JPS6027374Y2 - Automatic exposure adjustment device for cameras - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an automatic exposure amount adjustment device consisting of an electric shutter device and an automatic calibration value adjustment mechanism in a camera. The present invention relates to a device that is effective when the light response speed is fast.

Instead of cadmium sulfide photoconductors, photodiodes have been widely used as field light receiving elements in cameras due to their advantages such as fast response speed, responsiveness over a wide range of brightness changes, and little deterioration over time. It has become.

However, since this light receiving element has a fast response speed, when measuring light for a subject illuminated under a light source whose brightness is constantly changing, such as a fluorescent lamp, the light metering that follows the change in brightness of the light source is difficult. As a result of providing information, it is possible to use an electric shutter device that determines the exposure time value based on the photometry result immediately before shooting, an automatic calibration value adjustment device using a meter clamp method, other passing light amount control devices, and automatic aperture in movie cameras, etc. In a device, during photometry, especially the brightness of the field at the end of photometry and the brightness when the shutter is opened are often different, resulting in an exposure error in automatic control.

This kind of change in the brightness of the received light flux to which this light-receiving element is sensitive can be realized, for example, when the light-sensitive element is placed in the viewfinder optical system of a single-lens reflex camera with a preset aperture mechanism, and the aperture is set as the photometry point immediately before photography. This occurs when metering ends during oscillation of the diaphragm blades at the aperture position after the mechanism has apertured the aperture, and as a result, in such cases, the subject illuminated by natural light This can cause exposure errors even when photographing the world.

First, this problem will be explained in more detail using an example of a conventional automatic exposure adjustment device.

FIG. 1 is a circuit diagram showing an example of a conventional electric shutter circuit using a photodiode as a photosensitive element.

In the figure, Pd is a photodiode as a photosensitive element constituting the photometric section, and is connected to the input terminal of the amplifier A1.

The output terminal of the amplifier A1 is connected to the input terminal of the amplifier A2 as a high input impedance relay circuit via a memory switch Sw□ which is opened immediately before the mirror is raised in conjunction with the mirror raising operation in a single-lens reflex camera. It is.

A capacitor CM for storing photometric information, which is charged when the switch SW1 is closed, is arranged between the switch SW1 and the amplifier A2.

Further, a time-fixing capacitor C is connected to the output terminal of the amplifier A2.
A feedback circuit is connected to one pole of the photodiode Pd via a shutter opening synchronization switch SW2 connected in parallel to this, and a trigger that controls power supply to the electromagnet Mg that starts closing the shutter. It connects the input end of the circuit TR.

As the outline of the operation of the first illustrated circuit is already well known, first, during photometry, the switches Sw and SW2 are closed, and the Pd-A1-A1-3w1
-A2-3 Configure a closed circuit with a loop consisting of Pd, and use the amplifier to transmit the photocurrent of the photodiode Pd or a current proportional to the photocurrent so as to maintain the potential difference between both inputs of the amplifier A to zero. A feedback current is passed from the output to the photodiode Pd and the amplifier A□.

If the release switch is now pressed down from this state, the storage switch SW1 will be opened just before the mirror flips up, and photographing information such as the brightness of the subject will be stored in the storage capacitor CM.

This storage voltage is the input voltage of the amplifier A.
2 corresponds to the output current, that is, the charging current to the time-fixing capacitor C.

Next, at the same time as the shutter opens, the synchronous switch SW2 is opened, and the output current of the amplifier A2 charges the time-fixing capacitor C.

When the charging voltage of the capacitor C reaches a predetermined value, the trigger circuit TR operates to cut off the current to the magnet Mg and close the shutter.

In the above configuration, since the photodiode Pd has a fast optical response, the photocurrent ratio corresponds to the brightness of the subject, and the memory type I
Ev1 corresponds to the brightness of the subject.

Therefore, this circuit provides an excellent shutter circuit when the light source is natural light.

However, a problem arises when the light source is a fluorescent lamp, for example, which discharges every positive and negative half cycle depending on the power supply frequency.

FIG. 2 is a graph showing changes in brightness of an object illuminated by such a light source, with time ωt plotted on the horizontal axis and brightness plotted on the vertical axis.

As is clear from the figure, the brightness of the subject is changing.

The voltage of the memory capacitor CM also changes according to the change in brightness shown in the second figure, and depending on whether the memory switch SW1 leaves at the peak point a in FIG. 2 or has already left the bottom point, Memory values are different.

In other words, if the memory switch Sw□ is opened at the moment when the brightness is the value of point a, the brightest time will be stored as the brightness of the subject, and if the memory switch is opened at the moment when the brightness is turned on. The darkest time will be stored as the brightness of the subject.

