Variable magnification infrared objective lens assembly

Claim 2

An infrared objective lens assembly comprising a four-component zoom system arranged to accept from object space input radiation in the infrared waveband and a one-component collecting system arranged to form a real image from radiation delivered thereto by said zoom system, the components of said zoom and collecting system being formed by lens elements the refractive surfaces of which intercept a common optical axis, and wherein with respect to said collecting system the first and third components of said zoom system each have negative optical power and are mounted on a common carriage so as to be selectively positionable along said optical axis, the second and fourth components of said zoom system each have positive optical power and are fixedly positioned on said optical axis whereby said zoom system is optically-compensated and of variable effective focal length, said third zoom-system component being movable between a first location proximal to said fourth zoom-system component which first location establishes the lowest magnification factor of the zoom system and a second location, proximal to said second zoom-system component, which second location establishes the highest magnification factor of the zoom system, said zoom system being unstopped so that movements of the first and third zoom-system components give rise to movements in the axial position of the pupil formed by the assembly prior to the real image, said pupil moving between a lowest-magnification-factor position lying intermediate the collecting system and the first zoom-system component and a highest-magnification-factor position lying intermediate the third zoom-system component and the fourth zoom-system component, and said fourth zoom-system component comprises a lens element having an aspheric refractive surface, the refractive surfaces of all other lens elements of the zoom system being non-aspheric.

Claim 3

An assembly as claimed in claim 1, wherein said collecting system is mounted on a carrier and is movable along said optical axis at least to a limited extent to enable refocussing of the image in compensation of the limited defocussing which occurs throughout the range of movements of the zoom system and due to the effects of temperature variations.

Claim 4

An assembly as claimed in claim 2, wherein each component of said zoom and collecting systems is formed by a single lens element.

Claim 5

An assembly as claimed in claim 1, wherein each lens element is made of germanium.

Claim 6

An afocal refractor telescope comprising an objective lens assembly as claimed in claim 1 in combination with an eyepiece system.

Claim 7

An assembly as claimed in claim 1, wherein said fourth zoom system component is made of germanium and at least one lens element of said third zoom system component is colour correcting being made of a material listed in the following table: ______________________________________ Material Refractive Index* V-value.sup.# ______________________________________ BS2 2.85632 248 BSA 2.77917 209 TI 1173 2.60010 142 AMTIR 1 2.49745 169 BS1 2.49158 152 TI20 2.49126 144 ZnSe 2.40653 77 KRS 5 2.37044 260 CsI 1.73933 316 CsBr 1.66251 176 KI 1.62023 137 ______________________________________ *Refractive index is for a wavelength of 10 micrometers. .sup.# Over the wavelength range 8.5-11.5 micrometers.

Claim 8

An infrared objective lens assembly comprising a four-component zoom system arranged to accept from object space radiation in the infrared waveband and a one-component collecting system arranged to form a real image from radiation delivered thereto by said zoom system, the components of said zoom and collecting systems being formed by lens elements the refractive surfaces of which intercept a common optical axis, and wherein with respect to said collecting system the first and third components of said zoom system each have negative optical power and are mounted on a common carriage so as to be selectively positionable along said optical axis, the second and fourth components of said zoom system each have positive optical power and are fixedly positioned on said optical axis whereby said zoom system is optically-compensated and of variable effective focal length, wherein each of the first, second and fourth components of said zoom-system is formed by a single lens element and said third zoom-system component is formed by a lens doublet, and the lens elements of the zoom-system have refractive surface curvatures, separation distances between refractive surfaces (RS) as measured successively from the refractive surface proximal to the collecting system, materials, and maximum aperture diameters, as set forth in the following table: __________________________________________________________________________ Separation Magnif- Radius of Maximum Distance ication Curvature Aperture Item Surface (mm) Factor (mm) Material Diameter __________________________________________________________________________ First Component 1st RS 66.00 X1.04 -13869.63 Air 52.27 46.00 X2.17 26.00 X4.44 6.00 X8.99 2nd RS 3.25 any 154.89 Ge 51.44 Second Component 1st RS 5.59 X1.04 372.97 Air 78.19 25.59 X2.17 45.59 X4.44 65.59 X8.99 2nd RS 9.75 any -310.81 Ge 77.88 Third Component 1st lens 1st RS 68.30 X1.04 -116.62 Air 71.75 element 48.30 X2.17 28.30 X4.44 8.30 X8.99 2nd RS 4.00 any -549.06 Ge 73.84 2nd Lens 1st RS 2.00 any 3054.37 Air 75.96 element 2nd RS 4.25 any 660.41 ZnSe 77.42 Fourth Component 1st RS 20.41 X1.04 Aspheric Air 133.83 40.41 X2.17 60.41 X4.44 80.41 X8.99 2nd RS 12.5 any -95.15 Ge 142.63 __________________________________________________________________________ where the aspheric refractive surface has its profile governed by the equation; ##EQU3## Z being the distance parallel to the optical axis between the asperic surface and a line perpendicular to the optical axis which meets the optical axis where the datum spherical surface crosses the optical axis, the datum spherical surface being a theoretical surface constituting the spherical surface which would exist absent the aspheric; and C being the inverse of the radius of curvature of the datum surface and having a value of -101.83 -1 , B being a constant of value -1.2530×10 -8 , G being a constant of value -5.5100×10 -13 , and D being a constant value+7.5400×10 -17 .

