Single versus Multi-coated Lenses
by Robert Monaghan
Related Local Links:
Lens Flare (and Lens Hoods) (tips, homebrew hoods..)
Lens and Mirror/Prism Recoating FAQ
Ultraviolet Photography (using uncoated, older lenses)
Introduction
The advertisers and photo shop sales clerks would have you believe that
multicoating of lenses is absolutely essential to good photography. Why,
you should probably just toss out all those old single coated filters and buy brand new ones which are
now available in a multi-coated version (at a high price). Please don't
horrify them by pulling out your stock of uncoated filters!
Are they
right? Are multicoated optics and filters essential for good
photography? The short answer is NO!
Counterpoint
Laboratory studies reported below of identical coated and
multi-coated lenses clearly show that the benefits from multicoating are minimal
for typical medium format and similar lenses of up to 6 or 8 elements. If
you use a zoom lens with many elements, then multi-coating is
essential. But multicoating is much less
critical for fixed focal length lenses which usually have only 4, 5, 6 or at
most 7 elements typically. Consider this quote:
"Canon
should also be lauded for its attitude towards multicoating. They have publicly
acknowledged that the only really useful reason for multi-layer coatings is to
increase light transmission. They have, therefore, ignored any possible gains in
terms of flare and ghost elimination (which, as we've shown, isn't really such a
valid function of multicoatings in most cases), and instead, they have
concentrated on improving light transmission with their Super Spectra Coating."
[Source: Multi-Coating, Asset or Gimmick, Bennett Sherman
and Hiroshi Kimata, Modern Photography, June 1975, p.147; emphasis added]
Multicoating
| Multicoating vs. Single Coated Lenses
|
|---|
|
Although multi-coating is often more of a sales tool than a decisive
optical advantage, it does serve as a useful marker. If a lens is new
enough to be multi-coated, it is almost certainly equal in quality to just
about anything being made today. The advantages of multi-coating itself
will normally be apparent only in adverse conditions, as when shooting
under a white sky without a lens shade, or directly into the light. We
would never willingly use uncoated lenses. from Roger Hicks and Frances
Schultz in Medium and Large Format Handbook, p. 105
|
So the manufacturers have known that the real value of multicoating over
single coating is not reducing flare nor reducing ghosts, but only
slightly improving light transmission. Somehow, they have kept this news a
secret from their advertising copywriters, right?
If the differences between
single versus multicoated filters were really as dramatic as shown in some of
the magazine ads, shouldn't these differences be equally visible when you
compare a coated versus a multi-coated filter side by side? Try it
sometime. Have a magazine open to one of the ads, and see if you can get
the same huge differences in reflections they show in the ads? Can you? I can't!
Historical
Notes
Simply examining some of the great photographs in older magazines made with
older lenses should make you wonder about the magnitude of benefits from using
multi-coated lenses over single coated versions. The older lenses seem to do quite well in many of
these older photographs. Certainly, I have seen many nice original Ansel Adams
prints which I know were made using uncoated lenses, or at best single coated
Hasselblad lenses such as many of us still use today.
If you are using
an uncoated lens, you can even use the same tricks used by Ansel Adams and
others to compensate for lowered contrast during development [see Ansel Adams' series
The Camera..]. You can also use uncoated older lenses (with older natural
adhesives versus today's UV cured lens adhesives) to do ultraviolet
photography using such lenses and regular films with a UV-only pass filter
(e.g., Kodak #18A).
Many users of older medium format and 35mm
cameras can't buy multicoated lenses, since none are available for our
camera mounts (e.g., Kowa 6/66, Norita 66..). In the past, you could get
lenses coated inexpensively, but such
services are rare now.
Even if you have single coated older Hasselblad C
chrome lenses, you may wonder if the very high cost of upgrading to current
multicoated Zeiss T* lenses is worth it? In a similar case, are the multicoated Kiev
lenses worth a 50%+ price premium over the older single coated lenses? Due to
the tendency for fisheyes to flare thanks to their
wide coverage (180 degrees), I think the answer may be yes for the 30mm fisheye
lens, but what about the other optics?
Naturally, I have always wondered
just how much I was losing by not having the latest and most expensive
multicoated medium format and 35mm SLR optics. When I have been able to compare
single coated and multicoated lenses, I haven't been able to see significant
differences either, except perhaps in backlighted situations.
The good
news seems to be that single coated lens users aren't missing out on
very much as far as flare and ghost reduction goes, based on technical
laboratory tests on single versus multicoated (and uncoated) lenses reported
here.
Comparing Single vs. Multicoated Optics
Unfortunately, we usually can't compare identically constructed lens
which are uncoated, single coated, and multi-coated to precisely see what
benefits we are getting from various coatings and multicoatings. I guess
you could do this by finding a single coated design that was later multi-coated,
and by careful dis-assembly and removal of the lens coating from one such lens
example. Some lens recoating services could
do this for you, if you don't mind the expense. Careful lens reassembly would be
needed and require verification (e.g., so decentering or other problems weren't
the cause of observed flare and other optical aberrations). So you could
have 3 lenses, one uncoated thanks to a chemical bath, one earlier lens variant
that was single coated, and a later lens variant that was multi-coated. Now you
could compare photos with all three lenses to observe the benefits of coating
and multicoating over uncoated optics.
You can probably also find some
35mm lenses that were transitional, in which an earlier lens is single coated,
and the later lens is multicoated too (e.g., Pentax 50mm f/1.4 single coated and
SMC multicoated versions). In medium format, you might be able to compare
a late Hasselblad C chrome lens which is single coated against a later
multicoated T* lens of similar design too. So chances are good that you can run
your own multicoating benefits tests, in some limited ways, between single
coated and multicoated optics of identical construction, quality, and design.
But without spending kilobucks on spectrum analysis gear and lab chart
recorders, you would be hard pressed to produce a scientific comparison of your
test lenses that would stand up to challengers.
Modern Photography's
lab was able to get a 100mm f/2.8 lens with five elements in four groups
constructed in uncoated, coated, and multicoated versions for their lab study
and actual film shooting tests. So the results reported in their article are
unique among the flare and multicoating studies I have seen published by having
such identical lenses to study in their laboratory and practical photo shooting
tests. Since the lenses are new and carefully identically made, except for their
coatings, they provide an ideal test case to study coating effects.
Modern Photography's
Multi-coating Lab Tests
So I highly recommend that you obtain the original article in June 1975 Modern
Photography titled "Multicoating: Asset or Gimmick?" by
Bennett Sherman and Hiroshi Kimata (p. 90 et. seq.). The following quotes from
the article photos summarize some of their (and my) observations based on their
published flare comparision photos. If you are one of those who doubt lab
test results, you can simply look up the article and check out these
photographic examples. You should find them equally convincing as the authors
and I did:
A single coated lens, center, removes most of the ghosts. Multicoated lens,
right, offers little improvement over single-coated lens. [Ibid.,
p.91]
Single coating, center, improves matters in ghost
reduction, and again, multicoating, right doesn't really do much more.
[Ibid., p. 91]
You will quickly see that the difference in
ghost-producing ability between single- and multi-layer coated lenses is
really very little. [Ibid., p. 92]
Most flare with uncoated
lens: You can easily see flare over the entire picture at right when background
is five stops brighter than subject at foreground. [Ibid., p. 93]
Single
coat controls flare well: With normal exposures, flare is almost
invisible. [Ibid., p. 93]
Multicoating helps only a bit:
In practical picture taking, the flare caused by reflection from multicoated
lens surfaces is not much less than the flare from single layer coated
surfaces. Our picture taking results bear out the laboratory analysis.
Multicoating sometimes helps, but only a little bit more than
single-coating. [Ibid., p. 93]
The single layer anti-reflection coating is doing its job. With multicoating,
you hope that the background will be almost completely black. Unexpectedly, it
wasn't and, alas, we found just a modest improvement over the single-layer
coated lens. Why isn't multicoating as effective as we had hoped? The answer is
fairly simple. In the five-element 100mm lens, a single coating improved
transmission by about 20 percent. But multicoating only improved transmission by
12 percent over single coating. Therefore, the improvement between single- and
multicoating cannot be as dramatic as between no coating and single coating. ...[Ibid.,
p. 134]
Some Shocking Surprises from Lab Flare Tests
Just how bad was this overall flare we found in the background? .. We got
some shocking surprises.[Ibid., p. 134]
Using a very precise
laboratory analyzer.. we could detect virtually no
measurable difference in background flare between the single-coated and the
multicoated lenses. And in our portraits, which were shot against the
same backlit screen used by our analyzer, we could detect
no difference in flare within transparencies produced by single- and
multicoated leness (see photographs, page 93)! ...[Ibid., p. 134]
If
we overexposed our main subject by six f/stops or more, flare light could be
found in the dark areas of the subject. But, the
difference in the amount of flare (in such abnormal circumstances)
between single- and multicoated lenses was very minimal...[Ibid.,
p. 134]
Obviously, the real improvement of
multicoated over single coating does not have a lot to do with overall
flare. It seems to lie with increased light transmission and minimizing
ghosts, principally in lenses having many elements, such as zooms. And even in
the ghost and transmission area, multicoating is far from 100 percent effective.
[Ibid., p. 134]
If the thickness of any layer
is off by as little as 5 percent of the required thickness, the entire coating
will be bad - strong reflections will be noticed on one or more colors. ..A bad
job of multicoating can ruin a lens and prove to be far worse than no coating at
all. We have seen poorly multicoated optics which produced violently yellow
pictures. [Ibid., p. 138]
We compared the transmissions of many
lenses, both single-coated and multicoated. Sometimes improvement in
transmission was very dramatic, sometimes not as much. If a lens had a good
single coating and was well designed, improvement was not as great as with a
less efficient design or a less effective single coat. [Ibid., p.
138]
Even though some lens manufacturers do not indicate on the lens
whether it is multicoated or not, you can tell in most cases. You take the lens,
remove its front and back caps, and open it to full aperture. Hold the
lens under a bright light source, such as an overhead bulb, so that the bulb
will reflect on the surfaces of the lens elements. Look down into the lens at
these reflections. If all the reflections are light amber or blue, the lens is
single-coated. But if some are light amber or blue, and others are deep magenta,
dark green or a deep reddish yellow, the lens has multicoated elements. [Ibid.,
p. 138]
Some lens makers are claiming to multicoat every element of every
lens they make. But it's questionable whether this is either necessary or
optically sound. [Ibid., p. 138]
Since four is the minimum required for
so-called multicoating, Minolta's double or triple coatings are not advertised
as multicoatings. [Ibid., p. 147]
Multicoating improved light
transmission by only 1/2 f/stop or less over single coating. Flare elimination
was very minimal at most. Ghosts were minimized by multicoating,
principally in many-element lenses. [Ibid., p. 147]
The real
flare and ghost culprits of today are not products of the optical engineers.
They are caused by improper blacking of the mechanical parts of the lens barrels
and poor baffling within the film chamber. Anyone who chooses his lens solely on
the basis of multicoating is, in our opinion, putting the optical cart before
the mechanical horse. [Ibid., p. 147]
Photo-Myths Revisited
If you believe the photo ads and photo store sales clerks, multicoating is an
absolute must for any lens to produce a decent performance with
flare.
What Modern Photography's laboratory tests showed
instead was that they "could detect virtually
no measurable difference in background flare between the single-coated and
the multicoated lenses" and "the
real improvement of multicoated over single coating does not have a lot
to do with overall flare." [Emphasis added here and above]
In
other words, you should not and probably won't see any real improvement in flare
or ghost reduction from switching from single coated to multi-coated
lenses. I still advocate that you observe flare
reduction techniques such as the use of lens hoods as a common sense
precaution.
On the other hand, you may understand why Hasselblad's
newest lenses have worked on improving baffling as a low cost way to squeeze
some extra flare resistance from their lenses. Some Kiev
owners claim to have discovered that the supposed lens flare problems are due
mainly to shiny lens mounts and poor baffling and lack of blackening of
reflective surfaces in their cameras. So before you blame your lens or
decide to live with flare, you might take a closer look at your lenses and
cameras for shiny and reflective surfaces that may be the culprits, rather than
blame your lenses...
Notes:
From Modern Photography, January 1981, How to Choose a Lens (SLR Notebook), H. Keppler, p. 58.
"Most lenses today are multicoated; but don't avoid single coating.
There's not much difference in picture taking unless you have a highly
complex zoom or extremely fast wide angle"
From Modern Photography, November 1980, p. 18, View from Kramer column:
My protars are beautiful, but they are anything but crisp. Their contrast
is less than impressive, and having the lens coated (as I have) doesn't
help much. Coating has no effect in the scattering of light within the
glass. It cuts down on reflections between air spaced elements, but the
lower contrast of old lenses is a result mostly of poor scattering
characteristics due to the qualities of the old optical glasses. Generally
they [older lenses] are softer and flarier than modern lenses.
From Modern Photography, October 1982 p.63 in Herbert Keppler's SLR column:
Must all lens elements be multicoated? No. While it makes good ad copy to multicoat,
most lens designers agree that few lenses benefit from multicoating all surfaces. In fact,
with simple lenses having few elements, multicoating yields virtually no advantage at all
over single coating...
Related Postings
From: "Q.G. de Bakker" qnu@worldonline.nl
To: "Robert Monaghan" rmonagha@post.cis.smu.edu
Subject: Re: economics, zeiss and VHB marriage
Re: shift film, not lenses ;-) Re: converted & posted mf/photoads.html
Hello,
Funny thing about Hasselblad's sudden drop in price and many discount offers
is that they only happen in the US. Or should i say: not in Europe?
Perhaps the market in Europe is reacting differently to recent developmens
on the digital front. Or is the European market just not large enough? I
wonder. And remember, we here in Europe had to pay more for the privilege
than our friends the US anyway.
I've taken a look at your Blind Lens Test page. I wonder, are you really
planning to send out sets of slides all over the world? Would that not be a
very expensive way to obtain results that are rather predictable?
Re single- vs multicoating.
The importance of coating is something of a hype. Ever since Zeiss
"invented" coating, they have said that it makes a difference preventing
flare indeed, but only a tiny one. The main gain, and most important reason
to use coating is to increase transmission.
Using a lens shade does so much more to reduce flare. Yet multicoating has
become a marketing thing. They should push lens shades instead.
But now that it is extremely hard to find a lens that is not multicoated,
they need to find another marketing ploy. And they have found that in flare
repression using baffling and absorbant coatings. One really should perform
a Blind Test to see how great a difference this really makes, and
consequently debunk this scam. Sure, baffling does make a difference, and of
course flare would be unacceptable if all our lenses and camera bodies had a
highly polished metal internal surface. But they don't.
Notice how i am very sceptical about this?
A propos lenses bad enough to be bashed: try to find some Panagors.
(Or perhaps better not: you might find out they really are better than not
only what i thought they were, but better than my chosen ones as well... )
And you agree that you have more than your fair share of lenses, yet instead
on thinking how you could redress the balance and let other people have some
too, you are planning to take them all with you when your time has come?
Shocking!
Regards.
From: Stephe Thayer ms_stephe@hotmail.com>
Newsgroups: rec.photo.equipment.large-format
Subject: Re: non-coated..coated...multicoated
Date: Tue, 9 Oct 2001
benoit ulrich wrote:
> If you buy three lens with identical focal lengh, all with perfect
> condition glass,
> But one is uncoated, one coated and the other is multicoated,
> what will be the main differences if I shoot with them color and b&w.;
Depends on the lens design. Something with 3 or 4 elements might perform
well uncoated and the difference between a coated and multicoated might be
hard to see. The more elements you add, the greater difference you will
see. With large format lenses with 6 or less elements I wouldn't get real
concerned about the difference between a coated and a multicoated lens.
--
Stephe
From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: experimental result surprises Re: non-coated..coated...multicoated
Date: Thu, 11 Oct 2001
Tom Ferguson tomf2468@pipeline.com> wrote:
>From experience only..... there is far more differance between an uncoated
>lens and a single coated lens than there is between a single and multicoated
>lens. The original single coating was a huge advantage in lens design.
>Multi coating was a nice but small improvement. Someone earlier posted some
>info from ?Modern Photography? indicating that they tested this to be true.
>Multi coating is only slightly better than single coating.
>--
>Tom Ferguson
>http://www.ferguson-photo-design.com
>
I have both uncoated and single coated Kodak Ektar, f/4.7, 127mm
lenses. The difference between them is most apparent in the lack of a
ghost image in the coated version. There is undoubtedly some overall
contrast gain although the uncoated lens is not visually of low
contrast. There should be more visible difference in lenses with more
glass-air surfaces.
Multi-coated lenses may have more subtle differences in comparison
to single coated lenses, but they should be apparent in lenses like
Plasmats with eight surfaces, or in lenses with more. Most of the
better quality "normal" focal length LF camera and enlarging lenses of
today are Plasmat types.
Coating does not affect sharpness or other corrections.
Some older lenses have very low contrast because inner surfaces are
hazy. They get a lot better when cleaned.
I am also rather skeptical about tests run on anything by magazines.
These are often not very well controlled and are certainly not peer
reviewed. Lens testing is not straight forward because there are lots
of variables to be controlled. Testing on film is even more difficult
because the film and its processing become additional variables.
I think its safe to say that there is more difference between an
uncoated and a single coated lens than between a single and multiple
coated lens but beyond that one must be careful of generalizing.
>> From: brianc1959@aol.com (brian)
>> Subject: Re: experimental result surprises Re:
>> non-coated..coated...multicoated
>>
>> Hi Robert:
>> I once built a 4-element Gauss type lens (8 air-glass interfaces) for
>> my 11x14 view camera, and before I coated the elements I assembled the
>> lens and took a couple of shots. After coating there was noticeably
>> less overall flare in the images. Certain indoor stuff looked fine
>> uncoated, but outdoor shots were really washed out compared to my
>> coated version. I used moderately high index glass.
>
---
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: non-coated..coated...multicoated
Date: Thu, 11 Oct 2001
benoit ulrich ben.ulrich@videotron.ca> wrote:
>If you buy three lens with identical focal length, all with perfect
>condition glass,
>But one is uncoated, one coated and the other is multicoated,
>what will be the main differences if I shoot with them color and b&w.;
>
Coating supresses reflection from the glass-air surfaces in the lens.
Single coatings are most effecive at one color, having less effect on
colors of shorter or longer wavelength. Multi-coated lenses used
several layers to broaden out the spectrum of colors for which the
anti-reflection property is effective. Multi-coatings also tend to
have better suppression of reflection in general.
There are two effects of flare in a lens. The first is a sort of
general haze over the whole image. The second is ghost images or spots
of light from bright objects in the field of the lens, sometimes
outside of the image area. Ghost images are partly due to lens design
and some un-coated lenses either do not have them or have very little.
The effect of the general haze is to lower the contrast of shadows
for both color and B&W; images, and to reduce the saturation of colors
in color images. Because the haze is the color of the light entering
the lens it can also reduce the purity of the color of a color image,
especially where there may be a large area of bright color in the
image.
The amount of flare in a lens is proportional to the number of
glass-air surfaces, the more surfaces the worse the flare and the more
likely there will be ghost images. Before coatings the practical limit
was around eight surfaces but even these lenses were considered to be
a little flary. Lenses like Tessars have only six glass-air surfaces
and even uncoated ones have good contrast.
Before coating became generally available lens designers tryed to
reduce the number of glass-air surfaces by using cemented surfaces
instead. This explains such lens designs as the Dagor, Convertable
Protar, and original Zeiss f/1.5 Sonnar for the Contax camera. The
Sonnar had seven elements but cemented so that there were only six
glass-air surfaces. A complete Convertible Protar (two cells) has
eight elements, four in each cell, but they are all cemented so that
the complete lens has only four glass-air surfaces and low flare.
The availability of good anti-reflection coating changed the whole
approach to lens design after about 1945. Modern lenses use many
air-spaced surfaces because they give the lens designer much more
freedom in correcting lens faults. They no longer have to be concerned
with flare and can use air spacing to go after other problems. This is
one reason modern lenses are generally higher in performance than
those of the pre-WW-2 era (there are other reasons also).
Of course, modern zoom lenses would be impossible without effective
coatings.
---
Richard Knoppow
Los Angeles, CA, USA.
dickburk@ix.netcom.com
From: "skgrimes" skgrimes@ma.ultranet.com>
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Schneider Super Ang question
Date: Thu, 11 Oct 2001
Optical coatings are intended to minimize reflections from the glass
surfaces. That's all they do and they do nothing else. The more
sophisticated (multi) the coating the less the reflections.
"Color Correction" has to do with the design of the lens curves so that as
much of the color spectrum as possible focuses at the same plane.
