Taking pictures with the focus and exposure locked
In the above composition, the subjects (two people in this case) are not in the AF frame. Pressing the shutter button halfway at this point will result in the subjects being out of focus.
AF/AE lock is useful:
Use AF/AE lock to guarantee best result when shooting a subject that is not suited to autofocusing (➝p.30).
Using AF/AE lock
1 Move the camera slightly so that one of the
subjects is in the AF frame. 
Usingthe
Camera
2 Press the shutter button down halfway to focus on the subject.
Double
beep
250 F4.2
Halfway pressed
Continued Q
29