I have been looking at teleconverters for my Canon Rebel XS. It seems that most of them mount on the body and than the lens, from what I understand, mounts on the converter like it would the camera body. However some are made to screw into the threads of the lens. The differences in the 'why' of the different types are unclear to me, as well as the effectivness for the two types as far as IQ goes. Another area of confusion is that some of my lenses focus from turning the ring at the front of the lens, but my one lens focuses from the rear of the lens. I am uncertain if all teleconverters compatible with my camera body are also compatible with all my lenses. Some teleconverters seem to be compatible with auto focus and some with manual focus only. I have also read something about some not being compatible with zoom, but that doesn't seem right to me as that is from the lens itself. If anyone can help clear up any of my confusion, any help would appreciated.