JPS6236645A - Leading circuit for photographic information - Google Patents

Abstract

PURPOSE:To lead in highly accurately ASA information to a shutter control circuit and a finder display circuit with simple constitution by combining a logarithmic compressing circuit with a logarithmic expanding circuit. CONSTITUTION:When a resistance value of a log resistor 22 is RA, current IA flowing into a transistor (TR) 26 becomes Vref/RA (Vref is a reference voltage) and an equal ratio current flows into the TR 36. The current is logarithmically compressed by the logarithmic compressing circuit consisting of an operational amplifier 34 and the TR 36 and an output current from the amplifier 34 becomes an equal difference current, which is supplied to the non-inversion input terminal of an operational amplifier 40. The non-inversion input voltage of the amplifier 40 becomes an equal difference voltage corresponding to the ASA information. An optical current generated in a photodetecting element 42 is supplied to the inversion input terminal of the amplifier 40 and logarithmically compressed by a TR 44. Therefore, an output voltage obtained by adding both the inputs is outputted from the amplifier 40. Consequently, the ASA information and the equal difference voltage corresponding to the photodetecting information are supplied to the finder display circuit 46.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photographic information introduction circuit for a single-lens reflex camera using a reflection metering method.

[Conventional technology]

In recent years, in automatic aperture-priority reflex cameras, in addition to the memory system that controls the shutter based on the shutter speed calculated before shooting, the shutter curtain and film surface reflect light after the shutter is actually opened. The so-called reflection photometry method is used, which determines the shutter time by directly integrating.

This reflex metering type aperture-priority automatic exposure - Even in eye-reflex cameras, it is desirable to display the shutter speed in the viewfinder before taking a picture to prevent camera shake. The light receiving element is at the rear of the mirror,
That is, since it is disposed in front of the film surface, the finder display circuit is constructed separately from the shutter control circuit.

In conventional circuits, the shutter control circuit inputs logarithmic information because the photocurrent is logarithmic, and the viewfinder display circuit needs to input square information.
jt (hereinafter referred to as ASA) information introduction resistor is a log resistor whose resistance value changes in a linear geometric series for shutter control.
A linear resistor whose resistance value changes in an arithmetic manner is used for viewfinder display.

These resistors are connected to the ASA dial lO as shown in Figure 5.
Within the above ASA fixed angle i range, log for shutter control
Two resistors, a resistor 12 and a linear resistor 14 for 7-finder display, are distributed.

[Problem that the invention seeks to solve]

Is this a configuration like ASA? Since the A angle is set to a medium angle, the accuracy of reading the Af9A information deteriorates.

Also, the readings of the two resistance values may be off.

If both resistors are formed to prevent this, the configuration of the AHA dial will become complicated and the cost will also increase.

Furthermore, since the shutter control circuit and finder display circuit are provided separately, the circuit for reading the ASA information is also complicated.

This invention uses one ASA information resistor and a simple configuration. It is an object of the present invention to provide a photographing information introduction circuit for an eye reflex camera using a reflection photometry method, which can introduce 1& into a shutter control circuit and a finder display circuit.

[Means for solving problems]

The photographing information introducing circuit according to the present invention has a film sensitivity setting member, and a signal generating means for outputting an arithmetic signal that varies arithmetic with respect to an operating chamber of the member.

A logarithmic expansion means is provided for converting the output signal of the signal generation means into a signal that varies cyclically with respect to the operation chamber of the film sensitivity setting member.

[Effect]

In the photographing information introducing circuit according to the present invention, the output signal of the signal generating means is supplied to the display photometry circuit, and the output signal of the logarithmic expansion means is supplied to the M output control photometry circuit as film sensitivity information.

〔Example〕

An embodiment of the photographing information introducing circuit according to the present invention applied to an aperture υ priority automatic exposure eye reflex camera will be described below with reference to the five drawings. As shown in FIG. 2, the COM SA dial 20 is provided with only a log resistance 22 thereon. The resistance value of this log resistance 22 changes in a geometric series according to the rotation of the ASA dial 20.

Figure 1 shows the circuit diagram of the first embodiment. The anode of the light receiving element 24 for shutter control is connected to the non-inverting input terminal of an operational amplifier (hereinafter referred to as an operational amplifier) 26 and the differential ratio voltage terminal Vref.
, and its cathode is connected to the inverting input terminal of the operational amplifier 26. This light-receiving element 24 is disposed at the rear of the mirror and receives reflected light from the shutter curtain and film surface only during a shutter operation in which the mirror is raised. The output terminal of the operational amplifier 26 is connected to its inverting input terminal via a capacitor 28, and also to the inverting input terminal of an operational amplifier 30 which operates as a comparator.

