JPH0367216A - Liquid crystal projector - Google Patents

Abstract

PURPOSE:To prevent color shading from occurring when a condenser lens is disposed in front of a liquid crystal panel by eliminating an unnecessary spectrum from a light source from an optical system with the aid of the combination of the characteristics of a set of dichroic mirrors for separating and for composing. CONSTITUTION:The unnecessary spectrum the light source 1 is eliminated from the optical system by the combination of the characteristics of a set of dichroic mirrors for separating and for composing 3, 4, 12 and 14. For example, only a green color spectrum 6 between the green color spectrum G and the unnecessary spectrum N transmitted through the condensor lens 8 and the liquid crystal panel for G 9 is reflected on a second dichroic mirror for G 12 having the same characteristic as a conventional one, composed with a blue color spectrum B and supplied to the dichroic mirror for R 14. Then, the unnecessary spectrum N is transmitted as it is and eliminated from the optical system. Therefore, even when the characteristic of the dichroic mirror is shifted by the uncollimated beam of light, the hue unevenness of the light after it is composed is reduced. Thus, even when a projecting lens is miniaturized by disposing the condenser lenses 6, 8 and 10 in front of the liquid crystal panel, an image having the little color shading is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a liquid crystal projector using a liquid crystal display panel.

(B) Prior Art Conventionally, a liquid crystal projector using a liquid crystal display panel is disclosed in Japanese Patent Laid-Open No. 150487/1987. The optical system of the above-mentioned liquid crystal projector is as shown in FIG.

In the figure, a light source (1) containing three primary colors (R, G, B)
After the light other than visible light is filtered out by a UV filter (2), it is supplied to a B dichroic mirror (3) that reflects only blue light, and the blue light is separated. The light transmitted through this B dichroic mirror is supplied to the 111G dichroic mirror (4) which reflects only green light, and is separated into green light and red light.

The blue light is reflected by the reflecting mirror (5), then condensed by the condenser lens (6) and supplied to the B liquid crystal panel (7>).The green light is condensed by the condenser lens (8>). The red light is supplied to the G liquid crystal panel (9).Furthermore, red light is also collected by a condenser lens (10) and supplied to the G liquid crystal panel (11).Then, the B and G liquid crystal panels (7) (9), the blue light and green light whose brightness is modulated by the video signal are transmitted to the second G dichroic mirror (12).
) is synthesized. Further, the red light whose brightness has been modulated by the R liquid crystal panel (11) is reflected by the reflection mirror (13), and then combined with the blue and green lights by the R dichroic mirror (14). Further, this combined light is projected onto a screen (not shown) via a projection lens (5).

A metal halide lamp is used as a light source in the above optical system. The spectrum of this metal halide lamp is as shown in Figure 4, with blue (B) around 430nm, green (G) around 540r+m, and 60nm around 540r+m.
A red spectrum (R) exists from 0 to 700 nm.

Note that N is a spectrum of 580 nm that is close to the green spectrum, and is actually an unnecessary spectrum component.

Then, Tanu separates and synthesizes the above-mentioned necessary R, G, and B.
The characteristics of the B dichroic mirror (3) are shown in Figure 5 and Figure 1.
The characteristics of the second G dichroic mirrors (4) and (12) are set as shown in FIG. 6, and the characteristics of the R dichroic mirror (14) are set as shown in FIG.

In each characteristic diagram, the shaded portion is the reflected spectrum. Due to the above characteristics, each LCD panel (7
)(9) and (11) is condensed by a projection lens (15).

On the other hand, condenser lenses (6), (8), and (+o) are arranged in front of each of the liquid crystal panels to condense light, thereby reducing the size of the projection lens (15).

However, in the light condensed by the condenser lens, as shown in FIG. 8, the side lights (s 2 ) and (u 2 ) are generally no longer parallel to the central light (1). Therefore, for each dichroic mirror whose characteristics are set on the condition that the incident light is incident at an angle of 45° with respect to the normal to the reflecting surface, the side light (s) (u) is They are incident on the line at different angles of 45° + α and 45° - α (α is about 6°), and due to the angle-dependent characteristics of the dichroic mirror, the characteristics are as shown in Figure 9. In light (1) it is (w), but in side light (s)
(tl), respectively (V) (X), ±66-1
When turned on, the characteristics shift.

