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Lens review

Sigma A 135 mm f/1.8 DG HSM

14 April 2017
Maciej Lata³³o

10. Autofocus

As its name indicates, the Sigma A 135 mm f/1.8 DG HSM was equipped with an ultrasonic autofocus motor called the Hyper Sonic Motor by the producer. The mechanism is practically noiseless. Still running through the whole distance range and confirming the focus takes about 0.8-0.9 of a second, nothing impressive. That time can be shortened to about 0.4 of a second after choosing a range from 1.5 meters to infinity among the positions available in the AF limiter.

In studio conditions, where we use mainly the central autofocus point, there were almost no problems with the accuracy of the mechanism, with the number of misses never exceeding 2%. Sample shots outside were a bit a different story as I used side points of autofocus quite often. I didn’t notice any big mistakes but, with a shallow depth of field by f/1.8-2.0, even a small slip-up might be annoying. From f/2.8 upwards everything returned to norm.

As you see in photos below the Sigma didn’t have the slightest problems with any front or back focus tendencies, no matter what body we used in our test.

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Canon 50D, f/1.8
Sigma A 135 mm f/1.8 DG HSM - Autofocus
Canon 5D MkIII, f/1.8
Sigma A 135 mm f/1.8 DG HSM - Autofocus