GB2135470A

GB2135470A - 3-D Photography

Info

Publication number: GB2135470A
Application number: GB08400445A
Authority: GB
Inventors: Zoran Perisic
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-02-21
Filing date: 1984-01-09
Publication date: 1984-08-30
Also published as: GB2135470B; GB8400445D0

Abstract

Apparatus for filming and projecting film so as to provide a 3-D impression has a camera in which first and second eye images, spaced along parallel axes (L, R) (consistent with the interocular distance of a viewer) are passed alternately along the lens axis (L) of the camera (1) by means of mirror-shutter (4). The camera may be provided with a viewfinder in which the left and right eye images are separated out again by means synchronised with mirror 4 (see Fig. 6 - not shown) whereby the operator may see the 3-D effect being recorded. The images on the film strip may be projected by a projector synchronised with the camera so that alternate frames are polarised in opposite directions and viewed wearing spectacles with corresponding cross- polarised filters. <IMAGE>

Description

SPECIFICATION Method and apparatus for three-dimensional photography This invention relates to a method of threedimensional photography and to apparatus for carrying out the method.

Existing systems for producing threedimensional (3D) photography and cinematography fall broadly into two categories: namely, dual camera systems and single camera systems. Dual camera systems utilise two interlocked cameras positioned with the axis of their respective lenses at 900 to each other. A two-way mirror of 50-50 transmission to reflection ratio is placed between the two lenses which enables the effective separation between the entrance pupils of the lenses to be positioned at the correct interocular distance for the particular focal length of the lenses and the film format in use. By varying the position of the twoway mirror the interocular distance can be varied; in addition by angling the mirror away from the basic 450 setting convergence between the lenses can be altered as required.

An even simpler way is to place two interlocked cameras side by side, angling them in towards each other physically to control convergence. However, due to the physical size of camera and lenses themselves, the interocular distance is somewhat greater than that of human eyes and therefore only lenses of longer focal lengths can be used to produce satisfactory results. The main advantage of the dual camera systems is that there are no limitations with regards to formats and aspect ratios.

Single camera systems use only one camera to photograph both left and right eye images. These images can be positioned side by side on 65 mm format or one above the other on 35 mm format.

The latter is more common and means that both images are occupying the area of a normal 35 mm frame, i.e. alternate half frame sections, resulting in a limitation of the aspect ratio (Techniscope ratio). In all these cases both images are photographed simultaneously. The two images are produced by two prime lenses side by side and a group of optics and prisms therebetween which ensure that correct positioning of the images in both vertical and horizontal plane as well as having the correct orientation.

Single camera stereoscopic systems are known for example from U.S. Patent Specification No. 2365212 and U.K. Patent Specification No.

749675. In U.S. Patent Specification 2365212 a camera is disclosed which has a rotatable shutter which has openings alternately permitting the passage of light along two parallel paths forming the left and right eye images. The light conducted along either path is resolved downstream of the shutter by prisms so as to direct the light along the longitudinal centre line of the camera. The shutter mechanism is synchronised with the film actuator mechanism whereby an unexposed frame of film will move into position for each of the light transmissions passed by the shutter so that the left and right eye images are recorded alternately on the film.

In U.K. Patent Specification No. 749675 a camera is disclosed which has two parallel mirrors one of which is rotatable and arranged intermittently to cover the objective of the camera so that images transmitted by the two mirrors are recorded on to successive frames of film so as to form the left and right eye images of stereoscopic film. The two mirrors are positioned so that the images being recorded are images at right angles to the centre axis of the camera.

For the cinematograph film produced by either of the dual or single camera systems the viewing method depends on ensuring that the left eye sees only the left-eye image and the right eye only the right-eye image. Although U.S. Specification No. 2365212 proposes shutter spectacles, this is most commonly achieved (for colour film) with the use of crossed polarising filters placed in the beam of the appropriate image. The viewer (i.e.

the audience) sees the images through glasses with polarising filters whose polarisation axes are at 900 to one another corresponding to the polarisation axes on the projected images.

The projection is either by means of two interlocked projectors or by a single projector utilising a beam-splitting arrangement of mirrors whereby the two "over and under" images are separated out and superimposed on the projection screen.

Three-dimensional cinematography presents particular problems when it comes to special effects. Theoretically it is possible to project a stereoscopic background and to rephotograph it as a composite with suitable foreground action, using any of the existing systems. However, in practice, this is not so simple. In the case of the dual camera systems two cameras and two projectors would be required resulting in a very cumbersome piece of machinery. In the case of the existing single camera systems only one camera and one projector would be required utilising two identical lenses. Since both left and right eye images have to be projected on the same front-projection screen it is necessary to place crossed polarising filters in front of each lens - this cuts down the amount of projected light by about 1,5 f stops.Corresponding polarising filters have to be placed in front of the lenses on the camera unit so that the background images could be kept separated during rephotography; this cuts down the effective exposure by another 1,5 f stops, bringing the total up to 3 f stops. Moreover, in practice, polarising filters cause colour distortion which also needs to be corrected in order to produce a good match between the foreground and the background image. This can add up to at least another f stop - making the total loss of 4 f stops, which in turn makes it very impractical. Perhaps the biggest drawback to this method comes from the fact that the polarisation does not completely cancel the opposite image and this bleed through between the left and right eye images can result in a degradation of the image quality.It is also important that the operator can see what is taking place in front of him.

According to the present invention there is provided apparatus for providing left and right eye images along the lens axis of a camera whereby left and right eye images are recorded alternately on film strip so as to provide three-dimensional impression the apparatus comprising means for receiving a first eye image along a first axis, means for receiving a second eye image along a second axis spaced from the said first axis, the first and second axes extending substantially parallel to the lens axis of the camera, and means for resolving said first and second eye images alternately along the lens axis.

The invention also includes a camera for filming in three dimensions comprising upstream of the camera lens, a first fully reflective surface arranged to be positioned intermittently transverse to the lens axis of the camera in synchronism with the drive motor of the camera, and a second fully reflective surface laterally spaced from and parallel to the first reflective surface, the non-reflecting duration of the first reflective surface defining a first eye image and the reflecting duration of the first reflective surface defining, via the second reflective surface, a second eye image whereby the left and right eye images are separate from one another, the axes of the first and second eye images and the lens axis being substantially parallel.

According to another aspect of the invention there is provided a viewfinder for a camera recording alternate left and right eye images on film strip by using resolving means for resolving spaced left and right images alternately along the lens axis of the camera, the viewfinder comprising optical means defining an optical path for receiving the alternate left and right eye images passed along the lens axis of the camera, resolving means for separating out the images into left and right eye images and spaced left and right eyepieces for receiving the respective images, the resolving means of the viewfinder being synchronised with the resolving means of the camera whereby the camera operator may see the three dimensional effect being recorded alternately on the film strip in the camera.

According to another aspect of the invention there is provided a projector for projecting film with three-dimensional impression where left and right eye images are disposed alternately on the film, the projector comprising means for synchronising the speed of projection with the speed of the camera with which the images were recorded on the film, means four projecting light through the film so that a beam of light of said images on the film is projected towards a screen, and alternately positioning in said beam of light polarising means with their polarisation axes crossed, the positioning of the polarising means being synchronised with the speed of projection such that the left eye images on the film are polarised in one direction and the right eye images are polarised in another direction.

The invention will now be described by way of example with reference to the accompanying diagrammatic drawings in which: Figure 1 shows the apparatus of the invention in a first embodiment as applied to a camera; Figure 1 a is a front elevation of the shutter of the first embodiment; Figure 2 shows a second embodiment; Figure 2a is a front elevation of the shutter of the second embodiment; Figure 3 shows a third embodiment as applied to a camera; Figure 4 shows a fourth embodiment as applied to a camera; Figure 5 shows the conventional arrangement for viewing a subject being filmed; Figure 6 shows the apparatus of the invention in a fifth embodiment of a viewfinder for the camera operator to view the true 3D effect; Figure 7 is a second embodiment of an alternative viewfinder; Figure 8 is a third embodiment of a further alternative viewfinder;; Figure 9 is a side elevation of the viewfinder shown in Figure 8; and Figures 10a and lOb show an attachment for the projector for separating out the left and right eye images.

