JPH01100525A - Photometer for lens interchangeable camera - Google Patents

Abstract

PURPOSE:To perform proper exposure arithmetic even when a lens which has a large extension quantity is used by using an effective aperture value which varies with the lens extension quantity is used for the exposure arithmetic. CONSTITUTION:A TTL full-aperture photometric means 1 measures light arriving from a subject through an interchangeable lens IL in a full-aperture state to obtain a full-aperture photometric value Bvo'. An effective aperture value calculating means 2 reads a full-aperture value Av', focal length (f), a distance signal L, etc., from the interchangeable lens IL and calculates an effective full-aperture value effAv'=Av'+2log2(1+f/L) from those data. A correcting means 3A calculates a photometric error (Bvo-Bvo') by using the effective full-aperture value effAv' of the interchangeable IL. Consequently, even if the lens extension quantity increases and the full-aperture value varies greatly, the error in photometry can be corrected correctly.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a photometry device for an interchangeable lens camera, and is particularly suitable as a photometry device for a single-lens reflex camera using the TTL photometry method.

(Prior Art) Conventionally, in Japanese Patent Application Laid-Open No. 56-74226, a multi-photometering device is provided that divides the field into multiple areas and measures the light, and calculates an appropriate photometry output from the photometry results in each area. In a camera, it has been proposed to calculate a correction value for photometry results in each region using an open aperture value read from an interchangeable lens.

In addition, Japanese Patent Publication No. 1603/1983 states that in a camera that performs automatic exposure control using a luminance signal obtained from a TTL focus detection means, when performing aperture priority AE control, the set number of aperture steps is On the other hand, in order to determine a shutter speed that provides proper exposure, it has been proposed to use the maximum aperture value read from an interchangeable lens in exposure calculations.

(Problems to be Solved by the Invention) In TTL interchangeable lens cameras that measure the brightness of a subject through the photographic lens at an open aperture, exchanging lenses may cause a metering error, so the camera body You need to make the corrections on your side. Therefore, as disclosed in the above-mentioned Japanese Patent Laid-Open No. 56-74226, it has been proposed to read the maximum aperture value from an interchangeable lens and calculate a correction value for the maximum aperture metering value based on the maximum aperture value. ing. However, the maximum aperture value read from the interchangeable lens is the maximum aperture value when the interchangeable lens is retracted to infinity.
When the lens is extended, it becomes larger than this. In particular, for lenses with a large extension amount, such as macro lenses, close-up lenses, and bellows lenses, the open aperture value changes significantly, and there is a risk that photometry errors may not be corrected properly.

Furthermore, when photometric output is obtained from a TTL focus detection means, the light flux used for focus detection is, for example, FN
Since the light passes through an area smaller than 0.05.6, the photometric output is not linked to the maximum aperture value. Therefore, if the maximum aperture value of the interchangeable lens is not known, accurate exposure calculation cannot be performed even if the number of stops is set. Therefore, as disclosed in the above-mentioned Japanese Patent Publication No. 60-1603, it has been proposed to use the maximum aperture value for exposure calculation. There was a risk that the value would change significantly, causing an error in exposure calculation.

The present invention has been made in view of these points, and its purpose is to provide a photometry device for an interchangeable lens camera that can always perform appropriate exposure calculations even when the amount of lens extension changes. It is in.

(Means for Solving the Problems) In the photometry device for an interchangeable lens camera according to the present invention, in order to achieve the above object, FIGS.
As shown in b), in a camera with interchangeable lenses that is equipped with a photometer (1) that measures the brightness of a subject, the effective aperture value effAv', which changes depending on the amount of lens extension of the interchangeable lens (IL), is calculated. The present invention is characterized by comprising an effective maximum aperture value calculation means (2) for calculating an effective maximum aperture value, and an exposure calculation means (3) for performing an exposure calculation using the effective maximum aperture value effAv'.

(Operation) The operation of the present invention will be explained separately for the cases shown in FIGS. 1(a) and 1(b).

The photometry device shown in FIG. 1(a) corresponds to Example 1, which will be described later, and has a photometry means (1) of the TTL open photometry method. This photometry means (1) is an interchangeable lens (IL).
The light from the subject that has passed through the aperture is measured with the aperture open to obtain the aperture value B vo'. The effective open aperture value calculation means (2) reads the open aperture value Aν°, the focal length f, the distance signal, etc. from the interchangeable lens (IL),
Based on these data, the effective open aperture value effAv'
=Av'+21og2(1+f/L) is calculated. Open photometric value Bvo” obtained by photometric means (1)
includes a photometric error depending on the interchangeable lens (IL), so the correcting means (3A) corrects the photometric error to obtain the true aperture photometric value Bvo.

