Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE ~NVENTION
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This invention relates to focusing systems for photo-
graphic cameras and, more particularly, it concerns a focusing
system and method by which the variable depth of focus of a
camera lens is accounted for automatically in the focus setting
of the lens.
Automatic focusing systems for photographic cameras
are now well known as evidenced by such commercially available
cameras as those marketed by Polaroid Corporation of Cambridge,
0 Massachusetts under such names as "POLAROID SX-70 SONAR
ONE-STEP" and "P.RONTO ONE-STEP." In such cameras,
camera/subject distance is determined by the time re~uired
for an acoustical pulse to travel to and from a subject to
be photographed. Once the distance or range has been determined,
the objective lens of the camera is driven by an electric
motor to a focus position corresponding to the acoustically
determined range and the film exposure cycle of the camera
is carried out. The entire operation of range finding,
focusing and exposure occurs in a fraction of a second so
that the time required for focusing does not add noticeably
to the time normally associated with camera operation for
film exposure.
The range finding and lens adjusting functions of
such systems are accomplished by electronic circuitry including
a focus control pulse counter, a clock oscillator which, when
activated, transmits in accordance with subject range, a series
of pulses to the counter, and a lens-associated encoder wheel/
detector which generates and transmits to the same counter a
number of pulses representative of lens focusing movement from a
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known initial position to the proper focus setting. As camera/
subject dista~ce decreases, the number of pulses from the
clock oscillator will decrease. Since the lens movement is
from the infinity setting to the nearest focus distance
setting, the number of pulses resulting from lens focusing
movement will increase inversely in relation to camera/
subject distance. As a result of this organization of
components, lens focusing movement is terminated in response
to the focus control counter accumulating a predetermined
number of counted pulses.
Also, in cameras of this type manufactured by
Polaroid Corporation, a light integrating exposure control
system is used to determine automatically the quantity of
light permitted to pass to the film during exposure. While
like conventional cameras, proper exposure for a given film
speed is determined by a combination of aperture size and
shutter speed, these two parameters are combined or integrated
in a single pair of shutter blades positioned directly
behind the objective lens of the camera. When actuated for
exposure, these blades move from a closed position through a
progressively enlarged aperture setting until they stop and
return to a closed position. Auxiliary openings in the same
set of blades sweep a light detecting photocell associated
with a light integrating network which determines the aperture
size to which the shutter blades will move before returning
to an exposure terminating or closed position. This type of
exposure control is exemplified by the disclosures of U.S.
Patents No. 3,641,889, issued February 15, 1972 to Viato K.
Eloranta and No. 3,975,744, issued August 17, 1976, to Bruce
K. Johnson, et al.
929
As in all variable aperture or multi-stop lenses,
the distance along the lens axis within which objects will
be focused on the camera film plane for a given focus setting
of the lens, or depth of focus, will vary with the aperture
stop or diameter of the lens opening through which light is
passed for film exposure. Specifically, the depth of focus
varies inversely with aperture size. In cameras equipped
with a light integrating exposure control system of the type
mentioned, therefore, depth of focus will vary directly and
automatically with the brightness of the scene or object to
be photographed.
In acoustical lens focusing systems of the type
mentioned, the camera/subject distance is the distance between
the camera and the nearest sound reflecting subject portion or
object located close to the optical axis of the camera lens.
The lens will be focused, therefore, at a position such that
the nearest subject portion will lie midway between the near
and far limits of the in-focus distance or field provided
by the lens depth of focus. While this condition is perhaps
representative of the focusing position to which the lens
would be set manually by most amateur photographers, in many
cases it would be desirable for the medial plane of the
in-focus field to be positioned behind the nearest subject
so that the near limits of the depth of focus~distance
falls closely in front of the nearest object while the far
limit of the in-focus distance is extended rearwardly. This
situation is illustrated by three objects constituting a
total subject to be photographed and positioned, for example,
at seven, nine and twelve feet from the camera and illuminated
by ambient light calling for a lens aperture at which the
29
depth of focus distance is approximately five feet. If the
camera lens is focused for approximately seven feet as a
result of an acoustical range finder distance determination,
the first two objects will be in focus whereas the object
located twelve feet from the camera will be out of focus.
