JP3312057B2 - Objective lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens used for an optical system such as a microscope.

[0002]

2. Description of the Related Art Conventional objective lenses have a particularly high magnification and a high N.
In the case of A, a large number of cemented lenses were required to properly correct chromatic aberrations among various aberrations, and it was necessary to use anomalous dispersion glass. For this reason, there is no choice but to be expensive, and furthermore, in the case of an objective lens used for ultraviolet rays or infrared rays where the glass material is limited, it may not be possible to design the objective lens.

Recently, a diffractive optical element (DO) has been used as an optical element.
An optical system using E) has attracted attention. In the prior art similar to the objective lens of the present invention, an objective lens using this diffractive optical element is disclosed in JP-A-63-77003, JP-A-63-155432, JP-A-59-33636, and JP-A-59-33636. There are those described in JP-A-60-247611, JP-A-2-1-1109 and JP-A-4-361201.

A diffractive optical element utilizing the above-mentioned diffraction phenomenon, that is, a diffractive optical element
[Diffractive Optical Elem
ents (DOE)] , Optronics “Optical Elements for Optical Designers”, Chapters 6, 7
And William C.A. Newt by Sweat
METHODS OF DESIGNING HOL
OGRAPHIC OPTICAL ELEMENT
S "(SPIE.VOL.126, P46-53, 19)
77) etc., but the principle is briefly described as follows.

[0005] Ordinary optical glass is refracted according to Snell's law represented by the following equation in FIG.

N sin θ = n ′ sin θ ′ (1) where n is the refractive index of the incident side medium, n ′ is the refractive index of the exit side medium, θ is the incident angle of light rays, and θ ′ is the exit angle of light rays. is there.

On the other hand, in the diffraction phenomenon, light is bent according to the law of diffraction represented by the following equation as shown in FIG.

N sin θ−n ′ sin θ ′ = mλ / d (2) where m is the order of the diffracted light, λ is the wavelength, and d is the lattice spacing.

An optical element that refracts light according to the above equation (2) is a diffractive optical element. FIG.
In FIG. 7, the shielding portion and the transmitting portion are arranged side by side at a distance d. However, as shown in FIG. 18, a transparent surface is provided with a diffraction surface having a saw-tooth cross-section and blazed as shown in FIG. When the binary approximation is performed, high diffraction efficiency can be obtained.

Next, advantages of using the above-described diffractive optical element will be described.

In the case of a dioptric thin lens, the following equation (3) is used.
Is established.

1 / f = (n−1) (1 / r ₁ −1 / r ₂ ) (3) where f is the focal length, r ₁ and r ₂ are the radii of curvature of the entrance surface and the exit surface, respectively, and n Is the refractive index of the lens.

When both sides of the above equation (3) are differentiated by the wavelength λ, the following equation (4) is obtained.

Df / dλ = −f (dn / dλ) / (n−1) ∴Δf = −f ｛Δn / (n−1)｝ (4) Excluding the coefficient doubling effect, Δn / ( Since n-1) represents the dispersion characteristic, the dispersion value ν can be defined as follows.

Ν≡ (n−1) / Δn (5) Accordingly, the dispersion characteristic (Abbe number ν _d ) in the visible region is as follows.

Ν _d = (n _d −1) / (n _F −n _C ) (6) On the other hand, in the case of a diffractive optical element, the following equation holds. The focal length f of the diffractive optical element is the ray height h of the incident parallel light.
Assuming that the lattice spacing at the point is d _h , the following equation (7) is obtained.

[0017] f = h / (n'sin θ ' ) = (d h h) / (mλ) (7) If the diffractive optical element aplanatic, since d _h h is constant, f = C / λ (C is a constant). When both sides of f = C / λ are differentiated by λ, Expression (8) is obtained as follows.

Df / dλ = −C / λ ² = −f / λ Δf = −f (Δλ / λ) (8) Since Δn / (n−1) = ν, equations (4) and (8) From this, ν = λ / Δλ. Therefore, the Abbe number ν _d of the diffractive optical element in the visible region is as follows.

Ν _d = λ _d / (λ _F −λ _C ) = − 3.453 (9) As described above, the diffractive optical element has a very large negative dispersion characteristic. Since the dispersion characteristic of ordinary glass is about 20 to 95, it can be seen that the diffractive optical element has a very large inverse dispersion characteristic. Further, it can be seen from the same calculation that the diffractive optical element has anomalous dispersion .

Of the above conventional examples, Japanese Patent Application Laid-Open No. 63-7700
3, JP-A-63-155432, JP-A-59-33
No. 636 and JP-A-60-247611 each relate to a pickup lens of an optical disc, and include one or two diffractive optical elements or one refractive optical element (lens) and a diffractive optical element. Consisting of one optical element,
Basically, the light source is monochromatic, and the ability to correct chromatic aberration of the diffractive optical element is not used.

Further, Japanese Patent Application Laid-Open Nos.
The lens system disclosed in Japanese Patent No. 361201 relates to a photographing lens used for a stepper or the like, and is made of only quartz, and does not use a cemented lens. In particular, the former lens system disclosed in Japanese Patent Application Laid-Open No. 2-1109 is characterized in that a diffractive optical system is arranged at the pupil position, and the latter lens system disclosed in Japanese Patent Application Laid-Open No. In the peripheral portion, a higher order diffracted light is used than in the central portion.

However, these conventional examples are pickup lens types and cannot be used for microscope objective lenses that require a more complicated structure. The stepper lens type may be applicable to a low magnification microscope objective, but cannot be applied to a high magnification, high NA microscope objective. That is, when the chromatic aberration of the objective lens is corrected only by the diffractive optical element, the power of the diffractive optical element must be increased, and the minimum pitch of the diffractive optical element becomes small so that it cannot be manufactured.

[0023]

SUMMARY OF THE INVENTION An object of the present invention is to provide an objective lens which has a high magnification and a high NA and which corrects various aberrations, particularly chromatic aberration, without using many cemented lenses and anomalous dispersion glass. .

[0024]

SUMMARY OF THE INVENTION A microscope objective lens according to the present invention.
A lens (hereinafter referred to as an objective lens) is characterized by including at least one diffractive optical element and at least one cemented lens. The chromatic aberration is satisfactorily corrected.

A general objective lens corrects chromatic aberration by using a cemented lens in which lenses made of glass materials having different Abbe numbers are cemented. And Abbe number of normal glass material is 20 ~
95 are all positive values. On the other hand, the Abbe number of the diffractive optical element has a negative and small absolute value as described above. Therefore, if this diffractive optical element is combined with a normal glass lens, a strong chromatic aberration correcting action can be provided.

In a high-grade objective lens, it is necessary to use apochromat for color correction, so that anomalous dispersion glass must be used extensively. However, these glasses are expensive and often have poor workability, which makes these objective lenses more expensive. This problem can also be solved by using a diffractive optical element and utilizing its large anomalous dispersion.

If the color correction of the objective lens with high NA and high magnification is performed only by the diffractive optical element, the power becomes too strong and the minimum pitch becomes too small. The color correction can be shared with the mold optical element, and the minimum pitch can be relaxed.

For better correction of chromatic aberration, it is desirable to satisfy at least one of the following conditions (1) and (2). When only the condition (1) is satisfied,
The diffractive optical element is located near the pupil of the objective lens.
There should be.

(1) D ₁ /D>0.8 (2) (h × f) / (L × I)> 0.07 where D ₁ is the marginal luminous flux diameter at the position of the diffractive optical element, and D Is the maximum marginal luminous flux diameter, h is the principal ray height on the surface of the diffractive optical element, f is the focal length, I is the maximum image height on the sample surface, and L is the parfocal distance.

Chromatic aberration is roughly classified into two types, axial chromatic aberration and chromatic aberration of magnification. The former is a shift of the focal position by wavelength, and the latter is a shift of the focal length (magnification) by wavelength.

Of these chromatic aberrations, the most effective position for correcting the axial chromatic aberration is the pupil position in the objective lens, but it is not necessary to accurately set the pupil position.
A large light beam diameter (axial marginal light beam diameter) near the pupil is effective in correcting axial chromatic aberration. The condition (1) is determined in consideration of this. In this condition (1), if the lower limit is 0.8 or less, the axial chromatic aberration generated in another refractive optical element (lens) cannot be corrected by the diffractive optical element. Must be used, and extraordinary dispersion glass is required, and the effect of using the diffractive optical element is not sufficient.

On the other hand, the most effective position for correcting the chromatic aberration of magnification is not the pupil position but the position where the principal ray slightly away from the pupil position has a certain ray height. Condition (2) determines the arrangement position of the diffractive optical element for effectively correcting the chromatic aberration of this magnification. If the lower limit of 0.07 in this condition (2) is exceeded, chromatic aberration of magnification cannot be sufficiently corrected, and a large number of cemented lenses will be used for the refractive optical element,
It is necessary to use anomalous dispersion glass, and the effect of using the diffractive optical element cannot be sufficiently obtained. Condition (2)
Where f, L, and I are for normalizing this condition, f / I is a parameter for the principal ray angle, and L is a parameter for scaling the size of the entire optical system.

As described above, in the objective lens according to the present invention, a diffractive optical element suitable for the intended use satisfies at least one of the above conditions (1) and (2). It is more preferable to dispose them in particular in order to better correct chromatic aberration.

In order to use at least one cemented lens and at least one diffractive optical element in the lens system to share the correction of chromatic aberration, the Abbe number difference Δν between both lenses of at least one cemented lens must satisfy the following condition. It is preferable to satisfy (3).

(3) Δν> 20 If Δν is smaller than the lower limit of 20 of the condition (3), the effect of correcting chromatic aberration by the cemented lens becomes insufficient, and the minimum pitch of the diffractive optical element cannot be made too large.

Further, the diffractive optical element has a manufacturing feature that the grating interval can be arbitrarily set. Therefore, the diffractive optical element can obtain an effect equivalent to an arbitrary aspherical lens by changing the lattice spacing variously, and is designed more than a normal aspherical lens such that there may be many inflection points. The degree of freedom is high and the production accuracy is good. Moreover, it is possible to correct chromatic aberration that cannot be corrected by an aspheric lens. Also, the gradient index lens can correct chromatic aberration, but the refractive index gradient lens that can be actually produced is limited, and it cannot sufficiently cope with ultraviolet rays or infrared rays. As described above, the diffractive optical element has more excellent aberration correcting ability than the aspherical lens and the gradient index lens, and is advantageous in manufacturing. Therefore, by using this as an objective lens as in the present invention, it is possible to improve the performance of the objective lens and reduce the cost, and it is also possible to design a new objective lens which has been impossible in the past.

[0037]

Next, an embodiment of the present invention will be described. First, the diffractive optical element used in the embodiment of the present invention will be described in more detail. The diffractive optical element (DOE) used in the embodiments described later is as described above, but as a design method of an optical system including such a diffractive optical element,
Ultra-high index method
What is called index methods) is known. This is because a diffractive optical element is a virtual lens with an extremely large refractive index (Ultler high index).
Lens). This is described in SPIE 126, 46-53 (1977).
Year), but will be described briefly with reference to FIG. In FIG. 20, 1 is an ultra-high index lens, and 2 is a normal line. In this ultra-high index lens, the relationship represented by the following equation (11) is established.

(N _U −1) dz / dh = nsin θ−n′sin θ ′ (11) where n _U is the refractive index of the ultra-high index lens, and z is the optical axis direction of the ultra-high index lens. Coordinates, h is the distance from the optical axis, n and n 'are the refractive indices of the incident side medium and the exit side medium, and θ and θ', respectively.
Is the incident angle and the exit angle of the light beam. In the data of the embodiment described later, n _U = 1001 or 10001.

From equations (2) and (11), the following equation (1)
2) is obtained.

(N _U −1) dz / dh = mλ / d (12) That is, between the surface shape of the ultra-high index lens (a refractive lens having an extremely large refractive index) and the pitch of the diffractive optical element. Satisfies the equivalent relation given by equation (12), and through this equation, the pitch of the diffractive optical element can be determined from the data designed by the ultra-high index method.

A general axisymmetric aspherical surface is represented as follows.

Z = ch ² / [｛1-c ² (k + 1) h ² } ^1/2 ] + Ah ⁴ + Bh ⁶ + Ch ⁸ + Dh ¹⁰ + (13) where z is the optical axis (the direction of the image) ), H is the coordinate axis in the meridional direction among coordinate axes orthogonal to the z-axis with the intersection point of the plane and the z-axis as the origin, c is the curvature of the reference surface, and k is the conic constant, and A, B, C, D.・ Is 4th, 6th, 8th, and 10 respectively
The following are the aspheric coefficients.

From formulas (12) and (13), the pitch d of the diffractive optical element equivalent to the aspheric surface at a certain ray height is:
It is expressed by the following equation (14). d = mλ / [(n−1) ｛ch / (1-c ² (1 + k) h ² ) ^1/2 + 4Ah ³ + 6Bh ⁵ + 8Ch ⁷ + 10Dh ⁹ +...}] (14) In the example, the order of the aspherical terms is up to tenth, but the aspherical terms of the 12th, 14th,... May be used.

Next, data of each embodiment will be shown. Example 1 Focal length = 3.6 mm, NA = 1.1 (water immersion), magnification = 100, parfocal distance = 45 mm, maximum image height on the sample surface = 0.05 mm r ₀ = ∞ (object surface) d ₀ = 0.17 n ₀ = 1.521 ν ₀ = 56.02 r ₁ = ∞ d ₁ = 0.12 n ₁ , ν ₁ (water) r ₂ = ∞ d ₂ = 2.5814 n ₂ = 1.596 ν ₂ = 39.3 r ₃ = -2.0016 d ₃ = 0.15 r ₄ = -6.6313 _{d 4 = 2.2727 n 3 = 1.678} ν 3 = 55.34 r 5 = -4.4815 d 5 = 0.15 r 6 = 7.2872 d 6 = 3.7582 n 4 = 1.488 ν 4 = 70.21 r 7 = -5.6995 d 7 = 1.0 n 5 = 1.678 ν ₅ = 55.34 r ₈ = 8.2626 d ₈ = 3.3432 n ₆ = 1.497 ν ₆ = 81.14 r ₉ = -9.3735 d ₉ = 0.15 r ₁₀ = ∞ d ₁₀ = 1.5 n ₇ = 1.516 ν ₇ = 64.14 r ₁₁ = ∞ d ₁₁ = 0 r ₁₂ = -5.5443 × 10 ⁶ (DOE) d ₁₂ = 0.15 [n _U = 10001] r ₁₃ = 8.6431 d ₁₃ = 1.0 n ₈ = 1.678 ν ₈ = 55.34 r ₁₄ = 4.7497 d ₁₄ = 4.2904 n ₉ = 1.497 ν ₉ = 81.14 r ₁₅ = -5.7355 d ₁₅ = 1.0 n ₁₀ = 1.596 ν ₁₀ = 39.29 r ₁₆ = -55.2542 d _{16 = 0.15 r 17 = 12.1862 d 17} = 2.2382 n 11 = 1.497 ν 11 = 81.14 r 18 = -14.3804 d 18 = 7.0 n 12 = 1.596 ν 12 = 39.29 r 19 = 7.3769 d 19 = 8.5761 r 20 = -2.9707 d 20 = 2.0598 n ₁₃ = 1.678 v ₁₃ = 55.34 r ₂₁ = 11.1831 d ₂₁ = 7.0 n ₁₃ = 1.596 v ₁₄ = 39.3 r ₂₂ = -7.1268 (DOE surface) K = -1, A = 0.282845 × 10 ^-8 , B = -0.695088 x 10 ^-10 C = 0.643649 x 10 ^-11 , D = -0.321846 x 10 ^-12 D ₁ / D = 0.99, (h x f) / (L x I) = 0.064, minimum pitch = 130 m

[0045] Example 2 the focal length = 9 mm, NA = 0.6 (water immersion), magnification = 20, parfocal distance = 45 mm specimen surface maximum image height _{= 0.25mm r 0 = ∞ d 0} = 0.17 n 0 = 1.521 ν 0 = 56.02 r ₁ = ∞ d ₁ = 0.12 n ₁ , ν ₁ (water) r ₂ = ∞ d ₂ = 1.0 n ₂ = 1.516 ν ₂ = 64.15 r ₃ = ∞ d ₃ = 1.3056 r ₄ = -3.8226 d ₄ = _{1.5 n 3 = 1.744 ν 3 =} 44.79 r 5 = -96.9912 d 5 = 2.2154 n 4 = 1.755 ν 4 = 27.51 r 6 = -5.4626 d 6 = 0.15 r 7 = -19.8772 d 7 = 2.2181 n 5 = 1.487 ν 5 = 70.21 r ₈ = -6.7810 d ₈ = 0.15 r ₉ = -8.6681 d ₉ = 1.5 n ₆ = 1.639 ν ₆ = 34.48 r ₁₀ = 61.1760 d ₁₀ = 3.7076 n ₇ = 1.487 ν ₇ = 70.21 r ₁₁ = -7.8096 d _{11 = 0.15 r 12 = 58.3918 d} 12 = 3.5924 n 8 = 1.487 ν 8 = 70.21 r 13 = -9.6113 d 13 = 1.5 n 9 = 1.749 ν 9 = 34.96 r 14 = -41.0966 d 14 = 0.15 r 15 = 19.2027 d _{15 = 1.5 n 10 = 1.603 ν} 10 = 42.32 r 16 = 11.9017 d 16 = 3.6322 n 11 = 1.487 ν ₁₁ = 70.21 r ₁₇ = -76.0706 d ₁₇ = 0.15 r ₁₈ = -800896.0617 (DOE) d ₁₈ = 0 [n _U = 1001] r ₁₉ = ∞ d ₁₉ = 2.0 n ₁₂ = 1.516 ν ₁₂ = 64.15 r _{20 = ∞ d 20 = 14.1927 r} 21 = 23.9945 d 21 = 2.9486 n 13 = 1.762 ν 13 = 40.1 r 22 = -31.1050 d 22 = 1.5 n 13 = 1.487 ν 14 = 70.21 r 23 = 10.0681 (DOE surface) K = -1, A = 0.263441 × 10 ^-8 , B = -0.964788 × 10 ^-11 C = -0.315285 × 10 ^-13 , D = -0.299622 × 10 ^-15 D ₁ /D=0.99, (h × f) / ( L × I) = 0.205, minimum pitch = 87 μm

Embodiment 3 Focal length = 3.6 mm, NA = 0.75, magnification = 50, parfocal distance =
45 mm sample surface maximum image height = 0.265 mm r ₀ = ∞ d ₀ = 0.9498 r ₁ = -2.2690 d ₁ = 4.0409 n ₁ = 1.678 ν ₁ = 55.34 r ₂ = -3.4762 d ₂ = 0.1 r ₃ = 16.9526 d ₃ = _{3.3974 n 2 = 1.487 ν 2 =} 70.21 r 4 = -9.1604 d 4 = 0.1 r 5 = -28.7293 d 5 = 1.8 n 3 = 1.596 ν 3 = 39.29 r 6 = 6.5830 d 6 = 4.4396 n 4 = 1.487 ν 4 = 70.21 r ₇ = -15.6408 d ₇ = 0.1 r ₈ = ∞ d ₈ = 1.0 n ₅ = 1.516 ν ₅ = 64.15 r ₉ = ∞ d ₉ = 0 r ₁₀ = -5.7585 × 10 ⁶ (DOE) d ₁₀ = 0.1 [ _{n U = 10001] r 11 =} 20.2252 d 11 = 3.6611 n 6 = 1.487 ν 6 = 70.21 r 12 = -10.5398 d 12 = 1.8 n 7 = 1.596 ν 7 = 39.29 r 13 = 10.7283 d 13 = 3.4719 n 8 = 1.487 v ₈ = 70.21 r ₁₄ = -28.0713 d ₁₄ = 9.5097 r ₁₅ = 24.5125 d ₁₅ = 3.5584 n ₉ = 1.596 v ₉ = 39.21 r ₁₆ = -8.897 d ₁₆ = 1.8 n ₁₀ = 1.498 v ₁₀ = 65.03 r ₁₇ =- _{18.2382 d 17 = 4.0127 r 18 =} -7.0308 d 18 = 1.8 n 11 = 1.498 ν 11 = 65.03 r ₁₉ = 15.1697 (DOE surface) K = -1, A = 0.885874 x 10 ^-9 , B = -0.373681 x 10 ^-10 C = 0.171463 x 10 ^-11 , D = -0.455259 x 10 ^-13 D ₁ / D = 0.98 , (H × f) / (L × I) = 0.071, minimum pitch = 80 μm

Embodiment 4 Focal length = 3.6 mm, NA = 0.75, magnification = 50, parfocal distance =
45 mm sample surface maximum image height = 0.265 mm r ₀ = ∞ d ₀ = 0.9145 r ₁ = -2.6605 d ₁ = 4.1491 n ₁ = 1.678 ν ₁ = 55.34 r ₂ = -3.3609 d ₂ = 0.1 r ₃ = 59.4216 d ₃ = _{3.9495 n 2 = 1.617 ν 2 =} 62.8 r 4 = -4.8439 d 4 = 1.8 n 3 = 1.596 ν 3 = 39.29 r 5 = 8.9186 d 5 = 4.4558 n 4 = 1.439 ν 4 = 94.96 r 6 = -11.2459 d 6 = 0.1 r ₇ = ∞ d ₇ = 1.0 n ₅ = 1.516 ν ₅ = 64.15 r ₈ = ∞ d ₈ = 0 r ₉ = -7.2979 × 10 ⁶ (DOE) d ₉ = 0.1 [n _U = 10001] r ₁₀ = 19.9999 _{d 10 = 3.4234 n 6 = 1.439} ν 6 = 94.96 r 11 = -21.6675 d 11 = 14.4364 r 12 = 103.5371 d 12 = 6.0 n 7 = 1.596 ν 7 = 39.29 r 13 = -11.7643 d 13 = 3.0881 r 14 = - 6.5185 d ₁₄ = 2.7072 n ₈ = 1.498 ν ₈ = 65.03 r ₁₅ = 17.4388 (DOE surface) K = -1, A = 0.136333 × 10 ^-8 , B = -0.205407 × 10 ^-10 C = 0.275330 × 10 ^-12 , _{^{D = -0.502831 × 10 -14 D 1}} /D=0.96,(h×f)/(L×I)=0.076, minimum peak Ji = 157 μm

Embodiment 5 Focal length = 36 mm, NA = 0.20, magnification = 10, parfocal distance = 10
0 mm Sample surface maximum image height = 0.8 mm r ₀ = 0d ₀ = 10.8729 r ₁ = -10.1528 d ₁ = 7.0 SiO ₂ r ₂ = -12.8207 d ₂ = 0.2 r ₃ = 1185.9548 d ₃ = 7.0 SiO ₂ r ₄ = _{-20.8861 d 4 = 9.6560 r 5 =} 166976.3323 (DOE) d 5 = 0 [n U = 1001] r 6 = ∞ d 6 = 3.0 SiO 2 r 7 = ∞ d 7 = 36.8382 r 8 = 18.3786 d 8 = 5.2879 CaF _{2 r 9 = -14.5637 d 9 =} 5.2019 SiO 2 r 10 = 15.9489 d 10 = 3.5421 r 11 = -9.8983 d 11 = 6.6329 SiO 2 r 12 = -12.7649 d 12 = 0.2 r 13 = -107.5879 d 13 = 3.4872 SiO ₂ r ₁₄ = -38.6725 D ₁ /D=0.69, (h × f) / (L × I) = 0.344, minimum pitch = 8.9 μm, where r ₀ , r ₁ , r _2. Radius, d ₀ ,
d _1, d ₂ ··· spacing between surfaces, n _1, n _2, ··· is the refractive index of each lens, ν _1, ν _2, ··· is the Abbe number of each lens.

In the above data, r ₀ is the object plane. The Examples 1 and 2 n ₀ with water immersion objective lens, [nu ₀ is a cover glass, n _1, [nu ₁ is water, is d ₀ of Examples 3-5 are working distance. DO in the data
E is a diffractive optical element having a diffraction surface of a bitch d obtained by the equation (14).

FIG. 1 shows the first embodiment, and FIG.
The third embodiment has a configuration as shown in FIG. 7 and the fourth embodiment has a configuration as shown in FIG. The diffractive optical elements used in these embodiments have an aspherical effect, which allows for spherical aberration,
Coma is well corrected. Embodiment 5 is shown in FIG.
In the configuration shown in (1), since the NA is low and the magnification is low, the diffractive optical element does not need to have an aspherical surface effect, and the diffractive optical element corrects only chromatic aberration.

