jaapv Posted March 12, 2011 Share #41 Posted March 12, 2011 Advertisement (gone after registration) I shall put up some term explanation summaries after checking in with the Mods . I had hoped that there might have been comments/corrections on the information that I summarised since I have no formal expertise on the subject at all. You don't need to check with the mods, just follow the format of the posts in the thread. It is open to anybody, as long as it stays on topic. Link to post Share on other sites More sharing options...
Advertisement Posted March 12, 2011 Posted March 12, 2011 Hi jaapv, Take a look here Diopter Assistance. I'm sure you'll find what you were looking for!
hoppyman Posted March 12, 2011 Share #42 Posted March 12, 2011 Jeff I think we all agree and have commented that you need to try for yourself and get expert assistance (optometrist/ophamologist) if needed. My posts certainly were chock full of the technical 1 Link to post Share on other sites More sharing options...
tdtaylor Posted March 13, 2011 Author Share #43 Posted March 13, 2011 I gave my thoughts in post #35. While your two posts, Geoff, were quite erudite (as usual), much of it was technical, and while technical is often good and useful, in this instance there is no substitute for trial and error IMO. All the technical info in the world didn't get Terry to the right solution; trying it out did. Eyes are funny that way. Just my 2 cents. Jeff Geoff's comments were immersed in technical information, and I for one appreciated it. While it may have not yielded the final answer, it provided an excellent set of points and definitions that greatly helped me get a handle on the issues. As in any field, understanding some of the terms salient to that field can help the novice. And often FAQ's start with definitions (in the form of answers to questions). I would have come to a better understanding much more quickly if Geoff's post had been #1, and further understood more quickly the following posts with those understandings. Once again, thanks to everyone, although Jaap still owes me an explanation why the diopter measurement should be 2 meter instead of one . Link to post Share on other sites More sharing options...
hoppyman Posted March 13, 2011 Share #44 Posted March 13, 2011 (edited) It's all good, Terry. I sent a note to a Mod asking about setting up a Customer Service FAQ and making it a Sticky since this is not M9 specific. Shall look at this v soon. I follow Jeff's comments too and shall make it concise and usable, I hope. As to why two metres and not one please see my long winded technical waffle. For whatever reason Leica Camera and other manufacturers consider that is the best fit for our eyes. I recall that Nikon had the same in the old school film cameras. I have no idea about now. In their case they marked the correction eyepieces as the SUM not the individual values . More confusion. I know of a Leica shooting opthamologist to ask for a why (on the Leica User Group LUG). If I hear back I shall share of course. Alternatively I shall send a note to Customer Service and ask if anyone can explain for us. Edited March 13, 2011 by hoppyman 1 Link to post Share on other sites More sharing options...
jaapv Posted March 13, 2011 Share #45 Posted March 13, 2011 Once again, thanks to everyone, although Jaap still owes me an explanation why the diopter measurement should be 2 meter instead of one . Because that is the virtual distance of the framelines and rangefinder patch.Post #27 1 Link to post Share on other sites More sharing options...
tdtaylor Posted March 14, 2011 Author Share #46 Posted March 14, 2011 Missed it- what I get for using a DPA and mot a computer..... and probably not using my bifocals:D Thanks 1 Link to post Share on other sites More sharing options...
hoppyman Posted March 20, 2011 Share #47 Posted March 20, 2011 (edited) Advertisement (gone after registration) I trawled through some on-line archives and found a post from several years back when a Leica using optometrist (on the LUG) provided some helpful responses for me and to some others. I summarise a couple of this points here that may be of interest. The first example is using the example of a viewing eye with minus 0.50 diopter defect but illustrates the principle. Once again no substitute for trying for yourself and seeking expert assistance. Many camera systems are designed so that the user must accommodate (or focus) a little bit to see the distance. Human visual systems seem to prefer this minimal focus requirement. In many cases, just putting something close to your eye stimulates your visual system to focus a little. If you are less than 40-45 years old, your eye will focus this small amount without you being aware. The camera's optical system presents infinity at a virual point 2 metres in front of the camera. Your eye must focus 0.50 diopter to see this point in space clearly. When you combine the mild nearsightedness (minus 0.50 diopter) in your viewing eye with the minus 0.50 diopter focusing requirement of the viewfinder, you might think that you would need a minus 1.0 diopter correction lens. Well, its not that simple. You would be way overcorrected with a minus 1.0 diopter correction lens and although the viewfinder might seem clear when first viewing through it - you would not be comfortable. Your eye's focusing system would be working too hard. If you are over 45 yrs old you would definitely be uncomfortable..... Use the least amount of minus lens power to clear the image in the rangefinder. Better to be under corrected than over corrected. ..................................................................... (on progressive lens (bifocals without lines) with distance prescription +1.25 diopter Technically, you should use the distance prescription (+1.25) for an eyepiece correction lens. Some SLR viewfinders project the image of the ground glass out to about 1 metre and not optical infinity. So you may need an additional 0.50 to 1.0 above your distance prescription. The lens' total corrective power can simply be added for the final prescription..... For the M Leica, I would recommend your distance prescription (+1.25). If you can't get this power, you could then go with either +1.00 or even +1.50 ............................................................... On astigmatism with a shooter with minus correction If you have a mild amount of astigmatism, you can use the "spherical equivalent" by just adding more (-) minus correction. Usually you divide the astigmatism correction amount by two and just lump that in with the spherical correction. .. It is a compromise but will work when you have a mild astigmatic correction. Edited March 20, 2011 by hoppyman Link to post Share on other sites More sharing options...
chris_tribble Posted September 3, 2018 Share #48 Posted September 3, 2018 This is a bit tangential - but still relevant. I need to swap a diopter from M10 one body to another and realise that I've cross threaded the diopter INSIDE the leica viewfinder thread adapter. Do any engineers have an idea of how I might shift this without causing damage? I've tried gripping with rubber gloves, but this hasn't worked. Any advice gratefully received! Link to post Share on other sites More sharing options...
jaapv Posted September 3, 2018 Share #49 Posted September 3, 2018 Microtools provide a special brass wrench. https://www.micro-tools.de/en/Flexi-Clamps-oxid/ Link to post Share on other sites More sharing options...
chris_tribble Posted September 4, 2018 Share #50 Posted September 4, 2018 Jap - thanks! The good news is that a rubber glove gave me the purchase I needed and the dioptre is safely unscrewed. I may, however, get one of the micro-tools in case there's a future need. Again - grateful for the quick response Link to post Share on other sites More sharing options...
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