Patent Publication Number: US-2021181523-A1

Title: Reduced height penalty for folded camera

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/475,267 filed Jul. 1, 2019, which was a 371 application from international patent application No. PCT/IB2018/060203, which claims priority to U.S. provisional patent applications Nos. 62/626,306 filed Feb. 5, 2018, 62/658,819 filed Apr. 17, 2018, 62/672,754 filed May 17, 2018 and 62/677,012 filed May 27, 2018, the content of which applications is incorporated herein by reference in their entirety. 
    
    
     FIELD 
     Embodiments disclosed herein relate in general to digital cameras and in particular to thin folded optics cameras. 
     BACKGROUND 
     In recent years, mobile devices such as cell-phones (and in particular smart-phones), tablets and laptops have become ubiquitous. Many of these devices include one or two compact cameras including, for example, a main rear-facing camera (i.e. a camera on the back side of the device, facing away from the user and often used for casual photography) and a secondary front-facing camera (i.e. a camera located on the front side of the device and often used for video conferencing). 
     Although relatively compact in nature, the design of most of these cameras is similar to the traditional structure of a digital still camera, i.e. it comprises a lens assembly (or a train of several optical elements) placed on top of an image sensor. The lens assembly (also referred to as “lens module” or simply “lens”) refracts the incoming light rays and bends them to create an image of a scene on the sensor. The dimensions of these cameras are largely determined by the size of the sensor and by the height of the optics. These are usually tied together through the focal length (“f”) of the lens and its field of view (FOV)—a lens that has to image a certain FOV on a sensor of a certain size has a specific focal length. Keeping the FOV constant, the larger the sensor dimensions the larger the focal length and the optics height. 
     The assembly process of a traditional camera may include handling of a few sub-assemblies: a lens, a sensor board sub-assembly and an actuator. The lens may include a lens barrel made for example of plastic or metal and includes a few (3-7) lens elements which may be made of plastic or glass. The sensor board sub-assembly may include the image sensor, a printed circuit board (PCB) and electronics needed for the operation of the camera, as known in the art. The actuator is used to move the lens for optical needs (for example for focusing (and in particular auto focusing (AF)) and/or optical image stabilization (OIS)) and for mechanical protection of the other parts of the camera. In known art, the lens is inserted and attached (e.g. glued) to the actuator from one side, along the lens optical axis, whereas the sensor board is attached (e.g. glued) to the actuator from the opposite side along the optical axis. 
     “Folded camera modules” (or simply “folded cameras”) are known and have been suggested for incorporation in various “host” devices (e.g. smart-phones, tablets, laptops, smart TVs, etc.). In a folded camera, an optical path folding element (OPFE) e.g. a prism or a mirror (otherwise referred to herein collectively as “reflecting element”) tilts light arriving in a first optical path or direction (e.g. perpendicular to a back surface of a smart-phone) to a second optical path or direction (e.g. parallel to the smart-phone back surface). If the folded camera is part of a dual-aperture camera, this provides a folded optical path through one lens assembly (e.g. a Tele lens). Such a camera is referred to herein as “folded-lens dual-aperture camera” or “dual-aperture camera with a folded lens”. In general, the folded camera may be included in a multi-aperture camera, for example together with two “non-folded” (upright) camera modules in a triple-aperture camera, or in multi-aperture cameras with more than 3 cameras. 
     Actuators used for AF and OIS in smart-phone cameras are known. A commonly used actuator is based on voice coil motor (VCM) technology. In VCM technology, a permanent (or “fixed”) magnet and a coil are used to create actuation force. The coil is positioned in the vicinity of the magnetic field of the fixed magnet. Upon driving current in the coil, a Lorentz force is created on the coil, an in return an equal counter-force is applied on the magnet. The magnet or the coil is rigidly attached to an optical element to construct an actuating assembly. The actuating assembly is then moved by the magnetic Lorenz force. A VCM may also be referred to as “VCM engine” and an actuator including such a VCM (or VCM engine) may be referred to as to as “VCM actuator” or simply “actuator”. An actuator may be partially or fully surrounded by an envelope (sometimes also referred to as “shield”) having an envelope thickness. 
     In a folded camera with a moving lens mechanism (actuated by an actuator/VCM), at least one air gap is needed to allow movement. The envelope and other optional top and bottom elements or parts (e.g. a plate) added to protect the mechanism increase the total height of the actuator. A small height of a folded camera is important to allow a host device that includes it to be as thin as possible. The height of the camera is limited many times by the industrial design. In contrast, increasing the available height for the lens, sensor and OPFE may improve optical properties. 
     Envelope and other optional top and/or bottom parts add to the folded camera height. The height thus has a “penalty” that needs to be reduced. 
     In VCMs, in addition to the magnetic force, a mechanical rail is known to set the course of motion for the optical element. The mechanical rail keeps the motion of the lens in a desired path, as required by optical needs. One example of mechanical rail is known in the art as “spring-guided rail”, in which a spring or set of springs is used to set the motion direction. A VCM that includes a spring-guided rail is referred to as a “spring-guided VCM”. For example, US patent application No. 20110235196 discloses a lens element shifted in a linear spring rail to create focus. For example, international patent application PCT/IB2016/052179 discloses the incorporation and use of a spring guided VCM in a folded camera. The disclosure teaches a lens element shifted to create focus and OIS and an optical path folding element (OPFE) shifted in a rotational manner to create OIS. Also, PCT/IB2016/052179 teaches AF+OIS in a folded actuator where the actuator does not add to the folded camera height. 
     Another example mechanical rail is known in the art a “ball-guided rail”, see e.g. U.S. Pat. No. 8,810,714. With a ball-guided rail, the lens is bound to move in the desired direction by set of balls confined in a groove (also referred to as “slit”). A VCM that includes a ball-guided rail is referred to as a “ball-guided VCM”. A ball-guided VCM has several advantages over a spring-guided VCM. These include: (1) lower power consumption, because in a spring-guided VCM the magnetic force has to oppose a spring mechanical force, which does not exist in a ball-guided VCM, and (2) higher reliability in drops that may occur during the life cycle of a camera that includes the VCM. The actuation method in U.S. Pat. No. 8,810,714 is designed for an exemplary non-folded lens, where the lens optical axis is directly pointed at the object to be photographed and cannot be used in a folded camera. 
