Compact mobile cameras with curved image sensors and optical image stabilization

Abstract

A camera, comprising: a lens, a curved image sensor having a finite radius of curvature, and an optical image stabilization actuator. The optical image stabilization actuator moves the lens circularly with respect to the curved image sensor. The circular movement for optical image stabilization allows optical image stabilization while providing a relatively high image quality.

Description

[0001] COMPACT MOBILE CAMERAS WITH CURVED IMAGE SENSORS AND OPTICAL IMAGE STABILIZATION

[0002] FIELD

[0003] The presently disclosed subject matter is generally related to the field of digital cameras.

[0004] DEFINITIONS

[0005] In this application and for optical and other properties mentioned throughout the description and figures, the following symbols and abbreviations are used, all for terms known in the art:

[0006] Total track length (TTL): the maximal distance, measured along an axis parallel to the optical axis of a lens, between a point of the front surface Si of a first lens element Li and an image sensor, when the system is focused to an infinity object distance.

[0007] Back focal length (BFL): the minimal distance, measured along the optical axis of a lens, between a point of the rear surface S2N of the last lens element LN and an image sensor, when the system is focused to an infinity object distance.

[0008] Effective focal length (EFL): in a lens (assembly of lens elements Li to LN), the distance between a rear principal point P' and a rear focal point F' of the lens. f-number (f / #): the ratio of the EFL to an entrance pupil diameter (or simply aperture diameter “DA”).

[0009] BACKGROUND

[0010] Multi-aperture cameras (or “multi-cameras”, of which a “dual-cameras” having two cameras is an example) are today’s standard for portable electronic mobile devices (“mobile devices”, e.g. smartphones, tablets, etc.). A multi-camera usually comprises a wide field-of- view (or “angle”) FOVw camera (“Wide” camera or “W” camera) of about 20mm - 30mm 35mm equivalent focal length (“35eq.FL”), and at least one additional camera, e.g. with a narrower (than FOVw) FOV (Telephoto or “Tele” camera with FOVT) of about 35mm - 300mm 35eq.FL, or with an ultra-wide field of view FOVuw (wider than FOVw, “UW” camera) of about 9mm - 18mm 35eq.FL.

[0011] FIG. 1A illustrates a known dual-camera 150 that comprises a folded Tele camera 100 and a (vertical or upright) Wide camera 130. Folded Tele camera 100 comprises an optical path folding element (OPFE) 102, a lens included in a lens barrel 110 and an image sensor 106. Wide camera 130 includes a lens 132 with a plurality of lens elements (not visible in this representation) and an image sensor 138 having a (full) sensor diagonal (“SD”, marked in FIG. IB). Lens 132 is included in and fixedly coupled to a lens barrel 134. Wide camera 130 has an optical axis 136.

[0012] Modern cameras usually include optical image stabilization (OIS). OIS is required to mitigate undesired motion of a mobile device including the camera (“hand motion” or “handshake”). FIG. IB exemplarily shows Wide camera 130 in a cross-sectional view in a first optical image stabilization (“OIS”) position, referred to as “OIS center” (or “OIS zero”) position with respect to the 1stOIS direction. Wide camera 130 has a Depth of Focus (“DoFo”) measured along the z-axis, as shown. The DoFo defines a nearest and a farthest distance between a lens and an image sensor so that an object still is in acceptably sharp focus in an image. DoFo may be parallel to planar image sensor 138, which is oriented parallel to the y- axis. DoFo is given by DoFo = c x f / #, whereas “c” is a circle of confusion (in general, defined as size of one or two pixels) and f / # is a camera’s f number. In a camera used in a mobile device, DoFo may be in the range of about 0.5pm to 10pm. When Wide camera 130 is in focus, image sensor 138 is located within DoFo. For example, DoFo may extend symmetrically above and below image sensor 138, as shown. A ray pair 140 including two rays are shown. The two rays may originate from a center point in the scene including an object. In the OIS center position, ray pair 140 impinges on a center position of image sensor 138. A crisp image of the object is formed, as the two rays intersect at image sensor 138 within DoFo.

