A fixed focus lens

Abstract

The embodiment of the present invention discloses a fixed-focus lens. The fixed-focus lens includes a first lens, a second lens, a system aperture, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens arranged in sequence from the object side to the image side along the optical axis; the first lens is a convex-concave negative power lens, the second lens is a concave-convex negative power lens, the third lens is a biconvex positive power lens, the fourth lens is a concave-convex positive power lens, the fifth lens is a biconvex positive power lens, the sixth lens is a biconcave negative power lens, and the seventh lens is a biconvex positive power lens; the third lens is a glass spherical lens; the focal length F of the fixed-focus lens satisfies 5<F<8; the focal length F3 of the third lens satisfies 0.35<|F3 / F|<6. The embodiment of the present invention solves the problem that the existing monitoring equipment cannot take into account both large aperture and high resolution at the same time, and can ensure that the lens improves the imaging quality and more effectively highlights the subject under the premise of F1.6 large light transmission.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of security monitoring, and in particular to a fixed-focus lens. Background Art

[0002] With the increasing popularity of security monitoring facilities, monitoring equipment has higher and higher requirements for monitoring environment and images, and monitoring equipment needs to provide monitoring images with higher pixels and greater light transmittance.

[0003] In some cases, the monitoring process requires monitoring facilities to provide long-distance monitoring images. At present, ordinary lenses with a focal length of 4mm cannot highlight the focus subject at a long distance, the image distortion is relatively large, the peripheral illumination is relatively low, and the image is not clear. Lenses with a focal length of 6mm generally have a small aperture (F=2.0), and when a larger aperture is used, the image quality is poor, and the focusing difference between visible light and infrared light is large, which cannot meet the monitoring needs of day and night confocality. Summary of the invention

[0004] The present invention provides a fixed-focus lens to ensure high light throughput while improving imaging quality to meet day and night confocal imaging requirements.

[0005] An embodiment of the present invention provides a fixed-focus lens, including:

[0006] A first lens, a second lens, a system aperture, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens are arranged in sequence from the object side to the image side along the optical axis;

[0007] The first lens is a convex-concave negative power lens, the second lens is a concave-convex negative power lens, the third lens is a biconvex positive power lens, the fourth lens is a concave-convex positive power lens, the fifth lens is a biconvex positive power lens, the sixth lens is a biconcave negative power lens, and the seventh lens is a biconvex positive power lens; wherein the third lens is a glass spherical lens;

[0008] The focal length F of the fixed-focus lens satisfies the relationship: 5<F<8; the focal length F3 of the third lens satisfies the relationship: 0.35<|F3 / F|<6.

[0009] Optionally, the focal length F6 of the sixth lens satisfies the relationship: 0.1<|F6 / F|<4.

[0010] Optionally, the focal length F5 of the fifth lens and the focal length F6 of the sixth lens satisfy the relationship: 0.5<|F5 / F6|<4;

[0011] The focal lengths F6 of the seventh lens element F7 and the sixth lens element satisfy the relationship: 0.5<|F7 / F6|<4.

[0012] Optionally, the focal length F4 of the fourth lens satisfies the relationship: 1<|F4 / F|<7.

[0013] Optionally, the focal length F1 of the first lens satisfies the relationship: 1.5<|F1 / F|<4;

[0014] The focal length F2 of the second lens satisfies the relationship: 50<|F2 / F|<150.

[0015] Optionally, the focal length F5 of the fifth lens satisfies the relationship: 1<|F5 / F|<5.

[0016] Optionally, the focal lengths of the first lens F1 and the third lens F3 satisfy the relationship: 0.5<|F1 / F3|<5;

[0017] The focal length F2 of the second lens and the focal length F3 of the third lens satisfy the relationship: 10<|F2 / F3|<70;

[0018] The focal length F4 of the fourth lens and the focal length F3 of the third lens satisfy the relationship: 0.5<|F4 / F|<5;

[0019] The focal length F5 of the fifth lens satisfies the relationship: 0.5<|F5 / F|<5;

[0020] The focal length F6 of the sixth lens satisfies the relationship: 0.5<|F6 / F|<5;

[0021] The focal length F7 of the seventh lens satisfies the relationship: 0.5<|F7 / F|<5.

[0022] Optionally, the sixth lens and the seventh lens are glued to each other.

[0023] Optionally, the first lens, the second lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens are all plastic aspherical lenses.

[0024] Optionally, the first to seventh lenses meet the following conditions:

[0025] 1.40 <n1<1.60,50<v1<60;

[0026] 1.40 <n2<1.70,20<v2<60;

[0027] 1.40 <n3<1.60,70<v3<98;

[0028] 1.55 <n4<1.70,20<v4<38;

[0029] 1.40 <n5<1.60,50<v5<60;

[0030] 1.55 <n6<1.70,20<v6<38;

[0031] 1.40 <n7<1.60,50<v7<60;

[0032] Among them, n1~n7 are the refractive indices of the first lens to the seventh lens respectively, and v1~v7 are the Abbe numbers of the first lens to the seventh lens respectively.

[0033] Optionally, the fixed-focus lens satisfies BFL / TTL>0.22 and D1 / TTL<0.55, wherein D1 is the maximum aperture of the first lens, TTL is the distance from the first lens to the image plane, and BFL is the distance from the seventh lens to the image plane.

[0034] The fixed-focus lens provided by the embodiment of the present invention sequentially arranges the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens along the optical axis from the object side to the image side, wherein the first lens is a convex-concave negative power lens, the second lens is a concave-convex negative power lens, the third lens is a biconvex positive power lens, the fourth lens is a concave-convex positive power lens, the fifth lens is a biconvex positive power lens, the sixth lens is a biconcave negative power lens, and the seventh lens is a biconvex positive power lens; and the system aperture is set between the second lens and the third lens, and the focal length of the third lens of the glass spherical surface is set to meet 0.35<|F3 / F|<6, thereby improving the imaging quality of the fixed-focus lens. The fixed-focus lens provided by the embodiment of the present invention solves the problem that the existing monitoring equipment cannot take into account both large aperture and high resolution at the same time, and can improve the imaging quality to achieve 4K quality under the premise of ensuring that the lens has a large light transmission of F1.6. In addition, it can be used for long-distance monitoring, more effectively highlighting the subject, and can also ensure that the resolution meets the imaging requirements when used in an environment of -40 to 80°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a structural schematic diagram of a fixed-focus lens provided by an embodiment of the present invention;

[0036] Figure 2 yes Figure 1 The on-axis spherical aberration curve of the fixed focal length lens shown;

[0037] Figure 3 yes Figure 1 The ray fan diagram of the fixed focus lens shown;

[0038] Figure 4 yes Figure 1 Spot diagram of the fixed focal length lens shown;

[0039] Figure 5 is a schematic structural diagram of another fixed-focus lens provided by an embodiment of the present invention;

[0040] Figure 6 yes Figure 5 The on-axis spherical aberration curve of the fixed focal length lens shown;

[0041] Figure 7 yes Figure 5 The ray fan diagram of the fixed focus lens shown;

[0042] Figure 8 yes Figure 5 Spot diagram for the fixed focal length lens shown. DETAILED DESCRIPTION

[0043] 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.

[0044] Figure 1 is a schematic diagram of the structure of a fixed-focus lens provided by an embodiment of the present invention, with reference to Figure 1 The fixed-focus lens comprises: a first lens 11, a second lens 12, a system aperture (not shown in the figure), a third lens 13, a fourth lens 14, a fifth lens 15, a sixth lens 16 and a seventh lens 17 which are arranged in sequence from the object side to the image side along the optical axis; the first lens 11 is a convex-concave negative power lens, the second lens 12 is a concave-convex negative power lens, the third lens 13 is a biconvex positive power lens, the fourth lens 14 is a concave-convex positive power lens, the fifth lens 15 is a biconvex positive power lens, the sixth lens 16 is a biconcave negative power lens, and the seventh lens 17 is a biconvex positive power lens; wherein the third lens 13 is a glass spherical lens; the focal length F of the fixed-focus lens satisfies the relationship: 5<F<8; the focal length F3 of the third lens 13 satisfies the relationship: 0.35<|F3 / F|<6.

[0045] Among them, the focal length and optical power of the lens provided in the embodiment of the present invention are determined for a wavelength of 587.56nm. The first lens 11 and the second lens 12 are both negative optical power lenses, so that the front lens group before the system aperture is negative optical power, and the third lens 13, the fourth lens 14, the fifth lens 15, the sixth lens 16 and the seventh lens 17 form positive optical power, so that the positive optical power aberration of the rear lens group can be corrected by the negative optical power of the front lens group. Exemplarily, the first lens 11 is a negative optical power lens, which can be used to control the incident angle of the optical system of the fixed-focus lens and reduce optical distortion. The second lens 12 is a negative optical power lens, which can correct off-axis aberrations. The optical power of the fixed-focus lens optical system is approximately proportionally distributed to ensure the balance of the incident angle of the front and rear lens groups, thereby reducing the sensitivity of the lens and improving the possibility of production. By reasonably allocating the focal lengths of each lens, the spherical aberration and field curvature of the imaging system can be made small at the same time, ensuring the image quality of the on-axis and off-axis fields of view.

[0046] In addition, the third lens is the main element for converging the on-axis light in the entire fixed-focus lens. The third lens 13 is a positive focal lens, which can focus the light beam of the lens in front of the system aperture. At the same time, the third lens 13 uses a glass spherical lens. On the premise that the focal length F of the fixed-focus lens satisfies 5<F<8, the focal length F3 of the third lens 13 is set to meet 0.35<|F3 / F|<6. At the same time, it is made of glass lens material, which reduces the influence of high and low temperatures on the imaging quality of the fixed-focus lens, avoids the fixed-focus lens from producing defocus in different environments, and achieves the characteristic of no defocus from -40℃ to 80℃.

[0047] The fixed-focus lens provided by the embodiment of the present invention sequentially arranges the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens along the optical axis from the object side to the image side, wherein the first lens is a convex-concave negative power lens, the second lens is a concave-convex negative power lens, the third lens is a biconvex positive power lens, the fourth lens is a concave-convex positive power lens, the fifth lens is a biconvex positive power lens, the sixth lens is a biconcave negative power lens, and the seventh lens is a biconvex positive power lens; and the system aperture is set between the second lens and the third lens, and the focal length of the third lens of the glass spherical surface is set to meet 0.35<|F3 / F|<6, thereby improving the imaging quality of the fixed-focus lens. The fixed-focus lens provided by the embodiment of the present invention solves the problem that the existing monitoring equipment cannot take into account both large aperture and high resolution at the same time, and can improve the imaging quality to achieve 4K quality under the premise of ensuring that the lens has a large light transmission of F1.6. In addition, it can be used for long-distance monitoring, more effectively highlighting the subject, and can also ensure that the resolution meets the imaging requirements when used in an environment of -40 to 80°C.

[0048] On the basis of satisfying the above parameter requirements of the fixed-focus lens, the structural parameters of other lenses can be specifically adjusted as needed. The embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0049] Based on the above embodiments, Figure 1 Optionally, the focal length F6 of the sixth lens 16 satisfies the relationship: 0.1<|F6 / F|<4. The sixth lens 16 is the element with the largest negative focal length in the entire fixed-focus lens optical system. By setting the focal length ratio of the sixth lens and the entire lens to 0.1<|F6 / F|<4, its main function is to correct the magnification chromatic aberration and the axial chromatic aberration, thereby ensuring the imaging balance of the lens under high and low temperature conditions.

