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Picking your diopter correction
Old 06-13-2017   #1
roscoetuff
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Picking your diopter correction

So having read here on diopter adjustments, I had the eyeball chat with my Opthamologist about need at 1 meter. I bought a correction on that basis, but failed to take into account the camera's (Leica M4-2) internal reverse adjustment. Purchased a 1 diopter adjustment and it was a complete FAIL.

Shelved that and haven't missed it much... though I could probably do with something e-v-e-n-t-u-a-l-l-y.

BUT now I've picked up an SLR accompaniment to the RF... a Contax S2 because I have a number of old Contax CY mount Zeiss glass lying around the house. Ran some film through, and my focus is waaaaay off. So I really do need something to correct my vision (besides celebration of Rangefinder Appreciation Day). SLR's are "better" for macro photos of flowers, so it'd be good to solve.

Best recommendation I can find here is to go do a trial-and-error with corrective Drugstore glasses to see what works with the cameras. With an RF, this is simple. With an SLR, it becomes more a matter of... which lens to take with me? 50mm? and how far to focus? Thoughts? Suggestions? All comments appreciated. Thanks!
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Old 06-13-2017   #2
Darthfeeble
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I can only offer this. After I got my M9 I thought that contacts would be the best thing, and at that I thought that the bi-vision system would be the neatest thing. I could have the near vision in my right eye to see the focus patch and then get these crystal clear shots that I like. Turns out that because it's a mirror, the distance vision was all that was needed. Chimping was another issue that I could deal with reading glasses. Turns out that for me, the Rx in my contacts lets me see close enough to look at the lcd as well as the the focus patch and the long view. I have a +2 correction and astigmatism. I use the throwaway contacts on days when I want to do a lot of shooting or am trying for some serious stuff. For the rest of the time I just deal with glasses. A 10 pack of contacts has lasted me nearly 6 months which is very economical.
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Old 06-13-2017   #3
Spanik
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Lens and focus distance don't come into it. The only thing that matters is that you see your viewfinderscreen sharp. So if there are any marks on your screen like focus area, ring that indicates spot measurement, or even the line of a split prism, that is what you want to see sharp. It should be sharp even without a lens on it. Trying to focus before you have that solved it useless.
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Old 06-13-2017   #4
peterm1
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Quote:
Originally Posted by Spanik View Post
Lens and focus distance don't come into it. The only thing that matters is that you see your viewfinderscreen sharp. So if there are any marks on your screen like focus area, ring that indicates spot measurement, or even the line of a split prism, that is what you want to see sharp. It should be sharp even without a lens on it. Trying to focus before you have that solved it useless.


I think that is about right. The difference with an SLR is that a rangefinder camera's viewfinder uses a specific distance for the viewfinder itself. An SLR does not have a separate viewfinder hence that issue does not arise.

Hence you can conduct your test at any distance subject to what I have written below (I think).

In the following sense I would be inclined to disagree with Spanik however - I would use a fairly fast medium tele lens. One known to be sharp. The idea of using a tele is that it is easier to see details when shot appropriately. During the process of selecting a diopter, I would shoot it stopped down one stop (at which setting it should have maximum sharpness) and at a range that is not so short that it will compromise sharpness of that lens (some but not all tele lenses are less sharp close up) and not so far away as to make it hard to see details in your test subject. What you are looking to do is to eliminate any sharpness issues with the lens by using this regime. Any apparent residual sharpness issues should then be due to the finder.

While your S2 is MF the does not apply. But in cameras that support it, I would also use AF to eliminate any focusing errors. Then when you look through the finder any lack of sharpness should be attributable to the diopter correction because you have eliminated both lens and focusing issues. That is my reasoning in any event.