[0013] FIG. 1C exemplarily shows Wide camera 130 in a second OIS position with respect to the 1stOIS direction. In the second OIS position, lens barrel 134 is moved linearly by AOIS along the y-axis with respect to the OIS center position and image sensor 138. A position of lens barrel 134 in FIG. IB is indicated 139. DoFo did not change along the z-axis, so that also here, the two rays intersect at image sensor 138 within DoFo. For OIS in a 2ndOIS direction perpendicular to the 1stOIS direction, lens barrel 134 may be linearly moved along the x-axis. In other examples, image sensor 138 may be moved linearly by AOIS along the y-axis with respect to lens barrel 134, which provides an identical OIS effect.

[0014] Curved image sensors are known (FIGS. 2A-B). A light collecting surface is curved, which is beneficial as undesired effects such as field curvature and shading toward the sensor edges are reduced compared to a planar image sensor. Thus, a lower camera height (measured along the z-axis) is obtained, which is beneficial for slim mobile devices. It would be beneficial to have cameras including curved image sensors capable of performing OIS. Such cameras are disclosed herein.

[0015] GENERAL DESCRIPTION

[0016] According to a broad aspect, the present disclosure provides a camera, comprising: a lens; a curved image sensor having a sensor diagonal (SD) and a radius of curvature (ROC); an optical image stabilization (OIS) actuator; wherein the OIS actuator moves the lens circularly with respect to the curved image sensor, wherein the circular movement of the lens is around a virtual hinge axis located at a distance ROC from the image sensor, wherein the SD is in a range of 5mm to 30mm, wherein the ROC in the range of 2xSD to lOxSD.

[0017] According to some embodiments, the circular movement of the lens is around a first rotation axis for performing OIS along a first OIS direction.

[0018] According to some embodiments, the circular movement of the lens is around a second rotation axis perpendicular to the first OIS rotation axis for performing OIS along a second OIS direction.

[0019] According to some embodiments, the circular movement of the lens is in the range of 0.1 to 1 degrees.

[0020] According to some embodiments, wherein the circular movement of the lens is in the range of 0.1 to 0.35degrees.

[0021] According to some embodiments, wherein the circular movement of the lens is in the range of 0.1 to 0.25degrees.

[0022] According to some embodiments, the ROC is in the range of 2.5xSD to 5xSD.

[0023] According to some embodiments, the ROC is in the range of 3xSD to 4xSD.

[0024] According to some embodiments, the SD is in a range of 10mm to 23mm.

[0025] According to some embodiments, the image sensor is a 1” image sensor.

[0026] According to some embodiments, the image sensor is a 4 / 3” image sensor.

[0027] According to some embodiments, the lens has an effective focal length (EFL), and the EFL is in the range 2.5mm < EFL < 15mm.

[0028] According to some embodiments, the EFL is in the range 5mm < EFL < 12.5mm.

[0029] According to some embodiments, the EFL is in the range 7.5mm < EFL < 10mm. According to some embodiments, a f / # of the camera is in the range 1.2 < f / # < 3.

[0030] According to some embodiments, a f / # of the camera is in the range 1.5 < f / # < 2.25.

[0031] According to some embodiments, the camera has a 35mm equivalent focal length in the range of 20mm - 30mm.

[0032] According to some embodiments, the camera has a 35mm equivalent focal length in the range of 22mm - 25mm.

[0033] According to some embodiments, wherein the mobile device is a smartphone.

[0034] According to another aspect, the present disclosure provides a mobile electronic device comprising at least one camera, the camera comprising: a lens; a curved image sensor having a sensor diagonal (SD) and a radius of curvature (ROC); an optical image stabilization (OIS) actuator; wherein the OIS actuator moves the lens circularly with respect to the curved image sensor, wherein the circular movement of the lens is around a virtual hinge axis located at a distance ROC from the image sensor, wherein the SD is in a range of 5mm to 30mm, wherein the ROC in the range of 2xSD to lOxSD.

[0035] According to some embodiments, the mobile electronic device further includes a second camera, and wherein the second camera has a second effective focal length (EFL2) which is different from EFL.

[0036] In some embodiments, the mobile electronic devices described herein may be handheld devices, being a smartphone, tablet, smartwatch or any other handheld devices.

[0037] Generally, aspects of the present disclosure may include features described herein with respect to other aspects and embodiments of the present disclosure.

