JP2891369B2 - Microscope objective lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is intended to satisfactorily correct various aberrations with respect to a change in the thickness of a transparent parallel flat plate (cover glass) disposed on the object side. And a high magnification microscope objective lens.

[Prior Art] Generally, a microscope objective lens is designed on the assumption that the thickness of a cover glass is constant. Therefore, if the thickness of the cover glass changes, its imaging performance will deteriorate and the NA
This phenomenon becomes more remarkable as becomes larger. Therefore, the distance between the glass and the first lens unit is slightly changed by moving the entire objective lens so that the height of the light beam incident on the first lens unit becomes substantially constant.

In recent years, biotechnology fields such as cell culture and genetic manipulation have been developed. However, the thicknesses of glass dishes and plastic dishes used at that time vary widely, and aberrations are aggravated by the thickness of the dishes (thickness of the transparent parallel flat plate). Therefore, a microscope objective lens having a mechanism capable of compensating for the thickness and having a long working distance with a margin for a change in its thickness is required. As such a microscope objective lens, one described in JP-B-61-30245 is known. In this conventional example, the thickness of the cover glass is 0 to 2 mm.
Is a microscope objective lens with a long working distance that can correct aberrations for changes in

As a microscope objective lens with high magnification and high NA
The lens systems described in JP-A-100409, JP-A-60-205521 and JP-A-60-247613 are known. In this conventional example, the correction range of the thickness of the cover glass is narrow, but has a long working distance.

The conventional example described in JP-B-61-30245 is a microscope objective lens that maintains the magnification up to about 40 times, NA is 0.6 or less, and enables correction for the thickness of the cover glass.Compared over the entire thickness of the cover glass The aberration is corrected satisfactorily.

[Problems to be Solved by the Invention] Among these conventional examples, a microscope objective lens for correcting a cover glass having a high NA and a high magnification (Japanese Patent Application Laid-Open Nos.
60-205521, JP-A-60-247613) cannot sufficiently correct spherical aberration and coma due to a change in the thickness of the cover glass. In particular, with an objective lens having an NA of 0.8 and a magnification of about 100 × (Japanese Patent Application Laid-Open No. 60-247613), spherical aberration, chromatic aberration bending and coma aberration at the boundary of the correction range become large, and it is extremely difficult to correct the aberration. is there.

An object of the present invention is to provide a high-magnification, high NA, long working distance microscope objective lens in which various aberrations are satisfactorily corrected over the entire range that can be corrected for a change in cover glass thickness.

Microscope objective of the present invention [Means for Solving the Problems] includes a first group G ₁ having a positive refractive power the light flux is divergent light includes positive meniscus lens having a convex surface directed toward the image side, a negative Second group G ₂ having a positive refractive power and having at least one joining surface having a refractive power of
When the second group G in response to changes in the thickness of the transparent parallel flat plate disposed between the first group G ₁ and the object and a third group G ₃ having a negative refractive power (a cover glass or the like) ₂ is relatively movable with respect to the first group G ₁ and the third group G ₃ , and the distance between the first group G ₁ and the second group G ₂ when the plane-parallel plate becomes thicker the so moves the second group G ₂ to be shorter in the direction of the optical axis, the distance between the first group G ₁ and the second group G ₂ in the case of a plane-parallel plate becomes thinner becomes longer It is characterized by moving the 2 group G ₂ in the optical axis direction.

Generally, a microscope objective lens is moved to correct aberration caused by a change in the thickness of a cover glass. In the case of a high NA objective lens, spherical aberration, coma, and chromatic aberration vary greatly when the aberration varies. Therefore, unless the aberration generated in each of the fixed group and the moving group is reduced, the aberration generated in the entire system including the cover glass becomes large due to a change in the thickness of the cover glass, and correction cannot be performed.

In the microscope objective lens of the present invention, the first group G ₁ is have a positive refractive power, since the spherical aberration and the chromatic aberration is insufficiently corrected and the divergent light beam by the final surface of the first group G ₁ First
The aberration amount is small for the entire group. The second group G ₂ is a spherical aberration but has a positive refractive power generated in the entire second group by bonding surface having a negative refractive power refractive power weaker than the first group G _1, the chromatic aberration somewhat overcorrected , so that it cancels the aberration occurring in the first group G _1.