     There is a need for, and it would be advantageous to reduce height and length penalties in folded cameras both with respect to structures and to the design of a linear ball guided VCM. 
     SUMMARY 
     Embodiments disclosed herein relate to reduced height lens actuators (e.g. of VCM design) and folded cameras having such actuators. The term “lens” may refer to a lens assembly, comprising a train of several optical elements and a lens housing the lens elements. A lens is characterized by a fixed effective focal length (EFL), a clear aperture (CA), both of which are defined in international patent application PCT/IB2018/050988, which is incorporated herein by reference in its entirety, and a height, which is the distance along topmost and bottommost points on the lens. Lens elements may be made from plastic, glass and other materials known in the art. 
     The height of actuators and folded cameras is determined mainly by the lens diameter (height) and a “penalty”. In this description, any height that is additional to the lens diameter is considered herein to be a “penalty”. More specifically, a penalty is the sum of an upper (or top) height penalty and a lower (or bottom) height penalty, with the “upper”, “lower” and “penalty” terms described in detail below. 
     In various embodiments, a reduced height lens actuator disclosed herein may have an envelope with a bottom opening, a top opening or both bottom and top openings. A folded camera including such as actuator has a “reduced height penalty”, the reduction in height penalty brought about by the bottom opening, top opening or both bottom and top openings which allow to reduce the distance between the lens and outmost (e.g. top or bottom) surfaces of the envelope. The envelope may surround the lens actuator (e.g. be made of a sheet folded or bent around the lens actuator, or made of a few parts soldered or glued together. As mentioned, the envelope has an envelope thickness. The term “envelope thickness” refers to the thickness of the material forming the envelope (e.g. stainless steel, plastic, copper, etc.). If the envelope is made of different parts, the term “envelope thickness” refers to the thickness of each part. 
     In this description, an optical path-folding element (OPFE) is an optical element comprising a reflective plane, the OPFE capable of folding the light from one axis to a second axis, the two optical axes being substantially perpendicular to one another, with the reflective plane being tilted by 45 degrees relative to both optical axes. 
     In various embodiments, there are provided folded cameras, comprising: a movable lens positioned in an optical path between an OPFE and an image sensor, wherein the OPFE folds light from a first direction to a second direction and wherein the lens includes a lens optical axis parallel to the second direction, a lens height substantially aligned with the first direction, a first lens surface and a second lens surface diametrically opposed to the first surface, the first and second lens surfaces being in planes perpendicular to the first direction; and an envelope surrounding the lens in at least some sections and including, along the first direction, a first envelope section with a first opening positioned on a first side of the lens and a second envelope section without an opening positioned on a second, diametrically opposed side of the lens, wherein the first lens surface is distanced along the first direction from an external surface of the first envelope section by a first air gap, wherein the second lens surface is distanced along the first direction from an internal surface of the second envelope section by a second air gap, wherein the second envelope section has a second envelope section thickness and wherein the folded camera has a camera height substantially aligned with the first direction and substantially equal to a sum of the lens height, the first air gap, the second air gap and the second envelope section thickness. 
     In various embodiments, there are provided folded cameras, comprising: a movable lens positioned in an optical path between an optical path folding element (OPFE) and an image sensor, wherein the OPFE folds light from a first direction to a second direction and wherein the lens includes a lens optical axis parallel to the second direction, a lens height substantially aligned with the first direction, a first lens surface and a second lens surface diametrically opposed to the first surface, the first and second lens surfaces being in planes perpendicular to the first direction; and an envelope surrounding the lens and including, along the first direction, a first envelope section with a first opening positioned on a first side of the lens and a second envelope section with a second opening positioned on a second, diametrically opposed side of the lens, wherein the first lens surface is distanced along the first direction from an external surface of the first envelope section by a first air gap, wherein the second lens surface is distanced along the first direction from an external surface of the second envelope section by a second air gap, and wherein the folded camera has a camera height substantially aligned with the first direction and substantially equal to a sum of the lens height, the first air gap and the second air gap. 
     In some exemplary embodiments of a folded camera as above or below, each of the first and second air gaps may be in the range of 10-50 μm. In some exemplary embodiments, each of the first and second air gaps may be in the range of 10-100 μm. In some exemplary embodiments, each of the first and second air gaps may be in the range of 10-150 μm. 
     In some exemplary embodiments, the lens may be movable for focusing. 
     In some exemplary embodiments, the lens may be movable for optical image stabilization. 
     In some exemplary embodiments, the lens may be movable in two directions in a single plane for focusing and optical image stabilization, the single plane being perpendicular to the first direction. 
     In some exemplary embodiments, a folded camera as above has a height that does not exceed the lens height by more than about 600 μm. In some embodiments, the folded camera height does not exceed the lens height by more than 400 μm. In some embodiments, the folded camera height does not exceed the lens height by more than 300 μm. 
     In some exemplary embodiments, a folded camera as above may be included together with an upright camera in a dual-camera. 
     In an embodiment there is provided a folded camera, comprising: a lens actuator for moving a lens in at least one direction and including an envelope surrounding the lens in at least some sections and having an envelope thickness, the lens having a lens height and being positioned in an optical path between an optical path folding element and an image sensor and movable in the at least one direction, wherein the folded camera has a height smaller than the sum of the lens height, the size of a first air gap from the lens to the envelope, the size of a second air gap from the lens to the envelope and twice the envelope thickness. 
     In an embodiment there is provided a folded camera, comprising: a lens actuator for moving a lens in at least one direction and including an envelope surrounding the lens in at least some sections and having an envelope thickness, the lens having a lens height and being positioned in an optical path between an optical path folding element and an image sensor and movable in the at least one direction, wherein the folded camera has a height smaller than the sum of the lens height, the size of a first air gap from the lens to an external surface of the envelope, the size of a second air gap from the lens to the envelope and the envelope thickness. 
