I would definitely advise against the Canon MP-E 65mm. It is an excellent lens, but far too specialized here. You need to consider that at the absolute minimum magnification, you would be able to fit something 36mm long across the frame on the 5D, 22mm long on any crop body. The lens does not allow for normal focusing, the ring only controls magnification from 1x to 5x so you need a focusing rail to accomplish focusing. You also cannot shoot anything at less than 1:1 magnification. I would suggest a conventional macro lens going up to 1:1 magnification... the Nikon 60mm or 105mm AF-S micro-nikkors, or for Canon crop bodies (not the 5D) the 60mm EF-S or for any Canon the 100mm f/2.8 Macro. All are very good lenses, both Nikon versions are extremely new designs.