Automatic exposure control system for single reflex camera

A camera which permits change-over between different light measuring systems is disclosed. The camera includes a first light measuring element which measures light coming from an object to be photographed and an operational amplifier responsive to the element. A light measurement information producing circuit is included for producing a light measurement information signal for exposure computation. A change-over device is connected between the light measurement information producing circuit and the operational amplifier. The change-over device is arranged to be shiftable between a first position wherein the operational amplifier is connected to the light measurement information producing circuit and a second position wherein the operational amplifier is not so connected. An accessory device is attachable to the camera body. The accessory device includes a second light receiving element for measuring light from the object within a light measurement range different from that of the first light receiving element and another operational amplifier responsive thereto. A terminal is responsive to the signal from the latter operational amplifier. The terminal is disposed at the second position of the change-over device so that the signal from the latter operation is applied to the light measurement information producing circuit when the change-over device is in this position.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an exposure control system for a single 
reflex camera for controlling the current supply to each circuit in the 
camera. 
2. Description of the Prior Art 
Generally, the automatic exposure control system of a camera with electric 
shutter consists of many circuits such as a light sensing and processing 
circuit, a storage circuit, an exposure determining circuit, a shutter 
actuating circuit, a shutter time control circuit and an indication 
circuit to which the current is supplied from small cells set inside of 
the camera, whereby a current supply system for minimizing the power 
consumption in each circuit is needed in order to prolong the life of the 
cells. 
However, the conventional current supply system is constructed in such a 
manner that the current is supplied to each circuit by the shutter 
operation in the self-held state while the internal mechanisms are 
operated one by one. Then, when the rear plane of the focal plane shutter 
runs, the self-held state is released in such a manner that the current 
supply to each circuit is interrupted. Thus, during the operation of the 
camera, the current continues to be always supplied to each circuit so 
that the life of cells is very short. 
The first purpose of the present invention is to eliminate the above 
mentioned shortcoming in such a manner that the current supply to each 
circuit in a camera will be controlled efficiently. 
The second purpose of the present invention is to actuate the electric 
shutter electro-magnetically. 
The third purpose of the present invention is to adopt the mean light 
sensing and the partial light sensing which can be switched over 
selectively. 
The fourth purpose of the present invention will be disclosed in accordance 
with the explanation of the embodiments below.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be explained in accordance with the accompanying 
drawings. FIG. 1 shows a circuit system diagram of an embodiment of the 
current supply system in accordance with the present invention. The 
drawing shows an example adapted to a camera with an electric shutter of 
storage system. In the drawing, E is the current source, S.sub.1 and 
S.sub.2 are the switches in functional engagement with the shutter release 
button, S.sub.3 the switch for storage, C the condensor for storage, 
S.sub.4 the switch for the shutter time control circuit, S.sub.5 and 
S.sub.10 the normally closed switches which close at the termination of 
the winding up. 1 is the light sensing, information setting and processing 
circuit and 2 the indication circuit, whereby both are brought into the 
operation state when the switch S.sub.1 closes. 3 is the automatic 
exposure determining circuit which acts as diaphragm value determining 
circuit, when the priority is given to the shutter time. 4 is the 
electro-magnetic actuating circuit for releasing the set front plane of 
the focal plane shutter, 5 the shutter time control circuit. 6 is the 
current source self-holding circuit, 7 and 8 the switching circuits. The 
circuit shown in FIG. 1 operates in such a manner that the switches 
S.sub.5 and S.sub.10 are closed when the film and shutter winding up in 
the camera has finished. When the shutter-button R is pushed down to the 
first step in the above mentioned state, the switch S.sub.1 is closed by 
means of the stroke. When the switch S.sub.1 is closed, the applied 
voltage of the electric source E brings the light sensing, information 
setting and processing circuit 1 into the operation state, whereby the 
circuit 1 produces the exposure information, for example the diaphragm 
value information processed in Apex value so as to charge the storage 
condensor, because at this time, the storage switch S.sub.3 is closed. 
When the switch S.sub.1 is closed, the switching circuit 7 is brought into 
the conductive state in such a manner that the current is supplied to the 
indication circuit 2, namely the information coming from the circuit 1 is 
indicated in the indication circuit 2. Further, the indication circuit 
comprises an alarm circuit for giving an alarm when the photographing 
information lies beyond the limit of the AE operation range, whereby a 
means which brings the electro-magnetic actuation out of the operation in 
accordance with the signal coming from the alarm circuit is provided. 
