Camera capable of performing divisional photometry

The camera capable of performing divisional photometry according to the present invention includes a photometric sensor which is made up from a plurality of photoelectric conversion sub-elements arranged in close proximity to one another over a predetermined light receiving region in a two dimensional array and which performs divisionally photometry on the photographic field divided into a plurality of regions, an image projection optical system which projects an image of a photographic field upon light receiving surfaces of a proper subset of this plurality of photoelectric conversion sub-elements which occupies a region which is smaller than the predetermined light receiving region, and a calculation device which calculates an exposure value based upon the photometric outputs from the proper subset of the plurality of photoelectric conversion sub-elements.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a camera which is capable of performing 
photometry on the photographic field by dividing it up into a plurality of 
regions and of calculating an exposure value based upon the photometric 
outputs from these regions. 
2. Related Background Art 
Recently more and more cameras have been produced which perform a so called 
divisional photometry method. With this divisional photometry method, 
photometry is performed by dividing the photographic field into a 
plurality of regions, and a photometric signal is obtained for each of 
these regions; and, for this method, the photometric element (typically a 
photoelectric conversion element) is divided into a plurality of 
sub-elements which correspond to the above described plurality of regions 
on the photographic field. Further, an exposure value is calculated based 
upon the output photometric signals for the various regions, so that 
photography of the principal object to be photographed can be performed 
with appropriate exposure settings, without the illumination level of the 
background exerting any effect. 
With this type of divisional photometry method, the greater is the number 
of sub-elements into which the photometric element is subdivided, the 
greater is the resolution which can be obtained for the distribution of 
illumination over the principal object to be photographed and the area 
surrounding it, and accordingly the more appropriate is the exposure value 
which can be calculated; and therefore in recent years this number of 
sub-elements has increased steadily up to the range of several tens, and 
in the near future it is expected that in some devices the number of 
sub-elements will be in the range of several hundreds. For examples, 
reference should be made to Japanese Patent laid-open Applications Nos. 
4-215631 and 4-251230. 
However, with such a divided method of photometry as described above, if 
the position within the camera of the photometric sensor on which the 
light coming from the photographic field should fall has not been set 
accurately, then a proportion of the light emanating from the photographic 
field does not reach this photometric sensor, and deviation occurs between 
the divided photometric regions on the photographic field and the divided 
sub-elements of the photometric sensor which correspond to these 
photometric regions, so that an accurate photometric result for the object 
to be photographed cannot be obtained. In this connection, in the prior 
art, as shown in FIG. 11 of the drawings, the photometric sensor (denoted 
as 25) has been fixed to the body of the camera by a position adjusting 
construction which can provide fine adjustment both in the up and down 
directions and in the left and right directions. Thereby, the position of 
the photometric sensor 25 can be finely adjusted both upwards and 
downwards and also leftwards and rightwards, and can be set to correspond 
accurately to the position of the light emanating from the photographic 
field. 
In more detail, referring to FIG. 11, in this prior art the photometric 
sensor 25 is fixed to a first support plate 203, and this first support 
plate 203 is fixed to a second support plate 202, which itself is fixed to 
a support base 201. These constructions are built so as to be adjustable, 
in the following manner. Two slots 203a are formed through the first 
support plate 203 and extend in the direction denoted as "A" in the figure 
(which corresponds to the up and down direction when the camera is being 
used for photography), and two bolts 205 are passed through these slots 
203a and are threaded into bolt holes (not particularly shown in the 
figure) formed in the second support plate 202. Thereby, when these two 
bolts 205 are tightened up, the first support plate 203 and the 
photometric sensor 25 cannot move with respect to the second support plate 
202 in any direction; but, when the two bolts 205 are loosened somewhat, 
first support plate 203 and the photometric sensor 25 can be slid with 
respect to the second support plate 202 in the direction "A", but cannot 
be moved in the direction "B" perpendicular thereto. Similarly, two slots 
202a are formed through the second support plate 202 and extend in the 
direction denoted as "B" in the figure (which corresponds to the left and 
right direction when the camera is being used for photography), and two 
bolts 204 are passed through these slots 202a and are threaded into bolt 
holes (not particularly shown in the figure) formed in the support base 
201. Thereby, when these two bolts 204 are tightened up, both of the 
support plate 202 and 203 and the photometric sensor 25 affixed thereto 
cannot move with respect to the second support plate 202 in any direction; 
but, when the two bolts 204 are loosened somewhat, both of the first 
support plate 202 and 203 and the photometric sensor 25 affixed thereto 
can be slid with respect to the support base 201 in the direction "B", but 
cannot be moved in the direction "A". 
