CN113655595B

CN113655595B - Fixed focus lens

Info

Publication number: CN113655595B
Application number: CN202111062870.8A
Authority: CN
Inventors: 邓建伟; 陶雪; 翟林燕; 梁伟朝
Original assignee: Sunny Optics Zhongshan Co Ltd
Current assignee: Sunny Optics Zhongshan Co Ltd
Priority date: 2021-09-10
Filing date: 2021-09-10
Publication date: 2024-10-15
Anticipated expiration: 2041-09-10
Also published as: CN113655595A

Abstract

The invention relates to a fixed focus lens, which comprises a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4), a fifth lens (L5), a sixth lens (L6) and a seventh lens (L7) which are sequentially arranged from an object side to an image side along an optical axis. The day and night confocal fixed focus lens has the characteristics of high pixels, large image height, small volume and no virtual focus in the temperature range of-40 ℃ to 80 ℃.

Description

Fixed focus lens

Technical Field

The invention relates to the technical field of optical imaging, in particular to a fixed-focus lens.

Background

Along with the development of science and technology, security monitoring facilities are increasingly popularized, and fixed focus lenses are widely applied to various fields due to the advantages of high imaging definition, wide monitoring field of view, clear imaging under low illumination conditions and the like. However, in the night or in the environment with insufficient illumination conditions, the security monitoring lens is generally insufficient in brightness of the shot image, so that clear imaging cannot be realized, and therefore, the purpose of clear imaging is generally achieved by adopting an infrared light supplementing mode in the prior art. However, the infrared imaging range is smaller, and the shooting of real color information cannot be guaranteed, so that color distortion is serious. Therefore, in the night or in the environment with insufficient illumination conditions, how to ensure clear imaging of the lens is a technical problem to be solved in the security monitoring field.

Disclosure of Invention

The invention aims to provide a fixed-focus lens.

In order to achieve the above object, the present invention provides a fixed focus lens, including a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens, which are sequentially arranged from an object side to an image side along an optical axis, wherein the second lens has negative optical power, and the seventh lens is a biconvex or paraxial region biconcave lens.

According to an aspect of the present invention, an eighth lens on the image side of the seventh lens is further included.

According to one aspect of the invention, the first lens has negative power, the third lens has positive power, the fourth lens has positive power, the fifth lens has negative power, the sixth lens has positive power, the seventh lens has positive power, and the eighth lens has negative power.

According to one aspect of the present invention, the first lens is a convex-concave type lens, the second lens is a concave-convex type lens, the third lens is a convex-concave type lens, the fourth lens is a biconvex/plano-convex type lens, the fifth lens is a concave-convex type lens, the sixth lens is a biconvex/plano-convex type lens, and the eighth lens is a paraxial region biconcave type lens.

According to one aspect of the present invention, the first lens is an aspherical lens, the second lens is an aspherical lens, the third lens is an aspherical lens, the fourth lens is a spherical lens, the fifth lens is a spherical lens, the sixth lens is a spherical lens, the seventh lens is an aspherical lens, and the eighth lens is an aspherical lens.

According to one aspect of the present invention, the materials of the first lens, the second lens, the third lens, the seventh lens and the eighth lens are plastics.

According to one aspect of the invention, the first lens has negative power, the third lens has positive power, the fourth lens has positive power, the fifth lens has negative power, the sixth lens has positive power, and the seventh lens has negative power.

According to one aspect of the present invention, the first lens is a convex-concave type lens, the second lens is a convex-concave type lens, the third lens is a convex-concave type lens, the fourth lens is a biconvex type lens, the fifth lens is a convex-concave type lens, and the sixth lens is a biconvex type lens.

According to one aspect of the present invention, the first lens is an aspherical lens, the second lens is an aspherical lens, the third lens is an aspherical lens, the fourth lens is a spherical lens, the fifth lens is a spherical lens, the sixth lens is an aspherical lens, and the seventh lens is an aspherical lens.

According to one aspect of the invention, the fourth lens and the fifth lens are cemented to form a cemented lens group having positive optical power.

According to one aspect of the present invention, there is further included a diaphragm provided on an image side surface of the third lens, between the third lens and the fourth lens, or on an object side surface of the fourth lens.

According to one aspect of the present invention, the effective focal length f of the fixed focus lens and the effective focal length f1 of the first lens satisfy the following relationship: -2.ltoreq.f1-f is less than or equal to-1.3.

According to one aspect of the present invention, the effective focal length f of the fixed focus lens and the effective focal length f2 of the second lens satisfy the following relationship: -8.ltoreq.f2-f is less than or equal to-1.7.

According to one aspect of the present invention, the effective focal length f of the fixed focus lens and the effective focal length f4 of the fourth lens satisfy the following relationship: 1.1.ltoreq.f4-f is less than or equal to 2.2.

According to one aspect of the present invention, the effective focal length f of the fixed focus lens and the effective focal length f5 of the fifth lens satisfy the following relationship: -5.8.ltoreq.f5 ∈ -f is less than or equal to-2.0.

According to one aspect of the present invention, the effective focal length f of the fixed focus lens and the effective focal length f6 of the sixth lens satisfy the following relationship: 1.ltoreq.f6? f is less than or equal to 4.

According to one aspect of the invention, the Fno number and the effective focal length f of the fixed focus lens satisfy the following relationship: fno/f is less than or equal to 0.4.

According to one aspect of the invention, the effective focal length f and half image height h of the fixed focus lens satisfy the following relationship: f/h is less than or equal to 1.2.

According to one aspect of the invention, the effective focal length f and the total length TTL of the fixed focus lens satisfy the following relationship: f/TTL is less than or equal to 0.25.

According to one aspect of the present invention, the total length TTL, the maximum total image height H and the maximum field angle DFOV of the fixed focus lens satisfy the following relationship: TTL/H/DFOV is less than or equal to 0.02.

According to one aspect of the present invention, the object side maximum aperture D of the first lens, the maximum total image height H of the fixed focus lens, and the total length TTL of the fixed focus lens satisfy the following relationship: D/TTL/H is less than or equal to 4.3.

According to an aspect of the present invention, the relative refractive index temperature coefficient dn/dt of at least one of the fourth lens, the fifth lens and the sixth lens satisfies the following condition: dn/dt is less than or equal to 3.

According to one aspect of the present invention, the material of at least one lens is low dispersion glass, and Abbe number VD satisfies the following condition: VD is more than or equal to 60.

According to the conception of the invention, a high-pixel, large-image, small-volume, non-virtual focus and day-night confocal fixed focus lens is provided in the temperature range of-40 ℃ to 80 ℃.

According to the scheme of the invention, the relation between the effective focal length of part of lenses and the effective focal length of the fixed focus lens is reasonably set, so that the light trend of the whole optical system can be controlled, the aberration and chromatic aberration of the fixed focus lens can be effectively corrected, and the high-low temperature imaging can be corrected while higher image quality can be realized.

According to one scheme of the invention, the effective focal length, half image height, total length, maximum aperture of the first lens on the object side, maximum total image height and maximum field angle of the fixed-focus lens meet certain relations, so that the optical system can meet the requirements of miniaturization and small volume.

Drawings

Fig. 1 schematically shows a block diagram of a fixed focus lens according to a first embodiment of the present invention;

fig. 2 schematically shows an MTF diagram of a fixed focus lens of a first embodiment of the present invention;

FIG. 3 schematically shows a Through-Focus-MTF plot of a fixed Focus lens frequency of 125lp/mm for a first embodiment of the present invention;

FIG. 4 schematically shows a Through-Focus-MTF diagram of a fixed Focus lens of a first embodiment of the present invention having a frequency of 125lp/mm at a high temperature of 80 ℃;

FIG. 5 schematically shows a Through-Focus-MTF diagram of a fixed Focus lens of a first embodiment of the present invention having a frequency of 125lp/mm at-40℃at low temperature;

Fig. 6 schematically shows a block diagram of a fixed focus lens according to a second embodiment of the present invention;

fig. 7 schematically shows an MTF diagram of a fixed focus lens of a second embodiment of the present invention;

FIG. 8 schematically shows a Through-Focus-MTF plot with a fixed Focus lens frequency of 125lp/mm for a second embodiment of the present invention;

FIG. 9 schematically shows a Through-Focus-MTF diagram of a fixed Focus lens of a second embodiment of the present invention having a frequency of 125lp/mm at 80℃at high temperature;

FIG. 10 schematically shows a Through-Focus-MTF diagram of a fixed Focus lens of a second embodiment of the present invention having a frequency of 125lp/mm at-40℃at low temperature;

fig. 11 schematically shows a structure of a fixed focus lens according to a third embodiment of the present invention;

fig. 12 schematically shows an MTF diagram of a fixed focus lens of a third embodiment of the present invention;

FIG. 13 schematically shows a Through-Focus-MTF plot of a fixed Focus lens frequency of 125lp/mm in accordance with a third embodiment of the present invention;

FIG. 14 schematically shows a Through-Focus-MTF diagram of a fixed Focus lens of a third embodiment of the present invention having a frequency of 125lp/mm at 80℃at high temperature;

FIG. 15 schematically shows a Through-Focus-MTF diagram of a fixed Focus lens of a third embodiment of the present invention having a frequency of 125lp/mm at-40℃at low temperature;

Fig. 16 schematically shows a configuration diagram of a fixed focus lens according to a fourth embodiment of the present invention;

fig. 17 schematically shows an MTF diagram of a fixed focus lens of a fourth embodiment of the present invention;

FIG. 18 schematically shows a Through-Focus-MTF plot of a fixed Focus lens frequency of 125lp/mm according to a fourth embodiment of the present invention;

FIG. 19 schematically shows a Through-Focus-MTF diagram of a fixed Focus lens of a fourth embodiment of the present invention having a frequency of 125lp/mm at 80℃at high temperature;

FIG. 20 schematically shows a Through-Focus-MTF diagram of a fixed Focus lens of a fourth embodiment of the present invention having a frequency of 125lp/mm at-40℃at low temperature;

fig. 21 schematically shows a configuration diagram of a fixed focus lens according to a fifth embodiment of the present invention;

fig. 22 schematically shows an MTF diagram of a fixed focus lens of a fifth embodiment of the present invention;

FIG. 23 is a schematic representation of the Through-Focus-MTF plot at a fixed Focus lens frequency of 125lp/mm for a fifth embodiment of the present invention;

FIG. 24 schematically shows a Through-Focus-MTF diagram of a fixed Focus lens of a fifth embodiment of the present invention having a frequency of 125lp/mm at 80℃at high temperature;

FIG. 25 schematically shows a Through-Focus-MTF diagram of a fixed Focus lens of a fifth embodiment of the present invention having a frequency of 125lp/mm at a low temperature of-40 ℃.

Detailed Description

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments will be briefly described below. It is apparent that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained from these drawings without inventive effort for a person of ordinary skill in the art.

In describing embodiments of the present invention, the terms "longitudinal," "transverse," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are used in terms of orientation or positional relationship shown in the drawings for convenience of description and simplicity of description only, and do not denote or imply that the devices or elements in question must have a particular orientation, be constructed and operated in a particular orientation, so that the above terms are not to be construed as limiting the invention.

The present invention will be described in detail below with reference to the drawings and the specific embodiments, which are not described in detail herein, but the embodiments of the present invention are not limited to the following embodiments.

Referring to fig. 1, the glass-plastic mixed day-night confocal fixed focus lens of the invention comprises a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6 and a seventh lens L7 which are sequentially arranged from an object side to an image side along an optical axis. Of course, a protective sheet glass CG is also included. The fourth lens L4 and the fifth lens L5 are glued to form a glued lens set with positive focal power, so that the light trend between the third lens L3 and the sixth lens L6 can be adjusted, the tolerance sensitivity of the whole optical system is reduced, and the production yield is improved. In addition, the fixed-focus lens also comprises a STOP.

As shown in fig. 1, 11, 16 and 21, in some embodiments, the fixed focus lens further includes an eighth lens L8 located on the image side of the seventh lens L7. In these embodiments, the STOP may be disposed on the image side of the third lens L3, between the third lens L3 and the fourth lens L4, or on the object side of the fourth lens L4. The first lens L1 has negative power, the second lens L2 has negative power, the third lens L3 has positive power, the fourth lens L4 has positive power, the fifth lens L5 has negative power, the sixth lens L6 has positive power, the seventh lens L7 has positive power, and the eighth lens L8 has negative power.

The first lens L1 is a convex-concave type lens, the second lens L2 is a concave-convex type lens, the third lens L3 is a convex-concave type lens, the fourth lens L4 is a biconvex/plano-convex type lens, the fifth lens L5 is a concave-convex type lens, the sixth lens L6 is a biconvex/plano-convex type lens, the seventh lens L7 is a biconvex type lens, and the eighth lens L8 is a paraxial region biconcave type lens.

The first lens L1 is an aspherical lens, the second lens L2 is an aspherical lens, the third lens L3 is an aspherical lens, the fourth lens L4 is a spherical lens, the fifth lens L5 is a spherical lens, the sixth lens L6 is a spherical lens, the seventh lens L7 is an aspherical lens, and the eighth lens L8 is an aspherical lens. The materials of the first lens L1, the second lens L2, the third lens L3, the seventh lens L7 and the eighth lens L8 are plastic, so that the lens cost can be reduced.

In other embodiments, as shown in fig. 2, the fixed focus lens has only the first seven lenses. In these embodiments, the STOP is provided on the object side surface of the fourth lens L4. The first lens L1 has negative power, the second lens L2 has negative power, the third lens L3 has positive power, the fourth lens L4 has positive power, the fifth lens L5 has negative power, the sixth lens L6 has positive power, and the seventh lens L7 has negative power.

The first lens L1 is a convex-concave type lens, the second lens L2 is a concave-convex type lens, the third lens L3 is a convex-concave type lens, the fourth lens L4 is a biconvex type lens, the fifth lens L5 is a concave-convex type lens, the sixth lens L6 is a biconvex type lens, and the seventh lens L7 is a paraxial region biconcave type lens.

The first lens L1 is an aspherical lens, the second lens L2 is an aspherical lens, the third lens L3 is an aspherical lens, the fourth lens L4 is a spherical lens, the fifth lens L5 is a spherical lens, the sixth lens L6 is an aspherical lens, and the seventh lens L7 is an aspherical lens.

In the present invention, the effective focal length f of the fixed focus lens and the effective focal length f1 of the first lens L1 satisfy the following relationship: -2.ltoreq.f1-f is less than or equal to-1.3. The effective focal length f of the fixed focus lens and the effective focal length f2 of the second lens L2 satisfy the following relationship: -8.ltoreq.f2-f is less than or equal to-1.7. The effective focal length f of the fixed focus lens and the effective focal length f4 of the fourth lens L4 satisfy the following relationship: 1.1.ltoreq.f4-f is less than or equal to 2.2. The effective focal length f of the fixed focus lens and the effective focal length f5 of the fifth lens L5 satisfy the following relationship: -5.8.ltoreq.f5 ∈ -f is less than or equal to-2.0. The effective focal length f of the fixed focus lens and the effective focal length f6 of the sixth lens L6 satisfy the following relationship: 1.ltoreq.f6? f is less than or equal to 4. The optical system can control the light trend of the whole optical system, effectively correct the aberration and chromatic aberration of the fixed focus lens, and is beneficial to realizing higher image quality and correcting high-low temperature imaging.

In the invention, the FNO number and the effective focal length f of the fixed focus lens meet the following relation: fno/f is less than or equal to 0.4.

In the invention, the effective focal length f and the half image height h of the fixed focus lens meet the following relation: f/h is less than or equal to 1.2. The effective focal length f and the total length TTL of the fixed focus lens meet the following relation: f/TTL is less than or equal to 0.25. The total length TTL, the maximum total image height H and the maximum field angle DFOV of the fixed focus lens satisfy the following relationship: TTL/H/DFOV is less than or equal to 0.02. The maximum aperture D of the object side of the first lens L1, the maximum total image height H of the fixed focus lens and the total length TTL of the fixed focus lens meet the following relation: D/TTL/H is less than or equal to 4.3. The above relation is satisfied, and the optical system can satisfy the requirements of miniaturization and small volume.

In the present invention, the relative refractive index temperature coefficient dn/dt of at least one of the fourth lens L4, the fifth lens L5 and the sixth lens L6 satisfies the following condition: dn/dt is less than or equal to 3. Thus, the lens can be made to have no virtual focus within the temperature range of-40 ℃ to 80 ℃.

