A small face recognition lens and its imaging method

Abstract

The present invention relates to a small face recognition lens and an imaging method thereof, comprising a first lens, a second lens, a third lens and a fourth lens arranged in sequence along the incident direction of light in a lens structure, wherein the first lens is a positive meniscus lens, whose object side surface is convex and whose image side surface is concave; the second lens is a negative meniscus lens, whose object side surface is convex and whose image side surface is concave; the third lens is a positive meniscus lens, whose object side surface is concave and whose image side surface is convex; and the fourth lens is a negative meniscus lens, whose object side surface is convex and whose image side surface is concave. Compared with a traditional all-glass lens, the present invention uses a plastic aspheric lens to eliminate spherical aberration to the greatest extent by adjusting the quadratic surface coefficient and the aspheric surface coefficient, further improving the optical performance of the lens and reducing the number of optical elements, so that the total length of the optical lens is less than 8 mm and the diameter is less than 6 mm. While ensuring the imaging quality of the optical lens, the overall size is reduced to meet the requirements of system miniaturization.

Description

Technical Field

[0001] The invention relates to a small face recognition lens and an imaging method thereof. Background Art

[0002] With the continuous development of information technologies such as artificial intelligence, the Internet of Things, big data, and smart terminals, facial recognition has become increasingly popular and integrated into our daily lives. In the security field, it is used in monitoring and access control systems; in the financial sector, it can be used in service scenarios such as ATMs, mobile banking, and facial payment; and in education, it can be used in attendance and management systems, improving convenience and safety. At the same time, due to the overall aesthetic requirements of the system, the optical lens used for image capture at the front end must be small. While existing optical lenses meet basic optical performance requirements, they are large in size and cannot meet the miniaturization requirements of access control, attendance machines, and facial payment systems. Summary of the Invention

[0003] The present invention provides a small face recognition lens and an imaging method thereof, which achieve both small size and high imaging quality while meeting basic optical performance requirements.

[0004] The solution adopted by the present invention to solve the technical problem is a small face recognition lens: it includes a first lens, a second lens, a third lens and a fourth lens arranged in sequence along the incident direction of light in the lens structure, the first lens is a positive meniscus lens, whose object side surface is convex and the image side surface is concave; the second lens is a negative meniscus lens, whose object side surface is convex and the image side surface is concave; the third lens is a positive meniscus lens, whose object side surface is concave and the image side surface is convex; the fourth lens is a negative meniscus lens, whose object side surface is convex and the image side surface is concave.

[0005] Furthermore, the first lens and the second lens are glass aspheric lenses, and the third lens and the fourth lens are plastic aspheric lenses.

[0006] Furthermore, the focal length of the overall optical lens is f, and the focal lengths of the first lens, the second lens, the third lens, and the fourth lens are f1, f2, f3, and f4 respectively, wherein f1, f2, f3, and f4 satisfy the following ratio with f: 0.5 <f1 / f<1.5,-2.0<f2 / f<-1.0,0.0<f3 / f<1.0,-1.5<f4 / f<-0.5。

[0007] Furthermore, the first lens satisfies the relationship: N d ≥1.8, V d ≤50.0; the second lens satisfies the relationship: N d ≤1.5, V d ≥50.0; the third lens satisfies the relationship: 1.5≤Nd ≤1.8, V d ≤50.0; the fourth lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≥50.0; where N d is the refractive index, V d is the Abbe constant.

[0008] Furthermore, the air gap between the first lens and the second lens is 0-0.1 mm; the air gap between the second lens and the third lens is 0.5-1.0 mm; and the air gap between the third lens and the fourth lens is 0-0.1 mm.

[0009] Furthermore, the aspheric curve equations of the third lens and the fourth lens are expressed as:

[0010]

[0011] Among them, Z is the height of the aspheric surface from the vertex of the aspheric surface when it is at a height of h along the optical axis; c is the paraxial curvature of the aspheric surface; k is the cone constant; α1, α2, α3, α4, α5, α6, α7, and α8 are all high-order coefficients.

[0012] Furthermore, the total optical length TTL of the overall optical lens and the focal length f of the optical system satisfy: TTL / f≤1.6.

[0013] Furthermore, the F number of the overall optical lens is ≤2.0.

[0014] Furthermore, the image height H of the overall optical lens and the focal length f of the optical system satisfy: H / f≥1.0.

[0015] An imaging method for a small face recognition lens: when light is incident, the light path enters the first lens, the second lens, the third lens, and the fourth lens in sequence and finally forms an image on the image plane.

[0016] Compared with the prior art, the present invention has the following beneficial effects: Compared with traditional all-glass lenses, plastic aspheric lenses can eliminate spherical aberration to the maximum extent by adjusting the quadratic surface coefficient and the aspheric surface coefficient, further improve the optical performance of the lens, reduce optical components, and make the total length of the optical lens less than 8mm and the diameter less than 6mm. While ensuring the imaging quality of the optical lens, the overall size is reduced to meet the needs of system miniaturization. The use of plastic aspheric lenses, combined with the optimization of the tolerance sensitivity of each lens during optical design, can reduce the probability of defective products in the production process and reduce production costs. At the same time, the first and second lenses use glass spherical lenses. Due to the high and low temperature stability and wear resistance of glass, not only the high and low temperature performance of the lens is improved, but also the friction resistance of the lens surface is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is a schematic diagram of the optical structure of the first embodiment of the present invention;

[0018] Figure 2 This is a full-band axial chromatic aberration diagram of Example 1 of the present invention;

[0019] Figure 3 This is a vertical axis chromatic aberration diagram for the entire working band of the first embodiment of the present invention;

[0020] Figure 4 This is a field curvature distortion diagram for the entire working band of the first embodiment of the present invention;

[0021] Figure 5 is a schematic diagram of the optical structure of embodiment 2 of the present invention;

[0022] Figure 6 This is a full-band axial chromatic aberration diagram of Example 2 of the present invention;

[0023] Figure 7 This is a vertical axis chromatic aberration diagram of the full working band of embodiment 2 of the present invention;

[0024] Figure 8 This is a field curvature distortion diagram for the entire working band of the second embodiment of the present invention.

[0025] In the figure: STO - aperture; L1 - first lens; L2 - second lens; L3 - third lens; L4 - fourth lens; L5 - equivalent glass plate; IMA - imaging surface. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] Example 1: Figure 1-4 As shown, a small face recognition lens comprises a first lens, a second lens, a third lens and a fourth lens arranged in sequence along the incident direction of light in a lens structure, wherein the first lens is a positive meniscus lens, whose object side surface is convex and whose image side surface is concave; the second lens is a negative meniscus lens, whose object side surface is convex and whose image side surface is concave; the third lens is a positive meniscus lens, whose object side surface is concave and whose image side surface is convex; the fourth lens is a negative meniscus lens, whose object side surface is convex and whose image side surface is concave. By reasonably optimizing the quadratic surface coefficient and the aspheric surface coefficient, various aberration problems of the system are effectively optimized and the imaging quality is improved.

[0028] In this embodiment, the first lens and the second lens are glass aspheric lenses, and the third lens and the fourth lens are plastic aspheric lenses.

[0029] In this embodiment, the focal length of the overall optical lens is f, and the focal lengths of the first lens, the second lens, the third lens, and the fourth lens are f1, f2, f3, and f4, respectively, wherein f1, f2, f3, and f4 satisfy the following ratio with f: 0.5 <f1 / f<1.5,-2.0<f2 / f<-1.0,0.0<f3 / f<1.0,-1.5<f4 / f<-0.5。

[0030] In this embodiment, the first lens satisfies the relationship: N d ≥1.8, V d ≤50.0; the second lens satisfies the relationship: N d ≤1.5, V d ≥50.0; the third lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≤50.0; the fourth lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≥50.0; where N d is the refractive index, V d is the Abbe constant.

[0031] In this embodiment, the air gap between the first lens and the second lens is 0-0.1 mm; the air gap between the second lens and the third lens is 0.5-1.0 mm; and the air gap between the third lens and the fourth lens is 0-0.1 mm. While meeting the imaging requirements, the distance between the lenses is reduced, which is beneficial to the total optical length of the lens and ensures miniaturization.

[0032] In this embodiment, the aspheric curve equations of the third lens and the fourth lens are expressed as follows:

[0033]

[0034] Among them, Z is the height of the aspheric surface from the vertex of the aspheric surface when it is at a height of h along the optical axis; c is the paraxial curvature of the aspheric surface; k is the cone constant; α1, α2, α3, α4, α5, α6, α7, and α8 are all high-order coefficients.

[0035] In this embodiment, the total optical length TTL of the integral optical lens and the focal length f of the optical system satisfy the following relationship: TTL / f≤1.6.

[0036] In this embodiment, the F number of the entire optical lens is ≤2.0.

[0037] In this embodiment, the image height H of the overall optical lens and the focal length f of the optical system satisfy: H / f≥1.0.

[0038] An imaging method for a small face recognition lens: when light is incident, the light path enters the first lens, the second lens, the third lens, and the fourth lens in sequence and finally forms an image on the image plane.

[0039] The technical indicators achieved by the optical system of this embodiment are as follows:

[0040] Focal length: 4.5≤EFFL≤5.5mm; (2) Aperture F≤2.0; (3) Field of view: 2w≥60°; (4) Operating band: Infrared 940nm band.

[0041] To achieve the above design parameters, the specific design adopted by the optical system of this embodiment is shown in the following table:

[0042]

[0043]

[0044] The aspheric coefficients of the aspheric lenses of the optical system of this embodiment are as follows:

[0045]

[0046] The optical system of this embodiment achieves miniaturization of the lens group by reasonably allocating the optical power, surface shape, center thickness of each lens, and axial distance between lenses, thereby meeting the imaging performance requirements of the lens while reducing the total length of the lens and the radial dimensions of each lens.

[0047] Example 2: Figures 6 to 8 As shown, by rationally optimizing the quadratic surface coefficients and aspheric surface coefficients, various aberration problems of the system are effectively optimized and the imaging quality is improved. Since the overall structure is the same as that of Example 1, only the lens parameters are different, so this embodiment only describes the different parameters:

[0048] To achieve the above design parameters, the specific design adopted by the optical system of this embodiment is shown in the following table:

[0049]

[0050] The aspheric coefficients of the aspheric lenses of the optical system of this embodiment are as follows:

[0051]

[0052] The optical system of this embodiment achieves miniaturization of the lens group by reasonably allocating the optical power, surface shape, center thickness of each lens, and axial distance between lenses, thereby meeting the imaging performance requirements of the lens while reducing the total length of the lens and the radial dimensions of each lens.

[0053] Unless otherwise stated, for any of the technical solutions disclosed in the present invention, if a numerical range is disclosed, the disclosed numerical range is a preferred numerical range. Any person skilled in the art should understand that the preferred numerical range is merely a numerical range that is representative or has a more obvious technical effect among many feasible numerical values. Due to the large number of numerical values, it is impossible to enumerate them exhaustively. Therefore, the present invention discloses some numerical values to illustrate the technical solutions of the present invention. Moreover, the numerical values listed above should not be construed as limiting the scope of protection of the present invention.

[0054] If words such as "first" and "second" are used in this document to limit components, those skilled in the art should know that the use of "first" and "second" is only for the convenience of description to distinguish between components. Unless otherwise stated, the above words have no special meaning.

[0055] If the present invention discloses or involves components or structural parts that are fixedly connected to each other, then, unless otherwise stated, the fixed connection can be understood as: a detachable fixed connection (for example, connection using bolts or screws), and can also be understood as: a non-detachable fixed connection (for example, riveting, welding). Of course, the mutual fixed connection can also be replaced by an integrated structure (for example, manufactured by integrated molding using a casting process) (except where it is obviously impossible to use an integrated molding process).

[0056] In addition, the orientations or positional relationships indicated by terms such as "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", and "outside" used in any of the technical solutions disclosed in the above invention are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing this patent, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on this patent. Unless otherwise stated, the terms used to indicate shapes used in any of the technical solutions disclosed in the above invention include shapes that are approximate, similar, or close to them.

[0057] Any component provided by the present invention may be assembled from multiple separate components, or may be a separate component manufactured by an integral molding process.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and not to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention. They should all be included in the scope of the technical solution for protection of the present invention.

Claims

1. A small face recognition lens, characterized by: The lens structure comprises a first lens, a second lens, a third lens, and a fourth lens, which are arranged in sequence along the incident direction of light in the lens structure. The first lens is a positive meniscus lens, whose object side surface is convex and whose image side surface is concave; the second lens is a negative meniscus lens, whose object side surface is convex and whose image side surface is concave; the third lens is a positive meniscus lens, whose object side surface is concave and whose image side surface is convex; and the fourth lens is a negative meniscus lens, whose object side surface is convex and whose image side surface is concave. The first lens and the second lens are glass aspheric lenses, and the third lens and the fourth lens are plastic aspheric lenses; The focal length of the entire optical lens is f, and the focal lengths of the first lens, second lens, third lens, and fourth lens are f1, f2, f3, and f4 respectively, where f1, f2, f3, and f4 satisfy the following ratio with f: 0.5 <f1 / f<1.5,-2.0<f2 / f<-1.0,0.0<f3 / f<1.0,-1.5<f4 / f<-0.5; The first lens satisfies the relationship: N d ≥1.8, V d ≤50.0; the second lens satisfies the relationship: N d ≤1.5, V d ≥50.0; the third lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≤50.0; the fourth lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≥50.0; where N d is the refractive index, V d is the Abbe constant.

2. The small face recognition lens according to claim 1, characterized in that: The air gap between the first lens and the second lens is 0-0.1 mm; the air gap between the second lens and the third lens is 0.5-1.0 mm; and the air gap between the third lens and the fourth lens is 0-0.1 mm.

3. The small face recognition lens according to claim 1, characterized in that: The aspheric curve equations of the third lens and the fourth lens are expressed as follows: Among them, Z is the height of the aspheric surface from the vertex of the aspheric surface when it is at a height of h along the optical axis; c is the paraxial curvature of the aspheric surface; k is the cone constant; α1, α2, α3, α4, α5, α6, α7, and α8 are all high-order coefficients.

4. The small face recognition lens according to claim 1, characterized in that: The total optical length TTL of the overall optical lens and the focal length f of the optical system satisfy: TTL / f≤1.

6.

5. The small face recognition lens according to claim 1, characterized in that: The F number of the overall optical lens is ≤2.

0.

6. The small face recognition lens according to claim 1, characterized in that: The image height H of the overall optical lens and the focal length f of the optical system satisfy: H / f ≥ 1.

0.

7. An imaging method for a small face recognition lens, using the small face recognition lens according to claim 6, characterized in that: When light is incident, the light path enters the first lens, the second lens, the third lens, and the fourth lens in sequence and finally forms an image on the image plane.

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