(multi-coated)

OM-1 with mirror lockup

Vignetting = C @ f/2, B @ f/2.8
Distortion = pronounced waveform
Aperture Center Corner
f/2      C-     D-
f/2.8    B      C
f/4      B+     B
f/5.6    A      B+
f/8      A      A-
f/11     B+     A
f/16     B      B
Notes: Easy to focus due to bright viewfinder image. Lens hood selection critical since vignetting not predictable in viewfinder. Very contrasty at f/5.6, contrasty at other apertures.

OM-4T with mirror and aperture prefire
Vignetting = D @ f/2, B- @ f/2.8, A- @ f/4 and thereafter
Distortion = moderate waveforming with strong barrel tendency
Aperture Center Corner
f/2      C+     C
f/2.8    B-     C+
f/4      B+     B
f/5.6    A-     B+
f/8      B+     A-
f/11     B+     A-
f/16     B      B+
Notes: Moderately low contrast at f/2, moderate contrast at f/2.8,
moderately high contrast at f/11 and high contrast at f/4 to f/8.