Canon EOS 90D DSLR Camera with 18-135mm Lens - Manual (Page 562)

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Custom Function Setting Items
C.Fn II-5: 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
fi rst shot in continuous shooting.

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.

Shooting speed priority
Priority is given to the continuous shooting speed instead of achieving
focus.

Focus priority
Priority is given to achieving focus instead of the continuous shooting
speed. The picture will not be taken until focus is achieved.
o Even if [Shooting speed priority] is set, under shooting conditions that
activate fl icker reduction ( = 261), the continuous shooting speed may
become slower or the shooting interval may become irregular.
o If focus cannot be achieved in low-light conditions when [Equal priority] is
set, setting [Focus priority] may give better results.