KR20080062155A - Subminiature optical system - Google Patents

Abstract

A micro optical capturing system is provided to implement a mass production and reduce a manufacturing cost by using three lenses made of plastic material. A micro optical system includes a first lens(L1), a second lens(L2), and a third lens(L3). The first lens has a positive refraction ratio. Both surfaces of the first lens are convex. The second lens of a meniscus shape which is upward convex has a positive refraction ratio. The third lens has a positive refraction ratio. The size of the optical system in the optical axis direction satisfies an equation 1, 1.3<TL/f<1.4, where TL denotes a distance from the object side surface of the first lens to the upper surface of the first lens, and f denotes an effective focus distance of the total optical system.

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 various aberration diagrams of the first embodiment illustrated in FIG. 1.

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

3 is a graph showing the MTF characteristic of the first embodiment shown in FIG.

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

FIG. 5 illustrates various aberration diagrams of the second embodiment illustrated in FIG. 4.

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

FIG. 6 is a graph showing MTF characteristics of the second embodiment shown in FIG. 4.

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

FIG. 8 illustrates various aberration diagrams of the third embodiment shown in FIG. 7;

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

9 is a graph showing the MTF characteristic of the third embodiment shown in FIG.

Explanation of symbols on the main parts of the drawings

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

L3 ... third lens OF ... optical filter

IP ... Top (Image Sensor) AS ... Aperture Aperture

1,2,3,4,5,6,7,8,9,10 ... face number

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging optical system, and more particularly, to a microscopic imaging optical system mounted on a mobile communication terminal, a PDA, or the like and used for a surveillance camera, a digital camera, or the like.

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 have been strongly demanded for the imaging optical system installed in a camera phone, and the pixel size of image sensors such as CCD (solid-state imaging device) and CMOS (compensation compensation semiconductor) has been increased. 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 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.

Therefore, there is a need for a very small imaging optical system capable of realizing high resolution and miniaturization.

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 a compact imaging optical system having a high resolution and a small number of lenses using only three lenses and having a very short length.

In addition, an object of the present invention is to provide an ultra-small imaging optical system that can be reduced in weight and can be manufactured easily and can be mass-produced.

The present invention to achieve this object, the first lens having a positive refractive power and both sides are convex; A second lens of a meniscus shape having a positive refractive power and convex upward; And a third lens having positive refractive power; It provides a microscopic imaging optical system comprising a.

Preferably, the following Conditional Expression 1 regarding the optical axis dimension, the following Conditional Expression 2 regarding the refractive power of the first lens, the following Conditional Expression 3 relating to the refractive power of the third lens, and the Abbe number of the first lens. At least one of the following Conditional Expression 4 and the following Conditional Expression 5 regarding the shape of the third lens may be satisfied.

[Condition 1] 1.3 <TL / f <1.4

[Condition Formula 2] 0.8 <f1 / f <1.2

Conditional Expression 3 0.05 <f3 / f <0.14

[Condition Formula 4] V1 <60

[Condition Formula 5] 0.35 <R7 / f <0.55

TL: distance from the object-side surface of the first lens to the image surface

        f: effective focal length of the whole optical system

        f1: Focal length of the first lens

        f3: Focal length of the third lens

        V1: Abbe number of the first lens

        R7: radius of curvature of the image-side surface of the third lens

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 ultra-small imaging optical system according to the present invention has a first lens L1 having positive refractive power and convex on both sides, and a meniscus shape convex toward the image with positive refractive power, in order from the object side. A second lens L2 and a third lens L3 having positive refractive power are included.

At this time, by arranging the aperture stop AS between the first lens L1 and the second lens L2, the amount of light can be easily secured. That is, by reducing the F number to 2.8 or less in order to secure the maximum amount of incident light, it is possible to provide an optical system particularly suitable for a CMOS image pickup device.

In addition, by using a plastic material in the first lens (L1), the second lens (L2) and the third lens (L3) to facilitate the formation of aspherical surface, it is possible not only to improve workability and reduce manufacturing cost, but also to reduce the weight. have.

