I am using a Rodenstock Rodagon 135mm on my Omega enlarger to make prints on 16 x 20 paper from 4 x 5 negs. I have had some dust marks on prints recently and after cleaning the negs and filters finally noticed that the dust is always in the same pattern over and over. Ok so it must be the lens. After cleaning it several times I still have the dust issue. I can only assume that the offending dust must be inside the elements that I cannot take apart. Two questions, 1. where can I send this lens to be overhauled, and 2. Is it worth it for this lens. This is one of the lenses that came with the enlarger, so I don't really know if it is a decent lens, it is just the one I have always used. Maybe there is a really fantastic lens that I just don't know about?