Prime lens

Abstract

The utility model discloses a prime lens. The prime lens sequentially comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens from an object side to an image side along an optical axis, the object side surface of the second lens is a concave surface, and the image side surface of the second lens is a convex surface; the third lens has positive focal power; the object side surface of the fourth lens is a convex surface, and the image side surface of the fourth lens is a concave surface; the fifth lens has positive focal power; the sixth lens has negative focal power; the object side surface of the seventh lens is a convex surface, and the image side surface of the seventh lens is a convex surface; the fourth lens and the fifth lens form a balsaming lens group; the number of lenses with focal power of the prime lens is seven, the prime lens meets the condition that F7 / F is larger than or equal to 1.26 and smaller than or equal to 1.93, F7 is the effective focal length of the seventh lens, and F is the effective focal length of the prime lens.

Description

TECHNICAL FIELD

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

[0002] In recent years, with the continuous upgrading of security monitoring facilities, the monitoring equipment has higher and higher requirements for the monitoring environment and the picture. The monitoring equipment needs to provide all-weather monitoring pictures, clear imaging under low light conditions, and no defocus under high and low temperature environments to ensure that the lens still has high imaging quality under harsh weather conditions.

[0003] The existing fixed focus lens generally has the following technical problems:

[0004] 1. It is difficult to correct the system aberration well, resulting in poor lens imaging quality;

[0005] 2. The total optical length is long and the volume is large, resulting in high overall cost and weight of the lens;

[0006] 3. It is difficult to clearly image under low light conditions;

[0007] 4. The large-aperture lens does not have night vision function.

[0008] Therefore, in view of the current development status of fixed focus lenses, a fixed focus lens with high resolution, miniaturization, low cost, large aperture, and infrared confocal is one of the current market demands. CONTENT OF THE INVENTION

[0009] The present application provides a fixed focus lens, which comprises, in order from the object side to the image side along the optical axis: a first lens with negative optical power; a second lens with negative optical power, the object side surface of which is concave and the image side surface of which is convex; a third lens with positive optical power; a fourth lens with negative optical power, the object side surface of which is convex and the image side surface of which is concave; a fifth lens with positive optical power; a sixth lens with negative optical power; and a seventh lens with positive optical power, the object side surface of which is convex and the image side surface of which is convex; the fourth lens and the fifth lens form a cemented lens group; the fixed focus lens has seven lenses with positive optical power, and the fixed focus lens satisfies: 1.26≤F7 / F≤1.93, wherein F7 is the effective focal length of the seventh lens, and F is the effective focal length of the fixed focus lens.

[0010] According to an example embodiment of the present application, the object side surface of the first lens is concave, the image side surface of the first lens is concave, the object side surface of the third lens is convex, the image side surface of the third lens is concave, the object side surface of the fifth lens is convex, the image side surface of the fifth lens is convex, and the object side surface of the sixth lens is convex and the image side surface of the sixth lens is concave.

[0011] According to an example embodiment of the present application, the object side surface of the first lens is convex, the image side surface of the first lens is concave; the object side surface of the third lens is convex, the image side surface of the third lens is convex; the object side surface of the fifth lens is convex, the image side surface of the fifth lens is convex; and the object side surface of the sixth lens is concave, the image side surface of the sixth lens is convex.

[0012] According to an example embodiment of the present application, the focal length of the first lens is -1.88≤F1 / F≤-1.35, where F1 is the effective focal length of the first lens, and F is the effective focal length of the fixed focus lens.

[0013] According to an example embodiment of the present application, the fixed focus lens satisfies at least one of the following conditional expressions: 1.87≤F3 / F≤4.62, -6.38≤F2 / F≤-3.78, where F2 is the effective focal length of the second lens, F3 is the effective focal length of the third lens, and F is the effective focal length of the fixed focus lens.

[0014] According to an example embodiment of the present application, the fixed focus lens satisfies: 1.88≤F45 / F≤2.43, where F45 is the combined effective focal length of the fourth lens and the fifth lens, and F is the effective focal length of the fixed focus lens.

[0015] According to an example embodiment of the present application, the fixed focus lens satisfies at least one of the following conditional expressions: 4.77≤TTL / F≤7.13, 0.36≤D1 / TTL≤0.53, where TTL is the total track length of the fixed focus lens, F is the effective focal length of the fixed focus lens, and D1 is the maximum clear aperture of the object side surface of the first lens corresponding to the maximum field angle of view of the fixed focus lens.

[0016] According to an example embodiment of the present application, the fixed focus lens satisfies: -2.80≤(F1+F2+F6) / (F3+F7)≤-1.41, where F1 is the effective focal length of the first lens, F2 is the effective focal length of the second lens, F3 is the effective focal length of the third lens, F6 is the effective focal length of the sixth lens, and F7 is the effective focal length of the seventh lens.

[0017] According to an example embodiment of the present application, the fixed focus lens satisfies at least one of the following conditional expressions: 1.40≤F7 / F≤1.76, -1.71≤F1 / F≤-1.50, 2.07≤F3 / F≤4.20, -5.80≤F2 / F≤-4.20, 2.09≤F45 / F≤2.21, 5.30≤TTL / F≤6.48, 0.40≤D1 / TTL≤0.48, -2.54≤(F1+F2+F6) / (F3+F7)≤-1.56, -3.85≤F6 / F≤-1.38, -0.73≤F / (R21+R22)≤-0.30, -0.08≤F / (R31+R32)≤0.20, 9.17mm-1 ≤(V5-V4) / F≤13.71mm -1 , 0.04mm -1 ≤(Nd4-Nd5) / F≤0.07mm -1 , 0.21≤BFL / TTL≤0.30, 0≤(F2+F3) / F1≤2.73, 2.68≤TTL / H≤3.30, where F7 is an effective focal length of the seventh lens, F is an effective focal length of the fixed lens, F1 is an effective focal length of the first lens, F2 is an effective focal length of the second lens, F3 is an effective focal length of the third lens, F45 is a combined effective focal length of the fourth lens and the fifth lens, TTL is an optical total track length of the fixed lens, D1 is a maximum clear aperture of the first lens on the object side corresponding to a maximum field angle of the fixed lens, F6 is an effective focal length of the sixth lens, R21 is a curvature radius of the object side of the second lens, R22 is a curvature radius of the image side of the second lens, R31 is a curvature radius of the object side of the third lens, R32 is a curvature radius of the image side of the third lens, V5 is an Abbe number of the fifth lens, V4 is an Abbe number of the fourth lens, Nd4 is a refractive index of the fourth lens, Nd5 is a refractive index of the fifth lens, BFL is an optical back focal length of the fixed lens, and H is an image height corresponding to the maximum field angle of the fixed lens.

