You may see any fog the first time you try to use it. When we first used fog, we didn't see any either. We have fixed, or added warnings for many of the thing we ran into. But this list may help.
Most of these items are discussed later in the Volumetric Fog Article
- Enable Volumetric Fog on the Fog Setup Tab
If you forget this step you will not get any fog. - Use the Path Tracer Engine
We have added some warnings if you try to render with Fog enabled, but not the Path Tracer Engine. - Don't use Section Planes
There is currently a bug where Fog does not work when viewed through a section plane. You will need to hide or delete geometry instead if you want to see through walls, etc. until we get this fixed. - Wait long enough so that the lights creating the fog appear
The default is for only 1/3 of the lights to appear in each pass, so wait 6 to 10 passes before you give up on the fog. - Make sure Scattering is set properly
Scattering is the amoun that light is scattered by the fog. If you don't see any fog, set it to 50%. You can raise or lower it later once you are able to see the fog. - Don't set values too high - If Scattering or Absorption is too high, then you may just get a dark rendering with no light passing through.
- Check the Fog Boundary
For my first rendering I did not set the fog boundary. Since then we have added some default boundaries - such as the model boundary. - Make sure the fog boundary does not intersect any other faces.
We have made the default boundary 5% larger than the model. If you set your own boundary, make sure there are not any coplanar faces in th model which intersect the boundary.
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