Canon FD 20mm f/2.8 S.S.C.
Canon EF with mirror and aperture prefire

Vignetting = C @ f/2.8, B @ f/4, A- @ f/5.6, A thereafter
Distortion = waveform

Aperture Center Corner
f/2.8    B-     C+
f/4      B+     B
f/5.6    B+     A-
f/8      A-     B+
f/11     A-     A-
f/16     B+     B
f/22     B      B

Notes:
Moderately low contrast images at f/2.8;
moderate contrast images at f/4 and f/16 to f/22;
moderately high contrast images at f/5.6 and f/11;
high contrast images at f/8.