GB2516298A

GB2516298A - Camera lens assembly

Info

Publication number: GB2516298A
Application number: GB1312889.7A
Authority: GB
Inventors: Alan Perrett; Simon Vaitkevicius; James Dallas
Original assignee: OMG PLC
Current assignee: Oxford Metrics PLC
Priority date: 2013-07-18
Filing date: 2013-07-18
Publication date: 2015-01-21
Also published as: GB201312889D0

Abstract

A camera unit 1 is assembled using an adjustment tool 50 having a plurality of engagement pins capable of fitting in engagement recesses 26 of a lens assembly. The lens assembly is fitted into a tube 20 of a mounting element by engaging internal and external screw threads engaged, and the adjustment tool is engaged against the lens assembly with the engagement pins fitting in the engagement recesses. The lenses focus light passing through the central aperture onto the image sensor, and while monitoring a captured image the adjustment tool is used to adjust the position of the lens assembly relative to the mounting element to focus the image formed by the lenses on the image sensor. In the lens assembly, an infra-red filter is fixed across the rear rim and the central bore of the lens barrel, which location avoids a dust trap.

Description

Camera Lens Assembly The present invention relates generally to camera units that include image sensors.

The present invention is particularly concerned with a miniature camera unit having a simple construction compared to a conventional stills camera. In a typical construction, the camera unit may include an image sensor assembly that comprises an image sensor mounted on a printed circuit board support and a lens assembly that comprises a lens barrel and a plurality of lenses mounted inside the lens barrel for forming an image on the image sensor. The image sensor assembly and the lens assembly may be manufactured separately and assembled together to form the camera unit.

The first aspect of the present invention is concerned with the assembly of the camera unit. In particular, when the image sensor assembly and the lens assembly are assembled together, it is necessary to precisely position the lens assembly relative to the mounting element to focus the image formed by the lenses on the image sensor.

According to a first aspect of the present invention, there is provided a method of assembling a camera unit from an image sensor assembly and a lens assembly using an adjustment tool, wherein the image sensor assembly comprises: an image sensor mounted on a printed circuit board support; and a mounting clement fixed to the printed circuit board support, the mounting clement comprising a tube having a cylindrical bore aligned with the image sensor, the cylindrical bore having an intemal screw thread; the lens assembly comprises a lens barrel and a plurality of lenses mounted inside the lens barrel, the lens barrel having an external screw thread that matches the internal screw thread of the cylindrical bore of the mounting element, and the lens barrel having an annular front surface in which a plurality of engagement recesses are formed; and the adjustment tool comprises an annular body with a central aperture, the annular body having a plurality of engagement pins capable of fitting in the engagement recesses of the lens assembly, the method comprising: fitting the lens assembly into the mounting element with the internal and external screw threads engaged, and engaging the adjustment tool against the lens assembly with the engagement pins fitting in the engagement recesses and the central aperture of the annular body aligned with the lens barrel so that the lenses focus light passing through the central aperture onto the image sensor; and while monitoring an image captured by the image sensor, using the adjustment tool to adjust the position of the lens assembly relative to the mounting element to focus the image formed by the lenses on the image sensor.

This method uses an image sensor assembly including a mounting element that is fixed to the printed circuit board support on which the image sensor is mounted. The mounting element comprises a tube having a cylindrical bore aligned with the image sensor. By means of the cylindrical bore having an internal screw thread and the lens barrel of the lens assembly having a matching external screw thread, the position of the lens assembly relative to the mounting element may be adjusted by screwing. As the mounting element is fixed to the printed circuit board support, it is possible to provide precise control of the position of the lens assembly relative to the image sensor as necessary to provide good optical performance.

The use of adjustment tool with its particular construction, and the corresponding construction of the lens barrel provides particular advantages of providing for precise adjustment of the position of the lens assembly relative to the mounting element. The construction of the adjustment tool as an annular body having a plurality of engagement pins enables a robust engagement of the lens assembly while providing a central aperture that allows light to pass through the central aperture to be focused on the image sensor by the lenses of the lens assembly. This allows the adjustment to be performed while monitoring an image captured by the image sensor, permitting an accurate adjustment of the focus of the image formed by the lenses.

The annular front surface of the lens barrel has a construction with a plurality of engagement recesses in which the plurality of engagement pins are capable of engagement.

The engagement recesses co-operate with the engagement pins to provide a robust engagement that facilitates a precise adjustment to be made. This is achieved with engagement recesses that have minimal structural impact on the assembled camera unit.

