Electronic Flicker Apparatus with Automatic Frequency Variation*

Abstract

An electronic apparatus is described which delivers light flashes with intensity, light-dark ratio, and frequency as independent variables. The flash rate is varied automatically, and is proportional to the voltage on the control grid of the charging pentode. The control voltage is taken from a highly isolated condensor through a cathode follower with very low grid current. When the condensor is charged or discharged by a constant current, the control voltage, and hence the frequency, will change proportionally with time. The rate of frequency change is determined by the magnitude of the current, and can be started or reversed either manually or by a saw-tooth voltage. This automatic and variable frequency variation makes it possible to keep the conditions more constant from measurement to measurement for each rate of frequency change, and to compare the effect of varying speed of frequency variation as well as of the duration of series of exposures (prethreshold exposure time) upon FFF (flicker fusion frequency) with significant precision. These factors are important for the standardization of FFF determinations.