I got my 2nd copy of the Sigma 90mm. Unfortunately it also appears to be slightly decentered (although not as bad as the first copy). Serial number: 557788xx
Did any of you guys actually manage to get a well-centered copy?
keepcoding wrote:
I got my 2nd copy of the Sigma 90mm. Unfortunately it also appears to be slightly decentered (although not as bad as the first copy). Serial number: 557788xx
Did any of you guys actually manage to get a well-centered copy?
Mine is pretty decent for centering. I can only see any slight sharpness falloff on the very far right side/far corners at 42MP on my A7RIII and it goes away at f/5.6. My A7C (24MP and no LPF) says it's sharp all over at any aperture.
keepcoding wrote:
I got my 2nd copy of the Sigma 90mm. Unfortunately it also appears to be slightly decentered (although not as bad as the first copy). Serial number: 557788xx
Did any of you guys actually manage to get a well-centered copy?
I sampled three. One, which I now have, was very well-centered even at 400%, indeed all the way up to 800%. A second was well-centered, very much so at 100%, but a bit less good than the first. The third was ok also but the central image was just a bit less sharp than the other two. I am a bit extreme in my comparisons, running the X/Y comparisons in Lightroom all the way up to 800%. Generally, telephoto lenses should be easier to get good centering on than are wider lenses.
I do wonder about the upside down shooting that is used to do the centering test in Fred's directions. My experience is that it is very difficult for me to hold a camera as steadily upside down as it is right side up. Many of the "soft" corners I found when doing upside-down shooting were in the lower right corner (when viewed right side up), which led me to suspect that I could not hold the camera as steadily in the very awkward position used to shoot that corner as I could hold the camera for the other corners. Even at high shutter speeds, differences in hand-holding may be a factor in making critical comparisons at high magnifications.
It is not clear to me that the upside down manner of shooting test shots adds anything to the comparisons (and no one has offered an explanation that I have seen of why it is important to do two of the shots upside down) and I do wonder whether getting different decentered results from the upside-down shooting is often an artifact of the testing technique rather than an actual measurement of a characteristic of the lens.
I believe that Joshua in former days (I think he may have stopped testing his lenses this way), had a rig that would let him shoot the upside down shots from a tripod. If one is able to do that, it would obviate my concerns about hand-holding upside-down. But otherwise, at least for me, upside-down handholding is problematic, especially for the very-awkward-to-hold lower right corner shot.
chiron wrote:
I sampled three. One, which I now have, was very well-centered even at 400%, indeed all the way up to 800%. A second was well-centered, very much so at 100%, but a bit less good than the first. The third was ok also but the central image was just a bit less sharp than the other two. I am a bit extreme in my comparisons, running the X/Y comparisons in Lightroom all the way up to 800%. Generally, telephoto lenses should be easier to get good centering on than are wider lenses.
I do wonder about the upside down shooting that is used to do the centering test in Fred's directions. My experience is that it is very difficult for me to hold a camera as steadily upside down as it is right side up. Many of the "soft" corners I found when doing upside-down shooting were in the lower right corner (when viewed right side up), which led me to suspect that I could not hold the camera as steadily in the very awkward position used to shoot that corner as I could hold the camera for the other corners. Even at high shutter speeds, differences in hand-holding may be a factor in making critical comparisons.
It is not clear to me that the upside down manner of shooting test shots adds anything to the comparisons (and no one has offered an explanation that I have seen of why it is important to do two of the shots upside down) and I do wonder whether getting different decentered results from the upside-down shooting is often an artifact of the testing technique rather than an actual measurement of a characteristic of the lens.
I believe that Joshua in former days (I think he may have stopped testing his lenses this way), had a rig that would let him shoot the upside down shots from a tripod. If one is able to do that, it would obviate my concerns about hand-holding upside-down. But otherwise, at least for me, upside-down handholding is problematic, especially for the very-awkward-to-hold lower right corner shot.
In my experience the corner test is not always conclusive, especially since there is a normal sharpness falloff towards the corner.
