Canon FD 100mm f/2.8 pre-S.S.C. breech mount Canon F-1 w/ mirror and diaphragm prefire Vignetting: A- @ f/2.8, A thereafter Distortion: moderate pincushion Aperture Center Corner f/2.8 B+ B f/4 A- B+ f/5.6 A- A- f/8 A? A-? f/11 A- B+ f/16 B+ B+ f/22 B+ B Notes: provisional SQF grades at f/8 due to overexposure; moderately high contrast at f/2.8 and f/4; high contrast at f/5.6, f/22 and provisionally at f/8; very high contrast at f/11 and f/16.