However, the larger is the number of sub-elements into which the 
photometric sensor 25 is divided, the more strictly must the above 
described position adjustment process for the photometric sensor 25 be 
performed; and the problem arises that this position adjustment process 
takes a long time and is troublesome. Further, when the photometric sensor 
is fixed to the body of the camera via this type of position adjusting 
construction, it is not possible to be absolutely confident that the 
photometric sensor is solidly fixed in place, and there is a danger that 
its position may gradually change due to the effects of shock and 
vibration upon the camera or over the passage of time, in which case it 
may become impossible to perform accurate photometry. 
SUMMARY OF THE INVENTION 
The objective of the present invention is to provide a camera with which 
the position of the photometric sensor can be set comparatively roughly, 
and which further can perform divisionally photometry without any problem 
arising of deviation in the position of the photometric sensor due to 
vibration or the like. 
In order to attain this objective, the present invention provides a camera 
capable of performing divisional photometry, comprising: a photometric 
sensor having a plurality of photoelectric conversion sub-elements 
arranged in close proximity to one another over a predetermined light 
receiving region in a two dimensional array, and which performs 
divisionally photometry on the photographic field divided into a plurality 
of regions; an image projection optical system which projects an image of 
a photographic field upon light receiving surfaces of a proper subset of 
said plurality of photoelectric conversion sub-elements which occupies a 
region which is smaller than said light receiving region; and a 
calculation means which calculates an exposure value based upon the 
photometric outputs from said proper subset of said plurality of 
photoelectric conversion sub-elements. 
According to the present invention as specified above, the image of the 
photographic field is projected upon the light receiving surfaces of a 
proper subset of the plurality of photoelectric conversion sub-elements 
which occupies a region which is smaller than the total light receiving 
region of the photometric sensor. The calculation means calculates an 
exposure value based upon the photometric outputs from this proper subset 
of the plurality of photoelectric conversion sub-elements upon which the 
image of the photographic field is thus projected. Since any proper subset 
of the photoelectric conversion sub-elements upon which the image of the 
photographic field happens to be thus projected will do as well as any 
other, it is only necessary to fix the photometric sensor in place in a 
position such that the image of the photographic field definitely does not 
wander over its edge, and accordingly the fixing in place of the 
photometric sensor can be performed relatively roughly as compared with 
the prior art, so that the time required for such fixing is reduced. 
Further, since no adjustable construction is required for fixing the 
photometric sensor in place, it is possible to reduce the bulk of the 
camera, and also the photometric sensor can be fixed in place more solidly 
than was practicable with the prior art, so that there is no danger of the 
photometric sensor becoming displaced due to vibration or over the passage 
of time. 
Further, according to a specialization of the present invention, an 
accumulation type of image sensor which comprises M.times.N photoelectric 
conversion sub-elements which are arranged in a rectangular array 
measuring M vertically by N horizontally to constitute the above-mentioned 
light receiving region, and which performs photometry by dividing the 
photographic field into a plurality of regions, may be employed as the 
above-mentioned image sensor. By arranging the photometric sub-elements in 
a rectangular array in this manner, it is possible to perform photometry 
by dividing the entire photographic field up regularly into a plurality of 
regions, and accurate photometry can be performed. 
Further, according to another aspect of the present invention, there is 
provided a camera capable of performing divisional photometry, comprising 
a photometric sensor of the above described type, an image projection 
optical system also of the above described type, a mode setting means 
which sets either of a photographic mode and a field determination mode 
according to the actuation of an operating member, a determination means 
which, when the field determination mode is set, based upon the 
photometric outputs from the plurality of photoelectric conversion 
sub-elements, determines for each of the plurality of photoelectric 
conversion sub-elements whether it is a valid sub-element which is 
included in the proper subset of the plurality of photoelectric conversion 
sub-elements upon which the image of the photographic field falls, or an 
invalid sub-element which is not included in the proper subset of the 
plurality of photoelectric conversion sub-elements upon which the image of 
the photographic field falls, a storage means which stores the results of 
the determinations performed by the determination means, a selection means 
which based upon the information stored by the storage means selects the 
valid sub-elements from the plurality of photoelectric conversion 
sub-elements, and a calculation means which calculates an exposure value 
based upon the photometric outputs from the valid photoelectric conversion 
sub-elements selected by the selection means. 
