GB2103832A

GB2103832A - Improvements in or relating to electronic flash units

Info

Publication number: GB2103832A
Application number: GB08134200A
Authority: GB
Inventors: Yukio Nakajima; Isao Kondo
Original assignee: Olympus Optical Co Ltd
Current assignee: Olympus Corp
Priority date: 1978-07-04
Filing date: 1979-07-03
Publication date: 1983-02-23
Also published as: GB2131974B; GB2103832B; GB2102131B; GB2097136A; JPS557772A; JPH0160808B2; GB2102131A; GB2131974A; GB2097136B

Abstract

An electronic flash unit for use with and/or mounting on a camera with an electrical shutter has a flash discharge tube, a main capacitor for discharging the flash discharge tube, and a flashlight illumination detector circuit connected in the discharge path of the flash discharge tube for producing a signal which can be applied to a terminal of the camera electrical shutter circuit to enable an auxiliary shutter closing means for enforcing closure of the shutter. In an electronic flash unit, a discharge detector circuit responsive to discharge through the flash tube provides an externally available electrical signal which can be transmitted to a camera to enable a shutter closing circuit therein.

Description

1

SPECIFICATION. Improvements in or relating to electronic flash units

The present invention relates to electronic flash units and is more particularly concerned with 70 electronic flash units for use on cameras with electrical shutters.

When an electronic flash unit capable of automatically controlling the flashlight illumination is mounted on a camera having an electrical shutter of non-memory, TTL photometry type, a number of control schemes are possible depending on whether the control of the flashlight illumination from the electronic flash unit is controlled by a signal derived from a photometric light receiving element disposed within the camera and which is responsive to reflective light from an object being photographed and which is used for controlling the electrical shutter or by a signal from another photometric, light receiving element which is disposed within the electronic flash unit. In one instance, the control of the flashlight illumination is governed by one of these signals whichever occurs first. However, the user then is unable to know which signal controlled the flashlight illumination. If he wanted to take a picture according to the TTL photometry technique, the electronic flash may be controlled in respons to a control signal which is produced from the light receiving element contained therein, 95 thus defeating the very purpose of a single lens reflex camera having TTL photometry, light receiving element.

In another instance, there is provided a camera in which the TTL photometry is automatically 100 established whenever an electronic flash unit is mounted thereon. This arrangement suffers from the inability to control the flashlight illumination in response to an output from a light receiving element which is provided on the part of the 105 electronic flash unit.

There is also known a combination of a camera and an electronic flash unit, each of which is provided with its respective manual switching mechanism which enables the control of the flashlight illumination to be in response to an output from the light receiving element associated with the respective unit. In this instance, the two switching mechanisms must be individually operated to a desired position. In the event of the 115 camera being of the type which can be switched into a manual operation and in which the light receiving element associated with the camera can be disconnected from the circuit within the camera, the normal control of the flashlight illumination is lost if the selection made on the camera does not coincide with that on the electronic flash unit. Moreover, it is understood that the coincidence of such selections is liable to be forgotten, giving rise to an inadvertent use.

For a combination of an electronic flash unit capable of controlling its flashlight illumination automatically and a camera having an electrical shutter of the TTL photometry type, the shutter GB 2 103 832 A 1 can be closed in a number of ways, depending on the selection of a particular signal to which it responds. In one arrangement, an exposure period under the flashlight illumination is previously established within the camera, and synchro contacts are adapted to be closed at the end of running of a first shutter blind and at the beginning of running of a second shutter blind. In this instance, the shutter may be closed if the electronic flash unit fails to produce an illumination in the event of the power supply associated with the electronic flash unit being not properly connected or the charging capacitor thereof being not properly charged, resulting in a failure to take a picture.

In another arrangement, a fixed shutter period is established when an electronic flash unit is mounted or when the charging is complete. In this instance, the absence of the detection of illumination from the electronic flash unit allows the shutter to be closed if the illumination circuit fails to operate, resulting in a failure to take a picture. Because the photometric function provided on the part of the camera is not actuated, the exposure is solely determined on the part of the electronic flash unit, so that an overexposure may result for an object which is under bright illumination, thus destroying the very advantage of TTL photometry camera.

Finally, when an electronic flash unit having the capability of controlling its flashlight illumination automatically is used in combination with a camera having an electrical shutter of the nonmemory, TTL photometry type, it is desirable to provide a variety of functions including closing the shutter, display of the completion of a charging operation, luminescent display, and the display of the completion of flashlight illumination. However, in order to provide all these functions an increased number of electrical connections or contacts 'between the flash unit and the camera are required.

According to the present invention, an electronic flash unit for use with and/or mounting on a camera with an electrical shutter including a photometric circuit having a light receiving element for sensing light from a subject to be photographed, an electrical shutter control circuit of the non-memory type which controls an exposure period of the shutter in response to an output of the photometric circuit, a first terminal adapted to receive an electric signal from the electronic flash unit indicative of the occurrence of flashlight illumination by the electronic flash unit when used with and/or mounted on the camera, and auxiliary shutter closing means enabled by the electrical signal fed from the first terminal for enforcing closure of the shutter, includes:

a flash discharge tube, a trigger circuit for discharging the flash discharge tube, a main capacitor for flashing the flash discharge tube, a flashlight illumination detector circuit which is connected to the discharge path of the flash 2 GB 2 103 832 A 2 discharge tube and which has a switching element operative for producing said electric signal on discharge of the main capacitor, and a second terminal which is connected to the flashlight illumination detector circuit and which is adapted to be connected to the first terminal for applying the electric signal thereto when the electronic flash unit is used with and/or mounted on the camera.

Preferably the flashlight illumination detector circuit includes a series circuit which comprises a second capacitor and a current limiting circuit element and which is connected in parallel with the main capacitor, and the switching element has a control electrode connected to a junction between the second capacitor and the current limiting circuit element.

The invention will be further described by way of example with reference to the accompanying drawings in which:

Fig. 1 is a circuit diagram of an electionic flash unit according to a preferred embodiment of the invention, and Fig. 2 is a circuit diagram of a camera with which the electronic flash unit of Fig. 1 can be 90 used.

Referring first to Fig. 1, the electrical circuit of an electronic flash unit, hereinafter referred to as 1 electronic flash', generally comprises power supply circuit 501, flashlight illumination circuit 502, illumination control circuit 503, display circuit 504, and four connection terminals L, X, G, T which are adapted to be connected with corresponding connection terminals LO, XO, GO, TO provided in the electrical circuit of a camera 100 which will be described later in connection with Fig. 2.

Connection terminal L is used to transmit a display signal indicative of the completion of a charging operation, the completion of a flashlight 105 illumination or the occurrence of flashlight illumination to the camera from display circuit 504. Connection terminal X is connected with synchro contacts of the camera while connection terminal G represents a common ground material. 110 The electronic flash is actuated for flashlight illumination as synchro switch 202 (see Fig. 2) provided on the part of camera is closed in synchronized relationship with the opening of the shutter. Connection terminal T is used to transmit 115 an external control signal or an illumination control signal to the illumination control circuit 503 from the camera.

