Patent Publication Number: US-2023134656-A1

Title: Liquid lens having a fixed lens shaping element and a movable transparent window

Description:
The invention relates to a liquid lens, an optical system and a method for controlling the lens or the system. 
     In the art membrane-based liquid lenses are known. The lenses operate on a mechanical force applied to an incompressible liquid in a lens volume, wherein in response to the applied force a membrane covering the lens volume adjusts its curvature and thus the optical power of the lens. 
     For this purpose, the liquid lens has a first membrane and opposite the first membrane a rigid transparent cover element, wherein the liquid is arranged between the membrane and the cover element. 
     The lens further comprises a wall portion enclosing the liquid circumferentially. The first membrane may be connected to the wall portion. 
     The actuation force is provided to the liquid lens by means of a movable lens shaping element. The lens shaping element is outside of the lens volume arranged on the first membrane and comprises an aperture that defines an adjustable lens area of the first membrane within which the first membrane can adjust its curvature along the optical axis upon actuation. Around the aperture of the lens shaping element there is a free membrane portion of the first membrane allowing the membrane to bend and provide the necessary elasticity for actuation. 
     By moving the lens shaping element towards or away from the lens volume the curvature of the first membrane is adjusted. 
     This design has several disadvantages. 
     For example during assembly of the lens, an optical axis of the lens is defined by the lateral wall. The lens shaping element with its aperture therefore needs to be arranged perfectly centered on the optical axis in order to omit aberrations and beam displacements relative to the optical axis. 
     Moreover, when actuating the lens shaping element along the optical axis of the lens, residual lateral movement of the lens shaping element cannot be prevented. These lateral movements however lead to movement of the optical axis of the adjustable lens area of the membrane and also a potentially asymmetric membrane curvature with respect to the optical axis of the lens. This leads to undesired lateral image shifts when the optical power of the lens is adjusted. 
     Furthermore, the lens does not provide means for compensating or controlling a beam displacement. 
     Also, the first membrane has to provide a specific stiffness such that the desired optical properties of the lens can be achieved. For actuation however, it is more desirable to have a low stiffness which allows for low actuation forces and thus energy conserving control of the lens. This leads to a conflict of objectives in the lens design that cannot be solved without compromise. 
     In general the lenses known in the art require a certain predefined building space, which for many applications should be reduced. 
     An object of the present invention is to provide a lens that solves the problems of the lenses known in the art. The object is achieved by the liquid lens having the features of claim  1 . 
    
    
     Advantageous embodiments are described in the subclaims. 
     According to claim  1  the liquid lens has an adjustable optical power and comprises at least the following components:
         a lens volume with a first transparent liquid arranged between a first transparent, particularly elastically deformable, membrane and a second transparent, particularly elastically deformable, membrane opposite the first membrane,   wherein the first membrane has a first side facing outwards the lens volume and a second side facing in the opposite direction toward the lens volume,   wherein the second membrane has a first side facing toward the lens volume and a second side facing in the opposite direction outward the lens volume,   a lens shaping element arranged on, particularly connected to, more particularly fixedly connected to the first membrane, the lens shaping element having a circumferential aperture defining a lens area of the first membrane having an adjustable curvature,   a transparent, particularly rigid and/or massive window element connected to the second membrane, particularly wherein the window element is particularly fixedly connected to the second side of the second membrane, covering a window portion of the second membrane, wherein the window element is circumferentially surrounded by a free, particularly non-window covered portion of the second membrane, such that the window element can move relatively to the lens shaping element thereby bending the free portion of the second membrane and adjusting a liquid pressure in the lens volume, such that a curvature of the first membrane in the lens area and therefore the optical power of the lens is adjusted.       

