Electric shutter control device for use in a still video camera, for example, and a method of controlling same

An electronic shutter control system provided with an imaging device, a driving circuit to drive and control the imaging device and an exposure control circuit to output a signal to the drive circuit. The shutter opens in synchronization with a signal to read out electric charge in a photoelectric converter section to a vertical transfer section. The vertical transfer section is held in a state enabling readout of the signal after cleaning out an unnecessary electric charge. As a result, an electric charge is read out simultaneously with the close of the shutter. According to an electronic shutter controlling method, fast reverse transfer is stopped at a level of the proper exposure less the predetermined amount and an electric charge signal is read out to the vertical transfer section, waiting for the potential of the vertical transfer section to achieve a state wherein it can receive the electric charge signal.

BACKGROUND OF THE INVENTION 
This invention relates to an electronic shutter control device used for a 
still video camera, etc, and a method for controlling the same. 
So-called electronic shutter using a CCD which is a solid imaging device is 
generally used in a still video camera, etc. In a conventional shutter 
driving device in the still video camera, readout of an image signal 
representing an electric charge accumulated in the CCD (hereinafter 
referred to as an electric charge signal) to a vertical transfer section 
is synchronized with the vertical synchronous signal in an image 
processing circuit (for example, refer to "Television Technology", Aug. 
1987, pp. 37-39). 
This is necessary because a vertical transfer section in the CCD is 
provided to receive an electric charge signal from a photoelectric 
converter section in the CCD, the electric charge signal is read out as a 
TV signal and image recording is made at predetermined intervals, i.e., 
fundamentally a movie. 
In this prior art shutter control device, since said reading out of the 
electric charge signal to the vertical transfer section, i.e., the shutter 
closure is synchronized with a video vertical synchronous signal, timing 
of the shutter open timing is restrictedly determined at a timing 
preceding to a desired exposure time from the vertical synchronous timing 
so as to obtain a proper exposure. Additionally, since shutter release is 
made irrespective of the vertical synchronous timing, time irregularity 
may be observed from any release timing to the shutter open timing. 
Moreover, since the exposure time is obtained in advance of the shutter 
release on the basis of the light measurement before the shutter release, 
i.e., the exposure time is not based on the light measurement during the 
exposure, i.e., the real time photometry, incorrect exposure happens to 
occur especially at the flash photographing. 
Thus, the photometrical precision improvement was limited because the real 
time photometry could not be realized in the prior art techniques. 
Another known method consists in driving an electronic shutter 
synchronizing with a release switch (for example, refer to the Japanese 
Laid-Open Patent Publication No. 60-52173), but no consideration to obtain 
shutter open timing anytime, is given. 
SUMMARY OF THE INVENTION 
The present invention intends to overcome said shortcomings of the prior 
art and to provide an electronic shutter control device which permits 
arbitrary electronic shutter open and close independent of the video 
vertical synchronous signal timing so as to perform real time photometry 
during the exposure, and as a consequence, permits improvement in 
photometrical precision, i.e. exposure precision. 
According to the present invention, the shutter open is synchronized with 
the signal to read out electric charge in the photoelectric converter 
section to the vertical transfer section, and the vertical transfer 
section is held in a state enabling readout of the signal after cleaning 
out unnecessary electric charge, so as to read out electric charge 
simultaneously with shutter close. 
Therefore, it is possible to correspond the shutter open with the real 
accumulation beginning of electric charge and to read out the electric 
charge signal to the vertical transfer section with shutter close, and as 
a consequence, the real time photometry becoming possible, proper exposure 
control through high accuracy photometry can be realized. 
A further object of the present invention is to provide an electronic 
shutter controlling method which make possible to improvement in exposure 
precision. 
According to the present invention, electronic shutter controlling method 
comprises, stopping transfer at a level of the proper exposure less the 
predetermined amount, waiting for becoming a state that the potential of 
the vertical transfer section can receive an electric charge signal and 
reading out the electric charge signal to the vertical transfer section. 
Therefore, the electric charge signal accumulated up to an proper level in 
the imaging device can be read out anytime to the vertical transfer 
section, without synchronizing with the vertical synchronous signal, and 
the real time photometry is made possible so as to realize a shutter with 
high accuracy of exposure. Furthermore, an unnecessary electric charge in 
the vertical transfer section being cleaned out during the electric signal 
accumulation period (exposure period), the smear can be lowered. In flash 
photography, as the smear is apt to occur during the flash emission, an 
unnecessary electric charge being always cleaned out, then, the smear can 
be lowered. 
A further object of the present invention is to provide an electronic 
camera with an electronic shutter driving method which makes possible to 
improve in accuracy of exposure and realization of correct exposure 
control for fast shutter. 
According to the present invention, the electronic shutter close timing 
being realized through real time photometry independently from the 
synchronous signal, a high accuracy of exposure can be maintained and 
circuits and others for flashing stop, etc. are not necessary. 
