KR101070991B1 - Fisheye lens - Google Patents

Abstract

The present invention provides a fisheye lens having an angle of view greater than 180 °, a maximum correction distortion of 10% or less, and an ambient light ratio of 90% or more. One embodiment of the invention includes first to eighth lens elements. The refractive surfaces of all the lens elements are spherical, the first lens element is a negative meniscus lens element with the convex surface facing towards the object, the second lens element is a concave lens element, and the third lens element is the convex surface with the object A negative meniscus lens element directed towards, the fourth lens element is a positive convex lens element, the refractive index of the first to fourth lens elements is at least 1.7, and the Abbe number of the first to third lens elements is at least 40 And the Abbe number of the fourth lens element is 30 or less, and the aperture is located between the fourth lens element and the fifth lens element.

Fisheye lens, equidistant projection

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, the REAY operator in Zemax allows you to calculate the y-axis coordinate y on the focal plane of incident light with a given horizontal and vertical 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 requiring fisheye lenses with an angle of view of 180 ° or more. However, the 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 the hemisphere. 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 on 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 edges in the image will be severely different.

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, reference 1 shows a fisheye lens with an angle of view of 262 °. However, since the F-number is a dark lens with 14.94, it is difficult to use it unless it is a bright place. Reference 2 shows a fisheye lens with an angle of view of 170.8 °, which is also dark with an F-number of 7.98 and has a structure that is difficult for mass production because the shape of the second lens surface of the first lens element is close to the hemisphere. Reference 3 shows 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 face of the first lens element close to the hemisphere, and the modulation transfer function characteristic Insufficient to get Reference 4 presents 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 5 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 characteristics are not sufficient. Reference 6 presents 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 7 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 hyperhemisphere shape, which is very difficult for mass production. Reference 8 clearly shows the characteristics of various commercial fisheye lenses. 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 9 presents a landmark 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 10 presents a fisheye lens with an F-number of 2.8 and an angle of view of 182 ° that satisfies the projection 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 11 presents 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 production costs are high because of 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 12 shows various embodiments of the wide-angle lens that satisfies the useful projection method that can be implemented by the wide-angle lens, and References 13 to 15 have a horizontal angle of view of 190 ° in a 1 / 3-inch image sensor. , F-number is 2.8, fisheye lens with good modulation transfer function, good ambient light ratio and fabrication tolerance is presented.

[Reference 1] A. C. S. van Heel, G. J. Beernink, and H. J. Raterink, “Wide-angle objective lens,” US Pat. No. 2,947,219 (registration no.), Dated August 2, 1960.

[Reference 2] K. Miyamoto, "Fish eye lens", J. Opt. Soc. Am., Vol. 54, pp. 1060-1061 (1964).

[Reference 3] M. Isshiki and K. Matsuki, "Achromatic super wide-angle lens", US Patent No. 3,524,697 (registration number), dated August 18, 1970.

[Reference 4] T. Ogura, "Wide-angle lens system with corrected lateral aberration", US Pat. No. 3,589,798 (registration no.), Dated June 29, 1971.

[Reference 5] Y. Shimizu, "Wide-angle fisheye lens", US Patent No. 3,737,214 (registration number), registered September 29, 1971.

[Reference 6] R. Doshi, "Fisheye projection lens for large format film", Proc. SPIE, vol. 2000, pp. 53-61 (1993).

[Reference 7] J. B. Caldwell, "Fast IR fisheye lens with hyper-hemispherical field of view", Optics & Photonics News, p. 47 (July, 1999).

[Reference 8] J. J. Kumler and M. Bauer, "Fisheye lens designs and their relative performance", Proc. SPIE, vol. 4093, pp. 360-369 (2000).

[Reference 9] A. Ning, "Compact fisheye objective lens", US Pat. No. 7,023,628 (registration number), dated April 4, 2006.

[Ref. 10] K. Yasuhiro and Y. Kazuyoshi, "Fisheye lens and photographing apparatus with the same", Japanese Patent No. 2006-098942 (Publication No.), published April 13, 2006.

[Ref. 11] M. Kawada, "Fisheye lens unit", US Pat. No. 7,283,312 (registration number), registered October 16, 2007.

[Reference 12] Kwon Kyung-il, Milton Rykin, "Wide-angle lens", Republic of Korea Patent No. 10-0826571 (registration number), registration date April 24, 2008.

[Reference 13] Kwon Kyung-il, Milton Rykin, "fisheye lens", Republic of Korea Patent No. 10-0888922 (registration number), registration date March 10, 2009.

[Ref. 14] M. Laikin, G. Kweon and Y. Choi, "Day and night security camera", Proc. SPIE, vol. 7060, pp. 706009-1-706009-5 (2008).

[Reference 15] 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 commercially produce in large quantities. It is an object of the present invention to provide various embodiments of a fisheye lens having a mechanical structure suitable for mass production at a low cost without a large error.

In order to achieve the above object, it provides a specific embodiment having eight 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 or entertainment.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to FIGS. 1 to 18.

(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 2.339 mm so that the horizontal angle of view of the image captured by the camera using such an image sensor is 190 °.

This lens consists of first lens elements E ₁ to eighth lens elements E ₈ from the object side up. The first to eighth lens elements E ₁ to E ₈ are all refractive lens elements which are double-sided spherical surfaces, and the aperture S is located between the fourth lens element E ₄ and the fifth lens element E ₅ . The optical low pass filter F, located between the eighth lens element E ₈ and the sensor plane I, is not a component of the lens but is part of the components of the camera body covered over the image sensor surface of the camera. . The role of the optical low pass filter is to remove the moire effect from the image. 3 shows that the lens is designed considering this optical low pass filter.

As described above, the first to eighth 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 16th lens surface R ₁₆ . For convenience, the aperture is regarded as the ninth lens surface R ₉ .

The incident light originating from an object point toward the object enters the first lens surface R ₁ , which is the refractive surface of the first lens element E ₁ , and then sequentially passes through the first to eighth lens elements and the optical low pass filter F. Converges to sensor plane I.

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 15.471 0.910 1.8346 42.72 E-LASF05 2 R ₂ 3.885 2.690 3 E ₂ R ₃ -32.065 0.700 1.8346 42.72 E-LASF05 4 R ₄ 4.027 1.220 5 E ₃ R ₅ 10.444 0.800 1.8346 42.72 E-LASF05 6 R ₆ 5.449 1.130 7 E ₄ R ₇ 8.203 2.290 1.7616 26.56 E-SF14 8 R ₈ -8.203 3.540 9 S R ₉ infinity 0.200 10 E ₅ R ₁₀ 23.953 1.510 1.6399 60.09 E-LAK01 11 R ₁₁ -4.087 0.260 12 E ₆ R ₁₂ -3.190 0.710 1.8464 23.78 E-SF03 13 R ₁₃ -5.184 0.180 14 E ₇ R ₁₄ 12.877 0.600 1.8464 23.78 E-SF03 15 E ₈ R ₁₅ 3.763 2.410 1.6203 60.29 E-SK16 16 R ₁₆ -5.978 1.908 17 F R ₁₇ infinity 3.000 1.5167 64.10 E-BK7 18 R ₁₈ infinity 1,000 19 I R ₁₉

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 15.471 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 3.885 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 15.471 mm and the radius of curvature of the second lens surface is 3.885 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 concave surface facing toward the object side, and the fourth lens surface R ₄ is a concave surface facing upward. Such lenses are referred to as bi-concave lens elements. Amphipathic lens elements always have negative refractive power because their edges are thicker than the center region.

The third lens element E ₃ , like the first lens element E ₁ , is a negative meniscus lens element with a convex surface facing towards the object. On the other hand, the seventh lens surface R ₇ of the fourth lens element E ₄ is a convex surface facing toward the object side, and the eighth lens surface R ₈ 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 1.8346 and an Abbe number of 42.72. Hikari's product, which has the refractive index and the optical characteristic closest to Abbe's number, has the trade name E-LASF05. It is assumed that all of the second to eighth 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 main role of the third lens element E ₃ and the fourth lens element E ₄ is to compensate for the difference in refractive power according to the wavelength of the first to second lens elements, and the lens element having an Abbe number of 30 or less and the Abbe of 40 or more. Numbered lens elements are used together. In this embodiment, the third lens element has an index of refraction of 1.7 or more and an Abbe number of 40 or more, and the fourth lens element has a refractive index of 1.7 or more and an Abbe number of 30 or less. In particular, the third lens element is a negative meniscus lens element having a refractive index of at least 1.7, an Abbe number of at least 40, and a convex surface facing toward the object. On the other hand, the fourth lens element is a biconvex lens element having a refractive index of 1.7 or more and an Abbe number of 30 or less.

As described above, the aperture S is positioned between the fourth lens element E ₄ and the fifth lens element E ₅ . The iris is regarded as the ninth lens surface R ₉ 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 this embodiment, it is composed of the fifth to eighth lens elements. In particular, the fifth lens element E ₅ closest to the object side and the eighth lens element E ₈ closest to the image side both have positive refractive power.

In the first embodiment of the invention the fifth lens element E ₅ is a biconvex lens element with positive refractive power, similar to the fourth lens element E ₄ . On the other hand, the sixth lens element has a twelfth lens surface R ₁₂ and a thirteenth lens surface R ₁₃ , the twelfth lens surface is a concave surface facing toward the object, and the thirteenth lens surface is a convex surface facing upward. Since the direction vector of the twelfth lens face and the direction vector of the thirteenth lens face both point upward from the object side, this lens element is a meniscus lens element with the convex face facing upward. On the other hand, the radius of curvature of the twelfth lens surface is -3.190 mm, and the radius of curvature of the thirteenth lens surface is -5.184 mm. The sixth lens element is thus a negative meniscus lens element whose edge is thicker than the central portion. In total, the sixth lens element is a negative meniscus lens element with the convex surface facing upwards.

The seventh lens element E ₇ and the eighth lens element E ₈ , on the other hand, form a cemented doublet. The seventh lens element to the object side of the first 14 lens surfaces R ₁₄ and sangjjok claim 15 having a lens surface R _15, an eighth lens element of claim 15, the lens surface on the object side R ₁₅ and sangjjok 16th lens surface R ₁₆ of the Have The seventh lens element and the eighth lens element share the fifteenth lens surface R ₁₅ due to the nature of the bonded lens. Physically, the upper lens surface of the seventh lens element and the object-side lens surface of the eighth lens element are processed to have the same curvature and then bonded using optical cement. The seventh lens element is a negative meniscus lens element with the convex surface facing upwards, and the eighth lens element is a positive convex lens element.

The refractive index of the fifth lens element is 1.6 or more, the Abbe number is 50 or more, the refractive index of the sixth to seventh lens elements is 1.7 or more, the Abbe number is 30 or less, the refractive index of the eighth lens element is 1.6 or more and the Abbe number is 50 or more. Optical glass having an Abbe's number of 50 or higher and a refractive index of 1.7 or higher is not common. Therefore, the low dispersion lens of Abbe number 50 or more has a relatively low refractive index. The fifth lens element and the eighth lens element have Abbe's number as high as 50 or more, while the refractive index has a relatively low value of 1.6 or more. On the other hand, the sixth lens element and the seventh lens element are highly dispersed optical glass having Abbe number of 30 or less, and a material having a refractive index of 1.7 or more can be obtained.

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 0.2 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 almost 0.9 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 8% 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 25.058 mm, which makes the fisheye lens of this embodiment 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 eight lens elements, and there are 16 lens surfaces in total. 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.

(Second Embodiment)

Figure 7 shows the shape of the fisheye lens and the path of the light ray of the second embodiment of the present invention. The lens had an F-number of 2.0, an angle of view of 184 °, and a 1 / 3-inch CCD sensor. The image size corresponding to the incident angle of 92 ° is given as 2.329 mm so that the horizontal angle of view of the image captured by the camera using such an image sensor is 184 °.

The overall shape of the fisheye lens of this embodiment is the same as the overall shape of the fisheye lens of the first embodiment of the present invention, the specific shapes of which are shown in Table 2.

surface number element 표면 radius thickness index Abbe number glass object infinity infinity One E ₁ R ₁ 16.106 0.930 1.8346 42.72 E-LASF05 2 R ₂ 3.932 2.590 3 E ₂ R ₃ -30.461 0.770 1.8346 42.72 E-LASF05 4 R ₄ 4.111 1.120 5 E ₃ R ₅ 10.391 0.740 1.8346 42.72 E-LASF05 6 R ₆ 5.473 1.110 7 E ₄ R ₇ 8.219 2.380 1.7616 26.56 E-SF14 8 R ₈ -8.219 3.680 9 S R ₉ infinity 0.160 10 E ₅ R ₁₀ 22.797 1.500 1.6399 60.09 E-LAK01 11 R ₁₁ -3.963 0.220 12 E ₆ R ₁₂ -3.217 0.700 1.8049 25.43 E-SF6 13 R ₁₃ -5.619 0.200 14 E ₇ R ₁₄ 13.476 0.600 1.8049 25.43 E-SF6 15 E ₈ R ₁₅ 3.590 2.440 1.6203 60.29 E-SK16 16 R ₁₆ -6.032 1.925 17 F R ₁₇ infinity 3.000 1.5167 64.10 E-BK7 18 R ₁₈ infinity 1,000 19 I R ₁₉

