CN114637095B

CN114637095B - Imaging System

Info

Publication number: CN114637095B
Application number: CN202210243426.4A
Authority: CN
Inventors: 徐武超; 李晔; 戴付建; 赵烈烽
Original assignee: Zhejiang Sunny Optics Co Ltd
Current assignee: Zhejiang Sunny Optics Co Ltd
Priority date: 2022-03-11
Filing date: 2022-03-11
Publication date: 2024-07-12
Anticipated expiration: 2042-03-11
Also published as: CN114637095A

Abstract

The invention provides an imaging system. The imaging system comprises from an incident side to an emergent side: a first lens having a refractive power; the surface of the second lens close to the light incident side is a convex surface, and the surface of the second lens close to the light emergent side is a concave surface; a third lens having refractive power; the on-axis distance TTL from the surface of the first lens close to the light entrance side to the imaging surface of the imaging system and half of the diagonal length ImgH of the effective pixel area on the imaging surface satisfy: TTL/ImgH <1.6. The invention solves the problem that the lens in the prior art is difficult to miniaturize.

Description

Imaging system

Technical Field

The invention relates to the technical field of optical imaging equipment, in particular to an imaging system.

Background

In recent years, with the continuous upgrading and updating of electronic products such as mobile terminals, the demands of users for diversified functions of the products are increasing, and further, the demands of the lenses mounted on the mobile terminals are increasing, so that not only are the requirements for higher performance, but also the miniaturization of the lenses are required.

That is, the prior art lens has a problem in that it is difficult to miniaturize.

Disclosure of Invention

The invention mainly aims to provide an imaging system for solving the problem that a lens is difficult to miniaturize in the prior art.

In order to achieve the above object, according to one aspect of the present invention, there is provided an imaging system including, from an light-in side to a light-out side: a first lens having a refractive power; the surface of the second lens close to the light incident side is a convex surface, and the surface of the second lens close to the light emergent side is a concave surface; a third lens having refractive power; the on-axis distance TTL from the surface of the first lens close to the light entrance side to the imaging surface of the imaging system and half of the diagonal length ImgH of the effective pixel area on the imaging surface satisfy: TTL/ImgH <1.6.

Further, the effective focal length f3 of the third lens and the radius of curvature R5 of the surface of the third lens near the light-entering side satisfy: f3/R5<1.0.

Further, the on-axis distance TTL from the surface of the first lens close to the light-incident side to the imaging surface and the entrance pupil diameter EPD of the imaging system satisfy: 2.5< TTL/EPD <3.5.

Further, the height Do of the object and the minimum on-axis distance TOL between the object and the surface of the first lens near the light-incident side satisfy: 0.6< Do/TOL <1.2.

Further, the maximum half field angle Semi-FOV of the imaging system satisfies: semi-FOV >35 deg..

Further, the effective focal length f1 of the first lens and the effective focal length f2 of the second lens satisfy: f1/f2> -0.8.

Further, the combined focal length f12 of the first lens and the second lens and the combined focal length f23 of the second lens and the third lens satisfy the following conditions: 0.4< f12/f23<1.0.

Further, the curvature radius R1 of the surface of the first lens close to the light incident side and the curvature radius R2 of the surface of the first lens close to the light emergent side satisfy: R1/R2<2.5.

Further, the curvature radius R3 of the surface of the second lens close to the light incident side and the curvature radius R4 of the surface of the second lens close to the light emergent side satisfy: (R3-R4)/(R3+R4) | <0.8.

Further, the center thickness CT1 of the first lens on the optical axis of the imaging system and the center thickness CT3 of the third lens on the optical axis satisfy: 0.4< CT1/CT3<1.2.

Further, the air interval T12 on the optical axis of the imaging system between the first lens and the second lens, the sum Σat of the air intervals on the optical axis between any adjacent two lenses having refractive power among the first lens to the third lens, satisfies: 0.3< T12/ΣAT <0.9.

Further, the center thickness CT2 of the second lens on the optical axis of the imaging system, the air interval T23 of the second lens and the third lens on the optical axis, and the effective focal length f of the imaging system satisfy: (CT2+T23)/f <0.5.

Further, an on-axis distance SAG31 between an intersection point of the surface of the third lens close to the light entrance side and the optical axis of the imaging system and an effective radius vertex of the surface of the third lens close to the light entrance side, and an on-axis distance SAG32 between an intersection point of the surface of the third lens close to the light exit side and the optical axis and an effective radius vertex of the surface of the third lens close to the light exit side satisfy: 0.4< (SAG31+SAG32)/SAG 32<1.0.

Further, the on-axis distance SAG21 between the intersection point of the optical axis of the imaging system and the surface of the second lens close to the light entrance side and the effective radius vertex of the surface of the second lens close to the light entrance side, and the on-axis distance SAG22 between the intersection point of the optical axis and the surface of the second lens close to the light exit side and the effective radius vertex of the surface of the second lens close to the light exit side satisfy: (SAG 21-SAG 22)/(SAG21+SAG22) <0.7.

Further, the effective half-aperture DT11 of the surface of the first lens close to the light-incident side, the effective half-aperture DT21 of the surface of the second lens close to the light-incident side, and the effective half-aperture DT31 of the surface of the third lens close to the light-incident side satisfy: 0.5< (DT 11+DT 21)/DT 31<1.2.

Further, the distance BFL between the surface of the third lens close to the light emitting side and the imaging surface on the optical axis of the imaging system, and the axial distance SD between the aperture of the imaging system and the surface of the third lens close to the light emitting side satisfy: 0.4< BFL/SD <1.0.

According to another aspect of the present invention, there is provided an imaging system including, from an entrance side to an exit side: a first lens having a refractive power; the surface of the second lens close to the light incident side is a convex surface, and the surface of the second lens close to the light emergent side is a concave surface; a third lens having refractive power; the on-axis distance TTL from the surface of the first lens close to the light-in side to the imaging surface and the entrance pupil diameter EPD of the imaging system satisfy the following conditions: 2.5< TTL/EPD <3.5.

By applying the technical scheme of the invention, the imaging system comprises a first lens, a second lens and a third lens from the light incident side to the light emergent side. The first lens has refractive power; the second lens has negative refractive power, the surface of the second lens close to the light incident side is a convex surface, and the surface of the second lens close to the light emergent side is a concave surface; the third lens has refractive power; the on-axis distance TTL from the surface of the first lens close to the light entrance side to the imaging surface of the imaging system and half of the diagonal length ImgH of the effective pixel area on the imaging surface satisfy: TTL/ImgH <1.6.

By distributing the refractive power of part of the lenses of the imaging system and designing the surface type of the lenses, the low-order aberration of the imaging system can be effectively balanced, the sensitivity of the tolerance of the imaging system can be reduced, the miniaturization of the imaging system is kept, and the imaging quality of the imaging system is ensured. The refractive power and the surface shape of the second lens are reasonably controlled, so that the low-order aberration of the imaging system can be controlled. By controlling the ratio of the total length to the image height of the imaging system, the total size of the imaging system can be effectively reduced, and the ultra-thin characteristic and miniaturization of the imaging system can be realized.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:

FIG. 1 is a schematic diagram showing the structure of an imaging system according to an example I of the present invention;

Fig. 2 to 5 show on-axis chromatic aberration curves, astigmatism curves, distortion curves, and magnification chromatic aberration curves, respectively, of the imaging system in fig. 1;

FIG. 6 shows a schematic structural diagram of an imaging system of example two of the present invention;

fig. 7 to 10 show on-axis chromatic aberration curves, astigmatism curves, distortion curves, and magnification chromatic aberration curves, respectively, of the imaging system in fig. 6;

FIG. 11 shows a schematic configuration of an imaging system of example III of the present invention;

Fig. 12 to 15 show on-axis chromatic aberration curves, astigmatism curves, distortion curves, and magnification chromatic aberration curves, respectively, of the imaging system in fig. 11;

FIG. 16 is a schematic diagram showing the construction of an imaging system of example IV of the invention;

fig. 17 to 20 show on-axis chromatic aberration curves, astigmatism curves, distortion curves, and magnification chromatic aberration curves, respectively, of the imaging system in fig. 16;

FIG. 21 is a schematic diagram showing the construction of an imaging system of example five of the present invention;

fig. 22 to 25 show on-axis chromatic aberration curves, astigmatism curves, distortion curves, and magnification chromatic aberration curves, respectively, of the imaging system in fig. 21;

fig. 26 is a schematic diagram showing the configuration of an imaging system of example six of the present invention;

fig. 27 to 30 show an on-axis chromatic aberration curve, an astigmatism curve, a distortion curve, and a magnification chromatic aberration curve, respectively, of the imaging system in fig. 26.

Wherein the above figures include the following reference numerals:

STO and diaphragm; e1, a first lens; s1, a surface of a first lens, which is close to a light incident side, is provided; s2, the surface of the first lens close to the light emitting side; e2, a second lens; s3, the surface of the second lens close to the light incident side; s4, the surface of the second lens close to the light emitting side; e3, a third lens; s5, the surface of the third lens close to the light incident side; s6, the surface of the third lens close to the light emitting side; e4, a filter; s7, the surface of the filter close to the light incident side; s8, the surface of the filter close to the light emitting side; s9, an imaging surface.

Detailed Description

It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be combined with each other. The application will be described in detail below with reference to the drawings in connection with embodiments.

It is noted that all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs unless otherwise indicated.

In the present invention, unless otherwise indicated, terms of orientation such as "upper, lower, top, bottom" are used generally with respect to the orientation shown in the drawings or with respect to the component itself in the vertical, upright or gravitational direction; also, for ease of understanding and description, "inner and outer" refers to inner and outer relative to the profile of each component itself, but the above-mentioned orientation terms are not intended to limit the present invention.

It should be noted that in the present specification, the expressions of first, second, third, etc. are only used to distinguish one feature from another feature, and do not represent any limitation on the feature. Accordingly, a first lens discussed below may also be referred to as a second lens or a third lens without departing from the teachings of the present application.

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

Herein, the paraxial region refers to a region near the optical axis. If the lens surface is convex and the convex position is not defined, then the lens surface is convex at least in the paraxial region; if the lens surface is concave and the concave position is not defined, it means that the lens surface is concave at least in the paraxial region. The determination of the surface shape in the paraxial region can be performed by a determination method by a person skilled in the art by positive or negative determination of the concave-convex with R value (R means the radius of curvature of the paraxial region, and generally means the R value on a lens database (lens data) in optical software). The surface near the light incident side is judged to be convex when the R value is positive, and is judged to be concave when the R value is negative; the surface near the light-emitting side is determined to be concave when the R value is positive, and is determined to be convex when the R value is negative.

In order to solve the problem that the lens is difficult to miniaturize in the prior art, the invention provides an imaging system.

Example 1

As shown in fig. 1 to 30, the imaging system includes a first lens, a second lens, and a third lens from an incident light side to an exit light side. The first lens has refractive power; the second lens has negative refractive power, the surface of the second lens close to the light incident side is a convex surface, and the surface of the second lens close to the light emergent side is a concave surface; the third lens has refractive power; the on-axis distance TTL from the surface of the first lens close to the light entrance side to the imaging surface of the imaging system and half of the diagonal length ImgH of the effective pixel area on the imaging surface satisfy: TTL/ImgH <1.6.

Preferably, the on-axis distance TTL from the surface of the first lens close to the light entrance side to the imaging surface of the imaging system and half the diagonal length ImgH of the effective pixel area on the imaging surface satisfy: 1.0< TTL/ImgH <1.5.

In the present embodiment, the effective focal length f3 of the third lens and the radius of curvature R5 of the surface of the third lens near the light incident side satisfy: f3/R5<1.0. The ratio of the effective focal length of the third lens to the curvature radius of the surface of the third lens close to the light incident side is reasonably restrained, the refractive power of the imaging system can be reasonably distributed, and the third-order astigmatism of the imaging system can be controlled within a certain range, so that the imaging system has good imaging quality. Preferably 0.2< f3/R5<0.95.

In this embodiment, the on-axis distance TTL from the surface of the first lens near the light-incident side to the imaging surface and the entrance pupil diameter EPD of the imaging system satisfy: 2.5< TTL/EPD <3.5. The ratio of the total optical length to the entrance pupil diameter of the imaging system is controlled within a reasonable numerical range, so that the ultra-thin characteristic and miniaturization of the imaging system are realized, the collection capacity of the imaging system to object information is maintained, and the imaging quality of the imaging system is ensured. Preferably 2.7< TTL/EPD <3.3.

