GB2415265A - Adjustable stereoscopic viewer with rotatable prisms - Google Patents

Abstract

A stereoscopic viewer for viewing in three dimensions a scene defined by a pair of stereoscopic two dimensional mutually adjacent co-planer images, comprising a pair of eye pieces each of which includes at least one prism 21, 22, 34, 35. The prisms are substantially identical and adapted and arranged to be contra-rotateable for producing relative movement between two images as seen through respective eye pieces of the pair so that they are mutually superimposed, thereby to provide a three dimensional image of the scene as viewed. In a preferred embodiment each eye piece comprises a pair of prisms 21, 22, 34, 35.

Description

Adjustable Stereoscopic Viewer This invention relates to adjustable

stereoscopic viewers and more particularly it relates to stereoscopic viewers which use prisms.

Stereoscopic viewers which use prisms, hereinafter called prismatic stereoscopic viewers, are one kind among many different kinds of stereoscopic viewer. Known prismatic stereoscopic viewers, are used to view scenes defined by a pair of co-planer two dimensional stereoscopic adjacently positioned images, and comprise preset binocular eye pieces which serve to cause the images as viewed to converge so as to be mutually superimposed thereby to produce a single three dimensional image when the scene is viewed at one predetermined range.

For a given prism setting, a viewer must therefore be positioned a predetermined distance from a scene to be viewed and must be free to move back and forth to assume this position.

Moreover, because stereoscopic images can be presented in different sizes using many different kinds of media, the user of such a viewer must therefore make appropriate viewing distance adjustments to suit the image size presented. Physical constraints, such as the wearing of spectacles which limit the spectacle wearer's range of view, or an inappropriate distance between fixed seating and a stereoscopic image display, also introduce problems which may make known prismatic stereoscopic viewers impracticable for general use.

Additionally, with viewers of this kind a user may become confused as to how to move in order to make the appropriate distance adjustment, even if the user has freedom to move about. - 2

It is an object of this invention to provide a stereoscopic viewer which is adjustable, whereby there is no need for relative positional adjustment between a scene to be viewed and a viewer and whereby the associated disadvantages which result are obviated at least in part.

According to the present invention a stereoscopic viewer for viewing in three dimensions a scene defined by a pair of stereoscopic two dimensional mutually adjacent co-planer images, comprises a pair of eye pieces each of which includes a prism, the prisms being substantially identical and adapted and arranged to be contra- rotateable for producing relative movement between two images as seen through respective eye pieces of the pair so that they are mutually superimposed, thereby to provide a three dimensional image of the scene as viewed.

The term prism as used herein includes multi element prisms and prisms which include curved surfaces as may be used to improve optical performance, for example to correct for optical aberrations.

Although a viewer with one prism for each eye is generally satisfactory, a preferred embodiment comprises a pair of prisms for each eye and according to this embodiment a stereoscopic viewer for viewing in three dimensions a scene defined by a pair of stereoscopic two dimensional mutually adjacent co-planer images, comprises a pair of eye pieces at least one of which includes a pair of prisms through which the scene is viewed, the prisms being contra-rotateable for mutually superimposing the two images as seen through the eye pieces thereby to provide a resultant three dimensional image of the scene as viewed.

A stereoscopic viewer according to the invention thus has the advantage that a three-dimensional image may be produced without any need for undue relative positional adjustment between the viewer and a scene to be viewed.

The eye pieces may each comprise a front prism and a rear prism through which the scene is viewed, the front prisms being arranged to be adjustably rotateable via a first mechanism and the rear prisms being arranged to be independently adjustably rotateable via a second mechanism, whereby consequent upon appropriate adjustment of the two mechanisms the image as seen through the eye pieces are mutually superimposed so that a three dimensional image of the scene as viewed through the eyepieces is produced.

The first and second mechanisms may be similar, each comprising two similar gear trains which overlay each other in adjacent parallel planes.

Conveniently some gears of each train may be arranged mutually to align and are mounted for independent rotation on the same shaft.

The prisms may be similar and comprise angularly truncated cylinders each mounted coaxially within an annular gear, so that the eye pieces each comprise a pair of mutually aligned annular gears with the annular gears in which the front prisms are mounted being arranged in one gear train and the annular gears in which the rear prisms are mounted being arranged in the other gear train.

The first and second mechanisms may comprise first and second toothed thumb wheels by means of which the front and rear prisms respectively are a rotated via the gear trains.

Alternatively, the first and second mechanisms may comprise rack and pinion adjusters wherein the pinions form a part of respective gear trains and the racks each include an adjuster lever, or push rod by means of which the front and rear prisms respectively are a rotated via the gear trains.

The prisms may be made of glass or an optically stable plastics lens material.

The viewer may additionally comprise lens means arranged in front of the prisms of each eye piece, and for behind of the prisms of each eye piece, andior between the prisms of each eye piece, so as produce a magnified three dimensional image.

The lens means may be adjustable for the purposes of image framing and/or focusing.

The viewer may comprise housing means in which the prisms and other parts of the viewer are mounted.

