Canon POWERSHOT SX40HS User Manual page 86

You can change the AF (Auto Focus) frame mode to match the scene you
want to shoot.
Choose [AF Frame].
Press the
MENU
button to choose [AF
Frame] in the O tab, then press the ,_
buttons to choose an option.
A single AF frame will be used. This is effective for focusing on a specific
point. In [FlexiZone], you can change the position and size of the AF frame
(p. 88).
Changing the Composition with the Focus Lock
While you keep the shutter button pressed halfway, the focus and exposure
are locked. You can now recompose and shoot. This is called Focus Lock.
.... ::_iii!iiiiii!_,: ¸¸
Focus.
Center the subject you want in focus, and
press the shutter button halfway.
Confirm that the AF frame on the subject is
green.
:; Recompose.
Keep the shutter button pressed halfway
and move the camera to recompose the
scene.
shoot.
Press the shutter button fully.
86