Furthermore, proper exposure control can be achieved even at a high speed 
shutter operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a circuit diagram of a still video camera to which a first 
embodiment of an electronic shutter control device of the present 
invention is implemented in the still video camera. In this figure, a CCD 
1 as an imaging device for photoelectric conversion is a main part of an 
electronic shutter. As shown in FIG. 2, this CCD 1 mainly including a 
photoelectric conversion image section 22 and a storage section 24, is 
controlled by receiving driving pulses FI and FS respectively to the 
vertical transfer CCD 23 of the photoelectric conversion section 22 and to 
the vertical transfer CCD 25 of the storage section 24. Here, a frame 
interline transfer (FIT) type is used for CCD 1. The electronic shutter 
control device shown in FIG. 1 also comprises a vertical transfer CCD 
driver 2 for the photoelectric conversion section 22 and a vertical 
transfer CCD driver 3 for the storage section 24 to drive said CCD 1, a 
synchronous pulse generating circuit 4 for horizontal transfer, and a 
timing control circuit 5 which outputs signals to both vertical transfer 
CCD drivers 2 and 3 in order to control open and closure timings of the 
electronic shutter. 
This timing control circuit 5 is composed of a vertical timing control 
sections 51, 52 and 53 and a TV synchronous pulse generator section 54. 
The vertical timing control section comprises a circuit 51 which generates 
driving pulses FIN (FI1-FI4) to a vertical transfer CCD driver 2 for the 
photoelectric converter section 22, a circuit 52 which generates driving 
pulses FSN (FS1-FS4) to a vertical transfer CCD driver 3 for the storage 
section 24 and a circuit 53 which generates pulses FSAN and FSBN 
(corresponding respectively to a first field and a second field) in order 
to send out the electric charge accumulated in the photoelectric converter 
section 20 to the vertical transfer CCD 23. 
The automatic exposure control circuit 6 measures actual amount of exposure 
from the beginning of exposure and outputs an exposure stop signal to the 
timing control circuit 5 when the predetermined amount of exposure is 
attained. This automatic exposure control circuit 6 comprises a 
photometric element 7 monitoring amount of the exposure, a capacitor 8, a 
switch 9 connected in parallel with the capacitor 8, an operational 
amplifier 10, a comparator 11, a reference voltage source 12, an output 
circuit 13 generating a signal to open and close the electronic shutter, 
in other words, to begin and stop the exposure (called "EXP signal") and a 
timer 14 which determines a timing of flashing start. 
A release switch 15 gives an electronic shutter open command. Timer 16 
counts a power source start-up time in response to turn on of the release 
switch and then sends a START signal to enter sequence for still video 
photography, to circuits 51, 52 generating pulses FIN, FSN and an EXP 
signal output circuit 13. An image processing circuit 17 executes signal 
transfer from CCD 1 at a video rate. An image recording section 18 records 
a processed signal from the circuit 17 to a recording medium such as a 
magnetic disk or others. A flash control circuit 19 executes flash 
emission when the proper exposure value is not attained though the 
predetermined exposure time has passed. 
FIG. 2 shows the configuration of CCD 1 adopted for the present embodiment. 
In the photoelectric converter section 22, a plurality of photodiodes 21 
are arranged in a plural of rows, and a vertical transfer CCD 23 is 
located along each photodiode row. In the storage section 24, a vertical 
transfer CCD 25 is provided corresponding to each vertical transfer CCD 23 
and temporarily stores electric charge signal of the photodiode row read 
out and transferred at a high speed through each vertical transfer CCD 23. 
A clean-out drain 26 is used for cleaning out (draining off, or drawning 
out) unnecessary electric charges in the photoelectric converter section 
22 and the storage section 24 reversely transferred through the vertical 
transfer CCD 23. A horizontal readout CCD 27 transfers the electric charge 
signal stored at the vertical transfer CCD 25 to the image processing 
circuit 17 at a video rate. 
Electronic shutter operations of said configuration will be described in 
detail in connection with time charts of FIGS. 3 to 5 wherein FIGS. 4 and 
5 show enlargements along a time axis of a part of FIG. 3. In these 
figures, time t0, t1 and t2 correspond respectively to ON timings of the 
main switch (not shown), the photometric switch (not shown) and the 
release switch 15. Time t3 shows a generation timing of the first pulse of 
FASN pulse (a) and FSBN pulse (b) for reading out the stored electric 
charge (unnecessary electric charge) in the photoelectric converter 
section 22 and the storage section 24 to the vertical transfer CCD 23 
according to the start signal after release switch 15 is ON, and of a 
first pulse of FIN pulse (c) and FSN pulse (d) executing fast reverse 
transfer of the unnecessary electric charge from the vertical transfer CCD 
23 to the clean out drain 26. As evident from FIG. 4, time t4 corresponds 
to the last pulse generation timing of FSAN pulse (a) and FSBN pulse (b) 
for sending the unnecessary electric charge to the vertical transfer CCD 
23. 
The last pulse of the FSBN pulse (b) is also sent to the EXP signal output 
circuit 13 of the automatic exposure control circuit 6 to synchronously 
generate an EXP signal which in turn begins electric charge accumulation 
at the photoelectric converter section 22. The number of times of the 
unnecessary electric charge clean out should be determined conveniently 
(10 times for example) according to the structure of CCD 1. The exposure 
starts with the timing when an EXP signal shown in FIG. 4 becomes "OPEN". 