Then, by means of the second stroke of the shutter button, the switch 
S.sub.2 is closed. Thus, the switching circuit 8 is closed and kept in the 
self-held state in such a manner that the AE determining circuit 3 and the 
electro-magnetic circuit 4 are brought into the operation state so as to 
release the setting of the front plane of the focal plane shutter. In this 
manner, before the upward movement of the reflection mirror, the storage 
switch S.sub.3 is opened, while by means of the upward movement, the 
switch S.sub.4 of the shutter time control circuit is closed. When the 
circuit 6 is brought into the self-held state, by means of the signal 
coming from the circuit, the switching circuit 7 is opened so as to bring 
the indication circuit out of operation whereby the indication is put out. 
By means of the diaphragm information stored in C before the upward 
movement of the mirror the diaphragm value (AE) determining circuit 3 
determines the diaphragm value automatically, which value is kept in the 
balanced state of the circuit 3. When the diaphragm value is determined by 
means of the circuit 3 and the upward movement of the mirror is finished, 
the electro-magnetic actuating circuit 4 is inversed in such a manner 
that, by means of its output, the trigger switch S.sub.6 of the shutter 
time control circuit is opened. Thus the front plane of the focal plane 
shutter starts to run. After the shutter time set in advance in the CR 
circuit 5, the rear plane of the focal plane shutter is released by means 
of the output of the CR circuit 5 in such a manner that the rear plane of 
the focal plane shutter starts to run so as to complete the exposure. The 
already closed switch S.sub.10 is opened at the termination of the 
operation of the front plane of the focal plane shutter, while the switch 
S.sub.5 is opened when the rear plane of the focal plane shutter starts to 
run. When the switches S.sub.2 and S.sub.10 are opened, the self-holding 
circuit 6 is released. Because the switching circuit 7 is closed when the 
circuit 6 is opened, the current supply is interrupted only during the 
operation of the focal plane shutter when the self-holding circuit 6 is 
closed at the closed state of the indication circuit S.sub.2. While before 
and after the operation of the shutter, the current is supplied. When the 
shutter and the film are wound up after the termination of the first 
photographing, the initial state is restored again. 
FIG. 2 shows the circuit of FIG. 1 concretely, whereby in the circuit the 
switches S.sub.1 and S.sub.2, in functional engagement with the shutter 
button, are arranged in series with each other. In the drawing, P is the 
photoelectric converting element such as a silicon photo diode whose light 
responsive characteristics is superior, whereby the element is arranged at 
the proper position in the view finder optical system or the like. A.sub.1 
is the processing amplifier between whose two input terminals the 
photodiode P is connected while in the feed back circuit a logarithmic 
diode is inserted. To the (+) input terminal of the processing amplifier 
A.sub.1, a bias of a constant voltage is applied from a constant voltage 
source Vs. This amplifier for the light sensing circuit acts as a kind of 
impedance converting circuit presenting a high input impedance and low 
output impedance, which is the characteristic of a processing amplifier. 
The overall characteristic between the input and the output is the 
logarithmic characteristic so that the logarithmically compressed value of 
the input signal, namely the Apex value in the photography, is produced at 
the output. In the circuit shown in the drawing, the output of A.sub.1 is 
an Apex value, namely the value (Bv-Avo), determined by the brightness of 
the object to be photographed, the F value of the photographic lens at the 
time of the light sensing. When the light sensing is made by a completely 
opened lens, the deviation Avc of the F-value due to the curve 
characteristics at the lens opening is involved so that the output of 
A.sub.1 assumes the value Bv-(Avo+Avc). Then, to the input of the buffer 
amplifier A.sub.2 composing the photographic information setting circuit, 
various types of photographic information set at the variable resistance 
R.sub.1, through which a constant current flows from a constant current 
source Is.sub.1, are given and converted by the impedance of A.sub.2 into 
the Apex value of the photographic informations at the amplifier output. 
Namely, when the priority is given to the shutter time, the film 
sensitivity, the shutter time and the compensation value for the deviation 
of F value due to the curve characteristics at the lens opening are set 
while the signal (Sv-Tv+Avc) is produced at the output. 
