Verfahren zur Regelung der Belichtungszeit von Kopiergeräten

1,127,795. Controlling exposure in photoprinting. AGFA-GEVAERT A. G. March 1, 1966 [March 10, 19651, No. 8925/66. Heading G2A. In a method of regulating exposure in photoprinting, the exposure is terminated in dependence on a summation signal derived from two signals, one being time-dependent and initiated simultaneously with the exposure, and the other dependent on the illumination intensity. As shown, part of the light from source 1 falls on a photo-multiplier 5, the resultant current passing through a logarithmic amplifier 7, and then through a multiplier 8 where it is multiplied by a variable co-efficient y. When exposure is initiated, by closing the coupled switches 2 and 3, the linear timer 11 is started, and transmits a time-dependent signal via the logarithmic amplifier 12 to the multiplier 13, where it is multiplied by a variable co-efficient #. The two signals are passed on to an amplifier 18 where they are added together, and matched against a comparison voltage, which takes into account the film sensitivity, in a comparator 19. When a particular relationship is obtained between the two voltages (e. g. equality), a switch 4 is opened, which terminates the exposure. The exposure as regulated by this arrangement can constitute an overcorrection or undercorrection of that given by the reciprocity law, corresponding to the exponent p in the Schwarzchild equation I.tp = const., by suitably adjusting the values of the variable multipliers 8 and 13, and expressing the equation in the form y log I + # log t = const. Details of the various operative amplifiers shown diagrammatically in Fig. 1 are set out in Figs. 3-6 (not shown).