Sigma A 28-45 mm f/1.8 DG DN
10. Autofocus and focus breathing
Autofocus
According to the producers the tested Sigma features the original linear HLA motor (High-response Linear Actuator). The focus is supposed to be set very quickly and be exceptionally quiet. What's important, Sigma really means it – the performance of the autofocus joined with the Sony A7R IIIa and the Sony A7R V is noiseless and really quick. When you shoot in normal or good conditions it is really difficult to measure an exact time of running through the whole range and confirming the focus. It is, by and large, on the borderline of reflexes of the tester, rarely exceeding 0.2-0.3 of a second, a truly sensational result. What's more, it doesn't depend on the focal length and the direction. In worse lighting conditions that time can extend a bit, but usually it doesn't exceed 0.3-0.4 of a second.We also didn't notice any special problems with the accuracy of the autofocus. No matter whether we shot photos in our studio or outside the focus was always set where we aimed and the number of misses was negligible.
When it comes to front or back focus tendency the cooperation with the Sony A7R IIIa was completely problem-free. In case of the Sony A7R V the depth of field is slightly shifted towards the photographer but even at the minimum distance it still encompasses the aim so the problems are negligible.
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| A7R IIIa, 45 mm, f/1.8 |
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| A7R V, 45 mm, f/1.8 |
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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.
The test video of the Sigma lens is presented below:
