JPS6238690B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrical circuit for controlling and displaying exposure in a camera.

Conventionally, this type of electric circuit has been shown in Figure 1, and when the release button is pressed lightly and contact pieces 1 and 2 of switch SW ₁ are connected, power E _B is turned on and " It is in warning mode. In other words, if the trigger switch TR1SW is on, the exposure metering light receiving element Rcds and the comparison resistor
The divided voltage with _R1 is compared with the reference voltage Vref by the variable resistor _VR1 in the comparator COMP, and its output is applied to the resistor of the hand-wave warning light emitting diode LED.
Added via _R2 . Therefore, this light emitting diode LED turns on when the outside light is dark and turns off when it is bright. This is "warning mode". Next, when the release button is pressed deeper, contacts 1, 2, and 3 of switch SW ₁ are connected, and the camera enters "timer mode." At this time, the resistor _R1 is short-circuited by connecting the contacts 2 and 3 of the switch _SW1 , thereby forming a normal timer circuit. If the trigger switch TR1SW is on now, the shutter control magnet Mg and light emitting diode LED
turns on. Here, the light emitting diode LED turns on regardless of the brightness of the outside light, which causes an incorrect display. At this time, when the mechanical release is performed, the trigger switch TR1SW is turned off at the same time as the shutter blade opens, and integration is started by the light receiving element Rcds and the integrating capacitor _C1 . When the integrated voltage reaches the reference voltage Vref, the magnet Mg and the light emitting diode LED are turned off, the mechanical lock is released, the shutter blade closes, and the required shutter time is obtained.

The above operation is illustrated in Figure 2, and as you can see from this figure, the structure of the release button is such that if it can be easily stopped within the range where the above erroneous display of the light emitting diode LED is made, it can be stopped within that range. When this happens, the light-emitting diode LED lights up regardless of the brightness of the outside light, which is undesirable for operation.
Therefore, it is better for the stroke in the above range to be as small as possible, but if the release mechanism is a sensor type, the entire stroke itself is small, e.g.
Since it is 1.5 mm (usually about 6 to 8 mm), it is difficult to adjust the above range to a sufficiently small value, and it is currently impossible to completely eliminate erroneous display by light emitting diodes.

If only this erroneous display can be eliminated, the following configuration may be used. That is, the switch _SW1 may be switched to the timer mode after the mechanical release has been performed. In that case, it is necessary for the magnet Mg to be mechanically held before the trigger switch TR1SW is turned off (integration starts), and in order to hold it,
A time T ₁ of about 10 msec is required. This operation is illustrated in FIG. 3. As you can see in this figure, with this configuration, if the outside light is bright and the "warning mode" is activated, the magnet Mg and light emitting diode
If the above-mentioned time T ₁ is not longer than 10 msec when the LED is off, the magnet Mg cannot be held, so the magnet Mg "falls". To prevent this, turn on the mechanical governor until the trigger switch TR1SW turns on, and _then
It would be possible to make it 10 msec or more, but this would complicate the mechanism, which is not preferable.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrical circuit for a camera that eliminates the above-mentioned drawbacks and prevents erroneous display and shutter drop.

Embodiments of the present invention will be described below with reference to the drawings.

First, before explaining this embodiment, let us consider a normal timer circuit in a camera. In this timer circuit, the light receiving element for exposure metering is
Rcds and an integrating capacitor _C1 are connected in series between points A and B, and a trigger switch TR1SW is connected in parallel with the integrating capacitor _C1 . Also, a variable resistor _VR1 is connected between points A and B, and its sliding terminal is connected to the inverting input terminal of the comparator COMP. The connection point D of the light receiving element Rcds and the capacitor _C1 is connected to the non-inverting input terminal of the comparator COMP.
The power terminals of COMP are connected to points A and B. Furthermore, a shutter control magnet Mg is connected between the output terminal of the comparator COMP and point A, and both ends of a DC power source E _B are connected to points A and B.

When the trigger switch TR1SW is turned on now, the output of the comparator COMP becomes a low level, and the magnet Mg is driven. When the mechanical release is performed, the trigger switch TR1SW is turned off at the same time as the shutter blade opens, and the integration of the power supply voltage EB is started by the light receiving element Rcds and the capacitor _C1 . When the integrated voltage reaches the reference voltage Vref by variable resistor VR ₁ , the comparator
COMP output is inverted to high level and magnet
The Mg is turned off, the mechanical lock is released, the shutter blade closes, and the required shutter time is obtained. At this time, the timer time T from when the trigger switch TR1SW turns off to when the magnet Mg turns off is T=-C ₁ Rcds ln (1-Vref/EB)...(1), and the reference voltage Vref is set by the variable resistor. Since it is given by dividing the power supply voltage EB by VR ₁ , the voltage division ratio is α
Then, Vref=αEB ...(2), so equation (1) becomes T=-C ₁ Rcds ln(1-α) ...(3), and the timer time T is independent of the power supply voltage EB. However, it is assumed that there is no fluctuation in the power supply voltage during integration. Since the light receiving element Rcds, the capacitor _C1 , and the variable resistor _VR1 form a bridge in this way, a timer time T that is independent of power supply voltage fluctuations can be obtained.

