Note: Descriptions are shown in the official language in which they were submitted.
. 7569
TITLE: PREFLASH MEASUREMENT TECHNIQUE
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an automatic exposure control
system for an electronic flash camera, in general, and to a technique for
employing the electronic flash in such a camera for determining certain
photographic scene characteristics prior to exposure, in particular.
2. Description of the Prior Art
Automatic exposure control systems for electronic flash cameras
that cause an electronic flils)1 to illuminate a scene with artificial IigIU
prior to exposure, in order to determine certain photographic scene
characteristics for the purpose of adjusting one or more camera
functions, are known in the photographic arts. In, for example, U.S.
Patent No. 3,173,347 to Stimson et al., an automatic exposure control
system for a camera is disclosed in which a source of artificial light is
energized to illuminate a photographic scene prior to exposure and a
signal derived from sensing a reflection of this illumination from a
subject is employed to set a camera aperture.
In U.S. Patent No. 4,302,084 to Greenwald et al, a focusing
system for a photographic camera that also employs a pre-exposure flash
ZO is disclosed. This focusing system utilizes an electronic flash to direct
light toward a subject to be photographed prior to exposure. The
electronic flash light reflected from a subject within a scene is sensed
and integrated. When the amount of reflected flash liglo rcaclrcs ;i
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predetermined level a quench circuit is activated to generate a signal
which is used to extinguish the light emanating from the light source.
timer measures the elapsed time between the initiation of the electronic
flash and the generation of the quench signal. Converter means are
employed to translate the measured time interval into a range signal
that is functionally related to the distance between the focusing system
and the subject. This range signal may thus be employed to adjust or
focus the movable element of an adjustable focus lens system.
A major advantage of the above-described ranging portion ol'
the Greenwald et al. focusing system may be its ability to determine the
distance to subjects over a relatively wide range of subject clistances,
1-lowever, this advantage produces a major ciisacivan(gc which is the
inability to accurately determine subject distances of relatively close
subjects. More importantly though, this type of ranging sytcm conwn~cs
a relatively large amount of energy during the ranging process hecawc
light from the electronic flash must continue to illuminate a scene,
including a remote subject located therein, until a predetermined level
of reflected light has been sensed and integrated, a level that is
dependent, in large part, upon subject distance. Generally, the more
distant a subject the greater will be the energy consumption level.
'1'17e consumption of a large amount of energy for the prc-
exposure flash is not a problem in a ranging system where two separate
flash energizing or main discharge capacitors are provided, such as is
provided iri the electronic flash device described in U.S. Patent No.
2~ 4,25<,»5 to Ishida. However, in an exposure control system employing
an electronic flash unit that includes a single main discharge capacitor
for storing all of the electrical charge needed to fire the electronic flash
both before and during exposure, such as in the range-finding device
described in the above-noted Greenwald et al. patent, an excessive
consumption of this stored charge before exposure may excessively limit
the amount of charge available to fire the electronic flash for the
required amount c>f time during exposure.
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SUMMARY OF THE INVENTION
It is a primary object of the present invention, therefore, to
provide an electronic flash. system with a single main discharge capacitor
that is capable of fully firing the electronic flash from a single capacitor
charge both before and during an exposure interval.
It is another abject ~f the present invention to provide an
automatic exposure control system for an electronic flash camera
incorporating a pre-exposure flash subject reflectivity measurement
technique that is capable of accurately determining the distance to
relatively close subjects.
It is a further object of the present invention to provide an
automatic exposure control system for an electronic flash camera
incorporating a pre-exposure flash subject reflectivity measurement
technique of reduced cost and complexity.
Other objects, features and/or advantages of the present
invention will be readily apparent from the following detailed description
of a preferred embodiment thereof when taken in conjunction with the
accompanying drawings.
In accordance with a preferred embodiment of the present
invention an automatic exposure control system for an electronic flash
camera is provided that incorporates reduced complexity and energy
C()nStllllptl()11 rrleflrlS for measuring the reflectivity of a scene
illuminmed
by the electronic flash prior to exposure in order to determine
certain photographic scene characteristics for use in controlling a
2~ subsequent exposure. Means are provided for triggering the electronic:
flash to illuminate a scene with a pulse of light for an extremely short,
fixed period of time and for integrating a reflection of this IibIU from n
scene subject. The final integrated value of the reflected light is a
measure of subject reflectivity. Means are also provided for dcrivip
certain photographic scene characteristics from this final value of
integration for use in controlling a subseduent photographic exposure.
