Tamron SP 28-105mm f/2.8 Aspherical LD (multi-coated)
OM-4T with mirror and diaphragm prefire

@ 28mm setting

Vignetting = C @ f/2.8; B @ f/4; A- @ f/5.6, f/8; A thereafter
Distortion = pronounced barrel
Aperture Center Corner Popular Photography SQF
f/2.8    C      C-     C
f/4      B-     B-     B
f/5.6    A-     B+     B+
f/8      A      A-     A
f/11     A+     A-     B+
f/16     A-     A-     B+
f/22     B+     B      C+
Notes: Moderate contrast at f/2; moderately high contrast at f/4, f/11 and f/22; high contrast at f/5.6, f/8 and f/16. Difficult to precisely focus at any aperture due to relatively poor performance wide open and an extremely short focusing collar travel (rotation). Popular Photography SQF grades are from the Feb. 1998 issue and are for 22x magnification.

@ 35mm setting
Vignetting = B+ @ f/2.8, A- @ f/4, A thereafter
Distortion = moderate waveform with no tendency
Aperture Center Corner
f/2.8    B      C+
f/4      B+     B
f/5.6    A-     A-
f/8      A      A-
f/11     A      B+
f/16     A-     B+
f/22     B+     B
Notes: Moderate contrast at f/2.8; high contrast at f.4 to f/22.

@ 50mm setting
Vignetting = B+ @ f/2.8, A thereafter
Distortion = slight waveform with slight pincushion tendency
Aperture Center Corner
f/2.8    D+     D
f/4      C+     C+
f/5.6    B+     A-
f/8      A-     A-
f/11     A-     A-
f/16     B+     B+
f/22     B      B
Notes: Low contrast at f/2.8; moderately low contrast at f/4; moderately high contrast at f/5.6, f/16 and f/22; high contrast at f/8 and f/11.

@ 70mm setting
Vignetting = B- @ f/2.8, B+ @ f/4, A thereafter
Distortion = slight waveform with moderate pincushion tendency
Aperture Center Corner Popular Photography SQF
f/2.8    C      C-     F
f/4      C+     B-     C
f/5.6    B      B+     B+
f/8      A-     B+     A
f/11     A      B+     A
f/16     B+     B     B+
f/22     B      B-    C+
Notes: Moderately low contrast at f/2.8; moderate contrast at f/4; moderately high contrast at f/16 and f/22; very high contrast at f/8 and f/11.

@ 85mm setting
Vignetting = B- @ f/2.8, A- @ f/4, A thereafter
Distortion = pronounced pincushion
Aperture Center Corner
f/2.8    C      C
f/4      B      B-
f/5.6    B+     B
f/8      A      A-
f/11     A      A-
f/16     B+     B+
f/22     B      B
Notes: Moderately low contrast at f/2.8; moderate contrast at f/4; moderately high contrast at f/16; high contrast at f/5.6 to f/11 and at f/22.

@ 105mm setting
Vignetting = C+ @ f/2.8, A- @ f/4, A thereafter
Distortion = moderate pincushion
Aperture Center Corner Popular Photography SQF
f/2.8    C      C      F
f/4      B-     C      B
f/5.6    B-     B-     B+
f/8      B      B      B+
f/11     B      B      B+
f/16     B-     B-     B
f/22     B      B      C+
Notes: Moderately low at f/2.8 to f/5.6 and f/11 to f/16, moderate contrast at f/8 and f/22. Possible overexposure at all apertures makes data provisional for this focal length.