Canon EOS-1D X Af Setting Manualbook page 32

AF Area selection mode [AF point expansion]
For fast moving subjects that are difficult to track with a
Enlarge the active AF area to keep a larger focus area on moving subjects
AF point expansion (4 surrounding pts.)
[AF point expansion] mode can be excellent for subjects with erratic movement. [AF point expansion (4
surrounding points)] is well-suited for situations when the primary, central AF point may momentarily see a plain,
non-detailed area of a moving subject — focus-tracking can continue, using any surrounding AF point.
[AF point expansion] is an AF area choice that
is excellent when shooting sports. A single,
primary AF point is normally used — but with
either four or eight surrounding "stand-by"
points, the camera can immediately switch to
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AF point expansion (8 surrounding pts.)
an outer AF point if the subject suddenly moves
from the central point or if that central point
begins to fall on an area of a subject with little
detail, texture or contrast.
Any of the 61 AF points can be selected as
V iew finder display of
[AF point expansion].
The manually selected AF
point and surrounding
points lights up.