KR20080072333A - Subminiature optical system - Google Patents

Abstract

A micro optical system is provided to decrease a length of the optical system by decreasing the number of lenses in the optical system. A micro optical system includes first to third lenses, which are sequentially arranged from an object side. The first lens(L1) has a positive refractive power and has a meniscus shape convex toward the object side. The second lens(L2) has a negative refractive power and has a meniscus shape convex toward an image side. The third lens(L3) has a positive refractive power. A relation, 2.5 < V1/V2 < 3.5, is satisfied, where V1 and V2 and Abbe numbers of the first and second lenses, respectively.

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 top curvature, and (c) shows distortion aberration.

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 top curvature, and (c) shows distortion aberration.

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 top curvature, and (c) shows distortion aberration.

Explanation of symbols on the main parts of the drawings

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

L3 ... 3rd lens AS ... opening aperture

OF ... optical filter IP ... top

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, the mobile communication terminal initially had only a function of a communication means, but as its use is increased, a variety of required services such as photographing or image transmission or communication have been diversified. As a result, the functions and services have evolved. have. Recently, an expanded new concept mobile communication terminal, ie, a camera phone or a camera mobile phone, which combines digital camera technology and mobile phone technology, has been in the spotlight.

In particular, in recent years, compact, light weight, and low cost have been strongly demanded for imaging optical systems mounted in camera phones and PC cameras, and pixel sizes of image sensors such as CCD (solid-state imaging device) and CMOS (compensated metal semiconductor) ( As the pixel size becomes smaller, higher resolution is required for the imaging optical system using such an image sensor.

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

However, in such an imaging optical system, a lens made of a glass material and a lens made of a plastic material may be used to improve lens performance and correct aberrations, but a high pixel number may be satisfied. There was a limit to the miniaturized design that was small enough to meet the needs of consumers.

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 microscopic imaging optical system capable of effectively correcting chromatic aberration of a lens to prevent deterioration of color image quality.

In addition, an object of the present invention is to provide an ultra-small imaging optical system that is small in number of lenses, compact in size, very short in overall length, and obtains high resolution.

In addition, an object of the present invention is to provide an ultra-compact imaging optical system that is light in weight, less sensitive to temperature changes, reduces manufacturing costs, and is capable of mass production.

As one aspect for achieving the above object, the present invention, in order from the object side, the first lens having a positive refractive power, convex toward the object side; A second lens having a meniscus shape having negative refractive power and convex toward the image; And a third lens having positive refractive power; And a condition that the following conditional expression 1 is satisfied with respect to the Abbe number of the first lens and the second lens.

Conditional Expression 1 2.5 <V1 / V2 <3.5

Where V1: Abbe number of the first lens

        V2: Abbe number of the second lens

Preferably, the aperture stop for removing unnecessary light from the light incident from the first lens between the first lens and the second lens; It may further include.

Preferably, the first lens is made of glass, the second lens and the third lens are made of plastic, and at least one of the refractive surfaces of the second lens and the refractive surface of the third lens is an aspheric surface. Can be done.

More preferably, the following Conditional Expression 2 can be further satisfied with respect to the dimension in the optical axis direction.

[Condition Formula 2] 1.0 <TL / EFL <1.4

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

        EFL: Effective Focal Length of All Optical Systems

More preferably, the image sensor for sensing the light incident from the third lens and corresponding to the image surface; It further includes, and can satisfy the following conditional formula 3 with respect to the dimension of the optical axis direction.

[Condition 3] 0.8 <TL / D <1.0

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

        D: diagonal length of image sensor

More preferably, the following Conditional Expression 4 may be further satisfied with respect to the refractive indices of the first lens and the second lens.

Conditional Expression 4 N1 / N2 <0.95

Here, N1: refractive index of the first lens

        N2: refractive index of the second lens

More preferably, the following Conditional Expression 5 may be further satisfied with respect to the shape of the first lens.

Conditional Expression 5 0.30 <R1 / EFL <0.45

Where R1 is the radius of curvature of the object-side surface of the first lens.

        EFL: Effective Focal Length of All Optical Systems

More preferably, the following Conditional Expression 6 may be further satisfied with respect to the refractive power of the second lens and the third lens.

[Condition 6] 0.3 <| f2 / f3│ <0.8

Here, f2: focal length of the second lens

        f3: Focal length 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 microscopic imaging optical system according to the present invention includes a first lens L1 made of glass material having a meniscus shape convex toward the object side and having positive refractive power, in order from the object side, and the image side. And a second lens L2 of plastic material having a convex meniscus shape and having a negative refractive power, and a third lens L3 of plastic material having a positive refractive power. An aperture stop AS is provided between the second lenses L2. In this case, the first lens L1 is less sensitive to temperature change by using a glass material, and the second lens L2 and the third lens L3 are easily formed by using a plastic material.

On the other hand, between the third lens (L3) and the image surface (IP) is provided with an optical filter (OF) consisting 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 and the first lens L1 and the second lens L2 have a meniscus shape facing each other, thereby miniaturizing the optical system. In addition, the refractive surfaces of the second lens L2 and the third lens L3 are formed as an aspherical surface to correct the aberration so that the optical characteristic is excellent.

That is, through the first lens L1 having positive refractive power and the second lens L2 having negative refractive power, chromatic aberration can be corrected and high resolution can be realized. In particular, the second lens L2 and the third lens ( By using L3) as an aspherical lens, the resolution of the lens can be improved and various aberrations such as spherical aberration can be reduced, and a compact and excellent optical system can be realized.

