(multi-coated)

OM-1 with mirror lockup (sample 1)

Vignetting = C
Distortion = slight barrel
Aperture Center Corner
f/2.0    B-     C+
f/2.8    B      C+
f/4      B+     B
f/5.6    B+     B+
f/8      A-     B+
f/11     A      A-
f/16     A      A-
Notes: Contrasty lens.

OM-4T with mirror and diaphragm prefire (sample 2)
Distortion: NA
Aperture Center Corner Vignetting Contrast
f/2      C      B-     B-         moderate
f/2.8    C+     B-     B          moderate
f/4      B+     B+     A-         high
f/5.6    A      A-     A          very high
f/8      A      A-     A          high
f/11     A      A-     A          mod. high
f/16     A-     A-     A          mod. high

OM-4 with mirror @and diaphragm prefire (sample 3 - minty)
Vignetting = B- @ f/2, A- @ f/2.8, A @ f/4
Distortion = slight barrel
Aperture Center Corner
f/2.0    A-     C
f/2.8    A      C+
f/4      A-     B-
f/5.6    A-     B
f/8      A      A
f/11     A-     A-
f/16     B+     B+
Notes: Moderately high contrast in center and moderately low in corner at f/2 and f/2.8; moderately high contrast in center and moderate in corner at f/4 and f/5.6; moderately high contrast in corner and center at f/8 to f/16.