Photo, right: Vivitar underwater camera by bAnetz/b on Flickr. This photo also shows the 'sports finder', which is much more useful than a viewfinder once you're underwater. Your options will change depending on whether you want this to be a bvacation/b hobby or you want to become a gadget-tastic underwater photographer with all the bells, whistles, and a bathysphere with an espresso machine in the corner. Don't get me wrong, underwater photography can become very expensive, ...