They are two entirely different things which have no particular relation to
each other.
Poorly color corrected lenses take blurry pictures in either black and
white or color. They do not affect color fidelity. Excellently color
corrected lenses (whether optically coated or not) tend to make sharp images
in either black and white or color.
Optical coatings and color correction have nothing to do with each other.
Prescense or not in any order of coatings, no coatings, or multicoatings in
any production lens has nothing to do with "color fidelity" or inherent
suitability for color photography.
Although the term is seen from time to time there is no such thing as
"color coating"
SKG
--
S.K. GRIMES -- MACHINE WORK FOR PHOTOGRAPHERS
153 Hamlet Ave. (5th floor) Woonsocket RI, 02895
+ Lenses mounted into shutters.
+ Shutters repaired, restored.
+ For more info-- http://www.skgrimes.com.
(updated 8-1-01 Site Map)
Now: flat and pointed tip Spanner Wrenches
http://www.skgrimes.com/span/index.htm
"Two23" two23@aol.com wrote..
> I've been shooting 645 for four years now, mostly abandoned ranch buildings
> and "grand Western landscapes", half the time in color and the other half with
> Ilford Pan F b&w.; I've recently lost my mind and bought a 4x5 Calumet 45NX.
> Mostly, I wanted the movements. I bought a Scheider Super Angulon lens, 90mm
> f5.6 serial #9962722 from KEH for around $460, I think. Glass is perfect. Has
> Compur shutter I think. Lens does NOT say MC on it. Is this lens coated?
> Can't see the telltale greenish cast on the surface as I do my Nikon and
> Bronica lenses. Is it maybe monocoated? If so, will it likely meet my needs
> for color photography outdoors? If it's noncoated I will have to return it.
>
> Kent in SD
From: Martin Jangowski m.jangowski@phoenix-ag.de
Newsgroups: rec.photo.equipment.large-format
Subject: Re: experimental result surprises Re: non-coated..coated...multicoated
Date: 12 Oct 2001
Robert Monaghan rmonagha@smu.edu wrote:
> As you noted, the
> real gap is between uncoated and coated optics; the multicoated optics get
> better light transmission but not so much improved flare/ghosting unless
> they are more complex designs (e.g., zooms, more than 5 groups etc. ).
> That makes me feel better, at least, about continuing to use these older
> lenses and worry less about the flare performance I'm getting too ;-)
I have experiences with similiar lenses in MF format: a 3.5/75 lens from a
Mamiya 6 (multicoated, 6 lens Planar type) and a Rolleiflex E3 with a
3.5/75 6 lens Planar (single coated). The pictures made with both are
virtually undistingishable (sp?), the Mamiya lens is marginally more
contrasty. You'll readily see the effects of the much better film
guidance in the Mamiya, the two sharp corners in the Rollei can create
film flatness problems in the Rollei (I use a Stouffer resolution
target enlarged 10x in the center and all four corners of the picture).
It is nearly impossible to see the same high resolution in all four
corners on one negative. Even in high-flare situations it's very
difficult to see the differences between the coatings, Zeiss obviously
knew how to coat a lens even in the 1960s.
Martin
From: "skgrimes" skgrimes@ma.ultranet.com>
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Schneider Super Ang question
Date: Fri, 12 Oct 2001
My comments should have read "properly designed optical coatings" instead
of "optical coatings"
"color correction" and "color fidelity" are not the same thing.
This is not as important on factory made items as you would think. Properly
designed coatings which are universal on factory made items for the market
are appropriate for color fidelity and have nothing to do with "color
correction", which is a design characteristic of the lens itself and is a
factor in all lenses coated, not coated, or multi-coated.
There is a further problem with really well specified optical coatings in
that they are not detectable by casual inspection. The rich, expensive
looking blue or greenish color that we are used to regarding as high quality
is acutally a sign of deficient design since because we see the blue means
that it is passing some of the spectrum and not passing other parts of the
spectrum (that's what color is) A perfect coating looks totally
uncolored/white and is not apparent.
I have it anecdotally from working with some prototype military gunsight
optics that camera manufactures err on the side of blue looking, since there
was too much to explain about coatings that don't look like the coatings
photographers are used to.
This corroborates Nikon's problem about having good color fidelity yet
preserving the expensive blue look that photographers and magazine reviewers
are used to.
--
S.K. GRIMES -- MACHINE WORK FOR PHOTOGRAPHERS
153 Hamlet Ave. (5th floor) Woonsocket RI, 02895
+ Lenses mounted into shutters.
+ Shutters repaired, restored.
+ For more info-- http://www.skgrimes.com.
(updated 8-1-01 Site Map)
Now: flat and pointed tip Spanner Wrenches
http://www.skgrimes.com/span/index.htm
"Robert Monaghan" rmonagha@smu.edu> wrote
>
> hmmm? Nikon at least used to make a big deal in their ads and materials
> about NIC, that they had to formulate the coatings differently for each
> lens to balance their color fidelity among other properties. I used to
> think the coating was totally separate from lens coloration issues, but
> as the following quote makes clear, lens coatings can impact lens
> coloration:
>
> quote: If the thickness of any layer is off by as little as 5 percent of
> the required thickness, the entire coating will be bad - strong
> reflections will be noticed on one or more colors. ..A bad job of
> multicoating can ruin a lens and prove to be far worse than no coating at
> all. We have seen poorly multicoated optics which produced violently
> yellow pictures. [p. 138]
> end-quote: Source:
> June 1975 Modern Photography titled "Multicoating: Asset or Gimmick?" by
> Bennett Sherman and Hiroshi Kimata
>
> bobm
From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: experimental result surprises Re: non-coated..coated...multicoated
Date: Sat, 13 Oct 2001
rmonagha@smu.edu (Robert Monaghan) wrote:
>
>wow! not many of us hack our own lenses ;-) nor many places to get 'em
>coated if we could ;-) thanks for sharing this note on your experiences
>;-)
>
>my main interest in the quoted article was as the owner of a number of
>these coated but not multi-coated older optics, often simple designs
>(tessars etc.) in fixed focal length lenses. It is very hard (read
>impossible) to get an outdoor standardized setup for testing flare (dang
>sun keeps moving too fast for me ;-) to confirm/deny my suspicion that my
>multicoated versions work better in flarey situations than the older
>optics, and much of the literature and esp. marketing ads would have you
>believe single coated lenses are at a huge disadvantage. As you noted, the
>real gap is between uncoated and coated optics; the multicoated optics get
>better light transmission but not so much improved flare/ghosting unless
>they are more complex designs (e.g., zooms, more than 5 groups etc. ).
>That makes me feel better, at least, about continuing to use these older
>lenses and worry less about the flare performance I'm getting too ;-)
>
>grins bobm
>--
There ought to be a way of setting up using artificial light for
flare measurement. It would have the advantage of being more
reproducible. If spectral charistics are important strobe light is a
fair approximation of sunlight. Carefully controlled experiments
using film should be enough although some aerial image measurements
would also be useful.
I suspect a special camera might have to be constructed to eliminate
internal reflections as nearly completely as possible to isolate the
flare from the lens itself. There are probably existant set-ups for
doing all this but I don't know where they might be published. I
suspect that at review of the cumulateve indexes of the Journal of the
Optical Society of America might turn something up.
Beside coatings internal baffling of lens cells and mounts are
important. Kodak seems to have understood this and done a good job.
Ilex not so. I have a post war f/4.5 Paragon with very serious
internal reflections from the inside of the lens cells which requires
stopping down to f/8 to eliminate. Not damaged anti-reflection paint,
just bad design. This lens is a particularly egregious example but
shining a flashlight through other lenses will turn up those with bad
internal reflections. Coating won't fix this. Zeiss also seems to have
done a good job of reducing internal reflections on their lenses.
I would be very interested to see what differences can be measured
between uncoated, single coated, multicoated lenses of various types.
Single coating does make a noticable difference even for fairly simple
lenses (Tessars). Multi-coating should also make a noticable
difference but it may be subtle in comparison to single coating until
the lens becomes complex enough.
In principle multicoating should make some difference in color
purity even for fairly simple lenses since single coatings are not
very effective at the ends of the visible spectrum.
---
Richard Knoppow
Los Angeles, CA, USA.
dickburk@ix.netcom.com
From: Paul Butzi butzi@nwlink.com>
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Schneider Super Ang question
Date: Sat, 13 Oct 2001
Ilja Friedel ilja@blinky.caltech.edu> wrote:
>I think from this statement we can already see, why the outermost coating
>might have a "color". Actually, if I think of it - there is no need for
>any coating on the outermost surface of a lens. All reflections, which the
>coating is supposed to suppress, would go otherwise into the environment.
What about the light that travels through the first surface, strikes
some subsequent surface and is reflected, and reaches the first
surface traveling away from the lens? If it's reflected, it heads
back toward the film.
-Paul
--
http://www.butzi.net
From: Ilja Friedel ilja@sue.caltech.edu>
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Schneider Super Ang question
Date: 14 Oct 2001
Paul Butzi butzi@nwlink.com> wrote:
> What about the light that travels through the first surface, strikes
> some subsequent surface and is reflected, and reaches the first
> surface traveling away from the lens? If it's reflected, it heads
> back toward the film.
I have two answers for that. The optimistic one:
As stated before, reflection is on average 4 percent for each uncoated
surface and 2 percent for each single coated. For two subsequent
reflections you get at most 2/100*4/100 = 0.08 percent of the stray light
to the film.
The pessimistic answer: Light passing from glass to air might under large
angles exhibit "total internal reflection" - the surface acts as a perfect
mirror. (Coating should help against this effect too. But it might not be
very effective, because the lambda/4 thickness of the coating is stretched
by the angle.) Assuming our front surface acts as a backward mirror, then
the resulting flare would be as if our lens had one extra coated surface.
(e.g. N+1 instead of N surfaces) Those 100/N percent more flare _could_ be
noticable.
Assuming the second answer is correct, then the relative performance drop
is worst for Triotar and Tessar and insignificant for zoom lenses. ;-)
Mhh. As a consequence I'm now even more convinced to use a lens hood for
every shot. That should eliminate most of the vagabonding rays right from
the start.
Ilja.
From: bg174@FreeNet.Carleton.CA (Michael Gudzinowicz)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Schneider Super Ang question
Date: 14 Oct 2001
Paul Butzi butzi@nwlink.com> wrote:
> Ilja Friedel ilja@blinky.caltech.edu>
> wrote:
> >I think from this statement we can already see, why the outermost coating
> >might have a "color". Actually, if I think of it - there is no need for
> >any coating on the outermost surface of a lens. All reflections, which the
> >coating is supposed to suppress, would go otherwise into the environment.
>
> What about the light that travels through the first surface, strikes
> some subsequent surface and is reflected, and reaches the first
> surface traveling away from the lens? If it's reflected, it heads
> back toward the film.
As you suspect, every air-glass surface contributes to the problem,
as well as reflections from film and the bellows, and design
idiosyncrasies which may partially focus the bright aperture
onto the film leading to one or more hot spots.
Below, I've included the calculations to compare flare of uncoated,
single coated and multicoated 6/2 (Dagor) and 6/4 (Plasmat) designs,
though in fact any glass with 4 or 8 air-glass surfaces might be
considered.
After the calculations, if a description of the common apparatus used
to measure flare, and a home brew setup.
With modern MC lenses and filters, a large portion of the degradation
of contrast may be attributed to reflections from the bellows which
may be minimized with a lens hood, or compendium bellows. I have a
collection of articles from the 1970's promoting the virtues of
multicoating, however, one attributes large differences in flare
levels to the design and baffling of 35 mm cameras' mirror boxes.
>From old posts:
Flare Comparison Worksheet: Compares the effect of coatings and lens
design with respect to the flare levels they generate.
Lens Design: (note: only air glass interfaces have a difference in
refractive index sufficient to make a significant contribution to flare).
Uncoated Single coated Multicoated
6/2 6/4 6/2 6/4 6/2 6/4
Elements 6 6 6 6 6 6
Groups 2 4 2 4 2 4
Air surfaces 4 8 4 8 4 8
The reflectance at a 90 degree angle of incidence is approx. 4% for
uncoated lenses; 1.3% for single coated; 0.2% for multicoated.
Uncoated Single coated Multicoated
6/2 6/4 6/2 6/4 6/2 6/4
Reflectance 4.0% 4.0% 1.3% 1.3% 0.20% 0.20%
Transmission:
The total transmission through the lens is equal to
(1 - r)/(1 + (#_air-glass_surfaces)^r) where r is the reflectance.
Uncoated Single coated Multicoated
6/2 6/4 6/2 6/4 6/2 6/4
Total as % 85.7% 75.0% 95.0% 90.5% 99.2% 98.4%
The amount of reflected light as % is 100% - total%
Uncoated Single coated Multicoated
6/2 6/4 6/2 6/4 6/2 6/4
Reflected 14.3% 25.0% 5.0% 9.5% 0.8% 1.6%
The portion of transmitted light which contributes to the image is given
(1 - r)^( #_air-glass_surfaces)
Uncoated Single coated Multicoated
6/2 6/4 6/2 6/4 6/2 6/4
Image 84.9% 72.1% 94.9% 90.1% 99.2% 98.4%
The non-image portion of the total transmitted light is the total
less the image portion.
Uncoated Single coated Multicoated
6/2 6/4 6/2 6/4 6/2 6/4
Non-image 0.8% 2.9% 0.1% 0.4% 0.0% 0.0%
The ratio of transmitted image to non-image light is:
Uncoated Single coated Multicoated
6/2 6/4 6/2 6/4 6/2 6/4
Image/non-image 108.9 25.2 1002.5 221.6 41777.0 8999.3
One can take the log (base 10) of the ratio, and divide by log(2) to give the
number of doublings or "zones" separating the image/non-image contributions.
Uncoated Single coated Multicoated
6/2 6/4 6/2 6/4 6/2 6/4
Log 2.04 1.40 3.00 2.35 4.62 3.95
Zones 6.77 4.66 9.97 7.79 15.35 13.14
The film also reflects part of the total light back to the lens and baffles
of the camera. The amount of light reflected back to the lens, and then to
then back to film on axis may estimated as the ratio of the total transmitted
to the total reflected raised to a power equal to the film's reflectance.
The film's reflectance is approx. 15%, so the first data point would be
given by (85.7% / 14.3%)^0.15 = 1.8%
Uncoated Single coated Multicoated
6/2 6/4 6/2 6/4 6/2 6/4
Reflected from/
back to film 1.8% 2.8% 0.7% 1.3% 0.1% 0.2%
The non-image level given above may be revised to the "total" non-image
contribution by adding the amount reflected from film to lens to film.
Uncoated Single coated Multicoated
6/2 6/4 6/2 6/4 6/2 6/4
Total non-image 2.6% 5.7% 0.8% 1.7% 0.1% 0.2%
The flare level may be expressed as a percent of non-image to image light:
Uncoated Single coated Multicoated
6/2 6/4 6/2 6/4 6/2 6/4
Total non-image to
image ratio : 3.1% 7.9% 0.9% 1.9% 0.1% 0.2%
The image/non-image ratio, logs and zone or f/stop difference are recalculated.
Uncoated Single coated Multicoated
6/2 6/4 6/2 6/4 6/2 6/4
Image/non-image
ratio 32.5 12.7 117.5 53.0 821.8 403.5
Log ratio 1.5 1.1 2.1 1.7 2.9 2.6
f/stop difference 5.0 3.7 6.9 5.7 9.7 8.7
Suppose one photographed a card placed on zone 5 which had a small "black
hole" in the center. The "black hole" would fall on the following zones.
(zone of average placement - f/stop or zone difference)
Uncoated Single coated Multicoated
6/2 6/4 6/2 6/4 6/2 6/4
Zone for flare (5) 0.0 1.3 -1.9 -0.7 -4.7 -3.7
If the overall exposure were placed on zone 8, the "black hole" would
fall on the following zones:
Uncoated Single coated Multicoated
6/2 6/4 6/2 6/4 6/2 6/4
Zone for flare (8) 3.0 4.3 1.1 2.3 -1.7 -0.7
Using process lenses with lith film, one can still get a
complete black vs. white separation of tones over a small
exposure range, so coatings have not been as much of an issue
as flat field and lateral color requirements.
Uncoated lenses will result in problems when shooting
chromes, and complex single coated lenses will show
desaturation as well.
Using uncoated filters has the same effect as adding
uncoated groups to the lens design. Two filters will degrade
a multicoated lens' performance to something worse than the
uncoated Dagor example used above (6E/2G). Gelatin filters
have a refractive index close to that of air, and have
little effect.
Testing:
The SPSE handbook suggests one testing method which uses a
large white integrating light box with lamps surrounding a hole
into which a test lens is inserted. On the opposite wall, the
lens is focused on a small hole which has a mirror placed at a
45 degree angle behind it in a light tight box lined with black
velvet - essentially a "black hole". A very narrow angle probe
is used to determine the intensity of illumination of the white
surround, and the hole. Supposedly, "good" lenses give values
of 1-3% of the surrounding light. That method doesn't account
for reflection in the camera box or for the 10-15% of the
incident light reflected by film.
A simpler method is to use two large cards which extend well
outside the lens' view angle at 1/10 magnification. One card is
white with a small black area placed in the center (just large
enough on the negative to be read by a densitometer), and the
other card is completely black. (Black velvet is best for the black
areas.) The white area is placed on zone 8 or 9, and the target
exposed. The black card is substituted, and given the same
exposure. The difference between the black spot on the white
card and the black card density is due to flare, and if the
development process is well calibrated, an estimate of where
the flare exposure falls can be made.
From: Paul Butzi butzi@nwlink.com>
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Schneider Super Ang question
Date: Sun, 14 Oct 2001
bg174@FreeNet.Carleton.CA (Michael Gudzinowicz) wrote:
>The reflectance at a 90 degree angle of incidence is approx. 4% for
>uncoated lenses; 1.3% for single coated; 0.2% for multicoated.
It seems to me like the big culprit in generating flare has to be
light coming from far off the optical axis - that is, light which is
striking the surfaces quite a bit off from 90 angle of incidence.
Does the proportion of reflected light increase or decrease as you
move from 90 angle of incidence?
It seems to me like if it increases, then much of the flare must come
from light that strikes the front element but would never end up on
the film as part of the image - it's destined to just bang around
inside the camera until it's either absorbed or until it strikes the
film.
If that's so, then even minimal lens shades should reduce flare
pretty substantially.
-Paul
--
http://www.butzi.net
From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Schneider Super Ang question
Date: Sat, 20 Oct 2001
rmonagha@smu.edu (Robert Monaghan) wrote:
>again, I am under the impression that the purpose of multicoatings is to
>provide a series of layers "tuned" to different color bands, so each layer
>can provide cancellation of reflections for that color band, and the 3 or
>4 or more layers provide pretty good reflection control over a range of
>colors. With the right lighting, you can see reflections from each lens
>surface, sometimes in different colors, reflecting (pun intended) the
>specific tuned color band of that coating layer, at least in simpler fixed
>focus lenses.
>
>most of the current optical glasses offer better "water white" color
>options than in the past, yes? Some of the old flint/crown glass combos
>would drop violet response by 10% or so etc. Not important with b&w; films,
>but an issue with color films? Some lenses have a distinctly yellow color
>bias easily seen when held against a white sheet of paper and light
>source.
>
>re: front element coating?
>I suspect the front elements are coated not just because they are usually
>the biggest elements, but also as they are most subject to off-axis light
>sources which are likely to induce flare and ghosting etc.
>
>Front coatings may also play a role in protecting the lens surface, i.e.,
>small scratches in the coatings don't impact the lens' curvature as they
>might in the absence of a protective hard outer coating (not all older
>coatings were hard, but..).
>
>In a few lenses, the coating is also protective against staining the glass
>outer element (some glasses are susceptible vs. others) and finally, for
>odd-ball calcium fluoride lenses (cf Canon) the coatings may have a role
>in keeping the " " elements from reacting badly with environment (as in
>dissolving in water vapor from the air etc. ;-)...
>
>bobm
The coating on the ourside surfaces of a lens are important. Remember
the change in index there reflects light _both ways_. So, the amount
of light reflected back into the system from these interfaces is
reduced by the coatings. They also improve transmission, but that is a
minor consideration.
For those familiar with electronics, and especially radio frequency
transmission, a lens coating is exactly analogous to a quarter wave
impedance matching stub. It works perfectly at one wavelength but is
not sharply tuned. They are also analogous to lumped-constant LC
matching networks. Multi-coatings are analagous to either multiple
stepped stubs or to a complex impedance matching filter. The idea is
to broaden out the effective band of matching.
Single coatings might have some effect on the overall image color.
