A compact ten-times continuous zoom optical system for security

Abstract

The utility model discloses a compact type ten times continuous zoom optical system for security, it includes front fixed group, zoom group, compensation group, rear fixed group and image surface, front fixed group includes two pieces of spherical positive lens and a piece of spherical negative lens, corrects distortion and converges light beam, zoom group includes two pieces of spherical negative lens and a piece of spherical positive lens, corrects chromatic aberration, compensation group includes a piece of aspheric positive lens, a piece of spherical negative lens and a piece of spherical positive lens, corrects spherical aberration and converges light beam, rear fixed group includes a piece of aspheric positive lens and two pieces of spherical negative lens, corrects field curvature and converges to image surface and forms the image. The optical system provided by the utility model, its image side F number is 2.4, and the resolution is high, and the imaging quality is good, the system structure is compact and simple, and the total length is only 290mm, and the stability is high, and the cam curve is smooth and has no inflection point, and is easy to process and install and adjust, is used for security system, can realize fine identification in wide range, and has wide application prospect.

Description

Technical Field

[0001] This utility model relates to the field of optical design technology, specifically to a compact 10x continuous zoom optical system for security applications. Background Technology

[0002] Among the various cameras that come into direct contact with humans, security cameras are among the most important and closely related to daily life. Currently, the security field is undergoing a technological iteration from traditional fixed-focus systems to intelligent zoom systems. Fixed-focus security lenses no longer meet the security needs of various situations. Traditional fixed-focus systems, limited by their fixed focal length design, have significant shortcomings when dealing with complex monitoring scenarios—they can only achieve localized observation through digital magnification. This pixel-interpolation-based magnification method leads to a decrease in image resolution, making it difficult to meet the accuracy requirements of modern security in key areas such as target recognition and feature extraction.

[0003] Compared to traditional fixed-focus systems, the most significant advantage of zoom systems lies in their ability to continuously change the lens's focal length through the coordinated operation of a precision cam mechanism and a stepper motor. This allows for a continuous increase in the magnification of the observed object, enabling not only global monitoring but also high resolution and lossless local magnification for close monitoring. Therefore, zoom optical systems can not only perform wide-area searches of targets of interest but also precise tracking and detailed observation.

[0004] Currently, most security lenses designed by domestic lens manufacturers are fixed-focus or low-magnification zoom lenses, which are not suitable for large-scale regional monitoring and fine identification in various parking lots or warehouses. Prior to this invention, the literature "Design of a 10x Zoom Lens" ([D]. Changchun University of Technology, 2022) reported a 10x zoom lens for security. This article, through analysis of optical zoom principles and combined with Gaussian optical theory and optical lens design methods, provides a 14-element 10x continuous zoom lens. The system has a total length of 370mm and is achieved using 14 lenses. Each of the four lens groups adopts a single-lens-double cemented lens combination structure, which has many limitations in terms of size and weight for practical security applications. On the other hand, the system has a field of view of only 2.5° to 25°, which is small and results in a small detection range, making it difficult to obtain information over a wider area in the use of security lenses. Furthermore, the system distortion reaches 3%, and the imaging quality needs to be improved. In summary, the system has many shortcomings, such as excessive size, small detection field of view, and excessive distortion, which limits its practical use in security cameras. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a zoom imaging system that is simple and compact in structure, has a large zoom range, and is easy to manufacture and adjust.

[0006] The technical solution to achieve the purpose of this invention is to provide a compact 10x continuous zoom optical system for security purposes, which includes a front fixed group, a zoom group, a compensation group, a rear fixed group, and an image plane;

[0007] The aforementioned front fixing group is a Cook three-piece structure. According to the light incident direction, the front fixing group consists of a first positive lens, a negative lens, and a second positive lens. The radii of curvature of each lens surface are R11, R12, R13, R14, R15, and R16, respectively, satisfying the conditions 0.9mm≤R11≤2.3mm, -181mm≤R12≤-180mm, -4mm≤R13≤-3mm, -20.2mm≤R14≤-19.2mm, -3.8mm≤R15≤-3.1mm, and -8.2mm≤R16≤-7.4mm.

[0008] The zoom group includes a first negative lens, a second negative lens, and a positive lens. The radii of curvature of each lens surface are R21, R22, R23, R24, R25, and R26, respectively, satisfying the conditions 0.9mm≤R21≤2.3mm, -181mm≤R22≤-180mm, -4mm≤R23≤-3mm, -20.2mm≤R24≤-19.2mm, -3.8mm≤R25≤-3.1mm, and -8.2mm≤R26≤-7.4mm.

[0009] The compensation group includes a first positive lens, a negative lens, and a second positive lens. The radii of curvature of each lens surface are R31, R32, R33, R34, R35, and R36, respectively, satisfying the conditions 0.9mm≤R31≤2.3mm, -181mm≤R32≤-180mm, -4mm≤R33≤-3mm, -20.2mm≤R34≤-19.2mm, -3.8mm≤R35≤-3.1mm, and -8.2mm≤R36≤-7.4mm.

[0010] The rear fixing group includes a positive lens, a first negative lens, and a second negative lens. The radii of curvature of each lens surface are R41, R42, R43, R44, R45, and R46, respectively, satisfying the conditions 0.9mm≤R41≤2.3mm, -181mm≤R42≤-180mm, -4mm≤R43≤-3mm, -20.2mm≤R44≤-19.2mm, -3.8mm≤R45≤-3.1mm, and -8.2mm≤R46≤-7.4mm.

[0011] The aperture stop of the optical system is positioned between the compensation group and the rear fixing group, with a distance d from the rear fixing group of 0.9mm ≤ d ≤ 2.3mm.

[0012] The front and rear surfaces of the first positive lens in the compensation group and the positive lens in the rear fixed group are both aspherical. A Cartesian coordinate system is constructed with the intersection of the lens surface and the optical axis as the origin. The incident direction of the light is the positive Z-axis, the positive Y-axis is upward, and the positive X-axis is perpendicular to the paper and inward. The equation for the sag Z of the even-order aspherical surface is:

[0013]

[0014] Where c is the curvature; r is the radius; k is the quadratic surface coefficient; a i It is the coefficient of the monomial.

[0015] The front surface of the first positive lens of the compensation group described in this utility model has -0.5≤k≤0, and the coefficients of each monomial satisfy the following conditions: , , , , , The rear surface of the first positive lens in the compensation group, 17.5≤k≤19.1, and the coefficients of each monomial satisfy the following conditions: , , , , , .

[0016] The front surface of the positive lens of the rear fixed group, -0.1≤k≤0.1, and the coefficients of each monomial satisfy the following conditions: , , , , , The rear surface of the fixed positive lens, -2.1≤k≤-0.9, and the coefficients of each monomial satisfy the following conditions: , , , , , .

[0017] The present invention discloses a compact 10x continuous zoom optical system for security applications, wherein the image-side F-number ranges from 2.35 to 2.45; in the long-focus mode, the focal length ranges from 148mm to 152mm, and the object-side field of view ranges from 2.2° to 3.5°; in the short-focus mode, the focal length ranges from 14.5mm to 15.5mm, and the object-side field of view ranges from 29° to 31°.

[0018] The present invention describes a compact 10x continuous zoom optical system for security applications, wherein the total length L is in the range of 288mm≤L≤292mm.

[0019] This utility model provides a compact 10x continuous zoom optical system for security applications, suitable for use in large-area parking lots or warehouses. It can meet both the requirements for monitoring vehicles and goods over large areas and for precise license plate and facial recognition. Compared with existing technologies, the advantages of this utility model are:

[0020] 1. This utility model aims to achieve a continuous zoom optical system with a large zoom ratio. However, due to the contradiction between a large zoom ratio and a compact design, a large zoom ratio inevitably leads to a complex optical system structure and an increase in lens size and weight. Therefore, a positive group compensation mechanical compensation zoom method is adopted, which has stronger chromatic aberration and spherical aberration correction capabilities compared to negative group compensation. Furthermore, through zoom differential equation calculation, the optical power of each component is rationally allocated, ensuring a simple and compact system structure while achieving a large zoom ratio. This utility model achieves 10x continuous zoom, providing a large zoom range and meeting the needs of long-range monitoring and wide-angle precision identification.

[0021] 2. This invention addresses the high-resolution imaging requirements of security lenses. Through research on first-order aberration theory and aberration characteristics, it investigates the position of the aspherical surface, concluding that placing the aperture stop in front of the aspherical lens precisely suppresses spherical aberration without affecting other aberrations. The chosen aspherical surface position enhances the system's ability to balance various geometric aberrations. Corrections are made for spherical aberration and distortion in the optical system, effectively improving the overall imaging resolution. Compared to existing 10x zoom lenses, the imaging quality is significantly improved. For the commonly used 3.5μm pixel size in visible light detectors, this invention achieves an optical transfer function greater than 0.6 across the entire operating band and field of view at 100 lp / mm, demonstrating excellent imaging quality.

[0022] 3. This utility model addresses the design requirements of compact security lenses. During the design phase, structural optimization was implemented within the constraints of system aperture, ensuring that the optimized system achieves good image quality while remaining compact. The proposed 10x security lens has a total length of only 290mm, featuring a compact structure and good stability, laying the foundation for applications in various security fields where size and weight are limited. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the compact 10x zoom security optical system provided in this embodiment of the utility model.

[0024] Figure 2This is a schematic diagram of the zoom optical system provided in this embodiment of the invention under different focal length states.

[0025] Figure 3 This is a diagram showing the focused light spot pattern of the zoom optical system provided in this embodiment of the invention across the entire field of view and working wavelength at different focal lengths.

[0026] Figure 4 This is a graph of the MTF (Mean Transfer Function) of the zoom optical system provided in this embodiment of the present invention.

[0027] Figure 5 This is a distortion curve diagram of the zoom optical system provided in this embodiment of the utility model.

[0028] Figure 6 This is a curve showing the energy concentration of the zoom optical system provided in this embodiment of the present invention.

[0029] Figure 7 This is a cam curve diagram of the zoom optical system provided in this embodiment of the utility model.

[0030] Among them, 1. Front fixed group; 11. First positive lens of front fixed group; 12. Negative lens of front fixed group; 13. Second positive lens of front fixed group; 2. Magnification group; 21. First negative lens of zoom group; 22. Second negative lens of zoom group; 23. Positive lens of zoom group; 3. Compensation group; 31. First positive lens of compensation group; 32. Negative lens of compensation group; 33. Second positive lens of compensation group; 4. Rear fixed group; 111. Aperture stop; 41. Positive lens of rear fixed group; 42. First negative lens of rear fixed group; 43. Second negative lens of rear fixed group; 5. Image plane. Detailed Implementation

[0031] The technical solution of this utility model will be further described below with reference to the accompanying drawings and embodiments. Example

[0032] This embodiment provides a compact 10x continuous zoom optical system for security applications. The optical system consists of twelve lenses, has an image-side F-number of 2.4, operates in the 486~656nm wavelength range, and has a zoom range of 15~150mm, achieving a large zoom ratio of 10x. The system has a field of view of 3.1° at telephoto and 30° at focal length, and a total system length of 290mm.

[0033] The performance parameters of the zoom optical system provided in this embodiment are shown in Table 1.

[0034] Table 1:

[0035] Operating wavelength (nm) 486~656 F number 2.4 Focal length (mm) 15~150 Field of view Telephoto: 3.1°; Short telephoto: 30° System Length 290

[0036] See appendix Figure 1This is a schematic diagram of the zoom optical system structure described in this embodiment. According to the direction of light incident, the optical elements are as follows: front fixed group 1, zoom group 2, compensation group 3, rear fixed group 4, aperture stop 111, and image plane 5; wherein the front fixed group 1 includes a first positive lens 11, a negative lens 12, and a second positive lens 13; the zoom group 2 includes a first negative lens 21, a second negative lens 22, and a positive lens 23; the compensation group 3 includes a first positive lens 31, a negative lens 32, and a second positive lens 33; and the rear fixed group 4 includes a positive lens 41, a first negative lens 42, and a second negative lens 43.

[0037] In this embodiment, the front and rear surfaces of the first positive lens 31 of the compensation group and the positive lens 41 of the rear fixed group are both even-order aspherical surfaces. A Cartesian coordinate system is constructed with the intersection of the lens surface and the optical axis as the origin. The incident direction of the light is the positive Z-axis, the positive Y-axis is upward, and the positive X-axis is perpendicular to the paper and outward. The equation for the height Z of the even-order aspherical surface is:

[0038]

[0039] Where c is the curvature; r is the radius; k is the quadratic surface coefficient; a i These are the coefficients of the monomials; where the front surface of the first positive lens 31 in the compensation group has k=-0.282, and the coefficients of each monomial are respectively... , , , , , The rear surface of the first positive lens 31 in the compensation group has a value of k=18.259, and the coefficients of each monomial are as follows: , , , , , Wherein, the front surface k of the rear fixed group positive lens 41 is -0.016, and the coefficients of each monomial are respectively... , , , , , The rear surface of the fixed positive lens 41 has a k=-1.813, and the coefficients of each monomial are as follows: , , , , , .

[0040] The parameters of each optical element in this embodiment are shown in Table 2.

[0041] Table 2:

[0042] ,

[0043] See appendix Figure 2 This is a schematic diagram of the zoom optical system provided in this embodiment under different focal length states; in the figure, (a), (b), (c) and (d) correspond to the optical path structure of the zoom optical system provided in this embodiment under focal lengths of 15mm, 60mm, 110mm and 150mm respectively.

[0044] Table 3 shows the different air gap parameters of the structure of the zoom optical system provided in this embodiment under different focal length states.

[0045] Table 3:

[0046] .

[0047] See appendix Figure 3 It is a ray tracing point diagram of light passing through the zoom optical system provided in this embodiment. The root mean square radius of the point diagrams for each focal length corresponding to the four fields of view in the figure is less than 5.7 μm, and the average geometric radius of the point diagrams is less than 12.67 μm, indicating good imaging quality.

[0048] See appendix Figure 4 This figure shows the MTF (Mean Transfer Function) curves of the zoom optical system provided in this embodiment for each field of view on the corresponding image plane. In the figure, (a), (b), (c), and (d) correspond to the MTF curves of all fields of view on the corresponding image planes of the zoom optical system provided in this embodiment at focal lengths of 15mm, 60mm, 110mm, and 150mm, respectively. Figure 4 It can be seen that the optical transfer function of the entire working band and field of view within the zoom range of 100 lp / mm is greater than 0.6, which is close to the diffraction limit. The curve is smooth and compact, indicating that the system has clear and uniform imaging and good imaging quality in the entire band and field of view.

[0049] See appendix Figure 5 This figure shows the distortion curves of the zoom optical system provided in this embodiment at four focal lengths. Figures (a), (b), (c), and (d) correspond to the distortion curves of the zoom optical system provided in this embodiment at focal lengths of 15mm, 60mm, 110mm, and 150mm, respectively, on the image plane. The vertical axis represents the normalized field of view, and the horizontal axis represents the percentage of image distortion at each field of view. Distortion causes image deformation; a smaller percentage of distortion indicates less image deformation. Figure 4 It can be seen that the maximum distortion of the zoom optical system does not exceed 2.1% in the normalized field of view under different focal lengths.

[0050] See appendix Figure 6This is a graph showing the energy concentration curves of the zoom optical system provided in this embodiment at four focal lengths. In the graph, (a), (b), (c), and (d) correspond to the energy concentration curves of the zoom optical system provided in this embodiment on the image plane at focal lengths of 15mm, 60mm, 110mm, and 150mm, respectively. Figure 6 It can be seen that more than 85% of the energy is concentrated in the Airy spot area, indicating that the energy is relatively concentrated.

[0051] See appendix Figure 7 This is a cam curve diagram of the zoom optical system provided in this embodiment. In the diagram, the horizontal axis represents the distance the zoom group and compensation group move along the optical axis, and the vertical axis represents the rotation angle of the cam. Figure 7 It can be seen that the cam curve of the zoom optical system has a smooth transition without any inflection points, which facilitates the mechanical design of the cam, makes it easy to manufacture, and ensures high system stability.

Claims

1. A compact 10x continuous zoom optical system for security applications, characterized in that: It includes a front fixation group (1), a zoom group (2), a compensation group (3), a rear fixation group (4), and an image plane (5); The aforementioned front fixed group (1) is a Cook three-piece structure. According to the light incident direction, it consists of the first positive lens (11), the negative lens (12), and the second positive lens (13) of the front fixed group. The radii of curvature of each lens surface are R11, R12, R13, R14, R15, and R16, respectively, satisfying the conditions 0.9mm≤R11≤2.3mm, -181mm≤R12≤-180mm, -4mm≤R13≤-3mm, -20.2mm≤R14≤-19.2mm, -3.8mm≤R15≤-3.1mm, and -8.2mm≤R16≤-7.4mm. The zoom group (2) includes a first negative lens (21), a second negative lens (22), and a positive lens (23). The radii of curvature of each lens surface are R21, R22, R23, R24, R25, and R26, respectively, satisfying the conditions 0.9mm≤R21≤2.3mm, -181mm≤R22≤-180mm, -4mm≤R23≤-3mm, -20.2mm≤R24≤-19.2mm, -3.8mm≤R25≤-3.1mm, and -8.2mm≤R26≤-7.4mm. The compensation group (3) includes a first positive lens (31), a negative lens (32), and a second positive lens (33). The radii of curvature of each lens surface are R31, R32, R33, R34, R35, and R36, respectively, satisfying the conditions 0.9mm≤R31≤2.3mm, -181mm≤R32≤-180mm, -4mm≤R33≤-3mm, -20.2mm≤R34≤-19.2mm, -3.8mm≤R35≤-3.1mm, and -8.2mm≤R36≤-7.4mm. The rear fixing group (4) includes a rear fixing group positive lens (41), a rear fixing group first negative lens (42), and a rear fixing group second negative lens (43). The radii of curvature of each lens surface are R41, R42, R43, R44, R45, and R46, respectively, satisfying the conditions 0.9mm≤R41≤2.3mm, -181mm≤R42≤-180mm, -4mm≤R43≤-3mm, -20.2mm≤R44≤-19.2mm, -3.8mm≤R45≤-3.1mm, and -8.2mm≤R46≤-7.4mm. The aperture stop (111) of the optical system is set between the compensation group (3) and the rear fixing group (4), and the distance d from the rear fixing group is 0.9mm≤d≤2.3mm; The front and rear surfaces of the first positive lens (31) of the compensation group and the positive lens (41) of the rear fixed group are both aspherical. A Cartesian coordinate system is constructed with the intersection of the lens surface and the optical axis as the origin. The incident direction of the light is the positive direction of the Z-axis, the positive direction of the Y-axis is upward, and the positive direction of the X-axis is perpendicular to the paper and inward. The equation for the sag of the even-order aspherical surface Z is: ， Where c is the curvature; r is the radius; k is the quadratic surface coefficient; a i It is the coefficient of the monomial.

2. A compact 10x continuous zoom optical system for security applications according to claim 1, characterized in that: The front surface of the first positive lens (31) of the compensation group, -0.5≤k≤0, and the coefficients of each monomial satisfy the following conditions: , , , , , The rear surface of the first positive lens (31) of the compensation group, 17.5≤k≤19.1, the coefficients of each monomial satisfy the following conditions: , , , , , .

3. A compact 10x continuous zoom optical system for security applications according to claim 1, characterized in that: The front surface of the rear fixed positive lens (41) has -0.1≤k≤0.1, and the coefficients of each monomial satisfy the following conditions: , , , , , The rear surface of the rear fixed positive lens (41) has -2.1≤k≤-0.9, and the coefficients of each monomial satisfy the following conditions: , , , , , .

4. A compact 10x continuous zoom optical system for security applications according to claim 1, characterized in that: The system's image-side F-number ranges from 2.35 to 2.45; in telephoto mode, the focal length ranges from 148mm to 152mm, and the object-side field of view ranges from 2.2° to 3.5°; in short-focal-length mode, the focal length ranges from 14.5mm to 15.5mm, and the object-side field of view ranges from 29° to 31°.

5. A compact 10x continuous zoom optical system for security applications according to claim 1, characterized in that: The total length L of the system is in the range of 288mm ≤ L ≤ 292mm.

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