Maker's Name: 
A.J.Ashdown Ltd., London
Where made: 
16 × 14 × 18 cm

A patented shutter controlled by a gear connected to a centrifugal governor. A winding rod fits under the bottom handle to wind a spring. The speed of the gear is controlled by 5 sliding gear -coarse settings and an infinite graduation control achieved by a balanced centrifugal governor.

The Ashdown Rotoscope acts to gear human vision up to zero speed relative to an object having recurrent motion. A shutter turns at an accurate speed only allowing the viewer to see at instants certain time intervals apart. If the object under test executed a recurrent motion, then it is possible to view the object as stationary, or nearly so, by adjusting the time interval accordingly. The governor can be made to run between 50 and 125 RPM and thus by multiplying this with the gear ratio, the shutter speed may be calculated. The Rotoscope was used in two ways:

  • (a) To examine the workings of a machine running at a known speed, and determine speed variations.
  • (b) To measure the unknown speed of a machine, by setting the Rotoscope to run at a much higher speed than the machine and slowing the Rotoscope down until a steady picture is reached.