Patent Publication Number: US-2021173167-A1

Title: Lens stack with replaceable outer lens

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of International Application No. PCT/US2019/034804, filed on May 31, 2019, which claims the benefit of U.S. Provisional Patent Application No. 62/678,939 filed on May 31, 2018, both of which the contents are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to replaceable outer lenses. 
     BACKGROUND 
     Image capture devices, such as cameras, may capture content as images (e.g., still images or frames of video). Light may be received and focused via a lens and may be converted to an electronic image signal by an image sensor. The image signal may be processed by an image signal processor (ISP) to form an image, which may be stored and/or encoded. In some implementations, multiple images or video frames may include spatially adjacent or overlapping content. An outer lens may be subject to scratching, cracks, or other damage from impacts during use of an image capture device, which may cause optical distortion and degradation of quality of captured images. For example, lenses supporting a wide field of view (e.g., a fisheye les) may protrude from the body of an image capture device, and thus be particularly vulnerable to impact damage. 
     SUMMARY 
     The present disclosure describes, inter alia, apparatus and methods for replaceable outer lenses. 
     In a first aspect, the subject matter described in this specification can be embodied in image capture devices that include a lens barrel in a body of the image capture device, the lens barrel including multiple inner lenses; a replaceable lens structure that is mountable on the body of the image capture device, the replaceable lens structure including an outer lens and a retaining ring configured to fasten the outer lens in a position covering a first end the lens barrel in a first arrangement and configured to disconnect the outer lens from the body of the image capture device in a second arrangement; and an image sensor mounted within the body at a second end of the lens barrel, and configured to capture images based on light incident on the image sensor through the outer lens and the multiple inner lenses when the retaining ring is in the first arrangement. 
     In the first aspect, the outer lens may be a curved lens. In the first aspect, the outer lens may be a fisheye lens. In the first aspect, the retaining ring may be glued to the outer lens. In the first aspect, the outer lens may be secured in the retaining ring as a captured mount, such that the outer lens may be rotated within the retaining ring. In in some implementations of the first aspect, at least one of the multiple inner lenses is a curved lens. In the first aspect, the retaining ring may include a bayonet mechanism configured to facilitate transition between the first arrangement and the second arrangement. In the first aspect, the retaining ring may include a threaded mechanism configured to facilitate transition between the first arrangement and the second arrangement. In the first aspect, the retaining ring may include a snap-ring mechanism configured to facilitate transition between the first arrangement and the second arrangement. In the first aspect, the retaining ring may include screw holes that enable screws to fasten the retaining ring to the body in the first arrangement. In the first aspect, the image capture device may include a waterproofing O-ring that is positioned radially around the outer lens. In the first aspect, the image capture device may include a waterproofing O-ring that is positioned inside the outer lens, between the outer lens and the lens barrel. The first aspect may include any combination of the features described in this paragraph. 
     In a second aspect, the subject matter described in this specification can be embodied in image capture devices that include a lens barrel in a body of the image capture device, the lens barrel including a curved inner lens; a replaceable lens structure that is mountable on the body of the image capture device, the replaceable lens structure including an outer lens and a retaining ring configured to fasten the outer lens in a position covering a first end the lens barrel in a first arrangement and configured to disconnect the outer lens from the body of the image capture device in a second arrangement; and an image sensor mounted within the body at a second end of the lens barrel, and configured to capture images based on light incident on the image sensor through the outer lens and the curved inner lens when the retaining ring is in the first arrangement. 
     In the second aspect, the outer lens may be a curved lens. In the second aspect, the outer lens may be a fisheye lens. In the second aspect, the retaining ring may be glued to the outer lens. In the second aspect, the outer lens may be secured in the retaining ring as a captured mount, such that the outer lens may be rotated within the retaining ring. In the second aspect, the retaining ring may include a bayonet mechanism configured to facilitate transition between the first arrangement and the second arrangement. In the second aspect, the retaining ring may include a threaded mechanism configured to facilitate transition between the first arrangement and the second arrangement. In the second aspect, the retaining ring may include a snap-ring mechanism configured to facilitate transition between the first arrangement and the second arrangement. In the second aspect, the retaining ring may include screw holes that enable screws to fasten the retaining ring to the body in the first arrangement. In the second aspect, the image capture device may include a waterproofing O-ring that is positioned radially around the outer lens. In the second aspect, the image capture device may include a waterproofing O-ring that is positioned inside the outer lens, between the outer lens and the lens barrel. The second aspect may include any combination of the features described in this paragraph. 
     In a third aspect, the subject matter described in this specification can be embodied in methods that include disconnecting a first retaining ring from a body of an image capture device to remove a first outer lens from a position covering a first end of a lens barrel, the lens barrel including multiple inner lenses; and connecting a second retaining ring to the body of the image capture device to mount a second outer lens in a position covering the first end the lens barrel, in which an image sensor is mounted within the body at a second end of the lens barrel and configured to capture images based on light incident on the image sensor through the second outer lens and the multiple inner lenses. 
     In the third aspect, the first outer lens may be a curved lens. In the third aspect, the second outer lens may be a curved lens. In the third aspect, the first outer lens may be a fisheye lens. In the third aspect, the second outer lens may be a fisheye lens. In the third aspect, the first retaining ring may be glued to the first outer lens. In the third aspect, the second retaining ring may be glued to the second outer lens. In the third aspect, the first outer lens may be secured in the first retaining ring as a captured mount, such that the first outer lens may be rotated within the first retaining ring. In the third aspect, the second outer lens may be secured in the second retaining ring as a captured mount, such that the second outer lens may be rotated within the second retaining ring. In in some implementations of the third aspect, at least one of the multiple inner lenses is a curved lens. In the third aspect, the first retaining ring may include a bayonet mechanism configured to facilitate disconnecting the first retaining ring from the body of the image capture device. In the third aspect, the first retaining ring may include a threaded mechanism configured to facilitate disconnecting the first retaining ring from the body of the image capture device. In the third aspect, the first retaining ring may include a snap-ring mechanism configured to facilitate disconnecting the first retaining ring from the body of the image capture device. In the third aspect, the first retaining ring may include screw holes that enable screws to fasten the first retaining ring to the body of the image capture device. In the third aspect, the second retaining ring may include a bayonet mechanism configured to facilitate connecting the second retaining ring to the body of the image capture device. In the third aspect, the second retaining ring may include a threaded mechanism configured to facilitate connecting the second retaining ring to the body of the image capture device. In the third aspect, the second retaining ring may include a snap-ring mechanism configured to facilitate connecting the second retaining ring to the body of the image capture device. In the third aspect, the second retaining ring may include screw holes that enable screws to fasten the second retaining ring to the body of the image capture device. The third aspect may include any combination of the features described in this paragraph. 
     These and other aspects of the present disclosure are disclosed in the following detailed description, the appended claims, and the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosed embodiments have other advantages and features which will be more readily apparent from the detailed description, the appended claims, and the accompanying figures. A brief introduction of the figures is below. 
         FIG. 1  is a diagram of an example of an image capture system for content capture. 
         FIG. 2  is a block diagram of an example of an image capture device. 
         FIG. 3A  illustrates a camera system capable of capturing spherical content. 
         FIG. 3B  is a cross-sectional view of an example of an image capture apparatus including overlapping fields-of-view. 
         FIG. 4  illustrates a cross-sectional side view of an example of an interchangeable lens structure mounted over a lens barrel, over an image sensor. 
         FIG. 5A  illustrates an example of an interchangeable lens structure including a bayonet mechanism. 
         FIG. 5B  illustrates an example of an interchangeable lens structure including a threaded mechanism. 
         FIG. 5C  illustrates an example of an interchangeable lens structure including a snap-ring mechanism. 
         FIG. 5D  illustrates an example of an interchangeable lens structure including screw holes. 
         FIG. 6A  illustrates an exploded view of an example of an interchangeable lens structure with radial O-ring. 