On the other hand, when the shutter shutter is opened, the film is exposed to light with the brightness of the waveform shown in the second figure, and the shutter time is 1/2 cycle (for example, 1Qmsec if the power frequency is 5QHz) of the brightness that changes periodically. If there is, it can be considered that the light will be exposed at approximately the average brightness of the waveform shown in the second figure.

Therefore, if it is stored at point a, it will be underexposed, and if it is stored at point a, it will be overexposed.

In this way, under a light source such as a fluorescent lamp, which repeatedly discharges according to the power supply frequency, the brightness during storage differs from the brightness during film exposure, and as a result, proper exposure cannot be obtained.

In order to improve the above-mentioned drawbacks, under a pulsating light source such as a fluorescent lamp, it is necessary to store data as an average brightness or at least in a smoothed state.

Therefore, the inventor of the present invention proposed a circuit as shown in FIG. 3 as Utility Application No. 50-006741.

In the circuit shown in FIG. 3, a resistance element R is inserted in series with a storage capacitor CM, and the voltage IEV across the capacitor CM is
2, the stored values are averaged by causing a phase delay.

That is, since the output impedance of amplifier A1 is low, even if a relatively high resistance is used as impedance element R, it will not affect the operation of the feedback circuit, and A2-3W2-P
A current equal to or proportional to the photocurrent flows through the feedback loop of the d-A.

FIG. 4 shows the relationship between the conventional storage voltage under a fluorescent lamp and the storage voltage of the device according to FIG. 3, which was previously proposed by the inventor of the present invention.

Explaining based on the circuit shown in FIG. 3, the photodiode Pd receives brightness in a pulsating manner as indicated by the dotted line in FIG. 4, and the photocurrent is passed through a similar photocurrent feedback loop.

In order to cause a pulsating feedback current to flow, the input voltage V1 to the amplifier also pulsates as indicated by the dotted line in FIG.

Since both inputs of the amplifier A1 are pulsating in the same way, the potential difference between the two inputs of the amplifier A□ is kept at zero, and the circuit system operates normally.

On the other hand, the pulsating voltage V□ appearing at the input to the amplifier is smoothed by the resistive element R and the storage capacitor CM, and V2 shown by the solid line in the fourth figure appears at both ends of the storage capacitor CM.

Even if the memory switch Sw□ is opened at the peak point of point a, the stored value will be the average brightness a', and even if it is opened at the bottom point of the switch, the stored value will be the average brightness b' becomes.

Furthermore, since the input impedance of the amplifier A2 is very high, after the switch Sw□ is opened and the data is stored, the resistive element R becomes irrelevant to the storage level.

There is no problem in storing data at point a or point b shown in Figure 4 in this way, but if the capacitance of the storage capacitor is CM and the resistance value is R, it will have a time constant RCM. The terminal voltage of the capacitor becomes lower than its steady value.

for example? What is V2 at the time of r/2? It is lower than the voltage at time r+2.

Therefore, if it is memorized at an early stage, there will be a tendency for overexposure.

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic exposure adjustment device for a camera that can solve the problem regarding the response delay.

In order to achieve the above object, an automatic exposure adjustment device for a camera according to the present invention includes a photosensitive element consisting of a photodiode that receives field light, and the photosensitive element is connected to an input terminal. a first amplifier, a second amplifier whose input terminal is connected to the output terminal of the first amplifier, and a feedback circuit that feeds back the output of the second amplifier to the input of the first amplifier; In an automatic exposure adjustment device for a camera having a storage capacitor charged by the output of the first amplifier, the capacitor is connected to a non-linear circuit consisting of a resistor and a parallel circuit of a diode connected in parallel to the resistor. and when a relatively large voltage occurs between the capacitor and the output of the first amplifier, the capacitor is connected via a low forward resistance of a diode. When the voltage is low, the voltage is connected to the high forward resistance of the diode through a parallel circuit of the resistance.

According to the above configuration, the threat resistance of the parallel circuit of the diode and the resistor changes non-linearly depending on the difference between the terminal voltage of the capacitor and the output voltage of the first amplifier, so that it can quickly respond to sudden changes in the illumination light source. It can provide a smoothing effect as well as a response, and the purpose of the present invention can be fully achieved.

A more detailed explanation will be given below with reference to FIGS. 5 and 6.

FIG. 1 is a circuit diagram showing an embodiment of an exposure adjustment device according to the present invention;

In this embodiment, a parallel circuit (see FIG. 5) consisting of a resistor R and diodes D□ and D2 is connected between the input terminal of the amplifier N and the capacitor CM.

The diodes D□ and D2 are connected to have opposite polarities.

FIG. 7 is a graph for comparing the operation of the circuit according to the present invention and the operation of the circuit shown in FIG. 3 previously.

