JPS58192013A - Microscope objective lens - Google Patents

Abstract

PURPOSE:To obtain a lens of high magnification, which is capable of satisfactorily correcting various aberrations by a small number of constituting pieces, by making a lens group consisting of seven groups satisfy prescribed conditions. CONSTITUTION:A titled lens consists of the first group lens of a plano-convex lens whose plane faces an object side, the second group lens of a positive meniscus lens whose concave face faces the object side, the third group lens of a positive lens, the fourth group lens cementing three positive, negative and positive lenses, the fifth group lens of a biconvex lens, the sixth group lens of a cemented meniscus lens whose convex face faces the object side, and the seventh group lens whose concave face faces the object side, and this lens group is made to satisfy various conditions of the expressions I -VI. In the expression, r15, r16, d15, n9, nu8, f5 and (f) denote a radius of curvature of the face of an image side of the sixth group lens, a radius of curvature of the face of the object side of the seventh group lens, an air space between the sixth and the seventh group lenses, a refractive index of the lens of the image of the sixth group lens, Abbe number of the object side lens of the sixth group, a focal distance of the negative lens of the fourth group, and a focal distance of the whole system.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a high magnification microscope objective lens that is not used.

It is particularly difficult to correct spherical aberration and chromatic aberration in a high-magnification microscope objective lens because of its high magnification and large aperture. Furthermore, in order to obtain a plan objective lens, it is necessary to reduce the Petz Pearl sum, but in the case of high magnification, it is difficult to reduce the Petz Pearl sum because the focal length is small.

Generally, in order to correct field curvature, the object-side surface of the first lens is made strongly concave, and in oil immersion objective lenses, the first lens group is cemented and the radius of curvature of the cemented surface is made very small. A lens system in which field curvature is corrected by imparting negative power to that surface is well known.

In addition, a Gaussian-type lens group is placed relatively rearward, and the concave surface of this lens group corrects the field curvature, and a thick meniscus lens is placed to correct the field curvature and off-axis. Objective lenses that correct various aberrations are also known.

The problem is that spherical aberration occurs due to the large number of
In order to minimize this occurrence, it is necessary to use many lenses in the front group.

Also, due to the high magnification, residual chromatic aberration (chromatic aberration at the image position)
tends to become large, which reduces resolution. In order to correct this, conventionally it was common to make extensive use of anomalous dispersion materials and other special materials. , it is necessary to increase the number of lenses,
Furthermore, since many special materials are used, the number of processing steps increases.

For example, the objective lens described in British Patent No. 702,737 is a lens system consisting of 11 elements in 7 groups, and four of the lenses are made of a special material of CaF2. Also, British Patent No. 702,690 The objective lens described in the book is a lens system consisting of 12 elements in 8 groups, and 4 of the lenses use special paulownia material made of CaF2.As in these examples, conventional high-magnification microscope objectives Lenses have a large number of lenses and use many special materials, and therefore have the drawbacks mentioned above.

This provides a high-magnification microscope objective lens.

The present invention increases the power of each lens in order to reduce the Petzval sum without increasing the number of lenses, and thereby satisfactorily corrects residual chromatic aberration. In this way, the increase in the amount of aberration generated by each lens caused by increasing the power of each lens is corrected by canceling each other out by adjusting the lens arrangement.

Furthermore, regarding the front group, where spherical aberration is large, the spherical aberration is minimized as much as possible by using a lens with a shape similar to that of an aplanate lens.

Next, the microscope objective lens of the present invention based on the above idea will be explained.

The objective lens of the present invention includes a first lens group of a plano-convex lens with a flat surface facing the object side, a second lens group of positive meniscus lenses with a concave surface facing the object side, a third lens group of positive lenses, and a positive lens group. The fourth group lens is a three-piece cemented lens consisting of a negative lens and a positive lens, the fifth group lens is a biconvex lens, and the object side Q
This lens system is composed of a sixth lens group of a cemented meniscus lens with a convex surface facing the object side, and a seventh group lens of a meniscus lens with a concave surface facing the object side. Furthermore, present invention 7.
J objects are designed to satisfy the following conditions.

(1)], 1f≦r+5≦1.35f(2)1.7
f≦lr 161≦2.7f(3) 1.9 f
<d+5 ≦4.0f(4) 1.5
5 ≦ n, ≦ 165 (5) 2.4f≦ 1f, 1
≦2.8f(6) 65 ≦ ν8 where r15 is the radius of curvature of the image side surface of the sixth group lens, r
le is the radius of curvature of the object side surface of the seventh group lens, d15 is the air gap between the sixth group lens and the seventh group lens, n9 is the refractive index of the image side lens of the sixth group lens, and ν is The Abbe number f of the object-side lens of the 6N lens is the focal length of the negative lens in the third lens group, and f is the focal length of the entire system.

Next, the contents of each of the above conditions will be explained in detail. Condition (1) is a condition provided to reduce the Petzval sum. In the objective lens of the present invention, the positive contribution of the Petzval sum due to the strong convex surface of the first group lens is mainly corrected by the thick meniscus-shaped lenses of the sixth group lens and the seventh group lens. . Among them, the condition for the sixth group lens is condition (1). Under these conditions, if r15 exceeds the lower limit and becomes small, it is advantageous for correcting the Petzval sum, but at the same time, astigmatism occurring on this surface becomes large. If this astigmatism is attempted to be corrected by the seventh lens group, the residual amount of coma aberration generated in the sixth and seventh group lenses becomes large, which is undesirable because it becomes impossible to correct this satisfactorily.

Furthermore, if r15 exceeds the upper limit of condition (1), the burden of correcting the Petzval sum in the seventh lens group becomes large.

Moreover, since the height of the chief ray passing through this seventh group lens is high, astigmatism that occurs when trying to obtain a good Petzval sum with this lens becomes a problem.

Condition (2), like condition (1), is also provided to reduce the Petzval sum. If lr +el becomes smaller than the lower limit of the condition, it is advantageous to reduce the Petzval sum, but the occurrence of astigmatism increases. Also, when 1r161 exceeds the upper limit, t7 occurs in the 6th group lens.
Astigmatism cannot be corrected completely, and if this is attempted to be corrected using the fourth and fifth lens groups, comatic aberration increases.

Condition (3), together with conditions (1) and (2), is a condition for correcting astigmatism and coma aberration. If the seventh group lens is placed further back, the height of the chief ray incident thereon will increase, and its contribution to astigmatism and coma will be smaller. d15
If exceeds the lower limit of condition (3), in order to correct astigmatism, it is necessary to reduce the radius of curvature r16 of the object-side surface of the seventh lens group and increase the power of this surface. Coma aberration will be overcorrected. Also d1
If 5 exceeds the upper limit of the condition, then r+6 will have to be made weak in power, resulting in under-correction of coma aberration.

Condition (4) is a condition regarding the Petzval sum.

Since the power of the negative lens in the seventh lens group is very strong, the selection of the refractive index of this lens is also important in order to reduce the Petzval sum. If n exceeds the -1- limit of this condition and becomes a dog, the Petzval sum in this lens will be insufficiently corrected and flatness of the image plane will not be obtained. Further, the lower limit of this condition is set from the viewpoint of correcting chromatic aberration. In other words, n9
If it becomes smaller than the lower limit, it becomes necessary to use glass with a large Abbe number, which makes it difficult to correct chromatic aberration.

Conditions (5) and (6) are provided to correct spherical aberration and chromatic aberration.

In the present invention, spherical aberration is corrected by increasing the power of the negative lens of the fourth lens group. Furthermore, by increasing the power of this negative lens, the power of the positive lens of the fourth lens group can also be increased, which is convenient for correcting chromatic aberration. Residual chromatic aberration can be reduced by using a material with anomalous dispersion for the lens, which has a high axial ray height and strong power. If the focal length f5 of this negative lens exceeds the lower limit of condition (5), the spherical aberration will be overcorrected by this negative lens. 3. If this is attempted to be corrected by increasing the power of the seventh lens group, higher-order aberrations will occur, which is undesirable.

If the f5 value exceeds the upper limit of condition (5), the residual chromatic aberration cannot be reduced because the correction of chromatic aberration in the fourth group lens is insufficient.

The same thing as mentioned above can be said about the focal length f7 of the fifth group lens. Therefore, the 5th group lens also has spherical aberration and coma aberration generated in the 4th group lens.

It is desirable to set the power so that astigmatism can be corrected. Therefore, it is desirable that f7 be set to a level that satisfies the following conditions. .

8.2 t < 1f71 < 8.61 Next condition (6)
is related to chromatic aberration. The positive lens of the sixth lens group is a lens with relatively strong power. Therefore, it has a large effect on chromatic aberration, and if the Atsube number ν8 of this lens becomes smaller than the lower limit of condition (6), it is not suitable for correction of residual chromatic aberration.1) Next, the microscope objective of the present invention described above Each example of the lens is shown.

Example 1 r (1) d+ = 1.5833 1+ = 1.51825
ν, = 64.15r2-” 1.0460 d22 0.0361 r3= 4.3333 d3= 1.0000 n2= 1.68613
'2 = 44.65r4=-2,6128 d, = 0.0667 rs d5= 1.1278 13= 1.49846'
3=gl, 6°r, knee 3.3139 do” 0.4444 rt = 27.5822 d7”1.8167 n+=1.49846 c4
=81.60r8 knee 4.0328 ds = 1.1111 n! = 1.81990
ν5”44.45rg = 5.0850 do ”” 1.6111 n6 ” 1.4349
7 Shiro = 95.15rlo"" 9.4667 duo = 0.1222 ro = 6.4439 r, 2 = -10,9778 du2 = 0.4000 rt3" 4.0944 du: + = 2・3333 nt = 1. 434
97 νT=95.15ru ”-6,1833 (Ls ”” 1.1732 (L52 3.2722 r+a”’ 2.3550 (1+a-3,2389no = 1.72794
ν. =37.95r+7=3.5572 f=1. β=100X, NA=1.25 Example 2 rl −■ du = 1.5833 11 = 1.51825
shi, =64.15r2=-10497 d2= 0.0317 r:t ”” -4,3333 d3”” 0.9944 12= 1.68613
'2 = 44.65r, = -2,6128 d4 = 0.0833 r5 = -11,8822 d5 = 1.1278 ns" 1.49846
'3""81.6Or6" 3.3139 d62 0.4444 r7= 27.5822 d7 "" 1.8167 n4 = 1.
49846 9° = 8+, 60rg = -4,
0328 ds 21.1111 15= 1.81990 1'
5 = 44.45rQ = 5.0850 do = 1.6111 n6 ” 1.
43497 1'e = 95.15r,. =
-94667 d,. = 0.1222 1'+-2 6.4389 du = 1.6111 n7"" 1.49846
Schiff "81.6Or+2" 10.9778 cL2= 0.4000 r+3== 4.0944 du3=2.3333 na=1.43497
ν5=95.15r14=6.1833 d14=6.2833 no=1.59261
1'Q = 41.08r+i "" 1.169
9 d152 3.2722 rt62-2,3550 dua = 3.2389 1eo2 1.72794
ν+o ” 37.95r1□ =-3,5572 f=1, β=100X, NA=1.25 Example 3 r, 2ω du = 1.5833 11 = 1.51825
Si1=64.15r2=1.0460 d2=0.0361 r3 knee4.3333 d:+=1.0000 n2=1.68613
ν2""44.65r, =-2,6128 d, =0.0667 r5 knee 11.8822 ds" 1.1278 ns = 1.49846
shi3=81.60ra=3.3139 d, =0.4444 r, = 27.5822 d7" 1.8167 n4-' 1.49846
'4 = 81.60r &"' -4,0328 ds = 1.1111 n5 "1.81990
ν5=44.45ru=5.0850 d9=1.6111 ne=1.43497 'e
=95.15r,. =-9,4667 duo = 0.1222 rlt 264439 dll" 1.6111 n7 = 1.49846
Schiff=81.6Or+2 = 10.9778 dll-04000 rl3” 4.0944 du:+ = 2.3333 n@ = 1.434
97 νs = 95.15rn = -6,,1
833 dn = 6.2833 TI” 1.59261
&, = 41.081"+5" 1.173
2 (L5 = 3.2722 r+a = 2.3550 duo = 3.2389 1eo = 1.7279
4 shi, o= 37.95rl? "3.5572 f=1, β=100X, NA=1.25 Example 4 r+=ω du" 1.5833 nl = 1.51825
= 64.15 r2 knee 1.0618 d2 = 0.0327 r3 = 4.3564 ds” 0.9947 n2 = 1.68613
shi2=44.65r,=2.6089 d4=0.0865 r5=-11,7569 ds ” 1.1312 n3=1.49846
shi3=81.60ra ” 3.3051 do” 0.4474 r7= 30.9547 d7= 1.8208 14 = 1.49846
ν4”81.6Or,: 4.1679 ds” 1.1187 n5= 1.81990
ν5”44.45ro = 5.1423 do” 1.6124 no” 1.43497
νe=95.15r+o=9.3433 duo=0.1233 r,=6.4566 du=1.9281 nl” 1.49846
Schiff = 81. ．． 60r+2: 10.807
1 d, 2 = 0.3932 rl3 == 4.0908 d+3 = 2.3328 ns = 1.43497
νg=95.15r+<= 6.1647 dn=6.2822 no=1.59261
1'g=41.08r+s ° 1.1136 cp5= 3.8889 rl6= 2.5147 dua =3.2372 neo := 1.727
94 ν+o = 37.95rlt = 3.
6601 f-1, β-100X, NA=1.25 but rl +
+21 ”' + rlt is the radius of curvature of each lens surface,
dl+d2+..., d16 is the wall thickness and air gap of each lens, nl r 12 +...+ nl (1 is the refractive index of each lens, shi1.shi2..., ν1o is the Atsube number of each lens, β is a magnification.

Each of the above-mentioned embodiments has an infinite distance design and cannot form an image by itself. Therefore, the aberration curve is calculated using the lens configuration shown in Fig. 2 and the following data.
r, B = +4. shown in Publication No. 19. Kai Imabari 4 dus ” 2.2222 no-1, 48915ν
11= 70.15r+g-62,6306 dlQ21.1111 r2o: 31.9428 d2o = 1.1111 n+2" L74618
ν12 = 28.29r,, = -67,900
0 d2+ -” 8.3333 rz2 = 24.4072 d22”-1,0000n+3” 1.48915 1
'+3 = 70.15r, J-109122 The data of the above imaging lens is for f=1, and the aberration curves of each example are also drawn for f=1.

As explained above, the microscope objective lens of the present invention has a high magnification, a small numerical aperture, a small number of lenses, and a small number of special materials with anomalous dispersion, and yet various aberrations are well corrected. It is a lens system.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of the objective lens of the present invention, FIG. 2 is a diagram showing the configuration of an example of an imaging lens used together with the objective lens of the present invention, and FIGS. 3 to 6 are examples of the present invention, respectively. 1
6 is a diagram showing aberration situations in Examples to Example 4. FIG. Applicant Olympus Optical Co., Ltd. Agent Hiroshi Mukai Bosphere aberration o 5 G' Astigmatism Distortion, Aberration Chromatic aberration of magnification 5.0 Distortion Aberration Chromatic aberration of magnification -to 1.0 -2.0
20-+u
+u -tu
tiJ −'p, u
': +, u distortion aberration
Lateral chromatic aberration Spherical aberration o s c' Foot point aberration Distortion Lateral chromatic aberration

Claims (1)

[Claims] A first lens group of a plano-convex lens with a flat surface facing the object side, a second group lens of a positive meniscus lens with a concave surface facing the object side, a third lens group of positive lenses, and a positive lens group. a fourth lens group of a three-piece cemented lens consisting of a lens, a negative lens, and a positive lens;
It consists of a 5th group lens that is a biconvex lens, a 6th group lens that is a cemented meniscus lens that has a convex surface facing the object side, and a 7th group lens that is a meniscus lens that has a concave surface facing the object side, and meets the following conditions. A satisfying microscope objective lens. (1) 1.1f≦r15≦1.35f (2) 1.7f
≦Ir+el≦2.7f (3) 1.9f≦ dl5≦
4.0f (4) 1.55≦n, ≦1.65 (5) 2.4f≦1f, 1≦2,8f (6) 65≦ν8 However, r15 is the curvature of the image side surface of the 6th group lens radius, r
, 6 is the radius of curvature of the object side surface of the seventh group lens, dl is the air distance between the sixth group lens and the seventh group lens, n9 is the refractive index of the image side lens of the sixth group lens, ν8 is the Abbe number of the object-side lens of the sixth group lens, f is the focal length of the negative lens in the fourth group lens, and f is the focal length of the entire system.