JPS5836299B2 - exposure meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric exposure meter that digitally displays a digital signal corresponding to an exposure value using a digital display element.

Generally, when expressing exposure information, the aperture value is F number 1.4, 2, 2.8...11.16, and the shutter speed is 1/1000 seconds, 1/5.
Numerical sequences such as 0 0 seconds, 1/250 seconds, . . . 1/4 seconds, 1/2 seconds, etc. are commonly used.

Therefore, even when displaying exposure values digitally, it is most convenient to use a numerical display member to directly display the exposure information using the numbers.

Conventionally, a digital display type electric exposure meter configured in this manner has also been proposed.

Incidentally, the number sequence of exposure information can be expressed using the avex display method, which is an easy-to-handle arithmetic progression.

The above-mentioned normally used number sequence is in IE units in the Avex display system, and no consideration has been given to digitally displaying exposure values in units smaller than this.

An object of the present invention is to provide a light meter that can digitally display exposure information in units smaller than IEV and in a form that is extremely easy to read.

The present invention will be described below with reference to embodiments and the drawings.

FIG. 1 is a block diagram showing the basic configuration of the present invention.

The features of the present invention will be explained according to this figure.

The photoelectric conversion circuit 1 obtains an output corresponding to the brightness, which is used as one input to the comparator 2. In this state, the counting start command switch 4 applies a trigger pulse to the flip-flop circuit 3 for control.

This inverts the flip-flop output, puts the clock pulse generating circuit 5 into operation, and guides the clock pulses generated by the clock to the pulse counting circuits 6 and 6' for counting.

Feedback circuit 7 provided at the output end of counting circuits 6 and 6'
The current or voltage corresponding to the count is fed back to the other input terminal of the comparator 2.

The comparator 2 successively compares the brightness input from the photoelectric conversion circuit 1 and the feedback input.

When both inputs are balanced, the comparator 2 generates a pulse, inverts the output of the clock control flip-flop 3, and stops the operation of the clock pulse generation circuit 5.
The input pulse to the counting circuit 6 is cut off to fix the count.

In this way, the brightness information is converted into a digital signal as a count.

This digital signal is used as one input to the adder/subtractor 9.

Exposure determining factors other than brightness are converted into digital signals by a code conversion switch 8 serving as a film sensitivity setting circuit and are provided as the other input to the adder/subtractor 9.

In this way, the adder/subtractor 9 performs addition/subtraction, and a digital signal corresponding to the exposure value is taken out as the output of the adder/subtractor 9.

This digital output undergoes code conversion through a code conversion circuit 10 to match a display format such as 7-segment lighting or numeric lighting, and the elements of the digital display section 11 are lit to digitally display the intended exposure value. becomes.

In the digital display section 11, since the sensitivity series of commercially available films is (1/3) Ev step, the film sensitivity setting circuit is set according to the sensitivity series (1/3).
The structure is such that the film sensitivity can be set in the E'V step.

On the other hand, in commonly used cameras, the aperture is (
1/2) It is designed so that it can be set in Ev steps.

Therefore, there is no practical meaning in reducing the display unit of the exposure meter, so in this embodiment, the display unit is set to (173) Ev in accordance with the film sensitivity series.

Also, the aperture value written on the aperture setting member of the camera is, for example, 1.4, 2, 2.8...11.16.
Each step is Ev, and the middle can be selected by a click mechanism.

In view of this, in the digital display of this embodiment, as described above, the aperture value for each IEv step, that is, the part corresponding to the integer term of Av is displayed numerically using a 7-segment display member, and Light-emitting diodes are used to display lighting codes in the areas where the camera is connected, making it easy to understand the correspondence with the camera side.

Further, by displaying the portion of the aperture value that is not indicated on the camera by lighting the light emitting diode, the circuit structure is simplified and the current consumption is advantageously reduced.

The structure and operation will be described in detail below according to specific embodiments of the present invention.

FIG. 2 is a circuit diagram of an example of application of the present invention to a strobe light amount measuring device.

The APEX method is generally used to display the exposure amount of a camera.

