Camera with a stigmatic fresnel optical element

Claim 2

A reflex camera, comprising: housing means; objective lens means with an aperture stop, situate in a wall of said housing means, for forming a real image of a subject at a focal plane within said housing; and a focusing screen, at said focal plane, with a reflective surface for receiving said image, said reflective surface including a plurality of concentric grooves, each of said gRooves having a face that cooperates with the faces of the other of said grooves to receive light from said aperture stop and reflect it into an image of said aperture stop, said image of said aperture stop being separated from said aperture stop, said surface having a warp for ameliorating astigmatism otherwise present in said image of said aperture stop.

Claim 3

The reflex camera described in claim 1, wherein said surface having said warp has a generally cylindrical shape.

Claim 4

The reflex camera described in claim 2, further comprising: viewing means, superposed on said housing, for observing said image formed on said reflective focusing screen; an entrance aperture, in said housing means, for allowing optical communication between said housing means and said viewing means; and an optic axis for said reflective focusing screen, said entrance aperture and said aperture stop being arranged so both lie off said optic axis.

Claim 5

The reflex camera described in claim 3, wherein said reflective focusing screen forms an image of said aperture stop at said entrance aperture and the edges of said focusing screen furthest from a plane determined by said optic axis and said aperture stop are bent upwards an amount sufficient to minimize the astigmatism otherwise present in an image of said aperture stop formed by said reflective focusing screen means at said entrance aperture.

Claim 6

In a reflex camera of the type having: a housing; an objective lens with an aperture stop, situate in a forward wall of said housing; a focusing screen having a surface in the focal plane of said objective lens; a viewer; and an entrance aperture located in said housing so light from said focusing screen can enter said viewer; wherein said focusing screen is located so it forms an image of said aperture stop at said entrance aperture; the improvement comprising: a warp, in said surface of said focusing screen, for minimizing astigmatism in the image of said aperture stop at said entrance aperture, said surface including a plurality of grooves, each groove having a face and said face having a uniform slope with respect to said warp everywhere on said surface.

Claim 7

In a reflex camera of the type having: a housing; an objective lens with an aperture stop, situate in a forward wall of said housing; a focusing screen having a surface in the focal plane of said objective lens; a viewer; and an entrance aperture located in said housing so light from said focusing screen can enter said viewer; wherein said focusing screen is located so it forms an image of said aperture stop at said entrance aperture; the improvement comprising: a warp, in said surface of said focusing screen, for minimizing astigmatism in the image of said aperture stop at said entrance aperture, said surface including a plurality of grooves, each groove having a face and said face having a uniform slope with respect to said warp everywhere on said surface.

Claim 8

The improved reflex camera described in claim 5, wherein said plurality of grooves is concentric and has an axis of symmetry that defines the optic axis of said focusing screen, said optic axis bisecting the angle defined by the reflection of an axial light ray from said objective lens at the center of said concentric grooves.

Claim 9

The improved reflex camera described in claim 5, further comprising: means for specularly reflecting light from said faces, and wherein the lateral edges of said warp on said surface curve upwardly about the plane defined by the centers of said objective lens, said focusing screen, and said entrance aperture.

Claim 10

A reflex camera, comprising: housing means; objective lens means with an aperture stop, situate in a wall of said housing means, for forming a real image of a subject at a focal plane within said housing; and a focusing screen, at said focal plane, with a reflective surface for receiving said image, said reflective surface including a plurality of concentric grooves, each of said grooves having a face that cooperates with the faces of the other of said grooves to receive light from said aperture stop and reflect it into an image of said aperture stop, said image of said aperture stop being separated from said aperture stop, said surface having an anamorphic contour for ameliorating aberrations otherwise present in the image of said aperture stop formed by said focusing screen.

Claim 11

A reflex camera, comprising: housing means; objective lens means with an aperture stop, situate in a wall of said housing means, for forming a real image of a subject at a focal plane within said housing; and a focusing screen, at said focal plane, with a reflective surface for receiving said image, said reflective surface including a plurality of concentric grooves, each of said grooves having a face that cooperates with the faces of the other of said grooves to receive light from said aperture stop and reflect it into an image of said aperture stop, said image of said aperture stop being separated from said aperture stop, said surface having an anamorphic contour for ameliorating aberrations otherwise present in the image of said aperture stop formed by said focusing screen.

Claim 12

The reflex camera described in claim 8, wherein said anamorphic contour is a cylindrical curve for reflecting light from said aperture stop into a stigmatic image of said aperture stop.