(coating not specified)

OM-4 with mirror and diaphragm prefire

@ 35mm setting
Vignetting = B+ @ f/3.6, A- @ f/5.6, A elsewise
Distortion = moderate barrel
Aperture Center Corner
f/3.6    B      B-
f/5.6    B+     B
f/8      B+     A-
f/11     A      A
f/16     A-     B+
f/22     B      B
Notes: Moderately high contrast at all apertures, including corners.

@ 50mm setting
Vignetting = A at all apertures
Distortion = slight pincushion
Aperture Center Corner
f/3.6    B+     B-
f/5.6    B+     A-
f/8      A-     A-
f/11     A-     A
f/16     B+     A-
f/22     B+     A-
Notes: Apparent high resolution at the expense of contrast. Moderate contrast at f/3.6; moderately high thereafter, except only moderate in corner till f/16.

@ 70mm setting
Vignetting = A- @ f/3.6 & f/5.6, A thereafter
Distortion = moderate pincushion
Aperture Center Corner
f/3.6    B+     B
f/5.6    A-     B+
f/8      A      A
f/11     A      A
f/16     A-     A-
f/22     B+     A-
Notes: Low corner contrast at f/3.6 & f/5.6; moderately low contrast in center at f/3.6 and moderate at f/5.6; moderate contrast corner and center at f/8 on. Excellent handling lens with effective zooming lens shade. Greatly benefits from using mirror and diaphragm prefire on a tripod. Primary differences from 35-80mm f/2.8 Zuiko is that it requires f/11 for optimum performance (vs. f/8) and isn't as useable wide open.