Illumination control circuitry for a film video player electronic strobe light

摘要

A film video player includes an electronic strobe light operable for repetitively firing a flash tube to flash illuminate a solid state image sensor via a pulse of light projected via a photographic film during the vertical retrace interval of a standard television signal. Detector circuitry, responsive to a signal relating to an output of the image sensor, produces a control signal that is functionally related to whether or not the illumination of the image sensor is above, below, or within a predetermined range near the saturation level of the image sensor. A microprocessor adjusts an exposure level signal at the vertical retrace rate in accordance with the control signal. Logic switching circuitry, having an input coupled to the microprocessor and responsive to the exposure level signal and an output coupled to the electronic strobe light, causes the electronic strobe light to produce a pulse of light within each vertical retrace interval that is sufficient to illuminate the image sensor near its saturation level, without the illumination saturating the sensor, to optimize the signal-to-noise ratio of the image sensor. The amplitude of the flash-firing current through the electronic strobe light is adjusted to be one of two discrete levels, and the duration of the light pulse is adjusted to be greater than a minimum duration below which the energy of the light pulse cannot accurately be repeated, and less than the vertical retrace interval. Five stops of exposure variation in the photographic film can be accommodated.