[1]Patented May 29, 1951 215549532 UNITED STATES PATENT OFFICE 2,554,532 9TEREOSCOPY pi ierre Juillet, Albon (Drome), France, assignor to ReliefLyon@Fraiice, Lyon, France, a French joiht-stock c6mpainy AI)plicatioh July 11, 1946, SeriaI No. 682,749 In France November 20, 1942 Scletion 1, Public Law 690, August 8,1946 Patent expires November 20, 1962 9 Claims. (Cl. 88-16.6) 2 My inventioii relates to stereoscopic methods wherein the elementary images are of relatively large dimensio,.is, for instance, are formed on a projection screen, as in the case of stereoscopic einematograph. 5 In conventional stereoscopy the elerr-entary iin@ges are exactly dispos-ed before the observer's oyes. These images are seen in exactly the same manner and they are easily combined by the observer. But with images of large dimensions, 10 the distance between the awes of the t,,@To elementary t@vo imFLges is much greater than the distance between thp- eyes of tie -observar and the two images are not seen under the same angle. 1.5 Th6ir deformation due to perspective is different and their optical combination becomes difficult, j@ainfui or sometitnes-@quite impossible. 7nis difference between the t@vo stereoscbpic images is particularly rnarked for the spectat-3rs situated laterally of the screen who fail in practice to per- 20 c-,eive any stereoscopic effect with the known methods. Another drawback of stereoscopy with images of large dimensions is that it requires abnormally 25 largp screens if it is desired to retain for the stereoscopic image the same size as for the usual flat image. The known st,,reoscopic nietliods also require special photographic apparatus with two lens-es or objectives.. In stereoseop@ic cinematography i 30 has also been proposed to use a single film wherein 6ach pair of successive images correspond to a stereoseopi-- couple. A first object of my invention is to provide a method -wherein diiring the photographic or cine- 35 inato@raphic recording the axes of the objectives i3orresponding to each elementary image are angularly displaced with respect to one another in such 9, manner that the said images are subjepte4, owing to the difference of perspective 40 u@nder which th-ey have been taken, to deformations opposed and substantially equal to those which will result from the difference of perspective under which they will be viewed by the observer. 4,5 A further object of my invention is to record both elementary images with the same objective @y disposing in front thereof two systems of mir@ors or. prisms which lead to the same under two equal and opposed inclinations, the light rays 50 received from the subject at two points spaced 'from each other by the stereoscopic spacing selected. Still another object of my invention is a method @vberein the images are r6corded with a linear 55 defol-mation of the kind kno-wn under the nanie of ana--morphose, in such a manner that they are reduced in dimensions in the direction of their juxtapo.@ition on the filni or like support, the said -images being observed through an anamorphosing device coinplementary to the device used for their. recording. In the case of projected images, the surface of the screen is thus fully used and the def orniation resulting fro-m perspective is reduced. TI-ie device for observing the projected images preferably comprises two monocular el@ements adjustable with respect to each other by rotation about an axis substantially longitudinal with respect to each in such manner that it should be possible to deform the virtual images iintil they are substantially identical. My invention also relates to an optical device intended to be disposed in front of an usual plioto-raphic or cine--aiatographic camera to carry my iwlllention intg practice, such device cornprising two sets of reflecting prisms, symmetrical with respect to the longitud'nal axis of the objective and at such an angle in a plane transverse to the said axis, that a bundle of rays supposedly coming from the objective should be divided into two semi-bundles emerging at the same horizontal level, means being provided to maintain the optical axes of the said semi-bundles in one and the same plane. My improved optical device also comprises an auxiliary set of reflecting prisms with slightly oblique reflecting faces, disposed e ween e objective and the main set of prisms, this auxiliary set being adapted for rotation about a