Specifically considering the various parts of the electrical circuit, power supply circuit 501 functions to step up the voltage of power supply E for feeding the various circuit of the electronic flash. Thus, it comprises a DC-DC converter of a known form. More specifically, positive terminal of supply E is connected with fixed contact 2b of power switch 2, the movable contact 2c of which is connected to one end of supply auxiliary capacitor 3, the other end of which is returned to the negative terminal of supply E. A series circuit including resistor 4, feedback coil 8b of step-up 130 oscillator transformer 8 and diode 9, which protects transistor 7 from a counter-electromotive force developed during the oscillation, is connected in shunt with capacitor 3. Another series circuit including the emitter-to-collector path of switching power transistor 5 of NPN type and input coil 8a of transformer 8 is also connected in shunt with capacitor 3. Transistor 5 has its emitter connected to the negative terminal of power supply E, its base connected to the collector of converter transistor 7 of PNP type through resistor 6, and its collector connected to one end of input coil 8a and also connected to negative line E1 through a series combination of diode 10 and resistor 17. Transistor 7 has its emitter connected to contact 2c of switch 2, and its base connected to the junction between feedback coil 8b and diode 9. Connected to this junction is one end of secondary coil 8c of transformer 8, the other end of which is connected to the anode of rectifier diode 14. There is also provided external power switch 11 which is ganged with power switch 2, and which includes fixed contact 11 b connected to contact 2c of power switch 2, and transfer contact 11 c that is connected to the terminal 12a of terminal box 12 for connection with an external power supply which may be connected to the electronic flash and which is also connected to one terminal of capacitor 13, the other terminal of which is connected to terminal 12c of terminal box 12 and also connected to the cathode of rectifier diode 14 through a series combination of resistor 16 and diode 15. The anode of diode 15 is connected through resistor 19 to negative line E1 to which connection terminal G is also connected. Power switch 2 also includes fixed contact 2a which is connected to the junction between resistor 27 and light emitting element 28 in the flashlight illumination circuit 502 and which functions to indicate the completion of a charging operation.

When the power switch 2 is switched from fixed contact 2a to fixed contact 2b, a base current is supplied to transistor 7 through feedback coil 8b and resistor 4, whereby an amplified collector current is fed to the base of transistor 5, which in turn produces an amplified collector current flowing through input coil 8a and contacts 2b, 2c. The voltage that is developed across input coil 8a as a result of such current flow is stepped up according to the turns ratio of secondary coil 8c to input coil 8a, inducing a high voltage across secondary coil 8c. A stepped up voltage is also developed across feedback coil 8b to cause a further increase in the current flow. The positive feedback through feedback coil 8b drives transistor 5 to saturation through transistor 7. When the current reaches saturation, the feedback from input coil 8a to feedback coil 8b is interrupted, which causes a decrease in the base current of transistor 7, thus reducing the current flow through both transistors 5, 7. As a result, transistor 5 is rendered non-conductive instantaneously. Then the energy stored in input coil 8a produces a counter-electromotive force, 3 inducing a damped oscillation the frequency of which is determined by the inductance of the coil and the distributed capacitance. A component of the damped oscillation is coupled to feedback coil 8b in a direction to increase the base current to transistor 7, and this permits transistor 7 to conduct a collector current which then is effective to cause a flow of collector current through transistor 5. Coils 8a, 8b function to cause a rapid increase of these collector currents. This process is repeated to develop a high voltage across secondary coil 8c, which is rectified by diode 14 to supply an operating voltage on positive line E2 which feeds various circuits of the electronic flash.

The flashlight illumination circuit 502 includes flash discharge tube 62 and SCR 63 as well as a series controlled automatic illumination control circuit which includes commutating capacitor 71 and auxiliary discharge tube 75. A semiconductor switch trigger circuit is used which drives trigger capacitor 44 through SCR 35. More specifically, flashlight illumination circuit 502 includes main capacitor 18, a voltage divider formed by a series combination of resistors 22, 23, a series circuit including a parallel combination of coil 20 which limits the peak current flow through discharge tube 62 and SCR 63, and diode 21 which is adapted to conduct current arising from a counterelectromotive force developed across trigger transformer 45 upon interruption of the flashlight illumination, connected in series with a series combination of flash discharge tube 62 and main switching element formed by SCR 63, and another series circuit including diode 73, resistor 74 and auxiliary discharge tube 75, all connected between the cathode of rectifier diode 14 and negative line El. Also connected to the cathode of rectifier diode 14 is one end of resistor 27, the other end of which is connected to one terminal of display element 28, the other terminal of which is 105 connected to the collector of transistor 58 in display circuit 504. Display element 28 is operable to indicate the completion of a charging operation.

The anode of flash discharge tube 62 is also connected to line E 1 through a series combination 110 of capacitor 26 and resistor 31, with the junction therebetween being connected through resistor to the base of transistor 33, also in display circuit 504.

The junction between resistor 27 and display element 28 is connected through a series combination of resistor 34 and trigger capacitor 44 to one end of primary coil 45a of trigger transformer 45, the other end of the coil being connected to the cathode of a trigger switch formed by SCR 35. The cathode of this SCR is also connected to one end of secondary coil 45b of trigger transformer 45, with the other end of the coil connected to trigger electrode 62a of flash discharge tube 62.

The junction between resistors 22, 23 is connected through diode 25 to the terminal X which is adapted to be connected to synchro contacts, and is also connected through a series combination of capacitor 29 and resistor 36 to the130 GB 2 103 832 A 3 gate of SCR 35, with the junction therebetween being connected to the cathode of this SCR and also connected through a series combination of resistor 50 and diode 53 with the gate of SCR 63.

The gate of SCR 63 is also connected to line E1 through a parallel combination of capacitor 60 and resistor 61, and its cathode is directly connected to line El. The anode of SCR 63 is connected to the cathode of flash discharge tube 62, and also connected through commutating capacitor 71 to the junction between resistor 74 and auxiliary discharge tube 75, and is also connected through resistor 72 to line El. SCR 49 has its cathode connected to the anode of SCR 63, its gate connected to the junction between resistors 46, 47 which are connected in series with diode 48 between the junction between discharge tube 62 and SCR 63 and the junction between capacitor 29 and resistor 36, and its anode connected to the cathode of diode 67 in display circuit 504.

SCR 35, which serves as the trigger switch, has its anode connected to the junction between resistor 34 and trigger capacitor 44, and its cathode connected to the junction between capacitor 29 and resistor 36 and also to the anode of SCR 63 through the series circuit formed by components 46 to 48. As mentioned previously, its gate is connected through resistor 36 to the junction between capacitor 29 and resistor 50, and is also connected through resistor 37 to line El. The junction between resistor 34 and trigger capacitor 44 is connected to line E 1 through capacitor 43, which is utilized to fire SCR 63, and is also connected with diode 78 and capacitor 85, both forming part of the illumination control circuit 503.

The junction between resistor 50 and diode 53 or the anode of the latter is connected to line E 1 through diode 54 and PNP transistor 55. This transistor has its emitter connected to the cathode of diode 54 and also connected through resistor 51 to its base, which in turn is connected to line E1 through resistor 52 and is also connected to the anode of SCR 79, in illumination control circuit 503, through a series combination of resistor 56 and capacitor 57. The collector of transistor 55 is directly connected to line El.

In operation, flashlight illumination circuit 502 functions as follows: the voltage divider formed by resistors 22, 23 develops a voltage at their junction which is effective to charge capacitor 29. When synchro switch 202 (to be described later) on part of the camera is closed to connect terminal X with the common ground terminal G, a circuit is completed through diode 25, resistor 37, and a parallel combination of the gate-to-cathode path of SCR 35 and resistor 36 to cause discharge of capacitor 29 to produce a gate drive signal for SCR 35.

When SCR 35 is fired, trigger capacitor 43 is effective to drive SCR 63 through a series circuit including SCR 35, resistor 50, diode 53, and a parallel combination of the gate-to cathode path of SCR 63, capacitor 60 and resistor 61. The timing for this drive is chosen to be coincident 4 GB 2 103 832 A 4 with the time when a trigger signal is applied to trigger electrode 62a of flash discharge tube 62 as a result of the discharge of capacitor 44 through trigger transformer 45.

The circuit portion comprising transistor 55, diode 54, resistors 51, 52, 56 and capacitor 57 represents an auxiliary circuit which prevents a re firing of SCR 63 in response to noise signals which may be applied to the gate of SCR 63 when SCR 79 is subsequently fired by a signal from illumination control circuit 503 to discharge auxiliary discharge tube 75.

The purpose of illumination control circuit 30 is to terminate the flashlight illumination from the flash discharge tube by causing a discharge of the 80 auxiliary discharge tube in the flashlight illumination circuit 502 in response to an illumination complete or to a control signal which is produced when photometric light receiving element 92 has received a given amount of reflected light from an object being photographed and which is illuminated by the flashlight from the flash discharge tube, or in response to a similar signal fed from the camera.

Specifically, an operating voltage is fed from flashlight illumination circuit 502 between positive line E2 which is connected to the anode of trigger switch SCR 35 and negative line E1 which is connected to the electrical circuit of the camera at a common ground terminal G. A series circuit including diode 78, trigger capacitor 77, primary coil 76a of trigger transformer 76 and diode 80 is connected in series between these lines. The cathode of diode 78 is connected to capacitor 57. Also, a series circuit including capacitor 85, resistor 86 and Zener diode 103 is connected between these lines. Transformer 76 has secondary coil 76b which has its one end connected to the trigger electrode 75a, of an auxiliary discharge tube 7 5 in flashlight illumination circuit 302 and its other end connected to the anode of diode 80. The series combination of capacitor 77 and coil 76a is shunted by a trigger switch, formed by SCR 79, having its gate connected to its cathode through a parallel combination of capacitor 81 and resistor 82 and also connected with line E1 through resistor 83.

Connected in shunt with Zener diode 103 are capacitor 102; a series circuit including resistors 99, 100 and pre-set variable resistor 101; and another series circuit including a parallel combination of capacitor 96 and resistor 97 in series with light receiving element 92.

A series circuit including the collector-to emitter path of PNP transistor 88 and resistor 84 is connected between the anode of Zener diode 103 and the anode of diode 80. Transistor 88 has its collector connected to the anode of Zener diode 103, and its emitter connected through resistor 89 to its base which is connected to external control signal terminal T through resistor 90. The terminal T is connected to the collector of NPN transistor 104 through diode 91 and resistor 93 connected in series. Transistor 104 has its collector connected to line E l through resistor 94, its emitter connected to transfer contact 98d of an aperture value presetting changeover switch 98, and its base connected to the emitter of light receiving element 92 through resistor 95. Switch 98 has fixed contact 98a, which is connected to the junction between resistors 99, 100, and also includes another fixed contact 98b which is left without connection with the circuit, and a further fixed contact 98c which is connected to the junction between resistor 100 and pre-set resistor 101. By changing the resistance which is connected to switch 98, the threshold level of photocurrent detecting transistor 104 can be brought into coincidence with an aperture value of the camera on which the electronic flash is mounted.

In the illumination control circuit 503 thus constructed, transistor 88 is turned on in response to the conduction of photocurrent detecting transistor 104, or in response to a control signal from the camera which is supplied through connection terminal T. The conduction of transistor 88 causes SCR 79 to be fired, which then results in short-circuiting capacitor 77 through the primary coil 76a of transformer 76, thus applying a high voltage to the trigger electrode 75a of the auxiliary discharge tube 75 for firing it. The discharge of the auxiliary discharge tube 75 interrupts the illumination from the flash discharge tube. It is to be understood that Zener diode 103 and capacitor 102 constitute together a constant voltage circuit which is charged to a given voltage by a discharge current from the flash discharge tube flowing through a path including capacitor 85 and resistor 86 only during the time a trigger thyristor associated with the flash discharge tube is conducting. The charge in capacitor 102 is discharged through a circuit including resistors 99, 100 and 101 after a given time interval, thus preventing the element 92 from responding to illumination other than the flashlight illumination emitted by the flash discharge tube.

Display circuit 504 is operable to indicate the completion of a charging operation of main capacitor 18 or the completion of a flashlight illumination in response to signals fed from circuits 502 and 503. In addition, this circuit is connected with an electrical circuit which is internally contained in the camera of Fig. 2 through connection terminal L to feed such signals to the camera.

Specifically, Zener diode 32 has its cathode connected to line Ell and its anode connected to transfer contact 2c of power switch 2. Capacitor 24 is connected in shunt with this Zener diode. A series circuit including PNP transistor 33 and resistor 38 and another series circuit including diode 39, resistor 40 and NPN switching transistor 42 are connected in parallel with capacitor 24. Transistor 33 has its emitter directly connected to line El, its collector connected to connection terminal L and its base connected through resistor 30 to the junction between GB 2 103 832 A 5 capacitor 26 and resistor 31 in the flashlight illumination circuit so that it may be rendered conductive when capacitor 26 is short-circuited by the discharge of flash discharge tube 62. The transistor 42 has its collector connected to one end of resistor 40, the other end of which is connected to the anode of diode 39 which has its cathode connected to line El, with the junction between resistor 40 and diode 39 being connected to connection terminal L and also to the anode of Zener diode 32 through resistor 38.

The display element 28 has its one terminal connected to the collector of NPN transistor 58 which is also connected to the base of transistor 42 through diode 41. Transistor 58 has its emitter connected to the anode of diode 32, and its base connected to its emitter through resistor 59 and also connected through resistor 64 to the cathode of diode 67 and the anode of SCR 49 in flashlight illumination circuit 502. Diode 67 has its anode connected to the anode of SCR 63 and its cathode connected to line E 'I through capacitor 66 and also connected through resistor 68 to another display element 69 which is operable to indicate the completion of a flashlight illumination. The junction between resistor 68 and element 69 is connected through capacitor 70 to the anode of Zener diode 32.

In operation, when display element 28 is illuminated to indicate the completion of a 95 charging operation, its current flow is fed through diode 41 to forwardly bias switching transistor 42, which is thereby turned on. In this manner, display element 201 (Fig. 2) which is disposed in the camera is energized for illumination through the 100 electrical connection between connection terminal L and corresponding connection terminal LO provided on part of the camera. Alternatively, when display element 69 which indicates the completion of a flashlight illumination flashes, the 105 flashing current is similarly supplied to the base of the transistor 42 to cause a flashing operation of display element 201 disposed within the camera.

Furthermore, when flash discharge tube 62 discharges to produce flashlight illumination, transistor 33 is turned on, similarly causing an illumination of display element 201. When indicating the completion of a flashlight illumination, transistor 58 is turned on by the voltage across capacitor 66 which is applied thereto through resistors 64, 59, thus bypassing any current flow from display element 28 for a given time interval, thus assuring that only the flashing current from display element 69 passes through transistor 42.

Fig. 2 shows an electrical circuit that is contained in a camera and is adapted to be electrically connected with the described electrical circuit of the electronic flash. As shown, the electrical circuit of Fig. 2 includes connection 125 terminals LO, XO, GO, TO which correspond to the connection terminals L, X, G, T provided in the electrical circuit of the electronic flash shown in Fig. 1. It generally comprises logic circuit 601 which detects and stores any current flow through 130 display element 201, limiter circuit 602, reset circuit 603, photographing mode switching circuit 604, gate circuit 605 and usual shutter control circuit 606.

Connection terminal LO represents a terminal through which a signal to be displayed is transmitted. Connection terminal XO is associated with synchro contacts, and synchro switch 202 is connected between this terminal and common ground terminal GO. Synchro switch 202 is closed in timed relationship with the opening of the shutter to trigger a flashlight illumination from the electronic flash. Connection terminal TO conveys a control signal from gate circuit 605 to illumination control circuit 503 of the electronic flash, thus automatically interrupting the flashlight illumination from the electronic flash. This signal, representing an automatic illumination control signal, is derived as a proper exposure signal which is produced when a proper exposure is reached, as determined by photographic light receiving element 203 which forms part of the shutter control circuit 606 and which receives flashlight illumination from the electronic flash.

This signal is fed to illumination control circuit 503 of the electronicflash through gate circuit 605 and through the pair of connection terminals TO, T. This proper exposure signal also actuates shutter control circuit 606 to de-energize electromagnet Mg, thus closing the shutter. It is to be noted that display element 201 comprises a light emitting diode which is disposed within the viewfinder of the camera to indicate the completion of a charging operation of main capacitor 18 associated with the electronic flash by a continuous illumination thereof or the completion of a flashlight illumination by a flashing operation in response to a signal which is fed from the electrical circuit of the electronic flash as conveyed through the pair of connection terminals L, LO.

Now considering the specific construction of the respective circuits, logic circuit 601 is connected between a pair of lines E01, E02 which are connected to a series combination of power supply EO and main switch 204. One end of resistor 207 is connected to the terminal LO, and its other end is connected to the base of PNP transistor 211. Resistor 208 is connected between the base and line E01. Transistor 211 has its emitter connected to line E01 and its collector connected through resistor 209 with the base of NPN transistor 210. The emitter of transistor 210 provides an output to photographing mode switching circuit 604. The collector of transistor 210 is connected to the base of NPN transistor 206, which has its emitter connected to line E02 and its collector connected through resistor 205 to line E01 and also connected to one input of NAND circuit 213. Together with NAND circuit 212, NAND circuit 213 constitutes a flipfiop, with the output of NAND circuit 213 being fed back to one input of NAND circuit 212 and also providing an output to gate circuit 605, as will be further described later.

6 GB 2 103 832 A 6 The output of NAND circuit 212 is fed back to the other input of NAND circuit 213, and is also fed to the input of inverter 217. The output of inverter 217 is fed to one input of NAND circuit 214, the other input of which is connected to the collector of transistor 206. The output of NAND circuit 214 is fed to one input of NAND circuit 216, the other input of which is connected to the output of NAND circuit 215, with the output of NAND circuit 216 being fed back to one input of NAND circuit 215 and also providing an output to photographing mode switching circuit 604. The other input of NAND circuit 215 is connected to the other input of NAND circuit 212, to which a reset pulse signal is applied from reset circuit 603, as will be further described later.

The purpose of limiter circuit 602 is to cause a termination, at a given time, for example, when 1/60 second has elapsed representing a limiting time interval during which camera shake may be avoided, of a prolonged exposure which may be caused when the flashlight illumination emitted by the electronic flash is insufficient to provide a proper exposure of an object being photographed. It may comprise a form of RC timer having a time constant of 60 ms, for example, which starts with the closure of main switch 204. It comprises five series circuits connected between the line E01 and the line E02 or E03, a first one including resistor 219 and NPN transistor 218, a second one including NPN transistor 220 and capacitor 221, a third one including resistor 222 and NPN transistor 223, a fourth one including NPN transistor 230 and resistor 227, and a fifth one including NPN transistor 23 1, resistor 228 and NPN transistor 232.

Specifically, transistor 2 18 has its collector connected to the base of transistor 232, which has its collector connected through resistor 228 to the base of transistor 231 and which has its emitter connected to line E02 together with the emitter of transistor 218. Transistor 231 has its emitter connected to line E01 and its collector connected to produce an output signal through resistor 229. This output signal is fed to the base of NPN transistor 233 in the shutter control circuit 606. Time constant capacitor 221 is shunted by a series combination of time constant resistors 224, 225, with the resulting time constant circuit having a time delay of 60 ms, for example. When this delay time has elapsed, an output signal is produced from the collector of transistor 231 and is applied through resistor 229 to the base of transistor 233 to turn it on when photographing mode switching circuit 604 assumes a condition to permit the connection of limiter circuit 602, thus causing an illumination of display element 234 which is disposed adjacent to photometric element 203 in the shutter control circuit 606, the resulting irradiation of element 203 actuating shutter control circuit 606 to achieve a forced shutter closing operation.

The junction between resistors 224, 225 is connected to the base of transistor 218 while the base of transistor 220 is connected to the 130 collector of transistor 223. The base of transistor 223 is connected through resistor 226 to the collector of transistor 230, the base of which is connected through resistor 227 to line E02.

Capacitor 221 has its one end connected with the emitter of transistor 220 and its other end connected through line E03 to the negative terminal of power supply EO. Consequently, capacitor 221 is maintained charged through transistor 220 independently of the condition of main switch 204.

Reset circuit 603 functions to produce a reset signal which is applied to logic circuit 601, and is substantially similarly constructed as limiter 602.

It comprises three series circuits connected across the line E01 and the line E02 or E03, a first one including resistor 235 and NPN transistor 236, a second one including NPN transistor 237 and capacitor 238, and a third one including the emitter-to-base path of NPN transistor 244 and resistor 242. A series combination of resistors 239, 240 are connected between the emitter of transistor 237 and line E02, with their junction connected with the base of NPN output transistor 243, which has its collector connected with the other input of NAND circuit 212 and which has its emitter connected to fine E02. Transistor 244 has its emitter connected to line E01 and its collector connected through resistor 241 to the base of transistor 236 which has its emitter connected to line E02 and its collector connected with the base of transistor 237, which is in turn connected to fine E01 through resistor 235. The collector of transistor 237 is connected to line E01. Capacitor 238 has its one end connected to the emitter of transistor 237 and its other end directly connected to line E03, and forms part of a time constant circuit, which also includes resistors 239, 240. In this manner, capacitor 238 is maintained charged through transistor 237 independently of the condition of main switch 204.

In operation, when main switch 204 is closed, transistor 244 is turned on, thereby turning transistor 237 off. As a consequence, transistor 243 is turned on and remains on during a time interval which is determined by the values of capacitor 238 and resistors 239, 240, with a reset pulse from its collector being fed to the other input of NAND circuit 212 in logic circuit 601, thereby resetting the latter to its initial condition.

Switching circuit 604 permits a selection between a limited actuated photographing mode, an automatic photographing mode in which the exposure is controlled solely by the electrical shutter circuit in the usual manner, and a manual photographing mode in which the exposure factors are determined by manual operation. To this end, it includes mode selecting changeover switch 245A. This switch is ganged with mode selecting changeover switch 245B which forms part of the shutter control circuit 606 to be described later. Switch 245A includes a movable contact which can be selectively thrown into engagement with fixed contact 245Aa which is effective to couple limiter circuit 602 with shutter 7 GB 2 103 832 A 7 control circuit 606 to establish a limiter actuated photographing mode, with fixed contact 245Ab which actuates only shutter control circuit 606 to establish an automatic photographing mode, or with fixed contact 245Ac which establishes a manual photographing mode by operating shutter control circuit 606 in accordance with exposure factors which are manually established, by disconnecting photo-electric element 203 which is responsive to natural light, flashlight illumination, or light emitted by element 234 from the shutter circuit.

Switching circuit 604 includes three series circuits connected between the pair of lines E01, E02, a first one including PNP transistor 246, resistor 247 and NPN transistor 248, a second one including resistor 249 and NPN transistor 250, and a third one including resistor 251 and NPN transistor 252. Fixed contact 245Aa is connected to line E01 while fixed contact 245Ac is connected to line E02. In addition, it includes NPN transistors 253, 254 and resistors 255, 256, 257.

Specifically, resistor 255 has its one end connected to line E01 and its other end connected 90 to the base of transistor 253, the emitter of which is connected to the output of NAND circuit 216 and the collector of which is connected to the base of transistor 248. Transistor 248 has its emitter connected to line E02 and its collector connected to the base of transistor 254, which has its emitter connected to line E02 and its collector connected to the base of transistor 233.

A series circuit including resistors 256, 257 is connected between the base of transistor 246 and 100 the base of transistor 250, with the junction between these resistors being connected to the movable contact of switch 245A. It will be noted that fixed contact 245Ab is left without circuit connection. The collector or transistor 250 is connected to the base of transistor 252, the collector of which is connected to the emitter of transistor 210 contained in logic circuit 60 1.

The operation of switching circuit 604 will be described below in accordance with selected position of changeover switch 245k- (i) Limiter actuated photographing mode by throwing switch 245A to fixed contact 245Aa:- The emitter-to-base path of transistor 246 is short-circuited through resistor 256 and switch 245A and thus transistor 246 becomes cut-off, leaving the base of transistor 254 without a supply connection independently of the condition of transistor 248. Hence the collector output from transistor 254 is off, so that transistor 233 in the shutter control circuit 606 is controlled solely by the time constant circuit of limiter circuit 602 which has a time constant of the order of 60 ms. When such time length has elapsed after the initiation of an exposure, the emission of light from 125 element 234 impinges on photometric element 203 to cause a forced shutter closing operation.