Advantageously, the step of using the adjustment tool to adjust the position of the lens assembly may be performed while applying pressure from the adjustment tool onto the lens assembly. Such a positive pressure improves the precision of the adjustment process by reducing the freedom of movement and therefore reducing slippage of the lens asscmbly. This is a particular advantage when the position of the lens assembly is fixed relative to the mounting element, for example by adhesive, because it reduces the risk of relaxation or back-lash occurring prior to the fixing.

In one advantageous construction, the annular front surface of the lens assembly is planar and the adjustment tool has a planar annular rear surface from which the engagement pins extend. As a result, the adjustment tool may be engaged against the lens assembly with the annular front surface of the lens assembly and the annular rear surface of the adjustment tool in contact. In that case, the planar nature of those surfaces provides a robust engagement between the lens assembly and the adjustment tool that facilitates precise adjustment.

The present method is particularly suitable for a camera unit in which the lens assembly is fitted into the mounting element with the annular front surface of the lens asscmbly flush with or below the front surface of the mounting clement. In that case, construction with a plurality of engagement recesses in the annular front surface of the lens barrel allows engagement to be made without the need to insert a tool between the lens assembly and the mounting element.

The lens assembly may have a front portion which is radially wider than the remainder of the lens barrel. In that case, the annular front surface in which the engagement recesses are formed may be the front surface of that front portion. That width extra allows the engagement between the lens assembly and the adjustment tool to be improved.

The central aperture of the annular body may be frustoconical, widening forwardly.

That allows the method to be applied to lenses providing a relatively wide field of view without impacting on the operation of the adjustment tool.

The present method is particular suitable for a camera unit in which the plurality of lenses have a fixed focus. In the absence of the lens assembly providing an active, variable focus, precision in the adjustment made during assembly is particular important since the lenses are not focussed during use.

Further according to the first aspect of the present invention, there may be provided a camera unit that is adapted for use in the method.

The second aspect of the present invention is concerned with the design of the lens assembly. A particular issue is the collection of dust inside the camera. Over time, this can obscure the optics and cause defects or blemishes that reduce the quality of images captured by the image sensor.

According to a second aspect of the present invention, there is provided a camera unit comprising: an image sensor assembly that comprises: an image sensor mounted on a printed circuit board support; and a mounting element fixed to the printed circuit board support, the mounting clement comprising a tube having a cylindrical bore aligned with the image sensor, thc cylindrical bore having an intemal screw thread; and a lens assembly comprising: a lens barrel having a central bore, a rear rim and an external screw thread that matches the internal screw thread of the mounting element; a plurality of lenses mounted inside the central bore of the lens barrel; and an infra-red filter fixed across the rear rim and the central bore of the lens barrel, the lens assembly being fitted into the mounting element of the image sensor assembly with the internal and external screw threads engaged.

This aspect of the invention applies to a camera unit that includes an image sensor assembly including a mounting element that is fixed to the printed circuit board support on which the image scnsor is mounted. The mounting clement comprises a tube having a cylindrical bore aligned with the image sensor. By means of the cylindrical bore having an internal screw thread and the lens barrel of the lens assembly having a matching external screw thread, the position of the lens assembly relative to the mounting element may be adjusted by screwing. As the mounting element is fixed to the printed circuit board support, it is possible to provide precise control of the position of the lens assembly relative to the image sensor as necessary to provide good optical performance.

The location for the infra-red filter fixed across the rear rim and the central bore of the lens barrel provides advantages over a more usual arrangement in which an infra-red filter is fixed inside the central bore of a lens barrel. In that more usual arrangement, the construction effectively forms a dust-trap inside the lens barrel in the corners between the infra-red filter and the lens barrel itself, where dust tends to collect. This is avoided in the second aspect of the present invention, and so the collection of dust on the infra-rcd filter over time is reduced. That in turn limits the defects or blemishes caused by such collection of dust and that otherwise reduce image quality.

The first and second aspects of the present invention may be applied in combination. Thus, the optional features of each aspect of the present invention may be used in the other aspect of the present invention, in any combination.

An embodiment of the present invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which: Fig. I is an exploded perspective view from above of a camera unit; Fig. 2 is a perspective view from below of the camera unit; Fig. 3 is a schematic cross-sectional view, taken along the optical axis, of a lens assembly of the camera unit; Fig. 4 is a schematic cross-sectional view, taken along the optical axis, of a lens assembly in an alternative arrangement; Fig. 5 is a schematic perspective view from above of an assembly tool; Fig. 6 is a schematic cross-sectional view, taken along the optical axis, of the camera unit during assembly using the adjustment tool; Fig. 7 is a schematic cross-sectional view, taken along the optical axis, of the camera unit during assembly using the adjustment tool in an alternative form; and Fig. 8 is a perspective view of a camera incorporating the camera unit.

