Special thanks to Konrad Kandler for providing this lens for testing!

Introduction

The Sigma AF 12-24mm f/4.5-5.6 EX HSM DG is of three ultra-wide zooms made by Sigma – obviously
a primarily playing field for the company. The 12-24mm EX is a full format lens and within its
range it is currently unique in Sony Alpha mount. In fact there isn’t even a (mass production)
rectilinear SLR fix-focal this wide. Quite an achievement! On an APS-C DSLR the specifications
are not all that impressive anymore but the field-of-view is still equivalent to a classic
18-36mm lens so even here it keeps its ultra-wide character.

Due to the extreme design Sigma had to choose a very protruding front element
so there’s no front filter thread by default. However, when attaching the lens
cap holder there is a option to mount a filter here (82mm). At 12mm this causes slight
edges shading so front filters can only be used from about ~14mm. There’s a
gelatin filter slot at the rear of the lens (useful for color filters for B&W
photography).

The build quality of the lens is very impressive and among the best what Sigma has
to offer. The typical EX finish (smooth crinkle style) feels
very pleasant and the zoom and focus control rings operate very smooth.
Unlike the Canon and Nikon variant the Sony Alpha variant does still rely on the
conventional focusing system driven by the camera (via a slotted drive screw). The AF
produces a moderate degree of noise during operations but it is very fast and
reasonably accurate – although AF speed does hardly matter for an ultra-wide angle lens.