Note: Descriptions are shown in the official language in which they were submitted.
I IM~GE STABILIZATION SYSTEM FO~ CO~TINUOUS FILM SCANNING APPARATUS
1 BA<KC~q1ND O~ 51- INvEhlloN
2 - l. Field of the Inventio~
3 The present invention relates to an optical
4 immobilization apparatus for producing stationary images onto
51 or from a relatively moving object such as a continuously moving
6 film strip and more par~icularly to an improved illumination
-7''and projection lens system for complementing a scanner asse~ly
8I that is suitable ~or incorporation into projectors, cameras and
9loptical scanning equipment to optically immobili~e a moving
101 image with relatively minimal distortion.
11 1 2~ Description of the Prior Art
12 1 While the subject matter o the present invention
13 ¦is directed to a modular op~ical apparatus that can be
14~1incorpor~ted as an essential component in a number of optical
15¦1devicest reference will be made primarily to the field of
161j tion pictures.
17 ¦¦ . The conventional projec~ion of motion pictures has
1811 required an intermittent-motion film transport mechani~m. The
19~conventional projector has traditianally produced objectionable
2011noise, film weart frame and screen registration errors and frame
21 li rate limitations. The noise that is typically created by the
221 int~rmittent-motion projection system, has required a projection
2~i1booth in a commercial environment. The required intermittent
2411movement not only damages the perforations in the film but the
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2511continuous starting and stopping effects cause
26'severe speed limitations. Frequently, the projected images
27 appear to bounce due to vertical instability and flicker is still
28 present in conventional equipment. Additionally, the intermitten~
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1 motion creates interfacing problems between the correlations of
2 the sound and visual characteristics of the motion picture.
3 In one conventional projector, a three bladed shutter,
4 wherein each blade has a 55 sweep, will block a total of 165
; 5 of a ~otal of 360 of illumination. In effect, this means that
. 6 46% of the time the screen is blackened due to the light loss
,
7ll related to the shutter effect. This reduces the apparent image
8l!illuminance correspondingly by 46% . In addition, the complicated
9 structure of the inte~mittent-motion transport requires a
10li complex interfacing of the film into the projector.
1 11! A conventional projector when utilized in a video
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12~!con~erter application requires a compensator to immobilize th
131¦film frame on the screen for solving the synchronization problem
14¦¦associated with the normal projection rate of 24 frames per
1511second of a motion picture film interfaced with the 30 fields
16llper second scanning o~ the typical video system.
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17~l Various forms of optical compensating devices, have
18 been suggested over the last sixty years. Optical compensators
l9,lor image immobilizers have classically fa}len under these s~parate
20 ll categories; rotating and/or oscillating mirror de~ices~ rotating
21 ¦¦ lens devices and rotating polygon prism devicesO The German
22ljbuilt Mechau projector of U~S. Patent No. 1,401,346 is a classical
23 1l example of a mirror type o~ optical compe~sator. The Mechau
24, projector was built in the 1920's and was apparently the first
25ll technically successful continuous projector.
26 The Alexanderson U.S. Patent NoO 1.937,378 and ~he
27 Ripley et al U.S. Patent No~ 1,091,86~ disclose rela~ively
28, simple polygon reflecting projectors.
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1~ The Bauersfeld U.S. P~tent No. 1,154,835 is of particu-
2 lar interest since it discloses a reflector drum which has a
3 re1ector comprising three planar reflectors having perpendicular
4; reflecting surfaces which are respectively lying along a
5I Cartesian coordinate with a film window limiting the illumination
6 to one of the film frames. The inventor recognized that image
7j, movement particularly at the outer ed~es of a frame was a problem.
8l, The solution offered, however, causes dynamic distortion and
9 I! defocussing over the whole image during scan. The limitation of
10lllilluminating a single film frame creates defini~e light flicker
in the real image.
12¦' The Campbell U.S. Patent No. 3,583,798 discloses a
3¦¦high speed camera incorporating an optical compensator
141lcomprising a centrally fixed mirror for directing a ligh~ ray
15i; outward to a reflective rhombic configuration.
161 The Miller U.S. Patent No. 1,530,903, Barr U.S.
Patent No. 663,153 and U.S. Patent No. 1,156,596, Flogaus et al
U.S. Patent No. 3,885,857, Dahlquist U.S. Patent No. 3~889,102
1 .
19,and Rotter U.S. Patent No. 3,894,800 are cited of general
201' interest~
21 il The Thun German Patent Nos. 547,240 and 553,520 are
22¦ directed to a lenticular lens system for high speed photography.
23 ll Rotating lens devices have been less successful than
24llthe mirror devices or other methods due to the aberration
25~lproblems and the cost requirement for precision lensesO
26' Examples of the rotating prism optical compensators
27, can be found in the Leventhal U.S. Patent Nos. ~2,085,594;
28 2,417,002 and RE22,960. The Tuttle U.S. Patent No. 2,070,033,
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1 Eisler U.S. Patent No. 2,262,136 and Husted U.S. Patent
2 No. 3,539,251 are other examples of prism optical compensators. I
3j Optical immobilization can be described as a displace- i
4 ment of a light beam through the optical system in such a manner
5ll. that the portion of the beam coming from ~he subject, in the
6 case of a camera taking a picture, or the portion of a beam
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71l extend.ing from the projectox to ~he screen, i~ the case of a
8Ijmotion picture projection, is held rigidly stationary, centered
9¦lat the optical axis of exposure or projection respectively,
lo!,while the portion of the beam which is immediately adjacent the I-
11 lintersecting film, is optically displaced so as to move in
12 synchronism wi~h the movemen~ of tha film. A recurrent problem
13 ~that has been experienced is the inability to stabilize a virtual
14 limage during kinetic motion of the scanner system which, during
15 la resultant projection and magnification has produced image
6 ! movement on the screen. This problem has been frequently
1711 characterized as dynamic keystonlng.
