Canon FD 35mm f/2.8 bayonet mount Canon EF with mirror and diaphragm prefire Vignetting = B- @ f/2.8, A- @ f/4 & f/5.6, A thereafter Distortion = barrel Aperture Center Corner f/2.8 B+ B f/4 A- B+ f/5.6 A A f/8 A- A- f/11 B+ B+ f/16 B B f/22 B- B- Note: high contrast at f/4 and f/11 through f/22; very high contrast at f/5.6 to f/8; moderately high contrast at f/2.8.