KR101981645B1 - Fish-eye lens system - Google Patents

Abstract

The present invention comprises, in order from an object side to an image side, a first lens unit having a negative refractive power as a whole and a second lens unit having a positive refractive power as a whole, wherein the most object- S / Y1 < 2.5. Here, S represents the effective diameter of the most object-side lens of the first lens group, and Y represents the diameter of the image formed on the image plane of the lens system.

Description

Fish-eye lens system

The present invention relates to a fish-eye lens system.

The lens system of an electronic image pickup device such as a digital still camera, a video camera, a surveillance camera, a mobile phone camera and the like which implements an image by using an image pickup device such as a CCD or a CMOS, Various forms have been adopted. With the miniaturization and high quality of the electronic image pickup device, the demand for a lens system that can cope with mega pixels of a small size and a high resolution is steadily increasing.

Particularly, in an electronic image pickup apparatus such as a surveillance camera, a fish-eye lens system is sometimes used as a lens system in order to secure a wide field of view. The lens system must be well corrected to the aberrations occurring in the periphery of the screen in order to clearly record even the small information that the subject has. However, in order to achieve high performance, it is difficult to achieve miniaturization, and in order to miniaturize it, it is accompanied with an increase in manufacturing cost, so it is difficult to satisfy high optical performance such as high power and high resolving power and manufacturing cost.

An embodiment of the present invention relates to a fish-eye lens system including two lens groups.

According to an aspect of the present invention, there is provided a zoom lens comprising, in order from an object side to an image side, a first lens group having negative refracting power as a whole; And a second lens group having a positive refracting power as a whole, wherein the most object-side lens of the first lens group satisfies the following conditions.

1.5 < S / Y1 < 2.5

Here, S represents the effective diameter of the most object-side lens of the first lens group, and Y represents the diameter of the image formed on the image plane of the lens system.

According to one aspect of the present invention, the first lens group includes a first lens having a negative refractive power, a second lens having a negative refractive power, a third lens having a negative refractive power, and a fourth lens having a positive refractive power, A fifth lens of positive refractive power, a sixth lens of negative refractive power, and a seventh lens of positive refractive power.

According to still another aspect of the present invention, the fifth lens and the sixth lens satisfy the following conditions.

A5 / A6> 3.4

Here, A5 represents the Abbe number of the fifth lens and A6 represents Abbe number of the sixth lens.

According to another aspect of the present invention, the fish-eye lens system may satisfy the following conditions.

BFL / EFL> 4.0

Here, BFL represents the back focal distance of the fish-eye lens system, and EFL represents the effective focal length of the fish-eye lens system.

According to another aspect of the present invention, the fish-eye lens system may satisfy the following conditions.

6.0 < D / Y < 7.0

Here, D represents the distance from the apex of the object plane of the most object-side lens of the first lens group to the image plane.

According to still another aspect of the present invention, the most image side lens of the second lens group may satisfy the following condition.

A7 ≥ 80

Here, A7 represents the Abbe number of the most image-side lens of the second lens group.

According to the embodiment of the present invention as described above, it is possible to provide a fish-eye lens system that is compact and can sufficiently secure the resolution of not only the center but also the peripheral portion.

FIG. 1 schematically shows a configuration of a fish-eye lens system according to an embodiment of the present invention.
2 schematically shows the configuration of a fish-eye lens system according to the first embodiment of the present invention.
Fig. 3 shows aberration diagrams relating to longitudinal spherical aberration, astigmatism and distortion of the fish-eye lens system shown in Fig. 2. Fig.
Fig. 4 shows the distortion aberration according to the wavelength of 546.07 nm when the fisheye lens system shown in Fig. 2 is substituted into the equation of y = 2? F? Tan (? / 2).
Fig. 5 shows an aberration diagram relating to coma aberration of the fish-eye lens system shown in Fig. 2. Fig.
6 shows MTF (Modulation Transfer Function) characteristics in the visible light.
FIG. 7 shows Modulation Transfer Function (MTF) characteristics in infrared rays.
8 schematically shows a configuration of a fish-eye lens system according to a second embodiment of the present invention.
Fig. 9 shows aberration diagrams relating to longitudinal spherical aberration, astigmatism, and distortion of the fish-eye lens system shown in Fig. 8. Fig.
Fig. 10 shows the distortion aberration according to the wavelength of 546.07 nm when the fisheye lens system shown in Fig. 8 is substituted into the equation of y = 2? F? Tan (? / 2).
Fig. 11 shows an aberration diagram relating to coma aberration of the fish-eye lens system shown in Fig. 2. Fig.
12 shows MTF (Modulation Transfer Function) characteristics in the visible light.
13 schematically shows the configuration of a fish-eye lens system according to the third embodiment of the present invention.
Fig. 14 shows aberration diagrams relating to longitudinal spherical aberration, astigmatism, and distortion of the fish-eye lens system shown in Fig. 13;
Fig. 15 shows the distortion aberration according to the wavelength of 546.07 nm when the fisheye lens system shown in Fig. 13 is substituted into the equation of y = 2? F? Tan (? / 2).
Fig. 16 is an aberration diagram relating to coma aberration of the fish-eye lens system shown in Fig. 13;
17 shows the MTF (Modulation Transfer Function) characteristic in the visible light.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and particular embodiments are illustrated in the drawings and described in detail in the detailed description. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The terms first, second, etc. may be used to describe various elements, but the elements should not be limited by terms. Terms are used only for the purpose of distinguishing one component from another. The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises", "having", and the like are used to specify that a feature, a number, a step, an operation, an element, a component, Should not be construed to preclude the presence or addition of one or more other features, integers, steps, operations, elements, parts, or combinations thereof. In the following description, " / " may be interpreted as " and "

FIG. 1 schematically shows a configuration of a fish-eye lens system according to an embodiment of the present invention.

The fish-eye lens system according to the embodiment of the present invention is a fish-eye lens system according to a stereographic projection method of y = 2? F? Tan (? / 2) It is a lens system that can be used in an imaging device such as a camera. Here, f represents the focal length of the fish-eye lens system,? Represents the incident angle of light incident on the fish-eye lens system, and y represents the height of the image formed on the image plane IP.

The fish-eye lens system according to the present invention includes a first lens group 10, a diaphragm ST, and a second lens group 20 having a positive refractive power as a whole in order from the object side to the image side . An optical block G such as an ultraviolet cut filter or a dummy filter may be disposed between the second lens group 20 and the image plane IP.

The first lens group 10 may include four lenses. For example, the first lens group 10 includes a first lens 11 having a negative refractive power, a second lens 12 having a negative refractive power, a third lens 13 having a negative refractive power, and a fourth lens 14 having a positive refractive power .

The second lens group 20 may include three lenses. For example, the second lens group 20 may include a fifth lens 21 having a positive refractive power, a sixth lens 22 having a negative refractive power, and a seventh lens 23 having a positive refractive power. The fifth lens 21 and the sixth lens 22 may constitute a cemented lens. The chromatic aberration is corrected through the cemented lens, and aberration generation can be reduced.

The third lens 13, which is the third lens disposed from the object side, of the lenses included in the first lens group 10 may include at least one aspherical surface. The seventh lens 23, which is the most image-side lens among the lenses included in the second lens group 20, may include at least one aspherical surface. The first lens group 10 and the second lens group 20 include a lens having at least one aspherical surface to compensate for the distortion occurring in the periphery of the image along the direction away from the center of the image, Can be improved.

When the fish-eye lens system according to the embodiment of the present invention is used in a surveillance camera, the image taken by the fish-eye lens system must be clear not only to the center but also to the periphery. If both the first lens group and the second lens group are formed only of spherical lenses, the curvature of the lenses constituting each lens group is greatly increased to make the composition worse. Distortion occurs in the peripheral portion of the image, it's difficult.

The fish-eye lens system according to the embodiment of the present invention can satisfy the following conditions.

<Condition 1>

1.5 < S / Y1 < 2.5

Here, S represents the effective diameter of the most object-side lens of the first lens group 10, and Y represents the diameter of the image formed on the image plane IP of the fisheye lens system.

Condition 1 defines the ratio of the effective diameter of the first lens 11 which is the most object-side lens of the first lens group 10 to the diameter of the image plane IP of the fisheye lens system. By satisfying the condition 1, The lens system can be miniaturized, and the aberration that can be caused by miniaturization of the fish-eye lens system can be minimized. In other words, miniaturization of the fish-eye lens system becomes difficult if the upper limit of Condition 1 is exceeded, and if it is out of the lower limit of Condition 1, miniaturization can be achieved, but correction of aberration is difficult.

Meanwhile, the fifth lens 21 and the sixth lens 22 provided in the second lens group 20 of the fish-eye lens system according to the embodiment of the present invention may satisfy the following conditions.

<Condition 2>

A5 / A6> 3.4

Here, A5 represents the Abbe number of the fifth lens 21, and A6 represents Abbe number of the sixth lens 22.

Condition 2 defines the ratio of the Abbe number of the fifth lens 21 to the Abbe number of the sixth lens 22. It is difficult to correct the chromatic aberration of the fish-eye lens system if the Abbe number is out of the range of Condition 2.

The fish-eye lens system can satisfy the following conditions.

<Condition 3>

BFL / EFL> 4.0

Here, BFL represents the back focal distance of the fish-eye lens system, and EFL represents the effective focal length of the fish-eye lens system.

Condition 3 defines the ratio of the back focal length of the fisheye lens system to the effective focal length of the fisheye lens system.

In the case of a photographing device such as a surveillance camera, images should be taken not only during the day but also at night. The surveillance cameras use visible light and infrared light for daytime shooting and nighttime shooting, respectively, in order to obtain high-quality images, and appropriate filters should be provided according to the use of such light. At this time, an infrared ray cut filter is used as a daytime filter. A dummy filter may be used as the nighttime filter, and the daytime filter and the nighttime filter may be switched by a switching device (not shown). That is, the fisheye lens system must have a sufficient space for the filter and a space for conversion. Since the fisheye lens system according to the embodiment of the present invention has a back focal length of about four times or more as compared with the entire focal length, the switching and arrangement of the filter is easy. Thus, by providing a sufficient back focal distance necessary for the arrangement and switching of the filters, it can be effectively utilized for both daytime and nighttime photographing.

The fish-eye lens system according to the embodiment of the present invention can satisfy the following conditions.

<Condition 4>

6.0 < D / Y < 7.0

Here, D denotes a distance from the vertex of the object surface of the most object-side lens of the first lens group 10 to the image plane IP, that is, an over-all length (OAL), Y denotes an image plane IP). &Lt; / RTI &gt;

Condition 4 defines the ratio of the total length of the fisheye lens system to the diameter of the image, and a small fisheye lens system can be realized through Condition 4.

The most image side lens included in the second lens group 20, for example, the seventh lens 23, may satisfy the following condition.

<Condition 5>

A7 ≥ 80

Here, A7 represents the Abbe number of the most image-side lens of the second lens group 20.

Condition 5 defines the Abbe number of the image-side lens of the second lens group 20, and when the value falls outside the range of Condition 5, the ultraviolet rays used for night-time shooting are incident on the fish- It is difficult to correct aberrations. Therefore, degradation of resolution occurs at night.

The fish-eye lens system according to the embodiment of the present invention can obtain an image of a high resolving power not only at the center but also at the periphery. Therefore, it has been described above that it can be very usefully used in an electronic image pickup apparatus such as a surveillance camera which requires a high quality image while securing a wide field of view.

The definitions of the aspheric surface in the embodiment of the present invention are as follows.

The aspherical shape of the lens according to the embodiment of the present invention can be expressed by the following equation with the advancing direction of the ray as a positive direction when the direction of the optical axis is the x axis and the direction perpendicular to the optical axis direction is the y axis . Where x is the distance from the vertex of the lens to the optical axis direction, y is the distance in a direction perpendicular to the optical axis, k is a conic constant, A and B are aspheric coefficients, And the inverse number (1 / R) of the radius of curvature at the apex.

The following is a design data of a fish-eye lens system according to an embodiment of the present invention.

Hereinafter, EFL denotes the effective focal length of the fish-eye lens system, Fno denotes the F number, Rn denotes the radius of curvature, Field angle denotes the angle of view, and Dn denotes the distance between the lens surface and the lens surface on the optical axis. That is, Dn represents the thickness of the lens or the distance between the lens and the lens. And, nd is the refractive index of the material, and vd is the Abbe number of the material. And * denotes an aspherical surface.

&Lt; Embodiment 1 >

Table 1 shows design data of a fish-eye lens system according to the first embodiment of the present invention shown in Fig.

EFL: 1.103 mm

Fno: 2.47

Field angle: 181 °

Surface Rn Dn nd vd S1 11.5524 0.925 2.001 29.134 S2 5 2.512 S3 11.7624 0.6 1.883 40.8054 S4 4.2 1.897 S5 * -37.5477 0.6 1.772501 49.467 S6 * 4.8114 1.797 S7 53.1409 1.754 2.0027 19.317 S8 -9.36325 4.462 S9 (ST) INFINITY 2.539 S10 5.7026 1.2 1.496997 81.6084 S11 -4.8255 0.584 1.846663 23.7848 S12 999.7359 0.356 S13 * 5.9356 2.266 1.497103 81.5596 S14 * -3.304 0.311 S15 INFINITY 1.2 1.516798 64.1983 IP INFINITY 3.498

Table 2 shows the aspherical surface coefficients in the fish-eye lens system shown in Fig.

S5 S6 S13 S14 K 0 0 -8.8065 -1.004 A 4.18E-04 -1.85E-03 1.03E-04 1.88E-03 B -8.27E-05 -1.32E-04 0 2.69E-05

Fig. 3 is an aberration diagram relating to longitudinal spherical aberration, astigmatism and distortion of the fisheye lens system shown in Fig. 2. Fig. 4 is a graph showing the aberration diagram of the fisheye lens system shown in Fig. 2 with y = 2? 2), the distortion aberration according to the wavelength of 546.07 nm is shown. In Fig. 3, the astigmatism and distortion show the aberration according to the wavelength of 546.07 nm.

3 corresponds to an aberration diagram showing that the lens system shown in Fig. 2 is a fisheye lens system, and Fig. 4 is a graph showing the distortion in the fisheye system according to the embodiment of the present invention according to the stereographic projection method at a wavelength of 546.07 nm Respectively. Referring to FIG. 4, it can be seen that the fish-eye lens according to the embodiment of the present invention according to the stereoscopic projection method exhibits a distortion within ± 3% over a range of 0.00 ° to 100.00 °. That is, it can be confirmed that the fisheye lens system can obtain a clear image not only at the center but also at the periphery.

FIG. 5 shows an aberration diagram of the coma aberration of the fish-eye lens system shown in FIG. 2, FIG. 6 shows Modulation Transfer Function (MTF) characteristics in visible light, Respectively.

&Lt; Embodiment 2 >

Table 3 shows design data of a fish-eye lens system according to the second embodiment of the present invention shown in Fig.

EFL: 0.83 mm

Fno: 2.49

Field angle: 181 °

Surface Rn Dn nd vd S1 10.191 0.6 2.001 29.134 S2 4.4171 1.3761 S3 6.6809 0.5134 1.883 40.8054 S4 3.12 1.7023 S5 * 1759.6504 0.6841 1.772501 49.467 S6 * 3.62922 4.5514 S7 21.16329 2.0693 2.0027 19.317 S8 -13.47844 3.7767 S9 (ST) INFINITY 1.3 S10 4.7555 One 1.496997 81.6084 S11 -3.3111 2.0453 1.846663 23.7848 S12 71.9264 0.7513 S13 * 5.4892 1.8802 1.497103 81.5596 S14 * -2.8597 One S15 INFINITY 1.2 1.516798 64.1983 IP INFINITY 2.0998

Table 4 shows the aspherical surface coefficients in the fish-eye lens system shown in Fig.

S5 S6 S13 S14 K 0 0 5.4892 -0.553 A -4.5174 -9.89E-03 -9.6425 6.76E-03 B -2.10E-04 -1.42E-04 0 1.12E-04

Fig. 9 is an aberration diagram relating to the longitudinal spherical aberration, astigmatism and distortion of the fish-eye lens system shown in Fig. 8, and Fig. 10 is a diagram showing the aberration diagram of the fish- 2), the distortion aberration according to the wavelength of 546.07 nm is shown. In FIG. 9, the astigmatism and distortion show aberrations according to the wavelength of 546.07 nm.

9 corresponds to an aberration diagram showing that the lens system shown in Fig. 8 is a fish-eye lens system, Fig. 10 shows a distortion aberration according to the 546.07 nm wavelength of the fish- will be. Referring to FIG. 10, it can be seen that the fish-eye lens according to the embodiment of the present invention according to the stereoscopic projection method exhibits a distortion within ± 3% over a range of 0.00 ° to 100.00 °. That is, it can be confirmed that the fisheye lens system can obtain a clear image not only at the center but also at the periphery.

FIG. 11 is an aberration diagram relating to coma aberration of the fish-eye lens system shown in FIG. 8, and FIG. 12 shows Modulation Transfer Function (MTF) characteristics in visible light.

&Lt; Third Embodiment >

Table 5 shows design data of a fish-eye lens system according to the third embodiment of the present invention shown in Fig.

