Optical: systems and elements – Lens – Multiple component lenses
Patent
1999-05-25
2000-08-01
Epps, Georgia
Optical: systems and elements
Lens
Multiple component lenses
359717, G02B 904, G02B 1318
Patent
active
060975512
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to lenses for use with electronic imaging systems, e.g., systems employing charged coupled devices (CCDs) or similar light sensitive electronic components. Such systems are well known in the art and descriptions thereof can be found in various references, including Rose et al., "Physical Limits to the Performance of Imaging Systems," Physics Today, September 1989, pages 24-32 and the references cited therein; and Sequin et al., "Charge Transfer Devices," Advances in Electronics and Electron Physics, suppl. 8, L. Marton editor, Academic Press, New York, 1975, the relevant portions of all of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
Electronic imaging systems require lens systems which are capable of producing high quality images which have a small size, i.e., they require lens systems having short focal lengths. For example, CCDs having a diagonal of approximately 5.5 mm (known as 1/3 inch CCDs) are widely available. Within this small size, a typical CCD will have over 200,000 pixels, thus giving the device a resolution on the order of 40 cycles per millimeter at the surface of the CCD.
Short focal length lens systems typically comprise small lens elements. Such elements, if they are too small, can be difficult to handle and assemble into a finished unit. Cost is always a dominant factor for lenses for electronic imaging systems, especially where the system is to be part of a mass marketed product. Because CCDs have a high level of resolution, lenses used with such devices must be of high optical quality. This requirement exacerbates the cost problem. In particular, the requirement puts a high premium on achieving a high level of optical performance with a minimum of lens elements.
SUMMARY OF THE INVENTION
In view of above considerations, it is an object of the present invention to provide lens systems for electronic imaging systems which: (1) use only two lens elements to minimize costs; (2) use a minimum of general aspherical surfaces, e.g., only one general aspherical surface and in some cases, no general aspherical surfaces, again to minimize costs, in this case by simplifying the manufacturing process; (3) use lens elements having relatively large diameters to facilitate handling and assembly; and (4) have a level of optical performance compatible with that of CCDs and similar electronic imaging devices.
To achieve this and other objects, the invention provides a two element lens system wherein a first element, located on the object side of the lens system, has a negative optical power and is relatively thick, and a second lens element, located on the image side of the lens system, has a positive power and is relatively widely spaced from the first lens element and/or is relatively thick. Preferably, both lens elements have a large diameter relative to the lens system's entrance pupil.
In certain embodiments, the system includes one general aspherical surface on the first lens element and two conic surfaces on the second lens element. In other embodiments, no general aspherical surfaces are used. In connection with these embodiments, one conic surface can be employed on the first lens element and two conic surfaces can be employed on the second lens element, which is preferably a refractive-diffractive hybrid element. Alternatively, a spherical surface and a conic surface can be used on both the first and second lens elements. In some embodiments, in order to achieve color correction, the first lens element is composed of styrene and the second lens element is composed of acrylic. The first and second lens elements can both be composed of acrylic when a refractive-diffractive hybrid element is used for the second lens element.
The lens systems of the invention have focal lengths and optical performances suitable for use with conventional CCDs. For example, the lens systems can readily achieve a focal length of less than 5.0 mm, an f-number of 2.8 or faster, and a MTF at the CCD of 40 cycles/millimeter, thus making them s
REFERENCES:
patent: 5677798 (1997-10-01), Hirano et al.
Epps Georgia
Klee Maurice M.
Spector David N.
U.S. Precision Lens Inc.
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