JPS6339886B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a photometering method for a camera, in particular, a photometering method that makes it possible to switch between average metering and partial metering in the TTL metering method, which measures the brightness of a subject image formed on a focusing plate through a photographic lens. It is related to.

The TLL metering method, which measures the brightness of the subject image formed on the focusing plate through the photographic lens, has been used in single-lens reflex cameras and other devices, and various metering methods such as average metering, center-weighted average metering, and partial metering are available. It is used. Also known is a photometry method that uses two different types of light beams to switch between average and partial photometry.

Cameras that use this average/partial switching metering system have the advantage of being able to switch between average and partial metering as appropriate to obtain the desired exposure value, making them convenient for taking pictures. Many were equipped with separate photometry systems for and partial photometry, and the output could be switched. To give an example,
A photoelectric conversion element for average photometry is arranged in the pentaprism finder optical system to perform average or center-weighted average photometry of the subject image formed on the focusing plate,
The photoelectric conversion element for partial photometry is arranged so that it measures only the light mainly in the center of the screen using some spectroscopic means, and the appropriate exposure value is calculated by switching between these two systems of photometry output by average and partial photometry. be. In this way, in the conventional method, two photometry systems for average and partial photometry are provided separately and their outputs are switched, so the range of subject brightness that can be measured by both photometry systems is the same. In order to achieve this, an average photometry circuit and a partial photometry circuit should be provided separately, or if the same circuit is used, a circuit that amplifies the optical output more (electrical level adjustment) during partial photometry than during average photometry. However, it has the drawback that the photometric optical system is complicated, and the photometric device is also complicated.

An object of the present invention is to provide a new photometry switching method that eliminates the drawbacks of the conventional average and partial photometry switching methods as described above. A light-shielding member is provided near the focusing plate, and the light-shielding member is inserted or removed from the surface to measure the average and the brightness of a desired portion using a single photoelectric conversion element.
This is a partial switching photometry method. In other words, the difference between the photometric output obtained by inputting the entire screen of the light beam on the reticle to the photoelectric conversion element and the photometric output obtained by blocking a part of the light beam and inputting the light beam to the photoelectric conversion element is calculated, and the desired portion is calculated. This is a photometry method that obtains photometric values.

The present invention will be explained in detail below with reference to the drawings. FIG. 1 is a schematic diagram showing one embodiment of a photometric system of a single-lens reflex camera according to the present invention. In the figure, 1 is a photographing lens, 2 is a film surface, 3 is a movable reflecting mirror, 3a is a rotation axis, 4 is a focus plate, 5 is a condenser lens, and 6 is rotatable in a direction perpendicular to the finder optical path with 8 as the center of rotation. 7 is a holding arm for the light shielding member 6, 8 is a drive source that provides rotational driving force to the light shielding member 6, 9 is a pentaprism for a viewfinder, 10 is an eyepiece lens, and 11 is a subject image formed on a focusing plate. A photoelectric conversion element, such as a silicon photodiode, is placed at a position where it can photometer the average brightness of the entire surface.

FIG. 2 is a plan view showing the relative position of the focusing plate and the light shielding member. When the light shielding member 6 is in position a, that is, in a position separated from the focusing plate 4, the light flux from the entire screen of the focusing plate is transmitted to the photometric element. When the light enters and enters the state of average photometry and reaches the position b or c in the figure, the light beam in this portion is blocked by the light shielding plate 6 and does not enter the photometric element. This case becomes a state of partial photometry. Third
The figure is a circuit diagram showing an example of means for driving the light-shielding member 6. The resistor V _R is adjusted to apply current to the meter 12, and the light-shielding plate 6 provided at the light end of the pointer 7 is moved to a desired position as shown in FIG. It was designed so that they would come to Japan.

In the figure, the output of the photoelectric conversion element 11 when the light shielding plate 6 is in position a is now A, and the output of the photoelectric conversion element 11 when the light shielding plate 6 is in position b is A-.
If B, first place the light shielding plate 6 at position a and store and hold the photometric output A, then rotate the light shielding plate 6 to position b and store and hold the photometric output A-B at that time. When the difference between the two photometric outputs is electrically determined, the difference output is A-(A-B)=B, and brightness information B corresponding to the subject brightness of the portion shielded by the light-shielding plate 6 is obtained. Note that in the case of average photometry, the photometric output A is obtained when the light shielding plate 6 is placed at position a.

