View Full Version : Caustics dispersion and refraction

07-18-2011, 11:42 AM
Hey guys. I was reading something in the Lighting forum over at CGSociety and came across this image.


They say the look is caused by caustics dispersed refraction. I was wondering how we'd do that in the shaders in Lightwave.

Any suggestions? Thanks.

07-18-2011, 11:50 AM

In fact you don't need specific shader when using LW prior to version 9(no nodes), you can render 3 separate images with different IOR's and the channels from each image in PS, or better use the LW built-in MB and do an envelope in IOR channel, there was a thread somehwere here with files included

07-18-2011, 11:55 AM
Try adding a reflections node to Reflection Shading and crank the dispersion way up to 600% or so. Do the same for refraction and you're sorted.

If the example below (see the viewfinder) had faceting you'd get something along those lines.

07-18-2011, 12:06 PM
Dispersion is the way to get that lovely chromatic aberration, but note that you'll need some Roughness, or you won't see Dispersion at all.

07-18-2011, 12:17 PM
Use the refraction node plugged into the refraction shading input.

It has a setting for dispersion. Seems quite slow.....Zzzzzzz.


Edit :- Bah! Too slow.

07-18-2011, 12:44 PM
Are you talking about the aberration effect? The color prism that shows up because of the light splitting?

I wonder if it works with lumigons (+2 bounce gi) instead of lights?

07-18-2011, 02:05 PM
Thanks guys. I'll give this a shot... takes a long time huh?... figures.. oh well. Might just be worth the wait.
What are lumigons?

07-18-2011, 02:36 PM
A French friend, long LW user wrote a dispersion shader a few years back. Can't find his shader, but should be somewhere at his site:


07-18-2011, 07:33 PM
Thanks guys. I'll give this a shot... takes a long time huh?... figures.. oh well. Might just be worth the wait.
What are lumigons?

Luminous polygons. One old trick to get caustics back in the day, since the caustics button was basically useless, was to use luminous polygons in combination with 2 bounce GI to create cheap caustics.

This old thread was doing it with fprime 3.


post #6 was a couple of test renders using this method. But you can see the aberration was not cast on the floor in the sphere render.

07-19-2011, 01:04 PM
Are lumigons seperate objects or part of the mesh?

07-19-2011, 01:32 PM
Usually doesn't matter but I always made a separate light object. Just a polygon card with its own surface set 0% diffuse, and 100% or higher luminosity, sometimes would go up to 5000%.

If the refractive material is double sided you'll need more then 2 bounce GI. I usually wouldn't use double sided material for the glass.

07-19-2011, 02:11 PM
SvenArt has written a nice little L-Script that places an object of your choice to all or selected lights in your scene.


Look for Lights2Polys