Sony DSC-P9 Operating Instructions Manual page 52

Even if it is difficult to focus in Center AF
shooting because the subject is not in the
center of the frame, you can focus in this
situation
using the AF lock. For example,
when
~OLI are shooting two human subjects,
and there is a gap between them, the camera
may focus on the background visible in the
gap. In a case like [his, use AF lock to
ensure the subjects are in correct focus.
First, the focus for the subject you are
aiming at xvi99 be adjusted. When the
AE/AF lock indicator stops flashing
and remains on, and there is a beeping
sound, focus adjustment is completed.
The shutter clicks, the image will be
recorded with the proper focus for the
human subjects.
* You can carry out the AF lock adjujustment
process before you press the shutter baton fully
dowc.