JP2011013661A - Zoom lens for microscope, and the microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens for a microscope, which achieves a high zoom ratio and a size reduction and has high imaging performance, and to provide a microscope that has the zoom lens.SOLUTION: The zoom lens for the microscope includes, in order from an object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with negative refractive power. The fourth lens group G4 consists of, in order from the object side, an eleventh lens group G4a with positive refractive power, a twelfth lens group G4b with negative refractive power, and a thirteenth lens group G4c with positive refractive power. In varying power from a low varying power end to a high varying power end, the second and third lens groups G2 and G3 move in the direction of an optical axis. The zoom lens satisfies predetermined conditions.

Description

  The present invention relates to a microscope zoom lens and a microscope having the same.

  Conventionally, a microscope zoom lens used in a microscope and a microscope having a microscope zoom lens have been proposed (for example, Patent Documents 1 and 2).

JP-A-6-18784 Japanese Patent Laid-Open No. 7-56087

  In recent years, in a microscope, a stereomicroscope, a digital microscope, and the like, a microscope having a small and compact microscope zoom lens and a zoom lens while having a high zoom ratio is desired. The higher the zoom ratio, the larger the total length, and it was difficult to satisfy both the high zoom ratio and downsizing at the same time.

  The present invention has been made in view of the above problems, and provides a zoom lens for a microscope that achieves a high zoom ratio and miniaturization and has high imaging performance, and a microscope having the zoom lens.

In order to solve the above-described problems, the present invention provides, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power. And a fourth lens group having a negative refractive power. The fourth lens group includes, in order from the object side, an eleventh lens group having a positive refractive power, and a twelfth lens having a negative refractive power. And a thirteenth lens group having a positive refractive power, and the second lens group and the third lens group are arranged along the optical axis direction upon zooming from the low magnification end state to the high magnification end state. A zoom lens for a microscope is provided that moves and satisfies the following conditions.
| F1 / f2 |> 4
Z ^0.5 <V2 <Z ^0.6
(D1T-d1w) / fw <2.3
f ₁₁ / f ₁₃ > 3
However, f1 is the focal length of the first lens group, f2 is the focal length of the second lens group, Z is the zoom ratio of the zoom lens for microscope, V2 is the magnification of the second lens group, and d1T is the high magnification end. The distance between the most image side lens surface of the first lens group and the most object side lens surface of the second lens group in the state, d1w is the most image side lens surface of the first lens group in the low magnification end state Between the second lens group and the lens surface closest to the object side, fw is the focal length of the zoom lens at the low magnification end state, f ₁₁ is the focal length of the eleventh lens group, and f ₁₃ is the thirteenth position. This is the focal length of the lens group.

  The present invention also provides a microscope comprising the zoom lens for a microscope.

  According to the present invention, it is possible to provide a zoom lens for a microscope that achieves a high zoom ratio and miniaturization and has high imaging performance, and a microscope having the same.

It is a figure which shows the basic composition and zoom movement locus | trajectory of the zoom lens for microscopes concerning embodiment of this invention. It is a figure which shows the lens structure of the zoom lens for microscopes concerning 1st Example of this application. FIG. 4 is various aberration diagrams of the microscope zoom lens according to the first example in an infinitely focused state, where (a) is a low magnification end state, (b) is an intermediate focal length state, and (c) is a high magnification end state. Various aberration diagrams are shown. It is a figure which shows the lens structure of the zoom lens for microscopes concerning 2nd Example of this application. FIG. 6 is a diagram illustrating various aberrations of the microscope zoom lens according to the second example in an infinitely focused state, where (a) is a low magnification end state, (b) is an intermediate focal length state, and (c) is a high magnification end state. Various aberration diagrams are shown. It is a figure which shows the lens structure of the zoom lens for microscopes concerning 3rd Example of this application. FIG. 6 is a diagram showing various aberrations of the microscope zoom lens according to Example 3 in an infinitely focused state, where (a) is a low magnification end state, (b) is an intermediate focal length state, and (c) is a high magnification end state. Various aberration diagrams are shown. It is a figure which shows the lens structure of an example of the objective lens used in combination with the zoom lens for microscopes concerning embodiment of this invention. It is a figure which shows the optical system of the microscope provided with the zoom lens for microscopes concerning embodiment of this invention.

