Patent Application
20070091452
Digital light processing (DLP) projectors typically include an illumination system, some type of spatial light modulator (SLM), and a projection lens. The illumination system generally includes a light source which generates light and a reflector which directs the light from the light source to the SLM. The SLM forms an image beam by modulating the light, either via reflection (e.g. a digital micro-mirror device (DMD)) or transmission (e.g. a liquid crystal modulator), based on a data signal representative of the desired images to be projected. The projection lens receives and projects the image beam onto a projection surface, such as a projection screen, for viewing.
Projection lenses are typically designed to provide a desired magnification, or range of magnifications (i.e. zoom lens), and to minimize optical aberrations (e.g. chromatic aberrations, coma, diffraction, and geometric distortions) in order to provide a high quality projected image. In efforts to minimize such optical aberrations, projection lenses typically comprise complex systems of multiple lens elements arranged in a specific sequence which is often linear or barrel-like in configuration. Such projection lenses are often costly and may consume a relatively large amount of space within the projector.
One form of the present invention provides a projection system including an illumination source providing an illumination beam, a modulator configured to modulate the illumination beam based on an image signal to form an image beam, and a projection lens having an aberration profile and comprising a catadioptric lens. The image signal is adjusted based on the aberration profile of the projection lens. The catadioptric lens is configured to receive the image beam along a first optical axis and fold and direct the image beam along a second optical axis such that a fold angle between the first and second optical axes is within a desired range.
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.
As described herein, a projection lens is provided for a digital projector that folds a modulated image beam at a fold angle that is within a desired range using a catadioptric lens, wherein the image beam is modulated based on optical distortion characteristics of the projector including distortion characteristics of the projection lens. By folding the image beam in this fashion and modulating the image beam based on optical distortion characteristics of the projector, the projection lens has a folded architecture which is more compact in size relative to conventional projection lenses which, in-turn, enables a more compact digital projector relative to conventional digital projectors.
In one embodiment, illumination source 32 generates and directs an illumination beam along an illumination path 42 to modulation device 34 at a non-zero angle of incidence and in a fashion such that modulation device 34 is uniformly illuminated. Illumination source 32 may include a mercury ultra high pressure, xenon, metal halide, or other suitable projector lamp that provides a monochromatic or polychromatic illumination beam. In one embodiment, illumination source 32 comprises light emitting diodes (LEDs) configured to provide separate light components (e.g. red, green, and blue). Illumination source 32 may comprise any type of architecture generally known to those skilled in the art such as, for example, prism-based architectures and field lens based architectures.
In one embodiment, modulation device 34 modulates the illumination beam based on an image signal 44 to form an image beam which is directed to projection lens 36 along a first projection path having a first optical axis 46. Modulation device 34 comprises at least one SLM such as a transmissive-type modulator (e.g. liquid crystal display (LCD)), a digital light processing (DLP) type modulator (e.g. digital micro-mirror device (DMD)), or other suitable SLM which transmits or reflects selected portions of the illumination beam based on image signal 44. In one embodiment, illumination source 32 provides and separates the illumination beam along illumination path 42 into separate illumination components (e.g. red, green, and blue), with modulation device 34 including separate SLMs 34a, 34b, and 34c positioned to receive and modulate a corresponding illumination component.
In one embodiment, as described in greater detail below, catadioptric lens 38 includes at least a first refractive surface and a reflective last surface. Catadioptric lens 38 receives the image beam along optical axis 46 of the first projection path into the first refractive surface and, through refraction by the first refractive surface and reflection by the reflective last surface, folds and directs the image beam to an exit pupil 48 along a second projection path having a second optical axis 50.
In one embodiment, catadioptric lens 38 folds the image beam such that a fold angle (θ) 52 between first and second optical axes 46, 50 is within a desired range of angles. In one exemplary embodiment, the desired range of angles ranges from approximately 10 degrees to approximately 120 degrees. Although, as illustrated, exit pupil 48 appears to be positioned in a plane defined by modulation device 34 and catadioptric lens 38, exit pupil 48 can be positioned outside such a plane (e.g. into/out of the page on which
In one embodiment, as illustrated by the dashed lines in
In one embodiment, projection lens 36 is configured to magnify and relay an image of modulation device 34 (i.e. the image beam) onto projection surface 56 for viewing. Ideally, projection lens 36 forms an exact image, albeit enlarged (i.e. magnified), of modulation device 34 on projection surface 56. The actual image projected by projection lens 36 onto projection surface 56, however, may deviate from the exact image. The deviations of the projected image from the ideal image are referred to as lens aberrations. As known to those skilled in the art, lens aberrations include, for example, field curvature, chromatic aberration, coma, spherical aberration, distortion (e.g. barrel and pincushion distortion), and lateral color. In one embodiment, the distortion and lateral color aberration characteristics of projection lens 36 are referred to as the aberration profile of projection lens 36.
