US2336508A - Optical method and means - Google Patents

Description

Dec. 14, 1943. MacL, SMITH ET AL 2,336,508

OPTICAL METHOD AND MEANS Filed Nov. 16, 1940 4 Sheets-Shet 1 21 "6 D 14 J,- 22 I I 1 r so IN VEN TORJ. FRANC/S MACLEAN J M/ TH THONA! A QU/NASK/RBY ATTORNEY:

4 Dec. 14, 1943. Mac] sM T ET AL 2,336,508

OPTICAL METHODAND MEANS Filed Nov. 16, 1940 4 Sheets-Sheet 2 I o5 INVENTORJ'.

FRAN C15 MACLEAN J'MITH .j THOMAS AQU/NAS K/RBY ATTORNEX Dec. 14, 1943. F. MaoL. SMITH ET AL OPTICAL METHOD AND MEANS Filed Nov. 16, 1940 4 Sheets-Sheet 3 T u Hl s il M 6 6 k w: mm 1 7 n 5 i a n w n m a e m '5 A 5 mm m 1 W u r 1 4 a a m /m 3 .\.M.\. q I 8 CI 1 a F e no 9 .h 9 8 8 1.

IN V EN TORS.

FRANCIS MACLEAN SMITH THOMAS AQU/NAS K/RBY ATTORNEY Patented Dec. 14, 1943 OPTICAL METHOD AND MEANS Francis MacLean 'Smith and Thomas Aquinas Kirby, New York, N. Y.

Application November 16, 1940, Serial No. 365,914

18 Claims.

This invention in its broader aspectrelates to methods and means for increasing the effectiveness of an image, whether directly viewed by an observer or photographed for later reproduction. While designed primarily to apply to images which are originally formed in whole or in part by projection and particularly composite images which are formed either by the projection of two sets of images or of one set of images and the reflection of real objects, this invention in certain of its aspects may be applied also to ordinary rojection or to the direct viewing of real objects. Our invention is particularly applicable to single or composite images which are viewed in cabinets, but is not so limited.

A use to which our invention is widely applicable is in connection with illusions of a common type which embody composite images, whether for direct viewing or as a basis for photography. For almost a century transparent mirrors angularly disposed between an audience and real objects have been used to combine into a single unitary visible result those objects directly viewed and images of other real objects reflected by the mirror. In one such illusion known as Peppers ghosts, for example, actors representing real persons were positioned between an audience and an angularly and vertically disposed transparent mirror which reflected images of other actors who simulated ghosts and were actually placed at one side of the transparent mirror and of the stage or of the area visible to the audience, thus apparently merging the two groups of actors into a single composite scene. This illusion with Variations is described in the United States patent to J. H. Pepper and J. J. Walker, Number 221,605, dated November 11, 1879. Countless permutations of such arrangements have been proposed. For almost half a century, such illusions have been produced by similar combinations of pro- J'ected images and reflections of real objects or of'reflections of a plurality of projected images. It has beenproposed, for example, to project a motion picture of action upon the rear of a translucent screen between which and an audience is angularly disposed a transparent mirror which reflects real objects disposed as in a diorama, the real image projected from the motion picture furnishing a foreground or action component. and the virtual image reflected from the diorama furnishing a background or setting component which unite to form a composite image simulating depth and giving a stereoscopic eflect.

As a matter of convenience, in this specification we use the term foreground component to designate that portion of a composite image which represents the action or central theme of that which we are presenting. Ordinarily, such representations are of persons or objects in motion, and the term includes static objects either as principals or as supplementary to moving objects.

' For convenience in the sub-joined claims, we apment of the background component. Similarly,

a background component mayinclude furniture and other stage settings which may appear either forward or back of the images representing the actors. In the large majority of cases, however, these components appear to be spaced from each other thus giving an illusion of depth.

A motion picture film embodying a foreground component for use in such an illusion is produced by photographing persons or other objects making up foreground action against a background I which is as completely black as is possible. If the illusion of depth is to be created and maintained, it is essential that with the image projected from this film there be no suggestion what'- ever of a surface surrounding the image and forming a backgroundsince the appearance of such a surface or even a. suggestion thereof jointly with a foreground component interferes with the wanted background component which is produced by reflection as previously described. An observer should not be conscious of the presence of the screen or any part thereof. We have found it commercially possible to secure a negative motion picture of very excellent quality in which what would normally be the background iswholly' clear. In printing from this negative a positive 1 film for use in a projector, however, we have found it practically although not theoretically impossible to secure complete opacity in that portion of the positive film not occupied by the foreground action even though the correspondingportion of the negative film appears to be wholly clear. Unless exposure and development of this positive or one of such processes is carried to an extreme which produces an unsatisfactory foreground image, the remainder of the film permits the passage of a certain amount of light. This light seeps through the positive film, as it were, even by reflection from silver grain to silver grain, and emerges as diffused light, or light ma pass through very small transparent spaces suggesting minute pin heads. Even when printing is carried out under the best commercial conditions, enough light passes through this portion of the film which should be completely opaque seriously to interfere with the effectiveness of the illusion. Also, repeated projection causes scratches in the emulsion, known in the motion picture business as rain," and other damage which still further reduces this opacity.

This foreground component of a composite image must be projected upon a. so-called rearprojection screen. Such a screen, indeed, must be used practically speaking for all such projection since light bearing an image must be projected upon the rear surface of a flat translucent body and the image viewed from the front urface thereof. Projection of light through such a screen causes marked diffusion which as a practical matter is added to the diffused and even direct light which passes through what should be the opaque portion of the film carrying the foreground component. The result may even appear as a bluish haze or scrim tending to make visible the surface of the screen and apparently disposed between the observer and the apparent position of at least a portion of the background component. This surface visibility carried by this unwanted light in itself interferes with the quality of the reflected background and tends to obscure and confuse it, but more important is the fact that it reveals to the audienc that the foreground action is being projected on a surface thus indicating the presence of a background associated with the action. Since the illusion of depth depends upon the projection of the foreground action apparently spaced well apart from a background, including, in many cases, a proscenium arch and stage setting, which is produced solely by a wanted background component as by reflection as of a diorama, it will be readily understood that this visibility of what should be the opaque and unseen portion of the foreground surface destroys the illusion for which others have long striven.