If the focus setting of the lens is increased to nine and
one-half feet, all three objects would be in focus as a
result of the depth of focus under the ambient light conditions
indicated.
SUMMARY OF THE INVENTION
In accordance with the present invention, the focusing
adjustment of the camera lens is automatically modified to
account for the depth of focus in accordance with aperture size.
The lens focusing position, normally determined by the distance
between the camera and subject, is shifted through one or more
increments of focus adjustment toward the infinity focus setting
of the lens, with decreasing aperture size. As a result, the
nearest portions of the subject will lie in front of a medial
plane of in-focus distance, but within the depth of focus
distance extending in front of the medial plane and, correspond-
ingly, those portions of the subject as well as other scene
elements positioned behind the nearest subject portion will
still be in focus.
The modified lens focusing adjustment of the
invention is achieved in automatic lens focusing systems of
the type mentioned very simply by preloading the focus
control pulse counter of such systems with one or more pulse
counts representative of ambient light levels and correspondingly
representative of lens aperture setting and lens depth of
focus under such ambient lighting conditions. Since lens
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movement, as mentioned, is from the infinity setting position toward the
nearest focus distance setting, the preloaded pulse counts will terminate
focusing movement of the lens one or more increments of focus setting toward
the infinity setting, again depending on the depth of focus which results
from the lens aperture size at which the camera loaded film will be exposed
to an image of the subject. Moreover, ~he counter preloading pulses are
developed using the existing light integrating network presently incor-
porated in commercially available cameras of the type mentioned.
More generally, according to a first aspect of the present
invention, there is provided the method of focusing a variable aperture
obJective lens of a photographic camera having a range finder to determine
the distance from the camera to the near part of a subject to be photograph-
ed, focus control means for positioning said lens at a focus setting cor-
responding to the distance determined by said range finder and aperture
control means for determining the effective lens aperture value for proper
exposure of camera-contained film to said subject, said method comprising
the steps of: generating a signal representative of objective lens depth
of focus for the determined lens aperture value to be used; and transmit-
ting said signal to said focus control means to effect a focusing adjustment
~0 of said lens in accordance with said determined aperture value to a focus
setting corresponding to a distance greater than that determined by said
range finder.
According to a second aspect of the present invention, there
is provided in an automatic focusing system for a photographic camera, said
camera having a variable lens aperture, means for determining the effective
value of said lens aperture employed in a given photographic scene, range
finder means for determining camera/subject distance, and focus control
means for positioning a lens element of said camera within a range of focus
distance settings, the imProvement comprising: means for generating a signal
representative of the size of said lens aperture and correspondingly, the
lens depth of focus; and means for ad;usting said focus control system to
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position said lens element in response to both said range finding means
and said aperture determining means to a focus distance setting correspond-
ing to a camera/subject distance greater than the distance determined by a
said range Einder so as to exploit the depth of focus variation with
selected aperture value.
Among the objects of the present invention are, therefore,
the provision of an improved method and apparatus for automatically posit-
ioning the focus distance setting of a photographic camera lens; the pro-
vision of such a method and apparatus which takes advantage of increased
depth of focus resulting from reduced lens aperture sizes; and the provis-
ion of such a method and apparatus which maximizes use of mechanical and
electrical components in presently existing cameras.
Other objects and further scope of applicability of the
present invention will become apparent from the detailed descriptlon to
follow taken in conjunction with the accompanying drawings in w/hich like
parts are designated by like reference numerals.
