Device for Projecting Steroscopic, Anamorphotically Compressed Pairs of Images on to a Spherically Curved Wide-Screen Surface

The invention is in the field of optical image formation and relates to a device for projecting stereoscopic, linear anamorphotically compressed pairs of images on to a double-curved, particularly spherical wide-screen surface, comprising a lighting unit acting on the image plane of a projector, a basic lens arranged in the beam following the image plane and associated with the projector and a supplementary lens cooperating with the lighting unit.

When showing films attempts have frequently been made to give the viewer the impression that he is taking part in the photographically represented events. The attractiveness of the realistic representation of a usually optically dramatic sequence, such as e.g. objects flying towards the viewer and precipitous journeys, which give rise to many different reactions on the part of the viewer, have led to numerous technical solutions in this field.

Thus, U.S. Pat. No. 4,129,365 describes a wide-angle projection arrangement, in which a picture formed from three images is projected on to a cylindrically curved projection surface in order to offer the viewer a panoramic effect. Through the use of a special type of flexible mirror, projection can take place without any disturbing view of the projection machines, which are positioned somewhat below and in front of the viewer. The necessary aspect ratio of the partial images is produced with the aid of anamorphotically acting, optical means. The apparatus expenditure, namely three cameras and in each case two, i.e. six reflecting mirrors in all is considerable. Special measures are also required for a jointless transition of the partial images.

Much less expenditure is required by the projection device described e.g. in U.S. Pat. No. 4,154,514, by means of which an image can be produced on a projection plane which has a pronounced arcuate curvature on one side and as a result the viewer is given the impression of a three-dimensional effect. Projection takes place over an angle between 138.degree. and 153.degree. on to a cylindrically curved plane. Compared with conventional three D-systems, under an angle usually smaller than 90.degree., no additional optical viewing aid is required for producing the three-dimensional effect. The projection arrangement described in this specification merely consists of a single projection apparatus with upstream-connected, anamorphotic aids, in order to produce the necessary enormous width/height ratio. 35 mm standard films with anamorphotic images are used for projection purposes.

The impression of the optical three-dimensional effect is largely based on the pronounced curvature of the projection plane, which surrounds the viewer of the photographic scene or occupies the field of view of the eye to the extent that the image frame is no longer perceived. Thus, it is not a picture in the manner that it is perceived by both eyes with the given interoccular spacing and is processed to a three-dimensional image in the brain.

Another technical solution is known in which two anamorphotically compressed images, correlated to one another with an interoccular spacing are imaged on a 70 mm standard film in a ratio of 1:2. On projection, this leads to a stereo wide-screen picture with two images correlated with the interoccular spacing and also having different polarizations. Viewing takes place by means of a viewing aid, namely spectacles or glasses with two polarizers sloping towards one another.

For taking the pictures, two basic optics are connected upstream of in each case one anomorphotic lens, whose optical axes essentially have the average spacing of a pair of human eyes. Since on the film, the centre-to-centre distance of the photograph is determined by its size and is generally considerably smaller, the imaged object distances are adapted in known manner by reflecting mirrors. As a function of the conventional anamorphotic lens/basic optics combination, this requires relatively large overall length and consequently a limitation of the camera angle. The convergence control of the two correlated images is also made difficult in the case of the saught extreme wide-angle projection. The incident light beams of the two optics must be displaced transversely to the optical axis and at the same time focused, as soon as the camera distance changes.

In the case of all these projections on to oversize projection surfaces, there is the additional advantage of a very low light yield from the lighting unit. This is largely linked with the filters, which are arranged in the lens of such a projection apparatus and the polarization filters of the glasses worn by each viewer, in which approximately half of the light yield per polarization channel is lost. In addition, the projection surfaces are extremely large, so that image illumination is no longer particularly good. For a considerable time efforts have been made to overcome this disadvantage by more powerful light fittings. However, it is disadvantageous in this case that the illumination of a stereoscopic pair of images in the film plane also leads to light losses.

The problem of the invention, in connection with the reproduction of wide-angle stereo images, in which simultaneously anamorphotic decompression takes place, is to provide an optical arrangement, which has small overall lengths, few movable parts and which has a sufficiently high light intensity for image formation. Another problem of the invention is to provide an optical arrangement, which is suitable for projecting stereoscopic image pairs on to a spherical projection surface. Yet a further problem of the invention is to so equip an optical device, that it can be arranged on the mechanism and basic optics of normal commercially available projectors.

This problem is solved by the invention defined in the claims.

The invention is now described relative to the embodiment represented in the two drawings, wherein show:

FIG. 1 the apparatus for illuminating stereoscopic pairs of images.

FIG. 2 the supplementary lens for projecting stereoscopic pairs on to a spherical wide-screen surface.

As stated hereinbefore, by means of this device, a normal, commercially available cine projector can be upgraded into a projection apparatus for stereoscopic, linear anamorphotically compressed pairs of images on extremely large, spherically curved wide-screen surfaces. The problem is to supply the energy in the visible spectrum from the light sources as quantitatively as possible to the film trap and finally to anamorphotically laterally expand the transmitted image pairs and project them on to the oversize screen with an adequate light intensity, i.e. said screen is fully illuminated.

