JP2003098438A - Microscope objective lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microscope objective lens of an intermediate magnification and high numerical aperture of a wide correction range with respect to a fluctuation in the thickness of cover glass at a high numerical aperture. SOLUTION: The microscope objective lens is arranged, successively from the object side, a first lens group G1 of positive refracting power of a meniscus shape of which the concave face is directed to the object side, a second lens group G2 of positive refracting power as a whole having a plurality of cemented lenses including a cemented lens of positive refracting power bonded together with a biconvex lens Lp1, a biconcave lens Ln1 and a convex lens Lp2 and a third lens group G3 consisting of a cemented lens along of weak refracting power of a meniscus shape bonded together with a biconvex lens Lp3 and a concave lens Ln2 and satisfies the following relations 0.35<; |r1|/F<0.7, F2/F>; 1.5, |F3|/F>; 17 where F is the focal length of the entire system, r1 is the radius of curvature of the lens face closest to the object, F2 as the focal length of the second lens group G2 and F3 is the focal length of the third lens group G3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microscope objective lens, and more particularly, it relates to a microscope objective lens with a correction ring capable of correcting variation in aberration caused by variation in thickness of cover glass.

[0002]

2. Description of the Related Art A microscope objective lens is designed such that a cover glass, a glass petri dish and the like have a constant thickness. Therefore, when observed under a microscope using a cover glass or a glass petri dish other than the designed value, spherical aberration or the like occurs and the imaging performance deteriorates.

This deterioration of the imaging performance is caused by the numerical aperture NA (Nu
The larger the mercy Aperture, the more remarkable.

By the way, a glass dish is often used for microscopic observation in the field of biotechnology such as cell culture and gene manipulation.

The thickness of the glass petri dish is about 1 mm, which is thicker than the thickness (0.17 mm) of the cover glass generally used. Therefore, spherical aberration or the like is likely to occur and the imaging performance is likely to deteriorate, so that a microscope objective lens having a wide aberration correction range and a long working distance is required.

On the other hand, a microscope objective lens provided with a so-called correction ring, which corrects aberration fluctuations by changing the distance between lenses in the microscope objective lens according to the aberration caused by the variation in thickness, is disclosed in Japanese Patent Laid-Open No. H9-9-9. No. 292571 and Japanese Patent Laid-Open No. 10-142510.

[0007]

However, JP-A-9-2
The numerical aperture of the microscope objective lens described in Japanese Patent No. 92571 is as large as 0.85, but the thickness of the cover glass is 0.17 mm, the correction range is small as 0.1 mm, and the magnification is high (60 ×). Therefore, there is a problem that the field of view becomes narrow.

On the other hand, the cover glass of the microscope objective lens disclosed in Japanese Patent Laid-Open No. 10-142510 has a thickness of 1.2 mm and a large correction range of 2 mm, but has a small numerical aperture of 0.55 and a high magnification. Since it is (40 ×), there is still a problem that the field of view is narrowed.

The present invention has been made in view of the above circumstances, and its object is to provide a microscope objective lens having a high numerical aperture and a wide correction range with respect to a variation in the thickness of the cover glass, and a medium magnification and a high numerical aperture. It is to be.

[0010]

In order to solve the above-mentioned problems, the invention according to claim 1 is directed to a meniscus-shaped first lens group G1 having a positive refracting power with a concave surface facing the object side, and moved in the optical axis direction. It is possible to have a plurality of cemented lenses including a biconvex lens, a biconcave lens, and a cemented lens having a positive refracting power in which convex lenses are cemented together, and a second lens group G2 having a positive refracting power as a whole and a convex surface facing the object side , A third lens group G3 consisting of a meniscus-shaped cemented lens unit having a weak refractive power, in which a biconvex lens and a concave lens are attached, are arranged in order from the object side, F is the focal length of the entire system, and r1 is the lens on the most object side. When the radius of curvature of the surface, F2 is the focal length of the second lens group G2, and F3 is the focal length of the third lens group G3, the following conditional expressions are satisfied.

[0011]           0.35 <| r1 | / F <0.7 (1)           F2 / F> 1.5 (2)          ｜ F3 ｜ / F> 17 (3)

According to a second aspect of the present invention, in the microscope objective lens according to the first aspect, the Abbe numbers of the biconvex lens and the convex lens included in the second lens group G2 and having a positive refracting power are νdp, When the Abbe number of the biconcave lens is νdn, the most object-side radius of curvature of the third lens group G3 is RC1, and the most image-side radius of curvature is RC2,
It is characterized by satisfying the following conditions.

[0013]           νdp-νdn> 35 (4)           0.22 <(RC1-RC2) / (RC1 + RC2) <0.35 (5)

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

The microscope objective lens includes a first lens group G1.
The second lens group G2 and the third lens group G3 are sequentially arranged from the object side (see FIGS. 1 and 2).

The first lens group G1 is composed of a meniscus-shaped positive refracting power with a concave surface facing the object side. With this arrangement, the occurrence of spherical aberration is minimized, and the divergent light beam from the sample tends to converge to some extent. Can be

Conditional expression (1) defines the radius of curvature of the first lens group G1 closest to the object side. If the value deviates from this condition and becomes smaller, the concave surface becomes stronger, the Petzval sum becomes too small, and not only the field curvature becomes overcorrected but also the divergence becomes strong, so high-order spherical aberration becomes overcorrected. It becomes too much, and the correction by the lens group at the rear becomes difficult.

On the other hand, if the value exceeds this condition and becomes large, the Petzval sum becomes large and it becomes difficult to correct the image plane.

The divergent light flux that has converged by the first lens group G1 enters the second lens group G2. The second lens group G2 includes a plurality of cemented lenses including a biconvex lens Lp1, a biconcave lens Ln1, and a convex lens Lp2, which are cemented in this order, and includes a cemented lens with three lenses. The spherical aberration and the axial chromatic aberration generated in the lens group G1 are corrected.

The second lens group G2 is movable in the optical axis direction. By moving the second lens group G2 in the optical axis direction, the incident height h of the divergent light flux incident from the first lens group G1 to the second lens group G2 changes, and spherical aberration can be corrected. .

Conditional expression (2) defines an appropriate distribution of the refractive power of the second lens group G2. If this condition is exceeded and the size is reduced, the converging action of the second lens group G2 becomes too strong,
A negative spherical aberration amount is generated, and it becomes difficult to correct the spherical aberration generated in the first lens group G1.

Conditional expression (4) defines an appropriate range for the difference in Abbe number between the positive lens and the negative lens of the triplet cemented lens of positive refractive power included in the second lens group G2. If it is smaller than this condition, it becomes difficult to correct the axial chromatic aberration, and if it is attempted to correct it, the radius of curvature of the cemented surface becomes too small and high-order spherical aberration occurs.

When the positive refractive power of the second lens group G2 becomes large, the focal length of the entire microscope objective lens system changes when the correction ring is operated, and the focus is lost.

The third lens group G3 is composed of a meniscus-shaped cemented lens unit having a weak positive or negative refractive power, in which a biconvex lens Lp3 and a concave lens Ln2 are cemented in this order, with a convex surface facing the object side. Corrects lateral and lateral chromatic aberration.

Conditional expression (3) defines an appropriate distribution of the refractive power of the third lens group G3. If this condition is exceeded and the size is reduced, field curvature will occur.

Conditional expression (5) defines the meniscus shape of the third lens group G3. If it becomes smaller than this condition,
The meridional image plane becomes too large in the negative direction, and inward coma occurs. On the other hand, if this condition is exceeded, the meridional image surface becomes too large in the positive direction, and outward coma occurs.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a lens configuration of a microscope objective lens according to a first embodiment of the present invention, and FIG. 2 is a second view of the present invention.
It is a figure which shows the lens structure of the microscope objective lens which concerns on an Example.

(First Embodiment) Table 1 shows numerical examples of the first embodiment. In this embodiment, ri is the i-th order from the object side.
The radius of curvature of the th lens surface, d0 is the working distance, di is the thickness and air gap of the i th lens in order from the object side, ndi and ν
i is the d-line of the glass of the i-th lens in order from the object side
It is the refractive index and Abbe number for (λ = 587.56 nm). Further, β is a magnification.

[0029]

[Table 1] Example 1

Thickness CG of the cover glass in this example
Table 2 below shows the amount of change in the working distance d0 and the air distances d4, d12 due to the movement of the second lens group G2 in the case of 1.0 mm, 0.8 mm, and 1.2 mm (unit: mm).

[0031]

[Table 2]

As can be seen from Table 2, the correction range of this microscope objective lens is 0.4 mm.

FIG. 3 is an aberration diagram showing spherical aberration of the first embodiment when the cover glass thickness CG is 1.0 mm, and FIG. 4 is of the first embodiment when the cover glass thickness CG is 0.8 mm. Fig. 5 is an aberration diagram showing spherical aberration. Fig. 5 shows the thickness CG of the cover glass.
FIG. 9 is an aberration diagram showing spherical aberration of the first example when is 1.2 mm.

In FIGS. 3 to 5, the solid line, broken line, dash-dotted line and dash-dotted line are d line (λ = 587.56 nm) and C line, respectively.
(λ = 656.28nm), F line (λ = 486.13nm) and g line (λ = 435.84n)
m) is shown. 3 to 5, the vertical axis represents NA and the horizontal axis represents aberration.

As is clear from the aberration diagrams, according to the first embodiment, the spherical aberration is satisfactorily corrected for the cover glasses having different thicknesses. Also, since it has a medium magnification (20 ×), a wide field of view can be obtained.

(Second Embodiment) Table 3 shows numerical values of the third embodiment of the present invention. Since each reference numeral is the same as that in the first embodiment, its description is omitted.

[0037]

Table 3 Example 2

Thickness CG of the cover glass in this example
Table 4 below shows the amount of change in the working distance d0 and the air gaps d3, d12 due to the movement of the second lens group G2 in the case of 1.0 mm, 0.8 mm and 1.2 mm (unit: mm).

[0039]

[Table 4]

As can be seen from Table 4, the correction range of this microscope objective lens is 0.4 mm.

FIG. 6 is an aberration diagram showing the spherical aberration of the second embodiment when the cover glass thickness CG is 1.0 mm, and FIG. 7 is the second embodiment when the cover glass thickness CG is 0.8 mm. Fig. 8 is an aberration diagram showing spherical aberration, and Fig. 8 shows the thickness of the cover glass.
FIG. 8 is an aberration diagram showing spherical aberration of the second example when CG is 1.2 mm.

6 to 8, solid line, broken line, dash-dotted line and dash-dotted line are d line (λ = 587.56 nm) and C line, respectively.
(λ = 656.28nm), F line (λ = 486.13nm) and g line (λ = 435.84n)
m) is shown. 6 to 8, the vertical axis represents NA and the horizontal axis represents aberration.

As is clear from each aberration diagram, according to the second embodiment, spherical aberration is favorably corrected for cover glasses having different thicknesses. Also, since it has a medium magnification (20 ×), a wide field of view can be obtained.

Table 5 below shows numerical examples of the conditional expressions (1) to (5) in the first and second embodiments.

[0045]

[Table 5]

Further, the embodiments of the present invention are all designed at infinity, and are used in combination with the imaging lens having the configuration shown in Table 6 below. In Table 6, di is the thickness and air distance of the i-th lens in order from the object side, and ndi and νi are the refractive indices of the glass of the i-th lens in order from the object side with respect to the d line (λ = 587.56 nm). And Abbe number.

[0047]

[Table 6]

[0048]

As described above, according to the present invention,
It is possible to provide a microscope objective with a high numerical aperture and a wide range of correction for variations in the thickness of the cover glass, and a medium-magnification high numerical aperture microscope lens.

[Brief description of drawings]

FIG. 1 is a diagram showing a lens configuration of a microscope objective lens according to a first example of the present invention.

FIG. 2 is a diagram showing a lens configuration of a microscope objective lens according to a second example of the present invention.

FIG. 3 is an aberration diagram showing spherical aberration of the first example when the thickness CG of the cover glass is 1.0 mm.

FIG. 4 is an aberration diagram showing spherical aberration of the first example when the thickness CG of the cover glass is 0.8 mm.

FIG. 5 is an aberration diagram showing spherical aberration of the first example when the cover glass thickness CG is 1.2 mm.

FIG. 6 is an aberration diagram showing spherical aberration of the second example when the thickness CG of the cover glass is 1.0 mm.

FIG. 7 is an aberration diagram showing spherical aberration of the second example when the thickness CG of the cover glass is 0.8 mm.

FIG. 8 is an aberration diagram showing spherical aberration of the second example when the cover glass thickness CG is 1.2 mm.

[Explanation of symbols]

G1 first lens group G2 Second lens group G3 Third lens group Lp1 biconvex lens Lp2 convex lens Lp3 biconvex lens Ln1 biconcave lens Ln2 concave lens

Claims (2)

[Claims] 1. A meniscus-shaped first lens unit G1 having a positive refracting power with a concave surface facing the object side, and a biconvex lens, a biconcave lens, and a positive lens having a positive refracting power which are movable in the optical axis direction. A meniscus-shaped cemented lens unit having a plurality of cemented lenses, including a cemented lens, and a second lens group G2 having a positive refracting power as a whole, and a biconvex lens and a concave lens bonded to each other And a third lens group G3 consisting of 3 in order from the object side, F is the focal length of the entire system, r1 is the radius of curvature of the lens surface closest to the object side, F2 is the focal length of the second lens group G2, and F3 is 3 lens group G3
A microscope objective lens characterized by satisfying the following conditional expression when the focal length is 0.35 <｜ r1 ｜ / F <0.7 F2 / F> 1.5 ｜ F3 ｜ / F> 17 2. The Abbe number of the biconvex lens and the convex lens forming the cemented lens of positive refracting power included in the second lens group G2 is νdp, the Abbe number of the biconcave lens is νdn, and the third lens group G3 The radius of curvature on the most object side is RC
1. The microscope objective lens according to claim 1, wherein the following conditions are satisfied, where RC2 is the radius of curvature closest to the image side. νdp-νdn> 35 0.22 <(RC1-RC2) / (RC1 + RC2) <0.35