JPH0514254B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exposure amount control device for a programmable electric shutter that improves the accuracy of controlling the exposure amount.

[Prior Art and Problems to be Solved by the Present Invention] In the exposure amount control device for a so-called programmable electric shutter, the exposure amount in a high brightness state is generally controlled by the operation of only the triangular wave aperture characteristic region of the shutter blade which also serves as an aperture blade. .

On the other hand, the exposure amount in a low brightness state is controlled by calculating the operation of the triangular wave aperture characteristic area of the shutter blade and the trapezoidal wave aperture characteristic area following this area.

In the trapezoidal aperture characteristic region under such low brightness conditions, the shutter blades are fully open, and the aperture opening amount in this state is adjusted to prevent blades from remaining within the aperture due to mechanical errors, etc. The amount of movement of the blade is determined so that it is slightly larger than the diameter.

For this reason, during exposure control in low-brightness conditions, such programmed electric shutters obtain an opening amount larger than the aperture opening amount when the shutter blade opening amount is fully opened, and even when the shutter blade starts closing again, the aperture opening diameter remains the same. There is a delay in operation before returning, and this delay causes the exposure control amount to exceed.

Furthermore, as mentioned above, in a programmed electric shutter whose aperture characteristic has a triangular wave region and a trapezoidal wave region, the aperture is fully open in the trapezoidal wave region;
In the triangular wave region, the exposure amount is different because the shutter blade starts closing during its travel until it is fully opened. It is known that it is necessary to convert from the r characteristic of the case.

For this purpose, conventionally multiple (including complex types)
The shutter blade is provided with a photoconductive element, and the shutter blade operates by switching the element between a triangular wave region and a trapezoidal wave region, or operates in conjunction with the shutter blade operation. Since the light-receiving section is linked with the light-receiving diaphragm, it has the drawbacks of increasing costs and complicating the mechanism.

The present invention has been made in view of the above-mentioned drawbacks, and an object of the present invention is to provide an exposure amount control device for a programmable electric shutter that can perform appropriate exposure control with an inexpensive and simple configuration.

[Means for Solving the Problems] In order to achieve the above object, the exposure amount control device for a programmed electric shutter of the present invention provides an exposure time control device that controls the timing operation of the shutter blade when the exposure amount reaches a reference level. and a brightness determination circuit for determining an inflection point between the high brightness state where the aperture characteristic of the shutter blade starts to include only a triangular wave region and the low brightness state where the aperture characteristic of the shutter blade starts to include a trapezoidal wave region,
When the brightness determination circuit determines a low brightness state, the reference level of the exposure time control circuit is converted and latched, and the operation delay time is required until the shutter blade returns to the aperture opening amount in the trapezoidal wave opening characteristic region of the shutter blade. be compensated for.

Furthermore, an exposure time control circuit that controls a timing operation of the shutter blade when the exposure amount reaches a reference level, and an exposure time control circuit that controls a timing operation of the shutter blade when the exposure amount reaches a reference level; a luminance discrimination circuit for discriminating an inflection point with respect to a luminance state; a photoconductive element with r=1 which is used both as the discrimination circuit and an exposure time control circuit; and a photoconductive element circuit having a resistor that can be connected in parallel with the shutter blade, and when the brightness determining circuit determines a low brightness state, the reference level of the exposure time control circuit is converted and latched, and the trapezoidal wave aperture of the shutter blade is In addition to compensating for the operation delay time until the opening amount of the aperture returns to the opening amount of the aperture in the operation of the characteristic region, in a high brightness state, the apparent r of the photoconductive element circuit is changed from the beginning to 1 or less by the output of the brightness discrimination circuit. In addition, in a low brightness state, the output of the discrimination circuit corresponding to the change in the terminal voltage of the photoconductive element circuit accompanying the timing operation of the exposure time control circuit determines the apparent appearance of the photoconductive element circuit from the middle of the operation. r of 1
Change it to the following.

[Example] Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 1 is a circuit diagram showing an exposure amount control device of the present invention.

E is the battery power supply, S ₁ is the power switch, R _x is r=
1 photoconductive element, R _u is a correction resistor, C ₁ is a capacitor, R ₁ and R ₂ are resistors forming a voltage dividing circuit,
CM ₁ has the voltage at the connection point of resistors R ₁ and R ₂ applied as a control reference signal to the non-inverting input terminal (+),
Capacitor _C1 and correction resistor to inverting input terminal (-)
A comparator circuit for exposure time control to which the voltage at the connection point with R _u is applied, S ₂ is a switch for starting time measurement that is opened in conjunction with the start of opening of the shutter blade that also serves as an aperture blade (not shown), and MG is a switch for starting time measurement. This is an electromagnet that controls the closing timing of the shutter blades, and the above is the circuit configuration of a normal electric shutter.

