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Digital Camera Patent Abstract
A digital camera has an internally provided flash lamp and an externally
attached flash lamp. The internally provided flash lamp is set to
undergo a preliminary emission of light and thereafter a principal
emission of light. The externally attached flash lamp is controlled
to undergo a first emission of light in synchronism with the preliminary
emission and a second emission of light with the principal emission
as its trigger. The duration of the first emission is nearly the
same as or longer than that of the preliminary emission and the
quantity of light in the first emission is no less than the quantity
of light in the preliminary emission by said internally provided
flash lamp so as to be sufficient for determining the quantity of
light required by the camera for taking a picture, and the first
emission is controlled such that enough energy will be left for
the second emission.
Digital Camera Patent Claims
1. A method of controlling a digital camera having an internally
provided flash lamp and an externally attached flash lamp, said
internally provided flash lamp being set to undergo a principal
emission of light while said camera takes a picture and a preliminary
emission of light prior to said principal emission, said method
comprising the steps of: causing said externally attached flash
lamp to undergo a first emission of light in synchronism with said
preliminary emission by said internally provided flash lamp; and
causing said externally attached flash lamp to undergo a second
emission of light with said principal emission from said internally
provided flash lamp as a trigger; wherein the duration of said first
emission is nearly the same as or longer than that of said preliminary
emission by said internally provided flash light; and wherein the
quantity of light in said first emission is no less than the quantity
of light in said preliminary emission by said internally provided
flash lamp.
2. The method of claim 1 wherein said second emission of light
from said externally attached flash lamp is terminated independent
of the ending of said principal emission of light from said internally
provided flash lamp.
3. The method of claim 1 wherein said externally attached flash
lamp has a main capacitor for supplying power for emission of light
from said externally attached flash lamp, and wherein said first
emission of light is controlled such that enough energy is left
in said main capacitor for said second emission of light with a
specified quantity of light when said principal emission is effected.
4. The method of claim 1 wherein said first emission is stopped
by a first emission stopping signal that is generated by one or
more steps selected from the group consisting of the steps of: using
differential signals obtained by differentiating signals indicative
of said preliminary emission of light; using integrating signals
obtained by integrating signals indicative of said preliminary emission
of light; using a timer circuit for counting time of said preliminary
emission of light; and using a stop signal which causes said preliminary
emission of said internally provided flash lamp to stop.
5. The method of claim 1 wherein said second emission is automatically
stopped by providing an automatic stop signal generating circuit
for automatically generating a signal which causes said second emission
to stop.
6. A control device for controlling an externally attached flash
lamp of a digital camera including an internally provided flash
lamp, said internally provided flash lamp being set to undergo a
principal emission of light while said camera takes a picture and
a preliminary emission of light prior to said principal emission,
said control device comprising: means for causing said externally
attached flash lamp to undergo a first emission of light in synchronism
with said preliminary emission by said internally provided flash
lamp; and means for causing said externally attached flash lamp
to undergo a second emission of light with said principal emission
from said internally provided flash lamp as a trigger; wherein the
duration of said first emission is nearly the same as or longer
than that of said preliminary emission by said internally provided
flash light; and wherein the quantity of light in said first emission
is no less than the quantity of light in said preliminary emission
by said internally provided flash lamp.
7. The control device of claim 6 further comprising a main capacitor
for supplying power to said externally attached flash lamp; wherein
said first emission of light is controlled such that enough energy
is left in said main capacitor for said second emission of light
from said externally attached flash lamp with a specified quantity
of light when said principal emission is effected.
8. The control device of claim 6 wherein said externally attached
flash lamp further includes: a discharge tube; a DC-DC converter
for charging said main capacitor; a voltage-detection circuit for
indicating readiness of said capacitor for causing a discharge in
said discharge tube; and a trigger circuit for generating a voltage
pulse and applying said voltage pulse to said discharge tube.
9. The control device of claim 6 wherein said light emission controlling
means includes first emission stopping means for generating a first
emission stopping signal for stopping said first emission by one
or more steps selected from the group consisting of the steps of:
using differential signals obtained by differentiating signals indicative
of said preliminary emission of light; using integrating signals
obtained by integrating signals indicative of said preliminary emission
of light; using a timer circuit for counting time of said preliminary
emission of light; and using a stop signal which causes said preliminary
emission of said internally provided flash lamp to stop.
10. The control device of claim 6 further comprising automatic
stop signal generating means for receiving light, converting the
received light into electrical signals, processing said electrical
signals to obtain a result, and outputting a stop signal for stopping
emission of light from said externally attached flash lamp when
said result reaches a predetermined value.
11. The control device of claim 10 wherein said automatic stop
signal generating means incorporates inhibiting means for inhibiting
said stop signal from being outputted when said preliminary emission
is made.
12. The control device of claim 6 further comprising switching
means for selecting one of a plurality of predetermined quantities
of light to be emitted at said second emission.
13. An externally attached flash lamp of a digital camera including
an internally provided flash lamp, said internally provided flash
lamp being set to undergo a principal emission of light while said
camera takes a picture and a preliminary emission of light prior
to said principal emission, said externally attached flash lamp
comprising: a first discharge tube and a second discharge tube;
a first main capacitor for supplying power to said first discharge
tube for emission of light and a second main capacitor for supplying
power to said second discharge tube for emission of light; light
generating means for causing said externally attached flash lamp
to effect a first emission of light in synchronism with said preliminary
emission by said first discharge tube and a second emission of light
in response to said principal emission by said second discharge
tube; and light emission controlling means for stopping said second
emission of light when the quantity of light emitted by said second
emission has reached a specified quantity required by said camera
for taking said picture.
14. The externally attached flash lamp of claim 13 wherein said
light emission controlling means terminates said second emission
of light from said externally attached flash lamp independent of
the ending of said principal emission of light from said internally
provided flash lamp.
15. The externally attached flash lamp of claim 13 wherein the
duration of said first emission is nearly the same or longer than
that of said preliminary emission by said internally provided flash
light; and wherein the quantity of light in said first emission
is no less than the quantity of light in said preliminary emission
by said internally provided flash lamp.
16. The control device of claim 13 wherein said light emission
controlling means includes first emission stopping means for generating
a first emission stopping signal for stopping said first emission
by one or more steps selected from the group consisting of the steps
of: using differential signals obtained by differentiating signals
indicative of said preliminary emission of light obtained by integrating
signals indicative of said preliminary emission of light; using
integrating signals obtained by integrating signals indicative of
said preliminary emission of light; using a timer circuit for counting
time of said preliminary emission of light; and using a stop signal
which causes said preliminary emission of said internally provided
flash lamp to stop.
17. The control device of claim 13 further comprising an automatic
stop signal generating means for receiving light, converting the
received light into electrical signals, processing said electrical
signals to obtain a result, and outputting a stop signal for stopping
emission of light from said externally attached flash lamp when
said result reaches a predetermined value.
18. The control device of claim 17 wherein said automatic stop
signal generating means incorporates inhibiting means for inhibiting
said stop signal from being outputted when said preliminary emission
is made.
19. The control device of claim 13 further comprising switching
means for selecting one of a plurality of predetermined quantities
of light to be emitted at said first emission.
Digital Camera Patent Description
[0001] This is a continuation-in-part of application Ser. No. 10/117,972
filed Apr. 4, 2002, now pending.
BACKGROUND OF THE INVENTION
[0002] This invention is in the technical field of controlling
the quantity of light from a flash lamp externally attached to a
digital cameral.
[0003] FIG. 1 shows a digital camera (herein also referred to simply
as a "camera") 1 used for underwater photography, being
contained inside a watertight housing 4. Since there is generally
less light available in an underwater environment, a stroboscopic
lamp (herein referred to as a "flash lamp") is more frequently
used by an underwater photographer. If an internally provided flash
lamp ("inner lamp") 2 is used, however, the emitted flash
light is reflected by dust particles floating in water because the
light emitting element of the inner lamp 2 is positioned close to
the lens 3 of the camera 1, producing white spots in the image and
thereby giving rise to the so-called marine snow phenomenon. If
a wide conversion lens with a large outer diameter is attached to
the front frame 7 of the housing 4, on the other hand, the emitted
light from the inner lamp 2 tends to be screened by the wide conversion
lens, and a dark spot may appear on the target object to be photographed.
[0004] An externally attached flash lamp ("outer lamp")
9 is used in view of these problems, attached to the camera housing
4. In order to prevent the occurrence of a marine snow phenomenon,
it has been known to attach a back light screening plate 6 or a
tape on the front surface of a diffusion plate 5 on the housing
4. Such an outer lamp 9 is used also when the distance to the target
object is large and the light from the inner lamp 2 is not enough.
[0005] On the land, as inside water, an outer lamp 9 may be similarly
used when the light from the inner lamp 2 is not sufficient although
the waterproof housing 4 is not necessary unless there are many
water drops in the environment.
[0006] The outer lamp 9 must be synchronized with the inner lamp
2. A simple synchronization method without using an electric chord
between them is to detect the light from the inner lamp 2 by means
of a photodetector sensor 10 for the outer lamp 9. Since the light
from the inner lamp 2 normally reaches the sensor 10 dependably,
there is no need to provide any particular light transmitting means.
If the distance between the light emitting part of the inner lamp
2 and the outer lamp 9 is large or if there is a source of external
disturbance, however, an optical fiber 8 may be used as shown in
FIG. 1 to connect the light emitting part of the inner lamp 2 and
the sensor 10 such that the light from the inner lamp 2 can be received
by the sensor 10 dependably.
[0007] There are the following two methods of controlling the quantity
of light from the inner lamp of a digital camera. One is by causing
a weak preliminary emission of light immediately before the shutter
is opened, measuring the reflected light by a sensor through the
camera lens to determine the required quantity of light, and causing
the determined quantity of light to be emitted as the principal
emission as the shutter is opened. The other is by causing light
to be emitted only once as the shutter is opened, integrating signals
of reflected light detected by a sensor of the camera and stopping
the emission as the integrated total quantity of light reaches a
specified level. Both kinds have been in use but the former type
is becoming overwhelmingly more popular for digital cameras because
of the ease of control.
[0008] Throughout herein, according to the common usage, expression
"principal emission" will mean the emission of light for
taking a picture, whether or not the camera is of the kind that
opens a shutter for an exposure, and expression "preliminary
emission" will mean the emission of light prior to the principal
emission for the purpose of determining the required quantity of
light by the principal emission for taking a picture.
[0009] FIG. 2 shows the mode of light emission when a prior art
flash lamp or a manual flash lamp is externally attached to a digital
camera of the kind described above. FIG. 2A shows the operation
of the shutter and FIG. 2B shows the light emission from the inner
lamp 2, numeral 11 indicating the weak preliminary emission of light
for determining the required quantity of light for the principal
emission. The light emission from the outer lamp 9 is triggered
as the preliminary emission 11 from the inner lamp 2 is guided to
the sensor 10 but the triggered outer lamp 9 may emit a normal large
quantity of light such that there is not enough energy left for
it to emit a sufficient quantity of light, or to emit any light
at all, in synchronism with the opening of the shutter. This situation
happens especially if the distance between the camera and the target
object is large.
[0010] In order to avoid such a situation, it has been known to
provide a so-called preliminary emission canceling circuit for preventing
the outer lamp from emitting light at the time of the preliminary
light emission from the inner lamp and allowing the outer lamp to
emit light only at the time of the principal light emission from
the inner lamp. FIG. 2C shows the light emission 13 from the outer
lamp thus controlled, starting at time T1 and ending at time T2
when the total quantity of light emitted reaches a specified level.
The broken line portion of FIG. 2C shows how the emission would
proceed if it were not stopped.
[0011] According to the prior art technology explained above with
reference to FIG. 1, the back light screening plate 6 or a tape
covers the front surface of the diffusion plate 5 on the camera
housing 4. Thus, the light from the inner lamp 2 does not reach
the target object and hence is not reflected back. A similar result
is obtained also when a conversion lens or another accessory with
a large external diameter is attached.
[0012] Cameras according to prior art technology conclude that
the target object is at a large distance if no reflection of preliminarily
emitted light is received or the quantity of reflected light is
smaller than normal and do not stop the principal emission from
the inner lamp 2. The principal emission of light from the inner
lamp 2 is then a "full emission" as shown by the solid
line 12a in FIG. 2B. The time of full emission from the inner lamp
is usually about 3 milliseconds.
[0013] After such a full emission, the capacitor for the inner
lamp 2 must be recharged, and it usually takes 7-8 seconds with
an ordinary camera. This means that the shutter of the digital camera
becomes "locked". It also means that the battery for the
camera is consumed accordingly more, adversely affecting the number
of pictures that can be taken without replacing it with a new one.
[0014] Time for calculating photographic data and time for recording
in a memory are also required but some cameras are designed not
to be able to perform such processes while there is a drop in the
voltage of the battery, and this means that the user cannot take
the next picture in the meantime.
[0015] In the absence of an outer lamp, if the distance to the
target object is between about 0.5 m and 3 m, the emission of light
from the inner lamp is not a full emission but its principal emission
becomes as shown by the broken line 12b in FIG. 2B. In other words,
the quantity of emitted light is smaller and hence no time is required
for recharging the capacitor, allowing the user to take the next
picture immediately.
SUMMARY OF THE INVENTION
[0016] It is therefore an object of this invention to provide a
method and device for controlling the quantity of light from an
externally attached flash lamp of a digital camera such that the
quantity of light emitted as principal emission from the internally
provided flash lamp can be reduced and that the wait time required
until the next picture can be taken can be reduced and the useful
lifetime of the battery can be improved.
[0017] A method embodying this invention relates to a digital camera
having an internally provided flash lamp and an externally attached
flash lamp, the former being set to undergo a principal emission
of light while the camera takes a picture and a preliminary emission
of light prior to this principal emission and may be characterized
as comprising the steps causing the externally attached flash lamp
to undergo a first emission of light in synchronism with the preliminary
emission by the internally provided flash lamp and a second emission
of light with the principal emission by the internally provided
flash lamp as a trigger.
[0018] A control device of this invention may be similarly characterized
as relating to the control of an externally attached flash lamp
of such a digital camera including an internally provided flash
lamp set to undergo a principal emission of light while the camera
takes a picture and a preliminary emission of light prior to the
principal emission and as comprising means for causing the externally
attached flash lamp to undergo a first emission of light in synchronism
with the preliminary emission by the internally provided flash lamp
and a second emission of light with the principal emission from
the internally provided flash lamp as a trigger.
[0019] In the above, the duration of the first emission is nearly
the same as or longer than that of the preliminary emission by the
internally provided flash light, and the quantity of light in the
first emission is no less than the quantity of light in the preliminary
emission by the internally provided flash lamp so as to be sufficient
for determining the quantity of light required for taking the picture.
[0020] The control device of this invention may comprise not only
usual components of a flash lamp such as a DC-DC converter for charging
the main capacitor for supplying power to the externally attached
flash lamp, a so-called READY circuit for indicating that the main
capacitor is charged and ready to be used, a trigger circuit for
causing emission of flash light from a discharge tube and a gate
voltage generating circuit for generating a timing signal for adjusting
the timing of operations of the externally attached flash lamp,
but also means for causing a first emission of light from the externally
provided flash lamp in response to the preliminary emission of light
from the internally provided flash lamp and controlling this emission
of light such that enough energy is left in the main capacitor for
supplying power to the externally attached flash lamp with a specified
quantity of light required for the occasion.
[0021] The invention further relates to an externally attached
flash lamp for such a digital camera characterized as comprising
two discharge tubes and two respectively corresponding main capacitors,
one of the discharge tubes used for a first emission in response
to the preliminary emission from the internally provided flash lamp
and there being a control means for controlling the emission of
light from the other of the discharge tubes with a required quantity
of light at the time of the principal emission of light from the
internally provided flash lamp.
[0022] The invention also teaches the use of means for generating
a stopping signal for stopping the first emission from the externally
attached flash lamp. This may be done by one or more of the following
steps of or means for (1) using differential signals obtained by
differentiating signals which are indicative of the preliminary
emission of light, (2) using integrating signals obtained by integrating
signals which are indicative of the preliminary emission of light,
(3) using a timer circuit for counting time of the preliminary emission
of light, and (4) using a stop signal which causes the preliminary
emission of the internally provided flash lamp. Additionally, use
may be made of automatic stop signal generating means, automatic
stop signal generating means, inhibiting means for the time of the
preliminary emission, and a switching circuit for adjusting the
quantity of light of the preliminary emission.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a schematic diagram for showing how an external
flash lamp is attached to a digital camera according to prior art
technologies and also according to this invention.
[0024] FIG. 2, comprised of FIGS. 2A, 2B, 2C, 2D and 2E, is a timing
chart for the shutter operation and the emissions of light from
the internal and external flash lamps according to prior art technologies
and also according to this invention.
[0025] FIG. 3 is a block diagram for the circuit structure of a
flash lamp embodying this invention externally attachable to a digital
camera.
[0026] FIGS. 4A, 4B, 4C, 4D, 4E and 4F, together referred to as
FIG. 4, are timing charts of signals and waveforms for the emissions
of light.
[0027] FIG. 5 is a more detail circuit diagram of a portion of
FIG. 3.
[0028] FIG. 6 is a circuit diagram of a circuit as shown in FIG.
3 with an extra function.
[0029] FIG. 7 is a circuit diagram with another circuit structure.
[0030] FIGS. 8A, 8B, 8C, 8D, 8E and 8F, together referred to as
FIG. 8, are timing charts of signals and waveforms corresponding
to the circuit structure shown in FIG. 7.
[0031] FIG. 9 is a block diagram of a portion of a circuit with
another structure embodying this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0032] Externally, a combination of a digital camera and an outer
lamp incorporating the present invention may appear as shown in
FIG. 1. Thus, the invention will be described firstly with reference
to FIG. 1.
[0033] As explained above, numeral 1 indicates a digital camera
internally provided with a flash lamp (the inner lamp 2) and contained
inside a watertight housing 4 to which an outer lamp 9 is attached.
A black light screening plate 6 or a tape is pasted on the front
surface of a diffusion plate 5 on the housing 4 where the light-emitting
part of the inner lamp 2 faces such that the light from the inner
lamp 2 will not reach the target object to be photographed. It now
goes without saying that the housing 4 is not essential when the
camera 1 is used on land (not for underwater photography) except
where there are many water drops. The light emitting part of the
inner lamp 2 and a sensor 10 of the outer lamp 9 may be connected
by means of an optical fiber 8 for transmitting light from the former
to the latter.
[0034] FIG. 2D shows the light-emission curve of the inner lamp
2, and FIG. 2E shows the light-emission curve of the outer lamp
9. As shown, the inner lamp 2 of the camera 1 undergoes a preliminary
emission 14 immediately before the shutter is opened. As this light
from the inner lamp 2 is received by the sensor 10 as a detection
signal, the outer lamp 9 undergoes its preliminary emission 16 using
this detection signal as a trigger. A control circuit (not shown)
inside the outer lamp 9 serves at this time to prevent this light
emission from becoming a full light emission.
[0035] In FIG. 2D, T3 and T4 indicate respectively the start and
the end of the preliminary emission 14 by the inner lamp 2. In FIG.
2E, T7 indicates the start of the preliminary emission 16 by the
outer lamp 9, and it is nearly at the same time as T3. The end T8
of the preliminary emission 16 by the outer lamp 9 need not be the
same as T4. The end timing T8 is adjusted such that enough power
will be left in the main capacitor therefor will be left such that
the principal emission by the outer lamp 9 can be effected with
an appropriate quantity of light.
[0036] The quantity of light of this preliminary emission 16 by
the outer lamp 9 is preferably greater than that of the preliminary
emission 14 by the inner lamp 2 because there will be more reflected
light from the target object to be photographed but it is sufficiently
effective if it is about equal to that of the preliminary emission
14 by the inner lamp 2.
[0037] Because of the presence of the black light screening plate
6 as described above, there is no reflected light returning to the
lens 3 from the target object due to the preliminary emission 14
by the inner lamp 2 but the light of the preliminary emission 16
by the outer lamp 9 is returned by reflection from the target object.
If it is judged from this reflected light that the target object
is at a short distance of 0.5 m to 2 m, for example, the principal
emission by the inner lamp 2 may be relatively weak as shown at
15, starting at T5 and ending at T6.
[0038] In summary, because the principal emission from the inner
lamp 2 is weak, the power consumption therefor is small. This means
that the time for recharging the capacitor therefor for the next
emission (or the time for the user to wait until the next picture
can be taken by the camera 1) is reduced. The dotted line in FIG.
2D from the peak of the principal emission waveform 15 shows the
situation where there was no preliminary emission by the outer lamp
9. If there is no strong reflection from the target object, the
camera 1 will judge that the target object is at a large distance
and cause the inner lamp 2 to carry out a full-power principal emission.
The principal emission 17 by the outer lamp 9 starts at T1 substantially
simultaneously with that of the inner lamp 2, as shown in FIG. 2E,
and ends at T2, independent of the end of principal emission 15
by the inner lamp 2, when a specified quantity of light has been
emitted for taking a picture.
[0039] It is usually an automatically operating circuit that controls
the quantity of light emitted from the outer lamp 2, stopping the
emission of light when a specified suitable quantity of light has
been emitted. This specified suitable quantity of light is preliminarily
set according to the lens opening of the camera 1.
[0040] A suitable quantity of light can be set for the outer lamp
9 according to the distance to the target object even in the case
of a manual light emission. Since the power source for the outer
lamp 9 is independent of that for the camera 1, the capacity of
the power source battery and the source circuit can be appropriately
selected so as to adjust the charging time. Even after a full-power
emission for a principal emission, the wait period for the charging
may be 2-3 seconds.
[0041] The invention is described next by way of FIG. 3, which
is a circuit diagram, in part in the form of a block diagram, of
a flash lamp (such as shown at 9 in FIG. 1 and referenced herein
as the "outer lamp") attached externally to a digital
camera (such as shown at 1 in FIG. 1). Since this circuit structure
is similar to that of an outer lamp of a commonly known kind, it
will be described below only briefly.
[0042] Electrical power from a battery 18 is converted to a higher
voltage of up to about 330V by means of a DC-DC converter (DC-DC)
20 including a rectifier diode 21 to charge a main capacitor 22.
As the voltage of the main capacitor 22 increases gradually and
reaches a certain specified level such as 260V, it serves to light
up a neon tube contained in a voltage-detection circuit (the "READY
circuit" 23) to thereby inform the user that the lamp is ready
to be used. This lamp is normally referred to as the READY light
or the READY lamp. Thereafter, a transistor 37 connected to a trigger
circuit 24 becomes switched on, causing the trigger circuit 24 itself
to be switched on. This causes a high-voltage pulse of about 3000V
to be generated from a trigger coil to be applied to a discharge
tube 26. It may be parenthetically remarked here that the use of
the aforementioned voltage-detection circuit 23 is not a required
element. The ready condition of the lamp may be indicated by detecting
the voltage of the DC-DC converter circuit, and a light-emitting
diode may be used instead of a neon tube.
[0043] When the lamp is to be controlled from outside, use is made
of a shutter-operating terminal (sometimes known as the "X-junction")
25. For establishing synchronism with the internally provided flash
lamp (as shown at 2 in FIG. 1 and referenced as the "inner
lamp") of the camera 1, it is necessary to detect the light
therefrom. It may be accomplished by transmitting a signal indicative
of the principal light emission through a lead line from the shutter
operating terminal or by converting this electrical signal into
light by any known method and transmitting this light through an
optical fiber connected to the outer lamp. These are practical methods
because most digital cameras are provided with a shutter-operating
terminal.
[0044] At the moment when the discharge tube 26 begins to emit
flash light, an IGBT element 27 for controlling this light emission
is in a switched-on condition. A control signal is synchronously
emitted from the trigger circuit 24 and applied to a gate voltage
generating circuit 19, causing it to simultaneously generate a gate
voltage. A gate voltage may be provided alternatively from a discharge
tube circuit. As the gate voltage is generated, either an automatic
light emission control circuit 28 or a manual light emission control
circuit 30 is operated, depending on the condition of a switch (an
AUTO/MANUAL switch) 29. The gate voltage generating circuit 19 is
for generating a timing signal for adjusting the timing of operation
of the outer lamp 9. If the switch 29 is in the position as shown
in FIG. 3, an automatic stop signal generating circuit 43 is activated
when the discharge tube 26 emits light. This is carried out by a
sensor 44 comprising a photo-transistor which receives light reflected
from a target object, converts it to electrical signals and charges
an integrating capacitor 45 therewith. The integrating capacitor
45 is connected to a comparator 47. When the voltage of the integrating
capacitor 45 reaches a predetermined level (a comparison voltage
divided by resistor 46), this indicates that an appropriate exposure
has been made and the comparator 47 generates a signal which is
applied to the automatic light emission control circuit 28. A light
emission stopping signal is emitted thereupon from the automatic
light emission control circuit 28 and applied to the IGBT element
27 which forms a part of a light emission control circuit. The IGBT
element 27 is switched off and the discharge tube 26 ends its emission
of light.
[0045] Numeral 48 indicates a control terminal for control from
outside. It is used when automatic and manual stop signal generating
circuits or their equivalents are disposed externally and also when
a control signal for stopping the light emission is inputted from
the camera.
[0046] When the AUTO/MANUAL switch 29 is switched to MANUAL, the
gate voltage from the gate voltage generating circuit 19 is applied
to the integrating capacitor 31a through a resistor. When this voltage
reaches a predetermined level, the manual light emission control
circuit 30 is switched on and a signal for stopping the light emission
is applied to the IGBT element 27 such that the discharge tube 26
stops its emission of light.
[0047] The structures and operations of various components of this
invention will be described next with reference to FIGS. 3 and 4.
[0048] Since the outer lamp 9 embodying this invention is adapted
to emit light by using the preliminary light emission from the inner
lamp 2 of the digital camera 1 as the trigger, it requires a photodetector
circuit including a photodetector sensor 10 and a preliminary light
emission signal generating means including a first preliminary light
emission signal circuit ("FIRST") 39 and a second preliminary
light emission signal circuit ("SECOND") 33. The preliminary
light emission signal generating means is for controlling the quantity
of preliminarily emitted light to generate the signal for stopping
the light emission.
[0049] When the shutter button of the digital camera 1 is pressed,
the inner lamp 2 firstly emits a small quantity of light as preliminary
light emission, as shown by waveform 49 in FIG. 4A. This preliminarily
emitted light from the inner lamp 2 is detected by the photodetector
sensor 10 which may comprise a phototransistor (as shown at 24)
or its equivalent, and its signal is inputted through a capacitor
35 for cutting its DC portion to a timer circuit ("T")
36 and a transistor 37. The photodetector sensor 10 comprising the
photo-transistor 34 and the circuits near this photodetector sensor
10 may be a separate component not included in the outer lamp 9.
Such structures are intended to be also included within the scope
of this invention. For example, the photodetector sensor and its
peripheral circuits may be disposed near the inner lamp 2 inside
the camera 1 and a lead line may be used to connect them to the
outer lamp 9. The signal may be converted into an optical signal
and transmitted through an optical fiber. The output signal from
the transistor 37 after the detection signal from the phototransistor
34 is inputted will be as shown by waveform 51 in FIG. 4B. As explained
above, the trigger circuit 24 is activated, and the discharge tube
26 begins to emit flash light ("first emission").
[0050] The timer circuit 36 contained in the first preliminary
light emission signal circuit 39 is provided for detecting only
the preliminary emission of light from the inner lamp 2 because
it provides a most simple circuit structure.
[0051] It is to be remembered that the circuits for setting time
disclosed herein are intended to be examples of time setting means.
Integrating, differentiating and timer circuits described herein
are not essential components of this invention but may be substituted
with a one-shot multiple-purpose circuits, a latch circuit, other
equivalent circuits and other digitized equivalent circuits for
functioning similarly. In the case of a digitized method, a counter
(such as a decimal counter) 42 may be used to retrieve a signal
representing only the preliminary emission. Numeral 41 indicates
a waveform correction circuit which may be inserted whenever it
is considered necessary. Use may also be made of a microcomputer
programmed according to the timing shown in FIG. 4, although the
cost may be adversely affected. In such a case, other control circuits
can also be controlled at the same time.
[0052] As a signal from the capacitor 35 is inputted to this timer
36, the timer 36 is switched on as shown in FIG. 4C. Since this
timer 36 remains switched on for more than about 200 milliseconds,
it is not influenced by the second light emission from the inner
lamp 2 and serves to generate a signal for functioning only at the
time of the preliminary light emission as shown in FIG. 4. In response
to this signal, the first and second preliminary light emission
signal circuits 39 and 33 function only at the time of the preliminary
light emission.
[0053] The waveform shown in FIG. 4D is obtained if the output
signal from the timer 36 is differentiated from the position of
timing T9 shown in FIG. 4C by a differential circuit 38. If this
signal is inputted to the transistor 40, the its collector terminal
changes as shown in FIG. 4E. The signal width can be adjusted by
varying the constants of the differential circuit 38. Eventually,
the quantity of initially emitted light from the outer lamp 9 can
be controlled.
[0054] Explained again with reference to FIGS. 3 and 4, waveform
53 of FIG. 4D is for the case of the standard capacitance, and waveform
54 shows a situation where the capacitance has been somewhat increased.
Curves 55 and 56 of FIG. 4E are the corresponding waveforms of the
transistor 40, and curves 57a and 57b of FIG. 4F show the corresponding
quantities of light. In summary, the quantity of preliminarily emitted
light can be increased and decreased by adjusting the capacitance
and hence an optimum value can be selected according to the actual
condition.
[0055] The corresponding circuit includes differential capacitors
38a and 38b, as shown in FIG. 3. The total capacitance increases
if capacitor 38b is added to capacitor 38a. If a plurality of capacitors
are provided together with a switch as shown at SW1 (herein also
referred to as the "switching means"), the total capacitance
can be conveniently adjusted according to the situation. Although
an example is shown wherein the capacitance of a differential circuit
is made variable, it is equally effective to vary the resistance
of a resistor belonging to a differential circuit or making the
base resistance of the transistor 40 variable.
[0056] The transistor 40 is connected to the second preliminary
light emission signal circuit 33 and is adapted to have the aforementioned
signals inputted thereto.
[0057] The function of the second preliminary light emission signal
circuit 33 changes, depending on situations, as will be explained
more in detail below. In all cases, however, it functions as a part
of the means for stopping light emission by generating a signal
therefor when a specified level is reached and applying this signal
to the IGBT element 27 to switch it off and to cause the emission
of light from the discharge tube.
[0058] Firstly (1), when it is desired to make the flash light
emission time of the outer lamp at the time of preliminary light
emission considerably longer than that of the inner lamp, a timer
circuit or a similar circuit is connected to the second preliminary
light emission signal circuit 33 to increase the ON-time (operating
time) and then to the differential circuit 31. This is because the
second preliminary light emission signal circuit 33 becomes switched
off before the integrated value reaches a specified level unless
the time for the second preliminary light emission signal circuit
33 to supply power to the integrating circuit 31 is made sufficiently
long. FIG. 3 shows the integrating circuit 31 formed partially in
common with the manual light emission control circuit 30, another
equivalent circuit may alternatively be provided.
[0059] When the second preliminary light emission signal circuit
33 is switched on and the integrating capacitor 31a reaches a specified
level, the manual light emission control circuit 30 is activated
and a signal for stopping light emission is outputted and the discharge
tube 26 stops its emission of light.
[0060] If it is desired to adjust the flash light emitting time
from the outer lamp 9 at the time of the preliminary light emission,
an integrating circuit 31 may be provided with several different
C/R time constants such that a selection may be made therefrom by
means of a switch (such as shown by symbol SW2 in FIG. 3), depending
on the situation. The adjustment may be made in terms of resistance
by switching between resistors 31b and 31c. If it is to be made
in terms of capacitance, additional capacitors may be provided besides
capacitor 31a.
[0061] Since the integrating circuit 31, when combined with the
manual light emission control circuit 30, functions as an equivalent
of a timing circuit, it may be regarded as a part of what may be
herein referred to as a timer circuit. When made digital, in particular,
this portion may be said to serve as a digital timer circuit or
an equivalent thereof.
[0062] Secondly (2), when it is desired to make the flash light
emission time of the outer lamp at the time of preliminary light
emission about the same as or a little longer than that of the inner
lamp, the second preliminary light emission signal circuit 33 is
connected to the integrating circuit 31 only as a buffer circuit.
In this case, the switched-on time of the second preliminary light
emission signal circuit 33 is from waveform 55 to waveform 56 of
FIG. 4E. The time for the integrating capacitor 31a to reach the
specified level should be set within the switched-on time of the
second preliminary light emission signal circuit 33. Operations
thereafter are the same as in the case (1) described above.
[0063] Thirdly (3), if the flash light emission time of the outer
lamp at the time of preliminary light emission is to be adjusted
only by means of the differential circuit 38 and the transistor
40, the second preliminary light emission signal circuit 33 is directly
connected to a portion of the manual light emission control circuit
30 as a buffer circuit without going through the integrating circuit
31, as shown by the broken line 32. The timing of the discharge
tube 26 for stopping the emission of light in this case is as shown
by curves 55 and 56 in FIG. 4E. The signal for stopping the emission
of light is inputted from the second preliminary light emission
signal circuit 33 to the IGBT element 27 and the discharge tube
26 stops its emission of light.
[0064] Explained with reference to FIG. 4, the discharge tube 26
begins to emit light at T10 in FIG. 4F and stops its emission of
light at T11a of curve 57a corresponding to curve 55 of FIG. 5E
or at T11b of curve 57b corresponding to curve 56 of FIG. 4E.
[0065] These operations for three situations at the time of the
preliminary light emission, ("first emission") are carried
out such that enough electrical power will be left in the main capacitor
22 for the principal light emission. Especially when the target
object is at a large distance or the lens opening is narrow, a larger
quantity of light is required for the principal light emission than
for the preliminary emission. Explained more in detail, power from
the main capacitor 22 is mostly used for the light emission from
the outer lamp 9. So, if the outer lamp 9 undergoes a full emission
or a nearly full emission, there may not be enough energy left in
the main capacitor 22 for the occasion of the principal emission
("second emission"), resulting in an insufficient exposure
or a failure to emit any light at all.
[0066] About 100 milliseconds after the operations as described
above for a situation (1), (2) or (3), the inner lamp 2 of the camera
1 undergoes a principal light emission. Although the light from
the inner lamp 2 does not reach the lens 3 of the camera 1 because
it is screened, as explained above, the preliminarily emitted light
from the outer lamp 9 (from curve 57a to curve 57b of FIG. 4F) is
reflected by the target object (assumed to be at a distance between
0.5 m and 2 m) and makes incidence onto the lens 3 of the camera
1. As a result, the camera 1 is already aware that there is a target
at a near distance, and the principal light emission of light from
the inner lamp 2 is controlled such that the emission will be stopped
in the middle as shown by waveform 50 in FIG. 4A. In other words,
since there will be no full emission of light from the inner lamp
2, the object of controlling the quantity of light is hereby accomplished.
[0067] The principal emission of light from the inner lamp 2, thus
controlled, is detected by the photodetector sensor 10 with the
phototransistor 34, as explained above. The transistor 37 is thereby
switched on as shown by waveform 52 in FIG. 4B, and the discharge
tube 26 of the outer lamp 9 emits light as shown by waveform 58
shown in FIG. 4F. For this emission of light, neither the first
nor second preliminary light emission signal circuit 39 or 33 is
activated and no signal is outputted therefrom.
[0068] If the AUTO/MANUAL switch 29 is switched to AUTO, the automatic
stop signal generating circuit 43 is activated. A signal for stopping
the emission of light is outputted when a preliminarily determined
level of appropriate exposure is reached, and the discharge tube
26 stops its emission of light and the series of operations comes
to an end. Explained by way of FIG. 4, the emission of light is
started at T12 in FIG. 4F and ends at T13. If the AUTO/MANUAL switch
29 is switched to MANUAL, the emission of light from the discharge
tube 26, is similarly ended when the preliminarily determined level
is reached and the series of operations comes to an end.
[0069] It has been ascertained that timing variations of some degrees
in various operations described above do not seriously affect the
quality of pictures taken by the camera. Thus, expressions such
as "in synchronism" and "at the same time" within
the context of this invention are allowed to be interpreted leniently.
The timing charts in FIG. 4 should also be interpreted broadly.
As an example, the preliminary emission of light does not involve
a large quantity of light and its duration is only from about 20
to 50 microseconds. Thus, even if the emission of light from the
outer lamp 9 is started after that from the inner lamp 2 is stopped,
it can be considered sufficiently timely. In other words, a delay
of this order of magnitude is no problem. The emission of light
from the outer lamp 9 may be started even by using as its trigger
the signal for stopping the preliminary light emission from the
inner lamp 2. Such a delay will not be appreciated visually.
[0070] The invention is described next further in detail with reference
to FIG. 5. Conventionally known portions will be omitted and only
portions embodying this invention will be described. Terminal A5
is connected to the gate voltage generating circuit 19 shown in
FIG. 3 and terminal B5 is connected to the main capacitor 22 shown
in FIG. 3. Terminals G1 and G2 are grounded terminals and are connected
to the negative terminal of the battery 18. The positive terminal
of the battery 18 is connected to a plus circuit C5.
[0071] Numeral 67 indicates a timer circuit, shown more in detail
by way of an example, corresponding to the timer circuit 36 shown
in FIG. 3. As transistor 66 is switched on by a signal for starting
light emission, the capacitor in the timer circuit 67 is charged
up, causing the timer to start its functions.
[0072] The portion corresponding to the second preliminary light
emission signal circuit 33 includes transistor 64 and capacitor
65. The capacitor 65 is added when a timer is required. As explained
above, this portion may function as a timer in various ways. In
the example of FIG. 5, it is connected to the integrating circuit.
[0073] When this integrating circuit reaches a predetermined level,
transistors 63, 62 and 61 are all switched on, causing the IGBT
element 27 to be switched off and the discharge tube 26 to stop
its emission of light.
[0074] If the integrating circuit is not required, as explained
above, the collector of transistor 64 is connected to the base circuit
of transistor 61.
[0075] If the AUTO/MANUAL switch 29 is switched to AUTO when a
signal is received from the automatic stop signal generating circuit
43, transistors 60 and 59 are switched on, causing the IGBT element
27 to be switched off and stopping the emission of light from the
discharge tube 26.
[0076] It is here to be noted that the automatic stop signal generating
circuit 43 is activated both at the time of preliminary light emission
and at the time of principal light emission of the inner lamp. If
the distance to the target object at the time of the preliminary
light emission is relatively short (such as 0.5 m) and the lens
opening is relatively wide such as F2, the automatic stop signal
generating circuit 43 may reach the predetermined level with a smaller
quantity of light than that set by the signal circuit for the preliminary
light emission, generating a stop signal and stopping the emission
of light from the discharge tube 26. In other words, the quantity
of preliminarily emitted light from the outer lamp 9 becomes smaller
than the specified value.
[0077] As a practical matter, however, this phenomenon is not a
serious problem. If the target distance is short and the lens opening
is wide as stated above, although the quantity of reflected light
from the target object is somewhat diminished at the time of the
preliminary light emission, the quantity of light at the principal
emission from the digital camera becomes smaller as long as reflected
light returns from the target. Thus, no serious problem is to be
expected even if no measure is particularly taken, but an addition
of a simple circuit, as shown in FIG. 6, can eliminate the problem
as described above even when adverse conditions happen together
coincidentally.
[0078] The basic principle is to stop (inhibit) the action of the
automatic stop signal generating circuit 43 for the outer lamp which
emits light in synchronism with the preliminary light emission of
the inner lamp or the automatic light emission control circuit 28
only during the time of the preliminary light emission. FIG. 6 is
the same as FIG. 3 except for the addition of inhibit circuits.
[0079] A first inhibit circuit ("INHIBIT 1") 89 is added
for stopping the action of the automatic stop signal generating
circuit 43 at the time of the preliminary light emission. With the
circuit structure as shown in FIG. 6, the first inhibit circuit
89 is switched on when it receives a signal generated by the first
preliminary light emission signal circuit 39, and the action of
the automatic stop signal generating circuit 43 is stopped. A second
inhibit circuit ("INHIBIT 2") 86 is connected to the automatic
light emission control circuit 28 through a wire 87 for stopping
the operation of the latter. Either of these inhibit circuits can
eliminate the problem described above.
[0080] FIGS. 7 and 8 show another circuit structure for the first
preliminary light emission signal circuit (shown at 39 in FIG. 3)
functioning on another principle of matching the timing for stopping
the preliminary emission of light from the inner lamp with that
from the outer lamp. The remaining parts (not shown in FIG. 7) of
the circuit structure for controlling the principal light emission
are the same as explained above with reference to FIG. 3 and hence
will not be repetitiously presented.
[0081] In FIG. 7, terminal A6 is connected to the positive terminal
of a battery or an equivalent voltage level; terminal B6 is connected
to the automatic light emission control circuit 28 of FIG. 3; terminal
C6 is connected to the trigger circuit 24 of FIG. 3; and terminal
G6 is a ground terminal connected to the negative terminal of a
battery or an equivalent voltage level.
[0082] FIG. 8A shows the light emission from the inner lamp, curve
76 indicating its preliminary light emission. This signal is differentiated
by capacitor 68 to produce a differential signal 78 shown in FIG.
6B. As this differential signal 78 is amplified by AC amplifier
69 and applied to transistor 70, a signal with waveform shown at
80 in FIG. 8C is obtained because transistor 70 is switched on only
if its base is at a positive voltage. This signal 80 serves to stop
the emission of light, being applied through the automatic light
emission control circuit 28 to the IGBT element 27 of FIG. 3. As
a result, the emission of light from the discharge tube 26 is stopped
at the timing shown at T14 in FIG. 8C (and also at T15 in FIG. 8F).
The quantity of light by the preliminary emission can be controlled
by inserting a timer or an equivalent circuit on the upstream or
downstream side of the transistor 70 to vary the timing T15 of stopping
the light emission.
[0083] FIG. 8E shows the switching of transistor 75. It is switched
on in synchronism with the preliminary and principal light emission
of the inner lamp (shown at 76 and 77) to activate the trigger circuit
23, causing the (first and second) emissions of light from the outer
lamp with waveforms 84 and 85 shown in FIG. 8F.
[0084] The portion of the circuit shown in FIG. 7, including a
timer circuit 71, an integrating capacitor 72 and transistors 73
and 74, is an inhibit circuit for inhibiting the operation of transistor
70 at the time of the principal emission of light. If this circuit
were not provided, a pulse signal (shown at 79 in FIG. 8B) in synchronism
with the stopping of light emission from the inner lamp for the
second time (shown at 77 in FIG. 8A) would be applied to transistor
70 and the emission of light from the outer lamp would be stopped.
This inhibit circuit serves to prevent transistor 74 from becoming
switched on at T14 shown in FIG. 8 at the time of the preliminary
light emission by means of the timer circuit 71 and the integrating
capacitor 72.
[0085] At the time of the principal light emission thereafter,
transistors 73 and 74 are switched on, and signal 81 shown in FIG.
8D is applied to the base of transistor 70, thereby inactivating
transistor 70. Thus, the outer lamp becomes unaffected by the stopping
of the principal emission of light from the inner lamp.
[0086] The preliminary light emission from the inner lamp may take
place not only once but also for the second or third time. As well
known not only by persons skilled in the art but also by most people
who have ever used a flash lamp, however, most inner lamps are adapted
to undergo preliminary light emission only once. For this reason,
the present invention is primarily addressed to flash control methods
and devices wherein preliminary light emission from the inner lamp
takes place only once. Thus, expression such as "single preliminary
emission" used herein is intended to be interpreted as meaning
an embodiment wherein preliminary emission takes place only once,
not twice or more. On the other hand, this does not mean that such
embodiment characterized by the single preliminary emission from
the inner lamp is intended to limit the scope of the invention.
The invention is intended to further include additional embodiments
wherein the preliminary emission from the inner lamp may take place
twice or more. Even in such a situation, the timing of the inhibit
circuit may be adjusted for synchronism. This circuit structure
described above is convenient because the emission of light from
both the inner and outer lamps can be stopped nearly simultaneously
and hence the overall control becomes easier.
[0087] FIG. 9 shows still another circuit structure for the first
preliminary light emission signal circuit (shown at 39 in FIG. 3)
functioning on still another principle by providing a second main
capacitor 91. FIG. 9 shows the discharge tube separately but this
is for the clarity of explanation and the number of discharge tubes
is not intended to limit the scope of the invention.
[0088] With reference to FIG. 9, terminal G7 is a ground terminal
and is connected to the negative circuit of a battery; terminal
A7 is connected to the DC-DC converter 20 shown in FIG. 3; and terminal
D7 is connected to the automatic light emission control circuit
28 and the manual light emission control circuit 30. In this example,
the first preliminary light emission signal circuit 39 and the second
preliminary light emission signal circuit 33 of FIG. 3 are not required.
Terminal B7 is connected to transistor 37. Terminal C7 is connected
to the aforementioned preliminary emission canceling circuit of
a known type such that it can be activated only at the time of the
principal light emission.
[0089] The second main capacitor 91 is charged with power from
the DC-DC converter 20 through another rectifier diode 90. The capacitance
of the second main capacitor 91 is smaller than that of the first
main capacitor 22, being about 1/5 to 1/10 of the latter and hence
giving rise to a smaller quantity of light. The quantity of preliminary
emission of light can thus be adjusted by increasing and decreasing
this capacitance value.
[0090] A signal reaches terminal B7 first at the time of the preliminary
emission of light from the inner lamp, activating a second trigger
circuit 92 to cause a discharge tube 93 to emit light. A next signal
arrives at the time of the principal light emission of the inner
lamp but the discharge tube 93 does not emit light because the power
of the second main capacitor 91 is almost all used up at the time
of the preliminary light emission.
[0091] A signal comes to the trigger circuit 24 from terminal C7
only at the time of the principal light emission, activating the
trigger circuit 24 to start the light emission from the discharge
tube 26. This signal may be generated by a circuit of a known type
such as a combination of a timer circuit and an integrating circuit
or a digital circuit such as a counter circuit. A signal for stopping
the emission reaches terminal D7 thereafter, as explained above,
to switch off the IGBT element and to stop the light emission.
[0092] When two discharge tubes are used, as described above, they
may be set at different positions. The discharge tube for the preliminary
light emission may be placed near the camera while the discharge
tube for the principal light emission may be set farther away.
[0093] Although FIG. 9 shows an embodiment wherein two discharge
tubes are used, it is possible to use only the first discharge tube
26 to do way with the second trigger circuit 92. In such a situation,
a switch circuit of a known type for cutting off the circuit for
the first main capacitor 22 at the time of the preliminary light
emission may be required for preventing interference. Alternatively,
a circuit of another known type for connecting the circuit for the
first main capacitor 22 at the time of the principal light emission
may be required.
[0094] Although the circuit structure for the preliminary light
emission may be thus different, the ratio of quantity of light between
the preliminary and principal emission of light can be made similar
to the example shown by FIG. 3 and similar effects can also be obtained.
[0095] According to this invention, in summary, the preliminary
light emission from the outer lamp is started by using the preliminary
light emission from the inner lamp as the trigger and the quantity
of light by the principal emission from the inner lamp is controlled
according to the reflection of the preliminarily emitted light from
the outer lamp. Thus, the quantity of light from the inner lamp
at the time of its principal emission can be reduced and the capacitor
for the inner lamp can be more quickly recharged. This reduces the
possibility of the user missing the chance of taking a desired picture.
Additional advantages of this invention include a longer useful
lifetime of the battery for the digital camera and hence that the
battery need not be exchanged frequently.
[0096] The present invention is first characterized in that the
preliminary light emission ("first emission") of the outer
lamp is controlled such that sufficient energy will be left in the
main capacitor hence that the principal emission of light from the
outer lamp ("second emission") will not be adversely affected.
Thus, the principal light emission from the outer lamp can be dependably
effected with a sufficient quantity of light such that pictures
of a high quality can be expected independent of the distance of
the target object to be photographed.
[0097] The invention also teaches the preliminary emission of light
from the outer lamp through a discharge tube connected to a main
capacitor and the principal emission from the outer lamp through
another discharge tube connected to another main capacitor, the
principal emission from the outer lamp being stopped such that an
appropriate quantity of light is emitted. This also assures that
pictures of a high level of quality can be obtained dependably. |