RIEF DESCP~IPTION OF T~IE DRAWINGS
Fig. 1 is a schematic front elevational view of an automatic
focusing camera illustrating the mechanical components of its automatic
focusing system;
Fig. 2 is a similarly schematic elevation of the exposure
control system of the camera of Fig. 1 illustrating a fully open shutter
condition;
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Fig. 3 is a view like that of Fig. 2 with the
components of the illustrated exposure control system depicted
in an exposure taking position under high scene light conditions;
Fig. 4 is a front elevation view illustrating an
encoder wheel component of the automatic focusing system of
Fig. l;
Figs. 5a, b and c are schematic illustrations repre-
senting various focal setting positions of the camera lens; and
Fig. 6 is a schematic circuit diagram of electronic
components in the automatic focusing system of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Although the physical characteristics of the
present invention are embodied substantially in electronic
circuitry to be described with reference to Fig. 6 of the
drawings, reference is first made to Figs. 1-3 which illustrate
elementary lens focusing and exposure control components of
a camera in which the invention is particularly suited for
use. As will be apparent to those skilled in the art from
the ensuing description, however, the invention is equally
applicable to camera lens focusing and exposure control
systems different from that represented in Figs. 1-3. In
Fig. 1, therefore, the shutter and sound module housing
of a camera available commercially under the name
"POLAROID SX-70 SONAR ONE-STEP" is generally designated by
the reference numeral 10. Although many mechanical and
electronic components supported by the housing 10 in practice
have been omitted from Fig. 1 of the drawings in the interest
of more clearly illustrating parts which are relevant to the
present invention, it will be noted that a focusing lens
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element 12 is supported for movement on an optical axis 14
by a rotatable lens mount 16 having peripheral gear teeth
18. The gear teeth 18 mesh through an idler 20 with a
manual focusing wheel 22 and also through an idler 24 with a
gear train driven by an electric motor 26.
The electric motor 26 and associated gear train
are part of an acoustical range finding and automatic focusing
system by which the lens 12 is focused in response to the
time interval required for an acoustical pulse to be trans-
mitted from and received by a transducer supported by the
housing 10 and represented in Fig. 1 by a phantom line
circle 28. While the operation of the motor 26 and the
transducer 28 to focus the lens 12 will be described in
detail with reference to the circuit diagram of Fig. 6, it
will be noted at this point that operation of the motor 26
will effect focusing rotation of the lens mount 16 through
the gear train illustrated in Fig. 1.
In addition to rotating the lens mount 16, operation
of the motor 26 will rotate an encoder wheel 30 supported by
the housing 10. The encoder wheel 30 includes a circular
array of equally spaced openings 32 located to pass in
registry with a photoelectric detector 34 fixed with respect
to the housing 10. Although details of the photoelectric
detector 34 are not illustrated, it will suffice for purposes
of fully understanding the present invention that the
detector 34 will generate an electronic pulse once each time
an aperture 32 passes the detector 34. Also, the encoder
wheel 30 is provided with a series of latch teeth 36 on its
periphery, equal in number to the apertures 32 and adapted
to be engaged by a pawl 38 energized by a solenoid 40
supported by the housing 10.
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Exposure control components supported by the housing
10 but behind the lens 12 in the context of light passage from
a subject to be photographed to the film plane of the camera
including the housing 10, are illustrated in Figs. 2 and 3 of
the drawings. As shown in these drawing figures, a shutter/
diaphragm system or scanning shutter is employed, and includes
a pair of shutter blades 42 and 44, each having a primary
shaped aperture or opening 46 and 48, respectively, are supported
for relative lateral sliding movement by the housing 10. The
blades 42 and 44 are respectively connected to opposite ends
of a walking beam 50 supported by the housing 10 for pivotal
movement about a central axis 52 in response to an actuating
solenoid 54 having a return spring 56. In addition to the
primary openings 46 and 48, the shutter blades 42 and 44
include secondary or photocell sweep openings 58 and 60,
respectively. These openings cooperate on an axis 62 which
is the axis of a photocell (not shown) supported by the
housing 10. Though not shown in Figs. 1-3, the photocell
on the axis 62 forms part of a light integrating network 120
to be described below with reference to the circuit diagram
illustrated in Fig. 6.
The operation of the exposure control system
illustrated in Figs. 2 and 3 of the drawings is now well
known and described in several prior patents including, for
example, U.S. Patents No. 3,641,889 and No. 3,975,744 cited
above. A full appreciation of the present invention will be
facilitated, however, by summarizing at least certain
aspects of the exposure control operation effected by the
structure shown in Figs. 2 and 3.
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Because of the generally tear-shaped configuration
of the shutter blade openings 46 and 48, a maximum exposure
value or primary aperture value A is provided behind the
lens 12 when the shutter blades 42 and 44 are in the fully
open position as shown in Fig. 2 of the drawings. In this
condition, the solenoid 54 is de-energized and the walking
beam 50 is urged to the position shown by the spring 56.
