JPS61251827A - Camera - Google Patents

Abstract

PURPOSE:To reduce the influence of tandelta of a capacitor for detecting subject brightness or distance to a subject as much as possible and to obtain accurate detection data by providing the capacitor for range finding with a clipping circuit. CONSTITUTION:A range finding processing part B measures the time (when the output of a comparator 3 is at a high level) up to the coincidence of the voltage Vc of a capacitor Cs charge with a constant current with a range finding voltage Va proportional to the distance to the subject by a CPU 1, and range finding processing is carried out. The series circuit of two diodes D1 and D2 is connected across the capacitor C2 and the maximum charging voltage of this capacitor C2 is clipped. Consequently, the voltage of the capacitor C2 never becomes transient and a charge remaining after initialization is suppressed to an extent where there is no trouble to practical use.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a camera that can accurately detect external information for determining exposure or focus, such as subject brightness or distance to a subject.

[Prior art]

Automatic focus control for cameras with automatic exposure devices detects the brightness of the subject to determine exposure, then emits infrared rays to the subject to detect the distance to the subject, and uses the results to adjust the shooting lens. This is done by determining the focus (focus position) and automatically moving the photographic lens to the in-focus position.

By the way, when detecting the brightness of a subject or detecting the distance to the subject, the detection signal is usually obtained in the form of voltage, but in a camera that has a built-in computer to control the whole thing, it is difficult to capture the detection data. The voltage is converted to one hour. That is, this is done by measuring the time required to charge the capacitor.

However, capacitors have tan δ, and there is a delay in charging and discharging the capacitor itself, so it may not be possible to collect accurate time data during the above-mentioned one-hour voltage conversion. The image may be out of focus or out of focus.

[Purpose of the invention]

The present invention was made in view of these points, and its purpose is to eliminate the influence of tan δ of the capacitor as much as possible,
To provide a camera that can capture accurate data.

[Structure of the invention]

To this end, the present invention provides a camera that detects external information for determining exposure or focus, such as subject brightness acid t1, distance to the subject, etc., using the charging time of the capacitor. It is configured by providing a circuit.

〔Example〕

Examples of the present invention will be described below. In Figure 1, A is a subject brightness detection processing unit that uses the above-mentioned brightness one-time conversion method, and B is a system that converts a distance measurement signal obtained by a distance measurement IC (not shown) into time. The distance measurement processing section 1 is a CPU that controls the entire system.

The object brightness detection processing unit A includes a photoconductive element (1, dS) that reduces internal resistance as the brightness of the object increases, and a capacitor C1 that charges a current controlled by CdS.
At the initial stage, the capacitor CI is
Transistor Q1 initializes by discharging the charge of
, the voltage VCI of the capacitor ci is applied to the inverting input terminal, and the power supply voltage ■ is applied to the non-inverting input terminal through resistors R1 and R2.
, and a pull amplifier resistor R3 connected to the output side of the comparator 2.

The object brightness detection processing unit A detects a period of time after the initialization of the capacitor C1 by the transistor Q1 until the voltage VCI of the capacitor C1 matches the reference voltage Vr (this time is when the output of the comparator 2 is at a high level). The CPU 1 measures the time during which the object brightness remains.

For example, when the subject brightness is high, the voltage Vc of the capacitor C1 rises to the reference voltage Vr in a short time, and the measurement time becomes short. Conversely, when the subject brightness is low, the measurement time becomes long.

On the other hand, the distance measurement processing section B includes a capacitor C2 for charging a constant current regulated by a resistor R4, a transistor Q2 for initializing the capacitor C2, a diode D1 for clipping the maximum voltage of the capacitor C2,
D2, a comparator 3 to which the voltage VCZ of the capacitor C2 is applied to the inverting input terminal and a ranging voltage Va obtained by a ranging circuit (not shown) to the non-inverting input terminal, and the output side of the comparator 3. It consists of a pull-up resistor R5 connected to.

In this distance measurement processing section B, the time required for the voltage vex of the capacitor C2 charged with a constant current to match the distance measurement voltage Va proportional to the distance to the subject (during this time, the output of the comparator 3 is high time), cpu
The distance measurement process is performed by measuring at i.

By the way, when adjusting this distance measurement processing section B at the manufacturing stage, it is necessary to adjust the value of resistor R4 and the constant current value, but the result of this adjustment is the actual amount of movement of the photographing lens. And f11! However, this resistance R4
The area from the part to the part that detects the amount of movement of the photographing lens (the part that is made of a comb-teeth electrode and generates a feedback signal) is a so-called black box, and the adjustment result of the resistor R4 is accurately determined by the photographic lens. It is not possible to confirm whether or not this is reflected in the amount of movement. That is, for example, even if the amount of movement of the photographic lens moved by the output of the CPU 1 is incorrect for some reason, it cannot be confirmed.

Therefore, in this embodiment, dummy data (focus determination signal) indicating the current distance measurement data is obtained from the CPU at the terminal 4. Therefore, the resistor R4 can be adjusted while measuring and confirming the dummy data obtained at the terminal 4 by some method, and if there is any deviation in the movement of the photographic lens, it can be immediately discovered.

