Prime lens and monitoring equipment

Abstract

The invention discloses a prime lens and monitoring equipment. The prime lens comprises a convex-concave first lens with positive focal power, a field diaphragm, a second lens with negative focal power, a third lens with positive focal power, a convex-convex fourth lens with positive focal power, a concave-concave fifth lens with negative focal power and a sixth lens with positive focal power which are sequentially arranged from an object space to an image space along an optical axis, the vignetting diaphragm comprises a convex seventh lens with positive focal power and a concave eighth lens with negative focal power; the image side surface of the second lens is a concave surface, the object side surface of the third lens is a convex surface, the image side surface of the sixth lens is a convex surface, the second lens and the third lens are cemented into a first cemented lens, and the fourth lens and the fifth lens are cemented into a second cemented lens. And high resolution performance is achieved in visible light and near-infrared bands.

Description

Technical Field

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

[0002] With the development of technology, the working environment of surveillance lenses is becoming more and more severe. As the focal length of the lens increases, the lens diameter usually increases, which in turn increases the weight of the lens and the cost of processing materials. In order to control the lens diameter, the common solution on the market is to reduce the aperture, which sacrifices the lens's ability to work in low-light environments and reduces the lens's resolution. Summary of the invention

[0003] The present invention provides a fixed-focus lens and monitoring equipment, which can realize infrared confocality in the near-infrared band of 830-940nm and have high resolution performance in both visible light and near-infrared bands. The lens has a relative illumination of more than 50%, low cost, large aperture, long focal length and small distortion.

[0004] To achieve the above-mentioned purpose, an embodiment of the present invention provides a fixed-focus lens, comprising: a convex-concave first lens with positive focal power, a field stop, a second lens with negative focal power, a third lens with positive focal power, a convex-convex fourth lens with positive focal power, a concave-concave fifth lens with negative focal power, a sixth lens with positive focal power, a vignetting stop, a convex-convex seventh lens with positive focal power, and a concave-concave eighth lens with negative focal power, which are arranged in sequence from the object side to the image side along the optical axis;

[0005] Among them, the image side surface of the second lens is concave, the object side surface of the third lens is convex, the image side surface of the sixth lens is convex, the second lens and the third lens are cemented into a first cemented lens, and the fourth lens and the fifth lens are cemented into a second cemented lens.

[0006] Optionally, the object side surface of the second lens is concave or convex, and the image side surface of the third lens is concave or convex.

[0007] Optionally, the optical power of the first lens is The focal length of the fixed focal length lens The relationship between them is:

[0008] The refractive index ND1 of the first lens satisfies the relationship: 1.8 <ND1<2.1。

[0009] Optionally, the optical power of the second lens is The focal power of the third lens The optical power of the first doublet lens The relationship between them is:

[0010] The optical power of the second lens The optical power of the third lens The Abbe number vd2 of the second lens and the Abbe number vd3 of the third lens satisfy the relationship:

[0011] Optionally, the optical power of the fourth lens The optical power of the fifth lens And the optical power of the second cemented lens Satisfy the relationship:

[0012] The optical power of the fourth lens The optical power of the fifth lens The Abbe number vd4 of the fourth lens and the Abbe number vd5 of the fifth lens satisfy the relationship:

[0013] Optionally, the Abbe number vd3 of the third lens satisfies the relationship: 60 < vd3 < 96; the Abbe number vd4 of the fourth lens satisfies the relationship: 60 < vd4 < 96.

[0014] Optionally, the optical power of the sixth lens The optical power of the seventh lens The optical power of the eighth lens The optical power of the fixed-focus lens Satisfy the relationship:

[0015] Optionally, the semi-aperture SDmax of the first lens and the maximum image height H of the fixed-focus lens satisfy the relationship: 1 < SDmax / H < 1.2.

[0016] Optionally, the distance TTL from the center of the object side of the first lens to the center of the imaging surface and the focal length f of the fixed-focus lens satisfy the relationship: 1.1 < TTL / f < 1.3.

[0017] The embodiment of the present invention also provides a monitoring device, including the fixed-focus lens provided in any embodiment of the present invention.

[0018] According to the fixed-focus lens and monitoring device proposed in the embodiments of the present invention, the fixed-focus lens includes: a convex-concave first lens with positive focal power, a field stop, a second lens with negative focal power, a third lens with positive focal power, a convex-convex fourth lens with positive focal power, a concave-concave fifth lens with negative focal power, a sixth lens with positive focal power, a vignetting stop, a convex-convex seventh lens with positive focal power and a concave-concave eighth lens with negative focal power, which are arranged in sequence from the object side to the image side along the optical axis; the image side surface of the second lens is a concave surface, the object side surface of the third lens is a convex surface, the image side surface of the sixth lens is a convex surface, the second lens and the third lens are cemented into a first cemented lens, the fourth lens and the fifth lens are cemented into a second cemented lens, and the first lens to the eighth lens are all glass spherical lenses. By reasonably setting the optical focal length and surface shape of the eight lenses and matching them with glass materials, the following can be achieved at a relatively low cost: the focal length of the lens can be around 40mm, |optical distortion|<1.5%, image side F#=2.0, the maximum image height of the lens is 9.12mm, and while infrared confocality is achieved in the near-infrared band of 830nm~940nm, it has high resolution performance in both visible light and near-infrared bands.

[0019] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 is a schematic structural diagram of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0022] Figure 2 1 is a schematic diagram of the full-frequency MTF of the mixed light band of the fixed-focus lens provided in the first embodiment of the present invention;

[0023] Figure 3 1 is a schematic diagram of the full-frequency MTF of the fixed-focus lens in the infrared 850nm band provided in the first embodiment of the present invention;

[0024] Figure 4 1 is a schematic diagram of the central field of view defocus MTF after the mixed light of the fixed-focus lens provided in the first embodiment of the present invention and the 850nm light are superimposed;

[0025] Figure 5 is a schematic diagram of field curvature and distortion of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0026] Figure 6 is a schematic structural diagram of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0027] Figure 7 Schematic diagram of the full-frequency MTF of the mixed light band of the fixed-focus lens provided in the second embodiment of the present invention;

[0028] Figure 8 This is a schematic diagram of the full-frequency MTF of the infrared 850nm band of the fixed-focus lens provided in the second embodiment of the present invention;

[0029] Fig. 9 1 is a schematic diagram of the central field of view defocus MTF after the mixed light of the fixed focus lens provided in the second embodiment of the present invention and the 850nm light are superimposed;

[0030] Fig.10 is a schematic diagram of field curvature and distortion of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0031] Fig.11 is a schematic structural diagram of a fixed-focus lens provided in Embodiment 3 of the present invention;

[0032] Fig.12 Schematic diagram of the full-frequency MTF of the mixed light band of the fixed-focus lens provided in the third embodiment of the present invention;

[0033] Fig.13 This is a schematic diagram of the full-frequency MTF of the infrared 850nm band of the fixed-focus lens provided in the third embodiment of the present invention;

[0034] Fig.14 1 is a schematic diagram of the central field of view through-focus MTF after the mixed light of the fixed-focus lens provided in the third embodiment of the present invention and the 850nm light are superimposed;

[0035] Fig.15 Schematic diagram of field curvature and distortion of a fixed-focus lens provided in Embodiment 3 of the present invention. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0037] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions.

[0038] Figure 1 is a schematic structural diagram of a fixed-focus lens provided in Embodiment 1 of the present invention, Figure 6 is a schematic structural diagram of a fixed-focus lens provided in Embodiment 2 of the present invention, Fig.11 is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 3 of the present invention. Figures 1 to 11 As shown, the fixed-focus lens comprises: a convex-concave first lens L1 with positive focal power, a field stop, a second lens L2 with negative focal power, a third lens L3 with positive focal power, a convex-convex fourth lens L4 with positive focal power, a concave-concave fifth lens L5 with negative focal power, a sixth lens L6 with positive focal power, a vignetting stop, a convex-convex seventh lens L7 with positive focal power, and a concave-concave eighth lens L8 with negative focal power, which are arranged in sequence from the object side to the image side along the optical axis; wherein the image side surface of the second lens L2 is a concave surface, the object side surface of the third lens L3 is a convex surface, the image side surface of the sixth lens L6 is a convex surface, the second lens L2 and the third lens L3 are cemented into a first cemented lens, the fourth lens L4 and the fifth lens L5 are cemented into a second cemented lens, and the first lens L1 to the eighth lens L8 are all glass spherical lenses.

[0039] Specifically, the focal length is equal to the difference between the convergence of the image-side light beam and the convergence of the object-side light beam, and it characterizes the ability of the optical system to deflect light. The larger the absolute value of the focal length, the stronger the ability to bend light, and the smaller the absolute value of the focal length, the weaker the ability to bend light. When the focal length is a positive number, the refraction of light is convergent; when the focal length is a negative number, the refraction of light is divergent. The focal length can be used to characterize a certain refractive surface of a lens (i.e., a surface of a lens), can be used to characterize a certain lens, and can also be used to characterize a system formed by multiple lenses (i.e., a lens group). In the fixed-focus lens provided in this embodiment, each lens can be fixed to a lens barrel ( Figure 1 Not shown).

