Patent Publication Number: US-2020301116-A1

Title: Optical zoom device with focus tunable lens cores

Description:
The present invention relates to an optical zoom device using focus tunable lenses. 
     Particularly, regarding such optical zoom devices it is highly desirable to have a very compact form factor using known fluidic lenses with adjustable focal length. This allows one to construct compact optical zoom devices particularly comprising proven components. 
     The above-described objective is solved by an optical zoom device having the features of claim  1 . Preferred embodiments of the present invention are stated in the sub claims and are described below. 
     According to claim  1 , an optical zoom device is disclosed, comprising
         a first lens having an adjustable focal length and a second lens having an adjustable focal length, wherein each lens comprises a lens core filled with a transparent fluid, wherein the respective lens core comprises a transparent first wall in the form of an elastically deformable membrane and a transparent second wall facing the first wall, wherein the fluid is arranged between the two walls of the respective lens core, and wherein the respective lens comprises a lens shaping member interacting with the respective membrane for adjusting the focal length of the respective lens and/or for stabilizing an image generated with help of the two lenses,   wherein the optical zoom device comprises a first and a separate second lens barrel, wherein the first lens core is mounted on the first lens barrel and the second lens core is mounted on the second lens barrel   wherein the optical zoom device comprises at least one actuator associated to the first lens for generating said interaction of the lens shaping member of the first lens with the membrane of the first lens for adjusting said focal length of the first lens, as well as at least one actuator associated to the second lens for generating said interaction of the lens shaping member of the second lens with the membrane of the second lens for adjusting said focal length of the second lens.       

     In other words, more specifically, the current invention describes a new approach to make liquid-membrane based optical zoom lenses incorporating optical image stabilization. Particularly, the present invention also allows to use existing components such as the first and the second lens for making a reliable optical system. Furthermore, particularly, the use of simple components allows to build a complex camera module using component that can be tested separately before assembling them in the system especially the optical quality of the (e.g. plastic) lens stack and the tunable lens can be evaluated before building into a system. Using particularly linear actuators such as voice coil actuators, piezo actuators or shape memory alloys also helps in the implementation of a very compact form factor. 
     Furthermore, an optical zoom device according to the present invention can also be combined with an optical image stabilization system which can use either an image sensor shifting mechanism or a prism tilt mechanism or a tunable prism. Alternatively, the optical image stabilization can be achieved by appropriately deforming the first and/or the second lens so that the latter represent adjustable prisms. 
     Further, according to an embodiment of the present invention, the respective lens barrel holds at least one rigid lens, particularly a plurality of rigid lenses. Particularly, the first and the second lens each comprise an optical axis, which optical axes can be aligned with each other, i.e. form a common optical axis. The optical axis of the first lens particularly also forms an optical axis of the rigid lenses of the first lens barrel. Likewise, the optical axis of the second lens also forms an optical axis of the rigid lenses of the second lens barrel. 
     Furthermore, according to an embodiment, for achieving a compact device height, the first lens has an outer diameter (e.g. perpendicular to an optical axis of the first lens) that is equal to (or larger than) an outer diameter of the first lens barrel (e.g. perpendicular to said optical axis/radial direction of the lens barrel) in the same direction, wherein the first lens barrel comprises an opening for holding the first lens. Particularly, a lateral wall delimiting said opening of the first lens barrel that is configured to hold the first lens can comprise one or several recesses for receiving a portion of the first lens, respectively, which allows said diameters to be of equal size. Further, in the same manner, the second lens has an outer diameter (e.g. perpendicular to an optical axis of the second lens) according to an embodiment that is equal to (or larger than) an outer diameter of the second lens barrel (e.g. perpendicular to the optical axis of the second lens/radial direction of the second lens barrel) in the same direction in the same direction, wherein the second lens barrel comprises an opening for holding the second lens. Particularly, a lateral wall delimiting said opening of the second lens barrel that is configured to hold the second lens can comprise one or several recesses for receiving a portion of the second lens, respectively, which allows said diameters again to be of equal size. 
     Furthermore, according to an embodiment of the present invention, the optical device comprises a prism or a mirror. 
     Further, according to an embodiment of the present invention, the optical zoom device comprises a third barrel holding said prism or said mirror, which third barrel is connected to the first barrel, so that the first lens is arranged between the prism or mirror and the second lens in the optical path of the optical zoom device. 
     According to an alternative embodiment, the prism or mirror is arranged between the first lens and the second lens in the optical path of the optical zoom device. 
     Furthermore, according to an embodiment of the present invention, the optical device comprises an image sensor for generating said image to be stabilized. 
     Particularly, in an embodiment of the present invention, the image sensor is mounted to the second lens barrel, particularly such that it faces the second lens. 
     Further, according to an embodiment of the present invention, the at least one actuator of the first lens is configured to move the lens shaping member of the first lens with respect to the lens core of the first lens for adjusting the focal length of the first lens. Alternatively, the at least one actuator of the first lens is configured to move the lens core of the first lens with respect to the lens shaping member of the first lens for adjusting the focal length of the first lens. 
     Further, in an embodiment, the at least one actuator of the second lens is configured to move the lens shaping member of the second lens with respect to the lens core of the second lens for adjusting the focal length of the second lens. Alternatively, the at least one actuator of the second lens is configured to move the lens core of the second lens with respect to the lens shaping member of the second lens for adjusting the focal length of the second lens. 
     Particularly, having a fixed lens shaping member and a moving flat lens core of the respective lens results in an alignment insensitive design, due to the fact that a lateral shift of the respective flat lens core is optically not visible. 
     Further, according to an embodiment of the present invention, the first lens comprises two, three or particularly four actuators, that are configured to move the lens shaping member of the first lens with respect to the lens core of the first lens for adjusting the focal length of the first lens or that are configured to move the lens core of the first lens with respect to the lens shaping member of the first lens for adjusting the focal length of the first lens. 
     Furthermore, according to an embodiment, the second lens may also comprises two, three or even four actuators that are configured to move the lens shaping member of the second lens with respect to the lens core of the second lens for adjusting the focal length of the second lens or that are configured to move the lens core of the second lens with respect to the lens shaping member of the second lens for adjusting the focal length of the second lens. 
     Further, according to an embodiment of the present invention, the optical zoom device is configured to tilt the lens shaping member of the first lens with respect to the lens core of the first lens using said actuators of the first lens for stabilizing said image. Alternatively, the optical zoom device can be configured to tilt the lens core of the first lens with respect to the lens shaping member of the first lens using said actuators of the first lens for stabilizing said image. 
     Furthermore, according to an embodiment of the present invention, the optical zoom device is configured to tilt the lens shaping member of the second lens with respect to the lens core of the second lens using said actuators of the second lens for stabilizing said image. Alternatively, the optical zoom device can also be configured to tilt the lens core of the second lens with respect to the lens shaping member of the second lens using said actuators of the second lens for stabilizing said image generated by the optical zoom device. 
     Further, according to an embodiment of the present invention, the optical device is configured to use merely the first or the second lens for stabilizing said image. This means that the other lens not used for image stabilization merely adjusts its focal length and all image stabilization is performed by only one of the two focus adjustable lenses. 
     Further, according to an embodiment of the present invention, the optical device is configured to tune or tilt the prism or to tune or tilt the mirror for stabilizing said image. Here, both the first and the second lens can be configured to merely adjust their focal lengths for achieving the zoom function of the optical zoom device. 
     Particularly, according to an embodiment of the present invention, the optical device is configured to one of:
         shift the first lens perpendicular to an optical axis of the first lens with respect to the image sensor to stabilize the image and/or shift the second lens perpendicular to an optical axis of the second lens with respect to the image sensor to stabilize the image,   shift a rigid lens perpendicular to an optical axis of the first lens with respect to the image sensor to stabilize the image and/or shift a rigid lens perpendicular to an optical axis of the second lens with respect to the image sensor to stabilize the image and/or shift a rigid lens perpendicular to an optical axis of the third lens barrel with respect to the image sensor to stabilize the image, shift the image sensor perpendicular to an optical axis of the first lens with respect to the first lens to stabilize the image, and/or shift the image sensor perpendicular to an optical axis of the second lens with respect to the second lens to stabilize the image.       

     Further, according to an embodiment of the present invention, the first lens forms a zoom lens defining a field of view of the optical zoom device and the second lens is configured to refocus the image on the image sensor. 