As will be evident to those skilled in the art of making dramatic presentations, there are times when the stage, or in an illusion such as the one described above, that which passes for the stage, must be completely unoccupied. In an illusion such an effect is impossible if the screen is visible with no foreground component such as figures representing actors upon it. For example, it is highly desirable that the stage appear to be empty at the beginning and end of a presentation since otherwise much of the dramatic effectiveness is lost. Use of methods and means described and claimed herein, so far as we are aware, for the first time makes it possible to accomplish these new and desirable results in an illusion of this character.

The above difliculty as caused by unwanted light coming from a foreground component is much increased by interfering light from other sources.

Light from a diorama disposed as above described is in part reflected by a transparent mirror to an observer, as is necessary in order to produce the background component, and in part is transmitted through this mirror. A portion of this transmitted light falls upon and renders visible the portion of the scren surrounding the image of the action of the foreground component which should be maintained completely invisible if the illusion of a third dimension is to be maintained, as stated above. .Also this visibility, which is in the form merely of interferin light and not of images of the object making up the diorama, conflicts with the wanted and ponent.

A primary object of our invention is to overcome the above difficulties together with certain related difliculties, as will later appear, which in the past have caused the failure of all attempts to produce commercially such types of illusions, so far as we are aware. A particular object is to maintain the invisibility of the area surrounding a projected image of a foreground component of a composite picture which ha the illusion of depth which is produced by combining a foreground component with a reflection of a background component.

Difficulties in some respects similar to the above apply to projection within a cabinet or to any type of rear projection, even when a composite image is not desired.

For many years pictures of various types have been presented in cabinets, either by projection of stereopticon or motion picture type or for direct viewing. Conditions of use of such cabinets generally have required that they be employed in fully light rooms. As a consequence the definition of details, light and shade, quality and intensity of the picture as viewed have been seriously diminished by the effects of interfering light, which, as reflected back to an observer, is diffused to a not inconsiderable extent. Similarly it has long been proposed and in a limited measure practiced to show motion or still pictures upon so-called daylight screens likewise in rooms which are darkened only to a limited extent.

. being even greater with the projection of a composite image than with that of an ordinary single image. Another object of our invention, therefore, is to overcome the particularly damaging effects of outside interfering light in connection with such illusions.

We overcome the above difficulties and carry out the objects of our invention by simple method and means.

We absorb a portion of this interfering light, whether coming from a foreground component, from a background component or the objects which make it up, from the sight opening of a cabinet, or, in those cases in which a cabinet is not used, from the room generally within which a screen is placed. Since the interfering'light which does maximum damag is diffused, we presingle image as distinct from a composite control of this interfering light.

for tomake use of a wave filter which has mini mum transmission of light of those wave lengths which are diffused to a maximum extent and minimum absorption of those wave lengths relabe used alone to the end that a much improved image is secured. .We so apply these steps and means that they do not interfere noticeably with the images which are wanted while disposing of the interfering light which is not wanted.

All-projection lamps are relatively rich in light of the shorter wave lengths, ordinarily spoken our secondary protective reflecting means and filof as blue. According to accepted optical law,

light "of such wave lengths is diffused to a much greater relative extent than is light making up the remainder of the spectrum. Consequently by diminishing the light of thi character we reduce diffusion to a relatively greater extent than we reduce the total quantitative value of the light. It is diffused light which produces much of the difficulty which we overcome. W therefore prefer to interpose .a minus-blue filter in the light of the foreground component and in the interfering light from other sources so that we cut down the amount of light of the shorter wave lengths, ordinarily spoken of as blue light. This reduction in quantitative light value and indeed the qualitative change in sensory color value are so slight that they are practically imperceptible to an observer yet they destroy or at worst much reduce the diffused light which would render 'visible that area which we maintain invisible.

Also in rear-projection of a single image, we have found that the use of a filter particularly of this character is of value in that it reduces the diffused light coming from front or rear.

which is objectionable with any rear-projection screen.

Another measure which we employ is equally simple and its results equally striking. To reduce to a negligible point other interfering light, notably that coming from or associated with a background component, we place another protective transparent mirror between the primary refiecting mirror and the rear-projection screen at such an angle that it will reflect this unwanted light away both from the screen and from a viewing station. Likewise this secondary mirror infrom a projector rather than reflected from a tercepts interfering light coming from the viewing station infront of the screen and reflects a portion of it away from the real image and from the vicinity of the apparent position of the virtual image. Hence it is also valuable when a image i produced.

The acute angle at which this secondary mirror is placed relative to the plane of th rear-projection' screen is such that there is minimum interference with the strong primary image upon that screen. The intensity of the interfering light in relation to that of the foregroundim'age (and, indeed, to the amount of damage which it does) is so little that steps and means which virtually destroy it are without noticeable effect upon the foreground image.

Our filter also is of benefit in assisting in the -It causes a quantitative drop in intensity on account of transmission losses. This quantitative result is independent of the qualitative effect of the particular filter employed. It'will of course be unwhich will later appear.

ter asone sheet of plane glass preferably minus- =blue in filter factor readfly transparent and set at a slight angle to the plane of the screen.

Further details of the invention and other objects thereof and its novel features will be understood from the following description and drawings and particularly pointed'out in the ap claims. It will be understood, however, that the invention may be embodied in forms other than those shown and within the scope of th broader claims. The detailed descriptionwhich follows refers to the accompanying drawings which illus- I trate preferred embodiments.

