CN109445080B

CN109445080B - Lens

Info

Publication number: CN109445080B
Application number: CN201811643190.3A
Authority: CN
Inventors: 林法官; 刘凯
Original assignee: Zhejiang Dahua Technology Co Ltd
Current assignee: Zhejiang Dahua Technology Co Ltd
Priority date: 2018-12-29
Filing date: 2018-12-29
Publication date: 2021-02-02
Anticipated expiration: 2038-12-29
Also published as: CN109445080A

Abstract

The invention discloses a lens, which comprises a first positive focal power group, a first negative focal power group, a second positive focal power group and a third positive focal power group, wherein the first positive focal power group is provided with a first focal power; the first positive focal power group comprises a cemented lens consisting of a first concave lens and a first convex lens which are sequentially arranged from left to right, and a second convex lens; the first negative focal power group comprises a second concave lens, a third concave lens and a third convex lens which are sequentially arranged from left to right; the second positive focal power group comprises a fourth convex lens, a cemented lens consisting of a fourth concave lens and a fifth convex lens, and a cemented lens consisting of a sixth convex lens and a fifth concave lens, which are sequentially arranged from left to right; the third positive focal power group comprises a seventh convex lens, a cemented lens consisting of an eighth convex lens and a sixth concave lens, and a seventh concave lens which are sequentially arranged from left to right. The focal power group and the lens of the lens provided by the embodiment of the invention are reasonably distributed, and the requirement of a 4K resolution camera can be met.

Description

Lens

Technical Field

The invention relates to the technical field of optical imaging, in particular to a lens.

Background

Along with increasingly dense traffic networks and increasingly busy traffic, in order to maintain traffic safety, prevent traffic jam and realize order under busy road conditions; the lens with day and night confocal high resolution is provided for developing an intelligent traffic system, and has practical significance. Most of zoom lenses in the market have simple structure and low performance index, can only be adapted to standard definition CCD or CMOS cameras with 200 plus 300 ten thousand pixels in image definition, can only reach 600 ten thousand pixels in the existing lens with higher resolution, have common shooting effect and low picture value, and can only meet the requirement of watching in the monitoring field. Such a resolution has far failed to meet the requirements of the current 4K resolution cameras.

Disclosure of Invention

The embodiment of the invention provides a lens, which is used for solving the problem that the lens in the prior art cannot meet the requirement of a 4K resolution camera.

The embodiment of the invention provides a lens, wherein a first positive focal power group, a first negative focal power group, a second positive focal power group and a third positive focal power group are sequentially arranged in an optical system of the lens along the incident direction of light rays from left to right; a diaphragm is arranged between the first negative focal power group and the second positive focal power group, and an optical filter and an image plane are arranged on the right side of the third positive focal power group;

the first positive focal power group comprises a cemented lens consisting of a first concave lens and a first convex lens which are sequentially arranged from left to right, and a second convex lens; the first negative focal power group comprises a second concave lens, a third concave lens and a third convex lens which are sequentially arranged from left to right; the second positive focal power group comprises a fourth convex lens, a cemented lens consisting of a fourth concave lens and a fifth convex lens, and a cemented lens consisting of a sixth convex lens and a fifth concave lens, which are sequentially arranged from left to right; the third positive focal power group comprises a seventh convex lens, a cemented lens consisting of an eighth convex lens and a sixth concave lens, and a seventh concave lens which are sequentially arranged from left to right.

Further, the first concave lens, the third convex lens, the fifth concave lens and the sixth concave lens are all made of ultrahigh-refractive-index materials; the refractive indexes of the first concave lens, the third convex lens, the fifth concave lens and the sixth concave lens are all larger than 1.80.

Further, the absolute value of the ratio of the focal length of the second positive power group to the focal length of the first negative power group is greater than 2.1 and less than 2.8; the absolute value of the ratio of the focal length of the third positive power group to the focal length of the first negative power group is greater than 1.2 and less than 1.8.

Further, the first convex lens, the second convex lens, the third concave lens, the sixth convex lens and the seventh convex lens are made of low-dispersion materials; the abbe numbers of the first convex lens, the second convex lens, the third concave lens, the sixth convex lens and the seventh convex lens are all more than 65.

Further, the focal length range of the lens is greater than or equal to 8 millimeters and less than or equal to 40 millimeters.

Further, the field angle range of the lens is greater than or equal to 12 degrees and less than or equal to 65 degrees.

The embodiment of the invention provides a lens, wherein a first positive focal power group, a first negative focal power group, a second positive focal power group and a third positive focal power group are sequentially arranged in an optical system of the lens along the incident direction of light rays from left to right; a diaphragm is arranged between the first negative focal power group and the second positive focal power group, and an optical filter and an image plane are arranged on the right side of the third positive focal power group; the first positive focal power group comprises a cemented lens consisting of a first concave lens and a first convex lens which are sequentially arranged from left to right, and a second convex lens; the first negative focal power group comprises a second concave lens, a third concave lens and a third convex lens which are sequentially arranged from left to right; the second positive focal power group comprises a fourth convex lens, a cemented lens consisting of a fourth concave lens and a fifth convex lens, and a cemented lens consisting of a sixth convex lens and a fifth concave lens, which are sequentially arranged from left to right; the third positive focal power group comprises a seventh convex lens, a cemented lens consisting of an eighth convex lens and a sixth concave lens, and a seventh concave lens which are sequentially arranged from left to right.

The lens provided by the embodiment of the invention adopts a 4-group 15-piece type, namely 4 focal power groups, and 15 pieces of lenses are used in total. The optical power group and the lens are reasonably distributed, and the requirement of a 4K resolution camera can be met.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

Fig. 1 is a schematic view of a lens structure according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a lens provided in embodiment 1 of the present invention when the focal length is 8 mm;

fig. 3 is a schematic structural diagram of a lens provided in embodiment 1 of the present invention, the lens having a middle focal length of 25.1 mm;

fig. 4 is a schematic structural diagram of a lens provided in embodiment 1 of the present invention when the focal length is 40 mm;

fig. 5 is a transfer function curve diagram of a lens provided in embodiment 1 of the present invention in a white light scene when the lens is in a short focus;

fig. 6 is a transfer function graph of a lens provided in embodiment 1 of the present invention in a middle focus in a white light scene;

fig. 7 is a graph of a transfer function when a lens provided in embodiment 1 of the present invention is in a long focus in a white light scene;

fig. 8 is a transfer function curve diagram of the lens provided in embodiment 1 in the case of short focus in an infrared scene;

fig. 9 is a transfer function graph of a lens provided in embodiment 1 of the present invention in a middle focus in an infrared scene;

fig. 10 is a transfer function graph of the lens provided in embodiment 1 of the present invention when the lens is in a long focus in an infrared scene;

fig. 11 is a transfer function graph of a lens provided in embodiment 2 of the present invention in a short focus in a white light scene;

fig. 12 is a transfer function graph of a lens provided in embodiment 2 of the present invention in a middle focus in a white light scene;

fig. 13 is a graph of a transfer function when the lens provided in embodiment 2 of the present invention is in a long focus in a white light scene;

fig. 14 is a transfer function graph of a lens provided in embodiment 2 of the present invention in a short focus in an infrared scene;

fig. 15 is a transfer function graph of a lens provided in embodiment 2 of the present invention in a middle focus in an infrared scene;

fig. 16 is a transfer function graph of the lens provided in embodiment 2 of the present invention when the lens is in a long focus in an infrared scene.

Detailed Description

The present invention will be described in further detail with reference to the attached drawings, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Fig. 1 is a schematic structural diagram of a lens provided in an embodiment of the present invention, in an optical system of the lens, a first positive power group G1, a first negative power group G2, a second positive power group G3, and a third positive power group G4 are sequentially disposed along a left-to-right incident direction of light; a diaphragm P1 is arranged between the first negative power group G2 and the second positive power group G3, and a filter P2 and an image plane P3 are arranged on the right side of the third positive power group G4;

the first positive power group G1 comprises a cemented lens consisting of a first concave lens 1 and a first convex lens 2 which are sequentially arranged from left to right, and a second convex lens 3; the first negative power group G2 comprises a second concave lens 4, a third concave lens 5 and a third convex lens 6 which are arranged in sequence from left to right; the second positive power group G3 comprises a fourth convex lens 7, a cemented lens consisting of a fourth concave lens 8 and a fifth convex lens 9, and a cemented lens consisting of a sixth convex lens 10 and a fifth concave lens 11 which are arranged in sequence from left to right; the third positive power group G4 includes a seventh convex lens 12, a cemented lens of an eighth convex lens 13 and a sixth concave lens 14, and a seventh concave lens 15, which are arranged in this order from left to right.

