JPH08201602A - Projecting lens and projection optical device formed by using the same - Google Patents

Abstract

PURPOSE: To improve the contrast and focus of a blue projection optical system without lowering brightness by providing a projecting lens for blue with a light transmission means for attenuating the energy of the prescribed wavelength region of the light emission spectra of blue phosphors to the energy lower than other wavelength regions. CONSTITUTION: The element, for example, concave lens element 70C, constituting the blue projecting lens of the projecting optical system is provided with the light transmission means consisting of colored or multilayered interference films which is acted as a wavelength selective transmission type filter. The blue light energy after passing through the concave lens 70C falls down to 40% in the case of the absence of the light transmission means due to the transmittance characteristic and blue light emission spectra of the light transmission means. However, the blue luminance necessary for white display is 36% and, therefore, the blue luminance is equivalently improved by 10% in the case where the white display is made. As a result, the equivalently improved component of the blue luminance is appropriated to lessen the defocusing of electron beams. The spread of the blue spectra is suppressed by the light transmission means and the aberrations thereof are decreased and, therefore, the focusing performance of the blue projected image is exceedingly improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection television device or a projection display, and more particularly to a projection optical system suitable for improving the focus and contrast performance of the device.

[0002]

2. Description of the Related Art With the diversification of video sources, large-screen rear projection displays are becoming widespread in view of their excellent commercial properties (light weight, low cost, compactness).
In such a rear projection type display, projection tubes for red, green, and blue and a projection lens are independently provided inside a cabinet, and full-color images are displayed by synthesizing the respective projected images on a screen.

Among such recent rear projection type displays, as disclosed in Japanese Patent Laid-Open No. 3-224384, there is a device which employs a colored lens element as a projection lens of a projection optical system for green. The colored filter lens reduces spurious components near the red and blue wavelengths contained in the green emission spectrum, expands the color reproduction range of the display image, and improves the focus performance. Furthermore, by coloring the concave lens element close to the fluorescent screen of the projection tube, it is possible to absorb and reduce unnecessary light components reflected by the exit surface and returning to the fluorescent screen twice.
The contrast performance is also improved.

On the other hand, the brightness of a normal display set is represented by the brightness of white displayed on the screen. When displaying white in an actual set, other red and blue lights are added at a predetermined luminance ratio with reference to green light that is most dominant in brightness. In order to generate a predetermined brightness on the fluorescent screen of each color projection tube, it is necessary to set the cathode current to a predetermined value from the current-luminance characteristics of each projection tube. However, in general, the luminous efficiency of the blue phosphor is lower than that of the phosphors of other colors, and it corresponds to the brightness obtained when an allowable current is applied to the reference green projection tube in consideration of the phosphor life. , The emission brightness of the blue projection tube is insufficient. Therefore, in the blue projection tube, in order to compensate for insufficient brightness, the electron beam of the projection tube is defocused and the emission brightness is added to the current state.

Most of the projection lenses currently used do not have chromatic aberration correction. Although such a projection lens can obtain a performance close to the focusing performance intended in the design in the light of red and green which is originally close to a single wavelength spectrum, the focusing performance can be obtained in the case of blue light having a broad energy distribution with respect to the wavelength. Also tended to be inferior to the other colors.

Since blue light has lower visual sensitivity than green light, it has been left untreated by the above-mentioned treatments. However, in the actually displayed image, the blue flare covers the contours and the dark part like a veil, and there is a problem that the appearance quality of the focus and the contrast is deteriorated.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art and improve the contrast and focus of the blue projection optical system without reducing the brightness of the entire system as much as possible. It is to improve the quality of a display image of the entire device.

[0008]

In order to achieve the above object, the element of the blue projection lens is also provided with a light transmitting means having a predetermined transmittance characteristic. This light transmission means makes it difficult to transmit light on the longer wavelength side than the peak wavelength to the blue broad emission spectrum by absorbing or blocking it,
It has the property of transmitting light on the short wavelength side more easily.

[0009]

By the light transmitting means having the above-mentioned transmittance characteristic, the component on the long wavelength side in the emission spectrum of blue is less likely to be transmitted than the component on the short wavelength side. Therefore, the brightness of the blue projection optical system is lowered, but the chromaticity point of blue moves to the short wavelength side, and deep blue is expressed.

That is, since the degree of color deepening is greater than the decrease in the brightness of the blue optical system, the amount of red or green light necessary for expressing white is increased, and as a result, the brightness of white displayed is increased.

Further, since the wavelength band of the blue light transmitted through the optical system can be narrowed, the chromatic aberration of the projection lens is reduced.

