Did you know that it's possible to build a working compound microscope with nothing but LEGO elements? The key is the magnifying glass. All you need is several of these convex lenses, and some Power Functions LEDs.
This creation uses 4 LEGO magnifying glasses to create a fully functional compound microscope. Other features include separate coarse and fine adjustment knobs, power functions LEDs and a rotating stage.
LEGO Ideas - Working Microscope