Long-wave infrared afocal zoom telescope

Claim 2

In an afocal zoom lens attachment of variable magnification use with a prime imaging lens of fixed focal length, the improvement comprising: a. four optically coacting lens groups arranged sequentially along an optical axis to form a non-Galilean mechanically compensated zoom system, each of said groups comprising at least one lens, each of said lenses having a useful spectral bandpass in the infared wavelength region, the first group being a fixed focus front objective element, the second group being a zooming element moving in a first locus, the third group being a zooming element moving in a second locus, and the fourth group being a fixed focus eyepiece element; b. means to continuously vary the magnification of said system between minimum and maximum limits comprising means to simultaneously move said second and third group zooming elements through predetermined loci having a predetermined relationship to each other, one of said loci being substantially linear and the other of said loci being nonlinear; and, c. said four groups of lenses when said second and third group zooming elements are positioned to produce said minimum magnification of said system being arranged in relation to each other so that said first, second and third groups of lenses produce a real aerial image at a first intermediate image plane between said third and fourth groups of lenses which image is recollimated by said fourth group eyepiece element.

Claim 3

A system as in claim 1 wherein the locus of said third group zooming element is substantially linear and the locus of said second group zooming element is nonlinear.

Claim 4

A system as in claim 1 wherein said first lens group is a single fixed position front objective lens, said second lens group is a zooming doublet moving nonlinearly, one of the lenses of said doublet providing chromatic aberration correction for said system, and said third lens group is a zooming singlet moving substantially linearly.

Claim 5

A system as in claim 1 wherein said fixed focus eyepiece is a doublet which provides a collimated output beam of energy with an external exit pupil.

Claim 6

A system as in claim 3 wherein said fixed focus eyepiece is a doublet which provides a collimated output beam of energy with an external exit pupil.

Claim 7

A system as in claim 5 wherein the field of view of object space varies as a function of the variation in magnification of the zoom system whereas the field of view at said eyepiece exit pupil remains constant throughout the zoom range and wherein the entrance pupil diameter varies as a function of the variation in magnification of the zoom system whereas the exit pupil diameter remains constant throughout the zoom range.

Claim 8

A system as in claim 1 wherein: the loci of positions of said four groups of lenses are so related to each other that during the zooming motion of said second and third group zooming elements said third group zooming element at a predetermined position producing a magnification higher than said minimum magnification passes through said first aerial image plane thereby moving said aerial image plane for all higher magnification settings of said zoom elements, said motion of said aerial image plane contributing to aberration correction to maintain good image quality at magnifications higher than that at which said image plane beings to move.

Claim 9

A system in claim 3 wherein: the loci of positions of said four groups of lenses are so related to each other that during the zooming motion of said second and third group zooming elements said third group zooming element at a predetermined position produciing a magnification higher than said minimum magnification passes through said first aerial image plane thereby moving said aerial image plane for all higher magnification settings of said zoom elements, said motion of said aerial image plane contributing to aberration correction to maintain good image quality at magnifications higher than that at which said image plane begins to move.

Claim 10

A system as in claim 6 wherein: the loci of positions of said four groups of lenses are so related to each other that during the zooming motion of said second and third group zooming elements said third group zooming element at a predetermined position producing a magnification higher than said minimum magnification passes through said first aerial image plane thereby moving said aerial image plane for all higher magnification settings of said zoom elements, said motion of said aerial image plane contributing to aberration correction to maintain good image quality at magnifications higher than at which said image plane begins to move.

Claim 11

A system as in claim 1 wherein each of said lenses has a useful spectral bandpass for energy in the wavelength region between 2 and 20 microns, the total transmission loss of energy at any of said wavelengths by absorption in passing through said entire lens system being less than 60 percent; and, wherein the system has a zoom ratio of at least 5 to 1.

Claim 12

A system as in claim 3 wherein each of said lenses has a useful spectral bandpass for energy in the wavelength region between 2 and 20 microns, the total transmission loss of energy at any of said wavelengths by absorption in passing through said entire lens system being less than 60 percent; and, wherein the system has a zoom ratio of at least 5 to 1.