The correction means (3A) uses the effective aperture value ef f A v' of the interchangeable lens (IL) to calculate the photometry error (B v
o - B vo'), so even if the lens extension amount increases and the open aperture value changes greatly,
Photometry errors can be corrected correctly. The Ev calculation means (3B) calculates the true open photometry value Bv obtained in this way.
.

Then, the effective open aperture value efTAv' and the film sensitivity Sv are added to obtain the exposure value Ev, and the control aperture value Av and shutter speed Tv are obtained by program calculation or the like.

The photometric device shown in FIG. 1(b) corresponds to Example 2, which will be described later, and includes a photometric device (1) that also serves as a distance measuring device for automatic focus detection. The AF light flux for automatic focus detection is
This metering method (
The photometric value By obtained in 1) is not affected by the maximum aperture value of the lens. The exposure calculation means (3) determines the shutter speed Tv from the input number of aperture steps, but since the open aperture value when the number of aperture steps is zero changes depending on the amount of lens extension, the effective open aperture value Effective open aperture value ef calculated by value calculation means (2)
Exposure calculation is performed using fAv'', and the shutter speed Tv is determined after canceling the change in the open aperture value caused by the lens extension.

As described above, in the photometry device of the present invention, the effective open aperture value effAv' changes depending on the amount of lens extension.
is used for exposure calculation, so even if the amount of lens extension becomes large, appropriate exposure calculation can be performed.

(Example 1) FIG. 2 shows the configuration of a typical photometric optical system of a single-lens reflex camera. (11) is the photographing lens, (12) is the aperture, (13)
) is a quick return mirror, (14) is a focus plate, (1
5) is a pentaprism, (16) is a photometric lens, (17)
) is a light receiving element, (18) is an eyepiece lens, and (19) is a film surface. The photometric lens (16) is used for the purpose of condensing light when measuring light focusing on the center, and when dividing the photometric area as in the case of multi-segment photometry, the photometric lens (16) is used to focus the light on the focal plane and the light receiving element (17). ) is configured to be conjugate with the light-receiving surface. The light receiving element (17) is used by dividing the element when dividing the photometry area into multiple parts.

The photometric optical system shown in Fig. 2 has a configuration in which light is guided from the upper part of the exit of the pentaprism (15), but there is also an eyepiece lens (
18) A structure that guides light from both sides of the focusing plate (14)
Possible configurations include a configuration in which a light guide is provided nearby to receive light, and a configuration in which the quick return mirror (13) is a semi-transparent mirror and a light receiving element is placed in a mirror box to measure light.

FIG. 3 is an explanatory diagram in which the photometric optical system shown in FIG. 2 is expanded to include only the photometric portion. A Fresnel lens (14A) and a focal plane (14B) are formed on the focus plate (14). The focal plane (14B) is usually a diffusing surface for focusing. The focal plane (14B) and the light receiving surface of the light receiving element (17) have a conjugate relationship due to the photometric lens (16).

If the light-receiving element (17) is placed on the image plane (focal plane) created by the photographic lens, no photometry error will occur, but in reality, it is necessary to observe the screen through a finder, and it is observed from an oblique direction at a position slightly offset from the focal plane. Since the image is photometered, photometry errors occur due to differences in interchangeable lenses. For example, consider the case where even though taking lenses have the same F number (hereinafter referred to as FNO), the distance Pz from the focal plane to the exit pupil position differs as shown in Pza, Pzb, and Pze in FIG. 3. The light beam measuring the upper part of the focusing plate (14) is
, C1 is the light beam photometering near the center, and L is the light beam photometering the lower part. Since the light ray C photometrically measuring the vicinity of the center of the screen does not blur regardless of the exit pupil distance, the photometric value hardly changes depending on the exit pupil distance.

On the other hand, the light ray U that measures the upper part of the screen has a short exit pupil distance Pz
A lens with a long exit pupil distance Pza will not cause vignetting, but a lens with a long exit pupil distance Pza will cause blurring, and the image will be judged to be darker than it really is. On the other hand, the light ray that meters the lower part of the screen has a tendency opposite to that of the light ray U that meters the upper part of the screen.

In FIGS. 4(a), (b), and (c), the exit pupil distances are Pza and Pzb.

