Google to the rescue! It's a special lense that allows for adjusting the angles the image is actually being exposed on the film. Very cool, very expensive ($1,200 for one for my Canon). There's a site with instructions on how to build your own with an old lens and a plunger, but with the other site I perused I think I'll hold off until I get a digital SLR. Apparently a lot of trial and error in getting the right exposure times because of the way the camera sensors read the incoming light, you may end up with highly overexposed/underexposed areas on the print if you don't adjust your metering properly. Film developing is damn expensive if you're not getting payed for it.