I've been playing with my adaptall x-250mm zooms. These are 1:1 pixel peeping crops to illustrate. All at 250mm. Focus point was (attempted) to be on the eye(s). Samsung NX20.
Z250: the big old 80-250mm, constant f3.8, clearly derived from the adaptamatic version given their similarity. A premium lens of its time..
F8.
This old zoom is sharp! But soft wide open at this focus range (200mm, near infinity was much better - link below), and even on apsc dslr there is usually noticeable IQ loss away from the image centre. F3.8:
Z250's successor, the QZ-825M (aka QZ-250M), 80-250mm f3.8-4.5. Also a 2 ring zoom, more compact, no tripod mount.
Again impressive stopped down. But if anything even softer than the Z250 wide open, and more noticeable fringing/CA evident, most specifically on other test shots I did.
Adaptall-2 75-250mm f3.8-4.5. there are two versions of this, I have the later 104A.
This lens gives the most consistent results, and it is comfortably superior wide open.
You can see the comparison at 200mm, all f-stops to f11, on my
castle turret test page here. The performance of the Z250 is impressively the best to my eyes on this test.