(multi-coated)

Vignetting = A- @ f/4.5, A elsewise
Distortion = slight to moderate pincushion

Average of two samples; OM-1 with mirror lockup
Aperture Center Corner
f/4.5    B-     B-/C+
f/5.6    B      B/B-
f/8      B/B-   B-/B
f/11     B+     B-/B
f/16     B/B+   B
f/22     B+     B+
f/32     B+     B
Notes: Moderate contrast.

OM-2000 with Bogen Telephoto Lens Support and mirror/aperture prefire
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     A-     A-
f/32     B      B
Notes: Moderately low contrast at f/32 and f/22, moderate contrast elsewise. Insignificant SQF differences between using a Bogen Telephoto Lens Support on a OM-2000 and the tripod collar on an OM-1.

OM-4T with mirror/aperture prefire
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+
f/32     B+     C+
Notes: Moderately high contrast at f/4.5; high contrast at f/5.6 to f/32. Different lens than above tests.

300mm f/4.5 Zuiko (multi-coated) with Olympus 1.4X Teleconverter

OM-1 with mirror lockup
Vignetting = A (none)
Distortion = none!
Aperture    Center Corner
f/4.5 (6.3) F+     D-
f/5.6 (8)   C      C
f/8 (11)    C-     C-
f/11 (16)   B-     C+
f/16 (22)   B      C+
f/22 (32)   B-     C
f/32 (45)   C+     C
Notes: Poor wide open performance makes focusing difficult; low contrast; remarkable lack of distortion and vignetting.

OM-4T with mirror and aperture prefire
Aperture    Center Corner
f/4.5 (6.3) C-     C-
f/5.6 (8)   C+     C+
f/8 (11)    B-     B-
f/11 (16)   B      B-
f/16 (22)   A-     B+
f/22 (32)   B+     B
f/32 (45)   B      B-
Notes: Different lens than above test. Moderately low contrast at f/4.5 (f/6.3 effective); moderate contrast at f/5.6, 8, and 32; high contrast at f/11 to 22.

300mm f/4.5 Zuiko (multi-coated) with Olympus 2X Teleconverter
OM-1 with mirror lockup
Vignetting = B+
Distortion = slight pincushion
Aperture   Center Corner
f/4.5 (9)  F+     F
f/5.6 (11) C-     D
f/8 (16)   C+     C+
f/11 (22)  B-     B-
f/16 (32)  C+     C+
f/22 (44)  C+     B-
f/32 (64)  C      C
Notes: Moderately low contrast.