Sigma A 70 mm f/2.8 DG Macro review - Autofocus

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Sigma A 70 mm f/2.8 DG Macro

30 June 2018

Arkadiusz Olech

10. Autofocus

Contrary to other Art. series devices the Sigma A 70 mm f/2.8 DG Macro is not equipped with an HSM motor. In this case the lens is driven by a newly developed coreless DC (direct current) motor which, according to the producer, is supposed to ensure a quick and smooth performance of the lens, allowing you an access to full-time manual focus override without the necessity of switching to the MF mode. Still it should be noticed that manual focusing works only as long as you keep the shutter button slightly pressed down.

Practice indicates, however, that sometimes declarations of producers look nice only on paper. Firstly, the motor is hardly noiseless like its best HSM equivalents, when it works you can hear a distinct buzz, not very loud but still. Secondly, it is very slow. With the lens joined with the Canon 5D Mark III running through the whole distance scale and confirming the focus takes about 3 seconds and it’s a real snail’s pace. The situation is greatly improved by the focus limiter. When you employ the range from 0.5 of a meter to infinity the focusing time is shortened to about 0.7-0.8 of a second. It is far from record values but the speed seems more or less acceptable.

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What about switching the bodies? In the case of the EOS 50D the autofocus is still noisy and the focusing times don’t differ much from those we observed using the 5D Mark III.

If the autofocus mechanism was not only slow and audible but also imprecise, we would get a real tragedy. Fortunately it is not the case. The Sigma is perhaps slow but when it reaches its aim it locks on the object without a problem. Accordingly, we didn’t have any serious issues with the accuracy as, during our test, the number of misses never exceeded 2%. We consider it a very good result.

The tested lens also didn’t have any front- or back focus problems. The Sigma, attached to two different bodies during our test, always locked on the proper object without needing any calibration either done by microcalibration in the body or by the USB Dock.

Canon 50D, f/2.8