Sigma A 50 mm f/1.4 DG DN review - Autofocus and focus breathing

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Sigma A 50 mm f/1.4 DG DN

3 April 2023

Maciej Latałło

10. Autofocus and focus breathing

Autofocus

The autofocus of the new Sigma joined with the Sony A7R III is silent and smooth. In the AF-S mode its speed is not great – running through the whole distance range and confirming the focus takes about 0.9 of a second and this value doesn't depend on the direction from which you start. If you switch the AF-C mode on, autofocus speeds up and is able to focus in 0.5-0.6 of a second.

We can praise the accuracy of the autofocus – it didn't cause us any problems both inside the studio or outdoor.

The tested lens didn't show any front or back focus tendencies either.

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A7R III, f/1.4

Breathing

Focus breathing tests show refraiming images as you oversharp them. We conduct the test by manually passing from the minimum focusing ditance to infinity with the aperture stopped down; then we check how the field of view of the lens changed as a result. The test video of the Sigma lens is presented below:

After comparing freeze-frames from this video we can estimate that focus breathing of the tested lens amounts to about 19%, a significant value which is impossible to eliminate by breathing compensation algorithms, present in bodies of different producers. This flaw will defintely bother you in practice and the tested lens can't be praised in this category.