Photographic shutter

摘要

1,083,840. Camera shutter control. AGFAGEVAERT A.G. March 25, 1966 [March 25, 1965], No. 13353/66. Heading G2A. A camera has means for automatically controlling the exposure time which includes a photoresistor exposed to the prevailing illumination: if a sharp pulse of more intense illumination is received, as by ignition of a flash tube, the shutter is then closed immediately to terminate the exposure. As shown, when shutter release 15 is depressed, a detent 5 thereof engages a pin 4 on shutter opening ring 1, and rotates it clockwise against spring 3, until the pin moves clear of detent 5, whereupon ring 1 is pulled back to its original position. Mounted on ring 1 is the closing ring 2, which is carried round by ring 1 on its initial clockwise movement. When ring 1 is pulled back, however, ring 2 remains locked by a lever 12, which has been pushed (against spring 13) into latching engagement with a recess 14 on ring 2 by a lug 6 on release 15. This relative movement of ring 2 with respect to ring 1 opens the shutter blades. Lever 12 is held in this locking position, against spring 13, by an electromagnet 23, and when it is released, ring 2 is pulled anticlockwise by spring 10 to close the shutter again. The time control circuit 21 is set out in more detail in Fig. 2 (not shown). The load capacitor (31) is in series with the photo-resistor (32) by way of the primary (34) of a transformer (33). The secondary (35) is connected between the capacitor (31) and a switching device comprising two transistors (36, 40). When release 15 is pressed and the shutter opens, switch 20 is closed and switch 27 is open. The electromagnet 23 is energized by the transistor switching device, and consequently latches the shutter open by means of lever 12. For exposures with normal light, the capacitor (31) is charged by way of photo-resistor 32 until the trigger potential is reached. Electromagnet 23 is now de-energized, and lever 12 (and hence ring 2) is released to close the shutter. If a flash reaches the photo-resistor (32) before the capacitor has reached the triggering potential, the steepsided current impulse resulting is passed on by transformer (33) direct to the transistor switching device, and causes electromagnet 23 to become de-energized. Thus the shutter closes immediately after the flash.