The output of A.sub.1 and that of A.sub.2 are composed and put in the 
processing amplifier A.sub.3. A.sub.3 is the amplifier presenting the 
inversing efficiency, while to the (+) input terminal a constant bias 
voltage is applied from Vs. At the output of A.sub.3, the diaphragm value 
processed out of the above mentioned signal is produced. Namely, the 
output of A.sub.3 assumes the value-(Bv+Sv-Tv-Avo) whereby the output of 
A.sub.3 assumes the value-(Av-Avo) because Bv+Sv-Tv is equal to Av. 
This value corresponds to the number of steps with which, during 
photography, the diaphragm of the lens is closed from the F-value of the 
fully opened lens. Namely, a proper exposure value is reached when the 
lens is closed with this number of steps from the fully opened state. The 
output of the processing amplifer-(Av-Avo) is stored in the stored 
condensor C.sub.1 through the storage switch S.sub.3. The output of 
A.sub.3 is put in the (-) input terminal of the processing amplifier 
A.sub.4, while to the (+) input terminal, the voltage of a variable 
condensor R.sub.3 through which a constant current flows from a constant 
current source is applied. A signal showing the F-value of the fully 
opened photographic lens is set on R.sub.3, while at the output of A.sub.4 
the difference between the value-(Av-Avo) and the F-value information Avo, 
namely Av is produced. This value is the absolute value of the actual 
diaphragm value of the photographic lens at taking picture. Therefore, 
when this value is indicated in the view finder by means of some proper 
device, it is possible to know the diaphragm value in advance before the 
operation of shutter. In the case of the camera shown in the drawing, the 
above value is indicated digitally. The output of the compensation circuit 
of the F-value is analog information, which is converted into digital 
information by means of the A-D converter. The output of the A-D converter 
is put in the decoder driver DD to be decoded so as to illuminate the 
illuminating diode group In comprising seven segments. Namely by means of 
the LED element group of a plural number of positions arranged in the view 
finder, the diaphragm value for the proper exposure is indicated in 
letters or figures. In order to minimize the power consumption needed for 
the indication, the current supply to the indication circuit can be 
partially interrupted as is shown in FIG. 1 when the output of A.sub.3 is 
not necessary (for example, during the operation of shutter). Namely, the 
current is supplied to the indication circuit by means of the switching 
circuit Sw.sub.1, whereby Sw.sub.1 is closed by means of the first stroke 
of the shutter button and opened by means of the second stroke. Namely, 
the indication is extinguished during the shutter operation while even 
after the termination of the exposure the indication is visible. An alarm 
circuit is provided in such a manner that the output of A.sub.3 is 
supplied to the comparison circuit Co so as to be compared with the limit 
value of the automatic exposure control of the camera and an alarm is made 
when the output is beyond the limit value. Namely by controlling the 
oscillator G by means of the comparison circuit Co and further controlling 
the switching circuit Sw.sub.5 by means of the output of G, the limit 
F-value of the indication LED is lighted and extinguished repeatedly so as 
to indicate that the value is beyond the limit. Hereby when in accordance 
with the necessity LED is directly driven by means of the output of the 
oscillator G, the indication LED is lighted and distinguished repeatedly. 
Further, the output of the comparison circuit Co is applied to the 
electro-magnetic actuating circuit in such a manner that by bringing the 
electro-magnetic actuating circuit out of operation when Co produces an 
output the shutter time control circuit is brought out of the operation so 
as to stop the exposure beyond the limit of the AE operation. 
R.sub.4 and C.sub.2 compose the time constant circuit of the 
electro-magnetic actuating circuit whose time constant is chosen in such a 
manner that in case of the normal photographing the inversion is made in a 
very short time after the closing of the switch S.sub.2. By means of the 
electromagnet M.sub.2 of this circuit the trigger switch S.sub.6 of the 
shutter time control circuit is opened whereby the shutter time control 
circuit T.sub.2 is inversed with the shutter time set in advance on 
R.sub.5 in such a manner that by means of M.sub.3 the rear plane of the 
focal plane shutter starts to run so as to complete the exposure. Hereby 
in case of photographing by using a self-timer it is sufficient to attach 
a delay condensor C.sub.3 to the electromagnetic circuit while S.sub.8 is 
closed in such a manner that the shutter actuating time is delayed. The 
capacity of the condensors to be charged through the resistance by closing 
the switch S.sub.8 becomes C.sub.2 +C.sub.3, whereby when C.sub.3 is 
chosen sufficiently large it is possible to obtain a self-timer time as 
long as about 10 seconds. In this way, the operation of the shutter time 
control circuit driven by means of the electromagnet M.sub.2 can be 
automatically delayed by the self-timer time. Hereby C.sub.5 and S.sub.7 
of the shutter time control circuit is the condensor respectively the 
switch for the long time exposure, whereby by closing S.sub.7 the shutter 
time can be prolonged (for example 2-30 seconds). 
