Canon POWERSHOT SD3500 IS Digital ELPH User Manual page 82

While you keep the shutter button pressed halfway, the focus and exposure
are Iocked. You can now recompose and shoot. This is called Focus Lock.
_iJ Focus.
Center the subject you want in focus, and
press the shutter button halfway.
Confirm that the AF Frame is green.
2 Recompose.
........ Keep the shutter button pressed halfway
and recompose the scene.
3 s.oot.
Press the shutter button fully.
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