JP2005258179A - Projection lens and projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a projection lens that can be easily manufactured and processed, obtain a projection image with a low cost, smoothness, and a feeling of roughness, and a projector including the projection lens.
A projection lens 114 included in a projector 100, which is a prism that is a low-pass filter provided at a pupil position of the projection lens 114, a position conjugate to the pupil position, a vicinity of the pupil position, or a vicinity of the conjugate position. It has a group 210.
[Selection] Figure 2

Description

  The present invention relates to a projection lens and a projector including the same, and more particularly to a projector using a liquid crystal spatial light modulator.

  As an image display device, a dot matrix image display device such as a liquid crystal panel (liquid crystal display device), a CRT display device, or a plasma display device is often used. In the dot matrix image display device, a light blocking portion called a black matrix is provided in a region between pixels in order to reduce unnecessary light. In recent years, as a usage mode of an image display device, a large screen is often observed from a relatively short distance. For this reason, the observer may recognize the black matrix image. As described above, since the conventional dot matrix image display device is a black matrix image, the image quality is deteriorated such as an image with less smoothness or an image having roughness.

  In order to improve image quality, a configuration in which a dot matrix image display device and an optical element having a low-pass filter function, such as a diffraction grating, a diffusion plate, and a crystal plate are combined is proposed (for example, Patent Document 1). Patent Document 2, Patent Document 3).

JP 7-28046 A JP-A-8-122709 Japanese Patent Laid-Open No. 10-288754

  In the configurations proposed in Patent Document 1, Patent Document 2, and Patent Document 3 described above, an optical element having a low-pass filter function is disposed between the dichroic mirror and the projection lens, or between the liquid crystal panel and the projection lens. ing.

  When an optical element is disposed between the dichroic mirror and the projection lens, the area of the optical element increases. An optical element having a low-pass filter function needs to be formed with high processing accuracy and a predetermined surface roughness. For this reason, if the optical element is enlarged, it becomes difficult to manufacture and process. When an optical element is disposed between the liquid crystal panel and the projection lens, a three-plate projector requires three optical elements. For this reason, a manufacturing cost becomes high and is a problem. Further, as described above, there is a problem that it becomes difficult to easily manufacture and process the optical element.

  The present invention has been made in order to solve the above-mentioned problems, and can be easily manufactured and processed, and can provide a projection image that can be obtained at a low cost with a smooth and reduced feeling of roughness, and the projection lens. It aims at providing a projector provided with.

  In order to solve the above problems and achieve the object, according to the first aspect of the present invention, there is provided a projection lens provided in the projector, the pupil position of the projection lens, a position conjugate to the pupil position, the vicinity of the pupil position, or A projection lens having a low-pass filter provided in the vicinity of a conjugate position can be provided. Here, the low-pass filter refers to an optical element such as a diffraction grating, a diffusion plate, a crystal plate, and a prism element having a refractive surface. The pupil density of the projection lens and the vicinity thereof, or a position conjugate to these positions has the highest light density. In other words, the light beam diameter is smallest at the pupil position. Accordingly, the size of the low-pass filter disposed at the pupil position can be reduced. For this reason, a low-pass filter can be easily manufactured and processed with high processing accuracy. As a result, the projection lens itself provided with the low-pass filter can be easily manufactured and processed with high processing accuracy. In addition, the light beam diameter at the pupil position is smaller than the light beam diameter at other positions. For this reason, a small projection lens with a small low-pass filter can be obtained. Further, the projection lens only needs to have one low-pass filter regardless of the number of spatial light modulators. For this reason, an inexpensive projection lens can be obtained.

  Further, as described above, the light beam density is maximized at the pupil position. For this reason, when a low-pass filter is disposed at the pupil position, the function of the low-pass filter can be efficiently exhibited. As a result, the observer can recognize a good projected image with a reduced black matrix, for example. Furthermore, by arranging a low-pass filter at or near the pupil position of the projection lens, it is possible to reduce local non-uniformity of the projected image due to foreign matters such as dust.

