An imaging lens

Abstract

The present invention discloses an imaging lens, which comprises a first lens, a second lens, a third lens, an aperture, a fourth lens, a fifth lens, and a sixth lens sequentially arranged along an optical axis from an object side to an image side. The first lens has a negative diopter, the second lens has a negative diopter, the third lens has a positive diopter, the fourth lens has a positive diopter, the fifth lens has a negative diopter, and the sixth lens has a positive diopter. The lens satisfies: 5 < TTL / F < 5.5, where TTL is the overall optical length of the lens and F is the focal length of the lens. The imaging lens of the present invention is mainly used in the security field. It consists of six lenses, with fewer lens elements, a smaller overall volume of the lens, and a high resolution of the lens. At the same time, the lens has the characteristics of a large target surface and low distortion.

Description

Technical Field

[0001] The present invention relates to the technical field of optical lenses, and more particularly, to an imaging lens. Background Art

[0002] With the continuous progress of science and technology and the continuous development of society, in recent years, optical imaging lenses have also developed rapidly and are widely used in various fields such as smart phones, tablet computers, video conferencing, vehicle-mounted monitoring, and security monitoring. In the field of security monitoring, with the continuous improvement of technical indicators, while requiring the imaging area of the lens to match the imaging element with a large target surface, higher requirements are put forward for the volume and imaging quality of the lens. However, the existing security lens designs usually cannot simultaneously possess the advantages of a large target surface and a small volume while maintaining the imaging quality of the lens.

[0003] In view of this, the inventor of the present application has invented an imaging lens mainly used for security systems. Summary of the Invention

[0004] The purpose of the present invention is to provide an imaging lens with a small volume, a large target surface, high-definition imaging, and low distortion.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: An imaging lens includes a first lens, a second lens, a third lens, an aperture stop, a fourth lens, a fifth lens, and a sixth lens sequentially arranged along an optical axis from the object side to the image side. Each of the first lens to the sixth lens includes an object side facing the object side and allowing imaging light to pass through, and an image side facing the image side and allowing imaging light to pass through;

[0006] The first lens has a negative refractive power, and the object side of the first lens is a convex surface, and the image side is a concave surface;

[0007] The second lens has a negative refractive power, and the object side of the second lens is a concave surface, and the image side is a convex surface;

[0008] The third lens has a positive refractive power, and the object side of the third lens is a convex surface, and the image side is a convex surface;

[0009] The fourth lens has a positive refractive power, and the object side of the fourth lens is a convex surface, and the image side is a convex surface;

[0010] The fifth lens has a negative refractive power, and the object side of the fifth lens is a concave surface, and the image side is a convex surface;

[0011] The sixth lens has a positive refractive power, and the object side of the sixth lens is a convex surface, and the image side is a convex surface;

[0012] This lens satisfies: 5 < TTL / F < 5.5, where TTL is the total optical length of the lens, and F is the focal length of the lens.

[0013] Furthermore, the lens satisfies: TTL < 16 mm, where TTL is the overall optical length of the lens.

[0014] Furthermore, the lens satisfies: F < 3 mm, where F is the focal length of the lens.

[0015] Furthermore, the lens satisfies: nd2 > 2.0, where nd2 is the refractive index of the second lens.

[0016] Furthermore, the lens satisfies: |nd5 - nd4| > 0.25, |vd4 - vd5| > 65, where nd4 and nd5 are the refractive indices of the fourth lens and the fifth lens respectively, and vd4 and vd5 are the dispersion coefficients of the fourth lens and the fifth lens respectively.

[0017] Furthermore, the lens satisfies: 1.5 < nd1 < 1.6, 60 < vd1 < 80, 2.0 < nd2 < 2.2, 19 < vd2 < 30, 1.7 < nd3 < 1.8, 50 < vd3 < 60, 1.4 < nd4 < 1.5, 90 < vd4 < 95, 1.6 < nd5 < 1.7, 15 < vd5 < 25, 1.5 < nd6 < 1.6, 55 < vd6 < 60, where nd1, nd2, nd3, nd4, nd5, and nd6 are the refractive indices of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens respectively, and vd1, vd2, vd3, vd4, vd5, and vd6 are the dispersion coefficients of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens respectively.

[0018] Furthermore, the first lens, the second lens, the third lens, and the fourth lens are all glass spherical lenses, and the fifth lens and the sixth lens are both plastic aspherical lenses.

[0019] Furthermore, the effective diameters of the first lens to the sixth lens are all less than 7.4 mm.

[0020] After adopting the above technical solution, compared with the prior art, the present invention has the following advantages:

[0021] The imaging lens of the present invention is mainly used in the security field. It is composed of six lenses, with fewer lens elements, a smaller overall volume of the lens, and a high resolution. At the same time, the lens has the characteristics of a large target surface and low distortion. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the optical path diagram of Embodiment 1 of the present invention;

[0023] Figure 2: This is an MTF curve diagram of the lens under visible light in Example 1 of the present invention;

[0024] Figure 3 Graph showing field curvature and distortion of the lens under visible light in Example 1 of the present invention;

[0025] Figure 4 1 is a graph showing the magnification chromatic aberration curve of the lens under visible light in Example 1 of the present invention;

[0026] Figure 5 This is a light path diagram of Example 2 of the present invention;

[0027] Figure 6 This is an MTF curve diagram of the lens under visible light in Example 2 of the present invention;

[0028] Figure 7 Graph showing field curvature and distortion of the lens under visible light in Example 2 of the present invention;

[0029] Figure 8 1 is a graph showing the magnification chromatic aberration curve of the lens under visible light in Example 2 of the present invention;

[0030] Figure 9 This is a light path diagram of Example 3 of the present invention;

[0031] Figure 10 : This is an MTF curve diagram of the lens under visible light in Example 3 of the present invention;

[0032] Figure 11 Graph showing field curvature and distortion of the lens under visible light in Example 3 of the present invention;

[0033] Figure 12 : This is a graph showing the magnification chromatic aberration curve of the lens under visible light in Example 3 of the present invention;

[0034] Figure 13 This is a light path diagram of Example 4 of the present invention;

[0035] Figure 14 This is an MTF curve diagram of the lens under visible light in Example 4 of the present invention;

[0036] Figure 15 Graph showing field curvature and distortion of the lens under visible light in Example 4 of the present invention;

[0037] Figure 16 This is a graph showing the magnification chromatic aberration curve of the lens under visible light in Example 4 of the present invention.

[0038] Description of reference numerals:

[0039] 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Fifth lens; 6. Sixth lens; 7. Aperture diaphragm; 8. Protective glass & filter. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0041] Here, "a lens having a positive (or negative) refractive power" means that the lens's paraxial refractive power, calculated using Gaussian optics theory, is positive (or negative). The "object-side (or image-side) of a lens" is defined as the specific area of the lens surface through which the imaging light passes. The concavity or convexity of a lens's surface can be determined using the same method commonly used by those skilled in the art: the sign of the radius of curvature (abbreviated as R value). R values are commonly used in optical design software such as Zemax or CodeV. R values are also commonly found in lens data sheets within optical design software. For the object-side surface, a positive R value indicates a convex surface; a negative R value indicates a concave surface. Conversely, for the image-side surface, a positive R value indicates a concave surface; a negative R value indicates a convex surface.

[0042] The present invention discloses an imaging lens, comprising a first lens 1, a second lens 2, a third lens 3, an aperture 7, a fourth lens 4, a fifth lens 5, and a sixth lens 6, arranged in sequence along an optical axis from the object side to the image side. The first lens 1 to the sixth lens 6 each include an object-side surface facing the object side and through which imaging light passes, and an image-side surface facing the image side and through which imaging light passes.

[0043] The first lens 1 has a negative refractive power, and the object side surface of the first lens 1 is convex, and the image side surface is concave;

[0044] The second lens element 2 has a negative refractive power, and the object side surface of the second lens element 2 is concave, and the image side surface is convex;

[0045] The third lens element 3 has positive refractive power, and the object-side surface and image-side surface of the third lens element 3 are convex;

[0046] The fourth lens element 4 has positive refractive power, and the object-side surface and image-side surface of the fourth lens element 4 are convex.

[0047] The fifth lens element 5 has a negative refractive power, and the object-side surface of the fifth lens element 5 is concave, and the image-side surface is convex;

[0048] The sixth lens 6 has a positive refractive power, and the object side surface of the sixth lens 6 is convex, and the image side surface is convex.

[0049] In this lens, by continuously using two negative refractive power lenses (the first lens 1 and the second lens 2) to compress the field angle and expand the beam of light, the light can be deflected towards the direction of the optical axis, effectively reducing the outer diameter size of the subsequent lenses, and taking into account the large field angle and small volume of the lens.

[0050] In this lens, by designing the sixth lens 6 to have a positive refractive power and setting the image side surface of the sixth lens 6 to be convex, it is beneficial for the incident light beams of each field to be deflected and converged on the imaging surface after passing through the optical system, so that the spherical aberration, chromatic aberration, field curvature, and astigmatism of the optical system are better suppressed.

[0051] In this lens, the aperture stop 7 is located between the third lens 3 and the fourth lens 4. By adjusting the distance between the lens and the aperture stop 7, astigmatism can be corrected, and especially coma, distortion, and lateral aberration can be well corrected.

[0052] This lens satisfies: nd2 > 2.0, where nd2 is the refractive index of the second lens 2. Using a high refractive index material for the second lens 2 can reduce the lens spacing and effectively shorten the total length of the optical system.

[0053] This lens satisfies: |nd5 - nd4| > 0.25, |vd4 - vd5| > 65, where nd4 and nd5 are the refractive indices of the fourth lens 4 and the fifth lens 5 respectively, and vd4 and vd5 are the dispersion coefficients of the fourth lens 4 and the fifth lens 5 respectively. Using a positive focal power lens (the fourth lens 4) with a high dispersion coefficient material and a negative focal power lens (the fifth lens 5) with a low dispersion coefficient material in combination can effectively correct the chromatic aberration of the system and improve the imaging quality.

[0054] Specifically, this lens satisfies: 1.5 < nd1 < 1.6, 60 < vd1 < 80, 2.0 < nd2 < 2.2, 19 < vd2 < 30, 1.7 < nd3 < 1.8, 50 < vd3 < 60, 1.4 < nd4 < 1.5, 90 < vd4 < 95, 1.6 < nd5 < 1.7, 15 < vd5 < 25, 1.5 < nd6 < 1.6, 55 < vd6 < 60, where nd1, nd2, nd3, nd4, nd5, and nd6 are the refractive indices of the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, and the sixth lens 6 respectively, and vd1, vd2, vd3, vd4, vd5, and vd6 are the dispersion coefficients of the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, and the sixth lens 6 respectively.

[0055] The lens satisfies: 5 < TTL / F < 5.5, where TTL is the total optical length of the lens and F is the focal length of the lens. When the lens satisfies this relational expression, the volume of the optical system can be controlled. While ensuring the imaging quality, a small volume is taken into account. If TTL / F < 5, the volume of the lens is likely to be too small and the imaging quality will also decrease. When TTL / F > 5.5, the volume of the lens is likely to be too large and the miniaturization of the lens is not ideal.

[0056] The lens satisfies: TTL < 16 mm, F < 3 mm, where TTL is the total optical length of the lens and F is the focal length of the lens; meanwhile, the effective diameters of the first lens 1 to the sixth lens 6 are all less than 7.4 mm. The overall volume of the lens is small.

[0057] In this lens, the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4 are all glass spherical lenses, and the fifth lens 5 and the sixth lens 6 are both plastic aspherical lenses. The fifth lens 5 and the sixth lens 6 use aspherical lenses. By increasing the order of the even aspherical surface and using it, the utilization efficiency of each lens is improved, thereby reducing the number of lenses used, effectively reducing the volume of the lens, and also effectively controlling the peripheral distortion.

[0058] Among them, the fifth lens 5 and the sixth lens 6 are aspherical lenses, and both surfaces of the aspherical lens are aspherical. The equation of the surface curve of the aspherical lens is expressed as follows:

[0059]

[0060] Among them,

[0061] z: the depth of the aspherical surface (the vertical distance between the point on the aspherical surface at a distance y from the optical axis and the tangent plane at the vertex of the aspherical surface on the optical axis);

[0062] c: the curvature of the aspherical vertex (the vertex curvature);

[0063] K: the conic constant (Conic Constant);

[0064] radial distance;

[0065] rn: the normalized radius (normalization radius (NRADIUS));

[0066] u: r / rn;

[0067] am: the mth Qcon coefficient (is the mth Qcon coefficient);

[0068] Qmcon: the mth Qcon polynomial.

[0069] The MTF of this lens is greater than 0.4 at a frequency of 140lp / mm across the entire field of view, demonstrating excellent imaging quality. The lens target surface height is >7.2mm, compatible with a 1 / 2.5" sensor and boasts a large target surface. The lens F-Theta distortion is <6%, ensuring the image quality is not affected by excessive distortion.

[0070] The imaging lens of the present invention will be described in detail below with reference to specific embodiments.

[0071] Example 1

[0072] Reference Figure 1 As shown, the present invention discloses an imaging lens, comprising a first lens 1, a second lens 2, a third lens 3, an aperture 7, a fourth lens 4, a fifth lens 5, and a sixth lens 6, which are arranged in sequence along an optical axis from the object side to the image side. The first lens 1 to the sixth lens 6 each include an object-side surface facing the object side and allowing imaging light to pass through, and an image-side surface facing the image side and allowing imaging light to pass through.

[0073] The first lens 1 has a negative refractive power, and the object side surface of the first lens 1 is convex, and the image side surface is concave;

[0074] The second lens element 2 has a negative refractive power, and the object side surface of the second lens element 2 is concave, and the image side surface is convex;

[0075] The third lens element 3 has positive refractive power, and the object-side surface and image-side surface of the third lens element 3 are convex;

[0076] The fourth lens element 4 has positive refractive power, and the object-side surface and image-side surface of the fourth lens element 4 are convex.

[0077] The fifth lens element 5 has a negative refractive power, and the object-side surface of the fifth lens element 5 is concave, and the image-side surface is convex;

[0078] The sixth lens element 6 has positive refractive power, and the object-side surface and the image-side surface of the sixth lens element 6 are convex.

[0079] The detailed optical data of this specific embodiment are shown in Table 1-1.

[0080] Table 1-1 Detailed optical data of Example 1

[0081]

[0082] The aspheric surface data of this embodiment is shown in Table 1-2.

[0083] Table 1-2 Aspheric surface data of Example 1

[0084]

[0085] In this embodiment, please refer to the MTF curve of the lens under visible light. Figure 2 As can be seen from the figure, when the spatial frequency of this lens reaches 140lp / mm, the MTF value is greater than 0.4, the imaging quality is excellent, and the resolution of the lens is high.

[0086] Please refer to the field curvature and distortion diagram of the lens under visible light. Figure 3 As can be seen from the figure, the field curvature curves of each wavelength coincide, and the lens chromatic aberration correction is good; the distortion is <|-6%|, the distortion is small, and the imaging picture will not affect the viewing experience due to excessive distortion.

[0087] Please refer to the chromatic aberration curve of the lens under visible light. Figure 4 ,As can be seen from the figure, the magnification chromatic difference is less than 4um, the chromatic difference is small, and the image ,color reproduction is high.

[0088] Example 2

[0089] like Figure 5 As shown, the present embodiment is different from the embodiment 1 mainly in optical parameters such as the curvature radius of each lens surface and the lens thickness.

[0090] The detailed optical data of this specific embodiment are shown in Table 2-1.

[0091] Table 2-1 Detailed optical data of Example 2

[0092]

[0093] The aspheric surface data in this embodiment is shown in Table 2-2.

[0094] Table 2-2 Aspheric surface data of Example 2

[0095]

[0096] In this embodiment, please refer to the MTF curve of the lens under visible light. Figure 6 As can be seen from the figure, when the spatial frequency of this lens reaches 140lp / mm, the MTF value is greater than 0.4, the imaging quality is excellent, and the resolution of the lens is high.

[0097] Please refer to the field curvature and distortion diagram of the lens under visible light. Figure 7 As can be seen from the figure, the field curvature curves of each wavelength coincide, and the lens chromatic aberration correction is good; the distortion is <|-6%|, the distortion is small, and the imaging picture will not affect the viewing experience due to excessive distortion.

[0098] Please refer to the chromatic aberration curve of the lens under visible light. Figure 8 ,As can be seen from the figure, the magnification chromatic difference is less than 4um, the chromatic difference is small, and the image ,color reproduction is high.

[0099] Example 3

[0100] like Figure 9 As shown, the present embodiment is different from the embodiment 1 mainly in optical parameters such as the curvature radius of each lens surface and the lens thickness.

[0101] The detailed optical data of this specific embodiment are shown in Table 3-1.

[0102] Table 3-1 Detailed optical data of Example 3

[0103]

[0104] The aspheric surface data in this embodiment is shown in Table 3-2.

[0105] Table 3-2 Aspheric surface data of Example 3

[0106]

[0107] In this embodiment, please refer to the MTF curve of the lens under visible light. Figure 10 As can be seen from the figure, when the spatial frequency of this lens reaches 140lp / mm, the MTF value is greater than 0.4, the imaging quality is excellent, and the resolution of the lens is high.

[0108] Please refer to the field curvature and distortion diagram of the lens under visible light. Figure 11 As can be seen from the figure, the field curvature curves of each wavelength coincide, and the lens chromatic aberration correction is good; the distortion is <|-6%|, the distortion is small, and the imaging picture will not affect the viewing experience due to excessive distortion.

[0109] Please refer to the chromatic aberration curve of the lens under visible light. Figure 12 ,As can be seen from the figure, the magnification chromatic difference is less than 4um, the chromatic difference is small, and the image ,color reproduction is high.

[0110] Example 4

[0111] like Figure 13 As shown, the present embodiment is different from the embodiment 1 mainly in optical parameters such as the curvature radius of each lens surface and the lens thickness.

[0112] The detailed optical data of this specific embodiment are shown in Table 4-1.

[0113] Table 4-1 Detailed optical data of Example 4

[0114]

[0115] The aspheric surface data of this embodiment is shown in Table 4-2.

[0116] Table 4-2 Aspheric surface data of Example 4

[0117]

[0118] In this embodiment, please refer to the MTF curve of the lens under visible light. Figure 14 As can be seen from the figure, when the spatial frequency of this lens reaches 140lp / mm, the MTF value is greater than 0.4, the imaging quality is excellent, and the resolution of the lens is high.

[0119] Please refer to the field curvature and distortion diagram of the lens under visible light. Figure 15 As can be seen from the figure, the field curvature curves of each wavelength coincide, and the lens chromatic aberration correction is good; the distortion is <|-6%|, the distortion is small, and the imaging picture will not affect the viewing experience due to excessive distortion.

[0120] Please refer to the chromatic aberration curve of the lens under visible light. Figure 16 ,As can be seen from the figure, the magnification chromatic difference is less than 4um, the chromatic difference is small, and the image ,color reproduction is high.

[0121] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. An imaging lens, characterized in that: It includes a first lens, a second lens, a third lens, an aperture, a fourth lens, a fifth lens, and a sixth lens that are sequentially arranged along an optical axis from the object side to the image side. Each of the first lens to the sixth lens includes an object side facing the object side through which imaging light passes and an image side facing the image side through which imaging light passes; The first lens has a negative refractive power, and the object side of the first lens is convex, and the image side is concave; The second lens has a negative refractive power, and the object side of the second lens is concave, and the image side is convex; The third lens has a positive refractive power, and the object side of the third lens is convex, and the image side is convex; The fourth lens has a positive refractive power, and the object side of the fourth lens is convex, and the image side is convex; The fifth lens has a negative refractive power, and the object side of the fifth lens is concave, and the image side is convex; The sixth lens has a positive refractive power, and the object side of the sixth lens is convex, and the image side is convex; This lens satisfies: 5 < TTL / F < 5.5, where TTL is the overall optical length of the lens and F is the focal length of the lens.

2. The imaging lens according to claim 1, wherein: This lens satisfies: TTL < 16 mm, where TTL is the overall optical length of the lens.

3. The imaging lens according to claim 1 or 2, wherein: This lens satisfies: F < 3 mm, where F is the focal length of the lens.

4. The imaging lens according to claim 1, wherein: This lens satisfies: nd2 > 2.0, where nd2 is the refractive index of the second lens.

5. The imaging lens according to claim 1 or 4, wherein: This lens satisfies: 1.5 < nd1 < 1.6, 60 < vd1 < 80, 2.0 < nd2 < 2.2, 19 < vd2 < 30, 1.7 < nd3 < 1.8, 50 < vd3 < 60, 1.4 < nd4 < 1.5, 90 < vd4 < 95, 1.6 < nd5 < 1.7, 15 < vd5 < 25, 1.5 < nd6 < 1.6, 55 < vd6 < 60, where nd1, nd2, nd3, nd4, nd5, nd6 are the refractive indices of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens respectively, and vd1, vd2, vd3, vd4, vd5, vd6 are the dispersion coefficients of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens respectively.

6. The imaging lens according to claim 1, wherein: The first lens, the second lens, the third lens, and the fourth lens are all glass spherical lenses, and the fifth lens and the sixth lens are both plastic aspherical lenses.

7. The imaging lens according to claim 1, wherein: The effective diameters of the first lens to the sixth lens are all less than 7.4 mm.

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