Sigma AF 10-20mm f/4-5.6 EX DC (Pentax K) - Review / Test Report
Lens Reviews -
Wednesday, 26 December 2007 18:39
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Special thanks to Oliver Kirchner for providing this lens for testing!
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).
|Equiv. focal length||15-30 mm (full format equivalent)|
|Equiv. aperture||f/6-f/8.4 (full format equivalent, in terms of depth-of-field)|
|Optical construction||14 elements in 10 groups inc. 3 SLD and 3 aspherical (1x molded, 2x hybrid) elements|
|Number of aperture blades||6|
|min. focus distance||0.24 m (max. magnification ratio 1:6.7)|
|Dimensions||84 x 81 mm|
|Filter size||77 mm (non-rotating)|
|Hood||petal shaped, snap-on type (supplied)|