GB2531355A

GB2531355A - Improvements in image acquisition

Info

Publication number: GB2531355A
Application number: GB1418487.3A
Authority: GB
Inventors: David Watkins
Original assignee: Overview Ltd
Current assignee: Overview Ltd
Priority date: 2014-10-17
Filing date: 2014-10-17
Publication date: 2016-04-20
Also published as: WO2016059437A1; GB201418487D0

Abstract

An apparatus comprises a housing 10 for an image acquisition device 26, such as a security camera. The housing has a first hemispherical portion 14 and a first mount 28 disposed within. The first mount is configured to hold an image acquisition device and being movable within the housing relative to the housing wherein the housing and the first mount are configured such that an optical axis of an image acquisition device held by the first mount passes through a centre of the first hemispherical portion of the housing whilst the first mount moves relative to the housing. In a further invention the optical axis is configured to be perpendicular with the housing

Description

Improvements in Image Acquisition

Field of the Invention

The present invention relates to an apparatus, more particularly an apparatus comprising a housing for an image acquisition device.

Background of the Invention

Conventional camera apparatuses, such as closed-circuit television (CCTV) apparatuses, often take the form of a "dome" having a top portion and a bottom portion, with the top portion disposed vertically above the bottom portion with a horizontal interface between the top portion and bottom portion. A camera is disposed within the housing and is movable within the housing.

The top, or upper, portion is typically constructed from aluminium and is opaque so that it shades the camera and prevents the camera from being exposed to excess external light. The bottom, or lower, portion is typically hemispherical in shape, is constructed from plastic and is at least partially transparent. The camera is mounted within the housing such that its optical axis passes through the transparent bottom portion. In other words, it is through the hemispherical bottom portion that the camera points.

The bottom portion is intentionally hemispherical because this generally reduces distortion in images acquired by the camera. However, the camera cannot typically be positioned at the centre of the dome because such positioning would mean that the opaque top portion, which has to be opaque to shade the camera from external light, would restrict the field of view of the camera. In particular, the camera would not be able to point upwards because its optical axis would intersect the opaque top portion or, frequently, the interface between the top portion and the bottom portion.

Existing camera apparatuses typically counteract this issue in one of two ways. The first way is to position the camera low in the dome within the hemispherical bottom portion of the dome i.e. not centred within the dome or within the hemispherical bottom portion. However, this causes unwanted distortion in the acquired images because the optical axis of the camera intersects the bottom hemisphere of the dome at a range of angles when the camera moves within the dome.

The second way is to provide domes having a complex shape e.g. teardrop-shaped domes.

However, this significantly increases the complexity of the construction process and, consequently, the time and cost of manufacture.

Therefore, there exists a need for an improved apparatus which solves the problems identified above in a neat and efficient manner.

Summary of the Invention

In accordance with a first aspect of the present invention, there is provided an apparatus comprising: a housing for an image acquisition device, the housing having a first hemispherical portion; and a first mount disposed within the housing, the first mount being configured to hold an image acquisition device and being movable within the housing relative to the housing, wherein the housing and the first mount are configured such that an optical axis of an image acquisition device held by the first mount passes through a centre of the first hemispherical portion of the housing whilst the first mount moves relative to the housing.

The "centre" of a substantially hollow hemispherical or spherical portion or structure, which can also be described as the "focus", is a point which is equidistant from all points on an interior surface of the hemispherical or spherical portion. Therefore, the centre of the first hemispherical portion of the housing is a point which is equidistant from all points on an internal surface of the first hemispherical portion.

Providing an apparatus in which an optical axis of an image acquisition device held by the first mount passes through a centre of the first hemispherical portion of the housing whilst the first mount moves relative to the housing means that the angle of incidence of the optical axis of the camera on the first hemispherical portion remains constant. This is advantageous as it minimises distortion in any images which are acquired by the camera.

In accordance with a second aspect of the present invention, there is provided an apparatus comprising: a housing for an image acquisition device; and a first mount disposed within the housing, the first mount being configured to hold an image acquisition device and being movable within the housing relative to the housing, wherein the housing and the first mount are configured such that an optical axis of an image acquisition device held by the first mount remains perpendicular to the housing whilst the first mount moves relative to the housing.

