JP2926891B2 - Lighting device for oblique projection optical system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an oblique projection display device, and more particularly to an oblique projection optical system illumination device suitable for projecting a video image, a computer image, or the like in an enlarged manner.

(Prior art) Recently, a display device using a transmission type or reflection type dot matrix liquid crystal (hereinafter referred to as a light valve) has been used.
Attention has been paid to a magnified projection system in which an image displayed on the light valve is magnified and projected on a screen to be displayed as a large screen.

This is due to the limited size of the image display due to the cathode ray tube (CRT). To increase the screen size, the size of the cathode ray tube itself must be increased. In practice, the size is limited to about 40 inches. This is in order to respond to a request to obtain an image.

On the other hand, in order to increase the area of the light valve itself, it is not easy to obtain a large-sized liquid crystal display device having no defects in manufacturing, and even if obtained, it becomes extremely expensive.

For this reason, if a transmissive (or reflective) light valve is used to magnify and project an image displayed thereon, a powerful large screen can be obtained without being limited by the size of the screen. It is possible.

Therefore, a display type display device in which an optical system for magnifying and projecting using a light valve is housed in a cabinet, and a rear surface is projected on a screen provided on the front of the cabinet so that an enlarged image can be viewed from the front of the cabinet. Has been provided.

A conventional rear-projection display device using a light valve of this type is, for example, as disclosed in Japanese Utility Model Laid-Open No. 1-85778, in which a transmissive liquid crystal panel is illuminated from a light source and an image displayed on the liquid crystal panel is displayed. Is magnified by a projection lens, the optical path is changed by a reflection mirror, and the light is guided to the back of the screen. In this way, the entire projection optical system is housed in the cabinet, can be moved to an arbitrary place, and the image on the screen can be viewed even in a bright room.

(Problems to be Solved by the Invention) However, when the display device configured to enlarge and project the light on the screen using the light valve as described above, the amount of light transmitted through the light valve is greatly reduced, so that the illumination reaching the screen is reduced. It is inevitable that the amount of light will be significantly reduced and the image projected on the screen will be dark. Even if the light amount of the light source of the illumination device is increased, the effect cannot be obtained unless the light can be effectively guided on the screen.

In particular, when the oblique projection method as shown in FIG. 13 is employed with the intention of reducing the depth dimension of the display device using the light valve with respect to the screen of the cabinet, the above point is further reduced. Is a problem. This optical system includes an illuminating device 1, a light valve 2, a first lens 3, an imaging surface 4, a second lens 5, and a screen 6, and the first lens 3 and the second lens 5 are shaped like "C". The image formed on the image forming surface 4 by the first lens 3 and is obliquely projected on a screen 6 arranged on the side opposite to the inclination of the image forming surface 4 with respect to the optical axis 7 and enlarged. An image is obtained. In this case, the optical path from the second lens 5 to the screen 6 is bent by a reflection mirror, and the screen 6 is provided on the front of the cabinet and guided to the back of the cabinet, thereby achieving compactness. A display device using rear projection can be obtained as a simple optical system.

When such an optical system is employed, the optical axis of the first lens 3 and the second lens 5 has an angle and is obliquely incident on the lens, so that the amount of diffused light in the illumination light from the illumination device 1 increases, The rate of decrease in the amount of light reaching the screen 6 increases.

In view of the above, the present invention provides an illumination device of an oblique projection optical system that can guide the loss of illumination light from the illumination device to the screen with less light loss, and can prevent an image on the screen from being darkened. It is done for the purpose of.

(Means for Solving the Problems) As means for solving the problems of the prior art described above, the present invention is arranged such that it is inclined at a required angle with respect to the surface of a light valve arranged to be illuminated by illumination means. First
A lens, an image plane arranged at an image forming position of the first lens, and a lens arranged at a required angle to the image plane, distorting distortion caused by the first lens, and forming a required angle on the screen. An illumination system having a second lens for obliquely projecting light from the light source, wherein the illuminating means includes a condenser lens for condensing light from the light source between the light source and the light valve. Between the first lens and the first lens
Having a focal point at or near the object-side focal position of the lens,
The first lens enters the second lens as a substantially parallel beam.

