Nikon 105mm f/3.5 leaf shutter medium format lens
4 elements in 3 group design for Bronica S2/EC Users
Photo thanks to Bob - brpr1@alltel.net

Related Links:
Manufacture & Performance of Photographic Lenses By Heinz Richter
Photo Innovations - Lenses..
Sinclair Optics - Free OSLO Lens Design Software

Lens Elements - A Few Go A Long Way

My short answer was that the required quartz lens elements cost nearly $80 US each, so a minimum one lens element design was a desirable virtue! Moreover, designing and mounting a multi-element lens from the available off-the-shelf quartz lens elements was not an easy task for a beginner on a home lab bench, especially for a 4 to 6 or more element lens. A one element lens is lots easier to make and much harder to mess up!

Commercial shortwave UV quartz lenses are hard to find or rent, and they cost from $3,000 to $23,000 US and up each. So for those of us on a budget, a single element quartz lens that could produce usable shortwave UV results had a lot of good points!

My email in support of complex lens designs of many elements triggered this page and the associated simple lens design table. Lots of great photographs have been taken with simple lenses with anywhere from only 1 to 6 or 7 elements in their design. In fact, the photo directly below was taken without any lens elements at all!

F/238 Pinhole - Pool view - TMax 400, 15 secs thanks to Clint O'Connor - His First Pinhole Photo!

No Element Lenses

The main disadvantage of pinhole cameras is that the images are a bit diffuse, as you can see by close inspection of the above image. The pinhole camera works by diffraction effects and the basic laws of the physics of light. A tiny hole acts similar to a lens in generating an image, but the small size of the hole means you have to use very long exposure times. Longer exposure times also get you into reciprocity effects, which can produce even longer exposures in pinhole cameras (where you can't vary the aperture easily). That makes pinhole cameras a poor choice for fast moving subjects.

Naturally, adding a lens with one or more elements will hopefully improve the basic pinhole camera. A larger lens means faster f/stops and shorter exposure times. While lenses have faults and aberrations of their own, they produce such benefits as critically sharper images when used properly. The trick in lens design is to balance the number, shape, and placement of the lens elements to yield the optimal results for a given amount of time and money used in constructing them.

Single Element Lenses

A positive meniscus lens has one element in which there are two curved surfaces in the same orientation [e.g., lens (( ->| film ]. The light is focused to a point at the effective focal length of the meniscus lens.

Some 62 million "disposable" cameras were sold last year in the USA alone. That figure is nearly 100 times as many as all the 35mm SLRs sold in the USA in the same time frame. Many of these disposable cameras had simple single element lens designs. Moreover, most of today's simple lenses are made of plastic rather than glass to help keep costs down.

The major trick with a single element lens is to use them stopped well down, typically around f/11 or f/16. At this point, many lens aberrations will be minimized, and the resulting single element lens will do surprisingly well. See our lens faults pages for a listing of the lens aberrations improved by stopping down.

Single element lenses have also been created to provide levels of spherical aberration that are hard to attain in better quality lenses. Such lenses are very popular as portrait lenses which flatter the older client's egos. The high level of spherical aberrations wide open provides a smoothing out of wrinkles and other skin defects without smudging out the underlying face characteristics.

An example of such a single element soft-focus lens is from our weird lenses pages - the Sima/Spiratone soft focus 100mm lens. This lens was little more than a +10 diopter lens in a focusing holder with T-mount base. You could put in waterhouse stops (disks with patterns of central and surrounding holes of varying sizes) to vary the degree of softening.

The key point here is that if you stopped down these single element soft-focus lenses "too much", to the range of f/11 to f/16 and beyond, they frequently became "too sharp" to produce flattering portraits. While this single element lens won't perform as well as a multi-element portrait lens, if you use it stopped well down the results will probably surprise you. If you have a +10 diopter closeup lens, you can experiment with that single element 100mm focal length soft focus lens on a bellows with your camera and see for yourself.

My own suggested use for single element lenses in 35mm and medium format photography is in low cost shortwave ultraviolet photography. Unfortunately, you can't use glass lenses for shortwave UV photography (around 220-270 nanometers), so expensive quartz lenses have to be used instead. But commercial medium format lenses for shortwave UV cost $15,000 to $23,000 US, when you can find one. Even 35mm SLR UV quartz lenses are $3,000 and up. But a simple +10 diopter quartz lens element from Edmund Scientific Corp. for under $100 US can be used for many purposes (with a UV only pass filter such as Kodak #18A).

Two Element Lenses

My first experience with a two element achromatic lens was an eight inch diameter objective on a hundred year old Clarke refractor at Yale's astronomy department. Thanks to the long focal length of these lenses, the resulting telescope often enjoys surprisingly crisp and contrasty images of planets, gas clouds, and other astronomical sights.

You might be surprised to learn that many highly regarded and pricey long lenses (such as the early Leitz Telyt telephoto lenses) used in 35mm and medium format photography may consist of only two elements. My personal favorite is the low cost 500mm f/8 "cult classic" sharpshooter lenses. These lenses have only the simple matched glass objective and a focusing T-mount and preset diaphragm, which explains their low cost (under $100 US new in 1999, $129 US multicoated). Yet despite their simplicity, this lens rated all "excellents" both center and edge in Popular Photography lens tests.

500mm f/8 Lens - T-mount, air space tube, focusing mount + 2 element lens

The real reason I like this 35mm SLR format 500mm f/8 lens is that it has sufficient coverage to be remounted for medium format camera users up to 6x6cm. In fact, Cambridge Camera Corp. will sell you a remounted version of their $129 US multicoated Korean 500mm f/8 lens in mounts for pentax 645, mamiya 645, and various 6x6cm focal plane cameras (hasselblad 2000/x..) for under $400 US. That is a huge bargain compared to similar 500mm f/8 glass lenses for those same cameras which often start at $10,000 US and up - way up. For examples, see our homebrew lens hacking pages for sample photos and how to do its. Do you have a leaf shutter lensed medium format SLR camera? If so, you may be able to remount such a long 500mm f/8 lens in a junked normal lens in which the glass has been removed (see Kowa "shutter lens" near bottom of page).

Another major use of two element achromatic lenses in medium format and other areas of photography is in closeup or diopter lenses. A two element achromatic lens can be used to produce surprisingly sharp closeups without losing any lens speed (unlike extension tubes or bellows). In fact, tests of some 2 element achromatic lenses show they outperformed extension tubes, especially for shots of natural objects. If you intend to photograph flat documents, then you really do need a macro-lens. But if you are shooting flowers or other 3 dimensional objects, then you might be surprised at how great your closeups can look with a simple 2 element achromatic closeup lens in front of your regular normal lens.

Three Element Lenses

Some of the early Kodak Ektar lenses were also three element designs [see table]. The quality of these three element Ektar optics was such that the name Ektar was later applied to other lenses with more than three elements as a sign of their high quality and professional results.

Many three element lens designs are symmetrical. Some of the lowest cost wide angle lenses used in medium format and large format cameras are three element symmetrical designs. Unfortunately, most such lenses are relatively slow, partly due to the need to stop down to minimize their aberrations.

Medium format cameras often have three element lenses, but most such cameras are found on the economy side of most camera lines. For example, many Yashica TLRs of modest cost are three element Yashikor or Yashimar lenses (models A, B, C). The better performing Yashinon 4 element lenses (Tessar derivatives) were found on the more expensive or later camera models.

If you try to buy a low cost new TLR today, you are very likely going to end up with a Chinese made Seagull twin lens reflex camera. Here again, the better quality 4 element lenses are usually found in the higher end and higher priced Seagull models. Nonetheless, many users are happily taking suprisingly good photos using just the standard three element lenses in their TLRs, rangefinder, folder, or other medium format cameras.

I recently bought a "autofocus" 35mm point and shoot camera at a yard sale for $3 US (originally $39.95 US). That camera turned out to have a 30mm f/5.6 lens made up of three elements. The camera was "autofocus" since it was prefocused to have everything "automatically in focus" between infinity and eight feet. Just don't try to take any closeups with this camera, the fine print warned. My guess is that the majority of higher end cameras in the point and shoot class are similar three element designs. But don't despair. These lens can be hacked to produce suprising coverage (due to their symmetrical design) and closeups (due to their short focal lengths).

Origins of the Mystique Behind Lens Elements and Groups

The number of groups helped indicate whether the lens elements were separate or glued together into multi-element lens components. If a lens had 5 elements and 5 groups, that meant it had each of the five glass elements separately mounted with air spaces between them.

But with a design in which the lens has 5 elements in 3 groups, we can't tell how the elements are setup internally. For example, 5 elements can be made into 3 groups by having the first three elements cemented togther, the middle three cemented together, or the last three cemented together, or combinations of two pairs of lenses cemented together with a single element, and so on.

That's why internal lens diagrams are needed to evaluate the internal lens configuration and identify its design type and probable strengths and weaknesses. But today, photographers no longer concern themselves with the design of their lenses, just with how well they work and how much they cost!

Simple lenses usually have their elements mounted together in a rigid lens cell to maintain the needed high precision positioning of lens elements demanded by the lens design. The entire lens is moved during focusing. A few lens designs (e.g., in some folder cameras) moved some of the front lens elements, but not all of them, during focusing. Such designs often proved troublesome in practice. Today's modern prime zoom lens designs require various floating element (e.g., Nikon's CRC close focusing correction) and moving elements in internal focusing (e.g., Nikon's ED-IF..) designs using complex mechanics to achieve precision movements.

As photographers, we know that each air-glass interface offers a potential for flare. The more such air-glass interfaces in the lens, the more flare and the lower the lens contrast was likely to be. So combining lenses into groups cemented together removed or reduced the number of air-glass interfaces. The natural presumption was that these cemented lens designs improved the flare and contrast over similar air-spaced lens designs.

If you look at improvements in lens designs over time in prime lenses (e.g., Nikon), you find the earlier designs of the 60's and 70's giving way to more and more complex multi-element lenses. Extra elements were added to improve on close focusing or reduce aberrations or vignetting in an already useful design.

The practice of counting lens elements and groups has fallen out of favor, largely because of new low dispersion glasses. Thanks to such improved glasses, it is now possible to reduce the number of elements in many lens designs, while improving the lens in many aspects. Internal focusing designs have also changed the priorities of lens designers. A lens with fewer elements may now be better corrected, thanks to the new optical glasses. Computer lens design programs could also generate lenses with better performance and fewer elements by trying milliions of possible design combinations, something past lens designers couldn't easily try.

The biggest change has probably come about with the development of zoom lenses. While zoom lenses offer convenience, they still have more elements (often 12, 14 or more) and groups and hence more flare and lower contrast than most prime lenses. Because of the complexity of zoom lens designs, we have given up trying to guesstimate their quality from their number of lens elements or groups.

However, several facts remain to be discerned from the number of lens elements and groups. A simpler lens with fewer elements (such as a prime) will generally have lower levels of flare and higher contrast than a more complex lens (e.g., zoom) with many more elements and groups - other factors such as cost and quality of construction and multicoating being equal. This fact is one major reason that medium format and large format users so often use prime lenses to achieve the highest levels of optical quality. Even today (AD 2000), we are only seeing a handful of very expensive pro zoom lenses which are close enough to the quality of prime lenses as to be used in some or many professional applications.

From Rollei Mailing List:
Date: Tue, 02 Nov 1999
From: Paul Roark proark@silcom.com
Subject: Re: [Rollei] 2.8GX and its Planar

Marc J. S. wrote:

>... The 2.8 Planar remained a
>five-element lens from its introduction in the 2.8C through the last of the
>2.8GX cameras.  It was never redesigned or recomputed.  The only change was
>the introduction of multi-coating on the very late F's and GX's.

I might add that the original Planar design was a 6 element, but it was too flare prone to use at the time -- no coatings. The 3.5 f Planar was a 6 element design in the last runs, but the 2.8 TLR never had a 6 element. I suspect it's the difference between 75 mm and 80 mm. The five element lens had more trouble covering the wider view. The corners of the 5 element 75 mm got a bit rough by today's standards.

Paul Roark
http://www.silcom.com/~proark/photos.html

From Rollei Mailing List:
Date: Tue, 02 Nov 1999
From: Eric Goldstein egoldstein@usa.net
Subject: Re: [Rollei] Planar performance TLR vs. SLR

>Several years ago I heard Professor Rudolf Kingslake lecture about the Tessar
>lens design.  He recomputed it using a computer and found that its optimum
>point was unusually narrow.  He said the Tessar is "A vile design." Professor
>Kingslake always wondered how its designer found the optimum point without a
>computer.

This is just as true for the Cooke Triplet; placement and grind are critical, much more critical than in many other lenses. It is fascinating to realize that Dennis Taylor formulated this famous lens by trial and error computationally and on the bench, an exceedingly difficult task with only the benefit of hand calculation of a single ray at a time. When the lens was introduced, it was actually more expensive to produce than, say, a rapid rectilinear, but yielded more contrast and lower distortions in some important parameters and so was deemed worth the expense.

There were also process Triplets and Tessars, which raises the bar on calculation and fabrication still farther!

Eric Goldstein

From Rollei Mailing List:
[Ed. note: Mr. M.J. Small is a noted expert and author on Zeiss and related optics..]
Date: Wed, 03 Nov 1999
From: Marc James Small msmall@roanoke.infi.net
Subject: [Rollei] Lens Designs

Glen M. Robinson wrote:

>Most of the successful classic lenses were designed by a master lens designer
>      supported by a hundred or so clerks working with logarithm tables.  The
>      lens designer would create an algorithm to do the calculations in an
>      efficient manner.  Even a cohort of clerks could never produce the
>      mountains of calculations needed to design an optimized lens from scratch
>      so lens designers used special  tricks of the trade and insights to first
>      develop a working design and then used the clerks to finalize its
>      optimization.  These tools were kept as closely guarded trade secrets and
>      unfortunately many of these secrets went to the grave.

When Zeiss introduced the 2/5cm Sonnar for the Contax RF system, the original ad showed the designer, Bertele, standing beside the three-foot stack of paper representing the design work which went into the lens.

The notes of Rudolph, Wandersleb, Bertele, Sauer, &c;, are preserved at Jena, but five decades of Socialist Realism has meant that all of the Jena archives are simply one huge mess which needs sorting. The next time you have six months off, I can arrange access ...

Marc

msmall@roanoke.infi.net

From Rollei Mailing List:
Date: Wed, 03 Nov 1999
From: Marc James Small msmall@roanoke.infi.net
Subject: Re: [Rollei] What Makes a Planar a Planar?

Ben R. McRee wrote:

>The recent discussion of Planars and their permutations has got me
>wondering:  if some Planars have 5 elements, some have 6 elements, and some
>7, what is it that makes them all Planars?  After all, I have never heard
>of a Tessar with more (or fewer) than four elements.  Is there a particular
>component or underlying design principle that all the Planars share?
>
>While we're on the topic of lens design, I wonder if someone could explain
>what makes a retrofocus lens a retrofocus lens?  I understand that this
>design is commonly used in slr lenses because of limitations imposed by
>having to make room behind the lens for the mirror.  But what does it
>actually mean for a lens to "retrofocus" and how is that different from a
>lens that does not retrofocus?

On the first point, Dr Hans Sauer produced two modifications of the basic Rudolph symmetrical six-element Planar when Ernst Wandersleb instructed him to revisit the design in the late 1930's to incorporate lens coatings. The first was the five-element TLR lens, later to appear in a 3.5/75 six-element variant.

The second permutation was the six-element, later seven-element Hasselblad and Rolleiflex MF SLR lens.

Since then, "Planar" has just become a name given by Zeiss to lens designs between f/1.4 and f/2.8 in the normal focal length range of 50mm for miniature-format and 75mm or 80mm for MF.

On the second point, a "retrofocus" design is one whose physical length is less than its focal length, to allow the mirror its necessary travel room. Just as a telephoto is a compressed lens -- a "long-focus" 135mm is 5 1/2" long physically, a telephoto is shorter than this -- so is a "retrofocus" wide-angle lens: it may have an optical length of 28mm, but its physical length is short enough to allow that bloody SLR mirror to swing out of the way. ("Retrofocus" as a term is an Angenieux coinage, though the concept was developed twenty years earlier by Zeiss at Jena. Angenieux was the first to mass-market a range of such lenses.)

Marc

msmall@roanoke.infi.net

From Rollei Mailing List:
Date: Thu, 30 Dec 1999
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] German TLR lenses

you wrote:

>VMC@SOVER.NET     In addition to Rolleis, I have a few other German TLRs
>and I am wondering if anyone can comment on the design and quality of
>lenses such as the Steinheil Cassar 80mm/f2.8, or the Enna Werk Ennit of
>identical focal length and aperture, as compared to the Zeiss and Schneider
>lenses in 2.8 Rolleis.  Thanks.
>
>                                   Richard H,. Coutant

The Cassar is a triplet with its usual characteristics. Steinheil makes good lenses. I had a Cassar enlarging lens many years ago which was pretty good. I still have some of those prints and they were quite sharp. Nonetheless, its an economy model just as the Zeiss Triotar is.

I don't have much information on Enna, their lenses are not listed in Henney and Dudley or is the company listed in McKeown's guide. I have some other sources and will look. My guess is that its another triplet.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List:
Date: Wed, 22 Mar 2000
From: Marc James Small msmall@roanoke.infi.net
Subject: RE: [Rollei] 3.5 Planar question

Kotsinadelis, Peter (Peter) wrote:

>So far, and this is subjective using
>cameras and comparing results, my pre-war Tessars appear to do better than
>the post war models.  Don't know why, maybe QC was better in the late 30s
>than in the 60s. Maybe it was the recomputation that Zeiss did was not as
>accurate as it should have been.  Some folks say it may be who assembled
>them and when they took their beer breaks. I don't know.
>
>As to the 3.5 lenses, you are right.  The third version of the 3.5F did have
>a 6-element Planar and was later followed by a 6-element Xenotar.  But I
>would still say, that you would be hard pressed to see a difference between
>the older 5-element and newer 6-element lenses.  Some have say the newer
>6-elements lenses, although better in resolution may appear less sharp
>because of lower contrast.
>
>One question here for you.  The Xenotars have a bluish coating and the
>Planars almost a clear coating.  Does this have to do with the layers or the
>coating specific to a lens?  Seems odd since they are so similar in design.

Four comments.

I objected to your statement that "You might also consider the 3.5 Xenotar which has better edge sharpness from inception." I don't believe it had superior edge sharpness nor, for that matter, did its manufacturers, JSK.

I agree that there is no discernible difference in normal use between the five- and six-element Planars and Xenotars. I also do not see any discernible difference across the board between the Xenotar and Planar, nor did F&H;, JSK, nor Zeiss.

As to your experience between the Pre- and Post-War Tessars, I would posit that your sample group is just too small to be of any significance. F&H; produced hundreds of thousands of TLR's before the War, and the same, and more, after the War. A sample of two or five or even ten cameras becomes meaningless. But, to answer your short question, Jena quality control both before and after the War depended on hand-assembly of lenses, with a concomittant swathe of quality from exemplar to exemplar. Oberkochen began with hand-assembly but, by 1960, had pretty much shifted over to machine assembly, so QC/QA standards become substantially tighter.

It is generally accepted that the Tessar used in the T and the Xenar used in the last Rolleicords and T's were the finest of their designs. That has not been MY experience (the best Tessar I have ever used in a Rolleiflex TLR was on an immediate Post-War Automat III, an uncoated Wartime lens), but, as with you, my own experience is just too limited to serve as the foundation for sweeping generalizations.

Marc

msmall@roanoke.infi.net

FRom Rollei Mailing List:
Date: Sun, 31 Oct 1999
From: "John A. Lind" jlind@netusa1.net
Subject: Re: [Rollei] Rollei 35 lens quality?

The Triotar ranks third in the list of lenses (if one keeps the Schneider S-Xenar on the same rank as the Tessar). It is a single coated 3 element lens (the Tessar is 4 elements in 3 groups; the Sonnar is 5 elements in 4 groups). Only the Sonnar is "HFT" multi-coated. Because of the number of elements, there will be more measurable aberration, meaning measurable with bench tests.

However, the two lenses it ranks behind, the Tessar (and Xenar) and Sonnar are very, very fine lenses. From a results standpoint, your control of exposure and compositional creativity are more likely to make a much larger difference than which of the lenses is on the Rollei 35 (unless you are looking to make a lot of 11x14 prints). From a value standpoint, the "B35" (was also marked "35B") will be less than a 35, 35T or 35S; some because of collectors and some because of users. There are differences beyond just the Triotar; these are the more significant ones:

a. Selenium meter, no battery, supposedly uncoupled to aperture and shutter controls

b. slowest shutter speed is 1/30th (versus 1/2 on the Tessar and Sonnar models)

c. shutter speed and aperture controls are around the lens barrel

You can read more about the Rollei 35 optics on a Rollei 35 site here:

http://www.canalvip.com.br/nagano/rol_opt.htm

The URL for the site's main page:

http://www.canalvip.com.br/nagano/rollei_1.htm

I would make certain the Selenium meter is still accurate. Older Selenium meters have a habit of losing accuracy as the meter element ages. This is a phenomenon of Selenium meter elements in general, not who made the meter.

Mark wrote:

>Hi
>
>I'm planning on the purchase of a Rollei 35 B camera . I'm not
>looking for a classic collectable and plan to use the camera.
>My question is what is the quality of the Triotar 40mm 3.5
>lens? Is this lens considerably inferior to the Sonnar 40mm 2.8
>(not considering the speed advantage of the Sonnar)?
>
>Thanks
>Mark  

From Rollei Mailing List:
Date: Thu, 04 Nov 1999
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] What Makes a Planar a Planar?

you wrote:

>The recent discussion of Planars and their permutations has got me
>wondering:  if some Planars have 5 elements, some have 6 elements, and some
>7, what is it that makes them all Planars?  After all, I have never heard
>of a Tessar with more (or fewer) than four elements.  Is there a particular
>component or underlying design principle that all the Planars share?
>
>While we're on the topic of lens design, I wonder if someone could explain
>what makes a retrofocus lens a retrofocus lens?  I understand that this
>design is commonly used in slr lenses because of limitations imposed by
>having to make room behind the lens for the mirror.  But what does it
>actually mean for a lens to "retrofocus" and how is that different from a
>lens that does not retrofocus?  
>
>Ben

Some prototype lens designs are flexible enough to generate a lot of modifications which are still recognizable as being related to the original. At some point, as Kingslake points out about computer generated designs, they may reach a point where they are not classifiable as any conventional type.

The Planar was one of many lenses designed by Paul Rudolph of Zeiss, also the designer of the Tessar and Protar. He developed the lens from the basic "Double Gauss" type by compounding the inside elements. His original design had very good field flatness, hense the name. However it was symmetrical and limited in coverage. A very great many lenses are based on the Planar, it is a very powerful design.

Despite Marc's claim that the first attempts at developing the Planar were done at Zeiss Kingslake atributes it to Horace Lee at Taylor, Taylor, and Hobson, for the Opic lens which was patented in 1920. This lens broke away from Rudolph's symmetrical design and was asymmetrical enough to improve its corrections at infinity. The Planar was also the basis of the TT&H; Speed Panchro lenses for motion picture cameras, the standard lenses for twenty years.

The most famous version of the Planar was the Zeiss Biogon, which is the grandfather of nearly all f/2 or faster lenses for 35mm still cameras and motion picture cameras.

The Planar type consists of positive meniscus and negative compound meniscus lens on each side of the stop. All of the elements may be further compounded or split so the number of elements can be more than six.

The Rollei Planar and Schneider Xenotar are simplifications of the Planar where the positive part of one of the inside cemented elements is broken apart and combined with the outside positive element. This reduces the number of elements to five and make the lens less expensive to make. Since the Rollei lens was required to be only f/2.8 this could be done and still get performance which is better than a Tessar at f/2.8 where they really do not perform very well. A Planar at f/2 would need all six elements and for faster speeds often has seven or more.

Probably the reason for going back to six elements in the f/3.5 version is to get a little more coverage, or perhaps, the easier corrections proved easier to manufacture despite the additional element and need for another cemented surface (cemented surfaces are expensive due to the need for individual polishing of the cemented surfaces and the cementing process).

Kingslake attributes the five element Planar to C.G.Wynne of Wray for the Unilite type patented in 1944. Again Marc claims the type was developed before this at Zeiss. Possible, they may have come up with a lot of stuff they didn't commercialize.

A retrofocus lens is a reversed telephoto. The name "Retrofocus" was a trade-mark of P. Angnieux Co but has become generic. The priciple is to place a standard lens behind a large negative lens. The result is a lens where the rear principle point lies in back of the lens. The rear or second principle point is the point the image appears to be coming from. By doing this the distance from the back of the lens to the film may be made greater than its focal length.

Retrofocus lenses are necessary for SLR cameras and beam splitter cameras where there the mirror or beam splitter requires too much clearance to allow a standard type lens to get close enough to the focal plane to focus at infinity.

These lenses have a set of virtues and vices all their own but that is beyond this question.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Fri, 5 Nov 1999
From: bigler@jsbach.univ-fcomte.fr
Subject: [Rollei] on 5-element and 7-element f/2.8 planars

I think I found a good reason to explain why CZ designers *had to* add 2 elements to a 5-element planar in order to fit it onto a SLR body. The following was triggered by recent postings on what a retrofocus is (Peter K., Richard K.). I would really be happy to get a confirmation or a contradiction on what follows.

I considered the famous Rolleiflex cut-through of my 2.8 GX brochure. ;-)

After properly scaling the diagram (the image height in the film plane should be something between 56 and 59 mm, the input bunch of rays parallel to the optical axis has a diameter of 28 to 29 mm : it *is* a f/2.8, 80 mm lens !) I found that the distance between the rear lens vertex and the film plane for the f/2.8, 5-element taking lens planar is only 57 to 59 mm, in any cases smaller than 60 mm.

On the other hand, Wildi's Hasselblad Manual (2nd edition, p 244) tells us indirectly (75=138.5-63.5) that the distance from film plane to lens seat on the 'blad bayonet is *75 mm*. Allowing, say, 5 mm towards inside, implies that in no case the film to rear lens distance can be smaller than 70 mm on a 'blad.

The conclusion is then T*, no flare, and crystal-clear : the beloved 5-element, f/2.8 planar simply *cannot* be fitted on a 'blad body. And probably not on any R-F&H; SLR. Looking again at the Rolleiflex cut-through impressed me by the incredible economy of space involved: the film spools are located in places where the trapezoidal shape of the chamber allows "dead" space ; the viewing mirror takes some "dead" space from the underneath taking chamber, and it is incredible how close the f/2.8 twin lenses are, Und So Weiter.

So the story might be for a SLR, a new planar design was required, with an additional constraint : no rear lens closer to 70 mm from focus plane.

This would, very simply explain :

1) that the 7 element SLR, f/2.8 planar, has reasons not to be as good as his 5-element brother. He is constrained a little, not as much as a retrofocus, 40mm distagon, is constrained with respect to a 38mm Biogon, but the reasons are similar.

2) now scale the 5-element, 80 mm planar to 100 mm. (actually : 100.3). The rear distance becomes about 60x100/80=75mm !! The 100 mm, f/3.5, 5-element planar *will* fit on a 'blad body, nothing much in terms of clearance, but fits.

Now the last, virtual, reverse engineering attempt ;-) What are the MTF curves of the 80 mm, 5-element planar ?

I would try this. Take the 100 planar outstanding MTF curves.

(see: http://www.hasselblad.se/products/lenses/lens_cf/cf100/index.html)

Scale the horizontal axis (off-axis distance, in mm) by 80/100, i.e. from 0 to 32 mm (instead of 0 to 40). Then assume that there is no diffraction, assume the spot size due to residual aberrations scale like 80/100, i.e. 100/80 in terms of line pairs. Then you'll probably get a good idea of what the 5-element, 80 mm planar, Rollei TLR MTF curves are (at the center of the field) by taking the MTF readings on the same curves, but for 12.5, 25 and 50 lp/mm (instead of 10, 20 and 40). Still outstanding, if not better. But unfortunately this is a virtual quality evaluation...

Thanks for your patience, Ruggers ! and enjoy your planar.

--
Emmanuel BIGLER
bigler@lpmo.univ-fcomte.fr

From Rollei Mailing List:
Date: Mon, 8 Nov 1999
From: bigler@jsbach.univ-fcomte.fr
Subject: Re: [Rollei] 5-element Planar MTF and Tessars on SLRs

> From Paul R. :
> I doubt we can conclude much about the GX Planar from the MTF of the 100
> Hasselblad 3.5 Planar.  In addition to the angle of view being narrower

It might be a scaled design, used only at the center of the field. If you consider Hasselblad recommendations about shifting their SLR lenses on the Flex body, you'll find that the 100mm planar is the one that can shifted the most among all others, distagons being the more limited to this respect. The 100 mm planar probably covers slightly more that the normal 53 degrees, it means that it covers at least 100 mm in diameter, i.e. a 70x70mm square. So you can shift +- 15mm.

> and the lens being slower,

I agree this is the only difference.

> the 100 mm Planar appears to be a different design than the 80 2.8
> that is in the GX....

If we trust the Hasselblad printed brochure or the web site, you are right. However I am suspecting a left-right printing symmetry error, those kind of things being not uncommon in the press in general, and more precisely in the Hasselblad litterature : in one of the 'blad 50-th anniversary magazine issue, V.H. himself is shown on a left-right reversed pictured, handling, in his *right* hand a left-right reversed H'blad... may be a *very* special model manufactured for for Him only... ;-)

More seriously ; it was recently mentioned that the 6-element original, symmetric planar design, had evolved towards the asymmetric, 5-element design to improve the infinity-focus correction, an asymmetric objet-image ray-tracing situation. The 5-element planar on the 'blad brochure is *exactly* the symmetric of the Rollei TLR, the one we have on the 2.8 GX brochure. So if the R-TLR planar is OK, (and you *proove* it, see below) then the 'blad 5-element planar would be degraded in terms of this asymmetrical, on-purpose design. The second thing that makes me think that the 'blad 100 mm planar *is* actually the same as the R-TLR, but scaled by 100/80 is that I found on another page of Wildi's 'blad manual details on the design of all C lenses. The rear lens vertex to film plane distance for the 100 mm is 73 mm. If you scale this by 80/100, you find 58 mm, very close to what you can estimate on the 2.8 GX cut through. But again this is virtual reverse engineering ;-).

> In the meantime, I'll just continue to base my shooting on my tests
> and experience that show the GX 2.8 to be excellent. ....-- better
> than the HFT 7 element Planar in my SL66.)

I think the mirror relief distance is a good reason for the 7-element SLR planar to be (slightly ?) inferior. And the actual photographer's results, in the last resort are the only thing important as you mention it.

I have also found by measuring the rear lens vertex to film plane on my 75 mm Tessar (R-T), namely ~64 mm, that a scaled tessar design to 80 mm would just fit (~68mm) on a 'blad body, as it was on earlier models on the 50's. Thinking of a rectangular format SLR's (24x36 or 4.5x6) I realized that a square format SLR imposes a severe constraint in terms of mirror distance : on a rectangular format SLR, the mirror distance is something like 1.4 times the *short* side of the format. It was then probably easy to design a 24x36 SLR with an un-constrained tessar. For example, on my Bessamatic 35 mm SLR, the skopar (supposed to be a tessar clone) has the compur shutter *behind* the last element. And I would not be surprised if the 80 mm planar on the brand new 4.5x6 Contax does not suffer from the limitations of its elder brother on 6x6 SLR 80mm.

--
Emmanuel BIGLER
bigler@lpmo.univ-fcomte.fr

From ROllei Mailing List:
Date: Mon, 08 Nov 1999
From: Paul Roark proark@silcom.com
Subject: Re: [Rollei] 5-element Planar MTF and SLRs

you wrote:

>> From Paul R. :
>> I doubt we can conclude much about the GX Planar from the MTF of the 100
>> Hasselblad 3.5 Planar.  In addition to the angle of view being narrower
>....
>> In the meantime, I'll just continue to base my shooting on my tests
>> and experience that show the GX 2.8 to be excellent. ....-- better
>> than the HFT 7 element Planar in my SL66.)
>
>I think the mirror relief distance is a good reason for the 7-element
>SLR planar to be (slightly ?) inferior. And the actual photographer's
>results, in the last resort are the only thing important as you
>mention it. 

Let me clarify my comparison of the 7 and 5 element Planars. My SL66 version is the HFT, which I believe is the last version that was available for the SL66. Nonetheless, I've found that lenses are occasionally updated. The latest MTF of Hasselblad's 7 element Planar seems to be an improvement of that used by the Rollei -- at least of the era of the SL66.

My tests and use of the 5 element Planars on TLRs is consistent with what I was told by several -- including Rollei/HP reps. These people claimed that the GX Planar was updated and has a flatter field of focus than the older ones. (I understand this is contrary to the views generally expressed on this list.) I have experience only with the 3.5 Planars and Xenotars -- which were very similar to each other. So, my personal experience is just with respect to those 75 mm 5 element lenses. Compared to those lenses, the GX has a much flatter field wide open.

The wide open flatness of field is the primary area where the GX Planar is better than the 7 element Planar on the SL66. However, that may be because it is an updated design. I suspect that the newest 7 element Planar has a flatter field than the SL66 version.

Although the 7 element design is probably, in part, due to the need to clear the mirror, it may also have some performance advantages. The two that come to mind in comparing my samples is that the corners of the 7 element (outside the 8 by 10 framing) may be slightly better, and the 7 element seems to give better results with a # 29 red filter (thought the GX is fine/equal with a # 25 and may be better with an orange # 22 -- but this may be too close for my testing to reliably measure). Frankly, I generally use a tripod and prefer to use both lenses at f 11, which gives me enough margin of error to cover focus and film plane flatness problems. In my normal use on a tripod, it is very unlikely that either lens is the limiting factor in picture taking. They are both extremely good lenses.

>...Thinking of a rectangular format SLR's (24x36 or
>4.5x6) I realized that a square format SLR imposes a severe constraint
>in terms of mirror distance : on a rectangular format SLR, the mirror
>distance is something like 1.4 times the *short* side of the format.

...

So true, but the rectangular MF SLR formats are terrible when used in the vertical format. Not only is the camera generally awkward, but the focal plane shutters, when they are not moving vertically (so that the tripod mass is directly in line with the direction of the shutter movement), cause a lot of vibration that can degrade image quality substantially. Even the SL66, which has an extremely smooth, vertical-moving focal plane shutter, starts to have vibration problems from its shutter (mirror locked up) with a very light tripod. A major advantage of the TLR is the leaf shutter and ability to use the lightest of tripods. I'm always amused at how heavy the tripod (and thus system) of 35 mm SLR shooters has to be to get reasonably sharp shots. As a practical matter, my GX, using the 35 mm portion of the negative, outshoots my EOS 85 mm (which is optically excellent) in landscape type shots because of the lower vibration (and usually better focus).

On the SLR mirror clearance issue, I find the 7 element Planar, even if it is technically "retrofocus," does not have the negative optical characteristics of the Distagons and other retrofocus lenses I've used and tested. I must say, most of the SLR wide angles (including my 50 Distagon for the SL66) are real dogs compared to the Planar or range finder wide angles. This is especially the case up close, where the Distagon has major focus shift, field curvature and astigmatism. Rollei/Zeiss put an f 32 on the 50 for a reason. The 7 element Planar has none of these problems close up.

Happy shooting -- at least with non-retrofocus Rollei/Zeiss glass.

Paul Roark
http://www.silcom.com/~proark/photos.html

Date: Sat, 18 Dec 1999
From: "Shinichi Hayakawa" shaya@gol.com
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Biometar = Sonnar?

> David Foy wrote:
> >  
> > Is the Zeiss Biometar lens a Sonnar design? Anybody know? Thanks.
> >
> >
> Its a Planar.

I think Biometar is more like a "modified" Planar. The classic Planar is a 4-group/6-element configuration, but Biometar is 4-group/5-element. The third group consists of only one element in Biometar.

As far as physical configuration is concerned, Biometar and Xenotar (of Schneider) are identical.

Zeiss Jena's Biotar IS Planar type.

Shinichi

[Ed. note: example of doublet 2 element telephoto...]
From Bronica Mailing List:

> Sent: 16 October 1999 13:08
> To: bronica@iList.net
> Subject: Re: [BRONICA] Wanted: Sharp Focus- Sharp Film
>
>
> S. Sherman wrote:
> >
> > from: flexaret@sprynet.com  (Sam Sherman)   10-14-99
> >
> > to: Bronica List
> >       IDCC
> >
> > While tweaking the focus for maximum results on my Bronica S2-A I have
> > re-rested my old and Rare
> > 300MM f5 Astro-Berlin tele, mounted for S-2A. I also have mounts for
> > it for Pentax 42MM, Pentacon 6
> > Exakta 66 ('54) and Primarflex. Cleaning the optics I noted that all
> > this lens consists of is a cemented doublet
> > and  a long empty tube. Other long teles also use this design.... is
> > it good? The lens is reasonably sharp
> > by 1950s standards. 

.....

From Rollei Mailing List:
Date: Tue, 26 Oct 1999
From: ShadCat11@aol.com
Subject: Re: [Rollei] Re: {Rollei} planars and tessars

attaway@slip.net writes:

Stopped down to 5.6, it is very sharp.

I have had several Tessar and Tessar-type (Xenar, etc.) lenses over the years, and typical samples were centrally sharp at f5.6, but required @ f11 for edge to edge sharpness. Planars and Xenotars seem good to the edges by f5.6. Also, they are critically sharp at the center wide open while the Tessar is not (altho usable.) At present I have two 'flexes, one with a 3.5 Planar and the other with a Xenar. Optically, the way I use them, both are good enough to use interchangeably.

From Rollei Mailing List;
Date: Mon, 25 Oct 1999
From: bigler@jsbach.univ-fcomte.fr
Subject: Re: [Rollei] planars and tessars

> From  ellis feldman
> how do planars compare in performance to tessars.

The proper, modern way to answer this RUG FAQ ;-) would be to check various tessars and planars on Rolleiflexes with a modern MTF test bench and make average values to avoid some biases. However you may have a feeling of how a tessar compares to a planar by looking at the published MTF data for Hasselblad lenses :

http://www.hasselblad.se/products/lenses/

and compare the CB 160 Tessar MTF curves with, say, the 135 Macro planar curves. You may also have a look at the 100 mm 5-element Planar lens which seems better than the 80 mm planar. The comparison is not fair since all these lenses have different focal lenses and therefore are optimized for diferent purposes. However you can see that the CB160 MTF curves at f/8 are very close to those of the 135 planar at f/5.6 (magnification ratio 1:5, this is a mcro lens). I think this summarizes well my personal feeling about the difference in behavior between a planar and tessar of the same focal lens : you have to close down the tessar one f-stop to get a similar result.

So really it would be nice to have data measured with the same protocol for Rolleiflex planars (including the last 2.8 GX ones) and tessars (the last one being from '75) and make a side by side comparison with the modern Zeiss-'blad lenses.

BTW for people who have looked at all these 'blad MTF curves (conveniently available if you request the catalogs), the new Japanese zoom f/4.8 60-120 mm for the 2XX focal plane series seems damn' good if compared to well-known fixed focal Zeiss lenses offered in parallel...

--
Emmanuel BIGLER
bigler@lpmo.univ-fcomte.fr

From Rollei Mailing List:
Date: Mon, 25 Oct 1999
From: "Ben R. McRee" B_McRee@ACAD.FANDM.EDU
Subject: [Rollei] Tessars & Planars

By the time this message reaches the list, I'm confident that someone will have repeated the consensus on this question--that Tessars are fine lenses but that Planars have a distinct advantage in sharpness at the edges at most apertures and at the center at f8 and wider. As a Tessar user I can confirm that the edges do go soft at f3.5 and f4.0. I should add, however, that in practice I find it hard to disentangle the contribution of the lens towards softness from that of the shallow depth of field and slowish shutter speeds that usually accompany wide apertures. In any case, I get my best results at f8 or smaller, and, unless I'm looking for a particular effect, try not to go wider than f5.6. On a tripod it will almost always be f11 or f16. All that said, I have some great candid shots of my children taken with the lens wide open (though it could be a case of a father's critical faculties going soft in these cases).

Cheers,

Ben

From Rollei Mailing List;
Date: Thu, 16 Mar 2000
From: Tom Kline tkline@grizzly.pwssc.gen.ak.us
Subject: Re: [Rollei] Zeiss vs Schneider

>> http://home.sol.no/~lhusabo/Rollei/Rollei-9.html
>
>At the bottom of this link is a lens diagram with a caption indicating it is
>"the" Planar used on the Hasselblad. This I believe is outdated information,
>as there are now differing Planar formulations available for this camera.
>Eric Goldstein

You are correct. The early 80mm C lenses differ optically from all the rest. Now there is a CB version (Hassy 80 Planar#3) that has one element fewer than the more common #2. The Rollei 80mm SLR Planars are of the same design as the Blad 80 Planars optical version #2.

Tom

Date: Fri, 7 Apr 2000
From: "David Foy" nomail@thisaddress.please
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Stepping up to Med. Format

The Xenar lens produces results which I cannot distinguish from a Tessar (nor from a Yashica-Mat's Yashinon, Diacord's Rikenon, or Autocord's Rokkor). I consider them all capable of fully professional results when used with care (lens shade, tripod, stay away from extreme apertures). Others report the Planar and Xenotar (found on Rolleiflexes, not Rolleicords) are equivalent to each other and better than the Tessar and Xenar (probably -- I haven't tested them). The Planar and Tessar are Zeiss products, Xenar and Xenotar Schneider. Nobody makes better lenses than these two outfits, although others certainly make lenses that are as good.

I don't consider the Mamiya C series to be a comparable camera, so I've never done a side-by-side lens comparison. The reason I say this is that its weight, interchangeable lenses, and close-focus bellows put it in a significantly different (and more useful) class than the fixed-lens TLRs, easily worth a hefty price premium if you will benefit from those features. The shooting I've done with mine recently has been with the 80mm lens, and it's excellent in every way.

The latest Rolleicords, Va and Vb, can be found reasonably priced (about the same as near-mint Yashica-Mat 124-G's) and in excellent condition, usually with the Xenar lens for some reason (I've never seen one with a Tessar, but I assume they exist). You can fit them with a 6x4.5 kit for 24 exposures per 120 roll, and that is a very, very nice feature.

They are a better value than the Yashica 124-G unless you want to shoot 220 and find the built-in meter useful. As it happens I find 220 useful, and the meter gives me good, easy, fast results in many kinds of light, so I happen to prefer the 'Mat. Also, the later Yashica-Mats have f2.8 viewing lenses and fresnel brighteners, and are much easier for me to focus than the Rolleicords.

....

> Have any of you had experience with the cheaper Rolleicord models. Does the
> schneider lens measure up to the qaulity produced by the more popular zeiss
> and Mamiya optics?
>
> Thank you so much for all of the info thus far. It has truely shed an
> abundance of light on this issue. Keep it up you guys!
>
> Thanks again,
> Garry B.

Date: Thu, 6 Apr 2000
From: RHICKEY@webtv.net (Bob Hickey)
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Stepping up to Med. Format

I"ve had all of them. I can't tell the difference between any Rollei and Hassy, Zeiss or Schneider.

I think the Mamiya takes marginally better portraits, not as contrasty. I don't think the Yashica is in the same league, ESP. when it comes to longevity. They wear out very quickly, usually the film transport first. Lenses condensate easily. From cold to hot, they fog out, and then you have a mist.

Bob Hickey

From Rollei Mailing List;
Date: Mon, 02 Aug 1999
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Tessars optimumum aperture

you wrote:

>Emmanuel Bigler wrote:
>>
>> > > What are the "best" aperatures to use on the Rollei 35T. Rea1eye@aol.com
>>
>> > The best performance with a Rollei 35 Tessar 40/3.5 lens is
>> > typically between f/8 and f/11 ..... I see the same behavior in my
>> > Rolleiflexes, with 75/3.5 Tessar vs 75/3.5 Xenotar. < Godfrey >
>>
>> I totally agree, based on my own Rolleiflex T 75 mm Tessar. However
>> the homemade B&W print I consider one of my best B&W landscape image
>> taken with this 75 mm tessar, was in fact at f/5.6 with a medium-grade
>> yellow filter on 100 asa film. So f/5.6 is actually worth using with a
>> f/3.5 tessar if you make handheld pictures and like to use fine grain
>>snip
>
>I have fond nostalgia for f8/11! I think it is my all time favorite f stop, and
>most used on many lenes!
>I'ts good to have favorites! No matter how silly!
>Mark Rabiner

This is about the best range for an f3.5 Tessar. If you look at the aperture from the corners of the film gate you can see how far down the lens must be stopped for the diaphragm to be clear of vignetting. That is usually the largest stop where the corners will be sharp. The vignetting by the lens mount can creat some additional coma along with the light fall off. This point is typically where the diaphragm is half the clear aperture of the lens on axis or two stops down from maximum.

The effects will be chiefly in the corners although there may also be some improvement on axis from reduction of spherical aberration. The Tessars used in Rolleis seem to be pretty well corrected for spherical even wide open but there will always be some reduction when the stop limits the amount of light coming through the margins of the lens.

