JPH0823649B2 - Exposure control device - Google Patents

Description

The present invention relates to an exposure control device for a camera including a program shutter that uses shutter blades that also serve as aperture blades.
More specifically, while controlling the charging current of the integrating circuit with the current supply level being a level determined corresponding to the film sensitivity, the opening position of the shutter blades, and the field brightness,
The present invention relates to a novel exposure control device which gives a low brightness warning by the current supply level when the shutter blade is closed.

[Conventional technology and its problems]

As is well known, the exposure amount to the film surface is finally determined by the F value and the exposure time, and in the case of a camera that can control the F value and the exposure time independently, if the F value is determined, the field brightness is determined. Proper exposure can be obtained by determining the exposure time according to. Further, if the exposure time is determined, an appropriate exposure can be obtained by determining the F value corresponding to the field brightness.

However, in order to perform such exposure control, since it is necessary to provide independent driving devices for the diaphragm blade and the shutter blade (shutter curtain), the cost becomes high. A program shutter having both shutter blades and aperture blades is used. In the case of such a program shutter having both shutter blades and aperture blades, the shutter blades are opened in a linear approximation as shown in FIG. Close when you get.

By the way, even in such a program shutter, the exposure control is basically performed by integrating the photocurrent flowing through the light receiving element in accordance with the brightness of the field and closing the shutter blade when the integrated value reaches a certain value. However, in the program shutter of this type, the exposure amount is proportional to the exposure time after the shutter blade reaches the opening diameter, and in the so-called triangular area until the shutter blade reaches the opening diameter, the opening of the shutter blade is increased. At the same time, since the exposure amount per unit time is increasing every moment, proper exposure control cannot be performed unless the characteristics of the photometric circuit are corrected.

Various methods have been conventionally known for this correction, but basically they are roughly classified into the following two types.

First, the first method is to integrally form a sub aperture blade that opens and closes the light receiving element with the shutter blade, and increases the light receiving area of the light receiving element in conjunction with the opening of the shutter blade. According to the method, when the field brightness is constant, the photocurrent per unit time increases with the opening of the shutter blades, so that the integrated value of the actual exposure amount and the integrated value of the photocurrent substantially correspond to each other. It becomes possible to perform accurate exposure control.

However, in the case of this method, it is pointed out that the arrangement position of the light receiving element is extremely limited, and the shape of the shutter blade itself is also limited because the light receiving element is arranged. It is also possible to arrange the light receiving element arbitrarily and simultaneously operate the shutter blade and the sub diaphragm blade by the interlocking mechanism. However, if the interlocking mechanism is interposed, the exposure error may be amplified by the interlocking mechanism. is there.

As a second method, there is known a method of predicting the opening characteristic of the shutter blades in advance and electrically correcting the integrated value of the photocurrent. In this method, the arrangement position of the light receiving unit is a mechanism. However, since the traveling characteristics of the shutter blades are assumed to be extremely stable for the above prediction to be established, a complicated governor mechanism such as a governor is indispensable. At the same time, it is pointed out that the inertial weight of the actuating member increases due to these speed control mechanisms, and the charging force of the shutter increases. It has also been pointed out that an exposure error occurs when the traveling characteristics of the shutter blades fluctuate due to changes over time, changes in camera attitude, changes in temperature, changes in power supply voltage, and the like.

In addition, the shutter speed that does not cause camera shake in hand-held shooting is usually 1 / focal length or more in the case of a skilled person, and even if a wide-angle lens is used, a so-called low shutter speed is 1/30 seconds or less. It is desirable to give a brightness warning to encourage the use of tripods and strobes.

Since the shutter speed of the program shutter is determined by the film sensitivity and the field brightness, a calculation for calculating the shutter speed using the film sensitivity and the field brightness as variables has conventionally been performed in order to give this low brightness warning. It was necessary to separately provide a circuit in addition to the exposure control circuit.

[Means for solving problems]

The present invention has been made to solve such a problem, and effectively prevents an exposure error caused by a variation in the traveling characteristics of the shutter blades while giving a degree of freedom to the location where the light receiving element is arranged. An object of the present invention is to provide a novel exposure control device capable of issuing a low-luminance warning without separately providing an arithmetic circuit for calculating a shutter speed.

In summary, the exposure control device of the present invention includes: a shutter blade that also serves as a diaphragm blade that continuously opens within a maximum aperture, and a light receiving element whose exposure area to the field light is not affected by the opening position of the shutter blade. A logarithmic compression means for logarithmically compressing the photocurrent flowing corresponding to the amount of light received by the light receiving element, an integrating circuit for integrating a current obtained by logarithmically expanding the output of the logarithmic compression means, and an integral value of the integrating circuit is predetermined. On the premise of an exposure control device that includes shutter closing means for closing the shutter blade when the value of is reached; and a recognizable identification mark arranged in line on the operation line of the shutter blade; A blade position detecting means for detecting the continuously changing position of the shutter blade; a film sensitivity input means for inputting a film sensitivity; and a blade position detecting means for detecting the film sensitivity. Bias voltage generating means for applying to the logarithmic compression means a level corresponding to the root position corrected by the film sensitivity input from the film sensitivity input means, as bias voltage; and at a timing before the opening operation of the shutter blades. The above object is achieved by including low-brightness warning means for giving a low-brightness warning according to the output level of the logarithmic compression means.