     Further, according to an embodiment of the present invention, the lens shaping member of the first lens defines an area of the membrane of the first lens that has an adjustable curvature, and/or that the lens shaping member of the second lens defines an area of the membrane of the second lens that has an adjustable curvature. The area of the respective membrane can be defined by a circumferential or annular portion of the respective lens shaping member. 
     Particularly, the respective lens shaping member may comprise a circular portion resulting in a rotationally symmetrical area of the respective lens. However, the respective lens shaping member may also comprise a square portion which then results into a cylindrical lens. In principle, any other lens shaping member shape is possible. Further, particularly, the lens shaping member can be an injection molded part, a metal, glass or a silicon (etched) lens shaping member. 
     Particularly, the optical device can be configured to adjust the respective curvature by an interaction of the respective lens shaping member with the respective membrane, e.g. by pushing the respective lens shaping member against the respective membrane or by pulling on the respective membrane by means of the respective lens shaping member. 
     Particularly, the respective lens shaping member can contact the respective membrane directly or indirectly via another material layer (e.g. formed by a glue etc.). The respective lens shaping member can further be attached to the respective membrane by bonding it directly to the membrane or via another material layer such as a glue layer. 
     Particularly, according to an embodiment, the respective lens shaping member can be plasma bonded to the respective membrane. 
     Particularly, the notion according to which the respective lens shaping member defines an area of the membrane that has an adjustable curvature may mean that the respective lens shaping member delimits, by being attached to the membrane or by contacting the latter, an elastically expandable (e.g. circular) area of the respective membrane, wherein particularly the respective area extends up to an (e.g. circumferential) inner edge of the respective lens shaping member. The respective area may also be denoted as optically active area since the light passes through the respective area of the respective (first or second) lens and is affected by the curvature of the respective area. 
     When the respective lens shaping member presses against the membrane, the respective membrane is expanded and said curvature of said area of the membrane increases due to the fluid residing in the respective lens core. Likewise, when the respective lens shaping member pushes less against the respective membrane or even pulls the respective membrane, said curvature of the area of the respective membrane decreases. 
     Increasing curvature means that the area of the respective membrane may develop a more pronounced convex bulge, or that the area of the respective membrane changes from a concave or a flat state to a convex one. Likewise, a decreasing curvature means that the area of the respective membrane changes from a pronounced convex state to a less pronounced convex state or even to a flat or concave state, or changes from a flat or concave state to an even more pronounced concave state. 
     The respective membrane can be made of at least one of the following materials: a glass, a polymer, an elastomer, a plastic or any other transparent and stretchable or flexible material. For example, the membrane may be made out of a silicone-based polymer such as poly(dimethylsiloxane) also known as PDMS or a polyester material such as PET or a biaxially-oriented polyethylene terephtalate (e.g. “Mylar”). 
     Further, the membrane can comprise a coating, in particular an anti-reflection coating made of nanostructures, or nano-particles or sol-gel coatings. Further, the membrane can also be structured, e.g. comprises a structured surface or have a variable thickness or stiffness across the membrane. 
     Further, said fluid preferably is or comprises a liquid, a liquid metal, a gel, a gas, or any transparent, absorbing or reflecting material which can be deformed. For example, the fluid may be a silicone oil. 
     Further, according to an embodiment of the present invention, the optical zoom device comprises a wide mode in which the area of the membrane of the first lens is concave and the area of the membrane of the second lens is convex. 
     Furthermore, according to an embodiment of the present invention the optical zoom device also comprises a tele mode in which the area of the membrane of the first lens is convex and the area of the membrane of the second lens is concave. According to a further embodiment, the optical zoom device also comprises a mid zoom state in which the areas of the membranes of the two lenses are only slightly convex, or lightly concave, or even flat. In case both the first and the second lens are convex, the closest macro focus can be achieved. 
     Further, according to an embodiment of the present invention, the respective actuator is one of or comprises one of: a linear actuator, a piezo actuator, a shape memory alloy, a stepper motor, an electromagnetic actuator, a moving coil, a moving magnet. 
     Further, according to an embodiment of the present invention, the first lens comprises a single linear actuator (particularly a piezo actuator) that is configured to move the lens shaping member of the first lens with respect to the lens core of the first lens (or to move the lens core of the first lens with respect to the lens shaping member of the first lens) for adjusting the focal length of the first lens, and wherein the second lens comprises four linear actuators that are configured to move the lens core of the second lens with respect to the lens shaping member of the second lens for adjusting the focal length of the second lens and to tilt the lens core of the second lens about two different axes for stabilizing said image, wherein the respective linear actuator can comprise a shape memory alloy for moving and tilting the lens core of the second lens with respect to the lens shaping member of the second lens. 
     Further, according to an embodiment of the present invention, the respective actuator of the first lens is arranged outside the first lens barrel on a (e.g. circumferential) side wall of the first lens barrel. Further, in an embodiment, the respective actuator of the second lens is arranged outside the second lens barrel on a (e.g. circumferential) side wall of the second lens barrel. 
     Particularly, an advantageous minimal configuration of actuators comprises two actuators per lens. Here, according to an embodiment of the present invention, each of said two actuators of the first lens is connected to a region of the lens shaping member of the first lens to exert a force on the lens shaping member of the first lens via the respective region (e.g. so as to adjust the focal length of the first lens and/or for stabilizing said image) or each of said two actuators of the first lens is connected to a region of the lens core of the first lens to exert a force on the lens core of the first lens via the respective region (e.g. to adjust the focal length of the first lens and/or for stabilizing said image), wherein said two regions face each other in a first direction. Further, each of said two actuators of the second lens is connected to a region of the lens shaping member of the second lens to exert a force on the lens shaping member of the second lens via the respective region (e.g. to adjust the focal length of the second lens and/or for stabilizing said image) or each of said two actuators of the second lens is connected to a region of the lens core of the second lens to exert a force on the lens core of the second lens via the respective region (e.g. to adjust the focal length of the second lens and/or for stabilizing said image), wherein said two regions face each other in a second direction, and wherein said second direction is different from the first direction. Particularly, said first and second direction are skew and extend in parallel planes. Particularly, said two directions are orthogonal. 
     Particularly, in the following, embodiments are described in which the respective lens shaping member is moved by the respective actuators while the lens core of the first lens is fixed to the first lens barrel, and the lens core of the second lens is fixed to the second lens barrel. 
     Particularly, in an embodiment, the optical device is configured to adjust the focal length of the first lens by exerting on each region of the lens shaping member of the first lens a force using the respective actuator, wherein these two forces are equal so that the lens shaping member of the first lens pushes against the membrane of the first lens or pulls on the membrane of the first lens so as to adjust the curvature of said area of the membrane of the first lens and therewith the focal length of the first lens. 
     Further, in an embodiment, for stabilizing said image, the optical device is configured to shift said image in a first shifting direction by exerting on each region of the lens shaping member of the first lens a force using the respective actuator, wherein these two forces are opposite and particularly of equal or substantially equal magnitude, so that the lens shaping member of the first lens is tilted about a first axis thereby shifting said image in said first shifting direction. Particularly, due to the tilting of the lens shaping member of the first lens with respect to the lens core of the first lens, the lens core of the first lens is formed into a prism, i.e., said area of the membrane of the first lens is tilted relative to the second wall of the lens core of the first lens. 
     Furthermore, in an embodiment, the optical device is configured to adjust the focal length of the second lens by exerting on each region of the lens shaping member of the second lens a force using the respective actuator, wherein these two forces are equal or substantially equal so that the lens shaping member of the second lens pushes against the membrane of the second lens or pulls on the membrane of the second lens so as to adjust the curvature of said area of the membrane of the second lens and therewith the focal length of the second lens. 
     Further, in an embodiment, for stabilizing said image, the optical device is configured to shift said image in a second shifting direction by exerting on each region of the lens shaping member of the second lens a force using the respective actuator, wherein these two forces are opposite and particularly of equal or substantially equal magnitude, so that the lens shaping member of the second lens is tilted about a second axis thereby shifting said image in said second shifting direction. Particularly, due to the tilting of the lens shaping member of the second lens with respect to the lens core of the second lens, the lens core of the second lens is formed into a prism, i.e., said area of the membrane of the second lens is tilted relative to the second wall of the lens core of the second lens. 
     Furthermore, alternatively, the actuators may also exert the forces described above on the respective lens core. Here, the lens shaping member of the first lens is fixed to the first lens barrel, and the lens shaping member of the second lens is fixed to the second lens barrel (of course, mixed configurations are also conceivable, i.e. in one of the two lenses the lens shaping member is moved while in the other lens the respective lens core is moved). 
