Adjust and enhance your view with this Aquatica Zoom Gear, which is designed for use on the Canon EF-S 17-85 mm f/4-5.6 IS USM lens in a compatible port on an underwater housing. Mount the gear on the zoom ring of your lens, and then connect it to the zoom control knob of the housing compatible with your camera. Once beneath the surface, you'll be able to zoom in and out with the lens using the housing's exterior control.