It took a while to find one of these for a good price, but I now have an Nippon Kogaku (Nikon) El-Nikkor 80mm f/5.6 enlarger lens. It seems to work well as a macro lens when mounted on extension tubes using a M39→F-mount adaptor. Now I just need to find a 34.5x0.5mm→anything else adaptor and a BR3 reversing adaptor so that I can use filters on it.