Some embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which; Figure 1, is a perspective view of an adjustable stereoscopic viewer which comprises a first embodiment of the invention, Figure 2, is a front view of gearing within a half casing which forms a part of the viewer as shown in Figure 1, Figure 3A, is a front view on a line A-B of a geared prism housing forming one part of the gearing shown in Figure 2, Figure 3B, is a sectional side view on the line A-B of the geared prism housing shown in Figure 3A, Figure 4A, is a another front view on a line C-D of the geared prism housing shown in Figure 2, Figure 4B, is a sectional side view on the line C-D of the geared prism housing shown in Figure 4A, - 5 Figure 5A, is a front view on a line E-F of gearing which forms a part of the gearing shown in Figure 2, Figure 5B, is a sectional side view on the line E-F of the gearing shown in Figure 5A, Figure 6A, is a front view of further gearing on a line G-H which forms a part of the gearing shown in Figure 2, Figure 6B, is a sectional side view on the line G-H of the further gearing shown in Figure 6A, Figure 7A, is a front view of the half casing shown in Figure 2, but without the gearing, Figure 7B, is a plan view of the half casing as shown in Figure 7A, without the gearing, Figure 8A, is a further front view of the geared prism housing shown in Figure 3A, Figure 8B, is a sectional side view on a line H-H of the geared prism housing shown in Figure 8A, Figure 8C, is a sectional side view of a prism which fits within the housing as shown in Figure 8B, Figure 8D, is a front view of the prism as shown in Figure 8C, Figure 9, is a front view of a half casing in which is fitted an alternative gearing arrangement to that as shown in Figure 2, Figure 10, is a front view of a half casing in which is fitted another alternative gearing arrangement to that as shown in Figure 2, Figure 11A, is a front view of the viewer shown in Figure 1, Figure 11B, is a side view of flee right eye prism configuration of the viewer as shown in Figure 11A, in a neutral position, - 6 Figure TIC, is a side view of the left eye prism configuration of the viewer as shown in Figure 11A, in a neutral position, Figure 11D, is a plan view of the right and left eye prism configurations of the viewer as shown in Figure 11A, in a neutral position, Figures 11E, 11F, 11G, and 11H, correspond to Figures 11A, to 11D, but show the prisms after they have been contra-rotated to positions of maximum adjustment, Figure 12, is a perspective view of ail adjustable stereoscopic viewer comprising a second embodiment of the invention, Figure 13A, is a front view of gearing within a half casing which forms a part of the viewer as shown in Figure 12, Figure 13B, is a sectional plan view on a line I-J of the gearing shown in Figure 13A, Figure 14A, is a front view of gearing on the line K-L shown in Figure 13A, Figure 14B is a sectional side view on the line K-L of the gearing as shown in Figure 14A, Figure 15A, is a front view of gearing on a line M-N shown in Figure 13A, Figure 15B, is a sectional side view on the line M-N of the gearing as shown in Figure 15A, Figure 1GA, is a front view of gearing on a line P-Q shown in Figure 13A, Figure 16B, is a sectional side view on the line P-Qof the gearing as shown in Figure 16A, - 7 Figure 17A, is a sectional plan view of gearing on a line I-J shown in Figure 13A and, Figure 17B, is another sectional side view on the line I-J of the gearing as shown in Figure 13A.

Referring now to Figure 1 of the drawings, an adjustable stereoscopic viewer comprises a front half-casing 1 and a rear half-casing 2 in joining contact along the line 3; two apertures for geared housings in both half-casings shown on the front half-casing at 4 and 5; a cut-away for the nose at 6; four geared housings one for each of four identical prisms, the front parts of the two front housings in the front half-casing at 7 and 8; slots in the half-casings for thumbwheels at 9 and 10; thumbwheels at 11 and 12; screws joining the two half-casings, one of them at 13; registration marks on the prisms or their geared housings in the front half-casing at 14 and 15, with similar marks on the geared housings in the rear half-casing also, to assist a user to set up starting positions; registration marks on the front half- casing for setting up a starting position for viewing stereoscopic images in side-by-side format at 16 and 17, with similar marks on the rear half- casing also; registration marks on the front half-casing for setting up a starting position for viewing stereoscopic images in above-and-below format when the stereoscopic image for the le* eye is displayed above the image for the right eye at 18 and 19, or alternatively at 20 when the stereoscopic image for the right eye is displayed above the image for the left eye, with similar marks on the rear half-casing also except that left 'L' is exchanged for right 'R'; prisms for the left and right eyes in their geared housings in the front half-casing at 21 and 22 respectively. - 8

Referring to Figure 2, of the drawing one complete half of the adjustable stereoscopic viewer, the rear half shown in Figure 1, comprises one halfcasing 2; one thumbwheel 11 situated in a half-slot 9 and connected to gear 23 driving intermediate gear 24; this latter gear directly driving the geared housing 29 and indirectly driving a second geared housing 30 via three idler gears 26, 27 and 28 and a second intermediate gear 25; external bearings for the two housings of which 31 is typical; stub-axles for the bearings and gears integrally moulded with the half-casing of which 32 is typical; one prism 34 in its geared housing 29 and a second prism 35 in its geared housing 30; a cut-away for the nose 6; a second half-slot 10; and screw-hole posts of which 36 is typical. The geared housing 29 is retained in position by the four identical external bearings shown and also by the intermediate gear 24, these bearings being in contact on a peripheral surface 33 of the geared housing, a similar, but symmetrical, arrangement being used for geared housing 30.

