Flash photography system and electronic flash device for use in the system

A flash photography system includes an electronic flash device capable of light measurement for automatic flash light control and a camera capable of automatic shutter speed control at a daylight photography mode and at a flash photography mode. The flash device generates a flash readiness signal and a flash light control termination signal at a common terminal for the transmission of these signals to the camera through a corresponding common terminal, wherein these signals cause the camera to effect the automatic shutter speed control at the flash photography mode. The camera generates an interrupting signal at the corresponding terminal in response to a camera release operation and the electronic flash device interrupts the generation of the flash light control termination signal in response to the interrupting signal. In indicator which makes an indication in response to the flash readiness signal and the flash light control termination signal respectively is also provided in the camera.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a flash photography system and an 
electronic flash device for use in the system which transmits a flash 
readiness signal and a flash light control termination signal from the 
electronic flash device to a camera and switches the camera photography 
mode and/or its indication in accordance with the signals. 
2. Description of the Prior Art 
A Japanese Laid-Open Patent Application No. Sho 54-24625 discloses a flash 
photography system wherein an electronic flash device generates a flash 
readiness signal upon detecting that its main capacitor is fully charged, 
i.e., that it is ready to fire and when the flash readiness signal is 
transmitted to a camera, the camera is automatically switched to a flash 
photography mode which controls the shutter at a shutter speed tuned to 
the flash of the electronic flash device and, at the same time, an 
indication of the camera being switched to the flash photography mode is 
given in the camera viewfinder. That flash photography system also 
transmits a flash light control termination signal from the electronic 
flash device, upon termination of automatic flash light control, to the 
camera and indicates, in response to the signal, the flash light control 
termination in the camera viewfinder. In the system, both the flash 
readiness signal and the flash light control termination signal are 
transmitted from the electronic flash device to the camera through the 
separate terminals. However, providing the separate terminals between the 
electronic flash device and the camera for transmission of the two signals 
is not desirable in that it increases not only cost but also the frequency 
of terminal contact failure. Therefore, a desirable system is that it 
usually transmits a flash readiness signal from an electronic flash device 
to a camera through one terminal and transmits a flash light control 
termination signal through the same terminal for a predetermined period of 
time only upon termination of automatic flash light control so that 
re-transmission of the flash readiness signal is possible after the lapse 
of the predetermined period. Thus it reduces the number of terminals 
between the electronic flash device and the camera. However, such a system 
poses a new problem. That is, only the flash light control termination 
signal is transmitted during the predetermined period of time upon 
termination of automatic flash light control by the electronic flash 
device, making it impossible for the camera to judge whether the main 
capacitor of the electronic flash device is fully charged, i.e., whether 
the electronic flash device is ready to fire. In other words, since the 
same terminal is used for transmission of the two signals, the camera 
cannot identify a signal appearing at the terminal even if it is a flash 
light control termination signal and judges instead that the electronic 
flash device is ready to fire. Therefore, in case another shooting is 
performed for repeated photography in short cycles during the 
predetermined period of time when a flash light control termination signal 
is transmitted, the camera misjudges that the electronic flash device is 
ready to fire before it is so and actuates switching to the flash 
photography mode. The result is an underexposed picture. 
U.S. Pat. No. 4,349,260 discloses a flash photography system which 
eliminates the drawbacks of the above prior art system by use of a common 
terminal for the transmission of the flash readiness signal and the flash 
light control termination signal and a circuit for interrupting the 
generation of the flash light control termination signal in response to a 
camera release operation. This proposed system, however, employs a 
dedicated electronic flash device having no light receiving element for 
the flash light control, thereby necessitating a stop signal transmission 
from a camera to the flash device. In other words, the flash device is 
useful only for a camera capable of light measurement during an exposure 
operation and having an additional terminal for transmission of the stop 
signal for automatic flash light control. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the present invention to provide a flash 
photography system of the above described type which reduces the number of 
signal transmission terminals and which does not require a camera capable 
of light measurement during an exposure operation. 
Another object of the present invention is to provide an electronic flash 
device for use in the flash photography system. 