         FIG. 6B  illustrates a side view of an example of an interchangeable lens structure with radial O-ring. 
         FIG. 7A  illustrates an exploded view of an example of an interchangeable lens structure with radial glue. 
         FIG. 7B  illustrates a side view of an example of an interchangeable lens structure with radial glue. 
         FIG. 8  illustrates a cross-sectional side view of an examples of outer lenses. 
         FIG. 9  is a flowchart of an example process for replacing an outer lens mounted over a lens barrel. 
     
    
    
     DETAILED DESCRIPTION 
     Systems and methods for replaceable outer lenses are described below. Wide field of view lenses (e.g., hyperhemispherical lenses) often cannot be afforded the protection of a flat lens cover due to the field of view they need to cover. However, wide field of view lenses do scratch and suffer impact damage just like all other lenses. Without a mechanism to protect them or allow to repair/service/replacement of these lenses, the image quality afforded by an image capture device (e.g., a camera) could degrade significantly with the lens damage occurs during use of the image capture device, which may render the image capture device un-usable. Interchangeable outer lens structures are described herein that facilitate maintenance operations needed to preserve the image quality of a lens assembly within acceptable specifications. 
     Different techniques may be used to align replaceable outer lens with the optics (e.g., one or more inner lenses) of a lens barrel and/or an image sensor at the other end of the lens barrel. For example, press-fit, transition-fit, clearance-fit, conical, and/or threaded techniques may be used for alignment of an outer lens. Different mechanisms can be used for fastening an outer lens in a position covering an end of a lens barrel, such as screw thread, bayonet, and/or snap-in mechanisms. Different techniques may be employed for assembly of an interchangeable lens structure, such as a 1-piece snap-in lens, a retaining ring clamping a lens in position with a friction lock by fastening the retaining ring to a lens barrel or another part of a body of image capture device, a retaining ring mounted (e.g., using glue) to an outer lens, an outer lens mounted to a flange and a retaining ring, an outer lens mounted to a retaining ring and a lens barrel retention insert (e.g., including threads), or an outer lens mounted to a flange, a retaining ring, and a lens barrel retention insert. 
     The system and methods for replaceable outer lenses are described herein may provide advantages, such as saving the cost of replacing a lens barrel with inner lenses and when an outer lens has to be replaced due to scratches or other damage, and/or improving the captured image quality after an outer lens replacement by keeping a lens barrel with inner lenses in consistent alignment with an image sensor. 
     As used herein, the term “curved lens” refers to a lens (e.g., a plastic of glass lens) with substantial curvature of an optical surface that is used to focus light incident through the lens. For example, a curved lens may include a portion of an optical surface having a radius of curvature that is less than ten times the width or diameter of the optical surface. 
     Implementations are described in detail with reference to the drawings, which are provided as examples so as to enable those skilled in the art to practice the technology. The figures and examples are not meant to limit the scope of the present disclosure to a single implementation or embodiment, and other implementations and embodiments are possible by way of interchange of, or combination with, some or all of the described or illustrated elements. Wherever convenient, the same reference numbers will be used throughout the drawings to refer to same or like parts. 
       FIG. 1  is a diagram of an example of an image capture system  100  for content capture. As shown in  FIG. 1 , an image capture system  100  may include an image capture apparatus  110 , an external user interface (UI) device  120 , or a combination thereof. 
     In some implementations, the image capture apparatus  110  may be a multi-face apparatus and may include multiple image capture devices, such as image capture devices  130 ,  132 ,  134  as shown in  FIG. 1 , arranged in a structure  140 , such as a cube-shaped cage as shown. Although three image capture devices  130 ,  132 ,  134  are shown for simplicity in  FIG. 1 , the image capture apparatus  110  may include any number of image capture devices. For example, the image capture apparatus  110  shown in  FIG. 1  may include six cameras, which may include the three image capture devices  130 ,  132 ,  134  shown and three cameras not shown. 
     In some implementations, the structure  140  may have dimensions, such as between 25 mm and 150 mm. For example, the length of each side of the structure  140  may be 105 mm. The structure  140  may include a mounting port  142 , which may be removably attachable to a supporting structure, such as a tripod, a photo stick, or any other camera mount (not shown). The structure  140  may be a rigid support structure, such that the relative orientation of the image capture devices  130 ,  132 ,  134  of the image capture apparatus  110  may be maintained in relatively static or fixed alignment, except as described herein. 
     The image capture apparatus  110  may obtain, or capture, image content, such as images, video, or both, with a 360° field-of-view, which may be referred to herein as panoramic or spherical content. For example, each of the image capture devices  130 ,  132 ,  134  may include respective lenses, for receiving and focusing light, and respective image sensors for converting the received and focused light to an image signal, such as by measuring or sampling the light, and the multiple image capture devices  130 ,  132 ,  134  may be arranged such that respective image sensors and lenses capture a combined field-of-view characterized by a spherical or near spherical field-of-view. 
     In some implementations, each of the image capture devices  130 ,  132 ,  134  may have a respective field-of-view  170 ,  172 ,  174 , such as a field-of-view  170 ,  172 ,  174  that 90° in a latitudinal dimension  180 ,  182 ,  184  and includes 120° in a longitudinal dimension  190 ,  192 ,  194 . In some implementations, image capture devices  130 ,  132 ,  134  having overlapping fields-of-view  170 ,  172 ,  174 , or the image sensors thereof, may be oriented at defined angles, such as at 90°, with respect to one another. In some implementations, the image sensor of the image capture device  130  is directed along the X axis, the image sensor of the image capture device  132  is directed along the Y axis, and the image sensor of the image capture device  134  is directed along the Z axis. The respective fields-of-view  170 ,  172 ,  174  for adjacent image capture devices  130 ,  132 ,  134  may be oriented to allow overlap for a stitching function. For example, the longitudinal dimension  190  of the field-of-view  170  for the image capture device  130  may be oriented at 90° with respect to the latitudinal dimension  184  of the field-of-view  174  for the image capture device  134 , the latitudinal dimension  180  of the field-of-view  170  for the image capture device  130  may be oriented at 90° with respect to the longitudinal dimension  192  of the field-of-view  172  for the image capture device  132 , and the latitudinal dimension  182  of the field-of-view  172  for the image capture device  132  may be oriented at 90° with respect to the longitudinal dimension  194  of the field-of-view  174  for the image capture device  134 . 
     The image capture apparatus  110  shown in  FIG. 1  may have 420° angular coverage in vertical and/or horizontal planes by the successive overlap of 90°, 120°, 90°, 120° respective fields-of-view  170 ,  172 ,  174  (not all shown) for four adjacent image capture devices  130 ,  132 ,  134  (not all shown). For example, fields-of-view  170 ,  172  for the image capture devices  130 ,  132  and fields-of-view (not shown) for two image capture devices (not shown) opposite the image capture devices  130 ,  132  respectively may be combined to provide 420° angular coverage in a horizontal plane. In some implementations, the overlap between fields-of-view of image capture devices  130 ,  132 ,  134  having a combined field-of-view including less than 360° angular coverage in a vertical and/or horizontal plane may be aligned and merged or combined to produce a panoramic image. For example, the image capture apparatus  110  may be in motion, such as rotating, and source images captured by at least one of the image capture devices  130 ,  132 ,  134  may be combined to form a panoramic image. As another example, the image capture apparatus  110  may be stationary, and source images captured contemporaneously by each image capture device  130 ,  132 ,  134  may be combined to form a panoramic image. 
