KR101428180B1 - Optical system - Google Patents

Abstract

The optical system according to the embodiment includes a first lens, a second lens, and a third lens which are sequentially arranged from the object side to the image side, and satisfy the following expressions (1) and (2).
[Equation 1]
0.6 <| D 2 / Sag 2 |
Here, D2 is the effective radius of the upper surface of the first lens, and Sag2 is the Sag value of the upper surface of the first lens.
[Equation 2]
0.5 <| D 3 / Sag 3 |
Here, D3 is the effective radius of the upper surface of the second lens, and Sag3 is the Sag value of the upper surface of the second lens.

Description

Optical system {OPTICAL SYSTEM}

An embodiment relates to an optical system.

2. Description of the Related Art Recently, a compact digital camera or a digital video camera using a solid-state image pickup device such as CCD or CMOS is incorporated in a mobile phone or a mobile communication terminal. Such an imaging device has a tendency to be downsized, and accordingly, an optical system used for an imaging device is required to have high performance and miniaturization.

The conventional optical system includes a first lens, a second lens, a third lens, a fourth lens, a filter, and a light receiving element. At this time, the first lens, the second lens, the third lens, and the fourth lens are arranged in order from the object side to the image side. The first lens and the third lens may have a positive refractive power, and the second lens and the fourth lens may have a negative refractive power. The refractive power of the second lens may be designed to be larger than that of other lenses.

The first lens may have a convex surface on the object side, and the second lens may have a concave surface on the image side. The filter may be an infrared cut filter, and the light receiving element may be a CCD image sensor or a CMOS image sensor.

Such a small optical system is disclosed in Korean Patent Application No. 10-2007-0041825.

The embodiment is intended to provide an optical system having an improved performance and a small size.

The optical system according to the embodiment includes a first lens, a second lens, and a third lens which are sequentially arranged from the object side to the image side, and satisfy the following expressions (1) and (2).

[Equation 1]

0.6 <| D 2 / Sag 2 |

Here, D2 is the effective radius of the upper surface of the first lens, and Sag2 is the Sag value of the upper surface of the first lens.

[Equation 2]

0.5 <| D 3 / Sag 3 |

Here, D3 is the effective radius of the upper surface of the second lens, and Sag3 is the Sag value of the upper surface of the second lens.

When the optical system according to the embodiment is designed as described above, the following Equation 1 and Equation 2 can be satisfied.

[Equation 1]

0.6 <| D 2 / Sag 2 |

Here, D2 is the effective radius of the upper surface of the first lens, and Sag2 is the Sag value of the upper surface of the first lens.

[Equation 2]

0.5 <| D 3 / Sag 3 |

Here, D3 is the effective radius of the upper surface of the second lens, and Sag3 is the Sag value of the upper surface of the second lens.

Thus, the optical system according to the embodiment can realize a small-sized optical system by reducing the total length of the optical system through the combination of the first lens, the second lens, and the third lens satisfying the above-mentioned equations 1 and 2, By having improved performance, a high-resolution optical system can be realized.

Therefore, the optical system according to the embodiment can have a small size and an improved performance.

1 is a side cross-sectional view schematically showing an internal structure of a small optical system according to an embodiment.

Hereinafter, an optical system according to an embodiment will be described in detail with reference to the accompanying drawings.

1 is a side cross-sectional view schematically showing an internal structure of a small optical system according to an embodiment.

1, the compact optical system according to the embodiment includes a first lens 10, a diaphragm 15, a second lens 20 (in this order, ), A third lens 30, a filter 40, and a light receiving element 50.

The light corresponding to the image information of the subject is acquired through the first lens 10, the diaphragm 15, the second lens 20, the third lens 30 and the filter 40 in order to acquire the subject image, And is incident on the light receiving element 50.

The first lens 10 has a positive refractive power and the second lens 20 has a negative refractive power and the third lens 30 has a negative refractive power, ). &Lt; / RTI &gt;

At this time, the first lens 10 can satisfy the following equation (1).

[Equation 1]

0.6 <| D 2 / Sag 2 |

Here, D2 is the effective radius of the upper surface of the first lens, and Sag2 is the Sag value of the upper surface of the first lens.

In addition, the first lens 10, the second lens 20, and the third lens 30 may be formed of glass or plastic. Preferably, the first lens 10, the second lens 20, and the third lens 30 may be formed of plastic.

The object side surface R1 of the first lens 10 is convex and the upper surface R2 of the first lens 10 can be concave. In addition, the object side surface R1 and the image side surface R2 of the first lens 10 may be aspherical. Also, the first lens 10 may have a meniscus shape. In addition, a diffraction pattern may be formed on at least one surface of the object-side surface (R1) or the image-side surface (R2) of the first lens. Therefore, the performance of the entire optical summer can be improved by the diffraction pattern.

The second lens 20 may have a meniscus shape. The object side surface R4 of the second lens 20 is concave and the upper surface R5 of the second lens 20 is convex. In addition, the object side surface R4 and the upper side surface R5 of the second lens 20 may be aspherical.

The second lens 20 can satisfy the following equation (2).

[Equation 2]

0.5 <| D 3 / Sag 3 |

Here, D3 is the effective radius of the upper surface of the second lens, and Sag3 is the Sag value of the upper surface of the second lens.

The third lens 30 is formed to include at least one aspherical inflection point.

At this time, one or more aspheric inflection points may be formed on the object side R6 of the third lens 30. At least one aspheric inflection point may be formed on the upper surface R7 of the third lens 30. The aspheric inflection point formed in the third lens 30 can adjust the maximum emission angle of the principal ray incident on the light receiving element 50.

When the light receiving element 50 which is the image surface R10 is a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) sensor, there is an angle at which the amount of light is secured in each pixel. The shading of the periphery of the screen appears.

Therefore, in the present embodiment, the aspheric inflection point is formed on the upper surface R11 of the third lens 30 to adjust the maximum emission angle of the principal ray, thereby preventing the peripheral portion of the screen from becoming dark.

The diaphragm 15 is disposed between the first lens 10 and the second lens 20 to selectively focus the incident light to adjust the focus length.

The filter 60 may be formed of an IR cut filter 40 (IR cut filter). The infrared cut-off filter 60 blocks radiation heat emitted from external light from being transmitted to the light receiving element 50. That is, the infrared cut-off filter 40 has a structure for transmitting visible light and reflecting the infrared light to the outside.

The light receiving element 50 having an image formed thereon may be an image sensor for converting an optical signal corresponding to an object image into an electrical signal, and the image sensor may be a CCD or a CMOS sensor.

The compact optical system according to the embodiment satisfies the following expression (1).

[Equation 1]

0.6 <| D 2 / Sag 2 |

Here, D2 is the effective radius of the upper surface of the first lens, and Sag2 is the Sag value of the upper surface of the first lens.

Further, in addition to Equation (1), the compact optical system according to the embodiment can further satisfy Equation (2) below.

[Equation 2]

0.5 <| D 3 / Sag 3 |

Here, D3 is the effective radius of the upper surface of the second lens, and Sag3 is the Sag value of the upper surface of the second lens.

Thus, the optical system according to the embodiment can realize a small-sized optical system by reducing the total length of the optical system through the combination of the first lens, the second lens, and the third lens satisfying the above-mentioned equations 1 and 2, By having improved performance, a high-resolution optical system can be realized.

Therefore, the optical system according to the embodiment can have a small size and an improved performance.

Experimental Example

The compact optical system according to the experimental example has optical characteristics as shown in Table 1 below.

Lens face Radius of curvature (mm) Thickness (mm) Refractive index Abe number R1 * 1.1080 0.4839 1.530 55.84 R2 * 6.0921 0.1000 R3 ∞ 0.3132 R4 * -0.7903 0.3508 1.614 26.00 R5 * -1.3832 0.2946 R6 * 1.0786 0.6277 1.530 55.84 R7 * 1.5111 0.1148 R8 ∞ 0.2100 1.523 54.47 R9 ∞ 0.8613 R10 ∞ -0.0061

(* Indicates an aspherical surface)

The thickness shown in Table 1 represents the distance from each lens surface to the next lens surface.

Table 2 below shows the aspherical surface coefficient values for the aspherical lens in the experimental example.

Lens face K A ₁ A ₂ A ₃ A ₄ A ₅ A ₆ R1 -0.250467 0.566262E-02 -0.232440E-01 -0.318961E + 00 0.588935E + 00 -0.175168E + 01
0 R2 -90.000000 -0.632061E-01 -0.395617E + 00 -0.214306E + 00 0.726057E-01
0 0 R4 1.134436 -0.495858E-01 0.105215E + 01 0.210842E + 01 0.345141E + 02 -0.170979E + 03 0.436248E + 03 R5 0.267318 -0.782178E + 00 0.204004E + 01 -0.209377E + 01 -0.444919E + 00 0.999758E + 01 -0.115455E + 02 R6 -7.232056 -0.278586E + 00 0.239222E + 00 -0.773642E-01 -0.860328E-02 0.119174E-01 -0.238825E-02 R7 -0.839298 -0.353809E + 00 0.189503E + 00 -0.821451E-01 0.231764E-01 -0.333212E-02 -0.697239E-05

The aspherical surface coefficient values in Table 2 for the aspherical surface lens in the experimental example can be obtained from the following equation (3).

Equation 3

Z: distance from the apex of the lens in the optical axis direction

C: Basic curvature of lens

Y: Distance in the direction perpendicular to the optical axis

K: Conic constant

A ₁ , A ₂ , A ₃ , A ₄ , A ₅ : Aspheric constant

As described above, the aspherical shape for each lens in the experimental example was determined.

In the experimental example, each lens was designed as shown in Table 3 below.

Effective focal length (mm) Refractive index Abe number Refractive index (1 / ㎜) The first lens 2.461658 1.52996 55.84405 0.406230272 The second lens -3.853763 1.613995 26.00241 -0.259486637 Third lens 4.707574 1.52996 55.84405 0.212423639

When the compact optical system according to the experimental example was designed as described above, the performance as shown in Table 4 was obtained.

F (EFL) 2.8 ttl 3.452 f1 / F 0.879 ttl / F 1.232

Thus, when the small optical system according to the experimental example satisfies the equations (1) and (2), ttl and F can be obtained so as to satisfy the equation (2).

Therefore, the compact optical system according to the embodiment is designed as shown in Equations (1) and (2), and can have a small size and at the same time an improved performance.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood that various modifications and applications are possible. For example, each component specifically shown in the embodiments can be modified and implemented. It is to be understood that all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (9)

1. An optical system comprising a first lens, a second lens and a third lens which are sequentially arranged from an object side to an image side, and satisfy the following expressions (1) and (2).
[Equation 1]
0.6 <| D 2 / Sag 2 |
Here, D2 is the effective radius of the upper surface of the first lens, and Sag2 is the Sag value of the upper surface of the first lens.
[Equation 2]
0.5 <| D 3 / Sag 3 |
Here, D3 is the effective radius of the upper surface of the second lens, and Sag3 is the Sag value of the upper surface of the second lens. delete The method according to claim 1,
Wherein the first lens has a positive refracting power. The method of claim 3, wherein
And an aperture disposed between the first lens and the second lens. The method of claim 3,
Wherein the object-side surface and the image-side surface of the first lens, the second lens, and the third lens are aspherical surfaces. 6. The method of claim 5,
And the third lens includes at least one aspherical inflection point. The method according to claim 6,
And an optical system including a diffraction pattern on at least one surface of an object-side surface and an image-side surface of the first lens. The method according to claim 1,
And a filter and a light-receiving element next to the third lens in the upward direction from the object side. The method according to claim 1,
And an optical system including a diffraction pattern on one surface of at least one of the first lens and the second lens.

Images