JP2010210998A - Objective lens and microscope device having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective lens which is constituted, by incorporating respective elements, such as a polarizer, in advance and a quarter-wave plate necessary for extremely low magnification observation, thereby becoming capable of switching observation, from a very low magnification to a high magnification only by revolving operation of a revolver, and to provide a microscope device which includes the lens. <P>SOLUTION: The objective lens 10 has a first depolarizer 11, the polarizer 12, a first quarter-wave plate 13, a plurality of lens groups 14, and at least one optical element (second depolarizer 15) which are arranged in order from a light source side. The optical element is an element for making the polarization state change, between when a light enters and when a light exits. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an objective lens and a microscope apparatus having the objective lens.

In general, in a microscope apparatus equipped with a reflective illumination device, when using an objective lens with a long focal length, in other words, an objective lens with a low imaging magnification, a pair of crosses are formed in the reflective illumination device and the imaging optical system. By arranging a Nicol polarizer and placing a quarter-wave plate between the objective lens and the sample, it is possible to remove reflected noise light from the objective lens surface and detect only the signal light from the sample. (For example, refer patent document 1). According to this arrangement, the intensity of the noise light to the signal light from the sample can be attenuated to about 10 ^-4.

JP 11-271622 A

  On the other hand, in a conventional microscope apparatus, when using an objective lens with a short focal length, in other words, a high imaging magnification, the radius of curvature of each lens constituting the objective lens is reduced, etc. Since it is possible to design so that the reflected light is not condensed on the image plane, it is not always necessary to use the polarizer and the quarter wavelength plate as described above.

  Therefore, when a very low magnification (2.5 times or less) objective lens is used in a state where a plurality of objective lenses having different magnifications are mounted on the revolver, a pair configured to be detachable from the microscope apparatus. The polarizer is inserted into the optical path in a crossed Nicol state, and a quarter wave plate mounted in advance on the tip of the objective lens is rotated to set the position where the signal intensity from the sample is highest, and the observation is performed. In order to continue switching from a medium magnification to a high magnification objective lens, it was necessary to bring the pair of polarizers used for observation at extremely low magnification out of the optical path.

  That is, when switching the objective lens, there is a problem that not only the rotation operation of the revolver but also operations such as insertion and removal of the polarizer and adjustment of the quarter wavelength plate are necessary.

  The present invention has been made in view of such problems, and the revolver is rotated by incorporating each element such as a polarizer and a quarter-wave plate necessary for extremely low magnification observation in advance. It is an object to provide an objective lens capable of switching observation from extremely low magnification to high magnification and a microscope apparatus having the objective lens.

  In order to achieve such an object, an objective lens of the present invention includes a polarizer, a first quarter-wave plate, a plurality of lens groups, and at least one optical element, which are arranged in order from the image side. The optical element is an element that changes a polarization state between an incident time and an emitted time.

  A first depolarizing element (for example, the first depolarizer 11 in the present embodiment) is arranged on the image side of the polarizer so that its axis forms 45 degrees with the axis of the polarizer. preferable.

  The optical element preferably includes at least one of a second depolarizing element (for example, the second depolarizer 15 in the present embodiment) and a second quarter-wave plate.

  Further, when the optical element has both the second depolarization element and the second quarter-wave plate, the fast axis of the first quarter-wave plate and the second 1 / Arranged so that the fast axis of the four-wave plate is parallel to each other, and further, the axis of the second depolarizer and the fast axis of the second quarter-wave plate are orthogonal to each other. Is preferred.

  When the optical element has only the second quarter-wave plate, the fast axis of the first quarter-wave plate and the fast axis of the second quarter-wave plate are parallel to each other. It is preferable to arrange so that.

  Further, it is preferable that the polarizer axis and the fast axis of the first quarter-wave plate are arranged at 45 degrees with each other.

  The transmission surfaces of the first depolarization element, the polarizer, the first quarter-wave plate, the second depolarization element, and the second quarter-wave plate are the same as those of the objective lens. It is preferable to be inclined at 2 degrees or more and less than 6 degrees with respect to the optical axis.

  Moreover, the microscope apparatus of the present invention has any one of the above objective lenses.

  According to the present invention, it is possible to perform observation from extremely low magnification to high magnification only by rotating the revolver by constructing in advance elements such as a polarizer and a quarter wave plate necessary for extremely low magnification observation. It is possible to provide an objective lens capable of switching between and a microscope apparatus having the objective lens.