In the drawings:

Figure 1 is an isometric view partly broken away and partly in section and with certain parts omitted for clarity of an exterior of acabinet illustrating the practice of our invention.

Figure 2 is a sectional view of a cabinet illustrating the combination of a projected picture and a reflected diorama.

Figure 3 corresponds to Figure 2, the background image, however, being initially projected diorama.

I Figure 4 shows an embodiment of the invention similar to that of Figure 1 but includes the lacing or a stage setting, which for purposes of illustration is substituted for a diorama, in a preferred position which adds much to the effectiveness 0f the presentation. a

Figure 4a corresponds to Figure 4 but shows the use of a projected background component in place of real objects. Figure 5 illustrates certain of the optical principles involved in the practice of our invention.

Figure 5a represents a film of a type producing a foreground component of a composite image. Figure 6 (Sheet 2) illustrates the practice of our invention as applied to the production of a negative motion'picture film from a composite image formed according to the practice of our invention.

Figure 7 (Sheet 1) is a preferred variant of the form of our invention shown in Figure 3.

- Figure 8 (Sheet 3) is a diagram showing our invention as applied to rear-projection genersentially of a projection chamber I I (Figure 4), va viewing chamber I 3, and a background chamber H. The background chamber may be merely a recess in one side of the viewing chamber. In

fact, the various chambers to which we refer in this specification and in the sub-joined claims may be merelyparts of one chamber. A projecting machine I5 may be disposed within the projection chamber, or, as shown or indicated in Figures 2, 3 and 5, it may be placed directly back of a screen I! (Figures 1 and 2), sometimes hereinafter called a central surface for reasons This latter arrangement is of course a common one when our invention is practiced in a theatre. The projector may generally is the latter. If desired, in the structures shown in Figures 1, 2 and 3, the projector may be placed in a projection chamber preferably located below the viewing chamber, and the image reflected by suitable mirrors upon the screen IT.

The projection chamber l2 and background chamber I4 make up a roughly quadrilateral box with the background chamber l4 shown in Figure 2 as above the projection chamber. An observer looks from a viewing station through a protective window l8 as seen in Figure 2 placed in a forward sight opening l9 or as shown in Figure 6 a camera may be substituted for the observer. All other sides of the housing are closed, except that through which images are projected. The window 18 has no optical function and is intended merely to keep out of the apparatus the heads and fingers of observers who are curious as to how the illusion is obtained. In those locations in which external reflections are troublesome it may be omitted.

In the background chamber of Figure 2, a diorama is indicated containing for example a far background 2| disposed upon a wall of chamber I4, and wings '22 and 23 making up a stage setting, and, if desired, a simulation of a proscenium arch 24. In combination with a minus-blue filter, we have found blue an excellent color for the diorama or in fact any background component. The blue character of the one component imparted by the filter well cooperates with the slightly amber tone of the other component, to use sensory terms, to heighten the effect of depth and the effectiveness of the illusion, even though an observer may not be conscious of any color sensations as such. It is particularly to be noted, however, that the effectiveness of the methods and means herein described and claimed is in no way dependent upon this use of complementary colors. although it may be much assisted thereby. The diorama is illuminated as by an incandescent lamp 25 with a reflector 26 set in a housing 21 which if desired may be ventilated. In practice a plurality of light sources is used, but only one is shown for purposes of illustration.

A primary transparent mirror 28 is vertically and anguiarly disposed and comprises a front surface 29 and a rear surface 30. The angle at which the mirror is to be set depend upon the placing of the other elements of the device and the results which are desired, but an angle of forty-five degrees, as shown in Figure 5, is common. In practice for most purposes we prefer to employ a plane sheet of plate glass, but for certain uses the mirror may be silvered lightly.

Transmission relatively to reflection should be 7 high. As will be readily understood by persons skilled in this art, light from sources 25 is reflected from the objects making up the diorama and upon the forwardly facing surface 29 of the transparent mirror 28, which thereupon forms virtual images which make up a background component.

The optical principles involved will be clear by a consideration of Figures 1, 2 and 5. As shown in Figure 2, the optical axis of a cone of light representing a portion only of the diorama is indicated in dot and dash line as ABC and a projection of a portion CB of this line as CBC'B becomes the optical axis of the projector l5 which is producing the foreground component. DEF represents the actualreflection toward an observer 0 of point D of the diorama and GHI that place between the central surface I1 and the of an opposite point G. Similarly line JKL represents the actual reflection of point J toward the observer. The observer, however, views this background component, except that portion thereof which represents the proscenium arch, as if it were projected backwardly as indicated by the dotted lines HGG, KJJ and EDD respectively and disposed to the rear of the screen I! in the planes indicated by the dotted lines extending upwardly from GG, JJ and DD respectively which of course represent the planes of the respective virtual images. The proscenium arch properly appears as if before the screen II in the double plane indicated by dotted lines PP, which represent its virtua1 image. Therefore screen I! bearing a real image which forms a foreground component later discussed becomes a central surface since it appears as if central between the virtual image of the proscenium arch in the plane represented by PP and the remainder of the background along the planes represented as proceedingfrom GG, JJ and DD. The various elements making up each component need not be or appear to be in planes parallel to each other or to those of the other component. For example, the impression of perspective in a background component representing scenery may be heightened if its plane is slightly inclined. In the sub-joined claims, we speak of foreground and background components as disposed in adjacent planes, or as so appearing. We do not limit ourselves to a composite image in which these planes are but little separated, but wish merely to make clear that the planes must be sufficiently close to each other so that the resulting composite image has psychological unity.