     In various embodiments, there are provided lens actuators for moving a lens, the lens having a lens optical axis parallel to a second direction and a lens height substantially aligned with a first direction that is substantially perpendicular to the second direction, the actuators comprising: an envelope surrounding the lens in at least some sections and including, along the first direction, a first envelope section with a first opening positioned on a first side of the lens and a second envelope section without an opening positioned on a second, diametrically opposed side of the lens, wherein the first lens surface is distanced along the first direction from an external surface of the first envelope section by a first air gap, wherein the second lens surface is distanced along the first direction from an internal surface of the second envelope section by a second air gap, wherein the second envelope section has a second envelope section thickness and wherein the folded camera has a camera height substantially aligned with the first direction and substantially equal to a sum of the lens height, the first air gap, the second air gap and the second envelope section thickness. 
     In various embodiments, there are provided lens actuators for moving a lens, the lens having a lens optical axis parallel to a second direction and a lens height substantially aligned with a first direction that is substantially perpendicular to the second direction, the actuators comprising: an envelope surrounding the lens in at least some sections and including, along the first direction, a first envelope section with a first opening positioned on a first side of the lens and a second envelope section with a second opening positioned on a second, diametrically opposed side of the lens, wherein the first lens surface is distanced along the first direction from an external surface of the first envelope section by a first air gap, wherein the second lens surface is distanced along the first direction from an external surface of the second envelope section by a second air gap, and wherein the folded camera has a camera height substantially aligned with the first direction and substantially equal to a sum of the lens height, the first air gap and the second air gap. 
     In some exemplary embodiments of an actuator as above or below, each of the first and second air gaps may be in the range of 10-50 μm. In some exemplary embodiments, each of the first and second air gaps may be in the range of 10-100 μm. In some exemplary embodiments, each of the first and second air gaps may be in the range of 10-150 μm. 
     In some exemplary embodiments, the lens may be movable for focusing. 
     In some exemplary embodiments, the lens may be movable for optical image stabilization. 
     In some exemplary embodiments, the lens may be movable in two directions in a single plane for focusing and optical image stabilization, the single plane being perpendicular to the first direction. 
     In some exemplary embodiments, an actuator as above or below has a height that does not exceed the lens height by more than about 600 μm. In some embodiments, the actuator height does not exceed the lens height by more than 400 μm. In some embodiments, the actuator height does not exceed the lens height by more than 300 μm. 
     In various embodiments, there are provided folded cameras comprising: a lens positioned in an optical path between an optical path folding element and an image sensor, the lens having a lens height and an optical axis, wherein the folded camera has a height not exceeding the lens height by more than 500 μm. 
     In an exemplary embodiment, the folded camera above may have a height not exceeding the lens height by more than 400 μm. 
     In an exemplary embodiment, the folded camera above may have a height not exceeding the lens height by more than 250 μm. 
     In an exemplary embodiment, the folded camera above may be included together with an upright camera in a dual-camera. 
     In an embodiment there is provided an actuator for actuating a lens having a lens optical axis for AF and optical image stabilization OIS, the actuator comprising: a stationary sub-assembly that includes an OIS coil having an OIS coil plane and an AF coil having an AF coil plane; and a lens actuating sub-assembly movable relative to the stationary sub-assembly and including a lens holder holding the lens, wherein the OIS coil plane is perpendicular to AF coil plane and wherein the lens optical axis lies between the OIS coil plane and the AF coil plane. 
     In an exemplary embodiment, the stationary sub-assembly further includes a plurality of upper stepping yokes, wherein the lens actuating sub-assembly further includes a plurality of stepping magnets coupled to the plurality of upper stepping yokes, and wherein the plurality of stepping yokes and the plurality of stepping magnets are operable to create stepping forces in a direction perpendicular to the lens optical axis for stepping. 
     In some exemplary embodiments, an actuator as above or below further comprises a middle actuating sub-assembly for AF and OIS positioned between the stationary sub-assembly and the lens top actuating sub-assembly. 
     In some exemplary embodiments, the stationary sub-assembly further includes an OIS Hall sensor bar used in conjunction with one of the stepping magnets to perform position sensing. 
     In some exemplary embodiments, some yokes of the plurality of stepping yokes are positioned on a first surface, wherein other yokes of the plurality of stepping yokes are positioned on a second surface, and wherein the first and second surfaces are parallel. 
     In some exemplary embodiments, an actuator as above may be included in a folded camera. 
     In various embodiments, there are provided folded cameras comprising: a lens having a lens optical axis, an optical path folding elelement for folding light from a first direction to a second direction, the second direction being essentially aligned with the lens optical axis, an image sensor and an actuator for actuating the lens for AF and OIS, the actuator comprising an AF VCM that includes an AF coil positioned in an AF plane and is operable to move the lens in an AF direction, and an OIS VCM that includes an OIS coil positioned in an OIS plane and is operable to move the lens in an OIS direction, wherein the AF plane and the OIS plane are perpendicular to each other, and wherein the two VCMs are located on opposite sides of a plane defined by the first and second directions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting examples of embodiments disclosed herein are described below with reference to figures attached hereto that are listed following this paragraph. Identical structures, elements or parts that appear in more than one figure are generally labeled with a same numeral in all the figures in which they appear. The drawings and descriptions are meant to illuminate and clarify embodiments disclosed herein and should not be considered limiting in any way. In the drawings: 
         FIG. 1A  shows an embodiment of a folded camera disclosed herein; 
         FIG. 1B  shows a cross section along cuts A-A and B-B of the folded camera of  FIG. 1A ; 
         FIG. 1C  shows another folded camera disclosed herein; 
         FIG. 1D  shows a side cut along a line B′-B′ of the folded camera in  FIG. 1C ; 
         FIG. 2A  shows schematically the elements of a folded camera disclosed herein; 
         FIG. 2B  shows an embodiment of a reduced height folded lens actuator with a bottom opening disclosed herein in a top perspective view; 
         FIG. 2C  shows the actuator embodiment of  FIG. 2B  without an upper envelope from a top perspective view; 
         FIG. 2D  shows the actuator embodiment of  FIG. 2B  from a bottom perspective view; 
         FIG. 2E  shows the actuator embodiment of  FIG. 2B  in a front section view along sections between sections C-C and D-D; 
         FIG. 2F  shows an embodiment of a reduced height folded camera that includes a lens actuator as in  FIGS. 2B-2E ; 
         FIG. 2G  shows a side cut along a cut D′-D′ of the folded camera embodiment of  FIG. 2F ; 
         FIG. 3A  shows an embodiment of a reduced height folded lens actuator with a top opening disclosed herein in a top perspective view; 
         FIG. 3B  shows the actuator embodiment of  FIG. 3A  without an upper envelope from a top perspective view; 
         FIG. 3C  shows the actuator embodiment of  FIG. 3A  from a bottom perspective view; 
         FIG. 3D  shows the actuator embodiment of  FIG. 3B  from a bottom perspective view; 
         FIG. 3E  shows the actuator embodiment of  FIGS. 3A-3D  in a front section view along sections between sections A-A and B-B in  FIG. 3A ; 
         FIG. 4A  shows an embodiment of a reduced height folded lens actuator with a top opening and a bottom opening disclosed herein in a top perspective view; 
         FIG. 4B  shows the actuator embodiment of  FIG. 4A  with a separated upper envelope from a bottom perspective view; 
         FIG. 4C  shows the actuator embodiment of  FIG. 4A  with a top opening and a bottom opening from a bottom perspective view; 
         FIG. 4C  shows the actuator embodiment of  FIG. 4A  in a section view between sections H-H and I-I in  FIG. 4A ; 
         FIG. 5A  shows an exploded view of the reduced height folded lens actuator of  FIGS. 4A-C ; 
         FIG. 5B  shows another exploded view of the reduced height folded lens actuator of  FIGS. 4A-C ; 
         FIG. 6  shows an exploded view of an electronic sub-assembly in a reduced height folded lens actuator disclosed herein; 
         FIG. 7  shows an exploded view of a base sub-assembly in a reduced height folded lens actuator disclosed herein; 
         FIG. 8  shows an exploded view of a lens sub-assembly in a reduced height folded lens actuator disclosed herein; 
         FIG. 9  shows an exploded view of an OIS/AF plate sub-assembly in a reduced height lens actuator disclosed herein; 
         FIG. 10A  shows an exploded view of an embodiment and various parts of a folded camera lens sub-assembly according to some aspects of presently disclosed subject matter; 
         FIG. 10B  shows the positioning of the AF and OIS coils relative to the lens optical axis from one view; 
         FIG. 10C  shows the positioning of the AF and OIS coils relative to the lens optical axis from another view; 
         FIG. 10D  shows a envelope in the lens sub-assembly of  FIG. 10A  with an added top opening; 
         FIG. 10E  shows a lower plate in the lens sub-assembly of  FIG. 10A  with an added bottom opening; 
         FIGS. 11A and 11B  show exploded views from two perspectives of a first VCM actuator in the lens sub-assembly; 
         FIGS. 11C and 11D  show respectively rails in the middle chassis and rails in the base; 
         FIGS. 12A and 12B  show exploded views from two perspectives of a second VCM actuator in the lens sub-assembly; 
         FIGS. 12C and 12D  show respectively rails in the middle chassis and rails in the base; 
         FIGS. 13A and 13B  show parts of the lens sub-assembly related to the actuation; 
         FIGS. 14A and 14B  show the top actuating sub-assembly in respectively, an exploded perspective view and an assembled view; 
         FIGS. 14C and 14D  show two different embodiments in cross section along the optical axis of the top actuating sub-assembly of  FIGS. 14A, 14B  and a prism; 
         FIG. 15  shows an embodiment of a dual camera comprising an upright camera and a folded camera with an actuator disclosed above or below. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  shows an embodiment of a folded camera numbered  100 . Folded camera  100  comprises a lens actuator  102  carrying a lens  104 , an OPFE (e.g. a prism, a mirror. etc.)  106  and an image sensor  108 . Camera  100  may be used to image a photographed object or a scene  110 . In an example, light coming from the direction of object or scene  110  along a first direction (also referred to as “entrance optical axis”)  112  enters OPFE  106 , is folded to a second direction (also referred to as “lens optical axis”)  114 , enters lens actuator  102  and then arrives at image sensor  108 . Lens  104  may comprise several lens elements, which may be held in one lens barrel or in a plurality of lens barrels. Lens  104  may have a fixed focal length or a changing (variable) focal length (“zoom lens”). Lens  104  may be shifted (actuated) for example for the purposes of focus (or auto focus—AF) or optical image stabilization (OIS). The actuation of lens  104  dictates that an air gap should be kept between the lens and other stationary parts such as an envelope  122  (see  FIG. 1B ). Folded camera  100  may include other parts such as an actuation mechanism for OPFE  106  (as in PCT/IB2017/052383), a housing (not shown for simplicity) for image sensor  108  to prevent stray light and mechanical damages, and other components known in the art, not shown for simplicity. More details on the operation of such a folded camera may be found in co-owned patent applications PCT/IB2015/056004, PCT/IB2016/052179 and PCT/IB2017/058403, which are all incorporated herein by reference. 
       FIG. 1B  shows a cross section of lens actuator  102  along a cut A-A to B-B seen in  FIG. 1A . Lens actuator  102  has an actuator height HA  102  between an external surface  140  of a top (upper) section (or “side”)  126  of envelope  122  and an external surface  128  of a bottom (lower) section  130  of envelope  122 . The top and bottom envelope sections may be planar members with surfaces perpendicular to first direction  112  (i.e. with a plane normal aligned with first direction  112 ). As used herein, the terms “top” or “upper” refer to a side of the lens actuator (and of the folded camera) that is closer to and facing object or scene  110  along Y, while “bottom”, “below” or “lower” refers to a side of the lens actuator (and of the folded camera) that is farthest and facing away from the imaged object or scene along Y. Height H A    102  is measured along the Y axis, or parallel to the first optical axis  112 , as described below. As used herein, “height”, “part height”, “module height”, “actuator height” or “camera height”, refer to a dimension of the respective object along the Y axis, namely along an axis perpendicular to lens optical axis  114  and parallel to entrance optical axis  112  facing the object. 
