The present invention relates generally to projection lens systems for video display. More specifically, the present invention relates to a system and method for optimally coupling a projection system to a wave-guide structure.
This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Projection systems employed in video display units typically utilize lenses adapted to disperse light in a wide cone. The wide cone of light is usually projected on a screen disposed relatively far away form the projection system. As one of ordinary skill in the art would appreciate, such lenses typically have a structure by which chief light rays are made roughly parallel towards the front of the lens of the projection system. This is usually achieved by embedding an exit pupil deep within the lens, adapting the light rays to be parallel and attain a “wide waist.” In order to further widen the light beam, strong negative lens elements are disposed subsequent to the parallel rays, thus increasing their divergence. Further, wide angle projection systems are typically adapted to be disposed somewhat at a distance away from a display device rather than directly adjacent to it. In this manner, it may be possible to achieve a greater wide angle projection.
Although wide-angle projection is common, there are video systems for which the use of a wide-angle projection system may not be an optimal choice. In systems such as wedge displays comprising a screen in the form of a wedge, light exiting the projection lens system may be inserted into a small entrance aperture of the wedge display. The light entering the wedge display may be projected at an angle relative to the wedge display, such that the light undergoes multiple total internal reflections as it propagates through the wedge to form an image. In this manner, an image can be formed on a screen having a relatively small width. Consequently, due to the small entrance pupil and the manner in which the image is projected thereon, the use of a wide-angle projection system may be incompatible with a use of wedge display devices.
Such incompatibility stems from the mismatch between the large beam size produced by a wide-angle projection system and the small entrance pupil of the display device. Further, images projected onto wedge display systems are typically done so at some angle. Utilizing a wide-angle projection system for such a purpose may not be suitable. Such incompatibilities, as those mentioned herein, may cause a general loss of light-coupling efficiency between the display device and the projection system. Ultimately this may degrade the quality of the image displayed on a display device. A system and method that allows the use of medium wide-angle projection in such circumstances is desirable.
Certain aspects commensurate in scope with the disclosed embodiments are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.
The disclosed embodiments relate to a video unit, comprising an imaging system configured to create an image, a lens having a front surface and a back surface, the lens configured to receive an image on the back surface and produce a medium wide-angle representation of the image on the front surface, and an aperture stop positioned adjacent to the front surface of the lens to capture the medium wide-angle representation of the image from the lens.
Advantages of the invention may become apparent upon reading the following detailed description and upon reference to the drawings in which:
One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
Turning initially to
The video unit 10 may include a light engine 12. The light engine 12 is configured to generate white or colored light that can be employed by an imaging system 14 to create a video image. The light engine 12 may include any suitable form of lamp or bulb capable of projecting white or generally white light. In one embodiment, the light engine 12 may be a high intensity light source, such as a metal halide lamp or a mercury vapor lamp. For example, the light engine 12 may include an ultra high performance (“UHP”) lamp produced by Philips Electronics. The light engine 12 may also include a component configured to convert the projected white light into colored light, such as color wheels, dichroic mirrors, polarizers, and filters. Moreover, in alternate embodiments, the light engine 12 may include components capable of generating color light, such as light emitting diodes.
As described above, the light engine 12 may be configured to project, shine, or focus colored light at the imaging system 14. The imaging system 14 may be configured to employ the colored light to create images suitable for display on a screen 24. The imaging system 14 may be configured to generate one or more pixel patterns that can be used to calibrate pixel shifting in the video unit 10. In one embodiment, the imaging system 14 comprises a DLP imaging system that employs one or more DMDs to generate a video image using the colored light. In another embodiment, the imaging system may employ an LCD projection system. It will be appreciated, however, that the above-described exemplary embodiments are not intended to be exclusive, and that in alternate embodiments, any suitable form of imaging system 14 may be employed in the video unit 10.
As illustrated in
Accordingly,
The system 40 further includes a total internal reflection (TIR) prism 45, disposed adjacent to the cover glass 44. Colored light components comprising red, green, and blue (RGB) are emitted by the DMD 42 and projected through the TIR prism 45. In addition to the colored light components, image illumination light components (not shown) are also entering the TIR prism 45 enroute to the DMD 42 as well. The purpose of the TIR prism 45 is to direct these two different light bundles to their respective destinations. That is, the illumination light is directed to the DMD 42 and the colored light components are directed into first lens element 46. Accordingly, the TIR prism 45 is adapted to separate the image into RGB and illumination components.
The light rays exiting the TIR prism 45 are next projected onto a double negative lens 46. The lens 46 is adapted to increase the rate of spread and, thus, diverge chief light rays 41, 43, 47 and 49, as those emerge from the TIR prism 45. In this manner, the lens 46 initially formats light rays projected thereon before those are subsequently processed by additional lens elements of the system 40. Accordingly, the light rays 41, 43, 47 and 49, maximally divergent at this point, are next projected onto a large positive lens 48. The lens 48 comprises a large diameter and is adjacent to the lens 46, such that the two may be in physical contact. The lens 48 is further configured to initially converge the chief light rays 41, 43, 47 and 49, as these rays exit the double negative lens 46. Disposing the double negative lens 46 next to the large positive lens 48 allows spreading and, thereafter, converging the light relatively far forward in the lens system 40. This enables the light rays emerging from the lens assembly 40 to be parallel as they enter the display system 24 and, consequently, couple more efficiently therewith.
After emerging from the large positive lens 48, chief light rays 41, 43, 47 and 49 are next projected onto a positive doublet lens 50. The doublet lens 50 is disposed adjacent to the lens 48 and may be in physical contact thereto. The positive doublet lens 50 is utilized for color correcting the light exiting the large positive lens 48. Color correction is needed, as the RGB light components exiting the DMD 42 comprise various electromagnetic wavelengths. Accordingly, each wavelength of the light refracts at a different angle, as the light propagates through the lenses 46 and 48. Hence, the doublet lens 48 helps to ensure that images formed by the different colored-light components are focused appropriately. In focusing the light, the doublet lens 50 further converges the light as it reaches closer to the front of the lens.
Thereafter, the chief light rays 41, 43, 47 and 49 are projected onto an aspherical lens 52 disposed adjacent to the doublet lens 50, such that the two may be in physical contact with one another. The lens 52 is adapted to further converge the light rays emerging from the doublet 50 and, thus, “squeeze” the bundle of rays comprising the projected image. Once emerging from the aspherical lens 52, the chief light rays 41, 43, 47, and 49 are further made parallel to one another as they impinge on a plane mirror 54.
The plane mirror 54 is disposed adjacent to the lens 52. The mirror 54 is used to fold the light, so as to make the lens assembly 40 more compact. Accordingly, the mirror 54 is disposed at a forty five-degree angle relative to the horizontal and vertical components of the lens assembly 40. In this configuration, the mirror 54 reflects the image, causing it to propagate in a vertical direction. Absent the mirror 54, light rays emerging from the lens 52 would continue to propagate along a horizontal path, extending the length of the projection lens system 40. As further depicted in
Light reflected from mirror 54 is projected onto a focusing lens 55 disposed between the mirror 54 and the aperture stop 56. The light projected onto lens 55 is focused to from an image, which is in turn projected onto the aperture stop 56. As appreciated by those skilled in the art, an aperture stop determines an exit pupil of a lens. As illustrated by
Lens elements subsequent to the field lens 72 shown in
Spot diagrams of a projection system may be utilized to analyze performance of a projection system. Accordingly, data collected from such diagrams comprises pixel fields, whereby each field represents an image of a pixel on a display device. Further, each field represents a pixel having a unique root mean square (RMS) and geometrical (GEO) radius spot size for a certain box width, as may be appreciated by those of ordinary skill in the art. Accordingly, the performance of lens system 40 is analyzed via seven fields, each having a unique RMS and GEO radius for a box width of 12 micrometers. The fields represent an image of a pixel disposed on the DMD 42. The data of exemplary spot diagrams of system 40 is summarized in Table 1 below, where all units are in micrometers:
Similarly, the performance of lens system 70 is analyzed via seven fields, each having a unique RMS and geometrical (GEO) radius for a box width of 12 micrometers. The fields represent an image of a pixel disposed on the DMD 42. The data of the spot diagrams of system 70 is summarized in Table 2 below, where all units are in micrometers:
Further, the systems 40 and 70 have a modulation transfer function (MTF), which yields a value of 50%, considered as a worst case when evaluated at a spatial frequency of 45 lines per millimeter.
Furthermore, an exemplary embodiment of the system 40 produces a grid distortion of 0.3415%, while an exemplary embodiment of the system 70 produces a grid distortion of 0.2306%. In addition, the system 40 produces a 19% center to corner light fall-off across a screen. Similarly, the system 70 produces a 20% center to corner light fall-off across a screen. Accordingly, display units employing projection lens system, such as exemplary embodiments of the systems 40 and 70, may considerably out-perform display units employing cathode ray tubes (CRTs). CRT systems typically possess a 70% center to corner light fall-off across a screen, as may be appreciated to those of ordinary skill in the art.
Turning now to
An example of computer code useful for designing an exemplary embodiment of the present invention is given below:
A further example of computer code useful for designing an exemplary embodiment of the present invention is given below:
While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.
This application is a National Phase 371 Application of PCT Application No. PCT/US06/20852, filed May 26, 2006, entitled “Projection Lens with Exterior Stop”.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US06/20852 | 5/26/2006 | WO | 00 | 11/11/2008 |