A fixed focus lens

Abstract

The embodiment of the present application discloses a fixed focus lens, which comprises a first lens, a second lens, a third lens and a fourth lens arranged in sequence along the optical axis from the object side to the image side; the first lens has negative focal power, the second lens has positive focal power, the third lens has positive focal power, and the fourth lens has negative focal power; the object side surface and the image side surface of the first lens, the third lens and the fourth lens are all aspherical surfaces; the object side surface of the second lens is an aspherical surface, and the image side surface is a binary diffractive surface. In the embodiment of the present application, by adopting four optical lenses, the focal power of each lens element and the relative position of each lens element are optimized, and finally the design of the fixed focus lens with a large aperture, a compact structure and imaging requirements is realized; the aperture of the fixed focus lens is 1.4, the total optical length is not greater than 22.5 mm, and the 1 / 2.7'' sensor chip can be matched, and the comprehensive performance meets the use requirements of the general sensor of the security monitoring.

Description

Technical Field

[0001] This invention relates to the field of optical lens technology, and more particularly to a fixed-focus lens. Background Technology

[0002] 4mm prime lenses are popular in the security industry as mainstream products. However, most 4mm lenses on the market have 5 or more lenses with large apertures and an aperture of F1.6. There are very few lenses with a small number of lenses and a large aperture.

[0003] Therefore, designing a fixed-focus lens that uses four optical lenses, achieves a large aperture of F1.4, has a compact structure, and meets imaging requirements would have a broad market prospect. Summary of the Invention

[0004] This invention provides a fixed-focus lens to achieve a large-aperture fixed-focus lens with four lenses.

[0005] This invention provides a fixed-focus lens, comprising a first lens, a second lens, a third lens, and a fourth lens arranged sequentially along the optical axis from the object side to the image side;

[0006] The first lens has negative optical power, the second lens has positive optical power, the third lens has positive optical power, and the fourth lens has negative optical power.

[0007] The object-side and image-side surfaces of the first lens, the third lens, and the fourth lens are all aspherical; the object-side surface of the second lens is aspherical, and the image-side surface is a binary diffraction surface.

[0008] Optionally, the first lens is a concave-convex lens, the second lens is a biconvex lens, the third lens is a biconvex lens, and the fourth lens is a concave-convex lens or a biconcave lens.

[0009] Optionally, the first lens, the third lens, and the fourth lens are all plastic lenses.

[0010] Optionally, the first lens satisfies the following condition: -0.740≤Φ1 / Φ≤-0.600;

[0011] Wherein, Φ1 is the optical power of the first lens, and Φ is the optical power of the fixed-focus lens.

[0012] Optionally, the second lens satisfies the following condition: 0.49≤Φ2 / Φ≤0.62;

[0013] Wherein, Φ2 is the optical power of the second lens, and Φ is the optical power of the fixed-focus lens.

[0014] Optionally, the adjacent surfaces of the third lens and the fourth lens are cemented together to form a cemented lens group.

[0015] Optionally, the third lens and the fourth lens satisfy the following condition: 0.08≤(Φ3+Φ4) / Φ≤0.12;

[0016] Wherein, Φ3 is the optical power of the third lens, Φ4 is the optical power of the fourth lens, and Φ is the optical power of the fixed-focus lens.

[0017] Optionally, the third lens and the fourth lens also satisfy the following condition: 72≤(Vd3+d4)≤85;

[0018] Wherein, Vd3 is the Abbe number of the third lens, and Vd4 is the Abbe number of the fourth lens.

[0019] Optionally, the fixed-focus lens satisfies the following condition: 0.30 <T12 / TTL<0.38;

[0020] Wherein, T12 is the air gap on the optical axis between the image surface of the first lens and the object surface of the second lens, and TTL is the total optical length of the fixed-focus lens system.

[0021] Optionally, it may also include an aperture stop located between the first lens and the second lens.

