Photo.net have published an extremely comprehensive and useful overview of underwater housings for various film and digital cameras - essential reading if you ever intend to take your camera diving with you.

“Every housing works fundamentally the same way. It’s a metal or plastic case, usually molded to fit a specific camera, and uses silicone O-rings to create a watertight seal at the joints. Trusting a $5 O- ring to preserve your $2000 camera seems like madness, but the simplicity is what makes it work. Unless the O-ring is damaged or contaminated, it can work remarkably well. Ironically, as you dive deeper, the O-ring compresses under pressure and the housing becomes even more watertight.”

Website: Photo.net - Underwater Housings