Canon EOS-1D X Mark III Advanced User's Manual page 363

Case 3: Instantly Focus on Subjects Suddenly Entering
AF Points
Setting to focus on a series of subjects at different distances in the AF points, one after
another. Focus switches to any new subject that appears in front of the target subject. Also
effective when you want to always focus on the closest subject.
Note
Try setting [Tracking sensitivity] to [+2] if you prefer focusing that immediately
switches to new subjects that appear suddenly (
Default
• Tracking sensitivity: Responsive: +1
• Accel./decel. tracking: +1
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