Focal plane shift measurement and adjustment in a lens assembly

To compensate for this change in focal length due to a temperature change, an integrated image sensor and lens assembly includes a shift measurement module to measure a shift between optical elements to which the shift measurement module is coupled. The measured shift between optical elements is used to determine a shift of the focal plane in reference to the image plane. Optical aberration resulting from the shift of the focal plane in reference to the image plane may further be compensated.

TECHNICAL FIELD

This disclosure relates to a camera, and more specifically, to an integrated sensor and lens assembly of a camera.

BACKGROUND

Manufacturing of lens assemblies for high-resolution cameras typically require a high degree of precision in positioning components of the lens assembly to ensure that the lens will achieve proper focus. As a result, a challenge exists in achieving a fast, automated, and high-yielding assembly process for high-resolution cameras.

In an integrated image sensor and camera lens system, a lens mount is coupled to a lens barrel. In an assembly process, a lens barrel housing the camera lens (or multiple lenses) is placed within a housing assembly affixed to an image sensor such that the image sensor is properly aligned with the lens to maintain lens focus. Upon testing the lens barrel to position it for proper alignment, the lens barrel is affixed to the housing assembly. Imaging lenses tend to defocus due to various reasons such as temperature change or physical movement. For example, coefficient of thermal expansion (CTE) changes the physical scale in materials. CTE changes may cause the lens system to move. An individual lens may move with respect to one another and alter the physical dimensions of the lens. In addition, thermo-optic coefficient changes the refractive index of optical materials. Thermal expansion of lens assemblies cause changes in optical path lengths, which defocuses images when a camera is used in a temperature range other than the one under which the camera has been tuned. This affects the focus of the lenses and compromises performance and yield. This effect is especially detrimental to a high definition camera as the sensor is able to resolve details at the very limit of the optical focus and any defocusing is readily captured and appreciably degrades the picture quality.

DETAILED DESCRIPTION

Configuration Overview

An integrated image sensor and lens assembly is described herein. The integrated image sensor and lens assembly may include a lens barrel holding one or more lenses coupled to a lens mount. The lens mount may further be coupled to an image sensor substrate that has an image sensor lying on an image plane. During an assembly process, the optical distance between the camera lens and the image sensor may be tuned such that the focal plane of the camera lens coincides with the image plane. However, in operation, due to thermal expansion of the lens barrel and the lens mount, the optical distance between the lens window and the image sensor may vary with temperature change thereby causing the focal plane of the camera lens to shift from the image plane. To compensate for this change in focal length due to a temperature change, the integrated image sensor and lens assembly may further comprise a shift measurement module to measure a shift between a lens and an image sensor, two lenses, a lens window and an image sensor, or a lens window and a lens. The shift measurement module may include one or more strain gauges of which an electrical resistance changes responsive to a shift among optical elements. The measured shift may be used to determine a shift of a focal plane in reference to the image plane. Optical aberration resulting from the shift of the focal plane in reference to the image plane may accordingly be compensated.

Example Integrated Image Sensor and Lens Assembly

FIG. 1illustrates a cross-sectional view of an embodiment of an integrated image sensor and lens assembly100. The assembly100may include a camera lens barrel110, a camera lens mount120, an image sensor substrate140, and a shift measurement module150. The image sensor substrate140may have an image sensor assembly130(e.g., a high-definition image sensor) for capturing images (e.g., still images and/or video frames). The camera lens mount120may be physically affixed to the image sensor substrate140and also affixed to the camera lens barrel110.

The lens barrel110may include one or more lenses or other optical components to direct light to the image sensor assembly. The lens barrel110may comprise a lower portion116, one or more barrel arms114, and a lens window112. The lower portion116of the lens barrel is substantially cylindrical and structured to at least partially extend into the channel of the tube portion128of the camera lens mount120. The barrel arms114extend radially from the body of the lens barrel110and are outside the channel of the lens mount120when assembled. The lens arms114may be used to physically couple the lens barrel110to the camera body (not shown). The lens window112includes optical components to enable external light to enter the lens barrel110and be directed to the image sensor assembly130. The camera lens mount120includes a tube portion128that extends away from the image sensor assembly along the optical axis170and includes a substantially cylindrical channel for receiving the lens barrel110.

The image sensor substrate140comprises a printed circuit board for mounting the image sensor assembly130and may furthermore include various electronic components that operate with the image sensor assembly130or provide external connections to other components of the camera system. The image sensor assembly130houses an image sensor (e.g., a high-definition image sensor) for capturing images and/or video and includes structural elements for physically coupling the image sensor assembly130to the image sensor substrate140and to the camera lens mount120. The image sensor of the image sensor assembly130lies on an image plane171. The combined focal plane of the lens window112and lenses internal to the lens barrel116is maintained to coincide with the image plane171. The distance between the lens window112and the image sensor130is D. As illustrated, the lens barrel110and/or lens mount120expand or contract with temperature and cause a shift ΔB of a focal plane in reference to an image plane.

The shift measurement module150measures shifts between optical elements. In the illustrated example, the shift measurement module150is coupled between the lens window112and the image sensor130. The shift measurement module150measures a shift between the lens window112and the image sensor130. The shift measurement module150may be further coupled between the lens window112and a lens, between the lens and the image sensor130, and/or between two lenses.

In one embodiment, the shift measure module150includes one or more strain gauges. An electrical resistance of the strain gauge changes responsive to a shift between the lens window112and the image sensor130. A change in the electrical resistance of the strain gauge is measured. In various embodiments, the change in the electrical resistance of the strain gauge is converted to the shift ΔD between the lens window112and the image sensor130. A shift ΔB of the image plane171in reference to the focal plane172can be determined based on the shift ΔD between the lens window112and the image sensor130. For example, a shift ΔB between the image plane171and the focal plane172can be determined by looking up a shift ΔD between the lens window112and image sensor130in a table including values of ΔD and corresponding values of ΔB. As such, changes in the position of the focal plane (which results in a defocused image) caused, for example, by thermal expansion of the lens barrel110and/or lens mount120can be determined. The camera may compensate optical aberration as a result of a focal plane from an image plane.

FIG. 2Aillustrates an example shift measurement and compensation module202, according to one example embodiment. The shift measurement and compensation module202determines a shift of a focal plane in reference to an image plane and compensates the shift such that the image is focused. The shift of the focal plane in reference to the image plane may result in optical aberration (e.g., monochromatic aberration, chromatic aberration), and the shift measurement and compensation module202can correct for the optical aberration. As such, the image remains focused or substantially focused. The shift determination and compensation module202includes a shift measurement module150, a shift determination module204, and a shift compensation module206.

The shift measurement module150may measure one or more shifts. The one or more shifts may include a shift between a lens window and an image sensor. The one or more shifts may include a shift between a lens and an image sensor, a shift between a lens window and a lens, and/or a shift between two lenses. The shift measurement module150may include one or more strain gauges. The set of strain gauges may be integrated in the integrated image sensor and lens assembly, as illustrated inFIG. 1. The shift measurement module150measures one or more resistance changes caused by the one or more shifts. The shift measurement module150converts the measured one or more resistance changes to the one or more shifts between a lens window and an image sensor, between a lens and an image sensor, between the lens window and the lens, or between two lenses.

The shift determination module204may determine a shift of a focus plane in reference to an image plane based on the one or more shifts measured by the shift measure module150. The shift determination module204looks up the one or more measured shifts in a table to determine a shift of a focal plane in reference to the image plane. The table stores values of shifts between optical elements and values of a shift of the focal plane in reference to the image plane that correspond to the values of shifts between optical elements. A shift of the focal plane in reference to the image plane may result in an optical aberration.

The shift compensation module206may correct for the optical aberration resulting from the shift of the focal plane in reference to the image plane. For example, the shift compensation module206uses one or more digital image processing techniques to correct for the optical aberration. As a shift of the focal plane away from the image plane has been determined, the optical aberration can also be determined. Images are processed using various techniques to substantially minimize the determined optical aberration. For example the shift of the focal plane in reference to the image plane may cause the captured images that are out of focus. The captured images are processed to restore focus.

FIG. 2Billustrates an example process250of a camera measuring and compensating a shift of an optical plane from an image plane, according to one example embodiment. The camera may measure252one or more resistance changes due to one or more shifts between a lens window and an image sensor, between a lens and the image sensor, between the lens window and the lens, and/or between two lenses. The camera252may include one or more strain gauges. The one or more strain gauges may be coupled between the lens window and the image sensor, the lens window and a lens, two lenses, and/or a lens and the image sensor. The camera may determine254the one or more shifts between a lens window and an image sensor, between a lens and the image sensor, between the lens window and the lens, and/or between two lenses. The camera may convert the measured one or more resistance changes to determine the one or more shifts. The camera may further determine256a shift of a focal plane in reference to an image plane. The camera may look up the measured one or more shifts in a table to identify a corresponding shift of a focal plane in reference to the image plane. The table stores a one to one relationship between a shift of a focal plane from the image plane and one or more shifts. The camera may compensate for258the determined shift of the focal plane in reference to the image plane. In some embodiments, the camera may compare the determined shift of the focal plane in reference to the image plane to a threshold shift. The camera may compensate for the determined shift in response to determining that the determined shift exceeds the threshold shift. The camera may use one or more image processing techniques to correct for the optical aberration resulting from the shift of the focal plane in reference to the image plane.

Example Camera System Configuration

FIG. 3illustrates an embodiment of an example camera300that includes the integrated image sensor and lens assembly100described above. The camera300comprises a camera body having a camera lens structured on a front surface of the camera body, various indicators on the front of the 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 camera body for capturing images via the camera lens and/or performing other functions. The camera300is configured to capture images and video, and to store captured images and video for subsequent display or playback. As illustrated, the camera300includes a lens302configured to receive light incident upon the lens and to direct received light onto an image sensor internal to the lens. The lens302is enclosed by a lens ring304, which are both part of the integrated image sensor and lens assembly100discussed above.

The camera300can include various indicators, including the LED lights306and the LED display308. The camera300can also include buttons310configured to allow a user of the camera to interact with the camera, to turn the camera on, and to otherwise configure the operating mode of the camera. The camera300can also include a microphone312configured to receive and record audio signals in conjunction with recording video. The side of the camera300includes an I/O interface314.

Additional Configuration Considerations

Various embodiments as presented herein can advantageously measure focal length changes due to thermal expansion or contraction of the lens barrel and/or lens mount due to temperature changes and correct for optical aberration resulting from the focal length changes. The configurations as described herein can correct for optical aberration efficiently without compromising cameras' compact sizes.

Throughout this specification, some embodiments have used the expression “coupled” along with its derivatives. The term “coupled” as used herein is not necessarily limited to two or more elements being in direct physical or electrical contact. Rather, the term “coupled” may also encompass two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other, or are structured to provide a thermal conduction path between the elements.