Choosing the correct diopter for MP

[joseph_barbano]

I could use diopters for my MPs even though I already wear glasses. I need a

recommendation for how to choose the correct diopter without having access to

the diopter in advance since they are only available via mail order where I

live. Any suggestions? Thanks in advance.

[joseph_barbano]

BTW, I don't intend to use the diopter instead of my glasses (graduated bifocals). I just could use a slightly more crisp image when I focus.

[raymond_tai]

Do you have a camera with built-in diopter adjustment? If not then you can always borrow one. Most modern SLR's have this feature. You should get hold of such camera with preferably a standard lens attached, focus and adjust the diopters until crystal clear. You can then transfer the reading to the M. The M bodies has -1 diopter built-in so if you managed to borrow an R8 for example and based on the above requires an -2 adjustment then you should get a -1 diopter for your M.

[Rob F.]

Joseph, if your eyeglass prescription is current, you shouldn't need a diopter in addition to your glasses. Something about your wording makes me wonder if you are looking through the variable closeup part of your glasses when using the camera. You should look through the distance prescription, above the closeup part. Are you? If not, I think you should experiment with that idea before ordering a diopter. You should only need the diopter if you want to use the viewfinder without your eyeglasses.

[raymond_tai]

There are many situations where near sightness cannot be completely compensated with eye glasses, for example if you have severe astigmatism. For walking around and watching TV 100% correction is not necessary but for critical focusing dioptic correction is necessary so that is why these things are standard features in many cameras. Else why have them right?

[george_b1]

Joseph -

 

Go to: http://nemeng.com/leica/038b.shtml

 

George (The Old Fud)

[ron_h__portland_]

I'm an optometrist, so this should be within my bailiwick. Rob is correct. Your correction for

distant objects (the top part of any "bifocal" prescription) should suffice. Raymond,

astigmatism correction (even for "severe astigmatism") should be part of any pair of glasses.

 

Secondary dioptric correction lenses in camera viewfinders are used for people who DO NOT

want to wear their corrective spectacles or contact lenses while shooting.

 

Ron

[ron_h__portland_]

Also, Andrew Nemeng's description on how to choose a diopter correction lens is very good.

[raymond_tai]

Thanks Ron. That was the explanation I got from my optometrist. I should ask him again! I knew I would learn something valuable here eventually!

[alan_wilder1]

As an optometrist in my early 50's, I find even the distance correction of my glasses don't always give me the sharpest vision with my MP simply because the M viewfinder has a power of -0.6 diopters. This makes near focus espcially with goggled lenses like the 135/2.8 slightly unsharp at near. By using the +0.5 diopter lens on the camera's eyepiece, I find it helps especially when my eyes are fatigued.

[vinay_patel]

Alan and Ron highlight the frightening experience patients go through getting conflicting "facts" from two or more different healthcare providers. And like many cases, in this one Ron both are partly correct.

 

Unlike an SLR where the focusing is done on a flat plane that is fixed at a vitual distance regardless of the subject distance, the direct-view finder in the M is just that, similar to direct viewing. Therefore, it is subject to the same variability as looking directly at the world. Someone with nearsightedness who sees only blur through the M looking at far-off subjects, can take the camera and look through it without glasses at a very close subject (perhaps closer than the camera can focus if he's very nearsighted)and it will be sharp. The reverse is true for farsighted people. The unfortunate person is the one who requires correction for both near and far, i.e. the person who wears bi-, tri- or progressive-focal glasses. That person will find viewing compromised somewhere along the way regardless of what diopter he uses, or whether he uses one with or without glasses. The best advice I can give is to ask your opthalmologist what "add" correction he would prescribe for best sight at 1 to 3 metres (focusing is more critical at closer distances than far ones), add 0.5 (or subtract -0.5)to it (the amount of correction built into the finder itself), and that's the diopter you would use with the distance (upper)part of your glasses. I have an uncle who wears progressive focals and has learned to look through a different part of them (he's into Nikon rangefinders) depending on subject distance. That would work too I guess.

[alan_wilder1]

I have to disagree with Vinay on using an "add" power for 1 to 3 meters and on top of that add +0.5 diopters to compensate for the viewfinder. Anyone using a telephoto or fast 50 will still have to see sharply to critically focus beyond 3 meters (except of course for infinity). An "add" power for 1 to 3 meters translates to +1 to +0.33 diopters. The built in viewfinder power of -0.6 diopters nicely compensates for this low add power but an additional +0.5 diopters will cause a distinct distance blur through the finder. Try this if near focus is a problem but don't compensate for the viewfinder.