In this method, when the exposure value is Ev, the aperture value is Class, the shutter speed value is TV, the subject brightness value is By, and the film sensitivity value is Shi, Ev=Sv+Bv=Tv+Av
- There is the relationship (1).

In the embodiment shown in FIG. 2, the final display is the aperture value Av (
Since Av=
By-Tv+Sv...(2) as By
-Tv+Sv is measured and counted to obtain an Av value, which is then code-converted to obtain an aperture display.

1 in Figure 2 is a photoelectric conversion circuit for obtaining brightness information, and the applicant has already obtained a patent for it (Japanese Patent Publication No. 47-35
By using the circuit of 994, Patent No. 681415), a voltage proportional to (Bv-Tv) can be obtained at the output terminal 1a.

This output voltage is applied to one input terminal 2a of a certain comparator 2 from the differential amplifier.

Further, the output end 1b of the photoelectric circuit 1 gives a pulse to the input end 4a of the switch 4 when the photoelectric conversion operation is completed, and the output end 4b emits a counting start command pulse, and this pulse is used as a trigger signal for clock control. It is applied to the trigger input terminal 3a of the flip-flop circuit 3 for clock control.

Therefore, the flip-flop 3 is triggered, and the output terminal 3C of the flip-flop 3, which was in the H level state, is inverted to the L level, cutting off the signal applied to the clock control terminal 5a of the clock pulse generating circuit 5 via the diode 4a.

In this way, the holding state of the clock pulse generating circuit 5 is released and the clock pulse generating circuit 5 is brought into an operating state, and the clock pulse output is caused to be outputted from the output terminal 5b.

The circuit 18-21 for the film sensitivity value Sv will be described later.

In the case of this example, one level of exposure value (hereinafter referred to as IE ■)
IEv is counted using three clock pulses using a ternary counting circuit to provide a resolution of (1/3) of the clock pulse.

The clock pulses are applied to the input terminal 6a as an input to the primary pulse counting circuit 6 and counted.

Outputs 6b, . . . , 6d of the counting circuit 6 output outputs according to the truth table shown in FIG.

That is, an H level signal is output from the output terminal 6d every three counts.

Using this as a count corresponding to IEv, the output terminal 6 of the second pulse counting circuit 6' consisting of a 4-bit binary counting circuit
'a, and counting is performed for each exposure value IEv.

The counting circuit 6' has its output terminals 6'b, . . . 6'e
These output terminals 6 are constructed using known techniques to obtain an output corresponding to the count according to the truth table shown in Fig. 4.
b, 6 C j 6'b...6'e are connected to the constant current circuit CCT.

This constant current circuit CCT has a variable resistor 10a,...
, 10f,} transistor 11a,..., 11f
, 12 and resistors 13 and 14.

Variable resistor 10a of this constant current circuit CCT,...
, 10f and transistor 11a, ..., 11f
A resistor 9a+ is connected from each connection point of the emitter.
・The cathode side is connected to the output end 6bl6Ct via , 9f.
Diodes 8a+..., 8f arranged on the 6'b...6'e side are connected to these output terminals, respectively.

Therefore, the output terminal sb*sc, s'b...6'
When the output given to e is H level, diode 8a+
・・・・・・・・・The bias of 8f becomes in the opposite direction, and the transistors 11a, . . . , 11f become operational.

Therefore, the constant current output adjusted by the variable resistors 10a, . . . , 10f is the transistor 11a.
, ..., 11f is given as a collector current.

Since the collectors of these transistors are commonly connected to the feedback variable resistor 15, a current as the sum of the constant current values at each collector flows through the feedback variable resistor 15.

When each output terminal (3b, 5c, 6'b...6'e) is at the L level, each of the diodes 8a,..., 8f is in the forward direction. Biased from the power supply voltage +Vcc to each variable resistor 10a,...
..., 10f, each output terminal 6b via resistor 9a+..., 9f, diode 8a+..., 8f
A closed circuit is formed through +6 c s 6'b...6'e to the ground.

Therefore, the emitter voltage of each transistor 11a, . . . , 11f decreases, respectively.
. . , 11f is in a non-operating state, and no collector current flows through the variable resistor 15. Therefore, no feedback current flows through the variable resistor 15.