According to the photometric method of the present invention, at least one photometric element 11 is required, and there is no significant difference between the light amount during partial photometry and the light amount during average photometry, so unlike the conventional method, Amplification (electrical level) during average photometry and partial photometry in electrical circuits
There is no need to correct this, and furthermore, this allows partial photometry even for low-luminance objects. Furthermore, as shown in FIG. 1, the light shielding plate 6 is moved in and out of the screen near the focus plate 4, so when the light shielding plate 6 is confirmed with the viewfinder, partial photometry of that part is performed. It can be easily recognized from the viewfinder eyepiece.

As a result, there is no need to provide a separate means for indicating the photometry range in the case of partial photometry, and the apparatus can be configured extremely simply. Note that it is also possible to use a translucent member such as a color filter that has a light blocking effect as the light blocking member. Further, as will be described later, the same effect can be obtained by using an electro-optical light shielding member, such as a liquid crystal plate, and driving it in pulses instead of rotating the mechanical light shielding member.

FIG. 4 is a circuit connection diagram showing one embodiment of an electric circuit of a camera using the photometry method of the present invention. In the figure, the power switch Swo is turned on by pressing the first step of the shutter button (not shown), photometry is performed with the light shielding member inserted in the center of the screen, and the second step of pressing the shutter button (not shown) turns on the power switch Swo. The output is stored and held, and when the button is pressed in the third step, the light shielding member is retracted from the screen, and the photometric amount of the entire screen in that state is detected and stored. By electrically subtracting the photometric amount obtained when the light blocking member is inserted into the screen from the photometric amount of the entire screen, partial photometry of the subject image in the area blocked by the light blocking member is performed. It is. In Figure 4, OP1 to OP5 are operational amplifiers, BP1, BP
2 is a buffer amplifier, R ₁ to R ₁₂ are resistors, RT is a temperature compensation resistor, VR1 and VR2 are variable resistors C ₁ and C ₂ are memory capacitors for inputting shooting information, SP is a photoelectric conversion element for photometry, LD1, LD2 is a diode,
FT1 and FT2 are analog gates, RG is a constant voltage power supply for generating a reference voltage, E is a power battery, M is a meter for displaying exposure information, and CKT is an exposure control circuit that controls the shutter speed or aperture value. SW0～
SW4 is a switch, SW0 is a power switch,
SW1 and SW2 are memory retention switches that are turned off when the camera's film is wound up and turned on when the shutter button is pressed down, for example. In the circuit shown in the figure, when the release button (not shown) of the camera is pressed, the power switch SW0 is turned on in the first stage, and the circuit starts operating. The photoelectric conversion element Sp generates a photocurrent due to the light from the object, which is logarithmically compressed by the operational amplifier OP2 having a diode LD2 with logarithmic characteristics and outputted to the analog gates FT1 and FT2.
is applied to capacitors C ₁ and C ₂ through.
The second press of the release button turns off the switch SW1, which turns off the analog gate FT2 and stores the output of the photometry circuit OP2 in the capacitor _C2 . The output information of the photometric circuit when the light shielding member 6 is now in the position b in FIG. 2 is expressed as Bv-Avo-Avc-BM (1). Here, Bv is the subject brightness information, BM is the brightness information of the part shielded by the light shielding member, Avo is the open F value information of the attached lens, and Avc
is information on the bending of a large aperture lens near its maximum aperture.
The information in equation (1) is input to capacitor _C2 and stored.

