Immersion microscope objective and microscope with it

An immersion microscope objective comprises, in order from an object side, a first lens group having a positive refractive power comprising a cemented lens composed of a plano-convex lens whose plane surface faces the object side and a meniscus lens whose concave surface faces the object side, and at least one single lens having a positive refractive power; a second lens group having a positive refractive power comprising a three-piece cemented lens; and a third lens group having a negative refractive power including a Gaussian type lens structure, wherein the objective satisfies the following conditions when n1, NAob, d0 and β are a refractive index at a d-line of the single lens having the highest refractive index included in the first lens group, a numerical aperture on the object side of the objective, a working distance of the objective, and a magnification of the objective, respectively.1.7≦n10.75≦NAob≦1.450.4≦NAob*d0≦30.03≦NAob/β≦0.1.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application Nos. 2010-005503, filed on Jan. 14, 2010 and 2009-102954 filed on Apr. 21, 2009, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an immersion microscope objective and a microscope provided with it.

2. Description of the Related Art

Fluorescent observation is widely known as a method for observing a living body. Fluorescent observation is a method for observing a specimen by applying excitation light to a living body specimen to which a tag is attached by fluorescent dye and detecting fluorescent light generated from the fluorescent dye. The fluorescent dye is selectively combined with a specific molecule and a component object in the living body specimen and dyes them. Therefore, the behavior, combination state, movement state and the like of molecules in the specimen can be observed in addition to the structure of the specimen by detecting the fluorescent light.

Traditionally, the burden on a specimen due to dyeing with fluorescent dye has been heavy and living body targets that can be observed while living have been limited to a cell's level, such as a culture cell, and the like. However, recently, a fluorescent protein which can be expressed in a cell by introducing a gene has been put into practical use and damage to the living body specimen can be reduced by using this protein. GFP (green fluorescent protein), YFP (yellow fluorescent protein) or the like are examples of such a protein. The number of targets of fluorescent observation has been expanded by the commercialization of these fluorescent proteins and currently various living body specimens can be observed.

Japanese Laid-open Patent Publication No. 10-274742 discloses an immersion microscope objective usable for such a fluorescent observation.

SUMMARY OF THE INVENTION

One aspect of the present invention provides an immersion microscope objective which comprises a first lens group having a positive refractive power, including a cemented lens composed of a plano-convex lens whose plane surface faces the object side and a meniscus lens whose concave surface faces the object side, and at least one of a single lens having a positive refractive power, a second lens group having a positive refractive power, including a three-piece cemented lens, and a third lens group having a negative refractive power, including a Gaussian type lens structure, in order from the object side, and which satisfies the following conditions when n1, NAob, d0 and β are a refractive index at a d-line of the single lens having the highest refractive index included in the first lens group, a numerical aperture on the object side of the immersion microscope objective, a working distance of the immersion microscope objective and a magnification of the immersion microscope objective, respectively:
1.7≦n1
0.75≦NAob≦1.45
0.4≦NAob*d0≦3
0.03≦NAob/β≦0.1

Another aspect of the present invention provides an immersion microscope objective which comprises a first lens group having a positive refractive power, including a cemented lens composed of a plano-convex lens whose plane surface faces the object side and a meniscus lens whose concave surface faces the object side, and at least one single lens having a positive refractive power, a second lens group having a positive refractive power, including a three-piece cemented lens, and a third lens group having a negative refractive power, including a Gaussian type lens structure, in order from the object side, and in which the second lens group includes a first three-piece cemented lens composed of a positive refractive lens, a negative refractive lens and a positive refractive lens, a lens, and a second three-piece cemented lens composed of a positive refractive lens, a negative refractive lens and a positive refractive lens, in order from the object side.

Another aspect of the present invention provides an immersion microscope objective which comprises a first lens group having a positive refractive power, including a cemented lens composed of a plano-convex lens whose plane surface faces the object side and a meniscus lens whose concave surface faces the object side, and at least one of a single lens having a positive refractive power, a second lens group having a positive refractive power, including a three-piece cemented lens, and a third lens group having a negative refractive power, including a Gaussian type lens structure, in order from the object side, and in which the change in width of a focal position is within a focal depth between a visible light range and a near-infrared light range.

Another aspect of the present invention provides a confocal microscope which comprises an immersion microscope objective, a laser light source for emitting laser light, a separation unit for separating fluorescent light generated from a specimen to which the laser light is applied from the laser light, a scanning unit for scanning the specimen, a confocal stop disposed in a optically conjugate position with the focal position of the immersion microscope objective, and a detector for detecting the fluorescent light that has passed through the confocal stop. The immersion microscope objective comprises a first lens group having a positive refractive power, including a cemented lens composed of a plano-convex lens whose plane surface faces the object side and a meniscus lens whose concave surface faces the object side, and at least one single lens having a positive refractive power, a second lens group having a positive refractive power, including a three-piece cemented lens, and a third lens group having a negative refractive power including a Gaussian type lens structure and which satisfies the following conditions when n1, NAob, d0 and β are a refractive index at a d-line of the single lens having the highest refractive index included in the first lens group, a numerical aperture on the object side of the immersion microscope objective, a working distance of the immersion microscope objective and a magnification of the immersion microscope objective, respectively:
1.7≦n1
0.75≦NAob≦1.45
0.4≦NAob*d0≦3
0.03≦NAob/β≦0.1

Another aspect of the present invention provides a two-photon excitation microscope which comprises an immersion microscope objective, an ultra-short-pulse laser light source for emitting laser light that causes two-photon excitation in a specimen, a separation unit for separating fluorescent light generated from the specimen to which the laser light is applied from the laser light, a scanning unit for scanning the specimen, and a detector for detecting the fluorescent light. The immersion microscope objective comprises a first lens group having a positive refractive power, including a cemented lens composed of a plano-convex lens whose plane surface faces the object side and a meniscus lens whose concave surface faces the object side, and at least one single lens having a positive refractive power, a second lens group having a positive refractive power, including a three-piece cemented lens, and a third lens group having a negative refractive power including a Gaussian type lens structure, and which satisfies the following conditions when n1, NAob, dO and β are a refractive index at a d-line of the single lens having the highest refractive index included in the first lens group, a numerical aperture on the object side of the immersion microscope objective, a working distance of the immersion microscope objective and a magnification of the immersion microscope objective, respectively.
1.7≦n1
0.75≦NAob≦1.45
0.4≦NAob*d0≦3
0.03≦NAob/β≦0.1

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Firstly, matters common to respective preferred embodiments of the present invention will be explained. The configurations and functions of respective lens groups will be roughly explained with reference toFIG. 1.

