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 wave lengths 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.
Underwater photographers 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.