JP5206085B2 - Microscope objective lens - Google Patents

Description

  The present invention relates to a microscope objective lens.

The conventional microscope objective lens requires a large number of cemented lenses in order to satisfactorily correct chromatic aberration among various aberrations, and it is necessary to use anomalous dispersion glass. In recent years, a lens system using a diffractive optical element (DOE) capable of correcting various aberrations, particularly chromatic aberration, has been proposed with a high magnification and a high numerical aperture without using a cemented lens or anomalous dispersion glass (for example, patent documents). 1).
JP-A-6-331898

  However, in a lens system using such 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 at a high magnification and a high numerical aperture. There was a problem that the image performance of the image was low.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a microscope objective lens in which various chromatic aberrations are sufficiently corrected and various aberrations are well corrected in a sufficient field of view. And

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. And the first lens group includes a positive lens component including a lens surface located closest to the object side and having negative refractive power, and at least one cemented lens component having positive refractive power in combination. The second lens group includes a diffractive optical element having a diffractive optical surface in which two diffractive element elements made of different optical materials are bonded and a diffraction grating groove is formed on the bonded surface, and at least one or more diffractive optical elements . and a cemented lens component, the third lens group includes at least one or more color correction lens component, and the lens surface on the most image side of the third lens group, and a concave surface facing the image side Arranged and configured. The radius of curvature of the lens surface having negative refractive power of the positive lens component provided in the first lens group is r, and the refractive index with respect to d-line of the medium on the object side of the lens surface having negative refractive power is expressed as follows. When n1, the refractive index of the medium on the image side with respect to the d-line is n2, and the optical path length from the apex of the lens surface having negative refractive power to the object is dR,
| (N2-n1) / (r · dR) | ≦ 0.5
Where f is the focal length of the entire system, and h is 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.
0.1 ≦ | h / f |
It is configured to satisfy the following 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 off-axis light beam.

Further, such a microscope objective lens has the following formula when the focal length of the entire system is f and the combined focal length of the first lens group and the second lens group is f12:
1.5 ≦ | f12 / f | ≦ 2.5
When the focal length of the entire system is f and the focal length of the third lens group is f3, the following equation is satisfied:
10 ≦ | f3 / f | ≦ 20
It is configured to satisfy the following conditions.

Further, in such a microscope objective lens, when the focal length of the entire system is f and the focal length of the second lens group is f2, the following expression 30 ≦ | 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 ≦ 10
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 in which chromatic aberration is sufficiently corrected and various aberrations are well corrected in a sufficient field of view.

  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 closer to a parallel light beam. Therefore, a positive lens component (including a lens surface having negative refractive power) ( For example, the positive meniscus lens L1) in FIG. 1 and at least one achromatic lens component (a cemented lens CL11 in FIG. 1) formed by cementing a positive lens and a negative lens are configured. The positive lens component may be composed of a single lens or a cemented lens. Here, the radius of curvature of a lens surface having negative refractive power included in the positive lens component (for example, the first surface in FIG. 1) is r, the refractive index with respect to the d-line on the object side of the lens surface is n1, and the image When the refractive index with respect to the d-line on the side is n2, and the optical path length from the object to the apex of the lens surface closest to the object side (that is, the first surface in FIG. 1) is dR, the following conditional expression (1) Satisfied.

| (N2-n1) / (r · dR) | ≦ 0.5 (1)

  This conditional expression (1) defines the refractive power of the lens surface having the negative refractive power included in the above-mentioned positive lens component provided in the first lens group G1, and this conditional expression (1) If the upper limit is exceeded, it is difficult to correct the Petzval sum, and it becomes difficult to ensure image plane flatness up to a high angle of view. More preferably, if the upper limit value of conditional expression (1) is 0.4, the Petzval sum can be corrected more favorably.

  The second lens group G2 is a lens group that receives the substantially parallel light beam emitted from the first lens group G1 and corrects spherical aberration and chromatic aberration. In particular, the diffractive optical element GD is used to correct chromatic aberration. Is provided. 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 embodiment of the present application), large dispersion, and anomalous dispersion (in the embodiment of the present application). 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. 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, chromatic aberration can be favorably corrected by using the diffractive optical element GD.

