So do lens ever stop being sharp for some reason? I don't think my 24-70 is as sharp as it should be. It isn't front or back focusing. I checked that but the focus doesn't seem as sharp as I would expect from that lens or as sharp as it used to be. Has anyone had this happen? For awhile I was thinking that my eye at seeing clarity got better or I was having an off-focus few days but now I have my suspicions.