Referring to Figures 3A and 3B of the drawing the external bearing 31 has a peripheral contact surface 3 7 in contact with a peripheral contact surface on the geared housing 29 in order to constrain the geared housing in the radial direction, while the side of the external bearing is in sliding contact with the sides of the geared housing's gear teeth 38 thereby constraining the geared housing to its position at its aperture in the half-casing, the other sides of the gear teeth of the geared housing being in sliding contact with the inside surface of the fascia of the half-casing. Figure 3B shows that the external bearing is retained in position by a push-fit pin, or screw, 39 on the end of stub-axle 32, this retaining arrangement being used for all gears and bearings. Figure 3B also shows how the circular prism 34 is located within the geared housing 29.

Referring to Figures 4A and 4B of the drawing the intermediate gear 24 is shown in contact with the geared housing 29 as an external bearing while also providing the geared driving function required.

This gear, therefore, has a dual role. The radius of the peripheral contact surface on this intermediate gear should ideally be the same as the pitch-circle radius for the teeth of the attached gear to prevent sliding at the point of contact, this condition being closely approximated to in Figure 4B.

Referring to Figures 5A and 5B of the drawing the gear 23 is shown in mesh with the intermediate gear 24, the thumbwheel 11 being connected at 40 onto the gear 23 so that a user's rotation of the thumbwheel forces a rotation of gear 23.

Referring to Figures GA and 6B of the drawing the idler gear 26 is shown in mesh with the intermediate gear 24 while providing clearance for its bearing surface.

Referring to Figure 7A of the drawing the half-casing comprises a single injection moulding with facie 40 and side-walls 41; apertures in the facie 4 and 5 for the geared housings; half-slots 9 and 10 in the side- walls for the thumbwheels; stub-axles for the gears and bearings and screw-hole posts on the interior of the facie; registration marks on the interior surface of the facie to aid correct setting up of the geared housings during assembly 42 and 43; and registration marks on the outside of the facie, like those shown in Figure 1, but not shown here in Figure 7A. For simplicity of presentation in Figure 7B, only the gear stub-axles are shown in the left-hand part of this plan view and only the bearing stub-axles and screw-hole posts in the right-hand part. -

Referring to Figures tSA, 8B, SC and 8D of the drawing the geared housing 29 is shown with a ridged feature 44, and the prism 34 is shown with a grooved feature 45; these features ensuring that the prism's thickest part is precisely located with registration mark 46 on the outside of the geared housing. A mark of this kind may he integrally moulded with the geared housing, and will have a precise position relative to the gear teeth. In addition to a mark on the outside of the geared housing for the user, a corresponding mark could usefully be put on the inside of the geared housing for use during assembly with the aforementioned registration marks 42 and 43 on the inside of the half-casing. But, at least one of the gears in the gear train shown in Figure 2 must be positioned very carefully during the design process if proper gear teeth engagement is going to be obtained while both geared housings are registering accurately with their registration marks, and, of course, if one gear has to be repositioned then so may some or all of the others. In the case of Figure 2 the idler gear 27, in particular, has been positioned to meet this condition. Alternatively, perhaps, registration marks could to be put on the prisms, perhaps by etching during manufacture, rather than on the housings, and the prisms inserted into their housings after the gears have been assembled in their half-casings. A different method of prism location in its geared housing will then be required from that shown in this set of Figures.

Referring to Figure 9 of the drawing an alternative gearing arrangement from that in Figure 2 is shown in which the geared housing 30 is driven by a central intermediate gear 47, which, in turn, is now driven by the geared housing 29. The latter is now part of the gear driving sequence even though it does not have an axle to constrain its movements. Consequently, greater precision may be - 11 required of its bearings. This viewer has fewer components and could be made physically smaller. Registration marks 48 and 49 for assembly purposes are shown in alternative positions from those in Figure 7.

This gearing arrangement is less flexible for purposes of design modification than that shown in Figure 2 if changes are made in the separation of the prisms, with their geared housings, along the horizontal centre-line in Figure 2 in order to suit users having different inter-ocular distances. Moreover, as already pointed out above, the central intermediate gear must be positioned very carefully if proper gear teeth engagement is going to be obtained while the geared housings are registering accurately with their registration marks, and some very slight adjustment to the geared housing separation may be required.

Referring to Figure 10 of the drawing a further variation in the gearing arrangement from that in Figure 2 is shown which, like that in Figure 9, also has a central intermediate gear, but this is now connected to gear 23 via two idler gears 50 and 51. Both geared housings are now directly driven by one intermediate gear.