I say this because when I use my (say) Olympus OM D EM 5 and want to change the inbuilt diopter adjustment on its finder (which sometimes gets knocked out of whack because it uses an adjustment wheel which can get bumped accidentally) I use pretty much the above approach. There is however nothing more clumsy than trying to find focus manually and to focus to absolute maximum sharpness when the diopter is not right. Hence my preference for AF where possible. (But it can be done of course).
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Old 06-14-2017   #5
john_s
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Quote:
Originally Posted by roscoetuff View Post
So having read here on diopter adjustments, I had the eyeball chat with my Opthamologist about need at 1 meter. I bought a correction on that basis, but failed to take into account the camera's (Leica M4-2) internal reverse adjustment. Purchased a 1 diopter adjustment and it was a complete FAIL.

Shelved that and haven't missed it much... though I could probably do with something e-v-e-n-t-u-a-l-l-y.

BUT now I've picked up an SLR accompaniment to the RF... a Contax S2 because I have a number of old Contax CY mount Zeiss glass lying around the house. Ran some film through, and my focus is waaaaay off. So I really do need something to correct my vision (besides celebration of Rangefinder Appreciation Day). SLR's are "better" for macro photos of flowers, so it'd be good to solve.

Best recommendation I can find here is to go do a trial-and-error with corrective Drugstore glasses to see what works with the cameras. With an RF, this is simple. With an SLR, it becomes more a matter of... which lens to take with me? 50mm? and how far to focus? Thoughts? Suggestions? All comments appreciated. Thanks!
The drugstore glasses are positive diopters, for close viewing. Is that what you want? I am shortsighted, so I need a negative diopter added to my cameras, so drugstore glasses are not useful.

SLRs are easier because you are just looking at a screen which is always the same distance (equivalent optical distance) from the eye. For a rangefinder that is not the case: you are looking at the subject, not a screen image. So the diopter you need depends a little on the distance of the subject (especially if you're old like me and your eyes have almost no accommodation to different distances). Best to trial and error in not very bright light at the most critical distance for you (for me it's portraits at around 2m).

And as you've probably read here already, if your prescription has significant cylindrical correction (astigmatism) it's more problematical. Small cylindrical isn't much of a problem.
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Old 06-14-2017   #6
Rob-F
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My approach was to start with the idea of a corrective lens having the power closest my eyeglass prescription, and then take astigmatism into account by adding one-half of the astigmatism power (cylinder) to the spherical power. My optometrist verified that it is a satisfactory approximation of the astigmatism correction; but note my next paragraph.

By experimenting, I found that I needed a little less correction than the above calculation. I believe this is probably because when the corrective lens is closer to the eye than the distance at which eyeglasses are placed, the effective power of the lens increases with the decreased distance. When my optometrist prescribes contact lenses, she "regresses" the prescription slightly from the eyeglass power, perhaps 1/4 to 1/2 diopter or so. Apparently the same thing applies to a diopter lens, when the eye is up very close to the lens.

I can focus a rangefinder just fine with a correction that is only approximate: the split image is either lined up, or it ain't. With an SLR, where I have to actually judge the sharpness, I need it to be exact.

So "try before you buy" is advisable; the calculations are likely to get you in the right ball park, but could be off by maybe a quarter diopter or so.
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Old 06-14-2017   #7
Dwig
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Quote:
Originally Posted by john_s View Post
The drugstore glasses are positive diopters, for close viewing. Is that what you want? I am shortsighted, so I need a negative diopter added to my cameras, so drugstore glasses are not useful.
...
If you are looking for a diopter to use without any other corrective lenses (e.g. an eyeglass wearer shooting without their glasses) then you are correct.

One the other hand, if you wear contact lenses or are "of bifocal age" and looking for a diopter to use with your distance vision glasses, or bifocal segment, then the approach of using the drugstore reading glasses for Trial-and-Terror testing is valid.

With SLRs, the best approach is to remove the lens and view the screen in moderately low light. You need to see the screen sharply and any image will add to the confusion. You also need to do this in the lowest practical light so that your eye dilates significantly so there is minimal depth of field and focus is most critical.

I have some significant astigmatism and have always found shooting SLRs or eyelevel electronic VFs without my glasses impractical regardless of the diopter used. I combine my VFs diopter adjustment with my regular single vision glasses, whether using either my distance vision or "computer distance" glasses, though each require a somewhat different setting. Boy, do I like adjustable eyepieces!
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