WO1991019223A1

WO1991019223A1 - Stereoscopic photography

Info

Publication number: WO1991019223A1
Application number: PCT/GB1991/000882
Authority: WO
Inventors: Barry Leonard Wiseman; Alan Grayston Walmsley; David Gifford Burder; Jack Ezra
Original assignee: Hanimex (Uk) Limited
Priority date: 1990-06-01
Filing date: 1991-06-03
Publication date: 1991-12-12
Also published as: AU7989591A

Abstract

A camera, capable of generating a stereoscopic effect using a single optical path between the subject and the photosensitive medium, employs a coding member (75, 76), or assembly of elements such as an iris (82) having different coding effects to either side of a diametral centre line with the coding effects appropriate to decoding means such as spectacles in front of the eyes of an observer. The coding effect may be by way of filter material of different colorations to either side of the centre line or coding elements which are separately switchable between a transparent state and a less transparent or opaque state in synchronism between the switching of a coding element (23) and a decoding element (27) of viewing means such as spectacles.

Description

STEREOSCOPIC PHOTOGRAPHY

The present invention relates to improved apparatus for use in stereoscopic photography and is in particular concerned with a lens and a camera either of which enables stereoscopic photography to be achieved using a single or compound lens, with what we shall refer to herein as "duplex optical paths" in which two light beams pass side-by-side through the same lens system from the subject to the film plane.

It is known to provide for stereoscopic photography using twin lens systems which are separated laterally and which record respective images, one corresponding to the perspective view appropriate to the right eye and the other corresponding to the perspective view appropriate to the left eye. Normally such lenses will have a lateral separation corresponding to the separation between the left and right eyes of an average human being, although the important criterion is that the perspective appreciated by the viewer of two such images is realistic. The photograph resulting from such a stereoscopic photography process may either be recorded on spaced apart separate film regions or photographic paper sheet regions or be recorded overlapping one another on the same film or photographic paper sheet with some system for coding each image to be recognised only by the appropriate eye. One well known system of such coding involves the use of a red filter for the left eye in a pair of viewing spectacles, and a red filter in the camera in that part of the optical path corresponding to the left eye, and correspondingly a blue/green camera filter for the right eye and a blue/green filter for the optical path appropriate to the right eye.

It is an object of the present invention to provide for stereoscopic photography using a camera lens having a single optical system, thereby allowing for relatively straightforward manufacture or adaptation of a lens whether compound, simple, fixed, zoom, or varifocus, of glass, plastic, acetate or gelatine, or any combination of elements or prisms for the process of stereoscopic photograph .

By the term "camera" as used herein, we denote any apparatus for recording images electrically or chemically for viewing simultaneously or subsequently. Thus we include, for example, still photo cameras for conventional and specialised photography using either colour positive or negative film requiring processing, or "instant film" processed in the camera; cine-cameras; and video cameras used either for simultaneous broadcasting and/or viewing or for video recording. Other similar photographic and microscopic devices may fall within this definition.

Accordingly, one aspect of the present invention provides a camera including a lens having a duplex optical path (as herein defined) from subject to the photosensitive element of the camera; coding means adapted to be interposed in the light path through the lens and comprising different coding elements to either side of a coding means centre line which intersects the optical axis of said lens, whereby light passing to one side of said central line is coded appropriate to one eye of a viewer and light passing to the other side of said central line is coded to correspond to the other eye of the viewer; and means for selectively arranging said coding means in said light path and away from it.

Another aspect of the invention provides a camera lens comprising a plurality of lens elements in a lens body; coding means comprising different coding elements to either side of a centre line which orthogonally intersects the optical axis of said lens, whereby light passing to one side of said central line is coded appropriate to one eye of a viewer and light passing to the other side of said central line is coded to correspond to the other eye of the viewer; and means for displacing said coding means into and out of the light path through said lens.

Preferably but not essentially the lens is a multi¬ element system and the coding means is placed at or substantially at the nodal point of said lens system. More preferably the lens includes means for moving the positions of the lens elements for variation of the image perceived by said lens in a manner which will change the nodal point of the lens, and means for moving said coding means to restore coincidence or substantial coincidence between said coding means centre line and the nodal point of the lens.

One form of said coding means may, for example, comprise a two-component filter having its left-hand part coloured differently from the right-hand part, in which case the stereoscopic effect will be appreciated by a person using similarly coded filters, one in front of the left eye and the other in front of the right eye.

One form of the invention uses a displaceable coding means in the form of a pair of paddle-like elements having appropriate coloured panels and means for synchronously rotating the two paddle-like elements between a first position in which they are parallel and face towards the subject being viewed through the lens, and an out-of-the-way position in which they each have rotated through 90° to clear the light path through the lens. Preferably they also have a third position in which they are again parallel but face in the opposite direction, such that, whereas in said first position a red filter panel of one of said paddle-like members is alongside a blue or cyan filter panel of the other paddle-like member with the boundary between said red and cyan or blue panels intersecting the optical axis of the lens in a first diametral direction parallel to the axes of rotation of said paddle-like members, in said third position there are adjacent filter panels defined such that a red filter panel on each of said paddle-like members is disposed nearer one end of the boundary between said paddle-like members and a blue or cyan filter panel is nearer the opposite end of said boundary with the line of demarcation between the red filter panel and the blue or cyan filter panel of each of the paddle- like members in this third position coinciding with a line through the optical axis of the lens and perpendicular to said first diametral line.

A further possibility for the displaceability of the coding means comprises having a pair of pivotable filter members on pivot axes which are either coincident or close to one another parallel to a diameter of the lens incorporating the coding means, and able to be displaced between a filtering position in which they have closely adjacent edges defining a boundary between a red filter element and a blue or cyan filter element with the boundary extending along a line diametral of said lens, and an out-of-the-way position in which the lens is free from filtering effect by the two filter elements.

Yet a further possibility for arranging for the coding means to be alternately in the optical path and outside the optical path comprises providing a twin-lens camera in which one lens incorporates a said coding means permanently therein for stereoscopic photography, and another lens in which there is no such coding means and the lens is intended for two-dimensional photography, and light-affecting means able to define a first light path in which the light from said first lens impinges on the film plane, but light through the second lens does not, and a second light path in which light from said second lens impinges on the film plane but light from the first lens does not. Preferably said light-affecting means comprises a movable mirror.

