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3 Using Underwater Cameras
The rules of photography in air do not all apply in the water. Unlike in air, water absorbs light and modifies its colour and scatters it through suspended particles. Red light is filtered out first within a few meters, depending on visibility, leaving blue or green. In order to compensate for the loss of colour there are underwater colour corrected filters (UWCC) to bring back some of the reds. There is a mathematical calculation to work this out and there are different strengths of UWCC filters depending on depth and visibility. The downside is that UWCC's reduce the light reaching the film. Eventually there is no red left to enhance with a filter and they are of no use at depth. The solution is to have a strobe/flash to add light and bring back the colours. Flash photography If you want to get the best underwater photographs, the first accessory you should consider is a flashgun. They put the light and colour back into the shot and take away the monotone green or blue from available light shots. In addition a flash allows the use of smaller apertures giving a greater depth of field. First consideration is that the flash should have the same angle of coverage as the lens. For a 15mm lens the angle of coverage is 95 degrees. A wide-angle diffuser will widen the angle of coverage on a flash to cover the entire area with a slight drop off of light at the edges, which is acceptable in some individual fish shots, but noticeable on a shoal. Also how many flashes you get at full power and the recycle time should be considered. Next consideration is its power output. Is the flash powerful enough for the distance and lens you are using?
Does the Through The Lens exposure control (TTL) interface with your camera? There are several flash interfaces for Nikonos, Ikelite and Sea & Sea, make sure you get the right one to interface with your camera. Get advice before you attempt to plug any strobe into your camera. They don't all work together and may "fry" all of the camera's electronics.
Wide-angle lenses are great for wreck photography. These lenses allow you to get closer to the subject and minimises the column of water between the camera and subject giving clearer water and sharper images whilst getting the whole image in frame. Macro photography Macro lenses or extension tubes allow you to take pics close up of small objects. One-to-one macro photography gives an image exactly the same size as the subject. So, a prawn one-inch long will be one inch long on the film or CCD.
Camera Preparation Always prepare you camera in a dry, dust-free environment. Take your time and do it in a well-lit area. Many cameras are flooded through simply rushing and working in dimly lit places. Check that all seals are in perfect condition and have been seated properly. Finally, check all is OK by checking the complete system in a dip tank of fresh water. It is better for it to leak here than in salt water. If you are diving with a new housing for the first time, dive with it empty, without the camera, to check it does not leak. O-rings There are two kinds of o-ring seals. "Piston" o-rings seal one assembly into another,providing a flexible seal, such as in the back door of a Nikonos and on moving shafts. "Gasket" compression seals are squashed together by a lid, like used in the back of a SLR housing. Don't over grease the o-rings. Silicone grease is not a sealant. It is a lubricant that allows the o-ring to slide exactly into place. Too much grease can cause flooding.
0-rings made from Nitrile-butadiene Rubber (NBR) should be lubricated with petroleum gel, Vaseline or preferably silicone grease. Silicone rubber seals lubricated with the above will swell and fail. The correct lubricant for silicone seals is flurosilicone grease. Pre-dive check
Get someone to pass you your camera, gently slip below the surface with your camera. Jumping in with you camera in one hand is not advised. The sudden force of hitting the water can dislodge camera o-rings with disastrous results.
Immediately after diving immerse camera equipment in a wash tank with clean fresh water. Then dry with a clean cloth. Removing film or card procedure First rewind the film, then with dry hands, point back of camera downward to prevent any residual water drops in the o-rings falling into camera or housing. Finally remove film and rewind the leader fully into the film cassette. Film Processing Abroad Processing is an exact science that requires controlled conditions. Results vary from good to bad. It is good to have immediate feedback on your day's photography, which allows you to assess your photography. Then go back into the water and put right those mistakes and capitalise on your earlier successes. However, it is not worth having your films ruined if your films are being processed on a rolling and pitching boat. Try one roll out first before processing all of your precious films.
Flooded cameras can sometimes be recovered providing immediate action is taken. Salt water in contact with delicate electronic parts will cause irreparable corrosion. Immediately immerse the wet parts in preferably distilled water after first removing, lens, film and batteries. Then dry out completely and reassemble. Do not immerse flash capacitors in water, as there is a danger of electric shock. They can retain a high charge long after they have been switched off. After care and storage Clean and dry out all equipment thoroughly. A good ideas is to put all of your gear into a warm airing cupboard with the camera back and lenses open side up to ensure that they are thoroughly dry. Then clean all o-ring grooves and lightly lubricate with the appropriate grease before putting away. Remove re-chargeable batteries and only leave the mini internal function batteries. Store all equipment in a dust free environment, like a sealed camera box. Every few months inspect the camera, charge it up and fire off the strobe to keep the capacitors working at their optimum, rotate moving parts to keep free from seizing. 
HousingsA housing is a tough waterproof container, which allows you to take your land camera underwater. It has controls on the outside with levers to operate the camera controls and a plastic port for the lens to shoot through. Ports and domes There are many ports and domes available and this will depend on your lens. Each camera lens will require a different dome or port with its own length or diameter. Flat port for a standard or macro lens Flat ports increase the magnification of their lenses, often cause optical aberration and are best used with small apertures. The aberration will get worse as the focal length gets shorter so much so a 28mm lens behind a flat port will give shots with out of focus corners Dome port for wide angle lens. A dome port can restore lens angle, minimise chromatic abberation and restore focus range and depth of field as well as correcting pincushion effect. The dome when used in contact with water becomes a negative power lens and will need positive diopter to compensate for the negative effect of the dome. Housing cameras are larger than unhoused cameras. They are made from metal or plastic. Clear plastics advantage is that you have a clear view of the camera, and information control functions. It is corrosion free, you can see the seal and if it has sealed correctly. If it floods you can see the water seeping in and hopefully act before it causes damage. Metal housings are stronger and heavier on land but neutral in water. Return to PHOTOGRAPHY INDEX 
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