View Full Version : Mental Ray Caustics Not visible?

02 February 2006, 04:45 PM
I have attached a file. It is relatively simple. I have caustics on the water and close to default settings in the rendering options. I have tried all kinds of stuff to get the caustics to appear on the walls and ceiling. why aren't they showing up?

Take a look.


02 February 2006, 11:58 PM
A couple things:
First off, your water surface has no photon shader. You need a photon shader to describe how caustic photons interact with the water surface.
Similarly, none of your walls have photon shaders. And since the caustic light you're using has such a wide cone angle, thus making a large amount of the photons hit your walls before anything else, that's a bit of a problem! Also, if your walls or ceiling are going to be receiving any of these photons, they need a photon shader to tell MR to store photons on those surfaces. Every surface that generates or receives caustics has to have a photon shader. Default max shaders have photon shaders built into them. In your case, you should just apply photon basic shaders to your MR materials.
I'd also suggest creating a separate caustic-only light for things like this: If you have a light dedicated solely to caustics, you can adjust the cone angle so that all of the photons are focused on the water surface, instead of wasting half of them on other parts of the scene.
You've also placed your caustic light within another object that is set to receive caustics (the light geometry). And this light geometry also doesn't have a photon shader. So, what's happening is that your caustic photons are getting trapped in the ceiling light geometry. If you create a second caustic-only light, you can place that below this geometry - it really won't make that big of a difference. Or you could just uncheck receive caustics for the light geometry (with the material thats been applied to it, it won't matter anyway). Alternatively, you can place a transmat shader in the photon shader slot of your light material.
And finally, your scene isn't entirely closed off (no wall on the back side - the side that the camera is looking through. So, all of the photons that are being directed to that side are just shooting off into empty space. None of these photons can be stored anywhere, and so this slows the render time down dramatically.

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02 February 2006, 11:58 PM
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