Yet a further possibility for displacing the coding means into and out of the optical path through the lens comprises mounting a coding means having both a red filter panel and a blue or cyan filter panel pivotally for movement into a first position in which the boundary line between said red filter panel and said blue or cyan filter panel coincide with a diameter of the lens, and an out-of-the-way position in which the filter panels are both clear of the lens to allow unfiltered light to pass through the lens.

Yet a further possibility provides for the coding means to be defined by an iris assembly manufactured of transparent filtering material arranged such that when said iris is closed it defines a transparent wall having a dividing line between a first filtering zone of red filter material and a second filtering zone of blue or cyan filter material.

Preferably there are two of said irises, with the projections of the respective boundary lines between their red panels and blue or cyan panels onto a plane perpendicular to the optical axis of the lens mutually perpendicular, and control means for selectively closing a first said iris and opening a second said iris, and vice versa. Preferably the control means for the irises includes a possibility for both irises to remain open for two-dimensional photography. Another possibility appropriate for use with cine- photography or video photography may comprise a switchable coding member having means for rendering the coding element(s) to one side of the centre line of said coding means transparent while the coding element(s) to the other side of the coding means centre line is opaque or at least semi-transparent, and switchable for inverting the transparent state and the opaque or semi- transparent state on to the other coding element of said coding member. For example said switchability may be derived by the use of a liquid crystal layer which can be rapidly switched at will to render the layer opaque or transparent. In this switchable coding system the viewer will require a two component switchable decoding means before his or her eyes, with a left-hand switchable decoding element switched to synchronize with the said coding element corresponding to the light passing to the left eye, and a right decoding element switchable to synchronize with the other coding element.

In a preferred embodiment of the present invention the coding means orientation may be selected between two positions 90° rotated from one another in order that the lens and coding means combination can be used for both "full length portrait" photography and "landscape" photography, and including means for selecting an orientation of said coding means in each of said positions. Preferably the orienting means may comprise an automatic gravity-responsive switching system. However, alternatively, the orienting means may include an electrical (motor driven) or manual switch operated by the user of a camera with which the lens is being used.

In a preferred form of this embodiment of the invention, said coding means may include a weak close-up lens element in order to reduce the depth of field of the entire optical system with said coding means in place, thereby enhancing the stereoscopic effect to be derived by use of said coding means. For example, the weak close- up lens may be coated to represent the coding means optical characteristics, thereby combining both coding means and close-up lens in one.

The combination of a coding means with a weak close-up lens component is particularly useful in the context of an automatic camera such as the so-called 35 mm compact camera, or a 110 format camera, where a generous depth of field results during normal operation of the lens, and where the stereoscopic effect may be enhanced by reducing the depth of field/depth of focus.

In a further variation, the coding means may include a neutral-density filter to cause a "through-the-lens" exposure system of the camera to adopt a wider aperture at which the depth of field can be reduced and the stereoscopic effect enhanced. One possible form of such neutral-density filter may comprise cross-polarising filters which can be adjusted to vary the attenuation of the light passing through said coding means.

A further preferred embodiment of the present invention may comprise a coding means having its separate coding elements of non-uniform light transmission characteristics. For example, some lenses would benefit by part of said coding means further from said central line being opaque, or maybe transparent but of a higher optical density than the part of said coding means near said central line. More preferably the variation in optical density may be gradual between said central line and the perimeter of said coding means.

The coding means may be in the form of a two component filter having a red coding element corresponding to the light passing to the left eye, and a coding element, in this case cyan, corresponding to the light passing to the right eye, for use in combination with viewing decoding means comprising a red filter for the left eye and a cyan filter for the right eye of an observer, wherein the optical density of the filters of the viewing decoding means is higher than the optical density of the filter of the corresponding coding element. Preferably the difference in density is confined to the cyan filter components of both the viewing decoding means and the coding element of the coding means.

The present invention may be applied equally to a complete camera system such as a so-called compact still camera or a sub-miniature camera or a cine camera or video camera, where said coding means is preferably incorporated in the lens system, and also to a removable lens where again the coding means may be incorporated in the lens body which is detachable as a unit from the camera body, for example in the case of a single lens reflex camera.

In order that the present invention may more readily be understood the following description is given, merely by way of example, reference being made to the accompanying drawings, in which:-

Figures la and lb, respectively, show a front elevational view and a side perspective view of a coding means for use with stereoscopic photography, in accordance with the present invention.

Figure 2 is an overhead sectional view of a multi- component lens for a single lens reflex camera, or any still camera with interchangeable lenses, incorporating the coding means for stereoscopic photography in accordance with the present invention; Figure 3 is an overhead sectional view of an alternative form of detachable lens showing alternative positions for the coding means at la and lb, respectively;

Figures 4a and 4b show, respectively, a wide aperture position and a stopped down aperture position of an iris in combination with the coding means, showing the iris in two different positions for enhancement and/or attenuation of the stereoscopic effect;

Figures 5a and 5b show a typical still camera used in the "landscape" mode and in the "full length portrait" mode, respectively, with the orientation of the centre line of the coding means indicated, to illustrate the requirement for orientation of the coding means;

Figures 6a and 6b are a schematic front elevation and a horizontal section, respectively, of a coding means having an automatic orientation action;

Figure 7 shows a first embodiment of displaceable coding means for moving the coding means into and out of a filtering relationship with a camera lens, such that in a first position of filtering the lens is suitable for portrait photography, and in a second filtering relationship the lens is suitable for landscape photography;

Figure 8 illustrates a single lens compact camera incorporating switchable coding means;

Figure 9 illustrates the switchable coding means of the compact camera of Figure 8 in an out-of-the-way position suitable for two-dimensional photography;

Figure 10 illustrates the switchable coding means of the camera of Figure 8 in filtering position for three- dimensional photography;

Figure 11 illustrates a switchable twin-lens camera having a first lens with a coding means and a second lens without a coding means, with a movable mirror for selecting one or other of said lenses to guide light onto the film plane of the camera;

