Here is the official blurb:
"The Sigma 10-20mm f/4-5.6 EX DC HSM Lens is an ultra wide zoom lens for crop sensor "APS-C" cameras. Such a wide lens (equivalent focal range of approx. 15-30mm when used on a Pentax APS-C format DSLR camera) to is used in landscape photography as well as real estate photography, as well as anywhere for working space is limited. The Sigma 10-20mm f/4-5.6 EX DC HSM Lens is manufactured with Sigma's HSM (Hyper-Sonic Motor) focussing system which allows for fast, accurate focusing"