[0040] In this article, the paraxial area refers to the area near the optical axis. If the lens surface is convex and the position of the convex surface is not defined, it means that the lens surface is convex at least in the paraxial area; if the lens surface is concave and the position of the concave surface is not defined, it means that the lens surface is concave at least in the paraxial area. The surface of each lens close to the object side is called the object side surface of the lens, and the surface of each lens close to the image side is called the image side surface of the lens. The judgment of the surface shape in the paraxial area can be based on the judgment method of the general knowledge in this field, and the positive and negative R value (R refers to the radius of curvature of the paraxial area, usually refers to the R value on the lens database (lens data) in the optical software) is used to judge the convexity and concavity. When the R value is positive, the lens surface is convex to the object side, and when the R value is negative, the lens surface is convex to the image side.

[0041] Exemplarily, the first lens L1 is a convex-concave lens, then the object side surface and the image side surface of the first lens L1 are both convex toward the object side, the image side surface of the second lens L2 is a concave surface, then the image side surface of the second lens L2 is convex toward the object side, the object side surface of the third lens L3 is a convex surface, then the object side surface of the third lens L3 is convex toward the object side, the fourth lens L4 is a convex-convex lens, then the object side surface of the fourth lens L4 is convex toward the object side, and the image side surface is convex toward the image side. The fifth lens L5 is a concave-concave lens, then the object side surface of the fifth lens L5 is convex toward the image side, and the image side surface is convex toward the object side. The image side surface of the sixth lens L6 is a convex surface, then the image side surface of the sixth lens L6 is convex toward the image side. The seventh lens L7 is a convex-convex lens, then the object side surface of the seventh lens L7 is convex toward the object side, and the image side surface is convex toward the image side. The eighth lens L8 is a concave-concave lens, then the object side surface of the eighth lens L8 is convex toward the image side, and the image side surface is convex toward the object side.

[0042] Among them, the first lens L1 has a positive focal power, which is conducive to the convergence of light, can avoid excessive divergence of light on the object side, is conducive to controlling the aperture of the rear lens, and is conducive to realizing a miniaturized design. The first lens L1 preferably uses a high refractive index material, which is conducive to reducing the diameter of the front port, and the object side is designed to be convex, which can converge large-aperture light into the rear optical system, which is conducive to increasing the amount of light passing. The second lens L2 has a negative focal power, the image side is concave, and the object side can be concave or convex. When the negative focal power is conducive to light diffusion, and the object side is convex, the light emitted by the first lens L1 is almost vertically incident on the object side of the second lens L2, which is conducive to the smooth transition of light, can reduce light energy loss, is conducive to the illumination of the peripheral field of view, and reduces the sensitivity of the lens. The third lens L3 has a positive focal power, and the object side is convex, which can match the concave surface of the image side of the second lens L2, which is conducive to a smoother transition of light entering from the second lens L2, reduces light energy loss, is conducive to improving resolution, and is conducive to a smoother trend of light with the rear lens. The fourth lens L4 has a positive focal power, which is conducive to converging the light emitted from the previous lens and making the light smoothly transition to the rear lens. The fifth lens L5 has a negative focal power, which has a divergent effect on the light. By controlling the focal length of the fifth lens L5, various aberrations caused by the positive lens and the negative lens in front can be effectively corrected. The sixth lens L6 has a positive focal power, which is conducive to converging the light. On the one hand, it can make the divergent light enter the rear optical system smoothly, and on the other hand, it can lower the position of the light incident on the subsequent optical system and reduce the rear port diameter; and under the condition that the diameter of the object side of the sixth lens L6 is the same, the purpose of reducing the diameter of the front port of the lens and miniaturizing the lens can be achieved. The seventh lens L7 has a positive focal power, which can ensure that the lens shape is smooth, and can make the light emitted from the sixth lens L6 further converge and smoothly enter the rear lens, which is conducive to reducing sensitivity and improving resolution. The eighth lens L8 has a negative focal power, so that the light passes through the image side of the eighth lens L8 and tends to diverge upward, which can make the light quickly accumulate at the height of the imaging surface, which is conducive to expanding the imaging range.

[0043] In addition, by setting the second lens L2 and the third lens L3 to form a first cemented lens, and the fourth lens L4 and the fifth lens L5 to form a second cemented lens, the air gap between the second lens L2 and the third lens L3, and the air gap between the fourth lens L4 and the fifth lens L5 can be effectively reduced, thereby helping to reduce the total length of the lens. In addition, the cemented lens can minimize or eliminate chromatic aberration, so that various aberrations of the fixed-focus lens can be fully corrected. Under the premise of compact structure, it can improve resolution, optimize optical properties such as distortion, reduce light loss caused by reflection between lenses, and increase illumination, thereby improving image quality and improving the clarity of lens imaging. In addition, the use of cemented lenses can also reduce the assembly components between the two lenses, simplify the assembly procedures in the lens manufacturing process, reduce costs, and reduce the tolerance sensitivity of the lens unit due to tilt / eccentricity caused during the assembly process.

[0044] The field stop is located between the first lens L1 and the second lens L2. The aperture of the field stop determines the aperture size, which is conducive to effectively focusing the light entering the lens, reducing the lens aperture at the front of the lens, and reducing the sensitivity of the system. The vignetting stop is located between the sixth lens L6 and the seventh lens L7 to block light and improve the external field of view performance.

[0045] Therefore, the embodiment of the present invention adopts eight lenses, and by reasonably setting the optical focal length of each lens, it is conducive to realizing a fixed-focus lens with a large target surface, an ultra-large aperture and a long focal length. The focal length of the fixed-focus lens provided by this embodiment can be around 40mm, |optical distortion|<1.5%, image side F#=2.0, the maximum image height of the lens is 9.12mm, and while achieving infrared confocality in the near-infrared band of 830nm~940nm, it has high resolution performance in both visible light and near-infrared bands.

[0046] Optionally, the object side surface of the second lens L2 is a concave surface or a convex surface, and the image side surface of the third lens L3 is a concave surface or a convex surface. When the object side surface of the second lens L2 is a concave surface, the light passing through the field aperture can be collected and transmitted to the third lens L3 after being diverged. When the object side surface of the second lens L2 is a convex surface, the light passing through the field aperture can be collected and transmitted to the third lens L3 after being converged. When the image side surface of the third lens L3 is a concave surface, the light can be diffused. When the image side surface of the third lens L3 is a convex surface, the light can be converged.

[0047] Optionally, the optical power of the first lens L1 is Optical power of fixed focal length lens The relationship between them is:

[0048] The refractive index ND1 of the first lens L1 satisfies the relation: 1.8 < ND1 < 2.1. Meeting this condition is beneficial to reducing the incident angle of light entering the optical system, shrinking the aperture of the optical system, thereby reducing the volume and weight of the optical system.

[0049] Optionally, the optical power of the second lens L2 The optical power of the third lens L3 and the optical power of the first cemented lens satisfy the relation:

[0050] The optical power of the second lens L2 The optical power of the third lens L3 The Abbe number vd2 of the second lens L2 and the Abbe number vd3 of the third lens L3 satisfy the relation: Meeting this condition is beneficial for the doublet lens to exert its ability to correct chromatic aberration of the optical system, thereby improving the resolution of the optical system.

[0051] Optionally, the optical power of the fourth lens L4 The optical power of the fifth lens L5 and the optical power of the second cemented lens satisfy the relation:

[0052] The optical power of the fourth lens L4 The optical power of the fifth lens L5 The Abbe number vd4 of the fourth lens L4 and the Abbe number vd5 of the fifth lens L5 satisfy the relation: Meeting this condition is beneficial for the doublet lens to exert its ability to correct chromatic aberration of the optical system, thereby improving the resolution of the optical system.

[0053] Optionally, the Abbe number vd3 of the third lens L3 satisfies the relation: 60 < vd3 < 96; the Abbe number vd4 of the fourth lens L4 satisfies the relation: 60 < vd4 < 96. Meeting this condition is beneficial for correcting the axial chromatic aberration of the system to achieve infrared confocal.

[0054] Optionally, the optical power of the sixth lens L6 The optical power of the seventh lens L7 The optical power of the eighth lens L8 The optical power of the fixed-focus lens satisfy the relation: It is beneficial to improve the resolution of the lens.

[0055] Optionally, the semi-aperture SDmax of the first lens L1 and the maximum image height H of the fixed-focus lens satisfy the relationship: 1 < SDmax / H < 1.2. This is beneficial for reducing the volume and weight of the overall optical system, adapting to more usage environments, and reducing the material cost of the lenses.

[0056] Optionally, the distance TTL from the center of the object side surface of the first lens L1 to the center of the imaging surface and the focal length f of the fixed-focus lens satisfy the relationship: 1.1 < TTL / f < 1.3. This is beneficial for reducing the volume and weight of the overall optical system, adapting to more usage environments, and reducing the material cost of the lenses.

[0057] The following uses specific embodiments to introduce the fixed-focus lens proposed in the embodiments of the present invention.

[0058] Table 1 Parameter table of each relationship in Embodiment 1 to Embodiment 3

[0059]

[0060]

[0061] Embodiment 1

[0062] Figure 1 is a schematic structural diagram of the fixed-focus lens provided in Embodiment 1 of the present invention. As Figure 1 shown, the fixed-focus lens includes: a convex-concave first lens L1 with a positive optical power, a field stop STO, a concave-concave second lens L2 with a negative optical power, a convex-convex third lens L3 with a positive optical power, a convex-convex fourth lens L4 with a positive optical power, a concave-concave fifth lens L5 with a negative optical power, a convex-convex sixth lens L6 with a positive optical power, a vignetting stop 10, a convex-convex seventh lens L7 with a positive optical power, and a concave-concave eighth lens L8 with a negative optical power; as well as a filter 20 and an image plane 30. The second lens L2 and the third lens L3 are cemented into a first cemented lens, the fourth lens L4 and the fifth lens L5 are cemented into a second cemented lens, and the first lens L1 to the eighth lens L8 are all glass spherical lenses. Among them, the maximum image height H in the fixed-focus lens of Embodiment 1 is 9.12 mm, the image-side F# is 2, the TTL is 48.6 mm, and the lens focal length f is 42 mm. The parameters of each lens in the fixed-focus lens of Embodiment 1 are shown in Table 2.

[0063] Table 2 Parameters of each lens in the fixed-focus lens of Embodiment 1

[0064]

[0065]

[0066] The surface numbers S1 to S19 in Table 2 are numbered according to the surface order 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; "STO" represents the aperture of the lens; 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 a space represents that the current position is air, and the refractive index is 1.

[0067] In this embodiment, the optical power of the first cemented lens is The focal length of the second doublet is -0.0268. It is -0.0163.

[0068] Figure 2 Schematic diagram of the full-frequency MTF of the mixed light band of the fixed-focus lens provided in the first embodiment of the present invention. Figure 2 As shown, the hybrid light band includes the 436nm to 940nm band. The horizontal axis is the number of line pairs, the vertical axis is the modulation value, the central field of view is 150lp / mm, reaching 50%, and the edge field of view is 150lp / mm, reaching 37%.

[0069] Figure 3 This is a schematic diagram of the full-frequency MTF of the fixed-focus lens in the infrared 850nm band provided by the first embodiment of the present invention. The horizontal axis is the number of line pairs, the vertical axis is the modulation value, the central field of view is 150lp / mm, reaching 45%, and the edge field of view is 150lp / mm, reaching 40%.

[0070] Figure 4 It is a schematic diagram of the center field defocus MTF of the mixed light and 850nm light of the fixed-focus lens provided in Example 1 of the present invention. Among them, the horizontal axis is the defocus amount, and the vertical axis is the modulation value. The two lines in the figure, the blue one is the center field defocus MTF of the mixed light, and the green one is the center field defocus MTF of the 850nm band. The difference between the horizontal axes corresponding to the peak values ​​of these two curves reflects the infrared confocal capability. The smaller the difference, the smaller the defocus amount of the infrared 850nm. From Figure 4 It can be seen that the difference between the two is between -3μm and 3μm. Figures 2 to 4 This shows that the fixed-focus lens has good resolution in both the mixed light band and the infrared band.

[0071] Figure 5 Schematic diagram of field curvature and distortion of a fixed-focus lens provided in Embodiment 1 of the present invention. In the coordinate system on the left side of the figure, the horizontal coordinate represents the magnitude of field curvature, in μm; the vertical coordinate represents the normalized image height, in no unit; T represents meridian, S represents sagittal; Figure 5It can be seen that the fixed-focus lens provided in this embodiment is effectively controlled in field curvature for light with a wavelength of 546nm, that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small (wherein, in the field curvature diagram on the left, the maximum field of view is 6.111 degrees, the sagittal field curvature = 0.0180mm, and the meridian field curvature = 0.0223mm). In the coordinate system on the right, the horizontal coordinate represents the magnitude of the distortion, in %, and the vertical coordinate represents the normalized image height, without a unit; Figure 5 It can be seen that the distortion of the lens provided in this embodiment (in the distortion diagram on the right, the maximum distortion = 1.48%).

[0072] Embodiment 2

[0073] Figure 6 is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 2 of the present invention. Figure 6 As shown, the fixed-focus lens comprises: a convex-concave first lens L1 with positive focal power, a field stop STO, a convex-concave second lens L2 with negative focal power, a convex-concave third lens L3 with positive focal power, a convex-convex fourth lens L4 with positive focal power, a concave-concave fifth lens L5 with negative focal power, a concave-convex sixth lens L6 with positive focal power, a vignetting stop 10, a convex-convex seventh lens L7 with positive focal power, and a concave-concave eighth lens L8 with negative focal power, which are arranged in sequence from the object side to the image side along the optical axis; as well as a filter 20 and an image plane 30, the second lens L2 and the third lens L3 are cemented into a first cemented lens, the fourth lens L4 and the fifth lens L5 are cemented into a second cemented lens, and the first lens L1 to the eighth lens L8 are all glass spherical lenses. The maximum image height H of the fixed-focus lens of the second embodiment is 9.12 mm, the image side F# is 2, the TTL is 48.98 mm, and the lens focal length f is 38 mm. The parameters of each lens in the fixed-focus lens of the second embodiment are shown in Table 3.

[0074] Table 3 Parameters of each lens in the fixed focus lens of Example 2

[0075] Surface number Surface type Radius of curvature thickness Refractive Index Abbe number Dispersion dPgF Semi-caliber 0 Physical surface Infinity Infinity S1 Standard surface 23.1514 2.468 1.9200 23.30 0.000 9.580 S2 Standard surface 50.0334 7.082 9.376 STO Standard surface Infinity 0.579 7.771 S4 Standard surface 33.0445 1.182 1.6500 33.90 0.000 7.455 S5 Standard surface 7.2619 4.400 1.5900 68.60 0.019 6.484 S6 Standard surface 29.3885 0.368 6.285 S7 Standard surface 15.4406 3.084 1.5900 76.46 0.0199 6.130 S8 Standard surface -21.6487 4.944 1.8500 23.80 0.000 5.871 S9 Standard surface 15.2194 1.263 4.699 S10 Standard surface -26.3435 4.601 1.8700 20.10 0.000 4.692 S11 Standard surface -21.1069 0.099 5.036 S12 Standard surface Infinity 0.099 4.950 S13 Standard surface 20.7357 4.960 1.8500 24.50 0.000 5.098 S14 Standard surface -18.0705 1.745 4.904 S15 Standard surface -13.9430 0.997 1.910 35.30 0.000 4.189 S16 Standard surface 41.6622 0.308 4.138 S17 Standard surface Infinity 1.5000 1.520 64.20 0.000 4.142 S18 Standard surface Infinity 9.3000 4.182 S19 Image plane Infinity -

[0076] The surface numbers S1 to S19 in Table 3 are numbered according to the surface order 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; "STO" represents the aperture of the lens; 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 a space represents that the current position is air, and the refractive index is 1.

[0077] In this embodiment, the optical power of the first cemented lens is The focal length of the second doublet is -0.0791. It is -0.0212.

[0078] Figure 7 Schematic diagram of the full-frequency MTF of the mixed light band of the fixed-focus lens provided in the second embodiment of the present invention. Figure 7 As shown, the hybrid light band includes the 436nm to 940nm band. The horizontal axis is the number of line pairs, the vertical axis is the modulation value, the central field of view is 150lp / mm, reaching 50%, and the edge field of view is 150lp / mm, reaching 42%.

[0079] Figure 8 This is a schematic diagram of the full-frequency MTF of the fixed-focus lens in the infrared 850nm band provided by the second embodiment of the present invention. The horizontal axis is the number of line pairs, the vertical axis is the modulation value, the central field of view is 150lp / mm, reaching 50%, and the edge field of view is 150lp / mm, reaching 46%.

[0080] Fig. 9 It is a schematic diagram of the center field defocus MTF of the mixed light and 850nm light of the fixed-focus lens provided in Example 2 of the present invention. Among them, the horizontal axis is the defocus amount, and the vertical axis is the modulation value. The two lines in the figure, the blue one is the center field defocus MTF of the mixed light, and the green one is the center field defocus MTF of the 850nm band. The difference between the horizontal axes corresponding to the peak values ​​of these two curves reflects the infrared confocal capability. The smaller the difference, the smaller the defocus amount of infrared 850nm. From Fig. 9 It can be seen that the difference between the two is between -3μm and 3μm. Figures 7 to 9 This shows that the fixed-focus lens has good resolution in both the mixed light band and the infrared band.

[0081] Fig.10 Schematic diagram of field curvature and distortion of a fixed-focus lens provided in Embodiment 2 of the present invention. In the coordinate system on the left side of the figure, the horizontal coordinate represents the magnitude of the field curvature, in μm; the vertical coordinate represents the normalized image height, in no unit; T represents the meridian, S represents the sagittal; Fig.10 It can be seen that the fixed-focus lens provided in this embodiment is effectively controlled in terms of field curvature for light with a wavelength of 546nm, that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small (wherein, in the field curvature diagram on the left, the maximum field of view is 6.776 degrees, the sagittal field curvature = 0.0259mm, and the meridian field curvature = 0.0227mm). In the coordinate system on the right, the horizontal coordinate represents the magnitude of the distortion, in %, and the vertical coordinate represents the normalized image height, without a unit; Fig.10 It can be seen that the distortion of the lens provided in this embodiment (in the distortion diagram on the right, the maximum distortion = 1.0%).

