(12) United States Patent
`Mayhew
`
`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US006734900B2
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6, 734,900 B2
`May 11,2004
`
`(54) REAL TIME CAMERA AND LENS CONTROL
`SYSTEM FOR IMAGE DEPTH OF FIELD
`MANIPULATION
`
`(76)
`
`Inventor: Christopher Mayhew, 1155 Herndon
`Pkwy., Suite 200, Herndon, VA (US)
`22070
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/189,852
`
`(22) Filed:
`
`Nov. 12, 1998
`
`(65)
`
`Prior Publication Data
`
`US 2003/0164893 A1 Sep. 4, 2003
`
`Related U.S. Application Data
`(60) Provisional application No. 60/065,220, filed on Nov. 13,
`1997.
`
`Int. Cl? ................................................ H04N 5/225
`(51)
`(52) U.S. Cl. .................. 348/207.11; 348/239; 348/362;
`348/363; 348/368
`(58) Field of Search ................................. 348/239, 362,
`348/368, 207.11, 207.1, 221.1, 229.1, 363
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`4,532,553 A * 7/1985 Brill ........................... 348/364
`4,934,824 A * 6/1990 Ling .......................... 352/213
`
`5,051,770 A * 9/1991 Cornuejols .................. 396/125
`5,092,670 A * 3/1992 Preston ....................... 352/140
`5,245,379 A * 9/1993 Azuma et a!.
`.............. 396/299
`5,528,334 A * 6/1996 Lee ............................ 396/257
`5,610,654 A * 3/1997 Parulski et a!. .......... 348/229.1
`5,621,495 A * 4/1997 Yamamoto et a!. ......... 396/290
`5,721,981 A * 2/1998 Kosaka eta!. .............. 396/130
`5,861,917 A * 1!1999 Tariki et a!. ............. 348/230.1
`5,892,991 A * 4/1999 Hamada eta!. ............. 396/147
`5,912,774 A * 6/1999 Yoshida eta!. ............. 359/823
`5,999,215 A * 12/1999 Tamura ................... 348/224.1
`6,028,981 A * 2/2000 Hirasawa et a!. ........... 386/117
`* cited by examiner
`Primary Examiner-Andrew Christensen
`Assistant Examiner--Eric Wisdahl
`(74) Attorney, Agent, or Firm-Finnegan, Henderson,
`Farabow, Garrett & Dunner, L.L.P.
`
`(57)
`
`ABSTRACT
`
`A method is provided for real time control and manipulation
`of a moving imaging system lens's (prime, close-up, zoom,
`or anamorphic) depth of field. A computer control system is
`programed to perform a coordinated adjustment of a closed
`loop lens iris (aperture) and the shutter angle of a motion
`picture camera. The iris of the lens is reduced in size while
`simultaneously increasing the motion picture camera shutter
`angle an equal exposure (light transmission) amount,
`therefore, increasing the apparent image depth of field
`without a perceivable luminance shift. The image depth of
`field can be reduced by performing the above operation in
`reverse.
`
`14 Claims, 3 Drawing Sheets
`
`20
`
`CAMERA
`CONTROL
`SIGNALS
`
`LENS
`CONTROL
`SIGNALS
`
`USER
`SELECTION "\_.
`
`COMPUTER/CONTROLLER
`
`LENS AND CAMERA
`CONTROL
`
`GTL 1006
`
`

`
`U.S. Patent
`
`May 11,2004
`
`Sheet 1 of 3
`
`US 6, 734,900 B2
`
`40
`
`CAMERA
`
`CAMERA
`CONTROL
`SIGNALS
`
`LENS
`CONTROL
`SIGNALS
`
`(30
`rr=======~-~/
`
`USER
`
`SELECTION~ II~=~='§_=~-~~~j~ ~
`
`L.:
`
`COMPUTER/CONTROLLER
`
`LENS AND CAMERA
`CONTROL
`
`FIG. 1
`
`

`
`U.S. Patent
`
`May 11,2004
`
`Sheet 2 of 3
`
`US 6, 734,900 B2
`
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`200
`
`J
`
`d •
`\Jl
`•
`
`FIRST
`FIXED ANGLE SHUTTER
`
`SECOND VARIABLE
`SHUTTER {CLOSED DOWN)
`
`SECOND VARIABLE SHUTTER
`(OPEN)
`
`------
`
`, G- FILM OPENfNG
`
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`~ ,
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`MOTION PICTURE CAMERA
`ADJUSTAaLE SHUTIER
`
`FIG. 3
`
`

`
`US 6,734,900 B2
`
`1
`REAL TIME CAMERA AND LENS CONTROL
`SYSTEM FOR IMAGE DEPTH OF FIELD
`MANIPULATION
`
`This application claims the benefit of U.S. Provisional 5
`Application No. 60/065,220, filed Nov. 13, 1997.
`
`2
`increase the speed of a subject's motion by 100% during the
`shot without a visible exposure change, the shooting speed
`would be ramp down to 12 fps, while simultaneously
`reducing the shutter angle to 90°. This 90° shutter angle
`reduction is equivalent to one full f/stop or 50% of the
`original exposure.
`As the camera shooting speed is slowed down, the expo(cid:173)
`sure time is increased because the shutter is not turning as
`fast, and therefore, its angle must be reduced to compensate
`10 for the increase in light. Images shot at 12 fps and displayed
`at the standard 24 fps projection speed will exhibit a 100%
`increase in subject movement speed. The exposure time of
`12 fps is twice as long as 24 fps and therefore requires a
`shutter angle reduction of 50% to compensate for the
`15 increased exposure.
`One method of providing for the compensation in shutter
`angle size in accordance with a change in exposure time is
`to control the camera via a remote computer. Exemplary
`cameras that operate in response to commands from such a
`20 computer include the Arriflex 35 mm 435 and 535A and 16
`mm series motion picture 16SR3 cameras. This type of
`camera provides for the remote control of camera functions
`through the use of camera control software protocol via a
`computer interface. The camera and computer are also able
`25 to exchange data via the computer interface.
`The computer control sends messages to the camera and
`the camera responds to those messages. The computer
`control can send two types of messages: a command to
`perform a certain task and a request for information on tasks
`or other functions. The camera in turn will either perform the
`commanded task, provide the requested information or issue
`a warning message that the commanded task cannot be
`performed. The communications protocol consists of mes-
`35 sages to perform tasks and returned acknowledge or not
`acknowledge messages. The message format can be a string
`of characters with a defined format and meaning.
`The advent of the moving optical element lens for image
`parallax scanning as described in U.S. Pat. No. 5,448,322 to
`40 Bacs, which is hereby expressly incorporated herein by
`reference, has now made possible the interlocking of coor(cid:173)
`dinated settings changes of the lens iris and camera shutter
`angle. The moving optical element lens iris is controlled by
`a series of closed-loop actuators. The iris center can be
`45 positioned anywhere inside the lens's full effective aperture,
`frame-by frame. In addition, the iris can be scanned while a
`given frame is being exposed (as in 11 go motion" in
`animation).
`More commonly, a scan path of a particular size is set and
`the iris follows this path continuously while the camera runs.
`The scan path is usually a circle around the center (the
`nominal Z axis) of the lens. The diameter of this path can be
`increased or decreased on the fly while a given scene is
`being recorded. The shape of the path can also be modified
`on the fly, for example, from a perfect circle to an ellipse. In
`addition to the scan path, the scan frequency, focus position
`and f-stop can also be adjusted on the fly via remote control.
`The f-stop is inversely related to the diameter of the entrance
`pupil (N=F/D, wherein N is the f-stop, F is the focal length
`of the lens, and D is the diameter of the aperture).
`Another variable in optical photography is depth of field,
`which is explained by Rudolf Kingslake in his 1992 book
`Optics in Photography. As explained by Kingslake, if a
`camera is focused on an object at some definite distance
`from the camera's imaging plane, there will be a finite range
`of distances in front of and beyond the focused object in
`which everything will appear acceptably in focus. Outside
`
`FIELD OF THE INVENTION
`
`This invention relates to optical systems for creating
`moving images using motion pictures or video recording
`means. It is more closely related to computer control sys(cid:173)
`tems that provide real time adjustment of the lens and
`camera function settings.
