The Canon EF 16-35mm f/4L IS USM Lens is a wide-angle zoom lens featuring a constant f/4 maximum aperture to provide consistent performance throughout the zoom range. The optical design incorporates three aspherical elements, including one large-diameter aspherical element, as well as two UD (Ultra-low Dispersion) elements to minimize chromatic aberrations and contribute to high edge-to-edge sharpness and resolution. A fluorine coating has also been applied to the front and rear lens surfaces to reduce flare and ghosting for maintained color neutrality and image contrast. Benefitting working in difficult lighting conditions, an Optical Image Stabilizer has been integrated into the lens design to minimize the appearance of camera shake by up to an effective four shutter speed steps. For fast, smooth, and near-silent autofocus performance, a ring-type USM (Ultrasonic Motor) AF motor is employed and benefits from an internal focusing design to maintain the overall length of the lens during use. Full-time manual focus override can also be utilized for fine-tuned focusing precision as closely as 11″ throughout the zoom range.