The Ikelite 5509.28 Zoom/Focus Gear Set includes a zoom sleeve and lens clamp. It is designed for lenses with zoom rings measuring 2.8" (71mm) to 3" (76mm) in diameter. It is used with Ikelite housing units and allows you to maintain full lens operation, including smooth zoom control, when shooting underwater. It works with a wide variety of focal lengths, typically from 20-105mm. For more information on compatibility, be sure to review Ikelite’s port chart.