`
`BACKGROUND OF THE INVENTION
`
`The first camera was the camera obscura. It consisted of
`a light-tight box with a pin hole in one side. The later part
`of the Nineteenth Century saw the invention of flexible
`photographic film by George Eastman and a workable
`motion picture camera/projection system by Thomas Edi(cid:173)
`son's New Jersey laboratories. On Dec. 28, 1895, the
`Lumieres brothers held the first public screening of Cin(cid:173)
`ematographic films at the Grand Cafe, Boulevard des
`Capucines, Paris, and the "movies" were born.
`Motion picture lenses provide a cinematographer with
`four basic optical variables with which to compose a given
`scene. These are focus, iris (aperture), filtration and change
`in focal length. Mostly, the lens is used simply as a conduit
`to pass light to film. Over the years lens mechanics and 30
`optics have improved, but for all intents and purposes, a lens
`today and its role in motion photography is the same as it
`was 100 years ago.
`While modern motion pictures cameras operate on the
`same basic principles as those used by the Lumieres
`brothers, they differ in the recent use of computer control to
`allow for software driven adjustment of camera functions
`such as camera shooting speed and the camera shutter angle.
`Contemporary motion picture cameras provide for shutter
`angle adjustment to control the image exposure. The amount
`of shutter opening adjustment varies among camera manu(cid:173)
`factures and may range as high as 220° of angular change.
`This degree of shutter angle adjustment could theoretically
`provide as much as 5 f/stops of exposure change. In practical
`applications, however, a very small shutter angle creates a
`strobing effect in moving subjects and, therefore, limits the
`exposure compensation to perhaps 3 f/stops.
`Shutter angle adjustment is typically used when a cin(cid:173)
`ematographer desires to slow the camera shooting speed 50
`down without varying the lens iris (f/or T stop) to compen(cid:173)
`sate for the exposure change by modifying the image
`exposure time of the motion picture camera. Unlike a still
`camera, most modern motion picture cameras employ a
`spinning mirrored shutter system to provide for film expo- 55
`sure and reflex viewing. The reflective shutter is typically
`located at a 45° angle in front of the film plane. Since
`standard motion pictures are filmed at 24 frames per second
`(fps), the way to adjust the image exposure time and
`maintain a constant shooting speed is by changing the size 60
`of the opening in the shutter. The smaller the opening (angle)
`the shorter the exposure time for each image and vise versa.
`Motion picture camera systems have been developed
`which provide for an automatic shutter angle adjustment to
`compensate for exposure changes due to a camera shooting 65
`speed change. For example, if a cinematographer is shooting
`a scene at 24 fps with 180° shutter angle, and he wishes to
`
`

`
`US 6,734,900 B2
`
`3
`that range everything becomes more blurred at increasing
`distances from the plane of best focus. "The actual extent of
`this range of acceptably sharp definition depends mainly on
`the distance of the subject from the lens, the aperture [size]
`of the lens, and the manner in which we look at the final 5
`print, but it also depends to some extent on the type of
`subject being photographed, the resolving power of the film
`and paper emulsions, and the aberrations of the camera
`lens."
`While the camera systems and methods described above
`are useful in allowing in-shot camera shooting speed
`changes they do not provide for a coordinated computer
`control of both camera shutter angle and lens iris settings in
`order to manipulate image depth of field.
`
`15
`
`SUMMARY OF THE INVENTION
`
`4
`focus position and f/stop adjustment. These two features can
`be adjusted individually or together to produce a depth of
`field fade.
`In order to determine the depth of field for a camera
`arrangement, it is first necessary to determine a variable of
`the lens called the hyperfocal distance. The hyperfocal
`distance is defined as the distance to the closest point that
`will be acceptably in focus when the lens is focused at
`infinity. The lens is focused at infinity when the distance
`10 between the rear principal point of the lens (a characteristic
`distance value of the lens that depends on the index of
`refraction of the lens) and the film distance is equal to the
`focal length of the lens.
`It is also necessary to determine a value of acceptable
`focus in order to determine both hyperfocal distance and
`depth of field. When light from a single subject point passes
`through the lens of a camera, the light is focused as a cone
`of light onto the surface of the film. The point is perfectly in
`focus when the focused light that forms the cone converges
`at the film. When the point is out of focus, the cone of light
`20 will intersect the film either before or after the point of
`convergence, thereby forming a circle rather than a point on
`the film. This circle of light is called the circle of confusion.