(ii) Automatic photographing mode by throwing switch 245A to fixed contact 245Ab:

In this instance, the base of transistor 246 is 130 connected to the base of transistor 250 through resistors 256, 257, and hence is turned on. Transistor 254 is cut off and turned on when transistor 248 is turned on and cut off, respectively.

(iii) Manual photographing mode by throwing switch 245A to fixed contact 245Ac- Transistor 254 operates in the same manner as described in section 00 above, but because mode selecting changeover switch 245B is thrown to manual contact 24513c, photometric element 203 is disconnected, and a fixed resistor is connected instead, so that there is no interaction between elements 234 and 203. Consequently, shutter control circuit 606 is not influenced by the various circuits 601, 602, 603 and 605, but only responds to a manually established exposure period.

In this manner, switching circuit 604 forms a control circuit providing an output from transistor 254 which depends on the condition of transistor 248, this output controlling the conduction or non-conduction of transistor 233 in shutter control circuit 606.

The purpose of gate circuit 605 is to prevent resistors contained in the electrical circuit of the electronic flash from being connected as a load across the output of shutter control circuit 606 when the electronic flash is mounted on the camera but is not actuated, thus allowing the camera to be operated alone. Since the camera here disclosed is a single lens reflex camera having an electrical shutter of non-memory TTL (through the lens) photometry type, illumination produced by the electronic flash is determined by photometric element 203 disposed in the camera, and when it is determined that a proper exposure has been reached, shutter control circuit 606 is actuated to de-energize shutter closing electromagnet Mg, thereby closing the shutter. Simultaneously, the same control signal is fed to the illumination control circuit 503 of the electronic flash through connection terminal TO, thereby interrupting the flashlight illumination thereof.

The control signal which is obtained as a result of TTL photometry is derived from the output of comparator 2 58 which is located at the end of shutter control circuit 606. Through a resistor 259 having a high resistance this output is also connected to operate a switching transistor 260, which in turn controls the energization of the shutter closing electromagnet Mg. The presence of this high resistance resistor 259 causes a degree of instability in the exposure period during the high speed shutter operation. If resistors contained in the electrical circuit of the electronic flash were connected to the output of comparator 258 as the electronic flash is mounted on the camera, an increased instability could be caused in the exposure period during high speed shutter operation even though there is no problem whatsoever for an increased length of exposure period which utilizes a synchronized flashlight illumination from the electronic flash.

8 GB 2 103 832 A 8 To overcome this difficulty, an arrangement is made to prevent the resistors contained in the electrical circuit of the electronic flash from loading the output of shutter control circuit 606 when the camera is to be used alone even though the electronic flash is mounted thereon, by providing the gate circuit 605. Stated differently, only when synchronized photographing takes place by using the combination of the camera and the electronic flash, a control signal which results from TTL photometry in the camera is fed to illumination control circuit 503 of the electronic flash through gate circuit 605, thereby controlling the termination of the flashlight illumination thereof. The connection and disconnection 80 between the electrical circuits of the camera and the electronic flash are made by turning transistors 269, 271 on and off.

Specifically, gate circuit 605 comprises a series circuit including PNP transistor 26 1, resistor 262 and NPN transistor 263, another series circuit including PNP transistor 264, resistor 265 and NPN transistor 266, a further series circuit including PNP transistor 267 and NPN transistor 268, a fourth series circuit including PNP transistor 269, resistor 270 and NPN transistor 271, all connected between lines E01, E02. In addition, NPN transistor 271 has its collector connected through resistor 270 to the collector of transistor 269, its base connected to the junction between the collectors of transistors 267, 268, and its emitter directly connected to line E02.

Another NPN transistor 272 has its collector connected to the base of transistor 263, its base connected through resistor 276 to line E01 and its 100 emitter connected to the output of NAND gate 213. Additionally, NPN transistor 273 has its collector connected through resistor 277 to the base of transistor 269, and its emitter connected to line E02. The base of transistor 273 is connected to one cGilector of multi-collector transistor 274 which has its other collector connected to the base of transistor 268, its base connected to the collector of transistor 264 and its emitter connected to the collector of PNP transistor 275. The emitters of NPN transistors 261, 264, 275, 267 and 269 are connected to line E01, and the bases of transistors 261, 264, 275 and 267 are connected in common to one end of resistor 262, to which the collector of transistor 261 is also connected. The other end of resistor 262 is connected to the collector of transistor 263, which has its emitter connected to line E02. Transistor 266 has its collector connected through resistor 265 to the collector of 120 transistor 264, its emitter connected to line E02 and its base connected to the output of comparator 258 in the shutter control circuit 606.

The collector of transistor 268 is connected to the base of transistor 271 and also is connected to the 125 collector of transistor 267. The collector of transistor 269 is connected through resistor 292 to connection terminal TO.

Considering now shutter control circuit 606, it will be seen that it comprises mode selecting 130 changeover switch 245B which is ganged with photographing mode selecting changeover switch 245A, light emitting element 234, photometric light receiving element 203 and transistor 233.

Specifically, it includes a series combination of resistors 278, 279, 280 connected across lines E01, E02, with the junction between resistors 279, 280 connected to one end of a string of fixed resistors 282 to 286. Selection switch 28 1, which is used to establish an exposure period manually, includes a number of fixed contacts which are connected with the other end of the string and also with the junctions between adjacent resistors thereof and over which its movable contact may be switched. By operating switch 281 to change the value of resistors which are connected in circuit therewith, an exposure period can be manually established. The movable contact of selection switch 281 is connected with fixed contact 24513c of changeover switch 24513, which also includes fixed contacts 24513a and 24513b, which are interconnected and connected to one electrode of photometric element 203. Photometric element 203 may comprise any light responsive element having a rapid response such as silicon blue cell, for example. The other electrode of element 203 is connected to the junction between resistors 278, 279 and also to one input of operational amplifier 287. Light emitting element 234 is disposed adjacent to element 203 and comprises a light emitting diode. This diode is connected in series with resistor 288 between line EO 1 and the collector of transistor 233. Transistor 233 has its base connected to the collector of transistor 254 in mode selecting circuit 604, and its emitter connected to line E02.

Mode selecting changeover switch 245B may have its movable contact thrown into engagement with fixed contact 24513a to establish a limiter actuated photographing mode in which limiter circuit 602 co-operates with shutter control circuit 606. When the movable contact is thrown into engagement with fixed contact 24513b, an automatic photographing mode is established in which shutter controi circuit 606 operates alone. When switch 245B is thrown to fixed contact 24513c, photometric element 203 is disconnected from the shutter circuit, and instead fixed resistors 282 to 286 are selectively connected to switch 245B through selection switch 281 for connection to the other input of operational amplifier 287, thus establishing a manual photographing mode.

Operational amplifier 287 with integrating capacitor 289 and trigger switch 290 connected in shunt between its output and its other input, comparator 258, switching transistor 260, and electromagnet Mg constitute together an electrical shutter circuit of a known form. The output of amplifier 287 feeds one input of comparator 258, the other input of which receives a respective voltage from reference voltage circuit 607 which supplies a reference voltage. The reference voltage supplied by circuit 607 is varied by variable resistor 291 which is set according to input information such as film speed. Comparator 9 GB 2 103 832 A 9 258 compares the voltage developed across capacitor 289 with the reference voltage, and produces an output whenever the charged voltage exceeds the latter. This output is applied to the base of transistor 266 in gate circuit 605 and also to the base of switching transistor 260 through resistor 259 having a high resistance. When switching transistor 260 is rendered nonconductive, electromagnet Mg is de-energized, closing the shutter.

The operation of the electrical circuit of the camera will now be described for different modes of operation:- (1) When changeover switches 245A, 245B are thrown to fixed contacts 245Aa, 24513a, respectively, to establish a limiter actuated photographing mode, with the electronic flash being disconnected:- In this instance, the shutter of the camera is closed in response to a limiter signal from limiter circuit 602 even though the exposure of an object being photographed is insufficient. The resulting exposure period is short enough to prevent camera shake. When main switch 204 is closed as a result of the depression of a shutter release button of the camera, transistor 244 in reset circuit 603 is turned on while transistor 237 is turned off. As a consequence, the charge stored in capacitor 238 which is maintained connected to power supISly EO causes transistor 243 to be turned on for a time interval of the order of 1 ms, for example, which is determined by the values of capacitor 238 and resistors 239, 240, thus supplying a reset pulse of a lower potential than the ground potential to NAND circuits 212, 215 in 100 logic circuit 601 for a time interval of 1 ms starting with the closure of main switch 204.