[0018] According to one exemplary embodiment of the present application, the fixed lens satisfies at least one of the following conditional expressions: -3.50≤F6 / F≤-1.53, -0.66≤F / (R21+R22)≤-0.34, -0.07≤F / (R31+R32)≤0.18, 10.18mm -1 ≤(V5-V4) / F≤12.46mm -1 , 0.05mm -1 ≤(Nd4-Nd5) / F≤0.07mm -1 , 0.23≤BFL / TTL≤0.27, 0≤(F2+F3) / F1≤2.49, 2.98≤TTL / H≤3.00, where F6 is an effective focal length of the sixth lens, F is an effective focal length of the fixed lens, R21 is a curvature radius of the object side of the second lens, R22 is a curvature radius of the image side of the second lens, R31 is a curvature radius of the object side of the third lens, R32 is a curvature radius of the image side of the third lens, V5 is an Abbe number of the fifth lens, V4 is an Abbe number of the fourth lens, Nd4 is a refractive index of the fourth lens, Nd5 is a refractive index of the fifth lens, BFL is an optical back focal length of the fixed lens, TTL is an optical total track length of the fixed lens, F2 is an effective focal length of the second lens, F3 is an effective focal length of the third lens, F1 is an effective focal length of the first lens, and H is an image height corresponding to the maximum field angle of the fixed lens. BRIEF DESCRIPTION OF DRAWINGS

[0019] Other features, objects, and advantages of the present application will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. In the drawings:

[0020] Figure 1 A structural schematic diagram of a fixed focus lens according to Embodiment 1 of the present application is shown;

[0021] Figure 2 A structural schematic diagram of a fixed focus lens according to Embodiment 2 of the present application is shown;

[0022] Figure 3 A structural schematic diagram of a fixed focus lens according to Embodiment 3 of the present application is shown;

[0023] Figure 4 A structural schematic diagram of a fixed focus lens according to Embodiment 4 of the present application is shown; and

[0024] Figure 5 A structural schematic diagram of a fixed focus lens according to Embodiment 5 of the present application is shown. DETAILED DESCRIPTION

[0025] For a better understanding of the present application, various aspects of the present application will be described in detail with reference to the accompanying drawings. It should be understood that these detailed description is merely illustrative of exemplary embodiments of the present application and in no way limits the scope of the present application.

[0026] In the drawings, the thickness, size, and shape of the lenses have been slightly exaggerated for the sake of explanation. Specifically, the shape of the spherical or aspherical surface is shown by way of example. That is, the shape of the spherical or aspherical surface is not limited to the shape of the spherical or aspherical surface shown in the drawings. The drawings are merely examples and are not drawn to scale.

[0027] In this document, the paraxial region refers to a region near the optical axis. If a lens surface is convex and the position of the convex surface is not specified, it means that the lens surface is convex at least in the paraxial region. If a lens surface is concave and the position of the concave surface is not specified, it means that the lens surface is concave at least in the paraxial region. The surface of each lens closest to the object is called the object side surface of the lens, and the surface of each lens closest to the image surface is called the image side surface of the lens.

[0028] It should also be understood that the terms "comprise", "comprising", "have", "having", "include", "including", "contain", "containing", "provide", "provided", "provide for", "provided for" or "may provide for", when used in this specification, specify the presence of stated features, elements and / or components, but do not preclude the presence or addition of one or more other features, elements, components and / or groups thereof. It should be noted that the expressions first, second, third, etc. in the specification are only used to distinguish one feature from another feature, and do not represent any limitation on the features. It should be noted that the longitudinal direction stated herein is the direction perpendicular to the optical axis.

[0029] Unless otherwise defined, all terms used in this document have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terms should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0030] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0031] The fixed focus lens according to the exemplary embodiments of the present application can include, in order from the object side to the image side along the optical axis, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens.

[0032] In the exemplary embodiments, the first lens can have a negative refractive power, and an image side surface thereof can be a concave surface. The first lens having a negative refractive power and an image side surface being a concave surface can converge incident light rays into the optical system as much as possible, effectively expanding the field angle. In the exemplary embodiments, an object side surface of the first lens can be a convex surface or a concave surface.

[0033] In the exemplary embodiments, the second lens can have a negative refractive power, an object side surface thereof can be a concave surface, and an image side surface thereof can be a convex surface. The second lens having a negative refractive power, an object side surface being a concave surface, and an image side surface being a convex surface can effectively control the behavior of incident light rays of the optical system, reduce system aberration, and be conducive to improving image quality.

[0034] In the exemplary embodiments, the third lens can have a positive refractive power, and an object side surface thereof can be a convex surface. The third lens having a positive refractive power and an object side surface being a convex surface can effectively control light rays entering the rear of the optical system gently, reduce the generation of spherical aberration, balance the field curvature of the system, and be conducive to improving imaging quality. In the exemplary embodiments, an image side surface of the third lens can be a convex surface or a concave surface.

[0035] In the exemplary embodiments, the fourth lens can have a negative refractive power, an object side surface thereof can be a convex surface, and an image side surface thereof can be a concave surface. In the exemplary embodiments, the fourth lens can have a negative refractive power, an object side surface thereof can be a convex surface, and an image side surface thereof can be a concave surface.

[0036] In an example embodiment, the fifth lens can have positive refractive power, and a convex object side surface and a convex image side surface.

[0037] In an example embodiment, the fourth lens and the fifth lens form a doublet lens group with negative-positive refractive power, which can effectively control the light path and converge light, and shorten the total length of the lens, making the optical system more compact.

[0038] In an example embodiment, the sixth lens can have negative refractive power. The sixth lens having negative refractive power can effectively control the light path, converge light, correct chromatic aberration, and improve imaging quality. In an example embodiment, the object side surface of the sixth lens can be convex, and the image side surface can be concave, or the object side surface of the sixth lens can be concave, and the image side surface can be convex.

[0039] In an example embodiment, the seventh lens can have positive refractive power, and a convex object side surface and a convex image side surface. The seventh lens having positive refractive power, and a convex object side surface and a convex image side surface can correct edge field aberration, better meet the requirements of imaging quality, balance the aberration caused by the cemented lens, help achieve the performance of the lens in the infrared state, compress the light, help tighten the light beam, and reduce the chief ray angle to match the chip CRA curve requirements.

[0040] In an example embodiment, the fixed focus lens can further include a stop. The stop can be located between the second lens and the third lens, or between the third lens and the fourth lens, which can effectively converge the amount of light entering the optical system, shorten the total length of the optical system, and reduce the maximum light aperture of the front and rear lens groups.

[0041] In an example embodiment, the aperture Fno of the fixed focus lens can satisfy: Fno≤1.29, and further, Fno can satisfy: 1.283≤Fno≤1.286, which realizes the large aperture requirement of the fixed focus lens.

[0042] In an example embodiment, the total optical length TTL of the fixed focus lens can satisfy: TTL≤22.5mm, and further, TTL can satisfy: 22.428mm≤TTL≤22.451mm, which realizes the small volume requirement of the fixed focus lens.

[0043] In the example embodiments, any one of the first lens to the seventh lens can adopt a glass lens or a plastic lens. The glass lens can effectively suppress the shift of the back focal length of the fixed focus lens due to temperature change, improve the stability of the fixed focus lens, effectively avoid the imaging blur caused by high temperature environment or low temperature environment, ensure the normal use of the fixed focus lens, be conducive to realizing the athermalization of the fixed focus lens, and better correct the chromatic aberration of the system to improve the resolving power of the fixed focus lens. The plastic lens can effectively reduce the cost of the fixed focus lens. As an example, among the first lens to the seventh lens, the fourth lens and the fifth lens are glass lenses, and the remaining lenses are plastic lenses, which is conducive to reducing the cost of the fixed focus lens, balancing the high and low temperature performance of the fixed focus lens, realizing non-astigmatism in the range of -40°C to +80°C while maintaining high imaging quality, and using glass lenses is conducive to correcting the chromatic aberration of the optical system and improving the saturation of the lens color, which is conducive to improving the imaging quality.

[0044] In the example embodiments, the fixed focus lens can satisfy -1.88≤F1 / F≤-1.35, where F1 is the effective focal length of the first lens, and F is the effective focal length of the fixed focus lens. By making the fixed focus lens satisfy the above condition, the ratio range of the effective focal length of the first lens to the effective focal length of the fixed focus lens is controlled, which is conducive to converging large-angle light into the optical system and expanding the field angle of the fixed focus lens. Preferably, the fixed focus lens can further satisfy -1.71≤F1 / F≤-1.50, which is more conducive to expanding the field angle of the fixed focus lens.

[0045] In the example embodiments, the fixed focus lens can satisfy 1.87≤F3 / F≤4.62, where F3 is the effective focal length of the third lens, and F is the effective focal length of the fixed focus lens. By making the fixed focus lens satisfy the above condition, the ratio range of the effective focal length of the third lens to the effective focal length of the fixed focus lens is controlled, which is conducive to correcting the field curvature of the optical system, realizing 4K high resolution, and making the resolution of the fixed focus lens uniform. Preferably, the fixed focus lens can further satisfy 2.07≤F3 / F≤4.20, which is more conducive to realizing 4K high resolution.

[0046] In the example embodiments, the fixed focus lens can satisfy -6.38≤F2 / F≤-3.78, where F2 is the effective focal length of the second lens, and F is the effective focal length of the fixed focus lens. By making the fixed focus lens satisfy the above condition, the ratio range of the effective focal length of the second lens to the effective focal length of the fixed focus lens is controlled, which is conducive to correcting the field curvature of the optical system, realizing 4K high resolution, and making the resolution of the fixed focus lens uniform. Preferably, the fixed focus lens can further satisfy -5.80≤F2 / F≤-4.20, which is more conducive to realizing 4K high resolution.

[0047] In exemplary embodiments, the fixed focus lens can satisfy: -3.85≤F6 / F≤-1.38, where F6 is the effective focal length of the sixth lens, and F is the effective focal length of the fixed focus lens. By making the fixed focus lens satisfy the above condition, the ratio range of the effective focal length of the sixth lens and the effective focal length of the fixed focus lens is controlled, which is conducive to correcting the field curvature of the optical system, and helps to control the light ray trend to be gentle, reduce the aberration of the optical system, and achieve 4K high resolution. Preferably, the fixed focus lens can further satisfy: -3.50≤F6 / F≤-1.53, which is more conducive to achieving 4K high resolution.

[0048] In exemplary embodiments, the fixed focus lens can satisfy: -0.73≤F / (R21+R22)≤-0.30, where F is the effective focal length of the fixed focus lens, R21 is the curvature radius of the object side surface of the second lens, and R22 is the curvature radius of the image side surface of the second lens. By making the fixed focus lens satisfy the above condition, the ratio range between the effective focal length of the fixed focus lens and the sum of the curvature radius of the object side surface and the curvature radius of the image side surface of the second lens is controlled, which can converge light rays of different fields of view, can effectively ensure the maximum amount of light, improve the imaging brightness of the rear of the optical system, and is conducive to balancing the spherical aberration and improving the imaging quality. Preferably, the fixed focus lens can further satisfy: -0.66≤F / (R21+R22)≤-0.34, which is more conducive to improving the imaging brightness of the rear of the optical system and improving the imaging quality.

[0049] In exemplary embodiments, the fixed focus lens can satisfy: -0.08≤F / (R31+R32)≤0.20, where F is the effective focal length of the fixed focus lens, R31 is the curvature radius of the object side surface of the third lens, and R32 is the curvature radius of the image side surface of the third lens. By making the fixed focus lens satisfy the above condition, the ratio range between the effective focal length of the fixed focus lens and the sum of the curvature radius of the object side surface and the curvature radius of the image side surface of the third lens is controlled, which can well receive the light beams of the front group, compensate for the spherical aberration introduced by the first two lenses, further correct the aberration generated by the front lens group, and improve the imaging quality. Preferably, the fixed focus lens can further satisfy: -0.07≤F / (R31+R32)≤0.18, which is more conducive to improving the imaging quality.

[0050] In exemplary embodiments, the fixed focus lens can satisfy: 9.17mm -1 ≤(V5-V4) / F≤13.71mm -1, wherein V5 is the Abbe number of the fifth lens, V4 is the Abbe number of the fourth lens, and F is the effective focal length of the fixed-focus lens. By causing the fixed-focus lens to satisfy the above conditional expression, the ratio range between the difference between the Abbe number of the fifth lens and the Abbe number of the fourth lens and the effective focal length of the fixed-focus lens is controlled, which is conducive to balancing chromatic aberration and thus realizing a large aperture. Preferably, the fixed-focus lens can further satisfy: 10.18mm -1 ≤ (V5-V4) / F ≤ 12.46mm -1 , which is more conducive to realizing a large aperture.

[0051] In an example embodiment, the fixed-focus lens can satisfy: 1.26 ≤ F7 / F ≤ 1.93, wherein F7 is the effective focal length of the seventh lens, and F is the effective focal length of the fixed-focus lens. By causing the fixed-focus lens to satisfy the above conditional expression, the ratio range between the effective focal length of the seventh lens and the effective focal length of the fixed-focus lens is controlled, which is conducive to reducing the chief ray angle to match the chip CRA curve, while being conducive to correcting edge field aberration, better meeting the imaging quality requirement, and balancing the aberration generated by cemented lenses, and thus being conducive to meeting the performance of the lens in an infrared state. Preferably, the fixed-focus lens can further satisfy: 1.40 ≤ F7 / F ≤ 1.76, which is more conducive to reducing the chief ray angle to match the chip CRA curve, while being more conducive to better meeting the imaging quality requirement and meeting the performance of the fixed-focus lens in an infrared state.

[0052] In an example embodiment, the fixed-focus lens can satisfy: 0.04mm -1 ≤ (Nd4-Nd5) / F ≤ 0.07mm -1 , wherein Nd4 is the refractive index of the fourth lens, Nd5 is the refractive index of the fifth lens, and F is the effective focal length of the fixed-focus lens. By causing the fixed-focus lens to satisfy the above conditional expression, the ratio range between the difference between the refractive index of the fourth lens and the refractive index of the fifth lens and the effective focal length of the fixed-focus lens is controlled, which, by cementing the two lenses with positive and negative refractive powers, can offset the aberration generated by each other, realize high resolution, and, in combination with the glass material, further correct chromatic aberration and realize infrared confocal. Preferably, the fixed-focus lens can further satisfy: 0.05mm -1 ≤ (Nd4-Nd5) / F ≤ 0.07mm -1 , which is more conducive to realizing high resolution and infrared confocal.

