Sigma 18-250 mm f/3.5-6.3 DC OS HSM review - Autofocus

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Sigma 18-250 mm f/3.5-6.3 DC OS HSM

12 April 2011

Arkadiusz Olech

10. Autofocus

The Sigma 18–250 mm OS is equipped with an ultrasonic autofocus motor HSM so the mechanism works noiselessly. You don’t deal here with a speed merchant, though, because running through the whole distance scale takes about 0.8-0.9 of a second. What’s interesting, if passing from infinity downwards is smooth, the lens going the other way round can slow down for a moment somewhere in the middle of the distance. What’s more, during about two weeks of usage on the 50D, the autofocus jammed up several times. Something “buzzed” inside the lens, the mechanism didn’t want to move and you couldn’t take a photo. Moving the ring manually helped…until the next time.

When it comes to the accuracy the autofocus can be assessed positively. The number of misses in studio conditions reached 4.5% which is a good result if you take into account the class and the price of the equipment you deal with.

What’s important, the cooperation with the 50D, belonging to our editorial office, was seamless – the lens didn’t show any front or back focus tendencies.

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