It seems I cant post any screenshot, now, so I will try explaining the scene how it should look like and how it doesnt look like at all.... =p
A room; inside the room a table; on the table an oil lamp (old westerns kind); a camera: it looks at the table from a certain angle so that both the lamp and a door with a "hole" on it are in the field of view; from outside the door a free light; the free light has a volume light enviromental modifier on so the light through the crossed hole in the door casts a "noisy solid" light beam.....
Clear so far....?
.....in the same field of view you can see the "moon light beam" drawing the door hole bars' shadow on the floor.
Everything's alright, so far....the scene is ok. Now the problems... =p
1) using ray traced maps the light drawing on the floor is ok, but the volume light is a series of fog "dishes"
2) using mental ray shadow maps the fog looks realistic, but the light on the floor is...."squarey", even improving the floor shape segments
I've tried to turn the "foggy light" off but the squarey light on the floor persists...
With the mental ray shadow maps on, a singular black line appears on the boundary between the shadow and the light casted on the door hole depth....it's not a shadow nor a poly problem....nor a texture defect, since it appears even when the object is not textured at all...

Ask if you're not sure with some scene elements and tell me if you find I'm using the wrong tools....thank you =)


Not less important, but minor defect is that I've created a poligonal flame, a "pinched sphere" on the wick as subsitute of a light glow that I cant use cause it seems the glow cant be rendered from inside the lamp glass; the glass has been made by lathing a double sided section (closed spline) and applying a mental ray glass material.

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Walking Teapot