GB2343966A

GB2343966A - Bent optical projection lens unit for liquid crystal display

Info

Publication number: GB2343966A
Application number: GB9926818A
Authority: GB
Inventors: Jeong-Ho Nho; Chang-Wan Hong
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1998-11-17
Filing date: 1999-11-15
Publication date: 2000-05-24
Anticipated expiration: 2019-11-15
Also published as: KR20000032673A; CN1254101A; JP2000187274A; KR100292356B1; GB2343966B; DE19955332A1; GB9926818D0

Abstract

A rear-type liquid crystal display (LCD) projection apparatus having a light source (210), an image source (220) for generating an image, and a projection lens unit (230) for enlarging/projecting image light generated from the image source onto a screen (250), wherein the projection lens unit (230) includes a first optical lens group in which a plurality of optical lenses are sequentially arranged to focus the image light incident from the image source, means e.g. a prism (P, Fig 6), for shifting an optical path by bending the optical axis of the image light having passed through the first optical lens group at a predetermined angle, and a second optical lens group for focusing the image light whose optical axis is shifted by the optical path shifting means and enlarging/projecting the focused image light onto the screen. The focal distance of the projection lens (230) is reduced.

Description

2343966 REAR-TYPE LIQUID CRYSTAL DISPLAY PROJECTION APPARATUS The present

invention relates to a rear-type liquid crystal display (LCD) projection apparatus for displaying an image generated using a liquid crystal display device as an image source on a screen, and more particularly, to a rear-type LCD projection apparatus whose overall system is lighter and smaller by improving the optical lens lo arrangement of a projection lens unit for enlarging and projecting an image onto a screen.

A projection apparatus such as a video projector or a projection television forms an image using an image forming means such as a liquid crystal display (LCD) or a small-sized cathode ray tube (CRT), and enlarges and projects the image onto a large screen via a projection lens, thereby displaying a desired image on the screen. A large screen has been found to have a number of advantages for consumers, leading to an increase in demand.

Known projection systems are largely divided into a front-type projection system and a rear-type projection system according to the method of enlarging/projecting images, and are divided into a transmission-type projection system and a reflection- type projection system according to the type of image forming means.

Referring to Figure I showing a conventional rear-type LCD projection apparatus, a screen 150 on which an image is displayed is installed on the front surface of a cabinet 100, and a reflecting mirror 140 is slantingly incorporated at the rear side of the cabinet 100 to face 2 the screen 150. Disposed in the lower portion of the cabinet 100 is a projection apparatus for projecting an image light onto the screen 150 via the reflecting mirror 140, the projecting apparatus including a light source 110 for irradiating light generated using halogen or xenon, a liquid crystal display device 120 for generating an image using the light irradiated from the light source 110 and a projection lens unit 130 for enlarging/projecting the image generated by the liquid crystal display device 120 on the screen 150 via the reflecting mirror 140.

In the conventional rear-type LCD projection apparatus having the aforementioned configuration, as shown in Figure 3, an optical lens group L provided in the projection lens unit 130 has a linear optical arrangement.

Thus, the image light projected from the projection lens unit 130 are incident straightly onto the reflecting mirror 140. According to this optical arrangement, since the focus of the image light projected from the projection 20 lens unit 130 should be adjusted to land on the screen 150 via the reflecting mirror 140, the height of the cabinet is dependent on the focal distance of the optical lens group L, which obstructs attainment of a light and small projection system. 25 Figure 2 is a schematic diagram of another conventional rear-type LCD projection apparatus, in which a second reflecting mirror 140' is interposed between a projection lens unit 130 and a first reflecting mirror 140 which are equivalent to those of Figure 1, and the optical axes of an image projected from the projection lens unit 130 is shifted to be directed toward the second reflecting mirror 140', thereby adjust-;'_ng the focal distance of the 3 projection lens unit 130 to be shorter than the case shown in Figure 1, to reduce the height of a cabinet 100'.

However, since the arrangement of the optical lens group L provided in the projection lens unit 130 of the projection apparatus shown in Figure 2 is also linear, as shown in Figure 3, the optical axis of the image projected from the projection lens unit 130 is formed to be linear with respect to the second reflecting mirror 140'. Thus, io as the distance between the projection lens unit 130 and the second reflecting mirror 140' is limited to a predetermined distance, mainly due to the depth of the cabinet 100', that is, the width between the front and rear surfaces thereof, this obstructs the attainment of a light and small projection system.

