US20010002949A1 - Automatic exposure control device for a camera - Google Patents
Automatic exposure control device for a camera Download PDFInfo
- Publication number
- US20010002949A1 US20010002949A1 US09/725,118 US72511800A US2001002949A1 US 20010002949 A1 US20010002949 A1 US 20010002949A1 US 72511800 A US72511800 A US 72511800A US 2001002949 A1 US2001002949 A1 US 2001002949A1
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- transistor
- turned
- control device
- exposure control
- automatic exposure
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- 239000004065 semiconductor Substances 0.000 claims 1
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- 238000007599 discharging Methods 0.000 description 8
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- 229910052980 cadmium sulfide Inorganic materials 0.000 description 6
- 230000000994 depressogenic effect Effects 0.000 description 6
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- 230000000903 blocking effect Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 230000001681 protective effect Effects 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B7/00—Control of exposure by setting shutters, diaphragms or filters, separately or conjointly
- G03B7/08—Control effected solely on the basis of the response, to the intensity of the light received by the camera, of a built-in light-sensitive device
- G03B7/081—Analogue circuits
- G03B7/085—Analogue circuits for control of aperture
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B7/00—Control of exposure by setting shutters, diaphragms or filters, separately or conjointly
- G03B7/08—Control effected solely on the basis of the response, to the intensity of the light received by the camera, of a built-in light-sensitive device
- G03B7/091—Digital circuits
- G03B7/095—Digital circuits for control of aperture
Definitions
- the present invention relates to an automatic exposure control device of a camera, more particularly, the present invention relates to an automatic exposure control device for changing over a size of a stop opening according to subject brightness.
- Lens-fitted photo film units having pre-loaded photo films are widely sold as one kind of simple cameras.
- the lens-fitted photo film unit (hereinafter referred to as film unit)
- a fixed-focus lens and a shutter mechanism the shutter speed of which is fixed are used in the film unit in order to reduce the manufacturing cost.
- the exposure value is constant when the aperture size and the shutter speed are fixed.
- severe photographing condition there is a case in which an exposure amount is out of the latitude of the photo film, so that the photo film is extremely over-exposed.
- an automatic exposure control device in the film unit for controlling exposure amount according to subject brightness.
- the automatic exposure control device comprises a stop control circuit and a stop changeover mechanism.
- the stop control circuit drives an electromagnetic driving unit like a solenoid according to subject brightness measured by a light receiving element.
- the electromagnetic driving unit drives the stop changeover mechanism to change over size of stop opening.
- a large stop opening is set on a photographing optical axis when subject brightness is under the threshold level.
- a small stop opening is set on a photographing optical axis when subject brightness is equal to or more than the threshold level.
- a cadmium sulfide (CdS) element is popularly used.
- the CdS element is low priced, but have dispersion in sensitivity.
- the CdS element has characteristics to vary its resistance widely according to temperature and voltage of power source. Therefore, it is difficult to measure subject brightness precisely.
- a photo diode can be used as the light receiving element.
- the individual variation in sensitivity of the photo diode is less than that of the CdS element.
- the photo diode is less influenced by the fluctuation of the temperature and the power voltage (inversely biased voltage). With these reasons, the photo diode makes it possible to measure subject brightness precisely.
- the response speed of the photo diode is faster than that of the CdS element, so it is preferable to use the photo diode in the case where a momentary photometry is needed.
- the photo current of the photo diode is less than 1 ⁇ A when subject brightness is around the threshold level, it is difficult to decide precisely whether subject brightness is equal to or more than the threshold level. Accordingly, the photo current of the photo diode is needed to be amplified by an amplifier, such as an OP amp. It causes complication of the photometry circuit and high manufacturing cost. Furthermore, a 3V to 5V power supply is necessary to drive the amplifier. Although an R6 battery (1.5V) is provided in the film unit as a power source of flash device, it is impossible to apply the battery as a power source of the automatic exposure control device.
- an object of the present invention is to provide an automatic exposure control device that measures subject brightness precisely and operates with low voltage.
- Another object of the present invention is to provide an automatic exposure control device that is capable of being driven by a battery for driving a flash device.
- an automatic exposure device of the present invention is comprised of a photo diode for measuring subject brightness, a resistor connected to the photo diode, a field effect transistor (FET) having a gate and a source between which a terminal voltage across the resistor is applied.
- FET field effect transistor
- the FET is turned on when the voltage between the gate and the source is equal to or more than threshold level.
- the automatic exposure control device controls to power a solenoid according to state of the FET, and changes size of stop opening.
- a first transistor is connected to the FET.
- the first transistor is turned off when the FET is turned on, and is turned on when the FET is turned off.
- a second transistor is also turns on.
- the solenoid is connected to the second transistor.
- a stop plate is retracted from an optical axis of a taking lens, so an exposure is taken through a large stop opening.
- a stop plate is set on the optical axis, so an exposure is taken through a small stop opening.
- the automatic exposure control device comprises a latch circuit for keeping the first transistor turned on.
- the latch circuit prevents changing over size of stop opening even in a case where the state of the FET changes while exposing.
- the automatic exposure device comprises a capacitor for delaying operation of the first transistor. Since the state of the first transistor is defined after the state of the FET is stabilized, the automatic exposure control device operates stably. Electric power for driving the automatic exposure control device is supplied from a battery for a flash device. The charging operation of the flash device is forced to stop while the automatic exposure control device is in operation. Therefore, it is possible to prevent a faulty operation of the automatic exposure control device due to a decrease of the terminal voltage of the battery.
- the exposure control device having the photo diode and the FET decides whether a subject brightness is equal to or more than a threshold level, the exposure control device can operate reliably on low voltage. Moreover, the exposure control device of the present invention is provided at a low cost because the configuration of the electronic circuit is simple.
- FIG. 1 is a perspective view of a lens-fitted photo film unit
- FIG. 2 is an exploded perspective view of a lens-fitted photo film unit
- FIG. 3 is an exploded perspective view of an exposure unit
- FIG. 4A is an explanatory view of a stop plate at a time when a subject brightness is equal to or more than a threshold level
- FIG. 4B is an explanatory view of a stop plate at a time when a subject brightness is less than a threshold level
- FIG. 5 is a circuit diagram of a stop control circuit
- FIG. 6 is a circuit diagram of a flash circuit
- FIG. 7 is a time chart in controlling an exposure
- FIG. 8 is a circuit diagram of an another stop control circuit.
- a film unit is comprised of a housing 10 and a wrapping label 11 rolled around the housing 10 .
- a taking lens 12 , a viewfinder 13 , a flash projector 14 , a flash changeover plate 15 and a photometry window 16 a are provided on front wall of the housing 10 .
- a shutter button 17 , a frame counter 20 and an indication light guide 21 are provided on a top wall of the housing 10 , and a part of a winding dial 22 is exposed in a back wall of the housing 10 .
- the housing 10 includes a basic portion 23 , an exposure unit 24 , a flash device 25 , a front cover 30 and a rear cover 31 .
- the exposure unit 24 and the flash device 25 are removably attached to the front side of the basic portion 23 .
- the basic portion 23 is comprised of an exposure opening 32 for determining the frame region of the photo film 27 , a cassette chamber 33 for containing the photo film cassette 26 , and a photo film chamber 34 for containing a roll of the photo film 27 that is pulled out of the photo film cassette 26 .
- a winding dial 22 is rotatably attached to the top wall of the cassette chamber 34 .
- a shaft (not shown) provided below the winding dial 22 is engaged with a spool 26 a that is formed inside the photo film cassette 26 .
- One end of the photo film 23 is fixed to the spool 26 a .
- the spool 26 a rotates counterclockwise subsidiary to the rotation of the winding dial 22 a, the photo film 27 is wound into the photo film cassette 26 from the photo film chamber 34 .
