1. Field of the Invention
The present invention relates to an image display apparatus that performs magnified projection of an image supplied from an image generation source to thereby display the image on a light-transmissive projection screen. More particularly, the present invention relates to an image display apparatus that projects an image diagonal to the normal line of a projection screen to thereby form the image on the projection screen of a light-transmissive type, and to a projection screen and a fresnel lens sheet that are to be used in the image display apparatus.
2. Description of the Related Art
Conventionally, there are known so-called projection image display apparatuses that operate such that images formed in an image generation source, such as a liquid crystal display (LCD) device, are magnified and projected on a projection screen by using a projection optical unit. In a projection image display apparatus of that type, it is demanded that magnified images are obtained. Concurrently, it is demanded that the depth dimension of the device is reduced. A technique for satisfying such demands is known such as disclosed in Japanese Unexamined Patent Application Publication No. 2001-264627. The publication discloses a projection optical unit having the configuration that performs magnification and projection onto a projection screen from the direction diagonal to the projection screen. In addition, as described further below, in Japanese Unexamined Patent Application Publication No. 1998-282310, there is disclosed a technique of obtaining uniformity in the brightness of an image projected on a light-transmissive projection screen. The publication discloses forming of a plurality of focal distances of a fresnel lens on the light-transmissive projection screen.
According to the technique disclosed in the Publication No. 2001-264627, as shown in FIGS. 2 to 7, the center of the optical axis of a projection lens unit is positioned at the vicinity of the lower end (or, an outer side of the lower end) of the projection screen. In such an optical system, a fresnel center of a fresnel lens sheet (center point of a concentrically circular fresnel lens) has to be provided at the vicinity of the lower end of the fresnel lens sheet so as to be aligned with the optical axis center of the projection lens unit.
In the case as disclosed in Publication No. 2001-264627, considerations for brightly displaying the image on the projection screen are not taken into account. This is especially important for the reason that in the case where image light is projected onto the projection screen in the diagonal direction from the lower portion in order to reduce the depth of the device, the incident angle of light rays incident on the vicinity of an upper left, right end portion of the projection screen increases, such that light losses are increased thereby to reduce the brightness of the image in the vicinity of the end portion.
As disclosed in Publication No. 1998-282310, there is a case where, in order to brightly display the image on the projection screen, a conjugate point is provided on the image side (image viewing side), and the light rays are thereby directed to a viewer. The conjugate point refers to a point at which the projected image light is focused by the fresnel lens. According to the technique disclosed in Publication No. 1998-282310, considerations regarding the case where, as described above, the fresnel center is positioned at the vicinity of the lower end of the fresnel lens sheet.
The present invention is made in view of the problems described above. Accordingly, an object of the present invention is to provide a technique well suited for reducing the depth of an image display apparatus and concurrently for brightly displaying images on a projection screen.
In order to achieve the object, in the case that the fresnel center is positioned in either the vicinity/outside of a lower end of the fresnel lens sheet or the vicinity/outside of an upper end of the fresnel lens sheet, the present invention uses at least two types of fresnel lenses. More specifically, the invention uses a first fresnel lens portion formed inside a reference circumference with the fresnel center as a center point and a second fresnel lens portion formed outside the reference circumference. In the invention, a distance on an image-side conjugate point of the second fresnel lens portion is shorter than an image-side conjugate point of the first fresnel lens portion. The reference circumference may be a circumference of the fresnel lens that passes through vicinities of points whereat a horizontal centerline halving the fresnel lens sheet in upper and lower directions crosses with left and right ends of the fresnel lens sheet.
The second fresnel lens portion may include distances of a plurality of image-side conjugate points, in which the distances of the image-side conjugate points become gradually short toward the outside from the reference circumference. In addition, where a diagonal dimension of the projection screen is W, the distance of the image-side conjugate point may be about 10 W or longer or in a range of from about 10 W to 25 W. Further, where an angle (fresnel incident angle) formed between light incident on an arbitrary point of the second fresnel lens portion and a normal line of the projection screen is δ, a distance L of the image-side conjugate point at the point may be set to satisfy the conditions of the following equation:
L≧1.0583 exp(0.0387×δ)
According to the configuration described above, an image light ray at a screen corner portion which image light ray are incident at a relatively wide incident angle can be directed to a viewer, consequently enabling the image to be brightly displayed.
Thus, according to the present invention, an image display apparatus is formed to be thin, and concurrently, images can be brightly displayed.
In the accompanying drawings,
Embodiments of the present invention will be described herebelow with reference to the accompanying drawings.
An image generation source 1 displays small images. The image generation source 1 includes reflective or transmissive LC panel, or a light modulator element, such as a display element containing a plurality of small mirrors. The image generation source 1 also may be the one that includes a projection CRT. A projection lens 2, which is a component of a first optical system, projects an image generated by the image generation source 1 onto a projection screen 3. A reflecting mirror 4 is provided in the optical path extending from the projection lens 2 to the projection screen 3 in order to reduce the depth of the image display apparatus. A flexibly curved mirror 5 (“anamorphic aspheric mirror,” hereafter), which is a component of a second optical system, is installed between the projection lens 2 and the reflecting mirror 4. Light incoming from the projection lens 2 is reflected off of the anamorphic aspheric mirror 5, is led to the reflecting mirror 4, is reflected off of the reflecting mirror 4, and is then led to the projection screen 3. These components are housed inside a housing 6 and are fixed in predetermined positions therein. The image generation source 1, the projection lens 2, and the anamorphic aspheric mirror 5 are fixed to an optical system base 7 and are thereby integrated.
