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Description  |
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DETAILED EXPLANATION OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure control circuit, especially an
improved exposure control circuit of the APEX exposure system.
2. Description of the Prior Art
So far the APEX system has been proposed in order to treat the exposure of
the camera. According to this APEX system all the numerical values
concerning the exposure are converted into simple numbers in such a manner
that the exposure quantity is represented as the sum of the above
mentioned numbers. Hereby the exposure quantity (Ev), the time value (Tv),
the diaphragm value (Av), the ASA value (Sv), the luminance value (Bv) and
the illumination value (Iv) are represented in the exponent of 2 whereby
it can be defined in such a manner that Ev is equal to
##EQU1##
Av (diaphragm(A) ).sup.2, Sv a number proportional to ASA value, Bv a
value proportional to luminance (B.sub.fL or B.sub.e ai/ft.sup.2 and Iv a
value proportional to illumination.
However the above mentioned system is not utilized so much in the practice,
whereby only Ev (Exposure quantity) is used. One of the reasons seems to
be that the system serves nothing but as an equation merely for
calculation in practice and there take place irrational points when
considered in connection with the mechanism and the efficiency of the
camera so that its application is difficult.
For example according to the shutter time in the table of FIG. 1, the Tv
value for 1/1000 sec. is 10 and that for 1 sec. 1 while those for the time
more than one second are negative. Besides Tv assumes a value inversely
proportional to the time length so that it is unnatural and inconvenient
for the actual application. On the other hand is the larger the Tv value
is the larger the diaphragm value is. In consequence, it is impossible to
assume values inversely proportional to both of them, being connected with
the exposure. In consequence, in case the shutter time is controlled with
shutter in priority by means of the exposure control circuit of the above
mentioned APEX system, for the same luminance of an object to be
photographed, the Tv value which represents the shutter time value when a
large value is assumed for the diaphragm is smaller than the Tv value when
a small value is assumed for the diaphragm, which is quite contrary to the
relation of the actual shutter time value. Further the result of the case
with shutter time in priority is same as that with diaphragm in priority,
whereby it is inconvenient to offer an actual exposure control circuit
because it is unavoidable that the disposition of the circuit becomes
complicated.
Further in case the exposure is controlled in a digital way by applying the
conventional APEX system it is impossible to use as control pulse, the
pulse which corresponds to the actual shutter time or the actual diaphragm
in order to control the shutter speed or the diaphragm because as
explained above, the results of the exposure computation for the shutter
speed value or the diaphragm value assume a relation inversely
proportional to the actual shutter time value or the actual diaphragm
value whereby it becomes unavoidable to adopt the digital control system
according to;
(1) the actual time compression elongation system which adopts a binary
circuit such as flip-flop became the system of the shutter speed and other
mechanism of camera is of 2.sup.n series and has much to do with the
binary system, or
(2) logarithmic compression inverse logarithmic elongation system according
to which the input is compressed logarithmically while the output is
elongated in an inverse logarithmically whereby the computation between
the compression and the elongation is carried out in a digital way.
However, according to the system (1), the compression is necessary because
it takes much time to carry out the computation with the actual time
value, when the shutter speed is low, while when the shutter speed is
high, the upper limit of the compression is limited, being connected with
the upper limit of the frequency characteristics of the circuit and
further the power consumption is increased proportionally to the increase
of the frequency due to the low power consumption even when a
complementary MOS.IC is used, which also brings about a restriction.
Further, it is inconvenient that the conversion of the system can not be
done freely.
On the other hand, according to the system (2), the restriction on the
frequency can profitably be avoided while the possibility that the errors
should be introduced in the conversion circuit is increased so as to
reduce the accuracy because the conversion is carried out two times,
namely the logarithmic compression and the inverse logarithmic elongation.
Further, if the accuracy is tried to be increased, the device becomes
complicated and expensive, which is inconvenient for the exposure control
circuit of the camera.
SUMMARY OF THE PRESENT INVENTION
A purpose of the present invention is to offer an exposure computation
circuit in which the exposure factors such as the shutter speed, the
diaphragm value and so on can be computed as the values corresponding to
the actual numerical values.