As shown in Fig. I, a camera unit I comprises an image sensor assembly 2 and a lens assembly 3.

The image sensor assembly 2 includes a printed circuit board support 3 having an image sensor 4 mounted thereon. The image sensor 4 may be of any suitable type for example a CMOS (complimentary metal-oxide-semiconductor) device. In the following description, the terms "front" and "rear", and so on, are used to describe location with respect to forwards direction which the image sensor 4 faces for sensing light.

The printed circuit board support 3 has an arm 5 that supports a control circuit 6.

The control circuit 6 controls the image sensor 4 to capture still images that may be stored in a memory. The control circuit 6 may be implemented by a processor running an appropriate program. The control circuit 6 may include conventional elements to control the parameters of operation of the image sensor 4 such as exposure time.

The control circuit 6 may further include a sensor arrangement that includes plural sensors that sense different physical parameters of the camera unit 1 or its surroundings.

Some non-limitative examples include: sensing of the location of the camera unit 1 for example using a GPS (global positioning system) receiver; sensing of orientation and/or linear and/or rotational speed and/or acceleration of the camera unit I for example using a gyroscope sensor and/or accelerometer; sensing of magnetic fields using a magnetometer; sensing of ambient light conditions; sensing of motion of external objects using an external motion sensor, that may be for example an infra-red motion sensor; sensing of temperature using a thermometer; and sensing of sound.

The control circuit 6 controls the image sensor 4 to capture still images intermittently in response to the outputs of the sensors of the sensor arrangement. This allows the images to be captured without capture of individual images being triggered by the user. Capture of images may be triggered when the outputs of the sensors of the sensor arrangement indicate a change or a high level on the basis that this suggests occurrence of an event that might be of significance to the user. Capture may be triggered based on a single sensor or a combination of sensors. That allows for intelligent decisions on the timing of image captures, in a way that increases the chances of the images being of scenes that are in fact significant to the user. Images are captured intermittently over a period of time, for example by capturing an image when the period since the last capture exceeds a limit or by over time reducing the thresholds on the outputs of the sensors used for triggering.

The image sensor assembly 2 further includes a mounting clement 7 comprising a tube 8 having a cylindrical bore 9. As shown in Fig.2 The mounting element 7 is fixed to the printed circuit board support 3 by a pair of stud fittings 10 that provide a rigid fixing.

The cylindrical bore 9 is adapted to receive the lens assembly 3 as described below, for which purpose it has an internal screw thread II. Thus, when the mounting element 7 is fixed to the printed circuit board support 3, the cylindrical bore 9 is aligned with the image sensor 4. As the mounting element 7 is fixed to the printed circuit board support 3, it is possible to provide precise control of the position of the lens assembly 3 relative to the image sensor 4 as necessary to provide good optical performance.

As shown in Fig. 3, the lens assembly 4 comprises a lens barrel 20 and a plurality of lenses 21 mounted inside the lens barrel 20. Although two lenses 21 are shown in Fig. 3, in general the lens assembly 4 may include any number of lenses 21. The lenses 21 provide a fixed focus. In the absence of the lens assembly 3 providing an variable focus, it is important that the lens assembly 3 is precisely positioned relative to the image sensor 4, as the lenses 21 are not actively focussed during use.

The size of the image sensor 4 has a consequential effect on the size of the other components and hence the camera unit I as a whole. In general, the image sensor 4 may be of any size, but since the camera is to be worn, the image sensor 4 is typically relatively small. For example, the image sensor 4 may typically have a diagonal of 6.00mm (corresponding to a 1/3" type image sensor) or less, or more preferably 5.68mm (corresponding to a 1/3.2" type image sensor) or less.

In normal use, the camera unit 1 will be directed generally in the same direction as the user, but may not be directed at a scene that has a natural point of interest since the user does not know when image capture will occur. For this reason, it is desirable that the lens assembly 3 has a relatively wide field of view ("wide angle"). For example, the lens assembly 3 may typically have a diagonal field of view of 85 degrees or more, or more preferably 100 degrees or more.

