I received my fourth copy today, and it is the best one I've seen, with minimal decentering but some minor swing over the whole range that is masked by F4-5.6. After applying some temporary shims on the camera's mount it now looks fairly symmetric on my A7r4 even at 2.8, especially between 14 and 24mm. I may be able to improve 12mm symmetry with a bit more work, but even without that, when stopped down to 7.1 where I shoot focus-stacked landscapes it looks great. So I think I will call it quits with this copy.
In agreement with other reports, I clearly see best performance in the middle of the zoom range around 18mm, where it's phenomenally sharp all the way into the corners even wide open. Corner symmetry is also optimal at that focal length (nearly perfect), and worst at 12mm as also seen by several other FM members.
At 14mm I saw less corner asymmetry on average for the 4 Sigma 14-24 DG DN samples I tried last year than for these 4 GMs. But at 18mm it's been the other way around. At 24mm I didn't see a clear difference with these small numbers of lenses.
Sep 21, 2020 at 11:55 PM
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