`Cc is defined as the largest acceptable circle of confusion.
`This value is given a specific value, but is in fact subjective,
`25 and depends on the perceptions of the viewer of the pro(cid:173)
`duced image. One set of industry standard acceptable values
`for the largest circle of confusion Cc are 0.001 inches for 35
`mm film, and 0.006 inches for 16 mm film.
`The formula for hyperfocal distance using inches or
`30 fractions thereof is:
`
`Systems and methods consistent with the present inven(cid:173)
`tion provide depth of field fade capabilities in moving
`imaging systems through synchronized operation of the
`optical elements of a camera system.
`To attain the advantages and in accordance with the
`purpose of the invention, as embodied and broadly described
`herein, the motion picture system of the present invention
`includes a computer controller, a computer controlled lens,
`a computer controlled aperture, and a computer controlled
`adjustable shutter having a shutter angle, wherein the opera(cid:173)
`tion of the aperture, the shutter, and the lens are synchro(cid:173)
`nized by the controller to produce a depth of field fade
`without a visible luminance shift in a film exposed by the
`camera.
`Further, to attain the advantages and in accordance with
`the purpose of the invention, as embodied and broadly
`described herein, the method of producing a depth of field
`fade in a moving imaging system without a visible lumi- 35
`nance shift in accordance with the present invention includes
`the steps of: adjusting the object distance of the lens to
`change the depth of field of the camera; adjusting the
`aperture size to change the depth of field of said camera; and
`adjusting the exposure time to compensate for said aperture 40
`adjustment; wherein the aperture adjustment and exposure
`adjustment are synchronized to avoid a visible luminance
`shift in images produces by the camera.
`The following detailed description of the invention refers
`to the accompanying drawings. The following detailed
`description does not limit the invention. Instead the scope of
`the invention is defined by the appended claims.
`
`F2
`H= - (cid:173)
`NxCc
`
`(1)
`
`where F is the focal length of the lens, N is the f/stop
`number, and Cc is the circle of confusion. The hyperfocal
`distance, therefore, is inversely proportional to the f/stop
`number, which itself is inversely proportional to D, the
`diameter of the entrance pupil. A change in the aperture of
`the entrance pupil, therefore, has a direct relationship to a
`change in the hyperfocal distance.
`The two values of the depth of field are then calculated
`utilizing the value of the hyperfocal distance from equation
`(1) above. When rendering an image of an object at an object
`45 distance S from the camera, there is both a closest alternative
`point that is acceptably in focus, and a farthest alternative
`point that is acceptably in focus. The area within which a
`point will be imaged within acceptable focus is the depth of
`field, and is bounded at both extremes by the point at which
`50 the image of a point would create a circle greater than the
`defined accepted circle of confusion value.
`The near limit of the range of acceptable focus is found
`using the equation:
`
`55
`
`HxS
`DN camera to near limit= -;-H;-+-("'S-----,F"')
`
`(2)
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The accompanying drawings, which are incorporated in
`and constitute a part of this specification, illustrate preferred
`embodiments of the invention, and, together with the
`description, explain the goals, advantages and principles of
`the invention. In the drawings,
`FIG. 1 is a block diagram of the proposed control system;
`FIG. 2 is the front view of a lens iris; and
`FIG. 3 is the front view a motion picture adjustable
`shutter.
`
`60
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`As discussed in the Background section, the moving
`optical element lens provides a number of variables that can
`be independently adjusted to produce changes in the result- 65
`ing filmed images. Two features of interest that are utilized
`in the embodiments described below are remote control of
`
`The far limit of the range of acceptable focus is found
`using the equation:
`
`HxS
`DF camera to far limit= -;c;----c=-----c=(cid:173)
`H -(S-F)
`
`(3)
`
`The depth total is then calculated using the following
`equation:
`
`Depth Total=DF-DN
`
`(4)
`
`

`
`US 6,734,900 B2
`
`5
`As shown by the above equations, there are two variables
`of interest in the calculation of the depth of field. The first
`variable is the hyperfocal distance. As mentioned above, by
`changing the diameter of the aperture, the hyperfocal dis(cid:173)
`tance is changed. For example, changing the f/stop from f/2 5
`to f/4 would result in halving the hyperfocal distance. Using
`the changed value of the hyperfocal distance in the equations
`for near and far limit of depth of field above, it is shown that
`the near and far limits of the depth of field are also changed.
