JPH0435863Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an exposure control device in a so-called program shutter using shutter blades that also serve as aperture blades.

[Conventional technology]

The purpose of exposure control in still cameras is to give the photosensitive surface an amount of light that is determined according to its sensitivity. When a value is specified, the shutter speed is controlled according to the field brightness, and conversely, when the shutter speed is specified, the aperture value is controlled according to the field brightness to give the appropriate exposure. can.

However, in order to perform such exposure control, it is necessary to provide an aperture blade, a shutter blade (or shutter curtain), and a drive mechanism for each independently.
Mechanical members become expensive, and the expensive mechanism cannot be used effectively unless one has specialized knowledge regarding the aperture effect and shutter effect on drawings.

Therefore, so-called compact cameras have conventionally used a program shutter that uses shutter blades that also serve as aperture blades.

In this type of program shutter, at the same time as the exposure operation starts, the shutter blades that also serve as aperture blades open in a linear approximation as shown in Figure 6, and in conjunction with this, the integrating circuit is charged by the photocurrent flowing to the light receiving element. When the integral value reaches a predetermined level, the shutter blades that also serve as aperture blades are instantly closed and the exposure operation is completed. Therefore, when the field brightness is low, it takes longer for the integral value to reach a predetermined level, so the effective exposure time becomes longer and the aperture also becomes larger; conversely, when the field brightness is high, Since the time required for the integral to reach a predetermined level is shorter, the effective exposure time is also shorter and the aperture is smaller. and,
Various types of light-receiving elements are known, but
SPDs have been widely used in recent years because of their excellent responsiveness, especially in low-luminance areas.

By the way, in the case of such a program shutter that uses shutter blades that also serve as aperture blades, the exposure amount becomes proportional to the exposure time after reaching the full aperture, and in the so-called triangular region before the full aperture, the shutter blade becomes proportional to the exposure time. As the aperture increases, the amount of exposure per unit time increases moment by moment, so the γ value (in addition, γ
The value is one of the numerical values indicating the characteristics of the light receiving element.
In the case of a photovoltaic element, it refers to the value of γ when the photocurrent is proportional to the field brightness raised to the γ power. ) is 1, in addition to the opening of the shutter blade,
Appropriate exposure control cannot be performed unless the photocurrent for charging the integrating circuit is increased.

Therefore, conventionally, a sub-diaphragm blade that opens and closes in conjunction with the shutter blade is placed in front of the light-receiving surface of the light-receiving element, and by increasing the light-receiving area of the light-receiving element in conjunction with the opening of the shutter blade, the shutter blade The photocurrent was increased in conjunction with the aperture.

[Problem that the invention attempts to solve]

However, when sub-diaphragm blades are used in this way, there are many restrictions on the placement of the light-receiving element due to the need to place the photo-detector near the shutter mechanism, and the shape of the shutter blade itself is also affected due to the need to form the sub-diaphragm blade. The problem is that it gets bigger,
In particular, this was one of the reasons preventing the adoption of large-diameter lenses.

[Means for solving problems]

The present invention was made to solve these problems, and is a novel exposure method that makes it possible to control the charging current of the integrating circuit for exposure control by adapting it to the characteristics of the shutter blade without using a sub-diaphragm blade. The purpose is to provide a control device.

In summary, the exposure control device of the present invention controls the charging current of a capacitor by using a level determined corresponding to the field brightness as the current supply level, and determines the timing when the charging level of the capacitor reaches a predetermined level. In the exposure control device for a programmed shutter, which closes a shutter blade that also serves as an aperture blade, a level that increases in conjunction with the opening of the shutter blade that also serves as an aperture blade is superimposed on the current supply level, and the charging current is designed to approximate the aperture characteristics of the shutter blades that also serve as aperture blades.

[Effect]

Therefore, according to the present invention, at any point in the exposure operation, the integral value of the exposure amount to the photosensitive surface and the integral value of the charging current to the capacitor are approximate, making it possible to perform accurate exposure control. become.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the drawings.

