Sigma C 45 mm f/2.8 DG DN review - Coma, astigmatism and bokeh

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Sigma C 45 mm f/2.8 DG DN

28 February 2020

Maciej Latałło

7. Coma, astigmatism and bokeh

Standard lenses, especially these older ones, don't have good experience concerning coma correction. In the case of the Sigma 2.8/45 we didn't know what to expect because these coma-related problems concerns most often double gauss, fast f/1.4-1.8 lenses and here you deal with f/2.8 aperture and a more optically complex system. The Sigma proved, though, that even slower constructions can experience a lot of difficulties in this category. Coma in the corners of full frame is distinct – you can notice it even after stopping down the lens by 1 EV.

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

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

Astigmatism, understood as average difference between horizontal and vertical MTF50 function values, amounted to 5.2% and we consider it to be a low level. In this category we have no reservations, concerning the performance of the lens.

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The appearance of out-of-focus images is sensible but nothing more than that. Aspherical elements, present in the system,are the reason why you see a trace of onion ring bokeh and on stopping down you can notice a lighter rim. Mechanical vignetting also makes itself felt, visible without any problems by f/2.8 and f/4.0.

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

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