JPH1172701A - Two-step magnification switching optical system and stereoscopic microscope provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To switch magnification between low magnification and high magnification with compact and simple constitution by switching the position of a lens group which has negative refractive power among plural lens groups whose distances are specified on the same optical axis and which have positive refractive power. SOLUTION: This system is provided with the lens group L1 guiding a light beam from an axial object point O to a point on the optical axis and having the positive refractive power, the lens group L2 refracting and guiding the light beam in the same direction as the light beam emitted from the point on the optical axis and having the negative refractive power, and the lens group L3 guiding the light beam through the lens group L2 to an axial image point I and having the positive refractive power. By switching the position of the lens group L2 between the lens group L1 and the lens group L3, the magnification of an entire optical system is switched. The system satisfies relation: S=-f2(Z-1)/√Z, β2L=-1/√Z and β2H=$√Z. In the expressions, S means a moving distance along the optical axis of the lens group L2 between the lens groups L1 and L3, f2 means the focal distance of the lens group L2, Z means a magnification ratio, and β2L and β2H mean the magnification of the lens group L2 at respective positions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-stage magnification switching optical system and a stereo microscope provided with the optical system, and more particularly to a two-stage magnification switching in a stereo microscope.

[0002]

2. Description of the Related Art In a stereomicroscope disclosed in JP-A-7-104189, JP-A-64-88513, etc., an afocal system is rotated by 180 ° in a parallel beam path.
By rotating (reversing the object side and the image side of the afocal system), the magnification of the formed object image is switched. Further, in a stereoscopic microscope disclosed in Japanese Patent Application Laid-Open No. 62-35312, an object image formed by selectively inserting one of two afocal systems having different magnifications into a parallel light beam path. Is switched.

[0003]

As described above, in magnification switching in a conventional stereomicroscope, it is necessary to secure a parallel light beam path for rotating the afocal system by 180 ° and inserting and removing the same. There is an inconvenience that the degree of freedom in designing a microscope is greatly restricted. In addition, a space for rotating the entire afocal system by 180 ° and inserting and removing the entire afocal system in the optical path of the parallel light beam is required, and there is a disadvantage that the size of the stereomicroscope is increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and does not necessarily require a parallel light beam path, and is capable of switching magnification between high magnification and low magnification with a compact and simple configuration. It is an object of the present invention to provide a two-stage magnification switching optical system and a stereo microscope equipped with the optical system.

[0005]

In order to solve the above-mentioned problems, according to the present invention, a positive refraction for refracting a light beam from a predetermined on-axis object point and guiding the refracted light beam toward a first point on the optical axis. A first lens group having a power, and a negative refractive power for refracting a light beam passing through the first lens group and guiding the light beam in the same direction as a light beam emitted from a second point on the optical axis. A second lens group; and a third lens group having a positive refractive power for refracting a light beam passing through the second lens group and guiding the ray to a predetermined on-axis image point. By switching the position of the second lens group between the first position on the first lens group side and the second position on the third lens group side without changing the position of the third lens group, the entire optical system Is switched between a first magnification on the low magnification side and a second magnification on the high magnification side. , The distance along the optical axis from the to the second position is S, the focal length of the second lens group is f2, the magnification ratio of the second magnification to the first magnification is Z, and The magnification of the second lens group is β
2L and the magnification of the second lens group at the second position is β2H, the following relationship is satisfied: S = −f2 (Z−1) / ΔZβ2L = −1 / ΔZβ2H = −ΔZ A two-stage magnification switching optical system is provided.

The predetermined axial object point and the predetermined axial image point may be located at infinity from the optical system, and the optical system may be configured as an afocal optical system. Further, according to a preferred aspect of the present invention, the second lens group includes a first sub lens group configured to be insertable into and removable from an optical path at the first position, and an optical path at the second position. And a second sub-lens group configured to be insertable / removable, and by selectively inserting / removing the first and second sub-lens groups with respect to an optical path, the position of the second lens group can be changed. Switching between the first position and the second position.