In the embodiment of Figures 1 and 1 a the apparatus for converting an image into apparent three dimensions is applied to camera 1 where a single camera lens 2 is used for focussing the image to be recorded on film, the focal plane of which is included as 3. A segmented rotary shutter 4, shown in Figure 1 a, is placed at 450 in front and close to the front surface of the lens 2.

The shutter 4 is made of a front-silvered mirror with half the radius cut-away and is rotatable about an axis 5 by means of a drive motor 6.

When the cut-away section of tha shutter 4 is in front of the lens 2 the left eye image L is photographed and, when the mirrored part of the shutter 4 is rotated in front of the lens 2, the right eye image R is seen by the lens 2 via a second front silvered mirror 7 placed with its surface parallel to the mirrored surface of the shutter 4 and on the opposite side of the lens. The mirror 7 is pivoted about an axis 8 and is mounted upon a slidable support 9. The interocular distance between the left eye and right eye images L and R can be varied by moving the mirror 7 nearer or further away from the camera 1, and the convergence by varying the angle with the adjusted reading being indicated by convergence indicator 1 0.

The mirrored shutter 4 can be with a 1800 cutaway portion as shown or with two clear and two front silvered segments of 900 each (as shown in Figure 2a). The shutter 4 is driven by means of a motor 6 which is slaved to the camera motor (not shown) and is geared down appropriately. The camera 1 runs at 48 f.p.s. instead of the conventional 24 producing full frame left and right eye images in succession.

In the second embodiment shown in Figure 2, which is the preferred embodiment as applied to a camera, lenses of specific type of construction such as the Cook Speed Panchro 25 mm f 1,8 (inverted-telephoto type) 20 are used. These lenses, and lenses of this type of construction, have a fairly large gap between front and rear groups of elements. A rotary mirrored shutter 21 intersects the lens axis inside the body of the lens itself deflecting it 900 to the side of the lens wall which is cut off to accommodate another set of front elements. Beyond these elements lies a front-silvered mirror 22 set at 450 to the redirected lens axis which has much the same function as the mirror 7 in Figure 1. As indicated by the two arrows the mirror 22 may be moved in the same manner as the mirror Y in Figure 1.

The lens elements 20 are ground and readjusted with a new lens element 26 added to the front-facing lens element 20 so that both left and right eye images L and R focus at the same distance from the lens unit and that they are of identical size. Reference 23 indicates the real element of the primary lens unit in which the rotary shutter 21 is positioned.

This embodiment allows a correct arrangement between the focal length and interocular distance for a specific aspect ratio.

A relay lens 24 is placed between the split lens unit 20 and the camera (not shown) with a field lens 25 disposed intermediate the real element 23 of the primary lens unit and the relay lens 24 (an image reversing prism can also be incorporated as part of the relay system). This relay lens makes it possible to vary the final image size to be photographed and therefore the format.

The shutter 21 is again slaved to the camera motor (not shown) through gearing 27 preferably geared down in the ratio 4:1.

The embodiment of Figure 3 is designed to be used for both 25 mm and 18 mm lenses where the interocular distance needs to be varied from the normal (i.e. 2,5" for Academy with 25 mm) to zero. This is particularly useful for shooting scale models and miniatures.

This embodiment incorporates two lenses of the inverted telephoto type of construction such as the Cook Speed Panchro 18 mm and 25 mm.

The body of the lens 30 is cut at 450 to its axis in the gap at 31 between the front 32 and rear 33 groups of elements. A fixed silvered mirror is placed at the point of the cut 31 and the front group of elements 32 are re-assembled along the redirected lens axis, so that they lie at 900 to the rear group of elements 33. Two lenses 30 of identical construction are modified in this way and positioned with their exit and entrance axes running perpendicular to each other. A relay lens 36 is placed directly in line with the exit axis of one of the lenses 30 but at equal distance from the focal plane of both lenses. A segmented rotary shutter 34 placed at 450 and at the point where the exit axes of the two lenses 30 meet ensures that the images from the two lenses will be recorded on film by the camera, downstream of the relay lens 36, in succession.The lenses 30 are positioned so that their respective front elements 32 are at 90" to each other as shown. A two-way mirror 35 with 50-50 transmission to reflection ratio is placed at 450 then the two lenses produce identical images and the interocular distance is effectively zero. However, by moving the two-way mirror 35 towards the lens which is "looking through it" (the lens to the left in Figure 3), the deflected axis of the other lens (which is seeing a reflected image) is optically shifted to the opposite side. Thus, the lens which is seeing the scene reflected via the two-way mirror 35 and is positioned to the right of the lens which is looking directly at the scene through the two-way mirror 35 is in fact recording the left eye image. Convergence is controlled by varying the angle of the two-way mirror 35.

The two-way mirror 35 can be replaced in certain circumstances by another segmented rotary mirror which would prevent the loss of 1 f stop.

In Figure 4 a further embodiment is disclosed which uses two lenses 40 side by side - the minimum interocular distance being determined by the diameter of the two lenses one of which may be adjustable. Both lenses are facing forward and a mirror 41 is placed behind each lens at 450 to the lens axis so that the optical path of the light is reflected through 900 so that the two lens axes are now in line i.e. colinear. The reflected light then passes through respective relay lens element 44. An oscillating mirror 42 is positioned equidistant from the two lenses to direct the light alternately from one lens and then from the other towards a relay lens 43 positioned at 900 to the joint axis of the two lenses.The oscillation of the mirror 42 is produced by a suitable cam action (not shown) driven in synchronism with the motor of the camera positioned downstream of the relay lens 43. Convergence may be controlled by appropriate angular adjustment of the mirrors 41.

The main advantage of the 3D systems in accordance with the invention is that, in all cases, there are no limitations to the aspect ratio or film format. All 35 mm aspect ratios can be photographed including 2:1 Anamorphic squeeze (anamorphic attachment is added to the relay system). For flat release prints a C.R.I. is stepprinted from the original negative (printing every other frame) and the release prints can then be made from this in the conventional manner. This does not introduce another printing stage because it is a standard practice to make several duplicates of the original negative and make release copies from them. In the production of a C.R.I. dupe an optical printed is used in any case (to preserve the correct geometry of the image) - and skip-framing is an automatic operation on most printers.

All the conventional aspect ratios used on 35 mm can be photographed with the standard 35 mm camera. However if Techniscope format is to be used then the camera mechanism needs to be changed to pull down 2 perforations instead of four, with the appropriate mask in the camera. In this way two frames occupy the area of one conventional frame, and, although they are taken intermittently they can be projected simultaneously using conventional theatrical 3D projection methods. Flat copies from this method are made on 4 perforations with a 2:1 anamorphic squeeze. If a vertical anamorphic squeeze (instead of the conventional horizontal one) is introduced in the relay system during photography it is then possible to project an Academy aspect ratio using an anamorphic lens on the projector rotated through 900 from the conventional position.A suitable amended beam splitter attachment placed in front during projection would enable stereo viewing in the Academy aspect ratio. Flat release copies can also be made by de-squeezing the vertical during the printing of the C.R.I. at the same time as the skipframing is done.

By suitable adjustments to the relay system it is possible to shoot on larger formats such as Vista/Vision and 65 mm. This is particularly desirable for front-projection and other special effects work where duplication is necessary.

Naturally a Vista/Vision or 65 mm camera has to be used. For front-projection a plate produced in this way would then be rephotographed as a composite with the foreground on one of the conventional 35 mm aspect ratios.

As can be seen the Techniscope format can be used directly for theatrical presentation as though it had been shot by the conventional single lens 3D systems described earlier in the specification.

Other 35 mm aspect ratios can either be cropped and reprinted on the Techniscopic format or the left and right images can be separated out on two rolls of film and projected by means of two interlocked projectors, as would be the case if they had been produced by a two-camera system.

Either of the copies can be used for flat releasing.

It is also possible to project all the various aspect ratios directly as they were photographed.

For this it is necessary for the projector to run at double speed (48 f.p.s.) i.e. at the same speed as the camera during the original photography. In order to achieve the separation between the left and right eye images an attachment is placed in front of the projector lens.

This attachment can be of two types: 1. A shuttle arrangement is positioned perpendicular to the lens axis. Two pieces of polarising filters set in line next to each other with their polarisation axes crossed are moved in and out of the projector light beam in succession. The shuttle drive mechanism is synchronised with the projector drive motor.

2. This method involves the use of only one polarising filter mounted inside a circular device 101 (such as a large bearing) see Figures 10a and 1 Ob and positioned in front of the lens of the projector 102. This "circle" is driven through gearing 103 by an intermittent device (geneva movement) 104 which in turn through gearing 105, 106 is driven in synchronism with the projector motor 107, producing a rotation of 900 to coincide with the "pull down" action for the film advance of the projector controlled by a second intermittent device (geneva movement) 1 08. As a result the polarising filter is stationary during the projection of each frame and its polarising axis P will be in the appropriate position for each successive frame as the axis changes through 900 of rotation.

A major problem with the existing 3D systems is that the camera operator cannot see a true 3D effect through the viewfinder. This leads to the inaccurate setting of the interocular distance and most particularly convergence. The way the 3D effect is going to look when it is projected can only be guessed. In the case of front-projection this makes it difficult to see how the projected 3D images and the foreground interact making the matching of these elements possible. The conventional viewfinder for a camera is shown in Figure 5. The subject 51 is seen through the camera lens 52 via the camera shutter (reflex) 53, field lens 54, mirror 55, relay lens 56 and the eyepiece 57. This provides a view along the lens axis L of the same image as received at the film plane indicated at 58.The field lens 54 is positioned immediately behind the ground glass (not shown) and picks up the aerial image of the ground glass.

According to another aspect of the invention shown in Figure 6 I propose to use two angle viewfinder attachments 60 manufactured normally for single use with stills camera and an oscillating mirror 61 driven by suitable cam means as described in relation to Figure 4 which is used instead of the eyepiece 57. In this way it is possible for each eye to view its corresponding image on the ground glass 54 in the camera via the relay lens 56. The oscillating mirror 61 is driven by a cam (not shown) which is in turn driven by the camera motor.

This way the camera operator can at all times see the 3D effect so that both focus adjustments and convergence adjustments during a take can be scrutinised as they happen.

A second embodiment of viewfinder which may replace the conventional eyepiece 57 is shown in Figure 7. In this embodiment the image is separated into left and right eye images by a shutter 71 of the type shown in Figure 2a driven in synchronism with the camera motor and set at 450 to the image axis. The shutter 71 thus either allows light to pass straight through to a right eyepiece 72 or reflects the light to a mirror or prism 73 set at 900 to the shutter 71 which in turn reflects the light to a left eyepiece 74.

Respective relay lenses 75 and 76 are provided for the left and right eye images, the lenses being of different focal lengths to match the different lengths of the respective optical paths.

In Figures 8 and 9 a third preferred embodiment of viewfinder is shown which replaces the eyepiece 57 of a conventional viewfinder. In this embodiment light from the ground glass is passed to a field fens 81 supported on a mounting block 82 which bolts onto the camera by bolts (not shown). The image is then received by a relay lens 83 which transmits the light to a fully-reflective mirror shutter 84 of the bow-tie type shown in Figure 2a. The shutter 84 is driven by motor 85 in synchronism with the motor of the camera to which the viewfinder is secured. The shutter 84 thus either allows light to pass straight to the left eyepiece 86 via fully reflective mirrors 87 and 88 or reflects the light to fully reflective mirror 89 which in turn reflects the light to the right eyepiece 90.

As seen in Figure 8 the shutter 84 is positioned at 450 to the entrance axis by the fully reflective mirrors 88 and 89 which are set at 430 to provide a 40 divergence for each eyepiece which is more compatible with the natural focussing of the eyes.

