The EF 500mm f/4.5L USM is a professional L series lens, that is now discontinued. This lens is constructed with a metal body and mount, and with plastic extremities and switches. Features of this lens are: a wide rubber focus ring that is damped, a distance window with infrared index, the ability to limit the focus range, a focus-preset mechanism, and the ability to set the AF speed. A 9 blade, maximum aperture of f/4.5, gives this lens the ability to create depth of field effects. The optical construction of this lens contains 8 lens elements, including one fluorite lens element, and one UD (Ultra low Dispersion) Lens element. This lens uses an inner focusing system, powered by a ring type USM motor. The front of the lens does not rotate nor extend when focusing. This lens is compatible with the Canon Extender EF teleconverters.
Read more about this topic: Canon EF 500mm Lens