The Depth Of Field effect simulates a camera that’s focusing at one depth (focal plane) in a 3D scene, blurring objects at other depths. This effect uses the depth information from the auxiliary channel of an imported file representing a 3D scene. To use the depth information that After Effects calculates for a camera layer, see Create a camera layer and change camera settings.
This effect works with 8-bpc color.

To show the depth of an object in the Info panel,
click the object in the Composition panel or Layer panel using the
Selection tool while the effect is selected.