(multi-coated) Vignetting = C @ f/2, A- @ f/2.8, A @ f/5.6 Distortion = none OM-4 w/ mirror and aperture prefire Aperture Center Corner f/2 A B+ f/2.8 A+ A- f/4 A+ A f/5.6 A+ A+ f/8 A A- f/11 A- A- f/16 A- A- f/22 A- B+ Notes: Extremely high contrast and resolving power at all apertures with only a minor loss in the corners at f/2 and f/22. Strong vignetting at f/2, requiring exposure compensation for critical work. Probably the best overall image quality of any OM System Zuiko lens made. Brillant images with f/5.6 showing corner to corner clarity unsurpassed by any Zuiko tested. OM-1n with mirror lock-up Aperture Center Corner f/2 D C f/2.8 D+ C f/4 C C+ f/5.6 B- B- f/8 B- B- f/11 B+ B f/16 C+ C f/22 B- B Notes: Combination of vibrations from the auto diaphram mechanism and the horizontally traveling shutter of the OM-1n results in significant image deterioration, despite secure tripod mounting of the lens bracket. Note that differences between this test and the one above with the OM-4 are significant at the 1/3 grade level based on side by side comparisons. Test conditions were identical and I used the same lens. 250mm f/2 Zuiko with Olympus 1.4x teleconverter (both multi-coated) OM-4 w/ mirror and aperture prefire Vignetting = C+ @ f/2, A- @ f/2.8 Distortion = moderate pincushion Aperture Center Corner f/2 (2.8) A- B f/2.8 (4) A B+ f/4 (5.6) A A- f/5.6 (8) A A- f/8 (11) B+ B f/11 (16) B+ B f/16 (22) B+ B- f/22 (32) B- C+ Notes: Moderate to moderately high contrast. Exceptional wide open performance. 250mm f/2 Zuiko with Olympus 2X teleconverter (both multi-coated) OM-4T with mirror and aperture prefire and additional monopod support on camera Vignetting = B- @f/2.8 (5.6), A- @f/4 (8) and f/5.6 (11), A thereafter Distortion = very slight waveforming with no tendency Aperture* Center Corner f/2.8 (5.6) C+ C- f/4 (8) C+ C f/5.6 (11) C+ C f/8 (16) C+ C f/11(22) B- B- f/16 (32) B- B- f/22 (44) B B f/32 (64) C C- Notes: *Effective aperture in parenthesis (). Not an Olympus recommended combination. Moderately high contrast images atf/2.8 (5.6),f/4 (8), then f/11 (22) throughf/32 (64); high contrast images at f/5.6 (11) & f/8 (16).