Electronic exposure control apparatus

An electronic exposure control apparatus for a camera includes a setting means to set the exposure factor, a compression means connected to said setting means, for compressing the above-mentioned exposure factor logarithmically and an analogue-digital conversion means, being connected to said compression means, and generating a pulse number which corresponds to the output from the compression means. Also included is a first counter, which is connected to the output of the above-mentioned analogue-digital conversion means, for counting the pulse number from the above-mentioned analogue-digital conversion means, a pulse generating means, a binary counter having plural number of bits and connected to the output of the above-mentioned pulse generating means, wherein said counter counts the pulse number from the above-mentioned pulse generating means in association with shutter release, and the output of the counter is connected to the first counter for resetting the memorized content of the first counter. A coincidence detection means is connected to the output of the binary counter, wherein said means generates a signal when the memorized content of the first counter is reset, and a control means is connected to the above-mentioned coincidence detection means, wherein the opening and closing of the shutter is controlled by the signal from the above-mentioned coincidence detection means.

BACKGROUND OF THE INVENTION 
1. Field Of The Invention 
The present invention is related to an electronic exposure control 
apparatus of a single lens reflex camera, particularly to an electronic 
exposure control apparatus having an electronic shutter formed by a 
digital circuit which is digitally extended using the register. 
2. Description of The Prior Art 
In a conventional single lens reflex camera when an automatic exposure 
control is done by TTL photosensing, since photo-sensing is suspended 
during exposure of camera, as is well known, the brightness of an object 
just before exposure is detected and memorized and exposure control is 
performed based on this memorized value. And as such a device, a capacitor 
is used as a means to memorize the brightness of an object and the 
analogue amount of charged voltage at said capacitor is memorized. In 
another type, a register formed by flip-flop circuit is used to memorize 
the brightness as a digital amount. 
In the former method in which a capacitor is used to memorize analogue 
amount, the brightness of an object being electrically converted is 
compressed to several volts or less using a compression diode and is 
memorized with the use of a power source battery which is ordinarily used. 
Particularly in said device, a circuit to convert said memorized voltage 
to exposure time is an analogue circuit using a semiconductor. Therefore, 
said device has such shortcomings that it is apt to be influenced by 
temperature variation and variation in power source voltage and the 
memorized voltage can not be converted to proper exposure time. In 
addition, even when a compensation circuit, etc. is provided, said 
influence can not be sufficiently compensated. 
On the other hand, a method to digitally memorize an object information 
using a register is disclosed in the Japanese Patent Publication No. Sho 
45-4903, and in said method as the object information is digitally 
memorized in a register it will not be influenced by temperature variation 
and power source voltage variation. However, since the object information 
is memorized in a register in compressed manner for reducing the number of 
bits in the register, the output of the register needs to be expanded to 
convert what is memorized in the register to exposure time. But, as a 
circuit for said expansion purpose is an analogue circuit it is apt to be 
affected by temperature variation, power source voltage variation as in 
the former case, and it is difficult to obtain correct exposure time. 
SUMMARY OF THE PRESENT INVENTION 
An object of the present invention is to provide a device in which the 
above-mentioned shortcomings are eliminated, thus to provide an electronic 
shutter to digitally expand the content of the register memorizing the 
object brightness information being compressed. 
Another object of the present invention is to provide an electronic shutter 
in which an indication means is connected to an output end of the 
expansion circuit to digitally expand the content of the register. 
Still another object of the present invention will be apparent from the 
detailed explanations in which the invention is explained together with 
the drawings.

DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION 
FIG. 1 is a block diagram to shown an example of an electronic shutter 
control device of the present invention. In this figure, 1 is a variable 
resistor adjustable for film sensitivity, 2 is a light receiving element 
such as a CdS, silicon blue-cell (SBC), etc., to receive the light from an 
object and output photo-current 3 is an operational amplifier to which the 
output terminal of said light receiving element is connected, 4 is a diode 
having compressive characteristics being connected between the input 
terminal and the output terminal of the operational amplifier 3, 5 is a 
variable resistor varied by setting shutter time, 6 is a second 
operational amplifier being connected to the output terminal of the 
above-mentioned operational amplifier and the shutter time setting 
variable resistor 5, 7 is an integration waveform generator, 8 is a 
comparator to compare the outputs of the above-mentioned operational 
amplifier 6 and of the integration waveform generator 7 and to generate 
such pulse length as corresponds to such length of time required until the 
outputs of 6 and 7 coincide, 9 is a clock pulse generator and the 
oscillated frequency thereof can be varied, 10 is an AND gate, and such 
pulse number as corresponds to a proper diaphragm aperture value will be 
generated at its output, 11 is an AND gate, 12 is a generator which 
generates a pulse number corresponding to the limit value of the diaphragm 
aperture of a taking-lens (not shown) used in a camera (herein called as a 
limit diaphragm value), for example F = 1.4, and this generator 12 has 
various elements as shown in FIG. 1, e.g. a resistor 12a to be set at a 
resistance value corresponding to the limit diaphragm value, a capacitor 
12b forming a time constant circuit together with the resistor 12a, a npn 
type transistor 12c which becomes conductive when the output voltage of 
the time constant circuit reaches a present value, a standard value 
setting resistor 12d, a pnp type transistor 12l, a resistor 12e, 12q, 12h, 
a power source switch 12k, a clock pulse generator 12m and AND gate 12n. 
The generator 12 generates a pulse number from the output terminal or AND 
gate corresponding to the limit diaphragm value because it is 
non-conductive for a period of time corresponding to the resistance value 
set in the resistor 20 by the transistor 12l, 13 is a comparator circuit 
which compares the outputs of AND gate 10 and the generator 12 and is 
constituted, for example, by an up-down counter. 14 is a NOT gate which 
inverts the input and the output of this circuit and is connected to the 
other input of said AND gate. 15 is an AND gate which passes the output 
pulse generated from the AND gate 10 after the output of said comparator 
13 becomes 1. 16 is a pulse generator which generates a pulse with such 
pulse length as corresponds to shutter time information by setting of 
shutter time, and is composed of each of the above-mentioned circuits 5, 
6, 7 and 8. 17 is an AND gate having familiar function as that of the 
above-mentioned AND gate 10. 18 is an OR gate, 19 is a register connected 
to the AND gate 11. 20 is a D-A converter which makes the conversion to 
the amount of current which corresponds to the number of pulses of the 
register 19. 21 is a variable resistance which is varied in association 
with a diaphragm driving mechanism 22 of a camera. Element 22 may be a 
spring, for example. Element 22a itself a camera diaphragm. 23 is a 
comparator to compare the outputs of the D-A converter 20 and of the 
variable resistance 21 and generates a pulse when both outputs coincide. 
24 is a switching circuit such as a Schmitt circuit, etc. having its 
output state inverted by the output of the comparator 23. 25 is an 
electromagnet for locking the diaphragm driving member which is excited by 
24. Here, the above-mentioned variable resistances 5, 21 are resistances 
having logarithmic resistance variation corresponding to the set amount 
thereof. It is also possible to have the output of the register 19 drive 
the diaphragm by way of a conversion circuit and stepping motor. 
In terms of representative circuit elements, comparator 13 is of the type 
shown in FIGS. 1, 3 and 4 of the German laid-open Specification No. 
2,164,243 of July 29, 1972 which corresponds to U.S. Pat. No. 3,748,979. 
When the output terminal of AND gate 10 of the present invention is 
connected to the flip-flop 15 of DOLS No. 2,164,243 and the output 
terminal of the element 12 is connected to the input terminal of the 
flip-flop 5 of the above-mentioned DOLS, the desired function is achieved. 
It should be noted that comparator 13 has the function of both register and 
comparator. 
Register 19 is of the type disclosed as B.sub.0, B.sub.1, B.sub.2, B.sub.3, 
B.sub.4 on Page 675 of Pulse, Digital and Switching Waveforms (published 
1965, McGraw-Hill). Thus when the output terminal of AND gate 11 is 
connected to "T" of "B.sub.0," the required connection is achieved. The 
register shown in RCA Solid State Databook Series '72 type CD4014A may 
also be used. 
