Hi, I just bought an older, chrome base, 80/5.6 EL Nikkor to use on my Omega B22 Enlarger. However, when I try to mount it on the lensboard, the retaining ring will not start on the threads. The ring goes on off the board, it works fine with my 50/2.8 EL Nikkor, so it seems to be a problem with the length of the threads on the 80. Has anyone any suggestions? I could try to find a threaded lensboard, but it would probably be cheaper to buy an different lens.