Illuminating the scene with a pulse of light from an electronic flash for
a fixed period of time with energy from a single main cliscl~ar~c
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capacitor in this manner makes more energy available to
immediately fire the flash during a subsequent exposure with
energy from the same main discharge capacitor.
In accordance with the present invention, there is
provided apparatus for measuring the reflectivity of a subject
within a photographic scene comprising: a light source for
illuminating the photographic scene that is energizable for a
fixed period of time; light sensitive means for detecting light
emitted by said light source and reflected from the subject and
for generating a signal responsive to the reflected light;
integrating means coupled to said light sensitive means for
integrating said reflected light responsive signal for a
predetermined period of time that commences at a particular
delay time after the activation of said light source to
illuminate the scene and terminates at the end of the fixed
period of time that said light source is energized to
illuminate the scene, the final value of integration being a
signal that is a measure of subject reflectivity; and means for
energizing said light source to illuminate the scene and
thereby generate said subject reflectivity signal.
In accordance with the present invention, there is
also provided apparatus for measuring the reflectivity of a
subject within a photographic scene comprising: a light source
for illuminating the photographic scene that is energizable for
a fixed period of time; light sensitive means for detecting
light emitted by said light source and reflected from the
subject and for generating a signal responsive to the reflected
light; integrating means coupled to said light sensitive means
for integrating said reflected light responsive signal for a
predetermined period of time that commences at a particular
delay time after the activation of said light source to
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illuminate the scene and terminates before the end of the fixed
period of time that said light source is energized to
illuminate the scene, the final value of integration being a
signal that is a measure of subject reflectivity; and means for
energizing said light source to illuminate the scene and
thereby generate said subject reflectivity signal.
In accordance with the present invention, there is
further provided apparatus for measuring the reflectivity of a
subject within a photographic scene comprising: a light source
for illuminating the photographic scene that is energizable for
a fixed period of time; light sensitive means for detecting
light emitted by said light source and reflected from the
subject and for generating a signal responsive to the reflected
light; itegrating means coupled to said light sensitive means
for integrating said reflected light responsive signal for a
predetermined period of time that commences at a particular
delay time after the activation of said light source to
illuminate the scene and terminates after the end of the fixed
period of time that said light source is energized to
illuminate the scene, the final value of integration being a
signal that is a measure of subject reflectivity; and means for
energizing said light source to illuminate the scene and
thereby generate said subject reflectivity signal.
In accordance with the present invention, there is
further provided a method of measuring the reflectivity of a
subject within a photographic scene comprising the steps of:
energizing a light source so as to illuminate a subject within
the photographic scene, for a fixed period of time; detecting
light emitted by the light source and reflected from the
subject, and generating a signal responsive to the reflected
light; and integrating the reflected light responsive signal
for a predetermined period of time that commences at a
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particular delay time after the activation of the light source
to illuminate the scene and terminates at the end of the fixed
period of time that the light source is energized to illuminate
the scene, the final value of integration being a measure of
subject reflectivity.
In accordance with the present invention, there is
further provided a method of measuring the reflectivity of a
subject within a photographic scene comprising the steps of:
energizing a light source so as to illuminate a subject within
the photographic scene, for a fixed period of time; detecting
light emitted by the light source and reflected from the
subject, and generating a signal responsive to the reflected
light; and integrating the reflected light responsive signal
for a predetermined period of time that commences at a
particular delay time after the activation of the light source
to illuminate the scene and terminates before the end of the
fixed period of time that the light source is energized to
illuminate the scene, the final value of integration being a
measure of subject reflectivity.
In accordance with the present invention, there is
further provided a method of measuring the reflectivity of a
subject within a photographic scene comprising the steps of:
energizing a light source so as to illuminate a subject within
the photographic scene, for a fixed period of time; detecting
light emitted by the light source and reflected from the
subject, and generating a signal responsive to the reflected
light; and integrating the reflected light responsive signal
for a predetermined period of time that commences at a
particular delay time after the activation of the light source
to illuminate the scene and terminates after the end of the
fixed period of time that the light source is energized to
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illuminate the scene, the final value of integration being a
measure of subject reflectivity.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic diagram of a photographic
camera which incorporates a preferred embodiment of the pre-
exposure, reflectivity measuring, exposure control system of
the present invention;
Fig. 2A is an exploded perspective view of a scanning
type shutter blade mechanism which is also schematically shown
in Fig. l;
Fig. 2B is an unexploded top view, partly in section,
of the shutter blade mechanism of Fig. 2A;
Fig. 3A is a graph of the electronic flash energizing
and de-energizing signals, as a function of time, during an
exposure cycle and prior to an exposure interval;
Fig. 3B is a graph of the light output of the
electronic flash of the present invention, as a function of
time, during an exposure cycle and prior to an exposure
interval;
Fig. 3C is a graph of the time integration of the
output current of the infrared sensor employed in the exposure
control system of the present invention during an exposure
cycle, prior to an exposure interval; and
Fig. 4 is a graph showing primary and secondary blade
aperture size variations as a function of time during an
exposure cycle.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, and specifically to
Fig. 1, there is shown a single lens reflex (SLR) photographic
camera 10 of the self-developing type which incorporates a
preferred embodiment of the pre-exposure, reflectivity
measuring exposure control system of the present invention.