Referring to Figure 11A of the drawing a front view of the viewer is shown with the front prisms set up for side-by-side viewing, their registration marks 14 and 15 being aligned with the appropriate marks 1G and 17 on the front face of the viewer, the thickest part of the front prism for the right eye;21 being at the top and the thickest part of the front prism for left eye 22 being at the bottom, as shown in the side views in Figures 11B and 11C. The rear prisms in the latter Figures are shown rotated by 180 relative to the front prisms. Figure 11D shows the corresponding plan view of the four prisms. Figures 11E, 11F, 11G and 11H show the orientations of the prisms after each pair at each eye - 12 have been contra-rotated to positions for maximum adjustment, the front prisms having rotated 90 anticlockwise and the rear prisms 90 clockwise when viewed from the front.

The complete viewer shown in Figure 1, is formed by taking two assemblies, each like that shown in Figure 2, placing them with their screw postholes in contact and screwing or bolting them together. To allow users to clean the inside surfaces of the prisms the screws or bolts can be taken out to give the access required. The aforementioned screws or pins 39 shown in Figures 3B, 4B, 5B and 6B are needed principally to prevent the gears and bearings from falling off their stub-axles during assembly and during subsequent cleaning actions Both geared housings with their prisms in the front half of the viewer shown in Figure 1 are rotated simultaneously and in step by the user's rotation of the thumbwheel 12 on the right hand side of the viewer. Similarly, the two geared housings with their prisms in the rear half of the viewer are rotated simultaneously and in step by the user's rotation of the thumbwheel 11 on the left hand side of the viewer. A user will hold the viewer up to Fischer eyes after having set up an appropriate starting position and then, with, say, the index finger of each hand, rotate the thumbwheels by moving the fingers towards the centre of the viewer. From the user's point of view the thumbwheel on hisser left will rotate clockwise and the other thumbwheel anti-clockwise. Both of the geared housings with their prisms remote from the user will then rotate clockwise and those closest to the user anti-clockwise. Consequently, each pair of prisms for each eye will be contra-rotated by the user as the user makes adjustments to achieve stereoscopic viewing. Progressive contra-rotation of a pair of prisms from a neutral starting position will create a progressive amount of - 13 deviation of light rays incident on the prisms so that, when viewing stereoscopic pairs of images, the images can be progressively deviated to the extent required for three-dimensional viewing. Images presented in side-by-side format will be deviated along a horizontal axis and images in above-and-below format will be deviated along a vertical axis after the appropriate starting positions are set up and when, of course, a user views images with the head in a normal vertical position and makes equal adjustments to the two thumbwheels.

If a user views stereoscopic images with a relative inclination of the viewer, perhaps because of a naturally biased inclination of the head from the vertical, or perhaps because of a naturally biased inclination of the eye-line from the horizontal, then correction for this can be made by rotation of both thumbwheels in the same direction, rotation one way correcting for inclination in one direction, rotation the other way correcting for the other direction. An inexperienced user can be expected to learn quickly to rotate the two thumbwheels differentially, or together, to give the results required.

In order to simplify matters for manufacture of the half-casings, the registration markings shown on the front of the viewer in Figure 1 could be used on the rear facie also. Then, with suitable instructions provided for a user, the viewer shown in Figure 1 can be used either way around and the viewer need not have a formally recognised front and rear. If, however, a formally recognised front and rear for the viewer is provided then different positions for the registration markings on the rear from those on the front could simplify matters for the user, at least when setting up to view stereoscopic pairs presented in the above-and-below format. Registration markings for stereoscopic pairs of hnages presented in the side-by-side format on the other hand - 14 should be the same on both sides of the viewer anyway. The distinction for above-and-below viewing arises because, if, for example, the viewer is set up to suit a presentation in which the image for the left eye is over the image for the right eye, by using the positions marked L-o-R, of which one is shown at 20 in Figure 1, but the presented images are then viewed from the wrong side of the viewer, then the wrong images will be presented to the user's eyes and three- dimensional viewing will not be achievable.

The implementation of this embodiment described above so far will allow the two thumbwheels to rotate independently and without restriction. In practice, the front and rear prisms need only rotate by, at most, 180 relative to each other. Anything more than this is potentially confusing for a user. Physical restrictions to limit the rotational range of adjustment to this amount could, therefore, be useful. One method of implementing this restriction makes an axial extension to the geared housings so that the peripheries of the geared housings at the central plane of the viewer after final assembly (two half-casings with installed components having been brought together, as described above) interact and set limits to their relative rotation. A simple way of doing this limits the axial extension to the geared housings to a 90 arc, hereafter called a quadrant-arc, so that the quadrant-arc of one geared housing has freedom to move within the 270 of angular space left un-extended in the adjacent, co-axial, geared housing. A quadrant-arc on a geared housing may be arranged so that, when two geared housings (and therefore two quadrant-arcs) are brought together for each eye following assembly, their quadrant-arcs will come into contact at a neutral starting position at one end of their relative rotational range, and into contact again at a position of - is - maximum adjustment for the prisms at the other end of their relative rotational range. When quadrant-arcs are in contact the thumbwheels must rotate together, one thumbwheel indirectly turning the other thumbwheel in one direction of rotation. This can be expected to simplify the setting up of a starting condition because one thumbwheel can be used to rotate all four prisms together to a new position, and, moreover, the relative positions of the two prisms at each eye will be accurately established. All geared-housings in a viewer can still be physically identical, so there need not be act increase in the number of different components in the viewer as a result of introducing this feature.

