Chinese Leica M Diopters?
Old 07-17-2019   #1
Rob-F
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Chinese Leica M Diopters?

I ran across two diopter lenses for Leica M. The first one is Chinese, and is very interesting, since it comes in half-diopter increments, which I don't believe are available from Leica:

https://www.ebay.com/itm/Leica-M2-M3...53.m1438.l2649

And there is also this one, from Japan:

https://www.ebay.com/itm/From-JAPAN-...53.m1438.l2649

I'm not really tempted to try them, because I'd much rather have the Real Deal from Leica. Nevertheless, does anyone know anything about either of these?
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Old 07-17-2019   #2
peterm1
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Interesting development! I would be very interested to find out what people think of them.

I have no experience of these diopters and in fact never heard of aftermarket ones being on the market.

The only aftermarket diopter for Leica M cameras I am familiar with (I have one on my M8) is this one from Japan Exposures.
http://www.japanexposures.com/shop/a...r-leica-m.html

They are marketed as "viewfinder magnifiers" but the real attraction I find is that they have infinitely variable diopter adjustment within the range -3.0 to +1.0. This is very attractive as it means you do not have to know your exact eyepiece correction requirement up front. You can just buy the thing and adjust it till it gives the best result. Also if you eyes decline over time all you need to do is make further adjustments rather than needing to buy a new diopter. They also come in other magnifications, such as 1.35x (see their site).

The only slight gripe I have with them is that the adjustment ring has a tendency to move of its own accord when the camera it is mounted on is hanging from a camera strap around your neck as the eyepiece rubs against your clothes causing the adjustment lens to rotate. Not a big deal as you can (a) use some kind of fixative to make it harder to turn within its outer barrel and (b) mark the eyepiece surround and the barrel it goes in to with two dots of paint so you can see instantly if the two dots are still aligned or have moved out of alignment and need re adjustment.

Is the view through it as good as on a Leica diopter? I have no idea as I have not owned one. I suspect maybe not quite but the advantages it brings me outweigh this as it is in any event perfectly usable.
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Old 07-17-2019   #3
Rob-F
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Yes, I was aware of those. But most of the time I don't want that magnification, though. If I did, I would probably get one to try out.
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Old 07-17-2019   #4
peterm1
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Quote:
Originally Posted by Rob-F View Post
Yes, I was aware of those. But most of the time I don't want that magnification, though. If I did, I would probably get one to try out.
Yep, I fully understand that. However I find that I personally struggle a bit with the paltry 0.68 magnification of the M8 etc viewfinder. Folks with better eyesight than me may be OK and not require the added benefit of magnification - the diopter may well be enough. But I find I need more or else I take too long to focus thus missing shots.

Also the ones you have alluded to in your post have, as you say, the added advantage of half diopter adjustments. Its been a long time since I researched the Leica ones but I suspect the lack of this may have been a factor in me rejecting that option. However I cannot recall specifically but do seem to remember that when I tried to assess my own requirements it looked as if I needed a diopter lens that I could not get. - possibly because it was an "in between" one.
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Old 07-17-2019   #5
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The best diopter lens power may or may not be exactly the same as one's eyeglass prescription. Many of us have both near- or far-sightedness, which calls for a spherical correction; and astigmatism, the correction for which is called cylinder. Readymade off-the shelf correction lenses have only the spherical grind. In fact, it would not be feasible to correct cylinder with a lens that screws into place, because a cylinder correction has both a diopter strength and an axis, meaning that the correction must be rotated or oriented correctly to match the prescribed axis.

So if one orders a correction diopter based only on the spherical prescription, the astigmatism goes uncorrected. That can be good enough, if the cylinder power needed is mild.

