阅读说明：本技术 纳米激光直写物镜 (Nano laser direct writing objective lens ) 是由 黄木旺 刘旭 匡翠方 林法官 于 2021-07-02 设计创作，主要内容包括：本发明涉及镜头领域,特别为一种纳米激光直写物镜。包括沿光线入射方向依次设置的负光焦度的第一群组、正光焦度的第二群组、光阑、以及正光焦度的第三群组；其中各群组的焦距满足以下关系：0.65＜|fA/fB|＜3.5；4.0＜|fB/fC|＜15.0；-120mm＜fA＜-40mm；40mm＜fB＜80mm；5mm＜fC＜15mm,其中：fA为第一群组的焦距,fB为第二群组的焦距,fC为第三群组的焦距。本发明提供一种数值孔径NA至1.3左右且高分辨率的纳米激光直写物镜,该物镜为无限远复消色差类型系统,且无需使用超半球镜片,便于物镜的加工,能降低物镜的制造成本。(The invention relates to the field of lenses, in particular to a nano laser direct writing objective lens. The optical system comprises a first group with negative focal power, a second group with positive focal power, a diaphragm and a third group with positive focal power, which are sequentially arranged along the incident direction of light; wherein the focal lengths of the groups satisfy the following relationship: 0.65 < | fA/fB | < 3.5; 4.0 < | fB/fC | < 15.0; -120mm < fA < -40 mm; fB is more than 40mm and less than 80 mm; 5mm < fC < 15mm, wherein: fA is the focal length of the first group, fB is the focal length of the second group, and fC is the focal length of the third group. The invention provides a high-resolution nano laser direct writing objective lens with numerical aperture NA of about 1.3, which is an infinite apochromatic type system, does not need to use a hyper-hemispherical lens, is convenient for processing the objective lens and can reduce the manufacturing cost of the objective lens.)

1. A nanometer laser direct writing objective lens is characterized in that: the device comprises a first group (A) with negative focal power, a second group (B) with positive focal power, a diaphragm and a third group (C) with positive focal power, which are sequentially arranged along the incident direction of light;

wherein the focal lengths of the groups satisfy the following relationship:

0.65＜|fA/fB|＜3.5；

4.0＜|fB/fC|＜15.0；

wherein: fA is the focal length of the first group, fB is the focal length of the second group, and fC is the focal length of the third group;

the focal length fA of the first group is: -120mm < fA < -40 mm;

the focal length fB of the second group is: fB is more than 40mm and less than 80 mm;

the focal length fC of the third group is: fC is more than 5mm and less than 15 mm.

2. The nanolaser direct write objective lens of claim 1, wherein: in the second group (A), at least two lenses are made of ultra-low dispersion material, and the Abbe number of the ultra-low dispersion material is in the range of 90-100.

3. The nanolaser direct write objective lens of claim 1, wherein: and in the third group (C), at least one lens uses an ultra-low dispersion material, and the Abbe number of the ultra-low dispersion material ranges from 90 to 100.

4. The nanolaser direct write objective lens of claim 1, wherein: the first group (A) comprises a meniscus first lens (A1), a biconvex second lens (A2), a biconcave third lens (A3), a biconcave fourth lens (A4), a biconcave fifth lens (A5), a biconvex sixth lens (A6) and a seventh lens (A7) with positive focal power, which are arranged in sequence along the incident direction of light rays;

the second lens (A2) and the third lens (A3) form a close-connected double-adhesive combination, and the fifth lens (A5) and the sixth lens (A6) form a close-connected double-adhesive combination.

5. The nanolaser direct write objective lens of any one of claims 1 to 4, wherein: the second group (B) includes a biconcave eighth lens (B8), a biconvex ninth lens (B9), a biconvex tenth lens (B10), a biconcave eleventh lens (B11), a biconvex twelfth lens (B12), a biconvex thirteenth lens (B13), a meniscus fourteenth lens (B14), a biconvex fifteenth lens (B15), a biconcave sixteenth lens (B16), a meniscus seventeenth lens (B17), and a negative meniscus eighteenth lens (B18) which are sequentially arranged along the light incidence direction;

the eighth lens (B8) and the ninth lens (B9) form a sealed double-adhesive set, the tenth lens (B10), the eleventh lens (B11) and the twelfth lens (B12) form a sealed triple-adhesive set, and the fifteenth lens (B15) and the sixteenth lens (B16) form a sealed double-adhesive set.

6. The nanolaser direct write objective lens of any one of claims 1 to 4, wherein: the third group (C) comprises a first double-cemented lens, a second double-cemented lens and at least one meniscus lens which are sequentially arranged along the incident direction of light;

the first double-cemented combined lens is formed by closely gluing a first nineteenth lens (C19) of a negative meniscus type and a first twentieth lens (C20) of the negative meniscus type along the incident direction of light rays;

the second double-cemented lens group is formed by closely gluing a meniscus twenty-first lens I (C21) and a meniscus twenty-second lens I (C22).

7. The nanolaser direct write objective lens of claim 6, wherein: the number of the meniscus lenses in the third group (C) is two, and the meniscus lenses are respectively a twenty-third lens (C23) and a twenty-fourth lens (C24) which are sequentially arranged on the image side of the second double-cemented lens group along the incident direction of the light.

8. The nanolaser direct write objective lens of any one of claims 1 to 4, wherein: the second group (B) includes a biconcave eighth lens two (B8 '), a biconvex ninth lens two (B9'), a biconvex tenth lens two (B10 '), a biconcave eleventh lens two (B11'), a biconvex twelfth lens two (B12 '), a negative meniscus thirteenth lens two (B13'), a biconvex fourteenth lens two (B14 '), a biconcave fifteenth lens two (B15'), a biconvex sixteenth lens two (B16 '), a biconcave seventeenth lens two (B17'), a biconvex eighteenth lens two (B18 '), and a biconcave nineteenth lens two (B19') which are sequentially arranged along the light incidence direction;

the eighth lens group (B8 ') and the ninth lens group (B9 ') form a closely-connected double-cemented group, the tenth lens group (B10 '), the eleventh lens group (B11 ') and the twelfth lens group (B12 ') form a closely-connected triple-cemented group, the fourteenth lens group (B14 ') and the fifteenth lens group (B15 ') form a closely-connected double-cemented group, and the sixteenth lens group (B16 ') and the seventeenth lens group (B17 ') form a closely-connected double-cemented group; and the eighteenth lens II (B18 ') and the nineteenth lens II (B19') form a close-contact double-gluing set.

9. The nanolaser direct write objective lens of any one of claims 1 to 4, wherein: the third group (C) includes a meniscus-shaped second lens (C20 '), a meniscus-shaped second twenty-first lens (C21'), a meniscus-shaped second twenty-second lens (C22 '), a biconvex-shaped second twenty-third lens (C23'), a negative meniscus-shaped second twenty-fourth lens (C24 '), a meniscus-shaped second twenty-fifth lens (C25'), a meniscus-shaped second twenty-sixth lens (C26 '), and a meniscus-shaped second twenty-seventh lens (C27') which are sequentially arranged along the light incidence direction;

the twenty-first lens two (C21 ') and the twenty-second lens two (C22') form a close-connected double-adhesive combination, the twenty-third lens two (C23 ') and the twenty-fourth lens two (C24') form a close-connected double-adhesive combination, and the twenty-sixth lens two (C26 ') and the twenty-seventh lens two (C27') form a close-connected double-adhesive combination.

10. The nanolaser direct write objective lens of claim 8, wherein: the eighth lens two (B8 ') to the twelfth lens two (B12 ') constitute an inner focus group adjustably movably disposed between the seventh lens (a7) and the thirteenth lens two (B13 ') in the optical axis direction.

Technical Field

The invention relates to the field of lenses, in particular to a nano laser direct writing objective lens.

Background

A lithography machine is an apparatus for printing patterns on substrate materials such as chips, printed circuit boards, mask plates, flat panel displays, biochips, micromechanical electronic chips, optical glass plates, and the like. The chrome glass masks used in conventional lithographic processes need to be supplied by a professional supplier, but in a development environment, the design of the masks often needs to be changed frequently. Maskless lithography overcomes this problem by designing the electronic mask with software. Different from the traditional process of illumination through a physical mask plate, the laser direct writing is to directly expose and draw a required pattern on a photoresist by controlling the switch of a series of laser pulses through a computer. Laser direct writing techniques are commonly used for microstructure fabrication, such as diffractive optical elements, gratings, and the like.

In laser direct writing devices, the microscope objective is undoubtedly an important component. The microscope objective lens can realize high resolution by increasing numerical aperture NA to about 1.3, and usually, the working medium can be changed into liquid with refractive index of about 1.5 by air, so that the angle of light collection of the first lens can be increased, and the first lens needs to be designed to be a hyper-hemispherical lens, so that the lens is not easy to process, the coating difficulty is increased, and the cost of the objective lens is increased.

Disclosure of Invention

The invention aims to: the objective lens is an infinite apochromatic type system, a hyper-hemispherical lens is not needed, the processing of the objective lens is convenient, and the manufacturing cost of the objective lens can be reduced.

The invention is realized by the following technical scheme:

the first scheme is as follows:

a nanometer laser direct writing objective lens is characterized in that: the optical system comprises a first group with negative focal power, a second group with positive focal power, a diaphragm and a third group with positive focal power, which are sequentially arranged along the incident direction of light;

wherein the focal lengths of the groups satisfy the following relationship:

0.65＜|fA/fB|＜3.5；

4.0＜|fB/fC|＜15.0；

wherein: fA is the focal length of the first group, fB is the focal length of the second group, and fC is the focal length of the third group;

the focal length fA of the first group is: -120mm < fA < -40 mm;

the focal length fB of the second group is: fB is more than 40mm and less than 80 mm;

the focal length fC of the third group is: fC is more than 5mm and less than 15 mm.

In order to improve the resolution, at least two lenses in the second group are made of ultra-low dispersion materials, and the Abbe number of the ultra-low dispersion materials ranges from 90 to 100.

In order to further improve the resolution, at least one lens in the third group uses an ultra-low dispersion material, and the abbe number of the ultra-low dispersion material is in a range of 90-100.

Preferably, the first group includes a meniscus-type first lens, a biconvex-type second lens, a biconcave-type third lens, a biconcave-type fourth lens, a biconcave-type fifth lens, a biconvex-type sixth lens, and a positive power seventh lens, which are arranged in sequence along the light incidence direction;

the second lens and the third lens form a sealed double-gluing set, and the fifth lens and the sixth lens form a sealed double-gluing set.

Preferably, the second group includes a biconcave eighth lens one, a biconvex ninth lens one, a biconvex tenth lens one, a biconcave eleventh lens one, a biconvex twelfth lens one, a biconvex thirteenth lens one, a meniscus fourteenth lens one, a biconvex fifteenth lens one, a biconcave sixteenth lens one, a meniscus seventeenth lens one, and a negative meniscus eighteenth lens one, which are sequentially arranged along the light incidence direction;

the eighth lens and the ninth lens form a sealed double-adhesive combination, the tenth lens, the eleventh lens and the twelfth lens form a sealed three-adhesive combination, and the fifteenth lens and the sixteenth lens form a sealed double-adhesive combination.

Preferably, the third group comprises a first double-cemented lens, a second double-cemented lens and at least one meniscus lens which are arranged in sequence along the incident direction of the light;

along the incident direction of light rays, the first double-cemented combined lens is formed by closely bonding a first nineteenth lens of a negative meniscus type and a first twentieth lens of the negative meniscus type;

the second double-adhesive combined lens is formed by closely adhering a first meniscus twenty-first lens and a second meniscus twenty-second lens.

Preferably, the number of the meniscus lenses in the third group is two, and the meniscus lenses are respectively a twenty-third lens and a twenty-fourth lens which are sequentially arranged on the image side of the second double-cemented lens set along the incident direction of the light.

Scheme II:

the present solution is different from the first solution in that, preferably, the second group includes a biconcave eighth lens two, a biconvex ninth lens two, a biconvex tenth lens two, a biconcave eleventh lens two, a biconvex twelfth lens two, a negative meniscus thirteenth lens two, a biconvex fourteenth lens two, a biconcave fifteenth lens two, a biconvex sixteenth lens two, a biconcave seventeenth lens two, a biconvex eighteenth lens two, and a biconcave nineteenth lens two, which are sequentially arranged along the light incidence direction;

the eighth lens group and the ninth lens group form a close-joint double-gluing group, the tenth lens group, the eleventh lens group and the twelfth lens group form a close-joint three-gluing group, the fourteenth lens group and the fifteenth lens group form a close-joint double-gluing group, and the sixteenth lens group and the seventeenth lens group form a close-joint double-gluing group; and the eighteenth lens II and the nineteenth lens II form a tightly-connected double-gluing set.

Preferably, the third group includes a second meniscus lens, a second biconvex lens, a second negative meniscus lens, a second negative meniscus lens, a second positive lens, a second negative lens, a second positive lens, a third lens, a fourth lens, a third lens, a fourth lens, a third lens, a fourth lens, a third lens, a fourth lens, a third lens, a fourth lens, a third lens, a fourth lens, a third lens, a fourth lens, a third lens, a fourth lens, a third lens, a;

the twenty-first lens group and the twenty-second lens group form a close-joint double-gluing set, the twenty-third lens group, the twenty-fourth lens group form a close-joint double-gluing set, and the twenty-sixth lens group and the twenty-seventh lens group form a close-joint double-gluing set.

The eighth lens II to the twelfth lens II form an inner focusing group, and the inner focusing group is adjustably movably arranged between the seventh lens and the thirteenth lens II along the optical axis direction.

Compared with the prior art, the invention has the beneficial effects that:

1. the invention provides a high-resolution nano laser direct writing objective lens with numerical aperture NA of about 1.3, which is an infinite apochromatic type system, does not need to use a hyper-hemispherical lens, is convenient for processing the objective lens and can reduce the manufacturing cost of the objective lens.

2. According to the nano laser direct writing objective lens, the first group adopts a structure similar to double gausses, and vertical axis chromatic aberration, such as magnification chromatic aberration, coma aberration, distortion and the like, can be eliminated.

3. According to the nano laser direct writing objective lens, the second group adopts a plurality of double cemented lenses to be beneficial to eliminating the axial chromatic aberration of the system, the triple cemented lens plays the role of apochromatism, and the meniscus lens and the double concave lens can play the role of light ray transition

4. According to the nano laser direct writing objective lens, the third group of two meniscus lenses play a role of a collimating lens, the numerical aperture can be greatly improved to achieve the aim of NA1.3, and a traditional hyper-hemispherical lens is not used, so that the manufacturing difficulty is greatly reduced.

Drawings

FIG. 1 is a schematic structural diagram according to a first embodiment of the present invention;

FIG. 2 is a Seidel diagram according to a first embodiment of the present invention;

FIG. 3 is a diagram of optical path difference according to a first embodiment of the present invention;

FIG. 4 is a diagram of a multi-color optical focus drift according to a first embodiment of the present invention;

FIG. 5 is a diagram of chromatic aberration of magnification according to a first embodiment of the present invention;

FIG. 6 is a schematic structural diagram according to a second embodiment of the present invention;

FIG. 7 is a Seidel diagram (refractive index of working medium 1.484) of example two of the present invention;

FIG. 8 is an optical path difference diagram (refractive index of working medium is 1.484) of the second embodiment of the present invention;

FIG. 9 is a polychromatic light focus drift pattern (working medium refractive index of 1.484) according to the second embodiment of the present invention;

FIG. 10 is a diagram of chromatic aberration of magnification (refractive index of working medium is 1.484) in accordance with a second embodiment of the present invention;

FIG. 11 is an optical path difference diagram (the refractive index of the working medium is 1.479) of the second embodiment of the present invention;

FIG. 12 is a diagram of the shift of the multi-color focus of the second embodiment of the present invention (the refractive index of the working medium is 1.479);

FIG. 13 is a chromatic aberration of magnification diagram (refractive index of working medium 1.479) of the second embodiment of the present invention;

FIG. 14 is an optical path difference diagram (refractive index of working medium is 1.489) of the second embodiment of the present invention;

FIG. 15 is a diagram of the shift of the focus of polychromatic light according to the second embodiment of the present invention (refractive index of working medium is 1.489);

fig. 16 is a chromatic aberration of magnification diagram (refractive index of working medium is 1.489) of the second embodiment of the present invention.

Description of reference numerals:

a-first group, a 1-first lens, a 2-second lens, A3-third lens, a 4-fourth lens, a 5-fifth lens, a 6-sixth lens, a 7-seventh lens;

b-second group, B8-eighth lens one, B8 ' -eighth lens two, B9-ninth lens one, B9 ' -ninth lens two, B10-tenth lens one, B10 ' -tenth lens two, B11-eleventh lens one, B11 ' -eleventh lens two, B12-twelfth lens one, B12 ' -twelfth lens two, B13-thirteenth lens one, b13 ' -thirteenth lens two, B14-fourteenth lens one, B14 ' -fourteenth lens two, B15-fifteenth lens one, B15 ' -fifteenth lens two, B16-sixteenth lens one, B16 ' -sixteenth lens two, B17-seventeenth lens one, B17 ' -seventeenth lens two, B18-eighteenth lens one, B18 ' -eighteenth lens two, B19 ' -nineteenth lens two;

c-third group, C19-nineteenth lens one, C20-twentieth lens one, C20 '-twentieth lens two, C21-twenty-first lens one, C21' -twenty-first lens two, C22-twenty-second lens one, C22 '-twenty-second lens two, C23-twenty-third lens one, C23' -twenty-third lens two, C24-twenty-fourth lens one, C24 '-twenty-fourth lens two, C25' -twenty-fifth lens two, C26 '-twenty-sixth lens two, C27' -twenty-seventh lens two.

Detailed Description

The invention is described in detail below with reference to the accompanying drawings:

the first embodiment is as follows:

as shown in fig. 1-5, a nano laser direct writing objective lens includes a first group a of negative focal power, a second group B of positive focal power, a diaphragm, and a third group C of positive focal power, which are sequentially arranged along a light incidence direction;

the focal length of the system of the embodiment is 6.86, and the detailed structural data is as follows:

the serial numbers of the surfaces are sequentially arranged along the incident direction of the light;

the number marked with a symbol means that the surface is aspherical. The aspherical formula is as follows:

where c is the radius of curvature and the aspheric coefficients are as follows:

wherein the diaphragm is arranged on the 30 th surface;

the focal lengths of the groups satisfy the following relationship:

|fA/fB|＝1.88；

|fB/fC|＝12.72；

wherein: fA is the focal length of the first group, fB is the focal length of the second group, and fC is the focal length of the third group;

the focal length fA of the first group is: -111.04 mm;

the focal length fB of the second group is: 59.02mm for fB;

the focal length fC of the third group is: fC 8.73 mm.

In order to improve the resolution, at least two lenses in the second group A are made of ultra-low dispersion material with Abbe number ranging from 90 to 100, such as 16 th surface and 20 th surface.

In order to further improve the resolution, at least one lens in the third group C is made of an ultra-low dispersion material, and the Abbe number of the ultra-low dispersion material is in a range of 90-100, such as the 30 th surface.

Preferably, the first group a includes a meniscus-type first lens a1, a biconvex-type second lens a2, a biconcave-type third lens A3, a biconcave-type fourth lens a4, a biconcave-type fifth lens a5, a biconvex-type sixth lens a6, and a seventh lens a7 with positive power, which are sequentially arranged along the light incidence direction;

the second lens A2 and the third lens A3 form a closely-connected double-adhesive combination, and the fifth lens A5 and the sixth lens A6 form a closely-connected double-adhesive combination.

Preferably, the second group B includes a biconcave eighth lens B8, a biconvex ninth lens B9, a biconvex tenth lens B10, a biconcave eleventh lens B11, a biconvex twelfth lens B12, a biconvex thirteenth lens B13, a meniscus fourteenth lens B14, a biconvex fifteenth lens B15, a biconcave sixteenth lens B16, a meniscus seventeenth lens B17, and a negative meniscus eighteenth lens B18, which are sequentially arranged along the light incidence direction;

the eighth lens B8 and the ninth lens B9 form a close-coupled double-adhesive combination, the tenth lens B10, the eleventh lens B11 and the twelfth lens B12 form a close-coupled triple-adhesive combination, and the fifteenth lens B15 and the sixteenth lens B16 form a close-coupled double-adhesive combination.

Preferably, the third group C includes a first double-cemented lens, a second double-cemented lens, and at least one meniscus lens, which are sequentially arranged along the light incident direction;

along the incident direction of light rays, the first double-cemented combined lens is formed by closely gluing a negative meniscus nineteenth lens-C19 and a negative meniscus twentieth lens-C20;

the second double-cemented lens group is formed by closely cementing a meniscus twenty-first lens-C21 and a meniscus twenty-second lens-C22.

Preferably, the number of the meniscus lenses in the third group C is two, and the two meniscus lenses are respectively a twenty-third lens C23 and a twenty-fourth lens C24 which are sequentially arranged on the image side of the second double-cemented lens set along the incident direction of the light.

This embodiment can be seen from fig. 2 that Seidel values of all sides are less than 1.2mm, and the system is not sensitive and easy to manufacture.

As can be seen from fig. 3, the optical path difference of the entire system is within 1 wavelength except for the outermost margin field, and the performance of each field almost reaches the diffraction limit.

As can be seen from fig. 4, the type of systematic chromatic aberration correction is apochromatic, and the value of the axial chromatic aberration is also within the diffraction limit.

As can be seen from fig. 5, the chromatic aberrations within the wavelength bands are also within the diffraction limit.

Example two:

as shown in fig. 6-16, a nano laser direct writing objective lens includes a first group a of negative focal power, a second group B of positive focal power, a diaphragm, and a third group C of positive focal power, which are sequentially arranged along a light incidence direction;

the focal length of the system of this embodiment is 7.00, and the detailed structural data is as follows:

the serial numbers of the surfaces are sequentially arranged along the incident direction of the light;

the number marked with a symbol means that the surface is aspherical. The aspheric formula is the same as in the first embodiment:

where c is the radius of curvature and the aspheric coefficients are as follows:

wherein the diaphragm is arranged on the 31 st surface;

the focal lengths of the groups satisfy the following relationship:

|fA/fB|＝0.72；

|fB/fC|＝6.89；

wherein: fA is the focal length of the first group, fB is the focal length of the second group, and fC is the focal length of the third group;

the focal length fA of the first group is: -50.57.04 mm;

the focal length fB of the second group is: 69.92mm for fB;

the focal length fC of the third group is: fC 10.14 mm.

In order to improve the resolution, at least two lenses in the second group A are made of ultra-low dispersion material with Abbe number ranging from 90 to 100, such as 16 th and 22 th surfaces.

In order to further improve the resolution, at least one lens in the third group C uses an ultra-low dispersion material, and the abbe number of the ultra-low dispersion material is in the range of 90-100, such as 33 rd surface and 36 th surface.

Preferably, the first group a includes a meniscus-type first lens a1, a biconvex-type second lens a2, a biconcave-type third lens A3, a biconcave-type fourth lens a4, a biconcave-type fifth lens a5, a biconvex-type sixth lens a6, and a seventh lens a7 with positive power, which are sequentially arranged along the light incidence direction;

the second lens A2 and the third lens A3 form a closely-connected double-adhesive combination, and the fifth lens A5 and the sixth lens A6 form a closely-connected double-adhesive combination.

Preferably, the second group B includes a biconcave eighth lens two B8 ', a biconvex ninth lens two B9', a biconvex tenth lens two B10 ', a biconcave eleventh lens two B11', a biconvex twelfth lens two B12 ', a negative meniscus thirteenth lens two B13', a biconvex fourteenth lens two B14 ', a biconcave fifteenth lens two B15', a biconvex sixteenth lens two B16 ', a biconcave seventeenth lens two B17', a biconvex eighteenth lens two B18 ', and a biconcave nineteenth lens two B19' that are sequentially arranged along the light incidence direction;

the eighth lens group B8 ' and the ninth lens group B9 ' form a close-coupled double-gel-bonded group, the tenth lens group B10 ', the eleventh lens group B11 ' and the twelfth lens group B12 ' form a close-coupled triple-gel-bonded group, the fourteenth lens group B14 ' and the fifteenth lens group B15 ' form a close-coupled double-gel-bonded group, and the sixteenth lens group B16 ' and the seventeenth lens group B17 ' form a close-coupled double-gel-bonded group; the eighteenth lens element II B18 'and the nineteenth lens element II B19' form a sealed double-adhesive combination.

Preferably, the third group C includes a twenty-second meniscus lens C20 ', a twenty-first meniscus lens C21', a twenty-second meniscus lens C22 ', a twenty-third biconvex lens C23', a twenty-fourth negative meniscus lens C24 ', a twenty-fifth meniscus lens C25', a twenty-sixth meniscus lens C26 ', and a twenty-seventh meniscus lens C27' sequentially arranged along the light incident direction;

the twenty-first lens C21 'and the twenty-second lens C22' form a close-joint double-gluing set, the twenty-third lens C23 'and the twenty-fourth lens C24' form a close-joint double-gluing set, and the twenty-sixth lens C26 'and the twenty-seventh lens C27' form a close-joint double-gluing set.

In order to realize that the performance of the system is basically kept unchanged when the refractive index of the working medium fluctuates, the eighth lens II B8 ' to the twelfth lens II B12 ' form an inner focusing group, and the inner focusing group is adjustably and movably arranged between the seventh lens A7 and the thirteenth lens II B13 ' along the optical axis direction so as to be adjusted when the total length of the system (without the thickness of the working medium) is changed.

Wherein the variable data are as follows:

this example shows from fig. 7 that Seidel values for each side are less than 1.2mm, and the system is insensitive and easy to manufacture.

As can be seen from fig. 8, the optical path difference of the entire system is within 0.5 wavelength except for the outermost margin field, and the performance of each field almost reaches the diffraction limit.

As can be seen from fig. 9, the type of systematic chromatic aberration correction is apochromatic, and the value of the axial chromatic aberration is also within the diffraction limit.

As can be seen from fig. 10, each chromatic aberration in each wavelength band is also within the diffraction limit.

Fig. 11 to 13 are performance expressions of the working medium having a refractive index of 1.479, and fig. 14 to 16 are performance expressions of the working medium having a refractive index of 1.489. Therefore, the system performance is good when the refractive index of the working medium fluctuates within 1.479-1.489. However, the refractive index of the working medium is not limited to 1.479-1.489, but may be 1.516-1.526, or others.

The above two embodiments can achieve the following optical conditions:

1. the focal length is 6.6-7.2 mm;

NA value 1.315;

3. the total optical length is about 240 mm;

4. wavelength range: 0.522-0.79 um;

5.DFOV：8.4°；

6. all band wavelength OPD (performance index): on-axis OPD <1 wavelength;

1F OPD <2 wavelength.

While the invention has been illustrated and described with respect to specific embodiments and alternatives thereof, it will be understood that various changes and modifications can be made without departing from the spirit and scope of the invention. It is understood, therefore, that the invention is not to be in any way limited except by the appended claims and their equivalents.