There are housings for Hasselblad Superwides, and I'm pretty sure most of them will take the 70mm long-roll backs. They're far more common than the housings for other medium format cameras, with the possible exception of the Rolleimarin, which was a factory accessory (granted, they didn't sell that many of those either). But everything else that has been said about medium format underwater is true - I'd get used to shooting underwater with a digital, and only after you're sure you want to keep doing this and you've gotten better at it would I invest in a medium format housing. After digital, get a Nikonos V with a strobe to get used to the film+strobe bit - while the Nikonos V does have TTL strobe, it's still not as automated and idiot-proof as underwater digital is. When you're finally getting good, consistent results with the Nikonos, then upgrade to the medium format. IMHO, the way to go if/when you get to that point is to get the Hassy Superwide with the 70mm back. The 38mm lens is like a 20mm for 35mm/digital, so it'll be plenty wide, and if you couple it to a flash and reasonably fast film, you'll have the depth of field to be able to set the thing at hyperfocal and forget it. There are strobe setups that will work with those cameras too, but I'm not sure of the details on them. The whole medium format underwater thing is a bit of a mystery because it's so unusual.