longitudinal axis, whereby the stereoscopic angle under which a subject is seen at a given distance may be varied at will. In the annexed drawings: Fig. 1 is a diagrammatical elevation illustrating the phenomena which take place during observation of elementary st-areoscopic images of largedimensions on a screen. Fig. 2 shows the screen as it appears to the observer. Fig. 3 diagrammatically shows in elevation how the elementary images may be recorded with two obj ectives. Fig. 4 shows how these iw-ages may be recorded by means of only one objective. Fig. 5 is a plan view corresponding to Pig. 4. Figs. 6 and 7 are elevation and plan views diagrammatically showing how perspective deformation may be reduced by anamorphosing the images on the screen. Figs. 8 and 9 diagrammatically illustrate an
[2]a-kran,-ement similar to that of Figs. 3 and I@, but co,-nprising a double anar@iorphosing systerp.. Figs. 10 to 12 diagramrnatically show in side view, plan view and end view an optical system to be adapted in front of a camera with but oiie objective iii order to record two stereosco-o"@c images. Fig. 13 is a. front view of this opti-cal system. Fig. 14 is a side view thereof v@ith parts in sectioli. .C,@ig. 15 is a front v,'@ew, the cover with its Ienses being supposedly removed, and some parts b-aing shown in section. Fig. 16 is a longitu@dinal section through lin-XVI-XVI o@' Fig. 15. Fig. 1'7 is a section through line '"VI!-,',VT -I of Fig. 16. F,I,p@. 18 is a section throu.-h line XVIII-@'@VIII of Fi.-. 15. "ig. 19 is an end view of the stipport of the cylindrical convergin.@ lens, with p?,j:'@,ial sectioi, I rough 14 e XIX-XIX o@ Fig. 16. L,h @'Q Fig. 20 is a. longil@-iidi.r-al section. of the i,otatable r-ln,, of this sup-oort. Fi,@-. 21 is a seetlo-o through line C,, Fig. 16. Fig. 22 is a plan viev,7 iiith parts ir- sect@or, illuslrating ari obs-crv-lrg device for the elemelitary stercosco@pic iiiiages proiected on -- screen. Fig. 23 is a section thereof through line XXIIIXXIII of Fig. 22. Fig. 24 is a section through line =V-XXIV of Figs. 22 and 23, ilustrati-@i,@ the Dath of @bhe light rays. Fig. 25 is a diagrammatical plan view illusti-ating the position of an observer laterally disposed with respect to the screer. Figs. 26 to 28 are explanatory diagrams show.ing how the images are deformed by perspective for this observer aiid how the dev-lce of F-i.-s. 22 to 24 epables 'uh-@'s deforiiiation to be correctc-d. In 'E@igs. 1 and 2, A and -'c.3 are two stereoscopic images juxtaposed in heigh',, foi- iy-istance on a projection s@-i-een. 'fliese images are observed by an observer C t@irc-ugh an apparatVS D which enables hiiri to see respectively c-ne age with the r'lght eye ond the other -image v,.Fitfi the left eyc. The ir@nages are thus superil-posed and the observer perceives but onp- i---a,,@e relie@@'. But these eler,-ientary irr-,ages are vi@.ivcd -,inder two angles a and p which are algebraically different from each other (in the particular case of Fig. I they are opposed). It follows that they are not viewed with the same deformation due to perspective. In the case of Fig. I they Nvill a-,)pear as two inverted trapezes, as indicated in Fig. 2. A vertical line will appear as two lines La and Lb with opposed obliquity. It will easily be understood that the superposition of images A and B will be difficult and will cause fatigue for the observer's eyes. In order to avoid this drawback, the objectives Ed and Eb (Fig. 3) used fbr taking the elementary images of the subject MN are inclined in opposed direction, the first one being inclined towards the lower part of subject MN while the other is inclined towards the upper part thereof. The elementary images recorded on the photographic surfaces Fa and Fb are thus deformed by perspective, their res3jective deformations being opposed. If, for instance, MN is a rectangle, the two elementary images obtained will have the form of trape-zes and these trapezes will be in inverted respective relation. The images A and B projected on the screen wi2l thus 2,554,582 4 be deformed in opposed relation with respect to the deformation resulting from their observation by observer C and it will be understood that the two deformations may compensate each other. Of course, in the case of a hall perfect compensation can only be obtained for a given position of the observer, for instance for the central part of the hall. But for