Also, it will be noted that the sweep openings 58 and 60
define a secondary opening or aperture a through which light
may pass on the axis 62 to the lignt sensing element (not shown)
of the light integrating network 120. As is explained in the
aforementioned U.S. patents and as, in fact, occurs in the
aforementioned commercially available camera, the fully opened
position of the shutter blades is both the initial shutt~r
condition which permits reflex viewing of a scene, and also
provides the maximum aperture value achieved under low light
conditions.
Upon actuation of the exposure control system
illustrated in Figs. 2 and 3, the solenoid 54 is energized to
move the blades 42 and 44 to a position in which both apertures
A and a are fully closed. Film exposure then commences by de-
energizing the solenoid so that the spring 56 will move the
blades 42 and 44 to define enlarging aperture values and, for
example, under high scene light conditions only reach a position
in which the openings 46 and 48 define an exposure aperture value A'.
Similtaneously, the sweep openings 58 and 60 will define
enlarging secondary aperture values ultimately reaching an
aperture a'. When the sum total of light passing the secondary
aperture value is appropriate for proper exposure of the film
by light passing the exposure aperture, the solenoid 54 is again
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energized to ~uickly close both apertures; following which
the now exposed film is covered within the camera by a reflex
mirror (not shown), whereupon the blades are returned to their
full open position as shown in Fig. 2 for viewing of the next
scene.
The significance of the aforementioned exposure
control operation is that although shutter speed and lens
aperture size are integrated, the configuration of the openings
46 and 48 provide a variable lens aperture depending on illumi-
nation passing from the scene to be photographed or on ambient
scene light in the absence of some flash illumination. Also,
and as is well known in the photographic art, the size of the
lens aperture is determinative of the lens depth of focus or
the distance fore and aft of a given focus distance setting of
the lens within which all subject matter will be in focus at
the film plane of the camera. Specifically, for a given lens
the depth of focus will be minimal with a large aperture
represented, for example, by the fully opened condition of
the shutter blades 42 and 44 in Fig. 2 of the drawings. On
the other hand, with a relatively small aperture such as that
represented by A' in Fig. 3, the lens depth of focus will be
significantly increased.
In Fig. 5 of the drawings, various focus settings of
the lens 12 along the axis 14 thereof are depicted schematically
in relation to the film plane F of the camera in which the lens
12 is mounted. In Figs. 5b and 5c, the depth of focus distance
Fd for a given size lens aperture A' is also illustrated in
relation to a subject S, represented by three objects 64a, 64b
and 64c, located in a photographic scene at different distances
from the lens 12. Thus in Fig. 5b, the lens 12 is adjusted
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alony the axis 14 to the conventional focus position where the
first object 64a lies at or near a medial plane of focus Fm,
and the depth of focus Fd for the aperture A' straddles the
plane Fm 50 that two of the objects 64a and 64b will be in
focus as well as a distance o~ foreground in front of the first
object 64a. The farthest object 64c, however, will not be in
focus in this condition. However, if the setting of the lens
12 is adjusted through a distance d from the film plane F as
shown in Fig. 5c such that the subject distance to which the
lens 12 is focused is shifted toward infinity, the medial plane
of focus Fm is also thereby shifted so that all three objects
64a-c lie in the depth of focus distance Fd. The present
invention is addressed to the shifting of the focus position
of the lens 12 in a manner represented by Fig. 5c, and an
understanding of the method and apparatus by which this result
is obtained may be had by reference to Fig. 6 of the drawings.
Prior to describing the present improvement in detail,
the operation of the prior camera system will be briefly
reviewed with respect to Fig. 6, which illustrates a schematic
diagram of an automatic focus control system incorporating the
present invention, and shown to include generally, a range
finder 70 (e.g., a sonic range finder), a focus control segment
72 and an exposure control segment 74, each of which is repre-
sented by a dashed line enclosure in the illustrated diagram. A
source of electrical power (not shown) is supplied to one terminal
of a spring force biased, manually actuated, single pole switch ~1
and to one terminal of a lens movement actuated single pole switch
Sp through a terminal 76. Upon actuation of the switch Sl to a
closed condition, a signal Sl will appear at the output a~ the
switch. When the switch Sl is opened, a signal Sl will appear
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at the output thereof. A signal Sp will appear at the output
o the switch Sp when this latter switch is closed. It will
be noted further that in addition to the control or logic
signals provided by the switches Sl and Sp, these switches
can also be used to disconnect all loads from the power source
connected with the terminal 76. Thus, the outputs of both
switches Sl and Sp are also fed to an OR gate 78 and then to
as many electrical loads as desired. Also, it is to be under-
stood that when the switch Sl is eventually opened, power
continues to be supplied through the lens movement actuated
switch Sp. When the switch Sp is returned to its initial
opened condition, however, all electrical loads receiving
power from the terminal 12 are disconnected.
