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Lens review

Canon EF 8-15 mm f/4 L Fisheye USM

11 August 2011
Szymon Starczewski

7. Coma, astigmatism and bokeh

When you use an APS-C sensor camera, the coma shouldn’t be bothersome almost at all. On full frame, at the shortest focal length, this aberration’s level is also rather slight. It increases at longer focal lengths but remains still acceptable.

Canon EF 8-15 mm f/4 L Fisheye USM - Coma, astigmatism and bokeh

The assessment of astigmatism in fisheye lenses is always burdened with a lot of error. Because of image deformations the resolution measurement fields in the frame centre are moved much further away from the centre than in typical rectilinear lenses. Due to that fact the result we get is higher than in reality. Taking into account the fact that the value we got was 3.5% and that it constitutes rather the upper limit of the astigmatism, we can say this aberration is corrected by the Canon 8-15 mm in a perfect way.

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The huge depth of field you get in fisheye lenses means we not often deal with big areas of fuzziness. They are the easiest to spot at 15 mm focal length so, to assess the bokeh, we present unfocused photos of a diode taken at that focal value exactly.

Canon EF 8-15 mm f/4 L Fisheye USM - Coma, astigmatism and bokeh