A second embodiment of the invention will now be described by way of example with reference to Figure numbers 12 to 170f the drawing in which: Figure 12 shows, in isometric front view, an adjustable stereoscopic viewer having many features in common with the first embodiment described above, but being different in the following respects: as before, two thumbwheels are shown but these are now accessed from the front and rear surfaces of the viewer and movement of only one thumbwheel is now needed to effect the stereoscopic adjustments required; sufficiently large apertures in the front and rear surfaces have been provided so that each thumbwheel may be pulled to one side (to its side of the viewer) to effect a displacement of the thumbwheel and a disengagement of its drive from the geared housings and their prisms; one locking pin with each thumbwheel has been provided having a fixed mechanical relationship with its thumbwheel so that, when the thumbwheel has been displaced, this displacement can be retained by a simple locking-off process in which a slight - 16 rotation of the thumbwheel to turn the displaced locking pin is made so that it comes into contact with retaining shoulders; slots in the front and rear surfaces have been provided so that each locking pin may be seen protruding from the front and rear surfaces of the viewer during part of the locking pin's rotation with its thumbwheel; a narrow slot, operating as a gate', in the front and rear surfaces has been provided for each pin so that its thumbwheel is forced to take up a set position at the time of its displacement, thereby turning the geared housings and prisms to correspondingly set positions, e.g. for an original starting position; protruding from the top of the viewer are two gearwheels, subsequently called common idler gears, which are part of the drive systems connecting the thumbwheels to the geared housings and their prisms and which can be rotated freely to set up a new starting position for all prisms when the thumbwheel drives have been disengaged.

Figures 13A and 13B show, respectively, a front inside view of the rear half of the viewer's casing, and a simplified cross-sectioned plan view along the line marked I-J in Figure 13A. The rear half of the viewer comprises geared housings and bearings, substantially as before, but both geared housings are now driven by a single common idler gear which is driven in turn by a thumbwheel assembly comprising a bevelled drive gear, a shaft connecting the bevelled drive gear to its thumbwheel, pedestal bearings for the shaft, the aforementioned locking pin, and a compression spring on the shaft sandwiched between two collars. The apertures for the thumbwheels and locking pins, referred to above, are shown in the fascia for the rear half of the viewer. Also shown are means for gently restraining the common idler gear and geared housings from moving away from set positions as a result of random movements of the viewer, but still allowing controlled adjustments easily to be made, each device of this kind subsequently being referred to as a position holder.

Figure 14A shows one of the geared housings with two of its external bearings, and Figurel4B shows a cross-section through them along a line joining their centres, this line being marked as the line K-L in Figure 13A. As in Figure 3B, Figure 14B shows how a prism is mounted within its housing, slight dimensional changes having been made.

Figure 15A shows the prism in its geared housing with the common idler gear that drives it, and Figure 15B shows a cross-section through them along a line joining their centres, this line being marked as the line MN in Figure 13A.

Figure 16A shows the detail on the vertical centre-line marked P- QonFigure 13A for the common idler gear and two position holders confined here within the common idler's space and operating on a rack of very fine teeth or ridges on an inner periphery of the common idler.

Since the position holders exert only a relatively small force on the common idler gear, and therefore on its bearing, one only of the position holders will suffice in practice. Each position holder is implemented here as a leaf-spring mounted in a block attached to, or integrally moulded with, the rear half-casing. Figure 16B shows a cross-section on the line P-Q.

Figure 17A shows a simplified cross-section on the line marked I-J in Figure 13A when two mechanically identical half-casings with installed components, each like that shown in face view in Figure 13A, are placed face-to-face and joined together. Both thumbwheels are shown in their displaced positions, with both bevelled drive gears - 18 therefore disconnected from the common idler gears. The common idler gears can now be rotated in the same direction to set up of a new starting position for the geared housings and prisms. Figure 17B shows the same view as Figure 17A except that the thumbwheel assembly on the right hand side of the Figure (which would be on the user's left hand side in practice) is in the connected position ready for adjustments to be made. Either thumbwheel assembly can be used depending on whether left of right-handed use is preferred.

Referring to Figure 12 of the drawing the adjustable stereoscopic viewer comprises: components and markings very much like those described in the first embodiment, which will not be described again here; thumbwheels 60 and 61; apertures for the thumbwheels 62 and 63; locking pins 64 and 65; locking pin gates 66 and 67; locking pin shoulders 68 and 69; locking pin slots 70 and 71; rear and front common idler gears 72 and 73; ordinary gear teeth 74 and 75 on the common idler gears, driving the geared housings and prisms; bevelled gear teeth 76 and 77 on the common idler gears, connecting with the bevelled drive gears in the thumbwheel assemblies.

