Sigma 10-20 mm f/3.5 EX DC HSM
7. Coma and astigmatism
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Coma decreases noticeably with increasing focal length. At 10 mm the level of this aberration is too high, at 15 mm it’s medium and at 20 mm little. It’s probably coma that’s responsible for slightly lower results at the edge of the frame, at f/3.5 and the range 10-15 mm.
For a change, astigmatism is corrected perfectly. The mean difference between the horizontal and vertical MTF50 values amounted to mere 3.7%, which we consider a very good result.
