Small-diameter objective optical system
AssigneeOlympus Corporation
InventorMasato Fujiwara
Life of this patent
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Abstract
Reducing the outer diameter and effectively correcting various aberrations realizes a small-diameter objective optical system suitable for in vivo observation with a high numerical aperture. The invention provides a small-diameter objective optical system comprising, in order from an object plane a first lens group with positive refractive power, including at least one plano-convex lens whose convex surface faces an image plane; a second lens group with positive refractive power, including at least one concave lens; and a third lens group including a cemented lens of which a cemented surface has negative refractive power. The focal length of the third lens group is larger than the focal length of the first lens group.
Claims3
A small-diameter objective optical system comprising, in order from an object plane:
- a first lens group with positive refractive power, including at least one plano-convex lens whose convex surface faces an image plane;
- a second lens group with positive refractive power, including at least one concave lens;
- and
- a third lens group including a cemented lens of which a cemented surface has negative refractive power,
- wherein the focal length of the third lens group is larger than the focal length of the first lens group and conditional expression (1) below is satisfied:
- 0.2<(F1×h3)/(F3×h1)<0.3 (1)
- where
- F1 is the focal length of the first lens group,
- F3 is the focal length of the third lens group,
- h1 is a beam diameter of a substantially collimated beam at the first lens group side of the second lens group, and
- h3 is a beam diameter of a substantially collimated beam at the third lens group side of the second lens group.
A small-diameter objective optical system comprising;
- in order from an object plane:
- a first lens group with positive refractive power, including at least one piano-convex lens whose convex surface faces an image plane;
- a second lens group with positive refractive power, including at least one concave lens;
- and
- a third lens group including a cemented lens of which a cemented surface has negative refractive power,
- wherein the focal length of the third lens group is larger than the focal length of the first lens group and conditional expressions (2) and (3) below are satisfied:
- 0.25<(D1×NA)/(R1×n1)<0.35 (2)
- 1.5<d1/D1<2.5 (3)
- where
- D1 is a smallest lens diameter in the first lens group,
- NA is a numerical aperture at the object plane side of the small-diameter objective optical system,
- R1 is a smallest radius of curvature in the first lens group,
- n1 is a largest refractive index in the first lens group,
- d1 is a distance from the object plane to an image plane of a lens at the extreme image plane side in the first lens group.
A small-diameter objective optical system comprising, in order from an object plane:
- a first lens group with positive refractive power, including at least one piano-convex lens whose convex surface faces an image plane;
- a second lens group with positive refractive power, including at least one concave lens;
- and
- a third lens group including a cemented lens of which a cemented surface has negative refractive power,
- wherein the focal length of the third lens group is larger than the focal length of the first lens group and conditional expressions (4), (5), and (6) below are satisfied:
- 10<|ν31−ν32| (4)
- 0.12<|n31−n32|<0.2 (5)
- 4<F3/R3<5.5 (6)
- where
- ν31 is a d-line Abbe number of a lens with a large Abbe number in the cemented lens of the third lens group,
- ν32 is a d-line Abbe number of a lens with a small Abbe number in the cemented lens of the third lens group,
- n31 is a d-line refractive index of the lens with the large Abbe number in the cemented lens of the third lens group,
- n32 is a d-line refractive index of the lens with the small Abbe number in the cemented lens of the third lens group,
- F3 is the focal length of the third lens group, and
- R3 is a radius of curvature of the cemented surface in the cemented lens of the third lens group.
Dependencies are inferred from the claim text.