JP2001222038A - Automatc exposure controller for camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic exposure controller capable of performing the photometry of a subject with high accuracy and a low voltage. SOLUTION: When a photometric switch 75 is turned on, a photoelectric current corresponding to the luminance of a subject is generated in a photodiode 16 and a potential difference is generated across a resistance 77a. When the luminance of the subject is smaller than a threshold, since the potential difference of the resistance 77a is low, an FET 80 becomes to be in an OFF state. When the luminance is equal to or larger than a threshold, since the potential difference of the resistance 77a is high, the FFT 80 is turned on. When the FET 80 is in the OFF state, first and second transistors 81, 82 are turned on and a solenoid 60 is energized. The solenoid 60 makes a camera to be in a large diaphragm state by retreating a disphragm plate 63 from a photographing optical path. When the FET 80 is in the ON state, since the second transistor 82 is turned off, the solenoid 60 is not energized and the diaphragm plate 63 is positioned in the photographic optical path to make the camera to be in a small diaphragm state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic exposure control device for a camera, and more particularly, to an automatic exposure control device for switching the size of an aperture according to the brightness of a subject.

[0002]

2. Description of the Related Art As a kind of simple camera, a film unit with a lens in which a simple photographing mechanism such as a photographing lens and a shutter mechanism is incorporated, and a photo film is pre-loaded, is sold by the present applicant. Can easily take print photos of good image quality. In this lens-fitted film unit, a fixed-focus photographing lens and a shutter device having a constant shutter speed are used in order to reduce manufacturing costs.

[0003] Since the aperture value and the shutter speed are fixed, the exposure value is constant, and depending on the shooting conditions, the exposure may exceed the latitude of the photographic film and become extremely overexposed. Therefore, it has been proposed to provide an automatic exposure control device for controlling the exposure in accordance with the luminance of the subject in the film unit with the lens to widen the range of the luminance of the photographable subject. The automatic exposure control mechanism measures the light of a subject with a light receiving element, and drives an electromagnetic drive source such as a solenoid according to the result. The electromagnetic drive source operates the aperture switching mechanism to change the size of the aperture opening. For example, in an aperture switching mechanism that switches the aperture aperture in two stages, a large aperture aperture is set in the imaging optical path when the subject luminance is less than the threshold, and a small aperture aperture is set in the imaging optical path when the luminance is equal to or greater than the threshold.

[0004]

In such an automatic exposure control mechanism, cadmium sulfide (hereinafter referred to as C) is used as a light receiving element.
dS) is generally used. This CdS
Is inexpensive, but varies in sensitivity depending on individual components. Furthermore, it has a property that a change in resistance value due to a change in temperature or power supply voltage is large, so that it is difficult to perform high-precision photometry with CdS.

Therefore, a photodiode can be used instead of CdS as the light receiving element. Compared with CdS, this photodiode has the advantage that the component variation in sensitivity is small and the generated photocurrent is less affected by fluctuations in temperature and power supply voltage (reverse bias voltage). For this reason, the photodiode enables highly accurate photometry. Furthermore, since the photodiode has a faster response speed than CdS, it is suitable when instantaneous photometry is required.

However, when the brightness of the subject is near the threshold level, the photocurrent generated by the photodiode is very small, 1 μA or less, and it is difficult to accurately determine whether the brightness of the subject exceeds the threshold level. It is. For this reason, it is necessary to amplify the photocurrent generated by the photodiode with an amplifier such as an operational amplifier, which leads to a complicated circuit configuration and high cost. Further, to operate such an amplifier, 3V or 5V
A power supply voltage of V is required, and an AA battery (1.
5V) cannot be used as a power supply for the automatic exposure control device.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide an automatic exposure control device which enables high-precision photometry and operates at a low voltage by a strobe power supply at a low cost. I do.

[0008]

In order to achieve the above object, an automatic exposure control device according to the present invention comprises a photodiode for performing photometry of a subject, a resistor connected in series to the photodiode, and a A field-effect transistor in which a voltage between both terminals is applied between a gate and a source, and is turned on when the voltage is equal to or higher than a predetermined value, and turned off when the voltage is lower than a predetermined value; Electromagnetic force generating means whose energization is controlled in accordance with the state of the transistor, and a diaphragm plate which moves to a large or small aperture position depending on whether or not the electromagnetic force generating means is energized. . Note that the field effect transistor is preferably a MOS type.

Further, by providing a switch that is turned on by a shutter release operation and starting photometry by the photodiode when the switch is turned on, useless consumption of the battery can be effectively suppressed.
In addition, a small aperture opening is formed in the aperture plate, the small aperture opening is set in an imaging optical path at the small aperture position, and the aperture plate is retracted from the imaging optical path at the large aperture position, so that the size of the aperture is reduced. Can be switched.