Similarly, transistor 230 in limiter circuit 602 is turned on whi.le transistor 220 is turned off. As a consequence, the charge stored in capacitor 221 causes transistor 218 to be turned on for a time interval of 60 ms, for example, which is determined by the values of capacitor 22 1, and resistors 224, 225. This turns transistor 232 on and transistor 231 off. After the time interval has elapsed, transistor 218 is turned off as is transistor 232, while transistor 231 is turned, on, supplying to the base of transistor 233 in shutter control circuit 606 a limiter signal of a lower potential than the ground potential.

The reset pulse has a lower potential than the ground potential, and hence can be considered as a binary 0 when the ground potential is represented as binary 1. In the description to follow, the ground potential is considered to 120 represent binary 1 while a lower potential binary 0. In response to the reset pulse from reset circuit 603, one input of NAND circuit 212 redeives "0", outputting " 1 " which is then fed back to one input of NAND circuit 213. Because the electronic flash is not mounted on the camera, there is no input signal from connection terminal LO, whereby transistor 206 remains off, inputting '1 " to the other input of NAND circuit 213, which therefore produces "0" output. The f lipf lop circuit formed by 130 the pair of NAND circuits 212, 213 is stabilized in this condition, supplying a negative input to the emitter of input transistor 272 of gate circuit 605, thereby turning this transistor on. Consequently, transistor 263 is turned off as are transistors 26 1, 264, 275 and 267, with the result that transistors 269, 271 are also turned off, producing no output at connection terminal TO.

At this time, inverter 217 produces "0" output, and hence NAND circuit 214 receives "0" and '1 inputs, producing " 1 " output. This " 1 " output from NAND circuit 214 together with "1 " output from NAND circuit 215 which has received the reset pulse is fed to NAND circuit 216, causing it to produce "0" output. This output is fed to the emitter of transistor 253 in photographing mode switching circuit 604, and because the output potential is negative, this transistor is turned on, thereby turning transistor 248 off. Since switch 245A is thrown to fixed contact 245Aa, the emitter-to-base path of transistor 246 is shortcircuited by resistor 256, and is rendered off. Thus, the base of transistor 254 is left without connection independently of the on and off condition of transistor 248, producing no signal at the collector thereof. Consequently, switching transistor 233 in shutter control circuit 606 is controlled by the limiter signal which is derived from limiter circuit 602.

Specifically, when the exposure of an object being photographed is insufficient, as determined by the amount of light incident on photometric element 203, and a time interval of the order of 60 ms elapses since the closure of main switch 204 to produce a limiter signal, the latter signal turns transistor 233 on, whereby light emitting element 234 is actuated to produce light. The light thus produced impinges on photometric element 203, whereby photocurrent charged capacitor 289 until the voltage developed thereacross becomes equal to the reference voltage supplied from reference voltage circuit 607, whereupon comparator 258 ceases to produce its output, turning transistor 260 off to de-energize electromagnet Mg that has been holding the second shutter blind from running. In this manner, the second shutter blind is released for running, thereby closing the shutter. It should be understood that when a proper exposure has been given to an object being photographed before the time interval of 60 ms has elapsed, the shutter is controlled in accordance with the time at which the proper exposure has been reached.

In this manner, when the electronic flash is not mounted on the camera and a limiter actuated photographing mode is established by using the changeover switches 245A, 245B the shutter is automatically closed after an exposure period which is determined so as to avoid camera shake even under an underexposure condition. This provides a better result if the proper exposure is not reached since the object being photographed has been subject to a certain degree of illumination and the resulting photograph is free from adverse influences of camera shake.

GB 2 103 832 A 10 (2) When changeover switches 245A, 245B are thrown to fixed contacts 245Ab, 24513b to establish an automatic photographing mode with the electronic flash not connected therewith:

In this instance, the shutter of the camera remains open when an object being photographed is under an underexposure, the shutter remaining open until a proper exposure is reached unless the user manually closes the shutter. The principal difference over the limiter actuated operation described in section (1) above is the fact that changeover switch 245A is thrown to fixed contact 245Ab, whereby the base of transistor 246 is connected to the base of transistor 250 through resistors 256, 257, thus turning transistor 80 246 on. Because transistor 248 is off, transistor 254 is turned on, which in turn maintains switching transistor 233 off independently of an output from limiter circuit 602, so that light emitting element 234 produces no light output. As a result, the shutter remains open until the amount of light received by photometric element 203 reaches a predetermined value under natural illumination, whereupon shutter control circuit 606 is operated to close the shutter. It is also possible to close the shutter forcibly by an external operation by the user of the camera before the proper exposure is reached. However, a mechanism associated with such operation is known and hence will not be described herein.

(3) When changeover switches 245A, 245B are thrown to fixed contacts 245Ac, 24513c, respectively, to establish a manual photographing mode, without the connection of the electronic flash:

In this instance, the shutter is closed in accordance with a manually established exposure period which is chosen by a setting on selection switch 281, independently of the amount of illumination of an object being photographed. The primary difference over the operations described in sections (1) and (2) above is the fact that selection switch 245B is thrown to fixed contact 24513c, which prevents operation of photometric element 203 since one electrode thereof is disconnected. Consequently, the closure of the shutter takes place independently of the amount ofillumination on an object being photographed.

Fixed contact 24513c is connected to the movable contact of selection switch 281, which is manually preset to one of the fixed contacts thereof which are connected to the junctions between fixed resistors 282 to 286. Thus, the value of capacitor 289 and the sum of the resistances of these resistors which are connected in series therewith causes operational amplifier 287 to determine an exposure period. When such period has elapsed, comparator 258 ceases to provide an output, whereby the shutter is closed.

Since selection switch 245A is thrown to fixed contact 245Ac at this time, the base of transistor 246 is connected to line E02 through resistor 256, whereby it is turned on. This in turn causes transistor 248 to be turned off and transistor 254 to be turned on, maintaining switching transistor 130 233 off independently of an output from limiter circuit 602, to prevent element 234 from producing light output.

The base-to-emitter path of transistor 250 is short-circuited, and hence this transistor is turned off while transistor 252 is turned on. Accordingly, ---1---is fed to one input of NAND circuit 213, which produces -0- output, turning transistor 272 on and transistor 263 off in gate circuit 605, with the result that transistors 269, 27 1 are turned off, producing no output at connection terminal TO.

(4) When the electronic flash is mounted on the camera and selection switches 245A, 245B are thrown to fixed contacts 245Aa, 24513a, respectively, to establish a limiter actuated photographic mode:- In this instance, the flashlight illumination from the electronic flash is controlled by the photometric operation of element 203 disposed in the camera, and in the event of an underexposure, the shutter is responsive to a limiter signal from limiter circuit 602 and is closed within a preset time interval which is chosen to prevent camera shake.

When power switch 2 of the electronic flash (Fig. 2) is thrown to fixed contact 2b to connect power supply E to the circuit, DC-DC converter is set in oscillation to feed, through rectifier diode 14, flashlight illumination circuit 502, illumination control chuit 503 and display circuit 504. As main capacitor 18 begins to be charged, a signal is produced at connection terminal L which is of a very low level and of a polarity to flow out from this terminal. However, at this stage, the current flow through light emitting element 201 provided on part of the camera is of a level which is insufficient to permit recognition of the illumination thereof. Transistor 211 then detects a signal of such low level, and can be turned on simultaneously with the closure of main switch 204 located in the camera. This is advantageous to enable a limiter actuated photographing operation in the event the shutter is opened before tile capacitor is completely charged.