According to another aspect of the present invention, each of the pair of observation systems includes the above-described two-stage magnification switching optical system of the present invention, and sets the position of the second lens group to the first position. A stereo microscope, wherein the magnification of an object image formed through the observation system is switched between a low magnification and a high magnification by switching between the second position and the second position. I do.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining the principle of two-stage magnification switching in the present invention. In FIG. 1A, a light beam directed to a point O2 on the optical axis enters the negative lens unit L2, and is refracted in the same direction as the light beam emitted from the point I2 on the optical axis. That is, the point O2 forms the object point of the negative lens unit L2, and the point I2 forms the image point of the negative lens unit L2. Then, as shown in FIG. 1A, assuming that the object point distance of the negative lens unit L2 is D0 (positive) and the image point distance of the negative lens unit L2 is D1 (negative), the negative lens unit L2
Is represented by β2L = D1 / D0.

On the other hand, in FIG. 1B, as compared with the state of FIG. 1A, the position of the object point O2 and the position of the image point I2 of the negative lens unit L2 remain unchanged. Only the position changes to the right in the figure. In this case, the relationship between the object point distance and the image point distance of the negative lens unit L2 is shown in FIG.
The object image distance is unchanged. That is,
The object point distance of the negative lens unit L2 is -D1 (positive), the image point distance of the negative lens unit L2 is -D0 (negative), and the imaging magnification of the negative lens unit L2 is β2H = D0 / D1.

As described above, the position of the negative lens unit L2 is shown in FIG.
By switching between the position on the left side in FIG. 1A and the position on the right side in FIG. 1B, the position of the object point O2 and the position of the image point I2 of the negative lens unit L2 are not changed. The imaging magnification of the negative lens unit L2 can be switched between a low magnification magnification β2L (negative) and a high magnification magnification β2H (negative) in two steps.

As described above, the magnification β2L on the low magnification side and the magnification β2H on the high magnification side of the negative lens unit L2 are expressed by the following equation (1).
And (2). β2L = D1 / D0 (1) β2H = D0 / D1 (2) Therefore, the magnification ratio Z (Z> 1) of the magnification β2H on the high magnification side to the magnification β2L on the low magnification side of the negative lens unit L2 is expressed by the following equation ( It is represented by 3). Z = β2H / β2L (3)

Based on the relations of equations (1) to (3), the magnification β2L on the low magnification side and the magnification β2H on the high magnification side of the negative lens unit L2.
Can be represented by the following equations (4) and (5), respectively. β2L = −1 / ΔZ (4) β2H = −ΔZ (5) From the lens formula in FIG. 1A, the relationship shown in the following equation (6) is obtained. In Expression (6), f2 is the focal length (negative) of the negative lens unit L2. 1 / D1 = 1 / f2 + 1 / D0 (6)

The distance S (positive) along the optical axis from the position of the negative lens unit L2 in FIG. 1A to the position of the negative lens unit L2 in FIG. 1B is expressed by the following equation (7). Is done. S = D0 + D1 (7) The distance S can be expressed by the following equation (8) based on the relationships of the equations (1), (2), (3), (6) and (7). S = −f2 (Z−1) / √Z (8)

FIG. 2 is a diagram for explaining the overall basic configuration of a two-stage magnification switching optical system according to the present invention. As shown in FIG. 2, in the present invention, the above-described negative lens unit L2 is used as a second lens unit, and a first lens unit L1 having a positive refractive power on the object side and a positive refractive power on the image side. Third lens group L
The two-stage magnification switching optical system is configured by arranging the three lenses 3 respectively. The second lens unit L2 is located between the first position on the first lens unit side (the position in FIG. 2A) and the second position on the third lens unit side (the position in FIG. 2B). It is configured to be switchable.

Therefore, by switching the position of the second lens unit L2 between the first position and the second position without changing the position of the first lens unit L1 and the position of the third lens unit L3, the second position is obtained. The magnification of the lens unit L2 is switched between the magnification β2L on the low magnification side and the magnification β2H on the high magnification side, and thus the magnification of the entire optical system is changed to the magnification βL on the low magnification side and the magnification β on the high magnification side.
H. At this time, since the position of the object point O2 and the position of the image point I2 of the second lens unit L2 do not change, the relationship between the object point position and the image point position of the optical system also changes with the switching of the magnification. Instead, light from a predetermined on-axis object point O is guided to a predetermined on-axis image point I via an optical system.

