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  Compact high performance zoom lens systemUSPTO Application #: 20060238887Title: Compact high performance zoom lens system Abstract: A compact high performance objective zoom lens system is disclosed that provides optimum optical performance over the entire zoom focal length range at focus distances from close to infinity. The system comprises, from object space to image space, one focusing objective lens group (comprising a focus lens group and a stationary lens group) and three zoom lens groups aligned on the optical axis. The focus lens group and the zoom lens groups are axially movable along the optical axis for focusing and zooming. In one embodiment, the system has a focal length zoom region from about 19 mm to 90 mm, an aperture of F/2.7 and substantially the same optical performance as high quality fixed objective lenses of the same range. The performance characteristics of this system makes it suitable for use with both film and electronic detector cameras. (end of abstract) Agent: Morrison & Foerster, LLP - Los Angeles, CA, US Inventors: Jacob Moskovich, Iain A. Neil, Takanori Yamanashi USPTO Applicaton #: 20060238887 - Class: 359683000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20060238887. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] This invention relates to an optical objective lens system for cameras and, in particular, to a compact high performance zoom lens system that produces a high quality image over the full zoom range. [0003] 2. Description of Related Art [0004] High performance optical systems, such as for cinematography, high definition television ("HDTV") and advanced television ("ATV") require superior optical characteristics and performance that have historically been achieved using separate objective lenses of different fixed focal lengths to provide different photographic functions that are determined or influenced by the focal length. [0005] However, there are cinematographic advantages to using zoom lenses to vary the effective focal length of the objective lens without needing to change objective lenses. In addition, zoom lenses may provide a cost reduction as compared to the cost of several different fixed focal length lenses, particularly within the normal range of desired focal lengths that might be used in photographing normal scenes that require a range from very wide angle to standard focal lengths. Notwithstanding these advantages, previously available zoom lenses also had one or more undesirable limitations such as a limited range of focal lengths, the inability to focus adequately over the entire focal length range, the inability to focus on close objects, the lack of adequate optical performance over the entire focal length range and focus distance, the cost, the large size and the like. U.S. Pat. No. 6,122,111 (the '111 patent) discloses a high performance zoom lens system that improved upon previously available zoom lenses and provides improved optical performance over the entire zoom focal length range and at focus distances from very close to infinity. The zoom lens system of the '111 Patent has a focal length zoom region from about 14.5 mm to 50 mm and provides optical performance similar to that of high quality fixed objective lenses of the same range, including an aperture suitable for capturing images in low light conditions using conventional detectors. [0006] However, recent advances in detector technology such as in film and electronic sensors have created a need for objective lenses, including zoom lenses, to perform well with a multitude of detectors. In addition, the light sensitivity of these detectors has improved to the point where objective lenses, including zoom lenses, having lesser speed or full aperture are acceptable even in low light conditions. Thus, the smallest F-number, which is a commonly accepted technical term used to describe the speed or aperture of a lens (but in an inverse direction), can now be increased without substantially affecting low light sensitivity. For example, where a lens full aperture of F/2.0 was previously necessary with conventional detectors, a lesser lens full aperture of F/2.8 produces a similar result with these new detectors. With this reduction in apertures, compact objective lens designs, including zoom lenses, that are smaller in size (including length, diameter and weight) and cheaper to produce (as compared to a series of fixed focal length lenses) are now possible. SUMMARY OF THE INVENTION [0007] Embodiments of the present invention are directed to a compact high performance objective zoom lens system that provides optimum optical performance over the entire zoom focal length range and at focus distances from very close to infinity. The objective zoom lens system of the present invention collects radiation from object space and images the radiation at an image plane located just after the lens. [0008] In one embodiment, a compact zoom lens system is disclosed having a focal length zoom region from about 19 mm to 90 mm and substantially the same optical performance as high quality fixed objective lenses of the same range. Note that this embodiment was selected as providing a reasonably wide angle lens with a reasonably long focal length, yet maintaining a reasonable diameter lens at a reasonable length. In addition, an aperture of F/2.7 was chosen as being acceptable for use with state of the art detectors having lower light requirements, enabling the lens to be even more compact. However, it should be understood that although this embodiment is described herein for purposes of explaining the invention, embodiments of the present are not constrained to this embodiment. [0009] For purposes of comparison, the zoom lens system of the '111 Patent was designed to have an aperture of F/2.2, and has two focusing groups, two zoom groups, and one stationary group at the rear. There is an iris inside the last zoom group. However, significant design changes were required in order to design a lens having an aperture of F/2.7 as in the present invention. The compact high performance zoom lens system of the present invention comprises, in order from object space to image space, one focus lens group, a single stationary lens group, and three zoom lens groups aligned on the optical axis. The focus lens group and the zoom lens groups are axially movable along the optical axis for focusing and zooming but with the single stationary lens group and the real image plane of the camera remaining at fixed locations. One compact high performance objective zoom lens can take the place of a number (e.g. eleven) of fixed focal length lenses, and it is only slightly longer than fixed focal length lenses within the same range. BRIEF DESCRIPTION OF THE DRAWINGS [0010] FIG. 1 is an optical diagram of the compact high performance objective zoom lens system of the present invention; and [0011] FIGS. 2-9 are optical diagrams of the zoom lens system of FIG. 1 illustrating different positions of the focus lens groups and zoom lens groups to produce different focal lengths and focus distances. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [0012] In the following description of preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the preferred embodiments of the present invention. [0013] A preferred embodiment of the present invention will now be described by way of a design example with accompanying figures and tables. Referring first to FIG. 1, each lens element is identified by a numeral from 1 through 20 and the general configuration of each lens element is depicted, but the actual radius of each lens surface is set forth below in a table. The lens surfaces, including dummy optical surfaces used for design calculation purposes, are identified by the letter "S" followed by a numeral from S1 through S41. [0014] Each lens element has its opposite surfaces identified by a separate but consecutive surface number as, for example, lens element 1 has lens surfaces S2 and S3, lens element 12 has lens surfaces S22 and S23 and so forth, as shown in FIG. 1, except that for doublet lens components 1D, 2D and 3D the coincident facing lens surfaces are given a single surface number. For example, doublet 1D is comprised of lens element 5 having a front lens surface S10 and a rear lens surface S11 and lens element 6 having a front lens surface S11 (coincidental) and a rear lens surface S12. The location of the object to be photographed, particularly as it relates to focus distance, is identified by a vertical line and the letter "O" on the optical axis, and a dummy optical surface that is used in the optical data tables is identified by the vertical line numbered S40, and the real image surface is identified by the numeral S41. Dummy surface S40 used for making the calculations substantially coincides with real image surface S41 at all positions of the focus and zoom lens groups. All of the lens surfaces are spherical except lens surfaces S3 and S26 which are aspheric surfaces that are non-spherical, non-plano but rotationally symmetrical about the optical axis. [0015] Before describing the detailed characteristics of the lens elements, a broad description of the lens groups and their axial positions and movement will be given for the zoom lens system, generally designated 50, of this invention. Beginning from the end facing the object O to be photographed, i.e. the left end in FIG. 1, the focusing objective lens group 51 comprises a focus lens group 52 comprised of lens elements 1, 2 and 3 and a stationary lens group 53 comprised of lens element 4, a first doublet 1D comprised of lens elements 5 and 6, and lens element 7. A zoom lens group 54 comprises a first zoom lens group 55, a second zoom lens group 56 and a third zoom lens group 57 that together provide zooming