[Action]

As described above, the exposure control device of the present invention sequentially detects the actual position of the shutter blade, and uses the level obtained by correcting the voltage corresponding to the detected blade with the film sensitivity as the bias voltage of the logarithmic compression means. A sub-iris blade for mechanically adding so-called γ correction is not required, which improves the degree of freedom in the location of the light-receiving element, and integrates for photometry even if the aperture characteristics of the photographic lens fluctuate for some reason. Since the charging characteristics of the circuit can follow this, extremely accurate exposure control is possible, and the output voltage of the logarithmic compression unit at the timing before the opening operation of the shutter blades reflects only the film sensitivity and the subject brightness. The low brightness warning can be issued without separately disposing an arithmetic circuit for calculating the shutter speed with the film sensitivity and the field brightness as variables.

〔Example〕

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

The present invention is applied to a program shutter having shutter blades that also serve as aperture blades. First, FIG. 1 shows a basic configuration example of a program shutter having shutter blades that also serve as aperture blades.

In FIG. 1, reference numerals 1 and 2 denote shutter blades that also serve as aperture blades, respectively, and the shutter blades 1 and 2 are rotatably supported by shafts 1a and 2a, respectively. Reference numeral 3 denotes a blade opening / closing ring that is rotatably held about the optical axis. The blade opening / closing ring 3 is always biased counterclockwise by a spring 4 and is a pin planted in the blade opening / closing ring 3. 3a / 3b
Engage with long grooves 1b and 2b formed in the shutter blades 1 and 2, respectively. Reference numeral 5 denotes a solenoid which is an example of an actuator for rotating the blade opening / closing lever 3 clockwise.

The operation will be described. First, the solenoid 4 is demagnetized in the initial state, and the blade opening / closing ring 3 is
Is urged counterclockwise by a spring 4.
Therefore, the blade opening / closing ring 3 is stopped at the position where the claw 3c contacts the stopper 6, and the shutter blades 1 and 2 close the aperture 7.

When the solenoid 5 is excited in this state, the blade opening / closing ring 3 rotates clockwise against the tension of the spring 4 while the pins 3a and 3b lock the long grooves 1b and 2b. Respectively rotate counterclockwise around the shafts 1a and 2a to gradually open the aperture 7, and when the claw 3d of the blade opening / closing ring 3 comes into contact with the stopper 6, the aperture 7 is opened. Become. When the solenoid 5 is demagnetized at the timing when the proper exposure is obtained, the blade opening / closing ring 3 is rotated counterclockwise by the tension of the spring 4, and the shutter blades 1 and 2 close the aperture 7 to end the exposure operation. To do.

The structure and operation of this type of program shutter are well known in the prior art, but in the present invention, a feature is that means for detecting the actual aperture of the taking lens is provided.

As the means for detecting the aperture of the photographing lens, various modes such as a method of detecting the rotation amount of the shutter blade 1 (or 2) and a method of detecting the rotation amount of the blade opening / closing ring 3 are conceivable. An example in which a photoelectric encoder 8 for detecting the rotation amount of the shutter blade 1 is formed is adopted.

The details of the photoelectric encoder 8 are shown in FIGS.
Although the description will be made with reference to the drawings, the basic configuration and operation will be described. In the shutter blade 1, a large number of slits are formed on the circumference around the shaft 1a at a position that does not hinder the operation of other mechanism members. 8a is formed, and the number of pulses generated each time the slit 8a opens and closes the optical path from the light emitting element 8b to the light receiving element 8c is numerically detected to detect the amount of rotation of the shutter blade 1.

FIG. 2 is an enlarged view of the main part of this encoder 8, and FIG.
The figure is a sectional view taken along line A in FIGS. 1 and 2. The shutter blades 1 are supported so as to float in the gap between the base plate 8d and the base plate 8e, and the through hole formed in the base plate 8e has a light guide with extremely low reflectance and transmittance, which are the features of this embodiment.
8f is buried. A light guide slit 8g having a sufficiently smaller area than the slit 8a formed in the shutter blade 1 is formed at approximately the center of the light guide 8f, and the light flux emitted from the light emitting element 8b passes through the light guide slit 8g. The light passes through the base plate 8d or is reflected by the shutter blade 1 having a reflectance different from that of the base plate 8d to reach the light receiving element 8c. The characteristic of the encoder 8 in the present embodiment is that the reflectance of the light guide 8f is sufficiently smaller than the reflectance of the base plate 8d or the shutter blades 1,
The area of the light guide slit 8g is sufficiently smaller than the area of the slit 8a formed in the shutter blade 1,
The line connecting the light emitting element 8b and the light receiving element 8c is the shutter blade 1.
That is, it is orthogonal to the traveling direction of the slit 8a formed in. For this reason, in the present embodiment, only the light that has passed through the light guide slit 8g as if it were a pinhole in the luminous flux emitted from the light emitting element 8b reaches the light receiving element 8c, and the boundary between the shutter blade 1 and the slit 8a is the light guide Since the slit 8g is instantly crossed, the photocurrent generated by the light-receiving element 8c exhibits a sharp fall and rise, which enables accurate pulsing. Further, even considering the case where the shutter blade 1 travels unstablely due to a change in the camera posture and the like, in such a case, the shutter blade 1 inclines forward and backward in the advancing direction of the slit 8a. Since the line segment connecting the light emitting element 8b and the light receiving element 8c is orthogonal to the traveling direction of the slit 8a formed in the shutter blade 1 as described above, the shutter blade 1 of the light emitted from the light emitting element 8b is The incident angle with respect to is almost unaffected by the inclination of the shutter blade 1, and the passage through the slit 8a can be detected with high accuracy.

