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Patent Searching and Data

Document Type and Number:
Japanese Patent JPH01302310
Kind Code:
PURPOSE:To obtain a long back focus with a small number of lenses by forming the face on the image forming surface side of a lens of a second group into an aspherical face and specifying the focal length, the equivalent focal length, etc. CONSTITUTION:A lens system consists of lenses 1 and 3 of first and second groups, and a pupil 2 is provided between the lens 1 of the first group and the lens 3 of the second group, and at least the face on the image forming surface side of the lens 3 of the second group is formed to an aspherical face, and conditions of inequalities I-VI are satisfied. In these inequalities, F0, F1, F2, FB, CV, T2, A, and K are the focal length of the lens system, EFL (equivalent focal length) of the lens of the first group, EFL of the lens of the second group, the back focus of the lens system, the radius of curvature, the inverval, fourth-order contribution, and a constant (conic constant) respectively. Thus, a fixed focus lens of less aberrations and satisfactory performance is obtained with the small-sized and light-weight constitution consisting of two lens groups, and the back focus of the lens system is set to a long value.

Application Number:
Publication Date:
December 06, 1989
Filing Date:
May 31, 1988
Export Citation:
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International Classes:
G02B13/18; (IPC1-7): G02B13/18
Attorney, Agent or Firm:
Sada Ito (1 person outside)