(multi-coated)

OM-1 with mirror lockup

Vignetting = B+
Distortion = none

Aperture Center Corner
f/3.5    C+     C-
f/5.6    A-     B+
f/8      A-     A-
f/11     A-     A-
f/16     B+     B
f/22     B      B-

Notes: Moderately high contrast image which softens beginning at f/11 and is distinctly softer at f/22, thus yielding best performance at f/8; soft wide open; classic performance curve across aperture range.

OM-4 with mirror and aperture prefire

Vignetting = A- @ f/3.5, A @ f/5.6
Distortion = very slight pincushion

Aperture Center Corner
f/3.5    B-     C
f/5.6    A      A
f/8      A+     A
f/11     A      A
f/16     A-     A-
f/22     B+     B+

Notes: Moderately high contrast, except high at f/8. Different lens sample than the OM-1 test above.