KR101089881B1 - Optical system - Google Patents

Abstract

Disclosed is an imaging optical system mounted on a mobile communication terminal, a PDA, or the like and used for a surveillance camera, a digital camera, and the like.

The imaging optical system includes: a first lens having positive refractive power and convex on both surfaces, which are arranged in order from an object side to a front of an image surface; A second lens having negative refractive power and concave on both sides; A third lens having positive refractive power; A fourth lens having positive refractive power and a meniscus shape in which an image side surface is convex; And a fifth lens having negative refractive power and an image side surface having at least one inflection point.

Optics, lens system, lens, plastic, aspherical, focal length, radius of curvature, 5 elements

Description

Imaging optical system {OPTICAL SYSTEM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging optical system, and more particularly, to an 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.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging optical system, and more particularly, to an 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.

Recently, a camera module for a communication terminal, a digital still camera (DSC, digital still camera), a camcorder, and a PC camera (image pickup device included in a personal computer) have been studied in relation to an image pickup system. The most important component for such an image pickup system to obtain an image is a lens system that forms an image.

Since the lens system requires high performance in terms of resolution, image quality, and the like, the configuration of the lens is complicated. However, when the lens system is structurally or optically complicated, the lens system increases in size and is opposed to miniaturization and thinning.

For example, miniaturization of the entire module is essential for the camera module mounted in the mobile phone to increase its mountability. In addition, the image sensor of the CCD or CMOS is increasingly being reduced in size and the pixel size is reduced, and the corresponding lens system must not only require miniaturization and thinning, but also high resolution and excellent optical performance.

In this case, when using a 3 million pixel imaging device (CCD or CMOS), optical performance and miniaturization can be satisfied with a lens configuration of 3 sheets or less, but 3 or less sheets are required for a high resolution imaging device (CCD or CMOS) having 5 million pixels or more. When the lens of is used, the refractive power of each lens should be large, and accordingly difficult to process the lens, there is a problem that it is difficult to satisfy high performance and miniaturization at the same time. In addition, despite the configuration of four or more lenses, when using a spherical lens, there is a problem that the total length of the optical system is increased, making it difficult to achieve miniaturization.

Accordingly, there is a need for a lens system for a miniature camera module that can simultaneously realize miniaturization and optical performance.

The present invention provides a high resolution and miniaturization using five lenses, and a technical problem to be solved to provide an imaging optical system for a camera module excellent in optical performance.

In addition, the present invention is a technical problem to solve the low cost of manufacturing and mass production possible to provide a small-sized light-weight imaging optical system by implementing the five lenses included in the optical system with a plastic material.

According to an aspect of the present invention,

It is arranged in order from an object side to an upper surface front,

A first lens having positive refractive power and convex on both sides;

A second lens having negative refractive power and concave on both sides;

A third lens having positive refractive power;

A fourth lens having positive refractive power and a meniscus shape in which an image side surface is convex; And

A fifth lens having negative refractive power and having at least one inflection point capable of reducing an incident angle of light incident on the image plane onto the image plane;

It provides an imaging optical system comprising a.

An embodiment of the present invention further includes an aperture stop disposed in front of the object side of the first lens.

One embodiment of the present invention may satisfy at least one of the following Conditional Expressions 1 to 4.

[Condition 1] TTL / F <1.5

[Condition 2] 0.5 <F1 / F <1.2

[Condition 3] 0.5 <| F5 / F | <1.2

[Condition 4] V1-V2> 20

In the above Conditional Expressions 1 to 4, TTL represents an optical axis distance from the object-side surface of the first lens to the image surface, F represents the focal length of the whole optical system, F1 represents the focal length of the first lens, F5 Denotes a focal length of the fifth lens, V1 denotes an Abbe number of the first lens, and V2 denotes an Abbe number of the second lens.

In one embodiment of the present invention, the first to fifth lenses may be implemented in a plastic material.

In one embodiment of the present invention, the first to fifth lenses may be aspherical lenses.

According to the present invention, it is suitable for micro-optical devices such as cameras for mobile phones using image sensors such as CCD and CMOS, and adjusts the radius of curvature of the refractive surface of each lens constituting the optical system and minimizes various aberrations by using aspherical surface. As a result, an image of high definition can be obtained.

In addition, according to the present invention, the use of five plastic lenses can not only reduce the weight, but also make the production easy and mass production, and the manufacturing cost is low.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiment of this invention is provided in order to demonstrate this invention more completely to the person skilled in the art to which this invention belongs. Therefore, it should be noted that the shape and size of the components shown in the drawings may be exaggerated for more clear explanation.

1 is a lens configuration diagram showing a first embodiment of an 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.

In general, the camera module has at least one lens, a predetermined space formed therein, a housing accommodating the lens, an image sensor corresponding to an imaging surface by the lens, and a fixed installation at the other end of the housing, wherein the image is fixed on one surface of the camera module. The sensor may be mounted to a circuit board for processing an image sensed by the image sensor.

