KR20120076210A - Fisheye lens - Google Patents

Abstract

PURPOSE: A fisheye lens is provided to be used in the various applications such as security and monitoring or entertainment by having optical characteristics and mechanical characteristics. CONSTITUTION: A fisheye lens comprises first to seventh lens elements(E1-E7). The first and second lens elements are a negative meniscus lens element. A convex surface of the first and second lens elements is toward the object side. A refractive index of the first lens element and second lens element is greater than or equal to 1.7. The Abbe's number of the first lens element and the second lens element is greater than or equal to 40. The third lens element has positive refractive power. A refractive index of the third lens element is greater than or equal to 1.7. The Abbe's number of the third lens element is greater than or equal to30. A diagram is located between the third lens element and the fourth lens element. At least one among the fourth to seventh lens elements has the positive refractive power. At least one among the fourth to seventh lens elements has negative refractive power.

Description

Fisheye lens {FISHEYE LENS}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fisheye lens, and more particularly to a fisheye lens having an angle of view of 180 ° or more, having a high resolution and following an equidistant projection method.

1 is a conceptual diagram of a real projection scheme of a general imaging lens 112. The Z-axis of the world coordinate describing the object captured by the imaging lens coincides with the optical axis 101 of the imaging lens 112. Incident light 105 having a zenith angle θ with respect to this Z-axis is refracted by the imaging lens 112 and then reflected on the focal plane 132 as refracted ray 106. Converge to an image point P. The distance from the nodal point N of the lens to the focal plane approximately coincides with the effective focal length of the lens. The portion where the actual shop is formed in the focal plane is the image plane.

In order to obtain a clear image, the image plane and the image sensor plane 113 inside the camera body 114 must match. The focal plane and the image sensor plane are perpendicular to the optical axis. The distance from the intersection O between the optical axis 101 and the sensor surface 113 to the shop P is the image height r. The image size r in a general wide angle lens is given by Equation 1.

Here, the unit of the incident angle θ is radians, and the function r (θ) is a monotonically increasing function for the ceiling angle θ of the incident light.

The actual projection method of such a lens can be measured experimentally with a real lens, or can be calculated with a lens design program such as Code V or Zemax with a complete lens design. For example, using the REAY operator in Zemax, you can calculate the y-axis coordinate y on the focal plane of incident light with a given transverse and longitudinal angle of incidence, where the x coordinate in the x-axis direction is similar to the REAX operator. Can be calculated using.

A fisheye lens generally refers to a lens having an angle of view of 160 ° or more and having a generally proportional angle between an incident angle of incident light and an image size. In the true sense, however, a fisheye lens has a field of view of more than 180 ° and is generally proportional to the incident angle of the incident light and the image size. In many cases, such as security, surveillance and entertainment, there are applications that require fisheye lenses with an angle of view of more than 180 °. However, a fisheye lens according to the prior art may have a number of lens elements of 10 or more in order to achieve an angle of view of 180 ° or more, or may be very difficult to manufacture because some lens surfaces of the lens element are close to hemispheres. In addition, some lenses use a relatively small number of lens elements, such as six to eight, but may not have sufficient resolution to provide a clear image because of poor modulation transfer function characteristics. In addition, the manufacturing cost may be increased by using a high refractive index lens glass to keep the lens elements small.

Another factor to consider is the projection method. A preferred projection method of the fisheye lens is an equidistance projection scheme. In the equidistant projection method, an incident angle θ of incident light, an effective focal length f of a fisheye lens, and an image size r _ed on an image surface satisfy a proportional relationship as shown in Equation (2).

The actual projection method of the lens may show some error with the theoretical projection method given by Equation 2. If the image size on the image plane of the actual lens is r _rp , an error between the actual projection method of the lens and the ideal equidistant projection method may be calculated as shown in Equation (3).

Distortion of the fisheye lens is generally measured by f-θ distortion given by Equation 3, and the advanced fisheye lens relatively faithfully implements the equidistant projection method given by Equation 2. Although it is relatively easy to design a fisheye lens having an angle of view of more than 180 degrees, it is quite difficult to design a lens having an angle of view of more than 180 degrees and having a small error within 10% of an equidistant projection method.

However, an important fact in the industrial use of fisheye lenses is the fact that the incident angle of incident light is proportional to the image size on the image plane, and the proportional constant does not necessarily have to be an effective focal length. Therefore, the calibrated distortion of the virtual focal length f _c, in which the f-θ distortion given by Equation 3 is relatively maintained over the entire range of the angle of incidence, is also used as an indicator of the lens performance. In this case, the virtual focal length f _c is given as an optimal fitting constant by the least square error method regardless of the actual effective focal length of the lens. That is, the correction distortion indicates how close the incident angle of incident light and the image size on the sensor surface are to the linear function passing through the origin given by Equation (2).

2 is a conceptual diagram for understanding a field of view (FOV) of a fisheye lens. The image sensor 213 generally has a rectangular shape, and the ratio of the length B of the horizontal side to the length V of the vertical side is usually 4: 3, but an image sensor of 1: 1 or 16: 9 is also found. For example, in the case of the most commonly found 1 / 3-inch CCD sensor, the side length is 4.8 mm, and the length of the length is 3.6 mm. If the maximum incident angle of incident light formed by the fisheye lens is θ ₂ and the corresponding image size is r ₂ = r (θ ₂ ), the diameter 2r ₂ of the image plane is smaller than the length B of the horizontal side of the image sensor plane, When the length of the longitudinal side is greater than V, an image plane with identification number 233 is obtained. Therefore, an image obtained by such an image plane has a maximum angle of view in the horizontal direction and a smaller angle of view in the vertical direction. On the other hand, when the diameter 2r ₂ of the image plane is smaller than the length V of the longitudinal side of the image sensor plane, an image plane with identification number 234 is obtained. When an image plane such as the identification number 234 is obtained, a fisheye image having the same angle of view in all directions about the optical axis may be obtained.

Another consideration in the design of fisheye lenses is to keep the overall length of the lens itself small while ensuring sufficient back focal length. In addition, it is another difficulty to ensure that the ratio of light at the center and the edge of the upper surface, that is, the relative illumination is not too small. If the ambient light ratio is too small, the brightness of the center and the edge will be severely different in the image.

Even if all of these requirements are satisfied, it is difficult to design with sufficient manufacturing tolerances so as not to incur excessive manufacturing difficulties or costs.

For example, in Reference 1, a fisheye lens with an angle of view of 262 ° is presented. However, since the F-number is a dark lens with 14.94, it is difficult to use it unless it is a bright place. References [Film 1] shows a fisheye lens with an angle of view of 170.8 °, which is also dark with an F-number of 7.98, and the shape of the second lens surface of the first lens element is close to the hemisphere, making it difficult to mass-produce. Have. Reference [Exhibit 2] presents fisheye lenses with angles of view of 220 ° and 270 °, with a relatively dark F-number of 5.6, the shape of the second lens surface of the first lens element close to the hemisphere, and the modulation transfer function characteristics. Not enough to get this high resolution image. Reference 3 describes a fisheye lens with an F-number of 2.8 and an angle of view of 180 °. This lens has a relatively good resolution but has a severe distortion with correction distortion of more than 15%. Reference [Special 4] shows a fisheye lens with an F-number of 2.8 and an angle of view of 220 °, but likewise the shape of the second lens surface of the first lens element is close to the hemisphere, and the modulation transfer function characteristic is not sufficient. References [2] show a fisheye lens for projection with an F-number of 2.4 and an angle of view of 163 °, with a low ambient light ratio of 60% at the maximum angle of incidence. Reference [Non 3] presents a revolutionary infrared fisheye lens with an F-number of 0.7, an angle of view of 270 °, and only four lenses. This surprising property is partly due to the very high refractive index of Germanium, which is used as a lens material in the infrared region. However, even in this lens, the second lens surface of the first lens element has a hyper-hemispherical shape, which is very difficult for mass production. Reference [4] shows the characteristics of various commercial fisheye lenses at a glance. However, in most fisheye lenses, the ambient light ratio at the maximum angle of incidence is less than 60% and the correction distortion is as high as 10% or more. Reference [Special 5] shows an innovative fisheye lens with an F-number of 2.0, an angle of view of 180 ° and using only six lens elements. However, since the fisheye lens uses ultra high refractive index glass having a refractive index of 1.91, production costs are high. In addition, the modulation transfer function characteristic is not sufficient. Reference [Special 6] shows a fisheye lens with an F-number of 2.8 and an angle of view of 182 ° that satisfies the projection method given by a special function relationship. However, since the fisheye lens uses 11 lens elements, the structure is complicated and the production cost is high. In addition, the modulation transfer function characteristic is not sufficient. Reference [Special 7] shows a fisheye lens with an F-number of 2.8 and an angle of view of 180 °. This lens also uses only six lens elements, but the production cost is high due to the use of aspherical lens elements. In addition, the modulation transfer function characteristic is not sufficient, and the ambient light ratio at the maximum incident angle is relatively low, such as 70%. On the other hand, Reference [8] shows various embodiments of the wide-angle lens satisfying the useful projection method that can be realized by the wide-angle lens, and Reference [9] shows the horizontal angle of view in the 1 / 3-inch image sensor. The fisheye lens is 190 °, has an F-number of 2.8, and has a good modulation transfer function, good ambient light ratio and fabrication tolerance.

[Special 1] A. C. S. van Heel, G. J. Beernink, and H. J. Raterink, “Wide-angle objective lens,” US Pat. No. 2,947,219 (registration number), registered on August 2, 1960. [Special 2] M. Isshiki and K. Matsuki, "Achromatic super wide-angle lens", US Patent No. 3,524,697 (registration number), dated August 18, 1970. [Special 3] T. Ogura, "Wide-angle lens system with corrected lateral aberration", US Patent No. 3,589,798 (registration number), registration date June 29, 1971. [Special 4] Y. Shimizu, "Wide-angle fisheye lens", US Patent No. 3,737,214 (registration number), registered September 29, 1971. [Special 5] A. Ning, "Compact fisheye objective lens", US Patent No. 7,023,628 (registration number), dated April 4, 2006. [Special 6] K. Yasuhiro and Y. Kazuyoshi, "Fisheye lens and photographing apparatus with the same", Japanese Patent No. 2006-098942 (Publication No.), publication date April 13, 2006. [Special 7] M. Kawada, "Fisheye lens unit", US Patent No. 7,283,312 (registration number), registration date October 16, 2007. [Special 8] Kwon Kyung-il, Milton Rykin, "Wide-angle lens", Republic of Korea Patent No. 10-0826571 (registration number), date of registration April 24, 2008. [Special 9] Kwon Kyung-il, Milton Rykin, "fisheye lens", Republic of Korea Patent No. 10-0888922 (registration number), registration date March 10, 2009.

[Patent 1] K. Miyamoto, "Fish eye lens", J. Opt. Soc. Am., Vol. 54, pp. 1060-1061 (1964). [Non 2] R. Doshi, "Fisheye projection lens for large format film", Proc. SPIE, vol. 2000, pp. 53-61 (1993). [Patent 3] J. B. Caldwell, "Fast IR fisheye lens with hyper-hemispherical field of view", Optics & Photonics News, p. 47 (July, 1999). [Paper 4] J. J. Kumler and M. Bauer, "Fisheye lens designs and their relative performance", Proc. SPIE, vol. 4093, pp. 360-369 (2000). [Patent 5] G. Kweon, Y. Choi and M. Laikin, "Fisheye lens for image processing applications", J. Opt. Soc. Korea, vol. 12, no. 2, pp. 79-87 (2008).

