Modular infrared kepler telescope

Details Modular infrared kepler telescope Modular infrared kepler telescope

2000-02-03

2001-06-12

Spyrou, Cassandra (Department: 2872)

Optical: systems and elements

Having significant infrared or ultraviolet property

Including alternative optical path or optical element

C359S399000, C359S421000, C359S422000, C359S432000

Reexamination Certificate

active

06246516

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to an infrared Kepler telescope, that is, an afocal optical system providing an intermediate image and including an objective and an ocular. Optics of this kind are, for example, built into thermal imaging apparatus.
BACKGROUND OF THE INVENTION
A modular zoom reimager which includes an interchangeable compensator/ocular unit is disclosed in the paper of A. Mann entitled “Infrared zoom lenses in the 1980s and beyond” published in Optical Engineering, 31 (5), pages 1064 to 1071 (May 1992).
U.S. Pat. No. 5,044,706 discloses a telescope (Galilei, afocal) having a focal length (field of view) which can be changed by insertable lens groups. Diffractive optical elements and aspheric elements are provided in the additional lenses and in the base objective.
U.S. Pat. No. 5,214,532 discloses an achromatic two-lens accessory for thermal imaging apparatus to double the range. Aspheric lens elements are provided.
U.S. Pat. No. 5,229,880 discloses a reimager which is configured for three fields of view by omitting or inserting a first or second two-lens group behind the front lens of the objective. In the embodiments shown, this two-lens group has at least one diffractive optical element. Claim
9
of this patent, however, presents an embodiment without a diffractive optical element.
U.S. Pat. No. 5,257,133 describes a reimager having a diffractive optical element in the ocular as set forth in claim
1
or no diffractive optical element as set forth in claim
10
. The use of aspheric lenses in the objective and ocular is shown and these aspheric lenses are made of silicon, that is, for a 3 to 5 &mgr;m wavelength. An interchangeable optic is not provided.
U.S. Pat. No. 5,363,235 discloses a catadioptric reimager having interchangeable lenses for switching the image field.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a telescope of the kind described above which is adapted for use in thermal imaging apparatus. It is a further object of the invention to provide such a telescope which, for a compact configuration with as few lenses as possible, results in a system having interchangeable components for different fields of view and which is cost effective to manufacture.
The infrared Kepler telescope of the invention includes: an objective defining an optical axis and including a positive front group and a negative rear group all arranged on the optical axis; the objective further including an interchangeable optic interposed between the positive front group and the negative rear group; the interchangeable optic being configured to operate as a magnification changer; an ocular mounted on the optical axis rearward of the negative rear group; the rear group and the ocular being fixedly pregiven; the positive front group being a first positive front group and being exchangeable with at least a second positive front group; the interchangeable optic being a first interchangeable optic and being exchangeable with at least a second interchangeable optic; and, the first and second positive front groups being optically so configured that each one of the positive front groups undercorrects spherical aberration and coma forward of the negative rear group to the same extent with or without the interchangeable optic.
The afocal optical system of the invention defines an intermediate image plane and a real exit pupil. The afocal optical system includes: an objective having a focal length and defining an optical axis; the objective having a structural length and being configured as a telesystem including a positive front group and a negative rear group; the positive front group and the negative rear group conjointly defining a telefactor (TF) of less than 0.7 wherein the telefactor is the ratio of the structural length of the objective to the focal length thereof; an ocular defining a focal length and including at least two lenses arranged on the optical axis; the image plane and the real exit pupil defining a distance therebetween and the distance being greater than the focal length of the ocular by a factor of at least 1.3; and, the positive front group being exchangeable for changing the magnification of the system.
The afocal optical system according to another embodiment of the invention defines an intermediate image plane and a real exit pupil and the afocal optical system includes: an objective having a focal length and defining an optical axis; the objective having a structural length and being configured as a telesystem including a positive front group and a negative rear group; the positive front group and the negative rear group conjointly defining a telefactor (TF) of less than 0.7 wherein the telefactor is the ratio of the structural length of the objective to the focal length thereof; an ocular defining a focal length and including at least two lenses arranged on the optical axis; the image plane and the real exit pupil defining a distance therebetween and the distance being greater than the focal length of the ocular by a factor of at least 1.3; and, an interchangeable optic having at least two lenses and the interchangeable optic being insertable into the optical axis between the positive front group and the negative rear group for changing the magnification.
The method of the invention is for making an infrared Kepler telescope having a field-of-view as required. The method includes the steps of: fixedly pregiving a negative objective rear group and an ocular having overcorrected spherical aberration and coma; and, providing a positive objective front group configured in correspondence to the field-of-view.
The Kepler telescope according to the invention includes an objective and an ocular. The objective has adapted lens components which are arranged forward of the negative rear group of the objective. A permanent base optic of the Kepler telescope includes the negative rear group and an interface position between the permanent base optic and the adapted lens elements is provided forward of the rear group. A specific correction is provided at the interface position and especially spherical aberration and coma are undercorrected.


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“Infrared zoom lenses in the 1980s and beyond” by A. Mann, Optical Engineering, vol. 31, No. 5, May 1992, pp. 1064 to 1071.

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