Vray Light in Environment Fog

[Truffi]

Hi,

what is it that Standards Spotlights sample better in Environment Fog then Vray Lights do?
I am using Vray 2.2, the foggy scene is an interior, there is one light placed outside pointing inside the room.

When rendered with Vray Light the "godrays" look very natural, but I'll always end up with noisy fog.
In the same scene setup with a spotlight, rendertimes are way lower, there is less noise - I need less samples to get the fog look smooth. However the way the light spreads into the foggy room looks less natural than with the plane Vray Light.

Getting out the noise for the vray light by increasing both the light's and the fog's subdivs results in insane rendertimes. I had 100subdivs for the fog and 80subdivs for the light, which took 10hours+ without GI, that's too long since I need to render a sequence of 170frames.

Sorry if it has been asked before, but I didn't find a satisfying answer to this. I see in tutorials people tend to use Standard lights for the Vray Environment Fog, but I didn't get the reason. So anyone happens to know why 3ds using 3dsMax standard lights produces less noisy fog?

What is the best approach to get the natural look for foggy interiors, use the spotlight's decay?

[super gnu]

is it because standard lights dont have area/soft shadows unless you specifically set them?

also you could try playing around with

a) using vrayshadowmap instead of vray shadows for the standard light, this should allow you to get some fake "soft shadow" effects without the rendertime hit

b) play with attenuation on standard light to get a more natural look. by default a standard light has no decay over distance, hence the unnatural look.


you will almost certainly want to render this fog/ god ray effect seperately and comp. getting a light that plays nice with env. fog, but also shades the room nicely, might be a bit tricky.

[Truffi]

Yes. That makes sense to me, that the difference in rendertimes is simply due to more flexible shadow settings of the 3dsMax standard lights.

For the spotlight I was using standard shadow maps with a resolution of 512 to get less crisp godrays. I will try vrayshadowmaps for more soft shadow effects.

With the attenuation I am already messing around, I am still trying to find out what is better: A) using the decay option with inverse square - or B) using the attenuation settings to exactly adjust the distance of the light's fall-off..
The latter is more flexible but the fall off seems to be more linear.

For sheding the interior scene, I use seperate light sources that are not affecting the environment fog but geometry only. This way I don't need to make a compromise on how the fog reflects the light. I hope that's less tricky. In addition I am using the Atmo Renderpass to tweak the fog in After Effects to something I find optimal. But for that I now need to get that fog look smooth first. Now, hopely with Vray ShadowMaps..

Thanks!