Optical assembly

Abstract

An optical assembly comprises an optical element having an adaptable shape, and an actuator assembly. The actuator assembly comprises a support structure defining a first axis z, a primary intermediat

Description

Field The present application relates to an optical assembly, and in particular to an optical assembly comprising an optical element having an adaptable shape. Background An eye focuses on an object by focusing light from the object on the retina of the eye. The shape of the eye and the condition of the refractive elements of the eye can affect the eye’s ability to focus light on the retina. For example, a person may suffer from one or more of near-sightedness, far-sightedness and astigmatism. In the case of near-sightedness (also called myopia) and farsightedness (also referred to as hyperopia or hypermetropia), light from objects at certain distances may be focused in front of or behind the retina, respectively, such that the objects appear blurry. Astigmatism results in distorted or blurred vision, and is due to a rotational asymmetry in the refractive power of the eye. Glasses or contact lenses may be worn to correct for near-sightedness, far-sightedness and astigmatism. A prescription may comprise a spherical power (to correct for near-sightedness or far-sightedness) and / or a cylindrical power and direction (to correct for astigmatism). A person’s prescription may change over time. Furthermore, a person may also experience problems with adjusting the focus of the eye for objects at different distances. Glasses or contact lenses with fixed optical properties, such as a fixed focal length, may not be able to correct for this. Headsets such as virtual reality (VR) and augmented reality (AR) headsets present virtual objects to a user, either replacing or supplementing the visual environment around the user. The virtual objects may be presented as if being at certain simulated distances from the user. It is desirable that the user is able to focus on these objects at the simulated distance. The simulated distances may change, meaning that it is desirable for the VR or AR headset to change its optical properties such that the user’s eyes adjust and focus on the virtual objects as they would on real objects. The VR or AR headset may be worn by people having different interpupi I lary distances. It is advantageous for the comfort of a user that any headset is compact and lightweight. A VR or AR headset or, indeed, glasses, may be provided in a range of shapes and sizes. It is beneficial for optical assemblies used in glasses or headsets to be able to accommodate a range of shapes and sizes of headset. Furthermore, a VR or AR headset may be battery powered, so it is beneficial for components of the VR or AR headset to require little power to operate. Summary According to a first aspect of the present invention, there is provided: an optical assembly comprising: an optical element having an adaptable shape; and an actuator assembly comprising: a support structure, wherein a first axis is defined relative to the support structure; a primary intermediate part movable relative to the support structure in a primary plane perpendicular to the first axis and comprising a plurality of primary drive portions each extending out of the primary plane; a movable part comprising a plurality of driven portions each corresponding to one of the plurality of primary drive portions, wherein each driven portion is movable relative to the support structure to adapt the adaptable shape of the optical element; and one or more actuator units configured to drive movement of the primary intermediate part relative to the support structure in the primary plane; wherein movement parallel to the primary plane of the plurality of primary drive portions effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element. In this way, optical properties of the optical element may be altered by using a single actuator. The shape of the optical element may be changed by, for example, adding or adapting a spherical distortion, and / or adding or adapting a cylindrical distortion, and / or moving an optical axis. Use of one actuator to change the shape of the optical element saves power, compared to using multiple actuators positioned around an edge of the optical element. Actuation in a plane perpendicular to the first axis may be translated into movement parallel to the first axis, providing a compact device. Furthermore, additional actuation may be added by utilising two sides of the primary intermediate part and / or adding one or more additional intermediate parts. At least one of the one or more actuator units may comprise a shape memory alloy (SMA) element, e.g. an SMA wire. SMA elements are precise and reliable actuators, that are power-efficient and compact. The optical assembly may be configured to constrain movement of the movable part relative to the support structure in an absence of power to one or more actuator units of the actuator assembly. In other words, the optical assembly may be configured to hold the movable part in position (i.e. stationary) relative to the support structure in an absence of power to the one or more actuator units of the actuator assembly the In this way, power may be saved by only driving the actuating units when the movable part needs to be moved from its present position. In an event that the movable part needs to be held in place, power to the actuating units may not be required. The primary intermediate part may be movable relative to the support structure in a primary plane in two or more degrees of freedom; or the primary intermediate part may be movable relative to the support structure in a primary plane in a first degree of freedom, and wherein the actuator assembly further comprises a secondary intermediate part movable in a second degree of freedom relative to the support structure in a secondary plane perpendicular to the first axis, wherein: the secondary intermediate part comprises a plurality of secondary drive portions each extending out of the secondary plane. The second degree of freedom is different to the first degree of freedom. In this way, the optical assembly can move one or more intermediate parts in more than one degree of freedom, allowing for more than one distortion to be added to the optical element. Having more than one intermediate part increases the number of interfaces that may comprise drive portions, for example, so may increase the number of distortions that may be combined and / or may increase the magnitude of a distortion for a given movement of an intermediate part. Having more than one intermediate part may allow the movement in the first and second degrees of freedom to be independent, so that the magnitudes of the resulting distortions may be controlled independently. The primary intermediate part may be translatable relative to the support structure in the primary plane. The primary intermediate part may be rotatable relative to the support structure in the primary plane. The plurality of primary drive portions may each comprise a surface at an acute, non-zero angle with respect to the primary plane; and / or the plurality of primary driven portions may each comprise a surface angled at an acute, non-zero angle with respect to the primary plane. Advantageously, this allows driven portions of the movable part to slide or roll relative to the primary drive portions such that movement of the primary drive portions in the primary plane may be translated to movement of the movable part out of the primary plane. The plurality of primary drive portions may each comprise a surface at an acute, non-zero angle with respect to the primary plane, wherein either: the plurality of driven portions each comprise a mating surface corresponding to a surface of a corresponding primary drive portion; or the plurality of driven portions each comprise a rolling bearing; or the plurality of driven portions comprises a first sub-group of driven portions and a second sub-group of driven portions separate to the second sub-group of driven portions, wherein: the driven portions of the first sub-group of driven portions each comprise a mating surface corresponding to a surface of a corresponding primary drive portion; and the driven portions of the second sub-group of driven portions each comprise a rolling bearing. In this way, the driven portion may comprise either a mating surface or a rolling bearing, and may be chosen based on the primary drive portion. In other words, the movement of the movable part with respect to the primary intermediate part may be supported by a rolling bearing (e.g. only), a plain bearing assembly (e.g. only) or a combination of plain bearings and rolling bearings. In the case of one or more of the plurality of driven portions comprising a mating surface, a given mating surface may be in direct contact with the corresponding drive portion, i.e. the mating surface may slide over the surface of the corresponding drive portion when the primary intermediate part is driven to move relative to the support structure. This may be described as a plain bearing. Such a plain bearing may be arranged to have sufficient friction to restrain movement of the movable part with respect to the support structure when the one or more actuator units are unpowered, so as to hold the optical element in a particular configuration when the one or more actuator units are unpowered. This may be referred to as zero-hold-power functionality. The optical assembly may be arranged such that various components of the optical assembly (e.g. one or more of the primary intermediate part, the movable part and the support structure) are biased together. Such biasing may be achieved by use of a biasing assembly, which may comprise one or more resilient elements, such as springs, and / or one or more magnets. In the case of one or more of the plurality of driven portions comprising a rolling bearing, the optical assembly may comprise one or more rolling elements (e.g. ball bearings) disposed between the primary intermediate part and the movable part, for example between one of more primary drive portions and the corresponding driven portions. Such a rolling bearing arrangement may be low friction (e.g. as compared to a plain bearing). A combination of rolling bearings and plain bearings between the primary intermediate part and the movable part may be beneficial. For example, a driven portion comprising a mating surface (i.e. a plain bearing) may be appropriate for primary drive portions having a shallower angle with respect to the primary plane and a driven portion comprising a rolling bearing may be appropriate for primary drive portions having a steeper angle with respect to the primary plane. This is because that if a pair of driven / drive portions were arranged as a plain bearing with a steep angle with respect to the primary plane, the normal force between the two mating surfaces and hence the associated friction may be too high to overcome to drive relative movement. Accordingly, steep-angled surfaces may be arranged as (low friction) rolling bearings (to provide the necessary displacement of the driven portion out of the primary plane) and shallow-angled surfaces may be arranged as plain bearings (to provide zero-hold-power functionality). In the case of a non-spherical lens, driven portions which are further from the centre of the optical element will require a greater displacement out of the primary plane, as compared to driven portions closer to the centre of the optical element, to achieve a spherical deformation of the optical element. Such driven portions, which are relatively far from the centre of the optical element, may be supported to move relative to the primary intermediate part by rolling bearings and those driven portions which are relatively closer to the centre of the optical element may be supported to move relative to the primary intermediate part by plain bearings, for the provision of zero-hold-power functionality. The plurality of primary drive portions may each comprise: a body; and a linkage connected between the body and a corresponding driven portion; wherein movement of a body of a primary drive portion in the primary plane rotates the linkage of the primary drive portion such that the corresponding driven portion is moved out of the primary plane. In this way, movement of the primary drive portions in the primary plane may be translated to movement of the movable part out of the primary plane. The optical element may comprise a lens having at least one lens surface with an adaptable shape. The optical element may comprise a mirror with an adaptable shape. The movable part may comprise a first friction surface configured to engage with a second friction surface such that movement of the movable part relative to the support structure is constrained in an absence of power to one or more actuator units of the actuator assembly; and / or the primary intermediate part may comprise a first friction surface configured to engage with a second friction surface such that movement of the primary intermediate part relative to the support structure is constrained in an absence of power to one or more actuator units of the actuator assembly. In this way, movement of one or more parts of the optical assembly may be constrained in an absence of power to one or more actuator units of the actuator assembly. In the case that the movable part comprises a first friction surface, the second friction surface may be disposed on (e.g. may be part of) the primary intermediate part or the support structure. The first friction surface (and / or the second friction surface) may be at an acute, non-zero angle to the primary plane (i.e. the first friction surface may be a mating surface as described above). In the case that the primary intermediate part comprises a first friction surface, the second friction surface may be disposed on (e.g. may be part of) the movable part or the support structure. The first friction surface (and / or the second friction surface) may be at an acute, non-zero angle to the primary plane (i.e. the first friction surface may be a mating surface as described above). The primary intermediate part may be rotatable in the primary plane about the first axis. The optical assembly may be configured such that each driven portion moved out of the primary plane may have a component of movement that: is normal to the primary plane; and has a drive magnitude; wherein the drive magnitude for each of the driven portions is such that a spherical distortion of the optical element is adapted. In an event that the driven portions are arranged in a circle, the drive magnitude for each of the driven portions may be the same. In an event that the driven portions are not arranged in a circle, the drive magnitude for each of the driven portions may vary. The primary intermediate part may be translatable in the primary plane in a first degree of freedom and in a second degree of freedom. The optical assembly may be configured such that translation of the primary intermediate part along a secondary axis in the primary plane may effect movement of at least a subset of the plurality of driven portions out of the primary plane to add a first cylindrical distortion to the optical element, the first cylindrical distortion having a first cylindrical axis; and translation of the primary intermediate part along a tertiary axis in the primary plane may effect movement at least a subset of the plurality of driven portions out of the primary plane to add a second cylindrical distortion to the optical element, the second cylindrical distortion having a second cylindrical axis that is at a non-zero angle to the first cylindrical axis. In this way, two cylindrical distortions may be combined such that a cylindrical distortion may be obtained having an arbitrary angle of cylindrical axis. The secondary axis may be perpendicular to the tertiary axis and the second cylindrical axis is at 45° relative to the first cylindrical axis. In this way, two cylindrical distortions may be combined such that a cylindrical distortion may be obtained having an arbitrary angle of cylindrical axis. Furthermore, rotation of the primary intermediate part may result in translation of the optical axis in the primary plane. The primary intermediate part may comprise: a first region comprising the plurality of primary drive portions each extending out of the primary plane; and a second region comprising a plurality of secondary drive portions each extending out of the primary plane, wherein the plurality of secondary drive portions engage with corresponding portions of the support structure. For example, the first region may be disposed on a first side of the primary intermediate part and the second region may be disposed on a second side of the primary intermediate part. The first and second sides may be opposite each other and optionally may be separated from each other along the primary axis. As viewed along a direction in the primary plane, the first and second regions may be disposed on the top and bottom (respectively) of the primary intermediate part. In this way, more than one side of the primary intermediate part may be utilised to effect movement of the movable part. The first and second regions may effect the same magnitude and direction of movement of the movable part such that the movement is amplified by using both first and second regions, or the first and second regions may effect different magnitudes and directions of movement of the movable part. Rotation of the primary intermediate part in the primary plane may effect movement of at least a subset of the plurality of driven portions out of the primary plane to move an optical axis of the optical element.This may be in addition to the cylindrical distortion achieved by translating the primary intermediate part. The plurality of primary drive portions may each comprise a planar surface angled with respect to the primary plane and wherein a gradient of the planar surface with respect to the primary plane in a direction parallel to the secondary axis is proportional to cos(2a), where a is an angle to the secondary axis in the primary plane. Accordingly, the gradient of a primary drive portions may depend on its position on the circumference of the primary intermediate part. The optical element may be circular. According to a second aspect of the present disclosure, a head-mounted device is provided comprising an optical assembly according to the first aspect. The head-mounted device may comprise a display and an optical assembly according to the first aspect, wherein the display is configured to be viewed through the optical assembly. According to a third aspect of the present disclosure, there is provided a method of adapting a shape of an optical element having an adaptable shape using an actuator assembly comprising: a support structure, wherein a first axis is defined relative to the support structure; a primary intermediate part movable relative to the support structure in a primary plane perpendicular to the first axis and comprising a plurality of primary drive portions each extending out of the primary plane; a movable part comprising a plurality of driven portions each corresponding to one of the plurality of primary drive portions, wherein each driven portion is movable relative to the support structure to adapt the adaptable shape of the optical element; and one or more actuator units configured to drive movement of the primary intermediate part relative to the support structure in the primary plane; wherein the method comprises: moving the primary intermediate part in the primary plane such that the plurality of primary drive portions move parallel to the primary plane, effecting movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element. Further aspects of the present invention are provided according to the following numbered clauses: Clause A1: An optical assembly comprising: an optical element having an adaptable shape; and an actuator assembly comprising: a support structure, wherein a first axis is defined relative to the support structure; a primary intermediate part movable relative to the support structure in a primary plane perpendicular to the first axis and comprising a plurality of primary drive portions each extending out of the primary plane; a movable part comprising a plurality of driven portions each corresponding to one of the plurality of primary drive portions, wherein each driven portion is movable relative to the support structure to adapt the adaptable shape of the optical element; and one or more actuator units configured to drive movement of the primary intermediate part relative to the support structure in the primary plane; wherein movement parallel to the primary plane of the plurality of primary drive portions effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element. Clause A2: An optical assembly according to clause A1 wherein at least one of the one or more actuator units comprises a shape memory alloy (SMA) element. Clause A3: An optical assembly according to clause A1 or A2, wherein the optical assembly is configured to constrain movement of the movable part relative to the support structure in an absence of power to one or more actuator units of the actuator assembly. Clause A4: An optical assembly according to any of clauses A1 to A3, wherein the primary intermediate part is movable relative to the support structure in a primary plane in two or more degrees of freedom. Clause A5: An optical assembly according to any of clauses A1 to A5, wherein the primary intermediate part is translatable relative to the support structure in the primary plane. Clause A6: An optical assembly according to any of clauses A1 to A6, wherein the primary intermediate part is rotatable relative to the support structure in the primary plane. Clause A7: An optical assembly according to any of clauses A1 to A6 wherein the primary intermediate part is movable relative to the support structure in a primary plane in a first degree of freedom, and wherein the actuator assembly further comprises a secondary intermediate part movable relative to the support structure in a secondary plane perpendicular to the first axis and comprising a plurality of primary drive portions each extending out of the primary plane. Clause A8: An optical assembly according to any of clauses A1 to A7, wherein: the plurality of primary drive portions each comprise a surface at an acute, non-zero angle with respect to the primary plane; and / or the plurality of driven portions each comprise a surface angled at an acute, non-zero angle with respect to the primary plane. Clause A9: An optical assembly according to clause A8, wherein: the plurality of primary drive portions each comprise a planar surface at an angle with respect to the primary plane; and / or the plurality of driven portions each comprise a planar surface at an angle with respect to the primary plane. Clause A10: An optical assembly according to clause A8, wherein: the plurality of primary drive portions each comprise a curved surface at a varying angle with respect to the primary plane; and / or the plurality of driven portions each comprise a curved surface at a varying angle with respect to the primary plane. In this way, a magnitude of a distortion resulting from a given movement of a primary intermediate part may vary. Clause A11: An optical assembly according to any of clauses A8 to A10 wherein the plurality of driven portions each comprise a mating surface corresponding to a surface of a corresponding primary drive portion. Clause A12: An optical assembly according to any of clauses A8 to A10 wherein the plurality of driven portions each comprise a rolling bearing. Clause A13: An optical assembly according to any of clauses A8 to A12 wherein the plurality of primary drive portions each comprise a surface at an acute, non-zero angle with respect to the primary plane and wherein the plurality of driven portions comprises a first sub-group of driven portions and a second sub-group of driven portions separate to the second sub-group of driven portions, wherein: the driven portions of the first sub-group of driven portions each comprise a mating surface corresponding to a surface of a corresponding primary drive portion and configured to slide over the surface when the primary intermediate part moves relative to the movable part; and the driven portions of the second sub-group of driven portions each comprise a rolling bearing. Clause A14: An optical assembly according to any of clauses A1 to A7, wherein the plurality of primary drive portions each comprise: a body; and a linkage connected between the body and a corresponding driven portion; wherein movement of a body of a primary drive portion