Canon EF 50 mm f/1.8 STM review - Coma, astigmatism and bokeh

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Canon EF 50 mm f/1.8 STM

11 July 2015

Arkadiusz Olech

7. Coma, astigmatism and bokeh

The Canon EF 50 mm f/1.8 II dealt weakly with the coma and the new model seems to have even more problems in that category. The influence of that aberration is visible even in the corners of the APS-C sensor and in the corners of full frame the coma level is simply monstrous. In order to reduce it you have to close down the aperture by at least 2 EV - a serious problem indeed!

Center, f/1.8	Corner APS-C, f/1.8	Corner FF, f/1.8

Center, f/2.5	Corner APS-C, f/2.5	Corner FF, f/2.5

The astigmatism, understood as an average difference between horizontal and vertical MTF50 function values was 6.1%. It is a slight level and practically identical with the result of its predecessor which amounted to 6.2%.

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When it comes to the appearance of blurry areas the light spread in the circles hasn’t changed significantly and we still assess it very well. There is no trace of rims, onion rings or brightness loss on the edge. The increased number of aperture blades made the image more round, it is no longer as angular as that of the previous model.

Center, f/1.8	Corner APS-C, f/1.8	Corner FF, f/1.8

Center, f/2.5	Corner APS-C, f/2.5	Corner FF, f/2.5

Center, f/3.5	Corner APS-C, f/3.5	Corner FF, f/3.5