LensTip.com

Lens review

Pentax smc FA 31 mm f/1.8 AL

14 October 2011
Arkadiusz Olech

7. Coma, astigmatism and bokeh

The situation you can see in the crops below we don’t like at all. In a full frame lens coma on a smaller APS-C sensor should be corrected very well. In the case of the Pentax 1.8/31 the coma is very pronounced, though.

Pentax smc FA 31 mm f/1.8 AL - Coma, astigmatism and bokeh

When it comes to the astigmatism the performance is much better. Its average value amounts to 6.5% so this aberration is not bothersome.


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Photos below show off focus point-like diode images. The spread of light is more or less even but, as you stop down, more and more distinct concentric borders appear, especially visible near the edge of the light circle.

Pentax smc FA 31 mm f/1.8 AL - Coma, astigmatism and bokeh