A fixed-focus lens

Abstract

The embodiment of the present invention discloses a fixed-focus lens. The fixed-focus lens includes a first lens with negative focal power, a second lens with negative focal power, a third lens with positive focal power, a fourth lens with negative focal power, an aperture, a fifth lens with negative focal power, a sixth lens with positive focal power, a seventh lens with positive focal power, and an eighth lens with positive or negative focal power, which are arranged in sequence from the object side to the image side along the optical axis; wherein the first lens, the third lens, the fifth lens, and the sixth lens are all spherical lenses, and the fifth lens and the sixth lens constitute a cemented lens; the second lens, the fourth lens, the seventh lens, and the eighth lens are all aspherical lenses. The fixed-focus lens provided by the embodiment of the present invention has the characteristics of ultra-large light flux, is particularly suitable for monitoring requirements under complex conditions, can reach a large aperture of F0.8 to 1.2, supports an image plane of 1 / 1.8 inches, and the field of view angle range can reach 90° to 130°.

Description

Technical Field

[0001] The embodiments of the present invention relate to lens technology, and in particular to a fixed-focus lens. Background Art

[0002] As people's safety awareness improves, they have higher requirements for security, and surveillance lenses are born. Compared with zoom lenses, fixed-focus lenses are simple to design and manufacture, and the images of moving objects taken are clear and stable, with delicate pictures, making them occupy an important position in the security monitoring industry.

[0003] Currently, image sensor manufacturers have launched 1 / 1.8-inch large-image-area low-light image sensors with better light-receiving capabilities. However, existing lenses that can meet this demand have problems such as false aperture, large size, low yield, and only support up to 2 million pixels. Therefore, a 1 / 1.8-inch ultra-low-light lens with a small size, high cost performance, and a large aperture range is very necessary. Summary of the invention

[0004] An embodiment of the present invention provides a fixed-focus lens, which has the characteristics of ultra-large light throughput and is particularly suitable for monitoring needs under complex conditions. It can achieve a large aperture of F0.8 to 1.2, supports a 1 / 1.8-inch image plane, and has a field of view angle range of 90° to 130°.

[0005] An embodiment of the present invention provides a fixed-focus lens, comprising a first lens with negative optical power, a second lens with negative optical power, a third lens with positive optical power, a fourth lens with negative optical power, an aperture, a fifth lens with negative optical power, a sixth lens with positive optical power, a seventh lens with positive optical power, and an eighth lens with positive optical power or negative optical power, which are arranged in sequence from the object side to the image side along the optical axis;

[0006] Among them, the first lens, the third lens, the fifth lens and the sixth lens are all spherical lenses, and the fifth lens and the sixth lens form a cemented lens; the second lens, the fourth lens, the seventh lens and the eighth lens are all aspherical lenses.

[0007] Optionally, the focal lengths of the first lens to the seventh lens and the focal length of the fixed-focus lens satisfy:

[0008] 1.5<|f1 / f|<3.5;

[0009] 3.2<|f2 / f|<5.6;

[0010] 0.8<|f12 / f|<2.2;

[0011] 1.0<|f3 / f|<2.3;

[0012] 6.0<|f4 / f|<8.5;

[0013] 0.7<|f5 / f|<2.0;

[0014] 0.7<|f6 / f|<2.0;

[0015] |f56 / f|>10;

[0016] 2.0<|f7 / f|<4.0;

[0017] Wherein f1, f2, f3, f4, f5, f6 and f7 respectively represent the focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens, f12 represents the combined focal length of the first lens and the second lens, f56 represents the combined focal length of the fifth lens and the sixth lens, and f represents the focal length of the fixed-focus lens.

[0018] Optionally, the Abbe numbers of the second lens and the seventh lens are both greater than 50.

[0019] Optionally, the refractive index of the third lens is greater than 1.8, the refractive index of the fourth lens is greater than 1.6, and the refractive index of the fifth lens is greater than 1.8.

[0020] Optionally, the first lens is a meniscus lens, the second lens is a meniscus lens, the third lens is a biconvex lens, the fourth lens is a meniscus lens, the fifth lens is a biconcave lens, the sixth lens is a biconvex lens, and the seventh lens is a biconvex lens.

[0021] Optionally, the first lens is a convex-concave lens with the convex surface facing the object side, the second lens is a convex-concave lens with the convex surface facing the object side, and the fourth lens is a convex-concave lens with the convex surface facing the image side.