  Hereinafter, a zoom lens for a microscope according to an embodiment of the present invention will be described. The following embodiments are only for facilitating understanding of the invention, and exclude additions and substitutions that can be performed by those skilled in the art without departing from the technical idea of the present invention. Is not intended.

The zoom lens for a microscope according to this embodiment includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power. And a fourth lens group having a negative refractive power. The fourth lens group includes, in order from the object side, an eleventh lens group having a positive refractive power, and a twelfth lens having a negative refractive power. And a thirteenth lens group having a positive refractive power, and the second lens group and the third lens group are arranged along the optical axis direction upon zooming from the low magnification end state to the high magnification end state. The following conditional expressions (1), (2), (3), and (4) are satisfied.
(1) | f1 / f2 |> 4
(2) Z ^0.5 <V2 <Z ^0.6
(3) (d1T-d1w) / fw <2.3
(4) f ₁₁ / f ₁₃ > 3
However, f1 is the focal length of the first lens group, f2 is the focal length of the second lens group, Z is the zoom ratio of the zoom lens for microscope, V2 is the magnification of the second lens group, and d1T is the high magnification end. The distance between the most image side lens surface of the first lens group and the most object side lens surface of the second lens group in the state, d1w is the most image side lens surface of the first lens group in the low magnification end state Between the second lens group and the lens surface closest to the object side, fw is the focal length of the zoom lens at the low magnification end state, f ₁₁ is the focal length of the eleventh lens group, and f ₁₃ is the thirteenth position. The focal length of each lens group is shown.

  With this configuration, the zoom lens for a microscope can achieve downsizing and achieve high imaging performance by shortening the back focus while securing a high zoom ratio of 15 times or more.

  In addition, since the zoom lens for the present microscope has a positive and negative triplet configuration in the fourth lens group, the back focus can be shortened and the overall length can be reduced compared to the case where the most image side of the fourth lens group is configured as a negative lens. Further, it is possible to satisfactorily correct lateral chromatic aberration and the like. In the configuration where the fourth lens group has a negative lens on the most image side, the exit pupil position is too close to the image plane. A positive lens (a thirteenth lens group) is arranged on the image side of the (group) to keep the exit pupil position away from the image plane.

  Conditional expression (1) defines an appropriate range of the focal length ratio between the first lens group and the second lens group. By satisfying conditional expression (1), a zoom ratio of 15 times or higher can be secured, and a zoom lens for a microscope having high imaging performance can be achieved.

  In a state where the lower limit value of conditional expression (1) is not reached, the distance between the first lens group and the second lens group in the optical axis direction is narrowed and the first lens group and the second lens group interfere with each other. The zoom ratio cannot be reduced, and as a result, a high zoom ratio cannot be obtained. In addition, if the zoom ratio is increased by increasing the refractive power of the third lens group and the fourth lens group in a state where the lower limit value of conditional expression (1) is not reached, a high zoom ratio of 15 times or more is obtained. Absent.

  Conditional expression (2) defines an appropriate range of the magnification of the second lens group. Note that the “magnification ratio” indicates the “burden amount” with respect to the “zoom ratio” of the microscope zoom lens. By satisfying conditional expression (2), it is possible to achieve a microscope zoom lens having high imaging performance while maintaining the overall length of the microscope zoom lens compact.

  Giving the second lens unit having a negative refractive power a large refractive power and increasing the zoom ratio is advantageous for downsizing the zoom lens for a microscope. However, if the zoom ratio of the second lens group is too large, it is difficult to correct aberrations during zooming.

  When the upper limit of conditional expression (2) is exceeded, the refractive power of the second lens group increases and the “burden amount” of the second lens group increases, which is advantageous for downsizing the zoom lens for a microscope. . However, in this case, an increase in distortion, an increase in astigmatism due to the deterioration of Petzval sum, an increase in coma at the time of zooming, especially an increase in fluctuation of the lower coma, etc. occur in the low magnification end state. Increases spherical aberration and the like.

  Further, when the lower limit of conditional expression (2) is not reached, the zoom ratio of the third lens group increases when trying to obtain a high zoom ratio, and the amount of movement of the third lens group during zooming increases. As a result, it is necessary to increase the distance between the second lens group and the third lens group in order to prevent interference between the second lens group and the third lens group, and the overall length of the zoom lens for the microscope is increased. Cannot be achieved.

  Conditional expression (3) indicates that an appropriate distance between the lens surface closest to the image side of the first lens unit and the lens surface closest to the object side of the second lens unit is appropriate for zooming from the low magnification end state to the high magnification end state. Defines the range. By satisfying conditional expression (3), it is possible to achieve a zoom lens for a microscope having high imaging performance while maintaining the overall length of the zoom lens for microscope compact.

  When exceeding the upper limit value of the conditional expression (3), when changing the magnification from the low magnification end state to the high magnification end state, the most image side lens surface of the first lens group and the most object side lens surface of the second lens group Therefore, it becomes difficult to reduce the size. In addition, the negative refractive power of the second lens group increases, leading to an increase in distortion and astigmatism.

  In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (3) to 2.0.

  Conditional expression (4) defines an appropriate range for the refractive power of the eleventh lens group and the thirteenth lens group in the fourth lens group. By satisfying conditional expression (4), it is possible to achieve a zoom lens for a microscope having high imaging performance while shortening the back focus and keeping the overall length compact.

  Usually, in the positive / negative triplet configuration, the focal lengths of the object-side positive lens unit and the image-side positive lens unit are substantially equal. However, the zoom lens for this microscope increases the refractive power of the thirteenth lens unit having positive refractive power on the image side, thereby shortening the back focus and reducing the total length. In addition, this microscope zoom lens can satisfactorily correct various aberrations such as spherical aberration by reducing the refractive power of the eleventh lens group having positive refractive power on the object side of the fourth lens group.

  If the lower limit value of conditional expression (4) is not reached, the back focus becomes too short, and there is a possibility that a movable image plane range cannot be secured during optical adjustment after assembling the lens.

In addition, it is desirable that the zoom lens for the microscope satisfies the following conditional expression (5).
(5) 0.04 <f ₁₂ /f4<0.18
However, f ₁₂ is the focal length of the second lens subunit, f4 denotes a focal length of the fourth lens group.

  Conditional expression (5) defines an appropriate range of the refractive power of the twelfth lens group having a negative refractive power in the fourth lens group. By satisfying conditional expression (5), the exit pupil position can be set sufficiently far from the image plane, and a microscope zoom lens having high imaging performance can be achieved.

  In the zoom lens for this microscope, conditional expression (4) is satisfied, and the total refractive power of the thirteenth lens unit having positive refracting power on the image side of the fourth lens unit is increased to shorten the back focus and reduce the total length. However, when the refractive power of the thirteenth lens group is increased, the exit pupil position approaches the imaging position.

  Here, in consideration of the case where an image pickup device such as a CCD is arranged on the image plane, it is necessary to set the exit pupil position as far as possible from the image formation position and design the light beam to enter the device substantially perpendicularly. An image pickup device such as a CCD has an element structure, for example, a color filter or a light receiving portion located behind a light shielding portion of a charge transfer path. This is because there is a problem that peripheral light amount change (shading) occurs. Therefore, in order to move the exit pupil position sufficiently away from the image plane, it is necessary to define an appropriate range of the refractive power of the twelfth lens group having a negative refractive power in the fourth lens group.

  When the upper limit value of conditional expression (5) is exceeded, the back focus becomes too short, and there is a possibility that a movable image plane range cannot be secured during optical adjustment after assembling the lens.

  When the lower limit value of conditional expression (5) is not reached, the exit pupil position becomes too close to the image plane, and when an imaging device such as a CCD is arranged on the image plane, it becomes difficult to obtain high imaging performance. Further, the refracting power of the twelfth lens unit having the negative refracting power of the fourth lens unit becomes too large, and astigmatism and the like are deteriorated.

Further, it is desirable that the zoom lens for the microscope satisfies the following conditional expression (6).
(6) FNO> 12.0
However, FNO shows the F number of a low magnification end state.

  Conditional expression (6) defines an appropriate range of the F number in the low magnification end state of the microscope zoom lens. By satisfying conditional expression (6), a high zoom ratio can be achieved with a simple lens configuration.

  In the zoom lens for the microscope, the second lens unit moves only from the object side to the image side, and the third lens unit moves only from the image side to the object side during zooming from the low magnification end state to the high magnification end state. It is preferable to move. With such a configuration, the moving mechanism of the lens unit at the time of zooming can be simplified.

  In addition, the microscope of the present application includes the microscope zoom lens having the above-described configuration. Thereby, a small-sized microscope having a high zoom ratio and high imaging performance can be realized.

  Hereinafter, numerical examples of the microscope zoom lens according to the present embodiment will be described with reference to the accompanying drawings.

  FIGS. 1A and 1B are views showing a basic configuration and zoom movement locus of a microscope zoom lens common to each numerical example.

  The zoom lens for a microscope according to each example includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens having a positive refractive power. The lens group G3 includes a fourth lens group G4 having a negative refractive power.

  The zoom lens for the microscope has the air between the second lens group G2 and the third lens group G3 when zooming from the low magnification end state (FIG. 1 (a)) to the high magnification end state (FIG. 1 (b)). The second lens group G2 moves only from the object side to the image side, and the third lens group G3 moves only from the image side to the object side so that the interval decreases. In this way, the zoom lens for a microscope can take a locus that the second lens group and the third lens group move only in one direction and return in the middle when zooming from the low magnification end state to the high magnification end state. Absent.

(First embodiment)
FIG. 2 is a diagram illustrating a lens configuration of the zoom lens for a microscope according to the first example.

  The zoom lens for a microscope according to the first example includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a first lens group having a positive refractive power. The third lens group G3 includes a third lens group G3 and a fourth lens group G4 having negative refractive power.

  The first lens group G1 includes, in order from the object side, a cemented positive lens composed of a negative meniscus lens L1 having a convex surface facing the object side and a biconvex positive lens L2, and a positive meniscus having a convex surface facing the object side. It is composed of a lens L3.

  The second lens group G2 includes, in order from the object side, a cemented negative lens formed by cementing a biconcave negative lens L4, a biconcave negative lens L5, and a positive meniscus lens L6 having a convex surface facing the object side. Has been.

  The third lens group G3 includes, in order from the object side, a biconvex positive lens L7, and a cemented positive lens formed by cementing a negative meniscus lens L8 having a convex surface toward the object side and a biconvex positive lens L9. Has been.

  The fourth lens group G4 includes, in order from the object side, an eleventh lens group G4a having a positive refractive power, a twelfth lens group G4b having a negative refractive power, and a thirteenth lens group G4c having a positive refractive power. It is configured. The eleventh lens group G4a includes, in order from the object side, a cemented positive lens formed by cementing a positive meniscus lens L10 having a convex surface toward the object side and a negative meniscus lens L11 having a convex surface toward the object side. The group G4b includes, in order from the object side, a cemented negative lens formed by cementing a positive meniscus lens L12 having a convex surface toward the image side and a biconcave negative lens L13. The thirteenth lens group G4c is disposed on the image side. It is composed of a positive meniscus lens L14 having a convex surface.

  Table 1 below shows specification values of the zoom lens for a microscope according to the first example.

  In (lens data), the surface number is the order of the lens surfaces counted from the object side, r is the radius of curvature of each lens surface, d is the surface spacing of the lens surfaces, and nd is the refraction with respect to the d-line (wavelength λ = 587.56 nm). The ratio, νd, indicates the Abbe number for the d-line (wavelength λ = 587.56 nm). The object plane indicates the object plane, the variable plane indicates the variable plane spacing, and the image plane indicates the image plane I. Note that “∞” of the radius of curvature r indicates a plane.

  In (various data), f is the focal length, FNO is the F number, Y is the image height, NA is the numerical aperture on the object side, Bf is the back focus, and di (i: integer) is the variable surface spacing value at the surface number i. Respectively. (Conditional expression corresponding value) indicates the corresponding value of each conditional expression. Here, β represents the total magnification with the microscope zoom lens of the example when the objective lens shown in Table 4 described later is used.

  It should be noted that “mm” is generally used as a unit of focal length f, radius of curvature r, and other lengths listed in all the following specification values. However, the optical system is not limited to this because the same optical performance can be obtained even when proportionally enlarged or reduced. Further, the unit is not limited to “mm”, and other appropriate units may be used. Further, these symbols are the same in the other embodiments described below, and the description thereof is omitted.

(Table 1) First Example (Lens Data)
Surface number r d nd νd
Object ∞
1) 91.440 2.0 1.804540 39.61
2) 40.569 3.7 1.497820 82.52
3) -87.854 0.2
4) 35.614 2.5 1.497820 82.52
5) 59.009 Variable
6) -72.954 1.5 1.840421 43.35
7) 29.989 2.5
8) -90.563 1.0 1.670249 57.53
9) 15.187 2.2 1.805182 25.41
10) 71.267 Variable
11) 60.309 2.0 1.593189 67.87
12) -87.177 0.2
13) 36.370 1.5 1.803840 33.89
14) 19.588 2.6 1.497820 82.52
15) -289.370 Variable
16) 12.346 3.0 1.487490 70.41
17) 321.500 1.5 1.748099 52.30
18) 21.567 18.697
19) -69.302 2.5 1.620040 36.27
20) -5.188 1.5 1.804109 46.55
21) 10.474 16.811
22) -431.561 2.7 1.516800 64.10
23) -15.193
Image plane ∞

(Various data)
Zoom ratio (Z) 15.0

Low magnification end state Medium focal length state High magnification end state β 0.7 2.7 10.5
f 35 135 525
FNO 12.45 15.64 25.01
Y 4.45 4.45 4.45
NA 0.0281 0.086 0.21
Bf 19.46 19.46 19.46
d5 3.46869 31.14411 43.83989
d10 87.94900 44.98888 5.58363
d15 3.08730 18.31198 45.02145

(Zoom lens group data)
Group start surface f
1 1 79.0
2 6 -19.5
3 11 40.0
4 16 -163.9
11 16 105.2
12 19 -7.96
13 22 30.4

(Values for conditional expressions)
(1): | f1 / f2 | = 4.051
^{(2): Z 0.5 = 3.873} <V2 = 4.880 <Z 0.6 = 5.078
(3): (d1T-d1w) /fw=1.154
(4): f ₁₁ / f ₁₃ = 3.461
_{(5): f 12 / f4} = 0.0486
(6): FNO = 12.45

  3A and 3B are graphs showing various aberrations of the microscope zoom lens according to the first example in an infinitely focused state, where FIG. 3A is a low magnification end state, FIG. 3B is an intermediate focal length state, and FIG. 3C is a high magnification. Each aberration diagram in the end state is shown. When actually used as a microscope, it is used in combination with, for example, an objective lens shown in Table 3 to be described later. In each example of the present application, in order to show the performance of the microscope zoom lens well, the microscope zoom lens is used. Aberration diagrams only (ie ray tracing from infinity) are shown.

  In each aberration diagram, FNO represents an F number, and Y represents an image height. D is the d-line (λ = 587.56 nm), C is the C-line (λ = 656.27 nm), F is the F-line (λ = 486.13 nm), and g is the g-line (λ = 435.84 nm). An aberration curve is shown.

  In the astigmatism diagram, the solid line represents the sagittal image plane, and the dotted line represents the meridional image plane.

  In addition, in the various aberration diagrams of each example shown below, the same reference numerals as those in this example are used.

  From the various aberration diagrams, the zoom lens for the microscope according to the first example corrects various aberrations well in each of the low magnification end state, the intermediate focal length state, and the high magnification end state, and has excellent imaging performance. It can be seen that It can also be seen that the overall magnification in the low magnification end state is 0.7 times while having a high zoom ratio of 15 times, and a wide real field of view can be secured.

(Second embodiment)
FIG. 4 is a diagram illustrating a lens configuration of a zoom lens for a microscope according to the second example.

  The zoom lens for microscope according to the second example includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a first lens group having a positive refractive power. The third lens group G3 includes a third lens group G3 and a fourth lens group G4 having negative refractive power.

  The first lens group G1 includes, in order from the object side, a cemented positive lens composed of a negative meniscus lens L1 having a convex surface facing the object side and a biconvex positive lens L2, and a positive meniscus having a convex surface facing the object side. It is composed of a lens L3.

  The second lens group G2 includes, in order from the object side, a biconcave negative lens L4, and a cemented negative lens formed by cementing a biconcave negative lens L5 and a biconvex positive lens L6.

  The third lens group G3 includes, in order from the object side, a biconvex positive lens L7, and a cemented positive lens formed by cementing a negative meniscus lens L8 having a convex surface toward the object side and a biconvex positive lens L9. Has been.

  The fourth lens group G4 includes, in order from the object side, an eleventh lens group G4a having a positive refractive power, a twelfth lens group G4b having a negative refractive power, and a thirteenth lens group G4c having a positive refractive power. It is configured. The eleventh lens group G4a is composed of, in order from the object side, a cemented positive lens of a positive meniscus lens L10 having a convex surface facing the object side and a negative meniscus lens L11 having a convex surface facing the object side, and the twelfth lens group G4b is In order from the object side, the positive lens is composed of a cemented negative lens composed of a positive meniscus lens L12 having a convex surface directed toward the image side and a biconcave negative lens L13. The thirteenth lens group G4c includes a biconvex positive lens. L14.

  Table 2 below shows specification values of the zoom lens for a microscope according to the second example.

(Table 2) Second Example (Lens Data)
Surface number r d nd νd
Object ∞
1) 90.351 2.0 1.804400 39.58
2) 41.039 3.7 1.497820 82.52
3) -90.178 0.2
4) 33.918 2.5 1.497820 82.52
5) 50.405 variable
6) -45.414 1.5 1.834810 42.72
7) 26.079 2.5
8) -36.455 1.0 1.640000 60.09
9) 19.671 2.2 1.805180 25.43
10) -211.695 variable
11) 58.440 2.0 1.603000 65.47
12) -52.340 0.2
13) 47.276 1.5 1.804400 39.58
14) 18.782 2.6 1.497820 82.52
15) -95.853 variable
16) 14.053 3.0 1.487490 70.41
17) 9704.731 1.5 1.755000 52.31
18) 23.379 15.3
19) -62.097 2.5 1.620040 36.26
20) -15.822 1.5 1.804000 46.58
21) 15.187 16.2
22) 29.272 2.7 1.620040 36.26
23) -172.333
Image plane ∞

(Various data)
Zoom ratio (Z) 18.0

Low magnification end state Medium focal length state High magnification end state β 0.4944 2.1 8.9
f 24.72 105 445
FNO 12.47 15.67 22.28
Y 4.45 4.45 4.45
NA 0.02 0.067 0.20
Bf 17.40 17.40 17.40
d5 6.47392 37.16909 50.51459
d10 87.50351 43.19337 5.41855
d15 4.86543 18.48040 42.90972

(Zoom lens group data)
Group start surface f
1 1 83.1
2 6 -17.8
3 11 36.2
4 16 -78.3
11 16 177.34
12 19 -13.1
13 22 40.55

(Values for conditional expressions)
(1): | f1 / f2 | = 4.669
(2): Z ^0.5 = 4.243 <V2 = 5.398 <Z ^0.6 = 5.665
(3): (d1T-d1w) / fw = 1.782
(4): f ₁₁ / f ₁₃ = 4.373
(5): f ₁₂ /f4=0.167
(6): FNO = 12.47

  FIGS. 5A and 5B are graphs showing various aberrations in the infinitely focused state of the microscope zoom lens according to the second example. FIG. 5A is a low magnification end state, FIG. 5B is an intermediate focal length state, and FIG. Each aberration diagram in the end state is shown.

  From the various aberration diagrams, the microscope zoom lens according to the second example corrects various aberrations well in each of the low magnification end state, the intermediate focal length state, and the high magnification end state, and has excellent imaging performance. It can be seen that It can also be seen that the overall magnification in the low magnification end state is 0.5 times or less while having a high zoom ratio of 18 times, and a wide real field of view can be secured.

(Third embodiment)
FIG. 6 is a diagram illustrating a lens configuration of a microscope zoom lens according to the third example.

  The zoom lens for microscope according to the third example, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a first lens group having a positive refractive power. The third lens group G3 includes a third lens group G3 and a fourth lens group G4 having negative refractive power.

  The first lens group G1 includes, in order from the object side, a cemented positive lens composed of a negative meniscus lens L1 having a convex surface facing the object side and a biconvex positive lens L2, and a positive meniscus having a convex surface facing the object side. It is composed of a lens L3.

  The second lens group G2 includes, in order from the object side, a cemented negative lens formed by cementing a biconcave negative lens L4, a biconcave negative lens L5, and a positive meniscus lens L6 having a convex surface facing the object side. Has been.

  The third lens group G3 includes, in order from the object side, a biconvex positive lens L7, and a cemented positive lens of a negative meniscus lens L8 having a convex surface facing the object side and a biconvex positive lens L9. .

  The fourth lens group G4 includes, in order from the object side, an eleventh lens group G4a having a positive refractive power, a twelfth lens group G4b having a negative refractive power, and a thirteenth lens group G4c having a positive refractive power. It is configured. The eleventh lens group G4a is composed of, in order from the object side, a cemented positive lens of a biconvex positive lens L10 and a biconcave negative lens L11, and the twelfth lens group G4b is sequentially from the object side to the image side. And a positive negative meniscus lens L12 having a convex surface and a negative biconcave lens L13. The thirteenth lens group G4c includes a positive biconvex lens L14.

  Table 3 below shows data values of the microscope zoom lens according to the third example.

(Table 3) Third Example (Lens Data)
Surface number r d nd νd
Object ∞
1) 90.543 2.0 1.804400 39.58
2) 41.009 3.7 1.497820 82.52
3) -90.841 0.2
4) 34.250 2.5 1.497820 82.52
5) 49.221 Variable
6) -32.804 1.5 1.834810 42.72
7) 42.827 2.5
8) -41.814 1.0 1.640000 60.09
9) 18.098 2.2 1.805180 25.43
10) 485.631 Variable
11) 58.151 2.0 1.603000 65.47
12) -52.640 0.2
13) 44.626 1.5 1.804400 39.58
14) 18.841 2.6 1.497820 82.52
15) -146.156 Variable
16) 13.675 3.0 1.487490 70.41
17) -620.659 1.5 1.755000 52.31
18) 23.858 15.3
19) -64.442 2.5 1.620040 36.26
20) -23.810 1.5 1.804000 46.58
21) 13.218 16.2
22) 38.733 2.7 1.667550 41.96
23) -67.656
Image plane ∞

(Various data)
Zoom ratio (Z) 20.0

Low magnification end state Intermediate focal length state High magnification end state β 0.445 2.0 8.9
f 22.25 100 445
FNO 12.39 15.65 22.26
Y 4.45 4.45 4.45
NA 0.017 0.064 0.20
Bf 20.46 20.46 20.46
d5 3.29148 37.71572 52.22335
d10 93.96436 45.45442 5.20027
d15 3.02439 17.11009 42.85661

(Zoom lens group data)
Group start surface f
1 1 86.2
2 6 -18.5
3 11 37.0
4 16 -110.0
11 16 146.4
12 19 -12.52
13 22 37.27

(Values for conditional expressions)
(1): | f1 / f2 | = 4.660
(2): Z ^0.5 = 4.472 <V2 = 5.700 <Z ^0.6 = 6.034
(3): (d1T-d1w) /fw=2.199
(4): f ₁₁ / f ₁₃ = 3.928
_{(5): f 12 / f4} = 0.114
(6): FNO = 12.39

  FIGS. 7A and 7B are graphs showing various aberrations of the microscope zoom lens according to the third example in an infinitely focused state, where FIG. 7A is a low magnification end state, FIG. 7B is an intermediate focal length state, and FIG. Each aberration diagram in the end state is shown.

