Pentax SMC DA 17-70mm f/4 AL [IF] SDM - Review / Test Report
Lens Reviews -
Tuesday, 16 December 2008 21:00
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Lens kindly provided by Johannes Hildebrandt!
As of the time of this review Pentax is offering no less than 5 lenses covering the standard zoom range and the Pentax SMC DA 17-70mm f/4 AL [IF] SDM is the latest addition to this series. It can be seen as the sweet spot lens here because it offers the most attractive combination of range, speed, technology and price - on paper at least. It is a dedicated APS-C format lens with a field-of-view equivalent to 26-107mm (full format).
The build quality of the Pentax lens is very high thanks to quality materials and tight build tolerances - this positive impression is actually typical for the majority of the Pentax DA lenses. The lens uses a duo-cam system (2 inner lens tubes) to extend when zooming towards longer focal lengths. This may sound a bit worrisome at first but the tested sample showed no significant wobbling whatsoever here. Both the broad, rubberized zoom control ring as well as the smaller focus control rings operate very smooth. The lens has an internal focusing system (IF) resulting in a non-rotating front element. The Pentax Super Protect (SP) coating on the front element has been optimized to repel dust, water and grease.
The DA 17-70mm f/4 features the new near-silent Supersonic (ultrasonic) Dynamic Motor (SDM) AF. Unlike the DA* 16-50mm f/2.8 SDM it does not offer the old AF drive screw for legacy DSLR support but that's forgivable by now. Thanks to a very short focus path (make it 3-4cm for the whole range) the AF speed is very high. However, on the downside this approach has also the consequence that manual focusing is extremely difficult - a minor adjustment on the focus ring has a major impact on the focus. The AF accuracy was fine in field condition though. Thanks to a Quick-Shift system manual focus override is instantly possible in Single-Shot AF mode.
|Equiv. focal length||25.5-105 mm (full format equivalent)|
|Equiv. aperture||f/6 (full format equivalent, in terms of depth-of-field)|
|Optical construction||17 elements in 12 groups inc. 2 aspherical elements|
|Number of aperture blades||7|
|min. focus distance||0.28 m (max. magnification ratio ~1:3.2)|
|Dimensions||75 x 94 mm|
|Filter size||67 mm (non-rotating)|