Referring to Figures 13A and 13B of the drawing one complete half of the adjustable stereoscopic viewer, the rear half shown in Figure 12? comprises a half-casing with apertures, stub-axles and screw-hole posts, geared housings and prisms, and bearings for the geared housings very much like those described in the first embodiment and shown in Figure 2, but comprises also: the common idler gear 72, with its annulus of bevelled gear teeth 74 and, behind these, its annulus of ordinary gear teeth in mesh with the two geared housings; the leaf- springs 78 and 79 and the mounting blocks 80 and 81 for the leaf- springs for the two position holders; the rack of very fine teeth or - 19 ridges for the position holders 82; the thumbwheel 60; thumbwheel apertures 83 and 84, with bevelled features 99, 100, 101 and 102 allowing a close fit of the thumbwheels to the fascia, locking pin apertures 85 and SG and locking pin gates 87 and 88 all in the fascia of the rear half- casing; locking pin shoulder blocks 89 and 90; pedestal bearings 91 and 92; a pedestal bearing strap 93, of which one is required for each pedestal bearing; a shaft 94, supported by the pedestal bearings and connecting the thumbwheel 60 to the bevelled drive gear 95; a collar 96 which is fixed to shaft 94 supporting one end of spring 97 and, when in contact with pedestal bearing 91, sets the correct position for the bevelled drive gear when it is in mesh with the common idler gear; a sliding collar 98 in contact with pedestal bearing 92 supporting the other end of the spring.

Referring to Figure 17B of the drawing bevelled drive gear 95 is in mesh with the bevelled gear teeth on both common idler gears 72 and 73, thumbwheel GO is in its normal position for adjusting the viewer for stereoscopic viewing and pin 64 is aligned with its slot and is free to rotate.

The complete viewer shown in Figure 12 is formed, as in the first embodiment, by taking two assemblies, each like that shown in Figure 13, placing them with their screw post-holes in contact and screwing or bolting them together.

When a thumbwheel assembly is in its drive position (i.e. when its bevelled drive gear is in mesh with both common idler gears) all four geared housings with their prisms in the viewer are rotated simultaneously by the user's rotation of the thumbwheel, the two geared housings and prisms at the front rotating in one direction while those at the rear rotate in the opposite direction. A user will set up a - 20 starting position for one of the three formats of stereoscopic presentation by disengaging the thumbwheels so that both common idler gears can be rotated at the top of the viewer to align the registration marks on the geared housings with the appropriate registration marks on the front and rear fascias of the viewer. The thumbwheel will then be re- engaged and normal adjustments made, the thumbwheel being rotated in the normal right-handed screw direction to make an increase in adjustment. If a new starting position for a different format of stereoscopic presentation needs to be made then, in order to disengage the thumbwheel, its locking pin must be aligned first with its gate and this will return all prisms to their original starting set-up. A new starting position can then be obtained by rotating both common idler gears together in the same direction and by the same amount, checking alignments at the front and rear before re-engaging the thumbwheel. Because rotation of only one thumbwheel moves all four prisms simultaneously no independent adjustment for any variable other than for convergence of the stereoscopic images to effect 3D viewing is possible via the thumbwheel.

If the quadrant-arc extension to each geared housing, referred to at the end of the description for the first embodiment, were used for this second embodiment then it too would be easier to use because, when the quadrant-arcs come into contact at either of the two limits which define the useful range of adjustment, the thumb-wheels will lock-up' and further attempted adjustment outside the range will be prevented.

It will be appreciated that various other embodiments may be implemented without departing from the scope of the invention as - 21 claimed and for example a third embodiment of the invention comprises the second embodiment substantially as described above, but modified by: (i) having a simplified thumbwheel assembly with a bevelled drive gear which is permanently in mesh with the common idler gears, and (ii) providing means by which each prism can be rotated by hand within, and therefore relative to, its geared housing at the time of setting up a different startingposition for any one of the three positions required for stereoscopic viewing. The means referred to here may be implemented by dividing a geared housing, as shown typically in Figures and in other Figures, into two parts, one part comprising the prism with its own housing, subsequently referred to as the prism-housing, the second part comprising a separate housing with an annulus of gear teeth and a suitable surface for the external bearings, subsequently referred to now as the 'outerhousing', into which the prism-housing can be located. The prism-housing will fit closely within the outer-housing, but have freedom to be rotated within the outer-housing about their common axes. The means would include a bezel on the prism-housing accessible from the outside of the viewer allowing the prism-housing to be directly rotated by hand, and a springloaded latching feature, on the prism-housing, for example, which will flexibly locate the prism-housing at any one of three positions on the outer-housing. Rotation of the outer-housing via a thumbwheel will rotate the prism-housing, and therefore its prism, in the required manner.

