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Author Message   Tom_cheshire Tinkerer Username: Tom_cheshire Post Number: 327 Registered: 04-2009 Rating: N/A Votes: 0 Posted on Friday, June 18, 2010 - 10:36 am:    If it is anything like the 135mm then you undo the ring and the glass drops out. Quick clean and put together again. But the real question is "Why do Canon lenses get fungus on the backside of the front group so often?". It seems to be the location of choice for fungus in Canon.