DSLR uses every AF point in each shooting mode but often you can choose AF points manually

Auto select
By default, your DSLR uses every AF point in each shooting mode but often you can choose AF points manually. Press the AF Point Selection button at the top-right of the rear of the camera (this will differ by brand and model) and the display will confirm that multi-point Auto Select AF is in use.


Manual select
To switch from AF Auto Select to Manual Select mode, press the AF Point Selection button as in the previous step, but then press the Set button. The camera will now switch from multi-point selection to using only the central AF point for autofocus. Press the Set button again to revert to multi-point Auto Select.


Change the AF point
You’re not limited to using the central AF point in Manual Select mode. After switching to single-point AF, you can use the arrow keys to switch to any of the other eight AF points. To return to the central AF point, press the Set button again.

AF modes
Manual AF point selection works in any of the various AF modes, so you can couple use of selective AF points with One Shot AF for stationary subjects, AI Focus AF for erratic subjects, or AI Servo AF for tracking moving subjects. Select the most appropriate AF mode by pressing the AF arrow key.