CN110542993A

CN110542993A - Fixed focus lens

Info

Publication number: CN110542993A
Application number: CN201910849143.2A
Authority: CN
Inventors: 张品光; 李泽民; 何剑炜
Original assignee: Dongguan Yutong Optical Technology Co Ltd
Current assignee: Dongguan Yutong Optical Technology Co Ltd
Priority date: 2019-09-09
Filing date: 2019-09-09
Publication date: 2019-12-06

Abstract

The embodiment of the invention discloses a fixed-focus lens. The fixed-focus lens comprises a first lens with negative focal power, a second lens with positive focal power, a third lens with positive focal power and a fourth lens with negative focal power which are sequentially arranged from an object side to an image side along an optical axis; the first lens to the fourth lens are all plastic aspheric lenses; the third lens and the fourth lens constitute a cemented lens. According to the technical scheme of the embodiment of the invention, an optical structure of four plastic lenses is adopted, the aberration of the plastic aspheric lens is fully utilized, the high-low temperature compensation and infrared confocal are realized by utilizing the cemented lens, the resolution of 4 million pixels can be reached under visible light and infrared light on the premise of F2.0, and meanwhile, the lens does not focus at the ambient temperature of-10-60 ℃, so that the optical lens has the advantages of low cost, excellent performance, small volume and light weight.

Description

Fixed focus lens

Technical Field

The embodiment of the invention relates to a lens technology, in particular to a fixed-focus lens.

Background

with the development and progress of science and technology, various electronic components are developed towards miniaturization and integration, which makes miniaturization and portability of many electronic products possible. The same is true for security monitoring cameras, the smaller the camera volume is, the better the convenience of installation is, the lower the requirements on installation environment are, and meanwhile, the camera cost is also reduced. These all contribute to the popularization of security monitoring camera. Such a trend creates three major challenges for the design and manufacture of security lenses.

First, the camera is to be made small, and then the lens must also be made small, under the prerequisite of guaranteeing the camera lens image quality, make the camera lens size small, all very high to design, manufacturing and assembly requirement. Secondly, the heat released by the highly integrated camera chip cannot be dissipated in time in a narrow camera, the temperature of the camera chip can reach 80 ℃ at most when the camera chip is in a working state, and a common camera manufacturer is at the normal temperature of 25 ℃ when a lens is installed and debugged; therefore, the difference between the environment temperature and the installation and debugging time in the actual use process is too large, and if the lens has no compensation function aiming at temperature change, the display picture of the camera is blurred in the use process, so that the camera cannot be normally used. Thirdly, in consideration of cost, the cost of the camera needs to be reduced, the cost of the lens also needs to be reduced, the conventional security lens is usually a structure that a glass lens and a plastic lens are matched, and the use of the glass lens needs to be reduced in order to reduce the cost, so that great challenges are provided for ensuring the performances such as lens transmittance, high and low temperature defocusing and the like.

Disclosure of Invention

the embodiment of the invention provides a fixed-focus lens, which adopts an optical structure of four plastic lenses, fully utilizes the aberration elimination of the plastic aspheric lens, utilizes a cemented lens to realize high-low temperature compensation and infrared confocal, can reach 4 million pixels of resolution under visible light and infrared light on the premise of F2.0, simultaneously has no focus leakage of the lens under the state of ambient temperature of-10-60 ℃, and has the advantages of low cost, excellent performance, small volume and light weight.

the embodiment of the invention provides a fixed-focus lens, which comprises a first lens with negative focal power, a second lens with positive focal power, a third lens with positive focal power and a fourth lens with negative focal power, wherein the first lens, the second lens, the third lens and the fourth lens are sequentially arranged from an object space to an image space along an optical axis;

the first lens to the fourth lens are all plastic aspheric lenses;

The third lens and the fourth lens constitute a cemented lens.

Optionally, focal lengths of the first lens to the fourth lens satisfy the following relation:

0.8<︱f1/f2︱<1.3；

0.8<︱f3/f4︱<1.3；

wherein f 1-f 4 respectively represent focal lengths of the first lens to the fourth lens.

optionally, the first lens to the fourth lens satisfy the following parameters:

f1＝-8.2～-10.8	n1＝1.45～1.65	R1＝3.5～4.3	R2＝1.5～2.8
				f2＝9.5～11.5	n2＝1.45～1.65	R3＝-22.6～-28.2	R4＝-4.5～-6.0
f3＝3.2～4.6	n3＝1.45～1.65	R5＝4.1～5.2	R6＝-2.3～-3.5
				f4＝-3.2～-10.6	n4＝1.45～1.65	R7＝-2.3～-3.5	R8＝-160～-220.5

wherein f1 to f4 represent focal lengths of the first lens to the fourth lens in mm, n1 to n4 represent refractive indices of the first lens to the fourth lens, R1, R3, R5, and R7 represent radii of curvature of the first lens to the fourth lens toward the center of the object side surface, respectively, and R2, R4, R6, and R8 represent radii of curvature of the first lens to the fourth lens toward the center of the image side surface, respectively, in mm, and "-" represents a negative direction.

Optionally, the optical module further includes a diaphragm disposed between the first lens and the second lens.

Optionally, the first lens is a meniscus lens, the second lens is a barrel lens, the third lens is a biconvex lens, and the fourth lens is a meniscus lens.

Optionally, the first lens and the second lens are tightly fitted through a spacer, and the second lens and the third lens are tightly fitted through a spacer.

Optionally, the surface type of the plastic aspheric lens satisfies the formula:

Where z represents a distance vector from the vertex of the aspherical surface when the height of the aspherical surface in the optical axis direction is y, r represents a curvature radius of the center of the surface profile, k represents a conic coefficient, and A, B, C, D, E, F represents a high-order aspherical coefficient.

Optionally, the aperture F of the fixed-focus lens is greater than or equal to 2.0.

optionally, the total length of the fixed-focus lens is less than 23 mm.

The fixed focus lens provided by the embodiment of the invention comprises a first lens with negative focal power, a second lens with positive focal power, a third lens with positive focal power and a fourth lens with negative focal power, which are sequentially arranged from an object space to an image space along an optical axis; the first lens to the fourth lens are all plastic aspheric lenses; the third lens and the fourth lens constitute a cemented lens. By adopting the optical structure of four plastic lenses, the plastic aspheric lens has smaller quality and lower cost and has good aberration eliminating capability; the third lens and the fourth lens are arranged to form the cemented lens, so that high-low temperature compensation and infrared confocal are realized, 4 million pixel resolution can be achieved under visible light and infrared light on the premise of F2.0 by matching focal power of the lenses, and the lens does not leak focus under the state of ambient temperature of-10-60 ℃, so that the infrared confocal imaging lens has the advantages of low cost, excellent performance, small size and light weight.

Drawings

Fig. 1 is a schematic structural diagram of a fixed focus lens according to an embodiment of the present invention;

Fig. 2 is a schematic diagram of an MTF curve of a modulation transfer function of visible light according to an embodiment of the present invention;

Fig. 3 is a schematic diagram of MTF curves of infrared light provided by an embodiment of the invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.

The terminology used in the embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. It should be noted that the terms "upper", "lower", "left", "right", and the like used in the description of the embodiments of the present invention are used in the angle shown in the drawings, and should not be construed as limiting the embodiments of the present invention. In addition, in this context, it is also to be understood that when an element is referred to as being "on" or "under" another element, it can be directly formed on "or" under "the other element or be indirectly formed on" or "under" the other element through an intermediate element. The terms "first," "second," and the like, are used for descriptive purposes only and not for purposes of limitation, and do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

Fig. 1 is a schematic structural diagram of a fixed focus lens according to an embodiment of the present invention. Referring to fig. 1, the fixed focus lens provided in the present embodiment includes a first lens 10 with negative power, a second lens 20 with positive power, a third lens 30 with positive power, and a fourth lens 40 with negative power, which are arranged in order from the object side to the image side along the optical axis; the first lens 10 to the fourth lens 40 are all plastic aspheric lenses; the third lens 30 and the fourth lens 40 constitute a cemented lens.

It will be appreciated that the optical power is equal to the difference between the image-side and object-side beam convergence, which characterizes the ability of the optical system to deflect light. The larger the absolute value of the focal power is, the stronger the bending ability to the light ray is, and the smaller the absolute value of the focal power is, the weaker the bending ability to the light ray is. When the focal power is positive, the refraction of the light is convergent; when the focal power is negative, the refraction of the light is divergent. The optical power can be suitable for representing a certain refractive surface of a lens (namely, a surface of the lens), can be suitable for representing a certain lens, and can also be suitable for representing a system (namely a lens group) formed by a plurality of lenses together. In the present embodiment, each lens can be fixed in one lens barrel (not shown in fig. 1), by reasonably distributing the optical power and shape of the lens, for example, the first lens 10 with negative optical power is provided, and the light receiving surface of the first lens 10 is larger for receiving light, so as to increase the angle of field; the third lens 30 and the fourth lens 40 are arranged to be glued, so that high and low temperature confocal is realized; all the lenses are plastic aspheric lenses, the aspheric lenses are fully utilized to eliminate various aberrations, the plastic lenses are low in cost and easy to form, the lens can realize day and night confocal function in the wavelength range of 436 nm-880 nm, optionally, the aperture F of the fixed-focus lens provided by the embodiment is larger than or equal to 2.0, the total length of the fixed-focus lens is smaller than 23mm, the size of the lens can be favorably reduced, the size requirement of general security on the lens is met, and the visible light and infrared confocal function can be realized at the ambient temperature of-10-60 ℃.

according to the technical scheme of the embodiment, by adopting the optical structure of four plastic lenses, the plastic aspheric lens has smaller mass and lower cost and has good aberration eliminating capability; the third lens and the fourth lens are arranged to form the cemented lens, so that high-low temperature compensation and infrared confocal are realized, 4 million pixel resolution can be achieved under visible light and infrared light on the premise of F2.0 by matching focal power of the lenses, and the lens does not leak focus under the state of ambient temperature of-10-60 ℃, so that the infrared confocal imaging lens has the advantages of low cost, excellent performance, small size and light weight.

On the basis of the above technical solution, optionally, the focal lengths of the first lens 10 to the fourth lens 40 satisfy the following relational expressions:

0.8<︱f1/f2︱<1.3(1)；

0.8<︱f3/f4︱<1.3(2)；

Where f1 to f4 respectively represent focal lengths of the first lens 10 to the fourth lens 40.

the fixed-focus lens provided by the embodiment has the advantages that the third lens 30 and the fourth lens 40 are arranged to be glued, the specific value ranges of the focal lengths of the first lens 10, the second lens 20 and the third lens 30 and the fourth lens 40 are given, the confocal performance of the fixed-focus lens at high and low temperatures is guaranteed, and the resolution of 4 megapixels is achieved.

Alternatively, the first lens 10 to the fourth lens 40 satisfy the following parameters:

TABLE 1 lens parameters

Where f1 to f4 indicate focal lengths of the first lens 10 to the fourth lens 40 in mm, n1 to n4 indicate refractive indices of the first lens 40 to the fourth lens 40, R1, R3, R5, and R7 respectively indicate radii of curvature of the first lens 40 to the fourth lens 40 toward the center of the object side surface in this order, R2, R4, R6, and R8 respectively indicate radii of curvature of the first lens 40 to the fourth lens 40 toward the center of the image side surface in this order, and the unit is mm, "-" indicates a negative direction.

Optionally, with reference to fig. 1, the fixed-focus lens provided in the embodiment of the present invention further includes a diaphragm 50 disposed between the first lens 10 and the second lens 20. The diaphragm 50 can adjust the size of the view field, shield the far-axis light, avoid the far-axis light from influencing the imaging quality and improve the image quality.

Alternatively, the first lens element 10 is a meniscus lens element, the second lens element 20 is a barrel lens element, the third lens element 30 is a double convex lens element, and the fourth lens element 40 is a meniscus lens element.

It is understood that, in the implementation, the shape of the specific lens can be selected according to the design of the optical power, and the above is only a specific example and is not a limitation to the embodiment of the present invention.

Optionally, the first lens 10 and the second lens 20 are tightly fitted through a spacer, and the second lens 20 and the third lens 30 are tightly fitted through a spacer.

