JPS5837488B2 - Sotsukousouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photometric device that measures the maximum brightness and minimum brightness of a field.

When shooting with a camera, the exposure amount was set to match the maximum or minimum brightness of the subject. It was necessary to carry out complicated operations such as measuring light toward the area of maximum or minimum brightness, setting the exposure amount based on that, and then pointing the camera at the intended subject.

The present invention provides a photometry device that can detect and measure the maximum or minimum brightness at an unspecified position in a subject without having to point the photometer in that direction, and allows the photographer to perform photometry operations. The aim is to allow the user to concentrate solely on realizing his/her own drawing intentions without being bothered by the other factors.

In the present invention, a plurality of photocurrent elements are arranged on a screen, a current limiting element is connected in series to each photocurrent element, and the current of these current limiting elements is controlled by a common control signal. As a control signal, a gate circuit that detects the lowest or highest potential of each connection point between the photocurrent element and the current limiting element is switched depending on the detection of the lowest luminance or the highest luminance, and is passed through this gate circuit. This is a photometric device that uses the obtained signal and uses the output voltage of this gate circuit as a photometric value.

In this process, the photocurrent element is an element whose current changes depending on incident light, and photodiodes, phototransistors, etc. are suitable.

Although the current limiting element is a resistor, it is possible to control the current, and a transistor is more practical.

In addition, as a gate circuit for extracting the maximum value and the minimum value, there is an OR circuit using a diode, but in the present invention, the highest value of the voltage at the connection point between the photocurrent element and the current limiting element,
Since the lowest voltage is detected, if a large amount of current flows toward the gate, the potential of the highest and lowest potential parts will be averaged with other parts, reducing sensitivity, so special measures have been taken.

The present invention will be explained below with reference to Examples.

In FIG. 1, P1 to P4 are photodiodes as photocurrent elements, which are arranged on the screen 3 as shown in FIG.

Although only four are shown in FIG. 1, there are actually many.

As shown in Fig. 2, the screen 3 is an image formed in the camera's viewfinder through the photographing lens L1, reflected by the mirror M, and formed on the imaging surface 2 below the pentaprism PPO, which is further reduced by the lens L2. The image was formed by

Each of photodiodes P1 to P4 has a current limiting element.
C(7)} Transistors TO1 to TO4 are connected in series.

The emitters of TOI to TO4 are commonly connected to the negative pole of the power source E through switch S3, and the bases are commonly connected so that they can be connected to contact a side or b side by switch S2 as a changeover switch of the present invention. It has become.

A photometric output terminal OUT is provided on a common line of these bases.

Switches si, s2, and s3 are changeover switches for performing three types of photometry: maximum brightness, minimum brightness, and average brightness.

First, the circuit for maximum brightness measurement will be explained.

In this case, the switch 81 is turned on and the switches S2 and S3 are turned to the contact a side.

That is, the state shown in FIG. 1 is established. It is now assumed that the position of photodiode P2 is the position of maximum brightness.

The photocurrent of P2 is the maximum, and that current tends to flow through the transistor TO2 as it is.

Therefore, photodiodes P1 to P4 and transistor TO
Among the transistors T11 to T14 whose bases are connected to the connection points with I to TO4, the T120 base potential is the highest, and the common emitter of T11 to T14 has a voltage lower than the T120 base by the pace emitter voltage of T12. , the base potentials of the other T11, T13, and T14 are lower than this, so the voltage at the common emitter of T11 to T14 is ultimately determined by the photocurrent of the photodiode in the portion of maximum brightness.

This voltage is applied to the common base of transistors TO1-TO4 via contact 3 of switch S2.
The current of TO2 becomes equal to the photocurrent of photodiode P2.

To arrive at such a result, the voltage between the common base and the common emitter of TO1 to TO4 is the voltage between the base emitter of TO2 when the photocurrent of P2 flows through the transistor TO2, which is the voltage between the photoelectric output of P2 and the common emitter of the transistor TO2. This is logarithmically transformed according to the pace-emitter characteristics, and is output to the output terminal OUT.

In this case, the transistors TOI to TO4 have a common base, so the same collector current must flow through all of them, but the transistors other than P2 cannot allow that much current to flow, and the insufficient current is passed through the diode D11, etc., and the transistor T1 tT2. It is supplied from power source E.

Next, the case of measuring the minimum luminance will be explained.

At this time, the switch S2 is switched to the contact b side.

The other switches are shown in the figure.

When S2 is placed on the contact b side, the emitters of the transistors T11 to T14 are lifted from the circuit, so they are excluded from the circuit.

This time, assume that P2 is at the lowest brightness position.

