A fixed focus lens

Abstract

The present invention provides a fixed-focus lens, and relates to the technical field of lenses. The fixed-focus lens includes 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 plastic aspheric lens with negative optical power, the fourth lens is a glass lens with positive optical power, the fifth lens is a plastic aspheric lens with negative optical power, the sixth lens is a plastic aspheric lens with positive optical power, the seventh lens is a plastic aspheric lens with positive optical power, and the eighth lens is a plastic aspheric lens with positive optical power. 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 lenses, and in particular to a fixed-focus lens. Background Art

[0002] As the mainstream product in the security industry, fixed-focus lenses are very popular in the market. As the 1 / 1.8” chip is more and more widely used, the requirements for the size and aperture of the lenses that match it are becoming more and more stringent. At present, the mainstream 1 / 1.8” optical lenses on the market are relatively large (30mm) and have relatively small apertures, which is not conducive to the use and promotion of the product. 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, a sixth lens, a seventh lens and an eighth lens arranged in sequence from the object side to the image side along an optical axis;

[0005] The first lens is a plastic aspheric lens with negative power, the fourth lens is a glass lens with positive power, the fifth lens is a plastic aspheric lens with negative power, the sixth lens is a plastic aspheric lens with positive power, the seventh lens is a plastic aspheric lens with positive power, and the eighth lens is a plastic aspheric lens with positive power.

[0006] Optionally, the refractive index of the fourth lens is Nd4, and the Abbe number of the fourth lens is Vd4, which satisfies:

[0007] 1.44<Nd4<1.81, 45.0≤Vd4<95.1.

[0008] Optionally, the air spacing from the image side surface of the first lens to the object side surface of the second lens on the optical axis is T12, the air spacing from the image side surface of the fourth lens to the object side surface of the fifth lens on the optical axis is T45, the air spacing from the image side surface of the fifth lens to the object side surface of the sixth lens on the optical axis is T56, the air spacing from the image side surface of the seventh lens to the object side surface of the eighth lens on the optical axis is T78, and the total system length of the fixed focus lens is TTL, satisfying:

[0009] 0.1<T12 / TTL<0.19, 0.003<(T45+T56+T78) / TTL<0.006;

[0010] The image-side surface is a surface of the lens adjacent to the image side, and the object-side surface is a surface of the lens adjacent to the object side.

[0011] Optionally, the vertical height of the intersection of the principal ray of the maximum field of view and the image plane is H, satisfying:

[0012] 4.84<TTL / H<4.90.

[0013] Optionally, the focal power of the first lens is Φ1, and the focal power of the second lens is Φ2, satisfying:

[0014] -0.08<(Φ1+Φ2)<-0.06.

[0015] Optionally, the focal power of the third lens is Φ3, the focal power of the fourth lens is Φ4, and the focal power of the fixed-focus lens is Φ, satisfying:

[0016] 0.28<(Φ3+Φ4) / Φ<0.70.

[0017] Optionally, the maximum aperture of the image side light of the fifth lens is The maximum aperture of the light incident on the object side of the sixth lens is satisfy:

[0018]

[0019] The image-side surface is a surface of the lens adjacent to the image side, and the object-side surface is a surface of the lens adjacent to the object side.

[0020] Optionally, the focal power of the seventh lens is Φ7, the focal power of the eighth lens is Φ8, and the focal power of the fixed-focus lens is Φ, satisfying:

[0021] -0.153<(Φ7+Φ8) / Φ<0.110, 0.610<Φ8 / Φ<0.880.

[0022] Optionally, the aperture number of the fixed-focus lens is F / #, satisfying:

[0023] 1.03<F / #<1.08.

[0024] Optionally, the vertical height of the intersection of the principal ray of the maximum field of view and the image plane is H, and the focal length of the fixed-focus lens is f, satisfying:

[0025] 0.78<H / f<1.00.

[0026] The fixed-focus lens provided in the embodiment of the present invention includes 8 lenses. Among them, the first lens and the fifth lens are plastic aspheric lenses with negative optical power, the sixth lens, the seventh lens and the eighth lens are plastic aspheric lenses with positive optical power, and the fourth lens is a glass lens with positive optical power. By optimizing the optical power matching and relative position of each lens, a low-cost fixed-focus lens that can take into account both imaging requirements and compact structure is finally realized. The fixed-focus lens can match a maximum of 1 / 1.8″ sensor chip, meeting the requirements of small size and large aperture, and the comprehensive performance meets the use requirements of general sensors for security monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the structure of a fixed-focus lens in Embodiment 1 of the present invention;

[0028] Figure 2 is a spherical aberration curve diagram in the first embodiment of the present invention;

[0029] Figure 3 is a color difference curve diagram in the first embodiment of the present invention;

[0030] Figure 4 This is a light fan diagram of the light in the first embodiment of the present invention;

[0031] Figure 5 Schematic diagram of the structure of a fixed-focus lens in Embodiment 2 of the present invention;

[0032] Figure 6 is a spherical aberration curve diagram in the second embodiment of the present invention;

[0033] Figure 7 is a color difference curve diagram in the second embodiment of the present invention;

[0034] Figure 8 This is a light fan diagram of light rays in the second embodiment of the present invention;

[0035] Fig. 9 Schematic diagram of the structure of a fixed-focus lens in Embodiment 3 of the present invention;

[0036] Fig.10 is a spherical aberration curve diagram in the third embodiment of the present invention;

[0037] Fig.11 This is a color difference curve diagram in Embodiment 3 of the present invention;

[0038] Fig.12 This is a light fan diagram of light rays in the third embodiment of the present invention. DETAILED DESCRIPTION

[0039] 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.

[0040] Embodiment 1

[0041] Figure 1 is a schematic diagram of the structure of a fixed-focus lens in Embodiment 1 of the present invention, 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 from the object side to the image side along the optical axis. The first lens 1 is a plastic aspheric lens with negative power, the fourth lens 4 is a glass lens with positive power, the fifth lens 5 is a plastic aspheric lens with negative power, the sixth lens 6 is a plastic aspheric lens with positive power, the seventh lens 7 is a plastic aspheric lens with positive power, and the eighth lens 8 is a plastic aspheric lens with positive power.

[0042] The fixed-focus lens provided in the embodiment of the present invention includes 8 lenses. Among them, the first lens 1 and the fifth lens 5 are plastic aspheric lenses with negative optical power, the sixth lens 6, the seventh lens 7 and the eighth lens 8 are plastic aspheric lenses with positive optical power, and the fourth lens 4 is a glass lens with positive optical power. By optimizing the optical power matching and relative position of each lens, a low-cost fixed-focus lens that can take into account both imaging requirements and compact structure is finally achieved. The fixed-focus lens can match a maximum of 1 / 1.8″ sensor chip, meeting the requirements of small size and large aperture, and its comprehensive performance meets the use requirements of general sensors for security monitoring. The fourth lens 4 uses a glass lens, which can make the fixed-focus lens have good resolution in a relatively wide temperature range, suitable for more scenarios, and save the cost of the fixed-focus lens in another aspect.

[0043] For example, reference Figure 1 The fixed focus lens further includes an aperture 9 and a filter 10. The aperture 9 is located between the second lens 2 and the third lens 3. The filter 10 is located on a side of the eighth lens 8 away from the seventh lens 7.

[0044] Optionally, refer to Figure 1 , the refractive index of the fourth lens 4 is Nd4, and the Abbe number of the fourth lens 4 is Vd4. The refractive index and Abbe number of the fourth lens 4 satisfy: 1.44<Nd4<1.81, Vd4≥45.0. The fourth lens 4 is selected from a glass material with an Abbe number greater than or equal to 45.0, which can ensure that the chromatic aberration of the light just passing through the aperture 9 is well corrected, avoiding excessive chromatic aberration and high-order aberration at the tail end of the fixed-focus lens, which affects the image quality.