That is, at least one refractive surface of each of the refractive surfaces of each of the first lens L1 to the third lens L3 may be an aspherical surface for correcting aberration such as spherical aberration, and the aspherical refractive surface may be formed to facilitate the formation of the aspherical surface. The lens has a plastic material.

On the other hand, between the third lens (L3) and the image surface (IP) is provided with an optical filter (OF) made of an infrared filter, a cover glass or the like.

In the ultra-small imaging optical system according to the present invention, the refractive power of the first lens L1 is increased, the refractive power of the second lens L2 and the third lens L3 is reduced, and the first lens L1 is formed as a biconvex lens. Then, the second lens L2 is formed of a meniscus-shaped lens which is convex toward the image side, thereby miniaturizing the optical system. In addition, by forming at least one refractive surface of each of the refractive surfaces of each of the first lens L1 to the third lens L3 as an aspherical surface, it is possible to improve the resolution of the lens and to reduce various aberrations such as spherical aberration. It is possible to implement an optical system with excellent characteristics.

Then, the chromatic aberration is appropriately selected by selecting the Abbe number between the first lens L1 having a strong positive refractive power and the second lens L2 and the third lens L3 having a relatively weak positive refractive power than the first lens L1. It is possible to correct the resolution and realize high resolution.

Meanwhile, the third lens L3 has a positive refractive power, converges luminous flux, and provides an appropriate focal length.

The first lens L1, the second lens L2, and the third lens L3 have positive, positive, and positive refractive powers, respectively, and a meniscus shape and an aspherical surface are appropriately formed in each lens, thereby providing the lens. By reducing the angle of incidence at the edges, the light intensity in the center and periphery of the image sensor is equalized, and the amount of ambient light is secured as much as possible to prevent the phenomenon of darkening and distortion.

Look at the effect of the following Conditional Expressions 1 to 5 under such an overall configuration.

Condition 1 1.3 TL / f <1.4

Here, TL is the distance from the object side surface 1 of the first lens L1 to the image surface 10, and f is the effective focal length of the entire optical system.

Conditional Expression 1 defines the optical axis direction dimension of the entire optical system and is a condition for miniaturization. If the deviation from the upper limit of the conditional formula 1 is advantageous in terms of correction of various aberrations, the overall length is long, which is contrary to the point of view of the ultra-miniature feature of the present invention. In addition, if the deviation from the lower limit of Conditional Expression 1 may be advantageous in terms of miniaturization, the length of the electric field becomes too short, making it difficult to correct the aberration and satisfying an appropriate telecentric characteristic.

[Condition Formula 2] 0.8 < f1  / f <1.2

Here, f1 is a focal length of the first lens L1, and f is an effective focal length of the entire optical system.

Conditional Expression 2 is a conditional expression relating to a ratio of the focal length of the first lens L1 to the total focal length, that is, the refractive power of the first lens L1.

If it is out of the lower limit of Conditional Expression 2, the refractive power becomes large, making it difficult to correct spherical aberration. On the contrary, aberration correction becomes difficult when it exceeds the upper limit of Conditional Expression 2.

Conditional Expression 3 0.05 f3  / f <0.14

Here, f3 is the focal length of the third lens L3, and f is the effective focal length of the entire optical system.

Conditional Expression 3 is a conditional expression relating to a ratio of the focal length of the third lens L3 to the total focal length, that is, the refractive power of the third lens L3.

If it is out of the lower limit of Conditional Expression 3, the refractive power of the third lens L3 becomes large, which makes it difficult to correct the distortion aberration. On the contrary, when it exceeds the upper limit of Conditional Expression 3, the refractive power of the third lens L3 becomes small, making it difficult to satisfy the demand for miniaturization.

[Condition 4] V1  <60

Here, V1 is an Abbe number of the first lens L1.

Conditional Expression 4 relates to the material of the first lens L1, and is related to the correction of chromatic aberration and ease of manufacture.

That is, Conditional Expression 4 is a conditional expression for using a plastic material for the first lens L1. The first lens L1, the second lens L2, and the third lens L3 may be formed of a plastic material. .