D-A converter 20 is of the type disclosed in the McGraw-Hill text above 
(P.675). 
Comparator 23 is of the type disclosed in "Voltage Comparators/Buffers . . 
. LM106/LM206" on Page 135 of Linear Integrated Circuits published in 1971 
by National Semiconductor Corporation. Thus, by connecting the output 
terminal of element 20 of the present invention to the input terminal 2 of 
the element shown by a solid line on Page 135 of the above reference and 
by connecting the output terminal of the element 21 of the present 
invention to the other input terminal 3 of the reference and, further, by 
connecting the output 7 to the input terminal of the element 24, the 
desired interconnection is achieved. 
The output of the OR circuit 18 is added to the plural number of AND gates 
28 to 33. The outputs of the AND gates 28 to 33 are connected to the set 
terminals S of plural number of flip-flop circuits 34 to 28, respectively. 
The reset terminals R of these circuits 34 to 38 are connected to each of 
bits 2.sup.0, 2.sup.1 . . . of a binary counter 39. One of the output 
terminals Q at each of the circuits 34 to 38 is connected to the AND gate 
of the next stage, respectively, while the other output terminals Q are 
inputted to the AND gate circuit 40. The shutter time control circuit 41 
composed by, for example, Schmitt circuit is actuated by the output of the 
circuit 40, and by the same, a shutter closing member is driven by a 
magnet 42. A reference pulse is added to the input terminal CL of the 
above-mentioned binary counter from a reference pulse generator 44 through 
a switch 43, and a reset switch 45 is connected to the reset input 
terminal R. The output of the AND gate 33 is connected to an overflow 
indication lamp circuit 50 while the outputs Q, Q of each flip-flop 
circuit are connected to indication lamp circuits 46 to 49 through AND 
gates 51 to 54. 
Next, function of this device will be explained. First in a first state 
wherein there is no output pulse from the OR gate 18, the flip-flop 
circuits 34 to 38 are all reset and their outputs will be such that Q is 
"0", and Q is "1". As a shutter dial (not shown in the drawing) of a 
camera is rotated to set the same at a desired shutter time, shutter time 
information will be inserted into the resistance 5 in association 
therewith. As film sensitivity information is set at the resistance 1 
beforehand, such voltage as corresponds to film sensitivity and object 
brightness information is outputted from the operation amplifier 3. 
Therefore, the output of the second operation amplifier 6 becomes such as 
corresponds to proper diaphragm aperture value. Of course, the output of 
the amplifier 6 is logarithmically compressed as the diode 4 and the 
resistance 5 with its resistance value varying logarithmically are used. 
For example, as a photosensing starting switch (not shown in the drawing) 
is actuated, integrated waveform which ascends linearly is outputted from 
7, and at the same time the output of the comparator 8 becomes 1. As the 
output voltage of the generator 7 increases and becomes equal to the 
output of the amplifier 6, the output of the comparator 8 becomes again 0. 
By this operation, such pulse number, as is equal to the pulse number from 
the generator 9 being inputted while the output of the comparator 8 is 1, 
outputted from the AND gate 10. This pulse is mermorized in the register 
19 through the AND gate 11. On the other hand, such pulse number as 
corresponds to the set shutter time is outputted from the AND gate 17 and 
its pulse train is transferred to the output of the OR gate 18. 
The first one (first pulse) of said output pulse goes through the AND gate 
28 and is impressed on the set input S of 34, and in the output of 28, Q 
is inverted to "1" and Q is inverted to "0". When the next output pulse 
(second pulse) is sent out, the AND gate 29 becomes ON by said pulse and 
the Q "1" pulse from 34 and the second pulse is inputted into the S input 
of 35. By this, 35 is inverted and Q becomes "1" while Q becomes "0". 
Then, thereafter, every time the output pulse from 18 is sent out, the 
flip-flop circuits will be set in turn in the order of 34, 35 . . . and as 
great a number of FF circuits as the number of output pulse will be set. 
