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Discussion:

The above table of viewfinder magnifications highlights several points. First, 35mm SLR viewfinders make the viewed scene appear smaller than it is (magnifications below 1.00). Second, older viewfinders generally had larger magnification factors. By contrast, many medium format viewfinders such as prisms and chimney magnifiers have factors closer to 3X or even 5X!

Some early SLRs had magnifications of exactly 1.00 by careful design. You could look through the viewfinder with one eye and see the rest of the scene with the other eye (if more dimly). This trick allowed you to see the scene "normally", in stereo vision, with the SLR framing superimposed on the scene, at least with a bit of practice. You could also anticipate items entering the image from the sides or top of the scene. By contrast, I lost a few Christmas parade shots this week because people walked into the shot from the side just as I was pressing the shutter. My "one-eyed" view and viewfinder area limited to the image on film didn't provide any warning. By comparison with most SLRs, rangefinders usually have and display an area around the edges of the frame, if only as part of the parallax correction effort. So you can see or anticipate people or objects moving into or out of the shot with these old tricks. How many shots have you lost with your new SLR because somebody walked into the edges of the shot without warning?

Today's high eye relief viewfinders, started with the Nikon F3HP finder series in 1982, are handy if you must use glasses with your camera. The problem is that the chosen way to achieve such high eye relief is to reduce finder magnification factors. After all, if you are looking into the finder from farther away behind the eyepiece, you need less magnification if you are to avoid vignetting the image.

Do you really need to use a high eyepoint relief viewfinder? Can you correct your astigmatism problem with a custom ground lens from your optometrist? Or can you simply order a modest cost diopter correction (usual ranges -5 to +5 diopters in some lines)? Glasses also may make it harder to exclude extraneous light, such as a low cost rubber eyepiece eyecup could provide with greater contrast for a very modest cost. Side reflections and glare can also be a new problem.

Strangely, 35mm SLR viewfinders have gotten worse rather than better in some areas. Partly, the smaller magnification factors of newer cameras are the result of an attempt to reduce the size of the pentaprisms required on the cameras, lowering cost and weight of the cameras. The older cameras had heavier pentaprisms, but they provided higher magnification ratios too.

Some of the newer economy cameras use penta-mirror designs rather than a solid glass pentaprism. The cost of a pentamirror system is a good bit less, and more importantly the rather heavy solid glass prism is replaced by thin front surface mirrors and air spaces. The problem is that you lose circa 2% up of the light at each of the reflecting mirror surfaces. The total losses of a pentamirror design make the resulting prism view somewhat darker than an equivalent but heavier and more costly pentaprism design. How much heavier? Would you believe up to ten times heavier, per tests by David Phung (Ibid., p.90)!

Older cameras had very high contrast ground glass screens, rather than the low contrast but high brightness screens found on most of today's autofocus cameras. This change makes the newer cameras seem a lot brighter, but they are also harder to focus accurately than the older high contrast screens.

A partial solution to the older darker ground glass screens is to install one of the newer brighter laser etched screens. An optimized grid pattern of scoring of the screen provides higher and brighter amounts of light to reach the eye. In some cases, simply replacing the screen in your 35mm SLR can raise the screen brightness by the equivalent of a full stop or more. That is a lot cheaper (circa $100 US) than buying one stop faster lenses for a brighter focusing image!

Image Edge Cutoff in Finders

Before leaving this topic, we might note that the actual size of what you see in the finder has also shrunk on many modern cameras. In the past, many finders with their larger prisms were designed to give you a view of most of the film image - up to nearly 100% in some pro models (e.g., circa 97-98% with Nikon F..). But in many modern 35mm SLRs, you will not only see a smaller magnification factor image (see table above), but much of the edges of the image on film will NOT be shown on the camera. For example, many cameras opt to show only 22mm x 32mm of the full 24.2mm x 36.2mm film area. That design tradeoff yields a view of only 82% of the image that will actually be on the film in the viewfinder. Again, this trick helps reduce the size, cost, and weight of the pentaprism needed to provide the image.

Some folks will argue that this trimming process is useful since those edges will not show up in the slides shown on screen. The slide mounts will cover up some part of the edge of the slide, after all. So reducing what you see in the viewfinder to what you will see on the slide is a way to avoid cutoff in your slide shows. Sounds reasonable, but how many folks shoot slides anymore? After all, only 4% of consumer film sales are for non-color print emulsions, including both slides and black and white). For darkroom work, not being able to see in the viewfinder what will be in the edges of your film is less understandable.

Many of us want to use as much of the limited area of 35mm film as we can by cropping closely in the camera. If your viewfinder doesn't show the full film frame as it will appear on the film, then you can't crop as tightly. That is why pro photographers may opt for the more expensive pro models (Nikon F.., Canon F1..) which show closer to 100% of the on-film image in the viewscreen. Paradoxically, this full frame feature is more critical when shooting slides. You can't just crop in the darkroom when making a print. Unmounted slide film is required by many buyers who want to examine the full image with a loupe, particularly in the larger film formats (6x6cm, 6x7cm..).

So not being able to see what is in those edges when composing your shot in the viewfinder is a potential problem. You may find all sorts of intrusions such as wires or branches which intrude into the edge of your slide, ruining the shot. What if you elect to use your slide duplicator to "fix" and copy the slide? You introduce losses in quality (a second generation copy) and light and film color shifts too.

This problem is one good reason for having two cameras with you, besides the obvious benefits of camera backups. The pro camera with its nearly 100% film image could be used with slide film for critical shots. A backup lightweight prosumer or consumer 35mm SLR camera could be used with either slide film or print film (including black and white), depending on your shooting needs and goals. You can also opt to have more slide film loaded and ready (and avoid running out at a critical moment), along with two or more zoom or fixed lenses. With many of these backup cameras costing less than a fifth the price of the top of the line models, this flexibility costs very little.