Figure 12 illustrates a single-lens reflex camera having a teleconverter behind the lens and a switchable coding means between the teleconverter and the removable lens;

Figure 13 illustrates one form of the switchable coding means for the camera of Figure 12, in the out-of-the-way position corresponding to two-dimensional photography;

Figure 14 illustrates the coding means of Figure 13 in the filtering position corresponding to stereoscopic photography;

Figure 15 illustrates an iris body for a zoom lens having a switchable coding means in the form of a simple iris, shown open, alongside an aperture-controlling irish shown in an open aperture stop configuration;

Figure 15a is a front elevation of the coding means iris in its open poisition;

Figure 16 illustrates the iris coding means of Figure 15 in filtering position corresponding to steroscopic photography;

Figure 16a is a fron elevational view, schematic and partly exploded, showing the coding means iris in its closed or "stereoscopic photography" position;

Figure 17 illustrates a multiple iris lens in exploded view, with an aperture-controlling iris and two coding means irises to provide for landscape photography when one of the coding means irises is closed and the other is open, and portrait photography when the other iris closes and the first opens; Figure 18 illustrates an exploded view of a zoom lens having a coding means iris shown in partially closed configuration; and

Figure 19 is a perspective view of a video system comprising a video camera, a video cassette recorder, a television set or monitor, and a switching synchronizing controller for both switchable decoding viewing lenses and a switchable coding member requiring synchronous switching.

Referring now to Figures la and lb, there can be seen in Figure la an elevational view of a coding means 1 comprising a left-hand coding element 2 and a right-hand coding element 3.

In practice, the inversion of the light rays through the lens may result in the fact that the right-hand coding element 3 passes light intended for the left eye of the viewer, and vice versa, so the reference, with regard to Figures la and lb, to "left" and "right" is intended simply to denote their orientation as viewed in those drawings and not necessarily to imply the origin of the light rays passing through those coding elements.

The coding element 2 is shown by virtue of its cross- hatching as having a first characteristic appropriate to one eye, and the coding element 3 has its cross-hatching denoting a second characteristic (appropriate to the other eye) , and in this preferred example the coding elements in question are filter sheets one of which is a red filter and the other of which is a cyan filter. The use of red and blue, or red and green, or red and cyan for stereoscopic photography is well known in the art, but we have found that cyan is the preferred colour for the right eye coding and decoding elements. Although polarising filters of opposite polarity are possible for the coding elements, the use of colour filters is preferred as the coding information is then more easily recorded on colour films.

Figure 2 shows an overhead view, but in sectional form, of a detachable lens unit for use with a typical interchangeable lens camera, and comprises at the nodal point of the lens system a coding member 1, of the type shown in Figures la and lb. The left-hand part of the lens body 4 has bayonet pins 5 for attachment of the lens to the body of an SLR camera, and to that left-hand side of the coding member 1 (i.e. behind it) is a two component lens comprising firstly a bi-convex lens element 6 and secondly a bi-concave lens element 7. To the right-hand side (i.e. in front of) the coding member 1 is a three element lens system comprising a bi¬ concave lens element 8 followed by two meniscus lens elements 9 and 10, respectively.

The coding means 1 shown in Figure 2 is removable from the optical path either by bodily removal from the lens body 1 through a suitable closable opening, or by having it displaceably positioned within the lens body 1 so as to be able to be moved by operation of a suitable "stereoscopic in/out" switch on the lens body. Several constructions of such in/out mechanisms are disclosed herein.

Where the switchable stereoscopic effect uses any of these possible ways of removing the coding means from the optical path through the lens body 4, for certain lens designs it may be advantageous for the "stereoscopic in/out" switchability to control also the imposition of a further optical element in the optical path for the purposes of diminishing the depth of focus for reasons which will be explained later. This depth of focus diminution may, for example, be effected by use of a weak close-up lens which is also switchable into and out of the optical path (for example by being mounted on the same carrier with and directly contacting the coding member 1, or a neutral density filter of fixed density, or a variable density filter, for example of the cross- polarising type) .

As indicated above, the best results for stereoscopic photography in accordance with the present invention can be obtained when the coding means is on a nodal point of the lens. However, Figure 3 shows two alternative possibilities in which the same multi-element lens assembly 6, 7, 8, 9 and 10 may be used in conjunction with a coding means la positioned behind the lens body as a whole or a coding means lb positioned in front of the lens. In either case the coding means is associated with a protective lens assembly comprising weak lens elements 11a and 12a in the case of the coding means la mounted behind the lens body and lib and 12b in the case of the coding means lb mounted in front of the lens body.

In the case of the coding means la shown positioned behind the lens body, it is particularly advantageous for the protective lens elements 11a and 12a together to define a low power telephoto attachment (teleconverter) which can be used in association with the main lens body 4. Such an arrangement is shown in Figure 12.

The advantage of the systems shown in Figure 3 is that the removable coding element la or lb, respectively can be outside the lens body 4 and hence the lens body as a whole does not require modification. However, this provides a less dramatic stereoscopic effect because of the displacement of the coding means away from the nodal point of the main lens in use.

The stereoscopic effect to be achieved in accordance with the stereoscopic photographic process made possible with the present invention involves the use of colour separation techniques in order to generate colour fringing of those parts of the image which are out-of- focus, whereas no such fringing occurs where the image is in focus.

The fringing in the out-of-focus regions of the image is clearly polarised by colour separation into one component applicable to the left eye and another component applicable to the right eye, and the brain of the viewer causes the image to be appreciated as having a degree of perspective, although in fact there is no lateral separation of optical paths to give a true perspective view to the eyes of the viewer.

It is clear that the stereoscopic effect depends upon a distinct difference being generated between the field of the image which is in focus, and those two fields of the image which correspond to, on the one hand the part of the subject which was beyond the focal distance and, on the other hand the part of the subject which was closer than the focal distance. In order to enhance the differences between these three parts of the image, the degree of "out-of-focus" achieved in the parts of the image corresponding to the near and far regions of the subject should be enhanced, and this is best achieved by diminishing the depth of field in order to ensure that provided the main subject, for example a human figure in the case of a portrait, is correctly in focus then the background and any nearer foreground regions will be clearly out-of-focus and will be subject to acute red fringing and blue, or green, or cyan fringing (depending on the precise colour of the "right eye" coding element.

