Optical projection apparatus, transmission type screen, and projection type image display apparatus

#The present invention relates to a projection type image display apparatus of the type which is used as a projection TV set, etc., in which white light from a light source is separated into additive primary colors, each of the primary colors is modulated with the use of a display element, and images are expanded and displayed on a screen.

#Along with a diversity of video sources, projection type image display apparatuses are popular as optical projection apparatuses for a large screen as a result of its marketable properties, such as lightness in weight, low price, and compactness in size. In particular, the projection type image display apparatuses using a liquid crystal display element (hereafter, referred to as a liquid crystal panel) as a video generation source has come onto the market because of recent significant improvement of the definition and numerical aperture of a liquid crystal panel. Unlike the conventional projection type CRT, the liquid crystal panel does not emit light by itself, so it needs a light source. The projection type image display apparatus with a liquid crystal panel is composed so that a white light from its white light source is separated into additive primary colors and each of those primary colors are modulated in the liquid crystal panel, from which full-color images are displayed on the screen by expanding original images on the liquid crystal panel through a projection lens unit.

#The optical system of the projection type image display apparatus that employs this liquid crystal panel is divided into two types, i.e. a three-panel type that uses three liquid crystal panels and a single-panel type that uses only one liquid crystal panel.

#FIG. 1 is a cross sectional side view of the main portion of a rear side projection type image display apparatus for which an optical projection system in accordance with the present invention is employed.

#FIG. 2 is a cross sectional side view of the main portion of a rear side projection type image display apparatus for which an optical projection system in accordance with the present invention is employed.

#FIG. 3 is a diagram showing the configuration of the main portion of the optical system of the present invention.

#Hereunder, the preferred embodiments of the present invention will be described with reference to the accompanying drawings.

#FIGS. 1 and 2 show the overall configuration of different examples of a rear side projection type image display apparatus for which the optical system of the present invention to be described later is employed. FIGS. 1 and 2 are cross sectional views of the rear side projection type image display apparatus from the image viewing direction (image light ejecting direction) and from a side orthogonal to the horizontal direction.

#In FIGS. 1 and 2, 11 is an optical unit including a white light source and a liquid crystal panel. A light output from the optical unit 11 is expanded by a projection lens 12 connected to the optical unit 11. The expanded light from this projection lens 12 is reflected by a reflection mirror 13 at a predetermined angle so as to be projected on a screen 14 from the rear side thereof. Consequently, an image is displayed at the image viewing side of the screen 14. (The optical unit 11, the projection lens 12, and the reflection mirror 13 are housed in a cabinet 15. The screen 14 is disposed at the front side (image viewing side) of the cabinet 15. The term “various optical units” described above refers to the optical unit 11, the projection lens 12, the reflection lens 13, and the screen 14 in this embodiment, and the present invention has improved only the optical unit 11, the projection lens 12, and the screen 14 among those optical units.