In the prior commercially available camera (unlike
the circuitry illustrated in Fig. 6 as later explained in
detail), the range finder 70 operation is, in essence, the
first camera operation. Thus, in that application, closure
of the switch Sl energizes an acoustical transmitter 80 and
a clock oscillator 82 simultaneously. When energized, the
transmitter 80 causes an acoustical burst of energy to be
transmitted toward the subject 64. Similtaneously, the clock
oscillator 82 starts to generate a series of time related
pulses. A counter 84 counts the pulses being generated by
the clock oscillator 82 and transmits these pulses to a decoder
86 and to a focus control counter 88. Preferably, the clock
counter system is scaled in steps to match the linear range
parameter to the nonlinear lens focal position curve.
When an acoustical signal is reflected back to the
range finder from the nearest subject 64 in the acoustical
path, a signal is generated by a receiver 90 and transmitted
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to the clock oscillator 82 through a latching OR gate 92 to
stop the clock oscillator 92 at a point where the number of
pulses generated by the clGck oscillator 82 are representa-
tive of the total time taken for the acoustical burst of
energy initially transmitted by the transmitter 80 to return
to the receiver 90. As indicated above, the transmitting
and receiving functions are served by the same transducer
28, the transmitter 80 and receiver 90 being electrical
components associated with the transducer 28 in practice. If
the time required for the acoustical pulse to travel from
the range finder 90 to the subject 64 and back to the range
finder is such that the clock oscillator 82 generates 124
pulses, the decoder 86 will send a signal to the clock
oscillator through the latching OR gate 92 to stop the clock
oscillator at 124 pulses. In other words, the clock oscillator
82 is limited to 124 pulses by the decoder 86 on the basis
that the time required for generation of 124 pulses, given
the speed of sound, represents a subject distance ~t which the
focusing lens element 12 is at its infinity focus position.
Thus, an object located beyond that position and which would
otherwise result in the clock oscillator 82 generating more
than 124 pulses, is assumed to be in focus.
Because the gate 92 is a latching OR gate, if a
normal input to the gate 92 is removed, the output from the
gate 92 caused by such an input will be maintained. Thus, the
output from the gate 92 is removed only when the gate is reset
by a pulse generated, for example, by a one-shot multivibrator
94 which, in both the existing commercial camera and in the
embodiment shown in Fig. 6, is energized when the switch S
is actuated to its closed position.
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~rom the foregoing, it can be seen that the range
finder 70 provides ranging means which generates a range signal
(the time between transmit and receive of the sonic signal)
indicative of subject distance, and through the scaled clock 82
ultimately provides a series of pulse counts (accumulated by
counter 84) whose number is representative of the lens position
or lens setting at which a subject at that distance will be in
focus. Hence, the range finder 70 has a lens focus setting
corresponding to subject distance range.
In the illustrated system, focusing movement of
the lens 12 by the focus control portion 72 of the system is
not initiated until the camera/subject distance has been
first determined by the range finder 70. This determination
is made when an output appears at the latching OR gate 92.
In particular, the signal from the output of the latching OR
gate is combined with a signal S1 from the closed switch S
at an AND gate 96 which will conduct and transmit a drive
forward signal to a lens drive motor 26. The motor 26 will
drive the lens mount through the gear train described above
with respect to Fig. 1, causing axial movement of the
focusing lens element 12 and rotation of the encoder wheel
30. Because the wheel 30 is coupled through the gear train
with the lens mount 16, the angular or rotational position
of the encoder wheel is representative of the rotary position
of the lens mount and also of the axial focusing position of
the lens 12.
