Prime lens

Abstract

The utility model provides a prime lens, and relates to the technical field of optical lenses. The prime lens comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens which are sequentially arranged from an object space to an image space along an optical axis; the first lens is a glass spherical lens with negative focal power, the second lens is a plastic aspheric lens with negative focal power, the third lens is a plastic aspheric lens with positive focal power, the fourth lens is a glass spherical lens with negative focal power, and the fifth lens is a plastic aspheric lens with positive focal power. The fifth lens is a glass spherical lens with positive focal power, the sixth lens is a plastic aspheric lens with positive focal power, the seventh lens is a plastic aspheric lens with negative focal power, and the eighth lens is a plastic aspheric lens with positive focal power. According to the embodiment of the utility model, the prime lens which has the advantages of wide angle, compact structure, high image quality, large target surface and excellent comprehensive performance is realized.

Description

Technical Field

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

[0002] As people's awareness of security grows, the market demands higher and higher standards for surveillance cameras: the imaging range of lenses needs to be increasingly larger. The current mainstream 2-megapixel and 4-megapixel security lenses are gradually being replaced by higher-definition lenses such as 6-megapixel and 8-megapixel. Therefore, it is necessary to develop a high-quality lens with a wide field of view suitable for 1 / 1.8-inch cameras. Utility Model Content

[0003] The embodiment of the utility model provides a fixed-focus lens, which is a fixed-focus lens with excellent comprehensive performance, such as wide angle, compact structure, high image quality, and large target area.

[0004] The embodiment of the utility model provides a fixed-focus lens, comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens arranged in sequence from the object side to the image side along the optical axis;

[0005] The first lens is a glass spherical lens with negative optical power, the second lens is a plastic aspherical lens with negative optical power, the third lens is a plastic aspherical lens with positive optical power, the fourth lens is a glass spherical lens with negative optical power, the fifth lens is a glass spherical lens with positive optical power, the sixth lens is a plastic aspherical lens with positive optical power, the seventh lens is a plastic aspherical lens with negative optical power, and the eighth lens is a plastic aspherical lens with positive optical power.

[0006] Optionally, the fourth lens is cemented to the fifth lens.

[0007] Optionally, a stop is further included, and the stop is located between the third lens and the fourth lens.

[0008] Optionally, the focal power of the first lens is Φ1, and the focal power of the fixed-focus lens is Φ, satisfying:

[0009] -0.62<Φ1 / Φ<-0.42.

[0010] Optionally, the object-side surface of the first lens is convex toward the object side, and the image-side surface of the first lens is concave toward the image side.

[0011] Optionally, the focal power of the second lens is Φ2, the focal power of the third lens is Φ3, the focal power of the eighth lens is Φ8, and the focal power of the fixed-focus lens is Φ, satisfying at least one of the following conditions:

[0012] -0.88<Φ2 / Φ<-0.56;

[0013] 0.24<Φ3 / Φ<0.62;

[0014] 0.33<Φ8 / Φ<0.59.

[0015] Optionally, the common focal power of the fourth lens and the fifth lens is Φ45, and the focal power of the fixed-focus lens is Φ, satisfying:

[0016] 0.30<Φ45 / Φ<0.70.

[0017] Optionally, the focal power of the sixth lens is Φ6, and the focal power of the seventh lens is Φ7, satisfying:

[0018] 1.40<(Φ6+Φ7) / Φ<8.45.

[0019] Optionally, the Abbe number of the fourth lens is Vd4, and the Abbe number of the fifth lens is Vd5, satisfying:

[0020] 16.0 <Vd4<33.0,53<Vd5<96。

[0021] Optionally, the object-side surface of the fourth lens is convex toward the object side, and the image-side surface of the fourth lens is concave toward the image side;

[0022] The fifth lens is a biconvex lens;

[0023] The sixth lens is a biconvex lens;

[0024] The seventh lens is a biconcave lens;

[0025] The eighth lens is a biconvex lens.

[0026] The present invention provides a fixed-focus lens that utilizes a combination of three spherical glass lenses and five aspherical plastic lenses. These lenses, combined with a power design, are distributed to the first through eighth lenses. This lens is capable of effectively correcting aberrations, ensuring sufficiently good image quality, and simultaneously meeting the requirements of large-area imaging and a wide field of view. The lens has a total length of less than 25mm and can be used with an 8MP, 1 / 1.8-inch chip, achieving a FOV of up to 160°. This provides a fixed-focus lens with excellent overall performance, including wide angle, compact structure, high image quality, and a large target area. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic structural diagram of a fixed-focus lens provided in Example 1 of the present utility model;

[0028] Figure 2This is a spherical aberration curve diagram of a fixed-focus lens provided in Example 1 of the present utility model;

[0029] Figure 3 A schematic structural diagram of a fixed-focus lens provided in Example 2 of the present utility model;

[0030] Figure 4 This is a spherical aberration curve diagram of a fixed-focus lens provided in Example 2 of the present utility model;

[0031] Figure 5 This is a schematic structural diagram of a fixed-focus lens provided in Example 3 of the present utility model;

[0032] Figure 6 This is a spherical aberration curve diagram of a fixed-focus lens provided in Example 3 of the present utility model;

[0033] Figure 7 A schematic structural diagram of a fixed-focus lens provided in Example 4 of the present utility model;

[0034] Figure 8 This is a spherical aberration curve diagram of a fixed-focus lens provided in Example 4 of the present utility model. DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all of its components.

[0036] Example 1

[0037] Figure 1 This is a structural diagram of a fixed-focus lens provided in Example 1 of the present utility model, with reference to Figure 1 The fixed-focus lens comprises a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, a fifth lens 5, a sixth lens 6, a seventh lens 7, and an eighth lens 8, which are arranged in sequence along the optical axis from the object side to the image side. The first lens 1 is a glass spherical lens with negative optical power, the second lens 2 is a plastic aspherical lens with negative optical power, the third lens 3 is a plastic aspherical lens with positive optical power, the fourth lens 4 is a glass spherical lens with negative optical power, the fifth lens 5 is a glass spherical lens with positive optical power, the sixth lens 6 is a plastic aspherical lens with positive optical power, the seventh lens 7 is a plastic aspherical lens with negative optical power, and the eighth lens 8 is a plastic aspherical lens with positive optical power.

[0038] This embodiment of the utility model provides a fixed-focus lens that utilizes a combination of three spherical glass lenses and five aspherical plastic lenses. These lenses, combined with a design that optimizes the optical power, are distributed among the first through eighth lenses 1, 8. This lens effectively corrects aberrations, ensuring sufficiently good image quality while simultaneously meeting the requirements of large-area imaging and a wide field of view. The lens has an overall length of less than 25mm and is compatible with 8MP, 1 / 1.8-inch chips, achieving a FOV of up to 160°. This achieves a fixed-focus lens with excellent overall performance, offering wide angles, a compact structure, high image quality, and a large image area.

[0039] Optionally, refer to Figure 1 , the fourth lens 4 is cemented with the fifth lens 5. These two lenses can effectively correct the chromatic aberration, spherical aberration and field curvature of the fixed focus lens, thereby obtaining higher image quality.

[0040] Optionally, refer to Figure 1 The fixed-focus lens further includes an aperture STO, which is located between the third lens 3 and the fourth lens 4.

[0041] Optionally, refer to Figure 1 The focal power of first lens element 1 is Φ1, and the focal power of the fixed-focus lens is Φ, satisfying the following: -0.62 < Φ1 / Φ < -0.42. Within this range, object-side light is smoothly directed into the imaging system, allowing it to enter second lens element 2 at a smaller angle of incidence. This reduces the proportion of higher-order aberrations and also reduces the aperture of the fixed-focus lens, facilitating a wide field of view and shortening the overall lens length.

[0042] Optionally, refer to Figure 1 The object side surface of the first lens 1 is convex toward the object side, and the image side surface of the first lens 1 is concave toward the image side. The first lens 1 is a meniscus negative lens with a convex front and a concave back.

[0043] Optionally, refer to Figure 1 The focal power of the second lens is Φ2, the focal power of the third lens is Φ3, the focal power of the eighth lens is Φ8, and the focal power of the fixed-focus lens is Φ, which satisfies at least one of the following conditions: -0.88<Φ2 / Φ<-0.56; 0.24<Φ3 / Φ<0.62; 0.33<Φ8 / Φ<0.59. The second lens 2 and the third lens 3 can further smoothly shrink the light, giving the fixed-focus lens a looser tolerance sensitivity. The focal power of the eighth lens 8 within the range of 0.33<Φ8 / Φ<0.59 is conducive to the realization of a large target surface, and can also effectively reduce the light emission angle of the fixed-focus lens, facilitating better matching with the chip.

[0044] Optionally, refer to Figure 1The combined focal power of the fourth lens 4 and the fifth lens 5 is Φ45. The combined focal power of the fourth lens 4 and the fifth lens 5 refers to the focal power of the fourth lens 4 and the fifth lens 5 as a whole. The focal power of the fixed-focus lens is Φ, which satisfies the following conditions: 0.30 < Φ45 / Φ < 0.70.

[0045] Optionally, refer to Figure 1 , the focal power of the sixth lens is Φ6, and the focal power of the seventh lens is Φ7, satisfying the following: 1.40 < (Φ6 + Φ7) / Φ < 8.45. Meeting this focal power ratio range effectively corrects distortion and chromatic aberration in fixed-focus lenses, resulting in higher image quality.

[0046] Optionally, refer to Figure 1 , the Abbe number of the fourth lens 4 is Vd4, the Abbe number of the fifth lens 5 is Vd5, satisfying: 16.0 <Vd4<33.0,53<Vd5<96。

[0047] Optionally, refer to Figure 1 The object-side surface of the fourth lens element 4 is convex toward the object side, and the image-side surface of the fourth lens element 4 is concave toward the image side. The fourth lens element 4 is a convex-concave lens. The fifth lens element 5 is a biconvex lens. The sixth lens element 6 is a biconvex lens. The seventh lens element 7 is a biconcave lens. The eighth lens element 8 is a biconvex lens.

[0048] In summary, by rationally allocating parameters such as the material, optical power, center thickness of each lens, and on-axis spacing between lenses, the above-mentioned fixed-focus lens system can achieve at least one of the following beneficial effects: excellent imaging, compact structure, large target area, and wide field of view.

[0049] Exemplarily, the fixed-focus lens further includes a filter CG, which is located on the image-side surface of the eighth lens element 8. The filter CG is located on the side of the eighth lens element 8 away from the first lens element 1.

[0050] Table 1: Design values of the fixed-focus lens in Example 1

[0051] Surface number Face shape Radius of curvature thickness Refractive index Abbe number Semi-caliber k value S1 spherical surface 20.8001 0.7000 1.63 50.0 6.21 S2 spherical surface 3.6138 4.0189 3.45 S3 Aspheric -8.0478 0.7488 1.53 50.0 2.89 3.3566 S4 Aspheric 4.7010 0.5956 2.59 -4.1400 S5 Aspheric 5.1549 1.7309 1.71 18.1 2.36 0.9762 S6 Aspheric 534.9770 0.1915 2.16 -149.4987 STO Standard surface Infinity -0.1367 1.99 S8 spherical surface 9.7847 2.6185 1.75 18.0 2.16 S9 spherical surface 4.5692 2.3557 1.57 60.1 2.36 S10 spherical surface -8.6153 0.0550 2.61 S11 Aspheric 8.3551 2.4829 1.57 50.0 3.03 -1.0690 S12 Aspheric -3.7247 0.0802 3.12 -0.2819 S13 Aspheric -3.2061 1.1032 1.57 20.6 3.10 -3.0783 S14 Aspheric 14.1595 1.0861 3.39 10.4263 S15 Aspheric 8.3821 2.0717 1.69 19.0 4.04 -12.2656 S16 Aspheric -22.9270 4.5597 4.29 -116.1553 S17 Standard surface Infinity 0.7100 1.52 64.2 4.62 S18 Standard surface Infinity 0.0301 4.66 IMA Standard surface Infinity 4.51

[0052] Table 1 shows a design value of the fixed focus lens in Example 1. The specific value can be adjusted according to product requirements and is not a limitation to the embodiment of the present invention. 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 of the first lens 1 (i.e., the object side), the surface number "S2" represents the back surface of the first lens 1 (i.e., the image side), and so on, which will not be repeated here. It should be noted that "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 surface IMA side; 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 "Curvature Radius" column indicates 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 and next surfaces, representing the ability of the material between the current and next surfaces to deflect light. The blank space in the "Refractive Index" column represents the refractive index of air, which is 1. The Abbe number represents the dispersion properties of the material between the current and next surfaces. A blank space indicates that the current position is air. The value in the "Half-Aperture" column indicates the half-height of the light at the current surface, in mm. The k value represents the numerical value of the conic coefficient of the aspheric surface.