- the front cover 30 is attached to the front side of the basic portion 23 .
- the front cover 24 has several openings for emerging the taking lens 12 , the viewfinder 13 , and so forth.
- the rear cover 31 is attached to the rear side of the basic portion 23 .
- the rear side of the cassette chamber 33 , the photo film chamber 34 and a photo film passage provided between them are covered in light-tight fashion.
- the bottom lid 35 a is opened in taking the photo film cassette 26 outside.
- the flash device 25 has a printed circuit board 36 for forming a flash circuit 25 a.
- the printed circuit board 36 is disposed in a side of the exposure unit 24 .
- the flash projector 14 , a main capacitor 37 , a battery 38 , a synchronizing switch 40 and a push switch 41 are attached to the exposure unit 36 .
- An 1.5V R6 battery is used as the battery 38 .
- the synchronizing switch 40 is turned on when a shutter blade 62 (See FIG. 3) is fully opened.
- the push switch 41 is used for supplying electric power to the flash circuit 25 a.
- the flash changeover plate 15 is comprised of a changeover knob 15 a that is capable of being operated externally, and a plate portion 15 b that is integrated with the changeover knob 15 a.
- the flash changeover plate 15 is slidable up and down between a lower OFF position and an upper ON position.
- the push switch 41 is turned on when the changeover plate 15 is at the ON position, so that the flash circuit 25 a is active.
- the push switch 41 is turned off when the changeover plate 15 at the OFF position.
- the changeover plate 15 is click-stopped at the ON or the OFF position by a supporting plate 19 .
- the exposure unit 24 is comprised of a base frame 60 , a shutter cover 61 , a shutter blade 62 , a stop plate 63 and a solenoid 64 .
- a shutter opening 65 is formed in center of the base frame 60 .
- the viewfinder 13 , a shutter driving lever 66 and so forth are attached to the top wall of the base frame 60 .
- a lens holder 67 having a fixed stop opening 67 a is provided on the shutter cover 61 , and the taking lens 12 is put inside the lens holder 67 .
- a shutter driving unit moves the shutter driving lever 66 against bias of a spring from a released position to a charged position, wherein the shutter driving lever 66 is locked by a lock lever (not shown).
- the lock lever releases the shutter driving lever 66 . Then, the shutter driving lever 66 returns back to the released position by bias of the spring.
- the shutter blade 62 is comprised of a blade portion 62 a and a mounting portion 62 b, and is rotatably attached to the base frame 60 .
- the shutter blade 62 is held by a bias of a spring 70 at a closed position in which the blade portion 62 a lies on an optical axis PL to block subject light.
- the shutter driving lever 66 strikes an end of the mounting portion 62 b while moving to the released position from the charged position. Then, the shutter blade 62 rotates against bias of the spring 70 so as to open the shutter opening 65 . After the shutter opening 65 is fully opened, the shutter blade 62 returns back to the closed position by the bias of the spring 70 . While the shutter opening 65 is opened, the photo film 27 is exposed to subject light.
- the stop plate 63 is rotatably attached to the base frame 60 between the shutter blade 62 and the fixed stop opening 67 a .
- the stop plate 63 has a stop-down opening 71 .
- the fixed stop opening 67 a is larger than that of the stop-down opening 71 , so the fixed stop opening 67 a is used as the large stop opening.
- the stop plate 63 is held by bias of a spring 72 at a first position, in which the stop-down opening 71 is set on the optical axis PL. When the stop plate 63 is at the first position, the photo film 27 is exposed to subject light through the stop-down opening 71 .
- the reference numeral 73 is a stopper for keeping the stop plate 63 at the first position.
- the solenoid 64 is fixed on the base frame 60 , and is powered by a current conducted from a stop control circuit 74 .
- a plunger 64 a of the solenoid 64 is connected to the stop plate 63 through a pin 64 b.
- the plunger 64 b is pulled inside the solenoid 64 against bias of the spring 72 .
- the stop plate 63 moves to a second position in which the stop plate 63 is retracted from the optical axis PL. Therefore, the photo film 27 is exposed to subject light through the fixed stop opening 67 a.
- the stop control circuit 74 is comprised of a photometry section for measuring a subject brightness, a deciding section for deciding whether the output current of the photometry section is equal to or more than a threshold level, and a driving section for driving the solenoid 64 according to a result of a decision in the deciding section.
- the stop control circuit 74 , the solenoid 64 , the stop plate 63 and so forth comprise the automatic exposure control device.
- the stop control circuit 74 and the flash circuit 25 a are formed on the printed circuit board 36 .
- a photometry switch 75 is connected between the stop control circuit 74 and the battery 38 .
- the battery 38 supplies electric power to drive the stop control circuit 74 .
- the flash circuit 25 a is driven, a decrease in the terminal voltage of the battery 38 is so large. Therefore, the flash circuit 25 a is forced to stop while the stop control circuit 74 is driven.
- the battery 38 is used not only as a power source of the flash device 25 , but as a power source of the stop control circuit 74 .
- the shutter driving unit has a shutter delay mechanism (not shown).
- the shutter delay mechanism begins to work by depressing the shutter button 17 .
- the photometry switch 75 is turned on. After a predetermined time passes, the photometry switch 75 is turned off.
- the shutter delay mechanism release the shutter driving lever 66 after the necessary time for moving the stop plate 63 , that is 20 ms. Thereby, it is possible to prevent the photo film 27 from being exposed while the stop plate 63 is moving.
- the photometry switch 75 may be turned on while the shutter button 17 is depressed.
- the stop control circuit 74 has the photo diode 16 , a resistor 77 a, an FET 80 , a first trigger transistor 81 , a second trigger transistor 82 , a latch transistor 83 , and transistors 84 and 85 , and so forth.
- Power supplying terminals 88 a and 88 b are connected to the battery 38 (See FIG. 6), so the stop control circuit 74 is driven by electric power supplied from the battery 38 .
- the photo diode 16 and the resistor 77 a are connected in series, and they comprise a photometry section.
- the cathode of the photo diode 16 is connected to the positive electrode of the battery 38 through the photometry switch 75
- the anode of the photo diode 16 is connected to the negative electrode of the battery 38 through the resistor 77 a with high resistance.
- the photo diode 16 is inversely biased by the battery 38 when the photometry switch 75 is turned on. Then, the photo diode 16 generates a photo current according to an amount of incident light.
- a silicon photo diode may be used as the photo diode 16 .
- the anode of the photo diode 16 is connected to the gate of the N-channel type MOS FET 80 .
- the source of the FET 80 is connected to the negative electrode of the battery 38
- the drain of the FET 80 is connected to the base of the first trigger transistor 81 through a resistor 77 b. Since the photo current generated in the photo diode 16 flows through a resistor 77 a , a potential difference according to subject brightness is produced between both terminals of the resistor 77 a .
- the potential difference is applied between the gate and source of the FET 80 .
- the FET 80 is constructed to be turned off when the subject brightness is under a threshold level (hereinafter referred to as LV), and to be turned on when subject brightness is equal to or more than LV.
- LV threshold level
- the emitters of the PNP first trigger transistor 81 and the PNP second trigger transistor 82 are connected to each other, and are also connected to the photometry switch 75 through a resistor 77 c .
- the collector of the first trigger transistor 81 is connected to the negative electrode of the battery 38 through a resistor 77 d .
- the collector of the second trigger transistor 82 is connected to the base of the latch transistor 83 through a resistor 77 e .
- the circuit containing the first and the second trigger transistors 81 and 82 comprise the shumitt trigger circuit.
- the shumitt trigger circuit and the FET 80 comprise the deciding section.
- the base potential of the first trigger transistor 81 decreases due to the current flowing through the resistor 77 b , so that the first trigger transistor 81 is turned on. Then, the emitter potential and the base potential of the second trigger transistor 82 (equal to the collector potential of the first trigger transistor 81 ) are turned to be same, so the second trigger transistor 82 is turned off.
