Sigma A 18-35 mm f/1.8 DC HSM review - Autofocus

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Sigma A 18-35 mm f/1.8 DC HSM

18 June 2013

Arkadiusz Olech

10. Autofocus

The Sigma A 18-35 mm f/1.8 DC HSM, as its name indicates, is equipped with an ultrasonic autofocus motor called Hyper Sonic Motor. The work of the mechanism is, in fact, noiseless but far from fast. On the EOS 50D running through the whole distance range takes about one second which is not impressive. To defend the Sigma a bit you have to say that it has a lot to cover, its minimum focus distance being really short. It would be difficult to find a lens which focuses from a shorter distance among fast 17-55 mm zoom lenses designed for smaller sensors.

When it comes to the accuracy of the autofocus, our assessment is very positive. The number of misses in studio conditions reached less than 4% which is a very good result. What’s interesting, most of these misses were registered at 18 mm.

We didn’t notice any back or front focus tendencies and that result didn’t change with the zooming. You can see it in photos below where, both at 24 mm focal length and at 35 mm the depth of fields encompasses nicely the middle of the scale. In order to be meticulous it is worth adding that the 18 mm focal length diverges from this trend. In that case, in order to get the sharpest images possible we had to microcalibrate the lens by -2 units. The difference was visible in measurements but in real life photos it would be difficult to notice.

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