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Author Message   Casual_collector Tinkerer Username: Casual_collector Post Number: 8 Registered: 04-2009 Rating: N/A Votes: 0 Posted on Monday, June 15, 2009 - 03:19 pm:    I dropped a lens once. The impact separated the front doublet causing the interference ring effect. I looked at the lens some months later and the rings were gone. I assume some oil from the focus helicoid filled the gap caused by the fall.