It is preferable that the electromagnetic force generating means is a solenoid. It is preferable that a first transistor which is in a state opposite to a state of the field-effect transistor is provided, and energization of the solenoid is controlled according to a state of the first transistor. Further, it is preferable that a second transistor which is in the same state as the first transistor be provided, and the second transistor be connected in series with the solenoid.

Further, a first capacitor for delaying the operation of the first transistor is provided so that the first transistor is turned on after a predetermined time has elapsed since the switch was turned on. The operation of the field-effect transistor is stabilized. Further, by providing a latch circuit for latching the ON state of the first transistor, it is possible to prevent the state of the FET from fluctuating during exposure and switching of the aperture.

The photodiode, the field effect transistor, the first transistor, and the latch circuit are supplied with power from a battery through the switch, and
It is preferable that the transistor and the solenoid are supplied directly from a battery. Further, a second capacitor charged by the battery while the switch is turned on is provided, and after the switch is turned off, the photodiode, the field effect transistor, the first transistor and the second capacitor are charged. Preferably, power is supplied to the latch circuit.

Further, it is preferable that the voltage between terminals of the battery is set to 1.5 V, so that a battery for a strobe device can be used as it is, and an exposure control device can be provided at low cost. Further, while the switch is on, the charging operation of the strobe device is forcibly prohibited, so that a malfunction of the exposure control device due to a voltage drop can be prevented.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a film unit with a lens, which is a kind of a simple camera, will be described as an example.
As shown in FIG. 1, the lens-fitted film unit includes a unit main body 10 and an outer label 11 wound around the outer periphery of the unit main body 10. Unit body 10
On the front surface, a photographing lens 12, a finder 13, a strobe light emitting unit 14, and a strobe switching plate 15 are provided, and a photometric window 16a for exposing a photodiode 16 (see FIG. 2) is formed. A shutter button 17, a film counter 20, and a display light guide 21 are provided on the upper part of the unit body 10, and a part of the winding dial 22 is exposed to the outside on the back.

As shown in FIG. 2, a cartridge 26 and a photographic film 27 are loaded in the unit main body 10 in advance. The unit main body 10 includes a main body base 23,
An exposure unit 24, a strobe device 25, a front cover 30,
It comprises a rear cover 31. The exposure unit 24 and the strobe device 25 are attached to the main body base 23 so as to be removable. The main body base 23 houses an exposure frame 32 for determining an exposure range of the photo film 27, a cartridge storage room 33 for storing the cartridge 26, and a photo film 27 drawn out of the cartridge storage room 33 and wound into a roll. Photo film storage room 3
And 4. The hoisting dial 22 is attached to the upper part of the cartridge storage chamber 33.

The hoisting dial 22 has a shaft (not shown) provided at its lower part engaged with a spool 26 a formed on the cartridge body 26. Further, one end of the photo film 27 is fixed to a spool 26a.
When the winding knob 22 rotates in the counterclockwise direction, the spool 26a rotates, and the photo film 27 is pulled out from the inside of the cartridge storage chamber 34 and wound into the cartridge 26.

The front cover 30 is attached to the front of the main body base 23. The front cover 30 has an opening for exposing the photographing lens 12, the finder 13, and the like to the outside, in addition to the photometric window 16a. The rear cover 31 is attached to the back of the main body base 23, and
Also, the back of the photo film storage chamber 34 and the film passage therebetween are light-tightly covered. Bottom covers 35a and 35b are formed integrally with the rear cover 31, and cover the bottoms of the cartridge storage chamber 33 and the photo film storage chamber 34 in a light-tight manner. The bottom cover 35a is opened when the photographed cartridge body 26 is taken out.

The strobe unit 25 includes a strobe circuit 2
A printed circuit board 36 for forming 5a is provided. The printed circuit board 36 is arranged beside the exposure unit 24, and the strobe light emitting unit 14, the main capacitor 37, the battery 38, the synchro switch 40, and the push switch 41 are mounted on the printed circuit board 36. As the battery 38, an AA type (R6) dry battery having a terminal voltage of 1.5V is used. The synchro switch 40 is turned on when the shutter blade 62 shown in FIG. 3 is fully opened. Push switch 41
Is used as a power switch of the strobe circuit 25a.

The strobe switching plate 15 is composed of a switching knob 15a which can be operated externally, and a plate portion 15b formed integrally with the switching knob 15a, and has an upper ON position and a lower OFF position. Slide between. In the ON position, the push switch 41 is turned on and the flash circuit 25a
Operates, and in the off position, the push switch 41 is turned off.
The strobe switching plate 15 is provided with an auxiliary plate 1
9 stops the click at one of the ON position and the OFF position.

