JPH0567002B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field of the Invention) The present invention relates to a microscope objective lens with medium to low magnification and a flat image plane. (Background of the Invention) Recently, there have been increasing demands for objective lenses to have a long working distance, high resolution, wide field of view, good image flatness, and apochromat-level chromatic aberration correction. For this reason, conventional objective lenses are no longer able to adequately cope with this problem. As the working distance increases, the effective diameter of the lens increases, which worsens all kinds of aberrations, including spherical aberration, off-axis aberration, and chromatic aberration. Furthermore, as the numerical aperture increases, the depth of focus also decreases, and the tolerance range for various aberrations further narrows. Furthermore, high resolution and a wide field of view tend to be contradictory when it comes to correcting various aberrations, and it has been extremely technically difficult to satisfy both. (Objective of the Invention) The object of the present invention is to develop an apochromatic or semi-apochromatic class objective lens for medium to low magnification, which has an extremely larger working distance and higher resolving power than conventional ones, and which has a flat image over a wide field of view. Our goal is to provide the following. (Summary of the Invention) The objective lens according to the present invention includes, in order from the object side:
A first lens group G ₁ with a positive refractive power composed of at least one lens, a second lens group G ₂ of a cemented meniscus lens component consisting of a cemented positive lens and a negative lens with a convex surface facing the object side, and a negative a third lens group G ₃ consisting of a cemented meniscus lens component consisting of a cemented lens and a positive lens with a concave surface facing the object side;
A single positive lens and two negative and positive lenses
It has a fourth lens group _G4 having a positive refractive power and having a bonded positive lens component made of two lenses cemented together.
Then, the distance from the object plane O to the barrel mounting surface S of the objective lens (the surface where the objective lens is attached to the microscope body), that is, the so-called shoulder height, is l, and the distance from the apex of the object-side lens surface of the second lens group _G2 to the 3 lens groups
The distance to the apex of the image-side lens surface of G ₃ is D ₁₂ , and the Abbe numbers of the positive and negative lenses forming the cemented lens in the second lens group G ₂ are ν _2P , ν _2N , respectively.
The Atsube numbers of the positive lens and negative lens forming the cemented lens in the third lens group G ₃ are respectively ν _3P ,
ν _3N , refractive index N _3P , N _3N , fourth lens group
When the Atsube number of a single positive lens in G ₄ is ν _4P , 0.3l＜D ₁₂ ＜0.6l (1) N _3N ＞N _3P (2) ν _2P ＞ν _2N (3) ν _3N ＜50 <ν _3P (4) ν _3P <35.8 (5) is satisfied. The technical effects of the present invention as described above will be explained based on the optical path diagram of the first embodiment shown in FIG. First, the first lens group _G1 has a convergent effect,
The exit angle of the divergent light beam from the object plane is made small, and the second
By reducing the angle of incidence on the object-side lens surface of lens group _G2 , it contributes to correction of spherical aberration. By increasing the number of lenses constituting the first lens group _G1 , it is possible to increase the numerical aperture, angle of view, and working distance of the objective lens. By applying the above condition (1) to the second lens group G ₂ and the third lens group G ₃ , the composite center thickness of both groups is increased and the object of the third lens group G ₃ is We decided to provide a concave surface with a strong curvature on the side, and further conditions
By imposing (2), the cemented surface in the third lens group _G3 has a diverging effect, and the field curvature is effectively corrected. Condition (3) is for correcting chromatic aberration regarding the second lens group _G2 , and is based on the degree of Abbe number between the positive lens and the negative lens that form the cemented meniscus lens component of the second lens group _G2 . are the residual chromatic aberration of the first lens group G ₁ and the residual chromatic aberration of the third lens group G ₃ and the fourth lens group
It is determined by the degree of chromatic aberration of lens group _G4 .
Generally, the third lens group _G3 is the second lens group.
Since the effective diameter is larger than that of the G ₂ , it is possible to make stronger correction of chromatic aberration than the second lens group G ₂ .
Conditions such as equation (4) make it possible to satisfactorily correct the chromatic aberration of the entire system. Further, by applying the conditions as expressed in equation (5) to the positive lens in the fourth lens group _G4 having positive refractive power, chromatic aberration of magnification can be favorably corrected. Since this condition is a reverse correction for axial chromatic aberration and spherical aberration, that is, axially symmetrical chromatic aberration, it is necessary to correct it again using the next bonded positive lens component. In the fourth lens group _G4 ,
In order to correct both lateral chromatic aberration and axial chromatic aberration, the refractive power of the positive lens that satisfies the above condition (5) is strengthened, and the refractive power of the positive lens that forms the next bonded positive lens component is weakened. Therefore, it is necessary to provide the cemented surface with a sufficient effect of correcting chromatic aberration. Furthermore, a fourth lens group G ₄ that satisfies the above condition (5)
If a special glass material with a secondary dispersion coefficient suitable for a positive lens is used as the positive lens inside, it is possible to obtain an apochromatic objective lens with extremely good chromatic aberration correction. If the above condition (1) cannot be met,
The Petzval sum increases, the field curvature also increases, and the flatness of the image plane deteriorates. Furthermore, if condition (2) is not satisfied, the refractive power of the cemented surface of the third lens group _G3 becomes weak, which is disadvantageous for correcting spherical aberrations and the like. If conditions (3) and (4) are not met, it will be difficult to correct chromatic aberration, and if condition (5) is not met, lateral chromatic aberration will worsen, and an apochromatic objective lens will be required. becomes difficult. (Example) Examples according to the present invention will be described below.
The first embodiment shown in Fig. 1 has an NA of 4x magnification.
= 0.2 low magnification objective lens. As shown,
The first lens group _G1 consists of a single positive lens component _L11 , and the second lens group _G2 consists of a cemented double-convex positive lens _L21 and a double-concave negative lens _L22 , with the convex surface facing the object side. It consists of a meniscus lens component. Third
Lens group G ₃ is a negative lens L ₃₁ with a concave surface facing the object side.
It consists of a meniscus lens component with a concave surface facing the object side, and a positive lens _L32 .
The fourth lens group _G4 is composed of a positive lens component _L41 whose surface with a stronger curvature faces toward the image side and a bonded positive lens component _L42 . The second embodiment of the present invention has substantially the same configuration as the first embodiment and has similar specifications. Therefore, the lens configuration diagram has been omitted. Tables 1 and 2 below show the specifications of the first and second embodiments. In the table, the leftmost number represents the order from the object side, and the refractive index and Atsube number are values for the d-line (λ=587.6 nm). Also, WD is the working distance, and d _p is the first distance between the object plane and the objective lens.
The distance to the surface vertex, Bf is the distance from the final lens surface vertex to the image plane.

【table】

【table】

[Table] Various aberration diagrams for the first and second embodiments are shown in FIGS. 2 and 3, respectively. In each spherical aberration diagram, d
In addition to the reference ray of line C (λ=656.3nm),
F-line (λ=486.1nm) and G-line (λ=435.8nm)
I have also included the situation. A third embodiment according to the present invention shown in FIG.
Plan apochromat objective with 10x, NA=0.45. As shown, the first lens group
G ₁ is composed of, in order from the object side, a meniscus lens component L ₁₁ with a concave surface facing the object side and a single positive lens component L ₁₂ with a surface with a stronger curvature facing the object side. With this configuration of the first lens group _G1 , field curvature and spherical aberration are corrected, and chromatic aberration of magnification is corrected mainly by the balance with the fourth lens group _G4 . The second lens group G ₂ is composed of a meniscus lens component formed by cementing a biconvex positive lens L ₂₁ and a biconcave negative lens L ₂₂ in order from the object side, and has a convex surface facing the object side. ₃ is composed of a meniscus lens component formed by cementing a biconcave negative lens L ₃₁ and a biconvex positive lens L ₃₂ in order from the object side, with the concave surface facing the object side. The fourth lens group G ₄ includes, in order from the object side, a single positive lens component L _{41 with a surface with a stronger curvature facing the image side, a negative meniscus lens component with a convex surface facing the object side, and a single positive lens component L 41} with a surface with a stronger curvature facing the object side. It is composed of a bonded positive lens component L ₄₂ formed by bonding a biconvex positive lens with the strong side facing. Further, the fourth embodiment according to the present invention shown in FIG. 6 also has a magnification of 10 times and NA=0.45. The lens configuration is almost the same as that of the third embodiment, but the first
The difference is that the meniscus lens component _L11 closest to the object in the lens group _G1 is composed of a cemented double-concave negative lens and a double-convex positive lens. With such a configuration, it is advantageous to correct chromatic aberration, particularly chromatic aberration of magnification, and spherical aberration can also be corrected better. Tables 3 and 4 below show the specifications of the third and fourth embodiments, respectively, in the same way as the first embodiment. In addition, in both the third and fourth embodiments, a thickness of 0.17 mm, a refractive index of 1.52216, and an Atsube number are placed on the object plane.
It was designed to accommodate a 58.8 cover glass.

