To compose photographs with off-center subjects:
Focus: Position the subject in the focus frame and press the shutter button halfway to lock focus and exposure. Focus and exposure will remain locked while the shutter button is pressed halfway (AF/AE lock).
If AE-LOCK, AF-LOCK, or AE/AF LOCK is assigned to the Fn button, the focus and/or exposure will lock while the Fn button is pressed and remain locked even when the shutter button is pressed halfway.
Recompose: Keep the shutter button pressed halfway or keep the Fn button pressed.
This process can be repeated as often as desired before the picture is taken.
Shoot: Press the button all the way down.
Although the camera boasts a high-precision autofocus system, it may be unable to focus on the subjects listed below.