(Operation) The image formed on the light valve is illuminated through the condenser lens by the light from the light source of the illuminating means behind it, a real image is formed on the image forming surface by the first lens, and this image is formed by the second lens. It is enlarged and projected diagonally on the screen.
At this time, the light emitted from the light source of the illuminating means is condensed by the condenser lens, condensed near the object surface side focal position of the first lens, enters the first lens, and thereby emits light flux from the first lens. Become substantially parallel beams and enter the second lens. As a result, the illumination light beam emitted from the second lens is applied to a substantially entire area of the screen, and vignetting does not occur, so that the light from the light source can be used effectively.

(Embodiment) Hereinafter, the present invention will be described with reference to an embodiment shown in FIG. 1 to FIG.

FIG. 1 shows an embodiment in which the oblique projection display device according to the present invention is in a movable form, and FIG. 2 shows a longitudinal section thereof.

In this embodiment, a box-shaped cabinet having a small depth D is used.
10, a projection optical system 11 in the cabinet 10, a rear projection type screen 12 provided on the front surface of the cabinet 10, and a light beam emitted from the projection optical system 11 for guiding the light beam emitted from the projection optical system 11 to the rear surface of the screen 12. And the first and second reflection mirrors 13 and 14.

The projection optical system 11 used in the present invention has an illumination device 15 and an original optical system as shown in FIG. 3 (A) as an example of a transmission type optical system and FIG. 3 (B) as an example of a reflection type optical system. It comprises an example of a light valve 16, a first lens 17, an imaging surface 9, and a second lens 19 as a means for obtaining an image.

The light valve 16 uses a transmission type or reflection type dot matrix liquid crystal.
Is installed at a required angle with respect to
At a position where the image of the light valve 7 is formed by the lens 8, an image forming surface 18 is provided so as to be inclined to the opposite side to the light valve 7 with respect to the optical axis 20.

In the case of the transmission type, as shown in FIG.
A second lens 19 having an optical axis 21 bent at the image plane 18 with respect to the optical axis 20 is disposed with the image plane 18 interposed therebetween, and the first lens 18 and the second lens 19 Arrangement. The image formed on the image plane 18 is enlarged through the second lens 19 and is enlargedly projected onto the screen 12 inclined to the opposite side to the image plane 18 from an oblique direction. In the case of the reflection type, as shown in FIG. 3B, the imaging surface 18 is a reflection mirror (a part of which is enlarged in FIG. 3C), and a second lens 19 is provided on the reflection optical path. Be placed. As shown in FIG. 4 (A), for example, a micro-reflection surface 22, 22,..., Which is long in the horizontal direction and narrow in the depth direction, has a vertical length. The light from the first lens 17 is reflected by the minute reflecting surfaces 22, 22.
Are formed so as to reflect toward the first lens 19. It is preferable to use such a reflection means as an image forming surface because the loss of light amount is small. A screen may be used.

The illumination device 15 includes a light source 23, a parabolic or elliptical reflector 24 at which the light source 23 is located at a focal position, and a condenser lens 25 installed between the light source 23 and the light valve 16. The condenser lens 25 has a focal point 26 on the object plane side of the first lens 17 or a focal point 27 in the vicinity thereof. That is, the illumination optical path of the illumination device 15 and the first and second lenses 17, 1
The relationship with 9 is as shown in FIG. The light from the light source 23, which is reflected by the reflector 24 of the lighting device 15 and converted into parallel light, enters the condenser lens 25, and the light beam emitted from the condenser lens 25 covers the entire area of the light valve 16; It has a focal point 27 near the focal point 26 on the object plane side of the lens 17, and then diffuses and enters the first lens 17. The illuminating light beam 28 emitted through the first lens 17 becomes a substantially parallel beam including the image plane 18, enters the second lens 19, is refracted by the second lens 19, and has a focal point 29 on the image space side. After being condensed in the vicinity, the light is irradiated to a region including the entire area of the screen 12.

The screen 12 is incident so that a light beam projected obliquely (for example, at an incident angle of 60 °) from the rear surface of the screen 12 is not partially transmitted in the direction in which it extends, as shown in FIG. It is desirable to use a prism total reflection screen that directs the light flux in a direction substantially perpendicular to the front surface of the screen 12.

