The Focus-Mode Selector
When the focus mode selector (A) is set to S (single-servo autofocus) or C (con- tinuous-servo autofocus), the camera focuses automatically when the shutter-release button is pressed halfway (B).
A 
B
When your subject is stationary, single-servo AF allows you to lock focus on the subject by keeping the shutter-release button pressed halfway (or either of the AF- ON buttons pressed). The camera remains focused at the distance of the original subject as long as the shutter-release button is pressed halfway (or either or the AF- ON buttons held down), even if you re-frame the photograph so that the subject is no longer in the selected focus area. To ensure a sharp image, the shutter can only be released when the camera is in focus.
Continuous-servo AF can be used with moving subjects to allow the camera to continually reassess the distance to the subject in the focus area and adjust focus as necessary. The shutter can be released even when the camera is not in focus (re- lease priority).
In both single-servo and continuous-servo AF, the focus target is selected from one of five focus areas using the multi selector.
For more information on:
pg. 81 Manual focus