It is a schematic sectional drawing of the objective lens which concerns on this embodiment, and a microscope apparatus which has this. It is the figure which looked at the axial direction of each optical element (1st depolarizer, polarizer, and 1st quarter wave plate) from the upper part of the microscope apparatus. It is the figure which represented typically the cross-sectional block diagram of the objective lens which concerns on 1st Example, and the polarization state of the light beam which passes through the inside of this lens. It is the figure which represented typically the cross-sectional block diagram of the objective lens which concerns on 2nd Example, and the polarization state of the light beam which passes through the inside of this lens. It is the figure which represented typically the cross-sectional block diagram of the objective lens which concerns on 3rd Example, and the polarization state of the light beam which passes through the inside of this lens. It is a figure which shows an example of the wavelength characteristic of the quarter wavelength plate corresponding to a wide band.

  Hereinafter, the present embodiment will be described with reference to the drawings. FIG. 1 is a sectional view showing the configuration of a microscope apparatus having an objective lens according to this embodiment.

  As shown in FIG. 1, the microscope apparatus according to the present embodiment collects the light source 1, the collector lens 2 that converts light from the light source 1 into parallel light, and the parallel light converted by the collector lens 2. A relay lens group 3 that forms a light source image at the position of the aperture stop 4; a field stop 5 that is arranged at a position conjugate to the focal position of the rear side of the collector lens 2 (that is, the relay lens group 3 side); A field lens 6 that converts a light beam passing through the center of the light beam 5 into a light beam parallel to the optical axis, a half mirror 7 that deflects the parallel light beam converted by the field lens 6 downward in the drawing, and a lower side of the half mirror 7. It has a revolver 8 to which a plurality of objective lenses can be attached, and objective lenses 9 and 10 attached to the revolver 8. In FIG. 1, the objective lens 10 of extremely low magnification (2.5 times or less) is selected. Further, the microscope apparatus divides the imaging optical system, specifically, the second objective lens 18 that forms the primary image of the specimen 16, the first prism 19 that appropriately determines the depression angle, and the optical path suitable for binocular observation. The second prism 20 and the eyepiece 22 for magnifying and observing the primary image of the specimen 16 formed by the second objective lens 18 are included.

  According to the microscope apparatus having the above configuration, the light (illumination light) emitted from the light source 1 is deflected by the half mirror 7 via the collector lens 2, the relay lens group 3, the aperture stop 4, the field stop 5 and the field lens 6. Then, the specimen 16 on the stage 17 is illuminated via the selected objective lens 10. Thereby, reflection type bright field illumination is achieved.

  Further, the illumination light reflected by the specimen 16 passes through the selected objective lens 10 as the light (signal light) necessary for observing the specimen 16, passes through the half mirror 7, and passes through the second objective lens 18. The first prism 19 and the second prism 20 are sequentially guided to the eyepiece lens 22. The user of the microscope apparatus can enlarge and observe the primary image 21 of the specimen 16 with the eyepiece 22.

  Hereinafter, the selected internal configuration of the extremely low magnification objective lens 10 will be described in detail.

(First embodiment)
The objective lens 10 according to the first example will be described with reference to FIGS. The objective lens 10 according to the first embodiment is an extremely low magnification objective lens of 2.5 times or less, and as shown in FIG. 1, the first depolarizer 11 and the polarizer arranged in order from the light source side. 12, a first quarter-wave plate 13 (hereinafter referred to as a first λ / 4 plate 13), a plurality of lens groups 14, and a second depolarizer 15.

  The depolarizers 11 and 15 are optical elements having a function of canceling the polarization state of incident light (non-polarization state). The polarizer 12 is an optical element having a function of selectively transmitting a predetermined polarization component. Further, the λ / 4 plate 13 is an optical element having a function of generating a quarter wavelength phase difference between light oscillating in the fast axis direction and light oscillating in the orthogonal direction.

  The first depolarizer 11, the polarizer 12, and the first λ / 4 plate 13 are arranged so that the axis of the first depolarizer 11 is relative to the axis of the polarizer 12 when viewed from above the microscope apparatus as shown in FIG. The fast axis of the first λ / 4 plate 13 (oscillation direction in which the phase advances by 1/4 wavelength) so as to form 45 degrees and also with respect to the axis of the polarizer 12 (on the side opposite to the first depolarizer 11) ) Are arranged at 45 degrees. In the case of the present embodiment, the axial direction of the second depolarizer 15 may face either direction.

  According to the objective lens 10 having this configuration, the illumination light from the light source 1 first passes through the first depolarizer 11 (however, the polarization state is not particularly converted here) and enters the polarizer 12. As the illumination light incident on the polarizer 12, only the light polarized in the axial direction of the element 12 is selected and transmitted. Subsequently, the illumination light is converted into circularly polarized light by the first λ / 4 plate 13, is subjected to an image forming action by the plurality of lens groups 14, passes through the second depolarizer 15, becomes non-polarized light, and the specimen 16 Is irradiated.

  FIG. 3 schematically shows the polarization state of the light beam passing through the objective lens 10. The solid circle indicates the axial direction of each optical element, and the broken circles P1 to P12 all receive light. The polarization state seen from the side is shown. As shown in FIG. 3, when the illumination light (polarized state P1) from the light source 1 which is non-polarized light enters the objective lens 10, it proceeds in the direction indicated by the arrow A1 and first passes through the first depolarizer 11. However, the polarization direction of the light is not particularly converted here, and the illumination light remains unpolarized (polarization state P2). Next, the polarization direction of the illuminating light is selected by the polarizer 12 (polarization state P3), and the first λ / 4 plate 13 converts the light into a counterclockwise circularly polarized light (the polarization plane is counterclockwise when viewed from the light receiving side). Is converted (polarization state P4). And it injects into the some lens group 14 in this polarization state.

However, if the light reflected by any one of the lens surfaces constituting the plurality of lens groups 14 reaches the image plane, it becomes noise light and lowers the contrast of the sample image. Therefore, it is necessary to suppress the generation of noise light. . Here, the behavior of the noise light will be described. The noise light reflected by any lens surface of the plurality of lens groups 14 proceeds in the direction indicated by the arrow A2, but the polarization state is unchanged (the polarization state P5 (ie, the polarization state P5 (ie, , Counterclockwise circularly polarized light as in the polarization state P4)). Then, when the light travels in the direction indicated by the arrow A3 and passes through the first λ / 4 plate 13, it is converted into linearly polarized light (polarization state P6). The polarization state P6 at this time is in a relationship orthogonal to the previous polarization state P3. Therefore, the noise light is blocked by the polarizer 12, and the light intensity is attenuated to about 10 ⁻⁴ or less of the extinction ratio of the polarizer 12, so that even if it reaches the image plane, it becomes a level with no problem. In this way, noise light is avoided in the objective lens 10.

  Subsequently, the illumination light that has become circularly polarized light (polarization state P4) along the arrow A1 is subjected to an imaging action by the plurality of lens groups 14, proceeds in the direction indicated by the arrow A4, and is transmitted through the second depolarizer 15. After being converted to non-polarized light (polarization state P7), the specimen 16 is illuminated. The light (signal light) reflected by the sample 16 travels in the direction indicated by the arrow A5 and passes through the second depolarizer 15 (polarization state P9) while remaining unpolarized (polarization state P8). Then, the signal light travels in the direction indicated by the arrow A6 and is subjected to an image forming action by the plurality of lens groups 14, but the polarization state remains unpolarized even when transmitted through the first λ / 4 plate 13 ( Polarization state P10). For this reason, the signal light is not completely blocked by the polarizer 12, and can transmit light whose polarization direction is the same as the axial direction of the polarizer 12 (polarization state P <b> 11). Further, the signal light passes through the first depolarizer 11 and is converted into non-polarized light (polarization state P12), and then proceeds to the imaging optical system (see FIG. 1) constituting the microscope apparatus.

  Here, in the present embodiment, the reason why the first depolarizer 11 is arranged closest to the imaging optical system side (light source side) (in the objective lens 10) will be described. If the first depolarizer 11 does not exist at this position, the signal light from the sample 16 proceeds to the imaging optical system while maintaining the linearly polarized light selected by the polarizer 12 (polarization state P11), and the inside of the microscope apparatus. Depending on the polarization characteristics of the half mirror 7 arranged on the first mirror 19 and the polarization characteristics of the reflection films of the first prism 19 and the second prism 20, there is a risk of being affected by brightness and hue. Therefore, by arranging the first depolarizer 11 closest to the imaging optical system in the objective lens 10 and converting the signal light entering the imaging optical system to non-polarized light (polarization state P12), the previous half mirror This is because observation that does not depend on the polarization characteristics of the prisms 7 and 19 and 20 is possible.

  In the present embodiment, the reason why the second depolarizer 15 is arranged closest to the specimen 16 (in the objective lens 10) will be described. Since the specimen 16 is always irradiated with illumination light that is not polarized. This is because the effect that the observation independent of the 16 polarization characteristics is possible is obtained.

  In the objective lens configured as described above, the intensity of the signal light is approximately halved when the illumination light passes through the polarizer 12 once and the light reflected by the sample 16 passes twice. To do. That is, the intensity of the signal light is attenuated to about ¼ of the incident light. However, the low-magnification objective lens is sufficiently bright compared to the high-magnification objective lens, so even if the intensity of the signal light is about ¼ of the incident light, the intensity is sufficient for observation. is there.

  In this embodiment, each optical element inserted into the objective lens 10 such as the first depolarizer 11, the polarizer 12, the first λ / 4 plate 13, and the second depolarizer 15 is the same as the objective lens 10. It is desirable that they are arranged with an inclination of 2 degrees or more and less than 6 degrees with respect to the optical axis. If the method described so far is used, noise light generated by reflection on the lens surfaces constituting the plurality of lens groups 14 can be removed. However, the optical elements to be inserted (other than the lens group 14) as described above generally have a parallel plate shape, and reflected light from their surfaces cannot be removed. Therefore, by arranging each optical element so as to be inclined with respect to the optical axis of the objective lens 10, light reflected from the incident surface and exit surface of each optical element becomes noise light and avoids entering the observation field of view. ing.

  First, an element disposed between the plurality of lens groups 14 and the specimen 16 will be considered. The objective lens of the microscope apparatus is generally a specimen side telecentric. Therefore, the light beam incident on the element is a conical light beam whose principal ray is parallel to the optical axis and has an apex angle corresponding to the numerical aperture of the objective lens. Therefore, if the light beam reflected on the surface of the element can be tilted so as to be equal to or larger than the apex angle with respect to the optical axis, the light beam cannot pass through the pupil diameter of the objective lens and therefore does not reach the image plane.

  Further, since the numerical aperture of the ultra low magnification objective lens is about 0.03 and its apex angle is about 1.7 degrees, it has a conical shape from -1.7 degrees to +1.7 degrees with respect to the optical axis. Are guided to the image plane. That is, the inclination of the element with respect to the optical axis may be determined so that the reflected light on the surface of the element comes out of the cone. If the element is tilted by +1.7 degrees or more, the reflected light of the incident light at -1.7 degrees with respect to the optical axis will be +1.7 degrees or more with respect to the optical axis. .

  Next, an element disposed on the revolver 8 side from the plurality of lens groups 14 will be considered. For example, when the field number of the eyepiece 22 is 25 and the focal length of the second objective lens 18 constituting the imaging optical system is 200 mm, the maximum image of the light beam between the objective lens 10 and the second objective lens 18 is displayed. The angle is about 3.6 degrees. That is, if the light beam reflected by the surface of the element is tilted so as to be 3.6 degrees or more, the light beam can be out of the observation field. Therefore, it is more preferable that the tilt angle of the element with respect to the optical axis is 3.6 degrees or more because observation in a wide field of view is possible.

  Considering the upper limit of the tilt angle, for example, when the element to be inserted is a polarizing plate or a wide-band wave plate made of resin, the angle characteristics are relatively good. Less is. However, in the case of an objective lens having a limited focal length and a long focal length (that is, a low magnification), it is more convenient for aberration correction that the total length of the lens is as long as possible. Therefore, it is preferable to make the total thickness of elements inserted for noise removal as thin as possible. When the total thickness of the element group when arranged perpendicularly to the optical axis of the objective lens 10 is t, the diameter is D, and the inclination angle is θ, the total thickness t ′ of the element group when tilted is It is represented by (1).

  t ′ = D × sin θ + t × cos θ (1)

  For example, in the objective lens 10, when three types of elements are inserted on the revolver 8 side, each is 2 mm in thickness including the substrate glass, and is arranged with an air interval of 1 mm, the total number of cases when arranged perpendicular to the optical axis is obtained. The thickness is 8 mm. When such an element group is arranged at an inclination angle of 6 degrees, the total thickness t ′ is expressed by the following equation (2).

  t ′ = 25 × sin 6 ° + 8 × cos 6 ° = 10.6 [mm] (2)

  For example, assuming that the confocal distance is 60 mm, the total thickness t ′ of the element group occupies nearly 20% of the confocal distance of the objective lens 10 as can be seen from the above equation (2), and the degree of freedom in lens design. Therefore, the upper limit of the inclination is preferably about 6 degrees.

  Therefore, in this embodiment, the optical element inserted into the objective lens 10 is disposed with an inclination of 2 degrees or more and less than 6 degrees with respect to the optical axis of the objective lens 10 in order to remove noise light. It is desirable.

(Second embodiment)
Next, the objective lens 10 according to the second example will be described. In the present embodiment, those having the same configuration and function as those of the first embodiment are denoted by the same reference numerals and description thereof is omitted. In particular, the reason why the noise light reflected by the plurality of lens groups 14 is attenuated is the same as in the first embodiment, and thus the description thereof is omitted.

  As shown in FIG. 4, the objective lens of the second example has a second quarter wavelength between the second depolarizer 15 constituting the objective lens 10 of the first example and the plurality of lens groups 14. The plate 31 (hereinafter referred to as the second λ / 4 plate 31) is arranged. At this time, it arrange | positions so that the axis | shaft of the 2nd (lambda) / 4 board 31 and the axis | shaft of the 2nd depolarizer 15 may mutually orthogonally cross.

  In the objective lens according to the second embodiment having such a configuration, the illumination light passing through the first depolarizer 11, the polarizer 12, the first λ / 4 plate 13, and the plurality of lens groups 14 is circularly polarized ( Polarization state P4), when passing through the second λ / 4 plate 31, it is converted into linearly polarized light (polarization state P7a). The polarization direction of the linearly polarized light forms 45 degrees with the axial direction of the second depolarizer 15. The depolarizer has the property of depolarizing the linearly polarized light polarized in the direction of 45 degrees with respect to the axis most efficiently. Thus, the specimen 16 is illuminated with illumination light that is completely unpolarized. Note that the behavior of the light reflected from the specimen 16 (signal light) is almost the same as that in the first embodiment, and thus the description thereof is omitted here.

  According to the objective lens of the second embodiment, the performance of the second depolarizer 15 can be exhibited to the maximum, and the specimen 16 can be irradiated with completely non-polarized light, and observation that does not depend on the polarization characteristics of the specimen more. Is possible.

(Third embodiment)
Next, an objective lens according to Example 3 will be described. In the present embodiment, those having the same configuration and function as those of the first embodiment are denoted by the same reference numerals and description thereof is omitted. In particular, the reason for the attenuation of the noise light reflected by the plurality of lens groups 14 is the same, and thus the description thereof will be omitted.

  As shown in FIG. 5, the objective lens of the third embodiment is replaced with a second quarter-wave plate 31 ′ (hereinafter referred to as the first depolarizer 15) instead of the second depolarizer 15 constituting the objective lens 10 of the first embodiment. 2 λ / 4 plate 31 ').

  In the objective lens of the third embodiment having such a configuration, the illumination light that has passed through the first depolarizer 11, the polarizer 12, the first λ / 4 plate 13, and the plurality of lens groups 14 is circularly polarized (polarization state P4). However, after passing through the second λ / 4 plate 31 ′, it is converted into linearly polarized light (polarization state P7a). In this embodiment, the specimen 16 is illuminated with the linearly polarized light as it is. The light reflected by the sample 16 indicated by the arrow A5 remains in the same manner as linearly polarized light (polarization state P8a). Subsequently, the signal light travels in the direction indicated by the arrow A6, and when it passes through the first λ / 4 plate 13 again, it is converted into circularly polarized light (polarization state P9a). After that, when passing through the plurality of lens groups 14 and passing through the first λ / 4 plate 13 which is another wavelength plate, it is converted again into linearly polarized light (polarization state P10a). Since the polarization direction at this time coincides with the axial direction of the polarizer 12, the signal light from the sample 16 can pass through the polarizer 12 (polarization state P11). Then, the signal light passes through the first depolarizer 11 and is converted to non-polarized light (polarization state P12), and then proceeds to the imaging optical system (see FIG. 1) constituting the microscope apparatus.

