Build a Waterproof Camera
Underwater photography is the process of taking photographs while underwater. It is usually done while scuba diving, but can be done while snorkeling or swimming.
OverviewUnderwater 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 possibility 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. Camera EquipmentUnderwater 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. Sea and Sea continues to manufacture an amphibious range finder camera that utilizes 35mm film, the Motor Marine III. 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. Digital media can hold many more shots than standard photographic film (which rarely holds more than 36 frames). This is the primary advantage of using digital camera underwater, since it is impossible to change photographic film underwater. For this reason, most underwater photographers today choose to use a digital camera. 
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 may also have connectors to attach external flash units. Some basic housings allow the use of the flash on the camera, but the on-board flash may not be sufficiently powerful and are improperly placed for underwater applications. More advanced housings either redirect the on-board strobe to fire a slave strobe, or physically prevent the use of the on-board strobe. 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. Some housings also allow for the use of wet-coupled lenses, which thread on to the exterior of the lens port and increase the field of view. These wet-coupled lenses may be added or removed underwater, allowing for both macro and wide angle photography on the same dive. 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 Flash
The use of a flash or strobe is often regarded as the most difficult aspect of underwater photography. Some common misconceptions exist about the proper use of flash underwater, especially as it relates to wide-angle photography. Generally, the flash should be used to supplement the overall exposure and restore lost color, not as the primary light source. In situations such as the interior of caves or shipwrecks, wide-angle images can be 100% strobe light, but such situations are fairly rare. Usually, the photographer tries to create an aesthetic balance between the available sunlight and the strobe. Deep, dark or low visibility environments can make this balance more difficult, but the concept remains the same. Many modern cameras have simplified this process through various automatic exposure modes and the use of through-the-lens (TTL) metering. 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. An added complication is the phenomenon of backscatter, where the flash reflects off dirt or plankton in the water. Even seemingly clear water contains enormous amounts of this particulate, even if it is not readily seen by the naked eye. The best technique for avoiding backscatter is positioning the strobe away from the primary plane of the camera. Ideally, this means the flash will not light up the water directly in front of the lens, but will still strike the subject. Various systems of jointed arms and attachments are used to make off-camera strobes easier to manipulate. 
When using macro lenses, photographers are much more likely to use 100% strobe light for the exposure. The subject is normally very close to the lens, and the available sunlight is usually not sufficient. There have been some attempts to avoid the use of flash entirely, but these have mostly failed. In theory one could use color filters to overcome the blue-green shift, but this can be problematic. The amount of shift would vary with depth and turbidity, and there would still be a significant loss of contrast. Many digital cameras have settings that will provide color correction, but this can cause other problems. For example, an image shifted toward the "warm" part of the spectrum can create background water which appears purple or pink, and looks very unnatural. There have been some successful experiments using filters combined with the RAW image format function on some high-end digital cameras, allowing much more detailed manipulation in the digital darkroom. This approach will probably always be restricted to shallow to moderate depths, where the loss of color is less extreme. In spite of that, it can be very effective for large subjects such as shipwrecks which could not be lit effectively with any strobe. Although digital cameras have revolutionized many aspects of underwater imaging, it is unlikely that flash will ever be eliminated completely. From an aesthetic standpoint, the flash often adds "pop" and helps to highlight the subject. Ultimately the loss of color and contrast is a pervasive optical problem that cannot always be adjusted in software such as Photoshop. Split Images
Another format considered part of underwater photography is the over/under or split image; it is a composition that includes roughly half above the surface and half underwater. The traditional technique was pioneered by the 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. Over/under shots do present some technical challenges beyond the scope of most underwater camera systems. Normally a wide-angle lens is used, similar to the way they are used in everyday underwater photography. However, the exposure value in the "air" part of the image is often quite different from the one underwater. There is also the problem of refraction in the underwater segment, and how it affects the overall focus in relation to the air segment. 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. Some photographers will also rely on extremely wide or fisheye lenses, which have enough depth of field to overcome any differences in focus. Digital darkroom techniques can also be used to "splice" two images together, creating the appearance of an over/under shot. Timeline
See alsoExternal linksThis article is licensed under the GNU Free Documentation License. It uses material from Wikipedia Encyclopedia article "Underwater Photography" |