Further, in order to reset the electromagnetic circuit, it is sufficient to 
bring the switching circuit Sw.sub.4 connected parallel to C.sub.2 into 
the conductive state by closing the switch S.sub.11 and to discharge the 
charge remaining in C.sub.2 and C.sub.3. 
The voltage corresponding to the information of the number of steps of the 
diaphragm stored in the condensor C.sub.1 of the storage circuit is put in 
the high input impedance buffer amplifier A.sub.5 and kept even if the 
switch S.sub.3 is opened. The output of A.sub.5 is put in the comparison 
circuit A.sub.6 so as to be compared with the voltage applied to the other 
input terminal, of the variable resistance R.sub.2 through which a 
constant current supplied from the constant current source IS.sub.2. When 
the input voltages of A.sub.6 become equal to each other by the variation 
of the value of resistance R.sub.2 in functional engagement with the 
diaphragm mechanism, the electromagnet M.sub.1 is driven by means of the 
output of A.sub.6, so as to determine the diaphragm value producing a 
proper exposure. Thus when at taking photograph the lens is set at this 
diaphragm value and the shutter is operated with the predetermined shutter 
time, the proper exposure can be automatically obtained. Hereby the switch 
S.sub.9 is the auto-manual switching over switch which is closed when the 
diaphragm is manually set. 
FIG. 3 shows an example of the timing chart showing the operation of every 
parts of the camera in an embodiment of FIG. 2. In the drawing the 
abscissa shows the time, the lines drawn alng the abscissa shows the 
operation time of every circuit or the time during which each switch is 
closed. As is shown in the drawing, the operating time of the indication 
circuit as well as the electromagnet whose power consumption is large are 
chosen as short as possible. 
As explained above, by means of the exposure control system in accordance 
with the present invention an automatic exposure control with priority on 
shutter time can be made with the electric shutter. Further, it is 
possible to supply current to every part composing the electrical circuit 
of the camera efficiently and at the proper time whereby by means of the 
electromagnetic activating circuit the shutter time control circuit can be 
electromagnetically actuated with high accuracy while this circuit can be 
utilized for setting the timer time at taking photograph with self timer. 
The light sensing circuit shown inside of the dotted line in FIG. 2 can be 
composed in such a manner that the mean light sensing and the partial 
light sensing can be switched over as is shown in FIG. 4. Namely the part 
in the dotted line (I) shows the camera unit presenting the mean light 
sensing means, while the part in the dotted line (II) shows the partial 
light sensing unit. 115 is the diaphragm member for controlling the amount 
of the light beam coming from the object to be photgraphed in accordance 
with the set amount of the set lever 114 to be explained later, 116 the 
light sensing element such as cds, SBC and so on for measuring the mean 
brightness at the central part of the photographic field. 117 is the 
diaphragm for varying the view angle, 118 the view angle varying lever for 
varying the opening angle of the diaphragm, 119 the resistance being in 
functional engagement with the diaphragm member 117 and assuming the 
resistance value in accordance with the variation angle of the view angle 
so as to automatically compensate the exposure level error when the view 
angle is varied. 120 is the processing amplifier for amplifying the output 
of the light sensing element 116, 121 the diode for logarithmically 
compressing the photo current of the light sensing element 116, 122 the 
switch for switching over the light sensing systems whereby in the drawing 
the state in which the mean light sensing circuit at the camera side is 
chosen is shown. 123 is the constant voltage source for setting the 
operation level setting of the processing amplifier 126, 124 the 
processing amplifier for amplifying the output of the light sensing 
element 111, 125 the diode for logarithmically compressing the photo 
current of the light sensing element 111, 126 the processing amplifier, 
127 the diode for temperature compensation, 128 the constant current 
source for applying the bias voltage to the temperature compensating diode 
127, 129 the variable resistance for adjusting the output level of the 
light sensing circuit (I) and 130 the resistance with a positive 
temperature co-efficient. 131 is the temperature compensating amplifier 
whose output is put in the processing amplifier A.sub.3 shown in FIG. 2. 
