(multi-coated)

50mm f/1.8 Zuiko (multi-coated, earlier MC variant)
OM-2000 with mirror and aperture prefire

Vignetting = C+ at f/1.8
Distortion = none

Aperture Center Corner
f/1.8    C      C
f/2.8    B-     C+
f/4      A-     A-
f/5.6    A+     A-
f/8      A+     A
f/11     A-     A-
f/16     B+     B

Notes: Extremely high contrast at f/5.6 to f/8, high contrast at f/4 and f/11, moderately high contrast at f/2 to f/2.8 and at f/16.

50mm f/1.8 Zuiko (multi-coated, late "Made in Japan" variant)
OM-1 with mirror lockup

Vignetting = B
Distortion = moderate barrel

Aperture Center Corner
f/1.8    C-     C
f/2.8    B-     B
f/4      B      B+
f/5.6    A-     A
f/8      A-     A
f/11     A+     A
f/16     A      A

Notes: Moderately high contrast and extremely high resolution.

OM-2S with mirror and auto diaphragm prefire, serial number 3694244, paired comparison with sample below to examine potential production variation; identical coating

Vignetting = C- @ f/1.8, A- @ f/2.8, A thereafter
Distortion = slight barrel

Aperture Center Corner
f/1.8    B      C
f/2.8    A-     B+
f/4      A+     A
f/5.6    A      A-
f/8      A      A-
f/11     A-     B+
f/16     B+     B

Notes: High contrast at f/1.8 to f/2.8 and f/11 to f/16, very highcontrast at f/4 to f/8.

OM-2S with mirror and auto diaphragm prefire, serial number 5235157, paired comparison with sample above to examine potential production variation; identical coating

Vignetting = C @ f/1.8, A- @ f/2.8, A thereafter
Distortion = slight barrel

Aperture Center Corner
f/1.8*   B      C-
f/1.8    B+     C
f/2.8    A      B-
f/4      A+     A-
f/5.6    A      A-
f/8      A      A-
f/11     A-     B+
f/16     A-     B+

Notes: Moderately high contrast at f/2.8 and f/8 to f/16, high contrast at f/1.8, very high contrast at f/4 to f/5.6. * = with an Olympus 1A filter that "passed" a vertical autocollimator test; lens was refocused after attaching the filter; no detectable contrast difference with and without filter.