I don't know anything about enlarger lenses, other than the fact the El Nikkors are supposed to be good. I know nothing about types, sizes, brands, etc etc. I have an Omega B600 that has El Omegar 50mm and 75mm lenses with it. I also have a Beseler 67c that has a 50mm lens on it. I know that I have to have a 75mm lens to cover the 6x6 negative, so can I put the Omega lens on the 67c? Are they all threaded the same?