For the Pzc photographic lens, the relationship between the illuminance of the cell surface of the light receiving element (17) and the screen position is shown from the vignetting of the light rays. In a lens with a long exit pupil path @Pza, the cell surface illuminance at the top of the screen is low, as shown in Fig. 4(a), and in a lens with a short exit pupil distance Pzc, as shown in Fig. 4(a).
As shown in c), the cell surface illuminance at the bottom of the screen is low. For a lens with exit pupil distance Pzb, the focus plate (14)
Due to the imaging action of the Fresnel lens (14A) in
Since the pupil of the photometric optical system is projected onto the exit pupil position of the photographic lens, the light rays U and L above and below the focus plate (14) are converged at the exit pupil position, and the screen appears as shown in FIG. 4(b). There is almost no difference in illuminance between the top and bottom positions.Next, when the F'tio of the photographic lens changes, if the FNO becomes large (that is, the aperture is small) with a lens with a long exit pupil distance Pza, the upper part of the screen will change. There is a significant decrease in illuminance. On the other hand, with a lens having a short exit pupil distance Pzc, the illuminance at the bottom of the screen is significantly reduced.

The reference lens has a focal length of f=50 (mn+), FNol,
7 lens, the cell surface illuminance of the light receiving element when using the reference lens is Cs, the film surface illuminance is Is, the cell surface illuminance of the light receiving element when using an interchangeable lens is Ci, and the film surface illuminance is Ii. Then, Cs/Ci=Is
/ I i -(1), the exposure error caused by the photometric optical system will be zero. In reality, as explained in FIGS. 3 and 4, the cell surface illuminance varies depending on the exit pupil distance Pz and FNO, and the above relationship is not satisfied. Therefore, the exposure error caused by not satisfying equation (1) is called photometry error Wv, and is defined by the following equation.

Wv=log2Cs/Ci-1log2Is/
I i - (2) The Kuraray direction of the light flux varies greatly depending on the diffusion characteristics of the focus plate (14), but the characteristics in Figure 4 are simulated using the typical diffusion characteristics of the focus plate (14) used in cameras. The results are shown below.

FIG. 5 is a graph in which the tendency shown in FIG. 4 is replaced with exit pupil distance Pz and photometry error Wv. The photometric error Wv at the center of the screen is, as shown in FIG. 5(a),
It does not vary greatly depending on the exit pupil distance Pz. FNOl, 4
In the interchangeable lens, the aperture is larger than the light beam spread by the diffusivity of the focus plate (14), so the photometric value is almost the same as that of the reference lens. However, the amount of light reaching the film surface is 0.
Since it is 5Ev brighter, a photometry error of 0.5EV has occurred. Conversely, with an interchangeable lens that is darker than the reference lens of FNO1, 7, the cell surface illuminance is brighter than the decrease in illuminance due to the change in FNO. This is considered to be because even with the reference lens of FNO1, 7, the aperture is larger than the light flux entering the photometry section.

The photometry error Wv at the top of the screen is as shown in Figure 5(b), and since the aperture is larger than the luminous flux area required for photometry with the interchangeable lens of FNOl, 4, the photometry error Wv varies depending on the exit pupil distance Pz. do not. On the contrary, FN.

In an interchangeable lens with a large value, there is a large variation depending on the exit pupil distance Pz, and as the exit pupil distance Pz becomes short, the photometry error Wv becomes undervalued.

The photometry error Wv at the bottom of the screen is as shown in Figure 5 (C), and since the aperture is larger than the luminous flux area necessary for photometry with the interchangeable lens of FNOl, 4, the photometry error Wv varies depending on the exit pupil distance Pz. do not. On the other hand, in the case of an interchangeable lens with a large FNO, the variation depending on the exit pupil distance Pz is large, and as the exit pupil distance Pz becomes longer, the photometry error Wv becomes undervalued.

Figure 6 shows the interchangeable lens (IL) and camera body (B1
FIG. 1 is an explanatory diagram for explaining an overview of a data communication method with L-D). Memory means (ROM) in the interchangeable lens (IL)
The exit pupil distance Pz is held as data related to the exit pupil, the open aperture value Avo and the aperture change amount ΔAv due to zooming are held as data related to the aperture value, and various other data as described below are held. is retained. When the read signal from the camera body (BD) is given to the read signal input means (RD) of the interchangeable lens (TL), the data transmission means (DT) serially transmits each of the above data to the camera body (BD). Ru.

FIG. 7 is a circuit diagram of a camera system to which the present invention is applied. (DT) is a light receiving section for focus detection, and has a CCD image sensor array. (IFC) is an interface circuit, which controls the operation of the CCD image sensor array, and
The signals read from the CCD image sensor array are A/D converted and sent to the microcontroller (COM) via the data bus (DBAF).
The interrupt input terminal (INT,) of the microcomputer (COM>)
It has the function of transmitting information to other people. Note that the charge accumulation time in the CCD image sensor array is controlled by the output of a light receiving section (not shown) that monitors the brightness of the subject.

