A fixed focus lens

Abstract

The present invention provides a fixed-focus lens, which relates to the technical field of optical lenses, and includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens arranged in sequence from the object side to the image side along the optical axis, wherein the first lens, the second lens, and the sixth lens have negative optical focal lengths, and the fourth lens and the fifth lens have positive optical focal lengths; the object side surface of the first lens is a convex surface, and the image side surface of the first lens is a concave surface; the object side surface of the second lens is a convex surface, and the image side surface of the second lens is a concave surface; the object side surface of the fourth lens is a concave surface, and the image side surface of the fourth lens is a convex surface; the object side surface of the fifth lens is a convex surface, and the image side surface of the fifth lens is a convex surface; the object side surface of the sixth lens is a concave surface, and the image side surface of the sixth lens is a convex surface. An embodiment of the present invention provides a fixed-focus lens to achieve a low-cost fixed-focus lens design that takes into account both imaging requirements and compact structure.

Description

Technical Field

[0001] The present invention relates to the technical field of optical lenses, and in particular to a fixed-focus lens. Background Art

[0002] With the rapid development of science and technology and economy, society has higher and higher requirements for optical imaging lenses. For example, it is necessary to ensure that the imaging chip can be captured and observed at a long distance while requiring the lens to be smaller and smaller. However, existing optical lenses are difficult to meet the increasing demand. Summary of the invention

[0003] The embodiment of the present invention provides a fixed-focus lens to achieve a low-cost fixed-focus lens design that takes into account both imaging requirements and a compact structure.

[0004] An embodiment of the present invention provides a fixed-focus lens, comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens arranged in sequence from the object side to the image side along an optical axis, wherein the first lens, the second lens and the sixth lens have negative optical power, and the fourth lens and the fifth lens have positive optical power;

[0005] The object side surface of the first lens is a convex surface, and the image side surface of the first lens is a concave surface;

[0006] The object side surface of the second lens is a convex surface, and the image side surface of the second lens is a concave surface;

[0007] The object side surface of the fourth lens is a concave surface, and the image side surface of the fourth lens is a convex surface;

[0008] The object side surface of the fifth lens is a convex surface, and the image side surface of the fifth lens is a convex surface;

[0009] The object side surface of the sixth lens is a concave surface, and the image side surface of the sixth lens is a convex surface.

[0010] Optionally, a stop is further included, and the stop is located between the third lens and the fourth lens.

[0011] Optionally, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens are aspherical lenses.

[0012] Optionally, the first lens is a glass lens, and the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens are plastic lenses.

[0013] Optionally, the optical power of the first lens is , the focal power of the second lens is , the optical power of the fourth lens is , the optical power of the fifth lens is , the focal power of the sixth lens is , the focal length of the fixed-focus lens is , at least one of the following conditions is met:

[0014] -0.176≤ ≤-0.101;

[0015] -0.384≤ ≤-0.301;

[0016] 0.165≤ ≤0.242;

[0017] 0.451≤ ≤0.533;

[0018] -0.295≤ ≤-0.134.

[0019] Optionally, the focal length of the fourth lens is f4, the focal length of the fifth lens is f5, the focal length of the sixth lens is f6, and the focal length of the fixed-focus lens is f, satisfying at least one of the following conditions:

[0020] 6.024<(f4+f5) / f< 8.287;

[0021] -5.549<(f5+f6) / f<-1.497.

[0022] Optionally, the refractive index of the first lens is nd1, and the Abbe number of the first lens is vd1, satisfying:

[0023] 1.611≤nd1≤1.819;

[0024] 54.6≤vd1≤66.597.

[0025] Optionally, the lens diameter of the first lens is ΦL1, and the total optical length of the fixed-focus lens is TTL, satisfying:

[0026] 0.408≤ΦL1 / TTL≤0.487.

[0027] Optionally, the distance from the vertex of the last optical surface of the fixed-focus lens to the image plane is BFL, and the total optical length of the fixed-focus lens is TTL, which satisfies:

[0028] 0.091≤BFL / TTL≤0.109.

[0029] Optionally, the aperture number of the fixed-focus lens is FNO, and FNO≤1.17.