According to the present invention as specified above, when the field 
determination mode is set, for each of the plurality of photoelectric 
conversion sub-elements, it is determined, based upon the photometric 
outputs from the plurality of photoelectric conversion sub-elements 
included in the photometric sensor, whether it is a valid sub-element 
which is included in the proper subset of the plurality of photoelectric 
conversion sub-elements upon which the image of the photographic field 
falls, or an invalid sub-element which is not included in the proper 
subset of the plurality of photoelectric conversion sub-elements upon 
which the image of the photographic field falls. And the results of these 
determinations are stored. Further, when the photographic mode is set, 
based upon the stored information, the valid sub-elements are selected 
from the totality of the photoelectric conversion sub-elements, and an 
exposure value is calculated based upon the photometric outputs from the 
valid photoelectric conversion sub-elements thus selected, but not based 
upon the photometric outputs from the others of the photoelectric 
conversion sub-elements which are the invalid ones. Accordingly, it is 
possible accurately to select those ones of the photometric sub-elements 
upon which the image of the photographic field falls, and an accurate 
exposure value can be calculated based only upon the output signals from 
these valid photometric sub-elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A preferred embodiment of the present invention as applied to a single lens 
reflex camera will now be explained with reference to FIGS. 1 through 8 of 
the appended drawings. 
FIG. 1 is an external perspective view as seen from the upper left rear 
showing the outside of a single lens reflex camera according to this first 
preferred embodiment of the present invention. The reference numeral 1 
denotes the main body of the camera, and 2 denotes a detachable viewfinder 
which can be attached to and separated from a screen portion 8 on the 
upper surface of the camera body 1, while 3 denotes a film lid covering 
the rear surface of the camera body 1 which can be opened and closed for 
loading and removing film and 4 denotes a detachable photographic lens 
which can be attached to and separated from the front surface of the 
camera body 1. On the upper surface of the camera body 1 there are 
provided a release button 5, a liquid crystal display 6, and two setting 
buttons 7. The two setting buttons 7 are for setting the selection of 
photometric mode or exposure mode or film forwarding mode or the like. 
The viewfinder 2 comprises an eyepiece section 10 to view the photographic 
field therein, a photometric sensor 25 which is shown in FIG. 2, and an 
electrical circuit of which is shown in FIG. 5. When this viewfinder 2 is 
fitted to the screen portion 8 on the upper surface of the camera body 1, 
the contacts of a contact group 11 comprised in the electrical circuit of 
FIG. 5 are individually and respectively brought into contact with the 
contacts of a contact group 9 fitted in the camera body 1, and thereby the 
circuitry in the viewfinder 2 is brought into electrical communication 
with the circuitry in the camera body 1. 
FIG. 2 is a figure showing in schematic cross section the optical system 
(denoted collectively as 200) of this camera, and particularly showing a 
light beam from the object to be photographed which passes through the 
photographic lens 4, the camera body 1, and the viewfinder 2 to reach the 
eye of the camera user. The reference numeral 20 denotes an optical system 
which is provided within the photographic lens 4, and the light rays from 
the object to be photographed which have passed through this optical 
system 20 are reflected in the upward direction from a main mirror in the 
camera body 1, and these reflected light beams are focused upon a screen 
22 incorporated in the screen portion 8. After this focused light from the 
object to be photographed has been transmitted to a half silvered mirror 
24 via a pentaprism 23, a portion thereof passes through the half silvered 
mirror 24 and through the eyepiece section 10 to reach the eye of the 
camera user, while another portion thereof is reflected in the upward 
direction to reach a photometric sensor 25. 
The photometric sensor 25 of this preferred embodiment of the present 
invention is for example an image sensor made up of a CCD (charge coupled 
device), and as shown in FIG. 3 comprises, within a fixed light sensitive 
area, a total of M.times.N sub-elements (photoelectric conversion devices) 
arranged in the form of a matrix which has M rows and N columns, i.e. 
which measures M sub-elements in the vertical direction by N sub-elements 
in the horizontal direction. Further, the photometric sensor 25 comprises 
a charge accumulation section, a transmission section, and a voltage 
conversion section, none of which are shown in the figures. Each of the 
sub-elements receives light rays directed upon it as described above and 
originating from a portion of the photographic field which particularly 
corresponds to the sub-element and performs photoelectric conversion, and 
the charge accumulation section accumulates the electric charge which is 
generated by this photoelectric conversion process. These accumulated 
electric charges are read out by the transmission section in time series 
according to the receipt of a predetermined clock signal, and, after the 
voltages thereof have been converted by the voltage conversion section, 
these signals are input to a CPU 101 which is shown in FIG. 5 to be 
described hereinafter as digital photometric signals each of which is a 
function of the intensity of the illumination of its corresponding portion 
of the photographic field. In other words, in this preferred embodiment, 
the photometric sensor 25 divides the entire photographic field up into 
M.times.N regions and performs divided photometry for these M.times.N 
regions individually. 
