Non-distortion access control lens

Abstract

The application discloses a distortionless access control lens, which comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens arranged in sequence from an object plane to an image plane, wherein the first lens is a double-concave aspheric lens with negative focal power; the second lens is a convex-concave aspheric lens with positive focal power; the third lens is a concave-convex aspheric lens with positive focal power; the fourth lens is a double-convex spherical lens with positive focal power; the fifth lens is a concave-convex aspheric lens with negative focal power; and the sixth lens is a double-convex aspheric lens with positive focal power. By reasonably setting optical parameters, the access control lens meets the requirements of small size, light weight, low distortion, clear imaging under weak light, good ghost image, wide field of view, stable working performance under high and low temperature environments, low cost and wide application range.

Description

Technical Field

[0001] This invention belongs to the field of optical lens technology, specifically relating to a distortion-free access control lens. Background Technology

[0002] In the field of security cameras, the rapid development of access control cameras has led to a surge in demand. Access control cameras require a large shooting range and precise monitoring of object details during recording, placing higher demands on image quality and ghosting reduction. Therefore, as imaging systems become increasingly integrated and convenient, the matching lenses must be as small as possible in overall size while maintaining image quality to minimize space consumption. Furthermore, traditional access control cameras often produce images with severe distortion, making distortion correction difficult. A larger field of view also makes it more difficult to control the lens's dimensions, increasing design and manufacturing complexity. Therefore, it is essential to ensure that access control cameras can achieve a large field of view while remaining miniaturized, exhibiting low ghosting, and being distortion-free (in current technology, distortion less than 5% is considered distortion-free). Summary of the Invention

[0003] The purpose of this invention is to address the above-mentioned problems by proposing a distortion-free access lens that meets the requirements of small size and lightweight design, low distortion and weak ghosting under large target surfaces, clear imaging even in low light, wide field of view, high image quality, compact structure, and non-defocusing even under environmental conditions with large temperature differences. It also features stable performance, low cost, and wide applicability.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] The present invention proposes a distortion-free access control lens, comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens arranged sequentially from the object plane to the image plane, wherein:

[0006] The first lens is a biconcave aspherical lens with negative optical power;

[0007] The second lens is a convex-concave aspherical lens with positive optical power;

[0008] The third lens is a concave-convex aspherical lens with positive optical power;

[0009] The fourth lens is a biconvex spherical lens with positive optical power;

[0010] The fifth lens is a concave-convex aspherical lens with negative optical power;

[0011] The sixth lens is a biconvex aspherical lens with positive optical power;

[0012] And satisfy the following conditions:

[0013]

[0014]

[0015] Where f1 to f6 are the focal lengths of the first to sixth lenses, respectively, in mm; R 11 R 21 R 31 R 41 R 51 R 61 The following are the radii of curvature of the object-side mirror surfaces of the first to sixth lenses, in mm; R 12 R 22 R 32 R 42 R 52 R 62 The radii of curvature of the image-side mirrors of the first to sixth lenses are in mm, respectively; "-" indicates the negative direction.

[0016] Preferably, the first lens, the second lens, the third lens, the fifth lens, and the sixth lens are all plastic lenses, and the fourth lens is a glass lens.

[0017] Preferably, the distortion-free access control lens also meets the following conditions:

[0018] -0.35 <f1 / f2<-0.3,2.0<|f3 / f4|<2.5,-1.4<|f4 / f5|<-1.35,-0.95<|f5 / f6|<-0.85。

[0019] Preferably, the distortion-free access control lens also meets the following conditions:

[0020] <![CDATA[n d1 ]]> <![CDATA[n d2 ]]> <![CDATA[n d3 ]]> <![CDATA[n d4 ]]> <![CDATA[n d5 ]]> <![CDATA[n d6 ]]> 1.535±5％ 1.661±5％ 1.535±5％ 1.603±5％ 1.614±5％ 1.535±5％ <![CDATA[v d1 ]]> <![CDATA[v d2 ]]> <![CDATA[v d3 ]]> <![CDATA[v d4 ]]> <![CDATA[v d5 ]]> <![CDATA[v d6 ]]> 55.71±5％ 20.37±5％ 55.71±5％ 65.46±5％ 25.75±5％ 55.71±5％

[0021] Where, n d1 ~n d6 The refractive indices of the first to sixth lenses are shown in order, v d1 ~v d6 The Abbe numbers are for the first lens to the sixth lens, respectively.