The Xenotar and Planar are made with oversized front and rear elements. It is essentially an f/2 lens permanently stopped to f/2.8 so that the corner performance wide open is better than otherwise. Corner performance is still improved by stopping down but starts out better.

The rule of two to three stops down for best performance is pretty commonly correct amoung lenses but not universal. Beyone some stop, of course, the diffraction effects from the stop will degrade performance more than the reduction of aberration will improve it.

Keep in mind that not all aberrations are improved by stopping down. A really bad lens will be remain bad regardless:-)

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From ROllei Mailing List;
Date: Tue, 03 Aug 1999
From: Marc James Small msmall@roanoke.infi.net
Subject: RE: [Rollei] Planar vs Xenotar

Sean McTigue wrote:

>Buy the Xenotar!!  I have a 3.5E w/ a Xenotar and a 3.5F w/ a six element
>Planar. The old Xenotar is the equal of the updated Planar in every way.

What is an "old" Xenotar? What is an "updated" Planar? If by this you mean the five-element and six-element versions of each, they should be identical in performance save that the edge definition of the six-element lens should surpass that of the five-element lens.

Two points. First, Franke & Heidecke exhaustively tested both designs and found them absolutely identical in performance in all regards. Both JSK and CZ concurred in these findings. There is NO difference in performance between these lenses, save for the perceptual distinctions our minds impose on our evaluations!

Second, it is always dangerous to evalue ONE lens against ONE other lens, especially those lenses made back in the days of hand-assembled optics. Perhaps Mr McTigue's Planar was a Friday-afternoon lens and the Xenotar a Wednesday-morning one. Perhaps not. But an honest evaluation would consist of twenty cameras with each lens scattered through the production run. And I am sanguine that the evaluations F&H;, JSK, and CZ made four decades and more ago would be validated, that there is effectively no difference between Xenotar and Planar.

Marc

msmall@roanoke.infi.net

From Rollei Mailing List;
Date: Fri, 06 Aug 1999
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Consumers' Union

you wrote:

>Some years ago in one of their more ludicrous reports they tested an Alpa
>11el.  It was obvious to me as an Alpa owner at the time that they never
>even figured out how the rewind crank worked!!  It had me rolling on the
>floor laughing.
>
>Consumer Guide is about the same.  They had me do their camera section for
>a couple years, but it was obvious they wanted to cozy up to certain companies
>and dis others and not do any real testing, so I dropped out.
>
>Bob

In defense of CU, it is a non-profit organization which tries to stay isolated from the manufacturers of the products it tests. Consumers Guide is neither and is something of a fraud since it tries to fool people into thinking it _is_ CU with the very similar name etc.

CU has goofed more than once in testing products, and the goofs tend to be big ones. They were reponsible for killing off the gray baby Rollei by screwing up some test. They printed a retraction later but by that time the sales had been hurt too much and the camera was discontinued. Such goofs are actually quite rare.

Having said that, I think where they fall down is in very highly specialised testing, like optical testing, where they can't afford to maintain a staff of specialists. Different from testing cars and washing machines which they do all the time.

Testing lenses is pretty specialized. If someone reports on the relative merits of lenses I want to know just what tests were made and _how_ they were made, there are lots of pitfalls.

As far as Xenotar vs: Planar, it helps to know just which lenses are being discussed. Prochnow shows five different lenses. Two f/2.8 and three f/3.5. The f/2.8 lenses are both five elements in four groups. The Xenotar and Planar differ in the arrangement of cemented elements in the front. In the Xenotar, the second element is a cemented doublet. The order of the powers from the front being +, +, -. In the Planar the first component is compounded the order of powers being -, +, -. The rear half is nearly identical. What difference this makes in performance is beyond guessing, it may not make any. It probably makes a difference in manufacture. The cemented surface in the Xenotar is either plane or nearly so. In the Planar it is curved and the front element appears to be very thin. This is a more expensive assembly to make.

The f/3.5 version of the five element Planar has the cemented surface at the rear inside component and is very much like a reversed Xenotar, the cemented surface being plane.

Both the Xenotar and Planar six-element f/3.5 lenses are very similar in plan. They may have different glasses, one would have to have the design data or patents to know. Both lenses are more nearly conventional Biotar types. I don't quite understand why a more complex lens type was chosen for the f/3.5 lenses, it is the faster lens which should benefit for the extra element.

Someone mentioned contrast. This is a term with many meanings in photogrphy. For a lens it may mean overall image contrast or it may mean edge contrast or acutance. Overall contrast is a function of both internal reflection and residual aberrations, mainly spherical aberration. Internal reflections are nearly eliminated in modern lenses by coating. The difference between coatings is minimal compared to the uncoated condition. For lenses of the five or six element Planar type the additional gain in contrast of multi-coatings over single coatings will also be minimal, although noticable.

Uncorrected spherical can cause an overall haze in the image along with halos around highlights. None of the lenses used in Rollei cameras at any time, including the Triotar, should have enough residual spherical to do this. There reallly should be no noticable difference in such very well corrected lenses as any of the Xenotar or Planars used on Rolleiflex's . That leaves the acutance or edge contrast. This is determined by the designer in balancing the residual aberrations. A lens may have high resolution but low edge contrast, or the reverse. Depending on the final image size the high conrast lens will generally appear sharper to the eye than the one balanced for maximum resolution. The better the lens the less will be the difference between these conditions but there may be some visible difference in the images produced by two similar lenses where the designer has made a somewhat different choice in his/her compromise. There is something called the Strehl ratio which is a way of expressing the amount of energy in the main part of the diffraction pattern (Airy disc) compared to the total energy. the larger the Strehl ratio the higher the contrast of the lens.

It is also possible to make a compromise regarding marginal and axial correction. Again, this is done by choosing the balance of residual aberrations. Coma, particularly, may ruin the performance of a lens in the margins of the image even though the center is quite sharp. I've seen this condition in only a few lenses and I doubt that either the Xenotar or Planar suffer from it, the basic type has very good coma performance.

It certainly would be interesting to see the results of bench testing of a reasonable sample of all these lenses. They would have to be tested rather thoroughly, preferably for MTF at a variety of stops and positions in the field.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

Date: 10 Aug 1999
From: flexaret2@aol.com (FLEXARET2)
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Pentacon 6 Lenses on a Kiev 88 ?

from: flexaret2@aol.com (Sam Sherman) 8-10-99

Dear Bob,

In an issue of about 1953 of either Modern Photography or US Camera, some enterprising individual with lens polishing skills, cut off the bottom of a milk bottle (remember them?). He then ground and polished it into a single element lens and mounted it in some kind of camera mount, naming it a "Mootar".

The rest of the article was the pictures he proceeded to take with this lens. They were creative and interesting.

I have experimented with many 2x and other lens converters and even made some of my own. One converter in particular, which I made, allowed me to mount Kilar lenses on the leaf shutter Ricoh 126 SLR.

I am also aware that 2x converters can be rather good and Komura made a 7 element 2X converter that is very good. I have it in Minolta mount. I also once put 3 or 4 2x converters together for Exakta to take incredible long distance photos. All of this is relative to the task and budget one wants to achieve.

However, if one wants the best results out of a quality lens (and some of these can be bought inexpensively), no added glass elements in front of or behind the lens is the way to go.

But, on the subject of 2X converters, the was a rare 2x converter (called "Tiger") sold many years ago for Pentacon 6. I think it was a doublet - that was all that was around and it worked in a fashion.

Today there are tons of 2X converters around made in Ukraine for Kiev 60 and they work well on Pentacon 6. The converter has many glass elements, is well corrected and multicoated - this is a superb product.

Sometimes all of this works well and other times..................?

- Sam Sherman

From Rollei Mailing List;
Date: Sat, 18 Sep 1999
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Lens optimization

you wrote:

>      Are lens designs optimized for maximum sharpness at inf. per a given
>aperture.   John Kufrovich

Sort of. There is something called the Abbe since condition which dictates that a lens can be fully corrected for certain aberrations at only one distance. For camera lenses the distance is usually infinity. For lenses that are used at closer distances the optimum distance is where the manufacturer thinks its going to be used most. For copy lenses and process lenses it is the distance for 1:1 object to image size ratio. For enlarger lenses is is for the avarage distance for the range of magnifications the lens is intended for.

Different basic lens types vary in their sensitivity to changes in distance. The four-element air spaced design called a "Dialyte", the basis for many process lenses, is relatively insensitive so these lenses often perform very well at infinity even though corrected for 1:1. In general, the more complex and faster a lens is the more sensitive it will be to the object distance.

Generally a camera lens will have essentially full correction down to about 20X the focal length. Many will do well at much closer distances.

The main aberration to suffer is coma. It can be reduced by stopping the lens down.

As far as aperture, the optimisation is generally done for the lens wide open. Most lenses are corrected for spherical aberration at the center and at the edge. The greatest remaining error will be in the "zone" or a ring at 0.707 the radius. Some lenses have very little zonal spherical, the Planar and Plasmat being examples. Some have a lot, the Dagor being a prime example. Lenses with a lot of zonal spherical suffer from "focus shift" that is the apparent shift in the position of best focus as the aperture is stopped down. They way you judge focus has an effect on this so some people don't see it.

However, lenses like the Dagor are not really suitable for cameras which use rangefinders for focussing.

The focus shift can be nearly eliminated by changing the cross-over point of the spherical aberration curve to that it is zero at some point toward the zone of the lens rather than the edge. However, this compromizes the overall correction so such a lens is not quite as sharp as one with the zonal spherical but stopped down.

Most lenses have their optimum performance at about two stops down from maximum. That is partly due to eliminating most of the zonal aberrations but also because it is the point where most lenses are no longer vignetted by the lens mount. The maximum aperture without mechanical vignetting can be increased by using oversized outside elements, a trick used for the Xenotar/Planar lenses used on Rolleiflexes. These lenses were intended to provide better correction of the corners at large apertures than the Tessar type and the oversize elements are part of the method of obtaining this.

The "optimum" aperture, BTW, must be determined with a certain coverage in mind. Some very well corrected lenses will have their best performance near the center of the image when wide open but the corner performance will always require stopping down. The point is that for good performance at the margins of the image the best stop will nearly always be smaller than for best performance at the center of the image.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Sat, 18 Sep 1999
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Lens optimization

you wrote:

>      Are lens designs optimized for maximum sharpness at inf. per a given
>aperture.   John Kufrovich

I should have added to my previous long post that the sine condition limitation can be overcome by having a moving element or group coupled to the focussing. There are a number of current lenses with such "floating" elements. The reason for the change in correction is that the angle taken by the light rays when going through the lens will vary with the distance.

Obviously, the rays from an object at infinity or a very great distance will be different than those coming from a very close object. This changes the angles with which the light stikes every surface in the lens which in turn changes the effect each has on the light rays. By making one or more elements or groups movable in the right way the light paths through the lens can be kept more nearly to the optimum path.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Mon, 20 Sep 1999
From: Richard Knoppow dickburk@ix.netcom.com
Subject: [Rollei] Re: [Rollei] Off topic: Voigtlander Lanthar

you wrote:

>Hi RUG
>
>I just bought a Voigtl,nder rangefinder with a Lanthar 50 mm f2,8 lens.
>Does anyone here know what kind of design was used for this lens?
>
>Thanks
>Niels

Its a Cooke triplet. The Apo-Lanthar is a Heliar.

The name may or may not refer to Lanthanum glass. I can't remember how long Voigtlander has been using this name for a lens. Lanthanum is _not_ radioactive, I just checked a bunch of MSDS to confirm that.

Some radioactive materials have been used in glass formulas, notably Thorium, which was used in a few WW-2 vintage aerial lenses because there wasn't anything better at the time.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Tue, 21 Sep 1999
From: bigler@jsbach.univ-fcomte.fr
Subject: Re: [Rollei] Off topic: Voigtlander Lanthar

The Voigtlander Lanthar 50 mm f/2.8 lens is a 3-element type.

Reference : "Cameras: the facts, a collector's guide 1957-64" by W.D. Emanuel, A. Matheson, L. Gaunt - Focal Press, 1981, ISBN 0 240 51062 3 See: Voigtlander VITO section, pp 217-224.

BTW : for Rollei users this book presents a good summary of all Rolleiflex and Rolleicord models from the beginning to ~ 1960.

--
Emmanuel BIGLER
bigler@lpmo.univ-fcomte.fr

From 3D Mailing List;
Date: Mon, 24 Apr 2000
From: "Bob Porter" bporter3d@hotmail.com
Subject: Re: lenticular sources

Ken Conley is the premiere manufacturer of lenticular in the US, if not the world. Everyone else I know who sells lenticular has Ken somewhere in their supply chain.

And he's a wonderful guy to boot!

His company is Micro Lens Technology 704.847.9234.

- Bob Porter

From Rollei Mailing List:
Date: Fri, 05 May 2000
From: Bob Shell bob@bobshell.com
To: rollei@mejac.palo-alto.ca.us
Subject: Re: [Rollei] 2.8 planars TLR/Hassie

This is one of those little known secrets of photography. More elements is ALWAYS better. Now if they would just make a 9-element 80mm Planar we could all be happy with our photos.

Bob

....

[Ed. note: prize winning 3 element telephoto lens...]
From Pentax Mailing List:
Date: Wed, 07 Jun 2000
From: "Valery V. Zasedatel" vaza@eudoramail.com
Subject: Re: [Fwd: VALUE??? "PhotoSniper" lens...80yr old, russian built?!?]

It is a really military-looking thing. Because its predcessors were originaly designed for air documenting/intelligence. The lens is Tair-3 that was introdused in 1950-s (1955 if I am not mistaken) and it got a Grand Prix at Brussels Expo in 1958(!!!). With a butt attached (yes, Photo Sniper has a butt, but you can use a tripod as well) it is looking as a rifle. The modern version of FS (camera+lens+accessoires+metal box goes for some $200 in Russia). You may look in a Practical Photography magazine (I think it was in April issue) for the price - there was a small article about it. The lens has just 3 elements. Quality is really nice (just small positive distorsion as specialists in optics will say, but this is not noticeable at all).

Valery

http://dr.zet.tripod.com/zet.html
http://members2.clubphoto.com/valery197400/

From Rollei Mailing List:
Date: Thu, 01 Jun 2000
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] More QBM lenses Planar/Sonnar

you wrote:

 >      Many thanks to all those who responded to my original query.  I have a
 >better grip on the political and manufacturing reasons for the Planar's
 >pride of place in the Rollei stable, yet there is one thing I still do
 >not comprehend: Why did Zeiss see fit to continue researching and
 >producing Sonnar formula lenses (and still does) when the Planar is, at
 >least from a manufacturing standpoint, the better choice?  In other
 >words, what quality does the Sonnar possess that keeps it viable in the
 >market when there are Planars available in comparable focal
 >lengths/maximum apertures?  Is the Sonnar formula simply more adaptable
 >to longer focal lengths? (I've only ever heard of Planars in 50-85 mm
 >focal lengths - are there others?)  This is beginnin' to keep me up at
 >night . . . on the plus side, the nursery is really comin' along!
 >
 >Cheers,
 >Aaron

Most of the more recent Sonnars are long focus lenses. Essentially the Sonnar is a coupounded triplet using rather thick elements in the center negative component. In telephot type lenses these thick elements can help with certain corrections.

Very few standard focal length lenses of the original Sonnar type have been designed, either by Zeiss or by others. The original Nikkor 50mm f/1.4 lens for the rangefinder Nikon was an example. It is essentially a copy of the Zeiss lens for the Contax.

Rudolph's original Planar was derived from the double Gauss type lens. Rudolph compounded the two negative inside elements. The combination results in a lens with very good correction for spherical aberration and very little coma. The original Planar was symmetrical and f/4.5. In 1920 Horace Lee of TT&H; used this basic design for the Opic, a somewhat asymemtrical lens of f/2 speed. Making the lens asymmetrical allowed Lee to get better correction for a lens used at infinity focus. Other designers followed suit including Willy Merte of Zeiss who designed a series of lenses called the Biotar. Zeiss, and most other manufacturers, adopted this design as the basis for a very great variety of fast lenses. Nearly all f/2 or faster lenses for 35mm cameras are of the Opic or Biotar type, those faster than f/2 usually having additional elements.

The Biotar is a very powerful design. Zeiss certainly did not ignore it. The Sonnar type seems to perform well and to have low distortion when used for long focus lenses. I don't know of any standard FL lenses of the Sonnar type made by Zeiss after the Contax lens. The Contax type Sonnar has the advantage of lower flare than the Planar when coatings are not available. It is also a relatively shallow lens so is free from mechanical vignetting.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List:
Date: Thu, 01 Jun 2000
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] More QBM lenses Planar/Sonnar

you wrote:

 >--- Richard Knoppow  wrote:
 >
 >>    Most of the more recent Sonnars are long focus
 >> lenses.
 >
 >I seem to recall reading - perhaps in Kingslake - that
 >the Biogon design is essentially a Sonnar with a very
 >large rear element (or group).  If that is so - is it?
 >- then the Sonnar design may also live on in two Zeiss
 >Contax G lenses - the 21 and the 28 Biogon.
 >Gary Toop
 >

Zeiss used the Biogon name for two lenes of quite different design. The first was the lens yu refer to, a wide angle lens for the Contax designed by Bertele. The second form was later. This is the current Biogon type based on the Roosinov lens and similar to the Schneider Super Angulon, Rodenstock Grandagon, and many other WA lenes. This type can be analysed as a pair of back to back reversed telephoto types.

I am not familiar with the design used for the Contax G but would suspect it is of the second type.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List:
Date: Thu, 01 Jun 2000
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] More QBM lenses Planar/Sonnar

you wrote:

 >I enjoy all these lens discussions and thus thank the group for sharing them.
 >
 >Regarding the information below, where does the 40/2.8 Sonnar on the Rollei 35S
 >fit into the picture?
 >
 >Richard Knoppow wrote:
 > I don't know of any standard FL lenses of theSonnar type made by Zeiss
 >after the
 >Contax lens.

This is a interesting lens. It resembles the basic Ernostar type with the addition of a compounded rear element. The Ernostar is the lens Bertele designed for Ernamann, which is the prototype of the Contax Sonnar. The lens illustrated in Prochnow, _Rollei Report 3_ p.29-663 also looks very much like a Tessar with a split front element. Splitting the front element of a Triplett is a well known way of increasing its speed. This is essentially the approach Bertele took in designing the Ernostar. Since a Tessar is essentially a form of Triplett (although it was not derived from the triplett it can be analysed as one) the same trick would work for it. Bertele evidently designed the Ernostar from this basis, compounding the inner elements and rear element as needed for corrections.

The Contax 35S lens does not have the characteristic thick, low index, element as found on other Sonnar types. However, it certainly fits in with the series of Ernostar-Sonnar types.

So, I stand corrected. However I don't think the faster type of Sonnar was much duplicated.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List:
Date: Thu, 01 Jun 2000
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] More QBM lenses Planar/Sonnar

you wrote:

 >I enjoy all these lens discussions and thus thank the group for sharing them.
 >
 >Regarding the information below, where does the 40/2.8 Sonnar on the Rollei 35S
 >fit into the picture?
 >
 >Richard Knoppow wrote:
 > I don't know of any standard FL lenses of theSonnar type made by Zeiss
 >after the
 >Contax lens.

A brief addition to my last post.

Bertele's use of low index glass in very clever. While it is common now to replace cemented elements with an air space, giving the designer more surfaces to work with, in the old days this was avoided since it resulted in increased flare. Modern lens coatings virtually eliminate flare so the trick of splitting elements is quite practical. By splitting, the strength of each element is reduced thus reducing some of the aberrations produced by it. I think what Bertele did was to replace an air space with low index glass. This would have given him some of the advantages of splitting and air-spacing but retained the low-flare cemented surfaces. I have seen no direct references to this in the literature, other than Kingslake's mention of it in his book on lens history. He does not give the reason so I am guessing, but I think its a good guess.

The use of such low index glass rather than an air space might have other advantages too in some cases, so coatings would not have removed it from the designer's arsenal. However, it is likely to be used less than other design techniques since cemented elements are, in general, harder and more expensive to make (the surfaces to be cemented must match very closely) plus there is the cost of centering and cementing.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List:
Date: Mon, 29 May 2000
From: Marc James Small msmall@roanoke.infi.net
Subject: Re: [Rollei] Rollei 2.8B

ross bleasdale wrote:

>I was trying to figure out why the Biometar was used on the 2.8B and no
>other Rollei.
>Is it a poorer quality lens than say the Planar/Xenotar? I understand the
>Biometar was used following problems encountered with the 2.8A Carl Zeiss
>Jena Tessar which is reputed to be a little 'soft'. I'm not sure I would
>understand Sauer's formulation....so keep it simple!

As simply as the history will allow! In 1896, Paul Rudolph, Chief of Photographic Optical Design at Carl Zeiss Jena, developed the original six-element symmetrical Planar design, the first modern photographic lens. However, this lens, with its many elements and surfaces, was prone to flare. Hence, he then developed the less-capable, but less flare-prone, Tessar formula in 1902. (I am leaving out a LOT!). From 1902 until he retired in 1922, his main task was to 'open the Tessar' from its original f/6.3 configuration, and, to that end, he worked his assistant, Ernst Wandersleb, tirelessly. Wandersleb finally came up with the f/2.8 version of the lens, and, at that point, Rudolph retired, and went on to develop the Hugo Meyer lenses which were to be first coupled to the interchangeable-lensed Leica cameras nine years later.

Wandersleb inherited Rudolph's position. In 1935, another Zeiss scientist, Smakula, came up with lens coating, based on a number of other folks' works, including those of Taylor in England. Wandersleb, who had just suffered a huge embarrassment from a book he had written and dealing with those Two Titanic Egos, Ludwig Bertele and Willy Merte, tasked HIS assistant, the young Hans Sauer, to see what could be done with the flare-prone Planar design in light of lens coating. Sauer quietly went to work and completely redeveloped the lens. (I KNOW what Kingslake says about the five-element Planar, but he is, historically, wrong, at least from Sauer's own lips -- Sauer to a man now dead and thence to me, but I am happy with the citation.) Then the War ended, and Zeiss bifurcated into Jena and Oberkochen, and litigation resulted.

The Western Courts ruled that Zeiss Oberkochen owned the Planar name but acknowledged that the design was shared by both. Hence, Jena came up with the name 'Biometar' for Sauer's five-element design. And, in the early 1950's, Oberkochen could not produce the Planar lenses for Rollei but COULD supply East German glass, as the links from Jena to Oberkochen had not terminally died, though they were soon to do so.

And the use of the CZJ 2.8/8cm Tessar T on the 2.8A and the 2.8/80mm CZJ Biometar on the 2.8B resulted.

So, the short and long of it is that a Biometar IS a Planar, albeit the designer had voted with his feet and left the concern making the lens. A 2.8/80 CZJ Biometar in a 2.8B should perform identically to the 2.8/80 CZ Planar used on the 2.8C through F series.

The 2.8B is the rarest of the 2.8 Rolleis and is a collector's gem. Any of you owning these would earn my Eternal Gratitude by providing the body and both lens serial numbers to me for the Zeiss Historica archives, and thanks!

Marc

msmall@roanoke.infi.net

From Rollei Mailing List:
Date: Mon, 29 May 2000
From: Aaron Reece areece@intelos.net
Subject: [Rollei] QBM lenses - Wherefore art thou Sonnar?

Hi, everybody!

I'm glad to see this thread on the QBM lenses getting things back on topic, and thought I'd throw out a question that has been on my mind for a while:

I understand the advantage of the five- (or six-) element Planar design over the Tessar in terms of resolution, but what is the advantage of the Sonnar design? I know it has more elements than the Planar, but I'm not sure exactly how many. What was the rationale for employing this presumably more complicated design instead of the Planar formula in the 2.8/85 and 2.8/135 lenses?

On a similar note, what advantage would the 2.8/135 Sonnar have over the 4/135 Tele-Tessar, other than the extra stop? Is the Tele-Tessar even a true 4-element Tessar formula, or just a trademark (Like the JSK "Super-Angulon" lenses for 35mm cameras)?

For that matter, why was the Sonnar design chosen for the Tele-Rolleiflex? Is there a difficulty in applying the Planar formula to longer-focal-length lenses?

Ok, I know that was significantly more than one question, but with luck it will keep you chaps busy for a few days, while I convert my spare bedroom into a nursery!

Regards,
-Aaron

From Rollei Mailing List:
Date: Mon, 29 May 2000
From: "John A. Lind" jlind@netusa1.net
Subject: Re: [Rollei] QBM lenses - Wherefore art thou Sonnar?

I will dive in on this one hoping to draw Marc out of the woodwork to provide any necessary errata.

The Sonnar was designed specifically for the original Zeiss Ikon Contax I in 1930 by Ludwig Bertele of Carl Zeiss. Herr Bertele was one of the finest lens designers of the 20th Century and came to Carl Zeiss as a lens designer from Ernemann. Bertele went to Carl Zeiss when Ernemann was combined with several other German camera firms in 1926 (Ica, Contessa-Nettel and Goerz) to form Zeiss Ikon under the direction of Emanuel Goldman. Zeiss Ikon was established by the Zeiss Stiftung to compete with Ernst Leitz and the Leica (which had turned into a runaway sucess by mid-1920's standards). My guess is Zeiss Ikon wanted a super speed lens for the Contax and I know the Tessar cannot be reformulated that wide open without noticeable problems.

The original 1930 Sonnar was a 6 element, 3 group, f/2 5cm focal length lens. It was quickly followed in 1932 by a 7 element, 3 group formulation which opened it up the 5cm focal length to f/1.5 making it one of the fastest standard focal length lenses of its day (by comparison, most of its contemporaries were f/2.8 or f/3.5). The Sonnar was again reformulated at some point after the demise of the Zeiss Ikon Contax (1961) to 5 elements in 4 groups for a slower f/2.8 lens. These are the three basic formulations I am aware of for the standard focal length Sonnar. Since the Sonnar name has also been used on prime telephoto lenses, perhaps Marc (or another deep expert) can provide whatever basic formulation difference there is with them. There are also the much later Vario-Sonnar zoom lenses which may (??) have some basis in the original prime, but are unlikely to be anything but very distant cousins just by the nature of what must be done to design a zoom.

Unlike the Planar, it is an asymetric design, and I believe it has distant roots in the Cooke Triplet (the Tessar is closer to the Cooke). It is a stunning lens noted for near zero distortion with a very flat field, very low falloff, exceptional resolution and very high contrast. It has all the attributes sought for in a superb lens.

I have two of them. One is a mid-1950's coated Carl Zeiss f/1.5 50mm (7 elem. in 3 groups) for my Contax IIIa, and the other is a circa 1980 Rollei HFT f/2.8 40mm (5 elem. in 4 groups) on my Rollei 35S. For the Rollei 35S, Carl Zeiss reformulated the Sonnar for the 35S and Rollei manufactured them with their HFT multi-coating under a Carl Zeiss license. Carl Zeiss licensed a number of its designs for others to make, however they normally would not allow a Carl Zeiss lens name to be used on them. Rollei was allowed to use the Sonnar name on the lens which was very unusual. Both of them live up to the Sonnar's legendary reputation! The older f/1.5 50mm on the Contax IIIa is the best lens I have producing images rivaling 645 format in resolution; the newer f/2.8 40mm runs head-to-head with an f/1.2 50mm Zuiko, which is one of the finest lenses Olympus makes for its OM system. Not too shabby for a 1930 lens design. As with most lenses, the f/1.5 Sonnar is a tad softer at the wide open end.

One of the problems with the Sonnar is its very complex formulation. The original computations for it in 1930 consumed 3,000 pages. It requires extremely tight tolerances in its elements which makes manufacturing the Sonnar very difficult.

I have oft wondered why Carl Zeiss and Rollei opted for the reformulated Planar versus a Sonnar for the Rolleiflex. Not that the Planar is a better or worse. IMHO Carl Zeiss created three of the finest standard focal length lenses of the 20th Century: the Tessar, Sonnar and Planar.

-- John

...

From Rollei Mailing List:
Date: Tue, 30 May 2000
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] QBM lenses - Wherefore art thou Sonnar?

you wrote:

 > John A. Lind wrote:
 >>The Sonnar was designed specifically for the original Zeiss Ikon Contax I
 >>in 1930 by Ludwig Bertele of Carl Zeiss.  Herr Bertele was one of the
 >>finest lens designers of the 20th Century and came to Carl Zeiss as a lens
 >>designer from Ernemann.  Bertele went to Carl Zeiss when Ernemann was
 >>combined with several other German camera firms in 1926 (Ica,
 >>Contessa-Nettel and Goerz) to form Zeiss Ikon under the direction of
 >>Emanuel Goldman.  Zeiss Ikon was established by the Zeiss Stiftung to
 >>compete with Ernst Leitz and the Leica (which had turned into a runaway
 >>sucess by mid-1920's standards).
 >
 >Just a couple of minor additions.

Just a note in addition to Marc's very interesting history (one tends to forget there were real people behind all these designes).

One reason for choosing the cemented type of design for the Sonnar was to reduce flare. A Sonnar is really a compounded Triplet with six glass air surfaces, the same as for a Tessar. A Planar eight. Since the number of reflections in a lens go up rather fast with increasing number of surfaces the saving of two surfaces is more important thay might be apparent.

Later Sonnar lenses used the principle of filling a space between two elements with a rather thick low index glass, which Bertele devised for his lens.

It is interesting that the lens which made Nikon's reputation originally was a copy of the Sonnar.

The f/1.5 Sonnar for the Contax must have been a difficult and expensive lens to make. It has four cemented surfaces, one of which has quite steep curvature. Grinding and centering it must have been a chore.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List:
Date: Fri, 23 Jun 2000
From: Bob Shell bob@bobshell.com
Subject: Re: [Rollei] lens manufacturing

----------

>From: Richard Knoppow dickburk@ix.netcom.com
>To: rollei@mejac.palo-alto.ca.us
>Subject: Re: [Rollei] lens manufacturing
>Date: Thu, Jun 22, 2000, 6:43 PM
>

>   Where elements are to be cemented the mating surfaces must be very
>precisely ground and polished to exactly the same curvature. This is done
>one at a time, which adds to the cost of cemented surfaces.

This is one reason designers are using flat surfaces on some of their cemented doublets in lower priced lenses. A plano surface is relatively easy to make and cement. Look at optical sections of newer lenses and you see more and more flat cemented surfaces.

>   The method of checking the figure of the lens is to check it with a very
>precise guage using interference patterns. Probably a laser interferometer
>would make a more precise guage.

In my visits to optical manufacturing facilities the all seem to be doing final check on top-end optics by eye with a master blank and interference patterns.

Bob

From Rollei Mailing List:
Date: Thu, 22 Jun 2000
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] lens manufacturing

you wrote:

 >      i have hesitated for many months to get into the occasional
 >debates about zenar vs, tessar ad infinitum but here goes..
 >      granted my information and knowledge about these matters is
 >sparse but, but, but.
 >      my impression has been that at one time the figuring of a lens
 >formula, the grinding of a lens etc. was all a matter of much mental and
 >physical effort. We have all read stories of teams of mathematicians
 >spending months or years to compute a new lens. and of course as far as
 >grinding and polishing a lens let`s not discuss it. anyone who has ever
 >ground a telescope lens with his son or his dad has some input on that
 >subject.
 >      In fact to this day Leitz supposedly hand matches elements in
 >their camera lenses rather than taking one element after another and
 >placing it into the lens cell.
 >      However it was my understanding that, with computers, lens formulas
 >can be calculated in minutes in what used to take months or years. The
 >grinding and checking of lens elements i have assumed have progressed
 >proportionately.
 >      Now all of the above is based on a minimum amount of knowledge.
 >But from this i have derived the fact that schneider can copy whatever
 >zeiss has or visa versa unless it is patented or unless for whatever
 >the reason do not wish to.
 >      My own opinion? Pre- ww.11, tessar's are contrastier than most
 >other lens of similar age.
 >      Recently I built a collimator- i was shocked to find Tessars not
 >that sharp wide open. Now they were sharp but barely, and two stops
 >down perfect.
 > I know i am supposed to have known this beforehand but until i have
 >the time to test other tessar lens i am skeptical of what my eyes
>observed.
 >    Comments appreciated,
 >         regards fro the u.s.a.
 >           ellis feldman

Computers do speed up the process considerably. Lens designs are usually evaluated by ray tracing, a mostly trigonometic calculation. It can take half an hour to trace a single ray using a log table. A hand calculator will reduce this to a couple of minutes. A computer lens design progam will trace hundreds of rays and calculate the results, and chart them in a second.

The lens design program can not replace the designer but can help tremendously with the calculations. Theh program can also calculate such things as the sensitivity of various lens parameters, like glass constants. This can avoid having a design which calculates well but is impossible to build practically.

Spherical surfaces are a lot easier to generate than the parabolic ones needed for a telescope mirror. Modern computer controlled grinding machinery can make aspherical surfaces economically, as demonstrated by the number of commercial lenses with them, but, in the past they were very expensive to make and need to be made one at a time. Spherical surfaces are made many at a time on the same machine.

Where elements are to be cemented the mating surfaces must be very precisely ground and polished to exactly the same curvature. This is done one at a time, which adds to the cost of cemented surfaces.

The method of checking the figure of the lens is to check it with a very precise guage using interference patterns. Probably a laser interferometer would make a more precise guage.

After grinding and polishing the elements are "edged" by placing them on a centering machine and grinding the edges concentric and coaxial with the optical axis. For air spaced elements the precision required is not too great since the lens mount will automatically center spherical surfaces.

Elements which are to be cemented must be centered to a much greater degree of accuracy since the edge is the usual reference surface for aligning the elements for cementing. Again, this adds to the cost of a cemented surface.

Before any lenes are actually made the glass is checked for its constants. For the design to work the glass must be very close to the catalogue values the designer used. While slight adjustments may be made in the curvature of the surfaces to compensate for variations in glass, each change would amount to a new design so, in general, such an adjustment would be avoided.

No lens is at its best wide open unless designed that way especially. Lenses which must be best when wide open are generally either a faster lens which is effectively stopped down when wide open or lenses which are designed for rather narrow coverage, as is the case for projection lenses.

There are seven basic aberrations of lenses, sometimes called the Seidel aberrations after the mathematician who calculated them. They are: Spherical aberration, coma, astigmatism, longitudinal chromatic, lateral chromatic, curvature of field, and distortion. Of these spherical, coma, and astigmatism are reduced by stopping down the lens. Chromatic seems to be reduced as does field curvature because of the increase in depth of focus.

Beyond these first order aberrations there are higher orders. Up to seventh order aberrations must be taken into account in a complex lens. It is the balance of these higher order aberrations which often determine the subtle differences in lens performance among lenses of essentially similar design.

In addition to all this cerain aberrations can be minimised for only one subject distance. This is due to the geometry of the system. The rule is sometimes known as Abbe's sine condition, and sometimes as "the optical invariant". In any case, its why lenses are said to be "optimised" for a certain distance or degree of magnification. The lens can be corrected for spherical aberration, coma, and astigmatism at one point in the image field for only one distance. This is usually infinity for camera lenses and 1:1 magnification for process and copy lenses. For enlarging lenses it is usually the center of the range of magnlification the lens is intended to be used for. Some types of lenses are much more sensitive than others to change in subject distance. Generally the slower and simpler the lens the less its performance depends on object distance.

Tessars, and many other lens, vignet at full aperture. If the iris is looked at from an angle you will see that it changes from round to an eliptical shape. At some point the lens mount also cuts off part of the iris. A lens must be stopped down to the point where there is no longer any mechanical vignetting at the edges of the field before it has a chance of having good performance. Very often this is where the iris is about half the diameter it is when wide open, or about two stops down from maximum. Some lenses are better this way then others. For instance, the Kodak Ektar tessar type lenses have less residual spherical aberration in the center of the field when wide open than Tessars of the same age. Both the Ektar and Tessar have less coma than comparable Xenar or Wollensak Raptar or Optar (the last made for Graflex) lenses. Well designed f/4.5 Tessar type lenses will have best corner performance at around f/11. An f/3.5 lens at around f/8 to f/11. The center performance will be better for slower lenses, an f/6.3 Tessar generally outperforming an f/4.5 lens, etc.

The quality of glass is a key to good lenses. Glass does not bend light of all colors the same amount, blue light being bent more than red light. Optical glass comes in a variety of _indexes of refraction_ and _dispersion_. The Index of Refraction is the measure of how much the glass bends light. It is the _average_ of the bending over the range of colors the glass is intended to be use for. Dispersion is the amount the Index of Refractin changes with color. These two must be chosen carefully if a lens is to have a minimum of chromatic aberration.

There is a good tutorial and FAQ on lenses by David Jacobson on his web page at the Rochester Institute of Technology, there are links to it from the Graflex web page at http://www.graflex.org

For an example of a computer design program do a web search for "Oslo". Discard the travel stuff for Norway and you will come to the web page for this program. There is a free ware version which will handle up to (I think) twelve surfaces, the object and image surface are incuded. This program has a good graphical interface. It is not hard to set it up for the lens prescriptions from patent date. It comes with several sample lenses. This program will allow you to see what sort of differences are produced when a lens parameter, like bending or spacing, is changed.

Enough already!

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From: "Kent Gittings" bigplanetexec@email.msn.com
To: pentax-discuss@discuss.pentax.com
Subject: Re: Aspherical Lenses and Distortion
Date: Tue, 4 Jul 2000

I guess I need to get out a little more correct info in this field.

Aspheric lenses are basically designed to do one thing for the optical system. That is that spherical lenses, generally, will not make light waves at the edge of the field focus at the same point as the light passing near the center of the field. Has nothing inherently to do with color correction.

That's is why, for instance, Celestron Schmidt-Cassegrain optics have an aspheric corrector plate at the front. It allows the rest of the optical system to be made spherical instead of a more costly parabolic or hyperbolic curve on the optics. An aspheric element is made from one type of glass so it can't have any apochromatic qualities at all. It's non-spherical curve allows it to bring all the packets of white light together at the same point in conjunction with other spherical elements.

To make something apochromatic you need elements of different material, such as glass types like crown, flint, fluorite, or optical polymer coatings (plastic). Once the basic light is going to the same point you can them put in APO components to get as many of the colors to go through the same point (and not RGB but the range from 400-700 nm of visible light). And remember none of this addresses sharpness and contrast exactly either. Contrast will be better if the losses for every air-to-glass surface is kept to a minimum, so multilayer enhanced coatings like SMC are key. One of the problems with all this is that an optimum APO correction for film is not the same mix as you would want if using the optic visually. So optics from many years ago before APO type optics were used were generally corrected for a compromise of both or visual. So some earlier optics tended to have reputations as being "warmer" etc. All this meant was the designer opted to give the lens a color correction that was what he thought the user wanted not what is optically perfect as they couldn't do that then. So the affect was caused by whatever colors he decided to correct for and which he didn't. And depending on the type and color of the subject certain lenses got reputations as being better for one type of photography or another.

With APO you should theoretically be able to produce a lens corrected for all uses. That is depending on how much you want someone to pay for this lens, so their are compromises. The principles are the same no matter who builds the lens. Everybody has the same parameters to design from and the same problems to overcome. It is not rocket science exactly. Everybody could build the perfect lens on paper even the cheap companies. But can they produce it? Maybe and maybe not. Often times it's not whether they can make it but if they can sell it. If it costs them the same amount to build a lens as good as the best then they may not be able to sell it unless they are P-M-C-N. So they take away what they can get by with and sell it for less.

And since the advent of APO designs the best optics are better than the film all of us generally use. So some compromises will not show any differences on the film even on blowups. Mine own ratings, using both maker and third party lenses, indicate that in most instances it is virtually impossible to tell the difference between a photodo lens of 3-3.5 and one of 4 unless there are some distortions present unrelated to resolution and MTF. So if one has a bad pincushion problem you will see that but the sharpness may be indistinguishable ON FILM. So take the photodo tests as some kind of ballpark rating and look at things like the sharpest f-stop which is important and the range of resolutions across the f-stops tested.

Kent Gittings

....

[Ed. note: see archives for followup threads...l]

From: "Fred Whitlock" afc@skyenet.net
Newsgroups: rec.photo.equipment.35mm
Date: Thu, 20 Jul 2000
Subject: Re: fast lenses vs. slow lenses

The greatest cause of lost contrast in a lens revolves around the number of elements. The one with the fewer elements should display the higher contrast. I've never tested the 80~200 f4-5.6 but I don't think it would be an appropriate comparison with the f2.8 because it's not of the same quality of design and manufacture as the f2.8. So if the f2.8 were sharper then that wouldn't be a big surprise. We need to "keep other things equal" in order to interpret my comments.

I do own the 80~200 f2.8 Nikkor and it is a remarkable lens as zooms go. It is not, however, very contrasty and that's no surprise given the fact that its design incorporates 15 or so elements.

If you don't need the superior light gathering power of a fast lens, then it would make sense to me to use a slower, simpler lens and I do that sometimes. I wouldn't argue with that. Most of my lenses are of the "fast" variety, by the way. I'm a big believer in fast lenses, not because of corner sharpness at big apertures but because of all the other advantages they provide. Good shooting.

Fred
Maplewood Photography

[Ed. note: re: 3 element lens in the popular Olympus stylus camera P&S;]
From Contax Mailing List:
Date: Tue, 02 May 2000
From: "Bob Shell" bob@bobshell.com
Subject: Re: [CONTAX] T2/ standing up for the Stylus

When you consider that it only has a THREE ELEMENT lens, the performance of the lens is amazing.

Bob

- ----------

>From: mtm mtm@houston.rr.com
>To: contax@photo.cis.to
>Subject: Re: [CONTAX] T2/ standing up for the Stylus
>Date: Mon, May 1, 2000, 11:49 PM
>

> Granted
> it isn't on par with Contax anything but it makes a hell of a 'snap shot'
> camera.

From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: rec.photo.equipment.large-format
Date: Sat, 29 Jul 2000
Subject: Re: Aspheric Lens?

Nelson nelson@together.net wrote:

>Hi all,
>
>What is meant by the term "Aspheric" , as it relates to photographic
>lenes?
>
>Thanks
>Nelson

Lenses are made up of surfaces which are spherical. They are easy to generate. However, a spherical lens cannot produce a sharp image since different radiuses of the lens have different focal lengths. This is why an ordinary magnfying glass produces a blurry image.

Ordinarily, the lens designer uses a combination of negative and postive spherical surfaces to obtain the equivalent of a non-spherical surface which will produce a sharp image.

An aspherical surface can sometimes result in better correction of a lens, or to simplification of a lens. The effect of the aspheric surface can always be gotten by two or more spherical surfaces. The designer must determine if the expensive to make aspherical surface will be more economical in getting a certain level of performance than the spherical surfaces needed to emulate it.

Aspheres are hard to make, essentially the surface must be individually polished to shape. Automated machines allow much more economical production than in the past but such surfaces are used only when there is a good reason for them. Where an aspherical surface can eliminate a couple of elements or where it can give very improved performance they are justified.

Aspheres are used commonly in condenser systems, say for a slide projector, where the elements are made by molding rather than by grinding.

---
Richard Knoppow
Los Angeles, Ca.
dickburk@ix.netcom.com

From: h.nareid@nareid.demon.co.uk (Helge Nareid)
Newsgroups: rec.photo.equipment.large-format
Date: Sat, 29 Jul 2000
Subject: Re: Aspheric Lens?

"Rod Fleming" rodfleming@sol.co.uk wrote:

>Hi
>
>Aspherical elements have become commonplace in 35mm zoom lens design. These
>are plastic cast lens elements and their performance is surprisingly good. I
>have a couple of such lenses in my 35mm kit, and I am genuinely impressed by
>their performance compared to Nikon prime focus lenses.

As far as I am aware, the most common method for generating low-cost aspheric surfaces is by molding an aspheric surface onto a spherical surface. In that way, the thickness of plastic is minimized. Of course, there are also methods for making aspheric glass elements, but grinding and polishing such elements is costly.

>I think it is only a matter of time before plastic elements- both spherical
>and aspherical-  become commonplace in all formats- after all, there must be
>a market for a 300mm f5.6 which is lighter than a Symmar. Is there any real
>reason why glass should be the only material for the production of lenses?

Plastic (and there are of course a number of different plastics which can be used for optical purposes) has a number of problems for optical elements.

Firstly, the molecules are larger than in glasses, which means that they have larger inherent scatter than glass. That is one reason why plastic elements are normally as thin as possible.

Plastics also have thermal problems - their thermal expansion coefficients tend to be higher than glasses, which has optomechanical design implications.

Potential serious problems with plastics can be caused by birefringence, i.e. variations in optical properties as a function of polarisation - something which is highly undesirable in photographic optics. This can be an inherent property of the material (in which case it is a poor choice for photographic use, anyway), or a function of mechanical stresses on the material, so-called stress birefringence. Stress birefringence can also be observed in glasses, but is a much more serious problem for plastics, not the least because they tend to be more sensitive to thermal influences.