One could calculate the difference in transmission. However, it
wouldn't be that simple because one effect of flare is to desaturate
colors.
Most optical glass is very transparent and has little selectivity
for color within the visible range. Nonetheless, different lenses do
seem to have different color casts. I suspect the explanation of
balancing transmission using differently tuned coatings on different
surfaces is the correct one.
Because the flare from an uncoated lens can both desaturate color
and affect its purity an uncoated lens is probably not a good standard
of comparison. FWIW, some very early coatings were so soft they were
not used on outside surfaces. Kodak's first experiments in coating
used chemically applied coatings which can be wiped off with ordinary
lens cleaning. These coatings were applied to sealed surfaces on a few
lenses. The Eastman Ektar (predessor of the Commercial Ektar), the
lens in the Medalist, and the lenses for the Ektra camera were coated
this way.
Kodak "Luminized" lenses, bearing the circle-L symbol, are hard
coated on all surfaces.
---
Richard Knoppow
Los Angeles, CA, USA.
dickburk@ix.netcom.com
From: David Littlewood david@dlittlewood.demon.co.uk>
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Schneider Super Ang question
Date: Wed, 24 Oct 2001
Richard Knoppow dickburk@ix.netcom.com> writes
Sorry, I came late to this.
>rmonagha@smu.edu (Robert Monaghan) wrote:
>
>>again, I am under the impression that the purpose of multicoatings is to
>>provide a series of layers "tuned" to different color bands, so each layer
>>can provide cancellation of reflections for that color band, and the 3 or
>>4 or more layers provide pretty good reflection control over a range of
>>colors. With the right lighting, you can see reflections from each lens
>>surface, sometimes in different colors, reflecting (pun intended) the
>>specific tuned color band of that coating layer, at least in simpler fixed
>>focus lenses.
That is not quite the way I understood the purpose of multicoating.
IIRC, the optimum coating for reducing reflections at an interface
between air and glass of refractive index R would itself have an RI of
R^0.5. This would reduce reflections typically from say 5-10% to about
1-2%. These figures from memories from many years ago.
In order to improve on that, two coatings are required, with (in the
optimum case) each interface obeying the same ratio (hence, presumably,
R, R^0.5, R^0.25). Using such means (and acknowledging that materials
with the right RIs may not be available) the reflections can be cut down
to less than 0.2% per interface; maybe better now, since AIUI many more
than two coatings are applied.
I do suspect that something akin to what you say also applies,
especially as regards the thickness (as opposed to the RI) of the
coatings. The colour appearance of the coating is of course an
interference effect, as I imagine has been said earlier in bits I didn't
catch. However, if the sole purpose of multicoating was to broaden the
spectrum over which it worked, would it not be self-defeating? Each
interface, being optimised for one colour, might worsen the position for
others.
>>
>>most of the current optical glasses offer better "water white" color
>>options than in the past, yes? Some of the old flint/crown glass combos
>>would drop violet response by 10% or so etc. Not important with b&w; films,
>>but an issue with color films? Some lenses have a distinctly yellow color
>>bias easily seen when held against a white sheet of paper and light
>>source.
>>
>>re: front element coating?
>>I suspect the front elements are coated not just because they are usually
>>the biggest elements, but also as they are most subject to off-axis light
>>sources which are likely to induce flare and ghosting etc.
>>
>>Front coatings may also play a role in protecting the lens surface, i.e.,
>>small scratches in the coatings don't impact the lens' curvature as they
>>might in the absence of a protective hard outer coating (not all older
>>coatings were hard, but..).
>>
>>In a few lenses, the coating is also protective against staining the glass
>>outer element (some glasses are susceptible vs. others) and finally, for
>>odd-ball calcium fluoride lenses (cf Canon) the coatings may have a role
>>in keeping the " " elements from reacting badly with environment (as in
>>dissolving in water vapor from the air etc. ;-)...
Most of the Canon lenses with fluorite as their first optical element
have a plain glass element in front of them (e.g. 300/2.8, 400/2.8 etc).
I suspect the reason is that a thin coating may not be sufficient
protection, as fluorite is very soft. This, rather than water
sensitivity, seems most likely to me.
>>
>>bobm
>>--
>>
> The coating on the ourside surfaces of a lens are important. Remember
>the change in index there reflects light _both ways_. So, the amount
>of light reflected back into the system from these interfaces is
>reduced by the coatings. They also improve transmission, but that is a
>minor consideration.
Interesting; I suspect it may though be the least important at least
from a flare-creation point of view. If you think about it, the rear
face of the front element reflects say 0.5% of the light hitting it. The
front face then has an internal reflection of 0.5% of 0.5%. The
reflected light which escapes outwards has gone from the system (as has
the initially-reflected 0.5% or whatever). With all other interfaces,
the light which goes through or is reflected meets a myriad of other
possibilities. Hmm, maybe I am getting tied up here, better quit while I
am behind.
> For those familiar with electronics, and especially radio frequency
>transmission, a lens coating is exactly analogous to a quarter wave
>impedance matching stub. It works perfectly at one wavelength but is
>not sharply tuned. They are also analogous to lumped-constant LC
>matching networks. Multi-coatings are analagous to either multiple
>stepped stubs or to a complex impedance matching filter. The idea is
>to broaden out the effective band of matching.
> Single coatings might have some effect on the overall image color.
>One could calculate the difference in transmission. However, it
>wouldn't be that simple because one effect of flare is to desaturate
>colors.
> Most optical glass is very transparent and has little selectivity
>for color within the visible range. Nonetheless, different lenses do
>seem to have different color casts. I suspect the explanation of
>balancing transmission using differently tuned coatings on different
>surfaces is the correct one.
> Because the flare from an uncoated lens can both desaturate color
>and affect its purity an uncoated lens is probably not a good standard
>of comparison.
Perhaps a mirror lens would be a more neutral standard? Or does mirror
coating material have an uneven reflectivity across the visible
spectrum?
> FWIW, some very early coatings were so soft they were
>not used on outside surfaces. Kodak's first experiments in coating
>used chemically applied coatings which can be wiped off with ordinary
>lens cleaning.
Sounds like tobacco smoke stains!
> These coatings were applied to sealed surfaces on a few
>lenses. The Eastman Ektar (predessor of the Commercial Ektar), the
>lens in the Medalist, and the lenses for the Ektra camera were coated
>this way.
> Kodak "Luminized" lenses, bearing the circle-L symbol, are hard
>coated on all surfaces.
>---
>Richard Knoppow
>Los Angeles, CA, USA.
>dickburk@ix.netcom.com
--
David Littlewood
From: dickburk@ix.netcom.com (Richard Knoppow)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: flare and MC Re: Schneider Super Ang question
Date: Mon, 29 Oct 2001
rmonagha@smu.edu (Robert Monaghan) wrote:
>
>I will respond to the points I raised; Richard K. can do so if he likes
>for his own points too ;-) in the above interesting commentary...
>
Very briefly. Single coated lenses often had the individual surfaces
coated to different thicknesses. For instance, I have seen lenses
where some of the surfaces reflect magenta and some amber. I think
this was a trick to try to broadband the effect of the coating without
multi coating.
The whole purpose of multiple layer coating is to broaden out the
bandwidth of the coating. A single coating is most effective at a
single color or wavelength and fall off in its effectiveness on either
side of that wavelength. Because the band of wavelengths of interest
in general photography, or for visible light instruments (like
binoculars) is only about an octave wide, a single coating has
significant effect over the whole range.
To use an electronic analogy a coating is an impedance matching
devise. A single coating is exactly equivalent to a quarter-wave stub
used for matching radio frequencies, or an L network filter for
matching. Multiple coatings are equivalent to a series of stepped
stubs or to a more complex filter.
As the coating becomes more complex the sensitivity to error becomes
greater, just as it does in its electronic counterpart.
An ideal coating would have NO reflection at all. One which was
broad band but not quite a perfect match would look neutral gray, or
rather, there would be some reflection but it would be neutral in
color. The residual color in multi-coatings is due to the limitations
in how complex a practical coating stack can be made and still be
economical. The test really is the percentage of reflection from each
surface. There can be a noticable reflection even if its quite weak.
For instance, cemented surfaces, which have little reflectivity, can
still be seen.
Also note that the path length through the coating changes with the
angle of incidence of the light. I think in practice this is
insignificant in its effect but is interesting in terms of the theory.
A flashlight is a little more convenient way of inspecting lenses
than standing under a strong lightbulb:-)
The Optical Society Handbook has several pages of curves for both
anti-reflection coatings for lenses, and reflection boosting coatings
for mirrors.
>From Shutterbug Lens Flare Definitions and Solutions by Don Garbera, p.
>38, March 1989
> The color of multicoating on your lenses indicates the complimentary
>color of light the lens' multicoating is designed to control; purple, red
>and blue reflections mean that the coatings are controlling green, blue
>and yellow light...
>
>=====
>
>from Modern Photography's Multicoating: Asset or Gimmick article by
>Bennett Sherman and Hiroshi Kimata in June 1975 (p. 90..147) quote:
>
>Even though some lens manufacturers do not indicate on the lens whether it
>is multicoated or not, you can tell in most cases. You take the lens,
>remove its front and back caps, and open it to full aperture. Hold the
>lens under a bright light source, such as an overhead bulb, so that the
>bulb will reflect on the surfaces of the lens elements. Look down into the
>lens at these reflections. If all the reflections are light amber or blue,
>the lens is single-coated. But if some are light amber or blue, and others
>are deep magenta, dark green or a deep reddish yellow, the lens has
>multicoated elements. [Ibid., p. 138]
>
>Since four is the minimum required for so-called multicoating, Minolta's
>double or triple coatings are not advertised as multicoatings. [Ibid., p.
>147]
>
>Multicoating improved light transmission by only 1/2 f/stop or less over
>single coating. Flare elimination was very minimal at most. Ghosts were
>minimized by multicoating, principally in many-element lenses. [Ibid., p.
>147]
>
>====
>
>so the above is part of my basis for suggesting that these layers are
>tuned to specific light frequencies, as per the Shutterbug quote above...
>
>re: fluoride elements, you are quite right that canon can use a front
>protective glass on their telephoto lenses, so the coatings don't
>necessarily have a moisture protection effect in that case. However, on
>some UV lenses in which the design uses the extended ultraviolet range of
>specialty fluoride crystal elements, protective glass front elements can't
>be used as most glasses limit spectral response to below 320-360 nm (~3600
>Ang.). The particular crystals are known to absorb moisture out of the
>air, unfortunately. So the coatings may have such side benefits too, most
>often seen in pricey IC chip making lenses per some comments I've seen.
>
>I've seen suggestions that coatings can vary circa 5% or so within
>batches, but that larger variations can result in an off-color lens
>element effect and be cause for rejecting the element. This suggests that
>the risks and rejection costs of layering many layers may be part of the
>reason why many lenses are not coated more effectively, as the process can
>vary somewhat in practice, and more layers may mean more risk of costly
>failures, and is subject to higher costs and limited improvements too (as
>the above quotes from Modern Photography make clearer...)
>
>If anything, I am quite surprised at how high the cost of multicoating is,
>at least when judging from the few cases (like Kiev lenses) where you have
>the option of coated versus multicoated option variants - 50% or more
>higher price for the multicoated lens is not unheard of direct from the
>factory. Similarly, lenses in which single coating rather than
>multicoating was used, such as the Nikon series E 50mm f/1.8, seem to be a
>good bit cheaper.
>
>my main conclusions remain that multicoated lenses are nice, esp. for
>backlit situations or complex many element (zoom) lenses, but that many of
>the simpler MF and LF lenses which are simply coated can produce equally
>good results under many situations.
>
>bobm
>--
---
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: 28 Oct 2001
Hi Bob:
For environmentally sensitive elements made with materials like
calcium fluoride or acrylic, any sort of coating can provide valuable
environmental protection. I used to develop LCD and DMD projection
lenses, and some of the multi-coated aspheric plastic elements we used
were amazingly precise and stable.
As you probably know, single layer antireflective coatings nearly
always use MgF2, which has a refractive index of 1.38. A single layer
coating provides zero reflectivity for a normal incidence ray if its
refractive index is the square root of the refractive index of the
underlying lens material. So, if the lens has an index of 1.904 then
the best possible coating would be single layer MgF2. There are a few
optical glasses with an index of around 1.9, but they are pretty
expensive. The effectiveness of single layer coatings is reduced if
the index of the substrate is lowered, but it turns out that if the
substrate index is around 1.75 or more a single layer coating is quite
good. Its only when you get to really low index materials such as
calcium fluoride and the FK-type optical glasses with abnormal partial
dispersion that multilayer coating becomes really mandatory for decent
transmission and flare control.
The machinery used for single-layer coating of lens elements is fairly
simple and inexpensive, which is one of the main reasons that single
layer coatings are cheaper. It takes time to deposit multiple layers
precisely (to within a few nanometers tolerance), and everything has
to be done in batches in fairly expensive coating chambers. I've been
to some lens shops that had large rooms full of single layer machines,
but only a few coating chambers suitable for multi-layer coatings.
On UV lenses: the monochromatic designs always use very pure silica
glass for all the elements, and silica is the most durable and
environmentally stable glass available. The only thing that attacks
it is hydrofluoric acid, and it would be very suitable for use as a
protective plate. Calcium fluoride is used together with silica to
create UV achromats (and sometives UV-VIS-IR superachromats), and is
rarely if ever used by itself in an optical system.
Brian
rmonagha@smu.edu (Robert Monaghan) wrote
> I will respond to the points I raised; Richard K. can do so if he likes
> for his own points too ;-) in the above interesting commentary...
>
> From Shutterbug Lens Flare Definitions and Solutions by Don Garbera, p.
> 38, March 1989
> The color of multicoating on your lenses indicates the complimentary
> color of light the lens' multicoating is designed to control; purple, red
> and blue reflections mean that the coatings are controlling green, blue
> and yellow light...
>
> =====
>
> from Modern Photography's Multicoating: Asset or Gimmick article by
> Bennett Sherman and Hiroshi Kimata in June 1975 (p. 90..147) quote:
>
> Even though some lens manufacturers do not indicate on the lens whether it
> is multicoated or not, you can tell in most cases. You take the lens,
> remove its front and back caps, and open it to full aperture. Hold the
> lens under a bright light source, such as an overhead bulb, so that the
> bulb will reflect on the surfaces of the lens elements. Look down into the
> lens at these reflections. If all the reflections are light amber or blue,
> the lens is single-coated. But if some are light amber or blue, and others
> are deep magenta, dark green or a deep reddish yellow, the lens has
> multicoated elements. [Ibid., p. 138]
>
> Since four is the minimum required for so-called multicoating, Minolta's
> double or triple coatings are not advertised as multicoatings. [Ibid., p.
> 147]
>
> Multicoating improved light transmission by only 1/2 f/stop or less over
> single coating. Flare elimination was very minimal at most. Ghosts were
> minimized by multicoating, principally in many-element lenses. [Ibid., p.
> 147]
>
> ====
>
> so the above is part of my basis for suggesting that these layers are
> tuned to specific light frequencies, as per the Shutterbug quote above...
>
> re: fluoride elements, you are quite right that canon can use a front
> protective glass on their telephoto lenses, so the coatings don't
> necessarily have a moisture protection effect in that case. However, on
> some UV lenses in which the design uses the extended ultraviolet range of
> specialty fluoride crystal elements, protective glass front elements can't
> be used as most glasses limit spectral response to below 320-360 nm (~3600
> Ang.). The particular crystals are known to absorb moisture out of the
> air, unfortunately. So the coatings may have such side benefits too, most
> often seen in pricey IC chip making lenses per some comments I've seen.
>
> I've seen suggestions that coatings can vary circa 5% or so within
> batches, but that larger variations can result in an off-color lens
> element effect and be cause for rejecting the element. This suggests that
> the risks and rejection costs of layering many layers may be part of the
> reason why many lenses are not coated more effectively, as the process can
> vary somewhat in practice, and more layers may mean more risk of costly
> failures, and is subject to higher costs and limited improvements too (as
> the above quotes from Modern Photography make clearer...)
>
> If anything, I am quite surprised at how high the cost of multicoating is,
> at least when judging from the few cases (like Kiev lenses) where you have
> the option of coated versus multicoated option variants - 50% or more
> higher price for the multicoated lens is not unheard of direct from the
> factory. Similarly, lenses in which single coating rather than
> multicoating was used, such as the Nikon series E 50mm f/1.8, seem to be a
> good bit cheaper.
>
> my main conclusions remain that multicoated lenses are nice, esp. for
> backlit situations or complex many element (zoom) lenses, but that many of
> the simpler MF and LF lenses which are simply coated can produce equally
> good results under many situations.
>
> bobm
From: David Littlewood david@dlittlewood.demon.co.uk>
Newsgroups: rec.photo.equipment.large-format
Subject: Re: flare and MC Re: Schneider Super Ang question
Date: Tue, 30 Oct 2001
Robert Monaghan rmonagha@smu.edu> writes
[snip]
>
>I am also keeping my eyes out for some ultra cheapy badly coated zooms
>such as the green biased zooms I have heard about, as an example of an
>unusual lens flaw for my lens faults pages and collection ;-) I have seen
>stats that even small errors, in the 5% to 10% range, can be cause for
>rejection of some coatings as too thin/thick, and so adds to costs and
>rejection rates of these elements, and so may justify the higher costs of
>the multicoated elements. I'm still not sure why they don't just strip off
>the coatings chemically and start again? ;-) Maybe they do?
MgF2 is pretty insoluble; its solubility product (7.4 x 10^-11) is lower
than CaF2 (1.46 x 10^-10) so that gives you some idea. It would probably
(a guess from its composition) dissolve in HF, but then so would the
glass substrate. Polishing would seem to be the most likely way, but
then you would risk leaving the coating in varying thicknesses across
the surface.
--
David Littlewood
From: "Peter Klosky" peter.klosky@marcgs.com>
To: hasselblad@kelvin.net>
Subject: Re: [HUG] Silver C Lens vs CF or CFE
Date: Mon, 12 Nov 2001
Rob,
In my never-ending search for the highest quality, I bought an 80 CF to replace my 80C. Under the harshest flare situations,
shooting them side by side, I was not able to tell the difference, even using a 15x magnifier on the megatives. So I sold the 80C,
since it was older and Hasselblad keeps saying parts will become unavailable some day. It was running a little slow on the one
second speed, but not enough to make a difference on actual wedding jobs, only enough to cause undue concern on the part of a
potential buyer.
The 80C was under production for a while, and my understanding is that they are not all alike, in terms of the coating. You can see
different colors if you look at several samples, ranging from blue to yellowish brown. I suspect mine was fairly late in the line,
and had the better coating. Still, I had an experience where Hasselblad charged $344 to fix a 150C, so I bought all CF lenses
(50,80,150).
Peter
----- Original Message -----
From: "Dr. Rob" rob168@mediaone.net>
To: hasselblad@kelvin.net>
Sent: Monday, November 12, 2001 12:39 PM
Subject: [HUG] Silver C Lens vs CF or CFE
> I like the way the old silver 80mm 2.8 C lens looks.
> It is more compact and the Black lenses scratch
> too easily. So,
>
> 1. Is there any reason why you wouldn't want to
> own and use a Silver C lens?
>
> 2. Is the newer CFE lenses that much better that the
> CF or Silver C lenses?
>
> For a working wedding photographer, which lens
> would you want to own and operate.
>
> Dr. Rob
> 818 890-4542
> Van Nuys California
Date: Thu, 15 Nov 2001
Subject: Re: [Rollei] Planar lens design changes from 2.8E to 2.8F
From: Bob Shell bob@bobshell.com>
To: rollei@mejac.palo-alto.ca.us>
> From: Kip Babington cbabing3@swbell.net>
> Date: Wed, 14 Nov 2001
> To: rollei@mejac.palo-alto.ca.us
> Subject: Re: [Rollei] Planar lens design changes from 2.8E to 2.8F
>
> FWIW, my understanding is that John Van Stelten does single layer
> coating of lenses (and very well, too, from what I've heard) but that he
> does not do multicoating. I've read somewhere, probably on this or the
> Leica list, that multicoating is a very involved process that takes a
> substantial industrial plant to do, so that basically only the lens
> factories are equipped to do it.
The problem is really that different lens designs and glass types may
require different types of multicoating. If JVS or any other repairman
buys a single vacuum depositing machine he can do single coating very
easily, but for multicoating he would need to determine what's right for
a particular lens and then run the lens elements through the machine
multiple times. Multicoating has anywhere from about 7 to as many as
21 layers, so it would require running in the macine that many times.