Subsequently, when the charging of main capacitor 18 is completed, display element 28 is illuminated, and its current flow is fed to the base of transistor 42 through diode 41, thus turning this transistor on. In this manner, a sufficient current flow is supplied through display element 201 located within the viewfinder of the camera to illuminate it with sufficient brightness to enable recognition of it being illuminated and thereby of the completion of a charging operation.

When main switch 204 is closed in synchronism with a shutter release operation, transistor 211 is turned on, and causes transistor 206 to be forwardly biased into conduction through the base-to-col lector path of transistor 210, thus feeding -0- input to NAND circuit 213.

At the instant when main switch 204 is closed in synchronism with a shutter release operation, transistor 243 in reset circuit 603 is turned on for a time interval determined by capacitor 238 and resistors 239, 244 to supply a reset pulse to 11 GB 2 103 832 A 11 NAND circuits 212 and 215 in logic circuit 601, generally in the same manner as described in section (1) above. Simultaneously, transistor 218 in limiter circuit 602 is turned on for a time interval determined by capacitor 221 and resistors 70 224, 225, thereby supplying a limiter signal to transistor 233 of shutter control circuit 606 through transistors 232, 231.

In logic circuit 601, NAND circuit 213 produces ---1---output in response to a reset pulse from reset circuit 603 and receives "0" input when transistor 206 is turned on. NAND circuit 214 produces---11 output in response to "0" output from inverter 217 and "0" input when transistor 206 is turned on. Both of these outputs cause NAND circuit 216 to produce "0" output. " 1 " output from NAND circuit 213 permits a base current to be supplied to transistor 263 in gate circuit 605 through resistor 276 and tile base-to-col lector path of transistor 272, thus turning transistor 263 on.

This turns transistors 261, 264, 275, 267 on.

Since the base of transistor 266 is connected to the output of comparator 258 in shutter control circuit 606 which is turned on simultaneously with the closure of the main switch 204, transistor 266 90 is turned on, causing transistor 269 to be turned on and transistor 271 to be turned off.

After the closure of main switch 204, when a shutter release operation of the camera takes place to close synchro switch 202 in synchronized 95 relationship, the connection of power switch 2 (Fig. 1) to fixed contact 2b short-circuits the charged capacitor 29 in flashlight illumination circuit 502 through a circuit including diode 25, connection terminal X of the electronic flash, connection terminal XO of the camera (Fig. 2), synchro switch 202, connection terminal GO of the camera, connection terminal G of the electronic flash (Fig. 1) resistor 37 and the parallel combination of the gate-to-cathode path of SCR and resistor 36, thus firing the trigger switch SCR 35. Thereupon trigger capacitor 44 is short circuited, whereby the charge stored therein is discharged through primary coil 45a of trigger transformer 45, developing a high voltage pulse across secondary coil 45b. This high voltage is applied to trigger electrode 62a of flash discharge tube 62. At the same time, when SCR 3 5 is fired, trigger capacitor 43 is short-circuited through a path including the parallel combination of the anode-to-cathode path of SCR 35 and its gate and resistor 36, resistor 50, diode 53 and the parallel combination of capacitor 60, resistor 61 and the gate-to-cathode path of SCR 63, thereby firing SCR 63 to enable a flashlight illumination from discharge tube 62.

The flashlight illumination emitted by discharge tube 62 is reflected by an object being photographed and impinges on photometric element 203 disposed within the camera. 125 Photocurrent flow through element 203 charges capacitor 289 since trigger switch 290 is opened in synchronism with a shutter release operation.

The integrated voltage developed at the output of operational amplifier 287 is applied to comparator 258 for comparison with a reference voltage supplied by reference voltage circuit 607 in accordance with the setting of a variable resistor 29 1. When the integrated voltage exceeds the reference voltage, comparator 258 ceases to produce an output, thereby turning transistor 260 off to de- energize electromagnet Mg, whereby the latter releases the second shutter blind for running. In this manner, the shutter is closed. At this time, since the output of comparator 258 is connected with the base of transistor 266 in gate circuit 605, transistor 266 is turned off, which in turn causes transistor 269 to be turned off and transistor 271 to be turned on, supplying an illumination control signal to the electronic flash through connection terminal TO.

In the event of an insufficient exposure, or when the amount of light impinging on photometric element 203 does not reach a predetermined value, a limiter signal from limiter circuit 602 turns transistor 233 on after the predetermined time interval, thus causing element 234 to emit light. The light thus emitted impinges on photometric element 203 to compensate for the difference between the proper exposure and the insufficient exposure. This compensation causes comparator 258 to cease to provide an output, de-energizing electromagnet Mg and closing the shutter. In addition, transistor 269 is turned off while transistor 271 is turned on, supplying an illumination control signal through connection terminal TO.

The illumination control signal supplied to connection terminal TO is fed through connection terminal T (Fig. 1) on the electronic flash to the base of transistor 88 contained in illumination control circuit 503, thereby turning it on. Then the trigger switch SCR 79 is fired, whereby trigger capacitor 77 is discharged through primary coil 76a of trigger transformer 76, developing a high voltage pulse across its secondary coil 76b. This voltage is applied to trigger electrode 75a of auxiliary discharge tube 75 to fire it. Thereupon the anode of SCR 63 is driven to a negative potential, and hence SCR 63 is rendered nonconductive, interrupting the illumination from flash discharge tube 62. Capacitor 66 which has been charged by the firing of auxiliary discharge tube 75 causes display element 69 to flash, and the flashing current turns transistor 42 on and off repeatedly, thereby transmitting a signal through connection terminal L which causes a flashing operation of light emitting element 201 (Fig. 2) disposed in the camera to indicate the completion of a flashlight illumination.

At this time, reflected light from an object being photographed also impinges on light receiving element 92 disposed in the electronic flash, and the resulting photocurrent causes transistor 104 to be turned on when the amount of light reaches a predetermined value. By choosing a resistance of the order of 10 kg? for resistor 93 and a resistance of 1 kQ for resistor 292 connected to connection terminal TO on the camera, the potential at the junction between resistor 94 and 12 GB 2 103 832 A 12 the collector of transistor 104 is insufficient to turn transistor 88 on. Specifically, assuming that the voltage developed at the junction between resistor 94 and the collector of transistor 104 has a value of -10 volts, for example, the closed loop including resistor 94, connection terminals G, GO, the emitter-to-col lector path of transistor 269, resistor 292, connection terminals TO, T, diode 91 and resistor 93 reduces the voltage developed at connection terminal T to a value less than -1 volt, which is insufficient to turn transistor 88 on.

It will thus be seen that when the electronic flash is mounted on camera and photographing mode selecting changeover switches 245A, 245B are operated to establish a limiter actuated photographing mode, the flashlight illumination is controlled by photometric element 203 which is disposed within the camera, and the shutter will be automatically closed under an underexposure condition in a period of time which prevents camera shake. In this manner, a photograph can be obtained though it is of less than satisfactory quality.

(5) When changeover switches 245A, 245B are thrown to fixed contacts 245Ab, 24513b, respectively, to establish an automatic photographing mode, with the electronic flash connected with the camera:- In this instance, the flashlight illumination from the electronic flash is controlled by photometric element 203 disposed within the camera, and the shutter is closed in response to a limiter signal from limiter circuit 602 when the exposure of an object being photographed is insufficient. The principal difference over the mode of operation described in section (4) above is the fact that changeover switch 245A is thrown to engage fixed contact 245Ab, so that the base of transistor 246 is connected through resistors 256, 257 to the base of transistor 250, and thereby transistor 246 is turned on. This turns transistor 248 off, and thereby transistor 254 is turned on. Since the emitter-to-base path of transistor 233 is shortcircuited by transistor 254, switching transistor 233 is maintained off.