Claim 9

An infrared objective lens assembly comprising a four-component zoom system arranged to accept from object space radiation in the infrared waveband and a one-component collecting system arranged to form a real image from radiation delivered thereto by said zoom system, the components of said zoom and collecting systems being formed by lens elements the refractive surfaces of which intercept a common optical axis, and wherein with respect to said collecting system the first and third components of said zoom system each have negative optical power and are mounted on a common carriage so as to be selectively positionable along said optical axis, the second and fourth components of said zoom system each have positive optical power and are fixedly positioned on said optical axis whereby said zoom system is optically-compensated and of variable effective focal length, wherein each of the first, second and fourth components of said zoom-system is formed by a single lens element and said third zoom-system component is formed by a lens doublet, and the lens elements of the zoom-system have refractive surface curvatures, separation distances between refractive surfaces (RS) as measured successively from the refractive surface proximal to the collecting system, materials, and maximum aperture diameters, as set forth in the following table: __________________________________________________________________________ Separation Magnif- Radius of Maximum Distance ication Curvature Aperture Item Surface (mm) Factor (mm) Material Diameter __________________________________________________________________________ First Component 1st RS 66.00 X1.04 -13869.63 Air 52.27 46.00 X2.17 26.00 X4.44 6.00 X8.99 2nd RS 3.25 any 154.89 Ge 51.44 Second Component 1st RS 5.59 X1.04 372.97 Air 78.19 25.59 X2.17 45.59 X4.44 65.59 X8.99 2nd RS 9.75 any -310.81 Ge 77.88 Third Component 1st lens 1st RS 68.30 X1.04 -116.62 Air 71.75 element 48.30 X2.17 28.30 X4.44 8.30 X8.99 2nd RS 4.00 any -549.06 Ge 73.84 2nd Lens 1st RS 2.00 any 3054.37 Air 75.96 element 2nd RS 4.25 any 660.41 ZnSe 77.42 Fourth Component 1st RS 20.41 X1.04 Aspheric Air 133.83 40.41 X2.17 60.41 X4.44 80.41 X8.99 2nd RS 12.5 any -95.15 Ge 142.63 __________________________________________________________________________ where the aspheric refractive surface has its profile governed by the equation; ##EQU3## Z being the distance parallel to the optical axis between the asperic surface and a line perpendicular to the optical axis which meets the optical axis where the datum spherical surface crosses the optical axis, the datum spherical surface being a theoretical surface constituting the spherical surface which would exist absent the aspheric; and C being the inverse of the radius of curvature of the datum surface and having a value of -101.83 -1 , B being a constant of value -1.2530×10 -8 , G being a constant of value -5.5100×10 -13 , and D being a constant value+7.5400×10 -17 .