The addition of electrical elements based on the present invention will be described below.

That is, C ₂ is a capacitor, Q ₁ , Q ₂ and Q ₃ are transistors, R ₃ and R ₄ are resistors, and R ₅ is r that can be connected in parallel with the series-connected correction resistor R _u and the photoconductive element R _x . A correction resistor that includes the photoconductive element R _x and correction resistor R _u connected in series, and the r correction resistor.
A photoconductive element circuit is formed by connecting R ₅ and transistor Q ₂ in parallel. R ₆ and R ₇ are resistors that constitute a voltage divider circuit, and CM ₂ is a non-inverting input terminal (+) to which the voltage at the connection point of resistors R ₆ and R 7 is given as a reference signal for brightness status discrimination, and the voltage at the connection point of resistors R 6 and R ₇ is inverted. A correction resistor R _u and a photoconductive element R _x are connected to the input terminal (−).
A comparator circuit for brightness discrimination to which the voltage at the connection point is applied, D is a diode.

Next, the operation will be explained.

First, when the power switch S ₁ is closed at the beginning of the release operation for shooting, the entire circuit is energized, and first, the transistor Q ₁ becomes conductive and the resistor
By shorting R ₃ and capacitor C ₂ , transistor Q ₃ is placed in the cut-off state.

When the field is in a high brightness state, the resistance value of the photoconductive element R _x is small and the potential at point m is low, so the output of the comparator circuit CM ₂ is placed at the "H" level, and the transistor Q ₂ conducts and resistor R ₆
is connected in parallel to the series circuit of the correction resistor R _u and the photoconductive element R _x . Therefore, the r characteristic of the entire parallel photoconductive element circuit is corrected to 1 or less, for example 0.75.

Then, as the release operation progresses, the shutter blade is released and starts the opening operation, and in conjunction with this, when the switch S ₂ opens, the capacitor C ₁
Charging is started through the series circuit.

Here, as shown in Fig. 2, the operation is such that the potential change at the inverting input terminal (-) of the comparator circuit _CM1 is steep as shown by E, and the potential at point m is as shown by F. Comparator circuit CM ₂
The potential drops from a state lower than the potential of the non-inverting input terminal (+).

After that, when the potential of E reaches the potential of the non-inverting input terminal (+) of comparator circuit CM ₁ , the circuit
Since the output of CM ₁ is inverted to "H" level,
The electromagnet MG is activated, and the shutter blade starts its closing operation after a so-called mechanical delay time.

Therefore, in a high brightness state, the correction of the r characteristic is always maintained at 0.75, which is suitable for controlling the exposure amount by operating within the triangular wave aperture characteristic region of the shutter blade.

In particular, a case where the object field is in a low luminance state will be explained. Transistor Q ₁ is once conductive and transistor Q ₃ is cut off, but the resistance value of photoconductive element R _x is large and the potential at point m is high, so comparator circuit CM ₂
Since the output of Q1 becomes "L" level, transistor _Q1 immediately shuts off, and on the other hand, transistor
_Q3 becomes conductive, and this cutoff and conduction state is latched. Therefore, the connection of the resistor R ₃ works, and this means that the exposure time control reference level applied to the non-inverting input terminal (+) of the comparator circuit CM ₁ is raised, and the resistor R ₃ is short-circuited. The closing signal occurs relatively early compared to when the electromagnet MG
is demagnetized quickly, which compensates for the operation delay time from fully opening the shutter blade to returning to the opening amount of the aperture when the shutter blade is operated under the trapezoidal wave aperture characteristic state.

In FIG. 3, consider compensation for this operation delay time.

If we assume that the inflection point at which comparator CM ₁ discriminates between a high brightness state and a low brightness state is, for example, LV11, the r characteristic of the photoconductive element circuit is LV11.
It should be converted continuously from 0.75 to 1, but the amount that the start point of r = 1 is down from the end of r = 0.75 on the horizontal axis of the exposure time T means the compensation time. There is.

