Optical camera lens assembly

Abstract

There is disclosed an optical camera lens assembly comprising a substantially tubular main body having a front end and a rear end, and a subassembly comprising one or more subassembly lens elements surrounded by a substantially tubular mounting structure, wherein the front end of the main body defines a substantially cylindrical inner volume, wherein the substantially cylindrical inner volume is configured to receive the subassembly, and wherein the subassembly is removably received in the cylindrical inner volume.

Description

[0001] OPTICAL CAMERA LENS ASSEMBLY

[0002] This disclosure relates to an optical camera lens assembly and a lens accessory for engagement with a filter ring of an optical camera lens assembly.

[0003] BACKGROUND

[0004] Optical camera lens assemblies comprise a plurality of lens elements within a generally tubular housing. Conventionally, during assembly, the lens elements and an iris mechanism are successively inserted into the housing from one or both ends of the housing, either being secured onto the interior of the housing, for example by screws, or being held in place by other lens elements or the iris mechanism, commonly with intervening spacers. Assembly within the generally tubular housing may be slow and difficult, as is disassembly for servicing and changing lens elements.

[0005] A filter ring is commonly provided at the front end of optical camera lens assemblies, which has an internal thread at the forward end of the filter ring, enabling filters to be screwed into the front end of the optical camera lens assembly. Filters are provided in front of the front end of optical camera lens assemblies, and matte boxes may be provided around the front end of optical camera lens assemblies, by being mounted on rails extending beneath the optical camera lens assembly.

[0006] BRIEF SUMMARY OF THE DISCLOSURE

[0007] In accordance with a first aspect, there is provided an optical camera lens assembly comprising a substantially tubular main body having a front end and a rear end, and a subassembly comprising one or more subassembly lens elements surrounded by a substantially tubular mounting structure, wherein the front end of the main body defines a substantially cylindrical inner volume, wherein the substantially cylindrical inner volume is configured to receive the subassembly, and wherein the subassembly is removably received in the cylindrical inner volume.

[0008] By providing a removable subassembly, it is possible to more easily assemble and service the optical camera lens assembly.

[0009] By providing a removable subassembly, it is possible to change one subassembly for another subassembly, for example to change a focal length or other optical characteristics of the optical camera lens assembly. For example, the main body may be provided with one or more main body lens elements are not removable as part of the subassembly and which are disposed towards the rear end of the main body. The one or more main body lens elements may have certain predetermined optical characteristics. When combined with a first subassembly comprising one subassembly lens elements, the overall combination of lens elements may provide a first desired set of optical characteristics. When combined with a second, alternative, subassembly comprising at least one different subassembly lens elements, the overall combination of lens elements may provide a second desired set of optical characteristics.

[0010] A single main body and several subassemblies may comprise fewer lens elements overall than an equivalent number of separate main bodies. Moreover, the same main body may be used with several different subassemblies. In this way, it is possible to realise a set of different optical camera lens assemblies, for example with different focal lengths or other optical characteristics, that requires less glass and fewer components than an equivalent set of traditional optical camera lens assemblies each having fixed optical characteristics. A single main body and a set of different subassemblies may be lighter in weight and take up less space during transport than an equivalent set of traditional optical camera lens assemblies. There may also be cost savings by reducing the total number of lens assembles in the set, since the lens elements in the main body can be used with all of the different subassemblies.

[0011] The lens assembly may comprise an adjustable iris mechanism.

[0012] The lens assembly may comprise one or more lens assembly lens elements, wherein the one or more subassembly lens elements comprise all of the lens assembly lens elements between the front end of the lens assembly and the adjustable iris mechanism.

[0013] The subassembly may comprise the adjustable iris mechanism.

[0014] The adjustable iris mechanism of the subassembly may be operably connectable to an aperture adjustment ring on an outer circumference of the tubular main body.

[0015] The subassembly may comprise a plurality of subassembly lens elements. The subassembly may comprise three or more subassembly lens elements.

[0016] The subassembly may be secured to the main body by at least one screw.

