Hello. I have to create a simple scene in C4D with a mirror ball in a room reflecting its little mirrors on the ceiling, walls, and floor as it spins. I've done this before in C4D with the build in renderer by turning on caustics for the light and in the render setup. I can't figure out, or even come close, to do that in Arnold even if I have turn on caustics for the mirror material in the advance tab. The caustic reflections are very faint and not sharp at all like I've done in past with C4D. Am I missing something? This is on C4D R20 and Arnold 5. Thank you.
You have to use the Arnold surface shader and enable caustics, but it's not very good. Arnold is not optimized/biased for this. There's no photon mapping in Arnold and reflective caustics are anemic. You need a zillion specular samples and it takes forever and doesn't look good. Refractive/transmissive caustics aren't supported at all.
This would be far easier to achieve using a gobo with Atmosphere Volume.