Patent Application
20200371323
This invention relates generally to lens systems using free form lenses, and more particularly relates to lens systems configured to provide, selectively, an image space ranging from a relatively wide field of view to a substantially smaller field of view, thus effectively providing a zoom lens system.
The general task of an optical design is to make a perfect conjugation between the object space or plane and the image space or sensor plane, with no aberrations, distortions or other errors. Although many lenses are very good, such perfection is elusive. Even small increments can provide significant benefit. The issue becomes more problematic when the lens system is intended to provide multiple focal lengths, such as with a zoom lens system. When the design is intended to fit into a small form factor, such as a lens module and associated sensors for use as a camera in a smartphone or similar volume-limited application, the challenges become dramatically more acute.
Rotational symmetry is widely used in conventional lenses, with the field of view and the aperture stop both being rotationally symmetric. With only rare exception, this results in the final design comprising rotationally symmetric elements. However, most sensors—the photosensitive structures that record the image—are rectangular in shape. Thus, the image space created by a rotationally symmetric lens system creates a circular field of view, while the sensor that records the image is a rectangle. In an effort to optimize the mismatch, the diameter of the field of view of the lens system is matched to the diagonal size of the sensor.
One of the major shortcomings of current lens systems for smartphones is the lack of optical zoom. Volume, footprint, and z-height limitations in smartphones make it difficult, if not impossible, to achieve optical zoom using conventional rotationally symmetric lens elements. Recently, multi-camera solutions have been offered to provide a simulation of optical zoom, but these designs also suffer from a variety of deficiencies. Low distortion is difficult in a wide-angle lens, and particularly with low z-height. In addition, while creating a zoom without moving parts is desirable for a smartphone camera in many respects, zoom without moving parts (but with a large zoom ratio) is difficult to achieve using rotationally symmetric lenses. Use of rotationally symmetric lenses requires extra spacing between the lenses, which is undesirable when attempting to reconstruct, or stitch together, a wide angle image from multiple images taken at different points of view. Tilting of rotationally symmetric lenses allows an increased field of view, but adds a keystone distortion that is difficult to remove during processing.
As a result, there is a need for lens system designs that provide good image quality across a range of focal lengths extending from wide angle to zoom while still fitting within the z-height and volume available in a smartphone form factor.
The present invention provides a plurality of optical designs using free form lenses which provide selectable focal lengths ranging from a wide angle field of view to a narrow field of view representative of a zoom lens while still fitting within the form factor required for modern smartphones. In an embodiment, the range of focal lengths operates to provide approximately a 10× zoom. Alternative embodiments provide other ranges of focal lengths and thus function as zoom lens of different optical powers while still complying with the form factor requirements of modern smartphones.
To overcome the challenges mentioned above, the present invention provides a trio of cameras, arranged so that the sensors are co-planar. In an embodiment, the cameras are arranged in a linear fashion, with the lens system of the center camera providing an axially symmetrical image on the sensor although not necessarily rotationally symmetrical, whereas the right and left cameras use freeform lenses to provide an off-axis image to their respective sensors. It will be understand by those skilled in the art that the description of left/center/right can also mean top/center/bottom or up/center/down, depending upon the orientation of the smartphone. To avoid unnecessary complication and possible confusion, only the left/center/right terminology will be used hereinafter.
In an embodiment, the images created by the left and right cameras and associated lens systems are slightly overlapped, and the center camera substantially overlaps both the left and right cameras. In such an embodiment, sensor of the center camera can be a substantially higher resolution than the sensors of the left and right cameras. By selecting left and right cameras, a wide angle image is achieved. By selecting just one of the left, right, or center cameras, with a reduced resolution of the center camera (e.g., binning), a “normal” image is achieved. By selecting a portion of the center camera, a zoom image is achieved.
In an alternative embodiment, the images created by the left and center cameras only slightly overlap, and the images created by the center and right cameras only slightly overlap. Depending upon the fields of view of each of the cameras, an ultrawide image is created when the images from all three cameras are stitched together. In an embodiment, the center camera is substantially higher resolution than the left and right cameras, but the center sensor can be binned to match the resolution of the left and right cameras. By selecting only the image from one of the cameras, the user can select different points of view and create a “normal” image. By selecting the center camera at full resolution, a high resolution image can be achieved. Finally, by selecting only a portion of the center camera's sensor, a zoom image is achieved.
To achieve the foregoing results, while still complying with the space and form factor limitations imposed by modern smartphones, at least the lens systems for the left and right cameras comprise at least one freeform element. In addition to providing wide angle and zoom images, stereoscopic images can be provided by separately capturing the left and right images and then processing those images into left and right stereo views.
In a still further alternative embodiment, a center camera having a lens system comprising at least one Alvarez pair of free form lenses is combined with left and right cameras and their associated off-axis lens systems to provide optical zoom as well as wide angle and normal images. The images from the left and right cameras overlap slightly, and the image from the higher resolution Alvarez center camera overlaps both left and right images. The Alvarez center lens system can be configured with positive optical power to yield optical zoom.
