KR100920615B1 - Subminiature Optical System - Google Patents

Abstract

Provides an ultra-small imaging optical system.

The present invention provides a display device comprising: a second lens element having an object side surface bonded to an image side surface of a first lens element; And a third lens element having an object side surface bonded to the image side surface of the second lens element. And a lens group having a generally positive refractive power, including an aperture between an object side surface of the first lens element and an image side surface of the second lens element, and an object side surface of the first lens element. At least one of the image side surfaces of the third lens element is made of an aspherical surface, and the following conditional expression 1 is satisfied with respect to the shape of the third lens element with the image side surface convex toward the image side.

[Condition 1] 0.5 <│r2│ / f <0.74

Here, r2: paraxial radius of curvature of the image-side surface of the third lens element.

        f: effective focal length of the whole optical system

Imaging, optical system, lens, aperture stop, image, aspherical surface

Description

Subminiature Optical System

The present invention relates to an imaging optical system, and more particularly, is mounted on a mobile communication terminal, a PDA, and the like, to obtain a better image by increasing the resolution at the image periphery while reducing the incident angle of the periphery of the sensor while securing a wider angle of view. The present invention relates to an ultra-small imaging optical system capable of producing a small size and low cost optical system.

In general, mobile communication terminals initially had only the function of communication means. However, as the use thereof increases, required services such as photographing or image transmission or communication are diversified, and accordingly, functions and services are evolving. Recently, an expanded new concept mobile communication terminal, ie, a camera phone or a camera mobile phone, which combines digital camera technology and mobile phone technology, has been in the spotlight.

In particular, in recent years, compact, lightweight, and low cost have been strongly demanded for the imaging optical system mounted in a camera phone, and the pixel size of an image sensor such as CCD (charge coupled device) or CMOS (compensated metal semiconductor) As the size becomes smaller, higher resolution is also required for the imaging optical system using such an image sensor.

In addition, in order to satisfy the miniaturization and low cost, the imaging optical system mounted on a small device such as a mobile phone should reduce the number of lenses possible, but the degree of freedom in design becomes small and the optical performance is difficult to satisfy.

In particular, since a conventional imaging optical system is generally configured by arranging a diaphragm for adjusting the amount of light in a space outside the lens, a problem has been pointed out in terms of miniaturization and light weight.

Therefore, there is a need for an ultra-small imaging optical system capable of high resolution and excellent aberration performance and miniaturization and weight reduction.

In addition, in the case of an imaging optical system having a small aberration using a conventional sheet, the incident angle at the periphery of the sensor becomes large despite the relatively small angle of view, resulting in darkening of the brightness at the periphery of the sensor and deterioration of image periphery of the image. It acted as a factor to lower the.

The present invention has been made to solve the above problems, and as an aspect, an object of the present invention is to provide a microscopic imaging optical system that can improve the degradation of the resolution of the peripheral portion due to a serious increase in astigmatism outside the image.

In addition, another object of the present invention is to provide a microscopic imaging optical system capable of manufacturing a small-sized and inexpensive optical system while maintaining stable lens shape and optical characteristics even in a high temperature assembly process.

In order to achieve the above object, the present invention, the second lens element is bonded to the object side surface to the image surface of the first lens element; And a third lens element having an object side surface bonded to the image side surface of the second lens element. And a lens group having a generally positive refractive power, including an aperture between an object side surface of the first lens element and an image side surface of the second lens element, and an object side surface of the first lens element. At least one of the image-side surface of the third lens element is an aspherical surface, the image pickup surface is provided with an ultra-compact imaging system characterized in that the following conditional expression 1 is satisfied with respect to the shape of the third lens element convex toward the image.

[Condition 1] 0.5 <│r2│ / f <0.74

Where r2 is the paraxial curvature radius of the image-side surface of the third lens element, and f is the effective focal length of the entire optical system.

Preferably, the following Conditional Expression 2 is satisfied with respect to the length of the optical system.

