Agent Zaum Posted June 13, 2009 Share #1 Posted June 13, 2009 Advertisement (gone after registration) Hi, I have been following this forum for a while and just only registered because I have a question. I tried 2 different 90mm Summicrons, both ASPH, on my M8 today at a used equipment store. One was 6-bit coded, the other isn't. The coded lens focused without any problems and produced sharp images, even at f/2, when enlarged. For some reason, the uncoded one produced off-focused shots at every f-stop. Is it me or the lens? Link to post Share on other sites More sharing options...
Advertisement Posted June 13, 2009 Posted June 13, 2009 Hi Agent Zaum, Take a look here 90mm Summicron focusing problems. I'm sure you'll find what you were looking for!
BenMacPhoto Posted June 13, 2009 Share #2 Posted June 13, 2009 That is strange, I shoot with an early version 90 summicron from 1959. Not coded and focus is spot on, even wide open. Link to post Share on other sites More sharing options...
adan Posted June 13, 2009 Share #3 Posted June 13, 2009 The 90 Summicron pushes the envelope for the lower-magnification M viewfinders wide-open. Any straying within the tolerances of camera and lens can add up to a combination that is out of tolerance (cannot be focused reliably). I always test an individual M telephoto on my bodies before buying precisely because one will work better than another with a specific RF mechanism. I have heard from Leica sources that the company had to significantly tighten manufacturing tolerances as they found out how unforgiving a flat piece of silicon is compared to the jelly coating of a piece of film. The fact that the post-M8 (coded) lens did better than the pre-M8 (uncoded) lens tends to tie in with this info - although the coded 90 could have been coded after the fact. The 90 APO has a much more defined focus point than earlier 90 f/2s, which have more spherical aberration. The spherical aberration in older lenses makes them slightly more focus tolerant, as the light rays from the edge of the aperture focus at a different point than those from the center, or from in between. This creates a "tube" of more or less focused rays that allows some leeway in focusing - the image will not be as sharp as the APo is capable of, but the maximum sharpness will extend over a larger range of not-quite-focused. See this X-section of how SA (top and bottom) extends the almost-focused (brightest) area: File:Spherical-aberration-slice.jpg - Wikipedia, the free encyclopedia In fact I recall some members of the LUG reporting they got "less DoF" when they first switched to APO 90s. Technically, all 90 f/2s should have idenitcal DoF - but I think they were seeing this more abrupt defocusing effect. E.G. http://leica-users.org/v24/msg12281.html Finally, the APO 90 uses a pusher (sliding rail) to connect the lens focusing cam to the camera roller. These pushers can occasionally become sticky - although it is more likely in a 40-year-old 135 than in a 3-5-year-old 90 APO. The pusher tip is visible in this shot as the black trapezoidal metal piece in the cutout of the lens mount, left. http://www.kenrockwell.com/leica/images/90mm-f2-apo-asph/D3S_5316-600.jpg In your case I would say tolerance variation is the most likely explanation - one lens just played nicer with your particular rangefinder. Link to post Share on other sites More sharing options...
sfokevin Posted June 13, 2009 Share #4 Posted June 13, 2009 The 90 Summicron pushes the envelope for the lower-magnification M viewfinders wide-open. Any straying within the tolerances of camera and lens can add up to a combination that is out of tolerance (cannot be focused reliably). I always test an individual M telephoto on my bodies before buying precisely because one will work better than another with a specific RF mechanism. I have heard from Leica sources that the company had to significantly tighten manufacturing tolerances as they found out how unforgiving a flat piece of silicon is compared to the jelly coating of a piece of film. The fact that the post-M8 (coded) lens did better than the pre-M8 (uncoded) lens tends to tie in with this info - although the coded 90 could have been coded after the fact. The 90 APO has a much more defined focus point than earlier 90 f/2s, which have more spherical aberration. The spherical aberration in older lenses makes them slightly more focus tolerant, as the light rays from the edge of the aperture focus at a different point than those from the center, or from in between. This creates a "tube" of more or less focused rays that allows some leeway in focusing - the image will not be as sharp as the APo is capable of, but the maximum sharpness will extend over a larger range of not-quite-focused. See this X-section of how SA (top and bottom) extends the almost-focused (brightest) area: File:Spherical-aberration-slice.jpg - Wikipedia, the free encyclopedia Finally, the APO 90 uses a pusher (sliding rail) to connect the lens focusing cam to the camera roller. These pushers can occasionally become sticky - although it is more likely in a 40-year-old 135 than in a 3-5-year-old 90 APO. The pusher tip is visible in this shot as the black trapezoidal metla piece in the cutout of the lens mount, left. http://www.kenrockwell.com/leica/images/90mm-f2-apo-asph/D3S_5316-600.jpg In your case I would say tolerance variation is the most likely explanation - one lens just played nicer with your particular rangefinder. Or the older lens could just need a good CLA... Link to post Share on other sites More sharing options...
stevem7 Posted June 13, 2009 Share #5 Posted June 13, 2009 I just bought an older, used 90 APO, non coded and the focus is PERFECT with my M8. Not one issue. But yea, it is best to test a lens on your body before buying. I have had quite a few lenses come through that were off. My 90 review... THE LEICA 90 SUMMICRON APO ASPH LENS REVIEW Link to post Share on other sites More sharing options...
coup de foudre Posted June 14, 2009 Share #6 Posted June 14, 2009 i borrowed a friend's newer, coded lens and there was definitely a back-focus issue. yesterday, at a photo fair, i tried 3 90 Crons. the two Asphs where non-coded but worked brilliantly -- especially the titanium. a later model, non-asph, was way too soft and i doubt it was the lens itself. it likely needed some TLC and a CLA. the titanium is the one i really fell for (it actually may have more to do with the lighting and the subjects), but looked completely ridiculous on my black M8. unfortunately, both Asphs are kind of out of my price range right now but i think that's what i'll go for (i already have the 75 Lux for more dreamy shots) eventually. one thing is for sure, though -- i would not get one of these lenses sight unseen! at this focal length, the calibration really matters. Link to post Share on other sites More sharing options...
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