In this embodiment, the distance between the first lens element 10 and the edge of the second lens element 20 and the distance between the second lens element 20 and the edge of the third lens element 30 are larger, and a spacer is adopted for tight fitting, wherein the spacer may be a plastic spacer, so as to fix the relative positions of the lens elements and improve the stability of the fixed focus lens.

table 2 shows parameter design values of a specific embodiment of a fixed-focus lens provided in an embodiment of the present invention:

TABLE 2 design values for lenses in a refractive lens group

Wherein, the surface number 1 indicates that the first lens 10 is close to the front surface of the object, and so on, PL indicates that the surface is a plane, the surface number 7 indicates the cemented surface of the third lens 30 and the fourth lens 40, and the surface numbers 9 and 10 indicate the two surfaces of the lens protection glass; r represents the radius of the spherical surface, positive represents the side of the center of the spherical surface close to the image surface, and negative represents the side of the center of the spherical surface close to the object surface; d represents the distance on the optical axis from the current surface to the next surface; nd represents a refractive index of the lens; k denotes the conic coefficient of the aspheric surface.

Optionally, the surface shape of the plastic aspheric lens satisfies the formula:

table 3 shows the even coefficients for various aspheric surfaces of the above examples:

TABLE 3 aspheric parameters

Wherein, the surface numbers 1, 4 and 6 respectively correspond to the front surfaces of the first lens 10, the second lens 20 and the third lens 30 close to the object plane, the surface numbers 2, 5 and 8 respectively correspond to the rear surfaces of the first lens 10, the second lens 20 and the fourth lens 40 close to the image plane, the surface number 7 represents the gluing surface of the third lens 30 and the fourth lens 40, and-2.31314E-02 represents-2.31314 multiplied by 10-2.

The fixed-focus lens provided by the embodiment can achieve the resolution of 4 million pixels in visible light and infrared states, so that a clear picture can be obtained in a low-illumination environment at night. Meanwhile, the design does not run coke when used in an environment of-10 ℃ to 60 ℃.

Specifically, fig. 2 is a schematic diagram of an MTF curve of a modulation transfer function of visible light according to an embodiment of the present invention, and fig. 3 is a schematic diagram of an MTF curve of infrared light according to an embodiment of the present invention. The MTF curve shown in fig. 2 is obtained under the condition that the visible light wavelength is 436nm to 880nm, and the MTF curve shown in fig. 3 is obtained under the condition that the infrared light wavelength is 880nm, and to achieve the resolution of 4 megapixels, when the spatial resolution is 160 line pairs/mm, the MTF of the visible light of the central view field is greater than 0.4, and the MTF of the infrared light of the central view field is greater than 0.2. Referring to fig. 2 and 3, it can be seen that the condition of 4 megapixel resolution is satisfied for both visible light and infrared light.

It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. a fixed focus lens is characterized by comprising a first lens with negative focal power, a second lens with positive focal power, a third lens with positive focal power and a fourth lens with negative focal power, which are sequentially arranged from an object side to an image side along an optical axis;

The first lens to the fourth lens are all plastic aspheric lenses;

The third lens and the fourth lens constitute a cemented lens.

2. The prime lens according to claim 1, wherein the focal lengths of the first to fourth lenses satisfy the following relationship:

0.8<︱f1/f2︱<1.3；

0.8<︱f3/f4︱<1.3；

3. The prime lens according to claim 1, wherein the first to fourth lenses satisfy the following parameters:

4. The prime lens according to claim 1, further comprising a diaphragm disposed between the first lens and the second lens.

5. The prime lens according to claim 1, wherein the first lens is a meniscus lens, the second lens is a barrel lens, the third lens is a double convex lens, and the fourth lens is a meniscus lens.

6. the fixed focus lens as claimed in claim 5, wherein the first lens and the second lens are tightly fitted with a spacer, and the second lens and the third lens are tightly fitted with a spacer.

7. The prime lens according to claim 1, wherein the surface shape of the plastic aspherical lens satisfies the formula:

8. The prime lens according to claim 1, wherein an aperture F of the prime lens is greater than or equal to 2.0.

9. the prime lens according to claim 1, wherein the total length of the prime lens is less than 23 mm.