the other parts the residual deformation is relatively small and the above-described drawback is considerably reduced. It will also be understood that the vertical extension of the elementary images obtained on surfaces Pa and Fb is not the same and that it is necessary to suppress the upper portion of one image and the lower portion of the other to have two corresponding stereoscopic images. In lieu of two separate objectives Ea and Eb, there could be used but one objective, as illustrated in Figs. 4 and 5. The light rays from the subject are led to this objective m through two sets of prisms which displace their paths horizontally and vertically. A first set of two prisms p and q receives the rays from MN in a direc2,) tion inclined upwardly ivith respect to the objective axis XY. These rays are first reflected vertically and then in a direction inclined downwardly with respect to axis XY, in such a manner that they form the lower elementary image a 30 behind the objective m. A second set p' and q' also receives rays from MN in an upwardly oblique direction, but at a horizontal distance s from axis XY, s being equal to the desired stereoscopic spacing. They are reflected horizontally -,5 and are thus brought into the vertical plane of axis X-V where they are again reilected in an upwardly oblique direction to form the upper eleraentary image b. Images a and b are deformed in opposed relation by perspective. 40 For a better understanding of the phenomena involved, it is better to consider the reverse direction of the light rays, i. e. to suppose that It/IN is the projection of images a and b. It will be understood that if the latter correspond to two 4.@j different stereoscopic points of view in accordance with the stereoscopic spacing s, their combined projection may form a single image MN. It will also be understood that owing to the inclination of the mean axis of the rays from each image a or b towards the objective m with respqct to axis XY, the said images a and b should be deformed in opposed respective relation to enable the correct superimposition of their projections. ,55 When the elementary images are projected on a screen, they occupy a considerable surface. This requires an abnormally large screen, often difficult to dispose in a given hall, and moreover these elementary images of large dimensioi-is 6c) are viewed by a given observer under two materially different angles, which causes a difference of perspective liable to render diffleult or tiresome the correct perception of relief. According to my invention this is remedied 65 by reducing by one half the height of the images without modifying their width, by the so-called anamorphosing process. rlig. 6- illustrates a screen r on which the projected images A and B have been anamorphosed in height. They may 70 thus be disposed within a screen of normal dimensions whereas, if they had 1-iot been anamorphosed, they would have occupied a much higher space, as indicated in broken lines. Moreover, if one considers the angles (& and p (Fig. 7) 7.5 under which an observer C sees images A and
[3]5 33 ti@gpectively, their diff erence is considerably smallet than the difference of angles ai and pi under which this same observer C would see the unanamorphosed images. Figs. 8 and 9 illustrate how the images may 5 be anamorphosed when being recorded by mears of a device of the kind indicated in Figs. 4 and 5. Two -cylindrical diverging lenses t and t', with their axis of curvature horizontal, are disposed in front of prisms p and p' and between objec- 10 tive: m and the sets of prisms there is disposed a cylindrical converging lens u also with its axis 6f curvbture horizontal, in such a manner as to form A sort of double Galilean system. It will be @ observed that by appropriately displacin.