  According to a second aspect of the present invention, there is provided a projector comprising: a light source that supplies illumination light; a spatial light modulation device that modulates illumination light according to an image signal; and the projection lens described above. it can. As described above, a high-quality projected image with a reduced black matrix can be obtained. Further, the projection lens can be easily processed with high accuracy at a low price. As a result, a projector body equipped with this projection lens can be manufactured at a low price. The present invention is particularly suitable for a projector having a liquid crystal type spatial light modulation device.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(Explanation of the entire projector)
First, a schematic configuration of a projector according to Embodiment 1 of the present invention will be described with reference to FIG. Next, a characteristic configuration of the present embodiment will be described with reference to FIG. First, in FIG. 1, an ultra-high pressure mercury lamp 101 as a light source unit includes red light (hereinafter referred to as “R light”) as first color light and green light (hereinafter referred to as “G light”) as second color light. And blue light (hereinafter referred to as “B light”) which is the third color light. The integrator 104 uniformizes the illuminance distribution of the light from the ultrahigh pressure mercury lamp 101. The light whose illuminance distribution is made uniform is converted into polarized light having a specific vibration direction, for example, s-polarized light by the polarization conversion element 105. The light converted into the s-polarized light is incident on the R light transmitting dichroic mirror 106R constituting the color separation optical system. Hereinafter, the R light will be described. The R light transmitting dichroic mirror 106R transmits R light and reflects G light and B light. The R light transmitted through the R light transmitting dichroic mirror 106 </ b> R enters the reflection mirror 107. The reflection mirror 107 bends the optical path of the R light by 90 degrees. The R light whose optical path is bent enters the spatial light modulator for first color light 110R that modulates the R light as the first color light according to the image signal. The spatial light modulator for first color light 110R is a transmissive liquid crystal display device that modulates R light according to an image signal. Since the polarization direction of the light does not change even if it passes through the dichroic mirror, the R light incident on the first color light spatial light modulator 110R remains as s-polarized light.

  The first color light spatial light modulator 110R includes a λ / 2 phase difference plate 123R, a glass plate 124R, a first polarizing plate 121R, a liquid crystal panel 120R, and a second polarizing plate 122R. The detailed configuration of the liquid crystal panel 120R will be described later. The λ / 2 phase difference plate 123R and the first polarizing plate 121R are arranged in contact with a light-transmitting glass plate 124R that does not change the polarization direction. Thereby, the problem that the first polarizing plate 121R and the λ / 2 phase difference plate 123R are distorted by heat generation can be avoided. In FIG. 1, the second polarizing plate 122R is provided independently. However, the second polarizing plate 122R may be disposed in contact with the exit surface of the liquid crystal panel 120R or the entrance surface of the cross dichroic prism 112.

  The s-polarized light incident on the first color light spatial light modulator 110R is converted into p-polarized light by the λ / 2 phase difference plate 123R. The R light converted into p-polarized light passes through the glass plate 124R and the first polarizing plate 121R as it is and enters the liquid crystal panel 120R. The p-polarized light incident on the liquid crystal panel 120R is converted into s-polarized light by modulation according to the image signal. The R light converted into s-polarized light by the modulation of the liquid crystal panel 120R is emitted from the second polarizing plate 122R. In this way, the R light modulated by the first color light spatial light modulator 110R is incident on the cross dichroic prism 112 which is a color synthesis optical system.

  Next, the G light will be described. The light paths of the G light and the B light reflected by the R light transmitting dichroic mirror 106R are bent by 90 degrees. The G light and the B light whose optical paths are bent enter the B light transmitting dichroic mirror 106G. The B light transmitting dichroic mirror 106G reflects the G light and transmits the B light. The G light reflected by the B light transmitting dichroic mirror 106G is incident on the second color light spatial light modulator 110G that modulates the G light, which is the second color light, according to the image signal. The spatial light modulator for second color light 110G is a transmissive liquid crystal display device that modulates G light according to an image signal. The second color light spatial light modulator 110G includes a liquid crystal panel 120G, a first polarizing plate 121G, and a second polarizing plate 122G. Details of the liquid crystal panel 120G will be described later.

  The G light incident on the second color light spatial light modulator 110G is converted into s-polarized light. The s-polarized light incident on the second color light spatial light modulator 110G passes through the first polarizing plate 121G as it is and enters the liquid crystal panel 120G. The s-polarized light incident on the liquid crystal panel 120G is converted into p-polarized light by modulation according to the image signal. The G light converted into p-polarized light by the modulation of the liquid crystal panel 120G is emitted from the second polarizing plate 122G. Thus, the G light modulated by the second color light spatial light modulator 110G enters the cross dichroic prism 112, which is a color synthesis optical system.

  Next, the B light will be described. The B light transmitted through the B light transmitting dichroic mirror 106G passes through the two relay lenses 108 and the two reflection mirrors 107, and the third light that modulates the B light as the third color light in accordance with the image signal. The light enters the color light spatial light modulator 110B. The spatial light modulator for third color light 110B is a transmissive liquid crystal display device that modulates B light according to an image signal.

  The reason why the B light passes through the relay lens 108 is that the optical path length of the B light is longer than the optical path lengths of the R light and the G light. By using the relay lens 108, it is possible to guide the B light transmitted through the B light transmitting dichroic mirror 106G directly to the third color light spatial light modulator 110B. The spatial light modulator for third color light 110B includes a λ / 2 phase difference plate 123B, a glass plate 124B, a first polarizing plate 121B, a liquid crystal panel 120B, and a second polarizing plate 122B. Note that the configuration of the spatial light modulation device 110B for the third color light is the same as the configuration of the spatial light modulation device 110R for the first color light described above, and thus detailed description thereof is omitted.

  The B light incident on the spatial light modulator for third color light 110B is converted into s-polarized light. The s-polarized light incident on the third color light spatial light modulator 110B is converted into p-polarized light by the λ / 2 phase difference plate 123B. The B light converted into p-polarized light passes through the glass plate 124B and the first polarizing plate 121B as it is, and enters the liquid crystal panel 120B. The p-polarized light incident on the liquid crystal panel 120B is converted into s-polarized light by modulation according to the image signal. The B light converted into the s-polarized light by the modulation of the liquid crystal panel 120B is emitted from the second polarizing plate 122B. The B light modulated by the third color light spatial light modulator 110B is incident on the cross dichroic prism 112 which is a color synthesis optical system. As described above, the R light transmitting dichroic mirror 106R and the B light transmitting dichroic mirror 106G constituting the color separation optical system convert the light supplied from the ultrahigh pressure mercury lamp 101 into the R light that is the first color light, the second light, and the second light. The light is separated into G light, which is colored light, and B light, which is third color light.

  The cross dichroic prism 112, which is a color synthesis optical system, is configured by arranging two dichroic films 112a and 112b perpendicularly to an X shape. The dichroic film 112a reflects B light and transmits R light and G light. The dichroic film 112b reflects R light and transmits B light and G light. As described above, the cross dichroic prism 112 has the R light and G light modulated by the first color light spatial light modulation device 110R, the second color light spatial light modulation device 110G, and the third color light spatial light modulation device 110B, respectively. And B light. The projection lens 114 projects the light combined by the cross dichroic prism 112 onto the screen 116. Thereby, a full color image can be obtained on the screen 116.

  As described above, the light incident on the cross dichroic prism 112 from the first color light spatial light modulator 110R and the third color light spatial light modulator 110B is set to be s-polarized light. The light incident on the cross dichroic prism 112 from the second color light spatial light modulator 110G is set to be p-polarized light. In this way, by changing the polarization direction of the light incident on the cross dichroic prism 112, the light emitted from the spatial light modulators for the respective color lights in the cross dichroic prism 112 can be effectively combined. The dichroic films 112a and 112b are usually excellent in the reflection characteristics of s-polarized light. For this reason, R light and B light reflected by the dichroic films 112a and 112b are s-polarized light, and G light transmitted through the dichroic films 112a and 112b is p-polarized light.

(Configuration of low-pass filter)
Next, a schematic configuration of the projection lens 114 will be described with reference to FIG. The projection lens 114 magnifies and projects the modulated light from the spatial light modulators 110R, 110G, and 110B for each color light onto the screen 116. A prism group 210, which is a low-pass filter, is disposed at the pupil position, which is the conjugate position of the stop. FIG. 3A shows a perspective configuration of the prism group 210. A prism group 210 made up of a plurality of prism elements 211 is formed on the exit side surface of the transparent plate 206 made of glass or transparent resin.

  FIG. 3B illustrates a relationship between the black matrix forming layer 203 in the R-color light spatial light modulator 110R and the prism group 210 in the projection lens 114, for example. Here, in order to facilitate understanding, the illustration of other components other than the black matrix forming layer 203 and the prism group 210 is omitted. The R light transmitted through the opening 230 corresponding to one pixel portion travels as a conical divergent light. The R light is incident on at least some of the prism groups 210. The prism group 210 includes a prism element 211 having at least a refractive surface 212 and a flat portion 213. The flat portion 213 is a surface substantially parallel to the surface 230a where the opening 230 corresponding to the pixel portion is formed. A plurality of prism elements 211 are regularly arranged at a constant period to constitute a prism group 210.

