I recently bought a set of macro extension tubes for Nikon mount. I want to use these to make B&W dupes of color slides for making B&W prints. The only lens I have now is my 50mm f/1.4 AF-Nikkor. By stacking up the right number of extension tubes, I have found a combination that allows me to have focus at the 1:1 magnification required. Quality seems only OK. The question is, how much better quality will I get by buying a special macro lens? Would you care to recommend a Nikon mount macro lens that I should use?