LensTip.com

Autofocus

Autofocus of the tested lens is practically noiseless and very quick. Running through the whole distance range and confirming the focus takes here just 0.2-0.3 of a second, an excellent result. This time, while changing the working mode from AF-S to AF-C, we didn't notice any distinct differences. The lens also performed equally well no matter whether we attached it to the Sony A6700 or the Sony A7R V.

The accuracy of the autofocus was also very good. The lens set focus perfectly well no matter whether we worked outside or in our studio; we also didn't notice any significant differences in performance with the Sigma attached to the A7R IIIa, the A7R V or the A6700.

We didn't notice any front or back focus tendencies – the depth of field always included the aim, regardless of what camera body the tested lens was attached to.

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A6700, APS-C, f/1.4

A7R IIIa, APS-C, f/1.4

A7R V, APS-C, f/1.4

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 about 5% in the frame centre and about 7% on the edge. In this case the differences are caused by different distortion levels that change with oversharpening. After averaging out the results, we can say that you deal with an average level of this aberration that approaches a borderline of low levels. We think the Sigma engineers deserve to be neither praised nor criticized in this area.

It's worth noticing the fact that, like in the case on the wider end of the Sigma 17-40 mm f/1.8 DC Art, the focus breathing causes an enlargement of the frame, not a tightening, as you pass to the minimum focusing distances. It means that the field of view of the tested lens increases a bit when you work with small distances.