(MOAF) is the lens drive motor for AP, (M
DA) is a motor control circuit, which performs forward rotation, reverse rotation, brake, and OFF control using signals from output ports (PO) and (PL) of a microcomputer (COM). (DPA) is a display unit for displaying the moving direction of the lens, focusing, and warning that focus cannot be detected based on signals from the output ports (p2) and (pl) of the microcomputer (COM).

(ENL) is an encoder that outputs pulses to monitor the lens drive amount (motor rotation amount) by the lens drive motor (MOA F ), and (ENAP) is an encoder that outputs pulses to monitor the lens aperture amount. This is an encoder that outputs. (SEC) is the output port (p4
) is at the ``Lou+'' level, the pulse from the AP encoder (ENL) is sent, and when it is at the ``High'' level, the pulse from the aperture encoder (ENAP) is sent.
Each is a data selector for sending to an input terminal (CNTR) for an event counter. Microcomputer (CO
An event counter is provided inside the terminal (C), and data is preset in the event counter.
The contents of the event counter are counted down every time a pulse is input to the NTR), and when the contents of the event counter reach 0, an interrupt is generated.

(Sl) is a photometry switch that is closed at the first step of pressing the release button, and the closing signal of this photometry switch (Sl) is sent to the interrupt input terminal (INTO) of the microcomputer (COM>).
> is input to the input boat (p,). (S2) is a release switch that is closed in the second step of pressing the release button, and the closing signal of this release switch (S2) is as follows:
It is input to the input boat (p6). (S3) is a reset switch that is closed upon completion of the exposure control operation and opened upon completion of winding/charging, and the closing signal of this reset switch (S,) is input to the input port (p7).

(GV) is a power supply circuit, which operates when the power supply control signal (pwc) output from the output port (p,
High voltage (HV) and low voltage (L) based on the output of A)
V). High voltage (HV)
) and interface circuit (IFC). In addition, the low voltage (LV) is
EC), and the film sensitivity reading circuit (ISD) described below.
, lens circuit (LEC), photometry and A/D conversion circuit (MBC), decoder/driver (DDR), motor control circuit (MDA), (MDF), display unit (DSP), microcontroller (COM) ) receives power directly from the power battery (BA) via the power line (EV).

(ISD) is a film sensitivity reading circuit that reads ISO data indicating the film sensitivity on the film container.
When the film sensitivity reading circuit selection signal (C8IS) from the output port (p9) becomes l Lo, + level, the film sensitivity data is sent to the serial input terminal ( S.I.
N) serially. (LEC) is a lens circuit provided within the interchangeable lens. This lens circuit (LE
C) has a circuit configuration disclosed in, for example, Japanese Patent Application Laid-open No. 59-140408, and has an output port (p+
. ) The lens circuit selection signal (C3L) from
When the signal reaches the "L" level, various data stored in the ROM in the lens circuit (LEC) are serially sent to the serial input terminal (SIN) in synchronization with the serial clock (SCK). (The data fixedly stored in the ROM in L E C> will be explained separately for the fixed focus lens and the zoom lens.

(Margin below) Table 1 Table 2 Tables 1 and 2 show addresses and data contents in the interchangeable lens. Table 1 shows the ROM inside the fixed focus lens.
Indicates the memory contents of. Table 2 shows the R inside the zoom lens.
Shows the storage contents of OM. In each table, address 01 contains data common to all lenses.
) is fixedly stored. At address 02, the open aperture value (Avo) is stored, and in the case of a zoom lens, the open aperture value at the shortest focal length is stored.

Address 03 contains the aperture change amount (ΔAv
=O) is stored. Address 04 stores the exit pupil distance Pz of the single focus lens.

Address 05 stores the focal length f of the single focus lens. Address 06 contains the defocus amount for a single focus lens, which is set by the lens drive motor (MOA).
A coefficient K to be converted into a driving amount of F) is stored.

In the case of a zoom lens, the lower 4 bits 0 to 4F of addresses 10 to 4F are addressed by a signal obtained from a zoom encoder in accordance with zooming. address 1
0 to IF contains data Δ of the amount of aperture change due to zooming.
Av is located at addresses 20 to 2F, and exit pupil distance Pz, which changes according to zooming, is located at addresses 30 to 3F.
The focal length f that changes according to zooming is at address 4.
0 to 4F store a coefficient K that converts the defocus amount into the drive amount of the lens drive motor (MOAF) in the case of a zoom lens. Address 50-6
F stores object distance signals obtained from focusing lens position data for single focus lenses and zoom lenses.

