The present invention relates generally to image capture systems, more particularly, to image capture device systems that utilize a flat sparsely-filled aperture to provide a telephoto lens in a thin form factor and also provide zoom capabilities for the flat sparsely-filled aperture imaging device.
Many people utilize portable, handheld information handling devices (e.g., smart phones, tablets, smart watches, etc.) to capture images. For many people it is much easier to capture an image with a device that serves many purposes, instead of utilizing a dedicated imaging device. Additionally, dedicated imaging devices may be large and heavy and a person may not want to carry it everywhere in the event that the perfect photo opportunity arises. Thus, the portable, handheld information handling device solves some of these problems. Since these devices are utilized so frequently for image capturing, the imaging mechanisms, imaging optics, and on-board image processing have become more advanced to provide for better quality images as compared to older portable, handheld information handling devices. However, due to the form factor of the information handling device, these devices and imaging mechanisms suffer from some deficiencies as compared to larger, dedicated imaging devices. For example, some features that are found on dedicated imaging devices are not available on the described information handling devices due to the size of the information handling device.
For example, information handling devices do not have a true telephoto lens. The challenge is the diffraction limit. The diffraction limit of the human eye is set by the pupil diameter, which is typically 5 mm in daylight. For visible light, with a wavelength of 0.55 micrometers, that sets the Rayleigh limit at about 30 seconds of arc (0.5 minute of arc). A 7× set of binoculars can give no more detail unless it delivers a resolution of 30 sec/7 ≈ 4 sec of arc. To do that its diffraction limit, typically set by the front lens, must be at least 7× the diameter of the human pupil, that is, about 35 mm. When binoculars are designated 7×35, that means they magnify 7× compared to normal eyesight, and have a 35 mm aperture, thus allowing them to deliver adequate optical resolution at that magnification.
A telephoto lens is characterized by its long focal length. For standard 35 mm cameras, a 50 mm focal length gives the standard photographic image. A 100 mm focal length gives 2× magnification and a 350 mm lens delivers 7× magnification, the same as 7×35 binoculars. The necessary focal length for a telephoto lens causes a challenge in putting the telephoto lens on an information handling device, particularly one having a thin form factor. One technique for increasing the focal length within a thin form factor is by folding the optics, an example of which is shown in
In order to create a telephoto lens that will fit in a thin information handling device form factor, the described system provides an imaging device including a sparsely-filled optical aperture and imaging optics. The sparsely-filled optical aperture is in a shape that forms an outer portion of the optical aperture. In other words, and as an example, the optical aperture may be a ring shape, where the inner portion of the ring is not part of the optical aperture. This is in contrast to traditional telephoto lenses in which the entire area of the aperture is filled. For example,
Due to the thin form factor of the information handling device, the imaging optics may be in the folded optics design, for example, as found in
Thus, the system, device, and method described herein provide a novel technique for providing a telephoto lens within a thin form factor information handling device. Specifically, the described system and method utilizes a sparsely-filled aperture that provides a long focal length and a large-diameter aperture that can be included within a thin design, even if the sparsely-filled aperture is included in an information handling device that can support a thicker imaging device. Additionally, the described system and method provides a technique that allows for a zoom feature with the described telephoto lens utilizing one or more movable lenses.
In summary, one aspect provides an imaging device, including: a sparsely-filled optical aperture having a shape forming an outer portion of the optical aperture, wherein at least a portion of an inner portion formed by the outer portion of the optical aperture is not a part of the optical aperture; and imaging optics, wherein the imaging optics include at least one reflection device optically located after the optical aperture and at least one imaging sensor optically located after the at least one reflection device, wherein light entering the optical aperture reflects from the at least one reflection device onto the at least one imaging sensor.
Another aspect provides information handling device, including: an imaging device, including: an sparsely-filled optical aperture having a shape forming an outer portion of the optical aperture, wherein at least a portion of an inner portion formed by the outer portion of the optical aperture is not a part of the optical aperture; and imaging optics, wherein the imaging optics include at least one reflection device optically located after the optical aperture and at least one imaging sensor optically located after the at least one reflection device, wherein light entering the optical aperture reflects from the at least one reflection device onto the at least one imaging sensor; at least one memory device; and at least one processor operatively coupled to the imaging device and the at least one memory device.
Another aspect provides a method, including: receiving light through an sparsely-filled optical aperture, wherein the optical aperture is formed in a shape forming an outer portion of the optical aperture, wherein at least a portion of an inner portion formed by the outer portion of the optical aperture is not a part of the optical aperture; and reflecting the light using at least one reflection device optically located after the optical aperture onto at least one imaging sensor optically located after the at least one reflection device.
In accordance with the present application, the described system and method provide a technique for addressing the challenges of a long focal length and large-diameter aperture within a thin form factor or a thin imaging device. Specifically, the described system and method utilize an aperture that is not-completely-filled, also referred to as a sparsely-filled aperture. Such a sparsely-filled aperture allows for an imaging device that can be thin, for example, less than 10 millimeters in thickness.
Referring to
CPU 1002 and memory 1004 are connected to one another through a conventional interconnect 1006, which is a bus in this illustrative embodiment and which connects CPU 1002 and memory 1004 to one or more input devices 1008 and/or output devices 1010, network access circuitry 1012, and orientation sensors 1014. Input devices 1008 can include, for example, a keyboard, a keypad, a touch-sensitive screen, a mouse, and a microphone. Output devices 1010 can include one or more displays - such as an OLED (organic light-emitting diode), a microLED, or liquid crystal display (LCD), or a printed image of sufficiently high resolution - and one or more loudspeakers for associated audio. Network access circuitry 1012 sends and receives data through computer networks. Orientation sensors 1014 measure orientation of the device 1000 in three dimensions and report measured orientation through interconnect 1006 to CPU 1002. These orientation sensors may include, for example, an accelerometer, gyroscope, and the like, and may be used in identifying the position of the user.
One type of sparsely-filled aperture is referred to as a “ring aperture.” The ring aperture is an optical aperture having a circular shape that forms an outer portion of the optical aperture. At least a part of the area enclosed by the outer portion of the optical aperture is not a part of the optical aperture. In other words, the optical aperture forms a circular shape that has an inner portion that is not a part of the optical aperture. An example of a ring aperture is shown in
In
A cross-section of the
The diffraction pattern of the 7× lens (
Images in digital cameras can be “sharpened” by applying image processing. One of the best kinds of such processing is the application of a Wiener filter to the image. In many cases, a Wiener filter is the optimum method for improving the quality of an arbitrary image. Applying such filters typically consists of doing a fast-Fourier transform (FFT) to the image, dividing the result by the Wiener filter function, which is typically a function based on the Fourier transform of the aperture combined with an estimate of the image signal-to-noise ratio. Such filtering is well-known to those practiced in the art of image manipulation, and it typically improves the resolution of the image by a factor of 2 to 3.
This same type of sharpening can be accomplished with the ring aperture optics without applying an image processing or applying a Wiener filter to the image. It is expected the ring aperture will give a factor of 2-3 improved resolution. Note that we do not include this factor of 2-3 in our statement that the ring optics can improve over a filled circular aperture by a factor of 7× or more. If we included it, we would say that the ring aperture could improve over an unfiltered filled circular aperture by a factor of 14× to 21×. However, since such filtering is available to a filled circular aperture camera, to make a comparison to the filled aperture we do not include it.
The ring aperture has a series of secondary peaks, seen in
The properties of non-filled apertures are not widely known to optical designers, since in most camera and telescope designs, it is considered important to bring as much light as possible from the region of the aperture to the focus. The described system and method demonstrate that if the goal is not maximum light, but high resolution in an extremely compact space, then a sparsely-filled aperture can provide that. The value of a non-filled aperture is further enhanced when strong computing power is available, as is true when the camera is implemented in a modern mobile phone.
In the example of
The discussed example was chosen to match the dimensions of common mobile phones. However, the method described here (non-filled aperture, digital filters applied in image processing) has application in situations in which a thin imaging device is desired.
Since most of the space within the ring is empty (referred to as the inner portion formed by the outer portion of the optical aperture), additional cameras could be combined with the sparsely-filled optical aperture imaging device.
Thus, as shown in
The large but non-filled aperture can provide the angular resolution needed for a compact telephoto camera that can fit in a thin object such as a mobile phone. Additionally, image compensation can eliminate the image artifacts that otherwise could make the image less satisfactory. While the previously described example provides a particular geometry that achieves these objectives, other geometric layouts can achieve a similar high angular resolution. Two of these are shown in
In
Once the value of a ring geometry is recognized, with additional value obtainable by image processing, then other layouts can be used that would be evident to a person practiced in the field of camera optics.