To accomplish these objects, an electronic flash device for use in the 
flash photography system of the present invention includes a light 
receiving means which receives a light reflected from an object or a 
scene, an automatic flash light control means which generates a stop 
signal for stopping firing of a flash tube when integration of the light 
received by the light receiving means reaches a predetermined level, a 
detection means which generates a detection signal when a main capacitor 
is charged to a predetermined level, i.e., when the flash device is ready 
for flash photography, a flash readiness signal generating means for 
generating a flash readiness signal in response to the detection signal, a 
flash light control termination signal generating means for generating a 
flash light control termination signal in response to the stop signal and 
a terminal for common transmission of the flash readines signal and the 
flash light control termination signal. On the other hand, a camera for 
use in the flash photography system includes a terminal connectable to the 
terminal of the flash device and an automatic exposure control means 
capable of automatic shutter speed control at a daylight photography mode 
and at a flash photography mode and/or an indication means capable of 
making an indication. The flash readiness signal and the flash light 
control termination signal cause the automatic exposure control means to 
effect the automatic shutter speed control in the flash photography mode 
respectively and/or causes the indication means to make an indication. 
Additionally, the camera further includes an interrupting signal 
generating means for generating an interrupting signal at the terminal of 
the camera in response to a camera release operation and the flash device 
further includes a control means for causing the flash light control 
termination signal generating means to interrupt the generation of the 
flash light control termination signal in response to the interrupting 
signal transmitted to the terminal of the flash device. 
According to the flash photography system of the present invention, the 
common use of the terminal reduces the number of terminals to be provided 
on the camera and the flash device, and the camera is not required to have 
a light measurement capability during an exposure operation because the 
light receiving means is included in the flash device. 
The above and other objects and features of the present invention will 
become more apparent from the following description of a preferred 
embodiment of the present invention taken in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 2, which shows a camera circuit in an embodiment of the present 
invention, includes synchronization terminals (X terminals) J1 and J2, 
synchronous switch 87 and terminal J3 which receives the flash readiness 
signal and the flash light control termination signal from an electronic 
flash device shown in FIG. 1. When the potential at terminal J3 is below 1 
V, transistor 84 is OFF and the camera operates in the daylight 
photography mode. The flash readiness signal and the flash light control 
termination signal both input to terminal J3 are voltage signals which 
fluctuate between the levels of about 1 V and 2 V and differ only in 
frequency. Therefore, with these signals at terminal J3, transistors 81 
and 84 are ON, and the camera operates in the flash photography mode. 
Provided inside the camera viewfinder is indicator 99 which flickers at 
different frequencies in response to the two kinds of signals and 
indicates the flash readiness and the flash light control termination. The 
flash light control termination signal appears for about 2 seconds upon 
termination of automatic flash light control. The camera should be set to 
the daylight photography mode at X intervals during which the main 
capacitor of an electronic flash device is being charged. When the second 
shooting is performed at the timing of T2 with a flash readiness signal 
after the first shooting, normal flash photography is possible. Assuming 
that the shutter is then released at the timing of T3 with a flash light 
control termination signal, a voltage between 1 V and 2 V is applied to 
terminal J3 which turns transistor 84 ON, causing the camera to operate in 
the flash photography mode in the same manner as when a flash readiness 
signal is applied to terminal J3. Therefore, according to the present 
invention, switch 89 is turned ON in response to the shutter release 
operation to trigger one shot circuit 90 for reverse transmission of an 
interrupting signal to the electronic flash device through terminal J3 to 
thereby stop the occurrence of a flash light control termination signal. 
In other words, the remaining portion of a flash light control termination 
signal shown by a dotted line in FIG. 3 is eliminated at the timing of T3 
so that the camera is operated in the daylight photography mode. 
With reference to FIG. 1, description will now be given of an electronic 
flash device circuit in accordance with an embodiment of the present 
invention, wherein power battery 1 is connected to well-known booster 
circuit A when power switch 2 is closed. The high voltage generated by the 
booster circuit operation is applied through rectifier diode 12 to main 
capacitor 13 which is thus charged. Resistors 14 and 15, constant-voltage 
power supply 16 and comparator 17 together constitute flash readiness 
detection circuit D. When the charged voltage at main capacitor 13 exceeds 
a predetermined value, the output of comparator 17 is inverted from its L 
to H level. Resistor 20, capacitor 21, transformer 22 and SCR 19 together 
form trigger circuit B for triggering xenon flash tube 23. When the output 
of AND gate 18 becomes an H level, trigger circuit B operates to actuate 
xenon flash tube 23. Resistors 28, 30 and 32, capacitor 29 and SCR 31 
constitute flash-stop circuit E which stops the operation of xenon flash 
tube 23. Phototransistor 35, capacitor 36, constant-voltage power supply 
37 and comparator 38 constitute automatic flash light control circuit C. 