In the invention, at least one lens in the fixed focus lens is made of low-dispersion glass, and Abbe number VD meets the following conditions: VD is more than or equal to 60. Therefore, the aberration of the infrared light can be corrected, so that the system can meet the confocal characteristic of visible light and infrared light.

In conclusion, the fixed focus lens can realize large aperture and high pixel, FNo is less than or equal to 1.75, and visible light and infrared light are confocal. And then the positive and negative focal powers of the lenses are optimally configured, so that the aberration can be effectively corrected. In addition, the image plane height of the fixed focus lens can reach phi 9.1mm, and the fixed focus lens can be adapted to sensors such as 1/1.8 ', 1/2.5 ', 1/2.7 ', and the like, and has wide application prospect and higher market competitiveness. In addition, the fixed focus lens can realize no virtual focus in the temperature range of-40 ℃ to 80 ℃, thereby being applicable to different environments. Image capturing at a maximum field angle of 136 ° can also be achieved. And the total length of the fixed focus lens is less than or equal to 22.60mm (with the protection plate glass CG), so that the volume is smaller. The lens single part and the assembly tolerance are also good, so that the lens single part has good manufacturability.

In the following, the surfaces of the optical elements and the IMAGE plane IMAGE are denoted by S1, S2, …, and SN, respectively, in which the surface of the STOP may be denoted by STO, the IMAGE plane IMAGE may be denoted by IMA, and the bonding surface of the bonding lens group may be denoted by one surface.

The parameters of each embodiment specifically satisfying the above conditional expression are shown in table 1 below:

TABLE 1

In the invention, the plastic aspherical lens satisfies the following formula:

Wherein z is the axial distance from the curved surface to the vertex at the position with the height h perpendicular to the optical axis along the optical axis direction; c represents the curvature at the apex of the aspherical curved surface; k is a conic coefficient; a ₄、A₆、A₈、A₁₀、A₁₂、A₁₄、A₁₆ … represents fourth, sixth, eighth, tenth, fourteen, sixteen, … aspheric coefficients, respectively.

First embodiment

Referring to fig. 1, in the present embodiment, f#:1.65; total lens length: 22.50mm; angle of view: 135 deg..

The relevant parameters of each lens of the fixed focus lens of the present embodiment include the surface type, radius of curvature, thickness, refractive index of material, abbe number, as shown in table 2 below:

Face number	Surface type	R value	Thickness of (L)	Refractive index	Abbe number
						S1	Aspherical surface	5.872	1.16	1.55	55.99
S2	Aspherical surface	2.042	2.83
						S3	Aspherical surface	-3.626	0.98	1.55	55.99
S4	Aspherical surface	-4.971	0.1
						S5	Aspherical surface	6.579	1.03	1.64	23.35
S6	Aspherical surface	17.942	0.36
						S7(STO)	Spherical surface	Infinity	1.02
S8	Spherical surface	19.966	2.18	1.46	90.19
						S9	Spherical surface	-4.02	0.93	1.81	25.48
S10	Spherical surface	-6.425	0.1
						S11	Spherical surface	26.561	2.47	1.46	90.19
S12	Spherical surface	-10.508	0.1
						S13	Aspherical surface	9.023	2.33	1.55	55.99
S14	Aspherical surface	-9.861	0.22
						S15	Aspherical surface	-9.197	0.71	1.64	23.35
S16	Aspherical surface	29.295	4.98
						S17	Spherical surface	Infinity	0.7	1.52	64.2
S18	Spherical surface	Infinity	0.3
						S19(IMA)	Spherical surface	Infinity	-	-	-

TABLE 2

The aspherical coefficients of the respective aspherical lenses in the present embodiment are shown in table 3 below:

TABLE 3 Table 3

Wherein K is the quadric constant of the surface, and A ₄、A₆、A₈、A₁₀、A₁₂、A₁₄ is the aspheric coefficients of fourth order, sixth order, eighth order, tenth order and fourteen order respectively.

As can be seen from fig. 2 to fig. 5, the fixed focus lens of the present embodiment achieves a large target surface while ensuring the characteristics of good image-capturing power, high resolution and small volume; the confocal effect from visible light to infrared part day and night can be realized, and the virtual focus is avoided in the temperature range of-40 ℃ to 80 ℃.

Second embodiment

Referring to fig. 6, in the present embodiment, f#:1.65; total lens length: 19.46mm; angle of view: 135 deg..

The relevant parameters of each lens of the fixed focus lens of the present embodiment include the surface type, radius of curvature, thickness, refractive index of material, abbe number, as shown in table 4 below:

Face number	Surface type	R value	Thickness of (L)	Refractive index	Abbe number
						S1	Aspherical surface	3.066	0.7	1.54	55.99
S2	Aspherical surface	1.665	2.83
						S3	Aspherical surface	-2.815	1.06	1.64	23.53
S4	Aspherical surface	-4.793	0.1
						S5	Aspherical surface	6.422	2.59	1.64	23.53
S6	Aspherical surface	29.579	0.19
						S7(STO)	Spherical surface	9.36	2.61	1.46	90.19
S8	Spherical surface	-3.438	0.69	1.62	36.63
						S9	Spherical surface	-4.851	0.1
S10	Aspherical surface	6.962	2.23	1.54	55.99
						S11	Aspherical surface	-6.16	0.1
S12	Aspherical surface	-5.149	0.76	1.64	23.53
						S13	Aspherical surface	1534.293	4.5
S17	Spherical surface	Infinity	0.7	1.52	64.2
						S18	Spherical surface	Infinity	0.3
S19(IMA)	Spherical surface	Infinity	-	-	-

TABLE 4 Table 4

The aspherical coefficients of the respective aspherical lenses in the present embodiment are shown in table 5 below:

TABLE 5

As can be seen from fig. 7 to fig. 10, the fixed focus lens of the present embodiment achieves a large target surface while ensuring the characteristics of good image-capturing power, high resolution and small volume; the confocal effect from visible light to infrared part day and night can be realized, and the virtual focus is avoided in the temperature range of-40 ℃ to 80 ℃.

Third embodiment

Referring to fig. 11, in the present embodiment, f#:1.74; total lens length: 22.60mm; angle of view: 135.5 deg..

The relevant parameters of each lens of the fixed focus lens of the present embodiment include the surface type, radius of curvature, thickness, refractive index of material, abbe number, as shown in table 6 below:

Face number	Surface type	R value	Thickness of (L)	Refractive index	Abbe number
						S1	Aspherical surface	7.16	1.25	1.54	55.99
S2	Aspherical surface	2.364	2.9
						S3	Aspherical surface	-2.97	1.05	1.54	55.99
S4	Aspherical surface	-4.675	0.1
						S5	Aspherical surface	7.723	1.88	1.64	23.35
S6(STO)	Aspherical surface	38.678	0.06
						S7	Spherical surface	19.838	1.87	1.46	90.19
S8	Spherical surface	-4.309	0.99	1.81	25.48
						S9	Spherical surface	-7.5	0.1
S10	Spherical surface	30.753	2.77	1.50	81.56
						S11	Spherical surface	-9.746	0.1
S12	Aspherical surface	8.173	2.72	1.54	55.99
						S13	Aspherical surface	-8.676	0.06
S14	Aspherical surface	-8.68	0.58	1.64	23.53
						S15	Aspherical surface	40.111	5.17
S16	Spherical surface	Infinity	0.7	1.52	64.2
						S17	Spherical surface	Infinity	0.3
S18(IMA)	Spherical surface	Infinity	-	-	-

TABLE 6

The aspherical coefficients of the respective aspherical lenses in the present embodiment are shown in table 7 below:

TABLE 7

As can be seen from fig. 12 to 15, the fixed focus lens of the present embodiment achieves a large target surface while ensuring the characteristics of good image-capturing power, high resolution and small volume; the confocal effect from visible light to infrared part day and night can be realized, and the virtual focus is avoided in the temperature range of-40 ℃ to 80 ℃.

Fourth embodiment

Referring to fig. 16, in the present embodiment, f#:1.65; total lens length: 22.50mm; angle of view: 130 deg..

