Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 343)

: Zone AF
Uses auto selection AF in Zone AF frames to cover a larger area than AF point expansion,
which makes focusing easier than with AF point expansion.
Focusing areas are determined not only based on the nearest subject but also based on a
variety of other conditions such as faces, subject motion, or subject distance.
AF points in focus are displayed with <
>.
: Large Zone AF: Vertical
Uses auto selection AF in a vertical Large Zone AF frame to cover a larger area than Zone
AF, which makes focusing easier than with 1-point AF/AF point expansion and also effective
for moving subjects.
Focusing areas are determined not only based on the nearest subject but also based on a
variety of other conditions such as faces, subject motion, or subject distance.
AF points in focus are displayed with <
>.
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