[0053] Table 2 A design value of the aspheric coefficient of the lens in the fixed-focus lens in Example 1

[0054]

[0055] Table 2 shows a design value of the aspheric coefficient of the lens in the fixed-focus lens of Example 1. The specific value can be adjusted according to product requirements and is not a limitation to 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.

[0056] The aspheric cone coefficient can be defined by the following aspheric formula, but is not limited to the following expression method:

[0057]

[0058] Among them, z is the axial sagittal height of the aspheric surface in the Z direction; r is the height of the aspheric surface; c is the curvature of the fitted sphere, which is the inverse of the curvature radius; k is the fitted cone coefficient; A, B, C, D, E, F, and G are the coefficients of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspheric polynomial.

[0059] For example, in Example 1, Φ1 / Φ = -0.52, Φ2 / Φ = -0.68, Φ3 / Φ = 0.5, Φ45 / Φ = 0.35, (Φ6 + Φ7) / Φ = 7.73, Φ8 / Φ = 0.40, Vd4 = 18.00, and Vd5 = 60.1. The focal length of the fixed-focus lens is 3.66 mm, and the F# is 1.99.

[0060] Figure 2 This is a spherical aberration curve diagram of a fixed-focus lens provided in Example 1 of the present utility model, with reference to Figure 2 , the vertical direction represents the normalized aperture, 0 represents the optical axis, the vertical vertex represents the maximum pupil radius; 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, which are represented by Figure 2 It 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.

[0061] Example 2

[0062] Similarities with the above embodiment are not repeated here.

[0063] Table 3: Design values of the fixed-focus lens in Example 2

[0064] Surface number Face shape Radius of curvature thickness Refractive index Abbe number Semi-caliber k value S1 spherical surface 17.8604 1.3468 1.63 50.0 6.75 S2 spherical surface 3.7492 3.3809 3.61 S3 Aspheric -9.5411 0.8158 1.60 60.0 3.12 2.5985 S4 Aspheric 5.3948 0.7375 2.62 -1.5644 S5 Aspheric 7.4012 2.0001 1.70 18.0 2.36 2.6771 S6 Aspheric 30.2635 0.2233 2.11 -0.9499 STO Standard surface Infinity -0.1684 1.94 S8 spherical surface 6.0133 3.0089 1.88 18.0 2.17 S9 spherical surface 5.2771 2.2885 1.67 90.0 2.36 S10 spherical surface -7.0289 0.0550 2.53 S11 Aspheric 28.3005 1.5881 1.63 59.9 2.59 -37.5348 S12 Aspheric -4.7794 0.1485 2.78 0.2682 S13 Aspheric -3.1053 0.9201 1.63 20.0 2.77 -4.0741 S14 Aspheric 19.4977 0.6548 3.30 13.5862 S15 Aspheric 7.4037 2.4928 1.70 19.0 4.05 -17.9304 S16 Aspheric -12.3524 4.7676 4.25 -27.2265 S17 Standard surface Infinity 0.7100 1.52 64.2 4.64 S18 Standard surface Infinity 0.0301 4.68 IMA Standard surface Infinity 0.0000 4.51

[0065] Table 3 shows a design value of the fixed focus lens in Example 2. The specific value can be adjusted according to product requirements and is not a limitation to the embodiment of the present invention. Figure 3 As shown in .

[0066] Table 4: A design value of the aspheric coefficient of the lens in the fixed-focus lens in Example 2

[0067]

[0068] Table 4 shows a design value of the aspheric coefficient of the lens in the fixed-focus lens of Example 2. The specific value can be adjusted according to product requirements and is not a limitation to the embodiment of the present invention. The fixed-focus lens shown in Table 4 can be Figure 3 As shown in .

[0069] For example, in Example 2, Φ1 / Φ = -0.47, Φ2 / Φ = -0.66, Φ3 / Φ = 0.28, Φ45 / Φ = 0.64, (Φ6 + Φ7) / Φ = 1.49, Φ8 / Φ = 0.53, Vd4 = 18.00, and Vd5 = 90.0. The focal length of the fixed-focus lens is 3.66 mm, and the F# is 1.99.

[0070] Example 3

[0071] Similarities with the above embodiment are not repeated here.

[0072] Table 5: Design values of the fixed-focus lens in Example 3

[0073] Surface number Face shape Radius of curvature thickness Refractive index Abbe number Semi-caliber k value S1 spherical surface 18.4550 1.3468 1.68 68.2 6.35 S2 spherical surface 3.7568 3.1195 3.52 S3 Aspheric -10.2349 1.1168 1.60 60.0 3.11 4.3270 S4 Aspheric 5.6101 0.7211 2.64 -2.5421 S5 Aspheric 7.4280 2.0002 1.70 18.0 2.36 2.6890 S6 Aspheric 44.5785 0.2124 2.13 42.3323 STO Standard surface Infinity -0.1576 1.96 S8 spherical surface 5.8462 3.0100 1.79 29.8 2.20 S9 spherical surface 4.8846 2.3924 1.67 90.0 2.39 S10 spherical surface -7.0653 0.0560 2.53 S11 Aspheric 29.0345 1.5604 1.66 60.0 2.58 -49.9908 S12 Aspheric -4.7412 0.1569 2.75 0.2531 S13 Aspheric -3.0396 0.9269 1.66 20.0 2.74 -3.8846 S14 Aspheric 16.1736 0.7126 3.22 13.4915 S15 Aspheric 7.7626 2.5254 1.71 19.0 3.99 -19.1704 S16 Aspheric -11.6190 4.5597 4.24 -23.4977 S17 Standard surface Infinity 0.7100 1.52 64.2 4.62 S18 Standard surface Infinity 0.0301 4.66 IMA Standard surface Infinity 0.0000 4.51

[0074] Table 5 shows a design value of the fixed focus lens in Example 3. The specific value can be adjusted according to product requirements and is not a limitation to the embodiments of the present invention. Figure 5 As shown in .

[0075] Table 6 A design value of the aspheric coefficient of the lens in the fixed focus lens of Example 3

[0076]

[0077] Table 6 shows a design value of the aspheric coefficient of the lens in the fixed-focus lens of Example 3. The specific value can be adjusted according to product requirements and is not a limitation to the embodiments of the present invention. The fixed-focus lens shown in Table 6 can be Figure 5 As shown in .

[0078] For example, in Example 3, Φ1 / Φ = -0.51. Φ2 / Φ = -0.62. Φ3 / Φ = 0.30. Φ45 / Φ = 0.64. (Φ6 + Φ7) / Φ = 1.47. Φ8 / Φ = 0.53. Vd4 = 29.8. Vd5 = 90.0. The focal length of the fixed-focus lens is 3.66 mm, and the F# is 1.99.

[0079] Example 4

[0080] Similarities with the above embodiment are not repeated here.

[0081] Table 7: Design values of the fixed-focus lens in Example 4

[0082] Surface number Face shape Radius of curvature thickness Refractive index Abbe number Semi-caliber k value S1 spherical surface 19.1173 0.9857 1.66 50.0 6.13 S2 spherical surface 3.4638 3.7903 3.41 S3 Aspheric -6.4627 0.7249 1.56 50.0 2.79 2.3625 S4 Aspheric 4.4451 0.2407 2.53 -2.5576 S5 Aspheric 4.8229 2.0002 1.73 22.1 2.36 0.7560 S6 Aspheric -1705.1400 0.1788 2.13 52.0473 STO Standard surface Infinity -0.1239 1.95 S8 spherical surface 7.3975 3.0098 1.84 18.0 2.17 S9 spherical surface 4.9729 2.4779 1.65 62.5 2.55 S10 spherical surface -6.2419 0.0550 2.81 S11 Aspheric 11.8150 2.0611 1.52 50.0 3.07 -5.5116 S12 Aspheric -3.9620 0.1191 3.15 -0.1879 S13 Aspheric -2.9941 1.0725 1.62 20.0 3.13 -3.3495 S14 Aspheric 13.3650 0.5998 3.68 6.5512 S15 Aspheric 8.2673 2.5089 1.71 19.0 4.09 -18.3897 S16 Aspheric -11.3348 4.5597 4.40 -23.3262 S17 Standard surface Infinity 0.7100 1.52 64.2 4.62 S18 Standard surface Infinity 0.0301 4.66 IMA Standard surface Infinity 0.0000 4.51

[0083] Table 7 shows a design value of the fixed focus lens in Example 4. The specific value can be adjusted according to product requirements and is not a limitation to the embodiments of the present invention. Figure 7 As shown in .

[0084] Table 8: Design values of the aspheric coefficients of the fixed-focus lens in Example 4

[0085]

[0086] Table 8 shows a design value of the aspheric coefficient of the lens in the fixed-focus lens of Example 4. The specific value can be adjusted according to product requirements and is not a limitation to the embodiments of the present invention. The fixed-focus lens shown in Table 8 can be Figure 7 As shown in .

[0087] For example, in Example 4, Φ1 / Φ = -0.56, Φ2 / Φ = -0.80, Φ3 / Φ = 0.56, Φ45 / Φ = 0.56, (Φ6 + Φ7) / Φ = 1.71, Φ8 / Φ = 0.52, Vd4 = 18.0, and Vd5 = 62.5. The focal length of the fixed-focus lens is 3.66 mm, and the F# is 1.99.

[0088] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will appreciate that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, combinations, and substitutions are possible for 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 detail through the above embodiments, the present invention is not limited to the above embodiments and may include many other equivalent embodiments without departing from the scope of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. A fixed-focus lens, characterized in that: comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens arranged in sequence from the object side to the image side along the optical axis; The first lens is a glass spherical lens with negative optical power, the second lens is a plastic aspherical lens with negative optical power, the third lens is a plastic aspherical lens with positive optical power, the fourth lens is a glass spherical lens with negative optical power, the fifth lens is a glass spherical lens with positive optical power, the sixth lens is a plastic aspherical lens with positive optical power, the seventh lens is a plastic aspherical lens with negative optical power, and the eighth lens is a plastic aspherical lens with positive optical power.

2. The fixed-focus lens according to claim 1, wherein: The fourth lens is cemented to the fifth lens.

3. The fixed-focus lens according to claim 1, wherein: The optical system further includes a stop located between the third lens and the fourth lens.

4. The fixed-focus lens according to claim 1, wherein: The focal power of the first lens is Φ1, and the focal power of the fixed-focus lens is Φ, satisfying: -0.62<Φ1 / Φ<-0.

42.

5. The fixed-focus lens according to claim 4, wherein: The object-side surface of the first lens is convex toward the object side, and the image-side surface of the first lens is concave toward the image side.

6. The fixed-focus lens according to claim 1, wherein: The focal power of the second lens is Φ2, the focal power of the third lens is Φ3, the focal power of the eighth lens is Φ8, and the focal power of the fixed-focus lens is Φ, satisfying at least one of the following conditions: -0.88<Φ2 / Φ<-0.56; 0.24<Φ3 / Φ<0.62; 0.33<Φ8 / Φ<0.

59.

7. The fixed-focus lens according to claim 1, wherein: The common focal length of the fourth lens and the fifth lens is Φ45, and the focal length of the fixed-focus lens is Φ, which satisfies: 0.30<Φ45 / Φ<0.

70.

8. The fixed-focus lens according to claim 1, wherein: The focal power of the sixth lens is Φ6, and the focal power of the seventh lens is Φ7, satisfying: 1.40<(Φ6+Φ7) / Φ<8.

45.

9. The fixed-focus lens according to claim 1, wherein: The Abbe number of the fourth lens is Vd4, and the Abbe number of the fifth lens is Vd5, which satisfies: 16.0 <Vd4<33.0,53<Vd5<96。 10. The fixed-focus lens according to claim 1, wherein: The object-side surface of the fourth lens is convex toward the object side, and the image-side surface of the fourth lens is concave toward the image side; The fifth lens is a biconvex lens; The sixth lens is a biconvex lens; The seventh lens is a biconcave lens; The eighth lens is a biconvex lens.

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