Prime lens

Abstract

The utility model discloses a prime lens, which comprises a first lens with negative focal power, a second lens with positive focal power, a third lens with positive focal power and a fourth lens with negative focal power which are sequentially arranged from an object plane to an image plane along an optical axis. By setting the focal power matching mode and the specific focal power value of the four lenses, the half-aperture vector height and the full-aperture vector height of the object side surface of the first lens and the half-aperture vector height and the full-aperture vector height of the image side surface of the first lens, the characteristic of small distortion of the prime lens can be realized.

Description

Technical Field

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

[0002] As a mainstream product in the security industry, fixed-focus lenses with a focal length of 4mm are very popular in the market. The 4mm lens on the market that matches the 1 / 2.7″ chip has a horizontal field of view of about 90°, a diagonal field of view of about 110°, and a diagonal optical distortion of about -40%, which is relatively large.

[0003] Therefore, there is a great demand for fixed-focus lenses with small distortion. Utility Model Content

[0004] The utility model provides a fixed-focus lens, which realizes a fixed-focus lens with small distortion by reasonably setting a lens composition mode, a focal power distribution mode and sagittal height data of different surfaces of a first lens.

[0005] The present invention provides a fixed-focus lens, comprising a first lens, a second lens, a third lens and a fourth lens arranged in sequence from the object plane to the image plane along the optical axis; the first lens is a negative power lens, the second lens is a positive power lens, the third lens is a positive power lens, and the fourth lens is a negative power lens;

[0006] The sag height at half the aperture of the object side of the first lens is SAG-S1 0.5D , the sag height of the first lens at the full aperture of the object side is SAG-S1 1.0D , the sag height of the first lens at the half-aperture of the image side is SAG-S2 0.5D , the sag of the first lens at the full aperture of the image side is SAG-S2 1.0D ;

[0007] The focal power of the first lens is Φ1, the focal power of the second lens is Φ2, and the focal power of the fixed-focus lens is Φ;

[0008] Among them, 0.155≤SAG-S1 0.5D ≤0.215, 0.105≤SAG-S1 1.0D ≤0.185, 0.385≤SAG-S2 0.5D ≤0.515,1.515≤SAG-S2 1.0D ≤1.585, -0.325≤(Φ1+Φ2) / Φ≤-0.265.

[0009] Optionally, the air spacing on the optical axis from the image side surface of the first lens to the object side surface of the second lens is T12, and the air spacing on the optical axis from the image side surface of the second lens to the object side surface of the third lens is T23;

[0010] Among them, 0.225 <T12 / TTL<0.285,0.405<(T12+T23) / TTL<0.465。

[0011] Optionally, the focal power of the third lens is Φ3, and the focal power of the fourth lens is Φ4;

[0012] Among them, -1.125≤(Φ1+Φ4) / (Φ2+Φ3)≤-0.855.

[0013] Optionally, the focal power of the third lens is Φ3, and the focal power of the fourth lens is Φ4;

[0014] Among them, -0.825≤Φ1 / Φ≤-0.645; 0.425≤Φ2 / Φ≤0.515; 0.285≤(Φ3+Φ4) / Φ≤0.355.

[0015] Optionally, the back focus of the fixed-focus lens is BFL, and the total optical length of the fixed-focus lens is TTL;

[0016] Among them, 0.255 <BFL / TTL<0.285。

[0017] Optionally, the refractive index of the second lens is Nd2, and the Abbe constant of the second lens is Vd2;

[0018] Among them, 1.55≤Nd2≤1.72, 60.00≤Vd2≤75.50.

[0019] Optionally, the first lens includes a first object-side surface close to the object plane and a first image-side surface close to the image plane, the first object-side surface is a convex surface, and the first image-side surface is a concave surface;

[0020] The second lens comprises a second object-side surface close to the object plane and a second image-side surface close to the image plane, the second object-side surface is a convex surface, and the second image-side surface is a convex surface;

[0021] The third lens comprises a third object-side surface close to the object plane and a third image-side surface close to the image plane, the third object-side surface is a convex surface, and the third image-side surface is a convex surface;

[0022] The fourth lens includes a fourth object-side surface close to the object plane and a fourth image-side surface close to the image plane, the fourth object-side surface is a concave surface, and the fourth image-side surface is a convex surface.

[0023] Optionally, the first lens, the third lens and the fourth lens are all plastic aspheric lenses;

[0024] The second lens is a glass spherical lens.

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

[0026] The aperture is arranged in the optical path between the first lens and the second lens;

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

[0028] Optionally, the total optical length of the fixed-focus lens is TTL;

[0029] Among them, TTL≤22.5mm.

[0030] The fixed-focus lens provided in the embodiment of the utility model is provided with four lenses, so that the number of lenses in the entire optical system is small, which is conducive to realizing a miniaturized fixed-focus lens setting. In addition, in the fixed-focus lens provided in the embodiment of the utility model, by setting the focal power matching mode and specific focal power values ​​of the four lenses, as well as the half-aperture sag and full-aperture sag of the object side of the first lens, and the half-aperture sag and full-aperture sag of the image side of the first lens, it is ensured that the small distortion characteristic of the fixed-focus lens can be realized, which is conducive to improving the imaging quality.

[0031] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present utility model, nor are they intended to limit the scope of the present utility model. Other features of the present utility model will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 This is a structural schematic diagram of a fixed-focus lens provided in Embodiment 1 of the present utility model;

[0034] Figure 2 This is a schematic diagram of a spherical aberration curve of a fixed-focus lens provided in Embodiment 1 of the present utility model;

[0035] Figure 3 This is a schematic diagram of a light fan of a fixed-focus lens provided in Embodiment 1 of the utility model;

[0036] Figure 4 This is a schematic diagram of field curvature distortion of a fixed-focus lens provided in Embodiment 1 of the present utility model;

[0037] Figure 5 This is a structural schematic diagram of a fixed-focus lens provided in Embodiment 2 of the present utility model;

[0038] Figure 6 This is a schematic diagram of a spherical aberration curve of a fixed-focus lens provided in Embodiment 2 of the present utility model;

[0039] Figure 7 This is a schematic diagram of a light fan of a fixed-focus lens provided in Embodiment 2 of the present utility model;

[0040] Figure 8 This is a schematic diagram of field curvature distortion of a fixed-focus lens provided in Embodiment 2 of the present utility model;

[0041] Fig. 9 This is a schematic structural diagram of a fixed-focus lens provided in Embodiment 3 of the present utility model;

[0042] Fig.10 This is a schematic diagram of a spherical aberration curve of a fixed-focus lens provided in Embodiment 3 of the present utility model;

[0043] Fig.11 This is a schematic diagram of a light fan of a fixed-focus lens provided in Embodiment 3 of the present utility model;

[0044] Fig.12 This is a schematic diagram of field curvature distortion of a fixed-focus lens provided in Embodiment 3 of the present utility model;

[0045] Fig.13 This is a structural schematic diagram of a fixed-focus lens provided in Embodiment 4 of the present utility model;

[0046] Fig.14 This is a schematic diagram of a spherical aberration curve of a fixed-focus lens provided in Embodiment 4 of the present utility model;

[0047] Fig.15 This is a schematic diagram of a light fan of a fixed-focus lens provided in Embodiment 4 of the present utility model;

[0048] Fig.16 This is a schematic diagram of field curvature distortion of a fixed-focus lens provided in Embodiment 4 of the present utility model;

[0049] Fig.17 This is a structural schematic diagram of a fixed-focus lens provided in Embodiment 5 of the present utility model;

[0050] Fig.18 This is a schematic diagram of a spherical aberration curve of a fixed-focus lens provided in Embodiment 5 of the present utility model;

[0051] Fig.19 This is a schematic diagram of a light fan of a fixed-focus lens provided in Embodiment 5 of the present utility model;

[0052] Fig. 20 This is a schematic diagram of field curvature distortion of a fixed-focus lens provided in Embodiment 5 of the present utility model. DETAILED DESCRIPTION

[0053] In order to enable those skilled in the art to better understand the solution of the utility model, the technical solution in the embodiment of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiment of the utility model. Obviously, the described embodiment is only a part of the embodiment of the utility model, not all of the embodiments. Based on the embodiment of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the utility model.