[0050] Further optionally, the focal length F5 of the fifth lens and the focal length F6 of the sixth lens satisfy the relationship: 0.5<|F5 / F6|<4; the focal length F6 of the seventh lens F7 and the sixth lens satisfy the relationship: 0.5<|F7 / F6|<4. Among them, the fifth lens 15 and the seventh lens 17 can be used to correct chromatic aberration, and the focal length ratio of the fifth lens 15 and the seventh lens 17 to the sixth lens 16 is reasonably set to ensure that the entire fixed-focus lens has a better imaging quality under infrared light, that is, to achieve the correction effect of infrared light.

[0051] Furthermore, the fourth lens 14 in the rear lens group has the function of correcting field curvature, magnification chromatic aberration and axial chromatic aberration. Based on this, the focal length F4 of the fourth lens 14 can be set to satisfy the relationship: 1<|F4 / F|<7. At this time, the fourth lens 14 can converge the light and reduce the height of the light, while correcting the high-order spherical aberration, balancing various aberrations, and ensuring the imaging quality of light in each band.

[0052] It should be noted that while the rear lens group corrects aberrations such as magnification chromatic aberration and axial chromatic aberration, the front lens group can also optimize the imaging quality. Among them, the first lens and the second lens can correct field curvature, astigmatism and coma. Therefore, optionally, the focal length F1 of the first lens can be set to satisfy the relationship: 1.5<|F1 / F|<4; the focal length F2 of the second lens can satisfy the relationship: 50<|F2 / F|<150. At this time, the focal lengths of the first lens 11 and the second lens 12 can ensure that the optical system of the fixed-focus lens has a larger incident angle, reduce optical distortion, and correct off-axis aberrations. It should be noted that the first lens 11 adopts a convex-concave negative focal power lens, and the focal length is 1.5<|F1 / F|<4, which can ensure that the first lens has a relatively small size, thereby helping to reduce the total optical length of the entire fixed-focus lens and reduce the size of the fixed-focus lens.

[0053] Based on the above embodiment, optionally, the focal length F5 of the fifth lens 15 satisfies the relationship: 1<|F5 / F|<5. In this case, the fifth lens 15 can be used to correct spherical aberration, coma and related higher-order aberrations, which helps to improve and balance the imaging quality.

[0054] Furthermore, in order to make each lens more reasonably correct the aberration and chromatic aberration, balance the aberration of the entire lens, and optimize the imaging quality. Optionally, the focal length F3 of the first lens F1 and the third lens satisfies the relationship: 0.5<|F1 / F3|<5; the focal length F2 of the second lens and the focal length F3 of the third lens satisfy the relationship: 10<|F2 / F3|<70; the focal length F4 of the fourth lens and the focal length F3 of the third lens satisfy the relationship: 0.5<|F4 / F|<5; the focal length F5 of the fifth lens satisfies the relationship: 0.5<|F5 / F|<5; the focal length F6 of the sixth lens satisfies the relationship: 0.5<|F6 / F|<5; the focal length F7 of the seventh lens satisfies the relationship: 0.5<|F7 / F|<5. At this time, the lenses can cooperate with each other. On the one hand, the light line of the light beam can be adjusted by adjusting the focal length of each lens, ultimately achieving a large aperture and a large amount of light. On the other hand, through the cooperation of each lens, the aberrations and chromatic aberrations generated in various imaging processes can be corrected, optimized and balanced, thereby ensuring the imaging quality, achieving high resolution, and achieving day and night confocality to meet the monitoring imaging needs during the day and night.

[0055] In a preferred embodiment, considering that the sixth lens 16 and the seventh lens 17 can correct field curvature and astigmatism, in order to correct the axial chromatic aberration of the lens on this basis, the sixth lens and the seventh lens can be glued together to form a glued lens group. The glued lens group can not only correct the axial chromatic aberration, but also improve the field curvature and coma, thereby further optimizing the imaging quality of the fixed-focus lens.

[0056] In the fixed-focus lens provided in the above embodiments, optionally, the first lens 11, the second lens 12, the fourth lens 14, the fifth lens 15, the sixth lens 16 and the seventh lens 17 are all plastic aspherical lenses. On the one hand, aspherical lenses can meet the requirements of each lens for optical power while performing appropriate aberration correction; on the other hand, compared with glass lenses, the difficulty and cost of preparing plastic lenses are lower, and the use of aspherical lenses is also conducive to reducing manufacturing costs and mass production.

[0057] Specifically, the first lens to the seventh lens may be arranged to satisfy the following conditions:

[0058] 1.40 <n1<1.60,50<v1<60;

[0059] 1.40 <n2<1.70,20<v2<60;

[0060] 1.40 <n3<1.60,70<v3<98;

[0061] 1.55 <n4<1.70,20<v4<38;

[0062] 1.40 <n5<1.60,50<v5<60;

[0063] 1.55 <n6<1.70,20<v6<38;

[0064] 1.40 <n7<1.60,50<v7<60;

[0065] Among them, n1~n7 are the refractive indices of the first lens to the seventh lens respectively, and v1~v7 are the Abbe numbers of the first lens to the seventh lens respectively.

[0066] Optionally, when designing the fixed-focus lens, relevant parameters of each lens can be adjusted according to the actual lens size requirements, so as to set the ratio of the effective image plane IC and the total optical length TTL of the fixed-focus lens, so that the fixed-focus lens satisfies BFL / TTL>0.22 and D1 / TTL<0.55, wherein D1 is the maximum aperture of the first lens, TTL is the distance from the first lens to the image plane, and BFL is the distance from the seventh lens to the image plane.

[0067] The above-mentioned fixed-focus lens is described below with two specific embodiments. Figure 1 As shown, the fixed-focus lens comprises: a first lens 11, a second lens 12, a system aperture, a third lens 13, a fourth lens 14, a fifth lens 15, a sixth lens 16 and a seventh lens 17 arranged in sequence from the object side to the image side along the optical axis; the first lens 11 is a convex-concave negative power lens, the second lens 12 is a concave-convex negative power lens, the third lens 13 is a biconvex positive power lens, the fourth lens 14 is a concave-convex positive power lens, the fifth lens 15 is a biconvex positive power lens, the sixth lens 16 is a biconcave negative power lens, and the seventh lens 17 is a biconvex positive power lens; wherein the third lens 13 is a glass spherical lens; the focal length F of the fixed-focus lens satisfies the relationship: 5<F<8; the focal length F3 of the third lens 13 satisfies the relationship: 0.35<|F3 / F|<6.

[0068] In this embodiment, the design values ​​of the first lens 11 to the seventh lens 17 are shown in Table 1 below.

[0069] Table 1 shows a design value of the fixed focus lens (f=5.8mm; aperture F1.6):

[0070]

[0071]

[0072] The surface numbers in Table 1 are numbered according to the order of the surfaces of each lens, where "S1" represents the front surface of the first lens, "S2" represents the back surface of the first lens, and so on; 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; 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, and the refractive index is 1. It should be noted that the aperture is set between S4 and S5. In addition, S15 and S16 are essentially plane lenses.

[0073] The aspheric cone coefficient can be defined by the following aspheric formula, but is not limited to the following representation method:

[0074]

[0075] 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.

[0076] The aspheric surface parameters in this embodiment are shown in Table 2:

[0077] Table 2 shows a design value of the aspheric coefficient in the fixed focus lens

[0078]

[0079]

[0080] The optical system of this embodiment achieves the following technical indicators: focal length: f=5.8mm; relative aperture F=1.6; field of view: 2w≥69° (image side 2η≥Φ6.9mm); distortion: <-20%; resolution: compatible with 8-megapixel high-resolution CCD or CMOS camera; applicable spectral range: 420-850nm.

