Canon EOS-1DX Instruction Manual page 100

3 Customizing AF Functions
Select AF area selection mode
You can limit the selectable AF area selection modes to suit your
shooting preferences. Turn the <5> dial to select a selection mode,
then 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, left and 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 61 AF points are divided into nine zones for focusing.
: Auto selection: 61 pt AF
All of the AF points are used for focusing.
The <X> mark cannot be deleted from [Manual selection:1 pt AF].
If the attached lens belongs to group H (p.82, 83), you can only select
[Manual select.:Spot AF], [Manual selection:1 pt AF], and [Expand
AF area: ].
100
: Manual select.:Spot AF
For pinpoint focusing with a narrower AF
point than Single-point AF (manual
selection).
: Manual selection:1 pt AF
One of the AF points set by [Selectable
AF point] setting can be selected.