- 15 lenses t and t' vertically, the mean axis of the hght rays may be deviated in a vertical plane, the.lenses then acting as prisms. This permits of avoiding de-centering between the center of the subject MN and the objective axis XY, if de- 20 sired. Figs.:10 to 21 illustrate a modification where,.ii the bundles of rays of both images are deviated horizonta-Ily and vertically and they moreove,.. show how the difierent optical adjustments caii 25 be performed. In the diagram of Fig. 10, I designates a photographic surface such as a cinematographi-, film, on which the elementary images @hould be formed; 2 is the objective of the camera on which 30 the ste@eoscopic device is dispose@d. Thisidevice comprises a converging cylindrica, lens@3 in the immediate vicinity of the objective 2. aiid a set of two double prisms 4 adapted to ensure two reflections in a vertical plane. The 35 reflecting faces of these prisms are not quite@ parallel in such a manner that if one conside@.,s on film I the elementary images a and b, and if it is suppos ed that from each emanate a bundle 40 of light rays towards objecti-Ve 2, the axes of these bundles, wh,'@ch are oblique with respect to the objective axis, are displaced vertically in opposed respective relation and at the same time rendered horizontal, as clearly shown in Fig. 10. .. In front of prisms 4 there is disposed another 45 set of iv@6 do@ uble prisms 5 with parallel reflecting faces. These prisms are shown in super,mposed relation in Figs. 10 and 11 in such a man@er that the axes of the above-mentioned bundles of ray@ , are displaced the first one towards the right, the @@ 0 second one towards the left, while remaining horizor-tal and parallel. @ For the sake of clearness, prisms 4 will be termed auxiliary prisms, prisms 5 being the main prisms, since the former may be dispensed witli 55 in some cases, as explained thereafter. When the main pri@ms 5 are inclined by rotation o,,bout the longitudinal axis of the objective, a,s indicated in. Mg. 12, the axes of the b,,indles of rays may be brought into one and the same c)( horizontal plane@ viz. the mean horizontal plane of the objective, instead of being situated respectively above and below the sgid plane. The device also comprises two cylindrical diverging lenses 6 disposed in front of prisms 5. 65 Lenses 6 and 3 have their axis of curvature horizontal to form a dolible anamor-ohosing systein adapted to reduce the height of the images. if one again considers the rays from imgges a and b, it will be understood that they may 'Lorin 70 one and the same projected image MN if images a and b correspond to two different points of view of the same subject. Inversely, if MN is a subject from which light rays are radiated t-owards lenses 6, there are formed on surface I two 75 elementary images a and, @b of tho said subject, these images being reduced in height and correspondilig to the subject as seen bY the two lenses 6 respectively, which are spaced apart by the desired stereoscopic spacing s (Fig. 12). It is however to be remarked that the above-@ described device sli-ould be adjusted in accordance with th6 focal length of the objective 2 t@nd with the adjustment thereof. The improved dovi6i@ therefore comprises adjusting gearing8 by me ans of which it may be adapted to each individual, case. Adjustment in accordance'with the focal length of the objectivc A cinematographic,camera is generally adapted to receive a number of different objectives with different focal lengths. Since the vertical spacing of iniages,a and b on the film I should remaiii constant, the in-,Iination of the optical axis@ should vary in accordance with the focal length of the objective Qmployed. This is obtained by slightly inodi@.'Ying,the inclination of the set of raain prisms 5 about the longitudinal axis (angle a in Fig. 12). And in order to correct the difference of inclination of the said axes in front of the main prisms which would result from this adjustment, @-nses f-, a@@e slightly displaced verticall@y in op-- I:osed direction. For a better understanding, one may again considei- the reverse direction of the light rays. Supposing that these rays emanate from images a a,-id 1) any variation in the focal length causes - a modi--,-Ication in the inclination of the optical axes with respeet to the horizontal plane. These' 6@-es therefore enter prisms 5 higher or lower, respe,,t - ively, with respect to the mean horizontal plane of the device'. By modifying angle . they may nevertheless be brought to emerge from these prisms at the same horizontal level but with a different inclination with respect 'to a horizontal plane. By vertically disolacing lenses 6, this very slight inclination may - be correctidd and the said axes iii-ay again converge towards the center of pubject MN. The device is P'referably so constructed that with a-n average focal length lenses 0 have not to be displaced. Their displacement therefore remai-@is very limited. Adjustrrent in accordance with the adjustment of the objec I