US3836931A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Eye lens in a single lens reflex camera viewfinder providing field tilt compensation
Assignee: Polaroid Corp
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Filing: 1973-11-07
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Granted: 1974-09-17
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Expires: 1993-11-07
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 19:52
CPC Classifications
G; G03; G03B; G03B19/00; G03B19/02; G03B19/12
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
173 words
A camera comprising: an objective lens; an eye lens; and means defining an optical path between said objective lens and said eye lens, said optical path defining means including a reflective focusing screen positioned at a focal plane of said objective lens, a first mirror disposed to first reflect a primary real image formed by said objective lens onto said reflective focusing screen and to subsequently reflect light emanating from said primary image on said reflective focusing screen, said light emanating obliquely from said reflective focusing screen, a concave mirror for forming a real image of said reflective focusing screen using said light, an aperture disposed between said first mirror and said concave mirror to transmit said light, said eye lens arranged to form a magnified virtual image of said reflective focusing screen''s real image and having at least one non-rotational refracting surface for minimizing the field tilt, stemming from the oblique orientation of light rays emanating from said reflective focusing screen and reaching said concave mirror, otherwise associated with said virtual image.
Claim 2
Dependent Claim
173 words
A camera comprising: an objective lens; an eye lens; and means defining an optical path between said objective lens and said eye lens, said optical path defining means including a reflective focusing screen positioned at a focal plane of said objective lens, a first mirror disposed to first reflect a primary real image formed by said objective lens onto said reflective focusing screen and to subsequently reflect light emanating from said primary image on said reflective focusing screen, said light emanating obliquely from said reflective focusing screen, a concave mirror for forming a real image of said reflective focusing screen using said light, an aperture disposed between said first mirror and said concave mirror to transmit said light, said eye lens arranged to form a magnified virtual image of said reflective focusing screen''s real image and having at least one non-rotational refracting surface for minimizing the field tilt, stemming from the oblique orientation of light rays emanating from said reflective focusing screen and reaching said concave mirror, otherwise associated with said virtual image.
Claim 3
Dependent Claim
25 words
The camera described in claim 1, wherein said non-rotational refracting surface comprises the refracting surface of said eye lens situate away from said concave mirror.
Claim 4
Dependent Claim
18 words
The camera described in claim 1, wherein said concave mirror has a non-spherical surface derived from an ellipsoid.
Claim 5
Dependent Claim
148 words
The camera described in claim 1, wherein: a portion of a surface of revolution, about the Ym axis, for the positive values of X, of the curve described by the equation: Ym P1X + P2X2 + P3X3 + P4X4 + P5X5 + P6X6 represents the shape of said concave mirror; the surface of said lens toward said mirror has a radius of 0.8077 inches; and the non-rotational surface described by the equation:U (c(V2 + W2)/1 + Square Root 1 - c2(V2 + W2)) + Beta (V2 + W2)2 + gamma (V2 + W2)3 + G20V2 + G30V3 + G40V4 + G12VW2 + G22V2W2 + G04W4 represents the shape of said non-rotational refracting surface, wherein the constants have the values and meanings tabulated below: P1 0.0087470; P2 0.2698164/in.; P3 0.0193959/in.2; P4 0.0101742/in.3; P5 0.0090011/in.4; and P6 0.0017030/in.5. U, V, and W are coordinates, U coinciding with the viewfinder''s axis,
Claim 6
Dependent Claim
42 words
The camera described in claim 1, wherein the dioptric power of said refracting surface differs between adjacent areas in relation to the optical distance from said refracting surface of the portions of said reflective focusing screen''s real image associated with said areas.
Claim 7
Dependent Claim
20 words
The camera described in claim 5, wherein said refracting surface has a plurality of discrete zones of increasing refracTing power.
Claim 8
Dependent Claim
46 words
The camera described in claim 1, wherein said non-rotational refracting surface has a continuous contour, described by a polynomial expression 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 9
Dependent Claim
50 words
The camera described in claim 7, wherein said 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 10
Dependent Claim
102 words
The camera described in claim 8, wherein said polynomial comprises the terms: U (c(V2 + W2)/1 + Square Root 1 - c2(V2 + W2)) + Beta (V2 + W2)2 + gamma (V2 + W2)3 + G20V2 + G30V3 + G40V4 + G12VW2 + G22V2W2 + G04W4 wherein U, V and W designate coordinate directions, U being the direction of the viewfinder''s axis at said refracting surface, V and W being transverse to said axis and each other, c represents the reciprocal of the nominal radius of said refracting surface, and Beta , gamma , and the subscripted G terms represent preselected constants.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-09-16 | 1978-03-18 | 1978-09-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-09-16 | 1982-03-18 | 1982-09-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-09-16 | 1986-03-18 | 1986-09-17 | $7700.00 | Window Closed / Lapsed |