240-degree field fisheye lens and image capturing device

Abstract

The utility model provides a 240-degree field-of-view fisheye lens and an image capturing device, comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens and a tenth lens which are sequentially arranged along an optical axis from an object side to an image side, the object side surface of the first lens is a convex surface, and the image side surface of the first lens is a concave surface; the second lens has negative diopter, the object side surface of the second lens is a convex surface, and the image side surface of the second lens is a concave surface; the third lens has negative diopter, the concave-convex part of the object side surface of the third lens is not limited, and the image side surface of the third lens is a concave surface and the like; according to the utility model, the diopter of each lens is reasonably distributed, the optical performance of the lens is improved, the field angle FOV of the fisheye lens is 240 degrees, and the fisheye lens has a large image plane and a large field angle.

Description

Technical Field

[0001] The utility model relates to the technical field of fisheye lenses, in particular to a 240-degree field of view fisheye lens and an imaging device. Background Art

[0002] Fisheye lenses are extremely wide-angle lenses. Most existing fisheye lenses have one or more of the following defects:

[0003] First, the field of view of conventional fisheye lenses is about 180°. If the field of view is further increased, the design will be difficult and a large image surface cannot be achieved.

[0004] Second, the conventional fisheye lens has a large angle and the edge resolution is difficult to control, resulting in poor image quality and blurred edges.

[0005] Third, conventional fisheye lenses are prone to defocusing in high and low temperatures.

[0006] Fourth, conventional fisheye lenses have a large angle and severe chromatic aberration, which causes serious purple fringing.

[0007] Fifth, conventional fisheye lenses have large angles, complex structures, and large outer diameters. Utility Model Content

[0008] In view of the deficiencies in the prior art, the purpose of the present invention is to propose a 240° field of view fisheye lens, which can provide a lens with good imaging quality by reasonably allocating the refractive power of each lens and optimizing the surface shape of each lens, so as to solve the problems mentioned in the above background technology part.

[0009] The utility model is realized by the following technical solutions:

[0010] According to one aspect of the utility model, a 240° field of view fisheye lens is provided, comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens and a tenth lens arranged in sequence along an optical axis from an object side to an image side, wherein:

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

[0012] The second lens has a negative refractive power, the object side surface of the second lens is a convex surface, and the image side surface of the second lens is a concave surface;

[0013] The third lens has negative refractive power, and the image side surface of the third lens is a concave surface;

[0014] The fifth lens has positive refractive power, and the object side surface of the fifth lens is a convex surface;

[0015] The sixth lens has positive refractive power, and the image side surface of the sixth lens is a convex surface;

[0016] The seventh lens has a negative refractive power, the object side surface of the seventh lens is a convex surface, and the image side surface of the seventh lens is a convex surface;

[0017] The eighth lens has positive refractive power, the object side surface of the eighth lens is a convex surface, and the image side surface of the eighth lens is a convex surface;

[0018] The ninth lens has a negative refractive power, the object side surface of the ninth lens is a concave surface, and the image side surface of the ninth lens is a convex surface;

[0019] The tenth lens has positive refractive power, the object side surface of the tenth lens is convex, and the image side surface of the tenth lens is concave.

[0020] The beneficial effects of the above embodiment are: by reasonably allocating the diopter of each lens, the optical performance of the lens is improved, so that the field of view FOV of the fisheye lens is 240°, and it has a large image surface and a large field of view.

[0021] Furthermore, the lens satisfies the following relationship: Nd1>1.85, wherein Nd1 is the refractive index of the first lens.

[0022] The beneficial effects of the above embodiment are as follows: since the field of view angle of the lens is 240°, it has been found through multiple tests that if the refractive index Nd1 is less than 1.8, the front port diameter will be too large: by selecting a high refractive index material with a refractive index greater than 1.85 for the first lens, the outer diameter of the lens can be reduced while meeting performance conditions, thereby achieving a miniaturized design of the lens.

[0023] Furthermore, the lens satisfies the following relationship: 1.7<D12 / R12<1.95, wherein D12 is the aperture of the second surface of the first lens (i.e., the object side surface of the first lens), and R12 is the curvature radius of the second surface of the first lens (i.e., the image side surface of the first lens).

[0024] The beneficial effect of the above embodiment is: after multiple tests, it is found that if D12 / R12>1.95, the lens processing is extremely difficult, and if D12 / R12<1.7, the distortion will increase and the outer diameter of the lens will increase. Therefore, satisfying the above formula is conducive to optimizing the large field of view of the lens and reducing the difficulty of lens processing.

[0025] Furthermore, the lens satisfies the following relationship: 0.7<|f2 / f / f3|<1.2, wherein f2 is the focal length of the second lens, f is the focal length of the lens system, and f3 is the focal length of the third lens.

[0026] The beneficial effects of the above embodiment are as follows: satisfying the above formula is conducive to the reasonable distribution of optical power, so that large-angle light is transferred to the rear lens, thereby optimizing and improving the MTF of the lens.

[0027] Furthermore, the lens satisfies the following relationship: 0.8<|f2 / f5|<2.2, wherein f2 is the focal length of the second lens, and f5 is the focal length of the fifth lens.

[0028] The beneficial effect of the above embodiment is that satisfying the above formula is conducive to achieving high and low temperature athermalization of the lens and balancing high and low temperatures.

[0029] Furthermore, the lens satisfies the following relationship: Nd2>1.8, wherein Nd2 is the refractive index of the second lens.

[0030] The beneficial effects of the above embodiment are as follows: since the field of view angle of the lens is 240°, it has been found through multiple tests that if the refractive index Nd2 is less than 1.8, the front port diameter will be too large: by selecting a high refractive index material with a refractive index greater than 1.85 for the second lens, the outer diameter of the lens can be reduced while meeting performance conditions, thereby achieving a miniaturized design of the lens.

[0031] Further, the lens satisfies the following relationship: |Vd6-Vd7|>20, |Vd8-Vd9|>20, wherein the sixth lens and the seventh lens are glued together to form a double glued lens, the eighth lens and the ninth lens are glued together to form a double glued lens, Vd6 is the dispersion coefficient of the sixth lens, Vd7 is the dispersion coefficient of the seventh lens, Vd8 is the dispersion coefficient of the eighth lens, and Vd9 is the dispersion coefficient of the ninth lens.

[0032] The beneficial effects of the above embodiment are as follows: the two groups of cemented lenses are both made of a combination of high and low dispersion materials, which is beneficial to correcting the chromatic aberration of the lens imaging and making the color reproduction of the lens imaging high.

[0033] Furthermore, the third lens is an aspherical lens; and the tenth lens is an aspherical lens.

[0034] The beneficial effects of the above embodiment are as follows: the third lens and the tenth lens are aspherical lenses, which are beneficial to correcting temperature drift, and can also realize the miniaturization design of the lens, and is also beneficial to improving the resolution of the lens;

[0035] Furthermore, Nd5>1.8, where Nd5 is the refractive index of the fifth lens.

[0036] The beneficial effect of the above embodiment is that satisfying the above formula is conducive to improving the resolution of the lens.

[0037] On the other hand, the utility model provides an imaging device, comprising a 240° field of view fisheye lens as described in any one of the above items.

[0038] In the above embodiment, the imaging device using the above 240° field of view fisheye lens can achieve a large image plane and a large field of view suitable for panoramic stitching when the field of view angle FOV = 240°, and the transfer function can reach a high frequency of 200l p / mm, with the characteristics of high contrast and high image quality, good resolution control at the edge of the large field of view, and clear and delicate pictures. It can output high-definition images in high and low temperature environments (-40℃ to 80℃) without out-of-focus. In the wide spectrum of visible light, the chromatic aberration is small and the color reproduction is high BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a structural diagram of the optical system of the lens in Example 1.

[0040] Figure 2 This is the MTF curve diagram of Example 1.

[0041] Figure 3 This is the aberration curve diagram of Example 1.

[0042] Figure 4 This is the color difference curve diagram of Example 1.

[0043] Figure 5 This is a structural diagram of the optical system of the lens in Example 2.

[0044] Figure 6 This is the MTF curve diagram of Example 2.

[0045] Figure 7 This is the aberration curve diagram of Example 2.

[0046] Figure 8 This is the color difference curve diagram of Example 2.

[0047] Fig. 9 This is a structural diagram of the optical system of the lens in Example 3.

[0048] Fig.10 This is the MTF curve diagram of Example 3.

[0049] Fig.11 This is the aberration curve diagram of Example 3.

[0050] Fig.12 This is the color difference curve diagram of Example 3.

[0051] The above drawings include the following reference numerals:

[0052] L1, first lens; L2, second lens; L3, third lens; L4, fourth lens; L5, fifth lens; L6, sixth lens; L7, seventh lens; L8, eighth lens; L9, ninth lens; L10, tenth lens; ST, aperture; IM A, image plane. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, 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. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0054] Reference Figures 1 to 3 As shown, a 240° field of view fisheye lens (hereinafter referred to as lens) includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, an eighth lens L8, a ninth lens L9 and a tenth lens L10, which are arranged in sequence along the optical axis from the object side to the image side, and a stop ST is provided between the fifth lens L5 and the sixth lens L6, wherein:

[0055] The first lens L1 has a negative refractive power, the object side surface of the first lens L1 is a convex surface, and the image side surface of the first lens L1 is a concave surface;

[0056] The second lens L2 has a negative refractive power, the object side surface of the second lens L2 is a convex surface, and the image side surface of the second lens L2 is a concave surface;

[0057] The third lens L3 has a negative refractive power, the object side surface of the third lens L3 is not limited to be concave or convex, and the image side surface of the third lens L3 is a concave surface;

[0058] The refractive power of the fourth lens L4 is not limited, and the concave and convex sides of the object side and the image side of the fourth lens L4 are not limited;

[0059] The fifth lens L5 has a positive refractive power, the object side surface of the fifth lens L5 is a convex surface, and the image side surface of the fifth lens L5 is not limited to be concave or convex;

[0060] The sixth lens L6 has a positive refractive power, the object side surface of the sixth lens L6 is not limited to be concave or convex, and the image side surface of the sixth lens L6 is a convex surface;

[0061] The seventh lens L7 has a negative refractive power, the object side surface of the seventh lens L7 is a convex surface, and the image side surface of the seventh lens L7 is a convex surface;

[0062] The eighth lens L8 has a positive refractive power, the object side surface of the eighth lens L8 is a convex surface, and the image side surface of the eighth lens L8 is a convex surface;

[0063] The ninth lens L9 has a negative refractive power, the object side surface of the ninth lens L9 is a concave surface, and the image side surface of the ninth lens L9 is a convex surface;

[0064] The tenth lens L10 has positive refractive power, the object-side surface of the tenth lens L10 is convex, and the image-side surface of the tenth lens L10 is concave.

[0065] The beneficial effects of the above embodiments are: by reasonably allocating the diopter of each lens, the optical performance of the lens is improved, so that the fisheye lens field of view FOV = 240°, with a large image surface and a large field of view. Among them, the above non-limited lenses can refer to embodiments 1 to 3 provided by the utility model.

[0066] Furthermore, the lens satisfies the following relationship: Nd1>1.85, wherein Nd1 is the refractive index of the first lens L1.

[0067] The beneficial effects of the above embodiment are as follows: since the field of view angle of the lens is 240°, it has been found through multiple tests that if the refractive index Nd1 is less than 1.8, the front port diameter will be too large: by selecting a high refractive index material with a refractive index greater than 1.85 for the first lens L1, the outer diameter of the lens can be reduced while meeting performance conditions, thereby achieving a miniaturized design of the lens.

[0068] Furthermore, the lens satisfies the following relationship: 1.7<D12 / R12<1.95, wherein D12 is the aperture of the second surface of the first lens L1 (i.e., the object side surface of the first lens L1), and R12 is the curvature radius of the second surface of the first lens L1 (i.e., the image side surface of the first lens L1).

[0069] The beneficial effect of the above embodiment is: after multiple tests, it is found that if D12 / R12>1.95, the lens processing is extremely difficult, and if D12 / R12<1.7, the distortion will increase and the outer diameter of the lens will increase. Therefore, satisfying the above formula is conducive to optimizing the large field of view of the lens and reducing the difficulty of lens processing.

[0070] Furthermore, the lens satisfies the following relationship: 0.7<|f2 / f / f3|<1.2, wherein f2 is the focal length of the second lens L2, f is the focal length of the lens system, and f3 is the focal length of the third lens L3.

[0071] The beneficial effects of the above embodiment are as follows: satisfying the above formula is conducive to the reasonable distribution of optical power, so that large-angle light is transferred to the rear lens, thereby optimizing and improving the MTF of the lens.

[0072] Furthermore, the lens satisfies the following relationship: 0.8<|f2 / f5|<2.2, wherein f2 is the focal length of the second lens L2, and f5 is the focal length of the fifth lens L5.

[0073] The beneficial effect of the above embodiment is that satisfying the above formula is conducive to achieving high and low temperature athermalization of the lens and balancing high and low temperatures.

[0074] Furthermore, the lens satisfies the following relationship: Nd2>1.8, wherein Nd2 is the refractive index of the second lens L2.

[0075] The beneficial effects of the above embodiment are as follows: since the field of view angle of the lens is 240°, it has been found through multiple tests that if the refractive index Nd2 is less than 1.8, the front port diameter will be too large: by selecting a high refractive index material with a refractive index greater than 1.85 for the second lens L2, the outer diameter of the lens can be reduced while meeting performance conditions, thereby achieving a miniaturized design of the lens.

[0076] Further, the lens satisfies the following relationship: |Vd6-Vd7|>20, |Vd8-Vd9|>20, wherein the sixth lens L6 and the seventh lens L7 are cemented together as a doublet lens, the eighth lens L8 and the ninth lens L9 are cemented together as a doublet lens, Vd6 is the dispersion coefficient of the sixth lens L6, Vd7 is the dispersion coefficient of the seventh lens L7, Vd8 is the dispersion coefficient of the eighth lens L8, and Vd9 is the dispersion coefficient of the ninth lens L9.

[0077] The beneficial effect of the above embodiment is: by combining the sixth lens L6 and the seventh lens L7 with high and low dispersion materials, and by combining the eighth lens L8 and the ninth lens L9 with high and low dispersion materials, it is beneficial to correct the chromatic aberration of the lens imaging, so that the color reproduction of the lens imaging is high.

[0078] Furthermore, the third lens L3 is an aspherical lens.

[0079] The beneficial effects of the above embodiment are as follows: the third lens L3 is an aspherical lens, which is beneficial to correcting temperature drift, and can also realize the miniaturization design of the lens, and is also beneficial to improving the resolution of the lens.

[0080] Furthermore, the tenth lens L10 is an aspherical lens.

[0081] The beneficial effects of the above embodiment are as follows: the tenth lens L10 is an aspherical lens, which is beneficial to improving the resolution of the lens and realizing the miniaturization design of the lens;

[0082] Furthermore, Nd5>1.8, where Nd5 is the refractive index of the fifth lens L5.

[0083] The beneficial effect of the above embodiment is that satisfying the above formula is conducive to improving the resolution of the lens.

[0084] The present invention will be described in more detail below in conjunction with Tables 1 to 3. It should be noted that the following tables are only specific embodiments of the present invention, rather than limiting examples.

[0085] For the convenience of description, in the table, No. 1 and No. 2 are respectively the object side surface and the image side surface of the first lens L1; No. 3 and No. 4 are respectively the object side surface and the image side surface of the second lens L2; ​​No. 5 and No. 6 are respectively the object side surface and the image side surface of the third lens L3; No. 7 and No. 8 are respectively the object side surface and the image side surface of the fourth lens L4; No. 9 and No. 10 are respectively the object side surface and the image side surface of the fifth lens L5; No. 11 is the surface of the stop ST; No. 12 and No. 13 are respectively the object side surface and the image side surface of the sixth lens L6; No. 13 and No. 14 are respectively the object side surface and the image side surface of the seventh lens L7; No. 15 and No. 16 are respectively the object side surface and the image side surface of the eighth lens L8; No. 16 and No. 17 are respectively the object side surface and the image side surface of the ninth lens L9; No. 18 and No. 19 are respectively the object side surface and the image side surface of the tenth lens L10; and No. 20 is the surface of the image plane I MA. TC / AC is the ratio of the lens center thickness to the air gap thickness.

[0086] Table 1 is a specific arrangement table of parameters such as the curvature radius, refractive index, and dispersion coefficient of each lens in Example 1.

[0087]

[0088] In the lens group of Example 1, the focal length of the lens is f=1.55 mm, the field of view FOV=240°, the image plane I MH=7 mm, and the total length TTL=34.87 mm.

[0089] The following is an explanation of the various figures:

[0090] Figure 1 : is an optical system structure diagram of the lens in Example 1. In this example, the object side surface of the third lens L3 is concave; the fourth lens L4 has negative refractive power, the object side surface of the fourth lens L4 is concave, and the image side surface of the fourth lens L4 is convex; the object side surface of the sixth lens L6 is concave.

[0091] Figure 2 : is the MTF curve diagram of Example 1. The horizontal axis represents frequency and the vertical axis represents contrast. It can be seen from the figure that under the full field of view, the contrast at 200l p / mm is above 0.3, and the lens optical system has the characteristics of high resolution.

[0092] Figure 3 It is the aberration curve diagram of Example 1. It can be seen from the figure that at different wavelengths, the aberration is small and concentrated, the lens performance is excellent, the chromatic aberration is small, and the resolution is high.

[0093] Figure 4This is a color difference curve diagram of Example 1. It can be seen from the figure that different wavelengths cross each other, which plays a role in achromatization, the system color difference is extremely small, and there is no purple fringing phenomenon.

[0094] Table 2 is a specific arrangement table of parameters such as the curvature radius, refractive index, and dispersion coefficient of each lens in Example 2.

[0095]

[0096] In the lens group of Example 2, the focal length of the lens is f=1.62 mm, the field of view FOV=240°, the image plane I MH=7.02 mm, and the total length TTL=34.88 mm.

[0097] The following is an explanation of the various figures:

[0098] Figure 5 : is an optical system structure diagram of the lens in Example 2. In this example, the object side surface of the third lens L3 is concave; the fourth lens L4 has positive refractive power, the object side surface of the fourth lens L4 is convex, and the image side surface of the fourth lens L4 is convex; the object side surface of the sixth lens L6 is concave.

[0099] Figure 6 : is the MTF curve diagram of Example 2. The horizontal axis represents frequency and the vertical axis represents contrast. It can be seen from the figure that under the full field of view, the contrast at 200l p / mm is above 0.3, and the lens optical system has the characteristics of high resolution.

[0100] Figure 7 It is the aberration curve diagram of Example 2. It can be seen from the figure that at different wavelengths, the aberration is small and concentrated, the lens performance is excellent, the chromatic aberration is small, and the resolution is high.

[0101] Figure 8 This is a color difference curve diagram of Example 2. It can be seen from the figure that different wavelengths cross each other, which plays a role in achromatization, the system color difference is extremely small, and there is no purple fringing phenomenon.

[0102] Table 3 is a specific arrangement table of parameters such as the curvature radius, refractive index, and dispersion coefficient of each lens in Example 3.

[0103]

[0104] In the lens group of Example 3, the focal length of the lens is f=1.63 mm, the field of view FOV=240°, the image plane I MH=7.02 mm, and the total length TTL=34.66 mm.

[0105] The following is an explanation of the various figures:

[0106] Fig. 9: is an optical system structure diagram of the lens in Example 3. In this example, the object side surface of the third lens L3 is convex; the fourth lens L4 has positive refractive power, the object side surface of the fourth lens L4 is concave, and the image side surface of the fourth lens L4 is concave; the object side surface of the sixth lens L6 is convex.

[0107] Fig.10 : is the MTF curve diagram of Example 3. The horizontal axis represents frequency and the vertical axis represents contrast. It can be seen from the figure that under the full field of view, the contrast at 200l p / mm is above 0.3, and the lens optical system has the characteristics of high resolution.

[0108] Fig.11 It is the aberration curve diagram of Example 3. It can be seen from the figure that at different wavelengths, the aberration is small and concentrated, the lens performance is excellent, the chromatic aberration is small, and the resolution is high.

[0109] Fig.12 This is a color difference curve diagram of Example 3. It can be seen from the figure that different wavelengths cross each other, which plays a role in achromatization, the system color difference is extremely small, and there is no purple fringing phenomenon.

[0110] On the other hand, the utility model provides an imaging device, including a 240° field of view fisheye lens as described in any one of Examples 1 to 3. The imaging device using the above-mentioned 240° field of view fisheye lens can achieve a large image surface and a large field of view suitable for panoramic stitching when the field of view angle FOV = 240°, and the transfer function can reach a high frequency of 200lp / mm, with the characteristics of high contrast and high image quality, the resolution of the edge of the large field of view is well controlled, and the picture is clear and delicate. It can output high-definition images in high and low temperature environments (-40℃ to 80℃) without out-of-focus. In the wide spectrum of visible light, the chromatic aberration is small and the color reproduction is high.

[0111] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0112] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0113] The above description is only the preferred implementation of the utility model, and is not intended to limit the utility model. For those skilled in the art, the utility model can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model shall be included in the protection scope of the utility model.

Claims

1. A 240° field of view fisheye lens, characterized in that: The invention comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens and a tenth lens which are arranged in sequence along the optical axis from the object side to the image side, wherein: The first lens has a negative refractive power, the object side surface of the first lens is a convex surface, and the image side surface of the first lens is a concave surface; The second lens has a negative refractive power, the object side surface of the second lens is a convex surface, and the image side surface of the second lens is a concave surface; The third lens has negative refractive power, and the image side surface of the third lens is a concave surface; The fifth lens has positive refractive power, and the object side surface of the fifth lens is a convex surface; The sixth lens has positive refractive power, and the image side surface of the sixth lens is a convex surface; The seventh lens has a negative refractive power, the object side surface of the seventh lens is a convex surface, and the image side surface of the seventh lens is a convex surface; The eighth lens has positive refractive power, the object side surface of the eighth lens is a convex surface, and the image side surface of the eighth lens is a convex surface; The ninth lens has a negative refractive power, the object side surface of the ninth lens is a concave surface, and the image side surface of the ninth lens is a convex surface; The tenth lens has positive refractive power, the object side surface of the tenth lens is convex, and the image side surface of the tenth lens is concave.

2. The 240° field of view fisheye lens according to claim 1, characterized in that: The lens satisfies the following relationship: Nd1>1.85, where Nd1 is the refractive index of the first lens.

3. The 240° field of view fisheye lens according to claim 1, characterized in that: The lens satisfies the following relationship: 1.7<D12 / R12<1.95, wherein D12 is the aperture of the second surface of the first lens, and R12 is the radius of curvature of the second surface of the first lens.

4. The 240° field of view fisheye lens according to claim 1, characterized in that: The lens satisfies the following relationship: 0.7<|f2 / f / f3|<1.2, wherein f2 is the focal length of the second lens, f is the focal length of the lens system, and f3 is the focal length of the third lens.

5. The 240° field of view fisheye lens according to claim 1, characterized in that: The lens satisfies the following relationship: 0.8<|f2 / f5|<2.2, wherein f2 is the focal length of the second lens, and f5 is the focal length of the fifth lens.

6. The 240° field of view fisheye lens according to claim 1, characterized in that: The lens satisfies the following relationship: Nd2>1.8, where Nd2 is the refractive index of the second lens.

7. The 240° field of view fisheye lens according to claim 1, characterized in that: The lens satisfies the following relationship: |Vd6-Vd7|>20, |Vd8-Vd9|>20, wherein the sixth lens and the seventh lens are glued together to form a double glued lens, the eighth lens and the ninth lens are glued together to form a double glued lens, Vd6 is the dispersion coefficient of the sixth lens, Vd7 is the dispersion coefficient of the seventh lens, Vd8 is the dispersion coefficient of the eighth lens, and Vd9 is the dispersion coefficient of the ninth lens.

8. The 240° field of view fisheye lens according to claim 1, characterized in that: The third lens is an aspherical lens; the tenth lens is an aspherical lens.

9. The 240° field of view fisheye lens according to claim 1, characterized in that: The lens satisfies the following relationship: Nd5>1.8, wherein Nd5 is the refractive index of the fifth lens.

10. An imaging device, characterized in that: A 240° field of view fisheye lens comprising any one of claims 1 to 9.

Images