However, in this preferred embodiment, the area of the photometric sensor 
25 which actually corresponds to the photographic field, i.e. upon which 
light rays emanating from an object to be photographed can actually fall, 
is smaller than the total area of the photometric sensor 25 which is 
capable of reacting to light, i.e. than the total area of the M.times.N 
sub-elements of the photometric sensor 25, and may for example be like the 
rectangular area shown in FIG. 3 as 41. That is to say, the optical system 
of FIG. 2 is constructed in advance so that light from the object to be 
photographed can fall upon the light receiving surface of the photometric 
sensor 25 which is composed of the above described plurality of 
sub-elements only over a region narrower than the total light receiving 
area thereof. In the shown example, in concrete terms, light from the 
object to be photographed can only fall upon a central rectangle 41 
composed of K.times.L sub-elements included within the total area of the 
M.times.N sub-elements of the photometric sensor 25, and for this reason, 
even though the photometric sensor 25 is subdivided into a total of 
M.times.N sub-elements, in practice the entire photographic field is 
subdivided for photometric purposes into only a lesser number K.times.L of 
regions which correspond to this central rectangle 41 composed of 
K.times.L sub-elements of the photometric sensor 25. 
However, the above described region upon which light from the object to be 
photographed is not limited to being the region 41 described above. For 
example, the region upon which light from the object to be photographed 
can fall may be the rectangle outlined in FIG. 3 by the single dotted 
line. Accordingly, with the preferred embodiment of the present invention, 
its position on the photometric sensor 25 is only considered as being 
determined comparatively roughly. 
As an example, supposing that the size of a single one of the CCD 
sub-elements is 20 .mu.m by 20 .mu.m which is typical, and supposing that 
the matrix on the photometric sensor 25 is 200 sub-elements vertically by 
300 sub-elements horizontally, then the total size of the CCD will be 4 mm 
vertically by 6 mm horizontally. Further, supposing that on the other hand 
the region of the photometric sensor 25 upon which light from the object 
to be photographed can fall is a rectangle which is 3 mm vertically by 5 
mm horizontally, then the position setting of this region on the 
photometric sensor 25 can be performed within a margin of 0.5 mm either 
way, both in the vertical direction and in the horizontal direction. 
Wherever this region is positioned upon the total light sensitive surface 
of the photometric sensor 25, it will cover a rectangle of sub-elements 
thereof which measures 150 elements vertically by 250 elements 
horizontally. 
When in this manner it is possible to determine the position of the 
photometric sensor 25 roughly, it becomes possible to fix the photometric 
sensor 25 solidly into place. That is to say, whereas in the prior art as 
described above the photometric sensor was required to be fixed to the 
body of the camera via a position adjustment construction which allowed 
the position of the photometric sensor to be adjusted relative to the 
camera body both in the vertical direction and in the horizontal direction 
since it was necessary to be able to position the photometric sensor very 
accurately, by contrast, with this preferred embodiment of the present 
invention, the photometric sensor 25 can be fixed to the body of the 
camera without providing any position adjustment construction between 
them, because it is not necessary to perform fine adjustment of the 
position of the photometric sensor 25. For example, it will be quite 
satisfactory to provide a concave shaped depression in the camera body 
into which the photometric sensor 25 can be fitted, and to insert the 
photometric sensor 25 into this concave shaped depression and to fix it 
securely therein. According to such a method for fixing the photometric 
sensor 25 to the camera body 1, there is no danger of it becoming 
impossible to perform accurate photometry due to shifting of the position 
of the photometric sensor 25 by the shock and vibration upon the camera or 
even gradually over the passage of time. 
Next, electrical circuitry incorporated in the camera body 1 and in the 
viewfinder 2 will be explained. 
FIG. 4 is a block diagram showing circuitry within the camera body 1. 
Actuating electrical energy is supplied from a battery 70 via a DC/DC 
converter 71 to all of this FIG. 4 circuitry, and is also supplied to the 
circuitry in the viewfinder 2 (see FIG. 5), when the viewfinder 2 is 
fitted to the camera body 1, via a contact 83 included in the contact 
group 9 described above and via a corresponding and contacting contact 93 
of the contact group 11. In detail, the contact group 9 provided on the 
screen portion 8 of the camera body 1 (see FIG. 1) is made up of four 
contacts 83 through 86, and when the viewfinder 2 is fitted to the camera 
body 1 these contacts 83 through 86 come into respective contact with four 
contacts 93 through 96 of which the contact group 11 provided on the 
viewfinder 2 is composed. 