When the above-mentioned projection optical system 11 is viewed geometrically, the first lens 17 side is, as shown in FIG.
Reference numeral 18 denotes the first lens 17 at the imaging positions A ₁ and A ₂ , and the extension 30 of the light valve 16 and the extension 31 of the imaging plane 18 are aligned with the first lens 17.
It crosses at a zero point on a line 32 passing through the center of 17 and perpendicular to the optical axis 20. At this time, the enlargement ratio m ₀ is m ₀ = f / (χ ₁ −f) = (χ ₂ −f) / f = χ ₂ / χ ₁ . In other words, m ₀ = tan α ₂ / tan a ₁ (Scheimpflug's law).

By satisfying the above conditions, the image of the light valve 16 can be formed on the image plane 18 by the first lens 17. However, the image formed on this image plane 18 is the eighth
As shown in the figure, when the original image is an example of a square, this is an image distorted into a trapezoid.

The second lens 19 also enlarges the image on the image plane 18 by the second lens 19 by arranging the image plane 18 and the screen 12 in the same relation as the first lens 17. Image on the screen 12. This image is formed as an image having a magnification obtained by multiplying the magnification of the first lens 17 and the magnification of the second lens 19.

Here, the first lens 17 and the second lens 19 of the projection optical system 11 according to the present invention satisfy the following conditions.

That is, as shown in FIG. 7 (A), the normal to the optical axis 20 at the focal position f ₁ of the image space side of the first lens 17
Point C _{2 where} 33 intersects with extension line 31 of imaging surface 18 and second lens
Its perpendicular 34 to the optical axis 21 and the C ₃ point intersects the extension 31 of the imaging surface 18 is configured to conform 19 at the focal position f ₂ of the object space side.

In this case, as in the FIG. 7 (B), also the optical axis 21 of the optical axis 20 and the second lens 19 of the first lens 17 is not shifted in the image plane 18, the point C ₂ and C ₃ is one I just want to. This is the case where the image forming surface 18 is a reflecting surface as shown in FIG. 3C as shown in FIG. 7C and an optical system for guiding the light beam reflected by this reflecting surface to the screen 12 is used. It is the same as above.

By satisfying the above conditions, a normal image without trapezoidal distortion could be obtained on the screen 12 as shown in FIG.

 The analysis results are described below for the reason.

 First, the change in the image of the square screen will be considered.

In Figure 10, when the intersection between the focal plane and the object plane and C _1, It is.

The size of the object and the image in the directions shown in FIGS.
_1, when upsilon _2, magnification mυ of upsilon direction, Let u ₁ and u ₂ be the sizes of the object and the image in the u direction shown in FIG. Magnification defined as The magnification m ′ _{0 in the} u direction is U ₁ in FIG. 11, in upsilon ₁ face looking at the straight line that u ₁ = a, It turns out that it becomes a straight line of the same shape as.

Next, looking at the straight line of υ ₁ = b, On the image plane side, Here, the trapezoidal distortion generated in the optical system including the first lens 17 is corrected by the optical system including the second lens 19. In this optical system, the symbols are denoted by 3,4, and represented by μ instead of the magnification m, Becomes The optical axis as in the Fig. 12 in thisゝis when passing through A _2, so that the put and u ₃ = -u _2. Note that there is no need to consider the υ direction because there is no asymmetry in the vertical direction.

After all In general, a trapezoidal distortion type image is obtained. However, if g ₃ = m ′ ₀ g ₁ = g ₂ , the trapezoidal distortion disappears.

In the present invention, the first lens 17 is a reduction lens,
The elongation rate is set so as to be canceled by the elongation rate of the second lens 19.

Given the elongation rate σ and the main magnification m _0, the angles α ₁ and α _{2 in} FIG. 6 are determined, Since the elongation rate σ does not exceed the main magnification m ₀ , m ₀ >
σ.

Therefore, in the first lens 17, the elongation rate is temporarily set to 1 / σ.
Then, by returning the elongation rate to σ by the second lens 19, an image without trapezoidal distortion and elongation on the screen 13 can be obtained.

The projection optical system 11 is configured such that the optical axis 20 of the first lens 17 is
Although the case where the optical axis 21 of the lens 19 is arranged to be bent has been described, the optical axes 20, 21 are arranged on the same axis as shown by a dotted line in FIG. By placing the center of the light valve 16 and the center of the screen 12 on the axis thereof and maintaining the relationship of α + α ₄ = α ₄ ′ in the figure, it is possible to obtain a projection optical system having the same effect as described above.

