What does this mean? I'm thinking of buying a EL-Nikkor off of KEH.com. Is the ring like this?: Ring Lens Board Lens Ring screws onto 39mm threads on lens? IS this right? In addition, the main 2 choices are EX and UG. How would someone make a enlarger lens UG?! Its not like you are using it in the elements or having it on a camera that you drop or something.