I post the odd underwater blip such as this cuttlefish or this scallop , and usually that provokes questions about equipment. I've posted my other underwater cameras on here, including the disasterously flooded Olympus and my wee fuji with a borrowed strobe.
This is my current rig. At the heart is a Canon S90 compact about the size of a packet of cigarettes. It's got full manual control and very good performance in low light - both vital for underwater use. It's wrapped in an Ikelite housing, made of polycarbonate and waterproof to 60m. The door is sealed with an o-ring, which must be cleaned an inspected before sealing the camera in. All of the camera controls are accessible using knobs or buttons on the outside of the case that go through sealed fittings to activate the controls inside.
On the front of the housing is a white plate which stops the cameras flash leaking out, and attached to that is an optic fibre which connects the internal flash to the external flash, or "strobe" as they are known in underwater photography.
The housing is screwed on to a plastic plate, and attached to that is a flexible arm for the strobe, which is a specialist underwater device - an Epoque 150-DSa. It is triggered from the cameras internal flash using the optic fibre, and has a dial on the back to control how bright it is. The arm allows the strobe to be mounted well away from the lens, which reduces the amount of "back scatter" from particles in the water, giving much clearer pictures. You can move it around to get the best lighting position for your subject.
Also on the front of the housing is mounted an Epoque DCL-20 wide angle adapter. The optical properties of water mean that everything appears about 30% closer, which means the standard "wide angle" setting on the camera isn't very wide at all! This "wet" adapter lens fixes that problem.
To the left of the picture, you can see a wrist lanyard attached to the housing. When I'm using the camera this is attached to my wrist. The camera is also attached to a D-ring on my buoyancy jacket by the extending lanyard behind the wrist lanyard. For entry and exit from the water, this clips short to keep the camera steady. When in use the coiled section extends so I can move the camera freely. There is also a silver piston clip tied to the arm with yellow string to provide a second point of attachment for the camera rig during entry and exit.
In the UK I usually dive with the full setp as seen here, although sometimes I don't bother with the wide angle adapter - overseas the strobe is much less necessary so I don't always use it.
Very serious professionals do use SLR cameras underwater, but a typical SLR housing costs in the region of £1,500 to £3,000, and on top of that you need a special "port" for each lens, usually at least £500. SLR housings are also about 4 times the size of this kit and very heavy - so not convenient for travel, and you still need external strobes. All but the most serious photographers use rigs like this based on a compact, and the results from modern, high-spec compacts like the S90 are better than most SLRs from even a year or so back! This is still an expensive setup overall, but nothing like the price of taking an SLR under the waves.
So there you have it! Any more questions about underwater cameras will be referred here...
P.S. Please check out MrsCyclops truimphant blip - she is back from collecting her award and showing it off!