Optical system and projection type image display apparatus equipped with optical system

A light guiding member (40) for reflecting therein light entering through a light entering surface (40a) several times to cause light having a uniform illumination distribution to outgo from a light outgoing surface (40b) is inserted into an optical path between a lamp source (10) and a reflection type display device (80). The light outgoing surface (40b) of the light guiding member (40) is formed in a dissimilar shape with an image display region of the reflection type display device (80), and a region irradiated with light in the image display region of the reflection type display device (80) is formed smaller than the image display region. This prevents a whitening phenomenon in a projected image undisplay region and improves video effects given to viewers as well as effectively utilizing light emitted from a light source for images to be projected to display projected images brightly.

This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2003-075394 filed in JAPAN on Mar. 19, 2003, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical system and a projection type image display apparatus configured to guide light emitted from a lamp source to an image display region of a reflection type display device along a predetermined optical path, to reflect a light component which forms an image to be projected by the image display region, and to project the reflected light component onto a predetermined screen.

2. Description of the Background Art

A conventional reflection type image display apparatus is known in which light emitted from a lamp source is guided to an image display region of a reflection type display device along a predetermined optical path, and a light component which forms an image to be projected is reflected by the image display region, and the reflected light component is projected onto a predetermined screen (e.g., Japanese Patent Application Laid-Open No. 2000-98272 and 2001-183603).

In this type of apparatus, light emitted from a light source is converted into light having a substantially uniform illumination distribution by a rod lens or the like, and the converted light is guided to the reflection type display device, and light which forms an image reflected by the image display region of the reflection type display device is projected onto the screen.

In such projection type image display apparatus, a light outgoing surface of an optical member such as a rod lens for converting light into the state that illumination distribution is substantially uniform generally has a conjugate relationship with an image display region of a reflection type display device. Thus, the light outgoing surface of the optical member and the image display region of the reflection type display device are formed in a substantially similar shape.

Further, since an image reflected by the reflection type display device is scaled up or down to be projected onto the screen, the image display region of the reflection type display device and the projected image on the screen are in a similar shape.

Therefore, when an image having an aspect ratio (the ratio between the width and height of an image) of 4:3 is to be projected, the light outgoing surface of the optical member, the image display region of the reflection type display device and the screen size are all configured to have an aspect ratio of 4:3.

In the case that an image having an aspect ratio of 16:9 is projected with such apparatus, the optical member transmits light for irradiating the whole area of the image display region of the reflection type display device while the reflection type display device is controlled so as to perform image formation only in the central portion of the image display region and to prevent light entering the other portion from being reflected toward the screen.

In this case, however, part of light is also reflected by a portion other than the central portion of the image display region, and the reflected light is projected onto the screen. This causes a problem in that, although top and bottom regions of a image projection region on the screen where images are inherently unnecessary to be displayed need to be displayed in black, a part or the whole of the top and bottom regions is displayed brightly, that is, displayed in white (hereinafter referred to as a “whitening phenomenon”). Such whitened region appears in the vicinity of a projected image, causing another problem in that, particularly in the application to a video projector and in viewing video in a dimly lit room in order to enhance a realistic sensation of video, such region interferes with viewing and reduces the realistic sensation. Also, in the application to a data projector used for presentation or the like, viewers cannot concentrate on a projected image, causing the effect of presentation to be degraded.

Further, light outgoing from the light outgoing surface of the optical member is irradiated onto the whole area of the image display region of the reflection type display device, which means light incident upon a portion other than the central portion of the image display region is not utilized effectively. This disadvantageously causes images projected onto the screen to be darkened.

Due to these factors, a conventional projection type image display apparatus cannot display images having an aspect ratio of 16:9 in good condition.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an optical system and a projection type image display apparatus capable of preventing the whitening phenomenon and improving video effects given to viewers as well as effectively utilizing light emitted from a light source for an image to be projected to display a projected image brightly.

