Sigma 24-70 mm f/2.8 EX DG HSM review - Autofocus

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Sigma 24-70 mm f/2.8 EX DG HSM

3 June 2009

Arkadiusz Olech

10. Autofocus

Most of the Sigma lenses are equipped with the HyperSonic Motor (HSM) but the motors can differ greatly from one another when it comes to accuracy and speed. So far, one of the best mechanism we’ve found in a Sigma 70-200 f/2.8 EX HSM so in a classical reporter’s lens, where a good focusing mechanism simply cannot be overestimated. What mechanism are we dealing with in the case of the second of the classical reporter’s lenses?

The Sigma 24-70 mm autofocus mechanism is silent above all. Working either on the D200 or on the D3x we can’t hear practically anything. The speed is also beyond reproach. Running through the whole scale (which demands rotating the ring about 90 degrees), takes just about 0.5 second, no matter what end we’re traveling to.

When it comes to accuracy – and it’s an important issue for the Sigma lenses – we can find no serious fault either. The lens worked on the Nikkon D200 very well because the number of errors during the studio test didn’t exceed 2%. What’s interesting, there were a bit more problems while working on the D3x – the number of errors reached 6%. Still, you can’t complain. We got the real troubles when we tried the version with the Canon mount on an EOS 5D Mark II reflex camera. The lens had a frontfocus so big that even the built-in calibrating couldn’t manage it. We simply lack the scale.

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The issue of frontfocus or backfocus is an interesting one. On the D200, without any calibrating possibility, the Sigma had a strong backfocus tendency. On the D3x we corrected it without any problems and the lens was very accurate. You can see the proof in the crops below.