GI-Caustics - a unified light transportation model

finalRender Stage-2 offers a highly advanced approach to render physically accurate light transport between surfaces.  In Maya, usually a 2 pass rendering approach is used to get proper caustic light effects along with other illumination effects, in finalRender Stage-2, such things can be rendered in one pass within one unified light transportation model. Such an approach is much more efficient and creates accurate results in one go - instead of Maya's multiple independent rendering steps.  The main problem resulting from this separated rendering approach for direct illumination, indirect illumination and caustic light effects, is the lack of accuracy. In fact, such an approach does not really help in getting a physically correct light distribution. By treating the direct light sources as "Photon Shooters" with independent settings, the final result can only be a wild guess of the actual light energies that would be involved in creating a physically correct result.

The rendering shown below would be very hard, if not impossible, to render with Maya standard rendering tools. In this case, the only source of light is a HDRI light probe - no direct light of any kind is used.