Lens factories, of course, have that many machines and just move a
batch of elements from one machine to another until the process is
completed. These machines are not cheap, nor are they small!!
Bob
Date: Thu, 15 Nov 2001
To: rollei@mejac.palo-alto.ca.us
From: Richard Knoppow dickburk@ix.netcom.com>
Subject: Re: [Rollei] Planar lens design changes from 2.8E to 2.8F
you wrote:
>
>
>> From: Kip Babington cbabing3@swbell.net>
>> Date: Wed, 14 Nov 2001
>> To: rollei@mejac.palo-alto.ca.us
>> Subject: Re: [Rollei] Planar lens design changes from 2.8E to 2.8F
>>
>> FWIW, my understanding is that John Van Stelten does single layer
>> coating of lenses (and very well, too, from what I've heard) but that he
>> does not do multicoating. I've read somewhere, probably on this or the
>> Leica list, that multicoating is a very involved process that takes a
>> substantial industrial plant to do, so that basically only the lens
>> factories are equipped to do it.
>
>
>The problem is really that different lens designs and glass types may
>require different types of multicoating. If JVS or any other repairman
>buys a single vacuum depositing machine he can do single coating very
>easily, but for multicoating he would need to determine what's right for
>a particular lens and then run the lens elements through the machine
>multiple times. Multicoating has anywhere from about 7 to as many as
>21 layers, so it would require running in the macine that many times.
>Lens factories, of course, have that many machines and just move a
>batch of elements from one machine to another until the process is
>completed. These machines are not cheap, nor are they small!!
>
>Bob
>
Multiple coating can be done in a single run by having multiple
evaporators in the vacuum chamber. Multi coatings use two or more materials
of different indices of refraction which must be coated in the right order
to the right thickness. For single coatings the thickness can be judged
visually by the color of the reflection but multi coatings require much
tighter control of thickness since the whole stack acts together. As I have
mentioned before, multi coatings are somewhat analogous to a complex
electronic filter. For filters the tollerance for error in the components
becomes less as the filter becomes more complex. The same for multiple
coatings.
So I am nit-picking rather than disagreeing.
For a single coat the coating index should lie midway between the indexes
on either side, usually glass and air. For multiple coatings the index and
thickness depend on the position of the coating in the stack and its design.
My experience with vacuum coating was many years ago in the manufacture
of precision resistors. These were made from very carefully cleaned and
degassed ceramic blanks which were coated with several layers of verious
metals to give both the right resistance and the right temperature
coefficient. This last was a proprietary feature and produced by the exact
method and materials of coating. The company (long since sold) could meet a
spec for temperature coefficient, for instance to compensate for something
else. I think only two people in the company actually knew all the secrets.
Something like Kodak in the old days where only three people in the
company, one being George Eastman, actually knew everything about the
emulsion making procedures.
----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com
Date: Sat, 17 Nov 2001
To: rollei@mejac.palo-alto.ca.us
From: Richard Knoppow dickburk@ix.netcom.com>
Subject: Re: [Rollei] Planar lens design changes from 2.8E to 2.8F
you wrote:
>Are all elements coated in a tlr planar or just the outer
>surfaces.
>Do they AR coat the cemented sides of a doublet?
>John Kufrovich
>Katy, Texas
>
>
All glass-air surfaces are coated. Cemented surfaces don't need to be
coated because the cement has an index of refraction which is about the
average of the glass. Furthermore, the glass types don't differ so much
from each other in index as they do from air, so there is not much
reflection anyway.
Some very early chemical coatings were done to only internal glass air
surfaces because the coatings could be wiped off when cleaning. The coating
applied by Kodak to the early Medalist and Ektra lenses, and to Eastman
Ektars (the precessors of the Commercial Ektar) were done this way.
Vacuum deposited coatings are hard and bond with the glass so can be used
where they are exposed.
----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com
Date: Mon, 19 Nov 2001
To: hasselblad@kelvin.net
From: Marc James Small msmall@roanoke.infi.net>
Subject: Re: Fwd: Re: [HUG] 500C/M body vs 500C or 501CM - Lens
jchine@hushmail.com wrote:
>On the subject of C lenses, I had an interesting conversation with
someone a couple days ago regarding the non coated C lenses. Turns out
that the very early 150C is sought after by some wedding photographers in
Australia for darker skin tones in black and white work.
>
>The logic ran along these lines - Non coated lenses have a lower contrast
giving them a "softer" look without loosing sharpness.
All lenses for the Hasselblad are coated, whether they come from Kodak,
Zeiss, or Schneider. I have difficulty believing that this information has
not yet percolated to the Antipodes -- some of the more astute scholars of
Zeiss history reside down under. Beginning around 1973, Zeiss lenses began
to be multi-coated (the "T*" lenses), and JSK introduced this shortly
afterwards. So, from 1947 to 1973, the lenses were single-coated and, from
1973 or so to the present, they have been multi-coated.
Marc
=20
msmall@roanoke.infi.net
Date: Mon, 19 Nov 2001
To: hasselblad@kelvin.net
From: Marc James Small msmall@roanoke.infi.net>
Subject: [HUG] Coating and Multi-Coating
jchine@hushmail.com wrote:
>I was aware of the flare issues with the non multicoated lenses, but had
not heard a theory such as the one relayed below.
>
>If you want to be truly picky - the last lens to recieve the multicoating
was the 100C - the exact year escapes me as Nordin book is at home, but I'm
sure it was a lot later than '73
Multi-coating does not make as much of a difference as the marketing hype
would have us believe. For that matter, an uncoated lens will perform
identically to a single-coated or multi-coated lens under almost all
conditions if a proper lens hood is used. =20
Nordin states (p. 145) that the 3.5/100 Planar C received multi-coating
"about 1975". We really do not know EXACTLY when multi-coating began to be
used on any given lens: Zeiss often issued "test" lenses, marked as
multi-coated, for evaluation in the field, and, we are now understanding,
it became their practice, for reasons of industrial economy, to multi-coat
ALL lenses by around 1975 -- but, if you didn't pay the freight, you would
get a multi-coated lens without that "T*" marking. (There are a number of
late 2.8F and 3.5F Rolleiflex cameras which have appeared lacking the
marking -- one possible explanation for this is that Franke &
Heidecke/Rolleiwerke were going through the hard times that led to their
bankruptcy and simply couldn't afford to pay for the marking.)
Finally, there is one lens -- the 5.6/250 SuperAchromat -- which has never
been subjected to multi-coating due to its optical properties.
Marc
msmall@roanoke.infi.net
From: bg174@FreeNet.Carleton.CA (Michael Gudzinowicz)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Question about old, old uncoated lenses
Date: 19 Nov 2001
photoassistant@hotmail.com (WL) wrote
> I have a bunch of old lenses (everything from daguerrotype lenses to
> older uncoated aerial lenses from WWII) and wonder if I should put a
> yellow filter on them. What advantages/disadvantages will result from
> not using a filter on these older lenses? Basically, I am just
> wondering if it is worth the trouble to put yellow gels on these
> lenses. I am just shooting b&w; obviously.
If you don't want to test the lenses, you might want to consider their
original purpose, the materials for which they were optimized, and
the differences between the intended use and that which you might
cotemplate.
The oldest lenses (daguerrotype lenses) were used with blue-sensitive
materials, and weren't well corrected for color. Often, there was a
marked difference in blue focus, compared to that of visible light
(the eye responds well to green). The discrepancy led to the term
"chemical focus" referring to the blue focus shift when using
blue sensitive materials compared to focus on the GG by eye.
When those lenses were used with ortho materials (blue and green
sensitive), a yellow filter would block the blue component. The
use of the filter supressed blue light, so the focus shift due
to plate sensitivity was minimized. Also, chromatic aberrations were
decreased since the plate would primarily respond to green light.
With modern panchromatic materials, the contributions from red light
require consideration. With simple old lenses, I often use a green
filter to supress blue and red to some degree.
Later lens designs corrected the blue and green components for use with
ortho films. Generally, a yellow filter was recommended to partially
restore spectral balance, and darken skies. The use of graduated yellow
filters became popular. Red focus and chromatic aberrations were corrected
to varying degrees, but they were not that important since ortho plates
and films didn't respond to well to red. With panchromatic one would
expect that green and yellow-green filters might provide better results
with poorly corrected lenses, and that is often the case.
The next step in color correction was the inclusion of red and other
wavelengths which led to APO lenses and "modern color" lenses. Although
color materials had been around in one form or another from around 1900,
well corrected lenses were primarily process lenses. The popularity
of consumer films led to design and manufacturing refinements. Generally,
with modern lenses filter selection should be determined by the effect
desired.
Aerial lenses present another set of problems simce many were designed for
use with infrared film or red filters to maximize shadow contrast. If you
don't know the materials for which the lens was designed, red or yellow
filters might help.
Personally, I tend to use filters _all_ of the time. With modern lenses
and pan film, the standard rcommendation is a yellow filter. Although the
frequently cited reason for that selection is restoration of color
balance, outdoors the filter has the advantage of supressing blue skylight
or fill light. The blue attenuation usually increases local contrast, and
appearance of sharpness or texture. A yellow-green filter has a similar
effect. Those selections are modified depending upon specific subject
tones and relationships, and lighting.
I'd suggest that you run a comparison of your lenses with and without
a filter to see the effects, if any. Consider focusing with the filter
in place, and use film manufacturers' filter factors.
From: "Roland" roland.rashleigh-berry@virgin.net>
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Anyone actively shooting with uncoated lenses?
Date: Mon, 26 Nov 2001
Lassi Hippel,inen lahippel@ieee.orgies.invalid> wrote
> Roland wrote:
> ...>
> > Color rendition won't be as good as for a coated Color-Skopar lens. Your
> > lens may not be color corrected so you may notice a color corona on your
> > photographs.
>
> Really?
>
> I thought Skopar is just the Voigtl,nder name for Tessar, and that is a
> sharp lens at all colours. Or do you mean that the lens has a colour of
> its own, and that can be seen as an overall hue?
I'm not sure that the Skopar has exactly the same design as the
Color-Skopar. The Tessar patent has a fairly wishy-washy definition. Indeed,
the original patent had to be revised when someone discovered it actually
covered a lens already in production. The patent does not specify what
refractive index each element should be, what the color dispersion of the
glass material should be, what the radius of curvature of each surface
should be and how far the elements must be apart. Unfortunately, I do not
have the wording of the patent to hand.
Certainly, in my experience, the Color-Skopar is a better lens than a coated
Tessar. But they may have changed the Color-Skopar slightly from the Skopar
to get better colour correction. I don't think the addition of "Color" to
the name just applied to the coating they put on since this would add
nothing to the colour corrective properties of the lens.
The coatings on the Color-Skopar impart a hue that gives a very pleasing
effect for outdoors work.
As for a sharp lens at all colours, then this is difficult if not impossible
to attain. When a good colour corrected lens is designed it is designed such
that more than two colours will converge at a point. Colours inbetween will
be slightly out. Colours outside such as long red and short violet will be
out far more. You have only got to look at an ultra-violet lamp to see the
extent of the problem. Your eye would have to be 1.5 diopters too weak to
bring an ultra-violet lamp at a distance into focus, such is the extra
bending the ultra-violet light does in your eye lenses. Also, you will
notice for infra-red, that some lenses show a different infinity focussing
position for when you do infra-red photography. When designing a lens, this
same problem exists.
> Note that coating effects only the transparency of the glass surfaces,
> not their colour focusing.
I should think most people know that.
> -- Lassi
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
Date: Wed, 29 Aug 2001
To: rollei@mejac.palo-alto.ca.us
From: Marc James Small msmall@roanoke.infi.net>
Subject: Re: AW: [Rollei] Urgent-buying decision 2.8F Xenotar vs.
Planar vs. GX
Dirk Seffern wrote:
>according to the book of prochnow. both, the 2.8F Planar and the 2.8F
>Xenotar are single coated. But I do not know whether that is a reliable
>source....
>
>it seems to me that Rollei made many changes during the production of the
>same product line without marking it.
We have been over these points before and those interested might seek out
the Archives.
First, Rollei did not directly control whether or not Zeiss or Schneider
multi-coated their lenses. We have had a number of multi-coated Planars
surface but no Xenotars, so, presumably, Zeiss simply went from single
coating to multi-coating in the interests of production efficiences. That
is, until 1970 or so, every Zeiss made was single-coated. After 1974 or
so, you got a multi-coated lens whether you ordered single-coated or
multi-coated: the difference was one of price and permitted markings. If
you paid the extra money per lens, it would come marked "T*"; if you
didn't, you got an unmarked multi-coated lens. That is a speculation, of
course, but it is a pretty well-founded one.
Second, Prochnow is extremely reliable. But, as with any source, there are
some deficiencies.
Marc
msmall@roanoke.infi.net FAX:
Date: Wed, 29 Aug 2001
To: rollei@mejac.palo-alto.ca.us
From: Marc James Small msmall@roanoke.infi.net>
Subject: Re: [Rollei] MC v. coated lenses
Kotsinadelis, Peter (Peter) wrote:
>You guys have me going here. DID Rollei employ any multicoated lenses?
>I mean multi-coating was in the 60s if I am not mistaken first employed by
>Pentax.
It all depends on how you count or how precise you want to be. Zeiss and
Asahi pooled their research in 1967. By 1969, Zeiss was marketing lab and
medical test gear that was "T*" coated. I believe Asahi beat Zeiss into
the marketplace by a month or two in '71 or '72. So, Zeiss has priority
for getting it to the field first, while Asahi was the first to market
multi-coated camera lenses.
It really doesn't matter: the processes, coming from pooled research, were
identical.
Marc
msmall@roanoke.infi.net
Date: Wed, 29 Aug 2001
To: rollei@mejac.palo-alto.ca.us
From: Richard Knoppow dickburk@ix.netcom.com>
Subject: Re: [Rollei] Urgent-buying decision 2.8F Xenotar vs. Planar
vs. GX
you wrote:
>Is there a way to inspect such a lens to determine if it was multicoated
>without being so marked? The number of reflections or colors or whatever??
>
>Vincent L. Gookin
>vinlin92@cs.com
This is probably not 100% reliable but is true most of the time. Single
coatings absorb have a peak absorption at a single wavelength. The apparent
color is from wavelengths away from this absorption band. Single coatings
are usually peaked in either yellow-green, near the center of the visual
band, or shifted toward the blue end somewhat, where most films are most
sensitive.
The residual reflection will be either magenta or amber. Coatings on
different surfaces are sometimes peaked at different wavelengths to try to
average out the total internal reflection, so its possible to see a shift
in apparent color on inside surfaces, or sometimes on front and back
surfaces.
Multi-coatings absorb a much wider bandwidth of wavelengths and tend to
have residual colors which depend on the number of coatings and how uniform
the absorption is. Typically they have a double humped absorption curve
with some residual reflection in the green. A really good wide band coating
would have a neutral reflection of very low level.
Lens coatings are not equally effective at all angles. They are
calculated for light impinging perpendicularly on the lens surface. As the
angle is increased the effective depth of the coating is increased, hense
its most effective wavelength is shifted toward the red.
Those with a background in electronics, especially in RF, may recognize
the filter as a quarter-wave matching section as used in transmission lines
or its equivalent lumped-constant LC section. The effect of the coatings is
very similar to electronic wave filters although more complex if angle of
incidence is taken into account. A multiple coating is approximately
analogous to a horn.
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com
From: "Q.G. de Bakker" qnu@worldonline.nl>
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: SL66 questions
Date: Mon, 3 Dec 2001
eMeL wrote:
> All lenses in the current Rollei catalogue made for Rollei by Zeiss or
> Schneider are marked HFT (High Fidelity Transfer) and are supposedly
coated
> with a proprietary technique of the same name. Whether or not *T coating
> differs from HFT (esp. in practice) is open to speculation.
Let me quote Zeiss' Kornelius J. Fleischer:
"HFT is a multi-layer-anti-reflex-coating system co-developed by Zeiss and
Rollei during a time, when T* coating could be applied only at the Zeiss
plants to small lens production batches, but Rollei wanted to produce lenses
in their Singapore plant in large batches to gain economies of scale. This
was decades ago. Today the situation is this: HFT is a Rollei trademark for
their multi-layer coating. The performance of this Zeiss/Rollei development
is so close to the performance of T* that I cannot detect a difference in
practical testing at the Zeiss application department.
As you might know already, four lenses of Rollei's medium format SLR range
are manufactured by Rollei under Zeiss license. They don't bear the name
"Zeiss" anywhere on the product. They are treated with Rollei HFT by Rollei.
The Zeiss lenses of the Rollei 6000 system, manufactured at the Zeiss
Oberkochen plant, are coated by Zeiss with - guess what - T* coating! Just
the designation says "HFT" to keep them in line with all the other optics in
the Rollei 6000 system."
In fact i suspect there is very little difference between brands when it
comes to multicoating. I can't see how they could differ at all.
Date: Sat, 15 Dec 2001
Subject: Re: [HUG] Another lens question
From: Peter Rosenthal petroffski@mac.com>
To: hasselblad@kelvin.net>
If I had to rank ANY and ALL photographic properties that affect the quality
and characteristics of a given image, the type of lens coatings would be
near the bottom of the list (uncoated glass is something else). Coatings,
while important, have an infinitely greater effect on contrast than
"coloration" of emulsions. If we want to get into "coloration" perhaps our
time would be better spent discussing all aspects of developing chemistry,
printing processes, aging of film, before and after exposure, cleanliness of
all optical elements, color temperature of projection lamps and optical
train, and the most important element, in my opinion, the emulsion used in
the first place. While coatings do "contribute very specific properties of
light transmission to the lens", this is only an artifact of their primary
purpose, to eliminate internal and external glass-air reflections, thereby
increasing contrast and putting focused light where it belongs. Inhale,
exhale, inhale, exhale.... some of the greatest images ever taken were with
lenses having nothing more than a thin blush of magnesium flouride. Having
said all this, I can't stress enough the destructive power of scratched
coatings, especially on the exterior of the rear element of wide-angle
optics. Never touch a lens coating dry!! You should see what happens to an
MTF graph with scratched or dirty coatings. That is, scratched and dirty
coatings on lens glass, not on the graph paper itself. Studies show that
that has no effect on anything at all.
Peter - chairman of the Department of Redundancy Department
--
Peter Rosenthal
PR Camera Repair
111 E. Aspen #1
Flagstaff, AZ 86001
928 779-5263
> I have tested various Nikon 35mm lenses over the years and found that the
> different coating used for their lenses did influence the coloration of the
> slides. That the coating influences color should not be surprising; they do
> contribute very specific properties of light transmission to the lens.
>
> Clearly, however, different is not necessarily better. My early 1960's
> generation 80mm planar is an incredible lens that will always be better than
> my abilities as a photographer. Do not fall prey to the "specification game."
> The
> extent of the difference in coatings (to the extent they exist at all in
> Hasselblad lenses) is miniscule compared to the quantum leap that composition
> and lighting play in the photo game.
From: "Q.G. de Bakker" qnu@worldonline.nl>
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: *T
Date: Mon, 24 Dec 2001
Maarten delanghe wrote:
> > The *T lens are multicoated. The non *T are single coated.
>
> Will this affect image quaity much?
It will not. The difference between a single and multicoated lens is hardly
noticeable, if at all.
> Will this affect wide angle more ot tele?
Wide angle lenses ar more prone to internal reflections than telephotos.
From: ralf@free-photons.de (Ralf R. Radermacher)
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: *T
Date: Mon, 24 Dec 2001
Maarten delanghe maarten.delanghe@pandora.be> wrote:
> Will this affect image quaity much?
This depends on the subject and lighting conditions. Backlit scenes and
night-shots with strong light sources inside the frame or immediately
next to it, basically all subjects with very high contrast and bright
speculars are more likely to cause flare and reflections with
single-coated lenses.
Some of this may be prevented by means of the correct lens hood or,
better still, a compendium. If the troublemaker is within the frame, a
slight change of position to hide it behind another object, e.g. the
branches of a tree, often helps.
In most instances you won't see the difference between *decent*
single-coated or multi-coated lenses. There are, however, some
situations when my single-coated Zeiss Contarex lenses do cause trouble
while my Pentax SMC lenses won't bat an iris segment... :))
Happy holidays to one and all,
Ralf
--
Ralf R. Radermacher - DL9KCG - K"ln/Cologne, Germany
private homepage: http://www.free-photons.de
manual cameras and picture galleries - updated 26 Sept. 2001
Contarex - Kiev 60 - Horizon 202 - P6 mount lenses
From Leica Topica Mailing List:
Date: Fri, 28 Sep 2001
From: Dave Saalsaa SaalsD@cni-usa.com
Subject: Re: Harder coatings
Hi Roger,
With the advent of the Summicron M in 1969, Leica improved their
coatings to more durable types. The previous coatings of the 50's and
earlier as you are probably quite aware of were not the most abrasion
resistant especially when cleaned with old underwear and chewing tobacco
spit. ;-) Leica continued to increase the durability of the coatings to
this day with the latest version of lens coatings being the most
abrasion resistant. According to John Van Stelton of Focal Point, it is
not only the composition of the coating material but also the
temperature and method of application which determines the durabililty
of the coating. Leica improved their method of application greatly in
the late 60's and that is the main reason that we don't see the number
of cleaning marks on these later lenses that we do on the lenses from
the 40's and 50's.
