GB2485976A

GB2485976A - Interchangeable lens assembly and camera having same

Info

Publication number: GB2485976A
Application number: GB1020027.7A
Authority: GB
Inventors: Martin Brookfield
Original assignee: Infrared Integrated Systems Ltd
Current assignee: Infrared Integrated Systems Ltd
Priority date: 2010-11-25
Filing date: 2010-11-25
Publication date: 2012-06-06
Also published as: GB201020027D0

Abstract

A lens assembly for a camera comprises a cylindrical body 1c and one or more lenses 1b mounted in or on the cylindrical body, the body having a flat surface 1d at one end arranged to abut against a flat surface on a mounting plate 2 of the camera and one or more protrusions 1e from and/or openings in the flat surface each adapted to co-operate with a corresponding opening 2a in or protrusion from the camera mounting plate. Thus the axial position of the lens assembly with respect to the camera is defined by the facing flat surfaces of the lens assembly and the camera mounting plate and the assembly is secured against radial movement by the co-operation of the one or more protrusions and/or openings in the camera mounting plate and lens assembly respectively. The assembly may then be held in place against axial movement with respect to the camera by securing means which are optionally part of the lens assembly. The camera may also comprise imager electronics configured to read lens identification data provided on the lens assembly.

Description

Interchangeable Lens Assembly and Camera Having Same The present invention relates to cameras having interchangeable lenses and interchangeable lenses for cameras. The lens assembly to be described below has been designed particularly for a thermal imaging camera but is equally suitable for other types of camera.

It is known that high specification thermal cameras may use different lenses having different focal length and/or aperture. These lenses are usually interchangeable. They are therefore commonly provided in interchangeable lens assemblies designed to be attached to the same camera chassis.

In the current state of art there are two main types of camera mounts, i.e. mechanisms for attaching lens assemblies to cameras, namely screw type or bayonet type.

In the screw type mounts, inner threads and outer threads are formed on the camera chassis and the lens assembly respectively. These screw threads are used to connect the lens assembly to the camera chassis and position the lens assembly accurately in relation to the camera chassis. Screw type mounts are often machined from aluminum alloys. A disadvantage of this type of mount is that they are prone to binding and seizure.

Bayonet mounts usually consist of one or more lugs provided on the lens assembly and a locking ring on the camera chassis with matching slots and spring(s) to keep the two parts locked together. To assemble the lens assembly with the camera chassis, either the lens assembly or the locking ring is rotated by about a quarter of a turn to lock the lens assembly in place. However, bayonet mounts are prone to wobble and breakage. The locking lugs of such mounts have to be made to fine tolerance limits from high grade materials since they are highly stressed when the lens is knocked or the camera is dropped.

Furthermore, a common problem of screw and bayonet mounts is their cost. To achieve accurate alignment and positioning of the lens with respect to the camera imaging array, and hence good imaging effects, the mounts between the camera chassis and the interchangeable lens demand complex high precision machined metal parts. As the cost of thermal imaging cameras comes down the cost of these parts represents an increasingly significant element of the total.

GEN ERAL

In one aspect, there is provided in the following a lens assembly for a camera comprising a cylindrical body and one or more lenses mounted in or on the cylindrical body, the body having a flat surface at one end arranged to abut against a flat surface on a mounting plate of the camera and one or more protrusions from and/or openings in the flat surface each adapted to co-operate with a corresponding opening in or protrusion from the camera mounting plate.

Thus the axial position of the lens assembly with respect to the camera is defined by the facing flat surfaces of the lens assembly and the camera mounting plate and the assembly is secured against radial movement by the co-operation of the one or more protrusions and/or openings in the camera mounting plate and lens assembly respectively. The assembly may then be held in place against axial movement with respect to the camera by securing means which are optionally part of the lens assembly. The securing means may comprise one or more devices for securing the assembly with respect to the camera.

