View Full Version : MR caustics

10 October 2010, 10:26 PM
Hmm I dunno, if I am just reading tutorials wrong or just not getting it but I have a question on caustics, both reflective and refractive, is there like a general way of doing them?? Because I tried doing a quick test using glass physics phen shader in 2009 and am just not getting good results.

11 November 2010, 05:54 PM
What kind of results are you getting exactly?

11 November 2010, 12:06 AM
Well I just tried a basic setup with glass physics phen, 2 spheres and a plane

For the plane did a mental ray shader, added photon base shader to photon slot

the 2 spheres use glass physics phen

1 camera

1 mr area omni
1 mr area spot

set the spot light to inverse decay, have the 2 spheres generating caustics still not getting results.

11 November 2010, 03:27 PM
have the 2 spheres generating caustics still not getting results.
You should also have at least one light generating caustics, enable caustics under INDIRECT ILLUMINATION and have a sufficient amount of photons in AVERAGE CAUSTIC PHOTONS PER LIGHT

11 November 2010, 10:11 PM
Yea I tried that this mourning still not getting a good result...I'm thinking it may be the texture for the plane...or just the textures overall.

11 November 2010, 10:37 PM
okay I revisited this

made 3 wine glasses and 1 mr spot light - made all of em generate caustics.
Added a spotlight - which seemed to help...not sure how.

cranked caustic multiplier to 9 not sure if it should be that high

11 November 2010, 10:53 PM
You should try to lower the light intensity, i think it doesn't affect the caustics photon emission/intensity

11 November 2010, 08:26 AM
I think you're going about this the wrong way.

Caustics in mental ray are really much simpler than this. Use mia_material_x, not a phenomenon. Use this for all your objects, but use glass presets for your glass objects obviously.

Turn on photons and caustics in your light (should be a SPOTLIGHT, to focus photons) and it will render obscenely fast.

Also, use a linear lighting workflow. Your current scene is not - and it's extremely blown-out. It hurts the eyes to look at. And you shouldn't be cranking up multipliers all over, especially not for caustics.

11 November 2010, 10:26 PM
heh i guess...phenomena is a poor choice of words...well guess this is the best I'm gonna get because anyone else answering is going to give me even a harder time....

11 November 2010, 09:19 PM
Also side note. whats a quick way to get reflective caustics? is it raytrace map in the reflection slot?

also about mia_material_x don't think it exists in max, unless it's named something else.

11 November 2010, 09:39 PM
The mia_material_x is, broken down, "mental images architectural material_x". In Max, it's called the Architectural material, although this shader has nothing to do with architecture directly of course.

This shader is all you'll need for reflective and refractive caustics, and is also energy conserving and physically accurate. Takes the guesswork out of your rendering results... Well, not entirely, but at least the shader works properly!

12 December 2010, 11:34 PM
It's been mentioned already, but IMO this can't be mentioned enough...

I've found that the best way of making caustics is to have a light solely dedicated to casting photons for the caustics and nothing else - no spec, diffuse, shadows nothing but photons for caustics.
Preferably a spotlight, so you can focus it directly at your caustic material. It has to have Photons turned on for it and you obviously need Caustics enabled in the Indirect Lighting settings.
If you try to make a regular scene light cast caustic photons, you're going to often times have to turn it up so bright it will blow everything else out and you still probably won't get the effect you want.
And yeah, mia-x, and you can get even more control over your caustics if you add a (mental ray) dielectric_material_photon shader to the Photon Shader port on the mia-x SG node and override the mia_material Photon Shader (Under the mia-x SG Custom Shaders tab).

12 December 2010, 12:23 AM
Agree with all you're saying 'cept for the Dielectric part, Twosheds. I can't see any reason to use that shader - results are better for me from the mia_x alone, and it has far more control for refractions!

But yeah, an isolated spotlight is the best way for using photons. I can't think of any other reason to use GI at all these days; FG does fine by itself now!

12 December 2010, 12:42 AM
I just like the way the dielectric_material_photon shader makes it easier to adjust the color of the caustic patterns - seems to work better than changing the photon color in mia-x.
Now granted it's not particularly realistic to have, say blue caustics from an orange glass, but it looks cool as hell. :D

I suspect if one were so inclined you could add a ramp to it and maybe even make a spectrum caustic, but I haven't ever tried that.

12 December 2010, 12:54 AM
Good call! I wouldn't have even thought of using the Dielectric in this fashion. Thanks for the tip!

12 December 2010, 01:44 AM
No problem. :)

I'm playing with it right now, in Maya 2011. I decided to try to see if I could make a spectrum by plugging a ramp node into the color channel of the dielectric, but mental ray crashes every time I try to render it. *shrug*
There's probably a better way to do that though, but that seems like it should be the most obvious and easiest.

12 December 2010, 02:59 AM
Here's a quick and dirty example of the dielectric_material_photon shader plugged into the mia-x shader group Photon Shader on this gemstone, although in place of the basic color I used a ramp shader.
(Maya was crashing earlier, but got over it after closing and reopening the scene I was working on).
I don't know how to get the colors on the ramp close enough to even begin trying to simulate a spectrum, but if you look closely you can see some gradation between the colors that are there.
I don't have the time to tweak everything right now , but I'm going to try and figure this out.
There's an area light putting some basic light into the scene, but the caustic photons are all coming from a spotlight that has everything turned off except for photon emission.

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