     In some implementations, an image capture device  130 ,  132 ,  134  may include a lens  150 ,  152 ,  154  or other optical element. An optical element may include one or more lens, macro lens, zoom lens, special-purpose lens, telephoto lens, prime lens, achromatic lens, apochromatic lens, process lens, rectilinear lens, wide-angle lens, ultra-wide-angle lens, spherical lens, fisheye lens, infrared lens, ultraviolet lens, perspective control lens, other lens, and/or other optical element. In some implementations, a lens  150 ,  152 ,  154  may be a rectilinear lens and produce rectilinear field-of-view images. In some implementations, a lens  150 ,  152 ,  154  may be a fisheye lens and produce fisheye, or near-fisheye, field-of-view images. For example, the respective lenses  150 ,  152 ,  154  of the image capture devices  130 ,  132 ,  134  may be fisheye lenses. In some implementations, images captured by two or more image capture devices  130 ,  132 ,  134  of the image capture apparatus  110  may be combined by stitching or merging fisheye projections of the captured images to produce an equirectangular planar image. For example, a first fisheye image may be a round or elliptical image, and may be transformed to a first rectangular image, a second fisheye image may be a round or elliptical image, and may be transformed to a second rectangular image, and the first and second rectangular images may be arranged side-by-side, which may include overlapping, and stitched together to form the equirectangular planar image. 
     An image capture device  130 ,  132 ,  134  may include replaceable lens structures that allow an outer lens  150 ,  152 ,  154  of an image capture device to be replaced without replacing the underlying lens barrel that includes one or more inner lenses which may be curved. For example, the outer lens  150  may be part of an interchangeable lens structure (e.g., the interchangeable lens structure  500  of  FIG. 5A ). 
     Although not expressly shown in  FIG. 1 , In some implementations, an image capture device  130 ,  132 ,  134  may include one or more image sensors, such as a charge-coupled device (CCD) sensor, an active pixel sensor (APS), a complementary metal-oxide semiconductor (CMOS) sensor, an N-type metal-oxide-semiconductor (NMOS) sensor, and/or any other image sensor or combination of image sensors. 
     Although not expressly shown in  FIG. 1 , in some implementations, an image capture apparatus  110  may include one or more microphones, which may receive, capture, and record audio information, which may be associated with images acquired by the image sensors. 
     Although not expressly shown in  FIG. 1 , the image capture apparatus  110  may include one or more other information sources or sensors, such as an inertial measurement unit (IMU), a global positioning system (GPS) receiver component, a pressure sensor, a temperature sensor, a heart rate sensor, or any other unit, or combination of units, that may be included in an image capture apparatus. 
     In some implementations, the image capture apparatus  110  may interface with or communicate with an external device, such as the external user interface (UI) device  120 , via a wired (not shown) or wireless (as shown) computing communication link  160 . Although a single computing communication link  160  is shown in  FIG. 1  for simplicity, any number of computing communication links may be used. Although the computing communication link  160  shown in  FIG. 1  is shown as a direct computing communication link, an indirect computing communication link, such as a link including another device or a network, such as the internet, may be used. In some implementations, the computing communication link  160  may be a Wi-Fi link, an infrared link, a Bluetooth (BT) link, a cellular link, a ZigBee link, a near field communications (NFC) link, such as an ISO/IEC 23243 protocol link, an Advanced Network Technology interoperability (ANT+) link, and/or any other wireless communications link or combination of links. In some implementations, the computing communication link  160  may be an HDMI link, a USB link, a digital video interface link, a display port interface link, such as a Video Electronics Standards Association (VESA) digital display interface link, an Ethernet link, a Thunderbolt link, and/or other wired computing communication link. 
     In some implementations, the user interface device  120  may be a computing device, such as a smartphone, a tablet computer, a phablet, a smart watch, a portable computer, and/or another device or combination of devices configured to receive user input, communicate information with the image capture apparatus  110  via the computing communication link  160 , or receive user input and communicate information with the image capture apparatus  110  via the computing communication link  160 . 
     In some implementations, the image capture apparatus  110  may transmit images, such as panoramic images, or portions thereof, to the user interface device  120  via the computing communication link  160 , and the user interface device  120  may store, process, display, or a combination thereof the panoramic images. 
     In some implementations, the user interface device  120  may display, or otherwise present, content, such as images or video, acquired by the image capture apparatus  110 . For example, a display of the user interface device  120  may be a viewport into the three-dimensional space represented by the panoramic images or video captured or created by the image capture apparatus  110 . 
     In some implementations, the user interface device  120  may communicate information, such as metadata, to the image capture apparatus  110 . For example, the user interface device  120  may send orientation information of the user interface device  120  with respect to a defined coordinate system to the image capture apparatus  110 , such that the image capture apparatus  110  may determine an orientation of the user interface device  120  relative to the image capture apparatus  110 . Based on the determined orientation, the image capture apparatus  110  may identify a portion of the panoramic images or video captured by the image capture apparatus  110  for the image capture apparatus  110  to send to the user interface device  120  for presentation as the viewport. In some implementations, based on the determined orientation, the image capture apparatus  110  may determine the location of the user interface device  120  and/or the dimensions for viewing of a portion of the panoramic images or video. 
     In an example, a user may rotate (sweep) the user interface device  120  through an arc or path  122  in space, as indicated by the arrow shown at  122  in  FIG. 1 . The user interface device  120  may communicate display orientation information to the image capture apparatus  110  using a communication interface such as the computing communication link  160 . The image capture apparatus  110  may provide an encoded bitstream to enable viewing of a portion of the panoramic content corresponding to a portion of the environment of the display location as the image capture apparatus  110  traverses the path  122 . Accordingly, display orientation information from the user interface device  120  may be transmitted to the image capture apparatus  110  to control user selectable viewing of captured images and/or video. 
     In some implementations, the image capture apparatus  110  may communicate with one or more other external devices (not shown) via wired or wireless computing communication links (not shown). 
     In some implementations, data, such as image data, audio data, and/or other data, obtained by the image capture apparatus  110  may be incorporated into a combined multimedia stream. For example, the multimedia stream may include a video track and/or an audio track. As another example, information from various metadata sensors and/or sources within and/or coupled to the image capture apparatus  110  may be processed to produce a metadata track associated with the video and/or audio track. The metadata track may include metadata, such as white balance metadata, image sensor gain metadata, sensor temperature metadata, exposure time metadata, lens aperture metadata, bracketing configuration metadata and/or other parameters. In some implementations, a multiplexed stream may be generated to incorporate a video and/or audio track and one or more metadata tracks. 
     In some implementations, the user interface device  120  may implement or execute one or more applications, such as GoPro Studio, GoPro App, or both, to manage or control the image capture apparatus  110 . For example, the user interface device  120  may include an application for controlling camera configuration, video acquisition, video display, or any other configurable or controllable aspect of the image capture apparatus  110 . 
     In some implementations, the user interface device  120 , such as via an application (e.g., GoPro App), may generate and share, such as via a cloud-based or social media service, one or more images, or short video clips, such as in response to user input. 
     In some implementations, the user interface device  120 , such as via an application (e.g., GoPro App), may remotely control the image capture apparatus  110 , such as in response to user input. 
     In some implementations, the user interface device  120 , such as via an application (e.g., GoPro App), may display unprocessed or minimally processed images or video captured by the image capture apparatus  110  contemporaneously with capturing the images or video by the image capture apparatus  110 , such as for shot framing, which may be referred to herein as a live preview, and which may be performed in response to user input. 
     In some implementations, the user interface device  120 , such as via an application (e.g., GoPro App), may mark one or more key moments contemporaneously with capturing the images or video by the image capture apparatus  110 , such as with a HiLight Tag, such as in response to user input. 
     In some implementations, the user interface device  120 , such as via an application (e.g., GoPro App), may display, or otherwise present, marks or tags associated with images or video, such as HiLight Tags, such as in response to user input. For example, marks may be presented in a GoPro Camera Roll application for location review and/or playback of video highlights. 
     In some implementations, the user interface device  120 , such as via an application (e.g., GoPro App), may wirelessly control camera software, hardware, or both. For example, the user interface device  120  may include a web-based graphical interface accessible by a user for selecting a live or previously recorded video stream from the image capture apparatus  110  for display on the user interface device  120 . 
