The EF 300mm f/4L IS USM is Canon's latest introduction in a growing family of interchangeable SLR lenses with built-in Image Stabilizer technology. The new Dual Mode IS system is controlled by a 16-bit microcomputer that minimizes blurred images due to camera shake in Mode 1. When panning, simply switch to Mode 2, and the lens intelligently compensates for movement, providing sharp, stable images. The EF 300mm employs an optical design that compensates for all types of aberrations from infinity to the closest shooting distance of 4.9 feet. Two ultra-low dispersion (UD) glass elements ensure clear images and accurate color. The EF 300mm IS is extremely fast and quiet, too. Its Image Stabilization technology gives you the equivalent effect of up to 2 full shutter speeds faster than conventional lenses. And Canon's advanced ultrasonic focusing motor (USM) and rear focusing design provide silent, high speed auto focusing. Manual focusing is also smooth and easy, thanks to Canon's renowned mechanical focusing system and a wide rubber focusing ring. Whether stationary or panning, using either auto or manual focusing, the EF 300mm f/4L IS USM lens provides all users with the superior imaging performance they've come to expect from Canon.