- the FET 80 Since the photo current is not generated in the photo diode 16 just after the photometry switch 75 is turned on, the FET 80 is turned off. So, there is a possibility that the second trigger transistor 82 is turned on before the FET 80 is turned on even in the case where a subject brightness is more than LV. Therefore, a delay capacitor 86 is connected to the base of the second trigger transistor 82 for delaying operation of the second trigger transistor 82 .
- the NPN latch transistor 83 is provided for keeping the second trigger transistor 82 turned on.
- the collector of the latch transistor 83 is connected to the base of the second trigger transistor 82 through a resistor 77 f, and also connected to the base of the transistor 84 through a resistor 77 g .
- the collector of the latch transistor 83 is connected to the negative electrode of the battery 38 .
- the second trigger transistor 82 When the second trigger transistor 82 is turned on, its collector current flows into the base of the latch transistor 83 through the resistor 77 e. Then, the latch transistor 83 is turned on. Since a current flows to the collector of the latch transistor 83 , the base current of the second trigger transistor 82 increases more and more. Once the second trigger transistor 82 is turned on, the state of the second trigger transistor 82 is retained. Thereby, it is possible to prevent changing over the stops while exposing, and to expose the photo film 27 stably.
- the collector of the PNP transistor 84 is connected to the solenoid 60 and a cathode of a protective diode 87 .
- the emitter of the transistor 84 is connected to the positive electrode of the battery 38 .
- the latch transistor 83 When the latch transistor 83 is turned on, a current flows into the base of the transistor 84 through the resistor 77 g .
- the transistor 84 is turned on, and the solenoid 64 is powered. Then, as shown in FIG. 4B, the plunger 64 b is pulled into the solenoid 64 such that the stop plate 63 moves to the second position.
- the transistor 64 comprises the driving section.
- the protective diode 87 prevents the transistor 84 from being deteriorated or broken by inversed electromotive force produced at the moment when the solenoid 60 is turned on.
- the base of the NPN transistor 85 is connected to the photometry switch 75 through a resistor 77 h , and the corrector of the transistor 85 is connected to a terminal 56 .
- a resistor 77 i is connected to the emitter and the base of the transistor 85 .
- a capacitor 88 is connected to the battery 38 .
- the photometry switch 75 , and the capacitor 88 and the battery 38 comprise a charging circuit.
- the capacitor 88 is charged while the photometry switch 75 is turned on.
- the stop control circuit 74 is driven in a predetermined time (1500 ms to 1600 ms) by the electrical charge that is charged in the capacitor 88 .
- the electrostatic capacity of the capacitor 88 is determined in consideration of the time constant of the charging circuit and the necessary amount of the electrical charge for stop changeover.
- the value of the electrostatic capacity of the capacitor 88 may be set as 47 ⁇ F.
- the contact resistance of the photometry switch 75 is 1 ⁇
- the time constant of the charging circuit is 47 ⁇ sec. In this case, it is possible to charge the capacitor 88 while the photometry switch 75 is turned on.
- the solenoid 60 is powered from the battery 38 through the transistor 84 , not from the capacitor 88 . This is because the current that flows through the solenoid 60 is so large that the electrical charge in the capacitor 88 is disappeared at once.
- the flash circuit 25 a is comprised of the main capacitor 37 , the push switch 41 , an oscillating transistor 43 , an oscillating transformer 45 , a rectifying diode 49 , a trigger capacitor 51 , a trigger transformer 52 , a flash discharge tube and so on.
- the push switch 41 is comprised of a movable segment 42 , a first contact 43 a, a second contact 43 b and a third contact 43 c.
- One end of the movable segment 42 is fixed to the third contact 43 c.
- another end of the movable segment 43 contacts with the first and the second contacts 43 a and 43 b. Thereby, all contacts 43 a to 43 c are connected with one another.
- the NPN oscillating transistor 44 and the oscillating transformer 45 constitute a well-known blocking circuit, and the blocking circuit transforms a low-level voltage of the battery 38 into a high-level voltage about 300V for charging the main capacitor 37 .
- the oscillating transformer 45 is comprised of a primary coil 46 , a secondary coil 47 and a tertiary coil 48 which are inductively coupled to one another. One terminal of the primary coil 46 is connected to the positive electrode of the battery 38 , another terminal of the primary coil 46 is connected to the collector of the oscillating transistor 44 .
- One terminal of the secondary coil 47 is connected to the anode of the rectifying diode 49 , another terminal of the secondary coil 47 and one terminal of the tertiary coil 48 are connected to the positive electrode of the battery 38 .
- Another terminal of the tertiary coil 48 is connected to the third contact 43 c of the push switch 41 through a resistor 50 a.
- the cathode of the rectifying diode 49 is connected to the plus pole of the main capacitor 37 , and also connected to one pole of the trigger capacitor 51 . Another pole of the trigger capacitor 51 is connected to the first contact 43 a of the push switch 41 .
- the emitter of the oscillating transistor 44 is connected to the negative electrode of the battery 38 , and the base of the oscillating transistor 44 is connected to the second contact 43 b through a resistor 50 c.
- the trigger transformer 52 is comprised of a primary coil 52 a and a secondary coil 52 b which are inductively coupled to each other and have a common terminal.
- One terminal of the secondary coil 52 b is connected to a trigger electrode 54 that is located outside the flash discharging tube 53 .
- the flash discharging tube 53 is disposed inside the flash projector 14 .
- the common terminal of the trigger transformer 52 is connected to the push switch 41 through the synchronizing switch 40 .
- the flash discharging tube 53 is connected to the main capacitor 37 in parallel.
- the circuit from the positive electrode of the battery 38 , through the tertiary coil 48 , the resistor 50 a, the push switch 41 , the resistor 50 c, and the base-emitter circuit of the oscillating transistor 44 to the negative electrode of the battery 38 comprises a biasing circuit for conducting a biasing current to turn on the oscillating transistor 44 .
- the circuit from the secondary coil 47 , through the rectifying diode 49 , the push switch 41 , the resistor 50 c, the base-emitter circuit of the oscillating transistor 44 , and the battery 38 to the secondary coil 47 comprises a main charging circuit for conducting a secondary current to oscillate the oscillating transistor 44 and charge the main capacitor 37 .
- the circuit from the secondary coil 47 , through the rectifying diode 49 , the resistor 50 b, the trigger capacitor 51 , the push switch 41 , the resistor 50 c, the base-emitter circuit of the oscillating transistor 44 , and the battery 38 to the secondary coil 47 comprises a subsidiary charging circuit for conducting the secondary current to charge the trigger capacitor 51 .
- the circuit from the trigger capacitor 51 , through the primary trigger coil 52 a, the synchronizing switch 40 , and the push switch 41 to the trigger capacitor 51 comprises a trigger discharging circuit for conducting a current from the trigger capacitor 51 into the primary trigger coil 52 a at the moment when the synchronizing switch 40 is turned on.
- the oscillating transistor 44 When the push switch 41 is turned on, the oscillating transistor 44 is turned on for conducting the collector current through the primary coil 46 . Then, an electromotive force is generated in the secondary coil 47 according to the turn ratio of the secondary coil 47 to the primary coil 46 . The electromotive force causes the secondary current to flow as the base current of the oscillating transistor 44 . That is, because of positive feedback from the oscillating transformer 45 , the collector current of the oscillating transistor 44 increases. At that time, the secondary current generated in the secondary coil 47 conducts through the main charging circuit and the subsidiary charging circuit, causes to charge the main capacitor 37 and the trigger capacitor 51 respectively.
- the reference numeral 55 shows a light emitting diode (LED) provided below the indication light guide 21 .