Dave Saalsaa
>Since my only reference, Rogliati, pays little attention to coatings,
>does anyone have any information as to when or at what serial
>numbers Leitz began to use the modern much harder coatings?
>You know, those that Ted can rub the bejeepers on with his
>unmentionables without making the cleaning marks so often seen
>on the older glass.
>
>--
>Roger
From Leica Topica Mailing List:
Date: Fri, 28 Sep 2001
From: Dave Saalsaa SaalsD@cni-usa.com>
Subject: Re: Harder coatings
I think you're probably right, Roger. One other feature, which I
beleive may also factor into this, is the fact that Leitz was able to
make use of some newer optical glasses which also allowed for much
higher coating application temps which previously was not possible
because of the high failure rate of the older glass formulas. This also
from John Van Stelton at Focal Point. Failure rate due to thermal shock
of high temperature coatings accounted for an extremely high discard
rate until Leitz was able to come up with new optical glass formulas
which could withstand the application of high temperature coatings. This
probably accounted for some of increased durability of Leitz coatings of
later years.
Dave Saalsaa
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: Mon, 13 Aug 2001
"Nicholas O. Lindan" nolindan@ix.netcom.com> wrote:
>Mark Anderson wrote:
>>
>> I'm thinking of carrying two 6x9 cm. folders while hiking.
>> I'm thinking that the uncoated should be used for high contrast
>> subjects.....
>
>The flare from an uncoated lens is rarely uniform: one gets streaks,
>blobs and 'ghosts' in the 'wrong' section of the image. For black
>rocks on a snow field an uncoated lens may be a good choice,
>but for images with large low value (dark grey) areas the highlights
>are going to invade the shadows in an ugly fashion.
>
>Someone makes a diffusion disk you can mount on the lens for pre-
>flashing. Taking an out of focus picture of a uniform tone works
>just as well - use a grey card, uniform sky, snow, 3x5 index card...
>
>I would use the uncoated lens for low contrast subjects with
>muted highlights. A really good lens hood is a good idea with
>an uncoated lens.
>
>An alternative is a century graphic with two roll film holders
>or sheet film.
>
>--
>Nicholas O. Lindan, Cleveland, Ohio nolindan@ix.netcom.com
>Consulting Engineer: Electronics; Informatics; Photonics.
Ghost images depend a lot of the design of the lens. For example, I
have a couple of 135mm, f/4.5 Zeiss Tesssars on very old Speed
Graphics. They are late 1930's lenses, uncoated. They have no ghost
images at all. In comparison, an uncoated 127mm, f/4.7 Ektar has a
slight ghost image from bright objects near the center of the field.
The image is very dim but detectable on objects which cause no ghost
image with the Tessars (bare light bulb). The Ektar is also a Tessar
type lens and is of excellent performance. There is some slight
difference in curvature or spacing which allows the ghost image. A
coated version of this lens does not exhibit the ghost image but
otherwise the images are pretty much identical.
The more glass-air surfaces a lens has the more likely it is to have
ghost images or to project an image of the stop. Very complex lenses
even with good coatings are plagued by ghost images and stop images.
The corny effect of multiple images of bright objects (like the sun)
in movies, gotten with complex zoom lenses, is an example.
The primary effect of uncoated surfaces is a general haze over the
entire image. In B&W; it is similar to using a long toe film. In color,
it tends to either reduce saturation or to give a slight color cast if
there is a very bright object of a certain color in the image.
The effect can be subtle.
Again, this depends on the number of glass-air surfaces the lens
has. The amount of flare goes up very rapidly with the number of
surfaces. A lens with six uncoated surfaces, like a triplet or Tessar,
still has pretty good contrast, but at eight surfaces, the contrast
begins to suffer, and eight is about the maximum that can be tolerated
without coating.
It is the shadow contrast which is mostly affected. The amount of
haze is constant so mid and bright areas are not changed very much.
As far as scene contrast I don't think the lens will make much
difference, particularly a fairly simple lens like a Tessar.
Its important, BTW, that the lens be clean. Haze inside a lens, very
common in older lenses, does far more damage than lens flare. Most
lenses can be opened for cleaning without much surgery and the haze
comes off with any lens or glass cleaner.
Before good hard coatings became generally available around 1946,
lens designers tried to minimise air spaced elements in order to
reduce flare. Hence designs like the Dagor (three cemented elements in
each cell), the Double Protar (four cemented surfaces in each cell),
and the Zeiss Sonnar (a seven element f/1.5 lens with only six
glass-air surfaces), which have many cemented surfaces. 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.
---
Richard Knoppow
Los Angeles, Ca.
dickburk@ix.netcom.com
From: "Don Wallace" don.wallace@nlc-bnc.ca
Newsgroups: rec.photo.equipment.medium-format,rec.photo.equipment.large-format
Subject: Re: Uncoated lenses vs. high or low contrast subjects
Date: Mon, 13 Aug 2001
"Don Wallace" don.wallace@nlc-bnc.nospam.ca> wrote
> "Mark Anderson" andermar@teleport.com> wrote ...
> > I'm thinking of carrying two 6x9 cm. folders while hiking. I'd use one
> > for low contrast subjects and N+ development and one for high contrast
> > subjects and N- development. Both have 105 mm Tessar lenses. The
> > significant difference is that one has coated optics and one uncoated.
> > So, which should be used for which subjects?
> >
> > I'm thinking that the uncoated should be used for high contrast
> > subjects. As the flare will help to decrease the contrast and aid
> > shadow detail by essentially flashing the film. Is my thinking correct?
> >
>
> There are two kinds of flare which are the result of uncoated lenses:
> streaks
> or bright spots on the film because of bright light in the subject; and
> lowered
> overall contrast because of internal flare. The first kind can be reduced by
> a
> lens hood. You are referring mainly to the second kind, I think, so maybe
> using the uncoated lens for high contrast subjects will work. Try it out
> and get back to us.
I forgot to mention in my posting that there is a very good discussion of
this second type of lens flare and its effect on contrast in the first
edition of Ansel Adams "The Negative". The current version of this book is
a complete rewrite of the one Adams published in the 40s. Many libraries
have copies of the earlier edition. If you can't find it (or don't feel
like looking), I can send you a photocopy of the relevant chapter.
Don
From leica topica mailing list:
Date: Sat, 25 Aug 2001
From: *- CHILLED DELIRIUM -* sfunp@scfn.thpl.lib.fl.us>
Subject: Re: Lens coating color
Dear LEGgers --
This was sent to me by an old friend, and pertains directly
to the old-lens/new lens debate, specially about opening up
shadow detail, as mentioned before by a few of us. All
non-quoted commentary is by Ms. Fang. I thought those that have
eyes and might find these insights useful.
--- Luis
[It is taken directly from Adams' books]
=================================================================
[AA]
" Several years ago a motion-picture photographer was perplexed
because when he used an optical-flat neutral density filter to reduce
exposure he obtained a higher shadow value in relation to highlight
value than when he reduced exposure by simply using a smaller aperture.
Paul Strand found he obtained a smoother negative with his Cooke lens
than with his Dagor. Neither person could explain the reason for this
effect, nor could I; at that time there was scant mention of the subject
in photographic literature. " minor snip>
" The increased flare from the extra reflecting surfaces actually added
density to the negative (apparent in the shadow areas and other low-value
areas), "smoothing out" the contrast difference between high-value and
the shadow areas."
(from Book 4, under _Qualities of Natural Light_, Shade/Diffused
General Light)
[DF] On this same topic, Our Father Ansel also says...
[AA]
" In simple lenses the flare effect is immaterial. But as the number
of air-to-glass surfaces increases, the cumulative effect of the
internal reflections is to reduce image contrast seriously.
Flare therefore has a definite effect on the quality of the images
produced by any uncoated lens. The difference between the theoretical
contrast and the contrast actually obtained is called the flare factor,
it can be expressed as a ratio
Bs
------
Bi
The brightness range of the subject divided by the brightness range
of the image."
[DF] He goes on a little further down...
[AA] " Actually, flare can sometimes be used advantageously ".
and...
" Hence irrespective of the contrasts within the lower values,
the image from the coated lens will always be more brilliant --- that
is, have a greater contrast range --- than the image from an uncoated
lens. It will be obvious that with an uncoated lens we may obtain
" false " opacities for the lowest image values --- mistaking opacity
from flare as opacity from actual exposure. With a coated lens used with
the same subject and same exposure these low values would appear
quite underexposed "
****************** (highlights by La Fang)
(The above is from Book 2, _The Negative_, under Lens flare and image
contrast.)
[DF] Father Ansel seems to be in agreement what I was saying above
regarding the reduction of contrast in the image (he goes on to give
actual values, etc., too much to reproduce here) by adding opacity
in the low-value areas due to the effect of flare.
If most of your contrast problems are of the "too-little" kind
(and if so, believe me, you ARE blessed)
(or live in a fog bank)
then yes, by all means you want a hotshot, zero-flare optic.
But my contrast problems tend to run in the other direction (way too
much and too often), so the slight flare of the earlier lenses
is a proven, decided and visually apparent advantage. Specially when
using contrastier transparency films. I know it's
terribly distressing to embrace an "imperfection" like flare, but it
can work for you.
Remember, the right tool for the job...:-)
*= Doris Fang =*
[Tired from typing the above and hunting through her too-old
Adams books to find the stuff]
From leica topica mailing list:
Date: Fri, 24 Aug 2001
From: *- CHILLED DELIRIUM -* sfunp@scfn.thpl.lib.fl.us
Subject: Re: Lens coating color
Anthony Atkielski wrote:
> Luis writes:
>
> > This is untrue for shadow detail.
>
> Explain how light leaking from brightly-lit portions of the picture enhances
> detail in shadows.
It opens up the shadows, does not add details, only helps to reduce
the contrast from the shadow end.
From leica topica mailing list:
Date: Sat, 25 Aug 2001
From: "Anthony Atkielski" atkielski.anthony@wanadoo.fr
Subject: Re: Lens coating color
She misunderstood what he said. I don't see anything about improved shadow
detail, only reduced contrast. Obviously, the more you reduce contrast, the
easier you can fit the entire dynamic range on a negative or print, but you do
so at the expense of image detail, not the inverse.
From: "Q.G. de Bakker" qnu@worldonline.nl
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Rollei's MC coating before HFT?
Date: Tue, 26 Feb 2002
Ralf R. Radermacher wrote:
> There's T* inside only if it says "T*" on the outside... :))
Well, no.
As Bachchaconne added: "some current Rollei lenses made by Zeiss themselves,
are marked "HFT" for uniformity while in fact they are T* coated."
Zeiss's Kornelius Fleischer says about this:
"HFT is a multi-layer-anti-reflex-coating system co-developed by Zeiss and
Rollei during a time, when T* coating could be applied only at the Zeiss
plants to small lens production batches, but Rollei wanted to produce lenses
in their Singapore plant in large batches to gain economies of scale. This
was decades ago. Today the situation is this: HFT is a Rollei trademark for
their multi-layer coating. The performance of this Zeiss/Rollei development
is so close to the performance of T* that I cannot detect a difference in
practical testing at the Zeiss application department.
As you might know already, four lenses of Rollei's medium format SLR range
are manufactured by Rollei under Zeiss license. They don't bear the name
"Zeiss" anywhere on the product. They are treated with Rollei HFT by Rollei.
The Zeiss lenses of the Rollei 6000 system, manufactured at the Zeiss
Oberkochen plant, are coated by Zeiss with - guess what - T* coating! Just
the designation says "HFT" to keep them in line with all the other optics in
the Rollei 6000 system."
[Ed. note: for info only, caveat emptor! - for possible coating removal?]
From: "Roland" roland.rashleigh-berry@virgin.net
Newsgroups: rec.photo.equipment.medium-format
Subject: Using bleach on lenses
Date: Sat, 16 Feb 2002
I've recommended using bleach on lenses before, where they have been
affected by fungus. It works a treat (but you might lose your lens coating
in the process). I use window cleaner containing some acid for cleaning the
lens first. And if that does not do the trick then I use bleach on it and
leave it overnight. I thought I had a couple of lenses that had been etched
by fungus but I used thick bleach on one of the lenses last night to see if
that would shift it and it did. I highly recommend it for those fungus
affected lenses in your old cameras.
From: laren@qwest.net (Laren Miracle)
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Using bleach on lenses
Date: Sat, 16 Feb 2002
At our camera repair shop we use denatured alcohol to kill fungus.
It is also great for oily smears.
Vinegar is great for water spots and other things not affected by
alcohol. It is acidic, but it is safe.
We make out own lens cleaner to use afterwards but windex will work
fine as well.
I don't think I'd use bleach or acid, especialy if you risk loosing
the coatings.
Larr
From: bachchaconne@my-deja.com
Newsgroups: rec.photo.equipment.35mm
Subject: Re: Multi coated M42 lenses
Date: Thu, 21 Feb 2002
http://212.187.14.19/lenses.htm
http://www.gate.net/~hifisapi/lens1.htm
Multi-coated M42 lenses usually say so on the front ring. Since
they're made later than the single-coated models, some may have also
been re-computed.
Multi-coating improves flare-resistance, contrast, and reduces
ghosting. A lens hood, however, also help in these areas. Put one on
your lens whenever possible, especially with single-coated lenses.
Andrew
Mojtaba mojtabat@start.no wrote:
>How to detrmine if a lens is coated or multi coated?
>
>I have gathered several M42 lenses, all Auto Chinon from 70's. Only
>one of them (55 mm, macro) has this lable on it: Auto chinon MCM and
>outside on the barell: Multi coate dlens. Does it mean all others are
>not multi coated or coated?
>And to be honest, what difference does it make if the lens is coated
>or not?
>
>Thanks for your respons,
>
>Mojtaba
From: bachchaconne@my-deja.com
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Rollei's MC coating before HFT?
Date: Mon, 25 Feb 2002
Perhaps this may help:
http://www.sl66.com/HFT_coating.htm
If your lens doesn't say Made by Rollei, it's made by Zeiss. Also,
only Rollei-made lenses have the HFT coating.
AFAIK, the lenses for Zeiss-Ikon Contax cameras did not have T*
coating but those in Yashica-Contax SLR mounts do. Marc Small of the
Zeiss Historica Society will know the answer to your question, but I
believe your lens is single-coated. Having seen informal tests of
Zeiss lenses for the Hasselblad (the same 80 and 150 lenses with and
without T* coating), the single-coated ones were not any more
flare-prone. In fact, you will also be surprised at the Contax lenses
from 50s Oberkochen in this respect. But then of course, a hood is a
great companion for any lens, MC or not.
Andrew
"Denny Wong" dcywong@netvigator.com wrote:
>Hello all,
>
>I wonder if any of you have heard of Rollei or Zeiss was using Multi Coated
>on Rollei mount lenses prior the introduction of HFT? I believe T* was
>introduced before HFT and it was used on the Contarex and Contax lenses
>before Rollei.
>
>I have just received a Distagon 50/4 lens for SL66. It has a regular single
>coated and made in West Germany (Not made by Rollei) label. It has a serial
>number of 5581335. The SC lens has a light purple and yellowish coating.
>This lens has a deep purple/blue in the front and greenish/yellow/purple in
>the rear element, it looks a lot like my HFT Rollei lenses. I wonder if this
>lens is a MC version with T* prior HFT introduction? Thanks!
>
>Regards,
>Denny
From: Bob Salomon bobsalomon@mindspring.com
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Rollei's MC coating before HFT?
Date: Mon, 25 Feb 2002
bachchaconne@my-deja.com at bachchaconne@my-deja.com wrote
> only Rollei-made lenses have the HFT coating.
Nonsense.
Kiron made Rolleigons and Rolleinars, Schneider made lenses and Zeiss made
lenses as well as some Samsung and Ricoh made lenses as well as Apogon
lenses for Rollei 35mm and 6x6 cm cameras have HFT coatings. HFT is simply
Rollei's designation for their MC and is used on their lenses, regardless of
supplier, It is not just on Rollei made lenses.
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, Vue-All archival negative, slide and print protectors,
Wista, ZTS www.hpmarketingcorp.com
From: "Aaron" aaron@no.spam
Newsgroups: rec.photo.equipment.35mm
Subject: Re: Lens cleaning solution
Date: Tue, 19 Mar 2002
I've tried it before, and it didn't work for me. It decided to try to eat
though the single coating of my Hoya SMC filter. I use pure methanol
instead. But it leaves "water-marks".
Aaron
"Christopher Yeung" ktcy2@eng.cam.ac.uk wrote ...
> I wonder if the cleaning solution designed for spectale lens can be used
for
> camera lens? The label says it's good for multi-coated and uncoated
> spectacle lens. I figure that it probably works for camera lenses as well.
> Am I right in assuming that? Or will it do any harm to the lens coating or
> anything like that?
>
> Chris
From: Alan Browne alan.browne@videotron.ca
Newsgroups: rec.photo.equipment.35mm
Subject: Re: Lens cleaning solution
Date: Tue, 19 Mar 2002
Cleaning solutions for eyeglasses have detergents and solvents in them that you
might not want to get at the coatings on your lenses. The coatings on
eyeglasses are typically an ant reflection coating (which is a thick/rough film
and and anti-scratch (no idea what that is).
Kodak Lens Cleaner is sold in a 473 ml (16 oz) container that will last you
about 20 years (less than $10.00 US). Buy also a little squeeze bottle and fill
it from the large bottle for your c-bag and you're in business. I use this
fluid with Kodak lens papers and I have no complaints. Use sparingly.
Cheers,
Alan
From Russian Camera Mailing List:
Date: Tue, 19 Mar 2002
From: Marc James Small msmall@infi.net
Subject: Re: Re:Zeiss vs. Russian Lenses
eml@ce.net wrote:
>Sonnar, 5cm f1.5 (1939, COATED!!!!)
Why would this surprise you? Alexander Smakula had developed the modern
technique of vacuum-coating lenses while at Zeiss in 1935, and Carl Zeiss
Jena produced coated lenses from 1937 onwards, though most were for
military or technical applications. But several 1937 coated Contax lenses
are known to exist, though my oldest is only from early 1939.
Could I trouble you to send me the serial numbers from this mother-lode of
excellence? These are for the Zeiss Lens List maintained by Charlie
Barringer. Thanks!
Marc
msmall@roanoke.infi.net
From: bachchaconne@my-deja.com
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Rollei's MC coating before HFT?
Date: Tue, 26 Feb 2002
Even Zeiss themselves say their made-for-Rollei lenses have T*
coatings though the HFT label is retained. Would you call the
following "nonsense"?
http://www.zeiss.de/C12567A8003B58B9/allBySubject/35D433EB509B3DB4C1256A96005BD5
82#
Quote:
"How do Zeiss T* and Rollei HFT compare?
"Since this has recently grown into a frequently asked question we
feel it is appropriate to provide an official and unequivocal answer
from Carl Zeiss:
"HFT, meaning "High Fidelity Transfer", is a multi-layer
anti-reflection coating system co-developed by Zeiss and Rollei. This
occurred several decades ago at a time when Zeiss T* coating was new
on the market and could only be applied at the Zeiss Oberkochen plant
to rather small camera lens production batches. Rollei envisaged very
large volume production in their then new Singapore plant and
therefore encouraged this joint development.
"Today the situation is this: HFT has become a well established
trademark for Rollei's proprietary multi-layer anti-reflection
coating. The optical performance of this Zeiss/Rollei co-development
is so close to the performance of the original Zeiss T* that one can
hardly detect any difference in all practical picture taking.
"The Planarr, Distagonr, Sonnarr lenses that Rollei produces under
license from Carl Zeiss are all HFT coated by Rollei. All the lenses
that Carl Zeiss produces for Rollei at the Zeiss Oberkochen plant are
actually Zeiss T*. coated. However, the designation on these lenses is
"HFT" in the interest of remaining fully consistent throughout the
Rollei product range.
Camera Lens News No. 13, Spring 2001"
Unquote.