     Actuator height H A    102  is a sum of a lens height H L  of lens  104 , an upper height penalty  134  and a lower height penalty  136 . Upper height penalty  134  is defined as the distance between a topmost surface  138  of the lens and external top surface  140 . Lower height penalty  136  is defined as the distance between a lowest (bottom) surface  124  of the lens and external bottom surface  128 . In other words, upper height penalty  134  is the sum of the thickness of upper envelope section  126  and the size of an upper air gap  142  required between lens  104  and upper envelope section  126  (e.g. to allow actuation and movement of the lens for AF and/or OIS). Lower height penalty  136  is the sum of the thickness of lower envelope section  130  and the size of a lower air gap  144  needed between lens  104  and lower envelope section  130  e.g. to allow actuation and movement of the lens for AF and/or OIS). In turn, height H A    102  is the sum of the largest dimension of the lens in the Y direction (i.e. H L ) plus necessary air gaps  142  and  144  plus the thicknesses of the upper and lower envelope sections  126  and  130 . In other words, lens actuator height H A    102  is the largest dimension of actuator  120  along the Y direction. 
       FIG. 1C  shows another folded camera  150 , similar to camera  100 . Camera  150  includes a lens actuator section with lens actuator  102  holding the lens, an image sensor holder section  152  that includes the image sensor and has a height H S , and a prism holder section  154  that includes OPFE  106  and has a height H P . Additionally, an infra-red (IR) filter  156  may be positioned between lens  104  and image sensor  108 ,  FIG. 1D .  FIG. 1D  shows a side cut of camera  150  along a line B′-B′ seen in  FIG. 1C . In camera  150 , a folded camera height H FC  is limited by the maximum value of Hp, Hs and H A    102 . Thus H FC  may be limited by lens actuator height H A    102 , and a reduction in H A    102  may lead to a reduction of H FC . In other words, the folded camera height may be determined by (and may be equal to) the lens actuator height. 
       FIG. 2A  shows schematically the elements of a folded camera disclosed herein and numbered  200  in an exemplary coordinate system XYZ. Folded camera  200  includes a reduced height lens actuator  202  having a top opening  203 , a lens  204 , an OPFE  206  and an image sensor  208 , see also  FIGS. 2-9 . 
     OPFE  206  folds light arriving from an object or scene  210  along a first direction (entrance optical axis)  212  parallel to the Y direction, to a second direction (lens optical axis)  214  parallel to the Z direction toward image sensor  208 . 
       FIGS. 2B-2E  provide various views of lens actuator  202 .  FIG. 2B  shows lens actuator  202  in a top perspective view,  FIG. 2C  shows lens actuator  202  without an upper envelope section  216  from a top perspective view.  FIG. 2D  shows lens actuator  202  with a separated upper envelope section  216  from a bottom perspective view. Arrow  260  shows the direction from which upper envelope section  216  is installed.  FIG. 2E  shows lens actuator  202  in a section view between sections C-C and D-D in  FIG. 2A . Top opening  203  allows for an upper height penalty  234  smaller than upper height penalty  134  in lens actuator  102 . Upper height penalty (air-gap)  234  is measured between lens top surface  238  and an external top surface  224  of the upper envelope section  216 . Upper height penalty (air-gap)  234  is equal to the size of the air-gap between lens top surface  238  and an external top surface  224  measured along the first direction (Y axis). A second air gap  232  is positioned on the diametrically opposed side of lens  204  relative to air gap  234 . Air gap  232  is between lens  204  and an internal surface  236  of bottom envelope section  220 , and allows the motion of lens  204  relative to bottom envelope section  220 . In some examples, H A 202  is equal to the lens height H L  plus the size of two air-gaps  234  and  232  plus the thickness of a bottom envelope section  220 . Exemplarily, the size of air-gap  234  and/or  232  can be 50-150 μm, the thickness of bottom envelope section  220  is 100-150 μm, and lens actuator height H A    202  can be equal to H L  plus 250 μm-500 μm. All other dimensions being equal, a lens actuator height H A 202  in folded camera  200  will be smaller than lens actuator height H A    102  in folded camera  100 . 
       FIG. 2F  shows another embodiment of a folded camera disclosed herein and numbered  250 , similar to folded camera  200 . Camera  250  includes lens actuator  202  with lens actuator height H A    202  and carrying lens  204  Image sensor  208  is held in an image sensor holder  252 . An OPFE  206  is held in a prism holder  254 . Additionally, in some embodiments, an IR filter  256  is optionally positioned between lens  204  and image sensor  208 .  FIG. 2G  shows a side cut of camera  250  along a line D′-D′ seen in  FIG. 2F . In camera  250 , folded camera height H FC  is limited by the maximum of H A 202 , H P  and H S . Thus, a reduction H A 202  may lead to a reduction of H FC . 
     Alternatively, for a given folded camera height, a higher lens (i.e. a lens with large H L ) with better optical properties can be used in a design with an opening, relative to a design with no opening. Evidently, the design of camera  250  has an advantage over the design of camera  150  by either having a lower camera height for the same optics, or by having better optics for the same camera height. 
