Ronazle Posted September 17, 2017 Share #1 Posted September 17, 2017 Advertisement (gone after registration) In a couple of months I'll be cleaning up a cemetery about 1800 miles away. Part of my plan is to try IR photography to help discern markings on old and primitive tombstones. In preparation I've been trying different lenses on my M-8 and am a little surprised at the results: two very different lenses, an 18mm F4.0 Distagon and a 21mm 4.5 Biogon, are clearly rendering the sharpest results. In that regard I've tried simple and complex (formula wise) lenses from the past and present and none have come near those two in overall IR sharpness. I am doing multiple compensations for the shift in focal point, am using a rigid tripod. and am altering distances IAW focal length so that resultant images are have about the same coverage. I do not have a clue as to why these two lenses are so much better than all others. Can anyone explain it to me? The Distagon is one of the few modern lenses I have seen with IR compensatory focus marked on it. Thanks, Ron Quote Link to post Share on other sites More sharing options...
Advertisement Posted September 17, 2017 Posted September 17, 2017 Hi Ronazle, Take a look here IR Question. I'm sure you'll find what you were looking for!
tobey bilek Posted October 4, 2017 Share #2 Posted October 4, 2017 They are no longer marked because there are many filters/films with different frequency so it would be just a guess to calibrate. Years back there was one ir film and Leica supplied filter. The cut off at the filter may be different depending on filter. Some let in only IR, some allow a little visable along with IR and focus may be different. start with desired distance set at 5.6 and BRACKET FOCUS. If you are taking from 10 feet, set 10 at 5.6 instead of at infinity mark. Wides might be more forgiving and Zeiss designs perhaps are more traditional. Quote Link to post Share on other sites More sharing options...
Ronazle Posted October 4, 2017 Author Share #3 Posted October 4, 2017 Tobey, Thanks, as it were, I did bracket focusing points to no particular avail. Actually, the 21mm is the old true WA design while the 18mm is retrofocus. The whole experience is strange. Regards, Ron Quote Link to post Share on other sites More sharing options...
Michael Geschlecht Posted October 4, 2017 Share #4 Posted October 4, 2017 (edited) Hello Ron, There are a number of lenses, some of which are apochromatically corrected lenses, which are also corrected for infrared. I think that the 180mm, F3.4, Apo-Telyt for the Leicaflex may be 1 of them. A number of mirror lenses are infrared corrected because the mirrors, by reflecting & nor refracting (Except in the corrector lenses.), keep the different wave lengths together better. There might be some other Leitz/Leica lenses that are infrared corrected also. Best Regards, Michael Edited October 4, 2017 by Michael Geschlecht 1 Quote Link to post Share on other sites More sharing options...
tobey bilek Posted October 9, 2017 Share #5 Posted October 9, 2017 Do not bracket far. 2.8 to 8 in half stops on depth of field scale. If you are on a tripod, and you see no difference and images are out of focus, use another lens. Again there may be an issue of how much visible light gets in vs what the film is made for. 093 allows no visible light, Leica and 092 B+ W filters allow some visible. 092 and 093 work fine on my M8, but I do not have your lenses. 1 Quote Link to post Share on other sites More sharing options...
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