Exposure control apparatus for camera provided with multi metering device

An improved exposure control apparatus for camera comprises a metering circuit, exposure operational circuit, correction value calculating circuit and correction operational circuit. The metering circuit meters a plural number of divisional sections of the field of an object and generates a plural number of photoelectric outputs corresponding to the respective sections of the field. The exposure operational circuit calculates an exposure value from the plural number of photoelectric outputs. The correction value calculating circuit calculates correction values for correcting the distribution characteristics of said photometric outputs relative to the distribution characteristics of illumination on the focal plane of the photographing lens of the camera at the time of photographing, the correction values corresponding to the sections of the field respectively. The correction operational circuit makes a correction to the respective photoelectric outputs in accordance with the respective correction values found by above calculation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an exposure control apparatus for a camera 
and more particularly is directed to an improvement in such exposure 
control apparatus provided with multi metering means in which a plural 
number of divisional sections of an object field are metered 
photometrically to obtain a plural number of photoelectric outputs 
corresponding to the respective sections and a proper photometer output is 
operated and extracted from the photoelectric outputs to determine a 
proper exposure value for the whole object field. 
2. Description of the Prior Art 
The above mentioned type of multi metering device is well known in the art 
and there have been proposed various multi photometers for this purpose 
one example of which is disclosed in Japanese Patent Application laid open 
No. 12,828/1977 (its corresponding German Patent Laid Open Specification 
is DOS P No. 2,632,893). 
However, all of the improvements hitherto proposed for such type of 
divisional photometer have been directed solely to an operational method 
and apparatus for calculating a proper exposure value from a plural number 
of informations obtained by photometering. 
In practical use of known multi photometers in a camera, there arises such 
problem that the photoelectric outputs from the multi photometer can not 
be used directly as a proper photometer output because of the difference 
between the distribution of the photoelectric outputs in the object field 
and the distribution of illumination on the film plane. Hereinafter, the 
object field is referred to as the picture plane. 
In TTL open aperture metering, the above problem becomes particularly 
important. In this case, the difference between the distribution of 
photoelectric outputs obtained at the time of TTL photometering with fully 
open aperture and the distribution of illumination on the film plane 
obtained at the time of photographing with an aperture value then actually 
used becomes remarkably large and therefore the difference can not be 
ignored at all. This problem occurs even when the light receiving plane 
for multi metering is disposed conjugated with the film plane. Since a 
light receiving optical system is provided for the former plane, the above 
mentioned undesirable phenomenon can not be avoided even in such case. 
In the conventional photometering apparatus operable with one photoelectric 
output, the central part of a picture plane has been used as a main area 
to be metered. Since the central area of a picture plane generally 
exhibits good proportionality to lens aperture for both of the 
photoelectric output from the photo receptor and the illumination on the 
film plane, the above mentioned difference in distribution has no 
remarkable effect on the determination of proper exposure value. 
Therefore, in this single type of photometer it is seldom that such 
difference in distribution leads to exposure error. In contrast, in the 
case of multi photometer, the peripheral part of a picture plane is also 
to be metered independently of the main part and therefore the difference 
in distribution mentioned above can not be ignored. 
As an example, it is assumed that a picture plane is divided into segments 
in the form of 4.times.6 matrix as shown in FIG. 1 and these 4.times.6 
segments are to be metered by photo receptors P11 to P46 respectively. If 
the object is a surface having a uniform brightness all over, then the 
distribution of photoelectric output along A-A' in the picture plane shown 
in FIG. 1 will give a curve as shown in FIG. 2A. As seen from FIG. 2A, the 
level of photoelectric output drops down gradually from the center of the 
picture plane to both side end portions due to the vignetting effect of 
the lens and the effect of so-called Cos.sup.4 law (in FIGS. 2A and 2B, 
the distribution is plotted with the center of the picture plane as 0 and 
the locations of metered segments within the picture plane as the 
abscissa). However, when the aperture is stopped down for actually taking 
a picture, the effect of vignetting disappears and the distribution of 
illumination on the film plane gives a flattened curve (FIG. 2B) as 
compared with the curve of FIG. 2A. To obtain a proper exposure value, 
this difference between the distribution curves FIG. 2A and FIG. 2B has to 
be taken into consideration. Otherwise, the metered brightness for the 
peripheral sections of a picture plane will be unduly darker value than 
the real brightness thereof. This may lead the exposure to error. All the 
multi photometered hitherto proposed have no means for solving the 
problem. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the invention to provide a multi metering 
apparatus which enables minimization of the above exposure error. 
It is another object of the invention to provide a multi metering apparatus 
with which the possibility of exposure error mentioned above can be 
minimized by correcting the photoelectric outputs from a plural number of 
photo receptors so as to approximate the distribution thereof to the 
distribution of illumination on the film plane appearing at the time of 
the shot or exposure. 