[0017] The subassembly may be secured to the main body by a plurality of screws arranged about an optical axis of the lens in an arrangement that is not rotationally symmetric.

[0018] The main body may comprise one or more main body lens elements disposed between the cylindrical inner volume and the rear end of the lens assembly.

[0019] The one or more main body lens elements may be optically aligned with the one or more lens elements of the subassembly when the subassembly is received in the inner volume.

[0020] The lens assembly may further comprise a filter ring that fits around an end of the subassembly at the front end of the lens assembly and abuts an outer flange of the main body or the subassembly and that faces the front end of the lens assembly. The filter ring may be securable to the main lens body or the subassembly by way of at least one screw. The filter ring may help to secure the subassembly within the cylindrical inner volume.

[0021] In accordance with a second aspect, there is provided an optical camera lens assembly having an optical axis, a front end and a rear end, and comprising a substantially tubular filter ring having an exposed forward end, wherein, adjacent the forward end, the filter ring has an outer circumferential accessory engagement groove for receiving a lens accessory, wherein the accessory engagement groove comprises a rearward facing groove surface and a forward facing groove surface.

[0022] By providing an outer circumferential accessory engagement groove on the filter ring, lens accessories may be more conveniently, more securely and more accurately mounted onto the lens assembly.

[0023] The rearward facing groove surface and the forward facing groove surface may not be parallel and the accessory engagement groove may increase in width away from the optical axis.

[0024] The rearward facing groove surface and the forward facing groove surface may be axially separated by an axially extending cylindrical separation portion.

[0025] The rearward facing groove surface and the forward facing groove surface may each be angled by at least 30 degrees with respect to the optical axis.

[0026] One of the rearward facing groove surface and the forward facing groove surface may extend outwards perpendicular to the optical axis.

[0027] One or both of the rearward facing groove surface and the forward facing groove surface may be angled by 30 to 60 degrees with respect to the optical axis.

[0028] The rearward facing groove surface may be provided on a filter ring flange at the forward end of the filter ring.

[0029] The filter ring may have a cylindrical portion extending along the optical axis and the forward facing groove surface may be provided on the forward end of a reinforcement band extending around and projecting outwardly from the cylindrical portion.

[0030] The accessory engagement groove may have a depth of at least 2mm perpendicular to the optical axis.

[0031] In accordance with a third aspect, there is provided a lens accessory comprising a clamping mechanism configured for clamping into the accessory engagement groove of the filter ring of the lens assembly of the second aspect. By providing a clamping mechanism configured for clamping into the accessory engagement groove of the filter ring, lens accessories may be more conveniently, more securely and more accurately mounted onto lens assemblies.

[0032] The lens accessory may be configured to clamp about an optical axis of the lens assembly, and the clamping mechanism may comprise a rearward facing engagement surface and a forward facing engagement surface.

[0033] The rearward facing engagement surface and the forward facing engagement surface may be angled by at least 30 degrees with respect to the optical axis.

[0034] The rearward facing engagement surface and the forward facing engagement surface may not be parallel and the separation between the rearward facing engagement surface and the forward facing engagement surface may increase in width away from the optical axis.

[0035] One of the rearward facing engagement surface and the forward facing engagement surface may extend outwards perpendicular to the optical axis.

[0036] One or both of the rearward facing engagement surface and the forward facing engagement surface may be angled by 30 to 60 degrees with respect to the optical axis.

[0037] The lens accessory may comprise adjustable jaws for releasably engaging with the accessory engagement groove of the filter ring.

[0038] The lens accessory may be a matte box. The lens accessory may be a camera light, e.g. a ring light.

[0039] BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

[0041] • Figure 1A shows a cut-away view of an optical camera lens assembly;

[0042] • Figure 1 B shows the optical camera lens assembly of Figure 1A, after removal of the baffle ring.

