JPH0882746A - Objective lens system - Google Patents

Abstract

PURPOSE: To enable inexpensive working and correcting of chromatic aberrations without using embedded lenses and to improve flatness by providing the above objective lens system with first to forth lens groups and constituting the lens system so as to satisfy specific conditions. CONSTITUTION: This objective lens system consists, successively from an object side, a parallel flat plate L11, the first lens group G1 consisting of a lens L12 and positive meniscus lens of which the concave faces are directed to the object side, the second and third lens groups G2, G3 respectively having positive and negative refracting powers as a whole and the fourth lens group G4 having a combined lens of a positive lens and negative lens L42 and having the negative refracting power as a whole. The objective lens system is so constituted as to satisfy the conditions [(Nla'F)/rl(7)0.06, |(N1a.F)/r2 |<=10.06, 0.3<|r3 /(NIL-.F)1<0.4, 6<|f12/F1+|f42/F|<9 where the composite focal length of the entire lens system is defined as F, the radii of curvature of the object side face and image side face of the parallel flat plate Lll and the object side concave face of the lens L12 are respectively defined as r1, r2, r3, the refractive index of the parallel flat plate L11 is defined as Nla, the refractive index of the lens L12 as Nib and the focal lengths of the lenses 112, L42 are respectively defined as f12, f42.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens system, and more particularly to an immersion system plan apochromat class low magnification microscope objective lens.

[0002]

2. Description of the Related Art As a conventional liquid immersion type apochromat class objective lens, for example, an objective lens disclosed in Japanese Patent Laid-Open No. 59-155822 is known. In the objective lens disclosed in this publication, a cemented lens including an embedded lens is used for the front lens (the lens closest to the object). Then, by appropriately setting the radius of curvature of the cemented surface and the refractive index difference between the two lenses, the Petzval sum is reduced to correct the field curvature.

[0003]

As described above, the conventional method using the cemented lens consisting of the embedded lens in the front lens is as follows.
It is useful in design and is often used recently. However, in reality, there are difficulties in lens processing. First,
The concave surface on the embedded side becomes a curved surface with a strong curvature,
Glass having a refractive index of about 1.8 is selected for the lens on the embedded side. However, many glass types having a refractive index of about 1.8 are hard. As a result, there is a disadvantage that concave surface processing is very difficult, time consuming and costly tends to be high.

Further, the convex surface on the image side of the embedded lens has a strong curvature and is often used up to a hemispherical shape. Therefore, there is a problem that it is difficult to polish the effective range with high accuracy. The present invention has been made in view of the above-mentioned problems, and can be processed at a sufficiently low cost by using a conventional processing technique without using an embedded lens, the chromatic aberration is well corrected, and the flatness of the immersion type apochromat is good. It is an object to provide a microscope objective lens system.

[0005]

In order to solve the above-mentioned problems, in the present invention, a plane-parallel plate L11 consisting of two surfaces substantially parallel to each other in order from the object side, and a lens L12 having a concave surface facing the object side. A first lens group G1 having a positive meniscus lens, a second lens group G2 having two cemented lenses and having a positive refracting power as a whole, and a cemented lens having a negative lens and a positive lens as a whole are negative. A fourth lens unit G3 having a negative refracting power and a third lens unit G3 having a refracting power and a cemented lens made up of a positive lens and a negative lens L42.
With the lens group G4, the combined focal length of the entire lens system is F
The radius of curvature of the object side surface of the plane parallel plate L11 is r1, the radius of curvature of the image side surface of the plane parallel plate L11 is r2, and the radius of curvature of the object side concave surface of the lens L12 is r3. , The refractive index of the plane-parallel plate L11 is N1a
The refractive index of the lens L12 is N1b, the focal length of the lens L12 is f12, and the lens L42 is
When the focal length of is f42: | (N1a · F) /r1|≦0.06 | (N1a · F) /r2|≦0.06 0.3 <| r3 / (N1b · F) | <0 Provided is an objective lens system characterized by satisfying the condition of 6 <6f | / f12 / F | + | f42 / F | <9.

[0006]

As described above, the objective lens system of the present invention comprises, in order from the object side, a plane-parallel plate L11 consisting of two surfaces substantially parallel to each other, a lens L12 having a concave surface facing the object side, and a positive meniscus lens. And a second lens group G1 having a positive refractive power as a whole
A third lens group G3 having a lens group G2 and a cemented lens of a negative lens and a positive lens and having a negative refracting power as a whole.
And a fourth lens group G4 having a cemented lens of a positive lens and a negative lens L42 and having a negative refracting power as a whole.

In an immersion objective lens system for microscopes, the lens surface closest to the object side must be flat or slightly convex toward the object side so that air bubbles do not easily enter between the lens surface and the liquid. Therefore, in the objective lens system of the present invention, as described above, the plane-parallel plate having two planes substantially parallel to each other is arranged on the most object side. In addition, in the present specification, the parallel plane plate is a concept including a lens having an extremely gentle curvature.

Each conditional expression of the present invention will be described below. The objective lens system of the present invention satisfies the following conditional expressions (1) to (4). | (N1a · F) /r1|≦0.06 (1) | (N1a · F) /r2|≦0.06 (2) 0.3 <| r3 / (N1b · F) | <0.4 ( 3) 6 <| f12 / F | + | f42 / F | <9 (4)

Where F: composite focal length of the entire lens system r1: radius of curvature of the object-side surface of the plane parallel plate L11 r2: radius of curvature of the image-side surface of the plane parallel plate L11 r3: object side of the lens L12 Radius of curvature of concave surface N1a: d-line of the plane parallel plate L11 (λ = 587.6n
m) refractive index N1b: refractive index of lens L12 with respect to d-line (λ = 587.6 nm) f12: focal length of lens L12 f42: focal length of negative lens L42

Conditional expressions (1) and (2) define an appropriate range of the lens shape when the parallel plane plate L11 of the first lens group G1 is regarded as a lens having an extremely gentle curvature. In conditional expressions (1) and (2), if the upper limit value is exceeded, the Petzval sum increases and flatness deteriorates, which is inconvenient.

Conditional expression (3) defines an appropriate range for the concave surface shape of the lens L12 having the concave surface facing the object side of the first lens group G1. If the upper limit of conditional expression (3) is exceeded, the Petzval sum will become too large and the field curvature will deteriorate. In addition, the total lens length (the distance from the surface closest to the object side to the image plane along the optical axis) is increased. On the other hand, when the value goes below the lower limit of the conditional expression (3), the light flux spreads too much, spherical aberration deteriorates, and axial chromatic aberration is overcorrected.

Conditional expression (4) defines an appropriate range for the refractive power of the lens L12 having the concave surface facing the object side of the first lens group G1 and the refractive power of the negative lens L42 of the fourth lens group G4. , The conditions for flatness are defined. If the upper limit of conditional expression (4) is exceeded, the field curvature will be overcorrected, which is not preferable. On the other hand, when the value goes below the lower limit of conditional expression (4), the magnification becomes large, and as a result, the total lens length becomes large, which is inconvenient.

[0013]

EXAMPLE An objective lens system of the present invention is a plane-parallel plate L1 having two planes substantially parallel to each other in each example.
1, a first lens group G1 having a lens L12 having a concave surface facing the object side and a positive meniscus lens, a second lens group G2 having two cemented lenses and having a positive refracting power as a whole, and a negative lens A third lens group G3 having a cemented lens of a positive lens and a positive lens and having a negative refracting power as a whole, and a fourth lens group having a cemented lens of a positive lens and a negative lens L42 having a negative refracting power as a whole. And G4.

Each embodiment of the present invention will be described below with reference to the accompanying drawings. Example 1 FIG. 1 is a diagram showing a lens configuration of an objective lens system according to Example 1 of the present invention. The illustrated objective lens system is composed of a first parallel plane plate L11, a positive meniscus lens L12 having a concave surface facing the object side, and a positive meniscus lens L13 having a concave surface facing the object side, in order from the object side.
A lens group G1, a second lens group G2 including a cemented lens of a negative meniscus lens having a convex surface facing the object side and a biconvex lens, and a cemented lens of a biconvex lens, a biconcave lens, and a biconvex lens, and a biconcave lens and a biconvex lens. And a fourth lens group G4 including a cemented lens of a biconvex lens and a biconcave lens L42.

The following table (1) lists the values of specifications of the first embodiment of the present invention. In Table (1), f is the focal length,
N. A. Is the numerical aperture, B is the magnification, W. D. Represents the working distance, respectively. Furthermore, the leftmost number is the order of the lens surfaces from the object side, r is the radius of curvature of each lens surface, d is the distance between the lens surfaces, and n and ν are d lines (λ = 5).
The refractive index and the Abbe number for 87.6 nm) are shown.

[0016]

[Table 1] f = 1.0mm, NA = 0.75, B = -20.0, WD = 0.03 (Value corresponding to condition) (1) | (N1a · F) / r1 | = 0 (2) | (N1a · F) / r2 | = 0 (3) | r3 / (N1b · F) | = 0.323 ( 4) | f12 / F | + | f42 / F | = 8.5

FIG. 2 shows that the oil of Example 1 was used (refractive index n
= 1.51536). In each aberration diagram, FN is the F number, Y is the image height, H is the height of the incident height, D is the d line (λ = 587.6 nm), and G is the g line (λ = 435.8 nm). , C is the C line (λ = 65
6.3 nm) and F indicates the F line (λ = 486.1 nm).

In the aberration diagram showing astigmatism, the solid line shows the sagittal image plane and the broken line shows the meridional image plane. Further, in the aberration diagram showing the chromatic aberration of magnification, the d-line (λ = 5
87.6 nm) as a reference. As is clear from each aberration diagram, it is understood that various aberrations are satisfactorily corrected in this example.

Example 2 FIG. 3 is a diagram showing a lens configuration of an objective lens system according to Example 2 of the present invention. The objective lens system shown in the drawing has a plane-parallel plate L1 in order from the object side.
1, a positive meniscus lens L12 having a concave surface facing the object side,
And a positive meniscus lens L13 having a concave surface facing the object side
And a second lens group G2 including a cemented lens of a negative meniscus lens having a convex surface facing the object side and a biconvex lens, and a biconvex lens, a biconcave lens, and a biconvex lens. The third lens group G3 is composed of a cemented lens of a concave lens and a biconvex lens, and the fourth lens group G4 is composed of a cemented lens of a biconvex lens and a biconcave lens L42.

The following table (2) lists the values of specifications of the second embodiment of the present invention. In Table (2), f is the focal length,
N. A. Is the numerical aperture, B is the magnification, W. D. Represents the working distance, respectively. Further, the leftmost number is the order of the lens surfaces from the object side, r is the radius of curvature of each lens surface, d is the distance between the lens surfaces, and n and ν are d lines (λ = 5).
The refractive index and the Abbe number for 87.6 nm) are shown.

[0021]

[Table 2] f = 1.0mm, NA = 0.75, B = -20.0, WD = 0.03 (Condition corresponding value) (1) | (N1a · F) / r1 | = 0 (2) | (N1a · F) / r2 | = 0 (3) | r3 / (N1b · F) | = 0.340 ( 4) | f12 / F | + | f42 / F | = 7.1

FIG. 4 shows that the oil of Example 2 was used (refractive index n
= 1.51536). In each aberration diagram, FN is the F number, Y is the image height, H is the height of the incident height, D is the d line (λ = 587.6 nm), and G is the g line (λ = 435.8 nm). , C is the C line (λ = 65
6.3 nm) and F indicates the F line (λ = 486.1 nm).

In the aberration diagram showing astigmatism, the solid line shows the sagittal image plane, and the broken line shows the meridional image plane. Further, in the aberration diagram showing the chromatic aberration of magnification, the d-line (λ = 5
87.6 nm) as a reference. As is clear from each aberration diagram, it is understood that various aberrations are satisfactorily corrected in this example.

[0024]

As described above, according to the present invention, the flatness of the immersion microscope objective lens can be improved without using an embedded lens, and the conventional processing technique can be inexpensively manufactured. It is possible to expect a significant cost reduction and quality stability. Thus, according to the present invention, the magnification is about 20 and the numerical aperture (N
It is possible to realize an immersion type plan apochromat microscope objective lens in which A) is about 0.75, chromatic aberration is well corrected, flatness is good, and excellent imaging performance is maintained.

[Brief description of drawings]

FIG. 1 is a diagram showing a lens configuration of an objective lens system according to Example 1 of the present invention.

FIG. 2 is a diagram of various types of aberration when the oil according to the first embodiment is used.

FIG. 3 is a diagram showing a lens configuration of an objective lens system according to Example 2 of the present invention.

FIG. 4 is a diagram of various types of aberration when using oil in Example 2.

[Explanation of symbols]

 G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group

Claims (1)

[Claims] 1. A parallel plane plate L11 consisting of two surfaces which are substantially parallel to each other in order from the object side, a first lens group G1 having a lens L12 having a concave surface facing the object side and a positive meniscus lens, and two cemented lenses. A second lens group G2 having a lens and having a positive refracting power as a whole, a third lens group G3 having a cemented lens of a negative lens and a positive lens and having a negative refracting power as a whole, a positive lens and a negative lens A fourth lens group G4 having a cemented lens with the lens L42 and having a negative refracting power as a whole, and a composite focal length of the entire lens system is F, and the parallel plane plate L
The radius of curvature of the object-side surface of 11 is r1, the radius of curvature of the image-side surface of the plane-parallel plate L11 is r2, and the radius of curvature of the object-side concave surface of the lens L12 is r3. Let N1a be the refractive index of the lens L12
, N1b, the focal length of the lens L12 is f12, and the focal length of the lens L42 is f42: | (N1a · F) / r1 | ≦ 0.06 | (N1a · F) / r2 Objective lens system characterized by satisfying the condition of | ≦ 0.06 0.3 <| r3 / (N1b · F) | <0.4 6 <| f12 / F | + | f42 / F | <9 .