Pentax smc DA 15 mm f/4 ED AL Limited review - Coma, astigmatism and bokeh

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Pentax smc DA 15 mm f/4 ED AL Limited

16 August 2011

Arkadiusz Olech

7. Coma, astigmatism and bokeh

Coma is undoubtedly one of the more serious reasons why the image quality on the edge of the frame deteriorates so much. When the lens is wide open the coma level is really huge but fortunately it decreases significantly on stopping down to f/5.6. The crops below show it rather well.

Pentax smc DA 15 mm f/4 ED AL Limited - Coma, astigmatism and bokeh

When it comes to the astigmatism it doesn’t create any problems. Its value amounts to 3.7%, being exactly on the level appropriate for a solidly build and a quite slow “prime”.

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The crops below show off-focus images of a diode in the frame centre and in the frame corner. If you want to draw any conclusions from these photos concerning the bokeh of the lens, you are given a free hand – enjoy!