The present invention relates to an imaging optical system used in an ultra-compact camera module among such camera modules.

As shown in FIG. 1, an imaging optical system according to an exemplary embodiment of the present invention includes a first lens L1 having positive refractive power and convex surfaces 2 and 3, and a negative refractive power and double surfaces 4 and 5. The concave second lens L2, the third lens L3 having positive refractive power, the fourth lens L4 having positive refractive power and a meniscus shape in which the image side surface 9 is convex, and negative refractive power. The image side 11 may include a fifth lens L5 having at least one inflection point. The first to fifth lenses L1 to L5 may be arranged in that order from the object side to the front of the image surface. Such a lens configuration is advantageous for miniaturization by arranging lenses having positive, negative, positive, positive and negative refractive powers sequentially from the object side and appropriately distributing the refractive powers.

In addition, the first lens L1 may be configured to convexly form both surfaces 2 and 3 and to have positive refractive power for miniaturization.

In addition, the second lens L2 may be configured to concave the chromatic aberration generated in the first lens L1 by forming concave surfaces 4 and 5.

In addition, the fourth lens L4 may be configured such that the aberration correction and telecentric characteristics are advantageous by forming the image side surface 9 to have a convex meniscus shape.

In addition, the fifth lens L5 disposed at the most image side is formed such that the image surface 11 has at least one inflection point, thereby reducing the incident angle of light incident on the image surface IP to the image surface, thereby reducing the pixel size. Even in a small image sensor, it is possible to obtain an image having excellent image quality with reduced aberration.

In one embodiment of the present invention, the first to the fifth lens (L1-L5) has at least one surface aspherical surface to improve the resolution of the lens and at the same time can reduce distortion, spherical aberration, compact and optical It is possible to implement an optical system with excellent characteristics.

In one embodiment of the present invention, the first to fifth lenses L1 to L5 may be formed of a plastic material. Since the small image sensor applied to the small camera module has a small image plane size, the focal length of the electric field must be relatively shortened, and thus the curvature radius and the outer diameter of each lens are significantly reduced. Therefore, compared with the glass lens manufactured by the grinding | polishing process which is difficult to rework, all the lenses are comprised by the plastic lens manufactured by injection molding, and it is possible to mass-produce inexpensively even the lens with a small radius of curvature or an outer diameter. In addition, since the plastic lens can lower the press temperature, the wear of the molding die can be suppressed, and as a result, the number of replacement and maintenance of the molding die can be reduced, and the cost can be reduced.

In addition, since the area of the lens surface most exposed to the object side is small by arranging the position of the aperture stop in front of the object side of the first lens L1, it is easy to manage the infiltration of foreign objects and the like. By being located close to the top surface, it is possible to miniaturize the window of the external mechanism for fixing the camera module. In addition, the higher the resolution, the smaller the pixel size of the image sensor is required to have a brighter optical system (lens with a small F number), the aperture is located in front of the object side is an advantage that is easy to manufacture a bright optical system have.

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

[Condition 1]

TTL / F <1.5

Conditional Expression 1 above defines conditions relating to the length of the entire optical system. In Conditional Expression 1, TTL represents the optical axis distance from the object-side surface of the first lens to the image surface, and F represents the focal length of the whole optical system.

Deviation from the upper limit of Conditional Expression 1 is advantageous in terms of aberration correction, but is contrary to the miniaturization which is a feature of the present invention. Therefore, miniaturization of the optical system can be maintained by maintaining the condition of Conditional Expression 1.

[Condition Formula 2]

0.5 <F1 / F <1.2

Conditional Expression 2 defines a condition regarding the refractive power of the first lens L1, and represents the ratio of the focal length of the first lens L1 to the focal length of the entire optical system. In Conditional Formula 2, F1 represents a focal length of the first lens L1, and F represents a focal length of the entire optical system.

If the chromatic aberration of the optical system is increased beyond the upper limit of Conditional Expression 2, it is difficult to correct chromatic aberration. If the deviation is outside the lower limit of Conditional Expression 2, the refractive power is increased, making spherical aberration correction difficult.

[Condition 3]

0.5 <| F5 / F | <1.2

Conditional Expression 3 defines a condition regarding the refractive power of the fifth lens L5, and represents a ratio of the focal length of the fifth lens L5 to the focal length of the entire optical system. In Conditional Expression 3, F5 represents a focal length of the fifth lens L1, and F represents a focal length of the entire optical system.

If it is out of the upper limit of Conditional Expression 3, the refractive power decreases, making it difficult to satisfy the miniaturization. If the condition is out of the lower limit of Conditional Expression 3, the telecentric characteristic is lowered and correction of distortion aberration becomes difficult.

