This version of Canon's FD 500mm F/4.5 lens features a Canon mount which enables mounting with a simple twist. The lens incorporates BOTH Fluorite and Canon's UD (Ultra-low Dispersion) glass for performance that is not only superb, but extremely fast for a lens of its focal length. In addition, this suprisingly lightweight and compact lens features a plano-parallel glass protective flat used as a protective front element. It also features a built-in focus pre-setting mechanism which enables very rapid operation. The tripod mount has been changed to a built-in permanent type design. For sports, nature and surveillance photography, this is an ideal lens even under difficult lighting conditions. SPECIFICATIONS Type: super telephoto Construction: 7 elements in 6 groups Angle of view: 5 degrees Minimum Aperture: F/32 Closest Focusing Distance: 20ft Filter size: 48 drop-in with holder Lenshood: built-in Length: 15 9/16 in Weight: 5lbs 12oz.