KR102232977B1 - Optical system - Google Patents

Abstract

An optical system according to an embodiment of the present invention comprises: a first lens having negative refractive power in order from the object side, the object side surface being convex and the image side surface being concave; A second lens having positive refractive power and having a convex object-side surface and an image-side surface; A third lens having negative refractive power; A fourth lens having refractive power; A fifth lens having positive refractive power; And a sixth lens having negative refractive power.

Description

Optical system {Optical system}

The present invention relates to an optical system.

Recently, portable terminals are equipped with cameras to enable video calls and photographs. In addition, as functions occupied by cameras in portable terminals are gradually increasing, demands for high resolution and high performance of cameras for portable terminals are gradually increasing.

However, since portable terminals are gradually miniaturized or lightweight, there is a limit to implementing a high-resolution and high-performance camera.

In order to solve this problem, recently, the lens of the camera is made of a plastic material that is lighter than that of glass, and a lens module is composed of five or more lenses to realize high resolution.

An object according to an embodiment of the present invention is to provide a slim optical system while implementing a wide angle of view.

In addition, it is to provide an imaging optical system capable of improving aberration improvement effect and realizing high resolution.

In addition, it is to provide an optical system capable of reducing a difference between the brightness of an image in the central portion of the image sensor and the brightness of an image in the peripheral portion of the image sensor.

An optical system according to an embodiment of the present invention comprises: a first lens having negative refractive power in order from the object side, the object side surface being convex and the image side surface being concave; A second lens having positive refractive power and having a convex object-side surface and an image-side surface; A third lens having negative refractive power; A fourth lens having refractive power; A fifth lens having positive refractive power; And a sixth lens having negative refractive power.

According to the optical system according to an embodiment of the present invention, it is possible to provide a slim optical system while implementing a wide angle of view.

In addition, while improving the aberration improvement effect, it is possible to implement a high resolution.

In addition, it is possible to reduce a difference between the brightness of the image at the center of the image sensor and the brightness of the image at the peripheral part.

1 is a configuration diagram of an optical system according to a first embodiment of the present invention,
2 and 3 are curves showing aberration characteristics of the optical system shown in FIG. 1,
4 is a table showing the characteristics of each lens of the optical system shown in FIG. 1,
5 is a table showing aspheric coefficients of each lens of the optical system shown in FIG. 1,
6 is a configuration diagram of an optical system according to a second embodiment of the present invention,
7 and 8 are curves showing aberration characteristics of the optical system shown in FIG. 6,
9 is a table showing the characteristics of each lens of the optical system shown in FIG. 6,
10 is a table showing aspheric coefficients of each lens of the optical system shown in FIG. 6,
11 is a configuration diagram of an optical system according to a third embodiment of the present invention,
12 and 13 are curves showing aberration characteristics of the optical system shown in FIG. 11,
14 is a table showing the characteristics of each lens of the optical system shown in FIG. 11,
15 is a table showing aspheric coefficients of each lens of the optical system shown in FIG. 11.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. However, the spirit of the present invention is not limited to the presented embodiments, and those skilled in the art who understand the spirit of the present invention can add, change, or delete other elements within the scope of the same idea, Other embodiments included within the scope of the inventive concept may be easily proposed, but this will also be said to be included within the scope of the inventive concept of the present application.

In addition, components having the same function within the scope of the same idea shown in the drawings of each embodiment will be described using the same reference numerals.

In the following lens configuration diagram, the thickness, size, and shape of the lens are somewhat exaggerated for explanation, and in particular, the shape of the spherical or aspherical surface suggested in the lens configuration diagram is presented as an example, but is not limited thereto.

In addition, the first lens means the lens closest to the object side, and the sixth lens means the lens closest to the image side.

Further, the front means a side closer to the object side in the imaging optical system, and the rear side means the side closer to the image sensor or the image side in the imaging optical system. In addition, in each lens, the first surface means a surface close to the object side (or object side surface), and the second surface means a surface close to the image side (or image side surface). In addition, in the present specification, the values for the radius of curvature and thickness of the lens are all in mm.

In addition, the paraxial region refers to a very narrow region near the optical axis. For example, it may refer to a region in which a distance from which a ray falls from an optical axis is zero.

In addition, TTL is the distance from the object-side surface of the first lens to the image sensor, SL is the distance from the aperture limiting the amount of light incident to the optical system to the image sensor, and ImgH is the image. Half the diagonal length of the image surface of the sensor, BFL is the distance from the image surface of the lens closest to the image to the image sensor, and EFL is the total focal length of the optical system.

The optical system according to an embodiment of the present invention includes six lenses.

That is, the optical system according to an embodiment of the present invention includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens.

However, the optical system according to an embodiment of the present invention is not composed of only six lenses, and may further include other components as necessary. For example, the optical system may further include a stop for adjusting the amount of light. In addition, the optical system may further include an infrared filter for blocking infrared rays. In addition, the optical system may further include an image sensor for converting an image of an incident subject into an electric signal. In addition, the optical system may further include a gap maintaining member for adjusting a distance between the lens and the lens.

The first to sixth lenses constituting the optical system according to an exemplary embodiment of the present invention may be made of a plastic material.

In addition, at least one of the first to sixth lenses has an aspherical surface. In addition, each of the first to sixth lenses may have at least one aspherical surface.

That is, at least one of the first and second surfaces of the first to sixth lenses may be aspherical. Here, aspherical surfaces of the first to sixth lenses are expressed by Equation 1.

In Equation 1, c is the curvature (the reciprocal of the radius of curvature) at the vertex of the lens, K is the Konig constant, and Y is the distance in the direction perpendicular to the optical axis. In addition, constants A to F mean aspheric coefficients. And Z represents the distance from the apex of the lens in the direction of the optical axis.

The optical system including the first to sixth lenses has negative/positive/negative/negative/positive/negative refractive power in order from the object side.

The optical system configured as described above can improve optical performance by improving aberrations. The effect of each lens configuration will be described later.

The optical system according to an embodiment of the present invention satisfies Conditional Expression 1.

[Conditional Expression 1]

TTL/(ImgH*2) ≤ 0.75

In Conditional Equation 1, TTL denotes a distance from the object side surface of the first lens to the image sensor's upper surface, and ImgH denotes half the diagonal length of the image sensor's upper surface.

The optical system according to an embodiment of the present invention satisfies Conditional Expression 2.

[Conditional Expression 2]

TTL/(ImgH*2) ≤ 0.68

The optical system according to an embodiment of the present invention satisfies Conditional Expression 3.

[Conditional Expression 3]

-5 <f1/EFL <-4.6

In Conditional Expression 3, f1 is the focal length of the first lens, and EFL is the total focal length of the optical system.

The optical system according to an embodiment of the present invention satisfies Conditional Expression 4.

[Conditional Expression 4]

2.3 <f1/f3 <2.6

In Conditional Expression 4, f1 is a focal length of the first lens, and f3 is a focal length of the third lens.

The optical system according to an embodiment of the present invention satisfies Conditional Expression 5.

[Conditional Expression 5]

BFL/EFL <0.31

In Conditional Equation 5, BFL is the distance from the image-side surface of the sixth lens to the image sensor, and EFL is the total focal length of the optical system.

The optical system according to an embodiment of the present invention satisfies Conditional Expression 6.

[Conditional Expression 6]

0.95 <ER1/ER6 <1.05

In Conditional Expression 6, ER1 is an effective radius of an object-side surface of the first lens, and ER6 is an effective radius of an image-side surface of the third lens.

The optical system according to an embodiment of the present invention satisfies Conditional Expression 7.

[Conditional Expression 7]

79 <FOV <83

In Conditional Equation 7, FOV is the angle of view of the optical system. Here, the unit of the angle of view of the optical system is degrees.

Next, the first to sixth lenses constituting the optical system according to an exemplary embodiment of the present invention will be described.

The first lens has negative refractive power. In addition, the first lens may have a meniscus shape that is convex toward the object side. To further explain, the first surface of the first lens may be convex in the paraxial region, and the second surface of the first lens may be concave in the paraxial region.

At least one of the first and second surfaces of the first lens may be an aspherical surface. For example, both surfaces of the first lens may be aspherical.

The second lens has positive refractive power. In addition, the second lens may have a convex shape on both sides. To further explain, the first and second surfaces of the second lens may have a convex shape in the paraxial region.

At least one of the first and second surfaces of the second lens may be an aspherical surface. For example, both surfaces of the second lens may be aspherical.

The third lens has negative refractive power. In addition, the third lens may have a meniscus shape that is convex toward the object side. To further explain, the first surface of the third lens may be convex in the paraxial region, and the second surface of the third lens may be concave in the paraxial region.

At least one of the first and second surfaces of the third lens may be an aspherical surface. For example, both surfaces of the third lens may be aspherical.

The fourth lens has negative refractive power. In addition, the fourth lens may have a meniscus shape that is convex toward the image side. To further explain, the first surface of the fourth lens may be concave in the paraxial region, and the second surface of the fourth lens may have a convex shape in the paraxial region.

At least one of the first and second surfaces of the fourth lens may be an aspherical surface. For example, both surfaces of the fourth lens may be aspherical.

The fifth lens has positive refractive power. In addition, the fifth lens may have a meniscus shape that is convex toward the image. To further explain, the first surface of the fifth lens may be concave in the paraxial region, and the second surface of the fifth lens may have a convex shape in the paraxial region.

At least one of the first and second surfaces of the fifth lens may be an aspherical surface. For example, both surfaces of the fifth lens may be aspherical.

The sixth lens has negative refractive power. In addition, the sixth lens may have a meniscus shape that is convex toward the object side. To further explain, the first surface of the sixth lens may be convex in the paraxial region, and the second surface of the sixth lens may be concave in the paraxial region.

In the optical system according to an exemplary embodiment of the present invention, a wide angle of view can be realized by allowing the first lens to have negative refractive power, and the optical system is designed in a retro focus type.

The wider the angle of view, the shorter the focal length. In this case, the back focus, which is the distance between the lens closest to the image side and the image sensor's image surface, becomes shorter, so that the infrared filter can be placed between them. It becomes difficult to secure space.

Therefore, in the imaging optical system according to an embodiment of the present invention, the infrared filter is disposed between the sixth lens and the image sensor by making the back focus relatively long while implementing a wide angle of view by designing the imaging optical system in a retro focus type. Make sure you have a space that you can.

At this time, in order to prevent the length of the entire imaging optical system from increasing by making the back focus relatively long, the combined focal length of the second lens and the third lens is formed to be shorter than the total focal length of the imaging optical system.

Meanwhile, the optical system according to an embodiment of the present invention can easily correct chromatic aberration.

Chromatic aberration refers to aberration caused by the difference in refractive index according to wavelength, and it is a phenomenon that occurs because the longer wavelength light passes through the lens and focuses away from the lens rather than other light. Therefore, when the chromatic aberration is large, light spreads according to the wavelength, so it is necessary to correct it.

In the optical system according to an exemplary embodiment of the present invention, the first to third lenses have different refractive powers.

For example, the first lens has negative refractive power, the second lens has positive refractive power, and the third lens has negative refractive power.

Accordingly, the first to third lenses have refractive powers that are opposite to those of lenses adjacent to each other in the object-side direction.

Since adjacent lenses have opposite refractive powers, one lens emits light and the other lens converges light. Accordingly, it is possible to focus lights having different wavelengths at the same focus.

In the optical system according to an exemplary embodiment of the present invention, the distance between the first lens to the third lens is formed relatively narrow to maximize the effect of correcting chromatic aberration as described above.

For example, in the paraxial region, a distance between the first lens and the second lens and a distance between the second lens and the third lens may be narrower than that between other lenses. Accordingly, it is possible to have an effect similar to that of a triple junction lens in which the first to third lenses are bonded to each other, thereby maximizing the effect of chromatic aberration correction.

In addition, by narrowing the distance between the first to third lenses, the length of the entire imaging optical system can be reduced, and as a result, a slim optical system can be implemented.

As described above, the second lens of the optical system according to an embodiment of the present invention may have positive refractive power, and both surfaces may have a convex shape.

Here, in the second lens, an absolute value of a radius of curvature of an object-side surface is smaller than an absolute value of a radius of curvature of an image-side surface.

For example, when the radius of curvature of the object-side surface of the second lens is r3 and the radius of curvature of the image-side surface of the second lens is r4, |r4/r3| > 20 is satisfied.

Accordingly, in the second lens, the object-side surface has a relatively larger curvature than the image-side surface, and the image-side surface has a relatively smaller curvature than the object-side surface. With such a configuration, it is possible to easily correct spherical aberration.

Meanwhile, in the optical system according to an exemplary embodiment of the present invention, the third lens has a meniscus shape that is convex toward an object side, and the fourth lens and the fifth lens have a meniscus shape that is convex toward an image side.

In this way, the third lens and the fourth lens are configured to have a shape symmetrical to each other, or the third lens and the fifth lens are configured to have a shape symmetrical to each other so that the light incident on the optical system is It may be made to be vertically incident on the upper surface of the image sensor.

Accordingly, the optical system according to an exemplary embodiment of the present invention can reduce a difference between the brightness of an image in the central portion of the image sensor and the brightness of an image in the peripheral portion of the image sensor.

Accordingly, it is possible to alleviate lens shading, which is a phenomenon in which an image at the peripheral portion of the image sensor is formed relatively dark.

An optical system according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 5.

The optical system according to the first embodiment of the present invention includes a first lens 110, a second lens 120, a third lens 130, a fourth lens 140, a fifth lens 150, and a sixth lens. An optical system including 160 may be included, and a stop, an infrared filter 170 and an image sensor 180 may be further included.

Here, the lens characteristics (radius of curvature (radius), thickness of the lens, or distance between lenses (Thickness), refractive index (Index), Abbe number) of each lens are as shown in FIG. 4.

In the first embodiment of the present invention, the first lens 110 has negative refractive power and has a meniscus shape that is convex toward the object side. For example, the first surface of the first lens 110 is convex in the paraxial region, and the second surface of the first lens 110 is concave in the paraxial region.

The second lens 120 has positive refractive power and has a meniscus shape in which both surfaces are convex. For example, the first and second surfaces of the second lens 120 are convex in the paraxial region.

The third lens 130 has negative refractive power and has a meniscus shape that is convex toward the object side. For example, the first surface of the third lens 130 is convex in the paraxial region, and the second surface of the third lens 130 is concave in the paraxial region.

The fourth lens 140 has negative refractive power and has a meniscus shape that is convex toward the image side. For example, the first surface of the fourth lens 140 is concave in the paraxial region, and the second surface of the fourth lens 140 is convex in the paraxial region.

The fifth lens 150 has positive refractive power and has a meniscus shape that is convex toward the image. For example, the first surface of the fifth lens 150 is concave in the paraxial region, and the second surface of the fifth lens 150 is convex in the paraxial region.

The sixth lens 160 has negative refractive power and has a meniscus shape that is convex toward the object side. For example, the first surface of the sixth lens 160 is convex in the paraxial region, and the second surface of the sixth lens 160 is concave in the paraxial region.

In addition, at least one inflection point is formed on at least one of the first and second surfaces of the sixth lens 160.

Meanwhile, each surface of the first to sixth lenses 110 to 160 has an aspherical surface coefficient as shown in FIG. 5.

The diaphragm may include a first diaphragm for limiting an amount of light incident on the optical system and a second diaphragm for blocking light at a portion where an aberration excessively occurs.

The first stop may be disposed in front of the object-side surface of the first lens, and the second stop may be disposed between the first to fourth lenses.

In addition, the optical system configured as described above may have aberration characteristics illustrated in FIGS. 2 and 3.

An optical system according to a second embodiment of the present invention will be described with reference to FIGS. 6 to 10.

The optical system according to the second embodiment of the present invention includes a first lens 210, a second lens 220, a third lens 230, a fourth lens 240, a fifth lens 250, and a sixth lens. An optical system having 260 may be included, and a stop, an infrared filter 270 and an image sensor 280 may be further included.

Here, the lens characteristics (radius of curvature (radius), thickness of the lens, or distance between lenses (Thickness), refractive index (Index), Abbe number) of each lens are as shown in FIG. 9.

In the second embodiment of the present invention, the first lens 210 has negative refractive power and has a meniscus shape that is convex toward the object side. For example, the first surface of the first lens 210 is convex in the paraxial region, and the second surface of the first lens 210 is concave in the paraxial region.

The second lens 220 has positive refractive power and has a meniscus shape in which both surfaces are convex. For example, the first and second surfaces of the second lens 220 are convex in the paraxial region.

The third lens 230 has negative refractive power and has a meniscus shape that is convex toward the object side. For example, the first surface of the third lens 230 is convex in the paraxial region, and the second surface of the third lens 230 is concave in the paraxial region.

The fourth lens 240 has negative refractive power and has a meniscus shape that is convex toward the image. For example, the first surface of the fourth lens 240 is concave in the paraxial region, and the second surface of the fourth lens 140 is convex in the paraxial region.

The fifth lens 150 has positive refractive power and has a meniscus shape that is convex toward the image. For example, the first surface of the fifth lens 150 is concave in the paraxial region, and the second surface of the fifth lens 250 is convex in the paraxial region.

The sixth lens 260 has negative refractive power and has a meniscus shape that is convex toward the object side. For example, the first surface of the sixth lens 260 has a convex shape in the paraxial region, and the second surface of the sixth lens 260 has a concave shape in the paraxial region.

In addition, at least one inflection point is formed on at least one of the first and second surfaces of the sixth lens 260.

Meanwhile, each surface of the first to sixth lenses 210 to 260 has an aspherical surface coefficient as shown in FIG. 10.

The diaphragm may include a first diaphragm for limiting an amount of light incident on the optical system and a second diaphragm for blocking light at a portion where an aberration excessively occurs.

The first stop may be disposed in front of the object-side surface of the first lens, and the second stop may be disposed between the first to fourth lenses.

In addition, the optical system configured as described above may have aberration characteristics illustrated in FIGS. 7 and 8.

An optical system according to a third embodiment of the present invention will be described with reference to FIGS. 11 to 15.

The optical system according to the third embodiment of the present invention includes a first lens 310, a second lens 320, a third lens 330, a fourth lens 340, a fifth lens 350, and a sixth lens. An optical system having 360 is included, and a stop, an infrared filter 370 and an image sensor 380 may be further included.

Here, the lens characteristics (radius of curvature (radius), thickness of the lens or distance between lenses (Thickness), refractive index (Index), Abbe number) of each lens are as shown in FIG. 14.

In the third embodiment of the present invention, the first lens 310 has negative refractive power and has a meniscus shape that is convex toward the object side. For example, a first surface of the first lens 310 has a convex shape in a paraxial region, and a second surface of the first lens 310 has a concave shape in a paraxial region.

The second lens 320 has positive refractive power and has a meniscus shape in which both surfaces are convex. For example, the first and second surfaces of the second lens 320 are convex in the paraxial region.

The third lens 330 has negative refractive power and has a meniscus shape that is convex toward the object side. For example, the first surface of the third lens 330 is convex in the paraxial region, and the second surface of the third lens 330 is concave in the paraxial region.

The fourth lens 340 has negative refractive power and has a meniscus shape that is convex toward the image. For example, the first surface of the fourth lens 340 is concave in the paraxial region, and the second surface of the fourth lens 340 is convex in the paraxial region.

The fifth lens 350 has positive refractive power and has a meniscus shape that is convex toward the image. For example, the first surface of the fifth lens 350 is concave in the paraxial region, and the second surface of the fifth lens 350 is convex in the paraxial region.

The sixth lens 360 has negative refractive power and has a meniscus shape that is convex toward an object. For example, the first surface of the sixth lens 360 is convex in the paraxial region, and the second surface of the sixth lens 360 is concave in the paraxial region.

In addition, at least one inflection point is formed on at least one of the first and second surfaces of the sixth lens 360.

Meanwhile, each surface of the first to sixth lenses 310 to 360 has an aspherical surface coefficient as illustrated in FIG. 15.

The diaphragm may include a first diaphragm for limiting an amount of light incident on the optical system and a second diaphragm for blocking light at a portion where an aberration excessively occurs.

The first stop may be disposed in front of the object-side surface of the first lens, and the second stop may be disposed between the first to fourth lenses.

In addition, the optical system configured as described above may have aberration characteristics illustrated in FIGS. 12 and 13.

On the other hand, referring to Table 1, it can be seen that the optical system according to the first to third embodiments of the present invention satisfies the aforementioned Conditional Expressions 1 to 7, through which the optical performance of the lens can be improved. , It is possible to implement a slim imaging optical system while having a wide angle of view.

In the above, the configuration and features of the present invention have been described based on the embodiments according to the present invention, but the present invention is not limited thereto, and it is understood that various changes or modifications can be made within the spirit and scope of the present invention. It will be apparent to those skilled in the art, and therefore, such changes or modifications are found to be within the scope of the appended claims.

110, 210, 310: first lens
120, 220, 320: second lens
130, 230, 330: third lens
140, 240, 340: fourth lens
150, 250, 350: fifth lens
160, 260, 360: infrared filter
170, 270, 370: image sensor

Claims (18)

In order from the object side,
A first lens having negative refractive power, a convex object-side surface and a concave image-side surface;
A second lens having positive refractive power and having a convex object-side surface and an image-side surface;
A third lens having negative refractive power;
A fourth lens having refractive power;
A fifth lens having positive refractive power; And
Includes; a sixth lens having negative refractive power,
When the effective radius of the object-side surface of the first lens is ER1, and the effective radius of the image-side surface of the third lens is ER6,
An imaging optical system that satisfies 0.95 <ER1/ER6 <1.05.
The method of claim 1,
The third lens is an optical system in which an object-side surface is convex.
The method of claim 2,
The third lens is an optical system having a concave image-side surface.
The method of claim 1,
The fourth lens is an optical system in which an image-side surface is convex.
The method of claim 1,
The fifth lens is an optical system having a concave object-side surface.
The method of claim 5,
The fifth lens is an optical system in which an image-side surface is convex.
The method of claim 1,
The sixth lens is an optical system in which an object-side surface is convex.
The method of claim 7,
The sixth lens is an optical system having a concave image-side surface.
The method of claim 1,
The third lens has a convex object-side surface and a concave image-side surface, and the fifth lens has a concave object-side surface and a convex image-side surface.
The method of claim 1,
An optical system satisfying TTL/(ImgH*2) ≤ 0.75 when the distance from the object-side surface of the first lens to the image sensor is TTL, and half the diagonal length of the image sensor is ImgH.
The method of claim 1,
When the focal length of the first lens is f1 and the total focal length of the optical system including the first to sixth lenses is EFL, -5 <f1/EFL <-4.6.
The method of claim 1,
When the focal length of the first lens is f1 and the focal length of the third lens is f3,
An imaging optical system that satisfies 2.3 <f1/f3 <2.6.
The method of claim 1,
When the distance from the upper surface of the sixth lens to the upper surface of the image sensor is BFL, and the total focal length of the optical system comprising the first to sixth lenses is EFL,
Imaging optical system that satisfies BFL/EFL <0.31.
The method of claim 1,
When the angle of view of the imaging optical system is the FOV,
An imaging optical system that satisfies 79° <FOV <83°.
The method of claim 1,
In the paraxial region, the distance between the first lens and the second lens and the distance between the second lens and the third lens, respectively,
An optical system that is narrower than a distance between the third lens and the fourth lens, a distance between the fourth lens and the fifth lens, and a distance between the fifth lens and the sixth lens.
The method of claim 1,
A combined focal length of the second lens and the third lens is shorter than a total focal length of an optical system including the first to sixth lenses.
The method of claim 1,
An optical system in which an absolute value of a radius of curvature of an object-side surface of the second lens is smaller than an absolute value of a radius of curvature of an image-side surface of the second lens.
The method of claim 17,
When a radius of curvature of the object-side surface of the second lens is r3 and a radius of curvature of the image-side surface of the second lens is r4, |r4/r3| An optical system that satisfies> 20.

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