[0022] Preferably, an aperture stop is provided between the third lens and the fourth lens.

[0023] Preferably, the distortion-free access control lens also meets the following conditions:

[0024] 0.7 <SL / TTL<0.8,0.25<BFL / TTL<0.35,

[0025] Where SL is the distance from the aperture stop to the image plane, in mm; BFL is the back focal length, in mm; and TTL is the total optical length, in mm. The angle of incidence of the principal ray.

[0026] Preferably, the apertures of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are 5.0 mm, 3.173 mm, 2.594 mm, 3.218 mm, 3.957 mm, and 4.995 mm, respectively.

[0027] Preferably, the effective focal length f of the distortion-free access control lens is 3mm to 4mm, the F number is 2.0 to 2.05, the target surface IH is ≥ 1 / 2.7", and the total optical length TTL is ≤ 12mm.

[0028] Preferably, the mirror surfaces of the first lens, second lens, third lens, fifth lens, and sixth lens satisfy the following aspherical equation:

[0029]

[0030] In the formula, z is the sag, c is the curvature, y is the radial coordinate, k is the coefficient of the conic quadratic curve, and A i These are the coefficients of higher-order terms.

[0031] Preferably, the operating wavelength of the distortion-free access control lens is 435nm~656nm and 830nm~870nm.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1) This access control lens balances aberrations by combining spherical and aspherical surfaces, and reasonably sets the focal length and radius of curvature of each lens to correct various aberrations and improve edge image quality. The maximum image height can reach φ7mm, which corresponds to 1 / 2.7” of the target surface, achieving high imaging quality. The optical distortion is less than 4% within a field of view of 98°, meeting the distortion-free requirement under a large field of view, and enabling the lens to achieve clear imaging in both visible light and infrared bands.

[0034] 2) The 1G5P glass-plastic hybrid structure reduces costs while ensuring image quality. The lens structure is compact by reasonably allocating optical power. The large optical back focal space reduces ghosting and weakens it, which can further improve image clarity. The total optical length of the lens is within 12mm, and the head diameter and thread outer diameter are both within φ8mm, which meets the requirements of small size and lightweight.

[0035] 3) By reasonably setting the focal length ratio, the distance from the aperture stop to the image plane, the ratio of the back focal length to the total optical length, and by reasonably matching the materials, the lens can remain in focus under environmental conditions of -40℃ to +85℃, and its working performance is more stable. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the distortion-free access control lens of the present invention;

[0037] Figure 2 This is the optical path diagram of the distortion-free access control lens of the present invention;

[0038] Figure 3 This is the MTF chart of the present invention at room temperature (20°C).

[0039] Figure 4 This is the MTF plot of the present invention at a low temperature of -40°C.

[0040] Figure 5 This is the MTF diagram of the present invention at a high temperature of 85°C;

[0041] Figure 6 This is the MTF diagram of the present invention in the infrared band;

[0042] Figure 7 This is a field curvature and distortion diagram of the present invention.

[0043] Explanation of reference numerals in the attached diagram: L1, first lens; L2, second lens; L3, third lens; L4, fourth lens; L5, fifth lens; L6, sixth lens; IR, filter; CG, protective glass; IMA, image plane. Detailed Implementation

[0044] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0045] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application.

[0046] like Figure 1-7As shown, a distortion-free access control lens includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6 arranged sequentially from the object plane to the image plane, wherein:

[0047] The first lens L1 is a biconcave aspherical lens with negative optical power;

[0048] The second lens L2 is a convex-concave aspherical lens with positive optical power;

[0049] The third lens L3 is a concave-convex aspherical lens with positive optical power;

[0050] The fourth lens, L4, is a biconvex spherical lens with positive optical power;

[0051] The fifth lens, L5, is a concave-convex aspherical lens with negative optical power;

[0052] The sixth lens, L6, is a biconvex aspherical lens with positive optical power;

[0053] And satisfy the following conditions:

[0054] <![CDATA[f1=-3.922±5%]]> <![CDATA[R 11 =-5.78±5%]]> <![CDATA[R 12 =3.42±5%]]> <![CDATA[f2=11.978±5%]]> <![CDATA[R 21 =2.66±5%]]> <![CDATA[R 22 =3.56±5%]]> <![CDATA[f3=9.434±5%]]> <![CDATA[R 31 =-4.29±5%]]> <![CDATA[R 32 =-2.53±5%]]> <![CDATA[f4=4.297±5%]]> <![CDATA[R 41 =8.99±5%]]> <![CDATA[R 42 =-3.36±5%]]> <![CDATA[f5=-3.113±5%]]> <![CDATA[R 51 =-0.98±5%]]> <![CDATA[R 52 =-2.33±5%]]> <![CDATA[f6=3.42±5%]]> <![CDATA[R 61 =3.56±5%]]> <![CDATA[R 62 =-3.22±5%]]>

[0055] Where f1 to f6 are the focal lengths of the first lens L1 to the sixth lens L6, respectively, in mm; R 11 R 21 R 31 R 41 R 51 R 61 The radii of curvature of the object-side mirror surfaces of lenses L1 through L6, in mm, are as follows: R 12 R 22 R 32 R 42 R 52 R 62 The radii of curvature of the image-side mirrors of lenses L1 through L6 are in mm, respectively; "-" indicates the negative direction.

[0056] This access control camera consists of one spherical lens and five aspherical lenses. When light is incident, it passes sequentially through the first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5, and sixth lens L6. The angle of incidence is adjusted to form an image; that is, the positive power lens converges the light, while the negative power lens diverges it. An IR filter and a protective glass CG can be placed between the sixth lens L6 and the image plane IMA. These can be arranged in any order, and the protective glass CG provides effective protection for the photosensitive chip located on the image plane IMA. The combination of spherical and aspherical lenses balances aberrations, and the focal length and radius of curvature of each lens are appropriately set to correct various aberrations, improving edge image quality. The maximum image height can reach φ7mm, achieving high image quality. Optical distortion is less than 4% within a field of view of 98°, meeting the requirement of distortion-free imaging at large field of view, and enabling clear imaging in both visible and infrared bands. By rationally allocating optical power, the lens structure is made compact, and the large optical back focal length space reduces and weakens ghosting, further improving image sharpness. The overall optical length of the lens is within 12mm, and the head diameter and thread outer diameter are both within φ8mm, meeting the requirements of miniaturization and lightweight design. In addition, by rationally setting the ratio of focal length, the distance from the aperture stop to the image plane, the back focal length, and the overall optical length, and by using appropriate materials, the lens remains in focus in environmental conditions ranging from -40℃ to +85℃, resulting in more stable performance.

[0057] In one embodiment, the first lens L1, the second lens L2, the third lens L3, the fifth lens L5, and the sixth lens L6 are all plastic lenses, while the fourth lens L4 is a glass lens. This access control camera consists of one spherical glass lens and five aspherical plastic lenses, employing a 1G5P glass-plastic hybrid structure, which reduces costs while ensuring image quality. It is easy to understand that the material of each lens can also be adjusted according to actual needs.

[0058] In one embodiment, the distortion-free access control lens also satisfies the following condition:

[0059] -0.35 <f1 / f2<-0.3,2.0<|f3 / f4|<2.5,-1.4<|f4 / f5|<-1.35,-0.95<|f5 / f6|<-0.85。

[0060] The focal length of each lens can be set according to actual needs, and better image quality can be obtained when the above conditions are met.

[0061] In one embodiment, the distortion-free access control lens also satisfies the following condition:

[0062]

[0063]

[0064] Among them, n d1 ~n d6 are the refractive indices of the first lens L1 to the sixth lens L6 in sequence, and v d1 ~v d6 are the Abbe numbers of the first lens L1 to the sixth lens L6 in sequence.

[0065] In one embodiment, an aperture stop ST is further provided between the third lens L3 and the fourth lens L4, which is convenient for adjusting the light flux.

[0066] In one embodiment, the distortion-free access control lens further satisfies the following conditions:

[0067] 0.7 < SL / TTL < 0.8, 0.25 < BFL / TTL < 0.35,

[0068] where SL is the distance from the aperture stop ST to the image plane, with the unit of mm, BFL is the back focal length, with the unit of mm, and TTL is the total optical length, with the unit of mm. is the main ray incident angle.

