Prime lens

Abstract

The prime lens comprises a first lens with negative focal power, a second lens with positive focal power, a third lens with negative focal power and a fourth lens with positive focal power which are arranged from an object plane to an image plane along an optical axis, the object-side surface of the first lens is a convex surface, and the image-side surface is a concave surface. The object side surface of the second lens is a convex surface, and the image side surface is a concave surface; the object side surface of the third lens is a concave surface, and the image side surface is a convex surface; the fourth lens element has a convex object-side surface and a convex image-side surface. According to the technical scheme, the arrangement of the four lenses ensures that the number of the lenses in the prime lens is small, and the realization of small size and low cost is facilitated; and an M12 interface can be adopted, so that the cost can be further reduced. Furthermore, the focal power of the first lens and the third lens is negative, the focal power of the second lens and the fourth lens is positive, and the good imaging effect of the optical system can be ensured by reasonably distributing the focal power of each lens in the optical system.

Description

Technical Field

[0001] The embodiments of the present utility model relate to the technical field of optical devices, and in particular, to a fixed-focus lens. Background Art

[0002] In order to achieve high-precision detection and observation and other tasks, common machine vision lenses on the market usually cooperate with a larger-format Sensor to improve the detection accuracy. At the same time, when the total length of the optical system and the incident angle of the chief ray of the machine vision lens are fixed, the clear aperture of the lens near the image plane will inevitably increase with the increase of the Sensor format, resulting in an increase in the overall volume of the lens and the interface for connecting the lens to the camera. At the same time, after the lens aperture increases, the costs of lens materials, processing, etc. will also increase accordingly.

[0003] Currently, the common lens interfaces for 2 / 3” inch target surface Sensors are larger-aperture interfaces such as C interfaces or M16 interfaces, which require the use of more expensive interfaces, increasing the cost of machine vision lenses. Content of the Utility Model

[0004] The present utility model provides a fixed-focus lens. By reasonably setting the composition method, optical power distribution method, and lens surface type of the lens, a fixed-focus lens with a small volume and good imaging effect is realized. At the same time, an M12 interface can be used to reduce the cost of the fixed-focus lens.

[0005] The embodiments of the present utility model provide a fixed-focus lens, which includes a first lens, a second lens, a third lens, and a fourth lens arranged in sequence along the optical axis from the object plane to the image plane;

[0006] Both the first lens and the third lens are negative-power lenses, and both the second lens and the fourth lens are positive-power lenses;

[0007] The first lens includes a first object side close to the object plane and a first image side close to the image plane. The first object side is a convex surface, and the first image side is a concave surface;

[0008] The second lens includes a second object side close to the object plane and a second image side close to the image plane. The second object side is a convex surface, and the second image side is a concave surface;

[0009] The third lens includes a third object side close to the object plane and a third image side close to the image plane. The third object side is a concave surface, and the third image side is a convex surface;

[0010] The fourth lens includes a fourth object side close to the object plane and a fourth image side close to the image plane. The fourth object side is a convex surface, and the fourth image side is a convex surface.

[0011] Optionally, during the focusing process of the fixed-focus lens, the first lens, the second lens, the third lens, and the fourth lens move as a whole.

[0012] Optionally, the optical power of the first lens is The optical power of the second lens is The optical power of the third lens is The optical power of the fourth lens is

[0013] Wherein,

[0014] Optionally, the optical power of the first lens is The optical power of the second lens is The optical power of the fixed-focus lens is

[0015] Wherein,

[0016] Optionally, the optical power of the third lens is The optical power of the fixed-focus lens is The refractive index of the third lens is ND3;

[0017] Wherein, 1.6 < ND3 < 1.7.

[0018] Optionally, the optical power of the fourth lens is The optical power of the fixed-focus lens is

[0019] Wherein,

[0020] Optionally, the maximum principal ray incident angle of the fixed-focus lens is RD, the maximum semi-aperture of the fourth lens is SD4, the maximum image height of the fixed-focus lens is H, the distance from the midpoint of the object side of the first lens to the midpoint of the image plane is TTL, and the focal length of the fixed-focus lens is f;

[0021] Wherein, 10.5 < RD * SD4 / H < 13.5, 1.7 < TTL / f < 1.95.

[0022] Optionally, both the first lens and the third lens are meniscus lenses.

[0023] Optionally, both the first lens and the second lens are glass spherical lenses;

[0024] Both the third lens and the fourth lens are plastic aspherical lenses.

[0025] Optionally, the fixed-focus lens further includes a diaphragm and a filter;

[0026] The diaphragm is disposed in the optical path between the second lens and the third lens;

[0027] The filter is disposed in the optical path between the fourth lens and the image plane.

[0028] The fixed-focus lens provided by the embodiment of the present invention includes a first lens, a second lens, a third lens, and a fourth lens. The arrangement of the four lenses ensures that the number of lenses in the fixed-focus lens is small, which is beneficial to realizing a small-sized and low-cost fixed-focus optical system; and the small-sized optical system can be paired with an M12 interface to reduce the cost of the imaging lens. Further, the optical powers of the first lens and the third lens are both negative, and the optical powers of the second lens and the fourth lens are both positive. By reasonably distributing the optical powers of the respective lenses in the optical system, a good imaging effect of the optical system can be ensured.

