Sigma 50-150 mm f/2.8 APO EX DC OS HSM review - Coma, astigmatism and bokeh

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Sigma 50-150 mm f/2.8 APO EX DC OS HSM

13 February 2013

Arkadiusz Olech

7. Coma, astigmatism and bokeh

The Sigma 50–150 mm f/2.8 APO EX DC OS HSM corrects the coma in an exemplary way. At every focal length the shape of the diode, positioned in the very corner of the frame, doesn’t differ from its image in the frame centre. The crops below show it pretty clearly.

Sigma 50-150 mm f/2.8 APO EX DC OS HSM - Coma, astigmatism and bokeh

When it comes to the astigmatism the situation is a bit worse. The average difference between horizontal and vertical MTF50 function values amounts to 6%. It is a moderate result, not providing any reasons for complaining but it should be noted that the highest level of that aberration is registered at 150 mm. At shorter focal lengths it is practically imperceptible.

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The circles of light, created by defocusing point-like light images, don’t show anything unsettling. It is worth emphasizing that the image in the frame corner already by f/4.0 doesn’t differ at all from that you get in the frame centre. The intensity of the border, increasing on stopping down, is in fact the only thing that makes us worried a bit.