KR102369803B1 - Fisheye lens system - Google Patents

Abstract

According to an embodiment of the present invention, in order from the object side to the image plane side, the first lens group consisting of four lenses and having a negative refractive power; and a second lens group consisting of three lenses and having positive refractive power, wherein the fisheye lens system satisfies the following equations.
<expression>
1.0 < D/f < 2.0
Fno < 1.68
Here, D is the distance between the lens disposed on the most image plane side included in the first lens group and the lens disposed on the most object side included in the second lens group, f is the total focal length of the fisheye lens system, and Fno is It represents the F-number of a fisheye lens system.

Description

Fisheye lens system

The present invention relates to a fisheye lens system, and more particularly, to a fisheye lens system composed of seven lenses.

Recently, as solid-state imaging devices such as charge coupled devices (CCDs) and complementary metal-oxide semiconductors (CMOS) have been miniaturized and high-pixelated, digital cameras, video cameras, or monitoring devices equipped with imaging devices have been used. A lens system provided in an imaging optical device such as a camera is also required to have high optical performance.

In addition, as the importance of security increases, a CCTV (Closed Circuit Tele-vision) surveillance camera or precision measurement camera is widely used by individuals as well as public institutions or corporations.

Since the surveillance camera is used not only during the daytime but also at night, the need for a lens system for a bright surveillance camera that satisfactorily corrects aberrations in the visible to near-infrared range and has a small F-number is increasing. In addition, a user using a surveillance camera, etc., wants to obtain a high-resolution image without distortion not only in the center but also in the periphery over a wide range. Accordingly, the need for a wide-angle and low-distortion lens system provided in a surveillance camera increases. is becoming

Korean Patent Publication No. 2012-0076210 (2012.07.09)

An object of the present invention is to provide a bright fisheye lens system comprising seven lenses and having an F-number of 1.68 or less. However, these problems are exemplary, and the scope of the present invention is not limited thereto.

According to an embodiment of the present invention, in order from the object side to the image plane side, the first lens group consisting of four lenses and having a negative refractive power; and a second lens group consisting of three lenses and having positive refractive power, wherein the fisheye lens system satisfies the following equations.

<expression>

1.0 < D/f < 2.0

Fno < 1.68

Here, D is the distance between the lens disposed on the most image plane side included in the first lens group and the lens disposed on the most object side included in the second lens group, f is the total focal length of the fisheye lens system, and Fno is It represents the F-number of a fisheye lens system.

According to an embodiment, the following equation may be satisfied.

<expression>

-0.35 < f/f1 < -0.15

Here, f1 represents the focal length of the first lens group.

According to an embodiment, the following equation may be satisfied.

<expression>

14 < L/f < 14.5

Here, L denotes a distance from a surface disposed on the most object side of the first lens group to a surface disposed on the most image plane side of the second lens group.

According to an embodiment, the first lens group may include, in order from the object side, 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 positive refractive power.

According to an embodiment, the second lens may include at least one aspherical surface.

According to an embodiment, the following equation may be satisfied.

<expression>

0.925 < H1/2Y < 1.025

Here, H1 is the effective radius of the object-side surface of the first lens, and 2Y is the diameter of the image circle formed on the image surface.

According to an embodiment, the following equation may be satisfied.

Nd1 - Nd2 > 0.3

Here, Nd1 is the refractive index of the first lens, and Nd2 is the refractive index of the second lens.

According to an embodiment, the following equation may be satisfied.

Nd1 - Nd3 > 0.3

Here, Nd1 is the refractive index of the first lens, and Nd2 is the refractive index of the third lens.

According to an embodiment, the following equation may be satisfied.

6.7 < R2 < 7.3

Here, R2 represents the curvature of the object-side surface of the first lens.

According to an embodiment, the second lens group may include, in order from the object side, a fifth lens having positive refractive power; a sixth lens having negative refractive power; and a seventh lens having positive refractive power.

According to an embodiment, the fifth lens and the sixth lens may be junction lenses.

According to an embodiment, both surfaces of the seventh lens may be aspherical.

According to an embodiment, the following equation may be satisfied.

FOV > 185°

Here, FOV represents the angle of view of the fisheye lens system.

According to an embodiment, the diaphragm may further include a stop disposed between the first lens group and the second lens group.

Other aspects, features, and advantages other than those described above will become apparent from the following detailed description, claims and drawings for carrying out the invention.

According to the embodiments of the present invention as described above, it is possible to provide a bright fisheye lens system including seven lenses.

In addition, it is possible to provide a fisheye lens system having a high resolution and a wide viewing angle.

Of course, the scope of the present invention is not limited by these effects.

1 is an optical layout view of a fisheye lens system according to a first embodiment of the present invention.
FIG. 2 is an aberration diagram illustrating longitudinal spherical aberration, astigmatism, and distortion of the fisheye lens system shown in FIG. 1 .
FIG. 3 is an aberration diagram illustrating lateral aberration of the fisheye lens system shown in FIG. 1 .
4 is an optical layout view of a fisheye lens system according to a second embodiment of the present invention.
5 is an aberration diagram illustrating longitudinal spherical aberration, astigmatism, and distortion of the fisheye lens system shown in FIG. 4 .
FIG. 6 is an aberration diagram illustrating lateral aberration of the fisheye lens system shown in FIG. 4 .

Since the present invention can apply various transformations and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail in the detailed description. Effects and features of the present invention, and a method for achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the drawings. However, the present invention is not limited to the embodiments disclosed below and may be implemented in various forms.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, and when described with reference to the drawings, the same or corresponding components are given the same reference numerals, and the overlapping description thereof will be omitted. .

In the following embodiments, terms such as first, second, etc. are used for the purpose of distinguishing one component from another, not in a limiting sense.

In the following examples, the singular expression includes the plural expression unless the context clearly dictates otherwise.

In the following embodiments, terms such as include or have means that the features or components described in the specification are present, and the possibility that one or more other features or components will be added is not excluded in advance.

In the drawings, the size of the components may be exaggerated or reduced for convenience of description. For example, since the size and thickness of each component shown in the drawings are arbitrarily indicated for convenience of description, the present invention is not necessarily limited to the illustrated bar.

1 and 4 are optical layout views of a fisheye lens system according to a first embodiment and a second embodiment of the present invention, respectively.

1 and 4 , the fisheye lens system includes a first lens group G1 and a second lens group G2 sequentially arranged from the object O side to the image plane IP side. A stop ST may be disposed between the first lens group G1 and the second lens group G2 , and an optical block B may be disposed between the second lens group G2 and the image plane IP.

According to an embodiment, the fisheye lens system may be a zoom lens system in which chromatic aberration is well corrected from the visible region to the near-infrared region, and through this, it can be applied to imaging devices such as surveillance cameras used in the daytime as well as at night.

According to an embodiment, the optical block B is an optical filter such as a low pass filter (LPF) or an infrared cut filter (IR-cut filter), and a cover glass (CG) for protecting the imaging surface of the imaging device. ; cover glass) and the like.

The near-infrared cut filter may be turned on/off by a controller (not shown). For example, since the near-infrared cut filter performs photographing using visible light during the daytime, it may be disposed on the path of incident light between the second lens group G2 and the image surface IP, and photographing using near-infrared rays at night is performed. Therefore, it can be disposed outside the path of the incident light.

The first lens group G1 has a negative refractive power, in order from the object side O, a first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power, and a third lens having a negative refractive power (L3) and four lenses of the fourth lens L4 having positive refractive power.

The first lens L1 and the second lens L2 may be meniscus lenses having a convex surface facing the object side O, and the third lens L3 may be a biconcave lens and a fourth lens ( L4) may be a biconvex lens.

The first lens group G1 includes at least one aspherical lens, and according to an embodiment, the aspherical lens may be the second lens L2. According to an embodiment, by configuring at least one surface of the second lens L2 as an aspherical surface, aberrations occurring on the off-axis, that is, astigmatism and field curvature, etc. can be reduced.

The second lens group G2 includes, in order from the object side, a fifth lens L5 having a positive refractive power, a sixth lens L6 having a negative refractive power, and a seventh lens L7 having a positive refractive power. may include.

The fifth lens L5 and the sixth lens L6 may be junction lenses. That is, by configuring the fifth lens L5 and the sixth lens L6 as a junction lens, a stable optical quality can be obtained by reducing the influence of attachment errors during manufacturing while correcting aberrations such as chromatic aberration, and the configuration is improved. Because it can be simplified, it is suitable for miniaturization.

The seventh lens L7 may be a biconvex lens, and may include at least one aspherical surface. For example, both surfaces of the seventh lens L7 may be aspherical.

By configuring at least one surface of the seventh lens L23 as an aspherical surface, it is possible to reduce aberrations occurring on the off-axis, that is, astigmatism, field curvature, and the like.

The fisheye lens system according to an embodiment of the present invention includes only seven lenses, and through this, miniaturization can be realized. In addition, all of the seven lenses are made of an inorganic material such as a germanium (Ge) lens having a refractive index of 1.4 or more, and may not include a plastic lens. In the case of a plastic lens, it is easy to form an aspherical surface and thus aberration of the lens system can be reduced. However, when used in a surveillance camera installed outdoors for a long time, the performance may be deteriorated by heat. In addition, since the refractive index is relatively small compared to a lens made of an inorganic material, the radius of curvature must be formed to be small in order to realize the same refractive power, which may be a limitation in realizing a wide-angle lens.

The fisheye lens system according to embodiments of the present invention may satisfy the following <Conditional Expression 1>.

<Condition 1>

1.0 < D/f < 2.0

Here, D is the distance between the first lens group G1 and the second lens group G2, and f is the total focal length of the fisheye lens system. The distance between the first lens group G1 and the second lens group G2 is the image plane IP side of the fourth lens L4 disposed on the most image plane IP side included in the first lens group G1. It means the distance between ( S8 ) and the object (O) side surface S10 of the fifth lens L5 most disposed on the object (O) side included in the second lens group G2.

<Condition 1> defines the ratio of the distance between the first lens group (G1) and the second lens group (G2) to the total focal length of the fisheye lens system. It can be difficult to correct for aberrations and coma.

The fisheye lens system according to embodiments of the present invention may satisfy the following <Conditional Expression 2>.

<Condition 2>

Fno < 1.68

Here, Fno represents the F-number of the fisheye lens system. The fisheye lens system of the present invention can be used for surveillance cameras used in the daytime as well as at night, and therefore, the F-number must be small in order to realize the maximum image quality even in a dark environment. Therefore, when <Condition 2> has a value below the upper limit, a sufficiently bright lens system may not be implemented, and thus the image quality of an image photographed in a dark environment may be deteriorated.

The fisheye lens system according to embodiments of the present invention may satisfy the following <Conditional Expression 3>.

<Condition 3>

-0.35 < f/f1 < -0.15

Here, f1 is the focal length of the first lens group G1, and BFL is the rear focal length.

<Condition 3> defines the range of the ratio of the focal length of the first lens group G2 to the total focal length of the fisheye lens system. In the case of more than the upper limit of <Condition 3>, sufficient rear focal length cannot be secured, and in the case of less than the lower limit, aberration correction becomes difficult. The fisheye lens system of the present invention can be utilized as a surveillance camera, and in this case, the rear focal length must be sufficiently secured to arrange the optical block (B) and the like between the lens system and the image plane (IP). The fisheye lens system satisfies the range of <Conditional Expression 3>, so that a sufficient rear focal length can be secured and the aberration can also be corrected well.

The fisheye lens system according to embodiments of the present invention may satisfy the following <Conditional Expression 4>.

<Condition 4>

14 < |L/f| < 14.5

Here, L is the distance from the surface most disposed on the object O side of the first lens group G1 to the surface disposed on the most image plane side of the second lens group G2, that is, the first lens ( The distance from the surface S1 arranged on the object O side of L1 to the surface S14 arranged on the image surface IP side of the seventh lens L7 is indicated.

<Condition 4> defines the range of the ratio of the length of the entire lens system to the focal length of the fisheye lens system. Above the upper limit of <Conditional Expression 4>, optical performance in a region where the angle of view is 180 degrees or more is deteriorated, and it may be difficult to implement an angle of view of 180 degrees or more below the lower limit.

The fisheye lens system according to embodiments of the present invention may satisfy the following <Conditional Expression 5>.

0.925 < H1/2Y < 1.025

Here, H1 is the effective radius H1 of the object O-side surface of the first lens L1, and 2Y is the diameter 2Y of the image circle formed on the image surface IP. The image circle may be an image circle formed when light is incident on the fisheye lens system at the maximum viewing angle.

It is impossible to miniaturize the fisheye lens system above the upper limit of <Conditional Expression 5>, and it may be difficult to implement an angle of view of 180 degrees or more below the lower limit. Within the range of <Conditional Expression 5>, a high-performance fisheye lens system with little peripheral aberration can be implemented.

The fisheye lens system according to embodiments of the present invention may satisfy the following <Conditional Expression 6>.

<Conditional Expression 6>

Nd1 - Nd2 > 0.3

Here, Nd1 is the refractive index of the first lens L1, and Nd2 is the refractive index of the second lens L2.

<Conditional Expression 6> defines an appropriate range of the difference in refractive index between the first lens L1 and the second lens L2, and when the refractive index of the first lens L1 is sufficiently high, the radius of curvature of the first lens L1 is It can be enlarged, and thus the radius of the first lens L1 can be formed to be large, and it can be formed to have a gentle curvature even to the periphery. Through this configuration, a wide-angle bright lens system can be realized by making the angle of view large and the F-number sufficiently small.

The refractive power of the entire first lens group G1 may be appropriately adjusted by forming the refractive index of the second lens L2 to be relatively small while the refractive index of the first lens L1 is high.

That is, it may be difficult to implement a wide-angle and bright lens system below the lower limit of <Conditional Expression 6>.

The fisheye lens system according to embodiments of the present invention may satisfy the following <Conditional Expression 7>.

<Conditional Expression 7>

Nd1 - Nd3 > 0.5

Here, Nd1 is the refractive index of the first lens L1, and Nd2 is the refractive index of the third lens L3.

<Conditional Expression 7> defines an appropriate range of the difference in refractive index between the first lens L1 and the second lens L3, and when the refractive index of the first lens L1 is sufficiently high, the radius of curvature of the first lens L1 is It can be enlarged, and thus the radius of the first lens L1 can be formed to be large, and it can be formed to have a gentle curvature even to the periphery. Through this configuration, a wide-angle bright lens system can be realized by making the angle of view large and the F-number sufficiently small.

Instead of having a high refractive index of the first lens L1 , the refractive power of the entire first lens group G1 may be appropriately adjusted by making the refractive index of the third lens L3 relatively small.

The fisheye lens system according to embodiments of the present invention may satisfy the following <Conditional Expression 8>.

<Conditional Expression 8>

6.7 < R2 < 7.3

Here, R2 represents the radius of curvature of the object O side surface of the first lens L1.

If it is more than the upper limit of <Conditional Expression 8>, it is difficult to manufacture the first lens L1 and a ghost may be issued to the image. this may be lowered.

According to the above embodiments, it is possible to implement a bright fisheye lens system with an F-number of 1.68 or less with only 7 lenses, and a fisheye lens system with high resolution not only for visible light but also for near-infrared light, and having an angle of view of 185 degrees or more.

Hereinafter, design data of a fisheye lens system according to embodiments of the present invention will be described with reference to [Table 1] to [Table 4].

In the design data, R is the radius of curvature [mm] of each lens surface (however, the surface where the value of R is “infinity” indicates that the surface is planar), and Dn is the distance between the lens surface and the lens surface on the optical axis. As the distance [mm], it indicates the thickness of the lens or the distance between the lens and the lens. Nd represents the refractive index of each lens on the d line, and vd represents the Abbe number of each lens on the d line.

The definition of the aspherical surface (ASP) included in the embodiments of the present invention is as follows.

The aspherical shape included in the fisheye lens system according to the embodiments of the present invention, when the optical axis direction is the z axis and the direction perpendicular to the optical axis direction is the h axis, the propagation direction of the light beam is positive. It can be expressed by the above definition formula. Here, z is the distance from the vertex of the lens in the direction of the optical axis, h is the distance in the direction perpendicular to the optical axis, K is the conic constant, A, B, and C are the aspheric coefficients, and c is the It represents the reciprocal (1/R) of the radius of curvature at the vertex of the lens.

<First embodiment>

[Table 1] shows design data of a fisheye lens system according to an embodiment of the present invention shown in FIG. Reference numeral Si in FIG. 1 denotes the i-th surface, which is marked so that the object-side surface of the first lens is the first surface S1 and the surface number increases along the image-side direction.

In the above table, * denotes an aspherical surface. [Table 2] shows the aspheric coefficient of the aspherical surface included in the fisheye lens system according to the embodiment of the present invention shown in FIG. In the numerical value of the aspheric coefficient, the notation Em (m is an integer) means ×10 ^-m .

FIG. 2 shows the longitudinal aberration of the fisheye lens system shown in FIG. 1, and shows longitudinal spherical aberration, astigmatic field curves, and distortion, respectively. The longitudinal spherical aberration is plotted for light with wavelengths of 852.1100 nm, 656.2725 nm, 587.5618 nm, 546.0740 nm, 486.1327 nm and 435.8343 nm, and astigmatism and distortion are plotted for light with wavelengths 546.0740 nm. In the astigmatism, the dotted line indicates the astigmatism on the tangential surface (T), and the solid line indicates the astigmatism on the sagittal surface (S).

Referring to the longitudinal spherical aberration diagram of FIG. 2, when comparing the green light (546.0740 nm) among the near infrared (852.1100 nm) and visible light, the focal position over the entire region from the center to the periphery can be maintained with a difference of 30 μm or less. there is. That is, it may have high optical performance not only in the visible light but also in the near-infrared region.

FIG. 3 shows the lateral aberration of the fisheye lens system shown in FIG. 1 , and for light having wavelengths of 852.1100 nm, 587.5618 nm, 546.0740 nm, 486.1327 nm and 435.8343 nm, relative field heights of 0.00, 0.27; , 0.53, 0.8, and 1.00, respectively, represent lateral aberrations on a tangential surface and a sagittal surface, that is, chromatic aberration of magnification, coma, and the like.

<Second embodiment>

[Table 3] shows design data of a fisheye lens system according to an embodiment of the present invention shown in FIG.

In the above table, * denotes an aspherical surface. [Table 4] shows the aspherical coefficient of the aspherical surface included in the fisheye lens system according to the embodiment of the present invention shown in FIG. In the numerical value of the aspheric coefficient, the notation Em (m is an integer) means ×10 ^-m .

5 shows longitudinal aberration of the fisheye lens system shown in FIG. 4, respectively, longitudinal spherical aberration, astigmatic field curves, and distortion. The longitudinal spherical aberration is plotted for light with wavelengths of 852.1100 nm, 656.2725 nm, 587.5618 nm, 546.0740 nm, 486.1327 nm and 435.8343 nm, and astigmatism and distortion are plotted for light with wavelengths 546.0740 nm. In the astigmatism, the dotted line indicates the astigmatism on the tangential surface (T), and the solid line indicates the astigmatism on the sagittal surface (S).

Referring to the longitudinal spherical aberration diagram of FIG. 5, when comparing the green light (546.0740 nm) among the near infrared (852.1100 nm) and visible light, the focal position over the entire region from the center to the periphery can be maintained with a difference of 30 μm or less. there is. That is, it may have high optical performance not only in the visible light but also in the near-infrared region.

FIG. 6 shows the lateral aberration of the fisheye lens system shown in FIG. 4 , and for light having wavelengths of 852.1100 nm, 587.5618 nm, 546.0740 nm, 486.1327 nm and 435.8343 nm, relative field heights of 0.00, 0.27; , 0.53, 0.8, and 1.00, respectively, represent lateral aberrations on a tangential surface and a sagittal surface, that is, chromatic aberration of magnification, coma, and the like.

The following [Table 5] shows the total focal length (f), the F-number (fno), the rear focal length (BFL), and the angle of view (2ω) of the fisheye lens system according to embodiments of the present invention.

As shown in [Table 5], according to the embodiments of the present invention, it can be confirmed that a bright fisheye lens system having an F-number of 1.68 or less while having an angle of view of 185 degrees was implemented.

