Infra-red optical systems

Claim 2

An `eye-piece` system for a non-Galilean afocal infra-red optical system, the `eye-piece` system comprising a back lens element or group of positive power, and a front lens group of negative power which contributes towards astigmatism correction, which effects pupil matching, and which overcorrects the Petzval sum, said front lens group comprising a rear lens element with a convex rear surface, a front lens element with a concave front surface, and a biconvex or plano convex gas lens of negative power between the rear and front elements of the front lens group, said concave front surface of said front lens element having a radius of curvature greater than that of said convex rear surface of said rear lens element, and said front lens group spaced from said back lens element by a distance greater than that between said rear and said front elements of said front lens group.

Claim 3

An `eye-piece` system according to claim 1 in which said back lens element or group of positive power consists of a pair of positively powered meniscus elements disposed with their convex surfaces facing each other.

Claim 4

An `eye-piece` system according to claim 1 in which said back lens element or group of positive power comprises a meniscus element.

Claim 5

An `eye-piece` system according to claim 1 in which said front lens group of negative power has the rear lens element of positive power and the front lens element of negative power.

Claim 6

An `eye-piece` system according to claim 1 in which said gas lens of negative power is formed between a front concave surface of said rear element and a rear surface of said front element of the front lens group.

Claim 7

An `eye-piece` system according to claim 1 in which the front surface of said back lens element or group is closely adjacent or effectively in contact with the rear surface of the front lens group.

Claim 8

An `eye-piece` system according to claim 1 in which the ratio of the absolute focal length of the front lens group to that of said back lens element or group is in the range 1.5 to 3.5.

Claim 9

An `eye-piece` system according to claim 1 comprising lens elements 1 to 4 having axial thicknesses and separations, and whose surfaces R1 to R8 have radii of curvature substantially as follows: ______________________________________ Radius of Axial Thickness/ Element Surface Curvature Separation ______________________________________ R1 -146.54 1 4.20 R2 -96.505 0.50 R3 +125.22 2 4.65 R4 +183.66 19.75 R5 +68.285 3 5.50 R6 +117.64 4.02 R7 +500.38 4 6.60 R8 +91.034 ______________________________________

Claim 10

An `eye-piece` system according to claim 1 comprising lens elements 1 to 4 having axial thicknesses and separations, and whose surfaces R1 to R8 have radii of curvature, substantially as follows: ______________________________________ Radius of Axial Thickness/ Element Surface Curvature Separation ______________________________________ R1 -138.07 1 4.20 R2 -96.67 0.5 R3 +413.56 2 4.65 R4 -846.67 15.07 R5 +66.25 3 5.50 R6 +113.36 3.42 R7 -1110.3 4 6.60 R8 +80.03 ______________________________________

Claim 11

An `eye-piece` system according to claim 1 comprising lens elements 1 to 4 having axial thicknesses and separations, and whose surfaces R1 to R8 have radii of curvature, substantially as follows: ______________________________________ Radius of Axial Thickness/ Element Surface Curvature Separation ______________________________________ R1 -135.07 1 4.20 R2 -97.94 0.5 R3 -846.7 2 4.65 R4 -210.32 15.78 R5 +63.32 3 5.50 R6 +112.78 3.29 R7 -1947.0 4 6.60 R8 +76.42 ______________________________________

Claim 12

An `eye-piece` system according to claim 1 comprising elements 1, 3 and 4 having axial thicknesses and separations, and whose surfaces R1, R2 and R5 to R8 have radii of curvature, substantially as follows: ______________________________________ Radius of Axial Thickness/ Element Surface Curvature Separation ______________________________________ R1 -165.65 1 8.32 R2 -81.69 7.02 R5 +61.26 3 5.50 R6 +109.63 3.03 R7 PLANE 4 6.60 R8 +76.24 ______________________________________

Claim 13

A non-Galilean afocal infra-red optical system comprising an objective system in combination with an `eye-piece` system according to claim 1.

Claim 14

A non-Galilean afocal infra-red optical system according to claim 12 in which the objective system is a catadioptric system.

Claim 15

A non-Galilean afocal infra-red optical system according to claim 13 comprising lens elements 1 to 5, a Mangin secondary mirror 6, and a primary mirror 7 having axial thicknesses and separations, and whose surfaces R1 to R13 have radii of curvature, substantially as follows: ______________________________________ Radius of Axial Thickness/ Element Surface Curvature Separation ______________________________________ R1 -146.54 1 4.20 R2 -96.505 0.50 R3 +125.22 2 4.65 R4 +183.66 19.75 R5 +68.285 3 5.50 R6 +117.64 4.02 R7 -500.38 4 6.60 R8 +91.034 31.83 R9 -196.48 5 6.35 R10 -96.505 267.8 R11 -2980.4 6 12.7 R12 +2286.0 -12.7 R11 -2980.4 -308.1 7 R13 +845.25 ______________________________________

Claim 16

A non-Galilean afocal infra-red optical system according to claim 13 comprising lens elements 1 to 5, a Mangin secondary mirror 6, and a primary mirror 7 having axial thicknesses and separations, and whose surfaces R1 to R13 have radii of curvature, substantially as follows: ______________________________________ Radius of Axial Thickness/ Element Surface Curvature Separation ______________________________________ R1 -138.07 1 4.20 R2 -96.67 0.5 R3 +413.56 2 4.65 R4 -846.67 15.07 R5 +66.25 3 5.50 R6 +113.36 3.42 R7 -1110.3 4 6.60 R8 +80.30 36.85 R9 -176.21 5 6.35 R10 -94.00 267.8 R11 -3068.7 6 12.70 R12 +2247.1 -12.70 R11 -3068.7 -308.1 7 R13 +845.25 ______________________________________

Claim 17

A non-Galilean afocal infra-red optical system according to claim 13 comprising lens elements 1 to 5, a Mangin secondary mirror 6, and a primary mirror 7 having axial thicknesses and separations, and whose surfaces R1 to R13 have radii of curvature, substantially as follows: ______________________________________ Radius of Axial Thickness/ Element Surface Curvature Separation ______________________________________ R1 -135.07 1 4.20 R2 -97.94 0.5 R3 -846.7 2 4.65 R4 -210.32 15.78 R5 +63.32 3 5.50 R6 +112.78 3.29 R7 -1947.0 4 6.60 R8 +76.42 37.58 R9 -172.09 5 6.35 R10 -93.09 267.8 R11 -2812.8 6 12.7 R12 +2367.3 -12.7 R11 -2812.8 -308.1 7 R13 +845.25 ______________________________________

Claim 18

A non-Galilean afocal infra-red optical system according to claim 13 comprising lens elements 1 and 3 to 5, a Mangin secondary mirror 6, and a primary mirror 7 having axial thicknesses and separations, and whose surfaces R1, R2 and R5 to R13 have radii of curvature, substantially as follows; ______________________________________ Radius of Axial Thickness/ Element Surface Curvature Separation ______________________________________ R1 -165.65 1 8.32 R2 -81.69 7.02 R5 +61.26 3 5.50 R6 +109.63 3.03 R7 PLANE 4 6.60 R8 +76.24 47.96 R9 -202.77 5 6.35 R10 -106.68 267.8 R11 -2611.3 6 12.7 R12 +2494.6 -12.7 R11 -2611.3 -308.1 7 R13 +845.25 ______________________________________

Claim 19

An `eye-piece` system for a non-Galilean afocal infrared optical system comprising lens elements 1 to 4 having axial thicknesses and separations, and whose surfaces R1 to R8 have radii of curvature, substantially as follows: ______________________________________ Radius of Axial Thickness/ Element Surface Curvature Separation ______________________________________ R1 -105.94 1 4.20 R2 -92.83 0.50 R3 +104.66 2 4.65 R4 +155.33 0.51 R5 +60.15 3 6.14 R6 +72.83 5.21 R7 +309.18 4 6.60 R8 +100.24 ______________________________________

Claim 20

An `eye-piece` system for a non-Galilean afocal infrared optical system comprising lens elements 1 to 4 having axial thicknesses and separations, and whose surfaces R1 to R8 have radii of curvature, substantially as follows: ______________________________________ Radius of Axial Thickness/ Element Surface Curvature Separation ______________________________________ R1 -105.94 1 4.20 R2 -92.83 0.50 R3 +104.66 2 4.65 R4 +155.33 0.51 R5 +60.15 3 6.14 R6 +72.83 5.21 R7 +309.18 4 6.60 R8 +100.24 ______________________________________

Claim 21

A non-Galilean afocal infra-red optical system comprising lens elements 1 to 5, a Mangin secondary mirror 6, and a primary mirror 7 having axial thicknesses and separations, and whose surfaces R1 to R13 have radii of curvature, substantially as follows: ______________________________________ Radius of Axial Thickness/ Element Surface Curvature Separation ______________________________________ R1 -105.94 1 4.20 R2 -92.83 0.50 R3 +104.66 2 4.65 R4 +155.33 0.51 R5 +60.15 3 6.14 R6 +72.83 5.21 R7 +309.18 4 6.60 R8 +100.24 50.47 R9 +190.96 5 6.35 R10 +508.0 267.8 R11 PLANE 6 12.7 R12 +1578.4 -12.7 R11 PLANE -320.8 7 R13 +845.25 ______________________________________

Claim 22

A non-Galilean afocal infra-red optical system comprising lens elements 1 to 5, a Mangin secondary mirror 6, and a primary mirror 7 having axial thicknesses and separations, and whose surfaces R1 to R13 have radii of curvature, substantially as follows: ______________________________________ Radius of Axial Thickness/ Element Surface Curvature Separation ______________________________________ R1 -105.94 1 4.20 R2 -92.83 0.50 R3 +104.66 2 4.65 R4 +155.33 0.51 R5 +60.15 3 6.14 R6 +72.83 5.21 R7 +309.18 4 6.60 R8 +100.24 50.47 R9 +190.96 5 6.35 R10 +508.0 267.8 R11 PLANE 6 12.7 R12 +1578.4 -12.7 R11 PLANE -320.8 7 R13 +845.25 ______________________________________