Other and further objects, features and advantages of the present invention 
will appear more fully from the following description of preferred 
embodiments with reference to the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring first to FIG. 13 description is made of an example of a light 
receiving optical system mounted in a single lens reflex camera. To a 
camera body 330 is mounted detachably an interchangeable lens having a 
lens barrel 340. Light from an object to be photographed passes through a 
photographing lens system 332 in the lens barrel 340 and then is reflected 
by a movable mirror 333 toward a finder screen 335 on which the light is 
focused. When the movable mirror 333 is turned up to its retracted 
position in link with a photographing operation, the object light is 
focused on a film plane 334. The image of the object formed on the finder 
screen 335 is refocused on a surface 331 formed by a plural number of 
photoelectric elements through a refocusing lens 336. 
FIG. 3 shows the basic arrangement of a multi metering apparatus. Flow of 
signals for automatic control of shutter speed in aperture priority mode 
will be described hereinafter with reference to FIG. 3. In the following 
description there are used terms in APEX notation which include luminance 
value BV, aperture value AV, ASA speed value SV and time value TV. 
The multi metering apparatus shown in FIG. 3 comprises a metering circuit 
1, multi metering treatment circuit 2, APEX operational circuit 3, shutter 
control circuit 4, information setting portion 5 and display circuit 6. 
When TTL metering with fully open aperture is carried out for the 
divisional sections of a picture plane as shown in FIG. 1, there are 
obtained from the metering circuit 1 the following photoelectric outputs 
corresponding to the individual metered sections: 
EQU P11=BV11-AV0, P12=BV12-AV0, . . . , P46=PV46-AV0 
wherein the same number indicates the correspondency between photo receptor 
and photoelectric output from it. 
The multi metering treatment circuit 2 receives these outputs and carries 
out a series of operations and treatments to calculate an operational 
output P100=BVans-AV0 as an estimated value for proper exposure. Examples 
of such circuit are disclosed in Japanese Patent Application laid open No. 
12,828/1977 and U.S. Ser. No. 123,209 filed by the present applicant (its 
counterpart is DOS P. No. 3,007,575). 
The APEX operational circuit 3 receives information of film sensitivity 
P101=SV and information of aperture P102=(AV-AVO) from the information 
setting portion 5 as well as the above operational output P100=BVans-AV0 
relating to the brightness from the circuit 2, and carries out the 
following APEX operation: 
EQU (BVans-AV0)+SV-(AV-AV0) =BVans+SV-AV=TV(=P103) (1) 
The resultant TV value is introduced into the shutter control circuit 4 to 
control shutter speed. Also, it is put into the display circuit 6 to 
display the shutter speed displayed. 
FIG. 4 is a block diagram of a multi metering apparatus as formed by 
applying the present invention to the circuit shown in FIG. 3. A 
correction operational circuit 7 and a correction value calculating 
circuit 8 are added to the circuit shown in FIG. 3. 
In the multi metering apparatus shown in FIG. 4, the correction value 
calculating circuit 8 receives from the information setting portion 5 
information of the diameter of open aperture P105=AV0, information of 
aperture step number P102=AV-AV0 and signal P106=L informing of particular 
characteristics owing to the optical system of the lens. From these 
informations, the circuit 8 calculates correction values .delta.11 . . . 
.delta.ij . . . .delta.46 corresponding to the respective photoelectric 
outputs P11 . . . Pij . . . P46 from the respective sections. .delta.ij is 
given by the following general formula: 
EQU .delta.ij=f(AV0, AV-AV0, L) (2) 
Above general formula is experimentally obtainable. 
The correction operational circuit 7 comprises adders 7.sub.11, . . . 7ij, 
. . . 7.sub.46 which carry out adding the outputs .delta..sub.11 . . . 
.delta..sub.ij . . . .delta..sub.46 from the circuit 8 to the outputs P11, 
. . . Pij . . . P46 from the circuit 1 respectively. 
Let the photoelectric outputs from the metering circuit be represented 
generally in the matrix form by 
##EQU1## 
and let the outputs from the correction value calculating circuit be 
represented by 
##EQU2## 
Then, the operation carried out by the correction operational circuit 7 
can be represented by 
##EQU3## 
wherein Bij'-AV0 means a photoelectric output after correction. 
Consequently, the corrected photoelectric outputs P111=BV11'-AV0, . . . 
P146=BV46'-AV0 are introduced into the multi metering treatment circuit 2 
from the correction operational circuit 7 and then a proper exposure value 
P100'=BV'ans-AV0 is calculated by the circuit 2. Since the exposure value 
is found by calculation on the basis of corrected photoelectric outputs in 
this embodiment, it is much more proper than that obtainable by the 
apparatus shown in FIG. 3. Sequence subsequent to it in the apparatus 
shown in FIG. 4 is the same as in the apparatus shown in FIG. 3. 
