There is a phenomenon called shutter distortion, which occurs when you photograph fast moving objects using relatively long exposure time while NOT panning. When the first curtain slides up, the bottom of the sensor gets to be exposed first, and by the time the top part of the sensor is exposed the object could have (slightly) moved.


Knowing that your shutter will open and close predictably instead swinging back and forth, you can control or even apply the shutter distortion more effectively. I think...