A fixed focus lens

Abstract

The application discloses a kind of fixed focus lens, front lens group, diaphragm and rear lens group are sequentially arranged from object side to image side;Front lens group is sequentially arranged with the first lens, second lens and third lens with negative, negative, positive focal power from object side to image side;Rear lens group is sequentially arranged with the fourth lens, fifth lens, sixth lens and seventh lens with positive, negative, positive, positive focal power from object side to image side;Wherein, the fourth lens and the fifth lens are glued, form double glued lens.The fixed focus lens is composed of 7 lens elements, the number of lens is reasonable, simple and compact structure, the focal power and position of each lens element are reasonable, and the environmental adaptability is strong, the resolving power is high;The design of large field angle and large image height makes the lens system have greater competitiveness in the market.The fixed focus lens FNO is 2.50, the field angle is 138°, the imaging image height can match 1 / 1.8 inch chip, the optical total length is not more than 24.0mm, and the absolute value of optical distortion is less than 40%, to meet the super high definition imaging requirement.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical technology, in particular to a fixed focus lens. BACKGROUND

[0002] With the continuous progress of the security monitoring industry, society has put forward higher and higher requirements for security. The ultra-high-definition lens system with large field of view, large image height and good environmental adaptability is more and more favored by the security market. However, there are problems, that is, the lens with large field of view and large image height often contains many lenses, which are large in size and high in cost. In order to reduce the cost, a small part of the lens sacrifices part of the resolving power. SUMMARY

[0003] The present application provides a fixed focus lens, which adopts 7 glass-plastic lens elements, the field of view is 138°, the total length is less than 24.0mm, the absolute value of optical distortion is less than 40%, and the imaging image height can match the ultra-high-definition lens system of 1 / 1.8'' chip.

[0004] To achieve the above object, the embodiment of the present application provides a fixed focus lens, comprising: a front lens group, a diaphragm and a rear lens group arranged in sequence from the object side to the image side.

[0005] The front lens group is sequentially provided with a first lens with negative focal power, a second lens with negative focal power, and a third lens with positive focal power from the object side to the image side.

[0006] The rear lens group is sequentially provided with a fourth lens with positive focal power, a fifth lens with negative focal power, a sixth lens with positive focal power and a seventh lens with positive focal power from the object side to the image side.

[0007] Among them, the fourth lens and the fifth lens are glued to form a double-glued lens.

[0008] Optionally, the first lens is a glass spherical lens, the second lens is a plastic aspherical lens, the third lens is a glass spherical lens, the fourth lens is a glass spherical lens, the fifth lens is a glass spherical lens, the sixth lens is a plastic aspherical lens, and the seventh lens is a plastic aspherical lens.

[0009] Optionally, one surface of the first lens facing the object side is convex, one surface of the first lens facing the image side is concave, one surface of the second lens facing the object side is convex, one surface of the second lens facing the image side is concave, one surface of the third lens facing the object side is convex, one surface of the third lens facing the image side is concave, one surface of the fourth lens facing the object side is convex, one surface of the fourth lens facing the image side is convex, one surface of the fifth lens facing the object side is concave, one surface of the fifth lens facing the image side is convex, one surface of the sixth lens facing the object side is concave in the paraxial region, one surface of the sixth lens facing the image side is convex, one surface of the seventh lens facing the object side is convex in the paraxial region, one surface of the seventh lens facing the image side is concave.

[0010] Optionally, the front lens group satisfies the following relationship:

[0011] The rear lens group satisfies the following relationship:

[0012] wherein, is a combined focal power of the front lens group, is a combined focal power of the rear lens group, is a focal power of the fixed lens.

[0013] Optionally, a focal power of the first lens and a focal power of the fixed lens satisfy the following relationship: a focal power of the second lens and a focal power of the fixed lens satisfy the following relationship: a focal power of the third lens and a focal power of the fixed lens satisfy the following relationship:

[0014] Optionally, a refractive index ND3 of the third lens and an Abbe number VD3 of the third lens satisfy the following relationship: 1.75≤ND3≤1.88, 20.5≤VD3≤28.50.

[0015] Optionally, a focal power of the doublet lens is positive, a focal power of the doublet lens and a focal power of the fixed lens satisfy the following relationship:

[0016] Optionally, the refractive index ND4 and the Abbe number VD4 of the fourth lens satisfy the following relationship: 1.55≤ND4≤1.65, 65.0≤VD4≤75.5; the refractive index ND5 and the Abbe number VD5 of the fifth lens satisfy the following relationship: 1.755≤ND5≤2.1, 20.5≤VD5≤32.5.

[0017] Optionally, the refractive power of the sixth lens and the refractive power of the seventh lens satisfy the following relationship:

[0018] and the refractive power of the seventh lens satisfy the following relationship:

[0019] Optionally, the total optical length TTL of the fixed focus lens and the effective focal length f of the fixed focus lens satisfy the following relationship: 8.15≤TTL / f≤8.955.

[0020] Optionally, the optical back focal length BFL of the fixed focus lens and the effective focal length f of the fixed focus lens satisfy the following relationship: 1.252≤BFL / f≤1.554.

[0021] The technical scheme of the embodiment of the present application is that the front lens group, the diaphragm and the rear lens group are sequentially arranged from the object side to the image side; the front lens group is sequentially provided with the first lens with negative refractive power, the second lens with negative refractive power and the third lens with positive refractive power from the object side to the image side; the rear lens group is sequentially provided with the fourth lens with positive refractive power, the fifth lens with negative refractive power, the sixth lens with positive refractive power and the seventh lens with positive refractive power from the object side to the image side; wherein the fourth lens and the fifth lens are cemented to form a double cemented lens. Further, the fixed focus lens is composed of seven lens elements, the number of lens elements is reasonable, the structure is simple and compact, the refractive power and position of each lens element are reasonable, the environmental adaptability is strong and the resolving power is high; at the same time, the design of large field angle and large image height makes the lens system have greater competitiveness in the market. The fixed focus lens has an aperture number FNO of 2.50, a field angle of 138°, an imaging image height that can match a 1 / 1.8 inch chip, an optical total length of not more than 24.0 mm and an optical distortion absolute value of less than 40%, which meets the requirements of ultra-high definition imaging.

[0022] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present application, nor is it used to limit the scope of the present application. Other features of the present application will become apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0023] ​In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort based on these drawings.

[0024] Figure 1 is a structural schematic diagram of the fixed focus lens according to the first embodiment of the present application;

[0025] Figure 2 is an axial aberration curve diagram of the fixed focus lens according to the first embodiment of the present application;

[0026] Figure 3 is a lateral light fan diagram of the fixed focus lens according to the first embodiment of the present application;

[0027] Figure 4 is a field curvature distortion curve diagram of the fixed focus lens according to the first embodiment of the present application;

[0028] Figure 5 is a structural schematic diagram of the fixed focus lens according to the second embodiment of the present application;

[0029] Figure 6 is an axial aberration curve diagram of the fixed focus lens according to the second embodiment of the present application;

[0030] Figure 7 is a lateral light fan diagram of the fixed focus lens according to the second embodiment of the present application;

[0031] Figure 8 is a field curvature distortion curve diagram of the fixed focus lens according to the second embodiment of the present application;

[0032] Figure 9 is a structural schematic diagram of the fixed focus lens according to the third embodiment of the present application;

[0033] Figure 10 is an axial aberration curve diagram of the fixed focus lens according to the third embodiment of the present application;

[0034] Figure 11 is a lateral light fan diagram of the fixed focus lens according to the third embodiment of the present application;

[0035] Figure 12 is a field curvature distortion curve diagram of the fixed focus lens according to the third embodiment of the present application. DETAILED DESCRIPTION

[0036] In the following, the technical solutions in the embodiments of the present application will be described clearly and completely in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative effort should fall into the protection scope of the present application.

[0037] It should be noted that the terms "first", "second" and the like in the description and claims of the present application and the above drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in other sequences than those illustrated or described herein. In addition, the terms "comprise" and "have" and any variations thereof are intended to cover non-exclusive inclusion.

[0038] The embodiment of the present application provides a fixed focus lens, comprising: a front lens group, a diaphragm and a rear lens group arranged in sequence from an object side to an image side; the front lens group is sequentially provided with a first lens with negative focal power, a second lens with negative focal power and a third lens with positive focal power from the object side to the image side; the rear lens group is sequentially provided with a fourth lens with positive focal power, a fifth lens with negative focal power, a sixth lens with positive focal power and a seventh lens with positive focal power from the object side to the image side; wherein the fourth lens and the fifth lens are cemented to form a double cemented lens.

[0039] It should be noted that the fixed focus lens further comprises a flat glass and an image plane. The diaphragm of the fixed focus lens is located between the third lens and the fourth lens; the flat glass is located on the image side of the seventh lens. The diaphragm is located between the third lens and the fourth lens, which can effectively reduce the aperture size of the front lens group and reduce the weight of the lens; on the other hand, reducing the light passing aperture of the diaphragm position can increase the FNO value of the system and reduce the introduction of system diaphragm aberration; in the embodiment, the FNO value of the system is 2.5.

[0040] In the embodiment, the front lens group adopts three lens elements, and the focal power is negative-negative-positive. Reasonable adjustment of the focal power ratio of each element and the whole fixed focus lens can make the overall aberration of the front lens group be well controlled. The rear lens group adopts four lens elements, and the focal power is positive-negative-positive-positive. Reasonable adjustment of the focal power ratio of each element and the whole fixed focus lens can make the overall aberration of the rear lens group be well controlled. The focal power of each lens is reasonably matched, which is beneficial to realize mutual compensation of the focal power of each lens in the optical system and achieve the design purpose of super-clear imaging.

[0041] And the double-cemented lens is located behind the system stop, which is beneficial to correct chromatic aberration and improve the imaging quality of the optical system; meanwhile, the double-cemented lens can also gently transmit light and reduce the tolerance sensitivity of the optical system, thereby improving the assembly yield of the optical system.

[0042] Optionally, the first lens is a glass spherical lens, the second lens is a plastic aspherical lens, the third lens is a glass spherical lens, the fourth lens is a glass spherical lens, the fifth lens is a glass spherical lens, the sixth lens is a plastic aspherical lens, and the seventh lens is a plastic aspherical lens.

[0043] The glass elements arranged in the first lens, the third lens, the fourth lens and the fifth lens can ensure that the fixed-focus lens has good high-low temperature environment adaptability; the types of glass materials are various, and appropriate dispersion parameters can be selected to reduce chromatic aberration; the second lens, the sixth lens and the seventh lens are arranged as plastic aspherical lenses, which can effectively realize the design effect of large image height and low distortion. Reasonable matching of the materials, focal power, shape and position layout of the lenses can realize the design of a high-definition imaging lens system with a large field of view and a large image height.

[0044] Optionally, one side of the first lens facing the object side is a convex surface, and the other side facing the image side is a concave surface; one side of the second lens facing the object side is a convex surface, and the other side facing the image side is a concave surface; one side of the third lens facing the object side is a convex surface, and the other side facing the image side is a concave surface; one side of the fourth lens facing the object side is a convex surface, and the other side facing the image side is a convex surface; one side of the fifth lens facing the object side is a concave surface, and the other side facing the image side is a convex surface; one side of the sixth lens facing the object side is a concave surface in the near-axis region, and the other side facing the image side is a convex surface; one side of the seventh lens facing the object side is a convex surface in the near-axis region, and the other side facing the image side is a concave surface.

[0045] The object side surface of the first lens can be a convex surface, and the image side surface can be a concave surface. The first lens is designed as a meniscus negative lens with the convex surface facing the object side, which can make the light rays of a large field of view enter the system as much as possible, and is beneficial to improve the field of view angle of the optical system. The field of view angle of the fixed-focus lens is 138°. The object side surface of the second lens is a convex surface, and the image side surface is a concave surface. By setting the first lens and the second lens as similar convex-concave lenses, the optical distortion of the fixed-focus lens system can be effectively reduced. The object side surface of the third lens can be a convex surface, and the image side surface can be a concave surface. The third lens is designed as a convex-concave positive lens, which can effectively control the light rays to enter the rear of the optical system gently, reduce the spherical aberration of the optical system, and improve the imaging quality of the optical system. By setting the cemented lens material and reasonably setting the optical power, the color aberration of the fixed-focus lens can be balanced. The surface facing the object side of the sixth lens in the paraxial region is a concave surface, and the surface facing the image side is a convex surface. By using the plastic aspheric lens, the light ray trend can be effectively controlled, the light rays can be converged, and the total length of the system can be shortened, so that the system structure is more compact. The surface facing the object side of the seventh lens in the paraxial region is a convex surface, and the surface facing the image side is a concave surface. By using the plastic aspheric lens, the light ray trend can be effectively controlled, so that the light rays can enter the flat glass with a small deflection angle, which can effectively reduce the system tolerance sensitivity and reduce the risk of stray light at the flat glass.

[0046] Optionally, the front lens group satisfies the following relationship: The rear lens group satisfies the following relationship: wherein, is the combined optical power of the front lens group, is the combined optical power of the rear lens group, is the optical power of the fixed-focus lens.

[0047] The optical powers of the front lens group and the rear lens group of the lens have a reasonable distribution ratio, which is beneficial to control the incident light height of the front lens group, reduce the front aperture, and thus reduce the weight. In addition, the reasonable optical power distribution of the front and rear groups can increase the image surface as much as possible while ensuring the image surface illumination, so as to achieve the design purpose of large image height.

[0048] Optionally, the optical power of the first lens and the optical power of the fixed-focus lens satisfy the following relationship: The optical power of the second lens and the optical power of the fixed-focus lens satisfy the following relationship: The optical power of the third lens and the optical power of the fixed-focus lens satisfy the following relationship: Therefore, the first lens is arranged in such a way that the light rays with large field of view and large aperture can enter the second lens with a small deflection angle. The second lens is arranged in such a way that the trend of the light rays can be effectively controlled, the field curvature and spherical aberration of the optical system are reduced, and the image quality of the optical system is improved. The third lens is arranged in such a way that it is beneficial to balance the aberration of the light rays on the front side of the diaphragm.

[0049] Optionally, the refractive index ND3 and the Abbe number VD3 of the third lens satisfy the following relationship: 1.75≤ND3≤1.88, 20.5≤VD3≤28.50. The third lens is arranged in such a way that it is beneficial to balance the aberration, control the height of the light rays, and facilitate the miniaturization of the fixed-focus lens.

[0050] Optionally, the power of the doublet lens is positive, and the power of the doublet lens is smaller than the power of the fixed-focus lens satisfies the following relationship: Therefore, by setting the material of the doublet lens and reasonably setting the power of the doublet lens, the chromatic aberration of the lens system is balanced.

[0051] Optionally, the refractive index ND4 and the Abbe number VD4 of the fourth lens satisfy the following relationship: 1.55≤ND4≤1.65, 65.0≤VD4≤75.5; the refractive index ND5 and the Abbe number VD5 of the fifth lens satisfy the following relationship: 1.755≤ND5≤2.1, 20.5≤VD5≤32.5. The doublet lens is located behind the system diaphragm, which is beneficial to correct chromatic aberration and improve the imaging quality of the optical system; at the same time, it can also gently transfer the light rays, reduce the tolerance sensitivity of the optical system, and improve the assembly yield of the optical system.

[0052] Optionally, the power of the sixth lens is smaller than the power of the fixed-focus lens satisfies the following relationship: the power of the seventh lens is smaller than the power of the fixed-focus lens satisfies the following relationship: Therefore, it is beneficial to control the aberration, reduce the tolerance sensitivity, and improve the image quality.

[0053] Optionally, the total optical length TTL of the fixed-focus lens and the effective focal length f of the fixed-focus lens satisfy the following relationship: 8.15≤TTL / f≤8.955. It is beneficial to realize the small volume of the fixed-focus lens.

[0054] Optionally, the optical back focal length BFL of the fixed-focus lens and the effective focal length f of the fixed-focus lens satisfy the following relationship: 1.252≤BFL / f≤1.554. The optical back focal length BFL is the distance from the image side of the last lens to the image plane. It is beneficial to realize the small volume of the fixed-focus lens.

[0055] The technical scheme of the embodiment of the present application sequentially sets a front lens group, a diaphragm and a rear lens group from the object side to the image side; the front lens group sequentially sets a first lens with negative focal power, a second lens with negative focal power, and a third lens with positive focal power from the object side to the image side; the rear lens group sequentially sets a fourth lens with positive focal power, a fifth lens with negative focal power, a sixth lens with positive focal power, and a seventh lens with positive focal power from the object side to the image side; wherein the fourth lens and the fifth lens are cemented to form a double cemented lens. Further, the fixed focus lens is composed of seven lens elements, the number of lens elements is reasonable, the structure is simple and compact, the focal power and position of each lens element are reasonable, the environmental adaptability is strong, and the resolving power is high; at the same time, the design of large field angle and large image height makes the lens system have greater competitiveness in the market. The fixed focus lens has an aperture number FNO of 2.50, a field angle of 138°, an imaging image height that can match a 1 / 1.8 inch chip, an optical total length of not more than 24.0 mm, and an optical distortion absolute value of less than 40%, which meets the requirements of ultra-high definition imaging.

[0056] The following introduces the fixed focus lens proposed by the present application through three specific embodiments.

[0057] The specific parameters in the embodiment one, the embodiment two and the embodiment three are shown in Table 1.

[0058] Table 1: Specific parameters of different embodiments

[0059]

[0060]

[0061] Embodiment one

[0062] Figure 1 is a structure schematic diagram of the fixed focus lens proposed by the embodiment one of the present application. As shown in Figure 1As shown, the fixed focus lens is provided with, in order from the object side to the image side: a front lens group, a stop STO, a rear lens group, a flat glass PL, and an image plane IMA; the front lens group comprises: a first lens L1 which is a glass spherical lens, the first lens L1 has a negative focal power, one surface of the first lens L1 towards the object side is a convex surface, and one surface of the first lens L1 towards the image side is a concave surface; a second lens L2 which is a plastic aspherical lens, the second lens L2 has a negative focal power, one surface of the second lens L2 towards the object side is a convex surface, and one surface of the second lens L2 towards the image side is a concave surface; a third lens L3 which is a glass spherical lens, the third lens L3 has a positive focal power, one surface of the third lens L3 towards the object side is a convex surface, and one surface of the third lens L3 towards the image side is a concave surface; the rear lens group comprises: a fourth lens L4 which is a glass spherical lens, the fourth lens L4 has a positive focal power, both surfaces of the fourth lens L4 are convex surfaces; a fifth lens L5 which is a glass spherical lens, the fifth lens L5 has a negative focal power, one surface of the fifth lens L5 towards the object side is a concave surface, and one surface of the fifth lens L5 towards the image side is a convex surface; wherein the fourth lens L4 and the fifth lens L5 are cemented together as a cemented lens group; a sixth lens L6 which is a plastic aspherical lens, the sixth lens L6 has a positive focal power, the sixth lens L6 is in the paraxial region, one surface of the sixth lens L6 towards the object side is a concave surface, and one surface of the sixth lens L6 towards the image side is a convex surface; a seventh lens L7 which is a plastic aspherical lens, the seventh lens L7 has a positive focal power, the seventh lens L7 is in the paraxial region, one surface of the seventh lens L7 towards the object side is a convex surface, and one surface of the seventh lens L7 towards the image side is a concave surface; the stop of the fixed focus lens is located between the third lens L3 and the fourth lens L4; and the flat glass is located on the image side of the seventh lens L7. Figure 1 The structure, composition, shape and position of each element of the fixed focus lens are known, which are very important for the fixed focus lens. As shown in the figure, the optical system is composed of seven optical lenses, and the flat glass is located on the side of the seventh lens L7 towards the image plane.

[0063] In this embodiment, the focal length f is 2.687 mm, the F# is 2.50, the field of view angle is DFOV=138°, and the total optical length TTL is 23.82 mm; the optical physical parameters of the first lens L1 to the seventh lens L7 are shown in Table 2:

[0064] Table 2 Design values of the fixed focus lens of the embodiment

[0065] Surface No. Surface Type Radius of Curvature (mm) Thickness (mm) (nd) / (vd) Half Radius (mm) k Value S1 Standard Surface 11.272 1.207 1.755 / 52.33 8.18 S2 Standard Surface 6.217 3.236 5.72 S3 Even Aspherical Surface 13.143 0.868 1.535 / 55.71 5.42 2.534 S4 Even Aspherical Surface 2.178 3.863 3.28 -0.759 S5 Standard Surface 4.843 2.994 1.847 / 23.79 2.50 S6 Standard Surface 15.669 0.551 1.32 S7 STO INF 0.110 1.10 S8 Standard Surface 10.444 2.088 1.569 / 71.30 1.21 S9 Standard Surface -2.060 0.805 1.847 / 23.79 1.57 S10 Standard Surface -8.388 0.611 2.07 S11 Even Aspherical Surface -14.337 1.594 1.545 / 56.00 2.67 -56.674 S12 Even Aspherical Surface -3.444 0.027 2.86 -1.352 S13 Even Aspherical Surface 5.959 2.210 1.545 / 56.00 4.12 -10.524 S14 Even Aspherical Surface 7.993 2.723 4.20 -10.306 S15 Standard Surface INF 0.700 1.517 / 64.21 4.40 S16 Standard Surface INF 0.230 4.45 IMA Standard Surface INF 4.50

[0066] The surface sequence numbers S1-S16 in Table 2 are numbered according to the surface sequence of each lens, and "STO" represents the aperture of the lens; the radius of curvature represents the bending degree of the corresponding lens surface, a positive value represents that the surface is bent towards the image side, and a negative value represents that the surface is bent towards the object side, wherein "INF" represents that the surface is a plane, and the radius of curvature is infinite; the thickness represents the central axial distance from the current surface to the next surface, the refractive index represents the deflection ability of the material between the current surface and the next surface, and the space represents that the current position is air, and the refractive index is 1; Table 3 represents the aspherical surface coefficient values used in the current embodiment.

[0067] Table 3 Aspherical surface coefficients of the fixed focus lens of the embodiment

[0068] Surface No. A B C D E F G S3 -6.224324E-04 -2.077141E-05 1.156034E-06 -1.247189E-08 -3.380465E-11 -1.358838E-11 2.876792E-13 S4 -2.007909E-04 -1.021393E-04 -1.137823E-05 -9.161778E-07 1.772079E-07 8.018972E-09 -1.161599E-09 S11 2.910614E-04 3.219524E-04 1.127582E-04 -1.798642E-05 7.428775E-07 9.309057E-08 -7.905998E-09 S12 -7.032426E-04 2.937878E-04 1.000302E-04 -1.078097E-05 7.728304E-07 -2.987933E-08 1.860063E-09 S13 1.698379E-03 -2.191510E-06 2.569641E-06 -4.832158E-07 1.491300E-08 1.242029E-09 -6.241724E-11 S14 -3.281613E-03 2.053940E-04 -3.815619E-06 -5.943216E-08 8.898509E-09 1.655852E-11 -2.190213E-11

[0069] The aspherical conic coefficient can be defined by the following aspherical formula, but is not limited to the following representation method:

[0070]

[0071] Wherein, z is the axial height of the aspherical surface in the Z direction; r is the height of the aspherical surface; c is the curvature of the fitting sphere, which is the reciprocal of the radius of curvature in numerical value; k is the fitting conic coefficient; A-G are the 4th order, 6th order, 8th order, 10th order, 12th order, 14th order and 16th order term coefficients of the aspherical polynomial.

[0072] Figure 2 Fig. 1 is a schematic diagram of the axial aberration curve of the fixed focus lens according to the first embodiment of the present application, wherein the vertical direction represents the normalized aperture, 0 represents the optical axis, and the vertical direction vertex represents the maximum pupil radius (the pupil radius is 0.5373 mm); the horizontal direction represents the relative ideal focal point offset, and the unit is millimeter (mm). Different line curves in the figure represent different wavelengths of system imaging (wherein, blue represents 436 nm, green represents 486 nm, red represents 546 nm, yellow represents 587 nm, and purple represents 656 nm), and the system imaging is obtained by the fixed focus lens according to the first embodiment of the present application. Figure 2 It can be seen that the axial aberrations of different wavelengths are controlled within the range of (-0.05 mm, +0.05 mm), which indicates that the spherical aberration of the fixed focus lens at each wavelength is well controlled, and the wide spectrum application requirement can be met.

[0073] Figure 3The transverse light fan diagram of the fixed focus lens is one of the most commonly used evaluation methods in modern optical design. The horizontal coordinate is the beam aperture, and the vertical coordinate is the sagittal aberration. The most ideal curve is a straight line coinciding with the horizontal coordinate, indicating that all light rays are focused on the same point on the image plane. The corresponding interval on the vertical coordinate of the curve is the maximum dispersion range of the light beam on the ideal image plane. The light fan diagram can not only reflect the monochromatic aberration of different wavelengths (among them, blue represents 436nm, green represents 486nm, red represents 546nm, yellow represents 587nm, and purple represents 656nm), but also represent the size of the sagittal chromatic aberration. From the transverse light fan diagram of the fixed focus lens provided in the embodiment one of the present application, Figure 3 It can be seen that the system is close to the horizontal coordinate at each wavelength under each field of view, which indicates that the sagittal aberration of each wavelength of the system is well corrected. At the same time, there is no obvious dispersion of each wavelength, which indicates that the chromatic aberration of the system is also well corrected, thereby ensuring that the optical system can achieve high-resolution imaging requirements.

[0074] Figure 4 The field curvature distortion curve diagram of the fixed focus lens provided in the embodiment one of the present application is shown in the figure. In the left coordinate system, the horizontal coordinate represents the size of the field curvature, with units of mm; the vertical coordinate represents the normalized image height, without units; wherein T represents the meridian, and S represents the sagittal. From the field curvature distortion curve diagram of the fixed focus lens provided in the embodiment one of the present application, Figure 4 It can be seen that the fixed focus lens provided in the embodiment effectively controls the field curvature from light with a wavelength of 436nm to light with a wavelength of 656nm (among them, blue represents 436nm, green represents 486nm, red represents 546nm, yellow represents 587nm, and purple represents 656nm, the solid line in the figure represents the meridian, and the dashed line represents the sagittal). That is, the difference between the central image quality and the peripheral image quality is small during imaging (among them, in the left field curvature diagram, the maximum field of view is 69.000 degrees, the sagittal field curvature is 0.0392mm, and the meridian field curvature is 0.1001mm). In the right coordinate system, the horizontal coordinate represents the size of the distortion, with units of %; the vertical coordinate represents the normalized image height, without units; from the field curvature distortion curve diagram of the fixed focus lens provided in the embodiment one of the present application, Figure 4 It can be seen that the distortion of the lens provided in the embodiment (in the right distortion diagram, the maximum field of view is 69.000 degrees, and the maximum distortion is 36.0283%).

[0075] Embodiment two

[0076] Figure 5 The structure diagram of the fixed focus lens provided in the embodiment two of the present application is shown in the figure. As shown in the figure, Figure 5 the fixed focus lens is sequentially provided with a front lens group, a stop STO, a rear lens group, a flat glass, and an image plane from the object side to the image side. The front lens group includes a first lens L1, a second lens L2, and a third lens L3. The rear lens group includes a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. The fourth lens L4 and the fifth lens L5 are glued to form a double-glued lens.

[0077] In the embodiment, the focal length f is 2.766 mm, the F# is 2.50, the field angle is DFOV = 138°, and the total optical length TTL = 23.74 mm; the optical physical parameters of the first lens L1 to the seventh lens L7 are shown in Table 4.

[0078] Table 4 Design values of the fixed-focus lens of embodiment two

[0079]

[0080]

[0081] The surface serial numbers S1-S16 in Table 4 are numbered according to the surface order of each lens, and "STO" represents the stop of the lens; the radius of curvature represents the bending degree of the corresponding lens surface, and a positive value represents that the surface is bent toward the image side, and a negative value represents that the surface is bent toward the object side, wherein "INF" indicates that the surface is a plane, and the radius of curvature is infinite; the thickness represents the center axial distance from the current surface to the next surface, the refractive index represents the deflection ability of the material between the current surface and the next surface, and the space represents that the current position is air, and the refractive index is 1; Table 5 shows the aspherical coefficient values used in the embodiment.

[0082] Table 5 Aspherical coefficients of the fixed-focus lens of embodiment two

[0083] Surface No. A B C D E F G S3 -8.833809E-04 -4.412333E-06 1.152751E-06 -1.966412E-08 -2.446208E-10 -3.244532E-12 1.537720E-13 S4 -1.777238E-03 -2.210310E-04 -7.323004E-06 -3.797248E-07 1.182774E-07 1.478108E-09 -7.917610E-10 S11 9.818958E-04 1.490264E-04 1.061164E-04 -1.336553E-05 7.530762E-07 4.987956E-08 -6.352613E-09 S12 -4.403582E-04 2.141760E-04 7.462790E-05 -7.106536E-06 7.174557E-07 -1.829413E-08 1.760949E-09 S13 -7.930322E-04 -5.656581E-05 2.153137E-06 -2.733968E-07 2.989908E-08 1.477676E-09 -1.377818E-10 S14 -3.344818E-03 7.956412E-05 -6.919384E-06 2.334964E-07 1.144831E-08 -4.821004E-10 -1.826953E-11

[0084] The aspherical conic coefficient can be defined by the following aspherical formula, but is not limited to the following representation method:

[0085]

[0086] Wherein, z is the axial height of the aspherical Z direction; r is the height of the aspherical surface; c is the curvature of the fitting sphere, which is the reciprocal of the radius of curvature in value; k is the fitting conic coefficient; A-G are 4th order, 6th order, 8th order, 10th order, 12th order, 14th order and 16th order term coefficients of the aspherical polynomial.

[0087] Figure 6 Figure 1 is a schematic diagram of the axial aberration curve of the fixed-focus lens according to the embodiment two of the present application, the vertical direction represents the normalization of the aperture, 0 represents on the optical axis, and the vertical direction vertex represents the maximum pupil radius (the pupil radius is 0.5533 mm); the horizontal direction represents the offset amount relative to the ideal focus point, and the unit is millimeter (mm). Different line curves in the figure represent different wavelengths of system imaging (wherein, blue represents 436 nm, green represents 486 nm, red represents 546 nm, yellow represents 587 nm, and purple represents 656 nm), and the system imaging is obtained by the fixed-focus lens according to the embodiment two of the present application. Figure 6It can be seen that the axial aberration of different wavelengths is controlled in the range of (-0.05mm, +0.05mm), which shows that the spherical aberration of the fixed focus lens at each wavelength is well controlled, and the wide spectrum application requirement can be met.

[0088] Figure 7 is a lateral light fan diagram of the fixed focus lens provided in Embodiment Two of the present application. The lateral light fan diagram is one of the most commonly used evaluation methods in modern optical design. The abscissa is the beam aperture, and the ordinate is the sagittal aberration. The most ideal curve is a straight line coinciding with the abscissa, which shows that all light rays are focused on the same point on the image plane. The corresponding interval on the ordinate of the curve is the maximum dispersion range of the light beam on the ideal image plane. The lateral light fan diagram can not only reflect the monochromatic aberration of different wavelengths (among them, blue represents 436nm, green represents 486nm, red represents 546nm, yellow represents 587nm, and purple represents 656nm), but also represent the size of the sagittal chromatic aberration. From Figure 7 It can be seen that the system is close to the abscissa at each wavelength under each field of view, which shows that the sagittal aberration of the system at each wavelength is well corrected. At the same time, there is no obvious dispersion of each wavelength, which shows that the chromatic aberration of the system is also well corrected, thereby ensuring that the optical system can realize high-resolution imaging requirements.

[0089] Figure 8 is a field curvature distortion curve diagram of the fixed focus lens provided in Embodiment Two of the present application. In the left coordinate system in the diagram, the horizontal coordinate represents the size of the field curvature, with the unit of mm; the vertical coordinate represents the normalized image height, without unit; wherein T represents the meridian, and S represents the sagittal; from Figure 8 It can be seen that the fixed focus lens provided in the embodiment is effectively controlled on the field curvature from the light of 436nm to the light of 656nm (among them, blue represents 436nm, green represents 486nm, red represents 546nm, yellow represents 587nm, and purple represents 656nm, the solid line in the diagram represents the meridian, and the dotted line represents the sagittal), that is, the difference between the central image quality and the peripheral image quality is small during imaging (among them, in the left field curvature diagram, the maximum field of view is 69.000 degrees, the sagittal field curvature is 0.0563mm, and the meridian field curvature is 0.0749mm). In the right coordinate system, the horizontal coordinate represents the size of the distortion, with the unit of %; the vertical coordinate represents the normalized image height, without unit; from Figure 8 It can be seen that the distortion of the lens provided in the embodiment (in the right distortion diagram, the maximum field of view is 69.000 degrees, and the maximum distortion is 38.1940%).

[0090] Embodiment Three

[0091] Figure 9 is a structure diagram of the fixed focus lens provided in Embodiment Three of the present application. As Figure 9As shown, the fixed focus lens is sequentially provided with a front lens group, a diaphragm, a rear lens group, a flat glass and an image plane from the object side to the image side; the front lens group comprises a first lens L1, a second lens L2 and a third lens L3, and the rear lens group comprises a fourth lens L4, a fifth lens L5, a sixth lens L6 and a seventh lens L7. The fourth lens L4 and the fifth lens L5 are glued to form a double-glued lens.

[0092] In the embodiment, the focal length f is 2.766 mm, the F# is 2.50, the field of view angle is DFOV = 138°, and the total optical length TTL = 23.74 mm; the optical physical parameters of the first lens L1 to the seventh lens L7 are shown in Table 6.

[0093] Table 6 Design values of the fixed focus lens of the third embodiment

[0094]

[0095]

[0096] The surface numbers S1-S16 in Table 6 are numbered according to the surface order of each lens, and "STO" represents the diaphragm of the lens; the radius of curvature represents the bending degree of the corresponding lens surface, and a positive value represents that the surface is bent toward the image side, and a negative value represents that the surface is bent toward the object side, wherein "INF" represents that the surface is a plane, and the radius of curvature is infinite; the thickness represents the center axis distance from the current surface to the next surface, the refractive index represents the deflection ability of the material between the current surface and the next surface, and the space represents that the current position is air, and the refractive index is 1; Table 7 represents the aspherical surface coefficient value used in the current embodiment.

[0097] Table 7 Aspherical surface coefficients of the fixed focus lens of the third embodiment

[0098] Surface No. A B C D E F G S3 -8.833809E-04 -4.412333E-06 1.152751E-06 -1.966412E-08 -2.446208E-10 -3.244532E-12 1.537720E-13 S4 -1.777238E-03 -2.210310E-04 -7.323004E-06 -3.797248E-07 1.182774E-07 1.478108E-09 -7.917610E-10 S11 9.818958E-04 1.490264E-04 1.061164E-04 -1.336553E-05 7.530762E-07 4.987956E-08 -6.352613E-09 S12 -4.403582E-04 2.141760E-04 7.462790E-05 -7.106536E-06 7.174557E-07 -1.829413E-08 1.760949E-09 S13 -7.930322E-04 -5.656581E-05 2.153137E-06 -2.733968E-07 2.989908E-08 1.477676E-09 -1.377818E-10 S14 -3.344818E-03 7.956412E-05 -6.919384E-06 2.334964E-07 1.144831E-08 -4.821004E-10 -1.826953E-11

[0099] The aspherical conic coefficient can be defined by the following aspherical formula, but is not limited to the following representation method:

[0100]

[0101] Wherein, z is the axial height of the aspherical surface in the Z direction; r is the height of the aspherical surface; c is the curvature of the fitting sphere, which is the reciprocal of the radius of curvature in value; k is the fitting conic coefficient; A-G are 4th order, 6th order, 8th order, 10th order, 12th order, 14th order and 16th order term coefficients of the aspherical polynomial.

[0102] Figure 10is an axial aberration curve schematic diagram of the fixed focus lens provided in Embodiment Three of the present application, the vertical direction represents the normalization of the aperture, 0 represents on the optical axis, and the vertical direction top represents the maximum pupil radius (the pupil radius is 0.5533 mm) ; the horizontal direction represents the offset amount relative to the ideal focus point, with the unit of millimeter (mm). Different line curves in the figure represent different wavelengths of system imaging (among them, blue represents 436 nm, green represents 486 nm, red represents 546 nm, yellow represents 587 nm, and purple represents 656 nm), and the horizontal axis represents the field of view, with the unit of degree (°). Figure 10 It can be seen that the axial aberrations of different wavelengths are all controlled within the range of (-0.05 mm, +0.05 mm), which indicates that the spherical aberration of the fixed focus lens at each wavelength is well controlled, and the wide-spectrum application requirement can be met.

[0103] Figure 11 is the optical fan diagram of the fixed focus lens provided in Embodiment Three of the present application. The optical fan diagram is one of the most commonly used evaluation methods in modern optical design. The horizontal coordinate is the beam aperture, and the vertical coordinate is the sagittal aberration. The most ideal curve is a straight line coinciding with the horizontal coordinate, which indicates that all light rays are focused on the same point on the image plane. The corresponding interval on the vertical coordinate of the curve is the maximum dispersion range of the light beam on the ideal image plane. The optical fan diagram can not only reflect the monochromatic aberration of different wavelengths (among them, blue represents 436 nm, green represents 486 nm, red represents 546 nm, yellow represents 587 nm, and purple represents 656 nm), but also represent the size of the sagittal chromatic aberration. The horizontal axis represents the field of view, with the unit of degree (°). Figure 11 It can be seen that the system is well close to the horizontal coordinate at each wavelength under each field of view, which indicates that the sagittal aberration of the system at each wavelength is well corrected. At the same time, there is no obvious dispersion of each wavelength, which indicates that the chromatic aberration of the system is also well corrected, thereby ensuring that the optical system can realize the high-resolution imaging requirement.

[0104] Figure 12 is the field curvature distortion curve diagram of the fixed focus lens provided in Embodiment Three of the present application. In the left coordinate system in the figure, the horizontal coordinate represents the size of the field curvature, with the unit of mm; the vertical coordinate represents the normalized image height, without unit; among them, T represents the meridian, and S represents the sagittal; from Figure 12 It can be seen that the fixed focus lens provided in the embodiment is effectively controlled on the field curvature from the light with the wavelength of 436 nm to the light with the wavelength of 656 nm (among them, blue represents 436 nm, green represents 486 nm, red represents 546 nm, yellow represents 587 nm, and purple represents 656 nm, the solid line in the figure represents the meridian, and the dotted line represents the sagittal), that is, the difference between the central image quality and the peripheral image quality is small during imaging (among them, in the left field curvature schematic diagram, the maximum field of view is 69.000 degrees, the sagittal field curvature is 0.0559 mm, and the meridian field curvature is 0.0716 mm). In the right coordinate system, the horizontal coordinate represents the size of the distortion, with the unit of %; the vertical coordinate represents the normalized image height, without unit; fromFigure 12 It can be seen that the lens provided by the embodiment has distortion (in the right side distortion diagram, the maximum field of view is 69.000 degrees, and the maximum distortion = 38.1959%).

[0105] It should be noted that the structures and optical powers of the lenses in Embodiments One to Three can refer to the content before Embodiment One in the specific embodiment mode, and then, in each specific embodiment, it is not described again.

[0106] The above specific embodiments do not constitute a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A fixed focus lens characterized by, Comprise: a front lens group, a diaphragm and a rear lens group arranged in order from an object side to an image side; the front lens group is provided with a first lens with negative focal power, a second lens with negative focal power and a third lens with positive focal power in order from the object side to the image side; the rear lens group is provided with a fourth lens with positive focal power, a fifth lens with negative focal power, a sixth lens with positive focal power and a seventh lens with positive focal power in order from the object side to the image side; wherein the total number of lenses of the fixed focus lens is 7, the fourth lens and the fifth lens are cemented to form a double cemented lens; one side of the first lens towards the object side is a convex surface, the other side towards the image side is a concave surface, one side of the second lens towards the object side is a convex surface, the other side towards the image side is a concave surface, one side of the third lens towards the object side is a convex surface, the other side towards the image side is a concave surface, one side of the fourth lens towards the object side is a convex surface, the other side towards the image side is a convex surface, one side of the fifth lens towards the object side is a concave surface, the other side towards the image side is a convex surface, one side of the sixth lens towards the object side is a concave surface in the paraxial region, the other side towards the image side is a convex surface, one side of the seventh lens towards the object side is a convex surface in the paraxial region, the other side towards the image side is a concave surface.

2. The fixed focus lens of claim 1, wherein The first lens is a glass spherical lens, the second lens is a plastic aspherical lens, the third lens is a glass spherical lens, the fourth lens is a glass spherical lens, the fifth lens is a glass spherical lens, the sixth lens is a plastic aspherical lens, and the seventh lens is a plastic aspherical lens.

3. The fixed focus lens of claim 1, wherein The front lens group satisfies the following relational expression: -0.135 ≤ φ 前 / φ ≤ -0.003; The rear lens group satisfies the following relation: 0.485 ≤ φ 后 / φ ≤ 0.525; wherein φ 前 is the combined power of the front lens group, φ 后 is the combined power of the rear lens group, and φ is the power of the fixed focus lens.

4. The fixed focus lens of claim 1, wherein The focal power φ1 of the first lens and the focal power φ of the fixed focus lens satisfy the following relationship: -0.245≤φ1 / φ≤-0.115; the focal power φ2 of the second lens and the focal power φ of the fixed focus lens satisfy the following relationship: -0.615≤φ2 / φ≤-0.515; the focal power φ3 of the third lens and the focal power φ of the fixed focus lens satisfy the following relationship: 0.355≤φ3 / φ≤0.

425.

5. The fixed focus lens of claim 1, wherein, The refractive index ND3 of the third lens and the Abbe number VD3 satisfy the following relationship: 1.75≤ND3≤1.88, 20.5≤VD3≤28.

50.

6. The fixed focus lens of claim 1, wherein, The focal power of the double cemented lens is positive, and the focal power φ45 of the double cemented lens and the focal power φ of the fixed focus lens satisfy the following relationship: 0.02≤φ45 / φ≤0.

28.

7. The fixed focus lens of claim 1, wherein, The refractive index ND4 of the fourth lens and the Abbe number VD4 satisfy the following relationship: 1.55≤ND4≤1.65, 65.0≤VD4≤75.5; the refractive index ND5 of the fifth lens and the Abbe number VD5 satisfy the following relationship: 1.755≤ND5≤2.1, 20.5≤VD5≤32.

5.

8. The fixed lens according to claim 1, characterized in that, The focal power φ6 of the sixth lens and the focal power φ of the fixed focus lens satisfy the following relationship: 0.205≤φ6 / φ≤0.365; The focal power φ7 of the seventh lens and the focal power φ of the fixed focus lens satisfy the following relationship: 0.065≤φ7 / φ≤0.

12.

9. The fixed focus lens of claim 1, wherein, The total track length TTL of the fixed focus lens and the effective focal length f of the fixed focus lens satisfy the following relationship: 8.15≤TTL / f≤8.

955.

10. The fixed lens according to claim 1, characterized in that, The optical back focal length BFL of the fixed focus lens and the effective focal length f of the fixed focus lens satisfy the following relationship: 1.252≤BFL / f≤1.554.

Images