18 ll ~he use of a rotating solid polygonal prism can
9l produce a refraction of a light beam as lt enters the prism
~!Iand again as it leaves the prism to offset or displace a
2t¦~ section of the beam within the apparatus, while maintaining the
~2l,displiaced section parallel to the stationary portion of the beam.
23l!The displaced section of the light beam directly intersects the.
24~
film with the displacement being of a progressive
25llwiping nature such that the displacement portion of the beam
26 continually move~ in exact synchronism wi.th ~he moving film.
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1 A solid polygon having an appropr~ate refractive index
2 can provide frame lap dissolve. ~he refractive index would ha~e
3 to be in the order of 2.0 and the corresponding aberration con-
4 trol would demand a minimum of 26 facets which implies a maximum
5 il relative aperture of approximately f/7. In realizable solid
6" polygon systems a refractive index of approximately 2.0 cannot
1be achieved and each successive projected frame replaces its
8 jpredecessor frame in a top to bottom "wiping" motion with an
9 ¦inherent flicker that requires a corrective shutter be~ween the
10 Iframes.
11 An optical compensator that was developed for the
12 IPhilco Research Division for use as a motion picture film
13 ¦scanner for television transmission in the early 1950's
recognized some of the problems of a solid polygon. The ~udar
511u.s Patent Nos. 2,~72,280 and 2,8~0,542 described this work.
Basically, the Kudar patents disclose a hollow polygon device
¦1which utilized a set of prisms located within a cylindrical cavity
,lof the polygon to deviate the light beam su~iciently to permit
19l,a lap dissolved framing which was flicker free, required no
20¦!shutter, achieved a moderate relative aperture, for a 24 facet
21 ¦I system, while at the same time provided moderate control of
optical aberrations and film shrinkage compensation. The Kudar
3l;devices as described in the patents w~re developed upon the
24 theory that the parallelism of the stationary and displaced
25~ portions of the projected beam raquired, the bçam to be refracted
6 to the same extent upon entering and leaving the polygon prism.
Some of the disadvantages of the Kudar system include a limitation
of the relative aperture of the optical system, the requirement
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1 of expensive materials for the prisms, the existence of field
2 curvature aberra~ions and other refractive optical aberrations
3 which are particularly destructive in a projection system. The
4 Kudar device, however, has been utilized as a color television
5I film scanner as described in the paper, "New 35 mm Television
6 Film Scanner" Journal of SMPTE, Vol. 62, January 1954l Page 45.
7 The Kirkham U.S. Patent No. 2,817,995 suggests a
8~ modification of a hollow polygonal prism concept by the provision
9l;of a rotatable compensating core to permit adjustment for the
10l film shrinkage-
11l The Korb U.S. Patent No. 2,515,453 is cited of genexal
12, interest to disclose a sin~le pass prism optical compensator.
13i' Some devices of the prior art are càpable of providing
14ll flicker-free lap dissolve ~raming, no shuttering and film
~51l shrinkage adjustmentO For example the Kudar device taught the
16~ extension of the optical path through the compensator and the
171 compensation of film shrinkage by the various mounting of movable !
18 prisms within the hollow polygon. The result was accomplished
9! with relatively expensive oomponents and provided a limited
~ relative aperture while introduclng kinetic refractive aberrations.
21 Problems such as image displacement, dyhamic lceystoning
22 and ghost images still exist when applying prior art polygon
23, reflective scanners to motion picture projec~ors and cameras.
24 Thus, problems become fully apparent when the image is magnified,
25 for example, for motion picture pro jection. To date, the prior
~6 art has directed their primary efforts at modifying the scanner
27 assembly to remove these problems. The present invention
28 recognizes the inheren~ limitations of practical scanner
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configurations and nulli.fy the effects of these inherent limita-
tions such as dynamic keystoning by providing corrective illumin-
ating and projection systems that permit commercial magnification
of an image without discernible image movement by a viewer.
SUMMARY;O_ TXE;:INVENTION
` According to the present invention there is provided
an improved rotatable optical scanner system for the continuous
transmission of at least two dimensional successive images from
"~ a medium such as film, wherein each image is formed from a number
~`~ 10 of discrete points comprising:
....
a source of light energy;
means for creating virtual images of successive
film frames illuminated by the light energy with at least one
virtual image point of each film frame positioned on a stationary
locus point and at least another virtual image point offset from
the stationary virtual image locus point and relatively movable
during a scanning movement, and
; means for circuitous curvatures of the film about
a centroid of the stationary locus point while transmitting the
source of light energy, and
means for selectively illuminating different
regions of the real image of each film frame so that the light
- transmission is progressively decreased in the region of the real
image that has the greatest rate of defocussing and image
motion, and
projection means for generating real images from
~ the virtual image.
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The present invention provides a rotatable optical
scanner system for the transmission of at least two dimensional
successive images of objects to provide an image immobilization.
As can be appreciated, the objects can be considered reformed
from a number of discrete points. A scanner assembly creates
virtual images of successive objects with at least one vixtual
image point of each object positioned on a stationary locus
point and at least another virtual image point offset from the
stationary virtual image locus point and relatively movable
during a scanning movement. This relative movement can be
characterized as dynamic keystoning in the projected real image.
