Originally posted by lytrytyr If you're looking down obliquely on a flat scene,
focusing on the center,
field curvature may render the bottom corners sharp,
and the top corners soft.
Here is an image with a ZK 25/2.8 making use of that effect:
I don't take photos of brick walls to test for sharpness. I've tested the corners with CDAF, and no matter what I did. No matter how I focused or how far away, the top two corners were not sharp. I've tested it that way, since I'm aware of field curvature. Apparently I would get that effect thanks to misaligned glued lens element or some such thing.
Next time I consider getting 14-15mm prime I will look at it again and try to find sharp copy.
Some examples of this lens, in the first photo it even has a bit of a toy lens look:
I've a lot more photos, to prove that I had really bad copy.