     Particularly, in an embodiment, the optical device is configured to adjust the focal length of the first lens by exerting on each region of the lens core of the first lens a force using the respective actuator, wherein these two forces are equal or substantially equal so that the lens core of the first lens is pushed with the membrane of the first lens against the lens shaping member of the first lens or is moved away from the lens shaping member of the first lens so that the lens shaping member of the first lens pulls on the membrane of the first lens so as to adjust the curvature of said area of the membrane of the first lens and therewith the focal length of the first lens. 
     Further, in an embodiment, for stabilizing said image, the optical device is configured to shift said image in a first shifting direction by exerting on each region of the lens core of the first lens a force using the respective actuator, wherein these two forces are opposite and particularly of equal or substantially equal magnitude, so that the lens core of the first lens is tilted about a first axis with respect to the lens shaping member of the first lens thereby shifting said image in said first shifting direction. Particularly, due to the tilting of the lens core of the first lens, the lens core of the first lens is formed into a prism, i.e., said area of the membrane of the first lens is tilted relative to the second wall of the lens core of the first lens. 
     Further, in an embodiment, the optical device is configured to adjust the focal length of the second lens by exerting on each region of the lens core of the second lens a force using the respective actuator, wherein these two forces are equal or substantially equal so that the lens core of the second lens is pushed with the membrane of the second lens against the lens shaping member of the second lens or is moved away from the lens shaping member of the second lens so that the lens shaping member of the second lens pulls on the membrane of the second lens so as to adjust the curvature of said area of the membrane of the second lens and therewith the focal length of the second lens. 
     Further, in an embodiment, for stabilizing said image, the optical device is configured to shift said image in a second shifting direction by exerting on each region of the lens core of the second lens a force using the respective actuator, wherein these two forces are opposite and particularly of equal or substantially equal magnitude, so that the lens core of the second lens is tilted about a second axis with respect to the lens shaping member of the second lens thereby shifting said image in said second shifting direction. Particularly, due to the tilting of the lens core of the second lens, the lens core of the second lens is formed into a prism, i.e., said area of the membrane of the second lens is tilted relative to the second wall of the lens core of the second lens. 
     Furthermore, according to an embodiment, said two actuators of the first lens are arranged outside the first lens barrel on a [circumferential] side wall of the first lens barrel, wherein said two actuators face each other in a first direction running perpendicular to the optical axis of the first lens, and wherein said two actuators of the second lens are arranged outside the second lens barrel on a [circumferential] side wall of the second lens barrel, wherein said two actuators of the second lens face each other in a second direction running perpendicular to the optical axis of the second lens, wherein said second direction is different from the first direction. Particularly, said first and second direction are skew and extend in parallel planes. Particularly, said two directions are orthogonal. 
     Further, according to an embodiment of the present invention, each of the two actuators of the first lens comprises a pusher that is movable along an optical axis of the first lens, wherein each of said pushers of the first lens is connected to one of said regions of the lens shaping member of the first lens or of the lens core of the first lens to exert the respective force on the respective region. Further, in an embodiment, each of the two actuators of the second lens also comprises a pusher that is movable along an optical axis of the second lens, wherein each of said pushers of the second lens is connected to one of said regions of the lens shaping member of the second lens or of the lens core of the second lens to exert the respective force on the respective region. 
     Further, according to an embodiment of the present invention, the respective pusher is connected to the respective region via a latching connection, wherein particularly a section of the respective pusher engages with a recess of the respective region. 
     Further, according to an embodiment of the present invention, the respective pusher is connected to the respective region via a glued connection. 
     Further, according to an embodiment of the present invention, the respective pusher is connected to the respective region via a flexible piston. 
     Further, in an embodiment, each of said regions of the respective lens shaping member on which the respective actuator exerts a force can be formed as an arm protruding from said portion of the respective lens shaping member that defines the respective area of the membrane. Likewise, according to an embodiment, each of said regions of the respective lens core on which the respective actuator exerts a force can be formed as an arm protruding from the respective lens core, particularly from a lateral wall of the respective lens core. 
     Further, according to an embodiment of the present invention, each actuator of the two actuators of the first lens comprises an electrically conducting coil and a magnet structure comprising a first section having a first magnetization and an adjacent second section having a second magnetization, wherein the two magnetizations are antiparallel (i.e. are parallel but point in opposite directions), and particularly extend orthogonal to an optical axis of the first lens, wherein the coil comprises a first portion and a second portion, and wherein the first portion of the coil faces the first section of the magnet structure whereas the second portion of the coil faces the second section of the magnet structure. Further, particularly the coil comprises a conductor that extends around a coil axis of the coil, wherein the coil axis particularly extends parallel to said magnetizations. 
     Further, according to an embodiment, each actuator of the two actuators of the second lens may also comprise an electrically conducting coil and a magnet structure comprising a first section having a first magnetization and an adjacent second section having a second magnetization, wherein the two magnetizations are antiparallel (i.e. are parallel but point in opposite directions) and particularly extend orthogonal to an optical axis of the second lens, wherein the coil comprises a first portion and a second portion, and wherein the first portion of the coil faces the first section of the magnet structure whereas the second portion of the coil faces the second section of the magnet structure. Particularly, the coil comprises a conductor that extends around a coil axis of the coil, wherein the coil axis particularly extends parallel to said magnetizations of the respective magnet structure of an actuator of the second lens. 
     Further, according to an embodiment of the present invention, the magnet structure of the respective actuator of the first lens is rigidly coupled to the first lens barrel, whereas the coil of the respective actuator of the first lens is arranged on the pusher of the respective actuator of the first lens. Further, in an embodiment, the magnet structure of the respective actuator of the second lens is rigidly coupled to the second lens barrel, whereas the coil of the respective actuator of the second lens is arranged on the pusher of the respective actuator of the second lens. 
     Particularly, the optical zoom device can comprise two magnetic flux return structures, particularly in the form of an elongated plate, respectively. Particularly, each magnetic flux return structure is connected to both sections of a magnet structure of an actuator of the first lens as well as to both sections of a magnet structure of an actuator of the second lens. The respective return structure is configured to guide or return the magnetic flux from a section of the magnet structure to the adjacent section of the magnet structure to which it is connected. Particularly, the respective magnetic flux return structure can extend along the optical axis of the first lens and the optical axis of the second lens. Further, the two magnetic flux return structures face each other in a direction perpendicular to the said optical axes. Particularly, the respective magnetic flux return structure can be connected to or can be a part of a housing or shield enclosing the first and/or the second lens barrel. 
     Further, according to an embodiment of the present invention, the coil of the respective actuator of the first lens is rigidly coupled to the first lens barrel, whereas the magnet structure of the respective actuator of the first lens is arranged on the pusher of the respective actuator of the first lens. Further, in an embodiment, the coil of the respective actuator of the second lens is rigidly coupled to the second lens barrel, whereas the magnet structure of the respective actuator of the second lens is arranged on the pusher of the respective actuator of the second lens. 
     Further, according to an embodiment of the present invention, the respective coil can be embedded into a substrate, particularly in the form of a printed circuit board (PCB). Particularly, the optical zoom device can comprise two (e.g. elongated) substrates (e.g. PCBs), wherein each substrate comprises a coil of an actuator of the first lens as well as a coil of an actuator of the second lens. Particularly, the two substrates can be connected to a housing enclosing the first and/or the second lens barrel. Particularly, the two substrates can face each other in a direction perpendicular to the optical axis of the first lens and perpendicular to the optical axis of the second lens. 
     Alternatively, the optical zoom device can comprise two substrate assemblies, wherein each substrate assembly comprises two separate substrates electrically connected to each other by a flexible connector to provide electrical connections between the two substrates, wherein one of the two substrates comprises an embedded coil of an actuator of the first lens while the other substrate comprises a coil of an actuator of the second lens. Again, particularly, the two substrate assemblies can face each other in a direction perpendicular to the optical axis of the first lens and perpendicular the optical axis of the second lens. 
     Furthermore, in the present embodiments related to moving magnet structures arranged on pushers, each magnet structure is connected to a separate first magnetic flux return structure. The respective magnetic flux return structure is configured to guide or return the magnetic flux coming from one section of the magnet structure to the adjacent section of the magnet structure to which it is connected. Particularly, these first magnetic flux return structures are each rigidly coupled to the associated pusher and thus move together with the respective pusher. 