Claim 13

A system as in claim 4 wherein each of said lenses has a useful spectral bandpass for energy in the wavelength region between 2 and 20 microns, the total transmission loss of energy at any of said wavelengths by absorption in passing through said entire lens system being less than 60 percent; and, wherein the system has a zoom ratio of at least 5 to 1.

Claim 14

A system as in claim 7 wherein each of said lenses has a useful spectral bandpass for energy in the wavelength region between 2 and 20 microns, the total transmission loss of energy at any of said wavelengths by absorption in passing through said entire lens system being less than 60 percent; and, wherein the system has a zoom ratio of at least 5 to 1.

Claim 15

A system as in claim 8 wherein each of said lenses has a useful spectral bandpass for energy in the wavelength region between 2 and 20 microns, the total transmission loss of energy at any of said wavelengths by absorption in passing through said entire lens system being less than 60 percent; and, wherein the system has a zoom ratio of at least 5 to 1.

Claim 16

A system as in claim 9 wherein each of said lenses has a useful spectral bandpass for energy in the wavelength region between 2 and 20 microns, the total transmission loss of energy at any of said wavelengths by absorption in passing through said entire lens system being less than 60 percent; and, wherein the system has a zoom ratio of at least 5 to 1.

Claim 17

A system as in claim 15 wherein said four lens groups comprise the groups A, B, C and D as shown in FIG. 1 of the drawings and wherein said lenses are fabricated and mounted in accordance with the following construction Tables I and II wherein the "radius" refers to the radius of curvature of the lens surface indicated by the corresponding number, the "thickness" refers to the distance along the optical axis O from the indicated surface to the surface of next higher number, and the materials and lens outer diameters are as specified, the measured quantities being stated in inches as follows: TABLE I ______________________________________ Lens/ Thick- Lens Surface Radius ness Mat'l O.D. ______________________________________ A1 1 18.149 0.850 Ge 2 24.986 Tbl II Air 12.6 B1 3 4.879 .350 Ge 4 4.447 1.436 Air 6.4 B3 5 -24.428 .350 ZnSe 6 -45.901 Tbl II Air 5.8 C1 7 5.136 .350 Ge 8 7.687 Tbl II Air 4.2 D1 9 -3.393 .140 Ge 10 -3.186 .010 Air 2.2 D2 11 2.600 .160 Ge 12 3.846 1.298 Air 2.1 13 Exit pupil ______________________________________ TABLE II ______________________________________ Magni- Typical Zoom Spacings fication THK 2 THK 6 THK 8 ______________________________________ 20× 9.334 14.738 .984 15× 9.309 13.423 2.324 10× 8.435 12.758 3.862 5× 4.328 15.175 5.553 31/3× .750 18.237 6.069. ______________________________________

Claim 18

A system as in claim 10 wherein said four lens groups comprise the groups E, F, G and H as shown in FIG. 2 of the drawings and wherein said lenses are fabricated and mounted in accordance with the following construction Tables III and IV wherein the "radius" refers to the radius of curvature of the lens surface of corresponding number, the thickness refers to the distance along the optical axis O from the indicated surface to the surface of next higher number, and the materials and lens outer diameters are as specified in Tables III and IV as follows: TABLE III ______________________________________ Lens/ Thick- Lens Surface Radius ness Mat'l O.D. ______________________________________ 101 31.200 .700 Si 102 78.243 Tbl IV Air 11.0 F1 103 4.780 .400 Si 104 5.037 1.311 Air 5.75 F2 105 8.929 .300 ZnS 106 4.641 Tbl IV Air 4.70 G 107 2.759 .120 Si 108 4.891 Tbl IV Air 1.30 H1 109 -.3827 .050 Ge 110 -.3359 .010 Air 0.38 H2 111 .2183 .045 Ge 112 .2185 .168 Air 0.35 113 Exit pupil ______________________________________ TABLE IV ______________________________________ Magni- Typical Zoom Spacings fication THK 2 THK 6 THK 8 ______________________________________ 118× 8.792 12.448 0.658 89× 8.321 12.378 1.199 60× 7.017 13.111 1.769 33× 3.797 15.801 2.300 21× 0.599 18.794 2.505. ______________________________________