in the primary plane rotates the linkage of the primary drive portion such that the corresponding driven portion is moved out of the primary plane. Clause A15: An optical assembly according to clause A14, wherein the linkage comprises a flexure. Clause A16: An optical assembly according to any of clauses A1 to A15, wherein the optical element comprises a lens having at least one lens surface with an adaptable shape. Clause A17: An optical assembly according to clause A16, wherein the lens comprises a liquid lens or a gel lens having at least one lens surface with an adaptable shape. Clause A18: An optical assembly according to clause A17, wherein the lens comprises a cavity containing liquid or gel and having a cavity volume, and wherein the lens surface with an adaptable shape is under tension such that displacing a part of the membrane with respect to the support structure alters a curvature of the membrane with respect to the support structure such that the cavity volume of the lens is constant. In this way, altering a position of an edge of the lens surface can add or adapt a distortion to the lens surface. Clause A19: An optical assembly according to any of clauses A16 to A18, wherein the lens surface having an adaptable shape is a membrane with a stiffness value such that displacing a part of the membrane with respect to the support structure or altering an angle of a part of the membrane with respect to the support structure alters a curvature of the membrane with respect to the support structure. In this way, altering a position of an edge of the lens surface can add or adapt a distortion to the lens surface. Clause A20: An optical assembly according to any of clauses A1 to A15, wherein the optical element comprises a mirror with an adaptable shape. Clause A21: An optical assembly according to any of clauses A1 to A20 wherein at least one of the primary intermediate part and the movable part are flexible in a direction parallel to the first axis. Clause A22: An optical assembly according to any of clauses A1 to A21 wherein the primary drive portions are aligned with an edge portion of the optical element. Clause A23: An optical assembly according to any of clauses A1 to A22, wherein the primary intermediate part comprises between 50 and 100 primary drive portions. Clause A24: An optical assembly according to any of clauses A1 to A23, wherein the primary intermediate part is movable out of the primary plane. Advantageously, one or more additional intermediate parts may be used that may move the primary intermediate part in order to move the movable part. Clause A25: An optical assembly according to any of clauses A1 to A25, wherein at least one of the one or more actuator units comprises a voice coil motor actuator and / or a piezoelectric element. Clause A26: An optical assembly according to clause A3 or any of clauses A4 to A25 when dependent on clause A3, wherein either: the movable part comprises a first friction surface configured to engage with a second friction surface such that movement of the movable part relative to the support structure is constrained in an absence of power to one or more actuator units of the actuator assembly; or the primary intermediate part comprises a first friction surface configured to engage with a second friction surface such that movement of the primary intermediate part relative to the support structure is constrained in an absence of power to one or more actuator units of the actuator assembly. Clause A27: An optical assembly according to clause A26, wherein: the primary intermediate part comprises the second friction surface; or the support structure comprises the second friction surface; or the optical assembly further comprises a clamp comprising the second friction surface. Clause A28: An optical assembly according to any of clauses A1 to A27 further comprising a biasing means configured to bias the movable part and the primary intermediate part against each other. In this way, moving the primary intermediate part accurately effects movement of the movable part. Clause A29: An optical assembly according to clause A28, wherein the biasing means comprises: a resilient element; and / or a magnet. Clause A30: An optical assembly according to any of clauses A1 to A29, wherein the primary intermediate part is rotatable in the primary plane about the first axis. Clause A31: An optical assembly according to clause A30, wherein rotation of the primary intermediate part in the primary plane effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt a spherical curvature of the optical element. Clause A32: An optical assembly according to clause A31, wherein each driven portion moved out of the primary plane has a component of movement that: is normal to the primary plane; and has a drive magnitude; wherein the drive magnitude is the same for each of the driven portions. Clause A33: An optical assembly according to clause A31, wherein each driven portion moved out of the primary plane has a component of movement that: is normal to the primary plane; and has a drive magnitude; wherein the drive magnitude for each of the driven portions is such that a spherical distortion of the optical element is adapted. Clause A34: An optical assembly according to any of clauses A1 to A33, wherein the primary intermediate part is translatable in the primary plane in a first degree of freedom and in a second degree of freedom. Clause A35: An optical assembly according to clause A34, wherein translation of the primary intermediate part in the primary plane effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt a cylindrical distortion of the optical element. Clause A36: An optical assembly according to clause A35, wherein: translation of the primary intermediate part along a secondary axis in the primary plane effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt a first cylindrical distortion of the optical element, the first cylindrical distortion having a first cylindrical axis; and translation of the primary intermediate part along a tertiary axis in the primary plane effects movement at least a subset of the plurality of driven portions out of the primary plane to adapt a second cylindrical distortion of the optical element, the second cylindrical distortion having a second cylindrical axis that is at a non-zero angle to the first cylindrical axis. Clause A37: An optical assembly according to clause A36, wherein the secondary axis is perpendicular to the tertiary axis and the second cylindrical axis is at 45° relative to the first cylindrical axis. Clause A38: An optical assembly according to any of clauses A35 to A37, wherein the primary intermediate part comprises: a first region on a first side of the primary plane, the first region comprising the plurality of primary drive portions each extending out of the primary plane; and a second region on a second side of the primary plane, the second region comprising a plurality of secondary drive portions each extending out of the primary plane; wherein the first side and the second side are separated along the first axis. In this way more than one side of the primary intermediate part may be used to effect motion of the movable part, either to duplicate the movement effected by the primary drive portions or to introduce a different movement. Clause A39: An optical assembly according to clause A38, wherein the optical assembly further comprises a primary interface part comprising a plurality of primary interface portions each corresponding to a secondary drive portion and wherein movement parallel to the primary plane of the plurality of secondary drive portions effects movement of at least a subset of the plurality of secondary drive portions out of the primary plane. Clause A40: An optical assembly according to clause A39, wherein movement parallel to the primary plane of the plurality of the secondary drive portions effects movement of at least a subset of the plurality of secondary drive portions out of the primary plane such that a direction and magnitude of the movement of the primary intermediate part relative to the primary interface part is the same as a direction and magnitude of the movement of the movable part relative to the primary intermediate part. Clause A41: An optical assembly according to clause A39, wherein movement parallel to the primary plane of the plurality of secondary drive portions effects movement of at least a subset of the plurality of secondary drive portions out of the primary plane such that a direction and magnitude of the movement of the primary intermediate part relative to the primary interface part is different to a direction and magnitude of the movement of the movable part relative to the primary intermediate part. Clause A42: An optical assembly according to any of clauses A39 to A41, wherein the interface part is static relative to the support structure. Alternatively, the interface part may be movable relative to the support structure in a direction parallel to the first axis, and / or the interface part may be flexible out of the primary plane relative to the support structure. In other words, portions of the interface part may move relative to the support structure but the interface part may not translate or rotate as a whole relative to the support structure. Clause A43: An optical assembly according to any of clauses A34 to A42, wherein rotation of the primary intermediate part in the primary plane effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt a spherical curvature of the optical element. Clause A44: An optical assembly according to any of clauses A36 or clauses A37 to A43 when dependent on clause 36, wherein the plurality of primary drive portions each comprise a planar surface angled with respect to the primary plane and wherein a gradient of the planar surface with respect to the primary plane in a direction parallel to the secondary axis is proportional to cos(2a), where a is an angle to the secondary axis in the primary plane. Clause A45: An optical assembly according to any of clauses A36 to A43, wherein the plurality of primary drive portions each comprise a planar surface angled with respect to the primary plane and wherein: a gradient of the planar surface with respect to the primary plane in a direction parallel to the secondary axis is proportional to cos(2a), where a is an angle to the secondary axis in the primary plane; and a gradient of the planar surface with respect to the primary plane in a direction parallel to the tertiary axis is proportional to sin(2a), where a is an angle to the secondary axis in the primary plane. Clause A46: An optical assembly according to any of clauses A1 to A33, wherein the primary intermediate part is translatable relative to the support structure in the primary plane in a first degree of freedom and movable out of the primary plane, wherein the actuator assembly further comprises: a secondary interface part; a secondary intermediate part movable relative to the support structure in a secondary plane perpendicular to the first axis and separated from the primary plane along the first axis, the secondary intermediate part comprising a plurality of tertiary drive portions each extending out of the secondary plane, wherein the secondary intermediate part is translatable relative to the secondary interface part in the secondary plane in a second degree of freedom different to the first degree of freedom; and one or more actuator units configured to drive movement of the secondary intermediate part relative to the secondary interface structure in the secondary plane; and wherein the secondary interface part comprises a plurality of secondary interface portions each corresponding to one of the plurality of tertiary drive portions; and wherein movement of the secondary intermediate part parallel to the secondary plane effects movement of at least a subset of the tertiary drive portions out of the secondary plane to move the primary intermediate part out of the primary plane to adapt the adaptable shape of the optical element. The secondary interface part may be part of the support structure or static relative to the support structure. There are at least two interfaces, including between the primary intermediate part and the movable part and between the secondary intermediate part and the secondary interface part. There may be another interface between the primary intermediate part and the secondary intermediate part. Alternatively, the secondary interface part may be between the primary intermediate part and the secondary intermediate part. Clause A47: An optical assembly according to clause A46, wherein: translation of the primary intermediate part in the first degree of freedom in the primary plane effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt a first cylindrical curvature of the optical element, the first cylindrical curvature having a first cylindrical axis; and translation of the secondary intermediate part in the second degree of freedom in the secondary plane effects movement at least a subset of the plurality of tertiary drive portions out of the secondary plane to adapt a second cylindrical curvature of the optical element, the second cylindrical curvature having a second cylindrical axis at a non-zero angle to the first cylindrical axis. Clause A48: An optical assembly according to clause A47, wherein translation of the primary intermediate part in the first degree of freedom is perpendicular to translation of the secondary intermediate part in the second degree of freedom and wherein the second cylindrical axis is at 45° relative to the first cylindrical axis. Clause A49: An optical assembly according to any of clauses A46 to A48, wherein the primary intermediate part comprises: a first region on a first side of the primary plane, the first region comprising the plurality of primary drive portions each extending out of the primary plane; and a second region on a second side of the primary plane, the second region comprising a plurality of secondary drive portions each extending out of the primary plane; and wherein the secondary intermediate part comprises: a third region on a first side of the secondary plane opposing the second region of the primary intermediate part, the third region comprising a plurality of quaternary drive portions each corresponding to a secondary drive portion and extending out of the secondary plane; and a fourth region on a second side of the secondary plane, the second region comprising the plurality of tertiary drive portions each extending out of the secondary plane. Clause A50: An optical assembly according to clause A49, wherein the primary intermediate part is movable relative to the secondary intermediate part in the primary plane, wherein movement in the primary plane of the primary intermediate part relative to the secondary intermediate part effects movement of at least a subset of the secondary drive portions towards the primary plane. Clause A51: An optical assembly according to any of clauses A46 to A50, wherein the secondary interface portion is static relative to the support structure. Clause A52: An optical assembly according to any of clauses A1 to A24, wherein the primary drive portions of the primary intermediate part are movable out of the primary plane and movable in the primary plane and wherein the optical assembly further comprises: a secondary intermediate part movable relative to the support structure in a secondary plane perpendicular to the first axis and comprising a plurality of secondary drive portions each extending out of the secondary plane; one or more actuator units configured to drive movement of the secondary intermediate part relative to the support structure in the secondary plane and an interface part between the primary intermediate part and the secondary intermediate part, the interface part comprising a plurality of primary interface portions each corresponding to one of the plurality of secondary drive portions, wherein each primary interface portion is movable relative to the support structure to move the primary intermediate part to adapt the adaptable shape of the optical element; wherein movement parallel to the primary plane of the plurality of primary drive portions effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element; and wherein movement parallel to the secondary plane of the plurality of secondary drive portions effects movement of at least a subset of the plurality of primary interface portions out of the secondary plane to move the primary intermediate portion and adapt the adaptable shape of the optical element. Clause A53: An optical assembly according to clause A52, wherein: translation of the primary intermediate part along a secondary axis in the primary plane effects movement at least a subset of the plurality of driven portions out of the primary plane to adapt a first cylindrical curvature of the optical element, the first cylindrical curvature having a first cylindrical axis; and translation of the primary intermediate part along a tertiary axis that is in the primary plane and at a non-zero angle to the secondary axis effects movement at least a subset of the plurality of driven portions out of the primary plane to adapt a second cylindrical curvature of the optical element, the second cylindrical curvature having a second cylindrical axis different to the first cylindrical axis. Clause A54: An optical assembly according to clause A52 or A53, wherein rotation of the secondary intermediate part in the secondary plane effects movement of at least a subset of the plurality of primary interface portions out of the secondary plane to move the primary intermediate part to adapt a spherical curvature of the optical element. Clause A55: An optical assembly according to any of clauses A52 to A54, wherein the primary interface part further comprises a plurality of tertiary drive portions extending out of the primary plane and the interface part further comprises a plurality of secondary interface portions each corresponding to one of the plurality of tertiary drive portions. Clause A56: A headset comprising an optical assembly according to any of clauses A1 to A55. Clause A57: A headset comprising; a display; and an optical assembly according to any of clauses A1 to A55, wherein the display is configured to be viewed through the optical assembly. Clause A58: A method of adapting a shape of an optical element having an adaptable shape using an actuator assembly comprising: a support structure, wherein a first axis is defined relative to the support structure; a primary intermediate part movable relative to the support structure in a primary plane perpendicular to the first axis and comprising a plurality of primary drive portions each extending out of the primary plane; a movable part comprising a plurality of driven portions each corresponding to one of the plurality of primary drive portions, wherein each driven portion is movable relative to the support structure to adapt the adaptable shape of the optical element; and one or more actuator units configured to drive movement of the primary intermediate part relative to the support structure in the primary plane; wherein the method comprises: moving the primary intermediate part in the primary plane such that the plurality of primary drive portions move parallel to the primary plane, effecting movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element. Clause B1: An optical assembly comprising: a deformable optical element defining a primary axis; an actuator assembly configured to deform the deformable optical element, the actuator assembly comprising: a first part coupled to the deformable optical element; a support structure; a movable part configured to move relative to the support structure and which is coupled to the first part; a shape memory alloy, SMA, element configured to drive movement of the movable part relative to the support structure to effect movement of the first part relative to the support structure and thereby deform the deformable optical element; wherein the optical assembly is configured so as to retain the first part in position with respect to the support structure when the SMA element is unpowered. A deformable optical element is an example of an optical element having an adaptable shape, as used elsewhere in this document. The primary axis is an alternative term for the first axis. The first part is coupled to the deformable optical element, such that moving the first part relative to the support structure deforms the deformable optical element. This first part may be another term for the movable part used elsewhere in this document, wherein movement of one or more driven portions of the movable part adapts the shape of the optical element. The movable part of clause B1 moves relative to the support structure, and movement of the movable part effects movement of the first part (which may be referred to as the movable part elsewhere), so the movable part of clause B1 may be referred to as the primary intermediate part elsewhere. Clause B2: The optical assembly of clause B1, wherein the actuator assembly is configured to drive movement of the first part in a direction parallel to the primary axis. As for clause B1, the first part may be referred to elsewhere as the movable part, and the primary axis may be referred to as the first axis. Clause B3: The optical assembly of clause B1, wherein the actuator assembly is configured to rotate the first part about an axis perpendicular to the primary axis. As for clause B1, the first part may be referred to elsewhere as the movable part, and the primary axis may be referred to as the first axis. Clause B4: The optical assembly of any of clauses B1 to B3, wherein the movable part comprises a first friction surface which is engaged with a second friction surface so as to generate a friction force that resists movement of the movable part with respect to the first part and / or support structure. As for clause B1, the movable part of clause B4 may be referred to elsewhere as the primary intermediate part. Clause B5: The optical assembly of clause B4, wherein: the first part comprises the second friction surface; the SMA element is configured to drive movement of the first friction surface over the second friction surface to move the first part relative to the support structure and deform the deformable optical element. As for clause B1, the first part may be referred to elsewhere as the movable part. A deformable optical element is an example of an optical element having an adaptable shape. Clause B6: The optical assembly of clause B5, wherein at least one of the first friction surface and second friction surface defines an angled surface which is at an acute, non-zero angle to the primary axis. As for clause B1, the primary axis may be referred to elsewhere as the first axis. Clause B7: The optical assembly of clause B5 or clause B6, further comprising: a second part comprising a third friction surface; wherein the movable part further comprises a fourth friction surface which engages with the third friction surface so as to generate a friction force that resists movement of the movable part with respect to the first part and / or support structure. The second part of clause B7 may be referred to elsewhere as an interface part or as part of the support structure. As for clause B1, the movable part of clause B7 may be referred to elsewhere as the primary intermediate part and the first part may be referred to elsewhere as the movable part. Clause B8: The optical assembly of clause B7, wherein at least one of the third friction surface and fourth friction surface defines an angled surface which is at an acute, non-zero angle to the primary axis. As for clause B1, the primary axis may be referred to elsewhere as the first axis. Clause B9: The optical assembly of clause B8, wherein the acute, non-zero angle of the at least one of the first friction surface and second friction surface is defined in an opposite direction with respect to the primary axis to the acute, non-zero angle of the at least one of the third friction surface and fourth friction surface. As for clause B1, the primary axis may be referred to elsewhere as the first axis. Clause B10: The optical assembly of any of clauses B7 to B9, wherein the second friction surface and the third friction surface are spaced apart and the movable part is disposed between the first part and second part. As for clause B1, the movable part of clause B10 may be referred to elsewhere as the primary intermediate part. Clause B11: The optical assembly of any of clauses B4 to B10, wherein at least one of the first friction surface and the second friction surface comprises a first angled surface at a first acute, non-zero angle to the primary axis and a second angled surface at a second