From what I have read the C and C T* lenses take Bay 50 filters, the CF lenses take Bay 60 filters and the CFi lenses take Bay 70 filters. Some special lenses take other filters.

I own an 80mm CF lens. I have a conversion ring to 67mm and a step-up ring to 77mm so I can use my 77mm screw in filters as well as Bay 60 filters.