(DSP) is a display circuit, which performs display based on display data sent from a microcomputer (COM).

(MBC) is a photometry and A/D conversion circuit, and when low voltage (LV) power supply from the power supply circuit (GV) starts, it starts photometry operation and outputs the A/D conversion circuit from the output port (p12). When the D conversion enable signal (ADEN) becomes "Low" level, A/D conversion is repeated at a constant cycle. Then, when the photometry and A/D conversion circuit selection signal (C8ME) from the output port (pll) reaches the lLoIllII level, the A/D converted and latched data is synchronized with the serial clock (SCK). Microcomputer (CO)
M). (DDR) is a load driving circuit that decodes data sent from a microcomputer (COM) through a data bus (DBDR) and drives a load according to the decoded result.

The loads include a release magnet (RLM), an aperture control magnet (APM), and a leading curtain control magnet (
ICM), rear curtain control magnet (2CM), film advance and exposure control mechanism charge motor (MOCH)
and its driver (MDF).

(X) is an oscillator.

The operation of this camera system will be explained below based on the flowcharts shown in FIGS. 8 to 12.

In the following explanation, the symbol "#" means a step number of the program. When the release button is operated, the first press of the button closes the photometry switch (S,), an interrupt signal is input to the interrupt input terminal (INTo), and the microcomputer (COM) operates as shown in Fig. 8. Interrupt routine INT
, start the operation from.

First, the power supply control signal (pwc) output from the output port (p8) is set to the 'Lou+' level, and the power supply circuit (
GV) (#1). Next, interface circuit (IFC), display circuit (DSP), photometry and A/D
Reference clock (CK OUT) to conversion circuit (MBC)
) and sweeps out the charge accumulated in the CCD.
Perform CD initialization operation (#2, #3). next,
The charge accumulation operation of the CCD is started, and at the end of the charge accumulation operation, an interrupt signal to the interrupt input terminal (INTl) can be accepted, and an A/D conversion enable signal (ADEN) from the output port (p,) is accepted. Set the “Lou+” level and set the photometric value to A/
Convert to D (#4, #5, #6).

Next, the process moves to the photometry routine, and lens data is acquired from the interchangeable lens, and film sensitivity data (IS) is acquired from the film container.
0 data) respectively (#7, #8). next,
Determine the status of flags IFFI and IFF2. IFF
, is a flag that is set to 1 when the in-focus state is reached, and IFF2 is a flag that is set when photometric data is taken in after the in-focus state is reached. Therefore, when the camera is not in focus or when the photometric data is not captured even though it is in focus, the photometric data is captured, and when the data is captured after the focus is focused, the flag lFF2 is set to 1 and the process moves to the calculation routine. . Also, flag I
If FF, IFF2 are both 1, the process directly proceeds to the calculation routine without inputting photometric data (#9 to #13).

In the calculation routine, first, in step #15, it is determined whether or not the lens attachment signal ICP is input. If so, the process moves to step #19, and if not, the process moves to step #16. First, if no lens is attached, it is of course impossible to control the aperture, and the aperture must be assumed to be fixed. Therefore, in step #16, (photometric data) - B v - A v (B v is the subject brightness, A v is the fixed aperture value) is I that indicates the film sensitivity.
The exposure time Tv is calculated by adding the SO value Sv. In step #18, the exposure time is displayed, and the F value is displayed as a warning (for example, "--"). In step #19, as shown in the flowchart of FIG. 10 described later, the exposure value Ev is calculated based on the true photometry value obtained by correcting the photometry error.
Calculate. By performing program exposure calculation (#20) based on this exposure value Ev, the aperture value Av and exposure time T
v is calculated and displayed (#21).

When the above operations are completed, flag AEF is set to 1. This flag is set to 1 when the exposure calculation is completed. Next, determine the state of flag CF,
If CF=1, the process moves to the AP routine. This flag C
When the charge accumulation operation of the CCD is completed during the operation of the photometry routine or the calculation routine, if no exposure calculation has been completed, F will import the data from the COD and then perform the remaining exposure calculations. This step is provided to proceed from this step to the AF routine.

In step #24, it is determined whether the release switch (S2) is closed, and in step #25, it is determined whether the exposure control value is calculated from the photometry data after focusing. If so, the process moves to an exposure routine and performs exposure control operations.

On the other hand, if the conditions are not met, it is determined whether the photometry switch (Sl) is closed in step #251, and if it is closed, the process returns to the photometry routine, and if it is not closed, the stop routine is executed. perform the following actions.

