chiron wrote:
That is remarkable. I had such a different experience. I compared three copies and all were excellent and were very similar in performance, almost indistinguishable by my means of testing. My conclusion was that copy variation is very low with this lens.
I have never come across a complaint of uneven vignetting before. Do you have any speculation about what assembly error could cause uneven vignetting without causing uneven sharpness as well? I assume that somehow the image circle would have to be not centered on the sensor, for example if the lens barrel were curved or if the lens cell were tilted inside the barrel or were not centered in the barrel. But any of those seem certain to play havoc with sharpness as well as with the mechanical functioning of the lens.
I may just have incredibly bad luck. I feel bad mucking up Fred's review thread with my struggles to find a good copy cause it seems like most are receiving excellent copies, for which I'm very jealous, so this will be the last I'll post about it. I have 3 more copies on order just to hedge my bets one will be good. To answer your question, I have no idea, but I would imagine both the uneven sharpness and vignetting are caused by the same misalignment. Of the 4 lenses I tested, here are the best two, but all 4 exhibited the same behavior. You'll notice how both bottom corners are noticeably brighter than the top corners, and similarly, both bottom corners on both lenses are sharper than their top corner counterparts. I was initially concerned with decentering and sharpness, and I hadn't really noticed how uneven the vignetting was until I reviewed images I took over the weekend.
Regardless, it appears that there are plenty of sharp copies out there, so considering how phenomenal good copies are, I'm just going to keep trying.
May 04, 2021 at 11:27 PM
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chiron wrote:
That is remarkable. I had such a different experience. I compared three copies and all were excellent and were very similar in performance, almost indistinguishable by my means of testing. My conclusion was that copy variation is very low with this lens.
I have never come across a complaint of uneven vignetting before. Do you have any speculation about what assembly error could cause uneven vignetting without causing uneven sharpness as well? I assume that somehow the image circle would have to be not centered on the sensor, for example if the lens barrel were curved or if the lens cell were tilted inside the barrel or were not centered in the barrel. But any of those seem certain to play havoc with sharpness as well as with the mechanical functioning of the lens.
I may just have incredibly bad luck. I feel bad mucking up Fred's review thread with my struggles to find a good copy cause it seems like most are receiving excellent copies, for which I'm very jealous, so this will be the last I'll post about it. I have 3 more copies on order just to hedge my bets one will be good. To answer your question, I have no idea, but I would imagine both the uneven sharpness and vignetting are caused by the same misalignment. Of the 4 lenses I tested, here are the best two, but all 4 exhibited the same behavior. You'll notice how both bottom corners are noticeably brighter than the top corners, and similarly, both bottom corners on both lenses are sharper than their top corner counterparts. I was initially concerned with decentering and sharpness, and I hadn't really noticed how uneven the vignetting was until I reviewed images I took over the weekend.
Regardless, it appears that there are plenty of sharp copies out there, so considering how phenomenal good copies are, I'm just going to keep trying.
May 04, 2021 at 06:37 PM
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