[0053] In exemplary embodiments, the fixed focus lens can satisfy: 1.88≤F45 / F≤2.43, where F45 is the combined effective focal length of the fourth lens and the fifth lens, and F is the effective focal length of the fixed focus lens. By causing the fixed focus lens to satisfy the above conditional expression, the ratio range between the combined focal length of the fourth lens and the fifth lens and the effective focal length of the fixed focus lens is controlled, which is conducive to balancing various aberrations generated by the light passing through the diaphragm, improving the imaging quality, and realizing a large aperture. Preferably, the fixed focus lens can further satisfy: 2.09≤F45 / F≤2.21, which is more conducive to improving the imaging quality and realizing a large aperture.

[0054] In exemplary embodiments, the fixed focus lens can satisfy: 4.77≤TTL / F≤7.13, where TTL is the total optical length of the fixed focus lens, and F is the effective focal length of the fixed focus lens. By causing the fixed focus lens to satisfy the above conditional expression, the ratio range between the total optical length of the fixed focus lens and the effective focal length of the fixed focus lens is controlled, which is conducive to realizing the miniaturization of the fixed focus lens. Preferably, the fixed focus lens can further satisfy: 5.30≤TTL / F≤6.48, which is more conducive to realizing the miniaturization of the fixed focus lens.

[0055] In exemplary embodiments, the fixed focus lens can satisfy: 0.21≤BFL / TTL≤0.30, where BFL is the optical back focal length of the fixed focus lens, and TTL is the total optical length of the fixed focus lens. By causing the fixed focus lens to satisfy the above conditional expression, the ratio range between the optical back focal length of the fixed focus lens and the total optical length of the fixed focus lens is controlled, which is conducive to the fixed focus lens having a longer back focal length on the basis of realizing miniaturization, reserving space for optical element installation, facilitating the assembly of optical elements, and avoiding interference. Preferably, the fixed focus lens can further satisfy: 0.23≤BFL / TTL≤0.27, which is more conducive to the fixed focus lens having a longer back focal length on the basis of realizing miniaturization, facilitating the assembly of optical elements.

[0056] In exemplary embodiments, the fixed focus lens can satisfy: 0≤(F2+F3) / F1≤2.73, where F2 is the effective focal length of the second lens, F3 is the effective focal length of the third lens, and F1 is the effective focal length of the first lens. By causing the fixed focus lens to satisfy the above conditional expression, the ratio range between the sum of the effective focal length of the second lens and the effective focal length of the third lens and the effective focal length of the first lens is controlled, which is conducive to controlling the light trend, reducing the maximum aperture of the fixed focus lens, and realizing the vertical miniaturization of the fixed focus lens. Preferably, the fixed focus lens can further satisfy: 0≤(F2+F3) / F1≤2.49, which is more conducive to realizing the vertical miniaturization of the fixed focus lens.

[0057] In the example embodiment, the fixed-focus lens can satisfy: 0.36≤D1 / TTL≤0.53, where D1 is the maximum light aperture of the object side of the first lens corresponding to the maximum field angle of the fixed-focus lens, and TTL is the total optical length of the fixed-focus lens. By controlling the ratio range of the maximum light aperture of the object side of the first lens corresponding to the maximum field angle of the fixed-focus lens to the total optical length of the fixed-focus lens, the fixed-focus lens is miniaturized. Preferably, the fixed-focus lens can further satisfy: 0.40≤D1 / TTL≤0.48, which is more conducive to miniaturization of the fixed-focus lens.

[0058] In the example embodiment, the fixed-focus lens can satisfy: 2.68≤TTL / H≤3.30, where TTL is the total optical length of the fixed-focus lens, and H is the image height corresponding to the maximum field angle of the fixed-focus lens. By controlling the ratio range of the total optical length of the fixed-focus lens to the image height corresponding to the maximum field angle of the fixed-focus lens, the fixed-focus lens is miniaturized. Preferably, the fixed-focus lens can further satisfy: 2.98≤TTL / H≤3.00, which is more conducive to miniaturization of the fixed-focus lens.

[0059] In the example embodiment, the fixed-focus lens can satisfy: -2.80≤(F1+F2+F6) / (F3+F7)≤-1.41, where F1 is the effective focal length of the first lens, F2 is the effective focal length of the second lens, F3 is the effective focal length of the third lens, F6 is the effective focal length of the sixth lens, and F7 is the effective focal length of the seventh lens. By controlling the ratio range of the sum of the effective focal length of the first lens, the effective focal length of the second lens, and the effective focal length of the sixth lens to the sum of the effective focal length of the third lens and the effective focal length of the seventh lens, the fixed-focus lens is athermalized by reducing the focal length variation of the fixed-focus lens at different temperatures. Preferably, the fixed-focus lens can further satisfy: -2.54≤(F1+F2+F6) / (F3+F7)≤-1.56, which is more conducive to athermalization of the fixed-focus lens.

[0060] The fixed-focus lens according to the above-described embodiments of the present application adopts seven lenses, and by reasonably allocating optical parameters such as the focal power and surface shape of each lens, at least one of the following beneficial effects can be achieved: super-large aperture (Fno≤1.29), high resolution (4K), small size (TTL≤22.5mm), infrared confocal, and high and low temperature resistance (capable of long-term continuous operation under high and low temperature conditions of -40 to +80℃).

[0061] However, those skilled in the art should understand that the number of lenses constituting the fixed-focus lens can be changed without departing from the technical solutions claimed by the present application, to obtain the various results and advantages described in the specification.

[0062] The following describes in further detail, with reference to the accompanying drawings, specific embodiments of a fixed-focus lens applicable to the above-described embodiments.

[0063] Example 1

[0064] The following is for reference Figure 1 A fixed-focus lens according to Embodiment 1 of this application is described. Figure 1 This is a schematic diagram of the fixed-focus lens according to Embodiment 1 of this application.

[0065] like Figure 1 As shown, the fixed-focus lens includes, in sequence along the optical axis from the object side to the image side, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. An aperture stop STO is positioned between the second lens L2 and the third lens L3. The fourth lens L4 and the fifth lens L5 form a cemented doublet lens group.

[0066] The first lens L1 has negative optical power, and its object side S1 is concave, and its image side S2 is concave.

[0067] The second lens L2 has negative optical power, with its object side S3 being concave and its image side S4 being convex.

[0068] The third lens L3 has positive optical power, with its object side S5 being convex and its image side S6 being concave.

[0069] The fourth lens L4 has negative optical power, with its object side S7 being convex and its image side S8 being concave.

[0070] The fifth lens L5 has positive optical power, and its object side S8 is convex, and its image side S9 is convex.

[0071] The sixth lens L6 has negative optical power, with its object side S10 being convex and its image side S11 being concave.

[0072] The seventh lens L7 has positive optical power, and its object side S12 is convex, and its image side S13 is convex.

[0073] The fixed-focus lens also includes a filter CG disposed on the image side of the seventh lens L7, which has an object side side S14 and an image side side S15.

[0074] Light from the object passes through each surface S1-S15 in sequence and is finally imaged onto the imaging surface IMAGE.

[0075] Table 1 shows the basic parameters of the fixed-focus lens of Example 1, where the units for radius of curvature and thickness / distance are millimeters (mm).

[0076] Table 1

[0077]

[0078]

[0079] In Example 1, the object-side and image-side surfaces of the first lens, second lens, third lens, sixth lens, and seventh lens are all aspherical. The surface shape of the aspherical lens can be defined using, but is not limited to, the following aspherical formula:

[0080]

[0081] Where x is the distance vector from the vertex of the aspherical surface at a height of h along the optical axis; c is the paraxial curvature of the aspherical surface, c = 1 / R (i.e., the paraxial curvature c is the reciprocal of the radius of curvature R in Table 1 above); k is the conic coefficient; Ai is the i-th order correction coefficient of the aspherical surface. Table 2 below gives the conic coefficient k and higher-order coefficients A4, A6, A8, A10, A12, A14 and A16 that can be used for each aspherical mirror S1 to S6, S10 to S13 in Example 1.

[0082] Table 2

[0083] Face number k A4 A6 A8 A10 A12 A14 A16 S1 0.000 8.58E-04 -2.18E-05 6.02E-08 2.38E-09 0.00E+00 0.00E+00 0.00E+00 S2 -0.415 1.91E-03 2.19E-04 -9.45E-05 5.23E-05 -1.12E-05 1.18E-06 -4.85E-08 S3 -2.895 6.42E-03 -2.08E-04 -4.54E-06 -2.44E-06 9.57E-07 -1.19E-07 4.33E-09 S4 0.000 1.04E-02 -2.30E-04 2.04E-05 -4.72E-06 -8.98E-08 8.02E-08 -5.49E-09 S5 -0.575 -6.37E-04 1.11E-04 -2.42E-06 -4.64E-07 -1.12E-08 7.44E-09 -3.91E-10 S6 0.000 -2.35E-03 3.05E-04 -2.11E-05 7.11E-07 9.66E-08 -1.04E-08 2.91E-10 S10 -7.047 -2.71E-03 -1.96E-04 1.45E-05 -6.93E-08 2.43E-08 -5.02E-10 -2.68E-11 S11 -3.849 -3.11E-03 6.73E-05 -8.64E-06 3.35E-07 1.72E-07 -1.76E-08 5.96E-10 S12 -8.053 8.71E-04 7.38E-05 -2.85E-06 1.13E-06 -1.79E-07 1.23E-08 -3.68E-10 S13 -2.519 1.74E-04 1.11E-04 3.90E-06 1.01E-06 -1.04E-07 -8.19E-10 9.68E-11

[0084] In this embodiment, the aperture number Fno of the fixed-focus lens is 1.283, the maximum half field of view is 67°, and the effective focal length is 3.49mm. The MTF value of the center field of view at a spatial frequency of 160lp / mm exceeds 0.35. The defocus amount of infrared light 850nm and visible light 436nm-656nm in the center field of view is ≤10um. The defocus amount of -40℃ and +80℃ and +20℃ in the center field of view at visible light 436nm-656nm is ≤3um.

[0085] Example 2

[0086] The following is for reference Figure 2 Describes a fixed-focus lens according to Embodiment 2 of this application. Figure 2 This is a schematic diagram of the fixed-focus lens according to Embodiment 2 of this application.

[0087] like Figure 2 As shown, the fixed-focus lens includes, in sequence along the optical axis from the object side to the image side, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. An aperture stop STO is positioned between the second lens L2 and the third lens L3. The fourth lens L4 and the fifth lens L5 form a cemented doublet lens group.

[0088] The first lens L1 has negative optical power, and its object side S1 is concave, and its image side S2 is concave.

[0089] The second lens L2 has a negative focal power, with a concave object side surface S3 and a convex image side surface S4.

[0090] The third lens L3 has a positive focal power, with a convex object side surface S5 and a concave image side surface S6.

[0091] The fourth lens L4 has a negative focal power, with a convex object side surface S7 and a concave image side surface S8.

[0092] The fifth lens L5 has a positive focal power, with a convex object side surface S8 and a convex image side surface S9.

[0093] The sixth lens L6 has a negative focal power, with a convex object side surface S10 and a concave image side surface S11.

[0094] The seventh lens L7 has a positive focal power, with a convex object side surface S12 and a convex image side surface S13.

[0095] The fixed focus lens further includes a filter CG disposed on the image side of the seventh lens L7, having an object side surface S14 and an image side surface S15.

[0096] Light from an object passes through the surfaces S1-S15 in sequence and is ultimately imaged on the image plane IMAGE.

[0097] Table 3 shows a basic parameter table of the fixed focus lens of Example 2, where the units of the radius of curvature, thickness / distance are millimeters (mm).

[0098] Table 3

[0099]

[0100] In Example 2, the object side surface and the image side surface of the first lens, the second lens, the third lens, the sixth lens and the seventh lens are all aspherical surfaces, and the aspherical surface can be defined by, but not limited to, the following aspherical surface formula:

[0101]

[0102] where x is the distance from the vertex of the aspherical surface when the aspherical surface is at a height h along the optical axis, h is the height of the aspherical surface, c is the paraxial curvature of the aspherical surface, c = 1 / R (i.e., the paraxial curvature c is the inverse of the radius of curvature R in Table 1 above), k is the conic coefficient, and Ai is the correction coefficient of the i-th order of the aspherical surface. Table 4 below gives the conic coefficient k and the high-order term coefficients A4, A6, A8, A10, A12, A14 and A16 that can be used for the aspherical surfaces S1 to S6, S10 to S13 in Example 2.

[0103] Table 4

[0104]

[0105]

[0106] In this embodiment, the aperture number Fno of the fixed-focus lens is 1.285, the maximum half field of view is 67°, and the effective focal length is 3.46mm. The MTF value of the center field of view at a spatial frequency of 160lp / mm exceeds 0.35. The defocus amount of infrared light 850nm and visible light 436nm-656nm in the center field of view is ≤10um, and the defocus amount of -40℃ and +80℃ and +20℃ in the visible light 436nm-656nm in the center field of view is ≤3um.

[0107] Example 3

[0108] The following is for reference Figure 3 Describes a fixed-focus lens according to Embodiment 3 of this application. Figure 3 This is a schematic diagram of the fixed-focus lens according to Embodiment 3 of this application.

[0109] like Figure 3 As shown, the fixed-focus lens includes, in sequence along the optical axis from the object side to the image side, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. An aperture stop STO is positioned between the second lens L2 and the third lens L3. The fourth lens L4 and the fifth lens L5 form a cemented doublet lens group.

[0110] The first lens L1 has negative optical power, and its object side S1 is concave, and its image side S2 is concave.

[0111] The second lens L2 has negative optical power, with its object side S3 being concave and its image side S4 being convex.

[0112] The third lens L3 has positive optical power, with its object side S5 being convex and its image side S6 being concave.

[0113] The fourth lens L4 has negative optical power, with its object side S7 being convex and its image side S8 being concave.

[0114] The fifth lens L5 has positive optical power, and its object side S8 is convex, and its image side S9 is convex.

[0115] The sixth lens L6 has negative optical power, with its object side S10 being convex and its image side S11 being concave.

[0116] The seventh lens L7 has positive optical power, and its object side S12 is convex, and its image side S13 is convex.

[0117] The fixed-focus lens also includes a filter CG disposed on the image side of the seventh lens L7, which has an object side side S14 and an image side side S15.

[0118] Light from the object passes through each surface S1-S15 in turn and is ultimately imaged on the image plane IMAGE.

[0119] Table 5 shows the basic parameter table of the fixed focus lens of Example 3, wherein the units of the radius of curvature, thickness / distance are millimeters (mm).

[0120] Table 5

[0121]

[0122]

[0123] In Example 3, the object side and image side of the first lens, the second lens, the third lens, the sixth lens and the seventh lens are aspherical surfaces, and the surface type of the aspherical lens can be defined by, but not limited to, the following aspherical formula:

[0124]

[0125] wherein x is the sag of the aspherical surface at a height h along the optical axis from the vertex of the aspherical surface; c is the paraxial curvature of the aspherical surface, c = 1 / R (i.e., the paraxial curvature c is the inverse of the radius of curvature R in Table 1 above); k is the conic coefficient; and Ai is the correction coefficient of the i-th order of the aspherical surface. Table 6 below gives the conic coefficient k and the high-order term coefficients A4, A6, A8, A10, A12, A14 and A16 that can be used for the aspherical surfaces S1 to S6, S10 to S13 in Example 3.

[0126] Table 6

[0127] Face number k A4 A6 A8 A10 A12 A14 A16 S1 0.000 1.14E-03 -3.44E-05 4.21E-07 -1.75E-09 0.00E+00 0.00E+00 0.00E+00 S2 -0.428 1.57E-03 4.64E-04 -1.66E-04 6.22E-05 -1.15E-05 1.12E-06 -4.45E-08 S3 -2.818 8.24E-03 -3.33E-04 -8.64E-06 -4.81E-06 1.83E-06 -2.20E-07 8.34E-09 S4 0.000 1.41E-02 -4.39E-04 9.37E-06 -2.35E-06 -3.03E-07 9.78E-08 -6.42E-09 S5 0.177 -9.36E-04 1.03E-04 -5.51E-06 -3.98E-08 -2.49E-08 5.63E-09 -2.68E-10 S6 0.000 -2.22E-03 3.26E-04 -2.46E-05 8.97E-07 1.05E-07 -1.14E-08 3.13E-10 S10 -9.537 -2.09E-03 -2.49E-04 9.69E-06 6.62E-07 2.34E-08 -4.92E-09 1.60E-10 S11 -4.688 -2.05E-03 -4.56E-05 7.45E-07 3.51E-08 1.67E-07 -1.98E-08 7.45E-10 S12 -9.958 6.07E-04 1.47E-04 -6.03E-06 9.74E-07 -1.92E-07 1.38E-08 -3.97E-10 S13 0.247 1.12E-04 1.92E-04 -1.05E-05 1.67E-06 -5.10E-08 -8.01E-09 3.22E-10

[0128] In the present embodiment, the fixed focus lens has an Fno of 1.284, a maximum half field angle of 67°, and an effective focal length of 3.48 mm; the MTF value of the central field of view at a spatial frequency of 160 lp / mm is greater than 0.35, the defocus amount of infrared light 850 nm and visible light 436 nm-656 nm in the central field of view is ≤10 um, and the defocus amount of visible light 436 nm-656 nm in the central field of view at -40°C and +80°C and +20°C is ≤3 um.

[0129] Example 4

[0130] The following refers to Figure 4 A fixed focus lens according to Example 4 of the present application is described. Figure 4 A structural schematic diagram of the fixed focus lens according to Example 4 of the present application.

[0131] As Figure 4As shown, the fixed focus lens includes, in order along the optical axis from the object side to the image side, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. A stop STO is disposed between the third lens L3 and the fourth lens L4. The fourth lens L4 and the fifth lens L5 form a doublet lens group.

[0132] The first lens L1 has a negative refractive power, with a convex object side surface S1 and a concave image side surface S2.

[0133] The second lens L2 has a negative refractive power, with a concave object side surface S3 and a convex image side surface S4.

[0134] The third lens L3 has a positive refractive power, with a convex object side surface S5 and a convex image side surface S6.

[0135] The fourth lens L4 has a negative refractive power, with a convex object side surface S7 and a concave image side surface S8.

[0136] The fifth lens L5 has a positive refractive power, with a convex object side surface S8 and a convex image side surface S9.

[0137] The sixth lens L6 has a negative refractive power, with a concave object side surface S10 and a convex image side surface S11.

[0138] The seventh lens L7 has a positive refractive power, with a convex object side surface S12 and a convex image side surface S13.

[0139] The fixed focus lens further includes a filter CG disposed on the image side of the seventh lens L7, having an object side surface S14 and an image side surface S15.

[0140] Light from an object passes through each of the surfaces S1-S15 in order and is ultimately imaged on an image plane IMAGE.

[0141] Table 7 shows a basic parameter table of the fixed focus lens of Embodiment 4, where the units of the radius of curvature, thickness / distance are millimeters (mm).

[0142] Table 7

[0143]

[0144] In Embodiment 4, the object side surface and the image side surface of the first lens, the second lens, the third lens, the sixth lens, and the seventh lens are all aspherical surfaces, and the surface shape of the aspherical lens can be defined using, but not limited to, the following aspherical formula:

[0145]

[0146] wherein x is the sag of the aspherical surface at a position along the optical axis at a height h from the vertex of the aspherical surface; c is the paraxial curvature of the aspherical surface, c = 1 / R (i.e., the paraxial curvature c is the inverse of the curvature radius R in Table 1 above); k is the conic constant; and Ai is the correction coefficient of the i-th order of the aspherical surface. Table 8 below gives the conic constant k and the high-order term coefficients A4, A6, A8, A10, A12, A14 and A16 that can be used for each aspherical surface S1 to S6, S10 to S13 in Example 4.

[0147] Table 8

[0148] Face number k A4 A6 A8 A10 A12 A14 A16 S1 0.000 -4.97E-04 7.68E-05 -6.02E-06 2.50E-07 -5.91E-09 6.21E-11 0.00E+00 S2 -2.447 6.84E-03 -1.87E-04 5.86E-05 -7.88E-06 8.67E-07 -4.38E-08 9.66E-10 S3 -1.788 6.93E-03 -5.70E-04 7.46E-05 -7.89E-06 6.79E-07 -4.19E-08 1.22E-09 S4 -3.232 3.17E-03 5.42E-05 8.99E-06 -2.33E-06 1.87E-07 -7.19E-09 -5.95E-11 S5 1.372 -3.36E-03 1.26E-04 -1.21E-05 6.55E-07 -5.30E-08 3.70E-09 -1.36E-10 S6 0.000 -3.50E-03 3.72E-04 -3.23E-05 1.16E-06 1.04E-07 -1.16E-08 3.55E-10 S10 -4.523 1.05E-03 1.97E-04 -3.56E-05 7.15E-07 2.83E-07 -2.74E-08 8.33E-10 S11 -10.077 5.44E-03 -6.86E-05 -2.06E-05 2.49E-06 -1.22E-07 2.35E-09 -1.05E-11 S12 -14.993 1.47E-03 -8.86E-05 6.16E-06 -5.35E-07 4.87E-08 -2.40E-09 4.36E-11 S13 6.645 -4.36E-04 5.99E-05 6.34E-06 -1.70E-06 1.77E-07 -8.58E-09 1.73E-10

[0149] In this embodiment, the focal length of the fixed focus lens is 4.20 mm, the Fno is 1.284, and the maximum half field angle is 53.8°; the MTF value of the central field of view at a spatial frequency of 160 lp / mm is greater than 0.35, the defocus amount of infrared light 850 nm and visible light 436 nm-656 nm in the central field of view is ≤10 um, and the defocus amount of visible light 436 nm-656 nm in the central field of view at -40°C and +80°C and +20°C is ≤3 um.

[0150] Example 5

[0151] The following refers to Figure 5 a fixed focus lens according to Example 5 of the present application. Figure 5 A schematic diagram of the structure of the fixed focus lens according to Example 5 of the present application.

[0152] As Figure 5 shown, the fixed focus lens comprises, in order from the object side to the image side along the optical axis, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. A stop STO is arranged between the third lens L3 and the fourth lens L4. The fourth lens L4 and the fifth lens L5 form a doublet lens group.

[0153] The first lens L1 has a negative refractive power, the object side surface S1 is a convex surface, and the image side surface S2 is a concave surface.

[0154] The second lens L2 has a negative refractive power, the object side surface S3 is a concave surface, and the image side surface S4 is a convex surface.

[0155] The third lens L3 has a positive refractive power, the object side surface S5 is a convex surface, and the image side surface S6 is a convex surface.

[0156] The fourth lens L4 has a negative refractive power, the object side surface S7 is a convex surface, and the image side surface S8 is a concave surface.

[0157] The fifth lens L5 has a positive refractive power, the object side surface S8 is a convex surface, and the image side surface S9 is a convex surface.

[0158] The sixth lens L6 has negative refractive power, with a concave object side surface S10 and a convex image side surface S11.

[0159] The seventh lens L7 has positive refractive power, with a convex object side surface S12 and a convex image side surface S13.

[0160] The fixed focus lens further includes a filter CG disposed on the image side of the seventh lens L7, with an object side surface S14 and an image side surface S15.

[0161] Light from an object passes through the surfaces S1-S15 in sequence and is ultimately imaged on the image plane IMAGE.

[0162] Table 9 shows the basic parameter table of the fixed focus lens of embodiment 5, where the units of the radius of curvature, thickness / distance are all in millimeters (mm).

[0163] Table 9

[0164]

[0165] In embodiment 5, the object side surface and the image side surface of the first lens, the second lens, the third lens, the sixth lens and the seventh lens are all aspherical surfaces, and the aspherical surface can be defined by, but not limited to, the following aspherical surface formula:

[0166]

[0167] where x is the sag of the aspherical surface at a position along the optical axis at a height h from the vertex of the aspherical surface; c is the paraxial curvature of the aspherical surface, c = 1 / R (i.e., the paraxial curvature c is the inverse of the radius of curvature R in Table 1 above); k is the conic coefficient; and Ai is the correction coefficient of the i-th order of the aspherical surface. Table 10 below gives the conic coefficient k and the high order term coefficients A4, A6, A8, A10, A12, A14 and A16 that can be used for the aspherical surfaces S1-S6, S10-S13 in embodiment 5.

[0168] Table 10

[0169]

[0170]

[0171] In the embodiment, the Fno of the fixed focus lens is 1.286, the maximum half field angle is 53.8°, and the effective focal length is 4.23mm; the MTF value of the central field at a spatial frequency of 160 lp / mm exceeds 0.35, the defocus amount of infrared light 850nm and visible light 436nm-656nm at the central field is ≤10um, and the defocus amount of visible light 436nm-656nm at the central field at -40℃ and +80℃ and +20℃ is ≤3um.

[0172] In summary, the conditional expressions in Embodiments 1 to 5 satisfy the relationships shown in Table 11. In Table 11, the parameters Nd4, Nd5, V4, V5 have no units, and the units of the remaining parameters are millimeters (mm).

[0173] Table 11

[0174] Conditional expression / Example 1 2 3 4 F1 / F -1.701 -1.652 -1.603 -1.550 -1.500 F3 / F 4.192 4.083 4.088 2.131 2.079 F2 / F -4.200 -4.300 -4.400 -5.700 -5.800 F6 / F -3.500 -3.108 -3.065 -1.608 -1.536 F / (R21+R22) -0.344 -0.389 -0.408 -0.653 -0.660 F / (R31+R32) 0.176 0.163 0.171 -0.064 -0.066 (V5-V4) / F 12.374 mm -1 ]]> 12.459 mm -1 ]]> 12.391 mm -1 ]]> 10.273 mm -1 ]]> 10.189 mm -1 ]]> F7 / F 1.751 1.702 1.652 1.451 1.401 (Nd4-Nd5) / F 0.061 mm -1 ]] 0.061 mm -1 ]] 0.061 mm -1 ]] 0.051 mm -1 ]] 0.050 mm -1 ]] F45 / F 2.121 2.105 2.093 2.203 2.197 TTL / F 6.434 6.478 6.443 5.346 5.303 BFL / TTL 0.239 0.239 0.239 0.267 0.267 (F2+F3) / F1 0.005 0.131 0.195 2.302 2.481 D1 / TTL 0.471 0.476 0.469 0.409 0.405 TTL / H 2.988 2.993 2.993 2.998 2.998 (F1+F2+F6) / (F3+F7) -1.582 -1.566 -1.580 -2.473 -2.539

[0175] The present application also provides an imaging device, whose electronic photosensitive element can be a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), and the imaging device is equipped with the fixed focus lens described above.

[0176] The above description is merely preferred embodiments of the present application and a description of the principles of the technology used. It should be understood by those skilled in the art that the scope of the utility model involved in the present application is not limited to the technical solutions formed by the specific combinations of the technical features described above, and should also cover other technical solutions formed by any combination of the technical features described above or their equivalent features without departing from the inventive concept. For example, the technical solutions formed by the mutual replacement of the above-described features and the technical features disclosed in the present application (but not limited to) having similar functions.

Claims

1. A fixed focus lens characterized by, sequentially arranged along the optical axis from the object side to the image side include: a first lens having negative refractive power; a second lens having negative refractive power, the object side surface of which is concave, and the image side surface of which is convex; a third lens having positive refractive power; a fourth lens having negative refractive power, the object side surface of which is convex, and the image side surface of which is concave; a fifth lens having positive refractive power; a sixth lens having negative refractive power; and a seventh lens having positive refractive power, the object side surface of which is convex, and the image side surface of which is convex; the fourth lens and the fifth lens constitute a cemented lens group; the fixed focus lens has a total of seven lenses with refractive power, and satisfies: 1.26 ≤ F7 / F ≤ 1.93, wherein F7 is the effective focal length of the seventh lens, and F is the effective focal length of the fixed focus lens.

2. The fixed focus lens according to claim 1, wherein: the object side surface of the first lens is concave, and the image side surface of the first lens is concave; the object side surface of the third lens is convex, and the image side surface of the third lens is concave; the object side surface of the fifth lens is convex, and the image side surface of the fifth lens is convex; and the object side surface of the sixth lens is convex, and the image side surface of the sixth lens is concave.

3. The fixed focus lens according to claim 1, wherein: the object side surface of the first lens is convex, and the image side surface of the first lens is concave; the object side surface of the third lens is convex, and the image side surface of the third lens is convex; the object side surface of the fifth lens is convex, and the image side surface of the fifth lens is convex; and the object side surface of the sixth lens is concave, and the image side surface of the sixth lens is convex.

4. The fixed focus lens according to claim 1 or 2 or 3, characterized in that, the fixed focus lens satisfies: -1.88 ≤ F1 / F ≤ -1.35, wherein F1 is the effective focal length of the first lens, and F is the effective focal length of the fixed focus lens.

5. The prime lens according to any one of claims 1 or 2 or 3, characterized in that, the fixed focus lens satisfies at least one of the following conditional expressions: 1.87 ≤ F3 / F ≤ 4.62, -6.38 ≤ F2 / F ≤ -3.78, wherein F2 is the effective focal length of the second lens, F3 is the effective focal length of the third lens, and F is the effective focal length of the fixed focus lens.

6. The fixed focal length lens of claim 1 or 2 or 3, wherein, the fixed focus lens satisfies: 1.88 ≤ F45 / F ≤ 2.43, wherein F45 is the combined effective focal length of the fourth lens and the fifth lens, and F is the effective focal length of the fixed focus lens.

7. The fixed focus lens according to claim 1 or 2 or 3, characterized in that, the fixed focus lens satisfies at least one of the following conditional expressions: 4.77 ≤ TTL / F ≤ 7.13, 0.36 ≤ D1 / TTL ≤ 0.53, wherein TTL is the total track length of the fixed focus lens, F is the effective focal length of the fixed focus lens, and D1 is the maximum entrance pupil diameter of the object side surface of the first lens corresponding to the maximum field of view angle of the fixed focus lens.

8. The fixed focal length lens of claim 1 or 2 or 3, wherein, the fixed focus lens satisfies: -2.80 ≤ (F1+F2+F6) / (F3+F7) ≤ -1.41, wherein F1 is the effective focal length of the first lens, F2 is the effective focal length of the second lens, F3 is the effective focal length of the third lens, F6 is the effective focal length of the sixth lens, and F7 is the effective focal length of the seventh lens.

9. The fixed focal length lens of claim 1 or 2 or 3, wherein, the fixed focus lens satisfies at least one of the following conditional expressions: 1.40 ≤ F7 / F ≤ 1.76, -1.71 ≤ F1 / F ≤ -1.50, 2.07 ≤ F3 / F ≤ 4.20, -5.80 ≤ F2 / F ≤ -4.20, 2.09 ≤ F45 / F ≤ 2.21, 5.30 ≤ TTL / F ≤ 6.48, 0.40 ≤ D1 / TTL ≤ 0.48, -2.54 ≤ (F1+F2+F6) / (F3+F7) ≤ -1.56, -3.85 ≤ F6 / F ≤ -1.38, -0.73 ≤ F / (R21+R22) ≤ -0.30, -0.08 ≤ F / (R31+R32) ≤ 0.20, 9.17 mm -1 ≤ (V5-V4) / F ≤ 13.71 mm -1 , 0.04 mm -1 ≤ (Nd4-Nd5) / F ≤ 0.07 mm -1 , 0.21 ≤ BFL / TTL ≤ 0.30, 0 ≤ (F2+F3) / F1 ≤ 2.73, 2.68 ≤ TTL / H ≤ 3.30, Wherein, F7 is the effective focal length of the seventh lens, F is the effective focal length of the fixed focus lens, F1 is the effective focal length of the first lens, F2 is the effective focal length of the second lens, F3 is the effective focal length of the third lens, F45 is the combined effective focal length of the fourth lens and the fifth lens, TTL is the total optical length of the fixed focus lens, D1 is the maximum aperture of the object side of the first lens corresponding to the maximum field angle of the fixed focus lens, F6 is the effective focal length of the sixth lens, R21 is the curvature radius of the object side of the second lens, R22 is the curvature radius of the image side of the second lens, R31 is the curvature radius of the object side of the third lens, R32 is the curvature radius of the image side of the third lens, V5 is the Abbe number of the fifth lens, V4 is the Abbe number of the fourth lens, Nd4 is the refractive index of the fourth lens, Nd5 is the refractive index of the fifth lens, BFL is the optical back focal length of the fixed focus lens, and H is the image height corresponding to the maximum field angle of the fixed focus lens.

10. The fixed focal length lens of claim 1 or 2 or 3, wherein, The fixed focus lens satisfies at least one of the following conditional expressions: - 3.50 < F6 / F < -1.53, -0.66 < F / (R21+R22) < -0.34, -0.07 < F / (R31+R32) < 0.18, 10.18 mm < F < 10.50 mm -1 ≤ (V5-V4) / F ≤ 12.46 mm -1 , 0.05 mm -1 ≤ (Nd4-Nd5) / F ≤ 0.07 mm -1 , 0.23 < BFL / TTL < 0.27, 0 < (F2+F3) / F1 < 2.49, 2.98 < TTL / H < 3.00, Wherein, F6 is the effective focal length of the sixth lens, F is the effective focal length of the fixed focus lens, R21 is the curvature radius of the object side of the second lens, R22 is the curvature radius of the image side of the second lens, R31 is the curvature radius of the object side of the third lens, R32 is the curvature radius of the image side of the third lens, V5 is the Abbe number of the fifth lens, V4 is the Abbe number of the fourth lens, Nd4 is the refractive index of the fourth lens, Nd5 is the refractive index of the fifth lens, BFL is the optical back focal length of the fixed focus lens, TTL is the total optical length of the fixed focus lens, F2 is the effective focal length of the second lens, F3 is the effective focal length of the third lens, F1 is the effective focal length of the first lens, and H is the image height corresponding to the maximum field angle of the fixed focus lens.

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