The camera 10 includes an objective or taking lens 12, of the
fixed focus type, that may include one or more elements (only
one shown) for focusing image-carrying light rays of, for
example, an object 14 on a film plane 16 through an aperture
formed in a shutter blade mechanism or assembly 18.
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With additional reference to Figs. 2A and 2B of the
drawings, the blade mechanism 18, positioned intermediate the
lens 12 and the film plane 16, includes a pair of overlapping
shutter blade elements 20A and 20B of the "scanning" type.
Scene light admitting primary apertures 22A and 22B, are
respectively provided in the blade elements 20A and 20B to
cooperatively define a progressive and predictable variation of
effective aperture openings in accordance with simultaneous
longitudinal and lateral displacement of one blade element with
respect to the other blade element in a manner more fully
described in commonly assigned U.S. Patent No. 3,942,183 to
Whiteside. The blade element apertures are selectively shaped
so as to overlay the central optical axis of the lens 12 thereby
defining a gradually varying effective aperture size as a
function of the position of the blades of the blade mechanism
18. A shutter drive 24 is provided for displacing the blade
elements 20A and 20B. The shutter drive 24 includes a tractive
electromagnetic device in the form of a solenoid (not shown)
employed to displace the shutter blade elements with respect to
one another in a manner more fully described in the above-cited
Whiteside patent.
Each of the blade elements 20A and 20B of the blade
mechanism 18 includes two secondary apertures 26A, 28A and 26B,
28B, respectively. The aperture 26A in the blade 20A cooperates
with the aperture 26B in the blade 20B to form an opening 30 and
the aperture 28A in blade 20A cooperates with aperture 28B in
blade 20B to form an opening 32 through the shutter assembly 18.
These cooperating secondary apertures may be configured to track
in a predetermined corresponding relationship with respect to
the scene light admitting primary apertures 22A and 22B. With
the primary and secondary apertures being formed in the same
blade element and therefore being mechanically coupled to one
another, it is readily apparent that the secondary apertures can
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move in the same manner as the primary apertures when the blade
elements 20A and 20B are displaced, in the above-described
manner, with respect to one another. The amount of
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artificial light admitted to the film plane 1G through the primary
apertures 22A and 22B is controlled by a signal generated by a
combination of an infrared photosensitive element 34 within an infrared
sensor and ail integrator 38 that senses and integrates a corresponding
amount of infrared scene energy through the opening 30. The amount
of visible ambient light admitted to the film plane 16 through these
primary apertures is controlled by a signal generated by a combination
of a visible light photosensitive element 4U within a visible light sensor
42 and an integrator 43 that.senses and integrates a corresponding
amount of visible ambient light, through the opening 32. An example ol'
scanning blade elements having primary and secondary apertures that
cooperate to control the amount of scene light admitted to a film plane
is shown in U.S. Patent No. 3,942,183, supra.
The camera 10 is provided with a blade position sensor/cncoolcr
44. The sensor/encoder 44 senses the position of the blade elements
20A and 20B with respect to one another and generates a signs) 4~>
representative of the relative blade element position. The
sensor/encoder 44 comprises a light emitting diode 48, a photosensor SO
spaced therefrom, and a plurality of slots or openings S2 and S4 formed
in the blade elements 20A and 20B, respectively. The slots 52, 54 are
rectangular in shape, are of uniform size and are equally spaced in a
linear direction in their respective blade elements 20A and 2013. The
slots 52, 54 are interposed between the light emitting diode 48 and the
photosensor 50 such that they alternately block and unblock the
2S transmission of light between these two components to thereby cause the
photosensor SO to generate one or more pulses 4C representative ol' the
relative position of the blade elements 20A and 20B. The position of
the blade element 2UA with respect to the blade element 20B defines
the size of the effective or taking aperture formed by the primary
apertures 22A and 22B in the blade mechanism 18. 'l'heretore, the
relative position of the blade elements 20A and 20B represented by the
pulse or pulses 4(i is also a measure of the size of the effective or
taking aperture formed by the primary apertures 22A and 2213. The
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size of the slots 52, 54 in respective blade members 20A anti 20B is
kept to a minimum, in the direction of blade member movement, in
order to minimize any blade position errors between the actual size of
an effective aperture formed by the primary apertures 22A and 2213 and
S the relative blade position pulse signals 46 representative of this
particular aperture.