Providing an apparatus in which an optical axis of an image acquisition device held by the first mount remains perpendicular to the housing whilst the first mount moves relative to the housing is advantageous as it minimises distortion in any images which are acquired by the camera.

The housing and the first mount may be configured such that an optical axis of an image acquisition device held by the first mount remains perpendicular to the housing whilst the first mount moves relative to the housing. In particular, the housing and the first mount are positioned relative to one another such that an optical axis of an image acquisition device held by the first mount remains perpendicular to the housing whilst the first mount moves relative to the housing.

The housing may be a spherical housing. The housing may further comprise a second hemispherical portion which engages the first hemispherical portion to form a sphere. A portion, at least a portion, or all of the first hemispherical portion may be substantially transparent. The housing may comprise a substantially transparent or opaque window (sub-portion) which is shaped such that an optical axis of an image acquisition device held by the first mount remains incident on the window whilst the first mount moves relative to the housing. A portion, at least a portion, or all of a second hemispherical portion may be substantially transparent or opaque. In an alternative embodiment, whilst the first hemispherical portion may be hemispherical, a second portion may be non-hemispherical and the housing may therefore be non-spherical. A first sub-portion of the first hemispherical portion may be shaded, or covered (on its external or internal surface). A second sub-portion (e.g. the window) may be left uncovered or unshaded so that this second portion is transparent or opaque and is the portion through which the image acquisition device views objects which are external to the housing. As such, the image acquisition device's optical axis when viewing external objects at any position of the mount will always extend through a point of this second sub-portion. The second sub-portion may be shaped in the form of an ellipse, banana-like outline, rectangle, or rectangle having curved ends such that tilt movement of the image acquisition device moves the image acquisition device's optical axis across the second portion so that it remains within the sub-portion.

The apparatus may further comprise a second mount located at a mounting point on an external surface of the housing for attaching the housing to a surface. The surface may be a horizontal surface and may be parallel to the ground. The mount may extend perpendicularly to the surface.

A first plane defined by an interface between the first and second hemispheres may be neither parallel nor perpendicular to a second plane which passes through the mounting point and through a centre of the housing. In other words, the first plane defined by the interface between the first and second hemispheres may be tilted at an angle which is not 0°, 90°, 1800 or 270° to the ground and/or the surface to which the housing is attached. In other words, the first plane defined by the interface between the first and second hemispheres is neither horizontal nor vertical. The first mount may be located substantially at a centre of the housing and/or the first hemispherical portion. Again, the centre' of a substantially hollow hemispherical or spherical poition or structure, which can also be described as the "focus", is a point which is equidistant from all points on an interior surface of the hemispherical or spherical portion. Therefore, the centre of the first hemispherical portion of the housing is a point which is equidistant from all points on an internal surface of the first hemispherical portion.

Tilting the interface between the first and second hemispheres in this way means that the range of viewing angles of the camera which is positioned at the centre of the first hemispherical portion and whose optical axis passes through the centre of the first hemispherical portion increases when compared with a camera contained centrally within a housing having a horizontal interface between the two hemispheres. In particular, a camera contained centrally within the first hemispherical portion of the invention can point horizontally or upwards without its optical axis being blocked or obscured by the opaque second hemisphere or the interface between the first and second hemispheres. The reason that the camera is located at the centre of the housing and/or the first hemispherical portion is that the optical axis of the camera remains perpendicular to the first hemispherical portion and, consequently, distortion of any acquired image when the camera points through the first hemispherical portion is minimised. Therefore, the present invention provides a highly simple, elegant and compact arrangement in which i) the camera is centred within the first hemispherical portion to minimise distortion of any acquired images and U) the field of view (particularly with respect to tilt) of the camera is optimised e.g. the camera can point upwards without its view being obscured by the opaque second hemispherical poition.

The apparatus may further comprise a first motor for moving the first mount about a first axis. The apparatus may further comprise a second motor for moving the first mount about a second axis.

The first axis and the second axis may be substantially perpendicular to one another.

The first motor may be configured to move the first mount relative to the housing and the second motor may be configured to move the housing relative to the second mount. The first motor may be located within the housing and the second motor may be located outside the housing.

Alternatively, both the first motor and the second motor may be configured to move the first mount relative to the housing. Both the first motor and the second motor may be located within the housing.

