I was always turned off by the STIFF focus ring on the C lens, then someone told me "think about how OLD the grease in the lens is." That made me realize that the old dry grease is probably what makes the C lenses so hard to focus. I've dealt with old grease and oils on other stuff, the grease was like semi-dry clay, totally useless as a lubricant, and actually increased friction. I have not had the opportunity to try the focus on a recently serviced C lens, so I don't know how smooth it can get after removing that 40+ year old grease and relubing with new grease.