cpclee Posted October 21, 2017 Share #1  Posted October 21, 2017 Advertisement (gone after registration) I'm finding that at f2.0, the four corners of my copy of this lens perform more unevenly than I would have pictured.  This is true if my subject is near (say at 1.5m ) or far (infinity).  The difference becomes barely noticeable by 2.8, and by 4.0 it is completely gone.  I'm ruling out my SL or M adapter being at fault as I see much more consistent performance between the corners in all other lenses of mine including rather fast ones (1.4 to 2.0).  The lens went through a CLA by Leica three years ago and never took a knock or any impact.  So to me it is a mystery whether this is within tolerance or some adjustment is needed.  I'd also like to know if anyone would know what the adjustment would cost.  10 years ago when I bought an 80/1.4R that was badly decentered, it was about a US$350 job that only Solms could do.  Leica USA couldn't do it.  Pictures attached.  This was a quick test and AWB was on.  First up is center. Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/278003-75-summicron-aa-corner-degradation/?do=findComment&comment=3379467'>More sharing options...
Advertisement Posted October 21, 2017 Posted October 21, 2017 Hi cpclee, Take a look here 75 Summicron AA corner degradation. I'm sure you'll find what you were looking for!
cpclee Posted October 21, 2017 Author Share #2  Posted October 21, 2017 top left followed by bottom left Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/278003-75-summicron-aa-corner-degradation/?do=findComment&comment=3379468'>More sharing options...
cpclee Posted October 21, 2017 Author Share #3  Posted October 21, 2017 top right followed by bottom right.  In each of the five pictures it is the same subject and the lens is set to infinity.  All are 100% crops.  To me the top right and bottom right pictures are clearly worse. Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/278003-75-summicron-aa-corner-degradation/?do=findComment&comment=3379470'>More sharing options...
CJJon Posted October 21, 2017 Share #4  Posted October 21, 2017 Do you have an un-cropped image? Link to post Share on other sites More sharing options...
lct Posted October 21, 2017 Share #5  Posted October 21, 2017 All 75mm and 90mm lenses i know of have softer corners at f/2. As far as my lenses are concerned, the Summicron 75/2 apo is not significantly better or worse than the Summicron 90/2 apo from this viewpoint. Same for 90/2 v3. 90/2 v2 is sharper there but it is a bulky lens and f/2 is still softer than all other apertures of this superb lens. Link to post Share on other sites More sharing options...
UliWer Posted October 21, 2017 Share #6  Posted October 21, 2017 Sorry, I don't understand what the examples could show me. For me it seems as if all of them where different crops from the central part of a photo. Since the building was taken from an angle, parts which are further off should be different than nearer parts - especially at f 2. When I look at the brown wall in the middle, it seems as if it was forward leaning in some examples and backward leaning in others. Perhaps there is also some unsharpness due to shaking - though I am not sure.  To demonstrate differences between the left and the right outer edges of a lens, my advice would be, to take a photo of something which fills the whole frame and is exactly parallel to the sensor plane, using a tripod. Link to post Share on other sites More sharing options...
LocalHero1953 Posted October 21, 2017 Share #7 Â Posted October 21, 2017 Advertisement (gone after registration) What camera body are you using it on? You mention SL and M adapters........ Â At risk of asking the obvious, is the raw converter (which one?) using the correct lens profile? Link to post Share on other sites More sharing options...
cpclee Posted October 21, 2017 Author Share #8 Â Posted October 21, 2017 The SL. And yes the correct profile was used for all of the shots. Â What camera body are you using it on? You mention SL and M adapters........ Â At risk of asking the obvious, is the raw converter (which one?) using the correct lens profile? Link to post Share on other sites More sharing options...
cpclee Posted October 21, 2017 Author Share #9  Posted October 21, 2017 These were five different shots of the same building structure placed at the frame’s center and then the four corners. The building is far away enough that the change in angle would not have affected the focusing distance (infinity). I was following the decentering test referenced here:  http://www.fredmiranda.com/forum/topic/1432008/0 http://www.gletscherbruch.de/foto/test/dezentrierung/dezentrierung.html  Sorry, I don't understand what the examples could show me. For me it seems as if all of them where different crops from the central part of a photo. Since the building was taken from an angle, parts which are further off should be different than nearer parts - especially at f 2. When I look at the brown wall in the middle, it seems as if it was forward leaning in some examples and backward leaning in others. Perhaps there is also some unsharpness due to shaking - though I am not sure.  To demonstrate differences between the left and the right outer edges of a lens, my advice would be, to take a photo of something which fills the whole frame and is exactly parallel to the sensor plane, using a tripod.  Link to post Share on other sites More sharing options...
cpclee Posted October 21, 2017 Author Share #10  Posted October 21, 2017 I fully expected some corner degradation. However, what I didn’t expected was for the four corners to show noticeably different degrees of degradation from each other. Sometimes, but not always, that can be a sign that a lens element has de-centered.  Severely decentered lenses can show uneven corners when the lens is stopped down to f8 or more. In my case, though, the uneven corners is only at f2.0 so it may be very normal for this lens. That’s what I’m trying to find out about.  Thanks.  All 75mm and 90mm lenses i know of have softer corners at f/2. As far as my lenses are concerned, the Summicron 75/2 apo is not significantly better or worse than the Summicron 90/2 apo from this viewpoint. Same for 90/2 v3. 90/2 v2 is sharper there but it is a bulky lens and f/2 is still softer than all other apertures of this superb lens.  Link to post Share on other sites More sharing options...
