WO2023001017A1 - Fixed-focus lens - Google Patents

Abstract

A fixed-focus lens. The fixed-focus lens comprises: a first lens (11) having a negative optical power, a second lens (12) having a negative optical power, a third lens (13) having a positive optical power, a diaphragm (20), a fourth lens (14) having a positive optical power, a fifth lens (15) having a positive optical power, a sixth lens (16) having a negative optical power, a seventh lens (17) having a positive optical power, an eighth lens (18) having a positive optical power or having a negative optical power, and a ninth lens (19) having a positive optical power or a negative optical power, arranged in sequence along an optical axis from an object side to an image side. The fifth lens (15), the sixth lens (16) and the seventh lens (17) are a cemented triplet lens, and the second lens (12) is an aspheric lens.

Description

a fixed focus lens

This disclosure claims priority to a Chinese patent application with application number 202110825243.9 filed with the China Patent Office on July 21, 2021, the entire contents of which are incorporated herein by reference.

technical field

The embodiments of the present application relate to the technical field of optical imaging, for example, to a fixed-focus lens.

Background technique

With the advancement of technology and the development of 5G (fifth generation mobile communication), all walks of life have put forward higher requirements on the performance of lenses in various aspects, such as resolution, high and low temperature confocal and low-light photography. Generally, cameras can only obtain high-resolution images in places with good lighting conditions, but in low-light conditions, infrared fill lights or other auxiliary light sources need to be added, which will cause various light pollution, and the photo effect will be greatly lost.

Contents of the invention

An embodiment of the present application provides a fixed-focus lens, which does not require a supplementary light under low-light conditions, and at the same time can ensure a high-quality effect of a large image area and a large aperture.

An embodiment of the present application provides a fixed-focus lens. The fixed-focus lens includes: a first lens with negative refractive power, a second lens with negative refractive power, and sequentially arranged along the optical axis from object side to image side. A third lens with positive power, a diaphragm, a fourth lens with positive power, a fifth lens with positive power, a sixth lens with negative power, a seventh lens with positive power, an eighth lens with positive or negative power and a ninth lens with positive or negative power;

The fifth lens, the sixth lens and the seventh lens are triplet lenses; the second lens is an aspherical lens.

Description of drawings

FIG. 1 is a schematic structural view of a fixed-focus lens provided in an embodiment of the present application;

Fig. 2 is the axial aberration curve of fixed focus lens shown in Fig. 1;

Fig. 3 is the field curvature curve of the fixed-focus lens shown in Fig. 1;

Fig. 4 is the distortion curve of fixed-focus lens shown in Fig. 1;

Fig. 5 is the chromatic aberration curve of fixed-focus lens shown in Fig. 1;

FIG. 6 is a schematic structural diagram of another fixed-focus lens provided in an embodiment of the present application;

Fig. 7 is the axial aberration curve of the fixed-focus lens shown in Fig. 6;

Fig. 8 is the field curvature curve of the fixed-focus lens shown in Fig. 6;

Fig. 9 is the distortion curve of the fixed-focus lens shown in Fig. 6;

Figure 10 is the chromatic aberration curve of the fixed-focus lens shown in Figure 6;

Fig. 11 is a schematic structural diagram of another fixed-focus lens provided by the embodiment of the present application;

Fig. 12 is the axial aberration curve of the fixed-focus lens shown in Fig. 11;

Fig. 13 is the field curvature curve of the fixed-focus lens shown in Fig. 11;

Fig. 14 is the distortion curve of the fixed-focus lens shown in Fig. 11;

FIG. 15 is a chromatic aberration curve of the fixed-focus lens shown in FIG. 11 .

detailed description

The application will be described below in conjunction with the accompanying drawings and embodiments. It should be understood that the embodiments described here are only used to explain the present application. In addition, it should be noted that, for the convenience of description, only some structures related to the present application are shown in the drawings but not all structures.

