Canon FD 85mm f/1.8 S.S.C. breech mount
Canon EF with mirror and diaphragm prefire

Vignetting = B @ f/1.8, A- @ f/2.8, A thereafter
Distortion = moderate pincushion

Aperture Center Corner
f/1.8    D+     C
f/2.8    C+     C+
f/4      B-     B-
f/5.6    B-     B
f/8      B      B
f/11     A-     B
f/16     B      C+

Note:
moderately low contrast at f/1.8, f/2.8 and f/16;
moderate contrast at f/4, f/5.6 and f/11;
moderately high at f/8.