A foreground component may be provided by a positive film 32, which of course is printed from a negative. As shown for purposes of illus-' tration in Figure So, this positive film comprises essentially a background 33 and a figure 35, here.

shown as that of a dancing girl, which when projected create the true foreground component. As previously explained the area 33 of the film 32 surrounding the figure 35 must be completely opaque unless the illusion is to be destroyed. In Figure 5a light leakage or lack of opacity in area 33 is represented in an exaggerated form.

By means of the projector I5 a relatively intense image representing this .foreground component is projected upon the central surface ll. An observer 0 is able to see this image without realizing the presence of the transparent mirror 28. In addition to maintaining a complete absence of visibility on the central surface surrounding the figure 35, it is also desirable to maintain a careful balance between the relatively subdued image of the diorama reflected to form the background component and the relatively brilliant image which makes up the foreground component.

To overcome the difficulties caused by the visibility of the area surrounding the foreground component as viewed by an observer, such difiiculties having prevented the wide commercial use of all such illusions so far as we are aware, we

primary reflecting mirror 28 both a secondary transparent mirror designated as 40 in Figure 5, and also a filter 4|. This mirror should be of a high degree of transparency, preferably merely a thin plane sheet of plate glass. As a practical matter and as shown in Figure 2, we prefer to combine filter and secondary mirror as a single unit 42, but in order to make the scientific basis .are commonly called blue.

of our invention clearer in Figure we show the two elements as separated, as they may be in fact.

These two elements cooperate in a plurality of I ways to perfect the projection of such a composite image as above described.

As previously explained, in an illusion of this character a figure for example making up a foreground component of a composite image must be projected with its surroundings completely invisible. In Figure 5 asection of a total cone of light emanating from a projector not shown is bounded by the lines NM' and PC", but a section of a portion carrying an image such as 35 is shown as bounded by the lines NM and PO. Therefore, considering only one vertical section normal to the longitudinal axis of light from the projector, the portions of the screen between N and N and P and P must be maintained absolutely invisible while that between N and P bears the wanted image. Since the image produced by this light as it passes through a film or slide in the projector I5 is to be viewed from the opposite side of the screen I1, this screen must be translucent and permit emergence of an image-carrying cone shown in section in Figure 5 as bounded by NQ and PR. Passage of light through such a screen causes diffusion. In order to secure a relatively brilliant image, the color of this screen must be,

relatively light. Screens for rear projection are ordinarily blue white or grayish white in sensory terms. According to an accepted law of optics, light of shorter wave lengths is diffused to much greater extent than light of relatively longer wave lengths. The light making up these cones, including components which should be invisible as well as those which should be visible, coming as from a projector I5, whether equipped with an incandescent lamp or an arc, isrelatively richer in light of the shorter wave lengths which Consequently light relatively rich in the range of low wave lengths passing through a light colored screen will be diffused to a relatively large extent as indicated in Figure 5 for one beam taken as illustrative by the dash and double dot lines 43 much exaggerated for clarity. Also, the light which penetrates the theoretically opaque portion 33 of the film 32 is largely diffused. As a consequence of the two factors above, the side of the screen I! toward the observer is covered by a scrim ghost or haze which is generally blue in character from the standpoint of sensory perception. A relatively delicate image reflected from the diorama is in effect combined with this relatively strong image from the projector. haze (from the sensory standpoint) psychologically interferes with the relatively weak reflected background and causes great damage by rendering visible the area surrounding the foreground image as that of the dancer 35 thereby destroying the illusion. Merely a suggestion of a background other than that of the background component associated with the foreground figures tends to destroy the illusiom By the interposition of a minus-blue filter 4| preferably between the screen l1 and the primary mirror 28, we reduce this haze or visible sheen to a point where it no'longer destroys the effect and thus accomplish an important object of our invention.

In the projection of a single picture (as distinct from a component of a composite) through a translucent screen, diffused light interferes with the detail, clarity, and brilliance of the -feres with the enjoyment of the picture.

image, although to a less extent than in connection with the creation of a composite image as described above. Although in the projection of anordinary single picture, as distinct from a composite picture, an observer may not be conscious of this haze, it. none the less inter- A related object of our invention is to overcome this difliculty.

By using a filter which removes a substantial portion of light of the relatively short wave lengths we effect a qualitative rather than a quantitative change in the light forming our primary image upon the central surface. By removing the so-called blue light which is diffused to a greater extent than any other, we reduce diffusion to an extent relatively much greater than we reduce total light.

In sensory terms, a minus-blue filter is called amber. An image which is amber in color is supposed to be warm and pleasing. Whatever psychological benefit flows from this supposedly desirable quality of this color we secure but our choice of the filter is based upon sound physical reasons. Moreover, from the sensory standpoint, the color change imposed by the filter is so little as not to be noticed by the ordinary observer, but it should be stated that this fact does not necessarily indicate that the use of a 'a psychologically pleasing color though not noticed as a color is not of value.

While We much prefer to use a minus-blue filter, filters of maximum impenetrability by other sections of the spectrum may be employed.

' Since as already stated the light which we wish to remove is of relatively much less brilliance than that making up the foreground component, it is practicable to absorb a reasonable.

amount of the total light of the foreground component in the process of eliminating the unwanted interfering light. It is to be noted that we absorb no light whatever from the relatively weak background component. factor of any filter is of course helpful on a quantitative basis but we prefer but are not compelled to secure the qualitative as well as the quantitative effect of a minus-blue filter.

This filter has other and important uses as will later appear.

The above difliculty caused by projected light,

. largely diffused, is accentuated by light reflected This bluish line A'STU passes through the two surfaces of the primary mirror 28 and if unimpeded would reach the screen I! and render it visible. A portion is of course reflected by surface 29. If all of this unwanted light reached the central surface II, it would be suflicient to combine with the diffused projected light previously discussed and very seriously to impair the quality of the composite image. In fact this light alone and without the deleterious effects of the difiusedlight may be enough to destroy the effectiveness of the illusion.