`Consequent to the change in f/stop is a resultant change in 10
`the amount of light that is incident on the film. The ampli(cid:173)
`tude of the illumination at the film is directly proportional to
`the area of the aperture (i.e. for a circular aperture the area
`is proportional to the radius squared). This means that by
`halving the area of the aperture, the level of illumination 15
`striking the film is also halved.
`In order to provide a depth of field fade without a resulting
`change in the level of illumination, the time duration of the
`exposure of the film must be changed to compensate for the
`change in the aperture size. This could be accomplished, for 20
`example, by doubling the time of exposure for each frame of
`film for each halving of the area of the aperture. In motion
`picture cameras, this change in the exposure time is accom(cid:173)
`plished by changing the shutter angle (i.e. a doubling of the
`shutter angle is equal to a doubling of the exposure time). 25
`Therefore, for each change in the area of the aperture, a
`reciprocal change in the shutter angle is provided. When
`these are controlled to change in a synchronized indirect
`relationship, the system will produce a depth of field fade
`without a visible change in luminance.
`A first preferred embodiment of the invention is shown in
`FIG. 1, which shows a camera system 10. Camera system 10
`include computer/controller 30 coupled to camera 40 having
`lens 20. The functions of the camera and the camera lens are
`controlled by the operation of the computer/controller.
`FIG. 2 shows an exemplary aperture 100 for use in the
`camera of FIG. 1. Aperture 100 includes a plurality of
`aperture elements 110, which together form iris 120. As
`stated above, for circular apertures, the diameter of the
`aperture is related to the f/stop of the camera, and thereby, 40
`the hyperfocal distance and the depth of field of the image
`produced by the camera. The size of aperture 100 is actively
`controlled by computer/controller 30, which is able to
`change the size of iris 120 of aperture 100 via a command
`control signal produced by computer/controller 30. 45
`Computer/controller 30 is also able to choose the speed at
`which the change in iris size is accomplished.
`FIG. 3 shows an exemplary adjustable shutter 200 for use
`with a motion picture camera, as shown in FIG. 1. The
`adjustable shutter includes two shutters, first fixed angle 50
`shutter 210 and second variable shutter 220. The angle
`between first fixed angle shutter 210 and second variable
`shutter 220 (i.e. the remaining portion of the circle not
`occluded by either shutter) is the shutter angle. As shutter
`200 rotates, the amount of illumination striking the film is 55
`controlled by setting the shutter angle of adjustable shutter
`200. The setting of adjustable shutter 200 is controlled by
`computer/controller 30.
`A user of camera system 10 can produce a depth of field
`fade by inputting a signal via an interface to computer/ 60
`controller 30. Computer/controller 30 outputs a first signal
`to aperture 100 in accordance with the desired change in
`depth of field.
`Concurrently with the change in the setting of aperture
`100, computer/controller 30 outputs a second signal to 65
`adjustable shutter 200. The amount of change in the shutter
`angle of adjustable shutter 200 is used to compensate for the
`
`35
`
`30
`
`6
`difference in illumination striking the film as a result of the
`change in the area of iris 120.
`It is also desirable to be able to produce the depth of field
`fade in a controlled variable speed manner. The operator of
`the camera system might want to bring far elements, near
`elements or both into focus in a relatively rapid or slow
`manner. In the production of films, different optical effects
`would necessitate the use of variable speeds for different
`depth of field fades. By using the same computer control for
`both the aperture 100 and adjustable shutter 200, the user
`can operate both elements together at any desirable speed to
`produce the desired effect.
`An exemplary description of the operation of the
`computer/controller 30 follows. Upon receipt of a change
`request from the camera system user, the computer initiates
`the following exemplary steps of a depth of field fade. The
`change request from the user includes both a change in the
`f/stop value and a time duration for the system to produce
`the depth of field fade. A third value necessary to the
`production of the requested change is the update time rate of
`computer/controller 30. This is a variable rate that deter(cid:173)
`mines how often computer/controller 30 produces a signal to
`update the settings of the variables under its control.
