CN112462488A

CN112462488A - Optical system, lens module and electronic equipment

Info

Publication number: CN112462488A
Application number: CN201910849481.6A
Authority: CN
Inventors: 刘彬彬; 王妮妮; 邹海荣
Original assignee: Jiangxi Jingchao Optical Co Ltd
Current assignee: Jiangxi Jingchao Optical Co Ltd
Priority date: 2019-09-09
Filing date: 2019-09-09
Publication date: 2021-03-09

Abstract

The invention provides an optical system, a lens module and an electronic device. The optical system includes, in order from an object side to an image side in an optical axis direction: a first lens element with refractive power; a second lens element with positive refractive power; a third lens element with refractive power; a fourth lens element with refractive power; the optical system satisfies the conditional expression: t18/f is less than or equal to 0.6; where T18 is the distance on the optical axis from the object-side surface of the first lens element to the image-side surface of the fourth lens element, and f is the effective focal length of the optical system. By reasonably configuring the surface shape, the refractive power and the lens arrangement space of each of the first lens to the fourth lens, the telephoto function is realized, and meanwhile, the lengths of all lens barrels supporting the first lens to the fourth lens can be further shortened, and the processability of the optical lens group is improved.

Description

Optical system, lens module and electronic equipment

Technical Field

The invention belongs to the technical field of optical imaging, and particularly relates to an optical system, a lens module and electronic equipment.

Background

With the market requirement for high imaging quality of camera shooting, the telephoto lens comes along. The telephoto lens has the characteristics of longer focal length, is beneficial to capturing the details of a long-distance shooting object and realizes clear imaging. However, the lens barrel of the telephoto lens is long, and is not in line with the development trend of miniaturization integration.

In the prior art, the length and the imaging quality of a lens are difficult to balance due to poor distribution of the bending force of the four-piece photographing and image-taking module, the distortion cannot be controlled under the proper total system length, and the high-image-quality miniature telephoto lens cannot be realized. In order to solve this problem, it is necessary to further rationally configure the aspherical surface type and layout of the lens.

Disclosure of Invention

The invention aims to provide an optical system which meets the requirements of miniaturization, long focus and good imaging.

In order to realize the purpose of the invention, the invention provides the following technical scheme:

in a first aspect, the present invention provides an optical system, comprising, in order from an object side to an image side in an optical axis direction: a first lens element with refractive power; the second lens element with positive refractive power has a convex object-side surface at an optical axis; a third lens element with refractive power, wherein an object-side surface of the third lens element on an optical axis is concave; the fourth lens element with refractive power has a concave object-side surface at an optical axis; the optical system satisfies the conditional expression: t18/f is less than or equal to 0.6; wherein T18 is the distance on the optical axis from the object side surface of the first lens to the image side surface of the fourth lens, and f is the effective focal length of the optical system. By reasonably configuring the surface shape, the refractive power and the lens arrangement space of each of the first lens to the fourth lens, the telephoto function is realized, and meanwhile, the lengths of all lens barrels supporting the first lens to the fourth lens can be further shortened, and the processability of the optical lens group is improved.

In one embodiment, the optical system satisfies the conditional expression: sigma CT/T18 is more than or equal to 0.4 and less than or equal to 1; where Σ CT is the sum of thicknesses of all the first to fourth lenses of the optical system on the optical axis, and T18 is the separation distance on the optical axis from the object-side surface of the first lens to the image-side surface of the fourth lens. By reasonably setting the value of sigma CT/T18 and reasonably arranging the thickness of the lens, the optical structure is more compact, and the assembly process of the lens group can be improved.

In one embodiment, the optical system satisfies the conditional expression: TTL/f is more than or equal to 0.7 and less than or equal to 1.8; wherein, TTL is a distance on an optical axis from an object-side surface of the first lens element to an imaging surface of the optical system, and f is an effective focal length of the optical system. By setting a reasonable TTL/f value, the optical system has a long-focus characteristic, and meanwhile, a short total system length is obtained, and ultra-thinning is realized.

In one embodiment, the optical system satisfies the conditional expression: R12/R11 is more than or equal to 0.5 and less than or equal to 1; wherein R11 is a radius of curvature of an object-side surface of the first lens, and R12 is a radius of curvature of an image-side surface of the first lens. By reasonably setting the value of R12/R11, the incident ray angle of the optical system is reduced, the field angle is reduced, and the telephoto function is realized.

In one embodiment, the optical system satisfies the conditional expression: T23/CT2 is more than or equal to 0.3 and less than or equal to 0.9; wherein T23 is an air separation distance of the second lens and the third lens on an optical axis, and CT2 is a thickness of the second lens on the optical axis. Through the value of reasonable setting T23 CT2, rationally laying out optical structure, be favorable to compressing camera lens length size, slow down the direction change behind the light entering system simultaneously, help reducing stray light's intensity.

In one embodiment, the optical system satisfies the conditional expression: SAG21/f is less than or equal to 0.1; wherein SAG21 is the sagittal height of the object side surface of the second lens, and f is the effective focal length of the optical system. The value of SAG21/f is reasonably set, so that light is smoothly transmitted to the third lens, the sensitivity of the system is reduced, the production yield is improved, and the telephoto characteristic of the lens is met.

In one embodiment, the optical system satisfies the conditional expression: f2/f is less than or equal to 0.7; wherein f2 is the effective focal length of the second lens, and f is the effective focal length of the optical system. The value of f2/f is reasonably set, which is beneficial to the increase of the focal length of the optical system and simultaneously compensates the chromatic aberration of the system.

In one embodiment, the optical system satisfies the conditional expression: -1. ltoreq. R31/f. ltoreq.0; wherein R31 is a radius of curvature of an object side surface of the third lens, and f is an effective focal length of the optical system. By reasonably setting the value of R31/f, the shape of the lens is reasonably controlled, the long-focus characteristic of an optical system is met, and meanwhile, the system aberration is favorably balanced.

In one embodiment, the optical system satisfies the conditional expression: -1. ltoreq. SAG41/CT 4. ltoreq.0; wherein SAG41 is the rise of the object side surface of the fourth lens in the optical axis direction, and CT4 is the thickness of the fourth lens in the optical axis. The SAG41/CT4 value is reasonably set, which is beneficial to correcting distortion and curvature of field of the telephoto lens and ensuring the imaging quality.

In one embodiment, the optical system satisfies the conditional expression: FOV/IMGH is more than or equal to 4 and less than or equal to 6.5; the FOV is the maximum field angle of the optical system, and the IMGH is half of the diagonal length of the effective pixel area of the imaging surface. The FOV/IMGH value is reasonably set, so that a small view field can be realized while high pixels are ensured, and the long-focus characteristic is realized.

In a second aspect, the present invention provides a lens module including a lens barrel and the optical system of the first aspect, wherein the first to fourth lenses of the optical system are mounted in the lens barrel. Through installing each lens of this optical system's first lens to fourth lens at the camera lens module, guarantee that the camera lens module can satisfy the demand miniaturized, that long burnt and formation of image are good.

In a third aspect, the present invention further provides an electronic device, which includes a housing, the electronic photosensitive element, and the lens module of the second aspect, where the lens module and the electronic photosensitive element are disposed in the housing, and the electronic photosensitive element is disposed on an imaging surface of the optical system, and is configured to convert light rays of an object, which pass through the first lens to the fourth lens and are incident on the electronic photosensitive element, into an electrical signal of an image. Through adding this lens module in electronic equipment for electronic equipment can also carry out the long burnt shooting that the formation of image quality is good when miniaturized.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts. Detailed Description

FIG. 1a is a schematic structural diagram of an optical system of a first embodiment;

FIG. 1b is a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the first embodiment;

FIG. 2a is a schematic structural diagram of an optical system of a second embodiment;

FIG. 2b is a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the second embodiment;

FIG. 3a is a schematic structural diagram of an optical system of a third embodiment;

FIG. 3b is a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the third embodiment;

FIG. 4a is a schematic structural diagram of an optical system of a fourth embodiment;

FIG. 4b is a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the fourth embodiment;

FIG. 5a is a schematic structural diagram of an optical system of a fifth embodiment;

FIG. 5b is a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the fifth embodiment;

FIG. 6a is a schematic structural diagram of an optical system of a sixth embodiment;

FIG. 6b is a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the sixth embodiment;

FIG. 7a is a schematic structural diagram of an optical system of a seventh embodiment;

fig. 7b is a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the seventh embodiment.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

The embodiment of the invention provides a lens module, which comprises a lens barrel and an optical system provided by the embodiment of the invention, wherein first to fourth lenses of the optical system are arranged in the lens barrel. The lens module can be an independent lens of a digital camera, and can also be an imaging module integrated on electronic equipment such as a smart phone. Through installing each lens of this optical system's first lens to fourth lens at the camera lens module, guarantee that the camera lens module can satisfy the demand miniaturized, that long burnt and formation of image are good.

The embodiment of the invention also provides electronic equipment which comprises a shell, an electronic photosensitive element and the lens module in the second aspect, wherein the lens module and the electronic photosensitive element are arranged in the shell, and the electronic photosensitive element is arranged on an imaging surface of an optical system and used for converting light rays of objects which penetrate through the first lens to the fourth lens and are incident on the electronic photosensitive element into electric signals of images. The electron sensor may be a Complementary Metal Oxide Semiconductor (CMOS) or a Charge-coupled Device (CCD). The electronic device can be a smart phone, a Personal Digital Assistant (PDA), a tablet computer, a smart watch, an unmanned aerial vehicle, an electronic book reader, a vehicle event data recorder, a wearable device and the like. Through adding this lens module in electronic equipment for electronic equipment can also carry out the long burnt shooting that the formation of image quality is good when miniaturized.

An embodiment of the present invention provides an optical system, sequentially including, from an object side to an image side along an optical axis direction: the lens includes a first lens, a second lens, a third lens and a fourth lens. In the first lens to the fourth lens, an air space may be provided between any two adjacent lenses.

The optical system further comprises a diaphragm, and the diaphragm can be arranged at any position between the first lens and the fourth lens, such as between the first lens and the second lens.

Specifically, the specific shape and structure of the four lenses are as follows:

a first lens element with refractive power; the second lens element with positive refractive power has a convex object-side surface at the optical axis; the third lens element with refractive power has a concave object-side surface at the optical axis; the fourth lens element with refractive power has a concave object-side surface at the optical axis;

the optical system satisfies the conditional expression:

T18/f≤0.6；

where T18 is the distance on the optical axis from the object-side surface of the first lens element to the image-side surface of the fourth lens element, and f is the effective focal length of the optical system.

By reasonably configuring the surface shape, the refractive power and the lens arrangement space of each of the first lens to the fourth lens, the telephoto function is realized, and meanwhile, the lengths of all lens barrels supporting the first lens to the fourth lens can be further shortened, and the processability of the optical lens group is improved.

In one embodiment, the optical system satisfies the conditional expression: sigma CT/T18 is more than or equal to 0.4 and less than or equal to 1; where Σ CT is the sum of thicknesses of all the first lens to fourth lens of the optical system on the optical axis, and T18 is the separation distance on the optical axis from the object-side surface of the first lens to the image-side surface of the fourth lens. By reasonably setting the value of sigma CT/T18 and reasonably arranging the thickness of the lens, the optical structure is more compact, and the assembly process of the lens group can be improved.

In one embodiment, the optical system satisfies the conditional expression: TTL/f is more than or equal to 0.7 and less than or equal to 1.8; wherein, TTL is a distance on the optical axis from the object-side surface of the first lens element to the imaging surface of the optical system, and f is an effective focal length of the optical system. By setting a reasonable TTL/f value, the optical system has a long-focus characteristic, and meanwhile, the system with a smaller overall length is obtained, so that ultra-thinning is realized.

In one embodiment, the optical system satisfies the conditional expression: R12/R11 is more than or equal to 0.5 and less than or equal to 1; wherein R11 is a radius of curvature of the object-side surface of the first lens element, and R12 is a radius of curvature of the image-side surface of the first lens element. By reasonably setting the value of R12/R11, the incident ray angle of the optical system is reduced, the field angle is reduced, and the telephoto function is realized.

