Here are some shots taken with the Sigma 24mm and a Vivitar 2X Macro focusing teleconverter. This setup works Great! The teleconverter allows you to focus without a bellows. The focusing is quick and accurate. For reversing lenses, I highly recommend it. I also used an off camera flash. I used the on camera flash to optically trigger an external flash. It takes a lot of light at these magnifications.
The first shot is of a metal ruler to show the scale. The scale is in mm, so I measure about 2.5mm across the frame. I don't know the horizontal measurement of a K20D sensor, but I think I remember 24mm. That gives about 10:1 magnification!!!
This is a shot of the eye on top of the pyramid on the back of a dollar bill. I need to find something different to shoot, but I want something flat with a lot of detail that everyone is familiar with.