CN114859508A

CN114859508A - Optical system, camera module and electronic equipment

Info

Publication number: CN114859508A
Application number: CN202210346278.9A
Authority: CN
Inventors: 游兴海
Original assignee: Nanchang OFilm Optoelectronics Technology Co Ltd
Current assignee: Nanchang OFilm Optoelectronics Technology Co Ltd
Priority date: 2022-04-02
Filing date: 2022-04-02
Publication date: 2022-08-05

Abstract

An optical system, a camera module and an electronic device, the optical system sequentially comprises from an object side to an image side along an optical axis: the first lens element with refractive power has positive refractive power, and the fourth lens element with negative refractive power has negative refractive power, wherein the first lens element is a catadioptric lens element comprising a first refractive surface, a first reflective surface, a second reflective surface and a second refractive surface, the first refractive surface and the second reflective surface are located at an object side, the second reflective surface is a concave surface, the first reflective surface and the second refractive surface are located at an image side, the first reflective surface is a convex surface, and light rays sequentially pass through the first refractive surface, the first reflective surface, the second reflective surface and the second refractive surface. By reasonably designing the surface shape and the refractive power of each lens of the optical system, the characteristics of small optical total length, long focal length and high pixel are favorably met.

Description

Optical system, camera module and electronic equipment

Technical Field

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

Background

In recent years, portable electronic products with a photographing function have been increasingly thinner, and thus, demands for optical lens systems to satisfy high image quality and be miniaturized have been increasing. However, the total length of the optical system having the telephoto characteristic is increased by the increase in the length, and the focal length is limited by the thickness of the electronic product.

Therefore, how to achieve the effect of long focal length and high pixel under the premise of reducing the size of the lens becomes one of the problems that must be solved in the industry.

Disclosure of Invention

The invention aims to provide an optical system, a camera module and electronic equipment, which solve the problem that in the prior art, a long focal length and high pixels are needed on the premise that a lens is small in size.

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, in order from an object side to an image side along an optical axis, comprising: a first lens element with positive refractive power; a second lens element with refractive power; a third lens element with refractive power; a fourth lens element with negative refractive power; wherein, first lens are catadioptric lens, including first plane of refraction, second plane of refraction and second plane of refraction, first plane of refraction with the second plane of refraction is located the object side, just first plane of refraction is located the periphery of second plane of refraction, the second plane of refraction is the concave surface in paraxial region department, first plane of reflection with the second plane of refraction is located image side, just first plane of reflection is located the periphery of second plane of refraction, light passes through in proper order first plane of refraction first plane of reflection the second plane of reflection with the second plane of refraction.

The optical system satisfies the relation: 3.5< f/Imgh < 4.6; wherein f is the effective focal length of the optical system, and Imgh is half of the maximum field angle corresponding image height of the optical system.

The first lens has positive refractive power, so that the trend of incident light and reflected light can be controlled, and the total optical length of the optical lens can be shortened; the second lens has refractive power, so that the spherical aberration of the optical system is favorably reduced, and the imaging quality of the optical lens can be improved; the third lens element with refractive power is favorable for reducing the deflection angle of incident light, so that the incident light enters the fourth lens element at a proper angle; by making the fourth lens element have negative refractive power, the distortion, astigmatism and curvature of field generated by the incident light passing through the fourth lens element can be corrected, thereby obtaining high-quality imaging. Therefore, the surface type is satisfied, the optical system can realize the effects of long focal length and miniaturization, the incident angle of the incident light on the imaging surface is kept in a reasonable range, the characteristic of higher relative brightness of the edge of the imaging surface can be realized, and the requirement of a small-angle matching angle of the image sensor can be satisfied.

By enabling the optical system to satisfy the relational expression, the ratio of the effective focal length of the optical system to half of the maximum field angle corresponding image height is favorably and reasonably configured, the optical system has a longer effective focal length, good imaging quality is achieved, and the effects of ultra-thinning and high pixel are achieved. Below the lower limit of the relational expression, the focal length of the optical system is greatly limited, and the requirement that the optical system has a long focal length is difficult to meet; if the maximum angle of view of the optical system exceeds the upper limit of the relational expression, the half of the height of the image corresponding to the maximum angle of view of the optical system is too small, and it is difficult to satisfy the requirement that the optical system has high pixels.

In one embodiment, the optical system satisfies the relationship: 1.2< f/EPD < 1.5; wherein EPD is an entrance pupil diameter of the optical system. By enabling the optical system to satisfy the relational expression, the optical system can have the characteristic of a large aperture, so that the luminous flux of the optical system in unit time is increased, and the imaging effect in a dark environment is enhanced. Meanwhile, the first lens close to the diaphragm position can have a smaller aperture, and the design of structure miniaturization is facilitated. Below the lower limit of the relational expression, the diameter of the entrance pupil of the optical system is increased, so that the light rays entering the system are increased, the coma aberration of the edge light rays is difficult to correct, the imaging is unclear, meanwhile, the aperture of the first lens is increased, the thickness ratio is uneven, and the process forming difficulty is increased; when the light quantity exceeds the upper limit of the relational expression, the light flux of the optical system is insufficient, and under the condition of dark environment or insufficient light, the optical system is difficult to acquire clearer detail information of a measured object.

In one embodiment, the optical system satisfies the relationship: 0.4< TTL/f < 0.6; 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. By making the optical system satisfy the above relational expression, the optical system can have the characteristics of a telephoto lens and the miniaturization of the lens can be satisfied. The lower limit of the relational expression is not beneficial to the processing and manufacturing of the first lens, the second lens, the third lens and the fourth lens; exceeding the upper limit of the relation, the total optical length of the optical system is long, which is not favorable for meeting the requirement of miniaturization of the optical system.

In one embodiment, the optical system satisfies the relationship: -3.0< f/f4< -1.0; wherein f4 is the effective focal length of the fourth lens. Through making optical system satisfy above-mentioned relational expression, can rationally distribute the ratio of fourth lens and optical system's effective focal length to the spherical aberration that balanced first lens, second lens and third lens produced, and then finely tune and control optical system's spherical aberration, obtain the good imaging quality of epaxial visual field, be favorable to promoting optical system's the ability of taking a photograph of far away. When the refractive power of the fourth lens element is too low, the spherical aberration generated by the first lens element, the second lens element and the third lens element cannot be balanced easily by the fourth lens element in correcting the residual spherical aberration in the optical system; if the focal length of the fourth lens exceeds the upper limit of the relational expression, the focal length of the fourth lens is small, the focal length of the optical system is limited greatly, and the requirement that the optical system has a long focal length is difficult to meet.

In one embodiment, the optical system satisfies the relationship: 0< | f/f3| + | f/f2| < 1.2; wherein f3 is the effective focal length of the third lens, and f2 is the effective focal length of the second lens. By making the optical system satisfy the above relation, the contribution amounts of spherical aberration and coma of the second lens and the third lens can be effectively constrained, and the sensitivity thereof is made to be at a reasonable level after balancing. And when the upper limit of the relational expression is exceeded, the second lens and the third lens are sensitive, the processing precision is difficult to ensure, and the production yield of the optical lens is low.

In one embodiment, the optical system satisfies the relationship: 0.8< | (f1+ f3)/f3| < 2.0; wherein f3 is the effective focal length of the third lens. By enabling the optical system to satisfy the relational expression, reasonable positive third-order spherical aberration and negative fifth-order spherical aberration can be contributed, and the negative third-order spherical aberration and the positive fifth-order spherical aberration generated by the first lens and the second lens are balanced, so that the system has smaller spherical aberration, and good imaging quality of an on-axis view field is ensured. And when the spherical aberration exceeds the upper limit of the relational expression, the spherical aberration of the optical system is large, and the imaging quality of the on-axis field of view is poor.

In one embodiment, the optical system satisfies the relationship: 0.3< | f1+ f2|/| f1-f2| < 1.5; wherein f1 is the effective focal length of the first lens, and f2 is the effective focal length of the second lens. By enabling the optical system to satisfy the relational expression, the contribution range of the focal power can be reasonably controlled, and meanwhile, the contribution rate of the negative spherical aberration can be reasonably controlled, so that the positive focal power generated by the negative component can be reasonably balanced.

In one embodiment, the optical system satisfies the relationship: -2.1< f123/f234< -0.8; wherein f123 is a combined effective focal length of the first lens, the second lens, and the third lens, and f234 is a combined effective focal length of the second lens, the third lens, and the fourth lens. By enabling the optical system to satisfy the relational expression, the size of the combined focal length of the first lens, the second lens and the third lens can be well controlled, meanwhile, the size of the combined focal length of the second lens, the third lens and the fourth lens can also be well controlled, the spherical aberration balance of the optical system is realized, the good imaging quality of the on-axis view field is obtained, and the good processability of the optical system is also ensured. Below the lower limit of the relational expression, the spherical aberration of the optical system is large, and the imaging quality of the on-axis field of view is poor; exceeding the upper limit of the relation is not favorable for processing the lens.

In one embodiment, the optical system satisfies the relationship: 0.2< | (R2+ R3)/R4| < 1.3; wherein, R2 is a curvature radius of the first reflective surface of the first lens element on the optical axis, R3 is a curvature radius of the second reflective surface of the first lens element on the optical axis, and R4 is a curvature radius of the second refractive surface of the first lens element on the optical axis. By enabling the optical system to satisfy the relational expression, the light deflection angle of the optical system is small, and the optical system is easier to process. Lower than the lower limit of the relational expression is not beneficial to the processing of the optical system; the upper limit of the relational expression is exceeded, so that the refraction angle of the light at the second refraction surface of the first lens is large, the aberration of the off-axis field of view is large, and the imaging quality of the off-axis field of view is affected.

In one embodiment, the optical system satisfies the relationship: 0< | (R7-R8)/R7| < 2.1; wherein, R7 is a curvature radius of an object-side surface of the third lens element on an optical axis, and R8 is a curvature radius of an image-side surface of the third lens element on the optical axis. By enabling the optical system to satisfy the relational expression, the curvature radius of the object side surface and the curvature radius of the image side surface of the third lens are proper, the processability of the shape of the third lens can be ensured, the optical deflection angle born by the lens can be effectively distributed, the astigmatism of the off-axis field is improved, and the image quality of the middle field and the image quality of the aperture zone are reasonably controlled.

In one embodiment, the optical system satisfies the relationship: 1.8< TTL/(CT13+ CT2+ CT3+ CT4) < 3.0; 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, CT13 is a distance on the optical axis from the second reflecting surface to the second refracting surface of the first lens element, CT2 is a thickness of the second lens element on the optical axis, CT3 is a thickness of the third lens element on the optical axis, and CT4 is a thickness of the fourth lens element on the optical axis. By enabling the optical system to satisfy the relational expression, the range of residual distortion after the balance of the optical system can be reasonably controlled, the optical system has good distortion performance, the optical system is guaranteed to have good processing performance, and the miniaturization of the optical system is met. Below the lower limit of the relational expression, the distortion of the optical system is large and is not beneficial to the processing of the optical system; exceeding the upper limit of the relational expression, the total optical length of the optical system is long, which is not favorable for satisfying the demand for miniaturization of the optical system.

In a second aspect, the present invention further provides a camera module, which includes a photosensitive chip and the optical system of any one of the embodiments of the first aspect, where the photosensitive chip is disposed on an image side of the optical system. The light sensing surface of the light sensing chip is positioned on the imaging surface of the optical system, and light rays which penetrate through the lens and enter an object on the light sensing surface can be converted into electric signals of images. The photosensitive chip may be a Complementary Metal Oxide Semiconductor (CMOS) or a Charge-coupled Device (CCD). The camera module can be an imaging module integrated on the electronic equipment and can also be an independent lens. By adding the optical system provided by the invention into the camera module, the camera module has the characteristics of smaller total optical length, long focal length and high pixels by reasonably designing the surface shape and the refractive power of each lens in the optical system.

In a third aspect, the present invention further provides an electronic device, which includes a housing and the camera module set in the second aspect, where the camera module set is disposed in the housing. The electronic device includes but is not limited to a smart phone, a computer, a smart watch, and the like. By adding the camera module provided by the invention into the electronic equipment, the electronic equipment has the characteristics of smaller optical total length, long focal length and high pixels.

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.

Fig. 1 is a schematic configuration diagram of an optical system of a first embodiment;

fig. 2 shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the first embodiment;

FIG. 3 is a schematic structural view of an optical system of a second embodiment;

FIG. 4 shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the second embodiment;

fig. 5 is a schematic structural view of an optical system of a third embodiment;

fig. 6 shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the third embodiment;

fig. 7 is a schematic configuration diagram of an optical system of a fourth embodiment;

fig. 8 shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the fourth embodiment;

fig. 9 is a schematic configuration diagram of an optical system of the fifth embodiment;

fig. 10 shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the fifth embodiment;

fig. 11 is a schematic configuration diagram of an optical system of a sixth embodiment;

fig. 12 shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the sixth embodiment;

fig. 13 is a schematic configuration diagram of an optical system of the seventh embodiment;

fig. 14 shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the seventh embodiment;

fig. 15 is a schematic configuration diagram of an optical system of the eighth embodiment;

fig. 16 shows a longitudinal spherical aberration curve, an astigmatism curve, and a distortion curve of the eighth 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.

In a first aspect, the present invention provides an optical system, in order from an object side to an image side along an optical axis, comprising: a first lens element with positive refractive power; a second lens element with refractive power; a third lens element with refractive power; a fourth lens element with negative refractive power; the first lens is a catadioptric lens and comprises a first refraction surface, a first reflection surface, a second reflection surface and a second refraction surface, the first refraction surface and the second reflection surface are located on the object side, the first refraction surface is located on the periphery of the second refraction surface, the second reflection surface is a concave surface at a position close to an optical axis, the first reflection surface and the second reflection surface are located on the image side, the first reflection surface is located on the periphery of the second reflection surface, and light rays sequentially pass through the first refraction surface, the first reflection surface, the second reflection surface and the second refraction surface.

The optical system satisfies the relation: 3.5< f/Imgh < 4.6; where f is the effective focal length of the optical system, and Imgh is half the height of the image corresponding to the maximum field angle of the optical system.

In one embodiment, the optical system satisfies the relationship: 1.2< f/EPD < 1.5; where EPD is the entrance pupil diameter of the optical system. By enabling the optical system to satisfy the relational expression, the optical system can have the characteristic of a large aperture, so that the luminous flux of the optical system in unit time is increased, and the imaging effect in a dark environment is enhanced. Meanwhile, the first lens close to the diaphragm position can have a smaller aperture, and the design of structure miniaturization is facilitated. Below the lower limit of the relational expression, the diameter of the entrance pupil of the optical system is increased, so that the light rays entering the system are increased, the coma aberration of the edge light rays is difficult to correct, the imaging is unclear, meanwhile, the aperture of the first lens is increased, the thickness ratio is uneven, and the process forming difficulty is increased; when the upper limit of the relational expression is exceeded, the light flux of the optical system is insufficient, and under the condition of dark environment or insufficient light, the optical system is difficult to acquire clear detailed information of the measured object.

