GB2256992A

GB2256992A - Stereo camera

Info

Publication number: GB2256992A
Application number: GB9212289A
Authority: GB
Inventors: Stephen Patrick Murphy; Richard Paul Harvey
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1991-06-21
Filing date: 1992-06-10
Publication date: 1992-12-23
Anticipated expiration: 2012-06-10
Also published as: GB9212289D0; JPH05188502A; GB9113495D0; DE4219851A1; FR2679051B1; GB2256992B; FR2679051A1

Description

2 7 0) Stereo Camera This invention relates to a stereo camera and

paticularly but not exclusively to a stereo camera for providing stereoscopic television pictures.

According to the present invention there is provided a stereo camera comprising a single objective lens, a light-sensitive imaging device, a single image-focussing lens for focussing images onto the light-sensitive device, and a biprism between the objective lens and the image-focussing lens so that two images are created.

By using a single objective lens rather than two side-by-side objective lenses a much more compact stereo camera can be made, so enabling inspection in confined spaces for example. It will be appreciated that the objective lens and the image-focussing lens may both be compound lenses, that is to say each may comprise a plurality of lenses with a common optical axis.

Preferably a baffle is provided, extending between the light-sensitive device and the image-focussing lens in a plane parallel to the optical axis of the imagefocussing lens and in which the vertex of the biprism lies. This prevents any overlap of the two images. The baffle is desirably T-shaped, with the cross-bar of the T adjacent to the image-focussing lens and perpendicular to its optical axis.

Preferably the objective lens is a collimating lens, so light from a point on an object is incident as a parallel beam onto the biprism. Consequently the distance between the objective lens and the biprism is not critical. The camera is focussed by moving the objective lens towards or away from an object, and no movement of the other components is necessary. Alternatively the objective lens might have the nature of a telescope, comprising two converging lenses spaced apart and arranged to form an intermediate image between them, and to ensure light from a point on the object is incident onto the biprism as a parallel beam.

The image-focussing lens is preferably such that for an entrance pupil at the location of the biprism, the corresponding exit pupil, which is virtual, is as close as possible to the cross-bar of the baffle, so as to minimise the light loss due to the baffle. In the embodiment of the invention described below, the exit pupil would be only about 120 mm from the cross-bar (to the side of the cross-bar remote from the sensor); by contrast with a conventional lens the exit pupil would be about 200 mm. from the cross-bar.

The light-sensitive imaging device might be a photographic film, or might be an electronic image sensor. The two images may be produced side-by-side, and may be formed on a common imaging device, or by means of mirrors the two images may be formed on two separate imaging devices.

The optical components of the camera might also be used in reverse to recombine a pair of stereo images.

The invention will now be further described by way of example only, and with reference to the accompanying drawings in which:

Figure 1 shows a diagrammatic sectional view of a stereo camera; and Figure 2 shows a sectional view, in greater detail, of the camera of Figure 1.

1 Referring to Figure 1, there is shown a sectional view along the optical axis of a stereo camera 10. Light rays 12 from an object 13 are collimated by a collimating lens 14 so as to be incident as parallel rays onto a biprism 16. The biprism 16 splits the light into two parallel beams 17, 18 which diverge. The beams 17 and 18 are focussed by an image- forming lens 20 to form two side-by-side images 21, 22 above and below the optical axis of the camera 10 respectively. A baffle plate 24 extends along the optical axis from near the rear surface of the lens 20 to near the plane in which the images 21, 22 lie; this is a flat plate in the plane perpendicular to the Figure (i.e. the plane in which the vertex of the biprism 16 lies, that is to say the plane dividing the two parts of the biprism 16), and is T-shaped with a cross-bar 25 near the rear surface of the lens 20 and perpendicular to the opticall axis of the camera 10. The baffle plate 24 with its cross-bar 25 minimises any overlap of the two images 21 and 22.

In a modification to the above-described arrangement, indicated by broken lines, mirrors 30 are used so that the two images 21 and 22 are formed spaced well apart from each other. This modification is advantageous where the images 21 and 22 are to be formed on two separate electronic image sensors,' as more space is thereby provided for each sensor.