[0054] Embodiment 1

[0055] Figure 1 is a schematic diagram of the structure of a fixed-focus lens provided in the first embodiment of the utility model, such as Figure 1 As shown, the fixed-focus lens provided in the first embodiment of the present invention comprises a first lens 110, a second lens 120, a third lens 130 and a fourth lens 140 arranged in sequence from the object plane to the image plane along the optical axis; the first lens 110 is a negative power lens, the second lens 120 is a positive power lens, the third lens 130 is a positive power lens, and the fourth lens 140 is a negative power lens; the sagittal height at the half-aperture of the object side surface of the first lens 110 is SAG-S1 0.5D , the sag height of the first lens 110 at the full aperture of the object side is SAG-S1 1.0D , the sag at the half-aperture of the image side of the first lens 110 is SAG-S2 0.5D , the sagittal height of the first lens 110 at the full aperture of the image side is SAG-S2 1.0D ; The focal power of the first lens 110 is Φ1, the focal power of the second lens 120 is Φ2, and the focal power of the fixed focus lens is Φ; wherein, 0.155≤SAG-S1 0.5D ≤0.215, 0.105≤SAG-S1 1.0D ≤0.185, 0.385≤SAG-S2 0.5D ≤0.515,1.515≤SAG-S2 1.0D ≤1.585, -0.325≤(Φ1+Φ2) / Φ≤-0.265.

[0056] Specifically, the focal length is equal to the difference between the convergence of the image-side light beam and the convergence of the object-side light beam, and it characterizes the ability of the optical system to deflect light. The larger the absolute value of the focal length, the stronger the ability to bend light, and the smaller the absolute value of the focal length, the weaker the ability to bend light. When the focal length is a positive number, the refraction of light is convergent; when the focal length is a negative number, the refraction of light is divergent. The focal length can be used to characterize a certain refractive surface of a lens (i.e., a surface of a lens), can be used to characterize a certain lens, and can also be used to characterize a system formed by multiple lenses (i.e., a lens group). In the embodiment of the utility model, setting the first lens 110 as a negative focal length lens can ensure that the first lens 110 can effectively deflect large-angle incident light, thereby effectively increasing the field of view of the fixed-focus lens, and ensuring that the optical system can have wide-angle or even ultra-wide-angle characteristics. And setting the first lens 110 as a negative focal length lens can quickly expand the light aperture and increase the aperture of the lens. The second lens 120 and the third lens 130 are set as positive power lenses, so that the second lens 120 and the third lens 130 can timely correct the large aberrations generated by the first lens 110, especially the edge aberrations of the optical system, thereby improving the imaging resolution of the optical system. The fourth lens 140 is further set as a negative power lens, which can ensure the aberration balance and high and low temperature performance stability of the lens while eliminating the high-order aberrations of the lens as much as possible, and at the same time can control the target surface (size) and improve the image quality of the lens to meet the use requirements in more situations.

[0057] Furthermore, the object-side surface of the first lens 110 can be understood as the surface of the first lens 110 close to the object plane, and the image-side surface of the first lens 110 can be understood as the surface of the first lens 110 close to the image plane. 0.5D Satisfy 0.155≤SAG-S1 0.5D ≤0.215, the sag SAG-S1 of the object side of the first lens 110 at the full aperture 1.0D Satisfy 0.105≤SAG-S1 1.0D ≤0.185, the sag SAG-S2 at the half-aperture of the image side surface of the first lens 110 0.5D Satisfy 0.385≤SAG-S2 0.5D ≤0.515, the sag SAG-S2 of the full aperture of the image side of the first lens 110 1.0D Satisfy 1.515≤SAG-S2 1.0D≤1.585, the focal power Φ1 of the first lens 110, the focal power Φ2 of the second lens 120, and the focal power Φ of the fixed-focus lens satisfy -0.325≤(Φ1+Φ2) / Φ≤-0.265. The sagittal height data of the half-aperture and the full-aperture of the object side and the image side of the first lens 110, combined with the focal powers of the first lens 110 and the second lens 120, can realize the fixed-focus lens with small optical distortion.

[0058] In summary, the fixed-focus lens provided in the embodiment of the utility model is provided with four lenses, so that the number of lenses in the entire optical system is small, which is conducive to realizing a miniaturized fixed-focus lens setting. In addition, in the fixed-focus lens provided in the embodiment of the utility model, by setting the focal power matching mode and specific focal power values ​​of the four lenses, as well as the half-aperture sag and full-aperture sag of the object side of the first lens, and the half-aperture sag and full-aperture sag of the image side of the first lens, it is ensured that the small distortion characteristic of the fixed-focus lens can be realized, which is conducive to improving the imaging quality.

[0059] Based on the above embodiment, the fixed-focus lens may further include an aperture 150 and a filter 160; the aperture 150 is disposed in the optical path between the first lens 110 and the second lens 120; and the filter 160 is disposed in the optical path between the fourth lens 140 and the image plane.

[0060] Specifically, the aperture 150 can be set to adjust the propagation direction of the light beam, which is beneficial to improving the imaging quality. In addition, the aperture 150 in the fixed-focus lens is located in the light path between the first lens 110 and the second lens 120. The aperture 150 is located in the middle of the fixed-focus lens to minimize the front and rear aperture of the fixed-focus lens.

[0061] The filter 160 is disposed in the optical path between the fourth lens 140 and the image plane to filter out stray light and improve the imaging effect. Specifically, the filter 160 may be an infrared filter.

[0062] Furthermore, the fixed-focus lens provided in the embodiment of the utility model may also include a protective glass and an image acquisition element. The protective glass may be arranged on the image side of the filter, and the image acquisition element may be arranged on the image side of the protective glass. The protective glass protects the optical system, and the image acquisition element acquires the image, so as to realize the normal imaging function of the optical system.

[0063] Based on the above embodiment, the air gap between the image side surface of the first lens 110 and the object side surface of the second lens 120 on the optical axis is T12, and the air gap between the image side surface of the second lens 120 and the object side surface of the third lens 130 on the optical axis is T23; wherein, 0.225 <T12 / TTL<0.285,0.405<

[0064] (T12 + T23) / TTL < 0.465. When the optical system ratio is within the above range, the structure of the fixed-focus lens can be made more compact.

[0065] Furthermore, the overall optical length of the fixed-focus lens is TTL; among them, TTL ≤ 22.5 mm. Ensure an optical system with a compact and miniaturized structure.

[0066] On the basis of the above embodiments, the optical power of the third lens 130 is Φ3, and the optical power of the fourth lens 140 is Φ4; among them, -1.125 ≤ (Φ1 + Φ4) / (Φ2 + Φ3) ≤ -0.855. When the optical powers of the first lens 110, the second lens 120, the third lens 130, and the fourth lens 140 satisfy the above ratio range, the positive and negative optical power distributions of the optical system are reasonable, which is conducive to the balanced correction of system aberrations.

[0067] On the basis of the above embodiments, the optical power of the third lens 130 is Φ3, and the optical power of the fourth lens 140 is Φ4; among them, -0.825 ≤ Φ1 / Φ ≤ -0.645; 0.425 ≤ Φ2 / Φ ≤ 0.515; 0.285 ≤ (Φ3 + Φ4) / Φ ≤ 0.355.

[0068] Specifically, when the optical power Φ1 of the first lens 110 and the optical power Φ of the fixed-focus lens satisfy -0.825 ≤ Φ1 / Φ ≤ -0.645, the object-side light rays can enter the imaging system smoothly, and the light rays enter the second lens at a smaller incident angle, reducing the proportion of high-order aberrations. When the optical power Φ2 of the second lens 120 and the optical power Φ of the fixed-focus lens satisfy 0.425 ≤ Φ2 / Φ ≤ 0.515, the light rays can be further gently deflected and contracted, making the system have a looser tolerance sensitivity. When the optical powers Φ3 of the third lens 130, Φ4 of the fourth lens 140 and the optical power Φ of the fixed-focus lens satisfy 0.285 ≤ (Φ3 + Φ4) / Φ ≤ 0.355, the optical power distribution of the optical system is reasonable, which is more conducive to the correction of system aberrations.

[0069] On the basis of the above embodiments, the back focal length of the fixed-focus lens is BFL, and the overall optical length of the fixed-focus lens is TTL; among them, 0.255 < BFL / TTL < 0.285. The back focal length of the fixed-focus lens can be understood as the distance from the image-side vertex of the fourth lens to the image plane. Meeting the above requirements can ensure sufficient installation space for the imaging sensor and the filter.

[0070] Based on the above embodiment, the refractive index of the second lens 120 is Nd2, and the Abbe constant of the second lens 120 is Vd2; wherein 1.55≤Nd2≤1.72, 60.00≤Vd2≤75.50. When the refractive index Nd2 of the second lens 120 and the Abbe constant Vd2 meet the above conditions, the chromatic aberration of the optical system can be effectively corrected, which is beneficial to the improvement of the resolution of the optical system.

[0071] On the basis of the above embodiments, the first lens 110 includes a first object-side surface close to the object plane and a first image-side surface close to the image plane, the first object-side surface is a convex surface, and the first image-side surface is a concave surface; the second lens 120 includes a second object-side surface close to the object plane and a second image-side surface close to the image plane, the second object-side surface is a convex surface, and the second image-side surface is a convex surface; the third lens 130 includes a third object-side surface close to the object plane and a third image-side surface close to the image plane, the third object-side surface is a convex surface, and the third image-side surface is a convex surface; the fourth lens 140 includes a fourth object-side surface close to the object plane and a fourth image-side surface close to the image plane, the fourth object-side surface is a concave surface, and the fourth image-side surface is a convex surface.

[0072] Specifically, the object side of the lens can be understood as the surface of the lens close to the object plane, and the image side of the lens can be understood as the surface of the lens close to the image plane. Specifically, the object side of the first lens 110 is a convex surface, and the image side is a concave surface. It can be understood that the object side of the first lens 110 is convex toward the object plane at the near optical axis position, and the image side is concave toward the image plane at the near optical axis position, that is, the first lens 110 is a meniscus lens with a convex-concave structure. This lens shape combined with the negative optical power setting of the first lens 110 can further smoothly collect the object light into the imaging system, so that the light enters the second lens at a smaller incident angle, reducing the proportion of higher-order aberrations. The object side of the second lens 120 is a convex surface, and the image side is a convex surface. It can be understood that the object side of the second lens 120 is convex toward the object plane at a position close to the optical axis, and the image side is convex toward the image plane at a position close to the optical axis, that is, the second lens 120 is a lens with a double convex structure. The object side surface of the third lens 130 is convex, and the image side surface is convex. It can be understood that the object side surface of the third lens 130 is convex toward the object plane at the near optical axis position, and the image side surface is convex toward the image plane at the near optical axis position, that is, the third lens 130 is a lens with a double convex structure. The object side surface of the fourth lens 140 is concave, and the image side surface is convex. It can be understood that the object side surface of the fourth lens 140 is concave toward the object plane at the near optical axis position, and the image side surface is convex toward the image plane at the near optical axis position, that is, the second lens 120 is a lens with a concave-convex structure. By reasonably setting the surface shape of each lens, it can be ensured that the edge light trend is smoother, the relative illumination between the edge image and the center image is improved, and the imaging effect is improved.

[0073] On the basis of the above embodiment, the first lens 110 , the third lens 130 and the fourth lens 140 are all plastic aspherical lenses; and the second lens 120 is a glass spherical lens.

[0074] Specifically, the characteristic of the aspheric 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, the aspheric lens has a better curvature radius characteristic, and has the advantages of improving distortion aberration and improving astigmatism aberration. Setting the first lens 110, the third lens 130 and the fourth lens 140 to use aspheric lenses can eliminate the aberrations that occur during imaging as much as possible, thereby improving the imaging quality of the lens. On this basis, the aspheric lens can be a plastic aspheric lens, which is conducive to reducing the processing technology of the aspheric lens, and the cost of the aspheric lens is relatively low.

[0075] Furthermore, the spherical lens is characterized by having a constant curvature from the center of the lens to the periphery of the lens, ensuring 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 second lens 120 can be set as a glass spherical lens. The thermal properties of a glass spherical lens are more stable, and when it bears more optical power, it can ensure that the lens has good resolution in a wider temperature range (-40°C to 80°C). 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.

[0076] 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.

[0077] As a feasible implementation method, specific parameters of the fixed-focus lens are described below.

[0078] Table 1 Optical design values ​​of the fixed focus lens in Example 1

[0079] Conditional expression Example 1 Lower limit Upper limit <![CDATA[SAG-S1 0.5D ]]> 0.178 0.155 0.215 <![CDATA[SAG-S1 1.0D ]]> 0.157 0.105 0.185 <![CDATA[SAG-S2 0.5D ]]> 0.426 0.385 0.515 <![CDATA[SAG-S2 1.0D ]]> 1.550 1.515 1.850 (Φ1+Φ2) / Φ -0.308 -0.325 -0.265 Nd 1.59 1.55 1.72 Vd 68.35 60.00 75.50 T12 / TTL 0.254 0.225 0.285 (T12+T23) / TTL 0.441 0.405 0.465 (Φ1+Φ4) / (Φ2+Φ3) -0.993 -1.125 -0.855 Φ1 / Φ -0.779 -0.825 -0.645 Φ2 / Φ 0.471 0.425 0.515 (Φ3+Φ4) / Φ 0.319 0.285 0.355 BFL / TTL 0.273 0.255 0.285

[0080] Table 2 Design values ​​of optical physical parameters of a fixed-focus lens

[0081]

[0082] The surface numbers in Table 2 are numbered according to the order of the surfaces of each lens. "S1" represents the object surface of the first lens, "S2" represents the image surface of the first lens, and so on. "STO" represents the aperture of the lens; "S5" represents the virtual plane in the third lens, which is used to set the height of the light and thus determine the vignetting coefficient of the optical system; the radius of curvature represents the curvature of the lens surface, a positive value represents that the surface is bent toward the image side, and a negative value represents that the surface is bent toward the object side; "INF" 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, and the space represents that the current position is air with a refractive index of 1; the Abbe constant represents the dispersion characteristics of the material between the current surface and the next surface to the light; the k value represents the numerical value of the cone coefficient of the aspheric surface; the aperture represents the aperture size of the current surface.

[0083] The aspheric cone coefficient can be defined by the following aspheric formula, but is not limited to the following representation method:

[0084]

[0085] Among them, z is the axial vector height of the aspheric surface in the Z direction; r is the height of the aspheric surface; c is the curvature of the fitted sphere, which is the inverse of the radius of curvature; k is the fitting cone coefficient; AG is the coefficient of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspheric polynomial.

[0086] Table 3 Aspheric coefficients of a fixed-focus lens

[0087]

[0088] Among them, "-7.9576E-03" means -7.9576*10 -3 The remaining coefficients are expressed in this way.

[0089] Based on the above parameter definitions, the optical parameters that can be achieved by the fixed-focus lens in Example 1 of the utility model are as follows: focal length f is 4.30 mm, F# is 2.05, field of view angle DFOV=96°, and total optical length TTL: 22.39 mm.

[0090] Furthermore, Figure 2 This is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Example 1 of the utility model. The vertical direction represents the normalization of the aperture, 0 represents the optical axis, and the pupil radius is 1.0290mm; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). The different linear curves in the figure represent different wavelengths of system imaging (436nm, 487nm, 546nm, 587nm and 656nm, respectively), as shown in FIG. Figure 2It can be seen that the axial aberrations at different wavelengths are all controlled within the range of (-0.05mm, +0.05mm), indicating that the spherical aberration of this fixed-focus lens at each wavelength is well controlled and can meet the needs of wide spectrum applications.

[0091] Figure 3 This is a schematic diagram of the light fan of a fixed-focus lens provided in Example 1 of the utility model. The light fan diagram is one of the most commonly used evaluation methods in modern optical design. The horizontal axis is the beam aperture, and the vertical axis is the vertical axis aberration. The most ideal curve is a straight line that coincides with the horizontal axis, indicating that all light rays converge at the same point on the image plane, and the corresponding interval on the vertical axis of the curve is the maximum dispersion range of the light beam on the ideal image plane. The light fan diagram can not only reflect the monochromatic aberrations of different wavelengths, but also indicate the size of the vertical axis chromatic aberration. By Figure 3 It can be seen that each wavelength (436nm, 487nm, 546nm, 587nm and 656nm) in each field of view is close to the horizontal axis, indicating that the vertical axis aberration of each wavelength of the system is well corrected. At the same time, there is no obvious dispersion of each wavelength, indicating that the chromatic aberration of the system is also well corrected, thereby ensuring that the optical system can achieve high-resolution imaging requirements.

[0092] Figure 4 Schematic diagram of field curvature distortion of a fixed-focus lens provided in Embodiment 1 of the present utility model. In the coordinate system on the left side of the figure, the horizontal coordinate represents the magnitude of the field curvature, in units of mm; the vertical coordinate represents the normalized image height, in units of mm; Figure 4 As can be seen from the left figure, the field curvature of the lens provided by this embodiment is effectively controlled at each wavelength (436nm, 487nm, 546nm, 587nm and 656nm), that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small. In the coordinate system on the right, the horizontal coordinate represents the size of the distortion, in %, and the vertical coordinate represents the normalized image height, without unit; Figure 4 It can be seen from the figure on the right that the maximum distortion of the lens provided in this embodiment is controlled within -30%, the distortion is well corrected, the imaging distortion is small, and the difference between the image and the actual object is small.

[0093] In summary, the fixed-focus lens provided in the first embodiment of the present invention adopts a combination of a spherical glass lens and three aspherical plastic lenses, and achieves the design goal of small optical distortion by optimizing the focal length, surface shape, relative position of each lens element and optical parameters of each lens; it has the characteristics of high imaging resolution, compact structure and low cost, making the fixed-focus lens system highly competitive in the market. The maximum aperture of the fixed-focus lens is 2.0, the total optical length is not more than 22.5mm, and the maximum compatible sensor chip is 1 / 2.66″. Its comprehensive performance meets the general use requirements of security monitoring.

[0094] Embodiment 2

[0095] Figure 5 Schematic diagram of the structure of a fixed-focus lens provided in the second embodiment of the present utility model. Figure 5 As shown, the fixed-focus lens provided in the second embodiment of the present invention comprises a first lens 110, a second lens 120, a third lens 130 and a fourth lens 140 arranged in sequence from the object plane to the image plane along the optical axis; the first lens 110 is a negative power lens, the second lens 120 is a positive power lens, the third lens 130 is a positive power lens, and the fourth lens 140 is a negative power lens; the sagittal height at the half-aperture of the object side surface of the first lens 110 is SAG-S1 0.5D , the sag height of the first lens 110 at the full aperture of the object side is SAG-S1 1.0D , the sag at the half-aperture of the image side of the first lens 110 is SAG-S2 0.5D , the sagittal height of the first lens 110 at the full aperture of the image side is SAG-S2 1.0D ; The focal power of the first lens 110 is Φ1, the focal power of the second lens 120 is Φ2, and the focal power of the fixed focus lens is Φ; wherein, 0.155≤SAG-S1 0.5D ≤0.215, 0.105≤SAG-S1 1.0D ≤0.185, 0.385≤SAG-S2 0.5D ≤0.515,1.515≤SAG-S2 1.0D ≤1.585, -0.325≤(Φ1+Φ2) / Φ≤-0.265.

[0096] The configuration of the above-mentioned lens is the same as that in the first embodiment, and will not be described in detail here.

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

[0098] Table 4 Optical design values ​​of the fixed focus lens in Example 2

[0099] Conditional expression Example 2 Lower limit Upper limit <![CDATA[SAG-S1 0.5D ]]> 0.176 0.155 0.215 <![CDATA[SAG-S1 1.0D ]]> 0.174 0.105 0.185 <![CDATA[SAG-S2 0.5D ]]> 0.416 0.385 0.515 <![CDATA[SAG-S2 1.0D ]]> 1.532 1.515 1.850 (Φ1+Φ2) / Φ -0.300 -0.325 -0.265 Nd 1.59 1.55 1.72 Vd 68.35 60.00 75.50 T12 / TTL 0.248 0.225 0.285 (T12+T23) / TTL 0.434 0.405 0.465 (Φ1+Φ4) / (Φ2+Φ3) -0.985 -1.125 -0.855 Φ1 / Φ -0.785 -0.825 -0.645 Φ2 / Φ 0.484 0.425 0.515 (Φ3+Φ4) / Φ 0.325 0.285 0.355 BFL / TTL 0.273 0.255 0.285

[0100] Table 5 Design values ​​of optical physical parameters of a fixed-focus lens

[0101]

[0102] The surface numbers in Table 2 are numbered according to the order of the surfaces of each lens. "S1" represents the object surface of the first lens, "S2" represents the image surface of the first lens, and so on. "STO" represents the aperture of the lens; "S5" represents the virtual plane in the third lens, which is used to set the height of the light and thus determine the vignetting coefficient of the optical system; the radius of curvature represents the curvature of the lens surface, a positive value represents that the surface is bent toward the image side, and a negative value represents that the surface is bent toward the object side; "INF" 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, and the space represents that the current position is air with a refractive index of 1; the Abbe constant represents the dispersion characteristics of the material between the current surface and the next surface to the light; the k value represents the numerical value of the cone coefficient of the aspheric surface; the aperture represents the aperture size of the current surface.

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

[0104]

[0105] Among them, z is the axial vector height of the aspheric surface in the Z direction; r is the height of the aspheric surface; c is the curvature of the fitted sphere, which is the inverse of the radius of curvature; k is the fitting cone coefficient; AG is the coefficient of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspheric polynomial.

[0106] Table 6 Aspheric coefficients of a fixed-focus lens

[0107]

[0108] Among them, "-8.0514E-03" means -8.0514*10 -3 The remaining coefficients are expressed in this way.

[0109] Based on the above parameter definitions, the optical parameters that can be achieved by the fixed-focus lens in the second embodiment of the present invention are as follows: focal length f is 4.41 mm, F# is 2.06, field of view angle DFOV=95°, and total optical length TTL: 22.35 mm.

[0110] Furthermore, Figure 6 This is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Example 2 of the present utility model. The vertical direction represents the normalization of the aperture, 0 represents the optical axis, and the pupil radius is 1.0604mm; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). The different linear curves in the figure represent different wavelengths of system imaging (436nm, 487nm, 546nm, 587nm and 656nm, respectively), as shown in FIG. Figure 6It can be seen that the axial aberrations at different wavelengths are all controlled within the range of (-0.05mm, +0.05mm), indicating that the spherical aberration of the fixed-focus lens at each wavelength is well controlled.

[0111] Figure 7 This is a schematic diagram of the light fan of a fixed-focus lens provided in Example 2 of the utility model. The light fan diagram is one of the most commonly used evaluation methods in modern optical design. The horizontal axis is the beam aperture, and the vertical axis is the vertical axis aberration. The most ideal curve is a straight line that coincides with the horizontal axis, indicating that all light rays converge at the same point on the image plane, and the corresponding interval on the vertical axis of the curve is the maximum dispersion range of the light beam on the ideal image plane. The light fan diagram can not only reflect the monochromatic aberrations of different wavelengths, but also indicate the size of the vertical axis chromatic aberration. By Figure 7 It can be seen that each wavelength (436nm, 487nm, 546nm, 587nm and 656nm) in each field of view is close to the horizontal axis, indicating that the vertical axis aberration of each wavelength of the system is well corrected. At the same time, there is no obvious dispersion of each wavelength, indicating that the chromatic aberration of the system is also well corrected, thereby ensuring that the optical system can achieve high-resolution imaging requirements.

[0112] Figure 8 Schematic diagram of field curvature distortion of a fixed-focus lens provided in Embodiment 2 of the present utility model. In the coordinate system on the left side of the figure, the horizontal coordinate represents the magnitude of the field curvature, in units of mm; the vertical coordinate represents the normalized image height, in units of mm; Figure 8 As can be seen from the left figure, the field curvature of the lens provided by this embodiment is effectively controlled at each wavelength (436nm, 487nm, 546nm, 587nm and 656nm), that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small. In the coordinate system on the right, the horizontal coordinate represents the size of the distortion, in %, and the vertical coordinate represents the normalized image height, without unit; Figure 8 It can be seen from the figure on the right that the maximum distortion of the lens provided in this embodiment is controlled within -30%, the distortion is well corrected, the imaging distortion is small, and the difference between the image and the actual object is small.

[0113] In summary, the fixed-focus lens provided in the second embodiment of the present invention adopts a combination of a spherical glass lens and three aspherical plastic lenses, and achieves the design goal of small optical distortion by optimizing the focal length, surface shape, relative position of each lens element and optical parameters of each lens; it has the characteristics of high imaging resolution, compact structure and low cost, making the fixed-focus lens system highly competitive in the market. The maximum aperture of the fixed-focus lens is 2.0, the total optical length is not more than 22.5mm, and the maximum compatible sensor chip is 1 / 2.66″. Its comprehensive performance meets the general use requirements of security monitoring.

[0114] Embodiment 3

[0115] Fig. 9 Schematic diagram of the structure of a fixed-focus lens provided in Embodiment 3 of the present utility model. Fig. 9 As shown, the fixed-focus lens provided in the third embodiment of the present invention comprises a first lens 110, a second lens 120, a third lens 130 and a fourth lens 140 arranged in sequence from the object plane to the image plane along the optical axis; the first lens 110 is a negative power lens, the second lens 120 is a positive power lens, the third lens 130 is a positive power lens, and the fourth lens 140 is a negative power lens; the sagittal height at the half-aperture of the object side surface of the first lens 110 is SAG-S1 0.5D , the sag height of the first lens 110 at the full aperture of the object side is SAG-S1 1.0D , the sag at the half-aperture of the image side of the first lens 110 is SAG-S2 0.5D , the sagittal height of the first lens 110 at the full aperture of the image side is SAG-S2 1.0D ; The focal power of the first lens 110 is Φ1, the focal power of the second lens 120 is Φ2, and the focal power of the fixed focus lens is Φ; wherein, 0.155≤SAG-S1 0.5D ≤0.215, 0.105≤SAG-S1 1.0D ≤0.185, 0.385≤SAG-S2 0.5D ≤0.515,1.515≤SAG-S2 1.0D ≤1.585, -0.325≤(Φ1+Φ2) / Φ≤-0.265.

[0116] Among them, in the above lens setting method, the aperture is set in the light path between the third lens and the fourth lens, and the remaining settings are the same as those in the first embodiment, which will not be repeated here.

[0117] As another feasible implementation, specific parameters in the fixed-focus lens are described below.

[0118] Table 7 Optical design values ​​of the fixed focus lens in Example 3

[0119] Conditional expression Example 3 Lower limit Upper limit <![CDATA[SAG-S1 0.5D ]]> 0.186 0.155 0.215 <![CDATA[SAG-S1 1.0D ]]> 0.123 0.105 0.185 <![CDATA[SAG-S2 0.5D ]]> 0.426 0.385 0.515 <![CDATA[SAG-S2 1.0D ]]> 1.552 1.515 1.850 (Φ1+Φ2) / Φ -0.292 -0.325 -0.265 Nd 1.59 1.55 1.72 Vd 68.35 60.00 75.50 T12 / TTL 0.249 0.225 0.285 (T12+T23) / TTL 0.437 0.405 0.465 (Φ1+Φ4) / (Φ2+Φ3) -0.983 -1.125 -0.855 Φ1 / Φ -0.781 -0.825 -0.645 Φ2 / Φ 0.482 0.425 0.515 (Φ3+Φ4) / Φ 0.327 0.285 0.355 BFL / TTL 0.272 0.255 0.285

[0120] Table 8 Design values ​​of optical physical parameters of a fixed-focus lens

[0121]

[0122] The surface numbers in Table 8 are numbered according to the order of the surfaces of each lens. "S1" represents the object surface of the first lens, "S2" represents the image surface of the first lens, and so on. "STO" represents the aperture of the lens; "S5" represents the virtual plane in the third lens, which is used to set the height of the light and thus determine the vignetting coefficient of the optical system; the radius of curvature represents the curvature of the lens surface, a positive value represents that the surface is bent toward the image side, and a negative value represents that the surface is bent toward the object side; "INF" 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, and the space represents that the current position is air with a refractive index of 1; the Abbe constant represents the dispersion characteristics of the material between the current surface and the next surface to the light; the k value represents the numerical value of the cone coefficient of the aspheric surface; the aperture represents the aperture size of the current surface.

[0123] The aspheric cone coefficient can be defined by the following aspheric formula, but is not limited to the following representation method:

[0124]

[0125] Among them, z is the axial vector height of the aspheric surface in the Z direction; r is the height of the aspheric surface; c is the curvature of the fitted sphere, which is the inverse of the radius of curvature; k is the fitting cone coefficient; AG is the coefficient of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspheric polynomial.

[0126] Table 9 Aspheric coefficients of a fixed-focus lens

[0127]

[0128] Among them, "-8.0469E-03" means -8.0469*10 -3 The remaining coefficients are expressed in this way.

[0129] Based on the above parameter definitions, the optical parameters that can be achieved by the fixed-focus lens in Example 3 of the utility model are as follows: focal length f is 4.38 mm, F# is 1.98, field of view angle DFOV=98°, and total optical length TTL: 22.29 mm.

[0130] Furthermore, Fig.10 This is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Example 3 of the utility model. The vertical direction represents the normalization of the aperture, 0 represents the optical axis, and the pupil radius is 1.0539mm; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). The different linear curves in the figure represent different wavelengths of system imaging (436nm, 487nm, 546nm, 587nm and 656nm, respectively), as shown in FIG. Fig.10It can be seen that the axial aberrations at different wavelengths are all controlled within the range of (-0.05mm, +0.05mm), indicating that the spherical aberration of the fixed-focus lens at each wavelength is well controlled.

[0131] Fig.11 This is a schematic diagram of the light fan of a fixed-focus lens provided in Example 3 of the utility model. The light fan diagram is one of the most commonly used evaluation methods in modern optical design. The horizontal axis is the beam aperture, and the vertical axis is the vertical axis aberration. The most ideal curve is a straight line that coincides with the horizontal axis, indicating that all light rays converge at the same point on the image plane, and the corresponding interval on the vertical axis of the curve is the maximum dispersion range of the light beam on the ideal image plane. The light fan diagram can not only reflect the monochromatic aberrations of different wavelengths, but also indicate the size of the vertical axis chromatic aberration. By Fig.11 It can be seen that each wavelength (436nm, 487nm, 546nm, 587nm and 656nm) in each field of view is close to the horizontal axis, indicating that the vertical axis aberration of each wavelength of the system is well corrected. At the same time, there is no obvious dispersion of each wavelength, indicating that the chromatic aberration of the system is also well corrected, thereby ensuring that the optical system can achieve high-resolution imaging requirements.

[0132] Fig.12 Schematic diagram of field curvature distortion of a fixed-focus lens provided in Embodiment 3 of the present utility model. In the left coordinate system of the figure, the horizontal coordinate represents the magnitude of field curvature, in units of mm; the vertical coordinate represents the normalized image height, in units of mm; Fig.12 As can be seen from the left figure, the field curvature of the lens provided by this embodiment is effectively controlled at each wavelength (436nm, 487nm, 546nm, 587nm and 656nm), that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small. In the coordinate system on the right, the horizontal coordinate represents the size of the distortion, in %, and the vertical coordinate represents the normalized image height, without unit; Fig.12 It can be seen from the figure on the right that the maximum distortion of the lens provided in this embodiment is controlled within -30%, the distortion is well corrected, the imaging distortion is small, and the difference between the image and the actual object is small.

[0133] In summary, the fixed-focus lens provided in the third embodiment of the present invention adopts a combination of a spherical glass lens and three aspherical plastic lenses, and achieves the design goal of small optical distortion by optimizing the focal length, surface shape, relative position of each lens element and optical parameters of each lens; it has the characteristics of high imaging resolution, compact structure and low cost, making the fixed-focus lens system highly competitive in the market. The maximum aperture of the fixed-focus lens is 2.0, the total optical length is not more than 22.5mm, and it can match a maximum of 1 / 2.66″ sensor chip. Its comprehensive performance meets the general use requirements of security monitoring.

[0134] Embodiment 4

[0135] Fig.13 Schematic diagram of the structure of a fixed-focus lens provided in the fourth embodiment of the present utility model. Fig.13 As shown, the fixed-focus lens provided by the fourth embodiment of the present invention includes a first lens 110, a second lens 120, a third lens 130 and a fourth lens 140 arranged in sequence from the object plane to the image plane along the optical axis; the first lens 110 is a negative power lens, the second lens 120 is a positive power lens, the third lens 130 is a positive power lens, and the fourth lens 140 is a negative power lens; the sagittal height at the half-aperture of the object side surface of the first lens 110 is SAG-S1 0.5D , the sag height of the first lens 110 at the full aperture of the object side is SAG-S1 1.0D , the sag at the half-aperture of the image side of the first lens 110 is SAG-S2 0.5D , the sagittal height of the first lens 110 at the full aperture of the image side is SAG-S2 1.0D ; The focal power of the first lens 110 is Φ1, the focal power of the second lens 120 is Φ2, and the focal power of the fixed focus lens is Φ; wherein, 0.155≤SAG-S1 0.5D ≤0.215, 0.105≤SAG-S1 1.0D ≤0.185, 0.385≤SAG-S2 0.5D ≤0.515,1.515≤SAG-S2 1.0D ≤1.585, -0.325≤(Φ1+Φ2) / Φ≤-0.265.

[0136] The configuration of the above-mentioned lens is the same as that in the first embodiment, and will not be described in detail here.

[0137] As another feasible implementation, specific parameters in the fixed-focus lens are described below.

[0138] Table 10: Optical design values ​​of the fixed focus lens in Example 4

[0139] Conditional expression Example 4 Lower limit Upper limit <![CDATA[SAG-S1 0.5D ]]> 0.189 0.155 0.215 <![CDATA[SAG-S1 1.0D ]]> 0.124 0.105 0.185 <![CDATA[SAG-S2 0.5D ]]> 0.489 0.385 0.515 <![CDATA[SAG-S2 1.0D ]]> 1.760 1.515 1.850 (Φ1+Φ2) / Φ -0.310 -0.325 -0.265 Nd 1.57 1.55 1.72 Vd 71.31 60.00 75.50 T12 / TTL 0.264 0.225 0.285 (T12+T23) / TTL 0.426 0.405 0.465 (Φ1+Φ4) / (Φ2+Φ3) -1.085 -1.125 -0.855 Φ1 / Φ -0.796 -0.825 -0.645 Φ2 / Φ 0.454 0.425 0.515 (Φ3+Φ4) / Φ 0.335 0.285 0.355 BFL / TTL 0.269 0.255 0.285

[0140] Table 11 Design values ​​of optical physical parameters of a fixed-focus lens

[0141]

[0142] The surface numbers in Table 11 are numbered according to the order of the surfaces of each lens. "S1" represents the object surface of the first lens, "S2" represents the image surface of the first lens, and so on. "STO" represents the aperture of the lens; "S5" represents the virtual plane in the third lens, which is used to set the height of the light and thus determine the vignetting coefficient of the optical system; the radius of curvature represents the curvature of the lens surface, a positive value represents that the surface is bent toward the image side, and a negative value represents that the surface is bent toward the object side; "INF" 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, and the space represents that the current position is air with a refractive index of 1; the Abbe constant represents the dispersion characteristics of the material between the current surface and the next surface to the light; the k value represents the numerical value of the cone coefficient of the aspheric surface; the aperture represents the aperture size of the current surface.

