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Lens review

Sigma 17-70 mm f/2.8-4.0 DC Macro OS HSM

10 February 2010
Robert Olech

10. Autofocus

The focusing mechanism, as it befits an HSM motor, works silently. On setting the focus we can hear a barely audible swoosh. In this equipment class there should be no reservations when it comes to the speed either. Running through the scale, no matter from what end, takes 0.6-0.7 second. It is a good result but only slightly better than the predecessor’s.

The specimen of the Sigma 17–70 mm f/2.8–4.0 DC Macro OS HSM, which was tested in our editorial office, had a slight front focus. We were able to calibrate it without any problems though (it can be seen in the picture below) setting the 5-unit correction, accessible from the menu level of the Canon 50D. After the correction, the accuracy of the mechanism was difficult to fault. In well-lit studio conditions we noted just about 4% of misses.

Adding an HSM motor was definitely a very good move because the mechanism’s quality of work improved in practically every aspect.

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Sigma 17-70 mm f/2.8-4.0 DC Macro OS HSM - Autofocus