tive The objective 2 is adjusted as usu-al, in accordance with the distance of the subject but at the same time the double Galilean system should also be adjusted. This adjustment is preferably effected by axially displacing the converging cylindrical lens 3. In some cases the two diverging lenses 6 may also be displaced. BLit the adjustment of the objective also acts on the vertical @ spacing of images a and b on filn 1, since it modifies the distance between theobj@ective center and the photographic surface. This necessitates a correction, as in the case of a variation in the focal length, but since th-is correction is of minor importance it is preferabiy eff-ected by vertical displacement of but oiie lens 6. It must be added that the said correction is @a function of the focal length, being more important with objectives of longer focal lengths. This must be taken into account by tne adjusting gearing of the device.
[4]Ad7'usint6.,it z@n@ dccordance with ih@ ia i Pid@i@ in the objective fteld In conve,.,itional stereoscopy the rays from a. point at an infliiite distance sliould come parallel to the ooserver's eyes and on the other hand the eyeq sh6uld be convergent for any point at a shorter distance, which implies that the rays from the elementary images of this point should diverge tow . ards the respective eyes. But I have found that the perception of relief is considerably improved, if tl-ie axes of the observer's eyes are no more parallel for a point at an ir@i-inite distance, but for the last plane in the objective field behind the subject. For instance in the case of a subj'ect in front of a tapestry in the objective field, the observer's eyes will be para-Ilel when he views a point of this tapestry. For this purpose I arrange my iinproved device in :such a manner tnat a point of this tapestry will give r-' e to two rays in one ar@d the same IS vertical plane between the obj'ective and the photographic surface, although the said rays are divergent whc-n reachitig the device. This is very easily:obtained by a smal-I angular displacenient of the auxiliary prisms 4 about the longitudinal axis of the device. This limited rotatiori. does not materially modify the v-,rtical displaceme.-tit of the optical axes of the two elementary iniages, but since the reflecting faces of the said prisms are not parallel, it causes an inclination of thes-axes with respect to the roean vertical longitudinal plane of the device in such a ina-iiner that the rays supposedly comino@ from the images would be conve,.,gent when issuing from lenses C,. It will be noted that when the above-described adjustment is not desired, prisms 4 may be dispensed with. In such a case angle a of l@lig. 12 can be so selected that the optical axes (supposedly coming froin the irriages, and not from the subject) emerge frolii lenses 6 at the sarie horizontal level. And by vertically displacir-g lenses 6 it is possible to correct the oi)liqtiity 4af these axes with respect to the mean horizoiltal plane of the devic,-. But of course these vertical disl@lacements of lenses 6 @@equire lenses of hi@h qua@lity to avoid deforw-ations. It will a-iso be noted that the convergin.- cylindrical lens 3 only receiv,,s oii, respectively, its upl)er or lower ha@if one bundle (>f rays, viz. the rays respectively corresponding to the lower or upper ima,e b or a. The said lens iiiay th-Lis be cut alo-,ii,@ the meaii hor@@zontal plane of the apparatus and the tivo halves may be siightly incl-ined to be pc-rpendicular to the respective optical axes with - the ol--)Jective of average focal length. This reduces optical deformatiolis. Such a lev-s is illustrated in 3 in Fig. 16. Fi,@s. 13 to 21 illustritte a construction established iii accordance with the diagrammatical repre.-,bntation of F-igs. 10 to 12. The apparatus illustra-ted comprises a casing 7 intended to be fixed in -front of a usual camera. Casing 7 houses the main prisms 5 (forrled by juxtaposit4on of four elementary prisms, as indicated iii llig. 1"4). This prisms unit is clamped within a surport comprising two plates 8 (Fig. 16) connected by screws 9 (Fig. 17). This support is fixed to tL base IO (Fi,g-. 15) provided witl-i a gudgeon I I (Figs. 14, 15 ard '@-6) pivoted in a plate 12 forming a -froiit elosure for casin.- 7. Base I 0 e,xtends u-o,,@iardly iiito a lug carrying a rounded block 13 pressed by a pusher 14 (Figs. 15 and .91) carried by a sliding rod I.P o-n which there is mounted a, spr,'@iig 16 restin.