On the other hand, the output of comparator circuit CM ₂ is “L”
Transistor by being placed at the level
Since Q ₂ is cut off, the resistor R ₅ is disconnected from the series circuit of the correction resistor R _u and the photoconductive element R _x .
Therefore, the r characteristic of the photoconductive element circuit of the series circuit is set to 1.

Similarly, when the switch _S2 opens as the release operation progresses, charging of the capacitor _C1 starts via its series circuit.

Here, as shown in Figure 2, when it is dark to some extent in a low brightness state, the comparator circuit CM ₂
The change in the potential of the inverting input terminal (-) of is gradual as shown in A, and the potential at point m also drops as shown in B. Then, the potential at point m is the comparator circuit
When the potential of the non-inverting input terminal (+) of CM ₂ is reached,
Since the output of the circuit CM ₂ is inverted to the "H" level, the r characteristic of the photoconductive element circuit is converted to 0.75 from this point on, as described above. After that, when the potential of A reaches the potential of the non-inverting input terminal (+) of the comparator CM ₁ , the output of the circuit CM ₁ is inverted to the "H" level, so the electromagnet MG is demagnetized and the shutter blade is The closing operation begins after a mechanical delay time.

In Fig. 2, c and d are slightly dark operating characteristics in a low brightness state compared to a and b above, dotted line waveforms indicate the opening of the shutter blade in each state, and solid line waveforms respectively. It shows the conductive state of Q ₂ in the state of .

In other words, the lower the brightness of the subject, the more gradual the change in the _potential at point m.
The interval at which CM ₂ changes from "L" to "H" becomes longer, and the interval at r=1 becomes longer. Therefore, the region of r=1 increases as the length of the trapezoidal wave region of the aperture characteristic increases.

In this way, when the shutter blade performs an operation of scanning the triangular wave aperture characteristic area and the trapezoidal wave aperture characteristic area in a low brightness state of the object field, the r characteristic of the photoconductive element circuit changes to the trapezoidal wave characteristic area. Since the exposure amount changes depending on the length of the interval, the control of the exposure amount approaches the appropriate direction.

[Effects] As described above, the present invention provides a programmed electric shutter in which the operation of a shutter blade that also serves as an aperture blade includes a triangular wave aperture characteristic area and a trapezoidal wave aperture characteristic area, and in a low brightness state, the opening amount of the aperture of the shutter blade returns to that of the shutter blade. In addition, the r-characteristics of the photoconductive element circuit can be changed with an inexpensive and simple configuration, and appropriate exposure control can be performed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the operating characteristics of the circuit in a low brightness state, and FIG. 3 is an explanatory diagram showing an example of the r characteristics of the photoconductive element circuit. be. CM ₁ ...Comparator circuit for exposure time control,
CM ₂ ...Comparator circuit for determining brightness status.

Claims (1)

[Claims] 1. In a high brightness state, the exposure amount is controlled by the operation of a triangular wave aperture characteristic region of a shutter blade that also serves as an aperture blade, and in a low brightness state, the exposure amount is controlled by the operation of the triangular wave aperture characteristic region of the shutter blade and the region. The trapezoidal wave aperture characteristic formed by the region is controlled by the operation of the region,
In a programmed electric shutter in which the opening amount of the shutter blade is larger than the opening amount of the aperture in the trapezoidal wave aperture characteristic region, field light is received by a photoconductive element with r=1,
an exposure time control circuit that controls a timing operation of the shutter blade when the exposure amount reaches a reference level; and a discrimination between the high brightness state and the low brightness state based on the field light received by the photoconductive element. a luminance discrimination circuit; a photoconductive element circuit having a resistor that can be connected in parallel with the photoconductive element when the luminance discrimination circuit discriminates the constant luminance state; From the beginning, the apparent r of the photoconductive element circuit is set to 1 by the output of the circuit.
At the same time, in a low brightness state, the output of the discrimination circuit corresponding to the change in the terminal voltage of the photoconductive element circuit accompanying the time counting operation of the exposure time control circuit changes the voltage of the photoconductive element circuit from the middle of the operation. By changing the apparent r to 1 or less, and by causing the brightness discrimination circuit to determine a low brightness state, the reference level of the exposure time control circuit is converted and latched, and a shutter blade closing signal is generated early, so that the shutter blade closing signal is quickly generated. An exposure amount control device that compensates for an operation delay time until the opening amount returns to an aperture amount in an operation of a shutter blade in a trapezoidal wave aperture characteristic region.