[0069] When the access control lens satisfies 0.7 < SL / TTL < 0.8, it helps to ensure a large light passing aperture at a small F-number (such as 2.0 - 2.05) and meet the resolution requirements. When satisfying 0.25 < BFL / TTL < 0.35, the access control lens further has small distortion and good ghost images under the conditions of satisfying a small F-number and a compact structure.

[0070] In one embodiment, the apertures of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are 5.0mm, 3.173mm, 2.594mm, 3.218mm, 3.957mm, and 4.995mm in sequence.

[0071] Among them, the aperture of the first lens L1 being 5.0mm can make the head of the access control lens within φ8.0mm. For example, an aperture stop ST is provided between the third lens L3 and the fourth lens L4, and the apertures of the first lens L1, the second lens L2, and the third lens L3 decrease in sequence along the optical axis direction, achieving miniaturization of the overall structure while reducing costs; the apertures of the fourth lens L4, the fifth lens L5, and the sixth lens L6 increase in sequence along the optical axis direction, and the aperture of the sixth lens L6 being 4.995mm meets the requirement of the outer diameter M8 of the lens thread, and the use of plastic material realizes the compactness of the structure, ensuring small front and rear apertures in the case of a large target surface, and at the same time, the relatively long optical back focal length can optimize the ghost images. The main optical power is borne by the plastic aspherical surface, reducing the tolerance sensitivity, ensuring mass production, facilitating assembly, reducing costs, reducing manufacturing difficulty, and improving the yield.

[0072] In one embodiment, the effective focal length f of the distortion-free access control lens is 3mm to 4mm, the F number is 2.0 to 2.05, the target surface IH is greater than or equal to 1 / 2.7", and the total optical length TTL is less than or equal to 12mm.

[0073] In one embodiment, the mirror surfaces of the first lens L1, the second lens L2, the third lens L3, the fifth lens L5, and the sixth lens L6 satisfy the following aspherical equation:

[0074]

[0075] In the formula, z is the sag, c is the curvature, y is the radial coordinate, k is the coefficient of the conic quadratic curve, and A i These are the coefficients of higher-order terms.

[0076] In one embodiment, the distortion-free access control lens operates in the wavelength ranges of 435nm–656nm and 830nm–870nm. It can achieve clear imaging under both visible and infrared light.

[0077] The following detailed description is provided through specific embodiments.

[0078] like Figure 1 As shown, in this embodiment, the first lens L1 is a plastic biconcave aspherical lens, the second lens L2 is a plastic convex-concave aspherical lens, the third lens L3 is a plastic concave-convex aspherical lens, the fourth lens L4 is a glass biconvex spherical lens, the fifth lens L5 is a plastic concave-convex aspherical lens, and the sixth lens L6 is a plastic biconvex aspherical lens. Figure 1 The leftmost vertical line represents only a virtual surface, not a specific structure. The planes represented by the other vertical lines between lenses (such as between the second lens L2 and the third lens L3) are also virtual surfaces that act as light-blocking plates. A filter IR and a protective glass CG are also provided between the sixth lens L6 and the image plane IMA. The two can be arranged in any order. In this embodiment, the filter IR is set close to the sixth lens L6, and the filter IR and the protective glass CG are made of the same material. Figure 3-6 The vertical axis represents the OTF modulus, and the horizontal axis represents the spatial frequency in cycles per mm. Figure 3 , Figure 4 and Figure 5 The MTF charts for room temperature (20℃), low temperature (-40℃), and high temperature (85℃) are all in the visible light band; while Figure 6 This is the MTF plot at room temperature (20°C) in the infrared band. Figure 7 The left image is the field curvature diagram, and the right image is the distortion diagram.

[0079] The optical parameters of each lens in this embodiment are shown in Table 1, and the aspherical coefficients are shown in Table 2.

[0080] Table 1

[0081]

[0082] Table 2

[0083]

[0084]

[0085] The object-side mirror surfaces of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are respectively denoted as R11, R21, R31, R41, R51, and R61; the image-side mirror surfaces of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are respectively denoted as R12, R22, R32, R42, R52, and R62.

