Optical: systems and elements – Mirror – Including specified control or retention of the shape of a...
Reexamination Certificate
2000-05-02
2003-04-15
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Mirror
Including specified control or retention of the shape of a...
C359S354000
Reexamination Certificate
active
06547406
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to infra-red (e.g. thermal) imaging systems and to other optical systems, and in particular to optical systems in which at least two optical parameters can be controlled relative to one another.
2. Discussion of Prior Art
It is known to produce optical systems comprising two or more optical components of fixed focal length in which variation of at least two optical parameters of the system is achieved by moving two or more of the optical components relative to one another.
For example it is known to produce a variable magnification compound lens comprising at least two optical components of fixed focal length wherein the overall optical magnification of the system is varied by adjusting the spacing between the optical components whilst an in-focus image is maintained on a fixed image plane by relatively varying the distance from the final optical component to the fixed image plane.
The technology used in such systems is well developed and provides acceptable results in most applications. However, the mass and response time of these systems can be adversely affected by the need to physically move the optical components. Furthermore, for critical applications, especially in spacecraft optics, moveable optical components require complex counterbalancing arrangements.
It has also been known for nearly ten years from U.S. Pat. No. 4,836,661 to propose a refractive variable magnification system for zoom lenses in which a number of refractive lenses of variable refractive power are provided a fixed distance apart and are used to focus an image onto a fixed image plane.
U.S. Pat. No. 4,890,903, published in 1990, discloses a lens unit having variable focus refractive lenses which can be bodily rotated to alter their focal length, and which are gas or fluid filled. One lens have a positive power and the other a negative power. Uses in spectacles and cameras are disclosed.
U.S. Pat. No. 4,630,903 shows a complex multi-refractive lens system for a photocopies. it requires the ability to vary 3 system parameters from 6 in a refractive system.
It has also been known for many years in the field of thermal imaging to have detector, usually pixellated, upon which an image is focused and provided with a chopper whose function is to cause that image to dither over the detector, and to present a periodic reference signal to the detector. A typical chopper has three segments: a first transmissive prism, a second transmissive prism, and an opaque shutter region, the two prism sections causing an image to fall upon slightly different regions of the detector, and the shutter region providing a black body reference signal which can be used to allow the output voltage of a pixel to fall away from a scene-dependent value.
A paper by N. Butler, J. McClelland and S. Iwasa, employees of Honeywell, entitled “Ambient Temperature Solid State Pyroelectric I.R. Imaging Arrays”, dated March 1988, NE 8701-02 (SPIE), discusses using a de-focusing chopper having a thick transparent “blurring” portion.
It has also been known to compensate for movement of a detected image relative to a sensor/sensor array by introducing special, and additional, components into the optics of an imaging system, for example to compensate for atmospheric alteration, and camera shake.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided an optical system comprising two or more variable focal length optical components whose positions are fixed relative to one another; the system further comprising control means for varying the focal length of at least one of the said variable focal length optical components in relation to the focal length of at least one of the other said variable focal length optical components such that, in use, control over at least two optical parameters if the system is achieved.
The invention overcomes the drawbacks of much of the prior art because variation of certain optical parameters of the system can be achieved without the need to change the relative positions of the optical components within the system, i.e. without the need to, for example, move the optical components bodily, as a whole, towards or away from each other, or to rotate bodily the optical components. As a result system reprogramming can be achieved in time-scales shorter than those required for physical movement of the positions of the optical components, this being of particular benefit in active optical systems. (By active optical system it is meant an optical system in which the focal lengths of the optical components are varied in real time according to predictions regarding the required focal lengths, as opposed to being controlled by a feedback loop.) Furthermore, if the power supplies required for varying the focal length of the optical components are of low-mass design, then the overall mass of the system may be lower than for a conventional system due to the lack of mechanical positioning gear. Also the need for complex counterbalancing requirements is eliminated for critical applications such as spacecraft optics.
The optics may be used in a beam expander; or in a zoom lens unit; or in a camera; or in binoculars or a telescope. The optics may be reflective. An all-reflective optics device may be provided.
The control means in an optical system according the first aspect of the invention may comprise a mechanical linkage, electronic circuit or a computer program.
An optical system according to the first aspect of the invention may further have an image plane fixed relative to the said variable focal length optical components in the system.
One optical parameter that may be controlled is the magnification of the system. Alternatively, the focal lengths of the first and second components may be the two controlled parameters. Tilt means may be provided to apply a two-axis tilt to one or more of the optical components. De-focusing means may be provided to de-focus the image received by the detector/detector array.
In one application of an optical system according to the first aspect of the invention, variation of the focal length of at least one of the said variable focal length optical components in relation to the focal length of at least one of the other said variable focal length optical components varies the position of a principle plane of the system in dependence on a change in effective focal length of the compound system such that an image of variable magnification is obtained with maintenance of a substantially in-focus image in a fixed image plane.
In a further application of an optical system according to the first aspect of the invention, variation of the focal length of at least one of the said variable focal length optical components in relation to the focal length of at least one of the other said variable focal length optical components may vary the width of an optical beam whilst substantially maintaining collimation of the beam.
According to a second aspect of the present invention there is provided an optical system for varying the width of an optical beam, comprising two or more variable focal length optical components whose positions are fixed relative to one another, and control means for varying the focal length of at least one of the said variable focal length optical components in relation to the focal length of at least one of the other said variable focal length optical components such that, in use, the width of the optical beam is varied whilst substantially maintaining the collimation of the beam.
The width of the optical beam may be expanded, or may be contracted.
The optical components may comprise refractive optical components, or may comprise reflective optical components, such as mirrors.
According to a third aspect of the invention there is provided a variable magnification zoom lens unit comprising two or more variable focal length optical components whose positions are fixed relative to one an other and to an image plane of the lens unit; the lens unit further comprising means for var
Dickson Robin
Greenaway Alan H.
Harrison Paul
Amari Alessandro V.
Nixon & Vanderhye P.C.
Qinetiq Limited
Spyrou Cassandra
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