The output of the flip-flop circuits, which have been set according to the 
number of output pulse from the OR gate 18, as mentioned above, will be 
such that Q is "1" and Q is "0". Each of the Q outputs of the flip-flop 
circuits is inputted into the gate circuit 40 forming an AND gate so that 
the shutter time control circuit 41 is controlled by said output to 
actuate the magnet 42. But as the Q output of the flip-flop circuit being 
set by the output pulse from the OR gate 18 is then "0", the AND gate 40 
under such state will be OFF and control signal will not be sent to the 
control circuit 41. 
Next, the binary counter 39 is reset, for example, by having the switch 45 
connected momentarily from terminal a to terminal b at the time of film 
windup. Therefore, in this state, the signal for the reset input R of each 
flip-flop circuit will not be sent from each output of the counter. When a 
shutter release button (not shown in the drawing) is pressed one step in 
this state, the pulse memorized in register 19 is converted into an 
analogue amount by the D-A converter 20 and is then supplied into the 
comparator 23. At the same time, the diaphragm driving member 22 is 
actuated to stop down the diaphragm 22a. As the diaphragm driving member 
22 is actuated, the variable resistance 21 is varied in association 
therewith and such current as corresponding to the amount of rotation of 
the diaphragm will be inputted into one of the input terminals of the 
comparator 23. When the output current from the D-A converter 20 and the 
output current generated by the variable resistance 21 coincide, a pulse 
is generated by the comparator 23 and the magnet 25 is excited; thus the 
diaphragm driving member is locked. That is, it is always set at a desired 
diaphragm aperture value. When the shutter release button is further 
pressed down to a second step, the engagement of the shutter front screen 
is released. The switch 43 is turned ON at the same time the shutter front 
screen starts moving, and pulses with predetermined or periodic cycle will 
be sent to the binary counter 39 from the reference pulse generator 44. 
For example, if the cycle of the reference pulse is selected as 1 mS 
(1/1000 second), reset signal is generated at first bit 2.sup.0 of the 
binary counter in 1/1000 second after the shutter front screen starts 
moving, and it is sent to the reset input of the flip-flop circuit 34 to 
reset the FF circuit. By this, the output Q is inverted to "0" and Q to 
"1". Reset signal will be sent successively to the reset input of the 
flip-flop circuit in such manner that the second bit 2.sup.1 of the binary 
counter circuit is after 1/1000 .times. 2 = 1/500 second and the third bit 
2.sup.2 is after 1/1000 .times. 2.sup.2 = 1/250 second . . . . When there 
are four output pulses from the OR gate 14, the circuits 34 to 37 are in a 
set state, and the flip-flop circuits in the stages thereafter will be in 
a reset state. In this state, as the output of the binary counter is 
resetting FF1 to FF4, in turn, with a predetermined interval, the time 
required for the fourth bit 2.sup.3 of the counter to reset the circuit 37 
will be 1/1000 .times. 2.sup.3 = 1/125 second after the shutter starts 
moving, and at this time, the AND gate 40 is actuated and the magnet 42 is 
actuated by the control circuit 41 to close the shutter, thus exposure 
with 1/125 second will be made. 
As has been explained above, according to the present invention such 
arithmetical digital information (the pulse number from the AND gate) as 
is obtained by operating the logarithmically compressed information (the 
output of the amplifier 6) is expanded by a binary counter circuit to 
obtain shutter speed with multiple series (1/1000 second, 1/500 second, 
1/250 second . . . 1, 2, 4 . . .). 
It is possible to provide gate circuits 51 to 54 to AND, the Q output at 
front stage of the flip-flop circuit and the Q output at the latter stage 
as shown in the drawing for driving the lamp driving circuits 46 to 49 by 
their outputs, thereby digitally indicating shutter time beforehand with 
lamp. It is also possible to vary the illuminating color of said 
indication lamp to facilitate the identification of high speed shutter and 
low speed shutter. 
When the digital diaphragm aperture value information obtained from the AND 
gate 10 is greater than the marginal diaphragm value of the camera, 
operation will be as described below. 