[0022] The technical solution of this invention uses a fixed-focus lens composed of four lenses. The optical powers of these four lenses work together to achieve a fixed-focus lens design that meets the requirements of a large aperture, compact structure, and robust imaging. Specifically, the first lens has a negative optical power, which allows object-side light rays to enter the imaging system smoothly, causing light to enter the second lens at a smaller angle of incidence, thus reducing the proportion of higher-order aberrations. The second lens has a positive optical power, which further smooths out the angle of light deviation, giving the system a more relaxed tolerance. The third and fourth lenses have positive and negative optical powers, respectively, which is beneficial for correcting system aberrations. Furthermore, the object-side and image-side surfaces of the first, third, and fourth lenses, as well as the object-side surface of the second lens, are all aspherical lenses, which can further correct system aberrations. The image-side surface of the second lens is set as a binary diffraction surface, which can be used to correct chromatic aberration and also helps improve image quality. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0024] Figure 2 yes Figure 1 The spherical aberration curve of the fixed-focus lens is shown.

[0025] Figure 3 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0026] Figure 4 yes Figure 3 The spherical aberration curve of the fixed-focus lens is shown.

[0027] Figure 5 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 3 of the present invention;

[0028] Figure 6 yes Figure 5 The spherical aberration curve of the fixed-focus lens is shown. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0030] The terminology used in the embodiments of this invention is for the purpose of describing specific embodiments only and is not intended to limit the invention. It should be noted that directional terms such as "upper," "lower," "left," and "right" described in the embodiments of this invention are used to describe the angles shown in the accompanying drawings and should not be construed as limiting the embodiments of this invention. Furthermore, in the context, it should be understood that when referring to an element being formed "upper" or "lower" of another element, it can be formed not only directly "upper" or "lower" of the other element, but also indirectly "upper" or "lower" of the other element through an intermediate element. Terms such as "first," "second," etc., are used for descriptive purposes only and do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0031] The term "comprising" and its variations as used in this invention are open-ended, meaning "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment".

[0032] It should be noted that the concepts of "first" and "second" mentioned in this invention are only used to distinguish the corresponding contents and are not used to limit the order or interdependence.

[0033] It should be noted that the terms "a" and "a plurality of" used in this invention are illustrative rather than restrictive. Those skilled in the art should understand that, unless otherwise expressly indicated in the context, they should be understood as "one or more".

[0034] Figure 1 This is a schematic diagram of a fixed-focus lens provided in Embodiment 1 of the present invention, for reference. Figure 1 The fixed-focus lens includes a first lens 10, a second lens 20, a third lens 30 and a fourth lens 40 arranged sequentially along the optical axis from the object side to the image side;

[0035] The first lens 10 has negative optical power, the second lens 20 has positive optical power, the third lens 30 has positive optical power, and the fourth lens 40 has negative optical power.

[0036] The object-side and image-side surfaces of the first lens 10, the third lens 30, and the fourth lens 40 are all aspherical; the object-side surface of the second lens 20 is aspherical, and the image-side surface is a binary diffraction surface.

[0037] First, for optical lenses, optical power equals the difference between the image-side beam convergence and the object-side beam convergence; it characterizes the optical system's ability to deflect light. The larger the absolute value of optical power, the stronger the bending ability of light; the smaller the absolute value, the weaker the bending ability. When optical power is positive, the refraction of light is converging; when optical power is negative, the refraction of light is diverging. Optical power can be used to characterize a single refractive surface of a lens (i.e., one surface of the lens), a single lens, or a system formed by multiple lenses (i.e., a lens group).

[0038] In the fixed-focus lens provided in this embodiment, all lenses can be housed in a single lens barrel. Figure 1 (not shown in the image) such as Figure 1 As shown, in this embodiment of the invention, a fixed-focus lens is formed by setting four lenses. The optical powers of the four lenses work together to achieve a fixed-focus lens design that meets the requirements of a large aperture, compact structure, and robust imaging. Specifically, the optical power of the first lens 10 is negative, allowing object-side light rays to enter the imaging system smoothly, and enabling light to enter the second lens 20 at a smaller angle of incidence, reducing the proportion of higher-order aberrations. The optical power of the second lens 20 is positive, further smoothing out the angle of light deviation, giving the system a more relaxed tolerance sensitivity. The optical powers of the third lens 30 and the fourth lens 40 are positive and negative, respectively, which is beneficial for correcting system aberrations. Furthermore, the object-side and image-side surfaces of the first lens 10, the third lens 30, and the fourth lens 40, as well as the object-side surface of the second lens 20, are all aspherical lenses, used for further correction of system aberrations. The image-side surface of the second lens 20 is set as a binary diffraction surface, used for chromatic aberration correction, and also helps improve image quality.

[0039] Continue to refer to Figure 1 The fixed-focus lens also includes an aperture stop STO, which is located between the first lens 10 and the second lens 20.

[0040] As those skilled in the art will understand, the stop-gate (STO) in an optical system is used to limit the beam size, determining the amount of light entering the photosensitive element through the lens, i.e., controlling the light transmission of the lens; that is, the stop-gate directly determines the aperture size of the optical lens. Positioning the stop-gate between the first lens 10 and the second lens 20 essentially limits its specific position at the waist of the entire optical system, thereby enabling precise control of the light transmission, increasing the height of the central principal ray at the stop-gate position, widening the aperture, ensuring the amount of light passing through the stop-gate, and ensuring image brightness. Furthermore, the stop-gate can block off-axis light rays, effectively reducing off-axis aberrations and ensuring image sharpness. Therefore, this embodiment of the invention can achieve an aperture of f / 1.4, a total optical length of no more than 22.5 mm, and can be matched with a 1 / 2.7″ sensor chip, its overall performance meeting the requirements for general-purpose security monitoring sensors.

[0041] In one specific embodiment, optionally, the first lens 10 is a concave-convex lens, the second lens 20 is a biconvex lens, the third lens 30 is a biconvex lens, and the fourth lens 40 is a concave-convex lens or a biconcave lens.

[0042] In one specific embodiment, optionally, the first lens 10, the second lens 20, the third lens 30 and the fourth lens 40 are all plastic lenses.

[0043] It is understood that in this embodiment of the invention, the surfaces of the first lens 10, the third lens 30, and the fourth lens 40 are all set aspherical and made of plastic, which reduces the manufacturing difficulty and cost, and is beneficial for reducing manufacturing costs and mass production. Meanwhile, the object-side surface of the second lens 20 is set aspherical, and the image-side surface is set as a binary diffraction surface, which can achieve the function of correcting aberrations and chromatic aberrations using the aspherical and binary diffraction surfaces. Exemplarily, since the second lens 20 needs to be fabricated with both aspherical and binary diffraction surfaces, it can be specifically fabricated using acrylic material to reduce the manufacturing difficulty and cost.

[0044] In one specific embodiment, the first lens 10 may optionally satisfy the following condition: -0.740≤Φ1 / Φ≤-0.600; where Φ1 is the optical power of the first lens 10 and Φ is the optical power of the fixed-focus lens.

[0045] As can be seen above, in this embodiment of the invention, the first lens 10 can be configured as a convex-concave plastic aspherical lens with negative optical power. The optical power of this lens within this range can ensure that the object-side light rays are smoothly received into the imaging system, so that the light rays enter the second lens 20 at a smaller incident angle, thereby reducing the proportion of higher aberrations.

[0046] In a specific embodiment, optionally, the second lens 20 satisfies the following condition: 0.49≤Φ2 / Φ≤0.62; wherein Φ2 is the optical power of the second lens 20, and Φ is the optical power of the fixed-focus lens.

[0047] It can be seen from the above that in the embodiment of the present invention, the second lens 20 can be configured as a biconvex lens with positive optical power. When the optical power of the lens is within this range, it can ensure that light further achieves gentle deflection contraction, so that the system has relatively loose tolerance sensitivity.

[0048] In a specific embodiment, optionally, adjacent surfaces of the third lens 30 and the fourth lens 40 are cemented to each other to form a cemented lens group. Specifically, the third lens 30 and the fourth lens 40 can be bonded by glue.

[0049] Further optionally, the third lens 30 and the fourth lens 40 satisfy the following condition: 0.08≤(Φ3+Φ4) / Φ≤0.12; wherein Φ3 is the optical power of the third lens 30, Φ4 is the optical power of the fourth lens 40, and Φ is the optical power of the fixed-focus lens.

[0050] It can be seen from the above that in the embodiment of the present invention, both the third lens 30 and the fourth lens 40 can be configured as plastic aspheric lenses. When the optical power of the third lens 30 and the fourth lens 40 satisfies the above range, the optical power distribution of the system is reasonable, which is more conducive to the correction of system aberrations. Wherein, the third lens 30 and the fourth lens 40 are bonded by glue.

[0051] Further optionally, the third lens 30 and the fourth lens 40 further satisfy the following condition: 72≤(Vd3+Vd4)≤85; wherein Vd3 is the Abbe number of the third lens 30, and Vd4 is the Abbe number of the fourth lens 40.

[0052] Wherein, when the Abbe numbers of the third lens 30 and the fourth lens 40 satisfy this range, it is beneficial to the correction of chromatic aberration of the system, thereby further improving the image quality.

[0053] In a specific embodiment, optionally, the fixed-focus lens satisfies the following condition: 0.30<T12 / TTL<0.38; wherein T12 is the air gap on the optical axis from the image-side surface of the first lens 10 to the object-side surface of the second lens 20, and TTL is the total optical length of the fixed-focus lens system.

[0054] When the ratio of the optical system is within this range, the structure of the fixed-focus lens can be made more compact, the total optical length can be achieved to be no more than 22.5mm, it can be matched with a 1 / 2.7" sensor chip, and the comprehensive performance meets the application requirements of general sensors for security monitoring.

[0055] In this embodiment of the invention, by employing four optical lenses and optimizing the optical power of each lens element and the relative position of each lens element, a fixed-focus lens design with a large aperture, compact structure, and good imaging requirements is finally achieved. The fixed-focus lens has an aperture of f / 1.4, an optical length of no more than 22.5 mm, and can be matched with a 1 / 2.7″ sensor chip. Its overall performance meets the requirements of general security monitoring sensors.

[0056] Based on the same concept described above, this invention provides three different specific embodiments, the optical power relationship and related physical optical parameter design ranges of which are shown in Table 1:

[0057] Table 1. Optical power relationship and related physical and optical parameters in each embodiment.

[0058] Φ1 / Φ -0.625 -0.662 -0.721 -0.740 -0.600 Φ2 / Φ 0.536 0.519 0.597 0.490 0.620 (Φ3+Φ4) / Φ 0.087 0.085 0.107 0.080 0.120 Vd3+Vd4 75.71 82.00 78.00 72.00 85.00 T12 / TTL 0.36 0.34 0.32 0.30 0.38

[0059] In Embodiment 1 of the present invention, reference is made to Figure 1 The structure, shape, and location of each component in the system are known, which is crucial for the system. As shown in the figure, the optical system consists of four optical lenses, with the aperture stop STO located between the first lens 10 and the second lens 20. A filter 50 is also positioned along the object plane to the image plane; the filter 50 is located on the image-side surface of the fourth lens 40 and protects the image sensor chip, ensuring the imaging effect of the fixed-focus lens. The third lens 30 and the fourth lens 40 are cemented together, and the fourth lens 40 is a biconcave lens. This fixed-focus lens achieves a focal length f of 4.20mm and an aperture of F# 1.40.

[0060] like Figure 1 The parameter design values ​​of each lens in the fixed-focus lens of Embodiment 1 are shown in Table 2:

[0061] Table 2 shows a design value for each lens in the fixed-focus lens in Example 1.

[0062]

[0063]

[0064] The surface numbers in Table 2 are assigned according to the surface sequence of each lens. "STO" represents the aperture stop of a fixed-focus lens; "IMA" represents the image plane of a fixed-focus lens; the radius of curvature represents the curvature of the lens surface, with a positive value indicating that the surface bends towards the image plane and a negative value indicating that the surface bends towards the object plane. "Infinity" indicates that the surface is flat, with an infinite radius of curvature and an infinite distance; the thickness represents the central axial distance between the current surface and the next surface; the refractive index represents the ability of the material between the current surface and the next surface to deflect light, with a blank space indicating that the current position is air and the refractive index is 1; the Abbe number represents the dispersion characteristics of the material between the current surface and the next surface, with a blank space indicating that the current position is air; half-aperture represents the effective diameter of the lens; and the k-value represents the magnitude of the conic coefficient of the aspherical surface.

[0065] The conicity coefficients of aspherical surfaces can be defined using the following aspherical formulas, but are not limited to the following representations:

[0066]

[0067] Where z is the axial sagitta in the Z direction of the aspherical surface; r is the height of the aspherical surface; c is the curvature of the fitted sphere, which is numerically the reciprocal of the radius of curvature; k is the coefficient of the fitted cone; and AE are the coefficients of the 4th, 6th, 8th, 10th, and 12th order terms of the aspherical polynomial.