This corresponds to "shutter open". In order to obtain real shutter time 
by measuring brightness of an object during exposure, a switch 9 of the 
automatic exposure control circuit 6 is turned off simultaneously with the 
electric charge accumulation beginning so as to start integration of 
photoelectric current of the photometric element 7 to the capacitor 8. On 
the other hand, the last FIN, FSN pulses (c) and (d) are output in order 
to clean out unnecessary electric charge read out by the last FSAN pulse 
(a) and FSBN pulse (b) to the vertical transfer CCD 23. These pulses are 
output as soon as an EXP signal becomes "OPEN". 
Once said unnecessary electric charge is cleaned out through fast reverse 
transfer, the vertical transfer CCD 23 is held at an appropriate potential 
without outputting FIN and FSN pulses. The reason for this potential hold 
is to prepare for immediately reading out an electric charge accumulated 
in the photoelectric converter section 22 to the vertical transfer CCD 23, 
when an exposure stop signal generated when the amount of exposure 
measured by the automatic exposure control circuit 6 attains proper 
exposure to apply an EXP signal "CLOSE" corresponding to shutter close to 
the timing control circuit 5 and thus FSAN and FSBN pulses (a') and (b') 
for electric charge signal reading out are output. In other words, the CCD 
1 is in a state wherein the read out in response to an EXP signal "CLOSE" 
is possible, while accumulating the electric charge signal. As shown in 
FIG. 4, after one unnecessary electric charge clean out, the timing 
control circuit 5 fixes the potential of the generating FI1N-FI4N and 
FS1N-FS4N pulses at predetermined level when an EXP signal "OPEN" is input 
and keeps waiting for input of an EXP signal "CLOSE". This vertical 
transfer control section may be composed, for example, of a shift register 
arranging D flip-flops, and execute CCD 1 timing control upon receiving a 
START signal, an EXP signal and a "readout" signal mentioned later. 
Now, operation of the photodiode 21 and the vertical transfer CCD 23 will 
be described in connection with FIGS. 6 (a) and (b). In FIG. 6(a), 
supposing respective vertical portions V1-V4 of the vertical transfer CCD 
23 to which four-phase driving pulses FI1-FI4 are given, photodiodes 
PD1-PD4 are connected respectively to the portions V1, V3, V1 and V3. The 
vertical transfer CCD 23 is driven in four-phase by 3-value level pulses 
of "LOW", "MIDDLE" and "HIGH". FIG. 6(b) represents the potential of the 
dotted line X portion of FIG. 6(a) and FIG. 6(c) that of the dotted line Y 
portion of FIG. 6(a). As evident from these figures, the stored electric 
charge is read out by setting driving pulses FI1 and FI3 corresponding 
respectively to the portions V1 and V3, at "HIGH". As vertical transfer 
CCD drivers 2 and 3 are of an inversion type, pulses FI1 and FI3 are set 
at "HIGH" through the input of pulses FI1N, FI3N, FSAN and FSBN. 
Immediately before the stored charge readout, pulses FI1N and FI3N are set 
at "LOW" in order to keep pulses FI1 and FI3 at "MIDDLE" so that they can 
be set at "HIGH" anytime. Moreover, the pulse FI2 is set at "LOW" and FI4 
at "MIDDLE" in order to absorb potential variation during readout and to 
avoid undesirable mixing of read out electric charge. For this purpose, 
the pulse FI2N is kept at "HIGH" and FI4N at "LOW". In this way, 
potentials of pulses FI1N-FI4N are set at "LOW", "HIGH", "LOW" and "LOW", 
that is to say, in read out possible state. On the other hand, pulses 
FS1N-FS4N are in the state to be matched with said FI1N-FI4N. 
After starting exposure by shutter open, if proper exposure is not attained 
at the end of the predetermined time or is expected to be not attained, 
flashing is executed as shown in FIG. 3 by sending a flashing start signal 
to the flash control circuit 19. This flash emitting is necessary to 
restrict the exposure time within the predetermined period of time because 
too long exposure may increase an undesirable dark current due to the 
structure of CCD 1. Here, flashing start timing can be obtained through 
operation of a microcomputer (not shown) based on pre-photometric data 
measured in response to turn on of the photometry switch S1 before the 
release switch 15 is ON, and flash boosting for flashing, i.e., flash 
power supply should de done beforehand as shown in FIG. 3. 
The time t5 is a timing of which an exposure stop signal corresponding to 
shutter close, i.e. EXP signal "CLOSE" is outputted from the EXP signal 
output circuit 13. Upon receiving EXP signal "CLOSE", FSAN pulse (a') and 
FSBN pulse (b') are outputted, then, the stored signal electric charge in 
the photoelectric converter section 22 is readout to the vertical transfer 
CCD 23. And furthermore, fast transfer to the vertical transfer CCD 25 of 
the storage section 24 is executed through FIN pulse (e) and FSN pulse 
(f). At that time, a signal read out from the CCD 1 to outside is 
inhibited. On the other hand, said EXP signal "CLOSE" can not be sent 
during the fast reverse transfer of said unnecessary electric charge to 
the clean out drain 26. As a consequence, this fast reverse transfer time 
corresponds to the shortest shutter speed. Though a flashing stop signal 
is output at the same time as said EXP signal "CLOSE" in the present 
embodiment, the flash may be fully emitted by omitting stop operation of 
emitting. 