As shown in FIG. 3, the exposure unit 24
It comprises a dark box 60, a shutter cover 61, shutter blades 62, an aperture plate 63, a solenoid 64 and the like. Dark box 60
A shutter opening 65 for guiding subject light to the exposure frame 32 is formed at the center of the dark box 60, and a finder 13, a shutter drive lever 66, and the like are attached to the upper part of the dark box 60. The shutter cover 61 is provided with a lens holder 67 having a fixed aperture opening 67a formed therein, and the photographing lens 12 is fitted into the lens holder 67. An aperture control circuit 74 that determines whether to switch the aperture according to the brightness of the subject is connected to the solenoid 64.

The shutter drive lever 66 moves from a release position to a charge position against a spring by a shutter device (not shown) when the photographic film is wound up by one frame, and is locked by a lock lever (not shown).
When the shutter button 17 is pressed, the lock lever releases the locking of the shutter drive lever 66. The shutter drive lever 66 is returned to the release position by the urging force of the spring.

The shutter blade 62 includes a blade portion 62a and a mounting portion 62b, and is rotatably mounted on the dark box 60. The shutter blade 62 is held by a spring 70 at a closed position where the blade portion 62a closes the optical axis. The shutter drive lever 66 kicks off the tip of the mounting portion 62b when moving from the charge position to the release position. The shutter blade 62 rotates against the spring 70, and the shutter opening 65 is opened. After the shutter opening 65 is fully opened, the shutter blade 62 is returned to the closed position by the urging force of the spring 70. While the shutter opening 65 is open, exposure to the photographic film 27 is performed.

The diaphragm plate 63 is disposed between the shutter blade 62 and the fixed diaphragm opening 67a, and is attached to the dark box 60 so as to be rotatable. The aperture plate 63 has a small aperture opening 71 formed therein. The fixed aperture 67a has a larger aperture size than the small aperture 71 and is used as a large aperture. As shown in FIG. 4 (A), the aperture plate 63 has a small aperture opening 71 formed by a spring 72 so that the imaging optical axis PL
It is held in the first position set above. In this state, the photographic film 27 is exposed with the photographing light passing through the small aperture opening 71. Reference numeral 73 denotes a stopper provided on the dark box 60 to stop the diaphragm plate 63 at the first position.

The solenoid 64 is fixed to the dark box 60 and is driven by a drive signal from the aperture control circuit 74. The plunger 64a of the solenoid 64 is
b, it is connected to the aperture plate 63. When the solenoid 64 is driven, as shown in FIG. 4B, the plunger 64a is retracted against the spring 72, and the diaphragm plate 63 moves to the second position. In this second position, the diaphragm plate 63 is retracted from the photographing optical path PL, and the photographic film 27 is exposed with the subject light passing through the fixed diaphragm opening 67a.

The aperture control circuit 74 includes a photometric unit for measuring the luminance of the subject, a determining unit for determining whether or not the output from the photometric unit is equal to or greater than a threshold value, and a solenoid in accordance with the determination result of the determining unit. And a driving unit for driving the H.64. An automatic exposure control device is constituted by the aperture control circuit 74, the solenoid 64, the aperture plate 63, and the like.

The aperture control circuit 74 includes a strobe circuit 25a
In addition, they are formed on a printed circuit board 36 (see FIG. 2). A photometric switch 75 is connected between the aperture control circuit 74 and the battery 38.
Is turned on, power is supplied from the battery 38 to operate. During the operation of the strobe circuit 25a, the voltage fluctuation of the battery 38 is large.
The operation of the flash circuit 25a is forcibly stopped. The battery 38 is for driving the strobe device 25, but is also used as a power supply for the automatic exposure control device.

The shutter device for driving the shutter drive lever 66 is provided with a mechanical delay mechanism (not shown). The delay mechanism starts operating when the shutter button 17 is pressed, and turns on the photometric switch 75. Then, after a lapse of a predetermined time, the photometric switch 75 is turned off. The delay mechanism releases the locking of the shutter drive lever 66 after a lapse of time (20 ms) required for the movement of the diaphragm plate 63. This prevents exposure during the movement of the aperture plate 63. Note that the photometric switch 75 may be turned on when the shutter button 17 is pressed.

FIG. 5 is a circuit diagram of the aperture control circuit 74.
The aperture control circuit 74 includes the photodiode 16 and the resistor 77
a, an FET 80, a first trigger transistor 81, a second trigger transistor 82, a latch transistor 83, transistors 84 and 85, and the like. Power supply terminal 88
a and 88b are connected to the battery 38 (see FIG. 6) of the strobe circuit 25a, and the electric power from the battery 38 activates the aperture control circuit 74.

The photodiode 16 and the resistor 77a are connected in series and constitute a photometer. The cathode of the photodiode 16 is connected to the positive electrode of the battery 38 via a photometric switch 75, and the anode is connected to the negative electrode of the battery 38 via a high-resistance resistor 77a. The photodiode 16 is connected to the photometric switch 7.
When the switch 5 is turned on, a reverse bias is applied by the battery 38 to operate, and a photocurrent of a magnitude corresponding to the incident light is generated. As the photodiode 16, for example, a silicon photodiode can be used.