The light sensing element 11 and 16 of such a light sensing circuit are 
arranged as shown in FIG. 5. Namely the part in the dotted line (I) shows 
the camera unit presenting the mean light sensing member, while the part 
in the dotted line (II) shows the partial light sensing member. In the 
drawing 101 is the photographic lens optical system, 102 the diaphragm, 
103 the reflecting mirror provided slantly in the photographic optical 
path and movable around the axis 103, 104 the front plane and the rear 
plane of the focal plane shutter, 105 the film, 106 the film pressing 
plate, 107 the pint glass, 108 the condensor lens, 109 the pentagonal 
prism, 110 the eye piece, 111 the light sensing member such as cds, SBC 
and the like arranged at a position at which the mean brightness of the 
total picture plane of the photographic field can be measured, 112 the 
connecting member being provided on the upper part of the view finder in 
the camera body so as to dismountably mount the partial light sensing 
member (II) on the camera body, 113 the condensor lens system, 114 the set 
lever for setting the difference (Avo.sub.1) between the brightness of the 
photographic lens optical system 101 at the camera side and that of the 
condensor lens system 113 as well as the opening compensation amount 
(Avc.sub.1) of the condensor lens system 113, 115 the diaphragm member for 
controlling the amount of the light beam from the photographic field in 
accordance with the set amount of the set lever 114 and 116 the light 
sensing member such as cds, SBC and the like for measuring the mean 
brightness at the central part of the photographic field. Hereby the 
optical system for indicating the light sensing member (view angle) of the 
outer light sensing unit (II) is omitted. 117 is the diaphragm member for 
varying the view angle, 118 the view angle varying lever for varying the 
opening angle of the diaphragm member 117, 119 the resistance being in 
functional engagement of the diaphragm member 117 and asserming the value 
in accordance with the varied amount of the view angle so as to 
automatically compensate the exposure level error when the view angle is 
varied. First of all in case photograph is taken while the brightness of 
the photographic field is measured with partial measurement, the partial 
light sensing member shown with (II) in FIG. 5 is mounted on the 
connection member 112 provided on the camera body while the switching over 
switch 122 is set at the opposite side to that shown in FIG. 4. In this 
way, the output of the partial light sensing member is put in the input 
terminal of the processing amplifier A.sub.3. Further when photograph is 
taken while the mean brightness of the photographic field is measured, 
only the mean light sensing member shown with (I) in FIG. 5 is used, 
whereby the switching over switch 122 is set as is shown in FIG. 4. Hereby 
the photograph is taken by means of the partial light sensing member (II). 
After as mentioned above the partial light sensing member (II) is mounted 
on the camera body, the set lever 114 is slided either along the direction 
A or along the direction B so as to set the Avo.sub.1 as well as the 
opening compensation amount (Avc.sub.1). In case it is desired to alter 
the view angle, the view angle varying lever 118 is slided so as to set 
the view angle at the desired value. When then the shutter release button 
is pushed down, the switch S.sub.1 is closed in such a manner that the 
light measuring circuit is brought into the operation state. Thus the 
potential at the output terminal of the amplifier 120 of the light 
measuring circuit assumes the value Bv-(Avo.sub.1 +Avc.sub.1) whereby the 
brightness of the object to be photographed is Bv. In consequence to the 
input terminal of the processing amplifier A.sub.3 the output voltage 
{Bv-(Avo.sub.1 +Avc.sub.1)} of the processing amplifier 120 and the output 
voltage (Sv-Tv+Avc) of the processing amplifier A.sub.2 are put in so that 
at the output terminal of the amplifier A.sub.3 the voltage corresponding 
to {Bv+Sv-Tv-Avo.sub.1 -(Avc.sub.1 -Avc)}, namely 
(.vertline.Av.vertline.-Avo.sub.1 -Avc.sub.1 +Avc), in other wards the 
voltage corresponding to the number of the steps with which the diaphragm 
is to be closed from the fully opened state, is produced in such a manner 
that this diaphragm information is stored in the condensor C.sub.1 through 
the switch S.sub.3. 
As explained above, on the camera body the mean light sensing element is 
provided while the partial light sensing element is provided outside of 
the camera body so that the arrangement of the light sensing elements is 
easy, especially the pentagonal prism can be manufactured easily while the 
light measuring part for partial measurement can be mounted and dismounted 
easily so that the construction becomes compact. 
In the above mentioned embodiment the light sensing element provided at the 
camera side is for mean measurement while the light sensing element 
outside of the camera body is for partial measurement, whereby even if the 
arrangement is inversed, the effect of the present invention is not 
influenced.