Sigma C 50 mm f/2 DG DN
10. Autofocus and focus breathing
Autofocus
We attached the tested lens to the Sony A7R III in the first place. The autofocus performance was noiseless and sensibly quick – running through the whole focal range and confirming the focus took about 0.6-0.7 of a second. What's interesting, you are able to shorten it to an excellent result of about 0.4 of a second if you switch to the AF-C mode.In case of the newer Sony A7R V body the performance remains noiseless but is faster. In the AF-S mode the focusing time amounts to about 0.5 of a second and then it can be shortened to 03.-0.4 of a second if you pass to AF-C.
The accuracy of the autofocus was very good, no matter whether we used the lens in the studio or outdoors. Misses were really few and far between, never exceeding 1-2% of all shots.
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The tested lens didn't have any front or back tendencies either, no matter what body it was attached to.
| A7R III, f/2.0 |
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| A7R V, f/2.0 |
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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.After conducting a number of tests now we think we are able to determine some reference points. 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:
