Telescope objective system for the infrared range

Claim 2

A telescope objective system formed by a primary lens having a single lens element aligned on a common optical axis with a secondary lens having two lens elements forming a doublet, the shape and power distribution of the lens elements being such as to compensate for monochromatic aberration of the system, each lens element being made of a material which has a useful spectral bandpass in the infrared wavelength region and the lens elements of the secondary lens having refractive surfaces intercepting said optical axis which are substantially spherical, the system having a planar image surface, a postively-powered primary lens and a negatively-powered secondary lens whereby to provide an effective focal length greater than the axial distance between the image surface and the distal refractive surface, said distal refractive surface being formed by said primary lens element which is made of germanium, at least one of the two lens elements of the secondary lens being made of a chalcogenide glass such that the system is achromatic in the infrared wavelength region, wherein both lens elements of the secondary lens are made of chalcogenide glass having a refractive index of about 2.4916 and a dispersion coefficient of 0.00660, the radius of curvature of the respective refractive surfaces and the separations between successive refractive surfaces as listed from said distal refractive surface, in normalised units, being as follows: ______________________________________ ITEM Radius Separation ______________________________________ Primary Lens 1st Refractive Surface 0.5926 -- 2nd Refractive Surface 0.7692 .0427 Secondary Lens 1st lens 1st Refractive Surface -3.2968 0.3948 element 2nd Refractive Surface 0.3825 .0160 2nd lens 1st Refractive Surface 0.6204 .0267 element 2nd Refractive Surface -1.5895 .0267 ______________________________________ positive radius of curvature indicating a centre of curvature lying on th image plane side of the refractive surface and vice versa.

Claim 3

A telescope objective system formed by a primary lens having a single lens element aligned on a common optical axis with a secondary lens having two lens elements forming a doublet, the shape and power distribution of the lens elements being such as to compensate for monochromatic aberration of the system, each lens element being made of a material which has a useful spectral bandpass in the infrared wavelength region and the lens elements of the secondary lens having refractive surfaces intercepting said optical axis which are substantially spherical, the system having a planar image surface, a positively-powered primary lens and a negatively-powered secondary lens whereby to provide an effective focal length greater than the axial distance between the image surface and the distal refractive surface, said distal refractive surface being formed by said primary lens element which is made of germanium, at least one of the two lens elements of the secondary lens being made of a chalcogenide glass such that the system is achromatic in the infrared wavelength region, wherein both lens elements of the secondary lens are made of chalcogenide glass, the secondary lens element proximal the primary lens having a refractive index of about 2.7792 and a dispersion coefficient of 0.00479, the secondary lens element distal the primary lens having refractive index of about 2.4916, the radius of curvature of the respective refractive surfaces and the separations between successive refractive surfaces as listed from said distal refractive surface, in millimeters, being as follows: ______________________________________ Separa- ITEM Radius tion ______________________________________ Primary 1st Refractive 195.33 -- Lens Surface 2nd Refractive 268.99 15.65 Surface Secondary 1st lens 1st Refractive 825.5 113.37 element Surface Lens 2nd Refractive 109.22 6.05 Surface 2nd lens 1st Refractive 199.06 10.98 element Surface 2nd Refractive -2583.9 10.00 Surface ______________________________________ positive radius or curvature indicating a centre of curvature lying on th image plane side of the refractive surface and vice versa.

Claim 4

A telescope objective system formed by a primary lens having a single lens element aligned on a common optical axis with a secondary lens having two lens elements forming a doublet, the shape and power distribution of the lens elements being such as to compensate for monochromatic aberration of the system, each lens element being made of a material which has a useful spectral bandpass in the infrared wavelength region and the lens elements of the secondary lens having refractive surfaces intercepting said optical axis which are substantially spherical, the system having a planar image surface, a positively-powered primary lens and a negatively-powered secondary lens whereby to provide an effective focal length greater than the axial distance between the image surface and the distal refractive surface, said distal refractive surface being formed by said primary lens element which is made of germanium, at least one of the two lens elements of the secondary lens being made of a chalcogenide glass such that the system is achromatic in the infrared wavelength region, wherein both lens elements of the secondary lens are made of chalcogenide glass, the secondary lens element proximal the primary lens having a refractive index of about 2.7792 and a dispersion coefficient of 0.00479, the secondary lens element distal the primary lens having refractive index of about 2.4916, the radius of curvature of the respective refractive surfaces and the separations between successive refractive surfaces as listed from said distal refractive surface, in millimeters, being as follows: ______________________________________ Separa- ITEM Radius tion ______________________________________ Primary 1st Refractive 195.33 -- Lens Surface 2nd Refractive 268.99 15.65 Surface Secondary 1st lens 1st Refractive 825.5 113.37 element Surface Lens 2nd Refractive 109.22 6.05 Surface 2nd lens 1st Refractive 199.06 10.98 element Surface 2nd Refractive -2583.9 10.00 Surface ______________________________________ positive radius or curvature indicating a centre of curvature lying on th image plane side of the refractive surface and vice versa.

Claim 5

A telescope objective system formed by a primary lens having a single lens element aligned on a common optical axis with a secondary lens having two lens elements forming a doublet, the shape and power distribution of the lens elements being such as to compensate for monchromatic aberration of the system, each lens element being made of a material which has a useful spectral bandpass in the infrared wavelength region and the lens elements of the secondary lens having refractive surfaces intercepting said optical axis which are substantially spherical, the system having a planar image surface, a positively-powered primary lens and a negatively-powered secondary lens whereby to provide an effective focal length greater than the axial distance between the image surface and the distal refractive surface, said distal refractive surface being formed by said primary lens element which is made of germanium, at least one of the two lens elements of the secondary lens being made of a chalcogenide glass such that the system is achromatic in the infrared wavelength region, wherein the secondary lens element distal the primary lens is made of halide crystal material having a refractive index of about 2.3704, and a dispersion coefficient of 0.00385, the secondary lens element proximal the primary lens is made of chalcogenide glass having a refractive index of about 2.8563, the radius of curvature of the respective refractive surfaces and the separations between successive refractive surfaces as listed from said distal refractive surface, in normalised units, being as follows: ______________________________________ ITEM Radius Separation ______________________________________ 1st Refractive Surface .5117 -- 2nd Refractive Surface .6424 .0427 1st lens 1st Refractive Surface 7.6224 .3028 element 2nd Refractive Surface .3796 .016 2nd lens 1st Refractive Surface .5813 .0267 element 2nd Refractive Surface -1.2106 .0267 ______________________________________ positive radius of curvature indicating a centre of curvature lying on th image plane side of the refractive surface and vice versa.

Claim 6

A telescope objective system formed by a primary lens having a single lens element aligned on a common optical axis with a secondary lens having two lens elements forming a doublet, the shape and power distribution of the lens elements being such as to compensate for monchromatic aberration of the system, each lens element being made of a material which has a useful spectral bandpass in the infrared wavelength region and the lens elements of the secondary lens having refractive surfaces intercepting said optical axis which are substantially spherical, the system having a planar image surface, a positively-powered primary lens and a negatively-powered secondary lens whereby to provide an effective focal length greater than the axial distance between the image surface and the distal refractive surface, said distal refractive surface being formed by said primary lens element which is made of germanium, at least one of the two lens elements of the secondary lens being made of a chalcogenide glass such that the system is achromatic in the infrared wavelength region, wherein the secondary lens element distal the primary lens is made of halide crystal material having a refractive index of about 2.3704, and a dispersion coefficient of 0.00385, the secondary lens element proximal the primary lens is made of chalcogenide glass having a refractive index of about 2.8563, the radius of curvature of the respective refractive surfaces and the separations between successive refractive surfaces as listed from said distal refractive surface, in normalised units, being as follows: ______________________________________ ITEM Radius Separation ______________________________________ 1st Refractive Surface .5117 -- 2nd Refractive Surface .6424 .0427 1st lens 1st Refractive Surface 7.6224 .3028 element 2nd Refractive Surface .3796 .016 2nd lens 1st Refractive Surface .5813 .0267 element 2nd Refractive Surface -1.2106 .0267 ______________________________________ positive radius of curvature indicating a centre of curvature lying on th image plane side of the refractive surface and vice versa.