     In some implementations, the user interface device  120  may receive information indicating a user setting, such as an image resolution setting (e.g., 3840 pixels by 2160 pixels), a frame rate setting (e.g., 60 frames per second (fps)), a location setting, and/or a context setting, which may indicate an activity, such as mountain biking, in response to user input, and may communicate the settings, or related information, to the image capture apparatus  110 . 
       FIG. 2  is a block diagram of an example of an image capture device  200  in accordance with implementations of this disclosure. In some implementations, an image capture device  200 , such as one of the image capture devices  130 ,  132 ,  134  shown in  FIG. 1 , which may be an action camera, may include an audio component  210 , a user interface (UI) unit  212 , an input/output (I/O) unit  214 , a sensor controller  220 , a processor  222 , an electronic storage unit  224 , an image sensor  230 , a metadata unit  232 , an optics unit  234 , a communication unit  240 , a power system  250 , or a combination thereof. 
     In some implementations, the audio component  210 , which may include a microphone, may receive, sample, capture, record, or a combination thereof audio information, such as sound waves, which may be associated with, such as stored in association with, image or video content contemporaneously captured by the image capture device  200 . In some implementations, audio information may be encoded using, e.g., Advanced Audio Coding (AAC), Audio Compression—3 (AC3), Moving Picture Experts Group Layer-3 Audio (MP3), linear Pulse Code Modulation (PCM), Motion Picture Experts Group—High efficiency coding and media delivery in heterogeneous environments (MPEG-H), and/or other audio coding formats (audio codecs). In one or more implementations of spherical video and/or audio, the audio codec may include a three-dimensional audio codec, such as Ambisonics. For example, an Ambisonics codec can produce full surround audio including a height dimension. Using a G-format Ambisonics codec, a special decoder may be omitted. 
     In some implementations, the user interface unit  212  may include one or more units that may register or receive input from and/or present outputs to a user, such as a display, a touch interface, a proximity sensitive interface, a light receiving/emitting unit, a sound receiving/emitting unit, a wired/wireless unit, and/or other units. In some implementations, the user interface unit  212  may include a display, one or more tactile elements (e.g., buttons and/or virtual touch screen buttons), lights (LEDs), speakers, and/or other user interface elements. The user interface unit  212  may receive user input and/or provide information to a user related to the operation of the image capture device  200 . 
     In some implementations, the user interface unit  212  may include a display unit that presents information related to camera control or use, such as operation mode information (e.g., image resolution, frame rate, capture mode, sensor mode, video mode, photo mode), connection status information (e.g., connected, wireless, wired connection), power mode information (e.g., standby mode, sensor mode, video mode), information related to other information sources (e.g., heart rate, GPS), and/or other information. 
     In some implementations, the user interface unit  212  may include a user interface component such as one or more buttons, which may be operated, such as by a user, to control camera operations, such as to start, stop, pause, and/or resume sensor and/or content capture. The camera control associated with respective user interface operations may be defined. For example, the camera control associated with respective user interface operations may be defined based on the duration of a button press (pulse width modulation), a number of button presses (pulse code modulation), or a combination thereof. In an example, a sensor acquisition mode may be initiated in response to detecting two short button presses. In another example, the initiation of a video mode and cessation of a photo mode, or the initiation of a photo mode and cessation of a video mode, may be triggered (toggled) in response to a single short button press. In another example, video or photo capture for a given time duration or a number of frames (burst capture) may be triggered in response to a single short button press. Other user command or communication implementations may also be implemented, such as one or more short or long button presses. 
     In some implementations, the I/O unit  214  may synchronize the image capture device  200  with other cameras and/or with other external devices, such as a remote control, a second image capture device, a smartphone, a user interface device, such as the user interface device  120  shown in  FIG. 1 , and/or a video server. The I/O unit  214  may communicate information between I/O components. In some implementations, the I/O unit  214  may be connected to the communication unit  240  to provide a wired and/or wireless communications interface (e.g., Wi-Fi, Bluetooth, USB, HDMI, Wireless USB, Near Field Communication (NFC), Ethernet, a radio frequency transceiver, and/or other interfaces) for communication with one or more external devices, such as a user interface device, such as the user interface device  120  shown in  FIG. 1 , or another metadata source. In some implementations, the I/O unit  214  may interface with LED lights, a display, a button, a microphone, speakers, and/or other I/O components. In some implementations, the I/O unit  214  may interface with an energy source, e.g., a battery, and/or a Direct Current (DC) electrical source. 
     In some implementations, the I/O unit  214  of the image capture device  200  may include one or more connections to external computerized devices for configuration and/or management of remote devices, as described herein. The I/O unit  214  may include any of the wireless or wireline interfaces described herein, and/or may include customized or proprietary connections for specific applications. 
     In some implementations, the sensor controller  220  may operate or control the image sensor  230 , such as in response to input, such as user input. In some implementations, the sensor controller  220  may receive image and/or video input from the image sensor  230  and may receive audio information from the audio component  210 . 
     In some implementations, the processor  222  may include a system on a chip (SOC), microcontroller, microprocessor, CPU, DSP, application-specific integrated circuit (ASIC), GPU, and/or other processor that may control the operation and functionality of the image capture device  200 . In some implementations, the processor  222  may interface with the sensor controller  220  to obtain and process sensory information for, e.g., object detection, face tracking, stereo vision, and/or other image processing. 
     In some implementations, the sensor controller  220 , the processor  222 , or both may synchronize information received by the image capture device  200 . For example, timing information may be associated with received sensor data, and metadata information may be related to content (photo/video) captured by the image sensor  230  based on the timing information. In some implementations, the metadata capture may be decoupled from video/image capture. For example, metadata may be stored before, after, and in-between the capture, processing, or storage of one or more video clips and/or images. 
     In some implementations, the sensor controller  220 , the processor  222 , or both may evaluate or process received metadata and may generate other metadata information. For example, the sensor controller  220  may integrate the received acceleration information to determine a velocity profile for the image capture device  200  concurrent with recording a video. In some implementations, video information may include multiple frames of pixels and may be encoded using an encoding method (e.g., H.265, H.264, CineForm, and/or other codec). 
     Although not shown separately in  FIG. 2 , one or more of the audio component  210 , the user interface unit  212 , the I/O unit  214 , the sensor controller  220 , the processor  222 , the electronic storage unit  224 , the image sensor  230 , the metadata unit  232 , the optics unit  234 , the communication unit  240 , or the power systems  250  of the image capture device  200  may communicate information, power, or both with one or more other units, such as via an electronic communication pathway, such as a system bus. For example, the processor  222  may interface with the audio component  210 , the user interface unit  212 , the I/O unit  214 , the sensor controller  220 , the electronic storage unit  224 , the image sensor  230 , the metadata unit  232 , the optics unit  234 , the communication unit  240 , or the power systems  250  via one or more driver interfaces and/or software abstraction layers. In some implementations, one or more of the units shown in  FIG. 2  may include a dedicated processing unit, memory unit, or both (not shown). In some implementations, one or more components may be operable by one or more other control processes. For example, a GPS receiver may include a processing apparatus that may provide position and/or motion information to the processor  222  in accordance with a defined schedule (e.g., values of latitude, longitude, and elevation at 10 Hz). 
     In some implementations, the electronic storage unit  224  may include a system memory module that may store executable computer instructions that, when executed by the processor  222 , perform various functionalities including those described herein. For example, the electronic storage unit  224  may be a non-transitory computer-readable storage medium, which may include executable instructions, and a processor, such as the processor  222  may execute the instruction to perform one or more, or portions of one or more, of the operations described herein. The electronic storage unit  224  may include storage memory for storing content (e.g., metadata, images, audio) captured by the image capture device  200 . 
     In some implementations, the electronic storage unit  224  may include non-transitory memory for storing configuration information and/or processing code for video information and metadata capture, and/or to produce a multimedia stream that may include video information and metadata in accordance with the present disclosure. In some implementations, the configuration information may include capture type (video, still images), image resolution, frame rate, burst setting, white balance, recording configuration (e.g., loop mode), audio track configuration, and/or other parameters that may be associated with audio, video, and/or metadata capture. In some implementations, the electronic storage unit  224  may include memory that may be used by other hardware/firmware/software elements of the image capture device  200 . 