acute, non-zero angle to the primary axis, wherein the first and second angled surfaces are at different positions around the periphery of the deformable optical element and wherein the first angle is different to the second angle. As for clause B1, the primary axis may be referred to elsewhere as the first axis. A deformable optical element is an example of an optical element having an adaptable shape. Clause B12: The optical assembly of any of clauses B4 to B11, wherein the first friction surface and second friction surface are biased into engagement by at least one of an external biasing element and the deformable optical element itself. The biasing element may also be referred to as a biasing means. A deformable optical element is an example of an optical element having an adaptable shape. Clause B13: The optical assembly of any of clauses B1 to B12, wherein the movable part is coupled to the first part by a rotating linkage or flexure bearing, the rotating linkage or flexure bearing being arranged such that the first part is urged away from the movable part as the movable part moves relative to the support structure. As for clause B1, the movable part of clause B13 maybe referred to elsewhere as the primary intermediate part and the first part may be referred to elsewhere as the movable part. Clause B14: The optical assembly of any of clauses B4 to B13, wherein at least one of the first friction surface and second friction surface defines an undulating profile configured to rotate the first part about the axis perpendicular to the primary axis as the movable part moves relative to the support structure. As for clause B1, the movable part of clause B14 may be referred to elsewhere as the primary intermediate part and the first part may be referred to elsewhere as the movable part. Clause B15: The optical assembly of any of clauses B1 to B14, wherein the movable part extends around at least part of a periphery of the deformable optical element. As for clause B1, the movable part of clause B15 may be referred to elsewhere as the primary intermediate part. A deformable optical element is an example of an optical element having an adaptable shape. Clause B16: The optical assembly of any of clauses B1 to B15, wherein the movable part is a singular part, or a plurality of parts collectively forming the movable part. As for clause B1, the movable part of clause B15 may be referred to elsewhere as the primary intermediate part. Clause B17: The optical assembly of any of clauses B1 to B16, wherein the actuator assembly comprises at least one pair of opposing SMA elements, the opposing SMA elements being configured to drive the movable part relative to the support structure in opposing directions and / or senses. As for clause B1, the movable part of clause B15 may be referred to elsewhere as the primary intermediate part. Clause B18: The optical assembly of clause B17, wherein the opposing SMA elements are arranged substantially parallel to each other. Clause B19: The optical assembly of clause B17, wherein the opposing SMA elements cross over each other when viewed along the primary axis. Clause B20: The optical assembly of any of clauses B1 to B19, comprising one or more SMA elements located around a periphery of the deformable optical element. Clause B21: The optical assembly of any of clauses B1 to B20, further comprising one or more guide elements arranged to guide the SMA element around the periphery of the deformable optical element. A deformable optical element is an example of an optical element having an adaptable shape. Clause B22: The optical assembly of any of clauses B1 to B21, wherein the movable part comprises a plurality of parts; the optical assembly comprises a plurality of SMA elements of different lengths associated with the plurality of parts of the movable part; and the different lengths of the SMA elements are configured to drive the respective part of the movable part by different amounts. As for clause B1, the movable part of clause B22 may be referred to elsewhere as the primary intermediate part. Clause B23: The optical assembly of any of clauses B1 to B22, wherein the actuator assembly is located inside the deformable optical element. A deformable optical element is an example of an optical element having an adaptable shape. Clause B24: The optical assembly of any of clauses B1 to B22, wherein the actuator assembly is located on the outside of the deformable optical element. A deformable optical element is an example of an optical element having an adaptable shape. Clause B25: The optical assembly of any of clauses B1 to B24, wherein the actuator assembly is configured to adjust the focal length of the deformable optical element. A deformable optical element is an example of an optical element having an adaptable shape. Clause B26: The optical assembly of any of clauses B1 to B25, wherein the actuator assembly is configured to rotate the movable part about an axis parallel to or colinear with the primary axis. As for clause B1, the movable part of clause B26 may be referred to elsewhere as the primary intermediate part. Clause B27: The optical assembly of any of clauses B1 to B26, wherein the support structure comprises a frame located around the periphery of the deformable optical element for supporting the parts of the optical assembly. Clause B28: The optical assembly of any of clauses B1 to B27, wherein the support structure comprises a seal configured to seal a fluid or gel in at least part of the deformable optical element. A deformable optical element is an example of an optical element having an adaptable shape. Clause B 29: The optical assembly of any of clauses B1 to B28, wherein the support structure comprises a biasing means for biasing the first part and movable part into engagement. As for clause B1, the movable part of clause B29 may be referred to elsewhere as the primary intermediate part and the first part may be referred to elsewhere as the movable part. Clause B30: The optical assembly of any of clauses B1 to B29, wherein the optical element is a deformable lens and the primary axis is an optical axis. The primary axis may be referred to as the first axis. A deformable optical element is an example of an optical element having an adaptable shape. Clause B31: The optical assembly of any of clauses B1 to B29, wherein the optical element is a deformable mirror. Clause B32: A virtual reality headset comprising an optical assembly according to any of clauses B1 to B31. Clause B33: An augmented reality headset comprising an optical assembly according to any of clauses B1 to B31. Clause B34: A pair of glasses comprising an optical assembly according to any of clauses B1 to B31. Brief description of the drawings Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic top view of an optical assembly according to an embodiment of the present disclosure. Figure 2 is a schematic cross-sectional view of the optical assembly of Figure 1. Figure 3 is a schematic cross-sectional view of the optical assembly of Figure 1, showing two possible shapes of the second lens surface. Figure 4 is a schematic section of the view of the optical assembly of Figure 2, showing two possible shapes of the second lens surface. Figure 5 is a schematic section of the view of the optical assembly of Figure 2, showing three possible shapes of the second lens surface. Figure 6 is a schematic cross-sectional view of part of an optical assembly according to an embodiment of the present disclosure, wherein the primary intermediate part and the movable part are located inside the optical element. Figure 7 is a schematic cross-sectional view of part of an optical assembly according to an embodiment of the present disclosure, wherein the primary intermediate part and the movable part are located outside the optical element. Figure 8 is a schematic cross-sectional view of part of an optical assembly according to an embodiment of the present disclosure, wherein the primary intermediate part and the movable part are located inside the optical element. Figure 9 is a schematic cross-sectional view of part of the optical assembly of Figure 8, wherein the movable part is moved down. Figure 10 is a schematic cross-sectional view of part of the optical assembly of Figure 8, wherein the movable part is moved up. Figure 11 is a schematic side view of part of a primary intermediate part and a movable part of an optical assembly according to an embodiment of the present disclosure. Figure 12 is a schematic side view of part of the primary intermediate part and movable part of Figure 11, wherein the primary intermediate part is moved to the left. Figure 13 is a schematic side view of part of the primary intermediate part and movable part of Figure 11, wherein the primary intermediate part is moved to the right. Figure 14 is a schematic side view of part of a primary intermediate part, a movable part and an interface part of an optical assembly according to an embodiment of the present disclosure. Figure 15 is a schematic side view of part of a primary intermediate part, a movable part and an interface part of an optical assembly according to an embodiment of the present disclosure. Figure 16 is a schematic side view of part of the primary intermediate part, movable part and interface part of Figure 15, wherein the primary intermediate part is moved to the right. Figure 17 is a schematic side view of part of the primary intermediate part, movable part and interface part of Figure 15, wherein the primary intermediate part is moved to the left. Figure 18 is a schematic perspective view of part of a primary intermediate part and a support structure of an optical assembly according to an embodiment of the present disclosure, configured to add or adapt a spherical distortion of the optical element and with a membrane showing the shape of the optical element. Figure 19 is a schematic perspective view of part of a primary intermediate part and a support structure of Figure 18, with the primary intermediate part rotated and with a membrane showing the shape of the optical element. Figure 20 is a schematic perspective view of part of a primary intermediate part, a movable part, an optical element and a support structure of an optical assembly according to an embodiment of the present disclosure. Figure 21 is a schematic perspective view of part of a primary intermediate part, a movable part, an optical element and a support structure of Figure 20, with the primary intermediate part rotated. Figure 22 is a schematic top view of an optical assembly according to an embodiment of the present disclosure, showing an arrangement of SMA elements. Figure 23 is a schematic top view of an optical assembly according to an embodiment of the present disclosure, showing an arrangement of SMA elements. Figure 24 illustrates a shape of a cylindrical distortion with a cylindrical axis perpendicular to the z axis. Figure 25 shows a primary intermediate part, a movable part, and a support structure of an optical assembly according to an embodiment of the present disclosure. Figure 25A shows a schematic side view and Figure 25B shows a schematic top view. Figure 26 is a schematic perspective view of part of a primary intermediate part and a support structure of an optical assembly according to an embodiment of the present disclosure, configured to add or adapt a cylindrical distortion of the optical element and with a membrane showing the shape of the optical element and with the primary intermediate part translated along the x axis. Figure 27 is a schematic perspective view of part of a primary intermediate part and a support structure of an optical assembly according to an embodiment of the present disclosure, configured to add or adapt a cylindrical distortion of the optical element and with a membrane showing the shape of the optical element and with the primary intermediate part translated along the y axis. Figure 28 is a graph showing the gradient of the plurality of the primary drive portions. Figure 29 is a graph showing the gradient of the plurality of the primary drive portions. Figure 30 is a schematic side view of part of a primary intermediate part, a secondary intermediate part, a movable part and an interface part of an optical assembly according to an embodiment of the present disclosure. Figure 31 is a schematic side view of part of a primary intermediate part, a movable part, a support structure and an optical element of an optical assembly according to an embodiment of the present disclosure. Figures 31A and 31B show side views in different orientations. Figure 32 is a schematic side view of part of a primary intermediate part, a secondary intermediate part, a tertiary intermediate part, a movable part and an interface part of an optical assembly according to an embodiment of the present disclosure. Figure 33 is a schematic side view of part of an optical element, a movable part, a primary intermediate part, an interface part, a secondary intermediate part, and a support structure of an optical assembly according to an embodiment of the present disclosure. Figure 34 shows a schematic side view of the part of an optical element shown in Figure 33, with the secondary intermediate part rotated. Figure 35 shows a schematic side view of the part of an optical element shown in Figure 34, with the primary intermediate part translated. Figure 36 shows a schematic side view of the part of an optical element shown in Figure 36, with the secondary intermediate part rotated. Detailed description According to the present disclosure, an optical assembly is provided. The optical assembly comprises an optical element having an adaptable shape. The optical assembly further comprises an actuator assembly. The actuator assembly comprises a support structure wherein a first axis is defined relative to the support structure. Figure 1 shows a simplified front view of an example of an optical assembly 100 according to an embodiment of the present disclosure, wherein the optical assembly 100 comprises an optical element and an actuator assembly. Figure 1 illustrates an arrangement of the actuator assembly 120 relative to the optical element 110, wherein the actuator assembly 120 is arranged around an edge portion of the optical element 110. The hashed area 130 indicates an overlap between the optical element 110 and the actuator assembly 120. The arrangement shown is exemplary, and the arrangement of the actuator assembly 120 relative to the optical element 110 may differ. For example, the degree of overlap between the optical element 110 and the actuator assembly 120 may differ such that the actuator assembly 120 extends beyond an edge of the optical element 110 when viewed along the first axis, or the optical element 110 extends beyond an edge of the actuator assembly 120 when viewed along the first axis. The optical assembly 100 is an example, and an optical assembly according to the present disclosure may vary in shape or structure from that shown in Figure 1. The actuator assembly further comprises a primary intermediate part, a movable part and one or more actuator units. The support structure, primary intermediate part, movable part and one or more actuator units are not shown in Figure 1. The primary intermediate part is movable relative to the support structure in a primary plane perpendicular to the first axis. In Figure 1, the primary plane would be parallel to the page. The primary intermediate part further comprises a plurality of primary drive portions each extending out of the primary plane. The movable part comprises a plurality of driven portions each corresponding to one of the plurality of primary drive portions, wherein each driven portion is movable relative to the support structure to adapt the adaptable shape of the optical element. The one or more actuator units are configured to drive movement of the primary intermediate part relative to the support structure in the primary plane. Movement parallel to the primary plane of the plurality of primary drive portions effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element. In the context of the primary drive portions each extending out of the primary plane, extending out of the primary plane may mean any structure or part of a primary drive portion that is not parallel to the primary plane. The primary plane may intersect a primary drive portion or the primary plane may not intersect a primary drive portion. In the context of movement parallel to the primary plane of the plurality of primary drive portions, movement parallel to the primary plane may be any movement that has a component parallel to the primary plane. The movement of the plurality of primary drive portions may be the same for each primary drive portion or may differ between primary drive portions. In the context of movement of at least a subset of the plurality of driven portions out of the primary plane, movement out of the primary plane may be any movement having a component perpendicular to the primary plane. The movement may include translation and / or rotation. The direction of the component of the movement that is perpendicular to the primary plane may be towards or away from the primary plane. The movement may begin at, end at or pass through the primary plane, or the movement may not intersect with the primary plane. The actuator assembly comprises one or more actuator units configured to drive movement of the primary intermediate part relative to the support structure in the primary plane. In certain embodiments, at least one of the one or more actuator units may comprise a shape memory alloy (SMA) element, e.g.an SMA wire. The one or more actuator units comprising an SMA element may be connected directly or indirectly between the support structure and the primary intermediate part, such that actuation of the one or more actuator units drives movement of the primary intermediate part relative to the support structure in the primary plane. Or, the one or more actuator units comprising an SMA element may be connected directly or indirectly between the primary intermediate part and another part of the optical assembly. In certain embodiments, at least one of the one or more actuator units comprises an actuator element other than an SMA element. In certain embodiments, at least one of the one or more actuator units comprises a voice coil motor actuator and / or a piezoelectric element. The primary intermediate part may be movable in a first degree of freedom relative to the support structure in the primary plane. For example, the primary intermediate part may be translatable in a first degree of freedom in the primary plane. In another example, the primary intermediate may be rotatable in the primary plane. The primary intermediate part may be movable in one degree of freedom relative to the support structure in the primary plane. The primary intermediate part may be movable in more than one degree of freedom relative to the support structure in the primary plane. In certain embodiments, the primary intermediate part may be movable in two degrees of freedom relative to the support structure in the primary plane. For example, the primary intermediate part may be translatable in the primary plane in two degrees of freedom, or the primary intermediate part may be translatable in the primary plane in one degree of freedom and may be rotatable in the primary plane. In certain embodiments, the primary intermediate part may be movable in three degrees of freedom relative to the support structure in the primary plane. For example, the primary intermediate part may be translatable in the primary plane in two degrees of freedom (e.g. translatable along two axes which are perpendicular to each other) and may be rotatable in the primary plane. The actuator assembly may further comprise a secondary intermediate part movable relative to the support structure in a secondary plane. The secondary plane may be perpendicular to the first axis, and may be separated from the primary plane along the first axis. The primary intermediate part may be movable in a first degree of freedom relative to the support structure in the primary plane, and the secondary intermediate part may be movable in a second degree of freedom relative to the support structure in the secondary plane. The secondary intermediate part may comprise a plurality of secondary drive portions each extending out of the secondary plane. The first degree of freedom and the second degree of freedom may be different. Movement parallel to the secondary plane of the plurality of secondary drive portions may adapt the shape of the optical element. In the context of the secondary drive portions each extending out of the secondary plane, extending out of the secondary plane may mean any structure or part of a secondary drive portion that is not parallel to the secondary plane. The secondary plane may intersect a secondary drive portion or the secondary plane may not intersect a secondary drive portion. In the context of movement parallel to the secondary plane of the plurality of secondary drive portions, movement parallel to the secondary plane may be any movement that has a component parallel to the secondary plane. The movement of the plurality of secondary drive portions may be the same for each secondary drive portion or may differ between secondary drive portions. The optical element may comprise any optical element having an adaptable shape. In certain embodiments, the optical element may comprise a lens having at least one surface with an adaptable shape. The lens may comprise a liquid lens or a gel lens, wherein liquid or gel is contained within a cavity between a first lens surface and a second lens surface. The cavity may have a first cavity volume. One or both of the first and second lens surfaces may have an adaptable shape. In certain examples, the lens surface(s) having an adaptable shape may be under tension. In an event that a portion of the lens surface having an adaptable shape is moved with respect to the support structure, the shape of the lens surface having an adaptable shape may alter such that the cavity volume is constant. For example, the cavity may be filled with the liquid or gel without an air gap or other compressible gas. The lens surface having an adaptable shape may be under tension. In certain examples, the lens surface(s) having an adaptable shape may have a stiffness such that displacing a part of the lens surface or altering an angle of a portion of the lens surface with respect to the support structure alters a curvature of the lens surface with respect to the support structure. The lens surface(s) having an adaptable shape may be under tension and may have a stiffness. The lens surface(s) having an adaptable shape may comprise a membrane or other flexible material. In other embodiments, the optical element may comprise a mirror having an adaptable shape. The mirror may have a stiffness such that altering an angle of a portion of the mirror with respect to the support structure alters a curvature of the mirror with respect to the support structure. Figure 2 shows a simplified cross-section of the optical assembly 100 of Figure 1, taken along the line A-A in a plane parallel to the first axis 210. In the example shown, the optical element 110 comprises a lens comprising a curved first lens surface 111. The first lens surface 111 may be rigid, such that the shape of the first lens surface 111 is not adaptable. The optical element 110 may further comprise a second lens surface 112 that has an adaptable shape. The second lens surface 112 is shown in Figure 2 as being planar and parallel to the primary plane. The shape of the second lens surface 112 may be adaptable such that the second lens surface 112 is not planar. Figure 3 shows the same cross-section illustrated in Figure 2, illustrating how a shape of the second lens surface 112 might be adapted. Two examples of a shape of the second lens surface 112’, 112’ are shown, wherein the shape the second lens surface 112’, 112” has been adapted such that the second lens surface 112’, 112” is not planar. In a first example, the second lens surface 112’ is shown as being curved away from first lens surface 111. In a second example, the second lens surface 112” is shown as being curved towards the first lens surface 111. The amount by which the shape of the second lens surface 112 is adapted may vary. The second lens surface 112 may be adapted to form different shapes. The second lens surface 112 is shown as being either planar or having rotational symmetry about the first axis. The second lens surface 112 may have a different shape to those illustrated, and may not have rotational symmetry about the first axis. Figures 2 and 3 show the optical element 110 as comprising a lens comprising a first lens surface 111 and a second lens surface 