CN114609768B

CN114609768B - Optical system, lens module and electronic equipment

Info

Publication number: CN114609768B
Application number: CN202210507777.1A
Authority: CN
Inventors: 粘明德
Original assignee: Jiangxi Jinghao Optical Co Ltd
Current assignee: Jiangxi Jinghao Optical Co Ltd
Priority date: 2022-05-11
Filing date: 2022-05-11
Publication date: 2022-08-23
Anticipated expiration: 2042-05-11
Also published as: CN114609768A

Abstract

The invention relates to an optical system, a lens module and an electronic device. The optical system includes: a first lens element with positive refractive power having a convex object-side surface at paraxial region; a second lens element with refractive power having a concave image-side surface at paraxial region; a third lens element with negative refractive power having a convex object-side surface and a concave image-side surface; a fourth lens element with positive refractive power having a convex image-side surface at a paraxial region; the fourth lens element is movable along an optical axis on an image side of the third lens element; the optical system satisfies: TTL/fa is more than or equal to 0.8 and less than or equal to 1.5. The optical system can achieve both the telephoto characteristic and the compact design.

Description

Optical system, lens module and electronic equipment

Technical Field

The present invention relates to the field of camera shooting, and in particular, to an optical system, a lens module, and an electronic apparatus.

Background

With the rapid development of the camera shooting technology, the application of the optical system in electronic devices such as smart phones, tablet computers, electronic readers and the like is also more and more extensive, and meanwhile, the requirement of the industry on the shooting performance of the electronic devices is also higher and higher. The lens module with the focusing function is provided, and through focusing, the lens module can have good imaging quality for shot objects in different object distance ranges, and the use experience of a user is greatly improved. However, in the conventional lens module with focusing function, the whole optical system in the lens module is usually required to be moved during the focusing process, so that the lens module is difficult to be miniaturized.

Disclosure of Invention

Accordingly, it is desirable to provide an optical system, a lens module and an electronic device for solving the problem that the conventional lens module with a focusing function is difficult to be miniaturized.

An optical system includes, in order from an object side to an image side along an optical axis:

a first lens element with positive refractive power having a convex object-side surface at paraxial region;

a second lens element with refractive power having a concave image-side surface at paraxial region;

a third lens element with negative refractive power having a convex object-side surface and a concave image-side surface;

a fourth lens element with positive refractive power having a convex image-side surface at a paraxial region;

the fourth lens can move along the optical axis on the image side of the third lens to realize a focusing function;

and the optical system satisfies the following conditional expression:

0.8≤TTL/fa≤1.5；

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 fa is an effective focal length of the optical system in a telephoto state.

In a conventional optical system, all lenses in the system are generally required to be moved integrally in a focusing process, requirements on moving mechanical structures such as a motor are high, so that the size of a moving mechanism is too large, the size of a lens module is increased, the focusing speed is reduced, and meanwhile, a space larger than the total length of the system is required to be reserved in an electronic device for focusing the system. In the optical system, the second lens group is moved to enable the optical system to have an internal focusing function, and the system only needs to move by means of a back focus space in the focusing process without reserving a space larger than the total length of the system in the axial direction for the whole system, so that the occupied space of the system in the electronic equipment can be effectively reduced. Meanwhile, only part of the lenses of the system need to be moved to realize the design of the focusing function, the requirements on moving mechanical structures such as a motor and the like are lower, and the occupied space of the moving mechanical structures in the lens module is favorably reduced, so that when the system is applied to the lens module, the size of the lens module is favorably compressed, and the miniaturization design of the lens module is realized. In addition, only a part of lenses of the system needs to be moved to realize the design of focusing function, the part of the system needing to be moved is light in weight, and the moving speed of the moving mechanical structure is favorably improved, so that the focusing speed of the system is favorably improved, and the shooting experience of a user is further improved. Moreover, the moving part in the focusing process of the system has light weight and low requirement on driving force, and the stability of the focusing moving process is facilitated, so that the stability of imaging quality is improved.

In the optical system, the first lens element with positive refractive power is matched with the convex surface of the object side surface of the first lens element at the paraxial region, so that light rays can be effectively converged, the total length of the system can be shortened, and the miniaturization design can be realized. The image side surface of the second lens is in a concave surface type at the lower beam axis, and the convex-concave surface type at the lower beam axis is matched with the third lens, so that aberration can be effectively corrected, and the imaging quality of the system is improved. The third lens has negative refractive power, which is beneficial to reasonably deflecting the light rays converged by the first lens, thereby effectively correcting the aberration generated by the first lens and the second lens. The positive refractive power of the fourth lens element, in cooperation with the convex surface of the image-side surface of the fourth lens element at the paraxial region, is favorable for converging light rays, so that the light rays can better enter an imaging plane, and simultaneously, the rear focus of the system can be shortened, thereby shortening the total length of the system. And the fourth lens can move along the optical axis on the image side of the third lens, so that the focusing function is realized, and the system can adapt to more different shooting scenes.

When the conditional expressions are met, the ratio of the total optical length of the system to the effective focal length can be reasonably configured, and the system is favorable for having long-focus characteristics, so that the magnification of the system is favorably improved, the telephoto effect is realized, the total optical length of the system is favorably shortened, and the miniaturization design of the system is realized. Being lower than the lower limit of the above conditional expression, the system structure is too compact, light is difficult to deflect well, and the improvement of imaging quality is not facilitated. Exceeding the upper limit of the above conditional expression is disadvantageous for the system to realize the miniaturization characteristic and the char characteristic.

The optical system having the refractive power and the surface shape characteristics and satisfying the conditional expressions can achieve both the telephoto characteristic and the compact design.

In one embodiment, the optical system satisfies the following conditional expression:

1≤f4/f1≤3；

wherein f4 is the effective focal length of the fourth lens, and f1 is the effective focal length of the first lens. When the condition formula is met, the ratio of the focal length of the last lens to the focal length of the first lens of the system can be reasonably configured, so that focusing of the system is facilitated, and field curvature aberration of the system is corrected, so that the imaging quality of the system is improved.

10≤TTL/ImgH≤11；

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, that is, a total optical length of the optical system. When the condition formula is satisfied, the ratio of the total optical length to the half-image height of the system can be reasonably configured, and the total length of the system can be favorably shortened, so that the miniaturization design can be favorably realized.

13.5mm≤ImgH/tan（FOVa）≤14.5mm；

wherein ImgH is the radius of the maximum effective imaging circle of the optical system, and FOVa is the maximum field angle of the optical system in the telephoto state. When the condition formula is met, the half-image height and the maximum field angle of the optical system can be reasonably configured, so that the system can realize the long-focus characteristic, the magnification ratio of the system is favorably improved, the telephoto effect is realized, and the imaging quality of the system is favorably improved. If the lower limit of the above conditional expression is less than the lower limit of the above conditional expression, the achievement of the system char property is not facilitated. If the upper limit of the above relation is exceeded, the focal length of the optical system is too long, and it is difficult to compress the total optical length of the optical system, which increases the volume of the optical system, and is disadvantageous for the optical system to meet the design requirement for miniaturization.

In one embodiment, the optical system further includes an infrared cut filter disposed on the image side of the fourth lens, and the optical system satisfies the following conditional expression:

0.8≤map2/map1≤1；

the map2 is half of the maximum effective clear aperture of the light of the edge field on the image side of the infrared cut-off filter, and the map1 is half of the maximum effective clear aperture of the light of the central field on the image side of the infrared cut-off filter. When the condition formula is satisfied, the relative brightness of the system imaging is favorably improved, and the system can have a clear imaging effect under a low-light environment.

4≤TTL/（CT2+CT3）≤8.5；

wherein, TTL is an axial distance from an object-side surface of the first lens element to an image plane of the optical system, CT2 is an axial thickness of the second lens element, i.e., a central thickness of the second lens element, and CT3 is an axial thickness of the third lens element, i.e., a central thickness of the third lens element. When the condition is met, the ratio of the total optical length of the optical system and the sum of the central thicknesses of the second lens and the third lens can be reasonably configured, so that the arrangement of the second lens and the third lens is more compact, the reasonable transition of system light rays at the second lens and the third lens is facilitated, the refractive power of the second lens and the refractive power of the third lens in the system are reduced, the sensitivity of the system is reduced, and the imaging quality of the system is improved.

|（R5-R6）/（R5+R6）|≤1；

wherein R5 is a radius of curvature of an object-side surface of the third lens at an optical axis, and R6 is a radius of curvature of an image-side surface of the third lens at the optical axis. When the conditional expressions are met, the curvature radiuses of the object side surface and the image side surface of the third lens at the optical axis can be reasonably configured, so that the third lens can effectively correct the spherical aberration of the system, the first-order aberration of the system can be well corrected, and the imaging quality of the system is improved.

4≤FNO≤5.5；

wherein FNO is an f-number of the optical system. When the condition formula is satisfied, the system realizes the long-focus characteristic, and is favorable for improving the light flux of the system, so that the system can also have a clear imaging effect in a low-light environment.

In one embodiment, the second lens is cemented with the third lens. The arrangement of the cemented lens is matched with the surface type design of the second lens and the third lens, so that the chromatic aberration of the system can be effectively corrected by the second lens and the third lens, and the imaging quality of the system is improved.

vd2 is less than or equal to 30.5; wherein Vd2 is the Abbe number of the second lens. When the condition formula is satisfied, the chromatic aberration of the system can be corrected while the long-focus characteristic is realized, and the imaging quality of the system is improved.

vd3 is more than or equal to 55; wherein Vd3 is the abbe number of the third lens. When the condition formula is satisfied, the chromatic aberration of the system can be corrected while the long-focus characteristic is realized, and the imaging quality of the system is improved.

When the second lens and the third lens are cemented, and the abbe numbers of the second lens and the third lens satisfy the two conditional expressions, the surface shape design and the abbe number design of the second lens and the third lens can be matched with each other to effectively correct the chromatic aberration of the system.

A lens module includes a photosensitive element and the optical system of any of the above embodiments, where the photosensitive element is disposed on an image side of the optical system. By adopting the optical system in the lens module, the optical system can realize the inner focusing function by moving the second lens group, thereby being beneficial to reducing the size and the weight of the lens moving part in the lens module, being beneficial to reducing the size and the weight of moving mechanical structures such as a motor and the like in the lens module, further being beneficial to compressing the size of the lens module and improving the focusing speed of the lens module. Meanwhile, the stability of the imaging quality in the focusing process is improved.

An electronic device comprises a shell and the lens module, wherein the lens module is arranged on the shell. The electronic equipment adopts the lens module, and the lens module has an internal focusing function, so that the electronic equipment does not need to reserve a space which is larger than the total length of the optical system for the optical system to move and focus, the size of the electronic equipment is favorably reduced, and the miniaturization design is favorably realized.

Drawings

FIG. 1 is a schematic structural diagram of an optical system in a telephoto state according to a first embodiment of the present application;

FIG. 2 is a schematic structural diagram of an optical system in a short focus state according to a first embodiment of the present application;

FIG. 3 is a longitudinal spherical aberration diagram, an astigmatism diagram and a distortion diagram of the optical system in the telephoto state according to the first embodiment of the present application;

FIG. 4 is a longitudinal spherical aberration diagram, an astigmatism diagram and a distortion diagram of the optical system in the short-focus state according to the first embodiment of the present application;

FIG. 5 is a schematic structural diagram of an optical system in a telephoto state according to a second embodiment of the present application;

FIG. 6 is a schematic structural diagram of an optical system in a short focus state according to a second embodiment of the present application;

FIG. 7 is a longitudinal spherical aberration diagram, an astigmatism diagram and a distortion diagram of an optical system in a telephoto state according to a second embodiment of the present application;

FIG. 8 is a longitudinal spherical aberration diagram, an astigmatism diagram and a distortion diagram of an optical system in a short-focus state according to a second embodiment of the present application;

FIG. 9 is a schematic structural diagram of an optical system in a telephoto state according to a third embodiment of the present application;

FIG. 10 is a schematic structural diagram of an optical system in a short focus state according to a third embodiment of the present application;

FIG. 11 is a longitudinal spherical aberration diagram, an astigmatism diagram and a distortion diagram of an optical system in a telephoto state according to a third embodiment of the present application;

FIG. 12 is a longitudinal spherical aberration diagram, an astigmatism diagram and a distortion diagram of an optical system in a short-focus state according to a third embodiment of the present application;

FIG. 13 is a schematic structural diagram of an optical system in a telephoto state according to a fourth embodiment of the present application;

FIG. 14 is a schematic structural diagram of an optical system in a short focus state according to a fourth embodiment of the present application;

FIG. 15 is a longitudinal spherical aberration diagram, an astigmatism diagram and a distortion diagram of an optical system in a telephoto state according to a fourth embodiment of the present application;

FIG. 16 is a longitudinal spherical aberration diagram, an astigmatism diagram and a distortion diagram of an optical system in a short-focus state according to a fourth embodiment of the present application;

FIG. 17 is a schematic structural diagram of an optical system in a telephoto state according to a fifth embodiment of the present application;

FIG. 18 is a schematic structural diagram of an optical system in a short focus state according to a fifth embodiment of the present application;

FIG. 19 is a longitudinal spherical aberration diagram, an astigmatism diagram and a distortion diagram of an optical system in a telephoto state according to a fifth embodiment of the present application;

FIG. 20 is a longitudinal spherical aberration diagram, an astigmatism diagram and a distortion diagram of an optical system in a short-focus state according to a fifth embodiment of the present application;

FIG. 21 is a schematic view of a lens module according to an embodiment of the present application;

fig. 22 is a schematic diagram of an electronic device in an embodiment of the present application.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and are not to be considered limiting of the invention.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.

It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. As used herein, the terms "vertical," "horizontal," "upper," "lower," "left," "right," and the like are for purposes of illustration only and do not denote a single embodiment.

In some embodiments of the present disclosure, the optical system 100 includes, in order from an object side to an image side along an optical axis 110, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4, referring to fig. 1. Specifically, the first lens element L1 includes an object-side surface S1 and an image-side surface S2, the second lens element L2 includes an object-side surface S3 and an image-side surface S4, the third lens element L3 includes an object-side surface S5 and an image-side surface S6, and the fourth lens element L4 includes an object-side surface S7 and an image-side surface S8. The first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 are coaxially disposed, and an axis common to the lenses in the optical system 100 is an optical axis 110 of the optical system 100. In some embodiments, the optical system 100 further includes an image plane S11 located on the image side of the fourth lens L4, and the incident light can be imaged on the image plane S11 after being adjusted by the first lens L1, the second lens L2, the third lens L3 and the fourth lens L4.

The first lens element L1 with positive refractive power is matched with the convex object-side surface S1 of the first lens element L1 at the paraxial region 110 to converge light beams effectively, thereby shortening the total length of the system and realizing a compact design. The concave surface of the image-side surface S4 of the second lens element L2 near the optical axis 110 is matched with the convex-concave surface of the third lens element L3 near the optical axis 110 to effectively correct the aberration, thereby improving the imaging quality of the system. The third lens element L3 has negative refractive power, which is favorable for reasonably deflecting the light rays converged by the first lens element L1, so as to effectively correct the aberrations generated by the first lens element L1 and the second lens element L2. The positive refractive power of the fourth lens element L4, coupled with the convex surface of the image-side surface S8 of the fourth lens element L4 at the paraxial region 110, is favorable for converging light rays, so that the light rays can be better incident on the image plane S11, and the back focus of the system can be shortened, thereby shortening the total length of the system.

In some embodiments, the fourth lens L4 can move along the optical axis 110 between the third lens L3 and the image plane S11, so as to change the focal length of the optical system 100, so that the system has a focusing function, and thus can adapt to more different shooting scenes. Fig. 1 and fig. 2 are schematic structural diagrams of an optical system 100 in some embodiments in different object distance states, respectively, as shown in fig. 1 and fig. 2, where fig. 1 is a schematic structural diagram of the system in a long-focus state, and fig. 2 is a schematic structural diagram of the system in a short-focus state. It can be understood that when the fourth lens L4 moves along the optical axis 110 toward the third lens L3 and away from the imaging surface S11, the object distance of the optical system 100 gradually decreases, and the effective focal length also gradually decreases. In some embodiments, the object distance of the system is infinity when the system is in the tele state and 1m when the system is in the short state.

It should be noted that fig. 1 and fig. 2 are only examples of the optical system 100 in two different object distance states, and actually, the fourth lens L4 can move to a plurality of different positions between the third lens L3 and the imaging surface S11 according to different shooting scene requirements, and the position of the fourth lens L4 relative to the third lens L3 is different, and the effective focal length and the object distance of the system are also different. In some embodiments, the object distance of the optical system may be any value between 1m and infinity. For example, the fourth lens L4 is moved to realize a focusing function, so that the object distance of the system can be 2m, 5m, 10m, etc., thereby adapting to different shooting scenes, and enabling the system to acquire clear images of subjects with different object distances. Of course, when the fourth lens L4 moves between the third lens L3 and the image plane S11, the first lens L1, the second lens L2, the third lens L3 and the image plane S11 are relatively fixed.

In some embodiments, the optical system 100 is provided with the stop STO, which can be disposed on the object side of the first lens L1 or between any two lenses, for example, in the embodiment shown in fig. 1, the stop STO is disposed on the object side of the first lens L1. In some embodiments, the optical system 100 further includes an ir-cut filter L5 disposed on the image side of the fourth lens element L4, and the ir-cut filter L5 is configured to filter out interference light and prevent the interference light from reaching the image plane S11 of the optical system 100 to affect normal imaging. It should be noted that, in some embodiments, when the fourth lens element L4 moves along the optical axis 110 between the third lens element L3 and the image plane S11, the ir-cut filter L5 moves synchronously with the fourth lens element L4, in other words, the fourth lens element L4 and the ir-cut filter are fixed relatively, so that the ir-cut filter L5 can effectively filter the interference light emitted from the fourth lens element L4. Of course, in other embodiments, the ir-cut filter L5 may also be fixed with respect to the third lens L3 and the image plane S11, and only the fourth lens L4 moves with respect to the third lens L3 and the image plane S11.

In some embodiments, the object-side and image-side surfaces of at least one lens in optical system 100 are aspheric. The adoption of the aspheric surface structure can improve the flexibility of lens design, effectively correct spherical aberration and improve imaging quality. In some embodiments, the object-side surface and the image-side surface of the first lens L1 and the fourth lens L4 are both aspheric surfaces, so that spherical aberration of the system can be effectively corrected, and the imaging quality of the system is improved. In some embodiments, the object-side surface and the image-side surface of each lens of optical system 100 are both aspheric. It should be noted that the above embodiments are only examples of some embodiments of the present application, and in some embodiments, the surface of each lens in the optical system 100 may be an aspheric surface or any combination of spherical surfaces.

In some embodiments, each lens in the optical system 100 may be made of glass or plastic. The lens made of plastic material can reduce the weight of the optical system 100 and the production cost, and the light and thin design of the optical system 100 can be realized by matching with the small size of the optical system 100. The glass lens provides the optical system 100 with excellent optical performance and high temperature resistance. It should be noted that the material of each lens in the optical system 100 may be any combination of glass and plastic, and is not necessarily both glass and plastic.

It should be noted that the first lens L1 does not mean that there is only one lens, and in some embodiments, there may be two or more lenses in the first lens L1, and the two or more lenses can form a cemented lens, and the surface of the cemented lens closest to the object side can be regarded as the object side surface S1, and the surface closest to the image side can be regarded as the image side surface S2. Alternatively, although no cemented lens is formed between the lenses of the first lens L1, the distance between the lenses is relatively fixed, and in this case, the object-side surface of the lens closest to the object side is the object-side surface S1, and the image-side surface of the lens closest to the image side is the image-side surface S2. In addition, the number of lenses in the second lens L2, the third lens L3, or the fourth lens L4 in some embodiments may also be greater than or equal to two, and a cemented lens may be formed between any two adjacent lenses, or may also be a non-cemented lens.