The following [Table 6] shows that the fisheye lens system according to the embodiments of the present invention satisfies the above conditional expressions.

According to the above embodiments, it is possible to implement a bright fisheye lens system with an F-number of 1.68 or less with only 7 lenses, and a fisheye lens system having high resolution not only for visible light but also for near-infrared light and having an angle of view of 185 degrees or more can be provided. .

In addition, the fisheye lens system according to the embodiments of the present invention may be used in a photographing apparatus such as a surveillance camera, a digital camera, or a video camera having an image sensor (not shown).

The image sensor may be a solid-state imaging device such as a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) that receives light imaged by a fisheye lens system. The imaging plane of the image sensor corresponds to the image plane (IP) of the fisheye lens system.

Although the present invention has been described with reference to the embodiment shown in the drawings, which is merely exemplary, those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Accordingly, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

G1: first lens group G2: second lens group
L1: first lens L2: second lens
L3: Third lens L4: Fourth lens
L5: 5th lens L6: 5th lens
L7: 7th lens ST: Aperture
B: optical block

Claims (15)

In order from the object side to the upper surface side,
a first lens group consisting of four lenses and having a negative refractive power; and
Consists of three lenses and includes a second lens group having positive refractive power,
A fisheye lens system satisfying the following equations.
<expression>
1.0 < D/f < 2.0
Fno < 1.68
-0.35 < f/f1 < -0.15
Here, D is the distance between the lens disposed on the most image plane side included in the first lens group and the lens disposed on the most object side included in the second lens group, f is the total focal length of the fisheye lens system, and Fno is The F-number, f1, of the fisheye lens system represents the focal length of the first lens group. delete According to claim 1,
A fisheye lens system satisfying the following expression.
<expression>
14 < L/f < 14.5
Here, L denotes a distance from a surface disposed on the most object side of the first lens group to a surface disposed on the most image plane side of the second lens group. According to claim 1,
The first lens group, in order from the object side,
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 fisheye lens system comprising a fourth lens having positive refractive power. 5. The method of claim 4,
The second lens is a fisheye lens system including at least one aspherical surface. 5. The method of claim 4,
A fisheye lens system satisfying the following expression.
<expression>
0.925 < H1/2Y < 1.025
Here, H1 is the effective radius of the object-side surface of the first lens, and 2Y is the diameter of the image circle formed on the image surface. 5. The method of claim 4,
A fisheye lens system satisfying the following expression.
Nd1 - Nd2 > 0.3
Here, Nd1 is the refractive index of the first lens, and Nd2 is the refractive index of the second lens. 5. The method of claim 4,
A fisheye lens system satisfying the following expression.
Nd1 - Nd3 > 0.3
Here, Nd1 is the refractive index of the first lens, and Nd2 is the refractive index of the third lens. 5. The method of claim 4,
A fisheye lens system satisfying the following expression.
6.7 < R2 < 7.3
Here, R2 represents the curvature of the object-side surface of the first lens. According to claim 1,
The second lens group, in order from the object side,
a fifth lens having positive refractive power;
a sixth lens having a negative refractive power; and
A fisheye lens system comprising a seventh lens having a positive refractive power. 11. The method of claim 10,
The fifth lens and the sixth lens are junction lenses. 11. The method of claim 10,
A fisheye lens system wherein both surfaces of the seventh lens are aspherical. According to claim 1,
A fisheye lens system satisfying the following expression.
FOV > 185°
Here, FOV represents the angle of view of the fisheye lens system. According to claim 1,
The fisheye lens system further comprising a stop disposed between the first lens group and the second lens group. In order from the object side to the upper surface side,
a first lens group consisting of four lenses and having a negative refractive power; and
Consists of three lenses and includes a second lens group having positive refractive power,
A fisheye lens system satisfying the following equations.
<expression>
1.0 < D/f < 2.0
Fno < 1.68
14 < L/f < 14.5
Here, D is the distance between the lens disposed on the most image plane side included in the first lens group and the lens disposed on the most object side included in the second lens group, f is the total focal length of the fisheye lens system, and Fno is The F-number, L, of the fisheye lens system represents a distance from a surface most disposed on the object side of the first lens group to a surface disposed on the most image plane side of the second lens group.

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