[0081] Figure 2 yes Figure 1 The on-axis spherical aberration curve of the fixed-focus lens shown in the figure is Figure 3 yes Figure 1 The ray fan diagram of the fixed focus lens shown in the figure, Figure 4 yes Figure 1 The spot diagram of the fixed focal length lens shown is shown in Figure 1. Figure 2, the axial chromatic aberration of light of different wavelengths (0.486μm, 0.588μm, 0.656μm and 0.850μm) in the fixed-focus lens is no more than 0.02μm, and the axial chromatic aberration of the infrared light of 0.850μm is not much different from that of other visible light. Therefore, it can be seen that the fixed-focus lens provided by the embodiment of the present invention can not only correct the chromatic aberration well, but also ensure that there is a small difference in the imaging chromatic aberration of infrared light and visible light, which is conducive to achieving day and night confocality. It can be seen from the light fan diagram and the point diagram that the imaging range of different wavelengths under different field of view angles is within ±10μm, which ensures that the aberration difference in different field of view areas is small, which means that the fixed-focus lens has better corrected the aberration of the optical system, and the imaging quality is better, which is helpful to achieve high-resolution monitoring equipment.

[0082] Figure 5 is a schematic diagram of the structure of another fixed-focus lens provided by an embodiment of the present invention, referring to Figure 5 The fixed-focus lens comprises: a first lens 21, a second lens 22, a system aperture, a third lens 23, a fourth lens 24, a fifth lens 25, a sixth lens 26 and a seventh lens 27 arranged in sequence from the object side to the image side along the optical axis; the first lens 21 is a convex-concave negative power lens, the second lens 22 is a concave-convex negative power lens, the third lens 23 is a biconvex positive power lens, the fourth lens 24 is a concave-convex positive power lens, the fifth lens 25 is a biconvex positive power lens, the sixth lens 26 is a biconcave negative power lens, and the seventh lens 27 is a biconvex positive power lens; wherein the third lens 23 is a glass spherical lens; the focal length F of the fixed-focus lens satisfies the relationship: 5<F<8; the focal length F3 of the third lens 23 satisfies the relationship: 0.35<|F3 / F|<6. wherein the sixth lens 26 and the seventh lens 27 are glued to each other.

[0083] In this embodiment, the design values ​​of the first lens 21 to the seventh lens 27 are shown in Table 3 below.

[0084] Table 3 shows a design value of the fixed focus lens (f=6mm; aperture F1.6):

[0085]

[0086]

[0087] It should be noted that the aperture is arranged between S4 and S5. Furthermore, S14 and S15 are substantially plane lenses.

[0088] The aspheric surface parameters in this embodiment are shown in Table 4:

[0089] Table 4 shows a design value of the aspheric coefficient in the fixed focus lens

[0090]

[0091]

[0092] The optical system of this embodiment achieves the following technical indicators: focal length: f=6mm; relative aperture F=1.6; field of view: 2w≥69° (image side 2η≥Φ6.9mm); distortion: <-20%; resolution: compatible with 8-megapixel high-resolution CCD or CMOS camera; applicable spectral range: 420-850nm.

[0093] Figure 6 yes Figure 5 The on-axis spherical aberration curve of the fixed-focus lens shown in the figure is Figure 7 yes Figure 5 The ray fan diagram of the fixed focus lens shown in the figure, Figure 8 yes Figure 5 Spot diagram for the fixed focal length lens shown. Figure 6 , the axial chromatic aberration of light of different wavelengths (0.486μm, 0.588μm, 0.656μm and 0.850μm) in the fixed-focus lens is no more than 0.02μm, and the axial chromatic aberration of the infrared light of 0.850μm is not much different from that of other visible light. Therefore, it can be seen that the other fixed-focus lens provided by the embodiment of the present invention can also correct the chromatic aberration well, ensuring that there is a small difference in the imaging chromatic aberration of infrared light and visible light, which is conducive to achieving day and night confocal. At the same time, it can be seen from the light fan diagram and the point diagram that the imaging range of different wavelengths under different field of view angles is within ±10μm, ensuring that the aberration difference in different field of view areas is small, which means that the fixed-focus lens has better corrected the aberration of the optical system, and the imaging quality is better, which is helpful to achieve high-resolution monitoring equipment.

[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: include: A first lens, a second lens, a system aperture, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens are arranged in sequence from the object side to the image side along the optical axis; The first lens is a convex-concave negative power lens, the second lens is a concave-convex negative power lens, the third lens is a biconvex positive power lens, the fourth lens is a concave-convex positive power lens, the fifth lens is a biconvex positive power lens, the sixth lens is a biconcave negative power lens, and the seventh lens is a biconvex positive power lens; wherein the third lens is a glass spherical lens; The focal length F of the fixed-focus lens satisfies the relationship: 5<F<8; the focal length F3 of the third lens satisfies the relationship: 0.35<|F3 / F|<6; the focal length F1 of the first lens satisfies the relationship: 1.5<|F1 / F|<4; the focal length F2 of the second lens satisfies the relationship: 50<|F2 / F|<150.

2. The fixed-focus lens according to claim 1, characterized in that: The focal length F6 of the sixth lens satisfies the relationship: 0.1<|F6 / F|<4.

3. The fixed-focus lens according to claim 2, characterized in that: The focal length F5 of the fifth lens and the focal length F6 of the sixth lens satisfy the relationship: 0.5<|F5 / F6|<4; The focal lengths F6 of the seventh lens element F7 and the sixth lens element satisfy the relationship: 0.5<|F7 / F6|<4.

4. The fixed-focus lens according to claim 1, characterized in that: The focal length F4 of the fourth lens satisfies the relationship: 1<|F4 / F|<7.

5. The fixed-focus lens according to claim 1, wherein: The focal length F5 of the fifth lens satisfies the relationship: 1<|F5 / F|<5.

6. The fixed-focus lens according to claim 5, characterized in that: The focal lengths of the first lens F1 and the third lens F3 satisfy the relationship: 0.5<|F1 / F3|<5; The focal length F2 of the second lens and the focal length F3 of the third lens satisfy the relationship: 10<|F2 / F3|<70; The focal length F4 of the fourth lens and the focal length F3 of the third lens satisfy the relationship: 0.5<|F4 / F|<5; The focal length F6 of the sixth lens satisfies the relationship: 0.5<|F6 / F|<5; The focal length F7 of the seventh lens satisfies the relationship: 0.5<|F7 / F|<5.

7. The fixed-focus lens according to claim 5, characterized in that: The sixth lens and the seventh lens are cemented to each other.

8. The fixed-focus lens according to claim 1, wherein: The first lens, the second lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens are all plastic aspherical lenses.

9. The fixed-focus lens according to claim 8, characterized in that: The first to seventh lenses meet the following conditions: 1.40 <n1<1.60,50<v1<60; 1.40 <n2<1.70,20<v2<60; 1.40 <n3<1.60,70<v3<98; 1.55 <n4<1.70,20<v4<38; 1.40 <n5<1.60,50<v5<60; 1.55 <n6<1.70,20<v6<38; 1.40 <n7<1.60,50<v7<60; Among them, n1~n7 are the refractive indices of the first lens to the seventh lens respectively, and v1~v7 are the Abbe numbers of the first lens to the seventh lens respectively.

10. The fixed-focus lens according to claim 1, wherein: The fixed-focus lens satisfies BFL / TTL>0.22 and D1 / TTL<0.55, wherein D1 is the maximum aperture of the first lens, TTL is the distance from the first lens to the image plane, and BFL is the distance from the seventh lens to the image plane.

Images