The first copy of the script came with Poser 5, written by Stefan Werner, aka Stewer.  The script has been carried forward through Poser 6 AND 7 (not sure about newer versions of the software).  It's actually NOT at all hard to use, second MistyLaraPrincess ' above.  Just remember when rendering to check the 'Depth of Field' in the Render Settings window.

Here's an ealier thread about the subject:

http://market.renderosity.com/mod/forumpro/showthread.php?thread_id=2014883

bushi created a nice image to use as a guide/setup tool - located on page 4 of the thread.  I think we were playing with Poser 6*, not sure, but it works the same way in Poser 7.

Best Wishes,
Rªnce

EDIT: It was Poser 5 the folks in the thread were playing with.  Those were the days ...