The information setting portion 5 is formed in the following manner: 
In FIG. 13, the reference numeral 342 designates an aperture stop driving 
pin interlocked with an aperture stop 341 for the photographing lens 
system 332. The information setting portion 5 takes up the informations of 
AV0, AV-AV0 and L from the motion of the aperture stop driving pin 342 or 
from a signal pin 343 provided on the lens mount. Similarly, the 
information setting portion 5 takes up the information SV from ASA film 
sensitivity setting dial 337 mounted on the camera body and the 
information TV from the shutter speed setting dial 338. 
Hereinafter a detailed description is made as to what corrections are 
required. 
As an example, at first such case is considered wherein pictures of a 
surface having a uniform brightness are to be taken with use of two 
different lenses which have different open aperture values but have the 
same focal length. FIG. 5A shows the distributions of photoelectric 
outputs obtained when a lens of fully open aperture f/1.4 and another lens 
of f/2.8 are used respectively. The distributions are plotted with the 
photoelectric output as the ordinate and with the positions of the 
respective segments as the abscissa the origin "O" of which represents the 
center of the picture plane. As to the abscissa, the same is applied also 
to FIGS. 5B and 5C of which the ordinate is illumination on film plane 
(FIG. 5B) or correction value (FIG. 5C). 
As seen from FIG. 5A and as a matter of course, the photoelectric output 
produced in photometering with the aperture open using the lens having a 
larger relative aperture, f/1.4 is higher than that produced using the 
smaller aperture lens, f/2.8. However, because of vignetting, the drop in 
photoelectric output at the peripheral area of the picture plane becomes 
more remarkable in the case of larger aperture than in the case of smaller 
aperture. 
FIG. 5B shows the distribution of illumination of film plane obtained when 
a picture of the same object surface is taken through the lens whose 
aperture is stopped down to f/8. In this case, as seen from FIG. 5B, the 
distribution curve becomes almost flat for either of the two lenses. This 
means that for multi metering a particular treatment is required to 
transform the distribution of photoelectric output shown in FIG. 5A into 
that as shown in FIG. 5B. 
This problem is solved in the following manner: 
At first a reference lens (for example, f/2.8 lens) is preselected and 
using the selected lens the difference between the output in FIG. 5A and 
the output in FIG. 5B is determined. More particularly, one preliminarily 
knows the difference in output level between the photoelectric output at 
the time of fully open aperture metering and the output of illumination on 
film plane at the time of actual photographing with the aperture being 
stopped down to a certain step for the selected reference lens. This known 
difference constitutes a reference amount. Secondly, one finds out the 
difference in photoelectric output between two different lenses as shown 
in FIG. 5A to correct the difference caused by the difference in fully 
open aperture value between two lenses. Using the known difference, man 
obtains correction values are obtainable. FIG. 5C shows the distribution 
of correction value obtained in this manner. As seen from FIG. 5C, a 
larger correction value is applied to the photoelectric output derived 
from a remotor segment from the center of the picture plane, for a larger 
relative aperture lens. Here, it should be noted that the correction value 
for the central area of the picture plane is not 0 (zero) in FIG. 5C. This 
means that even at the central area the relation between photoelectric 
output and illumination on film plane does not correspond to the nominal 
step number for aperture value. 
Application of the above correction values is carried out depending upon 
whether the fully open aperture information P105=AV0 is large or small 
which is delivered from the information setting portion 5 in FIG. 4. When 
the lens is of a larger relative aperture, a larger correction value is 
applied to the peripheral area output. 
FIG. 6 shows another case wherein pictures of a surface having a uniform 
brightness are to be taken using the same lens but changing its aperture 
value variously. Similarly to the above case, FIG. 6A shows the 
distribution of photoelectric output, FIG. 6B the distribution of 
illumination on film plane and FIG. 6C the distribution of correction 
value obtained in this case. 
Since the same lens is used, there appears only one distribution of 
photoelectric output for every metering with fully open aperture as shown 
in FIG. 6A. However, the effect of vignetting on the distribution of 
illumination on the film plane varies depending upon the aperture value 
then used for actual photographing as shown in FIG. 6B. In particular when 
an aperture value at or near the fully open aperture is used, the drop in 
illumination output is much more remarkable as compared with other 
aperture values. Usually, pictures are taken with aperture values stopped 
down over a certain value. Therefore, it is required to use said certain 
aperture value as a reference value and to make a correction in such 
manner that in the case of taking a picture with an aperture value near 
the open aperture value of the lens, the photoelectric outputs from the 
peripheral sections of the picture plane can be corrected in the direction 
of minus(-) as shown in FIG. 6C. 
Application of above correction is carried out depending upon whether the 
aperture step number information P102=AV-AV0 is large or small which is 
delivered from the information setting portion 5 in FIG. 4. 
