There has to be a formula, I have seen tables on deep of field for real camaras. For a given focal length, focal distance, f-stop and film format, the deep of field is the same for every lens. It has to be a optical formula. Unfortunaly I can not find the actual formular in any of my photography books. :-( Anybody with an optics textbook around? I assume Poser simulates a 36 mm film format.