  From the various aberration diagrams, the zoom lens for the microscope according to the third example corrects various aberrations well in each of the low magnification end state, the intermediate focal length state, and the high magnification end state, and has excellent imaging performance. It can be seen that It can also be seen that the overall magnification in the low magnification end state is 0.5 times or less while having a high zoom ratio of 20 times, and a wide real field of view can be secured.

  The zoom lens for a microscope according to the present embodiment can be used in combination with, for example, an objective lens having specification values shown in FIG. 8 and Table 4 below.

  FIG. 8 is a diagram showing the lens configuration of this objective lens.

(Table 4)
(Lens data)
Surface number r d nd νd
Object ∞
1) -13.592 1.370 1.516800 64.10
2) -18.736 0.042
3) 28.447 2.271 1.803840 33.89
4) 125.000 0.988 1.696800 55.53
5) 28.256 2.463
6) -82.884 0.891 1.749500 35.33
7) 36.282 4.567 1.497820 82.52
8) -28.864 0.111
9) 123.608 0.950 1.517420 52.31
10) 46.000 4.510 1.497820 82.52
11) -28.210
Image plane ∞

(Various data)
Focal length = 50
Maximum NA = 0.2
Working distance = 29.7

  FIG. 9 is a diagram illustrating an optical system of a microscope including the microscope zoom lens according to the embodiment.

  The light from the object 1 is converted into parallel light by the objective lens 2, and then zoomed by the zoom lens 3 and simultaneously forms an image of the object on the image plane I. Then, for example, an observer observes this image through an eyepiece (not shown), or an imaging means such as a CCD is placed on the image plane and observed through a monitor. When an imaging means such as a CCD is arranged on the image plane, a relatively large object such as a metal specimen or a mechanical part (for example, a gear) can be observed well with a wide field of view.

G1: first lens group G2: second lens group G3: third lens group G4: fourth lens group G4a: eleventh lens group G4b: twelfth lens group G4c: thirteenth lens group I: image plane 1: object 2 : Objective lens 3: Zoom lens

Claims (5)

In order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens having a negative refractive power And having a group
The fourth lens group includes, in order from the object side, an eleventh lens group having a positive refractive power, a twelfth lens group having a negative refractive power, and a thirteenth lens group having a positive refractive power,
Upon zooming from the low magnification end state to the high magnification end state, the second lens group and the third lens group move along the optical axis direction,
A zoom lens for a microscope characterized by satisfying the following conditions.
| F1 / f2 |> 4
Z ^0.5 <V2 <Z ^0.6
(D1T-d1w) / fw <2.3
f ₁₁ / f ₁₃ > 3
However,
f1: Focal length of the first lens group f2: Focal length of the second lens group Z: Zoom ratio of the zoom lens for microscope V2: Variable magnification of the second lens group d1T: The first lens in the high magnification end state The distance between the lens surface closest to the image side of the lens group and the lens surface closest to the object side of the second lens unit; d1w: the lens surface closest to the image side of the first lens unit and the second lens unit in the low magnification end state; Distance from the lens surface closest to the object side fw: Focal length of the zoom lens at a low magnification end state f ₁₁ : Focal length of the eleventh lens group f ₁₃ : Focal length of the thirteenth lens group The zoom lens for a microscope according to claim 1, wherein the following condition is satisfied.
0.04 <f ₁₂ /f4<0.18
However,
f _12: the focal length of the second lens subunit f4: the focal length of the fourth lens group   In zooming from the low magnification end state to the high magnification end state, the second lens group moves only from the object side to the image side, and the third lens group moves only from the image side to the object side. The zoom lens for a microscope according to claim 1 or 2. The zoom lens for a microscope according to any one of claims 1 to 3, wherein the following condition is satisfied.
FNO> 12.0
However,
FNO: F-number in the low magnification end state   A microscope comprising: an objective lens; and the microscope zoom lens according to claim 1.

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