The camera 10 is also provided with an electronic flush
apparatus 56 together with apparatus for controlling its energization in
order to determined subject reflectivity and to provide a portion of tl~c
exposure value required to illuminate a scene to be photographed. '1'hc
electronic flash apparatus 56 comprises a main storage capacitor S8
which may be charted up to an oloerating voltage by any convcnlion;~l
voltage converter circuit (not shown) which would be included will~in a
DC-DC voltage converter 60. The l:)C-DC voltage converter l>(>
I~ operates in a conventional manner to convert a DC voltage as may be
derived from a battery 62 of the camera 10, which can be in the c7rder
of 6 volts, to a suitable operating voltage such as 280 volts. A flash
tube 64 and a series connected thyristor are collectively connected, in a
parallel relation, with respect to the main storage capacitor 58. The
flash tube 64 may be energized by a suitable trigger signal on a path 68
from a conventional trigger circuit (not shown) within an exposure
control electronic module 70, and the thyristor 66 may lie activated to
its open state by a suitable trigger signal on a path 71 from another
conventional trigger circuit (not shown) that is also included within the
exposure control electronics module 70. When energized, the flash ml~r.
64 illuminates the scene and subjects included therein with both visible
and infrared light.
The camera 10 additionally includes an empirically derived look-
up table 72. The primary purpose of the look-up tulle 72 is to comrol
the amount of image-carrying scene light rays focused on the film plane
16 by the lens 12 through the effective or taking aperture in the blade
mechanism 18 formed by the primary apertures 22A and 22B, as a
function of ambient scene light and of subject reflectivity.
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As previously explained, the amount of artificial and arnl>ient
scene light transmitted to the film plane 76 is indirectly measured by
sensing a portion of the artificial and ambient scene light through the
openings 30 and 32 in the blade mechanism 18 with the photosensor 34
located within the infrared light sensor 36 and its associated integrator
38 and the photosensor 40 located within the visible light sensor 42 and
its associated integrator 43. A signal generated by the infrared sensor
36 and its associated integrator 38 representative of reflected infrared
scene light is routed to the look-up table 72 through a path 74 and a
signal generated by the visible light sensor ~2 and its associated
integrator 43 representative of ambient scene light is routed to the look-
up table 72 through a path 76.
The Jook-up table 72 generates a plurality of different signals in
response to these two signals for controlling the amount of image-
1.5 carrying light rays transmitted to the film plane 16 through the primary
apertures in the blade mechanism 18. These plurality of different
signals are derived for each exposure cycle, prior to an exposure
interval. As an alternative, these signals may also be derived in the
early stages of an e;:posure interval.
The signals derived by the look-up table 72 are 7) an aperture
size signal tha controls the size of the Uking yocrlurc I'orroccl by tlu~
primary apertures 22A and 22B at which the flash tube 64 is fired, on
an output path 78; 2) a percentage of artificial light signal that controls
the amount of artificial light to be added to the scene to be
photographed by the flash tube 64, on an output path 80; 3) a
percentage of ambient light signal that controls the amount of imugc-
carrying light to be admitted to the film plane 16 through the primary
apertures 22A and 22B in t1e blade mechanism 18, on an output path
82; and 4) a signal to terminate the exposure interval at a time
dependent upon the magnitude of the artificial and ambient light signals
appearing tin the input paths 74 and 76, respectively, to the look-up
table 72, if the exposure interval is not sooner terminated, on an output
path 84.
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As mentioned above, the camera 10 is provided with an
electronic flash apparatus SG whose light output is employed to
determine subject reflectivity and to provide a portion of the exposure
value required to illuminate a scene to be photographed. The light
output of the electronic flash apparatus 56 is employed during an
exposure cycte prior to an exposure interval for the determination of
subject reflectivity.
