Waterproof digital cameras include those that can be totally submerged for underwater photography and those designed to operate in wet conditions on land. Many waterproof digital cameras are shockproof and resistant to low temperatures. Waterproof housings are available to protect non-waterproof cameras in wet or submerged conditions. Underwater photography is the process of taking photographs while under water. It is usually done while scuba diving, but can be done while snorkeling or swimming. Successful underwater imaging is usually done with specialized equipment and techniques. However, it offers exciting and rare photographic opportunities. Animals such as fish and marine mammals are common subjects, but photographers also pursue shipwrecks, submerged cave systems, underwater "landscapes", and portraits of fellow divers. Since underwater photography is often performed while scuba diving, it is important that the diver-photographer be sufficiently skilled so that it remains a reasonably safe activity. Good scuba technique also has an impact on the quality of images, since marine life is less likely to be scared away by a calm diver, and the environment is less likely to be damaged or disturbed. There is the possibility of encountering poor conditions, such as heavy currents, tidal flow, or poor visibility. Underwater photographers usually try to avoid these situations whenever possible. Underwater diving training providers such as the Professional Association of Diving Instructors (PADI) provides courses to help improve a divers diving skills and underwater photography skills. The primary obstacle faced by underwater photographers is the loss of color and contrast when submerged to any significant depth. The longer wavelengths of sunlight (such as red or orange) are absorbed quickly by the surrounding water, so even to the naked eye everything appears blue-green in color. The loss of color not only increases vertically through the water column, but also horizontally, so subjects further away from the camera will also appear colorless and indistinct. This effect is true even in apparently clear water, such as that found around tropical coral reefs.[2] Underwater pho

ographers solve this problem by combining two techniques. The first is to get the camera as close to the photographic subject as possible, minimizing the horizontal loss of color. Wide-angle lenses allow very close focus, or macro lenses, where the subject is often only inches away from the camera. Many serious underwater photographers consider any more than about 3 ft/1 m of water between camera and subject to be unacceptable. The second technique is the use of flash to restore any colour lost vertically through the water column. Fill flash, used effectively, will "paint" in any missing colors by providing full-spectrum visible light to the overall exposure. Some cameras are made for use underwater, including modern waterproof digital cameras. The first amphibious camera was the Calypso, reintroduced as the Nikonos in 1963. The Nikonos range are designed specifically for use underwater. Nikon discontinued the Nikonos series in 2001[4] and its use has declined as with other 35mm film systems, but not disappeared. Sea and Sea USA continues to manufacture an amphibious range finder camera that utilizes 35mm film, the Motor Marine III.[5] Cameras made for dry work can also work underwater, protected by special housings that are made for various digital point and shoot cameras, digital compact cameras with full exposure controls, and SLRs (single lens reflex cameras). Most such housings are specific to the camera. Materials range from relatively inexpensive plastic to high-priced aluminum cases. Housings allow many options, since the user can choose a housing specific to their everyday "land" camera, as well as utilize any lens in their collection. Underwater photographers generally use either wide-angle lenses or macro lenses, both of which allow close focus, thereby eliminating the need for long underwater distance between camera and subject. Digital media can hold many more shots than standard photographic film (which rarely holds more than 36 frames). This gives digital cameras an advantage, since it is impossible to change photographic film underwater. Other digital versus film photography comparisons apply, and the use of film underwater has declined, as it has on land.