Objective for microscope

Abstract

An objective includes, in order from an object side, first, second, and third lens groups. The first lens group includes, in order from the object side, a first lens, a second lens, and a third lens component. When NA represents an objective numerical aperture, f represents an objective focal length, f G1 represents a first lens group focal length, r 11 represents a radius of curvature of a lens surface on the object side of the first lens, r 12 represents a radius of curvature of a lens surface on an image side of the first lens, and d 012 represents a distance on an optical axis from a front-side focal plane of the objective to a lens surface on the image side of the first lens, the objective satisfies: 0.8≦ NA <1, 1.6≦ f G1 /f ≦6, −1.6≦ r 11 /f ≦−0.2, and −2≦ r 12 /d 012 ≦−0.86.

What is claimed is: 
     
         1 . A dry objective for a microscope, the dry objective comprising in order from an object side:
 a first lens group with positive refractive power;   a second lens group with positive refractive power, the second lens group including a cemented lens that is configured of a lens with positive refractive power that is made of a low dispersion material and a lens with negative refractive power that is made of a high dispersion material; and   a third lens group with negative refractive power,   wherein:   the first lens group includes in order from the object side:
 a first lens that is a single lens having a meniscus shape with a concave surface facing the object side; 
 a second lens that is a single lens with positive refractive power, the single lens having a meniscus shape with a concave surface facing the object side; and 
 a third lens component that is a single lens or cemented lens with positive refractive power, 
   the dry objective is configured in a manner such that a ray height of an on-axis marginal ray becomes maximum on a boundary surface of a lens component closest to an object in the second lens group or within the lens component, and   when NA represents a numerical aperture of the objective, f represents a focal length of the objective, f G1  represents a focal length of the first lens group, r 11  represents a radius of curvature of a lens surface on the object side of the first lens, r 12  represents a radius of curvature of a lens surface on an image side of the first lens, and d o12  represents a distance on an optical axis from a front-side focal plane of the objective to a lens surface on the image side of the first lens, the objective satisfies the following conditional expressions:
   0.8≦NA<1   (4)
 
   1.6≦ f   G1   /f≦ 6   (5)
 
   −1.6≦ r   11   /f≦− 0.2   (6)
 
   −2≦ r   12   /d   o12 ≦−0.86   (7).
 
   
     
     
         2 . The objective according to  claim 1 , wherein the third lens component has a meniscus shape with a concave surface facing the object side. 
     
     
         3 . The objective according to  claim 1 , wherein the second lens group includes a three-lens-cemented lens that is formed by respectively cementing lenses with positive refractive power that are made of a low dispersion material to both surfaces of a lens with negative refractive power that is made of a high dispersion material. 
     
     
         4 . The objective according to  claim 2 , wherein the second lens group includes a three-lens-cemented lens that is formed by respectively cementing lenses with positive refractive power that are made of a low dispersion material to both surfaces of a lens with negative refractive power that is made of a high dispersion material. 
     
     
         5 . The objective according to  claim 1 , wherein the first lens group includes a seventh lens component that is a single lens or cemented lens with positive refractive power, closer to the image side than the third lens component. 
     
     
         6 . The objective according to  claim 2 , wherein the first lens group includes a seventh lens component that is a single lens or cemented lens with positive refractive power, closer to the image side than the third lens component. 
     
     
         7 . The objective according to  claim 3 , wherein the first lens group includes a seventh lens component that is a single lens or cemented lens with positive refractive power, closer to the image side than the third lens component. 
     
     
         8 . The objective according to  claim 4 , wherein the first lens group includes a seventh lens component that is a single lens or cemented lens with positive refractive power, closer to the image side than the third lens component. 
     
     
         9 . The objective according to  claim 1 , wherein:
 the third lens group includes a front lens group closest to the object side,   the front lens group includes:
 an eighth lens with positive refractive power that is made of a low dispersion material; and 
 a ninth lens with negative refractive power that is made of a high dispersion material, 
 the eighth lens and the ninth lens being arranged so as to be adjacent to each other, 
   a lens surface on a ninth-lens side of the eighth lens and a lens surface on an eighth lens-side of the ninth lens have a radius of curvature having the same sign, and   when f G30  represents a focal length of the front lens group, the objective satisfies the following conditional expression:
   −0.3≦ f/f   G30 ≦0.3   (12).
 
   
     
     
         10 . The objective according to  claim 2 , wherein:
 the third lens group includes a front lens group closest to the object side,   the front lens group includes:
 an eighth lens with positive refractive power that is made of a low dispersion material; and 
 a ninth lens with negative refractive power that is made of a high dispersion material, 
 the eighth lens and the ninth lens being arranged so as to be adjacent to each other, 
   a lens surface on a ninth-lens side of the eighth lens and a lens surface on an eighth lens-side of the ninth lens have a radius of curvature having the same sign, and   when f G30  represents a focal length of the front lens group, the objective satisfies the following conditional expression:
   −0.3≦ f/f   G30 ≦0.3   (12).
 
