Restricted off-axis field optical system

Claim 2

In a restricted off-axis field optical system having a broad spectral range, which includes refracting means, the improvement comprising: said optical system being constructed and arranged so that the Petzval sum is substantially zero, and said refracting means including means for balancing the effects of the variation in said Petzval sum due to variation in color by introducing axial chromatic aberration of the opposite sense so that the position of focus at the off-axis field remains substantially constant.

Claim 3

A restricted off-axis field catadioptric optical system having a broad spectral range comprising, in combination: at least one convex and one concave mirror, said mirrors being nearly concentrically arranged along an optical axis; and refracting means; said optical system being constructed and arranged so that The Petzval sum is substantially zero, and said refracting means including means for balancing the effects of the variation in said Petzval sum due to variation in color by introducing axial chromatic aberration of the opposite sense so that the position of focus at the off-axis field remains substantially constant.

Claim 4

A restricted off-axis field catadioptric optical system having a broad spectral range comprising, in combination: at least one convex and one concave mirror, said mirrors being nearly concentrically arranged along an optical axis; and refracting means; said optical system being constructed and arranged so that The Petzval sum is substantially zero, and said refracting means including means for balancing the effects of the variation in said Petzval sum due to variation in color by introducing axial chromatic aberration of the opposite sense so that the position of focus at the off-axis field remains substantially constant.

Claim 5

An optical system according to claim 1 or claim 2 wherein said restricted off-axis field is an annular field.

Claim 6

An optical system according to claim 1 or claim 2 wherein the refracting means is constructed of a single optical material.

Claim 7

An optical system according to claim 1 or claim 2 wherein said means for compensating for the variation in field curvature with color in the restricted off-axis field by introducing axial chromatic aberration of the opposite sense comprises at least one pair of symmetrically disposed nearly concentric meniscus elements whose convex radii are larger than their concave radii and whose axial thickness is greater than the difference between their convex and concave radii, respectively.

Claim 8

An optical system according to claim 1 wherein said means for compensating for the variation in field curvature with color in the restricted off-axis field by introducing axial chromatic aberration of the opposite sense comprises one pair of symmetrically disposed nearly concentric meniscus elements whose convex radii are larger than their concave radii and whose axial thickness is greater than the difference between their convex and concave radii, respectively; and color trimming means.

Claim 9

An optical system according to claim 2 wherein said means for compensating for the variation in field curvature with color in the restricted off-axis field by introducing axial chromatic aberration of the opposite sense comprises one pair of symmetrically disposed nearly concentric meniscus elements whose convex radii are larger than their concave radii and whose axial thickness is greater than the difference between their convex and concave radii, respectively; and color trimming means.

Claim 10

The optical system of claim 6 or claim 7 wherein all of the refracting elements are constructed of a single optical material.

Claim 11

The optical system according to claim 2 wherein said mirrors are arranged so that there are three reflections from said concave mirror and two reflections from said convex mirror.

Claim 12

An annular field catadioptric optical system having a broad spectral range comprising, in combination: at least one convex and one concave mirror, said mirrors being nearly concentrically arranged along an optical axis; and refracting means; said optical system being constructed and arranged so that the Petzval sum is substantially zero, and said refracting means including means for balancing the effects of the variation in said Petzval sum due to variation in color by introducing axial chromatic aberration of the opposite sense so that the position of focus at the annular field remains substantially constant; said means for balancing the effects of the variation in said Petzval sum due to variation in color comprising at least one pair of symmetrically disposed nearly concentric meniscus elements whose convex radii are larger than their concave radii and whose axial thickness is greater than the difference between their convex and concave radii, respectively; and wherein the relationship between the annular radius of the system and the characteristics of the nearly concentric meniscus lens is defined by the formula: R.sub.2 >R.sub.1 and t≃R.sub.2 -R.sub.1 +(H.sup.2 /2N.sup.2) (1/R.sub.1 -1/R.sub.2) where: H=the annular radius of the system, R 1 =the concave radius of the meniscus lens, R 2 =the convex radius of the meniscus lens, t=the thickness of the meniscus lens, and N=the index of refraction of the meniscus lens.