In one embodiment, the optical system satisfies the relationship: 0.4< TTL/f < 0.6; 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. By making the optical system satisfy the above relational expression, the optical system can have the characteristics of a telephoto lens and the miniaturization of the lens can be satisfied. The lower limit of the relational expression is not beneficial to the processing and manufacturing of the first lens, the second lens, the third lens and the fourth lens; exceeding the upper limit of the relation, the total optical length of the optical system is long, which is not favorable for meeting the requirement of miniaturization of the optical system.

In one embodiment, the optical system satisfies the relationship: -3.0< f/f4< -1.0; where f4 is the effective focal length of the fourth lens. Through making optical system satisfy above-mentioned relational expression, can rationally distribute the ratio of fourth lens and optical system's effective focal length to the spherical aberration that balanced first lens, second lens and third lens produced, and then finely tune and control optical system's spherical aberration, obtain the good imaging quality of epaxial visual field, be favorable to promoting optical system's the ability of taking a photograph of far away. When the refractive power of the fourth lens element is too low, the spherical aberration generated by the first lens element, the second lens element and the third lens element cannot be balanced easily by the fourth lens element in correcting the residual spherical aberration in the optical system; if the focal length of the fourth lens exceeds the upper limit of the relational expression, the focal length of the fourth lens is small, the focal length of the optical system is limited greatly, and the requirement that the optical system has a long focal length is difficult to meet.

In one embodiment, the optical system satisfies the relationship: 0< | f/f3| + | f/f2| < 1.2; wherein f3 is the effective focal length of the third lens, and f2 is the effective focal length of the second lens. By making the optical system satisfy the above relation, the contribution amounts of spherical aberration and coma of the second lens and the third lens can be effectively constrained, and the sensitivity thereof is made to be at a reasonable level after balancing. And when the upper limit of the relational expression is exceeded, the second lens and the third lens are sensitive, the processing precision is difficult to guarantee, and the production yield of the optical lens is low.

In one embodiment, the optical system satisfies the relationship: 0.8< | (f1+ f3)/f3| < 2.0; where f3 is the effective focal length of the third lens. By enabling the optical system to satisfy the relational expression, reasonable positive third-order spherical aberration and negative fifth-order spherical aberration can be contributed, and the negative third-order spherical aberration and the positive fifth-order spherical aberration generated by the first lens and the second lens are balanced, so that the system has smaller spherical aberration, and good imaging quality of an on-axis view field is ensured. And if the upper limit of the relational expression is exceeded, the spherical aberration of the optical system is large, and the imaging quality of the on-axis field of view is poor.

In one embodiment, the optical system satisfies the relationship: -2.1< f123/f234< -0.8; where f123 is a combined effective focal length of the first lens, the second lens, and the third lens, and f234 is a combined effective focal length of the second lens, the third lens, and the fourth lens. By enabling the optical system to satisfy the relational expression, the size of the combined focal length of the first lens, the second lens and the third lens can be well controlled, meanwhile, the size of the combined focal length of the second lens, the third lens and the fourth lens can also be well controlled, the spherical aberration balance of the optical system is realized, the good imaging quality of the on-axis view field is obtained, and the good processability of the optical system is also ensured. Below the lower limit of the relational expression, the spherical aberration of the optical system is large, and the imaging quality of the on-axis field of view is poor; exceeding the upper limit of the relation is not favorable for processing the lens.

In one embodiment, the optical system satisfies the relationship: 0.2< | (R2+ R3)/R4| < 1.3; wherein, R2 is a curvature radius of the first reflective surface of the first lens element, R3 is a curvature radius of the second reflective surface of the first lens element, and R4 is a curvature radius of the second refractive surface of the first lens element. By enabling the optical system to satisfy the relational expression, the light deflection angle of the optical system is small, and the optical system is easier to process. Lower than the lower limit of the relational expression is not beneficial to the processing of the optical system; and if the refractive angle of the light ray at the second refractive surface of the first lens is larger than the upper limit of the relational expression, the aberration of the off-axis field of view is larger, and the imaging quality of the off-axis field of view is further influenced.

In one embodiment, the optical system satisfies the relationship: 0< | (R7-R8)/R7| < 2.1; wherein, R7 is a curvature radius of the object-side surface of the third lens element on the optical axis, and R8 is a curvature radius of the image-side surface of the third lens element on the optical axis. By enabling the optical system to satisfy the relational expression, the curvature radius of the object side surface and the curvature radius of the image side surface of the third lens are proper, the processability of the shape of the third lens can be ensured, the optical deflection angle born by the lens can be effectively distributed, the astigmatism of the off-axis field is improved, and the image quality of the middle field and the image quality of the aperture zone are reasonably controlled.

In one embodiment, the optical system satisfies the relationship: 1.8< TTL/(CT13+ CT2+ CT3+ CT4) < 3.0; 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, CT13 is a distance on the optical axis from the second reflecting surface to the second refracting surface of the first lens element, CT2 is a thickness on the optical axis of the second lens element, CT3 is a thickness on the optical axis of the third lens element, and CT4 is a thickness on the optical axis of the fourth lens element. By enabling the optical system to satisfy the relational expression, the range of residual distortion after the balance of the optical system can be reasonably controlled, the optical system has good distortion performance, the optical system is guaranteed to have good processing performance, and the miniaturization of the optical system is met. Below the lower limit of the relational expression, the distortion of the optical system is large and is not beneficial to the processing of the optical system; exceeding the upper limit of the relational expression, the total optical length of the optical system is long, which is not favorable for satisfying the demand for miniaturization of the optical system.

First embodiment

Referring to fig. 1 and fig. 2, the optical system of the present embodiment, in order from an object side to an image side along an optical axis direction, includes:

the first lens element L1 with positive refractive power has a first refractive surface S1 of the first lens element L1 being concave at a paraxial region and at a peripherical region, a first reflective surface S2 being convex at the paraxial region and at the peripherical region, a second reflective surface S3 being concave at the paraxial region and at the peripherical region, and a second refractive surface S4 being convex at the paraxial region and at the peripherical region.

The second lens element L2 with negative refractive power has a convex object-side surface S5 at a paraxial region and a concave object-side surface S6 at a paraxial region and a concave image-side surface S6 at a peripheral region of the second lens element L2.

The third lens element L3 with positive refractive power has an object-side surface S7 being convex at a paraxial region and concave at a paraxial region, and an image-side surface S8 being concave at a paraxial region and convex at a peripheral region of the third lens element L3.

The fourth lens element L4 with negative refractive power has a concave object-side surface S9 at the paraxial region and a convex image-side surface S10 at the paraxial region and at the peripheral region of the fourth lens element L4.

Further, the optical system includes a stop STO, an infrared cut filter IR, and an imaging surface IMG. In this embodiment, the stop STO is provided on the first reflection surface of the first lens of the optical system for controlling the amount of light entering. The infrared cut filter IR is disposed between the fourth lens L4 and the imaging surface IMG, and includes an object side surface S9 and an image side surface S10, and is configured to filter infrared light, so that the light incident on the imaging surface IMG is only visible light, and the wavelength of the visible light is 380nm to 780 nm. The material of the infrared cut filter IR is GLASS (GLASS), and the GLASS can be coated with a film. The first lens L1 to the fourth lens L4 are made of Plastic (Plastic). The effective pixel area of the electronic photosensitive element is positioned on the imaging surface IMG.

Table 1a shows parameters of the optical system of the present embodiment, in which the Y radius is a curvature radius of the object-side surface or the image-side surface of the corresponding surface number at the optical axis. Surface numbers S1, S2, S3, and S4 are the first refractive surface S1, the first reflective surface S2, the second reflective surface S3, and the second refractive surface S4 of the first lens L1, respectively, and surface numbers S5 and S6 are the object side surface S5 and the image side surface S6 of the second lens L2, respectively, that is, in the other lenses except the first lens, the surface with the smaller surface number is the object side surface, and the surface with the larger surface number is the image side surface. The first value in the "thickness" parameter column of the second lens element L2 is the axial thickness of the lens element, and the second value is the axial distance from the image-side surface to the rear surface of the lens element in the image-side direction. The focal length, material refractive index and abbe number are all obtained using visible light with a reference wavelength of 587.56nm, and the units of the Y radius, thickness and effective focal length are all millimeters (mm).

TABLE 1a

Wherein f is an effective focal length of the optical system, FNO is an f-number of the optical system, HFOV is a maximum field angle of the optical system, and TTL is a distance on an optical axis from an object-side surface of the first lens element to an image plane.

In the present embodiment, the object-side surface and the image-side surface of the first lens L1-the fourth lens L4 are aspheric, and the aspheric surface x can be defined by, but is not limited to, the following aspheric surface formula:

wherein x is the distance from the corresponding point on the aspheric surface to the plane tangent to the surface vertex, h is the distance from the corresponding point on the aspheric surface to the optical axis, c is the curvature of the aspheric surface vertex, k is the conic coefficient, and Ai is the coefficient corresponding to the i-th high-order term in the aspheric surface type formula. Table 1b shows the high-order term coefficients a4, A6, A8, a10, a12, a14, a16, a18, and a20 of the aspherical mirrors S1, S2, S3, S4, S5, S6, S7, S8, S9, and S10 that can be used in the first embodiment.

TABLE 1b

Fig. 2 (a) shows a longitudinal spherical aberration curve of the optical system of the first embodiment at wavelengths of 663.7725nm, 610.0000nm, 555.0000nm, 510.0000nm and 470.0000nm, in which the abscissa in the X-axis direction represents the focus shift, i.e., the distance (in mm) from the image plane to the intersection of the light rays and the optical axis, the ordinate in the Y-axis direction represents the normalized field of view, and the longitudinal spherical aberration curve represents the convergent focus deviation of the light rays of different wavelengths after passing through the lenses of the optical system. As can be seen from fig. 2 (a), the convergent focus deviation degrees of the light rays with different wavelengths in the first embodiment tend to be consistent, and the diffuse speckle or the chromatic halo in the imaging picture is effectively suppressed in the optical system, which shows that the imaging quality of the optical system in the present embodiment is better.