Fig. 1 is a schematic structural view of a fixed-focus lens provided by the embodiment of the present application. As shown in Fig. 1, the fixed-focus lens provided by the embodiment of the present application includes: The first lens 11 of power, the second lens 12 with negative power, the third lens 13 with positive power, the diaphragm 20, the fourth lens 14 with positive power, the fifth lens with positive power Lens 15, sixth lens 16 with negative power, seventh lens 17 with positive power, eighth lens 18 with positive power or negative power, and The ninth lens 19; the fifth lens 15, the sixth lens 16 and the seventh lens 17 are triplet lenses; the second lens 12 is an aspheric lens.

In one embodiment, the fifth lens 15 , the sixth lens 16 , and the seventh lens 17 are cemented together in sequence to form a whole, that is, a triplet lens.

In this embodiment, the focal power is equal to the difference between the image beam convergence degree and the object beam convergence degree, which represents the ability of the optical system to deflect light. The greater the absolute value of the focal power, the stronger the ability to bend light, and the smaller the absolute value of the focal power, the weaker the ability to bend light. When the focal power is positive, the refraction of light is converging; when the focal power is negative, the refraction of light is divergent. Optical power can be applied to characterize a certain refraction surface of a lens (that is, a surface of the lens), it can be applied to characterize a certain lens, and it can also be used to characterize a system formed by multiple lenses (that is, a lens group). In this embodiment, each lens can be fixed in a lens barrel, and the imaging effect of the optical lens can be improved by rationally allocating the optical power of the lens, wherein the optical power is the reciprocal of the focal length.

In this embodiment, by rationally allocating the first lens 11, the second lens 12, the third lens 13, the fourth lens 14, the fifth lens 15, the sixth lens 16, the seventh lens 17, the eighth lens 18 and The focal power ratio of the ninth lens 19, at the same time by setting the second lens 12 as an aspheric lens, can correct the field curvature caused by the large image surface, and the fifth lens 15, the sixth lens 16 and the seventh lens 17 form a triple cement The lens group can correct the chromatic aberration caused by the large aperture and increase the field of view, so that the fixed-focus lens provided by the embodiment of the present application can be used with a day and night full-color camera, and has a large aperture (for example, the lens light transmission ability parameter FNO.≤1.11 ), large target area, and high pixels, it can match up to 1/1.1-inch sensor (image sensor) chip, and the maximum can meet 1200W pixels.

In addition, an aperture 20 is provided between the third lens 13 and the fourth lens 14, which can improve the imaging quality. It should be noted that those skilled in the art can set the position of the diaphragm according to the actual situation.

At the same time, since the fifth lens 15 , the sixth lens 16 and the seventh lens 17 form a triplet lens group, the volume of the fixed-focus lens can be reduced, and the miniaturization of the fixed-focus lens can be realized.

Optionally, referring to Fig. 1, the object side of the first lens 11 is convex, the image side of the first lens 11 is concave; the object side of the second lens 12 is concave, and the image side of the second lens 12 is convex; the third lens 13 object The side surface is convex, and the third lens 13 image side is convex or concave; the fourth lens 14 object side is convex or concave, and the fourth lens 14 image side is concave or convex; the fifth lens 15 object side is convex, and the fifth lens 15 The image side is concave; the sixth lens 16 object side is concave, and the image side of the sixth lens 16 is concave; the seventh lens 17 object side is convex, and the seventh lens 17 image side is convex; the eighth lens 18 object side is convex Or concave, the image side of the eighth lens 18 is convex or concave; the object side of the ninth lens 19 is convex or concave, and the image side of the ninth lens 19 is convex or concave.

Optionally, the first lens 11, the third lens 13, the fifth lens 15, the sixth lens 16 and the seventh lens 17 are all glass spherical lenses; the second lens 12, the eighth lens 18 and the ninth lens 19 are all Plastic aspheric lens; the fourth lens 14 is a glass spherical or plastic aspheric lens.

The fixed-focus lens provided in the embodiment of the present application adopts a combination of glass lens and plastic lens, which can reduce cost and improve performance, and can meet the use conditions of -40°C to 80°C, that is, reduce cost while improving lens performance .

Optionally, the focal power of the first lens 11 and the focal power of the fixed-focus lens satisfy

in,

is the focal length of the fixed-focus lens,

is the power of the first lens. That is, the light incident aperture is compressed by the first lens 11 to reduce aberration.

Optionally, the refractive power of the first lens 11 and the thickness of the first lens 11 satisfy

in,

is the refractive power of the first lens, D1 is the thickness of the first lens; and the refractive index Nd1 of the first lens 11 satisfies Nd1>1.7. The advantage of this setting is that it can compress the light incident aperture and reduce aberration.

Optionally, the focal power of the second lens is 12 and the focal power of the fixed-focus lens satisfies

in,

is the focal length of the fixed-focus lens,

is the power of the second lens. That is, the curvature of field can be corrected by the second lens 12 .

Optionally, the refractive index Nd2 of the second lens 12 satisfies 1.5≦Nd2≦1.7. The advantage of this setting is that field curvature can be corrected.

Optionally, the third lens 13 is a glass spherical lens or a plastic aspheric lens, and the fourth lens 14 is a glass spherical lens or a plastic aspheric lens; and the refractive power of the third lens 13 and the refractive power of the fourth lens 14 satisfy:

in,

is the power of the third lens,

is the power of the fourth lens. With such settings, spherical aberration can be corrected. Optionally, the refractive index Nd3 of the third lens 13 may also be set to be greater than the refractive index Nd4 of the fourth lens 14 to correct spherical aberration.

Optionally, the dispersion coefficients of the fifth lens 15, the sixth lens 16, and the seventh lens 17 respectively satisfy: Vd5-Vd6>20, Vd7-Vd6>20; wherein, Vd5 is the dispersion coefficient of the fifth lens, and Vd6 is the dispersion coefficient of the fifth lens. The dispersion coefficient of the six lenses, Vd7 is the dispersion coefficient of the seventh lens. In this way, the ability of chromatic aberration correction can be improved to a certain extent, thereby improving the imaging quality of the fixed-focus lens.

Optionally, the thickness of the eighth lens 18, the thickness of the ninth lens 19 and the focal power of the fixed-focus lens satisfy

Wherein, D8 is the eighth lens thickness, D9 is the ninth lens thickness,

is the focal length of the fixed-focus lens.

By setting the eighth lens 18 and the ninth lens 19 as plastic aspheric lenses, and the eighth lens 18 thickness D8, the ninth lens 19 thickness D9 and fixed focus lens power

satisfy

It can correct high and low temperature and increase the lens aperture from the design.

The fixed-focus lens provided by the embodiment of the present application will be described below with reference to the following examples.

Exemplary: continue referring to Fig. 1, in this embodiment, the radius of curvature of each lens from the object side to the image side along the optical axis in the fixed-focus lens shown in Fig. Distance), refractive index and K value meet the conditions listed in Table 1:

Table 1 is a design value of the fixed focus lens:

Surf	Radius of curvature (mm)	Thickness (mm)	Refractive index	K value
S1	14.22	5.01	2.00	the
S2	8.17	5.40	the	0.12
S3	-7.27	4.33	1.64	-3.52
S4	-14.50	1.66	the	-11.13
S5	28.87	3.00	1.95	the
S6	-100.03	0.45	the	the
STO	PL	1.54	the	the
S8	14766.71	3.00	1.52	the
S9	-22.88	0.07	the	the
S10	13.27	4.02	1.70	the
S11	-21.95	0.94	1.75	the
S12	9.11	8.45	1.50	the
S13	-28.69	0.10	the	the
S14	-20.58	2.00	1.66	-101.71
S15	-13.72	0.05	the	-8.70
S16	9.56	2.73	1.54	-14.44
S17	7.49	4.6	the	-7.27
S18	PL	0.80	1.52	the
S19	PL	1.25	the	the