     In some implementations, the image sensor  230  may include one or more of a charge-coupled device sensor, an active pixel sensor, a complementary metal-oxide semiconductor sensor, an N-type metal-oxide-semiconductor sensor, and/or another image sensor or combination of image sensors. In some implementations, the image sensor  230  may be controlled based on control signals from a sensor controller  220 . 
     The image sensor  230  may sense or sample light waves gathered by the optics unit  234  and may produce image data or signals. The image sensor  230  may generate an output signal conveying visual information regarding the objects or other content corresponding to the light waves received by the optics unit  234 . The visual information may include one or more of an image, a video, and/or other visual information. 
     In some implementations, the image sensor  230  may include a video sensor, an acoustic sensor, a capacitive sensor, a radio sensor, a vibrational sensor, an ultrasonic sensor, an infrared sensor, a radar sensor, a Light Detection And Ranging (LIDAR) sensor, a sonar sensor, or any other sensory unit or combination of sensory units capable of detecting or determining information in a computing environment. 
     In some implementations, the metadata unit  232  may include sensors such as an IMU, which may include one or more accelerometers and/or gyroscopes, a magnetometer, a compass, a GPS sensor, an altimeter, an ambient light sensor, a temperature sensor, and/or other sensors or combinations of sensors. In some implementations, the image capture device  200  may contain one or more other metadata/telemetry sources, e.g., image sensor parameters, battery monitor, storage parameters, and/or other information related to camera operation and/or capture of content. The metadata unit  232  may obtain information related to the environment of the image capture device  200  and aspects in which the content is captured. 
     For example, the metadata unit  232  may include an accelerometer that may provide device motion information including velocity and/or acceleration vectors representative of motion of the image capture device  200 . In another example, the metadata unit  232  may include a gyroscope that may provide orientation information describing the orientation of the image capture device  200 . In another example, the metadata unit  232  may include a GPS sensor that may provide GPS coordinates, time, and information identifying a location of the image capture device  200 . In another example, the metadata unit  232  may include an altimeter that may obtain information indicating an altitude of the image capture device  200 . 
     In some implementations, the metadata unit  232 , or one or more portions thereof, may be rigidly coupled to the image capture device  200  such that motion, changes in orientation, or changes in the location of the image capture device  200  may be accurately detected by the metadata unit  232 . Although shown as a single unit, the metadata unit  232 , or one or more portions thereof, may be implemented as multiple distinct units. For example, the metadata unit  232  may include a temperature sensor as a first physical unit and a GPS unit as a second physical unit. In some implementations, the metadata unit  232 , or one or more portions thereof, may be included in an image capture device  200  as shown, or may be included in a physically separate unit operatively coupled to, such as in communication with, the image capture device  200 . 
     In some implementations, the optics unit  234  may include one or more of a lens, macro lens, zoom lens, special-purpose lens, telephoto lens, prime lens, achromatic lens, apochromatic lens, process lens, wide-angle lens, ultra-wide-angle lens, fisheye lens, infrared lens, ultraviolet lens, perspective control lens, other lens, and/or other optics component. In some implementations, the optics unit  234  may include a focus controller unit that may control the operation and configuration of the camera lens. The optics unit  234  may receive light from an object and may focus received light onto an image sensor  230 . Although not shown separately in  FIG. 2 , in some implementations, the optics unit  234  and the image sensor  230  may be combined, such as in a combined physical unit, such as a housing. 
     In some implementations, the communication unit  240  may be coupled to the I/O unit  214  and may include a component (e.g., a dongle) having an infrared sensor, a radio frequency transceiver and antenna, an ultrasonic transducer, and/or other communications interfaces used to send and receive wireless communication signals. In some implementations, the communication unit  240  may include a local (e.g., Bluetooth, Wi-Fi) and/or broad range (e.g., cellular LTE) communications interface for communication between the image capture device  200  and a remote device (e.g., the user interface device  120  in  FIG. 1 ). The communication unit  240  may communicate using, for example, Ethernet, 802.11, worldwide interoperability for microwave access (WiMAX), 3G, Long Term Evolution (LTE), digital subscriber line (DSL), asynchronous transfer mode (ATM), InfiniBand, PCI Express Advanced Switching, and/or other communication technologies. In some implementations, the communication unit  240  may communicate using networking protocols, such as multiprotocol label switching (MPLS), transmission control protocol/Internet protocol (TCP/IP), User Datagram Protocol (UDP), hypertext transport protocol (HTTP), simple mail transfer protocol (SMTP), file transfer protocol (FTP), and/or other networking protocols. 
     Information exchanged via the communication unit  240  may be represented using formats including one or more of hypertext markup language (HTML), extensible markup language (XML), and/or other formats. One or more exchanges of information between the image capture device  200  and remote or external devices may be encrypted using encryption technologies including one or more of secure sockets layer (SSL), transport layer security (TLS), virtual private networks (VPNs), Internet Protocol security (IPsec), and/or other encryption technologies. 
     In some implementations, the one or more power systems  250  supply power to the image capture device  200 . For example, for a small-sized, lower-power action camera a wireless power solution (e.g., battery, solar cell, inductive (contactless) power source, rectification, and/or other power supply) may be used. 
     Consistent with the present disclosure, the components of the image capture device  200  may be remote from one another and/or aggregated. For example, one or more sensor components may be distal from the image capture device  200 , e.g., such as shown and described with respect to  FIG. 1 . Multiple mechanical, sensory, or electrical units may be controlled by a learning apparatus via network/radio connectivity. 
       FIG. 3A  illustrates an image capture device  300  capable of capturing spherical content. The image capture device  300  includes a body  302  having two lenses  330  and  332  structured on front and back surfaces of the body  302 , various indicators on the front and/or back surface of the camera body (such as LEDs, displays, and the like), various input mechanisms (such as buttons, switches, and touch-screen mechanisms), and electronics (e.g., imaging electronics, power electronics, etc.) internal to the body  302  for capturing images via the lenses  330  and  332  and/or performing other functions. The two lenses  330  and  332  are oriented in opposite directions and couple with two images sensors mounted on circuit boards within the body  302 . Other electrical camera components (e.g., an image processor, camera SoC (system-on-chip), etc.) may also be included on a circuit board within the body  302 . 
     An image capture device  300  may include a replaceable lens structure that allows an outer lens (e.g., the lens  330  or the lens  332 ) to be replaced without replacing an underlying lens barrel that includes one or more inner lenses which may be curved. For example, the outer lens  330  may be part of an interchangeable lens structure (e.g., the interchangeable lens structure  500  of  FIG. 5A ) with a retaining ring  320  configured to fasten the outer lens  330  in a position covering an end of a lens barrel in the body of the image capture device  300 . For example, the outer lens  332  may be part of an interchangeable lens structure (e.g., the interchangeable lens structure  500  of  FIG. 5A ) with a retaining ring  322  configured to fasten the outer lens  332  in a position covering an end of a lens barrel in the body of the image capture device  300 . 
       FIG. 3B  is a cross-sectional view of an example of a dual-lens image capture device  300  including overlapping fields-of-view  310 ,  312 . In some implementations, the image capture device  300  may be a spherical image capture apparatus with fields-of-view  310 ,  312  as shown in  FIG. 3 . The image capture device  300  includes a first image sensor  340  mounted within the body  302 , behind the first lens  330  and configured to capture images based on light incident on the first image sensor  340  through the first lens  330 . The image capture device  300  includes a second image sensor  342  mounted within the body  302 , behind the second lens  332  and configured to capture images based on light incident on the second image sensor  342  through the second lens  332 . The first image sensor  340  and the second image sensor  342  may be arranged in a back-to-back or Janus configuration. The lenses  330  and  332  may be mounted on the body  302  of the image capture device  300  in their respective positions in relation to the first image sensor  340  and the second image sensor  342 . 