     According to an embodiment of the invention, an optical path extends through the window element and the lens area of the first membrane along the optical axis. 
     The term “optical path” particularly defines the portion of the lens, particularly the portion of the lens volume through which light propagates for being affected by the lens, i.e. the optical path does particularly not include residual stray light that might propagate through the lens in a manner that is not contributing to the intended alteration of the wave front of the light propagating through the lens. 
     The clear aperture of the lens shaping element defines the lens area of the first membrane by means of the circumferential enclosure of said lens area. When a pressure in the lens volume is adjusted, the lens area of the first membrane may alter its curvature in response to the pressure in the lens volume by either adopting a convex shape, i.e. in an outward protruding fashion, or by adopting a concave shape, i.e. in an inward protruding fashion. The change of curvature of the lens area of the first membrane allows the lens to adjust its optical power in a well-defined manner. Depending on the embodiment, the first membrane may also alter its curvature at other portions outside the lens area, however, these portion are outside the optical path of the lens and do not contribute to the optical properties of the lens. 
     According to another embodiment of the invention, in response to a change of pressure in the lens volume, the curvature of the first membrane causing the lens to change its optical power takes place only in the lens area of the first membrane. 
     Such change in pressure may be evoked by a relative movement or tilt of the window element toward or away from the lens shaping element. 
     The window element may be a plate-like window with no holes having at least one planar surface that is connected to the second side of the second membrane. 
     According to another embodiment of the invention, the lens comprises a lens body, wherein the lens body comprises at least the lens shaping element, the first membrane, the second membrane as well as the lens volume. 
     According to another embodiment of the invention, the lens shaping element is a fixed component of the lens body. Therefore, adjustment of the optical power or prism of the lens may be facilitated by moving the window element relatively to the lens body. 
     In a first embodiment, adjustment of the optical power and/or prism of the lens can be facilitated by means of an actuation force, for example provided by an actuator, configured to move the window element towards or away from the lens shaping element and thus the lens body, particularly while the lens body and the lens shaping element remain at a fixed position. In a second embodiment, adjustment of the optical power and/or prism of the lens may be facilitated by means of an actuation force, for example provided by an actuator, configured to move the lens body and/or the lens shaping element towards or away from the window element, particularly while the window element remains at a fixed position. Both embodiments provide a relative movement of the window element with respect to the lens shaping element and/or the lens body. 
     In other words, particularly, the optical power and/or prism of the lens may be adjusted by applying an actuation force to the lens shaping element, the window element or the lens body. The actuation force results in a relative motion of the window element and the lens shaping element. Said motion results in a displacement of the liquid in the lens volume, whereby the curvature of the first membrane in the lens area and/or the tilt of the first membrane in the lens area with respect to the window element is altered. 
     According to another embodiment of the invention, the lens comprises a housing, wherein the lens shaping element is rigidly, i.e. non-movable connected to the housing, wherein the window element is not connected to the housing or movably connected to the housing. 
     According to another embodiment of the invention, upon actuation, the housing is moved relatively to the window element, either by actuating the window element with respect to the fixed housing and/or by actuating the housing with respect to the fixed window element. The window element may be fixed to a holding device of the lens. 
     Even if the window element exhibits residual lateral movement relative to the lens body or housing upon actuation, the optical quality of the lens remains unaffected as the optical axis and the shape of curvature in the lens area is unaltered. 
     Moreover, actuation is not moving the lens shaping element relative to the lens body or housing which provides greater robustness and freedom of choice regarding the first and the second membrane. 
     Furthermore, impact of assembly tolerances on the position of the optical axis is reduced, because the position of the optical axis is essentially defined by the positon of the aperture of the lens shaping element. 
     Positioning tolerances of the window element on the second membrane do not affect the optical quality of the lens. 
     According to one embodiment, the lens comprises a prism function for deflecting a light beam relative to the optical axis of the lens. The prism function can be addressed by tilting the window element relative to the aperture of the lens shaping element. 
     According to an embodiment of the invention, the window element is formed as a planar plate. 
     According to an embodiment of the invention, the window element has a first planar surface that is fixedly connected, i.e. attached to the second membrane and a second surface that is facing in the opposite direction of the first planar surface. 
     According to an embodiment of the invention, the second surface of the window element is planar. In this case the window may introduce a prism capability but no optical power to the lens. 
     According to another embodiment of the invention, the first or the second surface of the window element is curved. In this case, the window element provides some additional optical power to the lens. In particular, the window element is a rigid lens, having a predefined optical power. 
     According to an embodiment of the invention, a z-axis of a Cartesian or cylindrical coordinate system extends orthogonally through the aperture of the lens shaping element. 
     According to an embodiment of the invention, an x-axis and a y-axis of a Cartesian coordinate system extend parallel to the aperture of the lens shaping element. 
     According to an embodiment of the invention, an optical axis of the lens extends orthogonally through the center of the aperture of the lens shaping element. 
     Depending on the physical requirement of the lens the relative sizes of the aperture and the second opening can be chosen. 
     The size of second opening essentially defines a stroke or force necessary for actuation of the window element, more precisely the actuation force and stroke depends on the size of the window element and the free portion of the second membrane as well as the stiffness of the second membrane. 
     It is noted that the actuation element is also referred to as piston shaper in the context of the specification. 
     It is further noted that the lens shaping element is also referred to as lens shaper in the context of the specification. 
     It is noted that the lens area does not need to be circular, but can have various shapes, such as oval, rectangular or polygonal. 
     It is further noted that the term deflection unit particularly refers to the lens area of the first membrane and to the lens shaping element in the context of the specification. 
     It is further noted that the term “container” particularly refers to the wall portion (see further below for details on the wall portion) with or without the lens shaping element in the context of the specification. 
     The lens shaping element may be also referred to as lens shaper in the context of the current specification. 
     With the lens according to the invention, either the window element might be actively moved with respect to a fixedly arranged lens shaping element or the fixedly arranged lens body. Movement of the window element might be facilitated with an actuator in order to adjust the optical power or the prism of the lens. 
     Alternatively, the lens body comprising the lens shaping element as well as the first and second membrane might be actively moved with respect to a fixedly arranged window element. Movement of the lens body, or the lens shaping element might be facilitated with an actuator in order to adjust the optical power or the prism of the lens. 
     It is noted that a movement of the lens shaping element alone, e.g. with respect to the first and the second membrane is not possible according to the invention, as the relation of the lens shaping element fixed with respect to the first membrane and the second membrane, particularly with respect to the lens body. This allows for the provision of a more robust lens with improved actuation properties as compared to liquid lenses where the lens shaping element is moved separately and relative to the lens body, e.g. the first membrane and the second membrane, and where the window element is in a fixed relation with respect to the lens body. 
     It is further noted, the relative movement of the window element with respect to the lens shaping element might be alternatively or additionally defined, if the lens comprises a wall portion, which disclosed for some embodiments of the invention. The relative movement in embodiments that have the wall portion may be defined by the window element being movable relative to the wall portion, wherein the lens shaping element remains at a fixed location and orientation with respect to the wall portion. The wall portion can be considered as being part of the lens body. 
     In the art, the lens shaping element is always moving relative to the wall portion. 
     In some embodiments the lens has an extension along the optical axis between 100 μm and 2 mm. 
     In some embodiments, the lens shaping element has an extension along the optical axis between 25 μm and 200 μm, particularly 100 μm. 
     In some embodiments, the window element has an extension along the optical axis between 50 μm and 200 μm, particularly 150 μm. 
     According to another embodiment of the invention, the lens volume is enclosed particularly exclusively, by the first and the second membrane only, wherein the first and the second membrane are connected in a sealing fashion to each other such as to form the lens volume, particularly wherein the first membrane and the second membrane are connected circumferentially at a lateral portion of the lens volume, particularly wherein the lateral portion extends circumferentially around the lens area of the first membrane and circumferentially around the free portion of the second membrane. 
     This embodiment provides a cushion-like lens, with no wall portion or rigid elements that might provide additional stability to the lens volume. This embodiment is therefore particularly light-weight and less-complex to manufacture. 
     Particularly, the lens shaping element is arranged between the lens area of the first membrane and the lateral portion. 
     This embodiment might also include a housing for rigid attachment of the lens shaping element, such that a motion of the window element relative to the lens shaping element does not cause the lens shaping element to move as well, such that actuation is not taking place efficiently. 
     According to another embodiment of the invention, the first membrane and the second membrane are integrally formed in form of a membrane sleeve that is sealingly connected at the openings of the membrane sleeve, particularly at the circumferential portion of the lens. 
     This embodiment allows for an even more facile manufacturing and provides a shorter seam length which in turn results in a more stable and robust lens. 
     The term sleeve in the context of the current specification particularly refers to a cylindrical or morphologically equivalent or similar geometry of a cylinder, wherein a cylinder wall is formed by the membrane that integrally comprises the first membrane and the second membrane. In other words, the membrane sleeve is a tube shaped membrane. 
     At the openings of the sleeve, the membrane is sealed in comprises the liquid of the lens. 
     According to another embodiment of the invention, the lens volume forms or comprises a first volume comprising the first liquid. 
     This embodiment allows for various types of lenses. According to a first alternative, the lens comprises only one liquid, namely the first liquid and the lens volume is the first volume. According to a second alternative, the lens comprises a plurality, for example two liquids that are both comprised in the lens volume, wherein the first liquid is comprised in the first volume and the other liquids are comprised in other (sub)-volumes of the lens volume. That is the lens volume might comprise a plurality of sub-volumes, when the lens comprises more than one liquid, wherein the first volume may be considered as a sub-volume of the lens volume as well. 
     According to another embodiment of the invention, the lens comprises a second liquid in a second volume, wherein the second volume is arranged at least partially on and/or completely centered around the optical axis of the lens, particularly along the z-axis of the lens, wherein the first liquid and the second liquid as well as the first volume and the second volume are separated from each other by a separating membrane portion. 
     The embodiment allows for acceleration-induced optical aberration compensation that for example occurs due to gravity. 
     By appropriately choosing the physical properties of the first and the second liquid acceleration-induced optical aberration compensation can be achieved. 
     Acceleration-induced optical aberrations may also be introduced by any force that attacks the lens obliquely to the optical axis. 
     According to this embodiment, the first and the second volume are essentially stacked on each other along the optical axis of the lens and are extending circumferentially around the optical axis of the lens. 
     The separating membrane portion may be a third membrane or it may be a particularly integral portion of the second membrane that is arranged such that it separates the first from the second volume. The latter is for example possible in case the second volume is arranged between a portion of the second membrane and the window element, wherein the second volume is sealed between said portion of the second membrane and the window element. 
     The first and the second volume are separated by each other in a liquid tight fashion, such that the liquids in the first and the second volume cannot exchange. It is noted that the membrane portion is not a liquid interface of the first and the second liquid but is made from a different material than the liquids. 
     According to another embodiment of the invention, the second liquid is arranged and sealed between the window element and the second membrane. In particular, the second membrane is connected with its second side only at a circumferential portion of the window element with the window element, thereby enclosing the second liquid between an integral portion of the second membrane and the window element, particularly wherein said integral portion forms the separating membrane portion, particularly wherein the separating membrane portion is in contact with the second liquid with a second side that corresponds to the second side of the second membrane and with the first liquid with a first side that corresponds to the first side of the second membrane. 
     Advantageously, this embodiment requires no third membrane and is thus less complex and more robust. 
     Moreover, upon actuation the second volume remains essentially at the same size and the integral portion of the second membrane (i.e. the separating membrane portion) does not change size which allows for low actuation forces, particularly as only the free portion of the second membrane and the lens area of the first membrane have to be changed in shape by a pressure change in the lens volume. 
     Particularly, the circumferential portion of the window element has a larger size than the clear aperture of the lens, particularly the clear aperture of the lens shaping element. Advantageously, the acceleration-dependent aberration compensation happens over the entirety of the clear aperture of the lens. In case the lens has a circular aperture, the circumferential portion of the second membrane surrounding the window element has a larger diameter than the clear aperture of the lens shaping element. In an analogue manner, this can be applied for different shapes of the clear aperture of the lens, particularly the clear aperture of the lens shaping element. 
     According to another embodiment of the invention, the separating membrane portion is comprised, particularly formed, more particularly integrally formed by a third membrane, wherein the third membrane has a first side and a second side, wherein the second side of the third membrane faces in the opposite direction than the first side of the third membrane. 
     This embodiment allows for a more differentiated structure of the lens volume in terms of separating the first from the second volume. For example, the third membrane may be attached to components of the lens, such as a wall portion, the first and/or the second membrane. 
     According to another embodiment of the invention, the first liquid is arranged between the first membrane and the third membrane. According to this embodiment, the first and the third membrane completely or partially limit the first volume. The third membrane may be attached to the first membrane such that the first volume is delimited by the first and third membrane only. For the perspective of manufacturing such a lens, there are several methods of producing such membrane-only first volume in conjunction with the second volume that might be formed as well from membranes only, e.g. by the first and the second membrane. 
     It is noted that all membranes are not solely liquid interfaces of the first and the second liquid but are made of a different materials than the liquids. 
     According to another embodiment of the invention, the second liquid, and thus the second volume is arranged between the third membrane and the second membrane. This embodiment complements for example the previous embodiment, where the first volume is arranged between the first and the third membrane. 
     Particularly, the lens volume is comprised between the first and the second membrane, wherein the third membrane is ranged inside the lens volume. 
     According to another embodiment of the invention, the second volume is comprised by the lens volume. 
     This embodiment is a clarification of the terms used in the specification. 
     According to another embodiment of the invention, the second volume is enclosed, particularly completely formed and enclosed by the third membrane and the second membrane. This embodiment might be used in combination with other embodiments to form a cushion-like lens which lens volume is essentially formed by membranes only. 
     According to another embodiment of the invention, the third membrane is circumferentially connected with its second side to the first side of the second membrane, particularly wherein the second volume with the second liquid is formed between a portion, particularly the window portion of the second membrane and a portion of the third membrane. 
     According to this embodiment, for example the second membrane is attached with its second side over an entire side of the window element to the window element and with the first side the second membrane faces the second volume. The third membrane in turn faces the second volume with its second side and with its first side the third membrane might face the first volume. Particularly, at some rim portions of the second and the third membrane, the membranes might be attached and sealingly connected to each other so as to form the second volume. 
     According to another embodiment of the invention, the third membrane is connected to the lens shaping element. 
     According to another embodiment of the invention, the first membrane is connected to the first side of the lens shaping element and wherein the third membrane is connected to the second side of the lens shaping element, such that the first volume is enclosed in the aperture of the lens shaping element. 
     This embodiment provides lateral structural stability to the first volume and the physical properties of the lens may be defined more precisely. Moreover, according to this embodiment, upon actuation both, the first and the third membrane (as well as the free portion of the second membrane) will be forced to change their curvature. This allows for additional optical power adjustment by the third membrane by exploiting changes in refractive index between the first and the second liquid. According to this embodiment, the curvature of the first and the third membrane will be either both convex or both concave. As both membranes are attached to the lens shaping element they exhibit the same clear aperture such that the clear aperture is perfectly overlapping and identical for both membranes, which allows for a high optical performance lens. The curvature of the first and the third membrane are moreover independent of a potential tilt of the window element and thus completely defined by the pressure change in the lens upon actuation and the clear aperture of the lens shaping element, which, to contributes to a high-quality lens. The actuation forces required for this embodiment are comparably higher, as according to this embodiment, three membranes have to be bent upon actuation (as compared to embodiments, where only two membranes, namely the first and the second membrane are bent). 
     According to another embodiment of the invention, the third membrane is circumferentially connected to the first membrane and the first volume is formed between the first membrane and the third membrane, particularly wherein the first side of the third membrane is in contact with the first liquid and the second side of the third membrane is in contact with the second liquid. Particularly, the first volume is formed by the first and the third membrane only. 
     According to this embodiment, actuation forces may be comparably low, as the third membrane is exposed only to very minor bending forces. 
     According to another embodiment of the invention, the third membrane is connected with its first side to the second side of the first membrane. 
     According to another embodiment of the invention, the first liquid has a first refractive index n 1  and the second liquid has a second refractive index n 2 , wherein the first and the second refractive index are different from each other. 
     This allows for various problems of the lens to be overcome. 
     One problem that may be solved with the two liquids having different refractive indices is temperature compensation of the optical power of the liquid lens. 
     According to another embodiment of the invention, the first liquid and the second liquid have different refractive indices, and the materials of the first liquid and the second liquid, the curvature of the membranes delimiting the first volume and the second volume are selected such that temperature-induced changes of the volume of the first and second liquid and temperature-induced changes of the refractive indices of the first and the second liquid are compensated, whereby the optical power of the lens remains essentially constant over a range of different temperatures. 
     For example, the first liquid may have a refractive index of 1.3±0.05 and the second liquid may have a refractive index of 1.45±0.05. Both, the first and the second liquid expand, when the temperature increases. Thereby, the curvatures of the membranes delimiting the first volume and the second volume respectively change in a similar fashion, when the temperature increases. Advantageously, a lens comprising two liquids with different refractive indices enables inherent temperature compensation, which results in a particularly reliable performance of the lens. 
     With differing refractive indices of the two liquids also acceleration-induced aberrations may be compensated or eliminated. 
     According to another embodiment of the invention, the first liquid has a first mass density and a first refractive index and the second liquid has second mass density and a second refractive index, wherein the first and the second refractive indices of the first and the second liquid as well as the first and the second mass densities are selected such that an acceleration-induced aberration of the lens, such as gravity-induced aberration, such as gravity coma or posture effects induced by orienting the lens along different directions with respect to gravity is compensated. 
     The person skilled in the art will understand that certain combinations of mass densities and refractive indices will behave just so that the optical path is adjusted by the two liquids such that said aberrations are compensated. 
     According to another embodiment of the invention, the second mass density of the second liquid is higher than the first mass density of the first liquid, and the second refractive index is smaller than the first refractive index of the first liquid or vice versa. 
     Such a combination of the physical properties of the liquids allows for acceleration-induced aberration compensation or at least reduction. 
     According to another embodiment of the invention, the first membrane has a first stiffness and the separating membrane portion, particularly the third membrane has a separating membrane portion stiffness, particularly wherein a thickness of the first membrane and the thickness of the separating membrane portion are essentially equal, wherein the first stiffness and the separating membrane portion stiffness are selected according to the relation 
     
       
         
           
             
               
                 k 
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                 k 
                 1 
               
             
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                     n 
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                     n 
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                     n 
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                   1 
                 
               
               ⁢ 
               
                 
                   
                     ρ 
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                     ρ 
                     1 
                   
                 
                 
                   ρ 
                   1 
                 
               
             
           
         
       
     
     wherein ρ 1  is the first mass density of the first liquid, ρ 2  is the second mass density of the second liquid, n 1  is the first refractive index of the first liquid and n 2  is the second refractive index of the second liquid. 
     According to another embodiment of the invention, the first membrane has a first thickness t 1  and the separating membrane portion has separating membrane portion thickness t s , particularly wherein a stiffness of the first membrane and a stiffness of the separating membrane portion are essentially equal, wherein the first thickness and the separating membrane thickness are selected according to the relation: 
     
       
         
           
             
               
                 
                   t 
                   s 
                 
                 
                   t 
                   1 
                 
               
               = 
               
                 
                   
                     
                       n 
                       1 
                     
                     - 
                     1 
                   
                   
                     
                       n 
                       1 
                     
                     - 
                     
                       n 
                       2 
                     
                   
                 
                 ⁢ 
                 
                   
                     
                       ρ 
                       2 
                     
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                       ρ 
                       1 
                     
                   
                   
                     ρ 
                     1 
                   
                 
               
             
             , 
           
         
       
     
     wherein ρ 1  is the first mass density of the first liquid, ρ 2  is the second mass density of the second liquid, n 1  is the first refractive index of the first liquid and n 2  is the second refractive index of the second liquid. 
     According to another embodiment of the invention, the stiffness of the first membrane and/or the stiffness of the separating membrane portion is/are in the range of 0.1 MPa and 10 MPa. 
     In this range one the one hand actuation forces are manageable and on the other hand membranes are rendered robust enough to last for a long time. 
     According to another embodiment of the invention, the membrane thickness of the first membrane and/or the thickness of the separating membrane portion is/are in the range of 2 μm and 200 μm. 
     This thickness range allows for a robust membrane and moderate actuation forces. 
     According to another embodiment of the invention, the first and/or the second refractive index is/are in the range of 1.26 and 1.6. Particularly, the first refractive index of the first liquid is in the range 1.3±0.05 and the second refractive index of the second liquid is in the range of 1.45±0.05. 
     According to another embodiment of the invention, the first and/or the second mass density is/are in the range of 1 kg*m −3  and 1.8 kg*m −3 . 
     According to another embodiment of the invention, the lens comprises an actuation element connected to the window element. Particularly the actuation element serves as a connection device for an actuation device. As such the actuation element may be integrally formed, glued to, or welded with the window element. 
     In some embodiments, the actuation element has an extension along the optical axis between 50 μm and 200 μm, particularly 100 μm. 
     The actuation element may have a clear aperture centered around the optical axis or may be asymmetrically formed with respect to the optical axis. 
     The actuation element may be formed from a different material than the window element or from the same material. The window element can be formed from glass or a transparent polymer. 
     According to another embodiment of the invention, the actuation element is connected, particularly in a rigid fashion to the window element at a circumferential portion of the window element, such that the window element can be tilted by the actuation element around at least one axis with respect to the aperture of the lens shaping element and/or translationally moved towards or away from the aperture of the lens shaping element. 
     Tilting of the window element may be achieved by providing an asymmetric force to the actuation element with respect to the optical axis of the lens. Tilting of the window element may be used in order to provide a prism function to the lens 
     Translation in turn may be achieved by providing a symmetric force to the actuation element. Translation of the window element along the optical axis may be used to adjust the optical power of the lens, as at least the curvature of the lens area of the first membrane is adjusted by such a translational motion of the window element. 
     According to another embodiment of the invention, the actuation element has a clear aperture enclosed by the actuation element such that light can pass through the clear aperture of the actuation element and through the window element. The clear aperture may be centered around the optical axis of the lens. Particularly, the clear aperture of the actuation element may be larger than the clear aperture of the lens shaping element. 
     According to another embodiment of the invention, the actuation element comprises a rigid portion and at least one damping element, wherein the damping element may be arranged at least partially between the window element and the rigid portion of actuation element, and/or wherein the damping element may be arranged at an outer portion of the rigid portion of the actuation element, wherein the damping element is softer than the window element and the rigid portion of the actuation element, pa wherein the damping element is connected to the window element, particularly at the circumferential portion of the window element. 
     The damping element for example allows for larger strokes for actuating the window element, which in turn allows for the use of a different kind of actuators that might be more cost-effective, due to reduced actuation-accuracy requirements. 
     Also the damping elements absorb external shocks. 
     According to another embodiment of the invention, the actuation element comprises a spring element such that an actuation force provided to the window element is transmitted via the spring element, particularly wherein the spring element is formed as an elastic metal sheet that extends essentially parallel to the window element. 
     The spring element particularly allows for larger strokes of the actuator, which leads to an increased actuation accuracy and tolerance and the manufacturing of the lens with less expensive actuators. 
     Moreover, the spring element may serve as an absorber for mechanical shocks. 
     According to another embodiment of the invention, the circumferential portion of the window element at which the actuation element is connected has a larger diameter, particularly a larger clear aperture than the aperture of the lens shaping element, particularly larger than the first opening of the wall portion (see further below), such that an optical path through the lens remains unobstructed by the actuation element, particularly wherein the diameter, particularly the clear aperture of the circumferential portion of the window element is so large that the optical path remains unobstructed by the actuation element, even if the actuation element is tilted with respect to the aperture of the lens shaping element. 
     When the apertures are circular the term diameter relates directly to the diameter of the circular aperture. If another shape of aperture is chosen for the lens, the aperture of the actuation element has to be so large that the actuation element does not obstruct the optical path through the clear aperture of the lens shaping element. 
     According to another embodiment of the invention, the lens shaping element is arranged fixed in space, while the window element is movably arrange din space, particularly wherein the lens shaping element is arranged fixedly at an external system or a housing or an optical system with respect to the movable window element, such that adjusting an optical power of the lens is facilitated by moving the window element relative to the lens shaping element that remains fixed in space, e.g. fixed relative to the external system, the housing or the optical system. 
     This embodiment essentially relates to a window element that is moved by an actuator. 
     Movement of the window element may comprise a tilting motion and/or a translational motion particularly parallel to or along the optical axis. 
     According to another embodiment of the invention, the lens body comprising the lens shaping element is configured to be actuated or moved, wherein the window element is fixedly arranged in space, while the lens body is arranged movably in space, wherein the window element may be rigidly connected to a housing of the lens, to an external system or to an optical system, such that adjusting an optical power or prism of the lens is facilitated by moving the lens body relative to the window element that remains fixed in space, e.g. fixed relative to the external system, the housing or the optical system. 
     According to another embodiment of the invention, the window element is configured to be actuated or moved, wherein the lens body, comprising the lens shaping element is fixedly arranged in space, while the window element is arranged movably in space, wherein the lens body and thus the lens shaping element may be rigidly connected to a housing of the lens, to an external system or to an optical system, such that adjusting an optical power of the lens is facilitated by moving the window element relative to the lens body that remains fixed in space, e.g. fixed relative to the external system, the housing or the optical system. 
     According to another embodiment of the invention, the lens comprises a lateral wall portion, particularly a rigid lateral wall portion extending circumferentially around the lens volume, particularly enclosing the lens volume at least laterally and/or radially, wherein the wall portion has a first side with a first opening facing toward the first membrane and a second side with a second opening opposite the first opening, wherein the second opening extends circumferentially around the free portion of the second membrane, particularly wherein the second side of the wall portion is connected, particularly bonded, plasma-bonded or glued, to the first side of the second membrane, thereby particularly sealing the first liquid in the lens volume, particularly wherein the lens shaping element is arranged at a fixed orientation and position with respect to the wall portion. 
     The wall portion is comprised by the lens body and has a fixed orientation relative to the lens body. 
     Particularly, an extension of the wall portion along the optical axis is in the range of 100 μm to 1.000 μm, particularly 350 μm. 
     The wall portion is particularly a structural stabilizing component of the lens. 
     The wall portion might be made of a non-transparent material such that stray light is reduced. 
     Thee wall portion might have a cylindrical or toroidal shape. 
     Depending on the lens design, the wall portion might also have polygonal or oval cross-section extending orthogonally to the optical axis. 
     The first and or second opening of the wall portion might differ from the clear aperture of the lens shaping element. 
     Particularly, the first and the second opening of the wall portion are centered on the optical axis of the lens, particularly the openings of the wall portion enclose the optical axis of the lens. 
     Particularly, the first and the second opening of the wall portion are concentrically arranged with respect to each other, centered on the optical axis of the lens. 
     According to another embodiment of the invention, the wall portion is connected with, particularly attached to the first side to the second side of the first membrane. 
     Connection may be facilitated by means of glue, bonding or welding techniques. 
     According to another embodiment of the invention, the lens shaping element is arranged inside the lens volume and circumferentially connected with the first side of the lens shaping element to the second side of the first membrane, thereby forming the lens area of the first membrane. In particular, the lens shaping element delimits the lens volume partially. For example, the lens shaping element is in direct contact with the liquid in the lens volume. 
     According to another embodiment of the invention, the aperture of the lens shaping element, particularly the lens area is smaller than the second opening of the wall portion. 
     According to another embodiment of the invention, the aperture of the lens shaping element, particularly the lens area is larger or of the same size than the second opening of the wall portion. 
     According to another embodiment of the invention, the third membrane is circumferentially connected to a wall portion and/or to the lens shaping element. The features of the wall portion are particularly defined in more detail in another embodiment. 
     According to another embodiment of the invention, the third membrane is connected with its first side to the first side of the wall portion. 
     According to another embodiment of the invention, the lens shaping element is connected, particularly with a second side of the lens shaping element to the first side of the wall portion. 
     This embodiment particularly comprises embodiments in which the lens shaping element is arranged inside the lens volume. 
     According to another embodiment of the invention, the wall portion is integrally formed with the lens shaping element, particularly wherein the first opening of the wall portion is formed by the clear aperture of the lens shaping element. In the same sense, the lens shaping element may be considered to be integrally formed with the wall portion, particularly wherein the aperture of the lens shaping element is formed by the first opening of the lateral wall portion. 
     This embodiment allows for a less complex lens manufacturing process, as fewer parts are required for lens assembly. 
     According to another embodiment of the invention, the lens shaping element is arranged on and connected to the first side of the first membrane, particularly wherein the lens shaping element is connected with its second side to the first side of the first membrane. 
     According to another embodiment of the invention, the first side of the wall portion is connected to the second side of the first membrane in a sealing fashion. 
     According to another embodiment of the invention, the aperture of the lens shaping element, particularly the lens area is smaller than the first opening of the wall portion. This embodiment allows for the lens to have a larger aperture on the side of the window element than on the side of the lens shaping element. Stray light may be reduced according to this embodiment. 
     According to another embodiment of the invention, the lens shaping element consists of a wall structure enclosing the aperture circumferentially, particularly wherein the wall structure has a toroidal shape, particularly wherein the wall structure forms a rectangular, square, oval, ellipsoid or circular aperture of the lens shaping element. According to this embodiment, the lens shaping element may be formed as a ring or a morphologically identical to a ring. 
     Particularly, the lens shaping element has an outer diameter and an inner diameter, wherein the inner diameter corresponds to the clear aperture of the lens shaping element. 
     The lens shaping element in this form is easy to manufacture, widely available and intrinsically stable. 
     According to another embodiment of the invention, the lens shaping element is a ring-shaped element, particularly wherein the ring-shaped element has a rectangular, square, oval, elliptical or circular aperture of the lens shaping element. 
     According to another embodiment of the invention, the lens shaping element is overlappingly arranged with the lateral wall portion, such that a rigid connection is formed between the wall portion and the lens shaping element or wherein the lens shaping element is arranged non-overlappingly with the lateral wall portion, particularly wherein the lens shaping element is connected to a part of the lens or an external member that may be arranged fixedly with respect to the window element. 
     According to another embodiment of the invention, the wall portion comprises a circumferential recess around the first opening, wherein the lens shaping element is arranged in the circumferential recess and connected to the wall portion, particularly wherein the lens shaping element is formed corresponding to a recess shape, such that a well-defined position with respect to the wall portion is adopted in the assembled state. This embodiment allows for a precise assembly of the lens during manufacturing. 
     According to another embodiment of the invention, the window element, particularly an area covered by the window element, more particularly the window portion of the second membrane, is larger than the aperture of the lens shaping element, particularly wherein the window element is larger than the aperture of the lens shaping element even if the window element is tilted with respect to the aperture of the lens shaping element. 
     This embodiment essentially renders the window element invisible at any orientation with respect to the clear aperture of the lens shaping element, as no edges of the window element can interfere with the incident light propagating through the lens. 
     According to another embodiment of the invention, the second opening of the wall portion is larger, smaller or equal in size than the first opening of the wall portion. 
     According to another embodiment of the invention, the first and the second opening of the wall portion extend parallel to each other, particularly in an x-y plane, particularly orthogonally to a z-axis of the lens. 
     According to another embodiment of the invention, the wall portion comprises a step-like contour, e.g. a discontinuity in the contour, between the first and the second opening at which the diameter of the wall portion changes, particularly wherein the step is formed by a protrusion of the wall portion that extends along a plane parallel to the first and the second opening of the wall portion, particularly wherein the protrusion is formed by the lens shaping element. 
     This embodiment allows for a larger degree of stray light reduction. 
     According to another embodiment of the invention, the first membrane has a first stiffness k 1  and/or a first thickness and the second membrane has a second stiffness k 2  and/or a second thickness, wherein the second stiffness k 2  and/or the second thickness is smaller than the first stiffness k 1  and/or the first thickness. 
     This embodiment allows for comparably low actuation forces, as the bending of the free portion of the second membrane may be facilitated with little force, while the first membrane is rendered comparably robust due to its increased stiffness/thickness as compared to the second membrane. 
     According to another embodiment of the invention, the first membrane has a first thickness t 1  and the second membrane has a second thickness t 2 , wherein the second thickness t 2  is smaller than the first thickness t 1 . 
     This embodiment allows for comparably low actuation forces, as the bending of the free portion of the second membrane may be facilitated with little force, while the first membrane is rendered comparably robust due to its increased stiffness/thickness as compared to the second membrane. 
     According to another embodiment of the invention, the lens shaping element forms the lateral wall portion for the lens volume, the first volume and/or the second volume. 
     According to another embodiment of the invention, the lens comprises the components of
         the actuation element that is rigidly connected, particularly attached to the window element, wherein said actuation element extends laterally from the window element with a lateral mover element beyond the wall portion and comprises a coil portion that is that is arranged laterally beyond the wall portion on the lateral mover element, wherein said coil portion comprises one or more coils, wherein said one or more coils are arranged such on the coil portion that the one or more coils extend with a coil axis of the at least one coil along the wall portion, particularly towards a lateral plane of the lens shaping element, particularly essentially parallel to the z-axis of the lens,   for each coil a corresponding magnetic portion, wherein said magnetic portion is arranged at the wall portion of the lens, such that a Lorentz force can be induced in the at least one coil that provides a tilting force to the actuation element and thereby to the window portion, such that a refractive power of the lens can be adjusted.       