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

In FIG. 1, 1 and 2 indicate shutter blades that also serve as aperture blades, and the shutter blades 1 and 2
are rotatably supported on shafts 1a and 2a, respectively. Further, 3 indicates a blade opening/closing ring which is rotatably held around the optical axis, and the blade opening/closing ring 3 is always urged counterclockwise by a spring 4 and is implanted in the blade opening/closing ring 3. pins 3a, 3
b denotes a long groove 1 formed in each of the shutter blades 1 and 2;
b, 2b. Further, 5 indicates a solenoid, which is an example of an actuator for rotating the blade opening/closing lever 3 clockwise.

To explain its operation, first, in the initial state, the solenoid 5 is demagnetized and the blade opening/closing ring 3 is biased counterclockwise by the 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 energized 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. rotate clockwise around the shafts 1a and 2a to gradually open the aperture 7, and when the pawl 3d of the blade opening/closing ring 3 comes into contact with the stopper 6, the aperture 7 becomes an open diameter. . Then, when the solenoid 5 is demagnetized at the timing when 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 and perform the exposure operation. end.

Note that 22 is a switch for detecting the opening operation, and the switch 22 is opened by rotating the blade opening/closing ring 3 clockwise.

In such a shutter mechanism, the shutter blades 1 and 2 open in a straight line approximation as shown in FIG. 6 due to the urging force of the solenoid 5, so in the so-called triangular area when the opening diameter is reached, the opening of the shutter blades 1 and 2 It is required to adapt the charging characteristics of the exposure control integrating circuit to the aperture characteristics of the shutter blades 1 and 2 by correcting the charging current of the exposure control integrating circuit in accordance with the characteristics.

FIG. 2 is a circuit diagram showing one embodiment of the present invention, in which the charging characteristics of the integrating circuit can be adapted to the opening characteristics of the shutter blades 1 and 2.

First, in FIG. 2, numeral 10 indicates an SPD which is an example of a light receiving element, and the SPD 10 is placed directly facing the field of view. The SPD 10 has its cathode side connected to the inverting input terminal of the operational amplifier 11, and its anode side connected to the non-inverting input terminal of the operational amplifier 11, and the output of the operational amplifier 11 is connected to the log diode 12.
The signal is fed back to the inverting input of the operational amplifier 11 via. When light corresponding to the field brightness enters the SPD 10, a photocurrent corresponding to the field brightness enters the SPD 10 through the log diode 12.
The photocurrent flows in the opposite direction through the photocurrent, and a voltage drop V ₂ corresponding to the photocurrent occurs between both terminals of the log diode 12.

Therefore, if the input level of the operational amplifier 11 is V ₁ , the output of the operational amplifier 11 has the input level
A level obtained by superimposing the voltage drop V ₂ due to the log diode 12 on V ₁ is derived.

The output of the operational amplifier 11 is connected to the base of a logarithmic expansion transistor TR ₁ connected in series with a capacitor 13 between the power supply and ground.
The base-emitter current of the transistor _TR1 is controlled by using the output level of the operational amplifier 11 as a current supply level, and the capacitor 13 is charged by the collector-emitter current of the transistor _TR1 .

Also, the charge level of capacitor 13 is applied to the non-inverting input of comparator 14,
A reference level is applied to the inverting input of the comparator 14, and the output of the comparator 14 is connected to the driving solenoid 5 and the power supply shown in FIG. ₁ via the resistor R1.
It is connected to the base of the transistor TR ₂ , which is connected in series between the ground.

Note that the transistor TR ₃ connected in parallel with the capacitor 13 is for short-circuiting the capacitor 13, and when the transistor TR ₃ is cut off, the charging operation of the capacitor 13 is started.

