KR101676424B1 - Imaging lens - Google Patents

Abstract

The present invention relates to an ultra-small imaging lens mounted on a camera module using a high resolution image sensor, comprising: a first lens having, in order from an object side, positive (+) refractive power; A second lens having a negative refractive power; A third lens having positive refractive power; A fourth lens having negative refractive power; And a diaphragm located between the first lens and the second lens.

Description

[0001] IMAGING LENS [0002]

The present invention relates to an imaging lens, and more particularly, to a miniature imaging lens mounted on a camera module using a high-resolution image sensor.

Recently, a camera module for a communication terminal, a digital still camera (DSC), a camcorder, a PC camera (an image pickup device attached to a personal computer), and the like have been studied in connection with an image pick-up system . The most important component for obtaining an image of a camera module related to such an image pickup system is an imaging lens for imaging an image.

The image pickup lens realizes a desired angle of view and resolution by variously designing the number of lenses, the shape of the lens, the focal length, the refractive index, and the Abbe number. That is, the imaging lens is variously applied depending on the object to which it is applied. The performance of the lens should be more stable in designing the imaging lens as desired.

The present invention provides a high-resolution micro-imaging lens having highly stabilized lens performance and improved aberration characteristics.

An imaging lens according to an embodiment of the present invention includes, in order from an object side, a first lens having positive refractive power; A second lens having a negative refractive power; A third lens having positive refractive power; And a fourth lens having negative refractive power, wherein a diaphragm is positioned between the first lens and the second lens, and a distance from an upper side of the first lens to the diaphragm is d2, D2 / d3 < 8, where d3 is the distance from the object side to the object side of the second lens.

The lens power of the four lenses can be arranged in PNPN (+ - + -), thereby providing an ultra-small, high-resolution lens module. By arranging the diaphragm in front of the second lens, distortion correction is excellent and lens performance can be stably maintained An imaging lens is provided.

Also provided is an imaging lens for stably maintaining the lens performance in the high-resolution lens module by arranging the position of the diaphragm close to the front side of the second lens as in conditional expression (4). The embodiment provided in the present invention shows excellent aberration characteristics and good aberration correction ability.

1 is a configuration diagram of an imaging lens according to the present embodiment.
2 is a graph showing aberration characteristics according to an embodiment of the present invention.
3 is a graph showing coma aberration according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, .

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein like or corresponding elements are denoted by the same reference numerals, and a duplicate description thereof will be omitted.

Fig. 1 is a configuration diagram of a camera lens module according to the present embodiment, and is a side view showing an arrangement state of lenses around an optical axis Z0. In the configuration diagram of Fig. 1, the thickness, size, and shape of the lens are shown somewhat exaggerated for explanatory purposes, and the spherical or aspherical shape is not limited to this shape, but only one embodiment.

1, the camera lens module of the present embodiment includes a first lens 10, a second lens 20, a third lens 30, a fourth lens 40, a filter 50, And a light receiving element 60 are arranged.

The light corresponding to the image information of the object passes through the first lens 10, the second lens 20, the third lens 30, the fourth lens 40 and the filter 50, .

Hereinafter, the term "object side" refers to a surface of the lens that faces the object side with respect to the optical axis, and "upper side" refers to a lens that faces the imaging surface with respect to the optical axis, .

The first lens 10 has a positive refractive power and the object side surface S1 is formed convexly. The second lens 20 has a negative refracting power, and both the object side surface S4 and the upper surface S5 are concave. A stop STOP is located between the first lens 10 and the second lens 20. Preferably, the diaphragm STOP is located closer to the object side surface S4 of the second lens 20 than the upper surface S2 of the first lens 10.

In the illustrated embodiment, the object side surface S4 of the second lens 20 is concave with a very high refractive index. The position of the diaphragm STOP is arranged close to the object side surface S4 of the second lens 20 by the following conditional expression and the embodiment. According to such a configuration, distortion correction is excellent and lens performance can be kept very stable.

The third lens 30 is a meniscus lens having a positive refractive power and the object side surface S6 is concave. The fourth lens 40 is a meniscus lens having a negative refractive power and the object side surface S8 being convex.