The first lens group LG1has, in order from an object side, a positive refractive power and includes a cemented lens CL1composed of a plano-convex lens L1whose plane surface faces the object side and a meniscus lens L2whose concave surface faces the object side, and a single lens L3having a positive refractive power. InFIG. 1, a cover glass CG is also exemplified together with an objective 1. The objective 1 is an immersion microscope objective and immersion liquid, which is not illustrated, is put between the cover glass CG and the plano-convex lens L1in order to realize a large numerical aperture.

In the objective 1, the numerical aperture and the working distance are balanced by using the plano-convex lens L1disposed nearest the object side, and the large numerical aperture and a long working distance are secured. Furthermore, the focal length of the cemented lens CL1is increased by cementing the plano-convex lens L1with the meniscus lens L2. Thus, a longer working distance can be secured. Since its Petzval sum can be corrected for by the meniscus lens, its field curvature can also be suppressed. As a result, a wide field of view (observation range) can be secured. In other words, the objective 1 can secure a long working distance while realizing both a wide observation range and the large numerical aperture by using the cemented lens CL1which is composed of the plano-convex lens L1and the meniscus lens L2and which is disposed nearest the object side.

Furthermore, the objective 1 is provided with a single lens L3having a positive refractive power in the first lens group LG1. The single lens L3suppresses the ray height of divergent light emitted from the meniscus lens L2and corrects high-order spherical and coma aberrations. Therefore, it becomes necessary for the single lens L3to have a strong positive refractive power. The objective 1 is structured in such a way that the single lens L3may attain a strong positive refractive power by using a material with a high refractive index for the single lens L3. Thus, the objective 1 can correct spherical and coma aberrations in the first lens group without increasing the total length of the first lens group excessively. The same effect can also be obtained by using a single lens group composed of the single lens L3and a single lens having a positive refractive power instead of the single lens L3.

The second lens group LG2has a positive refractive power. The second lens group LG2converts divergent light emitted from the first lens group LG1to convergent light and also corrects its chromatic aberration. For fluorescent light used in a fluorescent observation, light having various wavelengths in a visible light wavelength range is used. Therefore, for an objective used for a fluorescent observation, it is necessary for chromatic aberration to also be sufficiently corrected. The correction of a chromatic aberration is realized by the second lens group LG2including a three-piece cemented lens.

It is preferable that the second lens group LG2also include at least two cemented lenses and that the cemented lens CL2disposed nearest the object side of the second lens group LG2be a three-piece cemented lens composed of a positive refractive lens L4, a negative refractive lens L5and a positive refractive lens L6. It is preferable that the second lens group LG2also include a three-piece cemented lens CL2composed of a positive refractive lens L4, a negative refractive lens L5and a positive refractive lens L6, a lens L7, and a three-piece cemented lens CL3composed of a positive refractive lens L8, a negative refractive lens L9, and a positive refractive lens L10, in order from the object side.

The third lens group LG3has a negative refractive power, that is, a so-called Gaussian type lens structure. The third lens group LG3comprises a cemented lens CL4composed of a lens L11having a positive refractive power and a lens L12having a negative refractive power and a cemented lens CL5composed of a lens L13having a negative refractive power and a lens L14having a positive refractive power, in order from the object side. The lenses L12and L13are lenses whose concave surfaces face the image and object sides, respectively, and their concave surfaces are opposed to each other.

A single meniscus lens whose convex surface faces the object side can also be used instead of the cemented lens CL4.

The third lens group LG3converts convergent light from the second lens group LG2to parallel light and emits it while largely correcting an off-axis aberration. In other words, the objective 1 is an infinity corrected objective.

The objective 1 has the above structure and also satisfies the following conditions (1) through (4).
1.7≦n1  (1)
0.75≦NAob≦1.45  (2)
0.4≦NAob*d0≦3  (3)
0.03≦NAob/β≦0.1  (4)

In the above expressions, n1, NAob, d0 and β are the refractive index at the d-line of the single lens L3included in the first lens group LG1, the numerical aperture on the object side of the objective 1, the working distance of the objective 1, and the magnification of the objective 1, respectively. When the first lens group LG1includes a plurality of single lenses, n1 is the highest refractive index at the d-line of one of the single lenses included in the first lens group LG1.

Conditional expression (1) regulates the refractive index at the d-line of a single lens included in the first lens group LG1. When conditional expression (1) is satisfied, the occurrence of high-order spherical and coma aberrations can be suppressed in addition to the suppression of the occurrence of a chromatic aberration. If the value of conditional expression (1) falls below the lower limit (1.7), the ray height of the divergent light emitted from the meniscus lens L2excessively increases and the occurrence of high-order spherical and coma aberrations cannot be suppressed.

Conditional expression (2) regulates the numerical aperture on the object side of an objective. When conditional expression (2) is satisfied, the brightness necessary for a fluorescent observation can be secured and a light fluorescent image can be observed. If the value of conditional expression (2) falls below the lower limit (0.75), sufficient light cannot be taken in from the object side, sufficient brightness cannot be obtained, and a fluorescent image becomes dark. If the value rises beyond its upper limit (1.45), it becomes difficult to observe the inside of a living body specimen. In order to increase the numerical aperture on the object side beyond 1.45, it is necessary to increase the refractive index of immersion liquid beyond 1.45. However, generally the refractive index of a living body specimen is 1.4 or less. Therefore, if the refractive index of immersion liquid is 1.45 or more, a difference in a refractive index between a living body specimen and an immersion liquid increases and affects aberrations. Particularly when the inside of a living body specimen is observed, the quality of a fluorescent image greatly deteriorates.

Conditional expression (3) regulates a relation between the numerical aperture on the object side of an objective and working distance of an objective. When conditional expression (3) is satisfied, a numerical aperture and a working distance that are necessary to observe a living body specimen can be secured. If the value of conditional expression (3) falls below the lower limit (0.4), it becomes difficult to secure a working distance sufficient to observe the inside of a living body specimen. Even when a sufficient working distance can be secured, it becomes difficult to obtain a brightness necessary for a fluorescent observation. If the value rises beyond the upper limit (3.0), it becomes difficult to make an objective whose aberrations are sufficiently corrected small and the objective 1 becomes large.

Conditional expression (4) regulates a relation between the numerical aperture on the object side of an objective and magnification of an objective. When conditional expression (4) is satisfied, a brightness necessary for a fluorescent observation ranging particularly from a low to middle magnification can be secured. If the value of conditional expression (4) falls below the lower limit (0.03), it becomes difficult to obtain a sufficient brightness in the range from low to middle magnification and a fluorescent image becomes dark.

If the value rises beyond the upper limit (0.1), it becomes difficult to correct a wide range of aberrations within the limited total length of the objective 1. As a result, it becomes difficult to observe a wide range at a sufficient brightness.

Thus, an immersion microscope objective having a long working distance together with both a wide observation range and a large numerical aperture and having good optical performance can be provided.

It is preferable that the objective 1 further satisfy the following conditions (5) through (7) in addition to conditions (1) through (4).
0.3<f2a/f2b<2  (5)
|nx−ny|<0.35  (6)
30<|vx−vy|(7)

It is also preferable that the objective 1 further satisfy the following conditions (5-1) through (7-1) instead of conditions (5) through (7).
0.38<f2a/f2b<1.2  (5-1)
|nx−ny|<0.25  (6-1)
35<|vx−vy|(7-1)

In the above expressions, f2a, f2b, nx, vx, ny and vy are the focal length of the three-piece cemented lens CL2which is disposed nearest the object side of the second lens group LG2and which is composed of the positive refractive lens L4, the negative refractive lens L5and the positive refractive lens L6; the focal length of the three-piece cemented lens CL3disposed nearest the image side of the second lens group LG2; the refractive index at the d-line of the positive refractive lenses (lenses L4and L6) of the three-piece cemented lens CL2disposed nearest the object side of the second lens group LG2; the Abbe number at the d-line of the positive refractive lenses (lenses L4and L6) of the three-piece cemented lens CL2disposed nearest the object side of the second lens group LG2; the refractive index at the d-line of the negative refractive lens L5of the three-piece cemented lens CL2disposed nearest the object side of the second lens group LG2; and the Abbe number at the d-line of the negative refractive lens L5of the three-piece cemented lens CL2disposed nearest the object side of the second lens group LG2, respectively.

The nx and ny of conditions (6), (7), (6-1) and (7-1) can also be applicable to only the positive refractive lens (lens L4) disposed nearest the object side of the three-piece cemented lens CL2disposed nearest the object side of the second lens group LG2.

Conditional expression (5) regulates the ratio of the focal length of a cemented lens disposed nearest the object side to the focal length of a cemented lens disposed nearest the image side that is included in the second lens group. When conditional expression (5) is satisfied, a chromatic aberration can be effectively corrected by a cemented lens while ray height for effectively maintaining the Petzval sum is secured. If the value of conditional expression (5) falls below the lower limit (0.35), the refractive power of the cemented lens CL2disposed nearest the object side becomes excessive. Therefore, its ray height is excessively lowered and it becomes difficult to effectively maintain the Petzval sum. If the value rises beyond the upper limit (2), the refractive power of the cemented lens CL2disposed nearest the object side becomes insufficient. Therefore, its ray height is excessively raised and it becomes difficult to correct a chromatic aberration by a cemented lens.

Conditional expression (6) regulates a difference in a refractive index at the d-line between the positive and negative refractive lenses of a cemented lens disposed nearest the image side, which is included in the second lens group. Conditional expression (7) regulates a difference in an Abbe number at the d-line between the positive and negative refractive lenses of a cemented lens disposed nearest the image side that is included in the second lens group. When conditions (6) and (7) are satisfied in one of the positive refractive lenses (lenses L4and L6) and the negative refractive lens (lens L5) included in the cemented lens CL2disposed nearest the object side, an on-axis chromatic aberration can be sufficiently corrected. If the value of conditional expression (6) rises beyond the upper limit (0.35), it becomes difficult to correct an on-axis chromatic aberration since the amount of refraction on a cemented surface becomes insufficient. If the value of conditional expression (7) falls below the lower limit (30), it becomes difficult to correct an on-axis chromatic aberration since the difference in an Abbe number becomes insufficient.

It is also preferable that the objective 1 further satisfy the following conditions (8) through (11) in addition to conditions (1) through (4).
0.12≦d1/d0.3  (8)
−0.1≦fm/fs≦0  (9)
2.5≦fs/ds≦6.3  (10)
0.2≦Rmob/Rmim≦0.5  (11)

It is more preferable that the objective 1 satisfy the following conditions (8-1) through (11-1) instead of the above conditions (8) through (11).
0.12≦d1/d0.2  (8-1)
−0.4≦fm/fs≦−0.2  (9-1)
3≦fs/ds≦6  (10-1)
0.25≦Rmob/Rmim≦0.4  (11-1)

In the above expressions, d1, d and ds are the total length of the first lens group LG1, the total length of the objective1, and the total length of the single lens L3included in the first lens group or the summed total length of a single lens group including the single lens L3, respectively. fm and fs are the focal length of the meniscus lens L2and the focal length of the single lens L3included in the first lens group LG1or the composite focal length of a single lens group, respectively. Rmob and Rmim are the radius of curvature on the object side of the meniscus lens L2and the radius of curvature on the image side of the meniscus lens L2, respectively.

Conditional expression (8) regulates the ratio of the total length of the first lens group LG1to the total length of the objective 1. When conditional expression (8) is satisfied, the large numerical aperture and a long working distance can be realized while its optical performance is secured. If the value of conditional expression (8) falls below the lower limit (0.12), the first lens group LG1refracts light from a living body specimen by a short total length. Therefore, the refractive power of the first lens group LG1becomes excessively strong and it becomes difficult to correct high-order spherical and coma aberrations in a large numerical aperture. It also becomes difficult to secure a sufficiently long working distance. If the value rises beyond the upper limit (0.3), the total length of the first lens group LG1becomes excessively long and the space of the second lens group LG2and after decreases. Therefore, it becomes difficult to sufficiently correct a chromatic aberration in the second lens group LG2and after.

Conditional expression (9) regulates a relation between the focal length of the meniscus lens L2included in the first lens group and that of the positive refractive single lens L3(or the composite focal length of a single lens group). When conditional expression (9) is satisfied, the focal length of the first lens group can be secured while the Petzval sum is effectively maintained. If the value of conditional expression (9) falls below the upper limit (−1.0), the focal length of the positive refractive single lens L3(or the composite focal length of a single lens group) becomes excessively short. Therefore, the refractive power of the positive refractive single lens L3(or a single lens group) included in the first lens group becomes excessively strong and it becomes difficult to correct high-order spherical and coma aberrations when using a large numerical aperture, taking into consideration a refractive index regulated in conditional expression (1). If the value rises beyond the upper limit (0), the meniscus lens L2has a positive refractive index and it becomes difficult to correct the Petzval sum by the meniscus lens L2. Therefore, a field curvature becomes easy to occur and it becomes difficult to secure a wide field of view.

Conditional expression (10) regulates a relation between the focal length of a single lens L3(or the composite focal length of a single lens group) included in the first lens group and the total length of the single lens L3(total length of a single lens group). When conditional expression (10) is satisfied, sufficient refractive power can be secured while the occurrence of aberrations is suppressed in a single lens or a single lens group. If the value of conditional expression (10) falls below the lower limit (2.5), the focal length of a single lens or a single lens group in relation to the total length of the single lens (or the single lens group) becomes excessively short. Therefore, the refractive power of the single lens L3(or a single lens group) becomes excessively strong, taking into consideration the refractive index regulated in conditional expression (1), and it becomes difficult to correct high-order spherical and coma aberrations in a large numerical aperture. If the value rises beyond the upper limit (6.3), it becomes difficult for the single lens L3or the single lens group to obtain sufficient refractive power with a short total length and the total length of the first lens group increases. As a result, the space of the second lens group LG2and after decreases and it becomes difficult to sufficiently correct a chromatic aberration.

Conditional expression (11) regulates a relation between the curvature radii on the object and image sides of the meniscus lens L2included in the first lens group LG1. When conditional expression (11) is satisfied, a field curvature can be suppressed while a long working distance is secured. If the value of conditional expression (11) falls below the lower limit (0.2) of conditional expression (11), the radius of curvature on the image side excessively increases compared with that on the object side. Therefore, a divergence function on a curvature surface on the object side increases compared with a convergence function on a curvature surface on the image side and the height of a ray emitted from a meniscus lens becomes excessively large. As a result, it becomes difficult to secure a sufficiently long working distance. If the value of conditional expression (11) rises beyond the upper limit (0.5), the converging function in the meniscus lens increases and it becomes difficult to sufficiently correct the Petzval sum in the meniscus lens. Therefore, a field curvature becomes easy to occur and it becomes difficult to secure a wide field of view.

Although in the objective 1 a Gaussian type lens structure included in the third lens group comprises a cemented lens CL4whose concave surface faces the image side and a cemented lens CL5whose concave surface faces the object side, in order from the object side, the Gaussian type lens structure is not limited to this. A Gaussian type lens structure included in the third lens group can also comprise a single lens whose concave surface faces the image side and a cemented lens whose concave surface faces the object side, in order from the object side.

In this case, it is preferable that the objective further satisfy the following conditional expression (12) in addition to conditions (1) through (4).
0.05<|f3a/f3b|<0.5  (12)

It is more preferable that the objective satisfy the following conditional expression (12-1) instead of the above conditional expression (12).
0.07<|f3a/f3b|<0.2  (12-1)

In the above expressions, f3a and f3b are the focal length of a single lens whose concave surface faces the image side, composing a Gaussian type lens structure, and the focal length of a cemented lens whose concave surface faces the object side, also composing a Gaussian type lens structure, respectively.

Conditional expression (12) regulates a relation between the focal lengths of lenses whose concave surfaces face each other, composing a Gaussian type lens structure. When conditional expression (12) is satisfied, both the Petzval sum and a chromatic aberration can be effectively corrected in a compact Gaussian type lens structure. If the value of conditional expression (12) falls below the lower limit (0.05), the refractive power of a single lens whose concave surface faces the image side excessively increases. Therefore, its ray height becomes excessively large and it becomes difficult to correct a chromatic aberration. If the value rises beyond the upper limit (0.5), the refractive power of a single lens whose concave surface faces the image side excessively decreases. Therefore, a sufficiently large ray height cannot be secured and it becomes difficult to correct the Petzval sum.

The second lens group LG2can also comprise a cemented lens capable of moving along the optical axis in order to make one with an objective with a correction collar.

In this case, it is preferable that the objective satisfy the following conditional expression (13) in addition to conditions (1) through (4).
|f/f2c|<0.2  (13)

It is also preferable that the objective satisfy the following conditional expression (13-1) instead of the above conditional expression (13).
|f/f2c|<0.1  (13-1)

In the above expressions, f and f2c are the focal length of the entire objective and the focal length of the movable cemented lens included in the second lens group, respectively.

Conditional expression (13) regulates the ratio of the focal length of the entire objective to that of a movable cemented lens included in the second lens group. When conditional expression (13) is satisfied, a spherical aberration caused by a difference in thickness between individuals of cover glass can be effectively corrected by moving the movable cemented lens. If the value of conditional expression (13) rises beyond the upper limit (0.2), the positive or negative refractive power of the movable cemented lens increases excessively. Therefore, even though a spherical aberration can be corrected by the movement of the cemented lens, other aberrations, such as chromatic aberration, coma aberration and the like cannot be corrected and the performance of the objective deteriorates.

Conditions (1) through (13) can also be arbitrarily combined. Further, each conditional expression is restricted only by either its upper or lower limit.

First Embodiment

FIG. 1is a cross-sectional view of an immersion microscope objective according to this preferred embodiment.

An objective 1 comprises a first lens group LG1having a positive refractive power, a second lens group LG2having a positive refractive power, and a third lens group LG3having a negative refractive power, in order from the object side.

The second lens group LG2comprises a three-piece cemented lens CL2having a positive, negative and positive refractive power, respectively, in that order (lenses L4, L5and L6), a single lens having a positive refractive power (lens L7) and a three-piece cemented lens CL3having a positive, negative and positive refractive power, respectively, in that order (lenses L8, L9and L10), in order from the object side. Therefore, the second lens group LG2includes two cemented lenses.

The second lens group LG2corrects a chromatic aberration, using the three-piece cemented lens CL2having a positive, negative and positive refractive power, respectively, in that order. In order to secure a wider observation range, as exemplified in the objective 1, the second lens group LG2comprises the three-piece cemented lens CL3having a positive, negative and positive refractive power, respectively, in that order, after the three-piece cemented lens CL2and the positive refractive lens L7in that order. This is because, even though in order to secure a wider observation range it is effective to correct a curvature aberration by increasing the ray height, it becomes difficult to correct a chromatic aberration when the ray height is increased. A curvature aberration can be easily corrected while a chromatic aberration is corrected by using two three-piece cemented lenses having a positive, negative and positive refractive power, respectively, in that order, and using the positive refractive lens L7disposed between the two three-piece cemented lenses, compared with a case where there is only one such three-piece cemented lens.

The various data in this preferred embodiment will be described below.

The focal length f, magnification p, numerical aperture NAob on the object side, and working distance d0 of the objective 1 in this preferred embodiment are as follows.

The thickness dc, refractive index nc, and Abbe number vc of the cover glass CG exemplified inFIG. 1are also as follows.

It is also assumed that the surface number of an object surface (surface on the object side of the cover glass CG) and the surface number of the surface on an image side of the cover glass CG are S1and S2, respectively. In this case, the refractive index n and Abbe number v of an immersion liquid with which the area between the surface with surface number S2and the surface with surface number S3nearest the object side of the first lens group is filled are as follows.

The lens data of the objective 1 in this preferred embodiment is as follows, where “s” represents the surface number, “r” represents the curvature radius (mm), “ld” represents the space or thickness of a lens (mm), “nd” represents the refraction index with respect to the d line, and “vd” represents the Abbe number with respect to the d line.

In the above data, the surface with surface number S3in the objective 1 is the lens surface nearest the object side of the objective 1. The space or thickness of a lens with surface number S3indicates a space or thickness between the surfaces with surface numbers S3and S4. The refractive index at the d-line of a lens with surface number S3indicates the refractive index at the d-line of a medium between the surfaces with surface numbers S3and S4. The Abbe number at the d-line of the lens with surface number S3indicates the Abbe number at a medium between the surfaces with surface numbers S3and S4.

FIG. 2is a cross-sectional view of a tube lens according to this preferred embodiment. The tube lens2in this preferred embodiment comprises a cemented lens CTL1composed of lenses TL1and TL2and a cemented lens CTL2composed of lenses TL3and TL4as exemplified inFIG. 2.

The lens data of the tube lens2in this preferred embodiment is as follows, where “s” represents the surface number, “r” represents the curvature radius (mm), “ld” represents the space or thickness of a lens (mm), “nd” represents the refraction index with respect to the d line, and “vd” represents the Abbe number with respect to the d line.

In the tube lens2, surface numbers S1and S6indicate lens surfaces nearest the object and image sides, respectively. The space or thickness of a lens with surface number S1indicates the space or thickness between surfaces with surface numbers S1and S2. The refractive index at the d-line of a lens with surface number S1indicates the refractive index at the d-line of a medium between the surfaces with surface numbers S1and S2. The Abbe number at the d-line of a lens with surface number S1indicates the Abbe number at a medium between the surfaces with surface numbers S1and S2.

FIG. 3illustrates an aberration in the case where the objective 1 and tube lens2according to this preferred embodiment are combined and used and illustrates an aberration on the imaging surface on the image side. The space between the last surface of the objective 1 and the first surface of the tube lens2is 114.507 mm.FIG. 3illustrates spherical aberration, the amount of sine condition dissatisfaction, astigmatism, distortion aberration, and coma aberration. All of them are effectively corrected. “NA” and “FIT” inFIG. 3are the numerical aperture on the object side of the objective 1 and image height, respectively. “M” and “S” indicate a meridional component and a sagittal component, respectively.

Second Embodiment

FIG. 4is a cross-sectional view of an immersion microscope objective according to this preferred embodiment. An objective 3 comprises a first lens group LG1having a positive refractive power, a second lens group LG2having a positive refractive power, and a third lens group LG3having a negative refractive power, in order from the object side.

Firstly, only the points that are different from the objective 1 in the structures and operations of respective lens groups will be explained.

The objective 3 differs from the objective 1 in the structure of the first lens group LG1. The objective 3 comprises two single lenses having a positive refractive power (lenses L3and L4) on the image side of a cemented lens CL1. These positive refractive single lenses function to suppress the ray height of divergent light emitted from a meniscus lens L2and to correct high-order spherical and coma aberrations in the same way as the objective 1. The objective 3 increases the number of surfaces by providing a plurality of positive refractive single lenses. Thus, the objective 3 suppresses the ray height by gradually refracting divergent light from the meniscus lens L2on respective surfaces. Therefore, the objective 3 is advantageous compared with the objective 1, from the viewpoint of aberration correction.

Since the rest of the structure and the other functions of the objective 3 are the same as those of the objective 1, their explanations are omitted.

The various data in this preferred embodiment will be described below.

The focal length f, magnification β, numerical aperture NAob on the object side, and working distance d0 of the objective 3 in this preferred embodiment are as follows.

The thickness dc, refractive index nc, and Abbe number vc of the cover glass CG exemplified inFIG. 4are as follows and are the same as those of the first preferred embodiment.

The refractive index n and Abbe number v of immersion liquid with which the area between the surface with surface number S2on the image side of the cover glass CG and the surface with surface number S3nearest the object side of the first lens group is filled are as follows and are the same as those of the first preferred embodiment.

The lens data of the objective 3 in this preferred embodiment is as follows.

In the objective 3, a surface with surface number S3indicates a lens surface nearest the object side of the objective 3. The space or thickness of a lens with surface number S3indicates the space or thickness between the surfaces with surface numbers S3and S4. The refractive index at the d-line of a lens with surface number S3indicates the refractive index at the d-line of a medium between the surfaces with surface numbers S3and S4. The Abbe number at the d-line of the lens of surface number S3indicates the Abbe number at a medium between the surfaces with surface numbers S3and S4.

The objective 3 includes a plurality of positive refractive single lenses in the first lens group LG1. Therefore, in this preferred embodiment, n1 is the refractive index at the d-line of a single lens (lens L4) having the highest refractive index in single lenses included in the first lens group LG1. ds is the summed total length of a single lens group (lenses L3and L4) included in the first lens group LG1. fs is the composite focal length of a single lens group (lenses L3and L4) included in the first lens group LG1.

FIG. 5illustrates aberrations on the imaging surface on the image side in the case where the objective 3 and tube lens2according to this preferred embodiment are combined and used. The tube lens2is the same as that of the first preferred embodiment. The space between the objective 3 and tube lens2is also the same as that of the first preferred embodiment.FIG. 5illustrates spherical aberration, the amount of sine condition dissatisfaction, astigmatism, distortion aberration, and coma aberration. All of them are effectively corrected. “NA” and “FIT” inFIG. 5are the numerical aperture on the object side of the objective 3 and image height (mm), respectively. “M” and “S” indicate a meridional component and a sagittal component, respectively.

Third Embodiment

FIG. 6is a cross-sectional view of an immersion microscope objective according to this preferred embodiment. An objective 4 comprises a first lens group having a positive refractive power, a second lens group LG2having a positive refractive power, and a third lens group LG3having a negative refractive power, in order from the object side.

Firstly, only the different points from the objective 1 in the structures and operations of respective lens groups will be explained.

The objective 4 differs from the objective 1 in the structure of the second lens group LG2. In the objective 4, the second lens group LG2comprises a first three-piece cemented lens (cemented lens CL2), a second three-piece cemented lens (cemented lens CL3), and a cemented lens having a positive refractive (cemented lens CL4) in order from the object side. In this case, the cemented lens CL2is composed of lenses having a positive, negative, positive refractive power, respectively, which is composed of a biconvex lens, a biconcave lens, and a biconvex lens. The cemented lens CL3is composed of a lens having a negative-positive-negative refractive power, which is composed of a meniscus lens whose convex surface faces the object side, a biconvex lens, and a meniscus lens whose concave surface faces the object side. The cemented lens CL4is composed of a biconvex lens and a biconcave lens.

The second lens group LG2in this preferred embodiment corrects a chromatic aberration using the three-piece cemented lenses. In order to secure a larger numerical aperture, the second lens group LG2comprises two three-piece cemented lenses and a cemented lens having a positive refractive power, as exemplified in the objective 4. Thus, the objective 4 can secure a larger numerical aperture while correcting a chromatic aberration than the objective 1.

Since the rest of the structure and the other functions of the objective 4 are the same as those of the objective 1, their explanations are omitted.

