KR20190095226A - Optical system - Google Patents

Abstract

An imaging optical system according to one embodiment of the present invention comprises: a first lens having a negative refractive power; a second lens having a refractive power; a third lens having the refractive power; a fourth lens having the refractive power; and a fifth lens having a positive refractive power and having a concave upper side surface in a paraxial region, wherein the first to fifth lenses are arranged in order from an object side. A wide viewing angle and a high resolution can be realized while enhancing an effect of aberration improvement. In addition, a brightness of the image by the imaging optical system can be more brightly realized.

Description

Imaging Optical System

The present invention relates to an imaging optical system.

Recently, portable terminals are equipped with a camera to enable video call and picture taking. In addition, as the functions occupied by the camera in the portable terminal gradually increase, the demand for higher resolution and higher performance of the portable terminal camera is increasing.

However, since portable terminals are gradually miniaturized or lightweight, there are limitations in implementing a high resolution and high performance camera.

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

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

In addition, it is to provide an imaging optical system that can improve the aberration improvement effect and can realize high resolution.

In addition, it is to provide an imaging optical system that can reduce the difference between the brightness of the image in the center portion of the image sensor and the brightness of the image in the peripheral portion.

An imaging optical system according to an embodiment of the present invention includes a first lens having negative refractive power in order from an object side; A second lens having refractive power; A third lens having refractive power; A fourth lens having refractive power; And a fifth lens having a positive refractive power and a concave image surface in the paraxial region, to improve aberration improvement effect, and to realize a wide angle of view and a high resolution. In addition, the brightness of the image by the imaging optical system may be more brightly realized.

According to the imaging optical system according to the exemplary embodiment of the present invention, a slim imaging optical system may be provided while implementing a wide angle of view.

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

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

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

Hereinafter, with reference to the drawings will be described in detail a specific embodiment of the present invention. However, the spirit of the present invention is not limited to the embodiments presented, and those skilled in the art who understand the spirit of the present invention may degenerate other inventions or the present invention by adding, changing, or deleting other elements within the scope of the same idea. Other embodiments that fall within the scope of the present invention may be easily proposed, but this will also be included within the scope of the present invention.

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

In the lens configuration diagram below, the thickness, size, and shape of the lens are somewhat exaggerated for explanation, and in particular, the shape of the spherical or aspherical surface shown in the lens configuration is merely an example, and 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.

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

Also, the paraxial region refers to a very narrow region near the optical axis. For example, it may mean an area where a distance from which an 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 surface of the image sensor, SL is the distance from the aperture limiting the amount of light incident to the imaging optical system to the image surface of the image sensor, ImgH is the image Half of the diagonal length of the upper surface of the sensor, BFL is the distance from the upper surface of the lens closest to the image to the upper surface of the image sensor, and EFL is the total focal length of the imaging optical system.

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

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

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

In addition, at least one lens 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 aspheric. Here, the aspherical surfaces of the first to sixth lenses are represented by Equation 1.

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

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

The imaging optical system configured as described above can improve optical performance through aberration improvement. The effect by each lens structure is mentioned later.

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

[Condition 1]

TTL / (ImgH * 2) ≤ 0.75

In Conditional Expression 1, TTL is the distance from the object-side surface of the first lens to the image surface of the image sensor, and ImgH means half the diagonal length of the image surface of the image sensor.

The imaging optical system according to an embodiment of the present invention satisfies Condition 2.

[Condition Formula 2]

TTL / (ImgH * 2) ≤ 0.68

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

[Condition 3]

-5 <f1 / EFL <-4.6

In Condition 3, f1 is a focal length of the first lens, and EFL is an overall focal length of the imaging optical system.

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

[Condition 4]

2.3 <f1 / f3 <2.6

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

The imaging optical system according to an embodiment of the present invention satisfies Condition 5.

[Condition 5]

BFL / EFL <0.31

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

The imaging optical system according to an embodiment of the present invention satisfies Condition 6.

[Condition 6]

0.95 <ER1 / ER6 <1.05

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

The imaging optical system according to the exemplary embodiment of the present invention satisfies Condition 7.

[Condition 7]

79 <FOV <83

In Conditional Expression 7, FOV is an angle of view of the imaging optical system. Here, the unit of view angle of the imaging optical system is Degree.

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

The first lens has negative refractive power. In addition, the first lens may have a meniscus shape in which it is convex toward the object. In detail, 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 aspherical. For example, both surfaces of the first lens may be aspherical.

The second lens has a positive refractive power. In addition, both surfaces of the second lens may be convex. In detail, the first and second surfaces of the second lens may be convex in the paraxial region.

At least one of the first and second surfaces of the second lens may be aspherical. 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 in which it is convex toward the object. In detail, 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 aspherical. 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 in which it is convex toward the image. In detail, the first surface of the fourth lens may be concave in the paraxial region, and the second surface of the fourth lens may be convex in the paraxial region.

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

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

At least one of the first and second surfaces of the fifth lens may be aspherical. 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 in which it is convex toward the object. In detail, 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.

The imaging optical system according to an embodiment of the present invention may implement a wide angle of view by allowing the first lens to have negative refractive power, and design the imaging optical system 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 and the top surface of the image sensor, is shortened, so that the infrared filter can be disposed therebetween. It becomes difficult to secure space.

Accordingly, in the imaging optical system according to the exemplary embodiment of the present invention, the infrared filter may be disposed between the sixth lens and the image sensor by designing the imaging optical system in a retro focus type to realize a wide angle of view while relatively increasing the back focus. Make sure you have enough space.

In this case, the composite focal length of the second lens and the third lens is made shorter than the total focal length of the imaging optical system in order to prevent the length of the entire imaging optical system from being increased by relatively lengthening the back focus.

On the other hand, the imaging 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 the wavelength. The longer wavelength of light causes the focus to be farther from the lens than other light after passing through the lens. Therefore, if the chromatic aberration is large, the light is spread according to the wavelength, it is necessary to correct this.

In the imaging optical system according to the exemplary embodiment, refractive powers of the first to third lenses are configured differently.

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

Thus, the first to third lenses have refractive power opposite to that of the adjacent lens in the object-side direction.

Since adjacent lenses have opposite refractive powers, one lens emits light and the other lens converges light. Thus, light having different wavelengths can be collected at the same focal point.

In the imaging optical system according to the exemplary embodiment, the distance between the first lens and the third lens is relatively narrowed to maximize the effect of the chromatic aberration correction as described above.

For example, an interval between the first lens and the second lens and an interval between the second lens and the third lens in the paraxial region may be smaller than that between other lenses. Accordingly, the first to third lenses may have an effect similar to that of the triple junction lens bonded to each other, thereby maximizing the effect of chromatic aberration correction.

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

As described above, the second lens of the imaging optical system according to the embodiment of the present invention has a positive refractive power, and both surfaces thereof may be convex.

Here, the absolute value of the radius of curvature of the object-side surface of the second lens is smaller than the absolute value of the radius of curvature of the 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

Accordingly, the second lens has a larger curvature on the object side than the image side and a smaller curvature on the image side than the object side. This configuration makes it possible to easily correct spherical aberration.

On the other hand, in the imaging optical system according to an embodiment of the present invention, the third lens has a meniscus shape convex toward the object side, and the fourth lens and the fifth lens have a meniscus shape convex toward the image side.

As such, the light incident on the imaging optical system may be configured such that the third lens and the fourth lens have a symmetrical shape or the third lens and the fifth lens have a symmetrical shape. It may be incident to the upper surface of the image sensor perpendicularly.

Therefore, the imaging optical system according to the exemplary embodiment may reduce the difference between the brightness of the image at the center of the image sensor and the brightness of the image at the periphery.

Accordingly, lens shading, a phenomenon in which an image at the periphery of the image sensor is relatively dark, may be alleviated.

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

The imaging 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 the 160 may be further included, and may further include an aperture, an infrared filter 170, and an image sensor 180.

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

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

The second lens 120 has a positive refractive power and has a meniscus shape of 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 in which it is convex toward the object. For example, a first surface of the third lens 130 is convex in the paraxial region, and a 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 in which it is convex toward the image. For example, a first surface of the fourth lens 140 is concave in the paraxial region, and a second surface of the fourth lens 140 is convex in the paraxial region.

The fifth lens 150 has a positive refractive power and has a meniscus shape in which it is convex toward the image. For example, a first surface of the fifth lens 150 is concave in the paraxial region, and a 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 in which it is convex toward the object side. For example, a first surface of the sixth lens 160 is convex in the paraxial region, and a 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 lens 110 to the sixth lens 160 has an aspherical surface coefficient as shown in FIG. 5.

The diaphragm may include a first diaphragm for limiting the amount of light incident to the imaging optical system and a second diaphragm for blocking light of a portion where excessive aberration occurs.

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

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

6 to 10, an imaging optical system according to a second exemplary embodiment of the present invention will be described.

The imaging optical system according to the second exemplary 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. It includes an optical system having a 260, and may further include an aperture, an infrared filter 270 and an image sensor 280.

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

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

The second lens 220 has a positive refractive power and has a meniscus shape of 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 in which it is convex toward the object. For example, a first surface of the third lens 230 is convex in the paraxial region, and a 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 in which it is convex toward the image. For example, a first surface of the fourth lens 240 is concave in the paraxial region, and a second surface of the fourth lens 140 is convex in the paraxial region.

The fifth lens 150 has a positive refractive power and has a meniscus shape in which it is convex toward the image. For example, a first surface of the fifth lens 150 is concave in the paraxial region, and a 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 in which it is convex toward the object side. For example, a first surface of the sixth lens 260 is convex in the paraxial region, and a second surface of the sixth lens 260 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 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 the amount of light incident to the imaging optical system and a second diaphragm for blocking light of a portion where excessive aberration occurs.

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

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

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

The imaging optical system according to the third exemplary 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. It includes an optical system having a 360, and may further include an aperture, an infrared filter 370 and an image sensor 380.

Herein, the lens characteristics (radius of curvature, thickness of the lens or distance between lenses, refractive index, and Abbe's number) of each lens are as shown in FIG. 14.

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

The second lens 320 has a positive refractive power and has a meniscus shape of 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 in which it is convex toward the object. For example, a first surface of the third lens 330 is convex in the paraxial region, and a 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 in which it is convex toward the image. For example, a first surface of the fourth lens 340 is concave in the paraxial region, and a second surface of the fourth lens 340 is convex in the paraxial region.

The fifth lens 350 has a positive refractive power and has a meniscus shape in which it is convex toward the image. For example, a first surface of the fifth lens 350 is concave in the paraxial region, and a 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 in which it is convex toward the object side. For example, a first surface of the sixth lens 360 is convex in the paraxial region, and a 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 the aspherical surface coefficient as shown in FIG. 15.

The diaphragm may include a first diaphragm for limiting the amount of light incident to the imaging optical system and a second diaphragm for blocking light of a portion where excessive aberration occurs.

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

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

Meanwhile, referring to Table 1, it can be seen that the imaging optical system according to the first to third embodiments of the present invention satisfies the conditional expressions 1 to 7 described above, thereby improving the optical performance of the lens. In addition, it is possible to realize a slim imaging optical system with a wide field of view.

In the above description of the configuration and features of the present invention based on the embodiment according to the present invention, the present invention is not limited thereto, and 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 that such changes or modifications fall within the scope of the appended claims.

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

Claims (15)

In order from the object side,
A first lens having negative refractive power;
A second lens having refractive power;
A third lens having refractive power;
A fourth lens having refractive power;
A fifth lens having refractive power;
A sixth lens having refractive power; And
And an image sensor for converting an image of a subject incident through the first to sixth lenses into an electrical signal.
When the distance from the object-side surface of the first lens to the image surface of the image sensor is TTL, and half of the diagonal length of the image surface of the image sensor is ImgH, TTL / (ImgH * 2) ≤ 0.75 is satisfied.
And -5 < f1 / EFL < -4.6 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.
The method of claim 1,
And the second lens has positive refractive power, and the third lens has negative refractive power.
The method of claim 2,
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 are respectively,
An imaging optical system narrower than an interval between the third lens and the fourth lens, an interval between the fourth lens and the fifth lens, and an interval between the fifth lens and the sixth lens.
The method of claim 3,
The sum of the distance between the first lens and the second lens and the distance between the second lens and the third lens in the paraxial region,
And an interval between the third lens and the fourth lens, an interval between the fourth lens and the fifth lens, and an interval between the fifth lens and the sixth lens.
The method of claim 1,
An imaging optical system that satisfies TTL / (ImgH * 2) ≤ 0.68.
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 satisfying 2.3 <f1 / f3 <2.6.
The method of claim 1,
When the distance from the image side surface of the sixth lens to the image surface of the image sensor is BFL, and the total focal length of the optical system including the first to sixth lenses is EFL,
An imaging optical system that satisfies BFL / EFL <0.31.
The method of claim 1,
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 satisfying 0.95 <ER1 / ER6 <1.05.
The method of claim 1,
When the angle of view of the imaging optical system is FOV,
Imaging optics that satisfy 79 ° <FOV <83 °.
The method of claim 1,
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 | Imaging optics satisfying> 20.
The method of claim 1,
The fifth lens has a positive refractive power.
The method of claim 11,
The sixth lens has a negative refractive power.
The method of claim 12,
And the fourth lens has negative refractive power.
The method of claim 1,
The object-side surface of the first lens is convex and the image-side surface is concave,
The object-side surface and the image-side surface of the second lens are convex,
And an object-side surface of the third lens is convex and an image-side surface is concave.
The method of claim 1,
The first to sixth lenses are made of plastic,
At least one of the object-side surface and the image-side surface of the first to sixth lens is an aspherical surface.

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