Claim 10

An infrared objective lens assembly comprising a four-component zoom system arranged to accept from object space radiation in the infrared waveband and a one-component collecting system arranged to form a real image from radiation delivered thereto by said zoom system, the components of said zoom and collecting systems being formed by lens elements the refractive surfaces of which intercept a common optical axis, and wherein with respect to said collecting system the first and third components of said zoom system each have negative optical power and are mounted on a common carriage so as to be selectively positionable along said optical axis, the second and fourth components of said zoom system each have positive optical power and are fixedly positioned on said optical axis whereby said zoom system is optically-compensated and of variable effective focal length, wherein each of the first, second and fourth components of said zoom-system is formed by a single lens element and said third zoom-system component is formed by a lens doublet, and the lens elements of the zoom-system have refractive surface curvatures, separation distances between refractive surfaces (RS) as measured successively from the refractive surface proximal to the collecting system, materials, and maximum aperture diameters, as set forth in the following table: __________________________________________________________________________ Separation Magnif- Radius of Maximum Distance ication Curvature Aperture Item Surface (mm) Factor (mm) Material Diameter __________________________________________________________________________ First Component 1st RS 110.00 X4.02 -1902.59 Air 88.07 77.00 X6.49 44.00 X11.40 11.00 X20.02 2nd RS 4.5 any 604.52 Ge 87.92 Second Component 1st RS 7.00 X4.02 468.01 Air 129.96 40.00 X6.49 73.00 X11.40 106.00 X20.02 2nd RS 12.5 any -968.90 Ge 129.29 Third Component 1st lens 1st RS 109.00 X4.02 -279.82 Air 124.28 element 76.00 X6.49 43.00 X11.40 10.00 X20.02 2nd RS 5.50 any 3632.40 Ge 126.04 2nd lens 1st RS 6.00 any -989.90 Air 128.33 element 2nd RS 5.50 any -2315.89 ZnSe 130.66 Fourth Component 1st RS 44.12 X4.02 Aspheric Air 221.10 77.12 6.49 110.12 X11.40 143.12 X20.02 2nd RS 15.50 any -183.19 Ge 229.09 __________________________________________________________________________ where the aspheric refractive surface has its profile governed by the equation; ##EQU4## Z being the distance parallel to the optical axis between the asperic surface and a line perpendicular to the optical axis which meets the optical axis where the datum spherical surface crosses the optical axis, the datum spherical surface being a theoretical surface constituting the spherical surface which would exist absent the aspheric; and C being the inverse of the radius of curvature of the datum surface and having a value of -208.40 -1 , B being a constant of value -6.7000×10 -10 , G being a constant of value -3.0000×10 -15 , and D being a constant value+1.7000×10 -18 .

Claim 11

An infrared objective lens assembly comprising a four-component zoom system arranged to accept from object space radiation in the infrared waveband and a one-component collecting system arranged to form a real image from radiation delivered thereto by said zoom system, the components of said zoom and collecting systems being formed by lens elements the refractive surfaces of which intercept a common optical axis, and wherein with respect to said collecting system the first and third components of said zoom system each have negative optical power and are mounted on a common carriage so as to be selectively positionable along said optical axis, the second and fourth components of said zoom system each have positive optical power and are fixedly positioned on said optical axis whereby said zoom system is optically-compensated and of variable effective focal length, wherein each of the first, second and fourth components of said zoom-system is formed by a single lens element and said third zoom-system component is formed by a lens doublet, and the lens elements of the zoom-system have refractive surface curvatures, separation distances between refractive surfaces (RS) as measured successively from the refractive surface proximal to the collecting system, materials, and maximum aperture diameters, as set forth in the following table: __________________________________________________________________________ Separation Magnif- Radius of Maximum Distance ication Curvature Aperture Item Surface (mm) Factor (mm) Material Diameter __________________________________________________________________________ First Component 1st RS 110.00 X4.02 -1902.59 Air 88.07 77.00 X6.49 44.00 X11.40 11.00 X20.02 2nd RS 4.5 any 604.52 Ge 87.92 Second Component 1st RS 7.00 X4.02 468.01 Air 129.96 40.00 X6.49 73.00 X11.40 106.00 X20.02 2nd RS 12.5 any -968.90 Ge 129.29 Third Component 1st lens 1st RS 109.00 X4.02 -279.82 Air 124.28 element 76.00 X6.49 43.00 X11.40 10.00 X20.02 2nd RS 5.50 any 3632.40 Ge 126.04 2nd lens 1st RS 6.00 any -989.90 Air 128.33 element 2nd RS 5.50 any -2315.89 ZnSe 130.66 Fourth Component 1st RS 44.12 X4.02 Aspheric Air 221.10 77.12 6.49 110.12 X11.40 143.12 X20.02 2nd RS 15.50 any -183.19 Ge 229.09 __________________________________________________________________________ where the aspheric refractive surface has its profile governed by the equation; ##EQU4## Z being the distance parallel to the optical axis between the asperic surface and a line perpendicular to the optical axis which meets the optical axis where the datum spherical surface crosses the optical axis, the datum spherical surface being a theoretical surface constituting the spherical surface which would exist absent the aspheric; and C being the inverse of the radius of curvature of the datum surface and having a value of -208.40 -1 , B being a constant of value -6.7000×10 -10 , G being a constant of value -3.0000×10 -15 , and D being a constant value+1.7000×10 -18 .