In the stop routine, first, all flags are reset, the output port (p,) is set to the Lou+'' level, data is sent to the display circuit (DSP) to set the display to 0FF (nothing displayed), and the motor (MOAF ), stops the output of the reference clock (CKOUT), deactivates the power supply circuit (GV), and sets the signal (ADEN> to 'High'.
h” level, A/D conversion is disabled, and the microcomputer (C
OM) stops operating (#26 to #32).

At step #24 in Figure 8, release switch (S2
) is closed and the flag lFF2 is set to 1 in step #25.
If it is set, the process moves to the exposure control routine shown in FIG. First, use the #75 stabilizer to set the AF display to 0FFL.
, At step #76, remove the release magnet (RL M
) to start the operation of the exposure control mechanism. Then, determine whether or not an interchangeable lens is attached (#77) L
, if the lens is not attached, the process moves to step #83 and no aperture control operation is performed. On the other hand, if the lens is attached, first, in step #79, the control aperture value (A
v) is equal to the open aperture value (A vo), and if Av=Avo, the process similarly moves to step #83. On the other hand, if Av#Avo, the number of refinement stages (A
v Avo) in the event counter (EV C), set the port (p,) to High" level, and set the pulse from the encoder (ENAP) that monitors the aperture amount to be output from the selector (SEC). (#80, #81, #82). Then, #83, #8
Wait for a certain amount of time in step 4. During this time, if a narrowing operation is performed and an event counter interrupt occurs, #10
In step 4, the aperture magnet (APM) is operated to stop the aperture. Then, after a certain period of time has passed, the reflection mirror has finished rising and the leading curtain magnet (
ICM) to start running the front curtain and count the exposure time ($85. #86). When the count ends, the trailing curtain magnet (2CM) is operated to start running the trailing curtain (#87). Then, it waits for the trailing curtain to complete running and the reset switch (S,) to be turned on (#88). When the reset switch (S3) is turned ON, the charging motor (MOCH) is operated to wind the film and charge the exposure control mechanism, and when this operation is completed, the reset switch (S,) is turned OFF. (#89)

#90), and the reset switch (S, ) is OFF.
When this happens, wait until your finger is released from the release button and the photometry switch (Sl) is turned off (#91).

When the photometry switch (Sl) is turned OFF, the stop routine is performed, and then the photometry switch (S,) is turned ON.
and stops operating until the microcomputer (COM) is activated.

Here, the exposure calculation method will be explained. Let Ev be the exposure value expressed as an apex value, Av be the controlled aperture value, Tv be the shutter speed, By be the subject brightness, and Sv be the film sensitivity, then the relationship F,v=Av+Tv=Bv+Sv holds true. The subject brightness By is obtained through a photometric optical system as shown in FIG. 2, and the photometric data B vo' obtained from the camera body is expressed as follows.

B vo' −B v −(A vo+ΔAv) In the above equation, (Avo+ΔAv) indicates the open aperture value of the interchangeable lens. In reality, as shown in Figures 3 to 5,
The true photometric value Bvo requires correction depending on the photometric range and the configuration of the photometric optical system.

Therefore, the true photometric value Bvo is as follows, where Wv is the correction value (that is, photometric error). In the case of multi-division photometry, multiple correction values Wv are also required.

FIG. 13 shows an example of division when performing multi-division photometry on the screen. SP1 to SP5 indicate light receiving elements for photometry. SPI is a light receiving element that measures light at the center of the screen, and 8P2 to SP5 are light receiving elements that measure light at the periphery of the screen.

FIG. 10 shows the Ev calculation routine #19 in FIG. Assuming that the number of divisions in multi-division photometry is five, correction values are calculated by subroutines 5UB1 to 5UB5, respectively, when the cell number of the light receiving element SPi is i=1 to 5 (#
120 to #128), when the correction value Wvi corresponding to each light receiving element SPi is determined, the true brightness value Byi corresponding to each light receiving element SPi.

is found (#113). By weighting and adding each brightness value Byio with a coefficient ki set for each cell number i, an appropriate brightness Bvo is calculated (#129), and an exposure value Ev is obtained (#130). Note that when center-weighted spot photometry is performed instead of multi-segment photometry, the correction value W is set only for the light receiving element SP1 of cell number i-1.
v, and the light receiving element SP2 of cell number i=2 to 5
The calculation of the correction values Wv2 to Wvs for ~SP5 is omitted, and the exposure calculation speed is increased (#110 to #115
). In this case, in step #129, the corrected photometric value for the photodetector SPI, which measures the center of the screen, is directly 13
You can use vo.

