i'm trying to create a lighting effect of (volumetric) light rays coming through the doorway but whatever i do to the light and object settings, the light fog just keeps going through the object and doesn't give me the effect. How do i block the light with the wall and get the rays to come through only the opening in the wall?

the effect i'm after is a bit like lights rays shining from behind movie title text type thing...

please help!

thanks
lori