Plastics also have less resistance to mechanical damage than glasses, and for that reason, an optical designer would tend to avoid using plastics for any exposed surfaces.

Finally, there is a rather limited palette of plastics available for optical designs.

There are a number of good reasons to use plastics for optical elements, not the least the fact that they can easily be molded to non-spherical surfaces. There are also a number of problems with plastic lens elements, which is one reason why plastic elements are not more widely used.

--
- Helge Nareid
Nordmann i utlendighet, Aberdeen, Scotland

From: Mark Rabiner mark@rabiner.cncoffice.com
Newsgroups: rec.photo.equipment.large-format
Date: 30 Jul 2000
Subject: Re: Aspheric Lens?

>  Aspheres are used commonly in condenser systems, say for a slide
> projector, where the elements are made by molding rather than by
> grinding.
> ---
> Richard Knoppow
> Los Angeles, Ca.
> dickburk@ix.netcom.com

The newer line of much less expensive than before Aspheric's on the Leica M cameras are molded Pressed into place from soft glass suppled by Hoya!! The older ASPHs that were ground down cost thousands more. The new ones cost just a little more than regular spherical Leica optics cost before! Although this is off topic as it is 35mm I'm sure the same technology will be put into place to upgrade all glass from all formats.

I'm sure this is happening already! Aren't some of the LF Aspherics not so high end?

Mark Rabiner

Date: Wed, 2 Aug 2000
From: "Michael A. Covington" (see website for address)
Newsgroups: alt.astronomy,sci.astro.amateur
Subject: Re: Source for Surplus ACHROMAT Lenses

A company called American Science & Surplus has a separate optics catalogue (separate from their main catalogue; you have to request it) with lots of low-cost achromats in it.

Find them via web search.

--
Michael A. Covington / AI Center / The University of Georgia
http://www.ai.uga.edu/~mc http://www.CovingtonInnovations.com

From Leica Mailing List:
Date: Fri, 18 Aug 2000
From: "Erwin Puts" imxputs@knoware.nl
Subject: [Leica] Coatings and stuff

When evaluating lenses and/or discussing optical properties or develoments, some background knowledge is most certainly necessary. Otherwise it might be the case that attention is drawn to the wrong aspects or even characteristics are mentioned as discriminative in a negative or positive way do not have the relevance or importance attributed to it. The Rokkor topic does bring home this observation with some force. The study of lens drawings is a case in point. Without knowledge of optical design, without knowing the optical specs of a particular lens, the comparison of two diagrams is very dangerous and most certainly will lead to misleading conclusions. Two identical diagrams can deliver significantly different performance and two diagrams that look different, might give comparable performance. The assumption that the diagram reflects optical quality is erroneous.

If an optical designer is presented with whatever lens diagram and you would ask him/her to make any statement about performance or even assess differences, he/she would politely note that this is impossible without having access to much more important info. The noted difference of the third lens element between the Rokkor-CLE and the Summicron/Rokkor-C is obvious, assuming that the drawings are faithful. A Double Gauss lens is however, remarkably insensitive to small changes in glass thickness and without having any idea of the true radius of the glass and its type and the tracing of the rays, any conclusion, however tentatively, about design changes pointing to possible improvements, is a shot in the dark and because not based on analysis, inherently misleading. The only statement that can be corroborated is this: on the assumption that the diagramas are faithful, we note a difference in thickness of the third element, the purpose of which is unknown, without additional info.

Coating is a second topic that is easily mis-interpretated. Single coating is an obvious technique, as is multiple layer coating: in the first case a lens surface is coated with one layer of a certain and in the second technique, several layers are deposited, from two to nine and even more per surface. ML-coating is not in itself better than SL-coating, it depends on the design, on the glass types used and more. As example, when using high refractive glass, a SL-coating is more efficient than a ML-coating. If the Summicron were SL-coated, but used high RI glass, the effect might bettetr than a Minolta lens with ML and low refractive glass. ML-coating is often also used as a means to correct the colour transmission of a lens, again depending on the glass used. Leitz used three layer coating on selected surfaces of some lenses already in 1957, but did not mention it specifically, as they gave this aspect no public relation relevance. So if Leitz notes of a lens that it has coating, the inference that this has to imply SL-coating is incorrect and even if a certain lens does have single coating, that is not a sure sign of inferior performance.

The idea that MC-coating is more effective in flare reduction and repression of secondary images as SL-coating, is not true either as a general statement. And the claim of a Lugger that the Summicron-C must be a SL-coated lens, as his Summicron-C does have a significantly higher flare level than the Rokkor-CLE, is quite rash. Read what Mr Crawley, of BJP fame noted about the Summicron-C: "the lens is flare-free at full aperture". If the Summicron-C, as claimed, is of SL-coating type and as claimed, the SL-type is of inherently higher flare level, such a remark were hard to accept.

The type of coating is a lens characteristic that merits attention, but only in the context of the rest of the design parameters and without this knowledge, the singling out of coating properties as distinctive elements of the relative performance of a lens, is more reminiscent to a marketing act than enlighenment and advice for the user.

Erwin

From Rollei Mailing List:
Date: Tue, 22 Aug 2000
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Lens formulas

you wrote:

>Folks, I snipped this out of a response for a gentleman looking for the
>first Rolleiflex.
>
>> The 2.8D and 3.5E models introduced the five (sometimes six) -element
>> Planar and Xenotar. The greatest improvement you'll see with these lenses
>> over the Tessar or Xenar is in edge sharpness at larger apertures and
>> (depending on the age of the Tessar-design lens) an increase in contrast.
>
>
>Here is my question: what are the major strengths and weaknesses of the
>different formulas.  
>
>For example, this gentleman suggests that the Tessar formula gives higher
>contrast, while both the Tessar and Xenar are sharp wide open.  I'm not a
>student of optics, but is there something to be said for more "complex"
>designs?
>
>I guess this doesn't fall under the topic of a "Rollei" topic, more of a
>general photography question.
>
>Thanks.
>
>--
>Craig Stewart, VE9CES
>reddwarf@nbnet.nb.ca

Differences in contrast are mostly due to differences in coating. Single coated lenses are more contrasty than uncoated, multi-coated a little more contrasty than single coated.

The amount of flare is dependant on the number of glass air surfaces.

Tessar and Xenar lenses have six glass air interfaces, pre-WW-2 lenses were not coated, post about 1946 lenses are all single coated. The difference in a Tessar type lens is not great.

The f/2.8 Xenotar and Planar is a five element lens with eight glass air surfaces. They were all coated and do not have much flare. The f/3.5 Xenotar and Planar all have eight glass air surfaces regardless of the number of elements. The six element versions have an additional cemented surface, which does not contribute to flare. All these lenses are also coated.

I am not sure if any TLR lenses were multicoated before the current GX etc., probably Marc knows. In any case, the practical difference in contrast between a coated Tessar/Xenar and coated Planar/Xenotar is negligible.

The difference in performance between a Tessar and Xenar is probably too slight to be of concern, they are both excellent lenses. The same for the Xenotar and Planar although this is a matter of some controversy. The fact is that the differences in perceived performance between these two are slight, they are both exceptional lenses.

The main difference between a Tessar/Xenar and a Xenotar/Planar is that the more complex lens maintains its off axis performance at larger stops. A Rollei Tessar or Xenar is sharp at the corners at around f/8 and best at between f/8 and f/16. An f/3.5 Xenotar or Planar is probably sharp from around f/5.6 and better wide open (all standard lenses have some residual aberration off axis when wide open).

While there is probably not much if any difference between a Tessar and Xenotar at f/8 or f/11 I must say that the f/2.8 Xenotar in my Rollei 2.8E is astonishingly sharp.

I've found the main reason old lenses have low contrast is dirt. Most lenses acquire a coating of haze on the inside surfaces after ten or more years. A fifty year old lens which has never been cleaned, may be very hazy. Look through the lens with a flashlight to show up the haze. The good news is that the haze cleans off with ordinary lens cleaner and that getting the cells open for cleaning isn't too difficult. If you send a camera to a competent repair person (like Harry F.) he/she should be able to clean the inner surfaces if they need it. The difference in the visual image can be amazing.

A note. I just replaced the ground glass in a very old Speed Graphic because it was very dim and had a very noticeable hot spot. When examined with a loupe the glass seemed to be very coarse. I assumed it was a replacement made of very coarse glass. Well, while I had the GG out I cleaned it, along with the new one, using Bon Ami. Results, the old glass is perfectly good and the same as the new one. Evidently it had a coating of oil on it which was not removed by a casual cleaning with Windex. Warm water and Bon Ami did it. This is offered as a possibility to those with old Rolleis with very dim finder images. It may be that the GG is simply coated with oily grime which has gotten into the ground surface. Bon Ami is suggested but warm water and dishwashing detergent will likely work as well. Bon Ami is a mixture of soap and Sodium Silicate, long used for cleaning windows, chrome, and lenses from theatrical lights. In the US its available in hardware stores if not the market. The powder variety works as well as the older cake type. Do NOT use it on lenses!!!

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List:
Date: Wed, 23 Aug 2000
From: Laurence Cuffe Laurence.Cuffe@ucd.ie
Subject: OT Re: [Rollei] Lens formulas

>Folks, I snipped this out of a response for a gentleman looking for the
>first Rolleiflex.
>
>> The 2.8D and 3.5E models introduced the five (sometimes six) -element
>> Planar and Xenotar. The greatest improvement you'll see with these lenses
>> over the Tessar or Xenar is in edge sharpness at larger apertures and
>> (depending on the age of the Tessar-design lens) an increase in contrast.
>
>Here is my question: what are the major strengths and weaknesses of the
>different formulas.
>
>For example, this gentleman suggests that the Tessar formula gives higher
>contrast, while both the Tessar and Xenar are sharp wide open.  I'm not a
>student of optics, but is there something to be said for more "complex"
>designs?
>
>I guess this doesn't fall under the topic of a "Rollei" topic, more of a
>general photography question.
>
>Thanks.
>
>--
>Craig Stewart, VE9CES             

Each additional surface in a lens design introduces reflections and a consequent loss of contrast. Each additional surface also gives another degree of freedom to allow the lens designer to correct the aberrations of the lens. So its a trade off... before the war (roughly) the trade off came down on the side of less lens elements the Tessar (4 elements) is a classic example. After the war and the introduction of anti reflection coatings the balance swung in favour of the Plarar (5-6 elements) as the loss of contrast introduced by the extra elements could be mitigated by coating the elements. Now with the possibility of using aspherical elements at reasonable (roughly) prices it should be possible to design very good lenses with fewer elements. I think leica et at are now doing this. varifocal lenses zooms can have many elements say 10-12 and this is one reason that the contrast possible using such designs is low. Hope this helps

Larry Cuffe

Date: Fri, 01 Sep 2000
From: Anders Svensson anders.-.eivor.svensson@swipnet.se
Newsgroups: rec.photo.equipment.35mm
Subject: Re: Lens elements always glass vs plastic

Sure. They do all kinds, really.

Nikon grinds aspherics from molded blanks (as used in 28 f/1.4 and 20-35) as well as mold lenses in pecision metal forms (used in 24-120, among others). Nikon also makes hybrid lenses, molding plastic on top of a "special optical glass" - they say so in their own sales material.

I believe Nikon uses such hybrid lenses in some applications above kit lenses, too. But it is a fair guess that the 28-80 consumer lens has it, and perhaps the 28-200. They don't say exactly where they use them, but the asperic element on the 20-35 is the front lens - obviously a bad place to use plastic (and it is ground glass - the most expensive of these three).

It is likely that the third party 28-300 superzooms wouldn't be so well performing (price/performancewise) without plastic lenses here and there. It is not all lenses in a (say) 10 group/13 lens assembly that are plastic either - that would make them quite bad.

ss@randomc.com skrev:

Anders Svensson anders.-.eivor.svensson@swipnet.se wrote:

> >There are many lens manufacturers that use plastic in their lens designs.
>
> >Usually, only the cheapest of cheap lenses are all plastic material (like
> >in disposable, fix focus, f/8 "cameras"). On more expensive lenses,
> >plastic is used to make low cost aspheric lenses - it is much more cost
> >effective to mold these in plastic than to mold. grind and polish glass.
> They are sometimes molded, but I doubt plastic.  (Unless you mean in some kit
> lenses or something.)  Remember, glass can be molded.
>
> Steve

From Leica Mailing List:
Date: Mon, 9 Oct 2000
From: "Stanislaw B.A. Stawowy" watteau@krakow.neurosoft.net
Subject: Re: [Leica] Lens elements & groups

Ohhh, it is fairly simple.

Long long time ago, lenses were not coated. So they scattered light. Well, so we will use less elements, said constructors. But wait, Carl! You need many elements to correct optical errors! With three lenses you will have low sharpness in corners, not so flat field and little astigmatism! Ernst, what to do? Well, let's cement these elements together!

So then Carl (Zeiss) started production of Jupiter 3, later named Sonnar...

Jokes aside: every air-glass surface reflects some light. Despite of numerous efforts, even multi-extra-supercoated one. But you, as a constructor, want to correct aberrations. To do this, you have to have some lens surfaces to tweak their parameters. Also, with 2 lenses you simply cannot have flat field, nor good image. You need at least three elements, like in famous Cooke triplet. There you have six air-glass surfaces, because this lens is made from two plano-convex and one double-concave lens (I may be wrong, but then I will be flamed to death :-) Contemporary zooms have lot of these air-glass surfaces, so zooms have huge flare, low contrast and so. Jupiter/Sonnar have 7 lenses in three groups, what results in very good contrast and low flare. So is Leitz optics, How many air-glass surfaces famous Summicron have? Compare this to typical Sigma zoom :-)

St.
(Stanislaw B.A. Stawowy)

From Leica Mailing List:
Date: Mon, 09 Oct 2000
From: Bert Otten e.otten@med.rug.nl
Subject: [Leica] Re: Lens elements & groups

The fact that more than one piece of glass is used has to do with a number of factors:

1) Getting rid of chromatic aberration:

any piece of glass has two important properties: n, the refractive index, which determines how much light rays are bent the dispersive power, a measure of how different colours of light have a different refractive index

By combining different types of glass with different refractive indices and dispersive powers, it is possible to get rid of chromatic aberration, or the blue and red fringes in contrasty borders in the image

2) Getting rid of spherical aberration

All light rays coming from a pointsource need to be focussed in a single point. Thick lenses with spherical surfaces do not have that property. Partly this can be solved by combining lenses and using aspherical surfaces.

3) Getting rid of geometric deformation

Because single lenses have a thickness and are asymmetric, they do not behave perfectly in imaging straight lines in the object as straight lines in the image. By combining lenses this can be taken care of

4) Placing principal planes in agreement with the space in the camera

Sometimes lenses have a shorter focal length than space available between film and glass Then it is nice to place the back principal plane behind the lens. In telephoto lenses, you want to keep the physical length of the lens shorter than its focal length Again, you place the front principal plane in front of the frontlens.

This list is incomplete, but covers the main problems. So lenses with many pieces of glass can be better corrected for the above imperfections. So usually more pieces means a better lens.

However, each group of lenses has two air-glass surfaces, producing reflections, which reflect on and on in all groups. Thanks to multicoating, it is not as bad as it used to be.

Also, glass absorbs light, making it necessary to increase the aperture to reach the same effective aperture, making the lens even heavier.

If you look at the data of top lenses in large format phototgraphy, they tend to have fewer elements than hightly corrected lenses in medium and small format photography. This has to do with the principal planes: most large format lenses are more symmetrical, having the planes closer to the middle of the lens. Top prime lenses in small format photography can have up to 9 elements (for instance the 21/2.8 ASPH Elmarit). Zeiss produces the 40mm Distagon FLE for Hasselblad with 11 elements. This is a highly corrected lens with extreme demands on the principal planes.

So in short: many elements is usually a good sign, but only because of the multicoating and in the presence of skilled lens designers using good ray-tracing software.

Reference: Born, M and E. Wolf, Principles of Optics, Pergamon Press, Oxford, New York.

Hope this sheds some light (pun intended),

Bert Otten

From Contax Mailing List:
Date: Thu, 16 Nov 2000
From: Bob Shell bob@bobshell.com
Subject: Re: AW: [CONTAX] RE: Name of lenses

An apochromatic lens is one which brings all colors of visible light to focus at the same plane, and with all images the same size. This prevents color fringing. Apochromatic lenses have been around for a long time and were a necessity in the printing industry for color separation. Today they are often made with exotic glass types, but that is not essential. Older apochromats were usually completely symmetrical in design and the designer used the rear lens group(s) to cancel out the aberrations from the front lens group(s). I have an old 100mm f/2 Kinoptik Apochromat which was designed this way and is still capable of exceptional image quality.

Bob

...

From Contax Mailing List:
Date: Thu, 16 Nov 2000
From: Bob Shell bob@bobshell.com
Subject: Re: AW: [CONTAX] RE: Name of lenses

> From: Paul van Walree odobenus@xs4all.nl
> Date: Thu, 16 Nov 2000 
> To: contax@photo.cis.to
> Subject: Re: AW: [CONTAX] RE: Name of lenses
>
> Then these lenses must me saddled with other aberrations/limitations.
> Why would manufacturers resort to expensive low-dispersion glasses if there
> was an easier solution?
> Further, 100 mm is not a problematic focal length. Contax has the
> exquisite Planars 100/2 and 100/2.8 that do not contain LD glass.
> Do you know of a superior 300-mm lens that is symmetrical in design?

The idea is that a completely symmetrical lens can have almost no aberrations because the rear half being identical to the front half but reversed cancels them out.

The reason that exotic solutions were explored is that a symmetrical lens with a 500mm focal length, for example, will be physically awfully long and require a heavy barrel. To make an apochromatically corrected lens and simultaneously shift the rear nodal plane forward requires exotics. So a true telephoto with apochromatic correction can not be made from ordinary glass types.

Bob

[Ed. note useful resource link etc..]
From Nikon MF Mailing List:
Date: Sat, 2 Dec 2000
From: "Mark Vints" mark.vints@skynet.be
Subject: What makes a great lens?

In browsing through lens design schematics at http://www.laterna-magica.de/laterna-magica/nikon_forum/nikon_cd/content/java.ht m (sorry, it's in German), I noticed that two legendary Nikon lenses, the 35/1.4 and the 105/2.5, share a very thick optical element in their design, where other lenses make do with thinner lenses. Does anybody have any idea if there's a relation between this design fact and the perfromance of the lens? I for one would expect more chromatic aberration and light loss...

Mark

From Rollei Mailing List:
Date: Sat, 23 Dec 2000
From: Jon Hart jonhart51@yahoo.com
Subject: Re: [Rollei] Newbie - help me select an old Rolleiflex or Rolliecord TLR

--- Martin Jangowski martin@jangowski.de wrote:

> There were several lines of Rollei TLRs:
>
> Rolleicord with Triotar (3 lenses, a cheap entry
> model)
> I wouldn't buy a 'cord with a Triotar, the optics
> are inferior. A camera
> built before WW II (without coated lenses) isn't a
> very good user camera
> in my eyes, but there are fans of the soft looking
> pictures they will
> probably make.

Ummm, before our penis envy goes any further, I would like to categorically state that your opinion (as well as others' on this list) regarding "cheap, soft, (and worst offense of all) three-element" Triotars is a load of whale dreck. Further, the crack about lens coating being of utmost importance is in the same league. Not having a coating DOES NOT condemn a lens to producing inferior, soft-looking photos, thank you much. The only difference you can SEE between a Triotar and the other lenses mentioned is at or near full aperture up to the 11x14 size in my experience. You may see a slight difference at 16x20 in sharpness unless the Triotar is stopped down to f/8 or smaller. Having over 90 cameras in my accumulation, I have a number of uncoated lenses, few of which can be faulted because of being uncoated. For some uncorrected abberations, perhaps, but not because of a lack of coating. I have an ancient Bessa with uncoated Skopar that will knock the crap out of any 35mm lens produced on sharpness issues alone. However, being uncoated, extra care is taken to use the lens correctly, to prevent flare, the only real bug with this lens. And, just to pee in the Wheaties of those to whom this may matter, it is a front-cell focusing lens.

To sum up, a well-made three-element lens is nothing to sneer at, whether coated or not. Do you really believe Rollei would put a truly inferior lens on their equipment, especially way back when? Do you believe Zeiss would put their name on a lousy, cheap lens? They left that to others. Don't underestimate an uncoated lens of any type, especially something like a Tessar, which, coated or uncoated, can produce some stunning images. Of course, coating makes mindlessness a bit easier, in that one doesn't have to worry about flare as much so one needn't pay such close attention to where one is aiming the camera. I have always thought the folks on this list were considerably more discerning in their approach to photography than to do things that way.

Jon
from Deepinaharta, Georgia

From Rollei Mailing List
Date: Wed, 27 Dec 2000
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Off topic: Rapid Rectilinear

you wrote:

>As far as Rectilinear is concerned I'm not figuring it out!
>
>I found this:
>A double meniscus system in which two achromatized meniscus lenses are arranged
>symmetrically on either side of the aperture stop, reducing or eliminating distortion,
>coma and lateral color.
>
>Which I'm afraid is going right over my head.
>Can anybody put it in plain Grade school English? (Americain)
>
>mark :) rabiner

Well, meniscus means that all the outside surfaces of the lens are concave (or convex) in the same direction. Achromitized means that the lens is corrected for chromatic aberration, that is, it focuses light of all colors to the same point. Double meniscus means it has two separate lenses.

Arranged symmetrically means they are identical lenses and are spaced the same distance from a central stop, with the same curvature (either the convex or the concave side) of both lenses facing the stop. i.e., usually the convex side of both lenses faces the stop.

Symmetrical lenses are automatically corrected for geometrical distortion (pin-cushion or barrel distortion) straight lines are reproduced as straight lines. Lateral color is a difference in magnification, or the size of the image for different colors. It differs from the first kind of chromatic aberration in that the colors are focused to the same point but the size of the image is different. Coma is a very ugly directional bluring of the image away from the center of the image. The blur becomes tear-drop or comet shaped. The tail of the blur can point either toward or away from the center, depending on the source of the aberration in the lens. Coma is helped by stopping down but lenses with a lot of coma must be stopped down a lot to be reasonably sharp in the corners. Half a Dagor or half an R-R lens is not corrected for coma and has very poor image quality at anything larger than a largish pin-hole aperture.

For a good non-technical history of lenses see: A History of the Photographic Lens_ Rudolf Kingslake, 1989, San Diego, The Academic Press ISBN 0-12-408640-3 I think this is still in print. In it are also definitions of basic optical terms. It covers most familiar lenses and has a long section of one page biographies of optical pioneers.

Very strongly recommended. Kingslake is a particularly lucid writer. He was in charge of Kodak's optical design department from 1938 until about 1960. In this interval Kodak was making lenses the equal or superior to any made elswhere.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Thu, 28 Dec 2000
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Off topic: Rapid Rectilinear

you wrote:

>Can this Rapid Rectilinear be of the type I've heard someone call
>"Double-achromat"?
>
>/Patric

Yes, however "double acromat" is a very broad term which covers a lot of lenses, some older than the R-R and many later.

The description covers any lens with two components each of which is achromatized, but not necessarily symmetrical.

One of the oldest lenses fitting this description is the Ross-Collen lens of 1841. This is not a true symmetrical lens since the front component is + - and the rear also + - in the direction of light travel. A R-R lens has both positive elements facing the stop.

Lenses like the Dagor are also double acromats.

An acromatic lens is one corrected to bring two wavelengths of light (or colors) to a common focus. In very old designs the colors were often blue and yellow but later lenses are achromatized for blue and red. The remaining color error depends on the glass type. Modern glasses allow acromat lenses to have very small deviation at wavelengths other than those corrected for.

An apochromatic lens is corrected to bring three colors to a common focus. However, an apochromat may actually have larger deviations between the colors its corrected for than an achromat of better design.

There are seven basic aberrations in any lens:

Spherical
longitudinal chromatic
lateral chromatic
curvature of field
astigmatism
geometric distortion
coma

Of these the "lateral" aberrations, coma, lateral chromatic, and distortion are all automaticlly corrected by symmetry.

Where the entire optical path is symmetrical the cancellation is complete but it is substantial even for objects at infinity. The correction can often be improved for infinity by making the lens slightly asymmetrical by shifting some power from one end to the other. Completely asymmetrical lenses (like a Tessar) can also be highly corrected for these aberrations but it requires more effort by the lens designer to do. Kodak, for instance, claimed that its Ektar series of Tessar lenses (not all Ektars are Tessars) were completely corrected for lateral color.

A very good source of lens history is _A History of the Photographic Lens_ Rudolf Kingslake, 1989, San Diego, The Academic Press ISBN 0-12-408640-3 I think this is still in print.

(Did I just post this here?)

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Camera Makers Mailing LIst:
From: "G.Penate" penate@home.com
Subject: Re: [Cameramakers] Lens for box camera, DCX or PCX?
Date: Thu, 11 Jan 2001

----- Original Message -----
From: "John Sparks" jsparks@agilent.com

> Most of the box cameras that use a singlet used a meniscus lens rather than
> a plano-convex or double convex lens.  Best results come from using a stop
> between the subject and lens and concave side toward subject.

The kodak Autographic 3A has a great meniscus that just covers 4x5, I actually bought one of those cameras with the express purpose of removing its lens and use it in a 9x12 camera. I don't recall the 3A having the concave side facing the subject , tho, could someone corroborate that fact, please?

Guillermo

From Rollei Mailing List;
Date: Tue, 26 Dec 2000
From: Gene Johnson genej2@home.com
Subject: [Rollei] Off topic: Rapid Rectilinear

Hello All,

Sorry for the off topic message. Does anyone have anything to say about lenses of the Rapid Rectilinear design. I have seen some fairly impressive old pictures done with some of these. I know it is a fairly obsolete design, but it has interest for me since it might work out well for something I'm working on. The construction is comprised of two cemented achromats arranged with the more convex sides facing each other with the shutter or iris in the middle. There have been hints that this design has greater than usual covering power when stopped down, and I specifically was curious about that, but would be grateful for any observations. It seems it was quite popular around the turn of the century and for some time after. Thanks.

Gene Johnson

From Rollei Mailing List:
Date: Tue, 26 Dec 2000
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Off topic: Rapid Rectilinear

...

The R-R design originated in 1866 as the result of simultaneous invention by Steinheil and Dallmeyer. Both were issued patents although Steinheil had precedence. Steinheil worked with Seidel, one of the pioneers in mathematical optical design, so his version of the R-R was certainly designed with some knowledge of the principles of geometric optics.

Rapid Rectilinear lenses were used from the time of invention until the early 1930's. The R-R is not an anastigmat, that is, the radial and tangential fields do not coincide, so the lens must be stopped down considerably to be sharp away from the center. Astigmatism can be relieved to some degree by allowing some curvature of the field and this was done in most R-R designs.

The lenses are capable of quite good performance when stopped down.

Most R-R lenses are symmetrical but asymmetrical R-Rs were made as triple convertible lenses. A single cell of a R-R is not corrected for coma so they can be used only as very small stops (the same is true of a Dagor). They will also show some color fringing since the lateral color is no longer corrected by symmetry.

The coverage depends on the design of the lens. Generally, the longer the lens, i.e., the greater the apex to apex spacing for a given focal length, the narrower the coverage. Like other designs generally the lens must be made slower as the angle of coverage is increased in order to have reasonably correction.

Color performance can be quite good. Each half is corrected for longitudinal color and the symmetry corrects lateral color. The R-R is pretty well corrected for spherical aberration and complete lenses are well corrected for coma by the symmetry.

Bausch & Lomb made an enormous number of R-R lenses for Kodak for use in lower priced folding cameras. Eventually, the R-R was replaced by the Cooke Triplet, which is an anastigmatic and is rather cheaper to make. Rapid-Rectilinear lenses are actually fairly expensive to make since the cemented surfaces must be polished to an exact match one at a time and there is considerable extra labor in centering and cementing the elements. Triplets are air spaced and can be made considerably cheaper although spacing is quite sensitive to error so the mount must be accurately made.

Many R-R lenses, especially those made by B&L; have stops calibrated in the US system rather than f/stops. US 16 is equal to f/16 and US numbers halve or double for each stop; they are proportional to exposure time.

Typical medium coverage R-R lenses are around f/8 and perform well at around f/22 or smaller.

The R-R was made and sold by every major lens manufacturer under a great variety of trade names.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Camera Makers List:
Date: Sat, 13 Jan 2001
To: cameramakers@rosebud.opusis.com
From: Robert Mueller R.Mueller@fz-juelich.de
Subject: [Cameramakers] Re: Lens for a box camera;PCX or DCX (OPPS!!!)

In the process of writing the my last message on this I left a space for the title of a book by Warren J. Smith, expecting to add the title later, after I looked it up. But I forgot under the pressure of time and so I write again. The title of the book is "Modern Lens Design". However, contrary to what I wrote, the optimum when ONLY spherical abberation is considered is an unsymmetrical double convex lens. The trouble is that this yields a lot of field curvature and it so a little more spherical abberation is tolerated with a meniscus chosen to have low field curvature in a simple camera. The deign is known as the Wollaston simple meniscus and it has the concave side facing the subject to be photographed. The value of the design can be seen in a pair of photographs in "A History of the Photographic Lens" by Rudolf Kingslake. At the center of the images the double convex lens produces results as good (and probably even a bit etter) than the meniscus, but away from the center the meniscus soon looks far better when the image is made on a flat film. As I recall the original question in the thread, the application was to use a 40 to 50 mm lens to photograph on a 6x6 frame. This is already a wide-angle application and the issue of field curvature will be especially important, making the DCX look particularly inferior. In any case, at this wide an angle, a multiple element lens is probably worth looking for unless the outer portions of the image can be a little out of focus (sometimes desired in a portrait, but rarely does one want to make a serious portrait with a wide-angle- it makes the nose look too big!) Already a two element lens brings massive benefits (the Hypergon is an extreme example but though the design is old people are still making them and they bring impressive prices, yet they have only two elements of the same glass and are not even achromatic.)

Bob Mueller

From ROllei Mailing List;
Date: Wed, 10 Jan 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] OT Ross Xpres lens

you wrote:

>Marc wrote:
>>The Ross Xpress is generally credited with being a Tessar clone, but I
>>cannot claim sufficient familiarity with the breed to be certain that ALL
>>Xpress lenses are so configured.
>
>
>I get a little confused when I find information like this:
>
>http://www.cosmonet.org/camera/ensign_e.htm
>
>and this:
>
>http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=1205691125
>
>/Patric

I can see the confusion. The eBay poster may not know that its not a "Heliar" or is being delibrately misleading. Who knows?

The performance curves for the lens in the Xpres patent are shown on p.217 of _Modern Lens Design_ Warren J. Smith. Unless there is a typo the geometric distortion is very low but its other characteristics are no better than a good Tessar and not as good as some. The idea that more elements means better performance is not true. More elements can sometimes give a designer more degrees of freedom to make corrections, and cemented surfaces can be used to get the effect of some glass type that isn't available, but there is no guarentee that more is better.

Smith shows a number of compounded triplet lenses including several Tessars, Heliars, and other types, including the Pentac. The curves are for the most part computer analysis from patent data. Sometimes patent data is not quite reliable since it has to be only schematic, so the analysis of lens patents may not always be typical of actual productions lenses of the type.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List:
Date: Thu, 11 Jan 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] OT Ross Xpres lens

you wrote:

>Date sent:             Thu, 11 Jan 2001 
>From:                  J Patric Dahl,n jenspatricdahlen@hotmail.com
>Subject:               [Rollei] OT Ross Xpres lens
>
>>Does anyone here know the truth about the Ross Xpres lens, is it a four
>>element, three groups lens like the Tessar, or a five element three groups
>>design like the Heliar? I got one on my Ensign Selfix 820 camera.
>>
>Kingslake claims its a variation on the Tessar with three elements
>in the rear group i.e. two buried surface's both curving towards the
>central stop. it may be posible to confirm this by looking at
>reflections.
>All the best Larry Cuffe.

This is in fact what is shown in the patent. A buried surface is a cemented interface between two elements of similar index or refraction but different dispersion. The idea is that it can duplicate glass with some dispersion chacteristic not available. Accoding to Kingslake a buried surface can be used to correct nearly any amount of chromatic aberration without affecting other corrections. From the patent data it would appear that the cemented surface nearest the stop may be a buried surface but the last element is of rather higher index glass.

The curve shown for spherical in Smith's book shows considerable undercorrection at the margin. This would lead to a lens which is quite sharp when stopped down but somwhat soft wide open. This may or may not be an artifact of the patent data rather than a characteristic of actual production lenses.

The buried surface is attributed by Kingslake to Paul Rudolph, first used in the Planar.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Fri, 05 Jan 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] OFF TOPIC - Minolta Autocord

you wrote:

>>I have over 40 TLR's in my working/user collection, but as yet I have not
>>picked up either of these. What are your findings David? Seeing as how this
>>British made TLR doesn't have any electrical componets, I reckon it might
>>be alright....:-)
>>
>>Nolan Woodbury
>>
>>
>I was given an MPP Microcord Mk2 but have only run one roll through it, so
>far.  The engineering seems very good (milled knobs etc.) and very British
>(ie.very workmanlike, no flashiness).  The camera is like a Rolleicord but
>with shutter/aperture wheels as a Rolleiflex - a very good blend.  The
>shutter wheel is slipping though and needs some repair.  Shutter is a
>Prontor SVS, with XMV settings and a top speed of 1/300.
>
>The lens is a coated f3.5 Ross Xpres with a wonderful compromise focal
>length of 77.5mm, (four elements, rear pair cemented) and according to a
>1950s review, outperformed the Tessar on the Rolleicord III.  I have read
>that the British lenses of 1950s and 60s (Ross, TTH, Wray etc.) were very
>good and the equal of German equivalents.  However, I have yet to put this
>to the test!

FWIW, the Xpres is similar to a Tessar but has three cemented elements in the rear compenent. This may or may not have any effect on improving the performance. Sometimes extra cemented elements are used to get the effect of some glass type which is not available, sometimes simply to get around a patent. The Xpres has a good reputation. I don't have a copy of the patent so I don't know what the designer was getting at with the extra element.

There are other Tessar variations with three element rear components. The Zeiss Biotessar is an example where the extra elements are used to get improved performance for a faster lens. The Gundlach Radar is similar to the Xpres, although the arrangement of the elements is different. It was almost certainly intended to avoid the Zeiss Tessar patent. I don't think this was Ross's approach. Ross, BTW, was the British licensee of Zeiss as Bausch & Lomb was in the US.

Note that the _Wide Angle Xpres_ is another design altogether being a Plasmat.

I don't think Tessars were ever available on Rolleicord cameras. The III was available with a Schneider Xenar, which is a Tessar type lens, earlier Rolleicords were available only with the Zeiss Triotar, a Cooke Triplet type. While the Triotar is a very respectible triplet it is not in the same class with a good Tessar. It would be interesting to know if the comparison was with a Triotar or a Xenar. If the first, its not saying much, if the second its saying something because the Xenar, at least as found on Rollei cameras, is a very good lens.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing LIst;
Date: Sun, 7 Jan 2001
From: skeller keller.schaefer@t-online.de
Subject: Re: [Rollei] The Truth About the Sixth Element ...

TC Khoo,

Prochnow (whom I have not been able to prove to be wrong so far) states in his Rollei Report II (my own translation): "The new 6-element optical design made it easier than with the 5-element design for Zeiss and Schneider to achieve the optical performance that they had committed to deliver. Cost (for Rollei) did not increase. 2.8 Planar and Xenotar which did not have these problems (!!) remained 5-element."

To me that says that the 3,5 5-element Planar can have some production related problems (with tolerances?) whereas the 6-element lens should be as good as the 2,8 Planar. 3,5 and 2,8 Planar only share the name anyway - the basic design of both lenses is significantly different. The differences in performance cannot be that big, though. I personally would rate the Tessar sharp enough for almost everything. The 3,5 6-element Planar to me seems to be as sharp as a 7-element Planar (I don't have a 5-element Planar) but the 7-element (HFT) lens has more contrast.

Sven Keller
Cologne Germany

...

From Rollei Mailing List:
Date: Sun, 07 Jan 2001
From: Marc James Small msmall@roanoke.infi.net
Subject: Re: [Rollei] The Truth About the Sixth Element ...

TC Khoo wrote:

>What is the truth in the REAL reason for
>the 6th  element?? Was it a combination of what I have stated or something
>else? - Is there truth in the multi-coating of the last  batches??

The sixth element was added by Zeiss and Schneider to improve edge definition. I have used both five-element and six-element Planars and have never noticed an appreciable difference in performance but, then, I wasn't doing critical work looking for such distinctions. I suspect there were sound optical reasons for adding the additional element but that, in practical use, the differences in performance are minor.

On the second point, yes, the final F series cameras had multi-coated lenses, at least if they had Zeiss optics. The current state of analysis is that, by1973, Zeiss was multi-coating almost all production but consumers had to pay extra for the "T*" marking, and cash-strapped Rollei Fototechnik simply opted not to pay for the extra marking, though the lenses were multi-coated. No one has done research on the state of the Schneider Xenotar but I would be surprised if a similar occurrence didn't happen with these, as well.

Marc

msmall@roanoke.infi.net

From ROllei Mailing List;
Date: Sun, 07 Jan 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] The Truth About the Sixth Element ...

....

Its probably not possible to really know why the design was changed without access to someone who was privy to the change, or to the real prescriptions for the lenses. Even the patent data, if you could find it, might not tell you.

The six element version is the original type as designed by Paul Rudolph. He derived the lens from the "double Gauss" type, which is also the generic basis of the Kodak Wide Field Ektar, and a lot of other lenses. As embodied in a photographic objective this is a four-element, air-spaced type with all surfaces convex to the stop. This distinguishes this design from the "dialyte" type where the elements are bi-curved (in optical parlance they are not bent).

Rudolph expanded on the Gauss type by compounding the center (negative) elements and making them thicker. This resulted in an excellent lens but one which still had some zonal aberrations. Zeiss made some lenses based on this original design, but it was not popular. Around the early 1920's the design was taken up by Horace Lee of Taylor, Taylor, and Hobson, who designed a lens called the Opic. This was the first "modern" Planar type. Lee abandoned symmetry to obtain better correction of objects at a distance and improved the zonal problem. The lens was just another lens in the TT&H; catalogue so did not sell well.

Probably the first commercially successful design based on the original Planer was the TT&H; Speed Panchro, a lens designed for motion picture cameras. It became the most widely used lens in the industry from the late 1920's to about 1950.

The Planar is also the basis of the Zeiss Biotar of Merte and of most lenses of f/2 or faster speed for small format cameras.

The five element version of the Planar is attributed by Kingslake to C.G.Wynne c.1940. Marc says that Kingslake is mistaken, that the design originated at Zeiss c. mid 1930's. I have no way of substantiating either claim. Even though Kingslake is a very well respected historian he could well be wrong.

In any case, the Xenotar used in the f/2.8 Rolleiflex seems to be a design by Tronnier. The idea of the design is that two of the rear elements can be combined eliminating one element and one cemented surface. Cemented surfaces are expensive to make. The individual elements to be cemented must be individually ground to an exact surface contour match. The elements must be very accurately centered and edged, and there is the considerable extra labor of cementing and baking the component. Modern designers like to avoid cemented interfaces when possible.

OTOH, a cemented surface can have a very powerful effect on correcting aberrations, and, cemented elements can be used to obtain the effect of some type of glass which is not available, or is too expensive. This last may be a reason for the change from five to six elements. It my be that the five element form required some type of glass which was very expensive and that the more conventional six element form was actually cheaper to make for a given level of correction. This is a guess only and could be a mile off.

Another possible reason is simply that the slower lens is inherently lighter so that the lightness of the simpler lens was no longer a factor. The fact is that the original f/2.8 Xenotar is an excellent performer. I do not have the Planar version so can't compare the two. There is a general opinion that the Xenotar was sharper than the Planar, but since there were at least two versions of the Planar there is some (I think considerable) uncertainty about this opinion. The fact is that the plain, vanilla Tessar and Xenar are very sharp lenses when stopped down to f/8 or so suggests that at least some of the difference between the Xenotar and Planar is in the eye of the beholder rather than real.

The six element versions of both lenses are related more directly to the conventional Biotar type lens rather than to the five element type. The extra element _should_ allow better correction since it gives the designer at least one extra degree of freedom, OTOH, it is the f/2.8 lens which should benefit from the extra surface, not the slower and easier to correct f/3.5 lens.

It sure would be interesting to know what actually happened here.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing LIst
Date: Sun, 07 Jan 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] The Truth About the Sixth Element ...

....

It would be interesting to see some tests, or even computer analysis, if one could get the actual prescriptions (probably proprietary). Biotars are capable of excellent performance at f/2. The f/2.8 versions used for Hasselblad and Rolleis are excellent. An f/3.5 Biotar type should be outstanding.

Tessar types perform quite well at f/3.5 but must be stopped down to around f/8 for the residual coma to disappear at the corners. Optimum stop is probably around f/11. The Biotar type should be capable of good corner performance nearly wide open. Its optimum is probably around f/7 somewhere, a stop faster than a tessar of similar speed. The extra elements should allow better correction of higher order aberrations. Since the lens works at larger openings it is probably closer to being diffraction limited at larger stops, meaning its resolution is probably better. Some really excellent lenses of the tessar type have been made, the Kodak Ektar series being a prime example, however, even they are optimum at around f/11 to f/16(for an f/4.5 lens). The six element Biotar types should be capable of better performance at larger stops.

I call it a Biotar since I think it was Willy Merte's version of the Planar that put it on the map.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List:
Date: Fri, 12 Jan 2001
From: David Morris davidrobertmorris@lineone.net
Subject: Re: [Rollei] OT Ross Xpres lens

>>>Does anyone here know the truth about the Ross Xpres lens, is it a four
>>>element, three groups lens like the Tessar, or a five element three groups
>>>design like the Heliar? I got one on my Ensign Selfix 820 camera.
>>>

The 77.5 mm Ross Xpres lenses on my MPP Microcords are definitely four glass jobs. The Microcord instruction book says "The taking lens is a four-glass lens arranged as a single, single and cemented doublet assembly and is 3.5 aperture". The Focal Press Camera Guide says the same and carries a lens cross section which can be summarized as:

Film ()] )( [) Subject which I hope people can understand.

David Morris

David Morris (pbccon@gn.apc.org@gn.apc.org)

[Ed. note: thanks to Richard for sharing this nifty tip on counting lens elements nondestructively ;-)...]
Date: Mon, 08 Jan 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] How to determine number of lens elements

you wrote:

>No problem!  Take a large screwdriver, a beer can opener ("church key") or
>even a tire iron and gently pry the taking lens out.  then drop it into
>boiling water and simply count the elements as you drain the water off.
>100% accurate.  From there on, things get a little more difficult.  ;-)
>
>bob*

...

A rather less destructive method is to shine a flashlight or other small, bright source into the lens and cound the reflections. Glass-air surfaces, even coated ones, will be bright; cemented surfaces will be dim but visible. Care is necessary when looking for the reflections from cemented surfaces since a strongly curved one may result in very small or very large reflections which may be hard to see.

The five element Xenotar, both f/2.8 and f/3.5 has its cemented surface in the second front component (next to the stop). The Planar came in two versions; the f/2.8 had the cemented surface in the front component, the f/3.5 with the cemented surface in the rear component nearest the stop. Both the Xenotar and Planar six element f/3.5 lenses are conventional Biotar types with the cemented surfaces in the front and back components nearest the stop.

Using the flashlight method the five element lenses will have four reflections on one side and five (one very dim) on the other. Six element lenses will have five reflections (one very dim) on both sides.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Contax Mailing List:
Date: Tue, 09 Jan 2001
From: Bob Shell bob@bobshell.com
Subject: Re: [CONTAX] What is light Fall off ?

> From: "Ananth S" akrish@hotmail.com
> Reply-To: contax@photo.cis.to
> Date: Tue, 9 Jan 2001
> Subject: [CONTAX] What is light Fall off ?
>
> Is this similar to vignetting ?
> I have some slides which was shot using the TVS III , the central portion is
> fine but both the sides are little darker(not just the corners)
> I havent seen this issue with the Negative film prints, may be i should
> check the negatives itself.
>
> Thanks
> Ananth

This is more easily seen in transparencies than in print film, probably because the print film has more exposure latitude. The TVS III has known vignetting at high shutter speeds, so perhaps this is what you are seeing.

Light fall off is a simple optical fact of life. Areas away from the center of the lens get less light than the center because light passing through the diaphragm opening is less at more oblique angles. It's easy to see why. Hold a lens up in front of you and look through it at a white wall or bright surface. As you tilt the lens you will see that the diaphragm opening is a circle when you look straight along the optical axis, but becomes an oval as the lens is tilted. This oval has the same long dimension as the diameter of the round opening you see on axis, but a smaller area so less light passes. The more you tip the lens the narrower the oval gets, and the less light passes through. Lens designers can control this only to a limited extent by varying lens design.

Falloff is usually worse with wide angle lenses because more oblique light is used in forming the image.