Another purpose of the present invention is to offer a digital exposure
computing circuit in which the input is analog-digitally converted and
logarithmically compressed in such a manner that the figures to be
computed is reduced, so that the computation is carried out with reduced
figures, the actual time is treated when the result is enlarged into time,
whereby the time is directly given digitally without any digital-analog
conversion.
Another purpose of the present invention is to offer a digital exposure
computation circuit which can be manufactured at low cost.
A still further purpose of the present invention is to offer a digital
exposure computation circuit whose circuit composition is simple and whose
operation is correct.
Further purposes of the present invention will become clear from the
following explanation referring to the embodiments of the present
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the table of camera index according to the APEX system.
FIG. 2 shows the table of camera index according to the present invention,
shown in comparison with that according to the APEX system.
FIG. 3 shows a block diagram of a circuit as one embodiment of the present
invention.
FIG. 4 shows a diagram of a digital circuit as embodiment of the present
invention.
FIG. 5 shows a part of the circuit diagram shown in FIG. 4, in detail.
FIG. 6 shows a table of the shutter speed, the computation pulse and the
pulse number for shutter speed for explaining embodiments.
FIGS. 7a and b show a table of the computation counter indication and the
shutter time counter indication for a wide range of the shutter speed.
FIGS. 8 and 9 show respectively a further embodiment of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT:
FIG. 1 shows a table of the camera index according to the APEX system
showing the numerical values of the exposure factor according to the APEX
system in comparison with the numerical values of the actual exposure
factor, whereby the exposure (Ev), the shutter time (Tv), the diaphragm
(Av), the ASA (Sv) and the luminance (Bv) are indicated in the power index
of 2 and also in
##EQU2##
{Diaphragm value (A) }.sup.2, a value proportional to ASA value, a value
proportional to luminance (B.sub.fL or B.sub.e ai/ft.sup.2) and a value
proportional to illumination (fc). Hereby the relation according to APEX
is fulfilled as follows.
Ev = Av + Tv
= Bv + Sv
= Iv + Sv.
FIG. 2 shows a table of the exposure factor index according to the present
invention, shown in comparison with that according to the Apex system,
whereby the diaphragm value is kept same while other values are considered
as negative values and respectively indicated with Ev', Tv', Bv' and Iv'.
Hereby instead of the relation according to APEX, the following relation
is fulfilled.
-Ev' = Av - Tv'
= -Bv' - Sv'
= -Iv' - Sv'
Tv' = Av + Bv' + Sv'
According to thus converted relations, Tv' is determined as the sum of all
the other indexes (in case the diaphragm is set with priority), while Av
is determined by counting down the conditions of the light from outside or
of the film from Tv' (in case the shutter is set with priority).
Below an exposure computation is made by means of the converted relations.
When for example, the diaphragm is 2.8 (Av = 3), ASA 100 (Sv = 5), Ev 10,
the luminance B 32 (Bv = 5), Bv' = 9, Sv' = 7, Ev' = Bv' + Sv' = 16 and Av
= 3, so that Tv' = Av + Ev' = 19. The relation Tv' = 19 is to indicate
1/125 sec. as shutter time. Thus according to the computation system by
means of the exposure computation system by means of the exposure
computation circuit according to the present invention, the accomodation
to the camera becomes very easy. For example, it is sufficient to so
design that three pulses are produced, when the diaphragm is set from 1.0
to 2.8, Sv' of ASA 100 corresponds to seven pulses, Bv' 9 of the luminance
of the light beam means B(fL) to be 32 and nine pulses and altogether
nineteen pulses give out the shutter speed of 1/125 sec. Although B is
increased and Bv' is reduced for example down to 6, if six pulses are
produced when the diaphragm is set down to 8, the sum is 19 pulses whereby
the shutter speed of 1/125 sec. is resulted. Hereby it goes without saying
that the shutter speed varies accordingly when the sum of the total
impulses changes. As to how to produce shutter pulses in case of the table
shown in FIG. 2, it is sufficient to set in such a manner that no
operation takes place up to the 15th pulse and the 16th pulse gives the
shutter speed of 1/1000 sec., the 17th pulse that of 1/500 sec. and so on,
because the pulse number for Tv' is chosen above 16 or that a necessary
number of pulses are produced at a certain determined time set on a built
in storage circuit. So far is the explanation as to the relations. The
operation of the camera equipped with the circuit according to the present
invention will be explained below. The pulses produced in the standard
pulse generator (1), when the main switch (10) is closed enters into the
input light beam converted (2), in which the input light beam is converted
into pulses proportional to its logarithm. The pulses are given to one (U)
of the terminals of the up-down-counter (6) by means of an OR gate (11)
and a switching over switch (4) in functional engagement with a switch by
means of which the shutter speed in priority is switched over into the
diaphragm in priority or vice versa. On the other hand, the ASA converting
circuit (3), which receives the pulses from the standard pulse generator
(1) produces a number corresponding to the ASA value, of pulses, which
pulses are given to the terminal (U) as in the above mentioned case.