Suppose the marginal diaphragm aperture value of the register 12 is 
supplied to the comparator 13, as the pulse is sent from the AND gate 10, 
the content of the comparator 13 is successively deducted by said pulse 
and as the content of the comparator 13 becomes 0, the output of the 
comparator 13 becomes 1. By this, the AND gate 11 is closed and at the 
same time the AND gate 15 is opened and pulses are sent from the gate 10 
through the OR gate 18 to the flip-flop circuit, and the flip-flop 
circuits are set in turn according to the number of said pulses. On the 
other hand, since the gate 11 is closed, as mentioned above, such number 
of pulses as correspond to the marginal diaphragm value will be memorized 
in the register 19. As the shutter release button is pressed down to its 
second step, the diaphragm aperture is stopped down to the marginal 
diaphragm value. And the shutter will be opened for such period of time as 
corresponds to the diaphragm aperture value obtained after operation. That 
is, the device in the present invention is so made that in setting shutter 
speed beforehand, when the diaphragm device is driven by such pulse as 
corresponds to the set shutter speed and is set to the prescribed value 
and at the same time the diaphragm aperture value reaches the marginal 
value, the pulse memorizing device which memorizes the set shutter speed 
is reset to vary the shutter time. Thus, proper exposure can be obtained 
for a very wide range of object brightness without any manual operation 
and it is very effective. 
In the former case, explanations were made of the case wherein shutter time 
is set first, that is, so-called shutter preference, and the invention can 
naturally be applied to a diaphragm preference camera. Next, a device of 
the present invention, in which such control circuit is added as enabling 
the change-over to be made between diaphragm preference and shutter 
preference, will be explained using FIG. 2. Like parts as those in FIG. 1 
will be identified by like numbers. 
In FIG. 2, the outputs of a brightness input information circuit 112, a 
film sensitivity setting information circuit 113, a shutter time setting 
information circuit 114, and a diaphragm setting information circuit 115 
are connected to the input of a digital operation device 111, and either 
the proper diaphragm aperture information or shutter time information is 
outputted from the output of said operation device and passes through a 
prohibition gate 116 as a number of pulse trains with even intervals as 
correspond to said set information. The purpose of the brightness input 
information circuit 112 is to place the light receiving element 2 
(consisting of photoconductive element such as CdS cell, PbS cell, etc., 
or photo-electromotive force element such as photodiode, photo-transistor, 
etc.) at such position so as to receive the light of an object. The 
element 2 also is to logarithmically compress the analogue output thereof 
and impress the same into the input of an AD converter circuit 117 
composed of the 7, 8, 9 and 10 in FIG. 1. The A-D converter then converts 
the same to such linear digital pulse as is proportionate and corresponds 
to the analogue signal level and impresses the pulse signal thereof into 
the input of the operation device 111. 
The film sensitivity information circuit 113 is, as the information circuit 
112, to linearly impress into the operation device 111 through the 
information circuit 113 itself, the digital pulse signal which is 
proportional to the film sensitivity by a signal generator 118 which is 
composed of the elements 7, 8, 9 and 10 shown in FIG. 1 and has a function 
to A-D convert the analogue signal of the setting signal 1 which sets in 
the film sensitivity used. The output of the operation device 111 is 
supplied into a shutter time register 121, a diaphragm register 19 which 
is composed of the parts 28 to 45 shown in FIG. 1 through AND circuits, 
119 and 120 respectively. 
On the other hand, the output of a preference setting information circuit 
122 is added to the other input of the above-mentioned AND circuit and at 
the same time a shutter preference information circuit part 123 has such 
number of pulses, as corresponds to the set shutter time as is added to a 
shutter information signal generator 125 which is composed of the 7, 8, 9 
and 10 shown in FIG. 1, added to the shutter time setting information 
circuit 114 and the OR circuit 126, and the output of the above-mentioned 
OR circuit 126 is added to the shutter time register 121. 