I hope this quick, non-technical explanation makes sense.

Bob

From Rollei Mailing List;
Date: Tue, 16 Jan 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] front element focussing

you wrote:

>From Richard K. :
>>   The focal length of a front element focusing lens does change,
>> that's how it focuses. Most of the power in a Tessar is in the rear
>> component....It is, in effect, a very elementary zoom lens.
>
>Thanks very much Richard. So I was completely wrong by thinking that
>most of the power in a Tessar is in the front element. Consequently
>the amount you have to move the front element for focusing is
>certainly much smaller that is required when moving the whole lens
>according to Newton's formulae. Now I'm sure our RUGger friends would
>all like to get a comprehensive set of MTF charts for the
>front-focused 40mm f/3.5 Tessar at various focusing distances before
>making a major decision of purchase : a 'R-35 T/TE', or a 'R-35 S/SE'?
>;-);-) (The collector's answer : get'em all!!!)
>
>--
>Emmanuel BIGLER
>bigler@ens2m.fr

The Tessar, like the Protar from which it was derived has most of the power in the rear component. The front is composed of a fairly high power positive and negative element with a low combined power. Most of the correction is done in the front half of the lens, that is, its used to generate aberrations which cancel those of the rear lens. the cemented surface in the rear is used mainly for chromatic correction. Because both of the air spaced elements have considerable power, which is nearly cancelled changing the spacing between them a little has a rather large effect on the combined power, which is slightly negative. This, in turn, changes the focal length of the entire lens. Front element focusing can be used in any lens where ther is a balance of power between two elements such that moving one of them a little makes a magnified difference in overall focal length. Really a rather clever design.

In the Zeiss Super Ikonta cameras the rotating front of the lens is coupled to one side of a split rotating prism, making a simple but very accurate rangefinder. I think this rangefinder accounts in large part for the reputation these cameas have for sharpness.

----

Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List:
Date: Tue, 16 Jan 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Double-Anastigmats

you wrote:

>Maybe Mr. Knoppow can tell me the difference between a Tessar-type lens with
>the cemented rear elements, and the Double-Anastigmat like Unofocal which
>also is a four element lens, but with air-spaced elements?
>
>/Patric

I don't quite know how to approach this, its a simple question with a complicated answer.

Lenses are made with more than one element because simple elements with spherical surfaces can not make good images. Furtheremore, glass does not bend light of all colors equally, it bends blue more than red. Furthermore, the geometry of simple optics is such that a flat object is reproduced on a spherical image plane. There are other aberrations.

In order to make a lens which is corrected for these a multiplicity of elements is needed and, for correction of color, multiplicity of types of glass.

There are many arrangements for these elements to make the corrections.

The ability of a lens to bend light depends on its shape and on the difference in index of refraction of the lens material and the material surrounding it. When a lens is cemented to another lens the bending of the light depends on the difference in index of the two types of glass. This will be different than it would be in air. There are some types of corrections which are easier to make with a cemented surface.

Cemented surfaces have some advantages: they have very little reflection since the difference in index is smaller than in air. they can produce effects not possible in air, for instance, a double convex lens cemented to two lenses of higher index, looks like a negative lens rather than the positive lens it would be in air.

Air spaced elements have the advantage of both surfaces being independant. In a cemented lens the cemented suraface must have the radius of curvature and must be matched exactly. For a given number of elements the air spaced design gives the designer more to work with in making corrections. Air spaced elements however, have much more surface reflection even when coated. In the days before coating designers tried to minimise glass air surfaces, hense such lenses as the convertible Protar, with four cemented elements.

The Unofocal is a form of what is called generically a "dialyte", literally "two windows". in the Unofocal the lenses are all of equal power, the overall power is gotten by spacing. The Apochromatic Artar of Goerz, the Dogmar of Goerz and many other lenses are of this general type of design, but do not use the Unofocal approach of equal powers.

The Tessar was derived by Paul Rudolph from his earlier Protar type lens. This lens had a cemented pair of elements on both sides of the stop. It had problems with residual aberrations, so Rudolph split the front elements into an air spaced pair, thus giving him an additional curvature and the spacing to use in making corrections. Although the Tessar can be classified as a variation of the Cooke Triplet, it was not derived from the triplet.

In the Tessar the cemented surface is used for color correction. Most of the power in the lens, that is the power which contributes to its focal length, is in the rear pair. The front component is composed of a positive element of fairly high power and a negative element of similar power spaced so that the front has weak negative power but aberrations which are of equal magnitude but opposite sign to those of the rear component. The result is a lens with very good corrections.

The Unofocal makes the same sort of corrections in a different way. I don't have the patent for it so don't know exactly what its designer did in making corrections. The Unofocal is a very well corrected lens with rather narrower covering power than a Tessar.

One advantage of a design like the Unofocal is that it is either symmetrical or nearly symmetrical. Symmetrical lenses are automatically corrected for "lateral" aberrations, which include lateral color (the images in different colors are of the same size), geometrical distortion, and coma. Coma is a very unpleasant directional bluring of the image. Points are reproduced as tear-drop or commet (hense the name) shaped pointing toward or away from the center of the image. Coma is difficult to correct in a non-symmetrical lens, like the Tessar, but is automatically cancelled in a symmetrical lens like the Unofocal, Artar, Dagor, or modern Plasmat types. Although the cancellation is perfect only at 1:1, it is very good even at infinity. By making the lens slightly un-symmetrical i.e., shifting some power from one end to the other, the cancellation can be made perfect at infinity. Lenses like the Goerz Dogmar, or the famous Kodak Ektar, 203mm /f7.7 lens take advantage of this.

In short, an air spaced lens is simplly another approach to correcting the fundamental faults found in all lenses. Compared to a Tessar this type of lens has narrower coverage, but generally excellent correction especially for coma.

There is another form of four element - air spaced lens called the Double Gauss type. The difference between it and a dialyte is that the elements in a Double Gauss lens are all "bent" so that _all_ of the curved surfaces are convex toward the stop, while the elements in a dialyte are generally not bent. Double Gauss lenses can have very large coverage. The Kodak Wide Field Ektar is of this type. When the negative elements of a Double Gauss lens are compounded it becomes the Planar, prototype most of the f/2 or faster lenses used on 35mm cameras and many others. This is one of the most powerful generic designs.\

See Rudolf Kingslake's book on lens history for lots more on how lenses came to be and the people who designed them. Not technical and very well written.

_A History of the Photographic Lens_ Rudolf Kingslake, The Academic Press

I believe this is still in print.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing list:
Date: Wed, 17 Jan 2001
From: "Kotsinadelis, Peter (Peter)" peterk@avaya.com
Subject: RE: [Rollei] Serious lens design question

Richard Knoppow wrote:

See Kingslake's book for the history of these lenses.

The Ernostar and Sonnar were designed by Ludwig Bertele. He worked for Ernamann which became part of ICA which in turn became part of Zeiss-Ikon, so, Bertele became a designer for Zeiss.

The Sonnar is a further development of the Ernostar he designed for Ernamann. He was self taught: A quite remarkable man.

The f/1.4 Nikon lens used on the rangefinder Nikon camera is virtually a copy of the f/1.5 Zeiss Sonnar. This lens made Nikon's reputation.

_________________________________________________________________________

The Sonnar 50mm F1.5 was also an often used optic of HCB on his Leica. Interest note, many subsequent lenses were of the Planar design. The Konica rangefinders and others used copies of the Planar which were either 45mm or 50mm, and virtually identical to the Contax 45mm F2 lens found on todays G2 rangefinders. BTW, I picked up a really inexpensive Konica S2 rangefinder (about $40) on ebay which has this Planar clone. While I cannot change lenses, for a fraction of what it would cost to but the G-45mm F2 optic, I have a camera that produces amazingly sharp images.

Peter K

From Rollei Mailing List;
Date: Thu, 25 Jan 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] five element 2,8 Xenar

you wrote:

>I was looking through a book I just received called Kodak Lenses which
>gives lens and shutter data. The issue is from 1952. On one page is a
>description of the Anastar lens 80 mm/f3.5 for the Kodak Reflex TLR. This
>lens is quite similar to the 5 element Xenar described, except it is a four
>element lens, the difference being that the element closest to the film is
>not split and compounded. If it were it would be identical to the lens that
>Patric has described.  So this one is more like a Cooke Triplet with the
>extra element added between the first two elements.
>
>(]   ((   )(    |)
>
>Todd
>===========================
>
>Nope, there is a picture of the five element Xenar in the book. Maybe
>someone can translate this from german so we all can understand:
>
>"F_r die speziellen Zwecke der Universal-photograpie mit kleinen
>Bildformaten (bis 6x6 cm) haben wir ausserdem eine Sonderkonstruktion, das
>Xenar f:2,8 geschaffen, in der Form eines f_nflinsigen, halbverkitteten,
>unsymmetrischen Anastigmaten von besonders hoher Lichtst,rke und bester
>Koma-korrektur. Hier_ber steht ein Sonder-prospekt auf Anforderung zur
>Verf_gung.
>
>Unsere Xenare werden regul,r in Normalfassung oder Verschluss geliefert, in
>
>vielen Brennweiten auch mit Frontlinsen-Einstellung." (25 Jahre Schneider
>Optik, page 32.
>
>The lens looks like this in the pic:
>
>(]  ((  )(  )()
>
>and the book says it comes in 50 mm and 75 mm.
>
>/Patric

The lens in the Kodak Reflex is a variation of the "dialyte" type, a four element air spaced lens. It has front element focusing. There are many other lenses of this genric type. The Goerz Celor, Dogmar, Artar; the Kodak 203mm, f/7.7 Ektar, all Kodak 70 series lenses of the pre-ww-2 era; the Pentac, the Unofokal, and a bunch of others.

The type was first proposed by von Hoegh, of Dagor fame, who derived it from the Dagor by making one element an "air lens". It can also be derived from the triplet by spitting the center negative element in two and putting the halves on either side of the stop. I belive H.D.Taylor actually proposed this in his patent (but don't have a copy). The design can be either symmetrical or slightly asymmetrical, the later aollowing better correction of coma for distant objects. The design results in a lens of somewhat limited coverage but excellent correction and corrections which are relatively stable with subject distance (this is why an Apochromatic Artar is still excellent at infinity).

The Xenar as described above may actually be based on an idea similar to the Ernostar, with a negative meniscus lens in the front air space. Kingslake mentions this somewhere as one approach to increasing the aperture of a Tessar type lens. It would be interesting to know more about it. Splitting elements is a way of reducing spherical aberration. Spherical is proportional to the curvature of the elements, or rather, the angle at which the light hits the surfaces. By getting a give amount of power with two or more lenses the curvature of each is reduced so the overall spherical is reduced. This trick has been known for a very long time but not much practiced before lens coatings became available. Spherical can also be reduced by increasing the index of the glass (which reduces the curvature for a given power), one reason why modern lenses are better than similar older designs, but such glass was either not available or very expensive in the days when most of the classical lenses were designed.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Fri, 26 Jan 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] OT - An old Kodak Lens

you wrote:

>I've been reading where one of you all has a great big book on Kodak lenses.
>I believe it was Todd.  Perhaps you folks could tell me what I might have
>here.  It's a Kodak "Wide Field" Ektar F/6.3 190 mm mounted in a "No. 4 Acme
>Syncro Shutter".  The shutter has speeds from what appears to be 1 to 150
>and because the shutter is sticking, I don't know if these times are
>factions of a second or seconds.  It does have "M", "F" & "X" flash syncro.
>On the shutter band it says "Made in U.S.A. by Ilex Optical Co. Eastman
>Kodak Company, Rochester, New York.  I am wondering if this was used as a
>process camera lens or a view camera lens.  Any ideas?  .  I discovered this
>in an old box at work, which also contained an old Weston light meter, a
>Speed Graphic, a Crown Graphic and about twenty or so 4x5 film holders.
>Yippee!!!

Junk! I'll take it off your hands for no charge just so it won't be cluttering up your studio.

The WF Ektar is a double Gauss type lens (four air spaced elements, all surfaces concave to the stop) with coverage of around 80deg at infinity, not quite wide angle. These are very sharp lenses, corrected for lateral color, as are all Ektar lenses. The 190mm will cover an 8x10 without movements. They are single coated.

The shutter is an Ilex Acme Synchro shutter. Ilex shutters were very widely used on large format lenses. They are intended to operate without any lubrication. Your shutter is sticky because it got lubricated and the lubricant has oxidized becoming gummy. The shutter can be cleaned with lighter fluid which should free it up. Ilex shutters are not particularly accurate but are fairly reliable when clean.

I suggest getting the little shutter tester offered by Calumet. They were around $80 last time I looked. These are vaulable for any camera since they will tell you exactly what the shutter is doing.

I've found that a lot of Kodak lenses, and actually many others, develop a coating of haze on inside surfaces. This is visible if a flashlight is shown through the lens. Although it may not appear too dense visually it is devestating to contrast. The haze cleans off with any sort of lens cleaner.

I am not sure of the construction of the cells of the WF Ektar but it will have either a threaded back cap or a front retaining ring. The front ring can be removed with a friction tool made of any tubular thing the right size with double stick tape around its edge. This is used to unscrew the ring. If the threads for the ring are painted over you can remove the paint with Acetone applied carefully with cotton swabs. The difference in contrast after cleaning a hazy lens is astonishing.

These are excellent lenses, built in the period when Rudolf Kingslake was running Kodak's lens department.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: rec.photo.equipment.large-format
Date: Sun, 28 Jan 2001
Subject: Re: Brass Barell Lens Recommendations

benmarks@aol.com (BenMarks) wrote:

>Does anyone have a recommendation for a brass barrel lens with plenty of flare
>and/or coma wide open? I recently saw a (dented!) Voitlander Heliar on e-bay
>that fit my needs (but the price zoomed out of all proportion to anything I
>would consider paying).
>
>Lens should cover at least 5x7 wide open (but preferably 8x10).
>
>Personal anecdotes welcome!
>
>Ben Marks

I wonder what you really want. The Heliar is a very high performance lens. If its in good condition it will have little abarration of any kind.

Coma is one of the most disturbing aberrations, it is very ugly, so its at the top of the aberrations designers try to get rid of.

Most older lenses were designed to reduce flare by eliminating glass-air surfaces. Its only since c.1947 that modern coatings have encouraged designers to used "air lenses" for better correction. Most of the more flary of the old lenses are so because the designer took advantage of air spaced elements for better correction. They may be flary but are also very sharp.

If you want the effect of coma use the rear half of a Dagor. The cells of a Dagor are not corrected for coma, the symmetry of the combined lens being used for that correction, the single cells have _lots_ of coma.

If you are trying for an "authentic" look be aware that at no time in the history of photography were really awful lenses used. Even the earliest Wollaston mensicus lenses had resonable performance at the stops used. Have a look at Daguerreotypes and early wet-plate photos, they are usually exceptionally sharp, that sharpness is the authentic look.

For photographic purposes a desk magnifier will exhibit all the aberrations but will not have much flare since it has only two surfaces.

Brass barrels don't necessarily mean poor performance, some of these old timers are quite surprizingly good.

---
Richard Knoppow
Los Angeles, Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Sun, 21 Jan 2001
From: Eric Goldstein egoldstein@usa.net
Subject: Re: [Rollei] Planar, Heligon, Xenon, Xenotar...

J Patric Dahl,n wrote:

> I have a couple of Kodak Retina cameras with Heligon and Xenon lenses. Are
> they of the same type as the Xenotar and Planar?

Hi Patric:

They are different designs than the Xenotar and Planar. Kingslake attributes the Xenon to A. Tronnier (1925) based on the unsymmetrical six-element double-gauss type. The original Rudolf Planar of 1896 was a symmetrical double-gauss, but a later design is/was used in 'Flexes based on a five element design. The Xenons (and Heligons) are convertible lenses, with interchangeable front elements available which change the focal length of the system.

> Does anyone know which is the better lens of the Heligon and Xenon? Or are
> they the same, just different brands?

My understanding is that they are virtually the same design executed by different firms (Rodenstock and Schneider respectively) but the interchangeable lens elements cannot be mixed between the manufacturers.

I shoot the f/2 and f/2.8 Xenons in the 50 mm fl (IMO the Longar and Curtar are not great performers) and I really like the character of these fine lenses... retina cameras and these lenses are very under-appreciated and makes a wonderful alternative to the Rollei 35s for substantially less money...

Eric Goldstein

From Rollei Mailing List:
Date: Sun, 21 Jan 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Planar, Heligon, Xenon, Xenotar...

you wrote:

>Hello!
>
>I have a couple of Kodak Retina cameras with Heligon and Xenon lenses. Are
>they of the same type as the Xenotar and Planar?
>
>Does anyone know which is the better lens of the Heligon and Xenon? Or are
>they the same, just different brands?
>
>/Patric

I have no idea of the relative quality. Both are six element Biotar types. The Biotar is a somewhat asyemmetrical development from the original Planar. There were a number of similar, but not identical, lenses sold under both names (including some seven element Xenons). Xenon is a Schneider trade name, Heligon a Rodenstock trade name. Kodak bought lenses from both for the Retina camera, which BTW, has a pretty good reputation. There may well be a Retina list somewhere, there are certainly Retina clubs. The Retina was built by the former Nagle Werk, bought by Kodak c.early thirties.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List:
Date: Sun, 21 Jan 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] five element 2,8 Xenar

you wrote:

>I have a book from Schneider-Kreuznach from 1938, and it says that their 2,8
>Xenars for small format up to MF 75mm have FIVE elements.
>
>I will get a Rolleiflex 4x4 from 1938 soon, and it has a 2,8/60mm Tessar,
>and I assume that it has four elements. I wonder why the 2,8/80 Tessar on
>the 6x6 2,8A had four elements when Schneider used five elements for some
>extra corrections on their Xenar?
>
>/Patric

I think you are confusing the Xenar with the Xenotar. Xenars have always been Tessar clones wit four elements. The Xenotar is a five element lens derived from the Planar by air spacing one of the cemented elements and combining it with another. The idea was to get some additional degrees of freedom over the Tessar for lenses faster than those at which the Tessar performs well, but still be less complex than the Planar/Biotar type.

Although Tessars have been made as f/2.8 lenses for decades the design really is not at its best at speeds above f/3.5 and for larger sizes f/4.5. The focal length of the 4x5 is short enough so that the faster lens may be satisfactory there, but probably a five or six element lens would be noticably sharper, especially when opened up to larger stops.

Air spacing was avoided until good coatings became available. Older designs (pre WW-2) were compromised to reduce flare so lots of cemented surfaces were used. Air spacing often allows better correction but flare goes up quite rapidly with the number of elements so it was not until c.1950 that advantage was taken of the benefits of air spacing.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From: Godfrey DiGiorgi ramarren@apple.com
Newsgroups: rec.photo.equipment.35mm
Date: Mon, 12 Mar 2001
Subject: Re: Elements and Groups

A modern photographic lens is made up of several individual lens elements, some cemented together. Cemented elements constitute a group. So, for instance, the classic Zeiss Tessar optical formula is a four element design with three groups because two of the elements are cemented together.

The reason for more elements of different curvatures and dimensions, different glasses, is to improve the correction and image the incoming light as accurately as possible at the focus plane. Poorly designed or manufactured, yes, transmission losses and inaccuracies of the individual elements can harm the output image, so a 4 element Tessar, properly executed, can outperform a poorly designed/executed 6 element competitor. It's hard to make generalizations as, like with all other technologies, specific parameters and goals mean compromises of various kinds. Speed, focal length, size, cost, complexity of the assembly all have a hand in the total design and manufacture of a particular lens.

Taking as example a 40mm "normal" lens, a 3 element (Cooke triplet) can do a good job, but a 4 element Tessar does a much better job of correction. The premium lenses which can achieve fast speeds (f/2.8 and faster) generally require 5 to 7 elements for proper correction at all apertures and focus settings.

If you are interested in this subject, there is a HUGE amount of literature available on optical design and photographic lenses which any web search engine can help locate for you. It's a fascinating study.

Godfrey

Michael Henry wrote:

> Hi All,
>
>         I'm just beginning in photography and have a few questions
> about elements and groups (w.r.t. lenses). What is the definition
> of elements and groups? Is the total number of pieces of glass
> in a lens the product of these two numbers?
>
> What are the implications of more elements? more groups?
>
> I would imagine the more glass in a lens the more distortion and
> less light allowed through the lens. Is this assumption correct?
>
> Thanks,
>
>         Michael

From Rollei Mailing List:
Date: Tue, 13 Mar 2001
From: David Seifert dseifert@zyan.com
Subject: Re: [Rollei] slight OT : 4-element vs. 6-element 'standard' lens

I agree that the absolute test would be a full set of bench tests with contemporary lenses. That being said, perhaps something can be learned from studying the test reports from the current Zeiss lineup where such lens types are available. Specifically, the 45/2.8 Tessar and the 50/1.4 Planar for the current Contax SLR cameras. There are full test reports on these lenses at the Zeiss website (www.zeiss.de). I have taken a look and it appears the 6 element designs show substantially better performance (higher MTF) wide open but this advantage all but disappears when stopped down to f/5.6. Curiously, the Tessar shows signficantly less light falloff and less distortion.

Can one draw any conclusions about the 75/80mm TLR lenses bearing these appellations from these observations? Maybe, maybe not but it sure makes for fun speculation.

David

----- Original Message -----
From: bigler@ens2m.fr
Sent: Tuesday, March 13, 2001
Subject: Re: [Rollei] slight OT : 4-element vs. 6-element 'standard' lens

> Until somebody actually measures the different MTF values for a
> Tessar/Xenar vs. a Planar/Xenotar on the same vintage R-TLR, there
> will always be some uncertainties about the interest of spending extra
> money in a 5 or 6 element lens vs. a 4-element lens for general
> photograpy, when all lenses are closed to f/8-f/11.
>
> To add some quantitative information to this debate, may I recommend
> to compare the MTF charts published by Schneider Kreuznach for their
> 150mm (standard for 4"x5") view camera Xenar (4-element) and
> Apo-Symmar (6-element) lenses ?
>
> http://www.schneiderkreuznach.com/foto/sr_ap/sr_ap.htm
>  http://www.schneiderkreuznach.com/foto/sr_ap/pdf/SR_AP_56_150_R39105_2AD.PDF
>
> http://www.schneiderkreuznach.com/foto/xr/xr.htm
> http://www.schneiderkreuznach.com/foto/xr/pdf/XR_56_150_R36660_2AD.PDF
>
> From these charts (I assume they are simulated/computed and not
> actually measured) it is quite obvious that the 6-element lens is
> better and may worth the extra money you have to pay for it.
> Unfortunately for our R-TLR debate, the design for view cameras is
> quite different from a R-TLR lens design since view camera lenses are
> never used wide open but always stopped to f/11 or smaller. Moreover
> the question of shifting/tilting is irrelevant for a R-TLR and thus
> one of the well-known limitations of the Tessar/Xenar design, i.e. the
> lack of field coverage above ~57 degrees of angle, very obvious on
> Schneider's MTF charts, is not really relevant either for the R-TLR.
>
> --
> Emmanuel BIGLER
> bigler@ens2m.fr

From Rollei Mailing List;
Date: Sun, 25 Feb 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Which camera for Heidi

you wrote:

>ShadCat11@aol.com wrote:
>
>> My Y'mats ranged from good to poor, but even Rollei lenses vary.
>
>
>All lenses of this vintages varied between samples, often dramatically.  Hand
>grinding, fitting and matching was the order of the day, and tolerances  were
>much less stringent than today. It was reported in the photographic press  of
>the day and well into the 60's...
>
>
>Eric Goldstein

What hand grinding? Lenses were made on machines many at a time. Cemented surfaces were lapped to match individually but no hand polishing was done.

Centering is partly hand work. Centering of two accuracies were done. Air spaced lenses were often centered by simply clamping between two tubes and grinding the edges. Cemented elements were centered by sticking them on the end of a tubular tool and rotating slowly while watching the reflections though a telescope. The lens was pushed around on the tube until the images stood still. Then the element was clamped as above, and edge ground so that the edge was concentric and coaxial with the optical axis.

The main variation in old lenses is probably in glass characteristics. The designer assumes a certain value of index and dispersion (or v value) in making the design. If either varies much the corrections go to hell. One of the most important improvements in modern lenses is the improvement in reliability and consistency of glass.

For those interested and willing to do some searching the manufacturing techniques for lenses are covered in a couple of books published in the late thirties and late forties by Adam Hilger & Co. I don't have the specific titles.

Also, the manufacturing process at Zeiss Jena is covered very completely by post war reports by American and Brittish intellegence teams. I have some citations, but would have to really dig for others. These reports are hard to find. AFAIK the only complete (?) set is at the Library of Congress and you need to find a knowlegible librarian to help find them. These teams investigated all German industry. There is some pretty interesting stuff there if you can stand explaining what you want about fifty times. I have a little of the Zeiss information, and much more on various sound recording apparatus that I gathered years ago, in practcally another life, for a microphone history I wrote for the Audio Engineering Society.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Tue, 27 Feb 2001
From: Marc James Small msmall@roanoke.infi.net
Subject: Re: [Rollei] OT Voigtlander Lens

Gregory Fraser wrote:

>I read somewhere that Voigtlander was
>the first company to mathematically design their lenses. Anyone know if  this
>is true?

Well, in a sense, yes. The first mathematically designed photographic lens was the Petzval Portrait Lens, produced in the 1840's. Petzval licensed the Voigtlander firm in Vienna to manufacture the lens. The Petzval Portrait Lens became an overnight success, leading to the ennoblement of the Voigtlander family by Emperor Franz Joseph. It also caused Voigtlander to forget to pay Petzval his commission and, this being before "long-arm" jurisdictional statues, it also caused Voigtlander to move from Vienna to Braunschweig where, in turn, it engendered Franke & Heidecke.

So, it might be more accurate to say that Voigtlander stole the first mathematically designed lens!

Marc

msmall@roanoke.infi.net

From Rollei Mailing List;
Date: Tue, 27 Feb 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] OT Voigtlander Lens

you wrote:

>Can anyone tell me how the 1950's Voigtlander lenses compared with their
>peers? I have a Bessamatic with a 50 mm Color Skopar and a 35 mm Skoparex
>that seem to me to take extremely sharp pictures yet they don't seem to  go
>for very much money in today's market. I read somewhere that Voigtlander  was
>the first company to mathematically design their lenses. Anyone know if  this
>is true?
>
>Greg Fraser
>Technical Support Officer
>Canadian Commercial Corporation
>London, Ontario Canada

Can't answer for the quality other than the brand has a reputation for excellence.

The first Voigtlander lenses were those designed by Joseph Petzval. Petzval was a mathematician and developed an understanding of some of the optical theory needed for photographic lenses. He devised two types of lens and took the designs to Paul Voigtlander. Unfortunately, Petzval had no contract with Voigtlander and he essentially stole the designs. Petzval's lens was the first well corrected flat field lens good speed.

Many projection lenses to this day are based on this design.

Probably the first systematic study of the principles of lens design was conducted by von Seidel around 1850. The seven primary aberrations are called Seidel aberrations after him. Petzval predated Seidel, he derived the requirements for making a lens with a flat field around 1840.

For those interested in the detailed history of photographic optics I very highly recommend

_A History of the Photographic Lens_ Rudolf Kingslake, 1989, The Academic Press ISBN 0-12-408640-3 This book may still be in print. It is relatively non-technical and very well written. About one third of the book is composed of single page biographies of some of the pioneers in optical design.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Tue, 27 Feb 2001
From: David Morris davidrobertmorris@lineone.net
Subject: Re: [Rollei] OT Voigtlander Lens

you wrote:

>Can anyone tell me how the 1950's Voigtlander lenses compared with their
>peers?

I recently compared a Voigtlander Vito B Color Skopar f3.5 50mm with the f1,8 50mm Rollei Planar. There was a slightly better definition to the Planar at the edges of the picture in very small details. However, there was a slightly more attractive tonality to the Color Skopar. I was impressed with the Voigtlander as the Planar was twenty or thirty years younger and has more elements etc.

David Morris

From Rollei Mailing List:
Date: Sat, 24 Mar 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Optics question

you wrote:

>Hi!
>
>I've just seen a large format camera with a "Dialytar" lens. Has anyone
>heard of this lens? Can it be an early "Planar" type lens?
>
>And a silly question I've had in my mind for years:
>
>Why is it so difficult to make lenses with large openings? Why is it
>impossible to just use larger lens elements? I mean, a +5 close up lens  is a
>+5 close up lens even if it's in different mounts, 29mm or 72mm.
>
>/Patric

Dialytar is a trade-name used by Julius Laack Sohne of Rathnow Germany.

There are several types listed under this name:

f.3.5 and f/4.5, Celor (an actual Dialyte)
Dialytar P, a Cooke triplet type.
Dialytar T, a Tessar type.
Dialytar Wide Angle, A double Gauss of the Homocentric type.

A Dialyte is a generic type which is a four element air spaced type where the elements are not "bent" , that is each is either double convex, double concave or has one plano surface. The Double Gauss lens sometimes known as a Homocentric is also a four element air spaced lens but all the surfaces are concave to the stop. The famous Kodak Wide Field Ektar is a Homocentric type lens.

Dialytes were widely used as process lenses, the Apochromatic Artar is a dialyte.

The Celor, mentioned above, was an early version. The type was invented by Emil von Hoegh, the inventor of the Dagor. He reasoned that he could replace one of the cemented elements of the Dagor with an "air" lens. The result was the Celor. This type of lens has very little zonal sperical aberration, so it performs well even wide open. However, it has rather narrow coverage, perhaps 50 degrees, and the coverage does not get larger as the lens is stopped down.

While the original dialyte was a symmetrical lens they can be made somewhat unsymmetrical can improve the performance for distant objects. Examples of somewhat unsymmetrical dialytes are the Kodak f/7.7, 203mm Ektar (and its predecessor the No.77 Kodak Anastigmat), and the Goerz Dogmar. All of the old Series 70 Kodak Anastigmat lenses are dyalite types.

These lenses generally have excellent color correction so were popular for color work.

I have no idea of the relative quality of Laack lenses, perhaps someone on this list has had experience with them, or knows something of the history of the company.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From rollei mailing list: Date: Mon, 19 Mar 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Rollei f3.5 Lenses

you wrote:

>Hello Everyone-
>
>I see that the post-war Rolleis were furnished with a variety of f3.5
>lenses; the Tessar, or course, but also the Zeiss Jena Triotar, and the
>Schneider Xenars and Xenon.
>
>How do these lenses compare among each other? (leaving the Planar and
>Xenotar out of the discusion). Are the 3.5Tessar, Triotar, and Xenar
>essentially equivalent optics from different sources? Was the Xenon a
>premium offering relative to the other 3.5 lenses.
>
>Ed Balko

The Tessar is a four element lens and the Triotar a three element lens. The performance of the Tessar is superior, at least at larger stops. The Triotar was offered only on the Rolleicord, never on the 'flex.

The Schneider Xenar is a Tessar type lens. They were offered after WW-2 when Zeiss could not supply enough Tessars. While there is some controversey (similar to the Planar-Xenotar thing) Xenars are probably the equal of the Tessar, the ones I have are very sharp lenses.

Someone asked just today about Xenon lenses on Rolleis. AFAIK they were never used, at least on production cameras. The Xenon is a fast Biotar (six or seven element) lens. Most of them are f/2 or f/1.5 lenses for 35mm still cameras and motion picture cameras.

There is one Rollei which used an f/2.8 Zeiss Biometar, a five element lens similar (maybe identical) to the five element Planar but made at the Jena factory and reputedly of excellent quality.

The advantage of a Biometar, Planar, or Xenotar is that its performance is better when near wide open. Tessar type lenses have considerable coma until stopped down about two stops from maximum. The more complex lenses also do better when stopped down but are better near wide open.

Triotars, and other Cooke type triplets, tend to have over all spherical aberration which results in a somewhat soft focus effect until stopped down maybe three stops. The Tessar is considerably better this way although a good Triplet (and the Triotar was a good one) are quite sharp at around f/11.

If Rollei did use a Xenon on other than a 35mm camera I would sure like to know. I've managed to hide the appropriate volume of Prochnow from myself (or else the Pixies are looking at it) so I can't double check.

BTW, I strongly suspect the Pixies since I found a long lost jack knife this morning. They tend to trade things back and fourth. The Pixies who hang around here are probably interested in photography and like to read my books. I don't mind as long as I get them back. I have no idea of what they needed the knife for but it was in good condition when returned.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Tue, 20 Mar 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Re:(OT) Xenon ?

....

Kingslake gives a time line something like this:

1896, Paul Rudolph invents the Planar. It is a symmetrical double Gauss type lens but with the negative elements compounded in order to get the effect of a high dispersion glass not available at the time. He thickened these elements and reduced the air space between them in order to suppress excessive spherical aberration and reduce astigmatism. The name refers to the very flat field.

1920, Horace W. Lee, of Taylor, Taylor, and Hobson designed an f/2 lens by making the Planar unsymmetrical and using high index crowns. This lens was known as the Opic but was not popular because it was offered as just another catalogue lens.

1925, Tronnier, of Schneider designs the f/2 Xenon.

1927, Willy Merte, of Zeiss designs a series of lenses known as the Biotar in speeds of f/2 to f/1.4, the faster lenses being for 16mm motion picture cameras.

1931, H.W.Lee designs the TT&H; f/2 Speed Panchro for professional motion picture cameras.

1933, Max Barek designs the f/2 Summar for Leitz.

There was an f/1.5 version of the Xenon, with seven elements, designed for, or maybe by, Leitz for the Leica camera. Marc has some history about this. By memory it was a co-operative effort to get something which would match the f/1.5 Sonnar. The lenses were sold as Leitz Xenons, I don't know who actually made them.

The famous Kodak Aero-Ektar lenses (c.1944) are seven element Planars, designed by George Aklin. These were intended for night reconnaissance photography using flash bombs.

There are a perfectly enormous number of Planar type lenses. For some reason the generic name of Biotar is often used for these despite Lee's Opic being the first unsymmetrical version. Perhaps simply because it is a better known name.

...

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Tue, 13 Mar 2001
From: Eric Goldstein egoldstein@usa.net
Subject: [Rollei] Re: slight OT : 4-element vs. 6-element 'standard' lens

David Seifert wrote:

> I agree that the absolute test would be a full set of bench tests with
> contemporary lenses.  That being said, perhaps something can be learned  from
> studying the test reports from the current Zeiss lineup where such lens
> types are available.  Specifically, the 45/2.8 Tessar and the 50/1.4  Planar
> for the current Contax SLR cameras.  There are full test reports on  these
> lenses at the Zeiss website (www.zeiss.de).  I have taken a look and it
> appears the 6 element designs show substantially better performance  (higher
> MTF) wide open but this advantage all but disappears when stopped down  to
> f/5.6.  Curiously, the Tessar shows signficantly less light falloff and  less
> distortion.

In 35 mm and particularly with modern glass, the only advantages to designs more complex than Tessar-type construction is increased speed. This is less true for MF however, where coverage/corner resolution becomes more of a challenge with greater film area and the need to fabricate larger lens surfaces. Look for peak performance of MF Tessars at around f/11 and lower numbers away from the center than on 35 mm designs.

Eric Goldstein

From Minolta Mailing List:
Date: Sun, 22 Apr 2001
From: miata93@home.com
Subject: Re: Floating Elements (was Rotating front element on fixed lenses?)

--- In ManualMinolta@y..., Christian Deichert torgophile@y... wrote:

> Was out shooting with my MD W.Rokkor 24mm f/2.8 when I realized for the
> first time that the front element, and therefore any filter, rotated
> during focusing.  (Have owned the lens more than a year; can't believe
> I haven't noticed until now.)  I then checked out all ten of my lenses
> (all fixed length) and discovered that my MD Rokkor-X 20mm f/2.8 also
> has a rotating front element.

According to my Shipman Book, the following lenses have a floating element optical system:

17mm f/4 MD
20mm f/2.8 MD
24mm f/2.8 MD VFC
28mm f/2 MD
35mm f.2.8 Shift CA
(note that your 24mm f.2.8 is not included but this may be due to the date of the book (copyright 1980) or an error in the book (would not be the first one we have found).

Part of the description:

"An improvement in lens design, called the floating focusing system, changes the spacing between lens elements as they move along the focusing helecoid. In other words, the lens elements do not move in unison. Some appear to "float" in relation to others. This reduces aberrations at close focusing distances with short-focal-length lenses. Minolta uses the floating system in some lenses with focal lengths of 35mm or less, as you can see in the accompanying table. [Note: these are the lenses I listed above.] This improves image sharpness with close subjects and is especially beneficial at full aperature."

This seems to cover most of the lenses mentioned in this thread.

Ken

From Minolta Mailing List:
Date: Sun, 22 Apr 2001
From: "Ze'ev Kantor" zeevk@netvision.net.il
Subject: Re: Re: Floating Elements (was Rotating front element on fixed lenses?)

Hi,

To distinguish between "floating-element' and regular lenses you have to observe if while turning the focusing ring both the front and rear elements rotate together. If they do so - this in NOT a floating element lens. If the rear element moves back / forward but does not rotate - this is a "floating-element" lens.

Ordinary lens is constructed as a one-peace, that has to be moved forward / backward in order to focus. This is achieved by a rotating outer collar that swings on a static multy-thread helical (connected to the lens bayonet). This is the reason for the common " rotating front element" - actually, the whole optical assembly is rotated.

In a floating element design, in addition to the regular arrangement, the rotating main block has an additional helical (wit different pitch) and a rear optical group that is moving on a straight guides, propelled by the rotation of the secondary helical. Thus the rear floating element does not rotate. There are some very rare floating element designs, that work in opposite arrangement -resulting in a non-rotating front element. This is generally the case with macro lenses - like my MD 50/3.5.

BTW, the Mc/MD 24/2.8 is a floating element lens.

Ze'ev Kantor, Photographer
http://members.nbci.com/zeevk/

From Rollei Mailing List;
Date: Tue, 24 Apr 2001
From: Marc James Small msmall@roanoke.infi.net
Subject: [Rollei] A Very Brief Primer on Lenses

Jim Hemenway wrote:

>I'm very happy with my 2.8F. It is said to do a better job wide open
>than the 3.5s but I don't think that you'll notice much difference
>unless you print very large and maybe not even then depending on the
>aperture used
>
>The 2.8F has the mirror in the WLF, I don't know about the others.

Well, "received wisdom" is that the 3.5 Planar or Xenotar will outperform the f/2.8 lens save, obviously, for apertures wider than 3.5. But I have concentrated on the 2.8's for some years now, and a GX is my daily driver, having even supplanted my much-beloved collection of Leica RF's. In general, it is probably fair to assess the capacities of the lenses along the following schemata: j

Triotar Zeiss three-element lens. Okay, but not a sterling perfomer. Used in Rolleicords to the III.

Tessar/Xenar Zeiss or Schneider. Four element lenses from an epic design. These can be further broken down:

Uncoated Jena Tessar a landmark lens in a landmark camera, but the performance will be soft at wider apertures and will lack the fine resolution of later lenses. Good contrast, though. Used on all "big" Rolleiflex cameras from the original Standard through the Automat, Type III, and on the original "Black Baby".

Coated Jena or Oberkochen Tessar Coating improves contrast in contre-jour conditions. A fine lens. The Oberkochen lens was possibly a VERY slight reworking of the original design, though I've not seen any difference in performance. Used from the Automat, Type III, to the 3.5B/MX, and on the 2.8A. A recomputed version of this lens was used on the Rolleiflex T.

Xenar Schneider's version of the Tessar. Similar capacities. Used on the 3.5A and B, the Rolleicord IV, V, and Va, the Rolleimagics, the Postwar Babies, and on the final run of the T's.

Planar Five-element Zeiss lens, an epic design. Used from the 2.8C to the current GX and on the 3.5C/MX-EVS to the 3.5F. A Jena version of this lens, the Biometar, appeared briefly on the 2.8B. The 3.5/75 Planar was recomputed to accomodate a sixth element to improve edge definition and illumination from lens s/n 2,753,002 in the 3.5F, Type 3, and on the 3.5E3.

Xenotar A Schneider lens similar in performance to the Planar, though of slightly different construction. All Xenotars used in the 3.5F, Type 3, and the 3.5E3 were of six-element design similar to the recomputation of the f/3.5 Planar.

There was also a Distagon used in the Weitwinkel-Rolleiflex and a Sonnar used in the Tele-Rolleiflex.

Marc

msmall@roanoke.infi.net

From Rollei Mailing List;
Date: Wed, 25 Apr 2001
From: "Aaron M. Reece" areece@intelos.net
Subject: [Rollei] Re: A Very Brief Primer on Lenses

An excellent rundown, Marc. Two minor points:

1. The Rolleicord III was the first 'cord to use the Xenar, not the IV.

2. For the usage the original poster has in mind, a better question that "Which lens is best?" might be "Which lens best suits my particular photographic vision?" The original poster should consider whether he often shoots wide open for the sharp-foreground, blurred background effect that is so popular in portraiture. If so, a 2.8 Planar or Xenotar would be the best bet. If he works mostly at f/5.6 or smaller, a Tessar or Xenar would be worth investigating; I own a Rolleicord III with Xenar; when used at f/5.6 or smaller aperture, the sharpness is plenty good for most portraits, and the Tessar/Xenar has a reputation for imparting a certain "presence" to an image. I have seen this effect in my own photographs made with the Xenar; it's startling, in a subtle way, and I can't really explain it except to say that the photo seems to take on a three-dimensional quality which I have been unable to duplicate with any other lens/camera combination (I should point out that I have limited experience with TLRs, the Rolleicord III being my only one.)

3. OK, I thought of another one. This user also might be better off looking at the features of each TLR model, rather than obsessing about the lens. For example, in a fast-paced environment like wedding photography, my 'cord III would probably be a poor choice because it has no double exposure prevention; perhaps a pair of Automats or 2.8A's would be a better choice, since one could be reloaded by an assistant while the other is in use. Then there is the EVS question to consider, etc. etc.

Cheers,
Aaron
Fairmont, West Virginia
areece@intelos.net

From Contax Mailing List:
Date: Wed, 25 Apr 2001
From: Bob Shell bob@bobshell.com
Subject: Re: [CONTAX] Angenieur 70-210mm zoom for C/Y mount

> From: "Jiawei Ye" leafy@seed.net.tw
> Date: Wed, 25 Apr 2001
> Subject: Re: [CONTAX] Angenieur 70-210mm zoom for C/Y mount
>
> Hi Bob,
>
> Isn't the Planar supposed to be "symmetrical" too? Would you mind  elaborate
> a little on that?
>
> Thanks
>
> JY

The 100mm f/2 Planar is only semi-symmetrical. It has six elements in five groups. The three rear elements somewhat mirror the three front elements, but two are cemented rather than all being air spaced and the design shifts the rear nodal point forward allowing the lense to be physically shorter. A true telephoto, in other words. The rear element is quite close to the film at infinity focus and easily seen when you take the lens off the camera.

The 100mm f/2 Kinoptik is completely symmetrical. It has six elements in four groups with cemented doublets on both sides of the diaphragm and an air spaced front and rear element. Except for the rear group being slightly smaller in diameter, the front and rear lens groups are mirror images of each other. This was the original way to make an apochromatic lens. By having the front and rear groups absolutely symmetrical the rear group cancels out the aberrations of the front group. This symmetry, however, does not allow for shifting the nodal points, so the rear nodal point is located about where the diaphragm is, and this must be 100mm from the film plane at infinity focus, necessitating a long metal lens barrel to provide the spacing. When you take the lens off the camera you must look way down into the tube to see the rear element, and it is difficult to get to if it ever needs cleaning.

Bob

From hasselblad mailing list
Date: Fri, 6 Apr 2001
From: DBaker9128@aol.com
Subject: Re: 160mm CB Zeiss Tessar

> Has anyone any experience with this lens

Hi Dan

I have owned the 160 CB for the past couple years and have been really pleased with its performance and build quality. I would buy it again and for the price which you quoted in CDN $ I would say go for it without hesitation!

I like the fact that the 160 CB is a Tessar formula, I think it is an impressive lens on many fronts including its' high contrast, light weight and good balance on my 501 CM. My Provia F and E200 chromes just sparkle with the high contrast and the micro detail holds up really well when using my Rodenstock 3X and Schneider 8X loupes.

There are good things about Tessar designs in general (the Tessar and Biogon designs are my two favorite optical formulas) which current MTF charts don't capture, like resolution and contrast continuing to improve at F 11 to 16.

Nice features when one wants deeper depth of field using a MF telephoto without the concurrent diffraction limitations and performance slippage of lenses with a higher number of lens elements.

Dan if you take a look at the MTF graphs on the Hasselblad and Zeiss web sites I believe you will agree with me the 160 CB is on par in total performance with the 250 CFi and 120 CFi (in non-closeup mode). At F/8 the 160 CB matches the 150 CFi center to edge at the most important 10 LPM cycle but still lags a bit at the less crucial 20 LPM and 40 LPM cycles.

