This Sigma APO 500mm f/4.5 EX DG is a large aperture telephoto lens that can capture sharp images of fast-moving subjects. When doing sport or nature photography there is often no substitute for focal length. More millimeters get you closer to the subject whether it’s a running back in a football game or a monster moose grazing in a pasture. Two ELD (Extraordinary Low Dispersion) glass elements provide optimum color correction and sharpness throughout the entire zoom range and a new multi-layer lens coating technology and lens design formula reduce flare and ghosting. Rear insertion 46mm filters with provision for easy rotation of polarizing filters. Also, compatible with the Sigma APO Tele Converters to provide additional focal length as a 700mm f/8 or 1000mm f/11 lens. The Sigma 500mm provides excellent optical performance at a large aperture of f/4.5; and this lens is priced substantially lower than the competitive camera manufacturers’ lenses.