Then, if the change in the photocurrent of the light receiving element 8c that occurs each time the slit 8a passes through the light guide slit 8g is pulsed and this pulse is counted, the opening position of the shutter blade 1 that changes from moment to moment (that is, the current position). F-number) can be known.

In the present embodiment, the current supply level is determined in accordance with the opening position of the shutter blade 1 thus detected, the film sensitivity and the field brightness, and the charging current of the integrating circuit is controlled. Therefore, even if the light receiving element for photometry is arranged at a position irrelevant to the operation of the shutter blades 1 and 2, the charging characteristic of the integrating circuit can be made to follow the aperture characteristic of the shutter blades 1 and 2. Also, the shutter blade 1
Since the current supply level before 2 starts opening the aperture is determined only by the film sensitivity and the field brightness, the low brightness warning should be issued by the current supply level before the opening of the shutter blades 1 and 2. ing.

Next, referring to FIG. 4, a circuit for controlling the charging current of the integrating circuit by determining the current supply level corresponding to the opening position of the shutter blade 1, the film sensitivity and the field brightness.
An example of an exposure control circuit including a circuit that gives a low brightness warning according to the current supply level before the opening of the shutter blades 1 and 2 is described.

First, in FIG. 4, 8b and 8c respectively indicate the light emitting element and the light receiving element which have already been described, 10 is a waveform shaping circuit for pulsing the output of the light emitting element 8c, and 20 is a waveform shaping circuit 10.
Each of the counters for counting the output pulses of is shown. In addition, 30 is a photometric circuit that determines the exposure time according to the brightness of the field,
40 is a drive circuit for driving the shutter blades, 50 is a sequence circuit for performing various sequence controls, and 60 is a contact group for making and breaking corresponding to a conductive pattern provided at a predetermined portion of the DX film patrone. , 70 is contact group 60
The counter 83 is a DX circuit that encodes the film sensitivity corresponding to the pattern obtained by the make break of
Further, 84 denotes an arithmetic circuit supplied with the output from the DX circuit 70, and 84 denotes a digital-analog conversion circuit for converting the output of the arithmetic circuit 83 into a voltage value.

Although a camera compatible with DX film is assumed in this embodiment, the film sensitivity may be manually input as a terminal level of a variable resistor and digitally coded.

Next, a more specific structure and operation of this embodiment will be described.

 First, the photometric circuit 30 will be described.

In this embodiment, the light receiving element SPD31 is used without bias in order to eliminate the influence of dark current, and the log diode 32 is used as an operational amplifier in order to cope with a wide range of luminance.
It is used as a feedback resistor for 33. Specifically, SPD31
Has its anode side connected to the non-inverting input of the operational amplifier 33 and its cathode side connected to the inverting input of the operational amplifier 33, and its light-receiving surface is preferably arranged at an arbitrary position on the camera body so as to face the field. Has been done.

To explain the action, when light corresponding to the field brightness enters the SPD 31, a photocurrent flows through the SPD 31 in the opposite direction, and a voltage drop V ₂ due to this photocurrent occurs across the log diode 32. . Therefore, at the output terminal of the operational amplifier 33, a level is generated in which the voltage drop V ₂ of the log diode 32 due to the photocurrent is superimposed on the bias voltage V ₁ . And operational amplifier
The output voltage of 33 is applied as a current supply level to the base of the transistor 36 for logarithmic expansion, controls the collector current of the transistor 36, and the capacitor 37 is charged by the collector current of the transistor 36. Will be determined by the photocurrent flowing through the SPD 31 and the bias voltage V ₁ .

And the charge level of this capacitor 37 is the comparator
The shutter close signal generated by the comparator 38 when applied to the inverting input of 38, which matches the reference level applied to the non-inverting input of the comparator 38 from the power supply 39, is applied to the sequence circuit 50 to perform the shutter close operation. It is designed to let you. The transistor 310 connected in parallel with the capacitor 37 is cut off in conjunction with the shutter release, and the transistor 310 is cut off to start the charging operation of the capacitor 37.

