I did take many diving courses and start shooting underwater. The compact camera has some certain limits, regard the insufficient lighting. You'll need at least 2 extra external flashes to keep the picture look alright. Otherwise, you will need a DSLR housing for your DSLR camera for more control. Nevertheless, the picture quality is not what you expect without the flash. So far, I'm still tempting to take my EOS 20D and my 2 external flashes underwater. I lost my old Canon S-40 underwater when some water leaked into the housing. It could happen; there's no 100 % water proof guarantee, varied by the diving depth. Otherwise, you may end up spending a lot of money for more equipments. Any way, good luck. Start with what you've got and really need now.