The first axis may intersect the second hemisphere. The first motor and/or the second motor may be mounted on the second hemisphere. This helps to retain the structural integrity of the housing The first and second motors may be mounted substantially at a common mounting point inside or outside the housing. The second motor may be mounted on the second mount.

The first motor may be configured, in use, to rotate the first mount in a vertical direction. The first motor may be configured, in use, to provide tilt functionality.

The second motor may be configured, in use, to rotate the first mount in a horizontal direction. The second motor may be configured, in use, to provide pan functionality.

The apparatus may further comprise an image acquisition device mounted on the first mount, wherein the image acquisition device, first mount and housing are arranged such that the optical axis of the image acquisition device remains perpendicular to the housing whilst the first mount moves within the housing. The optical axis of the image acquisition device may be substantially parallel with a longitudinal axis of the image acquisition device. The optical axis of the image acquisition device may be the same as the longitudinal axis of the image acquisition device.

Brief Description of the Drawings

The present invention will now be described with reference to the accompanying drawings in which: Figs. 1 to 5 show perspective views of an apparatus according to an embodiment of the present invention from different sides; Figs. 6 to 10 show perspective views of the apparatus shown in Figs. ito 5 with a first hemispherical portion removed; Fig. 11 shows a top cut away view of an apparatus according to an embodiment of the invention; and Fig. 12 shows a further perspective view of an apparatus according to an embodiment of the invention.

Detailed Description of the Drawings

Figs. 1 to 5 show an apparatus 10 according to an embodiment of the invention. The apparatus 10 comprises a hollow, spherical housing 12 comprising a first hemispherical portion 14 and a second hemispherical portion 16. The first 14 and second 16 hemispherical portions are attached to one another at an interface 22 to form the spherical housing 12. The first 14 and second 16 hemispherical portions are typically attached to one another by gluing (e.g. using an adhesive) or bonding.

The first hemispherical portion 14 is typically constructed at least partially from transparent plastic.

Alternatively, glass or any other transparent material can be used. In the embodiment shown in Figs. ito 5, a shaded portion 18 of the first hemispherical portion 14 is covered (on its external or internal surface), and is, in the depicted embodiment painted black, leaving an unpainted portion which forms a transparent window 20. The shaded portion 18 typically remains partially or wholly transparent, although the shaded portion 18 can be partially or wholly opaque in some embodiments.

Figs. 6 to 10 show the apparatus 10 shown in Figs. ito 5 and described above with the first hemispherical portion 14 of the housing 12 removed to show the interior of the housing 12. As described above, the housing 12 is a hollow sphere.

The housing 12 is intended to contain an image acquisition device, such as a camera 26. The camera 26 is mounted on and/or held by a first mount 28 inside the housing 12. The first mount 28 is configured to permit the camera 26 to move relative to the housing 12, as will be described in more detail below. Moreover, a first motor 30 is in mechanical communication with the first mount 28, and is configured to move the camera 26 relative to the housing.

The first mount 28, and therefore the camera 26, is located at the centre or focus of the housing 12. This is also the centre or focus of the first hemispherical portion 14 i.e. the point which is equidistant from all points on an internal surface of the first hemispherical portion 14. The reason that the camera is located at the centre of the first hemispherical portion 14 is that the optical axis of the camera remains perpendicular to the first hemispherical portion 14 and, consequently, distortion of any acquired image when the camera 26 points through the first hemispherical portion 14 is minimised.

In one embodiment, the image acquisition device 26 is detachable from the first mount 28 and removable from the housing l2so that the apparatus 10 can be provided without the image acquisition device 26. In another embodiment, the image acquisition device 26 is integral with the first mount 28.

Referring again to Figs. 1 to 5, the apparatus 10 comprises a second mount 24 located at a mounting point on an external surface of the housing 12 for attaching the housing 12 to a surface, such as an interior of a roof, ceiling, ledge, beam or overhang. The second mount 24 is configured to permit the housing 12 to move relative to the second mount 24 (and therefore relative to the surface to which the mount is attached), as will be described in more detail below. Moreover, a second motor 25 is provided on the second mount 24 or attached to or in mechanical communication with the second mount 24 and is configured to move the housing 12 relative to the second mount 24. In some embodiments, the second motor 25 is mounted on the second hemispherical portion and may be mounted at a common mounting point with the first motor 30.

