In a shutter operating circuit wherein the shutter time is controlled by a photoelectric transducer disposed to receive the light transmitting through the objective lens, there are provided a first amplifier for amplifying the output from the photoelectric transducer, a second amplifier having a high input impedance and operating to generate an output corresponding to the output from the first amplifier, means for feeding back the output from the second amplifier to the input of the first amplifier, a capacitor connected on the input side of the second amplifier for holding the output from the first amplifier in accordance with the opening operation of the shutter of the camera, a first impedance element connected in series with the photoelectric transducer, a second impedance element connected in parallel with the series combination of the first impedance element and the photoelectric transducer, an integrating capacitor for integrating the output from the second amplifier in accordance with the opening operation of the shutter, and a shutter trigger circuit for closing the shutter when the voltage across the integrating capacitor reaches a predetermined valve value whereby the exposure time is determined by the output current from the second amplifier.
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1. A shutter operating circuit for a photographic camera, comprising a photoelectric transducer disposed to receive the light transmitting transmitted through the objective lens of said camera, first amplifier means for amplifying the output from said photoelectric transducer, second amplifier means having a high input impedance and operating to generate an output corresponding to the output from said first amplifier means, means for feeding back the output from said second amplifier means to the input of said first amplifier means, a capacitor connected on the input side of said second amplifier means for holding the output from said second amplifier means in accordance with the opening operation of the shutter of said camera, a first impedance element connected in series with said photoelectric transducer, a second impedance element connected in parallel with said series combination of said first impedance element and said photoelectric transducer, an integrating capacitor for integrating the output from said second amplifier means in accordance with the opening operation of said shutter, and a shutter trigger circuit for closing said shutter when upon the voltage across said integrating capacitor reaches reaching a predetermined value whereby the exposure time is determined by the output current from said second amplifier means which and is proportional to the output from said photoelectric transducer and varied by utilizing the impedances of said first and second impedance elements as parameters.
6. A shutter operating circuit for a photographic camera, comprising a photoelectric transducer disposed to receive the light transmitting transmitted through the objective lens of said camera for producing an output corresponding to the intensity of said light, an operational amplifier having a high input impedance and having said photoelectric transducer connected to the input thereof for amplifying said output, a feedback circuit for feeding back the output of said operational amplifier to the input thereof, an integrating capacitor connected in said feedback circuit for integrating the output from said operational amplifier in an interlocked relation with the opening operation of the shutter of said camera, a first impedance element having an impedance z1 connected in series with said photoelectric transducer to the input of said operational amplifier, a second impedance element having an impedance z2 connected in parallel with the series combination of said photoelectric transducer and said first impedance element said first and second impedance elements being included in and comprising a part of the load on said feedback circuit, and a shutter trigger circuit connected to said integrating capacitor for closing said shutter when the voltage across said integrating capacitor reaches a predetermined value whereby thereby to determine the exposure time in accordance with the output feedback current from said operational amplifier which is proportional to the output of said photoelectric transducer in accordance with the expression ##EQU22## where If is the feedback current of the operational amplifier and IL is the photocurrent of the photoelectric transducer and wherein the exposure time is varied dynamically by utilizing the impedances of said first and second impedance elements as the parameters. in the feedback circuit and the accuracy of setting the exposure time in dark areas is improved.
2. The shutter operating circuit according to
3. The shutter operating circuit according to
4. The shutter operating circuit according to
5. The shutter operating circuit according to
7. The shutter control circuit according to claim 5 6 wherein said first and second impedance elements comprise diodes having substantially the same characteristic.
8. The shutter control circuit according to claim 5 6 wherein said first and second impedance elements comprise resistors having substantially the same characteristic.
9. The shutter control circuit according to
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This invention relates to an electric shutter operating circuit E via resistors R10 and R11, respectively and switch SW4. A ninth transistor T9 is provided with its base electrode connected to the drain electrode of the field effect transistor T8 and the collector electrode connected to the movable contact of the transfer switch SW2, thus constituting the amplifier A2 shown in FIG. 1.
When the source switch SW4 is closed the fourth and fifth transistors T4 and T5 constituting the differential amplifier A1 shown in FIG. 1 are connected across the source E. Under these conditions, when the light from an object is projected upon the photocell SC, the photocell produces an output corresponding to the brightness of the object. Since the photocell is connected across the gate electrodes of the fourth and fifth transistors T4 and T5 these transistors produce on their outputs an output voltage corresponding to the output of the photocell SC. After being amplified by transistor T7, the output from the fourth and fifth transistors T4 and T5 is applied to the gate electrode of the field effect transistor T8 via switch SW1, now in the closed state. Since current holding capacitor C1 is connected between the gate electrode of transistor T8 and the ground, all signals supplied to this transistor via switch SW1 are stored in capacitor C1.
The signal supplied to transistor T8 is amplified by transistors T8 and T9 and is then applied to the juncture between impedance elements Z1 and Z2. Consequently, the circuit constructed as described above operates as a negative feedback circuit and the circuit will be balanced when the negative feedback signal reaches a value sufficient to cancel the terminal voltage across the photocell SC. As a consequence, under the balanced condition, the output from transistor T7, that is the negative feedback current assumes a value corresponding to the quantity of the light impinging upon the photocell. When the circuit is balanced at which the terminal voltage across the photocell SC is nearly zero volt, there is no adverse effect caused by the dark current of the photocell.
Substantially concurrently with the operation of the front diaphragm of the shutter, switches SW1, SW2 and SW3 are changed over, that is switches SW1 and SW3 are opened and switch SW2 is thrown to the left hand contact so that the current holding capacitor C1 continues to hold the condition existed before opening of the switch SW1 because the input impedance of transistor T8 is extremely high. As a consequence, the outputs of transistors T8 and T9 are maintained substantially at the same values as those provided before opening of the switch SW1. Since switch SW3 is now opened, the output of the transistor T9, that is the feedback current is supplied to the integrating capacitor C2 to gradually charge the same. When the terminal voltage across integrating capacitor C2 reaches the threshold level of transistor T1, this transistor is turned ON. Then transistors T2 and T3 connected to receive the output from transistor T1 are turned ON and OFF, respectively, whereby the rear diaphragm of the shutter which has been held by electromagnet M is operated to close the shutter. The interval between the operations of the front and rear diaphragms of the shutter, that is the charging time of the integrating capacitor C2, represents the shutter time. As it is possible to adjust the threshold level of transistor T1 by varying the variable resistor R1, it is advantageous to vary this resistor R1 in accordance with the sensitivity of the film used.
In this manner, the disclosed shutter operating circuit provides a correct shutter time corresponding to the quantity of light received by the photoelectric element without any trouble caused by the time lag of the photoelectric element at the time of quick variation of the light and by the dark current of the photoelectric element. Transistor T6 is effective to stabilize the circuit operation by improving the percentage of removing the in-phase component of the differential amplifier A1, while diodes D1 and D2 function to compensate for the temperature characteristic of transistor T6 acting as a constant current source and for the voltage variation of the source.
FIG. 3 shows another embodiment of this invention in which the same or corresponding elements to those shown in FIG. 2 are designated by the same reference charactors. In the modification shown in FIG. 3, diodes D3 and D4 are substituted for the impedance elements Z1 and Z2 utilized in the embodiment shown in FIG. 2, and tenth and eleventh transistors T10 and T11 are provided to form a constant voltage circuit. Furthermore, variable resistors VR1 through VR6 VR5 are provided to set such informations as the ASA sensitivity of the photographic film used, and the iris opening at the time of measuring light. Further, resistors R11 through R20 and switches SW5, SW6 and SW7 are connected as shown.
In operation, when switch SW5 is closed, photocell SC produces a photocurrent LL proportional to the quantity of light received, thereby to produce a voltage drop E1 across diode D3. When the characteristic of diode D3 is expressed by an equation Id= Is·exp(qE1 /kT) where Id represents a current flowing through the diode D3, Is the saturation current thereof, q the electric charge of an electron, E the terminal voltage across the diode D3, K the Boltzman's constant and T the absolute temperature (° K.) since Id= IL, the photocurrent IL is expressed by IL = Is·exp(qE1 /rT). Accordingly, the voltage drop across diode D3 is expressed by ##EQU4## A voltage expressed by an equation E2 = (KT/q)ln 2n is impressed upon the cathode electrode of diode D3. Since the terminal voltage of the photocell SC is set to be substantially zero volt by the balancing operation of the negative feedback circuit described above, the voltage E3 impressed across diode D4 is equal to (E1 + E2), namely ##EQU5## In this example, resistor VR1 is used to set an information regarding iris opening, resistor VR2 is used to set informations information regarding ASA sensitivity and manual shutter, resistor VR4 is used to automatically adjust the sensitivity of the circuit, and resistor VR3 to manually adjust the shutter. Resistors VR1 through VR5 are of the same type and switches SW6 and SW7 are thrown to their stationary contacts a for automatic operation. Accordingly, at the time of automatic operation, 1/3 of the voltages across resistors VR1 and VR2 is impressed upon the cathode electrode of the photocell SC. Under these conditions, in order to avoide avoid errors in various informations regarding ASA sensitivity and iris opening, it is necessary to set these resistors at low values.
As describe described above, since voltage drop E is created across diode D4 as has been pointed out herein above, if the characteristics of diodes D3 and D4 were identical. The current I2 flowing through diode D4 could be expressed as follows: ##EQU6##
At this time, when a voltage expressed by ##EQU7## is impressed upon the cathode electrode of the photocell SC, a current 2n will be produced on the output. Accordingly, even when the sum of three voltages, that is n= ASA information + iris opening information + sensitivity adjustment is impressed, since the resistors impressed with these voltages may be constructed to vary linearly their resistances, it is possible to readily set a large number of informations. Where n is selected such that 2n > 1, the collector current I0 of transistor T9 is nearly equal to I2, so that when switch SW1 is turned OFF and switch SW2 is transferred to stationary contact b, the time required by the voltage across the integrating capacitor C2 to reach the threshold level of the shutter trigger circuit ST is expressed by the following equation ##EQU8## where C2 represents the capacitance of capacitor C2. Thus, a condition wherein IL ·T1 that is the light quantity, is constant is fulfilled.
In the embodiment shown in FIG. 2, it is also possible to give an information by impressing a voltage E= A22 (where n= 1, 2. . .) upon the cathode electrode of photocell SC. Further, the transistors which constitute the differential amplifier should operate with a base or gate current which is sufficiently smaller than the photocurrent produced by the photocell. Where MOSFETs are used their gate leakage current is smaller than 10 PA so that such gate leakage current is negligible. The type of the amplifiers included in the succeeding stages is determined depending upon the capacitance of the current holding capacitor and the time required for storing. If a high degree of accuracy is desired, MOSFFT is preferred.
As described above, the invention provides a novel shutter operating circuit capable of using a photocell as a light receiving element without being adversely effected by the dark current of the photocell thus eliminating the problem of time lag which has been inevitable in the prior art shutter operating circuit when the high quantity varies quickly.
Further, the novel shutter operating circuit of this invention permits ready setting of informations information regarding ASA sensitivity, iris opening or the like and the resistors utilized to set such informations information may be resistors which vary their resistances linearly so that it is possible to readily set a large number of informations. As a differential amplifier having an extremely high input impedance is used as the first amplifier, it is possible to make effective use of the characteristic of the photocell and to greatly simplify the circuit construction.
In the following modified embodiments an operation operational amplifier is substituted for the first and second amplifiers utilized in the preceding embodiments. FIG. 4 shows a basic block diagram of such a modified embodiment which comprises an operational amplifier OA having a high input resistance and differential input terminals a and b across which is connected a photocell SC with a polarity as shown, the photocell being disposed to receive the light from an object to be photographed through an objective lens of the camera. The differential input terminal a of the operational amplifier OA is connected to an impedance element Z2 while the differential input terminal b is connected via an impedance element Z1 to a terminal EA to which is given an information regarding the iris opening or the ASA sensitivity.
An integrating capacitor C is connected between the output terminal O of the operational amplifier OA and input terminal a and a switch S1 interlocked with the shutter such that the switch is opened when the shutter is opened and is connected across the capacitor C for normally short circuiting the same. The output terminal O of the operational amplifier OA is also connected to the input terminal c of a shutter trigger circuit ST having an output terminal p connected to an electromagnet Mg for closing the shutter. The electromagnet Mg is constructed such that it is deenergized when the potential impressed upon the input terminal c of the shutter trigger circuit ST exceeds a predetermined value. A source of supply B is connected to the shutter operating circuit ST through a source switch S2. Instead of providing the first impedance element Z1 on the anode electrode side of the photocell SC, the impedance can be provided on the cathode electrode side.
When the camera is directed toward the object to project the light from the object upon the photocell SC, the operational amplifier OA begins to operate. When a shutter release button (not shown) of the camera is depressed at this time, switch S1 interlocked therewith is opened at a point OP shown in FIGS. 7A through 7B. Then, the charging of the integrating capacitor C by a current If fed back from the operational amplifier OA is commenced. If the brightness of the object does not vary, the information thereof has a constant value as shown by a dot and dash line m1 shown in FIG. 7A. As the terminal voltage across capacitor C builds up which is charged by the light from the object, the voltage appearing at the output terminal O of the operational amplifier OA also builds up as shown by dot and dash lines m2 shown in FIG. 7B. When this voltage reaches at point P the trigger voltage E1 of the shutter trigger circuit ST shown in FIG. 7B, the voltage appearing at the output terminal of the shutter trigger circuit ST varies from a level x to a level y as shown in FIG. 7C. At the level y, electromagnet Mg is deenergized to close the shutter. During an interval OP-CL shown in FIG. 7D the shutter is maintained opened. Solid line curves n1 and n2 shown in FIGS. 7A and 7B show an operation wherein the shutter is interlocked with a strobo flash. More particularly, the shutter release button, not shown, is depressed at an instant OP shown in FIGS. 7A and 7B, and at an instant L1 the strobo flash begins to luminesce. The light caused by this flash is projected upon the photocell SC from the object so that the voltage appearing at the operational amplifier OA begins to build up as shown by a solid line n2 shown in FIG. 7B. When this voltage reaches the trigger voltage Et of the shutter trigger circuit ST at point P the output voltage from the shutter trigger circuit ST jumps from x to y as shown in FIG. 7C. Thus, the electromagnet Mg is deenergized thereby completing the shutter control.
FIG. 5 shows a detailed connection of the circuit diagrammatically shown in FIG. 4. In the circuit shown in FIG. 5, variable resistors R1 and R2 are used as the impedance elements Z1 and Z2 shown in FIG. 4 and it is assumed that the information impressed across terminals EA has a voltage of 0 volt. Elements shown in FIG. 5 which are identical to those shown in FIG. 4 are designated by the same reference charactors and Q1 and Q2 show MOS type field effect transistors, Q3 through Q14 bipolar transistors, r a resistor, R a variable resistor, Q3 D3 and Q4 D4 diodes, D5 and D6 Zener diodes, and CD an electrolytic capacitor.
In operation, when the shutter release button is depressed after directing the camera toward the object to be photographed, switch S1 interlocked with the shutter release button is opened. Concurrently therewith the light from the object is received by the photocell SC to produce a photocurrent Il which is expressed by the following equation ##EQU9## in which I represents the total current flowing through the photocell, Is the saturation current thereof, q the electric charge of an electron, E the terminal voltage across the photocell SC, n a constant determined by the junction of the photocell, K the Boltzman's constant and T the absolute temperature (° K.).
By the operation of the operational amplifier OA, the terminal voltage across the photocell is made to be zero and since |Is|<< |Il|, the total current I shown by equation (9) becomes ##EQU10## While maintaining the condition shown by equation (10) the light from the object is amplified by the operational amplifier OA and is fed back to the input terminal a of the operational amplifier OA from the collector electrode of transistor Q7 of the amplifier through capacitor C, the feedback current being designated by If, thus gradually charging the capacitor C. At the same time photocurrent Il flows through variable resistor R1 thus creating a voltage drop IlR1 across the variable resistor R1 current (If - Il) flows through the variable resistor R2 so that a voltage drop (If - Il) R2 is produced across resistor R2. Since the voltage across the photocell SC is zero, Il R1 = (If -Il) R2. The feedback current If is expressed by the following equation ##EQU11##
As can be noted from this equation, the feedback current is equal to ##EQU12## times of the photocurrent Il so that it is possible to amplify current Il by suitably selecting the values of resistors R1 and R2. As described above, capacitor C is charged by feedback current If and the voltage across the capacitor C and the output voltage from the operational amplifier OA increase proportionally, the . The interval T1 required for the capacitor voltage to build up to the trigger voltage Et of the shutter trigger circuit ST is expressed by the following equation since CEt= If T1 ##EQU13## At an instant when this equation is satisfied, transistor Q14 of the shutter trigger circuit ST is turned OFF so that the electromagnet Mg is deenergized to close the shutter.
To assure the operation described above, it is necessary to maintain the quantity of the light arriving at the film of the cameral always at a constant value, and the circuit of this invention fulfills this requirements as follows. More particularly, since the quantity of the light is equal to the product of the brightness of the object and time, that is Il× T1, from equation (12) we obtain ##EQU14## Since the right hand term of this equation is constant the product Il× T1 is also a constant. In other words, with the novel shutter control circuit it is possible to project always a definite quantity of light upon the film surface. Where R1 >> R2 ##EQU15## In this equation, when the ratio between R2 and R1 is varied in accordance with the ASA sensitivity of the film or the iris opening, it is possible to set these informations this information in the circuit shown in FIG. 5.
For example, assuming ASA sensitivities of 25, 50, 100, 200, 400, 800 and 1600, and iris openings of 1.4, 2, 2.8, 4, 5.6, 8, 11, and 16, these informations may be set in resistors R2 and R1 respectively as shown in the following Tables.
| ______________________________________ |
| ASA |
| sensitivity 25 50 100 200 400 800 1600 |
| ______________________________________ |
| R2 64r2 |
| 32r2 |
| 16r2 |
| 8r2 |
| 4r2 |
| 2r2 |
| r2 |
| iris |
| opening 1.4 2 2.8 4 8 11 16 |
| ______________________________________ |
| R1 128r1 |
| 64r1 |
| 32r1 |
| 16r1 |
| 4r1 |
| 2r1 |
| r1 |
| ______________________________________ |
In these tables r2 and r1 show a resistance value of R2 corresponding to ASA sensitivity of 1600 and a resistance value of R1 corresponding to iris opening of 16, respectively. So long as the values of resistors R2 and R1 can be set as shown, informations information set in these resistors may be interchanged. Further, it is also possible to fix either one of these resistors and to vary the other in accordance with the ASA sensitivity or the iris opening. Alternatively, an iris diaphragm may be provided in front of the photocell so as to present the informations of both of information concerning both the ASA sensitivity and the iris opening as the intensity of light in which case both resistors R2 and R1 may be fixed. It is also possible to set the information regarding either one of the ASA sensitivity or iris opening as the degree of opening of the iris opening disposed in front of the photocell and to process the other information by either or both of the resistors R2 and R1.
In the embodiment shown in FIG. 6, impedance elements Z2 and Z1 shown in FIG. 4 are replaced by diodes D2 and D1 and an information regarding the ASA sensitivity and or iris opening is inserted into the shutter control circuit from a constant voltage circuit RE through variable resistors VR1, VR2 and VR3. Again, circuit elements identical to those shown in FIGS. 4 and 5 are designated by the same reference characters. In FIG. 6, if the impedances of diodes D2 and D1 are expressed by Z2 and Z1 respectively, the photocurrent Il will produce following voltage ED2 ED1 across diode D1 ##EQU16## Accordingly, a voltage ED2 will be created across diode D2 according to the following equation ##EQU17##
ED2 = ED1 + EB (17)
wherein EB represents an information voltage regarding the ASA sensitivity or iris opening. Since, the terminal voltage across the photocell SC is zero, by putting ##EQU18## From equations (14) through (18) ##EQU19## Accordingly
If =Il(2e + 1) (20)
If EB were large, 2e << 1, thus
If = 2e Il (21)
The instant at which the shutter trigger circuit ST operates or the shutter time T1 can be shown as follows: ##EQU20## and the light quantity Il· T1 is shown by ##EQU21## Since the right hand term of equation (23) is constant, the light quantity is also constant. The information regarding the ASA sensitivity or the iris opening can be represented by e of 2e. The information regarding the brightness of the object can be logarithmically compressed by diode D1 employed in the circuit shown in FIG. 6 and logarithmically expanded by diode D2. Consequently, the circuit shown in FIG. 6 can provide a positive control for the shutter.
According to the modified embodiments shown in FIGS. 4 to 6, a photoelectric transducer adapted to receive the light from an object is connected to the input of an operational amplifier, the output of the operational amplifier is fed back to its input through a capacitor so as to commence the charging thereof in an interlocked relation with the opening operation of the shutter of a camera, and to close the shutter when the voltage across the capacitor reaches a predetermined trigger voltage. Accordingly it is possible to greatly improve the response of the circuit to the brightness of the object, and to make always constant the quantity of light exposure of the photographic film over the entire range of the brightness of the object. Furthermore, as it is possible to project the light from the object over the entire surface of the photoelectric transducer, it is possible to simplify the construction of the shutter and reduce its cost. Use of a photocell greatly improves the response thereof to the light from an object of low brightness as well as the response of the control circuit as a whole. Moreover, as the measurement of light and shutter control are performed simultaneously, operation of the control circuit becomes simple. Also satisfactory flash control is possible even when an automatic storobo strobo flash is used.
| Patent | Priority | Assignee | Title |
| 4241280, | Jun 25 1979 | Polaroid Corporation | Light integrator circuit with built-in anticipation |
| Patent | Priority | Assignee | Title |
| 3626825, | |||
| 3641891, | |||
| 3648053, | |||
| 3678826, | |||
| 3690230, | |||
| 3712192, | |||
| 3731604, |
| Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
| Sep 02 1976 | Yashica Co., Ltd. | (assignment on the face of the patent) | / |
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