Patent EP0273476A1 successfully refreshed from Google Patents.
EP0273476A1
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EP
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Image projection system
Assignee: Koninklijke Philips NV
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Filing: 1987-11-18
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Granted: —
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Expires: 2007-11-18
Abstract
Abstract An image projection system is described with at least one display tube (3, 4, 5) provided with an interference filter for increasing the amount of light which is emitted within a small solid angle. By combination of such a display tube with a projection lens system (6, 7, 8) in accordance with a novel design the brightness of the picture on a projection screen (11) is enhanced whilst the brightness variation and the colour shading of this picture are reduced.
Inventors
- 👤 Johannes Hendrikus Maria Spruit
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 18:06
CPC Classifications
H; H04; H04N; H04N5/00; H04N5/74; G; G02; G02B; G02B5/00; G02B5/20; G02B5/28; G02B5/285; G02B13/00; G02B13/16; G02B13/18; H04N9/00; H04N9/12; H04N9/31
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
206 words
An image projection system comprising at least one display tube and a multi-element projection lens systems for imaging a display tube picture on a projection screen, said display tube comprising a display screen in an evacuated envelope, the display screen being arranged on the inside of a display window in the wall of the envelope and being provided with a luminescent material, a multi-layer interference filter being arranged between said material and the display window, characterized in that a first lens element of the projection lens system, viewed from the image end, is constituted by a positive lens element having a first refractive aspherical surface facing the image end and a second refractive surface facing the object end, which surface is convex and whose centre of curvature is located in the image end half of said lens element, in that the projection lens system comprises at least a second lens element having a negative power and whose surface facing the image end is concave and whose surface facing the display tube has a curvature which is adapted to that of the display window and in that the entrance pupil of the projection lens system is located in the image end half of the first lens element.
Claim 2
Dependent Claim
206 words
An image projection system comprising at least one display tube and a multi-element projection lens systems for imaging a display tube picture on a projection screen, said display tube comprising a display screen in an evacuated envelope, the display screen being arranged on the inside of a display window in the wall of the envelope and being provided with a luminescent material, a multi-layer interference filter being arranged between said material and the display window, characterized in that a first lens element of the projection lens system, viewed from the image end, is constituted by a positive lens element having a first refractive aspherical surface facing the image end and a second refractive surface facing the object end, which surface is convex and whose centre of curvature is located in the image end half of said lens element, in that the projection lens system comprises at least a second lens element having a negative power and whose surface facing the image end is concave and whose surface facing the display tube has a curvature which is adapted to that of the display window and in that the entrance pupil of the projection lens system is located in the image end half of the first lens element.
Claim 3
Dependent Claim
40 words
An image projection system as claimed in Claim 1, characterized in that the aspherical surface of the first lens element, viewed from the image end, is convex in a zone around the optical axis and is concave outside said zone.
Claim 4
Dependent Claim
23 words
An image projection system as claimed in Claim 2, characterized in that the second refractive surface of the first lens element is aspherical.
Claim 5
Dependent Claim
42 words
An image projection system as claimed in Claim 1 or 2, characterized in that a third bi-convex lens element supplying a part of the overall optical power of the projection lens system is arranged between the first and the second lens element.
Claim 6
Dependent Claim
30 words
An image projection system as claimed in Claim 4, characterized in that the optical power of the third lens element is approximately equal to that of the first lens element.
Claim 7
Dependent Claim
27 words
An image projection system as claimed in Claim 4 or 5, characterized in that the surface of the third lens element facing the image end is aspherical.
Claim 8
Dependent Claim
29 words
An image projection system as claimed in Claim 4 or 5, characterized in that the surface of the first and third lens elements facing the object end are aspherical.
Claim 9
Dependent Claim
43 words
An image projection system as claimed in any one of the preceding Claims, characterized in that the first lens element has a third surface which is reflective and is located in the radiation path between the first and the second refractive lens surface.
Claim 10
Dependent Claim
76 words
An image projection system as claimed in any one of the preceding Claims, characterized in that the display window of the display tube, viewed from the image end, is concave and has an angle of curvature φ wherein φ is the angle between the normal in the centre of the display window and a line perpendicular to the edge of the display window, which angle φ has a value in the range between 5° and 25°.
Claim 11
Dependent Claim
54 words
A colour picture projection device comprising three separate colour channels converging on a common projection screen and each being provided with a display tube and a projection lens system, characterized in that least one of the colour channels is provided with an image projection system as claimed in any one of the preceding Claims.
References Cited (Backward Citations)
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