[0038] BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Non-limiting examples of embodiments disclosed herein are described below with reference to figures attached hereto that are listed following this paragraph. The drawings and descriptions are meant to illuminate and clarify embodiments disclosed herein, and should not be considered limiting in any way.

[0040] FIG. 1 A illustrates a known dual-camera in a perspective view;

[0041] FIG. IB illustrates a known Wide camera in a cross-sectional view;

[0042] FIG. 1C illustrates the known Wide camera of FIG. IB when performing known linear optical image stabilization;

[0043] FIG. 2A illustrates a known Wide camera including a curved image sensor in a cross- sectional view;

[0044] FIG. 2B illustrates the known Wide camera of FIG. 2A when performing known linear optical image stabilization;

[0045] FIG. 3 illustrates a Wide camera when performing circular optical image stabilization as disclosed herein in a cross-sectional view;

[0046] FIG. 4A illustrates a Wide camera including a curved image sensor as disclosed herein in an optical image stabilization center position in a cross-sectional view;

[0047] FIG. 4B illustrates the Wide camera of FIG. 4A in an optical image stabilization noncenter position;

[0048] FIG. 4C illustrates a first, linear optical image stabilization contribution in a cross- sectional view;

[0049] FIG. 4D illustrates a second, rotational optical image stabilization contribution in a cross- sectional view;

[0050] FIG. 5 illustrates exemplarily a mobile device including a Wide camera including a curved image sensor and operational to perform optical image stabilization as disclosed herein.

[0051] DETAILED DESCRIPTION

[0052] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding. However, it will be understood by those skilled in the art that the presently disclosed subject matter may be practiced without these specific details. In other instances, well-known methods and features have not been described in detail so as not to obscure the presently disclosed subject matter.

[0053] FIG. 2A exemplarily shows a Wide camera 200 including a curved image sensor 202 in a cross-sectional view. Wide camera 130 may have an EFL in the range of 2.5mm to 15mm, or preferably in the range of 5mm to 10mm. A SD of curved image sensor 202 is measured along its curved surface, and SD may be in the range of 5mm to 30mm, or preferably in the range of 10mm to 23mm. In some examples, curved image sensor 202 may be a “1” sensor” (or “1-inch sensor”) or a “4 / 3 sensor” as known in the art. Wide camera 130 has a Depth of Focus (“DoFo”) measured parallel to curved image sensor 202, as shown. The degree of curvature of curved image sensor 202 is defined by a radius of curvature (“ROC”). A ROC may be in the range of two times to ten times larger than a SD of curved image sensor 202, i.e. ROC = SDx2 - SDxlO, e.g. 3x larger or 4x larger. Wide camera 200 is shown in a first optical image stabilization (“OIS”) center position. The two rays of ray pair 140 intersect at a center position of curved image sensor 202 within the DoFo, and a crisp image is formed.

[0054] FIG. 2B exemplarily shows Wide camera 200 in a second OIS position. In the second OIS position, lens barrel 134 is moved linearly by AOIS along the y-axis with respect to the OIS center position and image sensor 202. A position of lens barrel 134 in FIG. 2A is indicated 139. Here, the two rays do not intersect at curved image sensor 202 within the DoFo, so that a blurry image is formed. This is unbeneficial and demonstrates that linear OIS movements are not suitable for cameras including curved image sensors such as Wide camera 200.

[0055] FIG. 3 exemplarily shows a Wide camera 300 including curved image sensor 202 and an OIS actuator (not shown) operational to perform OIS as disclosed herein in a second OIS position with respect to a first OIS direction. A zero position of Wide camera 300 is identical with a zero position of Wide camera 200 (see FIG. 2 A). In the second OIS position, lens barrel 134 is rotated (or “moved circularly”) by an angle Aa with respect to the OIS center position and image sensor 202 around an axis parallel to the x-axis (perpendicular to the y-z coordinate system shown) and around a virtual hinge axis (or “pivot“) 302. Virtual hinge axis 302 is positioned at a distance ROC from a center of image sensor 202, as shown. A position of lens barrel 134 in FIG. 2A is indicated 139. Aa may be in the range of 0.1 to 1 degrees, e.g. 0.25degrees or 0.35 degrees. Here, the two rays intersect at curved image sensor 202 within the DoFo, so that a crisp image is formed. This is beneficial and demonstrates that circular (or “swing”) OIS movements are suitable for cameras including curved image sensors such as Wide camera 300. For OIS in a 2ndOIS direction perpendicular to the 1stOIS direction, lens barrel 134 may be circularly moved around an axis parallel to the y-axis and around virtual hinge axis 302.