By the way, as is well known, the proper exposure amount to the film is inversely proportional to the film sensitivity ratio. Therefore, when the field brightness is constant, the charging current of the capacitor 37 is increased as the film sensitivity is higher, and the shutter blades 1 and 2 have the same value. It is required to accelerate the closing timing. Then, as described above, the charging current of the capacitor 37 is controlled by the output level of the operational amplifier 33, and the voltage V ₂ and the bias voltage V ₁ determined corresponding to the brightness of the field are superimposed on the output of the operational amplifier 33. Since the level appears, if the bias voltage V _{1 is} determined according to the film sensitivity, the charging characteristic of the capacitor 37 can be determined according to the film sensitivity.

Further, as described above, in the case of the program shutter using the shutter blades 1 and 2 that also serve as the aperture blades, the shutter blades 1 and 2 can be used until the shutter blades 1 and 2 reach the opening diameter.
Since the exposure amount per unit time increases with the opening of 2, the shutter blades 1 and 2 will be fully opened unless the charging current of the capacitor 37 is increased in accordance with the increase curve of the exposure amount per unit time. It is not possible to perform proper exposure control in the so-called triangular area up to. Then, as described above, the charging current of the capacitor 37 is controlled by the output level of the operational amplifier 33, and the voltage V ₂ and the bias voltage V ₁ determined corresponding to the brightness of the field are superimposed on the output of the operational amplifier 33. Since the level appears, if the bias voltage V _{1 is} determined according to the opening position of the shutter blades 1 and 2, the charging characteristics of the capacitor 37 can be made to follow the opening characteristics of the shutter blades 1 and 2. Appropriate exposure control can be performed even in a so-called triangular area until 2 is fully opened.

Therefore, in this embodiment, the bias voltage V ₁ is basically determined according to the film sensitivity, and the shutter blade 1
・ Shutter blades 1 and 2 in the triangular area until 2 is fully opened
The bias voltage V ₁ is corrected in accordance with the opening position of the shutter blades 1 and 2, and the bias voltage V ₁ is increased in accordance with the opening of the shutter blades 1 and 2, so that the charging characteristic of the capacitor 37 is added to the opening characteristic of the shutter blades 1 and 2. I am able to follow.

Therefore, in the following, the circuit for determining the bias voltage V ₁ and the shutter blade 1
A circuit for increasing the bias voltage V ₁ corresponding to the opening position 2 will be described.

First, since this embodiment assumes a camera compatible with DX film, the film sensitivity is input as an on / off pattern of the contact group 60 that contacts the conductive pattern provided on the cartridge, and this on / off pattern is set. The pattern is DX circuit 70
Is coded in and added to the arithmetic circuit 83.

Further, the opening positions of the shutter blades 1 and 2 are input by the photoelectric encoder 8.

More specifically, the light emitted from the light emitting diode which is an example of the light emitting element 8b passes through the light guide slit 8g, is reflected by the base plate 8d or the shutter blade 1, and is converted into a phototransistor which is an example of the light receiving element 8c. Reach And
Since the ground plate 8d and the shutter blade 1 have different reflectivities, the light receiving element 8c is formed every time the slit 8a crosses the light guide slit 8g.
The light energy incident on the fluctuates and is applied to the waveform shaping circuit 10 as the terminal level of the resistor R ₁ .

FIG. 5 shows a specific configuration example of the waveform shaping circuit 10. The terminal level of the resistor R ₁ is an operational amplifier after the dark current equivalent of the light receiving element 8c is removed by the DC cut capacitor 11.
It is amplified at 12 and applied to the inverting input of comparator 13. The power supply 14 is connected to the non-inverting input of the comparator 13.
Since the reference level is added from the comparator 13, and the comparator 13 compares the output of the operational amplifier 12 with the reference level to pulse, a pulse is generated from the comparator 13 every time the slit 8a passes through the light guide slit 8g. The pulse is applied to the clock terminal of counter 20
Will count up (or count down),
The opening positions of the shutter blades 1 and 2 are digitized as a count value of the counter 20 and added to the arithmetic circuit 83.

Then, the arithmetic circuit 83 performs arithmetic processing using the numerically apertured aperture positions of the shutter blades 1 and 2 and the film sensitivity as variables, and supplies the answer to the digital-analog conversion circuit 84 to perform digital-analog conversion. Circuit 84 converts this to a voltage to generate bias voltage V ₁ .

Although the specific contents of the calculation executed by the calculation circuit 83 differ depending on the characteristics of the photometric circuit 30 and other mechanical characteristics,
Since the higher the film sensitivity is, the higher the charging speed of the capacitor 37 needs to be, and the higher the count value of the counter 20 increases with the opening of the aperture 7, it is necessary to increase the charging speed of the capacitor 37. The film sensitivity information added from the DX circuit 70 may be multiplied by the count value of the counter 20, and this may be multiplied by a constant determined by the characteristics of the photometric circuit 30 and other mechanical characteristics.

 The contents of this calculation are shown in (Equation-1).