The time t6 represents timing when a signal readout output "readout" 
indicative of completion of readout is given to the timing control circuit 
5 from the microcomputer (not shown) after a time necessary to complete 
transfer of the stored signal electric charge to the storage section 24. 
Before said "readout" signal is given, the timing control circuit 5 which 
drives and controls the CCD 1 is operated independently of the vertical 
and horizontal synchronous signals generated from the synchronous pulse 
generating section 54 for the video processing circuit 17 and the image 
recording section 18. While once the "readout" output is given, the timing 
control circuit 5 is operated synchronously with a TV synchronous signal 
to read out a signal to outside. That is to say, as shown in FIG. 5, FSN 
pulse (g) is output at the time t7-t8 after waiting for a vertical 
synchronous signal, electric charge signal is read out sequentially from 
the vertical transfer CCD 25 of the storage section 24 to the horizontal 
readout CCD 27 synchronizing at a video rate and then recorded in the 
image recording section 18 through the video processing circuit 17. In 
FIG. 3, this recording operation is represented as writing to a floppy 
disk. Here, the disk is driven by a spindle motor started to rotate by 
turning on the photometry switch S1. 
On the other hand, each pulse phase of FS1N-FS4N being deviated slightly, 
image data of one scanning line is obtained by a set of FS1N-FS4N pulses 
continuous in time and image data of one screen is composed of readout 
data of the time t7-t8. Moreover, fast reverse transfer of electric charge 
to the clean out drain 26 and fast transfer of electric charge to the 
vertical transfer CCD 25 of the storage section 24, can be switched over 
by phase deviation of each pulse of four phases of FIN and FSN. 
FIG. 7 shows another block diagram of a still video camera to which a 
second embodiment of the present invention is applied. In this figure, the 
electronic shutter is composed of a CCD 1 as an imaging device for 
photoelectric conversion, a vertical transfer timing control circuit 5 
generating vertical transfer and horizontal transfer pulses respectively 
in order to drive and control the CCD 1, vertical transfer CCD drivers 2 
and 3 and a horizontal transfer timing control circuit 4. The vertical 
transfer timing control circuit 5 comprises circuit sections for 
generating respectively four-phase pulses .phi.VN (hereinafter called 
.phi.VN) with a phase deviated each other, for driving (fast reverse 
transfer of unnecessary electric charge to clean out drain and fast 
transfer of signal electric charge to storage section) the vertical 
transfer CCDs 23 and 25 shown in FIG. 2, a pulse FSPN (hereinafter called 
FSPN) for transferring an electric charge of the photoelectric converter 
section 22 to the vertical transfer CCD 23, a signal EXP1 (hereinafter 
called EXP1) for giving a charge accumulation start to the CCD 1, in other 
words, giving shutter open timing and a vertical synchronous pulse 
V.sub.SYNC for .phi.VN. Vertical transfer CCD drivers 2 and 3 supply 
.phi.V and FSP to the CCD 1 according to .phi.VN and FSPN while the 
horizontal transfer timing control circuit 4 outputs pulses .phi.H which 
drive the horizontal readout CCD 27. An EXP1 signal becomes "HIGH" by ON 
signal of the release switch 15 and "LOW" by being synchronized with the 
predetermined FSPN. 
The photometry section 60 having a function to execute pre-photometry 
before exposure onto the CCD 1 and to execute real time photometry during 
exposure, is switched over from pre-photometry to real time photometry at 
a timing when the EXP1 signal is changed from "HIGH" to "LOW" as later 
mentioned and then outputs a signal EXP2 (hereinafter called EXP2) giving 
the timing to stop the fast reverse transfer of unnecessary electric 
charge to the clean out drain. As shown in the figure, this photometry 
section 60 is composed of a pre-photometry section, a real time 
photometric section, an operational amplifier 64 and a comparator 65. And 
the pre-photometry section comprises a pre-photometric element D1, an 
operational amplifier 61, resistors R, a correction voltage source 62, a 
photometry switch S1 and a capacitor C1. The real time photometry section 
comprises a real time photometric element D2, an operation amplifier 63, a 
capacitor C2, and a switch S2. 
The flash control circuit 19 controls flash by receiving EXP2 signal and a 
signal outputted from the timer 14 to which the EXP1 is inputted. The 
video processing circuit 17 receives a signal electric charge which is 
read out from the horizontal readout CCD 27 of the CCD 1, and converts it 
into a signal for image-recording on the image recording section 18 such 
as a magnetic floppy disk. The power supply section 100 provides each part 
of the circuit with power by receiving ON signal from the release switch 
15. 
Now the operation of the electronic shutter of the configuration will be 
described in connection with time chart of FIG. 8. 
