Adjustable focal length lenses and eyewear incorporating the same

Abstract

An adjustable focal length eyewear comprising at least one lens which is mounted to a frame for supporting the lens in front of a user's eyes, thereby defining a viewing direction through the lens; wherein the at least one lens is a variable focal length lens of the kind comprising two superposed lens elements having cooperating optical surfaces that are shaped such that the focal length of the lens is variable according to the relative lateral disposition of the lens elements in a direction transverse the viewing direction; wherein the lens elements are slidable relative to one another along a transverse path that is oriented transverse to the viewing direction for varying the focal length of the lens; wherein the lens further comprises: mutually cooperating guide parts on the lens elements which constrain relative lateral movement of the lens elements to the transverse path, and a magnetic fastener for releasably fastening the lens elements to each other, the magnetic fastener comprising an elongate magnetic strip on one of the lens elements or a part fixedly secured thereto and a cooperating magnetic slider provided on the other lens element or a part fixedly secured thereto, wherein the magnetic slider and magnetic strip are configured and arranged to: magnetically fasten the lens elements to each other during reciprocal relative lateral movement of the lens elements along the transverse path, and permit detachment of the lens elements from each other in the viewing direction.

Description

ADJUSTABLE FOCAL LENGTH LENSES AND EYEWEAR INCORPORATING THESAMEField of the disclosure

[0001] The present disclosure relates to adjustable focal length eyewear comprising at least one variable focal length lens of the kind that comprises two superposed lens elements having mutually cooperating optical surfaces that are shaped such that the focal length of the optical lens is variable according to the relative lateral disposition of the two lens elements in a direction transverse the viewing direction.Background

[0002] Optical lenses of the kind described above are well known in the art. An adjustable optical lens of this kind typically has two superposed lens elements with mutually cooperating cubic or higher order surfaces and a relative disposition that can be shifted in a transverse direction relative to a viewing direction through the lens for varying the optical power of the lens. Suitably, the transverse direction may extend in a generally horizontal plane relative to a user in normal use, but in some examples of lenses of this kind, it may extends in a sagittal plane or, at least theoretically, in any other plane with a component that extends substantially orthogonally to the viewing direction. An example of this kind of adjustable lens is the Alvarez lens disclosed by US 3,305,294 A, the contents of which are incorporated herein by reference.

[0003] While the adjustable glasses in the art operate generally satisfactorily, the adjusting mechanisms for adjusting the optical power of the lenses can be bulky and aesthetically unappealing. A common problem with glasses comprising such adjustable lenses is the weight of the glasses from the additional parts required for adjusting the lenses. Additionally, the focal length or the optical power of a pair of lenses may be continuously adjustable, which may cause discomfort to the user, particularly if the optical power changes unnecessarily during use.

[0004] An object of the present disclosure is to provide a pair of glasses or other wearable vision correcting apparatus of adjustable focal length which is more aesthetically attractive than similar kinds of eyewear known in the art. Another object of the disclosure is to provide eyewear, for example glasses, of adjustable focal length in which the user can selectively adjust the lenses between two or more discrete focal lengths using a simple manual adjustment mechanism.Summary of the disclosure

[0005] A first aspect of the present disclosure relates to an adjustable focal length eyewear comprising at least one lens which is mounted to a frame for supporting the lens in front of a user’s eyes, thereby defining a viewing direction through the lens. The at least one lens is a variable focal length lens of the kind comprising two superposed lens elements having cooperating optical surfaces that are shaped such that the focal length of the variable focal length lens is variable according to the relative lateral disposition of the lens elements in a direction transverse the viewing direction. The lens elements are slidable relative to one another along a transverse path that is oriented transverse to the viewing direction for varying the focal length of the lens.

[0006] The lens of the present disclosure further comprises mutually cooperating guide parts on the lens elements which constrain relative lateral movement of the lens elements to the transverse path, and a magnetic fastener for releasably fastening the lens elements to each other. The magnetic fastener comprises an elongate magnetic strip on one of the lens elements or a part fixedly secured thereto and a cooperating magnetic slider provided on the other lens element or a part fixedly secured thereto. The magnetic slider and magnetic strip are configured and arranged to: fasten magnetically the lens elements to each other during reciprocal relative lateral movement of the movable lens element along the transverse path, and to permit detachment of the moveable lens elements from each other in the viewing direction.

[0007] Preferably, while the guide parts on the lens elements constrain relative lateral movement of the lens elements to the transverse path, they permit the lens elements to be separated from one another against the attractive force of the magnetic fastener in the viewing direction in at least one relative lateral position and preferably in all relative positions of the lens elements.

[0008] Advantageously, the magnetic fastener prevents the lens elements from unintentionally detaching from each other when the lens elements are moved relative to each other. Additionally, the magnetic fastener allows the lens elements to be detached from each other when required. This may be useful for cleaning, repairing or replacing the lens elements.

[0009] A first one of the lens elements (either said “one of’ or said “other”) may be fixedly secured to the frame. A second one of the lens elements (either said “one of’ or said “other”) may be movable relative to the first lens element and the frame. The first lens element may be mounted in the frame in a conventional manner. For example, the first lens element may be surrounded bya rim which retains the lens element. Typically, the first lens element may be a front lens element, and the second lens element may be a rear lens element. The front lens element may be the lens element furthest form the eye, and the rear lens element may be the lens element closest to the eye, when the eyewear is operatively worn by a user. The second lens element may be disposed rearward of the frame in the viewing direction.

[0010] The adjustable focal length eyewear may comprise an lens element positioning mechanism. The positioning mechanism may define a plurality of discrete relative positions of the lens elements along the transverse path. The positioning mechanism may be arranged to restrain (laterally) the lens elements in each of the discrete relative positions. The positioning mechanism may be arranged such that, when the lens elements are not in one of the discrete relative positions, the lens elements are biased towards one of the discrete relative positions (e.g. the closest discrete relative position). In the absence of an external force (e.g. applied by a user), the lens elements may thereby move relative to each other to adopt one of the discrete relative positions. The bias force may suitably be provided by the magnetic fastener, which may pull the lens elements together. The magnetic fastener may restrain the lens elements in a direction generally parallel to the viewing direction.

