Patent US3810221A successfully refreshed from Google Patents.
US3810221A
Expired / Lapsed
US
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Viewfinder for a reflex camera
Assignee: Polaroid Corp
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Filing: 1971-11-11
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Granted: 1974-05-07
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Expires: 1991-11-11
Abstract
Abstract A special eye lens in a viewfinder for a reflex camera compensates for field tilt in a virtual image, thereby minimizing the depth accommodation required of an observer''s eye to focus the virtual image at top and bottom. The field tilt stems from an oblique orientation of the axis of the viewfinder at its incidence with a focusing screen in the reflex camera. To compensate for it, a special refracting surface is formed on the eye lens. The ophthalmic power of the special refracting surface varies with its vertical distance from the axis, causing the power of the eye lens to vary accordingly. A polynomial of at least the third order best describes the three-dimensional shape of the special refracting surface having mirror symmetry, but not rotational symmetry.
Inventors
- 👤 W Plummer
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 19:31
CPC Classifications
G; G03; G03B; G03B19/00; G03B19/02; G03B19/12
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
60 words
A viewfinder comprising: means for forming a real image of a focusing screen positioned at an oblique angle to the optic axis of said viewfinder; and means for magnifying said real image to form a virtual image thereof, said magnifying means including an optical surface with a non-rotational shape for minimizing the field tilt otherwise associated with said virtual image.
Claim 2
Dependent Claim
60 words
A viewfinder comprising: means for forming a real image of a focusing screen positioned at an oblique angle to the optic axis of said viewfinder; and means for magnifying said real image to form a virtual image thereof, said magnifying means including an optical surface with a non-rotational shape for minimizing the field tilt otherwise associated with said virtual image.
Claim 3
Dependent Claim
33 words
The viewfinder described in claim 1, wherein said means for forming a real image of a focusing screen comprises a concave mirror and said means for magnifying said real image comprises a lens.
Claim 4
Dependent Claim
32 words
The viewfinder described in claim 2, wherein said optical surface with a non-rotational shape comprises a continuously contoured shape on the refracting surface of said lens situate away form said concave mirror.
Claim 5
Dependent Claim
18 words
The viewfinder described in claim 3, wherein said concave mirror has a non-spherical surface derived from an ellipsoid.
Claim 6
Dependent Claim
20 words
The viewfinder described in claim 1, whErein said optical surface has a plurality of discrete zones of increasing refracting power.
Claim 7
Dependent Claim
60 words
A viewfinder, comprising: optical means, having a viewing axis, for forming a real image of a focusing screen oriented at an oblique angle with said viewing axis; eye lens means for magnifying said real image to form a virtual image; and correcting means for minimizing the field tilt of said virtual image otherwise apparent to a user of said viewfinder.
Claim 8
Dependent Claim
60 words
A viewfinder, comprising: optical means, having a viewing axis, for forming a real image of a focusing screen oriented at an oblique angle with said viewing axis; eye lens means for magnifying said real image to form a virtual image; and correcting means for minimizing the field tilt of said virtual image otherwise apparent to a user of said viewfinder.
Claim 9
Dependent Claim
47 words
The viewfinder described in claim 6, wherein said correcting means comprises: a refracting surface on said eye lens means whose dioptric power differs between adjacent areas in relation to the optical distance from said refracting surface of the portions of said real image associated with said areas.
Claim 10
Dependent Claim
20 words
The viewfinder described in claim 7, wherein said refracting surface has a plurality of discrete zones of increasing refracting power.
Claim 11
Dependent Claim
44 words
The viewfinder described in claim 7, wherein said refracting surface has a contour, described by a non-rotational polynomial of at least the third order, so said dioptric power varies continuously with the height, on said refracting surface, from the axis of said eye lens.
Claim 12
Dependent Claim
25 words
The viewfinder described in claim 7, wherein said refracting surface is situate away from said optical means and said optical means comprises a concave mirror.
Claim 13
Dependent Claim
18 words
The viewfinder described in claim 10, wherein said concave mirror has a non-spherical surface derived from an ellipsoid.
Claim 14
Dependent Claim
51 words
The viewfinder described in claim 9, wherein said non-rotational polynomial comprises the following terms: G20V2 + G30V3 + G40V4 wherein V designates a coordinate direction transverse to the axis of said viewfinder in which the height from said surface is to be measured, and the subscripted G terms represent preselected constants.
Claim 15
Dependent Claim
13 words
The viewfinder described in claim 12, wherein said non-rotational polynomial comprises the terms:
Claim 16
Dependent Claim
120 words
A viewfinder comprising: a concave mirror for forming a real image of a focusing screen positioned at an oblique angle to the optic axis of said viewfinder, said concave mirror having a shape that is a portion of a surface of revolution, about a Ym axis, for the positive values of X, of the curve described by the equation: Ym P1X + P2X2 + P3X3 + P4X4 + P5X5 + P6X6 an eye lens with two refracting surfaces for magnifying said real image to form a virtual image, the surface of said lens toward said mirror has a radius of 0.8077 inches and the surface away from said concave mirror has a continuously contoured non-rotational shape descrived by the equation:
Claim 17
Dependent Claim
120 words
A viewfinder comprising: a concave mirror for forming a real image of a focusing screen positioned at an oblique angle to the optic axis of said viewfinder, said concave mirror having a shape that is a portion of a surface of revolution, about a Ym axis, for the positive values of X, of the curve described by the equation: Ym P1X + P2X2 + P3X3 + P4X4 + P5X5 + P6X6 an eye lens with two refracting surfaces for magnifying said real image to form a virtual image, the surface of said lens toward said mirror has a radius of 0.8077 inches and the surface away from said concave mirror has a continuously contoured non-rotational shape descrived by the equation:
References Cited (Backward Citations)
US3634617A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-05-06 | 1977-11-05 | 1978-05-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-05-06 | 1981-11-05 | 1982-05-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-05-06 | 1985-11-05 | 1986-05-07 | $7700.00 | Window Closed / Lapsed |