If you just use the camera, it's pretty tough to shoot half underwater/ half and half photos, because the water line, filed of view and underwater magnification stop you doing that, so to even things out, you need this dome port. The dome pushes the waterline away from the lens, the field of view is increased, above and below the waterline, it gives you very cool pictures. The water magnifies things. This distorts the look of photos, making the above water objects look normal while the underwater objects look larger. With this dome port, it normalizes the field of the view, it matches up above and below the waterline, which gives you a real world.