Mental Ray Caustics 101

This tutorial will help you master the art of caustics in just a couple of easy-to-follow steps. In essence a caustic network is the projection of reflected or refracted light rays passing through a transparent surface. In 3DS Max this is handled by the renderer, in this case Mental Ray. It calculates the angle at which light hits a surface and how it is affected by the surface’s properties.

What You’ll be creating:

Mental Ray Caustics - Final

1/5 The Scene

We’ve prepared a simple scene for you. Please download and import this .FBX file.

You can create the scene yourself if you want to. It’s composed of a turbo-smoothed box with an open end and two Torus Knot objects inside it. The torus knots have a radius of roughly 13 standard units and a Cross Section radius of 7.5. One of the Torus Knots has Smoothing enabled for the sides in order to create some rough, diamond-like edges.

It should look something like this:

Mental Ray Caustics - the scene

2/5 Initial render setup

First of all, enable the mental ray renderer. Open the Render Setup window by pressing the “F10“ key and scroll down to the Assign Renderer tab. Click the Production: button and assign the mental ray renderer.

Mental Ray Caustics - enable mental ray

3/5 Lighting

As we’ve explained earlier, Caustics are light-dependent so we need to create one.
Click the Lights icon {Lights Tab} and create a Photometric Free Light. Remember to check the Shadow option and position it above the Knots but inside the rounded cube

Mental Ray Caustics - the photometric light

If we’d render the scene now, we’d see that the photometric light is way too bright. Photometric lights are scale dependent and our scene is just a bit too small. Select the light and click the Modify tab {Modify Tab} . Find the Intensity value-box and change it to 50.
Mental Ray Caustics - light intensity

Now render the scene. You should get something like this:

Mental Ray Caustics - light preview

The shadows look just about right and we can jump to the material section of this tutorial.

4/5 The material / Caustics

Caustics need transparent materials so we’re going to use Autodesk’s glass material. Open the Material Editor {Material Editor Icon} by pressing the “m” key and select the first empty material slot. Click the Standard button to the right of the material’s name and select the Autodesk Solid Glass from the mental ray tab. Users of older versions of 3DS Max can use the Glass (physics_phen) material.

Mental Ray Caustics - glass material

With the material still selected, select the Custom entry from the Color: dropdown and change the color to a light red

Mental Ray Caustics - first glass color

Apply {Apply Material} the material to the left Torus Knot, select the second empty material slot and repeat the same steps for the right Knot but set its color to a light blue. Also apply a standard material to the box.

Mental Ray Caustics - second glass color
Render the scene again and you should get this:

Mental Ray Caustics - glass preview

Continue on page 2

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