Canon FD 28mm f/2.8 S.C. breech mount Canon F-1 with mirror and diaphragm prefire Vignetting = B @ f/2.8, A- @ f/4, A thereafter Distortion = barrel Aperture Center Corner f/2.8 A- B f/4 A- B+ f/5.6 A- A- f/8 B+ A f/11 A- A- f/16 B B f/22 B+ B+ Note: high contrast at all apertures.