"surf" in Table 1 represents the surface number, and the surface number is numbered according to the surface order of each lens, where "S1" represents the front surface of the first lens, "S2" represents the rear surface of the first lens, and so on; " STO" represents the aperture of the lens; the radius of curvature represents the degree of curvature of the lens surface, a positive value represents that the surface is curved to the image plane side, and a negative value represents that the surface is curved to the object plane side, where "PL" represents the surface is a plane, and the radius of curvature is infinite; the thickness represents the central axial distance from the current surface to the next surface; the refractive index represents the deflection ability of the material between the current surface and the next surface for light, and a blank space represents the current position is air, and the refraction The rate is 1; the K value represents the numerical value of the best fitting conic coefficient of the aspheric surface, and the spherical lens has no K value, which is represented by a space.

Optionally, the conic coefficient of the aspheric surface can be expressed by the following aspheric surface formula:

In the above formula, z is the distance sagittal height of the aspheric surface from the apex of the aspheric surface at the position of height r along the optical axis direction; r is the height of the aspheric surface; c is the curvature of the fitting spherical surface, numerically it is the radius of curvature Reciprocal; k is the fitting conic coefficient; A, B, C, D, E, F are the 4th, 6th, 8th, 10th, 12th, and 14th order coefficients of the aspheric polynomial.

Table 2 is a kind of design value of aspheric coefficient in described fixed-focus lens:

the	A	B	C	D.	E.	f
S3	-5.40797E-04	2.00270E-05	-4.95875E-07	7.84382E-09	-5.33012E-11	0.00000E+00
S4	-1.82601E-04	9.87239E-06	-2.07542E-07	2.84138E-09	-1.57276E-11	0.00000E+00
S14	5.50674E-04	-8.90280E-06	4.61992E-08	1.73935E-10	-6.32110E-11	2.84448E-13
S15	4.38013E-04	-4.42015E-06	-1.97224E-07	8.63421E-11	2.51308E-11	-1.41158E-13
S16	-7.02572E-04	1.87462E-06	-9.15029E-08	-3.63303E-09	1.75534E-10	-1.08488E-12
S17	-6.44488E-04	8.91692E-06	-5.71557E-08	1.43485E-09	7.50325E-12	-5.36410E-14

Wherein, the scientific notation method is adopted in the above Table 2, for example, -5.40797E-04 means that the coefficient A of the surface number being the surface 3 is -5.40797×10 ^-4 . Fig. 2 is the axial aberration curve of the fixed-focus lens shown in Fig. 1, Fig. 3 is the field curvature curve of the fixed-focus lens shown in Fig. 1, Fig. 4 is the distortion curve of the fixed-focus lens shown in Fig. 1, Fig. 5 is the chromatic aberration curve of the fixed-focus lens shown in FIG. 1 . It can be seen from Fig. 2, Fig. 3, Fig. 4 and Fig. 5 that the fixed-focus lens provided by this embodiment has small axial aberration, small field curvature, small distortion and small chromatic aberration, high resolution, and maintains a good image quality at all working distances. image quality.

Exemplarily, FIG. 6 is a schematic structural diagram of another fixed-focus lens provided in an embodiment of the present application. As shown in FIG. 6, in this embodiment, the lens shown in FIG. The radius of curvature, center thickness (that is, the distance between adjacent mirror center points), refractive index and K value of each lens on the square meet the conditions listed in Table 3:

Table 3 is yet another design value of the fixed-focus lens:

Surf	Radius of curvature (mm)	Thickness (mm)	Refractive index	K value
S1	14.20	5.29	2.00	the
S2	8.03	5.40	the	the

