KR102386589B1 - Wide angle mobile optical system for high density pixel - Google Patents

Abstract

The present invention provides a compact mobile optical system. Mobile optical system according to the present invention, a first lens having a negative refractive power; a second lens having positive refractive power; a third lens having positive refractive power; a fourth lens having a negative refractive power; a fifth lens having positive refractive power; a sixth lens having negative refractive power, wherein the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are sequentially arranged from the object side to the image side, and the conditional expression 0.7 < BFL /EPD < 1.2 (BFL: Distance on the optical axis from the second surface (image side) of the sixth lens (L6) to the sensor surface (mm), EPD: Entrance Pupil Diameter (mm) )) can be satisfied.
According to the present invention, it is possible to provide a small mobile optical system that not only secures a wide angle of about 120 degrees, but also implements a high resolution corresponding to a high-pixel image sensor of 20 mega or more.

Description

High-pixel wide-angle mobile optical system {WIDE ANGLE MOBILE OPTICAL SYSTEM FOR HIGH DENSITY PIXEL}

The present invention relates to a high-pixel optical system mounted on a mobile device such as a smartphone, and more particularly, to a mobile optical system capable of realizing high resolution and a wide angle suitable for a high-pixel image sensor.

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

The technical requirements of the optical system can be generally divided into resolution, size, angle of view, etc. In the past, the demand for high resolution and miniaturization occupied a large proportion, but recently, the demand for a wide angle is also gradually increasing.

However, as the optical system becomes more difficult to correct aberration as the angle of view increases, it is difficult to realize high resolution. To realize a wide angle, the number of lenses must be increased for proper aberration correction. The reality is that it is very difficult to design.

In particular, as more and more high-pixel image sensors of 20 mega or more are installed in smart devices in recent years, it is necessary to develop an optimal optical system that can realize high-resolution and wide-angle in response to high-pixel image sensors while reducing the overall length by minimizing the number of lenses. .

Republic of Korea Patent Registration No. 10-2020032 (published on September 10, 2019)

The present invention has been devised against this background, and an object of the present invention is to provide an optical system capable of realizing a high resolution corresponding to a high-pixel image sensor while securing a wide angle and minimizing an optical electric field.

In order to achieve this object, an aspect of the present invention, a first lens having a negative refractive power; a second lens having positive refractive power; a third lens having positive refractive power; a fourth lens having a negative refractive power; a fifth lens having positive refractive power; a sixth lens having negative refractive power, wherein the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are sequentially arranged from the object side to the image side, and the conditional expression 0.7 < BFL /EPD < 1.2 (BFL: Distance on the optical axis from the second surface (image side) of the sixth lens (L6) to the sensor surface (mm), EPD: Entrance Pupil Diameter (mm) )) to provide an optical system that satisfies

In addition, in the optical system according to an aspect of the present invention, conditional expression 0.4 < (S21/S22) / (S11/S12) < 0.8 (S11: SAG value of the first surface of the first lens (mm), S12: of the first lens An optical system that satisfies the SAG value of the second surface, S21: the SAG value of the first surface of the second lens, S22: the SAG value of the second surface of the second lens).

In addition, the optical system according to an aspect of the present invention, the conditional expression |V4-V1| <5.0 (V4: Abbe's number of the fourth lens, V1: Abbe's number of the first lens) may be satisfied.

In addition, the optical system according to an aspect of the present invention, the conditional expression 15 < ET56 / CT56 < 35 (ET56: a straight line distance in the optical axis direction between the end of the effective mirror of the second surface of the fifth lens and the end of the effective mirror of the first surface of the sixth lens ( mm), CT56: the on-axis distance (mm) between the fifth lens and the sixth lens may be satisfied.

In addition, in the optical system according to an aspect of the present invention, an iris is disposed between the second lens and the third lens, and the conditional expression 0.5 < Td_BS / f < 0.8 (Td_BS: from the first surface of the first lens to the diaphragm The distance on the optical axis (mm) f: the focal length (mm) of the entire optical system can be satisfied.

In addition, the optical system according to an aspect of the present invention may satisfy the conditional expression 3.4 < FOV / AOI < 4.2 (FOV: angle of view (°), AOI: sensor incidence angle (CRA) (°) of chief ray of the outermost field)).

