Sigma A 14-24 mm f/2.8 DG DN review - Coma, astigmatism and bokeh

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Sigma A 14-24 mm f/2.8 DG DN

23 December 2019

Arkadiusz Olech

7. Coma, astigmatism and bokeh

On the APS-C sensor you can't notice any coma almost at all. In corners of full frame that aberration is clearly visible across the focal range but it seems the least pronounced at 14 mm. Still it would be difficult to call it high even at longer focal lengths so we don't have any serious reservations in this category. However, we think the reflex camera model corrected coma a tad better.

Center, 14 mm, f/2.8	Corner APS-C, 14 mm, f/2.8	Corner FF, 14 mm, f/2.8

Center, 19 mm, f/2.8	Corner APS-C, 19 mm, f/2.8	Corner FF, 19 mm, f/2.8

Center, 24 mm, f/2.8	Corner APS-C, 24 mm, f/2.8	Corner FF, 24 mm, f/2.8

Astigmatism, understood as an average difference between vertical and horizontal MTF50 function values, amounted to 4.6% and it is a low result. Still the reflex camera Sigma A 14-24 mm f/2.8 DG HSM once again fared a bit better because in its case we saw a result of 2.3%.

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Nice blurry areas in ultra wide angle lenses are rarely a priority so they are usually nothing you can call 'pleasing to the eye'. Because of oversharpening visible in frame corners, an effect forced by rectilinear projection, circles of light are elongated and they meet in the frame centre, creating a not exactly nice impression. Still it is more a feature characteristic of this type of lens, not a flaw – without that oversharpening you wouldn't get such wide angles of view or distortion would have to be much higher. You get nothing for nothing and you cannot cheat the laws of physics. In the case of the tested mirrorless model the circles themselves don't look so bad, quite the contrary, their middle is rather smooth especially when you think of all these aspherical elements inside the lens. The only thing that sticks out is the distinctly accentuated rim.

Center, 24 mm, f/2.8	Corner APS-C, 24 mm, f/2.8	Corner FF, 24 mm, f/2.8

Center, 24 mm, f/4.0	Corner APS-C, 24 mm, f/4.0	Corner FF, 24 mm, f/4.0

Center, 24 mm, f/5.6	Corner APS-C, 24 mm, f/5.6	Corner FF, 24 mm, f/5.6