The present invention recognizes this inherent
limitation in practical scanner geometries and seeks to provide
a specific projection lens assembly and illumination system
which tends to nullify the effects of dynamic keystonlng~
In this regard, the optical scanner system limits the effective
transmission of a pencil of rays of the offset virtual image
point from an o~ject to substantially a tangential interface
with a surface of focused real image point positions. The
surfaces being representative of the effective rotational
scan movement of the projected offset real image point. The
use of a projection means with a telecentric property and a
particular illumination
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1 system tha~ permits a vignetting of a transmitted light rays
2 so that they selectively illuminate different regions of the
3 real image of each ~ilm frame whereby the light transmission
4 will be progressively decreased in the region of each film frame
5 when the relative movement of the real offset image point
I are features of the present inv~ntion
6 becomes progressively greate~. Thus~ by selecting appropriate
7i number of facets to provide a rotation scan angle that is
81 optimum for the particular application, it is possible to in
- decrease the light tran~mission bo
9¦1effect, ~ that portion of the pxojected real image
101 that is expPriencing the greatest rate of defocussing thereby
! ef~ectively removing this source of p~rceptible image motion from
12,1the projected real image so that the viewer will perceive a
- 13j¦continuous projection of images.
141l The objec~s and features of the present invention
15~1which are believed to be novel are set forth with particularity
16 in the appended claims. The present invention, both as to its
17l¦ organization and manner of operation, together with further
1811objects and advantages therPof, may best be understood by
19 reference to the following description, taken in connection
20i1With the accompanying drawings.
- 21 ¦ BRIEF DESCRIPTION_OF THE l:~RAWINGS
22, Figure 1 is a schematic partial elevated view of a
2311scanner system of the present invention;
241! Figure 2 is a schematic partial top view of P'igure l;
.
!I Figure 3 is a schematic view disclosing the iliumination
26~system for a three mirror scanner before rotation;
27~ Figure 4 is a schematic view disclosing the three
281 mirror scanner illumination after rotation;
29 1'' " .
1 Figure S is a plot of the real image plane motion
2 produced by dynamic keystone aberratîon;
3 Figure 6 is a schematic viéw disclosing the effects
4;~of dynamic keystone aberration on a projection screen;
5. Figure 7 is a schematic disclosing effects of the
6 illumination projection system of the present invention in .
7''minimizing the effec~s of dynamic keystoning;
8, Figure 8 is a schematic of the two mirror scanner
911illumination sub-system before rotation;
10i; F.i~ure 9 is a schematic of the two mirror scanner . .
1illumination sub~system after rotation, and
12, Figure 10 is a schematic of a projection lens system.
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BRIEF DE~SCRIPTION _F THE P`REF~ u~n~D~ s
The followin~ description is provided to enable any
person skilled in the optical art to make and use the invention
and sets forth the best modes contemplated by the inventor of
carrying out his invention. ~arious modifications, howeverr
- will remain reaailv apparent to those skilled in the art since
the generic principles of the present invention have been defined
herein specifically to provide a modular optical device that can
be manufactured in a relatively economical manner.
Frequently, the term optical compensator or optical
immobilization will be utilized to describe a desired function
of the present invention. In this regard, re~erence may be
made to the Kudar U.S. Patent Nos: 2,972,280 and 2~860,542
simply to supplement the present disclosure with respect to
terminology and the theory relating to optical immobilization.
The present invention relates to a modular optical
device capable of performing a basic image transmitting
operation that could be incorporated into a large number of
optical systems such as a camera, movie editing table, dissolving
slide projector, tele-cine converters and optical scanning or
` image immobilization equipment. The preferred embodiments
herein will be disclosed in a projector system that is capable
of being commercially utilized. Obviously, other appllcations
of the basic scanner assembly would require modification such
as a rotating shutter in a camera embodiment.
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1 It should also be appreciated that the presen~. inven-
2 tion can be utili zed across the spectrum of energy transmission
3 and is not limited specifically to the visual spectrum of 400
4 nanometers to 700 nanometers. Utilizing the term light or
5 ll light rays, should be understood to be broad enough to encompass
6 both the ultraviolet and infrared range of energy in addition
7j, to the visual spectrum.
8,, ~eferring to Figure l, a partial schematic elevated
9~l cross~sectional view of the optical scanner system 2 of the
10,lpresen~ invention is disclosed.
~ The optical scanner system 2 can be'broadly subdivided
12, into three major sub-components; that is, the scanner assembly 4,
3llthe projection lens assembly 6 and the illumi~ation assembly 8.
14 ll The actual scanner assembly 4 configuration is a
1511pair of polygonal drums having planar reflective facets lO and l~ ¦
16,lpositioned at a 90-degree angle to each other. In an alternative
711embodiment, one half of a respective reflective member can be
1~ replaced by a ~0 degree roof angle formed from a pair of
19 individual roof mirxors. The choice of planar reflective facets
20ll with 90-degr~ee roof angle facets does not effect the basic
21,,image transmission bu~ would require a variance in the supportive
22i illumination assembly design. The number of mirror pairs or
23!,reflective members lO and 12 that are utilized is partially
24 dictated by the accuracy of the intended application of the
25~ polygon scanner con~iguration of the present i~vention.
26"
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1 Advantageouslyl each of the polygon reflecting members
2 that form the scanner assembly 4 can be injection molded from
3 plastic to either receive the individual reflecting members 10
4 and 12 or to directly provide surfaces that can be coated with
reflecting material. The respecting poly~on re~lecting members
6 can be appropriately fastened together to align the respective
7l reflecting segments 10 and 12 on each member and for movement
8; conjointly. As can be seen, the lower polygon reflecting
~i member 1~ can be provided with appropriate sprockets designed
10l1 to intermesh with perforations in the film strip 18. As can
11 ! be readily realized, a film transport system (not shown~ can be
12 utilized to drive the film strip 18 which in turn can drive
3l, the scanner assembly 4. Conversely, the polygon scanner
4l~assembly 4 can be utilized to drive the film strip 18. The use
5;of additional guide rollers, reels and audio e~uipment are
obvious expedients known to those skilled in the art and
17 ll accordingly, are~not disclosed or necessary for an understanding
18 of the present invention.
