Is it possible to change the viewfinder magnification on a SLR camera?

gone · Apr 20, 2022

I just bought a Canon camera w/ a cracked viewfinder, and found an inexpensive ($8) replacement for it on eBay. I also have a ME Super, and it's impossible to see the whole frame on it w/ my glasses on. It's even almost impossible w/ them off because the viewfinder's magnification is so great. Would changing the viewfinder have any effect on that, or is the magnification factor built in to the pentaprism? A little eye relief would sure help.

AgX · Apr 20, 2022

Canon offered (maybe still offer) an attachment lens for relief fitting their eyepieces with rails. I have not got the order number at hand.

gone · Apr 20, 2022

Good idea, but that probably extends the viewfinder out from the camera. It would dig into my back on the bike. I might just mask the viewfinder because it's very disconcerting to look in the finder as it is because of the way my eye has to wander around looking for the edges. If I can't see it, it ain't there

Ok, it will still be there (stuff at the edges of the frame). Maybe I'll crop it off in the enlarger. There will still be plenty of negative left for 11x14 papers, but it's really slowing down my ability to frame shots in the camera right now.

Alan Edward Klein · Apr 20, 2022

There are cameras made for eyeglass wearers that allow you to see the full frame while wearing glasses something most 35mm cameras don't do. It might be worth looking into.

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Marcelo Paniagua · Apr 20, 2022

Never heard about changing the magnification on SLR. Probably can be done but, based on what I've read over the years, the prism plays a part on the viewfinder magnification and coverage so it would be harder to modify. It doable on rangefinders since there is no prism in there.

Please correct me if I'm wrong. Just had my coffee and probably had not time to do its magic.

Ian C · Apr 20, 2022

SLR viewfinder magnification is determined by the built-in loupe between the rear surface of the pentaprism and the final eyepiece. The eyepiece is usually a single piece of flat glass, unless it is a corrective diopter to suit the user’s vision. So far as I know, the loupe assembly is not changeable. The loupe assembly is needed because the distance from the focusing screen to the eye is too close to see clearly.

Some SLR loupes are a cemented doublet. In the following diagram, it is an assembly (marked group 1) of 3 air-spaced elements. The final flat eyepiece at the rear has no optical effect on the view. It serves mainly as a protective cover and allows being interchanged with a diopter lens if needed. The loupe serves the same purpose as the flip-up magnifier in a reflex-viewing hood.

https://www.ephotozine.com/article/this-cutaway-diagram-shows-the-inside-of-a-dslr-30546

AgX · Apr 20, 2022

More modern cameras got eyepiece of adjustable diopter. These may be more complex.

reddesert · Apr 20, 2022

The quantity you're looking for is - distance behind the eyepiece that makes it easier to use with glasses - is called "eye relief" or high eyepoint. It's only tangentially related to magnification or field of view, in the sense that you need a larger finder to get more of any of them, so the available combination tends to be limited. For example, the Nikon F3 has a regular finder with 0.8x magnification, or the HP (high eyepoint) finder with 0.75x magnification, or the action finder that has a lot of eye relief but is enormous.

I don't think adjusting the diopter will give you more eye relief, or if it does you won't be able to see the edges of the frame.

Compact SLR cameras like the ME Super usually sacrificed viewfinder coverage and often eyepoint to keep the prism size and weight down.

Les Sarile · Apr 20, 2022

Manual focus Pentax SLRs generally tend to have higher magnifications - less eyerelief, then other brands. It's too bad your Canon has a cracked prism as they tend to have more eye-relief and could give you a good idea of which ones would better suit you.

gone · Apr 20, 2022

I thought that viewfinder magnification did indicate how much of the frame you saw. My N8008s has .75 magnification and I see the whole frame w/ glasses on. My Leicaflex had .9, I couldn't see the whole frame even w/ my glasses OFF. The Canon FT QL has .85, I can see the whole frame w/ my glasses off, not w/ them on.

gone · Apr 20, 2022

Alan Edward Klein said:
There are cameras made for eyeglass wearers that allow you to see the full frame while wearing glasses

That's true Alan, thanks. I own one, the n8008s, and it's perfect for us glasses wearers. But I need to address the Pentax and Canon cameras that I have

Les Sarile · Apr 20, 2022

momus said:
I thought that viewfinder magnification did indicate how much of the frame you saw. My N8008s has .75 magnification and I see the whole frame w/ glasses on. My Leicaflex had .9, I couldn't see the whole frame even w/ my glasses OFF. The Canon FT QL has .85, I can see the whole frame w/ my glasses off, not w/ them on.

