Patent US4926201A successfully refreshed from Google Patents.
US4926201A
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Finder optical system
Assignee: Minolta Co Ltd
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Filing: 1989-06-05
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Granted: 1990-05-15
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Expires: 2009-06-05
Abstract
Abstract A finder optical system comprises from the object side an objective lens having a positive refractive power as a whole, a condenser lens arranged in the vicinity of an image plane of the objective lens, an eyepiece consisting of a single lens element and having a positive refractive power, and further comprises a prism installed between the condenser lens and the eyepiece to introduce light fluxes having been passed through the condenser lens into the eyepiece, and wherein the finder optical system fulfills the following conditions; ν<50, 15 mm<fe<50 mm, 0.7<L/fe <1, wherein, ν represents an Abbe number of the prism, fe represents a focal length of the eyepiece, and L represents an optical path length of the prism defined as a ratio of thickness of the prism to the refractive index thereof. Thereby, axial chromatic aberration can be corrected well, and additionally, a finder image with high mangification is obtainable. Furthermore, compactness and cost reduction can be attained owing to the simple constitution.
Inventors
- 👤 Hiromu Mukai
- 👤 Ichiro Kasai
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 19:55
CPC Classifications
G; G02; G02B; G02B13/00; G02B13/08; G02B13/12; G02B23/00; G02B23/14
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
130 words
A finder optical system comprising from the object side: an objective lens having a positive refractive power as a whole; a condenser lens arranged in the vicinity of an image plane of said objective lens; an eyepiece consisting of a single lens element and having a positive refractive power; and further comprising: a prism installed between said condenser lens and said eyepiece to introduce light fluxes having been passed through said condenser lens into said eyepiece; and wherein the finder optical system fulfills the following conditions: ν<50 15mm<fe<50mm 0.7<L/fe<1 wherein, ν represents an Abbe number of the prism; fe represents a focal length of the eyepiece; and L represents an optical path length of the prism defined as a ratio of thickness of the prism to the refractive index thereof.
Claim 2
Dependent Claim
130 words
A finder optical system comprising from the object side: an objective lens having a positive refractive power as a whole; a condenser lens arranged in the vicinity of an image plane of said objective lens; an eyepiece consisting of a single lens element and having a positive refractive power; and further comprising: a prism installed between said condenser lens and said eyepiece to introduce light fluxes having been passed through said condenser lens into said eyepiece; and wherein the finder optical system fulfills the following conditions: ν<50 15mm<fe<50mm 0.7<L/fe<1 wherein, ν represents an Abbe number of the prism; fe represents a focal length of the eyepiece; and L represents an optical path length of the prism defined as a ratio of thickness of the prism to the refractive index thereof.
Claim 3
Dependent Claim
23 words
A finder optical system as claimed in claim 1, wherein said eyepiece has an aspherical surface on one of the lens surfaces thereof.
Claim 4
Dependent Claim
109 words
A finder optical system as claimed in claim 2, wherein said eyepiece fulfills the following conditions: ##EQU3## wherein, h represents a height from an optical axis (0≦h≦R F ); T(h) represents a thickness of the eyepiece at a height h; r B represents a radius of curvature of an exit pupil side surface of the eyepiece in the paraxial region; r F represents a radius of curvature of a prism side surface of the eyepiece in the paraxial region; D represents an axial thickness of the eyepiece; and R F represents a minimum value among |r B |, |r F | and an effective radius of the aspherical surface.
Claim 5
Dependent Claim
20 words
A finder optical system as claimed in claim 3, wherein said eyepiece has an aspherical surface on the prism side.
Claim 6
Dependent Claim
21 words
A finder optical system as claimed in claim 3, wherein said eyepiece has a aspherical surface on the exit pupil side.
Claim 7
Dependent Claim
16 words
A finder optical system as claimed in claim 3, wherein said eyepiece is a bi-convex lens.
Claim 8
Dependent Claim
129 words
A finder optical system comprising from the object side: an objective lens having a positive refractive power as a whole; a condenser lens arranged in the vicinity of an image plane of said objective lens; an eyepiece consisting of a single lens element and having a positive refractive power; and further comprising: a prism installed between said condenser lens and said eyepiece to introduce light fluxes having been passed through said condenser lens into said eyepiece; and wherein the finder optical system fulfills the following conditions: ν<50 15mm<fe<50mm l≦2.5mm wherein, ν represents an Abbe number of the prism; fe represents a focal length of the eyepiece; and l represents a distance between an exit pupil side surface of the prism and an object side principal point of the eyepiece.
Claim 9
Dependent Claim
129 words
A finder optical system comprising from the object side: an objective lens having a positive refractive power as a whole; a condenser lens arranged in the vicinity of an image plane of said objective lens; an eyepiece consisting of a single lens element and having a positive refractive power; and further comprising: a prism installed between said condenser lens and said eyepiece to introduce light fluxes having been passed through said condenser lens into said eyepiece; and wherein the finder optical system fulfills the following conditions: ν<50 15mm<fe<50mm l≦2.5mm wherein, ν represents an Abbe number of the prism; fe represents a focal length of the eyepiece; and l represents a distance between an exit pupil side surface of the prism and an object side principal point of the eyepiece.
Claim 10
Dependent Claim
44 words
A finder optical system as claimed in claim 7, wherein the finder optical system further fulfills the following condition: 0.7<L/fe<1 wherein, L represents a optical path length of the prism defined as a ratio of thickness of the prism to the refractive index thereof.
Claim 11
Dependent Claim
34 words
A finder optical system as claimed in claim 8, wherein the finder optical system still further fulfills the following condition: 1.7<n.sub.P wherein, n P represents a refractive index of the prism relative to D-line.
Claim 12
Dependent Claim
16 words
A finder optical system as claimed in claim 7, wherein said eyepiece is a bi-convex lens.
Claim 13
Dependent Claim
23 words
A finder optical system as claimed in claim 10, wherein said eyepiece has an aspherical surface on one of the lens surfaces thereof.
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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) | 1993-05-14 | 1993-11-13 | 1994-05-15 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-05-14 | 1997-11-13 | 1998-05-15 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-05-14 | 2001-11-13 | 2002-05-15 | $7700.00 | Window Closed / Lapsed |