The reference numeral 74 denotes a central processing control circuit 
(hereinafter referred to simply as a CPU) which comprises a CPU, ROM, RAM, 
etc. and which performs overall sequencing of this camera. To this CPU 74 
there are input the values of parameters related to exposure as calculated 
by the circuitry in the viewfinder 2 via the above described contact 85, 
while on the other hand the CPU 74 outputs the film ISO sensitivity and a 
position adjustment mode signal to the circuitry in the viewfinder 2 via 
the contact 84. Further, to the CPU 74 there is also connected certain 
circuitry described hereinafter. 
The reference numeral 72 denotes a film sensitivity detection circuit, 
which detects the ISO sensitivity of the film (not shown) loaded into this 
camera and inputs a signal representative thereof to the CPU 74. And 73 
denotes a switch group which comprises a plurality of switches and which 
inputs to the CPU 74 a signal representative of the ON/OFF states of these 
switches. These switches in the switch group 73 are not shown in detail, 
but include a first stroke switch which is turned ON when the release 
button 5 described (see FIG. 1) is partially depressed by the camera user 
as far as a first stroke position thereof, a second stroke switch which is 
turned ON when the release button 5 is further fully depressed by the 
camera user to a second stroke position thereof, setting switches which 
are turned ON and OFF in accordance with the operation of the above 
described two setting buttons 7, and the like. 
Further, in this preferred embodiment, by the use of a mode switch 
comprised in this switch group 73, a field determination mode can be 
selected, in which information of the location of the sub-elements which 
lies within the above described rectangular region 41 on which the light 
from the photographic field can fall is determined and is recorded. The 
operation when the field determination mode is selected will be described 
hereinafter in detail, but, since this field determination is an operation 
which is performed by a workman during the manufacture of the camera, the 
user of the camera never sets this mode. Accordingly, the above described 
mode switch is provided at a position internal to the camera which cannot 
be accessed by the user. Moreover, when the field determination mode is 
not selected, the camera is in a normal photography mode. 
Further, the CPU 74 is connected via a drive circuit 75 to a shutter 76, an 
aperture 77, a film forwarding motor 78, a focusing motor 79, and a focus 
detection element 80. The CPU 74 drives the focusing motor 79 based upon 
the output signal from the focus detection element 80 so as to perform 
focusing action, drives the aperture 77 and the shutter 76 based upon the 
aperture value and shutter speed as calculated on the side of the 
viewfinder 2 and performs exposure action, and drives the film forwarding 
motor 78 so as to perform film winding on action. 
FIG. 5 is a block diagram showing circuitry within the viewfinder 2. A CPU 
101 drives the photometric sensor 25 via a drive circuit 102, and inputs 
the photometric signal which the photometric sensor 25 outputs. This 
photometric signal is temporarily stored in a memory 104, and when 
required is read out by the CPU 101 and is used for calculating exposure 
parameters. The calculated exposure parameters are sent to the main body 1 
of the camera via the contact 95. 
In the following, the operation of this preferred embodiment of the present 
invention will be explained with reference to the flow charts shown in 
FIGS. 6 through 8. 
FIG. 6 is a flow chart showing the operation of the control program for the 
CPU 74 incorporated in the camera body 1. The operation of this control 
program is started, for example, when the above described first stroke 
switch included in the switch group 73 is turned ON. First, in the step 
S1, a decision is made as to whether or not the above described field 
determination mode is set, and if the result is YES then in the step S2 a 
field determination mode signal is sent via the contact 95 to the CPU 101 
on the viewfinder side, and then the flow of control returns to the step 
S1 in a loop. 
If in the step S1 the result of the decision is NO, i.e. when the normal 
photographic mode is set, then the flow of control proceeds to the step 
S3, in which the ISO sensitivity value of the film (not shown) loaded into 
this camera is detected by the film sensitivity detection circuit 72 and 
is read into the CPU 74, and next in the step S4 the detected film 
sensitivity value is transferred to the CPU 101 incorporated in the 
viewfinder via the contact 84. Next, in the looped decision step S5, the 
flow of control waits until a set of calculated aperture value and shutter 
speed are received from the viewfinder CPU 101 via the contact 85, and 
when such aperture value and shutter speed are received the flow of 
control passes to the step S6. In the step S6, the CPU 74 displays the 
aperture value and the shutter speed on the liquid crystal display 6. 
