LensTip.com

Autofocus

We tested the autofocus of the Sigma 1.4/12 by joining it to the Sony A7R V set in the AF-C mode. The performance of the mechanism was noiseless and flsh quick. Running through the full distance range and confirming the focus took about 0.3 of a second, an excellent value. As if it wasn't enough, we didn't notice any wavering or focus play and the focusing time didn't depend on the direction of work and lighting conditions – so far so good.

When it comes to the accuracy of the mechanism we don't have any reservations either. In our studio me mainly used the Sony A7R IIIa and outside we attached the tested lens to the Sony A7R V. In both cases there were practically no problems visible. Of course the fact that this lens features a huge angle of view and its depth of field is significant, able to masking any potential autofocus misses, helped a bit. Still, it doesn't change our high assessment of the tested Sigma in this category.

We also didn't notice any front or back focus tendencies and photos below prove that statement.

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A7R IIIa, APS-C, f/1.4

A7R V, APS-C, f/1.4

Focus breathing

Focus breathing tests show reframing images as you oversharp 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 constitute also 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 Viltrox lens:

On the basis of the recording above, comparing freeze-frames before and after oversharpening, we can estimate that the breathing of the tested lens amounts to about 3-4% for the frame centre and about 6% on the edge of the frame. How is it possible? The lens changes its distortion level significantly during oversharpening; that's why the further you go from the frame centre the more intensive focus breathing becomes. If you average out both results you can estimate that the focus breathing level of the Sigma 12 mm f/1.4 DC balances on the borderline between low and medium values. It shouldn't be bothersome in practical situation but we can't praise Sigma engineers for such a result either.