The anode of the photodiode 16 has N
The gate terminal of the channel MOS type FET 80 is connected. The source terminal of the FET 80 is connected to the negative electrode of the battery 38, and the drain terminal is connected to the base terminal of the first trigger transistor 81 via the resistor 77b. Since the photocurrent generated by the photodiode 16 flows through the resistor 77a, a potential difference occurs between both ends of the resistor 77a according to the luminance of the subject. This potential difference is the
Is applied between the gate and the source. The FET 80 is designed to be off when the subject brightness is lower than a threshold value (hereinafter, referred to as “LV”), but to be turned on when the subject brightness is equal to or higher than LV.

The judgment section is composed of a first trigger transistor 81, a second trigger transistor 82 and a FET 80 which constitute a Schmitt trigger circuit. The first trigger transistor 81 and the second trigger transistor 82 are PN
A P-type one is used, and the emitter terminals of both are common terminals, and this common terminal is connected to the photometric switch 75 via the resistor 77c. First trigger transistor 8
The collector terminal 1 is connected to the negative terminal of the battery 38 via the resistor 77d. The collector terminal of the second trigger transistor 82 is connected to the base terminal of the latch transistor 83 via the resistor 77e.

When the FET 80 turns on and a current flows through the resistor 77b, the base potential of the first trigger transistor 81 decreases, and the first trigger transistor 81 turns on. At this time, the emitter potential of the second trigger transistor 82 is
It becomes equal to the base potential (collector potential of the first trigger transistor 81), and the second trigger transistor 82 is turned off.

On the other hand, when the FET 80 is off, a base current flows to the second trigger transistor 82 through the resistor 77d, and the base potential decreases, so that the second trigger transistor 82 turns on. At this time, the first trigger transistor 81 is turned off. Therefore, FET8
0, two trigger transistors 81, 8
Only one of the two is turned on.

Here, immediately after the photometric switch 75 is turned on, the photocurrent of a magnitude corresponding to the luminance of the object is not generated from the photodiode 16, so that the FET 80 remains off. Therefore, even when the subject luminance is large, the second trigger transistor 82 may be turned on before the FET 80 is turned on. Therefore, a delay capacitor 86 is connected to the base terminal of the second trigger transistor 82 in order to delay the turning on of the second trigger transistor 82.

The NPN type latch transistor 83 is for maintaining this ON state when the second trigger transistor 82 is turned ON. The collector terminal of the latch transistor 83 is connected to the base terminal of the second trigger transistor 82 via the resistor 77f, and further connected to the base terminal of the transistor 84 via the resistor 77g. The collector terminal of the latch transistor 83 is connected to the negative electrode of the battery 38.

When the second trigger transistor 82 is turned on, its collector current flows to the base of the latch transistor 83 via the resistor 77e, and the latch transistor 83
Turns on. Since a current flows through the collector terminal of the latch transistor 83, the base current of the second trigger transistor 82 further increases, and the ON state of the second trigger transistor 82 is maintained. Therefore, once the second trigger transistor 82 is turned on, the on state of the second transistor 82 is maintained even if the state of the FET 80 changes during exposure. Thus, switching of the aperture during exposure is prevented, and stable exposure can be performed.

The collector terminal of the PNP switching transistor 84 is connected to the solenoid 60 and the cathode of the protection diode 87. The emitter terminal of the transistor 84 is connected to the positive electrode of the battery 38. When the latch transistor 83 conducts, the resistance 77 g
, A current flows through the base terminal of the transistor 84,
Transistor 84 conducts. When the transistor 84 is turned on, a current flows through the solenoid 60.
As shown in (B), the plunger 64a is sucked, and the aperture plate 63 moves to the second position. This transistor 8
4 constitutes a drive unit of the solenoid 60. In addition,
The protection diode 87 causes the transistor 84 to deteriorate due to the back electromotive force generated at the start of energization of the solenoid 60.
Prevent destruction.

The NPN transistor 85 has a base terminal connected to the photometric switch 75 via a resistor 77h, and a terminal 56 connected to a collector terminal. Also,
A resistor 77i is provided between the emitter and the base of the transistor 85.
Are connected to form a bias circuit together with the resistor 77h. When the photometric switch 75 is turned on, the transistor 85
, A constant voltage is applied between the base and the emitter, and the transistor 85 is turned on. When the transistor 85 is turned on, the charging operation of the strobe circuit 25a is forcibly stopped via the terminal 56. While the aperture control circuit 74 is operating, the strobe circuit 25a is stopped, so that the battery 38
The malfunction of the aperture control circuit 74 due to the voltage drop is prevented.