The relevant parameters of each lens of the fixed focus lens of the present embodiment include the surface type, radius of curvature, thickness, refractive index of material, abbe number, as shown in table 8 below:

Face number	Surface type	R value	Thickness of (L)	Refractive index	Abbe number
						S1	Aspherical surface	4.398	0.93	1.54	55.99
S2	Aspherical surface	1.99	2.5
						S3	Aspherical surface	-4.055	1.01	1.54	55.99
S4	Aspherical surface	-9.032	0.1
						S5	Aspherical surface	6.414	0.86	1.64	23.4
S6	Aspherical surface	34.903	0.15
						S7(STO)	Spherical surface	39.553	2.61	1.46	90.19
S8	Spherical surface	-4.212	0.7	1.81	25.48
						S9	Spherical surface	-7.488	1
S10	Spherical surface	Infinity	2.82	1.50	81.56
						S11	Spherical surface	-6.144	0.15
S12	Aspherical surface	7.662	2.80	1.54	55.99
						S13	Aspherical surface	-7.737	0.31
S14	Aspherical surface	-7.213	0.58	1.64	23.53
						S15	Aspherical surface	24.33	4.98
S16	Spherical surface	Infinity	0.7	1.52	64.2
						S17	Spherical surface	Infinity	0.3
S18(IMA)	Spherical surface	Infinity	-	-	-

TABLE 8

The aspherical coefficients of the respective aspherical lenses in the present embodiment are shown in table 9 below:

TABLE 9

As can be seen from fig. 17 to fig. 20, the fixed focus lens of the present embodiment achieves a large target surface while ensuring the characteristics of good image-capturing power, high resolution and small volume; the confocal effect from visible light to infrared part day and night can be realized, and the virtual focus is avoided in the temperature range of-40 ℃ to 80 ℃.

Fifth embodiment

Referring to fig. 21, in the present embodiment, f#:1.65; total lens length: 22.08mm; angle of view: 136 deg..

The relevant parameters of each lens of the fixed focus lens of the present embodiment include the surface type, radius of curvature, thickness, refractive index of material, abbe number, as shown in table 10 below:

Table 10

The aspherical coefficients of the respective aspherical lenses in the present embodiment are shown in table 11 below:

TABLE 11

As can be seen from fig. 22 to 25, the fixed focus lens of the present embodiment achieves a large target surface while ensuring the characteristics of good image-capturing power, high resolution and small volume; the confocal effect from visible light to infrared part day and night can be realized, and the virtual focus is avoided in the temperature range of-40 ℃ to 80 ℃.

The above description is only one embodiment of the present invention and is not intended to limit the present invention, and various modifications and variations of the present invention will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A fixed focus lens characterized by comprising a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4), a fifth lens (L5), a sixth lens (L6) and a seventh lens (L7) which are arranged in order from an object side to an image side along an optical axis, wherein the second lens (L2) has negative optical power, and the seventh lens (L7) is a biconvex or paraxial region biconcave lens;

Or further comprising an eighth lens (L8) located on the image side of the seventh lens (L7);

the first lens (L1) has negative power, the third lens (L3) has positive power, the fourth lens (L4) has positive power, the fifth lens (L5) has negative power, the sixth lens (L6) has positive power, and the seventh lens (L7) has positive power; the eighth lens (L8) has negative optical power;

The first lens (L1) is a convex-concave lens, the second lens (L2) is a concave-convex lens, the third lens (L3) is a convex-concave lens, the fourth lens (L4) is a biconvex/plano-convex lens, the fifth lens (L5) is a concave-convex lens, the sixth lens (L6) is a biconvex/plano-convex lens, and the eighth lens (L8) is a paraxial region biconcave lens.

2. The fixed focus lens according to claim 1, wherein the first lens (L1) is an aspherical lens, the second lens (L2) is an aspherical lens, the third lens (L3) is an aspherical lens, the fourth lens (L4) is a spherical lens, the fifth lens (L5) is a spherical lens, the sixth lens (L6) is a spherical lens, the seventh lens (L7) is an aspherical lens, and the eighth lens (L8) is an aspherical lens.

3. The fixed focus lens as claimed in claim 2, wherein the first lens (L1), the second lens (L2), the third lens (L3), the seventh lens (L7) and the eighth lens (L8) are made of plastic.

