Canon EOS 550D Instruction Manual page 44

Shooting Function Settings
@ _Shutter/AE Jock button
You can change the function assigned to the AE lock button and to
when you press the shutter button halfway.
AFIAE Jock:
Normal function. Press the shutter button halfway to execute AR
Press the <%> button for AE lock.
AE JocklAF:
Press the shutter button halfway for AE lock. For AF, press the
<_> button. Convenient when you want to focus and meter at
different parts of the picture.
AFtAF Jock, no AE Jock:
Press the shutter button halfway to execute AR While holding
down the <_> button, press the shutter button to take a still photo
without executing AR Convenient when you do not want to
autofocus when taking a still photo during movie shooting. AE lock
is not possible.
AEtAF, no AE Jock:
Press the shutter button halfway for metering. For AF, press the
<%> button. AE lock is not possible.
@ Remote controJ shooting
You can use the Remote Controller RC-6 (sold separately, p.204) to
start and stop the movie shooting. Set the shooting timing switch to
<2>, then press the transmit button, if the switch is set to <O>
(immediate shooting), still photo shooting wiii take effect.
The AE mede Settingwill also be reflected in Live view Shooting
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