FIG. 7 shows such case wherein pictures of a surface having a uniform 
brightness are to be taken using two different kinds of lenses which have 
different optical systems while the fully open apertures are entirely the 
same. Pictures are taken with the same aperture value in this case. Again, 
FIG. 17A shows the distribution of photoelectric output, FIG. 7B that of 
illumination on film plane and FIG. 7C that of correction value. 
As seen from FIG. 7A, there is no remarkable difference in photoelectric 
output between a lens having a longer focal length and a reference lens. 
However, when the aperture is stopped down for actual photographing, a 
considerable drop in illumination on film is observed at the peripheral 
areas for the reference lens which is caused by the effect of Cos.sup.4 
law. On the contrary, for the lens of longer focal length, the 
distribution of illumination on the film plane gives a nearly flattened 
curve (FIG. 7C). 
Therefore, when the lens having a longer focal length is used with an 
aperture value other than its fully open value, it is required to correct 
the photoelectric outputs from the peripheral sections of the picture 
plane in the direction of plus (+) in an amount corresponding to the 
difference between the output in FIG. 7A and the output in FIG. 7B, as 
shown in FIG. 7C. 
Application of this correction is made depending upon the lens 
chracteristics information signal P106=L which is delivered from the 
information setting portion 5. This signal L=P106 may be of, for example, 
focal length or distance of exit pupil of the lens. This signal is 
introduced into the correction value calculating circuit 8 to make it 
calculate those correction values which can not be represented by AV0 
(=P105) or AV-AV0 (=P102). 
In point of photometering only, what the signal L (=P106) has to do is only 
to transmit the correction value of the lens for metering. However, 
considering various automations on the camera, there are required a large 
number of signals. We have paid particular attention to this point and 
found that various purposes of correction can be attained by using such 
signal informing of data about the focal length of lens then used. Use of 
L (=P106) as focal length signal has an advantage that it may be used for 
other purposes than metering. 
In the shown embodiment in which a picture plane is divided into 
4.times.6=24 segments by photo receptors P11-P44, the number of correction 
values to be obtained by calculation reaches 24 in total, that is, 
.delta.11.about..delta.46. However, in general, lenses have such focusing 
characteristics that all the points in a lens lying on a concentric circle 
the center of which is the optical axis of the lens exhibit the same 
property. Therefore, for the sections equally distant from the center the 
same correction value may be used. For this reason, in case the metering 
system can be considered to have the same metering characteristics for 
every divisional area lying on a concentric circle with its center being 
the optical axis of the photographing lens, it is permissible to calculate 
the correction values as a function of the distance from the center of 
picture plane to the photo receptor. Namely, as seen from the following 
matrix formula and as illustrated in FIG. 8, five correction values 
.delta.0 . . . .delta.4 may be used as representatives of all the 
correction values: 
##EQU4## 
In addition, as seen from FIGS. 5C, 6C and 7C, the following relation holds 
among the five correction values: 
##EQU5## 
In case the metering system has such metering characteristics which are 
symmetrical about right and left only relative to the picture plane, it is 
desirable that the representative correction values be calculated as a 
function of the distance from the bisector of the picture plane to the 
respective photoreceptors to obtain such correction values which are 
symmetrical about right and left and asymmetric relative to the vertical. 
Making use of the above feature regarding the correction values, the 
embodiment shown in FIG. 4 can be simplified. FIG. 9 shows such simplified 
embodiment. 
In FIG. 9, reference numeral 108 designates a correction value calculating 
circuit. The circuit 108 receives from the information setting portion 5 
informations of the diameter of open aperture AV0 (=P105), aperture step 
number AV-AV0 (=P102) and lens signal L (=P106) and calculates the 
correction values .DELTA.0, .delta.1, . . . .delta.4 from the received 
informations. 
In the correction operational circuit 7, addition is carried out so as to 
add .delta.0 to P23, P24, P33, P34; .delta.1 to P13, P14, P22, P25, P32, 
P35, P43, P44; .delta.2 to P12, P15, P42, P45; .delta.3 to P21, P26, P31, 
P36 and .delta.4 to P11, P16, P41, P46. 
FIG. 10 shows a concrete form of the circuit used in the embodiment shown 
in FIG. 9. 
In FIG. 10, the metering circuit generally designated by 1 is constituted 
of a number of metering blocks each comprising an operational amplifier 
OPij, a photo diode PDij and a logarithmic compression diode LDij. The 
number of metering blocks in the metering circuit 1 corresponds to the 
number of the divisional sections in the metered picture plane. A 
reference bias E0 is applied to the in-phase input to the amplifier OPij. 
Metering current generated in photo diode PDij is logarithmically 
compressed by the logarithmic compression diode LDij. The logarithmically 
compressed output is: 
EQU V(Pij)=E0+(KT/q)ln(ILij/IS) (8) 
The correction value calculating circuit 108 receives from the information 
setting portion 5 informations P105=AV0, P102=AV-AV0 and lens signal 
P106=L. 