Only the co-operating surfaces of the lens assembly and the camera need to be accurately machined in order to ensure accurate positioning of the lens with respect to the camera imaging array. In this arrangement these surfaces comprise the abutting flat surfaces and the co-operating surfaces of the protrusion(s) and corresponding opening which can be very simple. In contrast to the bayonet and screw mechanisms, the means for axially securing the lens assembly with respect to the camera does not itself determine the position of the lens with respect to the camera and therefore the manufacture of this part of the mechanism does not require particular accuracy.

In a preferred embodiment, the one or more protrusions comprise a single protrusion encircling the lens aperture. Preferably this is in the form of an annular protrusion concentric with the cylindrical body having cylindrical outer and inner radial surfaces. Other arrangements are possible. For example the protrusion could have a non-cylindrical outer surface so as to prevent rotational movement of the lens assembly with respect to the camera chassis. In an alternative arrangement multiple protrusions could be provided in the form of locating pins protruding from the mounting plate or the cylindrical body to be received in corresponding openings in the camera mounting plate or cylindrical body respectively.

The cylindrical body preferably comprises a radially outwardly extending flange which provides the flat surface for abutment against the camera mounting plate.

The securing means is preferably separately formed and attached to the cylindrical body and is optionally made from a different material from that of the flat surface and the opening(s) or protrusion(s). The securing means can take any of a number of forms. For example the securing means may comprise one or more clamps or clips for securing the lens assembly to the camera chassis.

In the preferred embodiment the securing means comprise a collar encircling the cylindrical body having one or more features on its outer surface for engaging one or more corresponding features on the camera chassis, such as a screw thread or bayonet mechanism. Since this screw thread or bayonet mechanism is not responsible for precisely locating the lens assembly it need not be accurately machined. All that is required is that it secures the flat surface of the lens assembly against the corresponding flat surface of the camera mounting plate.

There is also provided in the following a camera having one or more lens assemblies as described above.

As noted above the means for securing the lens assembly may be pad of the lens assembly or pad of the camera or a separate item. Thus there is also provided a kit comprising one or more lens assemblies as described above, a camera comprising a mounting plate fixed with respect to the chassis having a flat surface, the flat surface having one or more openings in and/or protrusions from the flat surface each adapted to co-operate with a corresponding protrusion from or opening in the flat surface of the lens assembly; and means for securing the lens assembly against axial movement with respect to the camera.

Preferably the camera is a thermal imager.

The camera and lens assembly described above are not only suitable for designs in which the lens assembly is interchangeable. The advantages in terms of robustness and lowered manufacturing cost are useful in cameras having fixed lens assemblies.

DRAWINGS

Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a perspective view of a lens assembly as described above having a threaded collar; Figure 2 is a perspective view of the lens assembly of figure 1 with the threaded collar removed; Figure 3 is a perspective view of part of a camera chassis designed to receive the lens assembly of figure 1; and Figure 4 is schematic partial cross sectional view of the lens assembly of figure 1 coupled to the camera chassis of figure 3.

DETAILED DESCRIPTION

Lens assembly Referring to figures 1 to 4 of the drawings, a lens assembly I comprises a generally cylindrical body in the form of a cylindrical mounting tube I c on which focus lens I b is mounted. The focus lens will typically comprise several lens elements. Additional lenses may be housed in the tube I c. At the opposite end of the tube from the focus lens the tube I c is provided with a radially outwardly extending flange I a preferably of square or rectangular section. The rear surface I d of the flange I a is machined flat and abuts against a flat surface of the camera in use in a manner to be described in more detail below. A protrusion 1 e extends from the flat surface 1 d of the tube I c. This is an annular protrusion which encircles the lens aperture If.

The focus lens I b is rotatable and axially moveable in the mounting tube I c for focusing the camera. For this purpose the focus lens has a surround Ig having a knurled outer surface to facilitate gripping as shown most clearly in figures 1 and 2.

Preferably the flange I a is an integral part of the mounting tube I c. Preferably the mounting tube Ic and the flange Ia are made of metal machined with high precision.