Hereby in case of the diaphragm in priority for example, the pulses are
counted together with the counts for the diaphragm preset on the preset
switch (5). As the result Tv' ( = Bv' + Sv' + Av) is considered to have
entered into the up-down-counter (6). In consequence, the shutter time is
indicated in the indication device (7) in the above mentioned state. When
the shutter button is now pushed down the diaphragm is closed down to the
preset value. After a mechanical delay after the raise of the mirror the
shutter switch (9) is closed, when at the same time, the shutter is
opened. At the same time one pulse is produced by means of the storage
circuit every time, when the number of the counts reaches a certain value
which corresponds to the shutter time, whereby the pulse is given to the
other terminal (D) of the up-down-counter (6) in such a manner that in
case of the above mentioned embodiment the up-down-counter (6) becomes
empty when 19 pulses have entered into it, when the shutter is closed by
means of the output coming from the terminal (B) so as to obtain a certain
determined exposure time.
So far the case with the diaphragm in priority is explained, while in case
of the shutter in priority, the preset Tv' enters into the up-down-counter
(6) from the preset switch (5) and Bv' and Sv' are led to the terminal (D)
by means of the switching over switch (4) in such a manner that the
diaphragm value is indicated in the indication circuit (7) and the
diaphragm is closed down to the pulse number indicated by pushing the
shutter button. Further, the operation of the shutter in priority can be
achieved by leading the Tv' value in the preset switch (5) into the
up-down-counter (6) so as to operate the shutter after the raise of the
mirror, only after the signal that the up-down-counter (6) becomes empty.
FIG. 4 shows a circuit diagram of the further other embodiment of the
present invention, whereby (101) is a standard pulse generator for
continuously generating short pulses at a certain determined period and
(102) an input converter presenting a disposition as shown for example, in
FIG. 5, by means of the computation amplifier (203), the light receiving
elements (204) and the logarithmic diode (205) of which input converter
the input light is converted logarithmically by means of the photoelectric
effect whereby the photoelectrically converted output is integrated by
means of the integrating circuit (200) consisting of a condensor (207) and
a computation amplifier (206) together with the switching off operation of
a switch (208) in functional engagement with the switching on operation of
the main switch not shown in the drawing. (209) is a comparator whose
negative input terminal is connected with the output terminal of the above
mentioned integrating circuit and whose positive input terminal is
connected with a standard voltage presenting a value of the sum of Av and
Sv', whereby Av is a logarithmically compressed diaphragm value while Sv'
is a value inversely proportional to the logarithmically compressed ASA
value. (211) is an AND-gate which is connected with the output terminal of
the comparator (209) and that of the above mentioned pulse generator
(101). (109) is a computation counter which is connected with the output
terminal of the AND-gate (211), whereby the computation counter (109) is
connected with the storage circuit (110). (111) is an indication device
for indicating the information stored in the storage circuit. (112) is a
switch which closes when a shutter button not shown in the drawing, is
pushed, (113) a shutter time counter and (114) a comparison circuit of
matrix disposition for relating the pulse number counted by means of the
shutter time counter (113) to that counted by means of the above mentioned
computation counter according to a certain predetermined relation. (115)
is an output matching circuit for detecting the matching of the pulse
signal coming from the comparison circuit with that coming from the above
mentioned storage circuit, whereby the output signal is led to the shutter
closing relay (116) when the above mentioned both pulse signals are
matched with each other.