When the voltage at the positive terminal of capacitor 36 charged with the 
photocurrent of phototransistor 35 which receives the reflected light from 
an object or scene, reaches a predetermined level given by 
constant-voltage power supply 37, the output of comparator 38 is inverted 
to an H level. Flashstop circuit E of the electronic flash device operates 
with the inverted output of comparator 38 to thereby stop the flash firing 
of the electronic flash device. The level given by constant voltage power 
supply 37 is manually set in accordance with the film speed of the used 
film and an aperture value set on the side of the camera. 
Changeover switch circuit 43 is connected to constant-voltage power supply 
44 for generating the 1 V level output and constant-voltage power supply 
45 for generating the 2 V level output. When the output of OR gate 46 is 
at the H level, the output voltage of constant-voltage power supply 44 is 
generated from changeover switch circuit 43. When the output of OR gate 46 
is at the L level, the output voltage of constant-voltage power supply 45 
is generated from changeover switch circuit 43. On shot circuit 40 is 
triggered when input terminal J2 is short-circuited to ground to generate 
the H level one shot pulse at the time duration of approximately 10 m Sec. 
Transistor 50 is turned ON with the output of OR gate 57 becoming an H 
level when no voltage above the 1 V level is output at terminal J3, 
thereby short-circuiting terminal J3 to ground. Resistors 52 and 54, 
transistor 53, inverter 55 and AND gate 56 together constitute a detection 
circuit which detects that terminal J3 is short-circuited from the camera. 
When terminal J3 is short-circuited from the camera while transistor 50 is 
turned OFF to output the voltage above the 1 V level from terminal J3, the 
output of AND gate 56 becomes an H level, whereby one shot circuit 62 is 
triggered to output a one shot H level pulse for a predetermined period of 
time. This pulse time duration is set to that from the shutter release 
operation to the full shutter aperture and is normally 10 m Sec. One shot 
circuit 61 is triggered upon termination of automatic flash light control 
by the electronic flash device to output the one shot pulse voltage of an 
H level for about 2 seconds. 
When the charged voltage of main capacitor 13 exceeds a predetermined level 
after power switch 2 has been closed, the output of comparator 17 is 
inverted to an H level, and the outputs of AND gate 47 and OR gate repeat 
the H and L level oscillations at the frequency of a Hz in response to the 
output of oscillator 59 which oscillates at the frequency of a Hz. 
Generated from changeover switch circuit 43 is the voltage which 
oscillates alternately at the 1 V and 2 V levels in response to the output 
of OR gate 46 for transmission as a flash readiness signal to a camera 
through terminal J3. When the camera shutter is released, transistor 92 is 
turned ON for about 1 m Sec. with the output pulse of one shot circuit 90, 
whereby terminal J3 at the camera side is short-circuited to ground to 
trigger one shot circuit 62 which outputs the H level voltage for a 
predetermined period of time. This signal turns transistors 3 and 5 ON, 
whereby booster circuit A of the electronic flash device stops operating, 
thereby suspending charging main capacitor 13. This stop operation is 
performed to prevent a camera control circuit from malfunctioning due to 
noise occurring in the booster circuit of the electronic flash device. 
