Bill -
As a very rough general rule, the DOF is divided into thirds: 1/3 of the DOF is made up of the distance from the subject towards the camera, and the other 2/3 of the DOF is made up of the distance from the subject away from the camera. This is a helpful little rule for deciding if you want mostly foreground or mostly background to be in focus.
So, using inkista's lens as an example, on a full frame camera, if you were shooting at f/16 and if your subject was1.2 meters away, them everything from about 0.8 meters to about 2.3 meters would be in the DOF. If you were at f/4, then everything from just 1.1 meters to about 1.3 meters would be in the DOF.
Hope this helps.