Similarly, a diaphragm preference information circuit part 124 has such 
number of pulses, as corresponds to the diaphragm aperture which has been 
added to a diaphragm information signal generator 127 being composed of 
the 7 to 10 shown in FIG. 1 and has been set, added to the diaphragm 
setting information circuit 115 and the OR circuit 128, and the output of 
the above-mentioned OR circuit 128 is added to the diaphragm register 19. 
The contents of the above-mentioned registers are respectively sent to the 
shutter time indication circuit 130 and the diaphragm indication circuit 
131 being composed of the parts 46 to 54 shown in FIG. 1 to indicate the 
photographing information and at the same time the contents of the 
information are sent to the shutter control circuit 132 and the diaphragm 
control circuit 133 respectively, to effect the shutter control and the 
diaphragm control, respectively, with said content. 
The device is so composed that both outputs for shutter, diaphragm of the 
above-mentioned preference set information circuit are added to the AND 
circuit and the output sent to the prohibition gate 116, and at the same 
time the output is sent to a zero signal indication near the operating 
device. Now, the operation of the circuits will be explained in detail 
following each preference setting. 
(1) In case of shutter preference: 
When, for example, the indication marked on shutter dial is made to have 
the position of A (auto) set at any desired shutter speed by rotating a 
dial, a signal is issued to the shutter preference setting information 
circuit 123, and such number of pulses as corresponds to the shutter speed 
which has been sent to and set at the AND circuits 129, 120 and the 
shutter time setting information circuit 114. 
On the other hand, the brightness input information 112 which supplies such 
pulses from compressing the output of light receiving element and being AD 
converted and being in proportion with the logarithm of brightness, and 
the film sensitivity setting information 113 generated by film sensitivity 
setting are added to one of the inputs of the operation device 111. The 
above-mentioned shutter time setting information is added to the other one 
of the inputs, and from said operation device 111, a proper diaphragm 
aperture information output AV is outputted as such number of pulse train 
signal as correspond to the diaphragm aperture information. While the 
outputted diaphragm aperture signal is sent through the prohibition gate 
circuit 116 to the AND circuits 119 and 120, and since input is not 
impressed to one of the AND circuit 119, the signal will not pass through 
this circuit, but instead passes through the AND circuit 120 and is sent 
to the diaphragm register. By application of the signal of the diaphragm 
register, for example, a step motor, etc. is driven and the diaphragm is 
stopped down. When it falls outside of the linked movement zone of the 
diaphragm, signal is fed back by a detecting circuit 134 for detecting the 
association failure and is sent to the OR circuit 126 and reset the 
once-set shutter time so that proper exposure can be obtained. Of course, 
it is possible to issue a warning signal only without providing feedback 
and to reset manually. 
(2) In the diaphragm preference case: 
As the function of the diaphragm preference is entirely equivalent to the 
case of shutter preference, with the shutter preference signal, 
explanations will be omitted. In this case, 135 is a detecting circuit for 
detecting the association failure (i.e., a link-zone detecting circuit). 
(3) In the manual shutter case: 
When the shutter dial, the diaphragm ring are set at any desired value 
except A, EE, respectively, both the shutter preference signal circuit 
part 123 and the diaphragm preference signal circuit part 124 have their 
outputs generated and, as has been described above, have resets both the 
shutter register 121 and the diaphragm register 19. At the same time, 
signals are sent to the shutter time setting information circuit 114 and 
the diaphragm setting information circuit 115, and operation is performed 
other with the brightness input information and the film sensitivity 
setting information. The output of the operation device will not be sent 
to the AND circuit as the prohibition gate circuit 116 works thereon. 
Since the operation device is so composed as to provide zero signal, when 
the shutter or the diaphragm is operated until the zero signal indication 
is lighted so that the operation device becomes zero, proper exposure can 
be made. 
As has been explained above, in the electronic shutter control device 
according to the present invention such pulse number as corresponds to the 
shutter time obtained by operation of logarithmic information is memorized 
and it is read out by the read out pulse from the binary (notation) 
circuit, thereby the shutter speed of multiple series can be precisely and 
stably obtained, thus the invention has great effect as the most advanced 
automatic exposure control system.