Further, in some embodiments, the optical system 100 satisfies the conditional expression: imgH/tan (FOVa) is less than or equal to 13.5mm and less than or equal to 14.5 mm; where ImgH is the radius of the maximum effective imaging circle of the optical system 100, and FOVa is the maximum field angle of the optical system 100 in the telephoto state. Specifically, ImgH/tan (fova) may be: 13.99, 14.02, 14.04, 14.05, 14.07, 14.10, 14.12, 14.13, 14.15 or 14.19, in units of mm. When the above conditional expressions are satisfied, the half-image height and the maximum field angle of the optical system 100 can be reasonably configured, so that the system can realize the telephoto characteristic, thereby being beneficial to improving the magnification of the system and realizing the telephoto effect, and simultaneously being beneficial to increasing the magnification of the imaging of the system and improving the imaging quality of the system. If the lower limit of the above conditional expression is less than the lower limit of the above conditional expression, the achievement of the system char property is not facilitated. Having the above-described refractive power and surface shape characteristics and satisfying the above conditional expressions, the optical system 100 can achieve both the telephoto characteristic and the compact design. If the upper limit of the above relation is exceeded, the focal length of the optical system 100 is too long to compress the total optical length of the optical system 100, which increases the size of the optical system 100, and is disadvantageous for the optical system 100 to meet the design requirement for miniaturization.

It should be noted that in some embodiments, the optical system 100 may match a photosensitive element having a rectangular photosensitive surface, and the imaging surface S11 of the optical system 100 coincides with the photosensitive surface of the photosensitive element. At this time, the effective pixel region on the imaging plane S11 of the optical system 100 has a horizontal direction and a diagonal direction, the maximum angle of view can be understood as the maximum angle of view in the diagonal direction of the optical system, and ImgH can be understood as half the length of the effective pixel region on the imaging plane S11 of the optical system.

In some embodiments, the optical system 100 satisfies the conditional expression: f4/f1 is more than or equal to 1 and less than or equal to 3; where f4 is the effective focal length of the fourth lens L4, and f1 is the effective focal length of the first lens L1. Specifically, f4/f1 may be: 1.245, 1.415, 1.563, 1.725, 1.903, 2.412, 2.553, 2.749, 2.781, or 2.800. When the condition formula is met, the ratio of the focal length of the last lens to the focal length of the first lens of the system can be reasonably configured, so that focusing of the system is facilitated, and field curvature aberration of the system is corrected, so that the imaging quality of the system is improved.

In some embodiments, the optical system 100 satisfies the conditional expression: TTL/ImgH is more than or equal to 10 and less than or equal to 11; wherein, TTL is a distance from the object-side surface S1 of the first lens element L1 to the image plane S11 of the optical system 100 on the optical axis 110. Specifically, TTL/ImgH may be: 10.172, 10.185, 10.223, 10.257, 10.311, 10.375, 10.458, 10.512, 10.543, or 10.560. When the conditional expressions are satisfied, the ratio of the optical total length to the half-image height of the system can be reasonably configured, and the total length of the system is favorably shortened, so that the miniaturization design is favorably realized.

In some embodiments, the optical system 100 satisfies the conditional expression: TTL/fa is more than or equal to 0.8 and less than or equal to 1.5; wherein, TTL is a distance from the object-side surface S1 of the first lens element L1 to the image plane S11 of the optical system 100 on the optical axis 110, and fa is an effective focal length of the optical system 100 in a telephoto state. Specifically, TTL/fa can be: 0.990, 0.992, 0.996, 1.003, 1.012, 1.017, 1.025, 1.026, 1.030 or 1.032. When the conditional expressions are met, the ratio of the total optical length of the system to the effective focal length can be reasonably configured, and the system is favorable for having long-focus characteristics, so that the magnification of the system is favorably improved, the telephoto effect is realized, the total optical length of the system is favorably shortened, and the miniaturization design of the system is realized. Being lower than the lower limit of the above conditional expression, the system structure is too compact, light is difficult to deflect well, and the improvement of imaging quality is not facilitated. Exceeding the upper limit of the above conditional expression is disadvantageous for the system to realize the miniaturization characteristic and the char characteristic.

In some embodiments, the optical system 100 satisfies the conditional expression: map2/map1 of 0.8-1; the map2 is half of the maximum effective clear aperture of the light rays of the peripheral field of view on the image side surface S10 of the ir cut filter L5, and the map1 is half of the maximum effective clear aperture of the light rays of the central field of view on the image side surface S10 of the ir cut filter L5. Specifically, map2/map1 may be: 0.887, 0.894, 0.901, 0.913, 0.924, 0.935, 0.944, 0.950, 0.962 or 0.964. When the condition formula is satisfied, the relative brightness of the system imaging is favorably improved, so that the system can have a clear imaging effect under a low-light environment.

In some embodiments, the optical system 100 satisfies the conditional expression: TTL/(CT 2+ CT 3) is more than or equal to 4 and less than or equal to 8.5; wherein, TTL is a distance from the object-side surface S1 of the first lens element L1 to the image plane S11 of the optical system 100 on the optical axis 110, CT2 is a thickness of the second lens element L2 on the optical axis 110, and CT3 is a thickness of the third lens element L3 on the optical axis 110. Specifically, TTL/(CT 2+ CT 3) may be: 4.538, 5.201, 5.423, 5.938, 6.521, 7.305, 7.368, 7.874, 7.935 or 8.036. When the above conditional expressions are satisfied, the ratio of the total optical length of the optical system 100 to the sum of the central thicknesses of the second lens L2 and the third lens L3 can be reasonably configured, which is beneficial to making the arrangement of the second lens L2 and the third lens L3 more compact, so as to facilitate reasonable transition of system light at the second lens L2 and the third lens L3, further reduce the refractive power of the second lens L2 and the third lens L3 in the system, reduce the sensitivity of the system, and improve the imaging quality of the system.

In some embodiments, the optical system 100 satisfies the conditional expression: l (R5-R6)/(R5 + R6) l is less than or equal to 1; wherein R5 is a radius of curvature of the object-side surface S5 of the third lens element L3 along the optical axis 110, and R6 is a radius of curvature of the image-side surface S6 of the third lens element L3 along the optical axis 110. Specifically, | (R5-R6)/(R5 + R6) | may be: 0.039, 0.112, 0.135, 0.167, 0.213, 0.255, 0.278, 0.314, 0.355, or 0.460. When the above conditional expressions are satisfied, the curvature radii of the object-side surface S5 and the image-side surface S6 of the third lens element L3 at the optical axis 110 can be configured reasonably, so that the spherical aberration of the system can be effectively corrected by the third lens element L3, the first-order aberration of the system can be corrected well, and the imaging quality of the system can be improved.

In some embodiments, the optical system 100 satisfies the conditional expression: FNO is more than or equal to 4 and less than or equal to 5.5; wherein FNO is the f-number of the optical system 100. Specifically, FNO may be: 4.8, 4.9, 5.0, 5.1, 5.2 or 5.3. When the condition formula is satisfied, the system realizes the long-focus characteristic, and is favorable for improving the light flux of the system, so that the system can also have a clear imaging effect in a low-light environment.

In some embodiments, the second lens L2 is cemented with the third lens L3. The arrangement of the cemented lens, in cooperation with the surface type design of the second lens L2 and the third lens L3, enables the second lens L2 and the third lens L3 to effectively correct chromatic aberration of the system, and improves the imaging quality of the system. It should be noted that, in the present application, the description of the gluing of the second lens L2 and the third lens L3 can be understood as describing the relative position of the second lens L2 and the third lens L3, for example, the image side surface S4 of the second lens L2 is in contact with the object side surface S5 of the third lens L3, but cannot be understood as limiting the gluing process of the second lens L2 and the third lens L3. The second lens L2 and the third lens L3 are cemented together by optical cement, or are fixed by structural members, etc., which are all within the scope of the cementing of the second lens L2 and the third lens L3 described in this application.

In some embodiments, the optical system 100 satisfies the conditional expression: vd2 is less than or equal to 30.5; wherein Vd2 is the Abbe number of the second lens. Specifically, Vd2 may be 27.5. When the condition formula is satisfied, the chromatic aberration of the system can be corrected while the long-focus characteristic is realized, and the imaging quality of the system is improved.

In some embodiments, the optical system 100 satisfies the conditional expression: vd3 is more than or equal to 55; wherein Vd3 is the abbe number of the third lens. Specifically, Vd3 may be 59.3. When the condition formula is satisfied, the chromatic aberration of the system can be corrected while the long-focus characteristic is realized, and the imaging quality of the system is improved.

The gluing design of the second lens L2 and the third lens L3 is matched with the abbe number design and the surface type design of the second lens L2 and the third lens L3, so that the chromatic aberration of the system can be effectively corrected by the second lens L2 and the third lens L3 as a whole, and the imaging quality of the system is improved.

The reference wavelengths of the effective focal length values are 555nm, and the reference wavelengths of the Abbe numbers are 587.56 nm.

In light of the foregoing description of the various embodiments, the following provides more detailed description of the embodiments and accompanying drawings.

First embodiment

Referring to fig. 1, fig. 2, fig. 3, and fig. 4, fig. 1 is a schematic structural diagram of an optical system 100 in a long focus state in a first embodiment, and fig. 2 is a schematic structural diagram of the optical system 100 in a short focus state in the first embodiment. The optical system 100 includes, in order from an object side to an image side, a stop STO, a first lens element L1 with positive refractive power, a second lens element L2 with positive refractive power, a third lens element L3 with negative refractive power, and a fourth lens element L4 with positive refractive power, wherein the second lens element L2 is cemented with the third lens element L3. Fig. 3 is a graph of longitudinal spherical aberration, astigmatism and distortion of the optical system 100 in the first embodiment in the telephoto state from left to right, and fig. 4 is a graph of longitudinal spherical aberration, astigmatism and distortion of the optical system 100 in the first embodiment in the short-focus state from left to right, in which the reference wavelength of the astigmatism graph and the distortion graph is 555nm, and the other embodiments are the same. The first lens L1, the second lens L2 and the third lens L3 are fixed relative to the image forming surface S11, the fourth lens L4 can move between the image side surface S6 of the third lens L3 and the image forming surface S11, and when the fourth lens L4 moves in a direction of being close to the third lens L3 and being far away from the image forming surface S11, the object distance of the system gradually decreases, so that good imaging quality can be achieved for a subject at a closer distance. The system realizes the design of internal focusing by moving part of the lenses, is favorable for realizing the miniaturization design of the lens module, is also favorable for improving the focusing speed of the system, is also favorable for improving the imaging quality of the system, and is favorable for forming and assembling each lens of the system.

The object-side and image-side surfaces of the first lens L1 and the fourth lens L4 are aspheric, and the object-side and image-side surfaces of the second lens L2 and the third lens L3 are spherical.

The object-side surface S1 of the first lens element L1 is convex at a paraxial region 110 and convex at a peripheral region;

the image-side surface S2 of the first lens element L1 is concave at the paraxial region 110 and concave at the periphery;

the object-side surface S3 of the second lens element L2 is convex at a paraxial region 110 and convex at a peripheral region;

the image-side surface S4 of the second lens element L2 is concave at a paraxial region 110 and concave at a peripheral region;

the object-side surface S5 of the third lens element L3 is convex at the paraxial region 110 and convex at the peripheral region;

the image-side surface S6 of the third lens element L3 is concave at a paraxial region 110 and concave at a peripheral region;

the object-side surface S7 of the fourth lens element L4 is concave at a paraxial region 110 and concave at a peripheral region;

the image-side surface S8 of the fourth lens element L4 is convex at the paraxial region 110 and is convex at the periphery.

It should be noted that, in the present application, if a surface of a lens is aspheric, when it is described that a surface of the lens near the optical axis 110 (a central area of the surface) is convex, it can be understood that an area of the surface of the lens near the optical axis 110 is convex. When it is stated that the surface of the lens is concave at the circumference, it is understood that the surface is concave in the region near the maximum effective radius. For example, when the surface is convex at a paraxial region 110 and also convex at a peripheral region, the shape of the surface from the center (the intersection of the surface with the optical axis 110) to the edge direction may be purely convex; or a convex shape at the center is firstly transited to a concave shape and then becomes a convex shape near the maximum effective radius. Here, only examples are made to illustrate the relationship at the optical axis 110 and the circumference, and various shape structures (concave-convex relationship) of the surface are not fully embodied, but other cases can be derived from the above examples.

The first lens L1, the third lens L3 and the fourth lens L4 are all made of plastic, and the second lens L2 is made of glass.

Further, the optical system 100 satisfies the conditional expression: ImgH/tan (fova) =14.19 mm; where ImgH is the radius of the maximum effective imaging circle of the optical system 100, and FOVa is the maximum field angle of the optical system 100 in the telephoto state. When the above conditional expressions are satisfied, the half-image height and the maximum field angle of the optical system 100 can be reasonably configured, so that the system can realize a telephoto characteristic, thereby being beneficial to improving the magnification of the system, realizing a telephoto effect, simultaneously being beneficial to increasing the magnification of the imaging of the system, and improving the imaging quality of the system.

The optical system 100 satisfies the conditional expression: f4/f1= 2.800; where f4 is the effective focal length of the fourth lens L4, and f1 is the effective focal length of the first lens L1. When the condition formula is met, the ratio of the focal length of the last lens to the focal length of the first lens of the system can be reasonably configured, so that focusing of the system is facilitated, and field curvature aberration of the system is corrected, so that the imaging quality of the system is improved.