The time when the photometric switch 75 is turned on is several ms.
The storage capacitor 88 is connected to the battery 38 because it is very short and it is difficult to switch the aperture during this time. The light metering switch 75, the storage capacitor 88, and the battery 38 constitute a power storage circuit.
The storage capacitor 88 is charged while 5 is ON. After the photometric switch 75 is turned off, the storage capacitor 88
The aperture control circuit 74 operates for a certain period of time (1500 ms to 1600 ms) by the electric charge stored in. The capacitance of the storage capacitor 88 is determined in consideration of the time constant of the storage circuit and the amount of charge sufficient for switching the aperture, and may be, for example, 47 μF. In this case, when the contact resistance of the photometric switch 75 is 1Ω,
Since the time constant of the power storage circuit is 47 μsec, the power storage capacitor 88 can be charged while the photometric switch 75 is ON.

The solenoid 60 is connected to the transistor 8
4, and is not supplied from the storage capacitor 88. This is the solenoid 60
Is large, and the electric charge of the storage capacitor 88 disappears in a short time.

As shown in FIG. 6, the strobe circuit 25a
Is composed of a main capacitor 37, a push switch 41, an oscillation transistor 43, an oscillation transformer 45, a rectifying diode 49, a trigger capacitor 51, a trigger coil 52, a strobe discharge tube 53 and the like.

The push switch 41 is connected to the movable piece 42
The movable contact 42 is composed of third contacts 43a to 43c, and one end of the movable piece 42 is connected to the third contact 43c. When the strobe switch 15 moves to the ON position, the other end of the movable piece 42 comes into contact with the first contact 43a and the second contact 43b, and conduction between the contacts is established.

The NPN type oscillating transistor 44 and the oscillating transformer 45 constitute a known blocking oscillating circuit, and convert the voltage of the battery 38 to a high voltage of about 300 V to charge the main capacitor 37. Oscillation transformer 4
5 is composed of a primary coil 46, a secondary coil 47, and a tertiary coil 48, each of which is inductively coupled. One end of the primary coil 46 is connected to the positive electrode of the battery 38, and the other end is connected to the collector terminal of the oscillation transistor 44. One end of the secondary coil 47 is connected to the anode of the rectifying diode 49, and the other end is connected to the positive electrode of the battery 38 together with the tertiary coil 48. Also, the tertiary coil 48
Of the push switch 41 through the resistor 50a.
Connected to contact 43c.

The cathode of the rectifying diode 49 is connected to one end (positive side) of the main capacitor 37 and to one end of the trigger capacitor 51 via the resistor 50b. The other end of the trigger capacitor 51 is
It is connected to the first contact 43a of the push switch 41. The emitter terminal of the oscillation transistor 44 is connected to the negative electrode of the battery 38, and the base terminal is connected to the second contact 43b via the resistor 50c.

The trigger coil 52 comprises a primary trigger coil 52a and a secondary trigger coil 52b which are inductively coupled. One end of the primary trigger coil 52a is connected to one end of the trigger capacitor 51,
One end of “b” is connected to a trigger electrode 54 provided on the outer periphery of the strobe discharge tube 53. This strobe discharge tube 53
Are provided in the flash light emitting unit 14. The other end of each of the coils 52a and 52b is a common terminal, and is connected to the push switch 41 via the synchro switch 40. The strobe discharge tube 53 is connected to the main condenser 3.
7 are connected in parallel.

The strobe circuit 25 connected as described above
a, the tertiary coil 4 from the positive electrode of the battery 38;
8, resistor 50a, push switch 41, resistor 50c, battery 38
The path leading to the negative electrode forms a bias circuit for flowing a bias current for operating the oscillation transistor 44.

From the secondary coil 47 to the rectifying diode 4
9, main capacitor 37, push switch 41, resistor 5
0c, the path between the base and the emitter of the oscillation transistor 44, the battery 38, and the secondary coil 47 constitute a main secondary circuit for flowing a secondary current for causing the oscillation transistor 44 to oscillate. With this secondary current, the main capacitor 37
Is charged.

The path from the secondary coil 47 to the rectifier diode 49, the resistor 50b, the trigger capacitor 51, the push switch 41, the resistor 50c, the base-emitter of the oscillation transistor 44, the battery 38, and the secondary coil 47 is as follows. A secondary circuit for supplying a secondary current is formed.
The trigger capacitor 51 is charged by the secondary current.