     Furthermore, particularly, the optical zoom device can comprise two second magnetic flux return structures, particularly in the form of an elongated plate, respectively. Particularly, each second magnetic flux return structure faces both sections of a magnet structure of an actuator of the first lens as well as both sections of a magnet structure of an actuator of the second lens. The respective second return structure is configured to guide or return the magnetic flux coming from a section of the magnet structure to an adjacent section of the magnet structure. Particularly, the respective second magnetic flux return structure can extend along the optical axis of the first lens and the optical axis of the second lens. Further, the two second magnetic flux return structures face each other in a direction perpendicular to the said optical axes. Particularly, the respective magnetic flux return structure can be connected to or can be a part of a housing or shield enclosing the first and/or the second lens barrel. Thus, here, every coil of an actuator is arranged between a first and a second magnetic flux return structure. 
     Further, in an embodiment, the respective actuator of the first lens comprises a coil holder for holding a substrate (and the coil embedded therein) of a substrate assembly, via which coil holder the respective coil embedded into the substrate is rigidly connected to the first lens barrel. 
     Further, in an embodiment, the respective actuator of the second lens also comprises a coil holder for holding a substrate (and the coil embedded therein) of a substrate assembly, via which coil holder the respective coil embedded into the substrate is rigidly connected to the second lens barrel. 
     The respective coil holder can comprise a recess for accommodating said flexible connector that connects the two substrates of a substrate assembly. 
     Further, according to an embodiment of the present invention, the optical zoom device is configured to apply an electrical current to the coil of the respective actuator of the first lens for interacting with a magnetic field of the magnet structure of the respective actuator of the first lens such that the pusher of the respective actuator of the first lens is moved along the optical axis of the first lens, wherein, depending on the direction of the current in the coil of the respective actuator of the first lens, the pusher of the respective actuator of the first lens is either moved such along the optical axis of the first lens that the lens shaping member of the first lens presses against the membrane of the first lens or pulls on the membrane of the first lens to adjust the focal length of the first lens and/or to stabilize said image. 
     Further, in an embodiment, the optical zoom device is configured to apply an electrical current to the coil of the respective actuator of the second lens for interacting with a magnetic field of the magnet structure of the respective actuator of the second lens such that the pusher of the respective actuator of the second lens is moved along the optical axis of the second lens, wherein, depending on the direction of the current in the coil of the respective actuator of the second lens, the pusher of the respective actuator of the second lens is either moved such along the optical axis of the second lens that the lens shaping member of the second lens presses against the membrane of the second lens or pulls on the membrane of the second lens to adjust the focal length of the second lens and/or to stabilize said image. 
     Further, particularly, the respective current flows in opposite directions in said two portions of the respective coil. 
     Further, according to an embodiment of the present invention, the pusher of the respective actuator of the first lens is elastically coupled to the first lens barrel via a spring structure such that the pusher of the respective actuator of the first lens is movable along the optical axis of the first lens. Furthermore, in an embodiment, the pusher of the respective actuator of the second lens is also elastically coupled to the second lens barrel via a spring structure such that the pusher of the respective actuator of the second lens is movable along the optical axis of the second lens. 
     Further, according to an embodiment of the present invention, the pusher of the respective actuator of the first lens is supported on ball bearings such that the pusher of the respective actuator of the first lens is movable along the optical axis of the first lens. Further, according to an embodiment, the pusher of the respective actuator of the second lens is supported on ball bearings, too, such that the pusher of the respective actuator of the second lens is movable along the optical axis of the second lens. 
     Particularly, the respective pusher can be supported via said ball bearings on a housing that may surround the first and/or second lens barrel and that may be rigidly coupled to the first and/or second lens barrel. 
     Particularly, the respective actuator of the first lens and the second lens can comprise a cage, e.g. in the form of a frame, for holding the respective ball bearings. 
     Further, according to an embodiment of the present invention, the optical device is configured to measure a movement of the respective pusher of the first lens along the optical axis of the first lens using a sensor associated to the respective pusher. Further, in an embodiment, the optical device is also configured to measure a movement of the respective pusher of the second lens along the optical axis of the second lens using a sensor associated to the respective pusher. 
     Further, according to an embodiment of the present invention, the respective sensor is one of: a Hall sensor, an inductive sensor, a capacitive sensor, an optical sensor. 
     Further, according to an embodiment of the present invention, the optical zoom device is configured to adjust the focal length of the first and the second lens in concert to generate a particular zoom range and a sharp image on the image sensor. 
     Further, according to an embodiment of the present invention, the first lens is configured to define the field of view of the optical zoom device (zoom range) and the second lens is configured to focus an image generated by the optical zoom device on the image sensor. 
     Further, according to an embodiment of the present invention, the optical zoom device is configured to receive an output signal of a gyroscope coupled to the optical zoom device, which output signal is indicative of an unwanted movement of the optical zoom device, wherein the optical zoom device is configured to use said output signal to stabilize said image. 
     Further, according to an embodiment of the present invention, the optical zoom device is configured to use said output signal to control the respective actuator (particularly individually) for stabilizing said image. 
     Particularly, in an embodiment the optical zoom device can be calibrated in transmission by recording the focal power versus the actuation current applied to the respective actuator using a linear current source or alternatively by measuring the focal power versus one or more sensor signals. This enables a fast initial tuning without the image sensor data processing. 
     The algorithm can be based on one or more lookup tables for different sensor conditions and known physical properties of the first and/or second lens such as orientation dependence. Alternatively, the algorithm may also be based on a function such as a polynomial of order n for changing an actuation current applied to the respective actuator in a closed loop. 
     Furthermore, the environmental temperature can be used as an additional sensor signal to modify the lookup table and correct effects of the first and/or second lens due to changes in temperature. 
     Further, the calibration information can be stored into a memory of the optical zoom device such as an EEPROM. 
     According to yet another aspect of the present invention, a device comprising an optical zoom device according to the present invention and a camera having a wider field of view than the optical zoom device is disclosed, wherein said camera has a lower F-number than the optical zoom device. Particularly, the F-number of an optical system such as a camera lens is the ratio of the system&#39;s focal length to the diameter of the entrance pupil. 
     This allows to have a very good optical quality for wide field of view cameras and still give a good optical zoom effect with less constraints on the F-number. 
     Particularly, the present invention can be applied to the following technical fields/can be used in the following devices: 
     Ophthalmology equipment such as phoropter, refractometer, pachymeter, biometrics, perimeter, refrakto-keratometer, refractive lens analyzer, tonometer, anomaloskop, kontrastometer, endothelmicroscope, anomaloscope, binoptometer, OCT, rodatest, ophthalmoscope, RTA, machine vision, mobile phone cameras, medical equipment, robot cam, virtual reality or augmented reality cameras, microscopes, telescopes, endoscopes, drone cameras, surveillance camera, web cams, automotive cameras, motion tracking, binoculars, research, automotive, projectors, ophthalmic lenses, range finder, bar code readers, 3D sensing. 
    
    
     
       Further features and advantages of the present inventions as well as embodiments of the present invention shall be described in the following with reference to the Figures, wherein 
         FIG. 1  shows an embodiment of an optical zoom device comprising a piezo actuator for actuating a first lens as well as actuators comprising a shape memory alloy for actuating a second lens of the optical zoom device; 
         FIG. 2  shows a perspective and cross-sectional view of the embodiment shown in  FIG. 1 ; 
         FIG. 3  shows a detail of the embodiment shown in  FIGS. 1 and 2 ; 
         FIG. 4  shows a further detail of the embodiment shown in  FIGS. 1 to 3 ; 
         FIG. 5  shows a perspective and cross-sectional view of a variant of the embodiment shown in  FIGS. 1 to 4 ; 
         FIG. 6  shows a further aspect of the present invention, namely a device comprising a camera and a separate optical zoom device according to the present invention; 
         FIG. 7  shows different possible arrangements of the first and the second lens regarding the location of the respective lens shaping member; 
         FIG. 8  shows schematic illustrations of possible interactions of the respective lens shaping member with the associated membrane of a first or second lens for adjusting the focal length of the respective (first or second) lens; 
         FIG. 9  shows further possible arrangements of the first and the second lens, particularly regarding the location of the respective lens shaping member; 
         FIG. 10  shows a schematic illustration of a further embodiment of an optical zoom device according to the present invention; 
         FIG. 11  shows a schematic illustration of two further embodiments of an optical zoom device according to the present invention, wherein for each embodiment only one half of the device is shown, i.e. the first embodiment is shown above the optical axes A, A′; the second embodiment is depicted below the optical axes A, A′; 
         FIG. 12  shows a perspective view of an embodiment of an optical zoom device according to the present invention of the kind shown in  FIG. 11  (lower half); 
         FIG. 13  shows a schematical illustration of the minimal configuration of four actuators as used in the embodiments of  FIGS. 10 to 12 ; 
         FIG. 14  shows different embodiments regarding a connection between a pusher of an actuator and a lens shaping member (or lens core); 
         FIGS. 15 to 17  show details of the actuators of the embodiment of  FIGS. 11  (lower half) and  12 ; 
         FIG. 18  shows an electropermanent magnet that can be used as an actuator in the framework of the present invention; 
         FIG. 19  shows a schematical representation of an optical sensor that can be used to measure the movement of the pusher of the respective actuator; 
         FIG. 20  shows the principle of optical image stabilization and adjustment of the focal length of a (first or second) lens in case the respective lens core is moved by the actuators; 
         FIG. 21  shows the principle of optical image stabilization and adjustment of the focal length of a (first or second) lens in case the respective lens shaping member is moved by the actuators; and 
         FIGS. 22 to 23  illustrate the use of a tiltable prism for stabilizing an image generated with help of the optical zoom device. 