Information AV0 is introduced into the in-phase input terminal of 
comparator C1, information AV-AV0 into that of comparator C2 and signal L 
into that of comparator C3. Current I0 flows from a constant current 
source to resistors R15 and R16. A voltage I0 (R15+R16) is being applied 
to the inversion input terminals of comparators C1 and C3 and a voltage 
I0.multidot.R16 is being applied to the inversion input terminal of 
comparator C2. 
Comparator C1 has logic "1" at its output when 
EQU AV0.gtoreq.AV0th (I0(R15+R16)) (9) 
Comparator C2 has logic "1" at its output when 
EQU (AV-AV0).gtoreq.(AV-AV0)th(=I0R16) (10) 
and the output is inverted by a inverting circuit NOT. 
Comparator C3 has logic "1" at its output when 
EQU L.gtoreq.Lth(=I0(R15+R16)) (11) 
The output of NAND circuit becomes "0" only when both of the outputs from 
C2 and C3 are "1". 
In other words, the output of comparator C1 is "0" when the lens has a 
fully open aperture value lower than a certain determined value (AV0)th 
and the output of the circuit NOT becomes "1" when the aperture step 
number is smaller than a certain determined value (AV-AV0)th, namely when 
the aperture step number is a value near the open aperture for which 
correction is required. 
Assuming that the signal L is a signal of focal length, the output of the 
circuit NAND becomes "0" when the lens has a focal length longer than a 
certain determined value and the aperture value is not near the open 
aperture value, namely when correction is required because of the use of a 
lens different from the reference lens. 
A reference voltage E0 is being applied to between base and emitter of 
transistor TR3 and to between the base and resistor R14. Corrector current 
of TR3 is constant and therefore voltage at the both ends of resistor R13 
is constant. This constant voltage is referred to as E1. 
From the above it is understood that to the non-inversion input terminals 
of operational amplifier OP1 and OP2 such voltage is being applied which 
is dropped from Vcc by E1. Output terminals of OP1 and OP2 are connected 
to bases of transistors TR1 and TR2 respectively and their inversion input 
terminals are connected to emitters of TR1 and TR2 respectively. Between 
the emitter of TR1 and Vcc there are connected resistor R7 and a circuit 
comprising a resistor R8 and a field effect transistor FET1. R7 and the 
circuit R8, FET1 are parallel to each other, and R8 and FET1 are connected 
in series. Resistor R1 is connected to between the collector of TR1 and 
GND. Similarly, between the emitter of TR2 and Vcc there are connected a 
circuit comprising a resistor 10 and a field effect transistor FET 2, a 
circuit comprising R11 and FET3, and a circuit comprising R12 and FET4 and 
a resistor R9 in parallel with eath other. In each the circuit, resistor 
and field effect transistor are connected in series. Between the collector 
of TR2 and GND there is connected a resistor R2. 
Owing to the property of operational amplifier, the voltage between the 
emitter of transistor TR1 and Vcc and between the emitter of TR2 and Vcc 
are kept always at E1. In a state of non-correction, the output of 
comparator C1 is "1" and FET is On. Therefore, emitter current of TR1 
becomes E1/R7+E1/R8). So long as hfe is high, the emitter current is equal 
to the collector current and therefore the voltage at the both ends of R1 
is: 
EQU V(R1)=V(R1)normal=R1(1/R7+1/R8)E1 . . . non-correction (12) 
This voltage is the bias voltage to be applied to the photoelectric output 
from the central area. 
On the other hand, for a larger relative aperture lens, the output of 
comparator C1 is "0" and FET is turned off. Therefore, the collector 
current of TR1 becomes E1/R7 only. Namely, 
##EQU6## 
The second term is the correction term to the central area for a larger 
relative aperture. 
In a state of non-correction as to the peripheral area, the output of 
comparator C1 to "1", the output of NOT is "0" and the output of NAND is 
"1". FET 2 and FET 4 become On and FET 3 becomes Off. Therefore, the 
collector current of TR2 is (1/R9+1/R10+1/R12) and E1 and the voltage at 
the both ends of resistor R2 is: 
EQU V(R2)=V(R2) normal=R2(1/R9+1/R10+1/R12)E1 . . . non-correction (14) 
This voltage is the bias voltage to the peripheral area in the case of 
non-correction. In case that correction for larger relative aperture lens 
is required, the output of comparator C1 becomes "0" and FET is turned 
Off. Therefore, 
##EQU7## 
The second term is the correction term to the peripheral area in the case 
of large relative aperture. 
When correction is required for fully open aperture, the output of NOT 
becomes "1" and FET3 in turned On. Therefore, 
EQU V(R2)=R2(1/R9+1/R10+1/R11+1/R12)E1=V(R2) 
normal+(R2/R11)E1=V(R2)normal+Vf-fo, comp . . . correction for fully open 
aperture (16) 
The second term is the correction term for fully open aperture which is 
applied only to the peripheral area of the picture plane. 