It is interesting that Tessar lenses have had such a flourish of new design activity over the past few years. In the 35 mm world both Leica with its 50 mm F/2.8 Elmar-M, Contax with its 45 mm F/2.8 Zeiss Tessar and now Nikon with its brand new 45 mm F/2.8 Tessar have and are being well received because of the considerable Tessar strengths they offer. Why not the 160 CB? I shake my head and wonder if marking the lens as a "CB" sealed its fate with the prestige oriented consumer market profile of the Hasselblad consumer. If the 160 CB had been labeled a CFi from the beginning I think its strengths would have been more valued and its sales more successful.

Doug from Tumwater

From Rollei Mailing List:
Date: Wed, 11 Apr 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Re: New lenses on old Rolleiflex?

you wrote:

>Yes, according to one expert (and I agree) the 100mm f/3.5 Ektar
>on the Medalist is one of the finest lenses Kodak ever made.
>That's why I converted my Medalist to 120 use. Ed
>
>On Tue, 10 Apr 2001, Eric Goldstein wrote:
>
>> jerryleh@pacbell.net wrote:
>>
>> > Oh, no! That was a superb lens of 5 element Heliar
>> > construction, contrary to what Rick Nordin asserts
>> > in his otherwise excellent Hasselblad Compendium.
>> > It was just as sharp as my Medalist Ektar f3.5 100mm.
>>
>> Jerry-
>>
>> That would make sense, as f/2.8 exceeds the design parameters of Tessar-type
>> lenses for MF coverage. I think the 100 mm f/3.5 Medalist was also a  Heliar
>> variant from Altman... reputed to be a great lens...
>>
>>
>> Eric Goldstein

I don't know specifically about the Ektar lenses for the early Hasselblad, if someone has any I would appreciate a verification that they are Heliar types. It shoud be fairly easy to tell by counting reflections.

The Heliar type was exploited by Fred Altman of Kodak who designed a whole series of them. The Medalist lens is one and the Enlarging Ektars are others.

The type is covered in USP 2,279,384 which is worth reading. Altman says he uses the compounding strictly for chromatic correction and differentiates this from the approach used in the original Heliar by Hans Harting. Another variation of the Heliar is the Pentac designed by Lionel Booth and described in USP 1,421,156

Another interesting patent is USP 2,165,328 issued to George Aklin of Kodak. This is for a Tessar type lens with the order of powers in the cemented rear element reversed. Aklin claims this gives superior results when high index glass is used. I believe this design was used for an f/3.7 107 mm lens made for a couple of years but replaced about 1944 with Altman's f.3.7 105mm lens, essentially the same design as used on the Medalist. Kodak used this form for some front element focusing lenses later.

An f/2.8 Tessar, perhaps the one used in the Rolleiflex and Ikoflex cameras is described in USP 1,849,681 issued to Willie Merte and Ernst Wandersleb.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Wed, 11 Apr 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Re: New lenses on old Rolleiflex?

you wrote:

>----- Original Message -----
>From: "Richard Knoppow" dickburk@ix.netcom.com
>> I believe this design was used for an f/3.7
>> 107 mm lens made for a couple of years but replaced about 1944 with
>> Altman's f.3.7 105mm lens, essentially the same design as used on the
>> Medalist. Kodak used this form for some front element focusing lenses
>later.
>
>
>I have two of these f3.7 105mm Ektars.  One made in 1941 (uncoated) the
>other in 1947 (coated).
>I had the newer one CLAed by Ken Ruth about 2 years ago.   He did an
>excellent job and this lens has produced some of the best 6x9 Velvia
>transparencies I have ever seen!
>I also had a Medalist I that I carried with me during my tour of duty in
>Germany in the early '50s (that was when I bought my Rollei MX).  The  lens
>on that Medalist was truly outstanding.
>
>Bob C.

The 107mm lens shows up in the first edition of the lens booklet included in the _Kodak Reference Handbook_ but not in later editions. I don't have a first edition here but think the 105mm lens is not in it. I don't actually know when they started making the Heliar lens. Its essentially the same lens as used in the Medalist but of slightly longer focal length. The Medallist lens is actually coated, but only on inside surfaces, since the coating process was a chemical one and not vacuum deposited hard Kodak coated internal surfaces of the Medalist lens, the lenses for the Ektra, and Eastman Ektars, the pedicessors of the Commercial Ektar. The coating reportedly will come off with ordinary cleaning. The lenses in the Medalist II are hard coated.

Kodak lenses made after about 1946 are hard coated. Most have the L in a circle trademark for "Luminized" Kodak's trade name for their hard coating.

I tried to find out exactly when Kodak started vacuum coating lenses but the old records were given to RIT and are not available, or at least were not when I asked.

Kodak made their own optical glass and commerialized the rare-earth glassed developed by the National Bureau of Standards. From the patent literature I've been able to find they didn't seem to use any of this glass in their routine lenses, I don't think there is any in the Heliar series of Altman.

Kodak's lenes of the period when Rudolf Kingslake ran the lens department (1938 to 1961) seem to be the equal of any made anywhere. From experience with a lot of Ektars for Speed Graphics, it would also seem that their QC was superior.

Kodak also made some interesting lenses for the ill-stared Ektra camera. I dont' know anyone who has a working Ektra but reportedly the lenses were excellent. Perhaps someone on this list has had experience with them.

The Ektra seems to have been an attempt at a first-class 35mm system camera. It suffered from having been released just before the outbreak of WW-2. It also looks like it might have ergonomic problems and I've also heard it had shutter problems. Again, anyone out there with actual experience?

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Wed, 09 May 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: [Rollei] Books on Photographic Optics

In my previous posts I left out a good elementary book because I had lost track of my copy. I found it. _The Photographic Lens_ second edition, Sidney F. Ray, 1992, the Focal Press, ISBN 0-2405-1329-0

This is written on a fairly elementary level, no special math is required. It discusses camera lenses and special optics like endoscopes. It is AFAIK in print and not too expensive. Its not as well written as Kingslakes books but they are hard to find and Ray's covers subjects too recent for Kingslake like autofocus. There are a few small errors in it but nothing significant.

Ray also has an elaborate advanced text _Applied Photographic Optics_ second edition, 1994, the Focal Press 0-240-51499-8

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Mon, 30 Apr 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] RE: 2.8B Biometar

you wrote:

>I have taken the 2.8 Biometar lens apart in my 2.8 B and it appears to be  a
>clone of the Xenotar, not the Planar, although it does have a different
>coating than the Planar and Xenotar. It is quite sharp.
>
>Todd
>
>Marc James Small wrote:

The f/2.8 five element Planar has a cemented pair in the first component, at the front of the lens. the Xenotar has a cemented pair as the second component. Both the f/3.5 and f/2.8 five element Xenotars have the same construction. The f/3.5 Planar has the cemented element just in back of the stop. Prochnow doesn't show a diagram of the Biometar. While you can often tell how many elements a lens has by counting reflections its pretty hard to determine where a cemented surface is, only that its there. I would be interesting to know whether the Biometar is identical to one of the Planar designs, or something else. Marc may have some idea of how much communication there was between Jena and Oberchoken.

I've seen _one_ Rollei with a Biometar. It was being sold cheap at a camera sale but I didn't have the cash at the time. I knew the lens was similar to the Planar and was tempted. I didn't know it was so rare a bird.

It would be intesting to give some of these lenses real bench tests, something more than informal inspection of aerial images or photographic testing. The latter is subject to too many errors to be definitive. Of course, that last statement also carries the implication that if variations in film flatness and camera adjustment are sufficient to mask differences in lens performance perhaps that performance difference is inconsequential.

I expect the actual prescriptions for these lenses are not public. Although there may be patents its likely the patent data is not exactly the same as the production lens.

Boy, there are more damn ways to have a horse race without horses.:-)

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Fri, 25 May 2001
From: Eric Goldstein egoldstein@usa.net
Subject: [Rollei] Re: O.T. cold light head or condenser

Bob Shell wrote:

> Ctein has written on this effect.  Narrower spectrum does make a  difference,
> even with so-called apo lenses.

So-called APO lenses vary dramatically. Some barely bring spectra together at the requisite three points, others show remarkable convergence through broad ranges of the spectrum...

There can also be significant individual variation between the same brand of process lens, as even small variance in glass batches and element finish and fit are significant at this level of precision...

Eric Goldstein

[Ed. note: the definition of APO is not fixed, but up to mfger etc.!]
Date: Thu, 24 May 2001
From: "Kerry L. Thalmann" largeformat@thalmann.com
Newsgroups: rec.photo.equipment.large-format
Subject: Re: APOchromatic lenses?

Bob Salomon wrote:

> The DIN 19040 standard, part 5, specifies that there be a "specially  high
> level of chromatic correction" but does not specify what "specially  high"
> is.
>
> For Rodenstock, at 1:1 it is a secondary spectrum reduced to not more  then
> 0.4% of the focal length.
>
> Other manufacturers may use a different percentage.

In other words, the "new" definition of APO is imprecise and completely arbitrary. How it is used is left completely up to the manufacturers based on how they choose to randomly define "a specially high level of chromatic correction". Unlike the original "old" textbook definition Richard has been citing, which is very well defined.

Thanks for clearing this up. We now know beyond a shadow of a doubt that the term APO, as used currently by lens manufacturers, has been corrupted to he point that it is completely arbitrary and meaningless for anything other than marketing purposes (which has been exactly what Richard and others have been stating all along).

Kerry
--
Kerry's Large Format Homepage
http://largeformat.terrashare.com

Date: Fri, 25 May 2001
From: sanking@hubcap.clemson.edu (Sandy King)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: APOchromatic lenses?

Bob Salomon bob@hpmarketingcorp.com wrote:

> The DIN 19040 standard, part 5, specifies that there be a "specially  high
> level of chromatic correction" but does not specify what "specially  high"
> is.
>
> For Rodenstock, at 1:1 it is a secondary spectrum reduced to not more  then
> 0.4% of the focal length.
>
> Other manufacturers may use a different percentage.

If the DIN 19040 standard used by the German lens manufacturers for defining an apochromat is indeed no more precise than what you quote above, i.e. "specially (sic) high level of chromatic correct" then it is not much of a standard. The subjective terminology allows arbitrary and self-serving use of the word, which is apparently what Rodenstock has done in marketing their lenses. A difference in secondary spectrum of up to 0.4% of the focal length (at 1:1) appears to be a very high figure. Such a difference would certianly make it very difficult to do some of the thing true apochromats were intended to do, making separation negatives for example.

Does anyone know if the Japanese lens manufacturers work to a common standard?

Sandy King

From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: rec.photo.equipment.large-format
Date: Thu, 24 May 2001
Subject: Re: APOchromatic lenses?

....(quoted above post)

I intended to stay out of this until getting some material from Bob. However, in searching my texts I have run across something which tends to substantiate his side of this. This is from a book _Physical Optics in Photography_ Georg Franke, 1966, London: The Focal Press, translated from the German.

On p.161 appears the following statement in reference to reproduction (process) lenses: "Of the aberrations, transverse chromatic is the most persistent; in this class is comprises chromatic variation of magnification, distortion, astigmatisnm, and coma. Lenses with optimum correction in this respect are often called process apochromats. It should be noted that the term "apochromatic correction" is only defined for telescope and microscope objectives and not for camera objectives."

This is an interesting statement. No reference to exactly who it is who defines telescope and microscope objectives. This may well refer to a DIN standard, given that this is a translated German text. Indeed this sounds very much like the definition Bob Salomon is quoting and, evendently, Rodenstock uses. It also suggests that for microscope and telescope objectives a much more rigorous definition exists. I do not have access to a collection of either DIN or ISO standards. There are literally thousands of them covering all sorts of things. It would be quite expensive to get copies of the ISO standards applying to optial devices of all sorts to investigate what definitions of color correction exist there. The standards are not the sort of thing libraries tend to have (although I haven't checked with Cal Tech, who just might have some of this stuff). DIN standards are in German, which helps me not since I read German a word at a time with the aid of a dictionary. My German speaking friend who used to help with this got married and moved away. In any case, I think whatever is happening here is somethign rather deeper than Rodenstock trying to prevacate (I don't think they are) or Bob trying to save a losing argument (since he might be right) but rather a case where an odd definition of a scientific term may exist, and have existed for a long time, in, particularly, German technical terminology. If so, I can't really fault Rodenstock nor Bob. However, one onders how many other presumably well established technical or scientific terms are really not univesal or nearly as well defined as we think.

To their credit Rodenstock publishes the curves for logitudinal chromatic aberraton of their lenses. The performance is obvious to anyone who is familiar with this standard type presentation. Schneider does not publish this data. I am very curious to know what their APO lenses actually are. Someone in this thread (I can't find it now) says they were told by a Schneider person that their "APO" lenses _are_ actually apochromatic. However, I wonder if this meant that they meet the same DIN standard as we are discussing or if they were asked _specifically_ if their lenses were corrected to bring three wavelengths to a common focus.

Note that Bob is right in claiming that a true apochromat might not be any better than the achromats Rodenstock is making. The reduction of secondary spectrum, which is the remaining variation in focal length with color after achromatizing, is of critical importance. It is possible for a very well corrected achromat (two colors) to be superior to an apochromat, Kingslake shows an example of such a pair in one of his text books.

The point of this long disertation is that before throwing too many rocks at Bob Salomon one should look at the data he has to work with. The problem, I am strongly suspecting now, is in confusingly written standards rather than in some misunderstanding of a technical principle.

I have no idea who wrote the DIN standard or, again what other definitions may appear in other DIN standars applying to other kinds of optical devises.

I am going to go rest my back and fingers now.

---
Richard Knoppow
Los Angeles, Ca.
dickburk@ix.netcom.com

From: slberfuchs@aol.com (Ted Harris)
Newsgroups: rec.photo.equipment.large-format
Date: 24 May 2001
Subject: Re: APOchromatic lenses?

I went round and round on this same point a year + ago and thus have stayed out of the discussion until now. I finally reached the point of frustration where I just can't keep quiet.

We all know now that Rodenstockis NOT following the strict scientific definition of apochromatic in naming their lenses. Bob has implied that Leitz and Schneider, along with Rodenstock, don't follow the strict scientific definition either. He has implied that Leitz and Schneider follow the same ambiguous DIN standard followed by Rodenstock and cited by Bob.

My recollection was quite different regards Leitz and Schnieder so I called Schnieder. Michael Claimet (sp) at Schneider verified that when Schneider uses the term apochromatic and/or apo/APO as part of a lens description or in the name of a lens that the lens fully meets the standard scientific definitionof an apochromat. We discussed teh various Schneider LF lenses on the market and Michael reiterated that those that are apochromatically corrected are so noted in the discussion of the lenses. For example, the APO Symmars and Supoer Symmar HM's are apochromatically corrected, the Super Symamr XL's are not.

For more information you can reach Michael at michael@schneider.com

He no longer follows this newsgroup, he said, because it is difficult to access from their server at Schneider USA but has promised to try and chime in here, although it will be a few weeks. You willfind that he posts frequently in photo.net discussions.

This should further clarify the record. It is not all manufacturers who have abandoned science and clarity in the name of marketing, just Rodenstock!

It wouldnot be fair, however, tonot underscore the fact that the difference between a true apochromat and a highly corrected acromat will not matter for most photographic applications.

Cheers,

Ted
Ted Harris
Resource Strategy
Henniker, New Hampshire

From: Paul Butzi butzi@nwlink.com
Newsgroups: rec.photo.equipment.large-format
Date: Thu, 24 May 2001
Subject: apochromatic

When Bob Saloman offered to send a copy of the supporting documentation for his definition of apochromatic, I sent him my address and he sent me a copy.

It arrived today. I don't particularly care about the current discussion about the definition, having long ago concluding that marketing people will pretty much say or do anything to promote their own products and denigrate those of their competitors, without shame or decency.

Still, just so everyone knows what's being discussed, I'll describe what I've got.

What I am holding is a copy of three pages from "The Photonics Dictionary", published by Laurin Publishing Company.

The complete publication apparently comprises 4 volumes:

Book 1: The Photonics Corporate Guide to Profiles and Addresses
Book 2: The Photonics Buyers Guide to Products and Manufacturers
Book 3: The Photonics Design and Applications Handbook
Book 4: The Photonics Dictionary

Not being familiar with the world of optics, I can't tell if this document is of the authoritative variety or the comic book variety. If someone knows of it, perhaps they could comment.

Included was a copy of page D-8, which contains the following definitions relevant to the discussion:

Apochromat: Also known as apochromatic lens. A lens in which the secondary spectrum has been reduced, or in which three colors have been brought to a common focus, by the use of special glasses. It usually consists of three components of different kinds of glass.

Apochromatic System: An optical system that is corrected chromatically for three colors simultaneously.

Also included as a copy of a page titled "Lenses for Copying and Duplicating". The word "Kodak" is hand written at the top of the page, so I'd assume this is from some Kodak publication.

The relevant portion reads:

"Most process lenses available today are apochromatic lenses, that is, they are designed for better correction of chromatic aberrations. They are corrected so that the images formed by light of three specific different colors all focus sharply in the same plane, which means that they are corrected for longitudinal chromatic aberration.

They are also corrected for the difference in magnification of images in different colors, an aberration called lateral chromatic aberration. Apochromatic lenses *must* be used for critical work in color copying and duplicating, and, of course, they perform well with any kind of original.

It seems to me that the common thread here is that an optical system is apochromatic when three colors are brought to a common focus.

I guess I still don't understand what the discussion is about. It seems to me that everyone agrees on the definition, with the exception of the marketing drones. No one expect the marketing drones to do anything except lie shamelessly anyway, so surely it's no surprise to find out that they've done it again.

Perhaps a more interesting and productive direction for the discussion to go in would be for someone with some familiarity with optical design (Richard, Helge?) to comment on what sort of compromises must be made to make a lens an apochromat and how those tradeoffs will affect the images made with large format cameras.

I note that some lenses which are reputed to be stellar performers (e.g. Super Symmar/XL) are not even claimed to be apochromats.

It seems to me that optical design is surely a process of trading off one thing against another - coverage, contrast, resolution, various aberrations, cost, availability of glass. The fact that a lens is apochromatic surely does not mean that it is the acme of optical design.

But the amount I know about optical design is pretty small. I understand Snell's law, I understand the lens rule. Beyond that, I get out of my depth pretty fast.

Perhaps someone could comment on the tradeoffs?

-Paul

-- http://www.butzi.net

From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: sci.optics
Date: Mon, 21 May 2001
Subject: When is an "Apo" lens not apochromatic?

Both Rodenstock and Schneider sell photographic lenses which include "Apo" in their names and are called apochromatic in the data sheets. However, at least for the Rodenstock lenses the published longitudinal chromatic focus data indicates they are achromats, not apochromats. That is, the curve has the typical curved shape and crosses zero at two wavelengths, not "S" shaped with three zero crossings as I would expect for an apochromat. The sales rep makes the claim that because secondary spectrum is well corrected for these lenses that something in the ISO-9000 standards allows the manufacturer to call them apochromats. Rodenstock does this with at least two lenses. Schneider does not publish its chromatic aberration plots so its not possible to tell if their "Apo" lenses re actually apochromats. The language in the advertising is, however, nearly identical to that used by Rodenstock, so I suspect the worst.

What I am asking for here is some help. I am strictly an amateur at optics, fascinated by it but by no means an expert by any stretch. So, is anyone out there familiar with the ISO-9000 stuff to have any idea of what this is about, and am I correct in my understanding that an apochromatic lens is one which is corrected for longitudinal chromatic aberration at three wavelengths and for spherical aberration at two wavelengths?

Am I correct that a lens corrected for only two colors is an achromat no matter how little secondary spectrum it has?

I believe that ISO-9000 series standards apply to documentation and not to scientific or technical measurements or definitions as traditional standards do, it this understanding correct?

I am looking partly for some ammunition and partly simply to check the state of my own knowledge.

---
Richard Knoppow
Los Angeles, Ca.
dickburk@ix.netcom.com

From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: sci.optics
Date: Mon, 21 May 2001
Subject: Re: When is an "Apo" lens not apochromatic?

...(see above posting)

Thanks to all who responded to my question.

Rodenstock, as I stated, _does_ publish a chromatic error curve on its lens data sheets, so there is no question of the actual performance. I seems to me, however, that calling such a lens an apochromat is somewhat misleading despite its undoubted excellence. Apochromatic is associated by photographers at least with the special lenses made for process photography (before it all became electronic) and with other special, high performance, lenses which were actually corrected for three wavelengths. In fact, these modern lenses may have less deviation from focus with wavelength than these older lenses but IMHO, another name should have been found for them. AFAIK, the use of apochromatic for microscope and telescope objectives is much better defined than for photographic objectives and definitely requires correction for three wavelengths; I may be wrong about this.

I am probably not going to pursue this beyond testing my own knowledge. It is, BTW, very helpful to have had my understanding of ISO-9000 stuff confirmed. Not much of the material on the web is clear to a non-professional.

The source for the definition of apochromatic on which the rep is depending appears to come from a book written on a non-technical level for photgraphers. I prefer the definitions in Smith or Kingslake:-)

---
Richard Knoppow
Los Angeles, Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Tue, 17 Apr 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Slightly OT: Quality of Zeiss lens design versus new CAD designs

you wrote:

>First, before starting a flame war, I want to say that I love Zeiss  lenses.
>That said, I had a discussion yesterday with my father-in-law, who has a
>huge and complete workshop for designing, milling, and constructing just
>about anything, especially metals. He has a PhD from Yale in Chemistry  and
>Physics and has been doing high-level consulting for several major  companies
>for years from his home. He has an amazing library of technical books on
>math, sciences, materials, etc.  He really knows his stuff, but he is not  a
>photographer.
>
>We got to talking about lenses because I saw a book on optics design on  his
>shelf and I asked about Zeiss lenses (being the enthusiast I am). He  pulled
>the book and showed me the original long-hand calculations that were used  to
>develop the designs for Tessars, Planars, etc. He says these are "nice,   old"
>designs, but that they are not up to new (past 10 years) computer-aided  lens
>designs.  Since super-computers can calculate the results of millions of
>variations of lens designs (elements/groups), shapes, thickness, order,  etc.
>that could not be done thirty or more years ago, he contends that CAD  lenses
>are tested in ways that the older Zeiss lenses never were. He assumes  that
>lenses designed exclusively by CAD (maybe like new Mamiya, Tamron, etc)  are
>probably better lenses.
>
>I responded that the quality of a camera lens may not rest fully on the  best
>"technical" performance, but are optimized for photos, Bokeh, tonality,  etc,
>which are subjective measures.
>
>Questions:  are newer Zeiss lenses like the Zeiss Biogon 28mm designed  via
>computer??  Are the lenses optimized electronically or do they stay  within
>the original designs from 40-60 years ago?  How about it, lens gurus?
>
>Thanks,
>R.J.

I have no idea how the Biogon was calculated. However, calculators started to be used for lens calculations in probably the late 1940's. There is no doubt that a modern computer design program can fully characterize a proposed design within a few seconds.

Lenses are calculated by calculating ray paths through them. Hand calculation takes about 30min per ray. That is reduced to about 2 minuts using a hand calculator. A pc running a design program can trace thousands of rays in a fraction of a second and display the information in many ways. An automatic program can also optimize a design, but has to be told what to optimize and watched to make sure it doesn't get stuck or specify ultra-thin elements, etc. Computers also allow the use of physical optics rather than geometric optics to design lenses. This sometimes results in a definite improvment in performance. Geometrical optics assumes that light travels only in straight lines. In fact, the relativistic actions on light may modify their paths enough to have some effect in practical calculation.

The old system was for someone whith experience and an intuition design the lens. The lens was then constructed and tested. The actual lens was then modified to improve its performance. When done carefully, this procedure probably comes very close to duplicating the results of automatic computer design although, of course, it takes much longer. The point is that the old method recognized the limits of the practical computation and used empiracal techniques to overcome it.

H. Denis Taylor, the inventor of the Cooke Triplet, wrote a book on how to design lenses using only algebraic calculation and claimed not to have used ray tracing. However, he made extesive use of optical shop models of his lenses to determine their optimum design.

As far as computers go Kodak was using them by about 1950 according to Kingslake.

Also, some older lenses perform up to very high standards. The Kodak Ektar series are hard to match even with the most modern glass.

Glass has improved both in quality and in the range of indexes and dispersions available. This results in improved performance because lenses can be made with smaller radiuses for a given power. Since the aberrations are proportional to the radius of curvature they are automatically scalled down when higher index glass is used. The glass is also cleaner.

I would say that the performance may not be that much improved over the very best lenses of the past but that design is certainly simpler and the knowledge of what can be expected from a design is way ahead of where it was in the past.

In short, new lenses are better but some old ones are just as good (or something like that).

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: rec.photo.equipment.large-format
Date: Sun, 03 Jun 2001
Subject: Re: apochromatic

Bob Salomon bob@hpmarketingcorp.com wrote:

>DIN has defined the term. Not marketers.
>
>You tell the DIN the people what you think.
>
>HP Marketing Corp. 800 735-4373 US distributor for: Ansmann, Braun,
>CombiPlan, DF Albums, Ergorest, Gepe, Gepe-Pro, Giottos, Heliopan,  Kaiser,
>Kopho, Linhof, Novoflex, Pro-Release, Rimowa, Sirostar, Tetenal Cloths  and
>Ink Jet Papers, VR, Wista, ZTS www.hpmarketingcorp.com

Just to be clear, the DIN standard does NOT constitute a definition. In fact, it doesn't even try. In fact, the definition of apochromatic used by Rodenstock is defined by Rodenstock, according to the very material you sent to me. They get away with it precisely because they the DIN standard does not have a real definition and is so vague. So, Rodenstock made up a definition, which disagrees with a definition well established in optical science. The only reason for such a thing is to be able to use the term apochromatic in sales literature.

You have claimed in the past that apochromatic as used by Rodenstock was substantiated by the definition given in the Photonics dictionary. You sent me a Xerox of the pertinent pages. What I found was the traditional, and correct, scientific definition NOT the one used by Rodenstock.

The Xerox of Rodenstock's article describes what they have done, vis: to make up a definition because the DIN standard had none.

Further more, the claim that such a vague definition is acceptable because the term apochromatic is not rigorously definied for photographic lenses although it is for microscope lenses won't wash. In fact, its defined by a century of usage.

Another fact, Rodenstock is counting on its potential customers thinking that the definition of apochromatic is the scientific one. You can tell from the published data than the lenses are not actually apo's but its stated in the data sheets that they are and the name implies that they are.

I do not have a copy of the DIN standard you refer to, nor know if it is also an ISO standard. I don't know exactly what it is supposed to cover. In fact, it may not even be pertinent to this discussion. If it is not also an ISO standard, its application outside of Germany is questionable.

The fact that Rodenstock chose to use a vagueness in a German standard to justify its use of a definition used by no one else, rather than using a well established and accepted scientific definition, does not speak well for them.

Bob Salomon is not a bad guy, but his continued attempts to justify this use through obfuscation also does not sit well.

>> From: "alan duncanson" duncanson3@home.com
>> Newsgroups: rec.photo.equipment.large-format
>> Date: Sun, 03 Jun 2001 
>> Subject: Re: apochromatic
>>
>> Bob Salomon bob@hpmarketingcorp.com wrote in message
>>>
>>> " This older definition of
>>> "Apochromatic" did not include any limits for the longitudinal
>>> aberration for other colors than the three RGB colors. So the errors
>>> could have been rather large between the "zero" points.
>>>
>> And:
>>>
>>> Today it does not matter if the longitudinal color aberration is zero
>>> for three or only for two colors or wave lengths. It is only important
>>> that the residual color aberration from about 400 nm to about 700 nm 
>>> (visible range of the spectrum) will never exceed 0.1% ... 0.2% of the
>>> focal length.
>>
>> This confirms what I suspected when I began to see a spate of new
>> (old?) lens designs claiming to be Apo.  That is that marketeers
>> were mis-using a precisely defined technical term, long applied to
>> reveared old lens designs, to sell their products.
>>
>> On the other hand, he has made an intriguing proposition, that the
>> worst case residual color error is likely to be a better indicator of
>> lens performance than the number of wavelenths at which the
>> error is zero.  While the new designs may not be true Apo's,
>> nobody is denying that they are excellent.  Is anybody so
>> distresssed to learn that their Apo-Sironar is not a true Apo,
>> that they are ready to let it go for a song?
>>
>> We curmudgeons just wish that the marketeers would not redefine a
>> hallowed old term.  Richards suggestion, "Ultra-Achromat", would
>> have been less disturbing (and probably less effective at marketing.)
>>
>> - Alan

Ultra Achromat is not my suggestion. It is an established term in optical design and has been for a long time.

Yes, I would be very distressed if a lens sold to me as an apochromatic lens turned out not to be. There are applications where true apochromatism are important.

In any case, its not quite honest to use the term for an achromat no matter how good it is.

BTW, the appeal that the term is OK becaue _lateral_ color is corrected has nothing to do with apochromatish, which referes to longitudinal chromatic aberration.

The easiest way to correct later color is by symmetry. A symmetrical lens has no lateral color when the entire optical path is symmetrical (1:1 image to object ratio) and substantial cancellation of it even at infinity focus. Lenes like the Sironar are corrected for lateral color partly by the shifting of some power to maintain the cancellation at infinity conjugates.

Even non-symmetrical lenses can be corrected for lateral color although its not so easy. The Kodak Ektar series is very well corrected for lateral color, and BTW, also for longitudinal color. These lenses were made to sell color film.

---
Richard Knoppow
Los Angeles, Ca.
dickburk@ix.netcom.com

From: "Kerry L. Thalmann" largeformat@thalmann.com
Newsgroups: rec.photo.equipment.large-format
Date: Mon, 04 Jun 2001
Subject: Re: apochromatic

Joseph O'Neil wrote:

> On Mon, 04 Jun 2001, Bob Salomon
> bob@hpmarketingcorp.com wrote:
>
> >You couldn't be more wrong.
> >
> >Schneider as well as Rodenstock use the same definition as is set by  the
> >group.
>
>                 Mea culpa, I'll go crawl back into my corner.

Joe,

I wouldn't crawl too fast.

Bob also wrote:

"The DIN 19040 standard, part 5, specifies that there be a "specially high level of chromatic correction" but does not specify what "specially high" is.

For Rodenstock, at 1:1 it is a secondary spectrum reduced to not more then 0.4% of the focal length.

Other manufacturers may use a different percentage."

As has been said over and over an over.... in this thread, and as Bob CLEARLY proves with the above quote - the "standard" used by the German lens manufactures gives those same manufacturers the ability to define the term APO any way they like. Bob has shared Rodenstock's defintion, but we have no idea what Schneider's is (could be "better" could be "worse"). They may both adhere to the same "standard", but within that standard they are free to invent their own criteria, and hence their own definition, for the term APO. Based on this standard, there can be as many "definitions" as their are lens manufacturers based on their own interpretation of "specially high". Personally, I think whoever wrote that standard (if that is indeed how it is written) must have been "specially high" at the time.

So no, the lens manufacturers do NOT use the same definition, and there is no definition set by any group. What you have is a vague, imprecise "standard" that is open to interpretation and abuse (at least based on what Bob has posted of the standard in the above quote). There USED to be a very clearly defined, easily understood DEFININITION for the term APO, now it is nothing more than a marketing term bandied about to impress naive buyers.

I'm sure Bob will disagree yet again and say that they are just following the "standard", but as his quote above proves, it's not really much of a standard, and it certainly is NOT a definition.

Kerry
--
Kerry's Large Format Homepage
http://largeformat.terrashare.com

From: slberfuchs@aol.com (Ted Harris)
Newsgroups: rec.photo.equipment.large-format
Date: 05 Jun 2001
Subject: Re: apochromatic

Yes,

Take Kerry's advice; do not crawl too fast. In fact, you may not want to crawl at all. If you tuned into this thread a few ago you will recall that, in response to Bob's original post about the DIN standard, I called Mike Klayman at Schneider US. Mike stated unequivocally that all Schneider optics designated as apocchromats meet the strict, standard scientific definition of the term. Nonwithstanding what DIN 19040 may say!

Ted

From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: rec.photo.equipment.large-format
Date: Mon, 04 Jun 2001
Subject: Re: apochromatic

.....

There is a very complete discussion of chromatic correction in _Applied Photographic Optics_ second edition, Sidney F. Ray 1994, The Focal Press ISBN 0 240 51499 8 This is recent and in print.

He talks about the mis-use of the term apochromatic with reference to lenses with substantially reduced secondary spectrum due to the use of low dispersion glasses. He says "The term apochromatic lens is sometimes used for such colour-corrected lenses, but this is not strictly accurate as they only have much reduced secondary spectrum for two wavelengths and are not colour corrected for three wavelengths." He also defines the term "ultra-achromat" as a lens with low secondary spectrum using "ordinary" glasses. I think by "ordinary" he means not using fluorite but he isn't clear about this.

I've also seen the term "semi-apochromat" used. Ray doesn't have it but I think its in Warren Smith's book on lens design. It means about the same as ultra-achromat, i.e., an achromat with low secondary spectrum.

Fluorite is a glass made from Calcium Fluoride. It has a dispersion characteristic usefull for correcting the "anomolous dispersion" of other materials, but is used with discression because it is both expensive and chemically unstable.

AFAIK, the term apochromat is clearly defined for microscope objectives, and I thought, for telescope objectives.

I suppose I should add a note about anomolous dispersion. Most people know that glass, and many other transparent materials, bend light and bend different colors by different amounts. Blue is bent more than red. This is how a prism breaks light into a spectrum. Different kinds of glass have different amounts of dispersion.

When a lens is designed it must be corrected for this effect by using a combination of positive and negative elements of different kinds of glass so that the dispersion of one element cancells that of another but leaves some power. The problem is that the rate at which the idex of refraction changes with wavelength is not quite linear. When you get near the limit of the pass band of the glass, i.e., the colors it will transmit, the rate of change of index, which is the qulity we call dispersion, starts to change very rapidly. So, especially at the blue end of the spectrum it becomes very difficult to get rid of the color fringing. Fluorite glass and some other materials, have a charactreristic which is helpful in correcting this effect. Fluorite is sometimes used in camera lenses but is mostly found in very high performance microscope objectives.

Some of the newer low dispersion glasses also help reduce anomolous dispersion without the mecahanical problems of Fluorite. Fluorite is still very useful for lenses which must be corrected into the ultra-violet range.

Lenses are generally classified as:

1, Non color corrected: The focal length varies continuously with color (becoming shorter as we move from red to blue).

2, Achromatic: Color corrected so that two colors are brought to a single point of focus. Such lenses are also corrected for spherical aberration at one color. The colors chosen for correction can be any and different colors are used for different purposes. The choice depens partly on application and partly on what glass types are available. The error in focus away from the colors corrected for is known an secondary spectrum.

3, Apochromatic: A lens corrected to bring three colors to the same focus. Generally three kinds of glass must be used. In a well designed apochromat secondary spectrum is reduced but there is tertiary spectrum, the remaining error in correction.

4, Super-Achromat: A lens designed according the method of Herzberger and McClure. These researchers found a method for correcting a lens for any desired number of colors. The term is used for a lens corrected for four or more colors. Superachromats are expensive but are useful where a lens must be corrected for both visual spectrum and into the infrared or ultraviolet, or both, without focus shift.

All of the above terms are well established in the scientific literature. They are truely not a matter for debate.

I strongly recommend reading a good text on optics to get a better idea of the terminology and definitions of the various aberrations. Practical lenses use nearly all spherical surfaces. A spherical surface can not form an image. So, the use of combinations of such surfaces to make good lenses is something of a tour de force, a really remarkable feat despite having been reduced to nearly routine.

---
Richard Knoppow
Los Angeles, Ca.
dickburk@ix.netcom.com

From Contax Mailing List;
Date: Mon, 02 Jul 2001
From: Bob Shell bob@bobshell.com
Subject: Re: [CONTAX] Contax 645

> From: "Austin Franklin" darkroom@ix.netcom.com
> Date: Thu, 21 Jun 2001 
> Subject: RE: [CONTAX] Contax 645
>
>>>> All of the 645 lenses are new designs.
>>>
>>> I assume you really don't mean design in the optical sense, a
>> Planar IS a
>>> Planar design...from what I understand, and that design has
>> been around for
>>> quite some time.  Of course they are new in and unto themselves, in  that
>>> these lenses are designed specifically for the 645.
>>>
> Yes, new in the optical sense.
>
> So, it's NOT a Planar design?

Planar is the name Zeiss uses for a class of lenses having relatively flat fields, thus the name. The original Planar was computed in 1896 by Paul Rudolph at Zeiss, and was a modified double-Gauss type, completely symmetrical. Rudolph's genius was in making the third nd fourty elements of this six element design very thick, thus reducing the air space ( responsible for increased spherical aberration in other designs) to a minimum. At the time he was working there were no glass types with sufficiently his dispersion to make an achromatic lens in this design, though, so he resorted to the optical trick of making two cemented optical doublets each made from two types of glass with identical refractive indices but different dispersion powers.

This original Planar was pretty much stretched to its limits at a maxiumum aperture of f/4.5.

In the mid-1940s Zeiss optical designers went back to the drawing board and introduced a new series of Planar lenses, this time with five elements instead of six, and no longer even remotely symmetrical. These new Planars could be stretched all the way to f/2.8 with reasonable performance, and were exceptional at f/8. The front component looks much like that in Rudolph's original Planar, but with a plane surface between the second and third elements and without Rudolph's very thick third element. The rear component consists of one thin negative element and one relatively thick rear element. The Biometar is similar in design to this Planar.

If you look at the Contax Planars, you will find that the 50mm f/1.4 is a seven element design, having little in common with either of these two earlier Planar design. The 50mm f/1.7 Planar is similar, but not identical in design. The famous 85mm f/1.4 Planar is yet another different design with only six elements. The 100mm f/2.0 is a variation on this design. The closest modern lens to Rudolph's original Planar is the 60mm f/2.8 Makro-Planar which reverts to a near symmetrical design. The 100mm f/2.8 Makro-Planar, on the other hand, is not a design like any other Planar, and looks more like a Sonnar.

So Planar is really just a name used for lenses, and not a designation of a particular optical design.

Bob

From Contax Mailing List;
Date: Mon, 02 Jul 2001
From: Mark Rabiner mark@rabiner.cncoffice.com
Subject: Re: [CONTAX] Contax 645

>Snip
> It's in some Hasselblad literature where they say that it's an OK lens  and
> was good for its day but if you are really serious about maximum modern
> quality you should buy the 100mm instead.
>
> Bob

Bob, from the Zeiss site:

"And its performance is very constant over a wide range of imaging ratios, enabling such a versatile lens variety as the Makro-Planarr lens."

Victor had the 80 Planar because with the Rolleiflex this is what the people wanted but had the 100 designed for the Hasselblad system. As far as i go though 100mm does not a normal lens make!

Somebody i made up said:
Sometimes the 80 sees wide, sometimes it sees long, but it always sees something.

As far as the 80 being an embarrassment goes, maybe for post Victor - Hasselblad but for Zeiss on their site:

"The Planarr lens is the most successful camera lens design ever created.

This nearly symmetrical layout provides the lens designer with numerous means to correct aberrations extraordinarily well, even for wide open apertures. The ideal basis for high-performance lenses with great color correction, high speed, flat image plane (this is where the name comes from) and low distortion. The Planarr lens design is the basis for nearly all professional 'workhorse' lenses on earth and in space today, with the Planarr T* 2.8/80 CFE lens being the most popular in medium format SLR photography."

Mark Rabiner

http://www.rabiner.cncoffice.com/

Date: Tue, 21 Nov 2000
From: aries@selena.kherson.ua
Newsgroups: sci.astro.amateur
Subject: Re: Fast or Slow refractor, which is harder to make?

tony_miller@my-deja.com wrote:

> Here is a question for the optics wizards. I enjoy al the threads about
> the new refractor designs and the opinions expressed by Roland, Tom
> Back, Valery, Markus and others so was wondering just what there
> thoughts are on this subject.
> Is it harder for a manufacturer to achive a good optic when making a
> fast f/5 05 f/6 scope as compared to a long f/10 or f/15 design?
> I have heard that long focal lengths are more "forgiving" but is this
> inherent in simply the fact that the focus distance is long or more in
> manufacturing tolerances that don't have to be as critical?
> I look forward to your responses.
> Tony

Tony,

This is rethorical question. Of course, fast refractor scopes are more difficult to make than F/15 ones because of tolerances. Slower scopes with F/15 also does not necessary require such exotic glasses like fast apos. Excellent apo correction can be achieved with significantly cheaper glasses and with less efforts.

If it will be any kind of demand for such objectives/scopes we will be glad to make them relatively cheap.

Valery Deryuzhin.

From Rollei Mailing List;
Date: Fri, 06 Jul 2001
From: Eric Goldstein egoldstein@usa.net
Subject: Re: [Rollei] Tessar/Planar

Phil Swango wrote:

> "Creamy?"  I like that.  That's exactly the effect I noticed in a recent
> portrait I took with a Nettar with f/3.5 75mm Zeiss Novar, shot at about
> f/4-5.6.  With this particular image it's a wonderful look.

Know just what you mean, Phil. The Novars (and Triotars) are often pooh-poohed by people who don't put film in their cameras but folks who actually shoot with the lenses are usually impressed by the different characters they achieve open and stopped down.

Eric Goldstein

Date: Mon, 06 Aug 2001
From: "Eugene A. Pallat" eapallat@apk.net
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: lenses from computers? Re: Depth of Field - 35mm vs MF

Robert Monaghan wrote:

> most of the great lens designs were paper and pencil calculations, Cooke
> triplett, Tessar, and so on (see mf/history.html and mf/elements.html);
> probably 99% of lenses in use are five or less elements - though that's
> mostly due to cost factors, and disposable cameras ;-)

Most people don't realize that it's possible to design some multiple element lenses with graphical techniques. A friend and I did several eyepieces for telescopes which were excellent.

Gene Pallat

From Rollei Mailing List;
Date: Tue, 01 May 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] RE: 2.8B Biometar

you wrote:

>I have just taken the lens apart again to confirm and I can categorically
>state that the 2.8 Biometar as found on the Rollei 2.8 B is not the same  as
>the 2.8 Planar as found on the 2.8 Rollei. The 2.8 Rollei Biometar has a
>single front element and a cemented doublet in front of the shutter -  like
>the Xenotar.
>
>You can read as many books as you like to get information and come to a
>'logical' conclusion, but there is nothing like having the real thing in
>front of you to know for certain.
>
>todd

Very interesting. That makes the diagram shown on the Pentacon site accurate despite my guess that it wasn't. Boy it would be interesting to know more about where these designs came from and whether there is any patent literature describing them. Unfortunately, the US Patent Office web site offers only patent number searching for older patents.

I think the patent room at the LA Public Library has cross references by pattentee and asignee. I will have to look for Hans Saur next time I am there.

Two of the C.G.Wynne designs, shown by Kingslake in his book on lens history, are of similar design. An f/2 lens where the cemented interface is somewhat concave toward the stop, and an f/1.9 lens where it appears to be a plane surface, as in the Xenotar. This group of designs is dated from 1944.

The Xenotar is attributed to Tronnier, USP 2,683,398 (1952). Kingslake also lists six other patents for similar lenses, all with later patent dates. He referes to the Biometar is a "well known lens of a similar type" but does not give a patent number or date for it.

None of this means that Hans Saur, or someone else at Zeiss might not have anticipated the design.

Essentially, the Planar of Rudolph was a elaborated version of the double Gauss type with compounded negative elements. Rudolph thickened the negative elements to reduce astigmatism and compounded them to improve chromatic correction, since there were no suitable glass type available. By cementing two glasses of similar index but different dispersion, its possible to get the equivalent of a glass type with a dispersion not available.

Its difficult to tell if the five element Planar/Xenotar/Unilite type are really derived from the Planar or from the original Double Gauss type, one whould have to talk to the designer to know. One reason patent literature is interesting is that sometimes the approach is described.

>Marc James Small wrote:
>
>> of the 2.8/8cm CZJ Biometar and the 2.8/80 CZ Planar OUGHT to be  identical!

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Sun, 29 Apr 2001
From: Marc James Small msmall@roanoke.infi.net
Subject: Re: [Rollei] RE: 2.8B Biometar

DAVDOU9211@aol.com wrote:

> Sharpness, etc.?

The Carl Zeiss Jena Biometar (note spelling) was the East German variant of the five-element Carl Zeiss Planar -- both lenses were constructed from designs developed before the split of the two entities. The Biometar is fully equivalent to the Planar in performance, though the lens coatings on any of the early Postwar lenses may be a bit fragile.

The deeper question, of course, is whether a rather uncommon collectible camera should be used but I leave that to the owner's disgression -- on occasion, I use some very rare gear in my own possession. Only 5,000 2.8B's were made, and this makes them one of the rarer examplars of the breed.

Marc
msmall@roanoke.infi.net

From Rollei Mailing List;
Date: Sun, 29 Apr 2001
From: Marc James Small msmall@roanoke.infi.net
Subject: Re: [Rollei] RE: 2.8B Biometar

David Morris wrote:

>>The Carl Zeiss Jena Biometar (note spelling) was the East German variant  of
>>the five-element Carl Zeiss Planar -- both lenses were constructed from
>>designs developed before the split of the two entities.
>
>I think this lens also made its way into the lens range for the roll film
>Pentacons and Exactas.  Might be a cheaper and safer way of trying it  out.