The reflectivity of a subject within a scene is determined in the
following manner. With additional reference to Figs. 3A, 3B anti 3C of
the drawings, when an exposure cycle is initiated the conventional
trigger circuit (not shown) within the exposure control electronics
module 70 transmits a trigger signal 86 (Fig. 3A) on the path 68 to
energize or initiate the firing of the flash tube G4. After an inherent
delay of approximately five microseconds, the flash tube 64 starts to
illuminate the scene with visible and infrared light in the manner shown
in ,Fig. 3B. After a delay of approximately two microseconds from the
triggering of the flash tube 64, the integrator 38 at the output of the
infrared light sensor 36 is enabled by an enable signal from the
exposure control electronics module 70 on a path 87. This two
microsecond delay is to minimize the possibility of integrating error-
producing noise generated by the triggering of the flash tube 64 and toy
the sensing of ambient infrared light that might already be illuminating
the scene prior to its being illuminated with light from the flash tube
64. Fig. 3C is a graph of the integration of the output current from the
infrared sensor 36 as a function of time by the integrator 38.
Thirty-five microseconds after the triggering of the flash tube t=t
to illuminate the scene by the exposure control electronics module 70,
another conventional trigger circuit (not shown) within the exposure
control electronics module 70 transmits a trigger signal 8fi (Fig. 3~1) on
the path 71 to trigger the thyristor 66 to its open state and thereby
initiate the extinguishing of the light output of the flash tube 64. At the
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same time that the thyristor titi is triggered to initiate the cxtinguisl~ing
of the light output of the flash tube C4, the exposure control electronics
module 70 disables the integrator 38 through the path 87 to terminate
its integration of the output current of the infrared libht sensor 3ti. It
should be noted and as shown in Fig. 3B, even though the flash tube C4
is de-energized or triggered off at a particular time, it continues to
illuminate the scene with light for a significant period thereafter.
In some applications, the initiating of the extinguishing of the
light output from the flash tube C4 at the same time that the integrator
38 is disabled may introduce thyristor-generated-noise integration' errors
into the exposure control system of a magnitude that may not lie
tolerable. if this should occur, the integrator 38 could be disabled a
few tenths of a microsecond before the triggering of the thyriste>r C< and
thereby avoid such errors. In other exposure control applic<Uions tl~c
I~ disabling of the integrator 38 at the same tune or before the initiating
of the extinguishing of the light output from the flash tube C4 may
result in an integration signal of insufficient magnitude for proper
exposure control system operation. In such instances the integrator 38
may be disabled after the triggering of the thyristor 6< to its off or open
state in order to increase the amount of light integrated thereby.
However, additional circuitry may hove to lie added to compensate for
the integration errors that would normally be produced when the
integrator 38 integrates all of the noise generated by the actuation of
the thyristor C6 tc»ts off or open state, if such integration errors are
unacceptable. No matter what point in time the integrator 3S is
disabled, its final level of integration would constitute a signal
representative of subject reflectivity.
Prior tc~ the generation of the above-noted look-up table 72
output signals on the paths 78, 80, 82 and 84, the ambient visible light
signal generated by the visible light sensor 42, integrated by the
integrator 43 and applied to the look-up table 72 through the path 7f~, is
routed to a microcontrollcr 90 through ;r lalh 92, fr>r tcml>rary al r;yu.
Subsequent to the storage of this ambient visible light signal in the
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microccantrollcr JO and prior to the start of an exposure interval, an
infrared light signal generatcci by the infrared sensor 3<> and Il~c
integrator 38 in response to a pre-exposure interval flash of light from
the flash tube f4 containing an infrared light component that is reflected
from a scene subject, is routed to the look-up table 72 through the I:rrth
74. The ambient visible light signal already stored within the
microcontroller 90 is then routed to the look-up table 72 through a Irolr
94. This stored ambient visible light signal and the infrared signal
subsequently generated by the infrared light sensor 3C and integrated by
the integrator 38 are collectively employed within the took-up table 72
to generate the above-noted signals appearing on the output paths 7~,
$0, 82 and g4 from the look-up table 72.
The signals appearing at the output paths 78, 50, 82 and 84 of
the look-up table 72 in response to the infrared and ambient visil~l~
scene light signals respectively generated by the sensors 3ti and 42 and
their respective integrators 38 and 43, are empirically determined. The
look-up table 72 is constructed in accordance with the subjective analysis
of a multiplicity of photographic images of subjects located at various
subject distances and having a range of reflectivities that are produced
under a wide range of artificial and ambient scene light conditions, in
order to generate these look-up table output signals.