- the anode of the LED 55 is connected to one terminal of the tertiary coil 48
- the cathode of the LED 55 is connected to another terminal of the tertiary coil 48 .
- a terminal voltage of the tertiary coil 48 is over the set voltage such that LED 55 starts lighting.
- the trigger discharging circuit When the synchronizing switch 40 is turned on after the main capacitor 37 is charged up to the predetermined voltage, the trigger discharging circuit is closed. Then, the trigger capacitor 35 is discharged so that a current flows through the primary coil 52 a, inducing the high-level trigger voltage across the secondary coil 52 b. The trigger voltage is applied through the trigger electrode 54 to the flash discharging tube 53 . The main capacitor 37 is discharged through the flash discharging tube 53 . Thereby, flash light is projected through the flash projector 14 .
- the charge voltage of the main capacitor 37 is positive, and the casing of the main capacitor 37 is set to be ground. Therefore, it is possible to photograph without being shocked even in the case where the housing 10 is wet.
- the main capacitor 37 , the primary coil 46 , the rectifying diode 49 , the flash discharging tube 53 and the LED may be connected inversely.
- a terminal 56 of the stop control circuit 74 is connected to the resistor 50 c .
- the photometry switch 75 is turned on, the transistor 85 is also turned on. Then, the oscillating transistor 44 is turned off to stop charging operation of the flash circuit 25 a.
- the stop control circuit 74 is not operated, the flash circuit 25 a is operated if the push switch 41 is turned on.
- FIG. 7 shows a timing chart in controlling exposure in flash photography mode.
- the photometry switch 75 is turned on.
- the transistor 85 is turned on, the flash circuit 25 a is forced to stop the charging operation.
- the capacitor 88 is charged, and the photo diode 16 is driven for generating a photo current according to a subject brightness.
- the solenoid 60 is powered to move the stop plate 63 to the second position.
- the shutter delay mechanism keeps the shutter driving lever 66 at the charged position.
- the shutter driving lever 66 is released and rotates the shutter blade 62 . Thereby, an exposure is taken through the large stop opening.
- the capacitor 88 supplies the electric power to the photo diode 16 , the FET 80 , the shumitt trigger circuit and so forth. After the exposure is completed by returning back the shutter blade 62 to the closed position, the capacitor 88 is completely discharged. The operation of the stop control circuit 74 stops, and the solenoid 60 is not powered. Thereby, the stop plate 63 returns back to the first position by bias of the spring 72 . Since the transistor 85 is turned off, the flash circuit 25 a begins charging operation.
- the FET 80 and the first trigger transistor 81 are turned on.
- the latch transistor 83 and the transistor 84 are also turned off. Therefore, since the solenoid 60 is not powered, the stop plate 63 is kept at the first position to set the stop-down opening 71 on the optical axis PL.
- a subject is framed through the viewfinder 13 . Thereinafter, when the shutter button 17 is depressed, the photometry switch 75 is turned on, and the stop control circuit 74 is operated.
- the solenoid 60 is turned on for moving the stop plate 63 into the second position, shown in FIG. 4B.
- the solenoid 60 is turned off, so the stop plate 63 is kept at the first position, shown in FIG. 4A.
- FIG. 8 shows an another configuration of the stop control circuit of the present invention. Elements similar to those of the above embodiment are designated with identical reference numerals.
- the stop control circuit in this embodiment has an NPN transistor 90 and a PNP latch transistor 91 between the FET 80 and the transistor 84 .
- the drain of the FET 80 is connected to the photometry switch 75 through the resistor 77 j.
- the base of the transistor 90 is connected to the collector of the latch transistor 91 through the resistors 77 e and 77 k.
- the base of the latch transistor 91 is connected to the base of the transistor 84 through the resistors 77 f and 77 g.
- the emitter of the latch transistor 91 is connected to the photometry switch 75 .
- the photo diode 16 is driven for generating a photo current according to subject brightness.
- subject brightness is equal to or more than LV
- the FET 80 is turned on, so the current is conducted to the FET 80 through the resistor 77 j.
- the transistor 90 and the latch transistor 91 are turned off because their base currents are not conducted. Since the transistor 84 is not turned on, the solenoid 60 is not powered. Therefore, the stop plate 63 is kept at the first position, an exposure is taken through the stop-down opening 71 .
- the FET 80 when a subject brightness is less than LV, the FET 80 is not turned on, so the base current of the transistor 90 flows through the resistors 77 j and 77 e. Then, the latch transistor 91 is turned on. Once the transistor 90 is turned on, the latch transistor 91 keeps the transistor 90 on until the capacitor 88 is discharged. The collector current of the transistor 90 flows to the base of the transistor 84 , and the transistor 84 is turned on. Since the solenoid 60 moves the stop plate 63 to the second position, an exposure is taken through the fixed stop opening 67 a.
- the solenoid 60 is powered when subject brightness is less than LV, but the solenoid 60 may be powered when subject brightness is equal to or more than LV.
- the stop plate may be formed a large stop opening and a small stop opening, and each of them may be inserted according to a subject brightness.
- the solenoid 60 is used as electromagnetic force generating means, but it may be applied to the present invention to use an electromagnet for pulling a iron piece attached to the stop plate 63 .
- the present invention has been described with respect to the film unit, the present invention is also applicable to a compact camera and an electronic still camera.
Abstract
Description
- 1. Field of the Invention
- The present invention relates to an automatic exposure control device of a camera, more particularly, the present invention relates to an automatic exposure control device for changing over a size of a stop opening according to subject brightness.
- 2. Background Arts
- Lens-fitted photo film units having pre-loaded photo films are widely sold as one kind of simple cameras. In the lens-fitted photo film unit (hereinafter referred to as film unit), it is unnecessary to load and take out the photo film, so the film unit makes it possible to photograph by simple operation. Moreover, a fixed-focus lens and a shutter mechanism the shutter speed of which is fixed are used in the film unit in order to reduce the manufacturing cost.
- The exposure value is constant when the aperture size and the shutter speed are fixed. In severe photographing condition, there is a case in which an exposure amount is out of the latitude of the photo film, so that the photo film is extremely over-exposed. In order to widen the range of subject brightness for proper exposure, it is proposed to provide an automatic exposure control device in the film unit for controlling exposure amount according to subject brightness.
- The automatic exposure control device comprises a stop control circuit and a stop changeover mechanism. The stop control circuit drives an electromagnetic driving unit like a solenoid according to subject brightness measured by a light receiving element. The electromagnetic driving unit drives the stop changeover mechanism to change over size of stop opening. In the stop changeover mechanism for changing over size of stop opening by two steps, a large stop opening is set on a photographing optical axis when subject brightness is under the threshold level. A small stop opening is set on a photographing optical axis when subject brightness is equal to or more than the threshold level.
- As the light receiving element, a cadmium sulfide (CdS) element is popularly used. The CdS element is low priced, but have dispersion in sensitivity. Moreover, the CdS element has characteristics to vary its resistance widely according to temperature and voltage of power source. Therefore, it is difficult to measure subject brightness precisely.
- A photo diode can be used as the light receiving element. The individual variation in sensitivity of the photo diode is less than that of the CdS element. And the photo diode is less influenced by the fluctuation of the temperature and the power voltage (inversely biased voltage). With these reasons, the photo diode makes it possible to measure subject brightness precisely. Furthermore, the response speed of the photo diode is faster than that of the CdS element, so it is preferable to use the photo diode in the case where a momentary photometry is needed.
- However, since the photo current of the photo diode is less than 1 μA when subject brightness is around the threshold level, it is difficult to decide precisely whether subject brightness is equal to or more than the threshold level. Accordingly, the photo current of the photo diode is needed to be amplified by an amplifier, such as an OP amp. It causes complication of the photometry circuit and high manufacturing cost. Furthermore, a 3V to 5V power supply is necessary to drive the amplifier. Although an R6 battery (1.5V) is provided in the film unit as a power source of flash device, it is impossible to apply the battery as a power source of the automatic exposure control device.