Furthermore, if you press the release button to the 3rd step, the 3rd
The switch SW10 shown in the figure is turned off, the light shielding member 6 retreats from the screen, and then, after a short period of time, the switch SW10 is turned off.
SW2 turns on. This allows the photometric information of the entire screen to be transferred from the output of OP2 to the capacitor via FT1.
Stored in C ₁ . This photometric information is expressed as Bv−Avo−Avc (2). The information in equations (1) and (2) is applied to two inputs of a differential amplifier OP3 via buffer amplifiers BP2 and BP1, respectively, and is calculated by OP3, and difference information is output from OP3. The information is (Bv - Avo - Avc) - (Bv - Avo - Avc - BM) = BM (3) As shown in equation (3), it is information that corresponds to the brightness of the part of the subject that is shielded by the light shielding member. . That is, the second
This is partial photometry information at position b (or position C) in the figure. This is applied to the operational amplifier OP4 through the temperature compensation resistor RT, and then input to the operational amplifier OP5 together with the shooting information from VR2, such as the film sensitivity information Sv and the shutter time information Tv (or aperture information Av), where it is calculated. Information for exposure control, Av or Tv, is output to the output. This information is displayed on the exposure value display meter, and is also input to the exposure control circuit CKT to perform exposure control.

Next, the operation of the temperature compensation circuit will be explained.
Operational amplifier OP1 and diode LD in Figure 4
1 and resistor _R3 is the photoelectric conversion element SP
logarithmic diode for logarithmically compressing the photocurrent of
This is the temperature compensation circuit for LD2, and if the constant current from the reference voltage source RG flowing through the diode LD1 is is, and the constant voltage at the voltage dividing point of the voltage dividing circuits R ₁ and R ₂ is V _c , then the output V of the operational amplifier OP1 is _pp1 becomes V _pp1 −Vc−KT/qln(is/io+1) (3). Here, K is the Boltzmatsu constant, q is the elementary quantity of electrons, and io is the reverse saturation current of the diode.

Also, the output of buffer amplifiers BP1 and BP2
V _BP1 and V _BP2 are V _BP1 −V _OP1 +KT/qln(iBP1/io+1) (4) V _BP2 =V _OP1 +KT/qln(iBP2/io+1) (5), and iBP1 is the light intensity for the photometric amount of the entire screen. current,
iBP2 is the photocurrent for the amount of photometry when the central part of the entire screen is shaded.

When iBP1, iBP2≫io, OP3 output V _OP3 is (3),
From equations (4) and (5), V _OP3 = KT/qln (iBP1/iBP2) + Vc (6) Also, if the temperature compensation resistor RT has the characteristics RT=ROT/TO (7), the output of operational amplifier OP4 _VOP4
is V _OP4 = Vc + R ₁₀ /Ro KTo/qln (iBP1/iBP2) (8), and V _pp4 is information unrelated to temperature T.
In the case of average photometry, the light shielding plate 6 is retracted as described above,
When the switch SW ₃ is turned on, the photometric information when the light shielding plate 6 is placed on the screen is removed, and when the switch SW ₄ is turned on, the necessary exposure information is amplified through the variable resistor VR ₁ . input to device OP ₄ . For this average photometry, VBP ₂ equals Vc and VOP ₄
is VOP4=Vc+R ₁₀ /RO KTO/qln(iBP1/is) (9), and in both cases, photometric information that is not affected by temperature fluctuations can be obtained as shown in equations (8) and (9). .

