Animating DOF

Is there a way to animate Depth of Field? I know the basic set up for dof, but I’m not sure how to animate it. In animation I want to change the focus from foreground object to background object back and forth. I couldn’t find the way through search engines yet, and if any of you know a simple way to do that or have the link that will give me an idea, I would appreciate that.

Use an Empty Object as a point of interest for your camera.
Add an empty, then parent the camera to it. In the camera panel, type the name of your Empty (which is Empty by default) in the “DoF Ob:” entry.
Now animate your empty, your camera does follow and focus this empty.

Thanks, it works!