In general, when forming a photographic image at the film
plane lti of the camera 10, the smaller the taking aperture formed by
the primary apertures 22n and 2213, the greater will he tl~e dcll~ of
field of the fixed focus lens 12 and the darker will be the image
resulting from ambient scene light because of the reduction in the
amount of image-carrying scene light caused by the smaller taking
aperture. The look-up table 72 is constructed such that it performs n
tradeoff between the sharpness of a subject within the scene and an
overall photographic scene exposure. In pcrl.'orming this tradeoff, tl~c
look-up table 72 causes the flash tube (4 to fire at the smallest possible
aperture, and therefore the greatest depth of field, that will proviclc tl~c
optimum subject sharpness and overall scene exposure. The look-up
CA 02027515 1999-09-07
table 72 further improves the overall scene exposure in response
to the infrared and visible light level signal generated by the
sensors 36 and 42 by controlling the amount of artificial light
generated by the flash tube 64 during an exposure interval and
by controlling the maximum size of the taking aperture formed by
the primary apertures 22A and 22B.
As noted above, the camera 10 is of the SLR type and
therefore includes a conventional reflex mirror 96 that is
actuatable by the exposure control electronics module 70 through
the path 98. The mirror 96 is actuatable, in a conventional
manner, between a viewing position where it blocks the
transmission of scene light to the film plane 16 and where a
camera operator can view a scene to be photographed through the
lens 12, and a taking or unblocking position as shown in Fig. 1,
where it facilitates the transmission of scene light to the film
plane 16 during an exposure interval.
The camera 10 is preferably designed for use with a
self-developing film unit (not shown) similar to those described
in U.S. Patent No. 3,415,644 to Land, in common assignment
herewith. The self-developing film unit is packaged in a
lighttight film cassette 100 shown in the condition assumed just
after the cassette 100 has been fully inserted into the camera
10. The cassette 100 may enclose the 6 VDC battery 62.
Mounted within the camera 10 is a film advancing
apparatus 102 similar to that described in U.S. Patent No.
3,753,392 to Land that includes a motor for operating a gear
train (neither shown) which is coupled with the film advancing
apparatus 102 to provide for the continuous movement of an
exposed film unit from an exposure position within the camera 10
toward the exterior thereof. The film advancing apparatus 102
additionally includes a film-engaging arm member (not shown)
driven by the above-mentioned motor and gear train. The arm
member is adapted to extend into a slot in the cassette 100 and
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engage the upper most film unit located therein at or near its
trailing edge prior to moving it out of the cassette 100 and
into the bite of a pair of conventional processing rollers (not
shown) mounted adjacent the
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leading edge of the above-mentioned uppermost film unit. The
processing rollers, which are rotated by the motor and gear train
mentioned above, continue the uninterrupted movement of the exposed
film unit toward the exterior of the camera 10 while simultaneously
S rupturing a container of processing liquid at the loading end of the
exposed film unit. The processing rollers spread the liquid contents c>f
the ruptured container between elements of the film unit to initiate
formation of a visible image within the film unit in a manner that iv
well-known in the art.
OPERATION
A typical exposure cycle will nc>w be described in detail. hor
the purpose of this description it is assumed that the taking aperture of
the blade mechanism 18 is in its full open position, that the openings .s0
and 32 formed by the secondary apertures in the blade mechanism 1S
L5 are also fully opened, that the mirror J6 is in its viewing or light
blocking position, that the flash apparatus 56 has been energized by the
prior closure of a switch 104 that coupled the battery 62 to the DC-DC
voltage converter 60 through the exposure control electronics module 70
and a path 105 and that the main storage capacitor S8 is fully charged
and is ready for the initiation of an exposure cycle. Fig. 4 is a graph
showing primary and secondary blade aperture size variations as a
function of time during the typical exposure cycle. With reference m
Figs. 1, 2A, 2B, 3A, 3B, 3C and 4 of the drawings, a switch 106 is
actuated to its closed position by a camera operator to initiate an
2S exposure cycle. The closure of the switch 106 couples the battery 62 to
the exposure control electron?cs module 70 through a path 10~. With
the blade mechanism opening 32 formed by the secondary apertures 2,~n
and 28B adjacent the visible light sensor 42 in its full open position, the
exposure control electronics module 70 and the microcontroller >0
coupled thereto through a path 11U, in turn, activate the visible light
sensor 42 and the integrator 43 coupled to the visible light sensor 42,
through a path 112. When activated, the integrator 43 is enabled to
integrate ambient scene light for a fixed period of tune and then send
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the final integrated value thereof to the look-up table 72 through the
path 76 and then to the microcontroller 90 through the path 92 for
temporary storage.
Subsequent to the storage of the ambient scene light
information in the microcontroller 90, the exposure control electronics
module 70 energizes the shutter drive 24 to actuate the blade
mechanism 18 and therefore the taking aperture together with the
opening 30 formed by the secondary apertures 26A and 26(3, and the
opening 32 formed by the secondary apertures 28A and 28B, to their
fully closed positions. Subsequent to the closing of the opening 30 in
the shutter mechanism 18 and prior to the initiations of an exposure
interval, the shutter drive 24 causes the opening 30 to increase in size
toward its fully opened position. While the opening 30 is being moved
toward its fully opened position, the exposure control electronics module
IS 70 actuates means (not shown) for moving the mirror 96 from its
viewing or light blocking position, where it precludes the transmission of
image carrying light rays to the film plane 16, to its Light unblocking
position (as shown in Fig. 1), where it facilitates the transmission ol'
image-currying light rays to the film plane 1C during an exposure
interval through the path 98. When the opening 30 adjacent the
infrared light sensor 36 is in its fully opened position, tire exposure
control electronics module 70 triggers the flash tube 64 through the pnh
h8 to thereby illuminate a scene to be photographed with visible and
infrared light prior to the initiation of an exposure interval. The
exposure control electronics module 70 then triggers the thyristor GC to
its open or off state through the path 77 thirty-five microseconds after
turning on the flash tube 64 to thereby initiate the extinguishing of the
light output of the flash tube 64. This triggering on and off of the flash
tube 64 constitutes a first pulse of light directed toward the scene to I~c
photographed.
The exposure control electronics module 7U also activates the
infrared light sensor 36 and the integrator 38 coupled thereto throu~,l~
the path H9 for thirty-three microseconds or for two micrc>seconcls Icss
14
~~~'~5~.5
than the period of time that the strobe 64 is triggered to its on or scene
illuminating state. The exposure control electronics module 7U then
causes the final value of the integrator 38, which constitutes a measure
of subject reflectivity, to be sent to the look-up table 72 through the
path 74. Upon receipt of this subject reflectivity signal the loolc-up
table 72 combines ii with the ambient visible light signal previously
stored in memory in the microcontroller 90. These combined signals
are then employed to generate the aperture size flash fire signal, the
percentage of artificial light signal, the percentage of ambient light
signal and the end of exposure signal subsequently appearing on the
look-up table output paths 78, 80, 82 and 84, respectively, that are, in
turn, applied to the exposure control electronics module 7U. Upon
receipt of these look-up table generated signals, the exposure conlrc~l
electronics module 70 actuWcs the shutter drive 24 .md the I~I;rel~
mechanism 18 coupled thereto such that the opening 30 formed by the
secondary apertures 26A and 26B is placed in its fully closed position
and actuates the shutter drive 24 and the blade mechanism 18 to initiate
an exposure interval. The exposure control electronics module 70
includes four conventional comparators (not shown) to determine when
the four conditions represented by the look-up table output signals on
the paths 78, 8U, $2 and 84 and employed in the generation of an
exposure interval have been achieved. An exposure interval is defined
herein as the period of time that the shutter mechanism 18 allows
image-carrying light rays collected by the lens 12 to reach the film plane
16.
The first of the above-mentioned comparators compares the
reference or desired aperture size flash fire signal on look-up table
output path 78 with the blade position signal and therefore the taking
aperture size as represented by the pulses 46 from the blade position
sensor/encoder 44. When this first comparator determines that these
two signals are equal, the exposure control electronics module 7U once
again triggers the flash tube f4 through the path 68 and thereby
~o~~~~~
illuminates the scene being photographed with visible and infrared IibIU
during the exposure interval.
The second of the above-mentioned comparators compares tl~c
reference or desired percentage of artificial light signal on look-up table
S output path 80 with the actual level of artificial light illuminating the
scene as sensed by the infrared sensor 36, integrated by its associated
integrator 38 and then routed to the exposure control electronics module
70 through the path 114. When this second comparator determines that
these two signals are equal, the exposure control electronics module 70
triggers the thyristor 66 to its open state through the path 71 to thereby
cause the artificial light being generated by the flash tube 64 to be
extinguished. This illumination of the scene with artificial light
constitutes a second pulse of light that is directed toward the scene to
be photographed.
The third of the above-mentioned comparators compares the
reference or desired percentage of visible light signal on look-up table
output path 82 with the actual level of visible light illuminating the
scene as sensed by the visible light sensor 42, integrated by its
associated integrator 43 and then routed to the exposure control
electronics module 70 through the path 112. When this third
comparator determines that these two signals are equal, the exposure
control electronics module 7U activates the shutter drive 24 to close the
taking aperture in the blade mechanism 18 and thereby terminate the
exposure interval.
2~ Under certain scene lighting and subject reflectivity conditions
there may be insufficient ambient and/or artificial scene light reflected
from the scene for the infrared sensor 3ti and/or the visible liglu sensor
42 to generate a signal that is capable of causing the exposure control
electronics module 70 to terminate an exposure interval within a
reasonable amount of time. A fourth cornparator arrangement cony;rria
a signal on the look-up table output path 84 representative of the actual
level of ambient or reflected scene light with a precletern~inecl refercncu
signal stored within the exposure control electronics n~oclnle 7(), If tlrc
lh
wf
sibnal on Iltc lath S~4 is cclual to or greater than the reference sigltal,
the exposure interval will be limited to a relatively short t~eric>cl of
tilttc
such as 4U milliseconds whereas if this signal is less titan tire refer circa
signal the exposure interval will be limited to a relatively long period c>f
S time such as 400 milliseconds unless terminated sooner by the presence
of sufficient exposure levels of ambient and/or artificial scene light.
At the completion of the exposure interval, the exposure control
electronics module 70 actuates the mirror 96 toward its light-blocl<inb
position, and actuates the film advancing apparatus '102 and the drive
motor (not shown) included therein, through a path 116, to initiate the
transport and processing of an exposed, self-developing film unit. The
film advancing apparatus, in turn, moves the exposed film unit located
in the cassette 1()0, through a path 118, into the bite of the pair c>f
adjacent processing rollers (not shown), in the manner described above,
1~ to spread processing liduid between certain film layers and to move the
exposed film unit into an exit slot (not shown) in a housing 12U of tl~c
self-developing camera lU. After the mirror W has been actuated to its
light blocking position where it precludes the passage of light to the film
plane 16, the exposure control electronics module 70 actuates the
shutter drive 24 and the shutter mechanism 18 coupled thereto such th,U
the primary or taking aperture thereof is placed in its fully opened
position. After the film advancing apparatus 102 as moved the exposccl
film unit through the above-mentioned pair of rollers, a film movement
completion signal is routed to the exposure control electronics nu~dule
7() and the microcontroller )0 coupled thereto through a path 122,
Upon receipt of this film movement completion signal the exposure
control electronic module 70 initiates the charging of the electronic fl,tsl~
apparatus 56 through the path 105. When the main storage or
discharge capacitor 58 of the electronic flash apparatus 56 is fully
:i0 charged, as sensed through the path 10~, the exposure control electronic
module 70 places the exposure control system of the camera 10 in
condition for the initiation of the next exposure cycle.
17
In the exposure control system described above, a source of
artificial light generated by the flash tube G4 was employed to illumio,uc
the scene with both infrared and visible light. The flash tube' G4
illuminated the scene twice during an exposure cycle, once befi>re and
once during the exposure interval. A11 of the energy required by thr;
flash tube G4 to illuminate the scene both before and during an
exposure interval is provided by a single storage capacitor described
herein as the main discharge capacitor S8. The amount of time that
energy is available to the flash tube 64 from the main discharge
capacitor 58 prior to an exposure interval is limited to a predetermined
period of time. In this the preferred embodiment, that period of time
has been limited to 35 microseconds. Limiting the amount of time and
therefore the amount of energy available to the flash tulle C4 prior to
an exposure interval reduces the range of distances over which it can be
1S employed in the determination of subject reflectivity. However, by
limiting the amount of time that energy is available to the flash tube C4
for reflectivity determination purposes prior to an exposure interval, the
main discharge capacitor 58 is able to store sufficient energy, from a
single capacitor charge, to power the flash tube G4 both before and
during an exposure interval.
From the foregoing description of the invention it will be
apparent to those skilled in the art that various improvements and
modifications can be made in it without departing from its true scope.
The embodiment described herein is merely illustrative and should not
be viewed as the only embodiment that might encompass the invention.
lS