When the upper limit of Conditional Expression 4 is exceeded, the cost of the plastic material that can be used as the first lens L1 is greatly increased, thereby greatly increasing the manufacturing cost.

Conditional Expression 5 0.35 < R7  / f <0.55

Here, R7 is the radius of curvature of the image-side surface 7 of the third lens L3, and f is the effective focal length of the entire optical system.

Conditional Expression 5 is a conditional expression relating to the shape of the third lens L3 and is used for aberration correction. If it is out of the upper and lower limits of Conditional Expression 5, it is difficult to correct spherical aberration and distortion aberration.

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

As described above, in the following first to third embodiments, the first lens L1 having both positive refractive power and convex surfaces on both sides and the meniscus convex toward the image with positive refractive power in order from the object side. An aperture diaphragm AS including a second lens L2 having a shape and a third lens L3 having positive refractive power, and blocking unnecessary light between the first lens L1 and the second lens L2. It is provided. On the other hand, between the third lens (L3) and the image surface (IP) is provided with an optical filter (OF) made of an infrared filter, a cover glass or the like.

In each of the following embodiments, the first lens L1, the second lens L2, and the third lens L3 are all made of plastic to facilitate the formation of aspherical surfaces.

The aspherical surface used in each of the following examples is obtained from well-known Equation 1, and is used for the Conic constant (K) and the aspherical coefficients (A, B, C, D, and E), followed by the numerals. 'Represents a power of 10. For example, E + 01 represents 10 ¹ and E-02 represents 10 ⁻² .

Where Z is the distance from the apex 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 showing a lens arrangement of a microscopic imaging optical system according to a first embodiment of the present invention, and FIGS. 2A to 2C are spherical aberrations of the optical systems shown in Table 1 and FIG. , Astigmatism, and distortion, respectively, and FIG. 3 is a graph showing MTF characteristics of the optical system according to the first embodiment of the present invention shown in FIG. 1.

Here, MTF (Modulation Transfer Function) depends on the spatial frequency of the cycle per millimeter, and is a value defined by the following equation (2) between the maximum intensity (Max) and the minimum intensity (Min) of light.

In other words, if the MTF is 1, it is most ideal. If the MTF value decreases, the resolution drops.

On the other hand, "S" in the astigmatism drawings below represents sagital, and "T" represents tangential.

In the first embodiment, the F number FNo is 2.8, the angle of view is 60 degrees, and the distance TL from the object side surface 1 to the image surface 10 of the first lens L1 is 3.518. Mm, the effective focal length f of the optical system is 2.537 mm, the focal length f1 of the first lens L1 is 2.523 mm, the focal length f2 of the second lens L2 is 61.734 mm, and the third lens ( The focal length f3 of L3) is 24.941 mm.

In Table 1, * denotes an aspherical surface, and in the first embodiment, the object side surface 1 and the image side surface 2 of the first lens L1, and the object side surface 4 and image side surface of the second lens L2. (5) and the object-side surface 6 and the image-side surface 7 of the third lens L3 are aspherical surfaces.

The aspherical coefficients of the first embodiment 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.

4 is a lens configuration diagram showing the lens arrangement of the ultra-small imaging optical system according to the second exemplary embodiment of the present invention, and FIGS. 5A to 5C are spherical aberrations of the optical systems shown in Tables 3 and 4. , Astigmatism, and distortion, respectively, and FIG. 6 is a graph illustrating MTF characteristics of the optical system according to the second embodiment of the present invention shown in FIG. 4.

In the second embodiment, the F number FNo is 2.8, the angle of view is 60 degrees, and the distance TL from the object-side surface 1 to the image surface 10 of the first lens L1 is 3.517. Mm, the effective focal length f of the optical system is 2.547 mm, the focal length f1 of the first lens L1 is 2.535 mm, the focal length f2 of the second lens L2 is 31.023 mm, and the third lens ( The focal length f3 of L3) is 42.003 mm.

