KR20110008850A - Imaging lens - Google Patents

Abstract

PURPOSE: A photographing lens using a high resolution image sensor is provided to stabilize the lens performance and increase the aberration property. CONSTITUTION: A first lens(10) has plus refraction power and convexly forms an object side. A second lens(20) has the minus refraction power and concavely forms an image side. A third lens(30) has the refractive power and forms a meniscus shape. A fourth lens(40) has the refractive power and forms a meniscus form to the body side of the object.

Description

Imaging lens

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to imaging lenses, and more particularly, to a microscopic 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, and a PC camera (image pickup device included with a personal computer) have been studied in relation to an image pick-up system. . The most important component for the camera module associated with such an image pickup system to obtain an image is an imaging lens that forms an image.

Imaging lens designs the number of lenses, the shape of the lens, the focal length, the refractive index, the Abbe number, and the like to achieve a desired angle of view and resolution. That is, the imaging lens has been applied in various ways according to the object to which it is applied. In designing the imaging lens exactly as desired, the performance of the lens must be kept more stable.

The present invention provides a high resolution miniature image pickup lens that highly stabilizes lens performance and has improved aberration characteristics.

According to one or more exemplary embodiments, an imaging lens includes: a first lens having positive refractive power in order from an object side; A second lens having negative refractive power; A third lens having positive refractive power; And a fourth lens having negative refractive power, and an aperture is positioned between the first lens and the second lens.

The four lens powers can be arranged in PNPN (+-+-) to provide an ultra compact lens module, and the aperture can be placed in front of the second lens for excellent distortion correction and stable lens performance. It provides an imaging lens.

In addition, by positioning the stop close to the front of the second lens as shown in [Condition 4], an imaging lens for maintaining the lens performance more stably in the high pixel lens module is provided. The embodiment provided in the present invention has very good aberration characteristics and shows good aberration correction ability.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may be present in between. Should be.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, and the same or corresponding components will be denoted by the same reference numerals regardless of the reference numerals and redundant description thereof will be omitted.

1 is a configuration diagram of a camera lens module according to the present embodiment, and is a side configuration diagram illustrating an arrangement state of a lens centering on an optical axis Z0. In the configuration diagram of FIG. 1, the thickness, size, and shape of the lens are somewhat exaggerated for the sake of explanation, and the spherical or aspherical shape is presented as an example and is not limited thereto.

Referring to FIG. 1, the camera lens module of the present embodiment includes the first lens 10, the second lens 20, the third lens 30, the fourth lens 40, and the filter 50 in order from the object side. And the light receiving element 60 is arranged.

Light corresponding to the image information of the subject passes through the first lens 10, the second lens 20, the third lens 30, the fourth lens 40, and the filter 50. ) Is incident.

In the following description of the configuration of each lens, "object side" refers to the surface of the lens toward the object side with respect to the optical axis, and "image side" refers to the lens toward the imaging surface based on the optical axis It means

The first lens 10 has a positive refractive power, and the object side surface S1 is convex. The second lens 20 has a negative refractive power, and both the object side surface S4 and the image side surface S5 are concave. An aperture STOP is positioned between the first lens 10 and the second lens 20. Preferably, the stop STOP is positioned closer to the object side surface S4 of the second lens 20 than to the image side surface S2 of the first lens 10.

In the illustrated embodiment, the object side surface S4 of the second lens 20 is concave at a very high refractive index. Then, the position of the stop STOP is disposed close to the object side surface S4 of the second lens 20 according to the conditional expression and the embodiment described below. According to such a structure, the distortion performance is excellent and the lens performance can be kept very stable.

The third lens 30 has a positive refractive power and has a meniscus shape in which the object side surface S6 is concave. The fourth lens 40 has a negative refractive power and has a meniscus type lens in which the object side surface S8 is convex.

Here, the fourth lens 40 has an aspherical surface having both inflection points. As shown, the image side surface S9 of the fourth lens 40 is bent toward the image from the center of the optical axis Z0 toward the periphery, and is the outermost region in the peripheral portion away from the optical axis Z0. As it faces, it bends toward the object to form an aspherical inflection point.

The aspherical inflection point formed on the fourth lens 40 may adjust the maximum exit angle of the chief ray incident on the light receiving element 60. In addition, the aspherical inflection points formed on the object side surface S8 and the image side surface S9 of the fourth lens 40 adjust the maximum exit angle of the chief ray, thereby preventing shading of the periphery of the screen.

The filter 50 is at least one of an optical filter such as an infrared filter and a cover glass. As the filter 50, when an infrared filter is applied, radiant heat emitted from external light is blocked from being transmitted to the light receiving device 60. In addition, the infrared filter transmits visible light and reflects infrared rays to the outside.

The light receiving element 60 is an image sensor such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS).

As for the first lens 10, the second lens 20, the third lens 30, and the fourth lens 40, aspherical lenses are used as in the following embodiments, the resolution of the lens is improved and aberration characteristics are improved. This can be taken advantage of.

It will be apparent to those skilled in the art that the conditional expressions and examples described below are preferred embodiments that increase the effect, and the present invention is not necessarily composed of the following conditions. For example, even if only the conditional expressions of some of the conditional expressions described below are satisfied, the lens configuration of the present invention may have a synergistic effect.

[Condition 1] 0.5 <f1 / f <1.5

[Condition 2] -1.5 <f2 / f <-0.5

[Condition 3] 0.5 <∑T / f <1.5

[Condition 4] 2 <d2 / d3 <8

[Condition 5] 0.2 <bf / f <0.5

Where f is 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 of the first lens to the imaging surface

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

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

bf: Distance from the image side surface of the fourth lens to the imaging surface

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 refractive powers having proper spherical aberration correction and appropriate chromatic aberration according to conditional expressions 1 and 2. Conditional Expression 3 defines the dimension of the optical axis direction of the entire optical system, which is a condition for a micro lens and a condition for proper aberration correction.

Conditional Expressions 4 and 5 define the position S3 of the aperture. Referring to Conditional Expression 4, the stop is basically positioned closer to twice the object side surface S4 of the second lens 20 than the image side surface S2 of the first lens 10. As long as the stop position (S3) is closer to the second lens 20 or the stop (STOP) is close to the center of the optical system, the lens performance is more stable. Is implemented.

Hereinafter, the effect of the present invention will be described with reference to specific examples. The aspherical surface referred to in the following examples is obtained from the known Equation 1, and the 'E and subsequent numbers' used in the Conic constant k and aspherical coefficients A, B, C, D, E, and F are 10. Represents a power of. For example, E + 01 represents 10 ¹ and E-02 represents 10 ⁻² .

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

c: 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 satisfies the conditional expression described above.

Referring to Table 1, it can be seen that f1 / f is 0.747, which satisfies Condition 1, f2 / f is -1.247, which satisfies Condition 2, and ∑T / f is 1.26, which satisfies Condition 3. It can be seen that d2 / d3 is 7.5, which satisfies Condition 4, and Bf / f is 0.4345, which satisfies Condition 5. In particular, in the above embodiment, it is understood that the position S3 of the stop STOP is very close to the object side surface S4 of the second lens 20 and is located at a position close to the center of the entire optical system. This means that the lens performance of the imaging lens of this embodiment is very stable.

Cotton number Bending Radius (R) Thickness or distance (d) Refractive index (N) One* 1.57 0.7 1.53 2* 14.55 0.15 3 stop ∞ 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 ∞ 0.3 1.53 11 ∞ 0.77 image ∞ 0.06

In Table 2, * denoted by the surface number indicates an aspherical surface.

The example of Table 2 shows a more specific example compared with the example of Table 1.

In addition, in the embodiment of Table 2, the values of the aspherical coefficients of the respective lenses are shown in Table 3 below.

Cotton 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 illustrating aberration diagrams according to the above embodiment, in which spherical aberration, astigmatic field curves, and distortion are measured in order from the left.

In FIG. 2, the Y axis means an image size, and the X side means a focal length (mm unit) and a distortion degree (% unit). In FIG. 2, it is interpreted that the aberration correction function is better as the curves approach the Y axis. In the aberration diagram shown, the values of the phases are shown adjacent to the Y-axis in almost all fields, so that spherical, astigmatism, and distortion are excellent.

FIG. 3 is a graph measuring coma aberration, and FIGS. 3A and 3B show tangential aberrations and sagittals of wavelengths according to field heights of the upper surface. It is a graph measuring aberrations. In FIG. 3, the graph showing the experimental results is interpreted as having a better coma aberration correction function as the X axis is closer to each of the positive and negative axes. The measurement examples of FIG. 3 are interpreted as showing excellent coma aberration correction functions since the values of the phases appear in the nearly all fields adjacent to the X axis.

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. Therefore, it is not intended that the invention be limited to the above-described embodiments, but the present invention will include all embodiments within the scope of the following claims.

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.

<Explanation of symbols for the main parts of the drawings>

10: first lens 20: second lens

30: third lens 40: fourth lens

50 filter 60 light receiving element

Claims (9)

In order from the object side, A first lens having positive refractive power; A second lens having negative refractive power; A third lens having positive refractive power; And A fourth lens having negative refractive power, And an aperture lens positioned between the first lens and the second lens. The method of claim 1, The second lens is an imaging lens in which both the object side surface and the image side surface is concave. The method of claim 1, The third lens has a meniscus shape in which an object side surface is concave. The method of claim 1, The fourth lens is an aspherical lens having both an object side surface and an image side surface having an inflection point. The method of claim 1, When the total focal length of the imaging lens is f, the focal length of the first lens is f1, and the focal length of the second lens is f2, 0.5 <f1 / f <1.5 -1.5 <f2 / f <-0.5 An imaging lens that satisfies the conditional expression of. The method according to claim 1 or 5, When 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 An imaging lens that satisfies the conditional expression of. The method of claim 1, The aperture lens is positioned closer to the object side surface of the second lens than the image side surface of the first lens. The method according to claim 1 or 7, When the distance from the image side surface of the first lens to the aperture is d2, and the distance from the aperture surface to the object side surface of the second lens is d3, 2 <d2 / d3 <8 An imaging lens that satisfies the conditional expression of. The method of claim 1, When the distance from the image side surface of the fourth lens to the imaging surface is bf and the total focal length of the imaging lens is f, 0.2 <bf / f <0.5 An imaging lens that satisfies the conditional expression of.

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