Canon EOS-1D X Mark III Advanced User's Manual page 372

AI Servo 2nd image priority
With AI Servo AF for continuous shooting, you can preset the AF operation characteristics
and shutter-release timing for the subsequent shots after the first shot in continuous
shooting.
[0] Equal priority
Equal priority is given to focusing and continuous shooting speed. In low light or with
low-contrast subjects, continuous shooting speed may slow down.
[–2]/[–1] Shooting speed priority
Priority is given to the continuous shooting speed instead of achieving focus. –2
maintains fast continuous shooting better than –1.
[+2]/[+1] Focus
Priority is given to achieving focus instead of the continuous shooting speed. The picture
will not be taken until focus is achieved. +2 enables easier focusing than +1 in low-light
conditions, but continuous shooting may be slower under these conditions.
Caution
Even if [-1] or [-2] is set, shooting conditions that activate flicker reduction (
cause slower continuous shooting or an inconsistent interval between shots.
Note
If the camera cannot focus in low-light conditions when set to [0: Equal priority],
try setting to [+1] or [+2].
372
) may