It is for this reason of short depth of field that the stereoscopic effect is enhanced when using a telephoto lens as compared with using a wide angle lens and this effect is exploited in the camera shown in Figure 11. When an image photographed using a camera or lens in accordance with the present invention is viewed without filtering spectacles, the image has a relatively normal flat aspect with visible lack of focus in the foreground and background regions evident as distinct blue and red bands at the fringing regions.

When, on the other hand, the same image is viewed using viewing spectacles of the appropriate filtering colours, the "in-focus" region of the image is visible very clearly, and is distinctly in front of the out-of- focus background region and behind the out-of-focus foreground parts. The pronounced colour fringing resulting from the coding means gives a sense of perspective in providing the right eye with a view of the foreground and of the background which differs from that of the left eye, and it is this which gives the perceived stereoscopic effect.

It is preferred that the filters used for both the decoding viewing spectacles and the coding means in the lens be such that together the left and right elements of each system (the viewing spectacles on the one hand or the coding means on the other hand) give a cumulative "white light" effect so that the colours of the image are not distorted.

If the image is viewed through decoding spectacles which do not have precisely the correct colours, then provided the red filters are used on the correct sides of the coding system and the decoding system there will be a stereoscopic effect but with some "colour cast" effect. This "colour cast" is minimised when the preferred red and cyan filter elements are chosen.

Not only is it possible for the colours of the coding and decoding systems to differ slightly from one another, it is also possible for the same colours to be used for both coding and decoding but for the filter density of the decoding system to be different from that of the coding system.

Although, as indicated above, the stereoscopic effect is appreciable thanks to the fringing in the out-of-focus areas, it is additionally possible for a half prism or a bi-prism to be installed in the lens system in order to generate some degree of stereoscopic effect even in image areas which remain in focus.

As indicated above, it is important for the depth of field to be diminished in order to enhance the stereoscopic effect and Figures 4a and 4b are intended to illustrate the variation in diaphragm iris configuration for varying the depth of field. Figure 4a shows the wide aperture position which corresponds to diminished depth of field and hence enhanced stereoscopic effect, whereas Figure 4b shows the small aperture position which will give minimal stereoscopic effect because of the generous depth of field. Variation of the iris aperture may be achieved manually in the case of a camera and/or lens which can be fully overridden, whereas in the case of a camera with a fully automatic exposure control it may be necessary to deceive the automatic exposure system into operating with a wider aperture than would otherwise be the case, simply in order to reduce artificially the depth of field and thereby to enhance the stereoscopic effect. Thus whereas Figures 4a and 4b show wide open and stopped iris apertures, respectively, the way in which this is achieved may be either by rotation of the manual aperture control 13 to stop down or to open up the aperture, or by reducing the amount of light passing through the lens system in order to persuade the iris 14 to open automatically. This aperture-induced diminution of the depth of field is independent of the "supplementary lens"-induced diminution described above with reference to Figures 2 and 3. However, the two effects may, if desired, be used together.

Figures 5a and 5b illustrate a typical camera which in Figure 5a is oriented for photographing in the "landscape" format (where the width of the image is greater than its height) and in Figure 5b is oriented for "full length portrait" photographing where the height of the image is greater than its width.

In order to maintain the correct left-to-right coding separation of the image, the switchable coding means needs to be maintained with its central line 15 vertical as shown in Figures 5a and 5b.

Figure 6 shows that the coding means 1 has attached thereto an operating lever 16 which can move rightwardly or leftwardly along the directions of the double-headed arrow 17. Figure 6b shows a section on the line B-B of Figure 6a.

The operating lever 16 may be operated manually in order to ensure that the central line 15 remains vertical, for example by operation of a control on the exterior of the lens body having two extreme positions marked "portrait" (P) or "landscape" (L) shown in solid line and in broken line form, respectively in Figure 6.

Alternatively there may be a gravity-responsive switch such as a mercury switch which may be activated when the camera exposure system is switched on and may automatically drive the coding member 1 in rotation to bring its centre line 15 to an extreme position in which it is as near as possible vertical. On the assumption that the camera user will be holding the camera either horizontal or vertical, the orientation of the centre line 15 in this extreme position will be appropriate.

A further development of the orientable coding member device is that the same control switch which allows selection between "full length portrait" and "landscape" photography may additionally include a third position corresponding to the "stereoscopic out" configuration in which the coding means 1 is moved into a position in which it no longer intersects the optical axis of the lens system or even the paths of the extreme rays of the bundle passing through the lens.

Figure 7 illustrates a possible form of coding means which can readily be switchable into and out of the filtering position for stereoscopic and two-dimensional photography, respectively, but equally can be selected for both landscape photography and full-length portrait photography.

The device there shown comprises a pair of paddle-like members 31 and 32 each rotatable on respective spindles 33 and 34. The spindles have respective pinions 35 and 36, with pinion 36 on a shaft 37 driven from a control wheel 38 outside the lens body 39. The glass lens elements are illustrated by the dotted line circle 40.

Each of the paddle-like elements 31 and 32 is divided up into a larger rectangular filter panel (3la-red and 32a-blue or cyan) , as well as two smaller rectangular filtering panels 31b and 32b in blue or cyan filter material, and 31c and 32c in red filter material.

Clearly, in the configuration shown in Figure 7 the larger red filter panel 31a of paddle-like member 31 lies to the left of the boundary 41 between the two paddle- like members and the blue or cyan larger filter panel of the paddle-like member 32b lies to the right of said boundary 41 such that the boundary 41, coinciding with a diameter of the lens 40, defines the coding means centre line of vertical configuration for landscape photography, when in this position the two paddle-like members are parallel (in this coplanar) .

When each of the paddle members 31 and 32 has been rotated through 90° about its spindle 33 and 34, respectively, the paddles are in their out-of-the-way position clear of the light path through the lens 40, and non-stereoscopic photography (i.e. two-dimensional) is possible.

