JP3093835B2 - Microscope objective lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an image pickup apparatus having a magnification of about 20 times.
The present invention relates to an apochromat-class microscope objective lens having a large numerical aperture and a flat image surface.

[0002]

2. Description of the Related Art As the prior art closest to the present invention, there is an objective lens disclosed in JP-A-61-275811. this is,
The magnification is 20 times, the numerical aperture (NA) is 0.75, and the first lens has a meniscus lens having a strong concave surface facing the object side and a positive meniscus lens component having a concave surface facing the object side. A second lens group having a group, a single positive lens component and a cemented two positive lens component consisting of a cemented negative lens and a positive lens, and a cemented weakly refractive power cemented lens of a positive lens and a negative lens It comprises a third lens group having a compound lens component.

[0003] A prior art which is completely different from the specification of the present invention but slightly similar in the lens configuration is that of German Patent Specification DD288244. This means that the magnification is 100 times, the NA is 0.9, and the lens is composed of a first lens unit and a second lens unit having a positive refractive power with a concave surface facing the object side from the object side, and a biconvex first lens. A third group, a negative meniscus fourth group having a concave surface facing the object side, a fifth and sixth groups composed of a cemented negative lens and a positive lens, and a seventh and eighth groups of meniscus having a convex surface facing the object side. Ninth group of meniscus having a concave surface facing the object side.

[0004]

The prior art disclosed in Japanese Patent Application Laid-Open No. 61-275811 is characterized by a large NA of 0.75 and a flat image surface. Insufficient off-axis performance. In particular, astigmatism remains, and it is difficult to say that the coma aberration is good. Therefore, it cannot be said that the advantage of high NA is fully utilized. 2
At low magnifications of 0 or less, the entire field of view is often observed, and further image plane flatness is required.

The present invention has been made in view of such circumstances, and has as its object to provide a magnification of about 20 times, a large NA, excellent contrast and resolution, and an extremely flat image surface over a wide field of view. It is an object of the present invention to provide an apochromat-grade microscope objective lens.

[0006]

A microscope objective according to the present invention, which achieves the above object, includes, in order from the object, a meniscus lens component having a concave surface facing the object side, and the most image side surface has a convex surface facing the image side. A first lens group having a positive refractive power, a second lens group having a negative refractive power, having a meniscus shape having a concave surface facing the object side and emitting a light beam emitted from an object passing through the first lens group as a divergent light beam; A third lens group having a positive refractive power that converts the light into a convergent light beam, a fourth lens group having a negative refractive power in a meniscus shape having a convex surface facing the object side, and a fourth lens group having a weak refractive power having a concave surface facing the object side. It consists of five lens groups. When f ₃ , f ₄ , f ₅ , and f are respectively the third lens group, the fourth lens group, the fifth lens group, and the focal length of the entire system, (1) 0.2 <f / f ₃ < 0.5 (2) −0.5 <f / f ₄ <−0.1 (3) | f / f ₅ | <0.1

[0007]

The reason and operation of the above configuration will be described below. In general, in order to favorably correct off-axis aberrations such as curvature of field, astigmatism, and coma, a meniscus-shaped lens having a convex surface facing the object side is disposed on the most image side of the objective lens. There is known a method and a method of adding a meniscus lens having a concave surface facing the object side on the image side. The method is superior in off-axis performance.

[0008] Japanese Patent Application Laid-Open No. 61-275811
No. adopts the following method. This is because the magnification is about 20 times, and if the NA is 0.7 to 0.8, the emission side N
A (referred to as NA ') is related to a very large value of 0.035 to 0.04. If NA 'is large, the effective diameter of the final surface of the objective lens becomes large, so it is difficult to arrange the power in relation to the focal length of the entire system.
It is probable that this method could not be adopted.

By the way, when a higher magnification objective lens, for example, 100 × magnification and NA is 0.9, NA ′ is 0.0
09, which is 1/3 or less of the case of 20 times.
Therefore, the effective diameter of the final surface of the objective lens is also small,
There is no difficulty in adopting this method.

