CN215575891U

CN215575891U - Security lens

Info

Publication number: CN215575891U
Application number: CN202121285322.7U
Authority: CN
Inventors: 何明可; 程嘉健; 梁伟朝
Original assignee: Sunny Optics Zhongshan Co Ltd
Current assignee: Sunny Optics Zhongshan Co Ltd
Priority date: 2021-06-09
Filing date: 2021-06-09
Publication date: 2022-01-18
Anticipated expiration: 2031-06-09

Abstract

The utility model relates to a security lens, which comprises a first lens (L1) with negative focal power, a diaphragm (STO), a second lens (L2) with positive focal power, a third lens (L3) with positive focal power and a fourth lens (L4) with negative focal power, wherein the first lens (L1), the diaphragm (STO), the third lens (L3526) with positive focal power and the fourth lens (L4) with negative focal power are sequentially arranged from an object side to an image side along an optical axis. The security lens has the advantages of low cost, simple structure, small volume, no virtual focus in the temperature range of-40-80 ℃, infrared performance and dual-purpose use for day and night.

Description

Security lens

Technical Field

The utility model relates to the technical field of optical imaging, in particular to a security lens.

Background

Along with the popularization of work in the fields of security protection and public safety, the requirement for monitoring the fixed-focus lens is increasing day by day, the lower the cost of the lens is while ensuring the performance of the lens, the simpler and more reasonable the structure is, the more mass production can be realized, and the increasing security protection requirement can be met. The cost of the lens is closely related to the material of the lens and the structure of the lens, and the lenses of many lenses in the prior art are special in material selection, large in processing difficulty and complex in lens structure, so that the material cost and the processing cost of the lens are difficult to control, and the popularization of related lenses is not facilitated. Therefore, how to reduce the cost while ensuring the performance of the lens is a technical problem that needs to be solved urgently for monitoring the lens.

SUMMERY OF THE UTILITY MODEL

The utility model aims to solve the problems and provides a security lens.

In order to achieve the above object, the present invention provides a security lens, which includes a first lens with negative focal power, a diaphragm, a second lens with positive focal power, a third lens with positive focal power, and a fourth lens with negative focal power, which are arranged in order from an object side to an image side along an optical axis.

According to an aspect of the present invention, the first lens is a convex-concave aspheric lens, the second lens is a biconvex spherical lens, the third lens is a biconvex aspheric lens, and the fourth lens is a concave-convex aspheric lens.

According to an aspect of the utility model, the first lens element, the third lens element and the fourth lens element are made of plastic.

According to one aspect of the utility model, the lens further comprises a flat glass positioned on the image side of the fourth lens.

According to one aspect of the utility model, the effective focal length f3 of the third lens and the effective focal length f of the security lens satisfy the following relation: f3/f is more than or equal to 0.55 and less than or equal to 1.6.

According to one aspect of the utility model, the effective focal length f4 of the fourth lens and the effective focal length f of the security lens satisfy the following relation: f4/f is not less than-4.5 and not more than-0.8.

According to an aspect of the utility model, the effective focal length f1 of the first lens and the effective focal length f4 of the fourth lens satisfy the following relationship: f1/f4 is more than or equal to 0 and less than or equal to 1.5.

According to an aspect of the utility model, the effective focal length f3 of the third lens and the effective focal length f4 of the fourth lens satisfy the following relationship: f3/f4 is not less than 0.9 and not more than 0.3.

According to an aspect of the utility model, the effective focal length f2 of the second lens and the combined focal length f12 of the first and second lenses satisfy the following relationship: the absolute value of f2/f12 is more than or equal to 0.45 and less than or equal to 0.7.

According to an aspect of the utility model, the effective focal length f4 of the fourth lens and the combined focal length f34 of the third and fourth lenses satisfy the following relationship: the absolute value of f4/f34 is more than or equal to 0.35 and less than or equal to 1.65.