The optical system 100 satisfies the conditional expression: TTL/ImgH = 10.172; wherein, TTL is a distance from the object-side surface S1 of the first lens element L1 to the image plane S11 of the optical system 100 on the optical axis 110. When the condition formula is satisfied, the ratio of the total optical length to the half-image height of the system can be reasonably configured, and the total length of the system can be favorably shortened, so that the miniaturization design can be favorably realized.

The optical system 100 satisfies the conditional expression: TTL/fa = 0.990; wherein, TTL is a distance on the optical axis 110 from the object-side surface S1 of the first lens element L1 to the image plane S11 of the optical system 100, and fa is an effective focal length of the optical system 100 in the telephoto state. When the conditional expressions are met, the ratio of the total optical length of the system to the effective focal length can be reasonably configured, and the system is favorable for having long-focus characteristics, so that the magnification of the system is favorably improved, the telephoto effect is realized, the total optical length of the system is favorably shortened, and the miniaturization design of the system is realized.

The optical system 100 satisfies the conditional expression: map2/map1= 0.929; the map2 is half of the maximum effective clear aperture of the light rays of the peripheral field of view on the image side surface S10 of the ir cut filter L5, and the map1 is half of the maximum effective clear aperture of the light rays of the central field of view on the image side surface S10 of the ir cut filter L5. When the conditional expression is satisfied, the relative brightness of the imaging of the system is favorably improved, so that the system can have a clear imaging effect under a low-light environment.

The optical system 100 satisfies the conditional expression: TTL/(CT 2+ CT 3) = 7.036; wherein, TTL is a distance from the object-side surface S1 of the first lens element L1 to the image plane S11 of the optical system 100 on the optical axis 110, CT2 is a thickness of the second lens element L2 on the optical axis 110, and CT3 is a thickness of the third lens element L3 on the optical axis 110. When the above conditional expressions are satisfied, the ratio of the total optical length of the optical system 100 to the sum of the central thicknesses of the second lens L2 and the third lens L3 can be reasonably configured, which is beneficial to making the arrangement of the second lens L2 and the third lens L3 more compact, so as to facilitate reasonable transition of system light at the second lens L2 and the third lens L3, further reduce the refractive power of the second lens L2 and the third lens L3 in the system, reduce the sensitivity of the system, and improve the imaging quality of the system.

The optical system 100 satisfies the conditional expression: l (R5-R6)/(R5 + R6) | = 0.039; wherein R5 is a radius of curvature of the object-side surface S5 of the third lens element L3 along the optical axis 110, and R6 is a radius of curvature of the image-side surface S6 of the third lens element L3 along the optical axis 110. When the conditional expressions are satisfied, the curvature radii of the object-side surface S5 and the image-side surface S6 of the third lens L3 at the optical axis 110 can be reasonably configured, so that the third lens L3 can effectively correct the spherical aberration of the system, the first-order aberration of the system can be well corrected, and the imaging quality of the system is improved.

In addition, the parameters of the optical system 100 are given in table 1. In which elements from the object plane (not shown) to the image plane S11 are sequentially arranged in the order of elements from top to bottom of table 1. The Y radius in table 1 is the radius of curvature of the object-side or image-side surface of the corresponding surface number at the optical axis 110. Surface numbers S1 and S2 denote an object-side surface S1 and an image-side surface S2 of the first lens L1, respectively, that is, in the same lens, a surface with a smaller surface number is an object-side surface, and a surface with a larger surface number is an image-side surface. The first value in the "thickness" parameter list of the first lens element L1 is the thickness of the lens element along the optical axis 110, and the second value is the distance from the image-side surface to the rear surface along the image-side direction of the lens element along the optical axis 110. The thickness parameter of each lens is a numerical value of the system in the telephoto state.

Note that, in this embodiment and the following embodiments, the optical system 100 may not be provided with the infrared cut filter L5, but the distance from the image side surface S8 of the fourth lens L4 to the image plane S11 may be kept constant in the telephoto state.

In the first embodiment, the effective focal length fa =28.6mm in the telephoto state and fb =27.8mm in the short-focus state of the optical system 100; f-number FNO =4.8 of optical system 100; the maximum field angle FOVa =11.1deg in the telephoto state and the maximum field angle FOVb =11.07deg in the short-focus state of the optical system 100; total optical length TTL =28.32mm of optical system 100. It is understood that the refractive index, abbe number, and total length of the system of each lens are the same in the telephoto and the short focus states.

The reference wavelength of the effective focal length of each lens is 555nm, the reference wavelength of the refractive index and the abbe number of each lens is 587.56nm, and the same is also true for other embodiments.

TABLE 1

Further, aspheric coefficients of the object-side surface S1 and the image-side surface S2 of the first lens L1 and the object-side surface S7 and the image-side surface S8 of the fourth lens L4 are given by table 2. Where K-a14 from top to bottom respectively indicate the types of aspheric coefficients, where K indicates a conic coefficient, a4 indicates a quartic aspheric coefficient, a6 indicates a sextic aspheric coefficient, A8 indicates an octal aspheric coefficient, and so on. In addition, the aspherical surface coefficient formula is as follows:

wherein Z is the distance from the corresponding point on the aspheric surface to the plane tangent to the surface vertex, r is the distance from the corresponding point on the aspheric surface to the optical axis 110, 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 2

In addition, fig. 3 and 4 include Longitudinal Spherical Aberration plots (Longitudinal Spherical Aberration) of the optical system 100 in the telephoto state, where the Longitudinal Spherical Aberration plots represent the deviation of the converging focus of light rays of different wavelengths after passing through the lens, where the ordinate represents the Normalized Pupil coordinate (Normalized Pupil coordiator) from the Pupil center to the Pupil edge, and the abscissa represents the focus offset, i.e., the distance (in mm) from the image plane S11 to the intersection of the light rays and the optical axis 110. It can be known from the longitudinal spherical aberration diagram that the convergent focus deviation degrees of the light rays with different wavelengths in the first embodiment tend to be consistent, and the diffuse speckles or color halos in the imaging picture are effectively inhibited. Fig. 3 and 4 also include graphs of astigmatism (ASTIGMATIC FIELD CURVES) for the optical system 100, in which the abscissa represents focus offset, the ordinate represents image height in mm, and the S-curve and the T-curve in the graphs of astigmatism represent sagittal curvature at 555nm and meridional curvature at 555nm, respectively. As can be seen from the figure, the field curvature of the optical system 100 is small, the field curvature and astigmatism of each field are well corrected, and the center and the edge of each field have clear images. Fig. 3 and 4 further include DISTORTION graphs (distorsion) of the optical system 100, the DISTORTION curves representing values of DISTORTION magnitude corresponding to different angles of view, wherein the abscissa represents the DISTORTION value in mm, and the ordinate represents the image height in mm. As can be seen from the figure, the image distortion caused by the main beam is small, and the imaging quality of the system is excellent.

The following data reflects the relative positions of the fourth lens L4 and the third lens L3 and the image plane S11 under different object distances, wherein an object distance column from top to bottom represents the long-focus state and the short-focus state of the optical system 100, respectively, and in the present embodiment, the ir-cut filter L5 and the fourth lens L4 move synchronously during the focusing process of the system. S6-S7 are distances on the optical axis 110 from the image-side surface S6 of the third lens element L3 to the object-side surface S7 of the fourth lens element L4, and S10-S11 are distances on the optical axis 110 from the image-side surface S10 of the ir-cut filter L5 to the image-plane S11. As can be seen from the following data, when the object distance of the system is infinite, the distance between the image-side surface S6 of the third lens L3 and the object-side surface S7 of the fourth lens L4 on the optical axis 110 is 5.463mm, and the distance between the image-side surface S10 of the ir cut filter L5 and the image-side surface S11 on the optical axis 110 is 10.155 mm; when the object distance of the system is 1m, the distance between the image-side surface S6 of the third lens element L3 and the object-side surface S7 of the fourth lens element L4 on the optical axis 110 is 3.454mm, and the distance between the image-side surface S10 of the infrared cut filter L5 and the image-side surface S11 on the optical axis 110 is 12.166 mm. As can be seen from this, in the process of gradually decreasing the object distance of the system from infinity, the fourth lens L4 and the infrared cut filter L5 are gradually closer to the third lens L3 and further away from the image plane S11. In other embodiments, when the fourth lens element L4 gradually moves away from the third lens element L3 and approaches the image plane S11, the object distance of the system may also gradually increase from 1m, and the refractive power and the surface type configuration of each lens element of the system may be specifically adjusted according to the requirement.

Second embodiment

Referring to fig. 5, fig. 6, fig. 7, and fig. 8, fig. 5 is a schematic structural diagram of the optical system 100 in the second embodiment in the telephoto state, and fig. 6 is a schematic structural diagram of the optical system 100 in the second embodiment in the short-focus state. The optical system 100 includes, in order from an object side to an image side, a stop STO, a first lens element L1 with positive refractive power, a second lens element L2 with positive refractive power, a third lens element L3 with negative refractive power, and a fourth lens element L4 with positive refractive power, wherein the second lens element L2 is cemented with the third lens element L3. Fig. 7 is a graph sequentially showing the longitudinal spherical aberration, astigmatism and distortion of the optical system 100 in the telephoto state in the second embodiment from left to right, and fig. 8 is a graph sequentially showing the longitudinal spherical aberration, astigmatism and distortion of the optical system 100 in the short-focus state in the second embodiment from left to right.

the image-side surface S2 of the first lens element L1 is convex at a paraxial region 110 and convex at a peripheral region;

the object-side surface S5 of the third lens element L3 is convex at a paraxial region 110 and convex at a peripheral region;

the image-side surface S6 of the third lens element L3 is concave at the paraxial region 110 and is concave at the peripheral region;

the object-side surface S7 of the fourth lens element L4 is convex at the paraxial region 110 and convex at the peripheral region;

the image-side surface S8 of the fourth lens element L4 is convex at the paraxial region 110 and convex at the periphery.

In addition, the parameters of the optical system 100 are given in table 3, and the definitions of the parameters can be obtained from the first embodiment, which is not described herein.

TABLE 3

Further, the aspheric coefficients of the object-side surface S1 and the image-side surface S2 of the first lens element L1 and the object-side surface S7 and the image-side surface S8 of the fourth lens element L4 are shown in table 4, and the definitions of the parameters can be derived from the first embodiment, which is not described herein again.

TABLE 4

The following data reflect the relative positions of the fourth lens element L4 and the third lens element L3 and the image plane S11 under different object distances, and the definitions of the parameters can be obtained from the first embodiment, which will not be described herein.

According to the provided parameter information, the following data can be deduced:

in addition, as can be seen from the aberration diagrams in fig. 7 and 8, the longitudinal spherical aberration, astigmatism and distortion of the optical system 100 in different object distance states are well controlled, so that the optical system 100 of this embodiment has good imaging quality.

Third embodiment

Referring to fig. 9, 10, 11, and 12, fig. 9 is a schematic structural diagram of the optical system 100 in the third embodiment in the telephoto state, and fig. 10 is a schematic structural diagram of the optical system 100 in the third embodiment in the short-focus state. The optical system 100 includes, in order from an object side to an image side, a stop STO, a first lens element L1 with positive refractive power, a second lens element L2 with positive refractive power, a third lens element L3 with negative refractive power, and a fourth lens element L4 with positive refractive power, wherein the second lens element L2 is cemented with the third lens element L3. Fig. 11 is a graph sequentially showing longitudinal spherical aberration, astigmatism and distortion of the optical system 100 in the telephoto state in the third embodiment from left to right, and fig. 12 is a graph sequentially showing longitudinal spherical aberration, astigmatism and distortion of the optical system 100 in the short-focus state in the third embodiment from left to right.

the image-side surface S2 of the first lens element L1 is concave at the paraxial region 110 and concave at the peripheral region;

the object-side surface S3 of the second lens element L2 is convex at the paraxial region 110 and convex at the peripheral region;

the object-side surface S7 of the fourth lens element L4 is concave at the paraxial region 110 and concave at the peripheral region;

In addition, the parameters of the optical system 100 are given in table 5, and the definitions of the parameters can be obtained from the first embodiment, which is not described herein again.

TABLE 5

Further, the aspheric coefficients of the object-side surface S1 and the image-side surface S2 of the first lens element L1 and the object-side surface S7 and the image-side surface S8 of the fourth lens element L4 are shown in table 6, and the definitions of the parameters can be derived from the first embodiment, which is not repeated herein.

TABLE 6

in addition, as can be seen from the aberration diagrams in fig. 11 and 12, the longitudinal spherical aberration, astigmatism and distortion of the optical system 100 in different object distance states are well controlled, so that the optical system 100 of this embodiment has good imaging quality.

Fourth embodiment

Referring to fig. 13, 14, 15, and 16, fig. 13 is a schematic structural diagram of the optical system 100 in the fourth embodiment in the telephoto state, and fig. 14 is a schematic structural diagram of the optical system 100 in the fourth embodiment in the short-focus state. The optical system 100 includes, in order from an object side to an image side, a stop STO, a first lens element L1 with positive refractive power, a second lens element L2 with negative refractive power, a third lens element L3 with negative refractive power, and a fourth lens element L4 with positive refractive power, wherein the second lens element L2 is cemented with the third lens element L3. Fig. 15 is a graph sequentially showing longitudinal spherical aberration, astigmatism and distortion of the optical system 100 in the telephoto state in the fourth embodiment from left to right, and fig. 16 is a graph sequentially showing longitudinal spherical aberration, astigmatism and distortion of the optical system 100 in the short-focus state in the fourth embodiment from left to right.

The object-side surface S1 of the first lens element L1 is convex at the paraxial region 110 and convex at the peripheral region;

the object-side surface S3 of the second lens element L2 is concave at a paraxial region 110 and concave at a peripheral region;

the object-side surface S7 of the fourth lens element L4 is convex at a paraxial region 110 and convex at a peripheral region;

In addition, the parameters of the optical system 100 are given in table 7, and the definitions of the parameters can be obtained from the first embodiment, which is not described herein.

TABLE 7

Further, the aspheric coefficients of the object-side surface S1 and the image-side surface S2 of the first lens element L1 and the object-side surface S7 and the image-side surface S8 of the fourth lens element L4 are shown in table 8, and the definitions of the parameters can be derived from the first embodiment, which is not described herein again.

TABLE 8

in addition, as can be seen from the aberration diagrams in fig. 15 and 16, the longitudinal spherical aberration, astigmatism and distortion of the optical system 100 in different object distance states are well controlled, so that the optical system 100 of this embodiment has good imaging quality.

Fifth embodiment

Referring to fig. 17, 18, 19, and 20, fig. 17 is a schematic structural diagram of the optical system 100 in the fifth embodiment in a telephoto state, and fig. 18 is a schematic structural diagram of the optical system 100 in the fifth embodiment in a short-focus state. The optical system 100 includes, in order from an object side to an image side, a stop STO, a first lens element L1 with positive refractive power, a second lens element L2 with positive refractive power, a third lens element L3 with negative refractive power, and a fourth lens element L4 with positive refractive power, wherein the second lens element L2 is cemented with the third lens element L3. Fig. 19 is a graph sequentially showing longitudinal spherical aberration, astigmatism and distortion of the optical system 100 in the telephoto state in the fifth embodiment from left to right, and fig. 20 is a graph sequentially showing longitudinal spherical aberration, astigmatism and distortion of the optical system 100 in the short-focus state in the fifth embodiment from left to right.

In addition, the parameters of the optical system 100 are given in table 9, and the definitions of the parameters can be obtained from the first embodiment, which is not described herein.

TABLE 9

Further, the aspheric coefficients of the object-side surface S1 and the image-side surface S2 of the first lens element L1 and the object-side surface S7 and the image-side surface S8 of the fourth lens element L4 are shown in table 10, and the definitions of the parameters can be derived from the first embodiment, which is not repeated herein.

TABLE 10

The following data reflect the relative positions of the fourth lens element L4 and the third lens element L3 and the image plane S11 under different object distances, and the definitions of the parameters can be derived from the first embodiment, which are not repeated herein.

in addition, as can be seen from the aberration diagrams in fig. 19 and 20, the longitudinal spherical aberration, astigmatism and distortion of the optical system 100 in different object distance states are well controlled, so that the optical system 100 of this embodiment has good imaging quality.

Referring to fig. 21, in some embodiments, the optical system 100 may be assembled with the photosensitive element 210 to form the lens module 200. At this time, the light-sensing surface of the light-sensing element 210 coincides with the image formation surface S11 of the optical system 100. The lens module 200 may further include an ir-cut filter L5, wherein the ir-cut filter L5 is disposed between the image-side surface S8 and the image plane S11 of the fourth lens element L4. Specifically, the photosensitive element 210 may be a Charge Coupled Device (CCD) or a Complementary Metal-Oxide Semiconductor (CMOS) Device. The lens module 200 using the optical system 100 can achieve a focusing function, and can be adapted to various shooting scenes while achieving both a telephoto characteristic and a compact design.

Referring to fig. 21 and 22, in some embodiments, the lens module 200 can be applied to an electronic device 300, the electronic device 300 includes a housing 310, and the lens module 200 is disposed on the housing 310. Specifically, the electronic apparatus 300 may be, but is not limited to, a wearable device such as a mobile phone, a video phone, a smart phone, an electronic book reader, a vehicle-mounted image capturing apparatus such as a car recorder, or a smart watch. When the electronic device 300 is a smartphone, the housing 310 may be a middle frame of the electronic device 300. By adopting the lens module 200 in the electronic device 300, the focusing function can be realized, the long-focus characteristic and the miniaturization design can be considered, and more different shooting scenes can be adapted.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent should be subject to the appended claims.

Claims

1. An optical system, wherein four lens elements with refractive power are provided, the optical system sequentially includes, from an object side to an image side along an optical axis:

a second lens element with refractive power having a concave image-side surface at a paraxial region;

a fourth lens element with positive refractive power having a convex image-side surface at paraxial region;

the fourth lens can move along an optical axis on the image side of the third lens to realize a focusing function, and the first lens, the second lens and the third lens are fixed relative to an imaging surface of the optical system;

and the optical system satisfies the following conditional expression:

0.8≤TTL/fa≤1.5；

2. The optical system according to claim 1, wherein the following conditional expression is satisfied:

1≤f4/f1≤3；

wherein f4 is the effective focal length of the fourth lens, and f1 is the effective focal length of the first lens.

3. The optical system according to claim 1, wherein the following conditional expression is satisfied:

10≤TTL/ImgH≤11；

wherein, TTL is a distance on an optical axis from an object-side surface of the first lens element to an imaging surface of the optical system, and ImgH is a radius of a maximum effective imaging circle of the optical system.

4. The optical system according to claim 1, wherein the following conditional expression is satisfied:

13.5mm≤ImgH/tan（FOVa）≤14.5mm；

wherein ImgH is the radius of the maximum effective imaging circle of the optical system, and FOVa is the maximum field angle of the optical system in the telephoto state.

5. The optical system according to claim 1, further comprising an infrared cut filter provided on an image side of the fourth lens, wherein the optical system satisfies the following conditional expression:

0.8≤map2/map1≤1；

the map2 is half of the maximum effective clear aperture of the light rays of the marginal field of view on the image side surface of the infrared cut-off filter, and the map1 is half of the maximum effective clear aperture of the light rays of the central field of view on the image side surface of the infrared cut-off filter.

6. The optical system according to claim 1, wherein the following conditional expression is satisfied:

4≤TTL/（CT2+CT3）≤8.5；

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

7. The optical system according to claim 1, wherein the following conditional expression is satisfied:

|（R5-R6）/（R5+R6）|≤1；

wherein R5 is a radius of curvature of an object-side surface of the third lens at an optical axis, and R6 is a radius of curvature of an image-side surface of the third lens at the optical axis.

8. The optical system according to claim 1, wherein the following conditional expression is satisfied:

4≤FNO≤5.5；

wherein FNO is an f-number of the optical system.

9. A lens module comprising a photosensitive element and the optical system of any one of claims 1-8, wherein the photosensitive element is disposed on an image side of the optical system.

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