A primary method of avoiding this difliculty is by reflecting a major portion of this light away from the screen I! by the secondary in- The absorption that a portion of beam ASTU is reflected by miror 40 as shown by a dash line 8V to the bottom of the viewing chamber, which is preferably made dead black so that further reflection is prevented. A portion of this beam which as shown by a dash and dot line ST is transmitted by the transparent mirror 40 is absorbed by the color filter II. In such cases as we actually use the color fllter 4| as separate from the transparent mirror ll, further reflection TW takes place back to the mirror 40 andinpartbaclragaintothe fllter ti and so on until the emergent beam is too weak to. be of consequence. Internal reflection in a single element in such cases as we elect to combine fllter 4| and protective mirror 40 would produce somewhat the same effect. As our invention -is shown in Figure 2, however, the decreased transmission on account of the filter factor reduces to a" low value the intensity of the interfering light which actually reaches the screen II.

A portion of this interfering light, and as will laterbe explained other interfering light, does reach the screen II as at U and is reflected toward the observer, as for-one theoretical beam only indicated by line UK. It will of course be understood that this reflected light is relatively weak. On what might be termed its return trip, however, it encounters fllter 4| and protective mirror II which reduce it to such a negligible point that it is no longer a factor. were able to penetrate beyond the protective mirror 40 and within a fleld of vision it would be again reflected in part by surface 30 of the primary mirror 28 downwardly as shown in Figure 5 and out of the observer's fleld. As a matter of fact, the surface of screen ll toward an observer must be relatively rough and consists of a multitude of small particles. Consequently this (and other) interfering light, considered from the standpoint of a considerable quantity of it, is reflected, not so much as shown by ox. but more directly back toward an ob-v server. Also, since the screen must be translucent permit light from the projector to penetrate,

a portion of this interfering light before reflection also penetrates to a certain extent and consequently after reflection is in part diffused.

It of course must be understood that as a matter of fact much of the single section of the screen l'l represented by the line NP from time to time is not occupied by an image which the audience should see but represents the surroundings of that image which must be kept invisible. That is, each image from the fllm 32 is instantly succeeded by another, a section of which in any given plane is likely to be different from the preceding section in the same plane. For purposes of convenience, in this specification and in the appended claims the singular term image has been used, but it must be understood to include a succession of different images succeeding each other.

Not all interfering light, however, comes from the diorama and projector. projection chamber through the opening IS. A portion is cut all by an apertured member having bailles l8 and 41 (Figures 1 and 2) set above and below the screen I1. If desired, this member may itself form a proscenium arch or other decorative feature. So-called shadow boxes, not shown, projecting forwardly toward an observer from the viewing opening and other devices may be used further to reduce the interfering light, but they are clumsy, space-consuming and not Much enters the In fact 11' it asset cos clined mirror 40. From Figure 5 it will be seen very effective. Under ordinary conditions disregarding our particular arrangement above described, a large portion of this interfering light would reach the screen I! and hence would interfere with the effectiveness of an image in general and, an illusion in particular, An optical axis C'B" of the point A within the diorama image extended in Figure 5 as B"YZ may be taken as representing a. single path of interfering light. Stray interfering light will exist within the entire area opposite screen H. The forward surface 29 of the primary mirror 28 reflects a portion B"A' of this interfering light into the diorama where it is helpful rather than harmful. An additional portion follows B"YZ. The interposition of the secondary mirror 40, however, reflects a portion of this interfering light back upon the rear surface 30 of the primary mirror as indicated by the dash and triple dot lineYY' of Figure 5. For reasons stated above in connection with beam A'STU, this light upon reflection is in part diflused. As is clear, a portion of this light is harmlessly transmitted back toward the observer but another portion YY" is reflected downwardly to the blackened bottom of the projection chamber.

Similarly interfering light which may be considered as following the dot and dash line CBC'B', which represents the optical axis of the projector, is reflected by front surface 29 of the primary mirror as BA into the diorama where it is helpful. Similarly reflection from the front surface of protective mirror 40 as indicated by the dash and quadruple dot line CD is reflected to the back surface 30 of primary mirror 28 and as indicated in the quadruple dot line D'E thence downwardly to the bottom of the cabinet and out of the field of vision of observer 0.

The absorption factor of the filter 4| reduces the intensity of interfering light actually reaching the central surface l1, consequently increasing the effectiveness of the image there projected. Its minus-blue filter factor, if that factor is employed, is particularly valuable because much of this interfering light upon its return trip, so to speak, is diffused. It is also to be observed that our use of primary and secondary mirrors rather than decreasing the eflectiveness of the foreground image increases it by disposing of much of this interfering light. It will thus be seen that wholly independently of the diorama or of anyother image making up a composite, our system of a plurality of transparent mirrors angularly disposed between an observer and a projection l screen increases the efficiency of so-called daylight projection, as also does our use of a color filter either alone or in conjunction with one or more transparent mirrors.

To illustrate diagrammatically this use of our invention with a single and protective mirror, in Figure 8 we show a translucent rear projection screen 49 in a mount 50 upon which a projector 5| throws an image. Between an observer represented by 0 and the screen a protective transparent mirror 52 preferably embodying a filter factor preferably minus-blue is disposed. The

reflective capacity of this mirror and its position in relation to the image uponthe screen 49 are such that the observer is not conscious of any reflection from the screen although the mirror does reflect and absorb interfering light. So far as we have observed, such a protective mirror taken alone has no effect whatever in giving to a single image any impression of depth. Its function is solely protective.

motion or stereopticon, upon a translucent screen 55 protected by a transparent protective mirror 56. This image is reflected by a primary mirror 61 thus creating a virtual image forming a background which appears in a position indicated by dotted line 58. We prefer to make this secondary mirror 56 also in the form of a minusblue filter. A projector I throws a foreground image upon a translucent screen 6| which forms a central surface such as I! which in the manner previously described is protected by a combined transparent mirror and filter 63.