When the electronic flash has produced its flashlight illumination and a predetermined amount of reflected light from an object being photographed has been received by photometric element 203, shutter control circuit 606 is actuated to close the shutter. Because comparator 258 ceases to provide an output, an illumination control signal is supplied to connection terminal TO. In the event of a normal illumination control signal not being obtained from shutter control circuit 606 because of insufficient exposure though flashlight illumination has been given, the discharge of flash discharge tube 62 (Fig. 1) in the electronic flash turns transistor 33 on, so that a signal indicative of the illumination is supplied through connection terminals L, LO to light emitting element 201, thus temporarily shortcircuiting the circuit between terminals LO, GO. This turns transistors 211 and 206 off, supplying -1- input to NAND circuit 213. The output of NAND circuit 213 remains " 1 - in response thereto, but the output of NAND circuit 214 changes to "0" and that of NAND circuit 216 changes to - 1 -, with the consequence that transistor 254 in photographing mode switching circuit 604 is turned off. This permits switching transistor 233 in shutter control circuit 606 to be turned on in response to a limiter signal from limiter circuit 602, causing illumination of element 234, which illumination impinges on element 203. When the amount of light input to element 203 reaches a given value, shutter control circuit 606 is actuated to close the shutter, and produce an illumination control signal at connection terminal TO. Again a photograph can be taken though it may be of less than satisfactory quality, in the event of an underexposure.

(6) When changeover switches 245A, 245B are thrown to fixed contacts 245Ac, 24513c, respectively, to establish a manual photographing mode, with the electronic flash mounted on the camera:- In this instance, the flashlight illumination is controlled by photometric element 92 (Fig. 1) which is disposed in the electronic flash, and the shutter is closed in accordance with an exposure period which is previously established by selection switch 281 (Fig. 2) independently of the amount of exposure. The major difference over the mode of operation described in section (4) above is the fact that changeover switch 245B is thrown to fixed contact 24513c, so that photometric element 203 disposed in the camera is disconnected and hence is inoperative. As a consequence, the amount of illumination on an object being photographed has nothing to do with the closure of the shutter. Because switch 245B is thrown to fixed contact 245Bc, capacitor 289 is connected in series with selected resistors which are connected to the movable contact of selection switch 281. In this manner, operational amplifier 287 calculates an exposure period, at the end of which comparator 258 ceases to provide an output, whereupon electromagnet Mg is de energized to permit the shutter to be closed.

On the other hand, selection switch 245A is thrown to fixed contact 245Ac, so that the emitter-tobase path of transistor 250 is shortcircuited, and hence it is turned off while transistor 252 is turned on. Consequently, transistor 206 is turned off independently of a signal fed through connection terminal LO, so that NAND circuit 213 produces "0" output, turning transistor 272 on and transistor 263 off. This results in both transistors 269, 271 being turned off, which means that connection terminal TO is electrically disconnected. Hence, when comparator 258 ceases to provide an output, an illumination control signal is not transmitted to the electronic flash. In addition, connection terminal T (Fig. 1) of the electronic flash is electrically disconnected from the camera, so that light receiving element 92 provided in the electronic flash becomes operative to permit the voltage of the order of -10 volts, developed at the junction between 13 GB 2 103 832 A 13 resistor 94 and the collector of transistor 104 in response to the turning on of transistor 104, to be directly applied to the base of transistor 88 to thereby turn it on for firing auxiliary discharge tube 75 to interrupt the flashlight illumination from flash discharge tube 62, inasmuch as the closed loop described in connection with section (4) above is not formed.

In this manner, in a manual photographing mode with the electronic flash mounted on the camera, photometric element 92 is effective to control the flashlight illumination from the electronic flash, and the shutter of the camera is closed in accordance with an exposure period preset by means of selection switch 28 1, independently of the amount of illumination on an object being photographed.

In our copending patent application No. 7923103 from which the present application is divided we have claimed a camera and automatic electronic flash unit corn bi nation. comprising a camera having an electrical shutter of nonmemory, TTL photometry type, and an automatic electronic flash unit which is detachably coupled thereto to permit transfer of operating signals between the camera and the automatic electronic flash unit, the camera including a first photometric circuit including a first photometric light receiving element for automatically determining an exposure priod, a shutter control circuit responsive to an output from the first photometric circuit, a first terminal which is adapted to receive a shutter close signal from the shutter control circuit, a switching circuit for providing a connection or disconnection between the first terminal and the shutter control circuit, and a first 100 common ground terminal; the automatic electronic flash unit including a second photometric circuit including a second photometric light receiving element, an illumination control circuit responsive to an illumination control signal from the camera or an output of the second photometric circuit for interrupting flashlight illumination of a flash discharge tube, a second terminal connected to the illumination control circuit for receiving the shutter close signal, a second common ground terminal; the first terminal and the first common ground terminal being adapted to engage the second terminal and the second common ground terminal respectively when the camera and the automatic electronic flash unit are coupled to each other, whereby to allow the illumination control circuit to be controlled by the shutter close signal from the camera predominantly over an output from the second photometric circuit in the automatic electronic flash unit depending on the operative condition of the switching circuit.

Claims

1. An electronic flash unit for use with and/or mounting on a camera with an electrical shutter including a photometric circuit having a light receiving element for sensing light from a subject to be photographed, an electrical shutter control circuit of the non-memory type which controls an exposure period of the shutter in response to an output of the photometric circuit, a first terminal adapted to receive an electric signal from the electronic flash unit indicative of the occurrence of flashlight illumination by the electronic flash unit when used with and/or mounted on the camera, and auxiliary shutter closing means enabled by the electric signal fed from the first terminal for enforcing closure of the shutter, which electronic flash unit includes:

a flash discharge tube, a trigger circuit for discharging the flash discharge tube, a main capacitor for flashing the flash discharge tube, a flashlight illumination detector circuit which is connected to the discharge path of the flash discharge tube and which has a switching element operative for producing said electric signal on discharge of the main capacitor, and a second terminal which is connected to the flashlight illumination detector circuit and which is adapted to be connected to the first terminal for applying the electric signal thereto when the electronic flash unit is used with and/or mounted on the camera.

2. An electronic flash unit as claimed in claim 1, in which the flashlight illumination detector circuit includes a series circuit which comprises a second capacitor and a current limiting circuit element and which is connected in parallel with the main capacitor, and the switching element has a control electrode connected to a junction between the second capacitor and the current limiting circuit element.

3. An electronic flash unit as claimed in claim 2, in which the second capacitor has a capacitance smaller than that of the main capacitor.

4. An electronic flash unit for use with and/or mounting on a camera with an electrical shutter, having a discharge detector circuit constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 1 of the accompanying drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1983. Published by the Patent Office 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.

4. An electronic flash unit for use with and/or mounting on a camera with an electrical shutter, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 1 of the accompanying drawings.

New claims or amendments to claims filed on 22 Oct. 1982.

Superseded claims 1-4.

Ne or amended claims:- 1-4 1. An electronic flash unit for use with and/or mounting on a camera with an electrical shutter including a photometric circuit having a light receiving element for sensing light from a subject to be photographed, an electrical shutter control circuit of the nonmemory type which controls an exposure period of the shutter in response to an output of the photometric circuit, and an auxiliary shutter closing means for enforcing closure of the shutter and enabled by an external electric signal, which electronic flash unit includes:

a flash discharge tube, a main capacitor for storing electric energy for discharge through the flash discharge tube, 14 a trigger circuit for initiating an electric discharge through the flash discharge tube for producing flashlight illumination, a discharge detector circuit which is responsive to the discharge circuit of the flash discharge tube and which has a switching element operative for producing an externally available electric signal indicative of the occurrence of discharge through the flash discharge tube, and a second terminal which is connected to the detector circuit and which is adapted to receive said electric signal and to be connected to the first terminal on a camera when the electronic flash unit is used with and/or mounted on the camera, whereby said second terminal on the flash unit can apply to the first terminal on the camera a said electric signal which serves as said external signal to enable the auxiliary shutter closing means upon the occurrence of discharge through the flash GB 2 103 832 A 14 discharge unit in the electronic flash unit.

2. An electronic flash unit as claimed in claim 1, in which the detector circuit includes a series circuit which comprises a second capacitor and a current limiting circuit element and which is connected in parallel with the main capacitor, and the switching element has a control electrode connected to the junction between the second capacitor and the current limiting circuit element.