[0143] The aspheric cone coefficient can be defined by the following aspheric formula, but is not limited to the following representation method:

[0144]

[0145] Among them, z is the axial vector height of the aspheric surface in the Z direction; r is the height of the aspheric surface; c is the curvature of the fitted sphere, which is the inverse of the radius of curvature; k is the fitting cone coefficient; AG is the coefficient of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspheric polynomial.

[0146] Table 12 Aspheric coefficients of a fixed-focus lens

[0147]

[0148] Among them, "-7.9548E-03" means -7.9548*10 -3 The remaining coefficients are expressed in this way.

[0149] Based on the above parameter definitions, the optical parameters that can be achieved by the fixed-focus lens in the fourth embodiment of the present invention are as follows: focal length f is 4.31 mm, F# is 2.0, field of view angle DFOV=98°, and total optical length TTL: 22.38 mm.

[0150] Furthermore, Fig.14 This is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided by the fourth embodiment of the utility model. The vertical direction represents the normalization of the aperture, 0 represents the optical axis, and the pupil radius is 1.0273mm; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). The different linear curves in the figure represent different wavelengths of system imaging (436nm, 487nm, 546nm, 587nm and 656nm, respectively), as shown in FIG. Fig.14It can be seen that the axial aberrations at different wavelengths are all controlled within the range of (-0.07mm, +0.07mm), indicating that the spherical aberration of the fixed-focus lens at each wavelength is well controlled.

[0151] Fig.15 This is a schematic diagram of the light fan of a fixed-focus lens provided in Example 4 of the utility model. The light fan diagram is one of the most commonly used evaluation methods in modern optical design. The horizontal axis is the beam aperture, and the vertical axis is the vertical axis aberration. The most ideal curve is a straight line that coincides with the horizontal axis, indicating that all light rays converge at the same point on the image plane, and the corresponding interval on the vertical axis of the curve is the maximum dispersion range of the light beam on the ideal image plane. The light fan diagram can not only reflect the monochromatic aberrations of different wavelengths, but also indicate the size of the vertical axis chromatic aberration. By Fig.15 It can be seen that each wavelength (436nm, 487nm, 546nm, 587nm and 656nm) in each field of view is close to the horizontal axis, indicating that the vertical axis aberration of each wavelength of the system is well corrected. At the same time, there is no obvious dispersion of each wavelength, indicating that the chromatic aberration of the system is also well corrected, thereby ensuring that the optical system can achieve high-resolution imaging requirements.

[0152] Fig.16 Schematic diagram of field curvature distortion of a fixed-focus lens provided in Embodiment 4 of the present utility model. In the coordinate system on the left side of the figure, the horizontal coordinate represents the magnitude of the field curvature, in units of mm; the vertical coordinate represents the normalized image height, in units of mm; Fig.16 As can be seen from the left figure, the field curvature of the lens provided by this embodiment is effectively controlled at each wavelength (436nm, 487nm, 546nm, 587nm and 656nm), that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small. In the coordinate system on the right, the horizontal coordinate represents the size of the distortion, in %, and the vertical coordinate represents the normalized image height, without unit; Fig.16 It can be seen from the figure on the right that the maximum distortion of the lens provided in this embodiment is controlled within -30%, the distortion is well corrected, the imaging distortion is small, and the difference between the image and the actual object is small.

[0153] In summary, the fixed-focus lens provided in the fourth embodiment of the utility model adopts a combination of a spherical glass lens and three aspherical plastic lenses, and achieves the design goal of small optical distortion by optimizing the focal length, surface shape, relative position of each lens element and optical parameters of each lens; it has the characteristics of high imaging resolution, compact structure and low cost, making the fixed-focus lens system highly competitive in the market. The maximum aperture of the fixed-focus lens is 2.0, the total optical length is not more than 22.5mm, and the maximum sensor chip that can be matched is 1 / 2.66″. Its comprehensive performance meets the general use requirements of security monitoring.

[0154] Embodiment 5

[0155] Fig.17 : is a structural schematic diagram of a fixed-focus lens provided in Embodiment 5 of the present utility model, such as Fig.13 As shown, the fixed-focus lens provided in Embodiment 5 of the present invention comprises a first lens 110, a second lens 120, a third lens 130 and a fourth lens 140 arranged in sequence from the object plane to the image plane along the optical axis; the first lens 110 is a negative power lens, the second lens 120 is a positive power lens, the third lens 130 is a positive power lens, and the fourth lens 140 is a negative power lens; the sagittal height at the half-aperture of the object side surface of the first lens 110 is SAG-S1 0.5D , the sag height of the first lens 110 at the full aperture of the object side is SAG-S1 1.0D , the sag at the half-aperture of the image side of the first lens 110 is SAG-S2 0.5D , the sagittal height of the first lens 110 at the full aperture of the image side is SAG-S2 1.0D ; The focal power of the first lens 110 is Φ1, the focal power of the second lens 120 is Φ2, and the focal power of the fixed focus lens is Φ; wherein, 0.155≤SAG-S1 0.5D ≤0.215, 0.105≤SAG-S1 1.0D ≤0.185, 0.385≤SAG-S2 0.5D ≤0.515,1.515≤SAG-S2 1.0D ≤1.585, -0.325≤(Φ1+Φ2) / Φ≤-0.265.

[0156] The configuration of the above-mentioned lens is the same as that in the first embodiment, and will not be described in detail here.

[0157] As another feasible implementation, specific parameters in the fixed-focus lens are described below.

[0158] Table 13 Optical design values ​​of the fixed focus lens in Example 5

[0159] Conditional expression Example 5 Lower limit Upper limit <![CDATA[SAG-S1 0.5D ]]> 0.177 0.155 0.215 <![CDATA[SAG-S1 1.0D ]]> 0.158 0.105 0.185 <![CDATA[SAG-S2 0.5D ]]> 0.424 0.385 0.515 <![CDATA[SAG-S2 1.0D ]]> 1.546 1.515 1.850 (Φ1+Φ2) / Φ -0.307 -0.325 -0.265 Nd 1.62 1.55 1.72 Vd 63.41 60.00 75.50 T12 / TTL 0.254 0.225 0.285 (T12+T23) / TTL 0.442 0.405 0.465 (Φ1+Φ4) / (Φ2+Φ3) -0.993 -1.125 -0.855 Φ1 / Φ -0.777 -0.825 -0.645 Φ2 / Φ 0.470 0.425 0.515 (Φ3+Φ4) / Φ 0.319 0.285 0.355 BFL / TTL 0.272 0.255 0.285

[0160] Table 14 Design values ​​of optical physical parameters of a fixed-focus lens

[0161]

[0162] The surface numbers in Table 14 are numbered according to the order of the surfaces of each lens. "S1" represents the object surface of the first lens, "S2" represents the image surface of the first lens, and so on. "STO" represents the aperture of the lens; "S5" represents the virtual plane in the third lens, which is used to set the height of the light and thus determine the vignetting coefficient of the optical system; the radius of curvature represents the curvature of the lens surface, a positive value represents that the surface is bent toward the image side, and a negative value represents that the surface is bent toward the object side; "INF" 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, and the space represents that the current position is air with a refractive index of 1; the Abbe constant represents the dispersion characteristics of the material between the current surface and the next surface to the light; the k value represents the numerical value of the cone coefficient of the aspheric surface; the aperture represents the aperture size of the current surface.

[0163] The aspheric cone coefficient can be defined by the following aspheric formula, but is not limited to the following representation method:

[0164]

[0165] Among them, z is the axial vector height of the aspheric surface in the Z direction; r is the height of the aspheric surface; c is the curvature of the fitted sphere, which is the inverse of the radius of curvature; k is the fitting cone coefficient; AG is the coefficient of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspheric polynomial.

[0166] Table 15 Aspheric coefficients of a fixed-focus lens

[0167]

[0168] Among them, "-7.9581E-03" means -7.9581*10 -3 The remaining coefficients are expressed in this way.

[0169] Based on the above parameter definitions, the optical parameters that can be achieved by the fixed-focus lens in Example 5 of the utility model are as follows: focal length f is 4.28 mm, F# is 2.01, field of view angle DFOV=97°, and total optical length TTL: 22.38 mm.

[0170] Furthermore, Fig.18 This is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Example 5 of the utility model. The vertical direction represents the normalization of the aperture, 0 represents the optical axis, and the pupil radius is 1.0306mm; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). The different linear curves in the figure represent different wavelengths of system imaging (436nm, 487nm, 546nm, 587nm and 656nm, respectively), as shown in FIG. Fig.18 It can be seen that the axial aberrations at different wavelengths are all controlled within the range of (-0.07mm, +0.07mm), indicating that the spherical aberration of the fixed-focus lens at each wavelength is well controlled.

[0171] Fig.19 This is a schematic diagram of the light fan of a fixed-focus lens provided in Example 5 of the utility model. The light fan diagram is one of the most commonly used evaluation methods in modern optical design. The horizontal axis is the beam aperture, and the vertical axis is the vertical axis aberration. The most ideal curve is a straight line that coincides with the horizontal axis, indicating that all light rays converge at the same point on the image plane, and the corresponding interval on the vertical axis of the curve is the maximum dispersion range of the light beam on the ideal image plane. The light fan diagram can not only reflect the monochromatic aberrations of different wavelengths, but also indicate the size of the vertical axis chromatic aberration. By Fig.19 It can be seen that each wavelength (436nm, 487nm, 546nm, 587nm and 656nm) in each field of view is close to the horizontal axis, indicating that the vertical axis aberration of each wavelength of the system is well corrected. At the same time, there is no obvious dispersion of each wavelength, indicating that the chromatic aberration of the system is also well corrected, thereby ensuring that the optical system can achieve high-resolution imaging requirements.

[0172] Fig. 20 Schematic diagram of field curvature distortion of a fixed-focus lens provided in Embodiment 5 of the present utility model. In the coordinate system on the left side of the figure, the horizontal coordinate represents the magnitude of the field curvature, in units of mm; the vertical coordinate represents the normalized image height, in units of mm; Fig. 20 As can be seen from the left figure, the field curvature of the lens provided by this embodiment is effectively controlled at each wavelength (436nm, 487nm, 546nm, 587nm and 656nm), that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small. In the coordinate system on the right, the horizontal coordinate represents the size of the distortion, in %, and the vertical coordinate represents the normalized image height, without unit; Fig. 20 It can be seen from the figure on the right that the maximum distortion of the lens provided in this embodiment is controlled within -30%, the distortion is well corrected, the imaging distortion is small, and the difference between the image and the actual object is small.

[0173] In summary, the fixed-focus lens provided in the fifth embodiment of the present invention adopts a combination of a spherical glass lens and three aspherical plastic lenses, and achieves the design goal of small optical distortion by optimizing the focal length, surface shape, relative position of each lens element and optical parameters of each lens; it has the characteristics of high imaging resolution, compact structure and low cost, making the fixed-focus lens system highly competitive in the market. The maximum aperture of the fixed-focus lens is 2.0, the total optical length is not more than 22.5mm, and the maximum compatible sensor chip is 1 / 2.66″. Its comprehensive performance meets the general use requirements of security monitoring.

[0174] The above specific implementations do not constitute a limitation on the protection scope of the present utility model. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present utility model shall be included in the protection scope of the present utility model.

Claims

1. A fixed-focus lens, characterized in that: It comprises a first lens, a second lens, a third lens and a fourth lens which are arranged in sequence from the object plane to the image plane along the optical axis; the first lens is a negative power lens, the second lens is a positive power lens, the third lens is a positive power lens, and the fourth lens is a negative power lens; The sag height at half the aperture of the object side of the first lens is SAG-S1 0.5D , the sag height of the first lens at the full aperture of the object side is SAG-S1 1.0D , the sag height of the first lens at the half-aperture of the image side is SAG-S2 0.5D , the sag height of the first lens at the full aperture of the image side is SAG-S2 1.0D ; The focal power of the first lens is Φ1, the focal power of the second lens is Φ2, and the focal power of the fixed-focus lens is Φ; Among them, 0.155≤SAG-S1 0.5D ≤0.215, 0.105≤SAG-S1 1.0D ≤0.185, 0.385≤SAG-S2 0.5D ≤0.515,1.515≤SAG-S2 1.0D ≤1.585, -0.325≤(Φ1+Φ2) / Φ≤-0.

265.

2. The fixed-focus lens according to claim 1, characterized in that: The air distance between the image side surface of the first lens and the object side surface of the second lens on the optical axis is T12, and the air distance between the image side surface of the second lens and the object side surface of the third lens on the optical axis is T23; Among them, 0.225 <T12 / TTL<0.285,0.405<(T12+T23) / TTL<0.465。 3. The fixed-focus lens according to claim 1, characterized in that: The focal power of the third lens is Φ3, and the focal power of the fourth lens is Φ4; Among them, -1.125≤(Φ1+Φ4) / (Φ2+Φ3)≤-0.

855.

4. The fixed-focus lens according to claim 1, characterized in that: The focal power of the third lens is Φ3, and the focal power of the fourth lens is Φ4; Among them, -0.825≤Φ1 / Φ≤-0.645; 0.425≤Φ2 / Φ≤0.515; 0.285≤(Φ3+Φ4) / Φ≤0.

355.

5. The fixed-focus lens according to claim 1, wherein: The back focus of the fixed-focus lens is BFL, and the total optical length of the fixed-focus lens is TTL; Among them, 0.255 <BFL / TTL<0.285。 6. The fixed-focus lens according to claim 1, wherein: The refractive index of the second lens is Nd2, and the Abbe constant of the second lens is Vd2; Among them, 1.55≤Nd2≤1.72, 60.00≤Vd2≤75.

50.

7. The fixed-focus lens according to claim 1, wherein: The first lens comprises a first object-side surface close to the object plane and a first image-side surface close to the image plane, the first object-side surface is a convex surface, and the first image-side surface is a concave surface; The second lens comprises a second object-side surface close to the object plane and a second image-side surface close to the image plane, the second object-side surface is a convex surface, and the second image-side surface is a convex surface; The third lens comprises a third object-side surface close to the object plane and a third image-side surface close to the image plane, the third object-side surface is a convex surface, and the third image-side surface is a convex surface; The fourth lens includes a fourth object-side surface close to the object plane and a fourth image-side surface close to the image plane, the fourth object-side surface is a concave surface, and the fourth image-side surface is a convex surface.

8. The fixed-focus lens according to claim 1, wherein: The first lens, the third lens and the fourth lens are all plastic aspherical lenses; The second lens is a glass spherical lens.

9. The fixed-focus lens according to claim 1, wherein: The fixed-focus lens also includes an aperture and a filter; The aperture is arranged in the optical path between the first lens and the second lens; The filter is arranged in the optical path between the fourth lens and the image plane.

10. The fixed-focus lens according to claim 1, wherein: The total optical length of the fixed-focus lens is TTL; Among them, TTL≤22.5mm.

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