This new superzoom encompasses all popular focal lengths from the 50mm "normal" to 500mm ultra-telephoto; a 10:1 zoom ratio, providing tremendous versatility. The use of an apochromatic design and four elements composed of SLD (Special Low Dispersion) glass, plus a seven group zoom system and multi-coated optics, enable this wide-ranging zoom lens to provide a high level of performance, as well as versatility. It also employs a rear focus system to insure quick, convenient manual focus and a non-rotating front barrel. This, coupled with Sigma"s HSM (Hyper Sonic Motor), provide quiet, responsive autofocus function, plus "full time" manual focus. This lens also features a Zoom Lock mechanism to help eliminate "zoom creep" when the lens is tilted up or down. The use of magnesium in the tripod mount helps reduce the weight of this lens, while maintaining the strength and rigidity necessary to support it. A custom bayonet "Perfect Hood" is provided to protect the front of the lens from extraneous light. Nature and sports photographers will appreciate the performance and versatility of this amazing new superzoom lens from Sigma.