The Sigma 300-600mm F4 DG OS | Sports is a revolutionary large-aperture ultra-telephoto zoom lens that delivers all teh convenience and versatility of a zoom lens with the superior optical performance of an ultra-telephoto prime lens. With the Sigma 300-600mm F4 DG OS | Sports, photographers can move freely between focal lengths of 300mm and 600mm without changing lenses. The fast and precise AF performance of its High-response Linear Actuator (HLA)  and 5.5 stops* of optical stabilization at 600mm.