5.6 plus 2x = f/11 - there's no camera that AF at f/11....
you can manual focus though on bright daylight
My 1D Mark IIN and your 1D Mark IV will work on f/8 but not f/11 - none does
hope this helps your inquiry.
« Last Edit: September 04, 2012, 06:28:18 PM by Portrait_Moments_Photogra »
1DX, 1D Mark IIN, 1D Mark II, 5D Mark II, Rebel T3 and Canon XF300 ~ Mamiya 645AF and Medium Format View Camera with Petzval Lenses.
Lenses: 12mm to 400mm, Flashes: 580EX II (5), 600RT (2), Alien Bees (2) and White Lightning x1600 (1) Strobes
Canon CPS Member : 195 Points