Close range recognition lens

Abstract

The invention discloses a close-range identification lens, which is composed of an aperture (STO), a first lens (E1), a second lens (E2), a third lens (E3), a fourth lens (E4), and a chip protection glass (E5) in order from an object plane to an image plane; the first lens (E1) is a positive lens, the object side surface is a convex surface, the image side surface is a convex surface, and both are aspherical surfaces; the second lens (E2) is a negative lens, the object side surface is a concave surface, the image side surface is a concave surface, and both are aspherical surfaces; the third lens (E3) is a positive lens, the object side surface is a concave surface, the image side surface is a convex surface, and both are aspherical surfaces; the fourth lens (E4) is a negative lens, the object side surface is a convex surface, the image side surface is a concave surface, and both are aspherical surfaces; the four lenses are all made of plastic material, with a simple structure, low tolerance sensitivity, and are conducive to mass production; the positive lens and the negative lens are combined with each other, which is conducive to correcting astigmatism and distortion, and at the same time is conducive to reducing the total length of the optical system.

Description

Technical Field

[0001] The present invention relates to a close-range identification lens.

Background Art

[0002] With the development of society and the progress of technology, more and more high-end technological products have entered people's lives. Identification lenses such as face recognition and fingerprint recognition have also become an indispensable part of the market. The present invention relates to an identification lens with low tolerance sensitivity and suitable for mass production. It can not only meet the usage requirements of close-range identification, but also the optical lenses are all made of plastic materials, saving costs and being suitable for high-efficiency mass production.

Summary of the Invention

[0003] In view of the needs of the existing market and the room for improvement in research, the present invention provides a close-range identification lens, aiming to solve the technical problem that the optical aperture of the current identification lens is not small enough to ensure imaging quality while having low distortion.

[0004] To achieve the above object, the present invention provides a close-range identification lens, including a stop (STO), a first lens (E1), a second lens (E2), a third lens (E3), a fourth lens (E4), and a chip protection glass (E5) arranged in sequence from the object plane to the image plane;

[0005] The first lens (E1) is a positive lens, made of plastic material, and its focal length satisfies 0.5 < f1 / f < 1.1; the object side is a convex surface and an aspherical surface, and the image side is a convex surface and an aspherical surface;

[0006] The second lens (E2) is a negative lens, made of plastic material, and its focal length satisfies -1.86 ≤ f2 / f < -1.52; the object side is a concave surface and an aspherical surface, and the image side is a concave surface and an aspherical surface;

[0007] The third lens (E3) is a positive lens, made of plastic material, and its focal length satisfies 0.52 < f3 / f < 1.2; the object side is a concave surface and an aspherical surface, and the image side is a convex surface and an aspherical surface;

[0008] The fourth lens (E4) is a negative lens, made of plastic material, and its focal length satisfies -0.8 < f4 / f < 0; the object side is a convex surface and an aspherical surface, and the image side is a concave surface and an aspherical surface;

[0009] This close-range identification lens satisfies the following relationship: 1.28 < TTL / f < 1.5;

[0010] Among them, f1 is the effective focal length of the first lens, f2 is the effective focal length of the second lens, f3 is the effective focal length of the third lens, f4 is the effective focal length of the fourth lens, and TTL is the on-axis distance from the object side surface of the first lens to the imaging surface; f is the effective focal length of this close-range recognition lens.

[0011] Preferably, for the close-range recognition lens, the following relational expressions are satisfied: 0.02 < T12 / f < 0.03; 0.03 < T34 / f < 0.04;

[0012] Among them, T12 is the air spacing between the first lens and the second lens on the optical axis, and T34 is the air spacing between the third lens and the fourth lens on the optical axis.

[0013] Preferably, for the close-range recognition lens, the aperture stop is located between the object side surface of the first lens and the object to be photographed, and the following relational expression is satisfied: 0 < TDS / f1 < 0.4;

[0014] Among them, TDS is the aperture diameter of the aperture stop, and f1 is the focal length of the first lens.

[0015] Preferably, for the close-range recognition lens, the following relational expressions are satisfied: when DI < 0.8 * MDI, 0.09 mm < OAD < 0.42 mm; TTL < 3.6 mm; 75° < FOV < 85°; where OAD is the air spacing between the third lens and the fourth lens on a straight line parallel to the optical axis rather than the optical axis, DI is the diameter of the aspherical surface of the third lens near the image side perpendicular to the optical axis direction, MDI is the maximum effective diameter, TTL is the distance on the optical axis from the surface of the object side of the first lens to the image surface, and FOV is the maximum field of view angle of this close-range recognition lens.

