Impossible to increase Env Fog brightness in small steps

[ilmelovfx]

Hi all,

I searched the forum but I didn't find some clues about what I'm experiencing.
I want to add some sort of wall of fog on a high mountain grass field.

As you can see in the first image, I used a sliced tube mesh as a gizmo (with mesh falloff of 500) on a ForestPack grass plane, lit by an HDRI textured dome light. Scene scale in cm. The green box is about the height of a man (175cm circa).

All the scene is good to me but I want the fog to be a little brighter, so I add a 1 (only 1) to the RGB value of fog emission and bam... the fog turns totally white (RGB 255-255-255 8 bit, 65535 16 bit, everywhere), and the gizmo falloff disappear too (the smooth density gradient now turns completely dense, no gradient at all).
Is this a bug? Is this a light setting? I tried to deactivate "Use all lights" in fog settings, manually adding only the dome light, but nothing changes... I tried various fog densities, scatter gi on/off, scatter bounces, but nothing changes... I deleted the dome light and tried with a vray sun+sky but the issue persists, there's no way to brighten the fog in small controllable steps...
I don't want any fancy effect, I want only to control the brightness of the fog...
Can please someone give me any advice on how to solve this issue?

I'm using 3ds max 2020.3 with Vray Next 4 update 3.1, Windows 10.

Thank you

[hermit.crab]

Thanks for the report. We are aware of this issue (Bug-tracker id: VMAX-6850), it is present when using non-homogeneous environment fog (gizmo falloff in your case) and an emission color with values greater than 0. I'll bump its priority additionally.
As a workaround, try creating a dome light, in which no objects are included (Options>Exclude>Include) - this light would affect only the fog and you can use its multiplier as brightness control.

[ilmelovfx]

Thank you very much for answering, I'm very glad to hear that... I was going nuts trying all the env fog settings combinations
I tried your workaround and it works, btw in the meantime I tried another way using a volumeGrid with cutter geometry option (used some opacity texture to add some variations too).
I attached a couple of images to show the results.
(it's not perfect but now I can control the fog brightness and I will work on it...)
It seems to me that volumeGrid is also a lot faster to render
Thank you again