Television – Video display – Projection device
Reexamination Certificate
1998-10-27
2001-10-02
Hsia, Sherrie (Department: 2614)
Television
Video display
Projection device
C359S649000, C359S650000, C359S781000, C359S770000
Reexamination Certificate
active
06297860
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a wide field of view high numerical aperture lens systems with partial color correction for use in projection televisions and, in particular, in projection televisions employing cathode ray tubes (CRTs).
2. Description of the Prior Art
Prior art projection lenses for CRT projection televisions have comprised, from the long conjugate to the short conjugate, a weak aspherical corrector followed by a strong positive power unit, another weak aspherical corrector, and a strong negative power element in close proximity to the CRT. A description of this lens configuration can be found in a number of prior patents, including Betensky, U.S. Pat. No. 4,697,892, and Moskovich, U.S. Pat. Nos. 4,682,862, 4,755,028, and 4,776,681.
To achieve correction of chromatic aberrations, a color correcting doublet is often included in the strong positive power unit. U.S. Pat. No. 4,963,007 describes a lens configuration where color correction is achieved by adding negative power, high dispersion elements to both front units. In these lens forms, the glass elements and the shape of the plastic elements have resulted in higher manufacturing costs.
SUMMARY OF THE INVENTION
The lens systems of the invention provide means to achieve a partial correction of chromatic aberrations with a minimal increase in the difficulty and cost of manufacturing the lens. The lenses preferably comprise, from the long conjugate to the short conjugate, a weak power unit including at least one negative aspherical element of a high dispersion material followed closely by a positive aspherical element of a low dispersion material, a second strong positive power unit providing most of the power of the lens, followed by a weak power aspherical element and a strong negative power element in close proximity to the CRT on the short conjugate of the lens.
In the above described form of the lens, the first unit carries the burden of correction for pupil dependent aberrations like spherical aberration and coma. To correct for overcorrected spherical contributions coming from the power unit of the lens, the surfaces of the first unit take shapes which provide for increased negative power towards the edges of the lens. The use of even a weak power aspherical negative element made out of a high dispersion material in combination with a positive element of low dispersion material in the first unit significantly improves the correction of chromatic aberrations at the full aperture of the lens. It should be noted that having a negative element followed by a positive element allows the necessary correction of aberrations to be achieved with both elements having a fairly small variation in element thickness as a function of the diameter of the lens, thus providing shapes for these elements which are suitable for high volume manufacturing.
The invention thus provides a high speed wide field of view projection lens systems comprising in order from the long conjugate to the short conjugate:
a weak power aspherical corrector unit,
a strong power unit providing most of the positive power of the lens,
a weak power aspherical unit, and
a strong negative power unit close to the short conjugate of the lens and providing most of the correction to the field curvature of the lens,
where the corrector unit includes a negative power aspherical element of high dispersion material followed closely by a positive power element of low dispersion material. In certain embodiments, the positive power element may be aspherical.
REFERENCES:
patent: 4682862 (1987-07-01), Moskovich
patent: 4697892 (1987-10-01), Betensky
patent: 4755028 (1988-07-01), Moskovich
patent: 4776681 (1988-10-01), Moskovich
patent: 4963007 (1990-10-01), Moskovich
patent: 5251063 (1993-10-01), Baumann
patent: 5309283 (1994-05-01), Krietzer
patent: 5329363 (1994-07-01), Moskovich
patent: 5936776 (1999-08-01), Kreitzer
patent: 6141154 (2000-10-01), Kreitzer
patent: 764 865 (1997-03-01), None
Corning Precision Lens
Hsia Sherrie
Klee Maurice M.
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