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Home Jeff's Blog Volume Caustic Sample Scenes
Volume Caustic Sample Scenes PDF Print E-mail
Written by Jeff Patton   
Sunday, 12 April 2009 12:57
Volume Caustic render thumbnailWhile working on some content that required me to search through my scene archives I ran across some of my volume caustic scenes.  Figured it might be useful to someone out there so I knocked the dust off the scenes and figured I'd share a few of them for deconstructing purposes.
In the first scene the volume caustic effect is shot through a clear lens.  Well, it's almost clear it does have a slight green tint like you'd expect from glass.  As the volume caustics hit the colored reflectors it changes the color of the caustic pattern.

Click the image to enlarge:

In the second example scene the glass is strongly tinted green and this produces the green volumetric effect that is simply bouncing off mirrors (not colored surfaces).

Click the image to enlarge:


Fun things to try with these volume caustic scenes:
  • Explore changing the IOR (and/or shape) of the glass lens to achieve different patterns/results.
  • Put more reflectors in and try to spell something or draw different shapes.
  • Create a laser effect.
  • Try multiple lenses.

Notes:
The volume caustic effect here is rather strong mainly because I've decreased the decay on the photons and that let's them travel further.  If you increase it to the default value of 2.0 then it will shorten the volume caustic effect in a more natural way.  Likewise you may want to decrease it further than I have it set to extend the volume if you're making something like a laser effect.

Have fun.
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Ata Ul Munim Sipra wrote on April 13, 2009
 
Title: ...
Thanks for new addition.....
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William Munny wrote on April 13, 2009
 
Title: ...
Great stuff as always Jeff, big thanks!
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website
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Clan wrote on April 13, 2009
 
Title: Thank You
What would we do without you Jeff? Thank you for everything.

God Bless...
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Nik Clark wrote on April 15, 2009
 
Title: Thanks for the scenes, and a question.
Hi Jeff. Thanks for posting this.

Did you find this is quite unusable? I find that if I add geometry, it stops working. If I move things, it stops working. If I move things slightly, it works again, then doesn't? Simply adding a shell modifier to the lowest reflective plane stops it working for me.

This is on max 2009 and 2010.

I'd love to use this effect in a scene I'm working with, but it's too unstable to be of any use (like gemometry lights).

Thanks for posting it though!

/z
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Jeff Patton wrote on April 15, 2009
 
Title: ...
Hey Nik! It doesn't seem buggy here, just very picky. I can recreate the problem you mention about the shell modifier. However, that seems to be only an issue on the first reflector. If you don't add a shell modifier to the first reflector, but you do add it to all the other's it still works. Once you add it to the first reflector it stops working. Why? I dunno off the top of my head could be a material config issue or maybe a calculation issue when using modifiers, etc..

That being said, if you need to add thickness to the first reflector you can convert it to an editable poly and extrude the faces, that seems to work just fine.

As far as moving things breaking the effect, it only breaks it if things don't align properly as far as I can tell. For example, here's a working version in a different configuration with two light sources/set's of rays, shell modifiers, and extruded epoly objects: http://jeffpatton.net/Temp/Vol...dified.rar
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Nik Clark wrote on April 15, 2009
 
Title: Can't thank you enough.
Ha ha, thanks jeff!

You are quite right about the first reflector issue. I've spent some time with it, and armed with this information, I can use this reliably. I am ashamed I hadn't worked this out for myself!

This is an effect I prevously thought max was incapable of. I can't thank you enough for conrtibuting the sample scenes you do, and for always letting the community share your secrets.

Where would we be without your assistance?

:o)

/z
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Jeff Patton wrote on April 15, 2009
 
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No problemo my friend, glad to help.
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Goran Teodosiev Kissiov wrote on April 29, 2009
 
Title: ...
Hi, Jeff! I have a simple question - why do you use an object called "photon catcher", what does it really do... and why we need such kind of objects to generate volume caustics? Some time ago I spent a lot of time to archive this effect, but with no essential results. Now I see the key is in "photon catcher", but can not understand yet why we need this kind of extra object.
Thank you very much in advance!
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Jeff Patton wrote on April 29, 2009
 
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I saw a tutorial on creating this effect back in 2003: http://forums.cgsociety.org/sh...6&t=108789
and to date, I've never received an explanation as to why that photon catcher is required. So, I'm afraid I can't offer a real explanation.

Yes, I have my own theories but they are just guesses on my part so I'll keep those to myself as they are not based on hard facts and I don't want to spread misinformation.
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M. Botell wrote on May 14, 2009
 
Title: ...
Thanks alot for this! My own experiments didn't quite get me where I wanted to, but now when I look at your work, I notice that I was very very close to the correct answer all the time. These reflecting/refracting volumetric effects have been bugging me for a quite a while now but thanks to you I finally get them work the way I want to. Thank you for sharing some of your secrets :)
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MartinB wrote on August 11, 2009
 
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Hey Jeff,

thanks a lot for posting the scene. One question though: do you have any explanation, why the white light beam gets brighter after the lens? If you crank up the light, this gets even more noticeable, and it somehow doesn't look to realistic, does it?

MartinB
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Jeff Patton wrote on August 11, 2009
 
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I mentioned this a bit in my original post in the "notes" secion - "The volume caustic effect here is rather strong mainly because I've decreased the decay on the photons and that let's them travel further. If you increase it to the default value of 2.0 then it will shorten the volume caustic effect in a more natural way. Likewise you may want to decrease it further than I have it set to extend the volume if you're making something like a laser effect."

That being said, if you increase the photon decay to 2.0 the volume effect as it leaves the lens is still a bit brighter than the volume entering the lens.

Is it wrong? Maybe, I don't honestly know. I do know that lenses focus light sources so maybe it is accurate that the effect be slightly stronger due to the lens re-focusing (intensifying?) the effect...like a magnifying glass does the sun.

I suppose I could try to configure a similar scene with Maxwell or FryRender just for comparison sake...but I'd be afraid that would turn into a render engine pissing contest. :/
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MartinB wrote on August 11, 2009
 
Title: ...
Thanks for the comments, Jeff. I noticed the decay, but as you already said, that does not really explain why the illumination strength seems to be stronger after the lens than before. I tried focusing down the beam of light to basically a very thin ray (so to avoid any significant 'light bundling' effect of the lens) and this effect still exists. Same if you set the IOR to 1.0 or make the lens perfectly flat.
Could it be that the volume photons before the lens are different from the caustic photons behind it? Something seems weird here.

On a side note: If you take your initial scene and apply a Shell modifier to the first mirror, the volume effect breaks. Any ideas what's going on?
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Jeff Patton wrote on August 11, 2009
 
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"On a side note: If you take your initial scene and apply a Shell modifier to the first mirror, the volume effect breaks. Any ideas what's going on?" - Afraid I have no logical explanation for it. :/

However FWIW when this issue was discussed earlier in this thread I mentioned that you can convert the first mirror to an editable poly object and extrude it and that works if you need thickness on it.
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