OTOY Forums

Hi
As the title says, is it possible to achieve a light cone effect using Octane? I want to be able to put a light source behind a subject and have light rays emanating out from behind the subject through a dusty environment. I'm guessing this is to do with volumetric lighting so was wondering if Octane supports this?
Thanks in advance

Octane can do this using SSS (effectively). You need to create a volume (cube or whatever) that will contain the "fog". Make sure your camera is outside this volume.
Then assign it a specular material with IOR 1.0 (no light bending). Give it full transmission and zero reflection and roughness. Also enable fake shadows.
It should now be basically invisible.

Change the kernel to PMC or PT and then add a scattering medium to the fog volumes specular material.
Set the scattering to white then start with the scale at zero and slowly increase it until you start getting the haze created by the light scattering.

Hope that helps!

Thanks

I can suggest a nice tutorial about this tech:
OctaneRender Standalone Tutorial: Sunlight Rays / Fog Volume by OTOY New Zealand
http://www.youtube.com/watch?v=MqOZp77ZSLg

Hi Thanks for the explanation fooze. Unfortunately I'm not sure I quite understand. I wanted to simulate a spotlight having light cone. So the light should start at a point and radiate outwards. I tried creating a box with a hole in it and the light source outside the box and a material with your fog explanation above but all I get is a fuzzy looking box that doesn't send beams of light around the subject.
I also tried the tutorial but that did;t seem to do what I wanted either. Are there any other simpler tutorials out there?
Many thanks

Here's a simple test I did. The sphere and the spaceship are within the fog material (the camera is outside it and the scene is lit by an HDRI) image. I would have expected there to have been shadows cast by the two objects through the fog from the light above but all I can see is that fuzzy box!

This is the right concept, but i think the lighting is the problem. It is comming from too many directions.
Try putting a small emitter plane with a tight IES light (spotlight) at the top, this means there will be a controlled beam of light hitting the fog which should be visible.
If there is too much light coming from too many angles, this is what you will get (just an area of fog).

See the attached .orbx (for standalone)

Maybe you could have a look at the method I described some time ago about fog and God rays :

http://render.otoy.com/forum/viewtopic.php?f=9&t=38645

Hi Fooze
Thanks so much for the orbx file - it has helped a lot in trying to understand what you did. Here's an image thats starting to give the effect I'm looking for using your file. however theres a lot of grain so I think it will need some fine tuning. I also need to front-light the object too so that I can see the details so going to have to do a lot of experimentation. Anyway, its off to a good start
Thanks again

Yes, this fog (because it's pretty much SSS) can take some time to render out. PMC is almost a must.