Further, the path from the trigger capacitor 51 to the primary trigger coil 52a, the sync switch 40, the push switch 41, and the trigger capacitor 51 is such that when the sync switch 40 is turned on, the discharge current from the trigger capacitor 51 is transmitted to the primary trigger coil 52a. To form a trigger discharge circuit for flowing to

When the push switch 41 is turned on, the oscillation transistor 44 operates and a current (a collector current of the oscillation transistor 44) flows through the primary coil 46. Then, an electromotive force is generated in the secondary coil 47 according to the winding ratio between the primary coil 46 and the secondary coil 47, and the secondary current generated by the electromotive force flows as the base current of the oscillation transistor 44. . That is, the oscillation transistor 44 oscillates by increasing the collector current by the positive feedback action of the oscillation transformer 45. At the same time, the secondary current generated in the secondary coil 47 flows through the main secondary circuit and the sub secondary circuit, and the main capacitor 37 and the trigger capacitor 51 are charged.

The reference numeral 55 indicates the display light guide 2.
1 is a light emitting diode provided at the lower part of FIG. The anode of the light emitting diode 55 is connected to one end of the tertiary coil 48, and the cathode is connected to the other end of the tertiary coil 48. When the charging voltage of the main capacitor 37 reaches the specified charging voltage, the voltage between both terminals of the tertiary coil 48 exceeds a predetermined value, and the light emitting diode 55 turns on.

When the synchro switch 40 is turned on while the main capacitor 37 is charged, the trigger discharge circuit is closed, and the discharge current of the trigger capacitor 51 flows to the primary trigger coil 52a. When a discharge current flows through the primary trigger coil 52a, a high-voltage trigger voltage is generated on the secondary trigger coil 52b.
Is applied to the strobe discharge tube 53. Then, the electric charge of the main capacitor 37 is discharged in the strobe discharge tube 53, and strobe light is emitted.

In the case of the above circuit configuration, the main capacitor 37 is charged so as to have a positive voltage, and the case of the main capacitor 37 is on the ground side. Therefore, even when the unit body 10 is wet with water, there is no electric shock. . The main capacitor 37, the primary coil 46, the rectifying diode 49, the strobe discharge tube 53, the light emitting diode 5
The polarity of 5 may be reversed.

The terminal 56 of the aperture control circuit 74 is connected to the resistor 50
c. When the photometric switch 75 of the aperture control circuit 74 turns on, the transistor 85 turns on.
The oscillation transistor 44 is turned off, and the strobe circuit 25a
Is forcibly stopped. On the other hand, the aperture control circuit 74
Is not operating, the flash circuit 25a operates if the push switch 41 is on.

FIG. 7 is a timing chart of exposure control in the flash photography mode. When the shutter button 17 is pressed, the photometric switch 75 is turned on.
First, the transistor 85 is turned on, and the charging operation in the strobe circuit 25a is stopped. In addition, the electric charge is charged in the storage capacitor 88, and the photodiode 16 is operated to generate a photocurrent according to the luminance of the subject.

When the subject brightness is lower than LV, the FET 80
, The FET 80 and the first trigger transistor 81 do not turn on. Therefore, a base current flows through the second trigger transistor 82 via the resistor 77e, and the second trigger transistor 82 is turned on.
At this time, the delay capacitor 86 prevents the second trigger transistor 82 from turning on until the output of the photodiode 16 is stabilized.

When the second trigger transistor 82 turns on, the latch transistor 83 and the transistor 84 turn on. As a result, the solenoid 60 is energized and the aperture plate 63 is moved to the second position, so that the aperture becomes a large aperture. Even after the shutter button 17 is pressed, the shutter drive lever 66 is held at the charge position by the mechanical delay mechanism. After a time (about 20 ms) required for moving the aperture plate 63 has elapsed, the shutter drive lever 6
6 is released, the shutter blade 62 is kicked off, and exposure is started.

The photometric switch 75 is turned off immediately before the solenoid 60 is energized.
Power is supplied to the photodiode 16, the FET 80, the Schmitt trigger circuit, and the like. Then, after the shutter blade 62 closes and the exposure stops, the charge stored in the storage capacitor 88 disappears. As a result, the operation of the aperture control circuit 74 stops, the energization of the solenoid 60 stops, and the aperture plate 63 is returned to the first position by the spring 72. Further, since the transistor 85 is turned off, the charging operation of the strobe circuit 25a is started.

On the other hand, when the subject brightness is equal to or higher than LV,
The FET 80 and the first trigger transistor 81 are turned on. At this time, since the second trigger transistor 82 does not turn on, the latch transistor 83 and the transistor 84
Turns off. Accordingly, the solenoid 60 is not energized, and the diaphragm plate 63 is held at the first position.
1 is set in the photographing optical path LV.

The operation of the above configuration will be described below.
When the winding dial 22 is rotated, the unexposed photographic film 27 is pulled out from the photographic film storage chamber 34 and set behind the exposure frame 32. In conjunction with the movement of the photo film 27, the shutter drive lever 66 moves to the charging position and is locked by the lock lever. When the photographic film 27 is wound up by exactly one frame, the winding dial 22 is locked by a film winding stopping mechanism (not shown). In this state, the photometric switch 75
Is turned off and the aperture control circuit 74 does not operate, so that wasteful consumption of the battery 38 is suppressed.

