Reflex camera viewfinder with image correcting means

Claim 2

A viewer comprising: means for forming a rectified real image of a focusing screen having an oblique orientation to the optical path through said viewer, wherein the arrangement and the shape of said means for forming said rectified real image causes CACF in, and imparts field tilt to, said rectified real image; means, including a first aspheric optical surface, for minimizing said field tilt by providing different optical powers for viewing different parTs of said rectified real image; and means, including a second aspheric optical surface, for reducing said CACF by providing a compensating optical power gradient at a location substantially conjugate to the exit pupil of said viewer.

Claim 3

The viewer described in claim 1 further comprising means for defining an aperture stop optically conjugate to said exit pupil, and wherein said second aspheric optical surface is slightly displaced from said means for defining an aperture stop so light from different points on said focusing screen will use slightly different, but substantially overlapping regions of said second aspheric optical surface so as to impart differential corrections for reducing said CACF.

Claim 4

The viewer described in claim 2 wherein said second aspheric optical surface is tilted with respect to said optical path.

Claim 5

The viewer described in claim 1 wherein said second aspheric control surface has a non-rotational shape.

Claim 6

The viewer described in claim 4 wherein said means for forming a rectified real image includes an element having a varying power gradient thereon and the power of said second aspheric optical surface differs between adjacent areas such that light rays, emanating from a point on said focusing screen, incident on an optically weaker part of said element, relative to another part of said element, will have utilized an optically stronger part of said second aspheric optical surface, relative to another part of said second aspheric optical surface.

Claim 7

The viewer described in claim 5 wherein the general shape of said second aspheric optical surface is described by the equation U - P20V2 - P02W2 - P30V3 - P12VW2 - P40V4 - P22V2W2 - P04W4 wherein U, V, W represent a coordinate system and the directions designated by V and W are transverse to said optical path, and the subscripted P terms are preselected constants determined by the specific optical effects desired of said second aspheric optical surface.

Claim 8

The viewer described in claim 2 wherein said means for reducing said CACF comprises a corrector plate, said second aspheric surface constitutes at least a portion of one surface of said corrector plate and the surface of said corrector plate opposite said second aspheric surface is a plane surface and said plane surface is positioned against said means for defining an aperture stop, said displacement being determined by the thickness of said corrector plate.

Claim 9

The viewer described in claim 1 further comprising: an aperture stop optically conjugate to said exit pupil; and a support means; wherein said means for correcting said CACF comprises a corrector plate, said second aspheric surface constitutes at least part of one surface of said corrector plate and said corrector plate includes mounting means formed integrally with said corrector plate, said mounting means including at least one tenon for attaching said mounting means to said support means and at least one notch for orienting said corrector plate with respect to said support means.

Claim 10

The viewer described in claim 8 wherein said support means includes means for defining said aperture stop.

Claim 11

A viewer comprising: means for forming a rectified real image of a focusing screen having an oblique orientation to the optic axis of said viewer, wherein the shape of said image forming means causes CACF in, and imparts field tilt to said rectified real image; means for magnifying said rectified real image to form a virtual image thereof, said magnifying means including an optical surface with a first spheric shape for minimizing said field unit tilt otherwise perceived in said virtual image by providing different optical powers for viewing different parts of said rectified real image; and means, including an optical surface with a second aspheric shape, For reducing said CACF by providing a compensating power gradient, said CACF reducing means being located substantially conjugate, optically, to an exit pupil of said viewer.

Claim 12

A viewer comprising: means for forming a rectified real image of a focusing screen having an oblique orientation to the optic axis of said viewer, wherein the shape of said image forming means causes CACF in, and imparts field tilt to said rectified real image; means for magnifying said rectified real image to form a virtual image thereof, said magnifying means including an optical surface with a first spheric shape for minimizing said field unit tilt otherwise perceived in said virtual image by providing different optical powers for viewing different parts of said rectified real image; and means, including an optical surface with a second aspheric shape, For reducing said CACF by providing a compensating power gradient, said CACF reducing means being located substantially conjugate, optically, to an exit pupil of said viewer.

Claim 13

The viewer described in claim 10 wherein said means for forming a rectified real image comprises an aspheric concave mirror, said means for magnifying comprises an eye lens and said means for reducing said CACF comprises a corrector plate.

Claim 14

The viewer described in claim 10 wherein said optical surface with said first aspheric shape is continuously contoured and constitutes the side of an eye lens situate away from said image forming means.

Claim 15

The viewer described in claim 10 further comprising an aperture stop optically conjugate to said exit pupil, wherein said optical surface with said second aspheric shape is continuously contoured and is separated a small distance from said aperture stop so light from different points on said focusing screen will use slightly different, but substantially overlapping portions of said optical surface with said second aspheric shape.

Claim 16

The viewer described in claim 10 wherein the dioptric power of said optical surface with said first aspheric shape, on said magnifying means, differs between adjacent areas in relation to the optical distance from said optical surface with said first aspheric shape of portions of said rectified real image associated with said adjacent areas.

Claim 17

The viewer described in claim 10 wherein said means for forming said rectified real image includes an aspheric concave mirror having a power gradient thereon and the power of said optical surface with said second aspheric shape differs between adjacent areas such that light rays, emanating from a point on said focusing screen, incident on an optically weaker part of said aspheric concave mirror, relative to another part of said aspheric concave mirror, will have passed through an optically stronger part of said second aspheric shape, relative to another part of said second aspheric shape.

Claim 18

The viewer described in claim 10 wherein said optical surface with said second aspheric shape, has a continuous contour, described by a polynomial expression of at least the third order, so its dioptric power varies continuously as a function of height.

Claim 19

The viewer described in claim 11 wherein: the general shape of said aspheric concave mirror is a portion, away from the rotational axis, of the surface of revolution generated by rotating, about the Y axis, the curve described for positive values of X by the equation Y CmX2/(1 + Square Root 1 - (1 - e2) Cm2X2) + A2X2 + A3X3 + A4X4 + A5X5 + A6X6 + A7X7 + A8X8; the general shape of said first aspheric shape on said eye lens is described by the equation U - Ce (V2 + W2)/(1 + Square Root 1 - Ce2 (V2 + W2)) - Beta (V2 + W2)2 - gamma (V2 + W2)3 - G20V2 - G30V3 - G40V4 -G12VW2 - G22V2W2 - G04W4 - G50V5 - G60V6 - G32V3W2 - G42V4W2 -G14VW4 - G24V2W4 - G06W6; and the general shape of said second aspheric shape on said corrector plate is described by the equation U - P20V2 - P02W2 - P30V3 - P12VW2 - P40V4 - P22V2W2 - P04W4 wherein U, V, W, represent a coordinate system and the directions desIgnated by V and W are transverse to the optic axis of said viewer, the constants Cm and Ce represent nominal curvatures associated with said aspheric concave mirror and said first aspheric surface on said eye lens respectively, the values of the constants e2 and the subscripted A terms are preselected constants determined by the optical effects desired of said aspheric concave mirror, the values of the constants gamma , and the subscripted G terms are preselected constants determined by the optical effects desired of said first aspheric shape on said eye lens, and the subscripted P terms are preselected constants determined by the optical effects desired of said second aspheric shape on said corrector plate.

Claim 20

The viewer described in claim 16 further comprising: a spherical surface on the side of said eye lens toward said aspheric concave mirror; and a plane surface on the side of said corrector plate toward said aspheric concave mirror; wherein said spherical surface has a radius of 0.905 inch, centered below the viewer''s optical axis, and wherein the constants have the values tabulated herein: for said aspheric concave mirror Cm 0.078 13 /in e2 8.94 X 103 A2 0.269 76 /in A3 0.019 30 /in2 A4 0.010 04 /in3 A5 0.009 03 /in4 A6 0.001 70 /in5 A7 0.000 06 /in6 A8 0.000 16 /in7 and the center of the utilized portion of said surface of revolution is 0.707 inches in the X direction from the Y axis; for said first aspheric shape on said eye lens

Claim 21

A viewfinder comprising: aspheric reflecting means, having a viewing direction, for forming a rectified real image of a focusing screen oriented at an oblique angle with respect to said viewing direction, wherein the arrangement and the shape of said aspheric reflecting means causes CACF in, and imparts field tilt to, said rectified real image; eye lens means for magnifying said rectified real image to form a virtual image, said eye lens including accommodation reducing means for minimizing said field tilt of said virtual image corrector means located optically conjugate to the exit pupil of said viewfinder, for reducing said CACF otherwise apparent in said virtual image.

Claim 22

A viewfinder comprising: aspheric reflecting means, having a viewing direction, for forming a rectified real image of a focusing screen oriented at an oblique angle with respect to said viewing direction, wherein the arrangement and the shape of said aspheric reflecting means causes CACF in, and imparts field tilt to, said rectified real image; eye lens means for magnifying said rectified real image to form a virtual image, said eye lens including accommodation reducing means for minimizing said field tilt of said virtual image corrector means located optically conjugate to the exit pupil of said viewfinder, for reducing said CACF otherwise apparent in said virtual image.

Claim 23

The viewfinder described in claim 19 wherein; said accommodation reducing means comprises a first aspheric 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 portions of said rectified real image associated with said adjacent areas.

Claim 24

The viewfinder described in claim 19 wherein: said corrector means for reducing said CACF comprises a correcting plate with a second aspheric refracting surface whose power differs between adjacent areas such that light rays, emanating from a point on said focusing screen, incident on an optically weaker part of said aspheric reflecting means, relative to another part of said aspheric reflecting means, will have passed through an optically stronger part of said second aspheric refracting surface, relative to another part of said second aspheric refracting surface.

Claim 25

The viewfinder described in claim 21 further comprising an aperture stop optically conjugate to said exit pupil and wherein said corrector means is positioned, with respect to said aperture stop, so said second aspheric refracting surface is lightly displaced therefrom.

Claim 26

The viewfinder described in claim 21, wherein said second aspheric refracting surface, situate on said correcting plate, has a continuous contour, described by a polynomial expression of at least the third order, so its dioptric power varies continuously as a function of height.

Claim 27

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, an aspheric concave mirror for forming a rectified real image of said reflective focusing screen using said light wherein the shape and the arrangement of said aspheric concave mirror introduces field tilt into said rectified real image and said shape of said aspheric concave mirror causes CACF in said rectified real image, an aperture stop disposed between said first mirror and said aspheric concave mirror to transmit said light, a correcting plate disposed proximate said aperture stop, said eye lens arranged to form a magnified virtual image of said rectified real image, a first aspheric refracting surface, situate on said eye lens, for minimizing said field tilt otherwise associated with said magnified virtual image, and a second aspheric refracting surface, situate on said correcting plate, for reducing said CACF otherwise associated with said magnified virtual image.

Claim 28

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, an aspheric concave mirror for forming a rectified real image of said reflective focusing screen using said light wherein the shape and the arrangement of said aspheric concave mirror introduces field tilt into said rectified real image and said shape of said aspheric concave mirror causes CACF in said rectified real image, an aperture stop disposed between said first mirror and said aspheric concave mirror to transmit said light, a correcting plate disposed proximate said aperture stop, said eye lens arranged to form a magnified virtual image of said rectified real image, a first aspheric refracting surface, situate on said eye lens, for minimizing said field tilt otherwise associated with said magnified virtual image, and a second aspheric refracting surface, situate on said correcting plate, for reducing said CACF otherwise associated with said magnified virtual image.

Claim 29

The camera described in claim 24 wherein the dioptric power of said second aspheric refracting surface, situate on said correcting plate, differs between adjacent areas such that light rays, emanating from a point on said reflective focusing screen, incident on a less optically strong part of said aspheric concave mirror, relative to another part of said aspheric concave mirror, will have passed through an optically stronger part of said second aspheric refracting surface, relative to another part of said second aspheric refracting surface.

Claim 30

The camera described in claim 24 wherein said second aspheric surface is spaced a small distance from said aperture stop.

Claim 31

The camera described in claim 26 wherein said first aspheric refracting surface is the side of said eye lens situate away from said aspheric concave mirror and said correcting plate is on the side of said aperture stop situate away from said aspheric concave mirror and said second aspheric refracting surface is on the side of said correcting plate furthest from said aspheric concave mirror.

Claim 32

The camera described in claim 24 wherein said second aspheric refracting surface, siTuate on said correcting plate, has a continuous contour, described by a polynomial expression of at least the third order, so its dioptric power varies continuously as a function of height.

Claim 33

The camera described in claim 24 wherein: the general shape of said aspheric concave mirror is a portion, away from the rotational axis, of the surface of revolution generated by rotating, about the Y axis, the curve described for positive values of X by the equation Y CmX2/(1 + Square Root 1 - (1 - e2) Cm2X2) + A2X2 + A3X3 + A4X4 + A5X5 + A6X6 + A7X7 + A8X8; the general shape of said first aspheric surface, on said eye lens, is described by the equation U - Ce (V2 + W2)/(1 + Square Root 1 - Ce2 (V2 + W2)) - Beta (V2 + W2) 2 - gamma (V2 + W2)3 - G20V2 - G30V3 - G40V4 -G12VW2 - G22V2W2 - G04W4 - G50V5 - G60V6 - G32V3W2 - G42V4W2 -G14VW4 - G24V2W4 -G06W6; and the general shape of said second aspheric surface, on said corrector plate, is described by the equation U - P20V2 - P02W2 - P30V3 - P12VW2 - P40V4 - P22V2W2 - P04W4 wherein U, V, W, represent a coordinate system and the directions designated by V and W are transverse to the optic axis of said viewer, the constants Cm and Ce represent nominal curvatures associated with said aspheric concave mirror and said first aspheric surface respectively, the values of the constants e2 and the subscripted A terms are preselected constants determined by the optical effects desired of said aspheric concave mirror, the values of the constants gamma , and the subscripted G terms are preselected constants determined by the optical effects desired of said first aspheric surface, and the subscripted P terms are preselected constants determined by the optical effects desired of said second aspheric surface.

Claim 34

The camera described in claim 29 further comprising: a spherical surface on the side of said eye lens toward said aspheric concave mirror; and a plane surface on the side of said corrector plate toward said aspheric concave mirror; wherein said aperture stop separates said corrector plate from said aspheric concave mirror, wherein said spherical surface has a radius of 0.905 inches, centered below the system''s optical axis, and wherein said preselected constants have the values tabulated herein: for said aspheric concave mirror Cm 0.078 13 /in e2 8.94 X 103 A2 0.269 76 /in A3 0.019 30 /in2 A4 0.010 04 /in3 A5 0.009 03 /in4 A6 0.001 70 /in5 A7 0.000 06 /in6 A8 0.000 16 /in7 and the center of the utilized portion of said surface of revolution is 0.707 inches in the X direction from the Y axis; for said first aspheric surface

Claim 35

An optical element having an aspheric surface described by the equation U - P20V2 - P02W2 - P30V3 - P12VW2 - P40V4 - P22V2W2 - P04W4 wherein U, V and W represent a coordinate system and the directions designated by V and W are transverse to the optical path through said optical element and the subscripted P terms are constants having the values tabulated herein: P20 + 0.0341 P02 + 0.1015 P30 + 1.455 P12 + 2.303 P40 - 3.30 P22 - 8.1 P04 - 5.9 for the U direction oriented at 15* to said optical path.

Claim 36

An optical element having an aspheric surface described by the equation U - P20V2 - P02W2 - P30V3 - P12VW2 - P40V4 - P22V2W2 - P04W4 wherein U, V and W represent a coordinate system and the directions designated by V and W are transverse to the optical path through said optical element and the subscripted P terms are constants having the values tabulated herein: P20 + 0.0341 P02 + 0.1015 P30 + 1.455 P12 + 2.303 P40 - 3.30 P22 - 8.1 P04 - 5.9 for the U direction oriented at 15* to said optical path.