Canon EF 24 mm f/2.8 IS USM review - Coma, astigmatism and bokeh

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Canon EF 24 mm f/2.8 IS USM

17 October 2012

Arkadiusz Olech

7. Coma, astigmatism and bokeh

As long as you work on the APS-C sensor the coma shouldn’t be problematic at all. The situation changes drastically when you pass to the full frame. In that case the coma is really huge, visible even on stopping down to f/4.0.

Canon EF 24 mm f/2.8 IS USM - Coma, astigmatism and bokeh

The astigmatism correction looks much better. An average difference between horizontal and vertical MTF50 function values amounted to just 2.9% which is a very good result.

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One glance at the defocused images of a diode and you can notice a huge difference between the APS-C sensor and full frame. On the smaller detector the diode image in the frame corner looks the same as in the centre already by f/4.0. Apart from that the light in circles is very evenly spread. In the case of full frame corners the image is significantly distorted and you see a distinct lightness gradation so the blur in the frame corners can be sometimes less pleasant to the eye. When moving closer to the APS-C sensor corners the situation should improve, though.