  The diffractive optical element GD in the present embodiment joins two diffractive element elements (for example, optical members L6 and L7 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, when the focal length of the entire system of the microscope objective lens OL is f 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 is h, this diffractive optical The element GD is disposed at a position that satisfies the following conditional expression (2).

0.1 ≦ | h / f | (2)

However, in the microscope objective lens OL of FIG. 1, the principal ray of the light beam emitted from the off-axis object point is 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 on-axis object point is limited by the intersection of the image side surface of the lens L2 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 object 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. In order to prevent the minimum pitch of the diffraction grating grooves of the diffractive optical element GD from becoming small, it is necessary to perform the first order achromaticity to some extent with the refractive lens of the second lens group G2. For this reason, it is necessary to provide at least one achromatic lens component (a cemented lens component CL21 in FIG. 1) formed by cementing a positive lens and a negative lens in the second lens group G2.

  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 negative refractive power (a cemented lens component CL31 including the biconvex lens L11 and the biconcave lens L12 in FIG. 1). Further, the image side surface of the lens disposed closest to the image side of 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 the first lens group G1 and the second lens group G2 have positive refractive power. 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 element 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.

1.5 ≦ | f12 / f | ≦ 2.5 (3)

  Conditional expression (3) is a condition for securing a high numerical aperture. If the lower limit of conditional expression (1) 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 becomes difficult to ensure the numerical aperture. This makes it 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.

  The microscope objective lens OL preferably satisfies the following conditional expression (4), where f is the focal length of the entire system and f3 is the focal length of the third lens group G3.

10 ≦ | f3 / f | ≦ 20 (4)

  Conditional expression (4) is a condition for satisfactorily correcting spherical aberration including changes due to color and ensuring a sufficient field of view. If the lower limit of conditional expression (4) is not reached, the focal length f3 of the third lens group G3 becomes shorter than the focal length f of the entire system, and variations in spherical aberration occur for each color, as well as higher-order bending. Occurs. On the other hand, if the upper limit value of conditional expression (4) is exceeded, the focal length f3 of the third lens group G3 becomes longer than the focal length f of the entire system, and the correction of spherical aberration becomes insufficient, and the image performance is reduced. It is difficult to ensure a good and sufficient field of view.

  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 the microscope objective lens OL satisfies the following conditional expression (5), where f is the focal length of the entire system and f2 is the focal length of the second lens group G2.

30 ≦ | f2 / f | (5)

  Conditional expression (5) is a condition for controlling the incident angle to the diffractive optical element GD using power distribution. If the lower limit value of conditional expression (5) is not reached, the focal length f2 of the second lens group G2 becomes 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 (5) 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 (6) is satisfied. It is desirable to be satisfied.

2 ≦ N / H ≦ 10 (6)

  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 image-side surface of the lens L2 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 (6) is a conditional expression that defines an appropriate range of the number N of diffraction grating grooves and the effective radius H of the diffractive optical surface D. If the lower limit of conditional expression (6) is not reached, axial chromatic aberration will be insufficiently achromatic in the C-line and F-line when achromatic in the d-line and g-line (secondary spectrum). On the other hand, if the upper limit of conditional expression (6) is exceeded, axial chromatic aberration will be excessively achromatic in the C-line and F-line when achromatic in the d-line and g-line (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 (7) to (10) are satisfied.

nd1 ≦ 1.54 (7)
0.0145 ≦ nF1-nC1 (8)
1.55 ≦ nd2 (9)
nF2-nC2 ≦ 0.013 (10)

  Conditional expressions (7) to (10) respectively define the refractive indexes of the materials of the two diffractive element elements constituting the diffractive optical element GD, and the dispersion (nF-nC) with respect to the F line and the C line. 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 the conditional expressions (7) to (10) 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, five examples of the microscope objective lens OL according to the present embodiment will be described. In each example, the phase difference of the diffractive optical surface D formed on the diffractive optical element GD is a normal refractive index and will be described later. It calculated by the ultrahigh refractive index method performed using the aspherical surface formula (11). 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 (11) 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 (vertex radius of curvature) of the reference sphere, k is the conic constant, and An is the nth-order aspheric coefficient, and is expressed by the following equation (11). 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 (11)

  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 (11) indicates the performance of the diffractive optical surface. The specifications are shown.