In the present invention, as shown in FIG. 2, a predetermined on-axis object point O and a predetermined on-axis image point I are located at a finite distance from the optical system, and the optical system is shifted to a focal system (finite focal length system). ). In this case, assuming that the magnification of the first lens unit L1 is β1 (negative) and the magnification of the third lens unit L3 is β3 (negative), the magnification βL on the low magnification side and the magnification βH on the high magnification side of the entire optical system are: It is expressed by the following equations (9) and (10), respectively. βL = β1, β2L, β3 (9) βH = β1, β2H, β3 (10)

Although not shown, a predetermined on-axis object point O and a predetermined on-axis image point I are positioned at infinity from the optical system, and the optical system is set as an afocal system (infinite focal length system). It can also be configured. In this case, the first lens unit L1
If the focal length of the third lens group L3 is f3 (positive) and the focal length of the third lens unit L3 is f3 (positive), the magnification βL on the low magnification side and the magnification βH on the high magnification side of the entire optical system are expressed by the following equation (11). And (12) respectively. βL = β2L · (−f1 / f3) (11) βH = β2H · (−f1 / f3) (12)

The two-stage magnification switching optical system of the present invention configured as a focal system can be applied to, for example, an internal oblique stereo microscope. In this case, the object image is formed only through the two-stage magnification switching optical system of the present invention, and the position of the second lens unit L2 is switched between the first position and the second position to reduce the magnification of the object image. It is possible to switch between the magnification on the double side and the magnification on the high magnification side.

The two-stage magnification switching optical system of the present invention configured as an afocal system can be applied to, for example, a parallel system stereo microscope. In this case, the two-stage magnification switching optical system of the present invention is arranged in the parallel light beam path between the objective lens (common objective lens or individual objective lens) and the imaging lens, and the position of the second lens unit L2 is changed. By switching between the first position and the second position, the magnification of the object image formed via the objective lens, the two-stage magnification switching optical system, and the imaging lens can be changed between the low magnification and the high magnification. Can be switched between.

A first sub-lens group configured to be inserted into and removable from the optical path at the first position, and a second sub-lens group configured to be inserted into and removable from the optical path at the second position. Constitutes the second lens unit L2, and selectively inserts and removes the first and second sub-lens units with respect to the optical path, thereby shifting the position of the second lens unit L2 between the first position and the second position. You can switch between them. Also, the first position and the second position
The position of the second lens unit L2 can be switched between the first position and the second position by rotating the second lens unit L2 about the midpoint between the positions. Further, by selectively moving the second lens unit L2 along the optical axis direction between the first position and the second position, the position of the second lens unit L2 is shifted between the first position and the second position. You can also switch between them.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 3 is a diagram schematically showing a configuration of a two-stage magnification switching optical system according to the first example of the present invention.
In the first embodiment, the two-stage magnification switching optical system of the present invention is configured as a focal system. The two-stage magnification switching optical system of FIG. 3 includes, in order from the object side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a third lens unit L2 having a positive refractive power. And a lens unit L3. Then, the second lens unit L2 is arranged as shown in FIG.
It is configured to be switchable between a first position on the first lens group side shown in FIG. 3A and a second position on the third lens group side shown in FIG.

In the first embodiment, the focal length f1 of the first lens unit L1, the focal length f2 of the second lens unit L2, and the focal length f3 of the third lens unit L3 are set as follows. f1 = 54.279 f2 = −25 f3 = 61.403

In FIG. 3A, the second lens unit L2 is positioned at the first position, and the principal point distance D1L between the first lens unit L1 and the second lens unit L2 and the second lens unit L2 are set.
The principal point interval D2L between the second lens unit L3 and the third lens unit L3 is set as follows. D1L = 10 D2L = 49.679 Accordingly, in FIG. 3A, light from the on-axis object point O spaced apart from the principal point of the first lens unit L1 by D0 = 145 to the left in the figure is the first light. Lens group L1 to third lens group L
3, the distance from the principal point of the third lens unit L3 to the right side in FIG.
An on-axis image point I separated by 3 = 210.125 is reached.

On the other hand, in FIG. 3B, the second lens unit L2 is positioned at the second position, the distance D1H between the principal points between the first lens unit L1 and the second lens unit L2, and the second lens unit L2.
The principal point interval D2H between the second lens unit L3 and the third lens unit L3 is set as follows. D1H = 49.679 D2H = 10 Therefore, the distance S along the optical axis from the first position to the second position is S = 39.679. And FIG.
Also in FIG. 3B, light from the on-axis object point O located at the same position as in FIG. 3A is divided into the first lens unit L1 to the third lens unit L3.
To the on-axis image point I at the same position as in FIG.

In the first embodiment, by switching the position of the second lens unit L2 between the first position and the second position,
The magnification of the second lens unit L2 is switched between the magnification β2L on the low magnification side and the magnification β2H on the high magnification side, and thus the magnification of the entire optical system is switched between the magnification βL on the low magnification side and the magnification βH on the high magnification side. be able to. Specifically, the magnification β2L on the low magnification side and the magnification β2H on the high magnification side of the second lens unit L2, the magnification βL on the low magnification side and the magnification βH on the high magnification side of the entire optical system, and the magnification ratio Z = β2H / β2L = βH / ΒL is as follows.

Β2L = −0.483 β2H = −2.07 βL = −0.7 βH = −3 Z = 4.286 As described above, in the first embodiment, the interval is set by the distance of S = 39.679. By switching the position of the second lens unit L2 between the separated first position and the second position, the magnification of the entire optical system is set between -0.7 times on the low magnification side and -3 times on the high magnification side. Can be switched with.

FIG. 4 is a diagram schematically showing a configuration of a stereo microscope according to a second embodiment of the present invention. In the second embodiment, the two-stage magnification switching optical system of the first embodiment is applied to an internal oblique stereo microscope. In the stereo microscope of FIG. 4, the observation system for the right eye and the observation system for the left eye are arranged so as to be inclined inward. The two-stage magnification switching optical system of the first embodiment is incorporated in each observation system. Since the right-eye observation system and the left-eye observation system have the same configuration as each other, the second observation system focuses on only one observation system without distinguishing between the right-eye observation system and the left-eye observation system.
The configuration of the embodiment will be described.

Light from the observation object O illuminated by an illumination system not shown enters a two-stage magnification switching optical system having the same configuration as in the first embodiment. That is, the two-stage magnification switching optical system includes, in order from the object O side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a third lens unit L2 having a positive refractive power. And a lens unit L3. The second lens unit L2 is positioned between the first position on the first lens unit side indicated by a solid line in FIG.
Is configured to be switchable between a second position on the third lens group side indicated by a broken line.

The light from the object O forms an observation image I via a two-stage magnification switching optical system (L1 to L3). The observation image I thus formed is magnified and observed through the eyepiece Le. In the stereoscopic microscope of the second embodiment, the observation image I formed through the two-stage magnification switching optical system (L1 to L3) by switching the second lens unit L2 between the first position and the second position. Can be switched between -0.7 times on the low magnification side and -3 times on the high magnification side. In addition,
Needless to say, the observation magnification is a value obtained by multiplying the magnification of the eyepiece Le by the magnification of the observation image.

As described above, in the stereo microscope of the second embodiment, only the position of the second lens unit L2 of the two-stage magnification switching optical system (L1 to L3) arranged in the optical path other than the parallel light beam optical path is changed. Thus, the magnification of the observation image can be switched in two stages. Therefore, as compared with a conventional stereomicroscope in which the entire afocal system is rotated by 180 ° in the parallel light beam path or the entire afocal system is inserted into and removed from the parallel light beam path, space saving can be achieved, and As a result, the size of the entire stereomicroscope can be reduced.

FIG. 5 is a diagram schematically showing a configuration of a two-stage magnification switching optical system according to a third embodiment of the present invention. In the third embodiment, the two-stage magnification switching optical system of the present invention is configured as an afocal system. The two-stage magnification switching optical system in FIG. 5 includes, in order from the object side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a third lens unit L2 having a positive refractive power. And a lens unit L3. Then, the second lens unit L2 is arranged as shown in FIG.
It is configured to be switchable between a first position on the first lens group side shown in FIG. 5A and a second position on the third lens group side shown in FIG. 5B.

In the third embodiment, the focal length f1 of the first lens unit L1, the focal length f2 of the second lens unit L2, and the focal length f3 of the third lens unit L3 are set as follows. f1 = 80 f2 = −20 f3 = 80

In FIG. 5A, the second lens unit L2 is positioned at the first position, and the principal point distance D1L between the first lens unit L1 and the second lens unit L2 and the second lens unit L2 are set.
The principal point interval D2L between the second lens unit L3 and the third lens unit L3 is set as follows. D1L = 20 D2L = 50 Therefore, in FIG.
From the first lens group L1 to the third lens group L3, reaches an axial image point I at infinity. In other words, the first
The parallel light incident on the lens group L1 is divided into the first lens groups L1 to L1.
The light is emitted as parallel light through the third lens unit L3.

On the other hand, in FIG. 5B, the second lens unit L2 is positioned at the second position, and the principal point distance D1H between the first lens unit L1 and the second lens unit L2 and the second lens unit L2
The principal point interval D2H between the second lens unit L3 and the third lens unit L3 is set as follows. D1H = 50 D2H = 20 Therefore, the distance S along the optical axis from the first position to the second position is S = 30. Also, in FIG. 5B, the light from the infinite object point O at infinity, as in FIG. 5A, passes through the first lens unit L1 to the third lens unit L3, and To the on-axis image point I at infinity.

In the third embodiment, by switching the position of the second lens unit L2 between the first position and the second position,
The magnification of the second lens unit L2 is switched between a magnification β2L on the low magnification side and a magnification β2H on the high magnification side.
3) The overall magnification is defined as a lower magnification βL and a higher magnification βH.
And can be switched between. Specifically, the magnification β2L on the low magnification side and the magnification β2H on the high magnification side of the second lens unit L2,
Magnification βL on the low magnification side and magnification β on the high magnification side of the entire optical system
H and the magnification ratio Z = β2H / β2L = βH / βL are as follows, respectively.

Β2L = −0.5 β2H = −2 βL = 0.5 βH = 2 Z = 4 As described above, in the third embodiment, the first position and the second position are separated by a distance of S = 30. The second lens unit L2
, The magnification of the entire optical system can be switched between 0.5 times on the low magnification side and 2 times on the high magnification side.

FIG. 6 is a diagram schematically showing the configuration of a stereomicroscope according to a fourth embodiment of the present invention. In the fourth embodiment, the two-stage magnification switching optical system of the third embodiment is applied to a parallel stereo microscope. In the stereo microscope of FIG. 6, the observation system for the right eye and the observation system for the left eye share a common objective lens Lo.
And the two-stage magnification switching optical system of the third embodiment is incorporated in the parallel light beam path of each observation system. Since the observation system for the right eye and the observation system for the left eye have the same configuration, the configuration of the fourth embodiment will be described focusing on one observation system without distinguishing between the right eye and the left eye. I do.

Light from the observation object O illuminated by an illumination system not shown becomes parallel light through a common objective lens Lo and enters a two-stage magnification switching optical system having the same configuration as that of the third embodiment. I do. That is, the two-stage magnification switching optical system includes, in order from the object O side, a first lens unit L1 having a positive refractive power and a second lens unit L2 having a negative refractive power.
2 and a third lens unit L3 having a positive refractive power. The second lens unit L2 is configured to be switchable between a first position on the first lens unit side indicated by a solid line in FIG. 6 and a second position on the third lens unit side indicated by a broken line in FIG. I have. The light from the object O through the common objective lens Lo is transmitted to the two-stage magnification switching optical system (L1 to L
3) and the observation image I is formed via the imaging lens Lt. The formed observation image I is magnified and observed through the eyepiece Le.

In the stereo microscope of the fourth embodiment, the magnification of the two-stage magnification switching optical system (L1 to L3) is changed to the low magnification side by switching the second lens unit L2 between the first position and the second position. Between the magnification βL = 0.5 × and the magnification βH = 2 × on the high magnification side, and is formed via the common objective lens Lo, the two-stage magnification switching optical system (L1 to L3) and the imaging lens Lt. The magnification of the observed image I can be switched between a low magnification BL and a high magnification BH. Magnification BL on the low magnification side and magnification B on the high magnification side of observation image I
H is represented by the following equations (13) and (14). BL = βL · (−Ft / Fo) (13) BH = βH · (−Ft / Fo) (14) where Fo is the focal length of the common objective lens Lo, and is the focal length of the imaging lens Lt. is there.

The observation magnification is a value obtained by multiplying the magnification of the observation image I by the magnification of the eyepiece Le. As described above, in the stereomicroscope of the fourth embodiment, the two-stage magnification switching optical system (L1 to L3) disposed in the parallel beam path.
By simply switching only the position of the second lens unit L2, the magnification of the observation image can be switched in two stages. Therefore, as compared with a conventional stereomicroscope in which the entire afocal system is rotated by 180 ° in the parallel light beam path or the entire afocal system is inserted into and removed from the parallel light beam path, space saving can be achieved, and As a result, the size of the entire stereomicroscope can be reduced.