When the shutter button 17 is pressed after framing the subject, the photometric switch 75 is turned on, and the aperture control circuit 74 operates. When the subject brightness is lower than LV, the solenoid 60 is energized, and the aperture plate 63 moves to the second position shown in FIG. On the other hand, when the subject brightness is equal to or higher than the LV, the solenoid 60 is not energized, so that the diaphragm plate 63 is biased by the spring 72 as shown in FIG.
Are held at the first position shown in FIG.

When a predetermined time (about 20 ms) has elapsed since the shutter button 17 was pressed, the shutter drive lever 66 is unlocked and moves from the charge position to the release position. During this movement, the shutter blade 6
2 is kicked off, and the photographic film 27 is exposed.

When the subject is extremely bright, such as when photographing outdoors on a sunny day, exposure is performed through the small aperture opening 71. Since the exposure amount is reduced by the small aperture opening 71, appropriate exposure can be performed without overexposure. On the other hand, when the brightness of the subject is not sufficient as in the case of indoor photographing, exposure is performed through the fixed aperture 67. In this case, since the exposure amount increases, appropriate exposure can be performed without underexposure.

In a very dark situation such as at night, the switching knob 15a is slid to the ON position to switch from the daytime shooting mode to the flash shooting mode. In this flash photography mode, the flash circuit 25a operates,
The main capacitor 37 is charged. After the completion of charging is detected by turning on the display light guide 21, the shutter button 17 is depressed to perform photographing. In this case, the subject brightness is lower than LV, and the solenoid 6
Since 0 is energized, exposure is performed through the fixed stop aperture 67a.

FIG. 8 shows another aperture control circuit embodying the present invention. Except for the details described below, this embodiment is the same as the above-described embodiment, and substantially the same components are denoted by the same reference numerals, and description thereof will be omitted.

In this aperture control circuit, an NPN transistor 90 is provided between the FET 80 and the transistor 84.
And a PNP-type latch transistor 91. A photometric switch 75 is connected to the drain terminal of the FET 80 via a resistor 77j. The collector terminal of the latch transistor 91 is connected to the base terminal of the transistor 90 via the resistors 77e and 77k.
A resistor 77 is connected to the base terminal of the latch transistor 91.
f, a resistor 77g is connected to the base terminal of the transistor 84, and a photometric switch 75 is connected to the emitter terminal.

When the photometric switch 75 is turned on, the photodiode 16 operates and generates a photocurrent according to the luminance of the object. Here, when the subject luminance is large, the FET 8
0 turns on, and a current flows from the resistor 77j to the FET 80. At this time, since no base current flows through the transistor 90, the transistor 90 is not turned on. Further, since the base current does not flow through the latch transistor 91, the latch transistor 91 is not turned on. For this reason, since the transistor 84 is not turned on, the solenoid 60 is not energized. Accordingly, the aperture plate 63 is held at the first position, and exposure is performed through the small aperture opening 71.

On the other hand, when the subject brightness is low, the FET
Since the transistor 80 does not turn on, a base current flows through the transistor 90 via the resistors 77j and 77e. When the transistor 90 turns on, the latch transistor 91 also turns on. Once the transistor 90 is turned on, the latch transistor 91 keeps the transistor 90 on until the electric charge stored in the storage capacitor 88 disappears. When the transistor 90 is turned on, the collector current flows as the base current of the transistor 84, so that the transistor 84 is turned on. Solenoid 60
Is supplied, and the diaphragm plate 63 moves to the second position, so that exposure is performed through the fixed diaphragm opening 67a.

In the above embodiment, the solenoid 60 is energized when the subject brightness is low, but a structure in which the solenoid 60 is energized when the subject brightness is high may be employed. Also, a large aperture and a small aperture are provided on the aperture plate,
It is also possible to adopt a structure in which one of the aperture openings is inserted on the optical axis according to the magnitude of the subject brightness.

In the above embodiment, the solenoid 60 is used as the electromagnetic force generating means. However, an electromagnet which attracts an iron piece attached to one end of the aperture plate 63 may be used. Further, in the above-described embodiment, an example has been described in which the present invention is applied to a film unit with a lens. However, the present invention can also be applied to a compact camera or an electronic still camera.

[0071]

As described above, according to the automatic exposure control device of the present invention, a photodiode for photometry of a subject, a resistor connected in series to the photodiode,
A field-effect transistor having a gate and a source connected between terminals of the resistor, electromagnetic force generating means whose energization is controlled according to the state of the field-effect transistor, and whether or not the electromagnetic force generating means is energized. Since the aperture plate is moved to the large aperture position or the small aperture position, it is possible to accurately determine whether the subject brightness has exceeded a threshold value,
And it can operate at low voltage. Further, the automatic exposure control device of the present invention can be provided at low cost because the circuit configuration is simple.