As previously mentioned, the detector 34 is operative
to generate a pulse each time an aperture 32 in the encoder
wheel 30 passes the center of the detector 34. Thus, as the
3~ motor 26 is operated to drive the lens mount 16 and the
encoder wheel 30, the detector 34 will generate pulses that
are representative of lens mount movement. The pulses from
the detector 34 are transmitted to and are counted by a focus
control counter 88. When the number of pulses generated
by the clock oscillator 82 and the detector 34 reach a
combined total of 128 in the counter 88, a decoder 104
generates an output signal 106 indicating that focusing
movement of the lens 12 has been completed. The focus
complete signal 106 causes a one-shot multivibrator 108 to
momentarily energize the solenoid 40 causing the pawl 38 to
engage the encoder wheel 30 and thus stop motion of the
encoder wheel, the gear train associated therewith and the
lens 12. Simultaneously therewith, a focusing complete
signal 106 is inverted by an inverter 114 causing the AND
gate 96 to open, thereby shutting off the drive forward
signal to the motor 26. At this point, an image of the
object 64 has been focused at an image plane for viewing and
film exposure through the focus lens 12. Hence, the focus
control in the prior camera as described provides means for
automatically driving or adjusting the lens to the setting
defined by the range finder 70.
In addition to the focus complete signal 106, the
decoder 104 simultaneously generates an exposure initiate
signal 116 which is transmitted to an exposure control
actuator 118. The exposure initiate signal 116 is also
transmitted to a light integrating network 120 through an OR
gate 122. The output of the actuator 118 and of the light
integrating network are transmitted to the shutter mechanism
which in this instance may be assumed to include the shutter
blades 42 and 44 as well as the shutter blade actuating
1929
solenoid 54 described above with reference to Figs. 2 and 3.
Termination of shutter mechanism actuation is detected by an
end of exposure detector 124 which actuates a one-shot multi-
vibrator 126, the output of which is transmitted to an AND
gate 128 in the focus control segment 72.
As indicated, when the switch Sl is opened, it
generates a signal 51 and transmits such signal to the AND
gate 128 in the focus control segment 72 where it is combined
with the signal Sp and the output of the one-shot multivibrator
126, thereby causing the AND gate 128 to transmit a reverse
drive signal to the motor 26. The motor 26 will then drive
the lens mount 16 and the movable lens element 12 in an
opposite direction to which it was driven during focusing.
The signal S is generated when the switch Sp is actuated to
the closed position. The switch Sp is retained in its
closed position so long as the lens 12 is in any of several
in-focus positions to be described in more detail below.
Conversely, the switch Sp is actuated to its open position
upon movement of the lens mount 16 and the lens 12 to a
parking position also to be described.
As mentioned above, the decoder 104 signals both
completion of focusing and intiation of exposure when the
total number of pulses accumulated in the focus control
counter 88 reaches 128. Where this total count in the focus
control counter 88 is the sum only of pulses generated by
the counter 84 and by the detector 34, and where the clock
oscillator 82 generates 124 pulses to indicate a lens
setting at infinity, it will be appreciated that the detector
34 must generate at least four pulses before focusing is
complete. The reason for this is that the lens 12 and lens
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mount 16 are positioned originally in a park position P as
shown in Figs. 4 and 5a of the drawings. In other words, in
the park position P, the lens 12 will not focus any subject
on the film plane F of the camera. To reach the infinity
setting position from the park position P, the lens 12 must
be rotated and advanced axially from the park position
through an initial movement which, as indicated in Yig. 4,
causes movement of the encoder wheel so that at least four
apertures 32 pass the detector 34. Thus, it will be appreciated
that the lens will be properly positioned in the infinity
position when the range finder 70 develops 124 pulses and
the detector 34 transmits four additional pulses in the
focus control counter 88. Should the clock oscillator
82 generate a number of pulses lower than 124, thus indicating
a camera/subject distance requiring a lens setting of less
than infinity, the lens mount 16 and the encoder wheel 30
will be rotated by the motor 26 until the appropriate number
of apertures 32 pass the detector 34 to generate a number of
pulses equal in number to the difference between 128 and the
number of pulses counted by the range finder counter 84.