[0011] At each discrete relative position, the lens provides a different focal length. The discrete relative positions may typically be spaced such that the focal length varies by 0.5 diopters or 1 diopter between each discrete relative position. The positioning mechanism may allow user selection of the focal length of the lens, the positioning mechanism retaining the lens elements in the discrete relative position corresponding to the selected focal length. Thus, a user may select a particular setting of the lens according to their need; for example, a greater focal power may be needed for reading as compared with computer-work.

[0012] The positioning mechanism may be a manual positioning mechanism, i.e. a positioning mechanism manually operable by a user of the eyewear. It may be that the positioning mechanism does not comprise any electromechanical actuators.

[0013] The positioning mechanism may comprise a first positioning part associated with (e.g. formed in or fixedly secured thereto) one of the lens elements, and a second positioning part associated with (e.g. formed in or fixedly secured thereto) the other lens element. The first and second positioning parts may be arranged to inter-engage mechanically when the lens elements are fastened to each other. Said mechanical engagement may (e.g. in combination with the attractiveforce provided by the magnetic fastener) cause the lens elements to adopt, and be restrained in, one of the discrete relative positions (in the absence of an external force, for example applied by a user). The magnetic fastener may provide a bias force to bias the first and second positioning parts into said mechanical engagement. Advantageously, the magnetic fastener serves to hold the lens elements together in all relative positions of the lens elements, including between the discrete relative positions.

[0014] The positioning mechanism may suitably comprise a plurality of first positioning parts and a corresponding plurality of second positioning parts.

[0015] The first (or second) positioning part may be defined on a rearward facing surface of the front lens element or the frame, the second (or first) positioning part may be defined on a forward facing surface of the rear lens element. The (attractive) magnetic force between the magnetic slider and magnetic strip which acts magnetically to fasten the lens elements to each other may act in a direction substantially parallel to the viewing direction. The first and second positioning parts may thereby be urged into engagement by the magnetic force between the magnetic slider and magnetic strip.

[0016] The first positioning part may comprise a catch and the second positioning part may comprise a series of notches. The catch may extend generally in the viewing direction. The series of notches may be defined by a ridged surface of the respective lens element, for example a front surface of the rear lens element, that is oriented generally normal to the viewing direction. When the lens elements are fastened to each other, the catch may selectively engage one of the notches to restrain the lens elements laterally in one of the (e.g. a selected) discrete relative positions. The location of the notches relative to the catch may define the discrete relative positions along the transverse path. To change the focal length of the lens, the user may apply a force to move the lens elements relative to each other along the transverse path. As the lens elements move, the catch may ride over the notches. When the user applied force is removed, the catch may settle (e.g. under the action of the biasing force provided by the magnetic fastener) in the adjacent notch such that the lens elements are held in the desired discrete relative position.

[0017] The positioning mechanism may comprise a detent arrangement. The detent arrangement may define a series of detent positions, corresponding to the discrete relative positions of the lens elements. The detent arrangement may comprise a first detent part, for example formed by said catch, and a second detent part, for example formed by said series of notches.

[0018] The mutually cooperating guide parts may comprise a first guide part associated with (e.g. formed in or fixedly secured thereto) one of the lens elements and a corresponding second cooperating guide part associated with (e.g. formed in or fixedly secured thereto) the other lens element. The first and second guide parts constrain relative movement of the lens elements to the transverse path. For example, the first guide part may be or may comprise a guide pin, and the second guide part may be or may comprise a slot (e.g. forming a slide way) configured to receive the guide pin such that the guide pin is slidable within the slot. The slot may be configured to constrain movement of the guide pin to the transverse direction. The slot may be elongate and have a length extending in a direction generally transverse to the viewing direction.

[0019] In some implementation, the guide pin and slot may be configured to retain the pin in the slot in one or more relative positions of the lens elements, thereby to prevent detachment of the lens elements from one another, while permitting such detachment in one or more other relative positions. For example, the guide pin may comprise an enlarged head portion which engages with one or more retaining ribs that extend along part (but not all) of the length of the slot. However, in preferred implementations, the guide pin and slot are configured to allow removal of the guide pin from the slot at all relative positions of the lens elements.

[0020] In embodiments, the mutually cooperating guide parts also form part of (e.g. provide) the lens element positioning mechanism described above. The first and / or second guide parts may form part of (e.g. provide) the lens element positioning mechanism. For example, the first positioning part may comprise the guide pin. The guide pin may form a catch. The slot may provide the second positioning part. The second positioning part may comprise surface of the slot, the surface comprising a series of notches with which the guide pin (catch) engages to form the positioning mechanism described above.

[0021] There may be a plurality of mutually cooperating guide parts, for example spaced along the transverse direction. For example, there may be a plurality of first guide parts and a corresponding plurality of second guide parts. For example, there may be a plurality of slots, each slot comprising a corresponding guide pin. One or more of the mutually cooperating guide parts may form part of (e.g. provide) the positioning mechanism.

[0022] The adjustable focal length eyewear may comprise two or more sets of mutually cooperating guide parts spaced apart in the direction of the transverse path. This may help prevent the lens elements rotating relative to each other, for example about an axis that extends generallyin the viewing direction through the lens. In particular, the guide parts may be spaced apart for holding the lens elements together in a stable fashion in conjunction with the magnetic fasteners. The mutually cooperating guide parts may be arranged so as to minimise the tendency of the lens elements to twist, wobble or otherwise move relative to each other except along the transverse path.

