JPS6158766B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a photometric circuit for a camera, and more particularly to a photometric circuit using a CdS photodetector for a camera that controls exposure using electrical signals.

Conventionally, CdS light-receiving elements have been widely used in camera photometry circuits because they can be constructed at a lower cost than photovoltaic elements such as silicon diodes. However, in a photometry circuit using a CdS photodetector, even if the information on the amount of incident light obtained from the CdS photodetector is extracted as voltage information and adjusted with a correction resistor to be suitable for apex calculation, this alone will not allow the voltage to respond to changes in the amount of incident light. The rate of change and voltage level are low, making it unsuitable for cameras that control exposure using electrical signals.Moreover, the CdS photodetector is a composite type in which multiple CdS with different resistance ratios are sintered onto a single substrate.
Composite CdS has variations in characteristics such as the ratio of high resistance to low resistance and the rate of change in resistance value with respect to the amount of incident light. Since the accuracy is lower than that of a photometric circuit using an electromotive element, CdS
Information on the amount of incident light obtained by the light receiving element was extracted as current information to cause the meter needle to swing, and the swing angle of the needle was used as apex information in a camera that controlled exposure through mechanical control. .

The present invention provides a photometry circuit that can be used in a camera that extracts incident light amount information obtained by a CdS light receiving element as voltage information and uses it as apex information to control exposure using an electric signal. A detection circuit that outputs a voltage that changes according to a change in the amount of incident light using a light receiving element includes a proportional amplifier circuit that adjustably amplifies the rate of change in the output voltage of the detection circuit with respect to a change in the amount of incident light; The present invention is characterized in that it includes a substantial adder circuit that adjustably changes the level of the output voltage.

Hereinafter, the present invention will be explained based on the drawings.

1 and 3 are circuit diagrams showing embodiments of the present invention, and FIG. 2 is a graph showing the relationship between the amount of incident light and the output voltage of the circuit shown in FIG.

In the figure, a circuit consisting of a combination of a CdS light receiving element 2 connected to a constant voltage power supply 1 and correction resistors 3, 4 and 5 is a commonly used detection circuit, and a CdS light receiving element 2 consisting of a low resistance CdS 2a and a high resistance CdS 2b is used. When light is incident on the light receiving element, a voltage as shown by A in FIG. 2 is outputted to the sliding terminal of the variable correction resistor 5, which is proportional to the amount of incident light converted into an LV value. As mentioned earlier, this output voltage A is
Since the rate and level of change with respect to changes in the amount of light incident on the CdS light-receiving element are low, and these also vary depending on the characteristics of the CdS light-receiving element, it cannot be used as an electrical signal for exposure control as it is.

Therefore, the output voltage A of the above-mentioned detection circuit is inputted to the positive terminal of the amplifier 6, and the output voltage of the output terminal is distributed by the variable resistor 7 and inputted to the negative input terminal thereof. An amplifier circuit is provided to increase the rate of change and voltage level with respect to changes in the amount of incident light, and to correct variations in the rate of change due to the CdS light receiving element. That is, the output voltage of the detection circuit is connected to the output terminal of the amplifier 6 (R
A voltage B multiplied by +r)/r is output as shown in FIG. Note that R and r are distribution resistances of the variable resistor 7, and this distribution resistance inputs a voltage of Br/(R+r) to the negative input terminal of the amplifier 6.

With this proportional amplifier circuit, the rate of change and level of the output voltage of the detection circuit can be increased, and the variable resistance 7
Although variations due to the CdS light receiving element are corrected by this method, it can be used for almost all exposure control, but it is also affected by level variations due to the CdS light receiving element, so there is no universal compatibility.

