CA1108449A - Image stabilization system for continuous film scanning apparatus - Google Patents

Abstract

IMAGE STABILIZATION SYSTEM FOR
CONTINUOUS FILM SCANNING APPARATUS

ABSTRACT OF THE DISCLOSURE
An optical scanner system such as a projector for the continuous transmission of images to provide image immobilization is provided. The optical scanner system includes an illumination system, a scanner mechanism, and a projection lens system. The scanner mechanism is capable of creating virtual images of successive film frames 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 image locus point and relatively movable during a scanning movement. The scanner mechanism can, for example, be of a reflective or refractive polygon geometry. The specific para-meters of the projection lens system and illumination system recognizes the inherent limitations of the dynamic keystoning aberration in scanner assemblies and seeks to nullify its effect in the projected real image. The projection means is of a tele-centric design. The illumination system is matched to the vig-netting capabilities of the scanner and projection system to selectively illuminate different regions of a real image of each film frame so that the light transmission is progressively decreased in the region of each film frame when the relative movement of the real offset image point becomes progressively greater. Basically, the system deluminates during the greatest rate of defocusing of the real image.

Description

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 i .
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 jj .
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.
ii 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, 29 i 30!i 32 ! ~w ,1 .
- -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 !!
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.
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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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' 11S~8449 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 291; ' .

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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 29, ~2 ~ _ 11 ~
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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:
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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;
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!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;
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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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, L4g 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.
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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 31i ~
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Il 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 1i .
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 -: :
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 30lj ~2 Iy I! .

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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 . i, .
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 ., .
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 Il , ,1, 7~ ' ~2,1 ~

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li B4~0 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 I!
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 Il ~r I ~ ~ 17 li . I
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
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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 28, 2~

~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.

24 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 , 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 , 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 ~ 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 , , ii ~l, .

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 '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 2g 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

Claims (17)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. 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 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 curvature 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.

2. The invention of Claim 1 wherein the means for generating real images includes a projection lens having an entrance pupil, the means for transmitting virtual images includ-ing a movable scanner which causes an image of the light source to move through the projection lens entrance pupil as the scanner moves.

3. The invention of Claim 1 wherein the means for transmitting virtual images includes a movable scanner with a plurality of reflective facets, the movement of the scanner causing an image of the light source to move through the effect-ive aperture of the reflective facet.

4. The invention of Claim 2 wherein the means for transmitting virtual images includes a plurality of reflective facets that vignette the light transmission so that rays of light will focus along the tangent of a surface of sharply focussed real image point positions, the surface being representative of an effective rotational scan movement of the projected offset real image point.

5. The invention of any one of Claims 1 to 3 wherein the light source further includes an illumination system and means for moving the film medium having successive images of objects through the illumination system.

6. The invention of any one of Claims 1 to 3 wherein the light source further includes an illumination system and means for moving the film medium having successive images of objects through the illumination system, and wherein the illumination system includes an elongated source of light having its longi-tudial axis in the same direction as the film movement.

7. The invention of any one of Claims 1 to 3 wherein the light source further includes an illumination system and means for moving the film medium having successive images of objects through the illumination system, and wherein the means for transmitting virtual images is a reflective polygon scanner.

8. The invention of any one of Claims 1 to 3 wherein the light source further includes an illumination system and means for moving the film medium having successive images of objects through the illumination system, wherein the means for trans-mitting virtual images is a reflective polygon scanner, and wherein the reflective polygon scanner includes a plurality of planar reflective facets.

9. The invention of any one of Claims 1 to 3 wherein the light source further includes an illumination system and means for moving the film medium having successive images of objects through the illumination system, wherein the means for trans-mitting virtual images is a reflective polygon scanner, and wherein the reflective polygon scanner includes a condenser at least twice the size of an object image.

10. The invention of any one of Claims 1 to 3 wherein the light source further includes an illumination system and means for moving the film medium having successive images of objects through the illumination system, wherein the means for transmitting virtual images is a reflective polygon scanner, wherein the reflective polygon scanner includes a condenser at least twice the size of an object image, and wherein the source of light energy includes a condenser at least twice the size of an object image.

11. The invention of any one of Claims 1 to 3 wherein the light source further includes an illumination system and means for moving the film medium having successive images of objects through the illumination system, wherein the means for transmitting virtual images is a reflective polygon scanner, and wherein the polygon scanner includes plurality of reflective facets and the baffle means are positioned between respective facets.

12. The invention of any one of Claims 1 to 3 wherein the light source further includes an illumination system and means for moving the film medium having successive images of objects through the illumination system, wherein the means for transmitting virtual images is a reflective polygon scanner, wherein the polygon scanner includes plurality of reflective facets and the baffle means are positioned between respective facets, and wherein the baffle means are radial spokes.

13. The invention of any one of Claims 1 to 3 wherein the source of light energy includes a condenser at least three times the size of an object image.

14. The invention of any one of Claims 1 to 3 wherein the optical system has a telecentric characteristic to provide a substantially parallel position of the chief rays defining the image to an optical axis of the projection means.

15. The invention of any one of Claims l to 3 wherein the projection means includes a projection lens and an aperture on the real image side of the projection lens.

16. The invention of any one of Claims 1 to 3 wherein the projection means includes a projection lens and an aperture on the real image side of the projection lens, and further including baffle means for removing ghost images adjacent the projected real image.

17. The invention of any one of Claims 1 to 3 wherein the projection means for generating real images has an object field curvature characteristic complementary to the curvature of the film surface to minimize the relative movement of the real offset image point and to project a real composite image of perceptively stable registration between the film and real projected image.