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Autofocus

The autofocus of the tested Sigma is based on a double HLA motor (High-response Linear Actuator) that powers each of two focal groups with the help of a separate linear motor.

We checked the efficiency of this mechanism by joining the lens to two cameras, the Sony A7R IIIa and the Sony A7R V. The autofocus is really noiseless and relatively fast. In the AF-S mode, running through the whole distance range and confirming the focus takes about 0.5 of a second. This time could have been shorter; unfortunately, right after pressing the shutter release, the lens goes in the wrong direction and only after a moment finds the right position. We didn't observe such an effect in the AF-C mode, so the focusing time is shorter by about 0.3 of a second, exactly as it should be in a good-quality journalistic device.

The accuracy of the autofocus we assess very positively indeed. The mechanism is practically error-free, no matter whether you work in the studio or outside.

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We didn't notice any front or back focus tendencies either.

A7R IIIa, f/1.2

A7R V, f/1.2

Focus breathing

Focus breathing tests show reframing images as you oversharpen them. We conduct the test by manually passing from the minimum focusing distance to infinity with the aperture stopped down; then we check how the field of view of the lens changed as a result.

A frame change ranging from 0 to 5%, we consider to be low. Between 5 and 10%, you can speak about medium levels. Usually such values also constitute the maximum efficiency level of any breathing compensation algorithms, present in some bodies. Between 10 and 15% focus breathing is high; above 15%, its level can be called very high.

Below we present the test video of the Sigma lens:

Based on the recording above, comparing freeze-frames before and after oversharpening, we can estimate that the breathing of the tested lens amounts to zero within the margin of error. More precisely, the results range from 0% to 1%, depending for the frame you analyze, because, as you oversharpen the lens, its distortion increases. Still, the focus breathing is corrected in an almost perfect way – a round of applause!