[0029] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present invention, nor is it used to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0031] Figure 1 is a schematic structural diagram of a fixed-focus lens provided by Embodiment 1 of the present invention;

[0032] Figure 2 is a schematic diagram of the full-frequency MTF curve of a fixed-focus lens provided by Embodiment 1 of the present invention in the visible light band;

[0033] Figure 3 is a schematic diagram of the relative illumination curve of a fixed-focus lens provided by Embodiment 1 of the present invention;

[0034] Figure 4 is a schematic diagram of the field curvature and distortion curve of a fixed-focus lens provided by Embodiment 1 of the present invention;

[0035] Figure 5 is a schematic diagram of the chief ray incidence angle curve of a fixed-focus lens provided by Embodiment 1 of the present invention;

[0036] Figure 6It is a schematic structural diagram of a fixed-focus lens provided in the second embodiment of the present utility model;

[0037] Figure 7 It is a schematic diagram of the full-frequency MTF curve of a fixed-focus lens provided in the second embodiment of the present utility model in the visible light band;

[0038] Figure 8 It is a schematic diagram of the relative illumination curve of a fixed-focus lens provided in the second embodiment of the present utility model;

[0039] Figure 9 It is a schematic diagram of the field curvature and distortion curve of a fixed-focus lens provided in the second embodiment of the present utility model;

[0040] Figure 10 It is a schematic diagram of the chief ray angle of incidence curve of a fixed-focus lens provided in the second embodiment of the present utility model;

[0041] Figure 11 It is a schematic structural diagram of a fixed-focus lens provided in the third embodiment of the present utility model;

[0042] Figure 12 It is a schematic diagram of the full-frequency MTF curve of a fixed-focus lens provided in the third embodiment of the present utility model in the visible light band;

[0043] Figure 13 It is a schematic diagram of the relative illumination curve of a fixed-focus lens provided in the third embodiment of the present utility model;

[0044] Figure 14 It is a schematic diagram of the field curvature and distortion curve of a fixed-focus lens provided in the third embodiment of the present utility model;

[0045] Figure 15 It is a schematic diagram of the chief ray angle of incidence curve of a fixed-focus lens provided in the third embodiment of the present utility model. Detailed implementation manners

[0046] In order to enable those skilled in the art to better understand the solution of the present utility model, the technical solutions in the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all of the embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present utility model.

[0047] Embodiment 1

[0048] Figure 1 It is a schematic structural diagram of a fixed-focus lens provided in the first embodiment of the present utility model, as Figure 1As shown in the figure, the fixed-focus lens provided in the first embodiment of the present invention includes a first lens 101, a second lens 102, a third lens 103, and a fourth lens 104 arranged in sequence from the object plane to the image plane along the optical axis; both the first lens 101 and the third lens 103 are negative-power lenses, and both the second lens 102 and the fourth lens 104 are positive-power lenses; the first lens 101 includes a first object side facing the object plane and a first image side facing the image plane, the first object side is a convex surface, and the first image side is a concave surface; the second lens 102 includes a second object side facing the object plane and a second image side facing the image plane, the second object side is a convex surface, and the second image side is a concave surface; the third lens 103 includes a third object side facing the object plane and a third image side facing the image plane, the third object side is a concave surface, and the third image side is a convex surface; the fourth lens 104 includes a fourth object side facing the object plane and a fourth image side facing the image plane, the fourth object side is a convex surface, and the fourth image side is a convex surface.

[0049] Specifically, the fixed-focus lens provided in the embodiment of the present invention includes four lenses with optical power, specifically the first lens 101, the second lens 102, the third lens 103, and the fourth lens 104. The four lenses modulate the incident light to realize an optical system with a fixed focal length. Moreover, since the optical system only includes four lenses, its structure is simple, and it is easy to realize a miniaturized and low-cost optical system. Further, the optical system in the embodiment of the present invention can be connected to an M12 interface. The M12 interface can be understood as a lens interface with a thread size of 12 mm. Compared with the C interface or the M16 interface, the M12 is smaller and lighter, easier to manufacture, and can be produced at a lower cost than the C interface, and is very suitable for use in a compact camera system.

[0050] Furthermore, the optical power is equal to the difference between the converging degree of the image plane light beam and the converging degree of the object plane light beam, which characterizes the ability of the optical system to deflect light rays. The greater the absolute value of the optical power, the stronger the bending ability of the light rays; the smaller the absolute value of the optical power, the weaker the bending ability of the light rays. When the optical power is positive, the refraction of the light rays is convergent; when the optical power is negative, the refraction of the light rays is divergent. The optical power can be used to characterize a certain refracting surface of a lens (i.e., a surface of the lens), can be used to characterize a certain lens, or can be used to characterize a system formed by multiple lenses (i.e., a lens group). In the embodiments of the present invention, the first lens 101 and the third lens 103 are negative optical power lenses, and the second lens 102 and the fourth lens 104 are positive optical power lenses. Among them, the first lens 101, as the lens group that first adjusts the incident light rays in the fixed-focus lens, the setting of its negative optical power can effectively deflect the large-angle incident light rays, ensure that more light rays enter the optical system, and thus can effectively increase the field of view angle of the fixed-focus lens. The second lens 102 is a positive optical power lens, so that the second lens 102 can timely correct the large aberration generated by the first lens 101, especially can significantly correct the marginal aberration of the fixed-focus lens, thereby improving the imaging resolution of the optical system. Furthermore, the third lens 103 is a negative optical power lens, and the fourth lens 104 is a positive optical power lens. The optical powers of the third lens 103 and the fourth lens 104 cooperate with each other to achieve timely correction of the aberration.

[0051] Furthermore, the object side surface of the lens can be understood as the surface of the lens close to the object plane, and the image side surface of the lens can be understood as the surface of the lens close to the image plane. Specifically, the object side surface of the first lens 110 is a convex surface, and the image side surface is a concave surface. It can be understood that the object side surface of the first lens 101 bulges towards the object plane at the near optical axis position, and the image side surface depresses towards the image plane at the near optical axis position, that is, the first lens 101 is a convex-concave structure lens. The object side surface of the second lens 102 is a convex surface, and the image side surface is a concave surface. It can be understood that the object side surface of the second lens 102 bulges towards the object plane at the near optical axis position, and the image side surface depresses towards the image plane at the near optical axis position, that is, the second lens 102 is a convex-concave structure lens. The object side surface of the third lens 103 is a concave surface, and the image side surface is a convex surface. It can be understood that the object side surface of the third lens 103 depresses towards the object plane at the near optical axis position, and the image side surface bulges towards the image plane at the near optical axis position, that is, the third lens 103 is a concave-convex structure lens. The object side surface of the fourth lens 104 is a convex surface, and the image side surface is a convex surface. It can be understood that the object side surface of the fourth lens 104 bulges towards the object plane at the near optical axis position, and the image side surface bulges towards the image plane at the near optical axis position, that is, the fourth lens 140 is a double-convex structure lens. By reasonably setting the surface types of each lens, it can ensure that the edge light ray trend is smoother, improve the relative illumination between the edge image and the central image, and improve the imaging effect.

[0052] Further, the first lens 101 and the third lens 103 are meniscus lenses, that is, the first lens 101 is a meniscus lens convex in the front and concave in the rear, and the third lens 103 is a meniscus lens concave in the front and convex in the rear. The setting of the meniscus lens can further correct the field curvature of the optical system and improve the imaging effect.

[0053] In summary, the fixed-focus lens provided by the embodiment of the present invention includes a first lens, a second lens, a third lens, and a fourth lens. The setting of the four lenses ensures that the number of lenses in the fixed-focus lens is small, which is beneficial to realizing a small-size and low-cost fixed-focus optical system; and the small-size optical system can be matched with an M12 interface to reduce the cost of the imaging lens. Further, the optical powers of the first lens and the third lens are both negative, and the optical powers of the second lens and the fourth lens are both positive. By reasonably distributing the optical powers of the respective lenses in the optical system, a good imaging effect of the optical system can be ensured.

[0054] Based on the above embodiment, the fixed-focus lens may further include a diaphragm 105 and a filter 106; the diaphragm 105 is disposed in the optical path between the second lens 102 and the third lens 103; the filter 106 is disposed in the optical path between the fourth lens 104 and the image plane.

[0055] Specifically, setting the diaphragm 105 can adjust the propagation direction of the light beam, which is beneficial to improving the imaging quality. And in this fixed-focus lens, the diaphragm 105 is located in the optical path between the second lens 102 and the third lens 103. The diaphragm 105 being located in the middle of the fixed-focus lens can ensure the minimization of the front and rear apertures of the fixed-focus lens.

[0056] The filter 106 is disposed in the optical path between the fourth lens 104 and the image plane and is used to filter out stray light and improve the imaging effect. Specifically, the filter 106 can be an infrared filter.

[0057] Further, the fixed-focus lens provided by the embodiment of the present invention may further include a protective glass and an image acquisition element. The protective glass can be disposed on the image side of the filter, and the image acquisition element can be disposed on the image side of the protective glass. The optical system is protected by the protective glass, and an image is acquired by the image acquisition element to realize the normal imaging function of the optical system.

[0058] Based on the above embodiment, during the focusing process of the fixed-focus lens, the first lens 101, the second lens 102, the third lens 103, and the fourth lens 104 move as a whole.

[0059] Specifically, the first lens 101, the second lens 102, the third lens 103, and the fourth lens 104 move as a whole for focusing, which can achieve focusing at different object distances and clear imaging at different working object distances. Moreover, since the four lenses focus as a whole, the arrangement of the four lenses ensures that the overall weight of the fixed-focus lens is relatively light, making it more convenient to focus; when applied to autofocus, it can reduce the focusing error and improve the focusing sensitivity.

[0060] Based on the above embodiment, the optical power of the first lens 101 is The optical power of the second lens 102 is The optical power of the third lens 103 is The optical power of the fourth lens 104 is Among them, Satisfying this condition can constrain the optical system to have a reasonable optical power distribution, which is beneficial to the correction of system aberrations.

[0061] Based on the above embodiment, the optical power of the first lens 101 is The optical power of the second lens 102 is The optical power of the fixed-focus lens is Among them, Satisfying this condition is beneficial for the object-side light rays to smoothly enter the optical system, which is beneficial for the optical system to have a relatively high relative illumination, reduce high-order aberrations, and lower the tolerance sensitivity of the optical system.

[0062] Based on the above embodiment, the optical power of the third lens 103 is The optical power of the fixed-focus lens is The refractive index of the third lens 103 is ND3; among them, 1.6 < ND3 < 1.7. Satisfying this condition is beneficial for the correction of optical system distortion, and the incident and exit angles of light rays on the surface of the third lens 103 are relatively small, which is beneficial for the optical system to have a relatively high relative illumination.

[0063] Based on the above embodiment, the optical power of the fourth lens 104 is The optical power of the fixed-focus lens is Among them, Satisfying this condition is beneficial for reducing the CRA of the optical system and preventing problems such as a decrease in actual shooting illumination and color cast caused by too large a difference between the CRA of the lens and the CRA of the matched Sensor.

[0064] Based on the above embodiment, the maximum image height chief ray incident angle of the fixed-focus lens is RD, the maximum semi-aperture of the fourth lens 104 is SD4, the maximum image height of the fixed-focus lens is H, the distance from the midpoint of the object side of the first lens 101 to the midpoint of the image plane is TTL, and the focal length of the fixed-focus lens is f; among them,

[0065] 10.5 <RD*SD4 / H<13.5,1.7<TTL / f<1.95。满足此条件有利于减小整体光学系统的体积,使成品镜头能够采用M12接口的镜框,减少定焦镜头的材料成本。

[0066] On the basis of the above embodiment, the first lens 101 and the second lens 102 are both glass spherical lenses; the third lens 103 and the fourth lens 104 are both plastic aspherical lenses.

[0067] Specifically, the spherical lens is characterized by having a constant curvature from the center of the lens to the periphery of the lens, which ensures that the lens is set in a simple manner. Furthermore, since the thermal expansion coefficient of a glass lens is small and the stability is good, the first lens 101 and the second lens 102 can be set to be glass spherical lenses. The thermal properties of glass spherical lenses are more stable, and when they bear more optical power, they can ensure that the lens has good resolution within a wider temperature range. In addition, compared with plastic aspherical lenses, the range of glass materials available is wider, and the refractive index and Abbe constant are relatively free to choose. To a certain extent, the high-level aberrations and chromatic aberrations of the lens can be controlled to meet the use requirements under complex conditions.

[0068] The characteristic of an aspherical lens is that the curvature changes continuously from the center of the lens to the periphery of the lens. Unlike a spherical lens with a constant curvature from the center of the lens to the periphery of the lens, an aspherical lens has a better curvature radius characteristic, and has the advantages of improving distortion aberration and improving astigmatism aberration. Setting the third lens 103 and the fourth lens 104 to use an aspherical lens can eliminate the aberration that occurs during imaging as much as possible, thereby improving the imaging quality of the lens. On this basis, the aspherical lens can be a plastic aspherical lens, which is conducive to reducing the processing technology of the aspherical lens, and the cost of the aspherical lens is low.

[0069] In the fixed-focus lens provided in the embodiment of the utility model, a glass spherical lens and a plastic aspherical lens can be mixed and matched, so that the cost of the fixed-focus lens can be effectively controlled while ensuring the optical performance of the fixed-focus lens; at the same time, the materials of each lens have a mutual compensation effect, which can ensure that it can still be used normally in high and low temperature environments.

[0070] As a feasible implementation method, specific parameters of the fixed-focus lens are described below.

[0071] Table 1 Optical design values ​​of the fixed focus lens in Example 1

[0072]

[0073] Table 2 Design values ​​of optical physical parameters of a fixed-focus lens

[0074] Surf Surface type Radius of curvature Thickness Refractive index Abbe number k value Semi-aperture 0 Object surface Infinity 400.000 184.208 1 Standard surface 14.5909 2.582 1.7000 41.20 3.452 2 Standard surface 4.3841 1.078 2.406 3 Standard surface 4.3766 1.922 1.8000 47.00 2.231 4 Standard surface 30.3026 0.557 1.754 STO Standard surface Infinity 2.786 1.418 6 Aspherical surface -1.7794 0.860 1.6700 19.30 -4.1842 2.055 7 Aspherical surface -3.0403 0.048 -2.3389 2.608 8 Aspherical surface 5.6753 2.146 1.5400 55.70 -26.0835 3.431 9 Aspherical surface -15.0704 4.141(V) 1.7212 3.701 10 Standard surface Infinity 0.800 1.5200 64.20 4.564 11 Standard surface Infinity 5.000 4.657 12 Image surface Infinity - 5.610

[0075] The surface numbers in Table 2 are numbered according to the surface order of each lens. "0" represents the object surface, "1" represents the object-side surface of the first lens, "2" represents the image-side surface of the first lens, and so on. "STO" represents the aperture of the lens; the radius of curvature represents the degree of curvature of the lens surface. A positive value indicates that the surface is curved towards the image side, and a negative value indicates that the surface is curved towards the object side; among them, "Infinity" represents that the surface is a plane and the radius of curvature is infinite; the thickness represents the central axial distance from the current surface to the next surface, the refractive index represents the ability of the material between the current surface and the next surface to deflect light, a space represents that the current position is air and the refractive index is 1; the Abbe number represents the dispersion characteristics of the material between the current surface and the next surface to light; the k value represents the numerical value of the conic coefficient of the aspherical surface; the semi-aperture represents half of the aperture size of the current surface.

[0076] The aspherical conic coefficient can be defined by the following aspherical formula, but is not limited to the following representation:

[0077]

[0078] Among them, z is the axial sagittal height of the aspherical surface in the Z direction; r is the height of the aspherical surface; c is the curvature of the fitted spherical surface, numerically the reciprocal of the radius of curvature; k is the fitted conic coefficient; A - G are the coefficients of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspherical polynomial.

[0079] Table 3 Aspherical coefficients of a fixed-focus lens

[0080]

[0081] Among them, "-3.652281E-02" represents -3.652281×10 -2 , and the rest of the coefficients are represented in this way.

[0082] Table 4 Thickness data of the focusing interval of a fixed-focus lens

[0083] Object distance 100 mm 2000 mm Thickness of surface 9 (V) 5.331 mm 3.836 mm

[0084] Based on the above parameter definitions, the optical parameters that the fixed-focus lens in Embodiment 1 of the present utility model can achieve are as follows:

[0085] Full image height: 11.2 mm;

[0086] Image-side F#: 4.0;

[0087] Optical assembly TTL: 21.921 mm;

[0088] Focal length f: 12.30 mm.