Features of components of a projection optical unit according to the present embodiment will be described herebelow with reference to
As shown in
In the case that the image display device 11 is formed of the light modulator element, although illumination systems for the light modulator element, such as lamps, are necessary, the components are omitted from the drawings. The image display device 11 may be of a type, such as a so-called three-plate type, which synthesizes a plurality of images. Also omitted from the drawings are synthesis optical systems such as prisms.
In the example shown in
In the present embodiment, however, mirrors (not shown) are disposed between the anamorphic aspheric mirror 5 and the rear group 13 of the projection lens 2, between the front group 12 and the rear group 13 of the projection lens 2, or in the midway to the front group 12. Thereby, the depth can be prevented from being increased in the manner that the optical axis of the projection lens 2 is bent along the direction substantially perpendicular to the cross section shown in
According to the present embodiment, as shown in
By the above it is meant that the configuration passed through along the optical axis of the projection lens 2 is diagonally incident on the projection screen 3, and the optical axis of the projection lens 2 is provided substantially diagonally with respect to the projection screen 3. In the event of the diagonal incidence of the light ray in the manner described above, there occur not only a so-called trapezoidal distortion, which refers to the case where a projected rectangular shape is changed to a trapezoidal shape, but also various other aberrations not symmetrical with respect to the optical axis. According to the present embodiment, however, such aberrations are compensated for by using the rear group 13 of the projection lens 2 and the reflective surface of the second optical system.
In the cross section shown in
In
Operations of the respective optical elements will now be described herebelow.
The first optical system, i.e., the projection lens 2, is a primary lens for being used such that the front group 12 thereof projects the display screen of the image display device 11 onto the projection screen 3. The projection lens 2 functions to compensate for the fundamental aberrations occurring in the rotationally symmetrical optical system. The rear group 13 of projection lens 2 includes the rotationally asymmetrical anamorphic aspheric lens.
In the present embodiment, the anamorphic aspheric lens is arcuately formed with a concave surface facing the light radiation direction thereof. The curvature of a portion of the anamorphic aspheric lens through which the light ray directed to the lower end of the projection screen 3 passes is set wider than the curvature of a portion thereof through which the light ray directed to the upper end of the projection screen 3 passes.
The second optical system includes the anamorphic aspheric mirror having the rotationally asymmetrical anamorphic aspheric surface profile. In the present embodiment, the anamorphic aspheric mirror is formed of a rotationally asymmetrical convex mirror having a portion arcuately formed such that a convex portion faces the reflection direction of the light ray. More specifically, the curvature of a portion of the anamorphic aspheric mirror for reflecting the light ray directed to the lower end of the projection screen 3 is set wider than the curvature of a portion of the mirror for reflecting the light ray directed to the upper end of the projection screen 3. Alternatively, the configuration may be as follows. The portion of the anamorphic aspheric mirror for reflecting the light ray directed to the lower portion of the projection screen 3 may have a convex shape in the reflection direction of the light ray. Concurrently, the portion of the mirror for reflecting the light ray directed to the upper portion of the projection screen 3 may have a concave shape in the reflection direction of the light ray.
In accordance with the operations of the anamorphic aspheric lens and the anamorphic aspheric mirror, primarily, the compensation for the aberrations caused by the diagonal incidence is performed.
That is, according to the present embodiment, the second optical system compensates for, primarily, the trapezoidal distortions, and the rear group 13 of the projection lens 2, i.e., the first optical system, compensates for, primarily, asymmetrical aberrations such as image plane distortions.
Thus, in the present embodiment, the first optical system includes at least one rotationally asymmetrical anamorphic aspheric lens, and the second optical system includes at least one rotationally asymmetrical anamorphic aspheric mirror. This enables the compensation for both the trapezoidal distortions and aberrations caused by the diagonal projection.
According to the configuration described above, in the projection lens 2 including the refractive surfaces, the compensation of the trapezoidal distortions caused by the diagonal incidence can be accomplished without causing lens eccentricity and lens-diameter increase and without the need of increasing the number of lenses. Further, a projection optical unit reduced in the depth and easily manufacturable can be implemented. Further, according to the present embodiment, a compactly integrated device set reduced in the depth and the height of the lower portion of the projection screen 3 can be provided. Further, an optical system using a small anamorphic aspheric mirror and easily manufacturable can be provided.
Thus, the above-described configuration of the present embodiment implements the compactly integrated device set reduced in the depth and the height of the lower portion of the projection screen 3 by using the anamorphic aspheric lens and the anamorphic aspheric mirror. Basically, however, the device set is still one of eccentric projection optical systems. Accordingly, a projected image incident on the project screen 3 is eccentric with respect to the project screen 3, and the center thereof is present below a lower end P7 of the project screen 3 (refer to
The projection screen 3 according to the present embodiment, shown in
With reference to FIGS. 4 to 7, the following describes setting of the conjugate point of the fresnel lens sheet 31 for the projection screen 3 according to the present embodiment.