The lens barrel 20 has a central bore 40 inside which the lenses 21 are mounted and a rear rim 41. The lens assembly 3 further includes an infra-red filter 42, which is fixed across the rear rim 41 and the central bore 40 of the lens barrel 20.

This location of the infra-red filter 42 effectively closes the central bore 20 without creating any dust-traps. By way of comparison, Fig. 4 shows alternative arrangement for the lens assembly 3 that is identical to that of Fig. 3 except that the infra-red filter 42 is fixed inside the central bore 40 by an adhesive bead 43. With this location of the infra-red filter 42 a dust-trap is formed inside the central bore 40 in the corners between the infra-red filter 42 and the lens barrel 20 itself Over time dust tends to collect in this dust-trap causing defects or blemishes in the image captured by the image sensor 4 and so reduce the image quality. In contrast, this is avoided in the arrangement of the lens assembly 4 shown in Fig. 4 which therefore collects less dust and limits the consequent reduction in image quality.

To provide fitting of the lens assembly 3 in the mounting element 7, the lens barrel has an external screw thread 22 that matches the internal screw thread 11 of the cylindrical bore 9. This allows the position of the lens assembly 3 to be adjusted relative to the mounting elcment 7 by screwing.

The lens barrel 20 has a front portion 23 which is radially wider than the remainder 24 of the lens barrel 20. The front portion 23 has an annular front surface 25 that is planar and in which engagement recesses 26 are formed. In this example there are two engagement recesses 26, but in general there could be any number of engagement recesses 26, preferably evenly spaced around the annular front surface 25.

During assembly of the camera unit 1, adjustment of the position of the lens assembly 3 relative to the mounting element 7 is performed using an adjustment tool 50 as shown in Fig. 5. The adjustment tool 50 comprises an annular body 51 with a central aperture 52 that is frustoconical, widening forwardly. The annular body 51 has an annular rear surface 53 that is planar and from which a plurality of engagement pins 52 extend rearwardly. The engagement pins 52 match the engagement recesses 26 of the lens assembly 3 so that they are capable of fitting therewithin.

The method of assembling the image sensor assembly 2 and the lens assembly 3 to form the camera unit 1 will now be described.

The lens assembly 3 is fitted into the mounting element 3 with the internal screw thread II of the cylindrical bore 9 engaged with the external screw thread 22 of the lens barrel 20. As can be seen in Fig. 6, the lens assembly 3 fits in the mounting element 7 with the annular front surface 25 of the lens assembly 3 flush with (or in an alternative not shown, below) the front surface 12 of the mounting element 7.

Subsequently, or as part of the process of fitting the lens assembly 3 into the mounting clement 3, the adjustment tool 50 is engaged against the lens assembly 3 as shown in Fig. 6. The engagement involves the engagement pins 54 of the adjustment tool fitting in the engagement recesses 26 of the lens assembly 3, so that they co-operate together. There is also a secure contact between the annular front surface 25 of the lens assembly 3 and the annular rear surface 53 of the adjustment tool 50. This provides a robust engagement between the adjustment tool 50 and the lens assembly 3 that allows the adjustment tool 50 to provide precise control of the position of the lens assembly 3. This is achieved with a construction of the lens assembly 3 in which the engagement recesses 26 have minimal structural or visual impact on the assembled camera unit 1.

The robust engagement is also assisted by the extra width of the front portion 23 of the lens barrel 20, which increase the degree of contact and allows for larger engagement recesses 26, as compared to the lens barrel 20 being of a constant width.

This construction with a plurality of engagement recesses 26 in the annular front surface 25 of the lens barrel 20 allows the engagement to be made without the need to insert a tool between the lens assembly 3 and the mounting element 7.

The engagement the adjustment tool 50 against the lens assembly 3 also aligns the central aperture 52 of the annular body 51 with the lens barrel 20. As a result, the lenses 21 focus light passing through the central aperture 52 onto the image sensor 4. Accordingly the central aperture 52 allows the image sensor 4 to be operated during the adjustment.

Taking advantage of that, the adjustment tool 50 is used to adjust the position of the lens assembly 3 relative to the mounting element 7 while monitoring an image captured by the image sensor 3. The adjustment tool 50 may be moved by hand or by a mechanical drive arrangement that grips the annular body 51. Based on the image, the adjustment is performed to focus the image formed by the lenses 20 on the image sensor 4. Such monitoring of an image captured by the image sensor 4 permits accurate adjustment of the focus. The frustoconical shape of the central aperture 52 of the adjustment tool 50 allows the method to be applied to lenses 20 that provide a relatively wide field of view without impacting on the operation of the adjustment tool 50.