The preceding description represents essentially a
summary of the exposure control and automatic focusing system
of cameras presently commercially available under the name
"POLAROID SX-70 SONAR ONE STEP". In accordance with the
present invention, the existing system is modified to effect
a focusing adjustment of the lens 12 in accordance with
subject illumination or, that is, exposure aperture value
so that maximum advantage may be taken of the depth of focus
Fd available for a given lens aperture A'. Operation in t~is
3~ manner is achieved in the overall range finding and exposure
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cycle described above by preloading the focus control counter
88 with one, two or three pulses depending on the level of
ambient light in which the subject 64 to be photographed is
illuminated. As a result of this preloading of the counter 88,
the number of pulses which will be generated by the detector 34
during movement of the encoder wheel 30 and the lens 12 in
passing from the infinity focus position will be reduced, thus
positioning the lens 12 one, two or three focus increments
toward the infinity position from that in which it otherwise
would be positioned.
Specifically, and again with reference to Fig. 6 of
the drawings, it will be noted that closure of the switch Sl
to generate the signal Sl energizes a timer 130 (illustrated
within the focus control segment 72) whose output is transmitted
to and energizes the light integrating network 120 of the
exposure control segment 74 for a finite, short period of time
on the order of microseconds of duration. It will be recalled
that the secondary aperture a established by the sweep openings
58 and 60 of the shutter blades 42 and 44 (Figs 2 and 3) is
initially fully open at this time to pass light along the axis
62 to a photocell (not shown) associated with the light
integrating network 120. Thus, the light integrating network,
which will later be employed in the conventional manner to
determine the exposure interval (which also determines the
effective aperture value) is also employed for a pre-evaluation
of scene light level and, in turn, provides means for signalling
or indicating the effective aperture value.
The output of the light integrating network, when
energized only by the timer 130 through the OR gate 122, is
transmitted to a plurality of detectors, specifically three
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threshold detectors 134, 136 and 138 in the focus control segment
72, whose outputs feed respectively to single-shot pulse generators
140, 142 and 144 and to an OR gate 146. The output of the OR gate
146, if any, is transmitted directly to the focus control counter
88. Because the output of the light integrating network 120 is
time integrated, the cumulative output for a given time interval
will be representative only of the intensity of light passing the
opening a. Also, by staging the three detectors 134, 136 and 138
to detect successive threshold levels in the output of the network
120, an input will be transmitted in sequence to the three pulse
generators 140, 142 and 144, assuming that the photocell (not
shown) associated with the network 120 is exposed through the
opening a to high ambient light intensity. Thus, in the illus-
trated embodiment, the threshold detector 134 will develop a signal
and from pulse generator 140, generate a pulse at the OR gate 146
when the output of the light integrating network reaches a threshold
corresponding to an illumination level of 100 c/ft.2 (representative
of an anticipated effective aperture of f/10.8); the threshold
detector 136 will cause a pulse to be developed by the pulse
generator 142 upon the output of the light integrating network 120
reaching a threshold the equivalent of 300 c/ft. (an effective
aperture of f/14.9); and the threshold detector 138 will result in
a signal from the pulse generator 144 when the output of the light
integrating network 120 represents an illumination level or
threshold of 800 c/ft.2 (an effective aperture of f/19.2). With
lower levels of ambient light intensity, zero, one, or two pulses
may be developed at OR gate 146 by the output of the network 120
reaching thresholds of only detectors 134 or 136 before the output
of the timer is terminated to turn off and reset the light
integrating network 120.
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Z9
Hence, it can be seen that the light integrating
network 120, the detectors 134, 136, 138 and their respective
pulse generators 140, 142 and 144 provide an aperture deter-
mining means and, in coop~ration with the count accumulator,
focus control counter 88 provides means for altering the
distance related, lens position selection inversel~ with
aperture size. Consequently, the focus control 72 provides
means for adjusting the lens responsive to both the range
finder and the aperture determining means.
In order that the pulses from the OR gate 146 are
counted by the focus control counter 88 before signals are
transmitted from the range finding counter 84, the output of
the timer 130 is also transmitted to the range finder 70
through an inverter 148 to an AND gate 150. Since the signal
Sl is also an input to the AND gate 150, operation of the
transmitter 80 and of the clock oscillator 82 as described
above will not proceed until operation of the timer 130 has
ceased.
It will be recalled also that when the total number
of pulses transmitted to the focus control counter 88
reaches 128, the focusing operation is completed and the
exposure control system is actuated to initiate film exposure.
Also, it will be recalled that where a subject is sufficiently
remote from the camera that the lens 12 should be set at
infinity, four pulses must be generated by the encoder wheel
detector 34 to reach the infinity setting of the lens 12.