The various data in this preferred embodiment will be described below.

The focal length f, magnification β, numerical aperture NAob on the object side, and working distance d0 of the objective 4 in this preferred embodiment are as follows.

The thickness dc, refractive index nc, and Abbe number vc of the cover glass CG exemplified inFIG. 6are as follows and are the same as those of the first preferred embodiment.

The refractive index n and Abbe number v of the immersion liquid with which the area between the surface with surface number S2on the image side of the cover glass CG and the surface with surface number S3nearest the object side of the first lens group is filled are as follows and are the same as those of the first preferred embodiment.

The lens data of the objective 4 in this preferred embodiment is as follows.

In the objective 4, a surface with surface number S3indicates a lens surface nearest the object side of the objective 4. The space or thickness of a lens with surface number S3indicates the space or thickness between the surfaces with surface numbers S3and S4. The refractive index at the d-line of a lens with surface number S3indicates the refractive index at the d-line of a medium between the surfaces with surface numbers S3and S4. The Abbe number at the d-line of the lens of surface number S3indicates the Abbe number at a medium between the surfaces with surface numbers S3and S4.

FIG. 7illustrates aberrations on the imaging surface on the image side in the case where an objective 4 and a tube lens2according to this preferred embodiment are combined and used. The tube lens2is the same as that of the first preferred embodiment. The space between the objective 4 and tube lens2is also the same as that of the first preferred embodiment.FIG. 7illustrates spherical aberration, the amount of sine condition dissatisfaction, astigmatism, distortion aberration and coma aberration. All of them are effectively corrected. “NA” and “FIT” inFIG. 5are the numerical aperture on the object side of the objective 4 and image height (mm), respectively. “M” and “S” indicate a meridional component and a sagittal component, respectively.

Fourth Embodiment

FIG. 8is a cross-sectional view of an immersion microscope objective according to this preferred embodiment.

An objective 5 comprises a first lens group LG1having a positive refractive power, a second lens group LG2having a positive refractive power, and a third lens group LG3having a negative refractive power, in order from the object side.

Since the structure and functions of the objective 5 are the same as those of the objective 4, their explanations are omitted.

The various data in this preferred embodiment will be described below.

The focal length f, magnification β, numerical aperture NAob on the object side and working distance d0 of the objective 5 in this preferred embodiment are as follows.

The thickness dc, refractive index nc and Abbe number vc of the cover glass CG exemplified inFIG. 8are as follows and are the same as those of the first preferred embodiment.

the refractive index n and Abbe number v of an immersion liquid with which the area between the surface with surface number S2and the surface with surface number S3nearest the object side of the first lens group is filled are as follows and are the same as those of the first preferred embodiment.

The lens data of the objective 5 in this preferred embodiment is as follows.

In the objective 5, a surface with surface number S3indicates a lens surface nearest the object side of the objective 5. The space or thickness of a lens with surface number S3indicates the space or thickness between the surfaces with surface numbers S3and S4. The refractive index at the d-line of a lens with surface number S3indicates the refractive index at the d-line of a medium between the surfaces with surface numbers S3and S4. The Abbe number at the d-line of the lens of surface number S3indicates the Abbe number at a medium between the surfaces with surface numbers S3and S4.

FIG. 9illustrates aberrations on the imaging surface on the image side in the case where an objective 5 and a tube lens2according to this preferred embodiment are combined and used. The tube lens2is the same as that of the first preferred embodiment. The space between the objective 5 and tube lens2is also the same as that of the first preferred embodiment.FIG. 9illustrates spherical aberration, the amount of sine condition dissatisfaction, astigmatism, distortion aberration and coma aberration. All of them are effectively corrected. “NA” and “FIT” inFIG. 9are the numerical aperture on the object side of the objective 5 and image height (mm), respectively. “M” and “S” indicate a meridional component and a sagittal component, respectively.

Fifth Embodiment

FIG. 10is a cross-sectional view of an immersion microscope objective according to this preferred embodiment. An objective 6 comprises a first lens group LG1having a positive refractive power, a second lens group LG2having a positive refractive power and a third lens group LG3having a negative refractive power, in order from the object side.

Firstly, only the different points from the objective 1 of the structures and functions of respective lens groups of an objective 6 will be explained. The objective 6 differs from the objective 1 in the structures of the second and third lens groups LG2and LG3, respectively.

The second lens group LG2comprises a first three-piece cemented lens (cemented lens CL2), a two-piece cemented lens movable along the optical axis (cemented lens CL3), and a second three-piece cemented lens (cemented lens CL4). In this case, the cemented lens CL2is composed of lenses having a positive, negative, positive refractive power, respectively, which is composed of a biconvex lens, a biconcave lens, and a biconvex lens. The cemented lens CL3is composed of a biconvex lens and a meniscus lens whose concave surface faces the object side. The cemented lens CL4is composed of lenses having a positive, negative, positive refractive power, respectively, which is composed of a biconvex lens element, a biconcave lens element, and a biconvex lens element.

The second lens group LG2in this preferred embodiment can effectively correct a chromatic aberration using three-piece cemented lenses. Even when the thickness of the cover glass CG has some degree of individual difference, a spherical aberration can be effectively corrected by moving the cemented lens CL3along the optical axis.

The third lens group LG3includes a Gaussian type lens structure composed of a single lens (lens L12) whose concave surface faces the image side and a cemented lens (cemented lens CL5) whose concave surface faces the object side. In this case, the single lens is a meniscus lens and the cemented lens CL5is composed of two meniscus lens whose concave surface faces the object side.

In the third lens group LG3in this preferred embodiment, a Gaussian type lens structure comprises a single lens whose concave surface faces the image side. Therefore, the Gaussian type lens structure can be compactly composed.

Since the rest of the structure and the other functions of the objective 6 are the same as those of the objective 1, their explanations are omitted.

The various data in this preferred embodiment will be described.

The focal length f, magnification p, numerical aperture NAob on the object side and working distance d0 of the objective 6 in this preferred embodiment are as follows. In this case, the working distance d0 indicates the working distance in the case where the cover glass CG has a regulated thickness.

The thickness dc, refractive index nc, and Abbe number vc of the cover glass CG exemplified inFIG. 10are as follows and are the same as those of the first preferred embodiment. Although the thickness dc of the cover glass CG is regulated, it can be changed within a range to be described later.

The refractive index n and Abbe number v of an immersion liquid with which the area between the surface with surface number S2and the surface with surface number S3nearest the object side of the first lens group is filled are as follows and are the same as those of the first preferred embodiment.

The lens data of the objective 6 in this preferred embodiment is as illustrated in the following table.

