Problem with unusable noisy Environment Fog

[BeneZ]

Hello,

I'm new with rendering fog and have built a test scene.

It took me a day of testing and it's always slowly and noisy...
I tried now every setting. (Subdivs, step size, Scatter GI, Rendersettings...)

Attached some screenshots.
I created a cube and attached VrayEnvironment fog with VrayMaterial (opacity 0 and Fog as volume material to SG)

Lights:
There are only 2 rectangular lights attached to the set ("override light shapes"), but it takes like 10 minutes to get a grainy result and it never gets fine.
There are originally 9 Lights, I switched all others off to be sure they don't affect anything.

A texture still is not applied (because if the "base fog" doesn't work, it only would make it more complicated).

A final render in 1200 pixels would take 30 minutes and I stopped it, because it looks grainy, too.
When I see tutorials or show reels it goes instantly. In my setup it needs liek 5 moinutes until even it starts to show a picture...

Thanks for help!

VrayNext, Maya2018.6, CPU (on good doubleCPU workstation. also tried GPU render with 2 gtx1080ti but it is is not faster)

[BeneZ]

I found out, that "step size" makes a difference. Although small steps are finer, it did not go on anymore then because of that high distance value.
When I increased to 2500 it worked much better.

Although I would like to understand, if it is recommended to change:
- Subdivs?
- Max steps?
- Anything else?

- What means for fade out "multiply by density"? 300 x 5000 = 150.000 ? this would be 300 times larger than my set, but it does not seem so.

[dgruwier]

https://docs.chaosgroup.com/display/...ering+In-Depth there are some general tips on rendering volumes, try probabilistic rendering for example.

Have you set the shape type of your lights to disc by any chance? I've had trouble with those being much much slower than regular rectangle lights

[BeneZ]

Thanks. The main issue really only was the step size. When it is too small, it's not rendering correctly. In the manual is recommended to have a half or third of the fog distance.