The various components are mounted on an appropriate base plate 91.

The respective optical paths for the left and right eyepieces are arranged to be the same length so that adjustment by further relay lenses of differing focal lengths are not required. In Figure 9 the fully reflective mirror 89 is omitted for clarity.

As well as being a very useful system for conventional 3D cinematography, the present invention is also perfect for front-projection and back-projection (even if the backgrounds are originated by one of the existing 3D systems, they can be prepared and fused for front-projection in this way).

By tracking the entire camera/projector assembly towards or away from the frontprojection screen with the appropriate "follow focus" attachments on both lenses and an iris compensator on the projector lens, it is possible to create movement "in depth", an arrangement disclosed in detail in my prior U.K. Patent No.

1 5631 88 to which reference is directed; this arrangement can produce some quite remarkable effects in 3D.

Claims

1. Apparatus for providing left and right eye images along the lens axis of a camera whereby left and right eye images are recorded alternately on film strip so as to provide three-dimensional impression, the apparatus comprising means for receiving a first eye image along a first axis, means for receiving a second eye image along a second axis spaced from the said first axis, the first and second axes extending substantially parallel to the lens axis of the camera, and means for resolving said first and second eye images alternately along the lens axis.

2. Apparatus according to claim 1 wherein the resolving means comprises two reflective means, one reflective means aligned with said second eye axis and arranged to direct the second eye image transverse to the said lens axis, and the other reflective means being positioned to receive the second eye image and to reflect it substantially along said lens axis of the camera, said other reflective means being arranged alternately to reflect the second eye image along the lens axis whilst the first eye axis passes along the lens axis.

3. Apparatus according to claim 2 wherein the other reflective means is positioned substantially on said first axis whereby the first eye image axis and the lens axis are substantially coincident, the first eye image being permitted to pass along the lens axis of the camera when the second eye image is shielded from the lens axis.

4. Apparatus according to claim 1 wherein the resolving means comprises a first mirror, means for intermittently positioning the first mirror transverse to the lens axis in synchronism with the drive means of the camera, and a second reflective surface laterally spaced from and parallel to the first mirror.

5. Apparatus according to claim 4 wherein the first mirror is a front silvered, fully reflecting circular mirrored shutter with two 900 opposed portions cut-away.

6. Apparatus according to claim 1 wherein the resolving means comprises a reflective means aligned with each of the said first and second eye images and arranged to redirect the respective images such that their axes intersect one another at the lens axis, an alternating reflective surface being positioned at said intersection to direct the respective images alternately along the lens axis of the camera.

7. Apparatus according to claim 6 wherein the respective image axes are redirected to intersect with one another substantially at right angles, the alternating reflective surface being a fully reflecting mirrored shutter part of which is cutaway, the shutter being rotated in synchronism with the camera film drive to transmit alternate left and right eye images along the lens axis.

8. Apparatus according to claim 6 wherein the respective image axes are redirected so as to be colinear, the alternating reflective surface being an oscillating mirror.

9. A camera for filming in three dimensions comprising upstream of the camera lens, a first fully reflective surface arranged to be positioned intermittently transverse to the lens axis of the camera in synchronism with the drive motor of the camera, and a second fully reflective surface laterally spaced from and parallel to the first reflective surface, the non-reflecting duration of the first reflective surface defining a first eye image and the reflecting duration of the first reflective surface defining, via the second reflective surface, a second eye image whereby the left and right eye images are separate from one another, the axes of the first and second eye images and the lens axis being substantially parallel.

10. A camera according to claim 9 wherein the first fully reflective surface is positioned within a lens assembly comprising first and second lens elements, the axes of which form part of the optical paths of the respective left and right eye images, the reflective means intersecting the lens axes of the two lens elements.

11. Apparatus according to claim 1 or 9 wherein the optical path of one eye image is longer than the optical path of the other eye image, lens means being provided in one or both of the optical paths so that both the left and right eye images focus at the same point and are of identical size.

12. Apparatus according to claim 1 or 9 including means for varying the interocular distance between the first and second eye images.