`Upon receipt of the request, computer/controller 30 inter(cid:173)
`rogates camera 40 and lens 20 to determine the currents
`settings of the f/stop and shutter angle. Computer/controller
`then calculates the total change in f/stop necessary to
`produce the required f/stop. Following the calculation of the
`total change in the f/stop value, a calculation of the total
`change in shutter angle is performed in accordance with the
`change in the f/stop.
`By dividing the time duration of the change by its update
`time rate, computer/controller 30 then determines the num(cid:173)
`ber of steps necessary to produce the total change in f/stop
`and shutter angle. The total changes in aperture area and
`shutter angle are then divided by the number of steps, the
`resulting numbers being the required change in f/stop and
`shutter angle per update step. These values are then con(cid:173)
`verted to the proper signal form to produce the required
`change in aperture 100 and adjustable shutter 200.
`Computer/controller 30 then outputs a sequence of value
`change signals to both aperture 100 and adjustable shutter
`200 to produce the required changes in the f/stop and shutter
`angle.
`A second embodiment of the invention is disclosed again
`with reference to FIG. 1. As with changing depth of field by
`altering the hyperfocal distance, it is also possible to alter the
`depth of field by altering the object distance S, as shown by
`the near depth of field equation (2) and far depth of field
`equation (3). The following is the thin lens equation:
`
`1
`1
`1
`-+-=-·where
`S' F'
`S
`
`(5)
`
`S is the distance between the front principle point of the lens
`and the plane of focus, F is the focal length of the lens, and
`S' is the distance between the rear principle point of the lens
`and the plane of the film. Referring again to the discussion
`above with respect to near and far depth of field, it is
`possible to change the plane of focus of the lens without
`perceptibly changing whether the object will appear in
`focus. The object will appear in focus until the amount of
`blur exceeds the circle of confusion as defined above, though
`again this is a subjective value. The image distance S',
`therefore, can be changed, resulting in a change in the object
`distance S. As long as the object itself remains within the
`near and far limits of the depth of focus the object will be
`
`

`
`US 6,734,900 B2
`
`7
`acceptably in focus. (The change in object distance can also
`be accomplished by altering the focal length of the lens).
`As shown in FIG. 1, computer/controller 30 is connected
`to camera 40. Computer/controller 30 produces lens control
`signals, which alter the distance between lens 20 and the film 5
`in camera 40. By altering the distance between lens 20 and
`the film, the camera is able to change the object distance S.
`As shown by the two depth of field equations (2 and 3),
`changes in the object distance will result in a change in the
`depth of field.
`By constructively altering both the f/stop of the aperture
`and the object distance S, the system can further increase its
`ability to alter the area within the depth of focus. Because
`computer/controller 30 is able to control the operation of
`both lens 20 and aperture 100, the system can synchronously 15
`alter both elements together in order to produce a greater
`range of depth of field. Due to the coordinated control of
`these elements the system can produce a relatively slow
`optical effect by slowly altering the optical elements sepa(cid:173)
`rately or together. It is therefore possible to bring a broad 20
`range of elements into and out of focus at a selected speed
`without producing a visible luminance change in the result(cid:173)
`ing pictures. A viewer of the resulting images, could
`therefore, watch as elements within the field of the camera
`enter or leave focus during a single continuous shot, without 25
`a noticeable change in the brightness of the resulting image.
`An example of the operation of the second embodiment of
`the invention follows. If the correct exposure of a given
`scene is f/16 and the subject is located 11 ft from the camera
`image plane, a depth of field fade can be accomplished by 30
`an opposed reversal using a 50 mm lens focused at 10 ft with
`an iris setting of f/4 on a camera with shutter angle setting
`of 11 o. As the computer control increases the shutter angle
`to 180°, it also decreases the lens iris to f/16 at an identical
`exposure (light transmission) rate and moves the lens focus 35
`position from 10 ft to 20 ft. The resulting moving image
`would start with a range of depth of field from 8'11" to 11'5"
`(2'6" of the image in focus), and finish with a depth of field
`from 9' to infinity. This change in depth of field would be
`accomplished without a visible change in exposure. Of 40
`course the reverse is also possible. A cinematographer can
`therefore start a shot with a subject in shallow focus and
`slowly (or quickly) bring the background into focus while
`keeping the subject in focus with no visible image exposure
`changes. This technique, along with the other image 45
`enhancements of the invention, has tremendous creative
`applications.
