(multi-coated)

@ 50mm setting

OM-1 with mirror lockup and Bogen Telephoto Lens Support, sample 1
Vignetting = B+ @ f/5, A- @ f/8
Distortion = pronounced barrel
Aperture Center Corner
f/5      B+     B
f/8      A-     B+
f/11     A-     A-
f/16     A      A-
f/22     A-     B+
f/32     B+     B
Notes: Moderate contrast at f/5 and f/32. High contrast at f/11 and f/16.

OM-4T with mirror and diaphragm prefire, sample 2
Vignetting = B @ f/5, A- @ f/8, A thereafter
Distortion = slight barrel
Aperture Center Corner
f/5      B-     B
f/8      B      B
f/11     B      B
f/16     B+     B+
f/22     B+     B+
f/32     B-     C+
Notes: Low contrast at f/32, moderate contrast at f/5-11 and f/22, moderately high contrast at f/16.

@ 100mm setting

OM-1 with mirror lockup and Bogen Telephoto Lens Support, sample 1
Vignetting = A- @ f/5, A @ f/8
Distortion = moderate pincushion
Aperture Center Corner
f/5      B      B-
f/8      B+     B+
f/11     B+     B+
f/16     A-     B+
f/22     A-     B+
f/32     B+     B-
Notes: Moderately high contrast at f/11 and f/16.

OM-4T with mirror and diaphragm prefire, sample 2
Vignetting = B+ @ f/5,- A @ f/8, A thereafter
Distortion = slight pincushion
Aperture Center Corner
f/5      B-     B-
f/8      B      B
f/11     B+     B+
f/16     B+     B+
f/22     B      B
f/32     B-     B-
Notes: Low contrast at f/32, moderately low contrast at f/5, moderate contrast at f/8-22.

@ 200mm setting

OM-1 with mirror lockup and Bogen Telephoto Lens Support, sample 1
Vignetting = B @ f/5, B+ @ f/8, A @ f/11
Distortion = moderate pincushion
Aperture Center Corner
f/5      C-     C-
f/8      C+     C
f/11     B-     B-
f/16     B+     B
f/22     B      B
f/32     B      B
Notes: Moderately low contrast with poor resolution at wider apertures. Dip in SQF grades (versus 250mm) perhaps due to movements from the automatic diaphram mechanism.

@ 250mm setting

OM-1 with mirror lockup and Bogen Telephoto Lens Support, sample 1
Vignetting = B- @ f/5, A- @ f/8, A @ f/11
Distortion = pronounced pincushion
Aperture Center Corner
f/5      C+     B-
f/8      B+     B
f/11     A-     B
f/16     A      B+
f/22     B+     B
f/32     B      B-
Notes: Relatively easy to focus with 1-14 screen, despite the f/5 aperture. Not well balanced for tripod use. Probably demands use of a lens support to avoid lens movement during picture taking.

OM-4T with mirror and diaphragm prefire, sample 2
Vignetting = A- @ f/5, A thereafter
Distortion = moderate pincushion
Aperture Center Corner
f/5      B+     B
f/8      B      B
f/11     B+     B
f/16     B+     B
f/22     B      B-
f/32     B-     B-
Notes: Moderatly low contrast at f/32, moderate contrast at f/8-22, moderately high contrast at f/5.