Canon EOS Rebel SL3 DSLR Camera with 18-55mm Lens (Black) - Manual (Page 74)

74
Full Auto Techniques (Scene
Intelligent Auto)
Recomposing the Shot
Depending on the scene, positioning the subject toward the left or right
to include a balanced background will result in a picture with better
perspective.
In the < A > mode, pressing the shutter button halfway to focus on a
still subject will lock the focus on that subject. Recompose the shot while
keeping the shutter button pressed halfway, and then press the shutter
button completely to take the picture. This is called “focus lock”. Focus lock
is also possible in other Basic Zone modes (except < 8 : 5C >).
Shooting a Moving Subject
In the < A > mode, if the subject moves (distance to camera changes)
during or after focusing, AI Servo AF will take effect to focus on the subject
continuously. (The beeper will continue beeping softly.) As long as you keep
the AF point positioned over the subject while pressing the shutter button
halfway, focusing will be continuous. At the decisive moment, press the
shutter button completely to take the picture.