In FIG. 7, 11 is the circuit shown in FIG. 3 and the circuit shown in FIG. 6 according to the present invention; The voltage 1° indicates the terminal voltage of the capacitor CM of the circuit shown in FIG.

Note that in order to facilitate comparison, the magnitudes of CM and :R of each circuit are made equal.

As is clear from FIG. 7, 13 rapidly approaches 1□ compared to 1° and is smoothed.

Next, further explanation will be given with reference to FIGS. 8 and 9.

FIG. 8 is an enlarged view of the waveform shown in FIG. 7.

FIG. 9 is a diagram showing the rectification characteristics of a general diode.

As is clear from FIG. 9, the resistance of the diode when the threshold level Vs of the diode is exceeded is extremely low and shows a value close to zero, but below that level, the resistance value of the diode is extremely large.

In this embodiment, the resistance value shown at a voltage equal to or lower than Vs will be explained as being considerably larger than the resistance value of the resistor R.

In FIG. 8, the voltage V1 has a ripple voltage ■p-p so that the photodiode Pd faithfully responds to the incident light flux.

In the circuit shown in FIG. 6, when V□-v2>VS is established (between O and φ□ in FIG. 8), diode D2 conducts and capacitor CM is rapidly charged toward Vl.

That is, the moment the power is turned on, the memory capacitor CM is charged via the diode.

V□-V2〈VSl More specifically, IVl-V2
1<VS region (φ4 or more in FIG. 3), the diode D1. Since both D2 cannot conduct, capacitor C
M will be charged or discharged via resistor R,
V2 changes with a large time constant.

That is, the ripple of Vp-p is smoothed. Although the case where the light source fluctuates has been described above, the present invention is also effective when the incident light mechanically fluctuates.

There are two types of exposure control methods: aperture metering and aperture metering.
When instantaneous aperture metering using the aperture mechanism is performed under natural light, the switch SW1. If SW2 is closed, the input voltage V1,
The storage voltage V2 becomes as shown in Figure 11 and quickly approaches the reference value.

In conventional circuits, large exposure errors occur due to pulsation of the light source, etc., but with the device of the present invention, even if there is pulsation of the light beam incident on the photosensitive element, the brightness is used as the photometric information level and the shutter time etc. can be determined and the appropriate exposure can be obtained.

Although the device of the present invention was developed for an automatic exposure adjustment device, it can also be applied to an exposure meter device that uses an electric meter or the like to indicate the photometric value instead of automatically controlling the shutter, etc. Of course you can get it.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an example of a conventionally known electric shutter circuit using a photodiode, Figure 2 is a discharge characteristic diagram of a fluorescent lamp, Figure 3 is a circuit diagram for obtaining average brightness, Fig. 4 is an explanatory diagram of the storage voltage in the circuit shown in Fig. 3 above, Fig. 5 is a circuit diagram showing an example of the configuration of the main parts of the device of the present invention, and Fig. 6 is an illustration of the automatic exposure amount adjustment device for the camera of the present invention. A circuit diagram showing an example; FIG. 7 is a graph for comparing the operation of the circuit according to the present invention with the operation of the circuit shown in FIG. 3;
Figure 8 is an enlarged graph of the graph shown in Figure 7 and shown in correspondence with diode characteristics, Figure 9 is a graph showing diode characteristics, and Figure 10 is a graph showing the transient state of the aperture operation in the preset aperture mechanism. The explanatory diagram shown in Fig. 11 is the first
FIG. 2 is an explanatory diagram showing the operating characteristics of main parts of the device of the present invention under a transient state shown in FIG. Pd...Photodiode, A1. A2...
...Amplifier, TR...Trigger circuit, CM storage capacitor, R...Impedance element, S
wl...Memory switch, SW2...Synchronization switch, Mg...Electromagnet, C...
Time constant capacitor.

Claims (1)

[Scope of utility model registration request] a photosensitive element consisting of a photodiode that receives field light; and a first photosensitive element connected to an input terminal.
a second amplifier whose input terminal is connected to the output terminal of the first amplifier; a feedback circuit that feeds back the output of the second amplifier to the input of the first amplifier; In an automatic exposure adjustment device for a camera having a storage capacitor charged by the output of an amplifier No. 1, the capacitor is connected to the capacitor through a non-linear circuit consisting of a parallel circuit of a resistor and a diode connected in parallel to the resistor. When the capacitor is connected to be charged and a relatively large voltage occurs between the capacitor and the output of the first amplifier, the capacitor is connected through a low forward resistance of a diode, so that a relatively large voltage is generated between the capacitor and the output of the first amplifier. 1. An automatic exposure adjustment device for a camera, characterized in that the automatic exposure adjustment device for a camera is characterized in that it follows quickly and when the voltage is low, it is connected through a parallel circuit of a high forward resistance of a diode and the resistance.