- In view of the foregoing, an object of the present invention is to provide an automatic exposure control device that measures subject brightness precisely and operates with low voltage.
- Another object of the present invention is to provide an automatic exposure control device that is capable of being driven by a battery for driving a flash device.
- To achieve the above objects, an automatic exposure device of the present invention is comprised of a photo diode for measuring subject brightness, a resistor connected to the photo diode, a field effect transistor (FET) having a gate and a source between which a terminal voltage across the resistor is applied. The FET is turned on when the voltage between the gate and the source is equal to or more than threshold level. The automatic exposure control device controls to power a solenoid according to state of the FET, and changes size of stop opening.
- In the preferable embodiment of the present invention, a first transistor is connected to the FET. The first transistor is turned off when the FET is turned on, and is turned on when the FET is turned off. When the first transistor turns on, a second transistor is also turns on. The solenoid is connected to the second transistor. When the solenoid is turned on, a stop plate is retracted from an optical axis of a taking lens, so an exposure is taken through a large stop opening. When the solenoid is turned off, a stop plate is set on the optical axis, so an exposure is taken through a small stop opening.
- In the more preferable embodiment of the present invention, the automatic exposure control device comprises a latch circuit for keeping the first transistor turned on. The latch circuit prevents changing over size of stop opening even in a case where the state of the FET changes while exposing. Moreover, the automatic exposure device comprises a capacitor for delaying operation of the first transistor. Since the state of the first transistor is defined after the state of the FET is stabilized, the automatic exposure control device operates stably. Electric power for driving the automatic exposure control device is supplied from a battery for a flash device. The charging operation of the flash device is forced to stop while the automatic exposure control device is in operation. Therefore, it is possible to prevent a faulty operation of the automatic exposure control device due to a decrease of the terminal voltage of the battery.
- According to the present invention, since the exposure control device having the photo diode and the FET decides whether a subject brightness is equal to or more than a threshold level, the exposure control device can operate reliably on low voltage. Moreover, the exposure control device of the present invention is provided at a low cost because the configuration of the electronic circuit is simple.
- The above and other objects and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when read in association with the accompanying drawings, which are given by way of illustration only and thus are not limiting the present invention. In the drawings, like reference numerals designate like or corresponding parts throughout the several views, and wherein:
- FIG. 1 is a perspective view of a lens-fitted photo film unit;
- FIG. 2 is an exploded perspective view of a lens-fitted photo film unit;
- FIG. 3 is an exploded perspective view of an exposure unit;
- FIG. 4A is an explanatory view of a stop plate at a time when a subject brightness is equal to or more than a threshold level;
- FIG. 4B is an explanatory view of a stop plate at a time when a subject brightness is less than a threshold level;
- FIG. 5 is a circuit diagram of a stop control circuit;
- FIG. 6 is a circuit diagram of a flash circuit;
- FIG. 7 is a time chart in controlling an exposure; and
- FIG. 8 is a circuit diagram of an another stop control circuit.
- As shown in FIG. 1, a film unit is comprised of a
housing 10 and awrapping label 11 rolled around thehousing 10. A takinglens 12, aviewfinder 13, aflash projector 14, aflash changeover plate 15 and aphotometry window 16 a are provided on front wall of thehousing 10. Ashutter button 17, aframe counter 20 and an indicationlight guide 21 are provided on a top wall of thehousing 10, and a part of a windingdial 22 is exposed in a back wall of thehousing 10. - As shown in FIG. 2, a
photo film cassette 26 and aphoto film 27 are previously loaded inside thehousing 10. Thehousing 10 includes abasic portion 23, anexposure unit 24, aflash device 25, afront cover 30 and arear cover 31. Theexposure unit 24 and theflash device 25 are removably attached to the front side of thebasic portion 23. - The
basic portion 23 is comprised of anexposure opening 32 for determining the frame region of thephoto film 27, acassette chamber 33 for containing thephoto film cassette 26, and aphoto film chamber 34 for containing a roll of thephoto film 27 that is pulled out of thephoto film cassette 26. A windingdial 22 is rotatably attached to the top wall of thecassette chamber 34. - A shaft (not shown) provided below the winding
dial 22 is engaged with aspool 26 a that is formed inside thephoto film cassette 26. One end of thephoto film 23 is fixed to thespool 26 a. When thespool 26 a rotates counterclockwise subsidiary to the rotation of the winding dial 22 a, thephoto film 27 is wound into thephoto film cassette 26 from thephoto film chamber 34. - The
front cover 30 is attached to the front side of thebasic portion 23. Thefront cover 24 has several openings for emerging the takinglens 12, theviewfinder 13, and so forth. Therear cover 31 is attached to the rear side of thebasic portion 23. The rear side of thecassette chamber 33, thephoto film chamber 34 and a photo film passage provided between them are covered in light-tight fashion. There arebottom lids rear cover 31 to hold the bottom of thecassette chamber 33, thephoto film chamber 34 in light-tight fashion. Thebottom lid 35 a is opened in taking thephoto film cassette 26 outside. - The
flash device 25 has a printedcircuit board 36 for forming aflash circuit 25 a. The printedcircuit board 36 is disposed in a side of theexposure unit 24. Theflash projector 14, amain capacitor 37, abattery 38, a synchronizingswitch 40 and apush switch 41 are attached to theexposure unit 36. An 1.5V R6 battery is used as thebattery 38. The synchronizingswitch 40 is turned on when a shutter blade 62 (See FIG. 3) is fully opened. Thepush switch 41 is used for supplying electric power to theflash circuit 25 a. - The
flash changeover plate 15 is comprised of achangeover knob 15 a that is capable of being operated externally, and aplate portion 15 b that is integrated with thechangeover knob 15 a. Theflash changeover plate 15 is slidable up and down between a lower OFF position and an upper ON position. Thepush switch 41 is turned on when thechangeover plate 15 is at the ON position, so that theflash circuit 25 a is active. On the other hand, thepush switch 41 is turned off when thechangeover plate 15 at the OFF position. Thechangeover plate 15 is click-stopped at the ON or the OFF position by a supportingplate 19. - As shown in FIG. 3, the
exposure unit 24 is comprised of abase frame 60, ashutter cover 61, ashutter blade 62, astop plate 63 and asolenoid 64. Ashutter opening 65 is formed in center of thebase frame 60. Theviewfinder 13, ashutter driving lever 66 and so forth are attached to the top wall of thebase frame 60. Alens holder 67 having a fixed stop opening 67 a is provided on theshutter cover 61, and the takinglens 12 is put inside thelens holder 67. - When the
photo film 27 is wound by one frame, a shutter driving unit (not shown) moves theshutter driving lever 66 against bias of a spring from a released position to a charged position, wherein theshutter driving lever 66 is locked by a lock lever (not shown). When theshutter button 17 is pressed down, the lock lever releases theshutter driving lever 66. Then, theshutter driving lever 66 returns back to the released position by bias of the spring. - The
shutter blade 62 is comprised of ablade portion 62 a and a mountingportion 62 b, and is rotatably attached to thebase frame 60. Theshutter blade 62 is held by a bias of aspring 70 at a closed position in which theblade portion 62 a lies on an optical axis PL to block subject light. Theshutter driving lever 66 strikes an end of the mountingportion 62 b while moving to the released position from the charged position. Then, theshutter blade 62 rotates against bias of thespring 70 so as to open theshutter opening 65. After theshutter opening 65 is fully opened, theshutter blade 62 returns back to the closed position by the bias of thespring 70. While theshutter opening 65 is opened, thephoto film 27 is exposed to subject light. - The
