Patent GB-1523899-A (GB)
Title: Automatic exposure control apparatus for a single elns reflec camara
IPC: G03B7/091
Filed: 1975-10-07
Abstract: 1523899 SLR cameras CANON KK 7 Oct 1975 [7 Oct 1974 23 Dec 1974] 40947/75 Heading G2A An SLR camera is settable (1) to control diaphragm aperture automatically according to pre-set shutter speed and measured object brightness or (2) to control shutter speed automatically according to pre-set aperture and measured brightness. Mode (1). A resistor R18, Fig. 3 is set according to film speed and lens factors and R16 and R19 are both set according to the desired shutter speed. Upon shutter release:  (a) pulses from a generator PG pass through a gate G to a counter H2. A comparator CO1 has one input connected to counter H2, resistors R18, R16 and a photo-cell PD and the other to a reference voltage VC. When the count compares with VC, comparator CO1 turns off gate G (b) an electromagnet MR, Fig. 1 is energized to release levers 13, 14, 15, 16. Lever 16 releases a gear sector 18 which moves under the control of a governor 19 to set a diaphragm ring 3 via a lever 29 and at the same time to adjust R21. A second comparator C02, Fig. 3, compares R21 with the pulse count and when they compare, it energizes an electromagnet MA which halts sector 18 and thus ring 3 (c) lever 16, released in stage (b), releases a lever 11 which hinges up the mirror 38 and, via a lever 5, operates a rod 4 to stop down the diaphragm to the value determined by ring 3 (d) after a delay, an electromagnet MS is energized to release the shutter and a capacitor Cl, Fig. 3 charges through R19 to turn on an electromagnet MT which closes the shutter. Mode (2). The diaphragm ring 3 and R17 are set to a desired value, the pulse count is determined as in (1) except R17 replaces R16, and the shutter timing capacitor C1 is charged through a transistor ET controlled by the pulse count. Both aperture and shutter may be manually set. Aperture and shutter speed indicators Me and FW are provided. The photo-cell PD is connected to a temperature compensating circuit H1. A second embodiment is described with reference to Figs. 4 and 5 (not shown) having an alternative shutter speed control comprising a first generator/counter circuit (AD2) corresponding to that of Fig. 3 and a second generator/counter circuit (AD1), for providing a count representing manually set shutter speed. These are selectively connectible to a comparator (C3) which compares the selected one with a reference count (CC4) to control the shutter magnet MT1. This embodiment also includes:  (a) light emitting diodes (LED 1, LED 3) which go on or off to indicate which mode has been selected and which flash to indicate that gear sector 18 has been released or that the light is insufficient (b) a flash circuit (E, SUB 1, TROM, Fig. 5) which provides a fixed shutter speed and sets the aperture according to the flash guide number; a further LED (2) being energized when the flash capacitor is charged (c) a self-timer switch (S16) for delaying shutter release by 10 seconds, a further LED (4) indicating by the rate at which it flashes, whether or not the switch has been operated (d) a battery test switch (S17) which uses the same flashing light (LED 4) as the self-timer. Figs. 7, 8 and 9 (not shown) show circuits controlling release according to whether or not an eye-piece shutter (62, Fig. 4) is in its operative position. Fig. 10 (not shown) shows a memory (ME) which can be used to display exposure data after exposure e.g. for record purposes. It also shows a detachable film winding motor (MD). Fig. 11 (not shown) shows a circuit wherein, if both the diaphragm and shutter controls are set to "auto", the diaphragm is stopped down to a predetermined value and the shutter is controlled automatically.