Viewfinder magnfication is how close to real life it is. Most apparent when you have both eyes open with one eye looking through the viewfinder you can see the difference.

Viewfinders have the characteristics of magnification and coverage. For instance the ME Super has a magnification of 0.95X and shows 90% of the picture area - the other 10% is cropped from view but will show in the film. Back when this was desirable for people who shot slide as the mount would tend to cover that area.

As pointed out earlier, more magnification means less eye relief - distance of eye to viewfinder eyepiece. Less magnification is easier for people with glasses to see the full window.

reddesert · Apr 20, 2022

There are three things here:

1. Viewfinder coverage: how much of the 24x36mm frame is actually shown on the focusing screen.

2. Viewfinder magnification: (de)magnification by the eyepiece loupe relative to life-size, where life-size means looking with the non-camera eye. In the case of an SLR I think this is standardized as "life-size when a 50mm lens is mounted," since obviously the total magnification depends on what lens you're looking through. You can compare image sizes by putting on a 50mm lens, looking through the finder with one eye, and directly at the subject with the other eye.

3. How much of the image you can actually see with your eye up to the finder. Ideally, you should see all of the focusing screen and any info displays around it. If you wear glasses and the finder does not have a lot of eye relief, then you may not see all of the screen.

For the same size of glass, if the eyepiece has smaller magnification, then it makes the image smaller, so it's easier to see more of it. But if the manufacturer specs a larger prism and eyepiece, then they can get a larger field of view for the same magnification. So there's no absolute rule like "camera A has lower magnification than B so it has more eye relief." "Pro" top of the line cameras tended to have larger prisms and closer to 100% viewfinder coverage.

Alan Edward Klein · Apr 21, 2022

Les Sarile said:
Viewfinder magnfication is how close to real life it is. Most apparent when you have both eyes open with one eye looking through the viewfinder you can see the difference.

Viewfinders have the characteristics of magnification and coverage. For instance the ME Super has a magnification of 0.95X and shows 90% of the picture area - the other 10% is cropped from view but will show in the film. Back when this was desirable for people who shot slide as the mount would tend to cover that area.

As pointed out earlier, more magnification means less eye relief - distance of eye to viewfinder eyepiece. Less magnification is easier for people with glasses to see the full window.

Les, My Nikon N6006 35mm SLR has an eyepoint of 18mm. Also, it has 0.75X magnification with 50mm lens at infinity; 92% frame coverage. How does that fair for eyeglass wearers? Is there a minimum that the viewfinder should have for wearers to see the whole image in the finder?

Alan Edward Klein · Apr 21, 2022

momus said:
That's true Alan, thanks. I own one, the n8008s, and it's perfect for us glasses wearers. But I need to address the Pentax and Canon cameras that I have

The N8008 spec says the eyepoint is approx 19mm.

Alan Edward Klein · Apr 21, 2022

As an aside, eyepoint is important when you buy binoculars as well, especially for eyeglass wearers because if the eyepoint is too low, you can;t see the whole view when wearing glasses.

Les Sarile · Apr 21, 2022

Alan Edward Klein said:
Les, My Nikon N6006 35mm SLR has an eyepoint of 18mm. Also, it has 0.75X magnification with 50mm lens at infinity; 92% frame coverage. How does that fair for eyeglass wearers? Is there a minimum that the viewfinder should have for wearers to see the whole image in the finder?

Still don't need glasses so I can't really say other then to try them on for yourself. Besides, AF cameras have all gone away from high magnification since most users will depend on AF mechanism.

In my collection, Pentax started with high magnification - with the origonal Asahi Pentax, and generally continued that till AF. They did some in the high 0.8X. Canon and Nikon generally provided more eye-relief with their offerings. This allowed for viewfinder magnifiers.

Sirius Glass · Apr 21, 2022

momus said:
That's true Alan, thanks. I own one, the n8008s, and it's perfect for us glasses wearers. But I need to address the Pentax and Canon cameras that I have

OR you could switch to contact lenses and the problem will go away.

Is it possible to change the viewfinder magnification on a SLR camera?

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