     This embodiment of the lens allows for Lorentz force-induced actuation of the lens. 
     The coils particularly extend circumferentially around the lens volume with their respective coil axes essentially parallel to the optical axis of the lens. 
     Upon actuation of the lens, it might be that at least some coils will adopt a slightly tilted state with respect the optical axis. This tilt movement and also the lateral movement of the coils along the optical axis might be limited by a hard stop. 
     Particularly, the magnetic portion comprises at least one magnet, particularly one permanent magnet or a plurality of magnets that are correspondingly arranged to the coils at the wall portion. 
     This embodiment allows for robust actuation of the lens even in the presence of other, external magnetic fields. 
     According to another embodiment of the invention, the lens comprises a hard stop portion rigidly connected to the lens with respect to the shaping element, wherein the hard stop portion extends laterally over the coil portion at a distance, such that a movement along at least one direction of the z-axis of the coil portion particularly the mover element is mechanically limited by said distance between the coil portion and the hard stop element. 
     This embodiment provides a mechanical shock protection as well as an overdrive-protection for the lens, in case a control signal for the coils would cause the lens to be adjusted beyond an adjustment range. 
     According to another embodiment of the invention, the lens comprises a mechanical stop device that is arranged such at the lens that movement of the window element with regard to a fixedly arranged lens body, particularly the fixedly arranged lens shaping element along the optical axis and/or a movement orthogonally to the optical axis is limited by the mechanical stop device, particularly along a back and forth direction, or wherein the stop device is arranged such at the lens that a movement of the lens body, particularly the lens shaping element with respect to the fixedly arranged window element along the optical axis and/or a movement orthogonally to the optical axis is limited by the mechanical stop device, particularly along a back and forth direction. 
     For example, the stop device limits the relative motion of the window element and the lens shaping element along the optical axis. In particular, the stop device does not limit a tilt of the window element with respect to the lens shaping element. This embodiment allows for mechanical shock protection and overdrive states of the lens, particularly when the lens is built-in optical systems. 
     According to another aspect of the invention, the problem is solved by a lens barrel comprising an optical assembly, with at least one solid lens having a fixed focal length, and wherein the lens barrel further comprises the lens according to any of the preceding embodiments. 
     The lens barrel particularly comprises a rigid barrel wall that circumferentially encloses the optical assembly as well as the lens according to the invention, wherein the optical assembly and the lens are fixedly arranged in the lens barrel, such that the lens barrel may be used in an optical system as a pre-manufactured electro-optical component. 
     According to another embodiment of the lens barrel, the liquid lens is arranged at a first and/or a second opening of the lens barrel as the first optical component (apart from protective optical elements such as transparent windows), particularly wherein the optical assembly is arranged completely optically behind or in front of the liquid lens in the lens barrel. 
     The term optical component therefore particularly relates to an optical element that is configured to change the wavefront of incident light. 
     According to one embodiment, the lens may be altered from a negative to a positive lens by actuation or the lens may be changed from a positive lens to a negative lens by actuation. 
     For example, in a non-actuated state of the lens, the first membrane is concavely curved, and upon actuation the first membrane becomes convexly curved. Alternatively, the in a non-actuated state of the lens, the first membrane is convexly curved, and upon actuation the first membrane becomes concavely curved. Advantageously, switching between a negative and a positive lens enables a particularly large tuning range and a versatile application of the tunable lens. 
     According to a second aspect to the invention, the problem is solved by an optical system, comprising the lens according to any of the previous embodiments, wherein the system comprises at least one lens, i.e. a conventional rigid glass or polymer lens having a fixed focal length and an optical sensor, particularly an image sensor, arranged along an optical axis of the system, wherein the liquid lens and the at least one solid lens are fixedly arranged in a lens barrel, particularly the lens barrel, along the optical axis of the system, particularly wherein the first membrane of the liquid lens is closer to the sensor than the second membrane of the liquid lens. 
     According to another aspect of the invention, the problem is also solved by a reluctance motor assembly for adjusting the optical power of the liquid lens according to the invention. 
     According to another embodiment of the invention, the reluctance motor assembly is comprised by the optical system. 
     According to another embodiment of the invention, the optical system is a wide-angle, a macro-, a tele-, or a zoom-system. 
     According to another embodiment of the invention, the optical system comprises a first optical assembly with at least one lens having a fixed focal lens, and a second optical assembly comprising at least one lens having a fixed focal length, wherein the first and the second optical assembly are connected to a rigid lens barrel, particularly the lens barrel, wherein the liquid lens is arranged between the first and the second optical assembly with respect to the optical path of the optical system. 
     According to another embodiment of the invention, the system comprises a first control circuit that is configured to provide an electronic signal to an actuation assembly of the liquid lens configured to tilt the window element of the lens in response to a movement of the optical system such that an image on the sensor is stabilized, particularly wherein the first control circuit is configured to control a position of the at least one lens having fixed focal length. 
     This embodiment allows for image stabilization for example in hand-held devices such as mobile phone comprising an image sensor, such as a camera. 
     According to another embodiment of the invention, the liquid lens is arranged in the system for focusing an image to the sensor. 
     According to another embodiment of the invention, the liquid lens is arranged in the system for stabilizing an image position on the sensor. 
     Image stabilization can be achieved by tilting the window element in response to a recorded motion of the system accordingly. 
     As actuation of the lens is comparably fast, image stabilization is achieved fast as well such that sharper images may be acquired with the optical system. 
     According to another aspect of the invention, the problem is solved by a method, particularly a computer-implemented method for controlling the optical properties such as the optical power as well as prism of a liquid lens or an optical system according to the invention, wherein the method comprises the steps of:
         in response to a first control signal provided by a computer or a processor unit causing an actuation assembly particularly comprising the actuation element connected to the window element to tilt the window element relative to the aperture of the lens shaping element such that a light beam is deflected with respect to an optical axis of the liquid lens, and/or   in response to a second control signal provided by the computer or the processor unit causing the actuation assembly to move the window element translationally, particularly along the optical axis, with respect to the aperture of the lens shaping element such that an optical power of the liquid lens is adjusted.       

     According to another aspect of the invention, the problem is solved by a method, particularly a computer-implemented method for controlling the optical properties such as the optical power as well as prism of a liquid lens or an optical system according to the invention, wherein the method comprises the steps of:
         in response to a first or third control signal provided by a computer or a processor unit causing an actuation assembly connected to the lens body and/or the lens shaping element to tilt the lens body and/or the lens shaping element relative to window element, and/or   in response to a second or fourth control signal provided by the computer or the processor unit causing the lens assembly to move the lens body and/or the lens shaping element translationally, particularly along the optical axis, with respect to the window element such that an optical power of the liquid lens is adjusted.       