[0023] The mutually cooperating guiding parts may provide the above mentioned detent arrangement. For example, there may be a first detent part provided by the first guide part on the (e.g. movable) lens element which engages a second detent part provided by the second guide part on the (e.g. fixed) lens element or frame. Upon application of a progressively increasing force in a direction which urges the moveable lens element along the transverse path and relative to the fixed lens element, the inter-engaging detent parts may initially resist movement of the moveable lens element and retain the lens elements in a first discrete relative position (detent position). Eventually, the applied force may be sufficient to overcome the resistive force thereby allowing the movable lens element to move along the transverse path and allow the cooperating guiding parts to engage at a second discrete relative position (detent position).

[0024] As set out above, the lens elements are configured to provide a different predetermined focal length at each discrete relative position (detent position). In a straightforward example, the focal lengths may provide powers of -1.0 D, -0.5 D, 0 D, +0.5 D, +1.0 D. In another implementation, the focal lengths may provide powers of 0 D, +0.5 D, +1.0 D , +1.5 D, +2 D. More generally, the optical power of the lens may be adjustable between 0 D to +4 D. In some implementations, the minimum add power provided by the lens may be +0.25 D or +0.5 D.

[0025] It will be appreciated by those skilled in the art that in each relative lateral position of the lens elements, the variable focal length lens will define an optical (z) axis, i.e. an axis that is substantially perpendicular to the lens and represents a path of a ray of light through the lens with no net change in direction. Conveniently, the lens elements may be arranged such that as the focal length of the lens is decreased, the optical axis of the lens shifts inwardly, i.e. towards the user’s nose and, conversely, when the focal length of the lens is increased, the optical axis of the lens shifts outwardly, i.e. towards the user’s temple. This corresponds to how the eyes move to focus from far to near and may help improve the user’s optical experience.

[0026] The positioning mechanism may define at least two or three selectable discrete relative positions of the lens elements along the transverse path. The adjustment mechanism maydefine three, four or five selectable discrete relative positions of the lens elements along the transverse path. It will be appreciated that the adjustment mechanism may define greater or fewer than five discrete relative positions, depending on the optical power requirements of the variable focal length lens.

[0027] The transverse path may have two opposite lateral extremities where the lens elements cannot move beyond. The extremities of the transverse path may be defined by the mutually cooperating guide parts. For example, the extremities may be defined by the ends of the slot(s) in which the guide pins are received.

[0028] The variable focal length lens may be adjustable to alter the optical power of the lens by up to about +3.0 dioptres, which is suitable for most users when a change in optical power is required between reading closely and distance viewing. In some embodiments, each discrete detent may define + / - 0.5 diopter. In some embodiments, a wider range of variation may be provided, for example, each detent may define + / - 1, 2, 3 dioptres, which may assist with manufacturing the lens elements with fewer discrete detents.

[0029] The mutually cooperating guide parts may define a transverse path which is linear or curvilinear. In some embodiments, the optical surfaces of the lens elements may be formed on a base curve in a manner known to those skilled in the art. Thus, instead of being a straight line, the transverse path may in some embodiments be arcuate in a plane defined by the viewing direction, which substantially corresponds to the optical (z) axis in each relative position of the lens elements, and a horizontal (x) axis, the horizontal (x) axis being substantially perpendicular to the optical (z) axis and extending between temple and nasal sides of the lens, so that movement of the movable lens element along the transverse path substantially follows the base curve.

[0030]

[0031] The magnetic slider and magnetic strip are configured and arranged such that, as the lens elements move relative to each other along the transverse path, the magnetic slider slides relative to (e.g. along the length of) the magnet strip, thereby keeping the lens elements magnetically fastened to each other. The magnetic fastener may keep the lens elements magnetically fastened to each other throughout movement of the lens elements between adjacent discrete relative positions. The magnetic fastener may magnetically fasten the lens elements together across the whole range of relative movement (i.e. between the lateral extremities) of the lens elements along the transverse path. The magnetic fastener may be configured to provide asecuring force which is substantially independent of the relative position of the lens elements. It may be that the locations of the discrete relative positions of the lens elements along the transverse path are not defined by the magnetic fastener.

[0032] Advantageously, the magnetic fastener holds the lens elements together in a stable manner as they move relative to each other along the transverse path. Suitably, the strength of the magnetic fastener is sufficient to hold the lens elements firmly together in use whilst permitting a user to move the lens elements relative to one another between discrete detent positions defined by the positioning mechanism. Additionally, the magnetic fastener allows the moveable lens element to be removed when desired; for example by pulling, pushing or lifting the lens in a manner which overcomes the magnetic force fastening the lens elements to each other. Those skilled in the art would be able to select a magnetic fasteners of suitable strength to control the retention and sliding friction forces between the lens elements.

[0033] It will be appreciated that only one of the magnetic strip and the magnetic slider needs to be permanently magnetised (i.e. be a magnet); the other component may comprise a magnetic material (e.g. a ferromagnetic material) which is magnetically attracted to the magnetised component. In some embodiments, both the magnetic strip and the magnetic slider may be magnetised (with opposite poles facing each other). The magnetic axis of the magnetic slider and / or the magnetic axis of the magnetic strip are preferably substantially orthogonal to the plane in which the magnetic slider slides relative to the magnetic strip.

[0034] The elongate magnetic strip may be provided on one of the lens elements or provided on the frame. The elongate magnetic strip may comprise a generally rectangular shape, having a length extending generally in the transverse direction. In some embodiments, the elongate magnetic strip may be provided on the lens element or frame by being over-moulded into the lens element or the frame during manufacturing of those parts. The lens element or frame may comprise a recess which is configured to hold the elongate magnetic strip securely.

[0035] Similarly, the magnetic slider may be provided on one of the lens elements or provided on the frame. The cooperating magnetic slider may be in the form of a disc or dowel having a magnetic axis that extends generally in the viewing direction towards the magnetic strip. In some embodiments, the magnetic slider may be provided on the lens element or frame by being moulded into the lens element or the frame during manufacturing of those parts. The lens elementor frame may comprise a recess which is configured to hold the magnetic slider securely. In some implementations, the magnetic slider may be fixed in the recess, e.g. using a suitable adhesive.

