JP2010197536A - Microscope objective lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microscope objective lens where chromatic aberration is sufficiently corrected, which has a sufficient visual range, and where various aberrations in the visual range are satisfactorily corrected. <P>SOLUTION: The microscope objective lens OL includes, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 and a third lens group G3 having negative refractive power, wherein the first lens group G1 includes a positive lens component L1 located nearest to the object side, with a lens surface having negative refractive power, the second lens group G2 includes a diffraction optical element GD with a diffractive optical surface D in which two diffraction elements of different optical materials are cemented and a diffractive grating groove is formed on the cemented interface thereof, and the third lens group G3 includes at least one or more color correction lens components CL31 having negative refractive power. The lens surface nearest to the image side in the third lens group G3 is a concave surface directed to the image side. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a microscope objective lens.

  Conventional microscope objective lenses require a large number of cemented lenses to satisfactorily correct chromatic aberration among various aberrations, and it is necessary to use anomalous dispersion glass to correct the secondary spectrum. I had to. In recent years, a lens system using a diffractive optical element (DOE) has been proposed that can correct various aberrations, particularly chromatic aberration including the secondary spectrum, without using a cemented lens or anomalous dispersion glass with a high magnification and a high numerical aperture. (For example, refer to Patent Document 1).

JP-A-6-331898

  However, in such a lens system using a diffractive optical element, even if chromatic aberration can be corrected by the diffractive optical element, it is difficult to correct coma at a high angle of view, and the image performance at the periphery of the field of view is low. was there.

  The present invention has been made in view of such problems, and provides a microscope objective lens that is sufficiently corrected for chromatic aberration, has a sufficient field of view, and has various aberrations corrected well in the field of view. The purpose is to do.

In order to solve the above problems, a microscope objective lens according to the present invention includes, in order from the object side, a first lens group having a positive refractive power, a second lens group, and a third lens group having a negative refractive power. The first lens group has a positive lens component that includes a lens surface that is located closest to the object side and has a negative refractive power, and the second lens group has two diffractions made of different optical materials. A color correction lens having a diffractive optical element having a diffractive optical surface having a diffractive optical surface formed by bonding element elements and having a diffraction grating groove formed on the bonded surface, and having at least one negative refracting power The lens surface having the component and the most image side of the third lens group is disposed with the concave surface facing the image side. Of the lens surfaces having negative refractive power included in the positive lens component provided in the first lens group, the radius of curvature of the lens surface having negative refractive power arranged closest to the object side is defined as R. The refractive index for the d-line of the medium on the object side of the lens surface having negative refractive power is n1, and the refractive index for the d-line of the medium on the image side is n2, from the apex of the lens surface having negative refractive power to the object. Where d0 is the distance on the optical axis, the following formula | (n2-n1) / (R · d0) | ≦ 0.1
When the focal length of the entire system is f and the height from the optical axis of the principal ray of the light beam corresponding to the maximum angle of view passing through the diffractive optical surface is h, the following expression 0.01 ≦ | h / f | ≦ 0.04
Satisfy the conditions. However, the chief ray of the light beam emitted from the off-axis object point is the maximum light beam emitted from the on-axis object point, the light beam emitted from the off-axis object point in the direction farthest from the optical axis. The light beam emitted in the direction closest to the optical axis is defined as the light beam with the maximum numerical aperture emitted from the on-axis object point. When restricted at the intersection with an appropriate surface in the third lens group, it is set as the central ray of the luminous flux.

In such a microscope objective lens, when the combined focal length of the first lens group and the second lens group is f12, the following expression 1 ≦ | f12 / f | ≦ 1.5
It is preferable to satisfy the following conditions.

Further, in such a microscope objective lens, when the focal length of the second lens group is f2, the following expression 10 ≦ | f2 / f |
It is preferable to satisfy the following conditions.

Further, in such a microscope objective lens, when the number of diffraction grating grooves of the diffractive optical surface in the diffractive optical element is N and the effective radius of the diffractive optical surface is H, the following formula 2 ≦ N / H ≦ 5
It is preferable to satisfy the following conditions. However, the effective radius H is defined as the light beam having the maximum numerical aperture emitted from the on-axis object point and the light beam emitted from the off-axis object point in the direction farthest from the optical axis. The maximum ray emitted from the object point on the axis is limited by the intersection of the ray with the maximum numerical aperture emitted from the object point and an appropriate surface in the first lens group, and the ray emitted in the direction closest to the optical axis is emitted from the object point on the axis. It is determined by the outermost ray of the luminous flux determined when the beam is limited by the intersection of the ray having the numerical aperture and an appropriate surface in the third lens group.

Further, such a microscope objective lens has a refractive index with respect to the d-line of the material of the diffractive element having the lower refractive index and the smaller Abbe number of the two diffractive element elements in the diffractive optical element. The refractive index is nF1, the refractive index with respect to the C-line is nC1, and the refractive index with respect to the d-line of the material of the diffractive element element having the higher refractive index and the larger Abbe number among the two diffractive element elements in the diffractive optical element is nd2. When the refractive index for the F line is nF2, and the refractive index for the C line is nC2, the following formula nd1 ≦ 1.54
0.0145 ≦ nF1-nC1
1.55 ≤ nd2
nF2-nC2 ≦ 0.013
It is preferable to satisfy the following conditions.

  When the microscope objective lens according to the present invention is configured as described above, it is possible to provide a microscope objective lens that is sufficiently corrected for chromatic aberration, has a sufficient field of view, and is well corrected for various aberrations in the field of view. Can do.

It is a lens block diagram of the microscope objective lens which concerns on 1st Example. FIG. 6 is a diagram illustrating various aberrations of the microscope objective lens according to the first example. It is a lens block diagram of the microscope objective lens which concerns on 2nd Example. FIG. 5 is an aberration diagram of the microscope objective lens according to the second example. It is a lens block diagram of the microscope objective lens which concerns on 3rd Example. FIG. 10 is a diagram illustrating all aberrations of the microscope objective lens according to the third example. It is a lens block diagram of the imaging lens used with the said microscope objective lens.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. First, the configuration of the microscope objective lens according to the present embodiment will be described with reference to FIG. The microscope objective lens OL includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2, and a third lens group G3 having a negative refractive power. The

  In such a microscope objective lens OL, the first lens group G1 is a lens group for bringing a divergent light beam from an object close to a parallel light beam, and is therefore located closest to the object side and has a negative refractive power. A positive lens component including a surface (for example, a positive meniscus lens L1 in FIG. 1) is configured. The positive lens component may be composed of a single lens or a cemented lens. Here, among the lens surfaces having negative refractive power included in the positive lens component, the radius of curvature of the lens surface having negative refractive power arranged closest to the object side (for example, the first surface in FIG. 1) is set. Let R be the refractive index with respect to the d-line of the medium on the object side of the lens surface, n2, the refractive index with respect to the d-line of the medium on the image side is n2, and the distance on the optical axis from the object to the apex of the lens surface is d0. The following conditional expression (1) is satisfied.

| (N2−n1) / (R · d0) | ≦ 0.1 (1)

  This conditional expression (1) defines the refractive power of the lens surface having negative refractive power included in the above-mentioned positive lens component provided in the first lens group G1, and the conditional expression (1) When the upper limit is exceeded, it is difficult to correct the Petzval sum, and it becomes difficult to ensure image surface flatness up to a high angle of view.

  The second lens group G2 is a lens group for receiving a substantially parallel light beam emitted from the first lens group G1 and correcting chromatic aberration. A diffractive optical element GD is provided to correct the chromatic aberration. Yes. The diffractive optical element GD includes a diffractive optical surface D in which several to hundreds of fine groove-shaped or slit-shaped grating structures are formed concentrically per 1 mm, and the light incident on the diffractive optical surface D is grating pitch It has the property of diffracting in a direction determined by the (grating groove interval) and the wavelength of incident light. The diffractive optical element GD (diffractive optical surface D) has a negative dispersion value (Abbe number = −3.453 in the examples described later), a large dispersion, and anomalous dispersion (in the examples described later). Since the partial dispersion ratio (ng−nF) / (nF−nC) = 0.2956) is strong, it has a strong ability to correct chromatic aberration. The Abbe number of the optical glass is usually about 30 to 80, but the Abbe number of the diffractive optical element has a negative value as described above. In other words, the diffractive optical surface D of the diffractive optical element GD has a dispersion characteristic that is opposite to that of normal glass (refractive optical element), and the refractive index decreases as the wavelength of light becomes shorter. have. Therefore, a large achromatic effect can be obtained by combining with an ordinary refractive optical element. Therefore, by using the diffractive optical element GD, it becomes possible to correct chromatic aberration that cannot be achieved with ordinary optical glass.

  The diffractive optical element GD in the present embodiment joins two diffractive element elements (for example, optical members L7 and L8 in the case of FIG. 1) made of different optical materials, and diffracts by providing a diffraction grating groove on the joint surface. This is a so-called “contact multilayer diffractive optical element” constituting the optical surface D. Therefore, this diffractive optical element can increase the diffraction efficiency in a wide wavelength region including g-line to C-line. Therefore, the microscope objective lens OL according to the present embodiment can be used in a wide wavelength range. The diffraction efficiency indicates the ratio η (= I1 / I0 × 100 [%]) between the incident intensity I0 and the intensity I1 of the first-order diffracted light when the first-order diffracted light is used in the transmission type diffractive optical element.

  In addition, the contact multilayer diffractive optical element is compared to a so-called separated multilayer diffractive optical element in which two diffraction element elements formed with diffraction grating grooves are arranged close to each other so that the diffraction grating grooves face each other. Since the manufacturing process can be simplified, it has the advantages of high mass production efficiency and good diffraction efficiency with respect to the incident angle of light. Therefore, the microscope objective lens OL according to the present embodiment using the multi-contact diffractive optical element is easy to manufacture and improves the diffraction efficiency.

  Here, let f be the focal length of the entire system of the microscope objective lens OL, and the height from the optical axis of the principal ray of the light beam corresponding to the maximum field angle passing through the diffractive optical surface D (the twelfth surface in FIG. 1). When h, the diffractive optical element GD is disposed at a position that satisfies the following conditional expression (2).

0.01 ≦ | h / f | ≦ 0.04 (2)

  However, in the microscope lens OL of FIG. 1, the principal ray of the light beam emitted from the off-axis object point is changed to the light ray emitted in the direction farthest from the optical axis among the light beams emitted from the off-axis object point. The light beam having the maximum numerical aperture emitted from the upper object point is limited by the intersection of the object side surface of the lens L3 in the first lens group G1, and the light beam emitted in the direction closest to the optical axis is The light beam having the maximum numerical aperture emitted from the point is limited by the intersection point between the object side surface of the lens L11 in the third lens group G3, the off-axis light beam is determined, and the center light beam of the off-axis light beam is determined.

  By disposing the diffractive optical element GD at a position that satisfies the conditional expression (2), the chromatic aberration correcting ability of the diffractive optical element GD is effective not only for correcting axial chromatic aberration but also for correcting lateral chromatic aberration. Can be made. However, since it is not difficult to correct lateral chromatic aberration at low magnification, it is important to achieve a balance that is more effective in correcting axial chromatic aberration and moderately helps to correct lateral chromatic aberration. ) Represents a range that takes them into account.

  The third lens group G3 is a lens group that converts the convergent light beam emitted from the second lens group G2 into a substantially parallel light beam. The third lens group G3 includes at least one color correction lens component having a negative refractive power (for example, a cemented lens component CL31 including the biconvex lens L11 and the biconcave lens L12 in FIG. 1). Further, the image side surface (for example, the 18th surface in FIG. 1) of the lens disposed closest to the image side in the third lens group G3 is formed in a concave shape on the image side. The light beam incident on the third lens group G3 is a convergent light beam because it has a positive refractive power by the combination of the first lens group G1 and the second lens group G2. It is important that the third lens group G3 receives the convergent light beam and converts it into a parallel light beam while suppressing the occurrence of spherical aberration and coma aberration. The most image-side surface of the third lens group G3 is a surface that bears a large part of the negative refractive power of the third lens group G3. By constructing this surface as a concave surface on the image side, convergent light rays The incident angle with respect to the final surface can be made small, and in particular, the occurrence of higher-order coma and the like can be suppressed accurately. In addition, this color correction lens component may be constituted not only as a cemented lens but also by a plurality of lenses arranged with an air interval so as not to greatly reduce the chromatic aberration correction capability.

  Furthermore, this microscope objective lens OL satisfies the following conditional expression (3), where f is the focal length of the entire system and f12 is the combined focal length of the first lens group G1 and the second lens group G2. It is desirable.

1 ≦ | f12 / f | ≦ 1.5 (3)

  Conditional expression (3) is a condition for securing a sufficient numerical aperture (NA) while ensuring a sufficient working distance. If the lower limit of conditional expression (3) is not reached, the combined focal length f12 of the first and second lens groups G1 and G2 becomes shorter than the focal length f of the entire system, and it is difficult to ensure a sufficient numerical aperture. At the same time, it becomes difficult to correct spherical aberration. On the contrary, if the upper limit value of conditional expression (3) is exceeded, the combined focal length f12 of the first and second lens groups G1 and G2 becomes longer than the focal length f of the entire system, and the convergence of the light beam becomes insufficient. As a result, the overall length tends to be long, and it becomes difficult to correct various aberrations at high angles of view and the secondary spectrum of chromatic aberration.

  By the way, since the diffractive optical element GD has the thickness of the diffraction grating groove, the diffraction efficiency changes greatly even with a slight change in incident angle. That is, when the incident angle with respect to the diffractive optical surface D is increased, the diffraction efficiency is remarkably lowered, and the light beam of the order that is not blazed appears as flare. Therefore, it is desirable that this microscope objective lens OL satisfies the following conditional expression (4), where f is the focal length of the entire system and f2 is the focal length of the second lens group G2.

10 ≦ | f2 / f | (4)

  Conditional expression (4) is a condition for controlling the incident angle to the diffractive optical element GD using power distribution. If the lower limit of conditional expression (4) is not reached, the focal length f2 of the second lens group G2 is shorter than the focal length f of the entire system, and the refraction angle of the light beam in the second lens group G2 is large. Thus, the incident angle to the diffractive optical element GD is increased. In addition, since the conditional expression (3) defines the range of the combined focal length f12 of the first and second lens groups G1 and G2 with respect to the focal length f of the entire system, the lower limit of the conditional expression (4) If the value is below the value, the power of the first lens group G1 becomes weak, the aberration generated from the first lens group G1 decreases, the aberration in the second lens group G2, particularly the generation of spherical aberration, increases, and the first lens group It becomes difficult to balance the aberration between G1 and the second lens group G2.

  Further, in this microscope objective lens OL, when the number of diffraction grating grooves of the diffractive optical surface D in the diffractive optical element GD is N and the effective radius of the diffractive optical surface D is H, the following conditional expression (5) is satisfied. It is desirable to be satisfied.