(1) Unnecessary electric charge clean-out period 
When the release switch 15 is turned on, each part of the circuit is 
supplied with power and FSPN and .phi.VN are given to the drivers 2 and 3 
so as to drive the CCD 1. In other words, by the FSPN, unnecessary 
electric charge stored in the CCD 1 is transferred to the vertical 
transfer CCD 23 and fast reverse-transfer to the clean-out drain is 
executed by .phi.VN. Clean-out by .phi.VN is repeated several times (n 
times) in order to prevent any remaining unnecessary electric charge. At 
this time, EXP1 is at "HIGH" and the switches S1 and S2 are in ON state. 
(2) Signal electric charge accumulation period 
EXP1 is switched from "HIGH" to "LOW" synchronously with the n-th FSPN and 
unnecessary electric charge is transferred to the vertical transfer CCD 23 
with .phi.VN in order to start accumulation of signal electric charge 
(shutter open). Unnecessary electric charge transferred to the vertical 
transfer CCD 23 is cleaned out through fast reverse transfer to the 
clean-out drain 26. At this time, the fast transfer is continued so as to 
clean out as much smear component (unnecessary electric charge) generated 
in vertical transfer CCD 23, as possible. By the way, the potential at the 
vertical transfer CCD 23 should be ready to be able to receive electric 
charge in order to read out the stored signal electric charge to the 
vertical transfer CCD 23. Now, suppose the time required from the fast 
reverse transfer stop to the state enabling read out of a signal electric 
charge to the vertical transfer CCD, is T (constant). Even if it is 
commanded to read out the signal electric charge to the vertical CCD when 
proper exposure is realized through real time photometry from shutter 
open, electric charge storage will continue during the time T, resulting 
in overexposure of this much from the proper exposure value. However, 
since the brightness of the object is known by the real time photometry, 
the amount of over-exposure during the time T can be determined. Then, if 
the reverse transfer stop command is given at a lower level by said 
exposure during T, the readout signal can be proper exposure because the 
readout of signal electric charge to the vertical transfer CCD will be 
executed time T later. Although the switches S1 and S2 are turned off by 
the timing at which said EXP1 is changed from "HIGH" to "LOW", by 
measuring brightness of the object in advance of turn off these switches 
by a pre-photometric element D1, a lower voltage than proper exposure 
level by the exposure which may be obtained during time T is generated 
through the correction voltage source 62 and held in the capacitor C1. On 
the other hand, the real time photometry by the real time photometry 
element D2 and the capacitor C2, starts with the release switch 15 ON at 
the same time as the electric charge accumulation starts. When integration 
of the real time photometric value reaches a level held in the capacitor 
C1, i.e., a lower level than proper exposure level by the exposure which 
may be obtained during the time T, the output from the comparator 65, that 
is EXP2, is changed from "HIGH" to "LOW". This EXP2 signal stops the fast 
reverse transfer, generates FSPN after the time T and transfers the signal 
electric charge to the vertical transfer CCD 23 (shutter close). 
(3) Standby period after fast transfer to storage section 
A signal electric charge transferred to the vertical transfer CCD 23 is 
fast transferred to the storage section 24 by .phi.VN, and the storage 
section 24 waits for the vertical synchronous signal V.sub.SYNC being 
inputted. 
(4) Signal processing and recording period 
After V.sub.SYNC input, a signal electric charge is read out from the 
horizontal readout CCD 27 of the CCD 1 to the image processing circuit 17 
synchronously with a TV synchronous signal, converted into a signal for 
image-recording and recorded in the recording section 18. 
Now, the shortest shutter speed will be described. 
Unnecessary electric charge is transferred to the vertical transfer CCD 23 
when EXP1 is switched from "HIGH" to "LOW", but signal electric charge to 
be image-recorded can not be transferred to the vertical transfer CCD 23 
until the complete end of the unnecessary electric charge clean-out. 
Therefore, if one single clean-out needs time Tr, the shortest shutter 
speed will be Tr+T. If EXP2 is switched from "HIGH" to "LOW" during the 
time Tr, Tr+T will automatically be the shortest shutter speed. 
Now, cases when a flash is used, will be described. A flash is allowed to 
emit with time Tr delayed from timing of "HIGH" to "LOW" of EXP1. This is 
for preventing EXP2 from changing from "HIGH" to "LOW" during the time Tr. 
On the other hand, flash emitting is made stop with the timing of EXP2 
changing from "HIGH" to "LOW". 
FIG. 9 is a configuration of a third embodiment. 
This embodiment is different from the second embodiment, in the 
configuration of the photometry section 60 and the photometric timing 
operation. The photometry section 60 is composed of a photometric element 
D0, an operational amplifier 66, a voltage source E corresponding to the 
proper exposure level, a switch S0 turning on and off to connect or 
disconnect the voltage source E by the signal EXP0, a capacitor C0 charged 
by the voltage source E, a transistor Q discharging the electric charge of 
the capacitor C0 according to the output of the operational amplifier 66, 
and a comparator 65 operated by the voltage of the capacitor C0 and 
outputting EXP2. In the second embodiment, the fast reverse transfer is 
stopped at a lower exposure level than the proper exposure level by an 
exposure level during the time T, whereas in this embodiment, integration 
of the real time photometry value starts earlier by time T than the 
beginning of electric charge accumulation in the CCD and the fast reverse 
transfer stops when the proper exposure is attained by photometry. In this 
case, as the electric charge accumulation to the CCD starts later by time 
T than the photometry beginning, when the fast reverse transfer stops, the 
exposure lacks by the amount corresponding to the time T, but when the 
actual signal electric charge accumulation is completed, the proper 
exposure will be realized, as the actual accumulation completes later by 
time T than EXP2 changeover from "HIGH" to "LOW". 