  According to the objective lens of the third embodiment, since the specimen 16 is illuminated with linearly polarized light (polarization state P10a), if the specimen 16 has a polarization characteristic, the brightness changes depending on the orientation. Since the polarization state can be converted without any light loss, there is an advantage that about half of the incident light (excluding the attenuation of illumination light by the polarizer 12) can be used.

  As described above, according to the present invention, an objective lens is configured by incorporating in advance each optical element such as a polarizer and a quarter-wave plate necessary for observation at an extremely low magnification, thereby forming a microscope apparatus as in the conventional case. It is not necessary to attach the optical element to the lens, and the user can observe from the extremely low magnification to the high magnification only by rotating the revolver.

  In addition, in order to make this invention intelligible, although demonstrated with the component requirement of embodiment, it cannot be overemphasized that this invention is not limited to this.

  For example, the quarter-wave plate used in the present invention is preferably compatible with a wide band as much as possible. Specifically, when the retardation (phase difference) is about 80 to 100 degrees at a wavelength of 400 to 600 nm, the color of the sample does not change and good observation is possible.

  FIG. 6 is a graph showing an example of wavelength characteristics of a quarter-wave plate compatible with a wide band, in which the horizontal axis indicates the wavelength and the vertical axis indicates the retardation (phase difference) generated by the angle. In general, a phase plate such as a quarter-wave plate is an element that delays the phase of polarized light in a direction perpendicular to polarized light in a certain direction, but usually uses birefringence, and therefore depends on the wavelength of light. There is a feature that the phase difference changes. Therefore, as in the case of the first λ / 4 plate 13 used above, when the noise light is used twice for the purpose of attenuation by crossed Nicols, it may pass twice depending on the wavelength. Since it did not return to linearly polarized light, colored noise light was sometimes observed. Here, when a quarter-wave plate is produced by bonding two substances having different birefringence and refractive index distribution, a wave plate having a desired phase difference can be produced at specific two wavelengths. This is called a broadband wave plate or an achromatic wave plate. If a wave plate having such characteristics is used, noise can be removed at almost all wavelengths even when reflected illumination is observed with white light.

  In the objective lens according to each embodiment, a quarter wavelength plate may be used instead of the first depolarizer 11. Since the quarter-wave plate is a thin sheet, the space in the objective lens with a limited length can be effectively used as compared with a thick depolarizer.

10 Objective lens 11 First depolarizer (first depolarizer)
12 Polarizer 13 First λ / 4 Plate 14 Multiple Lens Group 15 Second Depolarizer (Second Depolarizer)
31 Second λ / 4 plate (second embodiment)
31 'second λ / 4 plate (third embodiment)

Claims (8)

Having a polarizer, a first quarter-wave plate, a plurality of lens groups, and at least one optical element, arranged in order from the image side,
2. The objective lens according to claim 1, wherein the optical element is an element that changes a polarization state between an incident time and an emitted time.   2. The objective lens according to claim 1, wherein the first depolarizing element is arranged on the image side of the polarizer so that an axis thereof forms 45 degrees with an axis of the polarizer. 3.   The objective lens according to claim 1, wherein the optical element includes at least one of a second depolarizing element and a second quarter-wave plate.   When both the second depolarizing element and the second quarter wave plate are used as the optical element, the fast axis of the first quarter wave plate and the second quarter wavelength are used. It is arranged so that the fast axis of the plate is parallel to each other, and the axis of the second depolarizing element and the fast axis of the second quarter-wave plate are arranged so as to be orthogonal to each other. The objective lens according to claim 3.   When the optical element has only the second quarter-wave plate, the fast axis of the first quarter-wave plate and the fast axis of the second quarter-wave plate are parallel to each other. The objective lens according to claim 3, wherein the objective lens is arranged as follows.   6. The objective lens according to claim 1, wherein an axis of the polarizer and a fast axis of the first quarter-wave plate are arranged to form 45 degrees with each other.   The transmission surfaces of the first depolarization element, the polarizer, the first quarter-wave plate, the second depolarization element, and the second quarter-wave plate are optical axes of the objective lens, respectively. The objective lens according to claim 3, wherein the objective lens is inclined at least 2 degrees and less than 6 degrees. The microscope apparatus which has the objective lens as described in any one of Claims 1-7.

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