Canon EOS-1DX Af Setting Manualbook page 62

Zone AF
With the [Zone AF] mode, one of nine
focusing zones can be selected, and the
AF point is automatically selected from
within that zone.
Effective for capturing subjects within
a known area
The selected AF points display in
[Zone AF].
Zone AF differs from [AF point expansion] with it's
manually selected AF point, which AF tracking is based
around. With Zone AF the camera decides where to
focus on the subject within the zone, rather than
targeting the subject (area) that you want to follow
closely. This is more suited for situations (the subject has
no obstacles that may block the AF points). This mode is
easy to use when you want to focus on areas of the
subject that are a larger size, making it possible to easily
capture the appropriate area.
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