This Ikelite Macro Lens Adapter allows the use of 67mm threaded macro lenses on Ikelite housings with 3.9" ports. This includes housings for the Canon G10 and G11 digital cameras. The adapter simply slides onto the front of the existing lens port.
The adapter can be added or removed while underwater. It does not limit the camera's zoom capabilities. The adapter blocks a significant portion of the port's front element, so it should only be used with a macro lens installed.