JPS5830566B2 - Denki Yatsuta Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric shutter circuit for a camera equipped with a programmable shutter whose shutter blades gradually open over time.

In this type of camera, in the exposure time range where the shutter opens at a constant aperture change rate with respect to time, a photoelectric conversion circuit with a γ-0.5 characteristic is required, and after the shutter, which also functions as an aperture, is fully opened, In the exposure time region of , a photoelectric conversion circuit having a characteristic of γ=1 is required.

In order to achieve this, in the past, the appropriate exposure time was
For a subject whose brightness is within the time it takes for the shutter to fully open, the photoelectric current exhibits a characteristic of γ-O,5, and for a brightness lower than that it exhibits a characteristic of γ=1. The conversion circuit was constructed by appropriately combining a photoconductive element and a resistor.

According to this conventional configuration, it is necessary to select a photoconductive element having photoelectric conversion characteristics suitable for the above-mentioned desired characteristics, and to adjust the photoelectric conversion circuit including the photoconductive element and a resistor so as to obtain the above-mentioned desired characteristics. This adjustment work required a considerable amount of work.

In view of these points, an object of the present invention is to provide an electric shutter circuit that does not require selection of photoelectric conversion elements or adjustment of the photoelectric conversion circuit for the desired characteristics.

For this reason, the present invention combines a photoelectric conversion circuit with a time-voltage generation circuit that generates a voltage approximately proportional to the logarithm of the time period from when the shutter starts opening to when the shutter is fully opened, and a time-voltage generation circuit that generates a voltage that is approximately proportional to the logarithm of the time from when the shutter starts opening to when the shutter is fully opened; A photometric circuit that generates a voltage approximately proportional to In the time domain between the two, a current proportional to the subject brightness and time is generated, this current is charged (including discharged) and integrated by an integrating capacitor, and the shutter is closed when the charging voltage reaches a predetermined value. Additionally, in the time domain when the shutter is fully open, the capacitor is configured to charge and integrate a current proportional to the subject brightness.

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

FIG. 1 is a block diagram showing the basic configuration of the present invention.

In FIG. 1, 1 is a photometric circuit that includes a photoelectric conversion element and generates a voltage signal proportional to the logarithm of the intensity of light incident on the element;
2 is a time-voltage conversion circuit that generates a voltage proportional to the logarithm of time during the period from when the shutter begins to open until it is fully opened.

3 is an adder circuit that outputs the sum of the output voltages of the circuits 1 and 2, and 4 is a logarithmic expansion circuit that converts the output voltage of the adder circuit 3 into a current proportional to its inverse logarithm.

A photoelectric conversion circuit is formed from these circuits 1 to 4.

C1 connected to the output of the circuit 4 is a capacitor that charges and integrates the logarithmically expanded current from the time when the switch SW1 is opened at the same time as the shutter is opened.

An integrating circuit is formed by this capacitor C1 and switch SW□.

When the charge level of the capacitor C1 reaches a predetermined level, the switching circuit 5 is activated to cut off the excitation current of the magnet Mg and close the shutter.

The operation in the above configuration will be explained.

As shown in Fig. 2, in a program shutter in which the shutter aperture area increases in proportion to time from the time of shutter release, the exposure amount Q at any time t from the time of full aperture to t1 is the amount of light incident on the subject lens. It is proportional to the product of light intensity and time squared.

On the other hand, if a current proportional to the incident light intensity and time is obtained and this current is integrated over time by a capacitor, the charging voltage of the capacitor becomes proportional to the product of the incident light intensity and the square of time.

Therefore, the time required for charging the capacitor and for the pressure to reach a predetermined level can be set as the exposure time.

Output voltage of photometry circuit 1 V B N time-voltage conversion circuit 2
It is assumed that the output voltage Vt of is expressed by the following equations, assuming that a PN junction is used as the logarithmic conversion element.

is obtained.

A voltage signal corresponding to the exposure amount Q can be obtained by time-integrating the current represented by equation (4) using the capacitor C1.

Next, the embodiment circuit of FIG. 3 according to the present invention will be described.

In FIG. 3, the base of the transistor Q1 is connected to the connection point P1 between the resistor R1 and the diode D1, the emitter is connected to one end P2 of the diode D1 via a capacitor C2, and the collector is connected to one end P3 of the resistor R1. The circuit constitutes a time-voltage conversion circuit.