     The Figures are appended to the claims and are accompanied by text explaining individual features of the shown embodiments and aspects of the present invention. Each individual feature shown in the Figures and/or mentioned in said text of the Figures may be incorporated (also in an isolated fashion) into a claim relating to the device according to the present invention. 
     In  FIG.  1 A  a schematic cross-section through a lens  1  according to the invention is shown. The lens  1  has on optical axis OA that extends along a z-axis of a Cartesian coordinate system (indicated as arrows with x, y and z). Laterally, the lens  1  extends along the x and y-axis of said coordinate system. While the x axis can point along the picture plane, the y axis might point outward the picture plane or vice versa. 
     The lens  1  comprises a lens volume VL that is enclosed by the first membrane  21 , the second membrane  22  and a rigid lateral wall portion  4  as well as the lens shaping element  3 . 
     The lateral wall portion  4  and the lens shaping element  3  are formed integrally with each other in the embodiment of  FIG.  1 A . 
     Nonetheless, for reasons of consistency with other embodiments of the lens  1 , the lens shaping element  3  and the wall portion  4  are treated as different members of the lens  1 . The wall portion  4  has a first side  4 - 1  (cf.  FIG.  4   ) facing toward the first membrane  21  and a second side  4 - 2  facing in the opposite direction. The wall portion  4  comprises a first opening  4   a  on the first side  4 - 1  and a second opening  4 - 2  on the second side  4 - 2 . The lens shaping element  3  has a clear aperture  3   a  comprising the optical axis OA of the lens  1 , such that a clear lens area  21   a  for the first membrane  21  is formed, wherein in the lens area  21   a  of the first membrane  21  is deformable and light can propagate through the lens  1  via the lens area  21   a.    
     The lens shaping element  3  is formed as a ring-shaped member with a clear aperture  3   a  that encircles the lens area, wherein the wall portion  4  is formed as a ring-shaped member as well. 
     The wall portion  4  and the lens shaping element  3  extend circumferentially around the optical axis OA of the lens  1 . 
     The first membrane  21  is a transparent distensible, i.e. an elastically deformable membrane, and has a first side  21 - 1  that faces away from the lens volume VL and a second side  21 - 2  that faces towards the lens volume VL. 
     The first membrane  21  is sealingly and circumferentially attached with its second side  21 - 2  to a first side  3 - 1  of the lens shaping element  3 . 
     The opening  4   a ,  4   b  of the wall portion  4  is larger than the aperture  3   a  of the lens shaping element  3 . The second membrane  22  is sealingly and circumferentially connected with a first side  22 - 1  of the membrane  22  to the second side  4 - 2  of the wall portion  4  and covers the second opening  4   b  of the wall portion  4 . 
     The second membrane  22  is a transparent and distensible membrane. 
     The first side  22 - 1  of the second membrane  22  faces toward the lens volume VL and a second side  22 - 2  of the second membrane  22  faces away from the lens volume VL. 
     The first side  22 - 1  of the second membrane  22  and the second side  21 - 1  of the first membrane  21  are in direct contact with a first liquid L 1  of the lens  1  that is enclosed in the lens volume VL by the first and second membrane  21 ,  22  and the wall portion  4  as well as the lens shaping element  3 . 
     A rigid, transparent window element  5  is connected to the second membrane  22  at the second side  22 - 2  of the second membrane  22 . 
     The window element  5  extends symmetrically around the optical axis OA over a window portion  22   a  of the second membrane  22 . The window portion  2   a  of the second membrane  22  is circumferentially enclosed by a free portion  22   b  of the second membrane  22  that is not covered by the window element  5 , such that the window element can be moved along the z-axis and to some extend also laterally along the x- and/or y-axis. Any motion of the window element  5  will cause the free portion  22   a  of the second membrane  22  to bend in order to allow the motion of the window element  5 . 
     Thus, the window element  5  is not directly connected (but only via the free portion  22   a  of the second membrane  22 ) to the wall portion  4  or the lens shaping element  3  and can therefore move relatively to the wall portion  4  as well as to the lens shaping element  3 . 
     An actuation element  6  is rigidly connected to the window element  5  at a connecting portion  5   b  and forms a clear aperture  5   a  of the window element  5 . The clear aperture  5   a  comprises the optical axis OA of the window element  5 . 
     The actuation element  6  extends laterally away from the window element  5  and allows an actuation force to be provided to the window element  5 . 
       FIG.  1 A  shows the lens  1  when no actuation force is applied to the actuation element  6 . 
       FIG.  1 B  shows the same lens as depicted in  FIG.  1 A , but with an actuation force (indicated by the arrows A next to the actuation element  6 ) applied to the actuation element  6 . On one side the actuation force pushes the window element  5  towards the clear aperture  3   a  of the lens shaping element  3  and on the other side of the window element  5  (facing outward the lens volume VL), the window element  5  is pulled away from the aperture  3   a  of the lens shaping element  3 . 
     As can be seen, the free membrane portion  22   b  of the second membrane  22  bends and stretches accordingly. 
     In the situation shown in  FIG.  1 B  a net movement of the window element  5  toward the clear aperture  3   a  of the lens shaping element  3  is achieved, which eventually produces a bending force also on the first membrane  21  such that the first membrane  21  is pushed away at the lens area  21   a  from the aperture  3   a  of the lens shaping element  3  forming a symmetric convex membrane surface Therefore, by moving the window element  5 , the refractive power of the lens  1  can be adjusted. 
     Despite the asymmetric tilted state of the window element  5  with respect to the wall portion  4  and the lens shaping element  3 , the bending of the lens area  21   a  of the first membrane  21  occurs symmetrically around the optical axis OA of the lens  1 . Particularly, the clear aperture  3   a  of the lens shaping element  3  defines the optical axis OA of the lens  1  independently of the actuation state of the window element  5 . This allows for greater manufacturing and assembly tolerances for the lens  1 . Also, with respect to the actuation of the window element  5 , greater tolerance is achieved by having the first and/or the second opening  4   a ,  4   b  of the wall portion  4  larger than the clear aperture  3   a  of the lens shaping element  3 . Particularly, the window element  5  has a larger aperture  5   a  than the clear aperture  3   a  of the lens shaping element  3 , which allows for even greater manufacturing tolerance without affecting the optical quality of the lens  1 . 
     The advantage of window element  5  moving with respect to the lens shaping element  3  is that the deformation of the lens area  21   a  is always symmetric with respect to the optical axis OA, independent of any asymmetric motion are lateral shift (e.g. along the x or y axis) of the window element  5  with respect to the lens shaping element  3 . This allows for a better optical performance of the lens  1  according to the invention, particularly any lateral offset of wave front propagating through the lens  1  due to a non-centered and/or non-symmetric surface shape of the lens area  21   a  is prevented. 
     In configurations known in the art, where the lens shaping element is moved relative the wall portion (or the window element), any lateral shift or asymmetric motion of the lens shaping element causes a correspondingly asymmetric deformation of the first membrane. 
     To illustrate this, in  FIG.  10    the same lens  1  is shown, but this time an actuation force is applied that pushes the window element  5  toward the aperture  3   a  of the lens shaping element  3  on both sides to the same extent. 
     Due to the incompressible first liquid L 1  in the lens volume VL, the actuation force causes the lens area  21   a  to bend outward of the aperture  3   a  of the lens shaping element  3 . The shape of the lens area  21   a  is symmetric to the optical axis OA as well. 
     Thus, by tilting the window element  5  accordingly, a wave front of light propagating through the lens  1  can be adjusted such as to compensate for slight offsets with regard to the optical axis of the lens  1  in a lens assembly or an optical system. In other words, an additional prism function can be integrated in the lens  1  by asymmetric actuation of the window element  5 . 
     With the lens  1  it is also possible to achieve negative refractive power, by pulling the window element  5  away from the aperture  3   a  of the lens shaping element  3 , which causes the lens area  21   a  to deform in a symmetric concave fashion. This is shown in  FIG.  1 D . 
     The second membrane  22  might be softer, i.e. less stiff, than the first membrane  21 , which allows for lower actuation forces of the lens  1 . 
     Moreover, a geometric extension along the z-axis of the lens  1  is reduced by having the lens shaping element  3  fixed relative to the movable window element  5 . 
     In  FIG.  2    a similar lens  1  as in  FIG.  1 A  is shown in equilibrium state by means of a schematic cross-sectional view of the lens  1 . In contrast to  FIG.  1   , in  FIG.  2    the aperture  3   a  of the lens shaping element  3  and the openings  4   a  and  4   b  of the wall portion  4  have the same size. Thus, the lens shaping element  3  and the wall portion are essentially formed as a cylinder. 
     It is noted that the aperture  5   a  on the window element  5  of actuation element  6  is smaller than the lens area  21   a.    
     This allows for an additional aperture function of the lens  1  provided by the aperture  5   a  that reduces stray light and ghosting effects of the lens  1 . 
     In  FIG.  3    an embodiment of the lens is shown, where the openings  4   a ,  4   b  of the wall portion  4  are smaller than the clear aperture  3   a  of the lens shaping element  3  and thus the lens area  21   a . This provides some additional aperture to the lens  1  that is particularly useful when the lens  1  is used for large incidence angles of light entering the lens  1  from the side of the window element  5 . This design suppresses stray light caused by large incident angles of light due to the smaller opening  4   a ,  4   b  of the wall portion  4 . 
       FIG.  4    shows an embodiment similar to the embodiment of  FIG.  1   , with the difference that the wall portion  4  and the lens shaping element  3  are formed as separate members that are connected to each other, e.g. by means of glue. 
     This allows for manufacturing the wall portion  4  and the lens shaping element  3  from different materials, particularly wherein the lens shaping element  3  might comprise a metal compound or a magnetic compound that might be essential used for an actuation capability of the actuation element  6 . 
