KR100616643B1 - Lens System For Subminiature Camera Module - Google Patents

Abstract

The present invention relates to a lens system for an ultra-compact camera module capable of obtaining small size, light weight and high resolution.

The lens system includes a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power, in order from the object side to the closest object aperture and then sequentially from the object side to the front of the image surface. And a fourth lens having negative refractive power, wherein at least three refractive surfaces of the refractive surfaces of the first to fourth lenses are aspherical, and at least three lenses are made of plastic.

According to the present invention as described above it is possible to obtain a compact, lightweight and high resolution lens system, which can be applied to an ultra compact camera module.

Lens system, plastic, aspherical, focal length, image sensor

Description

Lens System For Subminiature Camera Module             

1 shows a lens configuration of a first embodiment of a lens system for a compact camera module according to the present invention.

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

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

3 shows a lens configuration of a second embodiment of a lens system according to the present invention.

FIG. 4 illustrates the aberration diagram of the second embodiment shown in FIG. 3.

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

5 shows a lens configuration of a third embodiment of a lens system according to the present invention.

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

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

7 shows a lens configuration of a fourth embodiment of a lens system according to the present invention.

FIG. 8 illustrates a fourth aberration diagram of the fourth embodiment shown in FIG.

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

9 shows a lens configuration of a fifth embodiment of a lens system according to the present invention.

FIG. 10 illustrates a fifth aberration diagram of the fifth embodiment shown in FIG. 9.

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

Fig. 11 shows a lens configuration of a sixth embodiment of a lens system according to the present invention.

FIG. 12 illustrates the aberration diagram of the sixth embodiment shown in FIG.

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

Fig. 13 shows a lens construction of a seventh embodiment of a lens system according to the present invention.

FIG. 14 illustrates the aberration diagram of the seventh embodiment shown in FIG.

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

Explanation of symbols on the main parts of the drawings

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

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

S ... opening aperture IF ... infrared filter

CG ... cover glass IS ... image sensor

1,2,3,4,5,6,7,8 ... Refractive surface of lens 13 ... Upper surface

The present invention relates to a lens system used in an ultra-compact camera module using an image sensor such as a Charged Coupled Device (CCD) and a Complementally Metal Oxide Semiconductor (CMOS). It consists of four lenses with minus, plus, and minus refractive powers. At least three of them are made of plastic, so they can be applied to mobile phones, digital cameras, and PC cameras. A lens system for a micro camera module is provided.

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.

Such a lens system requires a high performance in terms of resolution, image quality, etc., but the configuration of the lens is complicated. However, when the lens system is structurally or optically complicated, there is a problem in that the size is increased and the size thereof 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 is to solve the above problems, it is an object to provide a lens system for a compact camera module that can implement high resolution and miniaturization with only four lenses, excellent optical performance.

In addition, an object of the present invention is to provide a lens system for a small size and light weight ultra compact camera module by using at least three or more plastic lenses, low production cost and mass production.

In order to achieve the above object, the present invention provides a lens system for use in an ultra-compact camera module having at least one lens mounted inside a housing and an image sensor corresponding to an image surface by the lens, the object system is the closest to the object side. A first lens having a positive refractive power, in order from an object side to an image plane front; A second lens having negative refractive power; A third lens having positive refractive power; And a fourth lens having negative refractive power; It includes, and provides a lens system for a miniature camera module at least three refractive surfaces of the refractive surfaces of the first to fourth lenses is aspherical surface.

Preferably, the lens system comprises at least three lenses of the first to fourth lenses made of plastic, and more preferably the second to fourth lenses are made of plastic.

Also preferably, each of the first to fourth lenses may include at least one refractive surface aspheric surface.

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 lens system for a compact camera module 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 fixedly installed at the other end of the housing. An image sensor is mounted to a circuit board for processing an image sensed by the image sensor.

The present invention relates to a lens system used in the small camera module of such a camera module.

As shown in Fig. 1, the lens system according to the embodiment of the present invention arranges the aperture stop S for removing unnecessary light to the nearest side of the object side, and then, in order from the object side, positive refractive power is applied. And a power arrangement including a first lens L1 having a second lens L2 having a negative refractive power, a third lens L3 having a positive refractive power, and a fourth lens L4 having a negative refractive power.