In the present embodiment, the height Do of the subject and the minimum on-axis distance TOL from the subject to the surface of the first lens on the light-incident side satisfy: 0.6< Do/TOL <1.2. The ratio of the height of the shot object to the minimum axial distance from the shot object to the surface of the first lens, which is close to the light incident side, is controlled within a reasonable numerical range, so that the collection capability of the imaging system on the object side information is improved, and the collection range of the imaging system on the object side information is ensured. Preferably 0.8< Do/TOL <1.1.

In the present embodiment, the maximum half field angle Semi-FOV of the imaging system satisfies: semi-FOV >35 deg.. And the half of the maximum field angle of the imaging system is restrained, so that a larger field range is obtained, the collection capacity of the imaging system to object information is improved, and the imaging effect of the imaging system with a small wide angle is realized. Preferably, 40 ° < Semi-FOV <50 °.

In the present embodiment, the effective focal length f1 of the first lens and the effective focal length f2 of the second lens satisfy: f1/f2> -0.8. The ratio of the effective focal length of the first lens to the effective focal length of the second lens is reasonably controlled, so that the spherical aberration contribution rate of the first lens and the second lens to the imaging system is favorably controlled, and the imaging system has good imaging quality on an on-axis view field. Preferably, -0.3< f1/f2< -0.75.

In the present embodiment, the sum focal length f12 of the first lens and the second lens and the sum focal length f23 of the second lens and the third lens satisfy: 0.4< f12/f23<1.0. The ratio of the synthesized focal length of the first lens and the second lens to the synthesized focal length of the second lens and the synthesized focal length of the third lens are controlled within a reasonable numerical range, so that the refractive power of the first lens, the refractive power of the second lens and the refractive power of the third lens are reasonably distributed in space, and further aberration of an imaging system is reduced. Preferably 0.6< f12/f23<10.95.

In the present embodiment, the curvature radius R1 of the surface of the first lens near the light entrance side and the curvature radius R2 of the surface of the first lens near the light exit side satisfy: R1/R2<2.5. The curvature radius of the surface of the first lens close to the light incident side and the curvature radius of the surface of the first lens close to the light emergent side are reasonably controlled, so that the deflection angle of the marginal light rays of the imaging system can be effectively controlled, and the sensitivity of the imaging system is effectively reduced. Preferably 0.2< R1/R2<2.4.

In the present embodiment, the curvature radius R3 of the surface of the second lens near the light entrance side and the curvature radius R4 of the surface of the second lens near the light exit side satisfy: (R3-R4)/(R3+R4) | <0.8. The ratio of the difference and sum of the surface curvature radius of the second lens close to the light incident side and the surface curvature radius of the second lens close to the light emergent side is controlled within a reasonable numerical range, so that the reasonable matching of the curvature radii of the two sides of the second lens is facilitated, the shape of the second lens, the refraction angle of the light beam and the contribution of the second lens to astigmatism of an imaging system can be effectively controlled, the second lens has good processability, and the imaging system has good imaging quality. Preferably, 0.2< | (R3-R4)/(R3+R4) | <0.7.

In the present embodiment, the center thickness CT1 of the first lens on the optical axis of the imaging system and the center thickness CT3 of the third lens on the optical axis satisfy: 0.4< CT1/CT3<1.2. The ratio of the center thicknesses of the first lens and the third lens is controlled within a reasonable numerical range, so that the thicknesses of the first lens and the third lens can be effectively balanced, the product yield is prevented from being influenced due to the fact that the thickness of the first lens is too thin, meanwhile, the stability of an imaging system can be improved, and the sensitivity of the imaging system is reduced. Preferably 0.6< CT1/CT3<1.1.

In the present embodiment, the air interval T12 on the optical axis of the imaging system between the first lens and the second lens, the sum Σat of the air intervals on the optical axis between any adjacent two lenses having refractive power among the first lens to the third lens, satisfies: 0.3< T12/ΣAT <0.9. The air interval on the optical axis between each lens is reasonably distributed, so that the processing and assembling characteristics can be ensured, and the problem of front and rear lens interference in the assembling process caused by too small interval is avoided. Meanwhile, the method is favorable for slowing down light deflection, adjusting field curvature of an imaging system, reducing sensitivity of the imaging system and further obtaining better imaging quality. Preferably, 0.4< T12/ΣAT <0.8.

In the present embodiment, the center thickness CT2 of the second lens on the optical axis of the imaging system, the air interval T23 of the second lens and the third lens on the optical axis, and the effective focal length f of the imaging system satisfy: (CT2+T23)/f <0.5. The ratio of the distance from the surface of the second lens close to the light incident side to the surface of the third lens close to the light incident side on the optical axis to the effective focal length is controlled within a reasonable numerical range, so that the imaging system has higher aberration correcting capability and better manufacturability can be obtained. Preferably 0.1< (CT2+T23)/f <0.3.

In the present embodiment, an on-axis distance SAG31 between an intersection point of the surface of the third lens close to the light entrance side and the optical axis of the imaging system to an effective radius vertex of the surface of the third lens close to the light entrance side, and an on-axis distance SAG32 between an intersection point of the surface of the third lens close to the light exit side and the optical axis to an effective radius vertex of the surface of the third lens close to the light exit side satisfy: 0.4< (SAG31+SAG32)/SAG 32<1.0. The ratio of the sum of the sagittal heights of the two surfaces of the third lens to the sagittal height of the surface close to the light emergent side is controlled within a reasonable numerical range, so that the shape of the third lens is favorably controlled, the processability of the third lens is improved, the deflection angle of light rays of an imaging system is favorably controlled, and the imaging system has better imaging quality. Preferably, 0.5< (SAG31+SAG32)/SAG 32<0.9.

In the present embodiment, an on-axis distance SAG21 between an intersection point of the surface of the second lens close to the light entrance side and the optical axis of the imaging system to an effective radius vertex of the surface of the second lens close to the light entrance side, and an on-axis distance SAG22 between an intersection point of the surface of the second lens close to the light exit side and the optical axis to an effective radius vertex of the surface of the second lens close to the light exit side satisfy: (SAG 21-SAG 22)/(SAG21+SAG22) <0.7. The ratio of the sagittal height difference and the sum of the two surfaces of the second lens is reasonably controlled, so that the shape of the second lens is controlled, the processability of the second lens is improved, the deflection angle of light rays of an imaging system is controlled, and the imaging system has better imaging quality. Preferably, 0< (SAG 21-SAG 22)/(SAG21+SAG22) <0.5.

In the present embodiment, the effective half-aperture DT11 of the surface of the first lens close to the light-incident side, the effective half-aperture DT21 of the surface of the second lens close to the light-incident side, and the effective half-aperture DT31 of the surface of the third lens close to the light-incident side satisfy: 0.5< (DT 11+DT 21)/DT 31<1.2. The effective half-caliber ratio of the surfaces of the first lens and the second lens close to the light incident side and the surface of the third lens close to the light incident side is controlled to be within a reasonable numerical range, so that the deflection height of the marginal light rays of the imaging system can be effectively controlled, and the sensitivity of the imaging system is effectively reduced. Preferably 0.6< (dt11+dt21)/DT 31<1.1.

In the present embodiment, the distance BFL between the surface of the third lens close to the light exit side and the imaging surface on the optical axis of the imaging system, and the on-axis distance SD between the aperture of the imaging system and the surface of the third lens close to the light exit side satisfy: 0.4< BFL/SD <1.0. The ratio of the distance from the surface of the third lens close to the light emitting side to the imaging surface on the optical axis to the distance from the aperture to the surface of the third lens close to the light emitting side is controlled within a reasonable numerical range, so that the optical back focal length and the height of the lens can be reasonably distributed, and the imaging system can be conveniently assembled. Preferably, 0.5< BFL/SD <0.9.

Example two

As shown in fig. 1 to 30, the imaging system includes a first lens, a second lens, and a third lens from an incident light side to an exit light side. The first lens has refractive power; the second lens has negative refractive power, the surface of the second lens close to the light incident side is a convex surface, and the surface of the second lens close to the light emergent side is a concave surface; the third lens has refractive power; the on-axis distance TTL from the surface of the first lens close to the light-in side to the imaging surface and the entrance pupil diameter EPD of the imaging system satisfy the following conditions: 2.5< TTL/EPD <3.5.

By distributing the refractive power of part of the lenses of the imaging system and designing the surface type of the lenses, the low-order aberration of the imaging system can be effectively balanced, the sensitivity of the tolerance of the imaging system can be reduced, the miniaturization of the imaging system is kept, and the imaging quality of the imaging system is ensured. The ratio of the total optical length to the entrance pupil diameter of the imaging system is controlled within a reasonable numerical range, so that the ultra-thin characteristic and miniaturization of the imaging system are realized, the collection capacity of the imaging system to object information is maintained, and the imaging quality of the imaging system is ensured.

Preferably, the on-axis distance TTL from the surface of the first lens close to the light entrance side to the imaging surface and the entrance pupil diameter EPD of the imaging system satisfy: 2.7< TTL/EPD <3.3.

Optionally, the imaging system may further include a filter for correcting color deviation and/or a protective glass for protecting the photosensitive element located on the imaging surface.

The imaging system in the present application may employ multiple lenses, such as the three described above. By reasonably distributing the refractive power, the surface shape, the center thickness of each lens, the axial distance between each lens and the like, the imaging quality of the imaging system can be effectively increased, the sensitivity of the imaging system can be reduced, and the processability of the imaging system can be improved, so that the imaging system is more beneficial to production and processing and can be suitable for portable electronic equipment such as smart phones and the like.

In the present application, at least one of the mirror surfaces of each lens is an aspherical mirror surface. The aspherical lens is characterized in that: the curvature varies continuously from the center of the lens to the periphery of the lens. Unlike a spherical lens having a constant curvature from the center of the lens to the periphery of the lens, an aspherical lens has a better radius of curvature characteristic, and has advantages of improving distortion aberration and improving astigmatic aberration. By adopting the aspherical lens, aberration occurring at the time of imaging can be eliminated as much as possible, thereby improving imaging quality.

However, those skilled in the art will appreciate that the number of lenses making up the imaging system can be varied to achieve the various results and advantages described in this specification without departing from the scope of the application as claimed. For example, although three lenses are described as an example in the embodiment, the imaging system is not limited to including three lenses. The imaging system may also include other numbers of lenses, if desired.

Examples of specific aspects, parameters, which may be applicable to the imaging system of the above-described embodiments are further described below with reference to the accompanying drawings.

Any of the following examples one to six is applicable to all embodiments of the present application.

Example one

As shown in fig. 1 to 5, an imaging system of an example one of the present application is described. Fig. 1 shows a schematic configuration diagram of an imaging system of example one.

As shown in fig. 1, the imaging system sequentially includes, from an object side to an image side: stop STO, first lens E1, second lens E2, third lens E3, filter E4, and imaging plane S9.

The first lens E1 has positive refractive power, a surface S1 of the first lens close to the light incident side is a convex surface, and a surface S2 of the first lens close to the light emergent side is a concave surface. The second lens E2 has negative refractive power, a surface S3 of the second lens close to the light incident side is a convex surface, and a surface S4 of the second lens close to the light emergent side is a concave surface. The third lens E3 has positive refractive power, a surface S5 of the third lens close to the light incident side is a convex surface, and a surface S6 of the third lens close to the light emergent side is a concave surface. The filter E4 has a surface S7 of the filter close to the light entrance side and a surface S8 of the filter close to the light exit side. Light from the object sequentially passes through the respective surfaces S1 to S8 and is finally imaged on the imaging surface S9.

In this example, the imaging system has an image height ImgH of 1.72mm. The total length TTL of the imaging system is 2.17mm.

Table 1 shows a basic structural parameter table of the imaging system of example one, in which the radius of curvature, thickness/distance, and focal length are all in millimeters (mm).

TABLE 1

In the first example, the surface of any one of the first lens E1 to the third lens E3 near the light incident side and the surface near the light emergent side are both aspheric, and the surface shape of each aspheric lens can be defined by, but not limited to, the following aspheric formula:

Wherein x is the distance vector height from the vertex of the aspheric surface when the aspheric surface is at the position with the height h along the optical axis direction; c is the paraxial curvature of the aspheric surface, c=1/R (i.e., paraxial curvature c is the inverse of radius of curvature R in table 1 above); k is a conic coefficient; ai is the correction coefficient of the aspherical i-th order. The following Table 2 shows the higher order coefficients A4, A6, A8, A10, A12, A14, A16, A18, A20, A22, A24, A26, A28, A30 that can be used for each of the aspherical mirrors S1-S6 in example one.