[0012]

1 is a sectional view showing the construction of a projection optical system according to the present invention in a plane view. In front of the fluorescent screens of the three projection tubes 20a, 20b, 20c of red, green, and blue, the corresponding projection lenses 40a, 40b, 40c are connected via brackets 30a, 30b, 30c, and are integrated. To form a projection optical system corresponding to each color. The concave lens elements 70a, 70b, 70c are fitted in the brackets 30a, 30b, 30c, and the projection tube cooling liquid 80a,
80b and 80c are enclosed.

Of these three projection optical systems, the optical axis of the green optical system having the highest relative luminous efficiency is set perpendicular to the screen 60, and the optical axes of the other red and blue projection optical systems are set to the screen 6.
The configuration is such that it is inclined at a predetermined angle α with respect to 0.

FIG. 2 is a sectional view showing a state in which the entire optical system is housed in a cabinet 10 of a projection type television. As shown in the figure, in order to make the set compact, a reflection mirror 50 is added to the configuration shown in FIG. 1 to bend the optical path.

With this configuration, the images displayed on the red, green, and blue phosphor screens 6 are projected and combined on the screen through the projection lens and the reflection mirror to form a full-color image.

FIGS. 3, 4 and 5 show the emission spectra of the phosphors of the red, green and blue projection tubes 20a, 20b and 20c, respectively.

As shown in FIG. 3, in the emission spectrum of the red phosphor, the component near 610 nm is extremely large as compared with the other wavelength components and is close to a single wavelength. As shown in FIG. 4, the emission spectrum of the green phosphor is composed of a main wavelength component around 545 nm and red-side and blue-side spurious existing on the long wavelength side and the short wavelength side. On the other hand, as shown in FIG. 5, the emission spectrum of the blue phosphor shows a mountain-shaped broad rise with respect to the change in wavelength.

The above three kinds of light are projected on the screen 60 by the respective projection lenses 40a, 40b and 40c shown in FIG. 1 to synthesize an image. 3, 4, and 5
The color of the projection tube having the characteristics shown in FIG. I.
E. FIG. In terms of chromaticity points on the chromaticity diagram, red is (0.675,
0.321), green is (0.358, 0.601), and blue is (0.143, 0.071).

As described above, the brightness of the set is represented by the white display brightness. The light from the projection tube at these chromaticity points is projected on the screen and combined, and white (here, color temperature 9300 ° K + 0MPCD, chromaticity point (0.285, 0.
294))), the red, green, and
The brightness ratio of the three colors of blue is 0.176: 1.0: 0.164.
Is.

FIG. 6 shows the red, green and blue projection tubes 20a, 2
The relationship between the cathode current and the projection tube surface brightness at 0b and 20c is shown. With respect to the brightness of green light at each current value, the brightness of red light can be about 60%. Based on the brightness of green light, the required relative brightness of red light is 0.1.
No. 76 has a margin in the red current-luminance characteristic, and is therefore sufficiently satisfactory. However, the emission brightness of blue is extremely small, 5 to 15% of the brightness of green at the same cathode current, and the required relative brightness of 0.164 to green is not satisfied. In order to balance the brightness of green, the current brightness characteristic of blue is
It is necessary to have the characteristics as shown by the blue 'in the broken line in FIG.
For this reason, as shown in the conventional example, on the phosphor screen of the blue projection tube, the electron beam incident on the phosphor is thickly defocused to take measures to compensate for the insufficient brightness.

On the other hand, in this embodiment, in the projection optical system as shown in FIG. 1, the element forming the blue projection lens, for example, the concave lens element 70c is colored,
Alternatively, a light transmission means using a multilayer interference film is provided to act as a wavelength-selective transmission filter.

FIG. 7 shows wavelength-transmittance characteristics of this light transmitting means. By this light transmitting means, the chromaticity point of the transmitted blue light is shifted to the short wavelength side, and (0.148,0.0
30).

Similarly to the above, the relative luminance ratio of red, green, and blue required to display white with reference to the luminance of green is
It changes to 0.122: 1.0: 0.059. Since the brightness of green is equal to the above, the brightness of blue light necessary for displaying white is 36% (=
0.059 / 0.164) is sufficient.

On the other hand, from the transmittance characteristics of the light transmitting means of FIG. 7 and the blue emission spectrum of FIG. 5, the energy of the blue light after passing through the concave lens 70c provided with the light transmitting means is the same as when the light transmitting means is not provided. It drops to 40%. However, since the brightness of blue required for white display is 36%, when displaying white, the brightness of blue is equivalently improved by 10%.

As a result, the equivalent improvement in the brightness of blue can be used for reducing the defocus of the electron beam. Also,
Since the spread of the blue spectrum is suppressed by the light transmitting means and the chromatic aberration is also reduced, the focus performance of the blue projected image is significantly improved by the synergistic effect of the projection tube and the projection lens.