Instead of projecting foreground and background pictures, any desired combination of images may be used.

Figure 4 illustrates a preferred variant of our invention in which a diorama or the like may be disposed in a position which increases the effectiveness of a composite image of which it forms a part.

In a cabinet II having a projection chamber I2 a motion picture or still projector I5" may be so disposed that by means of a mirror or prism 65 suitably supported as by a bracket 65 an image is projected through a translucent screen 66 forming a central surface placed at the bottom of an image chamber 61 equipped with a diagonally disposed primary transparent mirror 68 and a secondary or protective transparent mirror 69 placed between the pimary mirror and screen. If desired, a series of mirrors may be used. This secondary mirror preferably embodies a minus-blue filter and functions as does the mirror-filter 42 previously described. To the left of the image chamber as viewed in Figure 4, a diorama chamber 18 may contain a diorama or other small objects or stage settings. For purposes of illustration a chair 'II is shown. Illumination is furnished as by a battery of lamps of which one 12 is shown. It will be readily understood that the image of the chair II, which of course must be disposed in the diorama upside down in order to appear rightside up in the composite image, will be reflected through an opening "and by the mirror 68. The apparent position of the diorama, that is, its virtual image, is as shown in dotted lines 14 in the projection chamber I2. If desired, the area I5 surrounding opening 13 may be decorated to simulate a proscenium arch a virtual image of which appears as indicated by dotted lines I5' The image cast by the projector I5" upon the screen 66 and that reflected from the diorama by I the mirror 68 will be seen as a composite by an observer 0 through an' opening I6 of a viewing chamber I3 upon mirror 11 disposed directly above transparent mirror 68 and central surface 66.

The positioning of the diorama chamber I8. below the floor of the viewing chamber I3 and with its opening 13 completely shielded from view or access by an observer is of great value since otherwise the illusion is likely to be diminished or destroyed since an observer is likely to peer within the cabinet and discover the diorama.-

In the arrangement shown in Figure 4 such curiosity cannot be gratified. Also the diorama is completely protected from direct interfering light which might tend in certain circumstances to destroy the desired effect. Obviously the diorama must be illuminated but such illumination may well be controlled and standardized as can be done, for example, when the source or sources 12 represent all of the impinging light. Such positioning of a diorama or other objects or simulated stage settings is within the object of our invention.

Figure 4a shows an arrangement similar in general construction to that of Figure 4 but employing a plurality of projectors instead of one projector and a diorama or the like.-

Within a projection chamber 8| we dispose a motion picture or still projector 82 which by reflection from a mirror or prism 83 projects an image upon a translucent screen 84 forming a central surface. A second projector 86, which may be either motion picture or stereopticon, by

' reflection from a mirror or prism 81 and a mirror 88 projects an image upon a translucent screen 89 which is in line. with a transparent mirror 98 which is disposed within an image chamber 9| of which screen 84 forms a portion of the bottom. A secondary or protective transparent mirror 92, preferably also embodying a filter, is disposed at an acute angle to the plane of screen 84 and performs the function previously described for mirror- filters 42 and 69. A protective mirror 93 may be used in connection with screen 88. The virtual image reflected from the real image projected upon screen 89 is indicated in dotted lines 89'.

.It will be noted that in this instance, as previously stated might be done, the component which we for convenience term background" actually appears as if before the foreground component. The point of this phase of this construction and method is that two components, one a virtual and the other a real image, are united to form a composite image. The composite image thus formed is reflected by mirror 84 disposed within a viewing chamber 95 and through an opening 96 to an observer 0. It will of course be understood that the operation and principles of this form of our invention are similar to those previously described.

Figure 6 (Sheet 2) illustrates our invention as applied to the making of a composite photograph. A primary image as for example a foreground component of a composite picture may be projected as previously described upon a translucent screen I8I placed in an opening in a viewing chamber I82. Another or second image as previously described may be formed upon another translucent screen I83 disposed in an opening in another and contiguous wall of the viewing chamber. Alternatively real objects may be used. A transparent mirror I84 placed diagonally and in line with these two screens func-- of course be understood that even when both protective mirrors are employed, the photographic intensity of neither image is seriously reduced but instead the effectiveness of the images as photograph is increased. If protective mirror I86 is not used, as would be the case when real objects take the place of the pro-- jected image, the use of our protective devices and steps does not at all decrease the illumination of the second image, which then can be made relatively weak if desired.

In the variant of our invention shown in Fig- 6 ure '7 (Sheet 1) we may employ two projectors H l and I I2, either motion or still but preferably motion, in vertical alignment with each other, to form upon translucent screens H3 and ill a first image and a second image respectively, such images being foreground and background components respectively of a composite image. Within a duplex image chamber 6, in a rear wall of which screens H3 and Ill are disposed, a totally-reflecting mirror I I1 and a transparent mirror H8 are placed in alignment one above I illustrated the secondary or protective transparent mirror and filter as one integral unit. For.

a majority of purposes we prefer to construct these two instrumentalities as one because of simplicity, economy and other obvious advantages but it is to be understood that they may be constructed and used separately. In all forms of the invention both primary and protective mirrors should be of relatively low reflecting capacity. For most purposes. sheets of plane glass are adequate. We are aware that'all glass has more or less of color characteristics, but of course in speaking of a filter we refer to a scientifically planned and intelligently employed filter factor, and not to a quality which is haphazard accidental and unwanted.

