Sigma A 28 mm f/1.4 DG HSM review - Coma, astigmatism and bokeh

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Sigma A 28 mm f/1.4 DG HSM

21 January 2019

Maciej Latałło

7. Coma, astigmatism and bokeh

Full frame 1.4/28 lenses, tested by us so far, have never managed to correct coma in a perfect way - it was quite visible even in the case of the expensive Otus. The Sigma A 1.4/28 in the corners of full frame is not free of that aberration either but the images of point-like source of light seem to be slightly better than the respective images produced by the Otus and the Nikkor AF-S 1.4/28. In this category, despite the lack of ideal performance, the Sigma should be praised anyway.

Center, f/1.4	Corner APS-C, f/1.4	Corner FF, f/1.4

Center, f/2.0	Corner APS-C, f/2.0	Corner FF, f/2.0

When it comes to astigmatism, understood as an average difference between horizontal and vertical MTF50 function values, we don’t have the slightest reservations. The value, measured by us, amounted to 2.7% which means you don’t have to worry about this aberration at all. In this category the Sigma once again prevails over its rivals in a decisive manner – a round of applause!

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For a wide angle lens the appearance of out-of-focus areas is very nice indeed, with even light spread in the circles, without any local extreme points. If you examine these circles in the 1:1 scale you can notice a very delicately accented onion rings bokeh, most likely linked to aspherical elements of the lens. Still that effect is not distinct and you really have to look carefully in order to notice it. It’s also worth adding that mechanical vignetting makes itself felt rather strongly at the maximum relative aperture.

Center, f/1.4	Corner APS-C, f/1.4	Corner FF, f/1.4

Center, f/2.0	Corner APS-C, f/2.0	Corner FF, f/2.0

Center, f/2.8	Corner APS-C, f/2.8	Corner FF, f/2.8