Therefore, when the transistor TR ₃ is cut off and charging of the capacitor 13 is started, and the charging level of the capacitor 13 becomes lower than the reference level Vref applied to the inverting input of the comparator 14, the output of the comparator 14 becomes a low level. As a result, the transistor TR ₂ is cut off and the solenoid 5 is demagnetized, so the blade opening/closing ring 3 is rotated counterclockwise by the tension of the spring 4, and the shutter blades 1,
2 is also rotated counterclockwise to complete the exposure operation.

In the exposure control device having this basic structure, the capacitor 13 is charged by the collector-emitter current of the transistor _TR1 , and the collector-emitter current of the transistor _TR1 is controlled using the output level of the operational amplifier 11 as the current supply level.

The output of the operational amplifier 11 is the voltage drop of the log diode 12 due to the photocurrent flowing to the SPD 10.
Since the input voltage V ₁ of the operational amplifier 11 is superimposed on V ₂ , the input voltage to the operational amplifier 11 is adjusted to match the aperture characteristics of the shutter blades 1 and 2.
By determining V ₁ , it becomes possible to adapt the charging current of the capacitor 13 to the aperture characteristics of the shutter blades 1 and 2.

Therefore, in this embodiment, the input voltage V 1 to the operational amplifier 11 is increased in conjunction with the opening of the shutter blades 1 and 2 which also serve as aperture blades, and the input voltage V ₁ to the operational amplifier 11 is increased.
The charging current of the capacitor 13 flowing through the TR ₁ is made to approximate the opening characteristics of the shutter blades 1 and 2.

First, in FIG. 2, the output of a buffer 15 with a gain of 1 is added to the input of the operational amplifier 11, and the non-inverting input level of the buffer 15 is applied to the input of the operational amplifier 11.
Determined by the charge level. This capacitor 16 is connected in parallel with a bypass variable resistor 17 and a switching transistor TR ₄ , and current is supplied from a constant current source 18 to this parallel circuit.

To explain the outline of its operation, the capacitor 16 is charged from an initial state of 0 charge in conjunction with the opening of the shutter blades 1 and 2, and the charge level of the capacitor 16 is changed to the operational amplifier 1 through the buffer 15.
1 to determine the current supply level of the transistor TR ₁ , and the charging current of the capacitor 13 can be approximated to the aperture characteristics of the shutter blades 1 and 2 by logarithmic expansion by the transistor TR ₁ .

A switch 19 is linked to the shutter release operation, and is used to excite the solenoid 5 by making a shutter stroke or the like by the photographer. Further, 23 is a flip-flop for determining the base level of the transistor TR ₄ and the transistor TR ₅ to cause the transistor TR ₄ and the transistor TR ₅ to perform switching operations, and the flip-flop 23 normally receives a power clear signal.
Although cleared by the PUC, the switch 22 is activated in conjunction with the clockwise rotation of the blade opening/closing ring 3.
is set to cut off transistor _TR4 and transistor _TR5 .

Next, the operation of this embodiment will be explained with reference to the above matters.

First, in the initial state, the switch 22 is broken and the output of the flip-flop 23 is at a high level, so the bases of the transistors TR ₄ and TR ₅ are pulled up through the resistors 20 and 21, respectively, and are made conductive. There is.
When the transistor TR ₄ becomes conductive, the capacitor 16 is short-circuited and has an initial charge of 0, and when the transistor TR ₅ becomes conductive, the transistor TR ₃ also becomes conductive, and the capacitor 13
The terminal level of is set to the power supply level.

At the same time, in the initial state, the switch 19 is also broken and the solenoid 5 is demagnetized, so the blade opening/closing ring 3 in FIG. The shutter blades 1 and 2 are stopped at a position where they are in contact with the shutter blades 1 and 2, and the shutter blades 1 and 2 close the aperture 7.

Now, when the photographer presses the shutter button in this state, the switch 19 is activated. At this point, the terminal level of the capacitor 13 is at the power supply level, so the output of the comparator 14 is at a high level, the transistor TR ₂ is conductive, and the solenoid 5 is energized.

