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Author Message   Markkal Tinkerer Username: Markkal Post Number: 7 Registered: 08-2008 Rating: N/A Votes: 0 Posted on Sunday, June 10, 2012 - 07:32 am:    Hi friends, I have a pristine smc Pentax M 28mm 2.0 which has a problem I never encountered before, see pictures. There is a loose ring inside just behind aperture blades (When seen from backside) which moves around and interferes in half moon fashion with aperture. Blades are all there and they operate so I cannot understand what is the function of this ring, neither by which means it is attached. It looks like there is some glue or dried grease imprint on its rim. Have removed back elements but to fix it must go past blades removing front block too.. Any suggestions ?? Thanks al