Underwater photography

Animals such as fish and marine mammals are common subjects, but photographers also pursue shipwrecks, submerged cave systems, underwater "landscapes", invertebrates, seaweeds, geological features, and portraits of fellow divers.

Materials range from relatively inexpensive injection moulded plastic to higher-priced die-cast or machined from solid aluminum.

It is also not possible to change regular lenses underwater, though some wet connectable telephoto, fisheye and macro extensions are available for some housings.

Underwater housings have control knobs and buttons that reach the camera inside, allowing use of most of its normal functions.

High-end housings may use double O-rings on many of the critical pushbuttons and spindles to reduce the risk of leaks, which can destroy the electronics in cameras.

There is also a problem with some digital cameras, which do not have sufficiently wide lenses built in; to solve this, there are housings made with supplementary optics in addition to the dome port, making the apparent angle of view wider.

With macro lenses, the distortion caused by refraction is not a problem, so normally a simple flat glass port is used.

Refraction through a flat port increases the magnification of a macro lens; this is considered a benefit to photographers who are trying to capture very small subjects.

Ideally these should be incompressible at working depth range so the buoyancy remains constant throughout the dive, and can be set with considerable precision.

The primary obstacle faced by underwater photographers is the loss of color and contrast when submerged to any significant depth.

[9] 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.

The loss of color increases not only vertically through the water column, but also horizontally, so subjects farther away from the camera also appear colorless and indistinct.

The water is seldom optimally clear, and the dissolved and suspended matter can reduce visibility by both absorption and scattering of light.

The increasing use of digital cameras has reduced the learning curve of underwater flash significantly, since the user can instantly review photos and make adjustments.

For example, an image shifted toward the "warm" part of the spectrum can create background water which appears gray, purple or pink, and looks unnatural.

From an aesthetic standpoint, the flash emphasizes the subject and helps separate it from the blue background, especially in deeper water.

Considerably more energy is required for constant illumination in comparison with flash, and this method is best suited to cameras with sufficiently sensitive CCDs and for close up work.

One of the pioneers of the traditional technique was National Geographic photographer David Doubilet, who used it to capture scenes above and below the surface simultaneously.

Split images are popular in recreational scuba magazines, often showing divers swimming beneath a boat, or shallow coral reefs with the shoreline seen in the background.

There are specialized split filters designed to compensate for both of these problems, as well as techniques for creating even exposure across the entire image.

An external flash can also be very useful underwater, on a low setting, to balance the light: to overcome the difference in brightness of the elements above and below the water.

This can be avoided to some extent by wiping off the droplets with a chamois leather cloth above the water and lowering the camera to working position.

Keeping the port fully wet is an alternative option, which requires the shot to be taken before the water on the top part of the lens surface separates into droplets.

The technique requires a small f/stop—f/16 or smaller—for great depth of field, plus a lens capable of close-focus; you always focus on the subject below the water line.

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.

[14] Good diving skills are necessary to avoid damaging the environment when maneuvering close to benthic subjects on reefs.

[15] Underwater photography has become more and more popular since the early 2000s, resulting on millions of pictures posted every year on various websites and social media.

This mass of documentation is endowed with an enormous scientific potential, as millions of tourists possess a much superior coverage power than professional scientists, who can not allow themselves to spend so much time in the field.

As a consequence, several participative sciences programs have been developed, supported by geo-localization and identification web sites (such as iNaturalist), along with protocols for auto-organization and self-teaching aimed at biodiversity-interested snorkelers, in order for them to turn their observations into sound scientific data, available for research.

Technological advancements, like the invention of the first waterproof camera housings and improvements in diving equipment, have made underwater photography more accessible.