KR20220040962A - Mobile small telephoto optical system for high density pixel - Google Patents

Abstract

The present invention provides a small high-pixel mobile telephoto optical system. The small telephoto optical system according to the present invention comprises: a first lens having plus optical power; a second lens having minus optical power; a third lens having minus optical power; and a fourth lens having minus optical power, wherein the first lens, the second lens, the third lens, and the fourth lens are arranged sequentially from an object to an image to satisfy a conditional expression of 0.01 <(R1/R4)/f >< (R1/R4)/f < 0.05 (R1 is a radius of curvature on a surface of the first lens toward the object and R4 is a radius of curvature on a surface of the second lens toward an image). According to the present invention, high resolution performance can be achieved with regard to an 8 mega-level high-pixel image sensor and the lens number is minimized to realize a small telephoto optical system having a full length of about 6 mm.

Description

High-pixel mobile small telephoto optical system {MOBILE SMALL TELEPHOTO OPTICAL SYSTEM FOR HIGH DENSITY PIXEL}

The present invention relates to a telephoto optical system, and more particularly, to a small telephoto optical system for high pixels that can be used in mobile devices such as smartphones.

Recently, as cameras are installed as basic specifications not only in portable smart devices but also in driving devices such as automobiles and drones, the demand for small optical systems is rapidly increasing, and the technical requirements are also diversifying.

However, it is difficult for a small camera module installed in a smartphone to have various functions such as a DSLR camera due to a size limitation.

Recently, as a way to overcome the fundamental limitations of these small camera modules and to satisfy the various needs of users, the cases of mounting a plurality of camera modules specialized for different functions in a smartphone at once is increasing. For example, there is an increasing number of cases in which camera modules specialized for different functions, such as general use, wide-angle use, telephoto use, and depth-of-field use, are mounted on smartphones.

However, in general, since telephoto cameras have a large overall length compared to the focal length of the optical system, when mounted on a smartphone, it may be a factor that limits the design freedom of the smartphone.

Therefore, it is necessary to develop a compact telephoto optical system that can minimize the overall length of the optical system while exhibiting the performance corresponding to the high-pixel image sensor used in smartphones.

Republic of Korea Patent Publication No. 10-2020-62042 (published on June 3, 2020)

The present invention has been devised against this background, and an object of the present invention is to provide a small telephoto optical system for high pixels that can be mounted on a smart phone or the like.

In order to achieve this object, an aspect of the present invention, a first lens having a positive refractive power; a second lens having a negative refractive power; a third lens having a negative refractive power; a fourth lens having a negative refractive power, wherein the first lens, the second lens, the third lens and the fourth lens are sequentially arranged from the object side to the image side, 0.01 <(R1/R4)/f < 0.05 ( Provided is a compact telephoto optical system that satisfies the conditional expression of R1: radius of curvature of the object-side surface of the first lens, and R4: radius of curvature of the image-side surface of the second lens.

The compact telephoto optical system according to an aspect of the present invention may satisfy the conditional expression of 0.1 < T3/Td34 < 0.7 (T3: thickness of the third lens, Td34: center distance between the third lens and the fourth lens).

In addition, the compact telephoto optical system according to an aspect of the present invention may satisfy a conditional expression of 3 < FOV/TTL < 7 (FOV: angle of view (°), TTL: total length of optical system (mm)).

In addition, the compact telephoto optical system according to an aspect of the present invention may satisfy the conditional expression of 13 < HFOV / HIH < 17 (HFOV: horizontal angle of view (°), HIH: horizontal image height (mm)).

In addition, the compact telephoto optical system according to an aspect of the present invention may satisfy the conditional expression of 0.7 < TTL / f < 1 (TTL: the total length of the optical system, f: the focal length of the entire optical system).

In addition, the compact telephoto optical system according to an aspect of the present invention, 0.2 < |f1| / |f| < 0.8, -1.0 < f1/f2 < 0, 30 < V1-V2 < 40 (f: the focal length of the entire optical system, f1: the focal length of the first lens, f2: the focal length of the second lens, V1: the first All of the conditional expressions of the Abbe's number of the lens, V2: the Abbe's number of the second lens) may be satisfied.

In addition, in the compact telephoto optical system according to an aspect of the present invention, the first lens is a lens with both the object side and the image side being convex, the second lens is a lens with both the object side and the image side being concave, and the three lenses are the object side and the All of the image-side surfaces are concave lenses, the four lenses have a convex object-side surface and a concave image-side surface, and an iris may be disposed in front or around the first lens. In addition, each of the first lens, the second lens, the third lens, and the fourth lens may include at least one aspherical surface.

According to the present invention, a small telephoto optical system with a total length of about 6 mm can be realized by minimizing the number of lenses as well as exhibiting high resolution performance for an 8 mega-class high-pixel image sensor.

1A is a block diagram of an optical system according to a first embodiment of the present invention;
1B is an aberration diagram of an optical system according to a first embodiment of the present invention;
2A is a block diagram of an optical system according to a second embodiment of the present invention;
2B is an aberration diagram of an optical system according to a second embodiment of the present invention;

Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings.

First, FIGS. 1A and 1B are diagrams showing the configuration and aberration diagrams of an optical system according to a first embodiment of the present invention, and FIGS. 2A and 2B are diagrams and aberration diagrams of an optical system according to a second embodiment of the present invention. it has been shown

As shown in FIGS. 1A and 2A , the optical system according to an embodiment of the present invention includes first to fourth lenses L1 to L4 arranged in order from the object side to the image side.

Specifically, the first lens L1 may have a positive refractive power, and may be a lens in which both the object-side surface and the image-side surface are convex.

The second lens L2 may have a negative refractive power, and may be a lens in which both the object side surface and the image side surface are concave.

The third lens L3 may have a negative refractive power, and may be a lens in which both the object side surface and the image side surface are concave.

The fourth lens L4 may have a negative refractive power, and may be a lens having a concave surface and a concave surface on the object side.

On the other hand, it is preferable that both surfaces of the first to fourth lenses L1, L2, L3, and L4 are aspherical. However, since the present invention is not limited thereto, at least one of the lens surfaces of the first to fourth lenses L1 , L2 , L3 and L4 may be spherical.

The stopper STOP may be disposed in front of or around the first lens L1 . Also, a lens filter LF or the like may be disposed between the fourth lens L4 and the image sensor.

Meanwhile, the optical system according to an embodiment of the present invention is preferably designed to satisfy the following conditional expressions 1 to 8 in order to realize a high resolution corresponding to an 8 mega-class high-pixel image sensor and to minimize the overall length.

<Condition 1>

0.2 < |f1| / |f| < 0.8

f: Focal length of the entire optical system (mm)

f1: focal length of the first lens (L1) (mm)

The above conditional expression 1 relates to the focal length of the entire optical system and the focal length of the first lens L1, and |f1|/|f| If the value is larger than the upper limit, the refractive power of the lens unit becomes excessively large, and it is difficult to correct the curvature and distortion aberrations. If the value is smaller than the lower limit, the sensitivity becomes excessively large and it becomes difficult to shorten the total length.

<Condition 2>

30 < V1-V2 < 40

V1: Abbe number of the first lens

V2: Abbe number of the second lens

The above conditional expression 2 relates to the Abbe numbers of the first lens L1 and the second lens L2. If the value of V1-V2 is larger than the upper limit, it becomes difficult to secure the angle of incidence (CRA) of the chief ray incident on the image plane. is difficult to construct, and if it is smaller than the lower limit, it leads to an increase in unit price due to the use of expensive materials, making it difficult to secure price competitiveness of products.

<Condition 3>

0.7 < TTL / f < 1

TTL: Total length of optical system (mm)

f: Focal length of the entire optical system (mm)

Condition 3 above relates to the overall length and focal length of the optical system. If the TTL/f value is less than the lower limit, it is difficult to secure optical performance, and if the TTL/f value is smaller than the upper limit, it is difficult to reduce the size of the optical system.

<Condition 4>

-1.0 < f1/f2 < 0

f1: focal length of the first lens (L1) (mm)

f2: focal length of the second lens (L2) (mm)

The above conditional expression 4 relates to the focal lengths of the first lens L1 and the second lens L2. When the f1/f2 value is out of the upper or lower limit, while maintaining the power configuration of the lens according to the embodiment of the present invention. It becomes difficult to secure performance.

<Conditional Expression 5>

13 < HFOV / HIH < 17

HFOV: Horizontal angle of view (°)

HIH: Horizontal height (mm)

The above conditional expression 5 relates to the horizontal angle of view and the horizontal image height of the optical system. If the HFOV/HIH value is larger than the upper limit, it is difficult to image the light around the optical axis, so it is difficult to secure performance.

<Conditional Expression 6>

3 < FOV/TTL < 7

FOV: Diagonal angle of view (°)

TTL: Total length of optical system (mm)

The above conditional expression 6 relates to the angle of view and the overall length of the optical system. If the FOV/TTL value exceeds the upper limit, it is difficult to distribute the proper refractive power of the lens, making it difficult to maintain the lens configuration in its original state. .

<Conditional Expression 7>

0.1 < T3 /Td34 < 0.7

T3: Thickness of the third lens (L3) (mm)

Td34: center distance (mm) between the third lens (L3) and the fourth lens (L4)

The above conditional expression 7 relates to the third lens (L3) and the fourth lens (L4). If the T3/Td34 value is smaller than the lower limit or larger than the upper limit, it is difficult to manufacture a lens unit, and if it is smaller than the lower limit, the refractive power of the lens is reduced. This makes it difficult to secure high performance.

<Conditional Expression 8>

0.01 < (R1/R4) / f < 0.05

R1: Radius of curvature of the object-side surface of the first lens (L1) (mm)

R4: Radius of curvature of the image side of the second lens (L2) (mm)

Condition 8 above relates to the first lens (L1) and the second lens (L2). If the (R1/R4)/f value is greater than the upper limit, not only the characteristics of the telephoto lens for viewing distant objects are lost, but also It becomes difficult to correct distortion and aberration, and if it is smaller than the lower limit, the size of the optical system becomes large, making it difficult to downsize.

Table 1 below exemplifies specific design specifications of the optical system according to the first and second embodiments satisfying all of the above-described Conditional Expressions 1 to 7.

[Table 1]

Data for each example provided to calculate the values in Table 1 are as follows, and the optical system configuration of the first and second embodiments is as shown in FIGS. 1A and 2A , respectively.

Table 2 below shows the design specifications of the optical system according to the first embodiment - radius of curvature (mm), thickness (mm), lens spacing (mm), refractive index (Nd), Abbe number (Vd), etc. of each lens - Table 3 shows the aspheric coefficients applied to each lens surface of the first to fourth lenses L1, L2, L3, and L4 of the optical system according to the first embodiment.

[Table 2] Design specifications of the first embodiment

[Table 3] Aspheric coefficient of the first embodiment

In addition, Table 4 below shows the design specifications of the optical system according to the second embodiment, and Table 5 shows the lens surfaces of the first to fourth lenses L1, L2, L3, and L4 of the optical system according to the second embodiment. It shows the aspheric coefficient applied to .

[Table 4] Design specifications of the second embodiment

[Table 5] Aspheric coefficient of the second embodiment

Meanwhile, in each embodiment, the shape of the aspherical lens may be calculated through the following equation.

[Equation]

In the above equation, 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, c is the reciprocal of the radius of curvature at the vertex of the lens, K is the Conic constant, A4, A6, A8, A10, A12, A14, A16, .... are aspherical coefficients, respectively, as exemplified in Tables 3 and 5, respectively.

Meanwhile, FIGS. 1B and 2B show aberration diagrams of the optical system according to the first and second embodiments, respectively, and it can be confirmed that astigmatism and distortion aberration are good in each embodiment.

In addition, according to an embodiment of the present invention, it is possible to provide a small telephoto optical system for mobile use that can be used in an 8 mega-class high-pixel image sensor and has a minimum TTL of about 6 mm.

In the above, preferred embodiments of the present invention have been described, but the present invention is not limited to the above-described embodiments, and may be modified or modified in various forms and implemented. If the technical idea is included, it will be natural to fall within the scope of the present invention.

L1: first lens L2: second lens L3: third lens
L4: 4th lens STOP: Aperture LF: Lens filter

Claims (8)

a first lens having positive refractive power;
a second lens having a negative refractive power;
a third lens having a negative refractive power;
a fourth lens having a negative refractive power;
including, wherein the first lens, the second lens, the third lens, and the fourth lens are sequentially arranged from the object side to the image side, and the following conditional expression is satisfied.
0.01 < (R1/R4) / f < 0.05
(R1: radius of curvature of the object-side surface of the first lens, R4: radius of curvature of the image-side surface of the second lens) According to claim 1,
A compact telephoto optical system, characterized in that it satisfies the following conditional expression.
0.1 < T3 /Td34 < 0.7
(T3: the thickness of the third lens, Td34: the center distance between the third lens and the fourth lens) According to claim 1,
A compact telephoto optical system, characterized in that it satisfies the following conditional expression.
3 < FOV/TTL < 7
(FOV: Diagonal angle of view (°), TTL: Total length of optical system (mm)) According to claim 1,
A compact telephoto optical system, characterized in that it satisfies the following conditional expression.
13 < HFOV / HIH < 17
(HFOV: Horizontal angle of view (°), HIH: Horizontal image height (mm)) According to claim 1,
A compact telephoto optical system, characterized in that it satisfies the following conditional expression.
0.7 < TTL / f < 1
(TTL: the total length of the optical system, f: the focal length of the entire optical system) According to claim 1,
A compact telephoto optical system, characterized in that it satisfies all of the following conditional expressions.
0.2 < |f1| / |f| < 0.8
-1.0 < f1/f2 < 0
30 < V1-V2 < 40
(f: the overall focal length of the optical system, f1: the focal length of the first lens, f2: the focal length of the second lens, V1: the Abbe number of the first lens, V2: the Abbe number of the second lens) 7. The method according to any one of claims 1 to 6,
The first lens is a lens in which both the object side and the image side are convex,
The two lenses are lenses in which both the object side and the image side are concave,
The three lenses are lenses in which both the object side and the image side are concave,
The 4 lenses are convex on the object side and concave on the image side,
A small telephoto optical system, characterized in that the diaphragm is disposed in front or around the first lens According to claim 7,
The first lens, the second lens, the third lens, and the fourth lens each comprises at least one aspherical compact telephoto optical system.

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