EP0401912A2
Expired / Lapsed
EP
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Modulation system for projection display
Assignee: Koninklijke Philips NV
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Filing: 1990-06-01
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Granted: —
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Expires: 2010-06-01
Abstract
Abstract In a liquid crystal projection t.v. system the color gradient over the projected image, which is due to angular sensitivity of the dichroic mirrors, is minimized by introducing a field lens (61,62,63) next to the light values or LC-panels (21, 22, 23) in the light paths of the blue (b B ), green (b G ) and red (b R ) beams. By chosing different length light paths before and after the light valves and LC-panels a difference in angular sensitivity of the separation mirror (41,42) and the recombination mirrors (52,53) can be compensated for.
Inventors
- 👤 Jill Forer Goldenberg
- 👤 Wilhelmus Adrianus Gerardus Timmers
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 19:54
CPC Classifications
H; H04; H04N; H04N5/00; H04N5/74; H04N9/00; H04N9/12; H04N9/31; H04N9/3102; H04N9/3105
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
142 words
A modulation system for a color projection TV comprising at least two light valves, a color separation subsystem for separating an incoming lightbeam into a number of colored subbeams, each subbeam to be modulated by one of the light valves, and a color recombination subsystem for recombining the modulated subbeams to a projection beam, said color separation subsystem and said color recombination subsystem each comprising at least one dichroic mirror having a cut-off wavelength exhibiting a shift in dependence upon an angle of incidence, whereby said dichroic mirror in the separation subsystem and said dichroic mirror in the recombination subsystem are arranged such that for any picture element in the light valves the average shift in cut-off wavelength of the light rays passing that picture element is substantially equal in size and opposite in sign for the separation and recombination subsystems, respectively.
Claim 2
Dependent Claim
142 words
A modulation system for a color projection TV comprising at least two light valves, a color separation subsystem for separating an incoming lightbeam into a number of colored subbeams, each subbeam to be modulated by one of the light valves, and a color recombination subsystem for recombining the modulated subbeams to a projection beam, said color separation subsystem and said color recombination subsystem each comprising at least one dichroic mirror having a cut-off wavelength exhibiting a shift in dependence upon an angle of incidence, whereby said dichroic mirror in the separation subsystem and said dichroic mirror in the recombination subsystem are arranged such that for any picture element in the light valves the average shift in cut-off wavelength of the light rays passing that picture element is substantially equal in size and opposite in sign for the separation and recombination subsystems, respectively.
Claim 3
Dependent Claim
24 words
A modulation system according to Claim 1, which comprises three light values and whereby both the separation and recombination subsystem comprises two dichroic mirros.
Claim 4
Dependent Claim
24 words
A modulation system according to claim 1, whereby a field lens is arranged in the light paths of at least one of the subbeams.
Claim 5
Dependent Claim
179 words
A modulation system in accordance to Claim 3 having a dichroic mirror in the separation subsystem and a corresponding dichroic mirror in the recombination subsystem, which dichroic mirrors have different angular dependencies of the cut-off wavelength, which modulation subsystem is to be placed in between a light source and a projection system having an entrance pupil, said modulation subsystem comprising a field lens providing a first effective image of the light valve at a first effective position as seen from the light source and a second effective image of the light valve at a second effective position as seen from the entrance pupil and a magnification being the ratio of the size of the first and second effective images of the light valve, whereby the light valve and the field lens are arranged at positions such that the ratio between a distance from the light source and said first effective position and a distance between said second effective position and the entrance pupil is equal to the ratio between said angular dependencies of the cut-off wavelength times said magnification.
References Cited (Backward Citations)
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