JPH04207487A - Projector for projection television - Google Patents

Abstract

PURPOSE:To improve the contrast of a projection television by providing an optical element having a filter characteristic of a nearly specified transmittance to all wavelengths in front of a fluorescent surface and attenuating the unnecessary light reflected from a projection lens, etc. CONSTITUTION:Phosphors are applied on the rear surface of a face plate 1a made of glass on the front face of a projecting tube 1, by which the fluorescent surface 1b is formed. The projection lens L consisting of a meniscus lens 3 which corrects mainly the curvature of field and a lens group 4 which is housed in a lens barrel 5 and mainly enlarge projects images is disposed in front of the face plate 1a. A material which exhibits nearly the specified absorption characteristic to light of all the wavelengths is added to the meniscus lens 3 which is the lens nearest the fluorescent surface 1b of the projecting tube 1 of the projection lens L. The light which transmits the meniscus lens 3 is attenuated in the intensity alone without changing its spectral compsn. and the contrast of the projection television is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a projection device for a projection television that projects an image from a projection tube onto a screen using a projection lens.
In particular, it aims to improve the contrast of projection televisions by attenuating unnecessary light reflected toward the fluorescent screen side of the projection tube.

[Conventional technology]

As shown in FIG. 12, a conventional projection television includes a projection tube 11, a projection lens 14 that enlarges and projects an image emitted from the projection tube 11 onto a screen, and a projection tube 11 of the projection lens 14. A coupler 12 that optically couples the lens 13 closest to the projection tube 11 with the face plate lla of the projection tube 11 and is filled with a cooling liquid for cooling the projection tube 11 is known.

[Problem to be solved by the invention]

In the above conventional optical system, since the coupler 12 is provided for optical coupling, the phosphor screen 1 of the projection tube 11
The light I emitted from 1b is no longer reflected from the face plate 11a and the surface of the lens 13 on the face plate lla side.

However, the reflected light R on other surfaces of the projection lens 14 (the interface between the lens and the air) still exists. Then, these reflected lights R are returned to the phosphor screen 11b, further reflected by the phosphor screen 11b, and incident on the projection lens 14 as unnecessary light. As a result, the contrast of the projection television deteriorates. For example, when projecting a bright spot on a dark screen, a bright spot appears even in an area that should be dark.

Further, as shown in FIG. 13, the fluorescent screen 11. If the light rays emitted from b# enter the lens 13 at a critical angle (approximately 42 degrees or more in the case of acrylic resin) or more, they will be totally reflected by the lens 13 and reach the phosphor screen 11b, resulting in a similar decrease in contrast. There was.

The present invention has been made to solve the problems of the prior art described above, and an object of the present invention is to provide a simple projection device for a projection television that can improve the contrast of a projection television.

[Means to solve the problem]

The projection device for a projection television according to the present invention is a projection device for a projection television that projects an image emitted from a projection tube onto a screen using a projection lens disposed in front of the projection tube. In order to attenuate the light reflected from the projection lens, etc. toward the phosphor screen, the transparent optical element located there has a filter characteristic that makes the transmittance almost constant for all wavelengths from blue to red. The optical element is preferably a projection lens closest to the phosphor screen of the projection tube, a filter provided close to the face plate of the projection tube, or a face plate of the projection tube.

Further, in order to provide the above-mentioned filter characteristics, for example, a projection lens or the like is colored by adding a substance that has substantially constant absorption characteristics for all wavelengths from blue to red. Note that the above-mentioned filter characteristics only need to hold for light with wavelengths from at least blue to red, and may of course also hold for light in a wider visible range.

[Effect]

A portion of the light emitted from the phosphor screen of the projection tube is reflected by the surface of the projection lens, reaches the phosphor screen, is further reflected by the phosphor screen, and enters the projection lens as unnecessary light. During this time, these reflected lights pass through an optical element having filter characteristics with substantially constant transmittance for wavelengths from blue to red, and the amount of light decreases each time it passes. Since the filter has a nearly constant transmittance for all wavelengths from blue to red, only the intensity of the light transmitted through the optical element is attenuated without changing its spectral composition.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(Example 1) Figures 3111 and 2 show the first embodiment of the present invention.

In the figure, reference numeral 1 denotes a projection tube, the front of which is provided with a glass face plate la, and the back surface of the face plate 1a coated with phosphor to form a phosphor screen 1b. In front of the face plate 1a is a plastic meniscus lens 3 that mainly corrects field curvature.
and a lens group 4 (4, 42, . . . ) which is housed in the lens barrel 5 and mainly performs enlarged projection of an image.