From rollei mailing list:
Date: Sun, 07 Apr 2002
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Lens Coatings and Coverage for TLR
you wrote:
>At what point did coated lenses, especially multi-coated lenses, appear
>on the various TLRs? Are there some lenses that have "better" coatings
>than others?
>
>Do the various 75mm lenses lose anything in coverage compared to the
>80mm lenses, or are they adequate, or more than adequate, for the TLR
>negatives?
>
>Thanks.
>--
>Shel Belinkoff
>mailto:belinkoff@earthlink.net
Lens coating with vacuum deposited hard coatings became general after
about 1946. By the early 1950's most lenses were coated. I am not sure when
multi-coatings first became available, I think the mid 1960's but were not
widely applied until perhaps twenty years ago.
There is considerably less difference between a multi-coated and single
coated lens than between a single coated and uncoated lens. Multi coatings
become important in complex lenses such as zoom lenses.
The diagonal of a 2-1/4 negative is about 81mm. The angle for an 80mm
lens is about 53degrees, for a 75mm lens about 56degrees. This is well
within the wide open coverage of a Tessar type lens. The five element
Xenotar and Planar types have somewhat better wide open performance than a
Tessar. Neither type of lens is stretched much in a TLR.
FWIW, 135mm, f/4.5 Zeiss Tessars used to be the standard lens for the 4x5
Speed Graphic (slightly wide angle). The diagonal of a 4x5 film is 152mm.
This requires about a 59degree angle. The remarkable 127mm, f/4.7 Kodak
Ektar, a Tessar type, was a later standard on 4x5 Speed Graphics. That
requires a coverage angle of 62deg, which the lens will do stopped down to
f/8. The lenses in Rolleis are loafing.
----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com
From: Tony a_p@nospam.tv
Newsgroups: rec.photo.equipment.35mm
Subject: Re: Old Pentax Spotmatic users out there?
Date: Mon, 06 May 2002
Ron Todd rltodd@ix.netcom.com wrote:
>The only function of the super multi coating is to reduce flare. I have
>single coated Super Takumars and I assure you they perform excellently
>with color film.
The side-effect of good coating that's equally or more important than
flare reduction is that it obtains increased contrast. Increased
contrast means increased apparent sharpness. The contrast reduction
caused by less-than-optimal coating occurs all the time, not just when
flare is visible in the viewfinder or on the film.
The importance of this is that the lens designer need not over-correct
the lens's spherical aberration in order to optimise sharpness.
That's why lenses with very good AR coatings can obtain excellent
sharpness while retaining the wonderful out of focus effects that
characterise the truly *great* optics.
The difference between the Takumars and Super-Takumars was hugely
significant. The Super-Takumars were known to be sharper even if they
were of the identical optical design to their predecessors, all
because of the improved coatings, including some multi-coating.
The difference between the Super-Takumars and the Super-Multi-Coated
M42 Takumars was less significant. All the glass-to-air surfaces were
multi-coated but the improvement was relatively small. Yet the SMC
Takumars were among the very best lenses of their time, giving away
surprisingly little to Leica glass.
My own tests of M42 Super-Takumar and SMC-Takumar lenses and some of
their K- and M-mount successors seem to indicate that optical
standards dropped at Pentax. In particular, the superb contrast seems
to have been reduced. Sharpness appears to have been maintained more
by over-correction of aberrations than good coating and at the expense
of the more desirable qualities of a lens.
>BTW, the turning yellow with age problem. It wasn't the coating, it is
>the glass. Has something to do with the rare earth glass they were
>using at the time. I have one, it gives a nice warm effect on color
>slides.
None of my M42 Super-Takumar and SMC-Takumar lenses seem to have this
problem - yet. But I have a 20mm f/2.8 Flektogon (made in Jena) which
has a noticeable yellow cast. I use it only with black and white
film, when it offers a similar effect to a pale yellow filter. {g}
It has lost none of its sharpness or resistance to flare; another
example of the difference that good AR coatings can make.
From: "Jeremy 1952" jeremy@hotmail.com
Newsgroups: rec.photo.equipment.35mm
Subject: Re: Old Pentax Spotmatic users out there?
Date: Mon, 06 May 2002
1: The yellowing effect was seen ONLY on the f/1.4 normal lens, not the
f/1.8. And it was only on the older SMC Takumar lenses, not the newer ones
with rubber focusing rings. This was definitely a problem with the
multi-coating. The optical glass blanks that Pentax used in their lenses
were the same, the multicoating process was not.
The older 1.4s have the effect of a skylight filter, but it cannot be turned
off, the way one would do by removing a skylight filter from a lens. I
stand by my recommendation to get ONLY the later model 50mm 1.4 lens. If
you like the skylight filter effect, then buy a skylight filter.
This yellowing problem apparently has not been noticed on the 1.8 or the 2.0
normal lenses.
2: Here is what Herbert Kepplar said about multi-coating in his book, "The
Pentax Way" (1976):
"Asahi's exclusive Super Multi-Coating combats [flare] by the use of seven
ultra-thin anti-reflection layers using several kinds of rare elements.
Reflection from a surface is cut to 0.2 per cent. A 7-element lens
transmits an amazing 97.6 per cent of all light while the 14-element zoom
lens shows an incredible brightness increase of over 50 per cent more than a
single layer coating, bringing transmission up to 95.3 per cent. Ghost
images virtually disappear, contrast increases immensely, colours are
richer. In addition, Super Multi-Coating allows maximum light transmission
for all wavelengths of light while cutting off ultraviolet rays like a UV
filter."
He points out in an earlier paragraph that most untreated optical glass
reflects about 7 per cent of the light. A 7-element lens might transmit
only 41.8 per cent of all the light, while a zoom (14-elements) might
transmit only 17.5 per cent. In addition, the reflected light often reaches
the film in the form of ghost images and a general loss of brightness and
contrast (flare).
Given that a SMC lens on eBay is normally only a few dollars more than a
non-multi-coated Takumar, why would anyone buy anything but SMC lenses,
given the choice?
Super-Takumars were fine lenses, but the multi-coating technology was a big
step forward in lens production. He who buys a Super-Takumar does well,
but he who buys a SMC Takumar does even better . . . :-)
From hasselblad mailing list:
Date: Sat, 18 May 2002
From: DaveHodge@aol.com
Subject: [HUG] Re: hasselblad V1 #1591
In response to many requests, here is a Hasselblad technical question. Wildi
says that C lenses plus a hood are just as good as CT* lenses. I have a 50
and a 80 CT* and a 150 C. I don't see anything wrong with the photos shot
with the C lens with a hood. What would I gain with a T* lens? I am sure
everyone will have their own opinion, but I would like to know how much
variety there is in peoples' experiences.
Thanks and best regards,
David Hodge in scenic Churchville, MD.
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 - Cooke Lenses from England
Richard Knoppow wrote:
> Both Hans Harting and Eder have considerable respect for Taylor, about
>the only non German designer they think well of.
Taylor was quite a capable designer and thinker, and it was his observation
that marginally cloudy lenses transmitted more light than unclouded lenses
that led to the development of lens coatings four decades later.
Taylor's miscellaneous correspondence has recently surfaced and is being
vetted for publication. I have been in touch with the folks at Cooke about
this but do not know the present status.
Marc
msmall@infi.net
From rollei mailing list:
Date: Sat, 20 Jul 2002
From: Richard Knoppow dickburk@ix.netcom.com
Subject: RE: [Rollei] A Zeiss Question OFF Rollei topic - Cooke Lenses from England
...(quotes above)
It would be very intersting to see such a publication.
Taylor observed the effect of oxidation on lens transmission. Oxidation
does not result in cloudiness but rather in a film of oxide which makes the
lens look discolored. I have a few old lenses which show this effect. One
is a Tessar from about 1939 which has a light blue reflection, but only
from the front element. Another is a very old Rodenstock Trinar (Triplet)
which has an oil film rainbow reflection, again only on the front, one is
an ICA Maximar which is quite blue looking..
Taylor tried to find a method of artifically producing the tarnish but
was unsucessful so far as finding one sufficiently reliable for commercial
application. He did understand exactly why it worked.
Taylor wrote a famous book, published in 1923, on lens design. He
promoted an all algebraic method and claimed never to have traced rays.
According to Kingslake, who should know, the method is not very practical.
Taylor had access to an excellent optical shop and refined designs with
actual models.
Actually, this is a technique which was pretty universally used.
It may still be despite the ease and speed of computer analysis.
BTW, the Cooke Convertible lens of TT&H; is not a Triplet. I don't know
why the Cooke name is on it, perhaps it was designed there.
The Cooke Convertible is a four lens per cell design. It is something like
a Zeiss Convertible Protar with an air space in place of the middle
cemented surface. Since it has eight glass-air surfaces it would have had
some flare as an uncoated lens. I have no idea of its performance or what
advantage was gained by breaking apart the elements. This is the lens used
by Ansel Adams and others.
Curiously enough a similar lens was designed by Ernst Gundlach and made
by the Rochester Lens company as the Royal Anastigmat. It was continued by
Wollensak after they bought out Rochester as the Vitax.
Those interested in more about the triplet should see _A History of the
Photographic Lens_ Rudolf Kingslake, 1989, The Academic Press,
ISBN 0-12-408640-3
The patent is USP 568,062 (1893) available at http://www.uspto.gov
----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com
From: "Q.G. de Bakker" qnu@worldonline.nl
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Why has no one improved on the Blad?
Date: Fri, 5 Jul 2002
Lourens Smak wrote:
> Well, I have used both systems extensively, and in my experience the
> sharpness is the same, but the HFT coating is actually a bit better than
> T*, resulting in better contrast-rendering, and less flare.
Hey! You're very good!
May i quote Zeiss' dr. Kornelius J. Fleischer?
"HFT is a multi-layer-anti-reflex-coating system co-developed by Zeiss and
Rollei during a time, when T* coating could be applied only at the Zeiss
plants to small lens production batches, but Rollei wanted to produce lenses
in their Singapore plant in large batches to gain economies of scale. This
was decades ago. Today the situation is this: HFT is a Rollei trademark for
their multi-layer coating. The performance of this Zeiss/Rollei development
is so close to the performance of T* that I cannot detect a difference in
practical testing at the Zeiss application department.
As you might know already, four lenses of Rollei's medium format SLR range
are manufactured by Rollei under Zeiss license. They don't bear the name
"Zeiss" anywhere on the product. They are treated with Rollei HFT by Rollei.
The Zeiss lenses of the Rollei 6000 system, manufactured at the Zeiss
Oberkochen plant, are coated by Zeiss with - guess what - T* coating! Just
the designation says "HFT" to keep them in line with all the other optics in
the Rollei 6000 system."
Even the people producing the stuff can't see a difference.
And sometimes the only difference at all is in the name they put on the
lens.
But still: i'm impressed by your skills of perception.
Very much so! ;-)
From rollei mailing list:
Date: Mon, 17 Jun 2002
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] Coating Flaws in E Series
you wrote:
>I have a Planar 3.5 E front element that looks like it's been sandblasted.
>Under a very strong loupe it looks like something has eaten a thousand small
>pits in the glass. I'm contemplating wether I want to get it redone or not.
>In theory, taking off enough glass to fix the surface to fix the surface
>should change the figure, but all of the anecdotal feedback I've gotten from
>people who have had polishing/recoating done by reputable technicians have
>been very positive.
>
>Gene
I've seen this a number of times on lenses stored where there was a lot
of moisture. It may be the effect of fungus but I suspect it may be
something else.
Most coatings are Magnesium Flouride, a fairly hard and resistant
material. I don't know specifically what attacks it but have seen enough
lenses with damaged coatings, or damage which is much deeper than the
coating, to think it may be sensititve to moisture or the exudations of
fungus.
BTW, I also remember a runor that Schneider had coating problems in the
mid 1950s. My 2.8E shows some coating flaws on the outer surface but
neither of my Xenars do nor does a Componon enlarging lens from about the
same period. Actually, the Xenars are older, so may not have been coated in
the same way.
>----- Original Message -----
>From: "Craig Roberts" crgrbrts@netzero.net
>Sent: Sunday, June 16, 2002
>Subject: Re: [Rollei] Coating Flaws in E Series
>
>
>> Douglas Cooper said:
>>
>> "...the Xenotar had spots -- almost flakes -- in the coating...I had (it)
>> recoated by Focal Point, and it was stunning."
>>
>> Good morning,
>>
>> When I acquired my 2.8E Xenotar recently I noticed what looked like a
>slight
>> haze on the front element. However, when I examined the lens from the rear
>> with a strong light shining through it, I was shocked to see the same
>> "pin-prick field" coating damage you mentioned, Douglas. I suspected
>> mechanical damage (abrasive dirt blown onto it or something similar), but
>> the viewing lens was unmarred. Hmmmm.
>>
>> Well, even though the image quality produced by this Schneider lens was
>> outstanding and, as you say, seemingly unaffected, I sent it off to John
>Van
>> Stelten for recoating. He has it in his kind custody as we speak.
>>
>> In other words, you are not alone. Perhaps we should ask John if he sees a
>> disproportionate number of Xenotars exhibiting this coating anomaly. By
>the
>> way, have you noticed any improvement - especially in flare resistance -
>> since John performed his procedure?
>>
>> Craig Rioberts
>> Washington, DC
----
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com
From rollei mailing list:
Date: Tue, 18 Jun 2002
From: Jerry Lehrer jerryleh@postoffice.pacbell.net
Subject: Re: [Rollei] Coating Flaws in E Series
Peter
I've been told that alkaline cleaners may be injurious to coatings.
I tested the highly regarded lens cleaner ROR, and found it to be
alkaline, using pH test strips. I have never had a problem with
ROR though. It works.
For other than camera lenses, I use a 40% solution of ethyl alcohol
with a few drops of Kodak Photo-Flo. (Trader Joe's Vodka works
perfectly, and it's a hell of a lot cheaper than the proprietary cat-piss
that dealers charge for lens cleaner solutions).
Jerry Lehrer
From: rpn1@cornell.edu (Neuman - Ruether)
Newsgroups: rec.photo.equipment.35mm
Subject: Re: multicoating surprises Re: How important are multi-coated filters?
Date: Tue, 20 Aug 2002
Steffen Kluge kluge@dotnet.org wrote:
>According to Neuman - Ruether rpn1@cornell.edu:
>>You are quoting me, and as I pointed out in another post
>>in this thread (as I recall...;-), brilliance *is* slightly
>>improved with MC. This is a useful thing, though of a
>>considerably lower order of magnitude than the vast
>>difference in flare between single and multi-coated lenses
>>shown in sales brochure pictures, which is what I was
>>commenting about... As for the flare reduction in Nikkor
>>lenses, the only example I can think of (and the one I
>>was thinking of, when making the statement above) was the
>>one of the Nikkor MF 85mm f1.8, which in the single-coated
>>version was very sensitive to backlight.
>Yes, I did quote you, thinking that would be the safest way of
>soliciting your response ;-)
>
>I was worried you had changed your mind about what you say on
>your web site. You will know that SLE(MN) is among the most
>respected sources of subjective test results, and definitely is a
>certain stop for me before purchasing a lens.
>
>Being lazy and not wealthy enough to test any significant number
>of lens samples myself, I always put a lot of trust into SLE(MN)
>not the least because the testing method is well documented and
>the number of samples stated for each lens, so that everybody can
>make up their own minds about relevance and limitations of the
>resulting ranking.
Thanks for the comments. The URL for SLE(MN),
for those who have not yet run across it, is:
www.ferrario.com/ruether/slemn.html
>Your comments about the 35mm f/2 and 85mm f/1.8 pre-Ai actually
>made me avoid non-MC lenses in general, which turns out to be a
>bit overboard, after all. I wasn't sure when I read what you said
>in this thread, whether you've changed your mind about these
>lenses, or simply got carried away arguing for the pro-filter
>camp :)
Not the former, but perhaps a bit of the
latter...;-) I've been preoccupied with video
for a few years (though I try to keep SLE[MN]
current at least on Nikon's lens offerings, and
update ratings occasionally...), so some memories
of still-lens issues have faded a bit. The 35mm f2
MF, though of the same design as the original version,
does appear to be the other lens, besides the 85mm f1.8
MF, that did improve with newer manufacturing methods,
including, maybe, multicoating...;-)
>Ok, enough patronising, I conclude that it is best to evaluate
>flare resistance myself before purchasing a lens. In fact, the
>only little testing I'm regularly doing (shots of the night sky
>at various apertures) would point out flare quite brutally, at
>least at infinity focus. The stars did expose very bad flare on a
>Nikon field scope eyepiece that I'm using as a telescope
>eyepiece. Otherwise better than any other eyepiece I've ever
>used, those ghost images in the Nikon can be quite disturbing...
These may originate in the eyepiece...?
There is another issue with night shooting: coma.
Some lenses make a mess of point light sources
near the frame edges, turning them into "birds"
(head-on view...;-). In SLE(MN), assuming
characteristics that are not bad enough to stand
out, the primary standard for the evaluation number
is the sharpness (to the corners, or close enough...)
at the widest stop at which good performance can be
expected, when shooting in normal lighting. As
a result, some things that may "bug" some users may
not enter into the lens rating judgement at all...
In other words, an 85mm that produces a sharp-looking
image to the corners at all normal focus distances
shooting wide-open in normal lighting will get a
higher rating than one that is a bit soft in the
corners at the same stop, but has a tad less flare
in difficult lighting and maybe also has a tad less
linear distortion, since these will show in fewer
images than lack of sharpness will (and I'm a
sharpness nut...;-).
David Ruether
rpn1@cornell.edu
http://www.ferrario.com/ruether
From: rpn1@cornell.edu (Neuman - Ruether)
Newsgroups: rec.photo.equipment.35mm
Subject: Re: multicoating surprises Re: How important are multi-coated filters?
Date: Sat, 17 Aug 2002
>basically, if multicoating has so little impact in a multi-element lens,
>its benefits on a flat glass filter is likely to be even much less...
>
>grins bobm
When the first Nikkor multicoated versions of the
same single-coated lens designs appeared, I compared
a couple shooting with both the sun and dark areas in
the images. Guess what. They showed the same flare
and ghosting characteristics, except that the
multicoated lens' ghosts were multicolored instead
of neutral...;-) Brings to mind that old Barnum
saying, seeing ads that perported to "prove" the
superiority of multicoating for flare reduction...;-)
David Ruether
rpn1@cornell.edu
http://www.ferrario.com/ruether
From: rpn1@cornell.edu (Neuman - Ruether)
Newsgroups: rec.photo.equipment.35mm
Subject: Re: multicoating surprises Re: How important are multi-coated filters?
Date: Sun, 18 Aug 2002
Steffen Kluge
wrote:
>According to Neuman - Ruether rpn1@cornell.edu:
>>When the first Nikkor multicoated versions of the
>>same single-coated lens designs appeared, I compared
>>a couple shooting with both the sun and dark areas in
>>the images. Guess what. They showed the same flare
>>and ghosting characteristics, except that the
>>multicoated lens' ghosts were multicolored instead
>>of neutral...;-) Brings to mind that old Barnum
>>saying, seeing ads that perported to "prove" the
>>superiority of multicoating for flare reduction...;-)
>
>Hm, I've got a quote, too:
>"Multicoating ("IC", which appeared on Nikkor lenses just before
> "AI" appeared) seems to have improved lens image contrast a bit,
> and and to have reduced flare in lenses that were prone to
> showing it."
>
>;-)
>
>Cheers
>Steffen.
You are quoting me, and as I pointed out in another post
in this thread (as I recall...;-), brilliance *is* slightly
improved with MC. This is a useful thing, though of a
considerably lower order of magnitude than the vast
difference in flare between single and multi-coated lenses
shown in sales brochure pictures, which is what I was
commenting about... As for the flare reduction in Nikkor
lenses, the only example I can think of (and the one I
was thinking of, when making the statement above) was the
one of the Nikkor MF 85mm f1.8, which in the single-coated
version was very sensitive to backlight. I did not compare
this particular one with the MC version, but others
reported that MC cured this problem (perhaps I should not
have gone with "second hand" info, though - and in my direct
experience, I saw no great difference between the flare and
ghosting of the lenses I had available to compare - and
MC did not generally appear to "vastly" improve overall
lens quality, or even improve it enough generally to
recognize it as a distinct advantage unless one was
looking for subtleties...).
But, thanks for "keeping me honest"...;-)
David Ruether
rpn1@cornell.edu
http://www.ferrario.com/ruether
From: Rudy Garcia rudyg@jps.net
Newsgroups: rec.photo.equipment.35mm
Subject: Re: How important are multi-coated filters?
Date: Fri, 16 Aug 2002
...