FIG. 11 shows a subroutine 5UB1 for determining the correction value W v of the open photometry value corresponding to the center of the screen. The photometric value at the center of the screen is as shown in Figure 5(a).
The photometric value varies depending on the open aperture value, regardless of the exit pupil distance Pz of the interchangeable lens. Therefore, the photometric correction value W v + of the interchangeable lens is determined by the maximum aperture value A, as shown in Table 3.
It is determined by the value of v'(-Avo+ΔAv). In reality, as the amount of lens extension increases, the open aperture value Av' differs from that when the subject is at infinity.

If the actual open aperture value is the effective open aperture value effAv'', then effAv' = Av' + 2 Iogz (1
+β)...It can be expressed as ■. Here, β is a magnification; for example, when the magnification is the same (β = 1), effAv' = A
v' + 2, and it can be seen that it fluctuates greatly. Therefore, accuracy will be higher if the correction value is also determined using the effective open aperture value effAv'. Effective open aperture value effAv'
As shown in Tables 1 and 2, is determined by the distance signal obtained at addresses 50-6F and the focal length f obtained at addresses 05 or 30-3F. In simple calculation, the magnification β is β average f/L
...■, and by substituting this β into equation 0, the effective open aperture value effAv' is determined. In this embodiment, FIG.
In the correction value calculation subroutine shown in the figure, a more accurate correction value Wv is selected by performing the substitution Av'←Av' +21ogz (1+β).

First, in #131 if A v'< A v + +, Y++ is set as the address in #145, and then in #13
2, if A v 11≦A v'< A L+ 2, YI2 is set as the address in #146. Also, #1
33, if Avl□≦Av'< A V l 3, then #1
47, Y13 is set as the address, and Av'≧Av13
If so, Y is set as the address in #144. As a result, which position in Table 3 is the address data Y
+j makes it possible to set, and this address Y+j specifies the ROM table in which the correction values W1 to W in Table 3 are stored, and the correction values W1 to W stored there are specified.
Let one of them be the correction value Wv. Note that the correction values W1 to W in Table 3 are specifically A v' =
The log2F N02 is determined so that the relationship shown in FIG. 5(a) is satisfied.

FIG. 12 shows a subroutine 5UBi (i=
2. ..., 5) is shown. In the peripheral area of the screen, a data table is stored in advance in which the correction value of the photometric value is mapped by the value of the open aperture value Av' and the exit pupil distance Pz, and by reading this data table, the photometric correction value of the interchangeable lens is determined. Fourth
The table shows an example of a data table of correction values mapped by the maximum aperture value Av' and the exit pupil distance Pz.
It is also possible to change it depending on the element number i. Note that here as well, as the open aperture value, the effective open aperture value effAv
' is used.

In steps #121 to #123 in FIG. 10, the subroutine 5UB corresponding to element number 1 (-2,..., 5)
i is selected. In steps #150 to #153, an address Yij corresponding to the open aperture value Av' is set. In other words, if Av'<AvL in #150, Yi in #155
l is set as the address, and in #151 A v i +≦
If A v'< A v i 2, #156 yields Yi2
is set to the address, and in #152 A v i 2≦A
If v''< A v i 3, YL is set as the address in #157, and A v i 3≦Av'<A in #153.
If it is vi4, Yi4 is set as the address in #158,
Av'≧Avi.

If so, Yes is set to the address in #154.

Also, in steps #159 to #162, the exit pupil distance Pz
Address Xij is set according to. In other words, #15
If Pz<PzL in 9, Xil is set as the address in #164, and Pz i l≦Pz<Pzi in #160.
If it is 2, Xiz is set to the address in #165, and #1
If PzL≦Pz<PzL3 in 61, then Xiz in #166
is set as the address, and in #162 PzL≦Pz<Pz
If it is L4, Xi4 is set as the address in #167, and P
If z≧Pzi4, Xi5 is set as the address in #163. Set address (Xij.

R in which the data table in Table 4 above was stored in
Specify the OM table and input the data stored at that address to the correction value Wvi. In addition, specifically, the correction value in the data table of Table 4 is A v'
= l og2 F N02, the photometric correction value Wv 2 + W v 5 at the top of the screen is shown in Figure 5 (b
) is the photometric correction value at the bottom of the screen W v s +
For W V 4, the relationship shown in FIG. 5(e) is determined so that the grooves are filled.

