CN216526503U - Small-size liquid lens optical system - Google Patents

Abstract

The utility model discloses a small-sized liquid lens optical system, which sequentially comprises a liquid lens, a first lens, a second lens, a third lens, a fourth lens and a fourth lens from an object side to an image side along an optical axis, wherein the first lens, the second lens and the fourth lens respectively comprise an object side surface and an image side surface; the first lens element with positive refractive index has a convex object-side surface and a convex image-side surface; the second lens element with negative refractive index has a concave object-side surface and a concave image-side surface; the third lens element with positive refractive index has a convex image-side surface; the fourth lens element with negative refractive index has a concave object-side surface and a convex image-side surface; the lens with the refractive index only has the four lenses. The utility model adopts the scheme of matching with the liquid lens, carries out automatic focusing when different object distances are adopted, can obtain high resolution without changing optical back focus, and has wide working object distance range; the liquid lens is arranged in front, so that the liquid lens is convenient to take and place, and can be independently used as a single-focus lens after the liquid lens is removed.

Description

Small-size liquid lens optical system

Technical Field

The utility model relates to the technical field of lenses, in particular to a small liquid lens optical system.

Background

With the continuous progress of the industrial image processing technology, the machine vision system is widely applied in the field of precise detection or scanning code scanning, the eyes of the machine vision system are industrial cameras, the eye pupils of the industrial cameras are lenses, and the quality of the lenses directly determines the overall performance of the system.

At present, a plurality of defects exist in a lens applied to industrial detection or code scanning, for example, a single-focus lens is mostly adopted and used at a close object distance, and under different object distances, the back focus of the lens can generate deviation, so that the imaging quality is reduced, and the same lens cannot work at a plurality of different object distances simultaneously; at present, an optical system is matched with a liquid lens, and the liquid lens is usually arranged in the middle of the lens, so that when the liquid lens is removed, the image quality of the optical system per se is poor, and the optical system cannot be used independently; when the visual field range is large, the distortion of the lens is large, the image distortion affects the machine interpretation precision; in order to achieve high performance, the lens is large in size and long in total length.

SUMMERY OF THE UTILITY MODEL

It is an object of the present invention to provide a compact liquid lens optical system to solve at least one of the above problems.

In order to achieve the purpose, the utility model adopts the following technical scheme:

a small-sized liquid lens optical system sequentially comprises a liquid lens, a first lens, a second lens, a third lens and a fourth lens from an object side to an image side along an optical axis, wherein the first lens to the fourth lens respectively comprise an object side surface facing to the object side and allowing imaging light rays to pass and an image side surface facing to the image side and allowing the imaging light rays to pass;

the first lens element with positive refractive index has a convex object-side surface and a convex image-side surface;

the second lens element has negative refractive index, and has a concave object-side surface and a concave image-side surface;

the third lens element with positive refractive index has a convex image-side surface;

the fourth lens element with negative refractive index has a concave object-side surface and a convex image-side surface;

the lens with the refractive index only has the four lenses.

Preferably, the lens further comprises a diaphragm, and the diaphragm is arranged between the liquid lens and the first lens.

Preferably, the first lens is a plastic lens, and the second lens to the fourth lens are glass lenses.

Preferably, the lens satisfies the following conditional expressions: TTL is less than 11.5mm, wherein TTL is the total length of the lens.

Preferably, the lens satisfies the following conditional expressions:

1＜f1＜4，-3＜f2＜-1，2＜f3＜6，-7＜f4＜-2，

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

Preferably, the lens satisfies the following conditional expressions:

1.8＜nd1＜2.2，1.5＜nd2＜1.9，1.7＜nd3＜2.1，1.7＜nd4＜2.1，

wherein Nd1 is a refractive index of the first lens, Nd2 is a refractive index of the second lens, Nd3 is a refractive index of the third lens, and Nd4 is a refractive index of the fourth lens.

After adopting the technical scheme, compared with the background technology, the utility model has the following advantages:

1. the utility model takes the characteristics of industrial detection or code scanning into consideration, adopts a scheme of matching with a liquid lens, performs automatic focusing at different object distances, can obtain high resolution without changing optical back focus, and has wide range of working object distances.

2. The utility model adopts the scheme that the liquid lens is arranged in front, the liquid lens and the optical system can be directly connected by screw threads, the taking and the placing are convenient, and the single-focus lens can be independently used after the liquid lens is removed.

3. According to the utility model, four lenses are adopted in the direction from the object side to the image side, and the lenses are correspondingly designed, so that the optical distortion of the lens is controlled in | 1% |, the optical distortion is small, and the object image is not distorted.

4. The utility model adopts a miniaturized design, has small front port diameter, short total length and small integral volume, is beneficial to reducing the integral weight and cost of the lens and is suitable for mass production.

Drawings

FIG. 1 is a light path diagram according to the first embodiment;

FIG. 2 is a graph of MTF of the lens at 436nm-650nm in visible light and a long object distance in the first embodiment;

FIG. 3 is a graph of MTF of a lens at 436nm-650nm in visible light and a short object distance in the first embodiment;

FIG. 4 is a graph showing the distortion of a lens at 555nm in visible light in the first embodiment;

FIG. 5 is a light path diagram of the second embodiment;

FIG. 6 is a graph of MTF of the lens in the second embodiment at 436-650 nm of visible light and a long object distance;

FIG. 7 is a graph of MTF of the lens in the second embodiment at 436nm-650nm of visible light and a short object distance;

FIG. 8 is a graph showing the distortion of the lens at 555nm in visible light in the second embodiment;

FIG. 9 is a light path diagram of the third embodiment;

FIG. 10 is a graph of MTF of the lens in the third embodiment at 436-650 nm of visible light and a long object distance;

FIG. 11 is a graph of MTF of the lens in the third embodiment at 436nm-650nm of visible light and a short object distance;

FIG. 12 is a graph showing the distortion of the lens at 555nm in visible light in the third embodiment.

Description of reference numerals:

the lens comprises a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, a liquid lens 5 and a diaphragm 6.

Detailed Description

To further illustrate the various embodiments, the utility model provides the accompanying drawings. The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate embodiments of the utility model and, together with the description, serve to explain the principles of the embodiments. Those skilled in the art will appreciate still other possible embodiments and advantages of the present invention with reference to these figures. Elements in the figures are not drawn to scale and like reference numerals are generally used to indicate like elements.

The utility model will now be further described with reference to the accompanying drawings and detailed description.

In the present specification, the term "a lens element having a positive refractive index (or a negative refractive index)" means that the paraxial refractive index of the lens element calculated by the gauss theory is positive (or negative). The term "object-side (or image-side) of a lens" is defined as the specific range of imaging light rays passing through the lens surface. The determination of the surface shape of the lens can be performed by the judgment method of a person skilled in the art, i.e., by the sign of the curvature radius (abbreviated as R value). The R value may be commonly used in optical design software, such as Zemax or CodeV. The R value is also commonly found in lens data sheets (lens sheets) of optical design software. When the R value is positive, the object side is judged to be a convex surface; and when the R value is negative, judging that the object side surface is a concave surface. On the contrary, regarding the image side surface, when the R value is positive, the image side surface is judged to be a concave surface; when the R value is negative, the image side surface is judged to be convex.

The utility model discloses a small-sized liquid lens optical system, which sequentially comprises a liquid lens, a first lens, a second lens, a third lens and a fourth lens from an object side to an image side along an optical axis, wherein the first lens to the fourth lens respectively comprise an object side surface facing the object side and allowing imaging light rays to pass and an image side surface facing the image side and allowing the imaging light rays to pass;

the first lens element with positive refractive index has a convex object-side surface and a convex image-side surface;

the second lens element has negative refractive index, and has a concave object-side surface and a concave image-side surface;

the third lens element with positive refractive index has an object-side surface with concave-convex shape and a convex image-side surface;

the fourth lens element with negative refractive index has a concave object-side surface and a convex image-side surface;

the lens with the refractive index is only provided with the four lenses, the optical back focus is unchanged in different working object distances by matching the liquid lens, and the liquid lens is controlled to generate different curvature radiuses by changing the voltage value of the liquid lens, so that the lens optical system can obtain high resolution within the working object distance range from 50mm to 500 m.

Preferably, the lens further comprises a diaphragm, and the diaphragm is arranged between the liquid lens and the first lens.

Preferably, the first lens is a plastic lens, and the second lens to the fourth lens are glass lenses.

Preferably, the lens satisfies the following conditional expressions: TTL is less than 11.5mm, wherein TTL is the total length of the lens, so that the interface of the lens can be M8, and the requirement of miniaturization of the lens is met.

Preferably, the lens satisfies the following conditional expressions:

1＜f1＜4，-3＜f2＜-1，2＜f3＜6，-7＜f4＜-2，

wherein f1 is the focal length value of the first lens, f2 is the focal length value of the second lens, f3 is the focal length value of the third lens, and f4 is the focal length value of the fourth lens, and the performance of the system can be improved by reasonably distributing the focal power.

Preferably, the lens satisfies the following conditional expressions:

1.8＜nd1＜2.2，1.5＜nd2＜1.9，1.7＜nd3＜2.1，1.7＜nd4＜2.1，

wherein Nd1 is a refractive index of the first lens, Nd2 is a refractive index of the second lens, Nd3 is a refractive index of the third lens, and Nd4 is a refractive index of the fourth lens.

The optical system of the present invention will be described in detail below with specific embodiments.

Example one

Referring to fig. 1, the present embodiment discloses a small liquid lens optical system, which includes a liquid lens 5, a first lens 1, a second lens 2, a third lens 3 and a fourth lens 4 in sequence from an object side a to an image side a along an optical axis, wherein each of the first lens 1 to the fourth lens 4 includes an object side surface facing the object side a and allowing passage of imaging light and an image side surface facing the image side a and allowing passage of imaging light;

the first lens element 1 has a positive refractive index, and the object-side surface and the image-side surface of the first lens element 1 are convex and convex;

the second lens element 2 has a negative refractive index, and the object-side surface and the image-side surface of the second lens element 2 are concave;

the third lens element 3 has a positive refractive index, and the object-side surface and the image-side surface of the third lens element 3 are concave and convex respectively;

the fourth lens element 4 has a negative refractive index, and the object-side surface and the image-side surface of the fourth lens element 4 are concave and convex, respectively;

the lens with the refractive index only comprises the four lenses, and further comprises a diaphragm 6, wherein the diaphragm 6 is arranged between the liquid lens 5 and the first lens 1, the first lens 1 is a plastic lens, and the second lens 2 to the fourth lens 4 are glass lenses.

Detailed optical data of this embodiment are shown in table 1.

Table 1 detailed optical data of example one

In this embodiment, the field of view of the lens can reach 40 °, and TTL is 11.44 mm. Fig. 1 is a schematic diagram of an optical path of an optical imaging lens according to this embodiment. Please refer to fig. 2 for an MTF graph of the lens under a visible light range of 436nm to 650nm and a far object distance, where an abscissa in the graph is a half-image height at an image plane, a unit is mm, and an ordinate is a coefficient of OTF, i.e., an MTF value, and a unit is dimensionless, an upper two curves are MTF graphs at a spatial frequency of 50lp/mm, and a lower two curves are MTF graphs at a spatial frequency of 100lp/mm, and it can be intuitively obtained from the graph, where 50lp/mm and 100lp/mm are both greater than 0.65 and 0.4 in the whole visual field of the optical system, which indicates that the lens has a small astigmatism, good imaging quality, and high resolution. Please refer to fig. 3 for an MTF graph of the lens under a visible light of 436nm to 650nm and a near object distance, where an abscissa in the graph is a half-image height at an image plane, a unit is mm, and an ordinate is a coefficient of OTF, i.e., an MTF value, and a unit is dimensionless, an upper two curves are MTF graphs at a spatial frequency of 50lp/mm, and a lower two curves are MTF graphs at a spatial frequency of 100lp/mm, and it can be intuitively obtained from the graph, where 50lp/mm and 100lp/mm are both greater than 0.6 and 0.3 respectively in the whole visual field of the optical system, which indicates that the lens has a small astigmatism, good imaging quality, and high resolution. Please refer to fig. 4 for a distortion curve diagram of the lens under the visible light of 555nm, it can be seen from the diagram that the optical distortion is controlled within-1%, the wide-angle distortion is strictly controlled, the image quality is improved, the distortion is not required to be corrected by a later image algorithm, and the application is convenient.

Example two

As shown in fig. 5 to 8, the surface convexo-concave shape and the refractive index of each lens of the present embodiment are substantially the same as those of the first embodiment, and the optical parameters such as the curvature radius of the surface of each lens and the thickness of the lens are different.

The detailed optical data of this embodiment are shown in table 2.

Table 2 detailed optical data of example two

In this embodiment, the field of view of the lens can reach 40 °, and TTL is 10.25 mm. Please refer to fig. 5 for a light path diagram of the optical imaging lens in this embodiment. Please refer to fig. 6 for an MTF graph of the lens under a visible light range of 436nm to 650nm and a far object distance, where an abscissa in the graph is a half-image height at an image plane, a unit is mm, and an ordinate is a coefficient of OTF, i.e., an MTF value, and a unit is dimensionless, an upper two curves are MTF graphs at a spatial frequency of 50lp/mm, and a lower two curves are MTF graphs at a spatial frequency of 100lp/mm, and it can be intuitively obtained from the graph, where 50lp/mm and 100lp/mm are both greater than 0.7 and 0.4 respectively in the whole visual field of the optical system, which indicates that the lens has a small astigmatism, good imaging quality, and high resolution. Please refer to fig. 7 for an MTF graph of the lens under a visible light of 436nm to 650nm and a near object distance, where an abscissa in the graph is a half-image height at an image plane, a unit is mm, and an ordinate is a coefficient of OTF, i.e., an MTF value, and a unit is dimensionless, an upper two curves are MTF graphs at a spatial frequency of 50lp/mm, and a lower two curves are MTF graphs at a spatial frequency of 100lp/mm, and it can be intuitively obtained from the graph, where 50lp/mm and 100lp/mm are both greater than 0.6 and 0.3 respectively in the whole visual field of the optical system, which indicates that the lens has a small astigmatism, good imaging quality, and high resolution. Please refer to fig. 8 for a distortion curve diagram of the lens under the visible light of 555nm, it can be seen from the diagram that the optical distortion is controlled within 1%, the wide-angle distortion is strictly controlled, the image quality is improved, the distortion is not required to be corrected by a later image algorithm, and the application is convenient.

