Caustics are really great light effects that you can observe in liquids, glass objects and gems. We are able to simulate this effect with 3D Studio Max perfectly.
This tutorial about Caustics that I wrote for my students of the Florence Design Academy (href="http://www.florencedesignacademy.com">www.florencedesignacademy.com) will work only if you enable Mental Ray (this tutorial was made in Max 8).
Let's Create a small room like in the image below ( try to do that in realistic sizes, it is important that you make the setup of the unit system, only in this way Mental Ray will give you an optimal end result since it will consider all measurements of the objects in the scene for the final rendering).
There are several techniques to create a correct illumination. In the case of the room I have created 3 long free area lights as you can see in the image below ( you can find them under photometric lights).
Place them under three long boxes. Select the bottom polygons of the boxes and assign them a white self illuminated material like as I have done in the image below.
To get a more realistic illumination I have enabled Final Gather in indirect illumination. I have put a quite high number in samples to make the final render (600).
After you've made the room you must create the water. We can do that with a simple box. To create the small waves on the surface you have different possibilities (or with a material or by polygons). For a transparent water material create a Raytrace material (it must be transparent and a bit reflective). To create a wave effect put in the bump map a noise map with a quite small size; to simulate through geometry deformation the noise/wave effect you must apply to the box a noise modifier. The wave size will influence the caustic shapes. Big waves/noise = Big caustic shapes!
After you've made all the objects you must create a MR. Area Omni light on the top of the water in the center of the room as the image below shows.
Now right mouse click on the MR. Area Omni and disable Affect Specular and Affect Diffuse as the image below shows.
After doing this, the MR.Area Omni will not anymore affect the illumination of the room. We will use that MR.Area Omni only to create the caustic effects. Do it this way, we have much more control of the caustic position, color and the brightness. Disable the shadows of the MR.Area Omni. Now select the MR.Area Omni and all the other objects, except for the lights that you have created for illumination(Free area lights).
Right mouse click on all of the selections and select properties like in the image below.
Go to the Mental Ray panel and check Generate Caustics.This is necessary in order to have a caustic effect on the objects. Now we must go to the Indirect Illimination panel (panel for rendering), and enable Caustics.
To improve the quality of the caustics (better/clearer shapes) you must go to Light Properties and put a very high number in average caustic photons per light. I put a bit less than one million. For test renderings, I normal put about 10.000 as I find that is enough. The higher the number, the better the effect will be. Of course it will take much more longer to render all of the scene.
You can use very high numbers in the multiplier (MR.Area Omni) to create a very bright caustic effect. If you change the light color of the MR.Area Omni you will change the color of the caustics (blue omni color = blue caustics).
To have a blue color of the illumination under water the water material should have a blue color in diffuse and transparency like in the image below.
Well I hope you liked this tutorial.