A fourth embodiment of the invention comprises: two half- casings, with installed components, joined together after the manner described in the foregoing embodiments, each half-casing containing prisms in geared housings with bearings, as in the first embodiment - 22 and also two compound gears, one in mesh with each geared housing and located in a fixed position on the horizontal centre-line through the geared housing centres and at that part of the geared housing's periphery which is furthest from the vertical centre line of the viewer, both compound gears comprising two gears fixed together co-axially and having a typical gear ratio of 2:1, the larger of the two gears on each compound gear driving a geared housing and the smaller of the two gears being driven by a curved rack of gear teeth, hereafter called an arc-rack, on a curved arm, hereafter called an arc-arm, which can move on an axle which is located at a suitable point on the vertical centre-line of the viewer. Two arc-arms, therefore, are required in order to drive the two, separate, compound gears, the two arc-arms being part of a simple, plate-like, assembly (the two arc-arms and their arc-racks may be regarded as parts of one larger gear with an internal annulus of gear teeth). The compound gears are needed in order to reduce the length of the arc-racks on each arc-arm because they would otherwise be impracticably long. A handle, perhaps as a tab-like feature, extends from each arm to the outside of the viewer, approximately in the vicinity of the aforementioned horizontal centreline, for use with a user's index finger or thumb. One of the two arcarms carries a spring-loaded pawl, and the other arc-arm an arc of ratchet teeth, hereafter called an arc-ratchet, arranged such that, when two half-casings are joined together the pawl on an arc-arm in one halfcasing comes into play with the arc-ratchet on the opposite arc-arm in the other half-casing. The pair of arc-arms in a half-casing, when set to a starting condition, are offset from the horizontal centre-line by an appropriate angle so that in the assembled viewer the arc-arm handles for the two pairs of arc-arms are separated (opened) by a convenient - 23 distance for the index finger and thumb of one hand and can then be squeezed together' to rotate the arms (and, therefore, rotate the geared housings and prisms) when making adjustments for stereoscopic viewing. This squeezing action is opposed by a force exerted by a spring which acts to try to move the arm handles in the separated, open, direction, one end of the spring being connected to one pair of arms and the other end of the spring being connected to the other pair of arms. This spring is installed at the time when two assembled half-casings are brought together during final assembly.

When the arc-arm handles are squeezed together the new positions of the arc-arms are kept there by the pawls and ratchets. To reduce the amount of stereoscopic adjustment, or to return to the starting position, each pawl is released from its ratchet (by an extension from the pawl which is easily accessed by the index finger) and the arms allowed to open by spring action. In practice, only one pawl is needed.

However, a disadvantage of this embodiment is that a different starting position, for a different stereoscopic display format, is produced by rotating both sets of arms to a new position and then making the 'squeezing' action from there. This is potentially confusing for a user. One way of overcoming this disadvantage would be to utilise the arrangement referred to in the third embodiment above by providing means by which each prism can be rotated by hand within its geared housing at the time of setting up a different starting- position.

A fifth embodiment of the invention has much in common with the fourth embodiment above, but seeks to overcome the disadvantage referred to there by having only one arc-rack of gear teeth for one pair of arc-arms, this arc-rack being mounted on a separate plate which is - 24 pivoted on the same axle as the plate for the arc-arms and can be moved by hand to any one of three positions on the arc-arms in order to set up a starting condition for any one of the three formats of stereoscopic presentation. This single arc-rack of gear teeth drives a single compound gear, like that described in the fourth embodiment and provided for the same reasons, mounted on the viewer's vertical centre-line which, in turn, drives two idler gears, each connected to one geared housing and prism. This arrangement overcomes the disadvantage referred to above in the fourth embodiment by allowing the arm handles to assume the same position in the viewer for all three stereoscopic display formats. The plate carrying the arc of gear teeth has an extension, or handle, projecting from the top of the viewer and, because there are two plates of this kind in the fully assembled viewer, two handles will therefore project from the top and both may then be moved together to set up a different starting position.

Various modifications may be made to the arrangements hereinbefore described with reference to the drawings without departing from the scope of the invention and for example two prisms may provided, one for each eye which are arranged to be contra- rotatable. Although generally satisfactory, this simplified arrangement does have the disadvantage that the image as viewed tends to move consequent upon relative adjustment of the prisms and since the image is not positionally stable this arrangement may not be preferred. - 25

Claims (12)

CLAIMS.

1. A stereoscopic viewer for viewing in three dimensions a scene defined by a pair of stereoscopic two dimensional mutually adjacent co-planer images, comprising a pair of eye pieces at least one of which includes a pair of prisms through which the scene is viewed, the prisms being contrarotateable for mutually superimposing the two images as seen through the eye pieces thereby to provide a resultant three dimensional image of the scene as viewed

2. A stereoscopic viewer as claimed in Claim 1, wherein the eye pieces each comprise a front prism and a rear prism through which the scene is viewed, the front prisms being arranged to be adjustably rotateable via a first mechanism and the rear prisms being arranged to be independently adjustably rotateable via a second mechanism, whereby consequent upon appropriate adjustment of the two mechanisms, the images as seen through the eye pieces are mutually superimposed so that a three dimensional image of the scene as viewed through the eyepieces is produced.

3. A stereoscopic viewer as claimed in Claim 2, wherein he first and second mechanisms are similar, each comprising two similar gear trains which overlay each other in adjacent parallel planes.