4. The fixed focus lens according to claim 1, wherein the first lens (L1) has negative optical power, the third lens (L3) has positive optical power, the fourth lens (L4) has positive optical power, the fifth lens (L5) has negative optical power, the sixth lens (L6) has positive optical power, and the seventh lens (L7) has negative optical power.

5. The fixed focus lens as claimed in claim 4, wherein said first lens (L1) is a convex-concave type lens, said second lens (L2) is a convex-concave type lens, said third lens (L3) is a convex-concave type lens, said fourth lens (L4) is a biconvex type lens, said fifth lens (L5) is a convex-concave type lens, and said sixth lens (L6) is a biconvex type lens.

6. The fixed focus lens of claim 4, wherein the first lens (L1) is an aspherical lens, the second lens (L2) is an aspherical lens, the third lens (L3) is an aspherical lens, the fourth lens (L4) is a spherical lens, the fifth lens (L5) is a spherical lens, the sixth lens (L6) is an aspherical lens, and the seventh lens (L7) is an aspherical lens.

7. A fixed focus lens as claimed in claim 1, characterized in that the fourth lens (L4) is cemented with the fifth lens (L5) to form a cemented lens group with positive optical power.

8. The fixed focus lens according to claim 1, further comprising a STOP (STOP) disposed on an image side of the third lens (L3), between the third lens (L3) and the fourth lens (L4), or on an object side of the fourth lens (L4).

9. The fixed focus lens according to any one of claims 1-8, characterized in that the effective focal length f of the fixed focus lens and the effective focal length f1 of the first lens (L1) satisfy the following relation: -2.ltoreq.f1-f is less than or equal to-1.3.

10. The fixed focus lens according to any one of claims 1-8, characterized in that the effective focal length f of the fixed focus lens and the effective focal length f2 of the second lens (L2) satisfy the following relation: -8.ltoreq.f2-f is less than or equal to-1.7.

11. The fixed focus lens according to any one of claims 1-8, characterized in that the effective focal length f of the fixed focus lens and the effective focal length f4 of the fourth lens (L4) satisfy the following relationship: 1.1.ltoreq.f4-f is less than or equal to 2.2.

12. The fixed focus lens according to any one of claims 1-8, characterized in that the effective focal length f of the fixed focus lens and the effective focal length f5 of the fifth lens (L5) satisfy the following relationship: -5.8.ltoreq.f5 ∈ -f is less than or equal to-2.0.

13. The fixed focus lens according to any one of claims 1-8, characterized in that the effective focal length f of the fixed focus lens and the effective focal length f6 of the sixth lens (L6) satisfy the following relationship: 1.ltoreq.f6? f is less than or equal to 4.

14. The fixed focus lens of any one of claims 1-8, wherein the Fno number and effective focal length f of the fixed focus lens satisfy the following relationship: fno/f is less than or equal to 0.4.

15. The fixed focus lens of any one of claims 1-8, wherein the effective focal length f and half image height h of the fixed focus lens satisfy the following relationship: f/h is less than or equal to 1.2.

16. The fixed focus lens of any one of claims 1-8, wherein the effective focal length f and the total length TTL of the fixed focus lens satisfy the following relationship: f/TTL is less than or equal to 0.25.

17. The fixed focus lens of any one of claims 1-8, wherein the total length TTL, the maximum total image height H and the maximum field angle DFOV of the fixed focus lens satisfy the following relationship: TTL/H/DFOV is less than or equal to 0.02.

18. The fixed focus lens according to any one of claims 1-8, wherein the first lens (L1) object side maximum light transmission aperture D, the maximum total image height H of the fixed focus lens and the total length TTL of the fixed focus lens satisfy the following relationship: D/TTL/H is less than or equal to 4.3.

19. The fixed focus lens according to any one of claims 1-8, wherein the relative refractive index temperature coefficient dn/dt of at least one of the fourth lens (L4), the fifth lens (L5) and the sixth lens (L6) satisfies the following condition: dn/dt is less than or equal to 3.

20. The fixed focus lens of any one of claims 1-8, wherein the material of at least one lens is low dispersion glass, and the abbe number VD satisfies the following condition: VD is more than or equal to 60.