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OBJECTIVE OPTICAL SYSTEM FOR ENDOSCOPE

  • US 20180231749A1
  • Filed: 04/11/2018
  • Published: 08/16/2018
  • Est. Priority Date: 10/16/2015
  • Status: Active Grant
First Claim
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1. An objective optical system for endoscope, comprising in order from an object side:

  • a first group having a negative refractive power;

    an aperture stop; and

    a second group having a positive refractive power, whereinthe first group includes in order from the object side, a negative meniscus lens having a convex surface directed toward the object side, and a positive lens having a convex surface directed toward the object side, andthe second group includes in order from the object side, a predetermined lens, a positive cemented lens, and a positive single lens, or includes in order from the object side, the predetermined lens, the positive single lens, and the positive cemented lens, andthe negative meniscus lens has an aspheric surface, andthe predetermined lens is a meniscus lens having a convex surface directed toward an image side, andthe positive cemented lens includes an object-side lens positioned on the object side and an image-side lens positioned on the image side, andthe following conditional expressions (1′

    ), (2), and (4′

    ) are satisfied;


    0.7<

    |R1/R2|<

    1.1 



    (1′

    ),
    0.6<

    |R1/FL|<

    3 



    (2), and
    5≤

    |Fc/FL|≤

    7 



    (4′

    )where,R1 denotes a paraxial radius of curvature of a surface on the object side of the predetermined lens,R2 denotes a paraxial radius of curvature of a surface on an image side of the predetermined lens,FL denotes a focal length of the overall objective optical system for endoscope,Fc denotes a focal length at a cemented surface of the positive cemented lens,here,the focal length Fc at the cemented surface is expressed by the following expression (b)
    Fc=Rc/(nd′



    nd
    ) 



    (b)Rc denotes a paraxial radius of curvature of the cemented surface,nd denotes a refractive index of the object-side lens for a d-line, andnd′

    denotes a refractive index of the image-side lens for the d-line.

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