Tamron SP AF 90 mm f/2.8 Di Macro
7. Coma and astigmatism
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Even at the maximum aperture, coma in the tested Tamron is at a small level. Stopping down to f/4.0 eliminates the problem completely.
It is similar with astigmatism. The average value of the difference between vertical and horizontal values of the MTF50 function measured in the centre of the frame reached slightly less than 6%, which must be recognised as a very good result. It must be also added that astigmatism is noticeable only with the f/2.8 stop. Stopping down decreases this fault to the difficult to notice level.
