Patent Application
20100328471
The embodiments of the present invention disclosed herein relate generally to the fields of digital imaging, multi-lens cameras, and wireless imaging systems, and specifically to devices that feature integrated optics.
The replacement of film cameras with digital electronic cameras has revolutionized photography. The basic difference between a digital camera and a film camera is that a digital camera substitutes an electronic light sensor for the film. Both film and digital cameras employ lenses to focus an image onto an image plane, typically located at the camera “backplane,” at which the film or the electronic sensor records the focused image. Because film is a light-sensitive emulsion meant to be exposed in a controlled environment, use of multiple films within the same camera enclosure is generally impractical. In the past, this restriction limited the designs of traditional film cameras to those having a single optical axis. Restriction to a single optical axis dictates use of a single lens mounted in the optical path at any given time. Thus, photographers either had to swap lenses, or carry multiple camera bodies, each mounted with a different lens, in order to adjust the field of view of the camera.
Zoom lenses were developed to overcome this restriction, by extending a single optical path and thereby providing the flexibility of accessing multiple focal lengths within a single lens. A zoom lens thus enables close-up shots (telephoto) for magnification of far-away objects, or an increased field of view (wide angle) for capturing a panoramic scene, without the inconvenience of changing lenses. A zoom lens offers flexibility and convenience by including a greater number of optical elements than a fixed focal length compound lens, and by expanding and contracting to change relative distances between the optical elements. However, each zoom lens has a limited range, and the disadvantages compared to a fixed focal length lens become more severe as the range increases. A major disadvantage is that the additional optical elements in a zoom lens decrease the light intensity that reaches the image plane. Thus, the lens is “darker,” and the aperture must be held open longer at a given shutter speed in order to achieve adequate exposure. This tends to reduce the sharpness of the image, and precludes capturing high quality stop-action images of moving objects. A further disadvantage is that the combination of additional elements and moving parts for expansion and contraction of the optical path in a zoom lens tend to dramatically increase cost, increase weight, and reduce ruggedness and reliability.
With the advent of digital photography, the restriction to a single optical axis was lifted, providing an opportunity for even greater flexibility through the use of multi-lens camera designs. Despite this opportunity, many digital cameras currently in use continue to have only one optical axis, though they need not continue to be so restricted. Digital camera systems allow for multiple sensors and multiple fixed focal length lenses to be installed along multiple parallel paths within a common housing. A photographer using a digital camera may then electronically select a lens sub-assembly that is appropriate to capture a particular scene.
Thus, a multi-lens camera design using fixed focal length lenses allows retaining many of the advantages of a zoom lens without the drawbacks. Alternatively, a combination of fixed focal lengths and zoom lenses may be used in a multi-lens camera design. This concept is disclosed in a family of patents for digital cameras assigned to the Eastman Kodak Company that support multiple optical axes with multiple image sensors to provide an extended zoom range for still (non-video) photography. The Kodak patents include U.S. patent application Ser. No. 11/061,002, filed Feb. 18, 2005; U.S. patent application Ser. No. 11/060,845, filed Feb. 18, 2005; U.S. Pat. No. 7,305,180, filed Aug. 17, 2006; and U.S. Pat. No. 7,206,136, filed Feb. 18, 2005. However, the use of zoom lenses in such multi-channel systems continues to sacrifice image quality. Furthermore, both the lenses and the housings utilized in these systems have standard large-scale form factors i.e, the hand-held housing looks and feels like a traditional camera body, and each of the compound lenses is manufactured separately using discrete optical components. Finally, these and similar systems neglect to provide any capability for wireless communication of image data.
A wireless, remote, multi-channel camera system includes multiple fixed focal length lenses and multiple digital sensors in a compact package. The multi-channel camera system may be configured to support capture of still images or video images. A preferred embodiment of the invention is wearable, and is intended to be head-mounted near a user's eye to capture, in real time, the user's perspective view of a scene. In a preferred embodiment, the camera system is mounted in a standard BlueTooth™ cell phone headset. The multi-channel lens system sub-assembly preferably includes three fixed focal length lenses—a wide angle lens, a standard lens, and a telephoto lens,—each providing a different field of view. Lens elements are formed of transparent materials arranged in a monolithic integrated structure, and optionally separated from each other by light-absorbing baffles to minimize optical cross-talk between the multiple channels. The camera system includes control and processing circuitry to select at least one lens, capture and compress a series of images, and transfer the images for storage on a remote device. If multiple lenses are selected, a composite image may be formed from the multiple fields of view provided. The control and processing circuitry may be located either inside or outside the package enclosing the lens system sub-assembly. Electronic video compression enables wireless video data transfer via BlueTooth™ or other standard short-range communication protocols.
It is to be understood that this summary is provided as a means for generally determining what follows in the drawings and detailed description, and is not intended to limit the scope of the invention. Objects, features and advantages of the invention will be readily understood upon consideration of the following detailed description taken in conjunction with the accompanying drawings.
Embodiments of the present invention will be readily understood from the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements. Embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings.
In
Each channel may be implemented as a compound lens having a unique arrangement of four different optical elements. For example, first channel 402 is implemented as a wide-angle compound lens having f 2.7, comprising a plano-concave lens element 408, followed by a plano-convex lens element 410, a concave-convex lens element 412, and finally a convex-convex lens element 414, each of which is aligned along a first optical axis 416. Light travels through the compound lens from left to right, for perpendicular incidence on a first image plane 418. Second and third channels 404 and 406, respectively, are arranged similarly, centered about respective second and third optical axes 420 and 422, to focus incident light onto respective second and third image planes 424 and 426.
Electronic image sensors 419 located at image planes 418, 424, and 426, and superimposed thereon, are preferably a digital CMOS VGA-compatible Bayer type sensor. Image sensor chips suitable for implementing optical design 400 may be obtained from Omnivision Technologies, Inc. of Santa Clara, Calif. According to a preferred embodiment, a set of three 7670 VGA sensors having 3.6 micron pixels is used to acquire images from each of the three optical channels. The area of each image detector is defined by a circle, about 3 mm in diameter, encompassing a 640×480 pixel array of CMOS sensors, the array having a pixel separation of 3.6 microns. The photo-optic response of the image sensors 419 is preferably about 465 nm-642 nm, thus covering most of the visible spectral range. Image sensors 419 are preferably covered by a Bayer filter, typically provided on consumer digital cameras, which filters colors so as to mimic the human eye, which is more attuned to color resolution properties of the center of the spectrum (yellow-green) than the ends of the spectrum (red or blue), All three sensor chips preferably reside on a common circuit board. Image sensor chips may be flexibly attached to the board using, for example, Flexcircuit™ cabling.
To provide a constant image resolution over the full range of optical and digital zoom, which may be called “continuous zoom,” a technique known as “digital down-sampling ” is used. Digital down-sampling is a new approach for integrating disparate lenses to create a nearly seamless experience for the user. To implement digital down-sampling, a zoom factor is determined by computing the ratio of the larger field of view to the smaller field of view of two disparate optical systems. Then the number of pixels recorded by the optical system having the smaller field of view is reduced to give the appearance of continuity. Some existing digital zoom features zoom in on an image at the expense of cropping the edges of the image. Thus they provide a smaller number of pixels in the final image. In contrast, the present technique uses a lower resolution over the entire range of digital zoom to maintain consistency. A lower limit for the resolution is set at the largest digital zoom factor for which the image is cropped. Then images having larger fields of view are down-sampled to provide the same resolution at a smaller magnification. This concept is desirable for an optical system with more than one optical path in which each optical path has a different field of view, but in which the user desires continuous zoom over the entire range without loss of perceived quality.
Rather than manufacturing lens elements 408-414 as discrete optical elements and mounting them in a traditional compound lens assembly constructed along the optical axis 416, lens elements 408-414 are formed within separate transparent structures that include the corresponding lens elements that are components of the other two channels 404, and 406. Thus, a convex-concave lens element 428 within second channel 404, and a convex-convex lens element 430 within third channel 406 are integrated within a common first transparent lens plate 432 that also contains lens element 408. Lens plate 432 is indicated by dotted lines.
A comprehensive 3×4 lens element matrix is thus formed by integrating corresponding lens elements that are parts of the first, second, and third channels 402-406, respectively, within second, third, and fourth transparent lens plates 436, 438, and 440, similar to first lens plate 432. Lens plates may be formed from optically transparent glass using precision glass molding techniques, or plastic using injection molding. In a preferred embodiment, lens plates 432, 438, and 440 are made of acrylic, and lens plate 436 is made of a polycarbonate material. The use of two different plastic materials enables correction of color aberrations within the optical system. Thus, all optical components may be formed of injection-molded plastic, so that the lens elements may be lightweight and shatter-proof. In an alternative embodiment, a material such as Ultem may be used, if necessary, to maximize thermal stability. To compensate for thickness variations introduced during the molding process, selected distances between plates may be maintained by spacer adjustment plates inserted between the lens plates.