The operation of the photometry section 60 of the electronic shutter of 
this embodiment will be described in connection with the time chart of 
FIG. 10. 
(1) Unnecessary electric charge clean-out period 
When the release switch 15 is turned on, EXP0 changes from "LOW" to "HIGH" 
and the switch S0 turns on. In this condition, the capacitor C0 is charged 
with the voltage source E corresponding to the proper exposure level. By 
changing EXP0 from "HIGH" to "LOW" earlier by time T than the beginning of 
the signal electric charge accumulation with the timing of EXP1 changeover 
from "HIGH" to "LOW" by n-th FSPN, switch S0 is switched off, and thus the 
photometry is started. During the photometry, the electric charge of the 
capacitor C0 is discharged through the transistor Q according to the light 
received by the element D0. 
(2) Signal electric charge accumulation period 
EXP1 changes from "HIGH" to "LOW" at a timing of n-th FSPN, i.e., later by 
time T than the timing of EXP0 changeover from "HIGH" to "LOW", to start 
electric charge accumulation in the CCD 1 (shutter open). When the 
capacitor C0 has been completely discharged, EXP2 changes from "HIGH" to 
"LOW" to stop the fast reverse transfer which cleans out the unnecessary 
electric charge of the CCD 1 by .phi.VN. Thereafter, the CCD 1 continues 
to accumulate the signal electric charge during the time T and transfers 
the electric charge to the vertical transfer CCD 23 by FSPN (shutter 
close). The description of the subsequent operations is omitted because 
they are the same as mentioned before. Referring to said operation, the 
relation between the photometric element D0 and exposure of CCD 1 will be 
explained as below. Only the photometric element D0 receive light during 
the time T from EXP0 "HIGH" to "LOW" switching, to EXP1 "HIGH" to "LOW" 
switching (shutter open), whereas only the CCD 1 receive light during the 
time T from EXP2 "HIGH" to "LOW" switching, to FSPN (shutter close). 
Exposures during said both periods should, therefore, be equal. For this 
purpose, flash is controlled to emit between EXP1 "HIGH" to "LOW" 
switching and EXP2 "HIGH" to "LOW" switching. 
In these embodiments shown respectively in FIGS. 7 and 9, the charge 
accumulation time is controlled by the received light amount of 
photometric element other than the CCD 1 during the electric charge 
accumulation in the CCD 1, but it may also be controlled by calculating 
the proper exposure time according to the received light before the 
accumulation starts. In this case, the proper exposure time 2.sup.-Tv 
based on the received light signal of the photometric section 22 (here, Tv 
is an APEX value of exposure time, i.e., accumulation time) is calculated 
in advance of the charge accumulation start and a charge accumulation stop 
signal is output after the time 2.sup.-Tv has passed. Moreover, in flash 
photography, flashing start timing is determined such that full emission 
has completed at the passage of time 2.sup.-Tv, and the flashing stop 
signal is outputted when the amount of received light, reflected by the 
object and receive and integrated by a photometric element other than the 
CCD 1, reaches the predetermined level. 
FIG. 11 shows the configuration of a photometric section wherein such 
modification is implemented. This photometry section comprises a spot 
photometry section 71 measuring the brightness B.sub.vs of an object 
located at the center of the picture, a peripheral photometry section 72 
measuring the brightness B.sub.va of peripheral object, an exposure 
calculation section 73 receiving respective photometric values B.sub.vs 
and B.sub.va, a timer I receiving calculated output from the exposure 
calculation section 73 and EXP1 and outputting EXP2, a timer II receiving 
the calculated output and EXP1, a photometric section 74 controlling flash 
emitting, etc. This photometric section 74 is composed of a photometric 
element 75, a capacitor 76, a switch 77, an operation amplifier 78 and a 
comparator section 79. Here, AND output of a flash enable (EN) signal from 
the exposure calculation section 73 and signal from the timer II permits 
to start flash emission and to turn off the switch 77 which in turn starts 
charging the capacitor 77. Moreover, a flashing stop signal of flash 
emitting is outputted by comparing the output from the operation amplifier 
78 with the D/A converted output from the exposure calculation section 73 
by the comparator 79. 
