Canon EOS 70D Instruction Manual page 370

3 Custom Function SettingsN
C.Fn II -4
Equal priority:
Equal priority is given to focusing and continuous shooting speed. In low
light or with low-contrast subjects, shooting speed may slow down.
: Shooting speed priority
Priority is given to the continuous shooting speed instead of achieving focus.
The continuous shooting speed does not slow down. Convenient when you
want to maintain the continuous shooting speed.
: Focus priority
Priority is given to achieving focus instead of the continuous shooting speed.
The picture is not taken until focus is achieved. Effective when you want to
achieve focus before capturing the shot.
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AI Servo 2nd image priority
You can set the AF operation characteristics and
shutter-release timing during continuous shooting
after the first shot with AI Servo AF.