KR20100002623A - Image lens - Google Patents

Abstract

PURPOSE: An image lens is provided to improve the quality of the image in the various photographing environment by minimizing the lens size and by improving aberration correction capability. CONSTITUTION: A first lens(2) has positive refractive index to an object along the identical optical axis. A second lens(4) and a fourth lens(8) have the positive refractive index. A third lens(6), a fifth lens(10) and an iris diaphragm have the negative refractive index. The first lens has the surface which faces upward. The second lens has a convex side and a concave meniscus lens. The third lens is composed of a biconcave lens in which both sides are concave. The fourth lens is composed of the biconvex lens in which both sides are convex. The fifth lens has the concave side which faces to the fourth lens.

Description

Image Lens

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image lens, and more particularly, to an image lens capable of miniaturizing an image lens by reducing the overall length of the image lens and improving aberration correction capability even in a wide wavelength range.

Digital imaging lenses incorporated in surveillance cameras or digital cameras using solid-state imaging devices such as CCD (Charge Coupled Device) and CMOS (Complementary Metal-Oxide Semiconductor) are preferably provided to faithfully reproduce the subject. .

In addition, the imaging lens should have a short optical length defined by the distance from the object-side incident surface of the imaging lens to the imaging surface (image forming surface such as CCD).

For example, in a portable terminal, the optical distance should be at least shorter than the thickness of the portable terminal body.

On the other hand, the back focus defined by the distance from the image emitting surface of the imaging lens to the imaging surface is preferably as long as possible because a filter and other components need to be inserted between the imaging lens and the imaging surface. .

In addition to this reason, the imaging lens is required to be corrected such that the image aberration cannot be visually recognized and the various aberrations are reduced to a sufficient degree as required by the integration density of the imaging device (or also referred to as "pixel").

In the following, "the image aberration cannot be visually recognized and is corrected so that various aberrations are reduced to a sufficient degree as required by the integration density of the imaging element" is simply expressed as "various aberrations are sufficiently corrected" and the like.

At this time, an image in which various aberrations are sufficiently corrected will be expressed as a "good image".

On the other hand, in recent years, the CCD itself and the CCD camera have been miniaturized, and accordingly, the demand for miniaturization and compactness is inevitably increased also for the imaging lens for digital cameras in which they are assembled.

Moreover, in light receiving devices such as CCDs, the pixel size of the unit is high, in contrast to the miniaturization of the CCD, and the imaging lens used in the camera using the same is inevitably required to exhibit high optical performance.

As an imaging lens that satisfies such requirements, a lens designed with a small number of constituent lenses, a short scientific distance, and a compact design has been proposed.

However, these lenses must use lenses that cannot be made to have a small radius of curvature in order to shorten the optical distance due to the high cost and processing constraints using aspherical molded glass.

In addition, lens systems may use a single lens to achieve short optical distance, but in this case the aberrations are not sufficiently eliminated.

One of the imaging lenses for solving the above problems is composed of two groups of two lenses having a suitable length of back focus and a wide angle of field and small distortion aberration.

There is also an imaging lens having a form of two lenses, which is easy to manufacture with a sufficiently long back focus and a refractive index of an object-side lens and an image-side lens that can be set appropriately.

In addition, there is an image pickup lens that is compact, lightweight, has good telecentric characteristics, and is easy to astigmatism correction and fabrication assembly.

However, the above-described imaging lenses have a small numerical aperture, which may not only achieve desired characteristics in various imaging environments, but also have a limited wavelength range in which desired characteristics may be obtained. have.

Accordingly, the present invention is to provide an image lens to reduce the overall length of the image lens in order to solve the above-mentioned problems and to have a small numerical aperture while having a large numerical aperture to obtain the desired characteristics in a variety of shooting environment The purpose.

Another object of the present invention is to provide an image lens capable of miniaturizing an image lens and improving aberration correction capability in a wide wavelength range so that desired characteristics can be obtained.

The image lens according to the embodiment of the present invention is a first lens having a positive refractive index, a second lens having a positive refractive index, a third lens having a negative refractive index, an aperture, a positive in order from an object to an image along the same optical axis A fourth lens having a refractive index of and a fifth lens having a negative refractive index are disposed.

In the image lens according to the embodiment of the present invention, the first lens has a convex surface facing the object, and the second lens has a convex surface facing the first lens, and the other surface has a concave meniscus. ) And the third lens is a biconcave lens having both concave surfaces, and the fourth lens is a biconvex lens having two convex surfaces, and the fifth lens is The surface facing the fourth lens is formed concave.

In the image lens according to the embodiment of the present invention, the image lens is configured to satisfy the following conditions.

TL / f <1.25

Here, TL is the total distance of the image lens system from the object side of the first lens to the image surface, and f is the focal length of the image lens system.

In the image lens according to the exemplary embodiment of the present invention, the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are formed to have focal lengths that satisfy the following conditions, respectively.

1 <f1 / f <1.5,

1 <f2 / f <1.8,

4 <-f3 / f <0.6,

0.4 <f4 / f <0.6,

0.6 <-f5 / f <0.9

Where f is the focal length of the entire image lens, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, and f5 is the 5 The focal length of the lens.

In the image lens according to the embodiment of the present invention, the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are formed to have refractive indices satisfying the following conditions, respectively.

1.52 <N1 <1.72,

1.48 <N2 <1.7,

1.62 <N3 <1.8,

1.58 <N4 <1.75,

1.62 <N5 <1.8

Here, N1 is a refractive index of the first lens, N2 is a refractive index of the second lens, N3 is a refractive index of the third lens, N4 is a refractive index of the fourth lens, and N5 is a refractive index of the fifth lens.

In the image lens according to the embodiment of the present invention, the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are formed to have thicknesses satisfying the following conditions, respectively.

0.08 <d1 / f <0.1,

0.08 <d2 / f <0.1,

0.125 <d3 / f <0.5,

0.08 <d4 / f <0.125,

0.05 <d5 / f <0.1

Where f is the focal length of the entire image lens, d1 is the thickness of the first lens, d2 is the thickness of the second lens, d3 is the thickness of the third lens, d4 is the thickness of the fourth lens, and d5 is the thickness of the fifth lens. to be.

In the image lens according to the embodiment of the present invention, the third lens and the fourth lens are disposed to satisfy the following conditions.

d67 / f <0.2

Here, d67 is an interval between the third lens and the fourth lens.

In the image lens according to the exemplary embodiment of the present invention, the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are respectively disposed to satisfy the following conditions.

0.008 <d6 / f <0.125,

0.08 <d7 / f <0.125,

0.006 <d8 / f <0.01,

0.03 <d9 / f <0.04,

0.1 <d10 / f <0.4,

0.1 <d11 / f

Where d6 is the distance between the third lens and the aperture, d7 is the distance between the aperture and the fourth lens, d8 is the distance between the first lens and the second lens, d9 is the distance between the second lens and the third lens, d10 is an interval between the fourth lens and the fifth lens, and d11 is an interval between the fifth lens and the image surface.

In the image lens according to the exemplary embodiment of the present invention, the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are each formed to have an Abbe number satisfying the following conditions.

50 <v1 <60,

60 <v2 <70,

25 <v3 <35,

45 <v4 <55,

25 <v5 <35

Here, v1 is an Abbe number of the first lens, v2 is an Abbe number of the second lens, v3 is an Abbe number of the third lens, v4 is an Abbe number of the fourth lens, and v5 is an Abbe number of the fifth lens.

According to the present invention, the focal length of the image lens system is f, and when the total distance of the image lens system from the object side surface of the first lens to the image surface is TL, TL / f <1.25 can be realized to reduce the size of the image lens.

In addition, the present invention is produced to have a large numerical aperture has the effect of obtaining the desired characteristics in a variety of shooting environment.

In addition, the present invention has the effect of obtaining the desired characteristics by improving the aberration correction ability even in a wide wavelength range.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view illustrating an image lens according to an exemplary embodiment of the present invention.

Referring to FIG. 1, an image lens according to an exemplary embodiment may include a first lens 2 having a positive refractive index in order from an object to an image IP along an identical optical axis, and a second lens having a positive refractive index ( 4), a third lens 6 having a negative refractive index, an aperture stop ST, a fourth lens 8 having a positive refractive index and a fifth lens 10 having a negative refractive index are disposed.

In this case, when the focal length of the image lens system is f and the total distance of the image lens system from the object side of the first lens 2 to the image (IP) plane is TL, the image lens according to the embodiment of the present invention is represented by the following Conditional Expression 1; It is configured to satisfy.

TL / f <1.25 ---- (1)

By such a configuration, the image lens according to the embodiment of the present invention can shorten the overall length, thereby achieving miniaturization and thinning.

The first lens 2 is installed between the object and the second lens 4, is formed to have a positive refractive index, and the surface facing the object is convex.

The second lens 4 is provided between the first lens 2 and the third lens 6 and is formed to have a positive refractive index, and the surface facing the first lens 2 is convex and the other surface is concave. It consists of a meniscus lens.

The third lens 6 is provided between the second lens 4 and the diaphragm ST, is formed to have a negative refractive index, and consists of a biconcave lens having both surfaces concave.

The fourth lens 8 is provided between the diaphragm ST and the fifth lens 10, is formed to have a positive refractive index, and is composed of a biconvex lens having both sides convex.

The fifth lens 10 is provided between the fourth lens 8 and the image image IP, is formed to have a negative refractive index, and the surface facing the fourth lens 8 is concave.

This type of image lens is focused because the refractive index becomes weak when the total focal length of the first lens group composed of the first lens 2, the second lens 4, and the third lens 6 exceeds a predetermined value. It is difficult to correct the distortion and coma aberration caused by the second lens group because the refractive index of the second lens group including the fourth lens 8 and the fifth lens 10 must be strong to shorten the distance and the back focus. You won't get a good prize.

In addition, if the focal length of each of the first lens 2, the second lens 4, the third lens 6, the fourth lens 8 and the fifth lens 10 exceeds a predetermined value, Since the refractive index is weakened, the refractive index of the lens formed at the rear end of each lens must be strengthened to shorten the focal length and the back focus, so it is difficult to correct the distortion and coma aberration of the lens formed at the rear end of each lens, as well as the image. Miniaturization of the lens becomes difficult.

Accordingly, the first lens 2, the second lens 4, the third lens 6, the fourth lens 8, and the fifth lens 10 have the focal length as shown in Conditional Expression 2 below, It is formed to have the same refractive index.

1 <f1 / f <1.5,

1 <f2 / f <1.8,

4 <-f3 / f <0.6,

0.4 <f4 / f <0.6,

0.6 <-f5 / f <0.9 ---- (2)

Where f is the focal length of the entire image lens, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, and f5 is Focal length of the fifth lens.

1.52 <N1 <1.72,

1.48 <N2 <1.7,

1.62 <N3 <1.8,

1.58 <N4 <1.75,

1.62 <N5 <1.8 ---- (3)

N1 is a refractive index of the first lens, N2 is a refractive index of the second lens, N3 is a refractive index of the third lens, N4 is a refractive index of the fourth lens, and N5 is a refractive index of the fifth lens.

In other words, when the focal length f3 of the third lens 6 exceeds 0.6, since the refractive index becomes weak, the refractive index of the fourth lens 8 must be strengthened in order to shorten the focal length and the back focus. Not only is it difficult to correct the distortion aberration and coma aberration of the lens 8, it also becomes difficult to miniaturize the image lens.

In addition, the first lens 2, the second lens 4, the third lens 6, the fourth lens 8 and the fifth lens 10 reduce the overall length of the image lens system and ensure proper back focus. It is formed to have a thickness as shown in Conditional Expression 4 below to correct various aberrations well and obtain high optical performance.

0.08 <d1 / f <0.1,

0.08 <d2 / f <0.1,

0.125 <d3 / f <0.5,

0.08 <d4 / f <0.125,

0.05 <d5 / f <0.1 ---- (4)

Where f is the focal length of the entire image lens, d1 is the thickness of the first lens, d2 is the thickness of the second lens, d3 is the thickness of the third lens, d4 is the thickness of the fourth lens, and d5 is the thickness of the fifth lens. being.

In addition, the third lens 6 and the fourth lens 8 are disposed to satisfy the condition as in Equation 5 in order to reduce the overall length of the image lens system, to correct astigmatism and distortion aberration well, and to obtain high optical characteristics.

d67 / f <0.2 --- (5)

Where f is the focal length of the entire image lens, and d67 is the distance between the third and fourth lenses.

In addition, the first lens 2, the second lens 4, the third lens 6, the fourth lens 8 and the fifth lens 10 reduce the overall length of the image lens system and provide astigmatism and distortion aberration. In order to correct well and obtain high optical characteristics, the separation distance between lenses is arranged so as to satisfy the condition as in Equation 6.

0.008 <d6 / f <0.125,

0.08 <d7 / f <0.125,

0.006 <d8 / f <0.01,

0.03 <d9 / f <0.04,

0.1 <d10 / f <0.4,

0.1 <d11 / f -------- (6)

Where d6 is the distance between the third lens and the aperture, d7 is the distance between the aperture and the fourth lens, d8 is the distance between the first lens and the second lens, d9 is the distance between the second lens and the third lens, d10 is an interval between the fourth lens and the fifth lens, and d11 is an interval between the fifth lens and the image surface.

In addition, the image lens is formed to have an Abbe's Number, such as Conditional Expression 7, to facilitate chromatic aberration, in particular, axial chromatic aberration correction, where the first lens 2, the second lens 4, The third lens 6, the fourth lens 8 and the fifth lens 10 may be made of glass or plastic.

50 <v1 <60,

60 <v2 <70,

25 <v3 <35,

45 <v4 <55,

25 <v5 <35 --- (7)

Where v1 is the Abbe number of the first lens, v2 is the Abbe number of the second lens, v3 is the Abbe number of the third lens, v4 is the Abbe number of the fourth lens, and v5 is the Abbe number of the fifth lens.

(Example)

The image lens according to the embodiment of the present invention configured as shown in FIG. 1 exhibits the characteristics shown in Table 1 and FIGS. 2 to 8 at wavelengths 486.1 nm, 656.3 nm, and 852.1 nm.

2 is a diagram illustrating optical aberration according to the wavelength of the image lens illustrated in FIG. 1, and FIGS. 3A to 3C are diagrams illustrating a point spread function (PSF) of the image lens illustrated in FIG. 1, and FIG. 4. 1 is a diagram illustrating an adjustment transfer function (MTF) of the image lens illustrated in FIG. 1, and FIG. 5 is a diagram illustrating a relative illuminance of the image lens illustrated in FIG. 1.

6 is a diagram illustrating field curves of the image lens illustrated in FIG. 1, FIG. 7 is a diagram illustrating distortion aberrations of the image lens illustrated in FIG. 1, and FIG. 8 is a hardness of the image lens illustrated in FIG. 1. It is a figure which shows aberration.

At this time, the focal length f of the entire image lens is 48 mm, the angle of view 2w is 20 °, and the aperture ratio is 1: 1.6.

Bending Radius (RDY) THI Refractive index (Nd) Abbe number (vd) OBJ ∞ ∞ One 42.97676 5.0 1.6228 56.90 2 ∞ 0.3 3 24.38345 5.5 1.5924 68.39 4 102.59319 1.656193 5 -139.65430 8.0 1.7174 29.51 6 17.99462 5.558931 STO ∞ 4.310960 8 33.19807 5.5 1.6890 49.71 9 -36.142711 3.470308 10 -20.43449 3.6 1.7174 29.51 11 -106.20762 6.991107 IMG ∞

As described above, the image lens according to the exemplary embodiment of the present invention can properly correct optical aberration, distortion aberration and hardness aberration according to the angle of view as shown in FIGS. 2, 7 and 8 even in a wide wavelength range. Optical properties can be obtained.

1 is a view illustrating an image lens according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram illustrating optical aberration according to the wavelength of the image lens illustrated in FIG. 1.

3A to 3C are diagrams illustrating a point spread function (PSF) of the image lens shown in FIG. 1.

4 is a diagram illustrating an adjustment transfer function (MTF) of the image lens illustrated in FIG. 1.

FIG. 5 is a diagram illustrating a relative illuminance of the image lens illustrated in FIG. 1.

FIG. 6 is a diagram illustrating a field curve of the image lens illustrated in FIG. 1.

FIG. 7 is a diagram illustrating distortion aberration of the image lens illustrated in FIG. 1.

8 is a diagram illustrating hardness aberration of the image lens illustrated in FIG. 1.

<Explanation of symbols for the main parts of the drawings>

2: first lens 4: second lens

6: third lens 8: fourth lens

10: fifth lens

Claims (9)

A first lens having a positive refractive index, a second lens having a positive refractive index, a third lens having a negative refractive index, an aperture, a fourth lens having a positive refractive index and a negative in order from the object to the image along the same optical axis And an fifth lens having a refractive index. The method of claim 1, The first lens has a convex surface facing the object, the second lens is a convex meniscus lens having a convex surface facing the first lens and the other surface concave, and the third lens. The concave biconcave lens is concave on both sides, the fourth lens is composed of a biconvex lens convex on both sides, the fifth lens is formed with a concave surface facing the fourth lens Image lens, characterized in that. The method of claim 1, And the image lens is configured to satisfy the following conditions. TL / f <1.25 Where TL is the total distance of the image lens from the object side of the first lens to the image plane, and f is the total focal length of the image lens. The method of claim 1, And the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are formed to have focal lengths satisfying the following conditions, respectively. 1 <f1 / f <1.5, 1 <f2 / f <1.8, 4 <-f3 / f <0.6, 0.4 <f4 / f <0.6, 0.6 <-f5 / f <0.9 Where f is the total focal length of the image lens, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, and f5 is 5 Focal length of the lens. The method of claim 1, And the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are formed to have refractive indices satisfying the following conditions, respectively. 1.52 <N1 <1.72, 1.48 <N2 <1.7, 1.62 <N3 <1.8, 1.58 <N4 <1.75, 1.62 <N5 <1.8 N1 is a refractive index of the first lens, N2 is a refractive index of the second lens, N3 is a refractive index of the third lens, N4 is a refractive index of the fourth lens, and N5 is a refractive index of the fifth lens. The method of claim 1, And the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are formed to have thicknesses satisfying the following conditions, respectively. 0.08 <d1 / f <0.1, 0.08 <d2 / f <0.1, 0.125 <d3 / f <0.5, 0.08 <d4 / f <0.125, 0.05 <d5 / f <0.1 Where f is the total focal length of the image lens, d1 is the thickness of the first lens, d2 is the thickness of the second lens, d3 is the thickness of the third lens, d4 is the thickness of the fourth lens, and d5 is the thickness of the fifth lens. being. The method of claim 6, And the third lens and the fourth lens are arranged to satisfy the following conditions. d67 / f <0.2 Where f is the total focal length of the image lens and d67 is the distance between the third and fourth lenses. The method of claim 7, wherein And the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are arranged to satisfy the following conditions, respectively. 0.008 <d6 / f <0.125, 0.08 <d7 / f <0.125, 0.006 <d8 / f <0.01, 0.03 <d9 / f <0.04, 0.1 <d10 / f <0.4, 0.1 <d11 / f Where f is the total focal length of the image lens, d6 is the distance between the third lens and the aperture, d7 is the distance between the aperture and the fourth lens, d8 is the distance between the first and second lenses, and d9 is the second An interval between the lens and the third lens, d10 is an interval between the fourth lens and the fifth lens, and d11 is an interval between the fifth lens and the image surface. The method of claim 1, And the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are each formed to have an Abbe number satisfying the following conditions. 50 <v1 <60, 60 <v2 <70, 25 <v3 <35, 45 <v4 <55, 25 <v5 <35 Where v1 is the Abbe number of the first lens, v2 is the Abbe number of the second lens, v3 is the Abbe number of the third lens, v4 is the Abbe number of the fourth lens, and v5 is the Abbe number of the fifth lens.

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