cpclee Posted October 21, 2017 Author Share #11 Â Posted October 21, 2017 I should add that with all five shots the shutter was at 1/200s to rule out camera shake. Link to post Share on other sites More sharing options...
lct Posted October 21, 2017 Share #12 Â Posted October 21, 2017 I would not compare different shots. Too many variables then including field curvature which is significant at f/2. Posting one single shot (a raw file preferably) could help us to help you eventually. Link to post Share on other sites More sharing options...
Shac Posted October 21, 2017 Share #13 Â Posted October 21, 2017 Certainly looks like some decentering to me. I just ran some tests with a lens I have (not a Leica lens) and found decentering. How is it when you start to stop down? Link to post Share on other sites More sharing options...
wlaidlaw Posted October 21, 2017 Share #14  Posted October 21, 2017 Roger Cicala of Lens Rentals wrote a blog on lens testing on an optical bench with various adapters. He found that even the best quality manufacturers' adapters, OEM etc, caused very noticeable and asymmetric deterioration of lens MTF's. I wonder if what you are seeing is caused by the adapters.  Wilson Link to post Share on other sites More sharing options...
cpclee Posted October 21, 2017 Author Share #15 Â Posted October 21, 2017 The asymmetry is barely noticeably by f2.8 (all corners becoming very sharp) and completely gone by 4.0. Â Â Certainly looks like some decentering to me. I just ran some tests with a lens I have (not a Leica lens) and found decentering. How is it when you start to stop down? Link to post Share on other sites More sharing options...
cpclee Posted October 21, 2017 Author Share #16  Posted October 21, 2017 Yes I read that blog too which is why I’m not jumping to conclusions yet that anything is outside of tolerance. If you click on the fredmiranda.com link, someone actually talks about trying to find a perfect copy of a Zeiss Batis but ending up realizing that there is no perfect copy.  Roger Cicala of Lens Rentals wrote a blog on lens testing on an optical bench with various adapters. He found that even the best quality manufacturers' adapters, OEM etc, caused very noticeable and asymmetric deterioration of lens MTF's. I wonder if what you are seeing is caused by the adapters.  Wilson Link to post Share on other sites More sharing options...
cpclee Posted October 21, 2017 Author Share #17  Posted October 21, 2017 I’ll post more in the morning. But understand that the test I employed above is actually easier to conduct and more conclusive than trying to shoot a flat target that covers the whole frame. In the latter kind of test, trying to make sure the sensor plane is completely parallel to the target is almost impossible and that introduces even more uncontrollable factors.  Field curvature is a factor but in theory it affects all corners equally. What we are looking for isn’t how sharp the four corners are but how different are they from each other.  I would not compare different shots. Too many variables then including field curvature which is significant at f/2. Posting one single shot (a raw file preferably) could help us to help you eventually. Link to post Share on other sites More sharing options...
lct Posted October 21, 2017 Share #18  Posted October 21, 2017 [...] Field curvature is a factor but in theory it affects all corners equally. What we are looking for isn’t how sharp the four corners are but how different are they from each other.  I'm not good at theories but most if not all my fast lenses are affected by field curvature to variable degrees and i hardly see equality then between corners. Also decentering would be visible at various apertures i believe so instead of taking shots with different fields of view i would keep the same FoV and just change the aperture to see what happens. Could be useful to check focus shift as well. FWIW. Link to post Share on other sites More sharing options...
mdemeyer Posted October 21, 2017 Share #19 Â Posted October 21, 2017 Might suggest you try this test: Â http://blog.kasson.com/lens-screening-testing/ Â Uses the same general technique but is much easier to interpret than the building shot. Â By the way, the bad 35mm C-Biogon ZM included in the sample results was mine. Bought from an EBay seller and had to return. I saw the issues in normal images and used this to confirm. Link to post Share on other sites More sharing options...
cpclee Posted October 22, 2017 Author Share #20  Posted October 22, 2017 Thanks for sharing this.  A quick glance at the examples on that blog and I now realize that my copy is a much better than the what Kasson considers "good" for full frame lenses.  Like I said, the asymmetry between corners is mild and only visible at f2.  Where as on Kasson's blog the ones that are considered to be problematic are ones that exhibit asymmetry well into smaller apertures.  Here is an example I shot indoors (with a quick setup) at f2.8 using the same lens.  All corners perform quite equally.  I'm showing the whole frame.  Might suggest you try this test:http://blog.kasson.com/lens-screening-testing/Uses the same general technique but is much easier to interpret than the building shot.By the way, the bad 35mm C-Biogon ZM included in the sample results was mine. Bought from an EBay seller and had to return. I saw the issues in normal images and used this to confirm.  Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/278003-75-summicron-aa-corner-degradation/?do=findComment&comment=3379887'>More sharing options...
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