View Full Version : Mray Parti Volume Fog -- speed?

08-16-2009, 05:20 AM
Hey guys,

I have been going back over some old work and was wondering if anyone had any advice or alternate techniques to speed up the volume fog i'm doing here:

Rendertime -
No Volume Fog : 4mins
Volume Fog : 54 mins

Any ideas?


08-16-2009, 08:10 AM
hi there !
are you using final gather ? Parti volume isn't a party with final gather turned on. :D
If you do have it turned on..i recommend adding the lights on a different layer and then compositing them together. You can also try the ole video game trick.. create plane and apply a transparency. You can also skip all that and track a rotoshape in comp.
another one is to play with volume lights from the create lights panel.

there you go a couple of solutions you could try. I myself would go with the 1st one.


08-16-2009, 05:49 PM
Hey nfrancisj

FG is not on, I wonder if I might have too many lights participating in the fog calculations (8ish).

If possible I would like to keep a fog volume because as the camera pans the effect of the 3D volume VS 2D is quite nice.

Is there a specific place I can adjust the render stats of just the fog?
I am pretty sure I have not properly tweaked the render settings but I am not quite sure where to get at it.

Thanks for the suggestions!!

Kel Solaar
08-17-2009, 09:32 AM

Did you tried adjusting the Min / Max Step Len Attributes to higher values (it's the Ray Marching Steps, the smaller the values are, the more steps are taken along the Ray path, so the longer is the processing ) ? This can reduce the render time by a lot.


10-25-2009, 03:09 AM
Kel Solaar's on the right track - min and max step length will have the biggest effect on render times where parti volume's concerned.

also have a play with the "volume samples" attribute under the features tab in mental ray render settings - i have a sneaking suspicion this will have an effect on render times. can't be sure though :-/ just make sure you leave "auto volume" checked!

info on how to tweak the node with thumbnail examples here:

Alternatively you could use a simple volume fog and dmap shadow setup, render separately and composite in. faster, but lower quality and sometimes awkward.


10-25-2009, 04:38 PM
Thanks very much guys. I will have a go with it again soon and post back my results.

Many thanks,

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