Sigma A 50 mm f/1.4 DG HSM
10. Autofocus
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The Sigma A 50 mm f/1.4 DG HSM is equipped with an ultrasonic autofocus motor so the work of the focusing mechanism is silent. The speed is good in most of cases – running through the whole distance range with the focus confirmation take less than 0.5 of a second. What’s interesting, from time to time that result can be prolonged by almost another 0.5 of a second without any change of lighting conditions.
The autofocus performance depends strongly on the camera body. When the lens was attached to the Canon 50D and the 5D MkIII the whole set was pretty much predictable, with the number of misses reaching 6-7% which is good but also only a good result. The cooperation with the 1Ds MkIII was strange for a turn. The lens, even if positioned in a stable way in the same place before the testing chart, could oscillate for a short spells, jumping between two close focus positions several times; then it chose one of them but in a rather random way. More often than not the chosen position was correct but there were a lot of misses as well. The fact that the lens had also a pronounced front focus tendency didn’t help – once again you could observe it only when it was attached to the 1 Ds MkIII. While cooperating with the 50D and 5D MkIII the Sigma didn’t have such problems.
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