JP2001221904A - Lens, lens device, camera module and electric appliance equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system for a mobile terminal having enough brightness and resolution and a short optical path length. SOLUTION: The optical system is equipped with an image pickup system consisting of a lens 1 made of an acrylic resin PMMA with a concave face in the incident side for light and a convex face in the outgoing side for the light, an aperture stop 2 disposed in the entrance side for light of the lens 1 to cover the periphery of the optical face of the incident side for the light of the lens 1, and a field stop 3 to receive the light outgoing from the lens 1 and to shade the light at a specified or larger view angle of the outgoing light. Thus, 5.5 mm length of the optical system is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a portable electric device such as a portable telephone or a personal computer, and more particularly to an image pickup system mounted on a camera module mounted thereon.

[0002]

2. Description of the Related Art In recent years, camera modules for capturing images have been mounted on portable terminals such as portable telephones and notebook computers. In addition, mobile terminals themselves are continually being miniaturized. Accompanying this, there is an increasing demand for downsizing camera modules. On the other hand, CCD (Charge
Image sensors using Coupled Device) or CMOS
VGA format (640X480 pixels) and high quality, but 3.6X
It has realized a small area of 2.7mm (4.5mm diagonal). In addition, when this image sensor is mounted on a printed circuit board together with a drive circuit and a cover glass,
Its thickness is as thin as about 2.5 mm. VGA like this
When using an image sensor with a pixel density higher than that of the format, it is of course possible to take advantage of this.
A high-resolution imaging optical system is required. Such an optical system has conventionally been constituted by a plurality of lenses. For example, VG
When an image sensor having an image size of 3.6 × 2.7 mm in the A format is used, an optical system as shown in FIG. 6 is used. An imaging system 20 composed of these two lenses
Has an aperture ratio of F / 2.8, a focal length of 3.45 mm, and an optical system length L from the lens tip to the image plane of 5.93 mm. The field of view is 56 ° in horizontal angle and 67 ° in diagonal angle, including distortion. When this imaging system is a camera module, the thickness from the lens barrel to the back of the sensor is 8.9mm (= 5.93 + 2.5 + 0.5
(Projection of lens barrel)).

[0003]

By the way, for example,
When the above optical system is mounted on a 10.5 mm thick mobile phone composed of a 0.9 mm thick housing, the thickness of the space surrounded by the housing is about 8.7 mm, so the thickness in the optical axis direction However, a camera module of about 8.9 mm cannot be mounted on such a mobile phone. Therefore, for a camera module mounted on such a small portable terminal, the thickness in the optical axis direction needs to be at least 8.5 mm or less, and it fluctuates depending on the configuration of the wiring board and the like. It is required that the length is about 6.0 mm or less, including the length of the protruding portion of the lens barrel that protects the imaging system. In addition, the diameter of the lens itself is shortened by shortening the length of the imaging system to 6.0 mm or less, but it is difficult to mold a lens surface with a diameter of 1 cm or less into a highly accurate aspherical shape, The lens surface shape with good moldability is required. Therefore, an object of the present invention is to provide a lens and a camera module applicable to such a case, and an electric apparatus including the same.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is a single-lens, double-sided aspherical meniscus lens having a refractive index of n, a center thickness of t, and a radius of curvature of a concave surface. When r1, the radius of curvature of the convex surface is r2, and the focal length of the lens is f, the refractive index of the lens is n, the center thickness is t, the radius of curvature of the concave surface is r1, the radius of curvature of the convex surface is r2, and the focal length of the lens is f Are provided, respectively.
Further, the lens, an aperture stop provided on the incident surface side of the lens and restricting light incident on the lens, a lens barrel holding the aperture stop and the lens, and a hollow portion formed by the lens barrel An image sensor fixed to face the
And a camera module comprising: I will provide a. A lens device comprising: a lens; and an aperture stop provided on an incident surface side of the lens and configured to limit light incident on the lens, wherein the lens has a meniscus surface having a convex surface on an image surface side. An aspherical single lens having a refractive index n of the lens, a center thickness t, a radius of curvature r1 of a concave surface, a radius of curvature r2 of a convex surface, and a focal length f of the lens device, And a distance d1 between the concave surface of the lens and the aperture stop, Are provided, respectively. Further, the present invention provides a portable electric device that performs a predetermined operation, and includes the camera module mounted on a circuit board included in the electric device.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a camera module for a portable terminal according to the present invention will be described with reference to the drawings. The camera module shown in the sectional view of FIG. 1 includes an imaging system 10 and a photoelectric conversion unit 11. The imaging system 10 includes a lens 1 made of an acrylic resin PMMA having a concave surface on the incident light side and a convex surface on the outgoing light side, and is disposed on the incident light side of the lens 1 and has an optical surface periphery on the incident light side of the lens 1. And a field stop 3 that receives light emitted from the lens 1 and blocks light having a predetermined angle of view or more from the emitted light. The aperture stop 2 and the field stop 3 are supplied as components integrally formed with the lens barrel 4. The lens barrel 4 is formed by coloring a material such as an epoxy resin so as to prevent unnecessary light from being incident thereon, dividing the material in the optical axis direction, performing injection molding, and integrating the same with the lens 1 interposed therebetween. The light formed by the field stop 3 and taken out of only light having a predetermined angle of view that can reach the image plane linearly forms an image on an image plane separated by a predetermined distance. The photoelectric conversion unit 11 is arranged on this image plane.

As the photoelectric conversion means, an image sensor 5 such as a CCD or CMOS sensor capable of outputting an electric signal expressed in gradation is used. The image sensor 5 is mounted on a wiring board 6 on which a circuit for processing an electric signal output from the image sensor 5 is formed. Note that the imaging system 10 may be configured such that a field stop and a lens barrel are provided for a lens device obtained by integrating the lens 1 and the aperture stop 2 in advance.

Table 1 shows the radius of curvature, the distance from the next surface, the refractive index, the Abbe number, and the effective diameter of each surface of the imaging system according to the definition of each surface and each parameter in the schematic diagram shown in FIG. .

When the radius of curvature is R, the undulation Z at the diameter h of the aspheric surface is generally expressed by the following equation (1). Table 2 shows K, A, B, and C corresponding to the aspherical surface of the lens 1 at this time. With the configuration described above, the imaging system 10 of the present invention has a relatively bright and high-resolution imaging characteristic capable of supporting VGA,
The aperture ratio is F / 2.8, the focal length is 3.55 mm, and the optical system length from the aperture stop to the image plane is 5.526 mm. This imaging system 10
Is for an image size of 3.6 × 2.7 mm (4.5 mm diagonal) and can capture an image with a horizontal angle of view of 56 ° and a diagonal angle of view of 70 °. This angle of view is a value set in consideration of the distortion, and light rays exceeding this angle of view may cause disturbance.

FIG. 3 shows the spherical aberration, astigmatism,
FIG. 4 is a graph showing the angle of view characteristics of the distortion, and FIG. 4 is a graph showing the spatial frequency characteristics of the MTF (Modulation Transfer Function) at each angle of view, where the optical system of this embodiment is effective for a VGA format sensor. Is shown.

In order to obtain effective characteristics for the VGA format sensor as described above, in the definition according to FIG.
It has been confirmed that the lens preferably has a configuration satisfying at least the expressions (2) to (4). Regarding the lens of the present embodiment, the values based on the expressions (2) to (4) are -0.0220, 0.0805, and 0.507, respectively, and the meniscus lens satisfies the expressions (2) to (4). It was confirmed that it was suitable for an image sensor with an image size of 3.6X2.7mm. By designing the lens surface such that the lens surface satisfies the expressions (2) to (4), it is possible to configure a ridge line at an arbitrary cross section of the lens surface in a monotonous shape having no inflection point. became.

Further, it has been confirmed that, when the relationship between the lens and the aperture stop satisfies the expression (5), the aspherical shape of the lens surface is further simplified, and the lens surface is easily formed. The value in the camera module of the above embodiment is 0.028, which satisfies the expression (5).

As described above, when the lens surface satisfies the expressions (2) to (4), particularly when the optical system is assembled, and the expression (5) is also satisfied, a small lens surface having a diameter of 1 cm or less is obtained. It is possible to relatively easily mass-produce even a lens having. In addition, by performing imaging using such a lens, an image having a small spherical aberration can be obtained with a short focal length even in an optical system having a total length of 6 mm or less, and the camera can be manufactured without impairing the portability of electric equipment. Modules can be mounted.

