JP2009294518A - Objective lens for microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an extremely low magnification objective lens for a microscope which is favorably corrected in various aberrations and provides excellent observation up to the vicinity of a viewing field over a wide viewing field even in epi-illumination. <P>SOLUTION: The objective lens for the microscope is configured to include a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power in order from the side of an object O. The second lens group G2 includes at least two sets of cemented lenses L2 and L3 and the third lens group G3 includes at least two sets of cemented lenses L4 and L5. The respective two sets of cemented lenses are arranged so that their concave surfaces face each other and telecentric on the side of the object O. The objective lens satisfies the conditions of the following expressions: 0.02<¾f2/F¾<0.2 and 0.02<¾f3/F¾<0.2, wherein f2 is the focal length of the second lens group G2, f3 is the focal length of the third lens group G3, and F is the focal length of the entire system of the objective lens. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an objective lens, and more particularly to an extremely low magnification microscope objective lens.

Conventionally, macro observation for observing a specimen that can be seen with the naked eye over a wide field of view is widely used for biological and industrial purposes. When performing such macro observation, an objective lens having a low magnification (for example, 10 times or less) is generally used (see, for example, Patent Document 1), and an objective lens having an extremely low magnification (for example, 1 time). Has also been used. This macro observation has an advantage that it is easy to measure the size of a specimen and analyze an image because image data with a wide field of view can be captured at a time. Here, in the above observation, epi-illumination using reflected light from the specimen is generally used, but when correcting various aberrations of the objective lens so that a good image with small vignetting and color unevenness can be obtained, It is necessary to correct in consideration of aberration.
JP2007-11092

  By the way, since the total length of the objective lens is generally limited in size, it is necessary to shorten the total length of a very low magnification objective lens having a long focal length by adopting a configuration called a telephoto type. However, as the total length of the objective lens is shortened, there is a problem that correction of chromatic aberration of magnification and flatness of the image surface becomes difficult, and correction of pupil aberration is also difficult.

  The present invention has been made in view of such a problem, and various aberrations are corrected satisfactorily, and an NA which can be observed well around the field of view over a wide field of view even in epi-illumination is 0.03 and An object of the present invention is to provide a microscope objective lens having a very low magnification of about magnification -1.

  In order to achieve such an object, in the present invention, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a negative refractive power, arranged in order from the object side. A third lens group and a fourth lens group having a positive refractive power, and each of the second lens group and the third lens group has at least two sets of cemented lenses; The cemented lens is configured so that the concave surfaces face each other, is telecentric on the object side, the focal length of the second lens group is f2, the focal length of the third lens group is f3, and the entire objective lens system When the focal length of F is F, the following conditions (1) and (2) are satisfied.

0.02 <| f2 / F | <0.2 (1)
0.02 <| f3 / F | <0.2 (2)

The two sets of cemented lenses of the second lens group are configured by bonding a convex lens and a concave lens,
The Abbe numbers of the convex and concave lenses constituting the object-side cemented lens in the second lens group are νdp21 and νdn21, respectively, and the convex and concave lens materials constituting the image-side cemented lens in the second lens group When the Abbe numbers are νdp22 and νdn22, respectively, it is preferable that the conditions of the following expressions (3) and (4) are satisfied.

1.5 <νdp21 / νdn21 <5.1 (3)
1.1 <νdn22 / νdp22 <3.2 (4)

  Further, the two pairs of cemented lenses of the third lens group are formed into a meniscus shape by bonding a convex lens and a concave lens, and a glass material of a convex lens and a concave lens constituting the cemented meniscus lens on the object side in the third lens group. When the Abbe numbers are νdp31 and νdn31, respectively, and the Abbe numbers of the convex and concave lens materials constituting the cemented meniscus lens on the image side in the third lens group are νdp32 and νdn32, respectively, the following equations (5) and (6) It is preferable to satisfy the following conditions.

1.1 <νdn31 / νdp31 <3.2 (5)
1.5 <νdp32 / νdn32 <5.1 (6)

  The cemented lens on the object side in the second lens group is formed in a meniscus shape by bonding a convex lens and a concave lens, and the convex lens and the concave lens glass material constituting the cemented meniscus lens on the object side in the second lens group. When the refractive indexes are ndp2 and ndn2, respectively, it is preferable that the condition of the following formula (7) is satisfied.

  1.1 <ndn2 / ndp2 <1.5 (7)

  The cemented meniscus lens on the image side in the third lens group is configured by bonding a convex lens and a concave lens, and the refractive index of the glass material of the convex lens and the concave lens constituting the cemented meniscus lens on the image side in the third lens group. Is preferably ndp3 and ndn3, respectively, it is preferable to satisfy the condition of the following formula (8).

  1.1 <ndn3 / ndp3 <1.5 (8)

  Furthermore, when the distance from the object plane to the apex of the lens surface disposed closest to the image side is L, it is preferable that the condition of the following equation (9) is satisfied.

  0.25 <L / F <0.7 (9)

  As described above, according to the present invention, various aberrations (such as lateral chromatic aberration, image plane flatness, pupil aberration, etc.) are corrected well, and even in the epi-illumination, the wide field of view is good up to the periphery of the field of view. It is possible to realize an ultra-low magnification microscope objective lens that can be observed easily.

  Hereinafter, preferred embodiments of the present application will be described with reference to the drawings. First, the configuration of the microscope objective lens according to the present application will be described with reference to FIG. This microscope objective lens is a so-called infinite objective lens, and is arranged in order from the object O side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a negative lens group. A third lens group G3 having a refractive power and a fourth lens group G4 having a positive refractive power are provided. The first lens group G1 is provided with a convex meniscus lens (lens L1 in FIG. 1) having a convex surface directed toward the object O. The second lens group G2 is composed of a combination of a convex lens (lens L21 in FIG. 1) and a concave lens (lens L22 in FIG. 1) arranged in order from the object O side, and has a concave surface facing the image side as a whole. The cemented meniscus lens (lens L2 in FIG. 1), a concave lens (lens L31 in FIG. 1), and a convex lens (lens L32 in FIG. 1) are bonded together, and the cemented lens with the concave surface facing the object O as a whole (FIG. 1 and the lens L3).

  Further, the third lens group G3 is formed by bonding a convex lens (lens L41 in FIG. 1) and a concave lens (lens L42 in FIG. 1) arranged in order from the object O side, and has a concave surface directed toward the image side as a whole. A cemented meniscus lens (lens L4 in FIG. 1), a concave lens (lens L51 in FIG. 1), and a convex lens (lens L52 in FIG. 1) are bonded together, and a cemented meniscus lens having a concave surface facing the object O as a whole ( The lens L5) in FIG. The fourth lens group G4 is provided with a convex lens (lens L6 in FIG. 1).

  By the way, in a microscope for observing a metal specimen such as a circuit board, epi-illumination using reflected light from the specimen is generally used. In order to obtain an image with uniform brightness up to the periphery of the field of view, an objective lens It is necessary to illuminate substantially telecentrically on the object side. In addition, for example, when performing DIC observation (differential interference observation), it is necessary that the chromatic aberration and spherical aberration of the image side pupil of the objective lens are corrected to be sufficiently small in order to obtain an image without color unevenness. In this way, when performing macro observation at low magnification, the actual field of view is inevitably increased, but as the object height increases, the height of the luminous flux from the object point on the optical axis passing through the lens and the surrounding luminous flux. Since the difference between the two becomes large, it becomes difficult to correct the aberration of the pupil. Therefore, in order to obtain a good image, it is required to improve not only the imaging performance of the object and the image but also the imaging performance of the pupil. The microscope objective lens according to the present application configured as described above has a configuration that solves such a problem in order to obtain a good image, and details thereof will be described below.

  In the microscope objective lens having the above-described configuration, when the focal length of the second lens group G2 is f2, the focal length of the third lens group G3 is f3, and the focal length of the entire objective lens system is F, the following expression (1 ) And (2).

0.02 <| f2 / F | <0.2 (1)
0.02 <| f3 / F | <0.2 (2)

  Conditional expressions (1) and (2) are conditions for satisfactorily correcting field curvature and pupil aberration. If the upper limit value of the conditional expressions (1) and (2) is exceeded, the refractive power of the second lens group G2 or the third lens group G3 becomes too weak, so that the telecentricity with respect to the object O side cannot be maintained. It becomes difficult to uniformly illuminate the entire field of view. If the lower limit value of the conditional expressions (1) and (2) is exceeded, the negative refractive power becomes too strong, the Petzval sum becomes too negative, and the field curvature increases. In order to exhibit better imaging performance, it is preferable to set the upper limit value to 0.11 and the lower limit value to 0.03 in the conditional expressions (1) and (2).

  Further, the Abbe numbers of the glass goods of the convex lens (lens L21 in FIG. 1) and the concave lens (lens L22 in FIG. 1) constituting the cemented meniscus lens (lens L2 in FIG. 1) on the object O side in the second lens group G2, respectively. Let νdp21 and νdn21 be the Abbe numbers of the glass materials of the convex lens (lens L32 in FIG. 1) and the concave lens (lens L31 in FIG. 1) constituting the image-side cemented lens (lens L3 in FIG. 1) in the second lens group G2, respectively. When νdp22 and νdn22 are satisfied, it is preferable that the following expressions (3) and (4) are satisfied.

1.5 <νdp21 / νdn21 <5.1 (3)
1.1 <νdn22 / νdp22 <3.2 (4)

  The conditional expressions (3) and (4) give preferable conditions for correcting chromatic aberration, and the conditional expression (3) includes a convex lens constituting a cemented meniscus lens on the object O side in the second lens group G2. Defines the range of the Abbe number ratio with the concave lens. The conditional expression (4) defines the range of the Abbe number ratio between the convex lens and the concave lens constituting the cemented lens on the image side in the second lens group G2, and the conditional expressions (3) and (3) By satisfying 4) at the same time, it is possible to achieve both chromatic aberration correction of the entire objective lens system and chromatic aberration correction of the image side pupil. If the upper limit values of the conditional expressions (3) and (4) are exceeded, the achromaticity of the second lens group G2 becomes excessive, and it becomes difficult to correct the chromatic aberration of magnification. If the lower limit value of the conditional expressions (3) and (4) is exceeded, the achromaticity of the second lens group G2 becomes insufficient, and the axial chromatic aberration of the image side pupil of the objective lens increases. In order to more effectively correct the chromatic aberration of the entire objective lens system and the chromatic aberration of the image side pupil, the upper limit value of the conditional expression (3) is set to 2.9, and the lower limit value is set to 1.9. It is preferable to set the upper limit of conditional expression (4) to 2.9 and the lower limit to 1.9.

  Further, the Abbe numbers of the glass materials of the convex lens (lens L41 in FIG. 1) and the concave lens (lens L42 in FIG. 1) constituting the cemented meniscus lens (lens L4 in FIG. 1) on the object O side in the third lens group G3 are respectively νdp31. Νdn31 and the Abbe numbers of the glass materials of the convex lens (lens L52 in FIG. 1) and the concave lens (lens L51 in FIG. 1) constituting the cemented meniscus lens (lens L5 in FIG. 1) in the third lens group G3, respectively. When νdp32 and νdn32, it is preferable to satisfy the following expressions (5) and (6).