【table】

【table】

[Table] Various aberration diagrams for the third and fourth embodiments are shown in FIG. 5 and FIG. 7, respectively. From the various aberration diagrams, it can be seen that all the embodiments according to the present invention have a wide field of view due to the low magnification, and a flat image over the entire field of view, even though they have a large working distance. However, it can be seen that even chromatic aberrations are corrected extremely well. In addition,
As understood from the lens data of each example,
The shoulder heights l of the first to fourth embodiments are 45.44 (=D ₁₂ /0.45) and 45.59 (=
D ₁₂ /0.49), 45.13 (= _{D 12} /0.38), 45.11 (=D ₁₂ /
0.45). (Effects of the Invention) As described above, according to the present invention, an apochromat or semi-apochromat class medium-to-low magnification lens that has an extremely larger working distance and higher resolution than the conventional one, and has a flat image surface over a wide field of view. objective lens is achieved.

[Brief explanation of the drawing]

FIG. 1 is a lens configuration diagram of the first embodiment according to the present invention, FIGS. 2 and 3 are various aberration diagrams of the first and second embodiments according to the present invention, and FIG. 4 is a lens configuration diagram of the third embodiment. , FIG. 5 is a diagram of various aberrations of the third embodiment, FIG. 6 is a diagram of the lens configuration of the fourth embodiment, and FIG. 7 is a diagram of various aberrations of the fourth embodiment. Explanation of symbols of main parts, G ₁ ...first lens group,
G ₂ ...Second lens group, _G3 ...Third lens group, _G4 ...Fourth lens group, O...Object plane, S...Body mounting surface of objective lens, l...Shoulder height.

Claims (1)

[Claims] 1. In order from the object side, a first lens group G ₁ with a positive refractive power composed of at least one lens, a cementation consisting of a positive lens and a negative lens, with a convex surface facing the object side. 2nd lens group of meniscus lens component
G ₂ , a third lens group G ₃ consisting of a cemented meniscus lens component consisting of a negative lens and a positive lens with a concave surface facing the object side, a single positive lens, and two lenses consisting of a negative lens and a positive lens; The fourth lens group G ₄ has a positive refractive power and has a bonded positive lens component made of cemented lenses, and the distance from the object plane O to the barrel mounting surface S of the objective lens is l, and the second lens group G ₂
The distance from the apex of the object side lens surface of G3 to the apex of the image side lens surface of the third lens group _G3 is _D12 , and
Let the Atbe numbers of the positive lens and the negative lens forming the cemented lens in the lens group G ₂ be ν _2P and ν _2N respectively, and the Atsube numbers of the positive lens and the negative lens forming the cemented lens in the third lens group G ₃ be ν _3P , respectively
When ν _3N is the refractive index, N _3P and N _3N are respectively, and the Abbe number of the single positive lens in the fourth lens group G ₄ is ν _4P , 0.3l<D ₁₂ <0.6l (1) N _3N ＞N _3P (2) ν _2P ＞ν _2N (3) ν _3N ＜50＜ν _3P (4) ν _4P ＜35.8 (5) A microscope objective lens characterized by satisfying the following conditions.