Patent US4946252A successfully refreshed from Google Patents.
US4946252A
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US
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Focusing screen
Assignee: Pentax Corp
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Filing: 1988-08-04
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Granted: 1990-08-07
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Expires: 2008-08-04
Abstract
Abstract An improved focusing screen for a single-lens reflex camera or the like in which an unpleasant sensation caused by dark spots on the screen is eliminated. The inventive focusing screen includes a plurality of small lenses formed on the surface of the screen, each being a composite lens composed of a concave portion lens and a convex lens portion. The lenses may be disposed in such a way as to form a honeycomb pattern.
Inventors
- 👤 Saburo Sugawara
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 06:26
CPC Classifications
G; G03; G03B; G03B13/00; G03B13/18; G03B13/24
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
55 words
A focusing screen comprising: a substrate; and a plurality of small lenses formed on a surface of said substrate, each of said small lenses being a composite lens comprising a concave lens portion in right circular conical form and a convex lens portion in right circular conical form, both lens portions having a common axis.
Claim 2
Dependent Claim
55 words
A focusing screen comprising: a substrate; and a plurality of small lenses formed on a surface of said substrate, each of said small lenses being a composite lens comprising a concave lens portion in right circular conical form and a convex lens portion in right circular conical form, both lens portions having a common axis.
Claim 3
Dependent Claim
25 words
The focusing screen according to claim 1, wherein said plurality of small lenses are disposed in such a way as to form a honeycomb structure.
Claim 4
Dependent Claim
161 words
The focusing screen according to claim 1, wherein each of said small lenses comprises a concave lens portion of right circular conical shape disposed in a central portion of a convex lens portion of right circular conical shape, each of said small lenses satisfying the following conditions I: 0.2<(R.sub.B /R.sub.A)<0.2 85<(n-1)·P·Θ.sub.1 <115 0<Θ.sub.2 <2·Θ.sub.1 where n: the refractive index of the material of which each small lens is made; P: the distance between adjacent common axes; R A : the distance from a common axis to the boundary between adjacent small lenses; R B : the distance from the common axis to the boundary between a concave lens portion and a convex lens portion; Θ 1 : the angle formed between a line normal to the common axis and the sloping side of a convex lens portion; and Θ 2 : the angle formed between a line normal to the common axis and the sloping side of a concave lens portion.
Claim 5
Dependent Claim
21 words
The focusing screen according to claim 3, wherein (n-1)·P·Θ 1 in conditions I is set to a value of about 98.272.
Claim 6
Dependent Claim
161 words
The focusing screen according to claim 1, wherein each of said small lenses comprises a concave lens portion of right circular conical shape disposed in a central portion of a convex lens portion of right circular conical shape, each of said small lenses satisfying the following conditions I: 0.2<(R.sub.B /R.sub.A)<0.4 85<(n-1)·P·Θ.sub.2 <115 0<Θ.sub.2 <2·Θ.sub.2 where n: the refractive index of the material of which each small lens is made; P: the distance between adjacent common axes; R A : the distance from a common axis to the boundary between adjacent small lenses; R B : the distance from the common axis to the boundary between a concave lens portion and a convex lens portion; Θ 1 : the angle formed between a line normal to the common axis and the sloping side of a concave lens portion; and Θ 2 : the angle formed between a line normal to the common axis and the sloping side of a concave lens portion.
Claim 7
Dependent Claim
21 words
A focusing screen according to claim 5, wherein (n-1)·P·θ 2 in conditions II is set to a value of about 98.272.
Claim 8
Dependent Claim
25 words
A focusing screen according to claim 1, wherein the surface of each of said concave lens portion and convex lens portion is provided with asperities.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1993-08-06 | 1994-02-05 | 1994-08-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-08-06 | 1998-02-05 | 1998-08-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-08-06 | 2002-02-05 | 2002-08-07 | $7700.00 | Window Closed / Lapsed |