It is particularly to be noted that our protective steps and means when applied to a composite image neither by absorption or reflection or either thereof in any manner affect the intensity of a relatively weak virtual image reflected from real objects making up a background component. Neither do these factors, or either thereof, reduce the intensity of a relatively strong real image making up a foreground component to a point affecting its visible integrity or photographic effectiveness. Instead, the application of these measures or either of them, appears to increase the brilliance of this compo nent, and, in fact of a single image if applied thereto.

The advantages-of our invention will be understood from the foregoing specification, the

sub --joined claims, and the drawings which form a part hereof. They include the provision of method and means for creating an improved composite image or an improved single image produced by rear projection, such improvement ,fiowing primarily from the provision of method and means for overcoming the harmful effects of interfering light, particularly diffused light, and in positioning the various elements in an improved relation with each other.

We claim: 1. In-an optical device, a chamber with a viewing opening at one side, a primar transparent mirror angularly disposed in relation to said viewing opening and in line therewith, means for causing said primary transparent mirror to reflect a first or virtual image to a predetermined plane, said first image being one component of a composite image, a translucent screen disposed in said chamber in line with said primary mirror and with said viewing opening and in a plane adjacent but slightly separated from that of said virtual image, a projector disposed in the rear of said screen for placing a second image upon said screen during the existence of said first or virtual image formed by said transparent mirror, said second image being another component of said composite image, and a second or protective transparent mirror disposed between said screen and said primary transparent mirror and in vertically angular relation to each thereof, said protective mirror being so disposed in accordance with optical law that the opposite faces thereof reflect interfering and unwanted light out of an observer's field of vision without materially reducing the visibility of said composite image.

2. man optical device, a chamber with a viewing opening at one side, a primary transparent mirror angularly disposed in relation to said viewing opening. means for causing said primary transparent mirror to reflect a first or virtual image to a predeterminedplane, said image forming one component of a composite image, a translucent screen disposed in said chamber in a plane adjacent but slightly separated from that of said virtual image reflected by said primary mirror, means for placing a second image upon said screen while said virtual image is in existence, said second image forming another component of said composite image, and a second or protective transparent mirror including a minus-blue filter factor disposed between said screen and said primary transparent mirror and in vertically angular relation to each thereof, said protective mirror being effective to reduce the amount of interfering light affecting said composite image without interfering with said reflected image.

3. In an optical device, a chamber with a viewing opening at one side, a translucent screen disposed in said chamber in line with said opening, means for creating an image upon said screen, and a transparent plane minus-blue filter formin a transparent mirror disposed between said screen and said opening and in line with each thereof and in acute angular relation to said screen and adjacent thereto.

4. In an optical device, a chamber with a viewing opening at one side, a translucent screen disposed in said chamber in line with said opening, a projector for creating an imag upon said screen, a source of light for said projector rich in blue, and a minus-blue plane transparent filter disposed in line with said viewing opening and said screen and disposed in acute angular relation to said screen and adjacent thereto.

5. In an optical device, a first chamber formed with a viewing opening at one side, a second chamber adjacent said first chamber and having an opening communicating with said first chamber, real objects representing a stage setting or the like being disposed in said second chamber, means for illuminating said objects, a primary transparent mirror angularly disposed in relation to said viewing opening and in line therewith and with said objects within said second chamber for reflecting from said objects to a predetermined plane visible from said opening a virtual image of said objects when they are illuminated by said illuminating means, said reflected image being on component of a composite image, a translucent screen disposed in said chamber adjacent but slightly separated from the plane of said virtual'image, a projector disposed in the rear of said screen for projecting an image upon said screen, said image being another component of said composite image, and a second or protective transparent mirror so disposed in accordance with optical law between said screen and said primary transparent mirror in such angular and spatial relation to each thereof that opposite faces thereof reflect to points outside of the field of an observers vision interfering and unwanted light without materially reducing the visibility of said composite image.

6. In an optical device, a first chamber with a viewing opening at one side, a second chamber adjacent to said first chamber and having an opening communicating with said first chamber, real objects representing a stage setting or the like being disposed in said second chamber, means for illuminating said objects,a transparent mirror angularly disposed in relation to said viewing opening and in line therewith and with said objects within said second'chamber for refleeting to a predetermined plane visible from said viewing opening a virtual image of said objects when illuminated by said illuminating means, said reflected image being one component of a composite image, a screen in said first chamber in a plane adjacent but slightly spaced from that of said virtual image, mean for forming an image upon said screen during the existence of said virtual image, said image so formed being another component of said composite-image, 'said image forming means and said transparent mirror passing to the region adjacent said composite image unwanted and interfering light predominantly of a given group of related wave lengths, and a color filter disposed adjacent said composite image and between' said screen and said transparent mirror for absorbing that selected and unwanted portion of the light of said group of wave lengths which would otherwise interfere with said composite image thereby preventing said light so absorbed from interfering with said composite image while not-correspondingly reducing the over-all visibility of the image.

'7. In an optical device for producing a com posite image having depth of which a fore- 'jector for creating a second image upon saidground component is produced from a motion of an actor, the area surrounding the image of the actor in said film being'intended to be opaque but in fact and by necessity being permeable by light, and said composite image also having a background component which is produced by a virtual or reflected image; a screen, means for projecting an image of an actor from such a motion picture film upon said screen, means for reflecting a virtual image of a background to a plane adjacent said screen, and means for reducing to a negligible value the quantity of such unwanted light from said area surrounding said actor which is transmitted to an observer of said screen thereby inhibiting the visibility which otherwise would be imparted to said screen by unwanted light projected through said surrounding areas of said film thereby preventing the-destruction of the illusion of reality.