In Table 3, * denotes an aspherical surface, and in the second embodiment, the object side surface 1 and the image side surface 2 of the first lens L1, and the object side surface 4 and image side surface of the second lens L2. (5) and the object-side surface 6 and the image-side surface 7 of the third lens L3 are aspherical surfaces.

The aspherical coefficients of the second embodiment 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.

7 is a lens configuration diagram showing the lens arrangement of the ultra-small imaging optical system according to the third embodiment of the present invention, and FIGS. 8A to 8C are spherical aberrations of the optical systems shown in Tables 5 and 7. , Astigmatism, and distortion, respectively, and FIG. 9 is a graph illustrating MTF characteristics of the optical system according to the third embodiment of the present invention shown in FIG. 7.

In the third embodiment, the F number FNo is 2.8, the angle of view is 60 degrees, and the distance TL from the object-side surface 1 to the image surface 10 of the first lens L1 is 3.450. Mm, the effective focal length f of the optical system is 2.502 mm, the focal length f1 of the first lens L1 is 2.438 mm, the focal length f2 of the second lens L2 is 231.670 mm, and the third lens ( The focal length f3 of L3) is 23.525 mm.

In Table 5, * denotes an aspherical surface, and in the third embodiment, the object side surface 1 and the image side surface 2 of the first lens L1, and the object side surface 4 and image side surface of the second lens L2. (5) and the object-side surface 6 and the image-side surface 7 of the third lens L3 are aspherical surfaces.

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

Through the above embodiments, as well as the characteristics of various aberrations as illustrated in FIGS. 2, 5, and 7, as well as the optical system having excellent MTF characteristics as shown in FIGS. 3, 6, and 9 can be obtained. can confirm.

On the other hand, the values of Conditional Expressions 1 to 5 for the first to third embodiments are as shown in Table 7 below.

As shown in Table 7 above, it can be seen that the first to third embodiments of the present invention satisfy conditional expressions 1 to 5.

As described above, according to the present invention, by using only three lenses, the lens has a high resolution and a small number of lenses, so that a compact and extremely small imaging optical system can be realized.

In addition, by using three plastic lenses, not only the weight can be reduced, but also the production is easy, mass production is possible, and there is an advantageous effect that the optical system can be implemented with low manufacturing cost.

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

Claims (7)

A first lens having positive refractive power and convex on both sides; A second meniscus-shaped second lens having positive refractive power and convex toward the image; And A third lens having positive refractive power; Miniature imaging optical system comprising a. The method of claim 1, The ultra-small imaging optical system which satisfy | fills following Conditional expression 1 regarding the dimension of an optical axis direction. [Condition 1] 1.3 <TL / f <1.4 TL: distance from the object-side surface of the first lens to the image surface         f: effective focal length of the whole optical system The method according to claim 1 or 2, The microscopic imaging optical system according to claim 1, wherein the following conditional expression 2 is satisfied with respect to the refractive power of the first lens. [Condition Formula 2] 0.8 <f1 / f <1.2 Here, f1: focal length of the first lens         f: effective focal length of the whole optical system The method according to claim 1 or 2, The microscopic imaging optical system according to claim 3, wherein the following conditional expression 3 is satisfied with respect to the refractive power of the third lens. Conditional Expression 3 0.05 <f3 / f <0.14 Where f3 is the focal length of the third lens.         f: effective focal length of the whole optical system The method according to claim 1 or 2, A microscopic imaging optical system according to claim 4, wherein the following Conditional Expression 4 is satisfied with respect to the Abbe number of the first lens. [Condition Formula 4] V1 <60 Where V1: Abbe number of the first lens The method according to claim 1 or 2, A microscopic imaging optical system according to claim 3, wherein the following conditional expression 5 is satisfied with respect to the shape of the third lens. [Condition Formula 5] 0.35 <R7 / f <0.55 Where R7 is the radius of curvature of the image-side surface of the third lens.         f: effective focal length of the whole optical system The method according to claim 1 or 2, The microscopic imaging optical system according to claim 1, wherein an aperture stop is provided between the first lens and the second lens to block unnecessary light.

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