Prime lens and imaging device

Abstract

The invention provides a prime lens and an imaging device, and belongs to the technical field of optical imaging. The prime lens comprises a first lens with negative focal power, a second lens with negative focal power, a third lens with negative focal power, a fourth lens with positive focal power, a fifth lens with positive focal power, a sixth lens with negative focal power and a seventh lens with positive focal power which are sequentially arranged from the object side to the image side. The fixed-focus lens comprises a first lens, a second lens, a fifth lens, a sixth lens, a seventh lens, an image plane, an eighth lens with negative focal power, and an image plane, so that the total optical length of the fixed-focus lens is controlled within 20.5 mm, the diagonal field angle reaches more than 82 degrees, the aperture value is less than or equal to 2.8, and the second lens, the fifth lens, the sixth lens, the seventh lens and the eighth lens are plastic aspheric lenses. The first lens, the third lens and the fourth lens are spherical lenses. According to the scheme, the eight lenses are adopted, and the focal power and shape matching relation of the lenses are reasonably set, so that the prime lens which is small in size, high in imaging quality, low in cost, large in angle and free of virtual focus at high temperature is realized.

Description

TECHNICAL FIELD

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

[0002] With the development of science and technology, various components are more and more complex, and the requirements of consumers are also higher and higher. The lens product needs to have the advantage of wide shooting frame, and also needs to have good athermalization. At present, there is a common problem that it is difficult to balance large viewing angle, low cost, high pixel, high low temperature non-astigmatism and small size. For example, some lenses sacrifice part of the resolving power or use plastic aspherical surface in order to reduce cost, but due to large temperature difference in actual environment, such lenses are prone to astigmatism at high and low temperatures, which affects the use effect. Some lenses have high low temperature non-astigmatism and high imaging quality, but the price is expensive and not recognized by the consumer market. SUMMARY

[0003] The main purpose of the present application is to provide a fixed focus lens and an imaging device, which aims to provide a fixed focus lens with small size, large angle, high imaging quality and high low temperature non-astigmatism.

[0004] In order to achieve the above purpose, the present application provides a fixed focus lens, which has an object side and an image side arranged oppositely along the optical axis direction, and comprises a first lens with negative focal power, a second lens with negative focal power, a third lens with negative focal power, a fourth lens with positive focal power, a fifth lens with positive focal power, a sixth lens with negative focal power, a seventh lens with positive focal power, an eighth lens with negative focal power and an image plane arranged in sequence from the object side to the image side, so that the total optical length of the fixed focus lens is controlled within 20.5mm, the diagonal field of view angle reaches more than 82°, and the aperture value is less than or equal to 2.8. Among them, the second lens, the fifth lens, the sixth lens, the seventh lens and the eighth lens are plastic aspherical lenses, and the first lens, the third lens and the fourth lens are spherical lenses.

[0005] In an embodiment, the fixed focus lens further comprises a diaphragm arranged between the fourth lens and the fifth lens.

[0006] In an embodiment, the fixed focus lens further comprises a filter arranged between the eighth lens and the image plane in sequence from the object side to the image side, and the filter is used to filter stray light.

[0007] In an embodiment, the third lens and the fourth lens are connected by cementing.

[0008] In an embodiment, the first lens is a meniscus lens, and the object side surface of the meniscus lens is a convex surface. The second lens is a concave-convex lens, and its object-side surface is concave. The third lens is a concave-convex lens, and its object-side surface is convex. The fourth lens is a concave-convex lens, and its object-side surface is convex. The fifth lens is a biconvex lens; The sixth lens is a biconcave lens; The seventh lens is a biconvex lens; The eighth lens is a concave-convex lens, and its object-side surface is convex.

[0009] In one embodiment, the focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, the focal length of the fourth lens is f4, the focal length of the fifth lens is f5, the focal length of the sixth lens is f6, the focal length of the seventh lens is f7, and the focal length of the eighth lens is f8, wherein: -25<f1<-15, -220<f2<-160, -10<f3<-5, 3<f4<5, 3<f5<8, -12<f6<-5, 25<f7<40, -15<f8<-8.

