Macro Photography with Reversed Fixed Lens
Macro photography is a special case that need special lens to get the bigger magnification. Canon provide some lenses that can be used in macro photography such as: EF 100mm f/2.8 1:1, EF 180mm f/3.5L 1:1, and MP-E 65mm 1-5x; the last one has highest magnification about 5:1. All the macro lenses are quite expensive if you aren’t very lovely shoot a “macro” photo, because these lenses are built specialize only for macro photography although they also can be used for portrait.
Reversed lens maybe become the inexpensive way to get macro photography, it’s only need fixed lens (example: EF 50mm f/1.8 II) and also reversing ring that will fit your camera mount and filter thread size that your lens has. When you use this technique, AF will not work so you need to set the focus manually. Do not confuse it with stacking two lenses, this method is different from stacking two lenses.
More detail about macro photography: http://en.wikipedia.org/wiki/Macro_photography