KR101120964B1 - Imaging lens - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging lens mounted with a mobile device, and more particularly, to an imaging lens for mounting a mobile device composed of three lenses.

In the present invention, the mobile device-mounted imaging lens has a first lens, a second lens, and a third lens arranged in order from the object side, and the first lens has a positive convex surface facing the object side. A meniscus lens having power; the second lens is a meniscus lens having a concave surface facing the object side; and the third lens is a lens having positive power, and the first lens, the second lens, and the first lens. In the lens surface of the three lenses, the first surface of the second lens is a spherical surface, and both surfaces of the third lens are aspherical surfaces, and the aspherical surface of the third lens includes an imaging lens having one or a plurality of inflection points.

The imaging lens according to the present invention constitutes an aspherical surface and has an Abbe number of the second lens of 23 or less, and constitutes an optical system with chromatic aberration correction capable of realizing a high pixel of 3 Mega or more in 3P.

Lens, double-sided aspherical, meniscus

Description

Three pieces of imaging lenses {IMAGING LENS}

The present invention relates to an imaging lens for mounting a mobile device, and more particularly to an imaging lens for mounting a mobile device composed of three lenses.

Background Art In recent years, digital still cameras (hereinafter referred to as digital cameras) capable of inputting image information into personal computers are rapidly spreading with the spread of personal computers to general households. In addition, with the high functionality of mobile phones, mobile phones with cameras equipped with small imaging modules are also rapidly spreading. In addition, small-capacity information terminal devices such as PDAs are also widely used with mounting imaging modules.

In the apparatus with these imaging functions, imaging devices, such as a Charge Coupled Device (CCD) and a Complementary Metal 0xide Semiconductor (CMOS), are used. In recent years, these imaging devices have been extremely miniaturized. Therefore, in an imaging device using an imaging device such as a CCD, the device body and the lens mounted thereon are also required to be reduced in size and weight. In addition, in recent years, in order to achieve high image quality, an image pickup device having a large number of pixels has been developed, and accordingly, a higher resolution and higher contrast performance are required in a lens system.

As described above, miniaturization and high pixelation of image pickup devices in recent years are progressing, and therefore, high resolution performance and compactness of configurations are required for image pickup lenses, especially for digital cameras. On the other hand, imaging lenses for small information terminal devices such as mobile phones with cameras have been mainly required for price and compactness. However, in recent years, there has been a tendency for high pixel size of imaging devices to be advanced even in mobile phones with cameras. For example, those that support megapixels of 1 million pixels or more are put to practical use, and the demand for performance is also increasing. For this reason, it is desired to develop various kinds of lenses in consideration of price, performance and compactness.

For this request, for example, it is conceivable to use three or four lenses in order to achieve compactness and low cost, and to actively use an aspherical surface in order to achieve high performance. In this case, the aspherical surface contributes to compactness and high performance. However, since the aspherical surface is disadvantageous from the viewpoint of production and the price is likely to be high, the use of the aspherical surface is preferably taken into consideration of manufacturability.

In general, the lens of a three-piece configuration is likely to be insufficient in terms of performance for digital cameras, although it is sufficient for portable module cameras in performance. In addition, although the lens of the four-piece configuration can improve the performance compared to the three-piece configuration, it is likely to be disadvantageous in terms of price and compactness.

As an imaging lens for a small information terminal device corresponding to a high pixel, a lens system having a three-element structure consisting of one glass lens (1 g) and two plastic lenses (2 p) has been developed.

In the conventional lens system described above, a lens in which the first lens has a spherical shape and the third lens has a meniscus shape is employed.

However, there is a demand for a lens system with a small number of lenses, which is composed of plastic lenses rather than glass lenses in terms of price, and is high in performance, and able to meet the demand for miniaturization in recent years.

SUMMARY OF THE INVENTION An object of the present invention has been made in view of these problems, and an object thereof is to provide an imaging lens that can realize a high performance and a very compact lens system by effectively using an aspherical surface with a small number of lenses while being composed of a plastic lens. .

Another object of the present invention is to provide a compact imaging lens capable of solving the problem of defocusing due to processing error.

In order to achieve the above object, the imaging lens of the present invention

A first lens, a second lens, and a third lens arranged in order from the object side;

The first lens is a meniscus lens having a positive power of the convex side toward the object side, the second lens is a meniscus lens of a concave surface facing the object side, and the third lens is a positive power Branch is a lens,

Both surfaces of the first lens are aspherical, the second lens is spherical and the second surface is aspheric, and the third lens is both aspheric,

The aspherical surface of the third lens may have one or a plurality of inflection points.