Next, FIG. 5 is a circuit connection diagram showing another embodiment of the photometric system of the present invention, in which the mechanical light shielding member shown in FIGS. 1 to 3 is replaced with an electro-optic light shielding member. In other words, by using a liquid crystal as a light-shielding part and driving it in pulses, you can measure the amount of light measured over the entire surface when the liquid crystal is transparent,
Partial photometry is performed by taking the difference from the amount of photometry across the entire surface when the central portion is shaded when the liquid crystal is translucent. Fifth
The circuit shown in the figure is the same as the circuit shown in FIG. 4 except for the liquid crystal drive section, and the same parts are designated by the same reference numerals.
In the figure, AN1 and AN2 are AND gates,
IB1 and IB2 are inverters, PG is a pulse generator, _R13 is a resistor, and IC is a light shielding liquid crystal. Also
SW5 is a memory switch. In the circuit shown in the figure, when the power switch SW0 is turned on, the AND gate AN2 is
The analog gate FT2 becomes conductive with the output of , and the amount of photometry when the central portion of the entire screen is shaded is stored and held in the capacitor _C2 . Furthermore, when no voltage is applied to the liquid crystal, the analog gate FT1 is made conductive by the output of the AND gate AN1, and the photometric amount of the entire screen is stored and held in the capacitor _C1 . The output pulse of the pulse generator PG is applied to the liquid crystal via the inverter IB1, and new photometric information is alternately stored in the capacitors C ₁ and C ₂ in synchronization with this voltage, thereby creating the circuit shown in Fig. 4. The calculation is performed in the same way as
The output of OP5 is displayed by meter M. When the camera release is pressed further, the memory switch switches
5 is turned off, and the output of inverter IB2 becomes low level "L", so AND gate AN1
The outputs of AN2 and AN2 both become 0, analog gates FT1 and FT2 are turned off, and the photometric information accumulated in capacitors C ₁ and C ₂ at this time is stored and held. The subsequent circuit operation is similar to that of the circuit shown in FIG. 4, and the explanation thereof will be omitted here.

As described above, in the photometry method of the present invention, partial photometry can be performed by mechanical or electro-optical switching, and the dynamic range of partial photometry does not become narrow as in conventional methods, and the partial photometry It has the remarkable feature that switching between average and average photometry can be easily performed, and its effects are great as a photometry method for single-lens reflex cameras.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the single-lens reflex camera photometry system according to the present invention, FIG. 2 is a plan view showing the relative position of the focusing plate and the light shielding member, and FIG. 3 is a drive means for the light shielding plate. FIG. 4 is a circuit connection diagram showing an example of an electric circuit of a camera using the photometry method of the present invention. FIG. 5 is a circuit diagram showing another embodiment of the photometry method of the present invention. It is a connection diagram. 1...Photographing lens, 2...Film surface, 3...
Movable mirror, 4... Focusing plate, 5... Condenser lens, 6... Light blocking member, 7... Holding arm for light blocking member, 8... Drive source for light blocking member, 9... Pentaprism, 10... Eyepiece lens , 11...Photoelectric conversion element.

Claims (1)

[Scope of Claims] 1. A light-receiving element that receives a light flux incident through a photographic lens, and a light-receiving element disposed substantially on an optical imaging plane in the optical path of the light flux to the light-receiving element, and in front of the light-receiving surface of the light-receiving element. moves between a first position and a second position evacuated from the optical path, the first position blocks a part of the light flux to the light-receiving surface, and the second position blocks the light flux at the light-receiving surface. a light-shielding member that receives light without causing the light-shielding member to move; a displacement means that displaces the light-shielding member between a first and a second position; and a light-receiving member that receives light when the light-shielding member is in one of the first and second positions. a memory circuit that stores the element output; and the light shielding member that is connected to the first
or from said one of the second positions to the first position.
Alternatively, an arithmetic circuit is provided to calculate the difference between the light receiving element output when the light receiving element is moved to the other of the second positions and the value stored in the memory circuit, and the light shielding member is moved to the second position.
A camera characterized in that a photometric value in a first photometric mode is obtained from the output of the light receiving element in a state in which it has been moved to the position, and a photometric value in a second photometric mode is obtained from the output of the arithmetic circuit. photometric device. 2. A light-receiving element that receives the light flux incident through the photographic lens; an electro-optical light shielding member which is in a light shielding state in a first state, shielding a part of the light flux to the light receiving surface, and is in a non-light shielding state in a second state; and first and second states of the non-light shielding member. a control circuit that applies a control signal to the light shielding member; a memory circuit that stores a light receiving element output when the light shielding member is in one of the first or second state; an arithmetic circuit that calculates the difference between the output of the light receiving element and the value stored in the storage circuit in a state in which the state has transitioned from one of the first and second states to the other of the first or second state; and obtain a photometric value in a first photometric mode from the output of the light receiving element when the light shielding member is in a second state, and obtain a photometric value in the second photometric mode from the output of the arithmetic circuit. A camera photometry device featuring: