Review by Klaus Schroiff, published December 2005

Special thanks to Bernd Adam for providing this lens!

Introduction

The lens construction is made of 17 elements in 13 groups including 2 aspherical elements. Within its class it is a pretty big lens with a size of 87x132mm and a weight of 620g - this is even bigger than the Sigma AF 12-24mm f/4.5-5.6 EX. Its aperture mechanism features 8 aperture blades. The minimal focus distance is 0.30m resulting in a max. magnification of 1:6 at 30mm.

Due to the extreme wide-angle character Sigma implemented a very protruding front element so there's no front filter thread by default. However, when attaching the lens cap holder (see below) there is a filter mount here (82mm). This setup may cause edge shading at the widest setting though. There's a gelatin filter slot at the rear of the lens (useful for color filters for B&W photography).

Unlike its sister lens, the AF 12-24mm f/4.5-5.6 EX it doesn't feature HSM (an ultrasonic-driven AF drive) but a conventional micro motor - a quite noisy one. AF speed feels Ok though it isn't really relevant in this lens class. The lens incorporates a Dual-Focus (DF) mechanism which allows to decouple the focus ring from the focusing gear by pulling/pushing it back and forth (a little stiff). The idea is good but the implementation leaves something to be desired because you still have to switch the lens from AF to manual focusing - independent from the dual-focus mechanism that is.
The build quality of the lens is very good. The typical EX finish (smooth crinkle style) feels very pleasant and the zoom and focus control rings operate quite smooth and damped.