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Caustics in Cycles

Posted by Marius Oberholster on Tuesday, September 18, 2012 Under: General
Who knows what caustics are?
Well, as simply put as I can:
It's the light pattern you see after light has passed through a transparent medium, such as glass. Great examples are of course the following:
 - Light stripes at the bottom of the pool
 - Rainbow lights when light shines through cut crystal
 - That focus point you can get with a magnifying glass
 - And naturally this:

(Photo I took earlier this year that I wanted to maybe do as an exercise in Cycles)

Those white light spots you see that come because of the spheres is caustic light. It's a very cool element and a very new feature to Blender. In Blender Render this kind of light effect is not supported (which imo is the only thing it lacks in really needed features). There are many ways of faking it in Blender Render, using clever textures, like I did with these dolphins I did for my aunt's birthday:

(Blender Render image)

While it was a fun project and what not, the effect I had to make was not what I wanted it to be. Back then, this was great, but with Cycles, I should be able to get somewhat better results. So today, as part of the new part of the book, I tried my hand at caustics. I had heard somewhere about Cycles that if you shrink your light source and make it more powerful you get sharper caustics and of course the opposite is also true, so I took one of the dolphins from the above image's project, placed it in a cube with a platform and covered it with displacement procedural textures.
I don't think it was this source, but here someone says it too and there are some good example renders with LuxRender here too:

The idea works, so yey, and here is how the image developed:

This is the basic scene. A very simply modeled dolphin (and I mean very simply) and it is placed inside a cube as said above.

This one shows how much is direct light in this scene.

2416 samples. Took a while as you can tell in the image above. While this may look like Cycles would be useless, just take into account how much of this image is lit with caustic light and how little comes directly from the light source.

I think that if I left it to go maybe 30000 samples, it would be a perfect image, but as it sits, you can see this one took around 5.5 hours to render (click the image here for actual size). Each pass took just over 2 seconds.

Remember to take into account that this image is pretty much 99% caustic light (which is why it took so many samples and so long). As such it looks good and proves caustics work in the method described, but on my PC this is most certainly not practical in terms of speed, lol.
I am however super jazzed that procedural textures do have an effect on caustics, so double yey that this one is a successful experiment! Mind you, it would've been considered successful regardless of the outcome, since I would still have been given understanding as to how Cycles functions (or how it doesn't) for future reference.

While you are all waiting for the book, you can check out some cool stuff from Andrew Price here at Blender Guru. Especially check out the lantern tutorial. Very good explanation on materials and lighting in Cycles.

Will keep you posted!!

Thank YOU!!!!!!!

In : General 

Tags: caustics  cycles  render engine  textures  faking 

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