FIG. 8 shows modulation transfer function characteristics in the visible light region of the fisheye lens of FIG. 7 and has a resolution of 0.3 or more at 100 line pairs / millimeter. On the other hand, Figure 9 shows that the peripheral light ratio of the fisheye lens is more than 0.9, the left graph of Figure 10 shows the image surface curvature of the fisheye lens of the second embodiment, the right graph shows the correction distortion. From this graph, it can be seen that the maximum correction distortion is 8% or less. In other words, this lens implements an equidistant projection method fairly faithfully.

Another key feature of the lens is the full length, ie the distance from the apex of the first lens plane to the image plane I, 25.065 mm, which makes the fisheye lens of this embodiment quite compact and has a sufficient rear focal length, which is not at all suitable for industrial use. There is no inconvenience. In addition, the manufacturing tolerance of the fisheye lens of the second embodiment is better than the manufacturing tolerance of the first embodiment.

(Third Embodiment)

11 shows the shape of the fisheye lens and the path of the light beam of the third embodiment of the present invention. The lens had an F-number of 2.0, an angle of view of 184 °, and a 1 / 3-inch CCD sensor. The image size corresponding to the incident angle of 92 ° is given as 2.340 mm so that the horizontal angle of view of the image captured by the camera using such an image sensor is 184 °. The fisheye lens of the third embodiment of the present invention is a lens that improves optical performance by mitigating constraints on the overall length of the optical system.

The overall shape of the fisheye lens of this embodiment is the same as the overall shape of the fisheye lens of the first to second embodiments of the present invention, the specific shapes of which are shown in Table 3.

surface number element 표면 radius thickness index Abbe number glass object infinity infinity One E ₁ R ₁ 20.256 2.350 1.8346 42.72 E-LASF05 2 R ₂ 4.323 3.200 3 E ₂ R ₃ -22.855 1.660 1.8346 42.72 E-LASF05 4 R ₄ 4.645 1.230 5 E ₃ R ₅ 10.521 1.200 1.8338 37.16 E-LASF010 6 R ₆ 5.757 1.080 7 E ₄ R ₇ 8.413 2.520 1.7405 27.79 E-SF13 8 R ₈ -8.413 4.300 9 S R ₉ infinity 0.190 10 E ₅ R ₁₀ 18.122 1.540 1.6399 60.09 E-LAK01 11 R ₁₁ -4.266 0.250 12 E ₆ R ₁₂ -3.436 0.750 1.8049 25.43 E-SF6 13 R ₁₃ -6.452 0.230 14 E ₇ R ₁₄ 13.875 0.690 1.8049 25.43 E-SF6 15 E ₈ R ₁₅ 3.850 2.440 1.6203 60.29 E-SK16 16 R ₁₆ -6.220 1.982 17 F R ₁₇ infinity 3.000 1.5167 64.10 E-BK7 18 R ₁₈ infinity 1,000 19 I R ₁₉

12 shows the modulation transfer function characteristics in the visible light region of the fisheye lens of FIG. Meanwhile, FIG. 13 shows that the ambient light ratio of the fisheye lens is 0.9 or more, the left graph of FIG. 14 shows the image surface curvature of the fisheye lens of the third embodiment, and the right graph shows the correction distortion. From this graph, it can be seen that the maximum correction distortion is 7% or less. In other words, this lens implements an equidistant projection method fairly faithfully.

Another key feature of the lens is the total length, i.e. the distance from the apex of the first lens plane to the image plane I, 29.612 mm, which makes the fisheye lens of this embodiment quite compact and has a sufficient rear focal length, which is inconvenient for industrial use. There is no Moreover, it has a favorable manufacturing tolerance.

The fisheye lenses of the first to third embodiments of the present invention share the following features. That is, the fisheye lens of the first to third embodiments of the present invention is a fisheye lens having the first to eighth lens elements, wherein the refractive surfaces of all the lens elements are spherical surfaces, and the first lens elements are convex surfaces facing the object. A negative meniscus lens element, the second lens element is a cataclysmic lens element, the third lens element is a negative meniscus lens element with convex surfaces facing towards the object, and the fourth to fifth lens elements are positive The sixth lens element is a negative meniscus lens element with the convex surface facing upwards, the seventh lens element is a negative meniscus lens element with the convex surface facing towards the object, and the eighth lens element Is a biconvex lens element and an aperture is located between the fourth lens element and the fifth lens element.

(Fourth embodiment)

Figure 15 shows the shape of the fisheye lens and the path of the light ray of the fourth embodiment of the present invention. The lens had an F-number of 2.0, an angle of view of 184 °, and a 1 / 3-inch CCD sensor. The image size corresponding to the incident angle of 92 ° is given as 2.336 mm so that the horizontal angle of view of the image captured by the camera using such an image sensor is 184 °.

This lens is also composed of first lens elements E ₁ to eighth lens elements E ₈ from the object side upward. The first to eighth lens elements E ₁ to E ₈ are all refractive lens elements which are double-sided spherical surfaces, and the aperture S is located between the fourth lens element E ₄ and the fifth lens element E ₅ . The overall shape of the first to fourth lens elements in this embodiment is the same as that of the first to third embodiments.

The incident light originating from an object point toward the object enters the first lens surface R ₁ , which is the refractive surface of the first lens element E ₁ , and then sequentially passes through the first to eighth lens elements and the optical low pass filter F. Converges to sensor plane I. Table 4 shows the complete optical design for the fisheye lens of the fourth embodiment.

surface number element 표면 radius thickness index Abbe number glass object infinity infinity One E ₁ R ₁ 12.557 0.940 1.8346 42.72 E-LASF05 2 R ₂ 3.977 2.840 3 E ₂ R ₃ -22.464 0.750 1.8346 42.72 E-LASF05 4 R ₄ 3.646 1.390 5 E ₃ R ₅ 9.849 0.880 1.7290 54.66 E-LAK18 6 R ₆ 6.940 1.370 7 E ₄ R ₇ 7.988 2.230 1.7616 26.56 E-SF14 8 R ₈ -7.988 2.630 9 S R ₉ infinity 0.200 10 E ₅ R ₁₀ 10.159 1.840 1.5890 61.16 E-SK5 11 E ₆ R ₁₁ -2.414 0.490 1.8049 25.43 E-SF6 12 R ₁₂ 13.335 0.320 13 E ₇ R ₁₃ -53.978 1.430 1.6203 60.29 E-SK16 14 R ₁₄ -4.417 0.160 15 E ₈ R ₁₅ 10.118 1.700 1.7290 54.66 E-LAK18 16 R ₁₆ -14.555 1.887 17 F R ₁₇ infinity 3.000 1.5167 64.10 E-BK7 18 R ₁₈ infinity 1,000 19 I R ₁₉

Referring to Fig. 15 and Table 4, the first lens element E ₁ of the fisheye lens of the fourth embodiment of the present invention is a negative meniscus lens element with a convex surface facing toward the object, and the second lens element is a biconcave lens element. The third lens element is a negative meniscus lens with the convex surface facing towards the object, and the fourth lens element is a positive convex lens element. On the other hand, the fifth lens element is a biconvex lens element, the sixth lens element is a biconvex lens element, the seventh lens element is a positive meniscus lens element with the convex surface facing upwards, and the eighth lens element is positive Convex lens element.

Lens configurations such as glass composition and thickness of the spherical lens elements are given in Table 4, and all optical glasses were selected from Hikari glass. 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 the incident light, so that 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. 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 main role of the third lens element E ₃ and the fourth lens element E ₄ is to compensate for the difference in refractive power according to the wavelength of the first to second lens elements, and the lens element having an Abbe number of 30 or less and the Abbe of 40 or more. Numbered lens elements are used together. In this embodiment, the third lens element has an index of refraction of 1.7 or more and an Abbe number of 40 or more, and the fourth lens element has a refractive index of 1.7 or more and an Abbe number of 30 or less. In particular, the third lens element is a negative meniscus lens element having a refractive index of at least 1.7, an Abbe number of at least 40, and a convex surface facing toward the object. On the other hand, the fourth lens element is a biconvex lens element having a refractive index of 1.7 or more and an Abbe number of 30 or less.

As described above, the aperture S is positioned between the fourth lens element E ₄ and the fifth lens element E ₅ . The iris is regarded as the ninth lens surface R ₉ 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 this embodiment, it is composed of the fifth to eighth lens elements. In particular, the fifth lens element E ₅ closest to the object side and the eighth lens element E ₈ closest to the image side both have positive refractive power.

In a fourth embodiment of the invention the fifth lens element E ₅ is a biconvex lens element with positive refractive power, similar to the fourth lens element E ₄ . On the other hand, the sixth lens element is a biconvex lens element having an eleventh lens surface R ₁₁ and a twelfth lens surface R ₁₂ . The fifth lens element E ₅ and the sixth lens element E ₆ form a cemented doublet. The fifth and sixth lens elements share the eleventh lens surface R ₁₁ in the nature of the bonded lens.

The refractive index of the fifth lens element is 1.5 or more, the Abbe number is 50 or more, the refractive index of the sixth lens element is 1.7 or more, the Abbe number is 30 or less, the refractive index of the seventh and eighth lens elements is 1.6 or more, Abbe's number is over 50.

Optical glass having an Abbe number of 50 or higher and a refractive index of 1.7 or more is not common, and a low dispersion lens having an Abbe number of 50 or higher has a relatively low refractive index. Thus, the seventh lens element and the eighth lens element have Abbe's number as high as 50 or more, and the refractive index has a relatively low value of 1.6 or more. On the other hand, the sixth lens element is a highly dispersed optical glass having an Abbe number of 30 or less, and a material having a refractive index of 1.7 or more can be obtained.

The fisheye lens of the fourth embodiment of the present invention is a fisheye lens having first to eighth lens elements, wherein the refractive surfaces of all the lens elements are spherical, and the first lens element is a negative meniscus with the convex surface facing toward the object. The lens element, the second lens element is a amphipathic lens element, the third lens element is a negative meniscus lens element with the convex surface facing towards the object, and the fourth to fifth lens elements are biconvex lens elements, The sixth lens element is a biconvex lens element, the seventh lens element is a positive meniscus lens element with the convex surface facing upwards, and the eighth lens element is a biconvex lens element, and the fourth and fifth lenses. A diaphragm is positioned between the elements.

FIG. 16 shows modulation transfer function characteristics in the visible light region of the fisheye lens of FIG. 15, and it can be seen that the resolution has a resolution of 0.1 or more at 100 line pairs / millimeter. On the other hand, Fig. 17 shows that the peripheral light quantity ratio of this fisheye lens is 0.9 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. 18 shows a field curvature of the fisheye lens of the fourth embodiment, and the right graph shows calibrated distortion. From this graph, it can be seen that the maximum correction distortion is 6% 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 25.057 mm, which makes the fisheye lens of this embodiment quite compact. In addition, it has a sufficient rear focal length, so there is no inconvenience in industrial use, and the manufacturing tolerance is relatively good.

The fisheye lenses of the first, second and fourth embodiments of the present invention share the following features. That is, the fisheye lens of the first, second and fourth embodiments of the present invention is a fisheye lens having first to eighth lens elements, wherein the refractive surfaces of all the lens elements are spherical, and the first lens element is The convex surface is a negative meniscus lens element facing towards the object, the second lens element is a cataclysmic lens element, the third lens element is a negative meniscus lens element facing toward the object, and a fourth The lens element is a biconvex lens element, the refractive index of the first to fourth lens elements is 1.7 or more, the Abbe number of the first to third lens elements is 40 or more, the Abbe number of the fourth lens element is 30 or less, An aperture is positioned between the fourth lens element and the fifth lens element.

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.

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.

Fig. 7 shows the optical structure and the path of the light beam of the fisheye lens of the second embodiment of the present invention.

8 is a modulation transfer function characteristic of a fisheye lens of a second embodiment of the present invention.

9 is a graph showing the ambient light ratio of the fisheye lens of the second embodiment of the present invention.

10 is a graph showing image curvature and correction distortion of a fisheye lens of a second embodiment of the present invention.

FIG. 11 shows the optical structure and the path of light of the fisheye lens of the third embodiment of the present invention. FIG.

12 is a modulation transfer function characteristic of a fisheye lens of a third embodiment of the present invention.

Fig. 13 is a graph showing the ambient light quantity ratio of the fisheye lens of the third embodiment of the present invention.

14 is a graph showing image curvature and correction distortion of a fisheye lens of a third embodiment of the present invention.

Fig. 15 shows the optical structure and the path of the light beam of the fisheye lens of the fourth embodiment of the present invention.

16 is a modulation transfer function characteristic of a fisheye lens of a fourth embodiment of the present invention.

Fig. 17 is a graph showing the ambient light quantity ratio of the fisheye lens of the fourth embodiment of the present invention.

18 is a graph showing image curvature and correction distortion of a fisheye lens of a fourth embodiment of the present invention.

Claims (11)

A fisheye lens comprising first to eighth lens elements, The refractive surface of all lens elements is spherical, The first lens element is a negative meniscus lens element with the convex surface facing towards the object, The second lens element is a diorama lens element, The third lens element is a negative meniscus lens element with the convex surface facing towards the object, The fourth lens element is a biconvex lens element, The refractive index of the first to fourth lens elements is at least 1.7, The Abbe's number of the first to third lens elements is 40 or more, The Abbe's number of the fourth lens element is 30 or less, A fisheye lens, characterized in that the aperture is located between the fourth lens element and the fifth lens element. The method of claim 1, The fifth lens element is a biconvex lens element, The sixth lens element is a negative meniscus lens element with the convex surface facing upwards, The seventh lens element is a negative meniscus lens element with the convex surface facing towards the object, Fisheye lens, characterized in that the eighth lens element is a biconvex lens element. 3. The method of claim 2, The refractive index of the fifth lens element is at least 1.6 and the Abbe number is at least 50, The refractive index of the sixth to seventh lens elements is at least 1.7 and the Abbe number is at most 30, A fisheye lens, characterized in that the refractive index of the eighth lens element is at least 1.6 and the Abbe number is at least 50. The method of claim 3, wherein A fish-eye lens, characterized in that the seventh lens element and the eighth lens element constitute a joint lens. The method of claim 1, The fifth lens element is a biconvex lens element, The sixth lens element is a bilateral lens element, The seventh lens element is a positive meniscus lens element with the convex surface facing upwards, Fisheye lens, characterized in that the eighth lens element is a biconvex lens element. The method of claim 5, The refractive index of the fifth lens element is at least 1.5 and the Abbe number is at least 50, The refractive index of the sixth lens element is 1.6 or more and the Abbe number is 30 or less, A fisheye lens, characterized in that the refractive index of the seventh to eighth lens elements is at least 1.6 and the Abbe number is at least 50. The method of claim 1, The fisheye lens of claim 5, wherein the fifth lens element and the sixth lens element constitute a cemented lens. A fisheye lens comprising first to eighth lens elements, The refractive surface of all lens elements is spherical, The first lens element is a negative meniscus lens element with the convex surface facing towards the object, The second lens element is a diorama lens element, The third lens element is a negative meniscus lens element with the convex surface facing towards the object, The fourth to fifth lens elements are biconvex lens elements, The sixth lens element is a negative meniscus lens element with the convex surface facing upwards, The seventh lens element is a negative meniscus lens element with the convex surface facing towards the object, The eighth lens element is a biconvex lens element, A fisheye lens, characterized in that the aperture is located between the fourth lens element and the fifth lens element. delete A fisheye lens comprising first to eighth lens elements, The refractive surface of all lens elements is spherical, The first lens element is a negative meniscus lens element with the convex surface facing towards the object, The second lens element is a diorama lens element, The third lens element is a negative meniscus lens element with the convex surface facing towards the object, The fourth to fifth lens elements are biconvex lens elements, The sixth lens element is a diorama lens element, The seventh lens element is a positive meniscus lens element with the convex surface facing upwards, The eighth lens element is a biconvex lens element, A fisheye lens, characterized in that the aperture is located between the fourth lens element and the fifth lens element. 11. The method of claim 10, The refractive index of the first to fourth lens elements is at least 1.7, The Abbe's number of the first to third lens elements is 40 or more, The Abbe's number of the fourth lens element is 30 or less, The refractive index of the fifth lens element is at least 1.5 and the Abbe number is at least 50, The refractive index of the sixth lens element is 1.6 or more and the Abbe number is 30 or less, A fisheye lens, characterized in that the refractive index of the seventh to eighth lens elements is at least 1.6 and the Abbe number is at least 50.

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