[Condition 4]

V1-V2> 20

Conditional Expression 4 defines a condition related to dispersion of the first lens L1 and the second lens L2. In Conditional Expression 4, V1 represents an Abbe number of the first lens L1. , V2 represents the Abbe's number of the second lens L2.

Optical materials can be largely divided into a crown series having an Abbe number of 50 or more and a Flint series having an Abbe number of less than 50. Of these, the Flint-based optical material has a Abbe number less than 50, which is a medium having a large color dispersion. The present invention uses a flint-based medium having a large color dispersion so as to have negative refractive power in the second lens L2 located second from the object side, and the first lens disposed in front of the object side of the second lens L2. The chromatic aberration characteristics can be improved by employing a crown-based low dispersion lens at L1 to increase the dispersion difference between the first and second lenses L1 and L2.

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

As described above, the first to fourth embodiments all have the first lens L1 having positive refractive power and convex surfaces 2 and 3, and the second lens having negative refractive power and concave surfaces 4 and 5. L2), the third lens L3 having the positive refractive power, the fourth lens L4 having the meniscus shape having the positive refractive power and the convex image side 9 and the image side 11 having the negative refractive power A fifth lens L5 having at least one inflection point is included, and an aperture stop S is provided in front of the object side of the first lens L1. In addition, an optical filter OF corresponding to an infrared filter, a cover glass, or the like is provided between the fifth lens L5 and the image surface IP, and the image surface IP corresponds to an image sensor such as a CCD or a CMOS. .

The aspherical surface used in each of the following examples is obtained from well-known Equation 1, and is used in the Conic constant (K) and the aspherical surface coefficients (A, B, C, D, E, F) and The number following is the power of ten. For example, e + 01 represents 10 ¹ and e-02 represents 10 ⁻² .

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

In addition, in the MTF graph of each embodiment below, the MTF (Modulation Transfer Function) depends on the spatial frequency of cycles per millimeter, and the value defined by the following equation (2) between the maximum intensity (Max) and the minimum intensity (Min) of light. to be.

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

First Embodiment

Table 1 below shows a numerical example of the optical system according to the first embodiment of the present invention. 1 is a lens configuration diagram of an imaging optical system according to a first embodiment of the present invention, and FIG. 2 is an MTF graph of the optical systems shown in Table 1 and FIG. 3A to 3C show the aberration diagrams of the optical systems shown in Table 1 and FIG. 1.

In the first embodiment, the distance TTL from the object-side surface 2 of the first lens L1 to the image surface 12 is 4.734 mm, the effective focal length F of the optical system is 3.800 mm, and the first lens ( The focal length F1 of L1 is 2.798 mm, the focal length F2 of the second lens L2 is -4.296 mm, the focal length F3 of the third lens L3 is 16.706 mm, and the fourth lens L4 ) Has a focal length F4 of 2.817 mm and a focal length F5 of the fifth lens L5 of -2.659 mm. In addition, the first to fifth lenses L1 to L5 are made of a plastic material, and all of the refractive surfaces of the lenses are aspherical.

The aspherical coefficients of the first embodiment according to Equation 1 are shown in Table 2 below.

Example 2

Table 3 below shows numerical examples of the optical system according to the second embodiment of the present invention. 4 is a lens configuration diagram of an imaging optical system according to a second exemplary embodiment of the present invention, and FIG. 5 is an MTF graph of the optical systems shown in Table 3 and FIG. 4. 6A to 6C show the aberration diagrams of the optical systems shown in Table 3 and FIG. 4.

In the second embodiment, the distance TTL from the object-side surface 2 of the first lens L1 to the image surface 12 is 4.700 mm, the effective focal length F of the optical system is 3.792 mm, and the first lens ( The focal length F1 of L1 is 2.742 mm, the focal length F2 of the second lens L2 is -4.186 mm, the focal length F3 of the third lens L3 is 17.295 mm, and the fourth lens L4. ) Has a focal length F4 of 2.848 mm, and a focal length F5 of the fifth lens L5 of -2.681 mm. In addition, the first to fifth lenses L1 to L5 are made of a plastic material, and all of the refractive surfaces of the lenses are aspherical.

The aspherical coefficients of the second embodiment according to Equation 1 are shown in Table 4 below.

Example 3

Table 5 below shows numerical examples of the optical system according to the third embodiment of the present invention. 7 is a lens configuration diagram of an imaging optical system according to a third exemplary embodiment of the present invention, and FIG. 8 is an MTF graph of the optical systems shown in Table 5 and FIG. 9A to 9C show the aberration diagrams of the optical systems shown in Table 5 and FIG. 7.