FIG. 6 shows a table of the example of the shutter speed, the computation
pulse and the pulse number for shutter speed for explaining the embodiment
shown in FIG. 4.
Below the operation of the exposure computation circuit according to the
present invention shown in FIGS. 4 and 5 will be explained. When the main
switch not shown in the drawing is closed, the switch (208) is opened in
functional engagement with the main switch. On the other hand, the light
receiving element (204) produces a voltage which corresponds to the input
light beam, which voltage is logarithmically compressed by means of the
logarithmic diode (205) and the computation amplifier (203) and led to the
negative input terminal of the integrating circuit (200). The above
mentioned logarithmically compressed voltage is integrated by means of the
integrating circuit (200) and led to the negative input terminal of the
comparator (209). At the positive input terminal of the comparator (209)
exists a standard voltage corresponding to a value of the sum of A.sub.T
and Sv' which voltage is compared with the voltage at the negative
terminal of the comparator (209). The voltage to be led to the negative
input terminal of the comparator (209) varies proportionally to the input
light beam so that when the input light beam is strong enough the standard
voltage is reached in a short time, while the input light beam is weak it
takes longer time to reach the standard time. When the both input values
of the comparator (209) are matched with each other, the comparator does
not operate any more and does not produce the output to be led to the one
input terminal of the AND-gate. In consequence, the AND-gate (211) does
not operate any more. Because the AND-gate is connected with the standard
pulse generator (101), the pulse signals pass through the AND-gate (211)
until the comparator (209) stops its operation. As explained above, the
time until the comparator (209) ceases its operation is inversely
proportional to the logarithmically compressed value of the input light
beam so that the number of the pulses having passed through the AND-gate
(211) assumes a value which corresponds to Tv' ( = Bv' + Sv' + Av). The
pulses having passed through the AND-gate (211) are led to the computation
counter (109) and counted binarily in such a manner that the counts (Tv')
are stored in the storage circuit (110). (111) is the indication device
for the information stored in the storage circuit. The above mentioned
operations are finished only by aiming the object to be photographed with
a camera, whose shutter button has not yet been pushed. On the other hand,
the shutter opening switch (112) is closed when the shutter button is
pushed in such a manner that the standard pulses produced in the standard
pulse generator (101) are led to the shutter time counter (113) and
counted in it. This counting time is to present an actual time in unit of
the period of the standard pulses.
The comparison circuit (114) in the present embodiment is of the matrix
disposition, which relates the computation counts to the shutter time
counts according to a certain predetermined relation so as to detect the
time points at which the shutter time counts reach certain determined
counts in such a manner that the counts corresponding to the computation
counts can be obtained as output at each time point whereby this output
and the output of the above mentioned storage circuit (110) are compared
by means of the output matching circuit (115) consisting of a non-match
gate and a NOR-gate so as to detect the outputs matched with each other in
such a manner by means of this pulse the shutter closing relay (116) is
operated so as to close the shutter in a certain predetermined time.
The actual circuit diagram shown in FIG. 4 is the one in case seven steps
of the shutter speeds are provided whereby one step corresponds to 2.sup.n
and the computation pulse number corresponding to each shutter speed and
the shutter time pulse number are as shown in FIG. 6. The repetition
period of the standard pulse used as the shutter time pulse here is 50.mu.
sec. (Frequency: 20 KHz). As to other information corrections necessary
for taking photograph, it is so set that the pulse number be O when ASA is
100 and the computation pulse number be 5 basing upon the EV value and the
diaphragm value. In such a case as mentioned above. the digit of the first
and the fourth figure of the computation counter becomes a logic "1",
whereby in the storage circuit "101" in binary system is stored as Tv'
value. The shutter speed of 1/125 corresponding to 5 of the computation
pulses is 8 ms. The counts of the shutter time counter corresponding to
this time is 160 of pulses of 50 .mu.s and the figure of 128 and 32 of the
counter becomes logic "1", whereby in the shutter time counter (113),
"010100000" in binary system is counted. The third gate-circuit counted
from the above of the comparison matrix (114) on the drawing is switched
on in such a manner that "101" is led to the output matching circuit
(115). Namely the shutter is closed when the shutter time count reaches
"010100000" in such a manner that an exposure of 1/125 sec. is obtained.
