This application is the U.S. national phase under 35 USC § 371 of International Application No. PCT/US00/23124, filed Aug. 23, 2000, which was published in English under PCT Article 21(2) on Mar. 1, 2001 as International Publication No. WO 01/14927. This application claims the benefit under 35 USC § 119(e) of U.S. Provisional Application No. 60/150,451 filed Aug. 24, 1999, the contents of which in its entirety is hereby incorporated by reference.
This invention relates to rear screen projection systems including CRT, LCD, and DLP displays, as well as slide projectors.
A projection screen is an optical device which does not create an image but provides a required field of view in the vertical and horizontal directions of viewer space. By reducing the field of view in the vertical direction, the screen creates the effect of increasing the brightness of the image within the viewing area, an effect which is referred to in the art as gain.
The invention provides a new structure for a compound screen for a rear projection display. More particularly, the invention provides a rear projection screen for use with a projection lens which has an exit pupil (23 in
(a) a Fresnel structure (11 in
(b) a lenslet array (13 in
(c) an opaque layer (15 in
The lenslet array can comprise elements which have a square aperture in which case, in viewer space, the screen's half field of view α can be described by the equation:
α=tan−1(0.5·CA/f)
where CA and f are, respectively, the clear aperture and the focal length of the elements.
Alternatively, the lenslet array can comprise elements which have a rectangular aperture in which case the screen's vertical half field of view αv and horizontal half field of view αH, in viewer space, can be described by the equations:
αv=tan−1(0.5·CAv/f)
and
αH=tan −1(0.5·CAH/f)
where CAv, CAH, and f are, respectively, the vertical clear aperture, the horizontal clear aperture, and the focal length of the elements.
As a further alternative, the lenslet array can comprise anamorphic elements in which case the screen's vertical half field of view αv and horizontal half field of view αH, in viewer space, can be described by the equations:
αv=tan−1(0.5·CA/fv)
and
αH=tan−1(0.5·CA/fH)
where CA, fv, and fH are, respectively, the clear aperture, the vertical focal length, and the horizontal focal length of the elements.
The screen can comprise a protective layer on the light exiting side of the opaque layer. The Fresnel structure, the lenslet array, the opaque layer, and the protective layer can be arranged as subassemblies, e.g., the Fresnel structure and the lenslet array can be arranged in one subassembly and the opaque layer and the protective layer can be arranged in another subassembly.
When the screen is used with a pixelized panel, the lenslet array can comprise elements whose size is at least several times smaller than the magnified image of a pixel produced at the array by the projection lens. Similarly, when the screen is used with a cathode ray tube, the lenslet array can comprise elements whose size is at least several times smaller than the magnified image of a dot spot of the cathode ray tube produced at the array by the projection lens.
The accompanying drawings, which are incorporated in and constitute part of the specification, illustrate the various aspects of the invention, and together with the description, serve to explain the principles of the invention. It is to be understood, of course, that both the drawings and the description are explanatory only and are not restrictive of the invention.
The reference numbers used in the drawings refer to the following:
11 Fresnel structure
13 lenslet array
15 opaque layer with pinholes
17 smooth surface of protective layer
19 elements of lenslet array
21 magnified image of single pixel
23 exit pupil of projection lens
25 light from projection lens
27 parallel beam
29 light in viewer space
The structure of a screen constructed in accordance with the invention is shown in
As shown in this figure, the compound screen has four elements which are: (1) Fresnel structure 11; (2) lenslet array 13; (3) opaque layer 15 with two dimensional structure of precision pinholes; and (4) a protective layer having a smooth outer surface 17. These elements can be arranged in two components as shown in
The four elements listed above can be arranged in any combination of subassemblies but must have the following order from the projection lens to the viewer: Fresnel structure, lenslet array, and opaque layer with pinholes. The protective layer may not be necessary for all applications or may be unnecessary with the selection of a suitable opaque layer. When used, the flat protective layer on the viewer side provides an easy way to clean the screen with typical methods and products for cleaning. Also, this layer adds abrasion and impact resistance to the screen.
The work of the screen is illustrated in
The field of view in the viewer space can be calculated as:
where α is the half of field of view (angular dimension), CA is the clear aperture (optical diameter) of a single element of the lenslet array, and ƒ is the focal distance of the element.
To provide a different field of view in the vertical and horizontal directions two different solution can be implemented:
(1) Each element of the lenslet array can have a rectangular aperture as shown in
where αv and αH are the half angular fields of view in the vertical and horizontal directions, respectively, and CAv and CAH are the clear aperture of the element in these directions.
(2) Each element of the lenslet array can have a toroidal shape to provide different focal lengths in the vertical and horizontal directions (anamorphic property). For this case the equations for the vertical and horizontal fields of view are:
where ƒv' and ƒH' are the focal lengths of the element in the vertical and horizontal directions.
The opaque layer with the sets of pinholes can be done out of photoresist material. This material is exposed with an electromagnetic field and developed with an appropriate chemical process. The process of exposure is done after both components of the screen are assembled. The source of the electromagnetic field is located at the position of the exit pupil of the projection lens (see
To increase the contrast and reduce the reflection of ambient light in the viewer space the opaque layer can be further improved by the addition of materials which increases the absorption of this layer. All air contact surfaces of the screen can have antireflection coatings that reduce the reflectivity and increase the contrast.
By using identical materials or materials with appropriate thermal coefficients of expansion, the optical properties of the screen can be maintained throughout the temperature and humidity variations which can be expected from seasonal climate conditions and set operation.
From the foregoing, it can be seen that the benefits of the screen design of the invention include:
elimination of moiré effect;
full control of vertical and horizontal field of view in viewer space;
low loss for light propagation from the projection lens to the
viewer space and high loss of light (opaque property) in reverse
direction; and
a protective layer on the outside side of the screen.
Although specific embodiments of the invention have been described and illustrated, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the invention's spirit and scope. The following claims are thus intended to cover the specific embodiments set forth herein as well as such modifications, variations, and equivalents.
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/US00/23124 | 8/23/2000 | WO | 00 | 8/5/2002 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO01/14927 | 3/1/2001 | WO | A |
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Number | Date | Country |
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2000-035616 | Feb 2000 | JP |