From Chapter 9: Special FX

Cheats

You can also purchase special lights and cameras for atmospheric effects, but there is a fairly easy trick to accomplish some nice and easy atmospheric effects which render in a snap!  You can place a plane with a black and white image in the opacity channel, in front of your scene with the camera looking through the plane.  Anywhere there is black will be opaque and where it is white it will show.  This will also work for rain and some other effects.

Fog created using DAZ Studio Volumetrics                         Fog created using a plane

Rain effect using a plane