     
    
    
     The present invention relates to an optical zoom device  1 , wherein particular embodiments of this device are shown e.g. in  FIGS. 1 to 5 ,  FIGS. 7 to 17 , and  FIGS. 22 to 23 . 
     According thereto, an optical zoom device according to the present invention comprises a first lens  10  having an adjustable focal length and a second lens  20  having an adjustable focal lens, wherein, as e.g. shown in  FIG. 8(A) , each lens  10 ,  20  comprises a lens core  11 ,  21  filled with a transparent fluid (e.g. liquid)  12 ,  22 , wherein the respective lens core  11 ,  21  comprises a first wall  13 ,  23  in the form of an elastically deformable membrane and a transparent second wall  14 ,  24  facing the first wall  13 ,  23 , wherein the fluid  12 ,  22  is arranged between the two walls  13 ,  23 ;  14 ,  24  of the respective lens core  11 ,  21 , and wherein the respective lens  10 ,  20  comprises a lens shaping member  15 ,  25  interacting with the respective membrane  13 ,  23  for adjusting the focal length of the respective lens  10 ,  20  and, according to some embodiments, also for stabilizing an image generated with help of the two lenses  10 ,  20 . Further, the optical zoom device  1  particularly comprises a first and a separate second lens barrel  30 ,  31 , which are connected to each other, wherein the first lens core  11  is mounted on the first lens barrel  30  and the second lens core  21  is mounted on the second lens barrel  31 . Further, particularly, the optical zoom device  1  comprises an image sensor  2  that is mounted to the second lens barrel  31 , such that the image sensor faces the second lens  20  and particularly also the first lens  10 . Particularly, the first lens  10 , the second lens  20 , and the image sensor can be aligned with respect to a common optical axis A, A′ 
     For actuating the respective focus adjustable fluidic lens  10 ,  20  the optical zoom device  1  comprises at least one actuator  40  associated to the first lens  10 , namely for generating said interaction of the lens shaping member  15  of the first lens  10  with the membrane  13  of the first lens  10  for adjusting said focal length of the first lens  10 , as well as at least one actuator  41  associated to the second lens ( 20 ) for generating said interaction of the lens shaping member  25  of the second lens  20  with the membrane  23  of the second lens  20  for adjusting said focal length of the second lens  20 . 
     The principle of the adjustment of the focal length of the first or second lens  10 ,  20  is e.g. depicted in  FIGS. 8(B) , (C), and (D). Particularly, the lens shaping member  15 ,  25  of the respective lens  10 ,  20  defines an area  13   a ,  23   a  of the respective membrane  13 ,  23  that has an adjustable curvature. As can be seen from  FIGS. 8(A) to 8(D) , light L impinging on the respective area  13   a ,  23   a  will be deflected more strongly in case the respective area  13   a ,  23   a  has a larger curvature. Thus, the focal length of the respective lens  10 ,  20  can be adjusted by adjusting the curvature of said areas  13   a ,  23   a  using the respective lens shaping member  15 ,  25 . 
     Particularly, the optical device  1  is configured to adjust the respective curvature by an interaction of the respective lens shaping member  15 ,  25  with the respective membrane  13 ,  23 , e.g. by pushing the respective lens shaping member  15 ,  25  against the respective membrane  13 ,  23  as shown in  FIG. 8(B)  generating a more pronounces convex shape of the respective area  13   a ,  23   b  or lens  10 ,  20  or by pulling on the respective membrane  13 ,  23  by means of the respective lens shaping member  15 ,  25 , as shown in  FIG. 8(D)  which allows realizing a concave shape of the respective area  13   a ,  23   a  or lens  10 ,  20 . 
     Thus, by way of an axial movement of the respective lens shaping member  15 ,  25  towards or away from the respective lens core  11 ,  21 , the focal length of the respective lens  10 ,  20  can be adjusted. Of course, this can also be achieved by moving the respective lens core  11 ,  21  and keeping the respective lens shaping member  15 ,  25  in a fixed position. Basically, in all embodiments either the respective lens shaping member  15 ,  25  is moved or the respective lens core  11 ,  21 . 
     Furthermore, one of the lenses  10 ,  20  or both lenses  10 ,  20  can be used to also stabilize an image generated by means of the optical zoom device that is projected onto an image sensor  2  of the device  1 . Such a stabilization allows to counteract an unwanted (e.g. sudden) movement of the optical zoom device  1 . Such a movement can be detected by a gyroscope  100  as e.g. shown in  FIG. 1 , which generates an output signal indicative of the unwanted movement. This signal can be used to control the first and/or the second lens  10  in such a manner that the generated image is shifted so as to counteract the unwanted movement. Thus, the position of the image on the image sensor  2  can be maintained. This is denoted as optical image stabilization (OIS). 
     According to  FIGS. 20 and 21 , optical image stabilization can be achieved by shifting the image in 2D with respect to the image sensor in an image plane of the image sensor  2 . Such a shifting of the image is achieved by deflecting light L entering one of the lenses  10 ,  20  in two dimensions (i.e. in two different, particularly orthogonal direction) or by deflecting the incoming light L in a first direction with the first lens  10  and in a second direction with the second lens  20 . 
       FIGS. 20 and 21  show such an image shift as an example for a single direction using a single lens  10  or  20 . Particularly, according to  FIG. 20 , the respective lens core  11 ,  12  can be tilted with respect to a fixed lens shaping member  15 ,  25  which deforms the respective lens core  11 ,  21  so that the latter forms an (adjustable) prism that deflects the outgoing light L′ in a desired fashion. The amount of the tilt can be controlled using said output signal of the gyroscope  100 . Particularly,  FIGS. 20(A) to 20(C)  show tilting of the lens core  11 ,  21  with flat area  13   a ,  23   a , while  FIGS. 20(D) to 20(F)  show tilting of the respective lens core  11 ,  21  with a curved area  13   a ,  23   a  of the respective lens  10 ,  20 . 
     Alternatively, as shown in  FIG. 21 , the respective lens shaping member  15 ,  25  can be tilted with respect to a fixed lens core  11 ,  21  which also generates an adjustable prism. Also here,  FIGS. 21(A) to 21(C)  show tilting of the lens shaping member  15 ,  25  with flat area  13   a ,  23   a , while  FIGS. 21(D) to 21(F)  show tilting of the respective lens shaping member  15 ,  25  with a curved area  13   a ,  23   a  of the respective lens  10 ,  20 . Thus, optical image stabilization and focus adjustments can be carried out simultaneously. 
     However, it is also possible to not use the lenses  10 ,  20  for optical image stabilization. Particularly, in the individual embodiments also variants are conceivable in which the image stabilization is performed using a tiltable prism  5  as shown in  FIGS. 22  to and  23 . Here, the prism is arranged on a gimbal so that it can be tilted about two independent axes corresponding to a 2D shift of the image on the image sensor  2 . The gimbal  201  can be tilted using a magnet  202  connected to the gimbal, wherein the magnet is moved by means of electrical currents applied to coils arranged in or on the substrate PCB  204 . The movement of the gimbal  201 /prism  202  can be measured by measuring the movement of the magnet  202  by means of a Hall sensor  203  that can be arranged on the substrate/PCB  204 . 