Among the projection lenses L, the meniscus lens 3, which is the lens closest to the phosphor screen 1b of the projection tube 1, is doped with a substance that exhibits almost constant absorption characteristics for light of all wavelengths from blue to red. The meniscus lens 3 is colored gray like an ND filter that does not exhibit spectral selective absorption. The transmission characteristics of the meniscus lens 3 are shown in FIG. As shown in the figure, the transmittance is almost constant for wavelengths from blue to red, and the light incident on the meniscus lens 3 is transmitted with only the intensity reduced without changing the spectral composition. Note that by increasing or decreasing the concentration of the absorbing substance, it is possible to fabricate a device with an arbitrary transmittance, as shown in FIG.

A coupler 2 is provided between the face plate 1a and the meniscus lens 3, as shown in FIG. 2, for optically coupling them together. In FIG. 2, the coupler 2 is made of die-cast aluminum and mainly consists of a coupler body 2a in the shape of a rectangular cylinder and a large number of heat dissipation fins 2b formed on the outer periphery of the coupler body 2a.

A cooling liquid 8 is filled in the coupler 2 for the purpose of not only providing optical coupling between the face plate 1a and the meniscus lens 3, but also cooling the face plate b1. For this reason, gaskets 6 are interposed between the meniscus lens 3, the face plate 1a, and the front and rear openings of the coupler 2, respectively. The projection tube 1 and the coupler 2 are fixed by a fixed frame 9, and the meniscus lens 3 is attached to the coupler 2 by a lens attachment frame 7. Moreover, in order to keep the pressure of the coolant 8 constant, a pressure regulating part 2C including a diaphragm I and a pressure regulating valve above is provided in a part of the coupler body 2a.

A portion of the light incident on the projection lens L from the projection tube 1 is reflected by the surface of the projection lens L and returned to the fluorescent screen 1b (see FIG. 4). This reflected light (■) is transmitted through the meniscus lens 3 and attenuated as shown in FIG. imaged on top.

Now, if we assume that the meniscus lens 3 is colored with a transmittance of 90%, ignoring other factors that change the amount of light,
If the brightness of the reflected light ■ is 100%, the brightness of the light ■ that has passed through the meniscus lens 3 once is 100% x 0.9
=90%, and the brightness of the light ◎ that passes through the meniscus lens 3 again from the phosphor screen 1b is 100%X0.9X0.9
=81%. Therefore, the amount of unnecessary reflected light projected onto the screen can be reduced by about 20%, and the contrast of the image can be improved. Furthermore, if the transmittance of the meniscus lens 3 is 80%, the brightness of the light ■ is 6.
4%, which is a reduction of about 35%, and also reduces the transmittance by 70%.
%, the brightness of light (2) becomes 49%, which is a reduction of approximately 50%.

Furthermore, as shown in FIG. 5, contrast reduction caused by total reflection at the meniscus lens 3 can be similarly improved. In total internal reflection, the incident angle is greater than the critical angle, so
The distance through the meniscus lens 3 becomes longer. The transmittance when the passing distance of the meniscus lens 3 is 1=1 is τ
=τ 11/10, and if the passing distance t doubles, the transmittance decreases by the square of it. Therefore, in the case of total reflection, 100% is reflected, but the meniscus lens 3
Since the light passes over a long distance and is subject to large attenuation, it is possible to effectively improve contrast.

In order to improve the contrast by reducing the amount of reflected light, it is conceivable to color the coolant 8 to give it a filter effect, as shown in FIG. 7.

However, in this case, the light from the peripheral part (■) of the phosphor screen 1b has a longer passage distance through the coolant 8 than the light from the center part (2), resulting in a problem that the image in the peripheral part becomes darker. . However, when the meniscus lens 3 is colored, as shown in FIG. 6, the light from the peripheral part (2) and the light from the central part (2) pass the same distance through the meniscus lens 3, and the above problem does not occur.

Further, in this embodiment, since the absorbing substance is simply added to the meniscus lens 3, there is no increase in the number of optical components, and the lens can be adopted at low cost and easily.

(Example 2) FIG. 8 shows a second example of the present invention. In this example,
An ND filter or a thin plate filter lO having filter characteristics equivalent to an ND filter is attached to the face plate 1.
Install it just before a. In the above embodiment, the meniscus lens 3, which is the projection lens closest to the phosphor screen 1b, has filter characteristics, so it has a filtering effect on the reflected light from any of the projection lenses L. However, in this embodiment, the meniscus lens 3 has filter characteristics. Reflected light from the inner wall surface of the coupler body 2a, for example, as shown in the figure, can also be reduced at a location closer to the phosphor screen 1b than 3.

