Sigma 18-250 mm f/3.5-6.3 DC OS HSM
7. Coma and astigmatism
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As you can notice in the pictures below, at shorter focal lengths the coma is corrected well. When we pass to longer focal lengths that aberration increases slightly. It seems to be the highest near 100 mm but even there its level is not especially high.
The astigmatism won’t be a problem for a change. Its average value amounts to 4.3% which is low. If you look at particular focal lengths you can notice that this aberration reaches its peak near 120 mm (being 7% there) so exactly in the place where we observed the biggest resolution decrease on the frame edge.
