The Rays Panel

Enable Ray Tracing - Global control for enabling and disabling ray tracing. This causes MTOR to tag each object with visibility attributes required by PRMan's ray tracing subsystem. Only objects made visible to this subsystem will appear in ray traced reflections and shadows.

Trace Breadth Sample Factor - A global multiplier for all multi-sampling ray tracing operations. Set this to a value greater that 1 will increase sampling quality and slow down the rendering. Set this to a value less than 1 to speed up your renderings. Currently, this setting will only affect ray tracing shaders that are "trace sample factor savvy". This includes all factory slim shaders.

Trace Depth Sample Factor - A global multiplier for all multi-sampling ray tracing operations that varies the requested ray sample count according to the current ray depth. During preview rendering, a value less than 1 should be used. Smaller values result in a coarser approximation but yield significant speed improvement. And the gritty artifacts aren't entirely unpleasant. Currently, this setting will only affect ray tracing shaders that are "trace sample factor savvy". This includes all factory slim shaders.

Max Ray Depth - This sets a limit to the number of bounces any ray can travel regardless of its type.

Specular Threshold - This angle controls the categorization of a ray path. Rays scattered in regions smaller than this value are specular. Larger regions yield diffuse ray paths.

General Attributes 

This panel controls general ray tracing attributes. Values provided here act as scene-wide defaults and these can be overridden on a per-object basis. Here you can set the ray bias, limit the specular and diffuse ray depth and establish traced displacement policy.

Max Specular Depth - Limits the number of specular bounces (reflections and refractions) for rays trace from the associated primitive. To resolve the interaction between per-primitive values, we pass the current max down the ray tree and apply MIN(ray.depthMax, primitive.depthMax + ray.depth). You can use this attribute to limit the number of reflection and refraction bounces and thereby tune your rendering speed. A value of 1 or 2 is a reasonable default unless you need multi-bounce effects. This value acts as the scene default and you can override this value on a per-primitive basis via the Slim Ensemble. 

Max Diffuse Depth - Limits the number of bounces (diffuse or specular) for indirect illuminance relative to the associated primitive. To resolve the interaction between per-primitive values, we pass the current max down the ray tree and apply MIN(ray.depthMax, primitive.depthMax + ray.depth). You can use this attribute to limit the number of diffuse and specular bounces of photons in the photon tracing pass as well as to limit the depth of diffuse illuminance gathering shaders. A value of 1 is suggested. This value acts as the scene default and you can override this value on a per-primitive basis via the Slim Ensemble. 

Trace Displacements - Controls whether displacements are considered when ray tracing primitives. You can override this value on a per primitive basis via the Slim Ensemble. Since tracing displacements is much slower you'll want to avoid doing so in most circumstances. This value acts as the scene default and you can override this value on a per-primitive basis via the Slim Ensemble. 

Trace Bias - The default bias value for ray tracing. This value is added to the ray origin when tracing rays to overcome numerical precision issues resulting in false ray-primitive intersections. This value acts as the scene default and you can override this value on a per-primitive basis via the Slim Ensemble. 

Sample Motion - Controls whether motion blurred objects appear in ray traced results. If your reflective object is moving or deforming you should disable this parameter to avoid self-intersection artifacts. If your mirror isn't moving, set this to 1 to see the reflected objects properly blurred.