[0043] • Figure 1C shows the optical camera lens assembly of Figure 1 B, after removal of the screws or bolts holding the filter ring in place;

[0044] • Figure 1D shows the optical camera lens assembly of Figure 1C, after removal of the filter ring;

[0045] • Figure 1 E shows the optical camera lens assembly of Figure 1 D, viewed along the optical axis;

[0046] Figure 2A shows, in enlarged cut-away view, part of the front of an optical camera lens assembly having a filter ring; Figure 2B shows a cut-away view of part of the filter ring corresponding to Figure 2A; and

[0047] • Figure 2B shows a cut-away view of the filter ring of Figure 2A and a matte box connected to the filter ring.

[0048] DETAILED DESCRIPTION

[0049] Figures 1A to 1 D show , in cut-away view, an optical camera lens assembly 1 (e.g. a cinema camera lens assembly having a prime or zoom focal length) comprising a substantially tubular main body 2. The main body 2 has a front end 3, for receiving light, and a rear end 4, which is configured for detachable connection to an optical camera body (not shown). The main body 2 further comprises main body lens elements 5a, 5b, 5c and 5d (e.g. an optical lens element group, or one lens element) disposed within the main body 2 towards the rear end 4. The front end 3 of the main body 2 defines a substantially cylindrical inner volume 6 configured to receive a subassembly 7 (e.g. snugly received). The subassembly 7 comprises an outer, substantially cylindrical casing 8 in which one or more subassembly lens elements 9a, 9b and 9c (e.g. an optical lens element group) are mounted. The main body lens elements 5a, 5b, 5c and 5d and the subassembly lens elements 9a, 9b and 9c are substantially optically aligned with a common optical axis Z. The subassembly 7 further comprises an adjustable iris mechanism 10 (e.g. a diaphragm iris) that is operably connected to an aperture adjustment ring 11 on an outer circumference of the tubular main body 2.

[0050] One or more of the main body lens elements 5a, 5b, 5c and 5d of the main lens body 2 may be moved back and forth along a optical axis Z of the optical camera lens assembly 1 by way of a focus adjustment ring 12 on the outer circumference of the tubular main body 2. By moving the main body lens elements 5a to 5d relative to the subassembly lens elements 9a to 9c along the optical axis Z, it is possible to adjust a focus or a focal length of the optical camera lens assembly 1.

[0051] Alternatively or in addition, the subassembly lens elements 9a to 9c of the subassembly 7 may be moved back and forth along the optical axis Z of the optical camera lens assembly 1 by way of an adjustment ring (not shown) on the outer circumference of the main body 2, and which is operably connected with respective part(s) of the subassembly 7.

[0052] A mounting ring 13 is provided at the rear end 4 of the main body 2. The mounting ring 13 is configured to allow the optical camera lens assembly 1 to be mounted in a complementary mount (e.g. a bayonetted mounting system) of an optical camera body (not shown). In Figure 1A, the mounting ring 13 is provided with a removable dust cap 14 for transport and storage of the optical camera lens assembly 1. The subassembly 7 is held in place within the cylindrical inner volume 6 of the main body 2 by way of screws or bolts 15. The screws or bolts 15 may be disposed about the optical axis Z in an arrangement that is not rotationally symmetric which provides only one mounting orientation of the subassembly 7 with respect to the main body 2, thereby ensuring a correct rotational alignment between cooperating parts (mutually engageable parts) of the main body 2 and the subassembly 7 (e.g. ensuring correct alignment of the mechanism engaging between the aperture adjustment ring 11 of the main body 2 and the adjustable iris mechanism 10 of the subassembly 7). For example, as shown in Figure 1 E, three screws or bolts 15A may be spaced apart around the optical axis Z at 90 degree intervals, and a fourth screw or bolt 15B may be positioned to one side of the remaining 90 degree interval position.

[0053] The screws or bolts 15A, 15B may all be at the same radius from the optical axis Z. The screws or bolts 15A, 15B being positioned at the same radius from the optical axis Z simplifies manufacturing of the corresponding holes for receiving the screws or bolts.

[0054] As shown in Figure 1A, the subassembly 7 may be completely received within the cylindrical inner volume 6 (i.e. the subassembly 7 does not project beyond the end of main body 2). Being completely received within the main body 2 protects the subassembly 7 from direct mechanical impacts, and may simplify sealing against the ingress of dust and enable manufacture of a more mechanically robust optical camera lens assembly 1 .