(Leaving space below) Table 3 Table 4 In the above embodiment, in a zoom lens whose exit pupil distance Pz changes with zooming, the exit pupil distance Pz is set as a variable amount according to zooming, as shown in Table 2. However, in addition to this, even in lenses with a large extension amount, such as close-up lenses, it is desirable to make the exit pupil distance Pz variable according to the amount of edge extension. for example,
When extended to the same magnification with f=50mm, the exit pupil position is approximately 5
0mm will also move forward, and the exit pupil distance Pz will fluctuate by double the length, so select a more accurate correction value Wv based on the exit pupil distance Pz, which is variable according to the amount of extension. is desirable.

(Embodiment 2) FIG. 14 shows another example of the configuration of a photometric optical system used in a single-lens reflex camera. (11) is a photographing lens, (12) is a diaphragm, and (13H) is a quick return mirror consisting of a semi-transparent mirror. The light transmitted through the quick return mirror (13H) is reflected downward by the sub-mirror (SB), and is then reflected by the focus detection module (AF) located at the bottom of the mirror box.
). In a phase difference detection type focus detection device,
If the light flux that reaches the sensor in the focus detection module (AF) is eclipsed by the photographing lens, the distance measurement accuracy will deteriorate, so the AF light flux received by the focus detection module (AF) is the most important among the interchangeable lens groups. It's staring into a darker place than a lens with a dark F number. Therefore, when photometry is performed using the output of the focus detection module (AP), the photometry value does not change even if the aperture (12) is stopped until the AF light beam is eclipsed.

Therefore, in the photometric optical system of this embodiment, the brightness By of the subject is obtained that is independent of the aperture value of the photographic lens. As explained in step #80 above, the aperture value is controlled by the difference (Av-) between the control aperture value Av and the open aperture value Avo.
This is done by narrowing down the aperture value (Avo) from the open state, and if the accurate open aperture value Avo is not known, the aperture value will be inaccurate and cause an exposure error. For example, in the case of aperture priority AE, if the control aperture value is Av, the shutter speed Tv is calculated as Tv = Bv - Av + Sv, but in the above equation, Av is actually controlled by the number of stops from the aperture open state. Therefore, if it is assumed that the open aperture value changes by δAv as the lens is extended, the true aperture value will be (Av+δAv), and the appropriate shutter speed can be found as Tv=By-(Av+δAv)+Sv. However, δAv=effAv' −Av
'-21ogz(1+β). The true aperture value (A
v+δAv) can be effectively utilized with macro lenses,
This is a close-up lens, a lens with a large extension amount, such as a bellows.

Note that if exposure calculation is performed using the effective open aperture value efTAv', it is considered that it will contribute to higher precision of exposure control even when photometry is not performed through the photographing lens.

(Effects of the Invention) In the present invention, in an interchangeable lens camera equipped with a photometer, the effective maximum aperture value, which changes depending on the lens extension star, is used for exposure calculation. Even when a lens with a large amount of extension is used, there is an effect that appropriate exposure calculation can be performed.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are block diagrams showing the basic configuration of the present invention, Figure 2 is a schematic configuration diagram of a photometric optical system used in an embodiment of the present invention, and Figure 3 is the same photometric optical system as above. Explanatory diagram showing the relationship of light rays in FIGS. 4(a) and 4(b). (c) is a diagram showing the relationship between the cell surface illuminance of the photometric optical system and the screen position, and Figures 5 (a), (b), (c)
is a diagram showing the relationship between the photometric error and exit pupil distance of the same photometric optical system as above, FIG. 6 is a schematic configuration diagram of the communication system used in the above example, and FIG. 7 is a camera using the same photometric optical system. A block diagram of the system, FIGS. 8 to 12 are flowcharts showing the operation of the same as above, FIG. 13 is a diagram showing the photometry area in the photometry optical system of the above, and FIG. 14 is a photometry used in another embodiment of the present invention. FIG. 2 is a schematic configuration diagram of an optical system. (1) is a photometry means, (2) is an effective aperture value calculation means,
(3) is an exposure calculation means, and (IL) is an interchangeable lens.

Claims (3)

[Claims] (1) In a camera with interchangeable lenses that is equipped with a photometer for measuring the brightness of a subject, an effective aperture calculation means that calculates an effective aperture value that changes depending on the amount of lens extension of the interchangeable lens; A photometric device for an interchangeable lens camera, comprising an exposure calculation means for calculating exposure using an aperture value. (2) The photometry means is a means for fully metering the brightness of the subject through an interchangeable lens, and the exposure calculation means
2. The photometry device for an interchangeable lens camera according to claim 1, further comprising a correction means for correcting an error in photometry using an effective aperture value. (3) The lens interchangeable camera according to claim 1, wherein the photometry means also serves as a distance measurement means for detecting the distance to the subject by receiving the subject light incident through the interchangeable lens. photometric device.