Sigma's original full-frame ultra-wide zoom — rectilinear 12-24mm with bulbous front element, no filters.
The Sigma 12-24mm f/4.5-5.6 EX DG HSM launched in 2003 as one of the first rectilinear ultra-wide zooms to cover the full 35mm frame. At 12mm it offers an extremely wide 122-degree field of view with minimal distortion.
Optical quality is good considering the extreme focal length range — sharp in the centre but softer in the corners especially at 12mm wide open. Chromatic aberration is visible but manageable. The HSM motor provides fast and quiet autofocus.
Available in Canon EF, Nikon F, and Sony A mounts. Bulbous front element means no front filter thread — rear gel filter holder only. 600g. EX designation indicates Sigma's professional line. Minimum focus distance 28cm.
Available used at very reasonable prices. The Mark II version from 2011 improved coatings and corner sharpness. Check for decentering — ultra-wide zooms are sensitive to manufacturing tolerances. A bargain for full-frame ultra-wide on a budget.