19, A film sprocket 20 on the lower polygon reflecting
0l!member 14 includes cross bars 22 which are relatively positioned,
21~as can be seen in the cross-sectional top view of Figure 2,
22llbetween the respective upper and lower polygon reflecting
23l,members to provide an advantageous baffling effect to help elimi- ¦
24 nate`optical cross talk between xeflective facets or ghost
25~ images in the projected real image.
26~ It should be reali2ed that in an actual embodiment of
27~ithe scanner assembly 4, the respective lower polygon reflective
28~, member 14 and upper polygon reflective member 16 can be mounted
29 for relative movPme~t for adjustment to maintain a composite
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1 re~istration o-~ the film frames if any ad justment is required
2 due to shrinkage or expansion of the film.
3 Referring again to Figure 1 the film strip 18 is
4` schematically shown with the optical axis extending through
5` the centric of a frame. The optical axis can be traced from
6 the lower polygon reflective member 14 upward to the upper
7Ipolygon reflective member 16 to extend outward through the
8j projection lens assembly 6 parallel to the radially inward
9l~optical axis. The distance dl is the distance between the
10 li radially inward extending light trace from the centric of the ¦~
11 I film frame and the radi~lly outward extending optical axis for
12 the pro~ection o the image in o~her words dl is the dlstance
13~lbetween either a reflecting facet or roof mirror intersection on
14llthe lower polygon reflecting member 14 and a reflecting facet
1511 or roof mirror intersection on the upper polygon reflecting
16llmember 16 along the optical axis; d2 is the distance from a
17¦¦common axis of rotation or center of rotation of the scanner to
18l the optical axis between the lower and upper polygon rieflecting
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19l!members 14 and 16. d2 can also be described as a distance from
20llthe axis of rotation to a plane containing the reflected trans-
~ mission energy beam along the optical axis between the upper and
22 lower polygon reflecting members. d3 is the distance from the
common axis of rotation to the film strip 18 or an object being
24i scanned. The distance 1 refers to the back focal length of
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25; the pro~ection lens assembly 6. The specific iset of dimensions
2~ for a particular film format can be derived from the geometry
27l of a polygon. For example a 26 facet polygon scannier and a
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1 35 mm f.ilm format would have dimens~ons derlved as follows:
3 d2 = 2.298
; d3 = 3,095
5Ij The relationship between these distances can be
6 expressed as follows:
j d3 ~ 2d2 dl
'~ 8l, The specific dimensions given were derived for a 35 mm
91lcine format with a .748,inch frame separation and a 26 facet
0l~scanner geome~ry. All other formats and facet geometries are
equivalent in concept to this specific case and can be easily
derived by an optical designer from the present disclosure~
13 ¦ The embodiment of Figures l and 2 an~ the mathematical
14 ¦analysis was performed with a 24 facet scanner geometry,.
15 I Referring to ~he illumination sub-system 8, it performs
an important function in minimizing dynamic keystoning in the
17¦¦design of the scanner assembly 4. As c~n be seen, a pair of
--I 18'l~ondensors 24 and 26 are utilized with an HMI AC arc l mp 28, such
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9l,as a 575 w~tt HMI AC arc lamp having a 12 mm arc length~ The
20~ arc length is important, since the condensor elements 24 and 26
¦1combine to magnify the arc by a factor of about 1 to form an
22ilimage slightly forward of the cross bars 22 or baffle spokes.
23jlOne or more folding mirrors 30 can be inserted into the illumina-
24ltion assembly 8. The actions of the mirrors 30 are such to
25l orient the arc image so that the long directio~ of the arc image
26 is in the direction of motion of the film I8. The second
27 i!
' condensor 24 is large enough so that three frames of the film 1
23l~are simultaneously illuminated with a piane re~lecting facet
9'l,geometry for the upper and lower polygon reflecting membersO
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1 As will subsequently be seen with the use of a 90-degree~
2 roof reflector, the condensor 24 would be redesigned so that only
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3 two frames of the film need be simultaneously illuminated.
4 The projection lens assembly 6 is designed with its
5 ;, field cur~ature complementing the cylindrical film surface so
6 that it is capable of imaging the curved virtual image that
7l~passes through the center of rotation of the scanner into a real
8l'image on a screen. The projection lens assembly 6, has a
9lltelecentric property.
10ll The scanner assembly 4 is fundamental to the operation
of the optical scanner system 2. Ideally, the scanner assembly
~iS designed so that it does not introduce any aberrations of
3l¦its own while it performs its function of con~inuously changing
14 ¦I from one frame to the next without introducing any image motion
51jor intermittent illumination changes. The preferred embodiment
16l disclosed utilizes planar mirrors which will not introduce any
17 !1 aberrations provided the sur~aces are appropriately flat and
18l'properly aligned.
191l In the ini~ial experimental work, the projection lens
2ll6 was an achromat doublet purchased from Jaegers of Long Island,
21llNew'York, part number 14D3411, having"a double convex, with the
2211 negative side facing the scanner assem~ly. A circular aperture
23ljstop was used. The focal length was 94 mm.
24 ll The film condenser 24 was plano/convex with a focal
25j, length of 75 mm and diameter of 60 mm. The li~ht condenser 26 wa~
26 also~planojconvex wi~h a focal length of 45 mm and diameter of
27 65 ~
28 Il, The film condenser 24 was positioned as close as
29l possible to the film plane while still nok foeusing any dust on
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1 the surface of the condenser,that is approximately 10 mm. The
2 light condenser distance to the 12 mm arc of the lamp was 40 mm.
