CN217879791U

CN217879791U - Fixed focus lens

Info

Publication number: CN217879791U
Application number: CN202222488727.1U
Authority: CN
Inventors: 翟林燕; 梁伟朝; 应永茂; 张圆
Original assignee: Sunny Optics Zhongshan Co Ltd
Current assignee: Sunny Optics Zhongshan Co Ltd
Priority date: 2022-09-20
Filing date: 2022-09-20
Publication date: 2022-11-22
Anticipated expiration: 2032-09-20

Abstract

The utility model relates to a prime lens includes along the direction of optical axis from the thing side to picture side in proper order: the optical lens comprises a first lens (L1) with negative focal power, a second lens (L2) with positive focal power, a third lens (L3) with positive focal power, a diaphragm (STO), a fourth lens (L4) with positive focal power, a fifth lens (L5) with negative focal power, a sixth lens (L6) with positive focal power, a seventh lens (L7) with positive focal power and an eighth lens (L8) with negative focal power, wherein the first lens (L1) is an aspheric lens, and the sixth lens (L6) is a spherical lens; the seventh lens (L7) is a convex lens. The fixed-focus lens has the characteristics of large target surface, super-large aperture, large light flux, low cost, miniaturization and high imaging performance, and can clearly image within the temperature range of-40 ℃ to +80 ℃.

Description

Fixed focus lens

Technical Field

The utility model relates to an optical lens technical field especially relates to a tight shot.

Background

With the rapid development of work in the fields of security and public safety, the demand for monitoring fixed-focus lenses is also gradually rising. In order to have higher light transmission amount at night, the ultra-large aperture lens better meets the market demand, so the research and development design of the ultra-large aperture lens is necessary. However, most of the lenses in the lens market firstly ensure the imaging quality in the daytime, and the imaging quality at night is obviously reduced in the practical aperture. Therefore, aiming at the defects of the prior art, the ultra-large aperture security lens which has a large target surface, is low in cost and does not have virtual focus within the temperature range of-40 ℃ to 80 ℃ is needed.

SUMMERY OF THE UTILITY MODEL

The utility model aims to provide a large-target-surface, low-cost and virtually burnt super large aperture's tight shot not at-40 ℃ -80 ℃ temperature range.

To achieve the above object, the present invention provides a fixed focus lens, sequentially including, along an optical axis from an object side to an image side: the lens comprises a first lens with negative focal power, a second lens with positive focal power, a third lens with positive focal power, a diaphragm, a fourth lens with positive focal power, a fifth lens with negative focal power, a sixth lens with positive focal power, a seventh lens with positive focal power and an eighth lens with negative focal power.

According to an aspect of the present invention, in a direction from an object side to an image side along an optical axis,

the first lens is a paraxial region convex-concave lens;

the second lens is a concave-convex lens;

the paraxial region of the object side surface of the third lens is convex;

the shape of the image side surface of the fourth lens is convex;

the object side surface of the fifth lens is concave;

the sixth lens is a convex lens;

the seventh lens is a convex lens;

the eighth lens is a paraxial region meniscus lens.

According to an aspect of the present invention, the first lens, the second lens, the third lens, the seventh lens, and the eighth lens are aspheric lenses;

the fourth lens, the fifth lens and the sixth lens are spherical lenses.

According to an aspect of the present invention, the first lens, the second lens, the third lens, the seventh lens and the eighth lens are plastic lenses;

the fourth lens, the fifth lens and the sixth lens are glass lenses.

According to an aspect of the present invention, the fourth lens and the fifth lens are cemented to form a cemented lens group.

According to the utility model discloses an aspect, the focus F45 of veneer mirror group with the effective focal length F of tight shot satisfies: F45/F is more than or equal to-4.0 and less than or equal to 16.5.

According to the utility model discloses an aspect, the focus F45 of veneer mirror group with back crowd's focus FB of tight shot satisfies: F45/FB is more than or equal to-2.2 and less than or equal to 10.5.

According to the utility model discloses an aspect, the optics total length TTL of tight shot with the back focal length BFL of tight shot satisfies: TTL/BFL is more than or equal to 5.8 and less than or equal to 8.0.

According to the utility model discloses an aspect, the effective focal length F of tight shot with the back focal length BFL of tight shot satisfies: F/BFL is more than or equal to 1.0 and less than or equal to 1.5.

According to the utility model discloses an aspect, the effective focal length F of tight shot with the biggest image height IH of tight shot satisfies: F/IH is more than or equal to 0.4 and less than or equal to 0.8.

According to the utility model discloses an aspect, the focus F1 of first lens with the effective focal length F of tight shot satisfies: F1/F is more than or equal to-2.2 and less than or equal to-1.6.

According to an aspect of the present invention, the first lens reaches the center distance D12 of the second lens on the optical axis and the total optical length TTL of the fixed focus lens satisfies: D12/TTL is more than or equal to 0.1 and less than or equal to 0.3.

According to an aspect of the present invention, the refractive index Nd3 and the abbe number Vd3 of the third lens satisfy: nd3 is more than or equal to 1.6 and less than or equal to 1.7; vd3 is more than or equal to 20 and less than or equal to 30.

According to an aspect of the present invention, the refractive index Nd4 and the abbe number Vd4 of the fourth lens satisfy: nd4 is more than or equal to 1.70 and less than or equal to 1.8; vd4 is more than or equal to 50 and less than or equal to 60;

the refractive index Nd5 and the Abbe number Vd5 of the fifth lens respectively satisfy: nd5 is more than or equal to 1.70 and less than or equal to 1.9; vd5 is more than or equal to 20 and less than or equal to 30.

According to an aspect of the present invention, the refractive index Nd6 and the abbe number Vd6 of the sixth lens satisfy: nd6 is more than or equal to 1.40 and less than or equal to 1.5; vd6 is more than or equal to 90 and less than or equal to 95.

According to an aspect of the utility model, the focus F6 of sixth lens with the effective focal length F of tight shot satisfies: F6/F is more than or equal to 2.6 and less than or equal to 4.5.

According to an aspect of the present invention, the edge thickness ET8 of the eighth lens and the center thickness CT8 of the eighth lens satisfy: ET8/CT8 is more than or equal to 1.6 and less than or equal to 2.6.

According to an aspect of the utility model, the focus F8 of eighth lens with the effective focal length F of tight shot satisfies: F8/F is more than or equal to-4.6 and less than or equal to-2.6.

According to one aspect of the present invention, the prime lens further comprises a filter,

the optical effective aperture SDF of the optical filter and the optical effective semi-aperture SD1 of the first lens meet the following requirements: SDF/SD1 is more than or equal to 0.6 and less than or equal to 0.9.

According to an aspect of the present invention, the optical effective diameter SDS of the diaphragm and the optical effective half-aperture SD1 of the first lens satisfy: SDS/SD1 is more than or equal to 0.5 and less than or equal to 0.9.

According to the utility model discloses a scheme adopts eight pieces of lenses of above-mentioned arrangement and the focal power and different shapes, concrete material, focus relation and the camera lens each item parameter index of optimizing configuration, each lens of collocation, can make this tight shot possess high-quality imaging performance, and it is clear to image at-40 ℃ - +80 ℃ temperature range, has big target surface, super large light ring, big light flux volume, low cost and miniaturization concurrently, specifically can be applicable to 1/1.8' big target surface chip. Moreover, through the design of the two-gear type variable diaphragm, the fixed-focus lens can support two gears of F1.0/F1.6 under visible light, and the day and night confocal function is realized under the gear of F1.6.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for the embodiments will be briefly described below. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.

Fig. 1 schematically shows a schematic structural diagram of a fixed focus lens according to a first embodiment of the present invention;

fig. 2 schematically shows a light fan diagram of a fixed focus lens according to a first embodiment of the present invention;

fig. 3 schematically shows a schematic structural diagram of a fixed focus lens according to a second embodiment of the present invention;

fig. 4 schematically shows a light fan diagram of a fixed focus lens according to a second embodiment of the present invention;

fig. 5 schematically shows a schematic structural diagram of a fixed-focus lens according to a third embodiment of the present invention;

fig. 6 schematically shows a light fan diagram of a fixed-focus lens according to a third embodiment of the present invention;

fig. 7 schematically shows a schematic structural diagram of a fixed-focus lens according to a fourth embodiment of the present invention;

fig. 8 schematically shows a light fan diagram of a fixed focus lens according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

The embodiments described in this specification are to be considered in all respects as illustrative and not restrictive, and the appended drawings are intended to be part of the entire specification. In the drawings, the shape or thickness of the embodiments may be exaggerated and simplified or conveniently indicated. Further, the components of the structures in the drawings are described separately, and it should be noted that the components not shown or described in the drawings are well known to those skilled in the art.