     The first lens  330  of the image capture device  300  may have the field-of-view  310  shown above a boundary  350 . Behind the first lens  330 , the first image sensor  340  may capture a first hyper-hemispherical image plane from light entering the first lens  330 , corresponding to the first field-of-view  310 . 
     The second lens  332  of the image capture device  300  may have a field-of-view  312  as shown below a boundary  352 . Behind the second lens  332 , the second image sensor  342  may capture a second hyper-hemispherical image plane from light entering the second lens  332 , corresponding to the second field-of-view  312 . 
     In some implementations, one or more areas, such as blind spots  360 ,  362 , may be outside of the fields-of-view  310 ,  312  of the lenses  330 ,  332 , light may be obscured from the lenses  330 ,  332  and the respective image sensors  340 ,  342 , and content in the blind spots  360 ,  362  may be omitted from capture. In some implementations, the image capture device  300  may be configured to minimize the blind spots  360 ,  362 . 
     In some implementations, the fields-of-view  310 ,  312  may overlap. Stitch points  370 ,  372 , proximal to the image capture device  300 , at which the fields-of-view  310 ,  312  overlap may be referred to herein as overlap points or stitch points. Content captured by the respective lenses  330 ,  332 , distal to the stitch points  370 ,  372 , may overlap. 
     In some implementations, images contemporaneously captured by the respective image sensors  340 ,  342  may be combined to form a combined image. Combining the respective images may include correlating the overlapping regions captured by the respective image sensors  340 ,  342 , aligning the captured fields-of-view  310 ,  312 , and stitching the images together to form a cohesive combined image. 
     In some implementations, a small change in the alignment (e.g., position and/or tilt) of the lenses  330 ,  332 , the image sensors  340 ,  342 , or both may change the relative positions of their respective fields-of-view  310 ,  312  and the locations of the stitch points  370 ,  372 . A change in alignment may affect the size of the blind spots  360 ,  362 , which may include changing the size of the blind spots  360 ,  362  unequally. 
     In some implementations, incomplete or inaccurate information indicating the alignment of the image sensors  340 ,  342 , such as the locations of the stitch points  370 ,  372 , may decrease the accuracy, efficiency, or both of generating a combined image. In some implementations, the image capture device  300  may maintain information indicating the location and orientation of the lenses  330 ,  332  and the image sensors  340 ,  342  such that the fields-of-view  310 ,  312 , stitch points  370 ,  372 , or both may be accurately determined, which may improve the accuracy, efficiency, or both of generating a combined image. 
     In some implementations, optical axes through the lenses  330 ,  332  may be substantially antiparallel to each other, such that the respective axes may be within a tolerance such as 1°, 2°, 3°, and/or other tolerances. In some implementations, the image sensors  340 ,  342  may be substantially perpendicular to the optical axes through their respective lenses  330 ,  332 , such that the image sensors may be perpendicular to the respective axes to within a tolerance such as 1°, 2°, 3°, and/or other tolerances. 
     In some implementations, the lenses  330 ,  332  may be laterally offset from each other, may be off-center from a central axis of the image capture device  300 , or may be laterally offset and off-center from the central axis. As compared to an image capture apparatus with back-to-back lenses (e.g., lenses aligned along the same axis), the image capture device  300  including laterally offset lenses  330 ,  332  may include substantially reduced thickness relative to the lengths of the lens barrels securing the lenses  330 ,  332 . For example, the overall thickness of the image capture device  300  may be close to the length of a single lens barrel as opposed to twice the length of a single lens barrel as in a back-to-back configuration. Reducing the lateral distance between the lenses  330 ,  332  may improve the overlap in the fields-of-view  310 ,  312 . 
     In some implementations, images or frames captured by an image capture apparatus, such as the image capture apparatus  110  shown in  FIG. 1  or the image capture device  300  shown in  FIGS. 3A-3B , may be combined, merged, or stitched together, to produce a combined image, such as a spherical or panoramic image, which may be an equirectangular planar image. In some implementations, generating a combined image may include three-dimensional, or spatiotemporal, noise reduction (3DNR). In some implementations, pixels along the stitching boundary may be matched accurately to minimize boundary discontinuities. 
       FIG. 4  illustrates a cross-sectional side view of an example of system  400  including an interchangeable lens structure mounted over a lens barrel, over an image sensor. The system  400  includes a lens barrel  410  including a multiple inner lense  412  and  414 ; an image sensor  420 ; a replaceable lens structure including an outer lens  430  and a retaining ring  440 ; and an O-ring  450  for waterproofing. For example, the system  400  may be implemented as part of an image capture device, such as the image capture device  130  of  FIG. 1  or the image capture device  300  of  FIGS. 3A-3B . 
     The system  400  includes a lens barrel  410  a lens barrel in a body of an image capture device. The lens barrel  410  may be an integrated part of a body of an image capture device. The lens barrel  410  includes multiple inner lenses  412  and  414 . The lens barrel  410  includes a curved inner lens  412 . The curved inner lens  414  may refract light propagating through the lens barrel  410  to focus the light for capture by the image sensor  420 . The lens barrel  410  includes a second curved inner lens  414 . For example, the inner lenses  412  and  414  may be attached (e.g., using glue and/or ledges and flanges (not shown)) to inner walls of the lens barrel  410 . The inner lenses  412  and  414  may be oriented to direct light from a first end of the lens barrel  410 , roughly parallel to an optical axis  416  of the lens barrel  410  to a second end of the lens barrel  410 , where the light may be detected by the image sensor  420  to capture an image. 
     The system  400  includes a replaceable lens structure that is mountable on a body of the image capture device (e.g., image capture device  130  or the image capture device  300 ). The replaceable lens structure includes an outer lens  430  and a retaining ring  440  configured to fasten the outer lens  430  in a position covering a first end the lens barrel  410  in a first arrangement and configured to disconnect the outer lens  430  from the body of the image capture device in a second arrangement. The outer lens  430  may be configured (e.g., shaped and/or positioned) to facilitate capture of images with a desired field of view (e.g., a 90 degree field of view, a 135 degree field of view, or a 180 degree field of view). For example, the outer lens  430  may be a curved lens. For example, the outer lens  430  may be a fisheye lens. For example, the outer lens  430  may be a hyperhemispherical lens. In some implementations, the retaining ring  440  is glued to the outer lens  430 . In some implementations, the outer lens  430  is secured in the retaining ring  440  as a captured mount, such that the outer lens  430  may be rotated within the retaining ring  440 . For example, the outer lens  430  and the retaining ring  440  may be interlocked (e.g., using a flange and slot interface around a circumference of the outer lens  430 ) and travel together but the outer lens  430  may still be loose enough to turn inside the retaining ring  440  independently. In some implementations, the retaining ring  440  is firmly held in a fixed orientation in the first arrangement by a friction lock formed by pressing the retaining ring  440  against the outer lens  430  in its position covering the first end of the lens barrel  410 . For example, the process  900  of  FIG. 9  may be performed to replace the replaceable lens structure including the outer lens  430  and the retaining ring  440 . 
     In some implementations (not shown in  FIG. 4 ), the outer lens may be replaced by an outer lens such as one of the outer lenses described in relation to  FIG. 8 . 
     The retaining ring  440  may include a fastening mechanism configured to facilitate transition between the first arrangement and the second arrangement by removably fastening the retaining ring  440  to the lens barrel  410  or another nearby portion of the body of the image capture device. In the example depicted in  FIG. 4 , a threaded mechanism is employed to fasten the retaining ring  440  to the lens barrel  410  and fasten the outer lens  430  in a position covering a first end the lens barrel  410 . In some implementations (not shown in  FIG. 4 ), a retaining ring  440  may employ other fastening mechanisms to secure a retaining ring to a body of an image capture device. For example, a retaining ring may include a bayonet mechanism (e.g., such as the bayonet mechanism described in relation to  FIG. 5A ) configured to facilitate transition between the first arrangement and the second arrangement. For example, a retaining ring may include a threaded mechanism (e.g., such as the threaded mechanism described in relation to  FIG. 5B ) configured to facilitate transition between the first arrangement and the second arrangement. For example, a retaining ring may include a snap-ring mechanism (e.g., such as the snap-ring mechanism described in relation to  FIG. 5C ) configured to facilitate transition between the first arrangement and the second arrangement. For example, a retaining ring may include screw holes that enable screws to fasten the retaining ring to the body in the first arrangement (e.g., as described in relation to  FIG. 5D ). 
