There are two ways to approach underwater photography. One is to encase a surface camera in a housing and use it underwater, the second is to use a camera that is specially designed to be used underwater without a housing. Housing a camera can be very effective since you can put a good camera and the lenses you already own to use underwater. In addition, there are no SLR's currently available for underwater use without a housing, so if you want the advantages of an SLR, you need to used a housed SLR. On the other hand, no housed camera is as compact as an underwater camera, and underwater cameras are more durable.
There are two basic types of housings. Flexible housings are inexpensive, but can only be used near the surface. Hard housings are expensive, heavy and cumbersome, but offer greater protection and operating depths. Housings are becoming available for digital cameras as well as film cameras.
Available for almost every camera, flexible housings usually cost under $200. The better ones have a glass port for the lens and viewfinder, and some sort of glove arrangement to facilitate operating the controls. They do not add much bulk to the camera, and are very light. They are also good for simply waterproofing the camera for use in rainy, snowy, sandy or just plain icky environments.
In the water, these housings work well as long as you don't go too deep. Think about what happens to your feet when you wear tall rubber boots in a deep puddle. Well, pressure doubles for every 10 meters (33 feet) of depth. I've used these housings successfully at depths of up to 90 feet with my trusty Canon A1 (manual film advance and all), but it wasn't easy. The manufacturer only rates them to 60 feet, but even there they are tough to use.
Points to consider when looking at these housings are:
In general, get the biggest one you can. I found that with a little trickery I could leave the flash off my camera and put an extra roll or two of film in the bag and even switch film underwater (not too deep, though). I put velcro on the inside of the bag and the outside of my camera to make sure the viewfinder port stayed over the viewfinder.
To use the housing, place the camera inside it, along with all the accessories. Many models have an adapter ring which screws into the filter mount on the lens and then pops into the lens port of the housing. Some bags will also come with adapters to make the focusing ring of the lens easier to grip. Seal the bag up. The manufacturer usually recommends removing as much air as possible, but if you are going below 30 feet you may want to leave a little more air in the bag (this will make it very buoyant near the surface, however). As you go into the water, watch for bubbles; if you see them, return to the surface immediately. Since the plastic is clear, you can see any leaks as well.
For a very inexpensive underwater housing, put your camera in a ziplock bag. This works down to a foot or two, and don't do it with a camera you can't afford to lose. The results are about as good as you would expect.
While flexible housings are available for almost every camera, your choices are more limited when it comes to rigid housings. If you plan to house a camera, it is best to make sure in advance that a housing is available for it.
Rigid housings are made of metal or plastic. The metal housings tend to be more expensive, usually starting at around $1,000. Compared to plastic housings, they are tougher and more compact. Plastic housings are usually made of clear plastic; models for SLR's start at around $600. In both cases, special ports to accommodate different lenses, flash attachments, and other accessories will drive the cost up.
With most rigid housings, there will be oversized controls on the outside of the housing which actuate the camera's controls on the inside. With some cameras, it is not possible to actuate all of the controls, so only the more critical ones are available. In most cases, the controls will be somewhat awkward to use, at least at first. In some cases, there will be a special viewfinder extension to ensure that you can see through the viewfinder from outside the housing while wearing a mask underwater.
Because of the air they trap inside them, some rigid housings, particularly the plastic ones, may be positive buoyant, that is they will float if you let go of them. To make a larger housing neutral buoyant, it may be necessary to add a weight either inside or outside the housing. This, of course, makes the housing heavier and more unwieldy out of the water.
Some housings have a water alarm built into them, with others you simply have to watch for bubbles, or in the case of transparent housings, water inside the housing.
Using these housings is more of a production than using the flexible housings, but at least the controls operate with the same ease at the surface all the way down to their maximum depth. When buying such housings, look for ease of use and ease of handling in addition to durability.
Don't overlook the possibility of putting a compact autofocus camera in a rigid housing. The resulting rig is small and may be able to take some good pictures.
On the cheap end, you can get disposable cameras in plastic housings good to about 10 feet for about $10, or a housing for disposable cameras that costs around $70. The latter can be fitted with a strope and a macro kit.
There used to be a single type of underwater camera, the Calypso, developed by Jacques Cousteau. Over the years, the Calypso was taken up by Nikon, renamed the Nikonos, and evolved into the latest model, the Nikonos V. A host of other underwater cameras has also appeared on the market, including the amazing - and discontinued - Nikonos RS, and underwater autofocus SLR.
Today there are 3 basic levels of underwater cameras:
Flash is much more important below water than above it. Because of the attenuation of light in water, it is darker underwater, and because of the shift to blue light, a source of red light is needed.
There are a wide variety of possibilities for getting flash underwater. In many cases, a flash built into an underwater camera body, or into the body of a housed camera, or mounted on a hot shoe will be employed, but this can be problematic. Any suspended particle or planktonic organism in the water will reflect light back to the flash. If the flash is close to the lens (as most built-ins are), the light will be reflected back to the film as well, to appear as a bunch of distracting spots in the photograph. It is far better to get the flash off the camera, if possible.
Off the camera, it is possible to house an above water flash, but many people simply purchase underwater flashes or strobes. At this point, you need to be aware that there are several competing types of connectors available. One connector is used by Nikonos, another type by Sea & Sea, and some manufacturers produce both types. Whether buying an underwater strobe, or an underwater housing for a camera or strobe, you will have to figure out in advance what type of flash connector you want. Because of the inherent difficulty of making watertight connections, if a second flash is used underwater, it is often a slave model which gets its cues from the wired flash. Underwater photography tends to use wider angle lenses than above water photography, and to be done at closer distances. Therefore, flash power is usually not as much of an issue underwater as it is above water. Width of coverage is an important factor, however; underwater strobes need to cover the wide angles of view that are part of using wide-angle lenses.
Other Underwater Accessories
The Nikonos System