The lens assembly includes a collar 3 encircling the mounting tube Ic and having a threaded outer surface. Preferably the surround I g of the focus lens I b extends radially outwardly from the tube 1 c so that the collar 3 is trapped between the flange 1 a and the surround of the focus lens and cannot easily be removed from the tube I c. This is shown most clearly in figure 4.

Alternatively the collar 3 may be a separate component from the lens assembly I. In that case it is preferable for the surround I g of the focus lens I b not to extend radially beyond the outer surface of the tube Ic so that the collar can simply slide onto the tube over the surround I g of the focus lens lb. The collar has a flange 3a extending radially outwardly from the threaded surface to facilitate gripping as the flange is screwed into the camera chassis.

Camera Mounting Plate Referring now to figures 3 and 4, a mounting plate 2 is provided on the chassis 4 of the camera. The plate 2 has a central circular hole 2a. The inner diameter of the hole fits exactly with the outer diameter of the protrusion le of the cylindrical mounting tube Ic but is smaller than the diameter of the flange I a. Therefore the mounting plate 2 is able to receive the cylindrical mounting tube I c in an axial sliding fit and mounting tube I c is stopped at the position where the rearflat surface of the flange I a abuts against the front flat surface of the mounting plate 2. Due to this arrangement, the position of the focus lens I b is axially controlled by the interface between the flat surface of the flange Ia and the flat surface of the front plate 2. The radial position of the focus lens I b is controlled by the interface between the cylindrical outer surface of the protrusion le of the tube Ic and the inner surface of the hole 2a in the front plate 2. For this reason these surfaces need to be formed with high precision.

Chassis and Threaded Collar The mounting plate 2 may be fixed on the chassis 4 of the camera, part of which is shown in figures 3 and 4. The chassis 4 has a cylindrical recess 4a in front of the mounting plate 2 which is internally threaded to receive the threaded collar 3. The inner diameter of the collar is larger than the outer diameter of the cylindrical mounting tube I c but smaller than the outer diameter of the flange Ia. Therefore, the lens assembly I may be urged towards the front plate 2 or released by the action of rotating the threaded collar 3 in the recess 4a of the chassis 4.

Advantageously the thread is multi-start and relatively coarse. Advantageously the chassis 4 and the threaded collar 3 may be made of a moulded material such as diecast metal or engineering plastic therefore the cost of close tolerance machining is eliminated. The camera will have a housing for the camera components such as detector array, electronics, battery etc. Advantageously, the chassis 4 may be integral with the camera housing.

As noted above, optionally, the threaded collar 3 remains with each lens when it is removed.

Optionally the design of the threaded collar 3 may be different for each different interchangeable lens. This could be useful for lens identification as discussed in more detail below.

As noted above, it is advantageous for the chassis 4 to be made from a different and preferably less expensive material than that of the mounting plate 2. However some of the benefits described above can be achieved even if this is not the case and therefore the chassis and the mounting plate may be integral. For example, if the chassis and mounting plate are formed from the same material it is still the case that only the facing surfaces of the protrusion le on the lens assembly and the mounting plate need to be precisely machined As noted above, the fixing of the collar 3 or the lens assembly I with respect to the chassis 4 need not be by means of a screw thread. A bayonet fitting or any other axial clamping device may be used.

As noted above it is desirable to ensure that when the focus lensi b is rotated it rotates with respect to the tube I c and does not cause the tube I c to rotate with respect to the collar 3 and more importantly the chassis 4. This may be achieved by ensuring that the mounting tube Ic is tightly clamped to the mounting plate 2. Alternatively some other mechanism may be provided for ensuring that the tube does not rotate with respect to the chassis. One possibility is for the protrusion 1 e and the mating hole 2a in the mounting plate to be non circular.

[Another possibility is to secure the flange Ia to the mounting plate 2, for example by means of screws. This would require the flange to have a greater radial extent than that shown in the figures and would be suitable for arrangements in which the lens assembly was not to be interchanged or less frequently interchanged.

Another possibility that allows for easy removal of the lens assembly would be to provide one or more locating pins on the mounting plate or the annular flange each to be received in a corresponding recess provided in the annular flange or the mounting plate.