     The system  400  includes an image sensor  420  mounted within a body of an image capture device at a second end of the lens barrel  410 . The image sensor  420  may be configured to capture images based on light incident on the image sensor through the outer lens  430  and the multiple inner lenses  412  and  414  when the retaining ring  440  is in the first arrangement. The image sensor  420  may be configured to capture images based on light incident on the image sensor through the outer lens  430  and a curved inner lens  412  when the retaining ring  440  is in the first arrangement. The image sensor  420  may be configured to detect light of a certain spectrum (e.g., the visible spectrum or the infrared spectrum) and convey information constituting an image as electrical signals (e.g., analog or digital signals). For example, the image sensor  420  may include charge-coupled devices (CCD) or active pixel sensors in complementary metal-oxide-semiconductor (CMOS). In some implementations, the image sensor  420  includes a digital to analog converter. For example, the image sensor  420  may be configured to capture image data using a plurality of selectable exposure times. 
     The system  400  includes a waterproofing O-ring  450  that is positioned radially around the outer lens  430 . The O-ring may be composed of a rubbery material. For example, the O-ring  450  may be positioned to be compressed between the retaining ring  440 , the outer lens  430  and the body (e.g., the lens barrel  410 ) of the image capture device to form a waterproofing seal (e.g., as described in relation to  FIGS. 6A-B ). In some implementations, the O-ring  450  may be glued to the retaining ring  440  and/or to the outer lens  430 . In some implementations (not shown in  FIG. 4 ), a waterproofing O-ring that may be positioned inside the outer lens  430 , between the outer lens  430  and the lens barrel  410 . For example the O-ring may be positioned and compressed along the direction of the optical axis  416  (e.g., vertically) between the outer lens  430  and the lens barrel  410 . In some implementations (not shown in  FIG. 4 ), waterproofing may be provided by a ring of heat set glue (e.g., as described in relation to  FIGS. 7A-B ). 
       FIG. 5A  illustrates an example of an interchangeable lens structure  500  including a bayonet mechanism. The interchangeable lens structure  500  includes a lens barrel  510  (e.g., similar to the lens barrel  410  of  FIG. 4 ), which may include one or more inner lenses that may be curved. The lens barrel  510  is part of a body of an image capture device that includes a male bayonet ring  512 , which may be attached or otherwise integrated with the lens barrel  510  or another portion of the body. The interchangeable lens structure  500  includes a retaining ring  514  that includes a female bayonet ring. For example, the retaining ring  514  may be pushed onto the male bayonet ring of the body in an unlocked position and turned to a locked position to fasten the retaining ring  514  to the body and fasten an outer lens  516  (e.g., one of the lens depicted in  FIG. 8 ) in a position covering a first end of the lens barrel  510 . The interchangeable lens structure  500  includes an O-ring  518  that may be positioned radially around the outer lens  516  and compressed between the retaining ring  514  and the outer lens  516  and/or the body to waterproof the interchangeable lens structure  500 . For example, the retaining ring  514 , the outer lens  516 , and/or the O-ring  518  may be replaced using the process  900  of  FIG. 9 . The interchangeable lens structure  500  may offer advantages over alternative lens assemblies, such as robust reusability over many cycles of removing and replacing an outer lens, over-center locking, an enhanced user experience (e.g., easy to remove/replace), and the retaining ring maybe made sturdy out of a strong metal. A drawback may be a relatively large outer diameter of the retaining ring  514 . 
       FIG. 5B  illustrates an example of an interchangeable lens structure  520  including a threaded mechanism. The interchangeable lens structure  520  includes a lens barrel  530  (e.g., similar to the lens barrel  410  of  FIG. 4 ), which may include one or more inner lenses that may be curved. The lens barrel  530  is part of a body of an image capture device that includes a male threaded interface  534 , which may be attached or otherwise integrated with the lens barrel  530  or another portion of the body. The interchangeable lens structure  520  includes a retaining ring  532  that includes a female threaded interface. For example, the retaining ring  532  may be twisted onto the male threaded interface  534  of the body to fasten the retaining ring  532  to the body and fasten an outer lens  536  (e.g., one of the lens depicted in  FIG. 8 ) in a position covering a first end of the lens barrel  530 . The interchangeable lens structure  520  includes an O-ring  538  that may be positioned inside (e.g., vertically under) the outer lens  536  and compressed between the outer lens  536  and the body (e.g., the lens barrel  530 ) to waterproof the interchangeable lens structure  520 . For example, the retaining ring  532 , the outer lens  536 , and/or the O-ring  538  may be replaced using the process  900  of  FIG. 9 . The interchangeable lens structure  520  may offer advantages over alternative lens assemblies, such as a low profile. A drawback may be a risk of cross threading or stripping. 
       FIG. 5C  illustrates an example of an interchangeable lens structure  540  including a snap-ring mechanism. The interchangeable lens structure  540  includes a lens barrel  550  (e.g., similar to the lens barrel  410  of  FIG. 4 ), which may include one or more inner lenses that may be curved. The lens barrel  550  is part of a body of an image capture device that includes a male snap-ring interface  554 , which may be attached or otherwise integrated with the lens barrel  550  or another portion of the body. The interchangeable lens structure  540  includes a retaining ring  552  that includes a female snap-ring interface. For example, the retaining ring  552  may be pushed onto the male snap-ring interface  554  of the body to fasten the retaining ring  552  to the body and fasten an outer lens  556  (e.g., one of the lens depicted in  FIG. 8 ) in a position covering a first end of the lens barrel  550 . The interchangeable lens structure  540  includes an O-ring  558  that may be positioned radially around the outer lens  556  and compressed between the retaining ring  552  and the outer lens  556  and/or the body to waterproof the interchangeable lens structure  540 . For example, the retaining ring  552 , the outer lens  556 , and/or the O-ring  558  may be replaced using the process  900  of  FIG. 9 . The interchangeable lens structure  540  may offer advantages over alternative lens assemblies, such as ease of installation. A drawback may be difficulty removing the retaining ring  552 . 
       FIG. 5D  illustrates an example of an interchangeable lens structure  560  including screw holes. The interchangeable lens structure  560  includes a lens barrel  570  (e.g., similar to the lens barrel  410  of  FIG. 4 ), which may include one or more inner lenses that may be curved. The lens barrel  570  is part of a body of an image capture device that includes screw holes  574 , which may be attached or otherwise integrated with the lens barrel  570  or another portion of the body. The interchangeable lens structure  560  includes a retaining ring  572  that includes screw holes. For example, the retaining ring  572  may be fastened to body by driving screws  580  and  582  through the screw holes of the retaining ring  572 , into the screw holes  574  of the body to fasten an outer lens  576  (e.g., one of the lens depicted in  FIG. 8 ) in a position covering a first end of the lens barrel  570 . The interchangeable lens structure  560  includes an O-ring  578  that may be positioned radially around the outer lens  576  and compressed between the retaining ring  572  and the outer lens  576  and/or the body to waterproof the interchangeable lens structure  560 . For example, the retaining ring  572 , the outer lens  576 , and/or the O-ring  578  may be replaced using the process  900  of  FIG. 9 . The interchangeable lens structure  560  may offer advantages over alternative lens assemblies, such as robust fastening of the retaining ring  572  and the outer lens  576  into position. A drawback may be a large size and poor aesthetics of the retaining ring  572 . 
