Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B9/00—Optical objectives characterised both by the number of the components and their arrangements according to their sign, i.e. + or -
  • G02B9/04—Optical objectives characterised both by the number of the components and their arrangements according to their sign, i.e. + or - having two components only
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/0025—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration
  • G02B27/0037—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration with diffracting elements
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B13/00—Optical objectives specially designed for the purposes specified below
  • G02B13/04—Reversed telephoto objectives
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
  • G02B27/4205—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant
  • G02B27/4211—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant correcting chromatic aberrations
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B9/00—Optical objectives characterised both by the number of the components and their arrangements according to their sign, i.e. + or -
  • G02B9/04—Optical objectives characterised both by the number of the components and their arrangements according to their sign, i.e. + or - having two components only
  • G02B9/10—Optical objectives characterised both by the number of the components and their arrangements according to their sign, i.e. + or - having two components only one + and one - component

Definitions

• 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.
• CCDs charged coupled devices
• 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.
• CCDs having a diagonal of approximately 5.5 mm are widely available.
• 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.
• 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.
• 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.
• both lens elements have a large diameter relative to the lens system's entrance pupil.
• 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.
• 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.
• a spherical surface and a conic surface can be used on both the first and second lens elements.
• 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.
• 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 suitable for use with 1/3 inch CCDs.
• Figures 1-4 are schematic side views of lens systems constructed in accordance with the invention.
• the lens systems of the present invention consist of two lens elements.
• the first lens element has a negative optical power, i.e., f ⁇ ⁇ 0, and preferably has the following properties:
• f ⁇ is the focal length of the lens system
• f ⁇ is the focal length of the first lens element
• t ⁇ is the thickness of the first lens element
• D ⁇ is the diameter of the first lens element
• Dgp is the diameter of the entrance pupil of the lens system.
• the t ] / f ⁇ ratio is most preferably greater than 1.0.
• the diameter of a lens element is the element's largest clear aperture and the diameter of the entrance pupil of a lens system is the system's equivalent singlet focal length divided by the system's infinity f-number.
• the lens systems of Examples 1-4 set forth below have D ⁇ values of 9.5, 9.6, 11.9, and 5.6 mm, and Dgp values of 1.5, 1.5, 2.3, and 1.5 mm, so that their Di/Dgp ratios are 6.3, 6.4, 5.2, and 3.7, respectively.
• the D ⁇ /Dgp ratio is greater than 3.0.
• the second lens element has a positive optical power, i.e., f 2 > 0, and preferably has the following properties: f 2 / f 0 ⁇ 2.0; d 12 / f 0 > 0.25;
• D 2 /D E p > 1.3; and t 2 / f 0 > 0.5; where f is the focal length of the second lens element, d ⁇ 2 is the distance between the first and second lens elements, D 2 is the diameter of the second lens element, and t is the thickness of the second lens element.
• the lens systems of Examples 1-4 set forth below have D values of 4.0, 4.0, 4.5, and
• the D 2 /Dgp ratio is greater than 1.5.
• the lens systems of the invention satisfy the following relationships:
• the second lens element is a refractive- diffractive hybrid element.
• the fabrication of such elements is well known in the art. See, for example, C. Londono, "Design and Fabrication of Surface Relief Diffractive Optical Elements, or Kinoforms, with Examples for Optical Athermalization," Ph.D. diss., Tufts University, 1992, and the references cited therein, the relevant portions of all of which are incorporated herein by reference.
• Diffractive surfaces have the problem of diffraction efficiency, i.e., all orders do not come to a perfect focus. This effect is often seen as "glare". For an electronic imaging system application, the diffraction efficiency problem can be addressed by digital processing of the electronic image.