[0036] The magnetic slider moves relative to the elongate magnetic strip when the lens elements are moved relative to each other by the user.

[0037] The magnetic fastener may be disposed rearward of the frame and may be superposed with the frame. Preferably, the magnetic fastener is disposed entirely within the outline of solid parts of the frame when viewed from the front in the viewing direction. This may help conceal the magnetic fastener from view when the eyewear is operatively used by the user. Ideally, the guide parts and positioning mechanism are similarly disposed such that they are hidden when the eyewear is viewed from the front.

[0038] At least two magnetic fasteners may be spaced apart (e.g. one above another) in a top-to-bottom direction relative to the user, i.e. in a direction substantially orthogonal to both the transverse direction and the viewing direction. This may help stabilise the lens elements relative to each other in the viewing direction and prevent the lens elements from rotating relative to each other about the optical axis. In some embodiments, only one magnetic fastener is used per lens.

[0039] In some implementations, the eyewear may comprise a pair of the variable focal length lenses described above. In some implementations, the eyewear may be a pair of glasses (i.e. spectacles) or goggles. In some embodiments, the eyewear may be a headset such as, for example, an augmented or virtual reality head-up display.

[0040] A pair of lenses in accordance with the present disclosure (e.g. as described above) may be mounted in the frame to form the pair of glasses. The frame may be rimless or may include at least one rim portion for providing support around the periphery of each lens. The frame may comprise temple arms and nose-bridge. In some embodiments, the lens may be mounted to the frame such that both lens elements are movable relative to the frame. In some embodiments, the two lens elements may be connected for equal and opposite movement along the transverse path. In such case, the position of the optical axis will remain substantially fixed relative to the frame, regardless of the relative disposition of the lens elements.

[0041] At least one of the lens elements may comprise an engagement portion for engagement by a user to allow them to move the lens elements relative to each other and / or to allow them to detach the lens elements from each other. Conveniently, the engagement portion may extend beyond the periphery of the frame. For example, the engagement portion may extendbelow a lower portion of a rim portion of the frame. The engagement portion may comprise a ridged surface. This may improve the amount of grip provided by the engagement portion.

[0042] A second aspect of the present disclosure relates to a variable focal length lens comprising two superposed lens elements (i.e. that are mutually superposed in a viewing direction) having cooperating optical surfaces that are shaped such that the focal length of the lens is variable according to the relative lateral disposition of the lens elements in a direction transverse the viewing direction. The lens elements are slidable relative to one another along a transverse path that is oriented transverse to the viewing direction for varying the focal length of the lens.

[0043] The lens further comprises mutually cooperating guide parts on the lens elements which constrain relative lateral movement of the lens elements to the transverse path, and a magnetic fastener for releasably fastening the movable lens elements to each other . The magnetic fastener comprises an elongate magnetic strip on one of the lens elements or a part fixedly secured thereto and a cooperating magnetic slider provided on the other of the lens elements or a part fixedly secured thereto. The magnetic slider and magnetic strip are configured to: fasten magnetically the lens elements to each other during reciprocal relative lateral movement of the movable lens elements, and permit detachment of the lens elements from each other in the viewing direction.

[0044] The lens may have any of the features set out in relation to the first aspect of the disclosure. For example, the lens may comprise a lens element positioning mechanism as set out above.

[0045] The present disclosure also provides a vision correction apparatus comprising at least one adjustable lens and a wearable support for holding the adjustable lens in front of a user’s eye; the adjustable lens comprising two lens elements that are superposed one in front of the other in a direction of viewing through the adjustable lens and are configured such that the optical power of the adjustable lens is variable by shifting the lens elements laterally relative to each other; wherein the lens elements or parts fixedly secured thereto have mutually cooperating guide parts for constraining relative lateral movement of the lens elements to a path which is transverse the viewing direction; at least one of the lens elements or a part fixedly secured thereto comprises an elongate magnetic strip which extends in the transverse direction; and the other lens element comprises at least one magnetic slider which attaches magnetically to the magnetic strip, thereby holding the two lens elements together while permitting said relative lateral movement andpermitting the lens elements to be detached from one another against the magnetic force between the slider and the magnetic strip.

[0046] It will be appreciated that features described in relation to one aspect of the present disclosure may be incorporated into other aspects of the present disclosure. For example, the method of the present disclosure may incorporate any of the features described with reference to the apparatus of the present disclosure and vice versa.

[0047] Following is a description by way of example only with reference to the accompanying drawings of implementations of the present disclosure.Brief description of the drawings

[0048] In the drawings:

[0049] FIG 1 is a front view of a framed pair of glasses in accordance with a first embodiment of the present disclosure, which comprises a frame and two variable focal length lenses of the kind comprising front and rear lens elements that are arranged for lateral movement relative to one another for adjusting the optical power of the lens;

[0050] FIG. 2 is a top view of the framed glasses of FIG. 1 ;

[0051] FIG. 3 is a perspective view from above and to the left-hand side of the front of the glasses of FIG. 1 showing rear lens elements of the variable focal length lenses detached from cooperating front lens elements.