       FIGS. 3A-3E  provide various views of a second embodiment of a lens actuator numbered  302 , in which the lens actuator envelope  314  has a bottom opening  304  in a bottom lid  306 . Lens actuator  302  is similar to lens actuator  202  and can be installed in a folded camera such as folded camera  200  in a similar manner  FIG. 3A  shows lens actuator  302  actuating lens  310  in a top perspective view,  FIG. 3B  shows lens actuator  302  without an upper envelope section from a top perspective view.  FIG. 3C  shows lens actuator  302  from a bottom perspective view.  FIG. 3D  shows lens actuator  302  without an upper envelope section from a bottom perspective view, and  FIG. 3E  shows lens actuator  302  in a section view between sections E-E and F-F in  FIG. 3A . Bottom opening  304  allows for a lower height penalty (air-gap)  336  and equal to the air-gap between a bottom surface  324  of the lens and an external bottom surface  328  of a bottom envelope section  306  measured along the first direction (Y axis). That is, lower height penalty  336  is smaller than lower height penalty  136  in  FIGS. 1 . A second air gap  332  is positioned on the diametrically opposed side of lens  310  relative to air gap  336 . An air gap  232  is between lens  310  and the internal surface  362  of upper envelope section  360 , and allows the motion of lens  310  relative to upper envelope section  360 . In some examples, H A 302  is equal to H L  plus the size of the two air-gaps  332  and  336 , plus the thickness of upper envelope section  360 . Exemplarily, the height of each of air-gaps  332  and  336  can be 50-150 μm, the thickness of upper envelope section  360  can be 100-150 μm, and H A 302  can be equal to the lens height H L  plus 250 μm-500 μm. All other dimensions being equal, a lens actuator height H A 302  of camera  300  will be smaller than lens actuator height H A 102  in camera  100 . Like lens actuator  202 , lens actuator  302  may be combined in a folded camera between an OPFE and an image sensor, such that the height of the folded camera HFC may be equal to the height of the lens actuator H A    302 . 
       FIGS. 4A-4C  provide various views of a third embodiment of a folded lens actuator numbered  402  actuating a lens  410 , in which a lens actuator envelope  414  has both a bottom opening and a top opening.  FIG. 4A  shows lens actuator  402  in a top perspective view,  FIG. 4B  shows lens actuator  402  with a separated upper envelope section  416  from a bottom perspective view, and  FIG. 4C  shows lens actuator  402  in a section view between sections G-G and H-H in  FIG. 4A . Arrow  460  shows the direction from which upper envelope section  216  is installed. Lens actuator  402  includes upper envelope section  416  with an opening  403  like opening  203  in lens actuator  202  and a bottom envelope section  406  with an opening  404  like opening  304  in lens actuator  302 . The two openings  403  and  404  are positioned on diametrically opposed sides of lens  410 . Thus, lens actuator  402  combines the advantages provided by top opening  203  of lens actuator  202  and bottom opening  304  of lens actuator  302 , with a final lens actuator height H A    402  smaller than the lens actuator heights in actuators  102 ,  202  and  302 . In some examples, lens actuator height H A    402  is equal to the lens height plus the size of two air-gaps  418  and  432 . Exemplarily, the size of each of the air-gaps  418  and  432  can be 50-150 μm and lens actuator height H A    402  can be equal to H L  plus 100 μm or 250 μm or 300 μm. Like lens actuator  202 , lens actuator  402  may be combined in a folded camera between an OPFE and an image sensor, such that the height of the folded camera H FC  may be equal to the height of the lens actuator H A ,  402 . 
       FIGS. 5A, 5B, 6, 7, 8 and 9  show one exemplary lens actuator design using VCM actuation. Such a design may be used in conjunction with envelope designs of lens actuators  202 ,  302  and  402 . 
       FIG. 5A  and  FIG. 5B  show, respectively, exploded bottom and top perspective views of a VCM  502 . VCM  502  comprises an envelope  506 , an OIS/AF plate sub-assembly  508 , four upper balls  510 , a lens carrier sub-assembly  512 , lens  514 , four lower balls  516 , an electronic sub-assembly  530 , a base sub-assembly  540  and a lower plate  522 . VCM  502  is capable of actuating any of the lenses above in two orthogonal directions, for example for focusing and optical image stabilization. 
       FIG. 6  shows an exploded view of electronic sub-assembly  530 . Electronic sub-assembly  530  comprises an OIS Hall bar sensor  602 , an OIS coil  604 , an AF Hall bar sensor  606 , a first rigid printed board circuit (PCB)  608 , a second rigid PCB  610  and a flex PCB  612 . The control of the motion of any of the lenses above or below can be done in close loop mode using the position sensing allowed by Hall bar sensors  602  and  606 . 
       FIG. 7  shows an exploded view of base sub-assembly  540 . Base sub-assembly  540  comprises an AF VCM  704 , an AF stepping yoke  702  and a base  706 . 
       FIG. 8  shows an exploded view of lens carrier sub-assembly  512 . Lens carrier sub-assembly  512  comprises an OIS VCM magnet  804 , an OIS sensing magnet  802  and a lens carrier  806 . 
       FIG. 9  shows an exploded view of OIS/AF plate sub-assembly  508 . OIS/AF plate sub-assembly  408  comprises an AF motor magnet  902 , an OIS stepping yoke  904  and an OIS/AF plate  906 . 
       FIGS. 10-14  show another exemplary lens actuator design using VCM actuation.  FIG. 10A  shows an exploded view of a lens actuator  1004  using VCM actuation according to some aspects of presently disclosed subject matter, lens actuator  1004  comprises an envelope  1014  serving as protection for the lens and other mechanical parts, a lens  1016  with a lens optical axis  1012 , a lens carrier (holder)  1018 , a plurality (e.g. four) of stepping magnets  1020   a, b, c  and  d , an OIS magnet  1022 , four upper balls  1024 , an AF magnet  1026 , a middle chassis  1028 , four lower balls  1030 , a base  1032 , a plurality (e.g. four) of upper stepping yokes  1034   a, b, c  and  d , an AF Hall sensor bar  1036 , an AF coil  1038 , an OIS coil  1040 , a PCB  1042  serving as platform for placement of electrical components and electrical linkage between these electrical components, and OIS Hall sensor bar  1044  and a lower plate  1048  serving as bottom mechanical protection for the camera. In some embodiments, some of the stepping yokes may positioned on a first surface, and other stepping yokes may be positioned on a second surface, wherein the first and second surfaces are parallel. 