Any reference to directions and orientations to the description of the embodiments herein is merely for convenience of description and should not be construed as limiting the scope of the present invention in any way. The following description of the preferred embodiments refers to combinations of features which may be present independently or in combination, and the present invention is not particularly limited to the preferred embodiments. The scope of the present invention is defined by the appended claims.

As shown in fig. 1, an embodiment of the present invention provides a fixed focus lens, sequentially including, along an optical axis from an object side to an image side: a first lens L1, a second lens L2, a third lens L3, a stop STO, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8. Among them, the first lens L1, the fifth lens L5, and the eighth lens L8 are all negative power lenses, and the second lens L2, the third lens L3, the fourth lens L4, the sixth lens L6, and the seventh lens L7 are all positive power lenses.

In the direction from the object side to the image side along the optical axis, the first lens L1 is a paraxial region convex-concave lens, the second lens L2 is a concave-convex lens, the paraxial region of the object-side surface of the third lens L3 is convex, the image-side surface of the fourth lens L4 is convex, the object-side surface of the fifth lens L5 is concave, both the sixth lens L6 and the seventh lens L7 are convex-convex lenses, and the eighth lens L8 is a paraxial region convex-concave lens.

According to the technical scheme, the eight lenses in the arrangement mode are adopted, and the focal power, the object side and the image side of each lens are optimally configured to be different in shape, so that the fixed-focus lens has high-quality imaging performance, can clearly image within the temperature range of minus 40 ℃ to plus 80 ℃, realizes a large target surface and an ultra-large aperture, and can be suitable for a 1/1.8' large target surface chip. Moreover, through the design of the two-gear type variable diaphragm STO, the fixed-focus lens can support two gears F1.0/F1.6 under visible light, and under the gear F1.6, the lens can realize the day and night confocal function.

In the embodiment of the present invention, first lens L1, second lens L2, third lens L3, seventh lens L7 and eighth lens L8 are aspheric lenses, and fourth lens L4, fifth lens L5 and sixth lens L6 are spherical lenses. By adopting the aspheric lens and the combination thereof, the aberration of the fixed-focus lens optical system can be efficiently adjusted, and the performance of the lens is further improved.

In the embodiment of the present invention, the first lens L1, the second lens L2, the third lens L3, the seventh lens L7 and the eighth lens L8 are plastic lenses, and the fourth lens L4, the fifth lens L5 and the sixth lens L6 are glass lenses. By the optimized mixed arrangement of the lens glass and the plastic material, unstable correction of high and low temperature imaging and compensation of temperature drift can be realized, so that the cost of the lens is reduced, and the cost of the lens is reduced.

In the embodiment of the present invention, the fourth lens element L4 and the fifth lens element L5 are cemented together to form a cemented lens group. The cemented lens can correct the equiaxial external aberration such as field curvature, coma aberration and astigmatism, and further improve the imaging performance of the lens. Preferably, the focal length F45 of the cemented lens group and the effective focal length F of the prime lens satisfy: F45/F is more than or equal to-4.0 and less than or equal to 16.5. Preferably, in the cemented lens group, the refractive index Nd4 and the abbe number Vd4 of the fourth lens L4 satisfy the following conditional expressions, respectively: nd4 is more than or equal to 1.70 and less than or equal to 1.8; vd4 is more than or equal to 50 and less than or equal to 60. The refractive index Nd5 and the abbe number Vd5 of the fifth lens L5 satisfy the following conditional expressions, respectively: nd5 is more than or equal to 1.70 and less than or equal to 1.9; vd5 is more than or equal to 20 and less than or equal to 30. Thus, by properly arranging the cemented doublet and designing the refractive index and the abbe number of the fourth lens L4 and the fifth lens L5, the aberration in the lens optical system can be effectively reduced.

Preferably, the focal length F45 of the cemented mirror group and the back group focal length FB of the fixed focus lens satisfy: F45/FB is more than or equal to-2.2 and less than or equal to 10.5. The back group focal length FB here refers to a combined focal length of the fourth lens L4 to the eighth lens L8 from the object side to the image side. By designing the focal length ratio of the cemented lens group and the rear lens group, the aberration of incident light entering the optical system can be balanced.

The embodiment of the utility model provides an in, the effective focal length F of the total optical length TTL of tight shot, tight shot satisfies following conditional expression with the back focal length BFL of tight shot respectively: TTL/BFL is more than or equal to 5.8 and less than or equal to 8.0; F/BFL is more than or equal to 1.0 and less than or equal to 1.5. By reasonably and optimally designing the parameter indexes of the total optical length, the focal length and the back focal length of the lens, the miniaturization can be realized, and the performance requirement of small volume can be met. It should be noted that the back focal length BFL of the fixed-focus lens in the embodiment of the present invention refers to the distance from the image side of the last lens, i.e. the eighth lens L8, to the image plane IMA.

The embodiment of the utility model provides an in, the effective focal length F of tight shot and the biggest high IH of image of tight shot satisfy: F/IH is more than or equal to 0.4 and less than or equal to 0.8, which is beneficial to improving the resolving power of the fixed-focus lens and reducing the sensitivity of the lens.

The embodiment of the utility model provides an in, the effective focal length F of focus F1 and the tight shot of first lens L1 satisfies: F1/F is more than or equal to-2.2 and less than or equal to-1.6, so that light can correctly and stably enter the rear optical structure of the lens, the light flux is increased, and the resolution performance is improved.

The embodiment of the utility model provides an in, first lens L1 satisfies to the optics total length TTL of second lens L2 at the epaxial central distance D12 of optical axis and tight shot: D12/TTL is more than or equal to 0.1 and less than or equal to 0.3, and the deflection angle of the light emitted from the image side surface of the first lens L1 can be effectively controlled, so that the main light angle CRA of the lens can be effectively controlled.

In the embodiment of the present invention, the refractive index Nd3 and abbe number Vd3 of the third lens L3 satisfy the following conditional expressions respectively: nd3 is more than or equal to 1.6 and less than or equal to 1.7; vd3 is more than or equal to 20 and less than or equal to 30. Through carrying out so setting on the refracting index and the dispersion coefficient of plastic lens, can enough reduce cost, be favorable to promoting the resolution quality under the lens high low temperature state again.

In the embodiment of the present invention, the refractive index Nd6 and the abbe number Vd6 of the sixth lens L6 satisfy the following conditional expressions respectively: nd6 is more than or equal to 1.40 and less than or equal to 1.5; vd6 is more than or equal to 90 and less than or equal to 95. The focal length F6 of the sixth lens L6 and the effective focal length F of the prime lens satisfy: F6/F is more than or equal to 2.6 and less than or equal to 4.5. By satisfying the two conditional expressions, the confocal state of the lens in the visible light and infrared states can be balanced.

In the embodiment of the utility model, edge thickness ET8 of eighth lens L8 and center thickness CT8 of eighth lens L8 satisfy: ET8/CT8 is more than or equal to 1.6 and less than or equal to 2.6. Through carrying out reasonable setting to eighth lens L8's thickness index, can reduce the production degree of difficulty of plastic lens. The focal length F8 of the eighth lens L8 and the effective focal length F of the fixed-focus lens satisfy: F8/F is more than or equal to-4.6 and less than or equal to-2.6, so that light can smoothly enter the image plane IMA, the defocusing curve is concentrated, and the resolution performance of the lens is improved.

The embodiment of the utility model provides an in, tight shot still includes the light filter (in fig. 1 to fig. 4, record the light filter as one side S13), and the effective bore SDF of optics of light filter and the effective half bore SD1 of optics of first lens L1 satisfy: SDF/SD1 is more than or equal to 0.6 and less than or equal to 0.9, and can filter light, further improve the resolution performance and ensure the maximum light flux.

The embodiment of the utility model provides an in, the effective diameter SDS of optics of diaphragm STO and the effective semi-bore SD1 of optics of first lens L1 satisfy: SDS/SD1 is more than or equal to 0.5 and less than or equal to 0.9, so that the aperture is large enough, and the ultra-large aperture function of the infrared state of the lens is realized by changing the aperture.

In conclusion, by adopting the technical scheme, the fixed focus lens with the large target surface, the ultra-large aperture, the low cost, the miniaturization and the high imaging performance is obtained, the imaging is clear within the temperature range of minus 40 ℃ to plus 80 ℃, and the fixed focus lens can be suitable for a large target surface chip of 1/1.8'. Meanwhile, the lens can support two gears of F1.0/F1.6 under visible light, and the day and night confocal function is realized under the gear of F1.6.

The following describes four embodiments of the present invention with reference to the drawings and tables. In each of the following embodiments, the utility model discloses record diaphragm STO as the one side, record the cemented surface of cemented mirror group as the one side, record the light filter as the one side, record parallel flat board CG as two sides, record image plane IMA as the one side.

The parameters of each example specifically satisfying the above conditional expressions are shown in table 1 below:

table 1 in the embodiments of the present invention, the aspheric lens of the fixed-focus lens satisfies the following formula:

in the above formula, z is the axial distance from the curved surface to the vertex at the position of the height h perpendicular to the optical axis along the optical axis direction; c represents the curvature at the apex of the aspherical surface; k is a conic coefficient; a. The ₄ 、A ₆ 、A ₈ 、A ₁₀ 、A ₁₂ 、A ₁₄ 、A ₁₆ The aspherical coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth and sixteenth orders are expressed respectively.

Example one

Referring to fig. 1, the parameters of the fixed-focus lens of the present embodiment are as follows:

fno:1.09; total optical length TTL:30.30mm. The third lens L3 is a paraxial region convex-concave lens, the fourth lens L4 is a convex-concave lens, and the fifth lens L5 is a concave-concave lens.

The relevant parameters of each lens in the fixed-focus lens of the embodiment include: surface type, radius of curvature, thickness, refractive index of the material and abbe number, as shown in table 2 below.

TABLE 2

The aspheric coefficients of the aspheric lenses of the fixed-focus lens of the present embodiment include: the quadric surface constant K and the fourth-order aspheric surface coefficient A of the surface ₄ Sixth order aspherical surface coefficient A ₆ Eighth order aspheric surface coefficient A ₈ Ten-order aspheric surface coefficient A ₁₀ Twelve-order aspheric surface coefficient A ₁₂ Fourteen-order aspheric surface coefficient A ₁₄ And a sixteen-order aspheric coefficient A ₁₆ As shown in table 3 below.

TABLE 3

As shown in fig. 1 and fig. 2 and tables 1 to 3, the fixed focus lens of the present embodiment has the characteristics of large target surface, ultra-large aperture, low cost, miniaturization and high imaging performance, can clearly image in the temperature range of-40 ℃ to +80 ℃, and is applicable to 1/1.8' large target surface chips. Meanwhile, the lens can support two gears of F1.0/F1.6 under visible light, and the day and night confocal function is realized under the gear of F1.6.

Example two

Referring to fig. 3, the parameters of the fixed-focus lens of the present embodiment are as follows:

fno:1.09; total optical length TTL:29.64mm. The third lens L3 is a paraxial convex lens, the fourth lens L4 is a concave-convex lens, and the fifth lens L5 is a concave-concave lens.

The relevant parameters of each lens in the fixed-focus lens of the embodiment include: surface type, radius of curvature, thickness, refractive index of the material and abbe number are shown in table 4 below.

TABLE 4

The aspheric surface coefficients of the aspheric surface lenses of the prime lens of the embodiment include: the quadric surface constant K and the fourth-order aspheric surface coefficient A of the surface ₄ Sixth order aspherical surface coefficient A ₆ Eighth order aspheric surface coefficient A ₈ Ten-order aspheric surface coefficient A ₁₀ Twelve-order aspheric surface coefficient A ₁₂ Fourteen-order aspheric surface coefficient A ₁₄ And a sixteen-order aspheric coefficient A ₁₆ As shown in table 5 below.

TABLE 5

As shown in fig. 3 and 4 and tables 1, 4 and 5, the fixed focus lens of the present embodiment has the characteristics of large target surface, ultra-large aperture, low cost, miniaturization and high imaging performance, can clearly image in the temperature range of-40 ℃ to +80 ℃, and is suitable for 1/1.8' large target surface chips. Meanwhile, the lens can support two gears of F1.0/F1.6 under visible light, and the day and night confocal function is realized under the gear of F1.6.

EXAMPLE III

Referring to fig. 5, the parameters of the fixed-focus lens of the present embodiment are as follows:

fno:1.07; total optical length TTL:28.51mm. The third lens L3 is a paraxial convex-concave lens, the fourth lens L4 is a convex-concave lens, and the fifth lens L5 is a concave-concave lens.

