EXPOSURE CONTROL SYSTEMS

摘要

1523473 Shutter-diaphragm control WEST ELECTRIC CO Ltd 15 Oct 1975 [18 Oct 1974] 42112/75 Heading G2A A shutter-diaphragm is driven by a pulsed step motor 1 to provide an aperture and exposure time dependent on subject brightness, the motor being locked against movement when the shutterdiaphragm is closed in order to prevent accidental operation e.g. due to mechanical shock. As shown upon shutter release: (a) a switch 66 is closed to turn on a thyristor 69 which turns on a power supply transistor 67. This energizes an electromagnet 25 which pivots a brake arm 22, Fig. 2, from the dotted line to the solid line position to free motor 1 for rotation. (b) transistor 67 also turns on a transistor 63 after a time delay introduced by a capacitor 62 to ensure that brake arm 23 has completed its movement. Transistor 63 switches transistors 64, 65 which provide inputs to NAND gates 38, 39, so that these gates turn on an AND gate 37 to energize a driving circuit 26 which switches on the motor to open the shutter-diaphragm blades. The NAND gates 38, 39 also initiate charging of integrating capacitors 42, 50 through respective photo-cells 41, 16. (c) movement of the blades causes a grating 17 carried by the blades to admit light to a photo-cell 19 which turns on a transistor 44 to trigger a monostable multi-vibrator 27 to its unstable state. This turns off AND gate 37 to halt the motor. The aperture has by now opened to f/16. (d) when the multi-vibrator 27 returns to its stable state the motor 1 restarts, opens the blades to f/8 and is switched off again by reason of grating 17 and photo-cell 19. (e) pulsed opening of the blades continues until capacitor 42 is charged. This turns off AND gate 37 to stop further energization of drive circuit 26 and sends an instruction to input W of circuit 26 to ready it for reverse operation. (f) when capacitor 50 is charged and after a time delay introduced by a capacitor 32, an AND gate 56 is turned on to re-energize circuit 26 to close the blades. (g) the motor closes the blades as before in steps under the control of grating 17, photo-cell 19 and multi-vibrator 27. (h) when the blades are closed, a switch 59 is closed to turn on a transistor 71 which discharges a capacitor 70 to turn off thyristor 69. This turns off transistor 67 to de-energize the electromagnet 25, so that a spring 23 can return the arm 22 to its locking position. An alternative lock construction is shown in Figs. 5A, B, C (not shown).