In this case, chromatic aberration may be corrected through the first lens L1 having a strong positive refractive power and the second lens L2 having a strong negative refractive power, and a compact optical system may be realized at a small F number. In addition, by arranging the third lens L3 to have a weak positive refractive power and the fourth lens L4 to have a weak negative refractive power, the telecentric characteristic is improved while correcting the aberration such as spherical aberration, distortion, coma, and the like. The miniaturization of the entire lens system can be realized.

Further, by placing the aperture S of the optical system in front of the first lens L1, which is a curvature change part, the amount of defocus in which the change in curvature in the first lens L1 extends over the entire field is minimized. It becomes possible.

In addition, since at least three lenses of the first to fourth lenses L1, L2, L3, and L4 are made of plastic lenses, the manufacturing cost is low, mass production is possible, and a compact and lightweight lens system can be realized. .

Furthermore, each lens L1, L2, L3, L4 has at least one refracting surface as an aspheric surface, thereby enabling miniaturization of the lens system compared to the spherical lens.

Meanwhile, an optical low pass filter (OLPF) including an infrared filter IF, a cover glass CG, and the like is provided behind the fourth lens L4. The infrared filter IF and the cover glass CG may be replaced or omitted by other filters as necessary, and do not affect the optical properties of the present invention in principle.

In addition, the image sensor IS is formed of a Charged Coupled Device (CCD) and a Complementally Metal Oxide Semiconductor (CMOS), etc., and includes an image surface (photosensitive surface) 13 that receives an image formed by a lens. The cover glass CG is disposed behind the cover glass CG.

Look at the effect of the following Conditional Expressions 1 to 9 under such an overall configuration.

The lens system according to the present invention satisfies the following conditional expression 1 with respect to the refractive power of the first lens and the following conditional expression 2 with respect to the optical axis direction of the entire lens system. It can be provided.

(Condition 1) 0.4 <f _I / f <0.7

(Condition 2) TL / f <1.4

Where f is the composite effective focal length of the entire lens system.

f _Ⅰ : Effective focal length of the first lens

        TL: Distance from the dog stop to the top

Conditional Expression 1 above relates to the refractive power of the first lens. When the deviation from the lower limit of Conditional Expression 1 is exceeded, the refractive power of the first lens becomes excessively increased, so that the spherical aberration and coma aberration become large, and the radius of curvature of the first lens becomes small, resulting in lens processability. Will fall. On the other hand, when the upper limit value is exceeded, chromatic aberration increases, making it difficult to correct chromatic aberration in a subsequent lens.

Conditional Expression 2 defines the entire length of the lens system and is a condition related to miniaturization. A deviation from the upper limit of Conditional Expression 2 is advantageous in terms of aberration correction, but is contrary to miniaturization, which is a main feature of the present invention.

In addition, it is preferable that the following conditional expression 3 is satisfied with respect to the shape of the object-side refractive surface of the first lens.

(Condition 3) 0.3 <r ₁ / f <0.6

Where r ₁ : radius of curvature of the object-side refractive surface of the first lens

Conditional Expression 3 defines the shape of the first lens, and if it is out of the lower limit, the curvature radius of the first lens becomes smaller and the lens workability becomes inferior. Will act as a stumbling block.

Further, it is preferable that the following conditional expression 4 is satisfied with respect to the refractive power of the second lens, and the following conditional expression 5 is satisfied with respect to the shape of the second lens.

(Condition 4) 0.6 <| f _II | / f <1.2

(Condition 5) 0.4 <r ₄ / f <0.7

Where f _II : focal length of the second lens (f _II <0)

r ₄ : radius of curvature of the image-side refractive surface of the second lens

The second lens functions to interact with the first lens to reduce chromatic aberration.

Conditional Expression 4 defines the refractive power of the second lens, and if it is out of the lower limit, the radius of curvature becomes small, so that machining is difficult. If it is more than the upper limit, chromatic aberration correction becomes difficult.

Conditional Expression 5 relates to the shape of the second lens, which is difficult to process if it is out of the lower limit, and aberration correction becomes difficult in subsequent lenses, and beyond the upper limit, the postfocal length becomes long, which is contrary to miniaturization. In addition, when out of the upper limit or the lower limit of Conditional Expression 5, spherical aberration, coma aberration, distortion aberration is adversely affected.

Further, the following conditional expression 6 is satisfied with respect to the refractive power of the third lens, and the following conditional expression 7 is satisfied with respect to the shape of the image-side refractive surface of the third lens.