       FIGS. 10B and 10C  show the positioning of AF coil  1038  and OIS coil  1040  relative to the lens optical axis  1012  from two different views. Each coil has a stadium shape, such that it has two long dimensions (typically 1-5mm long) and one short dimension (typically 0.1-0.5 mm thick). Each coil typically has a few tens of windings (for example, in a non-limiting range of 50-250), with an exemplary resistance of 10-30 ohm. The plane in which the long dimensions of the coil reside will be considered henceforth to be the respective “coil plane”. In the example shown, an “OIS coil plane” of OIS coil  1040  is parallel to the XZ plane, namely its two long dimensions are in XZ plane while its short dimension is along the Y axis. In the example shown, an “AF coil plane” of AF coil  1038  is parallel to the YZ plane, namely its two long dimensions are in the YZ plane while its short dimension is along the X axis. Thus, in this example the OIS coil plane is perpendicular to the AF coil plane. In an embodiment, OIS coil  1040  faces OIS magnet  1022  ( FIG. 10A ). The OIS magnet is a fixed (i.e. permenant) magnet. Magnet  1022  may be fabricated (e.g. sintered, cut) such that it has a changing magnetic field polarity: on its positive X size, OIS magnet  1022  has a magnetic field facing the negative Y direction, while on its negative X side, OIS magnet  1022  has a magnetic field facing the positive Y direction. Upon driving of current in OIS coil  1040 , a Lorenz force is created by the magnetic filed of OIS magnet  1022  on OIS coil  1040  in the negative or positive Y direction. Consequently, an equal force is applied on OIS magnet  1022  in the Y direction. Having OIS coil  1040  in XZ plane has the advantage in that, while in actuation, OIS magnet is kept at a constant distance from OIS coil  1022 . That is, Lorentz force for OIS is uniform for different AF positions, and the OIS position reading is linear for OIS motion and uniform for different AF positions. 
     In the example of  FIG. 10B , lens optical axis  1012  is in the Z direction. Each of the OIS and AF planes is parallel to lens optical axis  1012 . In addition, relative to a plane defined by the first optical axis  1010  and the second (lens) optical axis  1012 , the OIS coil and the AF coil are on opposite sides of this plane. This feature has an advantage in that it reduces magnetic interference of the two VCMs. 
     In an embodiment, AF coil  1038  faces AF magnet  1026 . The AF magnet is a fixed (i.e. permenant) magnet. AF magnet  1026  may be fabricated (e.g. sintered, cut) such that it has a changing magnetic field polarity: on its positive Z size, AF magnet  1026  has a magnetic field facing the negative X direction, while on its negative Z side OIS magnet  1022  has a magnetic field facing the positive X direction. Upon driving of current in AF coil  1038 , a Lorenz force is created by the magnetic filed of AF magnet  1026  on AF coil  1038  in the negative or positive Z direction. Consequently, an equal force is applied on AF magnet  1026  in the Z direction. Having AF coil  1038  in YZ plane has the advantage in that, while in actuation, the AF magnet is kept at a constant distance from OIS coil  1040 . That is, the Lorentz force for AF is uniform for different OIS positions, and the AF position reading is linear for AF motion and uniform for different OIS positions. 
       FIG. 10D  shows an envelope  1014 ′ which is similar to envelope  1014  in VCM  1004 , with an added top opening  1062 .  FIG. 10E  shows a lower plate  1048 ′ similar to lower plate  1048  in VCM  1004 , with an added bottom opening  1064 . Openings  1062  and  1064  allow reducing the height of VCM  1004 , in a manner similar to openings  203  and  304  described above. All descriptions of embodiments  202 ,  302 ,  402 , with regard to benefits of top and bottom openings are applicable to the description of VCM  1004  and may be used in VCM  1004 . 
       FIGS. 11A and 11B  show exploded views from two perspectives of a first VCM actuator numbered  1100  included in lens actuator  1004 . In an example, VCM actuator  1100  may be used for AF. In another example, VCM actuator  1100  may be used for OIS. In VCM actuator  1100 , a top actuating sub-assembly  1110  is movable relative to an AF stationary sub-assembly  1120  in a direction parallel to oprtical axis  1012 . Top actuating sub-assembly  1110  comprises lens  1016 , lens holder  1018 , middle chasis  1028 , AF magnet  1026  and the four stepping magnets  1020   a, b, c  and  d , OIS magnet  1022 , and four upper balls  1024 . Middle chassis  1028  and AF magnet  1026  form a middle actuating sub-assembly  1130 . AF stationary sub-assembly  1120  comprises a lower stepping yoke  1050 , OIS Hall sensor bar  1044 , printed circuit board  1042 , OIS coil  1040 , AF coil  1038 , AF Hall sensor bar  1036 , four upper stepping yokes  1034   a, b, c  and  d  and base  1032  (only some of which are seen in these figures). Middle actuating sub-assembly  1130  is movable relative to an AF stationary sub-assembly  1120  in a direction parallel to optical axis  1012  and movable relative to lens actuating sub-assembly  1210  in a direction perpendicular to optical axis  1012 . 
       FIGS. 11C and 11D  show respectively four rails  1052  in middle chassis  1028  and four rails  1054  in base  1032 . While one of rails  1054  is hidden in  FIG. 11D , it is understood by a person skilled in the art that its location is symmetric with other visible rails. 
     In VCM actuator  1100 , each of the four rails  1052  faces one respective rail of rails  1054 , while one ball of lower balls  1030  is between the rails. The rails and ball structure confines the motion of top actuating sub-assembly  1110  relative to AF stationary sub-assembly  1120  in a direction parallel to optical axis  1012 . In addition, top actuating sub-assembly  1110  is pulled to AF stationary sub-assembly  1120  in the Y direction due to the magnetic force of magnets  1020  and upper stepping yokes  1034  (see below), while balls  1030  keep the distance between top actuating sub-assembly  1110  and AF stationary sub-assembly  1120  constant in the Y direction. In this description, the term “constant distance” with respect to moving parts refers to a distance between the parts in a direction perpendicular to the motion direction that is constant with a tolerance of ±10 μm, ±30 μm, ±50 μm, or even ±100 μm. 
