Patent
1985-02-13
1987-03-17
Arnold, Bruce Y.
350417, G02B 500, B29D 1100
Patent
active
046502750
DESCRIPTION:
BRIEF SUMMARY
The primary motive for this invention is to facilitate the development of inexpensive optical systems for use in infrared imaging systems. However, the invention could have wider application to optical systems used for other wavelength ranges.
The invention consists simply of an aberration-correcting optical element which corrects the aberrations of the optical system of which it is a part. The correcting element is in the form of a thin lenticular membrane of mouldable material stretched on a supporting perimeter frame such as a ring, the thickness of the membrane being varied as required to correct the aberrations of the optical system. The correcting element may be used as a separate element, or alternatively applied to another surface to vary the contour of the surface of the composite element so formed to correct the aberrations of the optical system.
The membrane is formed by injection moulding, forging or casting in a mould of which one surface may be optically flat and the other configured to produce the desired variation in membrane thickness.
Many methods of configuring the master surface of a mould for casting, moulding or forging are well known in the art. Even expensive methods of configuring the master surface could be economic if large numbers of elements are to be formed from a master surface. An advantage is that only one surface of the mould need be configured, the other being optionally an optically flat surface. When stretched the membrane will tend to form two surfaces of equal shape. The thickness variation of the membrane determines the correction of the aberrations.
A number of examples of prior art describe methods and means which have some bearing on the invention herein described. For example, Wu (U.S. Pat. No. 4,212,936) describes a method for conforming a thin sheet of thermoplastic material to glass surfaces of many different shapes and indeed his method of forming the matching pressing surface could be used to manufacture the configured master surface of the mould to form the herein described corrector lenses, but essentially, Wu does not deliberately alter the thickness of the sheet, but rather changes the contour of both surfaces of the sheet equally so that the thickness of the sheet remains constant and plays no part in correcting aberrations of the lens surface, whereas in the invention herein described the thickness is varied specifically for correcting aberrations.
On the other hand N. V. Philips Gloeilampenfabrieken (UK Pat. No. 698,772) describe a method of manufacturing a relatively rigid aberration correcting plate with an aspheric surface, with a supporting rim which may be reinforced by a metal ring. The rim and ring may not be essential depending on the rigidity of the plate, while the materials listed of which the correcting plate is made would not be suitable to transmit infrared radiation at longer wavelengths. Nor is there any description of using such a plate to modify the contour of another optical surface to improve the aberration correcting properties of that surface.
In the invention described herein, the correcting lens according to this invention comprises a lenticular membrane stretched on a frame, the membrane being made thin so that materials which in thick sections would block radiation of the required wavelength would be highly transmitting to those wavelengths. The lenticular membrane is thus deliberately made thin and necessarily must be stretched on a ring, which may or may not be reinforced, the ring ensuring that the thin non-selfsupporting membrane maintains a taut configuration necessary to achieve maximum possible definition. As an added advantage materials which are non-rigid even in thick sections, such as rubbers may be employed, thus increasing the range of materials that might be used.
In UK Pat. No. 1,295,157 WHITMARSH describes a thin metal sheet or metallised plastic foil stretched on a supporting frame and stretched by the application of air pressure to provide a mirror whose focal length varies with air pressure differential acr
REFERENCES:
patent: 3876734 (1975-04-01), Howden
patent: 3893750 (1975-07-01), D'Amato
patent: 3917766 (1975-11-01), Howden
patent: 3922327 (1975-11-01), Howden
patent: 4196961 (1980-04-01), Walter et al.
patent: 4212836 (1980-07-01), Wu
patent: 4378953 (1983-04-01), Winn
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