[0086] Based on the above data, by Figure 3 , 4 As shown in Figure 5, the lens did not exhibit severe defocusing in its MTF curves under extreme conditions including ambient temperature (20℃), low temperature (-40℃), and high temperature (85℃); Figure 6 As shown, this lens can also produce clear images when focusing in the infrared band; generally, a lens with distortion of less than 5% can be called a distortion-free lens. Figure 7 As shown, this lens can achieve distortion-free imaging over a wide field of view, with maximum optical distortion within 4%. The lens used effectively improves image quality and significantly shortens the overall optical length of the lens, with a TTL of 12mm, effectively saving assembly space and enabling further miniaturization. Furthermore, its F-number of 2.0 ensures clear imaging in low light, and the image height can reach φ7mm, resulting in better resolution.

[0087] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0088] The embodiments described above are merely specific and detailed examples of the embodiments described in this application, and should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. Therefore, the scope of protection of this patent application should be determined by the appended claims.

Claims

1. A distortion-free access control lens, characterized in that: The distortion-free access control lens includes a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4), a fifth lens (L5), and a sixth lens (L6) arranged sequentially from the object plane to the image plane. The distortion-free access control lens has six lenses with optical power, wherein: The first lens (L1) is a biconcave aspherical lens with negative optical power; The second lens (L2) is a convex-concave aspherical lens with positive optical power; The third lens (L3) is a concave-convex aspherical lens with positive optical power; The fourth lens (L4) is a biconvex spherical lens with positive optical power; The fifth lens (L5) is a concave-convex aspherical lens with negative optical power; The sixth lens (L6) is a biconvex aspherical lens with positive optical power; And satisfy the following conditions: Where f1~f6 are the focal lengths of the first lens (L1) to the sixth lens (L6), respectively, in mm; R 11 R 21 R 31 R 41 R 51 R 61 The radii of curvature of the object-side mirror surfaces of the first lens (L1) to the sixth lens (L6), in mm, are as follows: R 12 R 22 R 32 R 42 R 52 R 62 The curvature radii of the image-side mirrors of the first lens (L1) to the sixth lens (L6) are in mm, respectively; "-" indicates the negative direction.

2. The distortion-free access control lens as described in claim 1, characterized in that: The first lens (L1), the second lens (L2), the third lens (L3), the fifth lens (L5), and the sixth lens (L6) are all plastic lenses, and the fourth lens (L4) is a glass lens.

3. The distortion-free access control lens as described in claim 1, characterized in that: The distortion-free access control lens also meets the following conditions: -0.35<f1 / f2<-0.3,2.0<|f3 / f4|≤ 。 4. The distortion-free access control lens as described in claim 1, characterized in that: The distortion-free access control lens also meets the following conditions: Where, n d1 ~n d6 The refractive indices of the first lens (L1) to the sixth lens (L6) are, in order, v d1 ~v d6 The Abbe numbers are, in order, the first lens (L1) to the sixth lens (L6).

5. The distortion-free access control lens as described in claim 1, characterized in that: An aperture stop (ST) is also provided between the third lens (L3) and the fourth lens (L4).

6. The distortion-free access control lens as described in claim 5, characterized in that: The distortion-free access control lens also meets the following conditions: 0.7 <SL / TTL<0.8,0.25<BFL / TTL<0.35,17.5°<φ<19° Wherein, SL is the distance from the aperture stop (ST) to the image plane in mm, BFL is the back focal length in mm, TTL is the total optical length in mm, and φ is the principal ray incident angle.

7. The distortion-free access control lens as described in claim 1, characterized in that: The apertures of the first lens (L1), the second lens (L2), the third lens (L3), the fourth lens (L4), the fifth lens (L5), and the sixth lens (L6) are 5.0 mm, 3.173 mm, 2.594 mm, 3.218 mm, 3.957 mm, and 4.995 mm, respectively.

8. The distortion-free access control lens as described in claim 1, characterized in that: The distortion-free access control lens has an effective focal length f of 3mm to 4mm and an F-number of 2.0 to 2.

05.

9. The distortion-free access control lens as described in claim 1, characterized in that: The object-side and image-side mirrors of the first lens (L1), the second lens (L2), the third lens (L3), the fifth lens (L5), and the sixth lens (L6) satisfy the following aspherical equation: ； In the formula, z is the sag, c is the curvature, y is the radial coordinate, and k is the coefficient of the conic section. These are the coefficients of higher-order terms.

10. The distortion-free access control lens as described in claim 1, characterized in that: The distortion-free access control lens operates in the wavelength range of 435nm~656nm and 830nm~870nm.

Images