Canon PowerShot S3 IS Advanced User's Manual page 73

Changing shutter speed and aperture value
combinations
Automatically selected combinations of shutter speeds and
aperture values can be freely changed without altering the
exposure (Program Shift).
1
Turn the mode dial to
2
Focus on the subject on which you wish to lock the
exposure.
3
Press the ISO button while pressing the shutter
button halfway.
The exposure setting locks and
monitor (or viewfinder).
4
Press the
speed or aperture value is reached.
5
Recompose the image and shoot.
The setting will cancel after the shot is taken.
,
or button until the desired shutter
, or .
appears on the LCD
71