Solution = constant x (ISO / ISO100) x count value (Equation-1) By the way, as already explained, when the field brightness is low with respect to the film sensitivity, the shutter speed becomes slower than this value. When it becomes low, it is desirable to give a low brightness warning. In the present embodiment, the shutter speed is determined by the output level of the operational amplifier 33 which becomes the current supply level to the capacitor 37, and the output level of the operational amplifier 33 is the voltage of the log diode 32 which is determined corresponding to the field brightness as already described. Although it is determined by reflecting the drop V ₂ , the film sensitivity, and the bias voltage V ₁ that is determined corresponding to the shutter blade 1 and 2 opening position (that is, the count value of the counter 20), the half stroke of the shutter button (not shown) Sometimes the shutter blades 1 and 2 are completely closed and the count value of the counter 20 can be treated as a constant, so the bias voltage V ₁
Reflects only the film sensitivity, and therefore the output level of the operational amplifier 33 reflects only the film sensitivity and the field brightness. Then, the final shutter speed reflects the aperture characteristic of the shutter blades 1 and 2 introduced as the count value of the counter 20 in the output level of the operational amplifier 33 at this initial stage. Has a sufficient accuracy as a low-brightness warning even if some fluctuation is expected.

Therefore, in this embodiment, a low brightness warning is issued by a current comparator that compares the output current of the transistor 311 controlled by the output level of the operational amplifier 33 and the current value of the constant current source 313 during the half stroke of the shutter button. .

More specifically, the transistor 311 is connected between the current source 313 and the ground, and the output of the operational amplifier 33 is connected to the base of the transistor 311. Depending on the output level of the operational amplifier 33, the constant current source 313 causes the collector of the transistor 311 to operate. The amount of current injected between the emitters is controlled. Further, the base of the transistor 314 connected between the sequence circuit 50 and the ground is connected to the constant current source 313, and the current supply level to the base of the transistor 314 is the base of the transistor 312 having the base and emitter connected to function as a diode. -It is designed to be determined by the voltage between the emitters. Therefore, when the shutter button is half-stroked, if the amount of current flowing from the constant current source 313 to the transistor 311 is controlled by the output level of the operational amplifier 33 that changes in accordance with the film sensitivity and the field brightness, the constant current source 313 changes the transistor. The current supplied to the base of 314 is controlled to turn on / off the transistor 314, and the sequence circuit 50 monitors the on / off of the transistor 314 to know whether the shutter speed is above or below the handheld limit speed. I am doing it.

By the way, the guide number, which is a numerical value indicating the amount of strobe light emission, is defined as the product of the shooting distance and the F value when the film sensitivity is ISO 100, and when the film sensitivity is changed, the shooting distance is proportional to the square root of the film sensitivity ratio. .

Therefore, when using a strobe with a fixed guide number, the F value to be used is determined if the shooting distance and film sensitivity are determined, and if the strobe is synchronized at the timing when this F value is obtained, proper exposure can be obtained. Will be done.

In this embodiment, since the count value of the counter 20 indicates the F value, the film sensitivity information output by the DX circuit 70 and the shooting distance information output by the distance measuring circuit 90 are added to the arithmetic circuit 100.
In this arithmetic circuit 100, an F value for obtaining a proper exposure is calculated from the film sensitivity, the shooting distance, and the guide number, and is given to the digital comparator 110. In the digital comparator 110, the count output of the counter 20 matches the output of the arithmetic circuit 100. At this timing, a trigger pulse is applied to the EFU circuit 120 (abbreviation of electronics-flash-unit circuit, which is well known) to cause the strobe to emit light.

The arithmetic operation performed by the arithmetic circuit 100 is as follows
2).

However, in (Equation-2), F is an F value, GNo is a guide number, L is a shooting distance, and k is a constant determined by the characteristics of the shutter blades 1 and 2.

Further, the distance measuring circuit 90 may detect the amount of extension of the helicoid, or may use a distance measuring mechanism for autofocus using near infrared light, for example.

Next, the operation of this embodiment will be described with reference to the above items.

 First, the operation in the normal automatic exposure mode will be described.

In the initial state, the level of the signal applied by the sequence circuit 50 to the base of the transistor 41 constituting the drive circuit 40 is low, and the transistor 41 is cut off, so the solenoid 5 is demagnetized. Therefore, the blade opening / closing ring 3
Is rotated counterclockwise by the tension of spring 4,
3c is in contact with the stopper 6, and the pins 3a and 3b planted in the blade opening / closing ring 3 rotate the shutter blades 1 and 2 counterclockwise while locking the long grooves 1b and 2b, respectively. ,
The aperture 7 is closed by the shutter blades 1 and 2.

Further, in the initial state, the level of the signal applied to the base of the transistor 310 of the photometric circuit 30 by the sequence circuit 50 is also low, and the transistor 310 is conducting. Therefore, the terminal level of the capacitor 37 is pulled up to the power supply level, 37 is not charged.