In other words, according to the conventional reartype LCD projection apparatus, due to the optical arrangement of a projection lens' unit, if the depth of a cabinet is reduced, the height thereof increases, and if the height is reduced, then the depth increases. Thus, it is difficult to miniaturize the projection apparatus to less than a predetermined dimension.

It is an aim of at least preferred embodiments of the present invention to provide a light and small rear-type LCD projection apparatus while maintaining a large screen.

A -preferred aim is to provide a projection apparatus for use with a screen but reducing the optical projection distance between a projection lens unit and a screen, thereby reducing the space occupied by the projection apparatus.

4 According to the present invention there is provided a projection lens unit for use in a rear-type liquid crystal display (LCD) projection apparatus having a light source, an image source for generating an image using light irradiated from the light source, and a projection lens unit for enlarging/projecting image light generated from the image source onto a screen, wherein the projection lens unit comprises: a first optical lens group in which a plurality of optical lenses are sequentially arranged to lo focus the image light incident from the image source; means for shifting an optical path by bending the optical axis of the image light having passed through the first optical lens group at a predetermined angle; and a second optical lens group for focusing the image light whose optical axis is shifted by the optical path shifting means and enlarging/projecting the focused image light onto the screen.

Also according to the present invention there is provided a rear-type liquid display (LCD) projection apparatus comprising the projection lens unit.

The optical path shifting means is preferably an optical axis shifting prism constructed such that the main optical axis of the image light having passed through the first optical lens group is bent at an angle in the range of 900 to 1350 to then be shifted, and is preferably made of an optical plastic-based material.

The optical axis shifting prism preferably has an anti-reflective thin film having at least one layer formed on its light incoming and outgoing planes, and the anti reflective thin film made of either Al or Ag is preferably formed on its light reflection plane. Further, the optical axis shifting prism is preferably pentagonal and the light incoming and outgoing planes thereof are preferably perpendicular to the optical axis, respectively.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

Figure 1 is a schematic diagram illustrating a conventional rear-type LCD projection apparatus; Figure 2 is a schematic diagram illustrating another conventional rear-type LCD projection apparatus; Figure 3 is a schematic diagram illustrating the optical lens arrangement of a projection lens unit provided in the conventional projection apparatus shown in Figure 1 or 2; Figure 4 is a schematic diagram illustrating a reartype LCD projection apparatus according to a preferred embodiment of the present invention; Figure 5 is a schematic diagram illustrating the optical lens arrangement of a projection lens unit provided in the projection apparatus shown in Figure 4; and 6 Figure 6 is an extracted view schematically illustrating an optical axis shifting prism provided in the projection lens unit shown in Figure 5.

with reference to Figure 4, a screen 250 for displaying an image is arranged suitably at or near the front surface of a cabinet 200, and a reflecting mirror 240 is slantwise incorporated in the region of the rear side of the cabinet 200 to face the screen 250. Disposed in the lower portion of the cabinet 200 is a projection apparatus for projecting an image light onto the screen 250 via the reflecting mirror 240, the projecting apparatus including a light source 210 for irradiating light generated using, for example, halogen or xenon, a liquid crystal display device 220 for generating an image using the light irradiated from the light source 210 and a projection lens unit 230 for enlarging and projecting the image generated by the liquid crystal display device 220 on the screen 250 via the reflecting mirror 240.

The projection lens unit 230 is shown in Figure 5 and includes a first optical lens group L-I in which a plurality of optical lenses are sequentially arranged so as to focus the image light incident from the liquid crystal display device 220, an optical axis shifting prism P for shifting the optical axis of the image light having passed through the first optical lens group L-I by bending the optical axis at a predetermined angle, and a second optical lens group L-II in which a plurality of optical lenses are sequentially arranged so as to focus the image light whose optical axis is shifted by the optical axis shifting prism P to enlarge/project the same onto the screen 250.

7 The first optical lens group L-I includes at least one concave lens L1, a concave lens L2 and an aspherical lens L3 so as to focus incident light.

The second optical lens group L-II includes at least one concave lens L4, a meniscus lens L5, a concave lens L6 and an aspherical lens L7, and the optical axis thereof is coaxially positioned with respect to that of the first optical lens group L-I.

The optical axis shifting prism P is formed to be pentagonal so that the light incoming plane Pi and the light outgoing plane Po are perpendicular to the main optical axis, respectively, to bend the main axis of the image light having passed through the first optical lens group L-I at an angle in the range of 900 to 1350.