Therefore, in a two-legged optical system, the characteristics of the R dichroic mirror (14) are such that an unnecessary spectrum exists near the boundary between the transmission band and the reflection band, as shown in Figure 7. This results in so-called color shading, in which the hue of the image projected on the screen differs greatly between the top and bottom of the image.

(c) Problems to be Solved by the Invention The present invention has been developed in view of the above points, and provides a liquid crystal projector that can prevent color shading even if a condenser lens is disposed in front of the liquid crystal panel. It is something.

(d) Means for Solving the Problems The present invention removes unnecessary spectra from a light source from an optical system by combining the characteristics of a pair of separating and combining dichroic mirrors.

(e) Effect By the above means, even if the characteristics of the dichroic mirror are shifted by non-parallel light, the hue unevenness of the combined light is reduced.

(f) Example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an optical system in this embodiment, and the same parts as in FIG. 3 are given the same reference numerals and explanations are omitted.

The feature of this embodiment is that the characteristics of the first G dichroic mirror (4゛) are set so as to reflect both the green spectrum (G) and the unnecessary spectrum (N) existing in its vicinity, as shown in Figure 2. .

Therefore, the condenser lens (8) and the G liquid crystal panel (
9), the green spectrum (G) and unnecessary spectrum (N) are reflected by the 2nd G dichroic mirror (12), which has the same characteristics as before in Figure 6, where only the green spectrum (G) is reflected and becomes the blue spectrum (B). ) and is supplied to the R dichroic mirror (14). Then, the unnecessary spectrum (N) is transmitted as is and removed from the optical system.

On the other hand, the red spectrum (R) transmitted through the first G dichroic ink mirror (,1゛) is the condenser lens (1).
0) and R liquid crystal panel (11), and then the same 7th panel as before.
The light is incident on the R dichroic mirror (14) having the characteristics shown in the figure. And this dichroic ink mirror for R (1
Since the incident light to 4) has passed through the condenser lens (10), its characteristics shift as shown by the dashed line in Fig. 7, as explained in the conventional example, but the unnecessary spectrum (N) has already been removed from the incident light. Since it is removed, the hue of the reflected light does not change at either end of the light.

Therefore, color shading on the screen will be significantly reduced.

Incidentally, since the light incident on the second G-use Gikkreuzk mirror (12) also passes through the condenser lens (8), the characteristics of the mirror are also shifted, but the difference between the green spectrum (G) and the unnecessary spectrum (N) is Since they are separated by about 40 nm, by setting the shifted characteristic curve so that it does not intersect with the unnecessary spectrum (N), it is possible to prevent the unnecessary spectrum (N) from being included in the reflected light.

(g) Effects of the Invention As described above, according to the present invention, even if the projection lens is made smaller by disposing a condenser lens in front of the liquid crystal panel, an image with less color shading can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an optical system of a liquid crystal projector in one embodiment of the present invention, and FIG. 2 is a characteristic diagram of a first G clock mirror in this embodiment. Figure 3 is a schematic diagram of the optical system of a conventional liquid crystal projector, Figure 4 is a diagram showing the spectrum of a metal halide lamp,
Figure 5 is a characteristic diagram of the B dichroic mirror, Figure 6 is a characteristic diagram of the 1st and 2nd G dichroic mirrors, Figure 7 is a characteristic diagram of the R dichroic mirror, and Figure 8 is the main points of the optical system. FIG. 9 is an enlarged view showing a shift in the characteristics of the dichroic mirror. (])... Light source, (3)... Dichroic mirror for B (4) (4')... Dichroic mirror for 1st G, (6) (8) (10)... Condenser lens,
(7) (9) (13)...LCD panel, (12)...
- Dichroic mirror for 2nd G (14)... Dichroic mirror for R, (15)... Projection lens. Figure 1

Claims (1)

[Claims] (1) A light source that emits light of at least three components of red, green, and blue; a plurality of separation dichroic mirrors that separate the light from the light source into the three components of red, green, and blue; and the separated red, green, and blue components. , a liquid crystal panel that is inserted into each of the optical paths of the three components of green and blue, and modulates the light of the three components according to image information; a condenser lens that is placed in front of this liquid crystal panel; In a liquid crystal projector equipped with a plurality of synthesis dichroic mirrors for synthesizing three components of light, unnecessary spectra from the light source are removed from the optical system by a combination of characteristics of the pair of separation and synthesis dichroic mirrors. A liquid crystal projector that is characterized by: