Mods I hope this is ok. I copied and pasted the intro from the official Sigma webpage.
The large angle of view (122 degrees super wide angle of view at 12mm along the diagonal axis) is ideal for shootings indoor as well as landscape photography. It has a variable angle of view from 122 degrees at 84.1 degrees. Four Special Low Dispersion (SLD) glass elements are provided for effective compensation of color aberration, which is a common problem with super-wide angle lenses. Two pieces of Glass Mold and one-piece hybrid aspherical lenses offer excellent correction for distortion as well as all types of aberration. By effective arrangement of lens elements and advanced technology this lens has Super Compact dimensions of 3.9 inches full-length, and 3.4 inches maximum diameter.
It is equipped with Inner focusing system that will keep the length of the lens unchanged while controlling aberration. The models, which are equipped with HSM (Hyper Sonic Motor, available for Sigma, Canon and Nikon camera mount lens) system offer Full Time Manual Focusing. It has a minimum focusing distance of 11 inches (28cm) at all focal lengths. This lens is equipped with an integral Petal-type hood to block out extraneous light.
Available for SIGMA AF, Canon AF and Nikon AF: October 2003,
For Minolta AF and Pentax AF: November 2003
Focal length: 12-24mm
Maximum aperture: F4.5-5.6
Lens construction: 16 elements in 12 groups
Focusing system: Internal Focusing
Angle of view: 122.0 - 84.1 degrees
Number of diaphragm blades: 6
Minimum aperture: F22
Minimum focusing distance: 11 in. (28cm)
Maximum magnification: 1:7.1
Filter size: Rear (gelatin filter insert type)
External finish: EX finish
Lens hood: Petal shape hood (non-removable)
Dimensions: 3.4 in. (dia) x 3.9 in. (length)
87mm (dia) x 100mm (length)
Weight: 21.6 oz. (615g)
Mount: Sigma SA, Minolta (D), Nikon (D), Pentax, Canon