[0016] Preferably, for the close-range recognition lens, the following relational expressions are satisfied: 0 mm < T3 - T1 < 0.2 mm; 0 mm < T4 - T2 < 0.06 mm; where T1 is the distance on the optical axis from the surface of the object side of the first lens to the surface of the image side of the first lens, T2 is the distance on the optical axis from the surface of the object side of the second lens to the surface of the image side of the second lens, T3 is the distance on the optical axis from the surface of the object side of the third lens to the surface of the image side of the third lens, and T4 is the distance on the optical axis from the surface of the object side of the fourth lens to the surface of the image side of the fourth lens.

[0017] Preferably, for the close-range recognition lens, the following relational expression is satisfied: 0 mm < T3 - SA6 < 0.07 mm; where T3 is the distance on the optical axis from the surface of the object side of the third lens to the surface of the image side of the third lens. SA6 is the distance from the center of the aspherical surface of the image side of the third lens to the maximum effective diameter in the direction parallel to the optical axis.

[0018] Preferably, the short-distance recognition lens satisfies the following relational expressions: 0.23 < T1 / ∑T < 0.3; 0.01 < T2 / ∑T < 0.25; 0.30 < T3 / ∑T < 0.45; 0.1 < T4 / ∑T < 0.23; where ∑T is the sum of the lens thicknesses of the first lens, the second lens, the third lens, and the fourth lens on the optical axis, and T1, T2, T3, and T4 are the lens thicknesses of the first lens, the second lens, the third lens, and the fourth lens on the optical axis, respectively.

[0019] Generally speaking, compared with the prior art by the above technical solution conceived by the present invention, the following beneficial effects can be achieved:

[0020] 1. The short-distance recognition lens has a simple structure. All the lenses are made of plastic materials with low tolerance sensitivity, which is conducive to mass production. The second lens has the largest focal length, which is conducive to correcting high-order aberrations, and its aspherical shape increases the light angle, which is conducive to increasing the field of view angle. The combination of the first lens and the second lens, and the third lens and the fourth lens as positive and negative lenses is conducive to correcting astigmatism and distortion, and at the same time is conducive to reducing the total length of the lens.

[0021] 2. For the short-distance recognition lens, the aperture stop is located between the object side of the first lens and the object to be photographed, and satisfies the following relational expression: 0 < TDS / f1 < 0.4; which is conducive to reducing the total length of the lens and improving the imaging quality.

[0022] 3. The short-distance recognition lens satisfies the relational expressions: when DI < 0.8*MDI, 0.09mm < OAD < 0.42mm; TTL < 3.6mm; 75° < FOV < 85°; 0mm < T3 - SA6 < 0.07mm; The air gap between the third lens and the fourth lens is small, and the curvature of the image side of the third lens is large, which is conducive to the mutual compensation of astigmatism and distortion between the third lens and the fourth lens, correcting aberrations, and improving the imaging quality.

[0023] 4. The short-distance recognition lens satisfies the relational expressions: 0 < T3 - T1 < 0.2; 0 < T4 - T2 < 0.06. The center thicknesses of the front and rear two groups of lenses are similar, which is conducive to reducing the spherical aberration of the imaging system.

[0024] 5. The short-distance recognition lens satisfies the relational expressions: 0.23 < T1 / ∑T < 0.3; 0.01 < T2 / ∑T < 0.25; 0.30 < T3 / ∑T < 0.45; 0.1 < T4 / ∑T < 0.23; Controlling the center thickness of the lens and satisfying the relational expressions is conducive to correcting aberrations. Combining with the molding process of plastic lenses, the length of the lens is minimized to the greatest extent, realizing the miniaturization of the short-distance recognition lens.

Description of the Drawings

[0025] Figure 1 It is a schematic structural diagram of the close-range recognition lens;

[0026] Figure 2 It is the axial chromatic aberration diagram (mm) of the close-range recognition lens;

[0027] Figure 3 It is the astigmatism diagram (mm) of the close-range recognition lens;

[0028] Figure 4 It is the distortion diagram (%) of the close-range recognition lens.

[0029] Figure 5 It is the axial chromatic aberration diagram (mm) of a specific embodiment of the close-range recognition lens;

[0030] Figure 6 It is the astigmatism diagram (mm) of a specific embodiment of the close-range recognition lens;

[0031] Figure 7 It is the distortion diagram (%) of a specific embodiment of the close-range recognition lens.

Detailed Implementation Manner

[0032] In order to make the purpose, technical solutions and advantages of the invention more clear and understandable, the present invention will be further described in detail below with reference to 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 used to limit the present invention.

[0033] As Figure 1 shown, the close-range recognition lens proposed by the present invention includes, in sequence from the object plane to the image plane, a stop (STO), a first lens (E1), a second lens (E2), a third lens (E3), a fourth lens (E4), and a chip protection glass (E5); the first lens (E1) is a positive lens, made of plastic material, and its focal length satisfies 0.5 < f1 / f < 1.1; the object side is a convex surface and is an aspherical surface, and the image side is a convex surface and is an aspherical surface;

[0034] The second lens (E2) is a negative lens, made of plastic material, and its focal length satisfies -1.86 ≤ f2 / f < -1.52; the object side is a concave surface and is an aspherical surface, and the image side is a concave surface and is an aspherical surface;

[0035] The third lens (E3) is a positive lens, made of plastic material, and its focal length satisfies 0.52 < f3 / f < 1.2; the object side is a concave surface and is an aspherical surface, and the image side is a convex surface and is an aspherical surface;

[0036] The fourth lens (E4) is a negative lens, made of plastic material, and its focal length satisfies -0.8 < f4 / f < 0; the object side is a convex surface and is an aspherical surface, and the image side is a concave surface and is an aspherical surface;

[0037] The close-range recognition lens satisfies the relationship: 1.28 <TTL / f<1.5;

[0038] Among them, f1 is the effective focal length of the first lens, f2 is the effective focal length of the second lens, f3 is the effective focal length of the third lens, f4 is the effective focal length of the fourth lens, TTL is the axial distance from the object side of the first lens to the imaging surface; f is the effective focal length of the close-range identification lens.

[0039] The second lens has a larger focal length, which is conducive to correcting high-order aberrations. The first lens, the second lens, the third lens, and the fourth lens are combined with negative lenses and positive lenses, which is conducive to correcting astigmatism and distortion. By adjusting the focal length of each lens, it is conducive to reducing the total length, and on this basis, a larger field of view angle is guaranteed.

[0040] Preferably, the close-range recognition lens satisfies the following relationship:

[0041] 0.02 <T12 / f<0.03;

[0042] 0.03 <T34 / f<0.04;

[0043] Wherein, T12 is the air distance between the first lens and the second lens on the optical axis, and T34 is the air distance between the third lens and the fourth lens on the optical axis.

[0044] The lens spacing of the close-range recognition lens is very small, which helps to reduce the overall length of the system while ensuring the imaging quality.

[0045] Preferably, the aperture is located between the object side surface of the first lens and the object, and the close-range recognition lens satisfies the following relationship:

[0046] 0 <TDS / f1<0.4;

[0047] Where TDS is the aperture stop diameter, and f1 is the focal length of the first lens.

[0048] The close-range recognition lens has a relatively small aperture factor, which is beneficial to improving image quality and overall brightness.

[0049] Preferably, the close-range recognition lens satisfies the following relationship:

[0050] When DI<0.8*MDI, 0.09mm <OAD<0.42mm;

[0051] TTL<3.6mm;

[0052] 75° <FOV<85°

[0053] Among them, OAD is the air distance between the third lens and the fourth lens on a straight line parallel to the optical axis rather than the optical axis, DI is the diameter of the aspheric surface of the third lens close to the image side perpendicular to the optical axis, MDI is the maximum effective diameter, TTL is the distance from the object side surface of the first lens to the image plane on the optical axis, and FOV is the maximum field of view angle of this close-range identification lens.

[0054] The object side curvature of the third lens is relatively large, which is conducive to the mutual compensation of astigmatism, distortion, etc. between the third lens and the fourth lens, and improves the imaging quality. In addition, the close-range recognition lens has a larger field of view, and the lens has a wider camera range.