  In addition, the microscope objective lenses OL1 to OL5 in the following examples are of the infinity correction type, have the configuration shown in FIG. 11, 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 5.1 1.62280 57.0
2 -75.043 2.0 1.74950 35.2
3 1600.580 7.5
4 50.256 5.1 1.66755 42.0
5 -84.541 1.8 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 positive 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 L1 having a concave surface facing the object side, a biconvex lens L2, and a negative meniscus lens L3 having a convex surface facing the object side and a biconvex lens L4. The lens component (achromatic lens component) CL11 is included. Further, the second lens group G2 includes, in order from the object side, a diffractive optical element GD including the diffractive optical surface D, and a cemented lens component in which a negative meniscus lens L9 having a convex surface facing the object side and a biconvex lens L10 are cemented ( Achromatic lens component) CL21. Further, the third lens group G3 includes a cemented lens component CL31 in which a biconvex lens L11 and a biconcave lens L12 are cemented in order from the object side. As described above, in the first embodiment, the color correction lens component CL31 constituting the third lens group G3 is configured as a cemented lens component in which two lenses are cemented.

  Further, in the diffractive optical element GD, a flat optical glass L5, two flat optical members L6 and L7 formed from different resin materials, and a flat optical glass L8 are joined in this order, A diffraction grating groove (diffractive optical surface D) is formed on the joint surface of the optical members L6 and L7. 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. In the first embodiment, the second embodiment, and the third embodiment, d0 is from the sample to the apex of the lens surface (first surface) closest to the object side of the first lens (lens L1) closest to the object side. The distance on the optical axis is shown. DR indicates the optical path length from the apex of the lens surface having the negative refractive power located closest to the object side of the first lens group G1 to the object. The lens surface having the negative refractive power is In the first embodiment, the second embodiment, and the third embodiment, this is the first surface. Further, h represents 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 represents the focal length of the first lens group G1, and f2 represents the second lens group G2. F12 represents the combined focal length of the first and second lens groups G1 and G2, f3 represents the focal length of the third lens group G3, and N represents the diffractive optical surface D of the diffractive optical element GD. The number of diffraction grating grooves 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 image side surface (fourth surface) of the biconvex lens L2 and the object side of the biconvex lens L11. This is the surface (the 17th surface).

  The numbers of the optical surfaces shown in the first column m (* on the right indicate the lens surfaces formed as diffractive optical surfaces) correspond to the surface numbers 1 to 19 shown in FIG. 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 (10), that is, condition corresponding values. The description of these specification tables is the same in the following examples.

  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 = 4.005
NA = 0.8
β = 50x
d0 = 1.71
dR = 1.71
h = 0.69
f1 = 7.862
f2 = 140.481
f12 = 7.456
f3 = -45.026
N = 41
H = 6.89

m r d nd νd
1 -2.740 4.1 1.83481 42.7
2 -4.212 0.1
3 22967.611 5.5 1.49782 82.5
4 -10.771 0.2
5 92.682 1.3 1.79504 28.7
6 16.210 5.9 1.49782 82.5
7 -14.459 0.2
8 0.000 1.5 1.51680 64.1
9 0.000 0.2 1.55690 50.2
10 0.000 0.0 10001.00000 -3.5
11 * 0.000 0.2 1.52760 34.7
12 0.000 2.0 1.51680 64.1
13 0.000 0.5
14 34.600 1.5 1.74950 35.3
15 9.130 5.0 1.60 300 65.5
16 -2824.563 26.5
17 19.407 3.7 1.84666 23.8
18 -12.700 2.9 1.75692 31.6
19 8.699

Diffraction optical surface data 11th surface κ = 1.0000 A2 = -4.99472E-08 A4 = 1.32542E-13
A6 = -2.22321E-16 A8 = -1.44998E-18 A10 = 0.00000E-00

Condition corresponding value (1) | (n2-n1) / (r · dR) | = 0.178
(2) | h / f | = 0.17
(3) | f12 / f | = 1.86
(4) | f3 / f | = 11.2
(5) | f2 / f | = 35.1
(6) N / H = 6.0
(7) nd1 = 1.528
(8) nF1-nC1 = 0.0152
(9) nd2 = 1.557
(10) nF2-nC2 = 0.0111

  Of the condition corresponding values shown in Table 3, the conditional expression (1) is a value calculated from the curvature radius r of the first surface and the refractive indexes n1 and n2 with respect to the d-line of the medium before and after the first surface. Conditional expressions (7) and (8) correspond to the values of the eleventh surface, and conditional expressions (9) and (10) correspond to the values of the ninth surface. Thus, it can be seen that all the conditional expressions (1) to (10) 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 12.6 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 each wavelength, and the broken line indicates the meridional image plane for 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 negative refractive power. And a third lens group G3 having negative refractive power. The first lens group G1, in order from the object side, includes a positive meniscus lens L1 having a concave surface facing the object side, a positive meniscus lens L2 having a concave surface facing the object side, and a negative meniscus lens L3 having a convex surface facing the object side. It is composed of a cemented lens component (achromatic lens component) CL11 formed by cementing the biconvex lens L4. The second lens group G2 includes, in order from the object side, a cemented lens component (achromatic lens component) CL21 formed by cementing a biconvex lens-shaped diffractive optical element GD including the diffractive optical surface D, a biconcave lens L9, and a biconvex lens L10. Consists of. Further, the third lens group G3 includes a cemented lens component CL31 in which a biconvex lens L11 and a biconcave lens L12 are cemented in order from the object side. Thus, in the second embodiment, the color correction lens component CL31 constituting the third lens group G3 is configured as a cemented lens component in which two lenses are cemented. In the second embodiment, the refractive power of the second lens group G2 is negative. However, since the positive refractive power of the first lens group G1 is sufficiently strong, the light beam emitted from the first lens group G1. This is because there is a sufficient convergent luminous flux. Further, in the second embodiment, the lens surfaces for limiting the off-axis principal ray and the off-axis light beam that determines the effective diameter are the image side surface (fourth surface) of the positive meniscus lens L2 and the object side surface of the biconvex lens L11. (16th surface).

  Further, the diffractive optical element GD according to the second embodiment is also a close-contact multilayer diffractive optical element, and includes a plano-convex lens L5 having a convex surface facing the object side, and two optical members formed from different resin materials. L6 and L7 and a plano-convex lens L8 having a convex surface facing the image side are joined in this order, and a diffraction grating groove (diffractive optical surface D) is formed on the joint surface of the optical members L6 and L7.

  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 1-18 shown in FIG.

(Table 4)
f = 3.967
NA = 0.8
β = 50x
d0 = 1.71
dR = 1.71
h = 0.71
f1 = 7.289
f2 = -306.768
f12 = 7.265
f3 = -50.628
N = 22
H = 6.62

m r d nd νd
1 -2.722 4.3 1.90265 35.7
2 -4.398 0.1
3 -79.653 5.5 1.49782 82.5
4 -11.202 0.2
5 49.789 1.3 1.79504 28.7
6 15.062 5.9 1.49782 82.5
7 -12.303 0.2
8 36.594 1.3 1.51680 64.1
9 0.000 0.2 1.55690 50.2
10 0.000 0.0 10001.00000 -3.5
11 * 0.000 0.2 1.52760 34.7
12 0.000 3.0 1.49782 82.5
13 -10.999 1.2 1.66755 42.0
14 12.389 4.0 1.49782 82.5
15 -49.958 28.2
16 17.770 3.7 1.84666 23.8
17 -13.000 2.9 1.75692 31.6
18 8.383

Diffraction optical surface data 11th surface κ = 1.0000 A2 = -2.92088E-08 A4 = 1.20938E-13
A6 = -1.83902E-16 A8 = -3.40027E-19 A10 = 0.000000-00

Condition corresponding value (1) | (n2-n1) / (r · dR) | = 0.194
(2) | h / f | = 0.18
(3) | f12 / f | = 1.83
(4) | f3 / f | = 12.8
(5) | f2 / f | = 77.3
(6) N / H = 3.3
(7) nd1 = 1.528
(8) nF1-nC1 = 0.0152
(9) nd2 = 1.557
(10) nF2-nC2 = 0.0111

  Of the condition corresponding values shown in Table 4, the conditional expression (1) is a value calculated from the curvature radius r of the first surface and the refractive indexes n1 and n2 with respect to the d-line of the medium before and after the first surface. Conditional expressions (7) and (8) correspond to the values of the eleventh surface, and conditional expressions (9) and (10) correspond to the values of the ninth surface. Thus, it can be seen that all the conditional expressions (1) to (10) 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. The coma aberration diagram shown in FIG. 4 shows the amount of aberration when the image height Y is 12.8 mm, when it is 9.0 mm, when it is 6.0 mm, and when it is 0 mm. 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 negative refractive power. And a third lens group G3 having negative refractive power. The first lens group G1, in order from the object side, includes a positive meniscus lens L1 having a concave surface facing the object side, a positive meniscus lens L2 having a concave surface facing the object side, and a negative meniscus lens L3 having a convex surface facing the object side. It is composed of a cemented lens component (achromatic lens component) CL11 formed by cementing the biconvex lens L4. The second lens group G2 includes, in order from the object side, a cemented lens component (achromatic lens component) CL21 formed by cementing a biconvex lens-shaped diffractive optical element GD including the diffractive optical surface D, a biconcave lens L9, and a biconvex lens L10. Consists of. Further, the third lens group G3 includes a biconvex lens L11 and a biconcave lens L12 in order from the object side. Thus, in the third example, the color correction lens component CL31 constituting the third lens group G3 is composed of two lenses spaced apart from each other. In the third example as well, the second lens group G2 has a negative refractive power, and this reason is the same as the reason in the second example. 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 (fourth surface) of the positive meniscus lens L2 and the object side surface of the biconcave lens L12. (Eighteenth surface).

  Further, the diffractive optical element GD according to the third embodiment is also a close-contact multilayer diffractive optical element, a plano-convex lens L5 having a convex surface facing the object side, and two optical members formed from different resin materials, respectively. L6 and L7 and a plano-convex lens L8 having a convex surface facing the image side are joined in this order, and a diffraction grating groove (diffractive optical surface D) is formed on the joint surface of the optical members L6 and L7.

  Table 5 shows the specifications of the microscope objective lens OL3 according to the third example shown in FIG. Note that the surface numbers shown in Table 5 coincide with the surface numbers 1 to 19 shown in FIG.

(Table 5)
f = 4.018
NA = 0.8
β = 50x
d0 = 1.71
dR = 1.71
h = 0.56
f1 = 7.541
f2 = -243.716
f12 = 7.545
f3 = -60.190
N = 63
H = 7.16

m r d nd νd
1 -2.674 4.3 1.83481 42.7
2 -4.201 0.1
3 -23.463 5.6 1.49782 82.5
4 -12.063 0.2
5 39.359 1.4 1.79504 28.7
6 15.762 6.0 1.60 300 65.5
7 -15.718 0.2
8 38.466 1.2 1.51680 64.1
9 0.000 0.2 1.55690 50.2
10 0.000 0.0 10001.00000 -3.5
11 * 0.000 0.2 1.52760 34.7
12 0.000 3.0 1.56384 60.7
13 -19.843 1.2 1.72342 37.9
14 9.484 4.0 1.51680 64.1
15 -53.877 26.0
16 17.590 3.7 1.74950 35.3
17 -26.797 1.5
18 -25.258 2.9 1.67000 57.4
19 7.691

Diffraction optical surface data 11th surface κ = 1.0000 A2 = -7.15155E-08 A4 = 2.36388E-14
A6 = -3.33620E-16 A8 = -2.96788E-19 A10 = 0.000000-00

Condition corresponding value (1) | (n2−n1) / (r · dR) | = 0.183
(2) | h / f | = 0.14
(3) | f12 / f | = 1.88
(4) | f3 / f | = 15.0
(5) | f2 / f | = 60.7
(6) N / H = 8.8
(7) nd1 = 1.528
(8) nF1-nC1 = 0.0152
(9) nd2 = 1.557
(10) nF2-nC2 = 0.0111

  Of the condition corresponding values shown in Table 5, the conditional expression (1) is a value calculated from the curvature radius r of the first surface and the refractive indexes n1 and n2 with respect to the d-line of the medium before and after the first surface. Conditional expressions (7) and (8) correspond to the values of the eleventh surface, and conditional expressions (9) and (10) correspond to the values of the ninth surface. Thus, it can be seen that all the conditional expressions (1) to (10) 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. The coma aberration diagram shown in FIG. 6 shows the amount of aberration when the image height Y is 12.8 mm, when it is 9.0 mm, when it is 6.0 mm, and when it is 0 mm. 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.

[Fourth embodiment]
Next, as a fourth embodiment, a microscope objective lens OL4 shown in FIG. 7 will be described. The microscope objective lens OL4 shown in FIG. 7 has an immersion system objective used in a microscope in which a specimen (object) is placed under the cover plate C and the specimen is observed with the tip immersed in the immersion liquid. A first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power in order from the object side. Is done. The first lens group G1, in order from the object side, has a cemented lens component CL11 formed by cementing a planoconvex lens L1 having a flat object side and a negative meniscus lens L2 having a concave surface on the object side, and has a concave surface directed to the object side. It is composed of a positive meniscus lens L3 and a cemented lens component (achromatic lens component) CL12 in which a biconcave lens L4 and a biconvex lens L5 are cemented. The second lens group G2 includes, in order from the object side, a cemented lens component (achromatic lens component) CL21 obtained by cementing a negative meniscus lens L6 having a convex surface facing the object side and a biconvex lens L7, and a diffractive optical surface D. Is comprised of a diffractive optical element GD. Further, the third lens group G3 includes a cemented lens component CL31 in which a biconvex lens L12 and a biconcave lens L13 are cemented in order from the object side. Thus, in the fourth embodiment, the color correction lens component CL31 constituting the third lens group G3 is configured as a cemented lens component in which two lenses are cemented. Further, the lens surfaces for limiting the off-axis principal ray and the off-axis light beam that determines the effective diameter in the fourth embodiment are the image side surface (fifth surface) of the positive meniscus lens L3 and the object side surface of the biconvex lens L12. (Eighteenth surface).

  Further, the diffractive optical element GD according to the fourth embodiment is also a close-contact diffractive optical element, which is a flat optical glass L8 and two flat optical members L9 formed from different resin materials. , L10 and the flat optical glass L11 are joined in this order, and a diffraction grating groove (diffractive optical surface D) is formed on the joining surface of the optical members L9, L10.

  Table 6 shows the specifications of the microscope objective lens OL4 according to the fourth example shown in FIG. In the fourth and fifth embodiments using the cover plate C, d0 is the first lens (lens L1) closest to the object (specimen) excluding the thickness of the cover plate C. ) On the optical axis to the vertex of the lens surface (first surface) closest to the object side, dR represents the optical path length from the vertex of the second surface to the object, excluding the thickness of the cover plate C. ing. Here, the cover plate C has a thickness of 0.17 mm, a refractive index of 1.52216 with respect to the d-line, and an Abbe number of 58.8, and the immersion liquid has a refractive index of 1.51536 with respect to the d-line and an Abbe number of 41.4. is there. Further, the surface numbers shown in Table 6 coincide with the surface numbers 1 to 20 shown in FIG.

(Table 6)
f = 1.990
NA = 1.25
β = 100x
d0 = 0.174
dR = 0.871
h = 0.46
f1 = 4.374
f2 = 88.548
f12 = 4.672
f3 = -30.152
N = 23
H = 5.27

m r d nd νd
1 0.000 0.4 1.51823 58.9
2 -1.261 3.3 1.90265 35.7
3 -2.875 0.1
4 -112.396 3.2 1.60300 65.5
5 -7.930 0.2
6 -609.844 1.5 1.74950 35.3
7 10.980 6.2 1.49782 82.5
8 -8.898 0.1
9 36.907 1.7 1.75692 31.6
10 8.144 4.5 1.49782 82.5
11 -24.025 0.2
12 0.000 2.0 1.51680 64.1
13 0.000 0.2 1.55690 50.2
14 0.000 0.0 10001.00000 -3.5
15 * 0.000 0.2 1.52760 34.7
16 0.000 2.0 1.51680 64.1
17 0.000 26.5
18 105.388 2.4 1.69895 30.1
19 -8.220 3.4 1.51680 64.1
20 7.755

Diffraction optical surface data 15th surface κ = 1.0000 A2 = -5.00000E-08 A4 = 3.64816E-14
A6 = -1.91386E-16 A8 = -5.33683E-19 A10 = 0.000000-00

Condition corresponding value (1) | (n2−n1) / (r · dR) | = 0.350
(2) | h / f | = 0.23
(3) | f12 / f | = 2.35
(4) | f3 / f | = 15.2
(5) | f2 / f | = 44.5
(6) N / H = 4.4
(7) nd1 = 1.528
(8) nF1-nC1 = 0.0152
(9) nd2 = 1.557
(10) nF2-nC2 = 0.0111

  Of the condition corresponding values shown in Table 6, the conditional expression (1) is a value calculated from the curvature radius r of the second surface and the refractive indexes n1 and n2 with respect to the d-line of the medium before and after the second surface. Conditional expressions (7) and (8) correspond to values of the fifteenth surface, and conditional expressions (9) and (10) correspond to values of the thirteenth surface. Thus, it can be seen that all the conditional expressions (1) to (10) are satisfied in the fourth embodiment. FIG. 8 is a diagram showing various aberrations of spherical aberration, astigmatism, lateral chromatic aberration, and coma aberration of the microscope objective lens OL4 according to the fourth example. The coma aberration diagram shown in FIG. 8 shows the amount of aberration when the image height Y is 11.1 mm, when it is 8.0 mm, when it is 5.0 mm, and when it is 0 mm. As is apparent from the respective aberration diagrams, it is understood that aberrations are corrected well and excellent imaging performance is secured in the fourth embodiment.

[Example 5]
Next, as a fifth embodiment, a microscope objective lens OL5 shown in FIG. 9 will be described. The microscope objective lens OL5 shown in FIG. 9 is also an immersion system objective used in a microscope in which a specimen (object) is placed under the cover plate C and the tip is immersed in immersion liquid. A first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power in order from the object side. Is done. The first lens group G1, in order from the object side, has a cemented lens component CL11 formed by cementing a planoconvex lens L1 having a flat object side and a negative meniscus lens L2 having a concave surface on the object side, and has a concave surface directed to the object side. It comprises a positive meniscus lens L3, and a cemented lens component (achromatic 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 includes, in order from the object side, a cemented lens component (achromatic lens component) CL21 obtained by cementing a negative meniscus lens L6 having a convex surface facing the object side and a biconvex lens L7, and a diffractive optical surface D. The diffractive optical element GD including Further, the third lens group G3 includes, in order from the object side, a cemented lens component CL31 obtained by cementing a negative meniscus lens L12 having a convex surface toward the object side, a biconvex lens L13, and a biconcave lens L14. Thus, in the fifth example, the color correction lens component CL31 constituting the third lens group G3 is configured as a cemented lens component in which three lenses are cemented. The lens surfaces for limiting the off-axis principal ray and the off-axis light beam that determines the effective diameter in the fifth embodiment are the image side surface (fifth surface) of the positive meniscus lens L3 and the object side of the negative meniscus lens L12. This is the surface (18th surface).

  Further, the diffractive optical element GD according to the fifth embodiment is also a close-contact diffractive optical element, which is a flat optical glass L8, and two flat optical members L9 made of different resin materials. , L10 and the flat optical glass L11 are joined in this order, and a diffraction grating groove (diffractive optical surface D) is formed on the joining surface of the optical members L9, L10.

  Table 7 shows specifications of the microscope objective lens OL5 according to Example 5 shown in FIG. In addition, the surface number shown in Table 7 corresponds with the surface numbers 1-21 shown in FIG.

(Table 7)
f = 1.989
NA = 1.25
β = 100x
d0 = 0.174
dR = 0.871
h = 0.43
f1 = 4.322
f2 = 101.572
f12 = 4.650
f3 = -30.092
N = 25
H = 5.26

m r d nd νd
1 0.000 0.4 1.51823 58.9
2 -1.261 3.3 1.90265 35.7
3 -2.889 0.1
4 -86.403 3.2 1.60300 65.5
5 -7.861 0.2
6 140.533 1.5 1.74950 35.3
7 10.780 6.2 1.49782 82.5
8 -9.124 0.1
9 44.249 1.7 1.75692 31.6
10 8.181 4.5 1.49782 82.5
11 -22.375 0.2
12 37663.957 2.0 1.51680 64.1
13 0.000 0.2 1.55690 50.2
14 0.000 0.0 10001.00000 -3.5
15 * 0.000 0.2 1.52760 34.7
16 0.000 2.0 1.51680 64.1
17 0.000 25.0
18 58.830 1.5 1.61340 44.3
19 14.067 3.0 1.67270 32.1
20 -7.152 2.5 1.56883 56.3
21 8.451

