JP3071565B2 - Camera photometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photometer for a camera using a silicon photodiode (SPD) as a photometer.

[0002]

2. Description of the Related Art A technique using an SPD as a photometric device is disclosed in Japanese Patent Application Laid-Open No. 56-57028 (precedent).
Are known. In this precedent, light reflected from a film surface is received by an SPD, and an output current of the SPD is charged as an integrated voltage to a junction capacitor Cj between a cathode and an anode of the SPD to perform photometry. However, the junction capacitance Cj is a small capacitance, and SP j
Since the output current of D greatly changes, this junction capacitance Cj
There is a problem that it is not possible to cope with a change in luminance of external light with only the light source.

[0003] In addition, depending on the state of light rays illuminating the subject, there is a demand of the photographer who wants to select between photographing by average photometry and photographing by spot photometry, and a mechanism that can easily perform this selection is desired. ing.

[0004]

SUMMARY OF THE INVENTION In view of the above circumstances, the invention according to claim 1 of the present invention is directed to a comparison circuit in which a reference voltage is applied to a first input terminal, and a second input terminal of the comparison circuit. And two silicon photodiodes (hereinafter referred to as SPDs) for the spot and the periphery, which are connected in series to the peripheral SPD and closed to use both of the two SPDs, or opened to use the two SPDs for the spot A first switch for selecting whether to use only the SPD, a second switch for opening and closing the second input terminal and the Vss power supply, and a second switch connected to the second input terminal via a first capacitor. Three switch means, fourth switch means connected to the second input terminal via a second capacitor, and a control circuit for controlling the switch means, wherein both of the two SPDs are selected. When the light is bright, the third switch means is closed and the photocurrent is accumulated using the first capacitor. When the two SPDs are both selected, when the light is dark, the third SPD is turned on. Open the switch means and open the two S
The photocurrent is accumulated only by the junction capacitance of the PD, and when the spot SPD is selected, at least when it is bright, the fourth switch means is closed and the photocurrent is accumulated using the second capacitor. It is characterized by the following. Also,
According to a second aspect of the present invention, in the photometric device for a camera according to the first aspect, the first switch and the fourth switch are controlled by the same signal, and the fourth switch is turned on when the first switch is closed. The switch means is open, and when the first switch means is open, the fourth switch means is closed.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. FIG. 1 is a circuit diagram of a photometric device of a camera according to the present invention, FIG. 2 is an explanatory diagram showing a relationship between luminance and photometric time,
FIG. 3 is a flowchart according to the present invention.

In FIG. 1, a reference voltage source 2 is applied to a non-inverting input terminal of an operational amplifier 1 and an FE is connected to an inverting input terminal.
Drain of T transistor 3, capacitors 4 and 8, S
The anodes of PD5 and SPD6 are connected, and the output terminal is connected to the E terminal of CPU12. The collector of the pnp transistor 10 is connected to the cathode of the SPD 6, and the emitter is connected to the cathode of the SPD 5.
The cathode of the SPD 5 is connected to the collector of the pnp transistor 11 to which the voltage Vdd is applied to the emitter. The base of the transistor 11 is connected to the A terminal of the CPU 12 via a resistor. Transistor 1
The base of 0 and the base of the transistor 9 are connected to the B terminal of the CPU 12 via a resistor. The other end of the capacitor 4 is connected to the collector of an npn transistor 7, and the base of the transistor 7 is connected to the C terminal of the CPU 12 via a resistor. The gate of the FET transistor 3 is C
It is connected to the D terminal of PU12. The F terminal of the CPU 12 sends an inverted output to a shutter closing mechanism (not shown),
The shutter is closed, the G terminal is connected to a spot metering setting mechanism (not shown), and the H terminal is connected to a release mechanism (not shown).

In the present invention, photometry can be performed by switching between low-luminance average photometry, high-luminance average photometry, and spot photometry. The output of the B and C terminals of the CPU 12 and the selection capacitors in each case are shown in Table 1.

[0008]

[Table 1]

Here, the capacitor 4 is C4 = Cj
× 2 ^(17-10) , and the capacitor 8 is set as C8 = Kspd × C4, where Kspd is the photocurrent ratio between the SPD for spot 5 and both SPDs under the same illuminance. The range of photometric ranges in low-luminance average photometry, high-luminance average photometry, and spot photometry are the same, and quantization errors, etc.
The resolution is also equal.

