spent a lot of time messing with volume fog, got it working in VR ie steroscopic fog which is cool
The problem with fog in cycles is that it appears in the mist pass whether you like it or not, so you could have invisible fog in the raw render and bring it back in in the composite by bringing in the mist pass, then add a denoise to the mist pass. renders very clean too
This took about 12 mins to render, this is the cropped version of the left eye, but in order to make it VR you cannot crop the image, have to leave a big black border, so its stays at 4096x2048