As discussed above, the first 14 and second 16 hemispherical portions are attached to one another at an interface 22. The interface 22 takes the shape of a grand circle of the housing 12 and defines a first two-dimensional plane, the direction of which is shown by A-A in Figs. ito 5. A second two-dimensional plane is defined by the second mount 24 and a centroid (i.e. the centre) of the housing 12 i.e. the second two-dimensional plane passes through the second mount 24 and the centre point of the housing 12. The direction of the second two-dimensional plane is shown by B-B in Figs. ito 5.

As shown in Figs. ito 5, the interlace 22 is tilted at an angle with respect to horizontal and vertical directions. In other words, the first two-dimensional plane which is defined by the interface 22 between the first 14 and second 16 hemispheres is neither parallel nor perpendicular to the second two-dimensional plane which passes through the mount 24 and through a centroid of the housing.

The angle between the first A-A and second B-B planes is shown as angle C in Fig. 12. The magnitude (which can be measured in a clockwise or anti-clockwise direction) of this angle C between the first A-A and second B-B planes can be 5°, 100, 15°, 200, 25°, 300, 35°, 400, 450, 500, 550, 60°, 65°, 700, 750, 80°, 85° or indeed any value greater than 0° but less than 900. Fig. 12 therefore demonstrates the tilting of the interface 22 between the first i4 and second 16 hemispheres. In other words, the first plane A-A defined by the interface 22 between the first 14 and second 16 hemispheres is tilted at an angle which is not 00, 90°, 180° or 2700 to the ground and/or the suiface to which the housing i2 is attached. In other words, the first plane A-A defined by the interface 22 between the first 14 and second 16 hemispheres is neither horizontal nor vertical.

As described above, the apparatus comprises a first motor 30 for moving the first mount 28, and therefore the camera 26, relative to the housing and a second motor 25 for moving the housing 12 relative to the second mount 24. In particular, first motor 30 is configured to move the first mount 28, and therefore the camera, about a first axis and the second motor 25 is configured to move the housing 12 about a second axis which is perpendicular to the first axis.

In an exemplary embodiment, the first motor 30 is configured, in use, to rotate the first mount 28, and therefore the camera 26, in a vertical direction to provide tilt functionality. The second motor 30 is configured, in use, to rotate the housing 12 in a horizontal direction to provide pan functionality.

Figs. 6 to iO demonstrate the tilt movement of the first mount 28 and, therefore, the camera 26 which is driven by the first motor 30. As shown in Figs. 6 to 10, the camera 26 rotates vertically to different tilt angles. It can be seen that the provision of a housing 12 with a tilted interface 22 between the first 14 and second 16 hemispheres means that the range of viewing angles of the camera which is positioned at the centre of the first hemispherical portion 14 and whose optical axis passes through the centre of the first hemispherical portion increases when compared with a camera contained centrally within a housing having a horizontal interface between the two hemispheres. In particular, as shown in Fig. 7, the camera 16 can point upwards without its optical axis being blocked or obscured by the opaque second hemisphere 16. As discussed above, the reason that the camera is located at the centre of the first hemispherical portion 14 is that this means that the optical axis of the camera remains perpendicular to the first hemispherical portion 14 and, consequently, distortion of any acquired image when the camera 26 points through the first hemispherical portion 14 is minimised. Therefore, the present invention provides a highly simple, elegant and compact arrangement in which i) the camera 26 is centred within the first hemispherical portion 14 to minimise distortion of any acquired images and ii) the field of view (particularly with respect to tilt) of the camera 26 is optimised e.g. the camera 26 can point upwards without its view being obscured by the opaque second hemispherical portion 16.

As described above and shown in Figs. ito 5, the first hemispherical portion 14 comprises a transparent window 20. The transparent window 20 is shaped such that the optical axis of the camera 26 held by the first mount 28 remains incident on the window 20 whilst the first mount 28 moves relative to the housing 12. In other words, the transparent window 20 and the first mount 28 are arranged such that the camera 26 points towards the window 20 whilst the first mount 28, and therefore the camera 26, moves relative to the housing 12.

The window 20, can take any suitable shape depending on the positioning and orientation of the first mount 28 within the housing 12. As described previously, it is advantageous for the first mount 28, and therefore the camera 26, to be centred within the first hemispherical portion 14 because this minimises the distortion in any acquired images. For the same reason, it is advantageous for the optical axis of the camera 26 to pass through the centre of the first hemispherical portion.