EFL: 1.22524 mm

Fno: 2.72

Field angle: 181 °

Surface Rn Dn nd vd S1 11.7697 One 2.001 29.134 S2 5.5 2.14115 S3 * 10.2685 0.7 1.882023 37.2213 S4 * 4.2 2.317462 S5 -23.4055 0.68 1.7725 49.6243 S6 5.53745 4.843848 S7 13.2785 1.6 2.0027 19.317 S8 -39.3224 1.940893 S9 (ST) INFINITY 1.5 S10 7 2 1.496997 81.6084 S11 -4 0.6 1.846663 23.7848 S12 70.6119 0.4 S13 * 5.9869 2.4 1.497103 81.5596 S14 * -3.7098 0.5 S15 INFINITY 1.2 1.516798 64.1983 IP INFINITY 4.3

Table 6 shows the aspherical surface coefficients in the fish-eye lens system shown in Fig.

S3 S4 S13 S14 K 0 0 -6.7767 -0.7036 A 5.56E-04 -4.76E-04 1.6245 1.50E-03 B 9.04E-06 4.47E-05 1.14E-06 1.45E-05

Fig. 14 is an aberration diagram relating to the longitudinal spherical aberration, astigmatism and distortion of the fish-eye lens system shown in Fig. 13, and Fig. 15 is a diagram showing the aberration diagram of the fish- 2), the distortion aberration according to the wavelength of 546.07 nm is shown. In Fig. 14, the astigmatism and distortion show aberrations according to the wavelength of 546.07 nm.

14 corresponds to an aberration diagram showing that the lens system shown in Fig. 13 is a fish-eye lens system, Fig. 15 shows a distortion aberration according to the wavelength of 546.07 nm of the fish-eye lens system according to the embodiment of the present invention according to the stereoscopic method will be. Referring to FIG. 15, it can be seen that the fish-eye lens according to the embodiment of the present invention according to the stereoscopic projection method exhibits a distortion within ± 3% over a range of 0.00 ° to 100.00 °. That is, it can be confirmed that the fisheye lens system can obtain a clear image not only at the center but also at the periphery.

Fig. 16 is an aberration diagram relating to coma aberration of the fish-eye lens system shown in Fig. 13, and Fig. 17 shows Modulation Transfer Function (MTF) characteristics in visible light.

Table 7 below shows that the fish-eye lens system of each embodiment of the present invention satisfies the above condition.

Example 1 Example 2 Example 3 Condition 1 1.73 1.76 1.66 Condition 2 3.43 3.43 3.43 Condition 3 4.54 5.18 4.79 Condition 4 6.19 6.19 6.15 Condition 5 81.5596 81.5596 81.5596

Although the present invention has been described in connection with the above-mentioned preferred embodiments, it is possible to make various modifications and variations without departing from the spirit and scope of the invention. Accordingly, it is intended that the appended claims cover all such modifications and variations as fall within the true spirit of the invention.

10: first lens group 1: first lens
12: second lens 13: third lens
14: fourth lens 20: second lens group
21: fifth lens 22: sixth lens
23: seventh lens G: optical block
ST: Aperture P: Image plane

Claims (6)

In order from the object side to the image side,
A first lens group having a negative refractive power as a whole; And
And a second lens group having a positive refractive power as a whole,
A fish-eye lens system satisfying the following conditions.
FOV> 180 °
1.5 < S / Y1 < 2.5
Here, FOV represents the angle of view of the fish-eye lens system, S represents the effective diameter of the most object-side lens in the first lens group, and Y represents the diameter of the image formed on the image plane of the lens system. The method according to claim 1,
Wherein the first lens group includes a first lens having a negative refractive power, a second lens having a negative refractive power, a third lens having a negative refractive power, and a fourth lens having a positive refractive power,
The second lens group includes a fifth lens having a positive refractive power, a sixth lens having a negative refractive power, and a seventh lens having a positive refractive power,
Wherein the fifth lens and the sixth lens satisfy the following conditions.
A5 / A6> 3.4
Here, A5 represents the Abbe number of the fifth lens and A6 represents Abbe number of the sixth lens. delete The method according to claim 1,
Wherein the fish-eye lens system satisfies the following conditions.
BFL / EFL> 4.0
6.0 < D / Y < 7.0
A7 ≥ 80
EFL is the effective focal length of the fisheye lens system, D is the distance from the apex of the object side of the object-side lens of the first lens group to the image plane, A7 Represents the Abbe number of the most image-side lens of the second lens group. delete delete

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