CN113075783A

CN113075783A - Optical system, lens module and terminal equipment

Info

Publication number: CN113075783A
Application number: CN202010006668.2A
Authority: CN
Inventors: 乐宇明; 蔡雄宇; 兰宾利; 周芮
Original assignee: Tianjin OFilm Opto Electronics Co Ltd
Current assignee: Jiangxi Oufei Optics Co ltd
Priority date: 2020-01-03
Filing date: 2020-01-03
Publication date: 2021-07-06

Abstract

The embodiment of the application discloses an optical system, a lens module and terminal equipment. The optical system comprises a first lens from an object side to an image side along an optical axis direction and has negative refractive power; a second lens element with negative refractive power; a third lens element with positive refractive power; the fourth lens element with negative refractive power has a convex object-side surface at the paraxial region thereof and a concave image-side surface at the paraxial region thereof; the fifth lens element with positive refractive power has a convex image-side surface at the paraxial region thereof; the image side surface of the fourth lens is attached to the object side surface of the fifth lens, and the optical system meets the following conditional expression: TTL/(ImgH 2) <6 is more than 4; wherein, TTL is a distance on an optical axis from an object-side surface of the first lens element to an image plane of the optical system, and ImgH is a horizontal half-image height of the optical system. The surface shapes and the refractive powers of the first lens element to the fifth lens element and the ratio of TTL/(ImgH 2) are reasonably configured, so that the optical system has the imaging effect of wide angle of view and high imaging resolution, and is favorable for correcting system aberration.

Description

Optical system, lens module and terminal equipment

Technical Field

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

Background

In recent years, in order to meet the increasing market demand, an ultra-wide angle lens is widely applied to terminal devices such as mobile phones, monitors, vehicles and the like to obtain a larger field angle.

At present, an ultra-wide-angle lens generally comprises glass lenses and plastic lenses, a plurality of glass lenses or a plurality of plastic lenses are usually needed for obtaining a larger field angle, but the ultra-wide-angle lens has larger size and higher price and cannot meet the requirements of small size, low price and high performance of customers.

How to solve wide visual angle, miniaturization and optical performance of super wide-angle lens are not good, promote super wide-angle lens's imaging resolution should be the direction of industry research and development.

Disclosure of Invention

The embodiment of the application provides an optical system, a lens module and a terminal device, wherein the optical system is an ultra-wide-angle lens, the optical system has good optical performance and high imaging resolution, and the development requirement of miniaturization of the lens is met.

In a first aspect, an embodiment of the present application provides an optical system, in order from an object side to an image side along an optical axis direction, comprising: a first lens element with negative refractive power; a second lens element with negative refractive power; a third lens element with positive refractive power; the fourth lens element with negative refractive power has a convex object-side surface at a paraxial region thereof and a concave image-side surface at the paraxial region thereof; the fifth lens element with positive refractive power has a convex object-side surface at a paraxial region thereof and a convex image-side surface at the paraxial region thereof; the image side surface of the fourth lens element is attached to the object side surface of the fifth lens element, the fourth lens element and the fifth lens element form a cemented lens having positive refractive power, the cemented lens is formed by bonding the fourth lens element and the fifth lens element by photosensitive glue or the like, the optical system further includes a diaphragm, the diaphragm is located between the object side and the fourth lens element, and the optical system satisfies the following conditional expressions: TTL/(ImgH 2) <6 is more than 4; wherein, TTL is a distance on an optical axis from an object-side surface of the first lens element to an image plane of the optical system, and ImgH is a half-image height of the optical system in a horizontal direction.

The utility model provides a through the facial type and the specific value of refracting power and TTL/(ImgH 2) of restriction first lens to fifth lens in optical system, and set up the laminating of fourth lens and fifth lens and form cemented lens for optical system has wide visual angle, the imaging effect of high imaging resolution, be favorable to revising the miniaturization of system aberration and super wide angle lens, guarantee optical system's stability and the imaging system of high pixel, provide the good experience of user.

In one embodiment, the optical system satisfies the conditional expression: 11.8 < FOV/CRA < 21; the FOV is a field angle of the optical system in the horizontal direction, the CRA is a chief ray incident angle, and the chief ray incident angle is an included angle between a chief ray at the maximum image height and a normal direction of an imaging surface. The optical system has a larger angle of view by limiting the ratio of the angle of view to the incident angle of the chief ray, so as to meet the requirement of the large angle of view of terminal equipment such as mobile phones, monitoring equipment, vehicles and the like, and simultaneously reduce the angle of incidence of the chief ray to an imaging surface, so that the light sensing performance of a light sensing element can be improved, and the imaging quality of the optical system can be improved.

In one embodiment, the optical system satisfies the conditional expression: 3.5< f45/f < 7; wherein f45 is a combined focal length of the fourth lens and the fifth lens. The range of the ratio of the combined focal length of the fourth lens and the fifth lens to the effective focal length of the optical system is limited, the refractive power of the optical system is reasonably distributed, the assembly sensitivity of the optical system is favorably reduced, the problems of process manufacturing and assembly of the fourth lens and the fifth lens are solved, the yield is improved, the eccentricity sensitivity is favorably reduced, the system aberration is corrected, the imaging resolution is improved, and a better imaging effect is realized.

In one embodiment, the optical system satisfies the conditional expression: CT5/CT4 is more than or equal to 1 and less than 5; wherein CT4 is the thickness of the fourth lens element along the optical axis, and CT5 is the thickness of the fifth lens element along the optical axis. The thicknesses of the fourth lens and the fifth lens on the optical axis are reasonably configured, so that the gluing process of the fourth lens and the fifth lens is facilitated, the system aberration is corrected, and the imaging resolution is improved.

The range of the ratio of the combined focal length of the fourth lens and the fifth lens to the effective focal length of the optical system is limited, and the thicknesses of the fourth lens and the fifth lens on the optical axis are limited, so that the fourth lens and the fifth lens can be better attached to form a cemented lens, the aberration of the optical system can be corrected, and the imaging effect of the imaging resolution can be improved.

In one embodiment, the optical system satisfies the conditional expression: nd4-nd5 is more than 0; where nd4 is a refractive index of the fourth lens, and nd5 is a refractive index of the fifth lens. nd4-nd5 is more than 0, which is beneficial to correcting the off-axis chromatic aberration and improving the resolution of the optical system.

In one embodiment, the optical system satisfies the conditional expression: -6< f1/f < 0; wherein f1 is the focal length of the first lens, and f is the effective focal length of the optical system. The present embodiment adjusts the optical performance of the optical system by limiting the range of the ratio of the focal length of the first lens to the effective focal length of the optical system, and at the same time, the optical system has the characteristics of wide viewing angle, low sensitivity, and miniaturization.

In one embodiment, the optical system satisfies the conditional expression: -78 < RDY S3/RDY S2< -15; the lens is characterized in that RDY S2 is the curvature radius of the image side surface of the first lens, and RDY S3 is the curvature radius of the object side surface of the second lens. The size of the RDY S2 affects the degree of curvature of the first lens and the position where the ghost image appears, and the larger the RDY S2, the smaller the degree of curvature of the first lens, that is, the smoother the first lens, and the closer the position where the ghost image appears to the edge, which is beneficial to reducing the influence on the imaging quality of the optical system. The size of the RDY S3 will influence the brightness of the ghost image, and the larger the RDY S3, the darker the ghost image is, and the smaller the bending degree of the third lens is, which is beneficial to reducing the influence on the imaging quality.

By limiting the range of the ratio of the focal length of the first lens to the effective focal length of the optical system and limiting the curvature radius of the image side surface of the first lens and the curvature radius of the object side surface of the second lens, the method is beneficial to reducing the brightness of the ghost and enabling the position where the ghost appears to be closer to the edge on the basis of ensuring wide viewing angle, low sensitivity and miniaturization, and the imaging quality is improved.

In one embodiment, the optical system satisfies the conditional expression: -5< f2/f < -1.5; wherein f2 is the focal length of the second lens, and f is the effective focal length of the optical system. The embodiment strengthens the wide view angle capability of the optical system by limiting the range of the ratio of the focal length of the second lens to the effective focal length of the optical system, so that the optical system has the characteristics of wide view angle, low sensitivity and miniaturization.

In one embodiment, the optical system satisfies the conditional expression: RDY S4/f < 1.69; wherein RDY S4 is the radius of curvature of the image-side surface of the second lens. The curvature radius of the image side surface of the second lens is limited to the effective focal length ratio of the optical system, so that the second lens has a smaller curvature degree, and the ratio of ghost generation is reduced.

In one embodiment, the optical system satisfies the conditional expression: ET2/CT2 is less than or equal to 3.3; wherein ET2 is the edge thickness of the second lens at the maximum effective diameter, and CT2 is the thickness of the second lens at the optical axis. Through the limit to the thickness ratio of the edge thickness of the maximum effective diameter of the second lens to the optical axis, the forming difficulty of the second lens is favorably reduced, the manufacturability of the second lens is ensured, and the yield is improved.

In one embodiment, the optical system satisfies the conditional expression: 3< f3/f < 6; wherein f3 is the focal length of the third lens. The optical system has the characteristics of wide visual angle, low sensitivity and miniaturization by limiting the range of the ratio of the focal length of the third lens to the effective focal length of the optical system, and is favorable for correcting the aberration of the system and improving the imaging resolution.

In one embodiment, the optical system satisfies the conditional expression: 3mm < CT3<4.5 mm; wherein CT3 is the thickness of the third lens at the optical axis. The thickness of the third lens at the optical axis is limited, so that system aberration can be corrected conveniently, and imaging resolution can be improved.

In one embodiment, the optical system satisfies the conditional expression: sigma CT/L is more than 0.6 and less than 0.8; wherein Σ CT is a sum of thicknesses of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens of the optical system on an optical axis, and L is a distance from an object-side surface of the first lens to an image-side surface of the fifth lens of the optical system on the optical axis. The total length of the optical system can be effectively shortened by limiting the sigma CT/L, the compact structure among the lenses is ensured, the sensitivity is reduced, and the service life of the lenses is prolonged.

In a second aspect, the present application provides a lens module, comprising a lens barrel and the optical system of any one of the foregoing embodiments, wherein the optical system is installed in the lens barrel.

In a third aspect, the present application provides a terminal device, including the lens module.

According to the lens module, the surface shapes and the bending force of the first lens to the fifth lens and TTL/(ImgH 2) are limited in the optical system, and the fourth lens and the fifth lens are attached to form the cemented lens, so that the lens module has good optical performance, the user experience is improved, and excellent optical quality can be obtained.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments or the background art of the present invention, the drawings required to be used in the embodiments or the background art of the present invention will be described below.

FIG. 1 is a schematic diagram of an optical system provided herein in a terminal device;

FIG. 2 is a schematic diagram of an optical system according to a first embodiment of the present application;

FIG. 3 is a spherical aberration curve of the optical system of the first embodiment;

fig. 4 is an astigmatism curve of the optical system of the first embodiment;

fig. 5 is a distortion curve of the optical system of the first embodiment;

FIG. 6 is a schematic diagram of an optical system according to a second embodiment of the present application;

FIG. 7 is a spherical aberration curve of the optical system of the second embodiment;

fig. 8 is an astigmatism curve of the optical system of the second embodiment;

FIG. 9 is a distortion curve of the optical system of the second embodiment;

FIG. 10 is a schematic diagram of an optical system provided in a third embodiment of the present application;

FIG. 11 is a spherical aberration curve of the optical system of the third embodiment;

fig. 12 is an astigmatism curve of the optical system of the third embodiment;

fig. 13 is a distortion curve of the optical system of the third embodiment;

FIG. 14 is a schematic diagram of an optical system according to a fourth embodiment of the present application;

FIG. 15 is a spherical aberration curve of the optical system of the fourth embodiment;

fig. 16 is an astigmatism curve of the optical system of the fourth embodiment;

fig. 17 is a distortion curve of the optical system of the fourth embodiment.

Detailed Description

The embodiments of the present invention will be described below with reference to the drawings.

Referring to fig. 1, the optical system 10 according to the present application is applied to a lens module 20 in a terminal device 30. The terminal device 30 may be a mobile phone, a monitor, a vehicle-mounted device, or the like. The optical system 10 may be an ultra-wide angle lens, the optical system 10 is installed in a lens barrel of the lens module 20, and the lens module 20 is assembled inside the terminal device 30.

In one embodiment, an optical system includes five lens elements, which are sequentially disposed from an object side to an image side along an optical axis and include a first lens element, a second lens element, a third lens element, a fourth lens element and a fifth lens element, wherein the fourth lens element and the fifth lens element form a cemented lens having positive refractive power.