After the adjustment has been performed, the position of the lens assembly 3 is fixed relative to the mounting element 7 by adhesive that is inserted into the cylindrical bore 9 of the mounting element through a hole in the tube 8, although fixing by any suitable means could be performed.

While the adjustment tool 50 is used to adjust the position of the lens assembly, pressure is applied from the adjustment tool 50 onto the lens assembly 3. The positive pressure may be applied using magnets or by gravity, by arranging the camera unit 1 facing upwards so the weight of the adjustment tool 50 presses it down into the lens assembly 3.

Such a positive pressure improves the precision of the adjustment process by reducing the freedom of movement and therefore reducing slippage of the lens assembly 3. This reduces the risk of relaxation or back-lash of the lens assembly 3 occurring prior to the fixing.

Fig. 7 illustrates an alternative form of the adjustment tool 50 in a clamp arrangement 55 arranged to apply a positive pressure and constructed as follows..

The adjustment tool 50 has the same form as described above, but the annular body 51 is rotatably mounted in a bearing ring 56 of the clamp arrangement 55 that may provide any suitable form of bearing to allow rotation of the annular body 51. The clamp arrangement 55 includes a back plate 57 and a pair of arms 58 fixed to the bearing ring 56.

The back plate 57 mounts a pair of hinged clamps 59 that are arranged to engage respective catches 60 on the end of each arm 58.

To provide adjustment, the camera unit I is positioned on the back plate 57 and the adjustment tool 50 is engaged against the lens assembly 3 as shown in Fig. 8. The arms 58 have a gull-wing shape so that upon such engagement they extend around the camera unit 1 to position the catches 60 for engagement by the clamps 59. After such engagement of the adjustment tool 50, the clamps 59 arc engaged to generate the positive pressure from the adjustment tool 50 onto the lens assembly 3.

Thereafter, the annular body 5 1 is rotated inside the bearing ring 56, driven by hand or a mechanical drive, to adjust the position of the lens assembly 3 relative to the mounting element 7 while monitoring an image captured by the image sensor 3 in the manner described above.

The alternative form of the adjustment tool 50 shown in Fig. 7 provides the advantage of allowing the positive pressure to be applied as a separate step after the adjustment tool 50 is engaged against the lens assembly 3, thereby reducing the risk of the engagement pins 54 scratching the front surface 12 of the mounting element 7.

The assembled camera unit 1 may be incorporated into the housing 60 of a camera 61 as shown in Fig. 8.