[0052] FIG. 4 is an exploded perspective view from above and to the left-hand side of the rear of the glasses of FIGS. 1-3;

[0053] FIG. 5 is a rear elevation of a left-hand portion of the glasses of FIGS. 1-4, which shows the rear lens element engaged with the frame in use;

[0054] FIG. 6 is a perspective view from above and to the right hand side of the left-hand side rear lens element;

[0055] FIG. 7 is a perspective view from above and to the left hand side of the left-hand side front lens element mounted in the frame of the glasses;

[0056] FIG. 8 is an enlarged view of an upper rim portion of the frame of the glasses showing a magnetic fastener and guide pins when the rear lens element is mounted to the frame and front lens element;

[0057] FIG. 9 is an enlarged view of a lower rim portion of the frame of the glasses showing the magnetic fastener and a positioning mechanism when the rear lens element is mounted to the frame and front lens element;

[0058] FIG. 10a is an enlarged view of the lower rim portion of the frame of the glasses and part of the magnetic fastener; and

[0059] FIG. 10b is an enlarged view of the lower rim portion of the rear lens element and a cooperating part of the magnetic fastener and positioning mechanism.Detailed description of the drawings

[0060] FIGS. 1 to 4 show adjustable focal length eyewear in accordance with a first embodiment of the present disclosure. The adjustable focal length eyewear is in the form of a framed pair of glasses 100, but in other implementations, the eyewear may comprise another type of eyewear such for example as a headset, goggles, safety glasses or the like.

[0061] The glasses 100 comprise two variable focal length lenses 21, 22 which are mounted in a frame 12. The frame 12 comprises a frame front portion 13, which incorporates a left rim portion 17 and a right rim portion 18 and an integral nose-bridge portion 14. The frame 12 further comprises left and right hand side temple arms 15, 16, each of which is hinged to a respective one of the rim portions 17, 18 in a conventional manner.

[0062] Each of the variable focal length lenses 21, 22 comprises two superposed lens elements 31, 41 of the kind that are arranged to slide relative to one another along a transverse path in a direction transverse the direction of viewing for adjusting the focal power of the lens 21, 22. Lenses of this kind include Alvarez-type lenses.

[0063] The lenses 21, 22 each comprise a front and rear lens element 31, 41. The front lens element 31 of each lens 21, 22 is fixedly secured in the respective rim portion 17, 18, while the rear lens element 41 is slidable relative to the front lens element 31 in a direction indicated by axis x in FIGS. 2 and 4. Axis x extends transversely across the direction of viewing. The direction of viewing is indicated generally by axis z.

[0064] In some embodiments, the frame 12 and front lens elements 31 of the lenses 21, 22 are moulded as a single part. In other embodiments, the frame 12 and front lens elements 31 of the lenses 21, 22 are moulded as three parts (frame, left front lens element, right front lens element) and assembled in the traditional manner (for example with a traditional bevel fit).

[0065] In some embodiments, the front and rear lens elements 31, 41 are formed with a base curve in a manner well known in the art, so the transverse path followed by the rear lens element 41 as it moves relative to the front lens element 31 is arcuate in the x, z-plane instead of a straight line. However, in the present embodiment, the transverse path follows a substantially straight line.

[0066] The structure and operation of the left and right hand lenses 21, 22 is substantially the same, except that one is the mirror image of the other in a medial y, z-plane (not shown) that bisects the nose bridge 14 of the frame 12. In the following, therefore, only the left-hand lens 21 is described in detail, but the description applies equally to the right-hand lens 22.

[0067] As shown in FIG 4., the front lens element 31 has a front surface 32 and a rear surface 33. The front lens element 31 is generally rectangular, albeit with arcuate sides and corners. As shown in FIG. 7, the front lens element 31 has a top edge 34, a bottom edge 35, a temple side edge 36 and a nasal side edge 37. The top edge 34 of the front lens element 31 is mounted in an upper part 4 of the rim portion 17, while the bottom edge 35 of the front lens element 31 is mounted in a lower part 5 of the rim portion 17. The temple and nasal side edges 36, 37 of the front lens element 31 are mounted in the corresponding temple and nasal parts 6, 7 of the rim portion 17 of the frame 12, respectively.

[0068] As shown in FIGS 5, 7 and 8, the upper part 4 of the rim portion 17 of the frame 12 is formed with two upper guide pins 81, 82 that are spaced apart in the x-direction. The upper guide pins 81, 82 protrude rearwar dly of the rear surface of the rim portion 17. Intermediate the two upper guide pins 81, 82, at the rear surface of the upper part 4 of the rim portion 17, there is an upper magnetic strip 48. The upper magnetic strip 48 is formed from a ferromagnetic material, such for example as steel, and is elongate with a generally rectangular shape and has a length which extends in the x-direction. The upper magnetic strip 48 is fixed inside the upper part 4 of the rim portion 17, so that the magnetic strip 48 is not visible when the glasses are viewed from the front. In alternative embodiments, the upper magnetic strip 48 may have a different shape; for example, the upper magnetic strip may have an oblong shape. In some embodiments, the upper magnetic strip 48 is positioned flush with a rear surface of the upper part 4 of the rim portion 17.

[0069] As shown in FIGS. 5, 7, 9 and 10a, the lower part 5 of the rim portion 17 is formed with a similar arrangement of parts to the upper part 4 of the rim portion 17. A lower magnetic strip 49 is fixed in the lower part 5 of the rim portion 17 in a generally central location, the lowerpart 5 of the rim portion 17 has two lower guide pins 91, 92 which are positioned either side of the lower magnetic strip 49. The lower guide pins 91, 92 are aligned with the upper guide pins 81, 82. The lower guide pins 91, 92 protrude rearwardly of the rear surface of the rim portion 17, in the same way as the upper guide pins 81, 82.

[0070] As shown in FIG 4., the rear lens element 41 has front and rear surfaces 42, 43 and a shape that is similar to the front lens element 31. As shown in FIG. 6, the rear lens element 41 has a top edge 44, a bottom edge 45 and temple and nasal side edges 46, 47. In some embodiments, the width of the rear lens element 41 between the temple and nasal side edges 46, 47 is greater than the corresponding width of the front lens element 31.