Claim 13

An annular field catadioptric optical system having a broad spectral range comprising, in combination: at least one convex and one concave mirror, said mirrors being nearly concentrically arranged along an optical axis; and refracting means; said optical system being constructed and arranged so that the Petzval sum is substantially zero, and said refracting means including means for balancing the effects of the variation in said Petzval sum due to variation in color by introducing axial chromatic aberration of the opposite sense so that the position of focus at the annular field remains substantially constant; said means for balancing the effects of the variation in said Petzval sum due to variation in color comprising at least one pair of symmetrically disposed nearly concentric meniscus elements whose convex radii are larger than their concave radii and whose axial thickness is greater than the difference between their convex and concave radii, respectively; and wherein the relationship between the annular radius of the system and the characteristics of the nearly concentric meniscus lens is defined by the formula: R.sub.2 >R.sub.1 and t≃R.sub.2 -R.sub.1 +(H.sup.2 /2N.sup.2) (1/R.sub.1 -1/R.sub.2) where: H=the annular radius of the system, R 1 =the concave radius of the meniscus lens, R 2 =the convex radius of the meniscus lens, t=the thickness of the meniscus lens, and N=the index of refraction of the meniscus lens.

Claim 14

An annular field catadioptric optical system having a broad spectral range comprising, in combination: at least one convex and one concave mirror, said mirrors being nearly concentrically arranged along an optical axis; and refracting means; said optical system being constructed and arranged so that the Petzval sum is substantially zero, and said refracting means including means for balancing the effects of the variation in said Petzval sum due to variation in color by introducing axial chromatic aberration of the opposite sense so that the position of focus at the annular field remains substantially constant; said means for balancing the effects of the variation in said Petzval sum due to variation in color comprising at least one pair of symmetrically disposed nearly concentric meniscus elements whose convex radii are larger than their concave radii and whose axial thickness is greater than the difference between their convex and concave radii, respectively; and color trimming means; and wherein the relationship between the annular radius of the system and the characteristics of the nearly concentric meniscus lens is defined by the formula: R.sub.2 >R.sub.1 and t>R.sub.2 -R.sub.1 +(H.sup.2 /2N.sup.2) (1/R.sub.1 -1/R.sub.2) where: H=the annular radius of the system, R 1 =the concave radius of the meniscus lens, R 2 =the convex radius of the meniscus lens, t=the thickness of the meniscus lens, and N=the index of refraction of the meniscus lens.

Claim 15

An annular field catadioptric optical system having a broad spectral range comprising, in combination: at least one convex and one concave mirror, said mirrors being nearly concentrically arranged along an optical axis; and refracting means; said optical system being constructed and arranged so that the Petzval sum is substantially zero, and said refracting means including means for balancing the effects of the variation in said Petzval sum due to variation in color by introducing axial chromatic aberration of the opposite sense so that the position of focus at the annular field remains substantially constant; said means for balancing the effects of the variation in said Petzval sum due to variation in color comprising at least one pair of symmetrically disposed nearly concentric meniscus elements whose convex radii are larger than their concave radii and whose axial thickness is greater than the difference between their convex and concave radii, respectively; and color trimming means; and wherein the relationship between the annular radius of the system and the characteristics of the nearly concentric meniscus lens is defined by the formula: R.sub.2 >R.sub.1 and t>R.sub.2 -R.sub.1 +(H.sup.2 /2N.sup.2) (1/R.sub.1 -1/R.sub.2) where: H=the annular radius of the system, R 1 =the concave radius of the meniscus lens, R 2 =the convex radius of the meniscus lens, t=the thickness of the meniscus lens, and N=the index of refraction of the meniscus lens.

Claim 16

An annular field catadioptric optical system having a broad spectral range comprising, in combination: at least one convex and one concave mirror, said mirrors being nearly concentrically arranged along an optical axis; means defining a location for an object the image of which is a real image at a second location, said convex mirror being positioned to reflect to said concave mirror light from said object location initially reflected to said convex mirror from said concave mirror, whereby light from said object location will be reflected twice at said concave mirror and at least once at said convex mirror before being focused at said second location; and refracting means; said optical system being constructed and arranged so that the Petzval sum is substantially zero, and said refracting means including means for balancing the effects of the variation in said Petzval sum due to variation in color by introducing axial chromatic aberration of the opposite sense so that the position of focus at the annular field remains substantially constant; said means for balancing the variation in said Petzval sum due to variation in color including at least one pair of symmetrically disposed nearly concentric meniscus elements whose convex radii are larger than their concave radii and whose axial thickness is greater than the difference between their convex and concave radii, respectively; and color trimming means.

Claim 17

An annular field catadioptric optical system having a broad spectral range comprising, in combination: at least one convex and one concave mirror, said mirrors being nearly concentrically arranged along an optical axis; means defining a location for an object the image of which is a real image at a second location, said convex mirror being positioned to reflect to said concave mirror light from said object location initially reflected to said convex mirror from said concave mirror, whereby light from said object location will be reflected twice at said concave mirror and at least once at said convex mirror before being focused at said second location; and refracting means; said optical system being constructed and arranged so that the Petzval sum is substantially zero, and said refracting means including means for balancing the effects of the variation in said Petzval sum due to variation in color by introducing axial chromatic aberration of the opposite sense so that the position of focus at the annular field remains substantially constant; said means for balancing the variation in said Petzval sum due to variation in color including at least one pair of symmetrically disposed nearly concentric meniscus elements whose convex radii are larger than their concave radii and whose axial thickness is greater than the difference between their convex and concave radii, respectively; and color trimming means.

Claim 18

An annular field optical system according to claim 12 wherein said color trimming means is a substantially plane parallel plate mounted normal to the optical axis of said mirrors.

Claim 19

An annular field optical system according to claim 12 wherein said color trimming means is a plate having an aspheric surface.

Claim 20

An annular field optical system according to claim 12 wherein said color trimming means is a weak meniscus element mounted normal to the optical axis of said mirrors.

Claim 21

An annular field optical system according to claim 12 wherein said color trimming means is interposed between said mirrors and said object and image locations.

Claim 22

An annular field optical system according to claim 12 wherein said color trimming means is interposed between said meniscus elements and said mirrors.

Claim 23

An annular field optical system according to claim 15 wherein said system is characterized by the following construction data: __________________________________________________________________________ SURFACE NO. DISTANCE FROM OBJECT RADIUS TO NEXT TO IMAGE (mm.) SURFACE (mm.) MATERIAL __________________________________________________________________________ 0 (PLANE) 144.92 AIR OBJECT 1 -144.96 11.03 FUSED SILICA 2 -151.75 88.70 AIR 3 -957.30 16.75 FUSED SILICA 4 -967.84 295.25 AIR 5 -551.15 -279.07 AIR MIRROR 6 -267.18 279.07 AIR MIRROR 7 -551.15 -295.25 AIR MIRROR 8 -967.84 -16.75 FUSED SILICA 9 -957.30 -88.70 AIR 10 -151.75 -11.03 FUSED SILICA 11 -144.96 -144.92 AIR 12 (PLANE) IMAGE __________________________________________________________________________

Claim 24

An annular field optical system having a broad spectral range, which includes refracting means, said optical system comprising: a first half and a second half, each half including an optical system having an optical axis and having conjugate planes substantially normal to said axis; the first half and the second half being coaxially disposed in back-to-back relationship so that the conjugate planes are superposed on at least one side of the optical system, and means for providing spaced object and final image locations on the other side of the optical system, said optical system being constructed and arranged so that the Petzval sum is substantially zero, and said refracting means including means for balancing the effects of the variation in said Petzval sum due to variation in color by introducing axial chromatic aberration of the opposite sense so that the positions of focus at the annular field portions of the conjugate planes remain substantially constant.

Claim 25

An annular field optical system having a broad spectral range, which includes refracting means, said optical system comprising: a first half and a second half, each half including an optical system having an optical axis and having conjugate planes substantially normal to said axis; the first half and the second half being coaxially disposed in back-to-back relationship so that the conjugate planes are superposed on at least one side of the optical system, and means for providing spaced object and final image locations on the other side of the optical system, said optical system being constructed and arranged so that the Petzval sum is substantially zero, and said refracting means including means for balancing the effects of the variation in said Petzval sum due to variation in color by introducing axial chromatic aberration of the opposite sense so that the positions of focus at the annular field portions of the conjugate planes remain substantially constant.

Claim 26

An annular field optical system according to claim 19 wherein said means for balancing the effects of the variation in said Petzval sum due to variation in the color includes in said first half and in said second half a symmetrically disposed nearly concentric meniscus element whose convex radius is larger than its concave radius and whose thickness is greater than the difference between its convex and concave radii.

Claim 27

An annular field optical system according to claim 20 wherein said first half and said second half each further include color trimming means.

Claim 28

An annular field optical system according to claim 21 wherein said color trimming means is a plane parallel plate mounted substantially normal to the optical axis.

Claim 29

An annular field optical system according to claim 21 wherein said color trimming means is a plate having an aspheric surface.

Claim 30

An annular field optical system according to claim 21 wherein said color trimming means is a weak meniscus element mounted normal to the optical axis.

Claim 31

An annular field optical system according to any one of claims 19, 20, 22, 23, and 24, wherein said first half and said second half each include a concave mirror and a convex mirror, said mirrors being supported with their centers of curvature substantially coincident.

Claim 32

An annular field optical system according to claim 21 wherein said first half and said second half each include a concave mirror and a convex mirror, said mirrors being supported with their centers of curvature substantially coincident.

Claim 33

An annular field optical system according to claim 21 or claim 26 wherein said means for providing spaced object and final image locations comprises folding mirrors.

Claim 34

An annular field optical system according to claim 21 or claim 26 wherein said first half and said second half are substantially symmetrical with respect to an axis in said conjugate planes.

Claim 35

An annular field optical system according to any one of claims 19, 20, 21, and 26, wherein the optical system of the first half and the optical system of the second half are each substantially unit power optical systems.

Claim 36

An annular field optical system according to claim 26 wherein said meniscus elements are interposed between said mirrors and said object and final image locations, respectively.

Claim 37

An annular field optical system according to claim 26 wherein said meniscus elements are interposed between said mirrors and said intermediate image location, respectively.

Claim 38

An annular field optical system according to claim 26 wherein said color trimming means includes two elements which are interposed between said mirrors and said intermediate image location, respectively.

Claim 39

An annular field optical system according to claim 26 wherein said color trimming means includes two elements which are interposed between said mirrors and said object and final image locations, respectively.

Claim 40

An annular field optical system according to claim 26 wherein said color trimming means is a single element disposed at said intermediate image location.

Claim 41

An annular field optical system according to claim 19 wherein each half includes a concave mirror and a convex mirror facing said concave mirror and a convex mirror facing said concave mirror, said mirrors being substantially concentrically arranged along said axis; and wherein on the other side of the optical system the distance from the conjugate location to the two mirror component is different from the distance to the intermediate image location in at least one half, to thereby provide the spaced object and final image locations.

Claim 42

An annular field optical system according to claim 35 wherein said means for balancing the effects of the variation in said Petzval sum due to variation in color includes in said first half and in said second half a nearly concentric meniscus element whose convex radius is larger than its concave radius and whose thickness is greater than the difference between its convex and concave radii.

Claim 43

An annular field optical system according to claim 36 wherein said meniscus elements are interposed between said mirrors and said object and final image locations, respectively.

Claim 44

An annular field optical system according to claim 36 wherein said meniscus elements are interposed between said mirrors and said intermediate image location, respectively.

Claim 45

An annular field optical system according to claim 36 or claim 37 or claim 38 wherein said optical system further includes a color trimming element disposed substantially at said intermediate image location.

Claim 46

An annular field optical system according to claim 36 or claim 37 or claim 38 wherein said optical system further includes a plane parallel plate mounted substantially normal to the optical axis and substantially at said intermediate image location.

Claim 47

An annular field optical system according to claim 36 or claim 37 or claim 38 wherein said optical system further includes a plane parallel plate mounted substantially normal to the optical axis and substantially at said intermediate image location and wherein one of the faces of said plane parallel plate is made aspheric.

Claim 48

An annular field optical system according to claim 36 or claim 37 or claim 38 wherein said optical system further includes a weak meniscus element, mounted normal to the optical axis of said mirrors and substantially at said intermediate image location.

Claim 49

An annular field optical system according to any one of claims 35 to 38 wherein said first half and said second half are substantially symmetrical with respect to an axis through the intermediate image location.

Claim 50

An annular field optical system according to claim 19 wherein each half includes a concave mirror and a convex mirror facing said concave mirror, said mirrors being substantially concentrically arranged along an optical axis; and wherein the distance from the intermediate image to the two mirror component is greater than the distance from the other conjugate location to the two mirror component in at least one half to thereby space said object and final image locations one from the other, said means for balancing the effects of the variation in said Petzval sum due to variation in color includes in said first half and in said second half a meniscus element interposed between said mirrors and said intermediate image location, said meniscus element being nearly concentric but having a difference between the radii of its meniscus surfaces of less than its thickness so that it is not exactly concentric while its power is negative, and a color trimming element disposed substantially at said intermediate image location, said element being normal to the optical axis of said mirrors.

Claim 51

An annular field optical system according to claim 44 wherein said system is characterized by the following construction data: __________________________________________________________________________ SURFACE NO DISTANCE FROM OBJECT RADIUS TO NEXT TO IMAGE (mm.) SURFACE (mm.) MATERIAL __________________________________________________________________________ 0 (PLANE) 107.13 AIR OBJECT 1 -128.18 10.48 FUSED SILICA 2 -135.29 378.48 AIR 3 -541.32 -273.56 AIR MIRROR 4 -264.61 273.56 AIR MIRROR 5 -541.32 -590.28 AIR MIRROR 6 -1772.58* -7.01 FUSED SILICA ASPHERIC 7 (PLANE) -587.26 AIR 8 541.32 273.56 AIR MIRROR 9 264.61 -273.56 AIR MIRROR 10 541.32 378.48 AIR MIRROR 11 135.29 10.48 FUSED SILICA 12 128.18 107.13 AIR 13 (PLANE) IMAGE __________________________________________________________________________ *ASPHERIC SURFACE SYMMETRICAL ABOUT OPTICAL AXIS, and the RADIUS OF ANNULUS = 100 mm. and the DEPARTURE, X, FROM PLANE SURFACE AT DISTANCE r FROM AXIS. X = -1772.58 + 1772.58 - r.sup.2 + 1.732 × 10.sup.-8 r.sup.4 + 4.21 × 10.sup.-13 r.sup.6 + 8.278 × 10.sup.-18 r.sup.8 - 4.078 × 10.sup.-21 r.sup.10.

Claim 52

An annular field optical system according to claim 19 wherein said intermediate image location is axially displaced from the other conjugate plane in at least one half so that said final image location and said object location are crossed, and reflecting means interposed between the object and final image locations to reposition said locations to make them physically accessible.

Claim 53

An annular field optical system according to claim 46 wherein said first half and said second half each include a concave mirror and a convex mirror facing said concave mirror.

Claim 54

An annular field optical system according to claim 47 wherein said means for balancing the effects of the variation in said Petzval sum due to variation in color includes in said first half and in said second half a nearly concentric meniscus element whose convex radius is larger than its concave radius and whose thickness is greater than the difference between its convex and concave radii.

Claim 55

An annular field optical system according to claim 48 wherein said meniscus elements are interposed between said mirrors and said intermediate image location, respectively.

Claim 56

An annular field optical system according to claim 49 wherein said optical system further includes a color trimming element disposed substantially at said intermediate image location.

Claim 57

An annular field optical system according to claim 49 wherein said first half and said second half each further include a color trimming element.

Claim 58

An annular field optical system according to claim 49 wherein said first half and said second half each have a color trimming element interposed between said mirrors and said object and final image locations respectively, said element being normal to the optical axis of said mirrors.

Claim 59

An annular field optical system according to claim 52 wherein one of the faces of said color trimming element is made aspheric.

Claim 60

An annular field optical system according to claim 47 wherein in each half of the system, said concave and convex mirrors are supported with a distance between their centers of curvature of less than about three percent of the length of the shorter radius.

Claim 61

An annular field optical system according to claim 52 wherein said first half and said second half are substantially symmetrical with respect to an axis through the intermediate image location.

Claim 62

An annular field optical system according to claim 52 wherein said system is characterized by the following construction data: __________________________________________________________________________ SURFACE NO. DISTANCE FROM OBJECT RADIUS TO NEXT TO IMAGE (mm.) SURFACE (mm.) MATERIAL __________________________________________________________________________ 0 (PLANE) 151.33 AIR OBJECT 1 -726.89 28.69 FUSED SILICA 2 -730.32 410.82 AIR 3 -552.06 -280.16 AIR MIRROR 4 -267.18 280.16 AIR MIRROR 5 -552.06 -363.25 AIR MIRROR 6 -160.78 24.03 FUSED SILICA 7 -145.19 -272.77 AIR 8 145.19 -24.03 FUSED SILICA 9 160.78 -363.25 AIR 10 552.06 280.16 AIR MIRROR 11 267.18 -280.16 AIR MIRROR 12 552.06 410.82 AIR MIRROR 13 730.32 28.69 FUSED SILICA 14 726.89 151.33 AIR IMAGE 15 (PLANE) __________________________________________________________________________ and RADIUS OF ANNULUS = 100 mm.

Claim 63

An annular field optical system according to claim 19 wherein each half includes a concave mirror and a convex mirror facing said concave mirror, said mirrors being supported with their centers of curvature substantially coincident; and wherein the distance from the intermediate image to the two mirror component is greater than the distance from the other conjugate location to the two mirror component in at least one half, to thereby space said object and final image locations one from the other, said means for balancing the effects of the variation in said Petzval sum due to variation in color includes in said first half and in said second half a meniscus element interposed between said mirrors and said intermediate image location, said meniscus element being symmetrically disposed and nearly concentric having a convex radius larger than its concave radius and a thickness greater than the difference between its convex and concave radii.

Claim 64

An annular field optical system according to claim 57 wherein said first half and said second half each have a color trimming element interposed between said mirrors and said object and final image locations repectively, said element being normal to the optical axis of said mirrors.

Claim 65

An annular field optical system according to claim 58 wherein one of the faces of said color trimming element is aspheric.

Claim 66

An annular field optical system according to claim 58 wherein said color trimming element is a meniscus element.

Claim 67

An annular field optical system according to claim 58 wherein, in each half of the system, said concave and convex mirrors are supported with a distance between their centers of curvature of less than about three percent of the length of the shorter radius.

Claim 68

An annular field optical system according to claim 58 wherein said first half and said second half are substantially symmetrical with respect to an axis through the intermediate image location.

Claim 69

An annular field optical system according to claim 58 wherein said system is characterized by the following construction data: __________________________________________________________________________ RADIUS OF ANNULUS = 100 mm. DISTANCE TO NEXT SURFACE NO RADIUS (mm.) SURFACE (mm.) MATERIAL NOTE __________________________________________________________________________ 0 (PLANE) 88.41 AIR OBJECT 1 -212.36 8.37 FUSED SILICA 2 -217.77 394.30 AIR 3 -539.26 -271.74 AIR MIRROR 4 -264.45 271.74 AIR MIRROR 5 -539.26 -476.12 AIR MIRROR 6 -128.55 -6.68 FUSED SILICA 7 -123.91 -220.54 AIR 8 123.91 -6.68 FUSED SILICA 9 128.55 -476.12 AIR 10 539.26 271.74 AIR MIRROR 11 264.45 -271.74 AIR MIRROR 12 539.26 394.30 AIR MIRROR 13 217.77 8.37 FUSED SILICA 14 212.36 88.41 AIR 15 (PLANE) IMAGE __________________________________________________________________________

Claim 70

An annular field catadioptric optical system comprising: at least one concave and one convex mirror arranged around an optical axis in face-to-face relationship with their centers of curvature being substantially concentric and falling on said axis, the convex mirror being smaller than and having a smaller radius of curvature than the concave mirror; means defining an object location and a conjugate real image location, said convex mirror being positioned to reflect to said concave mirror light from said object location initially reflected from said concave mirror whereby light from said object location will be reflected at least twice at said concave mirror and at least once at said convex mirror before being focused at the image location; means for limiting the image field to an annular zone centered about the optical axis; and refracting means positioned in the light path between the object and image locations, said refracting means including means to reduce the spherical aberration of principal rays parallel to the optical axis, and means to introduce axial chromatic aberration of the opposite sense to balance out in said annular zone variations in focus resulting from curvature due to variations in wavelength.

Claim 71

An annular field catadioptric optical system comprising: at least one concave and one convex mirror arranged around an optical axis in face-to-face relationship with their centers of curvature being substantially concentric and falling on said axis, the convex mirror being smaller than and having a smaller radius of curvature than the concave mirror; means defining an object location and a conjugate real image location, said convex mirror being positioned to reflect to said concave mirror light from said object location initially reflected from said concave mirror whereby light from said object location will be reflected at least twice at said concave mirror and at least once at said convex mirror before being focused at the image location; means for limiting the image field to an annular zone centered about the optical axis; and refracting means positioned in the light path between the object and image locations, said refracting means including means to reduce the spherical aberration of principal rays parallel to the optical axis, and means to introduce axial chromatic aberration of the opposite sense to balance out in said annular zone variations in focus resulting from curvature due to variations in wavelength.

Claim 72

The system of claim 64 wherein the entirety of said refracting means is made from the same optical material.

Claim 73

The system of claim 64 or 65 further provided with color trimming means to maximize aberration reduction in said annular zone.