Here, the fourth lens 40 is an aspherical shape having both inflexion points on both sides. As shown in the figure, the upper surface S9 of the fourth lens 40 is curved upward toward the periphery from the central portion with the optical axis Z0 as the center, and again, at the peripheral portion away from the optical axis Z0, It is bent toward the object side to form an aspheric inflection point.

The aspheric inflection point formed in the fourth lens 40 can adjust the maximum emission angle of the principal ray incident on the light receiving element 60. [ The aspheric inflection point formed on the object side surface S8 and the upper surface side S9 of the fourth lens 40 adjusts the maximum projection angle of the principal ray to prevent shading of the peripheral portion of the screen.

The filter 50 is at least one of an infrared filter, an optical filter such as a cover glass, and the like. When the infrared filter is applied as the filter 50, the radiation heat emitted from the external light is blocked from being transmitted to the light receiving element 60. In addition, the infrared ray filter transmits visible light, and the infrared ray reflects the infrared ray to the outside.

The light receiving element 60 is an image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor).

The first lens 10, the second lens 20, the third lens 30 and the fourth lens 40 use an aspherical lens as in the following embodiments to improve the resolving power of the lens, This is an excellent advantage.

It will be apparent to those skilled in the art that the conditional expressions and embodiments described below are preferred embodiments for increasing the operating effect, and that the present invention is not necessarily constituted by the following conditions. For example, the lens configuration of the present invention may have an elevated action effect even if only the conditional formulas of some of the conditional expressions described below are satisfied.

[Conditional expression 1] 0.5 <f1 / f <1.5

[Conditional expression 2] -1.5 < f2 / f < -0.5

[Conditional expression 3] 0.5 < T / f < 1.5

[Conditional expression 4] 2 < d2 / d3 < 8

[Conditional expression 5] 0.2 <bf / f <0.5

Here, f: the total focal length of the imaging lens

f1: focal length of the first lens

f2: focal length of the second lens

T: Distance from the object side surface of the first lens to the image plane

d2: from the image side of the first lens to the aperture

d3: distance from the diaphragm to the object side surface of the second lens

bf: distance from the image side of the fourth lens to the image plane

Conditional expressions 1 and 2 define the refractive power of the first lens 10 and the refractive power of the second lens 20. The first lens 10 and the second lens 20 have a refractive power with proper chromatic aberration and correction of appropriate spherical aberration according to the conditional expressions 1 and 2. Conditional expression 3 defines the dimension in the optical axis direction of the entire optical system, and is a condition for a micro lens and a condition for proper aberration correction.

Conditional expression 4 and conditional expression 5 define the position S3 of the diaphragm. Referring to Conditional Expression 4, the aperture stop STOP is basically located closer to the object side surface S4 of the second lens 20 than the upper surface S2 of the first lens 10 by two times or more. The closer the position S3 of the diaphragm STOP is to the second lens 20 or the closer the diaphragm STOP is to the center of the optical system, the more stable the lens performance .

Hereinafter, the operation and effect of the present invention will be described with reference to specific examples. The aspherical surface referred to in the following embodiments is obtained from the known equation (1), and the 'E and the following number' used for the conic constant k and the aspherical coefficients A, B, C, D, Lt; / RTI &gt; For example, E + 01 represents 10 ¹ and E-02 represents 10 ^-2 .

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

c: The basic curvature of the lens

Y: Distance in the direction perpendicular to the optical axis

K: Conic constant

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

[Example]

Example f 4.35 f1 3.2505 f2 -5.4244 f3 1.8347 f4 -2.0780 f1 / f 0.747 T 5.5 T / f 1.26 d2 0.15 d3 0.02 d2 / d3 7.5 Bf 1.89

Table 1 shows an embodiment that conforms to the above-described conditional expression.

Referring to Table 1, it can be seen that f1 / f is 0.747, which is in accordance with the conditional expression 1, and that f2 / f is -1.247, which is in accordance with the conditional expression 2, and that T / f is 1.26, And d2 / d3 is 7.5, which is in accordance with the conditional formula 4. It can be seen that Bf / f is 0.4345 and the conditional formula 5 is satisfied. Particularly, in the above embodiment, it can be seen that the position S3 of the diaphragm STOP is very close to the object side surface S4 of the second lens 20, and is located close to the center in the entire optical system. This means that the imaging lens of this embodiment has a very stable lens performance.

Face number The radius of curvature (R) Thickness or distance (d) Refractive index (N) One* 1.57 0.7 1.53 2* 14.55 0.15 3 stops 8 0.02 4* -55.55 0.35 1.61 5 * 3.55 0.75 6 * -2.34 1.04 1.53 7 * -0.79 0.15 8* 36.32 0.4 1.53 9 * 1.06 0.77 10 8 0.3 1.53 11 8 0.77 image 8 0.06

In Table 2, an asterisk * next to the face number indicates an aspherical surface.

The embodiment of Table 2 shows a more specific embodiment in comparison with the embodiment of Table 1.

The values of the aspherical surface coefficients of the respective lenses in the example of Table 2 are shown in Table 3 below.

Face number k A B C D E F One* -0.125800 0.022432 -0.012502 0.09321 -0.141405 0.127804 -0.04126 2* 0 0.0404864 -0.006306 0.020487 -0.046358 0 0 4* 0 0.0302448 -0.0102585 -0.300037 0.7649432 -0.853334 0.025356 5 * 4.234675 0.0573070 -0.0362689 0.074805 -0.190018 0.151944 0.027700 6 * 2.614519 -0.0119960 -0.0399270 -0.010109 0.0609055 -0.008665 -0.004902 7 * -3.716436 -0.2009983 0.1283497 -0.088193 0.0183575 0.011293 -0.003772 8* -8.39785241E + 017 -0.0602964 -0.0184367 0.0300750 -0.0110296 0.0017842 -0.000111 9 * -8.986216 -0.08309047 0.0238778 -0.0052735 0.00067512 -2.816517E-05 -1.531881E-06

FIG. 2 is a graph showing aberration diagrams according to the above embodiment. FIG. 2 is a graph showing longitudinal spherical aberration, astigmatic field curves, and distortion in order from the left.

In Fig. 2, the Y axis means the size of the image, and the X side means the focal length (in mm) and the distortion degree (in%). In FIG. 2, as the curves approach the Y-axis, the aberration correction function is considered to be better. In the illustrated aberration diagrams, since the values of the images are adjacent to the Y axis in almost all fields, spherical aberration, astigmatism, and distortion aberration are all excellent values.

3 (a) and 3 (b) are graphs showing coma aberration. In FIG. 3, tangential aberrations and sagittal aberrations of respective wavelengths are plotted along the height of a top surface, Aberration is measured. In FIG. 3, as the graph showing the experimental results is closer to the X axis on the positive axis and the negative axis, it is interpreted that the coma aberration correction function is good. The measurement examples of FIG. 3 are interpreted as showing superior coma aberration correction functions because the values of the images appear near the X axis in almost all fields.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. You will understand. Accordingly, it is intended that the present invention covers all embodiments falling within the scope of the following claims, rather than being limited to the above-described embodiments.

10: first lens 20: second lens
30: third lens 40: fourth lens
50: filter 60: light receiving element

Claims (16)

delete delete delete delete delete delete delete delete In order from the object side,
A first lens having positive refractive power;
A second lens having a negative refractive power;
A third lens having positive refractive power;
A fourth lens having negative refractive power; And
And a diaphragm located between the first lens and the second lens,
The first lens, the second lens, the third lens, and the fourth lens are aspherical lenses,
D2 is the distance from the image side of the first lens to the diaphragm, and d3 is the distance from the diaphragm to the object side of the second lens,
2 < d2 / d3 < 8
Satisfies the following conditional expression. 10. The method of claim 9,
Wherein the diaphragm is closer to an object side surface of the second lens than an upper surface of the first lens. delete 10. The method of claim 9,
Wherein the second lens has both the object side surface and the image side surface concave. 10. The method of claim 9,
Wherein the third lens is in the form of a meniscus whose object side is concave. 10. The method of claim 9,
And the fourth lens has an inflection point on both the object side and the image side. 10. The method of claim 9,
The total focal length of the imaging lens is f, and the distance from the object side surface of the first lens to the imaging surface is T,
0.5 < T / f < 1.5
Satisfies the following conditional expression. 10. The method of claim 9,
A distance from an image side of the fourth lens to an imaging plane is bf, and a total focal length of the imaging lens is f,
0.2 < bf / f < 0.5
Satisfies the following conditional expression.

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