JPS6035048B2 - microscope objective lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an objective lens for a microscope with high magnification and high closure.

In order to correct field curvature in a microscope objective lens, it is necessary to arrange the concave surfaces facing each other like a Gaussian type lens, or to arrange lenses with concave surfaces as the first and last lenses. The sum must be made smaller.

In the case of an objective lens in which lenses having concave surfaces are arranged on the first and last lenses, it is not possible to provide a concave surface on the first lens in order to use this as an immersion system. Therefore, in order to use a lens with a flat image surface and an immersion system, it is sufficient to use a recessed lens for the front lens. As a microscope objective lens with such a recessed lens, US Pat. No. 359,847 is known.
No. 4, U.S. Patent No. 3,537,772, JP-A-51-72
No. 343 etc. are known.

Among these conventional examples, two US patent lenses are as follows:
As can be seen from the values of a, /r2l, the embedded lens of the first lens group, that is, the lens closest to the object side, has a thin thickness, so it is easy to work. U.S. Patent No. 3,598,474 0.3466 (Example 1) 0.3388 (Example 2)
U.S. Patent No. 3,537,772 0.3507 (Example 1)
0.3508 (Example 2) However, these lenses have poor image flatness and chromatic aberration is not well corrected.

Furthermore, since these objective lenses are designed to have an infinite distance, a barrel lens is actually used and the imaging system includes this barrel lens. Therefore, although it is possible to obtain flatness of the image with this barrel lens, it is still not possible to perform a sufficiently satisfactory correction. Furthermore, if there is no barrel lens, the objective lens itself must compensate for that amount, and sufficient compensation cannot be achieved unless the number of lens components is increased. Also, the lens of JP-A-51-72343 is la, /r
2l is 0.8818, and the flatness of the image is good, but the first
The lens to be embedded in the lens group is thick and has a strong curvature, making it difficult to process and resulting in an increase in cost.

The present invention is a microscope objective lens that uses a lens system in which the first group lens is a recessed lens, which further improves image flatness, and improves workability and reduces costs by increasing the radius of curvature of the recessed lens. Our goal is to provide the following. The objective lens of the present invention has a lens configuration as shown in FIG.

In other words, the first group lens is a hemispherical lens with an embedded lens, the second group lens is a positive meniscus lens with a concave surface facing the object, and the third group lens is a combination of a biconvex lens, a biconcave lens, and a biconvex lens. Three-piece cemented normal lens, the fourth group lens is a three-piece cemented normal lens with a negative meniscus with the convex surface facing the object side, a biconvex lens, and a negative lens, and the fifth group lens is a normal lens and a biconcave lens. This is a cemented negative lens that is cemented with a negative lens. In this lens system, the radius of curvature of the cemented surface of the first group lens is r2, the radius of curvature of the image side surface of the first group lens is r3, and the radius of curvature of the object side surface of the third group lens is t6.
, the radius of curvature of the cemented surface of the third group lens located on the elephant side is r8, the air distance between the fourth group lens and the fifth group lens is a, 3, and both lenses of the first group lens are It is characterized in that it satisfies the following conditions, where the refractive index is 3, the peak number of the second group lens is 3, and the focal length of the entire system is f. [1) 0.38<lr2l<0.56f ■ 1.37f<lr3l<1.75f (3} ri-n,>0.3 {4} shi3 <44 (51 3.1f<d,3< 6 is '6} 1.5<lr6/r8l<1.9 In the above objective lens, the first group lens is a built-in lens, and the Bebbard sum is in the negative direction due to the cemented surface with the concave surface facing the object side. It is designed to be.

By setting the radius of curvature r2 of the cemented surface as shown in the condition '1}', the shape of the lens is made to have good field curvature and good machinability. If the lower limit is exceeded under these conditions, the workability of the lens becomes extremely poor and astigmatism increases. When the upper limit is exceeded, the effect of making the Betubar sum negative becomes weaker, and the flatness of the image deteriorates. The radius of curvature of the image-side surface of this first group lens is set as shown in condition (2), and this makes the Bebbard sum a positive value and cancels each other out with the cemented surface described above, reducing the Bebbard sum to a small value. It's meant to be. In this condition '2}, if r3 is smaller than 1.37f, the Betzbar sum increases toward the positive side, which is not preferable. If r3 is larger than 1.75f, spherical aberration will be undercorrected. Furthermore, the refractive indexes n, and peaks of both lenses of this first lens group are selected as shown in the condition t31. If this condition (3) is violated, r2 must be made small in order to make the Betsuval sum small, and condition '1' is satisfied.
} is not preferable for the above-mentioned reason. Next, the Abbe number of the second group lens is set as shown in condition (4) so that the chromatic aberration of magnification becomes good.If 3 becomes larger than 44, the chromatic aberration of magnification becomes overcorrected.Also, The third group lens is a three-piece cemented lens, and the negative spherical aberration generated on the object side surface and the positive spherical aberration generated on the surface located on the wisteria side of the cemented surface cancel each other out. This is done to reduce spherical aberration.

Therefore, the radius of curvature of these surfaces r6,W or the condition '6}'
It is specified as shown below. If the upper limit of this condition [6} is exceeded, the spherical aberration will be under-corrected, and if the lower limit is exceeded, the spherical aberration will be over-corrected. The refractive index peaks of the object-side lens and the intermediate lens in this third group lens are set to almost the same value, and the Abbe numbers of these lenses are set to different values of 4 and 5 to make them hyperachromatic, and the surface r7 Axial chromatic aberration at high NA is corrected. Furthermore, the fourth group lens is a triple cemented lens to correct spherical aberration and longitudinal chromatic aberration.

Finally, the fifth group lens is a cemented lens, which corrects axial chromatic aberration and contributes to reducing the Bebbard sum by making the Bebbard sum negative by its image side surface.

Air distance a, 3 between the fourth group lens and this fifth group lens
is the condition (i.e., it is determined as shown below; under this condition, when a, 3 is smaller than 3.1f, the Betzval sum increases and the flatness of the image worsens, and when it becomes larger than 6.2, the axis Upper chromatic aberration worsens.

Examples of the objective lens of the present invention described above are shown below.

Example 1r,: alni〇. 248nl=1.51742 Hi1=52
．． 3r2=-0.4605a2 1.753 mountain 1.8
8300″2 d40.8r3=-1.6293a3
=0.018 r4=-5.3713 a4 d1.352 ratio=,. 72342 Re3 =38.
0r5=-2.9132a5=0.165 r6=5.4569 a6 2.444 mountains, . 69350re 4:50.8r
7=4.8766a7 d0.543 is d1.68893
〃5 d31.1r8=3.1659a8d2.44
4 Buddha 1.43389 6 95.2r9=-5.
7054a9=0.083 r,o=5.8861 al.

N〇． 〇667n7ni,. 66680ri7 =33.0
r,. =3.1499alld2.261n8:,. 4
3389 Re8 Ni95.2r・2=-3.1499a
12;〇. 767n9ni,. 66680 9 = 33
．． 0r13: -55.9032a・3=4.994 r・4=49.0626 a・4d 1.393nl.

D... 78472 Hi・〇ni 25.7r・5=-3.3
524d・5ni〇. 762nll Ni 1.50378 Re 11 Ni 66.8r, 6=2.8040f=1-0,8=
-100-OX, evening.

=○-182NA=1.25, ZP=0.059Example 2 Te・=.

〇al=〇. 250nl=1.51633 Reni 6
4.2r2=-0.4367a2d1.740&d1.
88300 Re2 Ni40.8r3ko-1.5989a
3=0.012 r4=-7.7218 a4 d1.341 mountain d1.72343 ″3 d38.
0r5=-3.1472a5=0.075 r6=5.7979 a6 2.371 mountain 1.69350 re 4 =50.
8r7=-4.8060a7 d0.536 is d1.68
893 hi5 d31.1r8=3.3082a8=2
．． 433~d1.433389 h6 =95.2r9
=-5.1042 also=0.162 r,o=7.5683 al.

=〇． 668n7=1.66680re7 ni33.0r
、． =3.3999alld2.246n8:,. 43
389 Hi8 Ni95.2r・2=-2.8334a is Ni〇, 761n9 Ni, 66680 Re9 Ni33,.

r・3=-13.8640a・3=4.810 r−4=a14=1.266nloni,. 78472 Hi・〇ni25.7r・5=-3.2040d15=〇. 561n
ll=1.50378 Re 11 Ni 668r, 6=2.8
353f=1-0, 8=-102-7X, so.

=○-175NA=1.25, 2P=0.062 Example 3 r-=target alni〇. 251nl d1.51633 hi1 =64
．． 2r2=-0.4345a2=1.674~=,. 8
8300re2 =41.0r3=-1.5643a3;
0.012 r4=-5.5216 a4 d1.328 ratio d1.72000 ″3 d43.
7r5: -2.8270a5=0.075 r6=4.8146 Father=2.256~D1.69350 〃4 D50.8
r7; 5.6249a7 ni 0.533 is: 1.6889
3 〃5 d31.1r8=2.7522a8;2.1
06=1.43389 Hi6=95.2r9=-7
．． 4580a9=0.282 r,o=6.0080 alo;〇. 658n7=,. 66680 Re7 Ni3
3.0r,. =2.8313all:1.974n8=
、． 43389 Re 8 =95.2r・2=-3.24
60a.2 〇. 877n9ni,. 66680hi9 ni33.0r13=-11.1057a・3=3.871 r,4=912.5575 a14=1.253nlOil. 76182 Sea.

;26.6r・5=-3.0105d15=〇. 557
nll=,. 50378 Re 11=66.8r, 6=2
．． 6978f=1-0, 3=-100.01X, evening.

=○-175NA=1.25, 2P=0.062 However, r,, r2. …r. 6 Radius of curvature of each surface of Shins, a,,
a2,...a,5 are the wall thickness and air spacing of each lens, n,
, mind,...n,. is the refractive index of each lens, shi, shi2,...
·death,. is the Abbe number of each lens, so is the working distance, 2
p is the Bebbard sum.

As shown in the above embodiments, the objective lens of the present invention has la,
/r2! The values of are 0.5386 (Example 1) and 0.5, respectively.
725 (Example 2) and 0.5777 (Example 3), a is relatively thin, r2 is also relatively large, and workability is good.

Moreover, the Bebbard sum is extremely small, the image has good flatness, and various aberrations are well corrected.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the objective lens of the present invention, and FIGS. 2 to 4 are aberration curve diagrams of Examples 1 to 3, respectively. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. A first lens group that is a hemispherical lens having an embedded lens, a second group lens that is a positive meniscus lens with a concave surface facing an object, a biconvex positive lens, and a biconcave negative lens. The third lens group is a positive three-piece cemented lens made by cementing a biconcave negative lens and a biconvex positive lens, a negative meniscus lens with a convex surface facing the object side, a positive three-piece cemented lens made by cementing a biconvex lens and a negative lens. A microscope objective lens comprising a fourth lens group consisting of a cemented lens and a fifth lens group consisting of a negative cemented lens formed by cementing a positive lens and a biconcave negative lens, and satisfying the following conditions. (1) 0.38<|r_2|<0.56f(2) 1
．． 37f<|r_3|<1.75f(3) n_2-n
_1>0.3(4) ν_3<44 (5) 3.1f<d_1_3<6.2f(6) 1.
5<|r_6/r_8|<1.9 where f is the focal length of the entire system, r_2 and r_3 are the radius of curvature of the cemented surface and image side surface of the first group lens, respectively, and r_6 and r_8 are the curvature radius of the third group lens, respectively. The radius of curvature of the object-side surface and the surface located on the image side of the cemented surface, d_1_3 is the air distance between the fourth group lens and the fifth group lens, and n_1 and n_2 are both lenses of the first group lens, respectively. The refractive index of ν_3 is the Abbe number of the second group lens.