First off, I think flat field lenses like enlarger lenses would be better than extension tubes and macro lenses. Do you want to copy 1:1 life size negs or photographs. For photographic prints, a good set up would be a copy stand with polarized light and a polarized lens. Also the larger the copy neg the better. You probably could find old copy stands for a song on Ebay. A lot of institutions are dumping them due to flat bed scanners. I'm sure some smart APUGer will give some great advice on copying photos.