112, wherein the shape of the second lens surface 112 is adaptable. In other examples, the first lens surface 111 may have an adaptable shape and the second lens surface 112 may be rigid, or the first lens surface 111 and the second lens surface 112 may each have an adaptable shape. The optical element 110 illustrated in Figures 2 and 3 may comprise a liquid or gel lens, wherein a cavity between the first lens surface 111 and the second lens surface 112 contains a liquid or a gel. In other examples, the optical element may have a different structure. For example, the optical element may comprise a sheet, such as a mirror, having an adaptable shape. A shape of a surface of an optical element may be adapted by tilting a surface of the optical element with respect to the support structure. The surface may have a stiffness value such that altering an angle of part of the surface with respect to the support structure alters a curvature of the surface with respect to the support structure. With reference to Figure 4, a section of the optical assembly 100 illustrated in Figure 3 is shown. The second lens surface 112 may be tilted about point 411, as indicated by the arrow 410. The second lens surface 112 may have a stiffness value such that tilting the second lens surface 112 with respect to the support structure alters the shape of the second lens surface 112 such that tilting the second lens surface 112 about point 411 alters the curvature of the second lens surface 112. Tilting the second lens surface 112 about the point 411 in the direction shown by arrow 410 may result in a second lens surface 112” that is curved towards the first lens surface 111. Tilting the second lens surface may be achieved by tilting one or more a driven portions of the movable part, wherein tilting the one or more driven portions has a component out of the primary plane. Tilting the second lens surface may be achieved by translating one or more a driven portions of the movable part, wherein translating the one or more driven portions has a component out of the primary plane. Tilting the second lens surface may be achieved by moving one or more a driven portions of the movable part with both rotational and translational components. A similar adaptation of shape may be effected for a mirror or other optical element having an adaptable shape, by tilting a portion of the mirror or other optical element. A shape of an optical element may be adapted by translating a portion of a surface of the optical element with respect to the support structure. The surface may be under tension and / or may have a stiffness such that the translating a portion of the surface with respect to the support structure alters a curvature of the surface with respect to the support structure. With reference to Figure 5, a section of the optical assembly 100 illustrated in Figure 3 is shown. The second lens surface 112 may be translated upwards as indicated by the arrow 420. The second lens surface 112 may have a stiffness value such translating a portion of the second lens surface 112 with respect to the support structure alters the shape of the second lens surface 112 such that translating a portion of the second lens surface 112 upwards alters the curvature of the second lens surface 112. Translating a portion of the second lens surface 112 upwards may result in a second lens surface 112” that is curved towards the first lens surface 111. Or, the second lens surface 112 may be under tension and the lens 110 may have a constant volume, such that translating a portion of the second lens surface 112 upwards results in a second lens surface 112’ that is curved away from the first lens surface 111. Translating the second lens surface 112 may achieved by translating one or more a driven portions of the movable part, wherein translating the one or more driven portions has a component out of the primary plane. Translating the second lens surface may be achieved by tilting one or more a driven portions of the movable part, wherein tilting the one or more driven portions has a component out of the primary plane. Translating the second lens surface may be achieved by moving one or more a driven portions of the movable part with both rotational and translational components. A similar adaptation of shape may be effected for a mirror or other optical element having an adaptable shape by translating a portion of the mirror or other optical element. A shape of a surface of an optical element may be adapted by a movement of the surface with respect to the support structure that has both rotational and translational components. The actuator assembly comprises a primary intermediate part and a movable part. The actuator assembly may further comprise a biasing means configured to bias the movable part and the primary intermediate part against each other. The biasing means may be further configured to bias the optical element (or part of the optical element) and the movable part against each other. In certain examples, the biasing means may comprise a resilient element, such as a spring. In certain examples, the biasing means may comprise a magnetic element. Part of the optical element and the movable part may be configured to be retained together in another manner, such that movement a driven adapts the adaptable shape of the optical element. In certain embodiments where the optical element comprises a liquid or gel lens, one or both of the primary intermediate part and the movable part may be located inside the lens. In certain embodiments, both the primary intermediate part and the movable part may be located inside the lens. The actuator assembly may further comprise a biasing means located outside the lens and configured to bias the lens and the movable part against each other. The biasing means may be further configured to bias the movable part and the primary intermediate part against each other. An example is illustrated in Figure 6, which shows a schematic diagram of a section of a cross-section of an optical assembly 600 taken in a plane parallel to the first axis. The optical assembly 600 comprises an optical element 610 that comprises a liquid or gel lens having a first lens surface 611 and a second lens surface 612. The first lens surface 611 may be rigid and the second lens surface 612 may have an adaptable shape. The actuator assembly 620 comprises a movable part 621 and a primary intermediate part 622, each located inside the optical element 610. The actuator assembly 620 further comprises a support structure that may comprise support part 623. The actuator assembly 620 may further comprise a biasing means 624 located outside the optical element 610 and configured to bias the movable part 621 and the primary intermediate part 622 against each other. The biasing means 624 may be further configured to bias the first lens surface 611 of the optical part and the movable part 621 against each other. In the view illustrated in Figure 6, the first axis may be in the page as indicated by arrow 630. The position of the first axis may vary from that illustrated by arrow 630. The primary plane is perpendicular to the first axis 630. An example of a position of the primary plane is illustrated by line 640. However, the primary plane could be any plane perpendicular to the first axis. Movement of the plurality of drive portions that has a component in the primary plane effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element. In the view illustrated in Figure 6, movement of a driven portion out of the primary plane may comprise moving the illustrated section of the movable part 621 with a component that is up or down. The illustrated section of the movable part 621 may comprise a driven portion. In certain embodiments where the optical element comprises a liquid or gel lens, one or both of the primary intermediate part and the movable part may be located outside the lens. In certain embodiments, both the primary intermediate part and the movable part may be located outside the lens. The actuator assembly may further comprise a biasing means located inside the lens and configured to bias the lens and the movable part against each other. The biasing means may be further configured to bias the movable part and the primary intermediate part against each other. An example is illustrated in Figure 7, which shows a schematic diagram of a section of a cross-section of an optical assembly 700 taken in a plane parallel to the first axis. The optical assembly 700 comprises an optical element 710 that comprises a liquid or gel lens having a first lens surface 711 and a second lens surface 712. The first lens surface 711 may be rigid and the second lens surface 712 may have an adaptable shape. The actuator assembly 720 comprises a movable part 721 and a primary intermediate part 722, each located outside of the optical element 710. The actuator assembly 720 further comprises a support structure that may comprise support part 723. The actuator assembly 720 may further comprise a biasing means 724 located inside the optical element configured to bias the movable part 721 and the primary intermediate part 722 against each other. The biasing means 724 may be further configured to bias the first lens surface 711 of the optical part and the movable part 721 against each other. In the view illustrated in Figure 7, the first axis may be in the page as indicated by arrow 730. The position of the first axis may vary from that illustrated by arrow 730. The primary plane is perpendicular to the first axis 730. An example of a position of the primary plane is illustrated by line 740. However, the primary plane could be any plane perpendicular to the first axis. Movement of the plurality of drive portions that has a component in the primary plane effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element. In the view illustrated in Figure 7, movement of a driven portion out of the primary plane may comprise moving the illustrated section of movable part 721 with a component that is up or down. The illustrated section of the movable part 721 may comprise a driven portion. As described above, movement of one or more driven portions out of the primary plane may adapt the shape of a surface of an optical element having an adaptable shape by translating and / or tilting a portion of the surface having an adaptable shape. An example of adapting the shape of a lens surface of an optical element by translating a driven portion out of the primary plane to translate a portion of the lens surface is illustrated in Figures 8 to 10. Figure 8 shows a schematic diagram illustrating a section of a cross-section of an example of an optical assembly 800, taken in a plane containing the first axis. The optical assembly 800 is similar to the optical assembly 100 illustrated in Figures 1 to 5, and the section shown in Figure 8 is similar to the section of the optical assembly 100 illustrated in Figures 4 and 5. The optical element of the optical assembly 800 comprises a lens 810 having a first lens surface 811 and a second lens surface 812. The first lens surface 811 is rigid and the second lens surface 812 has an adaptable shape. The optical assembly 800 comprises an actuator assembly 820, comprising a movable part 821 and a primary intermediate part 822 that are both located inside the lens 810. In the example illustrated, the actuator assembly 820 further comprises a support structure comprising support parts 823 and 824. The primary intermediate part 822 comprises a plurality of primary drive portions. The actuator assembly 820 may further comprise a biasing means 825 located inside the optical element configured to bias the movable part 821 and the primary intermediate part 822 against each other. The biasing means 825 may be further configured to bias the first lens surface 811 of the optical part and the movable part 821 against each other. In the view illustrated in Figure 8, the first axis may be in the page as indicated by arrow 830. The position of the first axis may vary from that illustrated by arrow 830. The primary plane is perpendicular to the first axis 830. An example of a position of the primary plane is illustrated by line 840. However, the primary plane could be any plane perpendicular to the first axis. Movement of the plurality of drive portions that has a component in the primary plane effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element. In the view illustrated in Figure 8, movement of a driven portion out of the primary plane may comprise moving the illustrated section of movable part 821 with a component that is up or down. The illustrated section of the movable part 821 may comprise a driven portion. Figure 8 shows the illustrated section movable part 821 in a position such that the second lens surface 812 is flat and is parallel to the primary plane. Figure 9 illustrates the same optical assembly as shown in Figure 8, wherein the primary intermediate part 822 has been moved in the primary plane such that the illustrated section of the movable part 821 has moved down (with respect to the view shown). This downwards movement has a component perpendicular to (and away from) the primary plane, and is therefore described as being out of the primary plane. The biasing means 825 is configured to bias the movable part 821 and the primary intermediate part 822 against each other and to bias the first lens surface 811 of the optical part and the movable part 821 against each other. Therefore, movement of the illustrated section of the movable part 821 out of the primary plane effects movement of a portion of the second lens surface 812 out of the primary plane. In the example shown, the optical element 810 is a liquid or gel lens having a cavity with a constant volume. Moving a portion of the second lens surface 812 down (away from the primary plane) effects movement of other portions of the second lens surface up (towards the primary plane) to maintain the constant volume of the cavity. The shape of the second lens surface 812’ is adapted to be curved towards the primary plane and the first lens surface. The radius of curvature of the second lens surface 812’ may be controlled by changing the amount by which the movable part 821 is moved out of the primary plane. Figure 10 illustrates the same optical assembly as shown in Figure 8, wherein the primary intermediate part 822 has been moved in the primary plane such that the illustrated section of the movable part 821 has moved up (with respect to the view shown). This upwards movement has a component perpendicular to (and towards) the primary plane, and is therefore described as being out of the primary plane. The biasing means 825 is configured to bias the movable part 821 and the primary intermediate part 822 against each other and to bias the first lens surface 811 of the optical part and the movable part 821 against each other. Therefore, movement of the illustrated section of the movable part 821 out of the primary plane effects movement of a portion of the second lens surface 812 out of the primary plane. In the example shown, the optical element 810 is a liquid or gel lens having a cavity with a constant volume. Moving a portion of the second lens surface 812 up (towards the primary plane) effects movement of other portions of the second lens surface down (away from the primary plane) to maintain the constant volume of the cavity. The shape of the second lens surface 812” is adapted to be curved away from the primary plane and the first lens surface. The radius of curvature of the second lens surface 812” may be controlled by changing the amount by which the movable part 821 is moved out of the primary plane. Figures 8 to 10 show the illustrated section of the primary intermediate part 822 changing in size as it effects movement of the movable part 821 out of the primary plane. This is illustrative of the movement of the primary intermediate part 822 in the primary plane, and does not indicate that the primary intermediate part 822 changes size. The change in size of the illustrated section of the primary intermediate part 822 is indicative of the primary drive portions that extend out of the primary plane being moved in the primary plane, such that more or less of a primary drive portion is visible in the cross-section shown in Figures 8 to 10. Movement of the primary drive portions may effect movement of the primary driven portions in any suitable way. For example, a primary drive portion and corresponding driven portion may comprise a bearing. The bearing may comprise a plain bearing or a rolling bearing. In other examples, a primary drive portion may comprise a body and a linkage connected directly or indirectly between the body and the driven portion corresponding to the primary drive portion, wherein movement of the body in the primary plane rotates the linkage relative to the body such that the corresponding driven portion is moved out of the primary plane. The linkage may comprise a flexure. The plurality of primary drive portions may each comprise a surface angled at an acute, non-zero angle with respect to the primary plane. To achieve this, the plurality of primary drive portions may each comprise a surface disposed on the primary intermediate part and angled at an acute, non-zero angle with respect the primary intermediate part. In certain embodiments, the plurality of primary drive portions may each comprise a planar surface at an acute, non-zero angle with respect to the primary plane. In other embodiments, the primary drive portions may each comprise a curved surface at a varying acute angle with respect to the primary plane. The plurality of driven portions may each comprise a mating surface corresponding to a surface of a corresponding primary drive portion, wherein in an event that the primary intermediate part moves relative to the movable part the mating surface is configured to slide with respect to the surface of the corresponding primary drive portion. The plurality of driven portions may each comprise a rolling bearing wherein in an event that the primary intermediate part moves relative to the movable part the rolling bearing is configured to roll with respect to the surface of the corresponding primary drive portion. The plurality of driven portions may comprise a first sub-group of driven portions and a second sub-group of driven portions separate to the second sub-group of driven portions. The driven portions of the first sub-group of driven portions may each comprise a mating surface corresponding to a surface of a corresponding primary drive portion. The driven portions of the second sub-group of driven portions may each comprise a rolling bearing. In this way, a combination of rolling bearings and plain bearings may be used. The plurality of driven portions may each comprise a surface angled at an acute, non-zero angle with respect to the primary plane. The plurality of driven portions may each comprise a planar surface angled at an acute, non-zero angle with respect to the primary plane. The plurality of driven portions may each comprise a curved surface angled at varying acute angle with respect to the primary plane. In an event that the optical assembly is configured to constrain movement of the movable part relative to the support structure in an absence of power to one or more actuator units of the actuator assembly, the surface of one or more primary drive portions may comprise a first friction surface configured to engage with a second friction surface such that movement of the primary intermediate part relative to the support structure is constrained in an absence of power to one or more actuator units of the actuator assembly. One or more driven portions may comprise the second friction surface, or the support structure may comprise the second friction surface. With reference to Figure 11, a section of a side view of a primary intermediate part 1110 and a movable part 1120 of an optical element according to an embodiment of the present disclosure are shown. The section of the primary intermediate part 1110 shown comprises a first primary driven portion 1111, a second primary drive portion 1112 and a third primary drive portion 1113, each comprising a planar surface angled at an acute, non-zero angle with respect to the primary plane. The section of the movable part 1120 shown comprises a first driven portion 1121 corresponding to the first primary drive portion 1111, a second driven portion 1122 corresponding to the second primary drive portion 1112, and a third driven portion 1123 corresponding to the third primary drive portion 1113. The first, second and third driven portions 1121,1122 and 1123 each comprise a planar surface angled at an acute, non-zero angle with respect to the primary plane. In the view shown in Figure 11, the first axis 1130 is vertical. The position of the arrow indicating the first axis 1130 is an example only, and is provided to indicate the direction of the first axis 1130. The primary plane (not shown) may be any plane that is perpendicular to the first axis 1130 (i.e. in the view illustrated, the primary plane is horizontal and extends into and out of the page). Movement of the primary intermediate part 1110 in the primary plane may be any movement with a component parallel to the primary plane. An example of movement of the primary intermediate part 1110 in the primary plane is indicated by arrow 1140. In an event that the primary intermediate 1110 is moved in the primary plane, the first, second and third driven portions 1121,1122 and 1123 slide with respect to the first, second and third primary drive portions 1111, 1112 and 1113, respectively, such that the movable part moves out of the primary plane. Movement of the movable part relative to the primary intermediate part in or parallel to the primary plane may be constrained in one or more degrees of freedom. Figure 12 shows the section of the side view of the primary intermediate part 1110 illustrated in Figure 11, with the primary intermediate part 1110 moved to the left as indicated by arrow 1210. The dashed lines indicate the original positions of the primary intermediate part 1110 and the movable part 1120 as illustrated in Figure 11. Movement of the movable part relative to the primary intermediate part in or parallel to the primary plane may be constrained in one or more degrees of freedom, such that upon movement of the primary intermediate part 1110 to the left, each of the first, second and third driven portions 1121,1122 and 1123 slide with respect to the first, second and third primary drive portions 1111,1112 and 1113 and the first, second and third driven portions move up out of the primary plane as indicated by arrow 1220. Figure 13 shows the section of the side view of the primary intermediate part 1110 illustrated in Figure 11, with the primary intermediate part 1110 moved to the right as indicated by arrow 1310. The dashed lines indicate the original positions of the primary intermediate part 1110 and the movable part 1120 as illustrated in Figure 11. Movement of the movable part relative to the primary intermediate part in or parallel to the primary plane may be constrained in one or more degrees of freedom, such that upon movement of the primary intermediate part 1110 to the right, each of the first, second and third driven portions 1121,1122 and 1123 slide with respect to the first, second and third primary drive portions 1111,1112 and 1113 and the first, second and third driven portions move down as indicated by arrow 1320. Downwards motion of the first, second and third driven portions has a component perpendicular to the primary plane, so as defined herein is movement out of the primary plane. The primary intermediate part may comprise primary drive portions disposed on a first side of the primary intermediate part. A second side of the primary intermediate part that is spaced apart from the first side along the first axis may be planar, as shown in Figures 11 to 13, or may be another shape. In certain embodiments, with reference to Figure 14, the primary intermediate part may comprise primary drive portions disposed on a first side of the primary intermediate part and may comprise secondary drive portions disposed on a second side of the primary intermediate part, wherein the first and second sides are separated along the first axis. Figure 14 shows a section of a side view of a primary intermediate part 1410 and a movable part 1420 of an optical element according to an embodiment of the present disclosure are shown. The section of the primary intermediate part 1410 shown comprises a first primary driven portion 1411, a second primary drive portion 1412 and a third primary drive portion 1413, each disposed on a first side of the primary intermediate part 1410 and each comprising a planar surface angled at an acute, non-zero