Projection display and illuminating optical system for it

Abstract

An apparatus which makes dark lines due to a central axis of a cross dichroic prism sufficiently inconspicuous. In a second lens array, minute lenses arranged on the same column include three different types of minute lenses having optical axes at different positions. Each row of the minute lenses consists of one of the three types of minute lenses. Partial light fluxes respectively passing through the minute lenses have optical axes at different positions relative to a center of a lighting area of a liquid-crystal light bulb, so as to illuminate different illumination areas.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a projection display apparatus with colored light combining means and a lighting optical system therefor.2. Discussion of the BackgroundA cross dichroic prism is often used for projection display apparatus that project a color image on a projection screen. For example, in a transmissive liquid-crystal projector, the cross dichroic prism is utilized as colored light combining means that combines three colored rays of red, green, and blue and emits the composite light in a common direction. In a reflective liquid-crystal projector, the cross dichroic prism is utilized as colored light separation means that separated a beam of white light into three colored rays of red, green, and blue and also as colored light combining means that recombines modulated three colored rays and emits the composite light in a common direction. A known example of the projection display apparatus with the cross dichroic pris...

AI Technical Summary

Benefits of technology

In a projection display apparatus, a lighting optical system with two lens arrays each including a plurality of small lenses (hereinafter referred to as an integrator optical system) as specified in WO94 / 22042 is known as the technique for dividing light from a light source into a plurality of partial light fluxes and thereby reducing an in-plane unevenness of the illuminance of light.

As shown by the rough dotted lines in FIGS. 1(A-1) and 1(B-1), light fluxes passing through a central axis 5 (along the y direction in the drawing) of the cross dichroic prism 4 are projected at positions Pa and Pb on the screen 7. As discussed previously in the prior art, scattering of the rays and no-reflection of the light to be reflected in the gaps between reflection films in the vicinity of the central axis 5 reduce the quantity of light passing through the vicinity of the central axis 5. As shown in FIGS. 1(A-2) and 1(B2), the reduction causes dark lines DLa and DLb, which have the lower luminance than the area around luminance on the projection screen 7.

As discussed previously, the partial light fluxes passing through the M small lenses arranged on the same column in the first and the second lens arrays 1 and 2 respectively form dark lines at substantially the same position on the projection screen 7. The degree of darkness of each resulting dark line is substantially equal to the summation of the degree of darkness of the dark lines formed by the respective small lenses. A desired arrangement accordingly causes dark lines to be formed at different positions on the projection screen 7 by the respective partial light fluxes passing through the M small lenses. Although increasing the total number of dark lines, this arrangement decreases the degree of darkness per each dark line, thereby making each dark line sufficiently inconspicuous. It is, however, not required to cause all the dark lines to be formed at different positions by the respective partial light fluxes passing through the M small lenses. One preferable application accordingly causes only part of the dark lines to be formed at different positions.

Problems solved by technology

FIG. 19 shows a problem arising in the case of utilizing the cross dichroic prism 48.

A similar problem arises in a cross dichroic mirror that includes two dichroic mirrors that are arranged in an X shape and respectively have selective reflection films, such as a red reflection film and a blue reflection film.

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