[0056] To clarify, methods for OIS as disclosed herein are beneficial for use in camera that is included in a mobile device such as a smartphone.

[0057] FIGS. 4A-D illustrate movements and movement contributions for “swing OIS” as disclosed herein.

[0058] FIG. 4A shows a Wide camera 400 operational to perform swing OIS as disclosed herein. Wide camera 400 includes curved image sensor 202 and lens 134. An EFL of lens 134 is shown. Wide camera 400 is shown in focus, so that its EFL expands from a “principal image plane” as known in the art to curved image sensor 202. A center ray (or “zero-field” ray) 402 is shown. FIG. 4A shows Wide camera 400 in a center OIS position. FIG. 4B shows Wide camera 400 in a non-center OIS position. With respect to FIG. 4A, lens 134 is rotated by an angle Aa around virtual hinge axis 302. This rotational (or circular) movement causes an OIS shift of center ray 402 by an OIS stroke “AOIS”.

[0059] FIG. 4C illustrates only a first linear (or “translational”) contribution to AOIS. As of the rotation of lens 134 by an angle Aa around virtual hinge axis 302, a center of lens 134 is linearly moved by AT together with center ray 402, as shown.

[0060] FIG. 4D illustrates a second rotational (or “circular”) contribution to AOIS. The rotation of lens 134 by an angle Aa around virtual hinge axis 302 leads to a linear displacement of center ray 402 by AR, as shown. OIS stroke AOIS is obtained by AOIS = AT + AR.

[0061] OIS example 1 - ROC= 4 x SD

[0062] We assume a 1” curved image sensor (SD ~ 16.4mm) having a ROC= 4 x SD =65.6mm with a typical FOVw of 83 degrees (about 23mm 35eq.FL), obtained by a lens having EFL = 9.3mm. A TTL of the lens may be in the range of 8mm - 15mm, and preferably in the range of 8mm - 12mm. In other examples, FOVw may be about 35mm 35eq.FL. Typically, a required OIS stroke AOIS is estimated by AOIS = EFL x tan(1.5deg) ~ 0.24mm. Here, including some tolerances, we aim for AOIS =0.3mm, which is obtained for an angle Aa=0.26 degrees. The linear contribution AT is given by AT = (ROC - EFL) x tan(Aa), the rotational contribution AR is given by AR = EFL x tan(Aa). This means that a ratio of ROCZEFL defines a relative size of the linear contribution versus the rotational contribution. For ROC= 4 x SD, we obtain AT = 0.255mm and AR = 0.045mm.

[0063] OIS example 2 - ROC= 3 x SD

[0064] In other examples having a 1” curved image sensor and a ROC= 3 x SD = 49.2mm, to obtain a same AOIS =0.3mm, an angle Aa=0.35 degrees is required. AT = 0.244mm and AR = 0.057mm. This shows that for smaller ROCs (i.e. image sensors having a stronger curvature), the rotational contribution becomes more dominant. In particular, this means that for e.g. ROC ~ EFL, only AR contributes, so that there is a rotational OIS movement only.

[0065] Table 1 shows examples of typical cameras that may be operational to perform “swing OIS” as disclosed herein. All values are given in mm. EFLMIN and EFLMAX give values for a minimum and maximum EFL respectively, TTLMIN and TTLMAX give values for a minimum and maximum TTL respectively.

[0066] Table 1

[0067] FIG. 5 shows schematically an embodiment of a mobile device (for example, a smartphone) numbered 500 and configured to perform swing OIS as disclosed herein. Mobile device 500 comprises a first camera 510 having a first camera FOV and including a curved image sensor 512. First camera 510 also includes a lens 514 and a swing OIS actuator 516 operational to actuate a swing OIS movement as disclosed herein. Swing OIS actuator 516 may for example include a voice coil motor (“VCM”). In some examples, swing OIS actuator 516 may include one or more curved rails, which may include balls and together act as curved ballbearings that are operational to translate a force provided by the VCM to a swing OIS movement as disclosed herein. The curvature of the rails may define a virtual hinge axis (or “pivot”), for example at a distance of ROC to curved image sensor 512. In some examples, swing OIS actuator 516 may include a first curved ball-bearing for a swing OIS movement in a first direction, and a second curved ball-bearing for a swing OIS movement in a second direction perpendicular to the first direction. In some examples, a swing OIS movement in the first direction may be independent from a swing OIS movement in the second direction.

