Canon POWERSHOT A1000IS User Manual page 21

The shutter button has two stops. To take images that are in focus, be sure
to first press the shutter button lightly (halfway) to focus, then take the shot.
Press halfway (lightly to the first
stop).
The camera focuses and automatically
makes necessary settings for shooting,
such as adjusting brightness and color.
When the camera focuses, it will beep
twice and the indicator will light green.
Press fully (to the second stop).
The camera takes the shot.
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