[0068] The coefficient values ​​of each aspherical surface in the above embodiment 1 are shown in Table 3:

[0069] Table 3 Aspheric coefficients of the lenses in Example 1

[0070] S1 -9.14303E-03 6.12773E-04 -2.42705E-05 5.42658E-07 -5.21925E-09 S2 1.10915E-02 -2.24348E-03 3.50044E-04 -2.66272E-05 8.72243E-07 S4 -6.97433E-04 7.86560E-06 -6.54616E-07 0.00000E+00 0.00000E+00 S5 -2.83418E-05 2.11145E-05 -5.41376E-07 0.00000E+00 0.00000E+00 S6 -3.70683E-05 9.35707E-06 -5.54947E-07 -8.21319E-08 2.31722E-09 S7 8.34852E-04 2.07922E-04 -1.14097E-05 -6.53922E-08 1.27589E-08 S8 2.53423E-03 -1.96186E-05 2.29673E-05 -2.29213E-06 8.96378E-08

[0071] Where -9.14303E-03 indicates that the coefficient A of surface number S1 is -9.14303 * 10 -3 And so on. The diffraction plane coefficients can be defined by the following diffraction plane equations, but are not limited to these representations:

[0072] Φ=A1Y 2 +A2Y 4 +A3Y 6 ;

[0073] Where Φ is the phase of the diffraction surface; Y is the half-aperture of the lens perpendicular to the optical axis; and A1, A2, and A3 are the phase coefficients of the diffraction surfaces.

[0074] The coefficient values ​​of the binary diffraction plane in the above embodiment 1 are shown in Table 4:

[0075] Table 4. Diffraction surface coefficients of the lenses in Example 1

[0076] S5 +1 3 2.5 -63.2797 14.4713 -3.6531

[0077] Figure 2 yes Figure 1 The spherical aberration curve of the fixed-focus lens shown is for reference. Figure 2 In the figure, the vertical direction represents the normalized aperture, 0 indicates being on the optical axis, and the vertical vertex represents the maximum pupil radius; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). The different linear curves in the figure represent different wavelengths of system imaging, determined by... Figure 2 It can be seen that the axial aberrations of different wavelengths are all controlled within the range of (-0.05mm, +0.05mm), indicating that the spherical aberration of this fixed-focus lens is well controlled at each wavelength, which can meet the requirements of wide-spectrum applications.

[0078] Figure 3 This is a schematic diagram of a fixed-focus lens provided in Embodiment 2 of the present invention. In Embodiment 2 of the present invention, reference is made to... Figure 3 The structure, shape, and location of each component in the system are crucial to its operation. As shown in the figure, the optical system consists of four optical lenses, with the aperture stop STO located between the first lens 10 and the second lens 20. A filter 50 is also positioned along the object plane to the image plane; the filter 50 is located on the image-side surface of the fourth lens 40 and protects the image sensor chip, ensuring the imaging effect of the fixed-focus lens. The third lens 30 and the fourth lens 40 are cemented together, and the fourth lens 40 is a concave-convex lens. This fixed-focus lens achieves a focal length f of 4.20mm and an aperture of F# 1.40.

[0079] like Figure 3 The parameter design values ​​of each lens in the fixed-focus lens of Embodiment 2 are shown in Table 5:

[0080] Table 5 shows a design value for each lens in the fixed-focus lens in Example 2.

[0081]

[0082]

[0083] The surface numbers in Table 5 are assigned according to the surface sequence of each lens. "STO" represents the aperture stop of a fixed-focus lens; "IMA" represents the image plane of a fixed-focus lens; the radius of curvature represents the curvature of the lens surface, with a positive value indicating that the surface bends towards the image plane and a negative value indicating that the surface bends towards the object plane. "Infinity" indicates that the surface is flat, with an infinite radius of curvature and an infinite distance; the thickness represents the central axial distance between the current surface and the next surface; the refractive index represents the ability of the material between the current surface and the next surface to deflect light, with a blank space indicating that the current position is air and the refractive index is 1; the Abbe number represents the dispersion characteristics of the material between the current surface and the next surface, with a blank space indicating that the current position is air; half-aperture represents the effective diameter of the lens; and the k-value represents the magnitude of the conic coefficient of the aspherical surface.

[0084] The conicity coefficients of aspherical surfaces can be defined using the following aspherical formulas, but are not limited to the following representations:

[0085]

[0086] Where z is the axial sagitta in the Z direction of the aspherical surface; r is the height of the aspherical surface; c is the curvature of the fitted sphere, which is numerically the reciprocal of the radius of curvature; k is the coefficient of the fitted cone; and AE are the coefficients of the 4th, 6th, 8th, 10th, and 12th order terms of the aspherical polynomial.

[0087] The coefficient values ​​of each aspherical surface in the above embodiment 2 are shown in Table 6:

[0088] Table 6 Aspheric coefficients of the lenses in Example 2

[0089]

[0090]

[0091] Where -1.00597E-02 indicates that the coefficient A of surface number S1 is -1.00597*10 -2 And so on. The diffraction plane coefficients can be defined by the following diffraction plane equations, but are not limited to these representations:

[0092] Φ=A1Y 2 +A2Y 4 +A3Y 6 ;

[0093] Where Φ is the phase of the diffraction surface; Y is the half-aperture of the lens perpendicular to the optical axis; and A1, A2, and A3 are the phase coefficients of the diffraction surfaces.

[0094] The coefficient values ​​of the binary diffraction plane in the above embodiment 2 are shown in Table 7:

[0095] Table 7. Diffraction surface coefficients of the lenses in Example 2

[0096] S5 +1 3 2.5 -78.7182 28.6306 -6.6082

[0097] Figure 4 yes Figure 3 The spherical aberration curve of the fixed-focus lens shown is for reference. Figure 4 In the figure, the vertical direction represents the normalized aperture, 0 indicates being on the optical axis, and the vertical vertex represents the maximum pupil radius; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). The different linear curves in the figure represent different wavelengths of system imaging, determined by... Figure 4 It can be seen that the axial aberrations of different wavelengths are all controlled within the range of (-0.05mm, +0.05mm), indicating that the spherical aberration of this fixed-focus lens is well controlled at each wavelength, which can meet the requirements of wide-spectrum applications.

[0098] Figure 5 This is a schematic diagram of a fixed-focus lens provided in Embodiment 3 of the present invention. In Embodiment 3 of the present invention, reference is made to... Figure 5 The structure, shape, and location of each component in the system are crucial to its operation. As shown in the figure, the optical system consists of four optical lenses, with the aperture stop STO located between the first lens 10 and the second lens 20. A filter 50 is also positioned along the object plane to the image plane; the filter 50 is located on the image-side surface of the fourth lens 40 and protects the image sensor chip, ensuring the imaging effect of the fixed-focus lens. The third lens 30 and the fourth lens 40 are cemented together, and the fourth lens 40 is a concave-convex lens. This fixed-focus lens achieves a focal length f of 4.26mm and an aperture of F# 1.41.

[0099] like Figure 5 The parameter design values ​​of each lens in the fixed-focus lens of Embodiment 3 are shown in Table 8:

[0100] Table 8 shows a design value for each lens in the fixed-focus lens in Example 3.

[0101]

[0102]

[0103] The surface numbers in Table 8 are assigned according to the surface sequence of each lens. "STO" represents the aperture stop of a fixed-focus lens; "IMA" represents the image plane of a fixed-focus lens; the radius of curvature represents the curvature of the lens surface, with a positive value indicating that the surface bends towards the image plane and a negative value indicating that the surface bends towards the object plane. "Infinity" indicates that the surface is flat, with an infinite radius of curvature and an infinite distance; the thickness represents the central axial distance between the current surface and the next surface; the refractive index represents the ability of the material between the current surface and the next surface to deflect light, with a blank space indicating that the current position is air and the refractive index is 1; the Abbe number represents the dispersion characteristics of the material between the current surface and the next surface, with a blank space indicating that the current position is air; half-aperture represents the effective diameter of the lens; and the k-value represents the magnitude of the conic coefficient of the aspherical surface.