[0041]

As described above, according to the present invention,
By switching only the position of the second lens group in an optical system having three positive / negative / positive lens units, the magnification of the optical system can be switched in two stages. The two-stage magnification switching optical system of the present invention can be configured as a focal system or an afocal system. The two-stage magnification switching optical system of the present invention configured as a focal system or an afocal system can be applied to a stereo microscope. In this case, by switching only the position of the second lens unit L2 in the two-stage magnification switching optical system, the magnification of the object image can be switched in two stages, so that the size of the entire stereomicroscope can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of two-stage magnification switching in the present invention.

FIG. 2 is a diagram illustrating an overall basic configuration of a two-stage magnification switching optical system according to the present invention.

FIG. 3 is a diagram schematically illustrating a configuration of a two-stage magnification switching optical system according to a first example of the present invention.

FIG. 4 is a diagram schematically showing a configuration of a stereo microscope according to a second embodiment of the present invention.

FIG. 5 is a diagram schematically showing a configuration of a two-stage magnification switching optical system according to a third embodiment of the present invention.

FIG. 6 is a diagram schematically showing a configuration of a stereomicroscope according to a fourth embodiment of the present invention.

[Explanation of symbols]

 L1 First lens group L2 Second lens group L3 Third lens group Le Eyepiece Lo Objective lens Lt Imaging lens

Claims (8)

[Claims] A first lens group having a positive refractive power for refracting a light beam from a predetermined on-axis object point and guiding the light beam toward a first point on the optical axis; A second lens group having a negative refracting power for refracting the light beam and guiding it along the same direction as the light beam emitted from the second point on the optical axis; and refracting the light beam passing through the second lens group. A third lens group having a positive refracting power to guide the second lens group to a predetermined on-axis image point, without changing a position of the first lens group and a position of the third lens group. Is switched between the first position on the first lens group side and the second position on the third lens group side, so that the magnification of the entire optical system is reduced to the first magnification on the low magnification side and the second magnification on the high magnification side. And the distance along the optical axis from the first position to the second position is S, The focal length of the lens group is f2, the magnification ratio of the second magnification to the first magnification is Z, the magnification of the second lens group at the first position is β2L, and the second lens at the second position is β2L. Group magnification β
A two-stage magnification switching optical system characterized by satisfying the relationship of S = -f2 (Z-1) / ZZ2L = -1 / ZZ2H = -Z when 2H. 2. The optical system according to claim 1, wherein the predetermined on-axis object point and the predetermined on-axis image point are located at infinity from the optical system, and the optical system constitutes an afocal optical system. Item 2. The two-stage magnification switching optical system according to Item 1. 3. The first lens group configured to be insertable into and removable from the optical path at the first position, and the second lens group configured to be insertable into and removable from the optical path at the second position. A second sub-lens group, and selectively inserting and removing the first and second sub-lens groups with respect to an optical path, so that the position of the second lens group is changed to the first position and the first position. The two-stage magnification switching optical system according to claim 1, wherein switching is performed between a second position and a second position. 4. The second lens group is rotated about an intermediate point between the first position and the second position, so that the position of the second lens group is shifted between the first position and the second position.
The two-stage magnification switching optical system according to claim 1, wherein the optical system is switched between positions. 5. The position of the second lens group is moved to the first position by selectively moving the second lens group along the optical axis direction between the first position and the second position. The two-stage magnification switching optical system according to claim 1, wherein switching is performed between the first position and the second position. 6. A stereo microscope having a pair of observation systems, wherein each of the pair of observation systems includes the two-stage magnification switching optical system according to any one of claims 1 to 5, and the second lens. By switching the position of the group between the first position and the second position, the magnification of the object image formed via the observation system is switched between a low magnification and a high magnification. A stereo microscope characterized by the following. 7. A stereomicroscope having a pair of observation systems, wherein each of the pair of observation systems is one of claims 1 and 3.
6. An object image is formed only via the two-stage magnification switching optical system according to any one of the above items 5 to 5, by switching the position of the second lens group between the first position and the second position. Wherein the magnification of the object image is switched between a low magnification and a high magnification. 8. A stereo microscope having a pair of observation systems, wherein each of the pair of observation systems includes an objective lens, an imaging lens, and a parallel light beam path between the objective lens and the imaging lens. An object image is formed via the two-stage magnification switching optical system according to any one of claims 2 to 5, which is disposed, and the position of the second lens group is defined by the first position and the second position. Wherein the magnification of the object image is switched between a lower magnification and a higher magnification.