Setup for getting the Canon 50mm f1.8 Lens attached to the Canon 100mm f2.8 Macro Lens. Focus point is about 1 inch or less, pretty limited. Autofocus works with this setup but I perfer to use manual focus.
With this setup you actually get about a 2.4:1 (if I recall when I figured this out a while ago), without this setup just with the Canon 100mm Macro I get 1:1 about a 1 foot away.