       FIG. 6A  illustrates an exploded view of an example of an interchangeable lens structure  600  with radial o-ring.  FIG. 6B  illustrates a side view of an example of the interchangeable lens structure  600  with a radial o-ring. The interchangeable lens structure  600  includes an outer lens  610  (e.g., one of the lens depicted in  FIG. 8 ), a retaining ring  620 , and an o-ring  630 . The retaining ring  620 , the o-ring  630 , and the outer lens may stacked as shown in  FIG. 6A , with the o-ring  630  fitting and being compressed radially between the outer lens  610  and the retaining ring  620 . A fastening mechanism (e.g., threads) of the retaining ring  620  may then be used fasten these components in a position covering a first end of a lens barrel  640 . In this position, the o-ring may be further compressed between the retaining ring  620  and the lens barrel  640  of the body. For example, the compressed o-ring  630  may provide a water seal to a depth of 10 meters with 1 mm=0.23 mm compression. 
       FIG. 7A  illustrates an exploded view of an example of an interchangeable lens structure  700  with radial glue.  FIG. 7B  illustrates a side view of an example of the interchangeable lens structure  700  with radial glue that has been set. The interchangeable lens structure  700  includes an outer lens  710  (e.g., one of the lens depicted in  FIG. 8 ), a retaining ring  720 , and a ring of glue  730 . The retaining ring  720 , the ring of glue  730 , and the outer lens may stacked as shown in  FIG. 7A , with the ring of glue  730  fitting radially between the outer lens  710  and the retaining ring  720 . The ring of glue  730  may be set (e.g., by applying heat or a laser) to secure the outer lens  710  to the retaining ring  720  and to provide waterproof seal. A fastening mechanism (e.g., threads) of the retaining ring  720  may then be used fasten these components in a position such that the outer lens  710  covers a first end of a lens barrel  740 . For example, the set ring of glue  730  may provide a water seal to a depth of 6 meters. 
       FIG. 8  illustrates a cross-sectional side view of an examples of outer lenses. The outer lens  810  has a cylindrical outer diameter. The outer lens  820  has a conical chamfer on its outer diameter. The outer lens  830  has a lower flange (upper cut). The outer lens  840  has a middle flange (upper cut and lower cut). The outer lens  850  has a middle cut (upper cut). For example, the outer lens  850  may be captured by a retaining ring with a snap-fit mechanism. The outer lens  860  has a cylindrical outer diameter with a greater thickness than the outer lens  810 . 
     The outer lens  870  is mounted to a ring  872  with glue. For example, the ring  872  may have thickness or height of 1 mm. The outer lens  880  is mounted to a ring  882  with glue. For example, the ring  872  may have thickness or height of 1.75 mm. In some implementations, a ring glued to an outer lens can have a larger thickness or height than the outer diameter of the outer lens. In some implementations, a ring can be mounted to an outer lens with shrink-fit. In some implementations, a ring can be mounted to an outer lens with shrink-fit. In some implementations (not shown), a ring can be mounted to an outer lens with shrink-fit. 
       FIG. 9  is a flowchart of an example process  900  for replacing an outer lens mounted over a lens barrel. The process  900  includes disconnecting  910  a first retaining ring from a body of an image capture device to remove a first outer lens from a position covering a first end of a lens barrel, and connecting  920  a second retaining ring to the body of the image capture device to mount a second outer lens in a position covering the first end the lens barrel. For example, the process  900  may be performed using the system  400  of  FIG. 4 . For example, the process  900  may be performed using the interchangeable lens structure  500  of  FIG. 5A . For example, the process  900  may be performed using the interchangeable lens structure  520  of  FIG. 5B . For example, the process  900  may be performed using the interchangeable lens structure  540  of  FIG. 5C . For example, the process  900  may be performed using the interchangeable lens structure  560  of  FIG. 5D . For example, the process  900  may be performed by an end user of the image capture device as a do-it-yourself repair or maintenance operation. For example, the process  900  may be performed by a technician. 
     The process  900  includes disconnecting  910  a first retaining ring from a body of an image capture device to remove a first outer lens from a position covering a first end of a lens barrel. For example, the lens barrel may include multiple inner lenses. For example, the lens barrel may include at least one curved inner lens. For example, where the first retaining ring includes a bayonet mechanism (e.g., as described in relation to  FIG. 5A ), disconnecting  910  the first retaining ring from the body may include twisting the first retaining ring from a locked to an unlocked position, and pulling the retaining ring away from the body to remove the first outer lens from a position covering a first end of a lens barrel. For example, where the first retaining ring includes a threaded mechanism (e.g., as described in relation to  FIG. 5B ), disconnecting  910  the first retaining ring from the body may include twisting the first retaining ring counterclockwise, and pulling the retaining ring away from the body to remove the first outer lens from a position covering a first end of a lens barrel. For example, where the first retaining ring includes a snap-ring mechanism (e.g., as described in relation to  FIG. 5C ), disconnecting  910  the first retaining ring from the body may include prying the first retaining ring away from the body (e.g., using fingers and/or a screwdriver) to remove the first outer lens from a position covering a first end of a lens barrel. For example, where the first retaining ring includes a screw holes (e.g., as described in relation to  FIG. 5D ), disconnecting  910  the first retaining ring from the body may include unscrewing screws through the screw holes, and pulling the retaining ring away from the body to remove the first outer lens from a position covering a first end of a lens barrel. 
     The process  900  includes connecting  920  a second retaining ring to the body of the image capture device to mount a second outer lens (e.g. a new outer lens) in a position covering the first end the lens barrel. For example, an image sensor may be mounted within the body at a second end of the lens barrel and configured to capture images based on light incident on the image sensor through the second outer lens and the one or more inner lenses of the lens barrel. In some implementations, the first outer lens is glued to the first retaining ring, and the second outer lens is glued to the second retaining ring. For example, where the second retaining ring includes a bayonet mechanism (e.g., as described in relation to  FIG. 5A ), connecting  920  the second retaining ring to the body may include pushing the retaining ring onto the body and twisting the second retaining ring from an unlocked to a locked position to mount the second outer lens in a position covering the first end the lens barrel. For example, where the second retaining ring includes a threaded mechanism (e.g., as described in relation to  FIG. 5B ), connecting  920  the second retaining ring to the body may include twisting the second retaining ring clockwise to mount the second outer lens in a position covering the first end the lens barrel. For example, where the second retaining ring includes a snap-ring mechanism (e.g., as described in relation to  FIG. 5C ), connecting  920  the second retaining ring to the body may include snapping the second retaining ring onto the body (e.g., using fingers) to mount the second outer lens in a position covering the first end the lens barrel. For example, where the second retaining ring includes a screw holes (e.g., as described in relation to  FIG. 5D ), connecting  920  the second retaining ring to the body may include screwing screws through the screw holes into the body to mount the second outer lens in a position covering the first end the lens barrel. 
     In the present specification, an implementation showing a singular component should not be considered limiting; rather, the disclosure is intended to encompass other implementations including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Further, the present disclosure encompasses present and future known equivalents to the components referred to herein by way of illustration. For example, the replaceable outer lens systems and techniques described herein may be applied to any number of lenses on an image capture device, such as multiple lenses for depth capture, or potentially to allow shorter TTL lenses (with smaller image sensors) that are then fused together to create the total light gathering power of a larger sensor/lens combination. 
     As used herein, the terms “camera,” or variations thereof, and “image capture device,” or variations thereof, may be used to refer to any imaging device or sensor configured to capture, record, and/or convey still and/or video imagery which may be sensitive to visible parts of the electromagnetic spectrum, invisible parts of the electromagnetic spectrum (e.g., infrared, ultraviolet), and/or other energy. 
     The above-described implementations and examples have been described in order to facilitate easy understanding of this disclosure and do not limit this disclosure. On the contrary, this disclosure is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation as is permitted under the law so as to encompass all such modifications and equivalent arrangements.