4. A stereoscopic viewer as claimed in Claim 3, wherein some gears of each train are arranged mutually to align and are mounted for independent rotation on the same shaft.

5. A stereoscopic viewer as claimed in Claim 4, wherein the prisms are similar and comprise angularly truncated cylinders each mounted cordially within an annular gear, so that the eye pieces each comprise a pair of mutually aligned annular gears with the annular gears in which the front prisms are mounted being arranged in one gear train and the - 26 annular gears in which the rear prisms are mounted being arranged in the other gear train.

6. A stereoscopic viewer as claimed in Claim 5, wherein he first and second mechanisms comprise first and second toothed thumb wheels by means of which the front and rear prisms respectively are rotated via the gear trains.

7. A stereoscopic viewer as claimed in Claim 5, wherein first and second mechanisms comprise rack and pinion adjusters wherein the pinions form a part of respective gear trains and the racks each include an adjuster lever or push rod by means of which the front and rear prisms respectively are a rotated via the gear trains.

8. A stereoscopic viewer as claimed in any preceding claim, wherein the prisms are made of glass or an optically stable plastics lens material.

9. A stereoscopic viewer as claimed in any preceding claim, wherein the viewer additionally comprises lens means arranged in front of the prisms of each eye piece, and for behind of the prisms of each eye piece, andfor between the prisms of each eye piece, so as produce a magnified three dimensional image.

10. A stereoscopic viewer as claimed in Claim 9, wherein the lens means is adjustable for the purposes of framing andior focusing.

11. A stereoscopic viewer as claimed in any preceding claim, wherein the viewer comprises housing means in which the prisms and other parts of the viewer are mounted.

12. A stereoscopic viewer as clamed in claim 1, and substantially as herein described with reference to Figures 12 to 1, 8, of the accompanying drawings.

12. A stereoscopic viewer as claimed in Claim 1, and substantially as herein described with reference to Figures 1 to 11H, of the accompanying drawings.

13. A stereoscopic viewer substantially as herein described with reference to Figures 12 to 17B, of the accompanying drawings.

14. A stereoscopic viewer for viewing in three dimensions a scene defined by a pair of stereoscopic two dimensional mutually adjacent co-planer images, comprising a pair of eye pieces each of whirls includes a prism, the prisms being substantially identical and adapted and arranged to be contra-rotateable for producing relative movement between two images as seen through respective eye pieces of the pair so that they are mutually superimposed, thereby to provide a three dimensional image of the scene as viewed.

Amendments to the claims have been filed as follows: 1. A stereoscopic viewer for viewing in three dimensions a scene defined by a pair of stereoscopic two dimensional mutually adjacent co-planer images, the said viewer comprising a pair of eye pieces each having a front prism and a rear prism through which the scene is viewed, the front prisms being arranged to be adjustably rotateable via a first mechanism and the rear prisms being arranged to be independently adjustably rotateable via a second mechanism, the front prisms and rear prisms being mutually contra-rotateable whereby consequent upon appropriate adjustment of the two mechanisms, the images as seen through the eye pieces are mutually superimposed so that a resultant three dimensional image of the scene as viewed through the eyepieces is produced.

2. A stereoscopic viewer as claimed in Claim 1, wherein he first and second mechanisms are similar, each comprising two similar gear trains which overlay each other in adjacent parallel planes.

3. A stereoscopic viewer as claimed in Claim 2, wherein some gears of each train are arranged mutually to align and are mounted for independent rotation on the same shaft.

4. A stereoscopic viewer as claimed in Claim 3, wherein the prisms are similar and comprise angularly truncated cylinders each mounted coaxially within an annular gear, so that the eye pieces each comprise a pair of mutually aligned annular gears with the annular gears in which the front prisms are mounted being arranged in one gear train and the annular gears in which the rear prisms are mounted being arranged in the other gear train.

S. A stereoscopic viewer as claimed in Claim 4, wherein he first and second mechanisms comprise first and second toothed thumb wheels 2q by means of which the front and rear prisms respectively are rotated via the gear trains.

6. A stereoscopic viewer as claimed in Claim 4, wherein first and second mechanisms comprise rack and pinion adjusters wherein the pinions form a part of respective gear trains and the racks each include an adjuster lever or push rod by means of which the front and rear prisms respectively are a rotated via the gear trains.

7. A stereoscopic viewer as claimed in any preceding claim, wherein the prisms are made of glass or an optically stable plastics lens material.

8. A stereoscopic viewer as claimed in any preceding claim, wherein the viewer additionally comprises lens means arranged in front of the prisms of each eye piece, and for behind of the prisms of each eye piece, andior between the prisms of each eye piece, so as produce a magnified three dimensional image.

9. A stereoscopic viewer as claimed in Claim 8, wherein the lens means is adjustable for the purposes of framing andior focusing.

10. A stereoscopic viewer as claimed in any preceding claim, wherein the viewer comprises housing means in which the prisms and other parts of the viewer are mounted.

11. A stereoscopic viewer as claimed in Claim 1, and substantially as herein described with reference to Figures 1 to 11H, of the accompanying drawings.