JP2003344757A - Image pickup lens unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image pickup lens unit whose optical length is made shorter with respect to a focal distance, and which has sufficient resolution and is miniaturized and thinned. <P>SOLUTION: The image pickup lens unit is equipped with a 1st lens 30, an aperture diaphragm 40 and a 2nd lens 50 successively arranged. When it is assumed that spaces between a convex surface 31 and a concave surface 32, the surface 32 and the aperture diaphragm 40, the diaphragm 40 and a concave surface 52, and the surface 52 and a convex surface 51 are d1 to d4, the radii of curvature of the surfaces 31, 32, 52 and 51 are r1 to r4, the refractive indexes of the 1st and the 2nd lenses 30 and 50 are n1 and n4, and the focal distance of an entire system is f, relation 0.057<ä(n<SB>1</SB>-1)/r<SB>1</SB>}/f<0.14, -0.14<ä(n<SB>1</SB>-1)/-r<SB>2</SB>}/f<-0.057, -0.1<ä(n<SB>4</SB>-1)/r<SB>4</SB>}/f<-0.05, -0.095<ä(n<SB>4</SB>-1)/-r<SB>5</SB>}/f<0.14 holds. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup lens unit mounted on a camera module used in a mobile terminal such as a mobile phone or a personal computer.

[0002]

2. Description of the Related Art In recent years, mobile phones, notebook computers, P
A camera module for capturing an image may be mounted on a portable electronic device such as a DA. As mobile electronic devices themselves are becoming smaller, there is an increasing demand for smaller and thinner camera modules. On the other hand, the image sensor using CCD or CMOS is VGA format (640 × 48
It has achieved a small area of 3.6 x 2.7 mm (diagonal length 4.5 mm) while maintaining high quality with 0 pixels. Not only that, but when this image sensor is mounted on a printed circuit board together with a drive circuit and a cover glass, the thickness is as thin as about 2.5 mm, which satisfies the demand for thinning.

[0003]

The image pickup lens unit described above has the following problems. That is, when using an image sensor having such a pixel density of VGA format or higher, high resolution imaging is required.
The optical system was composed of multiple lenses. Until now, V
When configuring a GA format camera module,
Whether the single lens 1 or the combination lens 2 is used depends on which of the image quality and the size is prioritized.
In addition, P has shown the light-receiving surface.

For example, when it is attempted to reduce the thickness in the optical axis direction, it is possible to use a single lens 1 as shown in FIG. 7A, but a sufficient image quality cannot be obtained. On the other hand, in order to obtain high image quality, it is conceivable to use the combination lens 2 as shown in FIG. 7B, but it has not been possible to achieve sufficient miniaturization and thinning.

Therefore, the present invention provides an imaging lens unit which can be made compact and thin by making the optical length short with respect to the focal length and having a sufficient resolution and comprising two meniscus lenses. The purpose is to do.

[0006]

In order to solve the above problems and achieve the object, the image pickup lens unit of the present invention is constructed as follows.

(1) A first lens, an aperture stop, and a second lens, which are sequentially arranged from the object side toward the image surface side, are provided, and the first lens has a convex surface on the object side and a lens surface on the image surface side. It is a meniscus lens formed as a concave surface, the second lens is a meniscus lens formed as a convex surface on the image side and a concave surface on the object side, and the distance between the convex surface and the concave surface of the first lens is d1, The distance between the concave surface of the first lens and the aperture stop is d2, the distance between the aperture stop and the concave surface of the second lens is d3, and the distance between the concave surface and the convex surface of the second lens is d.
4, the radius of curvature of the convex surface of the first lens is r1, the radius of curvature of the concave surface is r2, the radius of curvature of the concave surface of the second lens is r3, the radius of curvature of the convex surface is r4, and the refractive index of the first lens is n1 and the refractive index of the second lens are n4 and the focal length of the entire system is f, 0.057 <{(n ₁ −1) / r ₁ } / f <0.14 (1) −0 .14 <{(n ₁ −1) / − r ₂ } / f <−0.057 (2) −0.1 <{(n ₄ −1) / r ₄ } / f <−0.05 ... _{(3) -0.095 <{(n} 4 -1) / - r 5} / f <0.14 ... relationship (4) is characterized in that it holds.

