Problem Creating Light Fog

[georgep1]

i am trying to render a scene where a couple small lights give off a visible light fog but i dont want the larger lights that are illuminating the scene to have a fog. I created a box that serves as the environment for the fog and attached a transmat material shader to it and the parti volume shader to it, I also got rid of the connections between the box and the lights that dont give off a fog. When I render the scene the box shows up as a translucent black box, which is not what I want, I want the box to be invisible and to see fog coming from a couple small lights....what should I do?

[georgep1]

what if I rendered the fog seperately and composited the two images in photoshop? would this work? does anyone have any other suggestions? Thanks

[peterghill]

Hi there,

firstly Ill take you through a simple scene, so for the time being ignore what you have done so far.

Reset Max with a new scene
Make Sure MR is the renderer
clear all maps.

Below is in CM
Create a camera say X 0 Z100 Y500 with a target at 0,0,0

Create your MR spot lights say from top left/right with targets
pointing to 0,0,0

Create a back plane that covers the camera 1 vie completely but
is behind the spots with normals facing to the camera.

OK So far?

Now for the materials:

Go to the render panel and under MR renderer click thecamera shaders Volume and select
Parti Volume, drag an instance to the materials editor as an instance
and change the values:

Mode 0
scatt color to your volume colour
ext .001
0
0
0
0 ect
min step length.1
max step 5
0
and select lights
add your lights to the panel

Now create a new MR material and
surface select transmat (physics)
photon...select transmat (physics)
apply this material to the back plane

Lights:
check inverse (or square but I dont) (10cm?)
multiplier to around 2-4ish
RT shadows
Select a tight cone and fall off
RT shadows o Ray Bias 0.14
quad 7

Very untidy file here for you to download.

http://www.productionconsultants.co.uk/downloads/Max/