With such an arrangement, the burden on the lenses 17 and 19 can be reduced, and reasonable use of light can be achieved.

Referring to the embodiment shown in FIGS. 1 and 2, in this case, the projection optical system 11 is placed above the inside of the cabinet 10,
The light beam emitted from the projection optical system 11 is transmitted via a relay mirror 35 to a first reflection mirror installed at the bottom of the cabinet 10.
13, a second reflecting mirror 14 receiving the reflected light from the first reflecting mirror 13 is placed on the rear inner surface facing the screen 12 almost parallel to the rear surface of the screen 12, and the second reflecting mirror 14 is moved from the second reflecting mirror 14 to the screen. The image formed on the light valve 16 is projected on the screen 12 as an enlarged image by projecting from the oblique direction on the back surface of the 12.

By adopting the above arrangement structure, even when obliquely projecting from the back of the screen 12, a regular image can be projected without causing trapezoidal distortion and elongation in the enlarged image formed on the screen 12. However, the depth dimension D of the cabinet 10 can be greatly reduced, and an ultra-thin, large-screen display device can be obtained.

〔The invention's effect〕

As described above, according to the present invention, even if an oblique projection system is adopted for the projection optical system on the screen, the illumination light from the light source by the condenser lens of the illumination device is transmitted from the first lens to the second lens. The light from the light source can be used for illumination without waste, and the brightness of the image on the screen can be significantly increased. Also, since the light is incident on the first lens after being focused once before the first lens, the first lens may be a small-diameter only small-angle lens.
Since the second lens also enters the first lens as substantially parallel light, similarly small-diameter lenses can be used, and the constraints on these lenses can be remarkably reduced.

If an oblique projection optical system as in the illustrated embodiment is used, there is no trapezoidal distortion in the image on the screen, and there is no stretching between the images, and the quality of the image can be significantly improved. Also, even when projected obliquely onto the screen, no distortion or stretch occurs in the image, so when incorporated into a cabinet to form a display-type display device, the volume of the cabinet, particularly the depth, can be greatly reduced, A compact display device can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of the present invention, FIG. 2 is a longitudinal sectional view of the specific embodiment, and FIGS. 3 (A), (B) and (C).
FIG. 4A is an explanatory view of a projection optical system, FIG. 4A is an enlarged schematic cross-sectional view of a part of an example of the reflecting means when the reflecting means is used on the image forming surface in FIG. 3, and FIG. Is a partially enlarged view showing an example of the screen, FIG. 5 is an explanatory view of the operation of the illumination optical system, FIG. 6 is an explanatory view showing the projection optical system in FIG. 3 in geometrical optics, and FIG. , (B) and (C) are geometrical optical analysis diagrams of the projection optical system according to the present invention, FIG. 8 is an explanatory diagram showing trapezoidal distortion of an image formed by the first lens, and FIG.
FIG. 10 to FIG. 12 are explanatory diagrams showing an image corrected by a lens, FIG. 10 to FIG. 12 are diagrams for explaining that trapezoidal distortion does not occur, and FIG. 13 is an explanatory diagram of an oblique projection optical system. 1,15 lighting device, 2,16 light valve, 3,17 first lens, 4,18 image forming surface (reflecting means), 5,19 second
Lens, 6,12 ... Screen, 23 ... Light source, 24 ... Reflector, 25 ... Condenser lens.

Claims (1)

(57) [Claims] A first lens disposed at a predetermined angle with respect to a surface of a light valve arranged so as to be illuminated by an illuminating means; and an image forming surface arranged at an image forming position of the first lens. An optical system comprising: a second lens disposed at a required angle to the image plane and configured to correct distortion caused by the first lens and project obliquely at a required angle onto a screen. The means comprises a condensing lens between the light source and the light valve for condensing light from the light source, the condensing lens being located between the light valve and the first lens and the object-side focal position of the first lens. An illumination device for an oblique projection optical system, wherein the illumination device has a focal point in the vicinity thereof and enters the second lens as a substantially parallel beam at the first lens.