I sent in my 16-35 because it was back focusing too much. They sent it back saying that they calibrated it to factory specs and charged me almost $100. It still back focuses! They did say that "if I still have a problem to sent it back with the camera". Fuck that. They'd probably just adjust my 5D to correct the lens problem. All my other lenses focus where they're suppose to. Why the hell can't a $1000 lens focus properly.