When the cover glass is thickened, the height of the emitted light becomes higher, so that spherical aberration and chromatic aberration generated on the cover glass surface increase in the diverging direction. In this case, it is higher height of light rays incident on the first group G _1, the aberration converging action of the first group G ₁ is generated in the cover glass since stronger reverse aberration increases. But above aberrations of the diverging direction is increased by a change in thickness of the cover glass, since the change amount of the aberration occurring in the first group G ₁ is small, can not be corrected aberration change generated in the cover glass. Therefore the first group G ₁ and to lower the ray height of a ray incident on the distance shorter second group G ₂ between the second group G _2, reduced by the lens aberration of the diverging direction generated by the second group G ₂ The aberration of the entire system is reduced. If the thickness of the cover glass becomes thinner Conversely, the longer the first group G ₁ and the distance between the second group G ₂ second
Aberrations as a whole compensate the aberration of the diverging direction is reduced by a change in the thickness of the larger to cover glass aberrations of the diverging direction generated by the second group G ₂ by increasing the height of the light beam incident to the group G ₂ Balanced.

Third group G ₃ is performed to correct the longitudinal chromatic aberration and lateral chromatic aberration while reducing the Petzval sum has a negative refractive power. The third group G ₃ also the first group G _1, the amount of change in aberrations in the third group G ₃ due to the change in aberration is small cover glass thickness produced in the same manner as the second group G ₂ is small.

Microscope objective of the present invention, in order to correct the aberration variation due to change in thickness of the cover glass as described above, a relatively second group G ₂ with respect to the first group G ₁ and the third group G ₃ Move. Also between the first group G ₁ and the second group G ₂ is set to be in the divergent light beam in order to reduce the negative spherical aberration produced by the first group G _1. The radius of curvature r _i of the most image side surface of the first group G ₁ For that purpose, the following conditions (1), it is desirable to satisfy the (2).

(1) | r _i | / f> 50 (when r _i <0) (2) r _i /f>6.5 (when r _i > 0) where f is the focal length of the entire objective lens system.

Condition (1) than | r _i | is small when r _i second group from the surface G ₂
The divergence of the light rays going toward is weakened. That converging action of the first group G ₁ becomes strong, the spherical aberration occurring in the first group G _1, coma, chromatic aberration increases. Therefore the aberration caused by a change in thickness of the cover glass only movement of the second group G ₂ becomes impossible to correct.

When r _i is smaller than the condition (2), the second group
And divergence is too strong of a light beam towards the G _2, the incident light height of the change to the second group G ₂ when the second group G ₂ with the change of the thickness of the cover glass is moved is increased. Therefore it is impossible to change the chromatic aberration obtain vigorous sufficient performance when various aberrations generated in the second group G _2.

If the following conditions (3) and (4) are satisfied in the microscope objective lens of the present invention, it is possible to correct various aberrations more favorably.

(3) 2 <f ₁ / f <6 (4) 4 <f ₂ / f <10 where f ₁ and f ₂ are the focal lengths of the first group and the second group, respectively.

Condition (3) exceeds the lower limit too strong converging action of the first group G ₁ is, spherical aberration, coma aberration generated in the first group G ₁ is varied by a change in the increase of the cover glass thickness, only chromatic aberration moving the second group G ₂ can not sufficiently corrected. Also, the working distance of the objective lens is shortened. Converging action of Above the upper limit first group G ₁ of the condition (3) is weakened, the second group G _2, the spherical aberration in the third lens group G _3, must be a correction of the chromatic aberration, the second group G The ray height of the ray incident on ₂ becomes high, and it becomes difficult to largely correct the change in aberration due to the change in the thickness of the cover glass, especially the change in chromatic aberration.

Condition (4) the spherical aberration due to movement of the second group G ₂ the refractive power becomes too strong in the second group G ₂ is a mobile group out of the lower limit of the variation of chromatic aberration is large, and in the second group G ₂ Since the generated aberration increases in the diverging direction, the chromatic aberration of the entire system cannot be corrected. Condition (4) exceeds the upper limit refractive power of the second group G ₂ becomes weak, because the light flux from the first group G ₁ is for forming in place a light beam to a divergent light is first 3 groups
We must strengthen the refractive power of G ₃ in the positive direction. Therefore Petzval sum negative refractive power of the third group G ₃ becomes weaker increases. Further, the balance of various aberrations such as chromatic aberration, coma, and astigmatism is lost, and it becomes difficult to correct the aberration due to a change in the thickness of the cover glass.

Cover glass must be provided at least one surface of the bonding surface of the negative refractive power in the second group G ₂ to move in order to correct the aberration fluctuation to changes in the thickness of, this bonding surface of the following conditions (5) Is satisfied, aberration fluctuations can be corrected even more favorably.

(5) 0.02 <{(n N -n P) / r c} f <0.13 However r _c is the radius of curvature of the cemented surface with the negative refractive power,
n _N and n _P are the refractive indices of the concave lens and the convex lens before and after the joint surface, respectively.

When the value falls below the lower limit of the condition (5), the negative refractive power of the cemented surface is weakened, and the occurrence of aberration in the diverging direction is reduced. Therefore, when the thickness of the cover glass changes, spherical aberration and chromatic aberration of the entire system cannot be corrected. When the value exceeds the upper limit of the condition (5), the diverging action becomes strong in the second lens unit, and spherical aberration and chromatic aberration occur in the diverging direction. Therefore, similarly to the case where the upper limit of the condition (4) is exceeded, the convergence of the third lens group must be strengthened, and the variation in aberration becomes large with respect to the change in the thickness of the cover glass, so that sufficient satisfactory performance cannot be obtained. .

[Examples] Next, examples of the microscope objective lens of the present invention will be described.

Example _{1 f = 1.54, d 0 =} 1.065 r 1 = -9.84 d 1 = 2.1 n 1 = 1.755 ν 1 = 52.33 r 2 = -3.13 d 2 = 0.16 r 3 = 8.39 d 3 = 3.2 n 2 = 1.456 ν _{2 = 90.31 r 4 = -4.76 d} 4 = 0.8 n 3 = 1.6134 ν 3 = 43.84 r 5 = 15.12 d 5 ( _{variable) r 6 = 15.29 d 6 =} 1.05 n 4 = 1.6968 ν 4 = 56.49 r 7 = 8.48 d _{7 = 4.32 n 5 = 1.456 ν} 5 = 90.31 r 8 = -9.42 d 8 = 0.25 r 9 = 73.13 d 9 = 2.3 n 6 = 1.43389 ν 6 = 95.15 r 10 = -14.92 d 10 = 0.25 r 11 = 21.81 d _{11 = -3.39 n 7 = 1.43389 ν} 7 = 95.15 r 12 = -8.3 d 12 = 1.1 n 8 = 1.883 ν 8 = 40.78 r 13 = -88.45 d 13 = 0.15 r 14 = 12.64 d 14 = 7 n 9 = 1.618 ν ₉ = 63.38 r ₁₅ ==-7.21 d ₁₅ = 3.13 n ₁₀ = 1.53375 ν ₁₀ = 55.52 r ₁₆ = 8.06 d ₁₆ (variable) r ₁₇ = 6.56 d ₁₇ = 3.59 n ₁₁ = 1.7847 ν ₁₁ = 26.22 r ₁₈ = −6.13 d ₁₈ = 3.19 n ₁₂ = 1.74 ν ₁₂ = 31.7 r ₁₉ = 4.58 d ₁₉ = 1.39 r ₂₀ = −2.59 d ₂₀ = 0.7 n ₁₃ = 1.84666 ν ₁₃ = 23.78 r ₂₁ = −5.38 r _i (= r ₅ ) /F=9.8 f ₁ /f=3.09 f ₂ /f=5.45 ｛n ₄ −n5) / r ₇ ｝ f = 0.044 ｛(n ₈ −n ₇ / r ₁₂ ｝ f = 0.083 t d ₀ d ₅ d ₁₆ 0.7 1.164 2.57 3.99 1.1 1.065 1.9 4.66 1.5 0.974 1.08 5.49 Example 2 f = 1.54, d ₀ = 1.22 r ₁ = −8.17 d ₁ = 2.1 n ₁ = 1.755 ν ₁ = 52.33 r ₂ = −3.17 d ₂ = 0.16 r ₃ = 9.3 d ₃ = 3 n ₂ = 1.456 ν ₂ = 90.31 r ₄ = −5.38 d ₄ = 0.8 n ₃ = 1.6134 ν ₄ = 43.84 r ₅ = 18.99 d ₅ (variable) r ₆ = 12.85 d ₆ = 1.05 n ₄ = 1.72916 ν ₄ = 54.68 r ₇ = 7.61 d ₇ = 4.32 n ₅ = 1.456 ν ₅ = 90.31 r ₈ = −9.35 d ₈ = 0.4 r ₉ = 15.32 d ₉ = 1.1 n ₆ = 1.7865 ν ₆ = 50 r ₁₀ = 7.61 d ₁₀ = 5 n ₇ = 1.456 v ₇ = 90.31 r ₁₁ = -8.38 d ₁₁ = -1.1 n ₈ = 1.883 v ₈ = 40.78 r ₁₂ = -22.85 d ₁₂ = 0.2 r ₁₃ = 34.48 d ₁₃ = 2.2 _{n 9 = 1.456 ν 9 = 90.31} r 14 = -50.55 d 14 = 0.2 r 15 = 12.36 d 15 = 6.5 n 10 = 1.56907 ν 10 = 71.3 r 16 = -6.41 d 16 = 2.26 n 11 = 1.53375 ν 11 = 55.52 r ₁₇ = 7.15 d ₁₇ (variable ) R ₁₈ = 5.7 d ₁₈ = 3.76 n ₁₂ = 1.7847 ν ₁₂ = 26.22 r ₁₉ = −8.32 d ₁₉ = 2.81 n ₁₃ = 1.74 ν ₁₃ = 31.7 r ₂₀ = 3.21 d ₂₀ = 1.39 r ₂₁ = −2.2 d ₂₁ = 0.7 n ₁₄ = 1.84666 ν ₁₄ = 23.78 r ₂₂ = −4.06 r _i (= r ₅ ) /f=12.4 f ₁ /f=3.42 f ₂ /f=6.06 ｛(n ₄ −n ₅ ) / r ₇ ｝ f = 0.055 ｛(n ₆ −n ₇ ) / r ₁₀ ｝ f = 0.067 ｛(n ₈ −n ₇ ) / r ₁₁ ｝ f = 0.078 t d ₀ d ₅ d ₁₇ 0.7 1.333 2.59 2.47 1.1 1.22 1.9 3.16 1.5 1.119 1.06 4 example _{3 f = 1.54, d 0 =} 1.276 r 1 = -8.23 d 1 = 2.1 n 1 = 1.755 ν 1 = 52.33 r 2 = -3.2 d 2 = 0.16 r 3 = 9.17 d 3 = 3.1 n 2 = 1.456 ν ₂ = 90.31 r ₄ = −5.4 d ₄ = 0.8 n ₃ = 1.6134 ν ₃ = 43.84 r ₅ = 18.51 d ₅ (variable) r ₆ = 13.39 d ₆ = 1.05 n ₄ = 1.6968 ν ₄ = 56.49 r ₇ = 7.7 d ₇ = 4.32 n ₅ = 1.456 ν ₅ = 90.31 r ₈ = -10.51 d ₈ = 0.1 r ₉ = 26.46 d ₉ = 1.1 n ₆ = 1.6968 ν ₆ = 56.49 r ₁₀ = 8.78 d ₁₀ = 3.39 n ₇ = 1.497 ν _{7 = 81.61 r 11 = -16.68 d} 11 = 0.1 r 12 _{15.83 d 12 = 3.39 n 8 =} 1.456 ν 8 = 90.31 r 13 = -9.52 d 13 = 1.1 n 9 = 1.883 ν 9 = 40.78 r 14 = 109.35 d 14 = 0.15 r 15 = 15.66 d 15 = 7 n 10 = 1.618 _{ν 10 = 63.38 r 16 = -6.11} d 16 = 2.37 n 11 = 1.53375 ν 11 = 55.52 r 17 = 9.98 d 17 ( _{variable) r 18 = 5.81 d 18 =} 3.47 n 12 = 1.7847 ν 12 = 26.22 r 19 = - _{9.2 d 19 = 3.04 n 13 =} 1.74 ν 13 = 31.7 r 20 = 3.28 d 20 = 1.39 r 21 = -2.19 d 21 = 0.7 n 14 = 1.84666 ν 14 = 23.78 r 22 = -3.96 r i (= r 5) /f=12.1 f ₁ /f=3.44 f ₂ /f=6.05 ｛(n ₄ −n ₅ ) / r ₇ ｝ f = 0.048 ｛(n ₆ −n ₇ ) / r ₁₀ ｝ f = 0.035 ｛(n ₉ −n ₈ ) / r ₁₃ ｝ f = 0.069 t d ₀ d ₅ d ₁₇ 0.7 1.398 2.56 3.07 1.1 1.276 1.9 3.73 1.5 1.166 1.1 4.53 Example 4 f = 1.54, d ₀ = 1.08 r ₁ = −7.34 d ₁ = 2.1 n ₁ = 1.6968 v ₁ = 56.49 r ₂ = −2.92 d ₂ = 0.16 r ₃ = 13.37 d ₃ = 2.35 n ₂ = 1.43389 v ₂ = 95.15 r ₄ = −6.92 d ₄ = 0.8 n ₄ = 1.72916 v ₃ = 54.68 r ₅ = −200 d ₅ (possible Change) r ₆ = 13.04 d ₆ = 1.05 n ₄ = 1.79216 ν ₄ = 54.68 r ₇ = 7.84 d ₇ ＝ 4.32 n ₅ = 1.43389 ν ₅ = 95.15 r ₈ = −9.65 d ₈ = 0.4 r ₉ = 31.98 d ₉ = 1.1 n ₆ = 1.72916 ν ₆ = 54.68 r ₁₀ = 8.82 d ₁₀ = 3.39 n ₇ = 1.456 ν ₇ = 90.31 r ₁₁ = -15.69 d ₁₁ = 0.1 r ₁₂ = 35.18 d ₁₂ = 3.39 n ₈ = 1.456 ν ₈ = 90.31 _{r 13 = -9.31 d 13 = 1.1} n 9 = 1.883 ν 9 = 40.78 r 14 = -38.3 d 14 = 0.15 r 15 = 8.65 d 15 = 7 n 10 = 1.56907 ν 10 = 71.3 r 16 = -5.66 d 16 = 2.82 n ₁₁ = 1.56384 v ₁₁ = 60.69 r ₁₇ = 5.37 d ₁₇ (variable) r ₁₈ = 5.36 d ₁₈ = 3.48 n ₁₂ = 1.7552 v ₁₂ = 27.51 r ₁₉ = 33.53 d ₁₉ = 2.86 n ₁₃ = 1.6765 v ₁₃ = 37.5 _{r 20 = 3.68 r 20 = 1.39} r 21 = -2.3 d 21 = 0.7 n 14 = 1.80518 ν 14 = 25.43 r 22 = -4.13 | r i (= r 5) | /f=130.1 f 1 /f=3.66 f ₂ / f = 5.37 ｛(n _4- n ₅ ) | r ₄ ｝ f = 0.058 ｛(n _6- n ₇ ) / r ₁₀ ｝ f = 0.048 ｛(n _9- n ₈ / r ₁₃ ｝ f = 0.071 t d ₀ d ₅ d ₁₇ 0.7 1.193 2.48 3.7 1.1 1.08 1.8 4.37 1.5 0.977 0.98 5.19 Example 5 f = 1.54, d ₀ = 1.515 r ₁ = −6.83 d ₁ = 2.29 n ₁ = 1.7865 ν ₁ = 50 r ₂ = −3.47 d ₂ = 0.2 r ₃ = 10.99 d ₃ = 2.3 n ₂ = 1.456 ν ₂ = 90.31 r ₄ = −12.53 d ₄ = 0.85 n ₃ = 1.79216 ν ₃ = 54.68 r ₅ = 31.99 d ₅ (variable) r ₆ = 12.1 d ₆ = 1.1 n ₄ = 1.7865 ν _{4 = 50 r 7 = 7.57 d 7} = 4.27 n 5 = 1.43425 ν 5 = 95 r 8 = -10.31 d 8 = 0.5 r 9 = 12.97 d 9 = 1.1 n 6 = 1.7865 ν 6 = 50 r 10 = 7.8 d 10 = 3.8 n ₇ = 1.43425 ν ₇ = 95 r ₁₁ = −16.71 d ₁₁ = 0.15 r ₁₂ = 11.1 d ₁₂ = 3.2 n ₈ = 1.456 ν ₈ = 90.31 r ₁₃ = −9.06 d ₁₃ = 1 n ₉ = 1.874 ν ₉ = 35.26 r ₁₄ = 196.89 d ₁₄ = 1.3 r ₁₅ = −18.98 d ₁₅ = 3.1 n ₁₀ = 1.618 ν ₁₀ = 63.38 r ₁₆ = −4.97 d ₁₆ = 1.03 n ₁₁ = 1.5213 ν ₁₁ = 52.55 r ₁₇ = 53.97 d ₁₇ ( _{variable) r 18 = 4.83 d 18 =} 2.7 n 12 = 1.80518 ν 12 = 25.43 r 19 = 83.77 d 19 = 2.01 n 13 = 1.74 ν 13 = 31.7 r 20 = 2.65 d 20 = 1.7 r 21 = -2.29 d 21 _{0.7 n 14 = 1.7847 ν 14 =} 26.22 r 22 = -4.08 r i (= r 5) /f=20.8 f 1 /f=4.14 f 2 /f=6.98 {(n 4 -n 5) / r 7} f = 0.072 ｛(n ₆ −n ₇ ) / r ₁₀ ｝ f = 0.07 ｛(n ₉ −n ₈ ) / r ₁₃ ｝ f = 0.071 t d ₀ d ₅ d ₁₇ 0.9 1.618 2.31 8.52 1.2 1.515 1.8 9.03 1.5 1.418 1.21 9.62 where r ₁ , r ₂ , ... is the radius of curvature of each lens surface, d ₁ , d ₂ , ... is the thickness of each lens, n ₁ , n ₂ , ... is the refractive index of each lens, ν ₁ , ν
₂ ,... Are Abbe numbers of the lenses. D ₀ is the working distance, t
Is the thickness of the cover glass.

Examples 1 to 5 have the lens configurations shown in FIGS. 1 to 5, respectively. The amount of change in distance due to movement of the second group G ₂ corresponding to the thickness t of the cover glass in these examples are shown in the data.

In Examples 1 to 3 among these examples, the material of the cover glass is designed as a glass shear. Glass shear has a d-line refractive index of 1.52287 and an Abbe number of 59.89.
It is.

In Examples 4 and 5, the material of the cover glass is designed as plastic shear (polystyrene). Polystyrene has a d-line refractive index of 1.59108 and an Abbe number of 3.
0.85.

The correction range of the thickness of the cover glass is the same as in Examples 1 to 4.
0.7 to 1.5 mm, and Example 5 is 0.9 to 1.5 mm. Multiples, N
A, the image height is 100 ×, 0.8, and 10.5 in all examples.

The aberration states of the first embodiment are as shown in FIGS. FIG. 6 shows that the cover glass has a thickness t of 0.7 mm.
7 is for 1.1 mm and FIG. 8 is for 1.5 mm.

The aberration states of the second embodiment are as shown in FIGS. 9 to 11, wherein FIG. 9 is for t = 0.7 mm, FIG. 10 is for t = 1.1 mm, and FIG. 11 is for t = 1.5 mm. .

The aberration conditions of the third embodiment are as shown in FIG. 12 (t = 0.7 mm), FIG. 13 (t = 1.1 mm), and FIG. 14 (t = 1.5 mm).

The aberration states of the fourth embodiment are as shown in FIG. 15 (t = 0.7 mm), FIG. 16 (t = 1.1 mm), and FIG. 17 (t = 1.5 mm).

The aberration conditions of the fifth embodiment are as shown in FIG. 18 (t = 0.9 mm), FIG. 19 (t = 1.2 mm), and FIG. 20 (t = 1.5 mm).

[Effects of the Invention] The microscope objective lens of the present invention has a lens configuration as described above, and has a high magnification and a high NA by moving the second lens unit in the optical axis direction. Various aberrations are satisfactorily corrected.

[Brief description of the drawings]

1 to 5 show Embodiments 1 to 5 of the present invention, respectively.
6 to 8 are aberration curve diagrams of the first embodiment,
9 to 11 are aberration curve diagrams of the second embodiment, FIGS. 12 to 14 are aberration curve diagrams of the third embodiment, FIGS. 15 to 17 are aberration curve diagrams of the fourth embodiment, and FIGS. FIG. 20 to FIG. 20 are aberration curve diagrams of the fifth embodiment.

Claims (2)

(57) [Claims] 1. A first group having a positive refractive power, comprising a positive meniscus lens having a convex surface facing the image side, wherein an emitted light beam is divergent light;
A second group of positive refractive power having at least one joining surface of negative refractive power and movable on the optical axis; and a third group of negative refractive power. When the transparent parallel plane plate disposed between the first group and the second group is moved, the second group is moved in the optical axis direction so that the distance between the first group and the second group becomes shorter. A microscope objective lens characterized in that the second group is moved in the optical axis direction so that the distance between the first group and the second group becomes longer when the plane-parallel plate becomes thinner. 2. The radius of curvature of the most image side surface of the first lens unit is
r _i, when the focal length of the whole system is f, the microscope objective lens according to claim to satisfy the following condition (1). | r _i | / f> 50 (when r _i <0) r _i /f>6.5 (when r _i > 0)