GB1047866A - Improvements relating to photographic shutter timing apparatus - Google Patents

Abstract

1,047,866. Photographic cameras. INTER - NATIONAL POLAROID CORPORATION. March 26, 1964 [March 29, 1963], No.12870/64. Heading G2A. [Also in Division G1] A photographic camera shutter mechanism comprises a first shutter blade which is held in an open position by an electromagnet for a predetermined exposure time. The electromagnet is pulsed with a high current immediately prior to the release of another shutter blade initiating the exposure so that hysteresis in the magnet prevents premature release of the first blade on operation of the other blade. The shutter is initially cocked by actuating a lever 34, Fig. 1, whereby an arm 33 engages a rod 28 fixed to shutter vane 19 to push both vanes 19, 20 to the left until a pin 26 engages a latch 24. A keeper 40 on vane 20 completes the magnetic circuit of an electromagnet 37 operation of the release key 30 first closes a switch S 1 which connects the battery 56,Fig. 2, to the exposure control circuit. Transistor Q2 conducts to energize the electromagnet winding 38. Further movement of key 30 closes a switch S 5 which connects battery 56 across the winding 38 for a short period while latch 24 releases vane 19 to initiate exposure. This provides a high magnetic flux in keeper 40 to prevent premature release of vane 19 and also reduces the current needed from transistor Q2 to hold the electromagnet by utilizing the hysterisis effect. The release of vane 19 opens a switch 32, and capacitor C charges through the photoresistor 45. At a preset trigger potential, Q1 conducts, rapidly reducing the current through Q2 to an extent where vane 20 is released to terminate the exposure. Regenerative feedback provided by the common emitter resistor 53 increases the switching speed. Q1 is a planar silicon transistor, and resistor 60 limits the rate of discharge of C through Q1 when the latter conducts to give keeper 40 a chance to separate from electromagnet 37 before the current through winding 38 increases to its holding level again.