Never mentioned a 400mm lens so pls don't misquote. You are right in saying that the setup should be mounted on the lens collar and that you should be holding the lens instead of the body. However, try doing mf on a 300mm (for fine focusing) or basically having to manipulate any function on the lens and i think you will find that during that few moments, you are actually holding the camera body more than the lens. This of course only applies to hand holding shots. And before anyone asks, yes i do hand hold a 300mm f2.8 regularly when it is not convenient to mount up a tripod, monopod.