Lighting specific objects in cycles with volumetric atmosphere

Question

I'm trying to set up a night scene, and having trouble getting the lighting right. Here's my first stab at it:

I like the lighting on the tree, but the cloak on the left is too dark.

I wondered about splitting the scene into two render layers, kind of like this:

I thought I could adjust the levels of the cloak in the compositor, but I can't figure out how to recombine the layers. Similarly, I tried adding extra lights to the cloak layer, but that interferes with the volumetric effect in an undesirable way.

Is there a good way to light the cloak, without affecting the rest of the scene?

Answer 1

A possible soution is not using volumetrics in the world setting but creating a solid that contains the whole scene with volume scatter shader. Have that solid be in only one layer and have other layers with no volumetrics to light the objects.

For example on a scene like this:

I added a cube that surrounds the whole scene and added a volume scatter node as volume to create the volumetrics.

on a separate layer I have the object on the left with separate lighting and no volumetrics.

I render both layers separately and combine them in the compositor:

Answer 2

For a solution without compositing or adding render layers, you can create lights that ignore the volume scattering.

For example:

In a situation like this where you have two objects, a single light source and volume scattering as volume in the world.

The monkey is hard to see as there is no other light on the scene that help us see any more detail on the face.

If we were to add a new light to the scene it would also light the scattered particles in the environment, affecting the original effect.

To make the light invisible to volume scattering Disable the Ray Visiblity for to Volume Scatter in the Cycles settings for the new light.