An improved “spinning top” for exposure timer checking coupled with a light beam checking device

The time honoured “spinning top” test gives an accurate check for short exposure times, but the dots overlap if a hand spun top is used for times longer than about 0·25 second, and cannot be identified on three-phase and constant voltage generators. To remedy these shortcomings, a synchronous motor has been made to drive a “spinning top” of 6 in. diameter at a rate of one revolution in two seconds, and the arcs corresponding to exposure times are measured against a stationary scale which is reproduced on the film. The device is shown in Figs. 1 and 2.