Further, there is provided a first transistor for controlling the energization of the electromagnetic force generating means in a state opposite to the state of the field effect transistor, and a latch circuit for latching the ON state of the first transistor is provided. With this arrangement, it is possible to prevent the diaphragm plate from moving due to a change in the state of the field-effect transistor during exposure.

Further, since the first capacitor for delaying the conduction of the first transistor is provided, the state of the first transistor is determined after the operation of the field effect transistor is stabilized, so that the operation of the automatic exposure control device Becomes stable. In addition, the automatic exposure control device is driven by the battery for the flash device, and the charging operation of the flash device is prohibited while the automatic exposure control device is operating, preventing malfunction of the automatic exposure control device due to voltage drop. can do.

[Brief description of the drawings]

FIG. 1 is an external perspective view of a film unit with a lens.

FIG. 2 is an exploded perspective view of the film unit with a lens.

FIG. 3 is an exploded perspective view of the exposure unit.

4A and 4B are explanatory diagrams showing states of an aperture plate, wherein FIG. 4A shows a case where a subject is bright, and FIG. 4B shows a case where a subject is dark.

FIG. 5 is a circuit diagram of an aperture control circuit.

FIG. 6 is a circuit diagram of a strobe device.

FIG. 7 is a timing chart showing the operation of the exposure control mechanism.

FIG. 8 is a circuit diagram showing another embodiment of the aperture control circuit.

[Explanation of symbols]

 Reference Signs List 10 Film unit with lens 16 Photodiode 60 Solenoid 63 Aperture plate 80 FET 85 Transistor 86 Delay capacitor 88 Storage capacitor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03B 9/02 G03B 9/02 C 9/07 9/07 A 15/05 15/05 G03C 3/00 575 G03C 3/00 575A 575C 575B

Claims (14)

[Claims] 1. An automatic exposure control device for a camera for performing photometry of a subject prior to photographing and controlling the size of an aperture opening, comprising: a photodiode for performing photometry of the subject; and a resistor connected in series with the photodiode. A field-effect transistor in which a voltage between both terminals of the resistor is applied between a gate and a source and is turned on when the voltage is equal to or higher than a predetermined value, and turned off when the voltage is lower than a predetermined value; Electromagnetic force generating means whose energization is controlled in accordance with the state of the field effect transistor, and depending on whether or not the electromagnetic force generating means is energized, a large aperture position with a large aperture size or a small aperture size with a small aperture size An automatic exposure control device for a camera, comprising: an aperture plate that moves to a small aperture position. 2. The method according to claim 1, wherein the field-effect transistor is a MOS transistor.
The automatic exposure control device for a camera according to claim 1, wherein the automatic exposure control device is a mold. 3. A switch for starting photometry by said photodiode when turned on by a shutter release operation.
Or the automatic exposure control device of the camera according to 2. 4. A small aperture opening is formed in the aperture plate, the small aperture opening is set in a photographing optical path at the small aperture position, and the aperture plate is retracted from the imaging optical path at the large aperture position. The automatic exposure control device for a camera according to any one of claims 1 to 3, wherein: 5. The automatic exposure control device for a camera according to claim 1, wherein said electromagnetic force generating means is a solenoid. 6. A first control for controlling the energization of said solenoid by switching to a state opposite to a state of said field effect transistor.
6. The automatic exposure control device for a camera according to claim 5, further comprising: 7. The automatic exposure control device for a camera according to claim 6, further comprising a second transistor connected in series with said solenoid and in the same state as said first transistor. 8. A first capacitor for delaying the operation of the first transistor is provided so that the first transistor is turned on after a predetermined time has elapsed since the switch was turned on. 8. The automatic exposure control device for a camera according to claim 6, wherein 9. The automatic exposure control device for a camera according to claim 6, further comprising a latch circuit for latching an ON state of the first transistor. 10. The photodiode, the field-effect transistor, the first transistor, and the latch circuit are supplied with power from a battery via the switch, and the second transistor and the solenoid are directly supplied from the battery. 10. The automatic exposure control device for a camera according to claim 9, wherein power is supplied. 11. The battery is charged by a battery while the switch is turned on, and after the switch is turned off, power is supplied to the photodiode, the field effect transistor, the first transistor, and the latch circuit. 11. The automatic exposure control device for a camera according to claim 10, further comprising a second capacitor. 12. The automatic exposure control device for a camera according to claim 3, wherein a voltage between terminals of a battery for supplying power to the automatic exposure control device is 1.5V. 13. The automatic exposure control device for a camera according to claim 12, further comprising a strobe device driven by the battery. 14. An automatic exposure control device for a camera according to claim 13, further comprising a stop circuit for forcibly stopping a charging operation of said strobe device while said switch is on. .