Canon EOS-1DX Af Setting Manualbook page 57

Single-point AF
Single-point AF is an easy to use mode
for still life photos etc. in One-shot AF
Single-point AF is a mode where one
manually selected AF point is used to
focus.
For experienced photographers or when it is easy to track
the subject with a single AF point, AI Servo AF can be
utilized when continuously shooting moving subjects,
however, this mode is more effective for shooting still life
and landscapes with One-shot AF mode.
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