angle with respect to the primary plane. The section of the movable part 1420 shown comprises a first driven portion 1421 corresponding to the first primary drive portion 1411, a second driven portion 1422 corresponding to the second primary drive portion 1412, and a third driven portion 1423 corresponding to the third primary drive portion 1413. The first, second and third driven portions 1421,1422 and 1423 each comprise a planar surface angled at an acute, non-zero angle with respect to the primary plane. In the view shown in Figure 14, the first axis 1440 is vertical. The position of the arrow indicating the first axis 1440 is an example only, and is provided to indicate the direction of the first axis 1440. The primary plane (not shown) may be any plane that is perpendicular to the first axis 1440 (i.e. in the view illustrated, the primary plane is horizontal and extends into and out of the page). Movement of the primary intermediate part 1410 in the primary plane may be any movement with a component parallel to the primary plane. An example of movement of the primary intermediate part 1410 in the primary plane is indicated by arrow 1450. In an event that the primary intermediate 1410 is moved in the primary plane, the first, second and third driven portions 1421,1422 and 1423 slide with respect to the first, second and third primary drive portions 1411,1412 and 1413, respectively, such that the movable part moves out of the primary plane. Movement of the movable part relative to the primary intermediate part in or parallel to the primary plane may be constrained in one or more degrees of freedom. The section of the primary intermediate part 1410 shown further comprises a first secondary driven portion 1414, a second secondary drive portion 1415 and a third secondary drive portion 1416, each disposed on a second side of the primary intermediate part 1410 and each comprising a planar surface angled at an acute, non-zero angle with respect to the primary plane. The first side and the second side of the primary intermediate part 1410 are separated along the first axis 1440. A section of an interface part 1430 is shown, wherein the section of the interface part 1430 shown comprises a first interface portion 1431 corresponding to the first secondary drive portion 1414, a second interface portion 1432 corresponding to the second secondary drive portion 1415, and a third interface portion 1433 corresponding to the third secondary drive portion 1416. The first, second and third interface portions 1431, 1432 and 1433 each comprise a planar surface angled at an acute, non-zero angle with respect to the primary plane. The interface part 1430 may be static with respect to the support structure (and / or may be part of the support structure). The interface part 1430 may be movable with respect to the support structure. In an event that the primary intermediate 1410 is moved in the primary plane, the first, second and third interface portions 1431,1432 and 1433 may slide with respect to the first, second and third secondary drive portions 1414,1415 and 1416, respectively, such that the primary intermediate part 1410 and the interface part 1430 change their positions relative to one another in a direction out of the primary plane. Movement of the interface part relative to the primary intermediate part in or parallel to the primary plane may be constrained in one or more degrees of freedom. In certain embodiments, one or more primary drive portions may each comprise a body and a linkage connected directly or indirectly between the body and the driven portion corresponding to the primary drive portion, wherein movement of the body in the primary plane rotates the linkage relative to the body such that the corresponding driven portion is moved out of the primary plane. Figure 15 shows a side view of a primary drive portion 1510 of a primary intermediate part of an optical element according to an embodiment of the present disclosure. The primary drive portion 1510 comprises a body 1511 and a linkage 1512, wherein the body 1511 is movable in the primary plane. Figure 15 also shows a section of the movable part 1530, and an interface part 1520. The interface part 1520 may be part of the support structure, or may be separate to the support structure. The linkage 1512 of the primary drive portion 1510 is connected between the body 1511 of the primary drive portion 1510 and a corresponding driven portion of the movable part 1530. The linkage 1512 is rotatably connected to the body 1511 at connection point 1513, wherein the linkage 1512 may not be able to translate relative to the body 1511 at the connection point 1513. The linkage 1512 is rotatably connected to the corresponding driven portion of the movable part 1530 at connection point 1531, wherein the linkage 1512 may not be able to translate relative to the movable part 1530 at the connection point 1531. In the view shown in Figure 15, the first axis 1540 is vertical. The position of the arrow indicating the first axis 1540 is an example only, and is provided to indicate the direction of the first axis 1540. The primary plane (not shown) may be any plane that is perpendicular to the first axis 1540 (i.e. in the view illustrated, the primary plane is horizontal and extends into and out of the page). Movement of the primary drive portion 1510 in the primary plane may be any movement with a component parallel to the primary plane. An example of movement of the primary drive portion 1510 in the primary plane is indicated by arrow 1550. Movement of the primary drive portion 1510 in the primary plane results in rotation of the linkage with respect to the body 1512 of the primary drive portion 1510 and to a corresponding driven portion of the movable part 1530, such that the driven portion of the movable part 1530 is moved out of the primary plane relative to the body 1512 of the primary drive portion 1510 is altered. The driven portion of the movable part 1530 may be moved towards or away from the body 1512 of the primary drive portion 1510. Figure 16 illustrates a side view of the same primary drive portion 1510, interface part 1520 and movable part 1530 as shown in Figure 15, wherein the body 1511 of the primary drive portion 1510 has been moved to the right (in the view shown) in the primary plane, as indicated by arrow 1610. The dashed lines show the original positions of the primary drive portion 1510 and the movable part 1530 as illustrated in Figure 15. The solid lines show the positions of the primary drive portion 1510 and the movable part 1530 after the movement of the body 1511 to the right in the primary plane. The linkage 1512 has rotated relative to the body 1511 at connection point 1513 and relative to the movable part 1530 at connection point 1531, such that the driven portion of the movable part 1530 has moved out of the primary plane towards the body 1511 of the primary drive portion 1510. Figure 17 illustrates a side view of the same primary drive portion 1510, interface part 1520 and movable part 1530 as shown in Figure 15, wherein the body 1511 of the primary drive portion 1510 has been moved to the left (in the view shown) in the primary plane, as indicated by arrow 1710. The dashed lines show the original positions of the primary drive portion 1510 and the movable part 1530 as illustrated in Figure 15. The solid lines show the positions of the primary drive portion 1510 and the movable part 1530 after the movement of the body 1511 to the left in the primary plane. The linkage 1512 has rotated relative to the body 1511 at connection point 1513 and relative to the movable part 1530 at connection point 1531, such that the driven portion of the movable part 1530 has moved out of the primary plane away from the body 1511 of the primary drive portion 1510. In certain embodiments, the optical assembly is configured to constrain movement of the movable part relative to the support structure in an absence of power to one or more actuator units of the actuator assembly. In other words, in an event that the actuator units stop driving movement of the primary intermediate part relative to the support structure, the primary intermediate part may retain its position relative to the support structure. This may be known as zero hold power. The optical assembly may comprise a first friction surface configured to engage with a second friction surface such that movement of the movable part and / or the primary intermediate part relative to the support structure is constrained in an absence of power to one or more actuator units of the actuator assembly. In certain embodiments, the movable part may comprise a first friction surface configured to engage with a second friction surface such that movement of the movable part relative to the support structure is constrained in an absence of power to one or more actuator units of the actuator assembly. The second friction surface may be a surface of the optical assembly. For example, the primary intermediate part may comprise the second friction surface or the support structure may comprise the second friction surface. The optical assembly may further comprise a clamp comprising the second friction surface. In certain embodiments, the primary intermediate part may comprise a first friction surface configured to engage with a second friction surface such that movement of the primary intermediate part relative to the support structure is constrained in an absence of power to one or more actuator units of the actuator assembly. The second friction surface may be a surface of the optical assembly. For example, the support structure may comprise the second friction surface or the optical assembly may further comprise a clamp comprising the second friction surface. In certain examples, the first friction surface may engage with the second friction surface during actuation of the actuator units and in the absence of power to the actuator units. The actuator units may be configured to overcome the frictional force between the first friction surface and the second friction surface to drive movement of the primary intermediate part relative to the support structure. In the absence of power to the actuator units, movement of the movable part relative to the support structure may be constrained via the friction force between the first and second friction surfaces without a need to supply power to the one or more actuator units. In other examples, the first friction surface may not engage with the second friction surface during actuation of the actuator units, and the first friction surface may engage with the second friction surface in the absence of power to the actuator units. A clamp or biasing means may be configured to engage the first friction surface with the second friction surface in the absence of power to the actuator units. In an event that power to the actuator units changes from a non-zero power to zero power, the clamp or biasing means may engage the first friction surface with the second friction surface. The clamp or biasing means may continue to engage the first friction surface with the second friction surface in the absence of power to the actuating units. The clamp or biasing means may require power to continue engaging the first friction surface with the second friction surface while the actuator units are without power, or the clamp or biasing means may not require power to keep the first friction surface engaged with the second friction surface while the actuator units are without power. In an event that power to the actuator units changes from zero power to a non-zero power, the clamp or biasing means may release such that the first friction surface is no longer engaged with the second friction surface. The primary intermediate part is movable relative to the support structure in the primary plane. In certain embodiments, the primary intermediate part may be rigid. The primary intermediate part may be movable out of the primary plane, wherein movement of the primary intermediate part may comprise translational and / or rotational components. A rotational component of a movement of the primary intermediate part out of the primary plane may comprise rotating the primary intermediate part about an axis perpendicular to the first axis, such that the primary intermediate part rotates out of the primary plane. In an event that the primary intermediate part is rigid and is translated out of the primary plane, each of the plurality of drive portions may be moved out of the primary plane by the same amount and in the same direction. In an event that a movement of the primary intermediate part out of the primary plane has a rotational component, different portions of the primary intermediate part may move out of the primary plane by different amounts and / or in different directions. Otherwise, motion of the primary intermediate part out of the primary plane may be constrained. In other embodiments, the primary intermediate part may be flexible in a direction parallel to the first axis, wherein some or all of the primary intermediate part may be movable out of the primary plane. The primary intermediate part may be movable out of the primary plane as a whole in addition to being flexible in a direction parallel to the first axis. Or, the primary intermediate part may be fixed in place relative to the primary plane, but the primary intermediate part may be flexible in a direction parallel to the first axis such that portions of the primary intermediate part are movable out of the primary plane. The primary intermediate part may be flexible in a direction parallel to the first axis such that different portions of the primary intermediate part may be movable out of the primary plane by different amounts and / or in different directions. For example, the plurality of primary drive portions may each be movable out of the primary plane by different amounts and / or in different directions. The movable part comprises a plurality of driven portions each movable relative to the support structure. In certain embodiments, the movable part may be rigid. The movable part may be movable out of the primary plane, wherein movement of the movable part may comprise translational and / or rotational components. A rotational component of a movement of the movable part out of the primary plane may comprise rotating the movable part about an axis perpendicular to the first axis, such the movable part rotates out of the primary plane. In an event that the movable part is rigid and is translated out of the primary plane, each of the plurality of driven portions may be moved out of the primary plane by the same amount and in the same direction. In an event that a movement of the movable part out of the primary plane has a rotational component, different driven portions of the movable part may move out of the primary plane by different amounts and / or in different directions. In other embodiments, the movable part may be flexible in a direction parallel to the first axis. Different driven portions may be movable out of the primary plane by different amounts and / or in different directions. The driven portions may each be aligned with an edge portion of the optical element, such that movement of a driven portion out of the primary plane adapts a shape of the optical element at the edge portion of the optical element. For example, the driven portions may be arranged around a perimeter portion of an optical element, such that each driven portion is aligned with an edge portion of an optical element. Similarly, the primary drive portions may beach be aligned with an edge portion of the optical element. The primary intermediate part comprises a plurality of primary drive portions. The primary intermediate part may comprise any number of primary drive portions above one. In certain embodiments, the primary intermediate part comprises more than 10 primary drive portions, or more than 20 primary drive portions, or more than 30 primary drive portions, or more than 40 primary drive portions, or more than 50 primary drive portions. In certain embodiments, the primary intermediate part may comprise between 60 and 100 drive portions, or preferably between 80 and 100 drive portions. Spherical distortion In the case of near-sightedness (also called myopia), light from distant objects may be focused in front of the retina, while light from close objects may be focused on the retina. As a result, distant objects may appear to be blurry while closer objects are in focus. In the case of far-sightedness (also referred to as hyperopia or hypermetropia), light from objects may be focused behind the retina. Depending on the degree of far-sightedness, light from close objects may be focused behind the retina while light from distant objects may be focused on the retina, or light from both close and distant objects may be focused behind the retina. Nearsightedness and far-sightedness may be caused by various factors, such as an axial length of the eyeball being too long or too short, respectively, or by the curvature of the lens or cornea being increased or decreased, respectively. Near-sightedness and far-sightedness may be compensated for using a spherical power of a lens. An optical assembly according to an embodiment of the present disclosure may be used to alter the spherical power of the optical element by adapting the shape of the optical element such that the optical element undergoes a spherical distortion. Altering a spherical power of an optical element may be used for other applications, and may be applied to optical elements other than a lens. In certain embodiments, the primary intermediate part of the optical assembly may be rotatable in the primary plane about the first axis. Rotation of the primary intermediate part that has a component in the primary plane may effect movement of at least a subset of the plurality of driven portions out of the primary plane to add or adapt a spherical distortion to the optical element. Each driven portion moved out of the primary plane has a component of movement that is normal to the primary plane and has a drive magnitude. The drive magnitude may be the same for each of the driven portions. For example, in an event that the optical element is circular and / or the driven portions are arranged in a circle, a consistent drive magnitude for all the driven portions that are moved out of the primary plane results in a spherical distortion of the optical element. The drive magnitude may not necessarily be the same for each of the driven portions. For example, in an event that the optical element is not circular and / or the driven portions are not arranged around a circle, a consistent drive magnitude for all the driven portions that are moved out of the primary plane may not result in a spherical distortion of the optical element. The drive magnitude for each of the driven portions may be such that a spherical component of the curvature of the optical element is adapted, wherein the drive magnitude may vary between driven portions. With reference to Figures 18 to 21, an optical assembly according to certain embodiments of the present disclosure will be described, wherein a spherical power of a lens is adjusted by adapting a shape of the optical element. Figures 18 and 19 illustrate a primary intermediate part 1810 of an optical assembly according to certain embodiments of the present disclosure. A shape of an optical element having an adaptable shape is illustrated by membrane 1820. However, the position of membrane 1820 is not necessarily the position of the optical element, and is shown simply to illustrate how the shape of the optical element relates to the primary intermediate part 1810. A portion of the support structure is illustrated by a ring 1830. The first axis is indicated by the z axis. The primary plane is parallel to the x-y plane. The primary intermediate part 1810 comprises a plurality of primary drive portions 1811,1812,1813,1814,1815,1816,1817 and 1818, each comprising a planar surface at an acute, non-zero angle to the primary plane. Eight primary drive portions are illustrated, but the primary intermediate part 1810 may comprise any number of primary drive portions. In the example shown, the plurality of primary drive portions 1811,1812,1813,1814,1815,1816,1817 and 1818 are oriented such that the non-zero gradient of each primary drive portion with respect to the primary plane is in a direction along a tangent of a circle that aligns with an edge portion of the optical element. In an event that the optical element is non-circular, the plurality of primary drive portions 1811,1812,1813,1814,1815,1816,1817 and 1818 may be aligned such that the gradient of each primary drive portion with respect to the primary plane is in a direction parallel to a tangent to the non-circular optical element. Figure 18 shows the primary intermediate part 1810 in a first position. The membrane 1820 is near a lower side of each primary drive portion 1811,1812,1813,1814,1815,1816,1817 and 1818 relative to the z axis. The curvature of the membrane 1820 is positive, such that the centre of the membrane 1820 is higher relative to the edge of the membrane 1820, as measured along the z axis. Figure 19 shows the primary intermediate part 1810 rotated clockwise about the z axis, as indicated by arrow 1910. The rotation of the primary drive portions 1811,1812,1813,1814,1815,1816,1817 and 1818 results in corresponding driven portions of the movable part (not shown) sliding upwards along the surfaces of the primary drive portions 1811,1812,1813,1814,1815,1816, 1817 and 1818 such that the edge of the membrane has moved upwards along the z axis. The curvature of the membrane 1820 is negative, such that the centre of the membrane 1820 is lower relative to the edge of the membrane 1820, as measured along the z axis. Figures 20 and 21 show part of an optical assembly according to certain embodiments of the present disclosure, wherein a spherical power of a lens is adjusted by adapting a shape of the optical element. Similarly to Figures 18 and 19, the primary drive portions comprise each comprise a planar surface at an acute, non-zero angle to the primary plane. Figures 20 and 21 illustrate an example of an interaction between the primary drive portions and the movable part. Figures 20 and 21 show a primary intermediate part 2010, a movable part 2020, an optical element 2030 having an adaptable shape, and a support structure 2040. The optical element 2030 comprises a first lens surface 2031 that is flexible in directions parallel to the first axis (shown as the z axis). The optical element 2030 may comprise a liquid or gel lens, wherein the optical element 2030 further comprises a second lens surface 2032. The first and second lens surfaces 1231,1232 are separated along the first axis. In the example illustrated in Figures 20 and 21, the second lens surface 2032 is rigid and the primary intermediate part 2010 and the movable part 2020 are located within the optical element 2030. An example of a primary drive portion is labelled as 2011. A corresponding driven portion is labelled as 2021. The driven portions of the movable part 2020 each comprise a planar surface at an acute, non-zero angle to the primary plane, wherein each driven portion is configured to slide relative to the corresponding primary drive portion on actuation of the actuator assembly to rotate the primary intermediate portion 2010. Figure 20 shows the driven portions at a high position relative to the primary driven portions, such that the movable part is separated from the primary intermediate portion along the z axis. The movable part 2020 has moved an edge portion of the first lens surface 2031 upwards relative to the first axis (and thereby out of the primary plane). The curvature of the first lens surface 2031 is such that the separation between the first and second lens surfaces 2031, 2032 along the first axis is larger at an edge of the optical element 2030 than at a centre of the optical element 2030 (wherein the edge and centre are defined parallel to the primary plane). In certain embodiments, rotation of the movable part 2020 about the first axis may be constrained such that the movable part is translated parallel to the first axis. In other embodiments, movement of the movable part may have a component parallel to the first axis and a rotational component about the first axis. Figure 21 shows the primary intermediate part 2010 rotated anticlockwise relative to Figure 20, as shown by arrow 2110. The driven portions have slid downwards relative to the corresponding primary drive portions, such that the driven portions are at a lower position along the first axis than in Figure 20. The separation between the movable part and the primary intermediate portion along the first axis is smaller than that in