Claims

Claims A method of assembling a camera unit from an image sensor assembly and a lens assembly using an adjustment tool, wherein the image sensor assembly comprises: an image sensor mounted on a printed circuit board support; and a mounting clcment fixcd to thc printed circuit board support, the mounting clement comprising a tubc having a cylindrical borc aligned with thc imagc sensor, the cylindrical bore having an internal screw thread; the lens assembly comprises a lens barrel and a plurality of lenses mounted inside the lens barrel, the lens barrel having an external screw thread that matches the internal screw thread of the cylindrical bore of the mounting element, and the lens barrel having an annular front surface in which a plurality of engagement recesses are formed; and the adjustment tool comprises an annular body with a central aperture, the annular body having a plurality of engagement pins capable of fitting in the engagement recesses of the lens assembly, the method comprising: fitting the lens assembly into the mounting element with the internal and external screw threads engaged, and engaging the adjustment tool against the lens assembly with the engagement pins fitting in the engagement recesses and the central aperture of the annular body aligned with the lens barrel so that the lenses focus light passing through the central aperture onto the image sensor; and while monitoring an image captured by the image sensor, using the adjustment tool to adjust the position of the lens assembly relative to the mounting element to focus the image formed by the lenses on the image sensor.
2. A method according to claim 1, wherein said step of using the adjustment tool to adjust the position of the lens assembly is performed while applying pressure from the adjustment tool onto the lens assembly.
3. A method according to claim I or 2, further comprising, after using the adjustment tool to adjust the position of the lens assembly, fixing the position of the lens assembly relative to the mounting element by adhesive.
4. A method according to any one of the preceding claims, wherein the annular front surface of the lens assembly is planar, the adjustment tool has a planar annular rear surface from which the engagement pins extend, and the adjustment tool is engaged against the lens assembly with the annular front surface of the lens assembly and the annular rear surface of the adjustment tool in contact.
5. A method according to any one of the preceding claims, wherein the lens assembly is fitted into the mounting element with the annular front surface of the lens assembly flush with or below the front surface of the mounting element.
6. A method according to any one of the preceding claims, wherein the lens barrel has a front portion which is radially wider than the remainder of the lens barrel, the annular front surface being the front surface of that front portion.
7. A method according to any one of the preceding claims, wherein the central aperture of the annular body is frustoconical, widening forwardly.
8. A method according to any one of the preceding claims, wherein the step of using the adjustment tool to adjust the position of the lens assembly relative to the mounting element is performed whilst applying positive pressure from the adjustment tool onto the lens assembly.
9. A method according to claim 8, wherein the step of engaging the adjustment tool against the lens assembly farther comprises applying positive pressure from the adjustment tool onto the lens assembly by a clamping arrangement.
10. A method according to any one of the preceding claims, wherein the plurality of lenses have a fixed focus.
11. A method according to any one of the preceding claims, wherein the image sensor has a diagonal of 6.00mm or less.
12. A method according to any one of the preceding claims, wherein the lens assembly has a diagonal field of view of 85 degrees or more.
13. A method of assembling a camera unit from an image sensor assembly anda lens assembly substantially as hereinbefore described with reference to Figs. I to 4 and 6 of the accompanying drawings.
14. A camera unit comprising: an image sensor assembly that comprises: an image sensor mounted on a printed circuit board support; and a mounting element fixed to the printed circuit board support, the mounting element comprising a tube having a cylindrical bore aligned with the image sensor, the cylindrical bore having an internal screw thread; and the lens assembly comprises a lens barrel and a plurality of lenses mounted inside the lens barrel, the lens barrel having an external screw thread that matches the internal screw thread of the cylindrical bore of the mounting element, and the lens barrel having an annular front surface in which a plurality of engagement recesses are formed, the lens assembly being fitted into the mounting element with the internal and external screw threads engaged, and in a position relative to the mounting element in which it focuses the image formed by the lenses on the image sensor.
15. A camera unit according to claim 14, wherein the position of the lens assembly relative to the mounting element is fixed by adhesive.
16. A camera unit according to claim 14 or 15, wherein the annular front surface of the lens assembly is planar.
17. A camera unit according to any one of claims 14 to 16, wherein the lens assembly is fitted into the mounting element with the annular front surface of the lens assembly flush with or below the front surface of the mounting clement.
18. A camera unit according to any one of claims 14 to 17, wherein the lens barrel has a front portion which is radially wider than the remainder of the lens barrel, the annular front surface being the front surface of that front portion.
19. A camera unit according to any one of claims 14 to 18, wherein the plurality of lenses have a fixed focus.
20. A camera unit according to any one of claims 14 to 19, wherein the image sensor has a diagonal of 6.00mm or less.
21. A camera unit according to any one of claims 14 to 20, wherein the lens assembly has a diagonal field of view of 85 degrees or more.
22. A camera comprising a camera unit according to any one of claims 14 to 21 incorporated in a housing.
23. A camera unit constructed substantially as hereinbefore described with reference to Figs. 1,2,4 and 6 of the accompanying drawings.
24. A camera unit comprising: an image sensor assembly that comprises: an image sensor mounted on a printed circuit board support; and a mounting clement fixed to the printed circuit board support, the mounting element comprising a tube having a cylindrical bore aligned with the image sensor, the cylindrical bore having an internal screw thread; and a lens assembly comprising: a lens barrel having a central bore, a rear rim and an external screw thread that matches the internal screw thread of the mounting element; a plurality of lenses mounted inside the central bore of the lens barrel; and an infra-red filter fixed across the rear rim and the central bore of the lens barrel, the lens assembly being fitted into the mounting element of the image sensor assembly with the internal and external screw threads engaged.
25. A camera unit according to claim 24, wherein the lens assembly has a diagonal fidd of view of 85 degrees or more.
26. A camera unit according to claim 24 or 25, wherein the plurality of lenses have a fixed focus.
27. A camera unit according to any one of claims 24 to 26, wherein the lens barrel has an annular front surface in which a plurality of engagement recesses are formed.
28. A camera unit according to any one of claims 24 to 27, wherein the image sensor has a diagonal of 6.00mm or less.
29. A camera comprising a camera unit according to any one of claims 24 to 28 incorporated in a housing.
30. A lens assembly constructed substantially as hercinbeforc described with reference to Figs. 1,2,4 and 6 of the accompanying drawings.