(multi-coated) OM-1 with mirror lockup Vignetting = A- at f/2.8 Distortion = none Aperture Center Corner f/2.8 B- B- f/4 B B f/5.6 B+ B+ f/8 A- B+ f/11 A- A- f/16 B+ B f/22 B+ B Notes: Contrast loss at f/16 and f/22. No apparent contrast difference versus single-coated version, but sharper overall. OM-4T with mirror and diaphragm prefire Vignetting = A- at f/2.8, A thereafter Distortion = slight pincushion (none?) Aperture Center Corner f/2.8* D C f/2.8 C- B- f/4 B B f/5.6 B+ B+ f/8 A- B+ f/11 A- A- f/16 B+ B f/22 B+ B Notes: * = with a Canon 1A filter, which exhibits low contrast. Moderately low contrast at f/2.8 without filter, as well as f/4 and f/16-22, moderate contrast at f/8-11, moderately high contrast at f/5.6.