Next, in the decision step S7, a decision is made as to whether or not the 
above described second stroke switch included in the switch group 73 is 
turned ON. If the result of this decision is NO then the flow of control 
returns to the step S1, while if the result of this decision is YES then 
the flow of control passes to the step S8. 
In the step S8, the CPU 74 raises the main mirror 21, and in the next step 
S9 the CPU 74 controls the aperture 77 via the drive circuit 75 according 
to the calculated aperture value, and then in the step S10 the CPU 74 
controls the shutter 76 so as to open and close it according to the 
calculated shutter speed. Finally, in the step S11, the CPU 74 controls 
the film forwarding motor 78 so as to wind on the film, again via the 
drive circuit 75, and then the flow of control returns to the step S1. 
And, when the above described first stroke switch included in the switch 
group 73 is turned OFF, the execution of this program stops. 
FIGS. 7 and 8 together constitute a flow chart showing the operation of the 
control program for the CPU 101 incorporated in the viewfinder 2. This 
program is always continually executed in an endless loop as long as power 
continues to be supplied from the camera body 1 to the viewfinder 2. 
First, in the looped decision step S15, the flow of control waits until 
some information is received via the contact 84 from the CPU 74 
incorporated within the camera body 1 (such information will either be the 
ISO sensitivity value of the film loaded into the camera or the field 
determination mode signal) and when such information has been received the 
flow of control passes to the step S16. In the step S16, a decision is 
made as to whether or not this information received is the field 
determination mode signal, and if the result is YES then the flow of 
control passes to the step S30 of FIG. 8. The receipt of the field 
determination mode signal means that during manufacture of the camera a 
workman has operated the above described mode switch provided within the 
body of the camera so as to set the field determination mode. At this 
stage of production the photometric sensor 25 has already been fixed 
within the viewfinder 2. Moreover, when the field determination mode is 
thus set, the workman should have already set a uniformly illuminated test 
field of comparatively high brightness before the photographic lens. This 
test field is for causing light from the photographic field to fall 
uniformly over the rectangular region 41 shown in FIG. 3. 
Referring now to the FIG. 8 flow chart for field determination, in the step 
S30 the charge accumulation operation of the photometric sensor 25 is 
performed, and the light from the uniformly illuminated test field as 
received on its various sub-elements as shown in FIG. 3 is converted into 
electric charge, and the electric charge is accumulated by the charge 
accumulation section. Thus, only the sub-elements included in the 
K.times.L rectangular region 41 on which the light from the uniformly 
illuminated test field is currently falling will acquire a substantial 
electrical charge at this time, while the sub-elements outside this 
illuminated region 41 will not be very much charged up. Next, in the step 
S31, a photometric signal is read out from a current one of the 
sub-elements--i.e., the accumulated electric charges are read out one by 
one by the transmission section in time series according to the receipt of 
a predetermined clock signal, and, after the voltages thereof have been 
converted by the voltage conversion section, these signals are input to an 
A/D converter included in the CPU 101 and are successively converted into 
digital photometric signals. And next, in the decision step S32, a 
decision is made as to whether or not the value of the current photometric 
signal is greater than a predetermined value. 
If the current sub-element in fact lies within the K.times.L rectangular 
region 41 shown in FIG. 3 on which the light from the brightly illuminated 
test field is presently falling, then its photometric signal will be 
higher than the predetermined value, so that the result of the decision in 
the step S32 will be YES, and the flow of control will skip to the step 
S34; while, if the current sub-element in fact does not lie within the 
region 41, then its photometric signal will be lower than the 
predetermined value, so that the result of the decision in the step S32 
will be NO, and the flow of control will pass to the step S33. In this 
step S33, since the current sub-element lies outside the region 41 and 
accordingly is an invalid one (i.e.. is a sub-element whose photometric 
signal is not to be used for exposure value calculation), the address of 
this invalid sub-element is stored in the memory 104, and then the flow of 
control passes to the final decision step S34. In this decision step S34, 
a decision is made as to whether or not the above processing in the steps 
S31 through S33 has been performed for all of the M.times.N photometric 
signals from the photometric sensor 25 so that the addresses of all of the 
(M.times.N)-(K.times.L) invalid sub-elements thereof which lie outside the 
valid region 41 have been saved, and if the result of this decision is NO 
then the flow of control returns to the step S31 to check the value of the 
photometric signal from the next sub-element, while, when all of the 
M.times.N photometric signals from the photometric sensor 25 have been 
checked, then the flow of control returns to the initial step S15 of the 
FIG. 7 flow chart. 
