Here is an interesting contrast. I've included tests with the Olympus 2X
Teleconverter on the 90mm f/2 Zuiko Macro (a non-recommended combo which
requires an elimination of a tab off the back end of the 90) and the Tamron SP
2X Teleconverter on the Tamron SP f/2.5 macro.
Do you get what you pay for? Comments follow each chart:
Tamron SP 90mm f/2.5 Macro
Vignetting = A-
Distortion = slight pincushion
Aperture Center Corner
2.5 C- C
4 B- B
5.6 B B
8 B+ B+
11 A- A-
16 A- B+
22 B B
32 B- B-
Note: good detail in low contrast subject matter; at f/11 = slightly higher
image rendering performance at 1/3rd out from center of image than with 90mm
f/2 Zuiko.
Tamron SP 90mm f/2.5 Macro with Tamron SP 2X teleconverter
Vignetting = A
Distortion = slight pincushion
Aperture Center Corner
2.5 (5) ? ? (overexposed test shot)
4 (11) B- C-
5.6 (11) B C
8 (16) B C+
11 (22) B B-
16 (32) B- B-
22 (44) C C
32 (64) D- D-
Note: Remarkable contrast; clearly diffraction limited stopped down; little
quality loss in center of image at wider apertures.
90mm f/2.0 Zuiko Macro (multi-coated)
Vignetting = A-
Distortion = None
Aperture Center Corner
f/2 C B-
f/2.8 B- B-
f/4 B+ B
f/5.6 A- B
f/8 A A-
f/11 A A-
f/16 A- B+
f/22 B B-
Note: Image details in corners slightly lower than 50mm macros at optimum
apertures; delineation of low contrast details slightly inferior in center of
picture to 50mm f/3.5 Macro at optimum aperture; resolution of high contrast
details same as 50mm f/2 at optimum apertures; noticeably diffraction limited
at f/16.
90mm f/2.0 Zuiko Macro (multi-coated) with Olympus 2X Teleconverter
Vignetting = B+
Distortion = slight pincushion
Aperture Center Corner
f/2 (4) Unknown* C?* (* = overexposed test shots)
f/2.8 (5.6) C?* C?*
f/4 (8) C- C-
f/5.6 (11) C C-
f/8 (16) C+ C
f/11 (22) B- C
f/16 (32) C+ C
f/22 (45) C+ D+
Note: A non-recommended combination which requires modification of the 90mm
Macro to accomplish.
Detecting differences between the various 50mm and 90mm macros is mind
boggling! Remember that significant differences only occur across a full
letter grade. And it all depends on what part of a picture one is examining.
The ringer here might be ease of focusing. The 90mm f/2 Zuiko wins hands down
when used with a 1-8 screen.
Gary Reese
Las Vegas, NV
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