One of the finest telephoto zoom lenses in the EF line, comparable to a single focal length lens. It has four UD-glass elements to correct chromatic aberrations. Its constant f/2.8 maximum aperture and superb image quality make it one of the most popular professional SLR lenses in the world. This lens construction consists of one fluorite and five ultra-low dispersion optical elements which help deliver the sharpness and reduced aberrations. The IS II Optical Image Stabilizer provides up to 4 stops of correction at all focal lengths and features two modes for stabilization of still objects and while panning to follow moving subjects. An ultrasonic focusing motor provides fast, smooth and silent autofocus action. This lens has a minimum focusing distance of 3.9' (1.2m) at all zoom settings so you can shoot close to your subject even in smaller spaces. Like all Canon L-series lenses, this telephoto zoom is dust and moisture resistant and designed to keep on going even in the most challenging of environments.