KR20090019444A - Subminiature imaging lens for high-pixel - Google Patents

Abstract

A micromini imaging lens for high pixel applied in portable terminal is provided to perform high resolution with low cost and miniaturization by using a plastic non-spherical surface lens. A micromini imaging lens for high pixel applied in portable terminal comprises a first lens, a second lens, a third lens, and a fourth lens. The first lens has positive refractive power and non-spherical surface. The second lens has negative refractive power and non-spherical surface. The third lens has positive refractive power and non-spherical surface. The fourth lens has negative refractive power and non-refractive surface. The first, second, third, and fourth lenses are successively formed from an object to optical axis direction.

Description

Subminiature imaging lens for high-pixel

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging lens applied to a portable terminal employing an imaging device such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS).

In recent years, the use of a portable terminal or a personal computer has become common, and it has been less troublesome to check a landscape or a person photographed by printing a conventional silver salt film.

In addition, according to the spread of the digital camera, a mobile phone, a camcorder, a PDA, etc., the trend is being installed in a variety of digital electronic devices because of the convenience that can be recorded and confirmed, the subject to be recorded in real time.

In addition, with the spread of the imaging device, the user's portability has been emphasized very much, except for the basic specifications such as high quality, high performance, and low cost. The reality is that you are competing to meet your needs.

As an image pickup apparatus that can be mounted in a conventional image pickup apparatus, there is a Korean Patent Publication No. 2004-0010184 as shown in FIG. 1, and its configuration is composed of four lenses, between an object side and a first lens or between a first lens and a second lens. An aperture is disposed in the lens, and the first lens is a glass lens, and the second lens, the third lens, and the fourth lens are made of plastic lenses.

As described above, recent image pickup devices have been miniaturized and high performance. Accordingly, image pickup devices have also been required to have high resolution and miniaturization simultaneously.

The prior art has an advantage in terms of environmental resistance by employing the first lens as a glass lens from the object side, but when the image pickup device is mounted, the cover glass is mounted between the subject and the lens unit (lens assembly). 'Environmentality' is not a sensitive issue, but the issue of miniaturization, light weight, and low cost has been an issue, and the adoption of glass lenses has a problem that the manufacturing process is complicated, a cost increase factor, and is not suitable for light weight. There was a problem that it is impossible to reduce the size to shorter than the diagonal size.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an imaging lens capable of miniaturizing the optical electric field smaller than the sensor diagonal size and achieving high resolution and light weight at low cost.

The imaging lens of the present invention comprises a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens having a negative refractive power from an object side, By adopting the plastic aspherical lens for all of the lens to the fourth lens, the optical length is smaller than the diagonal size of the sensor, so that it is possible to apply a variety of applications including a slim handheld terminal by implementing sufficiently high resolution even in miniaturization, light weight and low cost. By configuring the F-number (= f / D) with a bright optical system of 2.8 or less, it is possible to show high performance even in a sensor having a small pixel size.

Detailed description of the invention will be described with reference to the accompanying drawings.

2 is an explanatory diagram of basic lens data according to the first embodiment of the present invention, FIG. 3 is an explanatory diagram of aspherical data according to the first embodiment of the present invention, and FIG. 4 is a first embodiment of the present invention. Fig. 5 is a cross-sectional view of the configuration of the imaging lens in the example, Fig. 5 shows aberration diagram showing spherical aberration, (B) diagram showing aberration aberration, (C) shows distortion as a first embodiment of the present invention. 6 is an explanatory diagram of basic lens data in the second embodiment of the present invention, FIG. 7 is an explanatory diagram of aspherical data in the second embodiment of the present invention, and FIG. 9 is a cross-sectional view of the configuration of the imaging lens in the second embodiment of the present invention, and FIG. 9 is a aberration diagram showing spherical aberration, and (B) aberration diagram showing astigmatism as a second embodiment of the present invention. And (C) are aberration diagrams showing distortion aberrations.

In the imaging lens of the present invention, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power and a fourth lens having a negative refractive power are arranged in order from the object side. The first lens, the second lens, the third lens, and the fourth lens are all aspherical.

0.9 <TL / 2Y <1.0.. … (One)

0.25 < bf / 2Y < 0.34 … (2)

Where TL represents the distance from the object-side lens surface of the first lens to the imaging surface, 2Y represents the diagonal size of the image sensor, and bf represents the distance from the lens surface on the imaging surface side of the fourth lens to the imaging surface (back focus distance). Indicates.

Conditional Expressions (1) and (2) are intended to reduce the size of the imaging lens system of the present invention. When conditional expression (1) is satisfied, the overall length of the entire optical system is shorter than the diagonal size of the sensor, which is very advantageous for miniaturization. If the lower limit of the conditional formula (1) is lower than the lower limit of the conditional formula (1), the manufacturing difficulty is increased, such as excessively thinner lenses, and the cost competitiveness is lowered in the imaging lens, which is mainly produced in mass production. This long optical system is obtained.

