This Modular 8" Dome Port with 2.75" Lens Extension Kit from Ikelite bundles their injection-molded acrylic dome port with 8" diameter and their Modular Lens Extension for lenses up to 2.75" in length and 3.3" in diameter. The dome includes a protective neoprene port cover and a 1cc tube of silicone lubricant, as well, and the extension includes an anti-rotation lock. This dome and extension kit is designed for use with compact, super wide-angle lenses, and offers a depth rating of 200'.
The extension threads onto the base of the dome port for easy assembly, and attaches to a compatible underwater camera housing body via bayonet mount. It works with all of Ikelite's 4-lock and 2-lock DSLR housings manufactured since March 2006. Additional extensions can be purchased separately and used with this dome, as well. You can also substitute the 8" dome for the optional Ikelite Modular Flat Front, though you will be unable to use the anti-rotation lock with this configuration.
The 8" dome is designed for super wide-angle DSLR lenses, and counteracts the decrease in coverage that occurs underwater by increasing your angle of view. It also reduces edge distortion to a greater degree than smaller 4" or 6" domes, and it has a shade that blocks out excess light for improved visibility and reduced flare. Additionally, the dome makes it easier to capture over-under shots, where the port is half-in and half-out of the water.