Apple Shake 4 Tutorials - Manual (Page 161)

Tutorial 4 Working With Expressions 161
When you view Move3D1, the transformation moves the fan image, but that’s not what
you want. You want to use the Move3D1 to generate motion blur only, so now you’re
going to tell Shake to use the input as a reference, but ignore the transform.
To apply fake motion blur to the fan:
1 In the Move3D1 parameters, set motionBlur to 0.5.
The result still is not correct—the fan is transformed.
2 At the bottom of the Move3D1 parameters, enable useReference.
The fan snaps back to its original position and the motion blur is applied to the fan.