3 While not shown, an extra heat reflecting mirror could
4 be inserted in the illumination subsystem 8.
5 ll As alternative embodiments, the more conventional
6 refractive prisms could also be utilized with appropriate
71 adjustments, for example, to compensate for chromatic aberrations.
8j Referring to Figure 2, it can be seen that the action
9 of the mirror facets in the scanner assembly is to place a
virtual image of the curved film frame a~ the axis of rotation
1lof the scanner, but displaced in such a way that it is centered
12 on the optical axis of the projection lens. As can be appreciated
- 13 la two dime~sional image can be considered to be formed from a
14 Inumber of discrete points and for the purposes of the present
Z 15 Idisclosure it can be seen that at least one virtual image point
6i,of each film frame will be positioned on a stationary locus
7~1point of the center of rotation of the scannerO Actually~ a line
.13l of points will be imaged along the axis of rotation which will
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9l;remain stationary as the scanner assembly 4 is rotated. Thus,
this portion of the film frame will appear to remain stationaxy
211l when two or more facets and film frames are simultaneously
221lilluminated and light from both are directed into the projection
23jllens 6.
24 ll Thus, two successive images will appear simultaneously
25l superimposed on the screen or real image plane, The rotation
26 of the scanner assembly will cause one of the film frame real
27 images to fade out as the other begins to dominate. As can also
28l be appreciated a single image will be projected when the normal
29l to the center of a film frame is parallel to the optical axis
30l,of the projection lens as shown in Figure 2. As can be further
31 ll seen from Figure 2, as the scanner rotates the virtual image
3 j,formed by the mirrors is only truly stable along the axis of
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l rotation and the off axis virtual image points will rotate at
~ the~same rate as the scanner assembly 4. The resulting effect
3` on the projected real imaye is to produce what can be called
4' dynamic keystoning. That is, the offset virtual image point
5li will be relatively movable to the stationary locus point during
6 a scanning movement. The result of dynamic keystoning is to
~:~ 7ll provide position dependent real image motions on the screen that
8 ll are perceptible to the viewer and are accented during any magni~
9I fication of the virtual image onto the real image plane. The
101 net effect at the real image screen is a projected real image
~ that begins tilted, gradually becomes co-planar with the image
121~screen and finally becomes tilted with respect ko the screen
13 l¦ in a direction opposite to the initial tilt. The actual visual
14lleffect perceived by the viewer is a geometric stretching at
15 1l the corners of the projected real image accompanied by a loss
16llin resolution. This effect perceived by the viewer can be
17l,ldefined as dynamic keystone distortion.
18l As can be further appreciated from Figure 2, the curved
19ll film strip 18 will likewise produce a curved virtual image
2~l about the centex of rotation. The particulax choice of a film
2l¦¦surface about a centroid of the stationary locus point or axis
;~ 22llof rotation of the scanner is important in preventing a lateral
23!;displacement of the image which would be experienced
` 24 with a flat film plane. In the mathematical embodiment disclosed
25 ll for the scanner assembly 4, 24 sets of mirrors were selected
26 so that each facet would subtend an angle of 15 degrees of the
. il i 27 l axis of rotation.
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1 The present invention recognizes that the scanner
2 assembly by itself is the source of dynamic keystoning and this
3 effect can only be minimized and not eliminated with a practical
4' scanner geometry. The present invention has accomplished this
5ll minimization by a projection lens design and by the controlled
6 interaction between the scanner assembly 4 and the illumination
7llsystem.
8I Mathematically, the imaging properties of the polygon
9Ireflecting facets can be represented by a transformation matrix
,using a four-by-four element matrix describing the properties
of the reflecting scanner facets. For purposes of reference to
12j this mathematical approach the article "Mirror-Image Kinematics"
131l by Joseph S. Beggs, Journal of the Optical Society of America~
14~ Volume 50, Number 4 (April 1960) pp. 388-393,~ieY~-u=~u-~ .
5¦lhcrcin b~ rc~erence.
16 , Thus, an object point P(x,y,z) on the film surface
17 Ican be related to its virtual image point p'~x',y',z') located
18 at the virtual image position described above by a simple
~9l matrix transformation. For a three mirror scanner this trans-
2ollformation is:
21 ~ Xcos~lZsin
24l Z' Xsin~-Zcos - ¦
This mathematical analysis is equally applicable to
26l both a planar reflective facet or a 90-degree roof reflector,
; 27 but i5 shown herein for the 90-degree roo reflector scanner
28llfor simplicityO
~9, ` I
30 l'
32 ~ /q
4~ 1
!
1 A distortion-free lens will project the virtual image
2 point P'(x',y',z') into the point P"(x",y"tz") at the projection
3 screen by the matrix transformation:
4 ~X" Y'l ~ m(X'+Z'a~) m(Y'-~Z'~')
~ 5 L~ J Lm - ~fZ' ~ ~ fZI- Yf
.. 7 ll In the above expressions, ~ = ~he scanner rotation
. il '
8 angle, m - the image magnification, f - the lens focal length,
9 !1 and the tan~ents of the ray angles are given by ~ , and ~
;ll Restricting the analysis ~o the chief ray (which will
lindicate the central ray of ~he fan of rays that construct an
12 image point), permits expressing the tangents of the ray angles
13jlas:
14~¦ ~ Zl~-t ~ Z+t
15 ~
16, Choosing a standard 35 mm film format and a typical
17jlmagnification o~ 440X, the above relationships have been plotted
- 13llfor a rotation angle of +7.5.
.. . .