(Condition 6) 0.5 <f _III / f <5

(Condition 7) 0.2 <| r ₆ | <0.5

Here, f _III : focal length of the third lens

r ₆ : radius of curvature of the image-side refractive surface of the third lens (r ₆ <0)

The third lens has a weak plus refractive power and functions to correct off-axis aberration while reducing the refractive power of the first lens and the second lens.

Deviation from the upper limit of the conditional expression 6 makes it difficult to correct the axial aberration, and below the lower limit, the occurrence of chromatic aberration by the third lens becomes excessive and the off-axis performance is weakened.

The conditional formula (7) defines the shape of the third lens having positive refractive power. If the deviation is outside the upper limit, the off-axis chief ray angle becomes too low, and the fourth lens deteriorates the telecentric characteristic. On the other hand, if the value falls outside the lower limit, the telecentric characteristic is advantageous, whereas the off-axis coma flare increases, resulting in poor performance.

In addition, it is preferable that the following conditional expression 8 is satisfied with respect to the refractive power of the fourth lens, and the following conditional expression 9 is satisfied with respect to the shape of the image-side refractive surface of the fourth lens.

(Condition 8) 0.5 <| f _IV | / f <5

(Condition 9) 0.2 <r ₈ <1.5

Here, f _IV : focal length of the fourth lens (f _IV <0)

r ₈ : radius of curvature of the image-side refractive surface of the fourth lens

The fourth lens has a weak negative refractive power, and serves to reduce the angle of the chief ray to reduce the difference in color sensitivity between the center and the periphery of the image plane.

Condition Equation 8 relates to the refractive power of the fourth lens, and when it is out of the upper limit value, the refractive power becomes small, the telephoto ratio becomes worse, and miniaturization becomes difficult. On the other hand, if it is out of the lower limit, it is advantageous for miniaturization, but the color sensitivity of the peripheral part is not good and distortion aberration increases.

Conditional Expression 9 relates to the shape of the image refracting surface of the fourth lens having a weak negative refractive power. If the upper limit of Conditional Expression 9 is exceeded, the refractive power decreases, which hinders miniaturization. If the lower limit is exceeded, the incident angle of the upper surface becomes large and the amount of light becomes insufficient. This becomes difficult.

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

As described above, in the following Examples 1 to 7, the aperture stop S1 is disposed closest to the object side, and then, in order from the object side, the first lens L1 having a positive refractive power, negative A second lens L2 having refractive power, a third lens L3 having positive refractive power, and a fourth lens L4 having negative refractive power, and between the fourth lens L4 and the image surface 13. An infrared filter IF and a cover glass CG are provided, and an image sensor IS is provided to detect an image corresponding to the image 13 of the fourth lens L4.

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, E21 has a 10 ^21, E-02 indicates the ^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

r: radius of curvature at the vertex of the lens

K: Conic constant

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

Example 1

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

1 is a lens configuration diagram illustrating a lens arrangement of a lens system for a micro camera module according to a first embodiment of the present invention, and FIGS. 2A to 2C illustrate aberrations of the lens systems shown in Tables 1 and 1. Indicates.

In addition, "S" shown in the astigmatism drawings below represents sagital, and "T" represents tangential.

In Example 1, the effective focal length f of the entire lens system is 8.305 mm, the F number F _No is 2.8, and the total angle of the lens (2ω) is 60 °. The total length TL from the aperture stop to the top surface is 9.9 mm.

In Example 2, the first lens L1 is a glass lens, and the second lens L2 is a plastic lens using OKP4 manufactured by Osaka Gas Chemical Co., Ltd., and the third lens L3 and the fourth lens ( L4) is a plastic lens using ZEONEX series E48R.

In Table 1, * denotes an aspherical surface, and the values of the koenic constant (K) and aspherical coefficients (A, B, C, D, and E) according to Equation 1 are shown in Table 2 below.

Example 2

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

In addition, Figure 3 is a lens configuration showing the lens arrangement of the lens system for a miniature camera module according to a second embodiment of the present invention, Figures 4a to 4c shows the aberration of the lens system shown in Table 3 and 3 .

In Example 2, the effective focal length f of the entire lens system is 8.499 mm, the F number F _No is 2.8, and the telephone angle (2ω) of the lens is 60 °, and the distance (TL) from the aperture stop to the upper surface (TL). ) Is 9.9 mm.

In Example 2, the first lens L1 is a glass lens, and the second lens L2 is a plastic lens using OKP4 manufactured by Osaka Gas Chemical Co., Ltd., and the third lens L3 and the fourth lens ( L4) is a plastic lens using ZEONEX series E48R.