The arrangement described above has the advantage that the mounting of the lens assembly on the camera chassis is very robust since the components which control the position of the lens assembly with respect to the camera chassis are not highly stressed.

Any stresses, such as might arise from the weight of a heavy lens assembly or dropping the camera, are borne by the separate means for securing the lens assembly to the chassis, i.e. the collar in the above example. The components engage with each other via flat and cylindrical surfaces. The cost of these components can be reduced as compared to the mounting mechanisms described above.

Suitable materials for the chassis 4 and/or the collar 3 include any mouldable materials, thermoplastic and thermosetting materials, cast metals and sintered metals.

Contactless ID System In one embodiment, the lens assembly is provided with identification to indicate to contactless sensing means provided in the camera which lens assembly has been inserted.

The identification may take any form that is detectable by a corresponding detector in the camera chassis. It may be a visible marking or it may be invisible. It may take the form of one or more indentations or protrusions or it may be a surface coating. The identification may be provided on a surface of the lens assembly which faces the camera housing in use.

The collar is particularly useful for this purpose. For example each lens assembly may be provided with its own collar and the identification may be either on a surface of the threaded portion or the rear surface of the flange 3a which faces the camera housing in use.

This latter possibility is partially illustrated in the figures 3. The chassis shown in figure 3 has three recesses 5a, 5b, 5c at different radial positions with respect to the camera axis.

Each recess can provide an optical path to the interior of the camera housing where light reflected or transmitted from the surface of the collar may be directed to the camera imager electronics (sensor array, signal processor etc). Alternatively the camera may be provided with dedicated means for identifying the lens assembly such as one or more suitably positioned transmitters or sensors. The collar 3 may be provided with a number (including zero) of identification marks at positions corresponding to the radial positions of the recesses ba, 5b, 5c. The identification marks are preferably annular so that they are visible through the recesses in use regardless of the rotational position of the collar 3. The presence or absence of an identification mark at a particular radial location provides a binary identification of the lens assembly.

The identification marks may be reflective and may be applied to the collar as stickers.

Alternatively the identification may take the form of a different colour for each different lens assembly in which case an analogue sensing arrangement would be needed in the camera housing to determine the colour.

Advantageously, the threaded collar 3 and the lens assembly I remain together even when removed from camera so that the identification on the threaded collar 3 always corresponds to the identified lens assembly I. While the invention is described through the above exemplary embodiments, it will be understood by those of ordinary skill in the art that modification to and variation of the illustrated embodiments may be made without departing from the inventive concepts herein disclosed.

