In real world, there is a relation between film speed and grain (or noise).
Can that can be done or is it nonsense?
Thanks
there is a relation, but it´s not like a=b…it varies for every manufacturer and film…Grain is a slippery bastard to match 
Thorsten
Yes, You are right.. But in this case, we could think Vray as a new film manufacturer. So they might have their own grain standards.. 
well there are various grain emulators out there that either try to mimic certain brands/filmtypes or analyse existing material. I assume that would be a faster and easier way to add grain (not to forget flexibility, imagine having to re-render 6000 frames cause you wanna change the grain :P)
Thorsten
I was thinking we could see different levels of noise in light and dark parts of a photo. Doing it in the post is possible but actually I mean controlling ‘noise threshold’ and/or subdivs etc by changing film speed parameter.
I am still not sure this may not be nonsense…
ah, i see…so you basically mean that the settings should adjust depending on the brightness…but i think they actually do already as the thresholds are not absolute values, but depend on the scene (esp. on the brightness if i recall right…so brighter parts are sampled higher by the rqmc sampler already).
Any techwiz ?
Thorsten
Exactly… Sorry I wasn’t clear at the beginning.
Do not confuse GI and artifact noise with fim grain. Film grain reacts diffrently in every channel (blue noise is thicker, more contrasted, and fatter) and responds at different light levels. Film grain should always be added in post, therefore, your CG image should be void of noise before adding film grain.
Thank for the info Chris. That’s very clear now.