The mental ray renderer can generate reflections and refractions by ray tracing. Ray tracing traces the path of rays sampled from the light source. Reflections and refractions generated this way are physically accurate.

Ray-traced reflections and Refractions

To reduce the time required to generate reflections and shadows, rays are limited by trace depth. Trace depth limits the number of times a ray can be reflected, refracted, or both.

You can turn off ray tracing. In this case, the mental ray renderer uses scanline rendering only. Turning off ray tracing makes the controls for all the effects that are specific to mental ray unavailable in the Renderer's rollouts.

You enable ray tracing and set trace depth with the Render Setup dialog Renderer panel Rendering Algorithms rollout controls.