Sigma 30 mm f/2.8 EX DN review - Coma, astigmatism and bokeh

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Sigma 30 mm f/2.8 EX DN

29 March 2012

Arkadiusz Olech

7. Coma, astigmatism and bokeh

On a small Micro 4/3 sensor the coma is corrected very well. The image of a diode positioned in the corner of the frame is only slightly distorted and in most cases this aberration won’t be bothersome at all.

Sigma 30 mm f/2.8 EX DN - Coma, astigmatism and bokeh

The situation with astigmatism looks a bit more serious. At the maximum relative aperture it is really noticeable, reaching 13%. It decreases a bit on stopping down the aperture to f/4.0 getting to about 10% there. It becomes imperceptible only by f/5.6.

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The images of defocused diode, shown below, are hardly perfect too. The light is spread out in distinct ring shapes which suggest some mild problems with the spherical aberration correction.