[0010] In one embodiment, the first lens has a refractive index of n1 and a dispersion coefficient of v1; the second lens has a refractive index of n2 and a dispersion coefficient of v2; the third lens has a refractive index of n3 and a dispersion coefficient of v3; the fourth lens has a focal refractive index of n4 and a dispersion coefficient of v4; the fifth lens has a refractive index of n5 and a dispersion coefficient of v5; the sixth lens has a refractive index of n6 and a dispersion coefficient of v6; the seventh lens has a refractive index of n7 and a dispersion coefficient of v7; and the eighth lens has a refractive index of n8 and a dispersion coefficient of v8, wherein: 1.50≤n1≤1.70, 1.60≤n2≤1.70, 1.50≤n3≤1.70, 1.70≤n4≤1.80, 1.50≤n5≤1.60, 1.60≤n6≤1.70, 1.60≤n7≤1.70, 1.50≤n8≤1.60, 55.0≤v1≤70.0, 18.0≤v2≤26.0, 45.0≤v3≤65.0, 50.0≤v4≤60.0, 50.0≤v5≤60.0, 18.0≤v6≤26.0, 18.0≤v7≤26.0, 50.0≤v8≤60.0.

[0011] In one embodiment, the effective focal length of the fixed-focus lens is EFL, and the total optical length of the fixed-focus lens is TTL, wherein: TTL / EFL≤3.4.

[0012] In one embodiment, the diameter of the first lens is D1, and the image plane diameter of the fixed-focus lens is IC, wherein: D1 < 13mm, IC ≤ 10.5mm.

[0013] The present invention also proposes an imaging device, which includes the aforementioned fixed-focus lens. The fixed-focus lens has an object side and an image side arranged opposite to each other along the optical axis. The fixed-focus lens includes, from the object side to the image side, a first lens with negative optical power, a second lens with negative optical power, a third lens with negative optical power, a fourth lens with positive optical power, a fifth lens with positive optical power, a sixth lens with negative optical power, a seventh lens with positive optical power, an eighth lens with negative optical power, and an image plane, so that the total optical length of the fixed-focus lens is controlled within 20.5 mm, the diagonal field of view reaches 82° or more, and the aperture value is less than or equal to 2.8. Among them, the second, fifth, sixth, seventh and eighth lenses are plastic aspherical lenses, and the first, third and fourth lenses are spherical lenses.

[0014] The technical solution provided by this invention, by setting the first lens with negative optical power, facilitates the collection of light from the optical system and effectively increases the field of view; by setting the fourth lens with positive optical power, it bears a larger optical power of the system, changes the propagation direction of the light beam, corrects aberrations in the off-axis field of view, and is more conducive to the image formation of the light beam on the image plane; by setting the second, fifth, sixth, seventh, and eighth lenses as plastic aspherical lenses, the proportion of glass lenses used is reduced, lowering costs, while correcting various aberrations, improving edge image quality, and resulting in high image quality. By setting the other lenses as spherical lenses, aberrations are effectively improved, ensuring that the lens does not defocus under high and low temperature conditions; the light path of this lens is smooth, allowing more light to be introduced while making the structure more compact, with the total optical length controlled within 20.5mm. In terms of aperture, the aperture value F satisfies F≤2.8, the image plane height can reach φ10.5mm, and the lens can also form clear images in low light. By rationally setting the focal length ratio, the optical system achieves excellent thermal aberration, resulting in more stable performance. Furthermore, the diagonal field of view can reach over 82°, allowing for the integration of a 1 / 1.56-inch chip and promising broad application prospects. By employing eight lenses and rationally configuring the optical power and shape relationships of each lens, a fixed-focus lens with a small size, large target surface, wide angle, high image quality, and no defocusing at high or low temperatures is achieved. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the structure of an embodiment of the fixed-focus lens provided by the present invention; Figure 2 for Figure 1 A schematic diagram of the spherical aberration curve for a medium focal length lens; Figure 3 for Figure 1 A schematic diagram of the vertical chromatic aberration curve of a medium focal length lens; Figure 4 for Figure 1 Aperture sector diagram of a medium prime lens; Figure 5 for Figure 1 A schematic diagram of field curvature distortion in a medium prime lens; Figure 6 for Figure 1 MTF curve of a medium prime lens at 20℃; Figure 7 for Figure 1 MTF curve of a medium prime lens at -30℃; Figure 8 for Figure 1 MTF curve of a medium prime lens at 70℃.

[0017] Explanation of icon numbers: 1000. Fixed focal length lens; 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Fifth lens; 6. Sixth lens; 7. Seventh lens; 8. Eighth lens; a. Aperture stop; b. Filter; c. Image plane.

[0018] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0021] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0022] With the development of technology, the structures of various components are becoming increasingly complex, and consumers' demands are also rising. Lens products need to have the advantage of a wide field of view while also possessing good thermal performance. Currently, they generally suffer from the inability to simultaneously achieve a wide angle of view, low cost, high resolution, no blurring at high and low temperatures, and small size. For example, some lenses sacrifice some resolution or use plastic aspherical surfaces to reduce costs, but due to large temperature variations in the actual environment, these lenses are often prone to blurring at high and low temperatures, affecting their performance. On the other hand, some lenses do not blur at high and low temperatures and have high image quality, but they are expensive and not accepted by the consumer market.

[0023] The main objective of this invention is to provide a fixed-focus lens and imaging device, which aims to provide a fixed-focus lens with small size, wide angle, high imaging quality, and no blurring at high and low temperatures.

[0024] Please see Figure 1This invention proposes a fixed-focus lens 1000, which has an object side and an image side arranged opposite to each other along the optical axis. The fixed-focus lens 1000 includes, from the object side to the image side, a first lens 1 with negative optical power, a second lens 2 with negative optical power, a third lens 3 with negative optical power, a fourth lens 4 with positive optical power, a fifth lens 5 with positive optical power, a sixth lens 6 with negative optical power, a seventh lens 7 with positive optical power, an eighth lens 8 with negative optical power, and an image plane c, so that the total optical length of the fixed-focus lens 1000 is controlled within 20.5mm, the diagonal field of view reaches more than 82°, and the aperture value is less than or equal to 2.8; wherein, the second lens 2, the fifth lens 5, the sixth lens 6, the seventh lens 7, and the eighth lens 8 are plastic aspherical lenses, and the first lens 1, the third lens 3, and the fourth lens 4 are spherical lenses.

[0025] The technical solution provided by this invention, by setting the first lens 1 with negative optical power, facilitates the collection of light from the optical system and effectively increases the field of view; by setting the fourth lens 4 with positive optical power, it bears a larger optical power of the system, changes the propagation direction of the light beam, corrects aberrations in the off-axis field of view, and is more conducive to the image formation of the light beam on the image plane; by setting the second lens 2, fifth lens 5, sixth lens 6, seventh lens 7, and eighth lens 8 as plastic aspherical lenses, the proportion of glass lenses used is reduced, lowering costs, while correcting various aberrations, improving edge image quality, and resulting in high image quality. By setting the other lenses as spherical lenses, aberrations are effectively improved, ensuring that the lens does not defocus under high and low temperature conditions; the light path of this lens is smooth, allowing more light to be introduced while making the structure more compact, with the total optical length controlled within 20.5mm. In terms of aperture, the aperture value F satisfies F≤2.8, the image plane height can reach φ10.5mm, and the lens can also form clear images in low light. By rationally setting the focal length ratio, the optical system achieves excellent thermal aberration, resulting in more stable operation and a diagonal field of view exceeding 82°. It can accommodate a 1 / 1.56-inch chip, offering broad application prospects. Through the use of eight lenses and the rational setting of their optical power and shape relationships, a 1000 fixed-focus lens with a small size, large target surface, wide angle, high image quality, and no defocusing at high or low temperatures has been achieved.

[0026] It should be noted that the characteristic of aspherical lenses is that the curvature changes continuously from the center of the lens to the periphery, unlike spherical lenses which have a constant curvature from the center to the periphery.

[0027] Furthermore, the fixed-focus lens 1000 also includes an aperture stop a, which is disposed between the fourth lens 4 and the fifth lens 5. The aperture stop a limits the light beam aperture along the optical axis, blocking some light rays, thereby reducing glare, improving image contrast, and also enlarging the target surface and improving image quality. Adjusting the light throughput of the aperture stop a according to actual conditions helps to further improve image quality.

[0028] Furthermore, the fixed-focus lens 1000 also includes a filter b disposed sequentially from the object side to the image side between the eighth lens 8 and the image plane c. The filter b is used to filter out stray light in non-working wavelength bands to reduce optical noise and reduce difficulties in subsequent optoelectronic module processing. The filter b can also be used to adjust the color saturation of the image during final imaging.

[0029] Furthermore, to improve the image quality of the optical system, reduce light energy loss, increase imaging clarity, protect the scale surface, and further optimize the manufacturing process to meet design requirements, the fifth lens 5 and the sixth lens 6 are cemented together. This rational use of cemented components and reasonable allocation of optical power effectively corrects aberrations and achieves a high-temperature, heat-free effect. It also effectively reduces chromatic aberration and improves image clarity.

[0030] Specifically, in a preferred embodiment, please refer to Figure 1 The first lens 1 is a concave-convex lens with a convex object-side surface; the second lens 2 is a concave-convex lens with a concave object-side surface; the third lens 3 is a concave-convex lens with a convex object-side surface; the fourth lens 4 is a concave-convex lens with a convex object-side surface; the fifth lens 5 is a biconvex lens; the sixth lens 6 is a biconcave lens; the seventh lens 7 is a biconvex lens; and the eighth lens 8 is a concave-convex lens with a convex object-side surface.

[0031] Further, the focal length of the first lens 1 is f1, the focal length of the second lens 2 is f2, the focal length of the third lens 3 is f3, the focal length of the fourth lens 4 is f4, the focal length of the fifth lens 5 is f5, the focal length of the sixth lens 6 is f6, the focal length of the seventh lens 7 is f7, and the focal length of the eighth lens 8 is f8, wherein: -25 < f1 < -15, -220 < f2 < -160, -10 < f3 < -5, 3 < f4 < 5, 3 < f5 < 8, -12 < f6 < -5, 25 < f7 < 40, -15 < f8 < -8. This embodiment is a preferred embodiment. Through the combination of different lenses and the reasonable allocation of their optical power, the entire lens has good performance such as low cost and high pixel count.

[0032] Further, the first lens 1 has a refractive index of n1 and a dispersion coefficient of v1; the second lens 2 has a refractive index of n2 and a dispersion coefficient of v2; the third lens 3 has a refractive index of n3 and a dispersion coefficient of v3; the fourth lens 4 has a focal refractive index of n4 and a dispersion coefficient of v4; the fifth lens 5 has a refractive index of n5 and a dispersion coefficient of v5; the sixth lens 6 has a refractive index of n6 and a dispersion coefficient of v6; the seventh lens 7 has a refractive index of n7 and a dispersion coefficient of v7; and the eighth lens 8 has a refractive index of n8 and a dispersion coefficient of v8, wherein: 1.50 ≤ n1 ≤1.70, 1.60≤n2≤1.70, 1.50≤n3≤1.70, 1.70≤n4≤1.80, 1.50≤n5≤1.60, 1.60≤n6≤1.70, 1.60≤n7≤1.70, 1.50≤n8≤1.60, 55.0≤v1≤70.0, 18.0≤v2≤26.0, 45.0≤v3≤65.0, 50.0≤v4≤60.0, 50.0≤v5≤60.0, 18.0≤v6≤26.0, 18.0≤v7≤26.0, 50.0≤v8≤60.0. This embodiment is a preferred embodiment. By combining different lenses and rationally allocating their refractive index and dispersion coefficient, the fixed-focus lens 1000 has the performance of low cost, high pixel count and good thermal differential performance.

[0033] In one embodiment of the present invention, the effective focal length of the fixed-focus lens 1000 is EFL, and the total optical length of the fixed-focus lens 1000 is TTL, wherein TTL / EFL ≤ 3.4. By reasonably limiting the size of EFL, the size of the total optical length can be further limited, making the entire optical system more compact and helping to control the focal length of the fixed-focus lens 1000.

[0034] In one embodiment of the present invention, the total optical length of the fixed-focus lens 1000 is TTL, the diameter of the first lens 1 is D1, and the image plane diameter of the fixed-focus lens 1000 is IC, wherein D1 < 13mm and IC ≤ 10.5mm. This design, by limiting the numerical relationships of the aforementioned optical system characteristics, avoids excessively large apertures in the fixed-focus lens 1000, thus meeting the installation space requirements of the final product. By limiting the specific values ​​of the total optical length and the diameter of the first lens 1, the lens size can be appropriately limited, contributing to lens miniaturization.

[0035] It is worth mentioning that the surface shape of the aspherical lens in the fixed-focus lens 1000 described in this embodiment should satisfy the following equation:

[0036] Where c is the curvature corresponding to the radius; y is the radial coordinate (its unit is the same as the lens length unit); k is the conic conic section coefficient, and A, B, C, D, E, F, G... represent the fourth, sixth, eighth, tenth, twelfth, fourteenth, sixteenth... aspherical coefficients, respectively. These parameters allow the setting of the shape and size of the aspherical surfaces facing the object and image sides of the lens.