[0055] Preferably, the close-range recognition lens satisfies the following relationship:

[0056] 0mm <T3-T1<0.2mm;

[0057] 0mm <T4-T2<0.06mm;

[0058] Wherein, T1 is the distance from the objective side surface of the first lens to the image side surface of the first lens on the optical axis, T2 is the distance from the objective side surface of the second lens to the image side surface of the second lens on the optical axis, T3 is the distance from the objective side surface of the third lens to the image side surface of the third lens on the optical axis, and T4 is the distance from the objective side surface of the fourth lens to the image side surface of the fourth lens on the optical axis.

[0059] The center thickness of the front and rear lens groups is similar, which is beneficial to reducing the spherical aberration of the lens.

[0060] Preferably, the close-range recognition lens satisfies the following relationship:

[0061] 0mm <T3-SA6<0.07mm;

[0062] Wherein, T3 is the distance from the object side surface of the third lens to the image side surface of the third lens on the optical axis, and SA6 is the distance from the center of the aspheric surface of the image side of the third lens to the maximum effective diameter in the direction parallel to the optical axis.

[0063] The difference between the two is small, so that the distortion and astigmatism are mainly generated on the image side of the third lens, and the fourth lens structure is optimized and controlled to compensate each other, which is beneficial to improving the imaging quality of the edge field of view.

[0064] Preferably, the close-range recognition lens satisfies the following relationship:

[0065] 0.23 <T1 / ∑T<0.3;

[0066] 0.01 <T2 / ∑T<0.25;

[0067] 0.30 <T3 / ∑T<0.45;

[0068] 0.1 <T4 / ∑T<0.23;

[0069] Among them, ∑T is the sum of the thickness of the first lens, the second lens, the third lens, and the fourth lens on the optical axis, respectively, and T1, T2, T3, and T4 are the thickness of the first lens, the second lens, the third lens, and the fourth lens on the optical axis, respectively. Controlling the thickness of each lens within the above range is conducive to correcting aberrations and mutual compensation, which can reduce tolerance sensitivity and reduce the difficulty in the molding process. At the same time, it is conducive to reducing the total length of the lens and realizing ultra-thin and miniaturized lenses. [Specific embodiment 1]

[0071] The following table is the lens data table of Example 1

[0072] Table 1 is the structural parameter table of the close-range recognition lens

[0073] Table 1

[0074]

[0075]

[0076] Table 2 shows the ratio range of the aspheric surface sagittal height to the radius R of the first lens E1 and the second lens E2

[0077] Table 2

[0078]

[0079] Table 3 shows the ratio ranges of the aspheric surface sagittal height to the radius R of the third lens E3 and the fourth lens E4.

[0080] Table 3

[0081]

[0082]

Claims

1. Close range recognition lens, characterized by: From the object plane to the image plane, it is composed of the aperture (STO), the first lens (E1), the second lens (E2), the third lens (E3), the fourth lens (E4), and the chip protection glass (E5); The first lens (E1) is a positive lens made of plastic, with a curvature radius of 1.2934 mm on the object side and an aspheric surface, and a curvature radius of -10 mm on the image side and an aspheric surface; the thickness of the first lens is 0.3363 mm, the refractive index is 1.546, and the distance between the first lens and the second lens is 0.059 mm; The second lens (E2) is a negative lens made of plastic, with a curvature radius of -21.2366 mm on the object side and an aspheric surface, and a curvature radius of 3.5125 mm on the image side and an aspheric surface; the thickness of the second lens is 0.23 mm, the refractive index is 1.649, and the distance between the second lens and the third lens is 0.6677 mm; The third lens (E3) is a positive lens made of plastic, with a curvature radius of -3.7877 mm on the object side and an aspheric surface, and a curvature radius of -0.7562 mm on the image side and an aspheric surface; the thickness of the third lens is 0.5357 mm, the refractive index is 1.546, and the distance between the third lens and the fourth lens is 0.0912 mm; The fourth lens (E4) is a negative lens made of plastic, with a curvature radius of 1.3899 mm on the object side and an aspheric surface, and a curvature radius of 0.489 mm on the image side and an aspheric surface; the thickness of the fourth lens is 0.27 mm, the refractive index is 1.537, and the distance between the fourth lens and the chip protection glass is 0.3848 mm; The thickness of the chip protection glass is 0.21 mm, and the distance between the chip protection glass and the imaging surface is 0.6525 mm.

Images