In addition, the optical system according to an aspect of the present invention, the conditional expression 1.0 < |f4 / f| < 3.0 and 1.0 < f / f5 < 3.0 (f: focal length of the entire optical system (mm), f4: focal length of the fourth lens (L4) (mm), f5: focal length of the fifth lens (L5) (mm) )) can be satisfied.

In addition, the optical system according to an aspect of the present invention may satisfy the conditional expression 0.6 < TTL / 2Y < 1.2 (TTL: the total length of the optical system (mm), 2Y: the diagonal length of the image sensor (mm)).

Further, in the optical system according to an aspect of the present invention, the object-side surface of the first lens is convex toward the object side and the image-side surface includes a concave surface toward the object side, and the object-side surface of the second lens is concave toward the image side and the image side surface is concave toward the image side convex, the object side surface of the third lens is concave toward the image side and the image side surface is convex toward the image side, the object side surface of the fourth lens is concave toward the image side and the image side surface is convex toward the image side, and the object side surface of the fifth lens is concave toward the image side and the image side surface is convex toward the image side, the object side surface of the sixth lens is convex toward the object side in the paraxial region and the image side surface is concave toward the object side, and the object side surface or the image side surface of the sixth lens has at least one An inflection point may be formed.

Also, in the optical system according to an aspect of the present invention, each of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens may include at least one aspherical surface.

According to the present invention, it is possible to provide a small mobile optical system that not only secures a wide angle of about 120 degrees, but also implements a high resolution corresponding to a high-pixel image sensor of 20 mega or more.

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;
3A is a block diagram of an optical system according to a third embodiment of the present invention;
3B is an aberration diagram of an optical system according to a third embodiment of the present invention;
4 is a reference diagram showing SAG and ET56

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

An optical system according to an embodiment of the present invention includes first to sixth lenses L1 to L6 sequentially arranged from the object side to the image side, as shown in FIGS. 1A, 2A, and 3A .

Specifically, the first lens L1 may include a negative refractive power, an object-side surface that is convex toward the object, and an image-side surface that is concave toward the object.

The second lens L2 may have a positive refractive power, and may be a lens having an object-side surface concave toward the image side and an image-side surface convex toward the image side.

The third lens L3 may be a lens having positive refractive power, an object-side surface concave toward the image side, and an image-side surface convex toward the image side.

The fourth lens L4 may have a negative refractive power, and may be a lens in which the object side surface is concave toward the image side and the image side surface is convex toward the image side.

The fifth lens L5 may be a lens having positive refractive power, an object-side surface concave toward the image side, and an image-side surface convex toward the image side.

The sixth lens L6 has negative refractive power, and in the paraxial region, the object side surface may be convex toward the object side and the image side surface may be concave toward the object side. In addition, at least one inflection point may be formed on the object side surface or the image side surface of the sixth lens L6 .

Meanwhile, it is preferable that both surfaces of the first to sixth lenses L1, L2, L3, L4, L5, and L6 are aspherical. However, since the present invention is not necessarily limited thereto, at least one of the lens surfaces of the first to sixth lenses L1 , L2 , L3 , L4 , L5 and L6 may be a spherical surface.

The stop STOP may be disposed between the second lens L2 and the third lens L3. Also, a lens filter LF or the like may be disposed between the sixth lens L6 and the image sensor.

On the other hand, the optical system according to an embodiment of the present invention is preferably designed to satisfy the following conditional expressions 1 to 9 in order to realize a wide angle of about 120 degrees and a high resolution corresponding to a high-pixel image sensor of 20M or more.

<Condition 1>

0.7 < BFL/EPD < 1.2

BFL: Distance on the optical axis from the second surface (image side) of the sixth lens (L6) to the sensor surface (mm)

EPD: Entrance Pupil Diameter (mm)

In Condition 1 above, when the BFL/EPD value exceeds the upper limit, it is difficult to construct a wide-angle and bright lens.

<Condition 2>

0.4 < (S21/S22) / (S11/S12) < 0.8

S11: SAG value of the first surface (object-side surface) of the first lens L1.

S12: SAG value of the second surface (image-side surface) of the first lens L1.

S21: SAG value of the first surface (object-side surface) of the second lens L2.

S22: SAG value of the second surface (image-side surface) of the second lens L2.

(The SAG value means the linear distance (mm) in the optical axis direction between the central vertex of the corresponding lens surface and the end of the effective mirror, as illustrated in FIG. 4 )

In the above condition 2, if the (S21/S22)/(S11/S12) value exceeds the upper limit, it is difficult to secure a space in the center thickness of the lens, making it difficult to manufacture, and if it is smaller than the lower limit, it becomes difficult to secure a wide viewing angle.

<Condition 3>

0.5 < Td_BS / f < 0.8

Td_BS: Distance (mm) on the optical axis from the first surface (object-side surface) of the first lens L1 to the diaphragm.

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

In the above condition 3, if the Td_BS/f value exceeds the upper limit, it becomes difficult to secure performance because the balance of the entire optical system is not appropriate. If it is less than the lower limit, it becomes difficult to secure performance while maintaining the current lens power configuration.

<Condition 4>

0.6 < TTL / 2Y < 1.2

TTL: The overall length of the optical system (mm).

2Y: The diagonal length of the image sensor (mm).

In the above condition 4, if the TTL/2Y value exceeds the upper limit, the electric length becomes too long and is not suitable for use in a mobile sensor, and if it is smaller than the lower limit, it becomes difficult to implement high performance.

<Conditional Expression 5>

3.4 < FOV / AOI < 4.2

FOV: Angle of View (°)

AOI: Sensor Chief Ray Angle (CRA) (°) of chief ray in full field

In condition 5 above, if the FOV/AOI value exceeds the upper limit, the corresponding optical system is not suitable for using a sensor generally used for a mobile lens, and if it is smaller than the lower limit, it becomes difficult to secure a wide viewing angle.

<Conditional Expression 6>

1.0 < f / f5 < 3.0

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

f5: Focal length (mm) of the fifth lens (L5).

In the above condition 6, if the f/f5 value exceeds the upper limit, it is difficult to configure the overall length of the optical system to be short, making it unsuitable for a mobile lens.

<Conditional Expression 7>

|V4-V1| < 5.0

V4: Abbe number of fourth lens L4

V1: Abbe number of the first lens L1

In condition 7 above, |V4-V1| When the value exceeds the corresponding range, the balance of refractive power in the optical system configuration according to the embodiment of the present invention is not appropriate, so that it is difficult to secure performance.

<Conditional Expression 8>

15 < ET56 / CT56 < 35

ET56: A linear distance (mm) in the optical axis direction between the end of the effective mirror of the second surface (image side) of the fifth lens L5 and the end of the effective mirror of the first surface (object side) of the sixth lens L6. (See Fig. 4)

CT56: On-axis distance (mm) between the fifth lens L5 and the sixth lens L6.

In the above condition 8, if the ET56/CT56 value exceeds the upper limit, it becomes difficult to secure a space for configuring the optical system, and if it is smaller than the lower limit, it becomes difficult to secure a refraction angle to satisfy the CRA.

<Conditional Expression 9>

1.0 < |f4 / f| < 3.0

f4: Focal length (mm) of the fourth lens (L4).

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

In condition 9 above, |f4/f| If the value exceeds the upper limit, it becomes difficult to secure high performance due to insufficient refractive power of the lens.

Table 1 below exemplifies specific design specifications of the optical system according to the first to third embodiments satisfying all of the aforementioned Conditional Expressions 1 to 9.

[Table 1]

The data for each example provided to calculate the values in Table 1 are as follows, and the optical system configuration of the first, second, and third examples is as shown in FIGS. 1A, 2A, and 3A, 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's number (Vd), etc. of each lens - Table 3 shows the aspheric coefficients applied to the respective lens surfaces of the first to sixth lenses L1, L2, L3, L4, L5, and L6 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 is the first to sixth lenses (L1, L2, L3, L4, L5, L6) of the optical system according to the second embodiment. shows the aspheric coefficient applied to each lens surface of .

[Table 4] Design specifications of the second embodiment

[Table 5] Aspheric coefficient of the second embodiment

In addition, Table 6 below shows the design specifications of the optical system according to the third embodiment, and Table 7 shows the first to sixth lenses (L1, L2, L3, L4, L5, L6) of the optical system according to the third embodiment. shows the aspheric coefficient applied to each lens surface of .

[Table 6] Design specifications of the third embodiment

[Table 7] Aspheric coefficient of the third 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, A18, and A20 are aspherical coefficients, respectively, as exemplified in Tables 3, 5 and 7, respectively.

Meanwhile, FIGS. 1B, 2B, and 3B show aberration diagrams of the optical systems according to the first, second, and third 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 an optical system for a high pixel with a minimized TTL while implementing a wide angle of about 120 degrees.

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 L5: 5th lens L6: 6th lens
STOP: Aperture LF: Lens filter

Claims (10)

a first lens having a negative refractive power;
a second lens having positive refractive power;
a third lens having positive refractive power;
a fourth lens having a negative refractive power;
a fifth lens having positive refractive power;
6th lens with negative refractive power
including,
The first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are sequentially arranged from the object side to the image side, and all of the following conditional expressions are satisfied.
0.7 < BFL/EPD < 1.2
0.4 < (S21/S22) / (S11/S12) < 0.8
(BFL: Distance on the optical axis from the second surface (image side) of the sixth lens (L6) to the sensor surface (mm), EPD: Entrance Pupil Diameter (mm), S11: SAG value of the first surface of the first lens (mm), S12: SAG value of the second surface of the first lens, S21: SAG value of the first surface of the second lens S22: SAG value of the second surface of the second lens SAG value) delete According to claim 1,
An optical system that satisfies the following conditional expression.
|V4-V1| < 5.0
(V4: Abbe number of the fourth lens, V1: Abbe number of the first lens) The method of claim 1,
An optical system that satisfies the following conditional expression.
15 < ET56 / CT56 < 35
(ET56: the linear distance in the optical axis direction between the effective mirror end of the second surface of the fifth lens and the effective mirror end of the first surface of the sixth lens (mm), CT56: the optical axis distance between the fifth lens and the sixth lens (mm) ))) According to any one of claims 1, 3, 4,
An optical system, characterized in that a stop is disposed between the second lens and the third lens, and the following conditional expression is satisfied.
0.5 < Td_BS / f < 0.8
(Td_BS: Distance on the optical axis from the first surface of the first lens to the aperture (mm). f: Focal length of the entire optical system (mm)) According to any one of claims 1, 3, 4,
An optical system that satisfies the following conditional expression.
3.4 < FOV / AOI < 4.2
(FOV: angle of view (°), AOI: sensor incidence angle (CRA) (°) of chief ray in the outermost field) According to any one of claims 1, 3, 4,
An optical system, characterized in that it satisfies all of the following conditional expressions.
1.0 < |f4 / f| < 3.0
1.0 < f / f5 < 3.0
(f: focal length of the entire optical system (mm), f4: focal length of the fourth lens (L4) (mm), f5: focal length of the fifth lens (L5) (mm)) According to any one of claims 1, 3, 4,
An optical system that satisfies the following conditional expression.
0.6 < TTL / 2Y < 1.2
(TTL: Total length of optical system (mm), 2Y: Diagonal length of image sensor (mm)) According to any one of claims 1, 3, 4,
The object-side surface of the first lens is convex toward the object and the image-side surface includes a concave surface toward the object,
The object side surface of the second lens is concave toward the image side and the image side surface is convex toward the image side,
The object-side surface of the third lens is concave toward the image side and the image-side surface is convex toward the image side,
The object side surface of the fourth lens is concave toward the image side and the image side surface is convex toward the image side,
The object side surface of the fifth lens is concave toward the image side and the image side surface is convex toward the image side,
The object side surface of the sixth lens is convex toward the object side in the paraxial region and the image side surface is concave toward the object side, and at least one inflection point is formed on the object side surface or the image side surface of the sixth lens,
Optical system, characterized in that the stop is disposed between the second lens and the third lens 10. The method of claim 9,
The first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens each include at least one aspherical surface.

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