Canon EOS 5DS Instruction Manual page 92

S Selecting the AF Area and AF PointN
Selecting the AF Area Selection Mode
With [24: Select AF area selec. mode], you can limit the selectable
AF area selection modes (p.125).
If you set [24: AF area selection method] to [S9Main Dial], you
can select the AF area selection mode by pressing the <S> button,
then turning the <6> dial (p.126).
92
1
Press the <S> button.
2
Press the <B> button.
Look through the viewfinder and
press the <B> button.
Each time you press the <B>
button, the AF area selection mode
changes.
(9)