KR100843465B1 - Subminiature optical system - Google Patents

Abstract

A subminiature optical system is provided to improve resolution and implement miniaturization by using only a single lens group. A subminiature optical system includes a single lens group(LG) which entirely has positive refractive power and includes a first lens element(L1), a second lens element(L2), and a third lens element(L3). An object side surface of the first lens element is convex toward an object on an optical axis. An object side surface of the second lens element is bonded to an upper surface of the first lens element. An object side surface of the third lens element is bonded to an upper surface of the second lens element. An upper surface of the third lens element is convex upward on the optical axis. An aperture stop(AS) is provided between the first and second lens elements to adjust light intensity.

Description

Subminiature Optical System

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

FIG. 2 illustrates a first aberration diagram of the first embodiment shown in FIG.

   (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.

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

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

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

FIG. 6 illustrates a third aberration diagram of the third embodiment illustrated in FIG. 5.

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

Explanation of symbols on the main parts of the drawings

L1 ... first lens element L2 ... second lens element

L3 ... 3rd lens element LG ... lens group

AS ... opening aperture IP ... top

1,2,3,4 ... face number

The present invention relates to an imaging optical system, and more particularly, by using only one lens having three lens elements, mounted on a mobile communication terminal, PDA, etc. having excellent optical performance and small size, or a surveillance camera, a digital camera, or the like. It relates to an ultra-small imaging optical system used.

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, small size, light weight, and low cost are 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 it becomes smaller, high resolution is also required for imaging optical systems using such an image sensor.

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

Therefore, there is a need for a microscopic imaging optical system capable of miniaturization while having high resolution and excellent aberration performance.

As such a microscopic imaging optical system, Japanese Patent Laid-Open No. 2004-109532 (published on April 4, 2004) includes a lens having a convex lens surface on the object side, includes an aperture diaphragm inside the lens, and an object side lens of the lens. Disclosed are a group 1 lens in which one of a surface and an image lens surface is formed as an aspherical surface.

In this lens, f is the focal length of the lens of the optical system, and if R1 is the radius of curvature of the object-side lens surface, the conditional expression of 0.35f <R1 <f must be satisfied.

However, if the value is out of the lower limit, the overall length becomes longer and the surface machining of the lens side of the object becomes difficult. If the value is out of the upper limit, the length is shortened, but the off-axis aberration cannot be corrected. There was a problem that the image quality is reduced.

In addition, in such a lens, although the angle of view is relatively small, the incident angle at the outside of the image sensor is increased so that the brightness is dark at the periphery of the image sensor.

The present invention is to solve the above problems, the object of which is to use a single lens is made of a very small, while reducing the angle of incidence at the periphery of the image sensor in the extended view angle to correct the off-axis aberration to improve the image quality The present invention seeks to provide an ultra-small imaging optical system that can be increased and is easy to mass-produce, and excellent in various optical performances.

In order to achieve this object, the present invention provides a first lens element in which the object side surface is convex toward the object side on the optical axis, a second lens element in which the object side surface is bonded to the image side surface of the first lens element, and the object side surface is A lens group bonded to an image side of the second lens element, the image side having a third lens element convex upward on the optical axis and having a positive refractive power as a whole; the first lens element and the second lens An aperture diaphragm for adjusting the amount of light is provided between the elements, and the following conditional expression 1 is satisfied with respect to the dimension in the optical axis direction, and the following conditional expression 2 is satisfied with respect to the radius of curvature, thereby providing a microscopic imaging optical system.

Condition 1 0.9 <T / bfl <1.7

[Condition 2] 0.65 <| r1 / r2 | <1.5

Where T is the distance from the object side surface of the first lens element to the image side surface of the third lens element, bfl is the distance from the image side surface to the image surface of the second lens element, r1 is the object side surface of the first lens element. Is the radius of curvature of r2: the radius of curvature of the image-side surface of the third lens element.

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

More preferably, the first and third lens elements are provided in a replica manner using a polymer material.

Further, preferably, the aperture stop is integrally provided in a plane formed on the object-side surface of the second lens element.

