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Which diopter?

Donald Carroll , Jan 11, 2005; 03:54 a.m.

Anyone have a quick 'n dirty way of guessing which diopter strength to use? For example, do camera diopter numbers have some rough relationship to those dime-store reading glasses with strengths like 1.5, 1.75, 2, etc.?

Or can something be guessed by where I would set the diopter setting on an SLR with an adjustment slider/dial? For example, with my normal glasses, I have to move the slider on my D70's viewfinder almost all the way to the top. On the other hand, with the glasses I had made for computer work the slider is almost at the bottom. Would ZERO on the diopter scale be like putting the slider in the middle? If so, would UP be POSITIVE or NEGATIVE?

Responses


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Jonathan Reynolds , Jan 11, 2005; 04:23 a.m.

Donald, do a search here on PN. In my few years of subscribing there have been at least two detailed threads on viewfinder correction lenses, containing expert advice from opticians.

Donald Carroll , Jan 11, 2005; 04:51 a.m.

Jonathan, I tried a search but didn't turn up anything.

Ray . , Jan 11, 2005; 04:56 a.m.

I don't remember the means by which I figured it, but I was only able to narrow the calculation to 2 possible numbers. If you're talking about a diopter lens for a Leica M, I think the way to determine it with certainty is to look through each of the lenses and compare them. Positive is magnification.

Donald Carroll , Jan 11, 2005; 05:13 a.m.

Going into a shop and looking at actual diopters on the camera is, unfortunately, not an option. Again what I'm looking for is some kind of quick and dirty way to get a rough handle on what sort of diopter is needed, i.e. a way to narrow the choices down to a minimum.

For example, can someone tell me if shifting the diopter control UP on the D70 is positive or negative? If so, then since the diopter range is from -1.6 to +0.5 then the top position would be a +0.5 diopter.

BTW, the viewfinder on the D70 appears slightly smaller with the diopter adjustment set to the top.

bruno menilli , Jan 11, 2005; 06:53 a.m.

Donald

From my own experience the M cameras are .5 dioptre less than R cameras, eg:

Leica R +2dioptre

Leica M +1.5 dioptre

These are the settings I use, but you, and your eyes, may need different settings.

Regards

Bruno

Ronald Moravec , Jan 11, 2005; 06:56 a.m.

There is no way to translate from an SLR to an M. SLRs may have some negative magnification built in, or may not.

The drug store glasses diopter is the same as Leica diopter. There is a scientific definition for a diopter which I do not remember.

The problem is few dealers carry the lenses. Tamarkin in New York does and were willing to exchange a few to get it right.

Then your eyes change and you start again! Have your eye doctor give you your perscription and see how it changes. Make the correction lens change the same absolute amount.

Jonathan Reynolds , Jan 11, 2005; 07:04 a.m.

Donald, I've just tried the search too and can't find the threads I remember. I may have printed them out - will have a hunt.

Meanwhile, here is what I remember of the discussion. Because the Leica M viewfinder is looking straight out into the world, the correction needed is that which enables your eyes to focus at infinity. Your optician should be able to quote this to you. Your focussing ability for close-distances is irrelevant. Thus I need reading glasses (only), but the M viewfinder is perfectly sharp (fortunate!).

bruno menilli , Jan 11, 2005; 07:16 a.m.

Donald

Whoops! thought you were talking about Leica !

regards

Bruno

Olivier Reichenbach , Jan 11, 2005; 08:08 a.m.

I wear reading glasses (farsightedness.) If I buy those cheap drugstore glasses, I take something around +2.5 which fit my left eye okay but not so well my right which has stronger astygmatism. But that's another story. On my M7 (0.72) I can't focus at all with my naked right eye, and much better with my naked left eye. So I ordered a +1D correction lens for the VF. Now, I can focus with my right eye. It's not perfect (again, that's a problem with astygmatism, not farsightedness), but it's a big improvement. I also have +1D correction lenses on my Nikon SLRs (F2 and F3.) So, first, the diopter correction apparently is not the same as your reading glasses, probably because the VF already has a correction in it and the virtual image is formed at a different distance than the naked view. Two, I think negative diopter corrections are for nearsightedness, while positive are for farsightedness. Also, all the cameras I've had with built-in VF correction go from - something to +1, no more, though correction lenses have a more extended range on the plus side. Go figure.

My $0.02.


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