S3	-7.23	4.13	1.64	-3.85
S4	-15.69	1.49	the	-15.71
S5	29.22	3.00	1.95	the
S6	-123.08	0.45	the	the
STO	PL	1.54	the	the
S8	-170.23	3.00	1.64	-100.00
S9	-21.83	0.07	the	-1.33
S10	13.43	3.93	1.70	the
S11	-23.14	0.94	1.85	the
S12	8.01	6.39	1.62	the
S13	-23.56	0.10	the	the
S14	-19.83	3.00	1.66	-44.96
S15	-17.52	0.05	the	-6.57
S16	11.75	3.14	1.54	-13.07
S17	9.84	4.34	the	-7.26
S18	PL	0.80	1.52	the
S19	PL	1.25	the	the

"surf" in Table 3 represents the surface number, and the surface number is numbered according to the surface order of each lens, where "S1" represents the front surface of the first lens, "S2" represents the rear surface of the first lens, and so on; " STO" represents the aperture of the lens; the radius of curvature represents the degree of curvature of the lens surface, a positive value represents that the surface is curved to the image plane side, and a negative value represents that the surface is curved to the object plane side, where "PL" represents the surface is a plane, and the radius of curvature is infinite; the thickness represents the central axial distance from the current surface to the next surface; the refractive index represents the deflection ability of the material between the current surface and the next surface for light, and a blank space represents the current position is air, and the refraction The rate is 1; the K value represents the numerical value of the best fitting conic coefficient of the aspheric surface, and the spherical lens has no K value, which is represented by a space.

Optionally, the conic coefficient of the aspheric surface can be expressed by the following aspheric surface formula:

In the above formula, z is the distance sagittal height of the aspheric surface from the apex of the aspheric surface at a position of height r along the optical axis direction; r is the height of the aspheric surface; c is the curvature of the fitting spherical surface, numerically it is the radius of curvature Reciprocal; k is the fitting conic coefficient; A, B, C, D, E, F are the 4th, 6th, 8th, 10th, 12th, and 14th order coefficients of the aspheric polynomial.

Table 4 is a kind of design value of aspheric coefficient in described fixed-focus lens:

the	A	B	C	D.	E.	f
S3	-5.00481E-04	2.12385E-05	-4.89365E-07	7.50339E-09	-5.40334E-11	0.00000E+00
S4	-1.11307E-04	1.09901E-05	-2.02722E-07	2.89741E-09	-1.87565E-11	0.00000E+00
S8	1.39834E-05	3.68068E-07	1.54330E-09	-6.62541E-11	3.36102E-12	0.00000E+00
S9	1.59520E-05	4.20321E-08	2.66276E-09	8.30723E-11	-3.71457E-13	0.00000E+00
S14	4.81170E-04	-9.55049E-06	6.79065E-08	3.59778E-10	-6.88488E-11	6.89079E-13
S15	3.91433E-04	-6.38302E-06	-2.21475E-07	6.75593E-10	4.83386E-11	-2.42974E-13
S16	-8.21711E-04	-3.52816E-07	-7.29460E-08	-2.60970E-09	1.86427E-10	-1.54397E-12
S17	-7.74776E-04	1.31524E-05	6.01485E-10	8.15424E-10	8.62122E-12	2.40001E-13

Wherein, the scientific notation method is adopted in the above Table 4, for example, -5.00481E-04 means that the coefficient A of the surface number is Surface 3 is -5.00481×10 ^-4 . Fig. 7 is the axial aberration curve of the fixed-focus lens shown in Fig. 6, Fig. 8 is the field curvature curve of the fixed-focus lens shown in Fig. 6, Fig. 9 is the distortion curve of the fixed-focus lens shown in Fig. 6, Fig. 10 is the chromatic aberration curve of the fixed-focus lens shown in FIG. 6 . It can be seen from Fig. 7, Fig. 8, Fig. 9 and Fig. 10 that the fixed-focus lens provided by this embodiment has small axial aberration, small field curvature, small distortion and small chromatic aberration, high resolution, and maintains good image quality at all working distances. image quality.