Also, the optical axis shifting prism P is preferably formed of an optical plastic-based material. As shown in the drawing, an anti-reflective thin film Pi consisting of at least one layer is formed on the light incoming plane Pi and the light outgoing plane Po, respectively, and another anti-reflective thin film P2 made of either aluminum (Al) or silver (Ag) is formed on a light reflection plane Pr.

In the preferred rear-type LCD projection apparatus, the image light formed by the liquid crystal display device 220 passes through the first optical lens group L-I installed in the projection lens unit 230 and is then incident into the light incoming plane Pi of the optical axis shifting prism P. Here, since the reflectivity of 8 the incident image light is reduced by the anti-reflective thin film Pi formed on the light incoming plane Pi, the transmittance thereof increases.

The main optical axis of the image light incident into the lightincoming plane Pi is bent at an angle in the range of 900 to 130' by the light reflection plane Pr of the optical axis shifting prism P so that the optical path thereof is shifted to pass through the second optical lens group L-II to then be emitted to the light outgoing plane Po. Here, since the reflectivity of the emitted image light is reduced by the antireflective thin film P2 formed on the light reflection plane Pr, the transmittance thereof increases.

In another preferred embodiment, when the incidence angle of ambient light of the optical axis of the image light incident into the light reflection plane Pr satisfies the total reflection condition in view of a refractive index, that is, a refractive index of a prism material, the anti-reflective thin film P2 formed on the light reflection plane Pr need not be formed. Also, the light incoming plane Pi and the light outgoing plane Po of the optical axis shifting prism P may be curved to have an arbitrary curvature.

As described above, the image light whose path is shifted by the optical axis shifting prism P and which has passed through the second optical lens group L-II is reflected by the reflecting mirror 240 to then be enlarged/projected on the screen 250, thereby displaying a desired image on the screen 250. Thus, since the focal distance of the projection lens unit 230 is shortened, the 9 projection distance of the image light is reduced, thereby reducing the space occupied by the projection lens unit 230 in the cabinet 200. Therefore, the overall projection system can be made lighter and smaller while maintaining a screen as large as the conventional screen. Likewise, while maintaining the same dimension of the overall projection system as that of the conventional system, a larger screen can be obtained.

As described above, in the rear-type LCD projection apparatus a projection lens unit is constructed such that the optical axis of an image light is bent at a predetermined angle to then be shifted for reducing the projection distance ranging from the projection lens unit and the screen, to reduce the space occupied by the projection lens unit in the overall projection apparatus, thereby making the overall system lighter and smaller while maintaining a screen as large as the conventional screen.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this

2S specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in thisspecification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, eachfeature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extend to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A projection lens unit for use in a rear-type liquid crystal display (LCD) projection apparatus having a light source, an image source for generating an image using light irradiated from the light source, and a projection lens unit for enlarging/projecting image light generated from the image source onto a screen, wherein the lo projection lens unit comprises:

a first optical lens group in which a plurality of optical lenses are sequentially arranged to focus the image light incident from the image source; means for shifting an optical path by bending the optical axis of the image light having passed through the first optical lens group at a predetermined angle; and a second optical lens group for focusing the image light whose optical axis is shifted by the optical path shifting means and enlarging/projecting the focused image light onto the screen.

2. The apparatus according to claim 1, wherein the optical path shifting means is constructed such that the main optical axis of the image light having passed through the f irst optical lens group is bent at an angle in the range of 900 to 135' to then be shifted.

3. The apparatus according to claim 1 or 2, wherein the optical path shifting means is an optical axis shifting prism.

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4. The apparatus according to claim 3, wherein the optical axis shifting prism is made of an optical plasticbased material.

5. The apparatus according to claim 3 or 4, wherein the optical axis shifting prism has an anti-reflective thin film having at least one layer formed on its light incoming and outgoing planes.

G. The apparatus according to any of claims 3 to 5, wherein the optical axis shifting prism has an antireflective thin film made of either Al or Ag formed on its light reflection plane.

7. The apparatus according to any of claims 3 to 6, wherein the optical axis shifting prism is pentagonal and the light incoming and outgoing planes thereof are perpendicular to the optical axis, respectively.

8. The apparatus according to any of claims 3 to 7, wherein the light incoming and outgoing planes of the optical axis shifting prism have an arbitrary curved plane, respectively.

9. A rear-type liquid crystal display (LCD) projection apparatus comprising a projection lens according to any of claims 1 to 8.

10. A projection lens unit substantially as hereinbefore described with reference to Figure 5 and 6 of the accompanying drawings.

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11. A rear-type liquid crystal (LCD) projection apparatus substantially as hereinbefore described with reference to Figures 4, 5 and 6 of the accompanying drawings.