V-Ray for Rhino Manual - Rum

Go back to the Caustic's control panel. Render it again with the Max Photons changed from 50 to
300, as the image on the right. Compare with last page you will find the Caustic effect is greater
this time and smoother.
Usually it's easier to spot the Caustic effect in a darker scene. If the scene is brighter, you can try
increase the Multiplier to offset the difference.
If you want to control the quality of Caustic even better, other than increase the intensity of light,
you can also increase the Subdivs under Sampling from 1000 to 2000 or even higher. But this will
increase the prepare time for render Caustic effect.
Image on the right is rendered with Caustic Subdivs set to 3000, you can see the better quality of
Caustic effect in this case.
V-Ray for Rhino 87