Since the photocurrent of P2 is the smallest, the anode of P2 has the lowest potential among the anodes of P1 to P4, and the potential of the anode of P2 is the lowest among the anodes of P1 to P4.
Diode DIl connected to each connection point of OI to TO4
~ Among D14, only D12 is conductive and the others are biased in the opposite direction.

Therefore, the emitter potential of transistor T2 connected to the common anode of D11 to D14 becomes approximately the same potential as the collector of TO2, and transistors TI, T2, and diode D
12. Current flows through transistor TO2, and the collector potential of T2 decreases. Since the collector of T2 is connected to the gate of transistor F (FET), the source potential of F decreases, and this potential flows through contact b of switch S2. Provided to the common base of transistors TOI-TO4.

TO2 is determined by the common base potential of TOI to TO4.
If the collector current flowing through P is less than the photocurrent of P2, then P
Since the anode potential of 2 tries to rise, the rise is T
2. It is transmitted to the common base of TOI to TO4 through F,
It acts to increase the collector current of TO2.

On the other hand, when the common base potential of TOI to TO4 is high and the collector current of TO2 is larger than the photocurrent of P2, more current flows from T2 through D12, the collector potential of T2 decreases, and this potential drop becomes TO1. ~ It is transmitted to the base of TO4 and acts to reduce the collector current of TO2.

Therefore, the collector current of transistor TO2 is equal to the photocurrent of P2, and the voltage between the common base and emitter of TOI to TO4 is the logarithmically transformed photocurrent of P2 at the lowest brightness position. Output terminal OUT
is output through.

During this time, the photocurrent of other photodiodes pLp3tp4 etc. receiving brighter light than P2 is transferred to transistors TO1,
Since it is limited by TO3, TO4, etc., it generates a photovoltaic force, which acts to raise the collector potential of the transistor TO1, etc. to a level higher than the anode of the power supply E, and deepens the reverse bias of the diode D11, etc. It does not interfere at all with the current corresponding to the lowest brightness flowing through P2 and TO2.

Finally, the case of full-plane average photometry will be explained.

In this case, open switch S1, set S2 to contact a side,
Set S3 to contact b side.

If you do this, the emitters of transistors TO1 to TO4 will float, so they will be removed from the circuit.
Since the collectors of the transistors T11 to T14 are also disconnected from the power supply E, the base and emitter of the transistors T11 to T14 function as diodes, and the photocurrents of P1 to P4 all flow to the transistor TOO through T11 to T14.

Since the sum of the photocurrents of P1 to P4 flows through TOO, its pace-emitter voltage is a logarithmic conversion of the sum of the total photocurrents of P1 to P4, and this is output to the output terminal OUT as the logarithmically converted average photometric output. be done.

The photodiodes are arranged in a picture panel as shown in Figure 3, but if each diode receives light from only a very small area of the screen, it may actually highlight tiny points that are not important in the screen composition. Since it responds to shadows, it is recommended that the array plane of these elements be slightly shifted from the image plane (3) in FIG. 2 so that each element receives light from a certain area of the screen.

Further, although a circuit switching method was used in the above embodiment to measure the average brightness, the array plane of the photodiodes may be shifted by an arbitrary amount from the imaging plane (3) of the lens L2 in FIG. Alternatively, other lenses may be inserted in addition to the lens L2.

The present invention has the above-described structure, and forms a circuit consisting of a current limiting element, a transistor, and a diode for each of a plurality of photocurrent elements arranged on a screen, and controls the common emitter voltage of the transistor or the diode. By providing the common anode voltage as a current control signal to the current limiting element, the minimum or maximum brightness can be detected.
The exposure can be set according to the brightness of the maximum or minimum brightness in the subject, allowing the camera user to concentrate on his or her own photographic intent without having to worry about special metering operations. .

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 is a diagram showing the arrangement position of the photometric element within the camera, and Fig. 3 is a diagram showing an example of the arrangement of the photometric element within the screen. be. P1-P4: Photovoltaic element, To1-To4: Current limiting element, T11-T142} transistor, DI1-D14:
Diode, S2: Selector switch, OUT: Photometry output terminal.

Claims (1)

[Claims] 1. A plurality of photocurrent elements arranged on a screen, a plurality of current limiting elements connected in series to each of the photocurrent elements, and a base at the connection point between each of the photocurrent elements and the current limiting element. A plurality of transistors having their emitters connected in common; a plurality of diodes having cathodes connected to the connection points of the respective photocurrent elements and the current limiting element and having a common anode; and a common transistor of the transistors. It consists of a changeover switch that transmits the voltage at the common anode of the emitter or the diode to the current limiting element as a current control signal, and the current limiting element is configured to allow a photocurrent corresponding to the maximum or minimum brightness to flow according to the current limiting signal. A photometric device, characterized in that the current control signal is controlled as a photometric output.