2 ≦ N / H ≦ 5 (5)

  However, in the microscope objective lens OL of FIG. 1, the effective radius H is farthest from the optical axis among the light beams having the maximum numerical aperture emitted from the on-axis object point and the light beams emitted from the off-axis object point. The light beam emitted in the direction is limited by the intersection of the light beam having the maximum numerical aperture emitted from the on-axis object point and the object-side surface of the lens L3 in the first lens group G1, and in the direction closest to the optical axis. The outermost ray of the luminous flux determined when the emitted ray is limited by the intersection of the ray with the maximum numerical aperture emitted from the on-axis object point and the object side surface of the lens L11 in the third lens group G3. Determined by

  Conditional expression (5) is a conditional expression that defines an appropriate range between the number N of diffraction grating grooves on the diffractive optical surface D and the effective radius H. If the lower limit of conditional expression (5) is not reached, axial chromatic aberration will be insufficiently achromatic in the C-line and F-line when the d-line and g-line are achromatic (secondary spectrum). On the other hand, if the upper limit of conditional expression (5) is exceeded, axial chromatic aberration will be excessively achromatic in the C-line and F-line when the d-line and g-line are achromatic (secondary spectrum). Further, the minimum pitch width of the diffraction grating grooves formed in the diffractive optical element GD becomes small, and it becomes difficult to ensure manufacturing accuracy.

  Further, this microscope objective lens OL has a refractive index with respect to the d-line of the material of the diffractive element having the lower refractive index and the smaller Abbe number of the two diffractive element elements in the diffractive optical element GD. The refractive index is nF1, the refractive index with respect to the C-line is nC1, and the refractive index with respect to the d-line of the material of the diffractive element element having the higher refractive index and the larger Abbe number is nd2 When the refractive index for the F-line is nF2 and the refractive index for the C-line is nC2, it is desirable that the following conditional expressions (6) to (9) are satisfied.

nd1 ≦ 1.54 (6)
0.0145 ≦ nF1-nC1 (7)
1.55 ≦ nd2 (8)
nF2-nC2 ≦ 0.013 (9)

  Conditional expressions (6) to (9) are based on the materials of the two diffractive element elements constituting the diffractive optical element GD, that is, the refractive indexes of two different ultraviolet curable resins, and the dispersion with respect to the F line and C line (nF-nC) Respectively. By satisfying these conditional expressions, it is possible to form a diffractive optical surface D by tightly bonding two different diffractive element elements with better performance, and thereby in a wide wavelength range from g-line to C-line. A diffraction efficiency of 90% or more can be realized. In addition, as an example of resin as such an optical material, it describes in Japanese Patent Application No. 2004-367607, Japanese Patent Application No. 2005-237573, etc., for example. When the upper limit value or lower limit value of each conditional expression (6) to (9) is exceeded, the diffractive optical element GD in the achromatic lens system according to the present embodiment obtains a diffraction efficiency of 90% or more in a wide wavelength region. It becomes difficult to maintain the advantages of the contact multilayer diffractive optical element.

  In the following, three examples of the microscope objective lens OL according to the present embodiment will be shown. In each example, the phase difference of the diffractive optical surface D formed on the diffractive optical element GD is the normal refractive index and will be described later. It calculated by the ultrahigh refractive index method performed using the aspherical surface formula (10). The ultrahigh refractive index method uses a certain equivalent relationship between the aspherical shape and the grating pitch of the diffractive optical surface. In this embodiment, the diffractive optical surface D is replaced by the ultrahigh refractive index method. As data, that is, an aspherical expression (10) described later and its coefficient. In this embodiment, d-line, C-line, F-line and g-line are selected as the calculation target of the aberration characteristics. The wavelengths of these d-line, C-line, F-line and g-line used in this example and the refractive index values used for calculation of the ultrahigh refractive index method set for each spectral line are shown in the following table. It is shown in 1.

(Table 1)
Wavelength Refractive index (by ultra-high refractive index method)
d-line 587.562nm 10001.0000
C line 656.273nm 11170.4255
F line 486.133nm 8274.7311
g-line 435.835nm 7418.6853

In each embodiment, the height of the aspheric surface in the direction perpendicular to the optical axis is y, and the distance (sag amount) along the optical axis from the tangential plane of the apex of each aspheric surface to each aspheric surface at height y. Is S (y), r is the radius of curvature of the reference sphere (vertex radius of curvature), κ is the conic constant, and An is the nth-order aspheric coefficient, and is expressed by the following equation (10). In the following examples, “E−n” indicates “× 10 ⁻ⁿ ”.

S (y) = (y ² / r) / {1+ (1−κ × y ² / r ² ) ^1/2 }
+ A2 × y ² + A4 × y ⁴ + A6 × y ⁶ + A8 × y ⁸ + A10 × y ¹⁰ (10)

  In each example, the lens surface on which the diffractive optical surface is formed is marked with an asterisk (*) on the right side of the surface number in the table, and the aspherical expression (10) indicates the performance of this diffractive optical surface. The specifications are shown.

  In addition, the microscope objective lenses OL1 to OL3 in each of the following examples are of the infinity correction type, have the configuration shown in FIG. 7, and are used together with the imaging lens IL having the specifications shown in Table 2. . In Table 2, the first column m is the number of each optical surface from the object side, the second column r is the radius of curvature of each optical surface, and the third column d is from each optical surface to the next optical surface. , The fourth column nd indicates the refractive index with respect to the d-line, and the fifth column νd indicates the Abbe number. Here, the refractive index of air of 1.0000 is omitted. The description of the specification table is the same in the following embodiments.

(Table 2)
m r d nd νd
1 75.043 5.10 1.62280 57.0
2 -75.043 2.00 1.74950 35.2
3 1600.580 7.50
4 50.256 5.10 1.66755 42.0
5 -84.541 1.80 1.61266 44.4
6 36.911

  The imaging lens IL includes a cemented lens in which a biconvex lens L21 and a biconcave lens L22 are cemented in order from the object side, and a cemented lens in which a biconvex lens L23 and a biconcave lens L24 are cemented.

[First embodiment]
FIG. 1 used in the above description shows a microscope objective lens OL1 according to the first embodiment. The microscope objective lens OL1 is a dry objective lens, and in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a negative refraction. And a third lens group G3 having power. The first lens group G1 includes, in order from the object side, a positive meniscus lens (positive lens component) L1 having a concave surface directed toward the object side, a positive meniscus lens L2 having a concave surface directed toward the object side, and a biconvex lens L3 and a biconcave lens L4. And a biconvex lens L5 are cemented lens component CL11. The second lens group G2 includes a cemented lens component CL21 in which a biconvex lens-shaped diffractive optical element GD and a biconcave lens L10 are cemented in order from the object side. Further, the third lens group G3 includes a cemented lens component (color correction lens component) CL31 in which a biconvex lens L11 and a biconcave lens L12 are cemented in order from the object side. Here, in the first embodiment, the positive lens component (positive meniscus lens L1) located closest to the object side of the first lens group G1 has one lens surface (first surface) having negative refractive power. In addition, the most image side lens surface (18th surface) of the third lens group G3 is disposed with the concave surface facing the image side.

  The diffractive optical element GD includes a plano-convex lens L6 having a convex surface facing the object side, two optical members L7 and L8 formed from different resin materials, and a plano-convex lens L9 having a convex surface facing the image side. The diffraction grating grooves (diffractive optical surfaces D) are formed on the bonded surfaces of the optical members L7 and L8. That is, the diffractive optical element GD is a contact multilayer diffractive optical element.

  Table 3 shows the specifications of the microscope objective lens OL1 according to the first example shown in FIG. In Table 3, f represents the focal length of the entire microscope objective lens OL1, NA represents the numerical aperture, and β represents the magnification. D0 is a lens having a negative refractive power located closest to the object among the lens surfaces having a negative refractive power included in the positive lens component (positive meniscus lens L1) closest to the object from the specimen (object). The distance on the optical axis to the top of the surface (first surface) is shown. In the first embodiment, an object (specimen) is observed using a cover glass having a thickness of 0.170 mm, a refractive index of 1.52216 with respect to d-line, and an Abbe number of 58.8. Therefore, the thickness of this cover glass is excluded from d0 described above.

  In Table 3, h indicates the height from the optical axis of the principal ray of the light beam corresponding to the maximum field angle passing through the diffractive optical surface D, f1 indicates the focal length of the first lens group G1, and f2 indicates the first 2 indicates the focal length of the second lens group G2, f12 indicates the combined focal length of the first and second lens groups G1 and G2, f3 indicates the focal length of the third lens group G3, and N indicates the diffraction in the diffractive optical element GD. The number of diffraction grating grooves on the optical surface D is indicated, and H indicates the effective radius of the diffractive optical surface. As described above, the lens surface for limiting the off-axis principal ray and the off-axis light beam that determines the effective diameter in the first embodiment is the object-side surface (fifth surface) of the biconvex lens L3 and the object of the biconvex lens L11. This is the side surface (the 16th surface).

  In Table 3, the numbers of the optical surfaces shown in the first column m (* on the right indicate lens surfaces formed as diffractive optical surfaces) correspond to the surface numbers 1 to 18 shown in FIG. ing. In the second column r, the curvature radius 0.000 indicates a plane. In the case of a diffractive optical surface, the second column r indicates the radius of curvature of the spherical surface that serves as a reference for the base aspherical surface, and the data used for the ultrahigh refractive index method is indicated in the specification table as aspherical data. Yes. Further, Table 3 also shows values corresponding to the conditional expressions (1) to (9), that is, condition corresponding values. The description of the above specification table is the same in the following embodiments.

  Unless otherwise specified, “mm” is generally used as the unit of the radius of curvature r, the surface interval d, the focal length f of the entire system, and other lengths that are listed in all the following specifications. Since the same optical performance can be obtained even when proportional expansion or reduction is performed, the unit is not limited to “mm”, and other appropriate units may be used.

(Table 3)
f = 10.030
NA = 0.75
β = 20x
d0 = 1.426
h = 0.234
f1 = 11.913
f2 = -2083.794
f12 = 11.339
f3 = -842.747
N = 25
H = 9.43

m r d nd νd
1 -5.203 10.00 1.72916 54.7
2 -8.542 0.15
3 -494.981 5.40 1.49782 82.5
4 -15.368 0.15
5 93.917 5.30 1.49782 82.5
6 -21.131 1.50 1.61340 44.3
7 17.138 7.65 1.49782 82.5
8 -24.188 0.15
9 57.175 4.00 1.51680 64.1
10 0.000 0.20 1.55690 50.2
11 0.000 0.00 10001.00000 -3.5
12 * 0.000 0.20 1.52760 34.7
13 0.000 3.80 1.60 300 65.5
14 -26.099 1.20 1.75520 27.5
15 166.877 14.80
16 24.623 4.60 1.71736 29.5
17 -41.588 1.15 1.51742 52.3
18 13.348

Diffraction optical surface data 12th surface κ = 1.0000 A2 = -1.6667E-08 A4 = 3.83938E-14
A6 = -1.86752E-16 A8 = -6.20047E-19 A10 = 0.000000 + 00

Condition corresponding value (1) | (n2-n1) / (R · d0) | = 0.098
(2) | h / f | = 0.02
(3) | f12 / f | = 1.1
(4) | f2 / f | = 207.7
(5) N / H = 2.7
(6) nd1 = 1.528
(7) nF1-nC1 = 0.0152
(8) nd2 = 1.557
(9) nF2-nC2 = 0.0111

  Of the values corresponding to the conditions shown in Table 3, the conditional expression (1) indicates that the radius of curvature R of the first surface, the refractive indexes n1 and n2 with respect to the d-line of the medium before and after that, and the light from the object to the first surface. It is a value calculated from the distance d0 on the axis. Conditional expressions (6) and (7) correspond to values on the twelfth surface, and conditional expressions (8) and (9) correspond to values on the tenth surface. Thus, it can be seen that all the conditional expressions (1) to (9) are satisfied in the first embodiment. FIG. 2 shows various aberration diagrams of spherical aberration, astigmatism, lateral chromatic aberration, and coma aberration for the d-line, C-line, F-line, and g-line rays in the first embodiment. Among these aberration diagrams, the spherical aberration diagram shows the aberration amount with respect to the numerical aperture NA, the astigmatism diagram and the lateral chromatic aberration show the aberration amount with respect to the image height Y, and the coma aberration diagram shows that the image height Y is 12.5 mm. In this case, the aberration amount is shown at 9.0 mm, 6.0 mm, and 0 mm. In the spherical aberration diagram, the lateral chromatic aberration diagram, and the coma aberration diagram, the solid line indicates the d line, the dotted line indicates the C line, the alternate long and short dash line indicates the F line, and the alternate long and two short dashes line indicates the g line. Further, in the astigmatism diagram, the solid line indicates the sagittal image plane for the light beams of each wavelength, and the broken line indicates the meridional image plane for the light beams of each wavelength. The explanation of these aberration diagrams is the same in the following examples. As is apparent from the respective aberration diagrams shown in FIG. 2, it is understood that various aberrations are corrected well and excellent imaging performance is secured in the first embodiment.

[Second Embodiment]
Next, as a second embodiment, a microscope objective lens OL2 shown in FIG. 3 will be described. The microscope objective lens OL2 shown in FIG. 3 is also a dry objective lens, and in order from the object side, a first lens group G1 having a positive refractive power, and a second lens group G2 having a positive refractive power. And a third lens group G3 having negative refractive power. The first lens group G1, in order from the object side, is a cemented lens component (positive lens component) CL11 obtained by cementing a negative meniscus lens L1 having a concave surface toward the object side and a positive meniscus lens L2 having a concave surface toward the object side. The lens includes a convex lens L3, and a cemented lens component CL12 in which a negative meniscus lens L4 having a convex surface facing the object side and a biconvex lens L5 are cemented. The second lens group G2 is a cemented structure in which, from the object side, a flat diffractive optical element GD including the diffractive optical surface D, and a biconvex lens L10 and a negative meniscus lens L11 having a concave surface facing the object side are cemented. Consists of a lens component CL21. Further, the third lens group G3 includes, in order from the object side, a cemented lens component (color correction lens component) CL31 in which a positive meniscus lens L12 having a concave surface facing the object side and a biconcave lens L13 are cemented. Here, in the second example, the positive lens component (junction lens component CL11) located closest to the object side of the first lens group G1 has two lens surfaces (first surface and first lens) having negative refractive power. The lens surface (20th surface) closest to the image side of the third lens group G3 is disposed with the concave surface facing the image side. The lens surfaces for limiting the off-axis principal ray and the off-axis light beam that determines the effective diameter in the second embodiment are the image side surface (third surface) of the positive meniscus lens L2 and the object side of the positive meniscus lens L12. This is the surface (18th surface).

  Further, the diffractive optical element GD according to the second embodiment is also a multi-layered diffractive optical element, which is a flat optical glass L6, two optical members L7, L8 each formed of a different resin material, And the flat optical glass L9 is joined in this order, and the diffraction grating groove | channel (diffractive optical surface D) is formed in the joint surface of the optical members L7 and L8.