[0037] Specifically, when k < -1, the corresponding lens surface curve is a hyperbola; when k = -1, the corresponding lens surface curve is a parabola; when -1 < k < 0, the corresponding lens surface curve is an ellipse; when k = 0, the corresponding lens surface curve is a circle; and when k > 0, the corresponding lens surface curve is an oval.

[0038] It should be noted that the basic parameters of the fixed-focus lens 1000 in one embodiment of the present invention are shown in Table 1, where the radius of curvature and thickness are in millimeters (mm).

[0039] Table 1

[0040] In this embodiment, the aspherical coefficients of the aspherical lens in the fixed-focus lens 1000 include: the quadratic surface coefficient k, the fourth-order aspherical coefficient A, the sixth-order aspherical coefficient B, the eighth-order aspherical coefficient C, the tenth-order aspherical coefficient D, the twelfth-order aspherical coefficient E, the fourteenth-order aspherical coefficient F, and the sixteenth-order aspherical coefficient G, as shown in Table 2 below.

[0041] Table 2

[0042] Please refer to Figure 2 Figure 1 is a schematic diagram of the spherical aberration curve of the fixed-focus lens 1000 in this embodiment. As can be seen from the figure, the spherical aberration of the fixed-focus lens 1000 at different wavelengths is controlled within the range of (-0.02mm, +0.02mm), indicating that the spherical aberration of the fixed-focus lens 1000 is well controlled.

[0043] Please refer to Figure 3 Figure 1 is a schematic diagram of the chromatic aberration curve of the fixed-focus lens 1000 in this embodiment. As can be seen from the figure, the chromatic aberration of the fixed-focus lens 1000 at different wavelengths is controlled within the range of (-1μm, +2μm), indicating that the chromatic aberration of the fixed-focus lens 1000 is well controlled and can meet the requirements of wide-spectrum applications across the entire wavelength range.

[0044] Please refer to Figure 4The figure shows the fan plot of the fixed-focus lens 1000 in this embodiment. The horizontal axis represents the normalized beam aperture, and the vertical axis represents the transverse aberration. Ideally, each curve should completely coincide with the horizontal axis, meaning all light rays in that field of view are focused at the same point on the image plane c. The vertical axis can also represent the maximum dispersion range of the beam on the ideal image plane c. The fan plot not only reflects monochromatic aberration at different wavelengths but also the magnitude of transverse chromatic aberration. As shown in the figure, the fixed-focus lens 1000 closely approximates the horizontal axis for each wavelength in each field of view, indicating that the transverse aberration at each wavelength is well corrected. Furthermore, the curves for each color do not show significant dispersion, indicating that the fixed-focus lens 1000 also provides good correction for chromatic aberration, ensuring the imaging requirement of sharp images across the entire wavelength range.

[0045] Please refer to Figure 5 The figure shows the field curvature distortion of the fixed-focus lens 1000 in this embodiment. Different colors represent different wavelengths. For the same color, the right curve represents the meridional direction, and the left curve represents the sagittal field curvature. The figure shows that the sagittal field curvature of this lens is no greater than 0.04mm, indicating that this lens can effectively correct chromatic aberration. The other curve in the figure is the system distortion curve. Distortion does not affect the system's sharpness, but it can cause image distortion. The optical distortion of this lens is less than 3%.

[0046] Please refer to Figures 6-8 The figure shows the MTF (Mean Transformer File) of the fixed-focus lens 1000 in this embodiment at 20℃, -30℃, and 70℃, respectively. It shows the imaging quality of three wavelengths of light. The horizontal axis represents the number of line pairs, and the vertical axis represents the resolving power. The higher the value of the vertical axis, the stronger the resolving power and the higher the image quality reproduction. It can be seen from the figure that the imaging quality of the fixed-focus lens 1000 in this solution is relatively stable under high and low temperature conditions, and basically achieves the state of not defocusing at high and low temperatures.

[0047] In this embodiment, the fixed-focus lens 1000 has a focal length of 6.1mm, an aperture of 2.66, an image plane diameter of 10.5mm, and a diagonal field of view of 83.2°. While having a large field of view, various aberrations of the lens are corrected, resulting in high image quality. It can also produce clear images in low light. Furthermore, the lens is small in size and does not defocus under high or low temperature conditions. In particular, it does not become out of focus within a temperature range of -30°C to 70°C, making its working performance more stable.

[0048] The present invention also proposes an imaging device, which includes the aforementioned fixed-focus lens 1000. Since the imaging device includes the fixed-focus lens 1000, the specific structure of the fixed-focus lens 1000 is as described in the above embodiments. As the fixed-focus lens 1000 of this imaging device adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.

[0049] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A fixed-focus lens, characterized in that, The fixed-focus lens has an object side and an image side arranged opposite to each other along the optical axis. The fixed-focus lens includes a first lens with negative optical power, a second lens with negative optical power, a third lens with negative optical power, a fourth lens with positive optical power, a fifth lens with positive optical power, a sixth lens with negative optical power, a seventh lens with positive optical power, an eighth lens with negative optical power, and an image plane arranged sequentially from the object side to the image side, so that the total optical length of the fixed-focus lens is controlled within 20.5mm, the diagonal field of view reaches more than 82°, and the aperture value is less than or equal to 2.

8. Among them, the second, fifth, sixth, seventh and eighth lenses are plastic aspherical lenses, and the first, third and fourth lenses are spherical lenses.

2. The fixed-focus lens as described in claim 1, characterized in that, The fixed-focus lens also includes an aperture stop, which is disposed between the fourth lens and the fifth lens.

3. The fixed-focus lens as described in claim 1, characterized in that, The fixed-focus lens also includes a filter disposed sequentially from the object side to the image side between the eighth lens and the image plane, the filter being used to filter out stray light.

4. The fixed-focus lens as described in claim 1, characterized in that, The third lens and the fourth lens are glued together.

5. The fixed-focus lens as described in claim 1, characterized in that, The first lens is a concave-convex lens, and its object-side surface is convex. The second lens is a concave-convex lens, and its object-side surface is concave. The third lens is a concave-convex lens, and its object-side surface is convex. The fourth lens is a concave-convex lens, and its object-side surface is convex. The fifth lens is a biconvex lens; The sixth lens is a biconcave lens; The seventh lens is a biconvex lens; The eighth lens is a concave-convex lens, and its object-side surface is convex.

6. The fixed-focus lens as described in claim 5, characterized in that, The focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, the focal length of the fourth lens is f4, the focal length of the fifth lens is f5, the focal length of the sixth lens is f6, the focal length of the seventh lens is f7, and the focal length of the eighth lens is f8, wherein: -25 < f1 < -15, -220 < f2 < -160, -10 < f3 < -5, 3 < f4 < 5, 3 < f5 < 8, -12 < f6 < -5, 25 < f7 < 40, -15 < f8 < -8.

7. The fixed-focus lens as described in claim 5, characterized in that, The first lens has a refractive index of n1 and a dispersion coefficient of v1; the second lens has a refractive index of n2 and a dispersion coefficient of v2; the third lens has a refractive index of n3 and a dispersion coefficient of v3; the fourth lens has a focal refractive index of n4 and a dispersion coefficient of v4; the fifth lens has a refractive index of n5 and a dispersion coefficient of v5; the sixth lens has a refractive index of n6 and a dispersion coefficient of v6; the seventh lens has a refractive index of n7 and a dispersion coefficient of v7; and the eighth lens has a refractive index of n8 and a dispersion coefficient of v8, wherein: 1.50 ≤ n1 ≤ 1.70, 1 .60≤n2≤1.70,1.50≤n3≤1.70,1.70≤n4≤1.80,1.50≤n5≤1.60,1.60≤n6≤1.70,1.60≤n7≤1.70,1.50≤n8≤1.60,55.0≤v1≤70.0,18.0≤v2≤26.0,45.0≤v3≤65.0,50.0≤v4≤60.0,50.0≤v5≤60.0,18.0≤v6≤26.0,18.0≤v7≤26.0,50.0≤v8≤60.

0.

8. The fixed-focus lens as described in claim 1, characterized in that, The effective focal length of the fixed-focus lens is EFL, and the total optical length of the fixed-focus lens is TTL, wherein: TTL / EFL≤3.

4.

9. The fixed-focus lens as described in claim 1, characterized in that, The diameter of the first lens is D1, and the diameter of the image plane of the fixed-focus lens is IC, wherein: D1 < 13mm, IC ≤ 10.5mm.

10. An imaging device, characterized in that, Includes a fixed-focus lens as described in any one of claims 1 to 9.

Images