Tamron 70-210mm f/3.5
OM-4T with mirror and diaphragm prefire

@ 70mm
Distortion: pronounced barrel
Aperture Center Corner Vignetting Contrast
f/3.5    B      B      B+         medium
f/5.6    A-     B+     A          medium
f/8      A      A-     A          medium
f/11     A-     A-     A          medium
f/16     A      A-     A          medium
f/22     A-     B      A          medium
f/32     B      B      A          medium

@ 120mm
Distortion: none
Aperture Center Corner Vignetting Contrast
f/3.5    B-     C      B          medium
f/5.6    B+     B-     A          medium
f/8      B+     B      A          medium
f/11     A-     A-     A          medium
f/16     B+     B+     A          medium low
f/22     B      B      A          medium low
f/32     B-     B-     A          medium low

@ 210mm
Distortion: pronounced pincushion
Aperture Center Corner Vignetting Contrast
f/3.5    B-     B-     B          medium
f/5.6    A-     B-     A          medium low
f/8      B-     B-     A          medium low
f/11     B      B-     A          low
f/16     B+     B      A          low
f/22     B      B-     A          low
f/32     B-     C+     A          low

Tamron 70-210mm f/3.5 with Tamron SP 2X Teleconverter
OM-4T with mirror and diaphragm prefire

@ 420mm

Distortion: not determined
Aperture   Center Corner Vignetting Contrast
f/3.5 (7)  C*     D+*    B*?        very low
f/5.6 (11) C+     C-     A          low
f/8 (16)   C+     C+     A          low
f/11 (22)  B-     C+     A          medium low
f/16 (32)  B-     C+     A          low
f/22 (45)  C      C      A          low*
f/32 (64)  Not determined
Notes: * = provisional grade, overexposed slide. Extremely difficult to focus, even with a 2-4 screen.