[vinay_patel]

If you need a "+1 ADD" to see clearly at 1 to 3 m in "real life", and the Leica finder already is at -0.5, you would need a +1.5 eyepiece correction lens. I agree with Alan that would cause a degradation of sharpness beyond 3m. As I said, unlike an SLR where one correction suffices regardless of subject distance, there will always be a compromise with the M finder. Perhaps, and I think this is what Alan is getting at, it might be better to choose a lower diopter strength (in the above example, perhaps a +1 or even a +0.5) which would optimize the finder for longer distances. I was basing my premise on the fact that critical focus is more demanded the closer the subject, and also perhaps a prejudice that many people consider the M more for close-range photography. A compromise is just that, and there is no perfect answer here.

[david j.lee]

now i'm confused. i though that the good thing about using diopters on an M body was

that you didn't have to use your glasses for focusing. am i wrong...?

[vinay_patel]

You're not wrong. However some people's vision has multiple challenges, like astigmatism and nearsightedness coupled with middle-aged reduced close-focus ability, which simple single-vision spherical correction lenses can't compensate.

[Rob F.]

And therefore, those who have significant astigmatism are probably better off to use their eyeglasses or contacts, rather than an off-the shelf diopter with no astigmatic correction. I believe some people do get their in-camera corrective lenses custom ground, though.

 

Most likely, we should not overly emphasize the problems of using the Leica finder at near and far distances. I don't guess it's much of a problem for most of us. My right eye is around -1.25 cylinder, at 90 to 100 degrees; and -4.00 spherical. At 65, I'm Mr. Presbyopia Plus. Yet I've noticed no problems using the finder at varying distances, near and far.

 

I'd like to hear from our optometrist members about the extent to which uncorrected astigmatism would interfere with the use of a rengefinder. Not that I'm planning on going uncorrected for it; I just think it's an interesting question.

[msitaraman]

I think Vinay is on the right track with this. The virtual image of the rangefinder patch in a Leica M is at approximately 1 meter. The viewing system has variously been said to have -1,-0.6,-0.5 diopter power on its own.

 

To the optical experts here

 

Question 1:

If my eyeglass prescription for vision at 1 meter is +1.3 diopters, what diopter should I choose for the Leica M, assuming that the Leica M itself has an x diopter correction built in.

 

A. 1.3+x

 

B. 1.3-x

 

C. 1.3

 

 

Question 2:

If my eyeglass prescription for vision at 1 meter is -1.3 diopters, what diopter should I choose for the Leica M, assuming that the Leica M itself has an x diopter correction built in.

 

A. -1.3+x

 

B. -1.3-x

 

C. -1.3

 

I've yet to receive an unambiguous and authoritative answer to this question in this or any other forum. A clear answer would save me or Joseph the trouble of going to a Leica store that has a large selection of eyepiece diopters, and trying each of them on for visual clarity.

 

Please shed some light! TIA

[eliot_rosen1]

I can't answer Mani's question but I can say that you are best off using the camera without corrective diopter with your regular eye glasses or better yet with contact lenses. The reason is that these diopters are very simple lenses, whereas eyeglasses or contacts are much more complex formulas that offer better correction. Imagine using one of those simple diopter correction lenses instead of your eyeglass prescription and you will see what I mean.

[alan_wilder1]

My answer to Mani's question is based on the assumption that you don't want to see blur at a long distance through the finder. The corrections given for 1 meter imply that for long distance -1 diopter is needed since a 1 meter focus requires +1 diopter supplied by the eye or the glasses. Assuming it's only by the glasses and the eye is completely at rest, the answer to #1 is: +1.3 + (-1) + (+0.6) = +0.9 or approx. +1 diopter. For question #2 it's -1.3 + (-1) + (+0.6) = +1.7 or approx. +1.5 diopter correction.

[alan_wilder1]

BTW, assume the built-in correction "x" is -0.6 diopters in the above response.

[rick_campbell]

I've been having trouble seeing the viewfinder in my Nikons for a long time. I just got my first Leica, a M6 TTL, and had the same issue. My glasses are very strong so I don't think I could use a diopter without glasses. Soon after getting the M6 I thought about trying my left eye with it instead on the right one. And the difference was amazing. Perfect view of the viewfinder. So I tried the Nikons with my left eye as well and also had a perfect view. What a surprise after all these years.

 

So, Joseph, have you tried your other eye? It might make a difference.

[msitaraman]

Alan,

 

Many thanks for the direct answers to the question. Just one clarification:

 

In the second answer my eyesight correction has gone from +1.3 to -1.3 diopters. Yet the change in the Leica diopter is only 0.8 diopters. I would be grateful if you could clarify...

TIA :-)

[alan_wilder1]

Oops, my bad, wrong sign. The answer to question 2 is -1.7 diopters, not +1.7 diopters.