The present invention has a relatively small number of lens elements and has an angle of view of 180 ° or more in place of a conventional fisheye lens having a mechanical structure that is difficult to manufacture or a manufacturing tolerance that is too small to be commercially produced in large quantities. It is an object of the present invention to provide an embodiment of a fisheye lens having a mechanical structure suitable for mass production at a low cost and does not have a large error.

In order to achieve the above object, it provides a specific embodiment having seven lens elements and simultaneously having desirable optical and mechanical properties.

By providing a fisheye lens having both desirable optical and mechanical properties, it can be widely used in various applications such as security, surveillance and entertainment.

1 is a conceptual diagram of a projection method of a general imaging lens.
2 is a conceptual diagram showing the size of an image plane of a preferred fisheye lens with respect to the image sensor plane.
3 is a view showing the optical structure and the path of light of the fisheye lens of the first embodiment of the present invention.
4 is a modulation transfer function characteristic of a fisheye lens of a first embodiment of the present invention.
5 is a graph showing the ambient light quantity ratio of the fisheye lens of the first embodiment of the present invention.
6 is a graph showing image curvature and correction distortion of a fisheye lens of a first embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to FIGS. 3 to 6.

(Embodiment 1)

Figure 3 shows the shape of the fisheye lens and the path of the light ray of the first embodiment of the present invention. The lens had an F-number of 2.0, an angle of view of 190 °, and a 1 / 3-inch CCD sensor. The image size corresponding to the incident angle of 95 ° is given as 2.350 mm so that the horizontal angle of view of the image captured by the camera using such an image sensor is 190 °.

This lens is composed of first lens elements E ₁ to 7 lens elements E ₇ from the object side upwards. The first to seventh lens elements E ₁ to E ₇ are all refractive lens elements which are double-sided spherical surfaces, and the stop S is located between the third lens element E ₃ and the fourth lens element E ₄ . The cover glass C located between the seventh lens element E ₇ and the sensor surface I is not a component of the lens, but is part of the components of the camera body that serve to protect the image sensor surface of the camera.

As described above, the first to seventh lens elements are all refractive lens elements and have two lens surfaces. For example, the first lens element has a first lens surface R _{1 on} the object side and a second lens surface R ₂ on the image side, and the second lens element E ₂ is a third lens on the object side. It has a surface R ₃ and an upper fourth lens surface R ₄ , and the remaining lens elements also have fifth lens surfaces R ₅ to 13th lens surface R ₁₃ . For convenience, the aperture is regarded as the seventh lens surface R ₇ .

Incident light originating from an object point toward the object is incident on the first lens surface R ₁ , which is the refractive surface of the first lens element E ₁ , and subsequently passes through the first to seventh lens elements and the cover glass C. Converge to

Table 1 shows the complete optical design for the fisheye lens of the first embodiment. In Table 1, the units of radius and thicknesses are millimeters. The radius here is exactly the radius of curvature. Since there is no confusion, the radius of curvature is called the radius for convenience.

surface number element 표면 radius thickness index Abbe number glass object infinity infinity One E ₁ R ₁ 12.902 0.98 1.88281 40.76 E-LASF08 2 R ₂ 3.801 2.41 3 E ₂ R ₃ 21.928 0.78 1.88281 40.76 E-LASF08 4 R ₄ 2.909 3.72 5 E ₃ R ₅ 6.700 1.59 1.84635 23.78 E-SF03 6 R ₆ -26.200 2.03 7 Stop R ₇ infinity 0.19 8 E ₄ R ₈ 10.608 1.82 1.74385 44.78 E-LAF2 9 E ₅ R ₉ -2.088 0.57 1.84635 23.78 E-SF03 10 R ₁₀ -7.733 0.20 11 E ₆ R ₁₁ 7.021 0.65 1.84635 23.78 E-SF03 12 E ₇ R ₁₂ 2.572 1.93 1.71987 50.23 E-LAK10 13 R ₁₃ 151.201 2.19 14 Cover R ₁₄ infinity 0.40 1.51673 64.10 E-BK7 15 R ₁₅ infinity 0.55 16 I R ₁₆

3 and Table 1, the first lens element E ₁ of the fisheye lens of the first embodiment of the present invention is a negative meniscus lens element with a convex surface facing towards the object. . In other words, the first lens surface R _{1, which} is the lens surface of the object side of the first lens element, has a convex shape when viewed from the object side, and the second lens surface R _{2, which} is the upper lens surface, is viewed from the upper side. It has the shape of a concave surface. Further, the radius of curvature of the first lens surface is 12.902 mm, and the center of the circle coinciding with the first lens surface is located to the right (i.e., image side) with respect to the first lens surface. Therefore, the direction from the center of the circle toward the vertex on the first lens surface, hereinafter referred to as the direction vector of the first lens surface, is the direction from the image toward the object. Here, the vertex means an intersection point between the lens surface and the optical axis. Further, the radius of curvature of the second lens surface is 3.801 mm, and the center of the circle coinciding with the second lens surface is also located to the right with respect to the second lens surface. Therefore, the direction vector of the second lens surface is also directed toward the object from the upper side. Such a lens element is referred to as a Meniscus lens element when the direction vector of the lens surface on the object side of an lens element coincides with the direction vector of the upper lens surface.

On the other hand, since the radius of curvature of the first lens surface is 12.902 mm and the radius of curvature of the second lens surface is 3.801 mm, the thickness of the lens element measured parallel to the optical axis of the first lens element is thicker at the edge than the center. The first lens element is therefore a lens element with negative refractive power. Putting these facts together, the first lens element is a negative meniscus lens element with the convex surface facing towards the object.

On the other hand, the third lens surface R ₃ of the second lens element E ₂ is a convex surface facing toward the object side, and the fourth lens surface R ₄ is a concave surface facing upward. Further, since the radius of curvature of the third lens surface is 21.928 mm and the radius of curvature of the fourth lens surface is 2.909 mm, the second lens element is also a negative meniscus lens element with the convex surface facing toward the object.

The fifth lens surface R ₅ of the third lens element E ₃ is a convex surface facing toward the object, and the sixth lens surface R ₆ is a convex surface facing upward. Such lenses are referred to as bi-convex lens elements. Biconvex lens elements are always positively refractive since they are thicker than the edges.

Lens configurations such as glass composition and thickness of the spherical lens elements are given in Table 1, and all optical glasses were selected from Hikari glass. For example, the first lens element E ₁ is a high refractive glass having a refractive index of 1.88281 and an Abbe number of 40.76. Hikari's product, which has the refractive index and the optical characteristic closest to Abbe's number, has the trade name E-LASF08. It is assumed that both the second to seventh lens elements use optical glass manufactured by Hikari. However, these designs can easily be adapted to the characteristics of other companies' products, such as Schott and Hoya.

In the present embodiment, the first to second lens elements have the purpose of converting the incident angle of incident light into small, and therefore, all of them have negative refractive power. In particular, since the first lens element is required to convert the incident angle of incident light having an incident angle of 90 ° or more to 90 ° or less, it is inevitably implemented as a negative meniscus lens whose convex surface faces toward the object. However, since the second lens element has the purpose of converting light rays having an angle of incidence of 90 ° or less into light rays having a smaller angle of incidence, it is not necessarily implemented as a negative meniscus lens. Therefore, it may be implemented in any lens form having negative refractive power, such as a plano-concave lens element or a biconcave lens element.

All of the first to second lens elements have a refractive index of at least 1.7 and an Abbe number of at least 40. Such a high refractive index is necessary to obtain a sufficient angle of view without the lens surface being close to the hemisphere, and a relatively high Abbe number is necessary to reduce the variation according to the wavelength.

The third lens element E ₃ mainly serves to compensate for the difference in refractive power according to the wavelength of the first to second lens elements, and has an Abbe number of 30 or less.

As described above, the aperture S is positioned between the third lens element E ₃ and the fourth lens element E ₄ . The aperture is regarded as the seventh lens surface R ₇ having a radius of curvature infinity (∞). Lens elements on the upper side of the aperture are necessary to form a real image on the image sensor surface and have a positive refractive power as a whole. In the present embodiment, the fourth to fourth lens elements are constituted. In particular, the fourth lens element E ₄ closest to the object side and the seventh lens element E ₇ closest to the image side both have positive refractive power.

In the first embodiment of the present invention the fourth lens element E ₄ is a biconvex lens element with positive refractive power, similar to the third lens element E ₃ . The fourth lens element E ₄ and the fifth lens element E ₅ form a cemented doublet. The fourth lens element and the fifth lens element share the ninth lens surface R ₉ due to the nature of the bonded lens. Physically, the upper lens surface of the fourth lens element and the object lens surface of the fifth lens element are processed to have the same curvature and then bonded using optical cement.

The fifth lens element has a ninth lens surface R ₉ and a tenth lens surface R ₁₀ , the ninth lens surface is a concave surface facing toward the object, and the tenth lens surface is a convex surface facing upward. Since both the direction vector of the ninth lens surface and the direction vector of the tenth lens surface point upwards from the object side, this lens element is a meniscus lens element with the convex surface facing upwards. On the other hand, the radius of curvature of the ninth lens surface is -2.088 mm, and the radius of curvature of the tenth lens surface is -7.733 mm. The fifth lens element is thus a negative meniscus lens element whose edge is thicker than the central portion. In sum, the fifth lens element is a negative meniscus lens element with convex surfaces facing upwards.

Meanwhile the sixth lens element E ₆ and the seventh lens element E ₇ also form a junction lens. The sixth lens element of the 11th lens surface R ₁₁ and sangjjok 12th lens surface having an R _12, a seventh lens element of claim 12, the lens surface R ₁₂ and sangjjok thirteenth lens surface R ₁₃ of the object side of the object side Have The sixth lens element is a negative meniscus lens element with the convex surface facing upwards, and the eighth lens element is a positive meniscus lens element with the convex surface facing upwards.

The refractive index of the fourth to seventh lens elements is at least 1.7. The Abbe number of the fourth lens element and the seventh lens element is 40 or more, and the Abbe number of the fifth to sixth lens elements is 30 or less.

In summary, the fisheye lens of the embodiment of the present invention is a fisheye lens having an angle of view of 180 ° or more including the first to seventh lens elements, and has the following characteristics. The first lens element and the second lens element are negative meniscus lens elements with convex surfaces facing towards the object, the refractive index of the first to second lens elements being at least 1.7 and the Abbe number being at least 40. The third lens element has a positive refractive power, wherein the refractive index of the third lens element is at least 1.7 and the Abbe number is at most 30. An aperture is positioned between the third lens element and the fourth lens element. Among the fourth to seventh lens elements are lens elements having at least one positive refractive power and lens elements having at least one negative refractive power. Among the fourth to seventh lens elements, the Abbe number of the lens elements having positive refractive power is 40 or more, and the Abbe number of the lens elements having negative refractive power is 30 or less.

Figure 4 shows the modulation transfer function characteristics in the visible light region of the fisheye lens of Figure 3, it can be seen that it has a resolution of 0.3 or more at 100 line pairs / millimeter. On the other hand, Fig. 5 shows that the ambient light quantity ratio of this fisheye lens is 0.8 or more. In general, if the ambient light ratio is 0.6 or more, it is considered to be good, so the ambient light ratio of this fisheye lens is very excellent. Meanwhile, the left graph of FIG. 6 shows a field curvature of the fisheye lens of the first embodiment, and the right graph shows a calibrated distortion. From this graph, it can be seen that the maximum correction distortion is 5% or less. In other words, this lens implements an equidistant projection method fairly faithfully.

The main characteristic of another lens, the overall length, i.e. the distance from the apex of the first lens plane to the image plane I, is 20.01 mm, so the fisheye lens of this embodiment is quite compact. It also has a sufficient back focal length, so there is no inconvenience in industrial use.

Lastly, the most important characteristic is that the manufacturing tolerance is relatively good. The lens of this embodiment has seven lens elements, and there are a total of 13 lens surfaces. In addition, a number of spacers, retainers and barrels are used to keep these lens elements precisely spaced as defined in Table 1. Since such lens elements and spacers must be mechanically processed, it is impossible to manufacture them accurately and without errors as designed. That is, there is some error. However, since Table 1 is a design that is optimized to have a given characteristic, if the design and the error has a degree of degradation occurs. However, according to the lens design, the range of processing error causing a certain amount of performance degradation is different. Good design results in relatively small degradation in performance even with large machining errors.

The manufacturing tolerances available with current production techniques vary among lens manufacturers, but general manufacturing tolerances are almost common. For example, the thickness tolerance is 20 µm, and the manufacturing tolerance of the radius of the lens surface is Newton ring 3 fringe. In this way, even if manufactured in the general manufacturing tolerances can be produced at low cost if the performance degradation is not large. However, if you try to produce a production tolerance smaller than the general production tolerances in order to reduce the performance degradation or defective rate, the production may be difficult or impossible, even if possible, the production cost is high, and mass production may be difficult. Therefore, a design that does not have sufficient manufacturing tolerances, even if it satisfies all desirable optical and mechanical properties, is not a good design.

The first embodiment of the present invention is a design that is good enough to maintain the failure rate at a general level even if fabricated with a general manufacturing tolerance. Such manufacturing tolerances can be identified through a process called tolerance analysis. If you have a complete lens design as shown in Table 1, you can easily check using a lens design program such as Zemax.

Preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings. However, the detailed description and the embodiments of the present invention are merely exemplary, and it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

The fisheye lens of the embodiment of the present invention has excellent optical properties and mechanical structure, but is large in manufacturing tolerance, and is suitable for mass production at low cost.

101: optical axis
112: lens
114: camera body
113, 213: sensor surface
132: focal plane
105: incident light
106: refractive light
233, 234: video plane
E ₁ to E ₇ : first to seventh lens elements
R ₁ to R ₁₆ : first to sixteenth lens surfaces
S: stop
C: cover glass
I: image sensor plane

Claims (4)

A fisheye lens comprising first to seventh lens elements,
The first lens element and the second lens element are negative meniscus lens elements with convex surfaces facing towards the object,
The refractive index of the first to second lens elements is at least 1.7 and the Abbe number is at least 40,
The third lens element has a positive refractive power,
The refractive index of the third lens element is at least 1.7 and the Abbe number is at most 30,
An aperture is located between the third lens element and the fourth lens element,
Among the fourth to seventh lens elements there are lens elements having at least one positive refractive power and lens elements having at least one negative refractive power,
The Abbe number of the lens elements having positive refractive power among the fourth to seventh lens elements is 40 or more,
Fisheye lens, characterized in that the Abbe number of the lens element having a negative refractive power of the fourth to seventh lens element is 30 or less.
The method of claim 1,
The third lens element and the fourth lens element are biconvex lens elements,
The fifth lens element is a negative meniscus lens element with the convex surface facing upwards,
The sixth lens element is a negative meniscus lens element with the convex surface facing towards the object,
The seventh lens element is a fisheye lens, characterized in that the convex surface is a positive meniscus lens element facing towards the object.
The method of claim 2,
The refractive indices of the fourth and seventh lens elements are between 1.7 and 1.8,
Fisheye lens, characterized in that the refractive index of the fifth to sixth lens element is 1.8 or more.
The method of claim 3,
The fourth lens element and the fifth lens element constitute a junction lens,
A fish-eye lens, characterized in that the sixth lens element and the seventh lens element also constitute a junction lens.

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