This winter I plan to go snorkeling with some manatees, but I currently only have a 60mm macro for underwater on my Canon 7D with an Ikelite housing. Obviously I need something a LOT wider for manatees, so have been looking at some of the 15mm lenses out there. I am wondering though...since I already have the Tamron 17-50mm VC f/2.8 for use on land, would that work ok for underwater? I'm assume if I got the right dome port I could at least get it working, but would it work well? I don't have much money to spend, thus if I don't have to get another lens then that would be best.
And I am assuming that 17mm on a cropped sensor wouldn't be wide enough for a good over/under, correct? That is an eventual goal of mine, and if I could get that shot with manatees that would be amazing.