"Dallas"dallas@nospam.ananzi.co.za
> > wrote:
> >
> > >To determine the sort of difference a MC filter will make as opposed to
> > > a non-MC filter, place one of each on a flat counter surface. Step back and
> > >look at about a 45 degree angle into the filters. One of them will
> > > reflect a lot of the ceiling and the other won't.
> > >
> > >No prizes for guessing which does which.
> >
> > Ok, so how does it affect the picture?
> >
> > What is important is the behavior of the light rays that bounce off the
> > lens and hit the back of the filter. Do they go through the filter, or
> > do they get re-reflected back to the lens?
I am perfectly sure. Light rays bouncing off of the external surface of
a fileter never become image making rays. Only light rays that bounce
off of the front lens element and hit the back of the filter are
problematic. If the back of the filter is coated, then these rays
escape the optical system and don't make an image. If the back of the
filter is not coated, the rays are re-flected back into the lens and
will cause flare or other artifacts.
The Hoya advert, although clever, doesn't really address how a frontal
coating (which is the effect displayed) is in any way better than a
filter with just rear multicoating. Now calm yourself down.
From rangefinder mailing list:
Date: Sun, 29 Sep 2002
From: ClassicVW@aol.com
Subject: Re: [RF List] black Hector 4.5/135
You're welcome, Mike, and I should have added- good luck with and enjoy the
lens. This book doesn't get into lens coatings, but the technology of
coating lenses was invented at Zeiss in 1935. I _thought_ I read somewhere
that it was not in widespread use until after the war, which would be very
close to when yours was produced. I also recall a discussion that said that
the serial numbers given for a particular year are ones that were allocated
ahead of time for that year, and actually may vary slightly from the exact
date of production.
Regards,
George
mbo5627310@aol.com writes:
Hello George
Thank you for looking up the Production year .1948 eh, An early coated lens ?
i wonder what year leitz began coating lens's ? And a short production run on
black ,It's a pretty lens for sure . Thanks again Mike
From rangefinder mailing list:
Date: Sun, 29 Sep 2002
From: Marc James Small msmall@infi.net
Subject: Re: [RF List] black Hector 4.5/135
mbo5627310@aol.com wrote:
> i wonder what year leitz began coating lens's ?
Some Wartime lenses were coated, as Zeiss was required to share its
vacuum-coating technology. Regular production of coated lenses began in
November, 1945, but Zeiss was then able to require Leitz to use the cruder
drip method which produced a much softer coating.
Marc
msmall@infi.net
From rangefinder mailing list:
Date: Sun, 29 Sep 2002
From: Jim Williams jimwilliams1@cox.net
Subject: Re: [RF List] black Hector 4.5/135
> This book doesn't get into lens coatings, but the technology of
> coating lenses was invented at Zeiss in 1935. I _thought_ I read
> somewhere that it was not in widespread use until after the war, which
> would be very close to when yours was produced.
The modern process of lens coating via vacuum deposition was proposed
by University of California professor John Strong in a 1936 academic
paper published in vol. 26 of the Journal of the Optical Society of
America. This doesn't mean that individual manufacturers' proprietary
processes might not have been in use earlier, but does provide a
convenient date for the technology* being *publicly* available. It took
a while for industry to ramp up for the process, but Kodak (for
example) was coating all its high-grade lenses on at least the internal
surfaces by late 1938. Disruption of consumer optics production in
general during the war years meant that coated lenses weren't widely
available to the public at first, but it's hard to find a high-quality
lens manufactured after about 1948 that isn't factory-coated.
To muddy the dating waters further, though, a lot of independent
suppliers in the late 1940s and early 1950s set up services to apply
coating to lenses that had been manufactured uncoated. This means that
while it's usually safe to assume that any high-grade UNCOATED lens you
encounter probably was manufactured prior to the 1936-48 period, you
can't assume that any COATED lens you encounter was manufactured
*during or after* that period -- it could be an older lens that the
owner had had coated independently.
*Actually, the basic principle of lens coating dates back to 1896, when
photographer H. Dennis Taylor published observations noting that some
old lenses with dark, tarnished surfaces actually (and contrary to what
you'd expect) transmitted MORE light than similar lenses with 'clean'
surfaces. Physicists soon recognized that this effect was caused by
reflections from the thin film of tarnish cancelling out the
reflections from the glass surface, and optical companies began
experimenting with techniques for producing this 'tarnish' or 'bloom'
in a controlled, uniform way.
From rangefinder mailing list:
Date: Sun, 29 Sep 2002
From: Marc James Small msmall@infi.net
Subject: Re: [RF List] black Hector 4.5/135
Jim Williams wrote:
>
>The modern process of lens coating via vacuum deposition was proposed by
>University of California professor John Strong in a 1936 academic paper
>published in vol. 26 of the Journal of the Optical Society of America.
Jim
This is most interesting, and I had been unaware of this paper. Smakula's
process -- a combination of the fluoride coatings with vacuum depositing --
had been patented in Germany in 1935 and commercial production of coated
Zeiss lenses began in 1937, although a variety of military and technical
items had been coated before this.
To be fair, the process of using vacuum deposits of fluoride compounds was
developed independently by Zeiss, Kodak, Wollensak, and Ross within a few
months of each other, but Zeiss and Kodak were the only ones to produce
commercial coated lenses before the outbreak of the Second World War.
Marc
msmall@infi.net
From rangefinder mailing list:
Date: Sun, 29 Sep 2002
From: Jim Williams jimwilliams1@cox.net
Subject: Re: [RF List] Coating history [long]
>> The modern process of lens coating via vacuum deposition was proposed by
>> University of California professor John Strong in a 1936 academic paper
>> published in vol. 26 of the Journal of the Optical Society of America.
>
> This is most interesting, and I had been unaware of this paper.
I admit I've never tracked down the actual paper. I just happened to
stumble across a citation to it in one of Kingslake's books.
> Smakula's
> process -- a combination of the fluoride coatings with vacuum depositing --
> had been patented in Germany in 1935 and commercial production of coated
> Zeiss lenses began in 1937, although a variety of military and technical
> items had been coated before this.
>
> To be fair, the process of using vacuum deposits of fluoride compounds was
> developed independently by Zeiss, Kodak, Wollensak, and Ross within a few
> months of each other, but Zeiss and Kodak were the only ones to produce
> commercial coated lenses before the outbreak of the Second World War.
This would be an interesting thesis topic for an "industrial historian"
(I'm not sure this academic discipline actually exists, but it
should!... the development of industrial processes probably having at
least as much impact on the shape of society as the development of
political ideas.)
Introduction of lens coating would be an especially clear-cut example
because it's a clearly better technology; it was developed almost
simultaneously in several countries, as Marc notes; and because it
became available just exactly at the beginning of the period when those
countries were beginning to go to war with each other.
If we could research it, I suspect we'd find that there was a clear-cut
correlation between war involvement and the availability of coated
lenses to the consumer. For example, Britain (Ross) definitely was at
war with Germany by 1939-40, so Ross's lens-coating capabilities
presumably were ramping up just as its production of consumer optics
was ramping down. Meanwhile, the US wasn't officially at war with
anyone until December 1941, so Kodak had a couple of years to exploit
coating technology for consumer optics. Germany would be an interesting
mixed case -- undoubtedly it was producing most of its coated optics
for war industries, but before 1941 was at least attempted to keep up
US trade (I recall reading an account of the Germans actually shipping
small, high-value specialties to US customers via U-boat!) so
lens-coating capacity presumably would have been split between military
and civilian production.
It would be interesting to chart the availability of 'consumer'
photographic lenses in all the combatant countries from 1937 to, say,
1943, as well as what percentage of those lenses were coated. I think
we'd find that by 1941, most every major optical house COULD coat
lenses, but most were NOT producing significant volumes of civilian
production by then.
An interesting side effect was that by the end of hostilities in 1945,
a large worldwide lens-coating capability was available thanks to the
demands of military production -- so from the viewpoint of civilian
optics, photography went very abruptly from a situation in which only a
trickle of lenses were coated (1937-38) to one in which just about
*everything* was coated (1947-48.) Wars are often cited for
accelerating the development of technology, but in this case it seems
that the effect was to simply make the *adoption* of technology very
abrupt rather than gradual.
I apologize for this long, rambling, not-terribly-RF-related essay, but
the technical history of photography interests me, and I feel it's
generally neglected by academic photo-historians. Lots of attention is
given to the development of artistic ideas in photography, but I feel
the historians often neglect the fact that those ideas can't be
expressed unless there's a technology available to realize them! (For
that matter, there also has to be a public receptive to the ideas, or
the artist's expressions won't get seen widely enough to have any
impact.)
Rangefinder photography is an especially good place to see this: the
notion of 'captured instants' was popularized artistically by the
Impressionists, after which public appetite for seeing real-life,
spontaneous images was developed by the picture press of the 1920s and
'30s -- which (NOT, I suspect, coincidentally!) is also the prime era
of development of the 35mm coupled-rangefinder camera, the ideal
instrument for expressing this type of idea by producing these types of
images.
From: "David Kieltyka" daverk@msn.com
To: contax@photo.cis.to
Subject: Re: [Contax] Different types of T* coating ? They have different colors.
Date: Fri, 18 Oct 2002
I picked up a 100mm f/3.5 MM not long ago (great lens, BTW...compact &
light, fine performance throughout its aperture range) and noticed the
greenish coating too. Maybe Zeiss simply uses more than one coating formula
and has criteria for determining which lenses get which coatings. Dunno...
-Dave-
----- Original Message -----
From: "Yuri Shchedov" ygs@strace.net
To: contax@photo.cis.to
Sent: Friday, October 18, 2002
Subject: [Contax] Different types of T* coating ? They have different
> Hello, Dear All,
>
> I recently accuared Distagon 28/2.8 and have found that its coating
> looks different to Planar 50/1.7 that I had.
>
> Distagon glass looks Green with some yellow, and Planar glass looks
> blue with some pink. Both lenses were made in Japan and both are
> AE-type.
>
> Does it mean that there are several types of T* coating available ?
>
> Is Planar 50/1.7 coating differs to planar 50/1.4 coating ?
>
> Which is better ?
>
> Thanks,
> Yuri
From: David Littlewood david@nospam.demon.co.uk
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Acetone a hazard to AR coatings?
Date: Sat, 4 Jan 2003]
mevansmi mevansmi@cbpu.com writes
>While at my opticians the head of the optical lab informed me that
>acetone is safe as a cleaner on uncoated glass but will cause
>anti-reflection coatings to turn opaque. Has anyone heard this or
>experienced such a result.Is the AR coating for eye glasses different
>than the ones used on camera lenses?
>Thanks for any information.
>mevansmi
The materials used to coat lenses are all (at least in normal use)
inorganic salts which are highly insoluble in water (for obvious
reasons)*. Now, I have no specialist knowledge of coating technology,
but from past experience as a chemist I know that inorganic salts which
are insoluble in water are likely to be even more insoluble in acetone.
Having said that, I question why you would want to use acetone on your
lens. It is, for example, possible that it would attack any plastic used
in the lens body (or even plastic used to create aspherical lens
surfaces, though these are unlikely to be at t he front surface), or
attack the balsam used to cement elements together. You would be far
better off using cleaning materials specially formulated for this
purpose.
I have no idea what is used on spectacle lenses; perhaps there is
something specific to these which causes the problem. I know plastic
lenses are quite common on these, and they could be attacked by acetone.
*Examples of the materials used on camera lenses are:
Magnesium fluoride
Cryolite (sodium hexafluoroaluminate)
Aluminium oxide
Silicon dioxide
Titanium dioxide
Cerium dioxide
Thorium fluoride
--
David Littlewood
From: "Richard Knoppow" dickburk@ix.netcom.com
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Acetone a hazard to AR coatings?
Date: Mon, 6 Jan 2003
...
The only coatings which could be removed by Acetone are
those used before vacuum coating became generally available
around 1946. Some early Kodak lenses have soft coatings on
protected interior surfaces only. This kind of coating will
come off with ordinary lens cleaning.
Hard coatings, single or multiple, are layers of metallic
salts deposited by vacuum evaporation. They are nearly as
hard as the glass and are bound very tightly to it. They can
be removed only by acid etching or by abrasion (polishing).
Generally modern eyeglass lenses are made of plastic.
Acetone will dissolve them. Pure Isopropyl alcohol,
avialable in many drugstores, makes a good cleaner for both
glass and many plastic lenses.
Acetone is an old standard cleaner for glass parts in
optical assembly. It must be rather pure to avoid deposition
of streaks on the glass.
It is not a good general purpose lens cleaner because it
will dissolve many plastics and some types of paint.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com
From: "Brian Ellis" bellis60@earthlink.net
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Multicoating Question
Date: Tue, 28 Jan 2003
I wouldn't worry about it. In 4x5 I have two single coated lenses and two
multicoated. I don't remember making a photograph with the single coated
lenses that looked technically inferior to those made with the muticoated
lenses. I certainly couldn't look back at my photographs over the years and
identify which photographs were made with single vs. multicoated lenses.
Maybe with color it would matter and I'm sure a specific situation could be
created where it would matter with black and white but if you do general
purpose photography I'd be surprised if it mattered in 1 out of 100
photographs. At least that's been my experience photographing outdoors,
mostly landscape and architecture, with the two types of lenses.
.llard@genuity.com wrote
> In this month's View Camera, an excellent article on Schneider lenses
> confirms what I had suspected, ie. my 90 mm f8 SA lens is not
> multicoated (sn dates the lens to the mid 70's). Since I only shoot B&W;,
> should I care? The article recommends one buy multicoated lenses, but
> doesn't state why.
>
>Thanks
From: Stacey fotocord@yahoo.com
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Multicoating Question
Date: Tue, 28 Jan 2003
john@stafford.net (J Stafford)
wrote:
> Stacey fotocord@yahoo.com wrote:
>
>> [...] I've had more problems with
>> crud that developed inside lenses than coatings showing much
>> difference. [...]
>
>See? That's what you get for _using_ your lens, and outside even! Sheesh.
>
>But seriously, it's fungus, right? Do you live in a warm, humid climate? I
>noticed far more of these fungi-optics in the tropics (like Florida and
>Trinidad) than I do up here in the Minnesota Tropics.
Actually I think this haze (it was on old kodak comercial ektar) came
from the lubricants in the shutter? I didn't really notice it until I
kept having flare problems and when I shinned a flash light through
the lens it was like "WOW what is that crap!" Couldn't really see it
just looking through the lens. Anyway after I cleaned it out the flare
problems were gone.
Stacey
From camera makers mailing list:
Date: Thu, 31 Oct 2002
From: Michael Briggs MichaelBriggs@earthlink.net
To: cameramakers@rosebud.opusis.com
Subject: [Cameramakers] Re: identifying multicoated lenses
> From: "Gene Johnson" genej2@cox.net
> Date: Tue, 29 Oct 2002
> Subject: [Cameramakers] identifying multicoated lenses
>
> Is there a way to determine by inspection if a lens is multicoated?
With experience, by visual examination one can distinguish between
single-coated and multi-coated. Distinguishing between uncoated and coated is
easy -- look at the reflection of a light bulb. If in doubt, compare to the
reflection from glass of known coating, e.g., a cheap filter for the uncoated
comparison. Telling single coating and multicoating apart is harder.
But this is a clue that it really doesn't matter that much. The difference in
performance between uncoated and single coated is quite large, the difference
in performance between single coated and multicoated is rather small.
Some clues for multicoating: good multicoating is designed for the refractive
index of the glass. Multicoating tends to have a stronger hue to the
reflections than single coating, and because the different glass elements
should have different coatings (because of their differing refractive indices),
the hues should differ from element to element. If all of the elements have
the same hue (blue is very common), then the glass is probably single-coated.
If the reflections have different hues, or if the reflections seem relatively
strongly colored, than the coating is probably multicoating. These clues are
not definitive.
> I have a set of 3 military surplus lenses which were intended for the
> KS-87B aerial recon camera. These date from the late 60's to early 70's
> I think. Being that these would be pretty close to cost-no -object
> items, I assume they would have been multicoated if that was available
> at that time. The color and contrast from the one I've used so far are
> wonderful. Looks like the kind of punch I get from my one known
> multicoated lens. But does anyone know a way I could tell?
It is conventionally stated that the first use of multicoating in commercial
lenses was by Pentax, in 1971 I think. Many people imply that Pentax and/or
Zeiss invented it. I just read somewhere that Pentax bought the technology
from an American company that had developed it for the Apollo program. I
don't know whether this is true. I think even military lenses from the
1960's are unlikely to be multicoated.
--Michael
Date: Fri, 1 Nov 2002
From: "Q.G. de Bakker" qnu@worldonline.nl
To: hasselblad@kelvin.net
Subject: Re: [HUG] Hasselblad Lenses (What is T*?)
Ayan George wrote:
> I am sure I am the only person on this list who
> does not know what at T* lens is and how it
> differs from a non T* lens.
>
> Can somoene point me to a resource that has this
> inforamtion about Hasselblad lenses?
T* is the Zeiss name for their 6 layer multicoating.
Early Zeiss Hasselblad C lenses did have a single layer coating. These
lenses are commonly referred to as non-T* lenses, the later lenses with
multicoating as T* lenses.
The change did not happen for all lenses at the same time, and did partly
coincide with the change from 'chrome' to black finnish lens barrel during
the 1970s. All Zeiss/Hasselblad lenses since are T* multicoated lenses.
From manual SLR mailing list:
Date: Mon, 6 Jan 2003
From: "Abdon" abdon@sillypages.com
Subject: RE: [SLRMan] Super-Multi-Coated vs. SMC
Multicoating technology was a stunning _MARKETING_ success. First of all,
benefits for multicoating are minimal for lenses of up to 6 to 8 elements,
which are your regular fixed focus lenses. For zooms with a gazillion pieces
of glass it does have its advantages. Second, all muticoating does is to
improve light transmission, it does nothing for flare nor ghosting. That's a
misconception that has been repeated soo long that now people think that it
is true.
You don't have to take my word for it. Modern photography did an article a
long time ago about Multicoating. They found that singlecoated lenses
significantly improved performance on both flare and ghosting, multicoated
lenses did very little (I think they said insignificant) over singlecoated
lenses.
Abdon
http://www.sillypages.com/
From manual SLR mailing list:
Date: Mon, 6 Jan 2003
From: "J. C. O'Connell" hifisapi@gate.net
Subject: RE: [SLRMan] Super-Multi-Coated vs. SMC
Dont mean to be argumentative tonight, but I
have responded to this one too.
See comments below.
> -----Original Message-----
> From: Abdon [mailto:abdon@sillypages.com]
> Sent: Monday, January 06, 2003
> To: SLRMAN@topica.com
> Subject: RE: [SLRMan] Super-Multi-Coated vs. SMC
>
>
> Multicoating technology was a stunning _MARKETING_ success. First of all,
> benefits for multicoating are minimal for lenses of up to 6 to 8 elements,
> which are your regular fixed focus lenses.
Ultrawides often have more than 8 elements and they are fixed
focal length ( not fixed focus as you mention). The really good
14mm to 18mm lenses we have today would not be possible without
good multi-coating.
> For zooms with a
> gazillion pieces
> of glass it does have its advantages. Second, all muticoating does is to
> improve light transmission, it does nothing for flare nor
> ghosting.
Huh? The more a piece of glass transmits light, the less reflections
there are to cause flare and ghosting. Multi-Coating greatly
reduces (especially in high element count lenses) both flare
and ghosting compared to single coated lenses.
> That's a
> misconception that has been repeated soo long that now people
> think that it
> is true.
>
I think it's because it IS true. Why do you think EVERY quality
lens being made for the last 20 years or so uses MULTI-coating?
Just for marketing? I think not. It adds to the cost of MFG.
If it didnt add value, it would have been eliminated long ago.
> You don't have to take my word for it. Modern photography did an article a
> long time ago about Multicoating. They found that singlecoated lenses
> significantly improved performance on both flare and ghosting,
OVER non-coated lenses, not over multicoated lenses.
> multicoated
> lenses did very little (I think they said insignificant) over singlecoated
> lenses.
May be true on 4-6 element designs, but not on the multi-element
(10-15 element designs...zooms...ultrawides) where the effect is downright
Dramatic.
JCO
From manual SLR mailing list:
Date: Tue, 7 Jan 2003
From: James Bielecki bieleckj@freeway.net
Subject: Re: Super-Multi-Coated vs. SMC
It all depends on how you define multi-coating. If multi-coating means
applying more than one layer of coating, then Canon's Super Spectra
Coating, which has three layers and was introduced back in 1967 on
their Super 8 and TV zoom lenses, pre-dates by Asahi by four years.