(2) The imaging lens unit described in (1) above, further comprising: 0.18 <d ₁ / n ₁ f <0.3 (5) 0.03 <d ₂ / f < 0.08 (6) 0.05 <d ₃ /f<0.1 (7) 0.19 <d ₄ / n ₄ f <0.28 (8) To do.

[0009]

1 is a schematic view showing an image pickup lens unit 20 according to an embodiment of the present invention, and FIG. 2 is an explanatory view showing positions corresponding to respective parameters in the image pickup lens unit 20. The imaging lens unit 20 includes a first lens 30, an aperture stop 40, and a second lens 50 that are sequentially arranged from the object side (left side in FIG. 1) toward the image plane side (right side in FIG. 1). The focal length of the entire system is f
Has become. In addition, P has shown the light-receiving surface.

[0010] The first lens 30 is a convex surface 31 of radius of curvature _{r 1} and the object side (surface number S1), the meniscus of the refractive index _{n 1} formed image surface side as a concave surface 32 of radius of curvature _{r 2} (surface number S2) It is a lens. The second lens 50 has a convex surface 51 (surface number S5) having a curvature radius r ₅ on the image side and a curvature radius r on the object side.
Refractive index n formed as a concave surface 52 of ₄ (surface number S4)
₄ meniscus lens. The surface number of the aperture stop 40 is S3.

The distance between the convex surface 31 and the concave surface 32 of the first lens 30 is d ₁ , and the concave surface 32 of the first lens 30 and the aperture stop 40.
Is d ₂ , the distance between the aperture stop 40 and the concave surface 52 of the second lens 50 is d ₃ , and the distance between the concave surface 52 and the convex surface 51 of the second lens 50 is d ₄ .

The following relationships are established among the refractive indices n ₁ , n ₄ , radii of curvature r ₁ , r ₂ and r ₄ , r ₅ , and the intervals d _{1 to} d ₄ . That is, 0.057 <{(n ₁ −1) / r ₁ } / f <0.14 (1) −0.14 <{(n ₁ −1) / − r ₂ } / f <−0. _{057 ... (2) -0.1 <{} (n 4 -1) / r 4} / f <-0.05 ... (3) -0.095 <{(n 4 -1) / - r 5} / f <0.14 (4) 0.18 <d ₁ / n ₁ f <0.3 (5) 0.03 <d ₂ /f<0.08 (6) 0.05 <d ₃ / f <0.1 (7) 0.19 <d ₄ / n ₄ f <0.28 (8) Here, each value in FIG. 2 will be described. In Table 1, in the imaging lens unit 10, the radii of curvature r ₁ , r ₂ and r ₄ , r ₅ , the distances d _{1 to} d _{4 from} the next surface, and the refractive index n ₁ ,
n ₄ and Abbe number are shown. When the radius of curvature is R, the undulation Z at the diameter h of the aspherical surface is: Z (h) = h ² / (R · (1 + √ (1- (1 + K) h ² / R ² ))) + Ah It is represented by ⁴ + Bh ⁶ + Ch ⁸ (9). Table 1 shows an example of the values of K, A, B and C in this lens system.

[0013]

[Table 1]

This lens system has an aperture ratio F / 2.8, a focal length of 3.6 mm, and an optical system length from the lens front surface to the image surface of 5.45 mm. The lens is made of PMMA resin.
This lens system has an image size of 3.6 x 2.7 mm.
It is for (diagonal length 4.5 mm) and can capture an image with a horizontal field angle of 53.4 ° and a diagonal field angle of 64.5 °.

FIGS. 3A and 3B show the angle-of-view characteristics of spherical aberration, astigmatism, and distortion of this image pickup system.
Further, FIG. 4 is a diagram showing the spatial frequency characteristic of the MTF at each angle of view ω, that is, the characteristic effective for the VGA format sensor. In addition, T shows the characteristic in the tangential direction, and R shows the characteristic in the radial direction.