1.1 <νdn31 / νdp31 <3.2 (5)
1.5 <νdp32 / νdn32 <5.1 (6)

  Conditional expressions (5) and (6) give preferable conditions for correcting chromatic aberration. The conditional expression (5) defines the range of the Abbe number ratio between the convex lens and the concave lens constituting the cemented meniscus lens on the object O side in the third lens group G3. The conditional expression (6) defines the range of the Abbe number ratio between the convex lens and the concave lens constituting the cemented meniscus lens on the image side in the third lens group G3. By satisfying the conditional expressions (5) and (6) at the same time, it is possible to satisfactorily correct the longitudinal chromatic aberration and the lateral chromatic aberration of the entire objective lens system. When the upper limit value of the conditional expression (5) is exceeded, the achromaticity of the third lens group G3 becomes excessive. On the other hand, when the lower limit value of the conditional expression (5) is exceeded, the achromaticity of the third lens group G3 is insufficient. Thus, the chromatic aberration of magnification of the entire objective lens system is increased. In order to more effectively correct the lateral chromatic aberration of the entire objective lens system, it is preferable to set the upper limit value of the conditional expression (5) to 2.9 and the lower limit value to 1.9.

  If the upper limit value of conditional expression (6) is exceeded, the achromaticity of the third lens group G3 becomes excessive. On the other hand, if the lower limit value is exceeded, the achromaticity of the third lens group G3 becomes insufficient and the entire objective lens system. This increases the longitudinal chromatic aberration. In order to more effectively correct the longitudinal chromatic aberration of the entire objective lens system, it is preferable to set the upper limit value of conditional expression (6) to 2.9 and the lower limit value to 1.9.

  In addition, when the refractive indexes of the glass materials of the convex lens and the concave lens constituting the cemented meniscus lens on the object O side in the second lens group G2 are ndp2 and ndn2, respectively, it is preferable that the following expression (7) is satisfied.

  1.1 <ndn2 / ndp2 <1.5 (7)

  The conditional expression (7) defines the range of the refractive index ratio between the convex lens and the concave lens constituting the cemented meniscus lens on the object O side in the second lens group G2. If the upper limit value of the conditional expression (7) is exceeded, the refractive index difference between the convex lens and the concave lens constituting the cemented meniscus lens on the object O side in the second lens group G2 becomes too large, and the astigmatism of the entire objective lens system is increased. Correction of aberration and spherical aberration of the image side pupil becomes difficult. In order to more effectively correct the spherical aberration of the image side pupil, it is preferable to set the upper limit value of the conditional expression (7) to 1.4 and the lower limit value to 1.25.

  Furthermore, when the refractive indexes of the glass materials of the convex lens and the concave lens constituting the cemented meniscus lens on the image side in the third lens group G3 are ndp3 and ndn3, respectively, it is preferable that the following expression (8) is satisfied.

  1.1 <ndn3 / ndp3 <1.5 (8)

  The conditional expression (8) defines the range of the refractive index ratio between the convex lens and the concave lens constituting the cemented meniscus lens on the image side in the third lens group G3. If the upper limit of conditional expression (8) is exceeded, the refractive index difference between the convex lens and concave lens of the cemented meniscus lens on the image side in the third lens group G3 becomes too large, and spherical aberration and coma aberration of the entire objective lens system. It becomes difficult to correct. In order to more effectively correct spherical aberration and coma aberration of the entire objective lens system, it is preferable to set the upper limit value of conditional expression (8) to 1.4 and the lower limit value to 1.25. .

  Furthermore, when the distance from the object surface to the apex of the lens surface disposed closest to the image side is L, it is preferable that the following expression (9) is satisfied.

  0.25 <L / F <0.7 (9)

  Conditional expression (9) defines the range of the ratio between the focal length F of the entire objective lens system and the distance L (lens length) from the object plane to the apex of the lens surface arranged closest to the image side. . If the upper limit value of the conditional expression (9) is exceeded, the total lens length becomes too long and the objective lens becomes large. On the other hand, if the lower limit value of the conditional expression (9) is exceeded, it becomes difficult to correct aberrations. The practical working distance WD and the number of visual fields required for observation cannot be secured.

  Embodiments of a microscope objective lens according to the present application will be described below with reference to the accompanying drawings.

  Tables 1 and 2 shown below are specifications of the lenses of the first and second examples of the microscope objective lens according to the present application. In any table, β is the corresponding magnification, NA is the object-side numerical aperture, D0 is the distance from the object O to the apex of the first lens surface (surface number 1 in the table) of the first lens group G1, and F is the objective. The combined focal length of the entire lens system is shown. The first column No. is the order of the lens surfaces from the object O side along the direction of travel of light (hereinafter referred to as surface number), the second column R is the radius of curvature of each lens surface, and the third column d. Is the distance on the optical axis from each optical surface to the next optical surface (or image surface) (hereinafter referred to as the surface interval), the fourth column nd is the refractive index for the d-line (wavelength 587.562 nm), the fifth column νd. Indicates the Abbe number on the d line.

  In the table, “mm” is generally used as the unit of focal length F, radius of curvature R, surface separation d, and other lengths. However, since the optical system can obtain the same optical performance even when proportionally enlarged or reduced, the unit is not limited to “mm”, and other appropriate units can be used. In the table, “INFINITY” of the radius of curvature R indicates a plane, and the description of the refractive index “1.00000” of air is omitted. In the table, values corresponding to the conditional expressions (1) to (9), that is, the condition corresponding values are also shown.

(First embodiment)
FIG. 1 used in the above description shows a first embodiment of the microscope objective lens according to the present application. The microscope objective lens according to the first embodiment is shown in FIGS. 1, 2, and 5A. This will be described with reference to Table 1. As described above, the microscope objective lens has a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a negative refractive power arranged in order from the object O side. A third lens group G3 having a positive refractive power, and a fourth lens group G4 having a positive refractive power.

  The first lens group G1 includes a convex meniscus lens L1 having a convex surface directed toward the object O. The second lens group G2 includes a cemented meniscus lens L2 having a concave surface facing the image side as a whole, a concave lens L31, and a convex lens L32. And a cemented lens L3 having a concave surface facing the object O as a whole. Further, the third lens group G3 includes a cemented meniscus lens L4 having a concave surface facing the image side as a whole, a concave lens L51, and a convex lens L52. And a cemented meniscus lens L5 having a concave surface facing the object O as a whole. The fourth lens group G4 has a configuration in which a convex lens L6 is provided.

  Table 1 shows a table of specifications in the first embodiment. The surface numbers 1 to 16 in Table 1 correspond to the surfaces 1 to 16 shown in FIG.

(Table 1)
[Overall specifications]
β = −1, NA = 0.03, D0 = 6.319, F = 198.054
[Lens specifications]
NO. R d nd νd
1 22.69900 5.200000 1.81600 46.6
2 174.64400 0.500000
3 13.31000 6.500000 1.43425 95.0
4 INFINITY 2.500000 1.84666 23.8
5 12.87300 15.207107
6 -9.35550 1.000000 1.90265 35.7
7 4.57300 2.800000 1.80809 22.8
8 111.81000 0.500000
9 18.19300 2.800000 1.80809 22.8
10 -4.71940 1.000000 1.90265 35.7
11 14.53020 8.669947
12 -28.65800 1.000000 1.90265 35.7
13 19.49200 3.500000 1.43425 95.0
14 -13.00200 1.526871
15 120.02800 4.300000 1.49782 82.5
16 -11.80120
[Conditional value]
Conditional expression (1) | f2 / F | = 0.031
Conditional expression (2) | f3 / F | = 0.103
Conditional expression (3) νdp21 / νdn21 = 3.99
Conditional expression (4) νdn22 / νdp22 = 1.57
Conditional expression (5) νdn31 / νdp31 = 1.57
Conditional expression (6) νdp32 / νdn32 = 2.66
Conditional expression (7) ndn2 / ndp2 = 1.29
Conditional expression (8) ndn3 / ndp3 = 1.33
Conditional expression (9) L / F = 0.32.

  As is clear from the table of specifications shown in Table 1 above, it can be seen that the first example satisfies all the conditional expressions (1) to (9).

  FIG. 2 shows the C-line (wavelength 656.279 nm) and d-line (wavelength 587.562 nm) calculated as ideal lenses having a focal length fk of 200 mm following the objective lens for the microscope of the first embodiment. The aberration diagrams (spherical aberration, astigmatism and coma aberration) for the F-line (wavelength 486.133 nm) and the g-line (wavelength 435.835 nm) are shown. Here, in the astigmatism diagram shown in FIG. 2, the solid line shows the sagittal image plane, and the broken line shows the meridional image plane. FIG. 5A shows a spherical aberration diagram of the pupil for each of the above lines. In each aberration diagram, NA represents the numerical aperture, and Y represents the image height. The explanation of this aberration diagram is the same in the second embodiment to be described later.

  As is apparent from each aberration diagram, in the microscope objective lens according to the first example, NA = 0.03 and a field number of 25 are satisfactorily corrected at each wavelength of C-line, d-line, F-line, and g-line. You can see that.

(Second embodiment)
2nd Example of this application is described using FIG. 3, FIG. 4, FIG.5 (b) and Table 2. FIG. The objective lens for a microscope according to Example 2 shown in FIG. 3 is similar to that shown in FIG. 1 except that the cemented lens on the image side of the second lens group G2 (the cemented lens L3 shown in FIG. 3) has a meniscus shape. The configuration is almost the same as that of the first embodiment shown in FIG. Therefore, in the following description, the same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted (see FIG. 3). Table 2 shows a table of specifications in the second embodiment. Surface numbers 1 to 16 in Table 2 correspond to surfaces 1 to 16 shown in FIG.

(Table 2)
[Overall specifications]
β = −1, NA = 0.03, D0 = 7.65, F = 198.037
[Lens specifications]
NO. R d nd νd
1 20.58079 5.200000 1.75500 52.3
2 87.93078 0.550000
3 14.99529 6.500000 1.43425 95.0
4 INFINITY 2.000000 1.84666 23.8
5 20.00000 13.300000
6 -10.04292 1.000000 1.90265 35.7
7 4.53365 3.000000 1.80809 22.8
8 -32.60227 2.000000
9 56.61271 3.000000 1.80809 22.8
10 -4.48893 1.000000 1.90265 35.7
11 11.17116 7.000000
12 -23.99958 1.000000 1.90265 35.7
13 13.99140 4.000000 1.43425 95.0
14 -10.85567 2.500000
15 -205.25741 4.300000 1.49782 82.5
16 -10.50822
[Conditional value]
Conditional expression (1) | f2 / F | = 0.062
Conditional expression (2) | f3 / F | = 0.045
Conditional expression (3) νdp21 / νdn21 = 3.99
Conditional expression (4) νdn22 / νdp22 = 1.57
Conditional expression (5) νdn31 / νdp31 = 1.57
Conditional expression (6) νdp32 / νdn32 = 2.66
Conditional expression (7) ndn2 / ndp2 = 1.29
Conditional expression (8) ndn3 / ndp3 = 1.33
Conditional expression (9) L / F = 0.32.

  As is apparent from the table of specifications shown in Table 2 above, it can be seen that all the conditional expressions (1) to (9) are satisfied in the second embodiment.

  FIG. 4 shows the C-line (wavelength 656.279 nm) and d-line (wavelength 587.562 nm) calculated as ideal lenses having a focal length fk of 200 mm following the imaging lens of the microscope objective lens of the second embodiment. The aberration diagrams (spherical aberration, astigmatism and coma aberration) for the F-line (wavelength 486.133 nm) and the g-line (wavelength 435.835 nm) are shown. FIG. 5B shows a spherical aberration diagram of the pupil for each line. As is apparent from each aberration diagram, in the microscope objective lens according to the second example, NA = 0.03 and a field number of 25 are satisfactorily corrected at each wavelength of C-line, d-line, F-line, and g-line. Has been.

  As described above, according to the objective lens for a microscope according to the present invention, various aberrations are satisfactorily corrected up to a field number of 25 at a magnification of 1 and a numerical aperture of 0.03. Can exhibit excellent imaging performance with little shading and color unevenness.

  In the first and second embodiments described above, by arranging a quarter-wave plate or a depolarizer (depolarizer) between the object O and the first surface of the objective lens, A configuration that prevents flare reflected at the surface is desirable. Further, at this time, in order to remove the reflected light from the surface on the object O side of the quarter wavelength plate or the depolarizer out of the field of view, it is more desirable to use these optical elements with the NA equivalent of the objective lens inclined.

  The present invention as described above is not limited to the above-described embodiment, and can be appropriately improved as long as it does not depart from the gist of the present invention.

It is a lens block diagram of the objective lens for microscopes concerning the 1st example of the present invention. FIG. 4 is a diagram illustrating various aberrations of the microscope objective lens according to the first example of the present invention. It is a lens block diagram of the objective lens for microscopes concerning 2nd Example of this invention. It is an aberration diagram of the objective lens for a microscope according to the second example of the present invention. (A) is a spherical aberration diagram of the pupil according to the first example, and (b) is a spherical aberration diagram of the pupil according to the second example.

Explanation of symbols

G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group L2 Joint lens on the object side constituting the second lens group L3 Joint lens on the image side constituting the second lens group L4 Third lens Cemented lens on the object side constituting the lens group L5 cemented lens on the image side constituting the third lens group

Claims (6)

A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power, arranged in order from the object side. A lens group,
The second lens group and the third lens group each have at least two sets of cemented lenses, and the two groups of cemented lenses are configured such that their concave surfaces face each other, and are telecentric on the object side,
When the focal length of the second lens group is f2, the focal length of the third lens group is f3, and the focal length of the entire objective lens system is F, the following expression 0.02 <| f2 / F | <0 .2
0.02 <| f3 / F | <0.2
The objective lens for microscopes characterized by satisfying the following conditions. The two sets of cemented lenses of the second lens group are configured by bonding a convex lens and a concave lens,
The Abbe numbers of the convex and concave lenses constituting the object-side cemented lens in the second lens group are νdp21 and νdn21, respectively, and the convex and concave lens materials constituting the image-side cemented lens in the second lens group When the Abbe numbers are νdp22 and νdn22, respectively, the following formula 1.5 <νdp21 / νdn21 <5.1
1.1 <νdn22 / νdp22 <3.2
The microscope objective lens according to claim 1, wherein the following condition is satisfied. The two cemented lenses in the third lens group are configured in a meniscus shape by bonding a convex lens and a concave lens,
The Abbe numbers of the convex and concave lens materials constituting the object side cemented meniscus lens in the third lens group are νdp31 and νdn31, respectively, and the convex lens and concave lens glass materials constituting the image side cemented meniscus lens in the third lens group, respectively. When the Abbe numbers of νdp32 and νdn32 are respectively given by: 1.1 <νdn31 / νdp31 <3.2
1.5 <νdp32 / νdn32 <5.1
The microscope objective lens according to claim 1, wherein the following condition is satisfied. The cemented lens on the object side in the second lens group is configured in a meniscus shape by bonding a convex lens and a concave lens,
When the refractive indexes of the glass materials of the convex lens and the concave lens constituting the cemented meniscus lens on the object side in the second lens group are ndp2 and ndn2, respectively, the following expression 1.1 <ndn2 / ndp2 <1.5
The microscope objective lens according to claim 1, wherein the following condition is satisfied. The cemented meniscus lens on the image side in the third lens group is configured by bonding a convex lens and a concave lens,
When the refractive indexes of the glass materials of the convex lens and the concave lens constituting the cemented meniscus lens on the image side in the third lens group are ndp3 and ndn3, respectively, the following expression 1.1 <ndn3 / ndp3 <1.5
The microscope objective lens according to claim 1, wherein the following condition is satisfied. When the distance from the object plane to the apex of the lens surface arranged closest to the image side is L, the following expression 0.25 <L / F <0.7
The microscope objective lens according to claim 1, wherein the following condition is satisfied.

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