The 18462 Port Extension Ring from Aquatica is for their bayonet style housings when using one of a variety of Canon, Nikon, Sigma and Tokina lenses. Insert the ring between the port and the housing. It is constructed from durable anodized aluminum.
To check lens and lens port compatibility, see the following charts:
Canon, Sigma and Tokina Type 1 Lens Chart
Canon, Sigma and Tokina Type 2 Lens Chart
Canon Type 4 Lens Chart
Nikon, Sigma and Tokina Type 1 Lens Chart
Nikon, Sigma and Tokina Type 2 Lens Chart
Nikon, Sigma and Tokina Type 3 Lens Chart
Nikon, Sigma and Tokina Type 4 Lens Chart