When correction is required for difference in lens optical system, the 
output of NAND becomes "0" and FET4 is Off. Therefore, 
##EQU8## 
The second term is the correction term for difference in lens optical 
system which is also applied to only the peripheral area of the picture 
plane. 
Operational amplifiers OP3 and OP4 constitute voltage follower circuits and 
inputs V(R1) and V(R2) to OP3 and OP4 become outputs from OP3 and OP4 as 
they are. 
Between the output terminals of operational amplifiers OP3 and OP4 there 
are connected resistors R3, R4, R5 and R6 in series. Let V(.delta.0), 
V(.delta.1), . . . V(.delta.4) denote their terminal voltages 
respectively. Then, 
##EQU9## 
These terminal voltages V(.delta.0) . . . V(.delta.4) are outputs from the 
correction value calculating circuit corresponding to .delta.0 . . . 
.delta.4 in the block diagram shown in FIG. 9. 
FIG. 11 is a graph in which correction value .delta. is plotted on the 
ordinate and the distance from the center of the picture plane on the 
abscissa. It is seen from the graph that the correction value .delta. 
changes describing a curve. The curve is variable in accordance with the 
content of correction as suggested by dotted line curves. However, the 
following relations hold for almost all of the cases: 
EQU .delta.1-.delta.0:.delta.2-.delta.0:.delta.3-.delta.0:.delta.4-.delta.0=K1: 
K2:K3:1 (23) 
where, K1, K2, K3 are constants. 
Determine the constants as follows: 
EQU R3/(R3+R4+R5+R6)=K1 (24) 
EQU (R3+R4)/(R3+R4+R5+R6)=K2 (25) 
EQU (R3+R4+R5)/(R3+R4+R5+R6)=K3 (26) 
Then, 
EQU V(.delta.0)=V(R1) (18) 
EQU V(.delta.i)=V(R1)+Ki{V(R2)+V(R1)}(i=1,2,3) (27) 
EQU V(.delta.4)=V(R2) (22) 
Thus, above corrections can be carried out. Referring again to FIG. 10, the 
correction operational circuit 7 is constituted of a number of blocks 723, 
. . . 734, . . . 746 each block comprising an operational amplifier 
(OP1ij), a transistor (Tr1ij) and two resistors (R1ij and R2ij). By way of 
example, operation relating to photoelectric output P23 will be described 
in detail hereinunder. 
When the output V(.delta.0) from the correction value calculating circuit 
108 is applied to the non-inversion input terminal of operational 
amplifier OP123, the emitter voltage of transistor TR123 becomes 
V(.delta.0). Since the output V(P23) from OP23 in the metering circuit 1 
is being applied to another end of resistor R123, the current flowing 
through R123 is {V(.delta.0)-V(P23)}/R123. So long as hfe of TR123 is 
sufficiently high, emitter current.apprxeq.collector current. Therefore, 
the current flowing through R123 is equal to that flowing through R233. 
From R123=R223, the voltage V23 at the both ends of resistor R223 becomes: 
##EQU10## 
The sign in the above formula is inverse to that in formula (5). This is 
merely by reason of the circuit structure. 
Hereinafter the manner of entering necessary corrections will be described 
in detail. 
At first description is made of the case where no correction is necessary. 
In this case, the formulas (12) and (14) hold and therefore 
EQU V(.delta.0)=V(R1)normal (34) 
EQU V(.delta.4)=V(R2)normal (35) 
V(R1)normal and V(R2)normal are not always equal to each other. This is 
because a substantial portion of the initial shift of photoelectric output 
may be incorporated into V(R1)normal, V(R2)normal. It is also possible to 
add a dark current term and/or temperature compensation term. At the time, 
outputs for other parts are obtained from the above formulas (28)-(33) as 
follows: 
EQU V(.delta.i)=V(R1)normal+Ki{V(R1)normal-V(R2)normal}(i=1, 2, 3)(36) 
Since they change little by little, there occurs no conflict. 
