The light in the fog is on but not added to the vrayfog light list.
Also increasing the max sample rate in the AA makes it disappear (top image has 4, second 10 and third 20 max subdivs).
This is quite annoying as i can handle a bit of noise, but not the extra render times from increasing the AA settings!
The images below have the fog subdivs at 24 where it is quite obvious… If you set the fog subdivs back to 8 the effect is less dramatic but still noticeable. (Why would 8 subdivs render better than 24???)
Is it something to do with using DMC?
Do you have the “subpixel mapping” option for the color mapping on or off?
The result is somewhat normal, because the sample distribution ends up being different for the two parts of the ray (even though it ends up giving the same result with enough samples). We might be able to fix this and I will look into it. Another work-around is to use a texture for the fog color (e.g. a VRayColor texture) so that the fog switches to the raymarching algorithm.
“subpixel mapping” was off, but with it on it made no difference.
It always worried me that hidden/invisible objects were treated as transparent! (having to turn up the max transparent level if i had a heap of hidden geo)
There is no problem with hidden objects - they don’t render at all (i.e. they are not part of the rendering in any way). In any case, you would get similar issues with opacity-mapped objects.
The only problem would be if some of the visibility settings for an object are enabled, but others are not (e.g. primary visibility is off, but secondary is on etc).
Also it seems that increasing the fog subdivs makes this effect worse. So the only way to get rid of grain is to turn up the DMC max subdivs… this seems a bit wastefull as I only want to get rid of noise in the fog, the rendered geometry is fine at DMC 1-8 but im needing 1-20+ for decent fog renders
