Water removes warm colors from sunlight with depth. It also magnifies subjects by about 33 percent. To compensate for these two effects of water on underwater video, it’s extremely important that the housing support the proper lens optics underwater. There are two fundamental requirements.
The housing should support a color-correcting filter that can optionally be selected underwater. This can mean one that is inside the housing and flips in front of or away from the lens using a mechanical control, or it can mean an external ‘wet’ filter that can be pushed on or pulled off the housing’s lens port. Most housing manufacturers incorporate the optional use of a color-correcting filter underwater. Optional is the key, because you only want to use the filter when your primary source of light is the sun. If you start out a dive in open sunlit water, but then penetrate a wreck or enter a swim-through where it becomes dark and you switch to artificial lights, you’ll need to remove the filter.
A decent housing should also allow for the addition of a wide-angle lens or wide-angle adapter. Water magnifies. Also, one usually shoots closer to a subject underwater than at the surface to reduce the effects of particles in the water. A proper wide-angle lens or wide angle adapter compensates for the magnification effects of water and enables one to get closer to a subject yet still fit it in the frame.