How to Change the Autofocus Point on Your Canon EOS 6D
By default, your EOS 6D displays 11 autofocus points. The camera focuses on subjects that intersect autofocus points. The default number of autofocus points works fine for most picture-taking situations.
However, at times, it makes sense to switch to a single autofocus point that you align with a single object, such as the edge of a building. This option is useful when you want to focus selectively on a single subject in a scene that has other objects that the camera may lock focus on. To change the autofocus point:
Press the AF Point Selection button in the upper right corner on the back of your camera as you point the camera toward the scene or subject you are photographing.
While looking at the viewfinder, or at the LCD monitor, move the Multi-controller to switch from multiple auto-focus points to a single auto-focus point.
This indicates the other possible points on which you can focus from.
Press the Multi-controller button to navigate to the desired autofocus point.
You can navigate to any of the autofocus targets (the small red squares) to designate the point from which the camera will focus. The camera focuses on an object under that autofocus point.
Press the Shutter button halfway.
You’re ready to take pictures with a single autofocus point. The autofocus point is the default autofocus point until you use the AF Point Selection button to designate another autofocus point.