Ockham, the script Rance1 mentions looks like what stewer posted and is used to calculate the distance between the camer and objects in focus or Focal Distance option. Maybe you can take a look at the method outlined by Stephen (on his website tutorial on this, which also has the py script) and see if that helps. I like the idea of being able to either pick a figure or place a ball prop where I want my focal point to be and the script do the calculation to give me the depth of field effect I want. So don't give up on this just yet. :O)