In the objective 6, a surface with surface number S3indicates a lens surface nearest the object side of the objective 6. The space or thickness of a lens with surface number S3indicates the space or thickness between the surfaces with surface numbers S3and S4. The refractive index at the d-line of a lens with surface number S3indicates the refractive index at the d-line of a medium between the surfaces with surface numbers S3and S4. The Abbe number at the d-line of the lens of surface number S3indicates the Abbe number at a medium between the surfaces with surface numbers S3and S4. Furthermore, the space between surface numbers S11and S12and the space between surface numbers S14and S15are variable values Da and Db which change according to the movement along the optical axis of the cemented lens CL3.

A relation among the thickness dc of a cover glass, the working distance d0 and the variable values Da and Db is as follows.

Thickness dc of a cover glass, and working distance d0 and surface space

FIG. 11illustrates aberrations on the imaging surface on the image side in the case where an objective 6 and a tube lens2according to this preferred embodiment are combined and used. The tube lens2is the same as that of the first preferred embodiment. The space between the objective 6 and tube lens2is also the same as that in the first preferred embodiment.FIG. 11illustrates spherical aberration, the amount of sine condition dissatisfaction, astigmatism, distortion aberration and coma aberration. All of them are effectively corrected. “NA” and “FIT” inFIG. 11are the numerical aperture on the object side of the objective 6 and image height (mm), respectively. “M” and “S” indicate a meridional component and a sagittal component, respectively.

Sixth Embodiment

FIG. 12is a cross-sectional view of an immersion microscope objective according to this preferred embodiment. An objective 7 comprises a first lens group LG1having a positive refractive power, a second lens group LG2having a positive refractive power, and a third lens group LG3having a negative refractive power, in order from the object side.

Since the structure and functions of the objective 7 are the same as those of the objective 6, their explanations are omitted.

The various data in this preferred embodiment will be described below.

The focal length f, magnification β, numerical aperture NAob on the object side and working distance d0 of the objective 7 in this preferred embodiment are as follows. In this case, the working distance d0 indicates the working distance in the case where the cover glass CG has a regulated thickness.

The thickness dc, refractive index nc and Abbe number vc of the cover glass CG exemplified inFIG. 12are as follows and are the same as those of the first preferred embodiment. Although the thickness dc of the cover glass CG is regulated, it can be changed within a range to be described later.

the refractive index n and Abbe number v of an immersion liquid with which the area between the surface with surface number S2and the surface with surface number S3nearest the object side of the first lens group is filled are as follows and are the same as those of the first preferred embodiment.

The lens data of the objective 7 in this preferred embodiment is as follows.

In the objective 7, a surface with surface number S3indicates a lens surface nearest the object side of the objective 7. The space or thickness of a lens with surface number S3indicates the space or thickness between the surfaces with surface numbers S3and S4. The refractive index at the d-line of a lens with surface number S3indicates the refractive index at the d-line of a medium between the surfaces with surface numbers S3and S4. The Abbe number at the d-line of the lens of surface number S3indicates the Abbe number at a medium between the surfaces with surface numbers S3and S4. Furthermore, the space between surface numbers S11and S12and the space between surface numbers S14and515are variable values Da and Db, respectively, which change according to the movement along the optical axis of the cemented lens CL3.

A relation among the thickness dc of a cover glass, the working distance d0 and the variable values Da and Db is as follows.

Thickness dc of a cover glass, and working distance d0 and surface space Da and Db

FIG. 13illustrates aberrations on the imaging surface on the image side in the case where an objective 7 and a tube lens2according to this preferred embodiment are combined and used. The tube lens2is the same as that of the first preferred embodiment. The space between the objective 7 and tube lens2is also the same as that in the first preferred embodiment.FIG. 13illustrates spherical aberration, the amount of sine condition dissatisfaction, astigmatism, distortion aberration and coma aberration. All of them are effectively corrected. “NA” and “FIT” inFIG. 13are the numerical aperture on the object side of the objective 7 and image height (mm), respectively. “M” and “S” indicate a meridional component and a sagittal component, respectively.

Seventh Embodiment

FIG. 14is a cross-sectional view of an immersion microscope objective according to this preferred embodiment. An objective 8 comprises a first lens group LG1having a positive refractive power, a second lens group LG2having a positive refractive power and a third lens group LG3having a negative refractive power, in order from the object side.

Since the structure and function of the objective 7 are the same as those of the objective 6 except that a cemented lens CL4included in the second lens group comprises a plano-convex lens L9whose surface is convex toward the object side, a plane-concave lens L10whose surface is convex toward the image side, and a biconvex lens L11, their explanation is omitted.

The various data in this preferred embodiment will be described below.

The focal length f, magnification 13, numerical aperture NAob on the object side and working distance d0 of the objective 8 in this preferred embodiment are as follows. In this case, the working distance d0 indicates a working distance in the case where the cover glass has a regulated thickness.

The thickness dc, refractive index nc, and Abbe number vc of the cover glass CG exemplified inFIG. 14are as follows and are the same as those of the first preferred embodiment. Although the thickness dc of the cover glass CG is regulated, it can be changed within a range to be described later.

the refractive index n and Abbe number v of an immersion liquid with which the area between the surface with surface number S2and the surface with surface number S3nearest the object side of the first lens group is filled are as follows and are the same as those of the first preferred embodiment.

The lens data of the objective 8 in this preferred embodiment is as follows.

In this case, in the objective 8, a surface with surface number S3indicates a lens surface nearest the object side of the objective 8. The space or thickness of a lens with surface number S3indicates the space or thickness between the surfaces with surface numbers S3and S4. The refractive index at the d-line of a lens with surface number S3indicates the refractive index at the d-line of a medium between the surfaces with surface numbers S3and S4. The Abbe number at the d-line of the lens of surface number S3indicates the Abbe number at a medium between the surfaces with surface numbers S3and S4. Furthermore, the space between surface numbers S11and S12and the space between surface numbers S14and S15are variable values Da and Db, respectively, which change according to the movement along the optical axis of the cemented lens CL3.

A relation among the thickness dc of a cover glass, the working distance d0 and the variable values Da and Db is as follows.

Thickness dc of a cover glass, and working distance d0 and surface space Da and Db

FIG. 15illustrates aberrations on the imaging surface on the image side in the case where an objective 8 and a tube lens2according to this preferred embodiment are combined and used. The tube lens2is the same as that of the first preferred embodiment. The space between the objective 8 and tube lens2is also the same as that in the first preferred embodiment.FIG. 15illustrates spherical aberration, the amount of sine condition dissatisfaction, astigmatism, distortion aberration and coma aberration. All of them are effectively corrected. “NA” and “FIT” inFIG. 15are the numerical aperture on the object side of the objective 8 and image height (mm), respectively. “M” and “S” indicate a meridional component and a sagittal component, respectively.

Microscope

A microscope for which objectives according to the above-described first through seventh preferred embodiments are suited to be used is particularly suitable for the usage to be explained below.

