This is how to make a cheap macro lens for a camera which does not have a built-in macro feature. The one I am showing here is designed around a housing for my cheap underwater camera, but you can easily re-design this to fit whatever camera you'd like. For those of you who don't know, the purpose of a macro lens is to allow your camera to take closeup photo's. Most cheap point-and-shoot cameras only let you get to within 1m or so of your subject. With the addition of a macro lens you can get much closer. A 2-3x magnifying lens will allow you to get within 10-15cm. This project is quick, simple, can be put together for a few bucks, and only takes an hour to do! I've made similar lenses to fit onto underwater video housings and an SLR housing. They all work fairly well. Unfortunately, I only took pics of the first, simplest lens I made. For you underwater SLR junkies out there, if you're using a flat port this is a way of getting a limited macro ability with a normal/wide-field lens. Unfortunately, it is not cross-compatible with dome ports. A few note on lenses: 1) The lens you pick will have a huge effect on your final results. Generally speaking you want a 2x-4x lens; any less and you won't get enough magnification; any more and your working distance will be too short to be useful. 2) Glass is better than plastic, especially for underwater use. Glass is more durable, and less prone to scratching. Under water, both types of lenses will loose magnification (because the refractive index of water is not the same as in air), but the effect will be less for a glass lens.
http://www.instructables.com/id/5-Macro-Lens---for-use-above-and-below-the-waves/