Sigma 18-125 mm f/3.8-5.6 DC OS HSM
7. Coma and astigmatism
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As you can see from the clippings of the diode below, coma makes life a misery at shorter focal lengths and vanishes almost absolutely for the range of 70-125 mm. It’s very similar to Nikkor 18-105 mm VR and slightly better than Nikkor 18-135 mm and Sony 16-105 mm, where coma influenced the shape of the diode for longer focal lengths as well.
As far as astigmatism is concerned, we have no particular reasons to complain. It’s quite far from ideal, but 8% is a level definitely acceptable in this class appliance.