[0055] The subassembly 7 comprises an outer circumferential flange 16 that abuts and is mounted to a mounting surface 17 (e g. an annular mounting surface) in the cylindrical inner volume 6 when the subassembly 7 is fully inserted through the front end 3 of the main body 2. The subassembly mounting flange 16 is provided with through holes (not shown) so as to allow the screws or bolts 15 to pass therethrough and to be secured in corresponding screw holes or bolt holes (not shown) in the mounting surface 17 of the main body 2.

[0056] The forward end of the subassembly 7 may be provided with inner circumferential ridges 29 to help reduce optical flare.

[0057] The main body 2 may have a support mount 21 (e.g. a threaded mount) for engagement with a tripod, in use.

[0058] A filter ring 18 is fitted around the subassembly 7 at the front end 3 of the main body 2 and secured to the front end 3 of the main body 2 by way of further screws or bolts 19. (Alternatively, the filter ring 18 may be secured to the subassembly 7.) By fitting around the end of the subassembly 7, the filter ring 18 may support the end of the subassembly 7, increasing the strength of the camera lens assembly 1. The filter ring 18 may help to reduce or prevent ingress of dust or other unwanted materials into the optical camera lens assembly 1. A seal 18S may be provided between the filter ring 18 and the subassembly 7. The filter ring 18 may be used for attachment of optical filters or a matte box (not shown in Figures 1 A to 1 D). In addition, a baffle ring 20 may be fitted over the filter ring 18 at the front end 3 of the main body 2. The baffle ring 20 may be provided with inner circumferential ridges to help reduce optical flare, and provides a neat appearance and additional protection from the ingress of dust or other unwanted materials.

[0059] Figure 1 B shows the optical camera lens assembly 1 of Figure 1A with the baffle ring 20 removed so as to allow access to the screws or bolts 19 that secure the filter ring 18 to the main body 2 (or to the subassembly 7).

[0060] Figure 1C shows the optical camera lens assembly 1 of Figure 1 B after removal of the screws or bolts 19 that hold the filter ring 18 in place.

[0061] Figures 1 D and 1 E show the optical camera lens assembly 1 of Figure 1C after the filter ring 18 has been removed. It can be seen that the screws or bolts 15 that hold the subassembly 7 in place are now easily accessible so as to allow the subassembly 7 to be removed from the cylindrical inner volume 6.

[0062] The easy connection and removal of the subassembly 7 within the main body 2 enables simplified construction of the optical camera lens assembly 1 , enabling the multiple components of the subassembly 7 to be assembled outside of the main body 2, with easier removal for subsequent access to the multiple components of the subassembly 7 than when within the main body 2. The easy connection and removal of the subassembly 7 within the main body 2 simplifies servicing of the optical camera lens assembly 1. Additionally, after it has been removed from within the main body 2, the subassembly 7 may then be switched for a different subassembly with a different set of subassembly lens elements 9a to 9c, thus changing the optical characteristics of the optical camera lens assembly 1 while making use of the same main body 2 and main body lens elements 5a to 5d.

[0063] Figure 2A shows, in enlarged cut-away view, of part of the front of an optical camera lens assembly 1 of Figure 1A, which has a filter ring 18. Figure 2B shows a corresponding view of part of the filter ring 18. Figure 2C shows a cut-away view of the filter ring 18 of Figure 2A and a lens accessory 40 connected to the filter ring 18.

[0064] The filter ring 18 has a generally tubular shape and is provided at the front end 3 of the optical camera lens assembly 1 , e.g. the forward end 18F of the filter ring 18 forms the front end 3 of the optical camera lens assembly 1.

[0065] The rearward end 18R of the filter ring 18 is configured to connect to the main body 2 (or may connect to the subassembly 7, where present) of the optical camera lens assembly 1. The illustrated filter ring 18 has a rearward filter ring mounting flange 23 that is secured to the main body 2 by screws or bolts 19 passing through holes 24 in the rearward flange 23. The filter ring 18 has an accessory engagement groove 22 adjacent the front end 3 of the optical camera lens assembly 1 , adjacent the forward end 18F of the filter ring 18, which extends circumferentially around (e.g. all the way around) the exterior of the filter ring 18.