In one embodiment, projection lens 36 is configured to provide a high quality resolution or modulation transfer function (MTF) with a known aberration profile. In one exemplary embodiment, the aberration profile of projection lens 36 is empirically determined at manufacture. As such, in one embodiment, image signal 44 is algorithmically adjusted or “pre-distorted” based on the aberration profile of projection lens 36 so as to counteract or pre-correct distortions such that distortion and lateral color aberrations that would otherwise be introduced by projection lens 36 are substantially reduced and/or eliminated from the projected image as displayed on projection surface 56.
By pre-processing image signal 44 to pre-correct the image data to compensate for or to counteract known distortion and lateral color aberration characteristics, the required distortion and lateral color tolerances of projection lens 36 can be relaxed. As a result, the complexity of projection lens 36 can be reduced relative to conventional projection lenses, thereby reducing expense and enabling a more compact lens architecture relative to conventional projection lenses. An example of such a compact lens architecture includes the folded architecture employing catadioptric lens 38 as described above with reference to
In one embodiment, catadioptric lens 138 includes a refractive front surface 170 and a rear surface 172 coated with a reflective material 174 such that rear surface 172 is a reflective surface. In one embodiment, catadioptric lens 172 comprises a bi-convex lens with both front surface 170 and rear surface 172 being aspheric in shape. In one embodiment, catadioptric lens 138 is centered on optical axis 146 and receives the image beam into front surface 170 such that front surface 170 refracts the image beam, rear surface 172 reflects the image beam, and front surface 170 again refracts and directs the image beam along a second illumination path having a second optical axis 150 to an exit pupil 148 at a pupil plane 158, such that a fold angle (θ) 152 between first optical axis 146 and second optical axis 150 is within a desired range.
In one embodiment, field lens 140 is positioned proximate to exit pupil 148 and includes a refractive surface 176 and a refractive surface 178. In one embodiment, field lens 140 comprises a negative meniscus type lens with refractive surface 176 being aspheric concave in shape and refractive surface 178 being aspheric convex in shape. In one embodiment, field lens 140 is configured to receive the image beam along optical axis 150 of the second projection path and to project the image beam along a projection path 154 to projection surface 56 for viewing. In one embodiment, field lens 140 is of low power relative to catadioptric lens 138 and is configured primarily to provide aberration correction in projection lens 136.
As illustrated in the embodiment of
Although illustrated in the embodiment of
In one embodiment, catadioptric lens 238 includes a refractive front surface 270 and a rear surface 272 coated with a reflective material 274 so that rear surface 272 is a reflective surface. In one embodiment, both front surface 270 and rear surface 272 are convex in shape. In one embodiment, catadioptric lens 238 is configured to be de-centered or off-axis from first optical axis 246. Catadioptric lens 238 receives the image beam into front surface 270 such that front surface 270 refracts the image beam, rear surface 272 reflects the image beam, and front surface 270 again refracts and directs the image beam along a second illumination path having a second optical axis 250 to an exit pupil 248 at a pupil plane 258, such that a fold angle (θ) 252 between first optical axis 246 and second optical axis 250 is within a desired range.
In one embodiment, field lens 240 is positioned proximate to exit pupil 248 and includes a refractive surface 276 and a refractive surface 278. Field lens 240 is configured to receive the image beam along optical axis 250 and project the image beam to projection surface 56 along a projection path 254. In one embodiment, field lens 240 comprises an asymmetric lens, having been truncated or “cut-off” in an asymmetric fashion opposite an optical axis so as further compact the architecture of projection lens 236.
At 304, an illumination beam is provided, such as by illumination source 32 as described above with reference to
At 308, the illumination beam along the first projection path is catadioptrically folded by the projection lens, such as by catadioptric lenses 38, 138, 238, and 238′ of the embodiments of
Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. Those with skill in the mechanical, electromechanical, electrical, and computer arts will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the preferred embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.