• the ratio of f 2 /f ⁇ , where f 2 includes the contribution of the diffractive surface is preferably greater than 1.0, e.g., the ratio is approximately 1.5.
• the f /f ⁇ ratio is preferably less than 1.0.
• the use of a refractive-diffractive hybrid element for the second lens element provides color correction for the lens system and allows both the first and second lens elements to be composed of a low dispersion material such as acrylic. If such a hybrid element is not used, the first lens element should have a higher dispersion than the second lens element.
• the first lens element can be composed of styrene and the second lens element can be composed of acrylic for such embodiments.
• Other plastics can, of course, be used if desired.
• polycarbonates and copolymers of polystyrene and acrylic (e.g., NAS) having flint-like dispersions can be used. See The Handbook of Plastic Optics, U.S.
• the second lens element is a refractive-diffractive hybrid element.
• the first lens element has a spherical surface and a conic surface and the second lens element also has a spherical surface and a conic surface. This arrangement facilitates manufacture of the lens system.
• the second lens element can have two conic surfaces
• the first lens element can have an object side surface which is spherical and an image side surface which in some embodiments is a conic and in other embodiments is a general asphere.
• the image side surface of the first lens element can be a conic when the second lens element is a refractive-diffractive hybrid element. Otherwise, for these embodiments, the image side surface of the first lens element is typically a general asphere to facilitate aberration correction.
• Conic surfaces are preferred to general aspherical surfaces since the polynomial used to define a general aspherical surface (see below) can lead to undesired surface configurations if the diameter is extended beyond the clear aperture, while a conic surface does not suffer from this problem.
• a surface is spherical if "k” and “D” through “I” are all zero, a surface is a conic if “k” is non-zero and “D” through “I” are all zero, and a surface is a general asphere if at least one of "D” through “I” is non-zero.
• a surface for which "k” is non-zero and at least one of "D” through “I” is nonzero, is a general aspherical surface.
• Figures 1 to 4 illustrate various lens systems constructed in accordance with the invention. Corresponding prescriptions and optical properties appear in Tables 1 to 4, respectively.
• the Hoya designation is used for the glass plate employed in Figures 2 and 4. Equivalent glasses made by other manufacturers can be used in the practice of the invention. Industry acceptable materials are used for the plastic elements.
• the designation "c” associated with various of the surfaces in the tables represents a conic surface.
• the designation "a” associated with surface 2 of Tables 1 and 2 represents a general aspherical surface.
• Surfaces 6 and 7 in Table 3 represent a diffractive surface.
• the asterisks used in this table represent the index of refraction and the Abbe numbers used in the Sweatt model for a diffractive surface, e.g., a N e value of 9999 and a V e value of -3.4. See W.C. Sweatt, "Mathematical Equivalence between a Holographic Optical Element and an Ultra High Index Lens," Journal of the Optical Society of America. 69:486-487, 1979.
• the diffractive surface is in fact part of the second lens element.
• Surface 3 in Tables 1-4 is a vignetting surface. All dimensions given in the tables are in millimeters.
• the figures are drawn with the long conjugate on the left and the short conjugate on the right. Accordingly, in the typical application of the invention, the object to be viewed will be on the left and an electronic imaging system, e.g., a system employing a CCD, will be on the right.
• an electronic imaging system e.g., a system employing a CCD

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• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Lenses (AREA)

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• 1997
  • 1997-11-12 CN CN97180169A patent/CN1119688C/zh not_active Expired - Fee Related
  • 1997-11-12 KR KR10-1999-7004735A patent/KR100506516B1/ko not_active Expired - Fee Related
  • 1997-11-12 EP EP97946529A patent/EP1010028B1/en not_active Expired - Lifetime
  • 1997-11-12 DE DE69728183T patent/DE69728183T2/de not_active Expired - Fee Related
  • 1997-11-12 WO PCT/US1997/020144 patent/WO1998023988A1/en not_active Ceased
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  • 1997-11-12 JP JP52466298A patent/JP2001504949A/ja not_active Ceased
  • 1997-11-12 US US09/308,798 patent/US6097551A/en not_active Expired - Fee Related
  • 1997-12-02 TW TW086118427A patent/TW393581B/zh not_active IP Right Cessation

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