[0068] In other examples, Swing OIS actuator 516 may include two or more springs that translate a force provided by a VCM to a swing OIS movement in a first and / or second direction as disclosed herein.

[0069] Optionally, mobile device 500 further comprise a second camera including a second image sensor 522 and a second lens 524. Mobile device 500 further includes an application processor (AP) 530. AP 530 includes an (optional) OIS controller 532, an image sensor controller 534 and an image signal processor (ISP) 536. Mobile device 500 includes in addition a memory 540 and a screen 570. Memory 540 may e.g. be used to store calibration data of first camera 510, and / or to store calibration data between first camera 510 and first camera 520. Mobile device 500 may as well include an inertial measurement unit (“IMU”) 550 operational for measuring a displacement of mobile device 500, which may be corrected by OIS. In some examples, mobile device 500 may include a micro controller unit (“MCU”) 560 operational to calculate OIS control data.

[0070] It is appreciated that certain features of the presently disclosed subject matter, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the presently disclosed subject matter, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

[0071] Unless otherwise stated, the use of the expression “and / or” between the last two members of a list of options for selection indicates that a selection of one or more of the listed options is appropriate and may be made. It should be understood that where the claims or specification refer to "a" or "an" element, such reference is not to be construed as there being only one of that element.

[0072] All patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual patent or patent application 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 disclosure.

Claims

WHAT IS CLAIMED IS:

1. A camera, comprising: a lens; a curved image sensor having a sensor diagonal (SD) and a radius of curvature (ROC); andAn optical image stabilization (OIS) actuator; and wherein the OIS actuator moves the lens circularly with respect to the curved image sensor, wherein the circular movement of the lens is around a virtual hinge axis located at a distance ROC from the image sensor, wherein SD is in a range of 5mm to 30mm, and wherein ROC in the range of 2xSD to lOxSD.

2. The camera of claim 1, wherein the circular movement of the lens is around a first rotation axis for performing OIS along a first OIS direction.

3. The camera of claim 2, wherein the circular movement of the lens is around a second rotation axis perpendicular to the first OIS rotation axis for performing OIS along a second OIS direction.

4. The camera of claim 1, wherein the circular movement of the lens is in the range of 0.1 to 1 degrees.

5. The camera of claim 4, wherein the circular movement of the lens is in the range of 0.1 to 0.35 degrees.

6. The camera of claim 4, wherein the circular movement of the lens is in the range of 0.1 to 0.25 degrees.

7. The camera of claim 1, wherein ROC is in the range of 2.5xSD to 5xSD.

8. The camera of claim 1, wherein ROC is in the range of 3xSD to 4xSD.

9. The camera of claim 1, wherein the SD is in a range of 10mm to 23mm.

10. The camera of claim 1, wherein the image sensor is a 1” image sensor.

11. The camera of claim 1, wherein the image sensor is a 4 / 3” image sensor.

12. The camera of claim 1, the lens having an effective focal length (EFL), and wherein the EFL is in the range 2.5mm < EFL < 15mm.

13. The camera of claim 12, wherein the EFL is in the range 5mm < EFL < 12.5mm.

14. The camera of claim 12, wherein the EFL is in the range 7.5mm < EFL < 10mm.

15. The camera of claim 1, wherein an f / # of the camera is in the range 1.2 < f / # < 3.

16. The camera of claim 15, wherein f / # is in the range 1.5 < f / # < 2.25.

17. The camera of claim 1, wherein the camera has a 35mm equivalent focal length in the range of 20mm - 30mm.

18. The camera of claim 17, wherein the 35mm equivalent focal length is in the range of 22mm - 25mm.

19. A mobile device including the camera of claim 1.

20. The mobile device of the claim 19, wherein the mobile device further includes a second camera, and wherein the second camera has a second effective focal length (EFL2) different EFL.

21. The mobile device of the claim 19,, wherein the mobile device is a smartphone.

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