JPH046511A - Objective lens for microscope - Google Patents

Abstract

PURPOSE:To obtain the objective lens usable in the ultraviolet ranges and far ultraviolet range at low cost by arraying 1st - 3rd specific lenses at specific air intervals from the object side to the image side in this order. CONSTITUTION:The 1st - 3rd lenses are arrayed at the specific air intervals from the object side to the image side in this order. The 1st lens 11 is a positive-power meniscus lens which is made of quartz or fluorite and has a concave surface 11a on the object side, the 2nd lens 12 is made of quartz and has negative power, and the 3rd lens 13 is made of fluorite and has positive power. Consequently, light in the ultraviolet range or far ultraviolet range can be transmitted through the objective, which is usable in the ultraviolet range and far ultraviolet range. Further, the 1st - 3rd lenses are isolated mutually across the specific air intervals, so the need for optical contact is eliminated and the objective lens can be obtained at low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an objective lens for a microscope that can be used even in the ultraviolet region, particularly in the far ultraviolet region with a wavelength of 300 nIll or less.

(Prior art and its problems) As is well known, in a microscope, if the numerical aperture (N^) of the objective lens is the same, the resolution limit increases as the wavelength becomes shorter. You can observe every detail of the sample. Furthermore, when a sample is irradiated with ultraviolet rays, more intense fluorescence is often emitted than when irradiated with visible light. Therefore, it is desirable to provide a microscope that can be used even in the ultraviolet region in order to obtain more information by observing a sample using a microscope. For this purpose, an objective lens that can be used in the ultraviolet and deep ultraviolet regions is required.

Therefore, for example, a microscope objective lens shown in FIG. 6 has been employed as an objective lens usable in the ultraviolet region or deep ultraviolet region. FIG. 6 is a diagram showing the configuration of this objective lens 70 for a microscope. This objective lens 70 is
Light Wave Jutsu] Contact Magazine Vol. 1.25 No. 2 (1987
(February 2013) P, 137.

As shown in the figure, the objective lens 70 consists of a first lens 71, a second lens, and a It is composed of third lens groups 72 and 73. Second lens group 72
The concave lens 72a made of quartz is replaced by the convex lens 72b made of fluorite,
72c and sandwiched and joined. Further, like the second lens group 72, the third lens group 73 is a concave lens 73a made of quartz and convex lenses 73b and 73C made of fluorite sandwiched and cemented together.

This objective lens 70 includes each lens 71.72a to 72.
Since C173a to C73C are all made of quartz or fluorite, they can transmit ultraviolet rays and far ultraviolet rays. Therefore, the objective lens 70 can be used even in the ultraviolet region or deep ultraviolet region.

Moreover, the second lens group 72 is composed of a concave lens 72a made of quartz and convex lenses 72b, 72c made of fluorite, and the third lens group 73 is composed of a concave lens 73a made of quartz and convex lenses 73b, 73C made of fluorite. Because of this configuration, it is also possible to correct chromatic aberration.

By the way, in the second lens group 72, the convex lens 72
b, the concave lens 72a and the convex lens 72C are in optical contact with each other.

Also in the third lens group 73, convex lenses 73b,
The concave lens 73a and the convex lens 73c are in optical contact with each other. The reason is that, at present, there is no practical adhesive that transmits deep ultraviolet rays. Therefore, the only way to eliminate total reflection at the lens cementation surface is to make optical contact with the cementation surface. Therefore, each cemented surface is required to be processed with high precision, and there is a problem in that the manufacturing cost of the objective lens 70 increases.

Therefore, the inventor of the present invention developed an objective lens for a microscope that solved the above problem in an earlier application (Japanese Unexamined Patent Publications No. 1-319719 and 1-319720, hereinafter simply referred to as the "earlier application"). Proposed. FIG. 7 is a diagram showing an example of the objective lens for a microscope according to this proposal.

According to this proposed example, the microscope objective lens 60 is composed of lenses 61 to 63 made of quartz or fluorite. And these first to third lenses 61 to 63
As shown in the figure, they are arranged in this order from the object side (left side in the figure) to the image side (right side in the figure) with a predetermined air interval. Therefore, this microscope objective lens 6
0 can be used in the ultraviolet region and deep ultraviolet region. Furthermore, the lenses 61 to 63 are spaced apart from each other; in other words, the objective lens 60 has no bonding surface. Therefore, this microscope objective lens 60 is
It becomes unnecessary to use optical contact, and the above problem is solved.