These outputs are, together with the metering outputs V(Pij), introduced 
into the correction operational circuit 7 which has then the following 
outputs: 
##EQU11## 
When correction is required for a lens of large relative aperture, the 
correction value calculating circuit 108 detects it by comparator C1 and 
issues outputs in accordance with formulas (13) and (15). Thus, the 
following outputs are obtained: 
##EQU12## 
Comparing the outputs before correction with the outputs after correction 
while omitting the respective bias terms, the following correspondency is 
seen: 
EQU V(P23).revreaction.V(P23)+Vfo comp1 (46) 
EQU V(P13).revreaction.V(P13)+(1-Kl)Vfo comp1+KlVfo comp2 (47) 
EQU V(P46).revreaction.V(P46)+Vfo comp2 (48) 
The second and the following terms in the right member of the above 
equations constitute correction terms for the corresponding sections. Vfo 
comp1 is a correction term which has been used also in the aforementioned 
conventional metering system with single photoelectric output wherein the 
central area of a picture plane is primarily metered. This correction term 
serves to compensate the drop in photoelectric output at the central area 
in the case of large relative aperture lens. The value of this correction 
term is relatively small. On the contrary, Vfo comp2 is a correction term 
serving to compensate the output from the area most distant from the 
center of a picture plane and therefore its value is relatively large (see 
FIG. 5C). To the intermediate distant area there is applied an 
intermediate correction value which increases up gradually toward the 
periphery of the picture plane. Information of photoelectric outputs 
corrected in this manner is delivered to the multi metering treatment 
circuit 2. 
When correction is required in the state of fully open aperture, comparator 
2 and NOT circuit detect the state of aperture and the correction value 
calculating circuit 108 has the following values in accordance with 
formulas (12) and (16): 
EQU V(.delta.0)=V(R1) normal (34) 
EQU V(.delta.i)=V(R1)normal+Ki{V(R2)normal-V(R1)normal}+KiVf-fo, comp(i=1, 2, 
3)(49) 
EQU V(.delta.4)=V(R2)normal+Vf-fo, comp (50) 
Therefore, the outputs from the correction operational circuit 7 become: 
EQU V23=V(R1)normal-V(P23) (37) 
EQU V13=V(R1)normal-Ki{V(R2)normal-V(R)normal}-V(P13)+KlVf-fo,comp(i=1,2,3)(51) 
EQU V46=V(R2)normal-V(P46)+Vf-fo,comp (52). 
Omit the bias terms and compare the outputs before correction with those 
after correction. Then, the following correspondency is seen: 
EQU V(P23).revreaction.V(P23) (53) 
EQU V(P13).revreaction.V(P13)-KlVf-fo,comp (54) 
EQU V(P46).revreaction.V(P46)-Vf-fo,comp (55) 
As for the central part, the photoelectric output remains uncorrected. As 
to other parts, a negative correction value is added which increases 
gradually toward the edge portion of the picture plane. This means that 
the correction illustrated in FIG. 6C is performed. 
Lastly, description is made of the case where correction is required by 
reason of the difference in type of optical system of the lens then used. 
When such lens is used for which a correction is necesssary, comparator C3 
detects the type of lens and comparator detects that the aperture value is 
not at or near its fully open aperture value. When both of the comparators 
have detected the requirements for such correction, NAND issues an output 
informing of the necessity of correction. At the time, the correction 
value calculating circuit 108 has the following outputs in accordance with 
formulas (12) and (17): 
EQU V(.delta.o)=V(R1)normal (34) 
EQU V(.delta.i)=V(R1)normal+Ki{V(R2)normal-V(R1)normal}-KiV.sub.L,comp(i=1,2,3) 
(56) 
EQU V(.delta.4)=V(R2)normal-V.sub.L,comp (57). 
Thereby, the outputs from the correction operational circuit become: 
EQU V23=V(R1)-V(P23) (37) 
EQU V13=V(R1normal+Kl{V(R2)normal-V(R1)normal}-V(P13)-KiV.sub.L,comp(i=1,2,3)(5 
8) 
EQU V46=V(R2)normal-V(P46)-V.sub.L, comp (59). 
Omitting the bias terms and comparing the outputs before correction with 
those after correction, the following correspondency is seen: 
EQU V(P23).revreaction.V(P23) (53) 
EQU V(P13).revreaction.V(P13)+KlV.sub.L,comp (60) 
EQU V(P46).revreaction.V(P46)+V.sub.L,comp (61). 
It is seen from the above that the photoelectric output of the central area 
remains uncorrected and that to the photoelectric output of the peripheral 
area is added a positive correction value which increases gradually toward 
the edge portion of the picture plane. This means that the correction 
illustrated in FIG. 7C is performed. 
In the above, the respective corrections have been described independently 
of each other. In case a picture is to be taken using a lens having a 
large relative aperture and at its fully open aperture value, the 
correspondency between the outputs before correction and those after 
correction will be represented by: 
EQU V(P23).revreaction.V(P23).revreaction.Vfo,comp1 (46) 
EQU V(P13).revreaction.V(P13)+(1-Kl)Vfo,comp1+KlVfo,comp2-KlVf-fo,comp(62) 
EQU V(P46).revreaction.V(P46)+Vfo,comp2-Vf-fo,comp (63). 
As seen from the above, in this case, the respective correction terms act 
in such direction that one negates the other. This means that use of such 
lens that is strongly affected by vignetting, at an aperture value near 
the fully open aperture is substantially equivalent to use of an ordinary 
lens at an ordinary aperture value. 