[0066] The accessory engagement groove 22 is formed between a rearward facing groove surface 25R and a forward facing groove surface 26F that each extend circumferentially around the exterior of the filter ring 18. The rearward facing groove surface 25R is angled A by at least 30 degrees (measured in a plane coplanar with the optical axis Z) with respect to the optical axis Z the optical camera lens assembly 1 (e g. being angled by 90 degrees, being angled by up to 90 degrees, or being angled by 30 to 60 degrees), e.g. being angled with respect to the optical axis Z extending centrally along the tubular filter ring 18. The forward facing groove surface 26F is angled B by at least 30 degrees with respect to the optical axis Z (e.g. being angled by up to 90 degrees, or being angled by 30 to 60 degrees). The rearward facing groove surface 25R and the forward facing groove surface 26F may be angled towards each other. The relative inclinations of the rearward facing groove surface 25R and the forward facing groove surface 26F (being non-parallel, providing a groove that increases in width away from the optical axis Z) enables a lens accessory 40 to be firmly clamped into the accessory engagement groove 22.

[0067] The rearward facing groove surface 25R and the forward facing groove surface 26F may be axially separated by an axially extending cylindrical separation portion 27 (a flat bottom of the accessory engagement groove 22), for example being axially separated by at least 2mm. Being axially separated enables connection of a lens accessory 40 having a stronger clamping mechanism 44, where it engages with the accessory engagement groove 22.

[0068] The accessory engagement groove 22 may have a depth D of at least 2mm (e.g. at least 3mm, at least 4mm) perpendicular to the optical axis Z, i.e. the rearward facing groove surface 25R and the forward facing groove surface 26F may each extend radially outwardly from the bottom of the accessory engagement groove 22 by at least 2mm. Having a depth D of at least 2mm (or at least 3mm, or at least 4mm) may enable accessories to securely engage within the accessory engagement groove 22.

[0069] One of the rearward facing groove surface 25R and the forward facing groove surface 26F may extend perpendicular to the optical axis Z, whilst the other of the rearward facing groove surface 25R and the forward facing groove surface 26F is angled by up to 60 degrees (e.g. 30 to 60 degrees) with respect to the optical axis Z. Providing one of the rearward facing groove surface 25R and the forward facing groove surface 26F extending perpendicularly to the optical axis Z may enhance axial alignment of a lens accessory 40 engaged in the accessory engagement groove 22. In the illustrated filter ring 18, the rearward facing groove surface 25R extends outwards perpendicular to the optical axis Z (angle A is 90 degrees), and the forward facing groove surface 26F is angled at 45 degrees with respect to the optical axis Z (angle B is 45 degrees).

[0070] As illustrated, the rearward facing groove surface 25R may be provided on a filter ring flange 25 at the forward end 18F of the filter ring 18, which extends perpendicularly outward from the optical axis Z. Providing the rearward facing surface 25R on the filter ring flange 25 enhances the strength of the filter ring 18 by providing a reinforced portion where the lens accessory 40 is engaged.

[0071] As illustrated, the forward facing groove surface 26F may be provided by the forward end of a raised reinforcement band (a circumferentially extending projection) 28 extending around, and projecting outwardly from, the axially extending cylindrical portion 27. Providing the forward facing groove surface 26F on the raised reinforcement band 28 enhances the strength of the filter ring 18 by providing a reinforced portion where the lens accessory 40 is engaged. The raised reinforcement band 28 also prevents the lens accessory 40 from moving backwards, away from the front end 3 of the lens assembly 1 , which could interfere with the focussing mechanism or aperture adjustment mechanism (or a zoom mechanism).

[0072] Providing a raised reinforcement band 28 with a radial height of at least 2mm and an axial length of at least 2mm (e.g. at least 4mm) reinforces the filter ring 18 where the lens accessory 40 is engaged.