  Table 4 shows the specifications of the microscope objective lens OL2 according to the second example shown in FIG. In addition, the surface number shown in Table 4 corresponds with the surface numbers 1-20 shown in FIG. D0 is a lens having a negative refractive power located closest to the object among the lens surfaces having a negative refractive power included in the positive lens component (junction lens component CL11) closest to the object from the specimen (object). The distance on the optical axis to the top of the surface (first surface) is shown.

(Table 4)
f = 9.962
NA = 0.45
β = 20x
d0 = 5.561
h = 0.336
f1 = 15.459
f2 = 116.019
f12 = 13.404
f3 = −36.215
N = 26
H = 7.89

m r d nd νd
1 -13.200 8.80 1.59270 35.3
2 -89.546 5.46 1.65160 58.5
3 -12.975 0.20
4 1362.063 3.65 1.49782 82.6
5 -24.083 0.30
6 51.899 1.00 1.64769 33.8
7 18.663 4.50 1.49782 82.6
8 -93.183 0.20
9 0.000 1.50 1.51680 64.1
10 0.000 0.20 1.55690 50.2
11 0.000 0.00 10001.00000 -3.5
12 * 0.000 0.20 1.52760 34.7
13 0.000 1.50 1.51680 64.1
14 0.000 0.20
15 30.634 5.10 1.49782 82.6
16 -18.485 1.00 1.66755 42.0
17 -1177.040 15.83
18 -550.436 3.70 1.74077 27.8
19 -14.581 2.80 1.51742 52.3
20 12.143

Diffraction optical surface data 12th surface κ = 1.0000 A2 = -2.50000E-08 A4 = 1.254542E-13
A6 = -2.23241E-16 A8 = -1.44998E-18 A10 = 0.000000 + 00

Condition corresponding value (1) | (n2−n1) / (R · d0) | = 0.008
(2) | h / f | = 0.03
(3) | f12 / f | = 1.3
(4) | f2 / f | = 11.6
(5) N / H = 3.3
(6) nd1 = 1.528
(7) nF1-nC1 = 0.0152
(8) nd2 = 1.557
(9) nF2-nC2 = 0.0111

  Of the values corresponding to the conditions shown in Table 4, the conditional expression (1) indicates that the curvature radius R of the first surface, the refractive indexes n1 and n2 with respect to the d-line of the medium before and after that, and the light from the object to the first surface It is a value calculated from the distance d0 on the axis. Conditional expressions (6) and (7) correspond to values on the twelfth surface, and conditional expressions (8) and (9) correspond to values on the tenth surface. Thus, it can be seen that all the conditional expressions (1) to (9) are satisfied in the second embodiment. FIG. 4 shows various aberration diagrams of spherical aberration, astigmatism, lateral chromatic aberration, and coma aberration of the microscope objective lens OL2 according to the second example. As is apparent from the respective aberration diagrams, it is understood that the aberration is corrected well and excellent imaging performance is ensured also in the second embodiment.

[Third embodiment]
Next, a microscope objective lens OL3 shown in FIG. 5 will be described as a third embodiment. The microscope objective lens OL3 shown in FIG. 5 is also a dry objective lens, and in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power. And a third lens group G3 having negative refractive power. The first lens group G1 includes, in order from the object side, a cemented lens component (positive lens component) CL11 obtained by cementing a biconcave lens L1 and a biconvex lens L2, and a biconvex lens L3. The second lens group G2 is composed of a plate-shaped diffractive optical element GD. Further, the third lens group G3 includes a cemented lens component (color correction lens component) CL31 in which a biconvex lens L8 and a biconcave lens L9 are cemented in order from the object side. Here, also in the third embodiment, the positive lens component (junction lens component CL11) positioned closest to the object side of the first lens group G1 has two lens surfaces (first surface and first lens) having negative refractive power. The lens surface (14th surface) closest to the image side of the third lens group G3 is disposed with the concave surface facing the image side. Further, the lens surfaces for limiting the off-axis principal ray and the off-axis light beam that determines the effective diameter in the third embodiment are the image side surface (third surface) of the biconvex lens L2 and the image side surface of the biconcave lens L9 ( 14th surface).

  Further, the diffractive optical element GD according to the third embodiment is also a close-contact multilayer diffractive optical element, which is a flat optical glass L4, two optical members L5, L6 each formed of a different resin material, And the flat optical glass L7 is joined in this order, and the diffraction grating groove | channel (diffractive optical surface D) is formed in the joint surface of the optical members L5 and L6.

  Table 5 shows the specifications of the microscope objective lens OL3 according to the third example shown in FIG. In addition, the surface number shown in Table 5 corresponds with the surface numbers 1-14 shown in FIG. D0 is a lens having a negative refractive power located closest to the object among the lens surfaces having a negative refractive power included in the positive lens component (junction lens component CL11) closest to the object from the specimen (object). The distance on the optical axis to the top of the surface (first surface) is shown.