       FIG.  5    shows an embodiment in which the lens shaping element  3  is arranged outside the lens volume VL. The wall portion  4  now forms the lateral container walls that enclose the lens volume VL in which the first liquid L 1  is comprised. 
     The first side  4 - 1  of the wall portion  4  is circumferentially and sealingly connected with the second side  21 - 2  of the first membrane  21  and the second side  4 - 2  of the wall portion  4  is circumferentially connected with the second side  22 - 2  of the second membrane  22 . 
     The first opening  4   a  of the wall portion  4  is smaller than the second opening  4   b  of the wall portion  4 . The wall portion  4  is essentially formed from two ring shaped portions having different diameter. 
     The lens shaping element  3  is connected with a second side  3 - 2  to the first side  21 - 1  of the first membrane  21 . The aperture  3   a  of the lens shaping element  3  is slightly smaller than the first opening  4   a  of the wall portion  4 . 
     The lens shaping element  3  is connected rigidly via the first membrane  21  to the wall portion  4  by having an overlapping portion with the wall portion  4 . 
     It is noted that the window element  5  and the corresponding aperture  5   a  is larger than the aperture  3   a  of the lens shaping element  3 , such that in a tilted actuation configuration of the window element  5 , the clear aperture  3   a  of the lens shaping element  3  is not obstructed or affected by the actuation element  6 . 
     In  FIG.  6    a similar embodiment of the lens  1  of  FIG.  5    is shown, wherein the lens shaping element  3  is arranged non-overlappingly with the wall portion  4 . The lens shaping element  3  can be fixed relative to the wall portion by a housing member (not shown) of the lens  1  or another external component (not shown). This embodiment allows for defining the clear aperture of the lens  1  by an external component (i.e. the lens shaping element  3 ) during assembly of the lens, which increases manufacturing tolerances during assembly and which provides increased flexibility for using differently shaped lens shaping elements  3  without the necessity of a redesign of the lens  1 , i.e. the body of the lens  1  remains the same, while the size and shape of the lens area  21   a  can be defined by choosing the appropriate lens shaping element  3  with an appropriate shaped clear aperture  3   a  (e.g. circular, rectangular or oval). 
     In  FIG.  7    another embodiment regarding the lens shaping element  3  and the wall portion  4  is shown. 
     The wall portion  4  comprises a recess in which the lens shaping element  3  is comprised inside the lens volume VL. This allows for a larger contact area of the lens shaping element  3  to the wall portion  4 , which in turn allows for a more stable connection between the lens shaping element  3  and the wall portion  4 . Moreover, the lens shaping element  3  might be made from a different material than the wall portion  4 . 
       FIG.  8    shows a similar embodiment as shown in  FIG.  1   . 
     In addition to the embodiment of  FIG.  1   , the actuation element  6  comprises a rigid portion  6   a  that extends laterally along a plane of the window element  5  without obstructing the window aperture  5   a . The rigid portion  6   a  might be ring-shaped or arm-shaped. The rigid portion  6   a  is connected to the window element  5  via a damping element  6   b  and at its outer portion the rigid portion  6   a  has another damping element  6   c  arranged. The damping elements  6   b ,  6   c  are softer than the rigid portion  6   a  of the actuation element  6  and the window element  5  and are configured to absorb vibrations and to provide a larger stroke of the actuation element  6  that is only partially translated to the lens area  21   a . A larger stroke of the actuation element  6  in turn increases an actuation sensitivity of the lens  1 , as the stroke is partially absorbed (e.g. by a deformation/compression/extension) by the damping elements  6   b ,  6   c , when the window element  5  is moved from its equilibrium position. This in turn allows to use actuators having a lower stroke resolution and that are more cost efficient. 
     As similar effect can be achieved with a lens  1  as shown in  FIGS.  9 A and  9 B . 
     Here, the actuation element  6  comprises a spring element  6   s  extending laterally from the window element  5 . Here, the spring element  6   s  allows for the larger stroke of the actuation element  6 . The stroke (i.e. movement of the actuation element  6 ) is not fully translated to the lens area  21   a  but is partially absorbed by a deformation of the spring element  6   s  as can be seen in  FIG.  9 B . 
       FIG.  10    shows an embodiment of the lens  1  devoid of the rigid wall portion  4 . 
     The lens volume VL with the first liquid L 1  is completely enclosed by the first membrane  21  and the second membrane  22  only. 
     In a first variant, the first  21  and the second membrane  22  are two separate membranes that are sealingly and circumferentially connected, e.g. glued or plasma-bonded, at a lateral membrane portion  21 - 22  of the lens volume VL, wherein the lateral portion  21 - 22  extends circumferentially around the lens area  21   a  of the first membrane  21  and circumferentially around the free portion  22   b  of the second membrane  22 . 
     This allows using different membranes for the first  21  and the second membrane  22 . 
     In another variant, the first  21  and the second membrane  22  are integrally formed, e.g. by a sleeve-like membrane and sealed at the openings of said sleeve. 
     The lens shaping element  3  is arranged outside the lens volume VL (but could also be arranged inside the lens volume VL) as shown in previous embodiments. 
     Upon actuation of the window element  5  relative to the lens shaping element  3  the lens area  21   a  bends outwards or inwards. At the same time, it might be that the lateral portion  21 - 22  and/or the free portion  22   b  also bend. This provides a damping effect, which in turn allows for larger stroke actuation resulting in a higher actuation resolution of the lens  1 . 
     The lens  1  according to this embodiment can be manufactured comparably cost-efficient as no wall portion is needed. 
     In the following, several advanced embodiments of the lens  1  according to the invention are described that can be combined with the embodiment of the  FIGS.  1  to  10   . The lens  1  according to some embodiments can be configured to compensate for acceleration-induced aberrations, such as gravity-induced coma. 
     For this purpose, the lens  1  comprises a first volume V 1  comprising the first liquid L 1  and a separate second volume V 2  with a second liquid L 2 . Thus, the lens volume VL is split into the first V 1  and the second volume V 2 . 
     The physical properties of the first and the second liquid L 1 , L 2  might be chosen such that the acceleration-induced aberrations are compensated. Such physical properties comprise the refractive index n 1 , n 2  as well as the mass density ρ 1  ρ 2  of the first and the second liquid L 1 , L 2 . Simultaneously, it is possible to adjust some properties of the first and the second membrane  21 ,  22  as well as a third membrane portion  20 ,  23 , such properties being for example the stiffness of the membranes or to adjust the thickness of the membranes that in turn might influence the stiffness of the membranes. 
     An example of one of such lens  1  that is configured to compensate acceleration in-induced aberrations is shown in  FIG.  11   . As many features of the lens of  FIG.  11    are identical to the features of  FIG.  1    only the differing features are elaborated in detail in order to avoid redundancy. It is obvious that also embodiments shown in  FIGS.  2  to  10    can be modified accordingly in order to provide the acceleration-induced aberration compensation. 
     The lens  1  of  FIG.  11    differs from the lens of  FIG.  1    in that the lens  1  additionally comprises a separating membrane portion  20 ,  23  that essentially divides the lens volume VL in the first volume V 1  comprising the first liquid L 1  and the second volume V 2  comprising the second liquid L 2 . The first and the second volume V 1 , V 2  are arranged such that along the optical axis OA and particularly over the complete lateral extent of the window element aperture  5   a  a layer of the first and second liquid L 1 , L 2  is arranged. 
     The separating membrane portion  20  has a first side  20 - 1  facing the first volume V 1  and that is in contact with the first liquid L 1  and a second side  20 - 2  that faces in the opposite direction and that is in contact with the second liquid L 2 . 
     In the embodiment of  FIG.  11    the separating membrane portion  20  is a separate third membrane  23 , with corresponding sides  23 - 1  and  23 - 2 . The third membrane  23  is sealingly and circumferentially connected with its second side  23 - 2  to the first side  22 - 1  of the second membrane  22 , such that the second volume V 2  is formed by the third  23  and the second membrane  22  only. The second  22  and the third membrane  23  can be connected for example by means of plasma bonding or glue. 
     The second membrane  22  and in some embodiments the third membrane  23  cover the second opening  4 - 2  of the wall portion  4  and thus, seals the first liquid L 1  together with the wall portion  4  and the first membrane  21  that covers the clear aperture  3   a  of the lens shaping element  3  such that the first volume V 1  is formed. 
     The window element  5 , as in  FIG.  1   , is connected to the second side  22 - 2  of the second membrane  22  on one side of the window element  5 . 
     Other features of the lens  1  of  FIG.  11    are essentially identical to the features of  FIG.  1   . 
     In response to a relative motion that changes the net volume of the lens volume VL of the window element  5  with respect to the lens shaping element  3 , the lens area  21   a  bends and forms either a concave or convex surface lens surface. The membrane shape of the third membrane  23  and the second volume V 2  is hardly affected by such a motion. 
     Therefore, the robust and accurate adjustment of the curvature of the lens area  21   a  that have been elaborated for the previous embodiments are maintained. In addition, the lens  1  of  FIG.  11    is configured to compensate for the acceleration-induced aberrations that might be caused by gravity or another accelerating force. 
     For this compensating effect to take place in a non-trivial fashion, the force has to have a force component that is not in alignment with the optical axis OA of the lens  1 . 
     By adjusting the refractive index n 1 , n 2  of the first and the second liquid L 1 , L 2  with respect to the first ρ 1  and the second mass density ρ 2  of the liquids L 1 , L 2 , such acceleration-induced aberrations can be compensated. 
     For example, the refractive index n 1  of the first liquid L 1  might be chosen higher than the refractive index n 2  of the second liquid L 2 , while the mass density ρ 1  of the first liquid L 1  is chosen to be smaller than the mass density ρ 2  of the second liquid L 1 . 
     This allows adjusting the optical path length through the lens volume VL such that the acceleration-induced aberrations can be compensated to full extend. 
     In addition, a relation between membrane stiffness k s  of third membrane  23  or the separating membrane portion  20  and the stiffness k 1  of the first membrane  21  can be found according to 
     