It is therefore one object of the present invention to provide optical zoom within the format factor limitations of a smartphone by providing a pair of cameras to create slightly overlapping images where the sensors of the pair are a first resolution, and further providing a third camera having a sensor of a higher resolution that creates a third, higher resolution image that substantially overlaps at least a central portion of the images created by the pair of cameras, such that the images from the pair of cameras provides a wide field of view, the image from a single camera provides a normal field of view, and the image from the centrally located camera provides either a high resolution image or a zoomed-in image of a portion of the sensor, all within the Z-height and other limitations of a smartphone.
It is a further object of the invention to provide an optical system that yields low distortion images at wide, normal and zoom fields of view.
These and other objects of the invention can be better appreciated from the following detailed description, taken in conjunction with the appended Figures.
Referring first to
Selection of the camera(s) to be used can be accomplished by any convenient means, including a simple switch, or other controls as are well known in the art. In some embodiments, the center camera comprises a larger sensor, and may also have a lens system with positive optical power or a different field of view from the right and left cameras. In such cases, selection of the center camera alone can yield a higher resolution image, or a larger field of view, or an optically zoomed image, and so forth. The center image can also be used to improve or correct the image created by the left or right image, particularly but not solely when the left and right images are stitched to form a wide angle image.
The free form lenses required for the embodiments shown herein can be developed using a variety of mathematical approaches, for example either the use of XY polynomials or the use of Zernike polynomials. For the embodiment shown in
The above example of a center lens system can be seen to comprise five elements L1 to L5, with an optional aperture in front of the first element L1. In an embodiment, the left and right cameras can have the characteristics shown in the below tables:
Further, the freeform lenses, element L5 in the above, can have the XY polynomial coefficients shown below:
Likewise, the aspheric coefficients for each of the surfaces of the lens elements for the center, left and right cameras can be appreciated from the below tables:
Those skilled in the art will recognize that the Extended XY Polynomial coefficients are for use in the following equation:
where z, x, y are cartesian coordinates of the surface, c is surface curvature, r is the surface radial coordinate, k is the conical constant, Ai are polynomial coefficients, Σ(x,y) are polynomials, as discussed in great detail in U.S. Patent Application Ser. No. 62/748,961 filed on 22 Oct. 2018 and incorporated herein by reference.
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In one embodiment of the configuration shown in
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The embodiment shown in the lower table uses a center sensor of 40 MP with left and right sensors of 20 MP each. The center lens system again has a 40 degree FOV, while the side cameras each have a FOV of 120 degrees, for a total FOV between then (accounting for overlap) of approximately 210 degrees, resulting in a higher zoom ratio.
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The GPU can be any of a variety of devices, such as those available from Intel, Nvidia, and others. The software operating on the GPU will typically depend on the specific implementation and which GPU is selected.
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Next, with reference to
While various embodiments of the invention have been disclosed in detail, it will be appreciated that the features of the exemplary embodiments discussed herein are not to be limiting, and that numerous alternatives and equivalents exist which do not depart from the scope of the invention. As such, the present invention is to be limited only by the appended claims.
This application is conversion of U.S. Patent Application Ser. No. 62/769,519 filed Nov. 19, 2018, and further is a continuation-in-part of U.S. patent application Ser. No. 15/958,804 filed on Apr. 20, 2018, entitled Low Distortion Lens Using Double Plane Symmetric Element, which is turn is a continuation-in-part of PCT Application PCT/IB2016/001630 having International Filing Date 20 Oct. 2016, which in turn claims the benefit of U.S. Patent Application 62/244,171, filed 20 Oct. 2015. The present application claims the benefit of priority of each of the foregoing applications, all of which are incorporated herein for all purposes. The present application also claims the benefit of PCT Application PCT/US2019/057467 filed 22 Oct. 2019 which in turn is a conversion of U.S. Patent Application Ser. No. 62/748,976, filed on 22 Oct. 2018, entitled Low Light Optical System Utilizing Double Plane Symmetry Defined by X-Y Polynomial, as well as U.S. Patent Application Ser. No. 62/748,961 entitled Lens Systems Using Free Form Elements to Match Object Space and Image Space, and Methods Therefor and also filed on 22 Oct. 2018. The present application claims the benefit of priority of each of the foregoing applications, all of which are incorporated herein for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 62769519 | Nov 2018 | US | |
| 62244171 | Oct 2015 | US | |
| 62748961 | Oct 2018 | US | |
| 62748976 | Oct 2018 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15958804 | Apr 2018 | US |
| Child | 16688955 | US | |
| Parent | PCT/IB2016/001630 | Oct 2016 | US |
| Child | 15958804 | US | |
| Parent | PCT/US19/57467 | Oct 2019 | US |
| Child | PCT/IB2016/001630 | US |