8. In an optical device for-producing a composite image having depth of which a foreground component intended to include only an image of an actor is projected upon th rear of a screen from a motion picture film, the area of the foreground component upon said screen surrounding the actor during the projection of said film being intended to be invisible, and said composite image also having a background component which is produced by a virtual or reflected image; a screen, means for projecting an image of an actor fromsuch a motion picture film upon said screen, means for reflecting a virtual image of such a background in a plane adjacent to that of said screen, unwanted light from said projecting means and said reflecting means making visible said area of said foreground component surrounding the image of said actor, and means associated with said screen for reflecting away from an observer's vision said unwanted light thereby reducing to a negligible value the visibility which otherwise would be imparted to the portions of said screen surrounding the image thereupon of the actor.

9. In an optical device, a primary transparent mirror disposed in vertical and angular relation to a viewing station, a first translucent screen disposed upon the side of said transparent mirror relatively distant from said viewing station and in line with both thereof, a first protectiv mirror disposed between said first screen and said primary reflecting mirror and in acute angular relation to said first screen and adjacent thereto, a first projector for creating a first image upon the rear of said first translucent screen, said first image forming one component of a composite image, a second translucent screen disposed in line with said primary transparent mirror upon the side thereof relatively distant from that upon which said first screen is disposed, a second protective transparent mirror disposed between said second screen and said primary reflecting mirror and in acute angular relation with said second screen and adjacent thereto, and a second proto form a virtual image in a plan adjacent that of said first image but slightly spaced therefrom thereby furnishing another component of said composite image, said first and second protective mirrors being so disposed in accordance with optical law that both faces thereof reflect interfering and unwanted light out of the vision of an observer of said composite image without materially reducing th visibility of said composite image.

10. .A method of creating a composite image in line with a viewing station which comprises forming by reflection a virtual image in a predetermined plane, said image being a first component of a composite image, projecting a real image in a plane adjacent but slightly spaced from said virtual image, said real image forming a second component of the composite image, intercepting such projected light which is of relatively short wave lengths thereby increasing the effectiveness of the composite image by reducing the amount of difiusion, and reflecting interfering light in a direction away from the composite image and from the viewing station thereby further increasing such effectiveness.

11. A method of creating a composite image which comprises reflecting to a first-predetermined plane a virtual image of real objects visible from a viewing station, creating a real image in a second predetermined plane adjacent but spaced from the plane of the reflected or virtual image. said images together forming a composite image visible from the viewing station, said creation of said composite image causing some "un wanted light adjacent said composite image, maintaining substantially invisible the area of said second plane surrounding said real imag by reflecting in a direction away from the viewing station a substantial portion of such unwanted light thereby increasing the effectiveness of the composite image.

12. A method of daylight projection which comprises projecting an image upon the side of a translucent screen opposite a viewing station by a light relatively rich in the shorter wave lengths thereby causing diffused light to e ate from the side of the screen relatively adjacent the viewing station, the screen being subjected to interfering light passing to it from the general direction of the viewing station, intercepting a portion of such light of the shorter wave lengths thereby decreasing the relative amount of diffused light emanating from the screen without propontionately reducing the total illumination upon the screen, and reflecting away from th viewing station and from the screen a portion of the interfering light while maintaining the visible integrity of the projected image.

13. A method of creating a composite image having depth which comprises forming a basis for a foreground component by photographing upon a negative film an actor disposed before a background which on account of the limitations of photographic technique when reproduced in a positive film will be largely but not completely opaque, reproducing said negative film as a positive film in which areas surrounding an image of the actor are not wholly opaque, projecting the positive film to form a real image of the foreground component upon an image receiving surface in a predetermined plane, forming a virtual image of a background component in a plane adjacent but slightiy spaced from that of the foreground component, said components uniting to provide said composite image, and reducing to a. negligible value light which passes to an observer from the areas in the positive film surrounding the image of the actor while transmitting said image substantially unimpaired thereby preventing the consequent visibility of areas in the foreground component surrounding the image of the actor from destroying the illusion of reality.

14. A method of creating a composite image having depth which comprises forming a foreground component by photographing upon a negative film an actor beforea background which on account of the limitations. of photographic technique when reproduced in a positive film will be largely but not wholly opaque, reproducing said both unwanted light which is transmitted alon with the reflection from said objects making up a background component and light which passes to the observer from the areas in the positive film surrounding the image of the actor while transmitting said image substantially unimpaired thereby preventing visibility of such areas surrounding an image of th actor in the foreground component from destroying the illusion of reality.

15. A method of creating a composite image having depth which comprises forming a foreground component by projecting an image of an actor in a predetermined plane, such projected image being intended to be surrounded by areas which are wholly invisible, reflecting a virtual image of a background component to a plane adjacent but slightly spaced from that of the foreground component, said reflecting step necessarily causing transmitted light to pass toward the image of the actor and the areas surrounding it making up the foreground component, and reflecting to a point outside of the field of vision of a person viewing the composite image asubstantial portion of such transmitted light thereby preventing it from rendering visible such areas in the foreground component, such visibility if present destroying the illusion of reality.

16. In an optical device, a chamber with a viewing opening at one side, a translucent screen disposed in said chamber in line with said opening, a projector disposed upon the side of said screen opposite said opening, said projector emitting light which is stronger in one group of related wave lengths than in others, and a transparent plane filter having a transmission band complementary to said group forming a transparentmirror disposed between said screen and said opening and in line with each thereof and in acute angular relation to said screen and adjacent thereto.

17. A method of producing a composite image having depth which comprises reflecting a cirtual image of a background component to a predetermined plane adjacent but slightly separated from a motion picture screen, while said background component is in existence projecting in motion a real image of a foreground component upon the screen, said foreground component not occupying all of said screen, said background component and said foreground com-' ponent uniting to form the composite image, and maintaining substantially invisible those portions of the screen not occupied by the foreground component.

posite image, and thereafter maintaining .sub-

stantiallyinvisible those portions of the screen not occupied by the foreground component.

FRANCIS MACLEAN SMITH. THOMAS AQUINAS KIRBY.

Images