It is important to note that lens elements common to each lens plate are generally not aligned with each other. The lens element positions are located along their respective optical axes 416, 420, and 422, at distances that yield a desired focal length, given the properties of the transparent materials, while maintaining a maximum depth of focus. This ensures that “focus adjustments” are not required for the three compound lenses. Thus, according to the preferred embodiment described herein, moving parts are not needed to focus the three lens systems, provided that the object is located a distance from the camera that is at least 0.5 m for the wide angle lens, and 3 m for the telephoto lens.
Adjacent lens plates 432-440 are substantially stationary, the plates assembled into a fixed, monolithic, interlocking structure. Such a monolithic structure may be assembled from the plates by snapping them together so as to establish a kinematic relationship using mechanical alignment features such as, for example, pins, holes, slots, or other such keys used for reliably and precisely attaching adjacent parts to lock them in place. Such a kinematic mount helps to ensure the relative lateral positions of the optical components are maintained as specified by preventing relative axial motion of the plates without over-constraining them and causing stress to the optics. Likewise, in a preferred embodiment, the positions of image planes 418, 424, and 426 may be staggered but still formed within a common structure. Such an integrated lens approach reduces the part count for building the lens matrix, from 12 individual optical elements to four lens plates, thereby reducing the cost of volume manufacturing by as much as 2-2.5 times compared to a traditional design that calls for building three separate and independent lens channels.
Custom-fabricated integrated lens structures suitable for applications such as those described above may be obtained from Apollo Optical Systems of Rochester, N.Y. A suitable design tool that may be used to define the system geometry and the lens characteristics needed for implementing such a multi-channel optical system is, for example, CODEV®, available from Optical Research Associates.
Referring to
After passing through first transparent lens plate 432, light within channel 402 is contained by a first light absorbing baffle 522, disposed between lens plates 432 and 436. First baffle 522 serves to minimize cross-talk between the three channels by absorbing, and thereby controlling, stray light. A second light-absorbing baffle 524 is similarly disposed in-between lens plates 436 and 438. Use of a third light-absorbing baffle was determined to be unnecessary during testing of the preferred embodiment shown, though one or more additional baffles may be provided without departing from the principles of the invention. Rings 521 extend through circular openings in baffles 522 and 524, the rings also serving to support three different aperture stops 526, one for each of the wide angle, mid-range, and telephoto lens fields of view. Aperture stops 526 function much like apertures in a conventional single lens reflex camera, but instead of being adjustable, their diameters are fixed at a pre-selected value. The f-number for each of the lenses is 2.8.
In addition,
Because image sensors 419 may crop images, there exist extra pixels, or “dark spaces” at the edges of the sensor that are not recorded. These dark spaces may be utilized to capture additional information. A preferred embodiment employs Electronic Image Stabilization (EIS), to sense movement of the camera by tracking differences in the edge pixels between one or more successive frames. Using EIS, the recorded image can dynamically track the field of view of interest by adjusting the cropped region of the sensor accordingly. Furthermore, the three sensors may each have a different resolution, allowing the system to shoot video at a lower resolution while still photographs may be shot at a high resolution. The frequency response of each of the three sensors may also be tuned to a different frequency range allowing, for example, one sensor to be a visible light sensor (e.g., 400 nm-700 nm), while a second sensor is tuned to the infrared (IR) range (e.g., 700 nm-1000 nm) to enable night vision.
Whereas
Second and third optical channels 404 and 406 comprise corresponding lens elements and prisms. Second optical channel 404 employs a prism 602 having one convex surface 603a, and third optical channel 406 employs a prism 602 having one concave surface 603c. Surfaces 603a-603c are designed so as to adjust the path lengths of the optical channels 402-406 to ensure that image planes 606 and 608 coincide with each other and with image plane 604. Thus, referring back to
In the second example, a fold mirror alternative optical design 610, shown in
Although certain embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a wide variety of alternative or equivalent embodiments or implementations calculated to achieve the same purposes may be substituted for the embodiments illustrated and described without departing from the scope of the present invention. Those with skill in the art will readily appreciate that embodiments in accordance with the present invention may be implemented in a very wide variety of ways. This application is intended to cover any adaptations or variations of the embodiments discussed herein.
The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, to exclude equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims that follow.
The present patent application claims benefit of U.S. Provisional Patent Application No. 60/075,317, filed on Jun. 24, 2008.