The first embodiment is an objective lens in which color correction is performed from near ultraviolet to visible light, and a diffractive optical element is arranged at a place having a large light beam diameter mainly for correcting axial chromatic aberration. The second embodiment is an objective lens in which color correction is performed from near-ultraviolet to visible light. In order to correct axial chromatic aberration and chromatic aberration of magnification with a single diffractive optical element, a position where the beam diameter is large and the principal ray height is high. Is provided with a diffraction optical element. The third embodiment is an objective lens that performs color correction in the visible region, and the fourth embodiment also corrects axial chromatic aberration and lateral chromatic aberration with one diffractive optical element. In the fifth embodiment, off-axis chromatic aberration is mainly corrected by a diffractive optical element, and axial chromatic aberration is mainly corrected by a lens in which quartz and fluorite are joined.

In the sectional views of the embodiments, the right side is the object side. In FIGS. 1, 4, 7, and 10, the symbol B indicates the body-attached position, and each is the final lens surface (the leftmost surface in the drawings).
3.6, 0.3526, 0.6477,
1.2300. The barrel attachment position in the fifth embodiment is 1.0808 on the image side from the last lens surface. Further, the aberration curve diagrams of the respective embodiments are drawn by reverse tracking.

[0053]

The objective lens of the present invention is a lens system which has a high NA, a high magnification, and excellently corrects various aberrations, particularly chromatic aberration, by using a diffractive optical element.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a diagram showing a spherical aberration, astigmatism, and distortion curve of Example 1 of the present invention.

FIG. 3 is a diagram showing a coma aberration curve according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a second embodiment of the present invention.

FIG. 5 is a diagram showing spherical aberration, astigmatism, and distortion curves of Example 2 of the present invention.

FIG. 6 is a diagram illustrating a coma aberration curve according to the second embodiment of the present invention.

FIG. 7 is a sectional view of a third embodiment of the present invention.

FIG. 8 is a spherical aberration, astigmatism, and distortion curve diagram of Example 3 of the present invention.

FIG. 9 is a diagram showing a coma aberration curve according to Example 3 of the present invention.

FIG. 10 is a sectional view of a fourth embodiment of the present invention.

FIG. 11 is a spherical aberration, astigmatism, and distortion curve diagram of Example 4 of the present invention.

FIG. 12 is a diagram showing a coma aberration curve according to Example 4 of the present invention.

FIG. 13 is a sectional view of a fifth embodiment of the present invention.

FIG. 14 is a diagram showing spherical aberration, astigmatism, and distortion curves of Example 5 of the present invention.

FIG. 15 is a coma aberration curve diagram according to the fifth embodiment of the present invention.

FIG. 16 is a diagram showing a state of refraction in normal glass.

FIG. 17 is a diagram showing a state of refraction of light due to a diffraction phenomenon.

FIG. 18 is a cross-sectional view of the diffractive optical element in a blazed state.

FIG. 19 is a sectional view of a diffraction-type optical element obtained by performing binary approximation.

FIG. 20 is a diagram showing a state of refraction of light in an ultra-high index lens.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 21/02 G02B 13/00 G02B 9/00

Claims (4)

(57) [Claims] An optical element having at least one diffractive optical element and at least one cemented lens ;
At least one sheet is arranged near the pupil position and the following condition (1)
Satisfy the microscope objective lens. ₍₁₎ D 1 /D>0.8 However, D ₁ is at a position of the diffractive optical element Majina
The diameter D of the light beam is the maximum marginal light beam diameter. 2. The method according to claim 1, wherein at least one diffractive optical element is provided.
At least one cemented lens, the diffraction optical element
At least one microscope objective satisfying the following condition (2)
lens. (2) (h × f) / (L × it)> 0.07 However, h is the principal ray height at the position of the diffractive optical element,
f is the focal length of the microscope objective lens, L is the microscope
The parfocal distance of the objective lens , I, is the maximum image height on the specimen surface. 3. The diffractive optical satisfies the condition (2).
3. The microscope pair according to claim 2, wherein the element further satisfies the condition (1).
Object lens. 4. The objective lens according to claim 1, wherein an Abbe number difference Δν between the two lenses of the at least one cemented lens satisfies the following condition (3). (3) Δν> 20