Specifically, the surface shapes and refractive powers of the five lenses are as follows:

a first lens element with negative refractive power; a second lens element with negative refractive power; a third lens element with positive refractive power; the fourth lens element with negative refractive power has a convex object-side surface at the paraxial region thereof and a concave image-side surface at the paraxial region thereof; the fifth lens element with positive refractive power has a convex object-side surface at a paraxial region thereof and a convex image-side surface at a paraxial region thereof.

The optical system further includes a diaphragm positioned between the object side and the fourth lens.

The optical system satisfies the following conditional expression: TTL/(ImgH 2) <6 is more than 4; wherein, TTL is a distance on an optical axis from an object-side surface of the first lens element to an image plane of the optical system, and ImgH is a horizontal half-image height of the optical system.

The surface shapes and the refractive powers of the first lens element to the fifth lens element are reasonably configured, and the cemented lens formed by the fourth lens element and the fifth lens element is favorable for meeting the requirements of miniaturization and high imaging resolution of an optical system. Meanwhile, the appropriate ratio of TTL/(ImgH x 2) is limited, the shorter TTL is realized, the compact structure of the optical system is facilitated, the stability of the optical system is ensured, and the high-pixel imaging system is obtained.

The aspherical surface curve equations of the second lens to the fifth lens are as follows:

wherein Z is a distance from a corresponding point on the aspherical surface to a plane tangent to the surface vertex, r is a distance from a corresponding point on the aspherical surface to the optical axis, c is a curvature of the aspherical surface vertex, k is a conic constant, and Ai is a coefficient corresponding to the i-th high-order term in the aspherical surface type formula.

The present application is described in detail below with reference to four specific examples.

Example one

As shown in fig. 2, the middle straight line represents the optical axis, and the left side of the optical system is the object side and the right side is the image side. In the optical system provided in this embodiment, the first lens L1, the second lens L2, the third lens L3, the stop STO, the fourth lens L4, the fifth lens L5, the infrared filter element IRCF, and the cover glass CG are arranged in order from the object side to the image side along the optical axis. The fourth lens L4 and the fifth lens L5 are cemented lenses, which is beneficial to reducing the assembly sensitivity of the optical system, solving the problems of lens manufacturing and lens assembly and improving the yield.

The first lens element L1 with negative refractive power has an object-side surface S1 being convex in a paraxial region thereof and an image-side surface S2 being concave in a paraxial region thereof.

The second lens element L2 with negative refractive power has an object-side surface S3 being concave in a paraxial region thereof and an image-side surface S4 being concave in a paraxial region thereof.

The third lens element L3 with positive refractive power has an object-side surface S5 being convex in a paraxial region thereof and an image-side surface S6 being convex in a paraxial region thereof.

The fourth lens element L4 with negative refractive power has an object-side surface S7 being convex in a paraxial region thereof and an image-side surface S8 being concave in a paraxial region thereof.

The fifth lens element L5 with positive refractive power has an object-side surface S9 being convex in a paraxial region thereof and an image-side surface S10 being convex in a paraxial region thereof.

The stop STO may be located between the object side of the optical system and the fourth lens L4, and the stop STO in this embodiment is located behind the third lens L3, which tends to be at a middle position of the optical system, and is beneficial to balance aberrations of the optical system.

The infrared filter element IRCF is arranged behind the fifth lens L5 and comprises an object side surface S11 and an image side surface S12, the infrared filter element IRCF is used for filtering infrared rays, the rays incident to the image side surface are visible rays, the wavelength of the visible rays is 380nm-780nm, and the infrared filter element IRCF is made of glass.

The protective glass CG is located behind the infrared filter element IRCF and comprises an object side surface S13 and an image side surface S14, and the protective glass CG is used for protecting the photosensitive element, so that the photosensitive element is prevented from being exposed outside, the photosensitive element is prevented from being influenced by dust and the like, and the imaging quality is ensured. The image formation surface S15 is an effective pixel region of the electrophotographic photosensitive member.

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

TABLE 1a

Wherein f is the effective focal length of the optical system, FNO is the f-number of the optical system, and FOV is the angle of view of the optical system in the horizontal direction.

S8/S9 indicates that the image-side surface of the fourth lens and the object-side surface of the fifth lens, and the image-side surface S8 of the fourth lens and the object-side surface S9 of the fifth lens are cemented together, and thus are represented as one surface on data.

Table 1b shows the high-order term coefficients A4, A6, a8, a10, a12, a14, a16, a18, and a20 that can be used for the respective aspherical mirrors S3, S4, S5, S6, S7, S8/S9, S10 in the first embodiment.

TABLE 1b

Wherein, S8/S9 refers to the image side surface of the fourth lens and the object side surface of the fifth lens, and the image side surface S8 of the fourth lens and the object side surface S9 of the fifth lens are glued together, so that the data is represented as one surface.

FIG. 3 shows a spherical aberration curve of the optical system of the first embodiment, which represents the deviation of the converging focal points of light rays of different wavelengths after passing through the lenses of the optical system;

fig. 4 shows astigmatism curves of the optical system of the first embodiment, which represent meridional field curvature and sagittal field curvature;

fig. 5 shows distortion curves of the optical system of the first embodiment, which represent distortion magnitude values corresponding to different angles of view;

as can be seen from fig. 3, 4, and 5, the optical system according to the first embodiment can achieve good image quality.

Example two

As shown in fig. 6, the middle straight line represents the optical axis, and the left side of the optical system is the object side and the right side is the image side. In the optical system provided in this embodiment, the first lens L1, the second lens L2, the third lens L3, the stop STO, the fourth lens L4, the fifth lens L5, the infrared filter element IRCF, and the cover glass CG are arranged in order from the object side to the image side along the optical axis. The fourth lens L4 and the fifth lens L5 are cemented lenses, which is beneficial to reducing the assembly sensitivity of the optical system, solving the problems of lens manufacturing and lens assembly and improving the yield.

The other structures of the second embodiment are the same as those of the first embodiment, and reference is made to the same.

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

TABLE 2a

Table 2b shows the high-order term coefficients A4, A6, a8, a10, a12, a14, a16, a18, and a20 that can be used for the respective aspherical mirrors S3, S4, S5, S6, S7, S8/S9, S10 in the second embodiment.

TABLE 2b

FIG. 7 shows a spherical aberration curve of the optical system of the second embodiment, which represents the deviation of the converging focal points of light rays of different wavelengths after passing through the lenses of the optical system;

FIG. 8 shows astigmatism curves of the optical system of the second embodiment, which represent meridional field curvature and sagittal field curvature;

fig. 9 shows distortion curves of the optical system of the second embodiment, which represent distortion magnitude values corresponding to different angles of view;

as can be seen from fig. 7, 8, and 9, the optical system according to the second embodiment can achieve good image quality.

EXAMPLE III

As shown in fig. 10, the middle straight line represents the optical axis, and the left side of the optical system is the object side and the right side is the image side. In the optical system provided in this embodiment, the first lens L1, the second lens L2, the third lens L3, the stop STO, the fourth lens L4, the fifth lens L5, the infrared filter element IRCF, and the cover glass CG are arranged in order from the object side to the image side along the optical axis. The fourth lens L4 and the fifth lens L5 are cemented lenses, which is beneficial to reducing the assembly sensitivity of the optical system, solving the problems of lens manufacturing and lens assembly and improving the yield.

The other structures of the third embodiment are the same as those of the first embodiment, and reference is made to the third embodiment.

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

TABLE 3a

Table 3b shows the high-order term coefficients A4, A6, a8, a10, a12, a14, a16, a18, and a20 that can be used for the respective aspherical mirrors S3, S4, S5, S6, S7, S8/S9, S10 in the third embodiment.

TABLE 3b

FIG. 11 shows a spherical aberration curve of the optical system of the third embodiment, which represents the deviation of the converging focal points of light rays of different wavelengths after passing through the lenses of the optical system;

fig. 12 shows astigmatism curves of the optical system of the third embodiment, which represent meridional field curvature and sagittal field curvature;

fig. 13 shows distortion curves of the optical system of the third embodiment, which represent distortion magnitude values corresponding to different angles of view;

as can be seen from fig. 11, 12, and 13, the optical system according to the third embodiment can achieve good image quality.

Example four

As shown in fig. 14, the middle straight line represents the optical axis, and the left side of the optical system is the object side and the right side is the image side. In the optical system provided in this embodiment, the first lens L1, the second lens L2, the third lens L3, the stop STO, the fourth lens L4, the fifth lens L5, the infrared filter element IRCF, and the cover glass CG are arranged in order from the object side to the image side along the optical axis. The fourth lens L4 and the fifth lens L5 are cemented lenses, which is beneficial to reducing the assembly sensitivity of the optical system, solving the problems of lens manufacturing and lens assembly and improving the yield.

The other structures of the fourth embodiment are the same as those of the first embodiment, and reference is made to the same.

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

TABLE 4a

Table 4b shows the high-order coefficient coefficients A4, A6, a8, a10, a12, a14, a16, a18, and a20 which can be used for each of the aspherical mirrors S3, S4, S5, S6, S7, S8/S9, S10 in the fourth embodiment.

TABLE 4b

FIG. 15 shows a spherical aberration curve of the optical system of the fourth embodiment, which represents the deviation of the converging focal points of light rays of different wavelengths after passing through the lenses of the optical system;

fig. 16 shows astigmatism curves of the optical system of the fourth embodiment, which represent meridional field curvature and sagittal field curvature;

fig. 17 shows distortion curves of the optical system of the fourth embodiment, which represent distortion magnitude values corresponding to different angles of view;

as can be seen from fig. 15, 16, and 17, the optical system according to the fourth embodiment can achieve good image quality.

Table 5 shows TTL/(ImgH × 2) values of the optical systems of the first to fourth embodiments, and as can be seen from table 5, the respective embodiments satisfy the condition: 4 < TTL/(ImgH 2) < 6.

TABLE 5

	TTL/(ImgH*2)
		First embodiment	4.54
Second embodiment	4.54
		Third embodiment	4.54
Fourth embodiment	4.54

Table 6 shows FOV/CRA values of the optical systems of the first to fourth embodiments, and as can be seen from table 6, the embodiments satisfy the conditions: 11.8 < FOV/CRA < 21.

TABLE 6

	FOV/CRA
		First embodiment	12.19
Second embodiment	12.27
		Third embodiment	12.04
Fourth embodiment	11.96

Table 7 shows f1/f values of the optical systems of the first to fourth embodiments, and as can be seen from table 7, the respective embodiments satisfy the conditions: -6< f1/f <0.

TABLE 7

	f1/f
		First embodiment	-5.92
Second embodiment	-5.71
		Third embodiment	-5.50
Fourth embodiment	-5.45

Table 8 shows RDY S3/RDY S2 values of the optical systems of the first to fourth embodiments, and as can be seen from table 8, the respective embodiments satisfy the conditions: -78 < RDY S3/RDY S2< -15.

TABLE 8

	RDY S3/RDY S2
		First embodiment	-45.87
Second embodiment	-49.23
		Third embodiment	-65.63
Fourth embodiment	-48.90

Table 9 shows f2/f values of the optical systems of the first to fourth embodiments, and as can be seen from table 9, the respective embodiments satisfy the conditions: -5< f2/f < -1.5.

TABLE 9

	f2/f
		First embodiment	-2.77
Second embodiment	-2.65
		Third embodiment	-2.86
Fourth embodiment	-2.88

Table 10 shows RDY S4/f values of the optical systems of the first to fourth embodiments, and as can be seen from table 10, the respective embodiments satisfy the conditions: RDY S4/f < 1.69.

Watch 10

	RDY S4/f
		First embodiment	1.53
Second embodiment	1.47
		Third embodiment	1.58
Fourth embodiment	1.59

Table 11 shows ET2/CT2 values of the optical systems of the first to fourth embodiments, and as can be seen from table 11, the respective embodiments satisfy the conditions: ET2/CT2 is less than or equal to 3.3.

TABLE 11

Table 12 shows f3/f values of the optical systems of the first to fourth embodiments, and as can be seen from table 12, each of the embodiments satisfies the conditions: 3< f3/f < 6.

TABLE 12

	f3/f
		First embodiment	4.30
Second embodiment	4.23
		Third embodiment	4.41
Fourth embodiment	4.41

Table 13 shows CT3 values of the optical systems of the first to fourth embodiments, and as can be seen from table 13, each of the embodiments satisfies the conditions: 3< CT3< 4.5.

