"A light weight and compact super telephoto lens suitable for hand-held shooting. This is a popular super telephoto lens among sports photographers. By restricting the maximum aperture to f/4.5, a motor-driven 500mm lens weighing only 3kg is realized. High picture quality from maximum aperture is realized by an optical system incorporating artificial crystal fluorite and UD (Ultra-low Dispersion) glass lens elements(2nd & 4th), which eliminate chromatic aberrations. High-speed and silent AF with full-time manual focusing, focus-preset mechanism and power manual focusing sensitivity control, are ensured by a ring USM(Ultrasonic Motor) and inner focusing system. Extenders EF1.4X and EF2X are compatible with this lens with manual focusing."
The EF 500mm f/4.5L USM is now discontinued. 
