JPH05281612A - Optical device for illumination - Google Patents

Abstract

PURPOSE:To obtain the illumination device which is useful for a slide projector, liquid crystal video projector, etc., is extremely high in the efficiency of utilizing light and produces luminous fluxes having good parallelism. CONSTITUTION:A ligh5 source 1 is placed in the first focal position of a spheroid mirror 2 and a spherical surface mirror 3 is arranged in such a manner that this mirror faces the mirror 2 and that its reflection surfaces come onto the second focus of the spheroid. An opening window 4 for emission of the luminous fluxes is provided near the second focal position of the spherical surface mirror 3 and further, a condenser lens 5 is arranged in front (illumination side) thereof. The size of the opening window 4, designated as W and the focal length of the lens 5, designated a Fc, are so determined as to satisfy the relation 1 deg.<=tan<-1>(W/2Fc)<=6 deg..

Description

Detailed Description of the Invention

[0001]

The present invention relates to a slide projector,
The present invention relates to a lighting device useful for liquid crystal video projectors, OHP sheet projectors, and the like.

[0002]

2. Description of the Related Art Hitherto, as this type of device, an illumination device has been used which is a combination of a light source such as a halogen lamp, a xenon lamp, a metal halide lamp, a parabolic mirror or a spheroidal mirror, and a condenser lens. (See, for example, “Design of Projection Television”, Chapter 3, Section 1 published by Trikeps Corporation).

[0003]

However, in any case in the prior art, the light emitted from the light source which emits light in a direction other than the direction of the paraboloidal mirror or spheroidal mirror is not effectively used as the illumination light. However, there is a problem that the utilization efficiency of the illumination light is low with respect to the total amount of light emitted from the light source.

[0004]

A light source that emits light in a wide range with a solid angle of approximately 2π or more from a range of a spherical region having a radius of approximately 10 mm or less, and a spheroid disposed behind the light source. An illumination optical system is configured by a body mirror, a spherical mirror and a lens arranged in front of the light source, and mutual relations and specifications of these parts are set as follows. That is,
The light source is located near the first focus of the elliptical mirror and near the center of curvature of the spherical mirror so that most of the light rays emitted from the light source are focused near the second focus of the elliptical mirror. Also, the radius of the spherical mirror is set to the first and second of the elliptical mirror.
The distance between the focal points is made almost equal, and the size W near the center
An opening of (diameter when circular, length of one side when rectangular) is provided. When the focal length of the lens is Fc, W and Fc are set to satisfy the relationship of 1 degree ≦ tan ⁻¹ (W / 2Fc) ≦ 6 degrees.

[0005]

According to the present invention, in addition to the illumination optical system including the light source and the spheroidal mirror, a spherical mirror whose center of curvature is located at the light source position is provided on the front surface of the illuminating optical system. The luminous flux emitted to is reflected by the spherical mirror, returns to the light source position again, passes through the light source as it is, and then is reflected by the spheroidal mirror.

Therefore, such a light beam originally emitted in a direction different from the direction of the spheroidal mirror is reflected by the spherical mirror and then travels in the same optical path as the light originally emitted in the direction of the spheroidal mirror. Since all of these light fluxes can be taken out through an opening window provided in a part of the spherical mirror, by placing a lens (condenser lens) at that position, collimated illumination light suitable for slide projectors, liquid crystal projectors, etc. Alternatively, slightly converged illumination light can be obtained with extremely high illumination utilization efficiency.

Further, the size W of the spherical mirror opening,
By setting the relationship with the focal length Fc of the condenser lens as 1 degree ≦ tan ^-1 (W / 2Fc) ≦ 6 degrees, it is possible to obtain high-brightness illumination light with high utilization efficiency of illumination light and high parallelism. it can.

[0008]

FIG. 1 shows an embodiment of the present invention. In the figure, reference numeral 1 denotes a light source, and a halogen lamp, a xenon lamp, a metal halide lamp, or the like having a light emitting portion within a spherical region having a diameter of several millimeters to several tens of millimeters is used. The light source 1 is disposed at the first focus position 21 of the spheroidal mirror 2, and is located behind the light source 1 (the direction in which the illumination light finally travels is called the front, and the opposite side is called the rear). The light rays 10 and 11 emitted in the lateral direction are reflected by the spheroidal mirror 2, and then travel toward the second focal position 22 of the spheroidal mirror 2.

A spherical mirror 3 is arranged so as to surround the front of the light source 1. The spherical mirror 3 is arranged so that its center of curvature coincides with that of the light source 1. Therefore,
Light rays 12 and 13 emitted forward from the light source 1 return to the direction of the light source 1 after being reflected by the spherical mirror 3 and, after passing through the light source position, proceed as if emitted from the light source 1 to the rear, and have a spheroidal surface. After being reflected by the mirror 2, the spheroidal mirror 2 advances toward the second focal position 22.

