An extremely high quality large aperture super telephoto lens used widely by professional photographers worldwide. The optical system utilizes artificial crystal fluorite and UD (Ultra-low Dispersion) glass lens elements (2nd & 3rd) to eliminate axial chromatic aberration, realizing extremely sharp, high-contrast imaging performance even at maximum aperture. Silent and super-fast AF is achieved by the inner focusing system (lens group between the front lens group and the diaphragm controls focusing) and USM (Ultrasonic Motor). The USM enables focus preset function, full-time manual focusing and electronic ring powered manual focusing, which allows the focusing speed adjustment in three steps. Those functions were applied to this lens for the first time and followed by other telephoto/super-telephoto lenses.