Canon FD 50mm f/1.4 breech mount (pre-S.S.C.)
Canon F-1 with mirror and diaphragm prefire

Vignetting = C+ @ f/1.4, B @ f/2, A- @ f/2.8, A thereafter
Distortion = slight barrel to none

Aperture Center Corner
f/1.4    B-     C
f/2      B+     C
f/2.8    A-     B
f/4      A-     A-
f/5.6    A-     A
f/8      A-     A
f/11     A-     A
f/16     B+     A-

Notes:
moderately low contrast at f/1.4;
moderate high center contrast and moderately low corner contrast at f/2;
moderately high contrast at f/2.8 through f/16.