stop plate 63 is rotatably attached to thebase frame 60 between theshutter blade 62 and the fixed stop opening 67 a. Thestop plate 63 has a stop-down opening 71. The fixed stop opening 67 a is larger than that of the stop-down opening 71, so the fixed stop opening 67 a is used as the large stop opening. As shown in FIG. 4A, Thestop plate 63 is held by bias of aspring 72 at a first position, in which the stop-down opening 71 is set on the optical axis PL. When thestop plate 63 is at the first position, thephoto film 27 is exposed to subject light through the stop-down opening 71. Thereference numeral 73 is a stopper for keeping thestop plate 63 at the first position. - The
solenoid 64 is fixed on thebase frame 60, and is powered by a current conducted from astop control circuit 74. Aplunger 64 a of thesolenoid 64 is connected to thestop plate 63 through apin 64 b. When thesolenoid 64 is powered, theplunger 64 b is pulled inside thesolenoid 64 against bias of thespring 72. Then, as shown in FIG. 4B, thestop plate 63 moves to a second position in which thestop plate 63 is retracted from the optical axis PL. Therefore, thephoto film 27 is exposed to subject light through the fixed stop opening 67 a. - The
stop control circuit 74 is comprised of a photometry section for measuring a subject brightness, a deciding section for deciding whether the output current of the photometry section is equal to or more than a threshold level, and a driving section for driving thesolenoid 64 according to a result of a decision in the deciding section. Thestop control circuit 74, thesolenoid 64, thestop plate 63 and so forth comprise the automatic exposure control device. - The
stop control circuit 74 and theflash circuit 25 a are formed on the printedcircuit board 36. Aphotometry switch 75 is connected between thestop control circuit 74 and thebattery 38. When thephotometry switch 75 is turned on, thebattery 38 supplies electric power to drive thestop control circuit 74. While theflash circuit 25 a is driven, a decrease in the terminal voltage of thebattery 38 is so large. Therefore, theflash circuit 25 a is forced to stop while thestop control circuit 74 is driven. Thebattery 38 is used not only as a power source of theflash device 25, but as a power source of thestop control circuit 74. - The shutter driving unit has a shutter delay mechanism (not shown). When the shutter delay mechanism begins to work by depressing the
shutter button 17, thephotometry switch 75 is turned on. After a predetermined time passes, thephotometry switch 75 is turned off. The shutter delay mechanism release theshutter driving lever 66 after the necessary time for moving thestop plate 63, that is 20 ms. Thereby, it is possible to prevent thephoto film 27 from being exposed while thestop plate 63 is moving. Thephotometry switch 75 may be turned on while theshutter button 17 is depressed. - As shown in FIG. 5, the
stop control circuit 74 has thephoto diode 16, aresistor 77 a, anFET 80, afirst trigger transistor 81, asecond trigger transistor 82, alatch transistor 83, andtransistors Power supplying terminals stop control circuit 74 is driven by electric power supplied from thebattery 38. - The
photo diode 16 and theresistor 77 a are connected in series, and they comprise a photometry section. The cathode of thephoto diode 16 is connected to the positive electrode of thebattery 38 through thephotometry switch 75, and the anode of thephoto diode 16 is connected to the negative electrode of thebattery 38 through theresistor 77 a with high resistance. Thephoto diode 16 is inversely biased by thebattery 38 when thephotometry switch 75 is turned on. Then, thephoto diode 16 generates a photo current according to an amount of incident light. A silicon photo diode may be used as thephoto diode 16. - The anode of the
photo diode 16 is connected to the gate of the N-channeltype MOS FET 80. The source of theFET 80 is connected to the negative electrode of thebattery 38, the drain of theFET 80 is connected to the base of thefirst trigger transistor 81 through aresistor 77 b. Since the photo current generated in thephoto diode 16 flows through aresistor 77 a, a potential difference according to subject brightness is produced between both terminals of theresistor 77 a. The potential difference is applied between the gate and source of theFET 80. TheFET 80 is constructed to be turned off when the subject brightness is under a threshold level (hereinafter referred to as LV), and to be turned on when subject brightness is equal to or more than LV. - The emitters of the PNP
first trigger transistor 81 and the PNPsecond trigger transistor 82 are connected to each other, and are also connected to thephotometry switch 75 through aresistor 77 c. The collector of thefirst trigger transistor 81 is connected to the negative electrode of thebattery 38 through aresistor 77 d. The collector of thesecond trigger transistor 82 is connected to the base of thelatch transistor 83 through aresistor 77 e. The circuit containing the first and thesecond trigger transistors FET 80 comprise the deciding section. - When the
FET 80 is turned on, the base potential of thefirst trigger transistor 81 decreases due to the current flowing through theresistor 77 b, so that thefirst trigger transistor 81 is turned on. Then, the emitter potential and the base potential of the second trigger transistor 82 (equal to the collector potential of the first trigger transistor 81) are turned to be same, so thesecond trigger transistor 82 is turned off. - On the other hand, when the
FET 80 is turned off, a current flows into the base of thesecond trigger transistor 82 through aresistor 77 d. Since the base potential of thesecond trigger transistor 82 decreases, thesecond trigger transistor 82 is turned on. Then, thefirst trigger transistor 81 is turned off. Thereby, only one among the twotrigger transistors FET 80. - Since the photo current is not generated in the
photo diode 16 just after thephotometry switch 75 is turned on, theFET 80 is turned off. So, there is a possibility that thesecond trigger transistor 82 is turned on before theFET 80 is turned on even in the case where a subject brightness is more than LV. Therefore, adelay capacitor 86 is connected to the base of thesecond trigger transistor 82 for delaying operation of thesecond trigger transistor 82. - The
NPN latch transistor 83 is provided for keeping thesecond trigger transistor 82 turned on. The collector of thelatch transistor 83 is connected to the base of thesecond trigger transistor 82 through aresistor 77 f, and also connected to the base of thetransistor 84 through aresistor 77 g. The collector of thelatch transistor 83 is connected to the negative electrode of thebattery 38. - When the
second trigger transistor 82 is turned on, its collector current flows into the base of thelatch transistor 83 through theresistor 77 e. Then, thelatch transistor 83 is turned on. Since a current flows to the collector of thelatch transistor 83, the base current of thesecond trigger transistor 82 increases more and more. Once thesecond trigger transistor 82 is turned on, the state of thesecond trigger transistor 82 is retained. Thereby, it is possible to prevent changing over the stops while exposing, and to expose thephoto film 27 stably. - The collector of the
PNP transistor 84 is connected to thesolenoid 60 and a cathode of aprotective diode 87. The emitter of thetransistor 84 is connected to the positive electrode of thebattery 38. When thelatch transistor 83 is turned on, a current flows into the base of thetransistor 84 through theresistor 77 g. Thetransistor 84 is turned on, and thesolenoid 64 is powered. Then, as shown in FIG. 4B, theplunger 64 b is pulled into thesolenoid 64 such that thestop plate 63 moves to the second position. Thetransistor 64 comprises the driving section. Theprotective diode 87 prevents thetransistor 84 from being deteriorated or broken by inversed electromotive force produced at the moment when thesolenoid 60 is turned on. - The base of the
NPN transistor 85 is connected to thephotometry switch 75 through aresistor 77 h, and the corrector of thetransistor 85 is connected to a terminal 56. Aresistor 77 i is connected to the emitter and the base of thetransistor 85. When thephotometry switch 75 is turned on, a certain amount of potential difference is applied between the base and the emitter of thetransistor 85, causes to turn on thetransistor 85. When thetransistor 85 is turned on, the charging operation of theflash circuit 25 a is forced to stop. Because theflash circuit 25 a stops while thestop control circuit 74 is in operation, it is possible to avoid a failure operation of thestop control circuit 74 due to the decrease in the terminal voltage of thebattery 38. - Because the