19!! To verify these analytical results, a computer
20llanalysis was performed to predict off-axis real image tracks
21 l¦ for different parameters of designO These plots graphically
22" predict the real image motion on the screenL Figure 5 discloses
23 ll these results for a three mirror scanner, that is a combination
24 ll roof reflector and planar facet with a flat ilm surface pro-
25!ijected with a normal projection lens onto a flat screen surface.
2~ Typical values were inserted in~o the equations ror a 35 mm format
27~ with a scanner excursion of plus or minus 7.5 degrees and a 440.0
28l magnification. The screen size was 9.2 by 6.7 meters. The plots
.; .i
-~ 29llare for the principal ray tracks and illustrate the nature and
30' magnitude of image degradation associated with uncompensated
31, scanner devices on the edge of the screen.
`' !l ,~_. . I
I
,
1 An advantage of the scanner assembly of the present
2 invention over that of a number of prior mirror scanners is the
3 fact that tlle object sur~ace or film medium always maint~ins a
4 constant distance away from the scanner axis of rotation. As
a result of this design parameter, a greater portion of the
6 image format is stabilized during scanner rotation. As can be
7 appreciated, the object surface or ~ilm curvaturet as well as
8 the virtual image realized on the axis of rotation will have a
~, cylindrical shape with a radius o~ curvature equal to the
10 scanner radius.
11 Referring to Figure 5, it is significant to note
12 that the slope of the real image motion error curves are
1 13l smallest when the scanner rotation angle is also small. An
14 object of the present invention is to minimize the impact of
- 15!lmotion errors on the real image as opposed to trying to eliminate j
,
16 them. Thus, the real image is held in sharp focus across the
17 screen when the scanner rotation angle is small. Thus, the
18 projection lens 6 of the present invention is designed to project
19 a cylindrical object onto a flat screen. It should also be
20 noted ~hat when a scanner rotation angle approaches zero the
21 projected real image will also be the brightest.
22
23
26
27
28,
2~
31
~7 ' I
32 ~
i
I
':- ' ' , ' ': '
. .
11~ 49
1 Minimum ima~c degradation is therefore achieved by
2 the use of a cylindrical film surface in concert with a pxojec-
3 tion optics component that utilizes a field flattening element
which serves to project the cylindrical film surface onto a flat
5 projection screen while maintaining sharp focus over the full
6 field of view and simultaneously eliminating geometric distortion.
7 Two specific embodiments have been established which satisfy
8 these constraints: a projection lens with a cylindrical or
9 toroidal field flattening element and a relay lens with a
10lcyl.indrical or toroidal field flattening element at the relayed
11 image plane. Thus, a projection system which ~enerates real
12 images from the virtual image should have an object field curva-
13lture characteristic complimentary to the curvature of the film
14 surface to minimiæe the relative movement of the real offset
. I
15,limage point.
1G It should be noted that this relative movement plott d
7 in Figure 5 is relatively small compared to the screen size
18 and because of thP present illumination system design and focus
19 effects, only about 4 degrees of scanner rotation are clearly
0~focused on the screen~ This amount of motion is only about l
21 centimeter at the edge of the format for a 440,0X screen and
22 represents less than one minute of arc at the projection lens.
23
24
26
27
28
29;
~2 ~ _ j
~8~
i
1 One minute of arc is normally the limit of perception of
2 unaid~d human vision. 0~ course, th~ audi~nce will be closPr,
3 but three or four minute image motions should not be noticeable
4`~in most projector applications. The important thing is that
5l the lens is in focus where the image motion changes are
6 the smallest. The foregoing analysis of the chief ray location
7!~ as a function of rotation angle will now be complemented by an
3 analysis of the positi.on of best focus attained by all of the
91,rays converging about the chief ray. This analysis will
10l disclose the effect of the illumination source position on the
apparent motion o~ the real image.
12i As the scanner rotates, the virtual image of the film
13 ll surface rotates about ~le scanner rotation axis with the same
4ll angular rate and angular displacement as the scanner. A fan of
15,l rays diverging from a point P'(x',y',z') located on the virtual
16" image surface will be focused at a point P"(x",y",z") near the
17i projection screen in accordance with the first-order parametric
18li eXpressions:
19 j, Y" = mhcos~ ~ Z" ~ -m2hsin~
201i ~ , ~ I
21,1 Note, that the ratio,
22;i z~
li yll = -mtana - ~tan~'
23!lis the Scheimpflug condition for tilted images. In other words,
24 the image of a plane object surface tilted through an angle
25llwill be sharply imaged on a tilted plane surface where the angle
26iof tile, ~', is determined by the above equation.
27~
28l i
~- 291,
30!'
il. '
- 31 ll
- ~2! ~ ~3:
:- ii ' '
il .
- ~ - . .
` . !
l The locus of the sharply focused points produced
2 durin~ the rotation of the scanner is determined by eliminating
3 the dependence upon ~ of the above expressions to obtain: l
Z " _ h 2 m ," ~ ¦
6 (~ ~) y,l 2 = 1 .
~8 Ih2/ ~ _ lJ ~ [h2,(h2 1 ~ ~
gll The locus of sharply focused points is therefore simply
10 conic section whose r~,:n n= coordinates is given by:
13l' These relationships are graphically disclosed in
14ll Figure 6 for the case when h2/f2 ~ l~m2. The physical inter-
151lpretation is of considerable signi~icance. The fan o~ rays which
Il
16 diverge from P'(x',y',z'~ are sharply focused on the screen when
1711the scanner angle is zero, but as the scanner rotation angle is
181gradually increased the fan of rays will be sharply focused
. . ! I . ¦
19!1along the hyperholic locus and will continue to diverge until
20jlthey are incident upon the screen. This implies that the real
211image blur on the screen will both become larger and will
22lappear to move as the scanner rotation angle is increased.