Next when terminal J2 at the camera side is short-circuited to ground 
after the leading shutter curtain has traveled and switch 84 has been 
closed at full shutter opening, one shot circuit 40 is triggered to output 
the one shot pulse. With the one shot pulse, the output of AND gate 18 
becomes an H level, whereby xenon flash tube 23 is triggered by trigger 
circuit B to fire, while SCR 25 is conductive by resistors 24 and 26 and 
capacitor 27 to thereby maintain xenon flash tube 23 operable. While the 
output of one shot circuit 40 remains at the H level, the output of OR 
gate 57 is at the H level, whereby transistor 50 is turned ON and the 
potential at terminal J3 is the same as that of ground. When the output of 
one shot circuit 40 is inverted to an H level, the output of inverter 63 
becomes an L level, causing transistor 34 to be turned OFF, whereby 
capacitor 36 inside automatic flash light control circuit C starts to be 
charged. When the voltage at the positive terminal of capacitor 36 reaches 
a potential level predetermined by constant-voltage power supply 37 after 
the electronic flash device has continued to be operated, the output of 
comparator 38 becomes an H level, whereby the firing of the electronic 
flash device is stopped by flash-stop circuit E. Similarly, the H level 
output of comparator 38 is a stop signal and causes one shot circuit 61 to 
be triggered to output the H level one shot pulses for 2 seconds. With 
this pulse output from one shot circuit 61, the output of AND gate 47 
becomes an L level through inverter 48, and the output of oscillator 60 
which oscillates at the frequency of b Hz is generated from AND gate 48 
and OR gate 46. As a result, changeover switch circuit 43 outputs the 
voltage which alternately changes to the 1 V and 2 V levels in response to 
the output of OR gate 46. This voltage output is transmitted as a flash 
light control termination signal to the camera through terminal J3. When 
the next camera shutter release operation is performed after the lapse of 
time determined by one shot circuit 61, a flash light control termination 
signal with the time duration of b Hz is output from terminal J3. After 
the lapse of that time duration, a flash readiness signal at the frequency 
of a Hz is then output from terminal J3 when main capacitor 13 of the 
electronic flash device is fully charged. When main capacitor 13 of the 
electronic flash device is not fully charged, transistor 50 turns ON and 
the output whose potential is identical to that of ground is generated at 
terminal J3. 
Next when the camera shutter release operation is performed within the time 
duration determined by one shot circuit 61, one shot circuit 90 outputs 
the one shot pulse for a duration of about 1 m Sec. after switch 89 has 
been closed in response to the camera shutter release operation. After a 
time duration of about 1 m Sec., transistor 92 turns ON, whereby terminal 
J3 at the camera side is short-circuited to ground. Therefore, transistor 
53 is turned OFF, causing the output of AND gate 56 to become an H level, 
whereby one shot circuit 61 is reset, and a flash light control 
termination signal at a frequency of b Hz is not output from terminal J3. 
When, at this time, main capacitor 13 of the electronic flash device has 
already been charged, a flash readiness signal at a frequency of a Hz is 
output at terminal J3, and if not, terminal J3 is short-circuited to 
ground. 
Referring further to the circuitry of FIG. 2, photo-voltaic element 70 
receives the light reflected from an object or scene and transmitted 
through the aperture of an objective lens and is connected to operational 
amplifier 71 with a high input impedance. Under the action of diode 72, 
operational amplifier 71 outputs the logarithmic compression voltage of a 
measured light equivalent to Bv-Av, for example, in the APEX notation, 
wherein Bv represents luminance values and Av aperture value. Sliding 
resistor 73 having slider A and connected to both ends of constant-voltage 
power supply 74 is used to set film sensitivity, and outputs the voltage 
equivalent to Bv+Sv-Av from node B. Sv is the set value of film 
sensitivity. Memory switch 75 is turned OFF immediately before the mirror 
(not shown) of a single-lens reflex camera is lifted, and with memory 
switch 75 OFF, the voltage at node B is stored into memory capacitor 76. 
Switch 80 is closed in synchronization with the start of the leading 
shutter curtain travel, while switch 78 is opened to turn on transistor 79 
whose collector current actuates memory capacitor 77 to be charged. When 
the charged voltage at memory capacitor 77 reaches a predetermined level, 
the output of comparator 82 is inverted to an H level to deenergizes 
electromagnet 83 for holding the trailing shutter curtain, which then 
travels and the shutter is closed. When main capacitor 13 of the 
electronic flash device is not fully charged, the voltage at terminal J3 
is identical in potential to ground, whereby transistors 81 and 84 are 
turned OFF and the shutter is automatically controlled to be at a shutter 
speed determined by the voltage at node B for shooting in the daylight 
photography mode. Switch 89 is closed in synchronization with the camera 
shutter release operation. One shot circuit 90 is triggered when switch 89 
is closed to output the H level one shot pulse for a duration of about 1 m 
Sec., while transistor 92 is ON and terminal J3 is short-circuited to 
ground. Thus, the potential at terminal J3 drops to the ground level and 
this dropping of the potential becomes the interrupting signal. 
