KR20130070439A - Optical system - Google Patents

Abstract

An optical system is disclosed. The optical system includes a first lens, a second lens, a third lens, and a fourth lens sequentially disposed from the object side to the image side, and satisfies Equations 1 to 3 below.
Equation 1
0≤R <0.01
Equation 2
0.5 <f3 / F <1.0
Equation 3
-10 <f4 / F <-0.5
Here, R is the curvature of the image side surface of the first lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, F is the overall focal length.

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 imaging devices tend to be miniaturized, and accordingly, optical systems used in imaging devices are also 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 may include a first lens, a second lens, a third lens, and a fourth lens that are sequentially disposed from the object side to the image side, and satisfy Equations 1 to 3 below.

Equation 1

0≤R <0.01

Equation 2

0.5 <f3 / F <1.0

Equation 3

-10 <f4 / F <-0.5

Here, R is the curvature of the image side surface of the first lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, F is the overall focal length.

In one embodiment, the image side surface of the first lens may be a plane.

The optical system according to an embodiment may satisfy Equations 4 and 5 below.

Equation 4

0.6 <f3 / F <0.9

Equation 5

-1 <f4 / F <-0.5

In example embodiments, the first lens may have positive refractive power, the second lens may have negative refractive power, the third lens may have positive refractive power, and the fourth lens may have negative refractive power. .

The optical system according to an embodiment may have a wide angle of 75 ° or more.

The optical system according to an embodiment may satisfy Equation 6 below.

Equation 6

1 <ttl / F <1.3

Here, ttl is the distance from the object side surface to the image side surface of the first lens, F is the total effective focal length.

In an embodiment, the image side surface of the fourth lens may be aspherical.

The optical system according to the embodiment may form an image side surface of the first lens to be close to a plane. Accordingly, the optical system according to the embodiment can reduce the sensitivity due to the tolerance.

In addition, since the optical system according to the embodiment satisfies 0.5 < f3 / f < 1.0, the peripheral light quantity ratio and chromatic aberration can be improved.

In addition, since the optical system according to the embodiment satisfies -10 < f4 / f <

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

Hereinafter, an imaging lens according to an exemplary 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.

As shown in FIG. 1, the compact optical system according to the embodiment has an aperture 5, a first lens 10, and a second lens 20 in order from an object side to an image side. ), A third lens 30, a fourth lens 40, a filter 60, and a light receiving element 70.

In order to acquire a subject image, light corresponding to image information of the subject passes through the first lens 10, the second lens 20, the third lens 30, the fourth lens 40, and the filter 60. Incident on the light receiving element 70.

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 positive refractive power, , And the fourth lens 40 may have a negative refracting power.

The first lens 10, the second lens 20, the third lens 30, and the fourth lens 40 may be formed of glass or plastic.

The object side surface R1 of the first lens 10 is convex and the upper surface R2 of the first lens 10 is convex or concave or may be planar. In addition, the object side surface R1 of the first lens 10 may be aspherical or spherical.

The curvature of the image side surface R2 of the first lens 10 may satisfy Equation 1 below.

Equation 1

0≤R <0.01

In more detail, the curvature of the image side surface R2 of the first lens 10 may satisfy Equation 2 below.

Equation 7

0≤R <0.001

In more detail, the curvature of the image side surface R2 of the first lens 10 may be zero.

That is, the image side surface R2 of the first lens 10 has a very small curvature. The image side surface R2 of the first lens 10 may include a plane. The image side surface R2 of the first lens 10 may be a flat surface or a nearly curved surface. Since the image side surface R2 of the first lens is close to the plane, the tolerance of the compact optical system according to the embodiment may be reduced.

The second lens 20 may have a meniscus shape. The object side surface R3 of the second lens 20 is concave and the upper surface R4 of the second lens 20 can be concave. That is, the second lens 20 may have a concave shape. In addition, the object side surface R3 and the upper surface R4 of the second lens 20 may be spherical or aspherical.

The object side surface R5 of the third lens 30 is concave and the upper surface R6 of the third lens 30 is convex. In addition, the object side surface R5 and the upper side surface R6 of the third lens 30 may be spherical or aspherical.

The focal length of the third lens 30 may satisfy Equation 2 below.

Equation 2

0.5 <f3 / F <1.0

Here, f3 is the effective focal length of the third lens 30, F is the total focal length of the compact optical system according to the embodiment.

In more detail, the focal length of the third lens 30 may satisfy Equation 4 below.

Equation 4

0.6 <f3 / F <0.9

The fourth lens 40 may have a meniscus shape. The object side surface R7 of the fourth lens 40 is convex and the upper surface R8 of the fourth lens 40 can be concave. In addition, the object side surface R7 and the upper surface R8 of the fourth lens 40 may be aspherical.

In addition, the fourth lens 40 is formed to include at least one aspherical surface inflection point.

At this time, one or more aspherical surface inflection points may be formed on the object side surface R7 of the fourth lens 40. [ At least one aspherical inflection point CP may be formed on the upper surface R8 of the fourth lens 40. [ The aspheric inflection point formed in the fourth lens 40 can control the maximum emission angle of the principal ray incident on the light receiving element 70.

The focal length of the fourth lens 40 may satisfy Equation 3 below.

Equation 3

-10 <f4 / F <-0.5

Here, f4 is the effective focal length of the fourth lens 40, F is the total focal length of the compact optical system according to the embodiment.

In more detail, the focal length of the fourth lens 40 may satisfy Equation 5 below.

Equation 5

-1 <f4 / F <-0.5

When the light receiving element 70 of the upper surface R11 is a Charge Coupled Device (CCD) or a Complementary Metal Oxide Semiconductor (CMOS) sensor, there is an angle at which light amount is secured at each pixel. Therefore, the periphery of the screen becomes dark.

Therefore, in this embodiment, the aspheric inflection point is formed on the upper surface R8 of the fourth lens 40 to adjust the maximum emission angle of the principal ray, thereby preventing the peripheral portion of the screen from becoming dark.

The diaphragm 5 is disposed on the object side of the first lens 10. The diaphragm 5 functions to adjust the focus length by selectively converging the incident light.

The filter 60 may be an infrared cut filter 60 (IR cut filter). The infrared cut filter 60 functions to block radiant heat emitted from external light from being transmitted to the light receiving device 400. That is, the infrared cut filter 60 has a structure that transmits visible light and reflects infrared light so as to flow out.

The light receiving element 70 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.

As described above, the optical system according to the embodiment may form the image side surface R2 of the first lens 10 close to a plane. Accordingly, the optical system according to the embodiment can reduce the sensitivity due to the tolerance.

In addition, since the optical system according to the embodiment satisfies Equation 2, the peripheral light quantity ratio and chromatic aberration can be improved.

In addition, since the optical system according to the embodiment satisfies Equation 3, ttl may be reduced and may be formed in a small size as a whole.

For example, the optical system according to the embodiment may satisfy Equation 6 below.

Equation 6

1 <ttl / F <1.3

Here, ttl is the distance from the object side surface to the image side surface of the first lens, F is the total effective focal length.

The optical system according to the embodiment may have a small ttl compared to the total effective focal length. That is, the distance from the object side surface R1 of the first lens 10 to the image surface R11, that is, the total distance of the optical system according to the embodiment may have a very small value.

In addition, the optical system according to the embodiment may be compactly formed and may have a wide angle WA of 74 ° or more.

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 surface Radius of curvature (mm) Thickness (mm) Refractive index Abe number Remarks R1 * 1.35008 0.673 1.5256 52.55 R2 * 0 0.102 R3 * -13.9707 0.172 1.61279 26.9 R4 * 3.9215 0.473 R5 * -3.41545 0.595 1.5311 55.7 R5 * -0.896963 0.100 R6 * 6.19778 0.540 R7 * 0.897863 0.480 1.5311 55.7

(* Indicates 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 surface K A ₁ A ₂ A ₃ A ₄ A ₅ A ₆ A ₇ R1 -0.26512 -0.01247 0.0626036 -0.226111 0 0 0 0 R2 5.23E + 10 -0.26108 -0.111212 0.0150532 0 0 0 0 R3 -1141.56 -0.35173 0.047436 0.223455 0 0 0 0 R4 3.72353 -0.00565 0.132789 0.0928787 0 0 0 0 R5 -3.0407 0.077338 -0.170015 0.0613954 0.0721348 -0.012891 -0.09641 0.055908 R6 -0.68251 0.259738 -0.185205 0.0372893 0.0491034 0.0273008 -0.0062364 -0.012733 R7 -953.428 -0.21890 0.0433275 0.0309563 -0.001856 -0.003297 -0.0009995 0.000449 R8 -6.36759 -0.12646 0.0542036 -0.015868 0.0014919 0.0002337 -0.000033 -0.000004

The aspherical coefficient values of Table 2 for the aspherical lens of the experimental example can be obtained from Equation 6 below.

Equation 6

Z = C * Y ² / (1 + √ (1- (1 + K) * C ² * Y ² )) + A ₁ * Y + A ₂ * Y ² + A ₃ * Y ³ + A ₄ * Y ⁴ + A ₅ * Y ⁵ + A ₆ * Y ⁶ + A ₇ * Y ⁷

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

C: basic curvature of the 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 2.568276 1.525697 52.55 1 / 2.568276 The second lens -4.982643 1.61279 26.9 1 / -4.982643 Third lens 2.120095 1.5311 55.7 1 / 2.120095 The fourth lens -2.054890 1.5311 55.7 1 / -2.054890

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 3.0863 ttl 3.84 R2 0 f3 / F 0.6869 f4 / F -0.66583 ttl / F 1.2442

As such, when the small optical system according to the experimental example satisfies Equations 1 to 5 and 7, ttl and F may be obtained to satisfy Equation 6.

Therefore, the compact optical system according to the embodiment is designed as Equation 1 to Equation 5 and Equation 7, and may have a small size and at the same time have improved performance.

In addition, the wide angle of the compact optical system according to the embodiment was about 74 °.

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 (7)

A first lens, a second lens, a third lens, and a fourth lens arranged sequentially from the object side to the image side,
An optical system that satisfies Equation 1 to Equation 3 below.
Equation 1
0≤R <0.01
Equation 2
0.5 <f3 / F <1.0
Equation 3
-10 <f4 / F <-0.5
Here, R is the curvature of the image side surface of the first lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, F is the overall focal length. The optical system of claim 1, wherein the image side surface of the first lens comprises a plane. The optical system of claim 1, which satisfies Equation 4 and Equation 5 below.
Equation 4
0.6 <f3 / F <0.9
Equation 5
-1 <f4 / F <-0.5 2. The objective lens of claim 1, wherein the first lens has positive refractive power, the second lens has negative refractive power, the third lens has positive refractive power, and the fourth lens has negative refractive power. . The optical system according to claim 1, which has a wide angle of 74 ° or more. The optical system of claim 1, wherein the following Equation 6 is satisfied.
Equation 6
1 <ttl / F <1.3
Here, ttl is the distance from the object side surface to the image side surface of the first lens, F is the total effective focal length. The optical system according to claim 1, wherein the upper surface of the fourth lens is an aspherical surface including an inflection point.

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