"Mount a longer-than-normal, say a 200 mm, lens on your camera. Owen refers to this as the primary lens. Then take your normal 50mm lens, set it to its widest f-stop opening, f/2.8 for example. Reverse this lens by flipping it 180 degrees and hold it directly in front of your longer lens so the two are touching, nose to nose.
Now look through the viewfinder. Cool, eh?
The working distance, between the end of the lens and the object, will only be a couple of inches. But you have instant high magnification."