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Author Message   Monopix Tinkerer Username: Monopix Post Number: 109 Registered: 11-2008 Rating: N/A Votes: 0 Posted on Monday, February 15, 2010 - 03:42 pm:    Looking at this picture... it looks like the ring you are trying to fit stands proud of the rear of the lens quite a bit. It looks like you are trying to put yours on too far, hence why it's hitting the back of the helicoid. But it's difficult to be specific without knowing how the lens is assembled.