There is a "sticky" on teleconverters, just do a forum search and you'll find lots of information and experience. The primary thing to know is that when you add a TC to a 100-400, planning to use it mainly at f 7.8 and 560mm, you lose autofocus and, because of the long length, you need to use a tripod for the sharpest pictures. Even with IS, you must shoot with an adequate speed to overcome vibrations due to many factors including all that glass hanging out there. OH, and IS is supposed to be shut off on a tripod with that lens, if I remember correctly. In terms of 35mm field of view, your lens at 400mm with 1.4 X TC would result in the equivalent of 896mm, which requires you to shoot at 1/1000 or thereabout to cut down vibration effects.