At this time, {(n ₁ -1) / r ₁ } /f=0.1247 (10) {(n ₁ -1) /-r ₂ } /f=-0.129 (11) {(N ₄ −1) / r ₄ } /f=−0.077 (12) {(n ₄ −1) / − r ₅ } /f=0.138 (13) (1) to (4) are satisfied. Under this condition, astigmatism and field curvature are small. By optimizing the aspherical surface coefficient in this state, spherical aberration and distortion can be reduced.
Further, d ₁ / n ₁ f = 0.19 (14) d ₂ /f=0.037 (15) d ₃ /f=0.07 (16) d ₄ / n ₄ f = 0.247 (17), which satisfies the equations (5) to (8). In this state, the optical length can be made compact with respect to the focal length f of the entire system.

Here, as a comparative example, each value of the combined lens 2 shown in FIG. 7B will be examined. In addition,
Consider the lens shown in Table 2 in the lens shown in FIG.

[0018]

[Table 2]

FIGS. 5A to 5C show the field angle characteristics of spherical aberration, astigmatism and distortion, and FIG. 6 shows the spatial frequency characteristics of the MTF at each field angle. It can be seen that the image quality obviously deteriorates as compared with the above-described image pickup camera unit 20.

As described above, according to the image pickup lens unit 20 of the present embodiment, the optical length can be shortened with respect to the focal length, it has sufficient resolution, and it is compact because it is composed of two meniscus lenses. It can be made thinner and thinner.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[0022]

According to the present invention, the optical length can be shortened with respect to the focal length, the optical length is sufficient, and two meniscus lenses can be used.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an imaging lens unit according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing positions corresponding to respective parameters of the imaging lens unit.

3A and 3B are diagrams showing optical characteristics of the imaging lens unit, where FIG. 3A is a spherical aberration, FIG. 3B is an astigmatism, and FIG. 3C is a distortion angle-of-view characteristic.

FIG. 4 is an MTF at each angle of view of the imaging lens unit.
The figure which shows the spatial frequency characteristic of.

5A and 5B are diagrams showing optical characteristics of an imaging lens unit in a comparative example, where FIG. 5A is a spherical aberration, FIG. 5B is an astigmatism, and FIG. 5C is a distortion angle-of-view characteristic.

FIG. 6 is an MTF at each angle of view of the imaging lens unit.
The figure which shows the spatial frequency characteristic of.

FIG. 7 is a schematic diagram showing a configuration of a conventional imaging lens unit.

[Explanation of symbols]

20 ... Imaging lens unit 30 ... First lens 31 ... Convex 32 ... concave 40 ... Aperture stop 50 ... Second lens 51 ... Convex 52 ... concave

Claims (2)

[Claims] 1. A first lens, an aperture stop, and a second lens, which are sequentially arranged from the object side toward the image surface side, wherein the first lens has a convex surface on the object side and a concave surface on the image surface side. The second lens is a meniscus lens having a convex surface on the image side and a concave surface on the object side, and the distance between the convex surface and the concave surface of the first lens is d1 and the first lens is the first lens.
The distance between the concave surface of the lens and the aperture stop is d2, the distance between the aperture stop and the concave surface of the second lens is d3, and the second distance is
The distance between the concave surface and the convex surface of the lens is d4, the radius of curvature of the convex surface of the first lens is r1, the radius of curvature of the concave surface is r2, the radius of curvature of the concave surface of the second lens is r3, and the radius of curvature of the convex surface is r4. Assuming that the refractive index of the first lens is n1, the refractive index of the second lens is n4, and the focal length of the entire system is f, then 0.057 <{(n ₁ -1) / r ₁ } / f < _{0.14 ... (1) -0.14 <{} (n 1 -1) / - r 2} / f <-0.057 ... (2) -0.1 <{(n 4 -1) / r 4 } / F <−0.05 (3) −0.095 <{(n ₄ −1) / − r ₅ } / f <0.14 (4) Lens unit. 2. Further, 0.18 <d ₁ / n ₁ f <0.3 (5) 0.03 <d ₂ /f<0.08 (6) 0.05 <d ₃ / f < The imaging lens unit according to claim 1, wherein the relationship of 0.1 (7) 0.19 <d ₄ / n ₄ f <0.28 (8) is established.