Prime lens

Abstract

The prime lens comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens which are sequentially arranged from an object plane to an image plane along an optical axis, the first lens is a negative-focal-power lens, the second lens is a negative-focal-power lens, the third lens is a positive-focal-power lens, the fourth lens is a positive-focal-power lens or a negative-focal-power lens, and the fifth lens is a positive-focal-power lens; the surface of the lens adjacent to the object surface is an object-side surface, and the surface of the lens adjacent to the image surface is an image-side surface; the curvature radius of the object side surface of the fourth lens is R41, the curvature radius of the image side surface of the fourth lens is R42, the focal length of the fourth lens is F4, the curvature radius of the object side surface of the fifth lens is R51, the curvature radius of the image side surface of the fifth lens is R52, and the focal length of the fifth lens is F5. According to the technical scheme provided by the embodiment of the invention, the design of the vehicle-mounted lens which is high in imaging quality, compact in structure, large in aperture and large in field angle can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of optical devices, and in particular to a fixed-focus lens. Background Art

[0002] With the development and application of technologies such as autonomous driving, smart cockpit and advanced driver assistance systems, the driver monitoring system (DMS) has become a research hotspot in the field of smart cars. The system is mainly used to monitor the driver's status and dangerous driving behavior, which can effectively reduce traffic accidents.

[0003] As an important part of the DMS system, the in-vehicle monitoring camera is generally installed in a position facing the driver, such as the rearview mirror, driving recorder, steering wheel, central control screen, and A-pillar. However, the existing cameras are too large, which is not conducive to lens integration and the aesthetics of the interior. Summary of the invention

[0004] The present invention provides a fixed-focus lens to achieve a vehicle-mounted lens design that takes into account imaging quality, compact structure, large aperture, and large field of view.

[0005] The fixed-focus lens provided by the present invention comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens which are arranged in sequence from the object plane to the image plane along the optical axis;

[0006] The first lens is a negative power lens, the second lens is a negative power lens, the third lens is a positive power lens, the fourth lens is a positive power lens or a negative power lens, and the fifth lens is a positive power lens;

[0007] The surface of the lens adjacent to the object plane is the object-side surface, and the surface of the lens adjacent to the image plane is the image-side surface; the curvature radius of the object-side surface of the fourth lens is R41, the curvature radius of the image-side surface of the fourth lens is R42, the focal length of the fourth lens is F4, the curvature radius of the object-side surface of the fifth lens is R51, the curvature radius of the image-side surface of the fifth lens is R52, and the focal length of the fifth lens is F5; wherein:

[0008]

[0009] Optionally, the first lens and the third lens are glass spherical lenses, and the second lens, the fourth lens and the fifth lens are plastic aspherical lenses.

[0010] Optionally, the object-side surface of the first lens is convex toward the object plane, and the image-side surface of the first lens is concave toward the image plane;

[0011] The object-side surface of the second lens is concave toward the object plane, and the image-side surface of the second lens is convex toward the image plane;

[0012] The object-side surface of the third lens is convex toward the object plane, and the image-side surface of the third lens is convex toward the image plane;

[0013] The object-side surface of the fourth lens is concave toward the object plane, and the image-side surface of the fourth lens is convex toward the image plane;

[0014] The object-side surface of the fifth lens is convex toward the object plane, and the image-side surface of the fifth lens is concave toward the image plane; or, the object-side surface of the fifth lens is convex toward the object plane, and the image-side surface of the fifth lens is convex toward the image plane.

[0015] Optionally, the refractive index of the first lens is Nd1, and the Abbe number of the first lens is Vd1; wherein:

[0016] 1.8 <Nd1<2.03,28.55<Vd1<60.90。

[0017] Optionally, the refractive index of the third lens is Nd3, and the Abbe number of the third lens is Vd3; wherein:

[0018] 1.91 <Nd3<2.1,24<Vd3<41。

[0019] Optionally, a refractive index of the fourth lens is greater than or equal to a refractive index of the fifth lens.

[0020] Optionally, the fixed focus lens further comprises an aperture;

[0021] The aperture stop is located in the optical path between the second lens and the third lens.

[0022] Optionally, the aspheric surface of the plastic aspheric lens satisfies:

[0023]

[0024] Among them, z represents the axial vector height of the aspheric surface in the Z direction; r represents the distance from the point on the aspheric surface to the optical axis; c represents the curvature of the fitted sphere, which is the inverse of the radius of curvature; k represents the fitted cone coefficient; A, B, C, D, and E represent the 4th, 6th, 8th, 10th, and 12th order coefficients of the aspheric polynomial, respectively.

[0025] The fixed-focus lens provided in the embodiment of the present invention can improve the resolution and image quality by using five lenses and reasonably matching the optical power of each lens, and limiting the relationship between the curvature radius and focal length of the fourth lens and the fifth lens close to the image side, and can also meet the design requirements of the vehicle-mounted lens for a large field of view, a large aperture and miniaturization.

[0026] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 is a structural schematic diagram of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0029] Figure 2 is an MTF curve diagram of the fixed-focus lens provided in Embodiment 1 of the present invention;

[0030] Figure 3 is a structural schematic diagram of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0031] Figure 4 is an MTF curve diagram of the fixed-focus lens provided in Embodiment 2 of the present invention;

[0032] Figure 5 is a structural schematic diagram of a fixed-focus lens provided in Embodiment 3 of the present invention;

[0033] Figure 6 This is an MTF curve diagram of the fixed-focus lens provided in Embodiment 3 of the present invention. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0035] The fixed-focus lens provided by the present invention comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens which are arranged in sequence from the object plane to the image plane along the optical axis; the first lens is a negative power lens, the second lens is a negative power lens, the third lens is a positive power lens, the fourth lens is a positive power lens or a negative power lens, and the fifth lens is a positive power lens; the surface of the lens adjacent to the object plane is the object-side surface, and the surface of the lens adjacent to the image plane is the image-side surface; the curvature radius of the object-side surface of the fourth lens is R41, the curvature radius of the image-side surface of the fourth lens is R42, the focal length of the fourth lens is F4, the curvature radius of the object-side surface of the fifth lens is R51, the curvature radius of the image-side surface of the fifth lens is R52, and the focal length of the fifth lens is F5; wherein:

[0036]

[0037] The above is the core idea of ​​the present invention. By using five lenses and reasonably matching the optical focal length of each lens, and limiting the relationship between the curvature radius and focal length of the fourth lens and the fifth lens close to the image side, the lens resolution can be improved, the image quality can be improved, and the design requirements of the vehicle-mounted lens for a large field of view, a large aperture and miniaturization can be met.

[0038] The technical scheme of the embodiment of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiment of the present invention. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Embodiment 1

[0040] Figure 1 is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 1 of the present invention, such as Figure 1 As shown, the fixed-focus lens provided by the present invention comprises a first lens 110, a second lens 120, a third lens 130, a fourth lens 140 and a fifth lens 150 which are arranged in sequence from the object plane to the image plane along the optical axis; the first lens 110 is a negative power lens, the second lens 120 is a negative power lens, the third lens 130 is a positive power lens, the fourth lens 140 is a positive power lens, and the fifth lens 150 is a positive power lens; the surface of the lens adjacent to the object plane is the object surface, and the surface of the lens adjacent to the image plane is the image surface; the curvature radius of the object surface of the fourth lens 140 is R41, the curvature radius of the image surface of the fourth lens 140 is R42, the focal length of the fourth lens 140 is F4, the curvature radius of the object surface of the fifth lens 150 is R51, the curvature radius of the image surface of the fifth lens 150 is R52, and the focal length of the fifth lens 150 is F5; wherein:

[0041] Specifically, the focal length is equal to the difference between the convergence of the image-side light beam and the convergence of the object-side light beam, and it characterizes the ability of the optical system to deflect light. The larger the absolute value of the focal length, the stronger the ability to bend light, and the smaller the absolute value of the focal length, the weaker the ability to bend light. When the focal length is a positive number, the refraction of light is convergent; when the focal length is a negative number, the refraction of light is divergent. The focal length can be used to characterize a certain refractive surface of a lens (i.e., a surface of a lens), can be used to characterize a certain lens, and can also be used to characterize a system formed by multiple lenses (i.e., a lens group). In the fixed-focus lens provided in this embodiment, each lens can be fixed to a lens barrel ( Figure 1 Not shown).

[0042] In this embodiment, by setting the first lens 110 as a negative power lens, the second lens 120 as a negative power lens, the third lens 130 as a positive power lens, the fourth lens 140 as a positive power lens or a negative power lens, and the fifth lens 150 as a positive power lens, the power of the entire fixed-focus lens is reasonably distributed, which can ensure the balance of the incident angles of the front and rear lenses, reduce the sensitivity of the lenses, improve the stability of the lenses, improve the imaging quality, and facilitate the realization of a large aperture. In this embodiment, the aperture number F of the fixed-focus lens can reach 1.2.

[0043] Specifically, the radius of curvature represents the curvature of the lens surface. A positive value of the radius of curvature represents that the surface is curved toward the object plane, with the center close to the image plane, and a negative value of the radius of curvature represents that the surface is curved toward the image plane, with the center close to the object plane. Specifically, the focal length (also known as focal length) is a measurement method for measuring the convergence or divergence of light in an optical system, and refers to the distance from the optical center of the lens to the focus of light convergence when parallel light is incident. In this embodiment, by setting the radius of curvature R41 of the object surface of the fourth lens 140, the radius of curvature R42 of the image surface of the fourth lens 140, the focal length of the fourth lens 140 to F4, the radius of curvature R51 of the object surface of the fifth lens 150, the radius of curvature R52 of the image surface of the fifth lens 150, and the focal length F5 of the fifth lens 150 to satisfy the above relationship, the shape and optical focal power distribution of the fourth lens 140 and the fifth lens 150 can be well defined, which is conducive to improving the field of view, reducing the total length of the lens, and improving the resolution, thereby ensuring image quality.

[0044] It should be noted that the first embodiment of the present invention is illustrated by taking the fourth lens 140 as a positive power lens as an example. In other embodiments, the fourth lens 140 may also be a negative power lens, which will be illustrated later.

[0045] In summary, the fixed-focus lens provided in the embodiment of the present invention can enhance the resolution and image quality by using five lenses and reasonably matching the optical focal length of each lens, and limiting the relationship between the curvature radius and the focal length of the fourth lens and the fifth lens close to the image side, and can also meet the design requirements of vehicle-mounted lenses for a large field of view, a large aperture and miniaturization.

[0046] On the basis of the above embodiment, optionally, the first lens 110 and the third lens 130 are glass spherical lenses, and the second lens 120 , the fourth lens 140 and the fifth lens 150 are plastic aspherical lenses.

[0047] Specifically, the characteristic of aspherical lenses is that the curvature changes continuously from the center of the lens to the periphery of the lens. Unlike spherical lenses that have a constant curvature from the center of the lens to the periphery of the lens, aspherical lenses have better curvature radius characteristics and have the advantages of improving distortion aberration and improving astigmatism aberration. After using aspherical lenses, the aberration that occurs during imaging can be eliminated as much as possible, thereby improving the imaging quality of the lens. The characteristic of spherical lenses is that they have a constant curvature from the center of the lens to the periphery of the lens, ensuring that the lens setting method is simple.

[0048] Furthermore, the material of the plastic aspherical lens can be various plastics known to those skilled in the art, and the material of the glass spherical lens can be various types of glass known to those skilled in the art, which will not be elaborated or limited in the embodiments of the present invention. The thermal expansion coefficient of the lens made of glass is small and the stability is good. When the ambient temperature of the fixed-focus lens changes greatly, it is helpful to maintain the focal length of the fixed-focus lens stable. The cost of the lens made of plastic is much lower than that of the lens made of glass. The use of the lens made of plastic is helpful to reduce the overall cost of the fixed-focus lens.

[0049] This embodiment adopts a mixed combination of glass spherical lenses and plastic aspherical lenses. By setting the first lens 110 and the third lens 130 as glass spherical lenses, and the second lens 120, the fourth lens 140 and the fifth lens 150 as plastic aspherical lenses, on the one hand, the cost of the fixed-focus lens can be effectively controlled and the processing technology of the aspherical lens can be reduced. On the other hand, the phase difference can be well corrected to ensure a sufficiently good image quality and to compensate each other between the lens materials, so as to ensure that the fixed-focus lens can still be used normally in high and low temperature environments and achieve stable high and low temperature resolution.

[0050] Optionally, the object-side surface of the first lens 110 bulges towards the object plane, and the image-side surface of the first lens 110 depresses towards the image plane; the object-side surface of the second lens 120 depresses towards the object plane, and the image-side surface of the second lens 120 bulges towards the image plane; the object-side surface of the third lens 130 bulges towards the object plane, and the image-side surface of the third lens 130 bulges towards the image plane; the object-side surface of the fourth lens 140 depresses towards the object plane, and the image-side surface of the fourth lens 140 bulges towards the image plane; the object-side surface of the fifth lens 150 bulges towards the object plane, and the image-side surface of the fifth lens 150 bulges towards the image plane.

[0051] Specifically, in this embodiment, by reasonably setting the surface shapes of the respective lenses, it is beneficial to ensure the image quality and can also ensure that the entire fixed-focus lens has a compact structure, achieving a miniaturized design. Exemplarily, the surface shape designs of the first lens 110 and the second lens 120 resemble a crescent moon, and their bending directions are opposite. In this way, light can enter the optics better, and during the propagation of light, it can be stable without excessive deflection, so as to avoid introducing greater aberration, ensure the image quality, and at the same time is beneficial to reducing the aperture and total length of the lens.

[0052] It should be noted that in the first embodiment of the present invention, only the case where the object-side surface of the fifth lens 150 bulges towards the object plane and the image-side surface of the fifth lens 150 bulges towards the image plane is taken as an example for illustration. In other embodiments, it is optional that the object-side surface of the fifth lens 150 bulges towards the object plane and the image-side surface of the fifth lens 150 depresses towards the image plane, which will be illustrated later.

[0053] Optionally, the refractive index of the first lens 110 is Nd1, and the Abbe number of the first lens 110 is Vd1; where: 1.8 < Nd1 < 2.03, 28.55 < Vd1 < 60.90. Specifically, the first lens 110 is a glass lens. By setting the refractive index and Abbe number of the first lens 110 to satisfy the above range, light can be converged better, the ratio of the lens aperture to the curvature radius can be reduced, and the marginal illuminance can be improved.

[0054] Optionally, the refractive index of the third lens 130 is Nd3, and the Abbe number of the third lens 130 is Vd3; where: 1.91 < Nd3 < 2.1, 24 < Vd3 < 41. Specifically, the third lens 130 is a glass lens. This lens undertakes the role of correcting defocus at high and low temperatures. By setting the refractive index and Abbe number of the third lens 130 to satisfy the above range and coordinating with the optical power of other lenses, it is beneficial to obtain stable resolution at high and low temperatures.

[0055] Optionally, the refractive index of the fourth lens 140 is equal to the refractive index of the fifth lens 150.

[0056] Specifically, the fourth lens 140 and the fifth lens 150 are plastic aspherical lenses. The matching of the refractive indexes of the fourth lens 140 and the fifth lens 150 is beneficial to chromatic aberration correction, further reducing the aberration of the system, and achieving high-definition image quality. In other embodiments, the refractive index of the fourth lens 140 can also be set to be greater than the refractive index of the fifth lens 150.

[0057] Optionally, the fixed focus lens further includes an aperture 160; the aperture 160 is located in the optical path between the second lens 120 and the third lens 130. By setting the aperture 160 relatively forward, the lens diameter at the front end of the lens can be effectively reduced, and it is also beneficial to achieve a large aperture.

[0058] Optionally, the fixed-focus lens further includes a protective glass 170 ; the protective glass 170 is located in the optical path between the fifth lens 150 and the image plane.

[0059] As a feasible implementation manner, the optical physical parameters such as the surface type, curvature radius, thickness, refractive index, Abbe number, and half-aperture of each lens in the fixed-focus lens are described below in conjunction with Table 1.

[0060] In Table 1, the surface numbers are numbered according to the order of the surfaces of each lens. For example, the surface number "S1" represents the object side of the first lens, the surface number "S2" represents the image side of the first lens, and so on; "STO" represents the aperture of the fixed-focus lens; "IMA" represents the image surface of the fixed-focus lens; the radius of curvature represents the curvature of the lens surface, a positive value represents that the surface is bent toward the object side, and the center of the circle is close to the image plane, and a negative value represents that the surface is bent toward the image side, and the center of the circle is close to the object plane, "PL" represents a plane, and the curvature radius of the plane is infinite; the thickness represents the central axial distance from the current surface to the next surface, where the focus has an error due to the different number of digits of the values ​​of each parameter, so the thickness of the 13th surface can vary slightly, and the value can be adjusted as needed to achieve the purpose of clear focus; the refractive index (Nd) represents the ability of the material between the current surface and the next surface to deflect light, and a blank represents that the current position is air, and the refractive index is 1; the Abbe number (Vd) represents the dispersion characteristics of the material between the current surface and the next surface to light, and a blank represents that the current position is air. The semi-aperture is the semi-diameter of the lens.

[0061] Table 1 Design values ​​of optical physical parameters of fixed focus lens

[0062]

[0063] Based on the above embodiment, optionally, the aspheric surfaces of the above aspheric lenses (i.e., the second lens 120, the fourth lens 140 and the fifth lens 150) satisfy:

[0064]

[0065] Among them, z represents the axial vector height of the aspheric surface in the Z direction; r represents the distance from the point on the aspheric surface to the optical axis; c represents the curvature of the fitted sphere, which is the inverse of the radius of curvature; k represents the fitted cone coefficient; A, B, C, D, and E represent the 4th, 6th, 8th, 10th, and 12th order coefficients of the aspheric polynomial, respectively.

[0066] Next, a feasible implementation manner is used to illustrate the data on the aspheric surface of the aspheric lens in combination with Table 2.

[0067] Table 2 Design parameter values ​​of each surface of the aspheric lens in the fixed focus lens

[0068]

[0069] Among them, 6.3626825E-03 means that the coefficient A of the surface number S3 is 6.3626825*10 -3 , and so on.

[0070] The optical system of this embodiment achieves the following technical indicators: focal length f is 1.674 mm, field of view angle is 144°, and aperture number is 1.2. The above scheme can make the fixed-focus lens take into account the imaging quality, compact structure, large aperture, and large field of view of the vehicle lens design.

[0071] Further, Figure 2 This is the MTF curve of the fixed focus lens provided in the first embodiment of the present invention. The MTF curve represents the comprehensive resolution level of an optical system. The vertical direction in the figure is the normalization of MTF, which indicates the quality of contrast and marks the resolution of the lens. The higher the better, and 1 is the full score. The horizontal direction represents the spatial frequency, 0 represents the spatial frequency of 0lp / mm, and the further to the right, the higher the spatial frequency. Figure 2 It can be seen that when the wavelength range is 0.92μm-0.96μm, the MTF value at the center field of view of 60lp / mm is ≥0.8, and the MTF value at the edge field of view of 60lp / mm is ≥0.45. The imaging from the center field of view to the edge field of view has excellent resolution.

[0072] Embodiment 2

[0073] Figure 3 is a structural schematic diagram of a fixed-focus lens provided in Embodiment 2 of the present invention, such as Figure 3As shown, the fixed-focus lens provided by the present invention comprises a first lens 110, a second lens 120, a third lens 130, a fourth lens 140 and a fifth lens 150 which are arranged in sequence from the object plane to the image plane along the optical axis; the first lens 110 is a negative power lens, the second lens 120 is a negative power lens, the third lens 130 is a positive power lens, the fourth lens 140 is a positive power lens, and the fifth lens 150 is a positive power lens; the surface of the lens adjacent to the object plane is the object surface, and the surface of the lens adjacent to the image plane is the image surface; the curvature radius of the object surface of the fourth lens 140 is R41, the curvature radius of the image surface of the fourth lens 140 is R42, the focal length of the fourth lens 140 is F4, the curvature radius of the object surface of the fifth lens 150 is R51, the curvature radius of the image surface of the fifth lens 150 is R52, and the focal length of the fifth lens 150 is F5; wherein:

[0074] Among them, the material of each lens and the range of other optical physical parameters such as refractive index and Abbe number are the same as those in Example 1, and will not be repeated here. The difference between this embodiment and Example 1 is that, first, the surface shape of the fifth lens is inconsistent. In this embodiment, the object surface of the fifth lens 150 is convex toward the object plane, and the image surface of the fifth lens 150 is concave toward the image plane; second, the refractive index of the fourth lens 140 in Example 1 is equal to the refractive index of the fifth lens 150, while the refractive index of the fourth lens 140 in this embodiment is greater than the refractive index of the fifth lens 150.

[0075] Table 3 describes in detail the specific setting parameters of each lens in the fixed-focus lens provided in Example 2 of the present invention in another feasible implementation manner. The fixed-focus lens in Table 3 corresponds to Figure 3 Prime lens shown.

[0076] Table 3 Design values ​​of optical physical parameters of fixed focus lens

[0077]

[0078] In Table 3, the surface numbers are numbered according to the order of the surfaces of each lens. For example, the surface number "S1" represents the object side of the first lens, the surface number "S2" represents the image side of the first lens, and so on; "STO" represents the aperture of the fixed-focus lens; "IMA" represents the image surface of the fixed-focus lens; the radius of curvature represents the curvature of the lens surface, a positive value represents that the surface is bent toward the object side, and the center of the circle is close to the image plane, and a negative value represents that the surface is bent toward the image side, and the center of the circle is close to the object plane, "PL" represents a plane, and the radius of curvature of the plane is infinite; the thickness represents the central axial distance from the current surface to the next surface, where the focus has an error due to the different number of digits of the values ​​of each parameter, so the thickness of the 13th surface can vary slightly, and the value can be adjusted as needed to achieve the purpose of clear focus; the refractive index (Nd) represents the ability of the material between the current surface and the next surface to deflect light, and a blank represents that the current position is air, and the refractive index is 1; the Abbe number (Vd) represents the dispersion characteristics of the material between the current surface and the next surface to light, and a blank represents that the current position is air. The semi-aperture is the semi-diameter of the lens.

[0079] Next, a feasible implementation manner is used to illustrate the data in the aspheric surface of the aspheric lens in combination with Table 4.

[0080] Table 4 Design parameter values ​​of each surface of the aspheric lens in the fixed focus lens

[0081]

[0082] Among them, 6.4409052E-03 means that the coefficient A of the surface number S3 is 6.4409052*10 -3 , and so on.

[0083] The optical system of this embodiment achieves the following technical indicators: focal length f is 1.673mm, field of view angle is 144°, and aperture number is 1.2. The above scheme can make the fixed focus lens take into account the imaging quality, compact structure, large aperture, and large field of view of the vehicle lens design.

[0084] Further, Figure 4 This is the MTF curve of the fixed focus lens provided by the second embodiment of the present invention. The MTF curve represents the comprehensive resolution level of an optical system. The vertical direction in the figure is the normalization of MTF, which indicates the quality of contrast and marks the resolution of the lens. The higher the better, and 1 is the full score. The horizontal direction represents the spatial frequency, 0 represents the spatial frequency of 0lp / mm, and the further to the right, the higher the spatial frequency. Figure 4 It can be seen that when the wavelength range is 0.92μm-0.96μm, the MTF value at the center field of view of 60lp / mm is ≥0.8, and the MTF value at the edge field of view of 60lp / mm is ≥0.55. The imaging from the center field of view to the edge field of view has excellent resolution.

[0085] Embodiment 3

[0086] Figure 5 is a structural schematic diagram of a fixed-focus lens provided in Embodiment 3 of the present invention, such as Figure 5 As shown, the fixed-focus lens provided by the present invention comprises a first lens 110, a second lens 120, a third lens 130, a fourth lens 140 and a fifth lens 150 which are arranged in sequence from the object plane to the image plane along the optical axis; the first lens 110 is a negative power lens, the second lens 120 is a negative power lens, the third lens 130 is a positive power lens, the fourth lens 140 is a negative power lens, and the fifth lens 150 is a positive power lens; the surface of the lens adjacent to the object plane is the object surface, and the surface of the lens adjacent to the image plane is the image surface; the curvature radius of the object surface of the fourth lens 140 is R41, the curvature radius of the image surface of the fourth lens 140 is R42, the focal length of the fourth lens 140 is F4, the curvature radius of the object surface of the fifth lens 150 is R51, the curvature radius of the image surface of the fifth lens 150 is R52, and the focal length of the fifth lens 150 is F5; wherein:

[0087] Among them, the material of each lens and the range of other optical physical parameters such as refractive index and Abbe number are the same as those in Example 1, and will not be repeated here. The difference between this embodiment and Example 1 is that, first, the optical focal length of the fourth lens 140 is inconsistent. In this embodiment, the fourth lens 140 is a negative optical focal length lens; second, the surface shape of the fifth lens 150 is inconsistent. In this embodiment, the object surface of the fifth lens 150 is convex toward the object plane, and the image surface of the fifth lens 150 is concave toward the image plane; third, the refractive index of the fourth lens 140 in Example 1 is equal to the refractive index of the fifth lens 150, while the refractive index of the fourth lens 140 in this embodiment is greater than the refractive index of the fifth lens 150.

[0088] Table 5 describes in detail the specific setting parameters of each lens in the fixed-focus lens provided in Example 3 of the present invention in another feasible implementation manner. The fixed-focus lens in Table 5 corresponds to Figure 5 Prime lens shown.

[0089] Table 5 Design values ​​of optical physical parameters of fixed focus lens

[0090]

[0091] In Table 5, the surface numbers are numbered according to the order of the surfaces of each lens. For example, the surface number "S1" represents the object side of the first lens, the surface number "S2" represents the image side of the first lens, and so on; "STO" represents the aperture of the fixed-focus lens; "IMA" represents the image surface of the fixed-focus lens; the radius of curvature represents the curvature of the lens surface, a positive value represents that the surface is bent toward the object side, and the center of the circle is close to the image plane, and a negative value represents that the surface is bent toward the image side, and the center of the circle is close to the object plane, "PL" represents a plane, and the radius of curvature of the plane is infinite; the thickness represents the central axial distance from the current surface to the next surface, where the focus has an error due to the different number of digits of the values ​​of each parameter, so the thickness of the 13th surface can vary slightly, and the value can be adjusted as needed to achieve the purpose of clear focus; the refractive index (Nd) represents the ability of the material between the current surface and the next surface to deflect light, and a blank represents that the current position is air, and the refractive index is 1; the Abbe number (Vd) represents the dispersion characteristics of the material between the current surface and the next surface to light, and a blank represents that the current position is air. The semi-aperture is the semi-diameter of the lens.

[0092] Next, a feasible implementation manner is used to illustrate the data in the aspheric surface of the aspheric lens in combination with Table 6.

[0093] Table 6 Parameter design values ​​of each surface of the aspheric lens in the fixed focus lens

[0094]

[0095] In Table 6, 4.0507006E-03 means that the coefficient A of the surface number S3 is 4.0507006*10 -3 , and so on.

