more 20-40 tests

angled view of test.  I centered my test image on
the brightly-colored recessed books in the middle.

A few more test-shots give comfort that this copy of the LimiZoom has minimal decentering if any, as test images look pretty symmetrical in appearance.  Colors and contrast are great, bokeh marvelous as advertised, and center sharpness is excellent.

Testing up close it's clear to me that field curvature is in play - at 20mm from a foot away, the center of an image looks great but not the sides.  I convinced myself of the issue by shooting a bookshelf with books at the edges pulled forward; by doing this I can have both center and edge books in focus.  Considering this only appears when shooting really close + wide and shooting a flat-plane surface, it is not a real-life kind of image for me; I'll let the Tamron 90/2.5 take care of those shots!