[0071] As can be seen in FIGS. 1, 5 and 9, the front and rear lens elements 31, 41 are mounted such that at least an engaging portion 78 of the bottom edge 45 of the rear lens element 41 protrudes slightly below at least a portion of the bottom edge 5 of the frame 12 to facilitate manual movement of the rear lens element 41 relative to the front lens element 31 and assists with the complete detachment of the rear lens element 41 from the front lens element 31. As best shown in FIGS. 5, and 9 and 10b, the bottom edge 45 of the rear lens element 41 comprises with an undulating (i.e. ridged) engaging portion 78. The engaging portion 78 may make the lens 21 easier for the user to manipulate by increasing the amount of friction between the user’s hand and the rear lens element 41.

[0072] With reference to FIG. 6, the rear lens element 41 is formed with two rebated shoulders 51, 52 adjacent the top edge 44. In the present embodiment, the rebated shoulders 51, 52 are formed in the front surface 42 of the rear lens element 41 and oriented along the x-axis. The rebated shoulders 51, 52 are defined by corresponding recesses in the front surface 42 of the rear lens element 41 and are arranged to engage with the guide pins 81, 82, thus, the rebated shoulders are configured to have a depth that corresponds to the height of each of the guide pins 81, 82 in the direction of the z-axis. In other embodiments, the rebated shoulders 51, 52 may extend completely through the rear lens element 41. As shown in FIGS. 5 and 8, each rebated shoulder 51, 52 is arranged to engage slidingly a respective one of the guide pins 81, 82. It will be appreciated that in a variant, the guide pins can be formed instead on the rear lens element 41, protruding forwards and engaged with a corresponding shoulder in the front lens element 31. As a further alternative, the rebated shoulders may be replaced by elongate slots or channels (not shown).

[0073] Between the two shoulders 51, 52, the front surface 42 of the rear lens element 41 has a protruding portion 60 which protrudes from the front surface 42 in the z-direction, as best seen in FIG. 6. The protruding portion 60 has a recess which receives an upper magnetic slider 58. Suitably, the magnetic slider is glued into the recess with an adhesive. In other embodiments, there may be more than one protruding portions, each protruding portion having a recesses to accommodate a magnetic slider. The upper magnetic slider 58 is formed of a permanent magnetic material and has a magnetic axis oriented along the z-axis for coupling with the upper magnetic strip 48 in the upper part 4 of the frame 12 as described in more detail below.

[0074] In alternative embodiments, there may be no protruding portion 60 and the upper magnetic slider 58 is flush with the front optical surface of the rear lens element 41

[0075] The front surface 42 of the rear lens element 41 is also formed with a recess 57 near the bottom edge 45 which is vertically aligned with the protruding portion 60. The lower recess 57 receives a lower magnetic slider 59 (as shown in FIGS 5, 9, and 10b) which is similarly glued therein with a suitable adhesive and has a magnetic axis oriented along the z-axis for coupling with the lower magnetic strip 49. The lower magnetic slider 59 is flush with the front optical surface of the rear lens element 41.

[0076] The present embodiment allows the upper and lower rear magnetic sliders 58, 57 to be a small size in comparison to the upper and lower front magnetic strips 48, 49 such that the rear moveable lens element 41 is manufactured with the fewest number of components. This reduces weight of the lens element and, as a result, the glasses 11 may be made thinner and less bulky than some other conventional adjustable lenses in the art. Making the product as similar in weight to that of a traditional set of eyeglasses may by important to ensure comfort and familiarity to the user. Additionally, a light-weight rear lens element 41 may assist with quick adjustments of the rear lens element 41 relative to the front lens element 31 along the transverse path.

[0077] The upper magnetic strip 48 and the upper magnetic slider 58 together form an upper magnetic fastener 20. The lower magnetic strip 49 and the lower magnetic slider 57 together form a lower magnetic fastener 40. The magnetic fasteners 20, 40 fasten the front and rear lens elements 31, 41 together magnetically with sufficient retention force to hold the lens elements 31, 41 together. The magnetic force is sufficiently strong that the rear lens element 41 stays fastened to the front lens element 31 and the frame 12 in the situations which the glasses would be expected to encounter during normal use. The magnetic fasteners 20, 40 furthermore allow the rear lenselement 41 to be slid laterally relative to the front lens element 31 and the frame 12 without becoming detached, and allow the rear lens element 41 to be manually detached from the front lens element 31 and the frame 12 by pulling the front and rear lens elements 31, 41 apart in the direction of the z-axis, for example, when the lens elements 31, 41 need cleaning.

[0078] The rear lens element 41 is formed with two elongate slots 61, 62 proximate its bottom edge 45, which are oriented along the x-axis and are positioned either side of the lower magnetic slider 59. The slots 61, 62 in the present embodiment have an oblong shape, but in other embodiments the slots may have another shape. The elongate slots 61, 62 are formed by recesses in the front surface 42 of the rear lens element 41. Each elongate slot 61, 62 is arranged to receive a respective one of the lower guide pins 91, 92. The elongate slots 61, 62 are configured to have a depth that corresponds to the height of each of the lower guide pins 91, 92 in the z-axis. It will be seen that the width of each slot 61, 62 is approximately equal to the diameter of each pin 91, 92, such that the engagement of the pins 91, 92 in the slots 61, 62 serves to hold the rear lens element 41 stably against the front lens element 31.

[0079] The guide pins 81, 82, 91, 92 each thus form a first guide part associated with the front lens element 31. The channels 51, 52 and slots 61, 62 each form a second guide part associated with the rear lens element 41. The first and second guide parts form mutually cooperating guide parts (there being four sets of mutually cooperating guide parts in total) which constrain relative lateral movement of the lens elements 31, 41 to the transverse path. The guide pins 81, 82, 91, 92 are not captive within the channels 51, 52 and slots 61, 62, which allows the rear lens element 41 to be detached from the front lens element 31 simply by pulling the rear lens element 41 against the magnetic force of the magnetic fastener.

[0080] As best shown in FIGS. 9 and 10b, within the temple side slot 61, an inner front surface of the recess has a series of formations 102. The formations 102 comprise projections 104 which project forwardly along the z-axis toward the opening of the slot 61. The projections 104 form a ridged surface and define a plurality of notches 106 distributed along the transverse direction, there being a notch 106 between each projection 104.