Figure 20. The movable part 2020 has moved an edge portion of the first lens surface 2031 downwards relative to the first axis (and thereby out of the primary plane). The curvature of the first lens surface 2031 is such that the separation between the first and second lens surfaces 2031, 2032 along the first axis is smaller at an edge of the optical element 2030 than at a centre of the optical element 2030 (wherein the edge and centre are defined parallel to the primary plane). In Figures 20 and 21, the primary intermediate part 2010 further comprises secondary drive portions. The primary drive portions are disposed on a first side of the primary intermediate part 2010, and the secondary drive portions are disposed on a second side of the primary intermediate part 2010. The first and second sides of the primary intermediate part 2010 are separated along the first axis. An example of a secondary drive portion is labelled as 2012. Each secondary drive portion comprises a planar surface at an acute, non-zero angle to the primary plane. The support structure 2040 comprises a plurality of interface portions (such as interface portion 2041) disposed on a base of the support structure 2040, each corresponding to a secondary drive portion. Each interface portion comprises a planar surface at an acute, non-zero angle to the primary plane. In an event that the primary intermediate part moves relative to the support structure 2040, each secondary drive portion is configured to slide with respect to the surface of the corresponding interface portion. Figure 20 shows the secondary drive portions at a high position relative to the interface portions, such that the primary intermediate part 2010 is separated from the base of the support structure 2040 along the z axis by a larger amount. Figure 21 shows the secondary drive portions at a low position relative to the interface portions, such that the primary intermediate part 2010 is separated from the base of the support structure 2040 by a smaller amount along the z axis. Movement of the primary intermediate part 2010 along the first axis effects movement of the movable part 2020 along the first axis, so the separation of the primary intermediate part 2010 from the base of the support structure 2040 affects the separation of the movable part 2010 from the base of the support structure 2040. The separation of the movable part 2020 from the base of the support structure 2040 along the z axis is therefore greater in Figure 20 than in Figure 21. In the example illustrated in Figures 20 and 21, the secondary drive portions correspond to interface portions disposed on a base of the support structure. In other embodiments, the optical assembly may further comprise an interface part comprising a plurality of primary interface portions each corresponding to a secondary drive portion. The primary interface portion may be static relative to the support structure. Or, the primary interface portion be separate to and movable relative to the support structure. Movement parallel to the primary plane of the plurality of secondary drive portions may effect movement of at least a subset of the plurality of secondary drive portions out of the primary plane. A direction and magnitude of the movement of the primary intermediate part relative to the interface part may be the same as a direction and magnitude of the movement of the movable part relative to the primary intermediate part. Otherwise, a direction and magnitude of the movement of the primary intermediate part relative to the interface part is different to a direction and magnitude of the movement of the movable part relative to the primary intermediate part. The primary intermediate part 2010 may be rotated by any suitable actuator assembly. In certain embodiments, the actuator assembly may comprise one or more SMA elements. Figures 22 and 23 show examples of an arrangement of four SMA elements that may be part of the actuator assembly and configured to actuate the primary intermediate part. A schematic illustration of a view of an optical assembly 2200 along the first axis (a top view) is shown in Figure 22, wherein the optical assembly comprises a primary intermediate part 2210 and a support structure 2220. The actuator assembly comprises a first pair of SMA elements 2231, 2232 and a second pair of SMA elements 2241, 2242, wherein the SMA elements are connected directly or indirectly between the support structure 2220 and the primary intermediate part 2210 such that actuation of one or more SMA elements rotates the primary intermediate part 2210 relative to the support structure 2220 and in the primary plane, as shown by arrow 2250. Other components of the optical assembly are not shown. A schematic illustration of a view of an optical assembly 2300 along the first axis (a top view) is shown in Figure 23, wherein the optical assembly comprises a primary intermediate part 2310 and a support structure 2320. The actuator assembly comprises a first pair of SMA elements 2331, 2332 and a second pair of SMA elements 2341, 2342, wherein the SMA elements are connected directly or indirectly between the support structure 2320 and the primary intermediate part 2310 such that actuation of one or more SMA elements rotates the primary intermediate part 2310 relative to the support structure 2320 and in the primary plane, as shown by arrow 2350. Other components of the optical assembly are not shown. Other numbers of SMA elements and other arrangements of SMA elements may be used. Cylindrical Distortion In certain embodiments of the optical assembly, adjustments other than spherical distortions may be made to the shape of the optical element, either instead of or in addition to spherical distortions. A cylindrical distortion of the optical element may, for example, be used to correct for astigmatism. Astigmatism results in distorted or blurred vision, and is due to a rotational asymmetry in the refractive power of the eye. Astigmatism may be a result of an irregular curvature of the cornea or lens of the eye. The curvature of the eye may be non-spherical, but symmetrical around the optical axis. For example, the curvature of the eye may be stretched or flattened along the optical axis. Or, the curvature of the eye may not be symmetrical. A prescription for astigmatism has two components: a cylindrical power, and a cylindrical direction. A cylindrical distortion may, simplistically, arise from a curvature of an optically active surface around an axis that is referred to as the axis of the cylindrical distortion, while there is no curvature about the perpendicular (optical) axis. In an event that two cylindrical distortions are combined, wherein the cylindrical direction of each is not colinear, a spherical distortion is introduced. Therefore, where cylindrical distortion is referred to in this document, it is cylindrical distortion with the component of spherical distortion removed. This gives rise to a saddle shape distortion as illustrated in Figure 24, wherein the saddle has two-fold rotational symmetry about the z axis. The saddle shape provides positive distortion along an axis perpendicular to the z axis and provides negative distortion along another axis perpendicular to the z axis, wherein the axes that provide positive and negative distortion are perpendicular to one another such that two saddle shaped distortions that are rotated about the z axis by 90 degrees relative to one another will cancel each other (and will therefore have no spherical distortion). In certain embodiments, the primary intermediate part is translatable in the primary plane in a first degree of freedom and in a second degree of freedom. Translation of the primary intermediate part in the primary plane may effect movement of at least a subset of the plurality of driven portions out of the primary plane to adapt a cylindrical component of the curvature of the optical element (or, in other words, add or adapt a cylindrical distortion to the optical element). Translation of the primary intermediate part along a secondary axis in the primary plane may effect movement of at least a subset of the plurality of driven portions out of the primary plane to add or adapt a first cylindrical distortion of the optical element, the first cylindrical distortion having a first cylindrical axis. Translation of the primary intermediate part along a tertiary axis in the primary plane may effect movement of at least a subset of the plurality of driven portions out of the primary plane to add or adapt a second cylindrical distortion of the optical element, the second cylindrical distortion having a second cylindrical axis that is at a non-zero angle to the first cylindrical axis. In certain examples, the secondary axis is perpendicular to the tertiary axis and the second cylindrical axis is at 45° relative to the first cylindrical axis. In an event that the secondary axis is perpendicular to the tertiary axis and the second cylindrical axis is at 45° relative to the first cylindrical axis, rotation of the of the primary intermediate part in the primary plane may effect translation of an optical axis of the optical element in the primary plane. For example, in an event that the optical element comprises a lens, the rotation of the of the primary intermediate part in the primary plane may result in a thickness of the lens (along a direction parallel to the first axis) increasing in an area of the lens and decreasing in another area of the lens, such that an optical axis of the lens is translated parallel to the primary plane. Moving the optical axis may, for example, be used to correct for a position of the lens relative to the eye. A combination of cylindrical distortion and moving the optical axis may be achieved by translating and rotating the primary intermediate part in the primary plane. With reference to Figure 25, an example of an optical assembly is illustrated wherein translation of the primary intermediate part in the primary plane effects movement of at least a subset of the plurality of driven portions out of the primary plane to add or adapt a cylindrical distortion to of the optical element. The optical assembly 2500 comprises a primary intermediate part 2510, a movable part 2520 and a support structure 2530. Other components of the optical assembly 2500 are not shown. Figure 25A shows a sideview of the arrangement of the primary intermediate part 2510, the movable part 2520 and the support structure 2530. Figure 25B shows a top view (wherein the x-y plane is shown, perpendicular to the first axis). The primary intermediate part is translatable along the x axis and along the y axis, wherein the x axis is perpendicular to the y axis and wherein both the x and y axes are perpendicular to the first axis. The x-y plane is parallel to the primary plane. Translation of the primary intermediate part along the x axis effects movement of the movable part to provide a cylindrical distortion with a first cylindrical axis 2541. Translation of the primary intermediate part along the y axis effects movement of the movable part to provide a cylindrical distortion with a second cylindrical axis 2542. The first and second cylindrical axes 2541, 2542 are parallel to the x-y plane and are at 45 degrees to one another. The primary intermediate part 2510 comprises a first region on a first side of the primary intermediate part, the first region comprising the plurality of primary drive portions each extending out of the primary plane. The driven portions of the movable part 2520 each correspond to a primary drive portion. In certain embodiments, the primary intermediate part further comprises a second region on a second side of the primary intermediate part, the second region comprising a plurality of secondary drive portions each extending out of the primary plane, wherein the first side and the second side are separated along the first axis. The optical assembly may further comprise an interface part comprising a plurality of primary interface portions each corresponding to a secondary drive portion. The interface portion may be part of the support structure or may be static relative to the support structure. Or, the interface portion may be separate to and movable relative to the support structure. Movement parallel to the primary plane of the plurality of secondary drive portions may effect movement of at least a subset of the plurality of secondary drive portions out of the primary plane. A direction and magnitude of the movement of the primary intermediate part relative to the interface part may be the same as a direction and magnitude of the movement of the movable part relative to the primary intermediate part. Otherwise, a direction and magnitude of the movement of the primary intermediate part relative to the interface part is different to a direction and magnitude of the movement of the movable part relative to the primary intermediate part. Figures 26 and 27 illustrate a primary intermediate part 2610 of an optical assembly according to certain embodiments of the present disclosure. A shape of an optical element having an adaptable shape is illustrated by membrane 2620. However, the position of membrane 2620 is not necessarily the position of the optical element, and is shown simply to illustrate how the shape of the optical element relates to the primary intermediate part 2610. A portion of the support structure is illustrated by a ring 2630. The first axis is indicated by the z axis. The primary plane is parallel to the x-y plane. The primary intermediate part 2610 comprises a plurality of primary drive portions 2611, 2612,2613,2614,2615,2616, 2617 and 2618, each comprising a planar surface at an acute, non-zero angle to the primary plane. Eight primary drive portions are illustrated, but the primary intermediate part 2610 may comprise any number of primary drive portions. In the example shown, the plurality of primary drive portions 2611, 2612, 2613, 2614, 2615,2616, 2617 and 2618 are oriented such that the non-zero gradient of each primary drive portion with respect to the primary plane is at a varying direction to a tangent of a circle that aligns with an edge portion of the optical element. In an event that the optical element is non-circular, the plurality of primary drive portions 2611, 2612, 2613, 2614, 2615, 2616, 2617 and 2618 may be aligned such that the gradient of each primary drive portion with respect to the primary plane is in a direction with a varying angle to a tangent to the noncircular optical element. Figure 26 shows the primary intermediate part 2610 in a first position, wherein the primary intermediate part 2610 has been translated along the x axis as indicated by arrow 2640. The membrane has a cylindrical distortion with a first cylindrical axis indicated by dotted line 2650. Figure 27 shows the primary intermediate part 2610 in a second position, wherein the primary intermediate part 2610 has been translated along the y axis as indicated by arrow 2710. The membrane has a cylindrical distortion with a second cylindrical axis indicated by dotted line 2720. The first and second cylindrical axes 2650, 2720 are examples only. The angles of the first and second cylindrical axes relative to each other and to the x and y axes may be different. Translation of the primary intermediate part 2610 that has components in both x and y may effect a cylindrical distortion that is a combination of the cylindrical distortions shown in Figures 26 and 27. The magnitude of the cylindrical distortion may be determined by a magnitude of a translation of the primary intermediate part 2610, and an axis of the cylindrical distortion may be determined by a direction of a translation of the primary intermediate part 2610. The plurality of primary drive portions may each comprise a planar surface angled with respect to the primary plane, as illustrated by Figures 26 and 27. In certain embodiments, a gradient of the planar surface with respect to the primary plane in a direction parallel to the secondary axis may be is proportional to cos(2a), where a is an angle to the secondary axis in the primary plane. This is illustrated in Figure 28. The primary drive portions illustrated in Figures 26 and 27 have this arrangement. In certain embodiments, the primary intermediate part may comprise a first region on a first side of the primary intermediate part, the first region comprising the plurality of primary drive portions each extending out of the primary plane. The driven portions of the movable part each correspond to a primary drive portion. The primary intermediate part may further comprise a second region on a second side of the primary intermediate part, the second region comprising a plurality of secondary drive portions each extending out of the primary plane, wherein the first side and the second side are separated along the first axis. In an event that moving the primary intermediate part in the primary plane effects a movement of the primary part (as a result of the secondary drive portions) having the same magnitude and direction as the movement of the movable part (as a result of the primary drive portions), the movement of the movable part out of the primary plane may be doubled for a given movement of the primary intermediate part in the primary plane relative to an optical assembly wherein the primary intermediate part has only primary drive portions. The gradient of the planar surface with respect to the primary plane in a direction parallel to the secondary axis may be proportional to cos(2a), where a is an angle to the secondary axis in the primary plane; and a gradient of the planar surface with respect to the primary plane in a direction parallel to the tertiary axis may be proportional to sin(2a), where a is an angle to the secondary axis in the primary plane. This is illustrated in Figure 29. Secondary Intermediate Part In the example described above with reference to Figures 25 to 27, the primary intermediate part is translatable in two degrees of freedom. In other embodiments, the optical assembly may comprise a primary intermediate part movable in a first degree of freedom and a secondary intermediate part movable in a second degree of freedom, different from the first degree of freedom. Movement in a particular degree of freedom may comprise translation or rotation. Movement of the primary intermediate part may apply a spherical distortion or a cylindrical distortion to the optical element. Movement of the secondary intermediate part may apply a spherical distortion or a cylindrical distortion to the optical element. With reference to Figure 30, a side view is illustrated of a structure of an optical assembly 3000 comprising a primary intermediate part 3010, a secondary intermediate part 3020, a movable part 3030 and a support structure 3040. Other components of the optical assembly 3000 are not shown. A direction of the first axis is indicated by arrow 3050. The primary intermediate part 3010 may be movable relative to the support structure 3040 in the primary plane in a first degree of freedom and movable out of the primary plane. The secondary intermediate part 3020 is movable relative to the support structure 3040 in a secondary plane perpendicular to the first axis and separated from the primary plane along the first axis. The secondary intermediate part 3020 comprises a plurality of tertiary drive portions each extending out of the secondary plane, wherein the secondary intermediate part is translatable relative to the support structure in the secondary plane in a second degree of freedom different to the first degree of freedom. The actuator assembly of the optical assembly 3000 further comprises one or more actuator units (not shown) configured to drive movement of the secondary intermediate part 3020 relative to the support structure in the secondary plane. The support structure comprises a plurality of secondary interface portions each corresponding to one of the plurality of tertiary drive portions. Movement of the secondary intermediate part 3020 parallel to the secondary plane effects movement of at least a subset of the tertiary drive portions out of the secondary plane to move the primary intermediate part 3010 out of the primary plane to move the movable part 3030 and adapt the adaptable shape of the optical element. Movement of the primary intermediate part 3010 parallel to the primary plane effects movement of at least a subset of the primary drive portions out of the primary plane to move the movable part 3030 out of the primary plane to adapt the adaptable shape of the optical element. Movement of the primary intermediate part 3010 out of the primary plane may comprise moving some or all of the primary intermediate part 3010 out of the primary plane. The primary intermediate part 3010 may be flexible in one or more directions out of the primary plane. In certain embodiments, the primary intermediate part 3010 is translatable relative to the support structure 3040 in the primary plane in a first degree of freedom and movable out of the primary plane. The secondary intermediate part 3020 is movable relative to the support structure 3040 in a secondary plane perpendicular to the first axis and separated from the primary plane along the first axis, the secondary intermediate part 3020 comprising a plurality of tertiary drive portions each extending out of the secondary plane, wherein the secondary intermediate part 3020 is translatable relative to the support structure 3040 in the secondary plane in a second degree of freedom different to the first degree of freedom. Movement of the secondary intermediate part 3020 parallel to the secondary plane effects movement of at least a subset of the tertiary drive portions out of the secondary plane to move the primary intermediate part 3010 out of the primary plane, thereby moving the movable part out of the primary plane to adapt the adaptable shape of the optical element. Translation of the primary intermediate part 3010 in the first degree of freedom in the primary plane may effect movement of at least a subset of the plurality of driven portions out of the primary plane to add or adapt a first cylindrical distortion of the optical element, the first cylindrical distortion having a first cylindrical axis. Translation of the secondary intermediate part 3020 in the second degree of freedom in the secondary plane may effect movement at least a subset of the plurality of tertiary drive portions out of the secondary plane to add or adapt a second cylindrical distortion of the optical element, the second cylindrical distortion having a second cylindrical axis at a non-zero angle to the first cylindrical axis. In certain embodiments, translation of the primary intermediate part in the first degree of freedom is perpendicular to translation of the secondary intermediate part in the second degree of freedom and the second cylindrical axis is at 45° relative to the first cylindrical axis. In a variation on the example illustrated in Figure 30, the primary intermediate part may comprise a first region on a first side of the primary intermediate part, the first region comprising the plurality of primary drive portions each extending out of the primary plane. The driven portions of the movable part each correspond to a primary drive portion. The primary intermediate part may further comprise a second region on a second side of the primary intermediate part, the second region comprising a plurality of secondary drive portions each extending out of the primary plane, wherein the first side and the second side are separated along the first axis. The secondary intermediate part may comprise a third region on a first side of the secondary intermediate part opposing the second region of the primary intermediate part. The third region may comprise a plurality of quaternary drive portions each corresponding to a secondary drive portion and extending out of the secondary plane. The secondary intermediate part may further comprise a fourth region on a second side of the secondary intermediate part, the fourth region comprising the plurality of tertiary drive portions each extending out of the secondary plane. The first side and the second side of the secondary intermediate part are separated along the first axis. Movement in the primary plane of the primary intermediate part relative to the support structure effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element. Movement in the secondary plane of the secondary intermediate part relative to the primary intermediate part results in movement of the quaternary drive portions in the secondary plane relative to the primary intermediate part, which effects movement of at least a subset of the plurality of the secondary drive portions out of the primary plane. As a result, at least part of the primary intermediate