Different design. The Postwar "Planar" and "Biometar" arose from the same design work conducted by Ernst Wandersleb and Hans Sauer at Jena immediately before and during the War (well, Wandersleb was forced to quit Zeiss by the Nazi Party, as his wife was Jewish, though he was returned to employment, with back pay, after the War). In any event, Sauer developed two different designs, both derived from the 1896 Rudolph six-element symmetrical Planar, and pace Kingslake. One design, of five elements, was used in the 2.8B (Biometar) Rolleiflex and in the 2.8C (Planar) and later TLR's, while the other was used in the Pentacon Six (Biometar) and Hasselblad (Planar). In short, the Biometar used in the 2.8B is to the Biometar used in the Pentacon Six as the Planar used in the 2.8C et sequentes TLR's is to that used in the Hasselblad 500C.

Sorry for getting the production figures wrong -- that's what happens when I don't Look Things Up!

Marc
msmall@roanoke.infi.net

From Rollei Mailing List;
Date: Thu, 26 Apr 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Introduction & Question

you wrote:

>   Mike Bischof nbg90455@usa.net said:
>
>>Also, while the difference between Planar and Xenotar is
>>largely philosophical, there appears to be a bigger difference between
>>Tessar and Xenar (with the Tessar the clear _winner_).
>
>I just plain don't believe it.
>
>---------------------------------------------
>les clark / edgewater, nj / usa

It would be interesting to bench test several Rollei Tessars against Rollei Xenars. From the images from carefully set up cameras I can see little if any difference. I can see some difference between longer focal length Xenars supplied for press cameras, particularly the 135mm Xenar compared to the 135mm Tessar. The Tessar has considerably less coma, the Xenar was similar to the Wollensak Raptar in this respect. The Tessar was free of coma at f/8. I can see no signs of this excessive coma in My Rollei Xenars when the corners of the image are examined with a high quality magnifier. All Tessar types have some coma but it should be gone when stopped down two or more stops.

The Planar-Xenotar lens should have less coma and may have less residual spherical aberration. I've found the f/2.8 Xenotar to be exceedingly sharp but have no Planars to compare it to.

I suggest using strobe illumination when testing cameras. It gets rid of motion bluring virtually completely. You may be surprized at how sharp a lens turns out to be when tested with strobe.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

From Rollei Mailing List;
Date: Fri, 27 Apr 2001
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Introduction & Question

you wrote:

>Richard,
>
>You got me wondering about a few things. Do you mean both the 135mm
>Tessar and the Rollei Tessar is free of coma at f8 or just the 135mm? At
>what f stop is there no signs of excessive coma in Rollei Xenar?
>
>If the Rollei Xenar and Tessar are free of coma at f8, do you see much
>difference between them and the Xenotar at f8?
>
>Thanks,
>Dale

The Xenars I checked were for press cameras. I looked at the aerial images of two. Both had excessive coma. Coma is related to spherical aberration but exists away from the center of the image, increasing with angle. It decreases with stoppig down. It looks like a tear drop shaped blur, the name indicating its commet like appearance.

The Xenar and Wollensak Raptar have coma at the corners of a 4x5 which does not go away entirely until they are stopped down to f/22. Both of my Zeiss Tessars, mid or late 1930's lenses have no coma beyond about f/8. The same for the 127mm f/4.7 Kodak Ektar, the coma disappears at around f/8. Best performance for both lenses is around f/11.

An examination of the Xenar in both a Rolleicord and Rolleiflex of about 1954 vintage shows no excess coma in the corners of the film gate at f/8 or maybe a bit less. There is some vignetting at the corners below f/11.

An examination of a Rollei Tessar of mid 1930's vintage shows about the same behavior. It would take much more elaborate and formal testing to give a true comparison.

When I got my Rolleicord IV (to replace my original which was stolen) some years ago I thought it was a little soft. Adjusting the finder lens and getting a good enlarging lens fixed that. Whet I first used a strobe with it I was aastonished at how sharp it was.

----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com

Date: Sun, 2 Sep 2001 
From: Jon Hart <jonhart51@yahoo.com>
To: rollei@mejac.palo-alto.ca.us
Subject: Re: [Rollei] Triplet Lenses/was Rollei TLR use in my work


--- Eric Goldstein <egoldstein@usa.net> wrote:
>This makes the
> lens extremely versatile
> and IMO if I could only have one lens for my camera
> I'd probably choose the
> Triplet... probably the most brilliant lens design
> of all time...

Eric, Dale, et al.,
I have to agree that for general use, a triplet
is quite sufficient, however, let's not forget why
there was such a push for more elements in lenses. The 
main reason, of course, was better performance at wide
apertures, the ultimate goal being to design a lens
that had the same performance from wide-open to fully
stopped-down. That being said, in most cases having
absolute performance at wide-open is not necessary
across the field. This is what allows a triplet to be
useful at fully-open apertures. Since the sharpest bit
is in the center (where most subjects end up, anyway),
one can let the rest of the field of view go soft and
concentrate the focus on the subject. This is where
the priorities of the photographer come in to play.
Some demand or need ultimate performance across the
field at wide-open. Hence, the demand for lenses with
higher correction at wide-open, therefore the need for
lenses with more elements to achieve that correction.
So, it boils down to: if you have no need for a lens
that performs at near-ultimate sharpness/flatness of 
field at wide-open, then why bother? A GOOD triplet
will accomplish most, if not all one's demands at the
smaller apertures and give you a great portrait lens
at the wider ones.
Teles are another area where less can be more.
Mirror lenses are generally of front plate,
main-surface mirror, secondary mirror, and, in some
cases, a corrector element. A refractor can employ as
few as two elements and still give good performance,
albeit, with loss of close-focus ability.
Just a few of my observations.

Jon
from Deepinaharta, Georgia 

From: artkramr@aol.com (ArtKramr)
Newsgroups: rec.photo.equipment.35mm
Date: 01 Oct 2001 
Subject: Re: Un-cementing lens elements

>One important lens design parameter for easy
>assembly would then be "uncritical" designs, where
>performance isn't dropping radically if tolerances add up
>instead of even out.  

Simply said but not so simply donen. When elements are manufactured  they are
"graded" as to how they fall plus or minus their design aim points. Then they
are grouped  so the the errors are compensating rather than additive. In cheap
lenses  extreme pluses are used to compensate for extreme minuses. But in
better lenses these extreme errors are discard for remelting and
remanufacturing .  There is a saying that how good a lens a company makes is a 
function of how much they ar willing to throw away. Leica throws a lot away. On
another point, not all of Leicas  optical performance is  totally due to lens
quality. The Leica pressure plate design contributes as well. But that is
another subject for another day.




Arthur Kramer
Now is the time for all good men to come to the aid of their country
Visit my WW II B-26 website at:
http://www.coastcomp.com/artkramer


From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: tele-Arton, tele-Xenar, tele-Optar
Date: Wed, 17 Oct 2001 

Georges Pelpel gpelpel@home.com> wrote:

>I have the 360mm Tele-Xenar and find it a good deal for 4x5 field
>cameras that have short bellow extension such as my Wista DX. It is
>heavy though and requires a long Arca-Swiss type plate as the
>camera/lens combo center of gravity is closer to the front standard than
>of the rear one. The lens is quite sharp. It usually comes with a old
>type Compound shutter that could be fragile from what I read (I have no
>experience with this shutter). I was lucky to got my lens with a Copal
>shutter (#3 so it's big), it turned out to be a good combo.
>Georges Pelpel
>

  I also have a 15" Tele-Optar. Mine is in a barrel but the cells will
screw directly into a #4 Alphax shutter (you have to make an f/stop
plate for it). The lens is a good performer, quite sharp. It will
cover 5x7 with good quality. It actually illuminates an 8x10 but the
image quality is not very good beyond about a seven inch image circle.
Probably it should have been baffled to reduce the circle of
illumination. 

  Wollensak could build good lenses and did although some of their
lenses are dogs.

  I've never seen a Tele-Optar in Compound. I suspect these must be
remounted lenses. Wollensak built perfectly good large shutters and
didn't have to go outside to obtain them. I am not sure if the
Tele-Optar or its non-Graflex version, the Tele-Raptar, was offered in
a shutter although the shorter focal length versions were available in
either shutter or barrel. 

  I bought this lens some time ago quite cheaply and was surprized and
very pleased at how good it is. 

  Of the other two lenses mentioned in the original post the
Tele-Arton is superior to the Tele-Xenar, its actually a very good
lens. It was substantially more expensive than the Tele-Xenar.

>
>Bogdan Karasek wrote:
>
>> Hello,
>>
>> Anybody in the group had any experience with these lenses
>> (tele-Arton, tele-Xenar, tele-Optar) for 4x5 in the 240mm to
>> 380mm range?
>>
>> Any comments would be appreciated.  Thanks.
>>
>> regards,
>> Bogdan
>> --
>>   Bogdan Karasek
>>   Montr,al, Qu,bec            e-mail: bkarasek@videotron.ca
>>   Canada
>

---
Richard Knoppow
Los Angeles, CA, USA.
dickburk@ix.netcom.com



From: andrew.sarangan@usa.net (Andrew Sarangan)
Newsgroups: sci.optics
Subject: Integrated Optics Online Simulation
Date: 17 Oct 2001 

Hello

I have been developing some online simulation software for a graduate
course I teach in Integrated Optics. The idea was to allow the user to
quickly run a simulation from any web browser. It was developed
primarily as a teaching aid.

This effort has been quite successful, and I would now like to invite
anyone who is interested in integrated optics to take a look at this
software. It is free. I am not asking for any money. Just your
comments.

The nice thing is, you don't have to download or install anything. The
interface is constructed from simple html files; no java or graphic
intensive frames. I think the menu is very intuitive to use. The
structure and simulation parameters are typed directly into the web
browser as simple text. Most of all, the computation is done at my
end, not on your computer. However, unlike the commercially sold
software, this one doesn't have extensive features or 3D capability.
But it does allow quick verification of ideas. It is also a great as a
taeching aid.

The following tools are available:
-  One- and Two- dimensional optical mode solver
-  Two-dimensional beam propagation method (BPM)

The BPM and the modesolvers are connected. That means, you can find
the mode of a waveguide structure, and then launch it using BPM.

Here is the address:

http://homepages.udayton.edu/~sarangan/lights.html


Andrew M. Sarangan
Assistant Professor
Electro-Optics Graduate Program
University of Dayton
300 College Park
Dayton, OH 45469-0245
Phone: (937) 229-3190
Fax:   (937) 229-2097
email:  sarangan@udayton.edu


From: bigler@ens2m.fr
Subject: [Rollei] slight OT : standard lens = tessar, an essay
To: RUG List rollei@mejac.palo-alto.ca.us>
Date: Fri, 19 Oct 2001 

Since we'll celebrate the centennial of the tessar next year, this is
a conjecture of mine for which I would be delighted to get
contradictory feedback from the group.

The question is an academic one (I like them as you know) : why do we
consider being "standard" a focal length equal to the diagonal of the
format. e.g. 43mm in 35m film (frame 24x36mm), 75 or 80 in 6x6 (56x56
diag = 79), 100mm in 6x9 (56x82) etc.. to be THE STANDARD FOCAL LENGTH?

Do not tell me because this coresponds to the angle of view of the
naked eye. The naked eye can see sharp in an angle of a few degrees
and can see color and movement up to 180 degrees. May be the muscles
can reasonably scan an angle of 54 degrees ? Hmm... doubtful.

So my conjecture is that it is simply combination of historical and
technical reasons, directly related to the triplet and tessar lens
designs. It has been proven almost 1 century ago that a 3 element
triplet and then, a 4-element tessar, make an excellent trade-off
between maximum useable aperture (6.3, then 4.5, then 3.5 and 2.8 for
the tessar) for an amazing small number of elements : only 4. The
coverage of the tessar is something like 57 degrees, a 75 tessar on a
R-TLR covering 55 degrees i.e. the standard 53 degrees plus a small
safety margin. It is well-known that the coverage angle does not
increase significantly when you stop daosn a tessar. Thus a reason why
view camera users demanding large shift+tilt capabilities are not
satisfied with the "simple" tessar design.

Then I assume that with the technology of the early fifties, a wide
angle would be less sharp and would require much more elements
wherearas a long focal lenght without modern glass and computer desing
techniques would generate a longitudinal chromatic aberration
proportional to the focal length.

So my conclusion is that Zeiss designers in 1902 have found an optimum
lens design, our beloved tessar, still alive and well *because* it is
an optimum, difficult to beat without relaxing one parameter : adding
a 5-th element (planar, heliar), accepting a slow aperture (early wide
angle f/8 designs lake the angulon) etc...

Now with modern computers, new glasses, this definition of standard
lens appears to me meaningless ; however from a technical point of
view, fixed-focal lengths corresponding to the diagonal of the format
are still in 2001 the best trade-off in terms of image quality vs.
price, weight, max aperture etc... but disregarded by 35mm camera
users due to the fantastic, and much welcome, progress in zoom lenses.

So RUGgers, what do you think of this definitive photographic equation : ;-)

STANDARD LENS = TESSAR DESIGN ? (or xenar, or elmar or.... its numerous clones)

and "STANDARD" because the Tessar is *the* standard against which all
other photographic lenses have been compared since 1902 ?

;-);-);-)

-- 
Emmanuel BIGLER         
bigler@ens2m.fr>


From: bigler@ens2m.fr
Subject: Re: [Rollei] slight OT : standard lens = tessar
To: rollei@mejac.palo-alto.ca.us
Date: Sat, 20 Oct 2001 

>From Gene:

> ...I'm inclined to agree with your basic premise....So I guess there
> is some natural magic that conspires to make the 'Normal" lens the
> happiest medium. There seems to be something like this at work for
> the number of elements too. For normal lenses again, it seems that
> the law of diminishing returns starts clamping down pretty heavily
> past four. Especially if those four comprise a Tessar.

Yes, this is exactly what I meant, and I was trying to imagine whether
this was a pure historical fact, that Zeiss found the Tessar design so
early, or if there was some more profound reason of technical optics,
something as fundamental as, say, the diffraction limit when you stop
down your lens at f/22 and above.

About the field angle seen by the eye, I realized that my old
Voigtlaender Bessamatic has a viewfinder setup so that when you put a
50mm lens you have a magnification close to 1 with respect to what you
see outside the camera. So somebody using this camera would say that
the 50mm gives a "normal" perspective simply because what you see in
the viewfinder through the 50mm is the same as what you see without
the instrument. But on my wife's Canon EOS, the focal length giving a
1:1 ratio vs. the naked eye is *not* 50mm, I do not know why. And on a
Leica RF camera, you can now chose 3 different magnifications for the
viewfinder !! so "what the eye sees through an eyepiece" is not the
good reference to tell what a standard lens is.

And what painters have used as an equivalent angle of view varies from
an ultra-wide panoramic to a telephoto angle. So no such thing as the
"standard painter's focal length" exists, either.

I think there is a story about the reason why Herr Barnack chose a
50mm ("f=5cm") on his elmar for the fisrt leica and not a 43mm. A good
question for the LUG of course.

-- 
Emmanuel BIGLER         
bigler@ens2m.fr>



Date: Sat, 20 Oct 2001 
To: rollei@mejac.palo-alto.ca.us
From: Richard Knoppow dickburk@ix.netcom.com>
Subject: Re: [Rollei] slight OT : standard lens = tessar

you wrote:
>From Gene:
>
>> ...I'm inclined to agree with your basic premise....So I guess there
>> is some natural magic that conspires to make the 'Normal" lens the
>> happiest medium. There seems to be something like this at work for
>> the number of elements too. For normal lenses again, it seems that
>> the law of diminishing returns starts clamping down pretty heavily
>> past four. Especially if those four comprise a Tessar.
>
>Yes, this is exactly what I meant, and I was trying to imagine whether
>this was a pure historical fact, that Zeiss found the Tessar design so
>early, or if there was some more profound reason of technical optics,
>something as fundamental as, say, the diffraction limit when you stop
>down your lens at f/22 and above.
>
>About the field angle seen by the eye, I realized that my old
>Voigtlaender Bessamatic has a viewfinder setup so that when you put a
>50mm lens you have a magnification close to 1 with respect to what you
>see outside the camera. So somebody using this camera would say that
>the 50mm gives a "normal" perspective simply because what you see in
>the viewfinder through the 50mm is the same as what you see without
>the instrument. But on my wife's Canon EOS, the focal length giving a
>1:1 ratio vs. the naked eye is *not* 50mm, I do not know why. And on a
>Leica RF camera, you can now chose 3 different magnifications for the
>viewfinder !! so "what the eye sees through an eyepiece" is not the
>good reference to tell what a standard lens is.
>
>And what painters have used as an equivalent angle of view varies from
>an ultra-wide panoramic to a telephoto angle. So no such thing as the
>"standard painter's focal length" exists, either.
>
>I think there is a story about the reason why Herr Barnack chose a
>50mm ("f=5cm") on his elmar for the fisrt leica and not a 43mm. A good
>question for the LUG of course.
>
>-- 
>Emmanuel BIGLER         
>bigler@ens2m.fr>
>

 Its hard to guess at why Barnak chose 50mm for the Leica lens. Perhaps it
was simply that the slightly narrower coverage made it easier to correct.
The Elmar is essentially a Tessar with the diaphragm in the front air space
instead of the rear air space. 

  Paul Rudolph came up with the Tessar design as a modification of his
earlier Protar. The Protar, which was the first commercially made
anastigmat lens (1890), had cemented groups in front and back. The front
group was composed of "old" glass, the rear of "new" glass. Rudolph
attempted to make a lens where both components were air spaced. This lens
was called the Unar and was not very satisfactory. He then went back to the
cemented pair in back and air spaced the front pair. The result was the
Tessar. In the Tessar, as in the Protar, the front component has little
power but has most of the corrections. 

  For any lens the angle of view will be duplicated when the print is
viewed from the same distance as the lens was when the picture was taken.
The distance is of course multiplied by the enlargement ratio when pictures
are enlarged. Generally the idea is that the viewing distance is about the
diagonal of the print for a "normal" view. However, the "distortion" from
wide angle lenses is due to the improper viewing distance. When such a
print viewed from the right distance the "distortion" disappears. 
  The best history on lens development is:

_A History of the Photographic Lens_ Rudolf Kingslake, 1989, San Diego,
Academic Press, Inc ISBN 0-12-408640-3  

  It may still be in print. It was reprinted a couple of years ago. At any
rate its worth finding. 

----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com



From: bigler@ens2m.fr
Subject: Re: [Rollei] slight OT : standard lens = tessar
To: rollei@mejac.palo-alto.ca.us
Date: Mon, 22 Oct 2001 

Thanks Richard for the details about the technical origins of Tessar
design.

> ....Generally the idea is that the viewing distance is about the
> diagonal of the print for a "normal" view. However, the "distortion"
> from wide angle lenses is due to the improper viewing distance. When
> such a print viewed from the right distance the "distortion"
> disappears.

I totally agree with you ; I did not have this key point in mind. So,
if you agree with me, this definitely means that the "standard lens"
concept (equal to the diagonal of the format) is something actually
arbitrary. Your remark about cancelling the apparent visual
"distorsion" by choosing the proper viewpoint for the final print
supports my conjecture that a lens with a focal lenght equal to the
diagonal of the format became "standard" between 1902 and now simply
because of the 57 degrees of coverage of the most successful tessar
design (and also the cheaper triplet like the triotar) used as the
only non-interchangeable lens fitting most amateur cameras in the last
100 years before the "zoom era". Does Mr. Kingslake say something
about the origins of the standrda lens concept itself ? (yes I should
buy the book ; I have some of "Prochnows", getting *the* "Kingslake"
will save me time and effort on historical issues ;-);-)

-- 
Emmanuel BIGLER         
bigler@ens2m.fr>



Date: Sun, 06 Jan 2002 
To: rollei@mejac.palo-alto.ca.us
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Re: Dynar lens?

you wrote:
>
>>From: Eric Goldstein J Patric -
>>
>>
>>Kinglake attributes this 1903 design to Voigtlander's Hans Harting, and
>>states that the design was largely ignored by designers until after WWI. It
>>was then picked up in 1919 by Dallmeyer in a Lionel Booth design called the
>>Pentac, a very successful design. Shortly thereafter, Voigtlander revived
>>the Dynar-type and renamed it the Heliar. It is this 5 element-in-3 group
>>Heliar which gained such fame and has recently been revived in 35 mm format
>>by Cosina/Voigtlander...
>>
>>So the answer to your question is the Dynar is a pre-WWI designation for
>>what we now know as the Heliar. Kingslake hypothesizes that the design is
>>derivative of Dennis Taylor's Triplet...
>
>
>
>I borrowed "A History of the Photographic Lens" by Kingslake from the 
>Library at Institute of Space Physics today. Yay! I got to buy this book! I 
>worked at that library for a couple of months in 1990, and looked in this 
>book many times. Very interesting!
>
>Kingslake says: "In 1903 Harting tried the effect of turning the outer 
>components around so that the cemented interfaces were convex towards the 
>stop instead of concave. He may have been influenced by the Tessar in which 
>this arrangement of the rear components was used. The new lens was called 
>the Dynar. The astigmatism was slightly worse than in the Heliar, but 
>otherwise the new design was better".
>
>So the Dynar is just similar to the Heliar, but not exactly the same.
>
>/Patric
>

 FWIW, there is a computer analysis of the original Heliar in _Modern Lens
Design: A resource manual_ Warren J. Smith, 1992, McGraw-Hill Book Co. ISBN
0-07-059178-4  On page 211. Six different Heliar variations are shown in
the book including Lionel Booth's Pentac, p.214

 The Fred Altman patent for the Kodak version of the Heliar is interesting
to read. Its USP 2,279,384  His approach is quite different than Hans
Harting's. 

 BTW, Harting describes his approach in his book on lenses, which was
translated into English. I've lost track of where my copy is at the moment
but will find it and post the publication data. 

  Both Harting and Eder are quite critical in their evaluation of
non-German lens designers. Harold Dennis Taylor is the only one they have a
healthy respect for. Interesting. 

----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com


Date: Sun, 06 Jan 2002 
Subject: [Rollei] Re: Dynar lens?
From: Eric Goldstein egoldstein@usa.net>
To: rollei@mejac.palo-alto.ca.us>

Richard Knoppow wrote:

 
> Both Harting and Eder are quite critical in their evaluation of
> non-German lens designers. Harold Dennis Taylor is the only one they have a
> healthy respect for. Interesting.

Even more interesting: Taylor was supposed to have forsaken calculations and
designed the triplet virtually exclusively with bench work!


Eric Goldstein



Date: Sun, 06 Jan 2002 
To: rollei@mejac.palo-alto.ca.us
From: Richard Knoppow dickburk@ix.netcom.com>
Subject: Re: [Rollei] Re: Dynar lens?

you wrote:
>Richard Knoppow wrote:
>
> 
>> Both Harting and Eder are quite critical in their evaluation of
>> non-German lens designers. Harold Dennis Taylor is the only one they have a
>> healthy respect for. Interesting.
>
>Even more interesting: Taylor was supposed to have forsaken calculations and
>designed the triplet virtually exclusively with bench work!
>
>
>Eric Goldstein
>
  Taylor wrote a classic book on lens design using entirely algebraic
methods rather than ray tracing. Kingslake comments on the difficulty of
actually designing a practical lens by this way.

  I don't have Taylor's book but I will have to try to find it. I think
Kingslake is quoting from it when he talks about finishing the design by
the use of actual models made up in an optical shop. This procedure was
used by other designers before computers made thorough evaluation of
proposed designs relatively easy, but, from what Kinglake implys, Taylor
went resorted to modeling at an earlier stage than usual because he
eschewed ray tracing. 

  The book for others who might want to search for it is _A System of
Applied Optics_ H. D. Taylor, 1906, London, Macmillan.

  I suspect its a rara avis. 

----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com


From: brianc1959@aol.com (brian)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: flare and MC Re: Schneider Super Ang question
Date: 31 Oct 2001 

Robert:

I did some quick design work and found that a two element quartz
system in the Hypergon configuration (all radii identical, optical
power introduced by lens thickness and element separation) would be
ideal for 4x5 or 8x10 in the violet-to-deep ultraviolet range. 
Extremely flat anastigmatic field and no coatings necessary.  At f/32
to f/64 the images will be as sharp as a plasmat one or two stops
faster in visible light.  If you're willing to put up with more
aberration (mainly lateral color and astigmatism) you could go with a
single element landscape lens.  Good fused silica is not necessarily
too expensive if you can find a surplus source.  Even a fused quartz
telescope blank might serve your purposes well.

Brian


rmonagha@smu.edu (Robert Monaghan) wrote 
> yes, I was interested in trying out UV photography, and found it
> delightful that some of the older lenses could be pushed into the longwave
> UV range (see notes at http://medfmt.8k.com/mf/uv.html), but the
> cost of shortwave UV quartz optics generally started in the multikilobuck
> range for 35mm and over $10k for the zeiss UV lenses for hasselblad on
> 6x6cm etc.  So I maintain an interest in other options, including possibly
> some simple lens designs replacing existing elements in a mounting with
> quartz elements in a modest simple design lens. But the coatings were 
> interesting since I would find it hard to evaluate flare assuming I was 
> shooting thru a UV only pass filter (quite dark), given the flare might be 
> in UV rather than visible light ranges ;-) grins bobm


From: "Kotsinadelis, Peter (Peter)" peterk@avaya.com>
To: "'rollei@mejac.palo-alto.ca.us'" rollei@mejac.palo-alto.ca.us>
Subject: [Rollei] Planar comparisons
Date: Thu, 15 Nov 2001 

Now I have an interesting question for the group. I know we are all Rollei
folks, but since the Xenotar and Planar F2.8 in the Rolleis are 5 element
and those in the Hasselblad and SLR are 7 element I was wondering if anyone
has ever compared the results from these lenses?  I understand the extra
element in SLRs for retrofocusing but wonder whether it has any notceable
differences in the final result even though I am sure Zeiss & JSK designed
them properly to minimized this. Several photographers have indicated that
the Xenotar F2.8 (no F2) for the Rolleiflex 6000 series is "the" killer 80mm
lens to get. Wonder if others feel this way? 

Peter K


Date: Thu, 15 Nov 2001 
From: Jerry Lehrer jerryleh@pacbell.net>
Subject: Re: [Rollei] Planar comparisons
To: rollei@mejac.palo-alto.ca.us

Peter

I can state with assurance that the Planar as used in
my H'blad is every bit the equal to the 2.8 Planar or
Xenotar as used in my Rolleis.

My H'blad had the later T* lens, and is 7 elements
but the earlier lenses had 6 elements.

Earlier yet, the H'blads had a 5 element Ektar, though
Nordin erroneously claims it was 4 elements. It was
NOT a retrofocus lens.  Fantastically sharp!  Come
to think of it, are you certain that the f2.8 80mm lenses
as used in Rollei and H'blad SLRs are retrofocus?

Jerry

Kotsinadelis, Peter (Peter) wrote:

>
>
> Now I have an interesting question for the group. I know we are all Rollei folks, but since the Xenotar and Planar F2.8 in the Rolleis are 5 element and those in the Hasselblad and SLR are 7 element
> I was wondering if anyone has ever compared the results from these lenses?  I understand the extra element in SLRs for retrofocusing but wonder whether it has any notceable differences in the final
> result even though I am sure Zeiss & JSK designed them properly to minimized this. Several photographers have indicated that the Xenotar F2.8 (no F2) for the Rolleiflex 6000 series is "the" killer
> 80mm lens to get. Wonder if others feel this way?
>
> Peter K



Date: Thu, 15 Nov 2001 
To: rollei@mejac.palo-alto.ca.us
From: Marc James Small msmall@roanoke.infi.net>
Subject: Re: [Rollei] Planar comparisons

Jerry Lehrer wrote:
>Earlier yet, the H'blads had a 5
>element Ektar, though=20
>Nordin erroneously claims it was 4 elements.

Jerry

What is the source for your contention?  Rick received his initial
information from Hasselblad and then confirmed this with Kodak and the
George Eastman House.  I have some difficulty believing that all three
would be wrong.

Marc

msmall@roanoke.infi.net  



Date: Thu, 15 Nov 2001 
From: Jerry Lehrer jerryleh@pacbell.net>
Subject: Re: [Rollei] Planar comparisons
To: rollei@mejac.palo-alto.ca.us

Marc

I remind you again of my friend's 2.8A and the
bad 2.8 Tessar, in1950/1.  We had Oscar
Heinnemann (sp?) replace the lens with a 2.8
80mm Ektar from a wrecked H'blad.  I saw the
Ektar apart, and OH said that it was almost a
twin to the 100mm f3.5 Ektar as used in a
Medalist.  That was a 5 element Heliar design.

Do you know of anyone else who has seen this
Ektar apart?

Jerry

Marc James Small wrote:

> Jerry Lehrer wrote:
> >Earlier yet, the H'blads had a 5
> >element Ektar, though
> >Nordin erroneously claims it was 4 elements.
>
> Jerry
>
> What is the source for your contention?  Rick received his initial
> information from Hasselblad and then confirmed this with Kodak and the
> George Eastman House.  I have some difficulty believing that all three
> would be wrong.
>
> Marc
>
* msmall@roanoke.infi.net  


From: bigler@ens2m.fr
Subject: Re: [Rollei] Planar comparisons
To: rollei@mejac.palo-alto.ca.us
Date: Fri, 16 Nov 2001 

  From Jerry L.:

> ....the Planar as used in my H'blad is every bit the equal to the
> 2.8 Planar or Xenotar as used in my Rolleis.

Ahh! *one of my favourite RUG-subjects. Can't resist (there are many
new RUG members, one of the RUG web archive is dead, so, you'll
hopefully forgive me...;-);-))

To be a little provocative, I would write this exactly in the reverse
order: despite the fact that the R-TLR 2.8 Planars or Xenonars are
"5-element" only and that the design for the 2.8/5-element planar did
not change for nearly 50 years, this non-retrofocus lens is as sharp
as the 7-element 80mm SLR planar, whether people like it or not.

> My H'blad had the later T* lens, and is 7 elements but the earlier
> lenses had 6 elements.

Yes, Nordin's book shows an interesting cut-through of the late '50s,
the first 6-element 80mm Zeiss Planar (probably introduced for the
500C). It looks very similar to the 5-element 2.8 R-TLR planar, with
its cemented front doublet. Probably Zeiss started from this 5-element
design and added the 6-th as an extra degree of design freedom to
accomodate for the (even "shortened") H-blad SLR mirror. Prochnow
shows a strange Rollei patent for a SLR mirror, folding in two halves,
intended to keep the non-retrofocus 5-element 80mm planar on the early
stage of development of the SL66. I think I've seen somewhere that the
early Bronicas SLRs had the same lens constraint solved with a complex
sliding/rotating movement for the mirror, a solution eventually
adopted by Hasselblad on the recent 500-series models.

Eventually the 6-element SLR planar was not satisfactory to
Oberkochen's masters who re-started from a different design, the one
with 7 elements still in use today on MF R-SLRs and H-blads. Now
everybody who has looked at official Zeiss MTF charts knows that the
100mm 3.5 planar with 5 elements "only" is better than the 7 element
80mm. I do not claim that for myslelf ; Zeiss put it on paper and
state that their MTF charts are *real* ones, not simulations. Now if
Schneider delivers 80 mm lens for R-MF-SLRs better than the 80 mm
planar (but is the Schneider lens better than the 100mm planar
?;-);-), this proves that Rollei's traditional approach for lens
supply, i.e. always keep a second source for lenses to maintain a
certain level of competition is still valid in Brauschweig... even if
Rollei actually manufactures the 80mm planar under a Zeiss licence.

Too bad that Rollei does not publish equivalent MTF charts for the
2.8GX "Rollei-made" "modern" 5-element 80mm planar to add some
"scienfic" elements to this beloved, often debated, RUG favourite
question.

-- 
Emmanuel BIGLER         
bigler@ens2m.fr>


Date: Sat, 17 Nov 2001 
To: rollei@mejac.palo-alto.ca.us
From: Richard Knoppow dickburk@ix.netcom.com>
Subject: Re: [Rollei] Re: Planar lens design changes from 2.8E to 2.8F

you wrote:
>>> I have replaced the front element of a badly scratched Triotar on a
>>> Rolleicord once, and it went perfect, maybe because it's a simpler lens
>>> design?
>> 
>> 
>> More likely you were just very lucky!
>
>
>If I'm remembering correctly, the front elements of Triplets and Tessars do
>not carry very much power, so variances may not show up all that
>dramatically... Richard Knoppow will know. Curious how you recentered the
>lens element?
>
>Don't the Planars have two elements in one group up front? Could mean more
>variance when swapping elements...
>
>
>Eric Goldstein
>
  The front _element_ has quite a bit of power. The front _cell_ does not.
Triplets are quite sensitive to variations in element power and spacing. 

  Centering is carried out in manufacture. The lens mount holds the lens by
clamping it between two narrow rings at front and back surfaces. If the
lens was centered properly in manufacture its automatically centered in the
mount. 

  After the element is polished its put into a centering machine which also
grinds the edge. The technique used for many years was to place the lens on
a hollow tube with some soft pitch. The operator then watched the
reflection of a point source reflected by the surfaces with the aid of a
low power microscope (or rather telescope since the image appears to be at
infinity). The lens is rotated slowly and pushed around on the pitch until
the reflections stop rotating. The lens is then clamped by a second tube
and the edge ground. For air spaced lenses approximate centering is enough
since the mount will pull the lens into alignment. For lenses to be
cemented the centering must be much more carefully done. One technique was
to cement the elements and to then adjust their position until all
reflections stood still. After curing the whole assembly is centered and
edged. Cemented elements which must be recemented will be centered when the
edges are clamped provided they were properly centered in the first place.
The difficulty is with lenses where the two or more cemented elements are
not of the same diameter, as in the Schneider Angulon.

  Another problem is recementing complex lenses which were not centered
accurately orinally since if they are centered optically the edges no
longer match and the must be re-ground. Reportedly, a lot of Turner-Reich
lenses were never centered properly. 

  A simple method of checking larger lenses for gross centering errors is
simply to rotate the lens in the mount while watching the reflection of a
distant small light. The reflection should stand still as the lens is
rotated. any orbiting of the reflection or relative movment of multiple
reflections is an indication of poor centering. 

  The sensitivity to centering depends on the lens design but it needs to
be pretty accurate for all types. 

  Another centering problem is a lens which is tilted. The centering and
edging should result in a lens which has an optical center line which is
exactly coaxial and parallel to its mechanical center line. A very small
amount of tilt will completly destroy the correction of a lens. 

----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com



Date: Fri, 23 Nov 2001 
To: rollei@mejac.palo-alto.ca.us
From: Richard Knoppow dickburk@ix.netcom.com>
Subject: Re: [Rollei] Lens names

you wrote:
>Hello,
>
>why do the names of lenses or lens groups finish by R (Tessar, Sonnar,
>Sekkor, Nikor...)?
>Sorry for possible OT posting.
>
>Jose Royo
>Logrono
>Spain
>

   Many lenses have names ending in "ar" or "tar" but many do not. I am not
sure what the origin of this is. The "at" ending somtimes found is from
Anastigmat". Many lenses have names made up of Latin or Greek roots,
sometimes a mixture of both. 

   Tessar comes from its having four elements. Sonnar means "like the sun"
meaning a bright image. Other lens names often indicate some property the
lens is supposed to have such as Planar (flat field) Rapid Rectilinear,
meaning no geometrical distortion and a fast lens (f/8 was fast in 1866),
Orthometar (correct measurement) originally an aerial mapping lens. Many
Zeiss lenses are named this way. Gon endings (Biogon) usually indicate a
wide angle lens, gon coming from a root for angle. 

  Some lenses are named after the manufacturer. Dagor means Dopple
Anastigmat- Goerz. Kodak Ektar is simply Eastman Kodak + tar.

  Boyer, an old French company, named their lenses after jewells, i.e.,
Saphir, Topaz, etc. 

  Some companies, Canon for example, don't name specific lenses, they are
all just Canon Lens. 

----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com



From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Convertible lenses
Date: Thu, 10 Jan 2002 

"Steve Wolverton" steve@wolvertonphotography.com> wrote:

>Hi,
>
>With convertible lenses, when you remove the rear element to increase focal
>length, does is affect aperture?
>
>Is there any quality change?  Does it ALWAYS double the focal, or never, or
>sometimes?
>
>Does anybody have a list of convertible lenses? (I'm shopping for one to
>maximize my spending dollars)
>
>Thanks
>

  The difference in focal length and aperture depend on the design of
the lens. For Goerz Dagors the FL of a single element is 1.8X the
combined lens and full aperture is about f/12.5. 

  For Convertible Protars the focal length is marked on each cell. All
are f/12.5 wide open. The combined focal length depends on the
individual cells as does the speed. 

  Single cells of convertibles should be used on the back of the
shutter or barrel for best performance. The location of the stop is
important in improving field flatness and in controlling some other
aberrations. However, since the principle points (which are where the
image appears to come from) both lie on the concave side of the lens
the bellows draw can be substantially reduced by using the lens on the
front. The image quality will be slightly worse but not by much.

  Symmetical lenses have automatic correction for distortion, coma,
and lateral color due to cancellation by the two elements. When a
single cell of a convertible is used this correction is lost.

  Convertible Protars are individually corrected for coma and have
fairly good performance, Dagor cells are not corrected for coma and
must be used at very small stops (f/45 or smaller) for decent
sharpness. Although the Dagor was patented and sold ans a convertible
it really isn't.  Single Protar cells are capable of quite
surprizingly good performance. I think they are slightly better than
the single cells of convertible Schneider Symmars. 

  The combined focal length of two lenses depends on their spacing so
the FL of a single element where the two are identical is always less
than half. 

---
Richard Knoppow
Los Angeles, CA, USA.
dickburk@ix.netcom.com


From: Martin Jangowski m.jangowski@phoenix-ag.de>
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Rolleiflex Planar Lens vs. Modern Hassy Planar Lens >?
Date: Sat, 12 Jan 2002 

Lassi Hippel,inen lahippel@ieee.orgies.invalid> wrote:

> Roland wrote:
>> 
>> "Xochitl" xochitlsells@hotmail.com> wrote...
>> > Hey everybody -
>> > just wondering if anyone knew the particulars of the planar lens
>> > design throught the years between my old rolleiflex 3.5 Type 4 75mm
>> > Zeiss Planar,  and the modern day Hassy 501c/m 80mm Zeiss
>> > Planar...other than probably an advance in lens coating technology.
>> > Do they have the same sharpness/resolution? Do 16x20 enlargments look
>> > as nice? Any differences in quality/workmanship? Any light shed would
>> > be much appreciated.
>> >
>> > XO
>> 
>> See if you can find mention of the number of elements in each lens. If you
>> find the more modern lens has extra elements then the more modern lens
>> should be a better lens since more has been corrected for.

> IIRC, the 3.5 Planar had 5 lenses. First 2.8 Planars had 6. Current 2.8
> Planars have 7.

There is a difference between the TLR Planars and the SLR Planars. The TLR
2.8/80 had always five lenses, the 3.5/75 had in the beginning five lenses
and then six lenses. The TLR lenses don't have to clear the swinging mirror
of a SLR, so the shorter SLR lenses have to be retrofocus lenses, which
is considerably more difficult than a normal lens. I don't know if the
80mm Hasselblad- (or Rollei SLR-) Planar is a retrofocus lens, it may be
borderline.

However, my own cameras show that the Rollei TLR lenses (Planar or Xenotar)
with the 2.8/80 or the 3.5/75 are second to none.

Martin



From: "Q.G. de Bakker" qnu@worldonline.nl>
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Rolleiflex Planar Lens vs. Modern Hassy Planar Lens >?
Date: Sat, 12 Jan 2002 

Martin Jangowski wrote:

> There is a difference between the TLR Planars and the SLR Planars. The TLR
> 2.8/80 had always five lenses, the 3.5/75 had in the beginning five lenses
> and then six lenses. The TLR lenses don't have to clear the swinging
mirror
> of a SLR, so the shorter SLR lenses have to be retrofocus lenses, which
> is considerably more difficult than a normal lens. I don't know if the
> 80mm Hasselblad- (or Rollei SLR-) Planar is a retrofocus lens, it may be
> borderline.

No. No Planar is a retrofocus design. All double Gauss derivatives.




From: hrphoto@aol.com (Heinz Richter)
Newsgroups: rec.photo.equipment.35mm
Date: 27 Nov 2001 
Subject: Re: OT: lenses from diamonds?

>Lens elements made out of cubic zirconia might be
>useful, because their refractive index is even higher than that of
>diamond.

A very high refractive index is useless unless it is accompanied by low
dispersion.  High refractive elements like diamonds, cubic circonia rtc. have
very high dispersion which makes them useless for lens production because of
the very high chromatic aberrations introduced by high dispersion.  Lens makes
instead use extra low dispersion glass, some of which approaches the refractive
index of a diamond, however, with very low dispersion.  The refractive index of
a diamond is 2.40, that of conventional flint glass 1.74, but the Leica Apo
glass has a refractive index of 1.99.

Heinz
GMP  Photography
FOTOgraphicART
GMB Custom Black & White Lab
http://www.goldmem.com



Date: Wed, 28 Nov 2001 
To: rollei@mejac.palo-alto.ca.us
From: Marc James Small msmall@roanoke.infi.net>
Subject: Re: [Rollei] Cosina 50mm F3.5 "Heliar"?!

B. D. Colen wrote:
>But the names? I understand your love of Voigtlander lenses and cameras.=
=20
>But the reality is the company died and the names were sold. There is=20
>really nothing more deceptive about Cosina using the names than there is=
=20
>in Chrystler's calling those tinny tanks it sells Jeeps.

It isn't a matter of MY emotions, such as they are.  It is a matter of
integrity.  The term "Skopar" and "Heliar" and "Ultron" and "Lanthar" and
so forth describe specific lens designs, just as does "Tessar" and
"Sonnar".  The Cosina offerings do not include a single true Heliar or
Skopar or Ultron or so forth.  In other words, the names are more than me=
re
brand-names:  they represent a specific lens design. =20

Recall the huge flack of protest when Leitz, in the 1960's, began to assi=
gn
its lens names based on apertures rather than designs.  Leitz was, on the
exact same grounds as I now raise, accused of everything from mopery and
dopery in the Spaceways to cheapening of a valued heritage in return for
cold, hard gelt.  (Of course, as more than one critic of the change point=
ed
out, the ultimate cause might just have been a lack of creative juices at
Wetzlar to come up with new names -- the LAST new name developed by Leitz
was the "Nokton" of 1966.)

Marc

msmall@roanoke.infi.net  


From: Glenn Stewart gstewart@inficad.com>
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Anyone actively shooting with uncoated lenses?
Date: Tue, 27 Nov 2001 

[This followup was posted to rec.photo.equipment.medium-format and a copy 
was sent to the cited author.]

kahhengNOSPAM@pacific.net.sg says...
> Hi

> I have just acquired (on its way) a nice pre-1940s coupled rangefinder Bessa
> (black) with an uncoated 105mm Skopar. (Is USD$100 too much to pay for one of
> these things in excellent condition?)

> Is anyone here using the same thing or something similar? 

> I am just wondering how colour corrected these pre-war uncoated lenses are, esp.
> the Skopar.

> If you have any advice, I'd appreciate it.

> Thanks!

> Tan

Tan,

Does a Brownie Hawkeye count? It's a single-element, uncoated "lens".

I've shot some fireworks with it using Fuji Provia (see my website under 
Gallery, Goofy-ing Around) and had excellent results. Ditto for B&W.; 
Granted, my Brownies are modified for tripod use, but it truly amazes me 
the quality of image they will produce. They're a little short on 
contrast for B&W;, but otherwise are pretty amazing.

Best regards,

Stew
-- 
--
Photo web pages at: http://www.inficad.com/~gstewart/



Date: Wed, 28 Nov 2001 
To: rollei@mejac.palo-alto.ca.us
From: Marc James Small msmall@roanoke.infi.net>
Subject: Re: [Rollei] Cosina's 50mm F3.5 Heliar (a True Heliar design)

Kotsinadelis, Peter (Peter) wrote:
> One exception at first glance though is the newest 50mm F3.5 Heliar in
Leica-M mount.  This is a true 5-element heliar design. Maybe Cosina
decided to follow a more traditional approach with this one lens and match
the design to the name. If you really wanted a Heliar for your Leica-M this
may be it. If nothing else I would love to see how well this "real" Heliar
design stands up to modern lenses. Should be quite interesting.
----------------------

Pete

Matthew Phillips had pointed this same thing to me off-line.  Interesting!

In defense of Cosina's practices, it should be noted that Emperor Hirohito
was especially pleased with a portrait of him taken with a Heliar in the
early 1920's, and raved about the qualities of this lens.  Thus, there is
some virtue to calling a lens a 'Helia' in a land which is still most
deferential to the Son of Heaven.

