KR101431980B1 - Optical System - Google Patents

Abstract

The present invention relates to an imaging optical system.
An imaging optical system of the present invention comprises: a first lens having positive refracting power in order from an object side, the object side surface being convex to the object side; A second lens having a negative refractive power; A third lens having negative refractive power; A fourth lens having positive refractive power; A fifth lens having negative refracting power and having an upward convex shape on the image side; And a sixth lens having a negative refracting power and having an upper side concave on the upper side.

Description

[0001]

TECHNICAL FIELD The present invention relates to an imaging optical system, and more particularly, to an imaging optical system constructed using six lenses.

2. Description of the Related Art Generally, mobile communication means such as a mobile communication terminal, a PDA, and a smart phone have increased usage and various services provided through communication technology have become diverse, so various types of additional functions are mounted in addition to basic communication functions.

In particular, the camera module mounted on the mobile communication means is increasingly demanding a variety of conference devices such as high-quality moving image shooting, automatic focus adjustment, and QR code recognition in addition to simple photography using a single focus.

In addition, the size of the camera module is gradually reduced, and a higher resolution is required, and the manufacturing cost of the camera module is gradually lowered due to the reduction of the price of the mobile communication device.

In order to lower the unit cost of the camera module, it is most preferable to lower the production cost of the lens group constituting the optical system built in the camera module. However, in order to satisfy the above-mentioned resolution improvement conditions, it is necessary to construct an optical system by applying a glass lens having excellent optical performance, but it is impossible to reduce the manufacturing cost of a camera module by using a plurality of expensive glass lenses .

In addition, when a large number of glass lenses are employed to solve the resolution problem, the optical system can not be lightened.

Korean Patent Publication No. 2011-24872

Accordingly, the present invention was conceived to solve the above-described problems and disadvantages in the conventional mobile camera optical system. By constructing an optical system using six aspheric plastic lenses, it is possible to provide a high- An optical system is provided.

The object of the present invention is attained by a zoom lens system comprising: a first lens having positive refractive power in order from an object side, the object side surface being convex toward the object side; A second lens having a negative refractive power; A third lens having negative refractive power; A fourth lens having positive refractive power; A fifth lens having negative refracting power and having an upward convex shape on the image side; And a sixth lens having a negative refracting power and having an upper side concave on the upper side.

Further, the optical system satisfies the following conditional expression for the chromatic aberration correction condition.

[Conditional expression] | V3 - V2 | <1.2

Here, V3 is the Abbe number of the third lens, and V2 is the Abbe number of the second lens.

Further, the optical system satisfies the following conditional expression for the optical system design conditions.

[Conditional expression] TTL / F <1.5

Here, TTL is the distance from the first lens to the image surface, and F is the focal length of the entire optical system.

Further, the above optical system satisfies the following conditional expression with respect to the condition of miniaturization by the focal length ratio of the optical system.

[Conditional expression 3] 1 <| F6 / F | <6

Here, F6 is the focal length of the sixth lens, and F is the focal length of the entire optical system.

In addition, the optical system satisfies the following conditional expression for the condition of miniaturization according to the radius of curvature of each lens of the optical system.

[Conditional expression 4] 0 < (R7 + R10) / (R7 - R10) < 1.3

Here, R7 is the radius of curvature of the object side surface of the fourth lens, and R10 is the radius of curvature of the image side of the fifth lens.

Further, the optical system satisfies the following conditional expression with respect to the condition relating to the aberration correction of the optical system.

[Conditional expression 5] | R7 / F | <5

Here, R7 is the radius of curvature of the object side surface of the fourth lens, and F is the focal length of the entire optical system.

Further, the optical system satisfies the following conditional expression for the condition relating to the chromatic aberration correction of the optical system.

[Conditional expression 6] | Nd2 - Nd5 | <0.11

Here, Nd2 is the refractive index of the second lens at the wavelength of the d line (587.6 nm), and Nd5 is the refractive index of the fifth lens at the wavelength of the d line (587.6 nm).

In addition, the optical system satisfies the following conditional expression with respect to the conditions for correcting the spherical aberration of the optical system.

[Conditional expression 7] F3 / F < -5

Here, F3 is the focal length of the third lens, and F is the focal length of the entire optical system.

The first to sixth lenses may be plastic lenses, and both surfaces of the first to sixth lenses may be aspherical.

In addition, an optical filter of a cover glass coated with an infrared cut filter for blocking excessive infrared rays contained in the light introduced from the outside may be further included between the sixth lens and the image plane.

INDUSTRIAL APPLICABILITY As described above, the imaging optical system according to the present invention is capable of reducing the manufacturing cost by forming six lenses of an aspherical plastic lens, improving the aberration correction efficiency, minimizing the chromatic aberration, There are advantages.

Further, in the present invention, the refractive power of the first lens and the fourth lens among the six lenses constituting the optical system is configured to have a positive refractive power, thereby making it possible to manufacture a high-resolution optical system by reducing the aberration value.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a configuration diagram showing a lens arrangement of an imaging optical system according to a first embodiment of the present invention; Fig.
2 is an MTF graph of the optical system shown in Fig.
3 is an aberration diagram of the optical system shown in Table 1 and Fig. 1, respectively.
4 is a configuration diagram showing a lens arrangement of an optical system for a camera according to a second embodiment of the present invention;
5 is an MTF graph of the optical system shown in Fig.
6 is an aberration diagram of the optical system shown in Table 3 and Fig. 4, respectively.
7 is a configuration diagram showing a lens arrangement of an optical system for a camera according to a third embodiment of the present invention;
8 is an MTF graph of the optical system shown in Fig.
9 is an aberration diagram of the optical system shown in Table 5 and Fig. 7, respectively.
10 is a configuration diagram showing a lens arrangement of an optical system for a camera according to a fourth embodiment of the present invention;
11 is an MTF graph of the optical system shown in Fig.
12 is an aberration diagram of the optical system shown in Table 7 and Fig. 10, respectively.

The matters relating to the operational effects including the technical structure of the above-mentioned object of the imaging optical system according to the present invention will be clearly understood by the following detailed description of the 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 an embodiment of an imaging optical system according to the present invention. As shown in the figure, the imaging optical system of the present embodiment has a first lens L1 having a positive refractive power and a second lens L1 having a negative refractive power. The second lens L2, the third lens L3 having a negative refractive power, the fourth lens L4 having a positive refractive power, the fifth lens L5 having a negative refractive power, and the negative refractive power And the sixth lens L6 may include the sixth lens L6.

In this case, the first lens L1 has a shape in which the object side is convex toward the object side, and the fifth lens L5 and the sixth lens L6 are convex on the upper side and concave, respectively.

Between the sixth lens L6 and the image plane 15, 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 .

In the optical system of the present invention, all of the first lens L1 to the sixth lens L6 may be made of plastic lenses, and any one of both surfaces of the first lens L1 to the sixth lens L6, Or both surfaces may be configured as an aspherical surface.

The reason why at least one of the lenses constituting the optical system according to the present invention is composed of an aspheric surface is to improve a degree of freedom of design that facilitates aberration correction including chromatic aberration and mitigates manufacturing tolerances, The reason why the lenses L1 to L6 are all made of a plastic lens is that the aspherical surface can be manufactured more easily than the glass lens and the weight of the aspheric surface can be reduced Thereby constituting an imaging optical system employable in a mobile device.

On the other hand, as mentioned above, the imaging optical system of the present invention enables the downsizing while using aberration correction and a plurality of lenses according to the following conditional expression 1 and conditional expression 2, and the condition formula and the operation effect will be described as follows.

[Conditional expression 1] | V3 - V2 | <41

Here, V3 is the Abbe number of the third lens, and V2 is the Abbe number of the second lens.

The conditional expression 1 is a condition for correcting the chromatic aberration of the optical system. The difference in the Abbe number between the third lens and the second lens is maintained at a predetermined value or less so that the chromatic aberration correction can be facilitated. At this time, the chromatic aberration can be minimized when the conditional expression 1 is satisfied, and the chromatic aberration can be generated when the upper limit is exceeded.

[Conditional expression 2] TTL / F < 1.5

Here, TTL is the distance from the first lens to the image surface, and F is the focal length of the entire optical system.

The conditional expression (2) is a condition for miniaturization due to the focal length ratio of the optical system, and is a conditional expression relating to the ratio of the distance from the first lens to the image surface to the focal length of the entire optical system. At this time, when the upper limit of the conditional expression (2) is exceeded, it is difficult to manufacture a compact optical system satisfying the characteristics of a predetermined angle of view or more required by a mobile camera.

[Conditional expression 3] 1 <| F6 / F | <6

Here, F6 is the focal length of the sixth lens, and F is the focal length of the entire optical system.

The conditional expression (3) is a condition for miniaturization due to the focal length ratio of the optical system, and is a conditional expression for the ratio of the focal length of the sixth lens to the focal length of the entire optical system. At this time, when the upper limit of the conditional expression (3) is exceeded, the refractive power of the entire optical system is lowered and it is difficult to satisfy the condition of miniaturization. When the lower limit is exceeded, the correction of the distortion aberration becomes difficult as the telecentric characteristic deviates.

[Conditional expression 4] 0 < ( R7  + R10 ) / ( R7  - R @ 10) <1.3

Here, R7 is the radius of curvature of the object side surface of the fourth lens, and R10 is the radius of curvature of the image side of the fifth lens.

The conditional expression (4) is a condition for miniaturization according to the radius of curvature of each lens of the optical system, and is a conditional expression for the ratio of the sum of the curvatures radii of the fourth and fifth lenses to the difference. At this time, if the upper limit of the conditional expression (4) is exceeded, the effective diameter of the lens becomes large, which makes it difficult to downsize the lens and increases the sensitivity of the lens.

[Conditional expression 5] | R7 / F | <5

Here, R7 is the radius of curvature of the object side surface of the fourth lens, and F is the focal length of the entire optical system.

Conditional expression 5 is a condition for aberration correction of the optical system, and is a conditional expression for the ratio of the radius of curvature of the object side surface of the fourth lens to the focal length of the entire optical system. At this time, if the upper limit of the conditional expression (5) is exceeded, it is difficult to correct the aberration of the optical system, and it may be difficult to realize a high resolution.

[Conditional expression 6] | Nd2  - Nd5 | <0.11

Here, Nd2 is the refractive index of the second lens at the wavelength of the d line (587.6 nm), and Nd5 is the refractive index of the fifth lens at the wavelength of the d line (587.6 nm).

The conditional expression (6) is a condition for correcting the chromatic aberration of the optical system, and is a conditional expression for the refractive index difference in the d line (587.6 nm) which is the specific wavelength band of the second lens and the fifth lens. At this time, when the condition of conditional expression (6) is satisfied, high resolution of the optical system can be realized and chromatic aberration can be minimized.

[Conditional expression 7] F3 / F < -5

Here, F3 is the focal length of the third lens, and F is the focal length of the entire optical system.

The conditional expression (7) is a condition concerning the correction of the spherical aberration of the optical system, and is a conditional expression relating to the ratio of the focal length of the third lens to the entire optical system. At this time, if the upper limit of the conditional expression (7) is exceeded, it may be difficult to correct the spherical aberration and it may be difficult to realize the high resolution of the optical system.

Hereinafter, the miniature wide-angle optical system according to the present invention will be described in more detail with reference to specific numerical examples.

As described above, the first through fourth embodiments described below all have the first lens L1 having a positive refractive power and the object side surface being convex toward the object side; A second lens L2 having a negative refractive power; A third lens L3 having a negative refractive power; A fourth lens L4 having positive refractive power; A fifth lens L5 having positive refracting power and having an upward convex shape on the image side; And a sixth lens L6 having a negative refracting power and having an upper side concave on the image side. The sixth lens L6 and the image plane 15 may be constituted by an infrared ray filter or an infrared ray filter An optical filter (OF) composed of a cover glass coated with an optical filter (OF) is provided.

The first lens L1 to the sixth lens L6 are composed of plastic lenses whose both surfaces are aspherical surfaces.

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 is the distance from the apex of the lens in the direction of the optical axis

Y: Distance in the direction perpendicular to the optical axis

c: the inverse 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 is an MTF graph of the optical system shown in FIG. 1, and FIG. 3 is a graph showing the MTF of the optical system shown in Table 1 and FIG. 1 In the optical system.

In the case of the first embodiment, the effective focal length F of the entire optical system is 4.09 mm, and the distance TTL from the first lens to the image surface is 5.0 mm. The first lens L1 to the sixth lens L6 are all made of an aspherical plastic lens.

In the first embodiment, the focal length F6 of the sixth lens is -5.98 mm, the refractive index is 1.6322 in the d line wavelength (587.6 nm) range of the second lens, and the d line wavelength of the fifth lens is 587.6 Nm), the refractive index is 1.6349, and the focal length F3 of the third lens is -100 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 sixth lens L6 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.

4 is a graph of MTF of the optical system shown in Fig. 4, and Fig. 6 is a graph showing the MTF of the optical system shown in Table 3 and Fig. 4, respectively, And shows an aberration diagram of the optical system shown.

In the case of the second embodiment, the effective focal length F of the entire optical system is 4.08 mm, and the distance TTL from the first lens to the image surface is 4.98 mm. The first lens L1 to the sixth lens L6 are all made of an aspherical plastic lens.

In the case of the second embodiment, the focal length F6 of the sixth lens is -4.45 mm, the refractive index is 1.6322 in the d-line wavelength (587.6 nm) band of the second lens, and the d- Nm), the refractive index is 1.6349, and the focal length F3 of the third lens is -100 mm.

In Table 3, an asterisk * in front of the surface number denotes an aspherical surface, and in the case of the second embodiment, both surfaces of the first lens L1 to the sixth lens L6 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.

7 is an MTF graph of the optical system shown in Fig. 7, and Fig. 9 is a graph showing the MTF of the optical system shown in Table 5 and Fig. 7, respectively, And shows an aberration diagram of the optical system shown.

In the case of the third embodiment, the effective focal length F of the entire optical system is 4.25 mm, and the distance TTL from the first lens to the image surface is 5.15 mm. The first lens L1 to the sixth lens L6 are all made of an aspherical plastic lens.

Further, in the case of the third embodiment, the focal length F6 of the sixth lens is -4.80 mm, the refractive index is 1.6322 in the d line wavelength (587.6 nm) range of the second lens, and the d line wavelength of the fifth lens is 587.6 Nm), the refractive index is 1.5255, and the focal length F3 of the third lens is -100 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 sixth lens L6 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.

10 is a diagram showing a lens arrangement of an optical system for a camera according to a fourth embodiment of the present invention, FIG. 11 is an MTF graph of the optical system shown in FIG. 10, and FIG. And shows an aberration diagram of the optical system shown.

In the fourth embodiment, the effective focal length F of the entire optical system is 4.07 mm, and the distance TTL from the first lens to the image surface is 5.01 mm. The first lens L1 to the sixth lens L6 are all made of an aspherical plastic lens.

In the fourth embodiment, the focal length F6 of the sixth lens is -23.26 mm, the refractive index is 1.6322 in the d line wavelength (587.6 nm) range of the second lens, and the d line wavelength of the fifth lens is 587.6 Nm), the refractive index is 1.6349, and the focal length F3 of the third lens is -24.42 mm.

In Table 7, an asterisk * in front of a surface number indicates an aspherical surface, and in the case of the fourth embodiment, both surfaces of the first lens L1 to the sixth lens L6 are aspherical surfaces.

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

The values of the conditional expressions for the first to fourth embodiments are shown in Table 9 below.

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 embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 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
L6. The sixth lens
OF. Optical filter
1, 2, 3, 4 ... 8, 9, 10 ... Surface number

Claims (11)

A first lens having positive refracting power in order from the object side, the object side surface being convex toward the object side;
A second lens having a negative refractive power;
A third lens having negative refractive power;
A fourth lens having positive refractive power;
A fifth lens having negative refracting power and having an upward convex shape on the image side; And
A sixth lens having a negative refracting power and having an upper concave shape on an upper side;
.
The method according to claim 1,
Wherein the imaging optical system satisfies the following conditional expression for a chromatic aberration correction condition.
[Conditional expression] | V3 - V2 | <41
Here, V3 is the Abbe number of the third lens,
V2 is the Abbe number of the second lens.
The method according to claim 1,
Wherein the imaging optical system satisfies the following conditional expression with respect to the design condition of the optical system.
[Conditional expression] TTL / F <1.5
Here, TTL is the distance from the first lens to the image surface,
F is the focal length of the entire optical system.
The method according to claim 1,
Wherein the imaging optical system satisfies the following conditional expression with respect to a condition of miniaturization by a focal length ratio of the optical system.
[Conditional expression] 1 <| F6 / F | <6
Here, F6 is the focal length of the sixth lens,
F is the focal length of the entire optical system.
The method according to claim 1,
Wherein the imaging optical system satisfies the following conditional expression with respect to a condition of miniaturization according to the radius of curvature of each lens of the optical system.
[Conditional expression] 0 < (R7 + R10) / (R7 - R10) < 1.3
Here, R7 is the radius of curvature of the object side surface of the fourth lens,
And R10 is the radius of curvature of the upper surface of the fifth lens.
The method according to claim 1,
Wherein the imaging optical system satisfies the following conditional expression for a condition relating to aberration correction of the optical system.
[Conditional expression] | R7 / F | <5
Here, R7 is the radius of curvature of the object side surface of the fourth lens,
F is the focal length of the entire optical system.
The method according to claim 1,
Wherein the imaging optical system satisfies the following conditional expression for a condition relating to chromatic aberration correction of an optical system:
[Conditional expression] | Nd2 - Nd5 | <0.11
Here, Nd2 is the refractive index of the second lens in the wavelength (587.6 nm) band of the d line,
Nd5 is the refractive index of the fifth lens in the wavelength (587.6 nm) band of the d line.
The method according to claim 1,
Wherein the imaging optical system satisfies the following conditional expression with respect to a condition relating to spherical aberration correction of the optical system.
[Conditional expression] F3 / F < -5
Here, F3 is the focal length of the third lens,
F is the focal length of the entire optical system.
The method according to claim 1,
Wherein the first lens to the sixth lens are made of a plastic lens.
The method according to claim 1,
And both surfaces of the first through sixth lenses are aspherical surfaces.
The method according to claim 1,
And an optical filter of a cover glass coated with an infrared cut filter for shielding excessive infrared rays contained in the light incident from the outside, between the sixth lens and the image plane.

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