In the present invention, the second lens has an Abbe number of 23 or less, preferably 1-23, more preferably 10-23, even more preferably 20-23, and most preferably 23. do.

In the present invention, the lens system preferably satisfies the following formula.

Φ = 1 / f = (n2-1) [(1 / R21)-(1 / R22) + (t (n2-1) / (R21R22n2))] <0 ... (1)

Is the power of the second lens, n2 is the refractive index of the second lens, R21 is the R1 of the second lens, R22 is the thickness of the lens, and R2 t is the thickness of the lens.

The Abbe number of L1 is 50 <Vd1 <60 (2)

Abbe's number of L2 is Vd2 &lt; = 23 (3)

0.6 <f1 / F <1.2

0.65 < tanθ <0.7

1.4 <L / (2ωx) <1.5

Where F is the focal length of the entire optical system, f1 is the focal length of the first lens, θ is the half angle of view at the maximum image height, x is the maximum image height, and 2ω (radian) diagonal angle of view, L Is the distance from the apex of the object-side surface of the first lens to the image pickup surface, υd1 is the Abbe's number with respect to the d-line of the first lens, υd2 is the Abbe's number with respect to the d-line of the second lens, and υd3 Is the Abbe's number for the d-line of the third lens.

Conditional Expression (4) is a condition for stably maintaining the spherical aberration and keeping the entire lens system compact. When the lower limit is lowered, the lens system can be made compact, but it is difficult to correct the spherical aberration. If the upper limit is exceeded, on the contrary, spherical aberration is easily corrected, but the entire lens system cannot be compactly constructed.

It is easy to reduce the axial color aberration by using the low Abbe number of the second lens. The smaller the color chromatic aberration, the higher the level of MTF, which is an optical performance. In terms of chromatic aberration correction, L2's Abbe number should be at least 23 to enable 3MegaPP chromatic aberration correction and performance. If the Abbe number exceeds 23, the chromatic aberration correction problem occurs, and the power of the lens should be stronger, causing loss in the tolerance part, which causes problems in product implementation.

In addition, in the present invention, both surfaces of the third lens are formed aspherical, and the aspherical surface of the third lens is formed to have one or a plurality of inflection points, thereby coma aberration and astigmatic aberration. Can be satisfactorily corrected, and distortion can also be satisfactorily corrected.

As described above, the present invention provides a lens consisting of three groups of three small-length full-length lenses suitable as a hair lens.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail with reference to drawings.

In addition, in the following description, when referring to the power of each lens and the uneven | corrugated shape of each lens surface, the state on an optical axis shall be shown as a rule. The imaging lens of the embodiment shown in FIG. 1 has a meniscus-shaped first lens L1 having a positive-side power and a double-sided aspherical surface with the object-side surface in order from the object side sequentially. And a second lens L2 having a meniscus shape having a diaphragm 2 and an object-side surface having a concave shape, a first surface having a spherical surface, a second surface having an aspheric shape, and having negative power. And a third lens L3 having an aspherical surface on both sides, having a positive power, and having a single tangent line parallel to a straight line perpendicular to the optical axis, and imaging light rays incident along the optical axis X. The imaging lens is configured to efficiently focus on the imaging position P of the element (imaging surface) 3.

In addition, the diaphragm 2 is disposed between the image side surface of the first lens L1 or between the first lens L1 and the second lens L2, and the cover glass 1 between the imaging lens and the imaging device 3. ) Is arranged.

In addition, both surfaces of the third lens L3 have an aspherical surface shape, and the third lens L3 has a shape such that one tangent line parallel to the straight line perpendicular to the optical axis exists. Here, the object-side surface of the third lens L3 has a shape similar to a straight line, and the image-side surface has a chevron shape.

In the imaging lens of the present invention, since the lens materials of the first lens L1 to the third lens L3 are all made of a plastic material, the aspherical surface can be effectively used while achieving low cost, and not only a portable module camera but also a digital camera can be used. A correspondingly high optical performance is obtained.

Next, the effect by this embodiment is demonstrated.

The length of the entire lens can be shortened by making the positive power of the first lens L1 relatively strong among the three lenses. Further, the first lens L1 is a double-sided aspherical lens, and by providing a lens having such aberration correction function, each aberration including image curvature and spherical aberration can be made good.

In addition, in the imaging lens of the present embodiment, an aperture 2 is disposed between the first lens L1 and the second lens L2, and between the first lens L1 and the second lens L2. As an axial air gap of, sufficient space must be secured to arrange the aperture mechanism.

In addition, in the imaging lens of the present embodiment, both surfaces of the air lens positioned between the second lens L2 and the third lens L3 are formed to follow each other, and the sign of the center curvature radius is also negative (object side). Concave in the direction). As described above, in the present embodiment, at least one surface of the second lens L2 focuses on the aspherical surfaces of both surfaces of the air lens positioned between the aspherical shape and the third lens L3, and the center of the aspherical surface of these surfaces By defining the magnitude relationship of the radius of curvature and the relationship of the height position of the poles as described above, even if the total length of the lens system is shortened by three lenses, the image surface curvature can be maintained well.

In addition, various aspects of the imaging lens of the present invention can be changed. For example, the curvature radius, lens spacing (or lens thickness), and aspherical shape of each lens can be appropriately changed.

In addition, by using a plastic material as the lens material, the weight can be reduced and the cost can be reduced. In addition, since both surfaces of the first lens L1 to the third lens L3 are aspherical, aberration correction can be performed on a plurality of surfaces to improve the optical performance.

Example 1

At F = 2.80 mm, the first lens has f1 = 2.26 mm, the object side R1 = 0.9823, the Abbe number is 55.7, the Abbe number of the second lens has 23, n2 = 1.632, R21 = -0.6887, R22 =- 1.1382, t = 0.360, spherical surface of the object surface, and aspherical data on the upper surface is K: -1.030008, A: -0.728294E + 00, B: 0.283034E + 01, C: -0.681991E + 01, D: 0.119451 E + 02, E: -0.779893E + 01. The third lens has an Abbe number of 55.7 and the aspherical data on the object surface is K: -16.405010

A: 0-.299280E + 00 B: 0.401788E + 00 C: -0.320001E + 00 D: 0.133831E + 00 E: -0.225859E-00

Aspheric data on the upper side has K: -12.091438, A: -0.229121E + 00, B: 0.140168E + 00 C: -0.761305E-01, D: 0.220029E-01, E: -0.348191E-02

Here, the aspherical shape of the lens is represented by the following aspherical formula.

Where Z denotes the amount of SAG, where the curvature on the optical axis of the lens surface is C, the cone coefficient is K, and the aspherical coefficients from 4th to 12th are A, B, C, D, and E, respectively. ) And the radius of curvature R are assumed to be in a relationship of C = 1 / R.

1 is a schematic cross-sectional view of an imaging lens according to an exemplary embodiment of the present invention.

2 is aberration diagrams for longitudinal chromatic aberration, image curvature aberration, and distortion aberration of the lens system of the embodiment of the present invention.

3 is an aberration diagram of coma aberration of Tangential (left view) and Sagittal (right view) for image heights 0F, 0.4F, 0.6F, 0.8F, and 1.0F of a lens system according to an embodiment of the present invention.

Claims (5)

An imaging lens in which a first lens, a second lens, and a third lens are arranged in order from an object side, The first lens having a convex surface facing the object side and being a meniscus lens having positive power; The second lens having a concave surface facing the object side and being a meniscus lens having negative power; And The third lens having positive power; Wherein both surfaces of the first lens and the third lens are aspherical, the second lens has an aspherical surface on an object side, and an image side is aspherical, and one or more inflection points exist on the aspherical surface of the third lens. And the lenses are configured to satisfy the following conditional expressions (1) to (6): (1) Φ = 1 / f = (n2-1) [(1 / R21)-(1 / R22) + (t (n2-1) / (R21R22n2))] <0 (2) 50 <υd1 <60 (3) υd2 ≤ 23 (4) 0.6 <f1 / F <1.2 (5) 0.65 <tanθ <0.7 (6) 1.4 <L / (2ωx) <1.5 Where Φ is the power of the second lens, n2 is the refractive index of the second lens, R21 is the curvature of the object side surface of the second lens, R22 is the curvature of the image side surface of the second lens, t is the thickness of the second lens, υd1 Is the Abbe's number with respect to the d-line of the first lens, υd2 is the Abbe's number with respect to the d-line of the second lens, F is the focal length of the entire optical system, f1 is the focal length of the first lens, and θ is the half angle of view at the maximum image height. Is the diagonal angle of view, x is the maximum image height, and L is the distance from the vertex of the object-side surface of the first lens to the image pickup device surface. The imaging lens of claim 1, wherein the paraxial region has a negative power. The imaging lens according to claim 1 or 2, wherein the power? Of the second lens is -0.25. delete The imaging lens according to claim 1 or 2, wherein an incident angle of chief rays of light to the sensor surface is 30 degrees or less.

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