According to an aspect of the present invention, a center thickness T3 of the third lens on an optical axis and a distance T34 of an object-side surface of the third lens to an image-side surface of the fourth lens on the optical axis satisfy the following relationship: T3/T34 is more than or equal to 0.5 and less than or equal to 0.85.

According to an aspect of the present invention, the effective focal length f1 of the first lens, the object side radius of curvature R1 of the first lens, and the image side radius of curvature R2 of the first lens satisfy the following relationship: 1.25 | (R1+ R2)/f1| is less than or equal to 20.5.

According to one aspect of the utility model, the Fno number of the security lens meets the following condition: fno is less than or equal to 2.4.

According to one aspect of the utility model, the chief ray angle CRA of the maximum field of view of the security lens satisfies the following condition: CRA is less than or equal to 16.5 degrees.

According to one aspect of the utility model, at least one lens is made of low dispersion glass, and the abbe number VD satisfies the following condition: VD is more than or equal to 55.

According to the scheme provided by the utility model, the day and night prime glass-plastic mixed security lens is low in cost, simple in structure, small in size, free of virtual focus within the temperature range of-40-80 ℃ and provided with infrared performance. According to one scheme of the utility model, the security lens is provided with four lenses, and the cost of the security lens can be lower by reasonably designing the focal power and the concave-convex property of each lens and selecting proper materials.

According to one scheme of the utility model, the system tolerance can be effectively adjusted and the sensitivity of the system tolerance is reduced by reasonably setting the relationship between the effective focal lengths of the lenses.

According to one scheme of the utility model, the thickness relationship of the third lens and the fourth lens, the relationship between the effective focal length of the first lens and the curvature radiuses of the two side surfaces of the first lens, the Fno number of the lens and the chief ray angle of the maximum field of view are properly set to meet a certain condition, and the Abbe number of at least one lens in the lens is larger than a certain numerical value, so that chromatic aberration correction and confocal of visible light and infrared light are facilitated, and high-temperature and low-temperature non-virtual focus is realized.

Drawings

Fig. 1 is a schematic diagram illustrating a structure of a security lens according to an embodiment of the present invention;

fig. 2 schematically shows an MTF chart of a security lens according to a first embodiment of the present invention;

FIG. 3 is a Through-Focus-MTF diagram schematically illustrating a frequency of a security lens of 125lp/mm according to a first embodiment of the present invention;

FIG. 4 is a Through-Focus-MTF diagram schematically illustrating a frequency of 125lp/mm at 80 ℃ for a security lens according to a first embodiment of the present invention;

FIG. 5 is a Through-Focus-MTF diagram schematically illustrating a low-temperature-40 ℃ frequency of a security lens according to a first embodiment of the present invention, wherein the frequency of the low-temperature-40 ℃ frequency is 125 lp/mm;

fig. 6 schematically shows an MTF chart of a security lens according to a second embodiment of the present invention;

FIG. 7 is a Through-Focus-MTF diagram schematically illustrating a frequency of a security lens of 125lp/mm according to a second embodiment of the present invention;

FIG. 8 is a Through-Focus-MTF diagram schematically illustrating a frequency of 125lp/mm at 80 ℃ for a security lens according to a second embodiment of the present invention;

FIG. 9 is a Through-Focus-MTF diagram schematically illustrating a low-temperature-40 ℃ frequency of a security lens according to a second embodiment of the present invention, wherein the frequency of the low-temperature-40 ℃ frequency is 125 lp/mm;

fig. 10 schematically shows an MTF chart of a security lens according to a third embodiment of the present invention;

FIG. 11 is a Through-Focus-MTF diagram schematically illustrating a frequency of a security lens of 125lp/mm according to a third embodiment of the present invention;

FIG. 12 is a Through-Focus-MTF diagram schematically illustrating a frequency of 125lp/mm at 80 ℃ for a security lens according to a third embodiment of the present invention;

FIG. 13 is a Through-Focus-MTF diagram schematically illustrating a low temperature-40 ℃ frequency of a security lens according to a third embodiment of the present invention, wherein the frequency of the Through-Focus-MTF diagram is 125 lp/mm;

fig. 14 is a MTF diagram schematically showing a security lens according to a fourth embodiment of the present invention;

FIG. 15 is a Through-Focus-MTF diagram schematically illustrating a fourth embodiment of the present invention, wherein the frequency of the security lens is 125 lp/mm;

FIG. 16 is a Through-Focus-MTF diagram schematically illustrating a frequency of 125lp/mm at 80 ℃ for a security lens according to a fourth embodiment of the present invention;

FIG. 17 is a Through-Focus-MTF diagram schematically illustrating a low temperature-40 ℃ frequency of a security lens according to a fourth embodiment of the present invention, wherein the frequency of the Through-Focus-MTF diagram is 125 lp/mm;

fig. 18 is an MTF diagram schematically illustrating a security lens according to a fifth embodiment of the present invention;

FIG. 19 is a Through-Focus-MTF diagram schematically illustrating a fifth embodiment of the present invention, wherein the frequency of the security lens is 125 lp/mm;

FIG. 20 is a Through-Focus-MTF diagram schematically illustrating a frequency of 125lp/mm at 80 ℃ for a security lens according to a fifth embodiment of the present invention;

FIG. 21 is a Through-Focus-MTF diagram schematically illustrating a low temperature-40 ℃ frequency of a security lens according to a fifth embodiment of the present invention, wherein the frequency of the low temperature-40 ℃ frequency is 125 lp/mm.

Detailed Description

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments will be briefly described below. It is obvious that the drawings in the following description are only some embodiments of the utility model, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.

In describing embodiments of the present invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer" are used in an orientation or positional relationship that is illustrated in the associated drawings for convenience and simplicity of description only, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus are not to be considered limiting of the present invention.

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

Referring to fig. 1, the security lens of the present invention includes a first lens L1 having negative power, a stop STO, a second lens L2 having positive power, a third lens L3 having positive power, and a fourth lens L4 having negative power, which are arranged in order from an object side to an image side along an optical axis. Of course, a protective plate glass CG is included and located on the image side of the fourth lens L4. In the present invention, the first lens L1 is a convex-concave aspheric lens, the second lens L2 is a biconvex spherical lens, the third lens L3 is a biconvex aspheric lens, and the fourth lens L4 is a concave-convex aspheric lens. The first lens element L1, the third lens element L3 and the fourth lens element L4 are made of plastic. Therefore, the security lens is low in cost, simple in structure and small in size.

In the utility model, the effective focal length f3 of the third lens L3 and the effective focal length f of the security lens satisfy the following relationship: f3/f is more than or equal to 0.55 and less than or equal to 1.6. The effective focal length f4 of the fourth lens L4 and the effective focal length f of the security lens satisfy the following relationship: f4/f is not less than-4.5 and not more than-0.8. The effective focal length f1 of the first lens L1 and the effective focal length f4 of the fourth lens L4 satisfy the following relationship: f1/f4 is more than or equal to 0 and less than or equal to 1.5. The effective focal length f3 of the third lens L3 and the effective focal length f4 of the fourth lens L4 satisfy the following relationship: f3/f4 is not less than 0.9 and not more than 0.3. The effective focal length f2 of the second lens L2 and the combined focal length f12 of the first lens L1 and the second lens L2 satisfy the following relationship: the absolute value of f2/f12 is more than or equal to 0.45 and less than or equal to 0.7. The effective focal length f4 of the fourth lens L4 and the combined focal length f34 of the third lens L3 and the fourth lens L4 satisfy the following relationship: the absolute value of f4/f34 is more than or equal to 0.35 and less than or equal to 1.65. The above arrangement is satisfied, which is beneficial to adjusting the tolerance of the system and reducing the sensitivity of the tolerance of the system.

In the present invention, the center thickness T3 of the third lens L3 on the optical axis and the distance T34 on the optical axis from the object-side surface of the third lens L3 to the image-side surface of the fourth lens L4 satisfy the following relationship: T3/T34 is more than or equal to 0.5 and less than or equal to 0.85. The effective focal length f1 of the first lens L1, the object-side radius of curvature R1 of the first lens L1, and the image-side radius of curvature R2 of the first lens L1 satisfy the following relationships: 1.25 | (R1+ R2)/f1| is less than or equal to 20.5. The Fno number of the security lens meets the following conditions: fno is less than or equal to 2.4. The chief ray angle CRA of the maximum view field of the security lens meets the following conditions: CRA is less than or equal to 16.5 degrees. At least one lens in the security lens is made of low dispersion glass, and the Abbe number VD meets the following conditions: VD is more than or equal to 55. The requirement of the above formula is favorable for chromatic aberration correction, confocal visible light and infrared light and no virtual focus at high and low temperatures.

The security lens has the advantages that the arrangement is met, the low-cost mass production can be realized, the material selection price is low, the structure is simple, the assembly difficulty is low, the first lens, the third lens and the fourth lens are plastic aspheric lenses, and the production cost of the security lens is reduced. The aberration is effectively corrected by optimally configuring the positive and negative focal powers of the respective lenses. In addition, the image plane height of the security lens can reach phi 6.6mm, the CRA is less than or equal to 16.1 degrees, the security lens can be adapted to multiple sensors, the application prospect is wide, and the market competitiveness is improved. In addition, the lens overcomes the defect that the plastic aspheric lens is easy to cause focus drift in high and low temperature environments due to large expansion coefficient, can realize no virtual focus in the temperature range of minus 40 ℃ to 80 ℃, and is suitable for different environments. The function of confocal of infrared light and visible light and the image capture of the maximum field angle of 102.2 degrees can be realized. The total length of the lens is less than or equal to 30mm (excluding the protection plate glass), the volume is small, the single part and the assembly tolerance are good, and the manufacturability is good.

The security lens of the present invention will be specifically described below in five embodiments. In the following embodiments, the surfaces of the lenses and the plate glass CG are represented by S1, S2,. and SN, and include an object plane OBJ, a stop STO, and an image plane IMA. The aspherical formula is as follows:

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

TABLE 1

First embodiment

In this embodiment, each parameter of the security lens is F #: 2.05; total lens length: 21.9023 mm; the field angle: 102 deg.

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

number of noodles	Surface type	R value	Thickness of	Refractive index	Abbe number
						S0(OBJ)	Spherical surface	Infinity	Infinity
S1	Aspherical surface	8.0000	1.4228	1.55	56.1
						S2	Aspherical surface	2.0255	5.2626
S3(STO)	Spherical surface	30.0300	3.0003	1.60	55.3
						S4	Spherical surface	-6.9784	3.1627
S5	Aspherical surface	4.9900	1.8151	1.55	56.5
						S6	Aspherical surface	-2.7005	0.0964
S7	Aspherical surface	-2.3441	1.3429	1.60	23.0
						S8	Aspherical surface	-8.9847	2.6169
S9	Spherical surface	Infinity	0.8000	1.50	62.0
						S10	Spherical surface	Infinity	2.3826
S11(IMA)	Spherical surface	Infinity	-	-	-

TABLE 2

The aspherical surface coefficients of the aspherical lenses in this embodiment are shown in table 3 below:

TABLE 3

Where K is the conic constant of the surface, and A, B, C, D, E, F are aspheric coefficients of fourth, sixth, eighth, tenth, twelfth, and fourteenth orders, respectively.

As can be seen from fig. 2 to 5, the security lens of the embodiment can achieve low-cost mass production, has low material selection price, simple structure and low assembly difficulty, and the first lens, the third lens and the fourth lens are aspheric lenses made of plastic materials, so that the production cost is reduced. The aberration is effectively corrected by optimally configuring the positive and negative focal powers of the respective lenses. In addition, the image plane height of the security lens can reach phi 6.6mm, the CRA is smaller than or equal to 16.1 degrees, the security lens can be adapted to multiple sensors, the application prospect is wide, and the market competitiveness is improved. In addition, the lens overcomes the defect that the plastic aspheric lens is easy to cause focus drift in high and low temperature environments due to large expansion coefficient, can realize no virtual focus in the temperature range of minus 40 ℃ to 80 ℃, and is suitable for different environments. The function of confocal of infrared light and visible light and the image capture of the maximum field angle of 102.2 degrees can be realized. The total length of the lens is less than or equal to 30mm (excluding the protection plate glass), the volume is small, the single part and the assembly tolerance are good, and the manufacturability is good.

Second embodiment

In this embodiment, each parameter of the security lens is F #: 2.2; total lens length: 22.3449 mm; the field angle: 102 deg.

Relevant parameters of the lens of the security lens of the embodiment include a surface type, a curvature radius, a thickness, a refractive index of a material, and an abbe number, as shown in table 4 below:

number of noodles	Surface type	R value	Thickness of	Refractive index	Abbe number
						S0(OBJ)	Spherical surface	Infinity	Infinity
S1	Aspherical surface	10.2354	1.0026	1.55	56.1
						S2	Aspherical surface	2.1455	5.9857
S3(STO)	Spherical surface	12.0773	3.7734	1.60	55.3
						S4	Spherical surface	-9.7656	2.9605
S5	Aspherical surface	5.3248	2.5107	1.55	56.5
						S6	Aspherical surface	-1.8997	0.0774
S7	Aspherical surface	-1.6798	0.5682	1.60	23.0
						S8	Aspherical surface	-6.4185	2.2830
S9	Spherical surface	Infinity	0.8000	1.50	62.0
						S10	Spherical surface	Infinity	2.3834
S11(IMA)	Spherical surface	Infinity	-	-	-

TABLE 4

The aspherical surface coefficients of the aspherical lenses in this embodiment are shown in table 5 below:

TABLE 5

As can be seen from fig. 6 to 9, the security lens of the embodiment can achieve low-cost mass production, has low material selection price, simple structure and low assembly difficulty, and the first lens, the third lens and the fourth lens are aspheric lenses made of plastic materials, so that the production cost is reduced. The aberration is effectively corrected by optimally configuring the positive and negative focal powers of the respective lenses. In addition, the image plane height of the security lens can reach phi 6.6mm, the CRA is smaller than or equal to 16.1 degrees, the security lens can be adapted to multiple sensors, the application prospect is wide, and the market competitiveness is improved. In addition, the lens overcomes the defect that the plastic aspheric lens is easy to cause focus drift in high and low temperature environments due to large expansion coefficient, can realize no virtual focus in the temperature range of minus 40 ℃ to 80 ℃, and is suitable for different environments. The function of confocal of infrared light and visible light and the image capture of the maximum field angle of 102.2 degrees can be realized. The total length of the lens is less than or equal to 30mm (excluding the protection plate glass), the volume is small, the single part and the assembly tolerance are good, and the manufacturability is good.

Third embodiment

In this embodiment, each parameter of the security lens is F #: 2.1; total lens length: 22.1031 mm; the field angle: 102 deg.

Relevant parameters of the lens of the security lens of the embodiment include a surface type, a curvature radius, a thickness, a refractive index of a material, and an abbe number, as shown in the following table 6:

number of noodles	Surface type	R value	Thickness of	Refractive index	Abbe number
						S0(OBJ)	Spherical surface	Infinity	Infinity
S1	Aspherical surface	108.0370	0.5920	1.55	56.1
						S2	Aspherical surface	2.8789	5.1421
S3(STO)	Spherical surface	36.7331	3.0094	1.60	55.3
						S4	Spherical surface	-7.0439	3.8262
S5	Aspherical surface	5.1549	2.8887	1.55	56.5
						S6	Aspherical surface	-3.2353	0.0975
S7	Aspherical surface	-2.5021	0.7387	1.60	23.0
						S8	Aspherical surface	-7.7278	2.6359
S9	Spherical surface	Infinity	0.8000	1.50	62.0
						S10	Spherical surface	Infinity	2.3726
S11(IMA)	Spherical surface	Infinity	-	-	-

TABLE 6

The aspherical surface coefficients of the aspherical lenses in this embodiment are shown in table 7 below:

TABLE 7

As can be seen from fig. 10 to 13, the security lens of the present embodiment can achieve low-cost mass production, has low material selection price, simple structure and low assembly difficulty, and the first lens, the third lens and the fourth lens are aspheric lenses made of plastic materials, thereby reducing the production cost. The aberration is effectively corrected by optimally configuring the positive and negative focal powers of the respective lenses. In addition, the image plane height of the security lens can reach phi 6.6mm, the CRA is smaller than or equal to 16.1 degrees, the security lens can be adapted to multiple sensors, the application prospect is wide, and the market competitiveness is improved. In addition, the lens overcomes the defect that the plastic aspheric lens is easy to cause focus drift in high and low temperature environments due to large expansion coefficient, can realize no virtual focus in the temperature range of minus 40 ℃ to 80 ℃, and is suitable for different environments. The function of confocal of infrared light and visible light and the image capture of the maximum field angle of 102.2 degrees can be realized. The total length of the lens is less than or equal to 30mm (excluding the protection plate glass), the volume is small, the single part and the assembly tolerance are good, and the manufacturability is good.

Fourth embodiment

In this embodiment, each parameter of the security lens is F #: 2.4; total lens length: 21.7823 mm; the field angle: 102 deg.

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

TABLE 8

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

TABLE 9

As can be seen from fig. 14 to 17, the security lens of the embodiment can be manufactured in a low-cost manner, has a low material selection price, a simple structure, and a low assembly difficulty, and the first lens, the third lens, and the fourth lens are plastic aspheric lenses, so that the manufacturing cost is reduced. The aberration is effectively corrected by optimally configuring the positive and negative focal powers of the respective lenses. In addition, the image plane height of the security lens can reach phi 6.6mm, the CRA is smaller than or equal to 16.1 degrees, the security lens can be adapted to multiple sensors, the application prospect is wide, and the market competitiveness is improved. In addition, the lens overcomes the defect that the plastic aspheric lens is easy to cause focus drift in high and low temperature environments due to large expansion coefficient, can realize no virtual focus in the temperature range of minus 40 ℃ to 80 ℃, and is suitable for different environments. The function of confocal of infrared light and visible light and the image capture of the maximum field angle of 102.2 degrees can be realized. The total length of the lens is less than or equal to 30mm (excluding the protection plate glass), the volume is small, the single part and the assembly tolerance are good, and the manufacturability is good.

Fifth embodiment

In this embodiment, each parameter of the security lens is F #: 2.3; total lens length: 22.1042 mm; the field angle: 102 deg.

The relevant parameters of the lens of the security lens of the embodiment include surface type, curvature radius, thickness, refractive index of the material, and abbe number, as shown in the following table 10:

watch 10

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

TABLE 11

As can be seen from fig. 18 to 21, the security lens of the present embodiment can achieve low-cost mass production, has low material selection price, simple structure and low assembly difficulty, and the first lens, the third lens and the fourth lens are aspheric lenses made of plastic materials, thereby reducing the production cost. The aberration is effectively corrected by optimally configuring the positive and negative focal powers of the respective lenses. In addition, the image plane height of the security lens can reach phi 6.6mm, the CRA is smaller than or equal to 16.1 degrees, the security lens can be adapted to multiple sensors, the application prospect is wide, and the market competitiveness is improved. In addition, the lens overcomes the defect that the plastic aspheric lens is easy to cause focus drift in high and low temperature environments due to large expansion coefficient, can realize no virtual focus in the temperature range of minus 40 ℃ to 80 ℃, and is suitable for different environments. The function of confocal of infrared light and visible light and the image capture of the maximum field angle of 102.2 degrees can be realized. The total length of the lens is less than or equal to 30mm (excluding the protection plate glass), the volume is small, the single part and the assembly tolerance are good, and the manufacturability is good.

