Light-correction system for printers of colour cinematographic films

Claim 1

A light-correction system for a cinematographic color film printing machine which is adapted to operate on the additive three-color principle in which the light flux emitted by a source is split up into three monochromatic beams which are each passed through a flux modulator and thereafter recombined, the system comprising, means for advancing a perforated programming tape on which correcting information is recorded step-by-step with the advance of a film to be printed, a programming tape reader for producing an output of electric pulses, a digital-analogue arrangement for converting the electric pulses into representative electrical voltages; means for separately adjusting the aperture of each of the flux modulators, said adjusting means including an aperture shutter and corresponding operating shaft for each flux modulator a separate electric motor for driving each of said adjusting means; separate positioncontrolling potentiometric assemblies for coupling each of the motors with one of the representative voltages; means for storing correction information supplied by the reader; means for sensing an index mark carried by the film; means for extracting the stored information when an index mark is sensed; a cam mounted in each of the flux modulators, for converting rotation of each corresponding motor into an angular displacement of a pivoting member mounted for rotation on an operating shaft of an aperture shutter of the respective flux modulator; means for making the operating shaft fast with the said pivoting member during a short time interval initiated by the index mark sensing means; the pivoting member comprising a lever journalled at one of the ends on the operating shaft of the corresponding aperture shutter and a blade articulated on the other end of the lever and provided at its free end with aligned lateral projections for engaging in corresponding recesses of the cam, said cam being keyed on the operating shaft, a spring for controlling the spacing between the cam and the blade and an electromagnet for engaging the blade with the cam when the latter receives an electric pulse indicative of a sensed index mark.