[Ricus.stormfire]

That's only the 'S' version, the 50 mm PS is 77 mm and (empirically determined) pretty sensitive to stuff building out on the front. That 67 mm across the line was one of the things that went by the wayside in the transition from S to PS. The 110 mm f/4.5 PS 1:1 macro takes a 72 mm filter. (Would I had bought 77s first and then some step-up rings! )

Thanks, I stand corrected.