`A third embodiment of the present invention will now be
`described with respect to the operation of a video camera.
`Both the operation of the aperture 100 and lens 20 are 50
`identical to that described above with respect to both the first
`and second embodiments.
`Unlike motion picture cameras, video cameras do not
`operate using a adjustable shutter having a shutter angle.
`Instead, video cameras include various electronic controlled 55
`"shutters" that produce a selected time duration of light
`exposure of the charge coupled elements (CCDs) in the
`camera. One example of the a light sensitive CCD element
`is called the Interline Transfer Chip. The central processing
`unit of the camera produces a timing signal that determines 60
`the rate at which the rows of charge coupled elements are
`interrogated. The time between interrogations of the indi(cid:173)
`vidual charge coupled elements is the exposure time of the
`element to the incident light. Analogous, therefore, to the
`change in shutter angle change for a motion picture camera 65
`is the length of time between consecutive interrogations of
`the charge coupled elements of a video camera. By changing
`
`8
`the time of exposure of the charge coupled elements to the
`incident light in accordance with changes in the area of the
`aperture, a depth of field fade can be accomplished in a video
`camera without a visible shift in luminance.
`It will be apparent to those skilled in the art that various
`modifications and variations can be made in the methods and
`apparatus consistent with the present invention without
`departing from the scope or spirit of the invention. Other
`modifications will be apparent to those skilled in the art from
`10 consideration of the specification and practice of the inven(cid:173)
`tion disclosed herein. The specification and examples should
`be considered as exemplary only, with the true scope and
`spirit of the invention being indicated by the following
`claims.
`I claim:
`1. A motion picture system, including a motion picture
`camera, said system comprising:
`a computer controller;
`a computer controlled aperture; and
`a computer controlled shutter having an adjustable shutter
`angle;
`wherein said aperture and said shutter are automatically
`controlled by said computer controller to produce a
`depth of field fade, over a user selected time duration,
`without a visible luminance shift in a film exposed by
`said camera.
`2. The system of claim 1, wherein as said controller
`causes a change in the area of said aperture, said controller
`causes a synchronized inverse change in said shutter angle.
`3. The system of claim 1, wherein said aperture and said
`shutter are automatically adjusted at a selectable update rate.
`4. A method of producing a depth of field fade in a moving
`imaging system without a visible luminance shift compris(cid:173)
`ing the steps of:
`adjusting an aperture size of a moving imaging camera to
`change a depth of field of an image recorded by said
`camera; and
`adjusting an exposure time of said camera to compensate
`for a change in illumination due to said aperture
`adjustment;
`wherein said aperture adjustment and said exposure
`adjustment are synchronized and automatically per(cid:173)
`formed by a computer controller over a user selected
`time duration to avoid a visible luminance shift in
`images produced by said camera.
`5. The method of claim 4, wherein said camera is a motion
`picture camera.
`6. The method of claim 4, wherein said camera is a video
`camera.
`7. The method of claim 4, wherein said aperture adjust(cid:173)
`ment and said exposure adjustment are automatically per(cid:173)
`formed by the computer controller at a selectable update
`rate.
`8. A motion picture system, including a motion picture
`camera, said system comprising:
`a computer controller;
`a computer controlled lens;
`a computer controlled aperture; and
`a computer controlled shutter having an adjustable shutter
`angle;
`wherein the operation of said aperture, said shutter, and
`said lens are synchronized and automatically controlled
`by said computer controller over a user selected time
`duration to produce a depth of field fade without a
`visible luminance shift in a film exposed by said
`camera.
`
`

`
`US 6,734,900 B2
`
`5
`
`9
`9. A method of producing a depth of field fade in a moving
`imaging system without a visible luminance shift compris(cid:173)
`ing the steps of:
`adjusting the focus distance of a lens to change a depth of
`field of an image recorded by a camera;
`adjusting an aperture size to change said depth of field;
`and
`adjusting an exposure time to compensate for said aper(cid:173)
`ture adjustment;
`wherein said aperture adjustment and said exposure
`adjustment are synchronized and automatically con(cid:173)
`trolled over a u