It will be appreciated also that if the counter 88 has
received a total of 124 pulses from the range finding
counter 84 and the counter 88 has also been preloaded with
one, two or three counts from the OR gate 146, the lens 12
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Z9
will not reach the infinity position from its park position
P and also will not focus any subject on the film plane F.
To prevent this unwanted situation ~rom occurring, the
output of the focus control counter 88 is transmitted to an
additional 124 count decoder 152 which develops an output signal
when the total count in the focus control counter 88 reaches
124. The output of the decoder 152 is transmitted through
an inverter 154 to an AND gate 156, the other input of which
is from the range finding counter 84. The net effect of
this arrangement is that the total number of pulses from the
combination of the counter 84 and the OR gate 146 may not
exceed 124. As a result, the effect of the pulses from the
OR gate 146 will be cancelled when the range finder 70
determines an infinity lens focus position and the counter
88 will always receive at least four pulses from the detector
34 before an output is generated by the decoder 104.
In light of the foregoing, the manner in which the
present invention may be advantageously used in practice may
be understood with reference again to Figs. 5b and 5c of the
drawings. Thus, in Fig. 5b, if it is assumed that the
ambient light in which the three objects 64a-c is 100 c/ft.
and that the objects are positioned at different distances
from the lens 12 as shown, but spaced from each other by
distance equal to the depth of focus distance Fd for an exposure
aperture value A' in such illumination, the lens 12 would be
ordinarily positioned to focus on the first object 64a as a
result of the acoustical pulse being reflected from that first
object. The result is that only the first two objects 64a and
64b would be included in the depth of focus distance Fd whereas
the farthest object 64c would be out of that distance and
correspondingly not in clear focus.
~1929
In Fig. 5c, the effect of the present invention is
illustrated. Specifically, the ambient light level of 100
c/ft. would preload the focus control counter 88 with one
pulse. After the number of pulses representing the range of
the nearest subject 64a have been transmitted from the counter
84 to the counter 88, the latter will include one count more
than that produced by the range finder. The motor 26 then
operates to drive the lens mount 16 and lens 12 from its park
position P past the infinity setting position and toward a
position represented by a total pulse count of 128 in the
counter 88. Focusing movement of the lens, however, will
terminate short of that position by the distance represented
by one count or, that is, by one aperture 32 in the encoder
wheel 30. The lens 12, therefore, will stop one step toward
its infinity focus position such that the medial plane of
focus Fm is at subject 64b. As a result, the depth of focus
distance Fd will bracket all three of the objects 64a, 64b
and 64c under the ambient light illumination given.
With higher levels of ambient light, and correspond-
ingly, with a further reduced size of the le~ns aperture A', the
depth of focus distance Fd will be increased. Because the near
and far limits of the depth of focus distance extend equally in
front of and behind a medial plane represented by the focus
setting of the lens 12, the final position to which the lens 12
is automatically adjusted will be advanced even further by one
or two additional increments of focus positioning.
The present system in effect adds p~llses to an
accumulator or focus control counter to shift the lens setting
accordingly, and lens movement operates to fill this counter.
However, the additional counts generated in accordance with
29
decreasing aperture size could be employed in a variety o~
pulse ranging systems to alter the final lens setting and
may also be effectively employed in some applications as
counts increasing with aperture size.
From the foregoing it will be appreciated that the
present invention represents an extremely economical modifi-
cation to existing camera structure and circuitry which
provides a highly effective focusing adjustment in an automatic
lens focusing system. While the present invention has been
described with respect to an automatic focusing camera and a
scanning shutter exposure system, it should be realized that
the invention has application to a variety of ranging and
focusing arrangements, and to any exposure system in which the
size of the taking aperture can be predicted or determined
prior to final movement of the lens. Consequently, while the
invention has been described in the context of the specific
camera organization illustrated in the drawings, it will be
appreciated by those skilled in the art that it may be adapted
to other types of automatic focusing systems and that it may
be modified without departure from the concepts manifested by
the illustrated embodiment. Accordingly, it is expressly
intended that the foregoing description is illustrative of a
preferred embodiment only, not limiting, and that the true
spirit and scope of the present invention be determined by
reference to the appended claims.
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