When the power switch is turned on, the contact group 60 turns on and off according to the DX pattern marked on the film cartridge set, and the DX circuit 70 turns on and off the contact group 60.
The film sensitivity information that encodes the off pattern is generated, and this film sensitivity information is calculated by the arithmetic circuit 83 and the arithmetic circuit 100.
Is added to

The count value of the counter 20 is also added to the arithmetic circuit 83, and the arithmetic circuit 83 executes the arithmetic processing shown in (Equation-1) using the film sensitivity and the count value of the counter 20 as variables, and the digital-analog conversion circuit 84 The calculation result of the calculation circuit 83 is converted into a voltage to generate the bias voltage V _1. However, since the count value of the counter 20 can be regarded as a constant when the shutter button is half-stroked, the bias voltage V ₁ is only the film sensitivity. It will be reflected.

On the other hand, a photocurrent corresponding to the field brightness flows through the SPD 31 via the log diode 32, and a voltage drop V ₂ corresponding to this photocurrent occurs across the log diode 32. Is a level in which the voltage V ₁ that reflects only the film sensitivity and the voltage V ₂ that reflects the field brightness are superimposed. The final shutter speed reflects the aperture characteristic of the shutter blade 1 introduced as the count value of the counter 20 in the output level of the operational amplifier 33 at this initial stage, and the aperture characteristic of the shutter blade 1 is expected to vary slightly. However, it has sufficient accuracy as a low brightness warning.

Then, as described above, the amount of current supplied from the constant current source 313 to the collector-emitter of the transistor 311 is controlled in accordance with the output level of the operational amplifier 33.
At half-stroke of the shutter button, operational amplifier 33
When the output level of the constant current source 313 is lower than the level determined according to the handheld limit shutter speed, a part of the current of the constant current source 313 flows through the transistor 311 and the rest of the transistor 311 flows.
Since it flows to the base of 14, the transistor 314 becomes conductive. When the transistor 314 conducts, the sequence circuit 50 determines that the field brightness is low with respect to the film sensitivity, and issues a low brightness warning to the LED or the like in the finder (not shown).

If the output level of the operational amplifier 33 is higher than the level determined according to the handheld limit shutter speed during the half stroke of the shutter button, all the current of the constant current source 313 flows into the collector of the transistor 311 and the constant current flows. Source 3
Since no current is supplied from 13 to the base of the transistor 314, the transistor 314 is cut off. When the transistor 314 is cut off, the sequence circuit 50 determines that the field brightness is sufficient for the film sensitivity and does not issue the low brightness warning.

After that, when the shutter button is pressed and the release signal is applied to the sequence circuit 50, the sequence circuit 50
Sets the base input of the transistor 41 of the drive circuit 40 and the base input of the transistor 310 of the photometry circuit 30 to high level, respectively, and applies a drive voltage to the light emitting element 8b.

First, the transistor 41 becomes conductive when the base becomes high level, and the solenoid 5 is excited accordingly. Therefore, since the blade opening / closing ring 3 rotates clockwise against the tension of the spring 4, the pins 3a and 3b implanted in the blade opening / closing ring 3 lock the long grooves 1b and 2b, respectively, and the shutter blade 1・ Since 2 is rotated clockwise, shutter blade 1
In No. 2, the aperture 7 is opened with the characteristic shown by the curve a in FIG. 6, and the exposure to the film surface is started.

In FIG. 6, the horizontal axis represents the exposure time and the vertical axis represents F.
Indicates the value.

Further, in the photometric circuit 30, the base of the transistor 310 becomes high level, so that the transistor 310 is cut off and the capacitor 37 can be charged.

In the case of the program shutter of this type, the exposure amount per unit time fluctuates with the opening of the shutter blades 1 and 2 in the triangular area before reaching the opening aperture. It is required to correct the charging characteristics of.

Therefore, in the present embodiment, the opening position of the shutter blade 1 is digitized as the count value of the counter 20, and the bias voltage V ₁ is increased in accordance with the increase of the count value of the counter 20 to increase the charging speed of the capacitor 37. I have to.

More specifically, when the shutter blades 1 and 2 start opening the apertures 7 by rotating the blade opening / closing ring 3 clockwise as described above, the slit 8a formed in the shutter blade 1 becomes a light guide slit. Cross 8g sequentially. At this point in time, the sequence circuit 50 applies a drive voltage to the light emitting element 8b, so the light flux emitted from the light emitting element 8b passes through the light guide slit 8g and enters the light receiving element 8c, and the reflection of the shutter blades 1 occurs. Since the reflectance and the reflectance of the main plate 8d are different, the slit 8a is the light guide slit 8g.
The amount of light incident on the light-receiving element 8c changes every time it crosses, and the terminal level of the resistor R ₁ also changes. Then, the waveform shaping circuit 10 compares the terminal level of the resistor ₁ with the reference level, and FIG.
Generates a pulse as shown in. This pulse is counter 20
Is added to the counter 20 to count up,
The opening position of the shutter blade 1 is digitized as a count value of the counter 20, and the count value of the counter 20 is added to the arithmetic circuit 83.

Then, the arithmetic circuit 83 corresponds to the film sensitivity information added from the DX circuit 70 and the count value of the counter 20 (equation −
Since the calculation 1) is performed and the digital-analog conversion circuit 84 converts the calculation result of the calculation circuit 83 into the bias voltage V ₁ ,
The bias voltage V ₁ rises stepwise, and the output of the operational amplifier 33 is the bias voltage V ₁ superposed with the voltage drop V ₂ of the log diode 32 determined in accordance with the field brightness. The output level of 33 also increases stepwise as shown in FIG.

