A small close-range recognition lens

Abstract

The present invention provides a small close-range recognition lens, which has the advantages of small size, easy processing, good imaging quality, etc., and has good resolution in close range. The small close-range recognition lens comprises an aperture stop (ST), a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4) and a chip protection glass (CG) in sequence from an object plane to an image plane; the first lens (L1) is a positive lens, and its object side surface and image side surface are both convex; the second lens (L2) is a negative lens, and its object side surface and image side surface are both concave; the third lens (L3) is a positive lens, and its object side surface is concave and its image side surface is convex; the fourth lens (L4) is a negative lens, and its object side surface and image side surface are both concave.

Description

[Technical field]

[0001] The invention relates to a small short-distance recognition lens. [Background technology]

[0002] As the degree of social informatization increases, people have also put forward higher requirements for information acquisition technology. In today's society, the application of intelligent recognition technologies such as fingerprint recognition, face recognition, and pupil recognition is becoming more and more widespread, and recognition lenses are the key to intelligent recognition technology. In order to meet market demand and solve the problems of the current lens's optical aperture not being small enough and large distortion, it is necessary to design a recognition lens with small size, simple structure, high imaging quality and low production cost.

[0003] The present invention is made based on this situation. [Summary of the invention]

[0004] In response to the defects or improvement needs of the prior art, the present invention provides a small close-range identification lens, which has obvious advantages such as small size, wide field of view, and easy production. While ensuring high imaging quality, it reduces distortion and the overall length of the lens. The overall length of the entire lens is less than 5mm, and the aspherical lenses used in the present invention are all made of plastic, which greatly reduces the processing difficulty and production cost.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A small close-range recognition lens comprises, from the object plane to the image plane, an aperture stop (ST), a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4) and a chip protection glass (CG); the first lens (L1) is a positive lens, and both the object side surface and the image side surface thereof are convex; the second lens (L2) is a negative lens, and both the object side surface and the image side surface thereof are concave; the third lens (L3) is a positive lens, and its object side surface is concave and its image side surface is convex; the fourth lens (L4) is a negative lens, and both the object side surface and the image side surface thereof are concave.

[0007] The above-mentioned small close-range recognition lens is characterized by:

[0008] 1.5 <TTL / f<1.8; (1)

[0009] Wherein, TTL is the distance from the object plane to the imaging plane of the small close-range identification lens on the optical axis, and f is the effective focal length of the lens.

[0010] The small close-range recognition lens can ensure that the lens has a shorter working distance and has a higher imaging quality in close range when satisfying formula (1).

[0011] The above-mentioned small close-range identification lens is characterized in that the first lens (L1), the second lens (L2), the third lens (L3), and the fourth lens (L4) are all plastic aspherical lenses, which greatly reduces the processing difficulty and production cost of the lenses and is conducive to mass production of lenses.

[0012] The above-mentioned small close-range recognition lens is characterized by:

[0013] 0.5 <f1 / f<0.9; (2)

[0014] -1.71 <f2 / f<-1.45; (3)

[0015] 0.61 <f3 / f<0.73; (4)

[0016] -0.59 <f4 / f<-0.53; (5)

[0017] Among them, f1 is the effective focal length of the first lens (L1), f2 is the effective focal length of the second lens (L2), f3 is the effective focal length of the third lens (L3), f4 is the effective focal length of the fourth lens (L4), and f is the effective focal length of the small close-range identification lens.

[0018] The focal length of the second lens (L2) is relatively large, which is conducive to more positive higher-order aberrations. The first lens (L1) and the second lens (L2) are matched with each other as positive and negative lenses, and the third lens (L3) and the fourth lens (L4) are matched with each other as positive and negative lenses, which are conducive to more positive chromatic aberration, astigmatism and distortion. The optical power of the first lens (L1), the third lens (L3), and the fourth lens (L4) is evenly distributed, which is conducive to reducing the sensitivity of tolerances and reducing aberrations.

[0019] The above-mentioned small close-range recognition lens is characterized by:

[0020] 0.22 <T1 / ∑T<0.28; (6)

[0021] 0.21 <T2 / ∑T<0.27; (7)

[0022] 0.29 <T3 / ∑T<0.33; (8)

[0023] 0.15 <T4 / ∑T<0.19; (9)

[0024] Wherein, ∑T is the sum of the thicknesses of the first lens (L1), the second lens (L2), the third lens (L3), and the fourth lens (L4) on the optical axis, and T1, T2, T3, and T4 are the lens thicknesses of the first lens (L1), the second lens (L2), the third lens (L3), and the fourth lens (L4) on the optical axis, respectively.

[0025] While satisfying equations (6)(7)(8)(9), this small close-range recognition lens is conducive to controlling the center thickness of each lens, reducing the sensitivity of tolerances, and maximally constraining the overall length of the lens on the basis of considering the injection molding process, thereby achieving miniaturization of the lens and ensuring good imaging quality.

[0026] The above-mentioned small close-range recognition lens is characterized by:

[0027] 30<|Vd1-Vd2|<35; (10)

[0028] Wherein, Vd1 is the Abbe number of the first lens (L1); Vd2 is the Abbe number of the second lens (L2).

[0029] Satisfying equation (10) can constrain the material range of the lens and reduce chromatic aberration.

[0030] The above-mentioned small close-range recognition lens is characterized by:

[0031] 4.5 <L / f<7.3; (11)

[0032] Wherein, L is the optimal imaging object distance of the small close-range recognition lens, and f is the effective focal length of the lens.

[0033] This small close-range recognition lens is conducive to balancing the relationship between object distance and focal length while satisfying equation (11), thereby optimizing the depth of field while ensuring imaging quality.

[0034] The above-mentioned small close-range recognition lens is characterized by:

[0035] 0.4 <D / f<0.7; (12)

[0036] Where D is the aperture diameter of the small close-range identification lens, and f is the effective focal length of the lens.

[0037] The small close-range recognition lens that satisfies formula (12) has a larger relative aperture, which is beneficial to improving the image quality and overall illumination of the lens.

[0038] The above-mentioned small close-range recognition lens is characterized by:

[0039] 1.68 <TTL / ImgH<2.31; (13)

[0040] 1.03 <f / ImgH<1.35; (14)

[0041] Wherein, TTL is the distance from the object plane to the imaging plane of the small close-range identification lens on the optical axis, ImgH is the maximum half-image height of the lens, and f is the effective focal length of the lens.

[0042] Formulas (13) and (14) can limit the overall length, imaging quality and field of view of the small close-range recognition lens to an appropriate range, thereby meeting the miniaturization requirements while ensuring that the image quality of the lens meets the needs of practical applications.

Brief Description of the Drawings

[0043] Figure 1 This is a schematic diagram of the structure of the small close-range identification lens;

[0044] Figure 2 Axial chromatic aberration graph of the lens for this small close-up identification;

[0045] Figure 3 Identify the aberration curves of the lens for this small close-up;

[0046] Figure 4 Identify the distortion map of the lens for this small close-up. [Specific implementation method]

[0047] In order to make the purpose, technical solution and advantages of the invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0048] like Figure 1 As shown, the small close-range recognition lens proposed by the present invention comprises, from the object plane to the image plane, an aperture stop (ST), a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4) and a chip protection glass (CG); the first lens (L1) is a positive lens, and its object side surface and image side surface are both convex; the second lens (L2) is a negative lens, and its object side surface and image side surface are both concave; the third lens (L3) is a positive lens, and its object side surface is concave and its image side surface is convex; the fourth lens (L4) is a negative lens, and its object side surface and image side surface are both concave.

[0049] The small close-range recognition lens involved in the present invention has the advantages of small size, easy processing, good imaging quality, etc. compared with previous recognition lenses. It has good resolution in close range, and the aspherical lenses of the lens are all made of plastic, which greatly reduces the production cost and processing difficulty, and is more suitable for mass production.

[0050] The following are some optical parameters of the small close-range identification lens embodiment. In the lens data table of this embodiment, the units of radius and thickness are mm, and S (solid line) and T (dashed line) in the aberration curve diagram represent the sagittal image plane and the meridional image plane, respectively.

[0051] The following table is the lens data table of the embodiment

[0052] Table 1 is the structural parameter table of the small close-range recognition lens

[0053] Surface Type Radius(mm) Thickness(mm) Glass Object Sphere Infinity 15.1953 Stop Sphere Infinity -0.15 2 Asphere 1.5818 0.5511 1.54:56.2 3 Asphere -14.3938 0.1271 4 Asphere -12.0000 0.6291 1.64:22.4 5 Asphere 4.4204 0.6233 6 Asphere -5.6299 0.7866 1.54:56.2 7 Asphere -0.9467 0.2215 8 Asphere 14.7203 0.4509 1.53:55.9 9 Asphere 0.8505 0.4883 10 Sphere Infinity 0.4000 1.51:64.2 11 Sphere Infinity 0.5963 Image Sphere Infinity 0.0000

[0054] Table 1

[0055] Table 2 shows the ratio of the sag height to the radius R of the first lens L1 of the small close-range recognition lens

[0056]

[0057]

[0058] Table 2

[0059] Table 3 shows the ratio of the sag height to the radius R of the second lens L2 of the small close-range recognition lens

[0060]

[0061] Table 3

[0062] Table 4 shows the ratio of the sag height to the radius R of the third lens L3 of the small close-range recognition lens

[0063]

[0064]

[0065] Table 4

[0066] Table 5 shows the ratio of the sag height to the radius R of the fourth lens L4 of the small close-range recognition lens

[0067]

[0068] Table 5.

Claims

1. A small close-range recognition lens, characterized in that: From the object plane to the image plane, it is composed of an aperture stop (ST), a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4) and a chip protection glass (CG); the number of lenses with optical power in the small close-range identification lens is 4, and the lens parameters are as follows: 。

Images