I have a question. I know that most Teleconverters say they won't AF on lenses that are not f4 or wider ( for a 1.4x ) and f2.8 or Wider for (2x ). I was just wondering if people have had their lenses AF with a 1.4x that wasn't f/4? I know that a lot of times the specs are understated to save from complaints. I have a Canon 70-300 f4-f5.6 IS USM. I can put 32mm worth of extension tubes ( a 20 and a 12 kenko ) and still have AF work. I am of course talking about outdoors daytime shooting. Nothing really dark or super cloudy etc. My reason for asking is I would rather get a 1.4x if I can AF, but if I am going to use a tripod either way I would go with a 2x or 3x instead. Thanks for your help everyone.