I've tried about 6 different adapters and 4 different Pentax 28's....while there may have been slight differences in the upper left corner, this adapter gives the best performance across the frame. The "better" adapters seem too thick. The cheaper ones seem to perform better, but then there's probably less adherence to tolerances so I can't rule that out. So far this is the best of the lenses and adapters.
One thing I will say is that I was focused a little short of infinity, and that may be aggravating that upper left corner. I will say that in other shots it's close in performance to the upper right. Although if there was any corner I've thought might be a little worse, that's the one.
-Tim
Tariq Gibran wrote:
Hey Tim. Just had a chance to check out the F5.6 and F8 examples and it looks like there is something going on with the Pentax in the top left corner. The Olympus looks noticeably sharper in that corner. It might be worthwhile to shoot a different subject with detail in the top right corner just to see if it's similarly soft (and rule out any adapter/ specific lens issue). I have not shot with my Pentax 28 in a while but I don't believe it's that soft at F8.