More preferably, the aperture stop is provided with a metal coating layer or a photosensitive resin layer.

Further, preferably, the position of the aperture stop satisfies the following conditional expression (5).

[Condition 5] 0.06 <d <0.25

Where d is the distance from the object-side surface of the first lens element to the aperture stop.

Further, preferably, an optical filter is further provided between the second lens element and the third lens element, and the optical filter is integrally provided on an image side surface of the second lens element.

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. 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 FIG. 1, the microscopic imaging optical system according to an exemplary embodiment of the present invention includes an image sensor corresponding to an aperture stop AS, a lens group LG, and an image surface IP in order from an object side. C).

The lens group LG has a positive refractive power as a whole, a first lens element L1 having an object-side surface convex toward the object side on the optical axis, and an object-side surface on the image side surface of the first lens element L1. The second lens element L2 to be bonded thereto, and a third lens element L3 having an object-side surface bonded to an image side surface of the second lens element L2 and having an image side convex toward the image side on the optical axis. Thus, it consists entirely of three lens elements.

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 lens bonded to the object-side surface of the second lens element (L2). Although the second lens element L3 bonded to the image-side surface of the 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.

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.

Here, the photosensitive resin refers to a polymer or a polymer composition in which a change in molecular structure occurs due to the action of light, and as a result, a change in physical properties occurs.

The components of the photosensitive resin are represented by a polymer, a solvent, and a photosensitizer, and are divided into a positive photosensitive resin and a negative photosensitive resin according to the developed form. In the case of the positive photosensitive resin, the exposed region disappears after development, and in the case of the negative photosensitive resin, the exposed region remains after development.

It is preferable that the light absorption in the visible light region of the photosensitive resin layer forming the aperture stop AS is 95% or more.

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 Preferably, the two lens element L2 is provided integrally with a flat portion formed on the image side surface.

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

The optical system according to the present invention can realize miniaturization by shortening the total length of the optical system through the lens group LG having a strong positive refractive power, and reduce off-axis aberration while reducing the angle of incidence of the peripheral part of the image in a more extended view angle. It can be improved.

In addition, as shown in FIG. 1, the lens group LG according to the present invention includes the first lens element L1 and the third lens element L3 on the object side surface and the image side surface of the second lens element L2, respectively. ) Is bonded and provided with one lens.

In this case, the lens group LG may be formed in both planar 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, manufacturing a wafer-scale lens using a replica method has the advantage that mass production is easy and the lens is formed when the SMT process is applied to reduce the cost of manufacturing a camera module for a mobile phone by forming the lens from a polymer material having excellent heat resistance. It has the advantage of preventing the breakdown phenomenon.

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.

That is, if aberration correction such as chromatic aberration can be made by differently forming a refractive index of some of the three lens elements constituting the lens group LG, the lens LG according to an embodiment of the present invention may be manufactured by conventional bonding lenses. It may be produced by a method.

In addition, the ultra-small imaging optical system according to the present invention is excellent in aberration characteristics by forming a curved surface aspherical surface and optimizing the radius of curvature of the refractive surface, it is possible to implement a high resolution.

In the lens group LG according to the present invention, both the object-side surface and the image-side surface of the second lens element L2 are formed in a plane, so that the first lens elements are respectively formed on both surfaces of the second lens element L2 by a replica process. And forming a second lens element, respectively, and then dicing the second lens element consisting of a lens substrate to produce a lens group.

In addition, there is an advantage that the image side surface of the third lens element (L3) is formed in a curved surface to maximize the resolution.

In addition, the optical system according to the present invention uses only one lens group LG and the aperture stop and the optical filter are integrally provided in the lens group, thereby minimizing the size of the optical system.

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

[Condition 1] 0.9 <T / bfl  <1.7

Here, T is the distance from the object side surface of the first lens element (L1) to the image side surface of the third lens element (L3), which is also the center thickness of the lens group LG, bfl is the The distance from the top face to the top face.

Condition 1 is a ratio of the distance of the second lens element L2 to the thickness of the lens group, and if it is outside the lower limit of Condition 1, the distortion aberration becomes worse, and if it is out of the upper limit, the incident angle of the chief-ray sensor becomes larger and the upper surface (IP The periphery of) darkens.

[Condition 2] 0.65 <| r1 // r2 | <1.5

Here, r1 is the radius of curvature of the object-side surface of the first lens element (L1), r2 is the radius of curvature of the image-side surface of the third lens element (L3).

Outside the lower limit of Conditional Expression 2, the incident angle of the chief ray sensor becomes large, and the periphery of the upper surface IP becomes dark.

[Condition 3] N> 1.4

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

[Condition 4] Vd  > 33

Where Vd is the Abbe's number 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.

[Condition 5] 0.06 <d <0.25

Here, d is the distance from the object side surface of the first lens element L1 to the aperture stop AS.

Condition Equation 5 relates to the position of the aperture stop AS. When the deviation from the lower limit of Condition Equation 5 is met, the first lens element L1 and the third lens are respectively formed on the object-side surface and the image-side surface of the second lens element L2. When the element L3 is hard to harden, it causes hardening, and when it is out of the lower limit, the object side of the second lens element L2 is made of polymer material as the first and third lens elements L1 and L3. It becomes difficult to shape the lens to be integrally bonded to the surface and the image side, respectively.

Hereinafter, the present invention will be described with reference to specific numerical examples.

As described above, the following first to third embodiments are all provided with an image sensor (not shown) corresponding to the aperture stop AS, the lens group LG, and the image surface IP in order from the object side.

The lens group LG has a positive refractive power as a whole, a first lens element L1 having an object-side surface convex toward the object side on the optical axis, and an object-side surface on the image side surface of the first lens element L1. The second lens element L2 to be bonded thereto, and a third lens element L3 having an object-side surface bonded to an image side surface of the second lens element L2 and having an image side convex toward the image side on the optical axis. Thus, it consists entirely of three lens elements.

In addition, the image sensor is positioned on an image surface IP, and an aperture stop AS is provided between the first lens element L1 and the second lens element L2, and the third lens element L3 and the image surface ( Between the IP) or between the second lens element L2 and the third lens element L3, an optical filter made of an infrared filter, a cover glass, or the like may be provided.

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, wherein (a) shows spherical aberration, (b) shows astigmatism and (c) shows distortion. 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 3.2, and the distance TTL from the object-side surface of the first lens element L1 to the image surface IP is 2.34661 mm. The effective focal length f of the optical system is 1.546 mm, the distance bfl from the image side surface of the second lens element LG2 to the image surface IP is 0.897 mm, and the object of the first lens element L1. The distance d from the side to the aperture stop AS is 0.2 mm.

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

In Table 1, * denotes an aspherical surface. In the first embodiment, an object side surface of the first lens element and an image side surface of the third lens element 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 a microscopic imaging optical system according to a second exemplary embodiment of the present invention, and FIG. 4 is a diagram illustrating a first aberration diagram of the second exemplary embodiment illustrated in FIG. 3, wherein (a) represents spherical aberration, (b) shows astigmatism and (c) shows distortion.

In the second embodiment, the angle of view is 60 degrees, the F number FNo is 3.0, and the distance TTL from the object-side surface of the first lens element L1 to the image surface IP is 2.332189 mm. The effective focal length f of the optical system is 1.523 mm, the distance bfl from the image side surface of the second lens element LG2 to the image surface IP is 0.875 mm, and the object of the first lens element L1. The distance d from the side to the aperture stop AS is 0.197 mm.

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

In Table 3, * denotes an aspherical surface. In Example 2, an object side surface of the first lens element and an image side surface of the third lens element are aspherical surfaces.

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

[Third Example ]

Table 5 below shows a numerical example according to the third embodiment of the present invention.

5 is a lens configuration diagram of a microscopic imaging optical system according to a third exemplary embodiment of the present invention, and FIG. 6 is a third aberration diagram of the third exemplary embodiment shown in FIG. 5, wherein (a) represents spherical aberration, (b) shows astigmatism and (c) shows distortion.