On the other hand, if in the step S16 of the FIG. 7 flow chart it is 
decided that the information received in the step S15 is not the field 
determination mode signal, i.e. is the film sensitivity value then in the 
step S17 the film sensitivity value is stored in the memory 104. Further, 
since the fact that the information received is the film sensitivity value 
implies that the camera is currently being used for normal photography, in 
the next step S18 the charge accumulation operation of the photometric 
sensor 25 is performed, and the light from the object to be photographed 
received on each of its sub-elements as shown in FIG. 3 is converted into 
electric charge and the electric charge is accumulated by the charge 
accumulation section. In the next step S19, a photometric signal is read 
out from a current one of the sub-elements, and next, in the decision step 
S20, a decision is made as to whether or not this current sub-element is 
an invalid one, i.e. as to whether or not it is a sub-element which lies 
outside the region 41 shown in FIG. 3, the locations of which were stored 
in the memory in the step S33 described above. If the current sub-element 
is an invalid one, then the flow of control simply returns to the step S19 
to read out the photometric signal from the next sub-element, while, if 
the current sub-element is a valid one, then in the next step S21 the 
photometric signal (converted into a digital signal) is stored in the 
memory 104, and next, in the decision step S22, a decision is made as to 
whether or not the above processing in the steps S19 and S20 has been 
performed for all of the M.times.N photometric signals from the 
photometric sensor 25 so that all of the K.times.L valid ones thereof 
which emanate from the K.times.L rectangular valid region 41 have been 
saved, and if the result of this decision is NO then the steps S19 through 
S22 are repeated, while when all of the M.times.N photometric signals from 
the photometric sensor 25 have been processed as above then the flow of 
control passes to the step S23. 
In this step S23, exposure value is calculated based upon the stored 
photometric signals and upon the above described film ISO sensitivity 
information which was input and was stored in the step S17, and an 
aperture value and a shutter speed are calculated based upon the exposure 
value. Next in the step S24 these calculated values are stored in the 
memory 104. And in the last step S25 these recorded exposure values are 
transferred to the CPU 74 in the camera body 1 via the contact 95. After 
this the flow of control returns to the step S15, and the above described 
process is repeated. 
The process described above and shown in the flow charts of FIGS. 6 through 
8 can be considered in summary as follows. 
As a step in the manufacture of the camera, after the photometric sensor 25 
has been fixed in a predetermined position in the viewfinder 2, a 
uniformly illuminated test field is positioned in front of the 
photographic lens, and the light from this test field falls upon the 
rectangular region 41 of the photometric sensor 25 as shown in FIG. 3. 
When in this condition the camera is set to the field determination mode, 
the charge accumulation action of the photometric sensor 25 is performed, 
and the photometric signals from all of the M.times.N sub-elements of the 
photometric sensor 25 are read in. Those of the sub-elements for which at 
this time the value of the photometric signal is higher than a 
predetermined value are deemed to be sub-elements which lie in the central 
rectangular region 41 on which the light from the photographic field can 
fall and which are valid for photometry, while those of the sub-elements 
for which at this time the value of the photometric signal is lower than 
the predetermined value are deemed to be surrounding sub-elements on which 
the light from the photographic field cannot fall and which are therefore 
not valid for photometry. The addresses of the latter sub-elements are 
therefore stored in the memory 104 as the addresses of invalid 
sub-elements. 
The camera is shipped from the factory in this condition with the addresses 
of the invalid sub-elements of the photometric sensor 25 stored in the 
memory 104. When a photograph is to be taken, initially the first stroke 
switch is turned on as the release button is depressed, and in the same 
manner as described above the charge accumulation action of the 
photometric sensor 25 is performed and the photometric signals from all of 
the M.times.N sub-elements of the photometric sensor 25 are read in. At 
this time, based upon the information recorded in the memory 104, the 
valid photometric signals from the K.times.L valid sub-elements of the 
photometric sensor 25 which lie within the rectangular region 41 are 
discriminated from the invalid photometric signals from the invalid 
sub-elements which lie outside the rectangular region 41, and only the 
K.times.L values of the valid photometric signals are stored. Accordingly 
divided photometry is performed by dividing the photographic field into 
K.times.L regions, and thereafter an exposure value is calculated based 
upon the K.times.L valid stored photometric signal values and upon the ISO 
sensitivity value of the film. 