Note also that, in the designs depicted in this document, many of the surfaces do not participate in required reflections. These surfaces can be blackened, that is, made to absorb stray light, by using methods well-known to those practiced in the art of camera design.
While the description has described an optical aperture having a ring shape, other shapes can be used. To achieve high (e.g. about 7×) resolution in all directions, the aperture needs to contain regions that are substantially separated in all directions (all azimuths). This can be done with rings, but it can be done in other ways. Example embodiments illustrating the use of different partially-filled apertures are shown in
In addition to the telephoto function of the previously described optical aperture and imaging device, a zoom capability can be included with the described optical aperture. To include a zoom capability, additional components are added to the imaging optics of the previously described imaging optics. Specifically, instead of the light or image that is captured hitting the imaging sensor from the central reflection device, it is reflected by a mirror to make it have a vertical orientation. This mirror may be a 45° mirror. The image location could also contain an optional field lens, which is common in optics design.
The optional field lens is normally placed at or near the location of an image. It is designed to focus the objective lens (in this diagram, that is the ring paraboloid) onto or near the objective lens of the microscope. Since in the described system and method the imaging array is moving, the fixed focus of the field lens would be somewhere along the path of motion of that lens. That microscope has an objective lens that reimages the initial image onto a sensor array.
The first image, that of the parabola-hyperbola combination, is called the primary image. The image of the field lens and objective lens of the microscope is called the secondary image. By motion of the objective lens and the imaging array, also referred to as an imaging sensor, the desired zoom effect can be achieved. This is most readily seen by making the assumption that the objective lens is a thin lens, and then using the thin lens approximation. If the objective lens has a focal length of f, and it is placed a distance d1 from the primary image, then the secondary image will appear a distance d2 from the objective lens, where, according to the thin lens formula:
To get an image that is in-focus, once d1 is chosen, then d2 must be chosen to match this formula. This can be done by mechanical linkages, or by separate control of the positions of the objective lens and the positioning array.
In this equation, f is fixed, but d1 and d2 are adjustable. The magnification M is given by:
Using Eq 2 to eliminate d2 from Eq 1, and solving for M, we get
Thus, by changing d1 and d2 according to Eq 1, we keep the image in focus, but achieve a variable magnification according to Eq 3.
In some designs, it might be desirable to have the sensor at a fixed position. For this case, a zoom telescope can be achieved by having two moving lenses. However, the positioning of the two lenses involves a complicated formula that is not easily achieved by mechanical means alone. However, it is easily achieved if a simple microprocessor is used to position the two lenses. A design for the zoom microscope that has a fixed position detector in shown in
In this Figure, the distance between the primary image (from the parabaloid-hyperbolide-45° mirror combination) is labeled “image 1”. (This is the same as “1st image plane” on
Similarly for the second lens, with focal length f2:
We have the length constraint equation:
The magnification of the microscope is the ratio of the sizes of image 3 to that of image 1. The magnification of lens 1 is I1/O1; the magnification of lens 2 is I2/O2; the magnification of the combination is the product of these:
The diagram also shows a field lens. In the optimum configuration, this lens would be positioned at image 2 and have a focal length that images lens 1 onto lens 2. However, a field lens need not be precisely focused and in many aspects can be fixed in a region in the center of the range of motion of image 2. In
For a given value of O1, we can consider equations 4, 5, 6, and 7 to be four equations with four unknowns: I1, 02, I2, and M. Thus, we can solve for all of these using algebra. The magnification M that results from these equations is a function of O1 (the placement of the first lens), assuming that the second lens is correctly placed at the location O1 + I1 + O2 from image 1. For the chart illustrated in
The chart of
Image stabilization can be achieved by lateral motion of the sensor array, using a separate tilt sensor to compute the required motion.
The above description is illustrative only and is not limiting. The present invention is defined solely by the claims which follow and their full range of equivalents. It is intended that the following appended claims be interpreted as including all such alterations, modifications, permutations, and substitute equivalents as fall within the true spirit and scope of the present invention.
This application claims priority to U.S. Provisional Pat. Application Serial No. 63/275,051, filed on Nov. 3, 2021, the content of which are incorporated by reference herein.
Number | Date | Country | |
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63275051 | Nov 2021 | US |