Next, the operation of the present invention will be described with reference to the drawings. When the voltage Vdd is applied, the A
Since the output of the terminal is L, the transistor 11 is on, the output of the terminal B is L, the transistor 10 is on, the transistor 9 is off, and the output of the terminal C is L, so that the transistor 7
Is off (101), and since the output of the D terminal is L and the transistor 3 is on, SPD5 and SPD6
Is charged to the potential Vdd. When the subject is darker than a predetermined brightness, a release signal enters the H terminal of the CPU 12 by closing a shutter button (not shown), and in response to the release signal, the D terminal of the CPU 12 becomes H, and the transistor 3 is turned off. Become. When the transistor 3 is turned off, the charge charged in the junction capacitance Cj of the SPD5 and SPD6 starts discharging (10
2). When the inverting input terminal voltage Vn of the operational amplifier 1 rises and reaches the reference voltage Vref of the non-inverting input terminal, the operational amplifier 1
Sends an inverted output to the terminal E of the CPU 12. If the output of the inverted output is longer than a predetermined time Tref measured from the time when the transistor 3 is turned off (103), CP
U12 receives the inverted input signal and sends a shutter closing signal to an F terminal to close a shutter (not shown). FIG.
As shown in the line S1, the light is measured only by the junction capacitance Cj of the SPD.

When the object is brighter than a predetermined brightness, when the transistor 3 is turned off, the electric charge charged in the junction capacitance Cj starts to be discharged (102). When the inverting input terminal voltage Vn of the operational amplifier 1 rises and reaches the reference voltage Vref of the non-inverting input terminal, the operational amplifier 1 sends out an inverted output. If the time is earlier than a predetermined time (103), the spot metering instruction is issued. It is determined whether or not the signal has entered the G terminal 12 (104), and if there is no command for spot metering, the L output is sent to the B terminal of the CPU 12 and the H output is sent to the C terminal (105), and the high brightness average metering Switch to (106).
At this time, the shutter closing signal is not sent to the F terminal, but the L output is sent to the D terminal for a short time, and the transistor 3 is turned off.
After n, the photometry is restarted. When the capacitor 4 is charged by the photocurrents of the SPDs 5 and 6, and the inverting input terminal voltage Vn reaches the reference voltage Vref, the operational amplifier 1
Sends an inverted output to the E terminal of the CPU 12,
Terminal F transmits a shutter closing signal and closes the shutter. When the image is brighter than the EV 10 as shown by the line S3 in FIG. 2, the photometry is performed by adding the condenser 4.

In the case of spot metering, when the operational amplifier 1 sends an inverted output within a predetermined time, it is determined whether or not there is a spot metering command (104). H and C terminals are L
Is output (107) and switched to spot metering (108). At this time, the shutter closing signal is not sent to the F terminal, but the L output is once sent to the D terminal for a short time, the transistor 3 is turned on, and then the photometry is restarted. SPD
When the capacitor 8 is charged by the photocurrent 5 and the inverted input voltage Vn reaches the reference voltage Vref, the operational amplifier 1 sends an inverted output to the E terminal of the CPU 12, and the F terminal of the CPU 12 sends a shutter closing signal to output the shutter closing signal. Is closed. Spot metering is performed as indicated by S2 in FIG. This
Here, the correspondence between the configuration of the claimed invention and the embodiment is described.
For the sake of clarity, the following is described in comparison. Structure of the invention Example (see FIG. 1) SPD for spot SPD for peripheral of SPD5 SPD6 first switch means Transistor 10 second switch means Transistor 3 third switch means ... Transistor 7 Fourth switch means Transistor 9 First capacitor Capacitor 4 Second capacitor Capacitor 8

[0013]

As described above, the photometric device for a camera according to the present invention can select between the case of using only the junction capacitance of the SPD and the case of adding a separate capacitor, and can increase the dynamic range of the photometric range. It can be expanded, and can switch between average photometry and spot photometry with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a photometric device for a camera according to the present invention.

FIG. 2 is an explanatory diagram showing a relationship between luminance and photometric time.

FIG. 3 is a flowchart according to the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 operational amplifier 2 reference voltage source 3 FET transistor 4 capacitor 5 silicon photodiode (SPD for spot ) 6 silicon photodiode (SPD for peripheral ) 7 transistor 8 capacitor

Claims (2)

(57) [Claims] 1. A comparison circuit in which a reference voltage is applied to a first input terminal, and two silicon photodiodes (hereinafter referred to as SP) for a spot and a periphery connected to a second input terminal of the comparison circuit.
D), and the two SPs connected in series to the peripheral SPD and closed.
D for both spots or open for S
A first switch for selecting whether to use only the PD, a second switch for opening and closing the second input terminal and a Vss power supply, and a second switch connected to the second input terminal via a first capacitor. Three switch means, fourth switch means connected to the second input terminal via a second capacitor, and a control circuit for controlling the switch means, when both of the two SPDs are selected. When the light is bright, the third switch means is closed and the photocurrent is accumulated by using the first capacitor. When both the two SPDs are selected, and when the light is dark, the third switch is turned on. Open the means and the two SPDs
Storing the photocurrent only by the junction capacitance of the above, and when the spot SPD is selected, at least when it is bright, closing the fourth switch means and storing the photocurrent using the second capacitor. A photometric device for a camera. 2. The photometric device for a camera according to claim 1, wherein the first switch and the fourth switch are controlled by the same signal, and when the first switch is closed, the fourth switch is activated. A photometric device for a camera, wherein the fourth switch is closed when the first switch is open and the first switch is open.