A diode D1 is connected between P1.
Given a constant voltage generated at P2, the charging pressure of capacitor C2 increases in proportion to the logarithm of time.

Such an operation is shown, for example, in Japanese Patent Publication No. 48-11167.

One end P3 of the resistor R1 is connected to the positive terminal of the power source E via a switch SW2 that operates in conjunction with a shack mechanism (not shown).

This switch SW2 is opened at time tl when the shutter is fully opened.

For example, a photoconductive element CDS for measuring exposure, which can directly receive the subject light and is installed at a predetermined position on the front of the camera, constitutes a photometry circuit together with a transistor Q2, one end of which is connected to the emitter of the transistor Q2, and one end of which is connected to the collector of the transistor Q2. is grounded P2.

Further, the base of the transistor Q2 is connected to a connection point P4 between the capacitor C2 and the emitter of the transistor Q1.

The characteristics of this photoconductive element cds are γ-1.

When object light is incident on the photoconductive element cds, a current proportional to the intensity of the incident light flows through the emitter-collector of the transistor Q2, and a voltage proportional to the logarithm of this current appears at the base-emitter of the transistor Q2.

SW3, which is connected to both terminals of capacitor C2, is a switch that is opened at the same time as the shutter opens, just like switch SW1. When switch SW3 is opened, a charging voltage due to capacitor C2 appears between points P2 and 44, so that the emitter of transistor Q2 and ground point P2. P5 represents the sum of the voltage of capacitor C2 and the base-emitter voltage of transistor Q2.

Point P2. The voltage across P5 is applied to the base and emitter of a transistor Q3 constituting an anti-log conversion circuit, and a current proportional to the anti-log of the voltage applied to the base and emitter is output to the collector of the transistor Q3.

The collector of the transistor Q3 is connected to the Schmitt circuit 5, and when the integrated value of the output current of the transistor Q3 by the capacitor C1 exceeds a certain value, the excitation of the electromagnet Mg for shifting connected to the Schmitt circuit 5 is cut off by a well-known operation. The shutter will be closed.

In the above configuration, when the shutter button of the camera is pressed, switches sw, , sw3 are opened, and switches SW2 . S
W4 is closed, and a voltage is applied to resistor R1 and photoconductive element cds.

At the beginning of the shutter operation, the voltage of the capacitor C2 is low, so the output current of the transistor Q3 is also small, the Schmitt circuit 5 is operated, the shutter electromagnet Mg is excited, and the shutter (not shown) is gradually opened. The aperture area increases in proportion to time, as shown in FIG. 2 between 0 and t1.

By closing switch SW2 and opening switch SW3, a constant forward voltage drop is generated across diode D1 as described above, and a constant voltage drop is generated across capacitor C2, which is proportional to the logarithm of the elapsed time since the shutter button was operated. A time voltage is generated.

This time voltage is applied to the base of transistor Q2.

On the other hand, when object light is incident on the photoconductive element cds, a current proportional to the intensity of the incident light flows between the emitter and collector of the transistor q.

Therefore, a voltage corresponding to the sum of the above-mentioned time voltage and a voltage proportional to the logarithm of the object light intensity is applied between the base and emitter of the transistor Q3. added to the base of.

The capacitor C1 is then charged with a current proportional to the inverse logarithm of this base input voltage.

If the luminous intensity of the object is shorter than the time t1 when converted into one shutter hour, the charging voltage of the capacitor C1 is changed by the Schmitt circuit 5 while the shutter opening area is gradually increasing.
, the electromagnet Mg is cut off and the shutter is closed.

In addition, if the subject luminosity is low, after the shutter operation, the time t1
Until time t1 elapses, the terminal voltage of capacitor C1 increases in proportion to the sum of the voltages in accordance with the time voltage and subject luminosity due to the same effect as described above, but before time t1, the terminal voltage of capacitor C1 The threshold value of the circuit 5 is not reached, and the electromagnet Mg remains energized.

After time t1, the opening degree of the shutter becomes constant.

When the time t1 is reached, the switch SW2 is opened, the transistor Q1 becomes inactive, and the voltage of the capacitor C2 becomes a constant value.

Therefore, after time 11 or more has elapsed since the shutter was operated, the collector current of transistor Q3 becomes proportional only to the intensity of light incident on the photoconductive element cds, regardless of time.

After a predetermined time, when the voltage of the capacitor C1 reaches the threshold of the Schmitt circuit 5, the electromagnet Mg is cut off and the shutter is closed, so that proper exposure control is carried out even after the shutter is fully opened.