[0096] The optical system of this embodiment achieves the following technical indicators: focal length f is 1.636 mm, field of view angle is 144°, and aperture number is 1.2. The above scheme can make the fixed-focus lens take into account the imaging quality, compact structure, large aperture, and large field of view of the vehicle lens design.

[0097] Further, Figure 6 This is the MTF curve of the fixed focus lens provided in the third embodiment of the present invention. The MTF curve represents the comprehensive resolution level of an optical system. The vertical direction in the figure is the normalization of MTF, which indicates the quality of contrast and marks the resolution of the lens. The higher the better, and 1 is the full score. The horizontal direction represents the spatial frequency, 0 represents the spatial frequency of 0lp / mm, and the further to the right, the higher the spatial frequency. Figure 6 It can be seen that when the wavelength range is 0.92μm-0.96μm, the MTF value at the central field of view of 60lp / mm is ≥0.8, and the MTF value at the edge field of view of 60lp / mm is ≥0.4. The imaging from the central field of view to the edge field of view has excellent resolution.

[0098] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A fixed-focus lens, characterized in that: It includes a first lens, a second lens, a third lens, a fourth lens and a fifth lens which are arranged in sequence from the object plane to the image plane along the optical axis; The first lens is a negative power lens, the second lens is a negative power lens, the third lens is a positive power lens, the fourth lens is a positive power lens or a negative power lens, and the fifth lens is a positive power lens; The surface of the lens adjacent to the object plane is the object-side surface, and the surface of the lens adjacent to the image plane is the image-side surface; the curvature radius of the object-side surface of the fourth lens is R41, the curvature radius of the image-side surface of the fourth lens is R42, the focal length of the fourth lens is F4, the curvature radius of the object-side surface of the fifth lens is R51, the curvature radius of the image-side surface of the fifth lens is R52, and the focal length of the fifth lens is F5; wherein:

2. The fixed-focus lens according to claim 1, characterized in that: The first lens and the third lens are glass spherical lenses, and the second lens, the fourth lens and the fifth lens are plastic aspherical lenses.

3. The fixed-focus lens according to claim 1, characterized in that: The object-side surface of the first lens is convex toward the object plane, and the image-side surface of the first lens is concave toward the image plane; The object-side surface of the second lens is concave toward the object plane, and the image-side surface of the second lens is convex toward the image plane; The object-side surface of the third lens is convex toward the object plane, and the image-side surface of the third lens is convex toward the image plane; The object-side surface of the fourth lens is concave toward the object plane, and the image-side surface of the fourth lens is convex toward the image plane; The object-side surface of the fifth lens is convex toward the object plane, and the image-side surface of the fifth lens is concave toward the image plane; Alternatively, the object-side surface of the fifth lens is convex toward the object plane, and the image-side surface of the fifth lens is convex toward the image plane.

4. The fixed-focus lens according to claim 1, characterized in that: The refractive index of the first lens is Nd1, and the Abbe number of the first lens is Vd1; wherein: 1.8 <Nd1<2.03,28.55<Vd1<60.90。 5. The fixed-focus lens according to claim 1, wherein: The refractive index of the third lens is Nd3, and the Abbe number of the third lens is Vd3; wherein: 1.91 <Nd3<2.1,24<Vd3<41。 6. The fixed-focus lens according to claim 1, wherein: A refractive index of the fourth lens is greater than or equal to a refractive index of the fifth lens.

7. The fixed-focus lens according to claim 1, wherein: The fixed-focus lens further includes an aperture; The aperture stop is located in the optical path between the second lens and the third lens.

8. The fixed-focus lens according to claim 2, wherein: The aspheric surface of the plastic aspheric lens satisfies: Among them, z represents the axial vector height of the aspheric surface in the Z direction; r represents the distance from the point on the aspheric surface to the optical axis; c represents the curvature of the fitted sphere, which is the inverse of the radius of curvature; k represents the fitted cone coefficient; A, B, C, D, and E represent the 4th, 6th, 8th, 10th, and 12th order coefficients of the aspheric polynomial, respectively.

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