Sigma AF 17-70mm f/2.8-4.5 DC (Pentax K) - Review / Test Report
Lens Reviews - Pentax

Review by Klaus Schroiff, published December 2007

Special thanks to Gerald Otte for providing this lens for testing!


The Sigma AF 17-70mm f/2.8-4.5 DC macro is one of the few third-party alternatives to the native Pentax standard zooms. The Sigma is a DC ("Digital Camera") lens specifically designed for the reduced image circle of today's APS-C DSLRs where its field-of-view is equivalent to 26-105mm (full format) - an attractive range suitable for a variety of applications.

Unlike its in-house cousin (Sigma AF 18-50mm f/2.8) the AF 17-70mm DC is not a designated EX lens (Sigma's pro grade lineup) but the build quality is still pretty good with tight controls and no wobbling. The lens has a slight crinkle ("ZEN") finish and broad rubberized control rings. The zoom ring operates pretty smooth whereas the focus action feels a little "lifeless". The tested sample showed a tendency for zoom creeping but Sigma has provided a transport lock (17mm only). The front element does not rotate so using a polarizer remains easily possible. As you can see in the product images below the Sigma uses a duo-cam system to extend its physical length when zooming towards the long end of the focal length range. FWIW the tested sample (a used one) has sucked in some dust over time.

Equiv. focal length25.5-105 mm (full format equivalent)
Equiv. aperturef/4.2-f/6.8 (full format equivalent, in terms of depth-of-field)
Optical construction15 elements in 12 groups inc. 1 SLD and 2 aspherical elements
Number of aperture blades7
min. focus distance0.20 m (max. magnification ratio 1:2.3)
Dimensions79 x 83 mm
Weight455 g
Filter size72 mm (non-rotating)
Hoodpetal shaped (supplied)
Other features-

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