(Example 3) Next, a third example of the present invention is shown in FIG. In this embodiment, the face plate 1a is colored to have filter characteristics. Fluorescent screen 1b of face plate 1a! The surface of the IJ is formed into a spherical or aspherical surface that is convex toward the electron gun (not shown) side of the projection tube 1. Therefore, as shown in FIG. 10, the distance that light from the center part (■) of the phosphor screen 1b passes through the face plate 1a and the distance that light from the peripheral part (2) passes through the face plate 1a are very different. The screen remains uniformly bright.

On the other hand, a flat front plate 1a as shown in FIG.
When the phosphor screen 1b is colored, the light from the peripheral part (2) of the phosphor screen 1b has a longer passage distance through the face plate la, resulting in a phenomenon that the peripheral part becomes darker.

In addition, in the present invention, unnecessary reflected light is reduced by using an optical element with filter characteristics that has almost constant transmittance for light of all wavelengths from blue to red.
It can be applied not only to three-tube projection devices that use three green and blue projection tubes, but also to single-tube projection devices that use color projection tubes, and in either case, the contrast of the projection TV Or image quality can be improved. Furthermore,
Optical elements with the same filter characteristics can be used for any of the red, green, and blue projection tubes.

Further, the projection device of the present invention can be applied to both front projection televisions using a reflective screen and rear projection televisions using a transparent screen.

〔Effect of the invention〕

In summary, in the present invention, an optical element having filter characteristics with almost constant transmittance for all wavelengths from blue to red is provided in front of a phosphor screen to attenuate unnecessary light reflected from a projection lens, etc. This has the effect of improving the contrast of the projection television.

In addition, since the filter characteristics have a nearly constant transmittance for wavelengths from blue to red, the spectral composition of the light transmitted through the optical element remains unchanged, only the intensity decreases, and color balance does not deteriorate. It has this effect.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional side view showing the first embodiment of the present invention, FIG. 2 is an exploded perspective view of the same embodiment, and FIG. 3 is a diagram showing the transmission characteristics of the meniscus lens in the embodiment of plan 1. 4, 5, and 6 are schematic side views for explaining the operation of the first embodiment; FIG. 7 is a schematic side sectional view of a comparative example compared with the first embodiment; FIG. 8 is a schematic side sectional view showing a second embodiment of the present invention, FIG. 9 is a schematic side sectional view showing a third embodiment of the present invention, and FIG. 10 is a diagram for explaining the operation of the same embodiment. FIG. 11 is a schematic side sectional view of a comparative example compared with the third embodiment; FIG. 12 is a side sectional view showing a conventional projection television projection device; FIG. 13 is a side sectional view of the same device. It is a figure for explaining an effect. 1... Projection tube 1a... Face plate 1b... Fluorescent screen 2... Coupler 2a... Coupler body 2b... Fin 2C... Pressure adjustment section 3... Meniscus lens 4... Lens Group 5... Lens barrel L, projection lens 6... Packing 7... Mounting frame 8... Coolant 9... Fixed frame 10... Filter 11... Projection tube 12... Coupler 13... Meniscus Lens 14... Projection Lens Applicant's Representative Yasushi Ishikawa Implementation + (RTM) 〆ML Invasion I Pressure in Niscus Lens 3 Figure 5 Figure/, fL/a Figure 10 Figure 110

Claims (1)

[Scope of Claims] 1. In a projection device for a projection television that projects an image emitted from a projection tube onto a screen using a projection lens disposed in front of the projection tube, the device is located in front of the fluorescent screen of the projection tube. A projection characterized in that the optical element has a filter characteristic that makes the transmittance almost constant for all wavelengths from blue to red in order to attenuate the light reflected from the projection lens etc. toward the phosphor screen side. Television projection device. 2. The projection apparatus for a projection television according to claim 1, wherein the optical element is a projection lens closest to the fluorescent screen of the projection tube. 3. The projection apparatus for a projection television according to claim 1, wherein the optical element is a filter provided close to the face plate of the projection tube. 4. The projection according to claim 1, wherein the optical element is a face plate of the projection tube, and the fluorescent screen of the face plate is formed into a convex curved surface on the electron gun side of the projection tube. Television projection device.