Canon POWERSHOT SD3500 IS Digital ELPH User Manual page 52

To save battery power, the camera shuts down automatically when it is not
operated for a certain time.
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The screen will turn off approximate}y 1 minute after the camera is last
operated. After about 2 more minutes, the lens wil! retract and the power will
turn off. When the screen has turned off but the lens has not yet retracted,
pressing the shutter button ha}fway (p_ 23) turns on the screen and shooting
can continue.
The power will turn off approximately 5 minutes after the camera is Jast
operated.
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