08-03-1967 дата публикации
Номер: GB0001061346A
1,061,346. Exposure control circuits. PENTACON DRESDEN KAMERA-UND KINOWERKE, VEB. May 3, 1965, No. 18505/65. Heading G2A. An electronic timing circuit includes an oscillator the oscillation of which can be delayed according to the required exposure time, and which, on commencement of oscillation, provides an impulse to an electromagnet which terminates the exposure period. The oscillator consists of a silicon transistor 1 and transformer 2. The secondary winding 3 of the transformer is connected between the base of transistor 1 and an RC member consisting of a photo-cell 5 and capacitor 7. The secondary winding 8 is connected to the base of a transistor 11 acting as a grid leak detector. In use, the switch 22 is closed to charge up condenser 7, which causes a positive potential to be applied to the base of transistor 1, so blocking it. In front of cell 5 is a grey filter 23, and also a diaphragm (not shown) which is set by hand. A switch 16, which is coupled to a further switch 17 (and also to the shutter release), is set to its first position, which includes in circuit a relay 18 giving a visual signal regarding exposure conditions. If this is satisfactory, switch 16 is brought, by operation of the shutter release, to its second position. In this position, a negative potential is applied via switch 17 to the base of transistor 11, which is thus opened and so maintains in the conductive state an electromagnet 12 which holds open the shutter. At the same time, switch 22 is opened, allowing capacitor 7 to be oppositely charged through cell 5. Thus the positive blocking voltage on transistor 1 is reduced until it suddenly begins to oscillate. This causes transistor 11 to be blocked, and hence electromagnet 12 is de-energised, so allowing the shutter to close and terminate the exposure. The transistor 11 may constitute the input of a D.C. amplifier, in which case the circuit variant shown in dotted lines is produced. For manual instead of automatic setting, a change- ...
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