Patent GB-1019932-A (GB)
Title: Automatic exposure control device for photographic purposes
IPC: G03B9/62
Filed: 1962-10-29
Abstract: 1,019,932. Photo-electrically controlled exposures; photographic shutters. INTERNATIONAL POLAROID CORPORATION. Oct. 29,1962 [Nov. 6, 1961], No. 40813/62. Heading G2A. An automatic exposure control for establishing an exposure value in accordance with the intensity of light from a scene being photographed has an electronic trigger circuit including photoelectric means which receives light from the scene, a delay in triggering after actuation being related to the intensity of scene light. Two solenoid windings 310, 312 Fig. 1, are included in a trigger circuit, Fig. 2 (not shown). The windings 310, 312 control the actuation of shutter blades 342, 344 Fig. 1. Blade 344 is normally disposed in a covering position with respect to aperture 346, while blade 342 is in uncovering position. Shutter operation is initiated by a Y-shaped lever 350 rotatable against the action of a spring 352. A timing device comprising a fly-wheel 354 biased by a spring 356 is provided for actuating switches 314, 326 in sequence following the release of the flywheel 354. In operation, the operator rotates the lever 350, thereby disengaging rockers 334, 336 and releasing flywheel 354. Switch 314, held closed by lug 360, then opens and after a short interval switch 326 is also opened by lug 360. Solenoid winding 310 is de-energized, thus permitting rocker 334 to move blade 342 out of its covering position and the initiating exposure through aperture 346. Capacitor 302, Fig. 2 (not shown) is charged by a current surge induced by de-energization of solenoid winding 310, the charge on the capacitor being a function of the resistance of a photo-electric cell 300. Similarly, the discharge rate of capacitor 302 is proportional to the resistance of cell 300. Solenoid winding 312 is de-energized and rocker 336 actuates blade 344 after an interval depending on the resistance of the cell 300 depending on the incidence of light. In another embodiment, Fig. 3, slidably mounted spring actuated shutter blades 404, 406 have apertures 408 and 410 at their opposite ends. In their rest position, the blades cover an exposure aperture 400. Lever 416 retains the blade 404 at rest against the action of spring 412 and through a shaft 430 the blade 406. Blade 432 has a magnetic element 432 adjacent solenoid 434 and is retained during energization. Switch S 2  is closed when the blades are in rest position while a switch S 1  is open in this position. The shutter is cocked by a bell crank lever 446. Depression of a button 426 releases latch 420 to allow blade 404 to move to exposure position and effect exposure through aperture 400. Solenoid 434 energized by depression of the button 426 is de-energized through trigger circuit Fig. 7'(not shown), thus allowing spring 414 to actuate blade 406. The circuit provides a delay in de-energization of the solenoid 434 depending on the resistance of a photo-electric cell 460, the resistance of the cell 460 varying inversely as function of the incidence of light. A plurality of capacitors covering a range in capacitance corresponding to a required range in film speed may be provided with suitable switching arrangements to select a particular capacitor. Flash synchronizing contacts may be arranged to close coincident with full shutter opening after release of blade 404, e.g. switch S 2  may have a second fixed contact which closes the flash bulb circuit when switch S 2  opens.