Currently I'm testing a scene in which a campfire (created using Fluids) is the main lightsource. By using FinalGather this is easily accomplished and it looks satisfactory (even with no lights at all in the scene).
The only problem is that the number of rays has to be quite high, otherwise the light given off by the flames dances around too much when making a movie out of it (it's a bit of a blobby effect). What would be the best way to keep the render time low without the effect becoming too distracting?
Here are some settings I've used:
Anti Aliasing Quality
Min Sample Level: 0
Max Sample Level: 1
Max Trace Depth: 8
Shadow Trace Depth: 2
Final gather Rays: 100
Precompute Photon Lookup: Off
Min Radius: 5
Max Radius: 50 (for this I've used the 1/10th scene size value)
Final Gather Scale: 2 (this gave the best distance for the light of the flames)
Falloff Start: 0.000
Falloff Stop: 0.000
Trace Depth: 2
Trace Reflection: 1
Trace Refraction: 1
Secondary Diffuse Bounces: Off
Rebuild Final Gather: On
These setting result in a render time of around 10 minutes a frame (this is with the dancing rays effect). It's not that much, but since the entire movie is going to be just over 1000 frames I'd like it if the render time didn't become too high.
Aside from the campfire there is an environmental sphere surrounding the scene (which gives of a blue- ish nightsky color) and 1 point light to simulate a bit of moonlight.
I have not used Global Illumination and do not intend to (it's not really necessary and would increase render time too much). Aside from the dancing effect everything else in the scene works fine (no flickering or any other render problems).
My experience with using MentalRay is rather limited (understatement), so if I did something completely wrong, please forgive me.
Help would really be appreciated.