JPS59220720A - Exposure control circuit of camera - Google Patents

Abstract

PURPOSE:To prevent the charging current of a capacitor from becoming excessive, and slow down voltage rising and adjust a shutter trigger switch and the start of opening operation easily by connecting a resistance with a properly large resistance value to a CdS photodetecting element in series. CONSTITUTION:An exposure control circuit has the high brightness correcting resistance connected to the CdS in series. The capacitor voltage (t) rises slowly with regard to the input and output of the comparator 6 of this control circuit and the opening waveform of a shutter, and time differences T1 and T2 are adjusted extremely easily even with high brightness. The resistance value Rs of the resistance 8 is set preferably so that 0.5REV10017<=Rs<=2REV10017, where EV10017 is the quantity of light and REV10017 is the resistance value of the CdS. This is applied similarly to a control circuit which performs discharge through a CdS.

Description

[Detailed description of the invention] (Field of industrial application) Is this invention a product of cameras? 1illllII411
1! The present invention relates to a circuit that facilitates exposure control for photographic subjects, especially for photographic subjects.

(Prior Art) Among automatic exposure control circuits for cameras, a shutter control circuit using CdS is well known.

An example is shown in FIG.

In the figure, turn on the IFi shutter trigger switch.
As a result, the capacitor 4 is charged through the CdS light-receiving element 2 and the shutter opening operation is started.

The voltage determined by the variable resistor 5 is input to the comparator 6 along with the voltage of the capacitor 4, and the capacitor 4 is charged, and the voltage is equal to the reference voltage determined by the variable resistor 5. At this time, the output of the comparator 6 is inverted, and the shutter control magnet 7 controlled by the output is activated, closing the shutter and ending the process.

Note that 3 is an ASA filter.

FIG. 2 shows the input and output waveforms of the comparator 6 and the shutter aperture waveforms. FIG. 6B shows the input to the comparator 6, where S is the reference voltage determined by the variable resistor 5. ) 1 shows the voltage change of the capacitor 40, and when the voltage t, which increases with the passage of time when the switch 1 is turned on at time T1, exceeds the reference voltage S, the figure (a)
The comparator output is inverted as shown in the figure, and the magnet 7 is activated. During this time, as shown in FIG. 1B (e), the shutter begins to open at time T2, which is a little later than time T1, starts its closing operation at time T4 when magnet 7 is activated, and closes at time T5. There is no problem when the brightness of the subject is relatively low, but a problem occurs when the brightness is high, the resistance is steep and small, and the pressure rises quickly.

However, as shown by the dashed line in FIG. 2(b), if the photoelectric current of the capacitor t4 is large and the voltage t' rises rapidly, the shutter will close at T3 before the shutter reaches the entire track. The closing operation begins. For this reason, in the case of extremely high-brightness subjects, deviations in the T3 or 12th place values will occur even when no light is used, and the shutter release will cause the switch 1v) ONv) timing control to minimize the time difference between T1 and T2. Subtle adjustments are required.

(Object of the invention) The present invention provides a control circuit that does not have the above drawbacks by connecting an appropriate resistor in series with Cda and appropriately suppressing the rising speed k of the capacitor voltage tυ. This is what we are trying to do.

(Structure of the Invention) As shown in FIG. 3, the exposure control circuit of the present invention has a high brightness correction resistor 8 connected in series with Cd52.

FIG. 4 shows the input/output waveform of the comparator 6 and the shutter opening waveform caused by this control circuit.

As shown in FIG. 2(b), the capacitor voltage tQ rises more slowly than in FIG. 2(b), and the time differences T, . . . T2 can be adjusted extremely easily even at high brightness. Of course,
The exposure time can be adjusted by reducing the reference voltage 8. If the resistance value of the inserted correction resistor 8υ is too small, the effect of suppressing the rise of the capacitor voltage will be small, and the time difference T1, T2 On the other hand, if it is too large, the rise of the capacitor voltage Q will be slow, and in order to obtain a short launch time, the reference voltage set by the variable resistor 5 must be low. This causes the problem of overloading. Therefore, the correction resistance 8 ■ resistance IRBI/'i
, the light amount value EV, the resistance value of CdS at oo17 is RE
0.5Rk when V10017; Vt oo 17
≦R8≦2 '1V1oo It is desirable to select the range of 17.

The above υ is implemented and 0 is the photoelectric control circuit of the capacitor v■
However, it goes without saying that the same can be applied to a type υ control circuit that discharges through CdS.

(Young fruit of invention Q) This invention, as in the above example, is based on a unique configuration in which a resistance straightener i7t of a size corresponding to IfL is connected to a CdS receiving water element element l. It prevents the photoelectric current of the capacitor from becoming excessive, ``slows the rise of voltage change, and
It is possible to easily adjust the timing of the start of the shutter trigger switch and shunter opening operation, to prevent accidents such as non-lighting even in the case of wedge-shaped, high-brightness objects, and to provide an exposure control circuit with f1 performance. I can do it.

[Brief explanation of drawings]

@Figure 1 is a circuit diagram of a conventional lace-drawing device, Figure 2 is a timing chart showing its operation, Figure 3 is a circuit diagram of one embodiment of the exposure control circuit of the present invention, and Figure 4 is a circuit diagram of the exposure control circuit of the present invention. See the timing chart. 1; Shutter trigger switch 2: CDS light receiving cable 3
:ASA filter 4:Capacitor 5:Variable resistor 6:
Comparator 7: Shutter control magnet 8: Compensation resistance Patent applicant Konishi Rokuyoshin Kogyo Niji Company applicant agent Patent attorney Fumi Sato (and 1 other person)

Claims (1)

[Claims] In an exposure control circuit that uses CdS as a light-receiving element, discharges the element to photodischarge a capacitor, and determines the exposure time by the time allowed for the voltage change, a correction resistor is connected in series to the light-receiving element, and the correction is performed. Resistance value R8f of resistor:, light exposure EV
CdS resistor in 1oo17 1LEV1oou
7, then 0.5aav10017 ≦R8≦2
Camera O exposure control circuit with special features in the range of REV10017