[0104] The conicity coefficients of aspherical surfaces can be defined using the following aspherical formulas, but are not limited to the following representations:

[0105]

[0106] Where z is the axial sagitta in the Z direction of the aspherical surface; r is the height of the aspherical surface; c is the curvature of the fitted sphere, which is numerically the reciprocal of the radius of curvature; k is the coefficient of the fitted cone; and AE are the coefficients of the 4th, 6th, 8th, 10th, and 12th order terms of the aspherical polynomial.

[0107] The coefficient values ​​of each aspherical surface in the above embodiment three are shown in Table 9:

[0108] Table 9 Aspheric coefficients of the lenses in Example 3

[0109]

[0110]

[0111] Where -9.84138E-03 indicates that the coefficient A of surface number S1 is -9.84138 * 10 -3 And so on. The diffraction plane coefficients can be defined by the following diffraction plane equations, but are not limited to these representations:

[0112] Φ=A1Y 2 +A2Y 4 +A3Y 6 ;

[0113] Where Φ is the phase of the diffraction surface; Y is the half-aperture of the lens perpendicular to the optical axis; and A1, A2, and A3 are the phase coefficients of the diffraction surfaces.

[0114] The coefficient values ​​of the binary diffraction plane in the above embodiment three are shown in Table 10:

[0115] Table 10 Diffraction surface coefficients of the lenses in Example 3

[0116] S5 +1 3 2.5 -58.5508 19.7396 -5.2386

[0117] Figure 6 yes Figure 5 The spherical aberration curve of the fixed-focus lens shown is for reference. Figure 6 In the figure, the vertical direction represents the normalized aperture, 0 indicates being on the optical axis, and the vertical vertex represents the maximum pupil radius; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). The different linear curves in the figure represent different wavelengths of system imaging, determined by... Figure 6 It can be seen that the axial aberrations of different wavelengths are all controlled within the range of (-0.05mm, +0.05mm), indicating that the spherical aberration of this fixed-focus lens is well controlled at each wavelength, which can meet the requirements of wide-spectrum applications.

[0118] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A fixed-focus lens, characterized in that, It includes a first lens, a second lens, a third lens, and a fourth lens arranged sequentially from the object side to the image side along the optical axis; the fixed-focus lens has four lenses with optical power. The first lens has negative optical power, the second lens has positive optical power, the third lens has positive optical power, and the fourth lens has negative optical power. The object-side and image-side surfaces of the first lens, the third lens, and the fourth lens are all aspherical; the object-side surface of the second lens is aspherical, and the image-side surface is a binary diffraction surface. in, When the focal length of the fixed-focus lens is 4.2mm and the aperture is F# 1.4, the first lens satisfies The second lens satisfies The third lens and the fourth lens satisfy The third lens and the fourth lens also satisfy the following: The fixed-focus lens satisfies The fourth lens is a biconcave lens; or When the focal length of the fixed-focus lens is 4.2mm and the aperture is F# 1.4, the first lens satisfies The second lens satisfies The third lens and the fourth lens satisfy The third lens and the fourth lens also satisfy the following: The fixed-focus lens satisfies The fourth lens is a concave-convex lens; or When the focal length of the fixed-focus lens is 4.26mm and the aperture is F# 1.41, the first lens satisfies The second lens satisfies The third lens and the fourth lens satisfy The third lens and the fourth lens also satisfy the following: The fixed-focus lens satisfies The fourth lens is a concave-convex lens; in, The optical power of the first lens is... The optical power of the second lens is [value missing]. The optical power of the fixed-focus lens. The optical power of the third lens is... The optical power of the fourth lens is... The Abbe number of the third lens. The Abbe number of the fourth lens. The air gap along the optical axis between the image-side surface of the first lens and the object-side surface of the second lens is denoted as . The total optical length of the fixed-focus lens system.

2. The fixed-focus lens according to claim 1, characterized in that, The first lens is a convex-concave lens, the second lens is a biconvex lens, and the third lens is a biconvex lens.

3. The fixed-focus lens according to claim 1, characterized in that, The first lens, the third lens, and the fourth lens are all plastic lenses.

4. The fixed-focus lens according to claim 1, characterized in that, The adjacent surfaces of the third lens and the fourth lens are cemented together to form a cemented lens group.

5. The fixed-focus lens according to claim 1, characterized in that, It also includes an aperture stop, which is located between the first lens and the second lens.

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