Canon EOS 5Ds Instruction Manual page 125

Select AF area selection mode
You can limit the selectable AF area selection modes to suit your
shooting preferences. Select the desired selection mode and press
<0> to append a checkmark <X>. Then select [OK] to register the
setting.
: Expand AF area:
The camera will focus with the manually-selected AF point and the
adjacent AF points (above, below, on the left, and on the right).
: Expand AF area:Surround
The camera will focus with the manually-selected AF point and the
surrounding AF points.
: Manual select.:Zone AF
The AF area is divided into nine focusing zones for focusing.
: Auto selection:61 pt AF
The Area AF frame (entire AF area) is used for focusing.
The <X> mark cannot be removed from [Manual selection:1 pt AF].
If the attached lens belongs to group H (p.104), you can only select
[Manual select.:Spot AF], [Manual selection:1 pt AF], and [Expand
AF area:
: Manual select.:Spot AF
: Manual selection:1 pt AF
].
3 Customizing AF FunctionsN
For pinpoint focusing with a narrower
area than single-point AF (manual
selection).
One of the AF points set by
[Selectable AF point] setting can be
selected.
125