1 3. A viewfinder for a camera recording alternate left and right eye images on film strip by using resolving means for resolving spaced left and right eye images alternately along the lens axis of the camera, the viewfinder comprising optical means defining an optical path for receiving the alternate left and right eye images passed along the lens axis of the camera, resolving means for separating out the images into left and right eye images and spaced left and right eyepieces for receiving the respective images, the resolving means of the viewfinder being synchronised with the resolving means of the camera whereby the camera operator may see the three dimensional effect being recorded alternately on the film strip in the camera.

14. A viewfinder according to claim 13 wherein the separated left and right eye images at the respective eyepieces are slightly diverging relative to one another.

1 5. A viewfinder according to claim 13 wherein the resolving means comprises a rotatable, front silvered, bow-tie shutter positioned on said optical path.

16. A viewfinder according to claim 13 wherein the resolving means comprises an oscillating mirror positioned on said optical path.

1 7. A projector for projecting film with threedimensional impression where left and right eye images are disposed alternately on the film, the projector comprising means for synchronising the speed of projection with the speed of the camera with which the images were recorded on the film, means for projecting light through the film so that a beam of light of said images on the film is projected towards a screen, and alternately positioning in said beam of light polarising means with their polarisation axes crossed, the positioning of the polarising means being synchronised with the speed of projection such that the left eye images on the film are polarised in one direction and the right eye images are polarised in another direction.

1 8. A projector according to claim 1 7 wherein the polarising means comprises a reciprocal shuttle containing two polarising filters with their polarisation axes crossed, the shuttle being moved to and fro to bring one filter and then the other filter in line with the projected beam in synchronism with the projection speed.

1 9. A projector according to claim 1 7 wherein the polarising means comprises a rotatable pola rising filter driven intermittently in synchronism with the projector so as to produce a 90" rotation coinciding with each pulldown of the projector, whereby frames are projected through the polarising filter so that the alternate left eye images are polarised in one direction and the alternate right eye images are polarised in the other direction.

20. Apparatus for filming and projecting film so as to provide three-dimensional impression comprising a camera, means for passing spaced left and right eye images alternately along the lens axis of the camera whereby left and right eye images are recorded alternately on film strip, a viewfinder in which the left and right eye images are separated out again whereby the camera operator may see the three-dimensional effect being recorded on the film strip, a projector for projecting the film at the same speed as the film was recorded by the camera, the projector including means whereby alternate left and right eye images on the film strip are cross-polarised and, viewing means with corresponding crosspolarised filters whereby the viewer is provided with a three-dimensional impression.

21. A film system for filming and projecting film so as to provide three-dimensional impression said system comprising: a camera having a lens axis; an assembly for providing left and right eye images along the lens axis of the camera whereby left and right eye images are recorded alternately on film strip, said assembly comprising means for receiving a first eye image along a first axis, means for receiving a second eye image along a second axis spaced from the said first axis, and means for resolving said first and second eye images alternately along the lens axis;; a viewfinder for the camera, said viewfinder comprising optical means defining an optical path for receiving the alternate left and right eye images passed along the lens axis of the camera, resolving means for separating out the images into left and right eye images, and left and right eyepieces for receiving the respective images, the resolving means of the viewfinder being synchronised with the resolving means of the camera whereby the camera operator may see the three dimensional effect being recorded on the film strip in the camera; ; a projection means for projecting the images recorded on the film strip with three dimensional impression, the projection means comprising means for synchronising the speed of projection with the speed of the camera, means for projecting light through the film so that a beam of light of said images on the film is projected towards the screen, and alternately positioning in said beam of light polarising means with crossed polarisation axes, the positioning of the polarising means being synchronised with the speed of projection such that the left eye images on the film are polarised in one direction and the right eye images are polarised in the other direction, and viewing means for the viewer having polarising filters for the left and right eye which have polarisation axes corresponding to the polarisation axes of projected images whereby the viewer's left eye only views the alternate projected left eye images and the viewer's right eye only views the alternate projected right eye images whereby the viewer is provided with a three-dimensional impression.