JPH11281891A - Infinity system objective lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately condense luminous flux at the surface or in the inside of an object without damaging an objective-lens by constituting the objective lens of a 1st lens group or a 3rd lens group, arranging a 2nd lens group so that it can be moved in an optical axis direction and satisfying a specified condition as the whole of them. SOLUTION: This objective lens is constituted of the 1st lens group G1 whose refractive power is positive and which is provided with three lenses, the 2nd lens group G2 obtained by sticking a positive lens and a negative lens and the 3rd lens group G3 whose refractive power is negative. Besides, the group G2 is arranged so that it can be moved in the optical axis direction. Then, the conditions by an expression I; 3.2<D/F, an expression II; 1.3<|r1 /F|<1.5, an expression III; 5.5<|r3 /F|<6.7 and an expression IV: 45<|r5 /F| are satisfied. In the expressions, F is the focal distance of the infinity system objective lens, D is the smallest gap between the groups G1 and G2, (r1 ) is the radius of the curvature of the object-side lens surface on the most object side, (r3 ) is the radius of the curvature of the 2nd object-side lens surface from the object side and (r5 ) is the radius of the curvature of the 3rd object-side lens surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infinity type objective lens, and more particularly to an infinity object for cutting an object or recording information on the object by converging a parallel light beam on or inside the object. The present invention relates to a system objective lens.

[0002]

2. Description of the Related Art In many cases, the surface of a sample to be observed by a microscope objective lens is covered with a cover glass. Although this cover glass is generally formed of a plane-parallel plate, its thickness is not always constant. Therefore, some lenses are arranged so as to be movable in the optical axis direction so that good imaging performance can be obtained even if the thickness of the cover glass changes.For this purpose, an objective lens with a correction ring is used. Have been. In recent years, as an objective lens of a microscope, a so-called infinity type objective lens in which emitted light becomes a parallel light beam has become mainstream. As described above, the microscope objective lens of recent years is formed so as to cope with a change in the thickness of the cover glass, and because it is an infinite distance system, it can be used for purposes other than the original observation purpose. There is. For example, a laser beam collimated with high accuracy is incident from the image side to the object side, and is imaged on the surface of the object or inside the object.

[0003]

Although the above-mentioned conventional objective lens is sometimes used for purposes other than the original observation purpose, the objective lens is not designed for such an application, but is merely an original objective lens. Designed for observation purposes. Therefore, if the objective lens is used for cutting an object or the like, the following problem may occur. That is, in order to cut an object or the like, high-intensity laser light is incident from the image side. In this case,
Reflected light reflected on the lens surface of each lens constituting the objective lens may be condensed on the inside of the lens or on the lens surface.In this case, the antireflection coat may be burned, or in the worst case, The lens may be broken.

[0004] Techniques for recording information three-dimensionally inside an ultraviolet curable resin or the like as an object have been developed. However, a three-dimensional laser has been used inside a transparent object using a high-intensity laser. In order to perform effective writing, it is necessary that the spherical aberration be properly corrected with respect to the change in the thickness of the object. Of course, even if a high-intensity laser is used, the objective lens must not be damaged. However, the conventional objective lens does not consider such usage at all. Accordingly, an object of the present invention is to provide an infinity type objective lens that can accurately condense a light flux on the surface or inside of an object without causing damage to the objective lens.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, that is, it has at least three single lenses or cemented lenses having a positive refractive power in order from the object side. A first lens group, a second lens group configured by bonding a positive lens and a negative lens,
A third lens group having a negative refractive power; the second lens group is arranged so as to be movable in the optical axis direction; and F: the focal length of an infinity objective lens D: the first lens group and the second lens group Minimum distance from lens group r ₁ : radius of curvature of object side lens surface of single lens or cemented lens arranged closest to object side r ₃ : object side lens of single lens or cemented lens arranged second from object side Radius of curvature of the surface r ₅ : radius of curvature of the object-side lens surface of the single lens or the cemented lens disposed third from the object side, 3.2 <D / FＦ (1) 1.3 <| r ₁ /F|<1.5‥‥(2) 5.5 <| r ₃ /F|<6.7‥‥(3) 45 <| r ₅ / F | ‥‥ (4) This is an infinite distance objective lens.

In this case, the first lens group has at least four single lenses or cemented lenses, and r ₈ is the curvature of the object-side lens surface of the fourth single lens or cemented lens from the object side. When the radius is set, it is preferable to satisfy the condition of 6.0 <| r ₈ /F|<8.0Ｆ(5).

In the present invention, it is assumed that light is incident from the image side as in the so-called epi-illumination method, and that a high-intensity laser beam is assumed as the light source. Then, the problem is the reflected light from the lens surface. Generally, the reflection from the surface not coated with the anti-reflection coating is about 4%.
% Of light is reflected. This reflected light becomes divergent light or convergent light depending on the radius of curvature of the reflecting surface. The problem lies in this convergent light. If the converged light is converged on the optical axis and the converging point is inside the glass, energy will be concentrated on that part. Since the light absorptance of glass is not zero, the portion where energy is concentrated is heated and expands, and in the worst case, the lens is broken due to the difference in the expansion coefficient from the surroundings.

Therefore, in order to protect the lens,
It needs to be focused off the optical axis or out of the lens. In the former case, the shape of the light condensing position is a ring shape, so that if its radius, that is, the height from the optical axis is sufficiently high, the energy density will be sufficiently low. That is, even if light is condensed in a ring shape in the lens, the possibility of damage to the lens is low. In the case of an objective lens with a correction ring, the reflection surface that may concentrate reflected light on the optical axis is the lens surface of the first lens group. Therefore, in the present invention, even if each reflected light from each lens surface of the first lens group is condensed on the optical axis, it condenses on the air gap between the first lens group and the second lens group. As described above, the above problem is solved by sufficiently increasing the air gap between the two lens groups.

That is, since the first lens group generally collects rays having a large numerical aperture and converts them into converged light, it is necessary to have a strong converging action, and therefore, a large negative spherical aberration occurs. Therefore, positive spherical aberration is generated in the second lens group, and negative spherical aberration generated in the first lens group is canceled. In an ordinary objective lens with a correction ring, it is desirable that the minimum distance D between the first lens group and the second lens group is short. The reason is that by bringing the second lens group closer to the first lens group, the incident height of light rays incident on the second lens group becomes higher, and more positive spherical aberration can be generated in the second lens group. Because you can. However, the minimum distance D
When the distance is shortened, it is difficult to position the condensing position of each reflected light from each lens surface of the first lens group within the short interval D.

Therefore, in the present invention, even if the reflected light is condensed on the optical axis, the minimum distance D is sufficiently set so as to be condensed in the air space between the first lens group and the second lens group. It is long. If the lower limit of the condition (1) is exceeded, the light condensing position of each reflected light from each lens surface of the first lens group may be located in the lens of the first lens group or the second lens group. Absent. When the configuration that satisfies the condition (1) is used, the incident height of the light beam incident on the second lens group is reduced, so that the positive spherical aberration generated in the second lens group is reduced. Therefore, the first lens group needs to be configured to bend light gradually so as not to generate a large negative spherical aberration. Also, the longer the minimum interval D, the better. When the interval D is long, the positive spherical aberration generated in the second lens group is reduced, and the tolerance for the change in the thickness of the cover glass or the like is reduced. Therefore, the value of D / F has a certain upper limit.

Here, it is preferable that the second lens group is a lens group having almost no refractive power. That is,
Even if the second lens group is moved in the optical axis direction for aberration correction, if the refractive power of the second lens group is weak, changes in the principal point and the focal position of the objective lens will be slight. Therefore, even if the correction ring is operated, the defocus becomes small, which is convenient.

Next, according to the condition (1), the air gap between the first lens group and the second lens group is sufficiently long, but each reflected light from each lens surface of the first lens group is In fact, it is necessary to collect at the air space between both lens groups. Conditions (2) to (5) are conditions for that. Condition (2)
If the absolute value of the radius of curvature of the lens surface becomes smaller than the lower limit of (5), each reflected light from each lens surface of the first lens group may be condensed inside the first lens group. Occurs. Conversely, if the absolute value of the radius of curvature of the corresponding lens surface is increased beyond the upper limit of the conditions (2) to (5), each reflected light may be condensed inside the second lens group. Neither is preferred.

Next, in the present invention, n _P : refractive index of the positive lens constituting the second lens group n _N : refractive index of the negative lens constituting the second lens group: 0.23 <| It is preferable to satisfy the following condition: n _P −n _N | <0.28 ‥‥ (6) Condition (6) is for making the amount of positive spherical aberration generated by the movable second lens group appropriate. If the difference in refractive index becomes smaller than the lower limit of the condition (6), the radius of curvature of the bonding surface needs to be reduced in order to generate the same spherical aberration. As a result, higher order spherical aberration occurs. As a result, it becomes difficult to correct the aberration over the entire correction range. Conversely, if the difference in refractive index is larger than the upper limit of the condition (6), the radius of curvature of the bonding surface needs to be increased, and the balance of aberration with the first lens group is deteriorated. Not preferred.

[0014]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment of an infinity objective according to the present invention, and FIG. 3 shows a second embodiment. Both embodiments are so-called objective lenses with a correction ring, and are of an infinity type that converts a light beam from an object into a parallel light beam. Each of the objective lenses of both examples has, in order from the cover glass CG side, four single lenses or cemented lenses L having a positive refractive power.
₁ and the first lens group G ₁ consisting of ~L _7, a positive lens L ₈ second lens group G ₂ constituted by bonding of the negative lens L _9, a third lens group having a negative refractive power G consists _{of three} Tokyo, the second lens group G ₂ is movably arranged in the optical axis direction.

Tables 1 and 2 show the first embodiment and the second embodiment, respectively.
The specifications of the embodiment are listed below. In [Main Specifications] of each table, NA indicates the image-side numerical aperture, and β indicates the imaging magnification. [Lens Specifications]
The first column No is the number of each lens surface from the cover glass CG side, the second column r is the radius of curvature of each lens surface, the third column d is the distance on the optical axis from each lens surface to the next lens surface, 4th column n
_s indicates the refractive index of each lens at a wavelength of 852.1 nm, column 5 indicates the Abbe number of each lens, and column 6 indicates the number of each lens. However, in the second embodiment, the Abbe number is omitted. The Abbe number is defined by the following equation. _{ν = (n A -1) /} (n r -n s) n A: refractive index n _r at a wavelength 768.2Nm: refractive index at a wavelength of 706.5nm n _s: the refractive index at a wavelength of 852.1nm Also, each table Working distance d ₁
Is about 1 mm. Further, the values of NA, β, and the like in the examples and the aberration diagrams described later are obtained when an image is formed using the second objective lens A (f = 200 mm) shown in Table 3 and FIG.

[0016]

[Table 1] [Main specifications] NA = 0.80 β = 100 F = 2mm [ Lens _{Data] No r d n s ν C} 1 ∞ (t) 1.5389 149.9 CG C 2 ∞ (d 1) 1 -2.901 2.6 1.8248 _{126.2 L 1 2 -3.382 0.1 3 -13.041} 2.5 1.5951 174.2 L 2 4 -6.634 0.1 5 100 1 1.6066 109.6 L 3 6 25.775 3.8 1.4927 22.9 L 4 7 -10.211 0.4 8 13.244 3 1.5951 174.2 L 5 9 -17.572 1 1.7346 87.9 _{L 6 10 7.978 3.4 1.4927 223.9 L} 7 11 -36.029 (d 2) 12 72.997 3.6 1.5603 153.7 L 8 13 -7.038 1 1.8248 126.2 L 9 14 -28.244 (d 3) 15 63.737 1.5 1.7815 81.7 L 10 16 -30.822 0.9 1.6829 152.3 L ₁₁ 17 7.956 [Variable interval] t 0.2 0.3 0.4 0.5 d ₁ 1.54 1.47 1.41 1.34 d ₂ 6.5 8.3 10.6 13.8 d ₃ 11 9.2 6.9 3.7 [Conditional value] (1) D / F = 3.25 (2) | R ₁ /F|=1.4055 (3) | r ₃ /F|=6.5202 (4) | r ₅ / F | = 50 (5) | r ₈ /F|=6.622 (6) | n _P -n _N | 0.2645

[0017]

[Table 2] [Main specifications] NA = 0.80 β = 100 F = 2mm [ Lens _{Data] No r d n s C 1} ∞ (t) 2.3 CG C 2 ∞ (d 1) 1 -2.901 2.6 1.8248 L 1 2 -3.315 0.1 3 -11.446 2.5 1.5951 L 2 4 -6.726 0.1 5 217.563 1 1.6066 L 3 6 16.537 3.8 1.4927 L 4 7 -9.699 0.4 8 15.429 3 1.5951 L 5 9 -16.761 1 1.7346 L 6 10 9.856 3.4 1.4927 L 7 _{11 -24.201 (d 2) 12 43.32} 3.6 1.5603 L 8 13 -6.97 1 1.8248 L 9 14 -35.039 (d 3) 15 24.351 1.5 1.7815 L 10 16 -24.634 0.9 1.6829 L 11 17 5.958 [ variable distance] t 0 0.1 0.2 _{0.3 0.4 0.5 d 1 1.57 1.52 1.48} 1.44 1.39 1.35 d 2 6.5 7.5 8.6 9.9 11.5 13.7 d 3 11 10 8.9 7.6 6 3.8 [ condition corresponding values] (1) D / F = 3.25 (2) | r 1 / F | = 1.4505 (3) | r ₃ /F|=5.723 (4) | r ₅ /F|=108.7815 (5) | r ₈ /F|=7.7145 (6) | n _P −n _N | = 0.2645

[0018]

[Table 3] Nor dn  ν 1 51.6 6.5 1.617 54 2 -87.1 2 1.749 35.2 3 348.5 8.2 4 49.1 5 1.67 41.9 5 ∞ 2.5 1.61 44.4 6 31.1

FIG. 2 shows the spherical aberration of the first embodiment. FIG.
(A), (B), and (C) are aberration diagrams when the thickness t of the cover glass CG is 0.2, 0.3, and 0.5 mm, respectively. Similarly, FIG. 8 shows the spherical aberration of the second embodiment. 8, (A), (B) and (C) show that the thickness t of the cover glass CG is 0, 0.3 and 0.
It is an aberration figure at the time of 5 mm. In addition, s
The line (852.1 nm) is used because the laser which can be used practically is in the infrared region, and therefore, it is necessary to correct the aberration in the wavelength region. Also,
In the present invention, since the imaging performance on the optical axis is regarded as important, only the spherical aberration is shown. 2 (A) to 2 (C) and FIG. 8 (A)
~ (C), the thickness t of the cover glass CG is 0
It can be seen that the spherical aberration is satisfactorily corrected even when it changes in the range of 0.5 mm.

Next, FIGS. 3 to 7 show the optical paths of light reflected by several lens surfaces when a light beam enters from the image side in the second embodiment. 3 shows the object-side lens surface r _{1 of} the single lens L ₁ disposed closest to the object.
In shows an optical path of the reflected light reflected, Figure 4 shows an optical path of light reflected by the object-side lens surface r ₃ of the single lens L ₂ that is disposed second outermost from the object side, 5 3 from the object side cemented lens L ₃ which is disposed in th, L shows an optical path of light reflected by the object-side lens surface r ₅ of the _4, 6 cemented lens L ₅ which is arranged in the fourth from the object side, L _6, L the _seven optical path of light reflected by the object-side lens surface r _8, and FIG. 7 is cemented with the lens L ₆ and L ₇ of the cemented lens L _5, L _6, L ₇ disposed fourth from the object side showing an optical path of light reflected by the surface r _10.

The reflected light from the lens surface r ₁ shown in FIG.
While it focused near the exit surface of the lens L _7, 1 on the optical axis
Instead of converging on a point, it converges on a ring.
The reflected light from the lens surface r ₃ shown in FIG. 4 is condensed into the air gap between the first lens group G ₁ and the second lens group G _2. The reflected light from the lens surface r ₅ shown in FIG. 5, lens L ₇
, But is not converged at one point on the optical axis but is converged in an annular shape. The reflected light from the lens surface r ₈ shown in FIG. 6 is condensed into the air gap between the first lens group G ₁ and the second lens group G _2. The reflected light from the lens surface r ₁₀ shown in FIG. 7 is converged near the exit surface of the lens L _7, rather than being focused on one point on the optical axis, condensing the zonal doing. Therefore, according to the present embodiment, even if a strong parallel light beam enters from the image side, there is no possibility that the objective lens will be damaged. The lens configuration of the first embodiment is almost the same as that of the second embodiment. Therefore, the optical path of the reflected light on each lens surface of the first embodiment is substantially the same as that of the second embodiment, and therefore is not shown. I do.

[0022]

As described above, according to the infinity-based objective lens of the present invention, when a high-intensity light beam such as a laser is incident from the image side, the light beam is accurately collected on the surface or inside of the transparent object. Can light. Moreover, at this time, there is no possibility that the objective lens is damaged by the reflected light on each lens surface.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an infinity-based objective lens according to the present invention.

FIGS. 2A and 2B are spherical aberration diagrams of the first embodiment, wherein FIG. 2A shows a cover glass having a thickness of 0.2 mm, FIG.
(C) shows a state of 0.5 mm.

[Figure 3] is a block diagram showing a second embodiment, light rays in the figure, showing an optical path of light reflected by the lens surface r _1.

[4] Also, showing an optical path of light reflected by the lens surface r _3.

[5] Also, showing an optical path of light reflected by the lens surface r _5.

[6] Also, showing an optical path of light reflected by the lens surface r _8.

[7] Also, showing an optical path of light reflected by the lens surface r _10.

8A and 8B are spherical aberration diagrams of the second embodiment, in which FIG. 8A shows a cover glass having a thickness of 0 mm, FIG.
Indicates a state of 0.5 mm.

FIG. 9 is a configuration diagram illustrating an example of a second objective lens.

[Explanation of symbols]

G ₁ ~G ₃ ... lens unit L ₁ ~L ₁₁ ... lens CG ... cover glass A ... second objective lens

Claims (3)

[Claims] 1. A second lens formed by laminating a first lens group having at least three single lenses or cemented lenses having a positive refractive power and a positive lens and a negative lens in order from the object side. An infinity type objective lens, comprising: a lens unit and a third lens unit having a negative refractive power, wherein the second lens unit is disposed so as to be movable in an optical axis direction and satisfies the following conditions. 3.2 <D / F 1.3 <| r 1 /F|<1.5 5.5 <| r 3 /F|<6.7 45 <| r 5 / F | However, F: infinity system Focal length of objective lens D: Minimum distance between first lens group and second lens group r ₁ : radius of curvature of object side lens surface of single lens or cemented lens arranged closest to object side r ₃ : from object side wherein are disposed in the second single lens or a cemented lens on the object side lens curvature radii r _5: wherein is located third from the object side is a radius of curvature of the object side lens surface of the single lens or a cemented lens. 2. The infinity objective according to claim 1, wherein the first lens group has at least four single lenses or a cemented lens, and satisfies the following condition. 6.0 <| r ₈ /F|<8.0 where r ₈ is the radius of curvature of the object-side lens surface of the single lens or the cemented lens arranged fourth from the object side. 3. The infinity objective according to claim 1, wherein the following condition is satisfied. _{0.23 <| n P -n N |} <0.28 where, n _P: refractive index of the positive lens constituting the second lens group n _N: a refractive index of the negative lens constituting the second lens group is there.