The position of the spherical surface of the spherical mirror 3 is set so that the second focal position 22 of the spheroidal mirror 2 is on the spherical surface. Further, an opening window 4 is provided on the spherical mirror 3 in the vicinity of the second focus position 22 on the spheroid. The size of this opening window is set so that most of the light rays traveling in the direction of the second focal point 22 can pass therethrough, and is generally the same size as the effective size of the light source 1, or the light source 1 is an ellipse. Second focus position 22 of the mirror
Is approximately the same as the effective size of the image formed in the vicinity of.

In the above apparatus, the light beams emitted from the light source 1, the light beam groups 10, 11 ... Which are emitted rearward and are reflected by the spheroidal mirror 2, and the light beams which are emitted forward and are once reflected by the spherical mirror 3. After that, all the light ray groups 12, 13 ... Reflected by the spheroidal mirror 2 pass through the aperture window 4 provided at the second focal position 22 and proceed.

Therefore, the above-mentioned device including the light source 1, the spheroidal mirror 2, and the spherical mirror 3 behaves as if the aperture window 4 is a secondary light source, and the lens 5 placed in front of the window 5 causes Collimated illumination with high directivity or slightly converged illumination. Incidentally, reference numeral 6 in the figure is a slide for projection.

When the aperture window 4 is a circular aperture having a diameter W and the focal length of the condenser lens 5 is Fc,
The parallelism α of the illumination light is

## EQU1 ## α = tan ^-1 [W / 2Fc] It is represented by (1). When the illumination optical system is used in a projection optical system such as a liquid crystal projector or a slide projector, if the parallelism of the illumination light is low (α is large), there is a disadvantage that a projection lens with a larger aperture is needed, and the like. It is necessary to set the parallelism of light to about α ≦ 6 degrees.

On the other hand, the light source 1 is not a point light source in fact, but has a finite size. Therefore, if the opening window 4 is made too small, light is eclipsed at the window portion, and the light utilization efficiency decreases. Therefore, it is not a good idea to make the value of α smaller than necessary, and it is necessary to make it large enough to increase the utilization efficiency of illumination light.
From this point of view, by setting α within the range of approximately 1 to 6 degrees, it is possible to realize an illumination optical system that is in good conditions in terms of both parallelism and light utilization efficiency. That is,

## EQU00002 ## It can be said that 1 degree.ltoreq.tan ^-1 (W / 2Fc) .ltoreq.6 degrees (2) is a proper condition.

As a typical numerical example, in FIG. 1, the depth Ds of the spheroidal mirror 2 is 35.4 mm, the radius of the mirror Rm is 50 mm, and the radius of the spherical mirror is Rms = 50.
mm (= distance between two focal points of the ellipse Df), diameter W of the opening window 4
= 5.2 mm, the focal length Fc of the condenser lens 5 = 5
With 0 mm, a parallelism α = 3 degrees and an illumination optical system with extremely high light utilization efficiency could be realized.

In FIG. 1, the slide 6 is a liquid crystal panel in the case of a liquid crystal projector. Further, practically, by raising a hole for air circulation in a portion between the spheroidal mirror 2 and the spherical mirror 3 and air-cooling with a fan, it is possible to suppress the temperature rise of the lighting device of the present invention.

[0017]

According to the present invention, most of the luminous flux (12 ', 13', etc. in FIG. 1) emitted from the light source to the front, which cannot be used as a conventional illumination device, is used as illumination light. It is possible to obtain an illuminating device that can be used and is extremely bright and has high utilization efficiency of light emitted from a light source.

Further, at this time, by setting the relationship between the size of the opening window 4 and the focal length of the condenser lens 5 as specified in the present invention, a lighting device having high light utilization efficiency and good parallelism. Can be realized.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 2 spheroidal mirror 3 spherical mirror 4 aperture window 5 lens 6 slide (liquid crystal panel) 10, 11 light beam emitted backward or laterally from light source 12, 13 light beam emitted forward from light source 12 ', 13' conventional Rays not used by the device 21 First focus of spheroid 22 Second focus of spheroid

Claims (1)

[Claims] 1. A light source that emits light in a wide range with a solid angle of approximately 2π or more within a range of a spherical region having a radius of approximately 10 mm or less, and a spheroidal mirror disposed behind the light source. An illumination optical system comprising a spherical mirror and a lens arranged in front of the light source, wherein the light source is located near the first focus of the elliptical mirror and near the center of curvature of the spherical mirror, Most of the light rays emitted from the light source are condensed near the second focus of the elliptical mirror, and the radius of the spherical mirror is substantially equal to the first and second focal lengths of the elliptical mirror, and is large near the center thereof. With an opening of size W (diameter in the case of a circle, length of one side in the case of a rectangle), and when the focal length of the lens is Fc, W and Fc are 1 degree ≦ tan ^-1 (W / 2Fc) ≦ 6 degrees. Illumination optics characterized by satisfying relationships apparatus.