A half-frame ultra-wide-angle circular fisheye lens

Abstract

This invention provides a half-frame ultra-wide-angle circular fisheye lens, comprising: a first lens, a second lens, a third lens, a fourth lens, an aperture stop, a fifth lens, a sixth lens, a seventh lens, an eighth lens, and a ninth lens, arranged sequentially from the object plane to the image plane; the first, second, third, sixth, seventh, and ninth lenses have negative refractive power, the fourth, fifth, and eighth lenses have positive refractive power, and the first, second, seventh, and ninth lenses are meniscus lenses; the fifth and sixth lenses are cemented together, and the eighth and ninth lenses are cemented together. This invention expands the incident light range by using a negative refractive power meniscus lens, adjusts the refractive power by combining biconcave and biconvex lenses to reduce aberrations, and eliminates chromatic aberration by cementing the fifth and sixth lenses and the eighth and ninth lenses together, thus achieving extreme wide-angle while ensuring image clarity and accurate color reproduction.

Description

Technical Field

[0001] This utility model relates to the field of optical lens technology, and more specifically to a half-frame ultra-wide-angle circular fisheye lens. Background Technology

[0002] With the iterative upgrades of imaging technology, imaging devices are rapidly developing towards miniaturization and high integration. Among them, mirrorless cameras and drones equipped with APS-C (half-frame) sensors, thanks to their excellent balance of performance and portability, have not only quickly occupied the mainstream consumer market but have also achieved widespread application in professional creative fields, driving imaging needs towards diversification and scenario-based extension. Currently, the demand for ultra-wide-angle imaging has surged significantly, with its application scenarios covering emerging fields such as architectural surveying, virtual reality content production, confined space surveying, and immersive sports recording, becoming an important support for professional tools and creative expression. In ultra-wide-angle imaging technology, fisheye lenses with a 180° circumferential field of view can capture complete hemispherical spatial information in a single frame, demonstrating irreplaceable value in target recognition, spatial relationship reconstruction, and visual effects creation, and gradually becoming a core technical indicator of industry focus. However, when faced with advanced needs such as capturing wider scenes and recreating more immersive spaces, the field of view coverage of existing lenses with 180° circular perspective is significantly limited. They still cannot meet the rigid demand of the new generation of miniaturized devices for extreme wide angles and cannot match the in-depth application scenarios of miniaturized devices in professional fields. Utility Model Content

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a half-frame ultra-wide-angle circular fisheye lens to solve the technical problem that existing half-frame circular fisheye lenses cannot meet the needs of extreme wide-angle viewing.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] This utility model provides a half-frame ultra-wide-angle circular fisheye lens, comprising: a first lens, a second lens, a third lens, a fourth lens, an aperture stop, a fifth lens, a sixth lens, a seventh lens, an eighth lens, and a ninth lens, arranged sequentially from the object plane to the image plane; the first lens and the second lens have negative refractive power and are meniscus lenses, with the object-side and image-side surfaces of the first lens being convex and concave, respectively, and the object-side and image-side surfaces of the second lens being convex and concave, respectively; the third lens has negative refractive power, and both its object-side and image-side surfaces are concave; the fourth lens and the fifth lens both have positive refractive power. The fourth and fifth lenses have convex object-side and image-side surfaces; the sixth lens has negative refractive power and has concave object-side and image-side surfaces; the fifth and sixth lenses are cemented together; the seventh lens has negative refractive power and is a meniscus lens, with its object-side and image-side surfaces being concave and convex respectively; the eighth lens has positive refractive power and has convex object-side and image-side surfaces; the ninth lens has negative refractive power and is a meniscus lens, with its object-side and image-side surfaces being concave and convex respectively; the eighth and ninth lenses are cemented together.

[0006] Among them, the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens are made of glass.

[0007] The focal length of the lens is 4.0±0.3mm, and the total optical length of the lens is 68±0.3mm.

[0008] The aperture of the lens is 2.2 ± 5.

[0009] The first lens, the second lens, the third lens, and the fourth lens form a front group, which satisfies -16.5 ≤ f1 ≤ -16, where f1 is the focal length of the front group; the fifth lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens form a rear group, which satisfies 14 ≤ f2 ≤ 14.6, where f2 is the focal length of the rear group.

[0010] The fifth lens and the sixth lens form a first cemented lens, wherein the first cemented lens satisfies -41.5≤f3≤-41, and f3 is the focal length of the first cemented lens; the eighth lens and the ninth lens form a second cemented lens, wherein the second cemented lens satisfies 18.5≤f4≤19, and f4 is the focal length of the second cemented lens.

[0011] The lens satisfies 3.4≤BFL / EFL≤3.8, where BFL is the equivalent air distance from the image side of the last lens in the lens to the image plane, and EFL is the focal length of the optical system in the infinity focusing state.

[0012] The third lens and the fourth lens form a focusing lens group, and the position of the focusing lens group in the optical axis direction of the lens is adjustable; the focusing lens group satisfies 112≤f5≤112.5, where f5 is the focal length of the focusing lens group.

[0013] Wherein, the refractive index of the first lens is greater than or equal to 1.87 and less than or equal to 1.89, the refractive index of the second lens is greater than or equal to 1.77 and less than or equal to 1.79, the refractive index of the third lens is greater than or equal to 1.48 and less than or equal to 1.5, the refractive index of the fourth lens is greater than or equal to 1.83 and less than or equal to 1.85, the refractive index of the fifth lens is greater than or equal to 1.48 and less than or equal to 1.5, the refractive index of the sixth lens is greater than or equal to 1.84 and less than or equal to 1.86, the refractive index of the seventh lens is greater than or equal to 1.89 and less than or equal to 1.91, the refractive index of the eighth lens is greater than or equal to 1.6 and less than or equal to 1.62, and the refractive index of the ninth lens is greater than or equal to 1.83 and less than or equal to 1.85.

[0014] The Abbe number of the first lens is greater than or equal to 39.1 and less than or equal to 39.3; the Abbe number of the second lens is greater than or equal to 47.4 and less than or equal to 47.6; the Abbe number of the third lens is greater than or equal to 81.5 and less than or equal to 81.7; the Abbe number of the fourth lens is greater than or equal to 23.7 and less than or equal to 23.9; the Abbe number of the fifth lens is greater than or equal to 81.5 and less than or equal to 81.7; the Abbe number of the sixth lens is greater than or equal to 29.9 and less than or equal to 30.1; the Abbe number of the seventh lens is greater than or equal to 31.2 and less than or equal to 31.3; the Abbe number of the eighth lens is greater than or equal to 63.3 and less than or equal to 63.5; and the Abbe number of the ninth lens is greater than or equal to 23.7 and less than or equal to 23.9.

[0015] The advantages of this invention compared to existing technologies are as follows: This invention expands the incident light range by using a meniscus lens with negative diopter, adjusts the diopter by combining biconcave and biconvex lenses to reduce aberrations, and eliminates chromatic aberration by cementing the fifth and sixth lenses and the eighth and ninth lenses. While achieving an extremely wide angle, it ensures image clarity and color reproduction accuracy, improves creative expression and image quality, breaks through the current limitation of a 180° field of view, increases the scene coverage, and better meets the wide-area capture needs in scenarios such as architectural surveying, virtual reality content production, and confined space surveying.

[0016] The above description is only an overview of the technical solution of this utility model. In order to better understand the technical means of this utility model, it can be implemented according to the contents of the specification. In order to make the above and other objects, features and advantages of this utility model more obvious and understandable, the following are preferred embodiments, which are described in detail below. Attached Figure Description

[0017] Figure 1 A schematic diagram of the structure of a half-frame ultra-wide-angle circular fisheye lens provided by this utility model;

[0018] Figure 2 MTF curves of a half-frame ultra-wide-angle circular fisheye lens provided for this utility model at spatial frequencies of 10, 20, and 30 within the entire field of view;

[0019] Figure 3 A relative illumination curve diagram of a half-frame ultra-wide-angle circular fisheye lens provided for this utility model.

[0020] Figure label:

[0021] 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. Ninth lens; 10. Aperture stop. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments. The technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0023] It should be understood that, when used in this specification and the appended claims, the terms “comprising” and “including” indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0024] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0025] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0026] See Figure 1 As shown, this embodiment discloses a half-frame ultra-wide-angle circular fisheye lens, comprising: a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, an aperture stop 10, a fifth lens 5, a sixth lens 6, a seventh lens 7, an eighth lens 8, and a ninth lens 9, arranged sequentially from the object plane to the image plane; the first lens 1 and the second lens 2 have negative refractive power and are meniscus lenses, the object-side surface and the image-side surface of the first lens 1 are convex and concave respectively, and the object-side surface and the image-side surface of the second lens 2 are convex and concave respectively; the third lens 3 has negative refractive power, and both the object-side surface and the image-side surface of the third lens 3 are concave; the fourth lens 4 and The fifth lens 5 has positive refractive power, and the object-side and image-side surfaces of the fourth lens 4 and the fifth lens 5 are both convex. The sixth lens 6 has negative refractive power, and the object-side and image-side surfaces of the sixth lens 6 are both concave. The fifth lens 5 and the sixth lens 6 are cemented together. The seventh lens 7 has negative refractive power and is a meniscus lens, with its object-side and image-side surfaces being concave and convex, respectively. The eighth lens 8 has positive refractive power and both its object-side and image-side surfaces are convex. The ninth lens 9 has negative refractive power and is a meniscus lens, with its object-side and image-side surfaces being concave and convex, respectively. The eighth lens 8 and the ninth lens 9 are cemented together.

[0027] This embodiment of the half-frame ultra-wide-angle circular fisheye lens expands the incident light range by using a meniscus lens with negative diopter, and adjusts the diopter by combining biconcave and biconvex lenses to reduce aberrations. Furthermore, it eliminates chromatic aberration by cementing the fifth lens 5 and the sixth lens 6, and the eighth lens 8 and the ninth lens 9. While achieving an extreme wide-angle view, it ensures image clarity and color reproduction accuracy, improves creative expression and image quality, breaks through the current limitation of 180° field of view, and increases the scene coverage, making the field of view reach 222°. This better meets the wide-area capture needs in scenarios such as architectural surveying, virtual reality content production, and confined space surveying.

[0028] Understandably, the field of view (FOV) refers to the angular range of objects that a lens can capture. Light rays originate from different angles of the subject and are refracted sequentially by the first lens 1 to the ninth lens 9 before being imaged on the image plane. The larger the field of view, the wider the range of angles of the subject that can be imaged by the lens. Diopter is a measure of a lens's ability to deflect light. Positive diopter converges light, while negative diopter diverges it. In this embodiment, the negative diopter of the first lens 1, second lens 2, third lens 3, sixth lens 6, seventh lens 7, and ninth lens 9, combined with the positive diopter of the fourth lens 4, fifth lens 5, and eighth lens 8, regulates the direction of light propagation to adapt to ultra-wide-angle imaging. Meniscus lenses, such as the first lens 1, second lens 2, seventh lens 7, and ninth lens 9, are lenses with one convex and one concave side, which can balance aberrations. Biconcave lenses, such as the third lens 3 and sixth lens 6, can enhance light divergence. Biconvex lenses, such as the fourth lens 4, fifth lens 5, and eighth lens 8, can enhance convergence, ensuring light processing efficiency. The cemented design of the fifth lens 5 and the sixth lens 6, as well as the eighth lens 8 and the ninth lens 9, facilitates the adjustment of light refraction through material matching, reduces light deviation, and achieves orderly guidance and imaging of light. Therefore, this embodiment, through the types and combinations of the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7, the eighth lens 8, and the ninth lens 9, can effectively receive light with a field of view of 222° and can ensure complete imaging and clear edges under ultra-wide-angle conditions.

[0029] In a further embodiment, the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7, the eighth lens 8, and the ninth lens 9 are made of glass. Glass has more stable optical properties, reducing the impact of temperature and humidity changes on the lens's refraction, avoiding imaging deviations caused by material deformation, and compared to resin, it can withstand greater light intensity, ensuring the lens maintains clear 222° ultra-wide-angle imaging even after long-term use. This improves the lens's durability and environmental adaptability, balancing the field of view and imaging capabilities of a half-frame circular lens.

[0030] In a further embodiment, the lens has a focal length of 4.0±0.3mm and an overall optical length of 68±0.3mm. The short focal length of 4.0±0.3mm allows the lens to capture a wider range of light within a limited size, enabling extreme wide-angle imaging; the overall optical length of 68±0.3mm adapts to the space requirements of miniaturized devices such as mirrorless cameras and drones, avoiding an excessively large lens that would affect device portability, and ensuring a 222° ultra-wide field of view while also considering the integration and flexibility of the imaging device.

[0031] In a further embodiment, the lens aperture is 2.2 ± 5. The large aperture of 2.2 ± 5% increases the amount of light entering the lens. Even in low-light scenes, such as surveying in confined spaces or architectural mapping in low-light environments, more light can enter the lens to participate in imaging, reducing image noise, improving image brightness and detail, and ensuring that the image quality in extreme wide-angle scenes still meets professional needs.

[0032] In a further embodiment, the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4 form a front group, satisfying -16.5 ≤ f1 ≤ -16, where f1 is the focal length of the front group. The fifth lens 5, the sixth lens 6, the seventh lens 7, the eighth lens 8, and the ninth lens 9 form a rear group, satisfying 14 ≤ f2 ≤ 14.6, where f2 is the focal length of the rear group. The negative focal length of the front group (-16.5 ≤ f1 ≤ -16) enhances the guidance of incident light divergence, expanding the field of view and laying the foundation for a 222° ultra-wide-angle lens. The positive focal length of the rear group (14 ≤ f2 ≤ 14.6) refocuses the diverged light from the front group onto the image plane, balancing the optical effect of the front group, preventing excessive light divergence that could lead to image blurring, and ensuring image clarity at ultra-wide angles.

[0033] In a further embodiment, the fifth lens 5 and the sixth lens 6 form a first cemented lens, which satisfies -41.5 ≤ f3 ≤ -41, where f3 is the focal length of the first cemented lens. The negative focal length of the first cemented lens (-41.5 ≤ f3 ≤ -41), combined with the refractive index differences of different materials, can assist in adjusting the optical path, further optimize the field of view, accurately eliminate chromatic aberration, and make the color reproduction of the image more accurate, avoiding color fringing problems at the edges in ultra-wide-angle scenes.

[0034] In a further embodiment, the eighth lens 8 and the ninth lens 9 form a second cemented lens, which satisfies 18.5 ≤ f4 ≤ 19, where f4 is the focal length of the second cemented lens. The positive focal length of the second cemented lens (18.5 ≤ f4 ≤ 19) complements the overall optical effect of the rear array, enhancing light convergence, further optimizing the field of view, accurately eliminating chromatic aberration, and making image color reproduction more accurate, thus avoiding color fringing issues at the edges in ultra-wide-angle scenes.

[0035] In a further embodiment, the lens satisfies 3.4 ≤ BFL / EFL ≤ 3.8. In this further embodiment, BFL is the equivalent air distance from the image side of the last lens to the image plane, and EFL is the focal length of the optical system at infinity focus. BFL / EFL is also called the back focal ratio. In this embodiment, the equivalent air distance refers to the distance traveled by light from the image side of the ninth lens 9 to the image plane within the lens medium, converted to its distance in air. The ratio of this distance to the lens's focal length of 4.0 ± 0.3 mm at infinity focus is the back focal ratio. The back focal ratio in this embodiment provides a suitable propagation distance for the light, allowing it to focus smoothly onto the image plane, reducing focusing deviations at large angles, and improving the stability and sharpness of ultra-wide-angle imaging.

[0036] In a further embodiment, the third lens 3 and the fourth lens 4 form a focusing lens group, the position of which is adjustable along the optical axis of the lens. The focusing lens group satisfies 112 ≤ f5 ≤ 112.5, where f5 is the focal length of the focusing lens group in a further embodiment. This adjustable position allows the focusing lens group to adjust the optical path according to the object distance, for example, from infinity to close-up distance, achieving clear focus. The focal length of 112 ≤ f5 ≤ 112.5 stably controls the light refraction angle, avoiding increased aberrations during adjustment. This ensures that at a 222° ultra-wide angle, focusing is achieved from infinity to an object distance of 0.2 meters, enabling clear images for both telephoto and close-up shots, further expanding the lens's shooting applicability.

[0037] In a further embodiment, the refractive index of the first lens 1 is greater than or equal to 1.87 and less than or equal to 1.89, the refractive index of the second lens 2 is greater than or equal to 1.77 and less than or equal to 1.79, the refractive index of the third lens 3 is greater than or equal to 1.48 and less than or equal to 1.5, the refractive index of the fourth lens 4 is greater than or equal to 1.83 and less than or equal to 1.85, the refractive index of the fifth lens 5 is greater than or equal to 1.48 and less than or equal to 1.5, the refractive index of the sixth lens 6 is greater than or equal to 1.84 and less than or equal to 1.86, the refractive index of the seventh lens 7 is greater than or equal to 1.89 and less than or equal to 1.91, the refractive index of the eighth lens 8 is greater than or equal to 1.6 and less than or equal to 1.62, and the refractive index of the ninth lens 9 is greater than or equal to 1.83 and less than or equal to 1.85. The refractive index is the ratio of the speed of light in a vacuum to the speed of light in a medium. It determines the angle of light refraction. In this embodiment, the first lens 1 to the ninth lens 9 are lenses made of glass with specific refractive index ranges. For example, using the first lens 1 and the seventh lens 7 with high refractive index can enhance the light deflection capability and adapt to the ultra-wide-angle optical path. The third lens 3 and the fifth lens 5 with low refractive index can balance the light path intensity and avoid excessive light deflection. The combination of different refractive indices can synergistically control the light propagation path to ensure that the light in the 222° field of view can be refracted in an orderly manner and focused on the image plane, ensuring complete and clear imaging.

[0038] In a further embodiment, the Abbe number of the first lens 1 is greater than or equal to 39.1 and less than or equal to 39.3, the Abbe number of the second lens 2 is greater than or equal to 47.4 and less than or equal to 47.6, the Abbe number of the third lens 3 is greater than or equal to 81.5 and less than or equal to 81.7, the Abbe number of the fourth lens 4 is greater than or equal to 23.7 and less than or equal to 23.9, the Abbe number of the fifth lens 5 is greater than or equal to 81.5 and less than or equal to 81.7, the Abbe number of the sixth lens 6 is greater than or equal to 29.9 and less than or equal to 30.1, the Abbe number of the seventh lens 7 is greater than or equal to 31.2 and less than or equal to 31.3, the Abbe number of the eighth lens 8 is greater than or equal to 63.3 and less than or equal to 63.5, and the Abbe number of the ninth lens 9 is greater than or equal to 23.7 and less than or equal to 23.9. The Abbe number reflects the degree of dispersion of light of different wavelengths by a lens material. Materials with high Abbe numbers have low dispersion, while materials with low Abbe numbers have high dispersion. By combining lenses with different Abbe numbers, the dispersion phenomenon in light propagation can be canceled, reducing chromatic aberration. In this embodiment, the high Abbe number third lens 3 and fifth lens 5 can reduce the dispersion of different wavelengths of visible light. Combined with the structure of the first cemented lens and the second cemented lens, chromatic aberration can be further reduced, allowing light of different colors in the image to be accurately focused, avoiding edge color shift in ultra-wide-angle scenes, improving color reproduction accuracy, and ensuring image quality.

[0039] See Figure 2 As shown, Figure 2The images show the MTF curves of the half-frame ultra-wide-angle circular fisheye lens in this embodiment at spatial frequencies of 10, 20, and 30 within the entire field of view. It can be seen that the MTF curve has a value of ≥0.85 at 30cyc / mm@MTF from the center to the edge and ≥0.5 at the edge, indicating high lens resolution and sharpness.

[0040] See Figure 3 As shown, Figure 3 This is a relative illumination curve of the half-frame ultra-wide-angle circular fisheye lens in this embodiment. As can be seen from the figure, the relative illumination at the edge is greater than 45%, which will not cause vignetting during photography and meets the imaging performance requirements.

[0041] This embodiment provides a half-frame ultra-wide-angle circular fisheye lens that expands the incident light range by using a meniscus lens with negative diopter, and adjusts the diopter by combining biconcave and biconvex lenses to reduce aberrations. Furthermore, it eliminates chromatic aberration by cementing the fifth and sixth lenses, and the eighth and ninth lenses. While achieving an extreme wide-angle view, it ensures image clarity and color reproduction accuracy, improves creative expression and image quality, breaks through the current limitation of a 180° field of view, increases the scene coverage, and better meets the wide-area capture needs in scenarios such as architectural surveying, virtual reality content production, and confined space exploration.

[0042] The above examples are merely illustrative of the technical content of this utility model to facilitate reader understanding, but do not imply that the implementation of this utility model is limited to these embodiments. Any technical extensions or re-creations made based on this utility model are protected by this utility model. The scope of protection of this utility model is defined by the claims.

Claims

1. A half-frame ultra-wide-angle circular fisheye lens, characterized in that, include: The system comprises, in sequence from the object plane to the image plane, a first lens, a second lens, a third lens, a fourth lens, an aperture stop, a fifth lens, a sixth lens, a seventh lens, an eighth lens, and a ninth lens; the first and second lenses have negative refractive power and are meniscus lenses; the object-side and image-side surfaces of the first lens are convex and concave, respectively, as are the object-side and image-side surfaces of the second lens; the third lens has negative refractive power and both its object-side and image-side surfaces are concave; the fourth and fifth lenses both have positive refractive power and both their object-side and image-side surfaces are convex. The sixth lens has negative refractive power, and both its object-side and image-side surfaces are concave. The fifth lens is cemented to the sixth lens. The seventh lens has negative refractive power and is a meniscus lens, with its object-side and image-side surfaces being concave and convex, respectively. The eighth lens has positive refractive power and both its object-side and image-side surfaces are convex. The ninth lens has negative refractive power and is a meniscus lens, with its object-side and image-side surfaces being concave and convex, respectively. The eighth lens is cemented to the ninth lens.

2. The half-frame ultra-wide-angle circular fisheye lens according to claim 1, characterized in that, The first lens, second lens, third lens, fourth lens, fifth lens, sixth lens, seventh lens, eighth lens and ninth lens are made of glass.

3. The half-frame ultra-wide-angle circular fisheye lens according to claim 1, characterized in that, The focal length of the lens is 4.0±0.3mm, and the total optical length of the lens is 68±0.3mm.

4. The half-frame ultra-wide-angle circular fisheye lens according to claim 1, characterized in that, The aperture of the lens is 2.2 ± 5.

5. The half-frame ultra-wide-angle circular fisheye lens according to claim 1, characterized in that, The first lens, the second lens, the third lens, and the fourth lens form a front group, which satisfies -16.5≤f1≤-16, where f1 is the focal length of the front group; the fifth lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens form a rear group, which satisfies 14≤f2≤14.6, where f2 is the focal length of the rear group.

6. The half-frame ultra-wide-angle circular fisheye lens according to claim 1, characterized in that, The fifth lens and the sixth lens form a first cemented lens, wherein the first cemented lens satisfies -41.5≤f3≤-41, where f3 is the focal length of the first cemented lens; the eighth lens and the ninth lens form a second cemented lens, wherein the second cemented lens satisfies 18.5≤f4≤19, where f4 is the focal length of the second cemented lens.

7. The half-frame ultra-wide-angle circular fisheye lens according to claim 1, characterized in that, The lens satisfies 3.4≤BFL / EFL≤3.8, where BFL is the equivalent air distance from the image side of the last lens in the lens to the image plane, and EFL is the focal length of the optical system in the infinity focusing state.

8. The half-frame ultra-wide-angle circular fisheye lens according to claim 1, characterized in that, The third lens and the fourth lens form a focusing lens group, and the position of the focusing lens group in the optical axis direction of the lens is adjustable; the focusing lens group satisfies 112≤f5≤112.5, where f5 is the focal length of the focusing lens group.

9. The half-frame ultra-wide-angle circular fisheye lens according to claim 1, characterized in that, The refractive index of the first lens is greater than or equal to 1.87 and less than or equal to 1.89; the refractive index of the second lens is greater than or equal to 1.77 and less than or equal to 1.79; the refractive index of the third lens is greater than or equal to 1.48 and less than or equal to 1.5; the refractive index of the fourth lens is greater than or equal to 1.83 and less than or equal to 1.85; the refractive index of the fifth lens is greater than or equal to 1.48 and less than or equal to 1.5; the refractive index of the sixth lens is greater than or equal to 1.84 and less than or equal to 1.86; the refractive index of the seventh lens is greater than or equal to 1.89 and less than or equal to 1.91; the refractive index of the eighth lens is greater than or equal to 1.6 and less than or equal to 1.62; and the refractive index of the ninth lens is greater than or equal to 1.83 and less than or equal to 1.

85.

10. The half-frame ultra-wide-angle circular fisheye lens according to claim 1, characterized in that, The Abbe number of the first lens is greater than or equal to 39.1 and less than or equal to 39.3; the Abbe number of the second lens is greater than or equal to 47.4 and less than or equal to 47.6; the Abbe number of the third lens is greater than or equal to 81.5 and less than or equal to 81.7; the Abbe number of the fourth lens is greater than or equal to 23.7 and less than or equal to 23.9; the Abbe number of the fifth lens is greater than or equal to 81.5 and less than or equal to 81.7; the Abbe number of the sixth lens is greater than or equal to 29.9 and less than or equal to 30.1; the Abbe number of the seventh lens is greater than or equal to 31.2 and less than or equal to 31.3; the Abbe number of the eighth lens is greater than or equal to 63.3 and less than or equal to 63.5; and the Abbe number of the ninth lens is greater than or equal to 23.7 and less than or equal to 23.9.

Images