According to a first aspect of the present invention, the optical system is configured to guide light emitted from a lamp source to an image display region of a reflection type display device along a predetermined optical path, to reflect a light component for forming an image to be projected by the image display region of the reflection type display device, and to project a reflected light component onto a predetermined screen. In the optical system, a light guiding member for reflecting therein light entering through a light entering surface several times to cause light having a uniform illumination distribution to outgo from a light outgoing surface is inserted into an optical path between the lamp source and the reflection type display device, and the light outgoing surface of the light guiding member is formed in a dissimilar shape with the image display region of the reflection type display device, and a region irradiated with light in the image display region is smaller than the image display region.

The optical system is configured such that the light outgoing surface of the light guiding member is in a dissimilar shape with the image display region of the reflection type display device and a region irradiated with light in the image display region is smaller than the image display region, which prevents the whitening phenomenon and improves video effects given to viewers as well as effectively utilizing light emitted from a light source for images to be projected to display projected images brightly.

According to a second aspect of the invention, the projection type image display apparatus is configured to guide light emitted from a lamp source to an image display region of a reflection type display device along a predetermined optical path, to reflect a light component for forming an image to be projected by the image display region of the reflection type display device, and to project a reflected light component onto a predetermined screen. In the projection type image display apparatus, a light guiding member for reflecting therein light entering through a light entering surface several times to cause light having a uniform illumination distribution to outgo from a light outgoing surface is inserted into an optical path between the lamp source and the reflection type display device, and the light outgoing surface of the light guiding member is formed in a dissimilar shape with the image display region of the reflection type display device, and a region irradiated with light in the image display region is smaller than the image display region.

The projection type image display apparatus is configured such that the light outgoing surface of the light guiding member is in a dissimilar shape with the image display region of the reflection type display device and a region irradiated with light in the image display region is smaller than the image display region, which prevents the whitening phenomenon and improves video effects given to viewers as well as effectively utilizing light emitted from a light source for images to be projected to display projected images brightly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Preferred Embodiment

FIG. 1illustrates the configuration of a projection type image display apparatus100, and more particularly, an optical system1which is an essential part thereof. This optical system1is configured such that light emitted from a lamp source10follows an optical path passing through a lamp reflector20, a color wheel30, a light guiding member40, a relay lens50, a plane reflection mirror60, a concave mirror70, a reflection type display device80and a projection lens90to be projected onto a screen91.

The lamp source10is a light source formed by a high pressure mercury lamp utilizing discharge or a halogen lamp, and light emitted from the lamp source10is reflected by the lamp reflector20provided to surround the lamp source10. The lamp reflector20has a spheroidal surface that faces the lamp source10and is mirror-finished. The lamp source10is provided at one of the focal points of the spheroidal surface, and light emitted from the lamp source10is reflected by the inner surface of the lamp reflector20to be condensed toward the other focal point.

At the other focal point, a light entering surface40aof the light guiding member40is placed. The light guiding member40is configured to reflect therein light entering through the light entering surface40aseveral times so that light having a uniform illumination distribution outgoes from a light outgoing surface40b.

FIG. 2illustrates an example of the light guiding member40. In the present embodiment, the light guiding member40is formed by a plurality of plate-like glass members41each having one side surface being mirror-finished. The glass members41are assembled such that the respective mirror surfaces face a hollow space to form a rectangular tube as a whole. Such light guiding member is generally called a light pipe.

FIG. 3conceptually illustrates light rays in the light guiding member40. The light guiding member40configured as described above is capable of reflecting light entering the inner hollow space through the light entering surface40aseveral times by the inner surfaces, thereby converting light outgoing from the light outgoing surface40bto have a uniform illumination distribution in section of luminous flux. The light guiding member40is arranged such that the light entering surface40ais provided at the focal point of the lamp reflector20with the center of opening on the light entering surface40asubstantially matching the optical axis of condensed light so that light emitted from the lamp source10is effectively taken in and is transmitted to the post-stage optical system.

Provided between the lamp reflector20and light guiding member40is the color wheel30having the function of time-dividedly changing the color of passing light.FIG. 4illustrates the color wheel30viewed from the lamp source10. As shown inFIG. 4, the color wheel30has a disk-shaped rotating part divided into, for example, three parts, on which color filters31,32and33for red (R), green (G) and blue (B), respectively, are provided and a motor34located at the center of each of the color filters31to33rotating in a single direction with a uniform speed, following which the color filters31to33also rotate.

Such color wheel30is inserted into an optical path between the lamp reflector20and light guiding member40and is arranged such that light condensed by the lamp reflector20always passes through a predetermined position35. Accordingly, as the motor34rotates, the respective color filters31to33sequentially pass through the position35, whereby a trajectory36is drawn on the color wheel30. With such operation, RGB lights are transmitted from the color wheel30to the post-stage optical system while being changed in sequence at regular time intervals.

On the other hand, light of a uniform illumination distribution outgoing from the light guiding member40passes through the relay lens50and is thereafter reflected by the reflection mirror60to enter the concave mirror70. The concave mirror70has both the reflecting function and condensing function and is configured to reflect all incident beams reflected by the reflection mirror60so as to condense the beams and to guide reflected light to the reflection type display device80.

The reflection type display device80modulates light entering from the concave mirror70on the basis of an image signal input to the projection type image display apparatus100, thereby forming a light figure constituting an image component to be projected. Examples of such reflection type display device80are a reflection type liquid crystal panel, a device having micromirrors arrayed two-dimensionally, each being capable of selectively switching the direction in which light is reflected, and a device having a great number of reflection mirrors which differ in height to cause interference with one another, thereby controlling the direction in which light is reflected.

FIG. 5illustrates the reflection type display device80viewed from the front (i.e., from an image display surface). As shown inFIG. 5, an image display region81for reflecting light from the concave mirror70to reflect a light figure constituting an image component to be projected is provided on the image display surface of the reflection type display device80. On the image display region81, the above-mentioned liquid crystal panel or micromirrors are provided and configured such that image formation is carried out on the basis of an input image signal.

A conventional well-known device may be used as the reflection type display device80, and the image display region81is formed to have an aspect ratio of 4:3, for example.

Light reflected by the image display region81is projected onto the screen91through the projection lens90.

By the action of the color wheel30, RGB lights are time-divided and sequentially enter the image display region81of the reflection type display device80, while, in synchronization with the color components passing through the color wheel30, image signals corresponding to the respective color components are input to the reflection type display device80. With such operation, images of the respective RGB colors are sequentially projected onto the screen91. By sufficiently shortening the color changing period, images of the respective colors are seen in combination, which allows full-color video to be perceived as a whole.

Then, in the present embodiment, the light outgoing surface40bof the light guiding member40(more strictly, an opening on the light outgoing surface40b) in the optical system1of the above configuration is formed to be in conformity with an aspect ratio of an image to be projected. For instance, in the case where an image having an aspect ratio of 16:9 is to be projected, the light outgoing surface40bof the light guiding member40is also formed to have an aspect ratio of 16:9. Therefore, the light outgoing surface40bis formed in a dissimilar shape with the image display region81of the reflection type display device80.

Then, optical devices (relay lens50, reflection mirror60and concave mirror70) between the light guiding member40and reflection type display device80causes light outgoing from the light guiding member40to be irradiated onto a part of the image display region81in the reflection type display device80which is smaller than the image display region81.

FIG. 6illustrates where light is irradiated onto the image display region81in the reflection type display device80. A broken line region40cinFIG. 6indicates a range in which the light outgoing surface40bof the light guiding member40is projected onto the image display region81by the optical devices provided between the light guiding member40and reflection type display device80. Thus, as shown inFIG. 6, light outgoing from the light outgoing surface40bof the light guiding member40is condensed and irradiated by the optical devices only onto a region82at substantially the center of the image display region81. This region82has a substantially similar shape with the light outgoing surface40bof the light guiding member40. Thus, other regions83(hatched regions inFIG. 6) in the image display region81are not irradiated with light.

The reflection type display device80then performs image formation on the basis of an image signal only in the central region82which is a light irradiated region, while image formation is not performed in the other regions83which are not irradiated with light. For instance, though the image display region81is formed to have an aspect ratio of 4:3, an image having an aspect ratio of 16:9 is formed only using the central region82. Then, all light components passing through the light guiding member40are effectively utilized as light for forming an image to be projected. An image brighter than in a conventional apparatus is then projected onto the screen91.

FIG. 7is a schematic view simply illustrating how light is transmitted through the light guiding member40and reflection type display device80to the screen91. As shown inFIG. 7, according to the above-described optical system1, light outgoing from the light outgoing surface40bof the light guiding member40formed in conformity with the shape of an image to be projected is irradiated only onto a partial region (the central region) of the image display region81of the reflection type display device80. Then, light for forming an image to be projected is generated in the light irradiated region and is projected onto the screen91.

Therefore, light is irradiated only onto an image forming region in the reflection type display device80, not onto the other regions (regions83inFIG. 6). This prevents unnecessary reflection in the region not irradiated with light and avoids the possibility that unnecessarily reflected light is projected onto regions adjacent to the image projection region on the screen91. As a result, the whitening phenomenon does not occur in the projected image undisplay region on the screen91, which allows video effects given to viewers to be improved.

As described, the optical system1according to the present embodiment is configured such that the light outgoing surface40bof the light guiding member40is formed in conformity with a projected image on the screen91and formed in a dissimilar shape with the image display region81of the reflection type display device80and such that the irradiation range of light irradiated onto the reflection type display device80through the light guiding member40is smaller than the image display region81. This allows all light outgoing from the light guiding member40to contribute to formation of an image to be projected, enabling projection of an image brighter than in a conventional apparatus. Further, the whitening phenomenon dose not occur in the projected image undisplay region on the screen91, which allows video effects given to viewers to be improved. Particularly, in the application to a video projector and in viewing video in a dimly lit room in order to enhance the realistic sensation of video, high-quality image projection can be achieved without loss of realistic sensation. Also, in the application to a data projector, viewers can concentrate on observing projected images, which allows more effective presentation to be achieved.

Therefore, even when a well-known device having an aspect ratio of 4:3 is used as the reflection type display device80, images having an aspect ratio of 16:9 can be projected onto the screen91in good condition.

Further, the use of the above-described optical system1to construct the projection type image display apparatus100allows the projection type image display apparatus100to provide the same effects as described above.

In the present embodiment, the light guiding member40is not limited to the above-described rectangular light pipe, but may be a conventionally used rod lens or the like.

Second Preferred Embodiment

In a second preferred embodiment, description will be directed to an improvement in the case of using the light guiding member40as shown inFIG. 2. More specifically, an example of the light guiding member40configured as the so-called light pipe will be described in which light passing outside the mirror surfaces that face the hollow space for guiding light is interrupted. In the present embodiment, the overall configuration of the projection type image display apparatus100and optical system1is the same as that described above, repeated explanation of which is thus omitted here.

FIG. 8illustrates the light guiding member40and a light shielding member45inserted into the optical path between the lamp source10and reflection type display device80. The light guiding member40shown inFIG. 8is the same as that described in the first preferred embodiment, and functions as a light pipe having a hollow space for guiding light formed by the plurality of glass members41.

By the action of the lamp source10and lamp reflector20, light rays8a, most part of light guided to the light guiding member40is condensed at the focal point of the lamp reflector20and is directed to the inner hollow space through the opening on the light entering surface40a. Being repeatedly reflected in the inner hollow space of the light guiding member40several times, the light rays8aare made uniform in illumination distribution and outgo through the opening on the light outgoing surface40b.

However, the light guided to the light guiding member40from the lamp source10and lamp reflector20contains light rays such as light rays8band8cshown inFIG. 8which do not enter the inner hollow space through the opening on the light entering surface40a. For instance, the light ray8benters the glass members41constituting the light guiding member40through end faces of the glass members41and is repeatedly reflected several times by the inner surfaces of the glass members41, following which outgoes from the end faces on the light outgoing side to be transmitted to the post-stage optical system. The light ray8cdoes not enter the glass members41but is transmitted outside the light guiding member40to enter the post-stage optical system. These light rays8band8care not made uniform in illumination distribution by the light guiding member40but follow an optical path that cannot be expected in optical design, which are thus unnecessary lights for forming an image to be projected.