The capacitor 37 is charged by the current flowing between the collector and the emitter of the transistor 36,
Since the collector-emitter current of is controlled in accordance with the output level of the operational amplifier 33, the output level of the operational amplifier 33 increases stepwise with the opening of the shutter blades 1 and 2, and the capacitor 37 The charging speed also increases.

Then, the charge level of the capacitor 37 is compared with the comparator 38.
The output of comparator 38 is inverted when it matches the reference level applied to its non-inverting input.

And the sequence circuit 50 is thus the comparator
When the output of 38 is reversed, the base of the transistor 41 is dropped to a low level, the solenoid 5 is demagnetized, the blade opening / closing ring 3 is rotated counterclockwise by the tension of the spring 4, and the shutter blades 1 and 2 are apertured. 7 is closed to end the exposure operation.

At this time, the sequence circuit 50 drops the base level of the transistor 310 of the photometric circuit 30 and the drive voltage of the light emitting element 8b, so that the photometric circuit 30 and the encoder 8 also end their operations.

By the way, as described above, the shutter blades 1 and 2 open the apertures when the solenoid 5 is excited. However, the opening characteristics of the shutter blades 1 and 2 change with time, the camera position changes, or the electromagnetic field changes. In the case of a shutter, it is undeniable that there is a possibility of fluctuation due to fluctuations in the power supply voltage.

For example, assuming that the curve a already described with reference to FIG. 6 is the ideal aperture characteristic in the design of the shutter blades 1 and 2, the shutter blades 1 and 2 have the above-mentioned reasons.
It is fully conceivable that the aperture opens with the characteristic shown by the curve b in FIG.

In order to give a proper exposure to the film surface, it is required to stop the exposure when the integrated value of the exposure amount reaches a value determined corresponding to the film sensitivity, so that the shutter blades 1 and 2 are curved. When the aperture characteristic as shown by b is shown, proper exposure cannot be given unless the exposure time is made longer than that of the ideal aperture characteristic as shown by the curve a.

However, in this embodiment, since the actual aperture characteristic of the shutter blades 1 and 2 is fed back as the count value of the counter 20 to determine the bias voltage V ₁ , the film surface is changed by the variation of the aperture characteristic of the shutter blades 1 and 2. Even if the integral characteristic of the exposure amount with respect to fluctuates, the charging characteristic of the photometric circuit 30 can be made to follow the integral characteristic of the exposure amount with respect to the film surface, and even if the aperture characteristic of the shutter blades 1 and 2 fluctuates, it is accurate. It is possible to control the exposure.

That is, the waveform shaping circuit 10 generates a pulse with the opening of the shutter blades 1 and 2, and this pulse is applied to the counter 20 as a count-up clock.
The pulse generated by 10 corresponds to the actual opening position of the shutter blade 1, so that the shutter blade 1 is curved by the curve b in FIG.
When the aperture characteristic as shown in FIG.
As shown in (1), since a slightly delayed pulse is generated, the rate of increase of the count value of the counter 20 also decreases. Since the bias voltage V ₁ generated by the digital-analog conversion circuit 84 increases stepwise each time the counter 20 counts up, if the increase rate of the count value of the counter 20 decreases, the increase rate of the bias voltage V ₁ increases. Has dropped. Since the rising speed of the charging current of the capacitor 37 also decreases, the time required for the charging level of the capacitor 37 to match the reference level is also delayed, and the exposure time is extended.

As described above, in the present embodiment, even if the aperture characteristics of the shutter blades 1 and 2 change due to some cause, the charging characteristics of the photometric circuit also change in accordance with the change of the aperture characteristics. It becomes possible to give a proper exposure regardless of the variation of the aperture characteristic of No. 2.

 Next, the operation during flash photography will be described.

When the photographer specifies the strobe mode, the sequence circuit 50 operates the EFU circuit 120 to start charging the main capacitor (not shown).

At the same time, the sequence circuit 50 is a distance measuring circuit 90 and an arithmetic circuit 100.
And activates the digital comparator 110.

First, the distance measuring circuit 90 is activated to obtain the shooting distance information indicating the distance to the target object scene from the arithmetic circuit 100.
Give to. Further, the film sensitivity information is given from the DX circuit 70 to the arithmetic circuit 100.

Then, in the case of a strobe with a fixed guide number, the F value for obtaining the proper exposure is uniquely determined if the shooting distance and the film sensitivity are determined, so that the arithmetic circuit 100 uses the film sensitivity information and the shooting distance information ( The calculation shown in Expression-2) is performed to calculate F value information indicating an appropriate F value, and the F value information is given to the digital comparator 110.