FIG. 1 shows in plan view the lighting unit for illuminating the stereoscopic pairs of images. This unit comprises two Xenon high pressure arc lamps, e.g. in each case with an output of 4 kW. Each of these arc lamps is surrounded by ellipsoidal mirror 2 in such a way that the light beams, as indicated by broken lines, pass in the direction of optical axis 11 to the first reflecting prism 3. Each of the ellipsoidal mirrors has focal lengths of substantially 60 and 540 mm. The diameter of the mirror at its edge is approximately 280 mm. It can also be seen that arc lamps 1 and mirrors 2 are arranged symmetrically to a plane of symmetry 7. The angle between plane of symmetry 7 and optical axes 11 is in the present case 18.5.degree.. It is obvious that, as a function of the spatial dimensions of an embodiment, the angle can differ from the given angular value. The first reflecting prism can be made from quartz with a refractive angle of 19.56.degree. or from the material "ZK N7 " with a refractive angle of 17.5.degree.. When made from quartz, the refractive index for the helium line n.sub.d =1.458 and the Abbe number .nu..sub.d =approximately 67. When made from "ZK N7", the refractive index for the helium line n.sub.d =1.5085 and the Abbe number .nu..sub.d =61.19. A first deflecting prism 3 is provided for each of the optical axes. The optical axis direction is consequently deflected by an angle of 9.3.degree. to the plane of symmetry 7, which is shown in broken line form in the drawing. The light passes in closely concentrated manner into area 8, which can e.g. contain the mechanical diaphragms of the film projector. At the end of area 8 there is a second deflecting prism 4, one of which is provided for each of the optical axes. This prism can either be made from quartz with a refractive index n.sub.d =1.458 and Abbe number .nu..sub.d =67 or from the material "Tempax" with the reflective index n.sub.d =1.485 and .nu..sub.d =approximately 62. In the second "Tempax" reflecting prism 4 with a refracting angle of 18.2.degree., the optical illumination axis is directed parallel to the plane of symmetry immediately in front of film plane 6. The light cone is extended by a spherical concave ground glass in the second deflecting prism, said glass being fitted to the side of the second prism 4, directed towards the projection optics 12. The radius of the ground glass is in the present case r.sub.4 =146 mm. The optical radius is a function of the arc lamp 1 used. The stereoscopic pair of images is completely illuminated in an optimum manner in film plane 6 and illumination losses no longer occur.

FIG. 2 shows in a partial sectional representation the supplementary lens arranged after the basic optics and which optically cooperates with the lighting unit according to the invention.

The stereoscopic pair of images 10, 11 is recorded on the film passing through image plane 6. Conventionally such films have a width of 35 or 70 mm. The centre-to-centre distance a of the two images 10, 11 is typically either 13 mm or 26 mm. As has been described, the lighting unit according to FIG. 1 is arranged behind the film. In the drawing, the optical axes of the two images 10, 11 are shown by dot-dash lines. For each image a so-called basic lens 12 is provided for projection, said lens can be considered as belonging to the camera in question. Each basic lens 12 is followed by a first pair of prisms 21, 22, which can be made from various optical materials and have the represented shape. The two partial prisms 21, 22 are cemented together. As a result the optical axis of the light beams is deflected to the right and left for anamorphotically decompressing the stereoscopic image paths. In the direction of the light beams, there now follows a second pair of prisms, comprising partial prisms 23, 24, which have the same or similar shape and operation to the first pair of prisms. The second pair of prisms 23, 24 is at a distance 1.sub.1 from the first pair of prisms 21, 22. This distance can either be lengthened or shortened, as is indicated by double arrow 15. The mechanisms for bringing about such a reciprocal displacement of the prism pairs are generally known and will not be discussed here. Distance b can be increased or decreased as a result of the change in distance 1.sub.1 between the prism pairs. This is dependent on the constructional width of the following lens elements A, B, C. The prism pairs 21, 22 and 23, 24 can also be pivoted in the corresponding fulcrum 13. As a result of this pivoting, which is indicated by the double arrows 14, the convergence of the stereo images projected on to the spherical projection screen can be adjusted in such a way that they offer the best stereo action without giving a disturbing optical impression.

The upper prism pairs 23, 24 of FIG. 2 is followed by an arrangement of three lens elements A, B, C for each of the two stereo images 10, 11. These lens elements have the same values for each image or for each image or picture channel. Thus, the reference numerals of the different constructional features of the lens elements are only shown for the right-hand arrangement. The following description and table also apply to the left-hand arrangement. The first element is positive and comprises a biconvex lens L.sub.1 and a concave/convex lens L.sub.2, which is followed by an air clearance with spacing 1.sub.2. The second element B has a negative action and comprises a biconcave lens L.sub.3, biconvex L.sub.4 and biconcave lens L.sub.5. The third lens element C is separated by an air clearance 1.sub.3 from the second lens element B. The third lens element has a negative optical path and comprises a menicus lens L.sub.6 and a biconcave lens L.sub.7, followed by the not shown, known polarization filters. The stereo image pair is projected with the base distance b on to the spherical projection surface, which is in the form of a hemisphere.

There now follows the Table of constructional data of the represented lens:

In this table, r stands for the radii and d the thicknesses of the individual lenses in mm. The thicknesses 1 of the air clearances are also given in mm. The refractive index n.sub.d relates to the helium line and .nu..sub.d indicates the Abbe number.