Canon EOS 5D Mark III Instruction Manual (en)

The AF modes available are [Live mode], [u Live mode] (face 
detection, p.210), and [Quick mode] (p.214).
If you want to achieve precise focus, set the lens focus mode switch to 
<MF>, magnify the image, and focus manually (p.216).
Select the AF mode.
Under the [z4] tab, select [AF 
]. In the <
A> mode, it is 
displayed under [z2].
While the Live View image is 
displayed, you can press the 
<o> button to select the AF 
mode on the setting screen displayed.
The image sensor is used to focus. Although AF is possible with the 
Live View image displayed, the AF operation will take longer than 
with the Quick mode. 
Also, achieving focus may be more difficult than 
with the Quick mode.
Display the Live View image.
Press the <0> button.
The Live View image will appear on 
the LCD monitor.
The AF point < > will appear.
Move the AF point.
You can use <
9> to move the AF 
point to where you want to focus. (It 
cannot go to the edges of the picture.)
Pressing <
9> straight down will 
return the AF point to the image 
Using AF to Focus
Selecting the AF Mode
Live Mode: d
AF point