[0045] Further, 45.0≤Vd4<95.1.

[0046] Optionally, refer to Figure 1 , the air spacing on the optical axis from the image side surface of the first lens 1 to the object side surface of the second lens 2 is T12, the air spacing on the optical axis from the image side surface of the fourth lens 4 to the object side surface of the fifth lens 5 is T45, the air spacing on the optical axis from the image side surface of the fifth lens 5 to the object side surface of the sixth lens 6 is T56, and the air spacing on the optical axis from the image side surface of the seventh lens 7 to the object side surface of the eighth lens 8 is T78. The total system length of the fixed-focus lens is TTL, and the fixed-focus lens satisfies: 0.1<T12 / TTL<0.19, 0.003<(T45+T56+T78) / TTL<0.006. Among them, the image side surface is the surface of the lens adjacent to the image side, and the object side surface is the surface of the lens adjacent to the object side. The lens includes 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. In the embodiments of the present invention, by limiting the interval between the first lens 1 and the second lens 2, the interval between two adjacent ones of the fourth lens 4, the fifth lens 5, and the sixth lens 6, and the interval between the seventh lens 7 and the eighth lens 8, the fixed-focus lens is made more compact, the volume of the fixed-focus lens can be effectively controlled, and the versatility of the fixed-focus lens is improved.

[0047] Furthermore, the vertical height of the intersection of the principal ray of the maximum field of view and the image plane IMA is H, and the fixed-focus lens satisfies: 4.84<TTL / H<4.90. This further makes the fixed-focus lens more compact, can effectively control the volume of the fixed-focus lens, and improves the versatility of the fixed-focus lens.

[0048] Optionally, refer to Figure 1 , the focal power of the first lens 1 is Φ1, the focal power of the second lens 2 is Φ2, and the first lens 1 and the second lens 2 satisfy: -0.08<(Φ1+Φ2)<-0.06. Therefore, the incident aperture of the light is increased before the aperture 9, the amount of light entering the fixed-focus lens is increased, and the requirement of a large aperture of the fixed-focus lens is met.

[0049] Optionally, refer to Figure 1 , the focal power of the third lens 3 is Φ3, the focal power of the fourth lens 4 is Φ4, the focal power of the fixed focus lens is Φ, and the third lens 3 and the fourth lens 4 satisfy:

[0050] 0.28<(Φ3+Φ4) / Φ<0.70. Therefore, when the light passes through the aperture 9 and enters the third lens 3 and the fourth lens 4, the light can be converged, which plays a certain role in achromatization.

[0051] Optionally, refer to Figure 1, the maximum aperture of the light emitting from the image side of the fifth lens 5 is φ52, and the maximum aperture of the light incident on the object side of the sixth lens 6 is φ61. The fifth lens 5 and the sixth lens 6 satisfy: 0.097<φ52 / φ61<0.105. Among them, the image side is the surface of the lens adjacent to the image side, and the object side is the surface of the lens adjacent to the object side. Therefore, the material, structure and optical power of the lens are reasonably matched to meet the above conditions, which can greatly correct the chromatic aberration of the fixed-focus lens, while avoiding the cemented structure and saving the cost of the fixed-focus lens.

[0052] Optionally, refer to Figure 1 , the focal power of the seventh lens 7 is Φ7, the focal power of the eighth lens 8 is Φ8, the focal power of the fixed focus lens is Φ, and the seventh lens 7 and the eighth lens 8 satisfy:

[0053] -0.153<(Φ7+Φ8) / Φ<0.110, 0.610<Φ8 / Φ<0.880. The seventh lens 7 is a plastic aspherical lens. After the light passes through the fifth lens 5 and the sixth lens 6 to eliminate a certain chromatic aberration, the seventh lens 7 can eliminate the higher-order aberrations and residual spherical aberrations that are not eliminated at the front end. When used with the eighth lens 8 which is also an aspherical lens, the remaining higher-order aberrations can be eliminated to the greatest extent. At the same time, the focal length of the eighth lens 8 within the above range can also make the main light angle of the fixed-focus lens within a suitable range, adapting to a variety of chips, and on the other hand, saving the cost of the fixed-focus lens.

[0054] Optionally, refer to Figure 1 , the aperture number of the fixed-focus lens is F / #, and F / # satisfies: 1.03<F / #<1.08. Therefore, the smaller the aperture number F / # of the fixed-focus lens, the stronger the light collection effect, which can achieve full-color imaging effect at night without infrared fill light, and can be used in special environments such as low illumination and all-weather monitoring.

[0055] Optionally, refer to Figure 1 , the vertical height of the intersection of the principal ray of the maximum field of view and the image plane IMA is H, the focal length of the fixed-focus lens is f, and the fixed-focus lens satisfies: 0.78<H / f<1.00. Therefore, by constraining the focal length of the fixed-focus lens and the vertical height of the intersection of the principal ray of the maximum field of view and the image plane IMA, the field of view angle of the fixed-focus lens can be controlled within a certain range to meet the use requirements.

[0056] For example, a mixed combination of 1 glass lens and 7 aspherical plastic lenses can be used, which can correct aberrations well and ensure sufficiently good image quality. The cost is low and can be used with 5MP / 4K and 1 / 1.8-inch chips, and has a wide range of applications.

[0057] For example, the distance from the last optical surface vertex of the fixed-focus lens to the image plane IMA is BFL, and the total system length of the fixed-focus lens is TTL, which satisfies: 0.16<BFL / TTL<0.23. This is conducive to compressing the total length of the fixed-focus lens, while ensuring that the imaging sensor and the filter 10 have sufficient installation space.

[0058] Table 1 A design value of the fixed focus lens in Example 1

[0059]

[0060]

[0061] 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 1 As 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 "STO" in the "Surface Number" column represents the plane where the aperture 9 is located. "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. "INF" 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 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 represents that the current position is air. The value in the "Half-Aperture" column represents half of the aperture of the current surface. The K value represents the numerical value of the aspheric cone coefficient.

[0062] Optionally, the surface of the aspheric lens satisfies the formula:

[0063]

[0064] Among them, z is the axial vector height of the surface in the Z direction, r is the height of the aspherical surface, that is, z is the distance vector height from the vertex of the aspherical surface when the aspherical surface is at a height of r along the optical axis; c is the curvature of the fitted sphere, numerically c is the inverse of the radius of curvature, c = 1 / R, R represents the paraxial curvature radius of the mirror; k is the cone coefficient, A, B, C, D, E, F, G are the aspherical coefficients, specifically, A, B, C, D, E, F, G are the 4th, 6th, 8th, 10th, 12th, 14th and 16th order coefficients of the aspherical polynomial, respectively.

[0065] Table 2 A design value of the aspheric coefficient of the lens in the fixed focus lens in Example 1

[0066]

[0067]

[0068] 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.

[0069] For example, in the first embodiment, the focal length f of the fixed-focus lens is 5.752 mm, and the F / # (ie, the aperture number) is 1.08.

[0070] Figure 2 is a spherical aberration curve diagram in the first embodiment of the present invention, referring to Figure 2 , the vertical direction represents the normalization of the aperture, 0 represents the optical axis, and 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 imaging, which are represented by Figure 2 It can be seen that the axial aberration of normalized apertures of different wavelengths from 0.3 to 1.0 is controlled within the range of (-0.01mm, +0.02mm), indicating that the spherical aberration of the fixed-focus lens at each wavelength is well controlled and can meet the needs of wide spectrum applications.

[0071] Figure 3 is a color difference curve diagram in the first embodiment of the present invention, referring to Figure 3 , the vertical direction is the normalized field of view, 0 represents the optical axis, and the vertex in the vertical axis represents the maximum field of view. The main wavelength uses 546.074nm, and the horizontal direction represents the offset relative to the main wavelength in micrometers (um). Figure 3It can be seen that the vertical chromatic aberration of different wavelengths is controlled within the range of (-1um, +7um), indicating that the vertical chromatic aberration of the fixed-focus lens is well controlled and can meet the requirements of full-band wide-spectrum applications.

[0072] Figure 4 is a light fan diagram of the light in the first embodiment of the present invention, referring to Figure 4 , the horizontal axis is the normalized beam aperture, and the vertical axis is the vertical axis aberration. Ideally, each curve should completely coincide with the horizontal axis, and all light rays in the field of view are focused on the same point on the image plane IMA. The vertical axis can also be expressed as the maximum dispersion range of the light beam on the ideal image plane IMA. The light fan diagram can not only reflect the monochromatic aberration of different wavelengths, but also indicate the size of the vertical axis chromatic aberration. Figure 4 It can be seen that the fixed-focus lens is close to the horizontal axis at each wavelength in each field of view, indicating that the vertical axis aberration of each wavelength is well corrected. In addition, the curves corresponding to each color wavelength are not obviously scattered, indicating that the fixed-focus lens also has good correction for chromatic aberration, ensuring the imaging requirements of this fixed-focus lens for clear images in the full band.

[0073] Embodiment 2

[0074] The same points as those in the first embodiment are not repeated here.

[0075] Table 3 A design value of the fixed focus lens in Example 2

[0076]

[0077] 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 5 as shown in .

[0078] Table 4 A design value of the aspheric coefficient of the lens in the fixed focus lens in Example 2

[0079]

[0080] 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 5 as shown in .

[0081] For example, in the second embodiment, the focal length f of the fixed-focus lens is 4.5002 mm, and the F / # (ie, the aperture number) is 1.08.

[0082] Figure 6 is a spherical aberration curve diagram in the second embodiment of the present invention, referring to Figure 6The axial aberration of normalized apertures of different wavelengths from 0.3 to 1.0 is controlled within the range of (-0.03mm, +0.03mm), indicating that the spherical aberration of the fixed-focus lens at each wavelength is well controlled and can meet the needs of wide spectrum applications.

[0083] Figure 7 is a color difference curve diagram in the second embodiment of the present invention, referring to Figure 7 The vertical chromatic aberration of different wavelengths is controlled within the range of (-1um, +10um), which means that the vertical chromatic aberration of this fixed-focus lens is well controlled and can meet the needs of full-band wide-spectrum applications.

[0084] Figure 8 is a light fan diagram of the light in the second embodiment of the present invention, referring to Figure 8 , the fixed-focus lens is close to the horizontal axis at each wavelength in each field of view, indicating that the vertical axis aberration of each wavelength is well corrected. In addition, the curves corresponding to each color wavelength are not obviously scattered, indicating that this fixed-focus lens also has good correction for chromatic aberration, ensuring the imaging requirements of this fixed-focus lens for clear images in the full band.

[0085] Embodiment 3

[0086] The same points as those in the first embodiment are not repeated here.

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

[0088]

[0089]

[0090] 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. 9 as shown in .

[0091] Table 6 A design value of the aspheric coefficient of the lens in the fixed focus lens in Example 3

[0092]

[0093]

[0094] 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. 9 It can be understood that the value of G corresponding to each face number in Table 6 can be 0.

[0095] For example, in the third embodiment, the focal length f of the fixed-focus lens is 4.776 mm, and the F / # (ie, the aperture number) is 1.03.

[0096] Fig.10 is a spherical aberration curve diagram in the third embodiment of the present invention, referring to Fig.10 The axial aberration of normalized apertures of different wavelengths from 0.3 to 1.0 is controlled within the range of (-0.01mm, +0.03mm), indicating that the spherical aberration of the fixed-focus lens at each wavelength is well controlled and can meet the needs of wide spectrum applications.

[0097] Fig.11 is a color difference curve diagram in the third embodiment of the present invention, referring to Fig.11 The vertical chromatic aberration of different wavelengths is controlled within the range of (-2um, +8um), which means that the vertical chromatic aberration of this fixed-focus lens is well controlled and can meet the needs of full-band wide-spectrum applications.

[0098] Fig.12 This is the light fan diagram of the third embodiment of the present invention, referring to Fig.12 , the fixed-focus lens is close to the horizontal axis at each wavelength in each field of view, indicating that the vertical axis aberration of each wavelength is well corrected. In addition, the curves corresponding to each color wavelength are not obviously scattered, indicating that this fixed-focus lens also has good correction for chromatic aberration, ensuring the imaging requirements of this fixed-focus lens for clear images in the full band.

[0099] 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: There are 8 lenses in total, and the fixed-focus lens includes 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 plastic aspheric lens with negative power, the fourth lens is a glass lens with positive power, the fifth lens is a plastic aspheric lens with negative power, the sixth lens is a plastic aspheric lens with positive power, the seventh lens is a plastic aspheric lens with positive power, and the eighth lens is a plastic aspheric lens with positive power; The focal power of the first lens is Φ1, and the focal power of the second lens is Φ2, satisfying: -0.08<(Φ1+Φ2)<-0.

06.

2. The fixed-focus lens according to claim 1, characterized in that: The refractive index of the fourth lens is Nd4, and the Abbe number of the fourth lens is Vd4, which satisfies: 1.44<Nd4<1.81, 45.0≤Vd4<95.

1.

3. The fixed-focus lens according to claim 1, characterized in that: 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, the air spacing on the optical axis from the image side surface of the fourth lens to the object side surface of the fifth lens is T45, the air spacing on the optical axis from the image side surface of the fifth lens to the object side surface of the sixth lens is T56, the air spacing on the optical axis from the image side surface of the seventh lens to the object side surface of the eighth lens is T78, and the total system length of the fixed focus lens is TTL, which satisfies: 0.1<T12 / TTL<0.19, 0.003<(T45+T56+T78) / TTL<0.006; The image-side surface is a surface of the lens adjacent to the image side, and the object-side surface is a surface of the lens adjacent to the object side.

4. The fixed-focus lens according to claim 3, characterized in that: The vertical height of the intersection of the principal ray of the maximum field of view and the image plane is H, which satisfies: 4.84<TTL / H<4.

90.

5. The fixed-focus lens according to claim 1, wherein: The focal power of the third lens is Φ3, the focal power of the fourth lens is Φ4, and the focal power of the fixed-focus lens is Φ, which satisfies: 0.28<(Φ3+Φ4) / Φ<0.

70.

6. The fixed-focus lens according to claim 1, wherein: The maximum aperture of the image side of the fifth lens for emitting light is φ52, and the maximum aperture of the object side of the sixth lens for emitting light is φ61, satisfying: 0.0971<φ52 / φ61<0.1003; The image-side surface is a surface of the lens adjacent to the image side, and the object-side surface is a surface of the lens adjacent to the object side.

7. The fixed-focus lens according to claim 1, wherein: The focal power of the seventh lens is Φ7, the focal power of the eighth lens is Φ8, and the focal power of the fixed-focus lens is Φ, which satisfies: -0.153<(Φ7+Φ8) / Φ<0.110, 0.610<Φ8 / Φ<0.

880.

8. The fixed-focus lens according to claim 1, wherein: The aperture number of the fixed focus lens is F / #, which satisfies: 1.03＜F / #＜1.08。 9. The fixed-focus lens according to claim 1, wherein: The vertical height of the intersection of the principal ray of the maximum field of view and the image plane is H, and the focal length of the fixed-focus lens is f, which satisfies: 0.78<H / f<1.00.

Images