When you render an animation, motion blur gives the effect of movement by blurring objects in the scene. For more information on motion blur, see Focus and blur.
mental ray for Maya supports only 3D motion blur.
You can enable Motion Blur in the Quality tab of the Render Settings window, and adjust the settings in the Motion Blur and Motion Blur Optimization sections.
In mental ray for Maya, you can choose between No Deformation and Full Motion Blur. Motion Blur in mental ray for Maya blurs everything: shaders, textures, lights, shadows, reflections, refractions, and caustics.
The No Deformation mode results in instance motion; shape changes are not considered. The Full Mode additionally exports motion vectors for every vertex of the moving object. Use it to motion blur objects with deforming shape. This mode requires more translation and render time.
The No Deformation mode just exports instance motion performed on transform nodes, any shape changes (even linear movements) are not considered.
The Shutter Open, Shutter Close setting of the Maya camera determines the actual motion blur path length. You can modify other settings, such as Motion Blur By, to further control the final motion blur calculation. Find these settings under Motion Blur (in the Features tab of the Render Settings window.).
A typical application of motion blur is the Export Motion Segments option, which approximates any non-linear movement with a set of linear segments.
Any transformation animation (instance translation, rotation etc.) with non-linear properties is not handled by the plug-in (there is no support in mental ray for more than 1 motion transform) but left to mental ray's built-in procedure to detect common cases of rotations (even pivot rotations) automatically. More complex transformation animation is not supported natively, but may be baked as shape deformation in Maya to be rendered correctly.