Sigma 180 mm f/2.8 APO Macro EX DG OS HSM
7. Coma, astigmatism and bokeh
The astigmatism correction can be described in a similar manner. An average difference between horizontal and vertical MTF50 function values amounted to just 3.5% which is a very good result.
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When it comes to the appearance of defocused light points here we also don’t have any major reservations. At the maximum relative aperture everything is as it should be. The light spread in the circles is very even; after stopping down you can notice a rim but it is nothing you should seriously worry about. Still, we are a little less impressed by the fact that even by f/5.6 the image is still far from a circle.