FIG. 8 shows changes in the cut-off wavelength at which the transmittance sharply changes and the equivalent luminance gain of white when the transmittance curve shown in FIG. 7 is translated in the direction of arrow A or arrow B. When the cutoff wavelength exists in the slope (460 nm or more) on the long wavelength side in the emission spectrum of blue in FIG. 5, the chromaticity point moves in the direction of deeper blue, so the equivalent luminance gain exceeds 100%. Cutoff wavelength is 480
In the vicinity of nm, the equivalent brightness gain is 1.11 times, which is the maximum.

The transmittance curve of the light transmitting means shown in FIG. 7 shows that the transmittance before and after the cutoff wavelength point is from about 100% to 0.
It changes sharply to around%. Such characteristics can be obtained with the multilayer interference film filter, but it is difficult to realize with the colored filter. However, as shown in (a), (b), and (c) of FIG. 9, in a colored filter having an effect of lowering the transmittance of light on the long wavelength side of blue than that on the short wavelength side, the effect of the same tendency is obtained. Can be obtained.

Further, as shown in FIG. 1, the concave lens element 70c closest to the phosphor screen in the projection lens absorbs energy in a predetermined wavelength region of the emission spectrum of the blue phosphor such as a colored filter more than other wavelength regions. When the light transmitting means for attenuating is provided, the effect of improving the contrast by absorbing unnecessary reflected light is large.

In this embodiment, the case where the concave lens element 70c in the blue projection lens is provided with the light transmitting means has been described, but when it is provided in another lens element, the projection tube panel, or the cooling liquid. As a matter of course, the effect of moving the chromaticity point that deepens the blue color can be obtained.

[0030]

According to the present invention, even if the emission energy of blue light is somewhat lost by the light transmitting means, the chromaticity point is moved to the short wavelength side so that the luminance based on white is equivalent. Since it can be improved or recovered, the focus of the blue projection optical system including the projection tube can be improved or the contrast can be improved.
Alternatively, the color purity is improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an optical system showing an arrangement of a projection tube, a projection lens, and a screen according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an optical system mounted on a set.

FIG. 3 is an emission spectrum diagram of a red phosphor.

FIG. 4 is an emission spectrum diagram of a green phosphor.

FIG. 5 is an emission spectrum diagram of a blue phosphor.

FIG. 6 is a characteristic diagram of current luminance of red, green, and blue projection tubes.

FIG. 7 is a characteristic diagram of the transmittance of the light transmitting unit.

FIG. 8 is a characteristic diagram of the transmittance and the brightness gain of the light transmitting unit.

FIG. 9 is a characteristic diagram of the transmittance of another light transmitting unit.

[Explanation of symbols]

6 ... Projection tube fluorescent screen, 20a, 20b, 20c ... Red, green,
Blue projection tube, 30a, 30b, 30c ... Red, green, blue bracket, 40a, 40b, 40c ... Red, green, blue projection lens, 60 ... Screen, 70a, 70b, 70c ...
Concave lens element for red, green and blue.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoyuki Ogura 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Hitachi Image Information Systems Co., Ltd.

Claims (6)

[Claims] 1. A projection lens for blue color in a projection lens for projecting an image displayed on a plurality of projection tube fluorescent screens corresponding to three primary colors of red, blue and green on a screen corresponding to each projection tube. A projection lens, wherein the lens is provided with light transmitting means for attenuating energy in a predetermined wavelength region of the emission spectrum of the blue phosphor more than other wavelength regions. 2. The projection lens according to claim 1, wherein the light transmitting means further attenuates a component on a long wavelength side with respect to a peak wavelength of an emission spectrum of the blue phosphor. 3. The projection lens according to claim 1, wherein the element provided with the light transmitting means is arranged closest to the fluorescent screen of the projection tube. 4. A projection optical apparatus using at least one of the projection lenses according to claims 1, 2, and 3. 5. Projection optics for enlarging and projecting an image displayed on a plurality of projection tube fluorescent screens corresponding to the three primary colors of red, blue and green on a screen by a projection lens provided corresponding to each projection tube. In the device, the liquid for cooling the blue projection tube is provided with a light transmission means for further attenuating the component on the long wavelength side with respect to the peak wavelength of the emission spectrum of the blue phosphor. Projection optics. 6. Projection optics for enlarging and projecting an image displayed on a plurality of projection tube fluorescent screens corresponding to three primary colors of red, blue and green on a screen by a projection lens provided corresponding to each projection tube. In the device, the phosphor screen panel of the blue projection tube is provided with a light transmitting means for further attenuating the component on the long wavelength side with respect to the peak wavelength of the emission spectrum of the blue phosphor. Projection optical device.