A large-aperture and ultra-low distortion 16mm fixed-focus optical system

Abstract

The present invention discloses a 16mm fixed-focus optical system with a large aperture and ultra-low distortion, which is applied to the machine vision field of intelligent security. The key points of its technical solution are as follows: It includes lens one, lens two, a cemented lens, a diaphragm, lens three, lens four, and lens five, which are arranged in sequence from the object plane to the image plane and rotate around the optical axis; the technical effect is that it can better reduce the distortion generated by the large aperture, and thus better improve the imaging quality. The system retains the optical design symmetric before and after the diaphragm, but introduces a group of doublet lenses to replace the single lens placed in front of the diaphragm instead of the traditional structure placed behind the diaphragm. Its main function is to converge the focusing positions of the chief rays and marginal rays in each field of view, and a heavy flint glass is specially arranged near the image plane of the system to correct the image plane curvature, correcting the original optical distortion of 5%-10% to within 0.1%.

Description

Technical Field

[0001] The present invention relates to the field of machine vision for intelligent security, and particularly to a 16mm fixed-focus optical system with a large aperture and ultra-low distortion. Background Art

[0002] Against the backdrop of the continuous development of intelligent security and intelligent vision products, as well as industrial automation vision inspection, it has become increasingly common in various fields of society to complete tasks such as the acquisition, processing, and judgment of some image data information through technical means such as visual image acquisition and image algorithms. How to collect more stable and less distorted images in various complex environments is a rather thorny problem faced by everyone. The 16mm fixed-focus optical system developed in this patent mainly solves two problems: one is the problem of still being able to clearly focus and image with sufficient image plane illumination in low-light environments. The developed optical system uses a large aperture with an F# of 1.2, replacing the mainstream F#1.6 - 2.4 on the market currently. The other is to control the optical distortion within 1%, meeting the design of nearly distortion-free images throughout the entire viewing angle. Currently, the optical distortion of similar products on the market is generally 10% or more, and obvious bending deformation can be seen in the edge area of the image. Summary of the Invention

[0003] The purpose of the present invention is to provide a 16mm fixed-focus optical system with a large aperture and ultra-low distortion, and its advantage is that it can better reduce the distortion generated by the large aperture, thereby better improving the imaging quality.

[0004] The above technical purpose of the present invention is achieved through the following technical solutions: A 16mm fixed-focus optical system with a large aperture and ultra-low distortion, characterized in that it includes a first lens, a second lens, a cemented lens, a diaphragm, a third lens, a fourth lens, and a fifth lens sequentially arranged from the object plane to the image plane, and with the optical axis as the rotation center;

[0005] Wherein:

[0006] The object plane of the first lens is a convex spherical surface with a curvature radius of 24.7mm,

[0007] The image plane of the first lens is a concave spherical surface with a curvature radius of 15.4mm;

[0008] The object plane of the second lens is a convex spherical surface with a curvature radius of 23.6mm,

[0009] The image plane of the second lens is a concave spherical surface with a curvature radius of 145mm;

[0010] The object plane of the first lens of the cemented lens is a convex spherical surface with a curvature radius of 13.85mm,

[0011] The image surface of the first lens of the glued lens is a convex spherical surface with a radius of curvature of -35.6 mm;

[0012] The object surface of the second lens of the glued lens is a concave spherical surface with a radius of curvature of -35.6 mm,

[0013] The image surface of the second lens of the glued lens is a concave spherical surface with a radius of curvature of 13 mm;

[0014] The object surface of the third lens is a convex spherical surface with a radius of curvature of 39.6 mm,

[0015] The image surface of the third lens is a convex spherical surface with a radius of curvature of -25.7 mm;

[0016] The object surface of the fourth lens is a convex spherical surface with a radius of curvature of 13.4 mm,

[0017] The image surface of the fourth lens is a convex spherical surface with a radius of curvature of -95.8 mm;

[0018] The object surface of the fifth lens is a concave spherical surface with a radius of curvature of -63.7 mm,

[0019] The image surface of the fifth lens is a concave spherical surface with a radius of curvature of 9.8 mm;

[0020] The present invention is further configured such that: the surface type tolerances of the curvatures of the first lens, the second lens, the glued lens, the diaphragm, the third lens, the fourth lens, and the fifth lens are f-number 3 - 4, and the local f-number is 0.3 - 0.5.

[0021] The present invention is further configured such that: the first lens is made of lanthanum flint glass,

[0022] The second lens is made of heavy lanthanum flint glass,

[0023] The first lens of the glued lens is made of light crown glass,

[0024] The second lens of the glued lens is made of heavy flint glass,

[0025] The third lens is made of heavy lanthanum flint glass,

[0026] The fourth lens is made of heavy lanthanum flint glass,

[0027] The fifth lens is made of heavy flint glass.

[0028] The present invention is further configured such that: the overall optical length of this optical system is 58 mm.

[0029] The present invention is further configured such that: the optical interval from the first lens to the second lens is 23.52 - 23.62 mm,

[0030] The optical distance from the second lens to the cemented lens is 4.47 - 4.53 mm,

[0031] The optical distance from the cemented lens to the diaphragm is 2.723 - 2.763 mm,

[0032] The optical distance from the diaphragm to the third lens is 0.123 - 0.143 mm,

[0033] The optical distance from the third lens to the fourth lens is 0.28 - 0.32 mm,

[0034] The optical distance from the fourth lens to the fifth lens is 0.15 - 0.19 mm, and the optical distance from the fifth lens to the lens image plane is 14.4 - 14.6 mm.

[0035] The present invention is further configured such that: the optical distance from the first lens to the second lens is 23.57 mm,

[0036] The optical distance from the second lens to the cemented lens is 4.5 mm,

[0037] The optical distance from the cemented lens to the diaphragm is 2.743 mm,

[0038] The optical distance from the diaphragm to the third lens is 0.133 mm,

[0039] The optical distance from the third lens to the fourth lens is 0.3 mm,

[0040] The optical distance from the fourth lens to the fifth lens is 0.17 mm,

[0041] The optical distance from the fifth lens to the lens image plane is 14.5 mm.

[0042] In summary, the present invention has the following beneficial effects:

[0043] 1. This optical system is a 16 mm fixed - focus optical system with an optical distortion of 0.9%, a maximum aperture of F#1.2, and a corresponding resolution of 5 million. This optical system has better improved the image illumination and clarity in low - light environments;

[0044] 2. Moreover, the maximum optical distortion is controlled within 0.9%, which better reduces the optical distortion so as to solve the accuracy error problem in image size calibration in the fields of intelligent vision and machine vision. Description of the Drawings

[0045] Figure 1 is a schematic diagram of the optical path structure of the optical system of this embodiment;

[0046] Figure 2 is the fan diagram of the optical system of this embodiment;

[0047] Figure 3 is the distortion and field curvature diagram of the optical system of this embodiment;

[0048] Figure 4 is the modulation optical transfer function curve diagram of the optical system of this embodiment;

[0049] Figure 5 is the image plane illuminance curve diagram of the optical system of this embodiment;

[0050] Figure 6 is the schematic diagram of the circle of confusion of the optical system of this embodiment.

[0051] Reference numerals: 1, the first lens; 2, the second lens; 3, the cemented lens; 4, the aperture stop; 5, the third lens; 6, the fourth lens; 7, the fifth lens; 8, the first lens element; 9, the second lens element. Detailed implementation manners

[0052] The present invention will be further described in detail below with reference to the accompanying drawings.

[0053] Embodiment:

[0054] Refer to Figure 1 , a large aperture and ultra-low distortion 16 mm fixed focal length optical system is composed of glass spherical lenses and an aperture stop 4, and all the spherical lenses and the aperture stop 4 are arranged in sequence with the optical axis as the rotation center; from the object plane to the image plane are successively the first lens 1, the second lens 2, the cemented lens 3, the aperture stop 4, the third lens 5, the fourth lens 6 and the fifth lens 7, wherein the cemented lens 3 is formed by cementing the first lens element 8 and the second lens element 9; the optical path of this optical system is a fixed focal length optical path, no fixed object plane is provided, and the object is at infinity; this optical system can be matched with a C-mount industrial camera, the C-mount flange distance is 17.526 mm, the back focal length is 14.5 mm, and the overall lens group deep into the interface is 3 mm.

[0055] The curvature surface type data of each lens are as follows:

[0056] The object surface of the first lens 1 is a convex spherical surface with a curvature radius of 24.7 mm, and the image surface is a concave spherical surface with a curvature radius of 15.4 mm;

[0057] The object surface of the second lens 2 is a convex spherical surface with a curvature radius of 23.6 mm, and the image surface is a concave spherical surface with a curvature radius of 145 mm;

[0058] The object surface of the first lens element 8 of the cemented lens 3 is a convex spherical surface with a curvature radius of 13.85 mm, and the image surface is a convex spherical surface with a curvature radius of -35.6 mm;

[0059] The object surface of the second lens element 9 of the cemented lens 3 has the same curvature as the image surface curvature of the first lens element 8 of the cemented lens 3, and the image surface is a concave spherical surface with a curvature radius of 13 mm;

[0060] The object surface of lens 35 is a convex spherical surface with a curvature radius of 39.6mm, and the image surface is a convex spherical surface with a curvature radius of -25.7mm;

[0061] The object surface of lens 46 is a convex spherical surface with a curvature radius of 13.4 mm, and the image surface is a convex spherical surface with a curvature radius of -95.8 mm;

[0062] The object surface of lens 57 is a concave spherical surface with a curvature radius of -63.7mm, and the image surface is a concave spherical surface with a curvature radius of 9.8mm;

[0063] The surface tolerance of all curvatures is aperture 3-4, the local aperture is 0.3-0.5, and interferometer is used for detection.

[0064] The material data of each lens is as follows:

[0065] All lenses are made of Chengdu Guangming colorless glass and are indicated by Chengdu Guangming's brand names. In order to ensure subsequent industrial production, all brands are currently recommended for mass production.

[0066] Lens 1 is made of lanthanum flint glass (H-LAF53); lens 2 is made of heavy lanthanum flint glass (H-ZLAF75A); the first lens 8 of the laminate 3 is made of light crown glass (H-QK3L), and the second lens 9 is made of heavy flint glass (H-ZF4); lens 3 5 is made of heavy lanthanum flint glass (H-ZLAF75A); lens 4 6 is made of heavy lanthanum flint glass (H-ZLAF75A); lens 5 7 is made of heavy flint glass (H-ZF50).

[0067] refer to Figure 1 The system has an optical path structure of six groups of seven lenses. The system aperture 4 of the entire optical system is set between the glued sheet 3-1 and the lens 3-5. The total optical length of the system (from the center of curvature of the first lens to the image plane) is 58mm.

[0068] The optical interval between lens 1 and lens 2 is 23.57 mm.

[0069] The optical distance from lens 1 to cemented sheet 3 is 4.5 mm;

[0070] The optical distance from the glued sheet 3 to the aperture 4 is 2.743 mm.

[0071] The optical interval from aperture 4 to lens three 5 is 0.133 mm;

[0072] The optical interval from lens three 5 to lens four 6 is 0.3 mm;

[0073] The optical interval from lens 4 6 to lens 5 7 is 0.17 mm;

[0074] The optical distance from lens five 7 to the image plane is 14.5 mm;

[0075] The designed focal length is 16 mm, the image plane is 11 mm in diameter, and the half field angle on the object side is 19.4°.

[0076] The working environment of this optical system is the visible light environment, and the working wavelength range is between 485 nm and 655 nm;

[0077] This optical system solves two main problems: 1. The maximum aperture is F#1.2. With the ultra-large aperture design, it can be better applied in low-light environments and has a larger diffraction limit at the same time. 2. The maximum optical distortion of the system is controlled within 0.1%, enabling it to complete visual imaging tasks for size detection at the 0.01 mm level during visual inspection applications;

[0078] Problem 1: The maximum aperture design of traditional industrial 16 mm fixed-focus optical lenses is generally between F#1.6 - 2.4. Calculated by f / D = F#, the entrance pupil diameter of the lens is between 10 - 6.6 mm. The larger the entrance pupil, the greater the spherical aberration, coma, and astigmatism of the system itself, the greater the difficulty of system correction, the more complex the optical path, and the more sensitive it is. For the already mature 5G (5 groups of optical lenses) system, it is very difficult to achieve a 5 million resolution with an image-side accuracy within 3.45 microns. This system adopts a six-group and seven-element structure, in which three pieces of heavy lanthanum flint glass with high refractive index are used, and the refractive index is above 1.8. At the same time, the overall optical length of the optical path is increased, and the optical length reaches 58 mm. Especially, the optical distance between the first lens and the second lens is greater than 10 mm, so that there is no more high-order spherical aberration between the marginal chief ray and the marginal ray of the marginal field of view. At the same time, the optical distance of more than 10 mm ensures that the object surface curvature of the first lens is not too small and difficult to process. This unique material selection and optical structure layout enable it to not only have good processability but also achieve an entrance pupil diameter of 13.3 mm on the basis of meeting the 5 million resolution, thus meeting the optical design requirements of F#1.2.

[0079] Problem 2: Fixed-focus imaging systems with a general focal length less than 25 mm will have an optical distortion within 1% - 10%. Moreover, as the focal length value becomes smaller, the optical distortion will increase rapidly. This is caused by the increase in the angle between the chief ray of the object-side edge field of view and the optical axis. Therefore, wide-angle lenses (lenses with a focal length of 35 or less than 25) generally have very obvious distortion. In this optical design, in order to control the distortion within 0.1%, the structure of the optical path has been changed on the basis of the traditional three-piece type. The system retains the optical design that is symmetric before and after the aperture 4, but introduces a group of doublet lenses to replace the single lens placed in front of the aperture 4, rather than the traditional structure placed behind the aperture 4. Its main function is to converge the focusing positions of the chief rays and marginal rays of each field of view. Moreover, a heavy flint glass is specially set at the position close to the image plane of the system to correct the image plane curvature, correcting the original optical distortion of 5% - 10% to within 0.1%. Of course, such a design introduces a new problem that a certain amount of vignetting will be brought into the edge field of view. However, from the result, the image plane illuminance of the edge field of view still ensures more than 70% of the illuminance of the central field of view, thus ensuring the performance of the product.

[0080] This specific embodiment is only an explanation of the present invention and is not a limitation thereof. Those skilled in the art can make modifications to this embodiment without creative contributions according to needs after reading this specification, but as long as it is within the scope of the claims of the present invention, it is protected by the patent law.

Claims

1. A large-aperture and ultra-low-distortion 16mm fixed-focus optical system, characterized in that, it includes a first lens (1), a second lens (2), a cemented lens (3), a diaphragm (4), a third lens (5), a fourth lens (6) and a fifth lens (7) sequentially arranged from the object plane to the image plane, and is centered on the optical axis for rotation; wherein: the object plane of the first lens (1) is a convex spherical surface with a radius of curvature of 24.7mm, the image plane of the first lens (1) is a concave spherical surface with a radius of curvature of 15.4mm; the object plane of the second lens (2) is a convex spherical surface with a radius of curvature of 23.6mm, the image plane of the second lens (2) is a concave spherical surface with a radius of curvature of 145mm; the object plane of the first lens (8) of the cemented lens (3) is a convex spherical surface with a radius of curvature of 13.85mm, the image plane of the first lens (8) of the cemented lens (3) is a convex spherical surface with a radius of curvature of -35.6mm; the object plane of the second lens (9) of the cemented lens (3) is a concave spherical surface with a radius of curvature of -35.6mm, the image plane of the second lens (9) of the cemented lens (3) is a concave spherical surface with a radius of curvature of 13mm; the object plane of the third lens (5) is a convex spherical surface with a radius of curvature of 39.6mm, the image plane of the third lens (5) is a convex spherical surface with a radius of curvature of -25.7mm; the object plane of the fourth lens (6) is a convex spherical surface with a radius of curvature of 13.4mm, the image plane of the fourth lens (6) is a convex spherical surface with a radius of curvature of -95.8mm; the object plane of the fifth lens (7) is a concave spherical surface with a radius of curvature of -63.7mm, the image plane of the fifth lens (7) is a concave spherical surface with a radius of curvature of 9.8mm; the surface tolerance of the curvature of the first lens (1), the second lens (2), the cemented lens (3), the diaphragm (4), the third lens (5), the fourth lens (6) and the fifth lens (7) is f-number 3-4, and the local f-number is 0.3-0.5; the first lens (1) is made of lanthanum flint glass, the second lens (2) is made of heavy lanthanum flint glass, the first lens (8) of the cemented lens (3) is made of light crown glass, the second lens (9) of the cemented lens (3) is made of heavy flint glass, the third lens (5) is made of heavy lanthanum flint glass, the fourth lens (6) is made of heavy lanthanum flint glass, the fifth lens (7) is made of heavy flint glass.

2. The large-aperture and ultra-low-distortion 16mm fixed-focus optical system according to claim 1, characterized in that, the overall optical length of this optical system is 58mm.

3. The large-aperture and ultra-low-distortion 16mm fixed-focus optical system according to claim 2, characterized in that, the optical distance between the first lens (1) and the second lens (2) is 23.52-23.62mm, the optical distance between the second lens (2) and the cemented lens (3) is 4.47-4.53mm, the optical distance between the cemented lens (3) and the diaphragm (4) is 2.723-2.763mm, the optical distance between the diaphragm (4) and the third lens (5) is 0.123-0.143mm, the optical distance between the third lens (5) and the fourth lens (6) is 0.28-0.32mm, The optical distance from the fourth lens (6) to the fifth lens (7) is 0.15 - 0.19 mm, and the optical distance from the fifth lens (7) to the lens image plane is 14.4 - 14.6 mm.

4. A large-aperture ultra-low distortion 16 mm fixed-focus optical system according to claim 3, characterized in that, the optical distance from the first lens (1) to the second lens (2) is 23.57 mm, the optical distance from the second lens (2) to the cemented lens (3) is 4.5 mm, the optical distance from the cemented lens (3) to the aperture stop (4) is 2.743 mm, the optical distance from the aperture stop (4) to the third lens (5) is 0.133 mm, the optical distance from the third lens (5) to the fourth lens (6) is 0.3 mm, the optical distance from the fourth lens (6) to the fifth lens (7) is 0.17 mm, and the optical distance from the fifth lens (7) to the lens image plane is 14.5 mm.

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