       FIGS. 12A and 12B  show exploded top and bottom perspective views of a second VCM actuator in lens sub-assembly  1004 , numbered  1200 . VCM actuator  1200  includes a lens actuating sub-assembly  1210  movable relative to an OIS stationary sub-assembly  1220 . VCM actuator  1200  may be used for OIS. Lens actuating sub-assembly  1210  comprises lens  1016 , lens holder  1018 , four stepping magnets  1020  and OIS magnet  1022  (which is also part of top actuating sub-assembly  1110 ). OIS stationary sub-assembly  1220  comprises lens holder  1018 , middle chasis  1028 , AF magnet  1026 , AF stationary sub-assembly  1120  and the four lower balls  1030 . 
       FIGS. 12C and 12D  show respectively four rails  1056  in lens carrier  1018  and four rails  1058  in middle chassis  1028 . In VCM actuator  1200 , each of the four rails  1056  faces one respective rail of rails  1058 , while one ball of upper balls  1024  is between the rails. The rails and ball structure confine the motion of lens actuating sub-assembly  1210  relative to OIS stationary actuating sub-assembly  1220  in a direction perpendicular to optical axis  1012 . In addition, lens actuating sub-assembly  1210  is pulled to OIS stationary sub-assembly  1220  in the Y direction due to the magnetic force of magnets  1020   a,b,c  and  d  and stepping yokes  1034   a,b,c  and  d  (see beolw), while upper balls  1024  keep the distance between lens actuating sub-assembly  1210  and OIS stationary sub-assembly  1220  constant in the Y direction. In some embodiments, the lens actuating sub-assembly is pulled toward the stationary sub-assembly, with the middle actuating sub-assembley positioned therebetween. 
     In use of actuator  1100  for AF, an electrical current in AF coil  1038  creates force on AF magnet  1026 , driving middle chassis  1028  in directions parallel to lens optical axis  1012 , for example along the positive or negative Z direction. Middle chassis  1028  holds lens actuating sub-assembly  1210  and while moving in the AF direction it carries lens actuating sub-assembly  1210  along, such that lens  1016  is operative to focus on image sensor  1006 , as required by optical demands The AF movement is directed by the rolling and/or sliding of the four lower balls  1030  inside the four respective rails  1052  located in middle chassis  1028  and inside four compatible rails  1054  located in base  1032 . 
     In use of actuator  1200  for OIS, electrical current in OIS coil  1040  creates force on OIS magnet  1022 , driving lens carrier  1018  in directions perpendicular to the lens optical axis  1012  and parallel to the X axis (shown in the examplary coordinate system XYZ). During this movement, lens carrier  1018  (which holds lens  1016 ) moves together with the lens in any OIS direction. The movement for OIS is directed by the rolling and/or sliding of four upper balls  1024  inside four rails  1056  located on lens carrier  1018  and inside another four compatible rails  1058  located on the middle chassis  1028 . 
     The four stepping magnets  1020   a ,  1020   b ,  1020   c  and  1020   d  located on the lens carrier  1018  are assocated with four stepping yokes  1034   a ,  1034   b ,  1034   c  and  1034   d  located on AF stationary sub-assembly  1120 , creating a stepping force indicated by arrows in a direction perpendicular to optical axis  1012 . Stepping magnets  1020 a-d and stepping yokes  1034   a - d  are seen in  FIG. 13A , which shows an exploded view of VCM  1100 , and in  FIG. 13B  which shows only the magnets and yokes along with the force direction, which is directed in the negative Y direction. In an embodiment, lens actuating sub-assembly  1210  is pulled toward AF stationary sub-assembly  1120 , while OIS stationary sub-assembly  1220  is positioned therebetween. Upper balls  1024  located between lens actuating sub-assembly  1210  and OIS stationary sub-assembly  1220  prevent contact between the two sub-assemblies. Similarly, lower balls  1030  located between OIS stationary sub-assembly  1220  and AF stationary sub-assembly  1120  prevent contact between the two sub-assemblies. At the same time, the pull force created between four stepping magnets  1020  and four stepping yokes  1034  hold actuator  1100  as one unit and prevent all moving parts from coming apart. In some examples, the three stepping magnets are used only for stepping, while the fourth magnet is used for stepping and sensing. 
       FIGS. 14A and 14B  show top actuating sub-assembly  1110  in, respectively, an exploded perspective view and an assembled view. In some embodiments, lens carrier  1018  has an an opening  1402  which allows light to pass from an OPFE to lens  1016 . Opening  1402  is surrounded by walls  1404   a, b, c and d . In an embodiment, middle chassis  1028  comprises walls  1406   a, b, c and d . Wall  1406   b  can be used to add mechanical strength and connect between the rails.  FIGS. 14C and 14D  show two different embodiments in cross section along the optical axis of top actuating sub-assembly  1110  and a prism  1410 . The embodiments shown in  FIGS. 14C and 14D  describe two relative positions of walls  1406   b  and  1404   b . In the embodiment of  FIG. 14C , wall  1406   b  is located below wall  1404   b  (in the −Y direction). 
     In contrast, in the embodiment of  FIG. 14D  wall  1406   b ′ replaces wall  1406   b  and is located beside wall  1404   b  (in the −Z direction). A distance  1408  denotes the minimal distance of top actuating sub-assembly  1110  from prism  1410 . Distance  1408  is determined by a stroke for AF of top actuating sub-assembly  1110 , as required by optical needs and assembly tolernces, as required by mechanical needs. Distance  1408  is constant in both configurations ( FIGS. 14C and 14D ). Thus, the configuration in  FIG. 14C  has an advantage, since it allows a shorter actuator along the optical axis direction (−Z direction), namely a reduction in the length of folded camera  1000  ( FIG. 10A ). 
       FIG. 15  shows a dual camera  1500  comprising an upright camera  1502  and a folded camera 1504 . Folded camera  1504  may include a lens actuator like any actuator/VCM disclosed above, for example actuators/VCMs  102 ,  202 ,  302 ,  402 ,  502  or  1004 . 
     While this disclosure describes a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of such embodiments may be made. In general, the disclosure is to be understood as not limited by the specific embodiments described herein, but only by the scope of the appended claims. 
     All references mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual reference was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present application.