A trigger switch 32 is connected to both ends of the capacitor 28 . This trigger switch 28 is closed while the mirror is lowering, and is opened in response to depression of the release button.

On the other hand, one end of the log resistor 22 is connected to the μ ground, and the other end is connected to the inverting input end of the operational amplifier 34. Reference voltage terminal Vr
ef is connected to the non-inverting input terminal of the operational amplifier 34. The output terminal of the operational amplifier 34 is connected to its inverting input terminal, the base of the transistor 38, and the non-inverting input terminal of the operational amplifier 40 via the collector-emitter path of a transistor 36 whose base and collector are shorted. The anode of the light receiving element 42 for finder display is connected to the inverting input terminal of the operational amplifier 40, and the cathode thereof is connected to the non-inverting input terminal of the operational amplifier 40. This light receiving element 42 is disposed in front of the mirror and constantly receives incident light and performs open photometry.

The output terminal of the operational amplifier 40 is connected to its inverting input terminal via the emitter-collector path of a transistor 44 whose base and collector are short-circuited, and is also connected to a finder display circuit 46 . This finder display image 1? ! r4
For example, 6 is an A-D conversion circuit.

A driver circuit, a shutter timer, and a light emitting diode are used to notify the shutter time by lighting a light emitting diode.

The DC power supply terminal VCa is connected to the emitters of transistors 48 and 50 whose bases are commonly connected. transistor 4
The base and collector of transistor 8 are short-circuited, and the collector thereof is connected to the collector of transistor 38. transistor 5
0 is connected to the non-inverting input terminal of the operational amplifier 30.

It is connected to the non-inverting input terminal of the operational amplifier 34 together with the emitter of the transistor 38 via a resistor 52 . The output terminal of the operational amplifier 30 is connected via a resistor 54 to a transistor 560 whose emitter is grounded. transistor 56
The collector is connected to the DC power supply terminal VCC via the shutter trailing curtain control electromagnetic coil 58, and is also connected to the cathode of a Zener diode 60 whose anode is grounded. The electromagnetic coil 58 is wound around an iron core of a permanent magnet, and the shutter rear curtain is normally wrapped around the electromagnetic coil 58.
is retained by. and,! Magnetic coil 58 is F
i) T& so as to cancel the magnetic force of the permanent magnet when magnetized
It is configured such that a force is generated. Here, transistors 36, 38, 48'.

50 are formed on one monolithic IC and have the same V
transistors 36 and 38,
Transistors 38 and 48 and transistors 48 and 50
constitute a current mirror circuit.

Next, the operation of the first embodiment will be explained. If the resistance value of the log resistor 22 is 8, the t current IA flowing through the transistor 36 will be Vref/HA. For example, the values are determined as follows.

That is, a geometric current flows through the transistor 36. This [fiE is logarithmically compressed by a logarithmic compression circuit consisting of an operational amplifier 34 and a transistor 36 that acts as a diode and whose base-collector distance is shortened, and the output current of the operational amplifier 34 is applied to the non-inverting input terminal of the operational amplifier 40, which becomes an arithmetic current. Supplied. The non-inverting input voltage v' of the operational amplifier 40 becomes an arithmetic voltage according to hsh@@ given by the following equation.

k: Boltzmann constant, q: charge factor 3: reverse saturation current The photocurrent generated in the light receiving element 42 is supplied to the inverting input terminal of the operational amplifier 4Q, and this photocurrent is logarithmically compressed by the transistor 44. Next, the output voltage v of the operational amplifier 40
1 is obtained by adding these two together as shown below.

Step α2: Due to the photocurrent of the light receiving element 42, the finder display circuit 46 is supplied with an arithmetic voltage according to the ASA information and the light receiving information.

Although not shown, since aperture information is also supplied to the finder display circuit 46, the shutter speed time is displayed.

In addition, to make the finder display a crest display, display circuit 4 is required.
All you have to do is supply the shirt time information to 6.

For a program 88 type camera, it is preferable to supply the output of the operational amplifier 40 to its tt display circuit 46.

When the release button is pressed down, the trigger switch 32 is opened, the mirror is raised, the shutter front curtain is moved, and the light receiving element 24 starts emitting secondary light.

This photocurrent is integrated by the operational amplifier 26 and the capacitor 28, and the output voltage of the operational amplifier 26 gradually increases and is supplied to the inverting input terminal of the operational amplifier 30. on the other hand,
Transistors 36, 38.