23~lThe increase in blur size can ~e substantially reduced, and
the motion of the image blur can be minimizeci by choosing
25j ,
26
27
28
29
3~i
!!
31''
~2 ~ y
- ,
~, ' -
I~
1 projection optic components havin~ ~ telec~ntric property and
2 specific illumination optic components that coordinate film
3; frame illumination, arc source size and entrance pupil
4~dimensions such that the effective transmission of a pencil of
5~;rays of ~le offset virtual image point is limited to substantially
6;a tangential inter~ace with a surface of ~ocused real image point
7I~positions. The surface being representative of the effective
8llrotational scan movement of the projected offset real image
9llpoints ~ormed in space. This condition of the present
1o! invention is shown in Figure 7.
When this condition is met, the image will appear to
12¦ remain station~ry throughout the scanner rotation angle range,
13 1I but will appear to become progressively softer in focus. Since
14l¦ the image is sharpest when ~he scanner angle is near zero, and
15 ll the rate of change of focus (and image motion) is smallest
16 when the scanner rotation angle is near zero, the image per
17 ¦¦ cPived by the viewer will appear to be stahle and in focus.
18li Additionally, the condition imposed upon the projection
19l optics components to satisfy the requirement that the chief
20 ¦I ray will be tangent to the hyperbolic locus is that the design
21llbe telecentric. Telecentricity means that the chief ray of the
22llprojection lens must be parallel to the lens optical axis on
23 ll the object side. The greater the deviation from telecentricity
24l the more pronounced the apparent image motion on the screen.
25 il ~igure 10 discloses one projection lens solution where
26 a toroid field flattener 40 is positioned ad]acent the film 18.
27 ~n astigmatism corrector 42 complements a tessar projection
28l lens 44.
29 1 .
30 i
31
, 32 ~1 ~/ '
2 s
.
l` ~
1 Complimenting the choice of projection optical
2 components is the particular illumination optical components
3 defined herein to further reduce dynamic keystoning. The
4 illumination subsys~em 8 provides corrections in two distinct
5I ways; first, operating in concer~ with a telecentric projection
6 lens the illumination system can restrict the fan of rays to a .
7l narrow ~an centered about the tangent to the hyperbolic locus
B, of sharp focus; and second, the lamp and illum.ination opti.cal
91. components can selectively vignette the fan of rays which are
lOIl projected to the screen.
Three mirror illumination optical system is quite
. 12~, unique by virtue of the fact that it is tailored to work in
` ~ 13ll concert with the paxticular scanner being used~ For example,
14l with the three mirror scanner having the arc image at the
15ll entrance pupil of the projection lens the scanning mechanism
` 16i,causes the image of the arc lamp source to move through the
. 17l'entrance pupil as the scanner rotates. A matrix transformation
.. ~ ., ~
. '. can provide tha ralationship between a fixed point on the
.. 19, arc lamp source and its projected image in the projection
; 20 il lens entrance pupil when the mirror scanner is rotated. As can
21, be determined ~rom the sequence rotation disclosed in Figures 3
22 ll and 4 for a three mirror scanner configuration (planar facet
. 23 plus roof reflector) and also from Figures 8 and 9 for the
24 two mirror scanner configuration (planar facet on both
. 25 upper and lower polygon scanner members1, the illumination
. 26 optics components provide a distinct interaction with the
scanner and the projection optics components for selectively
28, illuminating differ~nt regions of the real image of each film
29, frame so that the light transmission is progxessively decreased
.~ 3~1
. 1l
31
~ 321 ' ~ ~ . I
l,
I' .
4~9
. ' '
~
1 in the region wherein ~he relativ~ movement of the real ofset
2 ima~e point becomes progressive1y greater.
3 Mathematically, this can be verified by a matrix
4 transformation relating the source point and its image in the
5l projection lens entrance pupil as follows;
r s in ~ l O ~ X~rs in ~ .
8j, Y' _y ~ Y
g ! z~ -z-rcosa z~ = -z-rcos~
10jl Th ph sic ~l implic tion of the above expression is
that there is no cross-term dependence between x' and z' (imply-
ing that the image is not rotated in space). The negative signs
31 associated with ~' and y-' signify that the imàge is both inverted
4¦~and reverted in space. The r sin~ term in the expression for x'
¦1indicates that the arc image is displaced in the projection lens
,lentrance pupil by this amount while the r cos~ in the expression
7llfor z' indicates that the arc image moves along the optical
13" axis by thls very small amount. The net effect for the three
19l,mirror configuration that this relationship describes is that
201lthe image of the arc wiIl be displaced across the projection
jlens entrance pupil but will not be rotated in space. By means
22llof this novel arrangement it is possible to select an arc lamp
23iland condenser elements so that the lamp image always remains within
the projection lens entrance pupil while vignetting restricts
i'the fan of rays which illuminate the film to the set of rays that
are focused by the projection lens along the tangent line to the~
27l hyperbolic locus of best ~ocus.
~8 ,i, ~1
29~
30i
li , ,
3
32
ii ~l, .
3449
1 The experimental illumination optics con~iguration that
2 satisfied the above set of constraints was an HMI A.C. arc
3llamp with a 12 mm arc length combined with condenser elements
4 ! that magnify the arc so that its image just filled the projection
5;lens entrance pupil when the scanner is at ~ero rotation angle.
6 The axis of the arc image must be in the direction in which the
7ijfilm moves so that the arc image will be vignetted in a manner
that will minimize the dynamic keystone aberration.
