newest motor type
The HD Pentax DA 55-300mm F4.5–6.3 ED PLM WR RE is the first lens in brand history to use a pulse motor for autofocus, so we were especially interested to find out if it's a serious improvement over the DC and SDM lenses that came before. (Not to mention the ancient screw-drive motor in this lens's predecessor.) Read on for our full findings!
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HD Pentax-DA 55-300mm F4.5-6.3 PLM WR RE Review - Focusing | PentaxForums.com Reviews
current SDM type
The lens features two autofocus systems. On older bodies (predating the K10D), AF is driven by the traditional screwdrive shaft. On newer bodies, Pentax's in-lens Silent Drive Motor (SDM) is used, providing near-silent AF. In this review, we do not compare the speeds of the two systems, though we will say that Pentax's SDM motors are not known for their speed.
The SDM does feel accurate and responsive, however. A subtle whirring noise can be heard when listening closely in a silent environment, but for all practical matters the autofocus system is silent. It is therefore a big improvement over the dated screwdrive system.
Pentax's SDM motors have suffered from poor reliablity in the past. Fortunately, according to a survey we conducted in 2012, the SDM system on the DA* 60-250mm proved to be quite reliable. Only about 5% of 60-250mm users reported an SDM failure; failure rates for other lenses, such as the DA* 16-50mm, were as high as 30%. Recent reports from users and from Pentax engineers suggest that the SDM issues were resolved in late 2012, however.
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Pentax DA* 60-250mm F4 Review - Focusing | PentaxForums.com Reviews
DC type
The HD Pentax-D FA* 70-200mm features the newer silent DC motor which has proven to be far more reliable than SDM, as well as near-silent. In-lens focusing means that the lens won't autofocus with cameras older than the K10D (2006), which are quite dated by modem standards anyway. On the other hand, the newer AF systems are better adapted for contrast focusing using Live View.
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https://www.pentaxforums.com/reviews/hd-pentax-d-fa-star-70-200mm-f28/focusi...#ixzz58z4jlLLo