This lightweight, compact EF-S series ultra-wide-angle zoom lens is designed to take advantage of the short back focus and smaller image circle of the Advanced Photo System C size imaging element. It meets all the demands of both ultra-wide-angle zoom photography, and lightweight compactness. The optical system of thirteen elements in ten groups uses only environmentally friendly lead-free glass. Use of three aspherical lenses of two types(replica and molded glass), and one Super UD lens ensures outstanding picture quality over the entire zoom range, while the optical design and coatings have been optimized to reduce the flare and ghosts that are prone to occur with digital cameras, resulting in sharp images with excellent color banlance. Minimum focus is a constant 0.24m over the zoom range, and the round diaphragm provides exquisite bokey(blur effects). The internal focusing system with its ring-type USM is quick and quiet, while the full-time manual focus enables manual focusing even in autofocus mode. The lens mechanism is designed to ensure that it fits only EOS DIGITAL SLR cameras designed to take EF-S lense, and it is equipped with a special attachment indicator and protective rubber mount ring to prevent mistaken attempts to attach it to other EOS SLR cameras, and to prevent damage to the camera body.