Fluorine Coating. 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. 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.
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