Constant-voltage power supply 93 outputs a voltage between the 1 V and 2 V 
levels. The output of comparator 94 whose negative input terminal is 
connected with the output of constant-voltage power supply 93 is inverted 
to an H level when the 2 V level voltage from the electronic flash device 
is input through terminal J3 to the camera. If, at this time, the camera 
shutter release operation is not performed, i.e., if switch 89 is not 
closed, the output of AND gate 95 is similarly inverted to an H level, 
whereby transistor 97 turns ON and indicating light-emitting diode 99 
illuminates. When conversely the 1 V level voltage is transmitted through 
terminal J3 to the camera, the output of comparator 94 becomes an L level, 
causing LED 99 to go off. Therefore, when a flash readiness signal which 
alternately oscillates at the 1 V and 2 V levels at the frequency of a Hz 
is transmitted through terminal J3 to the camera, LED 99 flashes at a Hz. 
When a flash light control termination signal which alternately oscillates 
between the 1 V and 2 V levels at the frequency of b Hz is transmitted 
through terminal J3 to the camera, LED 99 flashes at b Hz. 
A camera indicator switch (not shown), i.e., a switch for connecting power 
supply Vcc to LED 99, is assumed to be ON. When a flash readiness signal 
is input from the electronic flash device to the camera through terminal 
J3, LED 99 flashes at the frequency of a Hz, whereby a photographer knows 
that main capacitor 13 of the electronic flash device has been fully 
charged. Next, with the camera shutter release operation, switch 89 is 
closed, causing LED 99 to go off and transistor 92 to run ON for about 1 m 
Sec., during which terminal J3 is short-circuited to ground. Memory switch 
74 is then turned OFF immediately before the mirror of a single-lens 
reflex camera is moved, and the voltage at node B is stored into memory 
capacitor 76. 
Next in synchronization with the start of the leading shutter curtain 
travel, switch 80 is closed and switch 78 is opened. At this time, 
voltages of the 1 V and 2 V levels are alternately input from the 
electronic flash device to terminal J3 as a flash readiness signal, 
whereby transistor 81 is ON and capacitor 77 is instantly charged to a 
predetermined potential with the collector current of transistor 81 and 
the output of comparator 82 inverted to an H level. However, transistor 84 
is also ON, whereby electromagnet 83 for holding the trailing shutter 
curtain is energized to maintain the shutter curtain restraint. When the 
shutter is fully opened, switch 87 in ON to make terminal J3 identical in 
potential to ground, whereby the electronic flash device begins to fire. 
With the firing of the electronic flash device, i.e., the discharge of 
main capacitor 13, the output of comparator 17 becomes an L level, causing 
the flash readiness signal to disappear from terminal J3. One shot circuit 
40 outputs the one shot pulse simultaneously with the firing of the 
electronic flash device, whereby transistor 50 turns ON and the potential 
at terminal J3 is identical to that of ground for about 10 m Sec. 
Therefore, transistor 84 is turned OFF and electromagnet 83 is 
deenergized, whereby the trailing shutter curtain travels and the shutter 
is closed. 
Next, with the automatic flash light control by the electronic flash device 
terminated, the output of comparator 38 becomes an H level, whereby one 
shot circuit 61 is triggered to transmit a flash light control termination 
signal from the electronic flash device to the camera through terminal J3 
for a predetermined period of time. As a result, LED 99 flashes at a 
frequency of b Hz and a photographer knows that the electronic flash 
device has terminated flash light control for correct exposure. 
Since both the flash readiness signal and the flash light control 
termination signal are transmitted through terminal J3, simultaneous 
transmission of both signals is not possible. Therefore, when a flash 
light control termination signal is generated as described above, AND gate 
47 is disabled through inverter 49 in response to the one shot pulse of 
one shot circuit 61, thereby generating a flash light control termination 
signal from terminal J3 by priority over a flash readiness signal.