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06-03-2008, 10:58 PM   #1
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About the new Pentax DA 17-70mm SDM Lens

PENTAX DA 17-70mm f/4 AL [IF] SDM Lens Announced

One noteworthy change compared to Pentax's pro-grade DA* lenses with SDM is the use of the KAF3 (rather than previous SDM lenses' KAF2) lens mount on the 17-70mm. The KAF3 mount is almost functionally identical to the KAF2, with two contacts driving the internal focusing motor, but the new mount eliminates the secondary focus drive option via the body's focusing motor found on KAF2 lenses. Hence, rather than reverting to body-driven auto focus on older Pentax bodies (anything further back than the K10D or K100D Super), the new DA 17-70mm is manual focus only in these applications.

While users with older Pentax digital bodies may be disappointed at the loss of AF compatibility with the latest lens, the move to KAF3 spells good news for current Pentax shooters: outside of its dimunitive DA Limited glass (which will retain body-driven AF), look for new lenses from the manufacturer to feature SDM focus drive exclusively going forward.

06-04-2008, 12:05 AM   #2
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Gubak, welcome to the Forums!

Actually, according to the FAQ at the bottom of the Pentax Imaging press release announcing the release of the DA 17-70 f/4, both SDM lenses and body drive lenses will be developed in the future. However, we can expect future lenses to feature only one of these AF lens drive technologies, not both, as in the DA* 16-50 f/2.8 and the DA* 50-135 f/2.8. See the excerpt below:

"Q: Will PENTAX be developing SDM-only lenses from now on?

A: No: Despite the great advantages of our SDM autofocus systems, we will continue to develop both SDM and body-based focus systems. In fact, different types of lenses have different requirements. For example, our unique Limited lenses are often so compact that there is no space for an SDM autofocus motor. Until time and technology present other options, we will continue to develop both types of autofocus systems.

Remark: Current DA* lenses (16-50mm, 50-135mm, 200mm and 300mm) contain both SDM and body-based focusing. While we will continue to develop lenses for each type of autofocus system, we will also phase out lenses that support both types of focusing simultaneously. Due to issues of cost, development timeframe and other factors, in the future, PENTAX lenses will either support SDM focusing or body-based focusing, but not both."
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