In the present invention, the following method is employed in order to correct off-axis aberrations extremely well. The fourth lens group and the fifth lens group correspond thereto. In order to make the aberration correction by the fourth and fifth lens groups effective, a meniscus lens having a negative refractive power and a concave surface facing the object side is arranged in the second lens group. As a result, the light beam emitted from the object passing through the first lens group is emitted as a divergent light beam. In the third lens group, a positive refractive power for converting the divergent light beam into a convergent light beam is arranged. The ray height is the largest in the third lens group and decreases toward the most image side surface of the fourth lens group. 4th
The Petzval sum is reduced by the negative refractive power on the most image side surface of the lens unit, and the off-axis aberration is corrected. Thereafter, a meniscus lens having a low refractive power is arranged in the fifth lens group, and the off-axis aberration is further corrected while increasing the ray height again.

The above conditions (1), (2) and (3) are for effectively performing the functions of the above-described lens groups. When the value exceeds the upper limit of the condition (1), the refractive power of the third lens unit becomes too large. When the value exceeds the lower limit, the refractive power becomes too small. Depending on the magnitude of this refracting power, the ray height on the most image side surface of the fourth lens group is different, and the symmetry of coma aberration is of course deteriorated.
Spherical aberration also worsens.

The condition (2) indicates the range of the refractive power of the fourth lens group. If the upper limit is exceeded, the refractive power becomes too small, and if the lower limit is exceeded, the refractive power becomes too large. In any case, if the ratio exceeds this range, the fifth lens group will have abnormal refractive power, and the symmetry of coma aberration will be deteriorated.

The condition (3) indicates the range of the refractive power of the fifth lens group. If the upper limit of the condition (3) is exceeded, the refractive power becomes too large. The symmetry of the aberration is deteriorated.

[0014]

Next, Embodiments 1 and 2 of the microscope objective lens of the present invention will be described. FIGS. 1 and 2 are cross-sectional views showing lens structures of Examples 1 and 2, respectively.

In the first embodiment, the first group G1 comprises three groups: a negative meniscus lens having a concave surface facing the object side, a biconvex lens, and a cemented lens of a negative meniscus lens having a convex surface facing the object side and a biconvex lens. The second group G2 is composed of one cemented lens of a biconcave lens and a biconvex lens, the third group G3 is composed of one biconvex lens, and the fourth group G4 is composed of one cemented lens of a biconvex lens and a biconcave lens. The fifth unit G5 includes one cemented lens composed of a concave flat lens and a plano-convex lens.

The second embodiment has a parallel plane plate P provided on the object side of the lens system for providing an oil immersion system.
The Petzval sum is kept small by an air convex lens between the lens and the front surface of the first group G1. ), The first group G1 comprises three groups: a negative meniscus lens having a concave surface facing the object side, a positive meniscus lens having a concave surface facing the object side, and a cemented lens of a biconcave lens and a biconvex lens. The third group G3 comprises one cemented lens of a biconcave lens and a biconvex lens.
Consists of one biconvex lens, the fourth group G4 consists of one cemented lens of a biconvex lens and a biconcave lens, and the fifth group G5
Consists of one cemented lens of a concave flat lens and a plano-convex lens. In addition, this embodiment employs an oil immersion system although the magnification is as low as 20 times as described later.
The reason for this is that when converting the magnification from low to high,
Oil immersion system must be adopted for high magnification, but if drying system is adopted for low magnification, drying system and oil immersion system are mixed, oil supply,
This is because it is desirable to employ an oil immersion system even at a low magnification because handling such as wiping becomes troublesome.

The lens data of each embodiment is shown below.
The symbols are β for magnification, NA for numerical aperture, f for the combined focal length of the whole system, WD for working distance, f ₃ , f ₄ , f
₅ are focal lengths of the third group G3, the fourth group G4, the fifth group G5, r ₁ , r ₂ ... Are the radii of curvature of the respective lens surfaces shown in order from the object side, and d ₁ , d ₂ . , N _d1 , n _d2 ... are the refractive indices of the d-line of each lens shown in order from the object side, and ν _d1 , ν _d2 ... are the Abbe of each lens shown in order from the object side. Is a number.

Example 1 β = 20 ×, NA = 0.7, f = 9, WD = 1.002 f ₃ = 24.497, f ₄ = −34.97 _{, F 5 = 3241 r 1 =} -2.9906 d 1 = 4.7738 n d1 = 1.67
790 ν _d1 = 55.33 r ₂ = -5.3974 d ₂ = 0.2000 r ₃ = 320.9597 d ₃ = 2.9000 nd ₂ = 1.43
_{875 ν d2 = 94.97 r 4 =} -7.1847 d 4 = 0.2000 r 5 = 30.2999 d 5 = 1.2000 n d3 = 1.61
_{340 ν d3 = 43.84 r 6 =} 9.6627 d 6 = 4.6000 n d4 = 1.43
_{875 ν d4 = 94.97 r 7 =} -13.1375 d 7 = 1.7000 r 8 = -10.4265 d 8 = 1.4000 n d5 = 1.61
340 ν _d5 = 43.84 r ₉ = 13.9904 d ₉ = 5.3000 nd ₆ = 1.43
_{875 ν d6 = 94.97 r 10 =} -11.9300 d 10 = 0.1000 r 11 = 18.5521 d 11 = 4.0000 n d7 = 1.43
_{875 ν d7 = 94.97 r 12 =} -23.8697 d 12 = 0.1000 r 13 = 20.4655 d 13 = 4.5000 n d8 = 1.57
501 ν _d8 = 41.49 r ₁₄ = -14.3511 d ₁₄ = 2.6000 _nd9 = 1.52
_{130 ν d9 = 52.55 r 15 =} 7.5061 d 15 = 5.0000 r 16 = -7.9296 d 16 = 1.5000 n d10 = 1.52
130 ν _d10 = 52.55 r ₁₇ = ∞ d ₁₇ = 3.7159 n _d11 = 1.57
135 ν _d11 = 52.92 r ₁₈ = -10.5558 f / f ₃ = 0.367 f / f ₄ = -0.257 f / f ₅ = 0.003
.

Embodiment 2 β = 20 ×, NA = 0.8, f = 9, WD = 0.19 f ₃ = 26.795, f ₄ = -45.43 , F ₅ = 536.32 Oil immersion liquid: n _d = 1.51548, ν _d = 43.10 r ₁ = ∞ d ₁ = 0.3000 n _d1 = 1.51
633 ν _d1 = 64.15 r ₂ = ∞ d ₂ = 0.2800 r ₃ = -2.9483 d ₃ = 4.4064 n _d2 = 1.67
_{790 ν d2 = 55.33 r 4 =} -4.7306 d 4 = 0.2000 r 5 = -103.1912 d 5 = 3.0000 n d3 = 1.49
700 ν _d3 = 81.61 r ₆ = -6.5185 d ₆ = 0.2000 r ₇ = -285.8879 d ₇ = 1.1500 nd ₄ = 1.61
340 ν _d4 = 43.84 r ₈ = 9.6803 d ₈ = 4.9500 n _d5 = 1.43
875 ν _d5 = 94.97 r ₉ = -9.9408 d ₉ = 1.6000 r ₁₀ = -9.7058 d ₁₀ = 1.2000 nd ₆ = 1.61
_{340 ν d6 = 43.84 r 11 =} 19.1518 d 11 = 5.6000 n d7 = 1.43
_{875 ν d7 = 94.97 r 12 =} -11.9628 d 12 = 0.1400 r 13 = 24.7125 d 13 = 4.4000 n d8 = 1.43
875 ν _d8 = 94.97 r ₁₄ = -21.2067 d ₁₄ = 0.1000 r ₁₅ = 22.7408 d ₁₅ = 4.5000 _nd9 = 1.57
_{501 ν d9 = 41.49 r 16 =} -19.0975 d 16 = 3.8550 n d10 = 1.52
_{130 ν d10 = 52.55 r 17 =} 8.9527 d 17 = 5.3000 r 18 = -8.7430 d 18 = 1.4000 n d11 = 1.52
130 ν _d11 = 52.55 r ₁₉ = ∞ d ₁₉ = 4.1000 n _d12 = 1.57
135 ν _d12 = 52.92 r ₂₀ = -11.2472 f / f ₃ = 0.336 f / f ₄ = -0.198 f / f ₅ = 0.017
.

The objective lens of each of the above embodiments has, for example, the following lens data and is used in combination with an imaging lens whose lens section is shown in FIG. Here, in the data, r ₁ ′, r ₂ ′... Are the radii of curvature of the respective lens surfaces shown in order from the object side, d ₁ ′, d ₂ ′. _d1 ', n _d2' ... d-line refractive index of each lens shown in order from the object _{side, ν d1 ', ν d2'} ... is the Abbe number of the lens shown in order from the object side.

R ₁ '= 68.7541 d ₁ ' = 7.7321
n _d1 '= 1.48749 ν _d1 ' = 70.20 r ₂ '= -37.5679 d ₂ ' = 3.4742 n _d2 '=
_{1.80610 ν d2 '= 40.95 r 3} ' = -102.8477 d 3 '= 0.6973 r 4' = 84.3099 d 4 '= 6.0238 n d3' =
1.83400 ν _d3 '= 37.16 r ₅ ' = -50.7100 d ₅ '= 3.0298 nd ₄ ' =
1.64450 v _d4 '= 40.82 r ₆ ' = 40.6619.

In this case, the distance between the objective lens of the first and second embodiments and the imaging lens of FIG. 3 may be any position between 50 mm and 170 mm. FIGS. 4 and 5 show aberration diagrams representing spherical aberration, astigmatism, distortion, and coma aberration of Nos. 1 and 2, respectively. In addition, when the above-mentioned interval is 50 mm to 170 mm, 10
At positions other than 5 mm, almost the same aberration is shown.

[0023]

As described above, according to the present invention,
In a microscope objective lens having a magnification of about 20 times and a large NA of 0.7 to 0.8, the resolution and contrast are excellent, and the image plane can be extremely flat over a wide field of view.

[Brief description of the drawings]

FIG. 1 is a sectional view of a microscope objective lens according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a lens according to a second embodiment.

FIG. 3 is a lens cross-sectional view of an imaging lens used with the microscope objective lens of each embodiment.

FIG. 4 is an aberration diagram showing a spherical aberration, an astigmatism, a distortion, and a coma of the first embodiment.

FIG. 5 is an aberration diagram showing a spherical aberration, an astigmatism, a distortion, and a coma of the second embodiment.

[Explanation of symbols]

 G1 first lens group G2 second lens group G3 third lens group G4 fourth lens group G5 fifth lens group P parallel plane plate

Claims (1)

(57) [Claims] 1. A first lens unit having a positive refractive power and a meniscus having a meniscus lens component having a concave surface facing the object side and a convex surface facing the image side, and a meniscus having a concave surface facing the object side. A second lens group having a negative refractive power that emits a light beam emitted from an object passing through the first lens group as a divergent light beam; a third lens group having a positive refractive power that converts the divergent light beam into a convergent light beam; With a meniscus shape with the convex surface facing the
A microscope objective lens comprising a fourth lens group having a negative refractive power and a fifth lens group having a meniscus-shaped weak refractive power having a concave surface facing the object side and satisfying the following conditions: (1) 0 _{.2 <f / f 3 <0.5} (2) -0.5 <f / f 4 <-0.1 (3) | f / f 5 | <0.1 , however, f _3, f _4, f ₅ and f are the focal lengths of the third lens unit, the fourth lens unit, the fifth lens unit, and the entire system, respectively.