part moves out of the primary plane, thereby moving at least part of the movable part out of the primary plane and adapting the adaptable shape of the optical element. Similarly, movement in the primary plane of the primary intermediate part relative to the secondary intermediate part effects movement of at least a subset of the plurality of the secondary drive portions out of the primary plane. As a result, at least part of the primary intermediate part moves out of the primary plane, thereby moving at least part of the movable part out of the primary plane and adapting the adaptable shape of the optical element. Movement in the secondary plane of the secondary intermediate part relative to the support structure effects movement of at least a subset of the plurality of tertiary drive portions out of the secondary plane. As a result, at least part of the secondary intermediate part moves out of the secondary plane, thereby moving at least part of the primary intermediate part out of the primary plane, which in turn results in at least part of the movable part moving out of the primary plane and adapting the adaptable shape of the optical element. The primary and secondary intermediate parts and the movable part may both be on the same side (along the first axis) of the part of the optical element having an adaptable shape. Alternatively, one or more of the primary and secondary intermediate parts and the movable part may on a first side of the part of the optical element having an adaptable shape and the remaining parts of the primary and secondary intermediate parts and the movable part may on a first side of the part of the optical element having an adaptable shape (wherein the first and second sides are separated along the first axis). In another variation, the optical assembly may comprise an interface part arranged between the primary intermediate part and the secondary intermediate part. The interface part may be movable in a direction parallel to the first axis. The interface part may be flexible in a direction parallel to the first axis, or may be rigid. The primary intermediate part may comprise a first region on a first side of the primary intermediate part, the first region comprising the plurality of primary drive portions each extending out of the primary plane. The driven portions of the movable part each correspond to a primary drive portion. The primary intermediate part may further comprise a second region on a second side of the primary intermediate part, the second region comprising a plurality of secondary drive portions each extending out of the primary plane, wherein the first side and the second side are separated along the first axis. The interface part may comprise a third region on a first side of the interface part opposing the second region of the primary intermediate part. The third region may comprise a plurality of primary interface portions each corresponding to a secondary drive portion and extending out of a tertiary plane perpendicular to the first axis. The interface part may further comprise a fourth region on a second side of the interface part, the fourth region comprising the plurality of secondary interface portions each extending out of the tertiary plane. The first side and the second side of the interface part may be separated along the first axis. The secondary intermediate part may comprise a fifth region on a first side of the secondary intermediate part opposing the fourth region of the interface part. The fifth region may comprise a plurality of quaternary drive portions each corresponding to a secondary interface portion and extending out of the secondary plane. The secondary part may further comprise a sixth region on a second side of the secondary intermediate part, the sixth region comprising the plurality of tertiary drive portions each extending out of the secondary plane. The first side and the second side of the interface part may be separated along the first axis. Movement in the primary plane of the primary intermediate part relative to the support structure effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element. Movement in the primary plane of the primary intermediate part relative to the interface part results in movement of the secondary drive portions in the primary plane relative to the interface part, which effects movement of at least a subset of the plurality of the secondary drive portions out of the primary plane. As a result, at least part of the primary intermediate part moves out of the primary plane, thereby moving at least part of the movable part out of the primary plane and adapting the adaptable shape of the optical element. Movement in the secondary plane of the secondary intermediate part relative to the interface part results in movement of the quaternary drive portions in the secondary plane relative to the interface part, which effects movement of at least a subset of the plurality of the quaternary drive portions out of the secondary plane. As a result, at least part of the interface part moves out of the secondary plane, resulting in movement of at least part of the primary intermediate part out of the primary plane, thereby moving at least part of the movable part out of the primary plane and adapting the adaptable shape of the optical element. Movement in the secondary plane of the secondary intermediate part relative to the support structure effects movement of at least a subset of the plurality of tertiary drive portions out of the secondary plane. As a result, at least part of the secondary intermediate part moves out of the secondary plane, thereby moving at least part of the interface part out of the secondary plane, resulting in movement of at least part of the primary intermediate part out of the primary plane, which in turn results in at least part of the movable part moving out of the primary plane and adapting the adaptable shape of the optical element. In other examples, one more of the interfaces between the primary intermediate part and the interface part, between the interface part and the secondary intermediate part, and between the secondary intermediate part and the support structure, may not comprise drive portions. Figure 31 shows two side views of an optical assembly wherein the primary intermediate part 3110 comprises a first region 3111 and a second region 3112 separated in a direction perpendicular to the first axis. The optical assembly may or may not have additional intermediate parts. The first region 3111 comprises a plurality of primary drive portions each extending out of the primary plane. The second region 3112 comprises a plurality of secondary drive portions each extending out of the primary plane. The movable part 3120 comprises a plurality of driven portions each corresponding to a primary drive option. The support structure 3130 comprises a plurality of interface portions each corresponding to a secondary drive portion. Movement parallel to the primary plane of the plurality of primary drive portions effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element 3140. Movement parallel to the primary plane of the plurality of secondary drive portions effects movement of at least a part of the primary intermediate part out of the primary plane, to adapt the adaptable shape of the optical element 3140. Tertiary Intermediate Part In certain embodiments, the optical assembly may comprise one or more further intermediate parts. With reference to Figure 32, in an example an optical assembly 3200 may comprise a primary intermediate part 3210, a secondary intermediate part 3220 and a tertiary intermediate part 3230. The optical assembly 3200 may comprise a movable part 3240 and a support structure 3250. The direction of the first axis is indicated by arrow 3260. Each of the primary intermediate part 3210, secondary intermediate part 3220 and tertiary intermediate part 3230 may be rotatable about the first axis. The primary intermediate part 3210 may be rotatable in the primary plane relative to the movable part 3240, such that a spherical distortion may be introduced to the optical element. The primary intermediate part 3210 may be rotatable relative to the secondary intermediate part 3220, creating a cylindrical distortion with a first cylindrical axis. The primary intermediate part 3210 may be rotatable relative to the secondary intermediate part 3220, creating a cylindrical distortion with a first cylindrical axis. The secondary intermediate part 3220 may be rotatable relative to the tertiary intermediate part 3230, creating a cylindrical distortion with a second cylindrical axis at a non-zero angle to the first cylindrical axis. The tertiary intermediate part 3230 may be rotatable relative to the support structure 3250, creating a cylindrical distortion with a third cylindrical axis at a non-zero angle to the first cylindrical axis and to the second cylindrical axis. Any of the interfaces between any of the movable part 3240, the primary intermediate part 3210, the secondary intermediate part 3220, the tertiary intermediate part 3230 and the support structure 3250 may comprise drive portions as described above. In certain embodiments, the first cylindrical axis is at 60 degrees to the second cylindrical axis and at 120 degrees to the third cylindrical axis. The overall magnitude and direction of the cylindrical distortion may be a combination of the cylindrical distortions that result from rotation of each of the primary intermediate part 3210, the secondary intermediate part 3220 and the tertiary intermediate part 3230 with the part below. In certain embodiments, a magnitude of the resultant cylindrical distortion from rotation of each of the primary intermediate part 3210, the secondary intermediate part 3220 and the tertiary intermediate part 3230 may arise from the relative amplitudes of the three constituent cylindrical distortions. For example, if all three of the primary intermediate part 3210, the secondary intermediate part 3220 and the tertiary intermediate part 3230 have the same relative rotation with the part below, the strength of the cylindrical distortion from all three interfaces will be the same and there will be no overall cylindrical distortion induced. However, there will be spherical distortion resulting from rotation of the primary intermediate part 3110 relative to the movable part 3140. The actuator assembly may comprise one or more actuating units configured to drive movement of the primary intermediate part relative to the support structure and the secondary intermediate part, one or more actuating units configured to drive movement of the secondary intermediate part relative to the tertiary intermediate part, and one or more actuating units configured to drive movement of the tertiary intermediate part relative to the support structure One or more actuating units may comprise SMA elements. Lines 3271 indicate a possible arrangement of a pair of SMA elements connecting the primary intermediate part 3210 and the secondary intermediate part 3220, such that on actuation the primary intermediate part 3210 rotates relative to the movable part 3240 and the secondary intermediate part 3220. Lines 3272 indicate a possible arrangement of a pair of SMA elements connecting the secondary intermediate part 3220 and the primary intermediate part 3230, such that on actuation the secondary intermediate part 3220 rotates relative to the tertiary intermediate part 3230. Lines 3273 indicate a possible arrangement of a pair of SMA elements connecting the tertiary intermediate part 3230 and the support structure 3250, such that on actuation the tertiary intermediate part 3230 rotates relative to the support structure 3250. Optical assembly configured to apply a cylindrical distortion and a spherical distortion to an optical element Figures 33 to 36 illustrate a structure of an optical assembly 3300 configured to add or adapt a spherical distortion and and / or a cylindrical distortion to the optical element 3340. The optical assembly 3300 may be further configured to move the optical axis of the optical element 3340 parallel to the primary plane. The optical assembly 3300 comprises a primary intermediate part 3310, a secondary intermediate part 3320, a movable part 3330, an interface part 3350 and a support structure 3360. The direction of the first axis is indicated by arrow 3370. The actuator units are not shown. The movable part 3330 may be movable in a direction parallel to the first axis. The movable part 3330 may be flexible out of the primary plane. The primary intermediate part 3310 may be movable in the primary plane. The primary intermediate part 3310 may be flexible out of the primary plane. The interface part 3350 may be movable in a direction parallel to the first axis. Movement of the interface part 3350 perpendicular to the first axis may be constrained. The interface part 3350 may be rigid. The secondary intermediate part 3320 may be movable in a direction parallel to the first axis. The secondary intermediate part 3320 may be rigid. The support structure 3360 may be rigid. The primary intermediate part 3310 may comprise a first region on a first side of the primary intermediate part 3310, the first region comprising the plurality of primary drive portions (such as 3311) each extending out of the primary plane. The driven portions (such as 3331) of the movable part 3340 each correspond to a primary drive portion. The primary intermediate part 3310 may further comprise a second region on a second side of the primary intermediate part 3310, the second region comprising a plurality of secondary drive portions (such as 3312) each extending out of the primary plane, wherein the first side and the second side are separated along the first axis. The interface part 3350 may comprise a third region on a first side of the interface part 3350 opposing the second region of the primary intermediate part 3310. The third region may comprise a plurality of primary interface portions (such as 3351) each corresponding to a secondary drive portion and extending out of a tertiary plane perpendicular to the first axis. The interface part 3350 may further comprise a fourth region on a second side of the interface part 3350, the fourth region comprising the plurality of secondary interface portions (such as 3352) each extending out of the tertiary plane. The first side and the second side of the interface part 3350 may be separated along the first axis. The secondary intermediate part 3320 may comprise a fifth region on a first side of the secondary intermediate part 3320 opposing the fourth region of the interface part 3350. The fifth region may comprise a plurality of quaternary drive portions (such as 3321) each corresponding to a secondary interface portion and extending out of the secondary plane. The secondary part 3320 may further comprise a sixth region on a second side of the secondary intermediate part 3320, the sixth region comprising the plurality of tertiary drive portions (such as 3322) each extending out of the secondary plane. The first side and the second side of the interface part 3350 may be separated along the first axis. The support structure 3360 may comprise a plurality of tertiary interface portions (such as 3361) each corresponding to a tertiary drive portion and extending out of the secondary plane. Translation in the primary plane of the primary intermediate part 3310 relative to the support structure 3360 effects movement of at least a subset of the plurality of driven portions out of the primary plane to add a cylindrical distortion of the optical element 3340. Rotation in the primary plane of the primary intermediate part 3310 relative to the support structure 3360 may effect movement of at least a subset of the plurality of driven portions out of the primary plane to move the optical axis of the optical element 3340. Translation in the primary plane of the primary intermediate part 3310 relative to the interface part 3350 results in movement of the secondary drive portions in the primary plane relative to the interface part 3350, which effects movement of at least a subset of the plurality of the secondary drive portions out of the primary plane. As a result, at least part of the primary intermediate part 3310 moves out of the primary plane, thereby moving at least part of the movable part 3330 out of the primary plane and adding a cylindrical distortion to the optical element 3340. Rotation in the primary plane of the primary intermediate part 3310 relative to the interface part 3350 may result in movement of the secondary drive portions in the primary plane relative to the interface part 3350, which effects movement of at least a subset of the plurality of the secondary drive portions out of the primary plane. As a result, at least part of the primary intermediate part 3310 moves out of the primary plane, thereby moving at least part of the movable part 3330 out of the primary plane and moving the optical axis of the optical element 3340. Rotation in the secondary plane of the secondary intermediate part 3320 relative to the interface part 3350 results in movement of the quaternary drive portions in the secondary plane relative to the interface part 3350, which effects movement of at least a subset of the plurality of the quaternary drive portions out of the secondary plane. As a result, at least part of the interface part 3350 moves out of the secondary plane, resulting in movement of at least part of the primary intermediate part 3310 out of the primary plane, thereby moving at least part of the movable part 3330 out of the primary plane and adding a spherical distortion to the optical element 3340. Rotation in the secondary plane of the secondary intermediate part 3320 relative to the support structure 3360 effects movement of at least a subset of the plurality of tertiary drive portions out of the secondary plane. As a result, at least part of the secondary intermediate part 3320 moves out of the secondary plane, thereby moving at least part of the interface part 3350 out of the secondary plane, resulting in movement of at least part of the primary intermediate part 3310 out of the primary plane, which in turn results in at least part of the movable part 3303 moving out of the primary plane and adding a spherical distortion to the optical element 3340. Figure 34 illustrates the optical assembly 3300 of Figure 33, wherein the secondary intermediate part 3320 has been rotated such that in the view shown, the secondary intermediate part rotates to the right. The interface part 3350 moves up out of the secondary plane, such that the primary intermediate part 3310 moves up out of the primary plane and the movable part 3330 moves up out of the primary plane. A spherical distortion of the optical element 3340 is adapted or added. Figure 35 illustrates the optical assembly 3300 of Figure 34, wherein the primary intermediate part 3310 has been translated to the right. As a result, the driven portions of the movable part move up by different amounts to add or adapt a cylindrical distortion of the optical element 3340. Figure 36 illustrates the optical assembly 3300 of Figure 35, wherein the secondary intermediate part 3320 has been rotated such that in the view shown, the secondary intermediate part rotates to the left. The interface part 3350 moves down (out of the secondary plane), such that the primary intermediate part 3310 moves down (out of the primary plane) and the movable part 3330 moves down (out of the primary plane). A spherical distortion of the optical element 3340 is adapted or added. The cylindrical distortion of Figure 35 is retained. In other embodiments, the primary intermediate portion may add or adapt a spherical distortion of the optical element and the secondary intermediate portion may add or adapt a cylindrical distortion of the optical element. Other optical properties of an optical element may be altered by adapting the shape of the optical element. For example, in an event that the optical element comprises a liquid or gel lens, sag (due to gravity) of the lens surface having an adaptable shape may be accounted for. In particular, sag of the lens surface having an adaptable shape may be corrected for in an event that the lens is oriented such that the optical axis is at an angle to the vertical, such as in spectacles where the optical axis will be close to horizontal. In an event that the optical element comprises a liquid or gel lens, the spherical power of the lens may be adjusted by using a pump to alter the volume of liquid or gel within the lens. An actuator assembly according to any of the embodiments described herein may be used to alter other properties of the lens, such as the cylindrical distortion. A headset may comprise an optical assembly according to any embodiment described herein. For example, the headset may be spectacles, or a virtual reality headset, or an augmented reality headset. The headset may comprise a display and an optical assembly according to any preceding claim, wherein the display is configured to be viewed through the optical assembly. A method of adapting a shape of an optical element having an adaptable shape may use an optical assembly according to any of the embodiments described herein. The method may use an actuator assembly comprising a support structure, a primary intermediate part, a movable part and one or more actuator units. A first axis is defined relative to the support structure. The primary intermediate part is movable relative to the support structure in a primary plane perpendicular to the first axis and comprises a plurality of primary drive portions each extending out of the primary plane. The movable part comprises a plurality of driven portions each corresponding to one of the plurality of primary drive portions, wherein each driven portion is movable relative to the support structure to adapt the adaptable shape of the optical element. The one or more actuator units are configured to drive movement of the primary intermediate part relative to the support structure in the primary plane. The method comprises moving the primary intermediate part in the primary plane such that the plurality of primary drive portions move parallel to the primary plane, effecting movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element. SMA The above-described SMA actuator assemblies comprise at least one SMA element. The term 'shape memory alloy (SMA) element’ may refer to any element comprising SMA. The SMA element may be described as an SMA wire. The SMA element may have any shape that is suitable for the purposes described herein. The SMA element may be elongate and may have a round cross section or any other shape cross section. The cross section may vary along the length of the SMA element. The SMA element might have a relatively complex shape such as a helical spring. It is also possible that the length of the SMA element (however defined) may be similar to one or more of its other dimensions. The SMA element may be sheet-like, and such a sheet may be planar or non-planar. The SMA element may be pliant or, in other words, flexible. In some examples, when connected in a straight line between two components, the SMA element can apply only a tensile force which urges the two components together. In other examples, the SMA element may be bent around a component and can apply a force to the component as the SMA element tends to straighten under tension. The SMA element may be beam-like or rigid and may be able to apply different (e.g. non-tensile) forces to elements. The SMA element may or may not include material(s) and / or component(s) that are not SMA. For example, the SMA element may comprise a core of SMA and a coating of non-SMA material. Unless the context requires otherwise, the term 'SMA element’ may refer to any configuration of SMA material acting as a single actuating element which, for example, can be individually controlled to produce a force on an element. For example, the SMA element may comprise two or more portions of SMA material that are arranged mechanically in parallel and / or in series. In some arrangements, the SMA element may be part of a larger SMA element. Such a larger SMA element might comprise two or more parts that are individually controllable, thereby forming two or more SMA elements. The SMA element may comprise an SMA wire, SMA foil, SMA film or any other configuration of SMA material. The SMA element may be manufactured using any suitable method, for example by a method involving drawing, rolling, deposition, sintering or powder fusion. The SMA element may exhibit any shape memory effect, e.g. a thermal shape memory effect or a magnetic shape memory effect, and may be controlled in any suitable way, e.g. by Joule heating, another heating technique or by applying a magnetic field.