Therefore, in the example of FIG. 1, the amplifier 8
The voltage of the constant voltage power supply 1 is distributed through a variable resistor 9 and inputted to the positive input terminal of the circuit, and the output of the amplifier 6 and the output of the amplifier 8 of the proportional amplifier circuit are connected to the negative input terminal through resistors 10 and 11, respectively. CdS
The variation in detection voltage level due to variation in light-receiving element characteristics is corrected. That is, by changing the distribution resistance of the variable resistor 9, the output voltage of the amplifier 8 changes in a manner that the output voltage B of the proportional amplifier circuit is shifted almost in parallel, as shown by C and C' in FIG. . However, depending on the resistance ratio of the resistors 10 and 11, the output voltage C of the amplifier 8 or
The rate of change of C' with respect to the change in the amount of incident light is different from the rate of change of the output voltage B of the proportional amplifier circuit, but since the rate of change can be adjusted by the proportional amplifier circuit, the above-mentioned adding circuit can be said to be a substantial adding circuit. .

As described above, the output voltage of the detection circuit using the CdS photodetector is increased by the proportional amplifier circuit to the extent that the rate of change and level in response to changes in the amount of incident light can be used for exposure control. of
Variations caused by the CdS photodetector are corrected, and the adder circuit further corrects level variations caused by the CdS photodetector, so the corrected output voltage of the photometry circuit is universally used as an electrical signal for exposure control. Available.

In Figure 3, the output information of the amplifier 6 of the proportional amplifier circuit is transferred between the proportional amplifier circuit and the adder circuit by ASA information,
This figure shows an example of a photometry circuit for an exposure control camera that prioritizes shutter speed and includes a correction circuit that performs correction based on aperture f-number information and shutter speed information.
Therefore, in FIG. 3, the same functional members as in FIG. 1 are designated by the same reference numerals.

In FIG. 3, variable resistors 12, 13, and 14 are resistances for setting ASA information, open F value information, and shutter speed information, respectively.
The information set by 14 is impedance-converted by amplifiers 15, 16, and 17, respectively, and is passed through resistors 18, 19, and 20 as voltage information with the same voltage change for a 1EV change, and is also transmitted to resistor 21. The signal is input to the amplifier 22 along with the output of the amplifier 6 of the proportional amplification circuit via. Thereby, the amplifier 22 receives the output of the amplifier 6, that is, the photometric information.
Outputs voltage information corrected with ASA information, open F value information, and shutter speed information. The output of this amplifier 22 is the output of the amplifier 6 of the proportional amplifier circuit shown in FIG.
The output of the amplifier 8 of the addition circuit is corrected in the same way as the output of the addition circuit, and the corrected output of the amplifier 8 of the addition circuit is used for setting the aperture.

In addition, in FIG. 3, if the variable resistor 14 is used as an aperture information setting resistor and the output of the amplifier 8 of the adder circuit is used to set the shutter speed, the circuit in FIG. It becomes a circuit. Also, if the input information is photometry information, ASA information, and aperture aperture information, and the output of amplifier 8 drives a circuit that uniquely determines the shutter speed and aperture, it can be applied to a program exposure control camera. It turns out.

As described above, the photometry circuit using the CdS light receiving element of the present invention can be widely applied to cameras that perform exposure control using electrical signals.

[Brief explanation of the drawing]

1 and 3 are circuit diagrams showing embodiments of the present invention, and FIG. 2 is a graph showing the relationship between the amount of incident light and the output voltage of the circuit shown in FIG. 1... Constant voltage power supply, 2... CdS light receiving element, 2a
...Low resistance CaS, 2b...High resistance CdS, 3, 4,
10, 11, 18-21...Resistance, 5, 7, 9,
12-14...variable resistor, 6, 8, 15-17,
22...Amplifier.

Claims (1)

[Claims] 1. A detection circuit that uses a CdS light receiving element and outputs a voltage that changes according to a change in the amount of incident light, a proportional amplifier circuit that adjustably amplifies the rate of change in the output voltage of the detection circuit with respect to a change in the amount of incident light; A photometry circuit for a camera, comprising a substantial adding circuit that adjustably changes the level of the output voltage of the circuit.