Sigma AF 10-20mm f/4-5.6 EX DC (Pentax K) - Review / Test Report
Lens Reviews - Pentax

Special thanks to Oliver Kirchner for providing this lens for testing!

Introduction

The Sigma AF 10-20mm f/4-5.6 EX DC is one of currently two Sigma alternatives to the native Pentax DA 12-24mm f/4 AL ED [IF]. The DC (Digital Camera) part of the lens name indicates that it can only be used on reduced image circle (APS-C) DSLRs. It is part of the Sigma's professional-grade EX ("Excellence") lineup. The field-of-view is equivalent to about 15-30mm on a full format camera so it is certainly an ultra-wide zoom pushing the limits here.

The build quality of the lens is very impressive - it feels like a solid block. The typical EX finish (smooth crinkle style) feels very pleasant and the zoom and focus control rings operate very smooth and well damped. There's no wobbling whatsoever here. The lens extends marginally when zooming towards the long end of the range. Thanks to an internal focusing group the lens does not extend during focusing and the front element does not rotate.


Typical for most Pentax-K mount lenses the Sigma has no internal AF motor and relies on a slotted drive screw operated by the camera. Consequently AF operations generate a moderate degree of noise. The AF speed is very fast on the K10D. The AF accuracy seems Okayish - probably a side effect of the extreme depth of field (on the AF sensor plane).

Specifications
Equiv. focal length15-30 mm (full format equivalent)
Equiv. aperturef/6-f/8.4 (full format equivalent, in terms of depth-of-field)
Optical construction14 elements in 10 groups inc. 3 SLD and 3 aspherical (1x molded, 2x hybrid) elements
Number of aperture blades6
min. focus distance0.24 m (max. magnification ratio 1:6.7)
Dimensions84 x 81 mm
Weight470 g
Filter size77 mm (non-rotating)
Hoodpetal shaped, snap-on type (supplied)
Other features-



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