In some embodiments, the window 20 may be positioned such that it is substantially centred within the first hemispherical portion i.e. neither left nor right of centre, such that an axis D-D which passes through the centre of the window 20 divides the first hemispherical portion 14 into two equal semihemispherical portions (i.e. quarters of a sphere). However, this would typically require the first motor 30 to be mounted on the interface 22 between the first 14 and second 16 hemispheres, which can be difficult to achieve and can weaken the housing structurally.

Therefore, as shown in Fig. 11, it is advantageous for an axis D-D passing through a centre of the window 20 to be shifted at an angle F to the front of the housing 12 i.e. at an angle F to an axis E-E (shown in Fig. 11) which divides the first hemispherical portion 14 into two equal semihemispherical portions as described above. The magnitude of this angle F (which can be measured in a clockwise or anti-clockwise direction) can be 5°, 100, 15°, 20°, 25°, 30°, 35°, 400, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85° or indeed any value greater than 0° but less than 90°.

This means that the first axis about which the first mount 28 and the camera 26 rotate intersects the second hemispherical portion 16, and the first motor 30 can therefore be mounted on the second hemispherical portion 16, not at the interface 22 between the first 14 and second 16 hemispherical portions. This is advantageous structurally over a situation in which the first motor is mounted on the interface 22 between the first 14 and second 16 hemispheres.

Since the window 20 is shaped such that the optical axis of the camera 26 held by the first mount 28 remains incident on the window 20 whilst the first mount 28 moves relative to the housing 12, if the first axis, or tilt axis, is angled with respect to the front of the housing 12, the window 20 typically takes the form of a curved or banana" shape, as can be seen in Fig. 1.

Therefore, the present invention provides a highly simple, elegant and compact arrangement in which i) the camera 26 is centred within the first hemispherical portion 14 to minimise distortion of any acquired images and ii) the field of view (particularly with respect to tilt) of the camera 26 is optimised e.g. the camera 26 can point upwards without its view being obscured by the opaque second hemispherical portion 16, and üi) the first motor 30 is mounted on the second hemispherical portion 16 to retain the structural integrity of the housing 12.

As mentioned above, Fig. 12 demonstrates the tilting of the interface 22 between the first 14 and second 16 hemispherical portions. The interface 22 is tilted at an angle with respect to horizontal and vertical directions. In other words, the first two-dimensional plane which is defined by the interface 22 between the first 14 and second 16 hemispheres is neither parallel nor perpendicular to the second two-dimensional plane which passes through the mount 24 and through a centroid of the housing. The angle between the first A-A and second B-B planes is shown as angle C in Fig. 12. The magnitude of this angle C (which can be measured in a clockwise or anti-clockwise direction) between the first A-A and second B-B planes can be 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85° or indeed any value greater than 0° but less than 90°.

Fig. 12 therefore demonstrates the tilting of the interface 22 between the first 14 and second 16 hemispheres. In other words, the first plane A-A defined by the interface 22 between the first 14 and second 16 hemispheres is tilted at an angle which is not 00, 900, 180° or 270° to the ground and/or the surface to which the housing 12 is attached. In other words, the first plane A-A defined by the interface 22 between the first 14 and second 16 hemispheres is neither horizontal nor vertical.

Whilst the second hemispherical portion 16 has been described as being hemispherical in nature, this is not essential. As long as the first portion 14 is hemispherical, and the first mount 18 and camera 26 are centred within the first hemispherical portion 14, the second portion 16 can take any suitable shape, as will be understood by the skilled person. However, to assist with the construction/moulding process, it is preferred that both portions 14, 16 are hemispherical.

The present invention has been described above in exemplary form with reference to the accompanying drawings which represent embodiments of the invention. It will be understood that many different embodiments of the invention exist, and that these embodiments all fall within the scope of the invention as defined by the following claims.