Further in case of the embodiment shown in FIG. 4, the value inversely
proportional to the logarithm of the luminance of the object to be
photographed and that of the film sensibility are used as input
information, while if the values corresponding to these exposure factors
are used the shutter time control can be carried out in the actual time,
when the comparison circuit is set so as to present a certain determined
comparison relation to the values corresponding to the above mentioned
exposure factors.
FIG. 7 shows a table of the dimensions corresponding to the shutter speed
of each step in case the range of the shutter time is 1/2000 to 8 seconds.
There are two series in the shutter speeds, namely 1/2000 series of
2.sup.n series and 1/1400 of 2.sup.n series. When the greatest common
divisor is taken into consideration, the standard period is 25 .mu.s and
the pulse number of this frequency becomes the pulse number of the shutter
counter. 1/60 instead of 1/62.5 is taken for the shutter time twice as
large as 1/125 in a series of 2.sup.n and 1/60 is calculated into the
pulse number, taking 25 .mu.s as standard. In this case, a circuit similar
to that shown in FIG. 4 using the computation counter of five figures and
the shutter time counter of nineteen figures. In case a certain degree of
error is allowed, the count can be made with only 2 - 3 digits in the
upper range of the shutter time counter and in this way, the gate of the
comparison circuit (114) can be made much more simple.
FIGS. 8 and 9 show a further other embodiment of the present invention. The
parts presenting the same effect as those in FIG. 1 are provided the same
numerical figures. In case of the comparison circuit (114) shown in FIG.
8, the computation count (stored in the storage circuit (110)
corresponding to the shutter speed and the count of the shutter time
counter are compared with each other by means of an AND-gate, whereby the
counts for the faster shutter speed are compared one after another so as
to detect the match point and are used to operate the shutter closing
relay through the output matching circuit or the NOR-gate in the present
embodiment. In FIG. 9. a up-down-counter (317) is used computation counter
to which the output of the input converter (102) is led, whereby every
time when the output of the shutter time counter (113) is matched with
each shutter speed one pulse is produced by the AND-gate and used to
reduce the counts through an OR-gate in such a manner that at a certain
predetermined shutter speed the counter (117) becomes empty and produces
an output by means of which the shutter closing relay is operated so as to
obtain a certain predetermined exposure.
As explained above in the exposure computation circuit according to the
present invention, the relations as to the exposure factors of the APEX
system is improved in such a manner that the computation is carried out
using values inversely proportional to the logarithms of all the exposure
factors excepting the diaphragm and by giving the shutter time value (Tv')
or the diaphragm value (Av) as the result of computation relation
proportional to the actual shutter speed value or the actual diaphragm
value the control can be carried out with the actual shutter speed or the
actual diaphragm value. In consequence, in case the computation and the
control are carried out digitally it is possible to convert the input
analog-digitally and compress the input logarithmically so as to reduce
the number of the computation figure, to carry out the computation with
the reduced figure number and to treat the actual time, when enlarging the
computation result into the time, whereby the time can directly obtained
digitally without using the digital-analog conversion. In consequence, it
is possible to realize not only a circuit disposition suitable for the
digital computation but also 2.sup.n series, 2.sup.n series and other
series freely besides the 2.sup.n series. Further, as to the reduction of
the computation time, in case the range of the shutter time is 1/2000 to 8
seconds, at least it takes 8 ms generally even if the compression of
1/1000 is taken into consideration, whereby a frequency more than 2 MHz is
necessary as the upper frequency limit, while according to the present
invention, for example, a frequency of 40 KHz - 80 KHz already suffices as
standard frequency, whereby even if 40 KHz is taken up as standard
frequency and the number of the steps of speed is 30, a time less than 0.8
ms already suffices for carrying out computation. Hereby the more the
frequency is increased the shorter the time needed for computation can be
made. Hereby it is very profitable to be able to choose the combination
freely depending upon other conditions. Thus the exposure computation
circuit according to the present invention offers remarkable effects.
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