Watch 13

	CT3
		First embodiment	3.50
Second embodiment	3.50
		Third embodiment	3.80
Fourth embodiment	4.00

Table 14 shows f45/f values of the optical systems of the first to fourth embodiments, and as can be seen from table 14, each of the embodiments satisfies the conditions: 3.5< f45/f < 7.

TABLE 14

	f45/f
		First embodiment	4.01
Second embodiment	3.78
		Third embodiment	3.96
Fourth embodiment	4.02

Table 15 shows CT5/CT4 values of the optical systems of the first to fourth embodiments, and as can be seen from table 15, the respective embodiments satisfy the conditions: 1 is less than or equal to CT5/CT4 is less than 5.

Watch 15

	CT5/CT4
		First embodiment	3.91
Second embodiment	4.43
		Third embodiment	4.23
Fourth embodiment	4.23

Table 16 shows the Σ CT/L values of the optical systems of the first to fourth embodiments, and as can be seen from table 16, each embodiment satisfies the condition: 0.6 < sigma CT/L < 0.8.

TABLE 16

	ΣCT/L
		First embodiment	0.63
Second embodiment	0.63
		Third embodiment	0.66
Fourth embodiment	0.68

Table 17 shows the nd4-nd5 values of the optical systems of the first to fourth embodiments, and it can be seen from table 17 that the respective embodiments satisfy the conditions: nd4-nd5 is more than 0.

TABLE 17

	nd4-nd5
		First embodiment	0.12
Second embodiment	0.12
		Third embodiment	0.12
Third embodiment	0.12

The foregoing is a preferred embodiment of the present application, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present application, and these modifications and decorations are also regarded as the protection scope of the present application.

Claims

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

a first lens element with negative refractive power;

a second lens element with negative refractive power;

a third lens element with positive refractive power;

the fourth lens element with negative refractive power has a convex object-side surface at a paraxial region thereof and a concave image-side surface at the paraxial region thereof;

the fifth lens element with positive refractive power has a convex image-side surface at the paraxial region thereof;

the image side surface of the fourth lens is attached to the object side surface of the fifth lens, and the optical system meets the following conditional expression:

4＜TTL/(ImgH*2)＜6；

wherein, TTL is a distance on an optical axis from an object-side surface of the first lens element to an image plane of the optical system, and ImgH is a half-image height of the optical system in a horizontal direction.

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

11.8＜FOV/CRA＜21；

wherein, the FOV is a field angle of the optical system in the horizontal direction, and the CRA is a chief ray incident angle.

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

3.5<f45/f<7；

wherein f45 is a combined focal length of the fourth lens and the fifth lens, and f is an effective focal length of the optical system.

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

1≤CT5/CT4＜5；

wherein CT4 is the thickness of the fourth lens element along the optical axis, and CT5 is the thickness of the fifth lens element along the optical axis.

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

nd4-nd5＞0；

where nd4 is a refractive index of the fourth lens, and nd5 is a refractive index of the fifth lens.

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

-6<f1/f<0；

wherein f1 is the focal length of the first lens, and f is the effective focal length of the optical system.

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

-78＜RDY S3/RDY S2<-15；

the lens is characterized in that RDY S2 is the curvature radius of the image side surface of the first lens, and RDY S3 is the curvature radius of the object side surface of the second lens.

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

-5<f2/f<-1.5；

wherein f2 is the focal length of the second lens, and f is the effective focal length of the optical system.

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

RDY S4/f<1.69；

where RDY S4 is the radius of curvature of the image-side surface of the second lens, and f is the effective focal length of the optical system.

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

ET2/CT2≤3.3；

wherein ET2 is the thickness of the second lens at the maximum effective diameter, and CT2 is the thickness of the second lens at the optical axis.

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

3<f3/f<6；

wherein f3 is the focal length of the third lens, and f is the effective focal length of the optical system.

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

3mm<CT3<4.5mm；

wherein CT3 is the thickness of the third lens at the optical axis.

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

0.6＜ΣCT/L＜0.8；

wherein Σ CT is a sum of thicknesses of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens of the optical system on an optical axis, and L is a distance from an object-side surface of the first lens to an image-side surface of the fifth lens of the optical system on the optical axis.

14. A lens module comprising a lens barrel and an optical system according to any one of claims 1 to 13, the optical system being mounted in the lens barrel.

15. A terminal device characterized by comprising the lens module according to claim 14.