JP5054178B2 - Microscope objective lens - Google Patents

Description

The present invention relates to a microscope objective lens, and more particularly to an apochromatic microscope objective lens having a magnification of about 4 to 10 times and various aberrations corrected favorably from the visible region to the near infrared region.

    In recent years, there are the following demands in the biological research market.

First, in the fluorescence observation method, using a fluorescent dye having a longer wavelength than before,
Fluorescence observation is performed in the near infrared region, and therefore, an optical system having good imaging performance in the near infrared region is desired.

Also, near-infrared DIC observation methods have come to be used, and good imaging performance in the near-infrared region is desired.

In multi-photon observation as typified by two photons, the sample is excited with long-wavelength light and observed with visible light. It is desirable that the deviation of the focal position at the lens is small.

Furthermore, simultaneous observation of the fluorescence observation method and the near-infrared DIC observation method may be performed, and it is desired that the deviation of the focal position on the specimen is small between the visible wavelength and the near-infrared wavelength. Yes.

For the reasons described above, an apochromatic microscope objective lens in which various aberrations are favorably corrected from the visible range to the near infrared range is desired.

2. Description of the Related Art Conventionally, an objective lens described in the following document has been known as an objective lens that favorably corrects various aberrations from the visible range to the near infrared range.
JP 62-49313 A Japanese Patent Publication No. 7-104488 (Japanese Patent Laid-Open No. 4-26813) JP-A-6-1775034 JP-A-11-174338 Among the above-mentioned documents, the objective lens described in Document 1 is an objective lens having a magnification of 50 times and an NA of 0.5, or an objective lens having a magnification of 60 times and an NA of 0.6. It is.

The objective lens described in Document 2 has a magnification of 5 times and NA of 0.14, a magnification of 10 times and NA of 0.26, a magnification of 20 times and a NA of 0.4, and a magnification of 50 times. NA is 0.42
The objective lens has a magnification of 100 and an NA of 0.5.

    Reference 3 describes an objective lens having a magnification of 50 times and an NA of 0.45.

Reference 4 also states that the magnification is 5 times and the NA is 0.13, the magnification is 10 times and the NA is 0.21.
An objective lens is described in which the magnification is 20 times, the NA is 0.35, the magnification is 50 times, the NA is 0.4, the magnification is 100 times, and the NA is 0.5.

    Further, Document 5 describes an objective lens having a magnification of 100 times and an NA of 0.7.

The objective lenses described in these conventional examples are used for observation and inspection of semiconductor ICs and liquid crystal panels. These objective lenses are YAG lasers (1064 nm)
Aberration correction is performed up to near-infrared for wiring defect repair. However, these objective lenses have a long working distance because the observation object is a semiconductor IC or a liquid crystal panel, and therefore have a small NA. Therefore, it is not suitable as an objective lens for observing cells, proteins, DNA, etc. that require high resolution and bright observation images.

The present invention has a high NA and from the visible region to the near infrared region, particularly t-line (λ = 1013.98 nm).
A microscope objective lens in which various aberrations are satisfactorily corrected to the vicinity.

The microscope objective lens of the present invention includes a first lens group and a second lens group in order from the object side. The first lens group includes a cemented lens in which a negative lens and a positive lens are bonded together in order from the object side. A positive lens, a positive lens, and a second cemented lens in which a positive lens and a negative lens having a concave surface facing the image side are bonded together, and the second lens group is concave on the object side in order from the object side. And a positive lens, which satisfies the following conditions (1), (2), (3), (4), (5) And
(1) ν _d (L1p) −ν _d (L1n)> 20
(2) ν _d (L2p)> 75
(3) −0.007 <{θCt (L2p) −θCt (L2n)} /
{Ν _d (L2p) −ν _d (L2n)} <0
(4) 15 <f <55
(5) | f (L2) / f | <4
Where ν _d (L1p) is the Abbe number of the second cemented lens in the first lens group with respect to the d-line of the positive lens, and ν _d (L1n) is the second cemented lens in the first lens group. Abbe number with respect to d line of negative lens with concave surface facing image side, ν _d (L2p) is Abbe number with respect to d line of positive lens of cemented lens in the second lens group, and ν _d (L2n) is the first number. Abbe number with respect to the d-line of the negative lens with the plane or concave surface facing the object side of the cemented lens in the two lens group, θCt (L2p) is a partial dispersion ratio of the cemented lens in the second lens group with respect to the t-line of the positive lens , ΘCt (L2n) is a partial dispersion ratio with respect to the t-line of the negative lens having a plane or concave surface facing the object side of the cemented lens in the second lens group, and f (L2) is a cemented lens in the second lens group. Focal length, f is the focal length of the entire objective lens system It is.

    The partial fraction θCt is given by the following equation.

θCt = (nC−nt) / (nF−nC)
Here, nC, nt, and nF are refractive indexes for the C-line, t-line, and F-line, respectively. G
The wavelengths of the line, F line, d line, C line, A ′ line, and t line are 435.835 nm and 486.13, respectively.
nm, 587.56 nm, 656.27 nm, 768.19 nm, 1013.98 nm.

As described above, the microscope objective lens according to the present invention includes the first lens group and the second lens group, and the first lens group includes a second lens in which a positive lens and a negative lens having a concave surface facing the image side are cemented. At least a cemented lens is included, and the second lens group is a lens system including at least a cemented lens in which a negative lens having a flat surface or a concave surface facing the object side and a positive lens are cemented.

In the objective lens according to the present invention, since the cemented lens of the first lens group is disposed on the front side (object side) of the lens system, the cemented lens is disposed at a location where the light beam height is large (a place where the light beam height greatly changes). Therefore, the second cemented lens included in the first lens group has a strong axial chromatic aberration correcting action. It also has a function of correcting various aberrations such as spherical aberration, astigmatism, and coma.

In addition, the cemented lens of the second lens group is disposed in the rear group of the objective lens, and thus is disposed in a place where light rays pass gently. Therefore, since the cemented lens included in the second lens group is disposed at a place where the light beam gently passes, the influence on various aberrations such as spherical aberration, astigmatism, and coma aberration is reduced. An upper chromatic aberration correction function can be provided.

    Therefore, in the present invention, the second cemented lens as described above is arranged in the first lens group so as to correct axial chromatic aberration mainly in the visible region, and the second lens group as described above. By arranging the cemented lens, the axial chromatic aberration in the near infrared region (for example, 750 nm to 1014 nm) is corrected together with the axial chromatic aberration in the visible region.

Furthermore, in order to satisfactorily correct chromatic aberration in the visible region in the second cemented lens having the above-described configuration arranged in the first lens group of the present invention, a concave surface is directed to the positive lens constituting the cemented lens and the image side. Further, the Abbe number ν _d of the negative lens is preferably a distant value, and it is desirable that the condition (1) is satisfied.

    In condition (1), it becomes difficult to correct chromatic aberration in the visible range below the lower limit of 20.

If the following condition (1-1) is satisfied instead of this condition (1), chromatic aberration can be corrected more satisfactorily.

(1-1) ν _d (L1p) −ν _d (L1n)> 25
Here, it is preferable that the Abbe number ν _d (L1p) of the positive lens of the second cemented lens in the first lens group satisfies the following condition (6).

(6) ν _d (L1p)> 75
By satisfying this condition (6), the chromatic aberrations of the d-line, C-line and F-line can be favorably corrected. Further, glass having an Abbe number exceeding 75 has a large anomalous dispersion in the g-line, so that the chromatic aberration of the g-line can be corrected well.

In the condition (6), if the lower limit of 75 is not reached, particularly correction of chromatic aberration of the g-line is not sufficiently performed.

Next, the cemented lens having the above-described configuration included in the second lens group enables correction of chromatic aberration in the visible region and the infrared region. In order to correct chromatic aberration in the visible range, condition (2) was set.

In this condition (2), if the lower limit of 75 is not reached, the chromatic aberration in the visible range becomes insufficiently corrected.

Examples of materials that satisfy the condition (2) and the condition (6) include fluorophosphate glass, phosphate glass, and fluorite.

Condition (3) is a condition provided for correcting chromatic aberration in the near infrared region by the cemented lens in the second lens group.

Normally, when using a cemented lens for the purpose of correcting chromatic aberration only in the visible range,
The value specified in 3) is often positive.

In the present invention, a chromatic aberration in the near infrared region is corrected by adding a cemented lens in which the value of the condition (3) is negative to the second lens group.

In the condition (3), when the lower limit value of −0.007 is not reached, the chromatic aberration in the near-infrared region is overcorrected, and the Abbe number of the negative lens and the positive lens constituting the cemented lens of the second lens group is excessive. The difference becomes small, and correction of chromatic aberration in the visible range becomes insufficient.

If the upper limit of 0 is exceeded in condition (3), it is advantageous for correcting chromatic aberration in the visible region, but chromatic aberration is insufficiently corrected in the near infrared region.

Condition (4) defines the application range of the microscope objective lens of the present invention. That is, the range of the magnification of the objective lens of the present invention is defined. In this condition (4), if the lower limit of 15 is not reached, the magnification of the objective lens becomes too large, and it becomes difficult to arrange a cemented lens that satisfies the condition (3) in the second lens group. If the upper limit of 55 is exceeded, the magnification of the objective lens becomes too small and the amount of chromatic aberration generated becomes large, making it difficult to correct this.

Condition (5) defines the refractive power of the cemented lens having the above structure included in the second lens group. In this condition (5), when the upper limit of 4 is exceeded, the refractive power of the cemented lens of the second lens group becomes weak, and when a low-magnification objective lens that is an application range of the present invention is used, the luminous flux is effectively transmitted. This is inconvenient and causes inconvenience in the focal length of the entire system. That is, it becomes difficult to increase the focal length of the objective lens (to reduce the magnification).

As the first lens group and the second lens group constituting the objective lens of the present invention, a single lens or a cemented lens may be arranged in addition to each cemented lens having the above-described configuration, for example, as in an embodiment described later.

In the objective lens of each configuration of the present invention described above, the light beam incident on the cemented lens in which the negative lens having the flat surface or the concave surface facing the object side in the second lens group and the positive lens are bonded together is a divergent light beam. It is desirable to make it.

In order to increase the degree of freedom in correcting the chromatic aberration by the cemented lens, it is preferable that the light beam incident on the cemented lens is a divergent light beam as described above. If this incident light beam is not a divergent light beam, it is difficult to dispose a cemented lens that satisfies the condition (3).
The optical microscope or the optical observation apparatus provided with the objective lens of the present invention described above is capable of high-resolution and bright observation of a specimen, and is effective for observation of cells and the like.

According to the present invention, a microscope objective lens having a high NA and well corrected for various aberrations such as chromatic aberration, spherical aberration, astigmatism, and coma from the visible region to the near infrared region is realized. obtain.

The figure which shows the structure of the objective lens of the reference example 1 of this invention The figure which shows the structure of the objective lens of the reference example 2 of this invention The figure which shows the structure of the objective lens of the reference example 3 of this invention. The figure which shows the structure of the objective lens of Example 1 of this invention. The figure which shows the structure of the objective lens of Example 2 of this invention. Aberration curve diagram of Reference Example 1 of the present invention Aberration curve diagram of Reference Example 2 of the present invention Aberration curve diagram of Reference Example 3 of the present invention Aberration curve diagram of Example 1 of the present invention Aberration curve diagram of Example 2 of the present invention The figure which shows the structure of one example of the imaging lens used in combination with the objective lens of this invention

Next, an embodiment of the microscope objective lens of the present invention will be described based on each example.
Reference example 1

Reference Example 1 of the present invention has a configuration as shown in FIG.
The first lens group G1 is composed of a lens group G2, and in order from the object side, the positive lens (r _{1 to} r ₂ ), the positive lens L1p (r _{3 to} r ₄ ), and the negative lens L1n with the concave surface facing the image side becomes more and (r ₄ ~r ₅₎ attaching the combined cemented lens L1 (r ₃ ~r _5). In addition, the second lens group G2 is a cemented lens in which a negative lens (r _{6 to} r ₇ ) and a positive lens (r _{7 to} r ₈ ) are bonded together in order from the object side.
r ₆ and ~r _8), and a positive lens (r ₉ ~r _10), a negative lens L2n having a concave surface on the object side (r ₁₁
~r ₁₂₎ and a positive lens L2p (r ₁₂ ~r ₁₃₎ attaching the combined cemented lens L2 (r ₁₁ ~r ₁₃
).

The data of this reference example 1 is as follows.
f = 45, β = 4 ×, NA = 0.16, number of fields = 26.5, WD = 13.327
r ₁ = 23.5100 d ₁ = 3.3114 n ₁ = 1.51633 ν ₁ = 64.14
r ₂ = -18.0816 d ₂ = 1.1909
r ₃ = 11.9099 d ₃ = 8.3841 n ₂ = 1.49700 ν ₂ = 81.54
r ₄ = -11.4327 d ₄ = 1.4037 n ₃ = 1.74100 ν ₃ = 52.64
r ₅ = 7.6802 d ₅ = 4.9712
r ₆ = -4.8583 d ₆ = 1.8582 n ₄ = 1.77250 ν ₄ = 49.60
r ₇ = 511.8307 d ₇ = 3.2971 n ₅ = 1.43875 ν ₅ = 94.93
r ₈ = -7.5362 d ₈ = 0.2307
r ₉ = -269.1995 d ₉ = 4.7695 n ₆ = 1.49700 ν ₆ = 81.54
r ₁₀ = -11.3589 d ₁₀ = 0.3500
r ₁₁ = −56.7065 d ₁₁ = 1.2469 n ₇ = 1.48749 ν ₇ = 70.23
r ₁₂ = 15.5159 d ₁₂ = 4.2171 n ₈ = 1.49700 ν ₈ = 81.54
r ₁₃ = -24.9502

ν _d (L1p) = 81.54
ν _d (L1n) = 52.64
ν _d (L2p) = 81.54
ν _d (L2n) = 70.23
θCt (L2p) = 0.8258
θCt (L2n) = 0.8924
f (L2) = 79.799
f = 45
(1) ν _d (L1p) −ν _d (L1n) = 28.9
(2) ν _d (L2p) = 81.54
(3) {θCt (L2p) −θCt (L2n)} /
{Ν _d (L2p) −ν _d (L2n)} = − 0.0059
(4) f = 45
(5) | f (L2) /f|=1.77
(6) ν _d (L1p) = 81.54
Where r ₁ , r ₂ ,... Are the radius of curvature of each lens surface, d ₁ , d ₂ ,... Are the thickness and air spacing of each lens, and n ₁ , n ₂ ,. Refractive index for d-line, ν ₁
, Ν ₂ ,... Are Abbe numbers for the d-line of each lens. The unit of length in the data is m
m. Further, f is a focal length, β is a magnification, NA is a numerical aperture, and WD is a working distance.

The glass used in Reference Example 1 is a glass having excellent transmittance in the ultraviolet region and less autofluorescence. Therefore, Example 1 is an objective lens that is optimal for fluorescence observation.
Reference example 2

Reference Example 2 is an objective lens as shown in FIG. That is, it consists of the first lens group G1 and the second lens group G2. The first lens group G1 includes positive lenses (r _{1 to} r _{2) in} order from the object side.
) And becomes more positive lens L1p (r ₃ ~r ₄₎ and a negative lens L1n (r ₄ ~r ₅₎ attaching the combined cemented lens having a concave surface on the image side L1 (r ₃ ~r _5). The second lens group G2, in order from the object side, a negative lens (r ₆ ~r ₇₎ and a positive lens (r ₇ ~r ₈₎ and a bonded cemented lens (r ₆ ~r _8), positive A lens (r _{9 to} r ₁₀ ) and a negative lens L2n (concave concave on the object side)
r _{11 to} r ₁₂ ) and a positive lens L2p (r _{12 to} r ₁₃ ) bonded to each other, a cemented lens L2 (r ₁₁ to r ₁₂
r ₁₃ ).
This Reference Example 2 also uses a glass having excellent transmittance in the ultraviolet region and little autofluorescence, and is a preferable configuration for fluorescence observation.

The data of this reference example 2 is as follows.
f = 45, β = 4 ×, NA = 0.16, number of fields = 26.5, WD = 13.128
r ₁ = 22.0338 d ₁ = 2.5851 n ₁ = 1.51633 ν ₁ = 64.14
r ₂ = -16.3327 d ₂ = 1.0057
r ₃ = 13.2301 d ₃ = 8.0333 n ₂ = 1.49700 ν ₂ = 81.54
r ₄ = -10.6413 d ₄ = 1.4762 n ₃ = 1.74100 ν ₃ = 52.64
r ₅ = 7.7218 d ₅ = 5.0902
r ₆ = -4.6759 d ₆ = 1.7801 n ₄ = 1.74100 ν ₄ = 52.64
r ₇ = -48.9050 d ₇ = 3.3001 n ₅ = 1.43875 ν ₅ = 94.93
r ₈ = -7.3261 d ₈ = 0.3451
r ₉ = ∞ d ₉ = 4.8401 n ₆ = 1.49700 ν ₆ = 81.54
r ₁₀ = -12.9154 d ₁₀ = 0.2325
r ₁₁ = -69.4925 d ₁₁ = 1.8817 n ₇ = 1.48749 ν ₇ = 70.23
r ₁₂ = 18.2063 d ₁₂ = 4.6804 n ₈ = 1.43875 ν ₈ = 94.93
r ₁₃ = -20.2479

ν _d (L1p) = 81.54
ν _d (L1n) = 52.64
ν _d (L2p) = 94.93
ν _d (L2n) = 70.23
θCt (L2p) = 0.8373
θCt (L2n) = 0.8924
f (L2) = 77.941
f = 45
(1) ν _d (L1p) −ν _d (L1n) = 28.9
(2) ν _d (L2p) = 94.93
(3) {θCt (L2p) −θCt (L2n)} /
{Ν _d (L2p) −ν _d (L2n)} = − 0.0022
(4) f = 45
(5) | f (L2) /f|=1.73
(6) ν _d (L1p) = 81.54
Reference example 3

Reference Example 3 is a microscope objective lens including a first lens group G1 and a second lens group G2 having a configuration as shown in FIG.

The first lens group G1 of Reference Example 3 includes, in order from the object side, a positive lens (r _{1 to} r ₂ ), a positive lens L1p (r _{3 to} r ₄ ), and a negative lens L1n (with a concave surface facing the image side) r ₄ ~r ₅₎ and becomes more and a bonded cemented lens L1 (r ₃ ~r _5). The second lens group G2, in order from the object side, a negative lens (r ₆ ~r ₇₎ and a positive lens (r ₇ ~r ₈₎ and a bonded cemented lens (r ₆
˜r ₈ ), a positive lens (r ₉ ˜r ₁₀ ), and a negative lens L2n (r ₁₁ ˜r with the plane facing the object side)
₁₂₎ and the positive lens L2p (r ₁₂ ~r ₁₃₎ and a bonded cemented lens L2 made of (r ₁₁ ~r _13).

The data of Reference Example 3 is as follows.
f = 18, β = 4 ×, NA = 0.16, number of fields = 26.5, WD = 13.074
r ₁ = 15.4116 d ₁ = 2.4262 n ₁ = 1.51633 ν ₁ = 64.14
r ₂ = -24.8478 d ₂ = 0.9700
r ₃ = 15.3969 d ₃ = 8.0632 n ₂ = 1.49700 ν ₂ = 81.54
r ₄ = -9.7470 d ₄ = 1.4344 n ₃ = 1.74100 ν ₃ = 52.64
r ₅ = 8.4888 d ₅ = 5.0716
r ₆ = -4.7470 d ₆ = 1.7813 n ₄ = 1.74100 ν ₄ = 52.64
r ₇ = -29.6562 d ₇ = 3.2984 n ₅ = 1.43875 ν ₅ = 94.93
r ₈ = -7.6436 d ₈ = 0.3428
r ₉ = 807.1999 d ₉ = 4.8337 n ₆ = 1.49700 ν ₆ = 81.54
r ₁₀ = -12.8532 d ₁₀ = 0.1456
r ₁₁ = ∞ d ₁₁ = 1.7263 n ₇ = 1.48749 ν ₇ = 70.23
r ₁₂ = 13.7643 d ₁₂ = 4.5524 n ₈ = 1.43875 ν ₈ = 94.93
r ₁₃ = -27.2037

ν _d (L1p) = 81.54
ν _d (L1n) = 52.64
ν _d (L2p) = 94.93
ν _d (L2n) = 70.23
θCt (L2p) = 0.8373
θCt (L2n) = 0.8924
f (L2) = 78.321
f = 45
(1) ν _d (L1p) −ν _d (L1n) = 28.9
(2) ν _d (L2p) = 94.93
(3) {θCt (L2p) −θCt (L2n)} /
{Ν _d (L2p) −ν _d (L2n)} = − 0.0022
(4) f = 45
(5) | f (L2) /f|=1.74
(6) ν _d (L1p) = 81.54
The objective lens of Reference Example 3 is also excellent in transmittance in the ultraviolet region and is made of glass with little autofluorescence, and has an optimum configuration for fluorescence observation.

The objective lens of Example 1 of the present invention has the configuration as shown in FIG.
It consists of a lens group G2. The first lens group G1 includes, in order from the object side, a negative lens (r
_{1 to} r ₂ ) and a positive lens (r _{2 to} r ₃ ), a cemented lens (r _{1 to} r ₃ ), and a positive lens (
r _{4 to} r ₅ ), a positive lens (r _{6 to} r ₇ ), a positive lens L 1 p (r _{8 to} r ₉ ), and a negative lens L 1 n (r _{9 to} r ₁₀ ) with a concave surface facing the image side. the more the combined cemented lens L1 (r ₈ ~r _10). The second lens group G2 includes a negative lens L2n having a concave surface directed toward the object side in order from the object side.
A cemented lens L2 (r ₁₁ ) in which (r _{11 to} r ₁₂ ) and a positive lens L2p (r _{12 to} r ₁₃ ) are bonded together
And ~r _13), the more the positive lens (r ₁₄ ~r _15).

The data of this Example 1 is as follows.
f = 18, β = 10 ×, NA = 0.4, the number of fields of view = 26.5, WD = 3.8
r ₁ = -10.0179 d ₁ = 6.0670 n ₁ = 1.67300 ν ₁ = 38.15
r ₂ = 55.2737 d ₂ = 2.7505 n ₂ = 1.49700 ν ₂ = 81.54
r ₃ = -9.2112 d ₃ = 0.2125
r ₄ = 83.9358 d ₄ = 4.0793 n ₃ = 1.56907 ν ₃ = 71.30
r ₅ = -35.6271 d ₅ = 1.1100
r ₆ = 11.8739 d ₆ = 4.5781 n ₄ = 1.43875 ν ₄ = 94.93
r ₇ = ∞ d ₇ = 6.5068
r ₈ = 10.2087 d ₈ = 3.6739 n ₅ = 1.43875 ν ₅ = 94.93
r ₉ = -9.8106 d ₉ = 1.2763 n ₆ = 1.55836 ν ₆ = 54.01
r ₁₀ = 8.2650 d ₁₀ = 5.6402
r ₁₁ = -6.3912 d ₁₁ = 2.7687 n ₇ = 1.48749 ν ₇ = 70.23
r ₁₂ = -19.9601 d ₁₂ = 3.2167 n ₈ = 1.49700 ν ₈ = 81.54
r ₁₃ = -12.7726 d ₁₃ = 0.1300
r ₁₄ = ∞ d ₁₄ = 3.0324 n ₉ = 1.49700 ν ₉ = 81.54
r ₁₅ = -16.8356

ν _d (L1p) = 94.93
ν _d (L1n) = 54.01
ν _d (L2p) = 81.54
ν _d (L2n) = 70.23
θCt (L2p) = 0.8258
θCt (L2n) = 0.8924
f (L2) = − 38.52
f = 18
(1) ν _d (L1p) −ν _d (L1n) = 40.92
(2) ν _d (L2p) = 81.54
(3) {θCt (L2p) −θCt (L2n)} /
{Ν _d (L2p) −ν _d (L2n)} = − 0.0059
(4) f = 18
(5) | f (L2) /f|=2.14
(6) ν _d (L1p) = 94.93
This Example 1 also has the characteristics that the glass to be used is excellent in transmittance in the ultraviolet region and has less autofluorescence, and is optimal for fluorescence observation.

The objective lens according to Example 2 of the present invention includes a second lens group G1 and a second lens group configured as shown in FIG.
This is a lens system including the lens group G2.

The first lens group G1 includes a negative lens (r _{1 to} r ₂ ) and a positive lens (r
And ₂ ~r ₃₎ a bonded cemented lens (r ₁ ~r _3), and a positive lens (r ₄ ~r _5), a positive lens (r ₆ ~r _7), a positive lens L1p (r ₈ ~r ₉ ) and a negative lens L1n (r
₉ ~r ₁₀₎ and the a bonded cemented lens L1 (r ₈ ~r ₁₀₎ becomes more. The second lens group G2 is a cemented lens L2 in which a negative lens L2n (r _{11 to} r ₁₂ ) and a positive lens L2p (r _{12 to} r ₁₃ ), which are concave on the object side, are bonded in order from the object side. (R _{11 to} r ₁₃ ) and a positive lens (r _{14 to} r ₁₅ ).

The data of this Example 2 is as follows.
f = 18, β = 10 ×, NA = 0.4, the number of fields of view = 26.5, WD = 3.949
r ₁ = -5.9965 d ₁ = 2.9820 n ₁ = 1.67300 ν ₁ = 38.15
r ₂ = 71.8587 d ₂ = 3.0905 n ₂ = 1.49700 ν ₂ = 81.54
r ₃ = -7.1299 d ₃ = 0.2125
r ₄ = 177.0850 d ₄ = 4.1851 n ₃ = 1.56907 ν ₃ = 71.30
r ₅ = -18.9259 d ₅ = 1.1100
r ₆ = 11.1707 d ₆ = 3.6235 n ₄ = 1.43875 ν ₄ = 94.93
r ₇ = ∞ d ₇ = 5.4744
r ₈ = 9.3475 d ₈ = 3.6935 n ₅ = 1.43875 ν ₅ = 94.93
r ₉ = -10.9268 d ₉ = 1.8214 n ₆ = 1.55836 ν ₆ = 54.01
r ₁₀ = 7.4855 d ₁₀ = 5.5110
r ₁₁ = -5.4188 d ₁₁ = 3.5673 n ₇ = 1.51633 ν ₇ = 64.14
r ₁₂ = 116.2141 d ₁₂ = 4.0903 n ₈ = 1.43875 ν ₈ = 94.93
r ₁₃ = -10.7940 d ₁₃ = 0.1300
r ₁₄ = ∞ d ₁₄ = 3.2380 n ₉ = 1.49700 ν ₉ = 81.54
r ₁₅ = -17.1112

ν _d (L1p) = 94.93
ν _d (L1n) = 54.01
ν _d (L2p) = 94.93
ν _d (L2n) = 64.14
θCt (L2p) = 0.8373
θCt (L2n) = 0.8687
f (L2) = − 28.379
f = 18
(1) ν _d (L1p) −ν _d (L1n) = 40.92
(2) ν _d (L2p) = 94.93
(3) {θCt (L2p) −θCt (L2n)} /
{Ν _d (L2p) −ν _d (L2n)} = − 0.001
(4) f = 18
(5) | f (L2) /f|=1.58
(6) ν _d (L1p) = 94.93
In Reference Examples 1, 2, and 3, and Examples 1 and 2 described above, as shown in the data, all of the conditions (1), (2), (3), (4), (5), and (6) Satisfied.

Reference Examples 1, 2, and 3 are all objective lenses having a magnification β of 4 and an NA of 0.16. In Examples 1 and 2, the magnification β is 10 times and the NA is 0.4.

The glass used in Example 2 is also an objective lens that has excellent transmittance in the ultraviolet region, has a feature of less autofluorescence, and is suitable for fluorescence observation.

The cover glass C used in Reference Examples 1 to 3 and Examples 1 and 2 has a thickness of 0.17 mm, a refractive index with respect to d-line of 1.521, and an Abbe number with respect to d-line of 56.02.
In addition, each of Reference Examples 1 to 3 and Examples 1 and 2 are infinity correction type objective lenses in which the emission destination from the objective lens is a parallel light beam, and no image is formed by itself. Therefore, for example, the configuration shown in FIG. 11 is used in combination with an imaging lens having the following data.
F = 180
R ₁ = 68.7541 D ₁ = 7.7321 N ₁ = 1.48749 V ₁ = 70.20
R ₂ = -37.5679 D ₂ = 3.4742 N ₂ = 1.80610 V ₂ = 40.95
R ₃ = -102.8477 D ₃ = 0.6973
R ₄ = 84.3099 D ₄ = 6.0238 N ₃ = 1.83400 V ₃ = 37.16
_{R 5 = -50.7100 D 5 = 3.0298} N 4 = 1.64450 V 4 = 40.82
R ₆ = 40.6619
Here, R ₁ , R ₂ ,... R ₆ are the radii of curvature of the lens surfaces of the imaging lens, D ₁ , D ₂
,... D ₅ is the thickness and air spacing of each lens of the imaging lens, N ₁ , N ₂ , N ₃ , N ₄ are the refractive indices of the lenses of the imaging lens, V ₁ , V ₂ , V _3. , V ₄ is the Abbe number of each lens of the imaging lens, and F is the focal length of the imaging lens.

    When this imaging lens is used in combination with each of the reference examples and examples, the imaging lens is used at a position where the distance between the objective lens and the imaging lens is 50 mm to 170 mm.

    Aberrations when combined with the imaging lens 120 mm apart from Reference Examples 1 to 3 and Examples 1 and 2 are as shown in FIGS. 6, 7, 8, 9 and 10.

    As is clear from these aberration states, in each of the reference examples and examples of the present invention, various aberrations including chromatic aberration are corrected well from the visible region to the near infrared region.

In addition, the objective lens of the present invention is an objective lens that can be used for wavelengths from the conventional visible range to the near-infrared range, such as in the above-mentioned literature, and has a high NA and a bright resolution compared with a lens of the same magnification. It is a high objective lens.

The microscope objective lens of the present invention is used for fluorescence observation, DIC observation, etc., and has a magnification of 4 to 4
Aberrations are well corrected from the visible range to the near infrared range at about 10 times. Moreover, it has a high NA and is therefore suitable for observation of cells, proteins, and DNA.

Claims (5)

In order from the object side, the first lens group and the second lens group are included. The first lens group includes, in order from the object side, a cemented lens obtained by bonding a negative lens and a positive lens, a positive lens, and a positive lens. And a second cemented lens in which a positive lens and a negative lens having a concave surface facing the image side are bonded together, and the second lens group includes, in order from the object side, a negative lens and a positive lens having a concave surface facing the object side And a positive lens, satisfying the following conditions (1), (2), (3), (4), (5).
(1) ν _d (L1p) −ν _d (L1n)> 20
(2) ν _d (L2p)> 75
(3) −0.007 <{θCt (L2p) −θCt (L2n)} /
{Ν _d (L2p) −ν _d (L2n)} <0
(4) 15 <f <55
(5) | f (L2) / f | <4
Where ν _d (L1p) is the Abbe number of the second cemented lens in the first lens group with respect to the d-line of the positive lens, and ν _d (L1n) is the second cemented lens in the first lens group. Abbe number with respect to d line of negative lens with concave surface facing image side, ν _d (L2p) is Abbe number with respect to d line of positive lens of cemented lens in the second lens group, and ν _d (L2n) is the first number. Abbe number with respect to the d-line of the negative lens with the plane or concave surface facing the object side of the cemented lens in the two lens group, θCt (L2p) is a partial dispersion ratio of the cemented lens in the second lens group with respect to the t-line of the positive lens , ΘCt (L2n) is a partial dispersion ratio with respect to the t-line of the negative lens having a plane or concave surface facing the object side of the cemented lens in the second lens group, and f (L2) is a cemented lens in the second lens group. Focal length, f is the focal length of the entire objective lens system It is. 2. The microscope objective lens according to claim 1, wherein the light beam incident on the cemented lens in the second lens group is a divergent light beam. The microscope objective lens according to claim 1 or 2, wherein the following condition (1-1) is satisfied instead of the condition (1).
(1-1) ν _d (L1p) −ν _d (L1n)> 25 The microscope objective lens according to any one of claims 1 to 3, wherein the Abbe number ν _d (L1p) of the positive lens of the second cemented lens in the first lens group satisfies the following condition (6).
(6) ν _d (L1p)> 75 An optical microscope or an optical observation apparatus using the objective lens according to any one of claims 1 to 4.

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