With thin wide angle filter installed you can't put the lens cap on to put the glass back in your bag. You have to either remove the filter or go without the cap. Kind of a pain in the butt, but it's such a great lens for the money, I really don't care so much about the cap.
Good filter but I was surprised when I try to close lens (Canon EF 24-70 1/2.8L USM) whit front lens cap. Filter is too thin for cap. But lens hood is realy big and protect front filter from fingerprints.