Use this Focus Gear from Sea & Sea to control manual focusing with your Nikon AF-S 16-35mm f/4G ED VR lens in a compatible lens port, which mounts onto a Sea & Sea MDX underwater camera housing. For compatibility, see MDX System Chart. The gear mounts onto the focus ring of the lens and is controlled by the housing's focus/zoom dial or a required extension ring with focus knob. Check the system chart for details. Built for durability, the gear is constructed from a corrosion-resistant aluminum alloy.