Endoscope optical system
An endoscope optical system has a first lens group having positive refractive power, an aperture diaphragm, a second lens group having negative refractive power and a third lens group having positive refractive group, the second lens group moving along an optical axis to perform focusing, the first lens group having a first lens having negative refractive power and a second lens having positive refractive power, and the optical system satisfying the following conditional equation: −5.0< H (76)*(1− nd 01)/ r 2<−0.2 (1) 0.5<( r 1+ r 2)/( r 1− r 2)<1.2 (2) where H(76) is a height at which a principal ray having an incidence angle of view of 76 degrees during normal observation passes through a surface on an image side of the first lens, nd01 is a refractive index of the first lens with respect to a line d, and r1 and r2 are respectively curvature radii of surfaces on the object side and the image side of the first lens.
1. An endoscope optical system consisting of a first lens group having positive refractive power, an aperture diaphragm, a second lens group having negative refractive power, and a third lens group having positive refractive power, in this order from an object side to an image side,
the second lens group moving along an optical axis to perform focusing, and
the first lens group comprising a first lens having negative refractive power and a second lens having positive refractive power, in this order from the object side and satisfying the following conditional equations:
−5.0< H (76)*(1− nd 01)/ r 2<−0.2 (1)
0.5<( r 1+ r 2)/( r 1− r 2)<1.2 (2)
where H(76) is a height at which a principal ray of an incidence angle of view of 76 degrees during normal observation transmits through a surface on the image side of the first lens, nd01 is a refractive index of the first lens with respect to a line d, and r1 and r2 are respectively curvature radii of a surface on the object side and the surface on the image side of the first lens.
2. The endoscope optical system according to claim 1 , satisfying the following conditional equation:
0.5< D — L 02/ ih< 5.0 (3)
where D_L02 is a thickness of the second lens on the optical axis, and ih is a maximum image height.
3. The endoscope optical system according to claim 1 , satisfying the following conditional equation:
1.65< nd 01<2.4 (4)
where nd01 is a refractive index of the first lens with respect to the line d.
4. The endoscope optical system according to claim 1 , wherein
the second lens group is composed of only a connected lens of a lens having negative refractive power and a lens having positive refractive power, and
the endoscope optical system satisfies the following conditional equation:
10<ν41−ν42<45 (5)
where ν41 and ν42 are respectively Abbe's numbers of the lens having negative refractive power and the lens having positive refractive power of the second lens group.
5. The endoscope optical system according to claim 4 , wherein the second lens group satisfies the following conditional equation:
0.2< LD 2/ ih< 3.0 (6)
where LD2 is a maximum drive amount upon focusing.
6. The endoscope optical system according to claim 4 , satisfying the following conditional equation:
−0.05< PW — G 2/ ih<− 1 (7)
where PW_G 2 is refractive power of the second lens group.
7. The endoscope optical system according to claim 4 , satisfying the following conditional equation:
−2.0< PW — L 01/ ih<− 0.1 (8)
where PW_L01 is refractive power of the first lens.
8. The endoscope optical system according to claim 4 , wherein
the first lens group is composed of a first lens having negative refractive power, a second lens having positive refractive power, and a connected lens of a lens having positive refractive power and a lens having negative refractive power, in this order from the object side toward the image side, and
the endoscope optical system satisfies the following conditional equation:
10<ν31−ν32<50 (9)
where ν31 and ν32 are Abbe's numbers of the lens having negative refractive power and the lens having positive refractive power constituting the connected lens of the first lens group.
9. The endoscope optical system according to claim 4 , wherein
the third lens group is composed of a lens having positive refractive power and a connected lens of a lens having positive refractive power and a lens having negative refractive power, and
the endoscope optical system satisfies the following conditional equation:
25<ν61−ν62<70 (10)
where ν61 and ν62 are Abbe's numbers of the lens having negative refractive power and the lens having positive refractive power constituting the connected lens of the third lens group.
10. The endoscope optical system according to claim 4 , satisfying the following conditional equation:
1.0< PW — G 1/ PW — G 3<2.0 (11)
where PW_G 1 is refractive power of the first lens group, and PW_G 3 is refractive power of the third lens group.
11. The endoscope optical system according to claim 4 , satisfying the following conditional equation:
5.0< L _all/ ih< 20.0 (12)
where L_all is an entire length of the endoscope optical system.