JPS6248957B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a video projector, and particularly to a cathode ray tube that supports each of the three primary colors of red (R), green (G), and blue (B) arranged in-line or in a delta shape. In a video projector that projects images individually onto a screen using a magnifying optical system and combines them into a color image, to maintain white balance well over time and to keep the drive current of the G cathode ray tube below a certain value. The purpose of this is to ensure high resolution by using acrylic lenses and to reduce costs by using acrylic lenses.

Among this type of video projectors, for example, the optical system of a so-called transmission type video projector has a configuration as shown in FIG. In this optical system, T _R , T _G , and T _B represent high-intensity cathode ray tubes that produce the three primary colors of red, green, and blue, respectively. The images from each of the cathode ray tubes arranged vertically inline are subjected to lenticular lens processing on the inside through corresponding magnifying lens systems L _R , L _G , and L _B , and uniform diffusion processing on the outside (viewing side). The images are projected onto a screen S and synthesized as a color image. The factors that determine the brightness of a color image on such a screen, apart from the characteristics of the screen itself, depend on the luminous efficiency of the cathode ray tube, that is, the type of phosphor and the characteristics of the projection lens.

By the way, the phosphors used in high-brightness cathode ray tubes for projection generally emphasize characteristics at high current densities, so R: Y ₂ O ₃ : Eu G: Gd ₂ O ₂ S: Tb B: ZnS: Ag , cl is used in combination.

In order to obtain a white color with a color temperature of 9300°K by combining three cathode ray tubes using such phosphors, each of the R, G, and B cathode ray tubes T _R , T _G ,
The current ratio of T _B is i _R :i _G :i _B =1:1.8:1.3. Of course, it is desirable that the current ratios be roughly equal. However, on the premise that the brightness of the projected image is to be improved as much as possible, it is impossible to satisfy such conditions only by a combination of phosphors. By the way, another factor, the characteristics of the projection lens, is determined by the F number and magnification.
Since it is actually composed of a combination of multiple single lenses, it has been found that the transmittance of each lens has a large effect.

On the other hand, in practical terms, if we focus on the fact that the brightness and resolution of the composite image on the screen are mostly controlled by the green component, the current ratio is determined based on the green cathode ray tube, and the overall brightness is It is no exaggeration to say that it depends on the situation.

Based on these considerations, the present invention has made the magnifying lens, as shown in the side cross-sectional view in Fig. 2, made of acrylic resin, and of which only the lens _LG , which magnifies and projects the image of the G cathode ray tube T _G , is coated with anti-reflection coating. By applying this correction, the current ratios of the R, G, and B cathode ray tubes _TR , T _G , and T _B are corrected so as to become smaller overall. Such antireflective coatings are formed by exposing the acrylic lens to a low temperature magnesium fluoride vapor atmosphere.

As shown in Figure 3, the difference in transmittance between the presence and absence of anti-reflection coating in the three-layer acrylic lens L ₁ , L ₂ , and L ₃ shown in Figure 2 can reach as much as 15% in the green wavelength region of 550 nm. Understood.

Taking advantage of these characteristics, anti-reflection coating is applied to only the acrylic magnifying lens L _G or L _G and L _B , and the overall current ratio for each of the R, G, and B phosphors is 1:1. : By approaching 1 and making the current densities as equal as possible, the phosphor becomes less susceptible to temperature effects, making it easier to maintain white balance over time. Since the spot diameter can be narrowed down, high-resolution images can be obtained, and the high cost of coating acrylic lenses can be saved, making it possible to take advantage of the cost advantages of using plastic lenses.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the optical system of this type of cathode ray tube, FIG. 2 is a side sectional view of a green magnifying lens system, and FIG. 3 is a diagram showing the wavelength of transmitted light versus the spectral transmittance characteristics of the lens.

Claims (1)

[Claims] 1 High-brightness cathode ray tube images corresponding to the three primary colors of red, green, and blue are selectively enlarged and projected onto a screen using an acrylic lens with anti-reflection coating applied to only the green or green and blue magnifying lenses. A video projector configured to synthesize images.