KR20180042182A - Optical system for camera - Google Patents

Abstract

An optical system for a camera of the present invention comprises: a first lens having a positive refractive power, and having a convex object side surface and a concave upper side surface; a second lens having a negative refractive power; a third lens having the positive refractive power and having both convex sides thereof; a fourth lens having the positive refractive power; and a fifth lens having the negative refractive power and formed with at least one inflection point on an upper side surface thereof. The present invention satisfies following conditional equation 1, f3/f < 2.0, wherein f3 in the conditional equation 1 is a focal length of the third lens, and f is a focal length of the entire of the optical system.

Description

Optical system for camera &lt; RTI ID = 0.0 &gt;

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a camera optical system, and more particularly, to an optical system for a camera which is small in size for mounting on a mobile device and can realize high resolution.

2. Description of the Related Art Recently, mobile communication means such as a mobile communication terminal, a PDA, and a smart phone has increased in usage and various services provided through communication technology have been diversified, so that various types of additional functions have been installed in addition to basic communication functions. Camera mounting for simple shooting is becoming common.

In recent years, the optical system of a camera used in a mobile device such as a mobile phone has exceeded 5 million pixels and has been made to have a high resolution of 8 million pixels or more, and an angle of view of 70 degrees or more than a normal angle of view of about 60 degrees is required.

However, if the angle of view of the lens is increased, the angle of incidence of the light incident on the lens surface becomes large, so that the performance deterioration may be increased even in the same manufacturing tolerance. In addition, as the pixel size of a sensor becomes smaller, a required spatial frequency becomes larger, and an optical system having a high resolution is required.

At this time, if the spatial frequency increases and the resolution increases, the sensitivity to the manufacturing tolerance of the optical system also increases, so it is necessary to develop an optical system capable of reducing the sensitivity with high resolution according to a high-resolution pixel.

On the other hand, conventionally, a high-resolution optical system that supports 8 million pixels as an optical system for a camera is mainly composed of four lenses (pixel size> 1.4 μm), and the first lens and the second lens, out of the four lenses, And the third lens and the fourth lens take charge of field curvature and distortion to correct aberrations that can not be corrected by the first lens and the second lens.

Further, the first lens and the second lens are used as a crown or flint-type glass lens, and in particular, the second lens uses a flint-type glass material having a negative refracting power There is a problem that it is difficult to meet the requirements of miniaturization and low cost by designing an optical system that takes into consideration the manufacturing cost of the optical system for a mobile camera

Especially, since plastic lenses are mainly applied in consideration of mass production, size, weight, and unit price of a camera optical system applied to mobile devices, it is difficult to satisfy optical performance and difficult to compensate for chromatic aberration have.

Japanese Patent Application Laid-Open No. 1997-211320

Accordingly, the present invention was conceived to solve the above-described problems and disadvantages encountered in the conventional optical system for a camera, in which five lenses having different chromatic aberration characteristics are sequentially arranged to realize a high-resolution wide angle, Is provided between the first lens and the second lens so that the peripheral light quantity ratio is improved.

According to an aspect of the present invention, there is provided an optical system for a camera, comprising: a first lens having positive refractive power, the object side being convex and the top side being concave; A second lens having a negative refractive power; A third lens having a positive refractive power and having a convex shape on both sides; A fourth lens having positive refractive power; And a fifth lens having a negative refracting power and having at least one inflection point formed on an upper side thereof, and the following conditional expression can be satisfied.

[Conditional expression] f3 / f < 2.0

In the conditional expression, f3 is the focal length of the third lens, and f is the focal length of the entire optical system.

The optical system for a camera according to an embodiment of the present invention can satisfy the following conditional expression.

[Conditional expression] R31 / f < 1.2

In the above conditional expression, R31 is the radius of curvature of the object side surface of the third lens, and f is the focal length of the entire optical system.

As described above, the optical system for a camera according to the present invention is advantageous in that the optical angle of view can be realized while reducing the manufacturing cost by constituting the five lenses of the aspheric plastic lens.

Further, in the optical system for a camera of the present invention, as the third lens performs correction of chromatic aberration with respect to the first lens in a state in which five lenses are arranged, the first lens having a concave shape upward is employed, So that the degree of freedom of design can be improved.

The optical system for a camera of the present invention can reduce the sensitivity to the manufacturing tolerance of the first lens by arranging the diaphragm between the first lens and the second lens, and can exert the action and effect that the peripheral light amount ratio can be improved .

1 is a block diagram showing a lens arrangement of an optical system for a camera according to a first embodiment of the present invention;
2A and 2B are the astigmatic aberration and distortion aberration of the optical system shown in Table 1 and Fig. 1, respectively.
3 is a lens configuration diagram showing a lens arrangement of an optical system for a camera according to a second embodiment of the present invention;
4A and 4B are the astigmatic aberration and distortion aberration diagrams of the optical system shown in Table 3 and Fig. 3, respectively.
5 is a lens configuration diagram showing a lens arrangement of an optical system for a camera according to a third embodiment of the present invention;
6A and 6B are astigmatism and distortion aberration diagrams of the optical system shown in Table 5 and FIG. 5, respectively.
7 is a lens configuration diagram showing a lens arrangement of an optical system for a camera according to a fourth embodiment of the present invention;
FIGS. 8A and 8B are astigmatism and distortion aberration diagrams of the optical system shown in Table 7 and FIG. 7, respectively.
9 is a lens configuration diagram showing a lens arrangement of an optical system for a camera according to a fifth embodiment of the present invention;
10A and 10B are astigmatism and distortion aberration diagrams of the optical system shown in Table 9 and FIG. 9, respectively.

The technical effects of the optical system for a camera according to the present invention, including the technical structure thereof, will be clearly understood from the following detailed description of preferred embodiments of the present invention with reference to the drawings.

It should be noted that the thickness, size, and shape of the lens in each of the following embodiments are exaggerated for the detailed description of the present invention. In particular, the shape of the spherical or aspherical surface shown in the lens configuration diagram is merely an example But is not limited to the shape.

1 is a lens configuration diagram showing a first embodiment of an optical system for a camera according to the present invention. As shown in the figure, the optical system for a camera according to the present invention has a meniscus shape concave upward from the object side A first lens L1 having a positive refractive power, a second lens L2 having a negative refractive power in an upward concave shape, a third lens L3 having a positive refractive power in a convex shape on the object side, A fourth lens L4 having a positive refractive power in a convex shape and a fifth lens L5 having a negative refractive power in a convex shape on the object side and concave upward.

At this time, an aperture diaphragm AS may be provided between the first lens L1 and the second lens L2.

An optical filter OF composed of a cover glass coated with an infrared filter or an infrared filter for shielding excessive infrared rays from light passing through the optical system is interposed between the fifth lens L5 and the image plane 11 .

The optical system for a camera according to the present invention is characterized in that the diaphragm AS is positioned behind the first lens L1, that is, between the first lens L1 and the second lens L2 to adjust the tolerance of the first lens L1 . That is, if the diaphragm AS is located in front of the first lens L1, the image height due to the light incident on the optical system becomes large, so that the first lens L1 can be sensitive to decentering . However, as in the present invention, when the diaphragm AS is positioned between the first lens L1 and the second lens L2, the angle of incidence of the rays incident on the first lens L1 can be reduced, L1) can be reduced, and the degree of freedom of design of the optical system can be increased.

When the diaphragm AS is positioned between the first lens L1 and the second lens L1, the magnitude of the incident motion imaged by the first lens L1 becomes larger toward the edge of the image plane Therefore, the effect of improving the peripheral light quantity ratio can be exhibited.

In the present invention, as the diaphragm AS is positioned between the first lens L1 and the second lens L2, the angle of incidence of the lower light ray increases and the angle of incidence at the upper surface side of the first lens L1 can be greatly increased It is possible to reduce the angle of incidence of the light beam on the first lens L1 by designing the first lens L1 to have a concave shape upward.

However, when a lens in which the first lens L1 is concave upward is used, the chromatic aberration correction function can be weakened. This is because the refractive power on the image side of the first lens L1 can be changed to a negative refractive power and therefore can be removed using the difference in dispersion characteristics due to the Abbe number of the first lens L1 and the second lens L2 The chromatic aberration correction function may be weakened.

Therefore, in the present invention, the third lens L3 is convexly formed on the object side, and the focal length f3 of the third lens L3 and the radius of curvature R31 of the object side surface of the third lens L3 So that the longitudinal chromatic aberration can be corrected through the relationship. This is explained in more detail in the following conditional expression.

At this time, the third lens L3 may be a lens having a convex shape on both sides.

Further, in the optical system of the present invention, the fourth lens L4 may be formed into a meniscus shape convex upward.

In the optical system of the present invention, the fifth lens L5 may be composed of a concave lens on the object side.

In the optical system of the present invention, all of the first lens L1 to the fifth lens L5 may be made of a plastic lens, and one of both surfaces of the first lens L1 to the fifth lens L5 , Or both surfaces may be composed of aspherical surfaces.

The reason for configuring at least one of the lenses constituting the optical system according to the present invention as an aspheric surface is to make the number of lenses capable of realizing a wide angle of view to be minimized so as to be compact, . The reason why the first lens L1 to the fifth lens L5 are all formed of plastic lenses is that the manufacturing cost can be reduced by constructing the optical system with a plastic lens which is easier to manufacture aspheric lenses than glass lenses, This is to improve chromatic aberration correction and design freedom to mitigate manufacturing tolerances.

On the other hand, as mentioned above, the optical system of the present invention corrects the chromatic aberration by the following conditional expression 1 and conditional expression 2, and the operation and effect thereof will be described below.

[Conditional expression 1] f3 / f < 2.0

Here, f3 is the focal length of the third lens, and f is the focal length of the entire optical system.

Conditional expression 1 is a condition relating to chromatic aberration correction of the optical system. When the upper limit of the conditional expression (1) is exceeded, the color adjustment of the photographed image may occur as the focus adjustment position of each wavelength is different in the entire optical system.

[Conditional expression 2] R31 / f < 1.2

Here, R31 is the radius of curvature of the object side surface of the third lens, and f is the focal length of the entire optical system.

Conditional Expression 2 Similarly to Conditional Expression 1, when the upper surface of the first lens L1 is concave, the radius of curvature of the third lens L3 is increased to correct the chromatic aberration. At this time, if the upper limit of the conditional expression (2) is exceeded, the back focal length (BFL) for each wavelength of the optical system can be abruptly changed in a short wavelength region. Therefore, the optical characteristics required in the present invention, It is hard to satisfy.

The aspherical surface used in each of the following embodiments is obtained from the well-known formula (1), and is represented by 'E' used in the conic constant K and aspherical surface coefficients A, B, C, D, And the following number 'denotes the power of 10. For example, E + 02 represents 10 ² and E-02 represents 10 ^-2 .

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

Y: Distance in the direction perpendicular to the optical axis

c is the reciprocal of the radius of curvature (r) at the apex of the lens

K: Conic constant

A, B, C, D, E, F: aspheric coefficient

[First Embodiment]

Table 1 below shows numerical examples according to the first embodiment of the present invention.

1 and 2 show the astigmatism and distortion aberration of the optical system shown in Table 1 and FIG. 1, respectively, and FIGS. 2A and 2B show the lens arrangement of the optical system for a camera according to the first embodiment of the present invention .

In the case of the first embodiment, the effective focal length f of the entire optical system is 4.05 mm. The first lens L1 to the fifth lens L5 are all made of an aspherical plastic lens.

In addition, focal lengths of the respective lenses employed in the first embodiment are 3.66 mm, f2 is -3.80 mm, f3 is 5.09 mm, f4 is 2.27 mm, and f5 is -2.10 mm.

An asterisk * in front of the surface number in Table 1 indicates an aspherical surface. In the case of the first embodiment, both surfaces of the first lens L1 to the fifth lens L5 are aspherical surfaces.

The values of the aspherical surface coefficients in the first embodiment according to Equation (1) are shown in Table 2 below.

[Second Embodiment]

Table 3 below shows numerical examples according to the second embodiment of the present invention.

3 is a lens configuration diagram showing a lens arrangement of an optical system for a camera according to a second embodiment of the present invention, and Figs. 4A and 4B show astigmatism and distortion aberration of the optical system shown in Table 3 and Fig. 3, respectively .

In the case of the second embodiment, the effective focal length f of the entire optical system is 3.94 mm. In addition, the first lens L1 to the fifth lens L5 are composed of an aspherical plastic lens.

In addition, focal lengths of each lens employed in the second embodiment are 3.68 mm, f2 is -4.63 mm, f3 is 5.55 mm, f4 is 3.80 mm, and f5 is -2.51 mm.

In Table 3, an asterisk * in front of the surface number indicates an aspherical surface, and in the case of the second embodiment, both surfaces of the first lens L1 to the fifth lens L5 are aspherical surfaces.

The values of the aspherical surface coefficients in the second embodiment according to Equation (1) are shown in Table 4 below.

[Third Embodiment]

Table 5 below shows numerical examples according to the third embodiment of the present invention.

Fig. 5 is a lens configuration diagram showing a lens arrangement of an optical system for a camera according to a third embodiment of the present invention, and Figs. 6A and 6B show astigmatism and distortion aberration of the optical system shown in Table 5 and Fig. 5, respectively .

In the case of the third embodiment, the effective focal length f of the entire optical system is 4.10 mm. In addition, the first lens L1 to the fifth lens L5 are composed of an aspherical plastic lens.

In addition, focal lengths of the respective lenses employed in the third embodiment are 3.694 mm, f2 is -4.620 mm, f3 is 6.119 mm, f4 is 2.402 mm, and f5 is -2.093 mm.

In Table 5, an asterisk * in front of the surface number indicates an aspherical surface. In the case of the third embodiment, both surfaces of the first lens L1 to the fifth lens L5 are aspherical surfaces.

The values of the aspherical surface coefficients in the third embodiment according to Equation (1) are shown in Table 6 below.

[Fourth Embodiment]

Table 7 below shows numerical examples according to the fourth embodiment of the present invention.

7 is a lens configuration diagram showing a lens arrangement of an optical system for a camera according to a fourth embodiment of the present invention, and Figs. 8A and 8B show astigmatism and distortion aberration of the optical system shown in Table 7 and Fig. 7, respectively .

In the case of the fourth embodiment, the effective focal length f of the entire optical system is 4.10 mm. In addition, the first lens L1 to the fifth lens L5 are composed of an aspherical plastic lens.

In addition, focal lengths of each lens employed in the fourth embodiment are 3.959 mm, f2 is -4.925 mm, f3 is 5.542 mm, f4 is 2.763 mm, and f5 is -2.302 mm.

In Table 7, an asterisk * in front of the surface number indicates an aspherical surface, and in the case of the fourth embodiment, both surfaces of the first lens L1 to the fifth lens L5 are aspherical surfaces.

The values of the aspherical surface coefficients in the fourth embodiment according to Equation (1) are shown in Table 8 below.

[Fifth Embodiment]

Table 9 below shows numerical examples according to the fifth embodiment of the present invention.

9 is a lens configuration diagram showing a lens arrangement of an optical system for a camera according to a fifth embodiment of the present invention, and Figs. 9A and 9B show astigmatism and distortion aberration of the optical system shown in Table 9 and Fig. 9, respectively .

In the case of the fifth embodiment, the effective focal length f of the entire optical system is 4.16 mm. In addition, the first lens L1 to the fifth lens L5 are composed of an aspherical plastic lens.

In addition, as the focal lengths of the respective lenses employed in the fifth embodiment, f1 is 3.749 mm, f2 is -4.198 mm, f3 is 4.042 mm, f4 is 4.365 mm, and f5 is -2.505 mm.

In Table 9, an asterisk * in front of a surface number indicates an aspherical surface. In the case of the fourth embodiment, both surfaces of the first lens L1 to the fifth lens L5 are aspherical surfaces.

The values of the aspherical surface coefficients in the fifth embodiment according to Equation (1) are shown in Table 10 below.

On the other hand, the values of Conditional Expression 1 and Conditional Expression 2 for the first to fifth embodiments are shown in Table 5 below.

As shown in Table 11, it can be seen that the first to fifth embodiments of the present invention satisfy the conditional expressions 1 and 2.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, and that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention. However, it should be understood that such substitutions, changes, and the like fall within the scope of the following claims.

L1. The first lens L2. The second lens
L3. Third lens L4. The fourth lens
L5. The fifth lens
AS. Aperture Aperture OF. Optical filter
1, 2, 3, 4 ... 9, 10, 11. Face number

Claims (12)

A first lens having positive refractive power and having a concave shape on an upper side;
A second lens having a refracting power and having an upper surface in a concave shape;
A third lens having a refractive power;
A fourth lens having a refracting power and having a concave shape on an object side; And
A fifth lens having a refractive power, the object side surface being convex and the at least one inflection point being formed on the image side;
Lt; / RTI &gt;
An optical system for a camera satisfying the following conditional expressions.
[Conditional expression 1] f3 / f < 2.0
[Conditional expression 2] R31 / f &lt; 1.2
(Where f3 is the focal length of the third lens, f is the focal length of the entire optical system, R31 is the radius of curvature of the object side surface of the third lens, and f is the focal length of the entire optical system) The method according to claim 1,
Wherein the first lens has a convex shape on an object side. The method according to claim 1,
And the second lens has a convex shape on an object side surface. The method according to claim 1,
And the third lens has a convex shape on an object side surface. The method according to claim 1,
And the third lens has an upward convex shape. The method according to claim 1,
And the fourth lens has an upward convex shape. The method according to claim 1,
Wherein the fifth lens has a concave shape on an upper side. The method according to claim 1,
And an aperture disposed between the first lens and the second lens. The method according to claim 1,
And the second lens has a negative refracting power. The method according to claim 1,
And the third lens has positive refractive power. The method according to claim 1,
And the fourth lens has positive refractive power. The method according to claim 1,
And the fifth lens has a negative refracting power.

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