In the case that a conjugate point is provided in the entirety of the fresnel lens, light rays transferred through respective portions of the fresnel lens propagate extended portions of the center of the lower end portion of the fresnel lens sheet 31. As such, especially, the image light on a portion below the horizontal centerline m of the fresnel lens sheet 31 propagates below the line of sight of the viewer, such that the image in that portion becomes dark. To avoid this, according to the present embodiment, a reference circumference n with the fresnel point o set as the center point is determined. Thereby, a conjugate point distance of a first fresnel lens portion formed outside the reference circumference n (outside the radius of the reference circumference n) is shorter than a conjugate point distance of a second fresnel lens portion formed inside the reference circumference n (inside the radius of the reference circumference n).
In the present embodiment, the first fresnel lens portion conjugate point distance is set to infinity. That is, light is radiated substantially parallel to the normal line of the projection screen 3 from the first fresnel lens portion. In addition, the present embodiment, the reference circumference n is set to a circumference of the fresnel lens of the fresnel lens passing through the vicinities of cross points of the horizontal centerline m and both left and right ends of the fresnel lens sheet 31. That is, in the present embodiment, the conjugate point of the fresnel lens is provided only in the area above the horizontal centerline m of the fresnel lens sheet 31. The fresnel lens is concentrically circular shape, such that the conjugate point is provided only in the portion (area) outside the reference circumference n. This portion (area) corresponds to the opposite side of the side where the fresnel point o exists, that is, the area distal from the point o, in which portion the light amount is reduced since the angle of viewing of the projection optical system is large. More specifically, this area corresponds to a portion where the incident angle of the light projected from the projection optical system to the projection screen 3 becomes largest, and the light loss increases.
According to the present embodiment, however, a light ray in a portion positioned outside the reference circumference n, that is, a portion where the light amount is relatively reduced, can be directed to the viewer. Consequently, images on the projection screen 3, especially, image in the vicinities of the both left and right end portions can be brightly displayed.
In order to reduce the conjugate point distance of the second fresnel lens portion positioned outside the reference circumference n to be shorter than the conjugate point distance of the first fresnel lens portion positioned inside the reference circumference n, a prism angle of the refractive surface of the second fresnel lens portion (angle formed between the refractive surface and the normal line of the projection screen 3) is set wider than a prism angle of the refractive surface of the second fresnel lens portion.
In the above-described example, although the conjugate point distance of the first fresnel lens portion is set to infinity, the distance need not be set to infinity inasmuch as the conjugate point distance is longer than the conjugate point distance of the second fresnel lens portion. Further, in the above-described example, although the respective prism angle of the refractive surface of the fresnel lens on the same circumference is set constant, the prism angle may be set variable depending on the position on the same circumference.
The conjugate point distance will be described herebelow with reference to
Referring to
L=kW (1)
In the above-described example, k is 10.3. In addition, it can be understood from
Thus, in the fresnel lens sheet 31 according to the present embodiment, the conjugate point is provided only in the fresnel lens formed outside the reference circumference n, or in other expression, formed in the portion above the horizontal centerline m. Then, where the conjugate point distance L is represented by the product of the multiplication between the diagonal dimension W of the fresnel lens sheet 31 and the coefficient k, k is set to a range of from 10.3 to 21.3. While the conjugate point distance is variable depending on the vertical viewing angle as viewed in
The present embodiment has thus been described with reference to the example cases where images are projected from the lower portion onto the projection screen 3. However, the configuration of the present embodiment can be similarly adapted even to the case where images are projected from an upper portion onto the light-transmissive projection screen 3. In this case, the fresnel lens sheet 31 is reversed upside down, the conjugate point is provided in a range below the horizontal centerline (m) of the fresnel lens sheet 31. Also in this case, the conjugate point distance is the same as in the case of projection performed from the lower portion onto the light-transmissive projection screen 3.
According to the fresnel lens sheet 31 provided with the conjugate point, the fresnel angle is increased, reflection losses in the fresnel lens are increased.
Referring to a graph of
kW=1.0583 exp(0.0387×δ) (2)
In this case, the coefficient k is “1.0583 exp(0.0387×δ)/W.” More specifically, when a maximum fresnel incident angle is δ (degrees), the conjugate point distance L has to be set to kW or longer, and more specifically, has to be set to satisfy equation (3):
L≧1.0583 exp(0.0387×δ) (3)
According to the embodiment described above, one conjugate point is provided to the second fresnel lens portion, a plurality of conjugate points may be provided thereto.
As described in conjunction with
The present invention has been described only with reference to preferred embodiments for example purposes and in the interest of brevity, and that the present invention is not limited to these embodiments. Those skilled in the art will understand that various alterations and modifications can be made to the embodiments discussed herein and that all such modifications are within the scope of the present invention.
Number | Date | Country | Kind |
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2005-194494 | Jul 2005 | JP | national |