A technique has been developed to film the entire trace of a ball tumbling in a rotary two-dimensional (2D) mill. With careful calibration, the positions of the ball before and after impact with the mill shell were precisely determined with an image analyzer. Because the image formation process was accurately timed using a digital strobe, the instantaneous speeds of the ball along its trajectory can also be calculated. This makes it possible to (I) investigate the end effect in the experimental two-dimensional mill; (2) evaluate the energy loss during impacts; (3) determine dynamic coefficient of restitution that is an essential parameter in Discrete Element Method (DEM) simulation. Furthermore, this technique permits the charge motion to be analyzed quantitatively in great detail hereby providing precise calibration of the DEM.