CN114442279B

CN114442279B - Imaging system

Info

Publication number: CN114442279B
Application number: CN202210134132.8A
Authority: CN
Inventors: 杨泉锋; 贺凌波; 戴付建; 赵烈烽
Original assignee: Zhejiang Sunny Optics Co Ltd
Current assignee: Zhejiang Sunny Optics Co Ltd
Priority date: 2022-02-14
Filing date: 2022-02-14
Publication date: 2024-03-22
Anticipated expiration: 2042-02-14
Also published as: CN114442279A

Abstract

The invention provides an imaging system, which comprises the following components from the light inlet side of the imaging system to the light outlet side of the imaging system: a first lens having negative optical power, a surface of the first lens close to the light incident side being a concave surface; a second lens having optical power; the surface of the third lens close to the light emergent side is a convex surface; a fourth lens having negative optical power, the fourth lens having an Abbe number of less than 20; a fifth lens having optical power; a sixth lens having optical power; wherein the maximum field angle FOV of the imaging system satisfies: FOV >120 °. The invention solves the problem that the imaging system 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

Along with the rapid development of electronic products such as smart phones and tablet computers, the demand of portable electronic products for lenses is increased, the quality requirement of people for imaging the lenses is also increased, and the trend is to push the portable electronic products to develop toward miniaturization. In order to meet the market demands, the lens needs to be as thin and small as possible, and thus the design difficulty increases. Meanwhile, as the performance of the image sensor is improved and the size of the image sensor is reduced, the degree of freedom of the design of the corresponding lens is smaller and smaller, and the design difficulty is increased.

That is, the imaging system in the related art has a problem in that it is difficult to miniaturize.

Disclosure of Invention

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

In order to achieve the above object, according to one aspect of the present invention, there is provided an imaging system including, from an entrance side of the imaging system to an exit side of the imaging system: a first lens having negative optical power, a surface of the first lens close to the light incident side being a concave surface; a second lens having optical power; the surface of the third lens close to the light emergent side is a convex surface; a fourth lens having negative optical power, the fourth lens having an Abbe number of less than 20; a fifth lens having optical power; a sixth lens having optical power; wherein the maximum field angle FOV of the imaging system satisfies: FOV >120 °.

Further, the effective focal length f of the imaging system and the entrance pupil diameter EPD of the imaging system satisfy: f/EPD < 2.3.

Further, the effective focal length f2 of the second lens and the effective focal length f5 of the fifth lens satisfy: 1.0 < f2/f5 < 2.5.

Further, the curvature radius R3 of the surface of the second lens on the light incident side and the curvature radius R11 of the surface of the sixth lens on the light incident side satisfy: R3/R11 is more than 2.0 and less than 5.0.

Further, the curvature radius R9 of the surface of the fifth lens on the light incident side and the curvature radius R12 of the surface of the sixth lens on the light exit side satisfy: R9/R12 is more than 1.5 and less than 2.6.

Further, the curvature radius R3 of the surface of the second lens on the light incident side and the curvature radius R12 of the surface of the sixth lens on the light exit side satisfy: R3/R12 is more than 2.0 and less than 5.0.

Further, the center thickness CT1 of the first lens on the optical axis and the center thickness CT2 of the second lens on the optical axis satisfy: CT2/CT1 is more than 1.5 and less than 4.0.

Further, the center thickness CT3 of the third lens on the optical axis and the air interval T34 of the third lens and the fourth lens on the optical axis satisfy: CT3/T34 is less than 2.0 and less than 3.0.

Further, the center thickness CT4 of the fourth lens on the optical axis and the center thickness CT6 of the sixth lens on the optical axis satisfy: CT6/CT4 is less than or equal to 1.5 and less than 2.0.

Further, the on-axis distance SAG11 between the intersection point of the optical axis and the surface of the first lens close to the light incident side and the effective radius vertex of the surface of the first lens close to the light incident side, and the on-axis distance SAG12 between the intersection point of the optical axis and the surface of the first lens close to the light exiting side and the effective radius vertex of the surface of the first lens close to the light exiting side satisfy: 1.0 < SAG12/SAG11 < 3.0.

Further, the on-axis distance SAG52 between the intersection point of the optical axis and the surface of the fifth lens close to the light exit side and the effective radius vertex of the surface of the fifth lens close to the light exit side, and the on-axis distance SAG61 between the intersection point of the optical axis and the surface of the sixth lens close to the light entrance side and the effective radius vertex of the surface of the sixth lens close to the light entrance side satisfy: 0.5 < SAG61/SAG52 < 2.5.

Further, the combined focal length f12 of the first lens and the second lens and the effective focal length f of the imaging system satisfy: -4.0 < f12/f < -2.5.

Further, the combined focal length f34 of the third lens and the fourth lens and the effective focal length f of the imaging system satisfy: f34/f is more than 3.0 and less than 5.0.

Further, the combined focal length f456 of the fourth lens, the fifth lens and the sixth lens and the effective focal length f of the imaging system satisfy: f456/f is more than 3.0 and less than 5.5.

Further, the abbe number V2 of the second lens satisfies: v2 < 25.

According to another aspect of the present invention, there is provided an imaging system, comprising, from an entrance side of the imaging system to an exit side of the imaging system: a first lens having negative optical power, a surface of the first lens close to the light incident side being a concave surface; a second lens having optical power; the surface of the third lens close to the light emergent side is a convex surface; a fourth lens having negative optical power, the fourth lens having an Abbe number of less than 20; a fifth lens having optical power; a sixth lens having optical power; the combined focal length f12 of the first lens and the second lens and the effective focal length f of the imaging system satisfy the following conditions: -4.0 < f12/f < -2.5.

Further, the abbe number V2 of the second lens satisfies: v2 < 25.

By applying the technical scheme of the invention, the imaging system comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens from the light incident side of the imaging system to the light emergent side of the imaging system. The first lens has negative focal power, and the surface of the first lens close to the light incident side is a concave surface; the second lens has optical power; the third lens has focal power, and the surface of the third lens close to the light emergent side is a convex surface; the fourth lens has negative focal power, and the Abbe number of the fourth lens is smaller than 20; the fifth lens has optical power; the sixth lens has optical power; wherein the maximum field angle FOV of the imaging system satisfies: FOV >120 °.

The positive and negative distribution of the focal power of each lens of the imaging system is reasonably controlled, so that 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. By limiting the FOV to a reasonable range, the imaging system can still have a good imaging range under a certain volume, meeting the needs of a wide-angle lens. That is, the imaging system still has better imaging effect while meeting miniaturization.

Drawings

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

FIGS. 2-4 show on-axis, astigmatic, and magnification chromatic aberration curves, respectively, of the imaging system of FIG. 1;

FIG. 5 shows a schematic structural diagram of an imaging system of example two of the present invention;

fig. 6 to 8 show on-axis chromatic aberration curves, astigmatism curves, and magnification chromatic aberration curves, respectively, of the imaging system in fig. 5;

FIG. 9 is a schematic diagram showing the structure of an imaging system of example III of the present invention;

FIGS. 10-12 show on-axis, astigmatic, and magnification chromatic aberration curves, respectively, of the imaging system of FIG. 9;

FIG. 13 is a schematic diagram showing the structure of an imaging system of example IV of the invention;

fig. 14 to 16 show on-axis chromatic aberration curves, astigmatism curves, and magnification chromatic aberration curves, respectively, of the imaging system in fig. 13;

FIG. 17 is a schematic diagram showing the construction of an imaging system of example five of the present invention;

fig. 18 to 20 show on-axis chromatic aberration curves, astigmatism curves, and magnification chromatic aberration curves, respectively, of the imaging system in fig. 17;

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

fig. 22 to 24 show an on-axis chromatic aberration curve, an astigmatism curve, and a magnification chromatic aberration curve, respectively, of the imaging system in fig. 21.

Wherein the above figures include the following reference numerals:

e1, a first lens; s1, a surface of a first lens, which is close to the light incident side, is provided; s2, a surface of the first lens, which is close to the light emergent side, is formed; 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; STO and diaphragm; 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 fourth lens; s7, a surface of the fourth lens close to the light incident side; s8, the surface of the fourth lens close to the light emitting side; e5, a fifth lens; s9, the surface of the fifth lens close to the light incident side; s10, a surface of the fifth lens close to the light emitting side; e6, a sixth lens; s11, a surface of the sixth lens close to the light incident side; s12, a surface of the sixth lens close to the light emitting side; e7, a filter; s13, a surface of the filter close to the light incident side; s14, the surface of the filter close to the light emitting side; s15, an imaging surface.

Detailed Description

It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other. The invention 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 determined to be convex when the R value is positive, and is determined 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 imaging system in the prior art is difficult to miniaturize, the invention provides an imaging system.

Example 1

As shown in fig. 1 to 24, the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are included from the light entrance side of the imaging system to the light exit side of the imaging system. The first lens has negative focal power, and the surface of the first lens close to the light incident side is a concave surface; the second lens has optical power; the third lens has focal power, and the surface of the third lens close to the light emergent side is a convex surface; the fourth lens has negative focal power, and the Abbe number of the fourth lens is smaller than 20; the fifth lens has optical power; the sixth lens has optical power; wherein the maximum field angle FOV of the imaging system satisfies: FOV >120 °.

Preferably 121 DEG < FOV < 140 deg.

In the present embodiment, the effective focal length f of the imaging system and the entrance pupil diameter EPD of the imaging system satisfy: f/EPD < 2.3. By limiting the f/EPD within a reasonable range, the imaging system can be ensured to have a larger aperture, so that the luminous flux of the imaging system is increased to enhance the imaging effect in dark environment, meanwhile, the aberration of the edge view field can be reduced, and the imaging quality of the imaging system is ensured. Preferably, 2.1 < f/EPD < 2.3.

In the present embodiment, the effective focal length f2 of the second lens and the effective focal length f5 of the fifth lens satisfy: 1.0 < f2/f5 < 2.5. By limiting f2/f5 to a reasonable range, better balance of aberration of the imaging system is facilitated, and resolution of the imaging system is improved. Preferably, 1.1 < f2/f5 < 2.4.

In the present embodiment, the curvature radius R3 of the surface of the second lens on the light-incident side and the curvature radius R11 of the surface of the sixth lens on the light-incident side satisfy: R3/R11 is more than 2.0 and less than 5.0. The ratio of the radius of curvature of the surface of the second lens close to the light incident side to the radius of curvature of the surface of the sixth lens close to the light incident side is limited within a certain range, so that the stability of the assembly of the imaging system can be improved. Preferably, 2.2 < R3/R11 < 4.8.