When the photographer presses the shutter button after the charging of the EFU circuit 120 is completed, the shutter blades 1 and 2 open the aperture 7 in the same manner as in the case of normal photographing, and the shutter blade 1 corresponds to the opening position. The count value of the counter 20 is updated. Therefore, the count value of the counter 20 always has a one-to-one correspondence with the actual F value regardless of the opening characteristics of the shutter blades. Therefore, if the count value of the counter 20 is compared with the F value information generated by the arithmetic circuit 100 by the digital comparator 110, and the digital comparator 110 gives a trigger signal to the EFU circuit 120 at the timing when the two coincide with each other, an appropriate F value is obtained. The strobe can be tuned at the obtained timing.

The trigger signal generated by the digital comparator 110 at this time is given to the sequence circuit 50, and the sequence circuit 50 stops the exposure operation by this trigger signal.

As a case of using a strobe, in addition to the case of using as a main light source when the field brightness is low as described above,
It may be used as an auxiliary light source for matching the brightness ratio of the field and the exposure area of the film as in the so-called daytime synchro.

And in this case, if the background is bright enough,
When the output of the comparator 38 is inverted at the timing when the proper exposure is given to the background, the output of the comparator 38 is given to the EFU circuit 120 as a trigger signal via the OR gate 130 to cause the strobe to emit light, so that the background is exposed. It will never be over.

Although the example in which the current comparator gives a low-brightness warning has been described above, it is also possible to compare the output levels of the operational amplifier 33.

〔effect〕

As described above, according to the present invention, the charging characteristic of the photometric circuit can be changed in accordance with the opening position of the shutter blade, so that the degree of freedom in the location of the light receiving element for photometry and the overall design The degree of freedom in design can be significantly improved.

Further, in the case of the present invention, since the actual opening position of the shutter blade is detected and the charging characteristic of the photometric circuit is changed, the opening characteristic of the shutter blade may change with time, the fluctuation of the power supply voltage, the change of the photographing attitude, or the like. Even if it fluctuates, the charging characteristic of the photometric circuit follows the fluctuation of the opening characteristic of the shutter blade, so that accurate exposure control can be performed.

Further, in the present invention, the output level of the operational amplifier 33, which is the current supply level to the capacitor 37, reflects only the film sensitivity and the field brightness at the half stroke of the shutter button, so that the dedicated circuit of the operational amplifier 33 is not provided. The output makes it possible to give a low brightness warning.

Further, according to the present invention, since the opening position of the shutter blade is digitized as the count value of the counter, it becomes easy to introduce a microcomputer which has become particularly popular in recent years.

Further, in the present invention, since the count value of the counter has a one-to-one correspondence with the F value at that time, it can be used as a criterion for determining the strobe synchronization timing in the flashmatic mode, and the opening position of the shutter blade can be used. It is possible to perform accurate exposure control in the flashmatic mode without separately providing a limiting mechanism.

Further, if the stroboscopic photographing mode is automatically selected when a low-brightness warning should be issued in the viewfinder, it is possible to prevent accidental camera shake.

[Brief description of drawings]

FIG. 1 is a mechanical view of a shutter mechanism according to an embodiment of the present invention, FIG. 2 is an enlarged view of a main part of FIG. 1, FIG. 3 is a sectional view taken along line A of FIG. 1 and FIG. FIG. 6 is a circuit diagram of one embodiment of the present invention, FIG. 5 is a circuit diagram showing a circuit example of a waveform shaping circuit, and FIG.
FIG. 7 is an aperture characteristic diagram of the shutter mechanism shown in FIG. 1, FIG. 7 is a characteristic diagram showing an output pulse of a waveform shaping circuit, FIG. 8 is a characteristic diagram showing an output waveform of a digital-analog conversion circuit, and FIG.
The figure shows the aperture characteristics of a general program shutter. 1, 2 ... Shutter blade, 5 ... Solenoid 8 ... Encoder, 8f ... Light guide 8g ... Light guide slit 20 ... Counter, 30 ... Photometric circuit 31 ... SPD, 35 ... Transistor 37 ... Capacitor, 311 ... Transistor 312 ... Transistor, 313 … Constant current source 314… Transistor, 83… Arithmetic circuit 84… Digital-analog conversion circuit

Claims (1)

[Claims] 1. A shutter blade that also serves as a diaphragm blade that continuously opens up to a maximum aperture, a light-receiving element whose exposure area to the field light is not affected by the opening position of the shutter blade, and a light-receiving element. Logarithmic compression means for logarithmically compressing the photocurrent flowing in accordance with the quantity, an integration circuit for integrating the current obtained by logarithmically expanding the output of the logarithmic compression means, and when the integrated value of the integration circuit reaches a predetermined value, In an exposure control device each comprising shutter closing means for closing the shutter blade, a recognizable identification mark arranged in a line on the operation line of the shutter blade, and the shutter blade of the shutter blade which is continuously changed by reading the identification mark. The blade position detecting means for detecting the position, the film sensitivity input means for inputting the film sensitivity, and the voltage corresponding to the blade position detected by the blade position detecting means The bias voltage generating means for applying the level corrected by the film sensitivity input from the film sensitivity input means to the logarithmic compression means as a bias voltage, and the output level of the logarithmic compression means at the timing before the opening operation of the shutter blades. An exposure control device comprising: a low-brightness warning means for issuing a low-brightness warning.