Canon EF 20 mm f/2.8 USM
7. Coma and astigmatism
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The coma in the tested lens is low but noticeable because an image of a diode is turned from a point into a comma in the frame corner. What’s interesting on stopping down by one stop we don’t see any decrease of this aberration.
The tested lens controls astigmatism very well for a change because the average difference between vertical and horizontal MTF50 function values in the frame centre amounts to only 3%.