When a camera module for a portable terminal is formed using this single lens, in order to reduce the size of the camera module, one aspheric meniscus lens is used, and an aperture stop is formed from the object side toward the image plane. A lens and a field stop were arranged, and the lens had a convex surface on the image side. As described above, in an imaging system in which the distance from the aperture stop to the image plane is short, it is preferable to provide a field stop in order to prevent incident light having an angle of view more than necessary from being incident on the image plane irrespective of the imaging operation. Furthermore, when this lens is incorporated into an imaging system to form a camera module, it is difficult to obtain such characteristics with a lens having a biconvex optical surface, and the convex is arranged on the image surface side using a meniscus lens. It has been confirmed that it is preferable to do so. In addition, since the lens is formed by injection molding of a resin material, an aspherical shape can be formed with higher precision, despite having a small lens surface.

When this camera module is built in not only a telephone but also an electronic device which performs each predetermined operation with an emphasis on portability, such as a personal computer having portability, a good image quality can be obtained without impairing portability. Can be provided. As one mode of such portable electrical equipment, FIG. 5 shows a schematic view of a telephone equipped with the camera module.

The telephone has an antenna 61 for transmitting and receiving radio waves, a radio unit 62 connected to the antenna 61 for converting radio signals into electric signals, and a speaker or microphone connected to a voice or electric signal. A communication circuit 63 for performing mutual conversion, a memory 64 for always storing temporary storage required when processing electric signals in the telephone, a desired telephone number, and the like; and a camera module shown in the above embodiment. 65, a control circuit 66 for integrally controlling them and enabling communication, and a key input unit 67 for arbitrarily controlling the control circuit 66 are mounted on a wiring board to constitute a circuit board; This is housed in a housing. With such a configuration, it is possible to transmit not only voice information realized by a normal telephone but also image information.

In addition, by mounting a display for displaying a received video signal in the control circuit 66, image information can be exchanged and via a connector 68 provided to be connectable to an external device. For example, it is possible to output video information to a personal computer or the like. It is assumed that the external device is a device that does not need to be portable. In that case, the video information projected by the device is an area formed by the display device of the device, for example, a large screen with a diagonal of 30 cm or more. Is also assumed. Even in such a case, since the image captured by the camera module 65 using the lens of the present invention has a low spherical aberration and is suppressed, it is possible to provide an image with less blur and an easily distinguishable display target. Becomes

As described in detail above, according to the present embodiment, spherical aberration and astigmatism can be made relatively small, and high-resolution imaging with a single lens becomes possible. In addition, by incorporating the above-described camera module into an electronic still camera, a mobile phone, or a computer, thinner products can be mass-produced and portability can be improved.

[0018]

As described above in detail, the present invention can provide a compact optical system capable of high-resolution imaging with a single aspherical lens, and can improve the portability of electrical equipment for handling image information. Can contribute.

[Brief description of the drawings]

FIG. 1 is a sectional view of a camera module of the present invention.

FIG. 2 is a schematic diagram of an imaging system of the camera module of the present invention.

FIG. 3 is a graph showing characteristics of the camera module of the present invention.

FIG. 4 is a graph showing characteristics of the camera module of the present invention.

FIG. 5 is a schematic view of a mobile phone equipped with the camera module of the present invention.

FIG. 6 is a schematic diagram of an imaging system of a conventional camera module.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... lens, 2 ... aperture stop, 3 ... field stop, 4 ... lens barrel,
5 image sensor, 6 wiring board, 10, 20 imaging system, 11 photoelectric conversion unit

Claims (4)

[Claims] 1. A meniscus lens having a single element and a double-sided aspheric surface, wherein the refractive index of the lens is n, the center thickness is t, the radius of curvature of the concave surface is r1, the radius of curvature of the convex surface is r2, and the focal length of the lens is f. When , Respectively. 2. The lens according to claim 1, an aperture stop provided on an incident surface side of the lens, for limiting light incident on the lens, a lens barrel holding the aperture stop and the lens, A camera module comprising: an image sensor fixedly opposed to a hollow portion formed by the lens barrel. 3. A lens device comprising: a lens; and an aperture stop provided on an incident surface side of the lens and for limiting light incident on the lens, wherein the lens has a meniscus having an image surface side as a convex surface. Is a single lens with a double-sided aspheric surface, having a refractive index n of the lens, a center thickness t, a radius of curvature r1 of a concave surface, a radius of curvature r2 of a convex surface, and a focal length of the lens device as f. And a distance d1 between the concave surface of the lens and the aperture stop, Wherein each of the lens devices is satisfied. 4. A portable electric device for performing a predetermined operation, comprising: the camera module according to claim 2 mounted on a circuit board of the electric device. .