The flow chart of FIG. 12 shows the operation procedure in the exposure 
calculation section 73. This operation proceeds as follows. First, the 
difference .alpha. [APEX value] between the spot brightness Bvs and the 
peripheral brightness Bva is determined (#1), and if .alpha. is smaller 
than 2 (in this case, object is in a normal light state), the program 
proceeds to #3, and if .alpha. is not less than 2 (in this case, object is 
in a back-light state) the program proceeds to #14. For front light, a 
mean value is calculated from Bvs and Bva (#3) and taking this mean value 
as Bvc, the exposure time Tv [APEX value] is calculated by Bvc+Svc-Avc, 
where Svc represents a CCD sensitivity and Avc represents an aperture 
value of photographing optical system [both APEX values]. Then, Tv and 
camera-shake limit time Tvh are compared and if Tv is smaller than Tvh, 
the program proceeds to low brightness front light processing starting 
from #6 to #10 and if Tv is not smaller than Tvh, high brightness front 
light processing starting from #17 to #13 will be executed. As for low 
brightness front light mode, proper exposure is realized by using the Tvh 
as exposure time control value Tvc (#6) and then enables the flash 
emission (#7). Then, 2.sup.-Tvc -T is set to the timer I which determines 
shutter close EXP2 (#8) and 2.sup.-Tvc -T-Tf (where Tf is a full emission 
time of flash) is set to the timer II which determines flash emission 
start timing (#9). CCD sensitivity Svc is outputted (#10) to a D/A 
conversion section which output is applied to the comparator 79 for 
outputting the flashing stop signal. In the high brightness front light 
mode, exposure time is controlled by Tv value based on the mean 
photometric value calculated in #4 (#11), the flash is set non emitting 
(#12) and 2.sup.Tvc -T is set in the timer I (#13). 
In back-light mode, Bva+Svc-Avc-1 is taken as Tv to control the time so 
that exposure onto the peripheral becomes 1 Ev over-exposure (#14). Then, 
Tv is limited by camera-shake limit time Tvh (#15 to #17) and flash 
emitting is enabled (#18). Moreover, the timers I and II are set as in 
said #8 and #9 (#19 and #20), Tvc+Avc-Svc-Bvs as corrected value .beta. is 
obtained (#21) and D/A conversion output of Svc+.beta. is obtained (#22) 
is given to the comparator 79 as mentioned before. The amount of flash 
emission, therefore, is controlled as much as the object located at the 
center will have an appropriate exposure, taking the central brightness 
Bvs into consideration. 
FIG. 13 shows the configuration of a fourth embodiment of an electronic 
camera with the electronic shutter according to the present invention. 
This embodiment is different from the first embodiment in that a timer 14b 
is provided in the automatic exposure control circuit 6. A field shift 
pulse FSP which is input to a EXP signal output circuit 13 is the last 
pulse of the FSBN pulse (b). 
The timer 14b counting the fastest shutter speed or the shortest exposure 
time, starts counting when an EXP signal changes from "HIGH" to "LOW" and 
outputs a "LOW" exposure stop inhibiting signal until the counting is 
completed. During this counting period, exposure will not be stopped even 
if the photometric circuit 6a generates an exposure stop signal EXP-STOP, 
and transfer of the electric charge being accumulated in the CCD 1 to the 
vertical transfer CCD 23 is inhibited. 
FIG. 14 shows a detailed circuit diagram of the EXP signal generating 
circuit 13. The circuit 13 receives a field shift pulse FSP, a release 
start signal START, an initialization signal INIT, an exposure stop signal 
EXP-STOP output from the photometric circuit 6a and an exposure stop 
inhibition signal output from the timer 14b, and outputs an exposure 
signal EXP. A counter 13a counts the time Tr necessary to clean out CCD 
unnecessary electric charge. After the START signal, the circuit 13 sets 
an exposure signal EXP at "LOW" synchronously with FSP after a certain 
time passage counted by said counter 13a, and thereafter, sets EXP at 
"HIGH" through the input of EXP-STOP signal with the exposure stop 
inhibition signal at "HIGH". 
Now, the operation of the fourth embodiment will be described referring to 
FIG. 15. When a release button (not shown) is depressed, the photometry 
starts upon turn on of the photometric switch (not shown), the timer 16 
starts counting upon turn on of the release switch 15 to output the START 
signal after the power supply start-up time (state I) to the timing 
control circuit 5 and the AE control circuit 6. Receiving this START 
signal, the timing control circuit 5 enters a repeating state of fast 
reverse transfer (FI, FS) and field shift (FSP), that is to say, 
unnecessary electric charge clean-out state (state II). As for the AE 
control circuit 6, receiving the START signal, the EXP signal generating 
circuit 13 counts the time from generation of the START signal and, after 
a sufficient period of time Tr to clean out unnecessary electric charge, 
sets an exposure signal EXP at "LOW" synchronizing with the FSP signal, 
and the photometry circuit 6a starts photometric integration. The timing 
control circuit 5 shifts to the state III when the exposure signal EXP is 
set at "LOW", executes a single fast reverse transfer, then enters an 
exposure stop wait state. Now, the flash control circuit 19 emits the 
flash after passage of a certain period of time from EXP changed to "LOW". 
As for the flash, flash emission is inhibited if the exposure time is 
shorter than the flash emitting start timing. On the other hand, the 
photometry circuit 6a outputs an EXP-STOP signal when photometric 
integration is completed. Operations of the EXP signal generating circuit 
13 relating to the EXP-STOP signal are different depending on output 
timing of the EXP-STOP signal as described below. 
