A fisheye security lens

Abstract

The present invention relates to the field of security lenses, and in particular to a fisheye security lens, which comprises, from the object side to the image side, a first lens, a second lens, a third lens, a fourth lens, an aperture, a fifth lens, a sixth lens, a seventh lens, and an eighth lens in sequence along an optical axis; the first to eighth lenses 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; and meet the following conditions: 1.73<nd1<1.80, 45<vd1<50, 1.75<nd2<2.00, 35<vd2<50, and 1.55<nd5<1.60, 68<vd5<69; the first, second, and fifth lenses are made of low-refractive-index, high-Abbe-number materials, and can correct off-axis astigmatism and off-axis chromatic aberration of magnification at wide angles.

Description

Technical Field

[0001] The present invention relates to the field of security lenses, and in particular to a fisheye security lens. Background Art

[0002] Security surveillance systems use optical fiber, coaxial cable, or microwaves to transmit video signals within a closed loop. From camera to image display and recording, they form a self-contained, complete system. They provide a real-time, vivid, and realistic view of the monitored object, replacing manual surveillance in harsh environments. Security lenses play a crucial role in surveillance systems. Patent application number 202222721327.0, titled "A Day / Night Athermal Glass-Plastic Hybrid Fisheye Lens," discloses a six-element fisheye lens. This lens achieves a relative illumination of only approximately 45% at its maximum field of view, and its MTF curve only reaches above 0.25 at a spatial frequency of 125 l p / mm. This lens suffers from a common problem with conventional security lenses: while the image center is bright, the brightness decreases gradually from the center toward the periphery, resulting in vignetting, color distortion, and blurred images. Summary of the Invention

[0003] In order to overcome the shortcomings of the existing technology, the present invention provides a fisheye security lens that can solve the technical problems of large distortion, severe distortion of the external field image, and low resolution under the premise of a large field of view.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] A fisheye security lens, characterized in that it includes, from the object side to the image side along an optical axis, a first lens, a second lens, a third lens, a fourth lens, an aperture, a fifth lens, a sixth lens, a seventh lens, and an eighth lens; each of the first to eighth lenses includes 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;

[0006] The first lens has negative optical power, a convex object-side surface, and a concave image-side surface;

[0007] The second lens has negative optical power, a convex object-side surface, and a concave image-side surface;

[0008] The third lens has negative optical power, a concave object-side surface, and a concave image-side surface;

[0009] The fourth lens has positive refractive power, a convex object-side surface, and a concave image-side surface;

[0010] The fifth lens has positive refractive power, a convex object-side surface, and a convex image-side surface;

[0011] The sixth lens has positive refractive power, a concave object-side surface, and a convex image-side surface;

[0012] The optical power of the seventh lens is opposite to that of the eighth lens;

[0013] And meet the following conditions:

[0014] 1.73<nd1<1.80, 45<vd1<50, 1.75<nd2<2.00, 35<vd2<50 and 1.55<nd5<1.60, 68<vd5<69; the nd1, nd2 and nd5 are the refractive indices of the first lens, the second lens and the fifth lens respectively, and the vd1, vd2 and vd5 are the Abbe coefficients of the first lens, the second lens and the fifth lens respectively.

[0015] Furthermore, the following conditional formula is met: 3.3<|f1 / f|<4.0, 3.0<|f2 / f|<6.5, 1.5<|f3 / f|<3.2, 2.0<|f4 / f|<3.5, 3.3<|f5 / f|<10.0, 2.5<|f6 / f|<4.2, 3.5<|f7 / f|<7.5, 3.5<|f8 / f|<7, where f1 to f8 are the focal lengths of the first lens to the eighth lens respectively, and f is the focal length of the fisheye security lens.

[0016] Furthermore, the following conditional expressions are met: |f1|<20, |f2|<25, |f3|<10, |f4|<15, |f5|<35, |f6|<15, |f7|<25, |f8|<25, where f1 to f8 are focal lengths of the first to eighth lenses, respectively.

[0017] Furthermore, the following conditional formula is met: 70<vd5+vd6<100, where vd5 and vd6 are the Abbe coefficients of the fifth lens and the sixth lens respectively.

[0018] Furthermore, the following condition is met: 6.01≤TTL / AAG, where TTL is the distance between the object side surface of the first lens and the imaging surface on the optical axis, and AAG is the sum of three air gaps on the optical axis between the first lens to the fourth lens.

[0019] Furthermore, the following conditional formula is met: ALT<6.51, ALT=CT1+CT2+CT3+CT4, and CT1 to CT4 are the center thicknesses of the first to fourth lenses, respectively.

[0020] Furthermore, the following conditions are met: TTL / F<15.05 and TTL<27.82mm, where TTL is the distance from the object side of the first lens to the imaging plane on the optical axis, and F is the clear aperture of the fisheye security lens.

[0021] Furthermore, the image-side surface of the fifth lens and the object-side surface of the sixth lens are cemented together to form a cemented lens group.

[0022] Furthermore, the first lens, the second lens, the fifth lens and the sixth lens are glass spherical lenses, and the third lens, the fourth lens, the seventh lens and the eighth lens are plastic aspherical lenses.

[0023] Furthermore, the surface shape of the object-side surface of the seventh lens is opposite to the surface shape of the image-side surface, the surface shape of the object-side surface of the seventh lens is the same as the surface shape of the object-side surface of the eighth lens, and the surface shape of the image-side surface of the seventh lens is opposite to the surface shape of the image-side surface of the eighth lens.

[0024] Furthermore, the object-side surface of the seventh lens is convex, and the image-side surface is concave; the object-side surface of the eighth lens is convex, and the image-side surface is convex.

[0025] Furthermore, the object-side surface of the seventh lens is concave, and the image-side surface is convex; the object-side surface of the eighth lens is concave, and the image-side surface is concave.

[0026] The beneficial effects of the present invention are:

[0027] In this solution, the first, second, and fifth lenses are made of low-refractive-index, high-Abbe-number materials to correct for off-axis astigmatism and wide-angle chromatic aberration. The combination of four glass spherical surfaces and four plastic aspherical surfaces enhances image quality, corrects for temperature drift, and significantly improves relative illumination. This results in a fisheye security lens with an MTF greater than 0.38 at all viewing angles at a spatial frequency of 100 l p / mm, demonstrating excellent imaging performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 Light path diagram of the fisheye security lens according to the first embodiment of the present invention;

[0030] Figure 2 MTF curve diagram of the fisheye security lens according to the first embodiment of the present invention;

[0031] Figure 3 A defocus curve diagram of the fisheye security lens according to the first embodiment of the present invention;

[0032] Figure 4 A relative illumination curve diagram of the fisheye security lens according to the first embodiment of the present invention;

[0033] Figure 5 A longitudinal chromatic aberration curve of the fisheye security lens according to the first embodiment of the present invention;

[0034] Figure 6 Field curvature and distortion diagram of the fisheye security lens according to Example 1 of the present invention;

[0035] Figure 7 Light path diagram of the fisheye security lens according to the second embodiment of the present invention;

[0036] Figure 8 MTF curve diagram of the fisheye security lens according to the second embodiment of the present invention;

[0037] Figure 9 A defocus curve diagram of the fisheye security lens according to the second embodiment of the present invention;

[0038] Figure 10 A relative illumination curve diagram of the fisheye security lens according to the second embodiment of the present invention;

[0039] Figure 11 A longitudinal chromatic aberration curve of the fisheye security lens according to the second embodiment of the present invention;

[0040] Figure 12 Field curvature and distortion diagram of the fisheye security lens described in Example 2 of the present invention;

[0041] Figure 13 Light path diagram of the fisheye security lens according to the third embodiment of the present invention;

[0042] Figure 14 MTF curve diagram of the fisheye security lens according to the third embodiment of the present invention;

[0043] Figure 15 A defocus curve diagram of the fisheye security lens according to the third embodiment of the present invention;

[0044] Figure 16 A relative illumination curve diagram of the fisheye security lens according to the third embodiment of the present invention;

[0045] Figure 17 A longitudinal chromatic aberration curve of the fisheye security lens according to the third embodiment of the present invention;

[0046] Figure 18 Field curvature and distortion diagram of the fisheye security lens described in Example 3 of the present invention.

[0047] Description of main component symbols

[0048] 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Fifth lens; 6. Sixth lens; 7. Seventh lens; 8. Eighth lens; 9. Aperture stop; 10. Protective sheet; 11. Imaging surface. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions 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 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 making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention for which protection is sought, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0050] Please refer to Figure 1-18 , the present invention provides a fisheye security lens, which includes a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, an aperture 9, a fifth lens 5, a sixth lens 6, a seventh lens 7 and an eighth lens 8 in sequence along an optical axis from the object side to the image side; the image side surface of the fifth lens 5 and the object side surface of the sixth lens 6 are glued to each other to form a glued lens group. In this embodiment, the first lens 1, the second lens 2, the fifth lens 5 and the sixth lens 6 are glass spherical lenses, and the third lens 3, the fourth lens 4, the seventh lens 7 and the eighth lens 8 are all plastic aspherical lenses, which can better improve the imaging quality, correct temperature drift, and also greatly improve the relative illumination. The first lens 1 to the eighth lens each include an object side surface facing the object side and allowing the imaging light to pass through, and an image side surface facing the image side and allowing the imaging light to pass through;

[0051] The first lens 1 has negative optical power, a convex object-side surface, and a concave image-side surface;

[0052] The second lens 2 has negative optical power, a convex object-side surface, and a concave image-side surface;

[0053] The third lens 3 has negative optical power, a concave object-side surface, and a concave image-side surface;

[0054] The fourth lens element 4 has positive refractive power, a convex object-side surface, and a concave image-side surface;

[0055] The fifth lens element 5 has positive refractive power, a convex object-side surface, and a convex image-side surface;

[0056] The sixth lens 6 has positive refractive power, a concave object-side surface, and a convex image-side surface;

[0057] The refractive power of the seventh lens element 7 is opposite to that of the eighth lens element 8;

[0058] The object side surface of the seventh lens element 7 is convex, and the image side surface is concave;

[0059] The object-side surface and the image-side surface of the eighth lens 8 are convex.

[0060] Alternatively, the object-side surface of the seventh lens element 7 is concave, and the image-side surface is convex;

[0061] The object-side surface and the image-side surface of the eighth lens 8 are concave.

[0062] The surface shape of the object-side surface of the seventh lens 7 is opposite to the surface shape of the image-side surface. The surface shape of the object-side surface of the seventh lens 7 is the same as the surface shape of the object-side surface of the eighth lens 8. The surface shape of the image-side surface of the seventh lens 7 is opposite to the surface shape of the image-side surface of the eighth lens 8.

[0063] Preferably, the following conditions are met: |f1|<20, |f2|<25, |f3|<10, |f4|<15, |f5|<35, |f6|<15, |f7|<25, |f8|<25, where f1 to f8 are the focal lengths of the first to eighth lenses, respectively. The optical power is evenly distributed, spherical aberration and off-axis aberration are well corrected, and the high and low temperature defocus curve shift is less than 2 μm, providing excellent imaging effects.

[0064] Preferably, the following conditions are met: 3.3<|f1 / f|<4.0, 3.0<|f2 / f|<6.5, 1.5<|f3 / f|<3.2, 2.0<|f4 / f|<3.5, 3.3<|f5 / f|<10.0, 2.5<|f6 / f|<4.2, 3.5<|f7 / f|<7.5, 3.5<|f8 / f|<7, where f is the focal length of the fisheye security lens.

[0065] Preferably, the following conditional expressions are met: 1.73<nd1<1.80, 1.75<nd2<2.00, 1.53<nd3<1.55, 1.65<nd4<1.69, 1.55<nd5<1.60, 1.95<nd6<1.97, 1.52<nd7<1.70, and 1.50<nd8<1.57; 45<vd1<50, 35<vd2<50, 55<vd3<56, 19<vd4<21, 68<vd5<69, 17.5<vd6<18.0, 19<vd7<57, and 19<vd8<57, wherein vd1 to vd8 are respectively the Abbe coefficients of the first lens 1 to the eighth lens 8, and nd1 to nd8 are respectively the refractive indices of the first lens 1 to the eighth lens 8. The first, second and fifth lenses are made of low refractive index and high Abbe coefficient lens materials, which can effectively correct off-axis astigmatism and off-axis chromatic aberration at wide angles, improve image quality, and have a flat lens shape and high processability.

[0066] Preferably, the following condition is met: 70<vd5+vd6<100, where vd5 and vd6 are the Abbe coefficients of the fifth lens 5 and the sixth lens 6, respectively. By individually controlling the Abbe coefficients of the cemented lens group, axial chromatic aberration is well corrected.

[0067] Preferably, the following condition is met: 6.01 ≤ TTL / AAG, where TTL is the distance on the optical axis from the object side of the first lens element to the imaging plane, and AAG is the sum of the three air gaps on the optical axis between the first lens element 1 through the fourth lens element 4. By controlling the ratio of optical length to air gap, the optical power between the various lens elements can be better distributed, the field curvature of the lens can be controlled, and image quality can be improved.

[0068] Preferably, the following condition is met: ALT<6.51, ALT=CT1+CT2+CT3+CT4, CT1 to CT4 are the center thicknesses of the first lens 1 to the fourth lens 4 respectively, and the lens structure is reasonable, so that the system has high resolution and is stable.

[0069] The following conditions are met: TTL / F < 15.05 and TTL < 27.8mm, where TTL is the distance from the object side of the first lens 1 to the imaging plane on the optical axis, and F is the clear aperture of the fisheye security lens. The overall structure is compact, miniaturized, and has greater practicality. The lens arrangement is rational, the sensitivity is low, and it is suitable for mass production.

[0070] In this solution, by controlling the refractive index and Abbe coefficient of the first lens 1, the second lens 2 and the fifth lens 5, the off-axis astigmatism, off-axis chromatic aberration of magnification and other aberrations of the fisheye security lens are effectively corrected; at the same time, the Abbe coefficient of the cemented lens group is separately controlled to optimize the on-axis chromatic aberration of the fisheye security lens, ensure the stability of light propagation in the lens, and set the seventh lens 7 and the eighth lens 8 with opposite optical powers to control the emission direction of the light, thereby further improving the imaging effect of the fisheye security lens.

[0071] The video imaging lens of the present invention will be described in detail below with reference to specific embodiments.

[0072] Example 1

[0073] Please refer to Figure 1-6 The present invention provides a fisheye security lens, which includes, from the object side to the image side along an optical axis, a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, an aperture 9, a fifth lens 5, a sixth lens 6, a seventh lens 7 and an eighth lens 8; the image side surface of the fifth lens 5 and the object side surface of the sixth lens 6 are cemented together to form a cemented lens group. In this embodiment, the first lens 1, the second lens 2, the fifth lens 5 and the sixth lens 6 are glass spherical lenses, and the third lens 3, the fourth lens 4, the seventh lens 7 and the eighth lens 8 are all plastic aspherical lenses. The first lens 1 to the eighth lens each include an object side surface facing the object side and allowing the imaging light to pass through, and an image side surface facing the image side and allowing the imaging light to pass through;

[0074] The first lens 1 has negative optical power, a convex object-side surface, and a concave image-side surface;

[0075] The second lens 2 has negative optical power, a convex object-side surface, and a concave image-side surface;

[0076] The third lens 3 has negative optical power, a concave object-side surface, and a concave image-side surface;

[0077] The fourth lens element 4 has positive refractive power, a convex object-side surface, and a concave image-side surface;

[0078] The fifth lens element 5 has positive refractive power, a convex object-side surface, and a convex image-side surface;

[0079] The sixth lens 6 has positive refractive power, a concave object-side surface, and a convex image-side surface;

[0080] The seventh lens element 7 has negative optical power, a convex object-side surface, and a concave image-side surface;

[0081] The eighth lens element 8 has positive refractive power, a convex object-side surface, and a convex image-side surface;

[0082] The detailed optical data of this specific embodiment are shown in Table 1.

[0083] Table 1 Detailed optical data of Example 1

[0084]

[0085]

[0086] In this specific embodiment, the third lens 3, the fourth lens 4, the seventh lens 7 and the eighth lens 8 are all plastic aspherical lenses. For detailed description of the aspherical surfaces of the third lens 3, the fourth lens 4, the seventh lens 7 and the eighth lens 8, please refer to the following Table 2:

[0087] Table 2: Aspheric coefficients

[0088]

[0089] The focal length of the fisheye security lens described in this embodiment is: TTL is 27.811mm; F ​​is 1.85, which increases the amount of light entering the lens and improves the image brightness; I MH is 8.52mm, I MH is the half image height of the lens, that is, half of the maximum image height of the lens imaging; DFOV is 133°, DFOV is the diagonal field of view.

[0090] In this specific embodiment, please refer to the attached diagram of the optical path of the fisheye security lens. Figure 1 Please refer to the attached MTF curves of the fisheye security lens disclosed in this embodiment at different focal lengths in the visible light band of 435nm-680nm. Figure 2 From the figure, it can be seen that when the spatial frequency reaches 100 1 p / mm, the full-view MTF of the fisheye security lens of this embodiment is greater than 0.46, which has a good imaging effect and meets the user's high-definition usage requirements. Please refer to the attached figure for the defocus curve of the fisheye security lens disclosed in this embodiment in the visible light band of 435nm-680nm. Figure 3 , different curves represent the defocus curves in the meridian and sagittal directions under different fields of view, as shown in the attached Figure 3 It can be seen that the peaks of almost all curves are near the zero offset vertical axis. At this time, the defocus characteristics of the fisheye security lens are relatively good, and a larger effective depth of focus range can be obtained. Please refer to the attached relative illumination diagram of the fisheye security lens disclosed in this embodiment in the visible light band of 435nm-680nm. Figure 4 , by the attached Figure 4 It can be seen that under the maximum field of view, RI>93%, the relative illumination is high, the image uniformity is high, and the imaging effect is good. Please refer to the attached longitudinal chromatic aberration curve of the fisheye security lens disclosed in this embodiment in the visible light band of 435nm-680nm. Figure 5 , by the attached Figure 5It can be seen that the maximum longitudinal chromatic aberration of the fisheye security lens working in the visible light band is 0.02mm, and the lateral chromatic aberration and longitudinal chromatic aberration of this optical lens are well corrected. Please refer to the attached figure for the field curvature distortion curve of the fisheye security lens disclosed in this embodiment in the visible light band of 435nm-680nm. Figure 6 , by the attached Figure 6 It can be seen that the optical distortion of the fisheye security lens is less than 11%, the image quality is good, and the difficulty of post-correction is reduced.

[0091] Example 2

[0092] Please refer to Figure 7-12 The present invention provides a fisheye security lens, which includes, from the object side to the image side along an optical axis, a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, an aperture 9, a fifth lens 5, a sixth lens 6, a seventh lens 7 and an eighth lens 8; the image side surface of the fifth lens 5 and the object side surface of the sixth lens 6 are cemented together to form a cemented lens group. In this embodiment, the first lens 1, the second lens 2, the fifth lens 5 and the sixth lens 6 are glass spherical lenses, and the third lens 3, the fourth lens 4, the seventh lens 7 and the eighth lens 8 are all plastic aspherical lenses. The first lens 1 to the eighth lens each include an object side surface facing the object side and allowing the imaging light to pass through, and an image side surface facing the image side and allowing the imaging light to pass through;

[0093] The first lens 1 has negative optical power, a convex object-side surface, and a concave image-side surface;

[0094] The second lens 2 has negative optical power, a convex object-side surface, and a concave image-side surface;

[0095] The third lens 3 has negative optical power, a concave object-side surface, and a concave image-side surface;

[0096] The fourth lens element 4 has positive refractive power, a convex object-side surface, and a concave image-side surface;

[0097] The fifth lens element 5 has positive refractive power, a convex object-side surface, and a convex image-side surface;

[0098] The sixth lens 6 has positive refractive power, a concave object-side surface, and a convex image-side surface;

[0099] The seventh lens element 7 has positive refractive power, a concave object-side surface, and a convex image-side surface;

[0100] The eighth lens element 8 has negative power, a concave object-side surface, and a concave image-side surface.

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

[0102] Table 3 Detailed optical data of Example 2

[0103]

[0104] In this specific embodiment, the third lens 3, the fourth lens 4, the seventh lens 7 and the eighth lens 8 are all plastic aspherical lenses. For detailed description of the aspherical surfaces of the third lens 3, the fourth lens 4, the seventh lens 7 and the eighth lens 8, please refer to the following Table 4:

[0105] Table 4: Aspheric coefficients

[0106]

[0107] The focal length of the fisheye security lens described in this embodiment is: TTL is 27.800mm; F ​​is 1.85, which increases the amount of light entering the lens and improves the image brightness; I MH is 8.52mm, I MH is the half image height of the lens, that is, half of the maximum image height of the lens imaging; DFOV is 133°, DFOV is the diagonal field of view.

[0108] In this specific embodiment, please refer to the attached diagram of the optical path of the fisheye security lens. Figure 7 Please refer to the attached MTF curves of the fisheye security lens disclosed in this embodiment at different focal lengths in the visible light band of 435nm-680nm. Figure 8 From the figure, it can be seen that when the spatial frequency reaches 100 1 p / mm, the full-view MTF of the fisheye security lens of this embodiment is greater than 0.38, which has a good imaging effect and meets the user's high-definition usage requirements. Please refer to the attached figure for the defocus curve of the fisheye security lens disclosed in this embodiment in the visible light band of 435nm-680nm. Figure 9 , different curves represent the defocus curves in the meridian and sagittal directions under different fields of view, as shown in the attached Figure 9 It can be seen that the peaks of almost all curves are near the zero offset vertical axis. At this time, the defocus characteristics of the fisheye security lens are relatively good, and a larger effective depth of focus range can be obtained. Please refer to the attached relative illumination diagram of the fisheye security lens disclosed in this embodiment in the visible light band of 435nm-680nm. Figure 10 , by the attached Figure 10 It can be seen that under the maximum field of view, RI>91%, the relative illumination is high, the image uniformity is high, and the imaging effect is good. Please refer to the attached longitudinal chromatic aberration curve of the fisheye security lens disclosed in this embodiment in the visible light band of 435nm-680nm. Figure 11 , by the attached Figure 11 It can be seen that the maximum longitudinal chromatic aberration of the fisheye security lens working in the visible light band is 0.05mm, and the lateral chromatic aberration and longitudinal chromatic aberration of this optical lens are well corrected. Please refer to the attached figure for the field curvature distortion curve of the fisheye security lens disclosed in this embodiment in the visible light band of 435nm-680nm. Figure 12 , by the attached Figure 12It can be seen that the optical distortion of the fisheye security lens is less than 12%, the image quality is good, and the difficulty of post-correction is reduced.

[0109] Example 3

[0110] Please refer to Figure 13-18 The present invention provides a fisheye security lens, which includes, from the object side to the image side along an optical axis, a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, an aperture 9, a fifth lens 5, a sixth lens 6, a seventh lens 7 and an eighth lens 8; the image side surface of the fifth lens 5 and the object side surface of the sixth lens 6 are cemented together to form a cemented lens group. In this embodiment, the first lens 1, the second lens 2, the fifth lens 5 and the sixth lens 6 are glass spherical lenses, and the third lens 3, the fourth lens 4, the seventh lens 7 and the eighth lens 8 are all plastic aspherical lenses. The first lens 1 to the eighth lens each include an object side surface facing the object side and allowing the imaging light to pass through, and an image side surface facing the image side and allowing the imaging light to pass through;

[0111] The first lens 1 has negative optical power, a convex object-side surface, and a concave image-side surface;

[0112] The second lens 2 has negative optical power, a convex object-side surface, and a concave image-side surface;

[0113] The third lens 3 has negative optical power, a concave object-side surface, and a concave image-side surface;

[0114] The fourth lens element 4 has positive refractive power, a convex object-side surface, and a concave image-side surface;

[0115] The fifth lens element 5 has positive refractive power, a convex object-side surface, and a convex image-side surface;

[0116] The sixth lens 6 has positive refractive power, a concave object-side surface, and a convex image-side surface;

[0117] The seventh lens element 7 has negative optical power, a convex object-side surface, and a concave image-side surface;

[0118] The eighth lens element 8 has positive refractive power, a convex object-side surface, and a convex image-side surface;

[0119] The detailed optical data of this specific embodiment are shown in Table 5.

[0120] Table 5 Detailed optical data of Example 3

[0121]

[0122]

[0123] In this specific embodiment, the third lens 3, the fourth lens 4, the seventh lens 7 and the eighth lens 8 are all plastic aspherical lenses. For detailed description of the aspherical surfaces of the third lens 3, the fourth lens 4, the seventh lens 7 and the eighth lens 8, please refer to the following Table 6:

[0124] Table 6: Aspheric coefficients

[0125]

[0126] The focal length of the fisheye security lens described in this embodiment is: TTL is 27.802mm; F ​​is 1.85, which increases the amount of light entering the lens and improves the image brightness; I MH is 8.52mm, I MH is the half image height of the lens, that is, half of the maximum image height of the lens imaging; DFOV is 133°, DFOV is the diagonal field of view.

[0127] In this specific embodiment, please refer to the attached diagram of the optical path of the fisheye security lens. Figure 13 Please refer to the attached MTF curves of the fisheye security lens disclosed in this embodiment at different focal lengths in the visible light band of 435nm-680nm. Figure 14 From the figure, it can be seen that when the spatial frequency reaches 100 1 p / mm, the full-view MTF of the fisheye security lens of this embodiment is greater than 0.48, which has a good imaging effect and meets the user's high-definition usage requirements. Please refer to the attached figure for the defocus curve of the fisheye security lens disclosed in this embodiment in the visible light band of 435nm-680nm. Figure 15 , different curves represent the defocus curves in the meridian and sagittal directions under different fields of view, as shown in the attached Figure 18 It can be seen that the peaks of almost all curves are near the zero offset vertical axis. At this time, the defocus characteristics of the fisheye security lens are relatively good, and a larger effective depth of focus range can be obtained. Please refer to the attached relative illumination diagram of the fisheye security lens disclosed in this embodiment in the visible light band of 435nm-680nm. Figure 16 , by the attached Figure 16 It can be seen that under the maximum field of view, RI>93%, the relative illumination is high, the image uniformity is high, and the imaging effect is good. Please refer to the attached longitudinal chromatic aberration curve of the fisheye security lens disclosed in this embodiment in the visible light band of 435nm-680nm. Figure 17 , by the attached Figure 17 It can be seen that the maximum longitudinal chromatic aberration of the fisheye security lens working in the visible light band is 0.02mm, and the lateral chromatic aberration and longitudinal chromatic aberration of this optical lens are well corrected. Please refer to the attached figure for the field curvature distortion curve of the fisheye security lens disclosed in this embodiment in the visible light band of 435nm-680nm. Figure 18 , by the attached Figure 18 It can be seen that the optical distortion of the fisheye security lens is less than 11%, the image quality is good, and the difficulty of post-correction is reduced.

[0128] Table 7 shows the values ​​of important parameters of three embodiments of the present invention:

[0129] Table 7: Important parameters of various examples

[0130]

[0131]

[0132] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0133] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and improvements fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A fisheye security lens, characterized in that: The lens system includes, in order from the object side to the image side along an optical axis, a first lens, a second lens, a third lens, a fourth lens, a stop, a fifth lens, a sixth lens, a seventh lens, and an eighth lens; each of the first to eighth lenses includes 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; The first lens has negative optical power, a convex object-side surface, and a concave image-side surface; The second lens has negative optical power, a convex object-side surface, and a concave image-side surface; The third lens has negative optical power, a concave object-side surface, and a concave image-side surface; The fourth lens has positive refractive power, a convex object-side surface, and a concave image-side surface; The fifth lens has positive refractive power, a convex object-side surface, and a convex image-side surface; The sixth lens has positive refractive power, a concave object-side surface, and a convex image-side surface; The optical power of the seventh lens is opposite to that of the eighth lens; And meet the following conditions: 1.73<nd1<1.80, 45<vd1<50, 1.75<nd2<2.00, 35<vd2<50 and 1.55<nd5<1.60, 68<vd5<69; nd1, nd2 and nd5 are the refractive indices of the first lens, the second lens and the fifth lens respectively, and vd1, vd2 and vd5 are the Abbe coefficients of the first lens, the second lens and the fifth lens respectively; 3.3<|f1 / f|<4.0, 3.0<|f2 / f|<6.5, 1.5<|f3 / f|<3.2, 2.0<|f4 / f|<3.5, 3.3<|f5 / f|<10.0, 2.5<|f6 / f|<4.2, 3.5<|f7 / f|<7.5, 3.5<|f8 / f|<7, where f1 to f8 are the focal lengths of the first lens to the eighth lens respectively, and f is the focal length of the fisheye security lens.

2. The fisheye security lens according to claim 1, characterized in that: The following conditional formula is met: |f1|<20mm, |f2|<25mm, |f3|<10mm, |f4|<15mm, |f5|<35mm, |f6|<15mm, |f7|<25mm, |f8|<25mm, where f1 to f8 are focal lengths of the first to eighth lenses, respectively.

3. The fisheye security lens according to claim 1, characterized in that: The following conditional formula is met: 70<vd5+vd6<100, where vd5 and vd6 are Abbe coefficients of the fifth lens and the sixth lens respectively.

4. The fisheye security lens according to claim 1, wherein: The following condition is met: 6.01≤TTL / AAG, where TTL is the distance from the object side surface of the first lens element to the imaging surface on the optical axis, and AAG is the sum of three air gaps on the optical axis between the first lens element to the fourth lens element.

5. The fisheye security lens according to claim 1, characterized in that: The following conditional formula is met: ALT<6.51 mm, ALT=CT1+CT2+CT3+CT4, and CT1 to CT4 are the center thicknesses of the first to fourth lenses, respectively.

6. The fisheye security lens according to claim 1, characterized in that: The following conditions are met: TTL / F < 15.05 and TTL < 27.82 mm, where TTL is the distance from the object side of the first lens to the imaging plane on the optical axis, and F is the clear aperture of the fisheye security lens.

7. The fisheye security lens according to claim 1, characterized in that: The surface shape of the object-side surface of the seventh lens is opposite to the surface shape of the image-side surface. The surface shape of the object-side surface of the seventh lens is the same as the surface shape of the object-side surface of the eighth lens. The surface shape of the image-side surface of the seventh lens is opposite to the surface shape of the image-side surface of the eighth lens.

8. The fisheye security lens according to claim 7, characterized in that: The object-side surface of the seventh lens is convex, and the image-side surface is concave; the object-side surface of the eighth lens is convex, and the image-side surface is convex.

9. The fisheye security lens according to claim 7, characterized in that: The object-side surface of the seventh lens is concave, and the image-side surface is convex; the object-side surface of the eighth lens is concave, and the image-side surface is concave.

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