When the solenoid 5 is energized in this manner, the blade opening/closing ring 3 rotates clockwise against the tension of the spring 4, and the shutter blades 1 and 2 are rotated around the shaft 1a.
As the aperture 7 is rotated clockwise around 2a, the aperture 7 opens.

Exposure is given to the film surface as the aperture 7 opens. At this time, the aperture 7 opens with the characteristic of linear approximation as shown in Fig. 6, so the amount of exposure per unit time is equal to the opening diameter. Until the maximum aperture is reached, the amount of exposure increases over time, and after the maximum aperture is reached, the amount of exposure per unit time remains constant as long as the brightness of the field remains constant.

Also, as the blade opening/closing ring 3 rotates clockwise, the switch 22 is closed and the flip-flop 2 is closed.
3 is set, so the output of flip-flop 23 becomes low level. Therefore, the transistor
TR ₄ and transistor TR ₅ each have their bases grounded and are cut off.

First, when the transistor TR ₅ is cut off, the base of the transistor TR ₃ also goes high and is cut off, allowing the capacitor 13 to be charged. And since the light receiving surface of SPD10 is always open,
A photocurrent corresponding to the field brightness flows through the SPD 10 via the log diode 12, and the operational amplifier 11
The output of the log diode 12 is caused by this photocurrent.
A level is obtained by superimposing the voltage drop V ₂ of V 2 and the input voltage V ₁ of the operational amplifier 11, and the output level of the operational amplifier 11 is set as the current supply level to the transistor.
A collector-emitter current flows through TR ₁ , and this collector-emitter current causes the capacitor 13 to
is being charged.

On the other hand, when the transistor TR ₄ is cut off, the constant current source 18 starts charging the capacitor 16, and its charge level increases. However, as the charge level of the capacitor 16 increases, the voltage across the terminals of the variable resistor 17 Also, the component flowing to the variable resistor 17 of the current supplied from the constant current source 18 increases, so the amount of charge injected into the capacitor 16 per unit time decreases as the charge level of the capacitor 16 increases. However, the rate of increase in the charge level of the capacitor 16 decreases as the charge level of the capacitor 16 increases. When the charge level of the capacitor 16 reaches a certain value, the amount of current flowing out from the variable resistor 17 due to the voltage applied to the variable resistor 17 matches the amount of current supplied from the constant current source 18, and at that point, the capacitor The charge level of 16 is stable.

The charge level of this capacitor 16 is 1
5 to the input of the operational amplifier 11, the input level of the operational amplifier 11 draws a curve as shown in FIG. As mentioned above, the output of the operational amplifier 11 is led to a level obtained by superimposing the voltage drop V ₂ of the log diode 12 determined according to the field brightness on the input voltage V ₁ , and the current of the transistor TR ₁ is Determine supply levels.

Since the transistor TR ₁ expands this logarithmically, the collector-emitter current of the transistor TR ₁ draws a curve as shown in Fig. 4, which approximates the aperture characteristics of the shutter blades 1 and 2 shown in Fig. 6. becomes.

Since the capacitor 13 is charged by the collector-emitter current of the transistor _TR1 , the charge level of the capacitor 13 draws a curve as shown in FIG. Then, at the timing when the charge level of the capacitor 13 falls below the reference level Vref applied to the inverting input of the comparator 14, the output of the comparator 14 becomes low level and the transistor TR ₂ is cut off, so the solenoid 5 is demagnetized. , vane opening/closing ring 3 in Fig. 1
is rotated counterclockwise by the tension of the spring 4, the shutter blades 1 and 2 close the aperture 7, and the exposure operation is completed.

