Aimed to satisfy the most demanding professionals and advanced amateur photographers, its enhanced optical design has multiple moving lens groups and features that adjust and compensate for a variety of conditions. Ultrasonic Motor (USM) technology and an internal focusing system enable silent, high speed autofocusing. A wide rubberized focusing ring and manual focusing capability in the autofocus mode provides maximum flexibility and ease of use. Key optical features include a replica aspherical lens element that minimizes distortion and a flare-cutting diaphragm that helps the lens maintain contrast in tough lighting conditions.