photometry switch 75 is turned on in a few micro seconds, it is difficult to do the stop changeover operation while thephotometry switch 75 is turned on. Therefore, acapacitor 88 is connected to thebattery 38. Thephotometry switch 75, and thecapacitor 88 and thebattery 38 comprise a charging circuit. Thecapacitor 88 is charged while thephotometry switch 75 is turned on. After thephotometry switch 75 is turned off, thestop control circuit 74 is driven in a predetermined time (1500 ms to 1600 ms) by the electrical charge that is charged in thecapacitor 88. The electrostatic capacity of thecapacitor 88 is determined in consideration of the time constant of the charging circuit and the necessary amount of the electrical charge for stop changeover. For instance, the value of the electrostatic capacity of thecapacitor 88 may be set as 47 μF. When the contact resistance of thephotometry switch 75 is 1Ω, the time constant of the charging circuit is 47 μsec. In this case, it is possible to charge thecapacitor 88 while thephotometry switch 75 is turned on. - The
solenoid 60 is powered from thebattery 38 through thetransistor 84, not from thecapacitor 88. This is because the current that flows through thesolenoid 60 is so large that the electrical charge in thecapacitor 88 is disappeared at once. - In FIG. 6, the
flash circuit 25 a is comprised of themain capacitor 37, thepush switch 41, an oscillating transistor 43, an oscillatingtransformer 45, a rectifyingdiode 49, atrigger capacitor 51, atrigger transformer 52, a flash discharge tube and so on. - The
push switch 41 is comprised of amovable segment 42, afirst contact 43 a, asecond contact 43 b and athird contact 43 c. One end of themovable segment 42 is fixed to thethird contact 43 c. When theflash changeover plate 15 moves to the ON position, another end of the movable segment 43 contacts with the first and thesecond contacts contacts 43 a to 43 c are connected with one another. - The
NPN oscillating transistor 44 and theoscillating transformer 45 constitute a well-known blocking circuit, and the blocking circuit transforms a low-level voltage of thebattery 38 into a high-level voltage about 300V for charging themain capacitor 37. The oscillatingtransformer 45 is comprised of aprimary coil 46, asecondary coil 47 and atertiary coil 48 which are inductively coupled to one another. One terminal of theprimary coil 46 is connected to the positive electrode of thebattery 38, another terminal of theprimary coil 46 is connected to the collector of the oscillatingtransistor 44. One terminal of thesecondary coil 47 is connected to the anode of the rectifyingdiode 49, another terminal of thesecondary coil 47 and one terminal of thetertiary coil 48 are connected to the positive electrode of thebattery 38. Another terminal of thetertiary coil 48 is connected to thethird contact 43 c of thepush switch 41 through aresistor 50 a. - The cathode of the rectifying
diode 49 is connected to the plus pole of themain capacitor 37, and also connected to one pole of thetrigger capacitor 51. Another pole of thetrigger capacitor 51 is connected to thefirst contact 43 a of thepush switch 41. The emitter of the oscillatingtransistor 44 is connected to the negative electrode of thebattery 38, and the base of the oscillatingtransistor 44 is connected to thesecond contact 43 b through aresistor 50 c. - The
trigger transformer 52 is comprised of aprimary coil 52 a and asecondary coil 52 b which are inductively coupled to each other and have a common terminal. One terminal of thesecondary coil 52 b is connected to atrigger electrode 54 that is located outside theflash discharging tube 53. Theflash discharging tube 53 is disposed inside theflash projector 14. The common terminal of thetrigger transformer 52 is connected to thepush switch 41 through the synchronizingswitch 40. Theflash discharging tube 53 is connected to themain capacitor 37 in parallel. - In this configuration of the
flash circuit 25 a, the circuit from the positive electrode of thebattery 38, through thetertiary coil 48, theresistor 50 a, thepush switch 41, theresistor 50 c, and the base-emitter circuit of the oscillatingtransistor 44 to the negative electrode of thebattery 38 comprises a biasing circuit for conducting a biasing current to turn on the oscillatingtransistor 44. - The circuit from the
secondary coil 47, through the rectifyingdiode 49, thepush switch 41, theresistor 50 c, the base-emitter circuit of the oscillatingtransistor 44, and thebattery 38 to thesecondary coil 47 comprises a main charging circuit for conducting a secondary current to oscillate the oscillatingtransistor 44 and charge themain capacitor 37. - The circuit from the
secondary coil 47, through the rectifyingdiode 49, theresistor 50 b, thetrigger capacitor 51, thepush switch 41, theresistor 50 c, the base-emitter circuit of the oscillatingtransistor 44, and thebattery 38 to thesecondary coil 47 comprises a subsidiary charging circuit for conducting the secondary current to charge thetrigger capacitor 51. - In addition, the circuit from the
trigger capacitor 51, through theprimary trigger coil 52 a, the synchronizingswitch 40, and thepush switch 41 to thetrigger capacitor 51 comprises a trigger discharging circuit for conducting a current from thetrigger capacitor 51 into theprimary trigger coil 52 a at the moment when the synchronizingswitch 40 is turned on. - When the
push switch 41 is turned on, the oscillatingtransistor 44 is turned on for conducting the collector current through theprimary coil 46. Then, an electromotive force is generated in thesecondary coil 47 according to the turn ratio of thesecondary coil 47 to theprimary coil 46. The electromotive force causes the secondary current to flow as the base current of the oscillatingtransistor 44. That is, because of positive feedback from the oscillatingtransformer 45, the collector current of the oscillatingtransistor 44 increases. At that time, the secondary current generated in thesecondary coil 47 conducts through the main charging circuit and the subsidiary charging circuit, causes to charge themain capacitor 37 and thetrigger capacitor 51 respectively. - The
reference numeral 55 shows a light emitting diode (LED) provided below the indicationlight guide 21. The anode of theLED 55 is connected to one terminal of thetertiary coil 48, and the cathode of theLED 55 is connected to another terminal of thetertiary coil 48. When themain capacitor 37 is charged up to a predetermined voltage, a terminal voltage of thetertiary coil 48 is over the set voltage such thatLED 55 starts lighting. - When the synchronizing
switch 40 is turned on after themain capacitor 37 is charged up to the predetermined voltage, the trigger discharging circuit is closed. Then, the trigger capacitor 35 is discharged so that a current flows through theprimary coil 52 a, inducing the high-level trigger voltage across thesecondary coil 52 b. The trigger voltage is applied through thetrigger electrode 54 to theflash discharging tube 53. Themain capacitor 37 is discharged through theflash discharging tube 53. Thereby, flash light is projected through theflash projector 14. - In the
flash circuit 25 a described above, the charge voltage of themain capacitor 37 is positive, and the casing of themain capacitor 37 is set to be ground. Therefore, it is possible to photograph without being shocked even in the case where thehousing 10 is wet. Themain capacitor 37, theprimary coil 46, the rectifyingdiode 49, theflash discharging tube 53 and the LED may be connected inversely. - A
terminal 56 of thestop control circuit 74 is connected to theresistor 50 c. When thephotometry switch 75 is turned on, thetransistor 85 is also turned on. Then, the oscillatingtransistor 44 is turned off to stop charging operation of theflash circuit 25 a. On the other hand, when thestop control circuit 74 is not operated, theflash circuit 25 a is operated if thepush switch 41 is turned on. - FIG. 7 shows a timing chart in controlling exposure in flash photography mode. When the
shutter button 17 is depressed, thephotometry switch 75 is turned on. Then, because thetransistor 85 is turned on, theflash circuit 25 a is forced to stop the charging operation. In addition, thecapacitor 88 is charged, and thephoto diode 16 is driven for generating a photo current according to a subject brightness. - When subject brightness is less than LV, the
FET 80 and thefirst trigger transistor 81 are not turned on because since the gate-source voltage of theFET 80 is low. Then, base current of thesecond trigger transistor 82 flows through theresistor 77 e, so that thesecond trigger transistor 82 is turned on. In this case, thedelay capacitor 86 keeps thesecond trigger transistor 82 turned off until the output current of thephoto diode 16 becomes stable. - When the