       
         
           
             
               
                 k 
                 s 
               
               
                 k 
                 1 
               
             
             = 
             
               
                 
                   
                     n 
                     1 
                   
                   - 
                   
                     n 
                     2 
                   
                 
                 
                   
                     n 
                     1 
                   
                   - 
                   1 
                 
               
               ⁢ 
               
                 
                   
                     ρ 
                     2 
                   
                   - 
                   
                     ρ 
                     1 
                   
                 
                 
                   ρ 
                   1 
                 
               
             
           
         
       
     
     Other relations relating thicknesses of the membranes  20 ,  23 ,  21  to the refractive indices n 1 , n 2  are given at another part of the specification and can be applied to this embodiment as well. 
     A variation of the embodiment of  FIG.  11    is shown in  FIG.  12   . Here, the separating membrane portion  20  is integrally formed  22   c  with the second membrane  22 . In order to provide the second volume V 2  the second membrane  22  is sealingly connected with its second side  22 - 2  to the window element  5  only at a circumferential portion  5   c  of the window element  5 , such that a volume is formed between an integral portion  22   c  of the second membrane  22  and the window element  5 . Thus, the second side  22 - 2  of the second membrane  22  faces the second volume V 2  over the area of integral portion  22   c.    
     For this embodiment, no third membrane is required, which reduces manufacturing costs. 
     The relation for the stiffness and thickness of the membranes might be applied for the first and the second membrane  21 ,  22  accordingly. 
     The embodiments shown in  FIGS.  11  and  12    allow for lower actuation forces and thus lower power consumption, as the third membrane  23  or the integral membrane portion  22   c  is not bent upon actuation of the window element  5 , but only the lens area  21   a  of the first membrane  21  (and the free portion  22   b  of the second membrane  22 ). 
     In  FIG.  13    another embodiment of the lens  1  according to the invention is shown having an acceleration-induced aberration compensation. 
     The lens  1  comprises a third membrane  23  as the separating membrane portion  20 . 
     In contrast to the embodiments of  FIGS.  11  and  12   , in  FIG.  13    the third membrane  23  is arranged along the optical axis OA between the wall portion  4  and the lens shaping element  3  and separates the lens volume into the first V 1  and the second volume V 2 , wherein with a first side  23 - 1  of the third membrane  23 , the third membrane  23  is in contact with the first liquid L 1  and with a second side  23 - 2  of the third membrane  23 , the third membrane  23  is in contact with the second liquid L 2 . 
     The first membrane  21  seals the lens volume VL and in particular the first volume V 1  at the first side  3 - 1  of the lens shaping element  3 , where the lens area  21   a  is formed by the clear aperture  3   a , wherein the second membrane  22  seals the lens volume VL and in particular the second volume V 2  at the second side  4 - 2  of the wall portion  4 . 
     Therefore, the first liquid L 1  is enclosed in the first volume V 1  formed by the first membrane  21 , the third membrane  23  and the lens shaping element  3 , wherein the second liquid L 2  is enclosed in the second volume V 2  formed by the second membrane  22 , the third membrane  23  and the wall portion  4 . 
     For assembly, the third membrane  23  is connected between the lens shaping element  3  and the wall portion  4 , particularly between the second side  3 - 2  of the lens shaping element  3  and the first side  4 - 1  of the wall portion  4 . The lens shaping element  3  and the wall portion  4  might be formed from different materials. Particularly, the wall portion  4  might comprise a permanent electro-magnetic compound and might be shaped in a non-round fashion (when viewed along the z-axis), while the actuating element  6  might comprise a corresponding metal compound such that a reluctance driving force can be induced by these two elements causing the actuation element  6  to move relatively to the wall portion  4  and thus adjustment of the refractive power of the lens  1  can be achieved. Alternatively, the actuation element  6  is comprises a permanent electro-magnetic compound and the wall portion  4  is made of a metal compound, such as steel. For this purpose, one or more coils (not shown) might be arranged next to the wall portion  4 . The lens shaping element  3  might be made of glass or a polymer. 
     The embodiment shown in  FIG.  13    causes the third membrane  23  to bend as well, when the window element is actuated, and thus depending on the refractive indices n 1 , n 2  of the first L 1  and the second liquid L 2 , the third membrane  23  might contribute to the refractive power of the lens  1 , which might be advantageous in certain instances. 
       FIG.  14    shows an embodiment of an acceleration-induced aberration compensating lens  1  according to the invention. The lens  1  has an integrally formed lens shaping element  3  and wall portion  4  like the lens shown in  FIG.  1   . In addition, the third membrane  23  forming the membrane portion  20  is sealingly connected with its first side  23 - 1 ,  20 - 1  to the second side  21 - 2  of the first membrane  21 , such that the first volume V 1  comprising the first liquid L 1  is formed between the first  21  and the third membrane  23 . The second volume V 2  comprising the second liquid L 2  is formed between the third membrane  23 , the second membrane  22 , the lens shaping element  3  and the wall portion  4 . 
     The first  21  and the third membrane  23  might be connected by plasma-bonding. 
       FIG.  15    shows an embodiment of the lens  1  that comprises an additional second wall portion  7  that contacts the second side  22 - 2  of the second membrane  22  circumferentially with a first side  7 - 1  of the second wall portion  7 . With a second side  7 - 2 , the second wall portion  7  is connected or integrally formed with the window element  5 . The opening  7   a  of the second wall portion  7  defines the window portion  22   a  to be a flexible lens area, within which the second membrane  22  might change its surface for adjusting the refractive power of the lens  1 . The first volume V 1  is enclosed between the first membrane  21 , the lens shaping element  3 , the wall portion  4  and the second membrane  22 . The second volume V 2  is enclosed by the second membrane  22 , the second wall portion  7  and the window element  5 . 
     The wall portion  4  is connected with its second side  4 - 2  to the first side  22 - 1  of the second membrane  22  and faces with its first  4 - 1  the second side  3 - 2  of the lens shaping element  3 . 
     As can be seen in  FIG.  15   , the openings  4   a ,  7   a  of the wall portions  4 ,  7  and the aperture of the lens shaping element  3  are all different, which allows a greater flexibility in terms of aperture design in combination with a reluctance motor. 
     While the lens shaping element  3  might be made of glass or a polymer, the wall portion  4  might be made of a metal compound such as steel and the actuation element  6  is made from a permanent electro-magnetic compound such that by means of a coil assembly (not shown) arranged at the wall portion  4 , the actuation element  6  can be moved relative to the lens shaping element, causing a change of refractive power of the lens  1 . The second wall portion  7  is made from a neutral material with respect to the electro-magnetic actuation. The second wall portion  7  can be regarded as a part of the window element  5 . In fact, the second wall portion  7  might be made from the same material as the window element  5  or even be integrally formed with the window element  5 . 
     Upon actuation with the actuation element  6 , the window element  5  and the second wall portion  7  exert a force on a contact portion  22   g  of the second membrane  22  that corresponds to the first side  7 - 1  of the second wall portion  7 . 
     This causes the first membrane  21  to alter its shape, i.e. its curvature, in the lens area  21   a  and the second membrane  22  to alter its shape in the window portion  22   a  accordingly, depending on the stiffness of the two membranes  21 ,  22 . This allows for providing a double convex or double concave lens  1  with acceleration-induced aberration compensation. 
     In yet another embodiment of the invention, the lens  1  as shown in  FIG.  16    comprises the first volume V 1  enclosed between the first membrane  21 , the cylindrical wall portion  4  that is integrally formed with the lens shaping element  3  and the third membrane  23 , wherein the first membrane  21  is connected to the first side  3 - 1  of the lens shaping element  3  and the third membrane  23  is connected to the second side  4 - 2  of the wall portion  4 . The second volume V 2  is enclosed between the third membrane  23  and the second membrane  22  that is circumferentially connected to the third membrane  23 , such that the second volume V 2  has a cushion like structure. On the second side  22 - 2  of the second membrane  22 , the window element  5  is arranged. This embodiment is structurally similar to the embodiment of  FIG.  11   , with the difference that the third membrane  23  is attached to the wall portion  4  rather than to the second membrane  22 . 
     The embodiment in  FIG.  17    is a further development of the embodiment of  FIG.  11   . In addition to the embodiment of  FIG.  11   , the cross-section of the integrally formed wall portion  4  and lens shaping element  3  slightly differs from the embodiment of  FIG.  11   , as the step-like contour is replaced by a more continuous contour  43 . The main difference, however, is that on the first side  21 - 1  of the first membrane  21  on the outside of the lens volume VL, an additional member  8  is connected to the lens  1  that serves as an aperture of the lens  1 . The additional member  8  has a central aperture  8   a  that is placed at a distance D to the first membrane  21  along the optical axis OA. This allows for manufacturing a lens  1  with various sizes of apertures that can be modularly applied to the lens  1 . The distance D allows the first membrane  21  to bend toward the aperture  8   a  of the additional member  8  without touching said aperture  8   a.    
     Embodiments shown in  FIG.  18    and  FIG.  19    concern a lens design that allows for a particularly light-weight lens  1 . The lenses  1  of  FIGS.  18  and  19    are similar to the lens of  FIG.  10    that discloses a pillow-like lens volume VL. 
     In addition to the lens of  FIG.  10   , the lenses  1  of  FIGS.  18  and  19    each are modified to compensate acceleration-induced aberrations by having the first and the second volume V 1 , V 2  with the first L 1  and the second liquid L 2 . The lens volume VL comprises the first volume V 1  and the second volume V 2 . The first volume V 1  is completely enclosed by the first membrane  21  and the second membrane  22  that are sealingly connected at a circumferential  21 - 22  portion to the second membrane  22 . The second membrane  22  is connected at a circumferential portion  5   c  of its second side  22 - 2  to the window element  5 , while the window portion  22   a  of the second membrane  22  integrally comprises the separating membrane portion  20 . Between the separating membrane portion  20  and the window element  5 , the second liquid L 2  is comprised in the second volume V 2 . This structure has been elaborated already for  FIG.  12    in detail, which is applicable to  FIG.  18    as well. The lens shaping element  3  is connected with a second side  3 - 2  to the first side  21 - 1  of the first membrane  21  from an outside of the lens volume VL. Any actuation of the lens  1  is provided via the window element  5 , wherein the lens shaping element  3  remains at a fixed position, which allows for the advantageous effects of a fixed lens shaping element  3  as elaborated previously. For this purpose, the lens shaping element  3  protrudes radially away from the optical axis OA, such that it can be rigidly connected to a fixing member (not shown). The window element  5  can be actuated at least along the z-axis, wherein the first membrane  21 , particularly the lens area  21   a  might change it curvature in the clear aperture  3   a  of the lens shaping element  3  in response to an actuation of the window element  5 . 
     In contrast of  FIG.  8   , where the window element  5  extends laterally beyond the clear aperture  3   a  of the lens shaping element  3 , which reduces stray light due to edge effects of the window element  5 , such that the window element  5  is essentially invisible, the situation is different in the embodiments of  FIG.  19 A  and  FIG.  19 B , where the window element  5  is smaller and does not extend beyond the clear aperture  3   a  of the lens shaping element  3  and more light-weight as compared to the window element of  FIG.  18   . 
     In  FIG.  19   , the second volume is formed by the second membrane  22  and the window element alone, wherein in  FIG.  19 B  the second Volume is enclosed by the third membrane  23  and the second membrane alone. In both embodiments, upon actuation the second lens volume V 2  essentially remains at the same size. 
     As elaborated in  FIG.  10   , the first  21  and the second membrane  22  might be two separate membranes or made of a sleeve-like membrane that is connected at the openings of the sleeve  21 - 22  for both embodiments  FIG.  19 A  and  FIG.  19 B . 