Upon a further 90° rotation in the same sense to bring the two paddles 31 and 32 in the opposite relationship to that shown in Figure 7, the two upper blue or cyan filter panels 31b and 32b will come together to define a substantially continuous cyan filter panel above a horizontal diameter of the lens 40, and equally the two red filter panels 31c and 32c will have come together to define a substantially continuous red filter panel below the horizontal diameter. This will then allow the entire lens to be rotated in the clockwise direction through 90° in order to enable full-length portrait photography to be taken (bearing in mind that the conventional 35 mm format is not square so that rotation of the camera to bring the major axis of the frame format vertical for full-length portrait photography is necessary, but in this case by appropriate manupulation of the control wheel 38 the switchable coding means comprising the two paddles 31 and 32 can be selected accordingly) .

If desired, the control wheel 38 may be replaced by a motor-driven pinion which can be electrically selected to the appropriate one of the three positions just described.

Figure 8 illustrates a single-lens reflex camera 50 having its film plane 51 in register with both (i) a removable lens 52 and (ii) a removable teleconverter 53 which has an integral switchable filter means 54. With the teleconverter 53 absent, the lens 52 operates as a wide-angle lens so no effective stereoscopic photography is possible. However, with the teleconverter 53 in place the switchable coding means 54 will allow either conventional photography (two-dimensional) using the telephoto combination of lens 52 and teleconverter 53, or stereoscopic photography using that same combination, depending on the state of switching of the switchable coding means 54. As explained elsewhere herein, the reduced depth of field with telephoto lens focal lengths is more conducive to stereoscopic photography than is the more generous depth of field with a wide-angle lens.

The coding means is illustrated in Figure 9 as comprising a left-hand semi-circular red filtering element 55a and a right-hand blue or cyan semi-circular filtering element 55b which are both pivoted about a common axis 56 lying on one end of the vertical diameter through the lens 52. This common pivot allows the two coding filter elements 55a and 55b to be moved from the out-of-the-way position shown in Figure 9 to the filtering position shown in Figure 10 upon appropriate manipulation of the switching control.

Although a common pivot axis has been illustrated, it may be geometrically preferable to have two separate pivot axes for the respective filter elements 55a and 55b which are close to one another and mutually parallel, rather than being coincident as shown.

Figure 11 illustrates a switchable twin-lens compact camera 60 having within its camera body 61 a wide-angle lens 62 (preferably one having a focal length of 35 mm) , and a telephoto lens (i.e. longer than 50 mm) 63, preferably having a focal length of 70 mm, and incorporating a coding means 64. A fixed mirror 65 is capable of deflecting the light entering through the telephoto lens 63 back towards a movable mirror 66, provided the mirror 66 is in the full- line position shown in Figure 11. This movable mirror 66 then reflects the light from the fixed mirror 65 onto the film plane 67. The presence of the mirror 66 will have, however, block light from the wide-angle lens 62 from reaching the film plane 67.

When the movable mirror 66 is moved to the broken line position shown in Figure 11, this path of light from the telephoto lens 63 to the film plane 67 is interrupted whereas the light path from the wide-angle lens 62 (not incorporating any coding means) to the film plane 67 is liberated.

As a result, when working with the wide-angle lens 62 (i.e. with the mirror 66 in the broken line position) when there would be no benefit from the stereoscopic effect, the light path from the subject to the film plane 67 does not intersect a coding filter such as 64.

On the other hand, when working with the telephoto lens 63 the presence of the coding filter 64 is able to take advantage of the shorter depth of field of the telephoto lens and can give the desired stereoscopic effect.

This is in some ways equivalent to the imposition of a neutral density filter or cross-polarising filter, as described above, in the light path through the lens when the stereoscopic effect is required.

Figure 12 shows an alternative form of compact camera in which the teleconverter is installed in the camera body (whereas in Figure 8 the teleconverter was outside the camera body) . This form of the compact camera 70 has a switchable coding means 71 between its lens 72 and the teleconverter 73 so that with the coding means 71 in its filtering position the image perceived at the film plane 74 will exhibit stereoscopic effect which, as with all embodiments of this invention, can be appreciated by viewing the resulting photograph using appropriately coded filtering spectacles, whereas with the switchable coding means 71 in its out-of-the-way position (shown in Figure 13) no such stereoscopic effect will be perceived.

Figures 13 and 14 show that the movement of the filter coding means 71 between the out-of-the-way position of Figure 13 and the filtering position of Figure 14 involves swinging the circular assembly of the red left- hand coding filter element 75 and the blue or cyan coding filter element 76 bodily from a position clear of the lens 72 (Figure 13) to a position in front of the lens and hence carrying out the appropriate filtering effect for stereoscopic photography (Figure 14) by pivoting about an axis 77 which is well clear of the outline 78 of the lens body.

Although in many of the drawings the filter has been illustrated as a circular assembly of two semi-circular filter elements, it is adequate for the filter panels to be of rectangular form which together define an overall filter of substantially 35 mm frame format.

Figure 15 shows a perspective view of an iris holder to go in a telephoto lens 80, and illustrates that at the front of the lens is an aperture-controlling iris 81 shown stopped down to a small aperture, and alongside it a four bladed coding means iris 82 which is fully open in Figure 15 but is closed in Figure 16. In practice this closed position of the iris 82 shows that it comprises a first cyan iris member 82a and a second adjacent cyan iris member 82b, as well as a third red iris member 82c and a fourth red iris member 82d, where all four of the iris members are of transparent material coloured with the appropriate filtering effect. When the iris 82 is shown in the closed position as shown in Figure 16, the image perceived at the film plane of the camera will exhibit stereoscopic effects, whereas with the iris 82a open as shown in Figure 1 there will be no stereoscopic effect.

In order to illustrate the construction of the four blades 82a,82b,82c and 82d of the iris 82, Figure 15a shows a front elevational view of the iris when open, and Figure 16a shows a front view, in schematic exploded form, of the iris 82 when closed.

As shown in Figure 16a, each iris blade element has a pivot pin 102 and a cam follower pin 103 which is driven by a cam slot on the iris ring.