EXAMPLE III

With reference to fig. 9 to 12, in the present embodiment, the object-side surface and the image-side surface of the third lens element 3 are convex surfaces, and the remaining lens elements of the present embodiment have substantially the same surface convexoconcave and refractive index as those of the first lens element, and have different optical parameters, such as the curvature radius of the surface of each lens element and the thickness of each lens element.

The detailed optical data of this embodiment are shown in table 3.

Table 3 detailed optical data of example three

In this embodiment, the field of view of the lens can reach 40 °, and TTL is 10.72 mm. Please refer to fig. 9 for a light path diagram of the optical imaging lens in this embodiment. Please refer to fig. 10 for an MTF graph of the lens under 436nm to 650nm of visible light and a long object distance, where an abscissa in the graph is a half-image height at an image plane, a unit is mm, and an ordinate is a coefficient of the OTF, i.e., an MTF value, and a unit is dimensionless, an upper two curves are the MTF graphs at a spatial frequency of 50lp/mm, and a lower two curves are the MTF graphs at a spatial frequency of 100lp/mm, and it can be intuitively obtained from the graph that both curves in the whole field of view of the optical system are greater than 0.7 at 50lp/mm and greater than 0.4 at 100lp/mm, which indicates that the lens has small astigmatism, good imaging quality, and high resolution. Please refer to fig. 11 for an MTF graph of the lens under a visible light of 436nm to 650nm and a close object distance, where an abscissa in the graph is a half-image height at an image plane, and a unit is millimeter, and an ordinate is a coefficient of the OTF, i.e., an MTF value, and a unit is dimensionless, an upper two curves are the MTF graphs at a spatial frequency of 50lp/mm, and a lower two curves are the MTF graphs at a spatial frequency of 100lp/mm, and it can be intuitively obtained from the graph that both 50lp/mm and 100lp/mm in the whole field of view of the optical system are greater than 0.6 and 0.3, which indicates that the lens has a small astigmatism, good imaging quality, and a high resolution. Please refer to fig. 12 for a distortion curve diagram of the lens under the visible light of 555nm, it can be seen from the diagram that the optical distortion is controlled within 1%, the wide-angle distortion is strictly controlled, the image quality is improved, the distortion is not required to be corrected by a later image algorithm, and the application is convenient.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (6)

1. A small-sized liquid lens optical system is characterized by sequentially comprising a liquid lens, a first lens, a second lens, a third lens and a fourth lens from an object side to an image side along an optical axis, wherein the first lens to the fourth lens respectively comprise an object side surface facing the object side and allowing imaging light rays to pass and an image side surface facing the image side and allowing the imaging light rays to pass;

the first lens element with positive refractive index has a convex object-side surface and a convex image-side surface;

the second lens element has negative refractive index, and has a concave object-side surface and a concave image-side surface;

the third lens element with positive refractive index has a convex image-side surface;

the fourth lens element with negative refractive index has a concave object-side surface and a convex image-side surface;

the lens with the refractive index only has the four lenses.

2. A compact liquid lens optical system as recited in claim 1, further comprising an optical stop disposed between the liquid lens and the first lens.

3. A compact liquid lens optical system as claimed in claim 1, wherein the first lens is a plastic lens, and the second to fourth lenses are glass lenses.

4. A compact liquid lens optical system according to claim 1, characterized in that the following condition is satisfied: TTL is less than 11.5mm, wherein TTL is the total length of the lens.

5. A compact liquid lens optical system according to claim 1, characterized in that the following condition is satisfied:

1＜f1＜4，-3＜f2＜-1，2＜f3＜6，-7＜f4＜-2，

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

6. A compact liquid lens optical system according to claim 1, characterized in that the following condition is satisfied:

1.8＜nd1＜2.2，1.5＜nd2＜1.9，1.7＜nd3＜2.1，1.7＜nd4＜2.1，

wherein Nd1 is a refractive index of the first lens, Nd2 is a refractive index of the second lens, Nd3 is a refractive index of the third lens, and Nd4 is a refractive index of the fourth lens.

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