48.50 constitutes a current mirror circuit, so
The t current IA also flows through the collector of the transistor 38. The collector current of this transistor 38 is
As a result, the collector of transistor 5Q also has a geometric ratio 'IIW.
mI people are flowing. Assuming that the resistance value of the resistor 52 is tRs, the collector voltage of the transistor 50, that is, the non-inverting input voltage (judgment voltage) (2) of the operational amplifier 30, becomes a geometric voltage as follows.

The operational amplifier 30 compares this determination voltage with the output of the operational amplifier 26, that is, the voltage corresponding to the light reflected from the shutter rear curtain and the film surface.

If both match, the transistor 56t is turned on and the electromagnetic coil 58 is excited. Therefore, the magnetic force of the permanent magnet core of the electromagnetic coil 58 is canceled, the shutter rear curtain is unlocked, and the shutter rear curtain is moved.

A second embodiment of the invention will now be described. here.

The same parts as in the first embodiment are given the same reference numerals.

The explanation will be omitted. In Figure 3, AHA dial 20
However, in the second embodiment, only the linear resistor 70 is provided above the ASA dial 2°.

Figure 4 is number 25! It is a circuit diagram of an example. Operational amplifier 34
A linear resistor 70 is connected between the output terminal and the inverting input terminal of 5.
The inverting input terminal is further grounded via a resistor 72. The line end Vcc is connected to the non-inverting input terminal of the operational amplifier 34 via a constant current source 74, and the non-inverting input terminal is further grounded via the collector-emitter of an NPN transistor 76 whose base and collector are short-circuited. be done.

Next, the operation of this embodiment will be explained. Assuming that a constant vL current IB flows through the transistor 76 by the constant current source 74,
The forward voltage of the transistor 76, ie, the potential V at the non-inverting input terminal of the operational amplifier 34, is as follows.

Therefore, the current IC flowing through the film sensitivity setting linear resistor 70 is as follows.

RB: resistance value of the resistor 72, and the output voltage V4 of the operational amplifier 34 is as follows.

V4=V, +Ic·Re Rc: resistance value of the linear resistor 70 This voltage (4) varies arithmetic in accordance with the change in the IJ=A resistor 70, and is supplied to the finder display circuit 46. Further, this voltage 4 flows between the base and emitter of the transistor 38 and is logarithmically expanded, and then is supplied to the base of the shutter control transistor 56 as a geometric signal.

According to this embodiment, film sensitivity information can be supplied to the finder display circuit and shutter control circuit with a single linear resistor.

As explained above, according to this output 8AVc, by using a combination of a logarithmic compression circuit and a logarithmic expansion circuit, ASA information is introduced from one AHA information introduction resistor to the shutter control circuit and the finder display circuit. It is possible to provide a photographing information introduction circuit for a reflective side light type eye reflex camera. In addition.

Since the AHA information is read from one resistor on the 8-person dial, there is no error in the information read to both circuits.

Moreover, it is possible to take a view to a high degree. Furthermore, temperature compensation for each element can be easily performed.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a first embodiment of the photographing information introducing circuit according to the present invention, Fig. 2 is a diagram showing an ASA dial used in the first embodiment, and Fig. 3 is a diagram showing an AHA dial used in the second embodiment.
Diagram showing the dial, Figure 4 is the circuit diagram of the second embodiment, Figure 5 is the circuit diagram of the second embodiment.
The figure shows a conventional AHA dial. 20...AHA dial, 22...log resistance, 2
4... Light receiving element for shutter control, 26, 30, 34° 40... Operational amplifier, 32... Trigger switch, 3
6°3B, 44.4B, 50.56...transistor. 42... Light receiving element for finder display, 46...7 finder display circuit, 58... Electromagnetic coil for shutter rear curtain control. Applicant's agent Patent attorney Atsushi Tsuboi Figure 2

Claims (3)

[Claims] (1) A signal generating means that has a film sensitivity setting member and outputs a signal that varies arithmetic with respect to the operating amount of this member, and the output signal of the signal generating means is used to operate the film sensitivity setting member. logarithmic expansion means for converting into a signal that changes geometrically with respect to the amount, the output signal of the signal generation means is sent to a display photometry circuit, and the output signal of the logarithm expansion means is sent to an exposure control photometry circuit. , a photographing information introduction circuit that supplies each as film sensitivity information. (2) The signal generating means includes a variable resistor whose resistance value changes geometrically according to the film sensitivity, and logarithmic compression that converts the output signal of the variable resistor into a signal that changes geometrically according to the film sensitivity. The photographic information introduction circuit according to claim 1, characterized in that the circuit comprises a circuit. (3) The photographing information introducing circuit according to claim 1, wherein the signal generating means is comprised of a variable resistor whose resistance value changes arithmetic in accordance with film sensitivity.