Exemplarily, FIG. 11 is a schematic structural diagram of another fixed-focus lens provided in the embodiment of the present application. As shown in FIG. 11, in this embodiment, the optical lens shown in FIG. 11 is from the object side to the The radius of curvature, center thickness (that is, the distance between adjacent mirror center points), refractive index and K value of each lens on the image side meet the conditions listed in Table 5:

Table 5 is a design value of the fixed focus lens:

Surf	Radius of curvature (mm)	Thickness (mm)	Refractive index	K value
S1	14.60	5.94	2.00	the
S2	7.98	5.40	the	the
S3	-7.79	4.14	1.64	-4.16
S4	-16.32	1.45	the	-16.91
S5	28.14	3.00	1.95	the
S6	-111.39	0.45	the	the
STO	PL	1.54	the	the

S8	-45.74	3.00	1.64	-100.00
S9	-20.76	0.07	the	-9.04
S10	14.02	5.25	1.70	the
S11	-12.29	0.94	1.85	the
S12	7.34	4.10	1.62	the
S13	-36.74	0.10	the	the
S14	33.00	3.00	1.66	-24.71
S15	-29.08	0.05	the	8.36
S16	23.23	5.00	1.54	1.27
S17	10.01	3.00	the	-0.33
S18	PL	0.80	1.52	the
S19	PL	1.57	the	the

"surf" in Table 5 represents the surface number, and the surface number is numbered according to the surface order of each lens, where "S1" represents the front surface of the first lens, "S2" represents the rear surface of the first lens, and so on; " STO" represents the aperture of the lens; the radius of curvature represents the degree of curvature of the lens surface, a positive value represents that the surface is curved to the image plane side, and a negative value represents that the surface is curved to the object plane side, where "PL" represents the surface is a plane, and the radius of curvature is infinite; the thickness represents the central axial distance from the current surface to the next surface; the refractive index represents the deflection ability of the material between the current surface and the next surface for light, and a blank space represents the current position is air, and the refraction The rate is 1; the K value represents the numerical value of the best fitting conic coefficient of the aspheric surface, and the spherical lens has no K value, which is represented by a space.

Optionally, the conic coefficient of the aspheric surface can be expressed by the following aspheric surface formula:

In the above formula, z is the distance sagittal height of the aspheric surface from the apex of the aspheric surface at a position of height r along the optical axis direction; r is the height of the aspheric surface; c is the curvature of the fitting spherical surface, numerically it is the radius of curvature Reciprocal; k is the fitting conic coefficient; A, B, C, D, E, F are the 4th, 6th, 8th, 10th, 12th, and 14th order coefficients of the aspheric polynomial.

Table 6 is a design value of the aspheric coefficient in the fixed-focus lens:

the	A	B	C	D.	E.	f
S3	-5.30555E-04	2.01159E-05	-4.91092E-07	8.68953E-09	-6.89591E-11	0.00000E+00

S4	-7.16557E-05	1.13725E-05	-1.97136E-07	2.66702E-09	1.56475E-12	0.00000E+00
S8	1.24022E-04	1.79952E-06	9.46488E-10	-3.70662E-10	1.49743E-11	0.00000E+00
S9	6.52120E-05	-3.47127E-07	1.40263E-08	3.39676E-10	4.62271E-12	0.00000E+00
S14	5.06858E-04	-1.03154E-05	6.14071E-08	5.46400E-10	-7.35402E-11	2.05302E-13
S15	1.72842E-04	-7.29999E-06	-1.65155E-07	1.98589E-09	5.26365E-11	-1.16269E-12
S16	-6.62192E-04	1.92590E-06	-7.82909E-08	-2.74654E-09	1.83175E-10	-1.54759E-12
S17	-4.41066E-04	1.45499E-05	-4.29123E-08	-2.50477E-09	1.55985E-10	-1.89024E-12

Wherein, the scientific notation method is adopted in the above Table 6, for example, -5.30555E-04 means that the coefficient A of the surface number being the surface 3 is -5.30555×10 ^-4 . Fig. 12 is the axial aberration curve of the fixed-focus lens shown in Fig. 11, Fig. 13 is the field curvature curve of the fixed-focus lens shown in Fig. 11, and Fig. 14 is the distortion curve of the fixed-focus lens shown in Fig. 11, Fig. 15 is the chromatic aberration curve of the fixed-focus lens shown in FIG. 11 . From Figure 12, Figure 13, Figure 14 and Figure 15, it can be seen that the fixed-focus lens provided by this embodiment has small axial aberration, small field curvature, small distortion and small chromatic aberration, high resolution, and maintains good image quality at all working distances. image quality.

