How do viewfinder diopters work?

darinwc · May 26, 2009

I've never worn glasses before, but I know I've been getting a bit nearsighted. I can see things fine up to about 15 feet or so. Distant objects are a bit fuzzy. Not too bad but not sharp.

The last 4 rolls of film I had developed were 90% out of focus. =[ I'm using a manually-focused SLR. I checked the registration of the focus screen to the film plane and that looks good.

So the only 2 possibilities are camera shake or bad focussing (user error).

chriscrawfordphoto · May 26, 2009

Go to the eye doctor, get your eyes examined. If you need glasses, get them, and ask the doctor what your prescription is. It'll be a diopter number. Buy that number for your camera. When you shoot, don't wear glasses to look through the camera. The diopter you put on it will correct your vision.

tessar · May 26, 2009

For nearsightedness, only negative diopter corrections (-1, -2 etc.) will work. I'm not sure they make these -- I've only seen positive diopters for attaching to viewfinders. These are for old-age sight (presbyopia), when nearby objects become more and more difficult to focus. I've been nearsighted for a long time and I used to wear glasses, which sometimes made it difficult to see the whole viewfinder image. Then I got contact lenses. These work very well for nearsightedness. You see clearly with the naked eye, and they also correct peripheral vision, which glasses won't do.

mrred · May 26, 2009

Do your shots of less that 15 feet suffer as well? What did you use to scan the image? Was it a negative scan?

Shooting %90 out of focus gives a hint of something else. I would look at the scanner.

I am far sighted and at 47, I too needed to put some "glass" on my nose. I was scanning with a flatbed and blamed a lot on me being blind. I was surprised when my new glasses didn't help here. I took a roll to the drug store and got them to develop and print it. The photo's were sharp. My scans did not match. It turned out to be crappy stock film holders on my Epson V350; they held the film out of focus. I ditched it and got an Epson 4490, but had the same problem. I could get adjustable replacement holders for Medium format but not small. I then got a Plustek for my 35mm work. It was amazing how much a difference it made.

Take your negs to someone that you know where it's known to have good scans. If you get the same result, then it's you. Otherwise you now know what to look for.

Q.G. · May 26, 2009

Remember that through the viewfinder, you do not see near or far objects. Everything is at the same distance: the (virtual) viewing distance from eyepiece to focussing screen.

This means that the correction you may need for your camera is not necessarily the same as your glasses's prescription.
This viewing distance typically is in the 10 - 15 ft range. Chosen to be that because it is the distance we are most comfortable viewing 'with intent'.
So find out what correction your eyes need for about that distance.

You say, Darin, that you can see things fine up to that distance. So maybe it's indeed not your eyesight.

ic-racer · May 26, 2009

I think that most will agree that wide angle lenses can be difficult to focus on SLRs. They don't 'snap' into focus, the screen is dark, the fresnel is not optimized for the focal length and any focusing aids in the middle probably don't work. So you need all the help you can get.

In that picture you presented, you will probably agree that zone focusing it at 'infinity' would have been better than what you got. One thing you can do to check you vision is check the viewfinder without a lens. But even then, you may not know how sharp it can really be without some comparison. I recommend a trip to the optician. I have found for nearsightedness the correction you need for your viewfinder will be the same as your glasses (or just wear your [new] glasses when focusing).

wiltw · May 26, 2009

Q.G. said:
Remember that through the viewfinder, you do not see near or far objects. Everything is at the same distance: the (virtual) viewing distance from eyepiece to focussing screen.

This means that the correction you may need for your camera is not necessarily the same as your glasses's prescription.
This viewing distance typically is in the 10 - 15 ft range. Chosen to be that because it is the distance we are most comfortable viewing 'with intent'.
So find out what correction your eyes need for about that distance.

You say, Darin, that you can see things fine up to that distance. So maybe it's indeed not your eyesight.

The viewfinder distance is typically 1 meter, while some use 30"...the virtual distance within the viewfinder is not uniform, from brand to brand!!

Q.G. · May 26, 2009

The viewing distance typically varies a lot.

nickandre · May 26, 2009

They're like little tiny glasses that screw in to the viewfinder. Many cameras have adjustable diopters these days, like my N80 and D50. Convenient. It is a pain to focus with glasses on, so I would personally get the diopter.

darinwc · May 26, 2009

For the record I was shooting with a Canon F1 and a 24mm f2.0 lens.

Since the images I have were all taken in near-sunset at ISO 160, it is likely to be caused by camera shake. But i would expect more of a linear blur and a wider variation than what I received.

Bob-D659 · May 26, 2009

Well you will need a diopter lens on the camera if you can't focus on an object 30-40 inches in front of your nose. Slr viewfinders are preset for this distance already. Removable diopter lenses are/were usually available in a range from -4 to +4. If you can't buy the one you need, most opticians can cut a premade lens to the right size if you have the mount to fit your camera. If you have severe astigmatism, having a custom made lens is almost your only option.

Sirius Glass · May 26, 2009

They work well. I tried them.

I usually wear contact lenses so I do not need the correction. I also do not have a problem when I am wearing glasses so again I do not bother.

If I wore glasses all the time, I would probably use them.

Steve

wiltw · May 26, 2009

Q.G. said:
The viewing distance typically varies a lot.

No it doesn't. It is the virtual distance to the surface of the focusing screen, and the same virtual distance to in-viewfinder displays. That is why it works to remove the lens, then look into the viewfinder to adjust a viewfinder with variable diopter correction built in.

Q.G. · May 27, 2009

wiltw said:
No it doesn't. It is the virtual distance to the surface of the focusing screen, and the same virtual distance to in-viewfinder displays. That is why it works to remove the lens, then look into the viewfinder to adjust a viewfinder with variable diopter correction built in.

You haven't read what went before.

L Gebhardt · May 27, 2009

If the in viewfinder objects are sharp then you do not need to adjust the viewfinder. Look at the exposure needle or other visible camera part. At least that's how I adjust the diopter for my SLRs with visible diopters. Your example looks like camera shake to me, as there isn't any area really in sharp focus.

wiltw · May 27, 2009

Q.G. said:
You haven't read what went before.

You started with the statement that virtual viewing distance is 'to the focusing screen', but then you continue on to say '10-15 ft range'.

The apparent distance to the screen is fixed at 30" or 1 meter, depending upon brand.

Q.G. · May 27, 2009

wiltw said:
You started with the statement that virtual viewing distance is 'to the focusing screen', but then you continue on to say '10-15 ft range'.

So what's wrong with that?

wiltw said:
The apparent distance to the screen is fixed at 30" or 1 meter, depending upon brand.

So there you are: "depending upon", i.e. "The viewing distance typically varies a lot".

How do viewfinder diopters work?

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