[0082] Embodiment 3

[0083] Fig.11 is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 3 of the present invention. Fig.11 As shown, the fixed-focus lens comprises: a convex-concave first lens L1 with positive focal power, a field stop STO, a convex-concave second lens L2 with negative focal power, a convex-concave third lens L3 with positive focal power, a convex-convex fourth lens L4 with positive focal power, a concave-concave fifth lens L5 with negative focal power, a convex-convex sixth lens L6 with positive focal power, a vignetting stop 10, a convex-convex seventh lens L7 with positive focal power, and a concave-concave eighth lens L8 with negative focal power, which are arranged in sequence from the object side to the image side along the optical axis; as well as a filter 20 and an image plane 30, the second lens L2 and the third lens L3 are cemented into a first cemented lens, the fourth lens L4 and the fifth lens L5 are cemented into a second cemented lens, and the first lens L1 to the eighth lens L8 are all glass spherical lenses. The maximum image height H of the fixed-focus lens of the third embodiment is 9.12 mm, the image side F# is 2, the TTL is 49.80 mm, and the lens focal length f is 40 mm. The parameters of each lens in the fixed-focus lens of the third embodiment are shown in Table 4.

[0084] Table 4 Parameters of each lens in the fixed focus lens of Example 3

[0085] Surface number Surface type Radius of curvature thickness Refractive Index Abbe number Dispersion dPgF Semi-caliber 0 Physical surface Infinity Infinity S1 Standard surface 22.9410 2.755 1.9200 20.70 0.000 10.100 S2 Standard surface 66.5869 6.310 9.940 STO Standard surface Infinity -0.003 8.034 S4 Standard surface 100.0000 0.999 1.6900 29.40 0.000 7.945 S5 Standard surface 11.2762 3.332 1.5000 81.60 0.0375 7.278 S6 Standard surface 89.6774 0.098 7.152 S7 Standard surface 15.1893 3.497 1.5000 74.30 0.009 6.920 S8 Standard surface -26.2111 4.948 1.9200 18.90 0.000 6.659 S9 Standard surface 16.0480 5.852 5.636 S10 Standard surface 62.2544 2.000 1.9200 19.70 0.000 6.034 S11 Standard surface -25.0596 1.289 6.029 S12 Standard surface Infinity 0.289 5.398 S13 Standard surface 13.3458 4.993 1.6400 36.10 0.000 5.412 S14 Standard surface -27.5446 0.807 4.694 S15 Standard surface -24.5078 1.030 1.910 35.30 0.000 4.250 S16 Standard surface 11.2631 0.803 3.937 S17 Standard surface Infinity 1.5000 1.520 64.20 0.000 3.943 S18 Standard surface Infinity 9.3000 4.001 S19 Image plane Infinity -

[0086] The surface numbers S1 to S19 in Table 4 are numbered according to the surface order 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; "STO" represents the aperture of the lens; the radius of curvature (mm) 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 (mm) 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 a space represents that the current position is air, and the refractive index is 1.

[0087] In this embodiment, the optical power of the first cemented lens is The focal length of the second doublet is -0.0159. It is -0.033.

[0088] Fig.12 Schematic diagram of the full-frequency MTF of the mixed light band of the fixed-focus lens provided in the third embodiment of the present invention. Fig.12 As shown, the hybrid light band includes the 436nm to 940nm band. The horizontal axis is the number of line pairs, the vertical axis is the modulation value, the central field of view is 150lp / mm, reaching 50%, and the edge field of view is 150lp / mm, reaching 50%.

[0089] Fig.13This is a schematic diagram of the full-frequency MTF of the infrared 850nm band of the fixed-focus lens provided in Example 3 of the present invention. The horizontal axis is the number of line pairs, the vertical axis is the modulation value, the central field of view is 150lp / mm, reaching 50%, and the edge field of view is 150lp / mm, reaching 50%.

[0090] Fig.14 It is a schematic diagram of the center field defocus MTF of the mixed light and 850nm light of the fixed-focus lens provided in Example 3 of the present invention. Among them, the horizontal axis is the defocus amount, and the vertical axis is the modulation value. The two lines in the figure, the blue one is the center field defocus MTF of the mixed light, and the green one is the center field defocus MTF of the 850nm band. The difference between the horizontal axes corresponding to the peak values ​​of these two curves reflects the infrared confocal capability. The smaller the difference, the smaller the defocus amount of infrared 850nm. From Fig.14 It can be seen that the difference between the two is between -3μm and 3μm. Figure 12 to Figure 14 This shows that the fixed-focus lens has good resolution in both the mixed light band and the infrared band.

[0091] Fig.15 Schematic diagram of field curvature and distortion of a fixed focus lens provided in Embodiment 3 of the present invention. In the coordinate system on the left side of the figure, the horizontal coordinate represents the magnitude of field curvature, in μm; the vertical coordinate represents the normalized image height, in no unit; T represents meridian, S represents sagittal; Fig.15 It can be seen that the fixed-focus lens provided in this embodiment is effectively controlled in terms of field curvature for light with a wavelength of 546nm, that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small (wherein, in the field curvature diagram on the left, the maximum field of view is 6.404 degrees, the sagittal field curvature = 0.0064mm, and the meridional field curvature = 0.0045mm). In the coordinate system on the right, the horizontal coordinate represents the magnitude of the distortion, in %, and the vertical coordinate represents the normalized image height, without a unit; Fig.15 It can be seen that the distortion of the lens provided in this embodiment (in the distortion diagram on the right, the maximum distortion = 1.49%).

[0092] An embodiment of the present invention further provides a monitoring device, comprising the fixed-focus lens provided by any embodiment of the present invention.

[0093] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A fixed-focus lens, characterized in that: Comprising: A positive meniscus first lens with positive optical power, a field stop, a second lens with negative optical power, a third lens with positive optical power, a positive biconvex fourth lens, a negative biconcave fifth lens, a sixth lens with positive optical power, a vignetting stop, a positive biconvex seventh lens and a negative biconcave eighth lens, which are arranged in sequence from the object side to the image side along the optical axis; Wherein, the image side surface of the second lens is concave, the object side surface of the third lens is convex, the image side surface of the sixth lens is convex, the second lens and the third lens are cemented into a first cemented lens, and the fourth lens and the fifth lens are cemented into a second cemented lens.

2. The fixed-focus lens according to claim 1, characterized in that: The object side surface of the second lens is concave or convex, and the image side surface of the third lens is concave or convex.

3. The fixed-focus lens according to claim 1, characterized in that: The optical power φ1 of the first lens and the optical power φ of the fixed-focus lens satisfy the relational expression: 0.8 < φ1 / φ < 1.5; The refractive index ND1 of the first lens satisfies the relational expression: 1.8 < ND1 < 2.

1.

4. The fixed-focus lens according to claim 1, characterized in that: The optical power φ2 of the second lens, the optical power φ3 of the third lens and the optical power φ23 of the first cemented lens satisfy the relational expression: |φ2 + φ3 - φ23| < 0.1; The optical power φ2 of the second lens, the optical power φ3 of the third lens, the Abbe number vd2 of the second lens and the Abbe number vd3 of the third lens satisfy the relational expression: |100 * (φ2 / vd2 + φ3 / vd3)| < 0.

5.

5. The fixed-focus lens according to claim 1, wherein: The optical power φ4 of the fourth lens, the optical power φ5 of the fifth lens and the optical power φ45 of the second cemented lens satisfy the relational expression: |φ4 + φ5 - φ45| < 0.1; The optical power φ4 of the fourth lens, the optical power φ5 of the fifth lens, the Abbe number vd4 of the fourth lens and the Abbe number vd5 of the fifth lens satisfy the relational expression: |100 * (φ4 / vd4 + φ5 / vd5)| < 0.

5.

6. The fixed-focus lens according to claim 1, wherein: The Abbe number vd3 of the third lens satisfies the relational expression: 60 < vd3 < 96; the Abbe number vd4 of the fourth lens satisfies the relational expression: 60 < vd4 < 96.

7. The fixed-focus lens according to claim 1, wherein: The optical power φ6 of the sixth lens, the optical power φ7 of the seventh lens, the optical power φ8 of the eighth lens and the optical power φ of the fixed-focus lens satisfy the relational expression: -0.5 < φ6 / φ + φ7 / φ + φ8 / φ < 0.

35.

8. The fixed-focus lens according to claim 1, wherein: The semi-aperture SDmax of the first lens and the maximum image height H of the fixed-focus lens satisfy the relational expression: 1 < SDmax / H < 1.

2.

9. The fixed-focus lens according to claim 1, wherein: The distance TTL from the center of the object side surface of the first lens to the center of the imaging surface and the focal length f of the fixed-focus lens satisfy the relational expression: 1.1 < TTL / f < 1.

3.

10. A monitoring device, characterized in that: Comprising the fixed-focus lens according to any one of claims 1-9.

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