JP3078400B2 - 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, since the junction capacitance Cj is a small capacitance and the output current of the SPD greatly changes in accordance with the change in the brightness of the external light, there is a problem that the junction capacitance Cj alone cannot cope with the change in the brightness of the external light. there were.

[0003]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a comparison circuit in which a reference voltage is applied to a first input terminal and a first circuit connected between the second input terminal and a Vss power supply. Switch means, and a second switch connected in series to the Vss power supply from the second input terminal via a sensitivity switching capacitor.
And switching means, and a control circuit for controlling said first and second switch means, when dark the first switch hands
Opening the stage, opening the second switch means, accumulating a photocurrent using only the junction capacitance of the silicon photodiode, and opening the first switch means and closing the second switch means when bright, Photometry is performed by accumulating a photocurrent using the junction capacitance of the silicon photodiode and the capacitor.

[0004]

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 for a camera according to the present invention, and FIG. 2 is an explanatory diagram showing a relationship between luminance and photometric time.

In FIG. 1, a reference voltage source 2 is applied to a non-inverting input terminal of an operational amplifier 1, and np is applied to an inverting input terminal.
Collector of n transistor 3, capacitor 4, and SP
The anode of D6 is connected, and the output terminal is connected to electromagnetic drive means for closing a shutter (not shown). SP
The voltage Vdd is applied to the cathode of D6. 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 CPU via a resistor.
8 is connected to the A terminal. The base of the transistor 3 is connected to the B terminal of the CPU 8 via a resistor. The external light luminance detection circuit 5 has a light receiving element inside, and its output is C
It is connected to the C terminal of PU8. The output terminal of the release 9 is connected to the D terminal of the CPU 8. Next, the operation of the present invention will be described with reference to FIGS. Voltage Vdd
Is applied, the output of the A terminal of the CPU 8 is L, the transistor 7 is off, the output of the B terminal is H, and the transistor 3 is on, so that the junction capacitance Cj of the SPD 6 is charged to the potential Vdd. I have. The external light luminance detection circuit 5 detects the luminance state of the subject and sends the information to the CPU 8. When determining that the subject is darker than the predetermined brightness, the CPU 8 keeps the terminal A at L, but when determining that the brightness is higher than the predetermined brightness, the terminal A is set to H and the transistor 7 is turned on. If the subject is darker than the predetermined brightness,
In synchronization with the opening of the shutter, a release signal from the release 9 enters the D terminal of the CPU 8, and in response to the release signal, the B terminal of the CPU 8 becomes L, and the transistor 3
Becomes off. When the transistor 3 is turned off, S
When the electric charge charged in the junction capacitance Cj of the PD 6 starts discharging, the inverting input terminal voltage Vn of the operational amplifier 1 rises and reaches the reference voltage Vref of the non-inverting input terminal. Close the shutter.
As shown in the line S1 in FIG.
6 is measured only by the junction capacitance Cj.

If the subject is brighter than a predetermined brightness, C
The A terminal of the PU 8 is H, and the transistor 7 is on. In synchronization with the opening of the shutter, a release signal from the release 9 enters the D terminal of the CPU 8, and in response to the release signal, the B terminal of the CPU 8 becomes L and the transistor 3 becomes off. As a result, the capacitor 4 starts charging, the terminal voltage Vn of the operational amplifier 1 increases, and when the terminal voltage Vn reaches the reference voltage Vref, the operational amplifier 1 sends an inverted output to close the shutter. When the image is brighter than the EV 10 as shown by the line S2 in FIG. 2, the condenser 4 is added and the photometry is performed.

In the embodiment, the external light luminance detecting circuit is provided separately. However, the present invention is not limited to this, and the luminance judging circuit is connected to the inverting input terminal of the operational amplifier 1 via the switch circuit. The light receiving element of the SPD 6 can be used to determine the brightness of the external light prior to the release operation.

[0008]

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. Can be spread.

[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.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 operational amplifier 2 reference voltage source 3 transistor 4 capacitor 5 external light luminance detection circuit 6 silicon photodiode (SPD) 7 transistor 8 CPU 9 release

Claims (1)

(57) [Claims] A comparison circuit having a reference voltage applied to a first input terminal; a second input terminal of the comparison circuit and a silicon photodiode reverse-biased to a Vdd power supply; a second input terminal and a Vss power supply; A second switch connected in series to a Vss power supply via a sensitivity switching capacitor from the second input terminal; and a control for controlling the first and second switch. A first switch means is opened and a second switch means is opened when dark, and a photocurrent is accumulated using only the junction capacitance of the silicon photodiode .
Opening the first switch means and closing the second switch means,
A photometric device for a camera, wherein photometry is performed by accumulating a photocurrent using a junction capacitance of the silicon photodiode and the capacitor.