Here's an approach to measuring or at least getting a feel for the DOF using the MeasureIt script (available in FreeStuff). I built a checkerboard grid in Photoshop (attached) and applied it to the ground plane. I used the script to measure the distance from the camera to the origin of the ground plane then used that as the value for the focal distance in the Render Options window. Setting this up is described in the next message.