In the embodiment shown in FIG. 3, the switch SW2 is opened at t1 when the shutter is fully open, and the output of the time-voltage conversion circuit is made independent of time, so that the photometric characteristics can be switched accurately, and the exposure accuracy is It gets extremely better.

Further, the circuit is adjusted by adjusting the terminal voltage of the diode D1 using the variable resistor R1.

For example, if the time t1 until full aperture is known, the appropriate exposure amount corresponding to that time t1 is determined.

Therefore, since an appropriate exposure time for the brightness of the reference light source is determined, the resistor R1 is adjusted so that the shutter closes within this time.

In this way, all appropriate exposures are controlled for other brightness levels.

In the circuit shown in FIG. 3, a photoconductive element is used as the photoelectric conversion element, but a photoelectric conversion element such as a photodiode may also be used.

Furthermore, if exposure accuracy is not required as a time-voltage conversion circuit, resistors R2 and R as shown in Figure 4 may be used.
3. A circuit consisting of the capacitor C3 may be used, or the switch SW2 may be turned off.

Approximately, it is better to increase the potential of the base of transistor Q2 over time.

The voltage across diode D1, in other words, point P1. P
The voltage produced at 2 may be varied not only for adjustment but also depending on exposure factors such as film sensitivity.

As described above, according to the present invention, a time-voltage signal is generated that generates a voltage that changes over time in relation to the elapsed time from when the shutter starts opening, but has a constant value after the shutter is fully opened. A circuit and a photometry circuit that generate a voltage with a value indicating the brightness of the subject received through the mouth are separately formed, and based on the sum voltage from both circuits, γ- Since the photoelectric conversion circuit is configured so that the circuit characteristics of 0.5 and γ-1 after full opening are obtained, the photoelectric conversion element of the photometry circuit generates an electrical signal with a value proportional to the received light intensity. A normal photoconductive element or photodiode with photoelectric conversion characteristics can be used as is, and there is no need to select a photoelectric conversion element having photoelectric conversion characteristics suitable for circuit characteristics, as in the past.

Furthermore, the desired circuit characteristics of the photoelectric conversion circuit are electrically switched depending on whether or not the output voltage from the time-voltage signal generation circuit changes with elapsed time. A highly accurate programmed shutter control circuit can be realized without requiring a lot of adjustment work such as adjusting the circuit characteristics using a resistor and a resistor.

[Brief explanation of the drawing]

Fig. 1 is a block circuit diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram of the operation of a program shutter, Fig. 3 is a circuit diagram showing a detailed embodiment of the invention, and Fig. 4 is a diagram illustrating the operation of the program shutter. FIG. 3 is a circuit diagram showing a modification of the time-voltage signal generation circuit of the circuit of FIG. 1, Cds, Q2-photometric circuit, 2, R1,
R2゜R3, Dl, Ql, C2, C3... Time, -voltage conversion circuit, 3, C2, C3, Q2... Addition circuit, 4
．． Q3...Logarithmic expansion circuit, 1,2,3,4...Photoelectric conversion circuit, C1°Swl...Integrator circuit, 5...Switching circuit, Mg...Shutter closing electromagnet.

Claims (1)

[Claims] 1. In the electric shutter circuit of a camera equipped with a programmed shutter in which the aperture area increases in proportion to time, a voltage is generated with a value related to the elapsed time from the start of the shutter opening, and after the shutter is fully opened, a time-voltage generating circuit that is provided to sustain the voltage at a point in time, and generates a voltage whose value changes approximately in proportion to the logarithm of the elapsed time from the start of opening in response to the start of opening of the shutter; It has the characteristic of generating an electric signal with a value proportional to the intensity of received light, and is equipped with a photoelectric conversion element that measures the intensity of light from a subject through a certain aperture, and generates a voltage proportional to the logarithm of the intensity of incidence on the photoelectric conversion element. A logarithm for converting the sum voltage from the generating photometering circuit and the circuit portion to which both circuits are connected so as to output the sum of the voltages from the time-voltage generating circuit and the photometering circuit into a current proportional to its inverse logarithm. an expansion circuit; an integration circuit that starts integrating the converted current from the logarithmic expansion circuit in response to the start of opening of the shutter; and switching when the integral value of the integration circuit reaches a predetermined level;
and a switching circuit for closing the shutter.