In this way, the counting output terminals 6b, 6c, 6'b,...
Each constant current output is obtained in response to only those to which the H level signal is applied as a counting output among the outputs 6'e, and a voltage proportional to the sum of the currents is fed back to the comparator 2.

Each variable resistor 10a,...10f is connected so that each constant current value, which is an analog quantity, corresponds to a count, which is a digital quantity.
By adjusting the variable resistor 15 to match the brightness information and the slope of the necessary feedback voltage, the constant current output corresponding to the output of the counting circuit can be adjusted by adjusting the variable resistor 15. As a result, a feedback voltage corresponding to the count is applied to the input terminal 2b of the comparator 2.

As the counting progresses, the comparator 2 performs a successive comparison between the voltage applied to the input terminal 2a (By-Tv) and the voltage applied to the input terminal 2b according to the count. When the output terminal 2C of the comparator 2 is balanced, a pulse output is given to the reset trigger terminal 3b of the flip-flop 3 for clock control.

Therefore, the output of flip-flop 3 is inverted from L level to H level, and this H level signal is applied to control terminal 5a of clock pulse generation circuit 5 through diode 4'a.

In this way, the clock pulse generation circuit 5 is brought into a non-operating state.
Stops the generation of clock pulses.

Therefore, the output of the counting circuit 6 and the feedback circuit 7 is fixed by the state when both inputs to the comparator 2 are balanced, that is, by the count corresponding to the brightness information.

Among the output terminals, diodes 16a, ..., 16C and resistor 1 connected to 6b, 6'C, 6'e
The AND circuit AD consisting of 6d is used to obtain a warning signal for the upper limit of the measurement range, and this AND circuit A is used only when all outputs given to these output terminals are at H level.
A well-known technique is used to obtain an H level signal at the output terminal 16e of D.

This H level signal at the output terminal 16e is fed back to the control terminal 5a of the clock pulse generation circuit 5 via the diode 4'b, and acts to stop the operation of the clock 5 and prevent further counting. .

In addition, an OR circuit OR from diodes 17a, . . . 17d and resistor 17e connected to the output terminals 6'b... When the outputs given to 6'b..., 6'e are all at L level, the output terminal 1 of this OR circuit
The structure is such that an L level output is obtained at 7f.

Using these lower limit warning L level signal and upper limit warning H level signal, it is possible to light up a known display element (not shown) for displaying a warning.

When the input of (Bv-Tv) is within the measurable range, the counting circuit output terminals 6bt6c-6'b...,6' e
The outputs are fixed at the input terminals 18'a, 18'b, 19'a of the 2-bit binary full adder circuit 18 and the 4-bit binary full adder circuit 19, respectively.
, -..., 1 9'd.

In this embodiment, the signal corresponding to the film sensitivity value Sv to be added as an exposure determining element is transferred to the code conversion switch 20.21.
Make using.

This signal is generated by converting the Sv value into a binary number according to the truth table shown in FIGS. 5 and 6, and is generated at the input terminals 18a, 18b, 19a, . . .
...I am led to 19d.

The adder 18 has input terminals 18a, 18b and 18a',
The inputs given to 18b' are added, and the adder 19 adds input terminals 1 9 a ,= , 1 9 d , and 1 9
The inputs given to a', = , 1 9a/ are added.

In this way, the output terminal 1 8c ,=, 18e , 1 9
At f,−,19i, an output is obtained according to the truth table shown in FIGS. 7 and 8.

At this time, the output of the carry signal output terminal 18e of the adder 18 is applied to the carry input terminal 19e of the adder 19 as a carry input, and the adder 19 is configured to add these signals together. There is.

With the above configuration, the outputs obtained at the adder output terminals 18c, 18d, and 19f, . . . , 191 are (B
y-Tv) value and the Sv value, that is, a signal corresponding to the aperture f axis Ay according to equation (2).

In this embodiment, for each IEv aperture display, for example, a 7-segment light emitting diode is used as a 2-digit numerical display element, and for each (1/3) Ev display, a 2-digit light emitting diode is used. Display using a display element that is carefully selected.