In the third embodiment, the distance TTL from the object-side surface 2 of the first lens L1 to the image surface 12 is 4.600 mm, the effective focal length F of the optical system is 3.726 mm, and the first lens ( The focal length F1 of L1 is 2.684 mm, the focal length F2 of the second lens L2 is -4.147 mm, the focal length F3 of the third lens L3 is 22.991 mm, and the fourth lens L4. ) Has a focal length F4 of 2.832 mm and a focal length F5 of the fifth lens L5 of -2.736 mm. In addition, the first to fifth lenses L1 to L5 are made of a plastic material, and all of the refractive surfaces of the lenses are aspherical.

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

Example 4

Table 7 below shows a numerical example of the optical system according to the fourth embodiment of the present invention. 10 is a lens configuration diagram of an imaging optical system according to a fourth embodiment of the present invention, and FIG. 11 is an MTF graph of the optical systems shown in Table 7 and FIG. 10. 12A to 12C show the aberration diagrams of the optical systems shown in Table 7 and FIG. 10.

In the fourth embodiment, the distance TTL from the object-side surface 2 of the first lens L1 to the image surface 12 is 4.500 mm, the effective focal length F of the optical system is 3.668 mm, and the first lens ( The focal length F1 of L1 is 2.638 mm, the focal length F2 of the second lens L2 is -4.080 mm, the focal length F3 of the third lens L3 is 32.088 mm, and the fourth lens L4. ), The focal length F4 is 2.736 mm, and the focal length F5 of the fifth lens L5 is -2.731 mm. In addition, the first to fifth lenses L1 to L5 are made of a plastic material, and all of the refractive surfaces of the lenses are aspherical.

The aspherical coefficients of the fourth embodiment according to Equation 1 are shown in Table 8 below.

As shown in FIGS. 3, 6, 9, and 12, the optical system having excellent characteristics of the aberration can be obtained through the above embodiments.

On the other hand, the values of the conditional formulas 1 to 4 for the above first to fourth embodiments are shown in Table 9 below.

TABLE 9

First embodiment Second embodiment Third embodiment Fourth Embodiment Conditional Expression 1 1.246 1.239 1.235 1.227 Conditional Expression 2 0.736 0.723 0.720 0.719 Conditional Expression 3 0.700 0.707 0.734 0.745 Conditional Expression 4 29 29 29 29

As shown in Table 9, it can be seen that the first to fourth embodiments of the present invention satisfy conditional expressions 1 to 4.

In the detailed description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the following claims and their equivalents.

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

FIG. 2 is an MTF graph of the first embodiment shown in FIG.

FIG. 3 shows a first aberration diagram of the first embodiment shown in FIG.

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

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

5 is an MTF graph of the second embodiment shown in FIG.

FIG. 6 shows the aberration diagram of the second embodiment shown in FIG. 4;

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

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

8 is an MTF graph of the third embodiment shown in FIG.

FIG. 9 shows a third aberration diagram of the third embodiment shown in FIG.

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

10 is a lens configuration diagram of an imaging optical system according to a fourth embodiment of the present invention.

FIG. 11 is an MTF graph of the fourth embodiment shown in FIG. 10; FIG.

12 illustrates a fourth aberration diagram of the fourth embodiment illustrated in FIG. 10.

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

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

L3 ... third lens L4 ... fourth lens

L5 ... 5th lens S ... opening aperture

OF ... optical filter IP ... top

1,2,3,4,5,6,7,8,9,10,11,12,13,14 ... face number

Claims (8)

It is arranged in order from an object side to an upper surface front, A first lens having positive refractive power and convex on both sides; A second lens having negative refractive power and concave on both sides; A third lens having positive refractive power; A fourth lens having positive refractive power and a meniscus shape in which an image side surface is convex; And A fifth lens having negative refractive power and having at least one inflection point capable of reducing an incident angle of light incident on the image plane onto the image plane; Imaging optical system comprising a. The method of claim 1, And an aperture stop disposed in front of the object side of the first lens. The method according to claim 1 or 2, An imaging optical system that satisfies the following Conditional Expression 1. [Condition 1] TTL / F <1.5 (TTL: distance on the optical axis from the object-side surface of the first lens to the image surface, F: focal length of the whole optical system) The method according to claim 1 or 2, An imaging optical system satisfying the following Conditional Expression 2. [Condition 2] 0.5 <F1 / F <1.2 (F1: focal length of the first lens, F: focal length of the whole optical system) The method according to claim 1 or 2, An imaging optical system that satisfies the following Conditional Expression 3. [Condition 3] 0.5 <| F5 / F | <1.2 (F5: focal length of the fifth lens, F: focal length of the whole optical system) The method according to claim 1 or 2, An imaging optical system satisfying the following Conditional Expression 4. [Condition 4] V1-V2> 20 (V1: Abbe number of the first lens, V2: Abbe number of the second lens) The method according to claim 1 or 2, The first to fifth lenses are imaging optical systems, characterized in that the plastic material. The method according to claim 1 or 2, And the first to fifth lenses are aspherical lenses.

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