I looked at a few other homemade underwater cameras but didn't see any that really fit all my needs. I needed a material that I could see through and that would allow me to work all the buttons. I also wanted something to protect the lens as it zoomed out but needed to be able to have a clean viewing area.
What I made was a double layer protective case with a special "zoom tube" attachment. The double layer of bags offer double waterproofing but also an early warning system. If you see water starting to collect on the inside of the outer bag then you know it's time to get out of there but the camera is still locked inside a second bag so it won't be damaged.
It's not the prettiest thing to look at but taking underwater pictures sure is fun so it more than makes up for it's ugliness.
Step 1: Materials
-2 zip-top bags big enough to fit your camera, see note below
-a portion of tube (empty tape rolls are perfect for this), see note below
-plastic to cover the tube, see note below
-tape, duct tape is strong and holds up under water well
-camera with power source (batteries or charged) and memory card, if necessary
You can test the bags for any leaks by sealing them about half full with air and submerging into a sink of water. If you see any bubbles coming out, get a different bag.
I used an empty tape roll for the tube portion which worked really well. The tube will be the protection for the zoom lens and also provide a crystal clear view of your underwater oasis. Make sure that the tube you choose will fit nicely around your camera's lens, especially of your camera has a slide open door like mine that is close to the lens. Also make sure that you take a few pictures while holding the tube up to your camera to make sure it doesn't show up in photos (if it does you'll have to cut it down a bit). I used a cardboard tube and it was fine but if you can find a plastic one I suggest using that just because it offers even more waterproofability (new word).
I used a cut open sandwich bag for the plastic that covers the zoom tube. I suggest you test various plastics by stretching them over the zoom tube and taking a picture through it. I found that name-brand plastic bags were too cloudy but that a store-brand bag was super clear. I tried plastic wrap but didn't trust the thin layer to protect my camera and two layers messed it up so I settled on the plastic bag. I've also hear of people using a condom to waterproof their camera and it working well so you could even try testing that.
Step 2: Zoom Tube
Attach one side using a small strip of tape. Pull the plastic as tight as you can (without tearing it, of course) to the opposite side of the tube and secure with a second piece of tape. This will leave you with two flappy wings like in the picture.
Add another layer of tape around where the plastic meets the tube, making sure there aren't any gaps where the plastic isn't taped down.
Position the tube under the "x" that you made in the last step. gentry stretch the plastic a bit to allow the tube to fit through. You want to only stretch the plastic to the point that the tube can push it's way through. Basically the goal is to have the plastic bag form a tight seal around the tube.
Since I didn't have the proper fitting usb on hand or the card slot on my laptop, I had to take a picture of the underwater pictures I took straight from the camera. You can see that even with a simple point and shoot that the pictures turned out really nice and clear.