In Table 3, * represents an aspherical surface, and the values of the koenic constant (K) and the aspherical coefficients (A, B, C, D, and E) according to Equation 1 are shown in Table 4 below.

Example 3

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

5 is a lens configuration diagram illustrating a lens arrangement of a lens system for a micro camera module according to a third exemplary embodiment of the present invention, and FIGS. 6A to 6C show aberrations of the lens systems shown in Tables 5 and 5. .

In Example 3, the effective focal length f of the entire lens system is 8.196 mm, the F number F _No is 2.8, the telephone angle of the lens (2ω) is 60 °, and the distance (TL) from the aperture stop to the upper surface (TL). ) Is 10.5 mm.

In Example 3, the first lens L1 is a glass lens, and the second lens L2 is a plastic lens using OKP4 manufactured by Osaka Gas Chemical Co., Ltd., and the third lens L3 and the fourth lens ( L4) is a plastic lens using ZEONEX series E48R.

In Table 5, * represents an aspherical surface, and the values of the koenic constant (K) and aspherical coefficients (A, B, C, D, and E) according to Equation 1 are shown in Table 6 below.

 Example 4

Table 7 below shows numerical examples according to the fourth embodiment of the present invention.

7 is a lens configuration diagram illustrating a lens arrangement of a lens system for a micro camera module according to a fourth exemplary embodiment of the present invention, and FIGS. 8A to 8C illustrate aberrations of the lens systems shown in Tables 7 and 7. .

In Example 4, the effective focal length f of the entire lens system is 8.297 mm, the F number F _No is 2.8, and the telephone angle 2ω of the lens is 60 °, and the distance from the aperture stop to the top surface TL ) Is 10.0 mm.

In Example 4, the first lens L1 is a glass lens, the second lens L2 is a plastic lens using OKP4 manufactured by Osaka Gas Chemical Co., Ltd., and the third lens L3 and the fourth lens ( L4) is a plastic lens using ZEONEX series E48R.

In Table 7, * represents an aspherical surface, and the values of the koenic constant (K) and the aspherical coefficients (A, B, C, and D) of Equation 1 are shown in Table 8 below.

Example 5

Table 9 below shows a numerical example according to the fifth embodiment of the present invention.

9 is a lens configuration diagram illustrating a lens arrangement of a lens system for a micro camera module according to a fifth embodiment of the present invention, and FIGS. 10A to 10C show aberrations of the lens systems shown in Tables 9 and 9. .

In Example 5, the effective focal length f of the whole lens system is 8.938 mm, the F number F _No is 2.8, and the telephone angle 2ω of the lens is 60 °, and the distance from the aperture stop to the top surface TL ) Is 10.0 mm.

In Example 5, the first lens L1 is a glass lens, and the second lens L2 is a plastic lens using OKP4 manufactured by Osaka Gas Chemical Co., Ltd., and the third lens L3 and the fourth lens ( L4) is a plastic lens using ZEONEX series E48R.

In Table 9, * represents an aspherical surface, and the values of the koenic constant (K) and the aspherical coefficients (A, B, C, and D) of Equation 1 are shown in Table 10 below.

Example 6

Table 11 below shows a numerical example according to the sixth embodiment of the present invention.

FIG. 11 is a lens configuration diagram illustrating a lens arrangement of the lens system for the ultra-compact camera module according to the sixth embodiment of the present invention, and FIGS. 12A to 12C show aberrations of the lens systems shown in Tables 11 and 11. .

In Example 6, the effective focal length f of the entire lens system is 8.646 mm, the F number F _No is 2.8, and the telephone angle (2ω) of the lens is 60 °, the distance from the aperture stop to the top surface (TL) ) Is 10.683 mm.

In addition, in Example 6, the second lens L2 is a plastic lens using OKP4 of Osaka Gas Chemical Co., Ltd., and the first lens L1, the third lens L3, and the fourth lens L4 are ZEONEX. Plastic lens using) series E48R.

In Table 11, * represents an aspherical surface, and the values of the koenic constant (K) and aspherical coefficients (A, B, C, D, and E) according to Equation 1 are shown in Table 12 below.

Example 7

Table 13 below shows a numerical example according to the seventh embodiment of the present invention.

13 is a lens configuration diagram showing the lens arrangement of the lens system for the micro camera module according to the seventh embodiment of the present invention, and FIGS. 14A to 14C show aberrations of the lens systems shown in Tables 12 and 12. .