In either of the two positions (Figures 15 and 16) of the colour filtering iris 82, the aperture-controlling iris 81 will select the appropriate wide aperture for the exposure required.

Figure 17 illustrates a multi-component iris assembly which can be incorporated in a zoom lens so as to provide, in a relatively compact manner, a switchable stereoscopic facility which can additionally be converted between landscape and full-length portrait formats.

The exploded view in Figure 17 shows a first ring component A having a plurality of sockets to receive the pivot pins of iris elements of an aperture-controlling iris B. Anti-clockwise motion of the ring A, driven by the bar 90 having upstanding end tabs 91 to engage the conventional aperture ring, carries the iris elements of iris B around the axis of the lens such that cooperation of the various drive pins 92 of the iris elements of the iris B with the cam slots 93 of the stationary ring C will move the iris elements of the aperture-controlling iris B towards a wide aperture condition at which the depth of focus will be shortest and stereoscopic effects can be best appreciated. A wide aperture of f 2.8 may be used with advantage.

A rotating ring D, again having a plurality of sockets to receive the pivot pins of the iris elements of a landscape stereoscopic filter iris E, is driven by the continued rotation of the ring A beyond the position in which it has opened the aperture-controlling iris B. A tab 94 on the ring D is for this purpose engaged by an appropriate end of the cam ramp 95 of the ring A.

The stereoscopic filter iris E is a more complex form of the iris 82 illustrated in Figures 15 and 16, and described above.

A further stationary cam ring F has cam slots 96 cooperating with the drive pins 97 of the landscape filter iris E in order to close the iris E upon continued movement of the ring A from a position corresponding to a threshold aperture stop (in this case f 2.8) at the aperture-controlling iris B.

A further drive ring G is rotated by the continued rotation of ring D, in order to close the full-length portrait filter iris H while at the same time this continued rotation of the control ring D of the landscape filter iris E will cause the landscape iris to re-open.

The operation of the portrait iris H results from cooperation of the drive pins 98 of its iris members with the slots 99 in a fixed final cam ring j.

It will be appreciated that the configuration illustrated in Figure 17 provides for progressive opening of the aperture of the iris B to the f 2.8 position (chosen for convenience in this case although any other wide aperture stop can be selected for the onset of stereoscopic effects) , and then continued rotation will firstly close the landscape iris E while the portrait iris H is open, and then open the landscape iris E and close the portrait iris H. It is thus possible to select stereoscopic effects in and out, and to switch between the landscape coding means E and the portrait coding means H all by simple rotation of the aperture control ring.

Figure 18 shows a conventional telephoto lens in which the aperture-controlling iris is illustrated at 110 but space is available for installation of the various iris components D to J can then be installed in front of the fixed control ring C which is shown in Figure 17.

Although the arrangement illustrated in Figure 18 shows the aperture-controlling iris with sufficient space for the landscape filter iris and the portrait filter iris be mounted alongside it, it is preferable for the filtering irises constituting the coding means to be positioned at the nodal point of the lens, in which case it is advantageous for some floating mechanism to be incorporated so that as each of the two filter irises closes to exert its filtering action for the purposes of stereoscopic photography, that iris moves into the nodal point of the lens. Such a floating mechanism is within the ability of the skilled expert in the art and is therefore not illustrated in detail in the present application.

Yet a further possibility for switching in and out of the filter coding means involves creating the filter disc of Figure 1 using liquid crystal diode coating material which can be energised electrically to become opaque, as in an LCD clock display. However, in this case the coating on the half 2 of the disc will show as a transparent red and the coating on the other half 3 of the disc will show as a transparent blue or cyan zone. A switch on the lens body or camera body in which such a disc is incorporated can be operated to switch in and out the stereoscopic effect.

By having two such discs virtually superposed and concentric at the nodal point of the lens, with separate energisation of each disc and with the boundary lines between their zones 2 and 3 perpendicular, a portrait/landscape switching is possible.

As a variation, separate LCD coatings, with separate perpendicular boundary lines, may be applied to the opposite surfaces of the same substrate.

Yet a further possible variation would be to employ a single LCD coating as a tricolour dot matrix, or even a simple two colour red/cyan dot matrix LCD coating in which the dots can be darkened in different zones so that a "landscape" left-red/right-cyan distribution can be employed in one state of energisation and a simple top-red/bottom- cyan distribution can be employed in a second state of energisation to allow the camera to be rotated anticlockwise for portrait photography.

When a three colour dot matrix is used with primary colours for the dots, it would be possible to use more than two energisation states so as to permit an overall colour filter configuration to be selected for "colour cast" effects. Equally colour filters of special shapes can be selected, if desired.

With this alternative possibility, the camera may be used either in the landscape configuration of Figure 5a or the portrait configuration of Figure 5b, and in either event it may either produce accurate full colour images, preferably with the minimum extent of out-of-focus effect (in the "stereoscopic out" selection) or may produce images with distinct red/cyan (or red/blue or red/green) fringing in the out-of-focus regions which will be exaggerated for the purposes of enhancing the stereoscopic effect.

By choice of the appropriate matching of the filtration colours of the left and right eye pieces of the viewing spectacles and of the left and right coding elements, the colour cast resulting from the presence of the coloured filters can be reduced.

As indicated above, in order to minimise the colour cast it may be appropriate to weaken or to strengthen the filtration density of the cyan (or blue or green) elements of the coding or decoding means.

As indicated above, the present invention is applicable both to a high quality detachable lens for an interchangeable lens type or single lens reflex (SLR) camera, and to compact cameras in which a less critical lens is built into the camera body. In addition to referring to a 35 mm compact camera, we intend the term

"compact camera" equally to cover roll film cameras (120/220) sheet film cameras, sub-miniature cameras and 110 size cameras, and in the case of any of these formats the lens may be either a fixed focus lens or a variable focus lens. Whereas the fixed focus lens does have a high depth of field, the combination of a weak close-up lens with the displaceable stereoscopic coding member allows for the depth of field to be diminished for the purposes of stereoscopic photography in accordance with the present invention.

When such a weak close-up lens is used, having a power a fraction of and determined by the power of the prime or main lens, the focal distance of the lens will change and the depth of focus will be relatively short.

