HOWTO:

 - Setup a scene with different objects at different distances to the camera,
   some very close
   
 - Select the camera, go to editbuttons, turn on DOF, "Show Focus", and AutoFocus.
 
 - Render. Press LEFTMOUSE in the render window, you will see a few values
   at the bottom while you drag over the image. Move to the faces of the
   render that are *closest* to the camera, note the Z: value.
   
 - Go back to camera editbuttons, set "ZMin:" slightly lower than that Z:
   value
   
 - In Scene buttons, turn on "DOF".
 
 - With the camera selected, go to Camera view (NUMPAD0), and press "F" with the
   mouse over the spot where you want the picture to be focused (crisp). This
   point will be used during the whole animation to automatically focus to
   the object that is at that point (like a real camera's Autofocus).
   
 - Render.
 

ADDITIONAL NOTES: 

 - In camera editbuttons, "Focus" can be used to set the focus distance manually
   (without AutoFocus - otherwise it is ignored). These values can be read in
   the renderwindow by dragging with LEFTMOUSE, it's "Z: ".
   
 - "Blur" defines the maximum amount of blur applied to any point in the
   picture.
   
 - Gamma and Sigma can be used to correct for brightness changes due to the
   Blur.
   
 - "Focus Lag" is a nifty feature that emulates the time the focus motor needs
   to adjust the lens when there's a different object in focus (in Autofocus
   Mode). 
   
   You have to render ONCE with usual F12 before rendering your animation.


CAVEATS:
   
 - Focus Lag doesn't work with network rendering or in general with rendering
   any arbitrary frame, it only works with sequential frames
 
 - DOF uses the Z-Buffer and thus doesn't work with Unified Renderer, which
   has no Z-Buffer