- Max Specular Depth - This is how many times a ray will reflect or refract for an object with a specular material lobe. Think of a mirror and how it reflects the light that reaches it instead of being absorbed.
- Max Diffuse Depth - This is how many times a ray will bounce off of objects with a diffuse lobe. Think of this as color bleeding from nearby objects.
- There is also a maximum combination of the two controlled by the integrator explained at the bottom.
These are per-object settings and not renderer options for RenderMan. Some bridge product UIs may expose this globally but that means on export for rendering the setting is applied to every object as though it were a rendering option.
Why are they separate?
It's possible that you only need higher depths of one interaction, specular or diffuse. So rather than trace more rays of a type that may be unnecessary visually, the user can decide which needs to travel further. Below are some examples. We'll begin with Diffuse Depth