- against, a guidi@ig washer 17 of rod 15. Block 13 is provided with 9, blind hole which receives the kbunded end of i6 screw I 8 s,,rewed through a spherical nut IS car@ ried by casing 7. Screw IS is pr i e wi an outer head 20. Actuation of hea 20 thus perr, mits of rotating sli@port 8-9-1 0 abol-,t pivot II (adj ustmeiit of angle a of Fig. 12). A finger 21 (Fig 14) is fixed to base IO to form a pivot for a pointer 22 provided with a slotted tadi engaged on a fixed rod 23, in such a manner 10 that when base 10 is axigularly displaced, pointer 22 is rotated in front of a dial 24 (Fig. 13). The transverse obliquity of prisms 5 can thus be readily adjusted in accordance with the focal length of the objective. 15 As above indicated, the cylindrical converging lens 3 is in two halves, each half being substantiauy perpendicular to the means directionof the optical axis of the corresponding image. Lens 3 is fixed within a support 25 (Figs. 16 and 17) slidably carried in a. ring 26. Ring 26 is in turn slidable in the rear cover 27 of casing 7, wherein it inay rotate while being axially retained in position. Support 25 is provided with radial fingers 28 engaged tl-irough longitudinal slots 29 25 of cover 27 and through helicoidal slots of ring 26 (such slots being illustrated in 30 in Figs. 19 and 20). NVh6n ring 26 is rotated by means of an actuatiiig lever 31, support 25 is moved axially whi'e beiiig retained angularly. This 30 p,-rmits adjustment of the anamorphosing system. Support 25 is not wholly cylindrical and it has two cut portigns i@Orming two crescent-shaped spaces within ring 26. In the first one there is disposed a pair of blocks 34 (Fig. 19) with a 35 compression spr;@ng 3@5 between them. In the second space there is arranged a member 36 fixed to cover 27. Blocks 34 act as wedges under the action of spring 35 and they press supp(rt 25 against mernber 36, whereby any lost motion in 40 the actuation of support 25 is suppressed in spite of the play of fingers 28 through slots 29. Moreover lens 3 is perfectly maintained with its curvature axis horizontal, which avoids aily twist of the images. 45 The diverging cylindrical lenses 6 are fixed ,,7ithin two supl)orts 37 (Fi.,s. 14, 16 and 17) vertically slidable c-n the front cover i2 of casing 7, such cover being therefor provided with a T-shaped ceiitral guide i2b. Each support 37 50 has t@vo f!nL,-ers passed t-lirough app,:opriate openi-,l,-s of cover 12. The upper finger 38 (Fig. 13) is pressed downwardly by one tnd of a lever 38 submitted to 'Z.he downward action of a compressL@n spring 40 which rests on the central part 55 thereof; the lower finlyer 41 c@-rries a nut 42 screwed or- a verti-Cal threaded spiiidle 43a or 43b. Sl$indle 43a extends downwardly through casing 7 and carries an outer actuaj'ing head 44. A gear wheel 45 is aiso fixed to spindle 43a and rests 60 a.-ainst a bridge member 46 in on,. NVith casing 7, in such a manner that rotation of head 44 causes vertical dispi-acement of the correspon I ding'finger @..l against the action of spring k'D. Spindle 43b also carries a gear wheel,47, equal c5 to wheel 45 and in mesh therewith; but this gear wheel 47 does not rest against bridge member 46. The lower end of spirdle 43b rests a_gainst a lever 48. The latter in turri rests on a finuer 49 ecceiitricall-y carried by a plate 50 keyed on a shaft 51 (Figs. 16 and 18) provided with an outer actua . @ing lever 52; and lev-r @18 also rests on the periphery of a wheel 53 (Iligs. 15 and 18) carried by a screw 54 provided @vith an outer actuating 75 head 55. Screw L54 -is screwedi-n bridge member
[5]9 46 and there is provided a spring 56 to suppress any lost motion. It will be understood that actuation of head 44 perinits of displacitig lenses 6 in opposed direc-tions any by the same quantity in accordance withthelselected focal length, as above-explained. Actuation I of lever 52 causes displacement of but one lens 6 and is used to effect corriection in accordance with the adjustmeiit of @he objective. The amplitude of the vertical d,.splacement of this lens 6 for a given angular displacement of lever 52 is dependent of the position 6f -xvheel 53 forming the fixed pivot of lever 48 aiid actuation of head 55 therefore permits of adapting the ab6ve correction to the focal length of the objective. A small lever 57 (Fig. 16) is articulated to nuts .42 iti such a manner as to oscillate when the latter @ are vertically disdlaced in opposed relation. Lever.'57 carries 0, --@-iexible blade 58 provided with a -oointer 59 slidabl6 in a vertical slot (Fig. 13) of the fronr, cover. An appropriate scale is disposed al@ong the said slot to enable the operator to readily adjust lenses 6 in accordance with the focal length of the objective.. There is also Drovided a horizontal slot for ano@,her pointer 60 .