On the other hand, in the capacitor C2 that is charged with a constant current, as described above, the transistor Q2 is set to CP before the start of charging.
Controlled by the UI, the capacitor C2 is made conductive for a certain period of time, short-circuited, and initialized, but the charge in the capacitor C2 must be completely discharged during that time.

However, as described above, capacitors generally have tan δ, which is a response delay element, and even if both ends of the capacitor are short-circuited, it takes a certain amount of time for discharge, resulting in a delay.

Therefore, the time required for complete discharge varies depending on the level of voltage of the capacitor C2, and complete discharge may not be possible within the predetermined conduction time of the transistor Q2, and charges may remain even after initialization is completed.

Therefore, in this embodiment, a series circuit of two diodes D1 and D2 is connected in parallel to both ends of the capacitor C2 to clip the maximum charging voltage of the capacitor C2.

As a result, the voltage of the capacitor C2 does not become excessively large, and the charge remaining at the time of initialization can be kept to a level that does not cause any practical problems.

Note that such a configuration can also be applied to the capacitor C1 of the subject brightness detection processing unit A, but since the charging time constant for this capacitor C1 is relatively large, the influence of residual charge can be ignored, and this implementation It was not applied in the example.

FIG. 2 shows an infrared light emitting circuit section for distance measurement. 5 is a battery built into the camera, Q3 is a switching transistor that turns on when the shutter switch S1 is turned on, 5 is a DC/DC converter that boosts the battery voltage (for example, 3V) to a DC voltage of about 20V, and C3 is for instantaneous discharge. A capacitor with a large capacity (for example, 56 μF), an infrared light-emitting diode made of galvanic arsenic, etc.
6 is a protection resistor, and Q5 is a transistor for driving the LED. 'B When the switch Sl is closed, the C/DC converter 5 generates a high voltage and starts charging the capacitor C3, and the capacitor C3 becomes D after a predetermined period of time.
It is charged to the output voltage of C/DCC/formula 5. Note that this capacitor C3 is initialized by switch S.
This is done at the start of turn-on of 1.

Then, when a control signal is generated from the CPU, the transistor Q5 turns on and instantly discharges the charge in the capacitor C3 to the LED, causing the LED to emit light with sufficient brightness.
Emit infrared light to the subject.

FIG. 3 shows a flowchart of the sequence from when the shutter button is pressed until distance measurement data is taken into the CPUI, and FIG. 4 shows a timing chart at that time.

First, when the shutter button is pressed, the switch S1 is turned on and the T1 timer (90n+s) is set in step 11, and then in the next step E2, the subject brightness is detected by the subject brightness detection section processing A in Figure 1. exposure will be set automatically. In this step 12, the internal resistance of the CdS changes considerably depending on the brightness of the object, and it takes about 1 ms for the voltage of the capacitor C1 to reach the reference voltage Vr in the short case, but as much as 70 m5 in the long case.

Therefore, in this embodiment, as mentioned above, a T1 timer of 90+ms is used with a little margin from 70m5, and the remaining time of step 12 is absorbed by step 13, thereby forming a waiting time after detecting the subject brightness. In this way, the time from turning on the switch S1 to moving to step 14 for distance measurement is made constant.

This is to keep the charging time constant until the high voltage is generated for distance measurement in step 15. LE for infrared emission
The high voltage applied to D is the voltage charged in capacitor C3, as shown in FIG.
1 is turned on, therefore, if the time from the time when the switch 81 is turned on until the transistor Q5 is turned on varies, a difference will occur in the emitted energy of the LED, and the distance measurement will be inaccurate. .

Therefore, by using the T1 timer as described above, the switch Sl
The time from the time to the LED light emission is made to be constant.

When the distance measurement is performed in step 14, a T2 timer (90n+s) is set in step 15 from the start of the distance measurement, and the 90n+s of the T2 timer is set via step 16.
When +s has elapsed, the distance measurement data is taken into the CPUI.

During distance measurement, the LED is made to emit light as described above, but when the emitted light is finished, charging of the capacitor C3 is started again. However, since this charging current has a fairly large value, the ground is shaking at the beginning of charging, and the ranging voltage Va obtained from the amount of reflected light of the emitted infrared light fluctuates.
Even if the voltage Va is converted into time in this state, accurate ranging data cannot be obtained.

Therefore, as described above, after the set time of the T2 timer has elapsed, the CPU turns the transistor Q2 from on to off, starts constant current charging to the capacitor C2, and converts the ranging voltage Va into time and imports it. This makes it possible to obtain accurate ranging data.

〔Effect of the invention〕

As described above, according to the present invention, since a clip circuit is provided in the capacitor for detecting the brightness of the subject or the distance to the subject, it is possible to minimize the influence of the tan δ of the capacitor and obtain accurate detection data. can.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a part for capturing a subject brightness signal and a distance measurement signal in an embodiment of the present invention, Fig. 2 is a circuit diagram of an infrared light emitting circuit for distance measurement, and Fig. 3 is a circuit diagram showing the subject luminance signal acquisition part. A flowchart from detection to acquisition of distance measurement data, and FIG. 4 is a timing chart corresponding to the flowchart.

Claims (1)

[Claims] (1) In a camera that uses the charging time of the capacitor to detect external information for determining exposure or focus, such as subject brightness or distance to the subject, a clip circuit is provided between both ends of the capacitor. A camera featuring