Canon EOS 5D Mark III Instruction Manual (en)

Lenses and Usable AF Points
Autofocusing with 61 points is possible. All of the AF area selection 
modes are selectable.
: Cross-type AF point. Subject 
tracking is superior and high-
precision focusing is achieved.
: AF points sensitive to horizontal 
Group I
EF200-400mm f/4L IS USM Extender 1.4x
When using a lens and an Extender in the combination marked with *, 
precise focus may not be achieved with AF. In such a case, refer to the 
instruction manual of the lens or Extender used.
Both “Extender EF1.4x” and “Extender EF2x” apply to all the I/II/III models 
(under this grouping).