Also as stated above, the invention may equally be applied to an "instant film" type of camera in which the film includes a peelable chemical sachet which allows the image to be developed in the camera prior to delivery of the developed and fixed photographic paper.

However, a way in which the absolute minimum of colour distortion effect can be appreciated is proposed in Figure 19 for use with a video camera or cine camera where synchronous switching between left and right halves of the coding member and the left and right eye pieces of viewing spectacles can be effected.

Figure 19 shows a video system, using a video cassette recorder (VCR) , but equally it can be applied to a closed circuit television (CCTV) system without a VCR and to a cine camera with appropriate synchronization of switching, but preferably with synchronization signals being recorded on the film.

The camera 18 has its output connected via a lead 19 but there could just as easily be an RF signal both to a video cassette recorder 20, and simultaneously along lead 21 to a synchronizing controller 22 for the coding and decoding systems.

The coding means 23, which in this case for simplifying the schematic illustration is shown as being exterior to the camera lens body, is driven by way of a lead 24 by the coding/decoding controller 22.

An output lead 25 from the VCR 20 applies the signal to the TV set or monitor 26, and in synchronism therewith the controller 22 feeds a signal to a pair of decoding viewing spectacles 27 by way of a lead 28.

When operating in the CCTV mode there will be no recording of the signal on the video cassette tape in the VCR 20. Instead there will be simultaneous application of the audio/video signal through the inlet port of the VCR 20 and on to the TV monitor through the lead 25, and application of the same audio/video signal to the synchronizer 22 along the line 21 and simultaneous emission of (i) a coding control signal via line 24 to the coding member 23 and (ii) a decoding control signal via line 28 to the viewing spectacles 27.

In operation, the transparency of the two coding elements of the split coding means 23 is switched between a high level and a low (or even opaque) level and this may be achieved by means of a liquid crystal display (LCD) coating on the surface of each coding element of the coding member 23. The same LCD switching system exists on the eye pieces of the viewing spectacles 27 such that when the image corresponding to the light passing to the right eye is being viewed by the image receiver, such as a charge coupled device (CCD) or a camera tube, by virtue of that side of the coding member 23 being transparent and the other side blocked to opaque by coloration of the LCD coating, the left eye piece of the viewing spectacles 27 is coloured to be opaque and the right eye piece is at maximum transparency. Immediately thereafter the synchronizing unit 22 switches over to the other coding element of the coding member 23 and to the other eye piece of the viewing spectacles 27 so that first of all the right eye will see only the image appropriate to the right eye and then the left eye will see only the image appropriate to the left eye, following which the cycle will repeat and will do so at a frequency of the order of 30 cycles per second.

Adaptation of the system to operate in the "time shift" mode will involve sophistication of the VCR so that it can receive and record synchronizing pulses emitted by the code/decode switching synchronizer 22. For this purpose there may be the need for an additional lead between an output of the code/decode switching synchronizer 22 and a coding synchronizer input of the VCR. This same input/output socket of the VCR will supply the synchronizer 22 with the recorded synchronizer signal to ensure that the same switchable viewing spectacles 27 can be used for viewing a recorded stereoscopic sequence.

It will be appreciated that the switchability may be derived in Figure 19 by arranging for both sides of the coding means filter 23 and both eyepiece filters of the spectacles 27 to be at maximum transparency simultaneously.

The system of Figure 19 can be used for direct transmission of stereoscopic broadcasts simply by incorporating the code/decode synchronizer signal in the transmission so that the signal received by the socket to which the input audio/visual signal 21 is shown as being connected will emanate from the receiver aerial rather than from a camera lead and will drive the synchronizer 22 to switch the spectacles 27 for appropriately decoding the image on the television screen.

The quality of a stereoscopic signal for video use will of course be enhanced with higher definition television cameras and monitor screens.

The switching system of Figure 19 can, of course, be incorporated in a twin-lens stereoscopic video or cine¬ camera.

Claims

C A I M S

1. A camera (18) (50) (60) (70) including a lens having a duplex optical path from subject to the photosensitive element of the camera; coding means (23) (54) (64) (71) adapted to be interposed in the light path through the lens and comprising different coding elements to either side of a coding means centre line which intersects the optical axis of said lens, whereby light passing to one side of said central line is coded appropriate to one eye of a viewer and light passing to the other side of said central line is coded to correspond to the other eye of the viewer; and means for selectively arranging said coding means in said light path and away from it.

2. A camera according to claim 1, and including an additional lens without a said coding member interposed in its optical path, and means for switching between the first mentioned lens and said additional lens to pass light to the film plane of the camera.

3. A camera according to claim 2, wherein said first mentioned lens is a wide-angle lens and the additional lens is a telephoto lens or a zoom lens.

4. A camera lens (4) (40) (52) (63) (72) (80) comprising a plurality of lens elements in a lens body; coding means (1) (31,32) (55a,55b) (64) (75,76) (82a,82b,82c,82d) (E or H) comprising different coding elements to either side of a centre line which orthogonally intersects the optical axis of said lens, whereby light passing to one side of said central line is coded appropriate to one eye of a viewer and light passing to the other side of said central line is coded to correspond to the other eye of the viewer; and means for displacing said coding means into and out of the light path through said lens.

5. A lens according to claim 4, wherein said coding means is positioned at or substantially at the nodal point of said lens.

6. A lens according to claim 4, wherein the coding means comprises at least one element (31,32) (55a,55b) (75,76) (82a,82b,82c,82d) pivoted between a first position in which it lies in the path of light through the lens, and an out-of-the-way position clear of said light path.

7. A lens according to claim 6, wherein said pivotal movement comprises movement between a first position in which the said at least one element (31,32) lies in a plane transverse to the optical axis of the lens, and said out-of-the-way position in which it lies in a plane perpendicular to said transverse plane.

