Sigma A 14 mm f/1.8 DG HSM review - Distortion

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Sigma A 14 mm f/1.8 DG HSM

14 July 2017

Arkadiusz Olech

6. Distortion

Let’s start this chapter from the performance of the rivals in the distortion category. The Samyang 14 mm f/2.8 ED AS IF UMC fared disastrously bad. In its case, already on the APS-C/DX that aberration reached a very high value of −5.44%. On full frame it was −7.21%, but, if not for distinct moustache distortion, it would be actually much closer to −10%.

The test of the Canon EF 14 mm f/2.8 USM II actually proved that, even with these parameters, you can correct distortion sensibly well and without help from its moustache version. On the smaller APS-C sensor this aberration level reached −1.23% and it was −3.18% on full frame.

The constructors of the Irix 2.4/15 optics took proper care of good distortion correction and with excellent results. On the smaller APS-C/DX sensor we noticed very low level of barrel distortion, amounting to −0.50%; it increased to −2.68% on full frame.

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As you see the differences in this category can be huge. The tested Sigma is much closer to good Irix results than to the Samyang disaster. On the small APS-C/DX sensor its distortion is almost imperceptible, amounting to just −0.24%. After passing to full frame it increases to −2.38%.Officially it’s a value even better than that of the Irix but in fact they are both interlocked, being on the borderline of margin of error.

It’s worth adding that, even though you can’t notice any moustache distortion its proper description in the case of the Sigma would need higher order expressions. Straight lines are bent here in a quite specific way and our measurements emphasize that fact. On the APS-C/DX sensor the distortion is practically zero, it starts to increase rather violently only later.