JPH0215049B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention provides a projection system that eliminates moiré.
This relates to a transparent screen for TV.

[Prior art] Conventionally, the transmission screens for projection TVs have been of the flat type with a light diffusing agent mixed in, the lenticular type with a lenticular lens molded on one side, and the lenticular type with a Fresnel lens molded on one side. Fresnel lens formats, double-sided molding formats in which a Fresnel lens is molded on one side and a lenticular lens is molded on the other side, and screens made from combinations of these have been used, but the requirements for optical properties such as brightness, color unevenness, and directional characteristics For reasons such as handling, cost, etc., a double-sided molded lens that combines a lenticular lens and a circular Fresnel lens has come into use. In other words, if there is no Fresnel lens, the light magnified and projected from the TV cathode ray tube will remain in the expanding direction, so unless this is converted into parallel light using a Fresnel lens, the surroundings will inevitably become dark. If a lens is used, and if there is no lenticular lens, the position suitable for viewing the screen is limited, so a lenticular lens is used to enlarge this position.

[Problems to be Solved by the Invention] By the way, in a double-sided molded transmission screen, a circular Fresnel lens is usually used on the projection lens side, and a lenticular lens is used facing the viewing side. In this case, in the conventional double-sided molded transmission screen, there is a part where the shadow of the concentric lines of the circular Fresnel lens and the line of the lenticular lens overlap almost in parallel, and this part creates a pattern called a moire pattern. This caused the appearance to deteriorate.

Conventionally, when it comes to moire, it is said that setting the pitch ratio of the Fresnel lens to the lenticular lens at 2:3 will make the moire pattern most difficult to discern, and it is important to keep such a ratio when manufacturing the lens. Because of this, due to processing technology, the pitch of Fresnel lenses was around 0.5mm, and the pitch of lenticular lenses was around 0.75mm. Therefore, at this pitch, it is not possible to make the focal length of the lenticular lens less than 1/2 of the plate thickness (usually about 3 mm) due to conflicts with the plate thickness and the radius that can be manufactured by the mold manufacturing tool. This was impossible and the focus was located close to the Fresnel lens surface.

[Means for Solving the Problems] The configuration of the present invention for solving the above problems will be explained with reference to FIG. 3 corresponding to the embodiment. In a transmission screen 1 formed by molding a Fresnel lens surface 2 on one side of a plate and a lenticular lens surface 5 on the other surface, the focal length F of the lenticular lens is set to 1/4 of the thickness D of the transmission screen. ~1/20, pitch D of lenticular lens is 1/4 of plate thickness D~
It is set to 1/40.

[Function] The double-sided molded transmission screen of the present invention has the following features:
As mentioned above, the focal length of the lenticular lens was set to 1/4 to 1/20 of the thick plate of the transmission screen, and the pitch of the lenticular lens was set to 1/4 to 1/40 of the same plate thickness, so Fresnel Moire patterns can be prevented from occurring regardless of the pitch ratio between the lens and the lenticular lens.

[Example] Hereinafter, an example of the present invention will be described in comparison with a conventional example according to the drawings.

FIG. 1 is a front view of a double-sided molded transmission screen 1 viewed from the projection side, in which a circular Fresnel lens surface 2 is formed on the front side and a lenticular lens surface 3 is formed on the back side. FIG. 2 is a partially enlarged cross-sectional view of FIG. 1, showing a conventional screen. The transmission screen 1 is made of a translucent resin plate mixed with a light diffusing agent, and its lenticule is The focal length F of the lens 3 was equal to or more than 1/2 of the plate thickness D. Therefore, when viewing the screen 1 from the lenticular lens 3 side, the distance from the surface of the Fresnel lens 2 to the focal point 4 of the lenticular lens 3 is shorter, so the shadow of the concentric lines of the Fresnel lens 2 is distorted. The light reaches the focal point 4 before being completely diffused by the incorporated light diffusing agent, causing a moiré pattern in the portion overlapping the line of the lenticular lens.

In order to eliminate such drawbacks, the present invention makes the focal length of the lenticular lens 3 smaller than the thickness of the plate of the transmission screen, the entire surface of which is a diffusion layer, so that the lenticular lens 3 has a smaller focal length than the surface of the Fresnel lens 2. The distance to the focal point 4 of the cyular lens 3 is increased so that the shadow of the concentric circles of the Fresnel lens 2 can be sufficiently diffused during this distance, and an embodiment according to the present invention is shown in FIG. This is a diagram similar to FIG. 2, and the lenticular lens 5 is made smaller in focal length and pitch than the conventional lens. In the transmission screen according to the present invention, the focal length F is 1/4 to 1/20 of the plate thickness D.
Therefore, the shadow of the concentric lines of the Fresnel lens 2 reaches the focal point 4 of each lenticular lens after being completely diffused by the light diffusing agent, so the phenomenon of overlapping with the lines of the lenticular lens does not occur, and This means that moiré patterns will not occur.

If a large amount of light diffusing agent is added to diffuse the shadows of the concentric lines of the Fresnel lens, the transparency will deteriorate, the brightness will decrease, the optical properties necessary for the screen will not be obtained, and the screen itself will be damaged. Although it is possible to increase the thickness and reduce the amount of diffusing agent, increasing the thickness increases both weight and cost, which poses a practical problem. Considering these points, the focal length F of the lenticular lens 5 is set to 1/4 to 1/4 of the plate thickness D.
They obtained values in the range of 1/20 and pitch P of 1/4 to 1/40 of the plate thickness.

[Effects of the Invention] Since the transmission screen of the present invention has the above-described configuration and function, according to the present invention, light incident from the Fresnel lens side is transmitted from the Fresnel lens surface to the focal point of the lenticular lens. Because of the long distance between them, the concentric shadows of the Fresnel lens are completely diffused by the light diffusing agent before reaching the focal point of the lenticular lens, and the part that overlaps with the line of the lenticular lens The generation of moire patterns can be reliably prevented, and a transmission screen with good appearance can be obtained.

[Brief explanation of drawings]

Fig. 1 is a front view of a double-sided molded transmission type screen as seen from the projection side, Fig. 2 is a partially enlarged view showing a cross section of Fig. 1 and shows a conventional screen, and Fig. 3 is a view of the present invention. FIG. 2 is a partially enlarged cross-sectional view similar to FIG. 2 of the transmission screen according to FIG. DESCRIPTION OF SYMBOLS 1... Transmissive screen made of translucent resin kneaded with a light diffusing agent, 2... Fresnel lens surface, 3... Lenticular lens surface, 4... Focal point, 5... Lenticular lens surface according to the present invention, D...Plate thickness,
F... Focal length, P... Lenticular lens pitch.

Claims (1)

[Claims] 1. In a transmission screen formed by molding a Fresnel lens surface on one side of a translucent resin plate into which a light diffusing agent has been kneaded and a lenticular lens surface molded on the other surface, the focal length of the lenticular lens is determined by the thickness of the transmission screen plate. A transmission screen characterized by having a lenticular lens pitch of 1/4 to 1/40 of the board thickness.