[0081] The attractive magnetic force between the magnetic slider 59 and magnetic strip 49 biases the lens elements 31, 41 to a position in which the guide pin 91 is received within a notch 106. The engagement of the notch 106 and the guide pin 91 restrains the rear lens element 31 against lateral movement relative to the front lens element 41. In order to move the rear lenselement 41 relative to the front lens element 31, it is necessary to move the rear lens element 41 relative to the front lens element 31 and frame 12, such that the guide pin 91 rides out of the notches 106 and over the projections 104. Doing so requires the rear lens 41 to be moved momentarily in a direction against the attractive magnetic force between the magnetic slider 59 and magnetic strip 49. The projections 104 help prevent the corresponding lower guide pin 91 from moving freely along the elongate slot 61, thus, the projections 104 help hold the front and rear lens elements 31, 41 stably together and help control the movement of the rear lens element 41 when it is moved manually between temple, intermediate and nasal positions.

[0082] The guide pin 91 and the formations 102 form a lens element positioning mechanism. The guide pin 91 functions as a catch and forms a first positioning part. The series of notches defined by the formations 102 form a second positioning part. The magnetic force provided by the magnetic fastener biases the first and second positioning parts into engagement with each other. The guide pin 91 and the formations 102 could be said to form a positioning mechanism in the form of a detent arrangement.

[0083] Each notch 106 defines a respective discrete relative position (detent position) of the lens elements 31, 41 along the transverse path. The number of notches 106 defines the number of discrete relative positions that the adjustable lens can adopt. In the present embodiment as shown in FIGS. 9 and 10b, there are five notches 106 that define five corresponding discrete positions that the guide pin 91 can be held, and thus five discrete relative positions that the lens elements 31, 41 can adopt along the transverse path. At each discrete relative position, the lens 21 has a different predetermined focal length. In the present implementation, the focal length varies by 1 diopter between each successive discrete relative position, although in other implementations, the differential may be different.

[0084] When a force is applied by the user to move the rear lens element 41 relative to the front lens element 31, the projections 104 resist such movement. Upon overcoming the projections 104 and moving into another notch 106, there may be an audible sound, for example a click. This may provide audible feedback for the user, allowing them to confirm that the rear lens element 41 has successfully moved from one notch to another. The movement of the guide pin 91 between notches 106 may also provide positive haptic feedback to the user.

[0085] In the present implementation, the projections 104 are arcuate in cross section, but in other embodiments, the projections 104 may have a triangular or another shape suitable for laterally restraining the guide pin 91 at discrete positions within the slot 61.

[0086] In the present embodiment, only the temple side elongate slot 61 has the formations 102. It will be appreciated that the nasal side elongate slot 62 may alternatively or additionally comprise such formations that are substantially similar to the formations in the temple side elongate slot 61. Having formations on both elongate slots 61, 62 may increase the retention force and may require a greater manual force from the user to move the rear lens element 41 relative to the front lens element 31 along the transverse path, although in such implementation, the formations in the slots 61, 62 would have to be aligned with one another. In some embodiments, one or both of the upper shoulders 51, 52 may comprise formations 102 substantially similar to the formations in the lower elongate slots 61, 62.

[0087] The shoulders 51, 52, slots 61, 62 and guide pins 81, 82, 91, 92 serve as guiding elements for guiding lateral movement of the rear lens element 41 in the transverse direction x across the direction of viewing z relative to the front lens element 31, while constraining movement of the rear lens element 41 relative to the front lens element 31 to the transverse path with a low tolerance. As mentioned above, the guide pins 81, 82 are dimensioned to form a close fit within the slots 51, 52 to prevent movement of the rear lens element 41 relative to the front lens element 31 in the y-direction orthogonal to the x axis and yawing of the rear lens element 41 relative to the front lens element 31 in the x,y-plane.

[0088] The temple and nasal side portions 6, 7 of the rim portion 17 are dimensioned such that, in each position of the rear lens element 41, the temple and nasal edges 46, 47 of the rear lens element 41 are masked by the frame 12 and thus “invisible” from the perspective of an onlooker viewing the user head-on. Additionally, the mutually cooperating guide parts, the magnetic fasteners and the positioning mechanism are all hidden behind the frame from an onlooker. The outer edges of the rear lens element may, however, remain visible when the user is viewed from the side.

[0089] While the present disclosure has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the present disclosure lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0090] Thus, in some implementations, the height of the rear lens element 41 between its top and bottom edges 44, 45 may be slightly greater than the height of the front lens element 31 such that both top and bottom edges 44, 45 of the rear lens element 41 protrude beyond the corresponding edges 34, 35 of the front lens element 31. In an alternative embodiment, the engaging portion 78 may be located on the top edge 44 of the rear lens element 41. In a variant, instead of forming the rear lens element 41 with an integral engaging portion 78, a small component providing increased friction may be attached to the bottom or top edge 45, 44 of the rear lens element 41. This may be achieved by bonding on extra media (such as transparent sandpaper), embedding small ball bearings or other media in the top or bottom edge 44, 45 or using coatings (e.g. dipped, sprayed) or by two-shot moulding (over-moulding) a high friction elastomeric (e.g. TPU) material.

[0091] The positioning mechanism may be located on the upper part 4 of the rim portion 17. The adjustment mechanism may be located on the upper part and lower part of the rim portion. This may improve the holding strength of the rear lens element against lateral movement relative to the frame.

[0092] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present disclosure, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the present disclosure that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the present disclosure, may not be desirable, and may therefore be absent, in other embodiments.

Claims

Claims:

1. Adjustable focal length eyewear comprising: at least one lens which is mounted to a frame for supporting the lens in front of a user’s eyes, thereby defining a viewing direction through the lens; wherein the at least one lens is a variable focal length lens of the kind comprising two superposed lens elements having cooperating optical surfaces that are shaped such that the focal length of the lens is variable according to the relative lateral disposition of the lens elements in a direction transverse the viewing direction; wherein the lens elements are slidable relative to one another along a transverse path that is oriented transverse to the viewing direction for varying the focal length of the lens; wherein the lens further comprises: mutually cooperating guide parts on the lens elements which constrain relative lateral movement of the lens elements to the transverse path, and a magnetic fastener for releasably fastening the lens elements to each other, the magnetic fastener comprising an elongate magnetic strip on one of the lens elements or a part fixedly secured thereto and a cooperating magnetic slider provided on the other lens element or a part fixedly secured thereto, wherein the magnetic slider and magnetic strip are configured and arranged to: magnetically fasten the lens elements to each other during reciprocal relative lateral movement of the lens elements along the transverse path, and permit detachment of the lens elements from each other in the viewing direction.

2. Adjustable focal length eyewear as claimed in claim 1, comprising a lens element positioning mechanism which defines a plurality of discrete relative positions of the lens elements along the transverse path, wherein the positioning mechanism is arranged to restrain the lens elements laterally in the discrete relative positions along the transverse path, wherein the lens provides a different focal length at each discrete relative position of the lens elements.

3. Adjustable focal length eyewear as claimed in claim 2, wherein the positioning mechanism comprises: a first positioning part associated with one of the lens elements, and a second positioning part associated with the other lens element,wherein the first and second positioning parts are arranged to engage mechanically when the lens elements are fastened to each other, the mechanical engagement causing, in the absence of external force applied by a user, the lens elements to adopt, and be retained in, one of the discrete relative positions.

4. Adjustable focal length eyewear as claimed in claim 3, wherein the positioning mechanism is configured to retain the lens elements in each discrete relative position until a threshold force acting to move the lens elements along the transverse path is exceeded.

5. Adjustable focal length eyewear as claimed in any of claims 2 to 4, wherein the positioning mechanism defines five selectable discrete relative positions of the lens elements along the transverse path.

6. Adjustable focal length eyewear as claimed in any of claims 2 to 5, wherein the magnetic fastener provides a bias force to bias the first and second positioning parts into the mechanical engagement.

7. Adjustable focal length eyewear as claimed in any of claims 2 to 6, wherein the positioning mechanism is a manual positioning mechanism which is manually operable by a user of the eyewear.

8. Adjustable focal length eyewear as claimed in any preceding claim, wherein the mutually cooperating guide parts comprise: a first guiding part comprising a guide pin, and a second guiding part comprising a slot configured to receive the guide pin such that the guide pin is slidable within the slot, wherein slot is configured to constrain movement of the guide pin to the transverse direction.

9. Adjustable focal length eyewear as claimed in claim 8, when dependent on claim 3, wherein the first positioning part comprises the guide pin, and the second positioning part comprises a surface of the other lens element within the slot, the surface having a series of notches with which the guide pin engages,wherein when the lens elements are fastened to each other, the guide pin selectively engages with the notches to restrain the lens elements laterally in a selected discrete relative position.

10. Adjustable focal length eyewear as claimed in claim 8 or 9, wherein the series of notches are provided on a surface of the other lens element that is oriented generally normal to the viewing direction, and the guide pin extends generally in the viewing direction.

11. Adjustable focal length eyewear as claimed in any of claims 8 to 10, comprising a plurality of the mutually cooperating guide parts spaced along the transverse direction.

12. Adjustable focal length eyewear as claimed in any preceding claim, wherein a first one of the lens elements is fixedly secured to the frame, and a second one of the lens elements is movable relative to the first lens element and the frame.

13. Adjustable focal length eyewear as claimed in claim 12, wherein the first lens element is a front lens element, and the second lens element is a rear lens element, the front lens element being the lens element furthest form the eye, and the rear lens element being the lens element closest to the eye, when the eyewear is operatively worn by a user.

14. Adjustable focal length eyewear as claimed in claim 12 or 13, wherein the magnetic strip is fixedly secured to the first lens element or the frame, and the magnetic slider is fixedly secured to the second lens element.

15. Adjustable focal length eyewear as claimed in any preceding claim, wherein the magnetic fastener is disposed rearward of the frame and is superposed with the frame.

16. Adjustable focal length eyewear as claimed in any preceding claim, comprising at least two of the magnetic fasteners spaced apart in a direction orthogonal to both the transverse direction and the viewing direction.

17. Adjustable focal length eyewear as claimed in any preceding claim, wherein the eyewear is a pair of glasses comprising a pair of the variable focal length lenses.

18. A variable focal length lens comprising: two superposed lens elements having cooperating optical surfaces that are shaped such that the focal length of the lens is variable according to the relative lateral disposition of the lens elements in a direction transverse the viewing direction; wherein lens elements are slidable relative to one another along a transverse path that is oriented transverse to the viewing direction for varying the focal length of the lens; wherein the lens further comprises: mutually cooperating guide parts on the lens elements which constrain relative lateral movement of the lens elements to the transverse path, and a magnetic fastener for releasably fastening the lens elements to each other, the magnetic fastener comprising an elongate magnetic strip on one of the lens elements or a part fixedly secured thereto and a cooperating magnetic slider provided on the other lens element or a part fixedly secured thereto, wherein the magnetic slider and magnetic strip are configured to: magnetically fasten the lens elements to each other during reciprocal relative lateral movement of the lens elements along the transverse path, and permit detachment of the lens elements each other in the viewing direction.

19. A variable focal length lens according to claim 18, comprising a lens element positioning mechanism which defines a plurality of discrete relative positions of the lens elements along the transverse path, wherein the positioning mechanism is arranged to laterally restrain the lens elements in the discrete relative positions along the transverse path, wherein the lens provides a different focal length at each discrete relative position of the lens elements.

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