By the way, the objective lens 60 shown in FIG. 7 cooperates with an imaging lens (the detailed structure of which will be described later) to form an image of an object with a predetermined imaging magnification M on the focal plane of the imaging lens. It is configured in such a way that

The imaging magnification M at this time is the ratio of the focal length f of the imaging lens to the focal length f1 of the objective lens 60. That is,
The imaging magnification M is M--f2/f1 (1).

Furthermore, in a microscope, the imaging lens is usually fixed and the objective lens is replaced to change the imaging magnification M.
Therefore, it is necessary to prepare objective lenses with mutually different focal lengths.

For example, consider a case where the objective lens 60 shown in FIG. 7 is replaced with a certain objective lens to increase the imaging magnification to 1/2.

In this case, as can be seen from equation (1), the imaging magnification is set to l/
In order to double the magnification, it is necessary to prepare an objective lens with a focal length of 2 f. Here, if jlt is sufficient to double the focal length, the objective lens 60 may be enlarged proportionally, for example.

However, when the objective lens 60 is replaced with an objective lens with 2x proportional magnification, as long as the position of the pupil is fixed, the distance from the objective lens to the object must also be doubled. After that, you may need to refocus. This significantly reduces the operability of the microscope and is not preferable. Conversely, if the object position is fixed, the position of the pupil will move, which is not preferable in a fixed illumination system because the illumination state will change. Moreover, by replacing the objective lens, the size of the pupil also doubles, and the amount of light used in a fixed illumination system decreases.

Therefore, by changing the objective lens, the imaging magnification can be reduced by 1/
In the case of 2, the objective lens after replacement is (1) the focal length is twice that of the objective lens 60, and (2) the objective lens does not need to be refocused even after the objective lens is replaced, that is, the objective lens (3) The position and size of the pupil are approximately equal to those of the objective lens 60.

(Object of the invention) This invention has been made in view of the above problems, and provides a microscope objective lens that can be used even in the ultraviolet region and deep ultraviolet region, with a different configuration from the objective lens according to the above-mentioned earlier application. The primary objective is to provide the following at low cost.

Furthermore, the present invention has a focal length that is approximately twice that of the objective lens of the above-mentioned earlier application, which cooperates with an imaging lens to form an image of an object on a focal plane with a predetermined imaging magnification. ,
A second object of the present invention is to provide a microscope objective lens which is parfocal and whose pupil position and size are approximately equal.

(Means for achieving the object) In order to achieve the above-mentioned first object, the invention as claimed in claim 1 is characterized in that the first to third lenses are arranged in this order with a predetermined air interval from the object side to the image side. Arranged. These first
Of the to third lenses, the first lens is a meniscus lens made of quartz or fluorite and has a positive power with a convex surface facing the object side, and the second lens is made of quartz and has a negative power, The third lens is made of fluorite and has positive power.

In order to better achieve the first object, in addition to the invention of claim 1, when the powers of the second and third lenses are φ and φ3, respectively, the objective lens satisfies the following: 1.1 < lφ3/ The inequality expressed as φ2|<1.3 is satisfied.

Further, the invention according to claim 3 cooperates with the imaging lens,
It is replaceable with an objective lens that forms an image of an object on the focal plane of the imaging lens with a predetermined imaging magnification, and when used in combination with the imaging lens instead of the objective lens, It is intended for microscope objective lenses that reduce image magnification by approximately half.

In order to achieve the second objective, the first to third lenses are arranged in this order from the object side to the image side with a predetermined air interval. Among these first to third lenses, the first lens is a meniscus lens made of quartz or fluorite and has a positive power with its convex surface facing the object side, and the second lens is made of quartz and has a negative power. has
The third lens is made of fluorite and has positive power.

Moreover, when the powers of the first to third lenses are respectively φ, φ, φ, the power of the composite system consisting of the second and third lenses is φ, and the power of the entire system is φ,
In the objective lens, 1.1 < l φ
/φ 2 l<1.30.901φ /φ1ku1φ1−/φ23■+ 1.001φ /φl>lφ1−/φ23■+ 0.80・1 (4φ/3φ −1)/φ1+1ull/
φ1-1+ 1.1 1 (4φ13φ -1)/φ1+1u11/
The inequality shown as φ1-1+ is satisfied.

Note that φ and φ are respectively 1+1= φ − (n 1) / r l ■＋ φ − (1n) / r 2 one Tatashi, n: refractive index of the first lens, rl: object side of the first lens The radius of curvature of the surface facing , r2: the image side of the first lens radius of curvature of facing surface It is.

(Function) According to the invention of claim 1, the first lens is made of quartz or fluorite, the second lens is made of quartz, and the third lens is made of fluorite. Therefore, light in the ultraviolet region or deep ultraviolet region can pass through the objective lens, and it can be used in the ultraviolet region and deep ultraviolet region. Further, the first to third lenses are spaced apart from each other by a predetermined air gap. Therefore, there is no need for an optical contact, and the objective lens can be provided at low cost. Moreover, while the third lens has positive power,
The second lens has negative power.

Therefore, various aberrations such as spherical aberration and chromatic aberration are corrected.

In particular, using the powers φ2°φ3 of the second and third lenses, the objective lens satisfies the following: 1.1 <+φ3/φ2|<1.3 (2)
If the inequality expressed by is satisfied, spherical aberration etc. will be better.

The reason for this is that when the value 1φ/φ21 becomes smaller than 1.1, the spherical aberration will be over-corrected, and conversely, if the value becomes larger than 1.3, the correction will be insufficient. It is.

According to the third aspect of the invention, achromatization is performed by the combination of the third lens having positive power and the second lens having negative power. Since the image side surface (hereinafter referred to as "second surface") of the first lens has a large negative power, the objective lens becomes a so-called telephoto type, and the focal length of the objective lens is shorter than the focal length of the objective lens. become longer.

Further, since the object side surface (hereinafter referred to as "first surface") of the first lens has positive power, the objective lens has telecentric characteristics on the object side.

Here, looking at the above content from a different angle, the composite system of the second surface, the second lens, and the third lens has a large focal length, and plays the role of a teleconverter with respect to the first surface. In other words, it can be said that the synthesis system expands the power of the first surface and adjusts the focal length of the objective lens to a desired value.

In order to accurately satisfy this condition, it is necessary to satisfy the following formula (3). However, in reality, the above synthetic system does not need to be a complete afocal system, and the above synthetic system has the following relationship: 0.901φ /φl<|φ1−/φ231...(4
A) l + t, oo +φ /φ1〉1φ1-/φ231...(
4B)■+ It is sufficient to satisfy the inequalities (4A) and (4B) shown below.

By the way, achromatization is achieved by the combination of the second and third lenses, as described above.

Here, when forming an image of the object only by the combination of the second and third lenses, the value 1φ/φ21 is set in the range of 1.3 to 1.4, taking into consideration the dispersion of fluorite and quartz. It is desirable to set it to . However, when the objective lens is composed of first to third lenses, it is preferable to set the correction by the second and third lenses excessively in order to correct the aberrations caused by the first lens. . Therefore, the value 1φ/φ21 is set to 1.1~
It is preferable to set it within the range of 1.3, that is, to set it so that the objective lens satisfies inequality (2).

Next, the conditions for aligning the parfocal distances, that is, the objective lens is 0.80・1 (4φ/3φ −1)/φ1+1u11/
φ1-1+ ... (5A) 1.1 1 (4φ/3φ -1)/φ, +1ull/
φ1−■+ (5B) The necessity of satisfying the inequality shown will be explained.

In this application, the parfocal length or 3 of the focal length of the objective lens is
/4 times, and the image-side focal point of the objective lens is assumed to be in close contact with the composite system of the second and third lenses. Therefore, if the distance between the principal points of the synthetic system and the second surface is e, then the condition expressed by the following formula (6) is obtained. In addition, in order for the objective lens to have telecentric characteristics on the object side, it is necessary to make the pupil of the composite system of the second surface, the second lens, and the third lens coincide with the focal point of the first surface. . Therefore, the condition expressed by the following formula % is obtained. And these conditions ([
1) and (7), the objective lens is required to satisfy the inequalities (5A) and (5B).

(Example) FIG. 1 is a diagram showing a first example of an objective lens for a microscope according to the present invention. As shown in the figure, this objective lens 10 is composed of first to third lenses 11 to 13. These first to third lenses 11 to 13 are
They are arranged in this order from the object side (left side 1i1 in the figure) to the image side (right side in the figure) with a predetermined air interval. Further, both the first and third lenses 11.13 have positive power. On the other hand, the second lens 12 has negative power. Note that, as shown in the figure, the convex surface 11a of the second lens 11 faces toward the object side.

Table 1 shows lens data of the objective lens 10 configured as described above.

(Margin below) Table 1 In addition, in the same table (and Table 3, which will be explained later), r
l is the radius of curvature of the i-th lens surface (i-1 to 6) counting from the object side, and d is the radius of curvature of the i-th (i-1 to 6) counting from the object side.
-1 to 5) and the (i+1)th lens surface on the optical axis Z. Also, as can be seen from the same table, the first and second lenses 11.12
is made of quartz, and the third lens 13 is made of fluorite.

Further, the focal length f of the objective lens 10 is 60, the numerical aperture (NA) is 1/24, and the image size is 1O16.

Also, the power φl+ of the convex surface 11a of the first lens 11 and the second lens 1 with respect to the wavelength 298.06 (nII+)
The powers φI− of the surface 11b facing the image side of 2 are φ −0, 1864, and φ1−−0.24671+, respectively. Also, the powers φ, φ of the second and third lenses 12.13 with respect to the wavelength 298,06 (r+m)
3, the power φ23 of the composite system consisting of the second lens 12 and the third lens 13, and the power φ of the entire system (objective lens 10)
are as follows.

φ--0.07670, φ3-0.09208.

φ23=0.02H6, φ=0.01667 Therefore, from the above data, φ/φ21−1.201 can be found, and it is clear that the objective lens 10 satisfies inequality (2).

Also, from the above data, 0.901φl+/φl-10,07.

1.001φl+/φl -11,18.

φ1−/φ231 −10.84 are respectively found. Therefore, it is clear that the objective lens 10 satisfies the inequalities (4^) and (4B).

Furthermore, from the above data, 080・1 (4φ/3φ −1)/φ, +1 = 3.7
80.

1+ 1.1 1 (4φ/3φ −1)/φ1+1 =5.
198.

1+ + 1/φ1-1-4.071 are respectively found. Therefore, it is also clear that the objective lens 10 satisfies the inequalities (5^) and (5B).

By the way, this objective lens 10 is a so-called infinity correction system in consideration of application to an epi-illumination type microscope. That is, it is configured to form an image of an object on a predetermined imaging plane in combination with an imaging lens described below.

Imaging Lens> FIG. 2 is a diagram showing the configuration of an imaging lens, which is the same as the imaging lens shown in the previous application. As shown in the figure, the imaging lens 50 includes first to third lenses 51 to 53. These first to third lenses 51 to 53 are arranged in this order from the object side (left side in the figure) to the image side (right side in the figure) with a predetermined air interval.

Table 2 shows lens data of the imaging lens 50 configured as described above.

Table 2 In the same table, R is the i-th (counting from the object side)
The radius of curvature of the lens surface (i-1 to 6), and Dl is the radius of curvature of the lens surface of the i-th (i-1 to 5) counting from the object side and (i+
1) It shows the distance between the lens surfaces on the optical axis Z with the th lens surface. Further, as can be seen from the table, the third lens 52 is made of fluorite, and the second and third lenses 52.5
3 is made of quartz. Further, the focal length f' of this imaging lens 50 is 300 mm.

Therefore, the imaging magnification M of the microscope composed of this imaging lens 50 and the objective lens 10 according to the first embodiment 1 is M--f'/f--300760--5.0.

FIGS. 3A and 3B are diagrams showing the spherical aberration and sine conditions of a lens system combining the objective lens 10 and the imaging lens 50, respectively. In both figures (and Figures 5A and 5B, which will be explained later), symbols A to D indicate wavelengths 298 and 06 (r+m), respectively.

202.54 (ns), 398.84 (nm), 2
The results are shown for light of 53.70 (nm).

FIGS. 3C and 3D show wavelengths of 2980 [1
It is a figure showing astigmatism and distortion aberration about (nm). In addition, Fig. 3C (and Fig. 5C, which will be explained later)
, the solid line S indicates the sagittal image plane, and the broken line M indicates the meridional image plane.

From FIGS. 3A and 3B, it can be seen that this objective lens 10 has little aberration for light in the ultraviolet region and deep ultraviolet region. Therefore, it is clear that this objective lens 10 can be used in the ultraviolet region and deep ultraviolet region. Also, from FIG. 3C and FIG. 3D, the objective lens 1
It is clear that the lens system using 0 has less astigmatism and distortion.

B. Second Embodiment FIG. 4 is a diagram showing a second embodiment of the objective lens for a microscope according to the present invention. The objective lens 20 according to the second embodiment has basically the same configuration as the objective lens 10. That is, the objective lens 20 includes first to third lenses 21 to 2 that are arranged in this order from the object side (left side in the figure) to the image side (right side in the figure) with a predetermined air interval.
It is composed of 3.

Table 3 shows lens data of the objective lens 20 configured as described above.

Table 3 As can be seen from the table, the second lens 22 is made of quartz, and the first and third lenses 2 and 23 are made of fluorite.

Further, the focal length f of the objective lens 20 is 60, the numerical aperture (NA) is 1/24, and the image size is 10.6.

Also, for the wavelength 298.06 (t+l11), the first
The powers φ1+ and E of the convex surface 21a of the lens 21 and the power φ1− of the image-facing surface 21b of the first lens 21 are φ −0,1637 and φ1−0.22071+, respectively. In addition, the powers φ and φ3 of the second and third lenses 22 and 23, the power φ23 of the composite system consisting of the second lens 22 and the third lens 23, and the entire system (objective lens 20)
The power φ of is as follows.

φ2--0.07676, φ3-0.09283
.

φ23- 0.02313. φ −0,0IH7
Therefore, it is clear that φ/φ21-1.210 can be found from the above data, and that the objective lens 20 satisfies inequality (2).

Also, from the above data, 0.901φ1+/φl -8,839.

1.001φ1+/φl -9,821.

φ1−/φ231 −9.5L1 are respectively found. Therefore, it is clear that the objective lens 20 satisfies the inequality (4A) and <4B>.

Furthermore, from the above data, 0.80・1 (4φ/3φ −1)/φ1+1! =4
．． 224.

■+ 1.1 1 (4φ/3φ −1)/φ1 and l −5,
808.

1+1/φ and l −4,531 are respectively found. Therefore, it is also clear that the objective lens 20 satisfies the inequalities (5^) and (5B).

This objective lens 20 is also a so-called infinity correction system, as in the first embodiment, and is combined with an imaging lens 50 shown in FIG. Therefore, this imaging lens 5
0 and the objective lens 20 according to the second embodiment described above, the imaging magnification M of the microscope is also M--f'/f--300/60--5.
．． It becomes 0.

FIGS. 5A and 5B are diagrams showing the spherical aberration and sine conditions of a lens system combining the objective lens 20 and the imaging lens 50, respectively. Also, Figures 5C and 5D
The figure shows a wavelength of 298. (It is a figure showing astigmatism and distortion aberration about H (nm).

From FIG. 5A and FIG. 5B, it can be seen that this objective lens 20 has little aberration for light in the ultraviolet region and deep ultraviolet region. Therefore, it is clear that this objective lens 20 can be used in the ultraviolet region and deep ultraviolet region. Also, from FIG. 5C and FIG. 5D, it is clear that the objective lens 2
It is clear that the lens system using 0 has less astigmatism and distortion.

Effects of C9 First and Second Examples As described above, the objective lenses 10.20 according to the first and second examples can be used in the ultraviolet region and deep ultraviolet region, and have excellent characteristics in these wavelength regions. have. Furthermore, in any of the embodiments, the first to third lenses are spaced apart from each other. Therefore, there is no need for an optical contact, and the objective lens can be provided at low cost.

Although not specifically explained above, all examples have little aberration in both the visible and infrared regions, and each objective lens 10.20 can be used in the range from the infrared region to the far ultraviolet region. It was confirmed that

By the way, the objective lens 60 (
FIG. 7) is combined with the imaging lens 50 (FIG. 2) to constitute a lens system with an imaging magnification M of 110 times. That is, the objective lens 60 (7+jC point distance is 30. In contrast, the objective lens 10.
The focal lengths of the 20 lenses are all 60. Therefore, by fixing the imaging lens 50 and replacing the objective lens 10 of the first embodiment with the objective lens 60, for example,
The imaging magnification M can be changed from 110 times to 15 times.

Furthermore, objective lenses 10 and 20 are both objective lenses 6 and 6.
It is parfocal with 0. As a result, even after replacing the objective lens (for example, replacing the objective lens 60 with the objective lens 10), there is no need to refocus, and the operability of the microscope is improved.

Moreover, the pupil diameter of each objective lens 10.20 is
It is almost the same as 0. Therefore, even when the lens is replaced, there is no significant change in the amount of light illuminating the object, and the object can be observed in good condition.

That is, the objective lenses 10 and 20 according to the above embodiments can all be said to be objective lenses that meet the second objective of the present application.

(Effects of the Invention) As described above, according to the invention of claim 1, the first lens made of quartz or fluorite, the second lens made of quartz, and the third lens made of fluorite can be attached to an object. Since the objective lenses are arranged in this order from the side to the image side with a predetermined air interval, the objective lens can be used in the ultraviolet region or deep ultraviolet region.

Furthermore, since the lenses are separated from each other by a predetermined air interval, there is no need for optical contacts, and the objective lens can be provided at low cost.

Furthermore, since the third lens has positive power and the second lens has negative power, various aberrations such as spherical aberration and chromatic aberration can be corrected.

In particular, in the invention of claim 2, the objective lens satisfies the inequality (2).
Since the following is satisfied, spherical aberration etc. can be further reduced.

According to the invention of claim 3, the second surface of the first lens has a large negative power, and the second surface, the second lens, and the third lens are arranged in this order from the object side to the image side. do,
It has a so-called telephoto type configuration. Therefore, the focal length of the objective lens of the present application can be approximately twice that of the objective lens of the previous application.

Also, the objective lens of this application is the inequality (5^), (5B>
Since the objective lens is configured to satisfy the above requirements, it is possible to make the objective lens almost at the same focal point as the objective lens to be replaced in the previous application.

[Brief explanation of drawings]

FIG. 1 shows the first objective lens for a microscope according to the present invention.
FIG. 2 is a diagram showing the configuration of the imaging lens, and FIG. 3A, FIG. 3B, FIG. 3C, and FIG.
FIG. 4 is a diagram showing the spherical aberration, sine condition, astigmatism, and distortion of a lens system that combines the objective lens shown in the figure and the above-mentioned imaging lens, and FIG. FIG. 5A, FIG. 5B, FIG. 5C, and FIG. 5D are diagrams showing the spherical aberration and sine of a lens system that combines the objective lens shown in FIG. 4 and the above-mentioned imaging lens, respectively. FIG. 6 is a diagram showing conditions, astigmatism, and distortion aberration, and FIGS. 6 and 7 are diagrams each showing the configuration of a conventional objective lens for a microscope. 10.20... Objective lens, 11.21... First lens, 11a, 21a... Convex surface 12.22... Second lens, 13.23... Third lens,

Claims (1)

[Scope of Claims] (1) First to third lenses are arranged in this order with a predetermined air interval from the object side to the image side,
The lens is a meniscus lens made of quartz or fluorite and has a positive power with a convex surface facing the object side, the second lens is made of quartz and has a negative power, and the third lens is made of fluorite. An objective lens for a microscope characterized by having positive power. (2) The powers of the second and third lenses are each φ
The objective lens for a microscope according to claim 1, which satisfies 1.1<|φ3/φ_2|<1.3 when _2 and φ_3. (3) It can be replaced with an objective lens that cooperates with the imaging lens to form an image of an object on the imaging plane with a predetermined imaging magnification, and can be combined with the imaging lens instead of the objective lens. An objective lens for a microscope that reduces the imaging magnification by approximately half when used in a microscope, comprising first to third lenses arranged in this order from the object side to the image side with a predetermined air interval, The first lens is a meniscus lens made of quartz or fluorite and has a positive power with its convex surface facing the object side, the second lens is made of quartz and has a negative power, and the third lens is made of fluorite. and has a positive power, and the powers of the first to third lenses are respectively φ_1 and
φ_2, φ_3, when the power of the composite system consisting of the second and third lenses is φ_2_3, and the power of the entire system is φ, 1.1<|φ_3/φ_2|<1.3 0.90|φ_1_+/φ |<|φ_1_-/φ_2_
3｜1.00｜φ_1_+/φ｜＞｜φ_1_-/φ_
2_3｜0.80・｜(4φ/3φ_1_+-1)/φ
＿１＿＋｜＜｜1/φ＿1＿｜1.1・｜(4φ/3φ
_1_+-1)/φ_1_+|>|1/φ_1_-|In addition, φ_1_+=(n-1)/r_1 φ_1_-=(1-n)/r_2 where, n: refractive index of the first lens, r_1: the above An objective lens for a microscope, characterized in that the radius of curvature of the surface of the first lens facing the object side satisfies r_2: the radius of curvature of the surface of the first lens facing the image side.