Monday, December 25, 2006

Underwater Camera

Underwater photographers have two basic options for equipment:

The first is using an amphibious or waterproof camera such as the Nikonos, which is designed specifically for use underwater. Nikon discontinued the Nikonos series in 2001 and it is a 35mm film system, so it is somewhat obsolete, but some photographers still choose this approach.

More often, underwater imaging is achieved by putting a traditional film or digital camera into an watertight underwater housing. This allows many more options, since the user can choose a housing specific to their everyday "land" camera, as well as utilize any lens in their collection. In practice, underwater photographers only use either wide-angle lenses or macro lenses, both of which allow close focus, thereby eliminating the need to have excessive water between the camera and subject. Since digital imaging has largely taken over the market, most underwater photographers today choose to house their regular digital camera with this approach.

All underwater housings are outfitted with controls knobs that access the camera inside, giving the photographer use of most of its normal functions. These housings also have connectors to attach external flash units, since any flash on the camera itself will be blocked by the housing. Like the Nikonos, housings are made waterproof through a system of silicone o-rings at all the crucial joints.

There are optical issues with using cameras inside a watertight housing. Because of refraction, the image coming through the glass port will be distorted, in particular when using wide-angle lenses. The solution is to use a dome-shaped or fish-eye port, which corrects this distortion. Most manufacturers make these dome ports for their housings, often designing them to be used with specific lenses to maximize their effectiveness. The Nikonos series allowed the use of water contact optics: ie, lenses designed to be used whilst submerged, without the ability to focus correctly when used in air. There is also a problem with some digital cameras which do not have sufficiently wide lenses built into the camera. 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 an issue, so normally a simple flat glass port is used. In fact, refraction increases the magnification of a macro lens, so this is considered a benefit to the photographer, who may be trying to capture very small subjects.

Underwater Photography Overview

Underwater imaging is considered an especially challenging area of photography, since it requires very specialized equipment and techniques to be successful. Despite these challenges, it offers the possibiltiy of many exciting and rare photographic opportunities. Animals such as fish and marine mammals are the most common subjects, but photographers also pursue shipwrecks, submerged cave systems, underwater "landscapes", and portraits of fellow divers.

The primary obstacle faced by underwater photographers is the extreme 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.

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. This is best achieved by using wide-angle lenses, which allow very close focus, or macro lenses, where the subject is often only inches away from the camera. In practical terms, 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 color 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.

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. Generally, underwater photographers try to avoid these situations whenever possible.

Source wikipedia