While in the above embodiment various informations to be put in the 
correction value calculating circuit 108 from the information setting part 
5 have been divided into two groups using the same reference level, it 
should be understood that two or more reference levels may be used to 
further improve the accuracy of correction. 
In the above embodiments, the present invention has been applied to a 
camera with aperture priority type automatic exposure control. As 
hereinafter described, the present invention is applicable also to a 
camera with shutter speed priority type automatic exposure control and a 
program control type of camera wherein shutter speed or aperture value is 
controlled in accordance with a program. 
In these types of cameras (shutter speed priority type and program control 
type), metering is generally carried out with the aperture stop for 
photographing lens being preset to the minimum aperture value. Information 
transmitted to the main body of the camera from the lens is that of said 
preset aperture value. Any information of the aperture value actually 
controlled at the time of the shot is not transmitted. Of course there is 
the possibility that the aperture value actually controlled at the time of 
the shot may be a value near the open aperture value. To attain the 
correction for fully or nearly opened aperture in accordance with the 
present invention, considering the above possibility, it is required, 
therefore, to introduce information of the actually controlled aperture 
value into the main body of such type of camera from the lens. 
FIG. 12 shows a further embodiment in which the present invention is 
applied to a camera provided with two automatic exposure control modes, 
namely aperture priority mode and shutter speed priority mode. Information 
of the actually controlled aperture value issued from an exposure 
operational circuit is introduced into the above described correction 
value calculating circuit. 
In FIG. 12, the information setting part designated by 205 generates 
information of preset aperture value P202=(AV-AV0).sub.M, information of 
preset shutter speed P203=TV.sub.M and information of selected mode P204 
in addition to ASA speed value information P101=SV, fully open aperture 
information P105=AV0 and lens signal P106=L. Thus, information of preset 
aperture value used in taking a picture in aperture priority mode is given 
by P202=(AV-AV0).sub.M and information of preset shutter speed used in 
taking a picture in shutter speed priority mode is given by P203=TV.sub.M. 
Of six informations mentioned above, P101=SV, P105=AV0, 
P202=(AV-AV0).sub.M, P203=TV.sub.M and P204 are put into APEX operational 
circuit 203 which receives also the operational output P100"=BV"ans-AV0 
from a multi metering treatment circuit 2 which is the same as that in 
FIG. 9 in structure and function. APEX operational circuit 203 carries out 
the following APEX operations based upon the received data (affix "M" 
means set value): 
For example, when aperture priority mode is selected by mode information 
P204, the operational circuit gives to the aperture control circuit 204a 
the following aperture control signal: 
EQU P204=P203=(AV-AV0).sub.M (64) 
and to the shutter control circuit 204b the following shutter speed control 
signal: 
##EQU13## 
To the display circuit 206 it gives the following display signal to 
indicate the shutter speed: 
EQU P209=P207=TV (66). 
When the shutter speed priority mode is selected by mode information P204, 
the following aperture control signal is given to the aperture control 
circuit 204a: 
##EQU14## 
and the following shutter control signal is given to the shutter control 
circuit 204b: 
EQU P207=P203=TV.sub.M (68) 
At the same time the following display signal is given to the display 
circuit 206 to display the controlled aperture value: 
EQU P209=P105+P208=AV0+(AV-AV0)=AV (69). 
The correction value calculating circuit 108 receives the open aperture 
information P105=AV0 and lens signal P106=L from the information setting 
part 205 and, when shutter priority mode is selected, the aperture control 
signal P208=AV-AV0 from APEX operational circuit and operates in the same 
manner as in the embodiment shown in FIG. 9. 
While in the above embodiment APEX operational circuit 203 has given the 
same aperture control signal (AV-AV0) to the aperture control circuit 204a 
and the correction value calculating circuit 8 to control them, signal 
applied to the circuit 204a and signal to the circuit 8 are not always 
necessary to be the same. Information which the correction value 
calculating circuit 8 requires is such information informing of whether 
the aperture value is near to the fully open aperture or not. On the 
contrary, the aperture control circuit 204a requires, in some case, a 
different information from the above to control the aperture according to 
the type of control system. For example, in the case of such control 
system where after releasing the quantity of light is continuously 
monitored and the driving of aperture stop is stopped when the quantity of 
light (BV-AV) has just reached a determinate value, the signal to be 
delivered to the aperture control circuit is TV-SV. Therefore, when 
EQU BV-AV.ident.TV-SV (70) 
holds, a proper exposure value is obtained. 
Also, while the present invention has been described mainly with reference 
to the case of metering with open aperture, the invention is applicable 
also to the case of metering with stopped down aperture wherein error of 
metering may take place for the same reason as above, in particular at the 
peripheral area of a picture plane. The present invention is also useful 
for correcting such error. It is therefore to be understood that within 
the scope of the appended claims, the invention may be practiced otherwise 
than as specifically described with reference to preferred embodiments 
thereof.