Face number

A4

A6

A8

A10

A12

A14

A16

S1

-3.2285E+00

4.8723E+02

-4.5202E+04

2.8210E+06

-1.2331E+08

3.8599E+09

-8.7609E+10

S2

-2.2148E+00

3.0496E+02

-2.2770E+04

1.0653E+06

-3.3906E+07

7.6766E+08

-1.2648E+10

S3

-1.7828E+00

-1.0686E+02

8.6249E+03

-3.6166E+05

1.0058E+07

-1.9461E+08

2.6725E+09

S4

-5.3242E+00

8.1098E+00

1.4875E+03

-4.3009E+04

6.9662E+05

-7.5274E+06

5.7125E+07

S5

-3.4131E+00

1.4698E+01

-7.5209E+01

3.3547E+02

-1.2274E+03

3.6236E+03

-8.3828E+03

S6

-3.6143E-01

-7.8792E+00

6.8453E+01

-3.5566E+02

1.2560E+03

-3.1264E+03

5.5934E+03

Face number

A18

A20

A22

A24

A26

A28

A30

S1

1.4488E+12

-1.7402E+13

1.4984E+14

-8.9962E+14

3.5708E+15

-8.4123E+15

8.8986E+15

S2

1.5288E+11

-1.3509E+12

8.5965E+12

-3.8225E+13

1.1234E+14

-1.9548E+14

1.5205E+14

S3

-2.6319E+10

1.8605E+11

-9.3455E+11

3.2508E+12

-7.4336E+12

1.0038E+13

-6.0583E+12

S4

-3.1081E+08

1.2183E+09

-3.4104E+09

6.6486E+09

-8.5715E+09

6.5666E+09

-2.2627E+09

S5

1.4663E+04

-1.8800E+04

1.7198E+04

-1.0862E+04

4.4886E+03

-1.0908E+03

1.1816E+02

S6

-7.2641E+03

6.8484E+03

-4.6342E+03

2.1909E+03

-6.8623E+02

1.2781E+02

-1.0703E+01

TABLE 2

Fig. 2 shows an on-axis chromatic aberration curve of the imaging system of example one, which represents the deviation of the converging focus of light rays of different wavelengths after passing through the imaging system. Fig. 3 shows an astigmatism curve of the imaging system of example one, which represents meridional image surface curvature and sagittal image surface curvature. Fig. 4 shows a distortion curve of the imaging system of example one, which represents distortion magnitude values corresponding to different angles of view. Fig. 5 shows a magnification chromatic aberration curve of the imaging system of example one, which represents the deviation of different image heights on the imaging plane after light passes through the imaging system.

As can be seen from fig. 2 to 5, the imaging system according to example one can achieve good imaging quality.

Example two

As shown in fig. 6 to 10, an imaging system of example two of the present application is described. Fig. 6 shows a schematic configuration of an imaging system of example two.

As shown in fig. 6, the imaging system sequentially includes, from an object side to an image side: stop STO, first lens E1, second lens E2, third lens E3, filter E4, and imaging plane S9.

In this example, the imaging system has an image height ImgH of 1.72mm. The total length TTL of the imaging system is 2.13mm.

Table 3 shows a basic structural parameter table of the imaging system of example two, in which the radius of curvature, thickness/distance, and focal length are all in millimeters (mm).

TABLE 3 Table 3

Table 4 shows the higher order coefficients that can be used for each of the aspherical mirror surfaces in example two, where each of the aspherical surface types can be defined by equation (1) given in example one above.

Face number

A4

A6

A8

A10

A12

A14

S1

-7.4746E-01

5.4483E+01

-2.1601E+03

5.0126E+04

-7.1246E+05

6.2229E+06

S2

-5.4814E-01

4.0593E+01

-1.4594E+03

2.8282E+04

-3.2081E+05

2.1254E+06

S3

-2.1938E+00

2.5295E+00

1.0057E+03

-3.2695E+04

5.5029E+05

-5.7065E+06

S4

-5.0521E+00

6.2730E+01

-6.8720E+02

5.6740E+03

-3.3190E+04

1.3354E+05

S5

-3.3022E+00

1.8886E+01

-1.1036E+02

4.4652E+02

-1.2050E+03

2.1721E+03

S6

-1.0169E+00

2.9856E+00

-1.3357E+01

4.0187E+01

-7.6453E+01

9.3348E+01

Face number

A16

A18

A20

A22

A24

S1

-3.2331E+07

9.0902E+07

-1.0570E+08

0.0000E+00

S2

-7.8106E+06

1.3528E+07

-6.3375E+06

0.0000E+00

S3

3.7651E+07

-1.5505E+08

3.6919E+08

-4.1357E+08

8.7458E+07

S4

-3.5981E+05

6.1916E+05

-6.1471E+05

2.6788E+05

0.0000E+00

S5

-2.6150E+03

2.0749E+03

-1.0422E+03

3.0067E+02

-3.7995E+01

S6

-7.3162E+01

3.5525E+01

-9.6912E+00

1.1306E+00

0.0000E+00

TABLE 4 Table 4

Fig. 7 shows an on-axis chromatic aberration curve for the imaging system of example two, which represents the deviation of the converging focus of light rays of different wavelengths after passing through the imaging system. Fig. 8 shows an astigmatism curve of the imaging system of example two, which represents meridional image surface curvature and sagittal image surface curvature. Fig. 9 shows a distortion curve of the imaging system of example two, which represents distortion magnitude values corresponding to different angles of view. Fig. 10 shows a chromatic aberration of magnification curve of the imaging system of example two, which represents the deviation of different image heights on the imaging plane after light passes through the imaging system.

As can be seen from fig. 7 to 10, the imaging system according to the second example can achieve good imaging quality.

Example three

As shown in fig. 11 to 15, an imaging system of example three of the present application is described. Fig. 11 shows a schematic configuration diagram of an imaging system of example three.

As shown in fig. 11, the imaging system sequentially includes, from an object side to an image side: stop STO, first lens E1, second lens E2, third lens E3, filter E4, and imaging plane S9.

In this example, the imaging system has an image height ImgH of 1.72mm. The total length TTL of the imaging system is 2.16mm.

Table 5 shows a basic structural parameter table of the imaging system of example three, in which the radius of curvature, thickness/distance, and focal length are all in millimeters (mm).

TABLE 5

Table 6 shows the higher order coefficients that can be used for each of the aspherical mirror surfaces in example three, where each of the aspherical surface types can be defined by the formula (1) given in example one above.

TABLE 6

Fig. 12 shows an on-axis chromatic aberration curve for the imaging system of example three, which represents the convergent focus offset of light rays of different wavelengths after passing through the imaging system. Fig. 13 shows an astigmatism curve of the imaging system of example three, which represents meridional image surface curvature and sagittal image surface curvature. Fig. 14 shows a distortion curve of the imaging system of example three, which represents distortion magnitude values corresponding to different angles of view. Fig. 15 shows a chromatic aberration of magnification curve of the imaging system of example three, which represents the deviation of different image heights on the imaging plane after light passes through the imaging system.

As can be seen from fig. 12 to 15, the imaging system of example three can achieve good imaging quality.

Example four

As shown in fig. 16 to 20, an imaging system of example four of the present application is described. Fig. 16 shows a schematic configuration diagram of an imaging system of example four.

As shown in fig. 16, the imaging system sequentially includes, from an object side to an image side: stop STO, first lens E1, second lens E2, third lens E3, filter E4, and imaging plane S9.

In this example, the imaging system has an image height ImgH of 1.72mm. The total length TTL of the imaging system is 2.24mm.

Table 7 shows a basic structural parameter table of the imaging system of example four, in which the radius of curvature, thickness/distance, and focal length are all in millimeters (mm).

TABLE 7

Table 8 shows the higher order coefficients that can be used for each of the aspherical mirror surfaces in example four, where each of the aspherical surface types can be defined by the formula (1) given in example one above.

Face number

A4

A6

A8

A10

A12

A14

A16

S1

-9.5073E-01

6.0257E+01

-2.1220E+03

4.3422E+04

-5.4630E+05

4.2707E+06

-2.0185E+07

S2

-2.7854E-01

1.2260E+01

-4.0963E+02

6.4539E+03

-5.7724E+04

2.9192E+05

-7.7327E+05

S3

-2.4821E+00

2.5441E+01

-1.7578E+02

-8.5261E+03

4.0266E+05

-9.0582E+06

1.2922E+08

S4

-4.1572E+00

2.6883E+01

7.6680E+01

-7.1358E+03

1.3365E+05

-1.5039E+06

1.1513E+07

S5

-2.1834E+00

6.0285E+00

-2.5724E+01

1.3807E+02

-8.3954E+02

4.0014E+03

-1.3135E+04

S6

-9.8282E-02

-4.9009E+00

3.4372E+01

-1.7671E+02

6.7178E+02

-1.8716E+03

3.8195E+03

Face number

A18

A20

A22

A24

A26

A28

A30

S1

5.2688E+07

-5.8171E+07

0.0000E+00

S2

7.8156E+05

1.8475E+05

0.0000E+00

S3

-1.2607E+09

8.6437E+09

-4.1761E+10

1.3954E+11

-3.0744E+11

4.0226E+11

-2.3696E+11

S4

-6.2322E+07

2.4120E+08

-6.6323E+08

1.2648E+09

-1.5891E+09

1.1822E+09

-3.9424E+08

S5

2.9405E+04

-4.5222E+04

4.7762E+04

-3.4066E+04

1.5691E+04

-4.2178E+03

5.0294E+02

S6

-5.7055E+03

6.1993E+03

-4.8252E+03

2.6125E+03

-9.3175E+02

1.9634E+02

-1.8479E+01

TABLE 8

Fig. 17 shows an on-axis chromatic aberration curve of the imaging system of example four, which represents the convergent focus deviation of light rays of different wavelengths after passing through the imaging system. Fig. 18 shows an astigmatism curve of the imaging system of example four, which represents meridional image surface curvature and sagittal image surface curvature. Fig. 19 shows a distortion curve of the imaging system of example four, which represents distortion magnitude values corresponding to different angles of view. Fig. 20 shows a magnification chromatic aberration curve of the imaging system of example four, which represents the deviation of different image heights on the imaging plane after light passes through the imaging system.

As can be seen from fig. 17 to 20, the imaging system as given in example four can achieve good imaging quality.

Example five

As shown in fig. 21 to 25, an imaging system of example five of the present application is described. Fig. 21 shows a schematic configuration diagram of an imaging system of example five.

As shown in fig. 21, the imaging system sequentially includes, from an object side to an image side: stop STO, first lens E1, second lens E2, third lens E3, filter E4, and imaging plane S9.

In this example, the imaging system has an image height ImgH of 1.72mm. The total length TTL of the imaging system is 2.29mm.

Table 9 shows a basic structural parameter table of the imaging system of example five, in which the radius of curvature, thickness/distance, and focal length are all in millimeters (mm).

TABLE 9

Table 10 shows the higher order coefficients that can be used for each of the aspherical mirror surfaces in example five, where each of the aspherical surface types can be defined by equation (1) given in example one above.

Face number

A4

A6

A8

A10

A12

A14

A16

S1

-9.5251E-01

5.4273E+01

-1.7669E+03

3.3347E+04

-3.8645E+05

2.7802E+06

-1.2087E+07

S2

-2.5151E-01

6.4506E+00

-2.2168E+02

3.2323E+03

-2.6359E+04

1.2089E+05

-2.9062E+05

S3

-1.6917E+00

1.6672E+00

1.5182E+02

-2.5998E+03

2.0498E+04

-1.1006E+05

1.2117E+06

S4

-3.2265E+00

-6.6530E+00

7.5404E+02

-1.5524E+04

1.9436E+05

-1.6760E+06

1.0357E+07

S5

-1.8471E+00

-1.4113E+00

8.3747E+01

-9.0988E+02

5.8760E+03

-2.5777E+04

8.0246E+04

S6

-8.8152E-02

-2.3480E+00

-9.2702E-01

7.8361E+01

-5.1901E+02

1.9678E+03

-5.0006E+03

Face number

A18

A20

A22

A24

A26

A28

A30

S1

2.9020E+07

-2.9476E+07

0.0000E+00

S2

2.6851E+05

5.4366E+04

0.0000E+00

S3

-1.9152E+07

1.9375E+08

-1.2047E+09

4.7196E+09

-1.1447E+10

1.5763E+10

-9.4513E+09

S4

-4.6554E+07

1.5238E+08

-3.5904E+08

5.9245E+08

-6.4903E+08

4.2354E+08

-1.2449E+08

S5

-1.8005E+05

2.9124E+05

-3.3547E+05

2.6764E+05

-1.4026E+05

4.3366E+04

-5.9889E+03

S6

8.9432E+03

-1.1430E+04

1.0396E+04

-6.5731E+03

2.7453E+03

-6.8046E+02

7.5729E+01

Table 10

Fig. 22 shows an on-axis chromatic aberration curve of the imaging system of example five, which represents the deviation of the converging focus of light rays of different wavelengths after passing through the imaging system. Fig. 23 shows an astigmatism curve of the imaging system of example five, which represents meridional image plane curvature and sagittal image plane curvature. Fig. 24 shows a distortion curve of the imaging system of example five, which represents distortion magnitude values corresponding to different angles of view. Fig. 25 shows a magnification chromatic aberration curve of the imaging system of example five, which represents the deviation of different image heights on the imaging plane after light passes through the imaging system.

As can be seen from fig. 22 to 25, the imaging system of example five can achieve good imaging quality.

Example six

As shown in fig. 26 to 30, an imaging system of example six of the present application is described. Fig. 26 shows a schematic configuration of an imaging system of example six.

As shown in fig. 26, the imaging system sequentially includes, from an object side to an image side: stop STO, first lens E1, second lens E2, third lens E3, filter E4, and imaging plane S9.

In this example, the imaging system has an image height ImgH of 1.72mm. The total length TTL of the imaging system is 2.38mm.

Table 11 shows a basic structural parameter table of the imaging system of example six, in which the radius of curvature, thickness/distance, and focal length are all in millimeters (mm).

TABLE 11

Table 12 shows the higher order coefficients that can be used for each of the aspherical mirror surfaces in example six, where each of the aspherical surface types can be defined by equation (1) given in example one above.

Table 12

Fig. 27 shows an on-axis chromatic aberration curve of the imaging system of example six, which represents the convergent focus deviation of light rays of different wavelengths after passing through the imaging system. Fig. 28 shows an astigmatism curve of the imaging system of example six, which represents meridional image surface curvature and sagittal image surface curvature. Fig. 29 shows a distortion curve of the imaging system of example six, which represents distortion magnitude values corresponding to different angles of view. Fig. 30 shows a magnification chromatic aberration curve of the imaging system of example six, which represents the deviation of different image heights on the imaging plane after light passes through the imaging system.

As can be seen from fig. 27 to 30, the imaging system given in example six can achieve good imaging quality.

In summary, examples one to six satisfy the relationships shown in table 13, respectively.

Conditional\example	1	2	3	4	5	6
							TTL/ImgH	1.26	1.24	1.25	1.30	1.33	1.39
f/f3	0.85	0.69	0.71	0.76	0.82	0.85
							f3/R5	0.89	0.26	0.27	0.28	0.29	0.28
TTL/EPD	3.17	3.04	3.05	2.88	2.80	2.75
							Do/TOL	0.99	1.01	0.99	0.95	0.93	0.88
Semi-FOV	44.6	45.3	44.8	43.7	43.0	41.4
							f1/f2	-0.69	-0.48	-0.49	-0.54	-0.59	-0.64
f12/f23	0.79	0.65	0.67	0.76	0.88	0.84
							R1/R2	2.37	0.44	0.44	0.39	0.37	0.35
\|(R3-R4)/(R3+R4)\|	0.65	0.40	0.40	0.36	0.32	0.33
							CT1/CT3	0.66	0.66	0.67	0.76	0.83	0.98
T12/∑AT	0.58	0.54	0.55	0.61	0.66	0.69
							(CT2+T23)/f	0.24	0.25	0.25	0.22	0.21	0.19
(SAG31+SAG32)/SAG32	0.61	0.73	0.73	0.70	0.82	0.68
							(SAG21-SAG22)/(SAG21+SAG22)	0.06	0.43	0.43	0.25	0.40	0.28
(DT11+DT21)/DT31	0.70	0.74	0.76	0.86	0.97	1.06
							BFL/SD	0.63	0.59	0.61	0.67	0.71	0.78

TABLE 13

Table 14 shows effective focal lengths f1 to f3 of the respective lenses of the imaging systems of examples one to six.

TABLE 14

The application also provides an imaging device, wherein the electronic photosensitive element can be a photosensitive coupling element (CCD) or a complementary metal oxide semiconductor element (CMOS). The imaging device may be a stand alone imaging device such as a digital camera or an imaging module integrated on a mobile electronic device such as a cell phone. The imaging device is equipped with the imaging system described above.

It will be apparent that the embodiments described above are merely some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.

It should be noted that the terms "first," "second," and the like in the description and the claims of the present application and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that embodiments of the application described herein may be implemented in sequences other than those illustrated or otherwise described herein.

The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An imaging system, wherein the imaging system has three refractive lenses, and the imaging system comprises, from an incident side to an emergent side:

the surface of the first lens close to the light incident side is a convex surface, and the surface of the first lens close to the light emergent side is a concave surface;

The surface of the second lens close to the light incident side is a convex surface, and the surface of the second lens close to the light emergent side is a concave surface;

the surface of the third lens close to the light incident side is a convex surface, and the surface of the third lens close to the light emergent side is a concave surface;

An on-axis distance TTL from a surface of the first lens near the light incident side to an imaging surface of the imaging system and a half of a diagonal length ImgH of an effective pixel area on the imaging surface satisfy: 1.0< TTL/ImgH <1.6;

the effective focal length f3 of the third lens and the curvature radius R5 of the surface of the third lens close to the light incident side satisfy: 0.2< f3/R5<1.0.

2. The imaging system of claim 1, wherein an on-axis distance TTL between a surface of the first lens near the light entrance side to the imaging surface and an entrance pupil diameter EPD of the imaging system satisfies: 2.5< TTL/EPD <3.5.

3. The imaging system of claim 1, wherein a height Do of a subject and a minimum on-axis distance TOL between the subject and a surface of the first lens near the light entrance side satisfy: 0.6< Do/TOL <1.2.

4. The imaging system of claim 1, wherein a maximum half field angle Semi-FOV of the imaging system satisfies: semi-FOV >35 deg..

5. The imaging system of claim 1, wherein an effective focal length f1 of the first lens and an effective focal length f2 of the second lens satisfy: f1/f2> -0.8.

6. The imaging system of claim 1, wherein a combined focal length f12 of the first lens and the second lens and a combined focal length f23 of the second lens and the third lens satisfy: 0.4< f12/f23<1.0.

7. The imaging system of claim 1, wherein a radius of curvature R1 of a surface of the first lens near the light entrance side and a radius of curvature R2 of a surface of the first lens near the light exit side satisfy: R1/R2<2.5.

8. The imaging system of claim 1, wherein a radius of curvature R3 of a surface of the second lens near the light entrance side and a radius of curvature R4 of a surface of the second lens near the light exit side satisfy:

|(R3-R4)/(R3+R4)|<0.8。

9. The imaging system of claim 1, wherein a center thickness CT1 of the first lens on an optical axis of the imaging system and a center thickness CT3 of the third lens on the optical axis satisfy: 0.4< CT1/CT3<1.2.

10. The imaging system according to claim 1, wherein a sum Σat of an air interval T12 on an optical axis of the imaging system between the first lens and the second lens, an air interval on an optical axis between any adjacent two lenses having refractive power of the first lens to the third lens satisfies: 0.3< T12/ΣAT <0.9.

11. The imaging system of claim 1, wherein a center thickness CT2 of the second lens on an optical axis of the imaging system, an air space T23 of the second lens and the third lens on the optical axis, and an effective focal length f of the imaging system satisfy: (CT2+T23)/f <0.5.

12. The imaging system according to claim 1, wherein an on-axis distance SAG31 between an intersection point of the surface of the third lens close to the light entrance side and an optical axis of the imaging system to an effective radius vertex of the surface of the third lens close to the light entrance side, an on-axis distance SAG32 between an intersection point of the surface of the third lens close to the light exit side and the optical axis to an effective radius vertex of the surface of the third lens close to the light exit side satisfies: 0.4< (SAG31+SAG32)/SAG 32<1.0.

13. The imaging system according to claim 1, wherein an on-axis distance SAG21 between an intersection point of the surface of the second lens near the light entrance side and an optical axis of the imaging system to an effective radius vertex of the surface of the second lens near the light entrance side, an on-axis distance SAG22 between an intersection point of the surface of the second lens near the light exit side and the optical axis to an effective radius vertex of the surface of the second lens near the light exit side satisfies:

(SAG21-SAG22)/(SAG21+SAG22)<0.7。

14. The imaging system of claim 1, wherein an effective half-caliber DT11 of a surface of the first lens near the light entrance side, an effective half-caliber DT21 of a surface of the second lens near the light entrance side, and an effective half-caliber DT31 of a surface of the third lens near the light entrance side satisfy: 0.5< (DT 11+DT 21)/DT 31<1.2.

15. The imaging system according to claim 1, wherein a distance BFL between a surface of the third lens on a light-emitting side and the imaging surface on an optical axis of the imaging system, and an on-axis distance SD between an aperture of the imaging system and a surface of the third lens on the light-emitting side satisfy: 0.4< BFL/SD <1.0.

16. An imaging system, wherein the imaging system has three refractive lenses, and the imaging system comprises, from an incident side to an emergent side:

An on-axis distance TTL from a surface of the first lens near the light entrance side to an imaging surface of the imaging system and an entrance pupil diameter EPD of the imaging system satisfy: 2.5< TTL/EPD <3.5;

17. The imaging system of claim 16, wherein a height Do of a subject and a minimum on-axis distance TOL between the subject and a surface of the first lens near the light entrance side satisfy: 0.6< Do/TOL <1.2.

18. The imaging system of claim 16, wherein a maximum half field angle Semi-FOV of the imaging system satisfies: semi-FOV >35 deg..

19. The imaging system of claim 16, wherein an effective focal length f1 of the first lens and an effective focal length f2 of the second lens satisfy: f1/f2> -0.8.

20. The imaging system of claim 16, wherein a combined focal length f12 of the first lens and the second lens and a combined focal length f23 of the second lens and the third lens satisfy: 0.4< f12/f23<1.0.

21. The imaging system of claim 16, wherein a radius of curvature R1 of a surface of the first lens near the light entrance side and a radius of curvature R2 of a surface of the first lens near the light exit side satisfy: R1/R2<2.5.

22. The imaging system of claim 16, wherein a radius of curvature R3 of a surface of the second lens near the light entrance side and a radius of curvature R4 of a surface of the second lens near the light exit side satisfy:

|(R3-R4)/(R3+R4)|<0.8。

23. The imaging system of claim 16, wherein a center thickness CT1 of the first lens on an optical axis of the imaging system and a center thickness CT3 of the third lens on the optical axis satisfy: 0.4< CT1/CT3<1.2.

24. The imaging system of claim 16, wherein a sum Σat of an air interval T12 on an optical axis of the imaging system between the first lens and the second lens, an air interval on an optical axis between any adjacent two lenses having refractive power of the first lens to the third lens, is satisfied: 0.3< T12/ΣAT <0.9.

25. The imaging system of claim 16, wherein a center thickness CT2 of the second lens on an optical axis of the imaging system, an air spacing T23 of the second lens and the third lens on the optical axis, and an effective focal length f of the imaging system satisfy: (CT2+T23)/f <0.5.

26. The imaging system of claim 16, wherein an on-axis distance SAG31 between an intersection of a surface of the third lens near the light entrance side and an optical axis of the imaging system to an effective radius vertex of a surface of the third lens near the light entrance side, an on-axis distance SAG32 between an intersection of a surface of the third lens near the light exit side and the optical axis to an effective radius vertex of a surface of the third lens near the light exit side, satisfies: 0.4< (SAG31+SAG32)/SAG 32<1.0.

27. The imaging system of claim 16, wherein an on-axis distance SAG21 between an intersection of a surface of the second lens near the light entrance side and an optical axis of the imaging system to an effective radius vertex of a surface of the second lens near the light entrance side, and an on-axis distance SAG22 between an intersection of a surface of the second lens near the light exit side and the optical axis to an effective radius vertex of a surface of the second lens near the light exit side satisfy:

(SAG21-SAG22)/(SAG21+SAG22)<0.7。

28. The imaging system of claim 16, wherein an effective half-caliber DT11 of a surface of the first lens near the light entrance side, an effective half-caliber DT21 of a surface of the second lens near the light entrance side, and an effective half-caliber DT31 of a surface of the third lens near the light entrance side satisfy: 0.5< (DT 11+DT 21)/DT 31<1.2.

29. The imaging system of claim 16, wherein a distance BFL between a surface of the third lens near the light exit side and the imaging surface on an optical axis of the imaging system, and an on-axis distance SD between an aperture of the imaging system and a surface of the third lens near the light exit side satisfy: 0.4< BFL/SD <1.0.