The Canon EF-S 10-22mm f/3.5-4.5 USM SLR Lens is a wide-angle zoom perfect for users of Canon's APS-C cameras like the Digital Rebels and the EOS 50D and 7D.
Cameras like the EOS 50D and 7D and those in the Rebel series like the Rebel T1I and T2I feature "crop factor" sensors that reduce width of wide-angle lenses. To get truly wide shots with these cameras, then, it's necessary to have a lens like the very wide EF-S 10-22mm.
According to Canon:
This exciting zoom lens provides ultra wide-angle coverage to the EOS 20D, 30D, 40D, 50D and Digital Rebel SLRs. Equivalent to a 16-35mm zoom, it offers excellent performance and optics designed from the ground-up for digital SLR use. Three Aspherical lens elements, plus a Super-UD element, assure image quality. Its ring-type USM means fast and silent AF along with full-time manual focus. It focuses as close as 9.5 inches.