What I've been doing instead is what I call "upside-down" test (flip camera by 180°). It is described here (the 2nd mentioned test a bit further down): https://keepcoding.ch/demo/decenteringtest/
This method only requires 2 photos and lets me compare each portion of the frame. Much easier to spot any sharpness difference. Had a few lenses where I did not see a decentering issue with the "4 corners" test but then the other method revealed obvious issues.
chiron wrote:
I sampled three. One, which I now have, was very well-centered even at 400%, indeed all the way up to 800%. A second was well-centered, very much so at 100%, but a bit less good than the first. The third was ok also but the central image was just a bit less sharp than the other two. I am a bit extreme in my comparisons, running the X/Y comparisons in Lightroom all the way up to 800%. Generally, telephoto lenses should be easier to get good centering on than are wider lenses.
I do wonder about the upside down shooting that is used to do the centering test in Fred's directions. My experience is that it is very difficult for me to hold a camera as steadily upside down as it is right side up. Many of the "soft" corners I found when doing upside-down shooting were in the lower right corner (when viewed right side up), which led me to suspect that I could not hold the camera as steadily in the very awkward position used to shoot that corner as I could hold the camera for the other corners. Even at high shutter speeds, differences in hand-holding may be a factor in making critical comparisons at high magnifications.
It is not clear to me that the upside down manner of shooting test shots adds anything to the comparisons (and no one has offered an explanation that I have seen of why it is important to do two of the shots upside down) and I do wonder whether getting different decentered results from the upside-down shooting is often an artifact of the testing technique rather than an actual measurement of a characteristic of the lens.
I believe that Joshua in former days (I think he may have stopped testing his lenses this way), had a rig that would let him shoot the upside down shots from a tripod. If one is able to do that, it would obviate my concerns about hand-holding upside-down. But otherwise, at least for me, upside-down handholding is problematic, especially for the very-awkward-to-hold lower right corner shot.
I don't want to wander too much off-topic here, but I perform Fred's decentering test 2-times:
* first starting with "left-hand side" corners before turning the camera upside down
* second starting with "right-hand side" corners
and the weaker corners remain in their (physical) position...
Do vendors package these tested but returned lenses(90i) up as new and resell them or do they end up as pristine used and resold? I have a feeling that some end up sold as new again in some situations. I am starting to think purchasing from slightly less common sellers might be a better choice.
MARKFER wrote:
Do vendors package these tested but returned lenses(90i) up as new and resell them or do they end up as pristine used and resold? I have a feeling that some end up sold as new again in some situations. I am starting to think purchasing from slightly less common sellers might be a better choice.
That depends very much on the seller. A reputable seller should not resell a returned product as "new" (e.g. Amazon usually advertises returned products on the marketplace and declares them as opened). Also, if a lens is returned as 'defective' to the seller, it will probably be sent back to Sigma (or at least the official distributor in the region). Would be interesting to know what Sigma / the distributor does with the returned lenses (probably just a brief inspection, cleaning, repackaging and then recirculate the lens).
Probably, I doubt centering is tested or reviewed as a fault with Sigma. Amazon is pretty good though with returns regardless. Who knows though with seemingly perfect returned merch. With an pretty average but not great tested lens, based on your testing measures, I would think 95% of people would not notice anyway. Maybe I'm in the group, ha, not sure.
Yes they won't test for decentering for sure (I've tried to send decentered lenses for repair to Sigma in the past, and they failed to identified a problem with the lens).
I agree that most people wouldn't notice that there is something wrong with the lens and would be totally happy with the results. In that perspective, it kind of makes sense to reuse the lenses (would be a waste to trash them).
Decentering issues may actually not have an impact to speak of for most use cases. Landscape photography is where decentering most prominently detriments image quality (especially wide open).
Went to some parties with 24mm f/2 DG DN and Panasonic S1.
I am not sure if my sample is decentered or not. It looks sharp enough in photos and that is enough so far. The lens works well and I hope Sigma releases a new 50mm lens with aperture ring too.
I just received my Sigma 90/2.8. Here are some initial shots all wide open. Will test for decentering when the weather cooperates a little more (35 deg F; 35 MPH winds)
First two = camera normal
Second two = upside down
This sounds nice to me.
I do not want to jump to any conclusion, but there is a clear focus shift when you compare DSC03072 and DSC03075 (either by accident or the lens is decentered).
I am assuming you did not refocus between the shots.
(although not as bad as the first copy). Serial number: 557788xx
