I recently started having trouble with my cherished 17-40mm 1:4 L USM lens. It won't properly auto-focus. It hunts and sometimes gets it right but usually doesn't. I can still manually focus. All my other lenses still auto-focus fine on my EOS 5D Mark II body. Furthermore, putting this lens on my old EOS 20D exhibits the same problem. So the finger is being pointed at the lens itself.
I've watch YouTube videos where people resolve this issue by taking the lens partially apart and cleaning the auto-focus sensor but I'm not sure I want to go down this road.
Canon doesn't even list this lens as serviceable on their site. I don't understand why.
Does anyone have any tips on getting this fixed? I just hope it doesn't cost more than a used version of the lens.
Thanks!