The diaphragm P1 can be automatically and continuously adjusted, and can meet the intelligent requirements of modern optical instruments. Filter P2 is an optical device for selecting a desired wavelength band of radiation. The right side of the filter P2 is an image plane P3.

The lens provided by the embodiment of the invention adopts 4 groups of 15-piece type optical lenses, namely 4 focal power groups, and 15 pieces of lenses in total. The optical power group and the lens are reasonably distributed, and the requirement of a 4K resolution camera can be met.

In order to improve the refractive index of the lens and reduce the total length of the lens, the first concave lens 1, the third convex lens 6, the fifth concave lens 11 and the sixth concave lens 14 are made of ultrahigh refractive index materials; the refractive indexes of the first concave lens 1, the third convex lens 6, the fifth concave lens 11 and the sixth concave lens 14 are all larger than 1.80. For example, the refractive indices of the first concave lens 1, the third convex lens 6, the fifth concave lens 11, and the sixth concave lens 14 may be 1.9, 2.0, 2.1, etc., and the refractive indices of the first concave lens 1, the third convex lens 6, the fifth concave lens 11, and the sixth concave lens 14 may be the same or different.

In addition, when light rays of a spherical lens enter the lens and then reach a focal plane, serious refraction and bending are easy to occur at the edge part of the spherical lens than at the central part of the spherical lens, and the phenomenon can cause the reduction of sharpness and contrast and the generation of light spots, thereby causing the reduction of image quality. The aberration generated by the spherical lens is called spherical aberration. In the embodiment of the invention, the refractive indexes of the first concave lens 1, the third convex lens 6, the fifth concave lens 11 and the sixth concave lens 14 are all larger than 1.80, so that the spherical aberration can be reduced, and the image quality can be improved.

The refractive index of the first concave lens 1 is nd1, the refractive index of the third convex lens 6 is nd6, the refractive index of the fifth concave lens 11 is nd11, and the refractive index of the sixth concave lens 14 is nd 14. Wherein nd1 is more than 1.80, nd6 is more than 1.80, nd11 is more than 1.80, and nd14 is more than 1.80.

The first concave lens 1, the third convex lens 6, the fifth concave lens 11 and the sixth concave lens 14 are all made of ultrahigh refractive index materials, so that the refractive index of the lens can be improved, and the resolution of the lens is further improved. Moreover, by adopting the ultrahigh-refractive-index material, the thicknesses of the first concave lens 1, the third convex lens 6, the fifth concave lens 11 and the sixth concave lens 14 can be reduced, and the total length of the lens can be further reduced.

In order to achieve a better imaging effect within the focal length range of the lens, in the embodiment of the present invention, the absolute value of the ratio of the focal length of the second positive power group G3 to the focal length of the first negative power group G2 is greater than 2.1 and less than 2.8; the absolute value of the ratio of the focal length of the third positive power group G4 to the focal length of the first negative power group G2 is greater than 1.2 and less than 1.8. Too small a ratio of group focal lengths may shorten the lens length, but may increase spherical aberration, affect image quality, and reduce lens manufacturability. The ratio of the group focal length is too large, which can reduce spherical aberration, improve image quality and lens manufacturability, but the lens length is larger. In order to take into account the lens length and the spherical aberration and manufacturability of the lens, in the embodiment of the invention, a range of absolute values of the ratio of the focal length of the second positive power group G3 to the focal length of the first negative power group G2, and a range of absolute values of the ratio of the focal length of the third positive power group G4 to the focal length of the first negative power group G2 are provided. The sequential structure of the first negative power group G2, the second positive power group G3 and the third positive power group G4 results in that the range of the absolute value of the ratio of the focal length of the second positive power group G3 to the focal length of the first negative power group G2 is different from the range of the absolute value of the ratio of the focal length of the third positive power group G4 to the focal length of the first negative power group G2. In the embodiment of the present invention, the absolute value of the ratio of the focal length of the second positive power group G3 to the focal length of the first negative power group G2 is greater than 2.1 and less than 2.8; the absolute value of the ratio of the focal length of the third positive power group G4 to the focal length of the first negative power group G2 is greater than 1.2 and less than 1.8. The lens length, the spherical aberration and the manufacturability of the lens can be better considered.

For example, the absolute value of the ratio of the focal length of the second positive power group G3 to the focal length of the first negative power group G2 may be 2.2, 2.5, 2.7, etc.; the absolute value of the ratio of the focal length of the third positive power group G4 to the focal length of the first negative power group G2 may be 1.2, 1.5, 1.7, etc.

The focal length of the first negative power group G2 is fg2, the focal length of the second positive power group G3 is fg3, and the focal length of the third positive power group G4 is fg 4. The relationship among fg2, fg3 and fg4 is: 2.1< | fg3/fg2| < 2.8; 1.2< | fg4/fg2| < 1.8.

In order to realize day and night confocal and athermalization in the full focal section of the lens, namely clear imaging can be realized at-40 ℃ to 80 ℃, in the embodiment of the invention, the first convex lens 2, the second convex lens 3, the third concave lens 5, the sixth convex lens 10 and the seventh convex lens 12 are made of low-dispersion materials; the abbe numbers of the first convex lens 2, the second convex lens 3, the third concave lens 5, the sixth convex lens 10 and the seventh convex lens 12 are all more than 65. In addition, the abbe numbers of the first convex lens 2, the second convex lens 3, the third concave lens 5, the sixth convex lens 10 and the seventh convex lens 12 are all larger than 65, and the chromatic aberration of the image can be reduced, so that the image quality is improved. For example, the abbe numbers of the first convex lens 2, the second convex lens 3, the third concave lens 5, the sixth convex lens 10, and the seventh convex lens 12 may be 68, 70, or the like. The abbe numbers of the first convex lens 2, the second convex lens 3, the third concave lens 5, the sixth convex lens 10, and the seventh convex lens 12 may be the same or different.

The abbe number of the first convex lens 2 is Vd2, the abbe number of the second convex lens 3 is Vd3, the abbe number of the third concave lens 5 is Vd5, the abbe number of the sixth convex lens 10 is Vd10, and the abbe number of the seventh convex lens 12 is Vd 12. The Vd2>65, the Vd3>65, the Vd5>65, the Vd10>65 and the Vd12>65 are included.

The focal length range of the lens provided by the embodiment of the invention is more than or equal to 8mm and less than or equal to 40 mm. The relative aperture of the lens may be 1.4, 1.5, 1.6, etc. The diameter of the image plane may be 9.0 mm, 9.2 mm, 9.4 mm, etc. The field angle range of the lens is greater than or equal to 12 degrees and less than or equal to 65 degrees. It should be noted that, if the field angle of the lens is too large, the occupation ratio of the face image in the picture is small, the face image is unclear, and the recognition of the face image is affected. On the other hand, if the angle of view of the lens is too small, the whole face image may not be visible on the screen, which may also affect the recognition of the face image. In order to ensure that the face image can be identified, the embodiment of the invention provides a range of the field angle of the lens. Moreover, the angle of view of the lens is within a range of 12 degrees or more and 65 degrees or less, and the face recognition requirements can be well satisfied.

The focal length range of the lens in the prior art is generally 12-50 mm, and the short-focus field angle of the lens cannot meet the requirement of face recognition. In the embodiment of the invention, the focal length of the lens is 8-40mm, the field angle is 65 degrees when the focal length is 8mm, and the field angle is 12 degrees when the focal length is 40 mm. The short-focus lens provided by the embodiment of the invention has a larger field angle, so that the requirement of face recognition can be met. The relative aperture of the lens can be preferably 1.5, and the corresponding aperture value is larger, so that the imaging quality under the condition of weak light can be improved.

Moreover, in the embodiment of the present invention, the length of the lens may be less than 110 mm; the length of the lens is the distance from the left vertex of the first concave lens to the image plane. The lens provided by the embodiment of the invention has small volume, and the total length TTL can be controlled within 110 mm, so that the requirement of miniaturization of a camera can be met, and the lens has strong adaptability. Of course, the length of the lens can be increased according to the needs of the product. Therefore, the length of the lens provided by the embodiment of the invention is not limited to be less than 110 mm.

In addition, the lens provided by the embodiment of the invention is designed by reasonably selecting the glass lens material, so that chromatic aberration is better corrected, the day and night imaging quality is improved, the day and night dual-purpose requirement of the monitoring camera is met, and the use requirement of the temperature range of-40 ℃ to 80 ℃ is also met.

The distance is described below with respect to the lens parameters provided by the embodiment of the present invention.

Example 1:

the focal length range of the lens is 8-40mm, the relative aperture Fno is 1.5, and the total lens length TTL is 105 mm. Data of curvature radius, center thickness, refractive index nd, and abbe constant Vd of each lens are shown in table 1:

TABLE 1

Note that the surface numbers in table 1 are surface numbers of the lenses from left to right in the lens configuration diagram shown in fig. 1.

The data of D5, D11, D20 and D29 in Table 1 at the corresponding focal lengths are shown in Table 2:

focal length of system	D5	D11	D20	D29
					8.0mm	1.492	33.476	4.541	1.967
25.1mm	24.999	9.974	2.957	3.546
					40.0mm	32.254	2.709	3.700	2.813

TABLE 2

fg2：-16.471mm；fg3：41.965mm；fg4：24.183mm。

|fg3/fg2|＝2.548；|fg4/fg2|＝1.468。

nd1:1.847；nd6:1.946；nd11:1.911；nd14:1.883。

Vd2：81.608；Vd3：81.608；Vd5：95.100；Vd10：95.100；Vd12:81.608。

The schematic structural diagrams of the lens at the short focus of 8mm, the middle focus of 25.1mm and the long focus of 40.0mm are respectively shown in fig. 2, fig. 3 and fig. 4.

The lens provided in embodiment 1 will be further described below by performing detailed optical system analysis on embodiment 1. The optical transfer function is used for evaluating the imaging quality of an optical system in a more accurate, visual and common mode, and the higher and smoother curve of the optical transfer function indicates that the imaging quality of the system is better, and aberration is well corrected.

Fig. 5, 6, and 7 are graphs of transfer function (MTF) curves of the lens in a white light scene in a short focus, a middle focus, and a long focus, respectively, and the curves are smoothly dropped and concentrated as shown in fig. 5, 6, and 7. The MTF value can still be ensured to be larger than 0.2 at 160 lp/mm. Therefore, the performance of the lens of the system can reach the resolution of 800 ten thousand pixels under white light.

Fig. 8, 9 and 10 are graphs of transfer function (MTF) curves of the lens in the infrared 850nm state, as shown in fig. 8, 9 and 10, respectively, the curves are smoothly descending and concentrated. The MTF value is still guaranteed to be larger than 0.1 at 160lp/mm, and the value is required to be lower than that of the white light state. Therefore, the high resolution of the lens can be ensured under the infrared 850nm state.

Example 2:

the focal length range of the lens is 8-40mm, the relative aperture Fno is 1.5, and the total lens length TTL is 105 mm. Data of curvature radius, center thickness, refractive index nd, and abbe constant Vd of each lens are shown in table 2:

TABLE 3

The data of D5, D11, D20 and D29 in Table 3 at the corresponding system focal length are shown in Table 4:

focal length of system	D5	D11	D20	D29
					8.0mm	1.423	34.411	2.417	1.549
26.0mm	25.981	9.858	0.706	3.255
					40.0mm	32.850	2.979	1.368	2.603

TABLE 4

fg2：-16.700mm；fg3：39.881mm；fg4：25.588mm。

|fg3/fg2|＝2.388；|fg4/fg2|＝1.532。

nd1:1.921；nd6:2.003；nd11:1.900；nd14:1.870。

Vd2：81.608；Vd3：81.608；Vd5：95.100；Vd10：95.100；Vd12:90.195。

The lens provided in embodiment 2 will be further described below by performing a detailed optical system analysis on embodiment 2. Fig. 11, 12 and 13 are graphs of transfer functions (MTF) of the lens in short, middle and long foci in a white light scene, respectively, and the curves are smoothly dropped and concentrated as shown in fig. 11, 12 and 13. The MTF value can still be ensured to be larger than 0.2 at 160 lp/mm. Therefore, the performance of the lens of the system can reach the resolution of 800 ten thousand pixels under white light.

Fig. 14, 15 and 16 are graphs of transfer function (MTF) curves of the lens in the infrared 850nm state, as shown in fig. 14, 15 and 16, respectively, the curves being smoothly dropped and concentrated. The MTF value is still guaranteed to be larger than 0.1 at 160lp/mm, and the value is required to be lower than that of the white light state. Therefore, the high resolution of the lens can be ensured under the infrared 850nm state.

The lens provided by the embodiment of the invention adopts 4 groups of 15-piece type optical lenses, namely 4 focal power groups, and 15 pieces of lenses in total. The optical lenses are sequentially arranged from left to right according to a specific sequence, and adaptive optical glass materials are adopted through the distribution of focal power of each optical lens, so that the structural form of the lens system, the refractive index, Abbe coefficient and other parameters of the lenses are matched with imaging conditions, and further, the spherical aberration, the coma aberration, astigmatism, field curvature, chromatic aberration of magnification and position chromatic aberration of the lens system are well corrected, so that a large field angle, a larger aperture and a higher resolution are achieved, and a 4K pixel camera, better infrared confocal property and better athermal property are supported to the maximum; the structure is compact, the overall dimension is small, all optical lenses adopt spherical surface design, the cold processing performance is good, and the production cost is low; the method can be widely applied to the field of security monitoring and achieves all-weather ultrahigh-definition picture display.

The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims

1. A lens is characterized in that a first positive focal power group, a first negative focal power group, a second positive focal power group and a third positive focal power group are sequentially arranged in an optical system of the lens along the incident direction of light rays from left to right; a diaphragm is arranged between the first negative focal power group and the second positive focal power group, and an optical filter and an image plane are arranged on the right side of the third positive focal power group;

the first positive focal power group comprises a cemented lens consisting of a first concave lens and a first convex lens which are sequentially arranged from left to right, and a second convex lens; the first negative focal power group comprises a second concave lens, a third concave lens and a third convex lens which are sequentially arranged from left to right; the second positive focal power group comprises a fourth convex lens, a cemented lens consisting of a fourth concave lens and a fifth convex lens, and a cemented lens consisting of a sixth convex lens and a fifth concave lens, which are sequentially arranged from left to right; the third positive focal power group comprises a seventh convex lens, a cemented lens consisting of an eighth convex lens and a sixth concave lens and a seventh concave lens which are sequentially arranged from left to right;

the absolute value of the ratio of the focal length of the second positive focal power group to the focal length of the first negative focal power group is greater than 2.1 and less than 2.8; the absolute value of the ratio of the focal length of the third positive power group to the focal length of the first negative power group is greater than 1.2 and less than 1.8.

2. The lens barrel as claimed in claim 1, wherein the first concave lens, the third convex lens, the fifth concave lens and the sixth concave lens are all made of ultra-high refractive index material; the refractive indexes of the first concave lens, the third convex lens, the fifth concave lens and the sixth concave lens are all larger than 1.80.

3. The lens barrel as claimed in claim 1, wherein the first, second, third, sixth, and seventh convex lenses are made of a low dispersion material; the abbe numbers of the first convex lens, the second convex lens, the third concave lens, the sixth convex lens and the seventh convex lens are all more than 65.

4. The lens barrel as claimed in claim 1, wherein the focal length range of the lens barrel is 8mm or more and 40mm or less.

5. The lens barrel according to claim 1, wherein a field angle range of the lens barrel is 12 degrees or more and 65 degrees or less.