Canon 500 HS - Manual (Page 119)

Shooting Range and Focusing
120
The focus can be locked. After you lock the focus, the focal position will not
change even when you release your finger from the shutter button.
Lock the focus.
z With the shutter button pressed halfway,
press the
q button.
X The focus is now locked, and % is
displayed.
z To unlock the focus, release the shutter
button and press the
q button again. In this
case, % is no longer displayed.
Compose the shot and shoot.
Shooting with the AF Lock
Still Images Movies
COP
Y