second trigger transistor 82 is turned on, thelatch transistor 83 and thetransistor 84 are turned on. Thereby, thesolenoid 60 is powered to move thestop plate 63 to the second position. After theshutter button 17 is depressed, the shutter delay mechanism keeps theshutter driving lever 66 at the charged position. After the necessary time for moving thestop plate 63, e.g. about 20 ms, theshutter driving lever 66 is released and rotates theshutter blade 62. Thereby, an exposure is taken through the large stop opening. - Although the
photometry switch 75 is turned off before powering thesolenoid 60, thecapacitor 88 supplies the electric power to thephoto diode 16, theFET 80, the shumitt trigger circuit and so forth. After the exposure is completed by returning back theshutter blade 62 to the closed position, thecapacitor 88 is completely discharged. The operation of thestop control circuit 74 stops, and thesolenoid 60 is not powered. Thereby, thestop plate 63 returns back to the first position by bias of thespring 72. Since thetransistor 85 is turned off, theflash circuit 25 a begins charging operation. - On the other hand, when subject brightness is equal to or more than LV, the
FET 80 and thefirst trigger transistor 81 are turned on. In this case, since thesecond trigger transistor 82 is turned off, thelatch transistor 83 and thetransistor 84 are also turned off. Therefore, since thesolenoid 60 is not powered, thestop plate 63 is kept at the first position to set the stop-down opening 71 on the optical axis PL. - Next, the operation of the above described configurations will be described. When the winding
dial 22 is rotated, anunexposed photo film 27 is drawn from thephoto film chamber 34 to be set behind theexposure opening 32. Accompanying with the movement of thephoto film 27, theshutter driving lever 66 is moved to the charged position in which the lock lever keeps theshutter driving lever 66. When the photo film is wound by one frame, a film winding mechanism (not shown) locks the windingdial 22. In this state, since thephotometry switch 75 is turned off, so thestop control circuit 74 is not operated. Therefore, it is possible to save power of thebattery 38. - A subject is framed through the
viewfinder 13. Thereinafter, when theshutter button 17 is depressed, thephotometry switch 75 is turned on, and thestop control circuit 74 is operated. When subject brightness is less than LV, thesolenoid 60 is turned on for moving thestop plate 63 into the second position, shown in FIG. 4B. On the other hand, when subject brightness is equal to or more than LV, thesolenoid 60 is turned off, so thestop plate 63 is kept at the first position, shown in FIG. 4A. - When a predetermined time, about 20 ms, passes after the
shutter button 17 is depressed, theshutter driving lever 66 is released, and moves to the released position from the charged position. In the movement of theshutter driving lever 66, theshutter blade 62 is struck, so an exposure is taken on thephoto film 27. - In cases where an outdoor photography is performed in a fine condition, the subject is so bright that the exposure is taken through the stop-
down opening 71. The exposure amount is decreased because of the stop-down opening 71, so it is possible to prevent an over-exposure. On the other hand, in an indoor photography, the subject is not so bright, the exposure is taken through thestop opening 67. In this case, the exposure amount is not decreased, so it is possible to prevent an under-exposure. - In a night photography, the subject is so dark that exposure is taken with flash, by sliding the
changeover knob 15 a to the ON position from the OFF position. Theflash circuit 25 a is operated to charge themain capacitor 37. When themain capacitor 37 is fully charged, indicating light emitted in theLED 55 passes through the indicationlight guide 21. Then, theshutter button 17 is depressed to take a photograph. In this case, since subject brightness is less than LV, thesolenoid 60 is powered. Therefore, the exposure is taken through the fixed stop opening 67 a. - FIG. 8 shows an another configuration of the stop control circuit of the present invention. Elements similar to those of the above embodiment are designated with identical reference numerals.
- The stop control circuit in this embodiment has an
NPN transistor 90 and aPNP latch transistor 91 between theFET 80 and thetransistor 84. The drain of theFET 80 is connected to thephotometry switch 75 through theresistor 77 j. The base of thetransistor 90 is connected to the collector of thelatch transistor 91 through theresistors latch transistor 91 is connected to the base of thetransistor 84 through theresistors latch transistor 91 is connected to thephotometry switch 75. - When the
photometry switch 75 is turned on, thephoto diode 16 is driven for generating a photo current according to subject brightness. In cases where subject brightness is equal to or more than LV, theFET 80 is turned on, so the current is conducted to theFET 80 through theresistor 77 j. Then, thetransistor 90 and thelatch transistor 91 are turned off because their base currents are not conducted. Since thetransistor 84 is not turned on, thesolenoid 60 is not powered. Therefore, thestop plate 63 is kept at the first position, an exposure is taken through the stop-down opening 71. - On the other hand, when a subject brightness is less than LV, the
FET 80 is not turned on, so the base current of thetransistor 90 flows through theresistors latch transistor 91 is turned on. Once thetransistor 90 is turned on, thelatch transistor 91 keeps thetransistor 90 on until thecapacitor 88 is discharged. The collector current of thetransistor 90 flows to the base of thetransistor 84, and thetransistor 84 is turned on. Since thesolenoid 60 moves thestop plate 63 to the second position, an exposure is taken through the fixed stop opening 67 a. - In the above described embodiments, the
solenoid 60 is powered when subject brightness is less than LV, but thesolenoid 60 may be powered when subject brightness is equal to or more than LV. The stop plate may be formed a large stop opening and a small stop opening, and each of them may be inserted according to a subject brightness. - In the above described embodiments, the
solenoid 60 is used as electromagnetic force generating means, but it may be applied to the present invention to use an electromagnet for pulling a iron piece attached to thestop plate 63. Although the present invention has been described with respect to the film unit, the present invention is also applicable to a compact camera and an electronic still camera. - Thus, the present invention is not to be limited to the above embodiments, but on the contrary, various modifications are possible to those skilled in the art without departing from the scope of claims appended hereto.
Claims (14)
Applications Claiming Priority (2)
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JP34167199 | 1999-12-01 | ||
JP11-341671 | 1999-12-01 |
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US20010002949A1 true US20010002949A1 (en) | 2001-06-07 |
US6363222B2 US6363222B2 (en) | 2002-03-26 |
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US09/725,118 Expired - Fee Related US6363222B2 (en) | 1999-12-01 | 2000-11-29 | Automatic exposure control device for a camera |
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Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6397011B1 (en) * | 1999-11-01 | 2002-05-28 | Fuji Photo Film Co., Ltd. | Camera with automatic stop change device |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6539176B2 (en) * | 2000-11-16 | 2003-03-25 | Fuji Photo Film Co., Ltd. | Photometry device for camera |
JP2007127718A (en) * | 2005-11-01 | 2007-05-24 | Fujifilm Corp | Photographing device |
JP4781251B2 (en) * | 2006-12-19 | 2011-09-28 | セイコープレシジョン株式会社 | Camera blade drive |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
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US4017873A (en) * | 1975-10-03 | 1977-04-12 | Polaroid Corporation | Exposure control system with braking capability |
JP3829995B2 (en) * | 1995-06-20 | 2006-10-04 | 富士写真フイルム株式会社 | Film unit with lens |
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2000
- 2000-11-29 US US09/725,118 patent/US6363222B2/en not_active Expired - Fee Related
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
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US6397011B1 (en) * | 1999-11-01 | 2002-05-28 | Fuji Photo Film Co., Ltd. | Camera with automatic stop change device |
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