JPH0618784A - Large aperture/high magnification zoom microscope - Google Patents

Abstract

PURPOSE:To obtain a large aperture, high NA, high magnification and a high zoom ratio, and also, a long operating distance by using a zoom tube lens of a high zoom ratio. CONSTITUTION:A zoom tube lens is constituted of lens groups of four groups consisting of a first group which has positive refracting power and consists of two pieces of positive lenses (an average value nu1 of Abbe number) and one piece of negative lens, a second group which has negative refracting power and consists of two groups of negative lenses, a third group which has negative refracting power, and a fourth group which has positive refracting power and consists of the first half part (an average value nuIV of Abbe number of a positive lens) having positive refracting power and the latter half part having negative refracting power in order from an object side. In the course of zooming, a first group is fixed, a second group moves, a third group executes a cam motion, and a fourth group is fixed. When a focal distance of the telephone end, and the image diameter are denoted as fT and phi, respectively, this microscope has conditions (1) 60phi>fT>30phi, (2) 95.2>=nuI>6.5, and (3) 95.2>=nuIV>65.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens and a tube lens of an infinity correction type microscope, and relates to a large-diameter, high-magnification zoom microscope in which the tube lens is zoomed.

[0002]

2. Description of the Related Art Conventionally, zoom microscopes have been known. These are, for example, Japanese Examined Patent Publication Nos. 41-16432 and 43-1.
No. 2714, No. 43-18355, No. 43-1835.
No. 6, No. 44-2916, No. 58-14650, No. 60-14327 and so on are so-called stereo zoom microscopes. However, all of them have a low magnification and a small NA. Taking the above Japanese Examined Patent Publication No. 43-18355 as an example, the magnification is 0.7 to 4.0 times,
A is 0.02-0.072.

On the other hand, there is Japanese Patent Publication No. 2-54925 in which a tube lens is zoomed, but this has an zoom ratio of only 2.0 and is an invention of only a tube lens, and should be used in combination with this. Since the invention of the objective lens has not been made, various problems occur as will be described later.

[0004]

Originally, a microscope is a tool for magnifying and observing a minute object that cannot be observed by the naked eye, and it has a magnification of 10 times, several tens of times, and sometimes 100 times. Front-to-rear magnification and large diameter suitable for it, namely high N
A and the aberration correction suitable for it are required.

However, the above-described conventional stereo zoom microscope has a magnification of 0.7 to 4.0 and an NA of 0.02 to 0.072, which is far from the above target, as described above.

On the other hand, in the above-mentioned zoom tube lens having a zoom ratio of 2.0, if the objective lens having a high magnification and a large aperture is used, a microscope objective can be achieved at the wide end of the zoom tube lens, but When zoomed up to the edge, the NA remains the same even though the magnification is doubled, and the NA that is appropriate for that magnification cannot be taken and the resolution does not increase. Further, the lateral aberration is increased by 2 times and the longitudinal aberration is increased by 4 times, so that a good image cannot be expected due to the combination of both, and on the other hand, the zoom ratio is only 2.0 and the effect of zooming is small.

The present invention was created in view of the problems of the prior art as described above, and it is an object of the present invention to realize a zoom microscope having a large aperture, high NA, high magnification, high zoom ratio and a long working distance. To aim.

[0008]

In order to achieve the above object, the present invention adopts a microscope of infinity correction type, and a first invention characterized by a zoom tube lens having a high zoom ratio, and this zoom. Disclosed are second and third inventions which are combinations of a tube lens and two kinds of objective lenses suitable for the tube lens.

(First Invention) According to the present invention, the first group has a positive refractive power in order from the object side, and includes two positive lenses and one negative lens.
The second lens group consists of two lenses and is fixed during zooming. The second lens group has negative refractive power. The second lens group includes two negative lens elements including a cemented lens. It has a negative refracting power and acts as a compensator with a cam motion during zooming to keep the image position constant.
The group has a positive refractive power, has a teletype configuration, and comprises a front half having a positive refractive power and a rear half having a negative refractive power, which is fixed during zooming and has a focal length at the tele end of f _T , If the average value of the Abbe numbers of the two positive lenses of the first group is ν _I , the average value of the Abbe numbers of only the positive lenses of the front half of the fourth group is ν _IV , and the image diameter is φ, then (1 ) 60φ> f _T > 30φ (2) 95.2 ≧ ν _I > 65 (3) 95.2 ≧ ν _IV > 65 Zoom tube for infinity correction type microscope composed of 4 groups having the condition Characterized by a lens.

(Second Invention) The present invention is composed of three positive lens groups including cemented lenses in order from the object side, and a cemented negative lens, and the Abbe numbers of three positive lenses in the three groups from the object side. Let ν _P1 , ν _P2 , and ν _P3 , respectively, and let the Abbe number of the positive lens in the cemented negative lens be ν _P4 ,

(1) 92> (ν _P1 + ν _P2 + ν _P3 ) / 3> 80 (2) 28 <ν _P4 <42

It comprises a combination of a relatively low-magnification objective lens for a microscope of infinity correction type and the zoom tube lens according to the first aspect of the present invention. (Third Invention) According to the present invention, there is a meniscus positive single lens with a concave surface facing the object side at a position closest to the object side, and a cemented negative lens at a farthest position, and a positive lens of at least three groups sandwiched between them. When there is a group, the Abbe number of the positive meniscus lens is ν ₁ , the average Abbe number of the positive lens of the intermediate lens group is ν _A , and the Abbe number of the positive lens in the cemented negative lens is ν _L ,

(1) 30 <ν ₁ <50 (2) 95.2 ≧ ν _A > 80 (3) ν _L <30

It is composed of a combination of an objective lens having a relatively high magnification for an infinity correction type microscope having the following condition and the zoom tube lens of the first invention.

[0015]

The operation of each of the above inventions is as follows. (First Invention) Regarding Conditional Expression (1): This condition defines the focal length of the zoom tube lens. The focal length f _T at the tele end of the zoom tube lens of the present invention is longer than the focal length of the tube lens of a general infinity correction type microscope. In the infinity-corrected type, the ratio of the focal lengths of the tube lens and the objective lens is a magnification, so the focal length of the objective lens used in the present invention is relatively long. f _T
When is greater than or equal to the right side of the conditional expression, the focal length of the objective lens is long because the focal length of the tube lens is long, which makes it possible to lengthen the working distance of the objective lens. Since each of the distances is long, the angle of the oblique light beam becomes gentle, which is advantageous for correcting the aberration related to the oblique light beam. However, when f _T is greater than or equal to the left side, that is, when the focal lengths of the objective lens and the tube lens are both too large, the entire system becomes large, and the longitudinal aberrations such as spherical aberration and chromatic aberration that increase in proportion to the focal length. The directional aberration cannot be corrected. As described above, the fact that f _T is relatively long is one of the major reasons for the successful solution of the problem.

Concerning condition (2): In the zoom lens of high magnification, high NA, and high zoom ratio as in the present invention, the achromatic correction of the positive lens of the first group affects the entire apochromat, especially at the tele end. Remarkable in. That is, it is necessary to increase the Abbe number. In this case, the effect of apochromat correction cannot be obtained unless the average value ν _I is larger than the right side of the conditional expression. Examples 5 and 6 which will be described later are examples in which the average value ν _I is a value close to the right side, and the above explanation is proved by showing the limit of the worse. On the other hand, the effect of apochromat correction increases as the average value ν _I approaches the left side of the conditional expression. Examples 1 and 2 which will be described later are examples in which the average value ν _I is a value close to the left side, and the above description is proved by showing the limit of the better one.

Conditional expression (3): The fourth group adopts a teletype system in which the front group is positive and the rear group is negative in order to shorten the back focus, so that the apochromat correction becomes worse. . Therefore, for the correction, it is necessary to set the average value ν _IV of the Abbe number of only the positive lens in the front half of the fourth lens group to be larger than the right side of the conditional expression. Example 5 described below
And 6 are examples in which the average value ν _IV is set to a value close to the right side, and the above explanation is proved by showing the worse limit. On the other hand, the effect of apochromat correction increases as the average value ν _IV approaches the left side of the conditional expression. The values on the left side are the values when fluorite is used, and the best correction effect can be obtained if all are fluorite.

(Second Invention) Regarding Conditional Expression (1): Although the objective lens of the present invention has a magnification of 20 times at the telephoto end as in Example 1 described later, the working distance is actually 41 m. / M has been reached. Therefore, apochromat correction becomes the most important and difficult problem. Conditional expression (1) is provided for the above apochromat correction, and is an indispensable condition for the objective lens of the present invention to be established. It is shown that apochromat correction is possible by taking the average value of the Abbe number of the positive lens, which is the main power of this objective lens, and the right side of the conditional expression is the minimum condition, below that the apochromat correction is impossible. Is. The left side of the conditional expression is the upper limit, but the reason why we did not set it to 95, which is the limit of optical glass, is that the Abbe number ν _P1 of the positive lens on the object side is higher than the Abbe numbers ν _P2 and ν _P3 of other positive lenses. This is because lowering it is advantageous for apochromat correction. That is, it is desirable that chromatic aberration is generated by using glass having a slightly large chromatic dispersion for the positive lens on the object side, and the chromatic aberration is corrected by another lens system. In the examples described below, both ν _P2 and ν _P3 are 95.

Conditional Expression (2): When the objective lens of the present invention is viewed from the opposite direction, the back focus, that is, the working distance is increased by adopting the retrofocus type in which the positive lens group comes next to the cemented negative lens. It has the same composition. In such a case, chromatic aberration, especially chromatic aberration of magnification, cannot be corrected unless the cemented negative lens is achromatic. Therefore, chromatic aberration of magnification cannot be taken unless a positive lens in the cemented negative lens has a large chromatic aberration, that is, a glass type having a low Abbe number. That is, if the Abbe number ν _P4 of the positive lens in the cemented negative lens is made smaller than the right side of the conditional expression, the above effect can be obtained, but if it exceeds the left side, vertical chromatic aberration occurs too much this time and apochromat correction is impossible. Is becoming.

(Third Invention) Regarding Conditional Expression (1): Generally, in a high-power objective lens, a positive lens closest to the object is made of glass with large chromatic dispersion to cause chromatic aberration, and then the chromatic aberration is generated at the subsequent intermediate portion. It is known that the apochromat correction will be successful if is canceled. This invention is not an example. Specifically, if the Abbe number ν ₁ of the positive meniscus single lens is made smaller than the right side of the conditional expression, the above effect begins to appear, but if the left side, which is the limit value, is exceeded, it will no longer be possible to correct in the middle part, Chromatic aberration is worsened, or chromatic spherical aberration is worsened.

Regarding Conditional Expression (2): This condition defines the average value ν _A of the Abbe number of the positive lens of the intermediate lens group, which is the main force of the apochromat correction of the objective lens of the present invention. It has already been mentioned that apochromat correction works well when a glass having a large chromatic dispersion is used for the positive lens closest to the object in the high magnification objective lens, but the chromatic aberration generated there must be corrected by the intermediate lens group. If ν _A is made larger than the right side, the chromatic aberration generated by the conditional expression (1) can be corrected. In this case, the best result can be obtained with the left side, which is the value when fluorite is adopted.

Regarding Conditional Expression (3): This condition is a condition for correcting lateral chromatic aberration, and the occurrence of lateral chromatic aberration according to the conditional expression in (1) must be canceled by the positive lens in the cemented negative lens. However, the chromatic aberration of magnification cannot be corrected unless the Abbe number ν _L is smaller than the right side of the conditional expression.

[0023]

EXAMPLES Examples of each invention related to this application will be described below. Here, for convenience of description, specific examples of the zoom microscope of the second invention are disclosed as the first, third, and fifth embodiments, and the third embodiment is also disclosed.
By disclosing specific examples of the zoom microscope of the present invention as Embodiments 2, 4, and 6, the embodiments will be collectively referred to as Embodiments of the first invention.

(Embodiment 1) FIG. 1 is a diagram showing a lens configuration of a zoom microscope of Embodiment 1. As shown in FIG. The optical system of this zoom microscope has an objective lens composed of three positive lens groups including cemented lenses in order from the object side, and a cemented negative lens,
The first group has a positive refractive power in order from the object side, and the positive lens 2
Negative lens 2 including a cemented lens and a second lens unit having a negative refracting power and fixed during zooming.
Consists of a group, which moves during zooming to form the main force of zooming, the third group has a negative refracting power, and acts as a compensator to make a cam motion during zooming to make the image position constant, The fourth group has a positive refracting power and is in a teletype configuration. The fourth group includes a front half having a positive refracting power and a rear half having a negative refracting power, and is fixed during zooming. It consists of a zoom tube lens. In the figure, reference numerals r ₁ ... r ₃₃ are the radii of curvature of the respective lenses, and d ₁ ... d ₃₂
Is the thickness and spacing of each lens, and s ₁ is the working distance. or,
In the following description, in addition to the above reference numerals, N ₁ ...
N ₂₀ is the refractive index of each lens, and ν ₁ ... ν ₂₀ is the Abbe number of each lens.

The specifications of the optical system in this embodiment are as shown in the following table.

[0026]

[Table 1]

In this embodiment, the following conditions are satisfied. Zoom tube lens: Condition (1) f _T = 1000.0, φ = 24.0 60 × 24.0 = 1440, 30 × 24.0 = 72
0.0 Condition (2) ν _I = (ν ₈ + ν ₉ ) / 2 = (95.0 + 95.0) /2=95.0 Condition (3) ν _IV = (ν ₁₅ + ν ₁₆ + ν ₁₈ ) / 3 = (70.2 + 95.0 + 70.2) /3=78.5 where f _T is the focal length at the telephoto end, and φ is the image diameter.

Objective lens: Condition (1) ν _P1 = ν ₁ , ν _P2 = ν ₂ , ν _P3 = ν ₄ (ν _P1 + ν _P2 + ν _P3 ) / 3 = (81.6 + 95.0 + 95.0) / 3 = 90.5 Condition (2) ν _P4 = ν ₆ = 36.3

Aberrations at the wide end (3.3 times), the middle (9.8 times), and the tele end (20 times) of this embodiment are shown in FIGS. 2, 3 and 4, respectively.

(Embodiment 2) FIG. 5 is a diagram showing a lens configuration of a zoom microscope according to a second embodiment. The optical system of this zoom microscope has a meniscus positive single lens with a concave surface facing the object side at the position closest to the object side, and a cemented negative lens at the farthest position, and at least three positive lens groups are sandwiched between them. The existing objective lens and the first group in order from the object side have a positive refracting power, are composed of two positive lenses and one negative lens and are fixed during zooming, and the second group has a negative refracting power. , Consists of two negative lens groups including a cemented lens, and moves during zooming to form the main force of zooming, the third group has negative refracting power, and cams as a compensator during zooming to achieve image position. The fourth group has a positive refracting power, has a teletype configuration, and has a front half having a positive refracting power and a rear half having a negative refracting power, and is fixed during zooming. Zoom zoom consisting of 4 groups Consisting of Burenzu. In the figure, reference symbols r ₁ ... R ₄₁ indicate radii of curvature of the respective lenses, d ₁ ... D ₄₀ indicate thicknesses and intervals of the respective lenses, and s ₁ indicates a working distance. Further, in the following description, in addition to the above reference numerals, N ₁ ... N ₂₅ refer to the refractive index of each lens, and ν ₁ ... ν ₂₅ refer to the Abbe number of each lens.

The specifications of the optical system in this embodiment are as shown in the following table.

[0032]

[Table 2]

In this embodiment, the following conditions are satisfied. Zoom tube lens: Condition (1) f _T = 1000.0, φ = 24.0 60 × 24.0 = 1440.0, 30 × 24.0 = 7
20.0 Condition (2) ν _I = (ν ₁₃ + ν ₁₄ ) / 2 = (95.0 + 95.0) /2=95.0 Condition (3) ν _IV = (ν ₂₀ + ν ₂₁ + ν ₂₃ ) / 3 = (70.2 + 95.0 + 70.2) /3=78.5 where f _T is the focal length at the telephoto end, and φ is the image diameter.

Objective lens: Condition (1) ν ₁ = 40.9 Condition (2) ν _A = (ν ₂ + ν ₄ + ν ₆ + ν ₇ + ν ₉ ) /
5 = (95.0 + 95.0 + 95.0 + 95.0 + 9
5.0) /5=95.0 Condition (3) ν _L = ν ₁₀ = 25.4

Aberrations at the wide end (10 times), the middle (29 times) and the tele end (60 times) of this embodiment are shown in FIGS. 6, 7 and 8, respectively.

(Embodiment 3) The details and the reference numerals of the lens of this embodiment are the same as those of the above-mentioned Embodiment 1, and the description thereof will be omitted.

The specifications of the optical system in this embodiment are as shown in the following table.

[0038]

[Table 3]

In this embodiment, the following conditions are satisfied. Zoom tube lens: Condition (1) f _T = 500.0, φ = 11.0 60 × 11.0 = 660.0, 30 × 11.0 = 33
0.0 Condition (2) ν _I = (ν ₈ + ν ₉ ) / 2 = (81.6 + 7
0.2) /2=75.9 Condition (3) ν _IV = (ν ₁₅ + ν ₁₆ + ν ₁₈ ) / 3 = (64.1 + 81.6 + 70.2) /3=72.0

Objective lens: Condition (1) ν _P1 = ν ₁ , ν _P2 = ν ₂ , ν _P3 = ν ₄ (ν _P1 + ν _P2 + ν _P3 ) / 3 = (81.6 + 95.0 + 95.0) / 3 = 90.5 Condition (2) ν _P4 = ν ₆ = 36.3

Aberrations at the wide end (3.3 times), the middle (9.8 times), and the tele end (20 times) of this example are shown in FIGS. 9, 10 and 11, respectively.

(Embodiment 4) The details and the reference numerals of the lens of this embodiment are the same as those of the above-mentioned Embodiment 2, and the description thereof will be omitted.

The specifications of the optical system in this embodiment are as shown in the following table.

[0044]

[Table 4]

In this embodiment, the following conditions are satisfied. Zoom tube lens: Condition (1) f _T = 500.0, φ = 11.0 60 × 11.0 = 660.0, 30 × 11.0 = 33
0.0 Condition (2) ν _I = (ν ₁₃ + ν ₁₄ ) / 2 = (81.6 + 7
0.2) /2=75.9 Condition (3) ν _IV = (ν ₂₀ + ν ₂₁ + ν ₂₃ ) / 3 = (64.1 + 81.6 + 70.2) /3=72.0

Objective lens: Condition (1) ν ₁ = 40.9 Condition (2) ν _A = (ν ₂ + ν ₄ + ν ₆ + ν ₇ + ν ₉ ) /
5 = (95.0 + 95.0 + 95.0 + 95.0 + 9
5.0) /5=95.0 Condition (3) ν _L = ν ₁₀ = 25.4

Aberrations at the wide end (10 times), the middle (29 times) and the tele end (60 times) of this embodiment are shown in FIGS. 12, 13 and 14, respectively.

(Embodiment 5) The details and reference numerals of the lens of this embodiment are the same as those of the above-mentioned Embodiment 1, and the description thereof will be omitted.

The specifications of the optical system in this embodiment are as shown in the following table.

[0050]

[Table 5]

In this embodiment, the following conditions are satisfied. Zoom tube lens: Condition (1) f _T = 500.0, φ = 11.0 60 × 11.0 = 660.0, 30 × 11.0 = 33
0.0 Condition (2) ν _I = (ν ₈ + ν ₉ ) / 2 = (70.2 + 6)
4.1) /2=67.2 Condition (3) ν _IV = (ν ₁₅ + ν ₁₆ + ν ₁₈ ) / 3 = (64.1 + 70.2 + 70.2) /3=68.2

Objective lens: Condition (1) ν _P1 = ν ₁ , ν _P2 = ν ₂ , ν _P3 = ν ₄ (ν _P1 + ν _P2 + ν _P3 ) / 3 = (81.6 + 95.0 + 95.0) / 3 = 90.5 Condition (2) ν _P4 = ν ₆ = 36.3

Aberrations at the wide end (3.3 times), the middle (9.8 times), and the tele end (20 times) of this embodiment are shown in FIGS. 15, 16 and 17, respectively.

(Embodiment 6) The details and the reference numerals of the lens of this embodiment are the same as those of the above-described Embodiment 2, and the description thereof will be omitted.

The specifications of the optical system in this embodiment are as shown in the following table.

[0056]

[Table 6]

In this embodiment, the following conditions are satisfied. Zoom tube lens: Condition (1) f _T = 500.0, φ = 11.0 60 × 11.0 = 660.0, 30 × 11.0 = 33
0.0 Condition (2) ν _I = (ν ₁₃ + ν ₁₄ ) / 2 = (70.2 + 6)
4.1) /2=67.2 Condition (3) ν _IV = (ν ₂₀ + ν ₂₁ + ν ₂₃ ) / 3 = (64.1 + 70.2 + 70.2) /3=68.2

Objective lens: Condition (1) ν ₁ = 40.9 Condition (2) ν _A = (ν ₂ + ν ₄ + ν ₆ + ν ₇ + ν ₉ ) /
5 = (95.0 + 95.0 + 95.0 + 95.0 + 9
5.0) /5=95.0 Condition (3) ν _L = ν ₁₀ = 25.4

Aberrations at the wide end (10 times), the middle (29 times), and the tele end (60 times) of this embodiment are shown in FIGS. 18, 19 and 20, respectively.

[0060]

The zoom microscope of the present invention has a high magnification and a high N.
It has the performance of a full-scale microscope with a long working distance and a high zoom ratio. That is, when the objective lens according to the second invention is used, the magnification is from 3.3 times to 2 times.
When the objective lens of the third invention is used up to 0 times, the magnification can be continuously varied from 10 times to 60 times,
If the objective lenses of the second invention and the third invention are used together, it is possible to obtain the effect that it is possible to set any magnification from 3.3 times to 60 times.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a zoom microscope according to a second invention.

FIG. 2 is a diagram of various types of aberration at the wide end of Example 1.

FIG. 3 is a diagram of various types of aberration in the middle of Example 1;

FIG. 4 is a diagram of various types of aberration at the telephoto end of Example 1;

FIG. 5 is a lens configuration diagram of a zoom microscope according to a third invention.

FIG. 6 is a diagram of various types of aberration at the wide end of Example 2;

FIG. 7 is a diagram of various types of aberration in the middle of Example 2;

FIG. 8 is a diagram of various types of aberration at the telephoto end of Example 2;

FIG. 9 is a diagram of various types of aberration at the wide-angle end of Example 3;

FIG. 10 is a diagram of various types of aberration in the middle of Example 3;

FIG. 11 is a diagram of various types of aberration at the telephoto end of Example 3;

FIG. 12 is a diagram of various types of aberration at the wide-angle end of Example 4;

FIG. 13 is a diagram of various types of aberration in the middle of Example 4;

FIG. 14 is a diagram of various types of aberration at the telephoto end of Example 4;

FIG. 15 is a diagram of various types of aberration at the wide-angle end of Example 5;

FIG. 16 is a diagram of various types of aberration in the middle of Example 5;

FIG. 17 is a diagram of various types of aberration at the telephoto end of Example 5;

FIG. 18 is a diagram of various types of aberration at the wide end of Example 6;

FIG. 19 is a diagram of various types of aberration in the middle of Example 6;

FIG. 20 is a diagram of various types of aberration at the telephoto end of Example 6;

[Explanation of symbols]

r ₁・ ・ ・ r ₄₁ Curvature radius of each lens d ₁・ ・ ・ d ₄₀ Thickness and interval of each lens s ₁ Working distance

Claims (3)

[Claims] 1. The first group has positive refracting power in order from the object side, is composed of two positive lenses and one negative lens and is fixed during zooming, and the second group has negative refracting power, It consists of two negative lens groups including a cemented lens and moves during zooming to form the main force of zooming, and the third group has negative refracting power. As a compensator, it cams and moves the image position during zooming. The fourth group has a positive refracting power,
It has a teletype structure and is composed of a front half having a positive refracting power and a rear half having a negative refracting power. It is fixed during zooming, the focal length at the tele end is f _T , and two positive lenses of the first group are used. When the average value of the Abbe number is ν _I , the average value of the Abbe number of only the positive lens in the front half of the fourth group is ν _IV , and the image diameter is φ, (1) 60φ> f _T > 30φ (2) 95.2 ≧ ν _I > 65 (3) 95.2 ≧ ν _IV > 65 The infinity-corrected large-diameter high-magnification zoom lens having a zoom tube lens composed of four groups satisfying the following conditions: microscope. 2. A positive lens group of three groups including cemented lenses in order from the object side, and a cemented negative lens, 3 out of 3 groups.
Abbe number of each positive lens is ν from the object side
_{When P1} , ν _P2 , ν _P3 and the Abbe number of the positive lens in the cemented negative lens is ν _P4 , (1) 92> (ν _P1 + ν _P2 + ν _P3 ) / 3> 80 (2) 28 <ν An infinity-correction type large-diameter high-magnification zoom microscope having an objective lens satisfying the condition of _P4 <42 and the zoom tube lens according to claim 1. 3. A meniscus positive single lens having a concave surface facing the object side is located closest to the object side, and a cemented negative lens is located farthest away from the object side, and at least three positive lens groups are sandwiched between them. , When the Abbe number of the positive meniscus single lens is ν ₁ , the average value of the Abbe numbers of the positive lenses in the middle lens group is ν _A , and the Abbe number of the positive lens in the cemented negative lens is ν _L , then (1) An infinity-corrected type having an objective lens having a condition of 30 <ν ₁ <50 (2) 95.2 ≧ ν _A > 80 (3) ν _L <30 and the zoom tube lens according to claim 1. Large-diameter, high-power zoom microscope.