Digital Camera Patent Abstract
For controlling emission of light from an outer flash lamp having
a light receiving part and externally attached to a camera, which
may be a digital camera and may be enclosed inside a watertight
housing for underwater photography, having an inner lamp which is
provided internally and includes a light emitting part, a filter
which passes infrared and near infrared light but prevents visible
light from passing through may be attached to the light emitting
part of the inner lamp or on the housing of the camera. Light emitted
from the inner lamp has sufficiently strong infrared intensity and
the portion passing through the filter is sufficiently strong to
activate the outer lamp. The filter may be substituted with a light
intensity-reducing filter for reducing the intensity of incident
light thereon with an amplifier added to the light receiving part
of the outer lamp such that the light with reduced intensity through
such a filter can activate the outer lamp. A light guide may be
used to deflect the forwardly propagating light emitted from the
inner lamp and to lead it to the light receiving part of the outer
lamp for activating it with a light screening plate provided to
screen off the forwardly propagating light from the camera. Digital Camera Patent Claims
What is claimed is:
1. A method of controlling emission of light from an outer flash
lamp having a light receiving part and externally attached to a
camera having an inner lamp which is provided internally to said
camera and includes a light emitting part, said method comprising
the steps of: preparing a filter which passes infrared light and
prevents visible light from passing through; providing said light
emitting part of said inner lamp of said camera with said filter;
and causing infrared light emitted through said filter to be received
by said light receiving part of said outer flash lamp and thereby
causing said light receiving part to control emission of light from
said outer flash lamp.
2. The method of claim 1 wherein said filter is pasted over said
light emitting part of said camera.
3. The method of claim 1 wherein said camera is enclosed in a watertight
housing and said filter is pasted on said housing.
4. A device for controlling emission of light from an outer flash
lamp having a light receiving part and externally attached to a
camera having an inner lamp which is provided internally to said
camera and includes a light emitting part, said device comprising:
a filter which passes infrared light and prevents visible light
from passing through, said filter being provided to said light emitting
part of said inner lamp; and a light receiving element in said light
receiving part of said light receiving part, said light receiving
element serving to control emission of light from said outer lamp
in response to infrared light received through said filter.
5. The device of claim 4 wherein said filter is pasted over said
light emitting part of said camera.
6. The device of claim 4 further comprising a watertight housing
enclosing said camera, said filter being pasted on said housing.
7. A method of controlling emission of light from an outer flash
lamp having a light receiving part and externally attached to a
camera having an inner lamp which is provided internally to said
camera and includes a light emitting part, said method comprising
the steps of: preparing a light-intensity reducing filter which
reduces intensity of incident light thereon from said light emitting
part and allows light with a lowered intensity to pass therethrough,
said light receiving part being designed to activate said outer
lamp in response to light with said lowered intensity; providing
said light emitting part of said inner lamp of said camera with
said light intensity-reducing filter; and causing said light with
said lowered intensity emitted from said inner lamp and passed through
said light-filter to be received by said light receiving part of
said outer flash lamp and thereby causing said light receiving part
to control emission of light from said outer flash lamp.
8. The method of claim 7 wherein said light intensity-reducing
filter is pasted over said light emitting part of said camera.
9. The method of claim 7 wherein said camera is enclosed in a watertight
housing and said light intensity-reducing filter is pasted on said
housing.
10. A device for controlling emission of light from an outer flash
lamp having a light receiving part and externally attached to a
camera having an inner lamp which is provided internally to said
camera and includes a light emitting part, said device comprising:
a light-intensity reducing filter which reduces intensity of incident
light thereon from said light emitting part and allows light with
a lowered intensity to pass therethrough; a circuit in said light
receiving part for activating said outer lamp in response to light
with said lowered intensity passed through said light intensity-reducing
filter.
11. The device of claim 10 wherein said light intensity-reducing
filter is pasted over said light emitting part of said camera.
12. The device of claim 10 further comprising a watertight housing
enclosing said camera, said light intensity-reducing filter being
pasted on said housing.
13. A method of controlling emission of light from an outer flash
lamp having a light receiving part and externally attached to a
camera having an inner lamp which is provided internally to said
camera and includes a light emitting part, said method comprising
the steps of: providing a light guide with a reflecting surface
to said light emitting part and internally deflecting and thereby
leading light from said light emitting part therethrough to said
light receiving part of said outer lamp; and providing a light screening
means in front of said light emitting part for screening light propagating
forward from said light emitting part.
14. The method of claim 13 wherein said light guide is pasted over
said light emitting part of said camera.
15. The method of claim 13 wherein said camera is enclosed in a
watertight housing and said light guide is pasted on said housing.
16. A device for controlling emission of light from an outer flash
lamp having a light receiving part and externally attached to a
camera having an inner lamp which is provided internally to said
camera and includes a light emitting part, said device comprising:
a light guide with a reflecting surface for internally deflecting
and thereby guiding light from said light emitting part to said
light receiving part of said outer lamp; and a light screening means
for screening off light propagating forward from said inner lamp.
17. The device of claim 16 wherein said light guide is pasted over
said light emitting part of said camera.
18. The device of claim 16 further comprising a watertight housing
enclosing said camera, said light guide being pasted on said housing.
19. The method of claim 7 wherein said light-intensity reducing
filter has a hole serving to allow a portion of the incident light
to pass through.
20. The device of claim 10 wherein said light-intensity reducing
filter has a hole serving to allow a portion of the incident light
to pass through.
Digital Camera Patent Description
BACKGROUND OF THE INVENTION
This invention is in the technical field of controlling the light
emission from a flash lamp internally contained in or externally
attached to a digital cameral adapted for use in underwater photography.
When a camera (such as a digital camera) is used for underwater
photography, it is usually enclosed inside a commercially available
transparent colorless watertight housing. A transparent colorless
container is used because the flash light emitted from a stroboscopic
lamp internally provided to the camera will have to pass through
the material of the housing to reach the target object to be illuminated.
A stroboscopic lamp ("flash lamp") is more frequently
used by an underwater photographer because the underwater environment
is generally darker than above the water. If an internally provided
flash lamp ("inner lamp") is used, however, the emitted
flash light is reflected by dust particles and microorganisms floating
in water because the light emitting element of the inner lamp is
positioned close to the lens of the camera 1, producing white spots
in the image and thereby giving rise to the so-called marine snow
phenomenon. If the existing particles are very fine, the picture
as a whole may become whiter, adversely affecting the contrast of
the picture.
An externally attached flash lamp ("outer lamp") is used
in view of these problems. Since the light emitting element of the
outer lamp can be farther removed from the lens of the camera, reflected
light from particles near the lens can be reduced and the effect
of the marine snow phenomenon becomes less severe, allowing it to
be possible to obtain clearer pictures.
The explanations given above are generally on the assumption that
the target objects are at distances in the range of 0.5 m-1.5 m.
FIG. 1 shows a prior art method of control of a digital camera
1 provided with a stroboscopic light emitting element (or the inner
lamp) 2 and a lens 3 and enclosed inside a watertight housing 4
to which an outer lamp 9 is attached. Numeral 7 indicates its outer
frame. The outer lamp 9 must be synchronized with the so-called
X-contact of the camera 1 (which is a switch on the part of the
camera 1 adapted to close when the shutter of the camera 1 is opened)
but commercially available camera housings are not equipped with
any synchronization terminal to be connected to an outer lamp because
it is troublesome to waterproof the portion of the housing at such
a terminal and also because some cameras are not provided with an
X-contact terminal.
A simple method of synchronizing the light emission from the outer
lamp 9 without a synchronization terminal is to provide the outer
lamp 9 with a sensor 10 for detecting the light emitted from the
inner lamp 2 such that the emission of light from the outer lamp
9 will be synchronized. Numeral 8 indicates an optical fiber. The
emission of light from the outer lamp 9 can be synchronized even
without the optical fiber 8 as long as the light from the inner
lamp 2 can reach the sensor 10. If the distance between the light
emitting part of the inner lamp 2 and the outer lamp 9 is large,
however, the optical fiber 8 serves to dependably transmit to the
sensor 10 the light from the inner lamp 2.
In order to reduce the effect of the aforementioned marine snow
phenomenon, a black light-screening plate 6, or a plate with a black
tape pasted thereon, is provided in front of a diffusing plate 5
such that the light from the inner lamp 2 will not reach the target
object for the reason given above. According to the example shown
in FIG. 1, the light emitted from the inner lamp 2 is passed through
the optical fiber 8 to be detected by the outer lamp 9. This method
is disadvantageous, however, in that the optical fiber must be provided
and it is costly to have it installed.
The user of a camera as shown in FIG. 1 will discover that a significant
amount of light emitted from the inner lamp 2 is leaking through
the portions around the light-screening plate. Even if the light-screening
plate is made wider, light continues to leak around the light-screening
plate because the watertight housing is transparent and colorless.
It is also because the walls of the light-emitting part of the camera
and the watertight housing are separated. This gives rise to the
aforementioned marine snow phenomenon because this leaked light
passes very close to the lens of the camera. The marine snow phenomenon
occurs also if there are many light-reflecting particles, whether
the distance to the target object to be photographed is large or
small. The light-screening plate is not very effective, although
it is better than not using it at all.
Another problem of the prior art technology is the so-called flare
phenomenon with a part of the light from the inner lamp reaching
the lens of the camera by being reflected inside the housing or
diffused near by because the housing is colorless and transparent.
As a result, the user may fail to obtain a picture with a good contrast.
In the case of a digital camera for underwater photography, the
camera itself is made watertight such that a housing as shown in
FIG. 1 is not required. Since the inner lamp must be caused to emit
light, however, there remains the same problem of the marine snow
phenomenon unless the inner lamp and the outer lamp are connected
by a synchronization cable for synchronizing their operations.
SUMMARY OF THE INVENTION
It is therefore a general object of this invention, in view of
the status of the prior art technology described above, to provide
a device for and method of controlling the emission of light from
a flash lamp externally attached to a digital camera ("the
outer lamp") for preventing as much as possible the occurrence
of marine snow and flare phenomena caused by the light from an internally
provided lamp ("the inner lamp") of the camera such that
pictures of a higher quality than was possible before can be obtained.
It is a more specific object of this invention to provide such
a device and a method characterized as using infrared light (inclusive
of near-infrared light) to which the image-taking element of the
camera is insensitive.
It is another more specific object of this invention to provide
such a device and a method characterized as reducing the quantity
of light coming from the light emitting part of the internally provided
lamp of the camera or its vicinity so as not to be photographed,
or as using a light guide to lead the flash light away so as not
to be incident on the target objects to be photographed.
In view of the objects of the invention as described above, one
of the methods of the invention may be described as comprising the
steps of preparing a filter which passes infrared light but prevents
visible light from passing through, providing the light emitting
part of the inner lamp of a camera (such as a digital camera for
underwater and/or above-water photography) with this filter, causing
infrared light emitted through this filter to be received by the
light receiving part of the outer flash lamp and thereby causing
the light receiving part to control emission of light from the outer
flash lamp. The filter may be pasted on the front surface of the
light emitting part of the inner lamp or on the inner or outer surface
of a watertight housing in which the camera may be enclosed when
it is used for underwater photography. A control device to be used
correspondingly may thus be characterized as comprising such a filter
which passes infrared light but prevents visible light from passing
through, being provided to the light emitting part of the inner
lamp and a light receiving element which is in the light receiving
part of the light receiving part and serves to control emission
of light from the outer lamp in response to infrared light received
through the filter.
In summary, this aspect of the invention is characterized as using
the infrared (inclusive of near infrared) portion of the flash light
from the inner lamp to generate a signal for activating the outer
flash lamp. The outer lamp usually comprises a xenon discharge tube
but xenon discharge tubes are well known for emitting infrared light
equally strongly as or more strongly than visible light. According
to this aspect of the invention, the visible portion of the emitted
light from the inner light is filtered off and the abundantly present
infrared portion is used to activate the outer flash lamp. For this
purpose, the light receiving part of the outer lamp must include
an element which has sensitivity to infrared light, or the capability
of generating an electrical signal for activating the outer lamp
in response to the infrared light received through the filter. Since
silicon phototransistors and silicon photodiodes of known kinds
have sufficient sensitivity to infrared light, they may directly
be used for the purpose of this invention.
In another aspect of the invention, use is made of a light intensity-reducing
filter, instead of a filter for preventing visible light from passing
through while allowing infrared (and near infrared) light to pass
through, either pasted on the light emitting part of the camera
or, if the camera is for underwater photography and is enclosed
inside a watertight housing, on the inner or outer surface of such
a housing. In this case, a circuit such as an amplifier circuit
may be provided in the light receiving part for amplifying the optical
signal with reduced intensity received through such a light intensity-reducing
filter such that a sufficiently strong electrical signal can be
obtained therefrom for activating the outer lamp.
In still another aspect of the invention, use is made of a light
guide serving to reflect (and deflect) the light emitted from the
light emitting part of the inner lamp and to lead the deflected
light therethrough to the light receiving part of the outer lamp
while a light-screening means is provided to screen off light propagating
forward from the camera. Such a light guide may be pasted onto the
light emitting part of the inner lamp. If the camera is for underwater
photography and is enclosed inside a housing, the light guide may
be pasted on the inner or outer surface of the housing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view of a camera with a prior art control device.
FIG. 2 is a front view of a camera with a control device embodying
this invention.
FIG. 3 is a graph of transmissivity characteristics of filters
usable for this invention.
FIG. 4 is a graph of sensitivity characteristic of a sensor for
the device embodying this invention.
FIG. 5 is a front view of a camera with another control device
embodying this invention.
FIG. 6 is a circuit diagram of the sensor of the control device
shown in FIG. 5.
FIG. 7 is a side view of another control device embodying this
invention including a light guide with various component shown separated
from one another.
FIG. 8 is a front view of a camera provided with the control device
of FIG. 7.
Throughout herein similar or like components are indicated by the
same symbols even where they are components of different systems
and may not necessarily be explained repetitiously.
DETAILED DESCRIPTION OF THE INVENTION
The invention is described next by way of examples. FIG. 2 shows
a control device according to a first embodiment of the invention
characterized as having a filter 11 pasted over the light emitting
part 2 of the camera as shown by numeral 12 before the camera is
inserted into its housing. The filter 11 is for allowing infrared
(and near infrared) light to pass through while preventing visible
light from passing through. With such a filter 11 placed over the
light emitting part 2 of the camera, visible light emitted from
the camera when its internally provided lamp is switched on does
not leak to the environment, causing no marine snow or flare phenomenon.
In the meantime, infrared light is transmitted through the filter
and the sensor 10 in the light receiving part is activated by this
transmitted infrared light to cause the externally attached flash
lamp ("outer lamp") 9 to emit light. The black light screening
plate as shown at 6 in FIG. 1 is no longer required, and since the
infrared light is emitted with a sufficient intensity, the optical
fiber cable 8 may be dispensed with so as to simplify the structure.
If it is desirable to make certain that the outer lamp 9 will function
such as when the outer lamp 9 is relatively far away, it is preferable
to make use of the optical fiber cable 8.
The filter 11 need not necessarily be pasted at the position indicated
by numeral 12 in FIG. 2. It may be pasted inside or outside the
housing (although not separately illustrated), or at any other place
where it can be as effective. Even if it is pasted outside the housing,
infrared light can be emitted with a sufficiently strong intensity
such that the outer lamp can be activated dependably even without
the use of the optical fiber cable 8. The filter may be made to
cover a relatively large area since it does not affect the transmission
of the infrared light. Thus, the leakage of light from areas around
the light emitting part can be significantly reduced compared to
the prior art technology.
In the case of a digital camera for both underwater and above-water
photography, such a filter may be pasted on the front surface of
its inner lamp for a similar effect.
FIG. 3 shows the filtering characteristics of some commercially
available examples of a filter which may be used for the purpose
of this invention. In FIG. 3, letters A, B and C refer to examples
commonly referred to as SC74, IR82 and IR84, respectively. The SC74
filter does not completely screen off visible light and allows near-infrared
light to pass through but this may be usable, depending on the type
of the camera and the environmental conditions such as brightness.
The IR82 and IR84 filters are seen to nearly completely screen off
light in the visible range of wavelength and hence may be used generally
without any problem.
It goes without saying that there are many other kinds of filters
which may be used, depending on their filtering characteristics.
A plastic resin material with such a filtering characteristics may
be molded into a suitable shape. If a sensor 10 with high infrared
sensitivity is used, it is possible to use a filter with a filtering
characteristic having a shielding threshold value moved in the direction
of longer wavelengths.
The image-taking light receiving element of the camera may comprise
a CCD or CMOS. Such devices produced in recent years are nearly
totally insensitive to infrared light and no infrared image will
be obtained. Since the pictures obtained will not have a good contrast
if the light receiving element is sensitive to infrared light, a
filter may be used over the light receiving element to reduce the
camera's sensitivity to infrared. The present invention takes advantage
of this characteristic of modern image-taking light receiving elements
having poor (little) or no sensitivity to infrared light.
The only light passing through the filter (such as indicated above
by letters A, B and C) is naturally infrared light which does not
form any image on the camera (although the filter A allows a small
amount of visible light to pass through). That the light from the
inner lamp does not form any image on the camera means that marine
snow and flare phenomena do not occur. The infrared light passing
through the filter A, B or C is made incident on the sensor 10 of
the outer lamp 9 through the optical fiber cable 8, directly or
by being reflected from a target object to be photographed. Since
the infrared light emitted from the inner lamp is sufficiently energetic,
the optical fiber cable 8 is not essential. The outer lamp 9 can
be activated either directly or by reflection, and this makes the
method of operation and the device structure simpler.
The sensor 10 may comprise an element such as a phototransistor
or a photodiode with a higher sensitivity to infrared light. FIG.
4 shows a representative characteristic of such a sensor, its vertical
axis representing relative sensitivity and its horizontal axis indicating
wavelength. In this example, the maximum sensitivity is at 800 nm,
the sensitive wavelength regions extending widely on both sides
thereof. Since the sensor 10 has such a high sensitivity in the
infrared region, it can function dependably by receiving the infrared
light through the aforementioned filter. As a matter of practical
fact, the sensor 10 need not be particularly sensitive because the
flash light from the discharge tube of the lamp is generally sufficiently
strong. The sensor 10 serves to convert the received infrared light
into an electrical signal with which the emission of light from
the outer lamp 9 is controlled.
FIG. 5 shows a control device according to a second embodiment
of the invention characterized as having a light intensity-reducing
filter 11' pasted over the light emitting part 2 of the camera as
shown by numeral 12 before the camera is inserted into its housing.
The light intensity-reducing filter 11' may be of any kind as long
as it is capable of reducing the intensity of light as it passes
therethrough. Examples of such a tape include ordinary ND (neutral
density) filters, cloth tapes with fine holes, sheets of colored
paper including white paper and vinyl tapes. Experiments have shown
that leakage of light around the inner lamp can be stopped when
it emits light and aforementioned marine snow and flare phenomena
can be sufficiently reduced if the light quantity is reduced to
1/10-1/100 of the original.
The quantity of light received by the sensor 10 is correspondingly
reduced according to this embodiment of the invention. Thus, the
signal from the sensor 10 must be amplified accordingly. If the
quantity of light is reduced to 1/10-1/100 of the original value,
an amplifier circuit for amplification of 10 times to 100 times
will be required for obtaining an equivalent signal. The original
light quantity may be reduced to less than 1/100 if an appropriate
amplifier circuit is used.
FIG. 6 shows a circuit structure for the sensor 10. Numeral 21
in FIG. 6 indicates an amplifier circuit including a transistor
19. Prior art sensors did not include such an amplifier circuit,
connecting a capacitor 16 for removing DC component directly to
a transistor 22 because this was sufficient if the quantity of light
from the inner lamp was sufficiently large. The amplifier circuit
21 shown in FIG. 6 is an AC amplifier circuit capable of amplification
by a factor of 10 to about 400, depending on the selection of the
components.
To explain the actual operation of the sensor 10 thus structured,
the light from the inner lamp is received by a phototransistor 14
serving as a sensor and converted into an electrical signal. Numeral
15 indicates a load resistor connected to the AC amplifier circuit
21 through a capacitor 16 for eliminating the AC component. Input
and output capacitors 17 and 18 are provided because it is an AC
amplifier circuit respectively on the input and output sides. The
transistor 19 has a bias voltage applied to its base through a bias
resistor 18. Amplified signals are applied to a second transistor
22 of which the collector is connected to a synchronization terminal
24.
When the second transistor 22 is switched on by such an amplified
signal, a trigger circuit (not shown) for the outer lamp is activated
and controls the emission of flash light from the outer lamp 9.
The black light-screening plate as shown at 6 in FIG. 1 may be dispensed
with but it is preferable to use such a plate for the purpose of
eliminating light propagating in forward directions. In FIG. 6,
numerals 23 and 25 indicate terminals for connecting to a voltage
source, a positive voltage and a negative voltage being respectively
applied thereonto.
Although the invention has been described by way of only a limited
number of examples, these examples are not intended to limit the
scope of the invention. Many modifications and variations are possible
within the scope of the invention. For example, the light intensity-reducing
filter 11' need not be pasted at the position indicated in FIG.
5 as long as a comparable effect of reducing the light intensity
can be obtained. It may be pasted inside the housing, for example,
because this will prevent the diffusion of light through the transparent
plastic housing. In such a case, a filter with a relatively large
area should be pasted in order to prevent leakage of light. Instead
of a light intensity-reducing filter as shown in at 11' in FIG.
2, a light-screening tape with a hole in the middle as shown at
13 in FIG. 5 may be pasted for obtaining an equivalent effect. It
goes without saying that the light-screening tape 13 may be substituted
with a light-screening plate structured similarly with a hole. With
such a light-screening device, the light emitted through is naturally
reduced from the total quantity of light from the inner lamp which
would otherwise be propagated out. The quantity of light actually
emitted out can be controlled by varying the size of the hole.
Another method is to make use of a light guide 27 which, as shown
in FIGS. 7 and 8, may be a bar-like elongated structure with a rectangular
cross-sectional shape with sides of 2-3 mm, made of a colorless
transparent resin material such as acryl, and having a reflecting
surface for changing the direction of incident light thereon. By
increasing the reflecting surface, it is possible to bend the incident
light into different directions.
With reference to FIG. 7, emitted light from a light emitting part
26 of the camera is propagated as indicated by the arrow and is
bent upward through the light guide 27. The emitted light need not
be deflected upward. It may be deflected in any other direction.
Since the area is small through which the deflected light is guided,
this light does not come to affect the photographed image.
An optical fiber may be used as a light guide. An optical fiber
as a light guide is advantageous because of an increased degree
of freedom of position.
A light-screening plate 28 is placed in front of the light guide
27 for screening the portion of emitted light propagating in forward
directions. FIG. 8 shows the light guide 27 and the light-screening
plate 28 as attached to a camera. In this example, the emitted light
is deflected upward. The camera as shown in FIG. 8 may be enclosed
in a housing (as shown at 4 in FIG. 5) directly.
With an optical fiber 8 as shown in FIG. 5 connected to the upper
surface of the housing 4, emitted light is led to and serves to
activate the outer lamp. In such an application, the amplifier circuit
21 described above may be dispensed with.
By using a light intensity-reducing filter or a light guide as
described above, the quantity of light emitted from the inner lamp
and reflected from the target object to be photographed becomes
negligibly small from the point of view of the camera. As a result,
the aforementioned phenomena of marine snow and flare due to the
inner lamp can be effectively prevented. The light passing through
the aforementioned filter or light guide is received by the sensor
10 at the light receiving part of the outer lamp 9 either through
the optical fiber cable 8, directly or by reflection from the target
object to be photographed. The sensor 10 serves to convert the received
light into an electrical signal and thereby controls the emission
of light from the outer lamp 9.
In summary, the disclosure is intended to be interpreted broadly.
It is to be noted in particular that throughout herein the term
"infrared" is intended to include near infrared and that
the precise definition of the term "near infrared" depends
on how the camera is sensitive to light of a particular wavelength
range and light in that wavelength range is desired to be eliminated
from affecting the quality of the obtained image.
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