[0022] Optionally, the first lens, the third lens, the fifth lens and the sixth lens are all glass spherical lenses; and the second lens, the fourth lens, the seventh lens and the eighth lens are all plastic aspherical lenses.

[0023] Optionally, the fixed-focus lens meets: 4.0 <TTL / f<7.0;

[0024] Wherein, TTL represents the total optical length of the fixed-focus lens, and f represents the focal length of the fixed-focus lens.

[0025] The fixed-focus lens provided by an embodiment of the present invention comprises a first lens with negative optical power, a second lens with negative optical power, a third lens with positive optical power, a fourth lens with negative optical power, an aperture, a fifth lens with negative optical power, a sixth lens with positive optical power, a seventh lens with positive optical power, and an eighth lens with positive or negative optical power, which are arranged in sequence from the object side to the image side along the optical axis; wherein the first lens, the third lens, the fifth lens, and the sixth lens are all spherical lenses, and the fifth lens and the sixth lens constitute a cemented lens; and the second lens, the fourth lens, the seventh lens, and the eighth lens are all aspherical lenses. By setting the first lens and the second lens with negative focal power, the optical system with a large field of view can collect light, and the second lens can correct the size of the distortion while collecting the light; by setting the third lens with positive focal power, the system spherical aberration can be corrected while turning the light path; by setting the fourth lens with negative focal power, it is more conducive to the correction of off-axis field aberration; by setting the fifth lens and the sixth lens in the form of a double cemented lens with negative and positive focal power, it is conducive to the correction of system chromatic aberration; at the same time, the third lens, the fourth lens, the fifth lens and the sixth lens form a Gaussian structure that is symmetrical about the aperture, which is more It is beneficial to the correction of the system's off-axis aberrations; by setting the seventh lens with positive optical power, it is beneficial to the correction of the system's field curvature and astigmatism, and at the same time, it can change the direction of the light and effectively reduce the inclination angle of the system's main light; the optical power of the eighth lens can be positive or negative, and is used to correct the residual aberration of the light after passing through the previous seven lenses; through the combination of spherical lenses and aspherical lenses, a large-light fixed-focus lens suitable for monitoring needs under complex conditions is realized, and a large aperture of F0.8 to 1.2 can be achieved, supporting a 1 / 1.8-inch image surface, and a field of view angle range of 90° to 130°. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a structural schematic diagram of a fixed-focus lens provided by an embodiment of the present invention;

[0027] Figure 2 is a schematic diagram of spherical aberration of a fixed-focus lens provided by an embodiment of the present invention;

[0028] Figure 3 is a schematic diagram of field curvature of a fixed-focus lens provided by an embodiment of the present invention;

[0029] Figure 4 Schematic diagram of distortion of a fixed-focus lens provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0031] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. It should be noted that the directional words such as "upper", "lower", "left", "right" and the like described in the embodiments of the present invention are described at the angles shown in the accompanying drawings and should not be understood as limitations on the embodiments of the present invention. In addition, in the context, it is also necessary to understand that when it is mentioned that an element is formed "on" or "under" another element, it can not only be directly formed "on" or "under" another element, but also indirectly formed "on" or "under" another element through an intermediate element. The terms "first", "second" and the like are only used for descriptive purposes and do not indicate any order, quantity or importance, but are only used to distinguish different components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0032] Figure 1 FIG. 1 is a schematic diagram of the structure of a fixed-focus lens provided by an embodiment of the present invention. Figure 1 The fixed-focus lens provided by the embodiment of the present invention comprises a first lens 10 with negative optical power, a second lens 20 with negative optical power, a third lens 30 with positive optical power, a fourth lens 40 with negative optical power, an aperture 90, a fifth lens 50 with negative optical power, a sixth lens 60 with positive optical power, a seventh lens 70 with positive optical power, and an eighth lens 80 with positive or negative optical power, which are arranged in sequence from the object side to the image side along the optical axis; wherein the first lens 10, the third lens 30, the fifth lens 50 and the sixth lens 60 are all spherical lenses, and the fifth lens 50 and the sixth lens 60 form a cemented lens; the second lens 20, the fourth lens 40, the seventh lens 70 and the eighth lens 80 are all aspherical lenses.

[0033] Among them, it can be understood that the optical 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 optical focal length, the stronger the ability to bend light, and the smaller the absolute value of the optical focal length, the weaker the ability to bend light. When the optical focal length is a positive number, the refraction of light is convergent; when the optical focal length is a negative number, the refraction of light is divergent. The optical 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 this embodiment, each lens can be fixed to a lens barrel ( Figure 1(not shown in the figure), by reasonably allocating the focal length of the lens, the lens can have a large light throughput. Optionally, the total optical length TTL of the fixed-focus lens provided in this embodiment satisfies 28mm≤TTL≤32mm, the aperture F can reach 0.8~1.2, supports a 1 / 1.8-inch image plane, and the field of view FOV range can reach 90°~130°. In one embodiment of the present invention, the focal length f=5.2mm, the aperture F=1.08, the field of view angle can reach 112°, and it can match a 1 / 1.8-inch imaging component, with the advantages of large light throughput and high resolution.

[0034] The technical solution of this embodiment, by setting the first lens and the second lens with negative focal power, plays the role of collecting light for the large field of view optical system, and the second lens can correct the size of the distortion while collecting the light; by setting the third lens with positive focal power, the spherical aberration of the system is corrected while turning the light path; by setting the fourth lens with negative focal power, it is more conducive to the correction of off-axis field aberration; by setting the fifth lens and the sixth lens in the form of a double cemented lens with negative positive focal power, it is conducive to the correction of system chromatic aberration; at the same time, the third lens, the fourth lens, the fifth lens and the sixth lens constitute a high symmetric lens about the aperture. The structure is more conducive to the correction of the system's off-axis aberrations; by setting the seventh lens with positive optical power, it is beneficial to the correction of the system's field curvature and astigmatism, and at the same time, it can change the direction of the light and effectively reduce the system's main light inclination angle; the optical power of the eighth lens can be positive or negative, and is used to correct the residual aberration of the light after passing through the previous seven lenses; through the combination of spherical lenses and aspherical lenses, a large-light fixed-focus lens suitable for monitoring needs under complex conditions is realized, and a large aperture of F0.8-1.2 can be achieved, supporting a 1 / 1.8-inch image plane, and a field of view angle range of 90°~130°.

[0035] On the basis of the above technical solution, optionally, the focal lengths of the first lens 10 to the seventh lens 70 and the focal length of the fixed-focus lens satisfy:

[0036] 1.5<|f1 / f|<3.5;

[0037] 3.2<|f2 / f|<5.6;

[0038] 0.8<|f12 / f|<2.2;

[0039] 1.0<|f3 / f|<2.3;

[0040] 6.0<|f4 / f|<8.5;

[0041] 0.7<|f5 / f|<2.0;

[0042] 0.7<|f6 / f|<2.0;

[0043] |f56 / f|>10;

[0044] 2.0<|f7 / f|<4.0;

[0045] Wherein f1, f2, f3, f4, f5, f6 and f7 respectively represent the focal lengths of the first lens 10, the second lens 20, the third lens 30, the fourth lens 40, the fifth lens 50, the sixth lens 60 and the seventh lens 70, f12 represents the combined focal length of the first lens 10 and the second lens 20, f56 represents the combined focal length of the fifth lens 50 and the sixth lens 60, and f represents the focal length of the fixed-focus lens.

[0046] By setting the focal length relationship between the first lens 10 to the seventh lens 70, the fixed-focus lens can meet the performance requirements of clarity while meeting the large light throughput. The positive and negative focal length range of the eighth lens 80 is not limited. The eighth lens 80 is used to correct the residual aberration of the first seven lenses, and is designed according to the actual imaging conditions during specific implementation.

[0047] Optionally, the first lens 10 is a meniscus lens, the second lens 20 is a meniscus lens, the third lens 30 is a biconvex lens, the fourth lens 40 is a meniscus lens, the fifth lens 50 is a biconcave lens, the sixth lens 60 is a biconvex lens, and the seventh lens 70 is a biconvex lens.

[0048] Optionally, the first lens 10 is a convex-concave lens with a convex surface facing the object side, the second lens 20 is a convex-concave lens with a convex surface facing the object side, and the fourth lens 40 is a convex-concave lens with a convex surface facing the image side.

[0049] Optionally, the Abbe numbers of the second lens 20 and the seventh lens 70 are both greater than 50.

[0050] Optionally, the refractive index of the third lens 30 is greater than 1.8, the refractive index of the fourth lens 40 is greater than 1.6, and the refractive index of the fifth lens 50 is greater than 1.8.

[0051] In a certain embodiment, the first lens 10 is set to be a convex-concave negative power meniscus lens, with the convex surface facing the object side, for collecting light and increasing the field of view angle; the second lens 20 is a convex-concave negative power meniscus lens, with the concave surface facing the image side, which can collect light and correct the size of distortion; the third lens 30 is a high refractive index (>1.8) positive power lens, which can correct the system spherical aberration while turning the light path; the fourth lens 40 is a convex-concave negative power meniscus lens, which is more conducive to the correction of off-axis field aberration; the fifth lens 50 and the sixth lens 60 are negative positive power lenses. The form of a double-cemented lens with focal length is conducive to the correction of system chromatic aberration; at the same time, the third lens 30, the fourth lens 40, the fifth lens 50 and the sixth lens 60 form a Gaussian structure symmetrical about the aperture 90, which is more conducive to the correction of the system's off-axis aberration; the seventh lens 70 adopts a double convex positive focal length lens, which is conducive to the correction of the system's field curvature and astigmatism, and can change the direction of the light, effectively reducing the size of the system's main light inclination angle CRA; the eighth lens 80 is mainly used to correct the residual aberration of the light after passing through the previous seven lenses, and the focal length can be positive or negative, and can be designed according to actual conditions during specific implementation. In this embodiment, the refractive index, Abbe number and other parameters of the lens are all parameter values ​​relative to the d line (587.6nm).

[0052] Optionally, the first lens 10 , the third lens 30 , the fifth lens 50 and the sixth lens 60 are all glass spherical lenses; the second lens 20 , the fourth lens 40 , the seventh lens 70 and the eighth lens 80 are all plastic aspherical lenses.

[0053] The fixed-focus lens provided in this embodiment adopts a glass-plastic hybrid structure design with four glass lenses and four plastic lenses. Through reasonable material matching, the glass spherical lens is easy to process, and the plastic aspherical lens has good aberration correction ability, which ensures the performance of the optical system while effectively controlling the cost. The maximum supported target surface reaches 1 / 1.8 inches, the maximum supported aperture is F0.8, and the maximum field of view angle can reach 130°, meeting the imaging needs in various application scenarios.

[0054] Optionally, the surface shape of the aspheric lens satisfies the formula:

[0055]

[0056] Where z represents the distance vector height from the vertex of the aspheric surface when the aspheric surface is at a height of y along the optical axis. r represents the radius of curvature of the surface center, k represents the cone coefficient, and A, B, C, D, E, F and G represent high-order aspheric coefficients respectively.

[0057] For example, Table 1 shows the focal length parameter design values ​​of a fixed-focus lens provided in an embodiment of the present invention:

[0058] Table 1 Focal length parameters of fixed focus lenses

[0059] f1＝-12.6 |f1 / f|=2.4 f2＝-21.56 |f2 / f|=4.2 f12＝-6.8 |f12 / f|=1.3 f3＝7.9 |f3 / f|=1.5 f4＝-40.4 |f4 / f|=7.79 f5＝-5.7 |f5 / f|=1.1 f6＝6.2 |f6 / f|=1.2 f56＝109.4 |f56 / f|=21.1 f7＝14.5 |f7 / f|=2.8

[0060] Wherein, f1 represents the focal length of the first lens 10, f2 represents the focal length of the second lens 20, f12 represents the combined focal length of the first lens 10 and the second lens 20, f3 represents the focal length of the third lens 30, f4 represents the focal length of the fourth lens 40, f5 represents the focal length of the fifth lens 50, f6 represents the focal length of the sixth lens 60, f56 represents the combined focal length of the fifth lens 50 and the sixth lens 60, f7 represents the focal length of the seventh lens 70, and f represents the focal length of the fixed-focus lens. The focal length of the fixed-focus lens is 5.2 mm, the aperture F=1.08, the field of view FOV=112°, and the total length of the optical system TTL=29.9 mm.

[0061] Table 2 shows a design value of a fixed-focus lens provided by an embodiment of the present invention:

[0062] Table 2 A design value of fixed focus lens

[0063]

[0064]

[0065] The surface numbers in Table 2 are numbered according to the order of the surfaces of each lens, where "S1" represents the front surface of the first lens 10 (the surface close to the object side), "S2" represents the back surface of the first lens 10 (the surface close to the image side), and so on, where "S11" is the bonding surface of the fifth lens 50 and the sixth lens 60; "S17" and "S18" represent the front surface and back surface of the lens protection glass, respectively. The radius of curvature represents the curvature of the lens surface, 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, where "PL" 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 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 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 K value represents the numerical value of the best fitting cone coefficient of the aspheric surface.

[0066] Table 3 shows the aspheric surface parameters in this embodiment:

[0067] Table 3 A design value of aspheric coefficient in fixed focus lens

[0068] Surface number A B C D E F G S3 -2.43E-03 -1.24E-04 1.21E-05 -6.46E-07 2.53E-08 -6.03E-10 5.87E-12 S4 -3.88E-03 -1.05E-04 1.34E-05 -4.67E-07 1.47E-08 -7.05E-10 1.42E-11 S7 -2.97E-04 -3.43E-06 6.83E-06 -4.45E-07 1.33E-08 -1.12E-10 0 S8 -1.37E-03 1.72E-05 5.02E-06 -4.10E-07 1.37E-08 -1.60E-10 0 S13 -4.12E-04 -2.62E-06 2.58E-07 -1.02E-07 4.52E-09 -1.04E-10 -7.67E-13 S14 -2.34E-03 6.59E-05 -2.87E-06 5.34E-08 -2.07E-10 -3.74E-11 8.01E-13 S15 -2.09E-04 -1.64E-04 2.30E-06 -2.40E-07 2.42E-08 -4.52E-10 0 S16 -1.73E-03 -5.32E-05 -6.56E-06 7.07E-07 -2.26E-08 3.32E-10 0

[0069] Among them, -2.43E-03 means that the coefficient A of the surface number S3 is -2.43×10 -3 .

[0070] Figure 2 FIG. 1 is a schematic diagram of spherical aberration of a fixed-focus lens provided by an embodiment of the present invention. Figure 3 FIG. 1 is a schematic diagram of field curvature of a fixed-focus lens provided by an embodiment of the present invention. Figure 4 FIG. 1 is a schematic diagram of distortion of a fixed-focus lens provided by an embodiment of the present invention, wherein Figures 2 to 4 It can be seen that the fixed-focus lens provided in this embodiment has good imaging capability.

[0071] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A fixed-focus lens, characterized in that: The invention comprises a first lens with negative optical power, a second lens with negative optical power, a third lens with positive optical power, a fourth lens with negative optical power, an aperture, a fifth lens with negative optical power, a sixth lens with positive optical power, a seventh lens with positive optical power, and an eighth lens with positive optical power or negative optical power, which are arranged in sequence from the object side to the image side along the optical axis; Wherein, the first lens, the third lens, the fifth lens and the sixth lens are all spherical lenses, and the fifth lens and the sixth lens form a cemented lens; the second lens, the fourth lens, the seventh lens and the eighth lens are all aspherical lenses; The Abbe numbers of the second lens and the seventh lens are both greater than 50; The first lens is a meniscus lens, the second lens is a meniscus lens, the third lens is a biconvex lens, the fourth lens is a meniscus lens, the fifth lens is a biconcave lens, the sixth lens is a biconvex lens, and the seventh lens is a biconvex lens.

2. The fixed-focus lens according to claim 1, characterized in that: The focal lengths of the first lens to the seventh lens and the focal length of the fixed-focus lens satisfy: 1.5<|f1 / f|<3.5; 3.2<|f2 / f|<5.6; 0.8<|f12 / f|<2.2; 1.0<|f3 / f|<2.3; 6.0<|f4 / f|<8.5; 0.7<|f5 / f|<2.0; 0.7<|f6 / f|<2.0; |f56 / f|>10; 2.0<|f7 / f|<4.0; Wherein f1, f2, f3, f4, f5, f6 and f7 respectively represent the focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens, f12 represents the combined focal length of the first lens and the second lens, f56 represents the combined focal length of the fifth lens and the sixth lens, and f represents the focal length of the fixed-focus lens.

3. The fixed-focus lens according to claim 1, characterized in that: The refractive index of the third lens is greater than 1.8, the refractive index of the fourth lens is greater than 1.6, and the refractive index of the fifth lens is greater than 1.

8.

4. The fixed-focus lens according to claim 1, characterized in that: The first lens is a convex-concave lens with a convex surface facing the object side, the second lens is a convex-concave lens with a convex surface facing the object side, and the fourth lens is a convex-concave lens with a convex surface facing the image side.

5. The fixed-focus lens according to claim 1, wherein: The first lens, the third lens, the fifth lens and the sixth lens are all glass spherical lenses; the second lens, the fourth lens, the seventh lens and the eighth lens are all plastic aspherical lenses.

6. The fixed-focus lens according to claim 1, wherein: The fixed-focus lens meets the following requirements: 4.0 <TTL / f<7.0; Wherein, TTL represents the total optical length of the fixed-focus lens, and f represents the focal length of the fixed-focus lens.

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