  Thereby, the flat part 213 transmits the R light from the opening 230 as it is. The refraction surface 212 refracts and transmits the R light from the opening 230. The refracting surface 212 is a projection image of the black matrix portion 220 that is a light shielding portion on the screen 116 that is a projection surface that is a predetermined distance away from the prism group 210 that is a refracting portion. The direction of the refracting surface 212 that leads to the black matrix image, and the tilt angle. As a result, an aperture image is formed on the screen 116 in a superimposed manner on the black matrix image region. Therefore, the observer can reduce the recognition of the black matrix image on the screen 116. Thereby, the observer can observe a smooth image with a reduced feeling of roughness.

  FIG. 4 shows the concept of functions of the low-pass filter. In an imaging apparatus such as a CCD, electrical processing is performed on a captured image signal using a low-pass filter. On the other hand, in the projector, in order to reduce the black matrix image of the projected image, instead of electrical processing, the light emitted from the spatial light modulator is optically processed as described above. FIG. 4 shows the intensity distribution of the projected image on the screen 116. The horizontal axis in FIG. 4 indicates an arbitrary position x, and the vertical axis indicates the intensity I (unit: arbitrary) of the projected image. For example, consider a case where a uniform white image without gradation is projected. In FIG. 4, when the low-pass filter is not used, an opening image having a high intensity and a black matrix image having a low intensity are repeated in a rectangular shape as indicated by a waveform a indicated by a solid line. In the state of the waveform a, the observer recognizes the black matrix image.

  Then, by arranging a low-pass filter such as the above-described prism group 210 at the pupil position of the projection lens 114, the intensity distribution of the projected image changes like a curve b indicated by a broken line or a curve c indicated by a one-dot chain line. To do. Both the curve b and the curve c are sinusoidal and have different maximum amplitude values. The maximum amplitude value of the curve c is smaller than the maximum amplitude value of the curve b. At this time, the observer can observe a smoother and more seamless projected image in the intensity distribution like the curve c than in the intensity distribution of the curve b. Most preferably, the intensity distribution of the aperture image and the intensity distribution of the black matrix image are substantially the same as the straight line d shown by the solid line.

  In the above embodiment, the prism group 210 is arranged at the pupil position of the projection lens 114. However, the present invention is not limited to this, and the position where the prism group 210 that is a low-pass filter is disposed may be a position conjugate to the pupil position, a vicinity of the pupil position, or a vicinity of the conjugate position. Furthermore, the low-pass filter is not limited to the above-described prism group. For example, a diffraction grating, a diffusion plate, a crystal plate, or the like can be used as the low-pass filter.

1 is a schematic configuration diagram of a projector according to a first embodiment of the invention. 1 is a schematic configuration diagram of a projection lens of Example 1. FIG. FIG. 3 is a perspective view of a prism group according to the first embodiment. FIG. 3 is a cross-sectional view of the prism group according to the first embodiment. Explanatory drawing of the function of a low-pass filter.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 Projector, 101 Super high pressure mercury lamp, 104 Integrator, 105 Polarization conversion element, 106R R light transmission dichroic mirror, 106GB B light transmission dichroic mirror, 107 Reflection mirror, 108 Relay lens, 110R Spatial light modulation device for 1st color light, 110G Spatial light modulator for second color light, 110B Spatial light modulator for third color light, 112 Cross dichroic prism, 112a, 112b Dichroic film, 114 Projection lens, 116 Screen, 120R, 120G, 120B Liquid crystal panel, 121R, 121G, 121B First polarizing plate, 123R, 123B λ / 2 phase difference plate, 124R, 124B glass plate, 210 prism group, 211 prism element, 212 refracting surface, 213 flat portion, 220 black mask Helix portion, 230 opening

Claims (2)

A projection lens provided in the projector,
A projection lens comprising a pupil position of the projection lens, a position conjugate to the pupil position, a vicinity of the pupil position, or a vicinity of the conjugate position. A light source for supplying illumination light;
A spatial light modulator that modulates the illumination light in accordance with an image signal;
A projector comprising the projection lens according to claim 1.

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