Sigma S 500 mm f/4 DG OS HSM review - Coma, astigmatism and bokeh

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Sigma S 500 mm f/4 DG OS HSM

5 September 2017

Arkadiusz Olech

7. Coma, astigmatism and bokeh

If you changed at random the layout of those thumbnails you see below, the results would remain the same – this is the proof how good the Sigma’s coma correction is. The image of a diode in the frame centre is practically the same as its image in the very corner of full frame. It means the comatic deformations and other effects connected to deformation of light points on the edge of the frame are negligible.

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

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

Astigmatism, understood as an average difference between horizontal and vertical MTF50 function values, amounted to just 1.1%. It is a very low result so the lens corrects that aberration very well.

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When it comes to the appearance of out-of-focus areas we almost have no reservations either. The spread of light in the circles is very even, without any local extreme points. The rim on the very edge is the only slightly accentuated area. You can also notice some truncation of circles connected to mechanical vignetting.

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

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

Center, f/8.0	Corner APS-C, f/8.0	Corner FF, f/8.0