Claims (10)

1. A fixed-focus lens, comprising: a first lens with negative refraction power, a second lens with negative refraction power, a third lens with positive refraction power, and an optical stop, fourth lens with positive power, fifth lens with positive power, sixth lens with negative power, seventh lens with positive power, positive or negative power an eighth lens and a ninth lens having positive optical power or negative optical power;

   The fifth lens, the sixth lens and the seventh lens are triplet lenses; the second lens is an aspherical lens.
2. The fixed-focus lens according to claim 1, wherein the object side of the first lens is convex, and the image side of the first lens is concave; the object side of the second lens is concave, and the image side of the second lens is concave. is a convex surface; the third lens object side is convex, and the third lens image side is convex or concave; the fourth lens object side is convex or concave, and the fourth lens image side is concave or convex; The object side of the fifth lens is convex, and the image side of the fifth lens is concave; the object side of the sixth lens is concave, and the image side of the sixth lens is concave; the object side of the seventh lens is convex, The image side of the seventh lens is convex; the object side of the eighth lens is convex or concave, and the image side of the eighth lens is convex or concave; the object side of the ninth lens is convex or concave, and the ninth lens is convex or concave. The image side of the lens is convex or concave.
3. The fixed-focus lens according to claim 1, wherein the first lens, the third lens, the fifth lens, the sixth lens and the seventh lens are all glass spherical lenses;

   The second lens, the eighth lens and the ninth lens are all plastic aspherical lenses;

   The fourth lens is a glass spherical lens or a plastic aspherical lens.
4. The fixed-focus lens according to claim 1, wherein the optical power of the first lens and the optical power of the fixed-focus lens satisfy

   

   in,

   

   is the focal power of the fixed-focus lens,

   

   is the optical power of the first lens.
5. The fixed-focus lens according to claim 1, wherein the first lens power and the first lens thickness satisfy

   

   in,

   

   is the optical power of the first lens, and D1 is the thickness of the first lens;

   And the refractive index Nd1 of the first lens satisfies Nd1>1.7.
6. The fixed-focus lens according to claim 1, wherein the optical power of the second lens and the optical power of the fixed-focus lens satisfy

   

   in,

   

   is the focal power of the fixed-focus lens,

   

   is the optical power of the second lens.
7. The fixed-focus lens according to claim 1, wherein the refractive index Nd2 of the second lens satisfies 1.5≤Nd2≤1.7.
8. The fixed-focus lens according to claim 1, wherein the third lens is a glass spherical lens or a plastic aspheric lens, and the fourth lens is a glass spherical lens or a plastic aspheric lens;

   And the optical power of the third lens and the optical power of the fourth lens satisfy:

   

   in,

   

   is the optical power of the third lens,

   

   is the optical power of the fourth lens.
9. The fixed-focus lens according to claim 1, wherein the dispersion coefficients of the fifth lens, the sixth lens, and the seventh lens respectively satisfy: Vd5-Vd6>20, Vd7-Vd6>20;

   Wherein, Vd5 is the dispersion coefficient of the fifth lens, Vd6 is the dispersion coefficient of the sixth lens, and Vd7 is the dispersion coefficient of the seventh lens.
10. The fixed-focus lens according to claim 3, wherein the thickness of the eighth lens, the thickness of the ninth lens and the focal power of the fixed-focus lens satisfy

    

    Wherein, D8 is the thickness of the eighth lens, D9 is the thickness of the ninth lens,

    

    is the focal power of the fixed-focus lens.

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