ive been reading a lot of reviews on line and cant really find a true answer. some say to put tape on some of the pins but the canon website says in wont work on my camera. has anyone used one on a rebel series camera if so how bad is it when they say autofocus is slow ? ill be getting a new lens in about a month , either a 300f4L or 400f5.6 and im thinking of an extender for a little extra reach for when the critters are a little far.