(Table 5)
f = 20.015
NA = 0.25
β = 10x
d0 = 11.600
h = 0.382
f1 = 24.397
f2 = 1200.063
f12 = 23.824
f3 = -2110.168
N = 27
H = 6.15

m r d nd νd
1 -20.000 9.70 1.80384 33.9
2 36.020 3.05 1.60 300 65.5
3 -15.779 0.75
4 40.984 4.50 1.60311 60.7
5 -39.626 0.30
6 0.000 1.50 1.51680 64.1
7 0.000 0.20 1.55690 50.2
8 0.000 0.00 10001.00000 -3.5
9 * 0.000 0.20 1.52760 34.7
10 0.000 1.50 1.51680 64.1
11 0.000 14.90
12 13.519 3.30 1.56883 56.3
13 -180.667 2.65 1.51823 58.9
14 10.140

Diffraction optical surface data 9th surface κ = 1.0000 A2 = -4.16667E-08 A4 = 1.32746E-13
A6 = -2.17799E-16 A8 = -1.31199E-18 A10 = 0.000000 + 00

Condition-corresponding value (1) | (n2-n1) / (R · d0) | = 0.003
(2) | h / f | = 0.02
(3) | f12 / f | = 1.2
(4) | f2 / f | = 60.0
(5) N / H = 4.4
(6) nd1 = 1.528
(7) nF1-nC1 = 0.0152
(8) nd2 = 1.557
(9) nF2-nC2 = 0.0111

  Of the condition corresponding values shown in Table 5, the conditional expression (1) indicates that the radius of curvature R of the first surface, the refractive indices n1 and n2 with respect to the d-line of the medium before and after the light, and the light from the object to the first surface It is a value calculated from the distance d0 on the axis. Conditional expressions (6) and (7) correspond to the value of the ninth surface, and conditional expressions (8) and (9) correspond to the value of the seventh surface. Thus, it can be seen that all the conditional expressions (1) to (9) are satisfied in the third embodiment. FIG. 6 is a diagram showing various aberrations of spherical aberration, astigmatism, lateral chromatic aberration, and coma aberration of the microscope objective lens OL3 according to the third example. As is apparent from the respective aberration diagrams, it is understood that aberrations are corrected well and excellent imaging performance is secured in this third embodiment.

OL (OL1 to OL3) Microscope objective lens G1 First lens group G2 Second lens group G3 Third lens group GD Diffractive optical element CL31 Color correction lens component

Claims (5)

From the object side,
A first lens group having a positive refractive power;
A second lens group;
A third lens group having negative refractive power,
The first lens group has a positive lens component including a lens surface that is located closest to the object side and has a negative refractive power;
The second lens group includes a diffractive optical element having a diffractive optical surface formed by bonding two diffractive element elements made of different optical materials and having a diffraction grating groove formed on the bonded surface.
The third lens group includes at least one color correction lens component having negative refractive power, and the lens surface closest to the image side of the third lens group faces a concave surface toward the image side. Has been placed,
Of the lens surfaces having negative refractive power included in the positive lens component provided in the first lens group, the radius of curvature of the lens surface having negative refractive power arranged closest to the object side is R, The refractive index for the d-line of the medium on the object side of the lens surface having the negative refractive power is n1, the refractive index for the d-line of the medium on the image side is n2, and the object from the apex of the lens surface having the negative refractive power When the distance on the optical axis up to d0 is d0, the following formula | (n2-n1) / (R · d0) | ≦ 0.1
Satisfy the conditions of
When the focal length of the entire system is f and the height from the optical axis of the principal ray of the light beam corresponding to the maximum angle of view passing through the diffractive optical surface is h, the following expression 0.01 ≦ | h / f | ≦ 0.04
Microscope objective lens that satisfies the above conditions. When the combined focal length of the first lens group and the second lens group is f12, the following expression 1 ≦ | f12 / f | ≦ 1.5
The microscope objective lens according to claim 1, which satisfies the following condition. When the focal length of the second lens group is f2, the following expression 10 ≦ | f2 / f |
The microscope objective lens according to claim 1 or 2, which satisfies the following condition. When the number of diffraction grating grooves of the diffractive optical surface in the diffractive optical element is N and the effective radius of the diffractive optical surface is H, the following formula 2 ≦ N / H ≦ 5
The microscope objective lens as described in any one of Claims 1-3 which satisfy | fills these conditions. Of the two diffractive element elements in the diffractive optical element, the refractive index for the d-line of the material of the diffractive element element having the lower refractive index and the smaller Abbe number is nd1, the refractive index for the F line is nF1, and the C line. The refractive index with respect to the d-line of the material of the diffractive element element having the higher refractive index and the larger Abbe number among the two diffractive element elements in the diffractive optical element with respect to nd2 and F-line is nC1. When the refractive index is nF2 and the refractive index for the C-line is nC2, the following formula nd1 ≦ 1.54
0.0145 ≦ nF1-nC1
1.55 ≤ nd2
nF2-nC2 ≦ 0.013
The microscope objective lens as described in any one of Claims 1-4 which satisfies these conditions.

Images