In this case, the code conversion circuit 2 also has a display element drive circuit that provides a lighting style according to the truth tables shown in FIGS. 9 and 10.
If code conversion is performed through 2.23, an aperture display corresponding to the intended Av value will be obtained on the digital display.

A preferred embodiment of the present invention includes a photometry circuit that outputs an analog voltage that is a function of subject brightness {ifBv in an abex display, an A-D conversion circuit that converts the analog voltage output of this photometry circuit into a digital output, and an A-D conversion circuit that converts the analog voltage output of this photometry circuit into a digital output. an encoder that generates a digital signal according to a photographic calculation variable in an Avex type display that is not included in the voltage; a digital addition/subtraction circuit that calculates the digital output of the A-D conversion circuit and the digital signal of the encoder; A code conversion circuit converts the calculation output of the digital addition/subtraction circuit into a signal suitable for display, and at least two numeric display members are used to convert the output of the digital addition/subtraction circuit into an integer term in units of IEv in the Avex display. Display in numbers and at least 1 for decimal terms.
The exposure meter can be summarized as an exposure meter characterized by displaying a lighting code using two blinking display members.

As described above, the present invention uses at least two number display members to narrow down integer values in IEv units such as 1.4, 2, 2, 8, 4, etc. A dedicated display member is provided to display the decimal term of IEv as well as to display the size of the decimal term, and exposure information is displayed by the combination of the display member for the integer part and the display member for the decimal part. It is designed to display the following information.

Therefore, the user can use the IEv displayed on the display member for the integer part.
The unit is the commonly used aperture value of 1.4,2.
, 2.8, etc., it is possible to accurately recognize the rough exposure value, while the display member for the decimal part allows to know by what fraction of IEv the exposure value deviates from the numerically displayed value.

For example, in the case of the embodiment, the numerical display is r2. s” decimal part represents 1/3, the user should immediately select r2.
．． It can be seen that a value is displayed that deviates from s-+ by 1/3 Ev toward "4".

In addition, when displaying in more detail than IEv units, use the numerical display member as is, for example, r2.8J to 1/3
It is also possible to display a value r3.2J that is shifted toward "4" by Ev.

However, an aperture value such as r3.2J is not a value that many people are accustomed to using, and users often think that r3.2J is r2. 8
Although it can be recognized that the value is between J and "4",
That's r2. It is extremely inconvenient to use this method because it is not immediately clear how many IEv the value deviates from 8 J toward "4".

As described above, the present invention allows exposure information to be read accurately and intuitively, and has a great advantage over conventional light meters.

[Brief explanation of the drawing]

Fig. 1 shows the structure of the principle of the present invention, Fig. 2 shows the structure of an embodiment of the invention, Figs. 3 and 4 show the truth table of the counting output of the counting circuit, and Figs. FIG. 6 shows a truth table showing the encoding of the film sensitivity value, and FIGS. 7 and 8 show the truth table of the adder output and the relationship between the truth value of the display element and the display. 9 and 10 are truth tables showing the relationship between the aperture value Av and each output terminal signal of the code converter. 1...Photoelectric conversion circuit, 2...Comparator, 3...Flip-flop for clock control, 4...Music counting start command switch, 5...Clock Pulse generation circuit, 6...Kiln type pulse counting circuit, 7...Feedback circuit, 8...Sign conversion switch, 9...Addition/subtraction device, 10... . . . code conversion circuit, 11 . . . display unit.

Claims (1)

[Claims] 1. A circuit that digitally outputs an exposure signal according to photometric output and setting information, a code conversion circuit that converts the digital output into a signal suitable for display, and a digital display section that performs a display according to the output of this code conversion circuit. In the exposure meter, the digital display section displays integer terms in units of IEV in the avex type display among the digital outputs as numbers using at least two numerical display members, and also displays a dedicated decimal term. What is claimed is: 1. A light meter comprising a display member, wherein exposure information is displayed by a combination of display by the display member for the integer part and display by the display member for the decimal part.