[0089] Furthermore, Figure 2 It is a schematic diagram of the full-frequency MTF curve of a fixed-focus lens provided in Embodiment 1 of the present utility model in the visible light band. The MTF graph is one of the most commonly used and authoritative evaluation methods in modern optical design. The abscissa is the spatial frequency at which line pairs in the object space are imaged on the image plane by the optical system, with the unit of cycle / mm, and the ordinate is the modulus value of the optical transfer function. For different fields of view (such as 0.00 mm, 1.1200 mm, 2.2400 mm, 3.3600 mm, 4.4800 mm, and 5.600 mm shown in the figure) in the meridional (such as T shown in the figure) and sagittal (such as S shown in the figure) directions, as the spatial frequency increases, the change trend of its optical transfer function. The most ideal curve is a straight line that coincides with the system diffraction limit, indicating that the geometric aberration of light rays at all positions is less than the wave aberration generated by the physical limitation of the system itself and can be ignored. From Figure 2 It can be seen that at 150 lp / mm for the imaging of each field of view of this system, its optical transfer function is greater than 0.3, achieving high resolution of the lens in the visible light environment.

[0090] Figure 3 It is a schematic diagram of the relative illumination curve of a fixed-focus lens provided in Embodiment 1 of the present utility model. Figure 3 The curve in the figure is illustrated by taking the light wavelength of 546 nm as an example. The horizontal coordinate in the figure represents the semi-field height, with the unit of mm, and the vertical coordinate represents the relative illumination. This attached figure reflects the relative illumination of the optical system at different fields of view, and the relative illumination at the maximum field of view is greater than 80%, which reflects the result that the system has high illumination mentioned above.

[0091] Figure 4 It is a schematic diagram of the field curvature and distortion curve of a fixed-focus lens provided in Embodiment 1 of the present utility model. In the left coordinate system in the figure, the horizontal coordinate represents the magnitude of the field curvature, with the unit of mm; the vertical coordinate represents the normalized image height, without a unit; from Figure 4 It can be seen from the left attached figure that the field curvature of the lens provided in this embodiment at each wavelength (436 nm, 487 nm, 546 nm, 587.6 nm, and 656 nm respectively) is effectively controlled, that is, when imaging, the image quality difference between the center and the periphery is small. In the right coordinate system, the horizontal coordinate represents the magnitude of the distortion, with the unit of %; the vertical coordinate represents the normalized image height, without a unit; from Figure 4 It can be seen from the right attached figure that the maximum distortion of the lens provided in this embodiment is controlled within -2%, the distortion is well corrected, the imaging distortion is small, and the difference between the image and the actual object is small.

[0092] Figure 5It is a schematic diagram of the chief ray angle of incidence curve of a fixed-focus lens provided in the first embodiment of the present utility model, which shows the CRA values at different image heights. The abscissa represents the true image height in mm, and the ordinate represents the CRA value in °. It can be seen from the figure that the CRA of this embodiment is < 18°, meeting the performance characteristics of a small CRA.

[0093] In summary, the fixed-focus lens provided in the first embodiment of the present utility model adopts two glass spherical surfaces and two plastic aspherical surfaces. Through reasonable selection of lens materials and reasonable distribution of lens optical powers, and by the method of overall moving focusing, within the object distance range of 100 - 2000 mm: |distortion| < 2%, focal length 12.3 mm, image-side F# 4.0 at the best working distance, target surface Φ11.2 mm, relative illumination > 80%, CRA < 18°, it can be used for a low-cost fixed-focus machine vision design solution with an M12 interface.

[0094] Embodiment 2

[0095] Figure 6 It is a schematic diagram of the structure of a fixed-focus lens provided in the second embodiment of the present utility model. As Figure 6 shown, the fixed-focus lens provided in the second embodiment of the present utility model includes a first lens 101, a second lens 102, a third lens 103, and a fourth lens 104 arranged in sequence along the optical axis from the object plane to the image plane; both the first lens 101 and the third lens 103 are negative optical power lenses, and both the second lens 102 and the fourth lens 104 are positive optical power lenses; the first lens 101 includes a first object side face close to the object plane and a first image side face close to the image plane. The first object side face is a convex surface, and the first image side face is a concave surface; the second lens 102 includes a second object side face close to the object plane and a second image side face close to the image plane. The second object side face is a convex surface, and the second image side face is a concave surface; the third lens 103 includes a third object side face close to the object plane and a third image side face close to the image plane. The third object side face is a concave surface, and the third image side face is a convex surface; the fourth lens 104 includes a fourth object side face close to the object plane and a fourth image side face close to the image plane. The fourth object side face is a convex surface, and the fourth image side face is a convex surface.

[0096] Among them, the setting method of the above lens is the same as that in the first embodiment, and will not be elaborated here.

[0097] As another feasible implementation manner, the specific parameters in the fixed-focus lens will be described below.

[0098] Table 5 An optical design value of the fixed-focus lens in Embodiment 2

[0099]

[0100] Table 6 Design values of the optical physical parameters of a fixed-focus lens

[0101] Surf Surface type Radius of curvature Thickness Refractive index Abbe number k value Semi-aperture 0 Object surface Infinity 400.000 191.521 1 Standard surface 12.9617 2.310 1.7000 40.50 3.848 2 Standard surface 4.3567 1.495 2.759 3 Standard surface 4.4819 1.965 1.7700 50.00 2.561 4 Standard surface 44.6848 1.145 2.112 STO Standard surface Infinity 2.517 1.331 6 Aspherical surface -1.8041 0.912 1.6600 20.00 -4.0410 1.972 7 Aspherical surface -3.1896 0.050 -3.0036 2.561 8 Aspherical surface 5.5442 2.052 1.5400 55.70 -17.8744 3.536 9 Aspherical surface -15.8254 3.424(V) 0.3396 3.720 10 Standard surface Infinity 0.800 1.5200 64.20 4.491 11 Standard surface Infinity 5.000 4.592 12 Image surface Infinity - 5.613

[0102] The surface numbers in Table 6 are numbered according to the surface order of each lens. "0" represents the object surface, "1" represents the object-side surface of the first lens, "2" represents the image-side surface of the first lens, and so on. "STO" represents the aperture stop of the lens; the radius of curvature represents the degree of curvature of the lens surface. A positive value represents that the surface bends towards the image side, and a negative value represents that the surface bends towards the object side; among them, "Infinity" represents that the surface is a plane and the radius of curvature is infinite; the thickness represents the central axial distance from the current surface to the next surface, the refractive index represents the ability of the material between the current surface and the next surface to deflect light, a space represents that the current position is air and the refractive index is 1; the Abbe number represents the dispersion characteristics of the material between the current surface and the next surface to light; the k value represents the numerical value of the conic coefficient of the aspherical surface; the semi-aperture represents half of the aperture size of the current surface.

[0103] The aspherical conic coefficient can be defined by the following aspherical formula, but is not limited to the following representation:

[0104]

[0105] Among them, z is the axial sagittal height of the aspherical surface in the Z direction; r is the height of the aspherical surface; c is the curvature of the fitted spherical surface, numerically the reciprocal of the radius of curvature; k is the fitted conic coefficient; A - G are the coefficients of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspherical polynomial.

[0106] Table 7 Aspherical coefficients of a fixed-focus lens

[0107]

[0108] Among them, "-3.567061E-02" represents -3.567061×10 -2 , and the rest of the coefficients are represented in this way.

[0109] Table 8 Thickness data of the focusing interval of a fixed-focus lens

[0110] Object distance 100 mm 2000 mm Thickness of surface 9 (V) 4.509 mm 3.143 mm

[0111] Based on the above parameter definitions, the optical parameters that the fixed-focus lens in the second embodiment of the present invention can achieve are as follows:

[0112] Full image height: 11.2 mm;

[0113] Image-side F#: 4.0;

[0114] Optical assembly TTL: 21.670 mm;

[0115] Focal length f: 11.80 mm.

[0116] Furthermore, Figure 7 This is a schematic diagram of the full-frequency MTF curve of a fixed-focus lens provided in the second embodiment of the present invention in the visible light band. The MTF graph is one of the most commonly used and authoritative evaluation methods in modern optical design. The abscissa is the spatial frequency at which the line pairs in the object space are imaged on the image plane by the optical system, with the unit of cycle / mm, and the ordinate is the modulus value of the optical transfer function. For different fields of view (such as 0.00 mm, 1.1200 mm, 2.2400 mm, 3.3600 mm, 4.4800 mm, and 5.600 mm shown in the figure) in the meridional (such as T shown in the figure) and sagittal (such as S shown in the figure) directions, as the spatial frequency increases, the change trend of its optical transfer function. The most ideal curve is a straight line that coincides with the system diffraction limit, indicating that the geometric aberration of the light rays at all positions is less than the wavefront aberration generated by the physical limitations of the system itself and can be ignored. From Figure 7 It can be seen that at 150 lp / mm for the imaging of each field of view of this system, its optical transfer function is greater than 0.3, achieving a high resolution of the lens in the visible light environment.

[0117] Figure 8 This is a schematic diagram of the relative illumination curve of a fixed-focus lens provided in the second embodiment of the present invention. Figure 8 In the figure, the curve is illustrated by taking the light wavelength of 546 nm as an example. The horizontal coordinate in the figure represents the semi-field height, with the unit of mm, and the vertical coordinate represents the relative illumination. This figure shows the relative illumination of the optical system at different fields of view, and the relative illumination at the maximum field of view is greater than 80%, which reflects the result that the system has high illumination mentioned above.

[0118] Figure 9 This is a schematic diagram of the field curvature and distortion curve of a fixed-focus lens provided in the second embodiment of the present invention. In the coordinate system on the left side of the figure, the horizontal coordinate represents the magnitude of the field curvature, with the unit of mm; the vertical coordinate represents the normalized image height, without a unit; from Figure 9 the left figure, it can be seen that the field curvature of the lens provided in this embodiment at each wavelength (436 nm, 487 nm, 546 nm, 587.6 nm, and 656 nm respectively) is effectively controlled, that is, when imaging, the image quality at the center and the periphery has a small difference. In the coordinate system on the right side, the horizontal coordinate represents the magnitude of the distortion, with the unit of %; the vertical coordinate represents the normalized image height, without a unit; from Figure 9 the right figure, it can be seen that the maximum distortion of the lens provided in this embodiment is controlled within -2%, the distortion is well corrected, the imaging distortion is small, and the difference between the image and the actual object is small.

[0119] Figure 10It is a schematic diagram of the chief ray angle of incidence curve of a fixed-focus lens provided in the second embodiment of the present utility model, which represents the CRA values at different image heights. The abscissa represents the true image height with the unit of mm, and the ordinate represents the CRA value with the unit of °. It can be seen from the figure that the CRA of this embodiment < 18°, meeting the performance characteristics of a small CRA.

[0120] In summary, the fixed-focus lens provided in the second embodiment of the present utility model adopts two glass spherical surfaces and two plastic aspherical surfaces. Through reasonable selection of lens materials and reasonable distribution of lens optical powers, it realizes within the object distance range of 100 - 2000 mm by the way of overall moving focusing: |Distortion| < 2%, focal length 11.80 mm, image-side F#4.0 at the best working distance, target surface Φ11.2 mm, relative illumination > 80%, CRA < 18°, and can use a low-cost fixed-focus machine vision design solution with an M12 interface.