In the present embodiment, the curvature radius R9 of the surface of the fifth lens on the light-incident side and the curvature radius R12 of the surface of the sixth lens on the light-exit side satisfy: R9/R12 is more than 1.5 and less than 2.6. The ratio of the radius of curvature of the surface of the fifth lens close to the light incident side to the radius of curvature of the surface of the sixth lens close to the light emergent side is limited within a certain range, so that the stability of the assembly of the imaging system is improved. Preferably, 1.6 < R9/R12 < 2.45.

In the present embodiment, the curvature radius R3 of the surface of the second lens on the light incident side and the curvature radius R12 of the surface of the sixth lens on the light exit side satisfy: R3/R12 is more than 2.0 and less than 5.0. The ratio of the curvature radius of the surface of the second lens close to the light incident side to the curvature radius of the surface of the sixth lens close to the light emergent side is limited in a certain range, so that the stability of the assembly of the imaging system is improved. Preferably, 2.1 < R3/R12 < 4.9.

In the present embodiment, the center thickness CT1 of the first lens on the optical axis and the center thickness CT2 of the second lens on the optical axis satisfy: CT2/CT1 is more than 1.5 and less than 4.0. By controlling CT2/CT1 within a reasonable range, the stability of lens assembly is improved. Preferably, 1.6 < CT2/CT1 < 3.6.

In the present embodiment, the center thickness CT3 of the third lens on the optical axis and the air interval T34 of the third lens and the fourth lens on the optical axis satisfy: CT3/T34 is less than 2.0 and less than 3.0. By limiting CT3/T34 to a reasonable range, the imaging system can be made to have a smaller field curvature to ensure the imaging quality of the imaging system. Preferably, 2.0 < CT3/T34 < 2.8.

In the present embodiment, the center thickness CT4 of the fourth lens on the optical axis and the center thickness CT6 of the sixth lens on the optical axis satisfy: CT6/CT4 is less than or equal to 1.5 and less than 2.0. The CT6/CT4 is limited in a reasonable range, so that the lens assembly is facilitated, and the stability and convenience of the lens assembly are improved. Preferably, CT6/CT4 is less than or equal to 1.5 and less than or equal to 1.99.

In the present embodiment, the on-axis distance SAG11 between the intersection point of the surface of the first lens close to the light entrance side and the optical axis and the effective radius vertex of the surface of the first lens close to the light entrance side, and the on-axis distance SAG12 between the intersection point of the surface of the first lens close to the light exit side and the optical axis and the effective radius vertex of the surface of the first lens close to the light exit side satisfy: 1.0 < SAG12/SAG11 < 3.0. By controlling SAG12/SAG11 within a reasonable range, the imaging system is beneficial to having smaller incidence angle and higher relative illumination when the chief ray is incident on the image plane, and is beneficial to having better processability of the first lens. Preferably, 1.1 < SAG12/SAG11 < 2.8.

In the present embodiment, the on-axis distance SAG52 between the intersection of the surface of the fifth lens on the light exit side and the optical axis and the effective radius vertex of the surface of the fifth lens on the light exit side, and the on-axis distance SAG61 between the intersection of the surface of the sixth lens on the light entrance side and the optical axis and the effective radius vertex of the surface of the sixth lens on the light entrance side satisfy: 0.5 < SAG61/SAG52 < 2.5. By controlling SAG61/SAG52 within a reasonable range, the fifth lens and the sixth lens are prevented from being excessively bent, the processing difficulty is reduced, and the imaging system has better stability. Preferably, 0.55 < SAG61/SAG52 < 2.4.

In the present embodiment, the combined focal length f12 of the first lens and the second lens and the effective focal length f of the imaging system satisfy: -4.0 < f12/f < -2.5. By limiting f12/f to a reasonable range, the imaging system is facilitated to have smaller spherical aberration, and good imaging quality of the on-axis field of view is ensured. Preferably, -3.9 < f12/f < -2.55.

In the present embodiment, the combined focal length f34 of the third lens and the fourth lens and the effective focal length f of the imaging system satisfy: f34/f is more than 3.0 and less than 5.0. By controlling f34/f within a reasonable range, the imaging system is facilitated to be able to better balance aberrations while the resolution of the imaging system is facilitated to be improved. Preferably, 3.1 < f34/f < 4.95.

In the present embodiment, the combined focal length f456 of the fourth lens, the fifth lens, and the sixth lens, and the effective focal length f of the imaging system satisfy: f456/f is more than 3.0 and less than 5.5. By controlling f456/f within a reasonable range, aberration of the marginal view field is reduced, and imaging quality of an imaging system is guaranteed. Preferably, 3.2 < f456/f < 5.4.

In the present embodiment, the abbe number V2 of the second lens satisfies: v2 < 25. By reducing the Abbe number of the lens, the chromatic aberration of the imaging system can be reduced, and the imaging quality of the imaging system can be ensured. Preferably, 20 < V2 < 25.

Example two

As shown in fig. 1 to 24, the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are included from the light entrance side of the imaging system to the light exit side of the imaging system. The first lens has negative focal power, and the surface of the first lens close to the light incident side is a concave surface; the second lens has optical power; the third lens has focal power, and the surface of the third lens close to the light emergent side is a convex surface; the fourth lens has negative focal power, and the Abbe number of the fourth lens is smaller than 20; the fifth lens has optical power; the sixth lens has optical power; the combined focal length f12 of the first lens and the second lens and the effective focal length f of the imaging system satisfy the following conditions: -4.0 < f12/f < -2.5.

The positive and negative distribution of the focal power of each lens of the imaging system is reasonably controlled, so that 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. By limiting f12/f to a reasonable range, the imaging system is facilitated to have smaller spherical aberration, and good imaging quality of the on-axis field of view is ensured.

Preferably, the combined focal length f12 of the first lens and the second lens and the effective focal length f of the imaging system satisfy: -3.9 < f12/f < -2.55.

In the present embodiment, the center thickness CT3 of the third lens on the optical axis and the air interval T34 of the third lens and the fourth lens on the optical axis satisfy: CT3/T34 is less than 2.0 and less than 3.0. By limiting CT3/T34 to a reasonable range, the imaging system can be made to have a smaller field curvature to ensure the imaging quality of the imaging system. Preferably, 2.0 < CT3/T34 < 2.8. In the present embodiment, the center thickness CT4 of the fourth lens on the optical axis and the center thickness CT6 of the sixth lens on the optical axis satisfy: CT6/CT4 is less than or equal to 1.5 and less than 2.0. The CT6/CT4 is limited in a reasonable range, so that the lens assembly is facilitated, and the stability and convenience of the lens assembly are improved. Preferably, CT6/CT4 is less than or equal to 1.5 and less than or equal to 1.99.

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 this application may employ multiple lenses, such as the six lenses described above. By reasonably distributing the focal power, the surface shape, the center thickness of each lens, the axial distance between each lens and the like of each lens, the aperture of an imaging system can be effectively increased, the sensitivity of a lens 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 mirrors of each lens is an aspherical mirror. 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 the specification without departing from the technical solutions claimed herein. For example, although six lenses are described as an example in the embodiment, the imaging system is not limited to including six 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.

It should be noted that 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 4, an imaging system of example one of the present application is described. Fig. 1 shows a schematic diagram of an imaging system configuration of example one.

As shown in fig. 1, the imaging system sequentially includes, from an incident side to an emergent side: a first lens E1, a second lens E2, a stop STO, a third lens E3, a fourth lens E4, a fifth lens E5, a sixth lens E6, a filter E7, and an imaging surface S15.

The first lens E1 has negative power, a surface S1 of the first lens close to the light incident side is a concave surface, and a surface S2 of the first lens close to the light exiting side is a concave surface. The second lens E2 has positive focal 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 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 exiting side is a convex surface. The fourth lens E4 has negative power, a surface S7 of the fourth lens adjacent to the light incident side is a convex surface, and a surface S8 of the fourth lens adjacent to the light exiting side is a concave surface. The fifth lens E5 has positive power, a surface S9 of the fifth lens close to the light incident side is a convex surface, and a surface S10 of the fifth lens close to the light exiting side is a convex surface. The sixth lens E6 has positive power, a surface S11 of the sixth lens close to the light incident side is a convex surface, and a surface S12 of the sixth lens close to the light exiting side is a concave surface. The filter E7 has a surface S13 on the light-incident side of the filter and a surface S14 on the light-emergent side of the filter. Light from the object sequentially passes through the respective surfaces S1 to S14 and is finally imaged on the imaging surface S15.

In the present example, the total effective focal length f of the imaging system is 1.57mm, the total length TTL of the imaging system is 6.50mm and the image height ImgH is 3.1mm.

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 sixth lens E6 near the light entrance side and the surface near the light exit side are both aspherical, and the surface shape of each aspherical lens can be defined by, but not limited to, the following aspherical 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-S12 in example one.

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 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 4, the imaging system according to example one can achieve good imaging quality.

Example two

As shown in fig. 5 to 8, an imaging system of example two of the present application is described. In this example and the following examples, a description of portions similar to those of example one will be omitted for the sake of brevity. Fig. 5 shows a schematic diagram of an imaging system configuration of example two.

As shown in fig. 5, the imaging system sequentially includes, from an incident side to an emergent side: a first lens E1, a second lens E2, a stop STO, a third lens E3, a fourth lens E4, a fifth lens E5, a sixth lens E6, a filter E7, and an imaging surface S15.

The first lens E1 has negative power, a surface S1 of the first lens close to the light incident side is a concave surface, and a surface S2 of the first lens close to the light exiting side is a concave surface. The second lens E2 has positive power, a surface S3 of the second lens adjacent to the light incident side is a convex surface, and a surface S4 of the second lens adjacent to the light emergent side is a convex surface. The third lens E3 has positive 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 exiting side is a convex surface. The fourth lens E4 has negative power, a surface S7 of the fourth lens adjacent to the light incident side is a convex surface, and a surface S8 of the fourth lens adjacent to the light exiting side is a concave surface. The fifth lens E5 has positive power, a surface S9 of the fifth lens close to the light incident side is a convex surface, and a surface S10 of the fifth lens close to the light exiting side is a convex surface. The sixth lens E6 has positive power, a surface S11 of the sixth lens close to the light incident side is a convex surface, and a surface S12 of the sixth lens close to the light exiting side is a concave surface. The filter E7 has a surface S13 on the light-incident side of the filter and a surface S14 on the light-emergent side of the filter. Light from the object sequentially passes through the respective surfaces S1 to S14 and is finally imaged on the imaging surface S15.

In the present example, the total effective focal length f of the imaging system is 1.57mm, the total length TTL of the imaging system is 6.50mm and the image height ImgH is 3.1 mm.

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.

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TABLE 4 Table 4

Fig. 6 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. 7 shows an astigmatism curve of the imaging system of example two, which represents meridional image surface curvature and sagittal image surface curvature. Fig. 8 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. 6 to 8, the imaging system according to the second example can achieve good imaging quality.

Example three

As shown in fig. 9 to 12, an imaging system of example three of the present application is described. Fig. 9 shows a schematic diagram of an imaging system configuration of example three.

As shown in fig. 9, the imaging system sequentially includes, from an incident side to an emergent side: a first lens E1, a second lens E2, a stop STO, a third lens E3, a fourth lens E4, a fifth lens E5, a sixth lens E6, a filter E7, and an imaging surface S15.

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.

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TABLE 6

Fig. 10 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. 11 shows an astigmatism curve of the imaging system of example three, which represents meridional image surface curvature and sagittal image surface curvature. Fig. 12 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. 10 to 12, the imaging system of example three can achieve good imaging quality.

Example four

As shown in fig. 13 to 16, an imaging system of example four of the present application is described. Fig. 13 shows a schematic diagram of an imaging system configuration of example four.

As shown in fig. 13, the imaging system sequentially includes, from an incident side to an emergent side: a first lens E1, a second lens E2, a stop STO, a third lens E3, a fourth lens E4, a fifth lens E5, a sixth lens E6, a filter E7, and an imaging surface S15.

The first lens E1 has negative power, a surface S1 of the first lens close to the light incident side is a concave surface, and a surface S2 of the first lens close to the light exiting side is a concave surface. The second lens E2 has positive focal 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 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 exiting side is a convex surface. The fourth lens E4 has negative power, a surface S7 of the fourth lens adjacent to the light incident side is a concave surface, and a surface S8 of the fourth lens adjacent to the light exiting side is a concave surface. The fifth lens E5 has positive power, a surface S9 of the fifth lens close to the light incident side is a convex surface, and a surface S10 of the fifth lens close to the light exiting side is a convex surface. The sixth lens E6 has positive power, a surface S11 of the sixth lens close to the light incident side is a convex surface, and a surface S12 of the sixth lens close to the light exiting side is a concave surface. The filter E7 has a surface S13 on the light-incident side of the filter and a surface S14 on the light-emergent side of the filter. Light from the object sequentially passes through the respective surfaces S1 to S14 and is finally imaged on the imaging surface S15.

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).

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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

1.6964E+00

-3.8705E-01

1.3309E-01

-5.7054E-02

2.1911E-02

-1.2735E-02

4.1455E-03

S2

4.5333E-01

-1.7280E-01

4.3417E-03

-6.1189E-03

4.7438E-03

8.1964E-04

3.0424E-04

S3

-7.5690E-02

-2.5637E-02

3.6834E-03

3.6895E-04

2.7596E-04

-1.6025E-05

9.6140E-05

S4

3.3825E-03

1.0163E-03

2.0407E-04

1.7874E-05

2.5552E-05

2.3269E-05

2.1168E-05

S5

1.3866E-02

-1.1889E-03

-2.6871E-04

3.3578E-05

2.5971E-05

1.1576E-05

-1.5484E-05

S6

-1.0279E-01

-2.0108E-03

5.6417E-04

3.0741E-04

-1.0183E-04

-1.4720E-05

2.5400E-05

S7

-3.3940E-01

1.8807E-02

3.0045E-03

2.9944E-03

-9.1291E-04

-2.3023E-04

-1.4656E-04

S8

6.3640E-03

8.8967E-02

-5.0959E-03

4.0915E-03

3.6577E-03

6.6274E-04

9.0737E-04

S9

-6.7787E-01

1.1446E-01

-4.0488E-02

1.0755E-02

-7.7655E-03

3.6105E-03

-2.1933E-03

S10

-1.0004E-01

1.5187E-01

-7.2916E-02

1.6930E-02

-7.1183E-03

4.5928E-03

-4.8123E-03

S11

-2.9293E+00

5.9948E-01

-1.2450E-01

4.4094E-02

-2.6933E-02

5.3094E-03

3.1650E-03

S12

-5.1434E+00

1.0775E+00

-3.2213E-01

1.0733E-01

-4.2033E-02

2.8451E-02

-1.4583E-02

Face number

A18

A20

A22

A24

A26

A28

A30

S1

-3.4471E-03

7.2555E-04

-1.0388E-03

1.0104E-04

-2.9059E-04

7.5707E-06

-5.9230E-05

S2

8.9615E-05

9.3605E-06

8.6477E-05

1.2589E-06

5.7052E-05

7.6573E-06

1.8270E-05

S3

3.5819E-05

1.6733E-05

6.8933E-06

1.3808E-07

-2.0110E-06

-3.9575E-06

-1.6258E-06

S4

1.4841E-05

9.2912E-06

1.0051E-05

1.0657E-05

1.0042E-05

6.6837E-06

2.7888E-06

S5

-2.4607E-05

-1.6931E-05

-3.3170E-06

7.3672E-06

8.4842E-06

5.0348E-06

1.4399E-06

S6

4.2729E-05

3.0301E-05

9.3754E-06

-1.2012E-05

-2.3894E-05

-1.7818E-05

-7.5894E-06

S7

1.4625E-04

6.3682E-05

4.3321E-05

3.7324E-06

6.6087E-06

3.0641E-06

2.9825E-06

S8

2.9472E-04

2.6607E-04

8.6110E-05

8.9177E-05

2.1151E-05

8.9942E-06

6.1839E-06

S9

6.7208E-04

-6.6166E-05

7.3526E-04

2.8263E-04

3.1348E-04

8.2058E-05

5.7997E-05

S10

-1.3682E-03

1.2513E-03

1.3107E-03

-5.9510E-04

-9.6474E-04

-5.5241E-04

-1.4419E-04

S11

-3.2437E-04

-5.9525E-04

-2.8122E-05

2.1913E-04

-5.5832E-05

-5.2446E-05

2.1626E-05

S12

-3.8397E-03

-7.4827E-04

2.1319E-03

1.5857E-03

8.9344E-04

1.9132E-04

-5.4556E-04

TABLE 8

Fig. 14 shows an on-axis chromatic aberration curve for 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. 15 shows an astigmatism curve of the imaging system of example four, which represents meridional image surface curvature and sagittal image surface curvature. Fig. 16 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. 14 to 16, the imaging system of example four can achieve good imaging quality.

Example five

As shown in fig. 17 to 20, an imaging system of example five of the present application is described. Fig. 17 shows a schematic diagram of an imaging system configuration of example five.

As shown in fig. 17, the imaging system sequentially includes, from an incident side to an emergent side: a first lens E1, a second lens E2, a stop STO, a third lens E3, a fourth lens E4, a fifth lens E5, a sixth lens E6, a filter E7, and an imaging surface S15.

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

1.7424E+00

-3.8536E-01

1.3343E-01

-5.5956E-02

2.1357E-02

-1.1851E-02

4.3207E-03

S2

4.6478E-01

-1.6973E-01

-7.1368E-03

-5.9484E-03

5.9748E-03

2.1254E-03

2.2827E-04

S3

-7.9480E-02

-2.3910E-02

3.0937E-03

4.6393E-04

4.5915E-04

7.5473E-05

6.7287E-05

S4

1.9917E-03

7.2961E-04

1.1040E-04

-2.5833E-05

2.7328E-05

5.2646E-05

7.8495E-05

S5

5.4046E-03

-9.9563E-04

-1.4424E-04

-3.0530E-06

7.4915E-06

4.4072E-06

5.6701E-06

S6

-1.0048E-01

1.6742E-03

-4.0013E-04

2.5292E-04

-1.6618E-04

7.6380E-06

-2.1837E-05

S7

-3.3431E-01

2.5793E-02

3.1534E-04

2.9972E-03

-6.3919E-04

1.5396E-04

-1.5377E-04

S8

-4.7756E-01

7.7345E-02

-1.2201E-02

6.3824E-03

-2.4977E-03

1.0580E-03

-5.2581E-04

S9

-6.5572E-01

1.0979E-01

-4.4857E-02

1.3426E-02

-7.9643E-03

4.0803E-03

-2.6962E-03

S10

-1.3294E-01

1.4243E-01

-9.0440E-02

2.2989E-02

-5.1977E-03

4.4930E-03

-6.4036E-03

S11

-2.9545E+00

6.1493E-01

-1.1802E-01

2.8534E-02

-2.4901E-02

7.1824E-03

4.6134E-03

S12

-5.1588E+00

1.0882E+00

-3.3298E-01

1.1994E-01

-3.9597E-02

2.7872E-02

-1.6548E-02

Face number

A18

A20

A22

A24

A26

A28

A30

S1

-2.8727E-03

9.5481E-04

-7.5019E-04

2.1431E-04

-2.0356E-04

2.5125E-05

-4.8826E-05

S2

-6.4242E-04

-7.1793E-04

-3.7267E-04

-1.5497E-04

1.3622E-05

1.5253E-05

1.3809E-05

S3

-1.1817E-05

-1.3090E-05

-5.1222E-06

-4.4359E-06

-2.5572E-06

-2.7296E-06

-8.1623E-07

S4

8.0700E-05

7.5866E-05

6.2775E-05

4.5957E-05

2.6405E-05

1.1436E-05

2.5303E-06

S5

3.0059E-07

2.7736E-07

-1.6502E-06

-2.1455E-06

-2.5705E-06

-1.4288E-06

-3.8644E-07

S6

1.8741E-05

-3.1708E-06

7.1137E-06

5.9222E-06

7.4140E-06

4.3867E-06

1.5649E-06

S7

1.0331E-04

2.8618E-05

3.9479E-05

6.3347E-06

8.0111E-06

2.5468E-06

1.9483E-06

S8

2.0279E-04

-9.9064E-05

4.4657E-05

-2.0914E-05

5.3889E-06

-1.9269E-06

-1.0527E-07

S9

1.2252E-03

-1.9124E-04

5.9499E-04

1.1789E-04

2.0457E-04

2.9267E-05

4.5904E-05

S10

-6.3456E-04

8.7240E-04

5.9470E-04

-1.8144E-04

1.5647E-04

1.2739E-04

6.8752E-05

S11

-9.6292E-04

-4.5344E-04

9.3608E-05

2.0773E-04

-4.5036E-05

-1.1987E-04

2.2317E-05

S12

-3.7778E-03

-1.4834E-03

1.6495E-03

2.2531E-03

7.6268E-04

2.1471E-04

-4.2671E-04

Table 10

Fig. 18 shows an on-axis chromatic aberration curve of the imaging system of example five, which represents the convergent focus deviation of light rays of different wavelengths after passing through the imaging system. Fig. 19 shows an astigmatism curve of the imaging system of example five, which represents meridional image plane curvature and sagittal image plane curvature. Fig. 20 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. 18 to 20, the imaging system of example five can achieve good imaging quality.

Example six

As shown in fig. 21 to 24, an imaging system of example six of the present application is described. Fig. 21 shows a schematic diagram of an imaging system configuration of example six.

As shown in fig. 21, the imaging system sequentially includes, from an incident side to an emergent side: a first lens E1, a second lens E2, a stop STO, a third lens E3, a fourth lens E4, a fifth lens E5, a sixth lens E6, a filter E7, and an imaging surface S15.

The first lens E1 has negative power, a surface S1 of the first lens close to the light incident side is a concave surface, and a surface S2 of the first lens close to the light exiting side is a concave surface. The second lens E2 has positive focal 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 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 exiting side is a convex surface. The fourth lens E4 has negative power, a surface S7 of the fourth lens adjacent to the light incident side is a convex surface, and a surface S8 of the fourth lens adjacent to the light exiting side is a concave surface. The fifth lens E5 has positive power, a surface S9 of the fifth lens close to the light incident side is a convex surface, and a surface S10 of the fifth lens close to the light exiting side is a concave surface. The sixth lens E6 has positive power, a surface S11 of the sixth lens close to the light incident side is a convex surface, and a surface S12 of the sixth lens close to the light exiting side is a concave surface. The filter E7 has a surface S13 on the light-incident side of the filter and a surface S14 on the light-emergent side of the filter. Light from the object sequentially passes through the respective surfaces S1 to S14 and is finally imaged on the imaging surface S15.

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.

Face number

A4

A6

A8

A10

A12

A14

A16

S1

1.9180E+00

-3.6695E-01

1.4502E-01

-5.5007E-02

2.0488E-02

-1.2409E-02

3.9138E-03

S2

4.4868E-01

-1.5978E-01

-1.1479E-02

-1.5092E-03

6.7063E-03

8.0761E-04

-1.8759E-03

S3

-1.2925E-01

-1.9461E-02

6.6361E-03

-1.5422E-04

-4.2298E-04

-3.0559E-04

1.4206E-04

S4

-2.1540E-04

1.1103E-03

2.6221E-04

3.8923E-05

4.0435E-05

2.5818E-05

2.8480E-05

S5

1.1212E-02

-1.1940E-03

-3.7445E-04

-6.7415E-05

-2.6888E-05

1.3675E-05

3.6522E-05

S6

-1.1944E-01

6.6001E-03

-8.8603E-04

-1.8746E-04

-4.5719E-04

-4.3729E-05

8.2207E-05

S7

-3.3373E-01

3.0311E-02

-2.3405E-04

2.0820E-03

-6.8796E-04

1.4286E-04

-2.3938E-04

S8

-4.6073E-01

7.7029E-02

-1.0678E-02

5.1585E-03

-2.2461E-03

9.6191E-04

-5.3980E-04

S9

-6.7555E-01

1.0091E-01

-3.5456E-02

1.1000E-02

-6.6815E-03

4.4921E-03

-2.3816E-03

S10

-2.6746E-01

1.8523E-01

-9.0686E-02

2.3298E-02

-1.1451E-02

6.2053E-03

-7.1631E-03

S11

-3.0004E+00

6.3984E-01

-9.1599E-02

8.6671E-03

-1.9795E-02

4.5380E-03

5.3129E-03

S12

-4.9953E+00

1.0985E+00

-3.0590E-01

8.1604E-02

-2.6224E-02

1.8208E-02

-1.4551E-02

Face number

A18

A20

A22

A24

A26

A28

A30

S1

-2.3550E-03

1.4536E-03

-2.7700E-04

4.7467E-04

-7.2136E-05

6.9514E-05

-3.4741E-05

S2

-1.9308E-03

-1.1819E-03

-7.0852E-04

-5.2847E-04

-3.4069E-04

-1.7468E-04

-5.1427E-05

S3

1.2850E-04

6.3796E-05

2.1402E-05

5.4443E-06

-4.1791E-07

-1.7067E-06

-8.5921E-08

S4

1.9426E-05

1.7234E-05

1.5981E-05

1.7076E-05

1.3504E-05

8.0392E-06

2.1754E-06

S5

2.8369E-05

1.0649E-05

8.4333E-07

-3.4945E-06

-1.6986E-06

-1.0275E-06

1.3312E-07

S6

1.5981E-04

7.6476E-05

1.7178E-05

-2.7106E-05

-2.9731E-05

-2.0103E-05

-7.5260E-06

S7

4.4255E-05

-2.7407E-05

2.3611E-05

-3.7689E-06

6.5544E-06

2.7560E-07

3.2319E-06

S8

2.0753E-04

-1.1352E-04

4.8168E-05

-2.3545E-05

6.8357E-06

-2.3961E-06

9.0876E-07

S9

1.2494E-03

-4.6828E-04

4.4122E-04

-9.3704E-05

1.2344E-04

-1.9452E-05

3.1956E-05

S10

-2.9752E-04

7.7044E-04

8.9519E-04

-1.3408E-05

3.1398E-04

2.5613E-04

1.7098E-04

S11

-1.8804E-03

-6.3807E-04

1.7087E-04

2.4815E-04

2.1003E-04

-1.2821E-04

-2.4039E-05

S12

-6.7062E-03

2.2968E-03

1.6579E-03

4.0505E-03

5.8735E-04

5.8636E-04

-3.2362E-04

Table 12

Fig. 22 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. 23 shows an astigmatism curve of the imaging system of example six, which represents meridional image surface curvature and sagittal image surface curvature. Fig. 24 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. 22 to 24, the imaging system of example six can achieve good imaging quality.

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

TABLE 13

Table 14 shows the effective focal lengths f of the imaging systems of examples one to six, and the effective focal lengths f1 to f6 of the respective lenses.

Example parameters	1	2	3	4	5	6
							f(mm)	1.57	1.57	1.57	1.57	1.57	1.57
f1(mm)	-1.96	-2.23	-2.11	-2	-2.05	-2.13
							f2(mm)	4.58	5.47	4.52	4.41	5.2	4.96
f3(mm)	2.46	2.47	2.54	2.41	2.3	2.37
							f4(mm)	-3.07	-2.76	-2.96	-2.77	-3.16	-3.26
f5(mm)	2.56	2.49	2.67	2.47	2.75	3.55
							f6(mm)	20.53	19.96	15.54	17.56	17.03	7.3
TTL(mm)	6.50	6.50	6.50	6.50	6.50	6.50
							ImgH(mm)	3.10	3.10	3.10	3.10	3.10	3.10
Semi-FOV(°)	63.8	61.4	61.9	62.0	62.2	61.4

TABLE 14

The present application also provides an imaging device, the electron-sensitive element of which may 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 example embodiments in accordance with 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 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 present application described herein may be implemented in sequences other than those illustrated or 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, comprising six lenses, from an entrance side of the imaging system to an exit side of the imaging system comprising:

a first lens with negative focal power, wherein the surface of the first lens close to the light incident side is a concave surface;

a second lens having positive optical power;

a third lens with positive focal power, wherein the surface of the third lens close to the light emergent side is a convex surface;

A fourth lens having negative optical power, the fourth lens having an abbe number of less than 20;

a fifth lens having positive optical power;

a sixth lens having positive optical power;

wherein the maximum field angle FOV of the imaging system satisfies: FOV >120 °;

the curvature radius R9 of the surface of the fifth lens close to the light incident side and the curvature radius R12 of the surface of the sixth lens close to the light emergent side satisfy the following conditions: R9/R12 is more than 1.5 and less than 2.6;

the combined focal length f12 of the first lens and the second lens and the effective focal length f of the imaging system satisfy the following conditions:

-4.0＜f12/f＜-2.5。

2. the imaging system of claim 1, wherein an effective focal length f of the imaging system and an entrance pupil diameter EPD of the imaging system satisfy: f/EPD < 2.3.

3. The imaging system of claim 1, wherein an effective focal length f2 of the second lens and an effective focal length f5 of the fifth lens satisfy: 1.0 < f2/f5 < 2.5.

4. The imaging system of claim 1, wherein a radius of curvature R3 of a face of the second lens on the light-entering side and a radius of curvature R11 of a face of the sixth lens on the light-entering side satisfy: R3/R11 is more than 2.0 and less than 5.0.

5. The imaging system according to claim 1, wherein a radius of curvature R3 of a face of the second lens on the light-incident side and a radius of curvature R12 of a face of the sixth lens on the light-exit side satisfy: R3/R12 is more than 2.0 and less than 5.0.

6. The imaging system of claim 1, wherein a center thickness CT1 of the first lens on an optical axis and a center thickness CT2 of the second lens on the optical axis satisfy: CT2/CT1 is more than 1.5 and less than 4.0.

7. The imaging system of claim 1, wherein a center thickness CT3 of the third lens on an optical axis and an air gap T34 of the third lens and the fourth lens on the optical axis satisfy: CT3/T34 is less than 2.0 and less than 3.0.

8. The imaging system of claim 1, wherein a center thickness CT4 of the fourth lens on the optical axis and a center thickness CT6 of the sixth lens on the optical axis satisfy: CT6/CT4 is less than or equal to 1.5 and less than 2.0.

9. The imaging system according to claim 1, wherein an on-axis distance SAG11 between an intersection of a face of the first lens near the light entrance side and an optical axis to an effective radius vertex of a face of the first lens near the light entrance side, and an on-axis distance SAG12 between an intersection of a face of the first lens near the light exit side and the optical axis to an effective radius vertex of a face of the first lens near the light exit side satisfy: 1.0 < SAG12/SAG11 < 3.0.

10. The imaging system according to claim 1, wherein an on-axis distance SAG52 between an intersection of a face of the fifth lens on the light exit side and an optical axis to an effective radius vertex of a face of the fifth lens on the light exit side, and an on-axis distance SAG61 between an intersection of a face of the sixth lens on the light entrance side and the optical axis to an effective radius vertex of a face of the sixth lens on the light entrance side satisfy: 0.5 < SAG61/SAG52 < 2.5.

11. The imaging system of claim 1, wherein a combined focal length f34 of the third lens and the fourth lens, an effective focal length f of the imaging system, satisfies: f34/f is more than 3.0 and less than 5.0.

12. The imaging system of claim 1, wherein a combined focal length f456 of the fourth lens, the fifth lens, and the sixth lens, an effective focal length f of the imaging system, satisfies: f456/f is more than 3.0 and less than 5.5.

13. The imaging system of claim 1, wherein the abbe number V2 of the second lens satisfies: v2 < 25.