Marc

msmall@roanoke.infi.net  


Date: Wed, 28 Nov 2001 
To: rollei@mejac.palo-alto.ca.us
From: Marc James Small msmall@roanoke.infi.net>
Subject: [Rollei] Voigtlander 

Jerry Lehrer wrote:
>Way back, in my day, Voigtlander was considered
>as a second rate company (maybe third), with Zeiss
>and Leitz vying for first and Franke& Heideke in
>second place.

Now, Jerry, that's really odd.  Zeiss lusted after the lens design team
Voigtlander had.  The only significant none-Zeiss lenses in the Prewar
Zeiss Lens Collection of significant designs were Voigtlander lenses.
Zeiss BOUGHT Voigtlander precisely to gut their lens guys, and did so.

Doesn't really sound much like a second-rate company!

Marc

msmall@roanoke.infi.net  



Date: Thu, 29 Nov 2001 
From: Laurence Cuffe Laurence.Cuffe@ucd.ie>
Subject: Re: [Rollei] Cosina 50mm F3.5 "Heliar"?!
To: rollei@mejac.palo-alto.ca.us

>B. D. Colen wrote:
>>But the names? I understand your love of Voigtlander lenses and cameras. 
>>But the reality is the company died and the names were sold. There is 
>>really nothing more deceptive about Cosina using the names than there is 
>>in Chrystler's calling those tinny tanks it sells Jeeps.
>
>It isn't a matter of MY emotions, such as they are.  It is a matter of
>integrity.  The term "Skopar" and "Heliar" and "Ultron" and "Lanthar" and
>so forth describe specific lens designs, just as does "Tessar" and
>"Sonnar". 

No.  They don't.  Sonnar describes a series of related lens designs 
as does Tessar.  there can, however, be considerable variation 
within a given design even the number of elements in a used may 
change  -thus the ongoing debate as to which planar's have a sixth 
element, or when a given lens design was changed.  

Apart from the use of "germany" what were dealing with here is the 
whole area of lens snobbery and trust.

 if I buy a cosina ultron I trust that I'm not buying a lens where 
quality control has been delegated to the costomer.  The voi..der 
name tells me this.  Some lens names refer to individual 
formulations, some such as ektar refer to a class of lenses, some 
such as commercial ektar refer to a price point.  A tessar 
formulated lens is, possibly for trademark reasons most likely to be 
sold under another name having been manufactured to that 
formulation after pattent protection ran out.  a Hexanon or a zukio 
as a lens name probably just gives rough guidance as to what 
camera it goes on.

my 2c. off soap box, 

Larry Cuffe 



Date: Wed, 19 Dec 2001 
To: rollei@mejac.palo-alto.ca.us
From: Richard Knoppow dickburk@ix.netcom.com>
Subject: Re: [Rollei] Rollei Users list digest V10 #100

you wrote:
>I have an Ektar I=on my 1000F which believe it our not works great, I would
>be happy to count the elements if someone tells me how to do so Mark
>

  If a lens is not too complex its possible to get some idea of its
construction by counting the reflections from a small source, like a pencil
flashlight. Uncoated glass air surfaces have a quite bright reflection.
Cemented surfaces have a very dim, but visible reflection, coated glass-air
surfaces are somewhere in-between, but even multi-coated surfaces are
usually a little brighter than a cemented surface and single coated
surfaces are much brighter.

  If the curvature of a surface, especially a cemented one, is extreme it
may be difficult to see but usually shining the light from both ends will
show up all surfaces. Its helpful if the cells are removable and can be
examined individually. 

  With some practice its possible to tell if the surface is convex or
concave toward you but mostly just the number of elements in each section
and whether they are air spaced or cemented is enough to identify a given
construction. 

----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com


Date: Thu, 20 Dec 2001 
To: rollei@mejac.palo-alto.ca.us
From: Marc James Small msmall@roanoke.infi.net>
Subject: [Rollei] Conrady and Kingslake

Thanks to the proddings of Richard Knoppow, I dug out my copy of AE
Conrady's APPLIED OPTICS AND OPTICAL DESIGN.  The first volume is as
Conrady wrote it -- but the second volume was edited from Conrady's notes
by one Rudolf Kingslake and was dedicated by his wife, Hilda, to the memo=
ry
of her father.

Volume II, incidentally, is the killer -- Conrady's thoughts on symmetric=
al
and unsymmetrical camera lenses are outstanding.

Thanks, Richard!

Marc

msmall@roanoke.infi.net  



From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: rec.photo.equipment.medium-format,rec.photo.equipment.large-format
Subject: Re: Uncoated lenses vs. high or low contrast subjects
Date: Wed, 15 Aug 2001 

andermar@teleport.com (Mark Anderson) wrote:

>Richard Knoppow dickburk@ix.netcom.com> wrote:
>
>>There are many
>> advantages to using air-spaced elements if flare can be controlled so
>> the whole design philosophy changed as soon as coating became
>> available. 
>
>What are those advantages?
>
>-- 
>Mark Anderson
> DBA Riparia    www.teleport.com/~andermar/
  
  Mainly that the two surfaces can be curved independantly of each
other. Cemented surfaces must be very carefully matched. In effect,
the air space between elements becomes an air lens. This gives the
designer more degrees of freedom to work with. 

  An example is the Plasmat type lens, now very commonly used for
large format camera lenses, copy machine lenses, and enlarging lenses.
The Schneider Symmar series and Componon series and Rodenstock Sironar
series are Plasmats. These are essentially derived from the Dagor by
air spacing one of the elements which is cemented in the dagor. There
are still six elements in the basic lens but one additional surface to
work with. The result is that the Plasmat type has much less zonal
spherical aberration than the Dagor. Zonal results in the focus shift
and somewhat soft image of a Dagor when used wide open. A well
designed Plasmat has very little zonal so can be made quite sharp,
even wide open, and has little or no focus shift. 

  If it is desired to make a convertible using the Plasmat basic type
the individual cells can be made to be free of coma. This can not be
done with a Dagor, it requires another element if cemented elements
are required. The Zeiss Series VII Protar is an example of such a
lens. 

  There are many other examples of air spaced elements allowing better
performance, or similar performance with fewer pieces of glass. A well
known one is the five element Planar/Xenotar as used on f/2.8
Rolleiflex cameras. In this lens two elements of the six element basic
Planar type are combined in one lens and an air lens is used to
complete the lens. The result is a very fine lens with one element
less than the Planar. Since the lens is working at f/2.8 rather than
f/2, a typical speed for Planars, its performance is excellent. 

 Cemented components are also expensive compared to air spaced ones.
Each surface must be polished individually so that it precisely
matches the other. In addition the elements must be centered much more
accurately since the edges are used as guides when the lenses are
cemented. An air spaced lens can be approximately centered since the
normal ring contact mounting automatically centers the lens on its
axis. Add to this the hand work of assembling the cemented elements.
They must be cleaned, cemented, baked, or otherwise cured,  and
cleaned afterward. So, there is often a cost saving in avoiding
cemented surfaces. 

  Before good lens coatings were avialable designers tried to avoid
adding glass-air surfaces. That's why so many of the older high
performance lenses had so many cemented surfaces. The Dagor has six
elements and four cemented surfaces. Result: only four glass air
surfaces. The Series VII Protar has four glass elements in each cell,
all cemented. Total in the combined lens: eight elements, six cemented
surfaces; four air surfaces. Another example is the f/1.5 Sonnar for
the Zeiss Contax. It is essentially a triplet. The center and back
componenst each consist of three cemented elements. A total of seven
elements is used in the lens but it has only six glass-air surfaces,
the same as a triplet or Tessar. It can be a very good lens but is
very espensive to make and equal or better performance can be gotten
from modified Planar types with fewer cemented surfaces. 

  It is also a common trick to split a positive lens into two lenses,
deviding the power. This reduces the angle of incidence of the light
rays at each surface thus reducing the aberratsions introduced at each
surface. This technique is very commonly used in high speed lenses for
35mm still cameras and motion picture cameras. For instance, an f/2
Planar type lens can be increased to f/1.5 by splitting the front
element into two air-spaced elements. 

  For lots more see Warren J. Smith's books on optical design.

---
Richard Knoppow
Los Angeles, Ca.
dickburk@ix.netcom.com


From: "skgrimes" skgrimes@ma.ultranet.com>
Newsgroups: rec.photo.equipment.medium-format,rec.photo.equipment.large-format
Subject: Re: Uncoated lenses vs. high or low contrast subjects
Date: Wed, 15 Aug 2001 

In simplest terms the lens designer's problem is to arrange the curved
surfaces of the glass so that the image made by the lens is projected to a
flat surface (the film)  This is not "natural"  A simple lens such as the
lens in the eyeball projects its image to a spherical surface, in that case
the back of the eyeball (which is approximatly a sphere)

It would seem to me that since film is now only one alternative to produce
an image that someone would come up with a spherical receiving surface for
digital image collection, such design would help simple biconvex lenses to
produce good images.

The more variables the designer has at his disposal (such as number of
elements and independently available curves to specify) the easier it is to
get the desired result of a projected flat image.  The designer's problem is
further complicated because some of the solutions have already been "taken"
and are protected by patents. So the lens designer may have the added
problem of getting the focus flat by using "some other way"

SKG

--
          S.K. GRIMES  --  MACHINE WORK FOR PHOTOGRAPHERS
          153 Hamlet Ave. (5th floor) Woonsocket RI, 02895
          http://www.skgrimes.com/span/index.htm

"Mark Anderson" andermar@teleport.com> wrote...
> Richard Knoppow dickburk@ix.netcom.com> wrote:
>
> >There are many
> > advantages to using air-spaced elements if flare can be controlled so
> > the whole design philosophy changed as soon as coating became
> > available.
>
> What are those advantages?
>
> --
> Mark Anderson
>  DBA Riparia    www.teleport.com/~andermar/


Date: Thu, 23 Aug 2001 
From: "Eugene A. Pallat" eapallat@apk.net
To: hasselblad@kelvin.net
Subject: Re: coke bottle lenses RE: a NEW SWC - 905SWC

As a joke, someone used the base of a Coke bottle for a camera to photograph stars.  
It actually worked.

Gebe Pallat



From: Benjamin M. ben@light-poet.com>
Subject: Re: f/2.8 lenses ...
Newsgroups: alt.photography
Date: Fri, 10 Aug 2001 


Irvine Dude wrote:

> Hi! I am an amateur photographer and have an "elementary" canon system
> (rebel g + 28-80 USM + 75-300 usm + 20-35 usm). I am in the market for
> a better system (see one of my previous post if you are interested in
> what I am considering buying).
> 
> Anyway, my questions are:
> * what's a "pro" quality lens?
> * what is "pro quality"?
> * why are f/2.8 lenses considered "pro" quality?
> * why are f/2.8 lenses so f***ing costly?
> 
> Thanks!

Howdy,

Basically, what makes a professional quality lens just that is the quality 
and number of lens elements and aperture blades. Other features like a 
maximum aperture of f/2.8 and larger, internal focusing motors, 
manual/auto switch, and overall construction also play into this 
distinction.

These lenses have a very fast aperture for a variety of reasons. 
Previously, in the days before super fast film, a 2.8 lens was crucial. 
Your typical National Geographic photographers in the field, for example, 
needed a lens capable of providing their Kodachrome 25 slides with enough 
light in a variety of conditions. f/8, while being a favorite 
aperture for many photojournalists ("f/8 AND BE THERE!"), simply wouldn't 
cut it on some low light shoots with slow film.

Another significant reason to use a lens with an aperture of f/2.8 or 
larger would be to isolate on your subject by reducing your depth of field. 
This creates the pleasing blurred backgrounds you have seen in most 
portraits. Personally, my favorite lens is a Nikkor 50mm f/1.4, which 
allows me to blast away the background into a pleasing blur when wide open. 

These lenses cost more due to the amount and quality of optical glass used 
in them. Also, since hardly any aperture photographers shoot such slow 
films these days, the old 50mm f/1.4 lens with a camera kit has been 
replaced by a 28-80mm f/3.5-5.6 (or something similar). However, the cost 
is worth it for the improved sharpness and color saturation that most of 
these faster lenses offer. Not to mention, of course, their amazing 
applications with available light photography.

Hope this helps! :)
-- 
Warm Regards,

Benjamin
www.light-poet.com
ben@light-poet.com


From: jenspatricdahlen@hotmail.com>
To: rollei@mejac.palo-alto.ca.us
Subject: [Rollei] 5 elem. Xenar patent
Date: Tue, 22 Jan 2002 

Got the patent info for this 2,8 Super-Xenar. The U.S patent is 2.105.799

Brittish patent 476.748

Numbers for the first patent try: 2.076.686

Brittish: 476.349

DRP-Nr. 753 329

http://photos.msn.se/Support/WorldWide.aspx



Date: Sat, 01 Dec 2001 
Subject: Re: [Rollei] Re: slighty OT Planar 2.8/80 patent issues
From: Bob Shell bob@bobshell.com>
To: rollei@mejac.palo-alto.ca.us>

> From: Eric Goldstein egoldstein@usa.net>
> Date: Sat, 01 Dec 2001 
> To: rollei@mejac.palo-alto.ca.us>
> Subject: [Rollei] Re: slighty OT Planar 2.8/80 patent issues
> 
> Now back to the original question... any modern MF camera/rangefinder use a
> Planar or Xenotar 5 element formula for their normal lenses?


Mamiya 7 and Bronica 645 both use six element/four group symmetrical
designs.  I couldn't find any tech specs on the lens used on the GW 670
and GW 690 Fuji cameras, so don't know what forumula they use.

Bob



From: brianc1959@aol.com (brian)
Newsgroups: rec.photo.equipment.35mm
Subject: Re: retrofocus Leica M lenses prejudices was Re: leica M weight
Date: 6 Dec 2001 

Q.G.:

You are correct about the confusing use of the name "Biogon".  I had
meant the symmetrical ultra-wide angle type Biogon.  However, Ludwig
Bertele, the inventor of the original Sonnar, developed a semi-wide
angle type Sonnar in the 1930's that could cover about 60 degrees full
field angle at f/2.8 or even f/2.  The symmetrical ultra-wide type
Biogon (typically covering 90-120 degrees) was also woked on by
Bertele in the 1950's and later, but this type was originally invented
by Michael Roosinov in Leningrad during WWII.  The Wild Aviogon and
symmetrical-type Biogon are very similar to the Schneider
Super-Angulon, and none of these is a reversed-telephoto design by any
stretch of the imagination.


Brian

"Q.G. de Bakker" qnu@worldonline.nl> wrote 
> brian wrote:
> 
> > Retrofocus lenses are certainly bigger and heavier than more classical
> > symmetrical types, but in many ways they have more optical potential.
> > For example, it is fairly straightforward to design an f/2 or even
> > f/1.4 retrofocus, but a symmetrical Biogon is really hard to correct
> > faster than f/4 or so.
> 
> The Biogon has been quoted before as an example of a symmetric lens design.
> It isn't!!!
> The Contax 35 mm Biogon designs (both versions) are a derivative of the also
> asymmetric Sonnar. I have seen this Biogon described as a remarkable lens,
> remarkable just because apparently no attempts were made to retain any form
> of symmetry... And when seeing the design, you cannot but agree.
> The other Biogon design, used for the Contax 21 mm and the 38 mm Hasselblad
> SW, is derived
> from the Aviogon aerial photography lens, and in fact is a reversed
> tele-photo (though it is not wildly asymmetric at all, But still...).


From: "Q.G. de Bakker" qnu@worldonline.nl>
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Hasselblad  - 120mm vs. 150mm vs. 180mm
Date: Wed, 12 Dec 2001 

DBaker9128 wrote:

> I like the 160 CB in part because I am a Tessar fan. The Tessar lens
formula
> was know as the "Eagle Eye of Zeiss" during the first half of the 20th
century.
> There is something very elegant and impressive about a lens which can
perform
> so well in the modern world of optics using just 4 elements of glass. I
also
> use modern Tessars with my 35mm equipment and I find them all to have
wonderful
> contrast, superior flatness of field and light weight. The last two
> characteristics are important to me and more complex formulas often
compromise
> these in the accumulation of glass in the search for faster maximum
apertures.

You do know that Tessar is a generic name used by Zeiss? You do know that
there are many, many Tessar designs, all of them different? You do also know
that there are good and there are not so good Tessar designs among them? And
that the praise given to the 1920's Tessar in no way tranfers to all Tessar
designs?

Good. Just thought i checked.


Date: Mon, 17 Dec 2001 
Subject: [Rollei] Re: LF Film cassettes (was: light leaks, black chord
From: Eric Goldstein egoldstein@usa.net>
To: rollei@mejac.palo-alto.ca.us>

Gene Johnson wrote:

> They are also front
> cell focus lenses which is a plus if you ask me.  If you leave it in
> it's infinity focused position it is at optimum correction

Doing this from memory Gene but I think Kingslake has it that typically the
front cell focusers go from over-corrected spherical up close to
under-corrected spherical at infinity. If I'm remembering correctly, the
thinking is that close up you're typically shooting heads at wide apertures
and the over-correction won't be objectionable (or possibly useful!) and at
infinity the lens is typically stopped down and so the spherical gets taken
care of...


Eric Goldstein



Date: Tue, 18 Dec 2001 
To: rollei@mejac.palo-alto.ca.us
From: Richard Knoppow dickburk@ix.netcom.com>
Subject: Re: [Rollei] Re: LF Film cassettes (was: light leaks, black
  chord

you wrote:
>Gene Johnson wrote:
>
>> Patric,
>> 
>> The only Kodak Heliar I know about is the Medalist 100mm.  I'm sure more
>> Kodak knowledgeable folks like Jerry and Richard will know others.  I
>> have an old Korelle Reflex with no lens.  I'm going to put a 101mm
>> Special Anastigmat on it I think, just to play with.  For a fp shutter
>> camera like the Korelle, I'll have to lock the shutter open on the B
>> setting, but on these shutters it's very easy to do.
>
>
>Patric/Gene-
>
>I believe there was a Kodak Heliar design (by Altman?) for 23 Graphics...
>I'm doing this from memory but think it is a 105/3.7 and reputed to be
>killer... I've been searching for a clean one for a loooong time but have
>yet to find... they were scarce then and now...
>
>
>Eric Goldstein

  Kingslake shows a series of Heliar type lenses designed by Altman. They
include the lens for the Medalist, a very similar lens for small press
cameras, some enlarging lenses, and a microfilm lens. The Enlarging Ektar
series were of this design. I think the early lenses for the Hasselblad
camera may also have been of this type. 

  I downloaded the patent. It claims to use the extra cemented elements for
better chomatic correction. Kodak literature describes all Ektar series
lenses as being virtually apochromatic. I don't think they are actually
corrected for three colors but that they have very little chromatic. Kodak
makes a point of these lenses having virtually no lateral color. 

  The Heliar form doesn't seem to have been exploited much outside of
Voigtlander. I suspect that other forms are more profitable in terms of
performance for a given number of elements, cost of manufacture, etc. 

  If someone has a Hasselblad Ektar I would appreciate it if they could use
a flashlight to see if it seems to be a Heliar by counting reflections. 

----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com


Date: Tue, 18 Dec 2001 
To: rollei@mejac.palo-alto.ca.us
From: Richard Knoppow dickburk@ix.netcom.com>
Subject: Re: [Rollei] Re: LF Film cassettes (was: light leaks, black
  chord

you wrote:
>Eric
>
>Yes, you are correct.  It was/is a super lens.  I was
>told that it is the same lens as the 100mm f3.5, with
>the elements closer together to give a 5mm longer
>focal length.
>
>BTW, if you space the elements further apart, you
>get an 80mm f2.8!  Well wadda ya know?
>
>Jerry

  I've heard the same thing, from someone who thinks they heard R.
Kingslake say so in a lecture long ago. 

  I have some skepticism since the corrections of a lens depend on the
spacing and triplet derived types are evidently quite sensitive to this.
Perhaps it was meant that the same prescription was used for each by
scaling it. 

  If someone has any two of these lenses measuring the power of the
components would tell pretty well if the only difference is spacing.  It
would be very interesting is this turns out to be true. 

  I have not heard recently if Rudolf Kingslake is still alive, he was a
couple of years ago, but is getting near the century mark. His son works at
RIT, I've contemplated sending a note just to say how much I value his
father's writing. 

  BTW. R.Kingslake was married to the daughter of A.E Conrady, a famous
pioneer in optical design and author of a text on optics which is still used. 

  >Eric Goldstein wrote:
>
>> Gene Johnson wrote:
>>
>> > Patric,
>> >
>> > The only Kodak Heliar I know about is the Medalist 100mm.  I'm sure more
>> > Kodak knowledgeable folks like Jerry and Richard will know others.  I
>> > have an old Korelle Reflex with no lens.  I'm going to put a 101mm
>> > Special Anastigmat on it I think, just to play with.  For a fp shutter
>> > camera like the Korelle, I'll have to lock the shutter open on the B
>> > setting, but on these shutters it's very easy to do.
>>
>> Patric/Gene-
>>
>> I believe there was a Kodak Heliar design (by Altman?) for 23 Graphics...
>> I'm doing this from memory but think it is a 105/3.7 and reputed to be
>> killer... I've been searching for a clean one for a loooong time but have
>> yet to find... they were scarce then and now...
>>
>> Eric Goldstein
----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com



From: "Roland" roland.rashleigh-berry@virgin.net>
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Zeiss 515/2 Nettar lenses
Date: Thu, 27 Dec 2001 

Ultimately it is you, and only you, who is the judge. Don't worry what
opinions other people have.

The three element Cooke triplet held sway for a long time. It was a very
good lens. Not great for color, but because it had only three groups (and
three elements) its light transmission was excellent and it outperformed
much better designed lenses that could not cope with flare. This light
transmission and the fewer glass/air surfaces was such an important factor
that this simple lens dominated consumer photography until the better
designed and older lenses with the benefit of coating came into their own.
Take the Tessar, for example, which was maybe a turning point in lens
design. It was only there because better designed lenses could not perform
up to their expectations due to the inherent flare. It was just a Cooke
triplet with the middle diverging lens cut in two with the post-iris half
cemented to the final diverging lens and the front half bent into a useful
shape for correction purposes. At the end of the day, you have corrected
another aberration without adding to the glass/air surfaces count and so you
have a better lens if correctly designed (which it was).

But as for the triplets, with old-fashioned photography you tend to use
smaller apertures the wider the format you use. So does a triplet at f16
giver better results than a Tessar-type or equivalent or multi-element
double-gauss multi-coated design?

Don't wait for an answer. Since it will be YOU taking the shots then YOU
decide. Take those shots, make the comparisons you want, and then choose, in
the fullness of time, what you prefer.

"Nomen Nescio" nobody@dizum.com> wrote...
>     I've recently picked up a second and third Zeiss Ikon Nettar,
> all models 515/2.  (Hey, I like the 6x9 format!).  I'm curious as to
> which lens is supposed to be the best - the Novar-Anastigmat or the
> Nettar-Anastigmat.  All are uncoated, and clean; I think I slightly
> prefer the shots taken with the Novar-Anastigmat - they seem
> contrastier, but maybe it's just me...
>
>
> NN


From: shadcat11@aol.com (ShadCat11)
Newsgroups: rec.photo.equipment.medium-format
Date: 23 Jan 2002 
Subject: Re: Rolleiflex Planar Lens vs. Modern Hassy Planar Lens >?

> > just wondering if anyone knew the particulars of the planar lens
> > design throught the years between my old rolleiflex 3.5 Type 4 75mm
> > Zeiss Planar,  and the modern day Hassy 501c/m 80mm Zeiss
> > Planar...other than probably an advance in lens coating technology.

Depending on year of manufacture; earlier Rollei f3.5 Planars were 5 element,
later ones 6 element.  Hasselblad 80 mm f2.8s are either 6 or 7 element
designs, different from the Rolleis.  

> > Do they have the same sharpness/resolution? Do 16x20 enlargments look
> > as nice?>>

I have both a Rolleiflex with a 5 element f3.5 Planar and a Hasselblad 500C
with an 80mm f2.8 Planar, not T*, so both are contemporary c. mid-60s. 
Centrally, they are equally sharp wide open, but the Rollei needs to be stopped
down to f5.6+ to match the 'blad edges at f4.  In practice, there is no real
difference visible under any field conditions when negs are enlarged up
to16X20, the largest size I print.  Both are superb lenses. 
These results may or may not be typical, but I suspect that in most samples,
given good condition, optical performance between Rollei and 'blad would be
comparable.  Later versions with improved coating offer a bit more contrast,
but a good lens shade minimizes even this difference.

Any differences in quality/workmanship? Any light shed would
> > be much appreciated.> >
> > XO

Both Rollei and Hasselblad lenses are built to the highest quality standards. 
In that regard there are none better.

> 
> See if you can find mention of the number of elements in each lens. If you
> find the more modern lens has extra elements then the more modern lens
> should be a better lens since more has been corrected for.

Sometimes otherwise comparable lenses with more elements outperform those with
fewer, but not always.  

Allen Zak


From minolta mailing list:
Date: Sat, 20 Oct 2001 
From: "Ze'ev Kantor" zeevk@bezeqint.net
Subject: RE: Re: Floating focusing

Floating Element just mean there is movement of the elements relative
to each other. In actuality, most of the time, this floating element
is the one in between, not the first or last. There being several
reason for it

ASAIK the "classic" floating element design is that the rear group(s) is
the floating one. The mechanism is very similar to zooming action.
In-between floating element is actually employed in "internal Focusing"
design, where an internal element is the only one that is moving during
focusing.

In fact, most usage of floating elements is not in Wide Angle lens,
but Macro Lens ( no prize for guessing why ).

Most Minolta wide angles (from 28 f/2 and wider) are floating element
design - I can verify this on my 17mm f/4, 24mm f/2.8 and 28mm f/2. My
MD 50mm f/3.5 is not a "floating element".

BTW, typical (but not mandatory) to floating element design is that the
front (main) objective body rotates during focusing but the rear
floating element does not. This is because the main moving / rotating
body includes additional cam or thread that controls the sliding
movement of the floating element.

Ze'ev Kantor
zeevk@netvision.net.il

...


From minolta mailing list:
Date: Thu, 1 Nov 2001 
From: "Daniel Hindes" Minolta@yakmilk.com
Subject: RE: Elements and Groups

The fist answer is that it has nothing to do with quality. The second
answer is that, ALL OTHER THINGS BEING EQUAL, fewer elements are
theoretically better. This is because as the light passes through each
group, there is an opportunity for a small bit of it to reflect instead
of being transmitted. This can then bounce around, creating a sort of
interference, the result of which is reduced contrast. Very small
amounts of this are present in all lenses. In fact, how well this is
controlled is fundamental to successful lens design. Multiple
antireflective coatings on all surfaces serve to bring the level of
reflection inside a modern lens down to miniscule amounts. Still, better
quality construction with more effective anti-reflective coating on a
lens with many elements will still produce a better lens than fewer
elements with lesser quality anti-reflective material. Further, the
interior of lenses is a matt black surface to absorb as much of the
reflected light as possible. This, too, can be done with greater or
lesser success. And finally, there is the precision of the elements to
begin with, so that a lens with few elements but poor manufacturing
tolerances will remain inferior to a lens with many elements and high
manufacturing precision.

Hope this is helpful.

Daniel


-----Original Message-----
From: Karen M. [mailto:karmona@home.com]
Sent: Thursday, November 01, 2001 
To: Minolta big group
Subject: [Minolta] Elements and Groups

Hi All,

When a lens description includes elements and groups, is a lens that has 9
elements in 10 groups "better" than a lens with 8 elements in 8 groups or
does it have nothing to do with quality?

Thanks
Karen M.
Low Moor, IA


From minolta mailing list:
Date: Fri, 2 Nov 2001 
From: "Kent Gittings" kent@ism.com
Subject: RE: Elements and Groups

There is some difference in optical performance. The more groups you have
the more light loss you have assuming the coatings are equal. This has
nothing to do with the actual optical performance of the lens as that is
part of the design. Has to do with the number of air-to-glass surfaces
that have to be coated. A 3 element group only need coatings on the front
and back of the group while 3 separate lenses have to have the coatings on
every lens surface. Often some of the extra elements are needed for
internal focus and some are needed for macro or close focusing. If they
left those out like earlier lenses they would be lighter and have a little
more contrast but you'd have to suffer through the parts you could no
longer do. For instance the old but excellent Pentax 500/4.5 has only 4
elements in 4 groups while the latest Sigma 500/4.5 EX APO has 12 elements
in 9 groups.

The Sigma is physically shorter (2/3rds the length), has internal
focusing, several low dispersion optical elements, and focuses down to 13
Ft. while the Pentax can't get closer than about 50 Ft. The Pentax only
needs 8 surfaces coated while the Sigma needs 18. Which is better? Pentax
still makes this lens after over 30 years of construction so it must still
be good, while the Sigma is current cutting edge optical design with AF,
greater range of use, and lighter to boot.

Kent Gittings



From zeiss interest group
Date: Mon, 17 Dec 2001 
From: Marc James Small msmall@roanoke.infi.net
Subject: Re: Planar=Biotar=Planar?

 you wrote:
>Is the Planar for Hasselblads, Rolleiflexes etc. constructed according to
the same scheme as the Planar of 1896? If it is, why is it not called 
Biotar?
>
>I have been looking for information on Plaubel Supracomar, which seems to
be of the same construction as Biotar/Planar-1896, when I started 
wondering about this.
>


The only information I can find on the Plaubel Supracomar is that it is a
2.5/80 lens and was made during the later 1950's for the Makiflex camera.

The basic Planar design of 1896 consists of six elements in four groups,
arranged symmetrically in a double-Gauss format.  The later Planar designs
were produced during the later 1930's to the later 1940's by Hans Sauer;
these began with five elements in four groups, arranged unsymmetrically.
The Hasselblad/Rolleiflex SLX/600x lenses have evolved from five to six to
the current seven elements.

the same scheme as the Planar of 1896? If it is, why is it not called 
Biotar?
>
>I have been looking for information on Plaubel Supracomar, which seems to
be of the same construction as Biotar/Planar-1896, when I started 
wondering about this.
>


The only information I can find on the Plaubel Supracomar is that it is a
2.5/80 lens and was made during the later 1950's for the Makiflex camera.

The basic Planar design of 1896 consists of six elements in four groups,
arranged symmetrically in a double-Gauss format.  The later Planar designs
were produced during the later 1930's to the later 1940's by Hans Sauer;
these began with five elements in four groups, arranged unsymmetrically.
The Hasselblad/Rolleiflex SLX/600x lenses have evolved from five to six to
the current seven elements.

The Biotar is an unsymmetrical double-Gauss design of six elements in four
groups designed by Willy Merte in 1927.  It is a distinct design from
either of the Planar types.

Marc
msmall@roanoke.infi.net



From: "Roland" roland.rashleigh-berry@virgin.net
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: I did a check on a Color-Skopar
Date: Fri, 8 Feb 2002


"Robert Monaghan" rmonagha@smu.edu wrote 

>
> I disagree.  You can tell some things about a lens from its design. An
> older three element lens (sans aspherics and fancy modern glasses) is
> probably going to be slightly less capable than a four element lens in
> which the designer had more flexibility, ditto five elements and so on.
> Some lenses do very well up to about f/3.5 or f/4.5 (e.g., biogon at
> f/4.5) but poorly in faster designs. Past four elements or so the quality
> differences are increasingly subtle and subject to refinements...

Past four elements, maybe. But within four elements I would say there would
be a lot of variation in what the theoretical lenses were capable of. They
didn't have the benefits of computers in those days to optimise designs. It
was a lot of hand calculation. And this costs money and is time consuming
and so must have a cut-off point such that only a certain number of
mathematical iterations could be done in practice. So the final design is
going to be a bit "hit and miss" and is open to improvement by another
company. And for all we know, other companies might have had a better range
of glass types, thus giving them an advantage. Also bear in mind that the
original Zeiss Tessar went through many design iterations (though mainly to
get it up to a wider aperture) so you might surmise that there was a great
deal of room for improvement in four element lens designs and it is quite
possible that one company could come up with a better design than that of
their rivals.

> On the other hand, the variability in mass producing lens may be larger
> than the variability between brands, as I have shown using some stats
> (see http://medfmt.8k.com/brontenmyths.html myth #31) for Canon,

I can't find the bit that shows the variability of production quality within
the same lens. And we would need to see these figures for Zeiss and
Voigtlander lenses made from that period in any case. I know that Zeiss coul
d make lenses to extremely tight tolerances for Rollei. I remember reading
something on your web site somewhere about the variability in quality of a
Russian zoom, or something like that, but then that's what you would expect.
hat's why most people don't buy them - given a choice. I would expect
better and more consistent quality from Zeiss and Voigtlander for their late
coated Tessars and Color-Skopars

> Nikon and Minolta (nearly identical in zooms lineup avg and std dev, very
> slight differences in fixed lenses) and lens variations studies
> (../third/variations.html). The bottom line is that you may be able
> to infer some differences between the older folder lenses, based on
> whether they are three or four element lenses and their quality of
> construction (e.g., more shutter speeds = better ;-). But I don't think
> that you can broadly endorse one Tessar variant (e.g., color skopar) over
> another Tessar variant without recognizing that on older folders, issues
> like use and abuse may have more impact than any small differences caused
> by the inherent superior design of one subvariant over another. This is
> why I advocate testing the lens you have in your hand, and that the rest
> of us can't tell you how good or bad it is, since we don't know its
> history etc.


Oh, did I forget to qualify? How remiss of me. I'll restate it then - a
color-skopar (correctly made and in excellent condition and rigidly mounted)
will beat the same focal length Zeiss Tessar (correctly made and in
excellent condition and rigidly mounted) for sharpness at f11 and f16 both
in the center and at the edges when set to infinity focus and projecting the
image onto a perfectly flat film plane any old day, ignoring such details
like the number of shutter speeds on the lens, who previously owned the
camera and any other matters not to do directly with lenses.

How about that?   :o)

It would be useful if somebody could get, let us say, 5 samples of the
Color-Skopar and the late coated Tessars of matching focal lengths and put
them through one of those setups that measures lens resolution over the
complete field at various apertures and then present the findings for all
ten lenses separately.

Maybe I'm just Mr. Lucky when it comes to Color-Skopars and Mr. Unlucky when
it comes to coated Zeiss Tessars.     :o)



From: Stephe ms_stephe@excite.com
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: I did a check on a Color-Skopar
Date: Sat, 09 Feb 2002


Roland wrote:

>
> Oh, did I forget to qualify? How remiss of me. I'll restate it then - a
> color-skopar (correctly made and in excellent condition and rigidly
> mounted) will beat the same focal length Zeiss Tessar (correctly made and
> in excellent condition and rigidly mounted) for sharpness at f11 and f16
> both in the center and at the edges when set to infinity focus and
> projecting the image onto a perfectly flat film plane any old day,
> ignoring such details like the number of shutter speeds on the lens, who
> previously owned the camera and any other matters not to do directly with
> lenses.


Sounds like TOTAL BS to me.. I've seen no such thing in the folders I've
owned. The skopar is a good lens but not some magical optic you claim it to
be.

>
>
> It would be useful if somebody could get, let us say, 5 samples of the
> Color-Skopar and the late coated Tessars of matching focal lengths and put
> them through one of those setups that measures lens resolution over the
> complete field at various apertures and then present the findings for all
> ten lenses separately.
>


I've owned 5 tessar 3.5's, two xenars 3.5's, 2 tessar 2.8's and 2 color
skopar camera's over the years and failed to see what you are claiming. The
3.5 tessar is sharper than the 2.8 no doubt about it. A couple of the 3.5's
weren't as good as the other three, One xenar was outstanding, the other
was pretty soft, one skopar was as soft or softer than the 2.8 tessar and
one was about the same as a good 3.5.

How many of these have you tested to make this blanket claim you keep
standing by? You say someone should test mulitple copies but proclaim one
is vastly superior like you have actually done this? Many people here are
TRYING to point out you aren't correct with this claim of your's, why won't
you listen?

--

  Stephe


From: Stephe ms_stephe@excite.com
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: DOF "overrated"?
Date: Sat, 16 Mar 2002


steven.sawyer@banet.net wrote:

>
>> even an old tessar version would equal 'blad glass at f22 and wouldn't
>> cost more than $150 for a mint sample.
>>
>
> I saw a post on this NG that Seagulls diffract at f22 (which incidentally
> LOMO
> optics do not).  But with respect to the quality of the lens, I would
> think that going to high f-stops like 22 and beyond (35, 45, etc.) would
> also require
> good optics.  Otherwise every lens would stop down to f45.


Most don't because of diffraction/quality loss. You do lose sharpness even
if actualy diffraction hasn't set in. Only long focal lengths and maybe
macro use lenses stop down this far in modern optics. Some VERY good lenses
only stop down to f22.

My point was many poor optics (like most 3 element front cell focusing
folder lenses) perform well at f22 and wouldn't be far off of "pro glass"
used at these same f stops. I know a 4 element tessar style will equal a
planar at this setting, I've tested it. It's at the wider settings that
lens defects really show up. If all one is going to use if f16 or f22 there
is no good reason to be concerned about getting high end optics, their
quality and cost isn't being utilized.

BTW Even one element miniscus lenses look pretty good at f22!  :-)
--
stephe



From: Stephe ms_stephe@excite.com
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Nice idea
Date: Sat, 16 Mar 2002



PSsquare wrote:

> Nice idea.  Have you any experience with the Holga.  (Toy camera, 6x6, two
> apertures, one speed, single element plastic lens)   Makes great old timey
> images of things like abandoned train depots and barns.  There is never a
> sharp image, but it really can have a lot of character.
>


What I started playing with is using an old normal lens gutted and removing
elements or using a single element in front of the diaphram and trying
different f stops to see what that turns out like. I just bought a "lot" of
70 different lens elements in bags (uncoated I hope!) on ebay to play with
this some more. I'm thinking a single element 180mm lens might make some
cool images! That way I can use this "dreamy" lens while doing normal
shooting and don't have to sweat light leaks or exposure screw ups.
--
stephe
http://www.geocities.com/kievgurl/


From rollei mailing list:
Date: Mon, 4 Dec 2000 
From: Guido Cova guido.cova@tin.it
Subject: R: [Rollei] Curved film planes?????

>...I have wondered
> myself that if one curves the negative to fit the
> curvature of the lens, wouldn't that imply one needs
> to curve not just horizontally, but vertically as
> well? In other words, ideally, the pressure plate
> would be dished out in the center as well as curved
> around the back of the camera. Or wouldn't that really
> be necessary?


Well, look at a disposable Kodak camera. They have done it very well.
The lens being a meniscus, it focuses on a spherical surface.
The film plane is curved and it is no more a plane but forms a cylindrical
surface.

I think these two surfaces have different radiuses: if the two radiuses were
equal, the focus would be perfect on a horizontal line in the middle of the
frame, where the sphere (focus surface) and the cylinder (film surface)
could be tangent.

Different radiuses cause the focus surface (sphere) intersect the film
(cylinder) defining an oval shape. On the border of this oval shape the
focus isperfect, inside it a little out of focus (short), outside a little
out of focus (long). Or the reverse.

I can'say which of the two radiuses is larger, but I think that stopping
down the lens to f/11 or smaller could result in a focus depth able to give
good results.

And this it does: prints from Kodak disposable cameras are surprisingly
good.

I reloaded one of these boxes wiht TRI-X, and got very good results: good
prints up to 18x24cm (and this is a lot more enlarging than what is expected
from a disposable camera).

Rollei contents: as I use my cameras for photogrammetry, I would neve trust
a camera with curved film, and that's why I use my TLRs, an Automat B
(Tessar) and a 3.5F (Planar).

Ciao
Guido Cova


From Rollei Mailing List:
Date: Tue, 26 Mar 2002 
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Re: 2.8C or D?

you wrote:
>J Patric Dahl,n wrote:
>
>> I have photos taken with pre-war Rolleicords with the three element Triotar
>> that are so sharp that you could say: "Oh, that must have been a Rollei
>> equipped with a Planar!".
>
>
>Thank you Patric for speak to the old saw that the triplets are not "good"
>lenses... just like the rest of the pre-70s cameras, if you find a good one
>that's clean and well set up, they are capable of great images with
>wonderful character...
>
>
>Eric Goldstein

 Triplets are capable of very good performance. Their downfall is in the
quality of the image near the margins at larger stops. A good Triplet
stopped down perhaps three stops from maximum aperture is quite sharp.

  Triplets tend to have more zonal spherical aberration than Tessars or
more complex lenses, giving them a soft-focus look when used at or near
maximum aperture. This can be a pleasing effect for portraits and some
other images.

  The Triplet has just enough degrees of freedom to correct all the first
order aberrations. They are not easy lenses to design since a less than
satisfactory design requires starting over. Everything is interactive.
Triplets are very sensitive to element spacing so require precision
mountings.
----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com


From Rollei Mailing List:
Date: Tue, 26 Mar 2002 
From: Edward Meyers aghalide@panix.com
Subject: Re: [Rollei] Triplets (was Re: 2.8C or D?)

It's refreshing to read about the virtues of aberrations and how
they can be utilized to produce desired images. Too much is put
on the race to a perfect lens. It's tough enough to make use with
what we have. There IS a place for a "perfect" lens, but not all
the time. 

Ed

Eric Goldstein wrote:
> Oblique spherical as well...
>
>
> Eric Goldstein



From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: lens names
Date: Wed, 27 Mar 2002


"David Smith" smith.david.dr@bhp.com wrote:
>Hi,
>I'm about to get into large format photography (4x5) by way of building my
>own camera. I have a Toyo back off a metallurgical microscope I found in a
>scrap yard. Attaching it to bellows and making the frame for the movements
>seems to be not too difficult.
>The lens is a question. I have been reading of Angulon...Super Angulon,
>Grandagon, Symmar and Sironar lenses.
>What do these lens descriptions mean?
>Thanks
>David

 Some of them refer to specific lens types, some are general
trade-names used for many different kinds of lenses. Ektar is an
example of the later as is Baltar (Bausch and Lomb + tar). The B&L;
Raytar is named after Ray, its designer. (There are at least two well
known lens designers named Ray. Intersting, I have long suspected some
people's names steer them into their professional fields).

  Many lens names come from Latin or Greek roots for some quality the
lens is supposed to have, or its construction.

  Symmar for symmetrical (the original Symmar was a Dagor type).
"ar" or "tar" is a frequent ending, I can't figure out what it comes
from other than sounding melifluous. "or" is also frequently found.

  Some names are derived from the maker's name. Again Ektar is an
example, meaning Eastman-Kodak + tar. Dagor is Doppple
Anastigmat-Goerz.

 Tessar means four elements.

Protar, the orginal. The first lens of this type was the first
anastigmat using the then new Jena glasses. It was called by Zeiss the
"Anastigmat" but the name soon became generic so it was re-named
Protar. There are several variations of this lens.

 Zeiss Sonnar, bright, like the sun (a very fast lens).

 Angulon, a wide-angle lens (large angle).

 "gon" or "on" is often found as a suffix to wide-angle lens names,
gon from angle (as in Hypergon, Metrogon, Angulon, Flektogon, &etc.;).

 Grandagon simply means large angle (excellent lenses BTW).

 Some makers used other kinds of names. Boyer, of France, named its
lenses after jewells, Opale, Beryl, etc.

  Some makers, like Nikon don't use individual names at all simply
marking all their lenses with a single trade-name (Nikkor).

  Some lens names have become synonomous with a generic type because
they were the first of the type or had someother outstanding quallity.
Planar (meaning flat field) was a Zeiss lens designed by Paul Rudloph,
also the inventor of the Tessar and Protar. The original Planar was a
symmetrical lens and not widely used. However, it was later made
semi-symmetrical by Horace Lee of Taylor, Taylor, and Hobson. This
design is the basis for most lenses of f/2 or faster speeds used on
35mm still cameras and a great many fast motion picture lenses.
Curiously enough the "generic" name for this type is Biotar, from a
later design by Willie Merte of Zeiss. Probably the reason is that the
Opic was a sort of stand-alone and while an excellent lens was not
widely sold.

  For more on lens history see:

_A History of the Photographic Lens_ Rudolf Kingslake, 1989, The
Academic Press ISBN 0-12-408640-3

  Probably out of print but may be available used and larger libraries
should have it.

---
Richard Knoppow
Los Angeles, CA, USA.
dickburk@ix.netcom.com




From: w.j.markerink@a1.nl (Willem-Jan Markerink)
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: APO isn't defined... Re: DOF "overrated"?
Date: Tue, 02 Apr 02

 rmonagha@smu.edu (Robert Monaghan) wrote:
>a discussion on APO revealed that there isn't any defined standard
>(ANSI/DIN) which covers what APO means for photographic lenses (microscope
>objectives, yes, lenses, no). So any mfger can call any lens they want APO
>regardless of its actual performance. This explains the low cost $200
>long zoom APO lenses which aren't very good at color fringing control ;-)
>
>regards bobm

More about this on: http://www.a1.nl/phomepag/markerink/apo_faqs.htm
(it's when dealing with IR (or UV) when you realize that APO is relative to
manufacturer)

--
Bye,
Willem-Jan Markerink

w.j.markerink@a1.nl
[note: 'a-one' & 'en-el'!]