Diffraction optical surface data 15th surface κ = 1.0000 A2 = -5.23715E-08 A4 = 2.66577E-13
A6 = -2.84237E-16 A8 = -3.93947E-18 A10 = 0.00000E-00

Condition corresponding value (1) | (n2−n1) / (r · dR) | = 0.350
(2) | h / f | = 0.22
(3) | f12 / f | = 2.34
(4) | f3 / f | = 15.1
(5) | f2 / f | = 51.1
(6) N / H = 4.8
(7) nd1 = 1.528
(8) nF1-nC1 = 0.0152
(9) nd2 = 1.557
(10) nF2-nC2 = 0.0111

  Of the condition corresponding values shown in Table 7, the conditional expression (1) is a value calculated from the curvature radius r of the second surface and the refractive indexes n1 and n2 with respect to the d-line of the medium before and after the second surface. Conditional expressions (7) and (8) correspond to values of the fifteenth surface, and conditional expressions (9) and (10) correspond to values of the thirteenth surface. Thus, it can be seen that all the conditional expressions (1) to (10) are satisfied in the fifth embodiment. FIG. 10 shows various aberration diagrams of spherical aberration, astigmatism, lateral chromatic aberration and coma aberration of the microscope objective lens OL5 according to the fifth example. The coma aberration diagram shown in FIG. 10 shows the amount of aberration when the image height Y is 11.1 mm, when it is 8.0 mm, when it is 5.0 mm, and when it is 0 mm. As is apparent from the respective aberration diagrams, it is understood that aberrations are corrected well and excellent imaging performance is secured in this fifth embodiment.

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 microscope objective lens which concerns on 4th Example. It is various aberrational figures of the microscope objective lens which concerns on the said 4th Example. It is a lens block diagram of the microscope objective lens which concerns on 5th Example. FIG. 10 is a diagram illustrating all aberrations of the microscope objective lens according to the fifth example. It is a lens block diagram of the imaging lens used with the said microscope objective lens.

Explanation of symbols

OL (OL1 to OL5) Microscope objective lens G1 First lens group G2 Second lens group G3 Third lens group GD Diffractive optical element

Claims (4)

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 includes a positive lens component including a lens surface located closest to the object side and having a negative refractive power, and at least one cemented lens component having a combined positive refractive power ,
The second lens group includes a diffractive optical element having a diffractive optical surface in which two diffractive element elements made of different optical materials are bonded and a diffraction grating groove is formed on the bonded surface, and at least one bonded lens component. And
The third lens group has at least one or more color correction lens components, and the lens surface closest to the image side of the third lens group is disposed with the concave surface facing the image side,
The radius of curvature of the lens surface having negative refractive power of the positive lens component provided in the first lens group is r, and the refractive index with respect to d-line of the medium on the object side of the lens surface having negative refractive power. Is n1, the refractive index of the medium on the image side with respect to the d-line is n2, and the optical path length from the apex of the lens surface having negative refractive power to the object is dR,
| (N2-n1) / (r · dR) | ≦ 0.5
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 field angle passing through the diffractive optical surface is h,
0.1 ≦ | h / f |
Satisfy the conditions of
When the focal length of the entire system is f and the combined focal length of the first lens group and the second lens group is f12, the following expression 1.5 ≦ | f12 / f | ≦ 2.5
Satisfy the conditions of
When the focal length of the entire system is f and the focal length of the third lens group is f3, the following expression 10 ≦ | f3 / f | ≦ 20
Microscope objective lens configured to satisfy the following conditions. When the focal length of the entire system is f and the focal length of the second lens group is f2, the following expression 30 ≦ | f2 / f |
The microscope objective lens according to claim 1, which satisfies the following condition. When the number of diffraction grating grooves on 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 ≦ 10
The microscope objective lens according to claim 1 or 2, which satisfies the following condition. 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 1-3 which satisfy | fills these conditions.

Images