In Example 7, the effective focal length f of the entire lens system is 8.656 mm, the F number F _No is 2.8, and the tele-angle (2ω) of the lens is 60 °, the distance from the aperture stop to the upper surface (TL) ) Is 10.5 mm.

In addition, in Example 7, the second lens L2 is a plastic lens using OKP4 manufactured by Osaka Gas Chemical Co., Ltd., and the first lens L1, the third lens L3, and the fourth lens L4 are ZEONEX. Plastic lens using) series E48R.

In Table 13, * represents an aspherical surface, and the values of the koenic constant (K) and aspherical coefficients (A, B, C, D, and E) according to Equation 1 are shown in Table 14 below.

The values of Conditional Formulas 1 to 9 for Examples 1 to 7 are shown in Table 15 below.

As shown in Table 15, Examples 1 to 7 of the present invention satisfy conditional expressions 1 to 9, and as shown in FIGS. 2, 4, 6, 8, 10, 12, and 14. It can be seen that a lens system having excellent characteristics of the aberration is implemented.

As described above, according to the present invention, there is an effect that a compact and ultra-compact lens system can be obtained with a high resolution and a small number of lenses.

In addition, by employing a large number of aspherical refracting surfaces, it is possible to obtain a lens system capable of simultaneously miniaturizing and high resolution with only four lenses.

In addition, by using a plastic lens, not only can be reduced in weight, but also has an advantageous effect that a lens system that can be easily manufactured, can be mass-produced, and the manufacturing cost is low.

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.

Claims (9)

A lens system for use in a micro camera module having at least one lens mounted inside a housing and an image sensor corresponding to an image surface by the lens, Place the aperture stop closest to the object side and then in sequence from the object side to the front face, A first lens having positive refractive power; A second lens having negative refractive power; A third lens having positive refractive power; And A fourth lens having negative refractive power; Including, At least three refractive surfaces of the refractive surfaces of the first to fourth lenses are aspherical, The following conditional expression 1 is satisfied with respect to the refractive power of said first lens, and the following conditional expression 2 is satisfied with respect to the optical axis direction dimension of the whole lens system. (Condition 1) 0.4 <f _I / f <0.7 (Condition 2) TL / f <1.4 Where f is the composite effective focal length of the entire lens system. f _Ⅰ : Effective focal length of the first lens         TL: Distance from the dog stop to the top delete The method of claim 1, And the following conditional expression 3 is satisfied with respect to the shape of the object-side refractive surface of the first lens. (Condition 3) 0.3 <r ₁ / f <0.6 Where r ₁ : radius of curvature of the object-side refractive surface of the first lens The method of claim 3, And the following conditional expression 4 is satisfied with respect to the refractive power of the second lens, and the following conditional expression 5 is satisfied with respect to the shape of the second lens. (Condition 4) 0.6 <| f _II | / f <1.2 (Condition 5) 0.4 <r ₄ / f <0.7 Where f _II : focal length of the second lens (f _II <0) r ₄ : radius of curvature of the image-side refractive surface of the second lens The method of claim 4, wherein The following conditional expression 6 is satisfied with respect to the refractive power of the third lens, and the following conditional expression 7 is satisfied with respect to the shape of the image-side refractive surface of the third lens. (Condition 6) 0.5 <f _III / f <5 (Condition 7) 0.2 <| r ₆ | <0.5 Here, f _III : focal length of the third lens r ₆ : radius of curvature of the image-side refractive surface of the third lens (r ₆ <0) The method of claim 5, The following conditional expression 8 is satisfied with respect to the refractive power of the fourth lens, and the following conditional expression 9 is satisfied with respect to the shape of the image-side refractive surface of the fourth lens. (Condition 8) 0.5 <| f _IV | / f <5 (Condition 9) 0.2 <r ₈ <1.5 Here, f _IV : focal length of the fourth lens (f _IV <0) r ₈ : radius of curvature of the image-side refractive surface of the fourth lens The method according to any one of claims 1 and 3 to 6, At least three lenses of the first to fourth lenses is a lens system for a micro camera module, characterized in that made of plastic. The method of claim 7, wherein The second to fourth lenses, the lens system for a micro camera module, characterized in that made of plastic. The method according to any one of claims 1 and 3 to 6, Each of the first to fourth lenses has at least one refractive surface consisting of aspherical surfaces.

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