A confocal microscope with a confocal aperture is suitable for the usage of an objective according to the above-described first through seventh preferred embodiments.

FIG. 16exemplifies the structure of a confocal microscope with a confocal stop. A confocal microscope9exemplified inFIG. 16comprises laser light sources (shortwave laser10and visible light laser11) for emitting laser light as illumination light, a separation unit (dichroic mirror13) for separating fluorescent light generated from a specimen from illumination light, a scanning unit (galvano-meter mirror21) for scanning a specimen, an objective25, a confocal stop27disposed in a position optically conjugate with the focal position of the objective25, and a detector31for detecting fluorescent light that has passed through the confocal stop27.

Laser light emitted from the shortwave laser10or the visible light laser11is input to a condensing lens14via the mirror12and the dichroic mirror13and condensed on a fiber coupling mechanism15by the condensing lens14. The position and inclination of the laser light input to a single-mode fiber16from the fiber coupling mechanism15is adjusted by a fiber adjustment mechanism17and is emitted from the single-mode fiber16. The laser light emitted from the single-mode fiber16is converted to parallel light by a collimating lens18and is input to the objective25via the mirror19, the dichroic mirror20, the galvano-meter mirror21apupil projection lens22, a lens23and a mirror24. The objective25applies the laser light to a specimen disposed at the focal position of the objective25.

Fluorescent light generated from the specimen by applying the laser light advances through the same optical path as that taken by the laser light in the opposite direction and enters the dichroic mirror20. The fluorescent light passes through the dichroic mirror20having a characteristic of reflecting laser light and enabling fluorescent light to be transmitted through it and is condensed on the focal stop27by a tube lens26. Since the focal stop27is disposed in a position optically conjugate with the focal position of the objective25, the only fluorescent light generated from the focal position passes through a pinhole provided in the confocal stop27. the fluorescent light that has passed through the focal stop27is transmitted through or is reflected by the dichroic mirror28depending on its wavelength. The fluorescent light passes through a barrier filter30and is detected by the detector31.

A confocal microscope such as the confocal microscope9exemplified inFIG. 16and the like is widely used for fluorescent observation targeting a living body specimen. Since the confocal microscope has a high resolution in the Z direction due to a confocal effect, it can observe the deep parts of a specimen. However, when observing the deep parts of a specimen, it is required that an objective have a long working distance in order to avoid contact between the objective and the specimen. In order to obtain a bright image while suppressing damage to a living body specimen, it becomes necessary for an objective to have a large numerical aperture. Therefore, a confocal microscope is suitable for the usage of the objectives exemplified in the first through seventh preferred embodiments.

The objectives exemplified in the first through seventh preferred embodiments are also suitably used for a two-photon excitation microscope.

FIG. 17exemplifies the structure of a two-photon excitation microscope. A two-photon excitation microscope32exemplified inFIG. 17comprises an ultra-short pulsed laser33for emitting laser light for causing two-photon excitation in a specimen43, a separation unit (dichroic mirror41) for separating fluorescent light generated from the specimen43from laser light, an objective42, a scanning unit (galvano-meter mirror35) for scanning the specimen43and a detector51for detecting fluorescent light generated from the specimen43by two-photon excitation. An ultra-short pulsed laser in a near-infrared range is preferable as the ultra-short pulsed laser33in order to enable laser light to reach the deep parts of a specimen.

Laser light emitted from the ultra-short pulsed laser33is input to a dichroic mirror37via an illumination lens34, the galvano-meter mirror35and a pupil projection lens36and passes through the dichroic mirror37. Laser light passed through the dichroic mirror37is input to the dichroic mirror41via a tube lens40and is reflected by the dichroic mirror41and is input to the objective42. The objective42applies the laser light emitted from the ultra-short pulsed laser33to the specimen43disposed at a focal position of the objective42.

The specimen43to which laser light is applied causes two-photon excitation to emit fluorescent light. The fluorescent light enters the objective42and is transmitted through the dichroic mirror41. The mirror44is disposed in an optical path in a detachable/attachable state. If the mirror44is removed from the optical path, laser light enters an eyepiece45. Thus, an observer can directly observe the specimen43. If the mirror44is inserted in the optical path, laser light is reflected on the mirror44and enters the dichroic mirror48via the pupil projection lens46and a laser-cut filter47. Laser light that has entered a dichroic mirror48is transmitted through or is reflected on the dichroic mirror48depending on its wavelength and is detected by the detector51via a barrier filter49and a pupil projection lens50.

Furthermore, a two-photon excitation microscope32has a laser38and an illumination lens39in order to illuminate the specimen43within a wide range. Thus, the specimen43can also be stimulated by the ultra-short pulsed laser33while the specimen43is illuminated within a wide range by the laser38.

A two-photon excitation microscope, such as the two-photon excitation microscope32exemplified inFIG. 17, is also used for fluorescent observation targeting a living body specimen. Therefore, a long working distance and a large numerical aperture are required for an objective used for a two-photon excitation microscope, for the same reason as an objective is used for a confocal microscope. In a two-photon excitation microscope, fluorescent light is generated only from a focal position. Therefore, it is necessary for an objective to take in as much fluorescent light as possible, including scattered fluorescent light. In this case, it is preferable that an objective have a low magnification. Therefore, a two-photon excitation microscope is suitable for the objectives exemplified in the first through seventh preferred embodiments.

FIG. 18explains the change characteristic of the focal position of an objective due to the wavelength in the two-photon excitation microscope exemplified inFIG. 17. The vertical and horizontal axes illustrated inFIG. 18indicate the amount of change (mm) of the focal position of an objective from the reference position and the wavelength (nm) of laser light, respectively. A broken line E5, a one-dotted chain line E6, and a solid line E7indicate the characteristic of the two-photon excitation microscope32using objectives according to the fifth, sixth and seventh preferred embodiments, respectively. A solid line FD indicates a depth of focus.

As exemplified inFIG. 18, the two-photon excitation microscope32using objectives according to the fifth through seventh preferred embodiments displays a good characteristic in a wide range of wavelength. More particularly, in the two-photon excitation microscope32, the change in width of the focal position of an objective stays within the focal depth in a near-infrared range including the wavelength range of laser light emitted from the ultra-short pulsed laser33in addition to a visible light range.

Besides a confocal microscope and a two-photon excitation microscope, a microscope for a time-lapse observation is suitable for objectives exemplified in the first through seventh preferred embodiments. In a time-lapse observation, a living body specimen contained in an incubator is observed for a long time. In this case, since it is necessary to suppress damage to a living body specimen as much as possible, a large numerical aperture is required for an objective. In order to observe the movement of a cell, a wide field of view is required for an objective. Therefore, a microscope for making time-lapse observation is suitable for the use of objectives according to the fifth through seventh preferred embodiments.