Ah,now those rocks sure add alot I would say(in a good way that is).And about the voulumetric slab,I was not aware of that technique at all,but now that you mention that is done that way I understand the mechanics of it.In the pics that I posted with caustics,I used a cone light with a gel,and made light visable for faked voulumetrics(my computer is slow,250mhz)for faster renders.I'll try your way though too,I cant pass up a new technique.thanks for the info.