Vivitar Series 1 200mm f/3.0
OM-1 with mirror lockup
Vignetting = B
Distortion = slight pincushion
Aperture Center Corner
f/3.0    D      D+
f/4      C      C
f/5.6    B-     B-
f/8      B      B
f/11     B+     B
f/16     A-     A-
f/22     B+     B+
Notes: Moderately high contrast @ f/8, but moderately low contrast wide open.