From: "Roland" roland.rashleigh-berry@virgin.net
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: I did a check on a Color-Skopar
Date: Wed, 6 Feb 2002 


Tut, tut. And you being a professor.

A Tessar is any lens that has a back converging cemented doublet and a front
diverging combination of a converging and a diverging lens. That is what the
patent covers and that is all it covers. When it comes to actually designing
and making the lens, the manufacturer can change the following:

1) The curvature of the front and rear surface of every lens element (so
long as the Petzval sum comes to zero or whatever it is supposed to come
to).

2) The spacing of the lens groups.

3) The type of glass used in every element (such that the refractive index
and dispersion properties of the glass can be varied).

4) The thickness of each element.

5) The back doublet could be reversed such that the converging element was
closest to the stop.

6) The front two elements could be reversed (not a good idea at all).

There might be more I've forgotten.

So a "Tessar" is a TYPE of lens. It isn't a specific design that details all
the features of the lens. So one man's Tessar can perform quite differently
to another man's Tessar because this TYPE of lens could be designed in an
infinite variety of ways. And what I am saying is the the Tessar made by
Zeiss is not as good as the Tessar-type-design Color-Skopar made by
Voigtlander.


"Robert Monaghan" rmonagha@smu.edu wrote 
> http://medfmt.8k.com/third/variations.html on lens variations
>
> you can say your sample of the color skopar beat the tessar you tested.
> Tessars have a lot of variants too, including, it appears, color skopar
> ;-) ;-0) ;-)
>
> see also
> http://medfmt.8k.com/mf/elements.html wherein emmanual bigler
> lists the color skopar like yours as a tessar variant.
>
> also note:
> Date: Thu, 30 Dec 1999
> From: dickburk@ix.netcom.com (Richard Knoppow)
> Newsgroups: rec.photo.equipment.large-format
> Subject: Re: old lens info needed
>
> quote
> Skopar was Voigtlander's Tessar type. I don't know if the Color Skopar was
> different in any way other than being coated.
> endquote from http://medfmt.8k.com/mf/lflenses.html
>
> so basically, you have compared two versions of the same lens design and
> illustrated that the same tessar design can produce different results ;-)
>
> grins bobm

Back to your books, Bob. I would recommend Rudolf Kingslake's "A History of
the Photographic Lens". Also maybe download the free and very good OSLO ray
tracing software so that you can play around with lens designs.

> --



Date: Fri, 08 Feb 2002 
From: Richard Knoppow dickburk@ix.netcom.com
To: rollei@mejac.palo-alto.ca.us
Subject: Re: [Rollei] 5 element Xenar

you wrote:
>That's interesting indeed! Remember to report your results with this lens!
>According to Schneider, this lens was also available with front cell
>focusing, but I guess your version is better!
>
>I've read that the Unofokal lens can be used with the two rear elements to
>get a tele effect. I will do some experiments with that. I guess I will have
>to extend the bellows more.
>
>/Patric

  A single element of most symmetrical or semi-symmetrical lenses can be
used alone, but the image quality will not be very good. Dialyte types,
like the Unofokal, Goerz Dogmar, Goerz Apochromatic Artar, Kodak 203mm,
f/7.7 Ektar or Anastigmat, etc., have no correction for coma. Neither does
the Dagor or Dagor derivatives like the Schneider Angulon (sold originally
as a tripple convertible!). Such lenses will perform at very small stops
vis: f/45. The Zeiss Convertible Protar (Series VII or VIIA) has individual
elements which are corrected for coma and perform much better as
convertibles although not any better as combined lenses.
----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com





Date: Sun, 03 Feb 2002 
From: Eric Goldstein egoldstein@usa.net
To: rollei@mejac.palo-alto.ca.us
Subject: Re: [Rollei] OT Easy service lens (was felt and plush : a possible source)

>> That sounds like a cool design.  I wonder why the newer
>> lenses aren't as easy to service as your older one?  Not
>> that you need to do it often, but dust and other particles
>> eventually creep in between the elements eventually.
>>
>>> I just got a Zeca 9 x 12 camera with Unofokal lens. This lens is
>>> great and
>>> really easy to clean. It's possible to screw lose all lens elements and
>>> clean them. No cemented lenses, never a risk for separation. :-)


It is a cool design... the Goerz Celor and Dogmar were also of this type;
Kingslake classifies them as Dialytes. Fine performers with decent lens
speed but a limited field, still used for enlarging lenses...

There are modern variants of the four element in four group-designs which
use asphericals to overcome the field limitations... I believe Olympus uses
this design for one of it's fast P&S; cameras with a 35 mm f/2.8 optic...

Eric Goldstein



From Rollei Mailing List:

Date: Sun, 03 Feb 2002 
From: Marc James Small msmall@roanoke.infi.net
Subject: Re: [Rollei] Rollei 35

John A. Lind wrote:
>You should be surprised by the sharpness and contrast of the Tessar, a lens
>design dating to about 1903.  It's elegantly simple and one of the finest
>lens designs of the 20th Century.  Also became one of the most copied and
>cloned designs after Zeiss' patents on it ran out.  Roughly translated from
>German, its nickname was "Eagle Eye."

Thanks, John.  "Tessar", however, comes from the Greek "tessaros", for
'four', as in four elements in three groups.  And the basic Zeiss patent
dates from 1902, and expired in 1922.  The Zeiss trademark, of course, goes
on.

Marc
msmall@roanoke.infi.net


From Rollei Mailing List:
Date: Sun, 03 Feb 2002 
From: "John A. Lind" jlind@spitfire.net
Subject: Re: [Rollei] Rollei 35

Jerry Lehrer wrote:
>John
>
>I never heard it called "Adler-Auge"
>
>Jerry

Scroll down about 20% of the page to the discussion about Dr. Paul Rudolph
and the Tessar in 1902:

   http://www.contaxcameras.com/home/history.html

Also see the 18th paragraph here (if I counted correctly):

   http://www.company7.com/zeiss/history.html

Last, but not least, from Carl Zeiss' international (German) website (you
may have to past the URL back together if your mail reader inserts a line
break):

http://www.zeiss.de/C12567A8003B58B9/allBySubject/48650323292A75EE41256A5300381623

-- John



From Rollei Mailing List:
Date: Mon, 4 Feb 2002 
From: "Kotsinadelis, Peter (Peter)" peterk@avaya.com
Subject: [Rollei] Lens elements and Greek naming conventions

Its all Greek to me....

Trio = 3 in Greek (as in 3-elements, hence Triotar)
Tessara = 4 in Greek (as in 4-element, Tessar lens)
Pente = 5 in Greek (I think there was a Pentar but I will leave this to the
lens experts).



From rangefinder mailing list:
From rangefinder mailing list:
Date: Wed, 13 Feb 2002 
From: Joachim Hein jhein@mail.lns.cornell.edu
Subject: Sonnar And Ernostar (RE: Hexar vs. G2)

Hi Dante,

thanks a lot for your reply.

> This is in reference to Jochim's last message, which I don't have in
> front
> of me.  Since that message is on my home computer (as are my collected
> block diagrams from various types of lenses), I am going from memory.

You replied very well for not having my text in front of you. I am quite
impressed.

> 1.  A block diagram as shown on a site does not give you enough
> information to build a lens.  It is an artist's conception, which gives
> only the relative arrangement and element types.  It does not give you
> refractive indices, millimetric spacing, or any detailed information.
> For
> this reason, even given the selfsame diagram, the Hexanon and "Sonnar"
> (more on this in a minute) could be completely different.  Or,
> depending on how drawn, could be exactly the same.
>
> What led me to the observation that they may be the same was having the
> two out at the same time -- and seeing what the basic arrangement was in
> the diagrams.
>
> 2.  The comment 
> [this] Sonnar variant is astounding, because neither of these lenses are
> Sonnars as we know them.

Ok, what I know for the configuration of the `original' Sonnar can be found on

http://www.mir.com.my/rb/photography/companies/canon/fdresources/fdlenses/index2.htm

I learned from the Zeiss literature that having 6 glass/air surfaces was
a design goal of the Sonnar, since no anti-reflective coatings have been
arround when the Sonnar was new. From what I know, the 3rd element from
the r.h.s (the central one in the cemented group) has a lower refractive
index than the neighbouring one. If you kick it out and replace it with
air you end up with the configuration as published for the lenses in
question. For my understanding this does not change too much about the
basic idea.

 Surely if you take the Ernostar config on the same site and replace
the last element with a cemented group, you also end up with the same
configuration. Perhaps not surprising, since the Sonnar is an improved
Ernostar (as you know, it is surprising how many postings of yourself in
other mailing groups come up if you search for Sonnar and Ernostar in
google ;-), I hadn't know that this is one of your pet topics.)
The configuration of the discussed can also be arrived at, by taking the
tessar and splitting the positive front group into two positive
elements. It seems there are just a handful (if at all) ideas arround in
classical lens design.

  I admit, with the optic book was a bit over the top. I am just so used
to this configuration being the Sonnar (e.g. 38/2.8 for Contax T2,
85/2.8, 135/2.8 for Contax MM, 90/2.8 for Contax G, all similar
arrangement) that I forgot about the cementing of the middle group.

> A long-focus Sonnar (85/2 Contax or Nikkor, for
> example) has a big fat triple-cemented element in the middle.  A
> *telephoto* "Sonnar" (where the back elements sit much closer to the
> film) has more in common in basic arrangement with the the Ernostar and
> the early Sonnars - where the middle groups are separate elements.  The
> heritage of the newer lenses is Sonnar but yet not Sonnar, because they
> take ancientnormal-focus designs and turn them into telephotos.  In
> fact,
> Konica calls this design an "Ernostar" in its Hexar RF catalog.
>

They would have gotten into trouble if they called it a Sonnar. Anyway,
they are related as you know.

Thanks again for the reply, Joachim


From rollei mailing list:
Date: Mon, 18 Mar 2002 
From: Cliff Travis cliff@allcamera.com
Subject: [Rollei] (rollei)Mismatched Tessar

Elements may work well together.and probably will.

There is a lot of mystique,hype,and hoke circulating about various types of
lenses and equipment which usually has no bearing on practical use and results.
Years ago there was an EXPERT  lens man in NY who polished, coated &
cemented etc all types of lenses,prisms,mirrors etc at prices so low that
you could have almost anything rejuvenated.. He was the rescuer of all the
Soft coated lenses like Summicrons

Elmars, Hektors Commercial and other Ektars. Front elements were polished
and recoated if required.

      The interesting point is that the ubiquitous Summicron  front
elements were often done in batches and  that  they were often remounted on
lenses other than those from which they came. No complaints were ever
received, even from those who took pictures of newspapers pinned to the wall

       I know that for a long time he was looking for  a new front element
for a Large Commercial Ektar  to replace one which had been damaged. He did
not see any problems in using it with the rear element..

      Incidentally ,in generla he would only POLISH glass to remove
cleaning marks in  coatings as this did not change the optical properties.
Some large and unscrupulous would request the grinding out of scratches in
glass, particularly when a rare lens was involved. This would only be done
on request.

      Unfortunately Al retired many years ago and we have had to live with
our lens problems. Fortunately a few scratches will not affect lens
performance in a noticeable manner.
Cliff

All Seasons Camera
Cliff Travis
5 Harvard Lane PO Box 111
Hastings on Hudson, NY 10706



From rollei mailing list:
Date: Wed, 17 Apr 2002 
From: Gene Johnson genej2@cox.net
Subject: Re: [Rollei] OT: Flash Bulb Help -- Thanks

Jerry,

The best 620's ( and I bet dad Lehrer would have had the best) had
Supermatic's with 4 element Special Anastigmats on them.  I have a several
of these.  Most of them have functional shutters.  The lesser Kodak shutters
are even more reliable, being a lot simpler and having fewer speeds.  I
really like some of the better Kodak cameras.  The Tourist, for example, is
a really handsome well made device.  I have one I converted to 120, and used
it for a while.  It made me mad once because the pictures I shot with it
were sharper than the ones I was getting from an Ikoflex IIA.  I later
figured out I was moving the IIA when I released the shutter. Still, the
triplet (Anaston) in the Tourist was very nice when used with a hood and
stopped well down.

Gene



Date: Tue, 9 Apr 2002 
From: Paul Shinkawa pshinkaw@yahoo.com
To: russiancamera-user@beststuff.com
Subject: Re: [Russiancamera] Re: Oil on the blades!!! Depth of field question....

Mike:

The simplistic explanation I once received about the
advantages of "stopping down" was that the smaller
aperture uses the "best part of the lens". I think in
a sense that is more or less true. For any given lens
design there is a theoretically perfect formulation
and shape of the elements. Most of the lenses we use
on Russian cameras are spherical, that is the curve is
based on a sphere. That theoretical execution of the
design cannot always be implemented. So, there will
always be variations in that perfect curvature. The
larger the surface area of the lens, the greater the
chances of such variations affecting the sharpness
being present. Conversely, the smaller the area, the
greater the chances that these imperfectly formed
spherical surfaces will not influence the image.

Coupled with that(or part of it) is the fact that
light has to bend through the lens elements. The
thickness varies even if the curvature is not supposed
to, and if the rays passing though the larger diameter
glass do not all meet at precisely the same focal
point, the image will lack sharpness. By making the
effecive diameter of the glass smaller, the light rays
pass through glass thickness and curvature which is
more uniform and less subject to scattering.

That is my amateur version of why we like to stop-down
(or not). I think I left out a lot of the details.

-Paul
...



Date: Tue, 09 Apr 2002 
From: Bob Shell bob@bobshell.com
To: russiancamera-user@beststuff.com
Subject: Re: [Russiancamera] Re: Oil on the blades!!! Depth of field question....

...

Paul,

Stopping down reduces spherical aberration, primarily.  Spherical
aberration has nothing to do with how accurately the lens is ground into a
spherical surface.  It is a simple fact that light entering the lens at
different angles to the central axis comes to focus at different planes.
Stopping down uses mostly central or near central axis light to form the
image, and makes it sharper.  But this applies only to spherical surface
lenses, and is a major reason the lens companies have spent vast amounts of
money to develop practical aspherical lens surfaces.  One or two aspherical
surfaces in a lens can just about completely eliminate spherical aberration.

Of course as your diaphragm opening becomes really small you encounter
diffraction, which degrades the image. So there is always a "sweet spot" in
the aperture range at which a lens will deliver its best performance.
Usually this is around f/8 for most lenses.


I generally shoot most of my photos at f/5.6 and f/8 .

Bob


From russian camera mailing list:
Date: Tue, 09 Apr 2002 
From: Kevin Kalsbeek krkk@earthlink.net
Subject: Re: [Russiancamera] Re: Oil on the blades!!! Depth of field question....

Mike,

With any lens shot wide open-- unless it is specifically corrected to
perform wide open, you will see some problems wide open if you look hard
enough, and especially if you have the entire negative printed. The
aberrations are there.

Some lens designs perform "better" wide open than others.
As to the 65mm Mir- this is a lens I seldom use and have never tried it
wide open, as i do not shoot that way. The same has been said about
other Kiev glass, usually wrongly.

Kevin



Date: Tue, 09 Apr 2002 
From: Bob Shell bob@bobshell.com
To: russiancamera-user@beststuff.com
Subject: Re: [Russiancamera] Re: Oil on the blades!!! Depth of field question....

Paul Shinkawa at pshinkaw@yahoo.com wrote:
> The rule I thumb I read somewhere is that this is
> usually 2 to 3 stops smaller than the maximum
> aperture. if this is true, the "sweet spot" can be
> inconveniently  large for a fast lens like an f1.4.


Like most rules of thumb, this one is frequently wrong.  Pop Photo just
found that one of the Cosina/Voigtl,nder lenses they tested was best at
f/11.  Like everything else, it depends on the lens design.  Some modern
high speed lenses are best almost wide open.

Bob


From nikon mailing list:
From: "Jim MacKenzie" photojim@yahoo.com
Subject: Re: [Nikon] Re:17-35 plastic lens
Date: Wed, 27 Mar 2002 

----- Original Message -----
From: "darrylchew" darrylchew@pacific.net.sg
To: nikon@photo.cis.to
Sent: Wednesday, March 27, 2002 
Subject: [Nikon] Re:17-35 plastic lens

> all plastic after exposure to sunlight for prolong period will exhibit
> fogging. just look around at sign boards around you...the older ones all
> will show fogging....will this happen to the 17-35? years back i have heard
> that sigma lens also uses plastic lens and they are well known for fogging
> problem.


This is due to UV exposure.  Don't forget that the plastic elements in
modern lenses are buried within the lens, not usually the outer element -
and that the glass elements in front will filter in the high 90% range of UV
light (which is compounded by each additional element).  While this may be a
real concern, it will happen at an exceedingly slow rate.  I also tend to
keep my lenses in the dark when I'm not using them; they are only in
daylight a few hours each month at most.

Jim


From nikon mailing list:
From: AlLofquist@aol.com
Date: Wed, 27 Mar 2002 
Subject: [Nikon] Plastic Lenses

The most probable plastic for forming aspheric lenses is methyl methacrylate
or "Lucite". It is extremely transparent in the visable portion of the
spectrum and in the ultraviolet: much more so than most glasses. It's
castability makes it almost ideal for internal elements that are protected
from abrasion. The other optical qualities, such as dispersion and refractive
index do not cause any serious design problems that I know of.

Alex


From: Ron Todd rltodd@ix.netcom.com
Newsgroups: rec.photo.equipment.35mm
Subject: Re: specs on throwaway camera was Re: An observation.. "HQ" Kodak
Date: Tue, 15 May 2001

Bob you have a very good point.

So, I just tried one of these little Rochester Leicas (joke, not flame
bait), WOW.  Very sharp, good contrast, decent color (Kodak Max 800 is
not one of my favorite film emulsions, but give it its due), twenty
seven good pictures.  Grain structure is reasonable up to 5x7 prints.  I
am very impressed.  Look at the economics, five bucks more than a roll
of film for the camera.  Twenty rolls before your Stylus Epic starts to
pay off, six hundred rolls before your M6 starts to pay off. (joke, not
flame bait) Great for always having a camera with you and not having too
worry about something damaging your precious p&s; (or better) hardware.
I like it and I'm very impressed.  I believe Kodak has pulled out a real
winner here.

Robert Monaghan wrote:
>
> too bad, you'll be missing out on an aspheric lens design which is capable
> of delivering 44 lpmm on even crappy 800 ASA kodak film, it is a very wide
> 30mm f/8 (shot stopped down at f/10) and with an aerial lens resolution
> circa 365 lpmm. Not bad for a two element plastic lens, eh? If you'd like
> to see a 28 times enlargement (!), see page 42 march 2001 Pop Photo ;-)
>


From: "Ron Andrews" randrew1@rochester.rr.com
Newsgroups: rec.photo.misc
Subject: Re: Quality of Kodak Brownie No. 2 Photos?
Date: Tue, 21 May 2002


"Mitch Monger" motiograph@yahoo.com wrote...
> Hi,
>    Anyone have experience using the Kodak Brownie No. 2 box camera? I'm
> wondering about the quality of it's meniscus lens. If you have had
> experience with any of the Brownie No. 2 box camera models, I would
> greatly appreciate hearing what you have to say.
> Thanks,
>    Mitch

     I shot some film in a 2A Brownie a few years back. With the large
format negatives, the prints were virtually grainless. That meniscus lens
isn't great, but the sharpness was about what you would get from a single
use camera today (not great, but passable)



From camera makers mailing list:
From: "Gene Johnson" genej2@cox.net
To: cameramakers@rosebud.opusis.com
Subject: Re: [Cameramakers] PRIMATIVE PHOTOGRAPHY BOOK and building your own lenses
Date: Tue, 28 May 2002 

Wouldn't that get you a Rapid Rectilinear?  I've seen shots taken with these
lenses which were pretty impressive.  I was interested in something similar
a while back and went so far as to glue some achromats to either side of an
old Agfa shutter. the fl is approximately half the fl of the achromats
involved.  in my case, two 150mm achromats yielded a lens of about 75mm in
fl.  The camera was an old agfa silette with a ruined bellows.  I replaced
the bellows with a box.  Focus was fixed at infinity.  I only shot one roll
of film with it, and they looked fine.  Reasonably sharp with great depth of
field at f32!  These arrangements have quite a bit of coverage when stopped
down by the way.  You might be able to make a moderately wide angle lens
this way.

Gene
----- Original Message -----
From: "John" john@darkroompro.net
To: cameramakers@rosebud.opusis.com
Sent: Tuesday, May 28, 2002 
Subject: Re: [Cameramakers] PRIMATIVE PHOTOGRAPHY BOOK and building your own lenses


> Personally I would simply get 2 identical achromats and mount them on
> either end of the tube. Good achromats are fairly inexpensive though of course
> you would need a little help in defining the focal length of the combination.
> There should be a program to help with this for simple lenses.
>
> Regards
>    John S. Douglas, Photographer
>      http://www.darkroompro.net
 you wrote:
>
> >Hello!
> >
> >I bought the book "Primitive Photography : A Guide to Making Cameras,
> >Lenses, and Calotypes"
> >by Alan Greene
> >
> >
> >Very nice book going into detail on building a large format camera for
> >Calotype and wet plate photography. i'm building an 8x10 film holder
> >right now.
> >
> >I'm mainly interested in making my own lens for this camera, which this
> >book discusses. Unfortunately, I'm not clear on what lenses (elements) I
> >need to buy to build this lens?
> >
> >My intent is for "Landscape" photography. I'm guessing 300mm. The
> >objective is not to get laser sharp pictures. I'm going for that ols look
> >"holga" like.
> >
> >Anyone with this book understand how I should purchase the lenses?
> >
> >The book has nice pictures showing how to cut PVC pipe to mke the barrel
> >and settings for the lenses.
> >
> >Thanks!
> >
> >Mac



From camera makers mailing list:
From: "Gene Johnson" genej2@cox.net
To: cameramakers@rosebud.opusis.com
Subject: Re: [Cameramakers] PRIMATIVE PHOTOGRAPHY BOOK and building your own lenses
Date: Tue, 28 May 2002 

I forgot some things.  I mounted mine with the convex surfaces facing each
other, and got them as close together as possible.  I was mimicking the
design of a Plossle telescope eyepiece, and only later learned that this was
basically the same design as the Rapid Rectilinear type design.  The (fl1 +
fl2)/4 formula is correct if the lenses are identical and touching I think,
but the fl gets shorter(?) as the lenses get farther apart. If you're making
your own barrel, and using a waterhouse stop or fixed stop, you'll be able
to get them pretty close.  For an 8x10 youll probably be looking for some
achromats of 500mm fl or longer.  Maybe you could use simple meniscus lenses
instead of achromats.  My guess is you would probably lose some performance
though.

Gene
...


from russian camera mailing list:
From: "Per Backman" perbackman@swipnet.se
Date: Thu, 25 Jul 2002 
Subject: Re: [Russiancamera] Re: Are Czech and Hungary Optics related to CZJ or Russian?

Jay Y Javier wrote:

>Nihao Zhang & Roman
>
>The 23.5 size was used for some Anaret and many Belar enlarging lenses.  Some
older enlarger lenses also came in this mount- I have Schneiders in this mount
as well which came with my Beseler.
>
>The Anaret 4.5/50 is an excellent lens, even for colour prints.   I've always
thought that it had 4 elements, but after dismantling it for clenaing, it
turned out that it had really 3 elements.

Hello,

Anaret; 3-element, Belar; 4-element, Meogon; 7-element.

Newer Meopta enlargers have 39mm mount.

Per
The PHOTO page;
Images (nude), B/W Formulae (lots of them);
http://hem.fyristorg.com/pbackman/



from rollei mailing list:
Date: Sat, 20 Jul 2002 
From: Marc James Small msmall@infi.net
Subject: Re: [Rollei] A Zeiss Question OFF Rollei topic

 Richard Knoppow wrote:
> FWIW, the old Henney and Dudley _Handbook of Photography_ (1939) lists
>three lenses under Zeiss-Ikon. This is a separate list from Carl Zeiss.
>Netter, f/3.5 to f/7.7,  Cooke Triplet

That should be "Nettar", Richard.  All of the Nettar and Novar lenses were,
to my relatively confident knowledge, of three elements.

Marc
msmall@infi.net  


From: "Q.G. de Bakker" qnu@worldonline.nl
Newsgroups: rec.photo.equipment.35mm
Subject: Re: Lenses - elements and groups.
Date: Sun, 22 Sep 2002



Jim wrote:

> Can anyone give or point me to some information on what I
> should take from "number of elements" and "in 'x' groups"
> from a lens spec? Cheers, Jim.

"Elements" are the different pieces of glass that are presnt in the lens.
"Groups" are one or more elements that are separated by an air space. Two
and more elements can be cemented to each other and then form a group.
For instance the classical Tessar triplet design has three elements in two
groups: a first group consisting of two differently shaped pieces of
different types of glass cemented to each other; then an airspace; and
finaly a single piece of glass forming the second group.

The number of elements and/or groups by itself does not say anything at all
about how good a particular design is. Only something about how many of
those the designer needed to find a way to meet the requirements set.
More elements and/or groups however means more chance for internal
reflections/flare.


From: Jeff four_season_photo@yahoo.com
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Old designs - still in production?
Date: Sat, 28 Sep 2002


Off the top of my head, I think the latest 50/2.8 Leica Elmar and the
current 40mm Nikkor are 4-element designs. But I'm not aware of anything
for MF cameras.

steven.sawyer@banet.net wrote:

> Are there any triplets or tessars still in production for modern
> cameras?  Or do you have to have at least six elements in order to merit
> a modern mount?



[Ed. note: not only do a few elements go a long way, they need not cost a lot either!]
From: artkramr@aol.com (ArtKramr)
Newsgroups: rec.photo.equipment.medium-format
Date: 04 Nov 2002
Subject: Re: Is Zeiss batch testing lenses?

>Subject: Re: Is Zeiss batch testing lenses?
>From: rmonagha@smu.edu  (Robert Monaghan)
>Date: 11/4/02
>what I find interesting about Brian's notes on the use of final MTF
>testing on low cost lenses (e.g., $10 scanner optics) is that it confirms
>my suspicion that it is possible to do a relatively low cost and fast
>(Nikon's six second test) MTF test of the final assembled lens, even


$10.00 sounds low, But it is quite expensive especially when we consider  mid
priced lenses.  If you went into the lens business you could get all elements
ground and polished to your specifications and even coated for less than $2.00
each. So all the elements in a Tessar would cost $8.00. And the maker is making
a profit on that sale. The lens mounts are  turned out by automatic computer
controlled machinery at a very low cost per mount so $10.00 is  a big number to
dump on all that especially with markups all along the way. The prices I
mentioned would vary with type of glass and  curvatures plus accuracy of
spherocity demanded.  And good centering adds to the costs as well. BTW, the
greatest problem with getting a good enlarging lens is lousy centering.

Arthur Kramer
Visit my WW II B-26 website at:
http://www.coastcomp.com/artkramer


From russian camera mailing list:
Date: Fri, 3 Jan 2003 
From: "Jay Y Javier" nikitakat@edsamail.com.ph
Subject: Re: Re: Re Lubitel 166

No, not a trick...  :-) There was a discussion of this at the zenit list.
Depending on whose glossary is used, a "triplet" would refer to a lens design
which has three components, though not necessarily the same number of elements.
Three components which do three things as light passes through them: converge,
diverge, and converge (or is it the reverse?)

I am following the definition set by Lester and Lester (or Morgan & Lester): in
the Leica manual, the Elmar (four element, and very close kin to the Tessar) is
classified as a triplet.  


From: "David Foy" nospam@this.address.please
Newsgroups: rec.photo.equipment.medium-format
Subject: Yashica D (was Re: Yaschimat 124G vs Rolleiflex-T ???)
Date: Wed, 08 Jan 2003

I've had the same general experience with several D's. They have never given
me disappointing images. There is a general tendency to under-rate
three-element lenses on principle, when in fact they can be excellent.
Having said that, there are many poor performers out there that are
triplets, which is how the name got tarnished.

David Foy
...


Date: Wed, 18 Dec 2002 
From: Dale Dickerson vze2g2z8@verizon.net
To: TLRList@topica.com
Subject: Re: [TLR List] Who says you need four elements!

I have may Father's Rolleicord II. It has a coated Triotar. It is a very
late model. He purchased it in fall of 1949. It was on close-out as the
Rolleicord III was coming out.

I had Mr. Rollei repairman Harry, did a cla on it in 2000. After he
calibrated it the lens performed very well for a Cook's Triplet design.
Below f16 is not good for edge to edge  for sharp work. However the
contrast is great and has a sharp but soft look even at f16.

I have used six Rolleicords with Triotar lens. All were post W.W.II and
all were coated. The best was able to give sharpness between f11 and f16
at the edges. I view it as a portrait camera for a creamy sharp/soft
center with soft edges. 

My  Xenar and Tessar design lenses are much sharper stopped down and
perform better at the edges at all f stops. The only time I use a
Xenotar is for super sharp images at 2.8-5.6. The Tessar design lenses
are very good at f8-f22 and much lighter to carry. (By the way, I have
not seen any advantage in the later MC six or seven element versions
over the single coated five element Xenotar lens. The five element
version has very good contrast.)

I like your TLR portraits in the LA magazine. I remember a series you
did last year of a radio station staff.  Which model are you using?

Dale   
Slobodan Dimitrov wrote:

>I didn't know that any of the Triotars were coated. Anyone have any info
>on this?
>Slobodan Dimitrov



Date: Mon, 16 Dec 2002 
From: Phil Marcus pmarcus@swbell.net
To: TLRList@topica.com
Subject: [TLR List] Who says you need four elements!

Recently I examined some negatives I took with a borrowed 'Cord.  It had a
Triotar lens that was coated.  During that period I was shooting a lot of
film, some with modern SLR medium format gear.  I owned a Mamiya RB67 at the
time.

The negs taken with the three-element lens from the old 'Cord are among the
sharpest I've ever seen.  The overall image quality is beautiful, nothing
I've seen since.  Showed me that there's more to optics than lots of glass
and expensive design.  And, yes, the prints (of a beautiful woman wearing a
jacket full of textures) look as good as anything I've ever seen or shot
myself.  I wish I could duplicated that look.  Makes me wonder if I just had
a well calibrated camera.

Phil



Date: Mon, 16 Dec 2002 
From: "Merritt, Robert" MerrittR1@ING-AFS.com
To: TLRList@topica.com
Subject: RE: [TLR List] Who says you need four elements!

No question -- you can get very nice results with a three element lens.  I
have a Zeiss Nettar with a Novar lens that produces fine pictures.  A four
element lens produces better results over a wider aperture range, I think,
but the "lesser" lenses work well.

I think the cheapest of the current Seagull TLR line has a "3."  Speaking of
which, has anybody used one of these cameras?  As far as I know they're the
only TLRs being made currently other than the Rolleiflexes, which are of
course astronomically priced.

Nick


From: John Stafford john@stafford.net
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: 6x9 used camera...
Date: Wed, 11 Dec 2002

Rabbitbert at rabbitbert@aol.com wrote 
> Hey, this is just a little off the topic of this thread but I want to ask. Is
> there a particularly strong reason or reasons why a person should seek out a
> 6x9 camera rather than a more common 6x7 camera?

It's something about the Golden Mean or some kinda unscheduled religious
thing.

>  I feel that I can
> get all the quality I could ever need from the 6x7 frame

Sally Man(n) gets all the quality she needs from a fungus filled, stepped-on
coke bottle bottom.


From: w-buechsenschuetz@web.de (Winfried Buechsenschuetz)
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Yashica D (was Re: Yaschimat 124G vs Rolleiflex-T ???)
Date: 8 Jan 2003 

"David Foy" nospam@this.address.please wrote 
> I've had the same general experience with several D's. They have never given
> me disappointing images. There is a general tendency to under-rate
> three-element lenses on principle, when in fact they can be excellent.
> Having said that, there are many poor performers out there that are
> triplets, which is how the name got tarnished.

I totally agree. I once got an east-german 6x6 folder with a
three-element Meyer Trioplan lens and was surprised with the quality
even wide open. I just made a test with several old 6x9 folders. One
(a Welta Trio) had a Trioplan lens, too. Its performance came close to
the four-element Tessar copy on the Moskva5. Only advantage of the
latter is that it offers 1/2 f-stop more.

A good three-element lens can come close to a four-element Tessar type
lens. But, as you mentioned, there are some three-element lenses which
are really poor. Worst one I found yet was a french Drestyl lens (on a
6x9 Drepy folder). Also the Zeiss Triotar lens is far from being sharp
edge to edge and is worse than the much less known Trioplan lens
mentioned.

Winfried



From Russian Camera mailing list:
Date: Mon, 14 Apr 2003 
To: Russiancamera-user russiancamera-user@mail.beststuff.com
From: nicha kapetanikolas@hotmail.com
Subject: [Russiancamera] skopars and skopars

The use of the name "Skopar" by the cosina manufacturers shows how
un-historical and ignorant some market techniques can be. They use a name
meaning historically "4-element lens" for a lens with god-knows how many
elements. It is like calling a 6-7 element lens 'Tessar'.

This weekend I saw a cheapo plastic 'Voigtl,nder' point and shoot with a
lens called: "Voigtl,nder Zoomar".

I understand that they have purchased the rights to the Voigtl,nder name but
I can't resist feeling that the use of some names and inscriptions (such as
the one "Voigtl,nder Germany since 1756") are purely sacrilegious.

Nikos


From: hemi4268@aol.com (Hemi4268)
Newsgroups: rec.photo.equipment.medium-format
Date: 19 Aug 2003 
Subject: Re: zeiss ikonta for shooting?

>Of course distortion and corner sharpness is something no one should be
>concerned with..
>
>The main point of the extra element is to improve performance at the larger
>f-stops and in the corners.

Could be but for most applications it's really to improve distortion. If you
look at any slightly complex lens design, these lenses have four elements. It
a copy lens, the front two elements will have the exact same design as the back
two elements. Two sets of two if you will.

The front two correct for resolution even in the corners and the second set
turned around correct for distortion.

The idea being that the distortion caused by the front two elements will be
completely backed out by having the light go through the rear end of the second
identical set of elements. Sort of having light go through a lens twice.
First through the front and then through the back thus no distoration.

Larry


From: w-buechsenschuetz@web.de (Winfried Buechsenschuetz)
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: The old TLR lenses
Date: 18 Aug 2003 

bill martin wcmartin@vnet.net wrote in 
> I don't know how you go about
> measuring the number of elements -- some say point it at a lite source
> and count the reflections in the lens. number of reflections = number of
> elements? I don't know how well that works. My Zeiss Tessar produces 4
> reflections ok, but so do most of my anastigmats.

Any lens element surface will produce a reflection. So with a
4-element lens (with cemented rear element) you should see 7
reflections and with a 3-element (air spaced) lens you should see 6
reflections. The four reflections you mentioned seem to refer to the
front lens cell only - the other lens elements are 'hidden' by the
shutter blades. Both triplet and Tessar designs have 2 (air spaced)
front lens elements.

It is difficult to distinguish all reflections you see from a lens at
a time. So you'd better check reflections from the front lens cell and
rear lens cell separately. A triplet rear lens element will add
another 2 reflections. Also, on a Tessar rear lens element you will
see just two reflections at first glance, although the Tessars have a
cemented rear lens element pair. The reflection from the cemented
surface (just one for the two surfaces meeting there) is hard to see,
since a cemented surface reflects much less light than an glass-to-air
surface, and it is also much smaller than the other two reflections.
But it IS possible to see them. Also, when checking the reflections
you should look at the lens from different distances. Some reflections
appear as a bright overall shine from certain distances and are not
similar to the image of the light source.

Winfried


From: "Stan Patz" SKP113@MINDSPRING.COM
Newsgroups: rec.photo.equipment.large-format
Subject: Re: crappy lens please
Date: Wed, 27 Aug 2003 

To Rocco and the group,

A number of years ago I faced the same problem. I wanted a "crappy lens"
(and cheap) for 4x5 field work. Here is how I solved the problem.

I collected a large number of old Kodak folders from flea markets and tested
their lenses. I found that many of these lenses, when cleaned, made very
nice images. But the real keepers are the "meniscus" lenses - simple two
cemented element lenses which are found in cameras with the painted brass
lens shades. (When you look at these lenses, they are hard to see, because
they are recessed behind the "shade".)

When these meniscus lenses are used as Kodak intended, they are good,
especially at small apertures. BUT, if you remove the "lens shade" and use
more of the glass, the image deteriorates smoothly to maximum opening. The
shade restricts the lens to about f8, but there is another stop or so
depending on focal length. Wide open the image is pretty smeary.

You could use the Kodak ball-bearing shutter the lens comes in. Crude, but
useful. I had a Copal shutter adapted to two choice lenses, a 101mm and a
120mm. I made a dual aperture scale for the lenses on the Copal, but I
seldom use the 120mm; the 101 covers 4x5 with very limited movements.

I think this thread bored a lot of people. If you (Rocco) want more info,
contact me off list. Even though you cannot see the softening effect in such
a small picture, you can go to my website and see a lake scene which has
some mist rising; it is in the "Infrared" section.

--
Stan Patz NYC

www.PatzImaging.com

> rbellant@yorku.ca (Rocco Bellantoni) wrote 
> > I am wondering if anyone can suggest a really bad lens for 4x5 work.
> > I'm serious. All of my large format lenses are super-sharp, and just
> > too good. I've grown tired of this look; I want my personal work to
> > take on a more impressionistic feel. Sort of like the Holga look,
> > except for large format. I don't want a new lens though as I don't
> > want to pay much for it. I'm looking for something old. This is not a
> > solicitation, I'm only looking for suggestions. Lens flare, low
> > contrast, low resolution, colour shifts and strong vignetting are all
> > welcome.



Date: Mon, 29 Dec 2003 
From: Gerald Newlands gnewland@ucalgary.ca
To: cameramakers@rosebud.opusis.com
Subject: [Cameramakers] Re:Meniscus lenses

Dear Michael,

The meniscus lens as a photographic lens was devised by Wollaston in
1812. By using appropriate radii it will yield a reasonably flat field.
It should also be noted that the aperture plate should be in front of
the lens tol reduce coma. Furthermore, the concave surface should face
the subject. Meniscus lenses are used in disposable cameras but the
aperture plate is behind the lens and the convex surface faces the
subject!. Have often wondered if a noticeable improvement would result
if they were set up as determined by the opticians. The meniscus lens
came to be known as a landscape lens.

The Goertz Hypergon of 1900, was a symmetrical lens composed of two
strongly curved mensicus lenses and it had a field of view of 140
degrees at f-22. Meniscus lenses can yield pretty sharp images.

Regards

Gerry


From: Stacey fotocord@yahoo.com
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Tominon 127mm Doesn't Match Shutter?
Date: Sun, 08 Feb 2004 
Bob Monaghan wrote:
> Since I suspect that spherical aberration is the source of much good
> bokeh, the fact that triplets and lens cells would have more uncorrected
> aberrations than a four element (tessar..) and fully corrected main lens
> would not be surprising. This may be one of those cases where older and
> cheaper (fewer elements..) may be better? ;=)

And with most of these lenses, when used at the small f-stops most LF
users use, these "defects" are corrected by stopping down.

I made a "soft focus" lens for my K-60 by taking a dead 80mm biometar and
removing all the glass except for the front element. I was shocked how good
it is at f16-f22 for 1 piece of glass.
--
Stacey




From: stacey fotocord@yahoo.com
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: when only bad lenses are good enough?
Date: Mon, 17 Nov 2003 

Bob Monaghan wrote:
> Nearly all of the soft lenses,
> even the dang +10 diopter single element lens SIMA-Soft gizmo, will yield
> surprisingly sharp photos stopped to f/8 or so, it is quite horrifying ;-)
>

Yep I "made" a soft focus lens out of a junk 80mm biometar using only the
front element stuck back into the lens housing just in front of the
diaphram and at f8 and smaller is amazing how sharp just one lens element is!
--
Stacey


From: steven.sawyer@banet.net
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Fewer elements - lesser Bokeh?
Date: Sat, 27 Mar 2004 

I believe "dimeniscus" is a term Kodak used to use for their "portrait" box
cameras that used a second meniscus lens for close ups. If you just put a
diopter in front of a meniscus lens, you'll get the same results, although
getting the right focus can only be done by inspection. I use measuring tape
for this purpose.

Bob Monaghan wrote:
> see the http://medfmt.8k.com/mf/soft.html pages on soft lenses; there is a
> +10 (100mm) single element diopter lens used in a focusing mount as a soft
> lens, often also praised for its bokeh too ;-0)
>
> dimeniscus - ;-)
>
> now I have another lens combo to try - thanks for the suggestion ;-)
>
> regards - bobm



From: "Nicholas O. Lindan" see@sig.com
Newsgroups: rec.photo.equipment.large-format
Subject: Re: How do I build my own large format lens?
Date: Fri, 02 Jul 2004


"Kirk Fry" kirkfry@msn.com wrote
> Someone spouted:
> > [3rd] Cheapest lens for a view camera? [Guy doesn't like pinholes
> > or zone plates].

> head for you your local drug store or Costco.
> Buy the cheapest reading glasses they have.

Two close-up lenses work well too - condition is irrelevant.
If you don't have a selection banging around in a box, well
then, get some: the more used, dusty, cracked and scratched
the better. A barrel can be made from a length of cardboard
tubing or black plastic pipe. Glue an aperture in the middle,
cut a slot(s) in the tube for a set of cardboard waterhouse
stops. Use a hat for a shutter.

Try 'sink strainer', 'wagon wheel' and other such apertures.

Performance will vary with lens spacing and stop position.

The use of two lenses clears up all of the distortion
and some of the aberrations.

You can do the same with a 35mm - use a close-up bellows
and a pair of +3's - results in a 167mm lens.
--
Nicholas O. Lindan


From: kirkfry@msn.com (Kirk Fry)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: How do I build my own large format lens?
Date: 1 Jul 2004 

Really cheap lens. First the shutter is going to be the most
expensive part. Try to find one from an old beat up folder that works
for really cheap then head for you your local drug store or Costco.
Buy the cheapest reading glasses they have. Costco has them for
$5.00. So 1.00 diaopter is 1000mm. 2 diaopters is 500mm. You are
going to cut two circles of plastic, one from each lens and then put
them back to back in the shutter to make a symetrical lens. So if you
stick two 500 mm ones together you will get 250 mm. That is a little
too short so maybe using a 1.50 set of glasses is the place to start.
The at f22 it will be pretty sharp.

Cutting the plastic lenses is not all that easy. I think I might try
something like a soldering iron to melt the edges and then sand paper.
Don't know for sure.

Kirk


camartsmag@aol.com (CamArtsMag) wrote 
> I'd like to build a simple lens for use with a large-format camera
> using 'off the shelf' lenses such as those available from a scientific
> catalog. Priorities are as follows (all are desireable - but 1 is most
> important and 5 is least important):
>
> View Camera magazine did an article about this a few issues ago. Call us at
> 800-894-8439 if you would like a copy
>
>
> www.viewcamera.com
>
> steve simmons


Date: Sat, 15 May 2004 
From: "Uptown Gallery" murray@uptowngallery.org
Subject: [Cameramakers] lens experiments
To: cameramakers@rosebud.opusis.com

OK - more questions for you lens experiementers out there.

Alan Greene's Primitive Photog. book enabled me to figure out the equations
I had started to figure out.

We know a single meniscus will work. We know that prior to Wollaston (I
think), double convex lenses were used, with more field abberations.

What's a field abberation? I've seen descriptions of coma, two types of
chromatic, spherical and som eother abberations, but not field.

Now, with Greene's help, we (we're all in this together right?) know that
lens powers can be added and the spacing accounted for simply to get a
resultant lens power for a combined pair of lenses.

This leads me to solution for a use for the Rodenstock-Ysarex front cells I
found - they are negative (say (-5) diopters for conversation's sake), but
if I combine them with a positive lens of greater than (+5) power, I have a
real instead of a virtual image! Abberations, too, I'm sure.

My main worry is coverage for a 5x7 camera...so I'm aiming for 210-250 mm
f.l. with the other lens elements I have lying around.

Now, Greene also cites formulae for calotype-era lens simple designs with
regard to spacing, diameter and diameter ratio of elements.

Has anyone come to any conclusions regarding what happens when you 'cheat'
and use smaller diameters or spacing out of necessity?

Lastly, I started to take apart a large lens I suspect is monochromatic
because the coatings and reflections are all yellow (looks like old sodium
street lights). Projected images from one element onto a wall have bad color
fringing - bright blue and other colors I can't identify.

Would such lenses be better than uncoated for a chromatic (as in not
achromatic and not APO-chromatic) lens because they already filter some of
the spectrum. There would still be a need to correct for bellows position
for visual vs 'actinic' focus position.

Anyone ever remove lens coatings without harming the glass? Acid?

Thanks

Murray



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