Thankfully the GoPro Hero 3 comes standard with a flat lens housing so you don't need to buy it as an extra like you had to for the Hero 2 which had a curved lens housing and gave a soft focus when taken underwater. The flat lens housing with the Hero 3 perfects the soft focus issue from before so you don't need to worry about that at all but the only thing that GoPro hasn't yet addressed is the colour absorption levels as you go deeper underwater.;
As you dive deeper underwater different colours are absorbed by the water. The first colour to be absorbed is red so a red wet suit for example will appear brown and a lot of the coral around you will look more dull than it is in reality. This can however be correct by placing a colour correction filter inside the Go Pro waterproof housing which adds more red to the shot and therefore brings the image back to where it should be.
UPDATE: Polar Pro have a specilased red clip on filter that does a perfect job of colour correcting what you see underwater. Click here to find out more about the Polar Pro Red Dive Filter.
In terms of the waterproof rating of the GoPro housing; it says on the box that the case is waterproofed down to 60m which may sound like overkill but most serious divers regularly go down to 50+ meters underwater. There used to be an issue with the older Hero 2 housing whereby the water pressure at these depths would push the case together leaving the clip to pop open, then when the diver came back up to regular pressures the clip wouldn't be in place so it would open and flood. Thankfully this is another improvement correction made by GoPro with the new Hero 3 Housings.
We're often been asked about the best ways to mount the camera when using it for diving. With the new Octomask now available, you can now easlily have hands free POV filming on your GoPro. The Octomask is a high grade diving mask that is specially designed to have a GoPro mounted securely right on the top of it. Most divers will also use the GoPro Head Strap which positions the camera above your diving goggles which is nice for a point of view shot and also allows for your hands to be free for prodding at rays. Another option used by some divers is to use the Chesty Harness which positions the camera on your chest. While this also lets you have hands free filming the camera isn't easily movable so if you want to film at something/ someone on your right then you need to rotate your entire body. If you don't need your hands to be 100% free then our recommended mounting options are the Grenade Grip or the Bobber. Both of these fit under the camera to allow for an easy-to-hold grip and the later of the two is great because floats :)
Speaking of floating and using the GoPro near water - it doesn't float. If you drop it overboard or while diving then it is going down. GoPro have their own solution for this called the GoPro Floaty which is great for all uses except if you have the GoPro Touch Screen LCD on your Go Pro because the Floaty sticks on the back of the housing and would block your view of the LCD screen. If you have the screen attached then we'll go back to our previous recommendation of using the GoPole Bobber which attaches underneath the camera.