According to the above described construction of this preferred embodiment, 
after the photometric sensor 25 has been fixed within the body of the 
camera, the ones of the plurality of sub-elements of which the photometric 
sensor 25 is composed which are invalid, i.e. upon which the light from 
the photographic field cannot fall, are determined and are recorded, and 
subsequently, based upon this recorded information, photometry is 
performed only using the photometric signals from the valid sub-elements. 
Therefore, it is only necessary to fix the photometric sensor 25 in a 
position such that the image of the photographic field definitely does not 
wander over its edge, i.e. in a position such that the entire image of the 
photographic field definitely falls upon the light receiving surfaces of a 
subset of the sub-elements of the photometric sensor 25, and then the same 
result as described above will be obtained, whichever in fact are the 
sub-elements included in said subset. Accordingly, even if the 
determination of the position of the photometric sensor 25 is performed 
relatively roughly, accurate photometric results can be obtained, and it 
is possible to determine an accurate exposure value. 
In the above described preferred embodiment the sub-elements of the 
photometric sensor 25 which lay on the boundary of the rectangular region 
41 were deemed to be valid sub-elements whose photometric signals could be 
used for purposes of exposure value calculation. In fact, however, the 
boundary of the actual region of the photometric sensor 25 upon which the 
light from the photographic field can fall inevitably does not accurately 
coincide with the divisions between the various sub-elements, and 
accordingly for some of these sub-elements on the boundary of the region 
41 light from the photographic field only falls upon a part of their light 
receiving surfaces, and therefore the values of the photometric signals 
from these boundary sub-elements are relatively small, as compared to the 
photometric signals from sub-elements which lie within the interior of the 
region 41. Therefore if, in a variant embodiment of the present invention, 
the exposure value calculation is performed by appropriately weighting the 
photometric signals from these boundary sub-elements, a more accurate 
exposure value can be calculated. Further, if in such a variant embodiment 
the photometric signals from these boundary sub-elements are thus 
appropriately weighted, even if the photometric sensor is mounted to the 
body of the camera in a slanting orientation with respect to the image of 
the photographic field which falls upon the photometric sensor, an 
accurate exposure value can be calculated. As another possible variant 
embodiment, the sub-elements on the boundary of the region 41 could be 
considered as invalid ones. 
Further, in the above described preferred embodiment, first in the field 
determination mode the addresses of the sub-elements which were deemed to 
be invalid were stored, and subsequently in the normal photographic mode 
the exposure value was calculated based upon the photometric output 
signals from the sub-elements (the valid ones) other than those whose 
addresses were thus stored. However, this is not limitative of the present 
invention; in another variant embodiment, in an opposite manner, it would 
be possible first in the field determination mode to store the addresses 
of those sub-elements which are deemed to be valid, and subsequently in 
the normal photographic mode to calculate the exposure .value based upon 
the photometric output signals from the sub-elements whose addresses were 
thus stored. In order to realize this variant embodiment in practice, the 
flow charts of FIGS. 7 and 8 need to be modified to the flow charts of 
FIGS. 9 and 10 respectively. The only differences between these flow 
charts are that the step S20 of the FIG. 7 flow chart has been replaced by 
the step S20' of the FIG. 9 flow chart, and correspondingly the step S32 
of the FIG. 8 flow chart has been replaced by the step S32' of the FIG. 10 
flow chart. The operation of this variant embodiment will be easily 
understood based upon the above disclosure, and accordingly detailed 
description thereof herein is omitted. 
Further, although in the above description it was stated that the process 
of determining and storing sub-element validity was performed as a step 
during the manufacture of the camera, as an alternative it would also be 
acceptable for this to be done after the camera has been completed and 
shipped. Moreover, although the above explanations were made in terms of a 
camera which had a viewfinder of the detachable type, the present 
invention could also be applied to a camera in which the viewfinder was 
provided integrally with the body of the camera. The manner of division of 
the photometric sensor is not to be considered as limited to that shown in 
FIG. 3, and also, provided that both the horizontal dimension and the 
vertical dimension of the total light receiving area of the photometric 
sensor are greater than the corresponding dimensions of the area thereof 
upon which the image of the photographic field falls, the ratio of these 
areas is not particularly restricted. Yet further, although the above 
explanation has been made in terms of a single lens reflex camera 
employing the so called TTL photometric method, as an alternative the 
present invention could also be applied to a lens shutter type camera 
employing an external type of photometry, in which photometry is performed 
upon light from an object to be photographed which has passed through an 
optical system which does not include the photographic lens. Therefore the 
position of the photometric sensor is not restricted to being within the 
viewfinder.