[0073] Figure 2C shows a lens accessory 40 engaged into the accessory engagement groove 22 of the filter ring 18. The accessory 40 has a clamping mechanism 44 for clamping into the accessory engagement groove 22 of the filter ring 18. The forward facing engagement face 44F and rearward facing engagement face 44R of the clamping mechanism 44 are respectively complementary in shape to the rearward facing groove surface 25R and the forward facing groove surface 26F of the accessory engagement groove 22, e.g. the engagement faces 44F, 44R are angled by at least 30 degrees with respect to the optical axis Z the optical camera lens assembly 1 (e.g.: one or both of the engagement faces 44F, 44R may be angled by up to 90 degrees or angled by 30 to 60 degrees to the optical axis Z; one of the engagement faces may be perpendicular to the optical axis Z). The angling of the engagement faces 44F, 44R respectively by angles A and B is indicated in Figure 2C.

[0074] The optical axis Z may be coplanar with a plane of mirror symmetry, or colinear with a line of rotational symmetry, of the rearward facing groove surface 25R and the forward facing groove surface 26F, and the angles specified with respect to the optical axis Z may alternatively be specified with respect to the plane of mirror symmetry or line of rotational symmetry of the engagement faces 44F, 44R of the clamping mechanism 44. The engagement faces 44F, 44R are angled away from each other. The relative inclinations of the engagement faces 44F, 44R (being non-parallel, providing a clamping mechanism 44 that increases in width away from the optical axis Z) enables the lens accessory 40 to be firmly clamped into the accessory engagement groove 22.

[0075] One of the engagement faces 44F, 44R may extend perpendicular to the optical axis Z, whilst the other of the engagement faces 44F, 44R is angled by up to 60 degrees (e.g. 30 to 60 degrees) with respect to the optical axis Z. Providing one of the engagement faces 44F, 44R extending perpendicularly to the optical axis Z may enhance axial alignment of the lens accessory 40 engaged in the accessory engagement groove 22.

[0076] In the lens accessory 40 illustrated in Figure 2C, the clamping mechanism 44 is a pair of opposed jaws that are radially adjustable C, with respect to the optical axis Z to clamp into the groove 22 of the filter ring 18.

[0077] In Figure 2C, the illustrated lens accessory 40 is a matte box. The illustrated matte box 40 has a lens hood 42 (e.g. provided by French flag adjustable fins). The lens accessory 40 may be a camera light, e.g. a ring light extending around the filter ring 18.

[0078] Although the illustrated optical camera lens assembly 1 described in relation to Figures 1A to 1 D has a removable subassembly 7 received within a main body 2, the filter ring 18 may also be provided on an alternative optical camera lens assembly that does not have a removable subassembly 7.

[0079] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0080] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0081] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

CLAIMS:

1. An optical camera lens assembly comprising a substantially tubular main body having a front end and a rear end, and a subassembly comprising one or more subassembly lens elements surrounded by a substantially tubular mounting structure, wherein the front end of the main body defines a substantially cylindrical inner volume, wherein the substantially cylindrical inner volume is configured to receive the subassembly, and wherein the subassembly is removably received in the cylindrical inner volume.

2. The lens assembly as claimed in claim 1, wherein the lens assembly comprises an adjustable iris mechanism.

3. The lens assembly as claimed in claim 2, wherein the lens assembly comprises one or more lens assembly lens elements, wherein the one or more subassembly lens elements comprise all of the lens assembly lens elements between the front end of the lens assembly and the adjustable iris mechanism.

4. The lens assembly as claimed in claim 2 or claim 3, wherein the subassembly comprises the adjustable iris mechanism.

5. The lens assembly as claimed in claim 4, wherein the adjustable iris mechanism of the subassembly is operably connectable to an aperture adjustment ring on an outer circumference of the tubular main body.

6. The lens assembly as claimed in any preceding claim, wherein the subassembly comprises a plurality of subassembly lens elements.

7. The lens assembly as claimed in any preceding claim, wherein the subassembly is secured to the main body by at least one screw.

8. The lens assembly as claimed in claim 7, wherein the subassembly is secured to the main body by a plurality of screws arranged about an optical axis of the lens in an arrangement that is not rotationally symmetric.

9. The lens assembly as claimed in any preceding claim, wherein the main body comprises one or more main body lens elements disposed between the cylindrical inner volume and the rear end of the lens assembly.

10. The lens assembly as claimed in claim 9, wherein the one or more main body lens elements are optically aligned with the one or more lens elements of the subassembly when the subassembly is received in the inner volume.

11. The lens assembly as claimed in any preceding claim, further comprising a filter ring that fits around an end of the subassembly at the front end of the lens assembly and abuts an outer flange of the main body or the subassembly and that faces the front end of the lens assembly.

12. The lens assembly as claimed in claim 11 , wherein the filter ring is securable to the main lens body or the subassembly by way of at least one screw.

13. An optical camera lens assembly having an optical axis, a front end and a rear end, and comprising a substantially tubular filter ring having an exposed forward end, wherein, adjacent the forward end, the filter ring has an outer circumferential accessory engagement groove for receiving a lens accessory, wherein the accessory engagement groove comprises a rearward facing groove surface and a forward facing groove surface.

14. The optical camera lens assembly of claim 13, wherein the rearward facing groove surface and the forward facing groove surface are not parallel and the accessory engagement groove increases in width away from the optical axis.

15. The optical camera lens assembly of claim 13 or claim 14, wherein the rearward facing groove surface and the forward facing groove surface are axially separated by an axially extending cylindrical separation portion.

16. The optical camera lens assembly of any one of claims 13 to 15, wherein the rearward facing groove surface and the forward facing groove surface are each angled by at least 30 degrees with respect to the optical axis.

17. The optical camera lens assembly of any one of claims 13 to 16, wherein one of the rearward facing groove surface and the forward facing groove surface extends outwards perpendicular to the optical axis.

18. The optical camera lens assembly of any one of claims 13 to 17, wherein one or both of the rearward facing groove surface and the forward facing groove surface is angled by 30 to 60 degrees with respect to the optical axis.

19. The optical camera lens assembly of any one of claims 13 to 18, wherein the rearward facing groove surface is provided on a filter ring flange at the forward end of the filter ring.

20. The optical camera lens assembly of any one of claims 13 to 19, wherein the filter ring has a cylindrical portion extending along the optical axis and the forward facing groove surface is provided on the forward end of a reinforcement band extending around and projecting outwardly from the cylindrical portion.

21. The optical camera lens assembly of any one of claims 13 to 20, wherein the accessory engagement groove has a depth of at least 2mm perpendicular to the optical axis.

22. A lens accessory comprising a clamping mechanism configured for clamping into the accessory engagement groove of the filter ring of the lens assembly of any one of claims 13 to 21.

23. The lens accessory of claim 24, wherein the lens accessory is configured to clamp about an optical axis of the lens assembly, and the clamping mechanism comprises a rearward facing engagement surface and a forward facing engagement surface.

24. The lens accessory of claim 23, wherein the rearward facing engagement surface and the forward facing engagement surface are each angled by at least 30 degrees with respect to the optical axis.

25. The lens accessory of claim 23 or claim 24, wherein the rearward facing engagement surface and the forward facing engagement surface are not parallel and the separation between the rearward facing engagement surface and the forward facing engagement surface increases in width away from the optical axis.

26. The lens accessory of any one of claims 23 to 25, wherein one of the rearward facing engagement surface and the forward facing engagement surface extends outwards perpendicular to the optical axis.

27. The lens accessory of any one of claims 23 to 26, wherein one or both of the rearward facing engagement surface and the forward facing engagement surface is angled by 30 to 60 degrees with respect to the optical axis.

28. The lens accessory of any one of claims 22 to 27, comprising adjustable jaws for releasably engaging with the accessory engagement groove of the filter ring.

29. The lens accessory of any one of claims 22 to 28, wherein the lens accessory is a matte box or a camera light.

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