The relevant parameters of each lens in the fixed-focus lens of the embodiment include: surface type, radius of curvature, thickness, refractive index of the material and abbe number are shown in table 6 below.

TABLE 6

The aspheric coefficients of the aspheric lenses of the fixed-focus lens of the present embodiment include: the quadric surface constant K and the fourth-order aspheric surface coefficient A of the surface ₄ Sixth order aspherical surface coefficient A ₆ Eighth orderAspheric coefficient A ₈ Ten-order aspheric surface coefficient A ₁₀ Twelve-order aspheric surface coefficient A ₁₂ Fourteen-order aspheric surface coefficient A ₁₄ And a sixteen-order aspheric coefficient A ₁₆ As shown in table 7 below.

TABLE 7

As shown in fig. 5 and fig. 6 and tables 1, 6, and 7, the fixed-focus lens of the present embodiment has the characteristics of a large target surface, an ultra-large aperture, low cost, miniaturization, and high imaging performance, and can clearly image in a temperature range of-40 ℃ to +80 ℃, and is applicable to a 1/1.8' large target surface chip. Meanwhile, the lens can support two gears of F1.0/F1.6 under visible light, and the day and night confocal function is realized under the gear of F1.6.

Example four

Referring to fig. 7, the parameters of the fixed-focus lens of the present embodiment are as follows:

fno:1.07; total optical length TTL:30.30mm. The third lens L3 is a paraxial convex-concave lens, the fourth lens L4 is a convex-convex lens, and the fifth lens L5 is a concave-convex lens.

The relevant parameters of each lens in the fixed-focus lens of the embodiment include: surface type, radius of curvature, thickness, refractive index of the material, and abbe number, as shown in table 8 below.

TABLE 8

The aspheric coefficients of the aspheric lenses of the fixed-focus lens of the present embodiment include: the quadric surface constant K and the fourth-order aspheric surface coefficient A of the surface ₄ Sixth order aspherical surface coefficient A ₆ Eighth order aspheric surface coefficient A ₈ Ten-step non-ballSurface coefficient A ₁₀ Twelve-order aspheric surface coefficient A ₁₂ Fourteen-order aspheric surface coefficient A ₁₄ And a sixteen-order aspheric coefficient A ₁₆ As shown in table 9 below.

TABLE 9

As shown in fig. 7 and fig. 8 and tables 1, 8 and 9, the fixed focus lens of the present embodiment has the characteristics of large target surface, ultra-large aperture, low cost, miniaturization and high imaging performance, can image clearly in the temperature range of-40 ℃ to +80 ℃, and is applicable to 1/1.8' large target surface chips. Meanwhile, the lens can support two gears of F1.0/F1.6 under visible light, and the day and night confocal function is realized under the gear of F1.6.

The above description is only for the preferred embodiment of the present invention, and should not be taken as limiting the invention, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A fixed focus lens, comprising, in order from an object side to an image side along an optical axis: a first lens (L1) with negative focal power, a second lens (L2) with positive focal power, a third lens (L3) with positive focal power, a diaphragm (STO), a fourth lens (L4) with positive focal power, a fifth lens (L5) with negative focal power, a sixth lens (L6) with positive focal power, a seventh lens (L7) with positive focal power and an eighth lens (L8) with negative focal power,

the first lens (L1) is an aspheric lens, and the sixth lens (L6) is a spherical lens;

the seventh lens (L7) is a convex lens.

2. The fixed focus lens according to claim 1, wherein in a direction from an object side to an image side along an optical axis,

the first lens (L1) is a paraxial region convex-concave lens;

the second lens (L2) is a meniscus lens;

the paraxial region of the object-side surface of the third lens (L3) is convex;

the shape of the image side surface of the fourth lens (L4) is convex;

the object side surface of the fifth lens (L5) is concave;

the sixth lens (L6) is a convex lens;

the eighth lens (L8) is a paraxial region meniscus lens.

3. The prime lens according to claim 1, wherein the second lens (L2), the third lens (L3), the seventh lens (L7), and the eighth lens (L8) are aspheric lenses;

the fourth lens (L4) and the fifth lens (L5) are spherical lenses.

4. The prime lens according to claim 1, wherein the first lens (L1), the second lens (L2), the third lens (L3), the seventh lens (L7) and the eighth lens (L8) are plastic lenses;

the fourth lens (L4), the fifth lens (L5), and the sixth lens (L6) are glass lenses.

5. Prime lens according to claim 1, characterized in that the fourth lens (L4) and the fifth lens (L5) are cemented together to form a cemented lens group.

6. The prime lens according to claim 5, wherein the focal length F45 of the cemented lens group and the effective focal length F of the prime lens satisfy: F45/F is more than or equal to-4.0 and less than or equal to 16.5.

7. The fixed-focus lens according to claim 5, wherein the focal length F45 of the cemented lens group and the back group focal length FB of the fixed-focus lens satisfy: F45/FB of-2.2 is less than or equal to 10.5.

8. The fixed-focus lens according to any one of claims 1 to 7, wherein an optical total length TTL of the fixed-focus lens and a back focal length BFL of the fixed-focus lens satisfy: TTL/BFL is more than or equal to 5.8 and less than or equal to 8.0.

9. The fixed-focus lens according to any one of claims 1 to 7, wherein an effective focal length F of the fixed-focus lens and a back focal length BFL of the fixed-focus lens satisfy: F/BFL is more than or equal to 1.0 and less than or equal to 1.5.

10. The fixed-focus lens according to any one of claims 1 to 7, wherein an effective focal length F of the fixed-focus lens and a maximum image height IH of the fixed-focus lens satisfy: F/IH is more than or equal to 0.4 and less than or equal to 0.8.

11. The prime lens according to any one of claims 1 to 7, wherein the focal length F1 of the first lens (L1) and the effective focal length F of the prime lens satisfy: F1/F is more than or equal to-2.2 and less than or equal to-1.6.

12. The prime lens according to any one of claims 1 to 7, wherein a center distance D12 of the first lens (L1) to the second lens (L2) on an optical axis and an optical total length TTL of the prime lens satisfy: D12/TTL is more than or equal to 0.1 and less than or equal to 0.3.

13. The fixed focus lens according to any one of claims 1 to 7, wherein the refractive index Nd3 and the Abbe number Vd3 of the third lens (L3) respectively satisfy: nd3 is more than or equal to 1.6 and less than or equal to 1.7; vd3 is more than or equal to 20 and less than or equal to 30.

14. The fixed focus lens according to any one of claims 1 to 7, wherein the refractive index Nd4 and the Abbe number Vd4 of the fourth lens (L4) respectively satisfy: nd4 is more than or equal to 1.70 and less than or equal to 1.8; vd4 is more than or equal to 50 and less than or equal to 60;

the refractive index Nd5 and the Abbe number Vd5 of the fifth lens (L5) respectively satisfy: nd5 is more than or equal to 1.70 and less than or equal to 1.9; vd5 is more than or equal to 20 and less than or equal to 30.

15. The fixed focus lens according to any one of claims 1 to 7, wherein a refractive index Nd6 and an Abbe number Vd6 of the sixth lens (L6) respectively satisfy: nd6 is more than or equal to 1.40 and less than or equal to 1.5; vd6 is more than or equal to 90 and less than or equal to 95.

16. The prime lens according to any one of claims 1 to 7, wherein the focal length F6 of the sixth lens (L6) and the effective focal length F of the prime lens satisfy: F6/F is more than or equal to 2.6 and less than or equal to 4.5.

17. The prime lens according to any one of claims 1 to 7, wherein the edge thickness ET8 of the eighth lens (L8) and the center thickness CT8 of the eighth lens (L8) satisfy: ET8/CT8 is more than or equal to 1.6 and less than or equal to 2.6.

18. The prime lens according to any one of claims 1 to 7, wherein the focal length F8 of the eighth lens (L8) and the effective focal length F of the prime lens satisfy: F8/F is not less than-4.6 and not more than-2.6.

19. The prime lens according to any one of claims 1 to 7, further comprising an optical filter,

the optical effective aperture SDF of the optical filter and the optical effective semi-aperture SD1 of the first lens (L1) satisfy: SDF/SD1 is more than or equal to 0.6 and less than or equal to 0.9.

20. The prime lens according to any of claims 1 to 7, wherein the optical effective diameter SDS of the Stop (STO) and the optical effective half-aperture SD1 of the first lens (L1) satisfy: SDS/SD1 is more than or equal to 0.5 and less than or equal to 0.9.