Claims

Claims 1. An apparatus comprising: a housing for an image acquisition device, the housing having a first hemispherical portion; and a first mount disposed within the housing, the first mount being configured to hold an image acquisition device and being movable within the housing relative to the housing, wherein the housing and the first mount are configured such that an optical axis of an image acquisition device held by the first mount passes through a centre of the first hemispherical portion of the housing whilst the first mount moves relative to the housing.
2. An apparatus comprising: a housing for an image acquisition device; and a first mount disposed within the housing, the first mount being configured to hold an image acquisition device and being movable within the housing relative to the housing, wherein the housing and the first mount are configured such that an optical axis of an image acquisition device held by the first mount remains perpendicular to the housing whilst the first mount moves relative to the housing.
3. An apparatus according to claim 1, wherein the housing and the first mount are configured such that an optical axis of an image acquisition device held by the first mount remains perpendicular to the housing whilst the first mount moves relative to the housing.
4. An apparatus according to any one of claims 1 to 3, wherein the housing and the first mount are positioned relative to one another such that an optical axis of an image acquisition device held by the first mount remains perpendicular to the housing whilst the first mount moves relative to the housing.
5. An apparatus according to any one of the preceding claims, wherein the housing is a spherical housing.
6. An apparatus according to any one of the preceding claims, wherein the housing further comprises a second hemispherical portion which engages the first hemispherical portion to form a sphere.
7. An apparatus according to any one of the preceding claims, wherein a portion, at least a portion, or all of the first hemispherical portion is substantially transparent.
8. An apparatus according to any one of the preceding claims, wherein the housing comprises a substantially transparent window which is shaped such that an optical axis of an image acquisition device held by the first mount remains incident on the window whilst the first mount moves relative to the housing.
9. An apparatus according to any one of claims 6 to 8, wherein a portion, at least a portion, or all of a second hemispherical portion is substantially opaque.
10. An apparatus according to any one of the preceding claims, further comprising a second mount located at a mounting point on an external surface of the housing for attaching the housing to a surface.
11. An apparatus according to claim 9, wherein a first plane defined by an interface between the first and second hemispheres is neither parallel nor perpendicular to a second plane which passes through the mounting point and through a centre of the housing.
12. An apparatus according to any one of the preceding claims, wherein the first mount is located substantially at a centre of the housing and/or the first hemispherical portion.
13. An apparatus according to any one of the preceding claims, further comprising a first motor for moving the first mount about a first axis.
14. An apparatus according to claim 13, further comprising a second motor for moving the first mount about a second axis.
15. An apparatus according to claim 14, wherein the first axis and the second axis are substantially perpendicular to one another.
16. An apparatus according to claim 14 or claim 15, wherein the first motor is configured to move the first mount relative to the housing and the second motor is configured to move the housing relative to the second mount.
17. An apparatus according to claim 16, wherein the first motor is located within the housing and the second motor is located outside the housing.
18. An apparatus according to claim 14 or claim 15, wherein both the first motor and the second motor are configured to move the first mount relative to the housing.
19. An apparatus according to claim 18, wherein both the first motor and the second motor are located within the housing.
20. An apparatus according to any one of claims 13 to 19, wherein the first axis intersects the second hemisphere.
21. An apparatus according to any one of claims 13 to 20, wherein the first motor and/or the second motor is mounted on the second hemisphere.
22. An apparatus according to any one of claims 13 to 21, wherein the second motor is mounted on the second mount.
23. An apparatus according to any one of claims 13 to 22, wherein the first motor is configured, in use, to rotate the first mount in a vertical direction.
24. An apparatus according to any one of claims 13 to 23, wherein the first motor is configured, in use, to provide tilt functionality.
25. An apparatus according to any one of claims 14 to 24, wherein the second motor is configured, in use, to rotate the first mount in a horizontal direction.
26. An apparatus according to any one of claims 14 to 25, wherein the second motor is configured, in use, to provide pan functionality.
27. An apparatus according to any one of the preceding claims, further comprising an image acquisition device mounted on the first mount, wherein the image acquisition device, first mount and housing are arranged such that the optical axis of the image acquisition device passes through a centre of the first hemispherical portion of the housing whilst the first mount moves relative to the housing.
28. An apparatus according to any one of the preceding claims, further comprising an image acquisition device mounted on the first mount, wherein the image acquisition device, first mount and housing are arranged such that the optical axis of the image acquisition device remains perpendicular to the housing whilst the first mount moves within the housing.
29. An apparatus according to claim 27 or claim 28, wherein the optical axis of the image acquisition device is substantially parallel with a longitudinal axis of the image acquisition device.
30. An apparatus according to any one of claims 27 to 29, wherein the optical axis of the image acquisition device is the same as the longitudinal axis of the image acquisition device.
31. An apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.