       FIG. 1  shows in conjunction with  FIGS. 2 to 4  an embodiment of the present invention, an embodiment in which the first lens is actuated by a single linear actuator, particularly a piezo actuator, while the second lens  10  is actuated by four actuators  41  comprising a shape memory alloy  411 , respectively. Here, these four actuators  41  are configured to adjust the focal length of the second lens  20  as well as for deflecting light passing through the second lens  20  for stabilizing an image generated with help of the lenses  10 ,  20  and projected onto the image sensor  2 . 
     Particularly, the linear actuator  40  of the first lens  10  is arranged outside the first lens barrel  30  on a lateral wall  30   a  of the first lens barrel  30  and is configured to move a pusher  400  in the form of a rod along the optical axis A of the first lens  10 , wherein the pusher  400  is connected to the lens shaping member  15  of the first lens  10 , so that the focal length of the first lens  10  can be adjusted as explained above by moving the lens shaping member  15  with respect to the lens core  11  of the first lens  10 , which lens core  11  is fixed to the first lens barrel  30  of the optical zoom device  1 . Here, the first lens  10  is merely configured for adjustments of the focal length of the first lens  10 , so that only a single actuator  40  is necessary. 
     In an alternative embodiment shown in  FIG. 5  such a single actuator  40  can be instead be formed by a voice coil motor comprising a coil  62  extending around the optical axis A which coil  62  faces a circumferential magnet  72  attached to the lens shaping member  15 . Here, the device  1  is configured to apply an electrical current to the coil  62  so that the magnet  72  is pushed away from the coil  62  or pulled towards the coil  62  depending on the direction of the current in the coil  62  (for a given magnetization of the magnet  72  that is parallel to the optical axis A) 
     Further, the four actuators  41  of the second lens  20  are arranged on a lateral wall  31   a  of the second lens barrel  31  outside the latter. The four actuators  41  each comprise an elongated member  411  formed out of a shape memory alloy, wherein each member  411  is connected on one end to a region  510  of the lens core  21  of the second lens  20  and on the other end to the lateral wall  31   a  of the second lens barrel  31 . Furthermore, a spring  412  is associated to each member  411  and also connected on one end to the respective region  510  and on the other end to the lateral wall  31   a  of the second lens barrel  31 . By heating the individual member  411  to a certain temperature the respective member contracts against the restoring action of the respective spring  412 . Thus, by actuating all members at the same time, the lens core  21  of the second lens can be pushed against the lens shaping member  25  of the second lens  20 , which lens shaping member  25  is fixed with respect to the second lens barrel  31 , or the lens core  21  can be moved away from the lens shaping member  25  so that the latter can also pull on the membrane  23  of the second lens  20  which allows to adjust the focal length of the second lens  20  as described above in conjunction with  FIGS. 8(A)  to (D). 
     By actuating the actuators  41  e.g. in pairs (e.g. two actuators  41  which face each other diagonally in  FIG. 1  with respect to the second lens barrel  31 , the lens core  21  can be tilted about at least two different axes which allows to stabilize an image projected by the optical zoom device  1  onto the image sensor  2  as described above. Here, the image sensor  2  is mounted to an end of the second lens barrel  31  so that the image sensor  2  extends perpendicular to the optical axis A′ of the second lens  20  and faces the second lens  20  in the direction of the optical axis A′. 
     Particularly, apart from the focus adjustable lenses  10 ,  20 , each lens barrel can hold further rigid lenses  3  as indicated e.g. in  FIG. 2 . Further, the first lens barrel  30  can comprise a tube  300  extending in a circumferential manner on an inside of the first lens barrel  30 , which tube  300  is configured to prevent stray light. 
     Furthermore, the optical zoom device  1  can comprise a front lens forming the first lens in the optical path of the device  1 , which lens  4  is followed by a prism  5 . Both prism  5  and front lens  4  are mounted to a third barrel  32  that is connected to the first lens barrel  30  so that the first lens barrel is arranged between the third (prism) barrel  32  and the second lens barrel  31 . 
     Furthermore, for allowing a fast assembly of the optical zoom device, each two adjacent barrels  30 ,  31 ,  32  are configured to be connected to each other via positive connection. 
     Furthermore, as indicated in  FIG. 2  for achieving a compact device height, the first lens  10  has an outer diameter D 1  perpendicular to the optical axis A of the first lens  10  that is equal to an outer diameter D 2  of the first lens barrel  30  perpendicular to said optical axis A of the first lens barrel  30 , wherein the first lens barrel  30  comprises an opening  301  for holding the lens core  11  of the first lens  10 . Particularly, a lateral wall  302  delimiting said opening  301  of the first lens barrel  30  comprises recesses  303  for receiving a portion of the lens core  11  of the first lens  10 , respectively, which allows said diameters D 1 , D 2  to be of equal size. This concept can also be applied to other interfaces between components of the device  1 . 
     Regarding the placement of the individual components, particularly the lenses  10 ,  20  in the optical path of the device  1 , various configurations are possible as shown in  FIGS. 7(A)  to (D) and  FIGS. 9(A)  to (D). 
     For instance, the first lens can be placed after a mirror  6  (or alternatively prism  5 ) in the optical path of the device as shown in  FIGS. 7(A)  to (D), wherein the lens shaping member  15  of the first lens  10  can face away from the prism  5 /mirror  6  ( FIGS. 7(A) and 7(B) ) or face the prism  5  or mirror  6  ( FIGS. 7(C) and 7(D) ). In the same manner, the lens shaping member  25  of the second lens  20  can face the prism  5 /mirror  6  ( FIGS. 7(A) and 7(C) ) or face away from the prism  5 /mirror  6  ( FIGS. 7(B) and 7(C) ). 
       FIG. 9  (A) to (D) also shows these configurations, wherein here, in contrast to  FIG. 8 , the first lens is arranged in front of the prism  5 /mirror  6  in the optical path of the device  1 , i.e., the prism  5 /mirror  6  is arranged between the first lens  10  and the second lens  20  in the optical path of the device. 
     The further embodiments of the optical device shown in  FIGS. 10 to 17  relate to configurations, where each lens  10 ,  20  comprises two actuators  40 ,  41 , wherein the two actuators  40  of the first lens  10  adjust the focal length and are configured to shift the image in a first shifting direction D, while the two actuators  41  of the second lens  20  also provide adjustment of the focal length, but are configured to shift the image in a different (e.g. orthogonal) second shifting direction D′ as is indicated schematically in  FIG. 13 . 
     This is done by arranging the two actuators  40  of the first lens  10  on a lateral wall  30   a  of the first lens barrel  30  (outside the lens first barrel  30 ) such that they can each act on a region  500  of the lens shaping member  15  of the first lens  10 , wherein these regions  500  face each other diagonally in the first shifting direction D′. In contrast thereto, regions  510  of the lens shaping member  25  on which the actuators  41  of the second lens  20  act face each other in a different (e.g. orthogonal) second shifting direction D′. Also here, the two actuators  441  are arranged on a lateral wall  31   a  of the second lens barrel  31  (outside the second lens barrel  31 ). This allows one to tilt the lens shaping member  15  of the first lens  10  about an associated axis B (perpendicular to D) while the lens shaping member  25  can be tilted about a different axis B′ (perpendicular to D′). Particularly, these two axes B, B′ can be oriented perpendicular with respect to each other. 
     In the following, it is assumed that the respective lens shaping member  15 ,  25  is moved while the respective lens core  11 ,  21  is fixed to the corresponding lens barrel  30 ,  31 . However, it is always possible in modified embodiments to move the lens core  11 ,  21  instead and fix the respective lens shaper  15 ,  25  to the associated lens barrel  30 ,  31 . 
     As shown in  FIG. 10 , each of the two actuators  40  of the first lens  10  comprises a pusher  400  arranged outside the first lens barrel  30 , wherein the respective pusher  400  is movable along the optical axis A of the first lens  10 , wherein each of said pushers  400  of the first lens  10  is connected to one of said regions  500  of the lens shaping member  15  of the first lens  10  as described above to exert a force on the respective region  500  of the lens shaping member  15 . Further, also each of the two actuators  41  of the second lens  20  comprises a pusher  410  that is movable along an optical axis A′ of the second lens  20 , wherein each of said pushers  410  of the second lens  20  is connected to one of said regions  510  of the lens shaping member  25  of the second lens  20  to exert a force on the respective region  510 . 
     Particularly, regarding all embodiments relating to pushers  400 ,  410 , different possibilities exist for connecting the respective pusher  400 ,  410  to its associated region  500 ,  510  of the respective lens shaping member  15 ,  25   
     Particularly, as shown in  FIG. 14(A)  the respective pusher  400 ,  410  can be connected to the respective region  500 ,  510  via a latching connection C 1 , wherein a section of the respective pusher  400 ,  410  engages with a recess of the respective region  500 ,  510 . 