Referring now to Figure 2, the stereo camera 10 is shown in greater detail. The collimating lens 14 is a compound lens with four spaced-apart component lenses 31, 32, 33, 34 held in a tubular metal support 35. The biprism 16 and the image-forming lens 20 are also held in a respective tubular metal support 36. The biprism 16 is of doublet construction to minimise chromatic aberration, and consists of a first biprism 37, plane on one side and on - 7.9 the other side defining two surfaces inclined at degrees to the plane surface, and two thin prisms 38 of vertex angle 15.6 degrees fixed to the inclined surfaces of the first biprism 37 with their vertices together (and intersecting the optical axis 39). The first biprism 37 is of type F2 glass and the prisms 38 are of type BK7 glass, these being the Schott glass type numbers. The image-forming lens 20 is also of compound form, comprising a thick doublet meniscus lens (lenses 40 and 41), and four other spaced-apart single lenses 42, 43, 44 and 45. The cross-bar 25 in this case is 8.5 mm high, and abuts the rear surface of the lens 45.

The characteristics of the lenses are listed in the Tables which indicate the radii of the successive surfaces, is the separation along the axis 39 between one surface and the next, the clear diameters, and the types of glass. The lenses of the collimating lens 14 are indicated in Table 1, and those of the imaging-forming lens 20 in Table 2. It will be appreciated that the overall diameter of the -ing lens 14 including the support 35 need be no collimat more than about 45 mm, while that of the image-forming lens 20 need be no more than about 55 mm.

As mentioned earlier, the optical components of the camera, that is the collimating lens 14, the biprism 16, and the image- forming lens 20, can be used in reverse to recombine a pair of stereoscopic images. In this case the stereoscopic images would be placed in the position of the images 21 and 22 of Figure 1.

i- Table 1

Radius/m Separation Diameter/mm Material Lens 250 40 -92 5.5 40 LAK9 31 4.1 air 78 40 6.0 BK7 32 -206 38 -55 7.4 38 air 2.0 SF8 33 91 38 19.6 air -112 38 -43 5.5 39 SK4 34 Table 2

Radius/mm Separation Diameter/mm Material Lens 10.6 air -24 35 1.5 LAK9 40 68 50 20.0 SSKS 41 -33 50 0.3 air -205 50 5.0 LAK9 42 -71 50 0.3 air 82 7.0 50 LAK9 43 -213 47 2.6 air -72 47 1.5 SF6 44 86 46 0.35 air 61 46 8.3 LAK9 45 -138 46

Claims

1. A stereo camera comprising a single objective lens, a light-sensitive imaging device, a single image-focussing lens for focussing images onto the light-sensitive device, and a biprism between the objective lens and the image-focussing lens so that two images are created.

2. A stereo camera as claimed in Claim 1 also comprising a baffle extending between the light-sensitive device and the image- focussing lens to prevent light crossing the plane parallel to the optical axis of the image-focussing lens in which the vertex of the biprism lies.

3. A stereo camera as claimed in Claim 2 wherein the baffle includes an element adjacent to the image-focussing lens, obstructing light emerging from the image-focussing lens in a region on each side of said plane.

4. A stereo camera as claimed in Claim 3 wherein the baffle is T-shaped, with the cross-bar of the T adjacent to the image-focussing lens and perpendicular to its optical axis.

5. A stereo camera as claimed in any one of the preceding Claims wherein the objective lens is a collimating lens.

6. A stereo camera as claimed in any one of the preceding Claims.wherein both the objective lens and the image focussing lens are compound lenses.

7. A stereo camera substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

8. An optical instrument for recombining a pair of 11 stereoscopic images, comprising a single converging objective lens for receiving light from the two stereoscopic images, the two images being at equal optical distances from the objective lens and light from the two images being received by respective non-overlapping segments of the objective lens, a single focussing lens, and a biprism between the objective lens and the focussing lens arranged such that the light received by the said segments passes through respective prisms of the biprism, 10 so the focussing lens creates a single image.

9. An optical instrument as claimed in Claim 8 also including a baffle arranged to prevent light from one image being received by the segment of the objective lens corresponding to the other image.

10. An optical instrument as claimed in Claim 8 or Claim 9 also including means to prevent light from either image being received by a region of the objective lens lying between the said segments.

11. An optical instrument for recombining a pair of stereoscopic images, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.