If the conditional expression (2) is satisfied, sufficient back focus distance is secured, and if the lower limit of the conditional expression (2) is lowered, it is difficult to obtain a sufficient back focus distance, and the performance of the optical system is degraded due to the heat generated from the image sensor. In addition, it is difficult to adopt the auto-focus module.

In addition, if the upper limit is exceeded, the back focus becomes longer, and thus the entire optical system length becomes longer, and if the length is not longer, the thickness of the lens becomes thinner, resulting in poor productivity.

To implement this, all of the first to fourth lenses were used as aspherical surfaces, and the aspherical surface coefficient of Conditional Expression (3) was adjusted appropriately.

In addition, the first to fourth lenses are all made of plastic material, and the first, third and fourth lenses are made of ZEON, Japan, and the second lens is made of Osaka Gas, Japan. Material was used.

……(3)

… … (3)

only,

Z: depth of aspherical surface from lens vertex to optical axis direction

c: curvature = 1 / R (R: radius of curvature)

Y: height in the vertical direction at the optical axis

K: conic constants

A, B, C, D, E,... Aspherical surface coefficient

0.55 < f1 / f < 0.85 … (4)

0.75 <| f2 / f | <1.3... … (5)

0.5 < f3 / f < … (6)

0.57 <| f4 / f | <0.9. … (7)

Where TL is the distance from the object side of the first lens to the imaging surface, f is the combined focal length of the entire optical system, f1 is the focal length of the first lens, f2 is the focal length of the second lens, and f3 is the focal length of the third lens. f4 denotes a focal length of the fourth lens.

Conditional Expression (4) defines the power of the first lens with respect to the power of the entire optical system, and aberration correction and miniaturization can be achieved by properly adjusting the power of the first lens as described above.

When a strong power is lower than the lower limit of the above conditional expression, the correction of spherical aberration becomes disadvantageous, and even in manufacturing, the edge thickness of the lens becomes thin, making it difficult to secure sufficient mass productivity.

Moreover, if it has power exceeding the upper limit of the said conditional expression, it will become unsuitable for miniaturization.

In addition, if the power of the first lens is properly adjusted to satisfy the following conditional expression (8), aberration correction can be more stably achieved while miniaturization.

0.6 < f1 / f < 0.72 … (8)

Conditional expression (5) defines the power of the second lens with respect to the power of the entire optical system, and aberration correction is advantageous if the power of the second lens is properly adjusted as described above.

Having a strong power below the lower limit of the conditional expression makes it difficult to correct higher order aberrations of 3rd order or higher, and having power above the upper limit of the conditional formula is disadvantageous in correcting spherical aberration and coma.

In addition, if the power of the second lens is properly adjusted to satisfy the following conditional expression (9), the numerical information can be more stably obtained.

0.9 <| f2 / f | <1.1. … (9)

Conditional expression (6) defines the power of the third lens with respect to the power of the entire optical system. When the power of the third lens is properly adjusted as described above, the aberration correction and miniaturization can be achieved.

Having a strong power below the lower limit of the above conditional expression makes it difficult to secure sufficient back focus, and increases the shrinkage rate since the plastic material is used, which is a disadvantage in securing performance.

In addition, sufficient aberration correction is difficult when it has power exceeding the upper limit of the conditional expression.

In particular, if the power of the third lens is properly adjusted to satisfy the following conditional expression (10), stable aberration correction is possible while ensuring sufficient back focus, and it is also advantageous to improve the telecentricity of the light incident on the image sensor. Done.

0.6 < f3 / f < 0.75 … 10

Conditional Expression (7) defines the power of the fourth lens with respect to the power of the entire optical system. When the power of the fourth lens is properly adjusted as in the conditional expression above, sufficient back focus and telecentricity can be improved. .

If a strong power is lower than the lower limit of the above conditional expression, the aspherical surface becomes too deep, or the double curvature becomes too large, making the plastic lens too sensitive to shrinkage after molding and heat generated from the sensor, making it difficult to secure stable performance.

In addition, having a power above the upper limit of the conditional expression is not only disadvantageous to aberration correction, but also difficult to secure telecentricity of light incident on the image sensor.

In particular, if the power of the fourth lens is properly adjusted to satisfy the following conditional expression (11), more stable aberration correction and telecentricity can be ensured.

0.62 <| f4 / f | <0.75. … (11)

Example

Hereinafter, an embodiment of the imaging lens of the present invention will be described with lens data and aberration.

FIG. 2 shows the configuration of the lens sectional view shown in FIG. 4 in detail. FIG. 2 shows basic lens data, and FIG. 3 shows aspherical data.

The formation principle of the aspherical data of FIG. 3 is expressed by the aforementioned conditional expression (3), and the first to third lenses are used in the 4th to 10th order, and the fourth lens is used in the 4th to 12th order. .

… … (3)

only,

Z: depth of aspherical surface from lens vertex to optical axis direction

c: curvature = 1 / R (R: radius of curvature)

Y: height in the vertical direction at the optical axis

K: conic constants

A, B, C, D, E,... Aspherical surface coefficient

In the basic lens data shown in FIG. 2, the surface number Si is a number given to the cross-sectional view of the imaging lens shown in FIG. And S10.

As shown in Fig. 4, the radius of curvature Ri of each lens is sequentially changed from the object side toward the image pickup surface R1, R2,... And R10.

In addition, the plane spacing Di represents a distance between the i-th lens surface Si and the i + 1th lens surface Si + 1 along the optical axis as shown in FIG. 4.

Nd and vd represent the refractive index and Abbe's number in the d-line (587.6 nm) of each lens.

In the upper part of FIG. 2, f denotes a focal length of the entire optical system, and a number F denotes a brightness of the optical system. A lower value indicates a brighter lens.

Can be expressed as "F number = f / D", f represents the focal length, D represents the size of the incident pupil, Example 1 of the present invention is F number of 2.6 Example 2 is 2.67, F number of 2.8 or more in the ordinary optical system Considering that, as a bright optical system, noise can be reduced in a dark environment as well as a general environment, and a faster frame speed can be realized even at a high pixel.

Considering that a sensor with a pixel size of 1.75㎛ is mass-produced, this is appropriate.

TL represents the distance from the object side to the imaging surface of the first lens, and 2Y represents the diagonal size of the image sensor.

In addition, 2ω represents the angle of view of the imaging lens, and "*" indicates that it is an aspherical lens.

5A to 5C sequentially show spherical aberration, astigmatism, and distortion aberration for Example 1. FIG.

For spherical aberration, aberrations for F-line (486.1nm), d-line (587.6nm), and C-line (656.3nm) wavelengths were shown.Astigmatism was measured in the sagittal direction on the d-line basis. The aberration diagram in the tangential direction is shown.

Distortion aberration is also shown on the d-line basis.

9 (A) to 9 (C) show spherical aberration, astigmatism, and distortion aberration for Example 2, and are applied in the same manner as described above.

As can be seen from the above lens data and the aberration diagram, the aberration is sufficiently stable while realizing miniaturization, and thus, it can be said that the lens is suitable for a high-pixel ultra-small imaging lens.

Embodiments described above through Examples 1 and 2 are examples of the present invention, and the spirit of the present invention is not limited thereto, and lens data (curvature radius, aspherical data, thickness, etc.) and materials (plastic or glass lenses) are used. By appropriately changing, various embodiments can be expressed within the scope of the present invention.

1 is a cross-sectional view showing the configuration of a conventional imaging lens.

2 is an explanatory diagram of basic lens data in the first embodiment of the present invention;

3 is an explanatory diagram of aspherical data in the first embodiment of the present invention;

Fig. 4 is a sectional view of the configuration of the imaging lens in the first embodiment of the present invention.

FIG. 5 is an aberration diagram showing spherical aberration, (B) aberration diagram showing astigmatism, and (C) aberration diagram showing distortion aberration as a first embodiment of the present invention.

6 is an explanatory diagram of basic lens data in the second embodiment of the present invention;

7 is an explanatory diagram of aspherical data in the second embodiment of the present invention;

Fig. 8 is a sectional view of the configuration of the imaging lens in the second embodiment of the present invention.

9 is a second embodiment of the present invention, (A) is an aberration diagram showing spherical aberration, (B) is an aberration diagram showing astigmatism, (C) is an aberration diagram showing distortion aberration

※ Explanation of code for main part of drawing

Sto: Aperture Stop

G1: first lens from the object side

G2: second lens from the object side

G3: third lens from the object side

G4: fourth lens from the object side

IRCF: IR Cut-off Filter

Si: i-th lens surface from the object side

Di: distance between the i th lens surface and the i + 1 th lens surface from the object side

Z: optical axis

Simg: image plane

Claims (4)

A first lens having positive refractive power and both surfaces thereof being aspherical; A second lens having a negative refractive power and an aspherical surface on both sides; A third lens having both positive refractive power and aspherical surfaces; A fourth lens having both negative refractive power and aspherical surfaces; To An ultra-small sized imaging lens for a high pixel, characterized by being configured in order from the object side in the optical axis direction to satisfy the conditional expressions 0.9 < TL / 2Y <1.0 and 0.25 < bf / 2Y <0.34 . The method of claim 1, wherein the power of each lens is 0.6 < f1 / f & lt; f2 / f | <1.1 and 0.6 < f3 / f <0.75 and 0.62 <| f4 / f | <, 0.55 <f1 / f < 0.85 and 0.75, including the condition 0.75 <| f2 / f | <1.3 and 0.5 < f3 / f <1.0 and 0.57 <| f4 / f | A miniature image pickup lens for high pixels, characterized by satisfying a condition of <0.9 . The ultra-small image pickup lens according to any one of claims 1 to 2, wherein all of the first to fourth lenses are plastic lenses. The ultra-small image pickup lens according to claim 1, wherein TL is 4.5 mm or less for a 1/4 inch 3 million pixel having a pixel size of 1.75 µm, and TL is 5.7 mm or less for 5 million pixels.

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