This is a method for calculating a Z depth distance fade
effect using material nodes and drivers.
I’m not 100% happy with the MIST effect; it produces a transparent alpha which is not going to work for my style of compositing, it also seems to be “stuck” on a blue atmospheric color.
The method here (see the blend file for the TLDR description ) uses drivers and a control object to create a Z-depth distance fade using material nodes:
Blend file here: https://docs.google.com/file/d/0B2uvwo42PkSmWVBSTk5COXk3anM/edit?usp=sharing