Viewfinder Cutoff Test

How can you test to see what you are missing in your viewfinder? The simplest way is to take a ruler with a millimeter scale and a closeup or macro lens. Now simply carefully align a few end-of-roll sample shots of the ruler, both horizontally and vertically, noting the limits you see in the viewfinder. Get the film developed, and look at the film - not the prints. Now see how much if the ruler is shown on the film, in millimeters, versus what you aligned and saw in the viewfinder. The result can be pretty surprising. The worst cases may cut off as much as 1/4 of the film area in the viewfinder, although these models are mostly from the former U.S.S.R. production designs.

A related test you can now do is to see how conservative your lab printers really are. Most lab printers decide to "compensate" for the cutoff in the viewfinders, and prevent surprises like wires and branches around the periphery of most photos. So they setup their printers to only print the center 80% to 90% or so of the image area. The really bad minilab printers in our area even slightly defocus your sharp lens images. They do this so as to hide the scratches and hairs and other gunk that would otherwise show up from their sloppy setups. So shop around!

If you really want your entire print, you will probably have to either do it yourself, or pay pro processing rates to get full frame printing.

How does this relate to vision issues in photography? Maybe it isn't you, maybe it is your minilab printers. If your images are out of focus on the prints, pull out a loupe and check the film. The film could easily be sharp, and your lab minions just messed up the printing and threw it out of focus to cover their own errors. Time to change labs!

Date: Sat, 02 Dec 2000
From: Jeff Cook jeff@cookstudios.com
Newsgroups: rec.photo.equipment.35mm
Subject: Re: 90% Viewfinder - What to do?

"Q.G. de Bakker" wrote:

> Why? Because all that matters is that what you need to be on film is indeed
> on film. Any extra is just that, an extra. And what you see in a less than
> 100% viewfinder is indeed ending up on film, isn't it?

If you have a reason to compose for a full frame, then this extra distance does have impact on the choices you would have had for perspective. If your viewfinder is even 90%, you would end up moving back farther for the framing. Moving back farther changes the wide angle appearance the subject; therefore, you are losing a portion of what you might have had the option to use.

And then of course, there's the increased grain when you make the same print you would if you had moved closer to fill the true frame. How much difference in grain? I dunno. How much more trouble do you go through to buy & use low grain films?

Any viewfinder that's not 100%...sucks. And yes, all my cameras suck.

--
Jeff Cook
jeff@cookstudios.com
http://www.cookstudios.com
Washington DC area

Date: Thu, 18 Jul 2002 From: Eric Rudd rudd@cyberoptics.com Newsgroups: sci.optics Subject: Re: Magnification in SLR viewfinder? AES wrote: > I'm trying to understand a statement concerning a certain SLR camera that > says if it's used with a 70 mm lens the magnification in the viewfinder > will therefore be unity > > Question: Is this some standard way in which SLRs are designed? Or is > it just a property of the viewfinder optics in this particular camera? The magnification one gets in the viewfinder of an SLR camera is the focal length (FL) of the taking lens divided by the focal length of the viewfinder eyepiece. For a 35-mm camera, the viewfinder eyepiece FL is typically a bit shorter than 70mm -- 50 to 60 mm is more common. I don't know if there's any standard for this, but there are constraints: the light from the viewfinder screen must travel through a penta roof prism, in order to be bent back horizontally and produce an image that is erect and correct left to right. (The shape of the prism is responsible for the oddly-shaped bulge on the top of SLR cameras.) The dimensions of this prism must be large enough to accept light from the entire 36x24 mm screen, so there are lower limits to its size, and therefore also the optical path length. A simple doublet is usually used for the eyepiece, which must be placed away from the screen by approximately its focal length, so this places a lower limit on the focal length of the viewfinder eyepiece. The upper limit on the focal length of the viewfinder eyepiece is imposed by the desire not to have too small an image to look at, and the desire to minimize the weight, bulk, and expense of the prism and camera. There are also medium-format SLR cameras, where all these dimensions must be scaled up correspondingly, and there are special viewfinder attachments that act like telescopes, to magnify the view of the central region of the focusing screen. -Eric Rudd rudd@cyberoptics.com

From camera makers mailing list: Date: Tue, 20 May 2003 From: Samuel Tang samueltang@austarmetro.com.au To: cameramakers@rosebud.opusis.com Subject: Re: [Cameramakers] Source for accessory shoe/cold shoe? Hi John, John Stafford wrote: > Jonathan King at jking_nh@charter.net wrote: > > > The subject says it all. > > > > I'm building a 6x12 pinhole/zoneplate camera and am looking for a metal > > accessory shoe/ cold shoe that I could put on the camera for a finder or > > level. Other that stripping an old camera that has one just attached, > > and not built into the body, is there a source for these things? > > If you can build an optical finder for a 6x12, then sign me up. But a frame > finder will almost certainly suffice. Frame finders aren't crude. They can > be quite accurate. Levels? You can buy flatbottomed levels from many > sources. That obviates the need for a shoe. Cement it to the camera body or > countersink it into the body. One of the cardboard "Film-In" cameras Konica used to produce had a 17mm panoramic lens, and its viewfinder is suitable for 6X18 with a 90mm lens. I think you can strip the finder assembly and use that with suitable modifications. I used to get shoes and other parts from the service department of a camera manufacturer, perhaps a camera repairer with lots of parts cameras would be able to sell you one for a very modest sum. Best, Sam.