In one embodiment, the optical system satisfies the conditional expression: T23/CT2 is more than or equal to 0.3 and less than or equal to 0.9; where T23 is an air separation distance on the optical axis of the second lens and the third lens, and CT2 is a thickness of the second lens on the optical axis. Through the value of reasonable setting T23 CT2, rationally laying out optical structure, be favorable to compressing camera lens length size, slow down the direction change behind the light entering system simultaneously, help reducing stray light's intensity.

In one embodiment, the optical system satisfies the conditional expression: SAG21/f is less than or equal to 0.1; where SAG21 is the rise of the object-side surface of the second lens, and f is the effective focal length of the optical system. The value of SAG21/f is reasonably set, so that light is smoothly transmitted to the third lens, the sensitivity of the system is reduced, the production yield is improved, and the telephoto characteristic of the lens is met.

In one embodiment, the optical system satisfies the conditional expression: f2/f is less than or equal to 0.7; where f2 is the effective focal length of the second lens, and f is the effective focal length of the optical system. The value of f2/f is reasonably set, which is beneficial to the increase of the focal length of the optical system and simultaneously compensates the chromatic aberration of the system.

In one embodiment, the optical system satisfies the conditional expression: -1. ltoreq. R31/f. ltoreq.0; where R31 is the radius of curvature of the object-side surface of the third lens, and f is the effective focal length of the optical system. By reasonably setting the value of R31/f, the shape of the lens is reasonably controlled, the long-focus characteristic of an optical system is met, and meanwhile, the system aberration is favorably balanced.

In one embodiment, the optical system satisfies the conditional expression: -1. ltoreq. SAG41/CT 4. ltoreq.0; wherein SAG41 is the rise of the object side surface of the fourth lens in the optical axis direction, and CT4 is the thickness of the fourth lens in the optical axis direction. The SAG41/CT4 value is reasonably set, which is beneficial to correcting distortion and curvature of field of the telephoto lens and ensuring the imaging quality.

First embodiment

Referring to fig. 1a and fig. 1b, the optical system of the present embodiment, in order from an object side to an image side along an optical axis, includes:

the first lens element L1 with negative refractive power has a convex object-side surface S1 of the first lens element L1 and a concave image-side surface S2 of the first lens element L1.

The second lens element L2 with positive refractive power has a convex object-side surface S3 at the optical axis, a concave object-side surface S3 at the circumference, and a convex image-side surface S4 of the second lens element L2.

The third lens element L3 with negative refractive power has a concave object-side surface S5 of the third lens element L3 and a convex image-side surface S6 of the third lens element L3.

The fourth lens element L4 with positive refractive power has a concave object-side surface S7 of the fourth lens element L4 and a convex image-side surface S8 of the fourth lens element L4.

The first lens element L1 to the fourth lens element L4 are all made of Plastic (Plastic).

Further, the optical system includes a stop STO, an infrared cut filter L5, and an image forming surface S11. A stop STO is disposed between the first lens L1 and the second lens L2, and is adjacent to the second lens L2, for controlling the amount of light entering. In other embodiments, the stop STO can be disposed between two other adjacent lenses. The infrared cut filter L5 is disposed on the image side of the fourth lens L4, and includes an object side surface S9 and an image side surface S10, and the infrared cut filter L5 is configured to filter out infrared light, so that the light entering the image plane S11 is visible light, and the wavelength of the visible light is 380nm-780 nm. The material of the infrared cut filter L5 is Glass (Glass), and a film may be coated on the Glass. The electron photosensitive element is disposed on the image side of the optical system to receive light of an image formed by the optical system, and the surface on which the image formed by the optical system is located is an image forming surface S11.

Table 1a shows a table of characteristics of the optical system of the present embodiment, and the units of the Y radius, thickness, and focal length are all millimeters (mm).

TABLE 1a

The EFL is an effective focal length of the optical system, the FNO is an f-number of the optical system, the FOV is a field angle of the optical system, and the TTL is a distance from an object side surface of the first lens to an imaging surface of the optical system on an optical axis.

In this embodiment, the object-side surface and the image-side surface of any one of the first lens L1 through the fourth lens L4 are aspheric surfaces, and the surface shape x of each aspheric lens can be defined by, but is not limited to, the following aspheric surface formula:

wherein x is the rise of the distance from the aspheric surface vertex to the aspheric surface vertex when the aspheric surface is at the position with the height of h along the optical axis direction; c is the paraxial curvature of the aspheric surface, c being 1/R (i.e., paraxial curvature c is the inverse of radius R of Y in table 1a above); k is a conic coefficient; ai is the correction coefficient of the i-th order of the aspherical surface. Table 1b shows the high-order coefficient A4, A6, A8, A10, A12, A14 and A16 which can be used for each of the aspherical mirrors S1-S8 in the first embodiment.

TABLE 1b

Fig. 1b shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the optical system of the first embodiment. The longitudinal spherical aberration curve represents the deviation of the convergence focus of the light rays with different wavelengths after passing through each lens of the optical system; the astigmatism curves represent meridional image surface curvature and sagittal image surface curvature; the distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from fig. 1b, the optical system according to the first embodiment can achieve good imaging quality.

Second embodiment

Referring to fig. 2a and fig. 2b, the optical system of the present embodiment, in order from an object side to an image side along an optical axis direction, includes:

The second lens element L2 with positive refractive power has a convex object-side surface S3 of the second lens element L2 and a convex image-side surface S4 of the second lens element L2.

The third lens element L3 with negative refractive power has a concave object-side surface S5 of the third lens element L3 and a concave image-side surface S6 of the third lens element L3.

The fourth lens element L4 with positive refractive power has a concave object-side surface S7 at the optical axis, a convex object-side surface S7 at the circumference, and a convex image-side surface S8 of the fourth lens element L4.

Other structures of the second embodiment are the same as those of the first embodiment, and reference may be made thereto.

Table 2a shows a table of characteristics of the optical system of the present embodiment, and the units of the Y radius, thickness, and focal length are all millimeters (mm).

TABLE 2a

Wherein the values of the parameters in Table 2a are the same as those of the first embodiment.

Table 2b gives the coefficients of high order terms that can be used for each aspherical mirror in the second embodiment, wherein each aspherical mirror type can be defined by the formula given in the first embodiment.

TABLE 2b

Fig. 2b shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the optical system of the second embodiment. The longitudinal spherical aberration curve represents the deviation of the convergence focus of the light rays with different wavelengths after passing through each lens of the optical system; the astigmatism curves represent meridional image surface curvature and sagittal image surface curvature; the distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from fig. 2b, the optical system according to the second embodiment can achieve good imaging quality.

Third embodiment

Referring to fig. 3a and 3b, the optical system of the present embodiment, in order from an object side to an image side along an optical axis direction, includes:

The second lens element L2 with positive refractive power has a convex object-side surface S3 of the second lens element L2 and a concave image-side surface S4 of the second lens element L2.

Other structures of the third embodiment are the same as those of the first embodiment, and reference may be made thereto.

Table 3a shows a table of characteristics of the optical system of the present embodiment, and the units of the Y radius, thickness, and focal length are all millimeters (mm).

TABLE 3a

Wherein the values of the parameters in Table 3a are the same as those of the first embodiment.

Table 3b gives the coefficients of high-order terms that can be used for each aspherical mirror surface in the third embodiment, wherein each aspherical mirror surface type can be defined by the formula given in the first embodiment.

TABLE 3b

Fig. 3b shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the optical system of the third embodiment. The longitudinal spherical aberration curve represents the deviation of the convergence focus of the light rays with different wavelengths after passing through each lens of the optical system; the astigmatism curves represent meridional image surface curvature and sagittal image surface curvature; the distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from fig. 3b, the optical system according to the third embodiment can achieve good imaging quality.

Fourth embodiment

Referring to fig. 4a and 4b, the optical system of the present embodiment, in order from an object side to an image side along an optical axis direction, includes:

The third lens element L3 with negative refractive power has a concave object-side surface S5 of the third lens element L3, a convex image-side surface S6 at the optical axis of the third lens element L3, and a concave image-side surface S6 at the circumference.

The fourth lens element L4 with negative refractive power has a concave object-side surface S7 of the fourth lens element L4 and a convex image-side surface S8 of the fourth lens element L4.

Other structures of the fourth embodiment are the same as those of the first embodiment, and reference may be made thereto.