[Condition 2] 0.59 <BFL / TTL <0.7

Here, BFL: distance from the image side surface of the third lens element to the image surface, and TTL: distance from the object side surface of the first lens element to the image surface.

Preferably, the following conditional expressions 3 and 4 are satisfied with respect to the material of the first and third lens elements.

[Condition 3] N> 1.4

[Condition 4] Vd> 33

Where N is the refractive index of the lens element and Vd is the Abbe's number of the lens element.

More preferably, the first and third lens elements are provided in a replica manner based on the UV curing polymer.

Preferably, the aperture stop is provided with a metal coating layer on the object-side surface of the second lens element.

Preferably, the aperture stop is provided with a photosensitive resin layer on the object side surface of the second lens element.

Preferably, the second lens element is provided with a filter member on either the object side surface or the image side surface.

 According to the present invention, an aperture diaphragm is disposed inside the lens, and the image side surface is convex toward the image side, and the lens group has positive refractive power, thereby reducing the incident angle of the sensor periphery while securing a wider angle of view, and at the same time, off-axis aberration. Can be properly corrected, so that the resolution at the periphery of the image can be increased to obtain a better image, and the effect of producing a small size and low cost optical system can be obtained.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a lens configuration diagram showing a first embodiment of a microscopic imaging optical system according to the present invention, and FIG. 3 is a lens configuration showing a second embodiment of the microscopic imaging optical system according to the present invention.

In the following lens configuration, the thickness, size, and shape of the lens have been somewhat exaggerated for explanation, and in particular, the shape of the spherical or aspherical surface shown in the lens configuration is merely an example and is not limited thereto.

As shown in FIGS. 1 and 3, the microscopic imaging optical system according to the exemplary embodiment of the present invention has an image sensor corresponding to the lens group LG and the image surface IP including the aperture stop AS in order from the object side. (Not shown).

The lens group LG has a positive refractive power as a whole, a second lens element L2 having an object side surface bonded to an image side surface of the first lens element L1, and an image side of the second lens element L2. The object-side surface is bonded to the surface, and the image-side surface is provided with a third lens element L3 having a shape which is convex toward the image side on the optical axis, and is composed of three lens elements as a whole.

Here, the object-side surface and the image-side surface of the second lens element (L2) is provided in a plane, the first lens element (L1) and the second bonded to the object-side surface of the second lens element (L2). Although the second lens element L3 bonded to the upper surface of the lens element L2 is illustrated and described as being made of all aspherical surfaces, the present invention is not limited thereto, and any one of them may be provided as an aspherical surface.

That is, the lens group LG may be formed at both side plane portions of the second lens element L2 corresponding to the transparent lens substrate to form the first lens element L1 and the third lens element L3. Each of the polymers having excellent heat resistance may be provided using a replica method of laminating them. As described above, the manufacturing of the wafer scale lens using the replica method has the advantage of easy mass production.

However, if at least one lens element among the first lens element L1, the second lens element L2, and the third lens element L3 may have a different refractive index from that of the other lens element LG, It is not limited to what is manufactured by such a replica method.

In addition, an aperture diaphragm AS is provided between the first lens element L1 and the second lens element L2 to adjust the amount of light. The aperture diaphragm reduces the installation space, thereby reducing the size of the optical system and assembling. In order to improve the performance, it is preferable to be provided integrally with a flat portion formed on the object side surface of the second lens element (L2).

The aperture stop AS may be formed of a metal coating layer made of a metal such as aluminum (Al) or chromium (Cr), but may be formed of a resin composition such as black photo-resist. It is preferable that the photoresist layer is formed integrally on the object side surface of the second lens element L2 corresponding to the lens substrate using the photoresist as a material.

Specifically, in the case of forming the aperture stop (AS) with a metal coating layer such as aluminum (Al) or chromium (Cr), since the adhesion to the UV-curable polymer is inferior due to the high hydrophobicity of the metal coating layer, a separate adhesion on the metal film Film formation is required.

In addition, in the case of forming the aperture stop AS with the photosensitive resin layer, since the adhesiveness with the UV curable polymer is excellent due to the high hydrophilicity of the photosensitive resin, there is no need to further form an adhesive film on the photosensitive resin layer.

On the other hand, when the aperture stop AS is formed of the metal coating layer, the sequential steps of exposure, metal film deposition, and metal film removal are necessary. However, when the aperture stop AS is formed of the photosensitive resin layer, the aperture stop AS is formed due to the characteristics of the photosensitive resin. The aperture stop AS can be formed only by the exposure process, and manufacturing cost and time can be shortened.

Meanwhile, an optical filter (not shown) made of an infrared filter, a cover glass, or the like may be provided between the lens group LG and the image surface IP of the image sensor.

Here, the optical filter may be provided between the second lens element (L2) and the third lens element (L3) in order to reduce the installation space to reduce the overall size of the optical system, and improve the assembling, in particular the 2 is preferably provided integrally with a flat portion formed on the image surface of the lens element (L2).

In addition, the image sensor corresponds to the upper surface IP, and consists of a CCD (charge coupled device) or a CMOS (compensation fast semiconductor) to detect an optical image passing through the lens group LG and convert it into an electrical signal.

Look at the effect of the following Conditional Expressions 1 to 4 under such an overall configuration.

[Condition 1] [Condition 1] 0.5 <│r2│ / f <0.74

Here, r2 is the paraxial curvature radius of the image-side surface of the third lens element L3, and f is the effective focal length of the whole optical system.

If the upper limit of Conditional Expression 1 is out of the range, the resolution of the peripheral portion of the image is lowered, and if the lower limit is removed, the shaping of the image side surface of the third lens element becomes difficult.

[Condition 2] 0.59 <BFL / TTL <0.7

Here, BFL is the distance from the image side surface of the third lens element L3 to the image surface IP, and TTL is the distance from the object side surface of the first lens element L1 to the image surface IP.

If it is out of the upper limit of Conditional Expression 2, the total length of the optical system becomes long, and the miniaturization design becomes difficult. If it is out of the lower limit, correction of the off-axis aberration is difficult, and the resolution of the image periphery is reduced.

[Condition 3] N> 1.4

Where N is the refractive index of the lens group consisting of the first, second and third lens elements.

[Condition 4] Vd  > 33

Here, Vd is the Abbe's number of the lens group consisting of the first, second and third lens elements.

Outside the lower limits of Conditional Expressions 3 and 4, chromatic aberration is increased, resulting in color degradation and material cost increase in the high resolution sensor.

The aspherical surface used in each of the following examples is obtained from known equation (1).

Z: Distance from the vertex of the lens to the optical axis direction

Y: distance in the direction perpendicular to the optical axis

c: inverse of the radius of curvature r at the vertex of the lens

K: Conic constant

A, B, C, D, E, F: Aspheric coefficient

[First Example ]

Table 1 below shows numerical examples according to the first embodiment of the present invention.

1 is a lens configuration diagram of a microscopic imaging optical system according to a first embodiment of the present invention, and FIG. 2 shows a first aberration diagram of the first embodiment shown in FIG. 1, and (a) shows spherical aberration. , (b) are astigmatism, and (c) are distortion graphs.

In the following astigmatism diagram, "S" represents sagittal and "T" represents tangential.

In the first embodiment, the angle of view is 60 degrees, the F number FNo is 3.0, and the distance BFL from the object-side surface of the third lens element L1 to the image surface IP is 1.5276 mm. The distance TTL from the object-side surface of the first lens element L1 to the image surface IP is 2.546 mm, and the effective focal length f of the optical system is 1.5 mm.

In Table 1, the unit of curvature radius R and thickness or distance D is mm.

In addition, in Table 1, * denotes an aspherical surface, and in the first embodiment, the object side surface 1 of the first lens element L1 and the image side surface 4 of the third lens element L3 are aspherical surfaces.

The aspherical coefficients of Example 1 according to Equation 1 are shown in Table 2 below.

[Second Example ]

Table 3 below shows a numerical example according to the second embodiment of the present invention.

3 is a lens configuration diagram of the ultra-small imaging optical system according to the second embodiment of the present invention, and FIG. 4 is a view showing the aberration diagram of the second embodiment shown in FIG. (b) is astigmatism and (c) is a graph showing distortion, respectively.

In the second embodiment, the angle of view is 60 degrees, the F number FNo is 3.0, and the distance BFL from the object-side surface of the third lens element L1 to the image surface IP is 1.66896 mm. The distance TTL from the object-side surface of the first lens element L1 to the image surface IP is 2.736 mm, and the effective focal length f of the optical system is 1.4 mm.

In Table 3, the unit of curvature radius R and thickness or distance D is mm.

In Table 3, * denotes an aspherical surface, and in Embodiment 2, the object side surface 1 of the first lens element L1 and the image side surface 4 of the third lens element L3 are aspherical.

The aspherical coefficients of Example 2 according to Equation 1 are shown in Table 4 below.

On the other hand, the values of Conditional Expression 1 and Conditional Expression 2 for the first and second embodiments are as shown in Table 5 below.

As shown in FIG. 2 and FIG. 4, it can be confirmed through the embodiments that a microscopic imaging optical system capable of obtaining a microscopic imaging optical system having excellent characteristics of the aberration is obtained.

As mentioned above, although this invention was demonstrated in detail using the preferable Example, the scope of the present invention is not limited to a specific Example and should be interpreted by the attached Claim. In addition, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

1 is a lens configuration diagram of a microscopic imaging optical system according to a first embodiment of the present invention.

FIG. 2 shows the aberration diagram of the embodiment shown in FIG. 1;

   (a) shows spherical aberration, (b) shows astigmatism, and (c) shows distortion.

3 is a lens configuration diagram of a microscopic imaging optical system according to a second embodiment of the present invention.

4 is a view illustrating the aberration diagram of the embodiment illustrated in FIG. 3;

   (a) shows spherical aberration, (b) shows astigmatism, and (c) shows distortion.

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

L1: first lens element L2: second lens element

L3: third lens element AS: aperture diaphragm

IP: Upper surface 1,2,3,4: Surface number

Claims (7)

A second lens element in which an object side surface is bonded to an image side surface of the first lens element; And A third lens element in which an object side surface is bonded to an image side surface of the second lens element; Including a lens group having a positive refractive power as a whole, An aperture is provided between the object side surface of the first lens element and the image side surface of the second lens element, and at least one of the object side surface of the first lens element and the image side surface of the third lens element is an aspherical surface. And the following conditional expression 1 is satisfied with respect to the shape of the third lens element whose image side surface is convex toward the image side. [Condition 1] 0.5 <│r2│ / f <0.74 Here, r2: paraxial radius of curvature of the image-side surface of the third lens element.         f: effective focal length of the whole optical system The method of claim 1, The ultra-small imaging optical system which satisfy | fills following Conditional expression 2 regarding the length of an optical system. [Condition 2] 0.59 <BFL / TTL <0.7 Here, BFL: distance from the image side surface to the image surface of the third lens element         TTL: distance from the object-side surface to the image surface of the first lens element The method of claim 1, And the following conditional expressions 3 and 4 are satisfied with respect to the material of the first and third lens elements. [Condition 3] N> 1.4 [Condition 4] Vd> 33 Where N is the refractive index of the lens element,         Vd: Abbe number of lens elements The method according to claim 1 or 3, The first and third lens elements are microscopic imaging optical system, characterized in that provided in a replica method using a UV-curing polymer material. The method of claim 1, And the aperture stop is provided with a metal coating layer on the object-side surface of the second lens element. The method of claim 1, And the aperture stop is provided with a photosensitive resin layer on the object-side surface of the second lens element. The method of claim 1, The second lens element is a miniature optical system, characterized in that the filter member is provided on any one of the object side surface or the image side surface.

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