Scene Creation
Photon Depth

The Photon Depth value controls the number of objects a photon can hit before it is absorbed. This has the effect of reducing unecessary rendering time as photons which reflected or transmitted many times will retain little energy and often have relatively no visible effect on the final image.

Different values can be specified for reflections, refractions and both together. XSI allows a maximum depth for reflection and refraction of 20 and the sum for both of 40.

If the specified photon trace depth is too small no photons will be stored in the scene therefore if a value is set to zero the caustics are disabled and an error message appears.

The default values in XSI are set to 2 and the default values in Mental Ray are 5. In this instance two layers of glass were used to investigate photon depth. A photon depth value of 1 does not penetrate the glass and produces no caustic effects. A minimum of depth of two is required for caustics.

Photon Depth (all values)
Further Information
Susan Windeatt