Table 4a shows a table of characteristics of the optical system of the present embodiment, and the units of the Y radius, thickness, and focal length are all millimeters (mm).

TABLE 4a

Wherein the values of the parameters in Table 4a are the same as those of the first embodiment.

Table 4b gives the coefficients of high-order terms that can be used for each aspherical mirror surface in the fourth embodiment, wherein each aspherical mirror surface type can be defined by the formula given in the first embodiment.

TABLE 4b

Fig. 4b shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the optical system of the fourth embodiment. The longitudinal spherical aberration curve represents the deviation of the convergence focus of the light rays with different wavelengths after passing through each lens of the optical system; the astigmatism curves represent meridional image surface curvature and sagittal image surface curvature; the distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from fig. 4b, the optical system according to the fourth embodiment can achieve good imaging quality.

Fifth embodiment

Referring to fig. 5a and 5b, the optical system of the present embodiment, in order from an object side to an image side along an optical axis direction, includes:

The other structure of the fifth embodiment is the same as that of the first embodiment, and reference may be made thereto.

Table 5a shows a table of characteristics of the optical system of the present embodiment, and the units of the Y radius, thickness, and focal length are all millimeters (mm).

TABLE 5a

Wherein the meanings of the parameters in Table 5a are the same as those of the first embodiment.

Table 5b shows the high-order term coefficients that can be used for each aspherical mirror surface in the fifth embodiment, wherein each aspherical mirror surface type can be defined by the formula given in the first embodiment.

TABLE 5b

Fig. 5b shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the optical system of the fifth embodiment. The longitudinal spherical aberration curve represents the deviation of the convergence focus of the light rays with different wavelengths after passing through each lens of the optical system; the astigmatism curves represent meridional image surface curvature and sagittal image surface curvature; the distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from fig. 5b, the optical system according to the fifth embodiment can achieve good image quality.

Sixth embodiment

Referring to fig. 6a and 6b, the optical system of the present embodiment, in order from an object side to an image side along an optical axis direction, includes:

The second lens element L2 with positive refractive power has a convex object-side surface S3 of the second lens element L2, a concave image-side surface S4 of the second lens element L2 at the optical axis, and a convex image-side surface S4 at the periphery.

The fourth lens element L4 with positive refractive power has a concave object-side surface S7 of the fourth lens element L4, a convex image-side surface S8 of the fourth lens element L4 at the optical axis, and a concave image-side surface S8 at the circumference.

Other structures of the sixth embodiment are the same as those of the first embodiment, and reference may be made thereto.

Table 6a shows a table of characteristics of the optical system of the present embodiment, and the units of the Y radius, thickness, and focal length are all millimeters (mm).

TABLE 6a

Wherein the values of the parameters in Table 6a are the same as those of the first embodiment.

Table 6b shows the high-order term coefficients that can be used for each aspherical mirror surface in the sixth embodiment, wherein each aspherical mirror surface type can be defined by the formula given in the first embodiment.

TABLE 6b

Fig. 6b shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the optical system of the sixth embodiment. The longitudinal spherical aberration curve represents the deviation of the convergence focus of the light rays with different wavelengths after passing through each lens of the optical system; the astigmatism curves represent meridional image surface curvature and sagittal image surface curvature; the distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from fig. 6b, the optical system according to the sixth embodiment can achieve good image quality.

Seventh embodiment

Referring to fig. 7a and 7b, the optical system of the present embodiment, in order from an object side to an image side along an optical axis direction, includes:

The other structure of the seventh embodiment is the same as that of the first embodiment, and reference may be made thereto.

Table 7a shows a table of characteristics of the optical system of the present embodiment, and the units of the Y radius, thickness, and focal length are all millimeters (mm).

TABLE 7a

Wherein the meanings of the parameters in Table 7a are the same as those of the first embodiment.

Table 7b shows the high-order term coefficients that can be used for each aspherical mirror surface in the seventh embodiment, wherein each aspherical mirror surface type can be defined by the formula given in the first embodiment.

TABLE 7b

Fig. 7b shows a longitudinal spherical aberration curve, an astigmatism curve, and a distortion curve of the optical system of the seventh embodiment. The longitudinal spherical aberration curve represents the deviation of the convergence focus of the light rays with different wavelengths after passing through each lens of the optical system; the astigmatism curves represent meridional image surface curvature and sagittal image surface curvature; the distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from fig. 7b, the optical system according to the seventh embodiment can achieve good image quality.

Table 8 shows values of T18/f, Σ CT/T18, TTL/f, R12/R11, T23/CT2, SAG21/f, f2/f, R31/f, SAG41/CT4, and FOV/IMGH of the optical systems of the first to seventh embodiments, and as can be derived from table 8, each embodiment satisfies: t18/f is less than or equal to 0.6, sigma CT/T18 is less than or equal to 0.4, TTL/f is less than or equal to 0.7 and less than or equal to 1.8, R12/R11 is less than or equal to 0.5 and less than or equal to 1, T23/CT2 is less than or equal to 0.9, SAG21/f is less than or equal to 0.1, f2/f is less than or equal to 0.7, -1 is less than or equal to R31/f is less than or equal to 0, -1 is less than or equal to SAG41/CT4 is less than or equal to 0, and FOV/.

TABLE 8

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. An optical system comprising, in order from an object side to an image side in an optical axis direction:

a first lens element with refractive power;

the second lens element with positive refractive power has a convex object-side surface at an optical axis;

a third lens element with refractive power, wherein an object-side surface of the third lens element on an optical axis is concave;

the fourth lens element with refractive power has a concave object-side surface at an optical axis;

the optical system satisfies the conditional expression:

T18/f≤0.6；

wherein T18 is the distance on the optical axis from the object side surface of the first lens to the image side surface of the fourth lens, and f is the effective focal length of the optical system.

2. The optical system according to claim 1, wherein the optical system satisfies a conditional expression:

0.4≤∑CT/T18≤1；

where Σ CT is the sum of thicknesses of all the first to fourth lenses of the optical system on the optical axis.

3. The optical system according to claim 1, wherein the optical system satisfies a conditional expression:

0.7≤TTL/f≤1.8；

wherein, TTL is a distance on the optical axis from the object-side surface of the first lens element to the imaging surface of the optical system.

4. The optical system according to claim 1, wherein the optical system satisfies a conditional expression:

0.5≤R12/R11≤1；

wherein R11 is a radius of curvature of an object-side surface of the first lens, and R12 is a radius of curvature of an image-side surface of the first lens.

5. The optical system according to claim 1, wherein the optical system satisfies a conditional expression:

0.3≤T23/CT2≤0.9；

wherein T23 is an air separation distance of the second lens and the third lens on an optical axis, and CT2 is a thickness of the second lens on the optical axis.

6. The optical system according to claim 1, wherein the optical system satisfies a conditional expression:

SAG21/f≤0.1；

wherein SAG21 is the rise of the object-side surface of the second lens.

7. The optical system according to claim 1, wherein the optical system satisfies a conditional expression:

f2/f≤0.7；

wherein f2 is the effective focal length of the second lens.

8. The optical system according to claim 1, wherein the optical system satisfies a conditional expression:

-1≤R31/f≤0；

wherein R31 is a radius of curvature of an object-side surface of the third lens.

9. The optical system according to claim 1, wherein the optical system satisfies a conditional expression:

-1≤SAG41/CT4≤0；

wherein SAG41 is the rise of the object side surface of the fourth lens in the optical axis direction, and CT4 is the thickness of the fourth lens in the optical axis.

10. The optical system according to claim 1, wherein the optical system satisfies a conditional expression:

4≤FOV/IMGH≤6.5；

the FOV is the maximum field angle of the optical system, and the IMGH is half of the diagonal length of the effective pixel area of the imaging surface.

11. A lens module comprising a barrel and the optical system according to any one of claims 1 to 10, wherein the first lens to the fourth lens of the optical system are mounted in the barrel.

12. An electronic apparatus comprising a housing, an electro-optic sensing element, and the lens module according to claim 11, wherein the lens module and the electro-optic sensing element are disposed in the housing, and the electro-optic sensing element is disposed on an image plane of the optical system, and is configured to convert light rays of an object incident on the electro-optic sensing element through the first lens to the fourth lens into an electrical signal of an image.