Photosensitive system for responding to different luminosities of an object

Claim 1

In an electrical system to be used when an object having regions of different luminosities is to be photographed, photosensitive detector circuit means for detecting those regions of the object which have maximum and minimum luminosities, respectively, and for transmitting signals respectively corresponding to said maximum and minimum luminosities, respectively, electrically-responsive means for producing, in response to an electrical input, an operation to be used in connection with the photographing of an object, and control circuit means electrically connected between said detector circuit means and said electrically-responsive means for receiving said signals from said detector circuit means and for transmitting to said electrically-responsive means said input to which the latter responds for producing said operation, said control circuit means including a transistorized comparison circuit for comparing the signals of said detector circuit means which respectively correspond to maximum and minimum luminosity, said control circuit means also including a capacitor for receiving a charge corresponding at least to a fraction of the difference between said signals, and switch means also forming part Of said control circuit means and having one position connecting said capacitor to the remainder of said control circuit means and another position connecting said capacitor to said electrically-responsive means for providing said input to which the latter responds, said control circuit means including a means connected with said switch means when the latter is in said other position thereof for transmitting through said switch means to said capacitor and through the latter to said electricallyresponsive means a signal according to which one of said signals according to maximum and minimum luminosity is arithmetically combined with the charge received by said capacitor, said control circuit means further including a means operatively connected to said comparison circuit for providing at said capacitor a charge according to one-half the difference between said maximum and minimum luminosity signals when said switch means is in said one position thereof, whereby said switch means when in said other position thereof transmits to said electrically-responsive means a signal according to which the charge of said capacitor is arithmetically combined with one of said maximum and minimum luminosity signals so as to transmit to said electricallyresponsive means an input corresponding to the average between the maximum and minimum luminosities at the object which is to be photographed.