Therefore, in the present embodiment, the light shielding member45is provided in the path of light outgoing from the light guiding member40as shown inFIG. 8. The light shielding member45is for transmitting the light rays8aoutgoing through the opening on the light outgoing surface40band shielding the unnecessary light rays8band8c. Used as the light shielding member45is, for example, a light shielding plate having at its center an opening of substantially the same shape of that of the light outgoing surface40b. The light shielding plate is formed to have an outside shape greater than a sectional outside shape of the light guiding member40in order to shield the unnecessary light ray8c. The light shielding member45is provided with the center of opening substantially matching the optical axis, so that the unnecessary light rays8band8cpassing outside the reflection surfaces that face the hollow space of the light guiding member40are both well shielded and are prevented from entering the post-stage optical system.

AlthoughFIG. 8illustrates the case in which the light shielding member45is provided on the light outgoing side of the light guiding member40, the light shielding member45may be provided on the light entering side or both on the light entering side and light outgoing side.

As described, in the present embodiment, the light shielding member45can shield the unnecessary light rays8band8cpassing outside the reflection surfaces that face the hollow space of the light guiding member40, which can prevent the unnecessary light rays8band8cfrom reaching the reflection type display device80. This can prevent the unnecessary light rays8band8cfrom being reflected by the reflection type display device80to be projected onto the screen91which causes irregular luminance and whitening phenomenon. That is, the configuration described in the present embodiment can even prevent the whitening phenomenon caused by the unnecessary light rays8band8c, allowing video effects given to viewers to be further improved.

Further, in the present embodiment, the light shielding plate as the light shielding member45is provided independently of the light guiding member40at least on one of the light entering side and light outgoing side of the light guiding member40. Thus, adjusting the light shielding member45alone allows the unnecessary light rays8band8cto be shielded well. That is, the light guiding member40is strictly positioned in connection with the other optical devices, but can be adjusted into such a condition that the unnecessary light rays8band8care shielded well, irrespective of the other optical devices, since the light shielding member45is provided independently of the light guiding member40.

Third Preferred Embodiment

In a third preferred embodiment, description will be directed to an improvement of the above-described light shielding member.FIG. 9illustrates the light guiding member40and a light shielding member46inserted into the optical path between the lamp source10and reflection type display device80. The light guiding member40shown inFIG. 9is the same as that described in the first preferred embodiment, and functions as a light pipe having a hollow space for guiding light formed by the plurality of glass members41.

In the present embodiment, the light shielding member46is provided on the light outgoing side of the light guiding member40and on the end faces of the glass members41. Such light shielding member46is formed by, for example, applying a light shielding coating or applying a light shielding tape on the end faces of the glass members41.

Providing such light shielding member46on the end faces of the glass members41allows the unnecessary light ray8bpassing outside the reflection surfaces that face the hollow space of the light guiding member40and inside the glass members41to be shielded well, which can prevent the unnecessary light ray8bfrom entering the post-stage optical system.

In this case, however, since the unnecessary light ray8cmay enter the post-stage optical system, it is preferable to attach a light shielding member for shielding the unnecessary light ray8con the end faces of the glass members41.

AlthoughFIG. 9illustrates the case in which the light shielding member46is provided on the light outgoing side of the light guiding member40, the light shielding member46may be provided on the light entering side or both on the light entering side and light outgoing side.

As described, in the present embodiment, the light shielding member46provided on the end faces of the members (i.e., glass members41) forming the light guiding member40of rectangular pipe can shield the unnecessary light ray8bpassing outside the reflection surfaces that face the hollow space of the light guiding member40, which can prevent the unnecessary light ray8bfrom reaching the reflection type display device80. This can prevent the whitening phenomenon caused by the unnecessary light ray8b, allowing video effects given to viewers to be further improved.

Further, the whitening phenomenon caused by the unnecessary light ray8bcan be prevented only by placing the light guiding member40having the light shielding member46on the end faces of the glass members41, in the light path. Moreover, the optical system1can be reduced in size and cost reduction can be achieved as compared to the case of providing a light shielding member independently.

Variant

Although some preferred embodiments related to the present invention have been described, the present invention is not limited to the above description.

For instance, the above preferred embodiments have been directed to, by way of example, the case where the image display region81of the reflection type display device80is formed to have an aspect ratio of 4:3 and the light outgoing surface40bof the light guiding member40is formed to have an aspect ratio of 16:9, however, this is only an illustrative example, and the present invention is not limited as such.