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

Claims

1. A security lens includes, in order from an object side to an image side along an optical axis, a first lens (L1) having negative power, a Stop (STO), a second lens (L2) having positive power, a third lens (L3) having positive power, and a fourth lens (L4) having negative power.

2. The security lens according to claim 1, wherein the first lens (L1) is a convex-concave aspheric lens, the second lens (L2) is a biconvex spherical lens, the third lens (L3) is a biconvex aspheric lens, and the fourth lens (L4) is a concave-convex aspheric lens.

3. The security lens of claim 1, wherein the first lens (L1), the third lens (L3) and the fourth lens (L4) are made of plastic.

4. The security lens according to any one of claims 1 to 3, wherein an effective focal length f3 of the third lens (L3) and an effective focal length f of the security lens satisfy the following relationship: f3/f is more than or equal to 0.55 and less than or equal to 1.6.

5. The security lens according to any one of claims 1 to 3, wherein an effective focal length f4 of the fourth lens (L4) and an effective focal length f of the security lens satisfy the following relationship: f4/f is not less than-4.5 and not more than-0.8.

6. A security lens according to any of claims 1 to 3, characterized in that the effective focal length f1 of the first lens (L1) and the effective focal length f4 of the fourth lens (L4) satisfy the following relationship: f1/f4 is more than or equal to 0 and less than or equal to 1.5.

7. A security lens according to any of claims 1 to 3, characterized in that the effective focal length f3 of the third lens (L3) and the effective focal length f4 of the fourth lens (L4) satisfy the following relationship: f3/f4 is not less than 0.9 and not more than 0.3.

8. A security lens according to any of claims 1 to 3, characterized in that the effective focal length f2 of the second lens (L2) and the combined focal length f12 of the first lens (L1) and the second lens (L2) satisfy the following relationship: the absolute value of f2/f12 is more than or equal to 0.45 and less than or equal to 0.7.

9. A security lens according to any of claims 1 to 3, characterized in that the effective focal length f4 of the fourth lens (L4) and the combined focal length f34 of the third lens (L3) and the fourth lens (L4) satisfy the following relationship: the absolute value of f4/f34 is more than or equal to 0.35 and less than or equal to 1.65.

10. A security lens according to any one of claims 1 to 3, wherein the central thickness T3 of the third lens (L3) on the optical axis and the distance T34 on the optical axis from the object side surface of the third lens (L3) to the image side surface of the fourth lens (L4) satisfy the following relationship: T3/T34 is more than or equal to 0.5 and less than or equal to 0.85.

11. A security lens according to any of claims 1 to 3, characterized in that the effective focal length f1 of the first lens (L1), the radius of curvature R1 of the object side of the first lens (L1) and the radius of curvature R2 of the image side of the first lens (L1) satisfy the following relations: 1.25 | (R1+ R2)/f1| is less than or equal to 20.5.

12. The security lens according to any one of claims 1 to 3, wherein the Fno number of the security lens satisfies the following condition: fno is less than or equal to 2.4.

13. The security lens according to any one of claims 1 to 3, wherein a Chief Ray Angle (CRA) of a maximum field of view of the security lens satisfies the following condition: CRA is less than or equal to 16.5 degrees.

14. The security lens according to any one of claims 1 to 3, wherein at least one lens is made of low dispersion glass, and an Abbe number VD satisfies the following conditions: VD is more than or equal to 55.