GB1373468A - Method of controlling exposure times in photographic apparatus - Google Patents

Abstract

1373468 Camera SOC D'OPTIQUE PRECISION ELECTRONIQUE ET MECANIQUE 15 March 1973 [15 March 1972] 12590/73 Heading G2A An exposure control system, especially for photo-micrography, comprises a generator 20 for applying pulses at a constant rate to a binary counter 22 which provides a shutter closing signal on reaching a predetermined count, the counter having a plurality of selectable stages to provide the signal, selection of the second or a succeeding stage giving rise to an exposure time twice that resulting from selection of the preceding stage. As shown, a photo-cell 3 produces a signal proportional to the illumination at the film plane and a log amp 4 and amp 5 produce a corresponding voltage V L . Film sensitivity and shutter time are set in on potentiometers 8 and 11 to produce voltages V S V P and these together with V L and a pre-set constant voltage V C are summed at 14 and fed to signal lamps 15, 16. Potentiometer 11 is adjusted until neither lamp is lit, the setting of potentiometer 11 determining the position of a stage selector 23 of the counter 22. When shutter release 26 is actuated a trigger 25 energizes an electromagnet 2 to open the shutter 1 and enables an AND gate 21 whereby pulses from clock generator 20 are fed to counter 22. The time taken for counter 22 to reach its predetermined count depends on the stage selected. When the count is reached, a signal from the counter resets the trigger 25 to de-energize the electromagnet 2, disable the AND gate 21 and reset'the counter 22.