Fig. 2 (b) also shows an astigmatism graph of the optical system of the first embodiment at a wavelength of 555.0000nm, in which the abscissa in the X-axis direction represents the focus shift and the ordinate in the Y-axis direction represents the image height in mm. The S curve in the astigmatism plot represents the sagittal field curvature at 555.0000nm, and the T curve represents the meridional field curvature at 555.0000 nm. As can be seen from fig. 2 (b), the curvature of field of the optical system is small, the curvature of field and astigmatism of each field are well corrected, and the center and the edge of the field have clear images.

Fig. 2 (c) also shows a distortion curve of the optical system of the first embodiment at a wavelength of 555.0000 nm. Wherein the abscissa in the X-axis direction represents a distortion value in units, and the ordinate in the Y-axis direction represents an image height in units of mm. The distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from (c) in fig. 2, at a wavelength of 555.0000nm, the image distortion caused by the main beam is small, and the imaging quality of the system is excellent.

As can be seen from (a), (b), and (c) in fig. 2, the optical system of the present embodiment has small aberration, good imaging quality, and good imaging quality.

Second embodiment

Referring to fig. 3 and 4, the optical system of the present embodiment, in order from an object side to an image side along an optical axis direction, includes:

the first lens element L1 with positive refractive power has a first refractive surface S1 of the first lens element L1 being convex at a paraxial region and concave at a peripheral region, a first reflective surface S2 being convex at the paraxial region and the peripheral region, a second reflective surface S3 being concave at the paraxial region and the peripheral region, and a second refractive surface S4 being concave at the paraxial region and convex at the peripheral region.

The third lens element L3 with positive refractive power has a convex object-side surface S7 at a paraxial region and a concave object-side surface S8 at a near circumference of the third lens element L3.

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

Table 2a shows parameters of the optical system of the present embodiment, in which the focal length, the refractive index of the material, and the abbe number are obtained using visible light having a reference wavelength of 587.56nm, and the units of the Y radius, the thickness, and the effective focal length are millimeters (mm), and other parameters have the same meanings as those of the first embodiment.

TABLE 2a

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. 4 shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the optical system of the second embodiment, wherein the longitudinal spherical aberration curve represents the convergent focus deviations of light rays of different wavelengths after passing through the lenses of the optical system; the astigmatism curves represent the meridian field curvature and the sagittal field curvature; the distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from the aberration diagram in fig. 4, the longitudinal spherical aberration, curvature of field, and distortion of the optical system are well controlled, so that the optical system of this embodiment has good imaging quality.

Third embodiment

Referring to fig. 5 and fig. 6, 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 S5 at a paraxial region and a concave object-side surface S6 at a paraxial region and a concave image-side surface S6 at a peripheral region of the second lens element L2.

The third lens element L3 with negative refractive power has a concave object-side surface S7 at a paraxial region and a concave image-side surface S8 at a paraxial region and at a paraxial region of the third lens element L3.

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

Table 3a shows parameters of the optical system of the present embodiment, in which the focal length, the refractive index of the material, and the abbe number are all obtained using visible light having a reference wavelength of 587.56nm, and the units of the Y radius, the thickness, and the effective focal length are all millimeters (mm), and other parameters have the same meanings as those of the first embodiment.

TABLE 3a

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. 6 shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the optical system of the third embodiment, wherein the longitudinal spherical aberration curve represents the convergent focus deviations of light rays of different wavelengths after passing through the lenses of the optical system; the astigmatism curves represent the meridian field curvature and the sagittal field curvature; the distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from the aberration diagram in fig. 6, the longitudinal spherical aberration, curvature of field, and distortion of the optical system are well controlled, so that the optical system of this embodiment has good imaging quality.

Fourth embodiment

Referring to fig. 7 and 8, 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 negative refractive power has an object-side surface S5 being convex at a paraxial region and concave at a paraxial region, and an image-side surface S6 being concave at a paraxial region and convex at a peripheral region of the second lens element L2.

The third lens element L3 with positive refractive power has a convex object-side surface S7 at a paraxial region and a concave object-side surface at a near circumference of the third lens element L3, and has a convex image-side surface S8 at a paraxial region and a concave image-side surface at a near circumference.

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

Table 4a shows parameters of the optical system of the present embodiment, in which the focal length, the refractive index of the material, and the abbe number are all obtained using visible light having a reference wavelength of 587.56nm, and the units of the Y radius, the thickness, and the effective focal length are all millimeters (mm), and other parameters have the same meanings as those of the first embodiment.

TABLE 4a

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. 8 shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the optical system of the fourth embodiment, wherein the longitudinal spherical aberration curves represent the convergent focus deviations of light rays of different wavelengths after passing through the lenses of the optical system; the astigmatism curves represent meridional field curvature and sagittal field curvature; the distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from the aberration diagram in fig. 8, the longitudinal spherical aberration, curvature of field, and distortion of the optical system are well controlled, so that the optical system of this embodiment has good imaging quality.

Fifth embodiment

Referring to fig. 9 and 10, 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 an object-side surface S5 being convex at a paraxial region and concave at a paraxial region, and an image-side surface S6 being concave at a paraxial region and convex at a peripheral region of the second lens element L2.

The third lens element L3 with positive refractive power has a concave object-side surface S7 at a paraxial region and a concave image-side surface S8 at a peripheral region of the third lens element L3.

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 parameters of the optical system of the present embodiment, in which the focal length, the refractive index of the material, and the abbe number are all obtained using visible light having a reference wavelength of 587.56nm, and the units of the Y radius, the thickness, and the effective focal length are all millimeters (mm), and other parameters have the same meanings as those of the first embodiment.

TABLE 5a

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. 10 shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the optical system of the fifth embodiment, wherein the longitudinal spherical aberration curves represent the convergent focus deviations of light rays of different wavelengths after passing through the lenses of the optical system; the astigmatism curves represent the meridian field curvature and the sagittal field curvature; the distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from the aberration diagram in fig. 10, the longitudinal spherical aberration, curvature of field, and distortion of the optical system are well controlled, so that the optical system of this embodiment has good imaging quality.

Sixth embodiment

Referring to fig. 11 and 12, 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 negative refractive power has an object-side surface S3 being convex at a paraxial region and concave at a paraxial region, and an image-side surface S4 being concave at a paraxial region and convex at a peripheral region of the second lens element L2.

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

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

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

Table 6a shows parameters of the optical system of the present embodiment, in which the focal length, the refractive index of the material, and the abbe number are all obtained using visible light having a reference wavelength of 587.56nm, and the units of the Y radius, the thickness, and the effective focal length are all millimeters (mm), and other parameters have the same meanings as those of the first embodiment.

TABLE 6a

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. 12 shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the optical system of the sixth embodiment, wherein the longitudinal spherical aberration curves represent the convergent focus deviations of light rays of different wavelengths after passing through the lenses of the optical system; the astigmatism curves represent the meridian field curvature and the sagittal field curvature; the distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from the aberration diagrams in fig. 12, the longitudinal spherical aberration, curvature of field, and distortion of the optical system are well controlled, so that the optical system of this embodiment has good imaging quality.

Seventh embodiment

Referring to fig. 13 and 14, the optical system of the present embodiment, in order from an object side to an image side along an optical axis, includes:

The second lens element L2 with positive refractive power has an object-side surface S5 being concave at a paraxial region and a near circumference of the second lens element L2, and an image-side surface S6 being convex at the paraxial region and concave at the near circumference of the second lens element L2.

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 parameters of the optical system of the present embodiment, in which the focal length, the refractive index of the material, and the abbe number are all obtained using visible light having a reference wavelength of 587.56nm, and the units of the Y radius, the thickness, and the effective focal length are all millimeters (mm), and other parameters have the same meanings as those of the first embodiment.

TABLE 7a

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. 14 shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the optical system of the seventh embodiment, wherein the longitudinal spherical aberration curves represent the convergent focus deviations of light rays of different wavelengths after passing through the lenses of the optical system; the astigmatism curves represent the meridian field curvature and the sagittal field curvature; the distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from the aberration diagrams in fig. 14, the longitudinal spherical aberration, curvature of field, and distortion of the optical system are well controlled, so that the optical system of this embodiment has good imaging quality.

Eighth embodiment

Referring to fig. 15 and 16, 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 negative refractive power has a convex object-side surface S5 at a paraxial region and a concave object-side surface S6 at a near circumference of the second lens element L2.

The third lens element L3 with positive refractive power has a convex object-side surface S7 at a paraxial region and a concave object-side surface S8 at a paraxial region and a concave image-side surface S8 at a peripheral region of the third lens element L3.

The fourth lens element L4 with negative refractive power has an object-side surface S9 being convex at a paraxial region and concave at a paraxial region, and an image-side surface S10 being concave at a paraxial region and convex at a peripheral region of the fourth lens element L4.

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

Table 8a shows parameters of the optical system of the present embodiment, in which the focal length, the refractive index of the material, and the abbe number are all obtained using visible light having a reference wavelength of 587.56nm, and the units of the Y radius, the thickness, and the effective focal length are all millimeters (mm), and other parameters have the same meanings as those of the first embodiment.

TABLE 8a

Table 8b shows the high-order term coefficients that can be used for each aspherical mirror surface in the eighth embodiment, wherein each aspherical mirror surface type can be defined by the formula given in the first embodiment.

TABLE 8b

Fig. 16 shows a longitudinal spherical aberration curve, an astigmatism curve and a distortion curve of the optical system of the eighth embodiment, wherein the longitudinal spherical aberration curve represents the convergent focus deviation of light rays of different wavelengths after passing through the lenses of the optical system; the astigmatism curves represent the meridian field curvature and the sagittal field curvature; the distortion curve represents the distortion magnitude values corresponding to different angles of view. As can be seen from the aberration diagrams in fig. 16, the longitudinal spherical aberration, curvature of field, and distortion of the optical system are well controlled, so that the optical system of this embodiment has good imaging quality.

Table 9 shows values of f/Imgh, f/EPD, TTL/f, f/f4, | f/f3| + | f/f2|, | (f1+ f3)/f3|, | f1+ f2|/| f1-f2|, f123/f234, | (R2+ R3)/R4|, | (R7-R8)/R7| and TTL 13+ CT2+ CT3+ CT4) in the optical systems of the first to eighth embodiments.

TABLE 9

As can be seen from table 9, the optical systems of the first to eighth embodiments all satisfy the following relations: 3.5< f/Imgh <4.6, 1.2< f/EPD <1.5, 0.4< TTL/f <0.6, -3.0< f/f4< -1.0, 0< | f/f3| + | f/f2| <1.2, 0.8< | (f1+ f3)/f3| <2.0, 0.3< | f1+ f2|/| f1-f2| <1.5, -2.1< f123/f234< -0.8, 0.2< | (R2+ R3)/R4| <1.3, 0< | (R7-R8)/R7| <2.1, and 1.8< TTL 13+ 2+ CT3+ 4.

The invention further provides a camera module, which comprises a photosensitive chip and the optical system of any one of the embodiments of the first aspect, wherein the photosensitive chip is arranged on the image side of the optical system. The light sensing surface of the light sensing chip is positioned on the imaging surface of the optical system, and light rays which penetrate through the lens and enter an object on the light sensing surface can be converted into electric signals of images. The photosensitive chip may be a Complementary Metal Oxide Semiconductor (CMOS) or a Charge-coupled Device (CCD). The camera module can be an imaging module integrated on the electronic equipment and can also be an independent lens. By adding the optical system provided by the invention into the camera module, the camera module has the characteristics of smaller total optical length, long focal length and high pixels by reasonably designing the surface shape and the refractive power of each lens in the optical system.

The invention also provides electronic equipment which comprises a shell and the camera module in the second aspect, wherein the camera module is arranged in the shell. The electronic device includes but is not limited to a smart phone, a computer, a smart watch, and the like. By adding the camera module provided by the invention into the electronic equipment, the electronic equipment has the characteristics of smaller optical total length, long focal length and high pixels.

While the invention has been described with reference to a number of illustrative embodiments, 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.

Claims

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

a first lens element with positive refractive power;

a second lens element with refractive power;

a third lens element with refractive power;

a fourth lens element with negative refractive power;

the first lens is a catadioptric lens and comprises a first refraction surface, a first reflection surface, a second reflection surface and a second refraction surface, the first refraction surface and the second reflection surface are positioned at the object side, the first refraction surface is positioned at the periphery of the second refraction surface, the second reflection surface is a concave surface at the position close to an optical axis, the first reflection surface and the second reflection surface are positioned at the image side, the first reflection surface is positioned at the periphery of the second reflection surface, and light rays sequentially pass through the first refraction surface, the first reflection surface, the second reflection surface and the second refraction surface;

the optical system satisfies the relation: 3.5< f/Imgh < 4.6;

wherein f is the effective focal length of the optical system, and Imgh is half of the maximum field angle corresponding image height of the optical system.

2. The optical system of claim 1, wherein the optical system satisfies the relationship:

1.2<f/EPD<1.5；

wherein EPD is an entrance pupil diameter of the optical system.

3. The optical system of claim 1, wherein the optical system satisfies the relationship:

0.4<TTL/f<0.6；

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.

4. The optical system of claim 1, wherein the optical system satisfies the relationship:

-3.0< f/f4< -1.0, and/or,

0< | f/f3| + | f/f2| <1.2, and/or,

0.8< | (f1+ f3)/f3| <2.0, and/or,

0.3<|f1+f2|/|f1-f2|<1.5；

wherein f1 is the effective focal length of the first lens, f2 is the effective focal length of the second lens, f3 is the effective focal length of the third lens, and f4 is the effective focal length of the fourth lens.

5. The optical system of claim 1, wherein the optical system satisfies the relationship:

-2.1<f123/f234<-0.8；

wherein f123 is a combined effective focal length of the first lens, the second lens, and the third lens, and f234 is a combined effective focal length of the second lens, the third lens, and the fourth lens.

6. The optical system of claim 1, wherein the optical system satisfies the relationship:

0.2<|(R2+R3)/R4|<1.3；

wherein R2 is a radius of curvature of the first reflective surface of the first lens element, R3 is a radius of curvature of the second reflective surface of the first lens element, and R4 is a radius of curvature of the second refractive surface of the first lens element.

7. The optical system of claim 1, wherein the optical system satisfies the relationship:

0<|(R7-R8)/R7|<2.1；

wherein R7 is a radius of curvature of an object-side surface of the third lens element on an optical axis, and R8 is a radius of curvature of an image-side surface of the third lens element on the optical axis.

8. The optical system of claim 1, wherein the optical system satisfies the relationship:

1.8<TTL/(CT13+CT2+CT3+CT4)<3.0；

wherein TTL is an axial distance from an object-side surface of the first lens element to an image plane of the optical system, CT13 is an axial distance from the second reflecting surface to the second refracting surface of the first lens element, CT2 is an axial thickness of the second lens element, CT3 is an axial thickness of the third lens element, and CT4 is an axial thickness of the fourth lens element.

9. An image pickup module comprising the optical system according to any one of claims 1 to 8 and a photosensitive chip, the photosensitive chip being located on an image side of the optical system.

10. An electronic device comprising a housing and the camera module of claim 9, wherein the camera module is disposed within the housing.