KR20140003129A - Fast lens for near infrared ray - Google Patents

Abstract

Introduced is a fast lens for near infrared ray which has wide angle of view and assures a small F-number as obtaining aberration correction by assembling a spherical lens and an aspheric lens. The fast lens for near infrared ray comprises a first lens, a second lens, a third lens, a fourth lens and an iris which are arranged sequentially to an image from a target object. The first lens is a meniscus lens which has a negative refractive index and has a convex surface which is facing the target object to photograph. The second lens includes at least one aspherical surface having a positive refractive index. The third lens is a meniscus lens or a biconvex lens which has a positive refractive index and a convex surface facing the side where the image is formed. The fourth lens has a negative refractive index, and is a meniscus lens having a concave surface facing the side where the image is formed. The iris is arranged between the second lens and the third lens. Here, the focal length (f1) of the first lens and the focal length (f2) of the second lens satisfy the relation in which f1/f2 is greater than -1.3 and is less than -1.1.

Description

Fast Lens for near infrared ray

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bright lens, in particular, a spherical lens and an aspherical lens, which are very bright and have excellent aberration correction characteristics, and can be used in a near-infrared bright lens that can be used in a near-infrared region without a change in performance even with heat inside the camera. It is about.

The general visible light and near-infrared surveillance camera lens is composed of a plurality of lenses, photographing the subject using a visible light wavelength band during the day, and photographing the subject using a separate lighting device such as a street lamp at night. When a surveillance camera is used in a streetlight installation at night, the camera is exposed to the camera, and thus it is not economical in terms of power consumption.

Recently, with the development of camera technology that can be used for surveillance in the dark as well as in the bright places, people are watching objects illuminated by near-infrared light emitting diodes, which are not easily seen by humans, and most surveillance cameras use this method.

The technical problem to be solved by the present invention is to provide a bright lens for near-infrared light having a wide F-number and a small F-number while achieving aberration correction by properly combining a spherical lens and an aspheric lens.

Another technical problem to be solved by the present invention is to provide a motion capture camera using the bright lens for the near infrared.

의 관계를 만족한다.
According to one aspect of the present invention for achieving the above technical problem, the bright lens for the near-infrared, the first lens, the second lens, the third lens, the fourth lens sequentially arranged from the object side toward the image And an aperture. The first lens is a meniscus-type lens having negative refractive power and a surface convex toward the object to be photographed. The second lens is a lens including at least one aspherical surface having positive refractive power. The third lens is a meniscus-type lens having a positive refractive power and a convex surface facing the image formation side. The fourth lens is a meniscus lens having a negative refractive power and a concave surface facing the image formation side. The aperture is disposed between the second lens and the third lens. Here, the focal length f _{1 of} the first lens and the focal length f ₂ of the second lens are

Lt; / RTI >

의 관계를 만족한다.
According to another aspect of the present invention for achieving the above technical problem, a bright lens for near-infrared light includes a first lens, a second lens, a third lens, and a fourth lens arranged sequentially from an object side to an image side. It has a lens and an aperture. The first lens is a meniscus-type lens having negative refractive power and a surface convex toward the object to be photographed. The second lens is a lens including at least one aspherical surface having positive refractive power. The third lens is a lens having a positive refractive power and a surface facing toward an object to be photographed and a surface facing toward an image are respectively convex. The fourth lens is a meniscus lens having a negative refractive power and a concave surface facing toward the image formation. The aperture is disposed between the second lens and the third lens. Here, the focal length f _{1 of} the first lens and the focal length f ₂ of the second lens are

Lt; / RTI >

Motion capture camera according to the present invention for achieving the above another technical problem, the near-infrared bright lens is a motion capture camera.

When the bright lens for the near-infrared light according to the present invention is used, there is almost no change in performance even in long time shooting, and therefore, there is an advantage that it is suitable as a photographing lens of a motion capturing camera that requires a photographing of a dynamic subject and a perspective.

1 illustrates an embodiment of a bright lens for near infrared rays according to the present invention.
Figure 2 shows another embodiment of a bright lens for the near infrared light according to the present invention.
FIG. 3 is an aberration diagram of the bright lens for the near-infrared shown in FIG. 1.
4 is an aberration diagram of the bright lens for the near infrared ray shown in FIG. 2.

In order to fully understand the present invention and the operational advantages of the present invention and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings, which are provided for explaining exemplary embodiments of the present invention, and the contents of the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference symbols in the drawings denote like elements.

In order to help the understanding of the present invention, terms to be used hereinafter will be described.

When the light emitted from the sunlight or the heating element is dispersed in the spectrum, infrared rays are located outside the end of the red spectrum, and infrared rays have a longer wavelength than visible rays, and among them, the shortest wavelength is 0.75-3 μm, which is near infrared ray).

Aperture is a mechanism that controls the amount of light passing through the lens. The numerical value obtained by dividing the focal length of the lens by the diameter of the aperture is called an F-number. The smaller the F-number, the greater the amount of light that passes through the lens, and the larger the smaller the amount of light that passes. The full opening of the iris is called the maximum aperture and the F-number at this time is called the open F-number. A lens with a small open F-number is called a fast lens or a large-diameter lens, and a lens with a large F-number is called a dark lens.

The present invention to be described below relates to a bright lens used in a near infrared camera.

1 illustrates an embodiment of a bright lens for near infrared rays according to the present invention.

Referring to FIG. 1, the near-infrared bright lens 100 according to the present invention is usable in the near-infrared region, and is composed of four lenses sequentially arranged in a direction in which an image is formed from an object.

The first lens L1 is a meniscus-type glass lens having negative refractive power and having a convex surface facing toward the object to be photographed. The second lens L2 is a plastic lens including at least one aspherical surface having positive (+) refractive power. The third lens L3 is a meniscus-type glass lens having positive refractive power and having a convex surface facing the image formation side. The fourth lens L4 is a meniscus-type plastic lens having a negative refractive power and having a concave surface facing the image formation side.

An aperture ST is disposed between the second lens L2 and the third lens L3.

Figure 2 shows another embodiment of a bright lens for the near infrared light according to the present invention.

2, the near-infrared bright lens 200 according to the present invention can be used in the near-infrared region, and is composed of four lenses sequentially arranged in a direction in which an image is formed from an object.

The first lens L1 is a meniscus-type glass lens having negative refractive power and having a convex surface facing the object to be photographed. The second lens L2 is a plastic lens including at least one aspherical surface having positive (+) refractive power. The third lens L3 is a glass lens having a positive refractive power and a surface toward the object to be photographed and a surface toward the image formation are convex. The fourth lens L4 is a meniscus-type plastic lens having a negative refractive power and having a concave surface that faces toward the image formation.

An aperture ST is disposed between the second lens L2 and the third lens L3.

Inflection points exist on the aspherical surfaces of the second lens L2 and the fourth lens L4 shown in FIGS. 1 and 2. Aspherical surface has aberration correction ability that spherical surface does not have, and in order to maximize aberration correction ability of aspherical surface, the degree of freedom of shape should be increased. Since the lens made of plastic resin is injected into the mold, it is possible to produce an aspherical surface having an inflection point, and the present invention utilizes this feature of the plastic lens.

1 and 2 denotes the lens curvature radius, and D denotes the thickness of the lens (D1, D3, D6, D8) or the distance between the lens (D2, D4, D7). DG1 to DG3 are the dummy glass used when designing the filter.

In addition, the Arabic numerals shown in FIGS. 1 and 2 are surface numbers of lenses.

Hereinafter, the focal lengths of the lenses used in the bright lenses illustrated in FIGS. 1 and 2 will be described.

The focal length f ₁ of the first lens and the focal length f ₂ of the second lens satisfy a condition as shown in Equation 1 below.

If the ratio f ₁ / f ₂ between the focal length f ₁ of the first lens and the focal length f ₂ of the second lens is less than −1.3, the angle of view increases with the decrease of the overall focal length and the peripheral attention is reduced. Aberration correction becomes difficult. The size of the entrance pupil is smaller, so the F-number is larger even though the focal length is reduced.

On the contrary, when the ratio f ₁ / f ₂ of the focal length f ₁ of the first lens and the focal length f ₂ of the second lens is larger than −1.1, the overall focal length increases and the angle of view decreases, thereby increasing the peripheral portion. It is easy to correct the aberration, but the amount of ambient light decreases and the angle of the chief ray incident on the upper surface increases, making it difficult to match the characteristics of the chief ray angle (CRA) of the image pickup device.

The focal length f ₄ of the fourth lens and the focal length f _t of the entire optical system using the bright lens satisfy the condition as in Equation 2.

When the ratio (f ₄ / f _t ) of the focal length f ₄ of the fourth lens to the focal length f _t of the entire optical system is less than −11, the focal length of the photographing lens is increased and the F-number is also increased. The larger and smaller angle of view makes it difficult to expect a bright lens.

On the contrary, when the ratio f ₄ / f _t between the focal length f ₄ of the fourth lens and the focal length f _t of the entire optical system is greater than −9, the refractive power of the fourth lens increases, so that the plastic In the case of the optical system configuration using the material of the amount of change depending on the temperature affects the entire optical system will cause a change in performance.

Referring to Equations 1 and 2, since the second lens and the fourth lens are used for aberration correction while having low refractive power, the change of refractive power according to temperature has little effect on the entire system. It is preferable. Plastic aspherical lenses are advantageous in terms of optical performance because they are less expensive than glass lenses and can realize free shapes with inflection points.

The refractive power N _L3 of the third lens is preferably greater than 1.80. If the refractive power N _L3 of the third lens is smaller than 1.80, the curvature radius of the image side surface becomes small, resulting in an increase in curvature of the image and difficulty in processing or poor workability, resulting in poor productivity.

The refractive power of a material changes with temperature, and its value varies depending on the material. Therefore, when the temperature increases or decreases, the focal length of the optical system increases or decreases, which causes the image to be out of focus. In the present invention, the arrangement of four lenses is determined so that the lenses compensate each other when the temperature changes.

The bright lens according to the present invention, which satisfies the above conditions, is capable of realizing a bright lens by using an aspheric lens for near-infrared rays, and arranging four lenses sequentially in consideration of appropriate temperature compensation as described above. Therefore, the change in performance is minimized even for long time shooting.

Table 1 below shows optical data of the bright lens for the near-infrared light shown in FIG. 1, and the focal length of the entire optical system is 3.43 mm, the F-number 1.12, the angle of view is 86.6 °, and the wavelength is 850 nm. * Indicates aspherical surface.

Face number Radius of curvature Thickness, distance Refractive power (nd) Variance (vd) One 7.2000 1.5000 1.62299 58.12 2 3.5807 4.6334 3 * 9.3926 0.8000 1.53240 56.00 4* -16.4249 0.1000 5 Infinity 0.8147 6 -99.1590 2.5681 1.88300 40.80 7 -4.1498 0.1000 8* 2.7672 0.9878 1.63278 23.30 9 * 2.1278 1.5000 10 Infinity 0.5000 1.52300 54.50 11 Infinity 0.2000 12 Infinity 0.5000 1.52300 54.50 13 Infinity 0.5000

Table 2 shows optical data of the bright lens for the near-infrared light shown in FIG. 2, and the focal length of the entire optical system is 3.37 mm, the F-number is 1.11, the angle of view is 87.1 °, and the wavelength is 850 nm. * Indicates aspherical surface.

Face number Radius of curvature Thickness, distance Refractive power (nd) Variance (vd) One 7.2000 1.5000 1.62299 58.12 2 3.5100 4.8400 3 * 8.1600 0.8000 1.53240 56.00 4* -20.0420 0.1100 5 Infinity 0.9600 6 338.9800 2.3500 1.88300 40.80 7 -4.2600 0.1000 8* 2.6800 0.9300 1.63278 23.30 9 * 2.0400 1.5000 10 Infinity 0.5000 11 Infinity 0.4585 12 Infinity 0.5000 1.52300 54.50 13 Infinity 0.0400

Table 3 shows coefficients of the aspherical surface of the bright lens for the near infrared ray shown in FIG.

3 sides Four sides 8 sides 9 k 0.000000 0.000000 -1.053331 -0.761349 A4 -.154070E-01 -.939450E-02 -.222069E-02 0.398262E-02 A6 0.184739E-02 0.152868E-02 -.117674E-02 -.399472E-02 A8 -.490413E-03 -.566647E-03 -.173287E-03 0.185954E-03 A10 -.265812E-03 0.120912E-03 0.160336E-04 0.112171E-04 A12 0.137196E-03 0.741812E-05 -.641394E-07 -.442421E-16 A14 -.145095E-04 -.465652E-06 0.216227E-18 -.711805E-19

Table 4 shows coefficients of the aspherical surface of the bright lens for the near infrared ray shown in FIG.

3 sides Four sides 8 sides 9 k 0.000000 0.000000 -1.113778  -0.978917 A4 -.138427E-01 -.809019E-02 -.280786E-02 0.677913E-02 A6 0.139824E-02 0.746546E-03 -.126334E-02 -.464039E-02 A8 -.367340E-03 -.339279E-03 -.223661E-03 0.294231E-03 A10 -.285369E-03 0.854491E-04 0.213733E-04 0.778827E-05 A12 0.137196E-03 0.741812E-05 -.641394E-07 0.548157E-15 A14 -.145095E-04 -.465652E-06 0.406378E-18 -.343797E-18

Table 5 shows actual values of the lenses in the embodiments shown in FIGS. 1 and 2.

Conditional expression Example 1 (FIG. 1) Example 2 (FIG. 2)

-1.197 -1.183

-10.599 -9.240 N _L3 > 1.80 1.883 1.883

FIG. 3 is an aberration diagram of the bright lens for the near-infrared shown in FIG. 1.

4 is an aberration diagram of the bright lens for the near infrared ray shown in FIG. 2.

3 and 4 show astigmatic field curves in the middle of the longitudinal spherical aber on the left side and distortion on the right side.

3 and 4, it can be seen that the bright lens according to the present invention has a good aberration correction state, and the resolution of the peripheral portion as well as the center portion is suitable.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope of the present invention.

L1: first lens L2: second lens
L3: Third lens L4: Fourth lens
1-13: Surface number of the lens

Claims (7)

In the near-infrared bright lens that can be used in the near-infrared region,
It is arranged sequentially from the object side up,
A meniscus-type first lens having negative refractive power and a surface convex toward the object to be photographed;
A second lens including at least one aspherical surface having positive refractive power;
A meniscus-type third lens having a positive refractive power and a convex surface facing the image forming side;
A meniscus fourth lens having a negative refractive power and a concave surface facing the image formation side; And
And an aperture disposed between the second lens and the third lens.
The focal length f _{1 of} the first lens and the focal length f ₂ of the second lens are

Near-infrared bright lens, characterized in that to satisfy the relationship. In the near-infrared bright lens that can be used in the near-infrared region,
It is arranged sequentially from the object side up,
A meniscus-type first lens having negative refractive power and a surface convex toward the object to be photographed;
A second lens including at least one aspherical surface having positive refractive power;
A third lens having a positive refractive power and a surface facing toward an object to be photographed and a surface facing toward an image being formed, respectively;
A meniscus fourth lens having a negative refractive power and a concave surface facing toward the image formation; And
And an aperture disposed between the second lens and the third lens.
The focal length f _{1 of} the first lens and the focal length f ₂ of the second lens are

Near-infrared bright lens, characterized in that to satisfy the relationship. 3. The method according to claim 1 or 2,
The focal length f ₄ of the fourth lens and the focal length f _t of the entire optical system of the camera are

Near-infrared bright lens, characterized in that to satisfy the relationship. The method of claim 3,
The refractive power N _L3 of the third lens is greater than 1.80, the bright lens for near-infrared. 5. The method of claim 4,
And the second lens and the fourth lens are made of plastic, and the first lens and the third lens are made of glass. The method of claim 5,
The bright lens for near-infrared light, wherein an inflection point exists on the aspherical surface of said second lens and said fourth lens.
A camera for motion capture, using the camera lens of claim 6.

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