       FIG.  20    shows an embodiment of a pillow-like embodiment of the lens  1  that arises from a combination of the embodiment of  FIG.  14    and  FIG.  10   . However, the embodiment of  FIG.  20   , in contrast to the embodiment of  FIG.  14   , has a pillow-like lens volume VL formed only by the first  21  and the second membrane  22  with no solid components inside the lens volume VL. The lens  1  comprises a third membrane  23  that is connected to the first membrane  21  on an inside of the lens volume VL, i.e. the third membrane  23  is connected with its first side  23 - 1  to the second side  21 - 2  of the first membrane  21 , such that the first volume V 1  is formed between these membranes  21 ,  23 . The second volume V 2  is formed exclusively by the first, the second and the third membrane  21 ,  22 ,  23 . Outside the lens volume VL, the lens shaping element  3  is connected to the first membrane  21  and the window element  5  is connected to the second membrane  22 . Actuation is facilitated by either moving the window element  5  relative to the lens volume VL and the lens shaping element  3  that remain fixed or by moving the lens volume VL and the lens shaping element  3  (as a whole) relative to the window element  5  that remains fixed. 
     As can be seen in  FIG.  20   , the first membrane  21  adopts a convex shape in its equilibrium position (i.e. while no actuation of the window element is performed), such that the lens  1  has a refractive power in its equilibrium state. This obviously, can be applied to all embodiments of the invention. Similarly, the lens  1  could be adjusted such, that in its equilibrium position, the first membrane  21  adopts a concave shape. Both equilibrium states can be achieved by adjusting a pressure of the first liquid L 1  inside the lens volume VL. 
       FIG.  21    discloses a lens  1  that is configured to compensate acceleration-induced aberrations as the lenses of previous figures. 
     Here, the lens volume VL is formed by a pillow-like second lens volume V 2  that is exclusively formed by the second  22  and the third membrane  23  with no rigid components on its inside. At its rim portions  22 - 23  the third  23  and the second membrane  22  are sealingly connected to seal the second liquid L 2  in the second volume V 2 . 
     The first lens volume V 1  is enclosed by the third membrane  23 , the lens shaping element  3  and the first membrane  21 . 
     The lens shaping element  3  is connected with the first side  3 - 1  to the first membrane  21  and with its second side  3 - 2  to the third membrane  23 . 
     The lens shaping element  3  protrudes radially away from the clear aperture  3   a , such that a fixing member (not shown) may be connected to the lens shaping element  3 . 
     The window element  5  is connected to the second side  22 - 2  of the second membrane  22  via the window portion  22   a  of the second membrane  22  to the second membrane  22 . 
       FIGS.  22  to  25    focus on actuation assemblies for the lenses according to the invention. While the embodiments only show lenses without acceleration-induced aberration compensation, it is noted that also embodiments having the lens volume VL separated in the first V 1  and the second volume V 2  for acceleration-compensation can be equipped with the actuation assemblies in the same manner. 
     The common design of the actuation assemblies shown in  FIG.  22    to  FIG.  25    is that the actuation coils  9  are arranged movable relative to the lens shaping element  3 . 
     In  FIGS.  22  to  25   , at the window element  5 , the actuation element  6  extends laterally away from the window element  5  such that it protrudes beyond the wall portion  4  of the lens  1 . In terms of a three-dimensional view, this might be by means of separate protruding arm members  6   a  or by means of a ring- or disc-like structure  6   a . This lateral protruding member is also referred to as the lateral mover element portion  6   a  in the context of the current specification. As elaborated for previous embodiments the actuation element  6  might comprise damping elements (not shown). The actuation element  6  can also serve as an aperture for the lens  1  as shown in  FIG.  22    to  FIG.  25   , limiting the aperture of the lens  1  on the side of the window element  5 . 
     At an outer portion  6   d  of the protruding member  6   a  that lies laterally beyond the wall portion  4 , a coil portion  6   e  is arranged, wherein said coil portion  6   e  comprises one or more coils  9 . Typically, four or more coils  9  are arranged on the protruding member  6   a  circumferentially around the wall portion  4 . In  FIGS.  22  to  25    only two coils  9  can be seen. The coils  9  extend with their coil axes essentially parallel to the optical axis OA of the lens  1 , when in equilibrium state. Correspondingly to the coils  9 , the lens  1  comprises magnetic portions  10 , particularly comprising a permanent magnet  10 , particularly in form of a permanent ring magnet or a plurality of separate magnets. The magnetic portions  10  are rigidly connected to the wall portion  4  on an outside of the lens volume VL that faces the coils  9 . As such the coils  9  are arranged opposite the corresponding magnetic portions  10  on the outside of the lens volume. Between the coils  9  and the magnetic portions  10  a predefined lateral distance or air gap  50  is provided, such that the coils  9  are free to move and tilt to some extent relative to the magnetic portions  10 . The magnetic poles N, S of the magnetic portions  10  are arranged in a radial or lateral fashion with respect to the optical axis OA, such that the magnetic dipole vector is oriented essentially orthogonal to the coil axes. The coils  9  overlap along the optical axis OA at least partially with the magnetic portions  10 . With the coil axes and the magnetic poles oriented and positioned as described, actuation of the window element  5  relative to the wall portion  4  and thus the lens shaping element  3  becomes possible by means of a Lorentz force. Therefore, by providing appropriate electrical currents to the coils  9  virtually any movement of the window element  5  relative to the lens shaping element  3  can be achieved. 
     The coils  9  can be wound around a solid axis of the coil portion (not shown). 
     The advantage of this actuation assembly is that is less susceptible to external magnetic fields as compared to reluctance-based actuation assemblies. 
     The embodiment of  FIG.  22    further comprises a silicon lens shaping element  3  that extends laterally beyond the wall portion  4  and the lens volume VL, such that it provides a hard stop for the coil motion along the optical axis. Further, a hard stop portion  11  is connected to the lens shaping element  3  at an outer portion  3   e  of the lens shaping element  3 , wherein said hard stop portion  11  extends in a housing-like fashion around the coil portion and the protruding member  6   d  of the actuation element  6 , such that a hard stop is provided also to the actuation element  6  from the other side of the lens  1 . 
     The two hard stops limit the range of the coil motion along the optical axis OA in both directions such that accidental overdrives or shock-induced motions will do no harm to the actuation assembly. 
     In  FIG.  23    the lens shaping element  3  is floatingly arranged on the first membrane  21 , i.e. it is not in rigid contact with the wall portion  4 . 
     In the embodiment of  FIG.  23   , the wall portion  4  consists of the magnetic portions  10 , which reduces the assembly complexity of the lens  1 . 
     The lens  1  comprises a separate hard stop portion  11  that is configured to limit the movement of the coils  9  toward the side of the lens  1 , where the lens shaping element  3  is located. 
     In  FIG.  24    a very similar embodiment as in  FIG.  22    is shown, however without any hard stop portions or housing-like features. 
     In contrast to  FIG.  22   , the coils  9  are attached to a rigid coil portion  6   e  and not wound around an axis of the coil portion  6   e.    
     In  FIG.  25   , an example is shown that illustrates an electric contacting of the coils  9 . For this purpose, for each coil  9  a contacting member  12  is arranged on the first side (i.e. the side of the lens  1  on which the first membrane  21  is arranged) of the lens  1 . The contacting members  12  comprise a spring-like member  12   a  that physically connects the coils  9  with the wall portion  4  and the magnetic portions  10  on a side of the coils  9  that faces away from the protruding member  6   a . The spring-like members  12   a  provide a restoring force, while at the same time said members  12   a  are configured to provide electricity to the coils  9  for controlling orientation and position of the window element  5  and thus, the refractive power of the lens  1 . 
     The spring like members  12   a  might be formed as leaf springs. 
     In  FIGS.  26  and  27    a different actuation assembly is shown. The actuation is based on a reluctance drive. 
     For this purpose, the coils  9  are arranged fixedly at the wall portion of the lens  1 , with an orientation of the coil axes pointing along the lateral plane (in the angular direction of the lens into the drawing plane or outwards the pane of drawing) extending orthogonal to the optical axis  9   a  of the lens  1 . The wall portion  4  is made of a metal compound, such as iron. Similarly, the actuation element  6 , particularly the protruding portion of the actuation element  6  comprises or consists of a metal compound such as iron. 
     An electrically conducting material may be used instead of the metal compound. 
     When an electrical current is applied to the coils  9  a reluctance force is induced in the protruding member  6   a  of the actuation element  6 , such that the position and orientation of the window element  5  can be controlled. The wall portion  4  amplifies said force up to a factor  1000 . As elaborated previously, the design of the lens  1  with regard to the arrangement of the lens shaping element  3 , the membranes  21 ,  22  (and particularly  20 ,  23 ) etc. can be adapted to previous embodiments in a similar fashion. 
     An example for the adaption of the embodiment of  FIG.  26    to a lens configured to compensate acceleration-induced aberrations is given in  FIG.  27   . 
     The lens of  FIG.  27    essentially corresponds to the lens  1  of  FIGS.  11  and/or  12   . In addition the lens of  FIG.  27    comprises the actuation assembly laid out in  FIG.  26   . 
     The reluctance-based actuation provides a very compact lens design. 
     In  FIG.  28    an example is shown in which the lens shaping element  3  in combination with the lens volume VL might be moved relative to the window element  5  as part of an optical system  100 . 
     The lens  1  of  FIG.  28    comprises an additional optics assembly  13  comprising a further lens  13   a  that might be glued to the window element  5 . The lens volume VL is enclosed by the first and the second membrane  21 ,  22  and the wall portion  4  that is integrally formed with the lens shaping element  3  (similar to  FIG.  2   ). 
     The window element  5  together with the optics assembly  13  is rigidly attached to some fixing member (not shown) that does not move, and might be connected to a housing of the lens. In order to adjust the refractive power of the lens  1 , an actuator  14 , e.g. a piezo actuator, is connected to the lens body comprising the lens volume VL, the first and the second membrane  21 ,  22  and the lens shaping element  3 . The actuator  14  might be rigidly connected with an end portion  14   e  to a fixing member (not shown) and with a connecting portion  14   c  to the lens body. 
     The lens body can be displaced relative to the window element  5 , by providing an actuation force generated by the actuator  14 , such that lens body is displaced relative to the window element  5 . This way, a relative movement of the window element  5  with respect to the lens shaping element  3  is achieved, while the lens shaping element  3  does not move relative to the wall portion  4 , the first and the second membrane  21 ,  22 , i.e. relative to the lens body. 
     In  FIGS.  29  to  30   , various embodiment of an optical system  100  comprising an optical sensor in form of an array detector  102 , such as a camera that is arranged on an optical axis of the system  100  that corresponds to the optical axis OA of the lens  1 . The system further comprises an optical assembly  101  comprising at least one hard lens  101 L. 
     In  FIG.  29   , the lens  1  and the optical assembly  101  are arranged at a fixed distance to each other while the lens  1  is located on an side of the system where the light is enters the system, i.e. the lens  1  that has the largest distance to the array detector  102 . 
     The lens  1  might provide focusing of an image to the array detector  102 . 
     In  FIG.  30 A , the system  100  comprises two lens assemblies  110 ,  120 , wherein between the lens assemblies  110 ,  120  the lens  1  according to the invention is located. This way, the lens  1  might be used for a zoom function of the optical system  100 . In  FIG.  30 A  the lens  1  faces with its first membrane  21  toward the array detector  102 , wherein in  FIG.  30 B  the lens  1  faces with its first membrane away from the detector  102 . 
     The lens  1  might provide optical image stabilization, e.g. by means of tilting the window element  5  accordingly, or superresolution imaging, also by way of tilting the window assembly, such that the induced prism of the lens  1  projects the image onto different portion on the array detector  102  in the latter case. 
     In  FIG.  31 A  and  FIG.  31 B  a two three-dimensional views of the lens  1  according to the invention are shown. In  FIG.  31 A , the lens shaping element  3  has a circular, disc-like shape, wherein in  FIG.  31 B  the lens shaping element  3  has additional protrusions that can be used for attaching and orienting the lens shaping element to external fixing elements (not shown). 
     In both Figures  FIG.  31 A  and  FIG.  31 B , the window element  5  is connected to the actuation element  6  that comprises a plurality of protruding members  6   a  to which an actuator might be connected. 
     In  FIG.  32    an example of the lens is shown that demonstrates that a relative movement of the window element  5  relative to the lens body or the lens shaping element  3  may be achieved by either by actuating the window element  5  actively and having the lens shaping element with the lens body fixed relative to the window element or by actuating the lens shaping element or the lens body actively and having the window element  5  fixed relative to the lens shaping element or the lens body. Both actuation methods provide the desired advantages of the lens novel lens design according to the invention. 
     The double arrow  200  indicates exemplary actuation directions.