Canon EOS-1D X Mark III Af Setting Manualbook page 33

An example where [Responsive: +1/+2] is
effective.
When you want to quickly switch between the athlete in
focus, while continuing to use AF.
On the track there's a lot of competition - in the first scene
on the start line, the center athlete was the target, but
then switched to the leading athlete one after another,
and in the finish line scene, the target was the athlete in
green running at the front. The [Responsive: +1/+2] setting
is effective when you want to quickly switch between
players while continuing to focus with AI Servo AF or Servo
AF. It is effective in a variety of cases such as in baseball
when you want to quickly switch subjects between a pitcher
starting to throw the ball, or a player running in an attempt
to steal a base.
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