Canon EOS 5D Mark III Instruction Manual page 73

Select the AF Area Selection Mode
With [24: Select AF area selec. mode], you can limit the selectable

AF area selection modes (p.99).
If you set [24: AF area selection method] to [ →Main Dial], you can

select the AF area selection mode by pressing the <S> button, then
turning the <6> dial (p.100).
AF point expansion (Manual
selection, surrounding points)
The manually-selected AF point <S>
and the surrounding AF points <w> are
used to focus.
Zone AF (Manual selection of
zone)
The 61 AF points are divided into nine
zones for focusing.
61-point automatic selection AF
All the AF points are used to focus. This
mode is set automatically in the <A>
mode.
Select the AF area selection
mode.
Press the <S> button.

Look through the viewfinder and

press the <B> button.
 Press the <B> button to switch the
AF area selection mode.
S Selecting the AF AreaN
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