So, a coworker loaned me his set of extension tubes, & I was playing around with the 12mm tube mounted to a 20-35mm f/3.5-4.5. Results were interesting: Note the extremely shallow DOF (lens was less than 1" from the subject in all of these): Another: More: Anyone else use these? I am thinking about picking up a 12mm tube. He let me borrow a 36mm one as well, but the DOF is way to shallow, and you have to have the subject virtually touching the lens. Any techniques I should try out while I still have the loaner tube?