In the third embodiment, the angle of view is 60 degrees, the F number FNo is 3.0, and the distance TTL from the object-side surface of the first lens element L1 to the image surface IP is 2.3171 mm. The effective focal length f of the optical system is 1.523 mm, the distance bfl from the image side surface of the second lens element LG2 to the image surface IP is 1.178 mm, and the object of the first lens element L1. The distance d from the side to the aperture stop AS is 0.22 mm.

In Table 5, the unit of curvature radius R and thickness or distance t is mm.

In Table 5, * denotes an aspherical surface. In the third embodiment, an object side surface of the first lens element and an image side surface of the third lens element are aspherical surfaces.

The aspherical coefficients of the third embodiment according to Equation 1 are shown in Table 6 below.

On the other hand, the values of Conditional Expression 1 and Conditional Expression 2 for the above first to third embodiments are shown in Table 7 below.

As shown in FIG. 2, FIG. 4, and FIG. 6, it can be confirmed that the ultra-small imaging optical system excellent in the characteristic of the aberration can be obtained through the above embodiments.

While the invention has been shown and described with respect to particular embodiments, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention as set forth in the claims below. I want to make it clear.

As described above, according to the present invention, an ultra-small imaging capable of efficiently correcting various aberrations such as chromatic aberration, distortion aberration, astigmatism, spherical aberration, and image curvature while having a small number of lenses through a lens group consisting of three lens elements There is an effect that an optical system can be obtained.

In addition, according to the present invention, it is possible to implement an optical system having a small size and high resolution using only one lens.

In addition, according to the present invention, by forming the lens refraction surface aspherical and properly forming the shape of the lens refraction surface, it is possible to obtain an ultra-small imaging optical system that is excellent in characteristics of various aberrations and can realize high resolution.

Furthermore, in the case of using the replica method, the lens manufactured at the wafer scale is used to realize a microscopic optical system and to produce a lens made of a polymer made of a polymer having excellent heat resistance and suitable for mass production. The effect which can improve reliability more can be acquired.

Claims (8)

A first lens element whose object side surface is convex toward the object side on the optical axis, A second lens element having an object side surface bonded to an image side of the first lens element, An object-side surface is joined to an image-side surface of the second lens element, the image-side surface comprises a lens group having a total of positive refractive power with a third lens element convex toward the image side on the optical axis, and the first lens element And an aperture stop for adjusting the amount of light between the lens element and the second lens element, and satisfying the following Conditional Expression 1 with respect to the dimension of the optical axis direction, and satisfying the following Conditional Expression 2 with respect to the radius of curvature. Condition 1 0.9 <T / bfl <1.7 [Condition 2] 0.65 <| r1 / r2 | <1.5 Where T is the distance from the object-side surface of the first lens element to the image-side surface of the third lens element bfl: distance from the image surface of the second lens element to the image surface r1: radius of curvature of the object-side surface of the first lens element r2: radius of curvature of the image-side surface of the third lens element The ultra-compact optical system according to claim 1, wherein the first and third lens elements satisfy the following conditional expressions 3 and 4 with respect to materials. [Condition 3] N> 1.4 [Condition 4] Vd> 33 Where N is the refractive index of the first, second and third lens elements. Vd: Abbe number of the first, second and third lens elements The micro-optical optical system according to claim 1 or 2, wherein the first and third lens elements are provided in a replica manner using a polymer as a material. The microscopic imaging optical system of claim 1, wherein the aperture stop is integrally formed in a plane formed on an object-side surface of the second lens element. The ultra-small imaging optical system of claim 4, wherein the aperture stop is provided with a metal coating layer. The microscopic imaging optical system according to claim 4, wherein the aperture stop is provided with a photosensitive resin layer. The micro-imaging optical system according to claim 1, wherein the position of the aperture stop satisfies the following conditional expression (5). [Condition 5] 0.06 <d <0.25 Where d is the distance from the object-side surface of the first lens element to the aperture stop The micro-optical optical system of claim 1, further comprising an optical filter between the second lens element and the third lens element, wherein the optical filter is integrally provided on an image side surface of the second lens element.

Images