Sigma A 30 mm f/1.4 DC HSM review - Coma, astigmatism and bokeh

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Sigma A 30 mm f/1.4 DC HSM

15 April 2013

Arkadiusz Olech

7. Coma, astigmatism and bokeh

When it comes to the coma, there is hardly any improvement compared to the lens’s predecessor. The coma makes itself felt at the maximum relative aperture and also after the stopping down to f/2.0. The Sigma’s result in this category is very similar to that of the Nikkor 1.8/35G and a bit better than that of the Sony DT 1.8/35.

Sigma A 30 mm f/1.4 DC HSM - Coma, astigmatism and bokeh

One of the most serious problems of the previous model of the Sigma was the astigmatism which, next to the chromatic aberration, was the main optical aberration limiting the performance of the lens. We counted on a significant improvement in this category and we weren’t disappointed. The average difference between vertical and horizontal MTF50 function values amounts to 8.4%. It is perhaps not a perfect result but certainly much better than that of the predecessor. What’s more, in the new Sigma the influence of that aberration can be noticed only by f/1.4 and f/2.0. In the case of the previous Sigma model its influence reached even f/5.6.

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The appearance of defocused light points is beyond reproach. The light spread is even, the concentric rings are very fine and with just small differences in brightness. It’s worth emphasizing that even by f/2.0 the light circle in the corner is not very distorted, looking more like that you get in the centre. All of it together indicates that blur areas, provided by the tested lens can be pleasing to the eye.