@Figs. 13 and 18) carried by another flexible blade Of fixed at the end of a fork C2 pivoted at 63. Fork 62 (Fig. 18) is engaged on screw 54 and it is pressed against wheel 53 by the eiasticity of blade 61 in such a manner as to oscillate when head 55 is actuated, whereby pointer 60 is moved along an appropriate scale. Lever 52, which contro4 vertical displace-rient of bne of lenses 6 to adjust the anamorphosing system in accordance with the adjustinent of the bbiec',ive, and lever 26a (Figs. 17 and 19) @vriich controls adjlistment of lens 3, are connected with each other and with the lever (not illustrated) controlling adjustment of the obiective oi the camera in such a manner that the operator may effect the tlaree adjustments at the same '@ime. The auxiiiary prism unit 4 is carried by a support 64 (Fig. 14) fixed to one end of a longitiidinal shaft 63. The latter is disposed between jarisms 5 and its front end carries an arrri 66 (Mg. 13) provided with an actuating head 67 movable withiii a guid(, 68 provided with an apliropriate scale. As above-explained actuation of head 67 enatiles the operator to determ4@-ne the distance for which the s@,ereoscopic angie will be null. The apparatus described thus permits all the adjustments rientioiied in reference to Figs. 10 and 12. Figs. 22 and 24 illustrate an apparatus for viewing theelementary stereoscopic images projected on a screen one above tl-ie other and in the anarr-,orpl,iosed state. This device comp-ris6s two mofioci.ilar Galilean systems with cylindrical lenses with their curvature axi@ horizontal. tach monocular syster@l has a casing 14 with a cylindrical diverging lens 75 at one end and a cylindrical converging lens '16 at the o-.her end. The two casings 74 are connected with each other by means of a spl-ierical articulation comprising a ball 77 with a vertical rod 78 driven therethrough, the ulper and lower ends of rod 78 receiving nuts 79 adapted -Lo pre.-s against casin.-s 74 tvio spherical washers 80 (rig. 23). This connection permits of rotating casings 74 -with respect to each other about a transverse axis and also @-bout a longitudinal axis (arroivs 81 and 82 of F@@gs. 23 and 24). The device is held in fron, of the observer or spectator by an articulated support @iot shown provided with a spherical joint 2.554,532 10 83 (Mg. 22) frictionally mounted in a bearing 84 fixed to one casing 74. By rotating casings 74 with respec@. to one another about a transverse axis (arrow 8 1, Fig. 24) one eye can see the upper elementary image while the other one sees the lower image. E,,tch casing is prbv-ided with a small screen 65 adapted to screeli the lower image for the eye which must see the upper one and the upper image for the eye 10 which must see the lower one. T'his first adjustment i-S sufficient for an observer disposed substg.,ntially in front of the projection screen. Bdt, in the case of an observer C (Fig. 25) disposed laterally with respect to the projection i.@) screen, the elemeiitary images appear to the naked eYe as indicated in Fig. 26, i. e. as deformed in opposed rel@ation. When viewed through the device adjusted as above explained (by rolation according to arrow 81 of Fig. 24), thev will ap20 pear as shown in Fig. 27, i. e. they will be twisted in opposed directioyi by tiie anomorpliosing systems of casi-n.-s 74. Their optical superimpo@itiori will be very diff-iclilt or even impossible. Bu@t if casings 74 are rotated with respect to one an2;-) other about a longitudinal axis (arro)v@ 82 of @Mg. 23) the virtual images seer- by the observer will rotate in opposed di-rection and for a correc,'; adjiistr@ient their perfect superiripositioia will be'come easy, as indicated in Fig. 28. ;i( Lenses 75 and 76 are preferably sl4@ghtly prismatic, as illustrated by the see@uion of Fig. 2-), whereby the axes of [,he bundles of rays reaching the eyes are slightly displaced, which permits of uslng the full width of lenses 76. @', 5 I
