The center crop shows that my lens did not focus properly. I chose to keep this as an example of the difference in sharpness that the tiniest of mismatch will produce, even at a focal length where the depth of field is huge. I have tried to use the micro AF adjust function to try to correct the problem, but I have not been very successful. It seems that AF is not 100% accurate at 20mm on that lens. The CZ appears to be better in this respect, probably because of the USM AF system.
However, this problem is not really relevant in usual photographic practice. One does not shoot landscapes at f/2.8.
Center performance, first CZ 16-35, then Minolta 20mm, both at f/2.8.
And corner performance, first CZ 16-35, then Minolta 20mm, both at f/2.8:
