DE2129275A1 - Electrical circuit for operating a camera shutter - Google Patents

Description

Electrical circuit for operating a camera shutter Die Invention relates to an electrical circuit for operating a camera shutter, with the automatic shutter speed of a reflex camera with a single Lens determined as a function of the brightness of an object to be photographed is, and in particular to such an electrical circuit for operating one Camera shutter with which the exposure time depends on the Objective lens system, the amount of light passing through is determined.

In a known device of this type, the brightness (lumen) measured near the photosensitive layer by a photoconductive element that is arranged in the housing of a camera on the optical axis of the lens and with the help of which it is possible to accurately measure the lumens at the time in where the lens is exchanged and photographic film is inserted.

With this camera, however, it is necessary to have the photoconductive element to withdraw from the optical axis at the moment the shutter is opened will. Therefore the must be measured at a point in time before the opening of the shutter Light value can be saved so that the correct exposure time, i.e. the time while the shutter is held open., can be adjusted. To this end a device known from US Pat. No. 3,324,779 is used.

In this direction, the light value is that of the photoconductive It has been measured while it is on the optical axis before opening the element Shutter is arranged, stored in a capacity so that the exposure time can be determined according to the stored value. Although this facility the stored exposure value with a relatively simple construction can save, the saved value is the same as the light value before opening the Shutter and does not correspond to the light value during the period during which the shutter is actually open. Hence, no correct exposure can be expected because the stored measured value differs from the actual brightness of the Object during the opening period of the contract distinguishes especially when the brightness of the object changes.

The invention is therefore based on the object of an electrical To create a circuit for operating a camera shutter, in which, while avoiding of the disadvantage mentioned, the brightness of the object can be precisely determined. while the aperture is open is so the correct exposure time is set.

Furthermore, the circuit according to the invention should have a compact structure and no moving parts, such as an iris and a drive motor for that, need.

An electrical circuit used to operate a camera shutter is therefore characterized according to the invention by an outer on the front a camera arranged electromotive element, an internal electromotive element Element to which the light passing through the lens of the camera can be acted upon is a switching device that has a first capacity for charging by the external and the inner electromotive element connected in series against each other are, applied to a constant voltage source and the output of the first Capacitance with a first input of a differential amplifier, which is the balanced Samples state between the first input and a second input, connects and the outer electromotive element with reverse polarity between the output and the second .Eingang of the differential amplifier simultaneously with the opening of the shutter of the camera turns on, a second capacity, which is through a Einriehtung is chargeable as a function of the output of the differential amplifier, and by a control circuit for the closure of the to a predetermined terminal voltage responds to the second capacitance and closes the shutter.

The switching device is with the release button for the shutter coupled, so that when the release button is slightly depressed, the switching device operated in a first working position in which she is the first Capacity with the constant current source via the inner and the outer electrical circuit Element connects, and that when the shutter button continues to open the shutter is depressed, the switching device is operated in another operating position in which it is the capacitance with the first input of the differential amplifier connects and the upside-down, outer electromotive element between the output and the second input of the differential amplifier turns on.

An embodiment of the invention will now be made with reference to the enclosed Drawings described. It shows: Fig. 1 is a block diagram of the invention electrical circuit; and.

2 shows a detailed circuit diagram of an embodiment of the inventive Circuit.

The preferred embodiment shown schematically in FIG a power source B, for example a battery, and a series circuit, which is connected to the source and a constant voltage device E and a includes variable resistor R f. An inner electromotive element P1 which is located at a location that allows light passing through a camera lens receives, and an outer electromotive element P2 that is on the front des- camera body are arranged in series between the movable arm R of the variable resistance Rf and a stationary contact B one Switch S switched. The electromotive elements can for example be solar cells be. The moving contact a of the switch S is connected to the contact b, when the shutter release button (not shown) for the shutter of the camera is pressed slightly at the same time with the opening movement of the shutter is depressed. The contact is brought to the neutral position when the shutter is closed. One capacity C1 is connected to the movable contact a so that it can match the differential voltage between the output voltages of the inner and outer electromotive voltage Element P1 or P2 is loaded. Another stationary contact c of the switch S is connected to a first input Q1 of a differential amplifier A1, the has a high input impedance. The second input Q2 of the differential amplifier A1 is connected to the outer electromotive element P2, which is included in the circuit is switched using a switch S4 at the same time when the movable Contact a of switch S is switched to contact c. The output of the differential - Stronger A1 is applied to the base electrode of the first transistor T1, the is grounded by a diode 9 connected in the forward direction, while the collector electrode of the second transistor T2 is grounded by a capacitance C2, which is through a The current corresponding to the brightness of an object is charged.

A control circuit F for the shutter is parallel to the capacitance C2 switched to close the previously opened shutter when the voltage is on the capacitance C2 reaches a predetermined value.

Mode of operation: When the release button (not shown) is pressed down slightly, the movable contact a of the switch S is connected to the contact b, while at the same time the electromotive elements P1 and P2 generate output voltages depending on the brightness of the object. A current I, which is given by the following equation, flows through a conventional electromotive element: I = Io where IO: saturation current -V: terminal voltage of the element IL: photocurrent q: charge of the electron K: Boltzmann constant T: absolute temperature (degrees K) means.

When the electromotive element is connected to a circuit with a high input impedance, the current I flowing through the element is negligibly small. Under the condition IL> I0 (this condition is always fulfilled when light hits the element fl1-lt} the terminal voltage of the electromotive element is given by: V = kT / q log e IL / I0 ........ ........ (2) Accordingly, when the inner electromotive element Pi and the outer electromotive element P2 are connected in series with opposite polarity to each other, as shown in FIG. 1, the voltage Vp is P2 across them Elements given by: where Vpl: terminal voltage across element P1 Vp2: terminal voltage across element P2.

If the elements P1 and P2 have the same course, then IoPl = I0P2 applies and equation 3 can be written as follows: Since the photocurrents ELp1 and ILp2 correspond to the brightness of the light incident on the elements P1 and P2, the voltage VplP2 is proportional to the ratio of the brightnesses at the front of the camera housing and that in the vicinity of the photosensitive medium.

When the output of the constant current source E is applied to the variable resistor Rf, a voltage VR is generated between the movable arm R and the earth. The voltage VR is applied to the capacitance C1 through the inner and outer electromotive elements P1 and P2. Therefore, the voltage Vc1 across the capacitance C1 is given by the following equation: When the shutter release button is further depressed, the movable contact a is switched to the contact c simultaneously with the opening of the shutter. The capacitance C1 is connected to the first input Q1 of the differential amplifier A1.

The outer electromotive element P2 is when closing the Switch S4 between the second input Q2 of the differential amplifier A1 and the first transistor-D with such a polarity, that a negative potential is delivered to the differential amplifier. When the capacitance C1 anodes first Input Q1 of the differential amplifier A1 is connected, and if the outer Electromotive element B2 to the second input Q2 with the polarity shown connected, the differential amplifier produces an output signal that is proportional to the difference between those applied to the first and the second input Input voltages is., This output voltage is amplified by the amplifier A2 and applied to the base electrode of the first and second transistors T1 and T2. A current that corresponds to the output voltage then flows. of amplifier A2 corresponds, - through the emitter collector circuit of the first transistor T1 and the diode D. Thereby a voltage drop VD- is generated across the diode D, so that the i difference between this voltage drop and the voltage Vp2 given by the external electromotive Element P2 is generated at the second input Q2 of the differential amplifier A1 is present.

If the second input voltage is greater than the first input voltage, the-Di, fferential amplifier A1 lowers its output voltage, so that the output voltage of the amplifier A2 and the collector current Ic of the first transistor T1 is reduced will.

The voltage drop VO then drops across the [diode D] in order to reduce the differential voltage VD-Vp2, which is applied to the second input Q2 of the differential amplifier A1. On the other hand, if the second input voltage is lower than the first input voltage, the output voltage of the differential amplifier A1 increases to increase the output voltage of the amplifier A2 and the collector current Icl of the first transistor T1 of the differential amplifier A1 is applied. After repeating this operating cycle, the differential amplifier A1 reaches a balanced state in which the first input voltage is equal to the second input voltage5 when the condition VD - Vp2 = Vc1 is fulfilled. This process is almost instantaneous. The voltage drop VD across the diode D at this point in time is given by the following equation: VP1 - VP2 + VR = VD - V # 2 VD = (VP1 - VP2 + VR) + V # 2 2 where IL'P2 is the photocurrent of the outer element after opening the P2 shutter. The current ID that flows through the diode when the voltage drop VD is present at the diode D is given by: qVD ID = I0D 1xp kT where Io is the saturation current of the electromotive element P2 and IoD is the saturation current of the diode D. Although these values change with temperature, temperature has no effect on the IoD / Io ratio. The diode current ID given in equation 7 is determined by the collector current Ic1. Therefore, when the first and second transistors T1 and T2 have the same characteristics, the diode current ID is substantially equal to the collector current Ic2 of the second transistor T2. The collector currents Icl and Ic2 of the first and the second transistor are determined by the low base currents and are not so much influenced by the size of the load and the emitter-collector voltages - therefore the current Ic2 flowing through the capacitance C2 is which is connected to the collector electrode of the second transistor T2, equal to or proportional to the collector current Icl of the first transistor T1. For this reason, the voltage Vc2 at the capacitance C2 builds up essentially linearly according to the following equation: Vc2 = Ic2 t = ID t ....................... ..... (8) C2 Inserting equation 8 into equation 7 results in: Since C2, IoD / IDs ILP1 / IlP2 and 2n are constants, we get: Vcz = A. IL'P2. t .............. (10) where A is a constant.

Therefore, if the voltage of the capacitance C2 to the control circuit F for the shutter is applied, the shutter closes when the voltage is applied to the Capacity reaches a predetermined value.

In this way, the shutter is from the time the movable contact a of the switch 5 is closed with the contact b, up to a time kept open when the terminal voltage of the capacitance C2 the desired Value reached.

This interval coincides with the charging time of the capacitance C2 and is proportional to the ratio of the output voltage of the outer and inner electromotive element P2 and P1 multiplied by the output of the outer electromotive element P2 or the brightness (lumen) (the one on this at the moment photographing incident light).

With the described circuit for actuating the lock, wherein the relationship between the external brightness and the internal brightness before Photographing multiplied by the external brightness at the time of photographing it is possible to get the exact value of the internal brightness at the time of the To determine photographing.

Fig. 2 shows in detail a circuit of an embodiment of the electrical circuit according to the invention for activity a camera shutter. In this figure, three transistors constitute T1A, T2A and TDA the constant voltage source E. Four transistors T4> T5, T6 and T7 have a part of a differential amplifier circuit K on. The field effect transistors FET1 and FET2 form the other part of the differential amplifier circuit.

To boost the output voltage of transistor T7, two more are needed transistors T8 and T9 connected in parallel are provided. The connections between the transistors T8 and T9 and the diode D2, the capacitance C2 and the control circuit F are arranged similarly to FIG. 1. Switches S1, S2 and S3 that attach to the trigger button (not shown) are coupled, are provided for the connection between the inner electromotive element P1, the outer electromotive element P2, to change the capacitance Cl and the field effect transistor FET1, as described below will.

In the following description, it is assumed that the slide arm R of the variable resistance Rfs that is connected to the output of the constant voltage source E connected, is set to simplify the description..When the shutter button is depressed a little, the movable contacts a become the switch S1 and 53 brought to the stationary contacts b to form a circuit which from the slide arm R to the capacitance Cl through the inner and outer electromotive Element P1 and P2 extend to charge the capacitance C1. As described above the terminal voltage of the capacitance C1 is given by an equation- Vcl = Vf + VP1 - Vp given and is proportional to the 2 difference between the output voltage VP1 and VP2 of the two electromotive elements when Vf the Voltage between the slide arm R of the variable resistor Rf and earth.

When the shutter button is further depressed, at the same time the shutter (not shown) is opened, the movable contacts a of Switches S1ß-S2 and S3 switched on their stationary contacts c to the outer electromotive element P2 between the gate electrode of the field effect transistor FET2 and the collector electrode of transistor T3 with opposite polarity to turn on with respect to the field effect transistor FET2.

When the capacitance C1 to the gate electrode of the field effect transistor FET1 is connected, and when the outer electromotive element with the gate electrode of the field effect transistor FET2 is connected as described above, the terminal voltage the capacitance C1 is connected to the gate electrode of the transistor FET1 and the sum of the voltage drop VD across the diode D2, which is derived from the collector current of the Transistor T8 is caused, and the output voltage VP2 of the external electromotive Element P2 is applied to the gate electrode of the field effect transistor FET2.

When VD> VP2, the voltage V2> the difference VD -VP2 is positive because VD is positive while VP2 is negative with respect to the field effect transistor FET2 is. Then the 4 * voltage V2 of the field effect transistor FET2 is greater than the input voltage V1 of the field effect transistor FET1 or the terminal voltage the Capacitance 01> so that the load current of the field effect transistor FET2 is greater than the load current 11 of the other field effect transistor FET1. Therefore the base voltage of the transistor T5 falls, which is determined by the difference 1 1R5 - 12, R9 is given, in order to reduce the output voltage of the transistor T5. Through this in turn, the output voltage of the transistor T6, whose base electrode is on the collector electrode of the transistor t5 is connected, and the output voltage of the transistor T7> its base electrode to the collector electrode of the transistor T6 is connected, reduced.

As a result, the collector currents I3 and I4 of the transistors decrease T8 and Tg, while their emitter electrodes to the collector electrode of the transistor T7 are connected. The drop in the collector current 13 reduces the voltage drop VD. On the diode D2 in order to reduce the voltage V2 = VD - Vp2, which is applied to the gate electrode-e of the field effect transistor FET2 is applied.

Otherwise, if the voltage V2 = VD - VP2 is less than the first Input voltage V1 increases due to the decrease in load current 12 des Field effect transistor FET2 has the base voltage 11R5 - I2R9 of the transistor T5 a higher value than in the previous case, so that the output voltages of the Transistors T6 and T7 rise. This will make the collector current I3 of the transistor T3 is increased in order to increase the voltage drop VD across diode D, so that the gate voltage V2 of the field effect transistor FET2 is increased.

After repeating the process described, the differential amplifier circuit reaches Not a balanced state, if the gate voltage V1 of the field effect transistor FET1 is equal to the gate voltage V2 of the other field effect transistor FET2.

The time it takes to reach this balanced state is exceptionally short because the circuits are transistorized.

If the transistors T8 and T9 have the same characteristics, the collector currents I3 and I4 of these transistors are equal or proportional. Therefore, a current ID flows which is the product of the ratio of the output voltages of the inner and the outer electromotive element Pl and P2 immediately before corresponds to photography and the output voltage of the external electric motor Element during the photographing due to the capacitance C2> the one with the collector electrode of the transistor T9 is connected. Therefore, the capacitance C2 becomes a substantial one constant current charging, so that the voltage Vc2 across the capacitance Ca increases linearly. When the voltage Vc2 across the capacitor C2 reaches a predetermined value, it closes the control circuit F the previously opened lock in that a pawl (not shown) is notched. When the shutter is closed in this way switches S1, S2 and S3 are returned to their neutral position, so that the photographing process is completed. In this way, the shutter from a point in time at which the movable contacts a of the switches S1, S2 and Attack S3 at contact b until a point in time at which the Voltage Vc2 across the capacitance C2 reaches the above-described value.

In the described circuit for operating the lock, if a film with a different speed is used, the slide arm R of the variable Resistance Rf shifted in order to vary the charging voltage of the capacitance C1.

In the circuit according to the invention, the ratio between the values of light emitted by the inner and outer electromotive elements be measured, determined and the - exposure time is dependent on the Ratio and the value of the light determined by the external electromotive Element is measured, so that it is possible at any time to -the.brightness of the ~ object to be determined while the shutter is open.

Even if the brightness of the object changes; it is therefore possible to quickly follow such a change and the correct exposure time to determine. In the circuit according to the invention, it is also possible to adjust the brightness to measure with an accuracy that with the measurement of the internal brightness (L-umen) at the time of photographing is comparable, so that the correct shutter speed can be set that corresponds to the measured brightness (lumen), where only an electronic circuit is used and the need for an iris diaphragm and a drive motor for this is omitted. By the fact that the iris diaphragm and Its drive motor is eliminated, the construction becomes simpler and the size becomes simpler and the manufacturing cost is reduced. Since the circuit according to the invention has an electronic circuit that has no moving parts, it is possible to Quickly determine the shutter speed. Furthermore, the circuit is robust against vibrations and shocks.

Claims (4)

Claims 1.) Electrical circuit for operating a camera shutter characterized by an outer, arranged on the front of a camera, electromotive element (P2), an inner electromotive element (P1) that can be acted upon by the light passing through the lens of the camera, one Switching device (5) which has a first capacity for charging through the outer and the inner electric motor element, which are connected in series against each other, to a constant voltage source (E) and the output of the first Capacitance with a first input of a differential amplifier (A), the balanced Samples state between the first input and a second input, connects and the outer electromotive element (P2) with reverse polarity between the Output and the second input of the differential amplifier (A) simultaneously with opening the shutter of the camera turns on, a second capacity that through a device depending on the output of the differential amplifier (A) is chargeable, and by one Control circuit (F) for the lock, which responds to a predetermined terminal voltage on the second capacitance and closes the shutter. 2. Circuit according to claim 1, characterized by a diode and a transistor that depends on the output voltage of the differential amplifier (A) conducts a current through the diode (D), the switching device (S) the Difference between the output voltage of the external electromotive element and the voltage drop across the diode (D) to the second input of the differential amplifier (A) 'creates. 3. Circuit according to claim 2, characterized in that the differential amplifier (A) two field effect transistors (FET1, FET2), the gate electrode of a field effect transistor through the switching device can be connected to the first capacitance and the gate electrode of the other field effect transistor can be switched on so that it has the differential voltage between the output voltage of the external electromotive element and the voltage drop at the diode. 4. Circuit according to claim 1, characterized in that the switching device (, s) has two working positions and one neutral position and with the release button of the camera shutter is linked in such a way that when the shutter button is pressed slightly is depressed, the switching device (S) can be actuated into a working position is where she has the first capacity with the constant voltage source (E) connects by the inner and outer electromotive elements, and that, if the release button is further depressed, the switching device (S) in another working position can be actuated in which it increases the capacity with the first The input of the differential amplifier (A) connects and the reverse connected, outer electromotive element between the output and the second input of the Differential amplifier (A) turns on.