[0121] Embodiment Three

[0122] Figure 11 It is a schematic structural diagram of a fixed-focus lens provided in the third embodiment of the present utility model. As Figure 11 shown, the fixed-focus lens provided in the third embodiment of the present utility model includes a first lens 101, a second lens 102, a third lens 103, and a fourth lens 104 arranged in sequence along the optical axis from the object surface to the image surface; both the first lens 101 and the third lens 103 are negative optical power lenses, and both the second lens 102 and the fourth lens 104 are positive optical power lenses; the first lens 101 includes a first object side surface close to the object surface and a first image side surface close to the image surface, the first object side surface is a convex surface, and the first image side surface is a concave surface; the second lens 102 includes a second object side surface close to the object surface and a second image side surface close to the image surface, the second object side surface is a convex surface, and the second image side surface is a concave surface; the third lens 103 includes a third object side surface close to the object surface and a third image side surface close to the image surface, the third object side surface is a concave surface, and the third image side surface is a convex surface; the fourth lens 104 includes a fourth object side surface close to the object surface and a fourth image side surface close to the image surface, the fourth object side surface is a convex surface, and the fourth image side surface is a convex surface.

[0123] Among them, the setting method of the above lens is the same as that in Embodiment One, and will not be elaborated here.

[0124] As another feasible implementation manner, the specific parameters in the fixed-focus lens will be described below.

[0125] Table 9 An optical design value of the fixed-focus lens in Embodiment Three

[0126]

[0127] Table 10 Design values of the optical physical parameters of a fixed-focus lens

[0128] Surf Surface type Radius of curvature Thickness Refractive index Abbe number k value Semi-aperture 0 Object surface Infinity 400.000 186.384 1 Standard surface 8.8249 2.260 1.7000 41.20 4.443 2 Standard surface 4.9995 4.261 3.286 3 Standard surface 4.5234 2.192 1.8000 47.00 2.225 4 Standard surface 33.3517 0.266 1.579 STO Standard surface Infinity 3.526 1.420 6 Aspherical surface -1.7412 0.851 1.6700 19.30 -2.4753 2.137 7 Aspherical surface -2.9767 0.077 -3.3031 2.703 8 Aspherical surface 5.2990 1.921 1.5400 55.70 -16.6860 3.753 9 Aspherical surface -84.7046 1.744(V) 362.3882 3.997 10 Standard surface Infinity 0.800 1.5200 64.20 5.285 11 Standard surface Infinity 5.000 5.391 16 Image surface Infinity - 5.597

[0129] The surface numbers in Table 10 are numbered according to the surface order of each lens. "0" represents the object surface, "1" represents the object-side surface of the first lens, "2" represents the image-side surface of the first lens, and so on. "STO" represents the aperture of the lens; the radius of curvature represents the degree of curvature of the lens surface. A positive value represents that the surface bends towards the image side, and a negative value represents that the surface bends towards the object side; among them, "Infinity" represents that the surface is a plane and the radius of curvature is infinite; the thickness represents the central axial distance from the current surface to the next surface, and the refractive index represents the ability of the material between the current surface and the next surface to deflect light. A space represents that the current position is air and the refractive index is 1; the Abbe number represents the dispersion characteristics of the material between the current surface and the next surface to light; the k value represents the numerical value of the conic coefficient of the aspheric surface; the semi-aperture represents half of the aperture size of the current surface.

[0130] The aspheric conic coefficient can be defined by the following aspheric formula, but is not limited to the following representation methods:

[0131]

[0132] Among them, z is the axial sagittal height of the aspheric surface in the Z direction; r is the height of the aspheric surface; c is the curvature of the fitted spherical surface, numerically the reciprocal of the radius of curvature; k is the fitted conic coefficient; A - G are the coefficients of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspheric polynomial.

[0133] Table 11 Aspheric coefficients of a fixed-focus lens

[0134]

[0135] Among them, "-1.153551E-02" represents -1.153551×10 -2 , and the rest of the coefficients are all represented in this way.

[0136] Table 12 Thickness data of the focusing interval of a fixed-focus lens

[0137] Object distance 100 mm 2000 mm Thickness of surface 9 (V) 2.864 mm 1.456 mm

[0138] Based on the above parameter definitions, the optical parameters that the fixed-focus lens in Embodiment 3 of the present invention can achieve are as follows:

[0139] Full image height: 11.2 mm;

[0140] Image-side F#: 4.0;

[0141] Optical assembly TTL: 22.900 mm;

[0142] Focal length f: 12.0 mm.

[0143] Furthermore, Figure 12 It is a schematic diagram of the full-frequency MTF curve of a fixed-focus lens provided in Embodiment 3 of the present utility model in the visible light band. The MTF graph is one of the most commonly used and authoritative evaluation methods in modern optical design. The abscissa is the spatial frequency of the line pairs in the object space imaged on the image plane by the optical system, with the unit of cycle / mm, and the ordinate is the modulus value of the optical transfer function. In the meridional (such as T shown in the figure) and sagittal (such as S shown in the figure) directions corresponding to different fields of view (such as 0.00 mm, 1.1200 mm, 2.2400 mm, 3.3600 mm, 4.4800 mm, and 5.600 mm shown in the figure), as the spatial frequency increases, the change trend of its optical transfer function. The most ideal curve is a straight line that coincides with the system diffraction limit, indicating that the geometric aberration of the light rays at all positions is less than the wave aberration generated by the physical limitation of the system itself and can be ignored. From Figure 12 It can be seen that at 150 lp / mm for the imaging of each field of view of this system, its optical transfer function is greater than 0.3, achieving a high resolution of the lens in the visible light environment.

[0144] Figure 13 It is a schematic diagram of the relative illumination curve of a fixed-focus lens provided in Embodiment 3 of the present utility model. Figure 13 In the figure, the curve is described by taking the light wavelength of 546 nm as an example. The horizontal coordinate in the figure represents the semi-field height, with the unit of mm, and the vertical coordinate represents the relative illumination. This figure shows the relative illumination of the optical system at different fields of view, and the relative illumination at the maximum field of view is greater than 80%, which reflects the result of the high illumination of the system mentioned above.

[0145] Figure 14 It is a schematic diagram of the field curvature and distortion curve of a fixed-focus lens provided in Embodiment 3 of the present utility model. In the left coordinate system in the figure, the horizontal coordinate represents the magnitude of the field curvature, with the unit of mm; the vertical coordinate represents the normalized image height, without a unit; from Figure 14 the left figure, it can be seen that the field curvature of the lens provided in this embodiment at each wavelength (436 nm, 487 nm, 546 nm, 587.6 nm, and 656 nm respectively) is effectively controlled, that is, when imaging, the image quality difference between the center and the periphery is small. In the right coordinate system, the horizontal coordinate represents the magnitude of the distortion, with the unit of %; the vertical coordinate represents the normalized image height, without a unit; from Figure 14 the right figure, it can be seen that the maximum distortion of the lens provided in this embodiment is controlled within -1%, the distortion is well corrected, the imaging distortion is small, and the difference between the image and the actual object is small.

[0146] Figure 15It is a schematic diagram of the chief ray angle of incidence curve of a fixed-focus lens provided in the third embodiment of the present utility model, which shows the CRA values at different image heights. The abscissa represents the true image height in mm, and the ordinate represents the CRA value in °. It can be seen from the figure that the CRA of this embodiment is <18°, meeting the performance characteristics of a small CRA.

[0147] In summary, the fixed-focus lens provided in the third embodiment of the present utility model uses two glass spherical surfaces and two plastic aspherical surfaces. Through reasonable selection of lens materials and reasonable distribution of lens optical powers, and by the way of overall moving focusing, within the object distance range of 100 - 2000 mm, |distortion| < 2%, focal length 12.00 mm, image-side F# 4.0 at the best working distance, target surface Φ 11.2 mm, relative illumination > 80%, CRA < 18°, and it can be used for a low-cost fixed-focus machine vision design solution with an M12 interface.

[0148] The above specific embodiments do not constitute a limitation to the protection scope of the present utility model. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present utility model shall be included within the protection scope of the present utility model.

Claims

1. A fixed-focus lens, characterized in that, It includes a first lens, a second lens, a third lens, and a fourth lens arranged in sequence along the optical axis from the object plane to the image plane; Both the first lens and the third lens are negative focal length lenses, and both the second lens and the fourth lens are positive focal length lenses; The first lens includes a first object side face close to the object plane side and a first image side face close to the image plane side. The first object side face is a convex surface, and the first image side face is a concave surface; The second lens includes a second object side face close to the object plane side and a second image side face close to the image plane side. The second object side face is a convex surface, and the second image side face is a concave surface; The third lens includes a third object side face close to the object plane side and a third image side face close to the image plane side. The third object side face is a concave surface, and the third image side face is a convex surface; The fourth lens includes a fourth object side face close to the object plane side and a fourth image side face close to the image plane side. The fourth object side face is a convex surface, and the fourth image side face is a convex surface.

2. The fixed-focus lens according to claim 1, wherein, During the focusing process of the fixed-focus lens, the first lens, the second lens, the third lens, and the fourth lens move as a whole.

3. The fixed-focus lens according to claim 1, characterized in that The focal length of the first lens is φ1, the focal length of the second lens is φ2, the focal length of the third lens is φ3, and the focal length of the fourth lens is φ4; Wherein, -0.8 < (φ1 + φ3) / (φ2 + φ4) < -0.

65.

4. The fixed-focus lens according to claim 1, wherein The focal length of the first lens is φ1, the focal length of the second lens is φ2, and the focal length of the fixed-focus lens is φ; Wherein, 0.7 < (φ1 + φ2) / φ < 1.

5. The fixed-focus lens according to claim 1, characterized in that, The focal length of the third lens is φ3, the focal length of the fixed-focus lens is φ, and the refractive index of the third lens is ND3; Wherein, -1.5 < φ3 / φ < -1.3, 1.6 < ND3 < 1.

7.

6. The fixed-focus lens according to claim 1, wherein The focal length of the fourth lens is φ4, and the focal length of the fixed-focus lens is φ; Wherein, 1.1 < φ4 / φ < 1.

6.

7. The fixed-focus lens according to claim 1, wherein The maximum image height chief ray incident angle of the fixed-focus lens is RD, the maximum semi-aperture of the fourth lens is SD4, the maximum image height of the fixed-focus lens is H, the distance from the midpoint of the object side face of the first lens to the midpoint of the image plane is TTL, and the focal length of the fixed-focus lens is f; Wherein, 10.5 < RD * SD4 / H < 13.5, 1.7 < TTL / f < 1.

95.

8. The fixed-focus lens according to claim 1, wherein Both the first lens and the third lens are meniscus lenses.

9. The fixed-focus lens according to claim 1, wherein, Both the first lens and the second lens are glass spherical lenses; Both the third lens and the fourth lens are plastic aspherical lenses.

10. The fixed-focus lens according to claim 1, characterized in that, The fixed-focus lens further includes a diaphragm and a filter; The diaphragm is arranged in the optical path between the second lens and the third lens; The filter is arranged in the optical path between the fourth lens and the image plane.

Images