But the astigmatism can be partially corrected. Years ago I read someplace that you can algebraically add one-half of the cylinder to the spherical figure. I asked one eye doctor about this, and the answer was "never heard of that." But then I asked my present optometrist. She smiled and said, "Yep." In fact, I had already confirmed it empirically. I have known for years that the best diopter choice for me is a little stronger than my spherical prescription. When my spherical was about -4.25 or so, a -5 diopter gave me a sharper image in the viewfinder than a -4. And now that my spherical prescription is more like about -3, a -4 is a little better than a -3. I don't yet have a -3 Leica diopter, but I have -3 and -4 for my Nikons ($10 instead of $212 for the Leica). So the "add one-half of your cylinder" trick works for me. My spherical is close to -3, and my cylinder is around -1.5 at 100 degrees. So -3 + ( -1.5/2) = -3.75 comes out closer to -4 than -3, and that is my best choice at the moment.

I had surgery last month to remove cataracts, and they replaced my lenses with plastic implants. They reduced my nearsightedness, so I no longer needed my -5 diopter lenses. Tomorrow I will find out what my exact final numbers will be. One doctor predicts it will be -2.5 spherical. So I may wind up needing only a -3 diopter lens. But, it could also be that a -3.5 will be best, which would make that Chinese lens my best choice.

Peter M, depending on what your spherical plus cylinder is, one of those Chinese lenses might be best for you as well. But I think we first ought to know if they are a good product.
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Old 07-17-2019   #6
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Leica diopters do come in half-diopters, at least for some values. I've seen +0.5 and +1.5. Not sure what other values are available.

They are expensive as blazes though, so I'd be interested in checking into the other options mentioned here.
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Old 07-17-2019   #7
davidnewtonguitars
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Careful buying from the Chinese seller, not a good feedback.
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Old 07-17-2019   #8
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Keep in mind that you may need to add the native viewfinder correction, usually between -0.5 and -1.5 (don't now about M Leicas), to that of the correction lens. Or not, it may be worked into the number on the correction lens, so that the actual optical power is not what it says. There's no universal convention.
If you need cylinder correction, you could always have the glass in one of these rings replaced, some optometrists can do it, and it shouldn't be very expensive compared to what an off the shelf one already costs. For a simple screw-on ring one would need to glue it in place in the correct orientation, but that's perfectly doable. Of course the view will be fuzzy in portrait orientation, but that could be acceptable for some.
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Old 07-17-2019   #9
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Quote:
Originally Posted by retinax View Post
Keep in mind that you may need to add the native viewfinder correction, usually between -0.5 and -1.5 (don't now about M Leicas), to that of the correction lens. Or not, it may be worked into the number on the correction lens, so that the actual optical power is not what it says. There's no universal convention.
If you need cylinder correction, you could always have the glass in one of these rings replaced, some optometrists can do it, and it shouldn't be very expensive compared to what an off the shelf one already costs. For a simple screw-on ring one would need to glue it in place in the correct orientation, but that's perfectly doable. Of course the view will be fuzzy in portrait orientation, but that could be acceptable for some.
Nikon does work the finder's optical power into their correction lenses. The intention is for us to simply buy the lens that matches our prescription, and not worry about compensating for the finder's power. Like Retinax, I haven't seen anything on how Leica handles this. I suspect however that they do it the same as Nikon, just based on my results. My Spherical plus 1/2 my cylinder gets me a sharp image, with no further adjustments.
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Old 07-17-2019   #10
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Also, when deciding between two diopters, when one is a little too weak and the other is a little too strong, I have found that the slightly higher negative power is better. The slightly lower one will look a little soft to me (but still good enough); the slightly higher (negative) power still looks sharp. But if it is more than slightly higher, I won't use it, because I get a sense of eyestrain looking through it. It may still be useable, but it's uncomfortable. With a rangefinder camera, the diopter can be a little off, and I can still see when the images are lined up. So even the slighter softer one is really OK.

Edit: I am stressing that my remarks are for the negative diopters, because I don't know if the same idea works for the positive ones.

With an SLR, I would be concerned about how a diopter that is too far off, might affect my ability to judge focus.
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