Pentax HD DA 20-40 mm f/2.8-4.0 ED Limited DC WR
10. Autofocus
The speed of the autofocus is hardly impressive, though. Running through the whole distance scale takes almost one second - an average result, taking into account the narrow working range of the focusing ring. At such a price point I think you have every reason to expect a really efficient and quick ultrasonic motor, which is, after all, a common feature in the rival devices, even those noticeably cheaper.
When it comes to the accuracy of the focusing mechanism it wasn’t perfect – the number of misses in studio conditions amounted to 4 %. On the other hand such a result still might be considered good or even very good at a push.
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As you can notice in the photos below, the autofocus of the Pentax 20-40 mm needed some microcalibration because of its noticeable tendency to set the focus behind the photographed object.
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