This tutorial is for 3d studio max version 6 ONLY. It will guide you on how to create a good caustic effect using the mental ray 3.2 renderer in-built to 3d studio max 6 and hopefully explain a little about the effects of each settings. A little knowledge of the program interface is helpful however this tutorial can be tackled by a complete beginner.

1. Start a new 3dsmax file. Firstly press f10 to go to the render dialogue box (alternatively you can click rendering>render on the program tool bar. In the common tab, inside the render dialogue scroll to the bottom and enlarge the "assign renderer" rollout. Click the box containing 3 dots "..." on the slot for "production" and change this from "default scanline" to "mental ray". You can now close the render dialogue. NB: you may wish to "save as defaults" for this setting as mental ray is a much faster and more powerful renderer than scanline making scanline almost obselete.

2. If not already selected, click the create tab on the right hand side of the max interface (its symbol is a cursor pointing to a star). Under "standard primatives" click plane, underneath are a set of options for the plane, expand the "keyboard entry" rollout and use the following values, X=0 , Y=0 , Z=0 [these are the positioning co-ordinates for the plane, in this case set to the centre of the max viewports] Length = 200 Width = 200 [These are the dimensions of the plane being created]. Then click the "create" button. There should now be a square plane visible in all 4 viewports.

3. Open up the materials editor by pressing m, within the "blinn basic parameters" rollout there is a colour box next to the word diffuse, click this box and change the tone of grey to a slighty lighter shade (or any other colour of your choice). Then click the "assign material to selection" button [this button is just below the spheres and looks like a sphere with an arrow pointing to a box].

4. We will now create an object which is going to create the caustics in the scene, a torus knot is always a good choice. Select the top viewport by clicking inside it. Then goto the create panel again, click the combo box which currently says "standard primatives" in it and change this to "extended primatives". Choose torus knot and once more extend the keyboard entry rollout. Use the following settings X=0 , Y=0 , Z=28.5 , major radius = 20 , minor radius = 8 and click the "create" button.

5. There should now be a torus knot sat on the plane, it may need a little tweaking to get it set exactly on the plane, simply use the move tool along the 5 axis to do this. You may wish to increse the number of sides to the torus knot to give it a smoother appearance in rendering, you can do this simply by going to the modify panel and increasing the number of segments and sides. I use 200 segments and 24 sides. IMPORTANT: Ensure the torus knot is selected, right-click inside one of the viewports and goto properties. In the mental ray tab check the box next to generate caustics.

6. The torus knot now needs a refractive material, open up the material editor again and choose an empty slot (sphere). On the right hand side of the material editor there is a box saying "standard" in it, this is the type of material being used, in this case we want a refractive material and so the best choice to use is raytrace. Click the box and change the material from standard to "raytrace". We now have a more complex looking set of material options. Change the colour in the diffuse slot to a colour of your choice, im using a rustic orange colour, then also change the transparency colour to the same shade. [my settings Red=205, Green=140, Blue=0 ]. Change the specular level to 300, and the glossiness to 60, apply this material to the torus knot.

7. Now the scene needs lighting, since without it caustics would not be possible. Goto the creat tab again, and this time click the lights button, choose "mr area omni" and create it abve the centre of the torus. Now goto the modify panel, in the light options rollout the combo box that says "omni" in it and change this to "directional", ensure that the light is casting shadows by checking the box and choose raytrace shadows. Rotate the light so that the beam falls on to the torus knot, then increase the hotspot/falloff values under "directional parameters" to hotspot=60 , falloff=80. Now scroll down to "mental ray inderect illumination" rollout and expand it. Uncheck "use global settings" and check the "on" box which has now become active. Set the energy to 50,000 decay to 2. And set the number of caustic photons to 150,000.

8. We're now ready to render the scene. Ensure the perspective viewport is selected and open up the render dialogue box again, click the "indirect illumination" tab, check the enable box under caustics. Change the filter from box to cone and click the render button at the bottom. Hey presto some groovy looking caustics:

I hope that this tutorial has helped you learn a little more about max interface, and the tools that it encompasses. Here is my final scene with HDRI added: