(multi-coated, serial number higher than 500,000)

OM-4T with mirror and diaphragm prefire

@ 35mm setting
Vignetting = B @ f/3.5, B+ @ f/5.6, A- @ f/8, A thereafter
Distortion = slight waveform with no tendency
Aperture Center Corner
f/3.5    B-     C
f/5.6    B      B-
f/8      B+     B-
f/11     B+     B
f/16     B+     B+
f/22     B      B
Notes: Moderately low contrast images atf/3.5 (perhaps due to
overexposure); moderately high at f/5.6 and f/22; high at f/8 to f/16. Focusing impossible with a 2-4 series focusing screen. Requires a biprism screen for ease of focusing.

@ 70mm setting
Vignetting = B @ f/4, A- @ f/5.6, A thereafter
Distortion = slight waveform with slight pincushion tendency
Aperture Center Corner
f/4.0    B-     B-
f/5.6    A-     B
f/8      A      A
f/11     B+     A-
f/16     B      B
f/22     B-     B-
Notes: Moderately high contrast images at f/4 and f/22; high contrast images at f/11 to f/16; very high contrast images at f/5.6 to f/8. Focusing difficult with a 2-4 series screen.

@ 105mm setting
Vignetting = B @ f/4, A- @ f/5.6, A thereafter
Distortion = moderate pincushion
Aperture Center Corner
f/4.5    B      B
f/5.6    B+     B
f/8      B      B+
f/11     A-     B+
f/16     B+     B
f/22     B-     B
Notes: Very high contrast images atf/4.5 (perhaps due to underexposure); high contrast images at all other apertures. Focusing difficult with a 2-4 series screen.