     Alternatively, as shown in  FIG. 14(C) , the respective pusher  400 ,  410  can be connected to the respective region  500 ,  510  via a glued connection C 2 . 
     Furthermore, the respective pusher  400 ,  410  can be connected to the respective region  500 ,  510  via a flexible piston C 3 . 
     Furthermore, referring to  FIG. 10 , each actuator  40  of the two actuators  40  of the first lens  10  comprises an electrically conducting coil  60  and a magnet structure  70  comprising a first section  70   a  having a first magnetization M 1  and an adjacent second section  70   b  having a second magnetization M 2 , wherein the two magnetizations M 1 , M 2  are antiparallel (i.e. are parallel but point in opposite directions) and particularly extend orthogonal to the optical axis A of the first lens  10 . Furthermore, the respective coil  60  comprises a first portion  60   a  and a second portion  60   b , wherein the first portion  60   a  of the coil  60  faces the first section  70   a  of the magnet structure  70  whereas the second portion  60   b  of the coil  60  faces the second section  70   b  of the magnet structure  70 . Further, particularly, the respective coil  60  comprises a conductor that extends around a coil axis C of the respective coil  60 , wherein the coil axis C particularly extends parallel to the magnetizations M 1 , M 2 . 
     In the same fashion, also each actuator  41  of the two actuators  40  of the second lens  20  comprises an electrically conducting coil  61  and a magnet structure  71  comprising a first section  71   a  having a first magnetization M 1  and an adjacent second section  71   b  having a second magnetization M 2 , wherein the two magnetizations M 1 , M 2  are antiparallel and particularly extend orthogonal to an optical axis A′ of the second lens  20 . Further, the respective coil  61  comprises again a first portion  61   a  and a second portion  61   b , wherein the first portion  61   a  of the respective coil  61  faces the first section  71   a  of the respective magnet structure  71  whereas the second portion  61   b  of the respective coil  61  faces the second section  71   b  of the respective magnet structure  71 . Further, particularly, the respective coil  61  comprises a conductor that extends around a coil axis C′ of the respective coil  61 , wherein the respective coil axis C′ particularly extends parallel to the magnetizations M 1 , M 2 . 
     As can be seen from  FIG. 10 , the embodiment realizes a so called moving coil configuration, i.e., the magnet structure  70  of the respective actuator  40  of the first lens  10  is rigidly coupled to the first lens barrel  30 , whereas the coil  60  of the respective actuator  40  of the first lens  10  is arranged on the pusher  400  of the respective actuator  40  of the first lens  10  and thus moves with the respective pusher  400 . 
     In the same fashion, the magnet structure  71  of the respective actuator  41  of the second lens  20  is rigidly coupled to the second lens barrel  31 , whereas the coil  61  of the respective actuator  41  of the second lens  20  is arranged on the pusher  410  of the respective actuator  41  of the second lens  20  and thus moves with the respective pusher  410 . 
     Furthermore, the pusher  400  of the respective actuator  40  of the first lens  10  is elastically coupled to the first lens barrel  30  via a spring structure  9  such that the pusher  400  of the respective actuator  40  of the first lens  10  is movable along the optical axis A of the first lens  10 . In the same manner, the pusher  410  of the respective actuator  41  of the second lens  20  is elastically coupled to the second lens barrel  31  via a spring structure  9  such that the pusher  410  of the respective actuator  41  of the second lens  20  is movable along the optical axis A′ of the second lens  20 . 
     Further, in order to properly guide magnetic fluxes generates by the magnet structures  70 ,  71 , the optical zoom device  1  can comprise two magnetic flux return structures  800 , particularly in the form of an elongated plate, respectively. Particularly, each magnetic flux return structure  800  is connected to both sections  70   a ,  70   b  of a magnet structure  70  of an actuator  40  of the first lens  10  as well as to both sections  71   a ,  71   b  of a magnet structure  71  of an actuator  41  of the second lens  20 . The respective return structure  800  is configured to guide or return the magnetic flux from a section  70   a ,  70   b ,  71   a ,  71   b  of the magnet structure  70 ,  71  to the adjacent section  70   a ,  70   b ,  71   a ,  71   b  of the magnet structure  70 ,  71  to which it is connected. Particularly, the respective magnetic flux return structure  800  can extend along the optical axis A of the first lens  10  and the optical axis A′ of the second lens  20 . Further, the two magnetic flux return structures  800  face each other in a direction perpendicular to the said optical axes A, A′. Particularly, the respective magnetic flux return structure  800  can be connected to or can be a part of a housing  7  or shield  8  enclosing the first and/or the second lens barrel  30 ,  31 . 
     Now, in order to move the pushers  400 ,  410  of the actuators so as to adjust the focal lengths of the lenses and to provide image stabilization, the optical zoom device  1  is configured to apply an electrical current to the coil  60  of the respective actuator  40  of the first lens  10  for interacting with a magnetic field of the magnet structure  70  of the respective actuator  40  of the first lens  10  such that the pusher  400  of the respective actuator  40  of the first lens  10  is moved along the optical axis A of the first lens  10  wherein, depending on the direction of the current in the coil  60  of the respective actuator  40  of the first lens  10 , the pusher  400  of the respective actuator  40  of the first lens  10  is either moved such along the optical axis A of the first lens  10  that the lens shaping member  15  of the first lens  10  presses against the membrane  13  of the first lens  10  or pulls on the membrane  13  of the first lens  10  to adjust the focal length of the first lens  10  and/or to stabilize said image. In each case the respective force is exerted by the respective pusher  400  on the lens shaping member  15  of the first lens  10  via the respective region  500 . In case of equal forces on the regions  500 , just the focal length of the first lens  10  is adjusted (see above). In case e.g. opposite forces are exerted on said regions  500  of the lens shaping member  15 , the latter can be tilted for shifting the image in the first shifting direction D for providing optical image stabilization. 
     Analogously, the optical zoom device  1  is also configured to apply an electrical current to the coil  61  of the respective actuator  41  of the second lens  20  for interacting with a magnetic field of the magnet structure  71  of the respective actuator  41  of the second lens  20  such that the pusher  410  of the respective actuator  41  of the second lens  20  is moved along the optical axis A′ of the second lens  20 , wherein, depending on the direction of the current in the coil  61  of the respective actuator  41  of the second lens  20 , the pusher  410  of the respective actuator  41  of the second lens  20  is either moved such along the optical axis A′ of the second lens  20  that the lens shaping member  25  of the second lens  20  presses against the membrane  23  of the second lens  20  or pulls on the membrane  23  of the second lens  20  to adjust the focal length of the second lens  20  and/or to stabilize said image. In each case the respective force is exerted by the respective pusher  410  on the lens shaping member  25  of the second lens  20  via the respective region  510 . In case of equal forces on the regions  510 , again just the focal length of the second lens  20  is adjusted (see above). In case e.g. opposite forces are exerted on said regions  510  of the lens shaping member  25 , the latter can be tilted for shifting the image in the second shifting direction D′ for providing optical image stabilization. Thus, tilting both lens shaping members  15 ,  25  allows realizing a 2D shift of the image on the image sensor  2  if necessary. Particularly, the respective current flows in opposite directions in said two portions  60   a ,  60   b ,  61   a ,  61   b  of the respective coil  60 ,  61 . 
     In contrast to  FIG. 10 ,  FIG. 11  shows an embodiment comprising an actuator configuration having so called moving magnets. 
     Here, the coil  60  of the respective actuator  40  of the first lens  10  is rigidly coupled to the first lens barrel  30 , whereas the magnet structure  70  of the respective actuator  40  of the first lens  10  is arranged on the pusher  400  of the respective actuator  40  of the first lens  10 . Furthermore, the coil  61  of the respective actuator  41  of the second lens  20  is rigidly coupled to the second lens barrel  31 , whereas the magnet structure  71  of the respective actuator  41  of the second lens  20  is arranged on the pusher  410  of the respective actuator  41  of the second lens  20 . 
     According to the upper half of  FIG. 11 , the respective coil  60 ,  61  can be embedded into a substrate  600 , particularly in the form of a printed circuit board. Particularly, the optical zoom device  1  can comprise two (e.g. elongated) substrates  600  (e.g. printed circuit boards), wherein each substrate  600  comprises a coil  60  of an actuator  40  of the first lens  10  as well as a coil  61  of an actuator  41  of the second lens  20 . Particularly, the two substrates  600  can be connected to a housing  7  enclosing the first and/or the second lens barrel  30 ,  31 . Particularly, the two substrates  600  can face each other in a direction perpendicular to the optical axis A of the first lens  10  and to the optical axis A′ of the second lens  20 . 