[0030] The fixed-focus lens provided in the embodiment of the present invention includes 6 lenses. Among them, the first lens is a convex-concave lens. The second lens is a convex-concave lens. The fourth lens is a concave-convex lens. The fifth lens is a biconvex lens. The sixth lens is a concave-convex lens. The optical power design of the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens is combined. By optimizing the optical power matching and the surface shape of each lens, a low-cost fixed-focus lens that can take into account both imaging requirements and compact structure is finally realized. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0032] Figure 2 A schematic diagram of an axial aberration curve provided in Embodiment 1 of the present invention;

[0033] Figure 3 A schematic diagram of field curvature provided in Embodiment 1 of the present invention;

[0034] Figure 4 A distortion schematic diagram provided in Embodiment 1 of the present invention;

[0035] Figure 5 A schematic diagram of MTF provided in Example 1 of the present invention;

[0036] Figure 6 A schematic structural diagram of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0037] Figure 7 A schematic diagram of an axial aberration curve provided in Embodiment 2 of the present invention;

[0038] Figure 8 A schematic diagram of field curvature provided in Embodiment 2 of the present invention;

[0039] Fig. 9 A distortion schematic diagram provided for the second embodiment of the present invention;

[0040] Fig.10 A schematic diagram of an MTF provided in Embodiment 2 of the present invention;

[0041] Fig.11 A schematic structural diagram of a fixed-focus lens provided in Embodiment 3 of the present invention;

[0042] Fig.12 A schematic diagram of an axial aberration curve provided in Embodiment 3 of the present invention;

[0043] Fig.13 A schematic diagram of field curvature provided in Embodiment 3 of the present invention;

[0044] Fig.14 A distortion schematic diagram provided in Embodiment 3 of the present invention;

[0045] Fig.15 This is a schematic diagram of MTF provided in Embodiment 3 of the present invention. DETAILED DESCRIPTION

[0046] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0047] Embodiment 1

[0048] An embodiment of the present invention provides a fixed-focus lens. Figure 1 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 1 of the present invention, referring to Figure 1 The fixed focus lens includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5 and a sixth lens L6 arranged in sequence from the object side to the image side along the optical axis. The first lens L1, the second lens L2 and the sixth lens L6 have negative optical power, and the fourth lens L4 and the fifth lens L5 have positive optical power. The third lens L3 has optical power.

[0049] The object side surface of the first lens L1 is convex, and the image side surface of the first lens L1 is concave. Among them, the object side surface is the surface of the lens on the side adjacent to the object side, and the image side surface is the surface of the lens on the side adjacent to the image side. The object side surface of the first lens L1 is convex toward the object side, and the image side surface of the first lens L1 is concave toward the image side. The object side surface of the second lens L2 is convex, and the image side surface of the second lens L2 is concave. The object side surface of the second lens L2 is convex toward the object side, and the image side surface of the second lens L2 is concave toward the image side. The object side surface of the fourth lens L4 is concave, and the image side surface of the fourth lens L4 is convex. The object side surface of the fourth lens L4 is concave toward the object side, and the image side surface of the fourth lens L4 is convex toward the image side. The object side surface of the fifth lens L5 is convex, and the image side surface of the fifth lens L5 is convex. The object side surface of the fifth lens L5 is convex toward the object side, and the image side surface of the fifth lens L5 is convex toward the image side. The object side surface of the sixth lens L6 is concave, and the image side surface of the sixth lens L6 is convex. The object-side surface of the sixth lens L6 is concave toward the object side, and the image-side surface of the sixth lens L6 is convex toward the image side.

[0050] Among them, the object side of the first lens L1 is convex, the purpose is to receive light incident at a large angle. The optical focal length of the first lens L1 and the second lens L2 is negative, which is used to bend the light, so that more light enters the fixed-focus lens to participate in imaging, and also avoids the problem of the subsequent lens having an overly large aperture. The high and low refractive index combination of the fifth lens L5 and the sixth lens L6 is used to eliminate chromatic aberration and other aberrations, and also improves optical performance such as resolution and distortion while maintaining a compact structure.

[0051] The fixed-focus lens provided in the embodiment of the present invention includes 6 lenses. Among them, the first lens L1 is a convex-concave lens. The second lens L2 is a convex-concave lens. The fourth lens L4 is a concave-convex lens. The fifth lens L5 is a biconvex lens. The sixth lens L6 is a concave-convex lens. The optical power design of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 is combined. By optimizing the optical power matching and surface shape of each lens, a low-cost fixed-focus lens that can take into account both imaging requirements and compact structure is finally realized.

[0052] Optionally, refer to Figure 1 The fixed focus lens also includes an aperture STO, which is located between the third lens L3 and the fourth lens L4. The cooperation between the second lens L2 and the third lens L3 allows light to pass through the aperture STO more smoothly. The fourth lens L4 is used to converge the light passing through the aperture STO.

[0053] Optionally, refer to Figure 1 , the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 are aspherical lenses. Aspherical lenses are beneficial for correcting aberrations, increasing illumination, and reducing the number of lenses in a fixed-focus lens.

[0054] Optionally, refer to Figure 1 , the first lens L1 is a glass lens. The second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 are plastic lenses. The second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 are plastic aspherical lenses, which have the advantages of low price, easy processing and light weight.

[0055] Exemplarily, the first lens L1 is a glass spherical lens.

[0056] Optionally, refer to Figure 1 , the focal power of the first lens is , the focal power of the second lens is , the focal power of the fourth lens is , the optical power of the fifth lens is , the focal power of the sixth lens is , the focal length of the fixed-focus lens is , satisfies at least one of the following conditions: -0.176≤ ≤-0.101;-0.384≤ ≤-0.301; 0.165≤ ≤0.242; 0.451≤ ≤0.533; -0.295≤ ≤-0.134.

[0057] The focal length is the difference between the convergence of the image-side beam and the convergence of the object-side beam. Its size determines the ability of the fixed-focus lens 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. This design controls the focal length of the entire fixed-focus lens to be distributed in a certain proportion to ensure the balance of the incident angles of the front and rear lenses, thereby reducing the sensitivity of the lens to processing tolerances. It is also beneficial to reduce distortion and improve the stability of the fixed-focus lens.

[0058] Optionally, refer to Figure 1 , the focal length of the fourth lens L4 is f4, the focal length of the fifth lens L5 is f5, the focal length of the sixth lens L6 is f6, and the focal length of the fixed-focus lens is f, which satisfies at least one of the following conditions: 6.024< (f4+f5) / f< 8.287; -5.549<(f5+f6) / f<-1.497. The fourth lens L4 and the fifth lens L5 are both positive lenses, which play a role in converging light. The sixth lens L6 is a negative lens, which plays a role in diverging light. Reasonable setting of the focal lengths of the fourth lens L4, the fifth lens L5, and the sixth lens L6 is conducive to improving image quality, reducing tolerance sensitivity, and improving processing yield.

[0059] Optionally, refer to Figure 1 , the refractive index of the first lens is nd1, and the Abbe number of the first lens is vd1, which satisfies: 1.611≤nd1≤1.819; 54.6≤vd1≤66.597. The first lens L1 is used to receive light into the fixed-focus lens. The first lens L1 needs to refract the light, but it should not bring too much dispersion. Therefore, the first lens L1 needs to meet the requirements of appropriate refractive index and not too low Abbe number.

[0060] Optionally, refer to Figure 1 , the lens diameter of the first lens L1 is ΦL1, and the total optical length of the fixed-focus lens is TTL, which satisfies: 0.408≤ΦL1 / TTL≤0.487. The above conditions can effectively control the volume of the entire fixed-focus lens, so that the fixed-focus lens meets the requirements of miniaturization. And the lens diameter ΦL1 of the first lens L1 is reasonably selected, which is conducive to achieving a larger field of view angle and a higher amount of light input.

[0061] Optionally, refer to Figure 1 , the distance from the vertex of the last optical surface of the fixed-focus lens to the image plane is BFL, which is also the back focus of the fixed-focus lens. The total optical length of the fixed-focus lens is TTL, which satisfies: 0.091≤BFL / TTL≤0.109. The back focus BFL of the fixed-focus lens is reasonably selected, leaving enough space for the installation of the bottom optical sensor and the flat glass CG.

[0062] Optionally, refer to Figure 1 , the aperture number of the fixed-focus lens is FNO, FNO≤1.17. FNO satisfies FNO≤1.17, indicating that the fixed-focus lens has a large aperture. The aperture number can be used to measure the amount of light entering. A smaller aperture number will bring more light entering, which is very conducive to clear imaging.

[0063] Exemplarily, the fixed-focus lens further includes a flat glass CG, which is located on the image side of the sixth lens L6, and the flat glass CG can protect the photosensitive chip in the optical sensor. The photosensitive chip is used to convert the optical signal collected by the fixed-focus lens into an electrical signal, thereby ensuring the imaging effect of the fixed-focus lens.

[0064] Table 1 A design value of the fixed focus lens in Example 1

[0065]

[0066] Table 1 shows a design value of the fixed-focus lens in Example 1, and its specific value can be adjusted according to product requirements and is not a limitation of the embodiment of the present invention. The fixed-focus lens shown in Table 1 can be Figure 1As shown in . A lens generally includes two surfaces, each of which is a refractive surface. The surface numbers in Table 1 are numbered according to the surfaces of each lens. Among them, the surface number "S1" represents the front surface (i.e., the object side) of the first lens L1, the surface number "S2" represents the back surface (i.e., the image side) of the first lens L1, and so on, which will not be repeated here. It should be noted that "OBJ" in the "Surface Number" column represents the object surface of the fixed-focus lens. "IMA" in the "Surface Number" column represents the image surface of the fixed-focus lens. The radius of curvature represents the degree of curvature of the lens surface. A positive radius of curvature value indicates that the center of curvature is on the side of the surface close to the image side, that is, a positive value represents that the surface is bent toward the image side IMA; a negative radius of curvature value represents that the center of curvature is on the side of the surface away from the image side, that is, a negative value represents that the surface is bent toward the object side. "INFINITY" in the "Radius of Curvature" column represents that the surface is a plane and the radius of curvature is infinite. The value in the "Thickness" column represents the central axial distance from the current surface to the next surface. The "Refractive Index" column indicates the refractive index of the medium between the current surface and the next surface, representing the ability of the material between the current surface and the next surface to deflect light. The blank space in the "Refractive Index" column is the refractive index of air, which is 1. The Abbe number represents the dispersion characteristics of the material between the current surface and the next surface to light, and the blank space represents that the current position is air.

[0067] Table 2 A design value of the aspheric coefficient of the lens in the fixed focus lens in Example 1

[0068]

[0069] Table 2 shows a design value of the aspheric coefficient of the lens in the fixed-focus lens in Example 1. The specific value can be adjusted according to product requirements and is not a limitation of the embodiment of the present invention. The fixed-focus lens shown in Table 2 can be Figure 1 The meaning of the column "surface number" in Table 2 is consistent with that of the column "surface number" in Table 1. "E" in each embodiment of the present invention represents an index with base 10.

[0070] Optionally, the surface of the aspheric lens satisfies the formula:

[0071] . Among them, Z is the sagittal height of the aspheric surface, is the basic curvature at the vertex, is the conic constant, is the radial coordinate perpendicular to the optical axis, is the coefficient of the higher order term, is a high-order term of the aspheric surface. i is a positive integer from 2 to 11.

[0072] For example, in the first embodiment, the focal length f of the fixed-focus lens is 0.591, the TTL (ie, the total optical length) is 8.925, the field of view angle is 202°, ​​and the image plane size is φ2.1 mm. = -0.101, -0.384, 0.206, 0.528, -0.295. BFL / TTL= 0.091. ΦL1 / TTL= 0.469. FNO= 1.13. (f4+f5) / f=6.744. (f5+f6) / f= -1.498.

[0073] Figure 2 This is a schematic diagram of an axial aberration curve provided in Example 1 of the present invention, with reference to Figure 2 , the vertical direction is the normalized aperture, 0 means on the optical axis, the vertical vertex corresponds to the maximum pupil radius; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). Different linear curves in the figure represent different wavelengths of imaging, Figure 2 It can be seen that the axial aberration of normalized apertures of different visible light wavelengths from 0 to 1.0 is controlled within the range of (-0.02mm, +0.02mm), indicating that the spherical aberration of the fixed-focus lens at each wavelength is well controlled.

[0074] Figure 3 A schematic diagram of field curvature provided in the first embodiment of the present invention is shown in FIG. Figure 3 As shown in the figure, the horizontal coordinate represents the magnitude of the field curvature, in mm; the vertical coordinate represents the normalized image height, in units. Figure 3 It can be seen that the fixed-focus lens provided in this embodiment is effectively controlled in field curvature from light with a wavelength of 0.436 μm to light with a wavelength of 0.650 μm, that is, when imaging, the difference between the best imaging surfaces of the central field of view and the edge field of view is small.

[0075] Figure 4 A distortion diagram provided in the first embodiment of the present invention, referring to Figure 4 , the horizontal coordinate represents the size of the distortion (F-Theta), the unit is %; the vertical coordinate represents the normalized image height, no unit; the maximum field of view is 101 degrees. The distortion of the large field of view fixed focus lens is within 6%, the imaging distortion is reasonable, and meets general requirements.

[0076] Embodiment 2

[0077] The similarities with the above-mentioned embodiment are not repeated here.

[0078] Table 3 A design value of the fixed focus lens in Example 2

[0079]

[0080] Table 3 shows a design value of the fixed-focus lens in Example 2, and its specific value can be adjusted according to product requirements and is not a limitation of the embodiment of the present invention. The fixed-focus lens shown in Table 3 can be Figure 6 as shown in .

[0081] Table 4 A design value of the aspheric coefficient of the lens in the fixed focus lens in Example 2

[0082]

[0083] Table 4 shows a design value of the aspheric coefficient of the lens in the fixed-focus lens in Example 2. The specific value can be adjusted according to product requirements and is not a limitation of the embodiment of the present invention. The fixed-focus lens shown in Table 4 can be Figure 6 as shown in .

[0084] For example, in the second embodiment, the focal length f of the fixed-focus lens is 0.617, the TTL (ie, the total optical length) is 8.370, the field of view angle is 202°, ​​and the image plane size is φ2.2 mm. = -0.106, -0.377, 0.242, 0.528, -0.134. BFL / TTL= 0.093. ΦL1 / TTL= 0.487. FNO= 1.09. (f4+f5) / f=6.027. (f5+f6) / f= -5.548.

[0085] Embodiment 3

[0086] The similarities with the above-mentioned embodiment are not repeated here.

[0087] Table 5 A design value of the fixed focus lens in Example 3

[0088]

[0089] Table 5 shows a design value of the fixed-focus lens in Example 3, and its specific value can be adjusted according to product requirements and is not a limitation of the embodiment of the present invention. The fixed-focus lens shown in Table 5 can be Fig.11 as shown in .

[0090] Table 6 A design value of the aspheric coefficient of the lens in the fixed focus lens in Example 3

[0091]

[0092] Table 6 shows a design value of the aspheric coefficient of the lens in the fixed-focus lens in Example 3. The specific value can be adjusted according to product requirements and is not a limitation of the embodiment of the present invention. The fixed-focus lens shown in Table 6 can be Fig.11 as shown in .

[0093] For example, in the third embodiment, the focal length f of the fixed-focus lens is 0.590, the TTL (ie, the total optical length) is 8.221, the field of view angle is 202°, ​​and the image plane size is φ2.2 mm. = -0.176, -0.301, 0.165, 0.451, -0.231. BFL / TTL= 0.109. ΦL1 / TTL= 0.408. FNO= 1.17. (f4+f5) / f=8.286. (f5+f6) / f= -2.116.

[0094] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, combinations and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A fixed-focus lens, characterized in that: The fixed-focus lens comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens which are sequentially arranged along the optical axis from the object side to the image side, and the number of lenses in the fixed-focus lens is 6; the first lens, the second lens and the sixth lens have negative optical power, and the third lens, the fourth lens and the fifth lens have positive optical power; The object side surface of the first lens is a convex surface, and the image side surface of the first lens is a concave surface; The object side surface of the second lens is a convex surface, and the image side surface of the second lens is a concave surface; The object side surface of the fourth lens is a concave surface, and the image side surface of the fourth lens is a convex surface; The object side surface of the fifth lens is a convex surface, and the image side surface of the fifth lens is a convex surface; The object side surface of the sixth lens is a concave surface, and the image side surface of the sixth lens is a convex surface; The optical power of the fourth lens is , the optical power of the fifth lens is , the focal length of the fixed-focus lens is ,satisfy: 0.165≤ ≤0.242； 0.451≤ ≤0.533； The aperture number of the fixed focus lens is FNO, FNO≤1.17; The distance from the vertex of the last optical surface of the fixed-focus lens to the image plane is BFL, and the total optical length of the fixed-focus lens is TTL, which satisfies: 0.091≤BFL / TTL≤0.

109.

2. The fixed-focus lens according to claim 1, characterized in that: Also included is an aperture stop located between the third lens and the fourth lens.

3. The fixed-focus lens according to claim 1, characterized in that: The second lens, the third lens, the fourth lens, the fifth lens and the sixth lens are aspherical lenses.

4. The fixed-focus lens according to claim 3, characterized in that: The first lens is a glass lens, and the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens are plastic lenses.

5. The fixed-focus lens according to claim 1, wherein: The optical power of the first lens is , the focal power of the second lens is , the focal power of the sixth lens is , at least one of the following conditions is met: -0.176≤ ≤-0.101； -0.384≤ ≤-0.301； -0.295≤ ≤-0.134。 6. The fixed-focus lens according to claim 5, characterized in that: The focal length of the fourth lens is f4, the focal length of the fifth lens is f5, the focal length of the sixth lens is f6, and the focal length of the fixed-focus lens is f, satisfying at least one of the following conditions: 6.024<(f4+f5) / f< 8.287; -5.549<(f5+f6) / f<-1.

497.

7. The fixed-focus lens according to claim 1, wherein: The refractive index of the first lens is nd1, and the Abbe number of the first lens is vd1, which satisfies: 1.611≤nd1≤1.819; 54.6≤vd1≤66.

597.

8. The fixed-focus lens according to claim 7, characterized in that: The diameter of the first lens is ΦL1, which satisfies: 0.408≤ΦL1 / TTL≤0.487.

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