while maintaining a constant image location. The first zoom lens group 55 includes, from left to right in FIG. 1, lens element 8, a second doublet 2D comprised of lens elements 9 and 10, and a singlet lens element 10. The second zoom lens group 56 includes a singlet lens element 12. The third zoom lens group 57 includes, from left to right in FIG. 1, an adjustable optical stop (iris) S24, singlet lens elements 13-16, a third doublet 3D comprising lens elements 17 and 18, and singlet lens elements 19 and 20. [0016] The positive or negative power of each lens element is set forth below in TABLE 1. The resultant optical power of each subgroup of lenses is as follows; the focus lens group 52 is negative, the stationary lens group 53 is positive, the first zoom lens group 55 is negative, the second zoom lens group 56 is positive, and the third zoom lens group 57 is positive. The combined optical power of the focusing objective lens group 51 is positive. [0017] Each of the lens groups 52, 55, 56 and 57 are movable in both directions along the optical axis. Lens group 52 moves for focusing, while lens groups 55, 56 and 57 move for zooming. The stationary lens group 53 remains stationary and at a fixed distance from the real image surface S41. The horizontal arrows with arrowheads on both ends in the upper portion of FIG. 1 indicate that each of the lens subgroups 52, 55, 56 and 57 are movable in both axial directions but in a monotonic manner (i.e. in only one direction when progressing from one extreme to the other of adjustments). [0018] While only the lens elements are physically shown in FIG. 1, it is to be understood that conventional mechanical devices and mechanisms are provided for supporting the lens elements and for causing axial movement of the movable lens groups in a conventional lens housing or barrel. [0019] The lens construction and fabrication data for the above described zoom lens system 50 is set forth below in TABLE 1, which is extracted from data produced by CODE V.RTM. optical design software that is commercially available from Optical Research Associates, Inc., Pasadena, Calif., U.S.A., which was also used for producing the optical diagrams FIGS. 1-9. All of the data in TABLE 1 is given at a temperature of 25.degree. C. (77.degree. F.) and standard atmospheric pressure (760 mm Hg). Throughout this specification, including the Tables, all measurements are in millimeters (mm) with the exception of wavelengths which are in nanometers (nm). In TABLE 1, the first column "ITEM" identifies each optical element and each location, i.e. object plane, dummy surface, etc., with the same numeral or label as used in FIG. 1. The second and third columns identify the "Group" and "Subgroup," respectively, to which that optical element (lens) belongs with the same numerals used in FIG. 1. The fourth column "Surface" is a list of the surface numbers of the object (line "O" in FIG. 1 and "Object Plane" in TABLE 1), the dummy optical surface S41, the Stop (iris) S24 and each of the actual surfaces of the lenses, as identified in FIG. 1. The fifth and sixth columns "Focusing Position" and "Zoom Position," respectively, identify three typical focus positions (F1, F2 and F3) of the focus lens group 52 and five typical positions (Z1, Z2, Z3, Z4 and Z5) of the zoom lens groups 55-57 wherein there are changes in the distance (separation) between some of the surfaces listed in the fourth column, as described below more thoroughly. The seventh column, headed by the legend "Radius of Curvature," is a list of the optical surface radius of curvature for each surface, with a minus sign (-) meaning the center of the radius of curvature is to the left of the surface, as viewed in FIG. 1, and "Flat" meaning either an optically flat surface or a dummy optical surface. The asterisk (*) for surfaces S3 and S26 indicate these are aspheric surfaces for which the "radius of curvature" is a base radius, and the formula and coefficients for those two surfaces are set forth as a footnote to TABLE 1 at the * (asterisk). The eighth column "Thickness or Separation" is the axial distance between that surface (fourth column) and the next surface. For example, the distance between surface S2 and surface S3 is 3.000 mm. [0020] The last three columns of TABLE 1 relate to the "Material" between that surface (fourth column) and the next surface to the right in FIG. 1, with the column "Type" indicating whether there is a lens (Glass) or empty space (Air) between those two surfaces. All of the lenses are glass and the column "Code" identifies the optical glass. For convenience, all of the lens glass has been selected from glass available from Ohara Corporation and the column "Name" lists the Ohara identification for each glass type, but it is to be understood that any equivalent, similar or adequate glass may be used. Continue reading... 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