Sigma A 50 mm f/1.4 DG DN review - Coma, astigmatism and bokeh

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Sigma A 50 mm f/1.4 DG DN

3 April 2023

Maciej Latałło

7. Coma, astigmatism and bokeh

The Sigma A 50 mm f/1.4 DG DN doesn't have any serious problems with coma and fares in this category much better than its predecessor. In the corner of full frame diode images are just slightly deformed, an effect minimally lower than the one we observed in the case of the rival Sony lens. If we really wanted to pick holes in this performance we could only carp about the fact that coma appears very quickly. Slight diode image deformations are visible already in the corner of the APS-C sensor. Fortunately, further increase of that aberration, as you move away from the frame centre, is slow. As we wrote earlier, in the corners of full frame coma is kept firmly in check.

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

Astigmatism, understood as an average difference between horizontal and vertical MTF50 function values, amounted to 4.1%. It is a very low level, not giving you any reasons to worry. In this category the new Sony model fares slightly better than its predecessor and also slightly weaker than the Sony FE 50 mm f/1.4 GM.

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Out-of-focus images seem to be quite nice. Light spread in the circles seems to be even and onion-ring bokeh, despite apherical elements in the system, is just slightly visible but it can be noticed if you look carefully. The new model fares weaker than its predecessor but you have to remember that the new Sigma lens features more aspherical elements so its task was more difficult.

Mechanical vignetting is a noticeable problem, though – it remains visible even on stopping down the aperture by 2 EV. It's a big regress compared to the model designed for reflex cameras – its mechanical vignetting disappeared already by f/2.0. For a change the new Sigma seems to fare a tad better than the smaller Sony model.

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