Claudia Herbst-Tait
Professor
Pratt Institute
Department of Digital Arts



A Look at Setting Up Caustics

Open the file mental_ray_caustics_ring.mb located in my folder on DDA transfer

Note that in the Render Settings, Common tab, Enable Deafult Light is turned off and, under the
Maya Software tab, Raytracing is turned on.

Familiarize yourself with the scene; we should be inside a cube, looking at a ring up close;
it has a metal/gold blinn material assigned to it. There's a spot light at close range.

Select the spot light, turn on Ray Trace Shadows. Do a quick test render. Sort of looks like a gold ring...


Getting Started:
Now, in the Render Settings, switch the renderer to Mental Ray. Set Quality Presets to Custom.

Select the Indirect Lighting tab, turn on Caustics.

Further down, in the Photon Tab section, turn on Enable Map Visualizer.

Do a quick test render -- nothing's happening yet because the light does not emit any Photons yet...
Select the spot light, open the Mental Ray section, in the Caustic and Global Illumination section, check Emit Photons.

Do another test render: the magic should be starting to happen... at this point, the caustics effect is
quite sublte but the light should be bouncing off the ring and create a yellowish relfection on the ground.

Btw, in the Maya scene, notice the dots/sparkles. These represent the photons and are visible because you
turned on the Enable Map Visualizer option a moment ago. If you don't see any results in your rendered
image, the Map Visualizer lets you see if Photons are there -- if so, getting results will depend on tweaking
some of the values, i.e., upping the Photon Intensity, Caustic Photons value, and Caustic Accuracy & Radius
values, which is what we do next to achieve a better result.


Tweaking and Andjusting:
Int he Render View, keep the last rendered image for comparison. Now, select the spot light, in the
Caustics and Global Illumination section, change Photon Intensity from the default 8000 to 12000.
Test render; compare the before and after. The caustics effect should be more pronounced at this point.
Keep this image as well.

Next, select the spot light, in Caustics and Global Illumination section, change the Caustic Photons value
to 2000. Test render; compare the before and after. Keep the image.

In the Render Settings, go to the Caustics and Globale Illumination section, change the Caustics Accuracy
from 100 to 300; do as test render and compare the before and after; next, change the value from 300 to 600,
do as test render and compare the before and after... also, try a low value of 50... keep each render in the
Render View so that you can compare...


Ok, so this was easy... in part this is due to the setup, the envrionment's & object's size. In the next scene,
we'll look at a scenario that took a bit more time tweaking.

Open the file mental_ray_caustics_vase.mb located in my folder on DDA transfer.

Note that in the Render Settings, Common tab, Enable Deafult Light is turned off and Raytracing is turned on.
Familiarize yourself with the scene; we should be inside a cube, looking at the looking at our favorite vase...

Do a test render but make sure to set the render Test Resolution (main menu, Render), to 50%.

Now take a look at the values we've just tweaked in the above example. These include the Photon Intensity,
Caustic Photons value, and Caustic Accuracy & Radius values, which is what we do next to achieve a better
result. See how much bigger the values had to be in order to get a smooth caustics effect in this scene...
We'll further experiment in class with this...