Our two drinking glasses are now turned to glass. It's time to return our Raytrace glasses to the scene, enable caustics and try a Quick Render to see what we've created.
Step 4: Enabling mr Caustics
Before enabling caustics, let's first tell mental ray which of our objects shall be generating caustics. Click anywhere in the Camera viewport where there's no object, and from the Quad Menu select Unhide All. This returns to our scene the two hidden raytrace objects.
Next, hit H to call up the Select Objects list and from this list selects the following items: Camera01, Camera01.Target and Enclosure.
Click Invert, then select. Right click on any of the three glasses, and from the Quad Menu, select Object Properties > mental ray tab, and in the Indirect Illumination section enable Generate Caustics. Click OK. Hit F10 to bring up the Render Scene dialog panel. Click the Indirect Illumination tab, and depending on the version of Max/mental ray you're using, slide down the panel to the Caustics and Global Illumination (GI) rollout. For now, enable Caustics only, leaving all other settings to their default values and hit F9.
At default settings our render is quite sloppy. Let's take care of both the photon size and clarity problems before moving onward. In the Caustics group, enable Maximum Sampling Radius and set a value of 6 inches. Next, slide down the panel to the section Light Properties and increase the Average Caustic Photons per Light from 10000 to 35000. Your next Quick Render should yield a result similar to this:
This would be a good point to start making further adjustments to improve the quality of the render. The last matter we need to tend to concerns the trace depth of our project, this is especially notable by the lack of caustic light in the shadow field of the raytrace glass.
On the Render Scene panel (F10), click the Indirect Illumination tab and slide down to the area Caustics and Global Illumination (GI) to the Trace Depth Section. Set the Maximum Depth to 10, Maximum Reflections to 2 and Maximum Refractions to 8. And try your Quick Render (F9) again.
Which one is better? I'll leave that to you to decide. Imagine the possibilities with HDRI and/or a better background. You'll be surprised at what you can learn by experimenting with the settings to these materials. And here's a parting shot of the GPP and DMS in a real world scene. Good luck to all in your work.