To create motion blur for a specific object in a scene, you must assign it a motion blur property. This is useful when you want to force motion blur off for a given object, or if you want to optimize rendering performance by setting the more render-intensive deformation blur only for a specific object.
Select the object for which you want to create the motion blur property.
From the Render toolbar, choose Get 
Property Motion Blur. This creates a motion blur property for the selected object. The motion blur property editor opens.
In this property editor, do the following:
If you wish to remove the motion blur from more than one object in a scene, repeat the same steps, but first create a group with all the non-motion blurred objects. Then open the explorer and expand the group. You should see the motion blur subnode beneath the group. You can now follow the previous steps.
In frames where motion blur is active and both the camera and the scene objects are moving, each of them will contribute to the motion blur.
If you want to deactivate the motion blur created by the camera, follow the previous procedure to apply a motion blur property to the camera. Make sure to set the motion blur to be Off.
Deformation motion blur consumes a lot of memory and may affect render times adversely. The most efficient way to work with deformation motion blur is to use localized deformation blur properties, as in the following example.
You have a large static set and three characters in a scene.
Place your characters in a group and put a motion blur property on the group (or put properties on each separate character) and then activate Deformation Blur in that property editor.
Set the motion blur options as describe in Defining and Rendering Motion Blur.
Do not enable Deformation Blur in the Scene Render Options property editor because this will active deformation motion blur globally for the scene and generate additional motion data for all objects even if they do not require deformation blur.
You can set the number of motion steps for the deformation motion blur by entering a value for the Motion Steps Deformation slider in the mental ray Render Options property editor. This value is pushed to mental ray as long as an object with local
deformation blur is detected in the scene.
The result is that only the characters use the extra memory required to blur them, while the rest of the scene remains static. If a character picks up a prop, for example, the movement is transformation-based, so the moving prop blurs as well (as long as standard motion blur is enabled).
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