Optical: systems and elements – Compound lens system – With curved reflective imaging element
Reexamination Certificate
1994-07-28
2001-12-25
Chang, Audrey (Department: 2872)
Optical: systems and elements
Compound lens system
With curved reflective imaging element
C359S365000, C359S728000, C359S729000, C359S859000
Reexamination Certificate
active
06333811
ABSTRACT:
BACKGROUND OF THE INVENTION
Some earth-orbiting satellites contain optical imaging systems for tracking earth-bound targets. Generally, these systems generate real images that are converted into electrical signals and transmitted to the ground.
Depending upon the satellite's angle of inclination in relationship to the earth, the distance between the satellite and an earthbound target will vary. As a result, the image size of fixed sized objects will also change. A similar effect arises in scanning telescopic systems in aircraft. Here, as the telescope scans the terrain over which the aircraft is passing, depending on the telescope's angle inclination, the changing distance between the telescope and the various targets affect the relative image sizes.
The solution to maintaining image size independent of the distance between the satellite and the target is to use a zoom optical system that can increase magnification in response to the satellite's angle of inclination relative to the earth. One problem that arises, however, is the fact that traditional zoom optical systems have utilized refractive optical elements. Optical glass is the preferred material for refractive lenses, but this is restricted in wavelength from 500 to 950 nm. A few materials are available for wavelengths outside of the range but these have severe limitations in size and durability. One of the major defects of refractive optics is chromatic aberration which becomes more serious as the wavelength band increases. If this is a problem for a particular application, one has to use several lenses made of different materials which increases the weight of the optics. The weight of refractive optics is a problem in any event because refractive lenses are not lightweight as in the case of mirrors. Refractive optics are also much more susceptible to thermal effects than reflective optics, and controlling to thermal environment in space or airborne systems is not an easy task. A final problem in refractive optics relative to reflective optics is that they are subject to the deleterious effects of radiation because the light has to go through the material of which the lens is made, and the optical characteristic of materials are more sensitive to radiation effects than their physical characteristics.
SUMMARY OF THE INVENTION
An all-reflective zoom optical system solves the above-identified problems. Such a system comprises a plurality of curved relay mirrors successively reflecting electromagnetic radiation received by the system to generate a real image with the electromagnetic radiation at a focal surface. These curved relay mirrors are movable in relationship to each other in order to effect magnification.
In a particular embodiment of this invention, the focal surface remains fixed as the curved relay mirrors move in relationship to each other in order to change the magnification. Further, the entrance aperture is constant across the zoom range. Also in the embodiment of the invention, the optical system further comprises a primary mirror for collecting and reflecting received electromagnetic radiation and a secondary mirror for receiving the electromagnetic radiation from the primary and reflecting the electromagnetic radiation to the curved relay mirrors.
In other embodiments, the curved relay mirrors comprise a first relay mirror, a second relay mirror receiving the electromagnetic radiation from the first relay mirror, a third relay mirror receiving the electromagnetic radiation from the second relay mirror, and a fourth relay mirror receiving the electromagnetic radiation from the third relay mirror and reflecting the electromagnetic radiation onto the focal surface. The first and fourth relay mirrors have aspheric curvatures with only bilateral symmetry. The second relay mirror has a convex curvature. Of the mirrors, only the second and the third relay mirrors move to effect the magnification. Further, these mirrors move in parallel tracks. The third relay mirror has a spherical curvature. Finally, the focal surface has an aspheric curvature with only bilateral symmetry.
According to a different aspect of the invention, the system comprises relay mirrors successively reflecting electromagnetic radiation received by the system to generate a real image at a fixed focal surface. These relay mirrors are removable in relationship to each other in order to effect the magnification.
According to another aspect of the invention, a reflective zoom optical system comprises a primary mirror for collecting electromagnetic radiation, a stationary secondary mirror co-axial with the primary mirror for receiving the electromagnetic radiation from the primary mirror and a plurality of curved relay mirrors positioned behind the primary mirror for receiving and successively reflecting the electromagnetic radiation. These curved relay mirrors are movable in relationship to each other in order to effect magnification.
According to a particular embodiment of the invention, the curved relay mirrors generate a real image at an focal surface. Still further, the focal surface remains fixed as the curved relay mirrors move in relationship to each other producing the change in magnification.
The above and other features of the invention including various novel details of construction and combinations of parts will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular all-reflective zoom optical imaging system embodying the invention shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed and varied in numerous embodiments without departing from the scope of the invention.
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Tatian Berge
Wientzen Richard
Chang Audrey
The B. F. Goodrich Company
Winstedt Jennifer
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