As already explained, the exposure to the film surface is the integral value of the amount of light passing through the aperture 7,
The amount of light passing through the aperture 7 at a certain point in time is determined by the aperture characteristics of the shutter blades 1 and 2. On the other hand, since the charging level of the capacitor 13 is the integral value of the charging current to the capacitor 13, if the charging current to the capacitor 13 is approximated to the aperture characteristics of the shutter blades 1 and 2 as described above, then The integral value of the exposure amount corresponds to the charge level of the capacitor 13, and if the exposure operation is terminated when the charge level of the capacitor 13 reaches a predetermined value, it will remain constant with respect to the film surface regardless of the height of the field brightness. can give exposure to

In addition, when the film sensitivity is changed, the required exposure amount changes, but in this case, the variable resistor 17
This can be easily handled by adjusting the current value according to the film sensitivity or by varying the current value of the constant current source 18.

Further, when it is necessary to stabilize the opening characteristics of the shutter blades 1 and 2, a governor or the like may be added to the drive mechanism member.

〔effect〕

As explained above, according to the present invention, the charging current of the integrating circuit for exposure control can be approximated to the aperture characteristics of the shutter blade that also serves as the aperture blade.
It is possible to approximate the integral value of the exposure amount to the photosensitive surface and the integral value of the charging current to the capacitor at any point in the exposure operation without providing a member that mechanically varies the photocurrent such as a sub-diaphragm blade. This makes it possible to perform accurate exposure control.

Furthermore, by eliminating the need for sub-diaphragm blades, there are no restrictions on where the light-receiving element can be placed, and it is also easier to set the light-receiving angle of the light-receiving element to match the angle of view of the photographic lens. , more appropriate exposure control becomes possible.

Furthermore, by eliminating the need for sub-diaphragm blades, it becomes easier to increase the effective area of the shutter blades and aperture, and it becomes easier to use a large-diameter lens.

[Brief explanation of the drawing]

Figure 1 is a mechanical diagram showing an example of a program shutter using shutter blades that also serve as aperture blades.
The figure is a circuit diagram showing one embodiment of the present invention, Figure 3 is a characteristic diagram showing the change over time of the input voltage of the operational amplifier linked to the light receiving element, and Figure 4 is the change over time of the charging current of the integrating circuit for exposure control. Figure 5 is a characteristic diagram showing the change in charge level of the integrating circuit for exposure control over time. Figure 6 is the change in aperture over time of a program shutter using shutter blades that also serve as aperture blades. Characteristic diagram showing. 1, 2...Shaft blade, 5...Solenoid,
7... Aperture, 10... Light receiving element, 11...
...Operational amplifier, 12...Log diode, 13...
...Capacitor, 14...Comparator, 15...
Buffer, 16... Capacitor, 17... Variable resistor, 18... Constant current source, TR ₁ , TR ₂ , TR ₃ ,
TR ₄ , TR ₅ ...transistors.

Claims (1)

[Claims for Utility Model Registration] A light-receiving element that receives field light, and a photocurrent flowing through the light-receiving element corresponding to field brightness is logarithmically compressed, and the voltage obtained by this logarithmic compression is used as a bias voltage. an amplification means for outputting a superimposed voltage on the output voltage; a logarithmic expansion means for logarithmically expanding the output voltage of the amplification means; and a logarithmic expansion means for integrating the current supplied from the logarithm expansion means in conjunction with the opening operation of a shutter blade that also serves as an aperture blade. A program shutter comprising: a received light amount integrating means; and a comparing means that compares the output voltage of the received light amount integrating means with a reference voltage and generates a closing signal to close the shutter blade that also serves as an aperture blade at a timing when both voltages match. The exposure control device includes a parallel circuit of a capacitor and a resistor, a constant current source circuit that supplies a constant current to the parallel circuit in conjunction with the opening operation of the shutter blade that also serves as an aperture blade, and the amplification of the terminal voltage of the capacitor. and a voltage output circuit for applying a bias voltage to the device, the current flowing through the resistor due to the terminal voltage of the capacitor is substantially equal to the current supplied by the constant current source circuit. The exposure control device is characterized in that the time required for the shutter blade to fully open is made substantially equal to the time required for the shutter blade that also serves as an aperture blade to fully open.