US4609945A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Video projection apparatus with temperature compensation device
Assignee: Hitachi Ltd
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Filing: 1984-06-15
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Granted: 1986-09-02
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Expires: 2004-06-15
Abstract
Abstract In a video projection apparatus including a projection lens, a cathode-ray tube and a projection screen, a layer of a medium whose refractive index n p decreases with a temperature rise is disposed between the projection lens and the faceplate of the cathode-ray tube, and the thickness l p of the medium layer is selected to substantially satisfy the following equation thereby compensating the temperature-dependent variation of the focal length of the principal lens: ##EQU1## where ΔT is a temperature variation; Δn p is a variation of the refractive index n p due to the temperature variation ΔT; f is the focal length of the projection lens; K is a constant representing the proportion of the power of plastic lenses to the total power when the projection lens is of a hybrid type; Δf is a variation of the focal length f due to the temperature variation ΔT; and M is the magnification of projected images.
Inventors
- 👤 Masanori Oguino
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 02:25
CPC Classifications
H; H01; H01J; H01J29/00; H01J29/86; H01J29/89; H01J29/894; H04; H04N; H04N5/00; H04N5/74; H04N5/7408
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
171 words
In a video projection apparatus including at least a cathode-ray tube, a projection lens and a projection screen, a temperature compensation device comprising a layer of a medium disposed between said projection lens and a faceplate of said cathode-ray tube, said medium having a refractive index n p decreasing with a temperature rise and having a thickness l p on an optical axis, thereby compensating a temperature-dependent variation of a focal length of said projection lens, the thickness l p of said medium layer being selected to satisfy an equation ##EQU20## where ΔT is a temperature variation; Δn p is a variation of the refractive index n p due to the temperature variation ΔT; f is the focal length of the projection lens; K is a constant representing the proportion of the power of plastic lenses to the total power when the projection lens is of a hybrid type, Δf is a variation of the focal point due to the temperature variation ΔT; and M is the magnification of projected images.
Claim 2
Dependent Claim
171 words
In a video projection apparatus including at least a cathode-ray tube, a projection lens and a projection screen, a temperature compensation device comprising a layer of a medium disposed between said projection lens and a faceplate of said cathode-ray tube, said medium having a refractive index n p decreasing with a temperature rise and having a thickness l p on an optical axis, thereby compensating a temperature-dependent variation of a focal length of said projection lens, the thickness l p of said medium layer being selected to satisfy an equation ##EQU20## where ΔT is a temperature variation; Δn p is a variation of the refractive index n p due to the temperature variation ΔT; f is the focal length of the projection lens; K is a constant representing the proportion of the power of plastic lenses to the total power when the projection lens is of a hybrid type, Δf is a variation of the focal point due to the temperature variation ΔT; and M is the magnification of projected images.
Claim 3
Dependent Claim
24 words
A video projection apparatus according to claim 1, wherein the thickness l p of said medium layer is selected to satisfy an equation ##EQU21##
Claim 4
Dependent Claim
145 words
In a video projection apparatus including at least a cathode-ray tube, a projection lens and a projection screen, a temperature compensation device comprising a layer of a medium disposed between said projection lens and a faceplate of said cathode-ray tube, said medium having a refractive index n p decreasing with a temperature rise and having a thickness l p on an optical axis, thereby compensating a temperature-dependent variation of a focal length of said projection lens, the thickness l p of said medium layer being selected to satisfy an equation ##EQU22## where ΔT is a temperature variation; Δn p is a variation of the refractive index n p due to the temperature variation ΔT; f is the focal length of the projection lens; Δf is a variation of the focal point due to the temperature variation ΔT; and M is the magnification of projected images.
Claim 5
Dependent Claim
145 words
In a video projection apparatus including at least a cathode-ray tube, a projection lens and a projection screen, a temperature compensation device comprising a layer of a medium disposed between said projection lens and a faceplate of said cathode-ray tube, said medium having a refractive index n p decreasing with a temperature rise and having a thickness l p on an optical axis, thereby compensating a temperature-dependent variation of a focal length of said projection lens, the thickness l p of said medium layer being selected to satisfy an equation ##EQU22## where ΔT is a temperature variation; Δn p is a variation of the refractive index n p due to the temperature variation ΔT; f is the focal length of the projection lens; Δf is a variation of the focal point due to the temperature variation ΔT; and M is the magnification of projected images.
Claim 6
Dependent Claim
24 words
A video projection apparatus according to claim 3, wherein the thickness l p of said medium layer is selected to satisfy an equation ##EQU23##
References Cited (Backward Citations)
US4405949A
Cited
US4511927A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1989-09-01 | 1990-03-03 | 1990-09-02 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-09-01 | 1994-03-03 | 1994-09-02 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-09-01 | 1998-03-03 | 1998-09-02 | $7700.00 | Window Closed / Lapsed |