Thanks everyone, bruno021, "I create alpha planes in PS and place them in my scene, so they look like patches of fog, like volumetric spheres, but the render time is a lot quicker. To creates the planes in Photoshop, use the free "cumulus" plug in from Flaming Pear." I went to Flaming Pear but I didn't see the "cumulus" plug-in anywhere. Did they rename it or do you know where else I can get it? What exactly does this plug-in do it sounds so interesting? Also, I am interested in creating the alpha planes in Photoshop like you mentioned. I have made alpha planes before, but not for fog. Could you explain a little more on how to do this?