(a) When EXP-STOP signal is output after the end of the fast reverse 
transfer; 
Receiving EXP-STOP signal, the EXP signal generating circuit 13 sets the 
EXP at "HIGH" to stop the electric charge accumulation in the CCD 1. 
(b) When EXP-STOP signal is output during the fast reverse transfer; 
During the fast reverse transfer, the exposure stop inhibition signal 
output from the timer 14b being set at "LOW", the EXP does not shift to 
"HIGH" even if the EXP-STOP signal is outputted, whereas after the fast 
reverse transfer completion, when the exposure stop inhibition signal 
becomes "HIGH", the EXP becomes "HIGH" to stop the electric charge 
accumulation of the CCD 1. 
In this way, even if the object brightness is high and the exposure time is 
shorter than the fast reverse transfer time, exposure control can be 
realized though slight overexposure compared to the proper exposure level 
may occur. As for the timing control circuit 5, when the EXP shifts to 
"H", the circuit 53 (hereinafter referred to a field shift pulse 
generating circuit 53) outputs a field shift pulse FSP and enters the 
state IV, and then, the vertical transfer pulse generating circuit 52 
generates the pulse which permits fast transfer of signal electric charge 
from image section of the CCD 1 to the storage section. Thereafter, signal 
electric charge of the CCD 1 is read out synchronously with a TV 
synchronous signal generated separately, processed in the video processing 
circuit 17 so as to be recordable and then recorded in the recording 
section 18. 
Now, a fifth embodiment will be described referring to FIG. 16. This 
embodiment is different from the fourth embodiment in that it does not use 
the timer 14b used in the previous one and that the timing control circuit 
5 comprises a shutter close timing generating circuit 55. An example of 
the circuit 55 is shown in FIG. 17. The shutter close timing generating 
circuit 55 receives a reverse transfer end signal RTF END, a clock signal 
CK2, an initialization signal INIT and an exposure signal EXP, and outputs 
a signal FS ON which controls a field shift pulse. In other words, the 
circuit 55 stores an EXP signal switching from "LOW" to "HIGH", i.e., 
shutter close signal which is output from the AE control circuit 6, then 
receives a reverse transfer end signal RTF END ("LOW" to "HIGH") from the 
vertical transfer pulse generating circuit 52 and commands output of a 
field shift pulse corresponding to shutter close, to the field shift pulse 
generating circuit 53. 
As for the operation of the present embodiment, as is the case of the 
fourth embodiment, the state shifts to III through I and II of the time 
chart in FIG. 15 and to the exposure stop wait state, and the EXP signal 
generating circuit 13 sets an EXP signal at "HIGH" receiving an EXP-STOP 
signal from the photometric circuit 6a to stop the electric charge 
accumulation of the CCD 1. 
Here, the operation of the EXP signal generating circuit 13 is different 
depending on the timing at which an EXP signal shifts to "HIGH". 
(a) When EXP signal is shifted to "HIGH" after the completion of fast 
reverse transfer; 
The shutter close timing generating circuit 55 sends a field shift pulse 
output command to the field pulse generating circuit 53 when the EXP 
signal shifts to "HIGH". With this command, the circuit 53 outputs a field 
shift pulse, and thereafter, the vertical transfer pulse generating 
circuit 52 fast transfers signal electric charge from the CCD 1 image 
section to the storage section. 
(b) When EXP signal is shifted to "HIGH" during the fast reverse transfer; 
The EXP signal having shifted to "HIGH", the shutter close timing 
generating circuit 55 stands by until the fast reverse transfer end pulse 
is input. After being inputted of the fast reverse transfer end pulse, the 
output command of said pulse is sent to the field shift pulse generating 
circuit 53. When this pulse is input, the circuit 53 outputs a field shift 
pulse, and thereafter, the vertical transfer pulse generating circuit 52 
outputs pulses for fast transferring the signal electric charge from the 
CCD 1 image section to the storage section. In this way, as 
aforementioned, even if the object brightness is high and the exposure 
time is shorter than the fast reverse transfer time, exposure control can 
be realized though slight overexposure compared to the appropriate one may 
occur. In both cases, thereafter, signal electric charge is read out 
synchronously with a TV synchronous signal generated independently, 
processed as necessary for recording in the video processing circuit 17, 
and then recorded in the recording section 18. 
Further, a sixth embodiment will be described referring to FIG. 18. This 
embodiment is similar to the abovementioned second embodiment shown in 
FIG. 7. However, this embodiment is so modified that a timer 69 and switch 
69' are provided in a photometry section 60. The switch 69' is interposed 
on an outline of a comparator 65, and driven by an output of the timer 69. 
The timer 69 is for counting shortest exposure time, commences the count 
operation with an input of EXP1, and forbids outputting EXP2 signal until 
the timer 69 terminates the count operation. 
Also, in this embodiment, as like the abovementioned embodiment shown in 
FIG. 16, even if an exposure time is shorter than the fast reverse 
transfer time, correct exposure control can be realized.