(multi-coated)

OM-1 with mirror lockup

Vignetting = B- @ f/2, A- @ f/2.8, A @ f/4
Distortion = moderate barrel

Aperture Center Corner
f/2      C      C
f/2.8    B+     A-
f/4      B+     A-
f/5.6    B+     A-
f/8      A      A
f/11     A-     A-
f/16     A-     B+

Notes: Moderate contrast images with high resolution.

OM-4T with mirror and diaphragm prefire, different sample from above OM-1 test

Vignetting = B @ f/2, A- @ f/2.8, A thereafter
Distortion = none

Aperture Center Corner
f/2      C+     C-
f/2.8    B+     C
f/4      A-     B
f/5.6    B      B+
f/8      A-     A
f/11     A      A
f/16     A      A-

Notes: Moderately low contrast in center and low contrast in corners at f/2; moderate contrast in center and moderately low in corners at f/2.8; moderately high contrast in center and moderate contrast in corners at f/4; moderately high contrast in center and corners at f/16; high contrast in center and corners at f/11; very high contrast in center and corners at f/8.