Photographs of sunken wrecks, of animals on the seabed, or of fish swimming about coral reefs, are often seen nowadays. Free-divers hunting fish or exploring in shallow waters take photographs of features in their surroundings. Oceanographers who formerly had to reconstruct the appearance of the seabed from the jumbled contents of a dredge, are now taking photographs which throw light on the little-known habits of the bottom fauna.
Many different varieties of underwater camera exist. The design of the camera will depend on whether it is to be held by a diver or lowered from a ship, and whether it is for taking still photographs or moving pictures. A typical hand-held submarine camera would consist of a normal camera mounted inside a light-weight, watertight, pressure-resistant case with a window and fitted with controls passing to the outside of the case, which enable the diver to operate and adjust the camera under water. Often electronic flashlight or simpler flash bulb outfits are modified for use under water and coupled to the camera. Lighting for underwater movie cameras is more complicated, as a steady source of light is required. Waterproofed floodlamps, connected with a source of electricity on a boat or dry land, are usually used.
Remote underwater cameras normally used by research ships must have chambers which can withstand considerable hydrostatic pressure. O-ring seals are commonly used to seal the window and entrance into such chambers, as well as to seal lead-ins for the triggering switch and the coupling between camera and flash. The camera mechanism in remote underwater cameras may be specially built, and such cameras are normally fitted with an electric or clockwork mechanism to advance the film.
Light is absorbed by sea water and is scattered by suspended matter always present, to a greater or lesser degree, in the sea. Because of this photographs taken in oceanic water are usually of better quality than those taken near sources of sediment, such as wave-beaten shores, or river mouths, or in muddy harbours. In average oceanic water, about 96 percent of the light from the surface has been absorbed at a depth of 100 ft. In clean sea water, blue light penetrates deeper than red, but if much suspended matter is present blue light will be scattered to a greater extent than will red. To restore the colour balance, especially in submarine colour photography, filters are often used, both with artificial and with natural light. When light passes between water and air, it is refracted or bent. This introduces two effects to be considered when submarine photographs are taken. First, the camera must be focused at three-quarters the actual camera-to-object distance, and, secondly, when a light beam is refracted, it becomes a diverging spectral band (as when light passes through a glass prism), with the result that unless a supplementary lens is used, the photograph is blurred towards the edges.
Submarine photography has become a valuable technique in oceanographic research. No longer can the saying, “Out of sight is out of mind” apply to the depths of the ocean.
When plans were being made to join the North and South Islands of New Zealand by an electric power cable, oceanographers and engineers took bottom photographs along the proposed routes across tide-swept Cook Strait. The appearance of the sea-floor in these photographs gave essential information on the conditions the cable might have to withstand.
A submarine camera has been used in the clear, oceanic water in Foveaux Strait to photograph the valuable oyster beds and adjacent sea floor. These photographs reveal oysters in their natural surroundings: they show the type of substrate that oysters prefer, as well as the other animals that live there, such as the snake-tailed brittlestars, starfish, and sponges.
In the Ross Sea, photographs of the sea floor reveal a remarkable fauna of sponges, horny corals, and sea-mosses as luxuriant as the surface of the Antarctic Continent is barren.
by John Sidney Bullivant, M.SC., New Zealand Oceanographic Institute, Department of Scientific and Industrial Research, Wellington.