Claims

Claims 1. A lens assembly for a camera comprising a cylindrical body and one or more lenses mounted in or on the cylindrical body, the body having a flat surface at one end arranged to abut against a flat surface on a mounting plate of the camera and one or more protrusions from and/or or openings in the flat surface each adapted to co-operate with a corresponding opening in or protrusion from the camera mounting plate.
2. A lens assembly as claimed in claim I in which the one or more protrusions extend from the flat surface of the cylindrical body.
3. A lens assembly as claimed in claim 2 in which the one or more protrusions comprise a protrusion extending from the flat surface of the cylindrical body encircling the lens aperture.
4. A lens assembly as claimed in claim 3 in which the protrusion encircling the lens aperture comprises an annular protrusion concentric with the cylindrical body.
5. A lens assembly as claimed in any preceding claim in which the protrusion(s) and recess(es) are arranged to prevent rotation of the cylindrical body with respect to the mounting plate.
6. A lens assembly as claimed in any preceding claim in which the cylindrical body comprises a flange extending radially outwardly which provides the flat surface for abutment against the camera mounting plate.
7. A lens assembly as claimed in any preceding claim further comprising means for securing the lens assembly against axial movement with respect to the camera
8. A lens assembly as claimed in claim 7 in which the securing means comprise a collar encircling the cylindrical body having one or more features on its surface for engaging one or more corresponding features on the camera body.
9. A lens assembly as claimed in claim 8 in which the securing means comprise a screw thread provided on a surface of the collar.
10. A lens assembly as claimed in claim 9 in which the screw thread is provided on an outer annular surface of the collar.
II. A lens assembly as claimed in any of claims 7 to 10 in which the collar is made from a moulded or cast or sintered material.
12. A lens assembly as claimed in any preceding claim comprising identification means on a surface of the lens assembly facing towards the mounting plate in use.
13. A lens assembly as claimed in any preceding claim in which flat surface and the surfaces of the protrusions and/or recesses which co-operate with the mounting plate are precision machined.
14. A lens assembly as claimed in any preceding claim in which the portion of the cylindrical body providing the flat surface and the recesses and/or protrusions is made of metal.
15. A lens assembly as claimed in any preceding claim comprising identification provided on a surface which faces the camera housing in use.
16. A lens assembly as claimed in claim 15 when dependent on claim 8 in which the identification is provided on a surface of the collar.
17. A camera comprising a chassis, a lens assembly as claimed in any preceding claim and a mounting plate fixed with respect to the chassis having a flat surface, the flat surface having one or more openings in and/or openings protrusions from the flat surface each adapted to co-operate with a corresponding protrusion from or opening in the flat surface of the lens assembly.
18. A camera as claimed in claim 15 in which the chassis comprises a portion in front of the mounting plate to which securing means may be attached for securing the lens assembly to the chassis.
19. A camera as claimed in claim 16 in which the portion provides a recess into which at least a pad of the lens assembly may be inserted.
20. A camera as claimed in claim 15 or 16 in which the portion has one or more features on its surface for engaging corresponding features on the lens assembly.
21. A camera as claimed in claim 20 in which the one or more features comprise a screw thread.
22. A camera as claimed in any of claims 15 to 21 in which the chassis is made from a moulded or sintered material.
23. A kit comprising: one or more lens assemblies as claimed in any of claims I to 6, a camera comprising a mounting plate fixed with respect to the chassis having a flat surface, the flat surface having one or more openings in and/or protrusions from the flat surface each adapted to co-operate with a corresponding protrusion from or opening in the flat surface of the lens assembly; and means for securing the lens assembly against axial movement with respect to the camera.
24. A kit as claimed in claim 23 in which the securing means comprise a collar encircling the cylindrical body having one or more features on its surface for engaging one or more corresponding features on the camera body.
25. A kit as claimed in claim 23 or 24 in which the securing means comprise a screw thread provided a surface of the collar.
26. A kit as claimed in claim 25 in which the screw thread is provided on an outer annular surface of the collar.
27. A kit as claimed in any of claims 22 to 26 in which the camera chassis comprises a portion in front of the mounting plate to which securing means may be attached for securing the lens assembly to the chassis.
28. A kit as claimed in claim 27 in which the portion provides a recess into which at least a part of the lens assembly be inserted.
29. A kit as claimed in claim 27 or 28 in which the portion has one or more features on its surface for engaging corresponding features on the lens assembly.
30. A kit as claimed in claim 29 in which the one or more features comprise a screw thread.
31. A kit as claimed in any of claims 23 to 30 in which the or each lens assembly comprises identification provided on a surface of the assembly which faces the camera housing in use.
32. A lens assembly as claimed in claim 31 when dependent on claim 24 in which the identification is provided on a surface of the collar.
33. A camera or kit as claimed in any of claims 17 to 32 in which the camera comprises imager electronics, in which the camera imager electronics are configured to read identification provided on the lens assembly.
34. A camera or kit as claimed in any of claims 17 to 32 comprising one or more transmitters or sensors provided on the camera chassis arranged to read identification provided on the lens assembly.
35. A camera as claimed in claim 33 or 34 in which the camera imager electronics or the one or more transmitters or sensors are configured to recognise the presence or absence of one or more marks at different radial positions with respect to the camera axis.
36. A lens assembly substantially as hereinbefore described with reference to the accompanying drawings.
37. A camera substantially as herein before described with reference to the accompanying drawings.
38. A kit substantially as herein before described with reference to the accompanying drawings.