In this embodiment, as shown in FIG. 5, in the timer circuit, point B is connected to point E via a resistor _R1 , and the power terminal of the comparator COMP is connected to points A and E. Further, the switch SW ₁ has two contact pieces 1 and 2, the contact piece 1 is connected to the negative terminal of the DC power source E _B , and the contact piece 2 is connected to the point E. variable resistance
Both ends of VR ₂ are connected to points A and E, and the sliding terminal is connected to the inverting input terminal of the comparator COMP via a capacitor C ₂ . A hand shake warning light emitting diode LED is connected between points A and E via a resistor _R2 , and a thyristor SCR is connected in parallel with this light emitting diode LED. The gate of thyristor SCR is connected to the output terminal of comparator COMP via resistor _R3 , and capacitor _C3 is connected between the gate of thyristor SCR and point E.

In the electrical circuit constructed in this manner, when the release button is pressed lightly and the contacts ₁ and 2 of the switch SW1 are connected, the DC power source E _B is connected between points A and E. If the trigger switch TR1SW is on, the divided voltage of the light receiving element Rcds and the resistor _R1 is input to the comparator COMP. On the other hand, when the switch SW ₁ is turned on, the reference voltage from the variable resistor VR ₂ is transiently applied to the comparator COMP through the capacitor C _2. This reference voltage and the above divided voltage are compared by the comparator COMP, and the output is sent to the thyristor SCR. Added between gate and source. For this reason, the thyristor SCR
If the outside light is bright, that is, the subject is bright, it will turn on and turn off the light-emitting diode LED, and if the outside light is dark, it will turn off and turn on the light-emitting diode LED to issue a hand wave warning. This is the warning mode, and its state is held by the thyristor SCR regardless of the stroke of the release button. In this case capacitor _C3 is connected to the thyristor SCR when the outside light is dark.
This prevents the switch from accidentally turning on due to a delay in the operation of the comparator COMP. Also, the timer circuit operates in the same manner as described above.

In the electric circuit of such a camera, the warning mode state is held by the thyristor SCR, so the above-mentioned adjustment in the conventional electric circuit is not necessary, and erroneous display of the light emitting diode LED and shutter drop are eliminated. The trigger switch TR1SW is either closed only when the shutter is set or closed when the shutter is not in operation, but the light emitting diode LED displays correctly in either case. In addition, a comparator is used to determine hand gestures.
Since it is performed using COMP, voltage dependence is small.

Next, other embodiments of the present invention will be described. In this embodiment, as shown in FIG. 6, in the above embodiment, variable resistor VR ₂ , capacitors C ₂ and C ₃ ,
_R3 is omitted and the gate of thyristor SCR is connected to point B. Therefore, in warning mode, the light receiving element
The divided voltage of Rcds and resistor _R1 is applied directly between the gate and source of thyristor SCR, and the thyristor
The SCR and light emitting diode LED operate in the same manner as described above. Also, in timer mode, point B is the thyristor.
The gate-source voltage of the SCR is locked to approximately 0.65V, and the shutter time is maintained accurately.

Note that the present invention can also be constructed using a switching element having a hold function, such as a programmable union transistor, instead of the thyristor.

As described above, in the electric circuit of the camera according to the present invention, since the warning mode state is held by the switching element, it is possible to eliminate erroneous display and shutter drop.

Furthermore, since the light receiving element for exposure metering is also used for hand shake detection without using a mechanical switch to change the circuit, there is no need to provide a light receiving element dedicated to hand shake detection or the above-mentioned mechanical switch.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of the electric circuit of a conventional camera, Fig. 2 is a timing chart of the same electric circuit, Fig. 3 is a timing chart of another example of the electric circuit of a conventional camera, and Fig. 4 is a circuit diagram showing an example of the electric circuit of a conventional camera. FIGS. 5 and 6 are circuit diagrams showing an ordinary camera timer circuit, and FIGS. 5 and 6 are circuit diagrams each showing an embodiment of the present invention. Rcds...Photodetector for exposure metering, _C1 to _C3 ...Capacitor, _R1 to _R3 , _VR1 , _VR2 ...Resistor, TR1SW...Trigger switch, COMP...Comparator, Mg...
Shutter control magnet, LED...light emitting diode for hand wave warning, SCR...thyristor, SW ₁ ...switch, E _B ...DC power supply.

Claims (1)

[Claims] 1 In a camera, a bridge including a series circuit of a shutter control magnet, a light receiving element for exposure metering, and an integrating capacitor, a trigger switch connected in parallel with the integrating capacitor, and a trigger switch connected in parallel with the integrating capacitor, A drive means for driving the shutter control magnet, a switch that turns on the power when the release button is pressed over a predetermined stroke, a resistor connected between the bridge and the power source via the switch, and the resistor. 1. An electric circuit for a camera, comprising: a switching element having a hold function that is turned on by a signal voltage generated in the camera; and a camera shake warning means driven by the switching element.