Optical: systems and elements – Lens – With field curvature shaping
Reexamination Certificate
2002-07-30
2004-07-06
Ton, Toan (Department: 2871)
Optical: systems and elements
Lens
With field curvature shaping
C349S095000
Reexamination Certificate
active
06760162
ABSTRACT:
This application claims the benefit of the Korean Application No. P2001-46116 filed on Jul. 31, 2001, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection display system, and more particularly, to a projection display system having project lenses that enable aberration correction and movement.
2. Discussion of the Related Art
Recently, with increase of request for a large sized screen and high picture quality, projection systems that enlarge and project small images using a projection lens have been rapidly spread.
Examples of a projection system include a front projection system and a rear projection system depending on a direction of an image projected on a screen.
The rear projection system has received much attention due to an advantage that a relatively bright image can be displayed even in a place where surroundings are bright.
A good example of the rear projection system includes a projection television.
In the projection TV, a cathode ray tube (CRT) mode has been used as a light source for displaying small images.
The projection TV of a CRT mode has a limitation in obtaining a small and lightweight size due to a weight of the CRT. For this reason, it is difficult to display a large sized screen and obtain luminance required for high resolution in the projection TV.
To solve such problems, there has been suggested a projection TV based on a flat display that can obtain a large sized screen at a thin thickness.
Examples of a flat display include liquid crystal display (LCD), plasma display panel (PDP), field emission display (FED), and electro-luminescence (EL) device.
Of them, a projection TV based on LCD projects light emitted from a light source onto the LCD and displays an image of a liquid crystal panel on a screen using a projection lens system.
Since the image is enlarged and projected on the screen using the liquid crystal panel of high picture quality and a small size, a large sized screen image can easily be obtained and a small and lightweight sized projection system can be obtained.
The projection display system based on a liquid crystal panel can obtain relatively high resolution and high luminance compared to the CRT. Therefore, it is expected that a large sized screen can be displayed.
FIG. 1
illustrates a related art projection display system based on a liquid crystal panel.
Referring to
FIG. 1
, the related art projection display system includes an optical engine
11
, a total reflection mirror
14
, and a screen
15
. The optical engine
11
includes a lighting system
11
, a liquid crystal panel
12
, and a projection lens system
13
.
The lighting system generates light and irradiates the generated light onto the liquid crystal panel
12
. The liquid crystal panel
12
displays an image by controlling transmittivity of incident light from the lighting system
11
in accordance with an image signal. The projection lens system
13
enlarges and projects the image from the liquid crystal panel
12
and displays the image on the screen
15
. Thus, a viewer can view the image displayed on the screen
15
.
In this case, the image projected by the projection lens system
13
is totally reflected by the total reflection mirror
14
to change a light path. The image moves to the screen by the changed light path and then is displayed on the screen
15
.
If the projected image is directly projected from the rear of the screen
15
without any change of the light path by the total reflection mirror
14
, the thickness of the system becomes great. Accordingly, it is desirable to change the light path using the total reflection mirror
14
so as to reduce the thickness of the system.
In more detail, as shown in
FIGS. 2 and 3
, the related art projection display system includes first and second fly eye lenses (FEL)
22
and
24
arranged between a light source
20
and a first dichroic mirror
30
, a polarizing beam splitter array (PBS array)
26
, and a focusing lens
28
.
The related art projection display system further includes a first total reflection mirror
32
, a second dichroic mirror
34
, a first relay lens
36
, a green liquid crystal panel
44
G, a second relay lens
36
, a third total reflection mirror
42
, a dichroic prism
46
, a projection lens
48
, and a screen
50
.
The first total reflection mirror
32
is arranged between the first dichroic mirror
30
and a red liquid crystal panel
44
R. The second dichroic mirror
34
and the first relay lens
36
are arranged between the first dichroic mirror
30
and a second total reflection mirror
38
. The second relay lens
40
and the third total reflection mirror
42
are arranged between the second total reflection mirror
38
and a blue liquid crystal panel
44
B. The dichroic prism
46
is arranged on three surfaces of the liquid crystal panels
44
R,
44
G, and
44
B.
It is a general tendency that the aforementioned projection display system has a small size and is lightweight.
To make the size of the screen great and reduce the thickness of the system in accordance with such a general tendency, it is necessary to make a projection distance between the screen
50
and the projection lens
48
short.
The projection lens system includes a first lens group having a positive refractive power, and a second lens group having a negative refractive power. A total reflection mirror for changing the light path is disposed between the first lens group and the second lens group to form an “L” shaped projection lens system. Thus, the thickness and the height of the system can be reduced.
However, the “L” shaped projection lens system should make the negative refractive power of the second lens group great to obtain a short projection distance. In this case, aberration such as distortion, coma, and astigmatism occurs.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a projection display system that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a projection display system that enables aberration correction and can reduce the size of the system.
Another object of the present invention is to provide a projection display system that enables movement of lenses to obtain an image of high definition.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a projection display system includes a liquid crystal panel displaying an image, a first lens group having a positive refractive power, formed by combination of two or more lenses, and correcting aberration of incident light from the liquid crystal panel, a total reflection mirror reflecting the incident light from the first lens group in a predetermined direction, and a second lens group having a negative refractive power, formed by combination of two or more lenses, and correcting aberration of the incident light from the total reflection mirror.
The distance between the liquid crystal panel and the first and second lens groups is based on a focal distance and is determined to satisfy the following conditions:
2.0<bf
1
/f
1
<2.8;
0.6<f
2
/f
1
<1.0; and
4.0<d/f
2
<5.0,
wherein bf
1
represents a focal distance between the liquid crystal panel and a lens included in the first lens group nearest to the liquid crystal panel, fl represents a focal length of the whole projection lens system including the total reflection mirror, the first lens group, and the second lens grou
Caley Michael H.
Lee, Hong, Degerman, Kang & Schmadeka P.C.
LG Electronics Inc.
Ton Toan
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