Patent GB-1371995-A (GB)
Title: Photographic exposure control systems
IPC: G03B7/16
Filed: 1972-04-18
Abstract: 1371995 Photographic camera exposure control POLAROID CORP 18 April 1972 [19 April 1971 ] 17885/72 Heading G2A A photographic camera has an exposure aperture control system having an exposure aperture regulator means 124 Fig. 2 movable between a first terminal position to fully close the exposure aperture 114 and a second terminal position in which the exposure aperture is fully uncovered (as shown), wherein during movement of the aperture regulator means 124 to establish an exposure aperture an electromagnet 174, Fig. 4, is operated, the position of the electromagnet being adjustable to control the point in the path of movement of the exposure aperture regulator means at which the movement is arrested. The position of the electromagnet may be adjusted in accordance with the setting of a focus setting device 170. The exposure aperture regulator means is coupled via slots 130, 132 and pins 134, 136 to aperture blades 106, 108 which slide in a guide 109. The blades have apertures 110, 112 which co-operate with exposure aperture 114 and apertures 118, 120 which co-operate with a photocell 122. The regulator means 124 has a driving hub 126 around which and fixed thereto is a flexible cable 150, the other end of the cable being fixed to a plunger 148 of a solenoid 144. A spring 138 biases the blades to their second terminal position. The camera is designed to operate under ambient light conditions, during which the photo-cell controls the energisation of the electromagnet so that the blades operate as a shutter-diaphragm, or under flash illumination conditions. In the latter event, the electromagnet 174 is energized when the blades are in their first terminal position so that subsequent de-energization of electromagnet 144 enables a plunger 192, Fig. 4, of electromagnet 174 to lie in the path of movement of an extension 200 of the regulator means 124. Electromagnet 174 is mounted on a rack 178 sliding on a plate 184 and having teeth 186 meshing with a pinion 180. Pinion meshes with a distance setting member 26 which is coupled via an idler gear 172 with focussing bezel 170. The camera is preferably a single-lens reflex camera having a mirror assembly (50) Fig. 1 (not shown), movable between a viewing position and an exposure position by the selective energization of a motor M, Fig. 7, in which figure the circuit diagram for controlling the exposure mechanism is shown. Photo-cell 370 replaces photo-cell 122 of Fig. 2. During exposure control under ambient illumination, the exposure time is determined by the timing circuit of photo-cell 370 and capacitor 372, and during flashlight exposure, a pre-set time is obtained by the timing circuit formed by resistor 946 and capacitor 372. The flash apparatus is preferably built into the camera and upon hinging it out ready for use, a switch 420 is closed. In either mode, the shutter is closed before the movement of the mirror and the attainment of the mirror in the exposure position closes a switch 294 which switches on transistor 0 9  and Q 10  to energize the exposure controlling power line 356. In the flash made the arrangement of the plunger 192 and extension 200 forms a detent so that the blades are held in the set position upon de-energization of solenoid 174. Upon de-energization a voltage pulse is delivered to the flash apparatus 444 via line 442.