     Further, according to  FIG. 11  (upper half), instead of having a common return structure  800  for two neighboring actuators  40 ,  41  of the first and the second lens  10 ,  20 , each magnet structure  70 ,  71  is connected to a separate first magnetic flux return structure  80 ,  81 . The respective magnetic flux return structure  80 ,  81  is configured to guide or return the magnetic flux coming from one section  70   a ,  70   b ,  71   a ,  71   b  of the magnet structure to the adjacent section  70   a ,  70   b ,  71   a ,  71   b  of the magnet structure  70 ,  71  to which it is connected. Particularly, these first magnetic flux return structures  80 ,  81  are each rigidly coupled to the associated pusher  400 ,  410  and thus move together with the respective pusher  400 ,  410 . 
     The lower half of  FIG. 11  shows a further embodiment of the present invention in a schematical fashion. The  FIGS. 12, 14 to 17  show further illustrations of an embodiment of this kind. 
     Here, particularly, the optical zoom device  1  can comprise two substrate assemblies  610 , wherein each substrate assembly  610  comprises two substrates  611 ,  612  electrically connected by a flexible connector  613  to provide electrical connections between the two substrates  611 ,  612 , wherein one of the two substrates  611  comprises an embedded coil  60  of an actuator  40  of the first lens  10  while the other substrate  612  comprises a coil  61  of an actuator  41  of the second lens  20 . Again, particularly, the two substrate assemblies  610  can face each other in a direction perpendicular to the optical axis A of the first lens  10  and the optical axis A′ of the second lens  20 . 
     Furthermore, besides the first return structures  80 ,  81  described in conjunction with  FIG. 11  (upper half), the optical zoom device  1  can comprise two second magnetic flux return structures  800 , particularly in the form of an elongated plate, respectively. Particularly, each second magnetic flux return structure  800  faces both sections  70   a ,  70   b  of a magnet structure  70  of an actuator  40  of the first lens  10  as well as both sections  71   a ,  71   b  of a magnet structure  71  of an actuator  41  of the second lens  20 . The respective second return structure  800  is configured to guide or return the magnetic flux coming from a section  70   a ,  70   b ,  71   a ,  71   b  of the magnet structure  70 ,  71  to an adjacent section  70   a ,  70   b ,  71   a ,  71   b  of the magnet structure  70 ,  71 . Particularly, the respective second magnetic flux return structure  800  can extend along the optical axis A of the first lens  10  and the optical axis A′ of the second lens  20 . Further, the two second magnetic flux return structures  800  face each other in a direction perpendicular to the said optical axes A, A′. Particularly, the respective magnetic flux return structure  800  can be connected to or can be a part of a housing  7  or shield  8  enclosing the first and/or the second lens barrel  30 ,  31 . Thus, here, every coil  60 ,  61  of an actuator  40 ,  41  is arranged between a first and a second magnetic flux return structure  80 ,  81 ,  800 . 
     Further, as particularly shown in  FIGS. 12 and 15 to 17 , the respective actuator  40  of the first lens  10  comprises a coil holder  620  for holding a substrate  611  (and the coil  60  embedded therein) of a substrate assembly  610 , via which coil holder  620  the respective coil  60  embedded into the substrate  611  is rigidly connected to the first lens barrel  30 . 
     Further, the respective actuator  41  of the second lens  20  also comprises a coil holder  630  for holding a substrate  612  (and the coil  61  embedded therein) of a substrate assembly  610 , via which coil holder  630  the respective coil  61  embedded into the substrate  612  is rigidly connected to the second lens barrel  31 . 
     The respective coil holder  620 ,  630  can further comprise a recess  621 ,  631  for accommodating said flexible connector  613  that connects the two substrates  611 ,  612  of a substrate assembly  610 . 
     Furthermore, as shown in  FIG. 11  (lower half) and  FIGS. 15 to 17  the pusher  400  of the respective actuator  40  of the first lens  10  is supported on ball bearings  641  such that the pusher  400  of the respective actuator  40  of the first lens  10  is movable along the optical axis A of the first lens  10 . In the same fashion also the pusher  410  of the respective actuator  41  of the second lens  20  is supported on ball bearings  651  such that the pusher  410  of the respective actuator  41  of the second lens  20  is movable along the optical axis A′ of the second lens  20 . 
     Particularly, the respective pusher  400 ,  410  can be supported via said (e.g. four) ball bearings  641 ,  651  on the coil holder  620 ,  630  that may surround the first and/or second lens barrel  30 ,  31 , and that may be rigidly coupled to the first and/or second lens barrel  30 ,  31 . 
     Particularly, the respective actuator  40  of the first lens  10  can comprise a cage  640 , e.g. in the form of a frame, for holding the respective ball bearing  641 , particularly four ball bearings  641  can be held by corner regions of the cage  640 . Likewise, the respective actuator  41  of the second lens  20  can comprise a cage  650 , e.g. in the form of a frame, for holding the respective ball bearing  651 . Also here four ball bearings  651  can be held by corner regions of the cage  650 . 
     Furthermore, in the above-described embodiments the optical device  1  according to the present invention is preferably configured to measure a movement of the respective pusher  400  of the first lens  10  along the optical axis A of the first lens  10  using a sensor  90  associated to the respective pusher  400 . Further, in the same fashion, the optical device  1  is preferably configured to measure a movement of the respective pusher  410  of the second lens  20  along the optical axis A′ of the second lens  20  using a sensor  91  associated to the respective pusher  410 . 
     Particularly, the respective sensor  90 ,  91  is a Hall sensor for measuring the movement of the respective magnet structure  70 ,  71   
     According to  FIGS. 11, 15 and 17 , the respective Hall sensor can be arranged on the respective substrate  611 ,  612 . Alternatively other positions that allow sensing the movement of the magnet structures  70 ,  71  are also conceivable (cf.  FIG. 11 ). Further, in  FIG. 15  also a possible current direction I is indicated for the coil  60 . 
     Alternatively also inductive sensors, or capacitive sensors can be employed. According to  FIG. 19  also an optical sensor  90 ,  91  can be used. Such a sensor can comprise a moving mirror  900  (e.g. arranged on the respective pusher  400 ,  410 ) and a light source (e.g. LED)  901  that impinges light on the moving mirror. Reflected light is then detected by a photosensitive element (e.g. photo diode)  902 . The intensity of the reflected light depends on the position of the moving mirror  900 . 
     Furthermore, in the above embodiments generally all suitable actuator types can be used for the actuators  40 ,  41 . 
     Particularly, according to  FIG. 18 , also actuators comprising electropermanent magnets  40 ,  41  can be used. Such an actuator  40 ,  41  comprises a first magnet  75  comprising a magnetization that can be switched by applying an electrical current to a coil  65  surrounding the first magnet. The actuator  40 ,  41  further comprises a permanent second magnet  76  extending along the first magnet. In case the two magnets  75 ,  76  comprise an antiparallel magnetization, no external magnetic field is generated. In case the magnetization of the first magnet is switched by means of a current pulse applied to coil  65 , magnet flux is guided via the return structure and the (air) gap G to the magnetic flux guiding structure  78  and the latter is attracted towards the return structure against the action of the spring structure  79  that connects the magnetic flux guiding structure  78  to the return structure  77 . 
     Particularly, the magnetic flux guiding structure can be connected to a lens shaping member  15 ,  25  or to a lens core  11 ,  21  to adjust the focal length or to provide optical image stabilization as described herein. 
     Furthermore, different current levels in the coil  65  results in different Hc values. These magnetic fields from the coil  65  program the electropermanent magnet  40 ,  41  on a desired Mr value. 
     A tuning of the actuator  40 ,  41  can be achieved by using the inductivity of the coil  65 , e.g. by means of the switching time, by means of the applied voltage, by means of a PWM signal (any shape). 
     Finally,  FIG. 6  shows a further aspect of the present invention which relates to a device  1 ′ comprising an optical zoom device  1  according to the present invention and a camera  1 ″ having a wider field of view than the optical zoom device  1 , wherein said camera  1 ″ has a lower F-number than the optical zoom device  1 . Such a device  1 ′ can e.g. be used in mobile phones or other handheld devices and allows to have a very good optical quality for wide field of view cameras and still give a good optical zoom effect with less constraints on the F-number.