9 The respective Fiyures 3, ~, 8 and 9 disclose the
0llvignetting for both ~he three mirror facet and two mirror facet
scanner geometry. These views illustrate how the displaced
12l arc image, the rotated ~lrtual image of the film, the effective
131 facet aperture, and the fixed projection lens entrance pupil
~41 combined to vignette the ray fan with increasing rotation angle.
15i The virtual film images rotate about the scanner center-
line as previously described. The illumination system arc lamp
7l¦image, however, is displaced in the direction of motion of the
18 scannerO As the edges of the film being to go out of focus with
19" increasing scanner rotation, the image of the arc lamp source is
~ ~ 2olldisplaced so that tha vignetting introduced by the scannin~
211mirror effective facet aperture allows only the upper portion of
22lthe arc image to be incident at the lower portion of the projec-
23lltion entrance pupil; by choosing the pupil to be the same size
24 as the film frame, this arc lamp displacement just compensates
1 25,~for the dynamic ~eystone aberration by permitting only the
26 restricted fan of rays to pass through the projection lens
27
28
29
'311' ~
~2 ~ .
,~ .
!
1 entranc~ pupil that will focus along the tangent to the hyper-
2 bolic locus of best focus.
3;j Other effects are also present that influence the
4 quality of the perceived screen image. ~he image goes out of
focus with increasing scanner rotation angle at the same rate
6; that the illumination system vignetting reduces the screen
7 !I brightness. In addition, the illumination across the film frame
8~, decreases from a maximum on one edge to a minimum on the other
9 ed~e. This "shading" is enhanced by the arrangement of the arc
1011 lamp and condenser elements so th~t the minimum illumination
- 11lll occurs when the film defocus is at the greatest ~alue that it
` 12 ¦I will attain-
~3~1 As can be seen in Figures 8 and 9, by increasing the
; 14licondenser si~e and reducing condenser focal length to insure
15~ illumination of three full frames a two mirror scanner
~ 16 configuration is possible.
., 11
; 171¦ Summariæing the above, it can be seen that the present
~ 18 ll invention recognizes that practical configurations of reflective
., ,1
19!! and/or refractive scanners will experience a dynamic keystone
20 ll aberration and that the amoun~ of aberration can be only
211~ minimized to a modest degree by increasing the number of
22, scanner facets. Accordingly, the present invention provides a
23l particular projection optics and illumination optics that can
24 ll operate in concert to nullify the perception of the dynamic
25l! keystone aberration in the real image by a viewer even with
26~ commercial movie projection magnification.
27~ !
28 l,l
29,i
;. 31 1!
32 ~,
. .
-\ ~
1 The derivation of the locus of the chief rays
2 intersec~ion point with a surface of best focus indicates that
3 the real image on the screen must be held in sharp focus during
4l that period of time when the scanner rotation angle is nearly
5l 2ero, due to the fact that the image motion r~mains small for a
~` 11
6 large angular range about the zero rotation angle but becomes
!
: 7 ll quite large for the small amount of time when the scanner
8 ll rotation angle is approaching its maximum value~ To maintain
9~sharp focus vver the full film frame during the time that the
~` 10 I scanner rotation angle is nearly zero re~uires either a cylindric ¦l
11 I or a toroidal field flattening element to project the cylindrical
12 ~ film frame onto a flat screen. The film record must be
I cylindrical rather than flat, and the design qf the field flat-
1`4 ¦ tening element must also avoid introducing distortion that will
-~ 15 ~ contribute to image motion errors.
I 161 It should be fully realized that the particular
17¦ projector lens design can be subjective to a particular
,18 ! app~ication of the continuous projector of the present invention
Il
19 ll and accordingly, the presen-t invention should not be limited to
~¦¦the specific examples shown herein.
21~¦ The following conditions would provide sufficient
22 li guidelines for an optical designer to provide a specific
231;projection lens;
24 1l l . The lens must image the film sharply when the film
25ll and scanner facet are in the "head on" position.
26 i~ This implies the lens must be able to image a
27
28
2g
31
32 j I . ~
Il ,, 3~5
.~.. ~ .
:`
-` !'
g
1 cylindrical ficld as flat. Field flatteners near
2 the film are undesirable since scratches or
3 dust may be projected.
4 2. The lens must have sufficient back focal length
5l to clear the scanner and sharply image the film,
6 i.e., the back focal length must be equal to the
7 radius of the scanner wheel or greater~
B 3. The exit pupil of the projection lens should be
9~ equal to the size of the film format.
10,l 4. Minimum dynamic keystoning will result if the lens
is~designed to be telecentric on the film side.
5. In addition, baffles should be included in the lens
,
13ll or the scanner to eliminate "ghost" images.
14'l 6. The numerical aperture (f-number) is determined
15~j by the number of facets. The greater the number
!!
16, of facets, the slower must be the projection lens.
17 ¦l The preferred embodiments for the projection optics
1g required to satisfy these conditions consist either of (l) a
9 cylindrical or toroidal ~ield flattening element designed into a
: 20ll projection lens and located in ~lose proximity to the film record,
21 (2) a relay lens with a cylindrical or toroidal element desigr.ed
22llto be in close proximity to the relayed image surface so that
23iiany commercial projection lens can be utilized for projection
24 of the relayed image surface onto the scr~en~ I
!
25i While the above embodiments have been disclosed as
.. ,,
26; the best mode presently contemplated by the inventor, it should
27 be realized that these examples should not be interpreted as
28~, limiting, because artisans skilled in this field, once given the
29lpresent teachings, can vary from these specific embodiments.
30l,Accordingly, the scope of the present invention should be deter-
: 31 ll mined solely from the following claims in which I claim:
~2 ~
~ ~` .74j 3 1
