Yes, there is a Focus Distance guide that you can use to help you with DOF in Poser. I know at least in Poser 7 there was a script where you could select an object, run the script and it could tell you how far the object was from the camera. Not sure if it's in Poser 8 - I don't have it open right now and I haven't used it in Poser since version 7...hehe.

Laurie