   
     
     
         11 . The objective according to  claim 3 , wherein:
 the third lens group includes a front lens group closest to the object side,   the front lens group includes:
 an eighth lens with positive refractive power that is made of a low dispersion material; and 
 a ninth lens with negative refractive power that is made of a high dispersion material, 
 the eighth lens and the ninth lens being arranged so as to be adjacent to each other, 
   a lens surface on a ninth-lens side of the eighth lens and a lens surface on an eighth lens-side of the ninth lens have a radius of curvature having the same sign, and   when f G30  represents a focal length of the front lens group, the objective satisfies the following conditional expression:
   −0.3≦ f/f   G30 ≦0.3   (12).
 
   
     
     
         12 . The objective according to  claim 4 , wherein:
 the third lens group includes a front lens group closest to the object side,   the front lens group includes:
 an eighth lens with positive refractive power that is made of a low dispersion material; and 
 a ninth lens with negative refractive power that is made of a high dispersion material, 
 the eighth lens and the ninth lens being arranged so as to be adjacent to each other, 
   a lens surface on a ninth-lens side of the eighth lens and a lens surface on an eighth lens-side of the ninth lens have a radius of curvature having the same sign, and   when f G0  represents a focal length of the front lens group, the objective satisfies the following conditional expression:
   −0.3≦ f/f   G30 ≦0.3   (12).
 
   
     
     
         13 . The objective according to  claim 5 , wherein:
 the third lens group includes a front lens group closest to the object side,   the front lens group includes:
 an eighth lens with positive refractive power that is made of a low dispersion material; and 
 a ninth lens with negative refractive power that is made of a high dispersion material, 
 the eighth lens and the ninth lens being arranged so as to be adjacent to each other, 
   a lens surface on a ninth-lens side of the eighth lens and a lens surface on an eighth lens-side of the ninth lens have a radius of curvature having the same sign, and   when f G30  represents a focal length of the front lens group, the objective satisfies the following conditional expression:
   −0.3≦ f/f   G30 ≦0.3   (12).
 
   
     
     
         14 . The objective according to  claim 6 , wherein:
 the third lens group includes a front lens group closest to the object side,   the front lens group includes:
 an eighth lens with positive refractive power that is made of a low dispersion material; and 
 a ninth lens with negative refractive power that is made of a high dispersion material, 
 the eighth lens and the ninth lens being arranged so as to be adjacent to each other, 
   a lens surface on a ninth-lens side of the eighth lens and a lens surface on an eighth lens-side of the ninth lens have a radius of curvature having the same sign, and   when f G30  represents a focal length of the front lens group, the objective satisfies the following conditional expression:
   −0.3≦ f/f   G30 ≦0.3   (12).
 
   
     
     
         15 . The objective according to  claim 7 , wherein:
 the third lens group includes a front lens group closest to the object side,   the front lens group includes:
 an eighth lens with positive refractive power that is made of a low dispersion material; and 
 a ninth lens with negative refractive power that is made of a high dispersion material, 
 the eighth lens and the ninth lens being arranged so as to be adjacent to each other, 
   a lens surface on a ninth-lens side of the eighth lens and a lens surface on an eighth lens-side of the ninth lens have a radius of curvature having the same sign, and   when f G30  represents a focal length of the front lens group, the objective satisfies the following conditional expression:
   −0.3≦ f/f   G30 ≦0.3   (12).
 
   
     
     
         16 . The objective according to  claim 1 , wherein:
 the third lens group includes a rear lens group with negative refractive power closest to the image side, and   when f G3I  represents a focal length of the rear lens group, the objective satisfies the following conditional expression:
   −10≦ f   G3I   /f≦− 1.5   (15).
 
   
     
     
         17 . The objective according to  claim 16 , wherein the rear lens group includes two or more lens components with negative refractive power. 
     
     
         18 . The objective according to  claim 16 , wherein:
 the third lens group includes:
 a front lens group arranged closest to the object side; and 
 an intermediate lens group arranged between the front lens group and the rear lens group, and 
   the intermediate lens group includes a tenth lens component that is configured of a single lens or cemented lens having a meniscus shape with a concave surface facing the object side.   
     
     
         19 . The objective according to  claim 1 , wherein when r 12  represents the radius of curvature of the lens surface on the image side of the first lens, and r 21  represents a radius of curvature of a lens surface on the object side of the second lens, the objective satisfies the following conditional expression:
   0.8≦ r   21   /r   12 ≦2   (16).
   
     
     
         20 . The objective according to  claim 1 , wherein a lens component closest to an image plane in the second lens group is a lens component with positive refractive power that is closest to the object among lens components other than lens components included in the first lens group and a lens component which the maximum ray height of the on-axis marginal ray passes through.