8. A lens according to claim 7, wherein said element (31) comprises a plate of filter material divided along a line parallel to the axis (33) of pivoting of said plate into a first panel (31a) having an outer edge remote from said axis which is parallel to said axis (33) and in which the plate has a red filter characteristic, and a second panel having an outer edge remote from said axis and over a first part (31c) of which the filter material has red filter characteristics and along a second part (31b) of which the filter material has blue or cyan filter characteristics, and the coding means further comprises a second said plate (32) having a first panel (32a) adapted in one position of said plates to lie alongside the first panel (31a) of the first plate and having a blue or cyan filter characteristic, and a second panel with a red first part (32c) and a blue or cyan second part (32b) adapted to lie adjacent said second and third parts (31b and 31c) of the first plate in a third position of said plates 180° displaced from said first position; wherein in said third position of said plates the boundary between the first and second parts (31b,31c and 32b,32c) of the two second panels is continuous and extends perpendicular to the axes of rotation (33,34) of said plates; and including means (37,38) for rotating said plates between said first position, said out-of-the-way perpendicular second position, and said third position.

9. A lens according to claim 6, and wherein said coding means comprises at least one filter element

(55a,55b) (75,76) pivotable about an axis parallel to the optical axis of said lens, between said first and out-of-the-way positions, and wherein in said first position the lens optical path is completely in register with filter material having a red characteristic to one side of said central line and a blue or cyan characteristic to the other side of said central line.

10. A lens according to claim 9, and wherein said coding means comprises an iris (82) consisting of iris elements (82a,82b,82c,82d) formed of optical filtering material, with each of said iris elements pivotable about its own pivot axis between said out-of-the-way position, and said first position in which all of the iris elements cooperate to close the light path by means of the filter material of the iris elements, and are arranged such that the closed iris has a red filter characteristic to one side (82c,82d) of said central line and a blue or cyan filter characteristic to the other side (82a,82b) of said central line.

11. A lens according to claim 10, and including an aperture-controlling iris (81) (B) in addition to said coding means iris (82) (E) , and drive means (90,95,94) interconnecting said aperture control iris and said coding means iris whereby over a range of aperture stops of said aperture control iris the coding means iris (E) remains in said out-of-the-way position, and upon attainment of a threshhold wide aperture stop position of said aperture control iris (B) further operation of the aperture control iris drive closes said coding means iris (E) .

12. A lens according to claim 11, and including a further coding means iris (H) mechanically linked to the first mentioned said coding means iris (E) whereby said first mentioned coding means iris is in its said first position only while said further coding means iris is in its out-of-the-way position, wherein said further coding means iris is in its said first position only while said first mentioned coding means iris is in its out-of-the-way position; and wherein the projection of the central line of said first mentioned coding means iris (E) and the projection of the central line of said further coding means iris (H) onto any plane perpendicular to the optical axis of the lens are mutually perpendicular.

13. A lens according to claim 12, wherein said further coding means iris is also driven by said aperture control iris (B) whereby movement of the aperture control iris drive beyond said threshhold wide aperture stop position firstly closes said first mentioned coding means iris (E) to its first position while the further coding means iris (H) is in its out-of-the-way position, and then still further movement of the aperture control iris (B) opens said first mentioned coding means iris (E) and closes said further coding means iris (H) to its first position.

14. A lens according to claim 13, wherein said lens is a zoom lens and means are provided for varying the axial positioning of said first mentioned coding means iris and said further coding means iris along the optical axis of said lens for ensuring that when either of said first mentioned and further coding means irises arrives at its first position, that coding means iris is at the nodal point of the lens.

15. A camera according to claim 1 or a camera lens according to claim 6 or 7, and further including a close-up lens switchable between an operative position in which light passing along the optical path through the lens also passes through both said coding means and said close-up lens, and an inoperative position in which such light passes along the optical path without encountering either the close-up lens or the coding means.

16. A camera according to claim 1 or a camera lens according to claim 6 or 7, and further including a neutral density filter switchable between an operative position in which light passing along the optical path through the lens also passes through both said coding means and said neutral density filter, and an inoperative position in which such light passes along the optical path without encountering either the neutral density filter or the coding means.

17. A camera according to claim 1 or a camera lens according to claim 6 or 7, and further including an adjustable cross-polarising filter in the optical path through the lens and adjustable between an aligned configuration in which a higher amount of light passes along the optical path through both said coding member and said cross-polarising filter, and a cross-polarised condition in which a lesser quantity of light passes along the optical path through the cross-polarising filter and the coding means.

18. A camera according to claim 1 or 2 or a camera lens according to any one of claims 4 to 10, and including means (17) for rotating the coding means relative to the camera or camera lens in which it is incorporated, whereby it may be rotated through 90° between a "landscape" position in which the width of an image is greater than its height and a "portrait" position in which the height of an image is greater than its width.

19. A camera or camera lens according to claim 18, and including gravity responsive means for driving said coding member between said first and second positions 90° apart, and means for selecting that one of said positions which is nearer to the vertical than is the other.

20. The combination of a camera according to claim 1 or 2 or a camera lens according to any one of claims 4 to 10, with a viewing decoder means having decoder elements appropriate to the left eye and to the right eye of an observer, wherein the optical density of at least one of said decoder elements is different from that of the corresponding side of the coding means.

21. A combination according to claim 20, wherein the optical density of said coding element which is blue or green or cyan, is different from the optical density of the corresponding said coding element.

22. A camera according to any one of claims 1 to 3 or a camera lens according to claim 4 or 5, wherein each of said coding elements has a liquid crystal coating, and including means for switching between a first configuration in which a said coding element is transparent and a second configuration in which that coding element is opaque.

23. A camera or camera lens according to claim 22, wherein in said first configuration a first one of said coding elements is transparent while the second is less transparent or even opaque, and in said second condition said second coding element is transparent and the first coding element is less transparent or opaque.

24. A camera or camera lens according to claim 22, and including separate liquid crystal coatings having the boundary between the elements formed by one said coating perpendicular to the boundary between the coding elements formed by the second coating; and including switching means for energising said coatings alternately or not at all.

25. A camera or camera lens according to claim 22, in combination with viewing spectacles having liquid crystal-coated eye pieces and synchronizing switching means for ensuring that the right eye piece is transparent while the corresponding coding element is also transparent and simultaneously the other eye piece and coding element are less transparent or opaque, and vice versa.