Underwater conversion lenses are generally divided into two categories; wide-angle and close-up lenses. (The latter are often also called macro lenses). Most of today's UW lenses have a 67mm thread and will fit on to various housings and ports. All the lenses below are also so-called wet- or wet- interchangeable conversion lenses. This means that they are fully sealed units and can be exchanged underwater. This enables you to capture macro and wide-angle photos during one dive by just simply swapping the lens when needed. Don't leave the surface without one!