Canon also used Super Spectra Coating on the FD 55mm F1.2 lens which
was introduced late in 1970. I can also tell you that Canon's
multi-coating process is/was not the same as used by Asahi. All this
is from the "British Journal of Photography's" review of the Canon F-1
published back in the early 1970's.
Jim Bielecki
...
From rangefinder mailing list:
Date: Mon, 10 Mar 2003
From: Dante Stella dante@umich.edu
Subject: Numerical Aperture vs. Actual Transmission
DFStein@aol.com wrote:
> Is there a theoretical limit for maximum aperture?
No, but the maximum T-stop (transmission) of a lens can diminish
considerably if it has a lot of elements. Given even a 3% light loss
per surface for a multicoated lens, a 10-element f/1.2 lens can be a
lot slower than that in practice, it is more like a 1.4. T-stops are
used in cinema applications, where screwing up exposure is a much
bigger issue.
The transmission dropoff was something I discovered in practice when
comparing a 50/1.5 Canon to a 50/1.2 Canon. There was about a 1/3 stop
difference in f/stops, but the light transmission difference was really
a lot smaller in practice (as in imperceptible on film or in scans).
Then I did some research on light loss and learned that the entire
difference could be swallowed by light transmission loss in a
single-coated system. I surmised that this was because the 50/1.5 had
6 air-glass surfaces, and the 50/1.2 had something like 10. This is why
you almost have to chuckle at the prices that 85/1.5 Summarexes and
Canons get; they are not nearly as fast in reality as they seem to be
on paper.
I would propose that a quick and dirty way to estimate the T-stop of a
lens is (TE= estimated T-stop):
TE = (1/(1-L)^S) * F
Where L is the transmission loss (decimal) per surface, S is the number
of air-glass surfaces in the lens (generally, twice the number of
single elements and cemented groups), and F is the numerical aperture.
This formula does not take into account mechanical vignetting, flare
from the barrel or element edges or light absorption by lens elements
themselves. T-stops really have to be measured through the lens.
According to Schneider, the light loss for each air-glass interface is
4% for uncoated glass
2% for single-coated glass
0.5% for MRC glass
Hoya (an equally reputable source, since they make Leica elements)
claims that it is
4-4.5% for uncoated glass
2-2.5% for single-coated glass
0.5-1% for HMC glass
Applying this to the two lenses above, assuming 2% per surface, you get
TE=1.69 for the 50mm f/1.5 lens and TE=1.46 for the f/1.2 lens. Not
much.
Effective speed also partially explains the success of the f/1.5 Sonnar
over the Xenon before the war. A Sonnar has a 7/3 construction (6
interfaces). Assuming 4.5% loss per interface, a "perfect" uncoated
f/1.5 Sonnar would have TE=1.97 (in other words equal to a
theoretically-perfect f/2 multicoated lens). A "perfect" uncoated
Xenon (10 interfaces) would have TE=2.38, getting close to 50% slower.
Post-war (2% per surface), the Sonnar would rate a TE of 1.69; the
Summilux 50/1.4 (7/5) would hit 1.71. The difference is that the
Summilux could have superior correction through a greater number of
elements.
It will be interesting to see just how fast the CV 35/1.2 is in
practice. Assuming that the Summilux and Nokton are true to their
numerical apertures, and taking 1% as the conservative loss, it may be
very close. The 35 Summilux ASPH has 10 air-glass surfaces (TE=1.55);
the new Nokton will have 14 (TE=1.38). As a result, the realistic
difference in light-gathering could be as little as 1/5 of a stop.
The numerical aperture of a lens can be a red herring. As the
numerical aperture gets bigger, you definitely get shallower depth of
field, but you do not necessarily get improved light-gathering ability.
Aspherics help by giving you correction without as many added
elements. It is probable that without aspherics, the Nokton would have
needed as many as three additional elements to perform corrections, and
these would have degraded its speed considerably. That's probably why
we haven't seen a 35/1.2 until now.
Cheers
Dante Stella
http://www.dantestella.com
From rangefinder mailing list:
Date: Wed, 12 Mar 2003
From: Gerry Szarek gszarek@hotmail.com
Subject: RE: Numerical Aperture vs. Actual Transmission
I also forgot some minor details, called coating fall off. The ideal
glass element to coat is FLAT. The worst element to coat is a pure
sphere (ie an old fish eye lens from the early 80's). What happens is
the coating will be perfect at the center an less than perfect at the
edges. Most coating failures will start at the edges.
The other issue is coating stress, after that beautiful lens element is
polished you coat it typically around 60 to 80C for the high stuff, some
of the easy stuff is done at room temperature. The problem comes in
that the coating is actually stressed which will bend the glass, yes in
the worst case it BREAKS the glass. So if you have a camera that works
fine at room temperature but gets fuzzy either in the cold or hot
extreme you now know why, your glass is changing focus.
BTW did you know most early lenses where coated with Mag Flouride?
Gerry
Dante Stella wrote:
> Gerry:
>
> That's an interesting point about the glass size. I hadn't even
> thought of that. I did know that large elements are much harder to
> grind than small.
From rangefinder mailing list:
Date: Wed, 12 Mar 2003
From: Winfried Buechsenschuetz w-buechsenschuetz@gmx.de
Subject: RE: Numerical Aperture vs. Actual Transmission
I am not an expert in optics manufacturing, but I think there are a few
errors in this message.
Gerry Szarek wrote:
> I also forgot some minor details, called coating fall off. The ideal
> glass element to coat is FLAT. The worst element to coat is a pure
> sphere (ie an old fish eye lens from the early 80's). What happens is
> the coating will be perfect at the center an less than perfect at the
> edges. Most coating failures will start at the edges.
Usually coating is applied via a vacuum depositing process. That's at
least what Mr Smakula did. I don't think that in this case the shape of
the surface matters too much. There are many lens elements inside lens
barrels of which the curvature has a much smaller radius than the front
lens elements of wide angle lenses.
>
> The other issue is coating stress, after that beautiful lens element is
> polished you coat it typically around 60 to 80C for the high stuff, some
>
> of the easy stuff is done at room temperature. The problem comes in
> that the coating is actually stressed which will bend the glass, yes in
> the worst case it BREAKS the glass.
I don't know how much the glass has to be heated. But I have severe
doubts that the coating which has a thickness of less than a wavelength
of visible light (required by physics for anti reflective coating) will
break a piece of glass of several mm thickness when it expands or
shrinks. There are some types of optical glass which break very easily
when heated but this will occur even if no coating will be applied.
So if you have a camera that works
> fine at room temperature but gets fuzzy either in the cold or hot
> extreme you now know why, your glass is changing focus.
I don't know the thermal expansion data of glass but in most cases these
figures are rather low. I have severe doubts whether this affect focus
in a range of some ten deg. C.
> BTW did you know most early lenses where coated with Mag Flouride?
Not only the most early, MgF is still used as a standard coating, for
example for many lens elements from Edmund Scientific. MgF was chosen
because its refraction index is somewhat lower than that of glass (which
is required for anti-reflection coating) and because it is very
transparent in the visible range.
Winfried
From rangefinder mailing list:
Date: Wed, 12 Mar 2003
From: Marc James Small msmall@infi.net
Subject: Re: [RF List] Zeiss lenses???
Jim Williams wrote:
>
>No; the prewar 50/1.5 Sonnar also went only to f/11, right, Marc?
>
>I've been told that this was because of a mechanical limitation of the
>size of aperture blades that could be fitted inside the barrel.
Jim
I believe that the f/11 limit was due to diffraction limits on uncoated
lenses. The very first coated lenses only stopped to f/11, then, later, to
f/16 and, with some of them, late production stopped to f/22.
Marc
msmall@infi.net
From rangefinder mailing list:
Date: Thu, 13 Mar 2003
From: Winfried Buechsenschuetz w-buechsenschuetz@gmx.de
Subject: RE: Zeiss lenses???
Marc James Small wrote:
> I believe that the f/11 limit was due to diffraction limits on uncoated
> lenses.
I don't think so. The laws of diffraction apply to any optical system,
whether it's coated or not, and only deal with the relationship between
absolute lens opening and wavelength of the light. Of course a lens with
f/11 and f=50mm will have a similar amount of diffraction like a lens
with f/22 and f=100mm, since in both cases the diameter of the opening
is the same. But many 50mm lenses were made prior to the f/1.5 Sonnar,
and they stopped down to f/16 or f/22.
Winfried
From rangefinder mailing list:
Date: Thu, 13 Mar 2003
From: Winfried Buechsenschuetz w-buechsenschuetz@gmx.de
Subject: RE: Numerical Aperture vs. Actual Transmission
Allan Ostling wrote:
> So, you're saying that a coating about 500 nm thick will not have the
> strength to break a lens element which is 10,000,000 nm thick. Makes
> sense to me!
Yes, I have severe doubts whether the coating itself is the reason for
cracking glass during (or after) the coating process. Coating is applied
in a thickness of 1/4 lambda, where lambda is the dominant wavelength. I
think the main reason is improper heating of the glass. There are some
types of optical glass which will expand approx. 5 my-m for each 10mm of
thickness (or diameter). If the glass is heated to fast, outer parts
will expand more than the inner (not yet heated) parts. Remember that
optical glass is much less 'heat resistant' than the glass used for
dishes.
Winfried
From: Don Stauffer stauffer@usfamily.net
Newsgroups: rec.photo.equipment.35mm
Subject: Re: Color of Lens Reflections
Date: Wed, 23 Apr 2003
Well, it is possible to widen the AR range, but not indefinitely.
For starters, there is the standard quarter wave single layer filter.
This filter is a quarter wavelength thick at the wavelength you want to
minimize reflection at. RI should be as close as possible to geometric
mean between 1 and RI of first element.
That single layer coating is QUITE selective. One can either increase
or decrease selectivity by adding layers, and with some slight variation
in thickness and RI in some layers. However, again one can only broaden
so far (though one can NARROW the notch to a very sharp degree).
Normally AR filters are tuned to maximize transmittance (minimize
reflectance) of green. Therefore, they look magenta (minus green) in
reflectance.
David Littlewood wrote:
> Don Stauffer stauffer@usfamily.net writes
> >The type of coatings (thin film interference coatings) designed to
> >prevent reflection are to some degree wavelength sensitive. In general,
> >the coatings prevent reflection at one wavelength, but actually enhance
> >reflection at complementary colors or other wavelengths.
>
> This is not true; a coating which is designed to reduce reflections at
> one wavelength will also reduce it at others, but not quite so
> effectively. It will not actually increase reflection. Note I am not
> saying that it would not be possible to give a coating which increased
> reflection - it would - but AFAIK it would do so for all wavelengths.
> >
> >Now, a useful coating tries to cover as wide a band as possible, but
> >there are limits, so AR coatings DO reflect strongly at some
> >wavelengths.
> >
> >These filters never absorb light, they can only reflect or transmit it.
>
> They are not filters.
> >
> >The exact colors seen in reflection are dependent on the exact design of
> >the AR coatings (and, to some degree the angle- AR coatings ARE angle
> >sensitive also).
>
> This is true, as the optical path length changes.
> >
> >"Gregory L. Hansen" wrote:
> >>
> >> I've seen reflections from lenses, not just camera lenses, that were red,
> >> green, blue, and purplish. What is the significance of the reflected
> >> colors? Are the coatings designed that way, or is it just incidental?
> >>
> >> I know that some lines of lenses are known to be "warm" (redder pictures)
> >> or "cool" (bluer pictures). Is that related?
> >>
> >> --
> >> "Don't try to teach a pig how to sing. You'll waste your time and annoy
> >> the pig."
> --
> David Littlewood
--
Don Stauffer in Minnesota
stauffer@usfamily.net
webpage- http://www.usfamily.net/web/stauffer
From: David Littlewood david@nospam.demon.co.uk
Newsgroups: rec.photo.equipment.35mm
Subject: Re: Color of Lens Reflections
Date: Wed, 23 Apr 2003
Gregory L. Hansen glhansen@steel.ucs.indiana.edu writes
>David Littlewood david@nospam.demon.co.uk wrote:
>> Don Stauffer stauffer@usfamily.net writes
>>>The type of coatings (thin film interference coatings) designed to
>>>prevent reflection are to some degree wavelength sensitive. In general,
>>>the coatings prevent reflection at one wavelength, but actually enhance
>>>reflection at complementary colors or other wavelengths.
>>
>>This is not true; a coating which is designed to reduce reflections at
>>one wavelength will also reduce it at others, but not quite so
>>effectively. It will not actually increase reflection. Note I am not
>>saying that it would not be possible to give a coating which increased
>>reflection - it would - but AFAIK it would do so for all wavelengths.
>
>If the coating is the thickness of lambda/2 it would increase reflections.
>But I don't think visible covers that large a spectrum. So halfway
>between, 3*lambda/8, would be a "no effect" point? So a coating designed
>to pass 600nm light would have no effect at 400nm and enhance reflection
>below 400nm which is in the ultraviolet. How about that?
>
You forgot the fact that coating the glass with a lower RI material
reduces reflections anyway, even before the interference effects. This
is because Fresnel's law, which describes the variation in reflection in
terms of the RI of the two media is very sensitive to the difference
between the RIs. Thus, applying it twice to two smaller difference gives
a smaller answer than applying it once to a bigger difference equal to
the sum of the two smaller ones.
(For the very curious, R=(n2-n1)^2/(n2+n1)^2, where R is the fraction
reflected, n1 is the RI of the incident medium, and n2 of the receiving
medium.)
If n1 is equal to the square root of n2, then reflection is
approximately halved.
The interference effect will act on top of this, but you will see that
constructive interference would have a lot of ground to make up.
As to the interference effects, note I specifically said that it would
be possible to design a coating to increase reflection; all I am saying
is that I do not believe a coating stack designed to minimise reflection
at one colour will not increase it at another.
To look at your example specifically, the visible spectrum runs from
approximately 400 nm to 700 nm. Green light is usually taken to be about
550 nm. Taking a single coating optimised for 550 nm (i.e. 137 nm),
light of 400 nm wavelength would have to travel 3lambda/4 wavelengths to
make a positive contribution, which requires a reflected optical path
through 3lambda/8 in thickness, i.e. 150 nm. That is to say, its optical
path is still not great enough to constructively interfere, though the
destructive interference will indeed be very small. As you will see, the
ratios for green (550 nm) to red (700 nm) are even closer, so it does
not work there either.
Real life coatings are often much more complex that this simple case. If
you want to study it further, I suggest you take a look at Ray, or one
of the other standard textbooks.
--
David Littlewood
From: Stacey fotocord@yahoo.com
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Camera and lens questions
Date: Thu, 07 Aug 2003
CamArtsMag wrote:
> Lens: (from around the front ring) "Carl Zeiss Jena Nr 758976 Tessar 1:4.5
> f = 16.5 cm". It's mounted in a Compur shutter; above the lens it says
> "Zeiss Ikon"; below the lens is: ".D.R.P No258646 D.R.G.M."; on the side is
> "No108019". Lens glass appears to be
> uncoated
>
> This is an older lens, 165mm which is essentially a normal lens. If it is
> uncoated I might use it for black and white but not for color unless you
> want an image w/o a great deal of saturation and sharpnesss. In black and
> white you can partially make up for this lack of contrast and sharpness by
> developiong your negs a little longer. Remember, I said partially overcome
> the effects of no coatings. Even a lens with a single coating would be a
> great improvement.
I wouldn't expect to see a "great" improvement on a lens this simple unless
you're shooting back lite subjects or not shading the lens. I have shot
with coated and uncoated tessars and if I'm careful using them, can't see
any difference in contrast. Coatings would make no difference at all in
sharpness.
--
Stacey
From nikon mailing list:
Date: Sat, 28 Feb 2004
From: "John Owlett" owl@postmaster.co.uk
Subject: Re: Nikon 35mm f1.4 lens and Nikkor 35mm f2 O-C
I'm a bit of an anorak when it comes to lens coatings (I guess that's
a warning of obsessional detail to come). Before I finally bought a
Nikon I used a 1936 Rolleiflex, whose uncoated Tessar lens gives me
beautiful slides but tends to flare if used against the light.
After studying what I could find about Nikon coatings, I came to
much the same conclusion as Rick Housh when he wrote on Saturday
21 February 2004:
> There is a lot of confusion on this "C", and you can read almost
> anything you can imagine on Nikon's coating practices, "C" and
> "NIC".
>
> snip
>
> In short, I'm not sure there was ever a single bright line
> distinguishing NIC multicoating from previous multicoatings.
Doug Coartney, in his post of Friday 27 February 2004, at 20:28 Zulu,
has advanced my knowledge by tracking down a quote from a Nikon
brochure of 1973-74:
> "'C' marking after the code letter on lens front rim represents NIC
> (Nikon Integrated Coating)."
Nikon Marketing was using the NIC label earlier than I'd previously
seen documented.
The story of lens coatings goes back a surprisingly long way -- to
about 1900 and Dennis Taylor's laboratory -- but nothing seems to
have reached production until 1945. So the earliest Nikon lenses --
the ones made in the 1930s for the early Canon cameras -- were not
coated.
The idea of quarter-wave coating is straightforward. If you have a
coating on a lens that is exactly one quarter of a wavelength think,
then the light reflected from it will be one half of a wavelength
out of phase with the light reflected from the surface ... and will
therefore cancel out.
Of course, a single coating will cancel out only one wavelength, so
you have to choose the most useful. Early coatings were designed in
the days of highly blue-sensitive black-and-white films, so they
cancelled out blue, giving the coatings a yellow hue. As colour and
panchromatic black-and-white films came in, the maximum cancelling
was moved to green, and coatings gained a magenta hue.
In Germany in the 1930s, Zeiss had made progress in depositing a
precision quarter-wave layer, and its post-war lenses carried a red
"T" proclaiming this. In response to this, Nikon's lenses for its
own rangefinder cameras, all of which were single coated, carried a
"C".
By 1959, single coating was nothing special, so the single coating
"C" was never used on SLR lenses, and was dropped on the last of the
rangefinder lenses.
I have seen reports, quite credible reports, but never anything
definitive, that the most successful of the multicoating teams in
the 1960s was at Asahi Optical. Certainly the Super Multi-Coated
Takumar lenses for the Pentax cameras of the early 1970s were very
good at controlling veiling flare. The reports say that Zeiss,
Rollei and Nikon leased the SMC technology from Asahi, and used
it as the basis of their own developments: T*, HFT and NIC.
While multicoating was new, Nikon introduced the "C" suffix to SLR
lenses for the first time, to indicate that some sort of multicoating
had been used. As with the single coating "C", this was dropped
when multicoating ceased being remarkable.
As Rick says, Nikon's multicoating has changed gradually over the
years. I suspect that the new name of Super Integrated Coating
(SIC) is more a piece of marketing, drawing attention to 25 years
of enhancements, than another step change in quality.
The last of the non-SIC lenses was the AF Zoom-Nikkor 35-80mm
f/4.5-5.6D which dropped from the lens brochure in year 2000.
In his post, Rick says
> Today we have, what? Super Nikon Integrated Coating (SNIC)?
Surely he must know that SNIC is reserved for the gentle sound of
a Compur shutter opening and closing as smoothly as it did in the
1930s? :-)
Which brings me back to my Rolleiflex.
Later,
Dr Owl
----------------------------
John Owlett, Southampton, UK
From: mpate@oscintl.com (Michael Pate)
Newsgroups: sci.optics
Subject: Re: Coating Design
Date: 14 Apr 2004
sandivp@hotmail.com (sankar) wrote
> sandivp@hotmail.com (sankar) wrote
> > Dear Optical Coating Design Experts,
> >
> > For optical coating designs (for example edge filter designs), how
> > to do Tolerance Analysis using statistical techniques like ANOVA, DOE,
> > etc. so as to make the design robust.
> >
> > Any useful leads will be highly appreciated.
>
> In other words, how an Optical Coating design can be made robust?
Sankar:
You can tolerance your coating designs using many of the coating
design and analysis programs such as:
Essential Macleod from Thin Film Center http://www.thinfilmcenter.com
Some of the books on the subject are:
Thin Film Optical Filters, Angus Macleod ISBN 0750306882
Optical Thin Films; User Handbook: User Handbook, James Rancourt, ISBN
0819422851
I believe both of these authors teach courses in the area of thin
films, design, and tolerancing through their own companies and with
SPIE conferences.
In order to use the analysis of variables and design of experiments,
it is my opinion, that in addition to the coating design sensitivity
from the programs you would need to know quite a bit about the coating
chamber. You would have to characterize the chamber under the various
deposition conditions and processes for each material in the coating
design. Finally you would probably want to know how each of the
materials and their properites vary under the environmental conditions
in which the coating is used within.
Michael
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