Canon EF 28 mm f/1.8 USM review - Coma and astigmatism

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Canon EF 28 mm f/1.8 USM

6 July 2010

Arkadiusz Olech

7. Coma and astigmatism

The Canon EF 28 mm f/1.8 USM can be quoted as a textbook example of coma. The change of the point source of light is really impressing. At the maximum aperture the coma is clearly visible even in the APS-C sensor’s corner and in the corner of the full frame sensor it becomes simply monstrous. The situation improves swiftly on stopping down the aperture by one stop. The APS-C corner coma stops being bothersome then but in the full frame corner it remains still huge.

The rival Sigma 1.8/28 had also quite big coma but it wasn’t as big as in the case of the Canon.

Canon EF 28 mm f/1.8 USM - Coma and astigmatism

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The astigmatism is corrected a lot better than the coma but it is still far from perfect. The average difference between horizontal and vertical MTF50 function values amounted to 13% - a medium result which is a bit better than 16% we got in the case of the Sigma 1.8/28.