Claims

1. An optical assembly comprising:an optical element having an adaptable shape; andan actuator assembly comprising:a support structure, wherein a first axis is defined relative to the support structure;a primary intermediate part movable relative to the support structure in a primary plane perpendicular to the first axis and comprising a plurality of primary drive portions each extending out of the primary plane;a movable part comprising a plurality of driven portions each corresponding to one of the plurality of primary drive portions, wherein each driven portion is movable relative to the support structure to adapt the adaptable shape of the optical element; andone or more actuator units configured to drive movement of the primary intermediate part relative to the support structure in the primary plane;wherein movement parallel to the primary plane of the plurality of primary drive portions effects movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element.

2. An optical assembly according to claim 1 wherein at least one of the one or more actuator units comprises a shape memory alloy (SMA) element.

3. An optical assembly according to claim 1, wherein the optical assembly is configured to constrain movement of the movable part relative to the support structure in an absence of power to one or more actuator units of the actuator assembly.

4. An optical assembly according to any preceding claim, wherein the primary intermediate part is movable relative to the support structure in a primary plane in two or more degrees of freedom;orwherein the primary intermediate part is movable relative to the support structure in the primary plane in a first degree of freedom, and wherein the actuator assembly further comprises a secondary intermediate part movable in a second degree of freedom relative to the support structure in a secondary plane perpendicular to the first axis, wherein:the secondary intermediate part comprises a plurality of secondary drive portions each extending out of the secondary plane.

5. An optical assembly according to any preceding claim, wherein the primary intermediate part is translatable relative to the support structure in the primary plane.

6. An optical assembly according to any preceding claim, wherein the primary intermediate part is rotatable relative to the support structure in the primary plane.

7. An optical assembly according to any preceding claim, wherein:the plurality of primary drive portions each comprise a surface at an acute, non-zero angle with respect to the primary plane; and / orthe plurality of primary driven portions each comprise a surface angled at an acute, non-zero angle with respect to the primary plane.

8. An optical assembly according claim 7 wherein the plurality of primary drive portions each comprise a surface at an acute, non-zero angle with respect to the primary plane and wherein either:the plurality of driven portions each comprise a mating surface corresponding to a surface of a corresponding primary drive portion; orthe plurality of driven portions each comprise a rolling bearing; orthe plurality of driven portions comprises a first sub-group of driven portions and a second sub-group of drivenportions separate to the second sub-group of driven portions, wherein:the driven portions of the first sub-group of driven portions each comprise a mating surface corresponding to a surface of a corresponding primary drive portion; andthe driven portions of the second sub-group of driven portions each comprise a rolling bearing.

9. An optical assembly according to any of claims 1 to 6, wherein the plurality of primary drive portions each comprise:a body; anda linkage connected between the body and a corresponding driven portion;wherein movement of a body of a primary drive portion in the primary plane rotates the linkage of the primary drive portion such that the corresponding driven portion is moved out of the primary plane.

10. An optical assembly according to any preceding claim, wherein the optical element comprises a lens having at least one lens surface with an adaptable shape.

11. An optical assembly according to any of claims 1 to 9, wherein the optical element comprises a mirror with an adaptable shape.

12. An optical assembly according to claim 3 or any of claims 4 to 11 when dependent on claim 3, wherein either:the movable part comprises a first friction surface configured to engage with a second friction surface such that movement of the movable part relative to the support structure is constrained in an absence of power to one or more actuator units of the actuator assembly; and / orthe primary intermediate part comprises a first friction surface configured to engage with a second friction surface such that movement of the primary intermediate part relative to the support structure is constrained in an absence of power to one or more actuator units of the actuator assembly.

13. An optical assembly according to any preceding claim, wherein the primary intermediate part is rotatable in the primary plane about the first axis.

14. An optical assembly according to any preceding claim, wherein each driven portion moved out of the primary plane has a component of movement that:is normal to the primary plane; andhas a drive magnitude;wherein the drive magnitude for each of the driven portions is such that a spherical distortion of the optical element is adapted.

15. An optical assembly according to any preceding claim, wherein the primary intermediate part is translatable in the primary plane in a first degree of freedom and in a second degree of freedom.

16. An optical assembly according to claim 15 configured such that:translation of the primary intermediate part along a secondary axis in the primary plane effects movement of at least a subset of the plurality of driven portions out of the primary plane to add a first cylindrical distortion to the optical element, the first cylindrical distortion having a first cylindrical axis; andtranslation of the primary intermediate part along a tertiary axis in the primary plane effects movement at least a subset of the plurality of driven portions out of the primary plane to add a second cylindrical distortion to the optical element, the second cylindrical distortion having a second cylindrical axis that is at a non-zero angle to the first cylindrical axis.

17. An optical assembly according to claim 16, wherein the secondary axis is perpendicular to the tertiary axis and the second cylindrical axis is at 45° relative to the first cylindrical axis.

18. An optical assembly according to any of claims 15 to 17, wherein the primary intermediate part comprises: a first region comprising the plurality of primary drive portions each extending out of the primary plane; and a second region comprising a plurality of secondary drive portions each extending out of the primary plane, wherein the plurality of secondary drive portions engage with corresponding portions of the support structure.

19. An optical assembly according to any of claims 15 to 18, wherein rotation of the primary intermediate part in the primary plane effects movement of at least a subset of the plurality of driven portions out of the primary plane to move an optical axis of the optical element.

20. An optical assembly according to any of claims 16 or claims 17 to 19 when dependent on claim 16, wherein the plurality of primary drive portions each comprise a planar surface angled with respect to the primary plane and wherein a gradient of the planar surface with respect to the primary plane in a direction parallel to the secondary axis is proportional to cos(2a), where a is an angle to the secondary axis in the primary plane.

21. A head-mounted device comprising an optical assembly according to any preceding claim.

22. A head-mounted device comprising;a display; andan optical assembly according to any of claims 1 to 20, wherein the display is configured to be viewed through the optical assembly.

23. A method of adapting a shape of an optical element having an adaptable shape using an actuator assembly comprising: a support structure, wherein a first axis is defined relative to the support structure;a primary intermediate part movable relative to the support structure in a primary plane perpendicular to the first axis and comprising a plurality of primary drive portions each extending out of the primary plane;a movable part comprising a plurality of driven portions each corresponding to one of the plurality of primary drive portions, wherein each driven portion is movable relative to the support structure to adapt the adaptable shape of the optical element; andone or more actuator units configured to drive movement of the primary intermediate part relative to the support structure in the primary plane;wherein the method comprises:moving the primary intermediate part in the primary plane such that the plurality of primary drive portions move parallel to the primary plane, effecting movement of at least a subset of the plurality of driven portions out of the primary plane to adapt the adaptable shape of the optical element.

Images