The chromatic aberration can be sufficiently corrected by ideally setting the difference between the Abbe number of the first lens L1 and the second lens L2. In addition, the third lens L3 has a positive refractive power, converges luminous flux, and provides an appropriate focal length.

Meanwhile, since the first lens L1 is formed of a glass material having a small change in refractive index at the time of temperature change, the positional change of the shop is minimized due to the temperature change, and the second lens L2 and the third lens L3 are processed. By forming a plastic material, it is possible to reduce the manufacturing cost and improve the light weight and processability, and to realize a high resolution and ultra-small imaging optical system using only three lenses.

The first lens L1, the second lens L2, and the third lens L3 have positive, negative, and positive refractive forces, respectively, and the meniscus shape and the aspherical surface are appropriately formed in each lens, thereby providing the lens. By reducing the angle of incidence of the edges of the image sensor, the amount of light in the center and the 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 6 under such an overall configuration.

Conditional Expression 1 2.5 <V1 / V2 <3.5

Here, V1 is the Abbe number of the first lens L1, and V2 is the Abbe number of the second lens L2.

Condition 1 is related to the correction of chromatic aberration, and if it is out of the lower limit of Condition 1, the chromatic aberration increases, and the color of the high resolution sensor is deteriorated. This raises the manufacturing cost.

[Condition Formula 2] 1.0 <TL / EFL <1.4

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

Conditional Expression 2 defines the dimensions of the entire optical system and is a condition for miniaturization. If the length of the optical system is shorter than the lower limit of Conditional Expression 2, the length of the optical system may be shortened. However, as the angle of view becomes larger, the shape of the lens may not be actually manufactured. The length becomes longer and contrary to the point of view of the ultra-small which is a feature of the present invention.

[Condition 3] 0.8 <TL / D <1.0

Here, TL is the distance from the object side surface 1 of the first lens L1 to the image surface 10, and D is the diagonal length of the image sensor IP.

Conditional Expression 3 defines the dimensions of the entire optical system and is a condition for miniaturization. If the upper limit value of Conditional Expression 2 is removed, it is advantageous in terms of correction of the aberration, but the length of the electric field is longer, which is contrary in view of the ultra-miniature feature of the present invention. In addition, the deviation from the lower limit of Conditional Equation 3 may be advantageous in terms of miniaturization, but since the overall length becomes too short, it is difficult to satisfy the optical characteristics required for the optical system.

Conditional Expression 4 N1 / N2 <0.95

Here, N1 is a refractive index of the first lens L1, and N2 is a refractive index of the second lens L2.

Condition 4 is related to the material as a condition regarding the refractive indices of the first lens L1 and the second lens L2.

Conditional Expression 4 is for forming the second lens L2 from a plastic material, and considering the fact that at least one of the refractive surfaces of the second lens L2 is formed as an aspherical surface, Condition 4 is a condition for manufacturing the lens with low cost and high productivity. .

If out of the upper limit of Conditional Expression 4, chromatic aberration is increased, the color is degraded in the high resolution sensor, and the material cost is increased, which is contrary to the viewpoint of low cost.

Conditional Expression 5 0.30 <R1 / EFL <0.45

Here, R1 is the radius of curvature of the object-side surface 1 of the first lens L1, and EFL is the effective focal length of the entire optical system.

Conditional Expression 5 relates to the shape of the first lens L1, and is for aberration correction.

If the deviation from the lower limit of Conditional Expression 5 is difficult to correct spherical aberration and coma aberration, the radius of curvature of the object-side surface 1 of the first lens L1 is reduced, making the first lens L1 difficult. On the contrary, if it deviates from the upper limit of Conditional Expression 5, the total length of the optical system becomes long, which is contrary to the point of view of the ultra-miniature feature of the present invention.

[Condition 6] 0.3 <| f2 / f3│ <0.8

Here, f2 is the focal length of the second lens L2, and f3: the focal length of the third lens L3.

Conditional Expression 6 defines the ratio of the focal lengths of the second lens L1 and the third lens L3, and is a conditional expression relating to the refractive power of the second lens L2 and the third lens L3. When the value falls outside the lower limit of Conditional Expression 6, correction of the distortion aberration becomes difficult, and the telecentric characteristic becomes self. On the contrary, the deviation from the upper limit makes it difficult to correct the aberration due to the occurrence of the distortion aberration, as well as the correction of the upper surface curvature.

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

As described above, the first to third embodiments below all have a meniscus shape convex toward the object side in order from the object side, and have a first lens L1 of glass material having positive refractive power. And a second lens L2 of plastic material having a meniscus shape convex toward the image and having negative refractive power, and a third lens L3 of plastic material having positive refractive power. An aperture stop AS is provided between the lens L1 and the second lens L2.

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 following embodiments, the first lens L1 is made of glass material so as not to be sensitive to temperature change, and the second lens L2 and the third lens L3 are easy to form aspherical surface by using a plastic material. It was made.

In addition, the following embodiments are for an optical system having an F number of approximately 2.8, an angle of view of 60 degrees or more, a full length of 5 mm or less, and suitable for a 2 megapixel CCD or CMOS, but without departing from the spirit of the present invention. Alternatively, an optical system suitable for the type of imaging device may be set.

On the other hand, the aspherical surface used in each of the following examples is obtained from the known equation (1), 'E and used in the Conic constant (K) and aspherical coefficients (A, B, C, D, E) The number following is the power of ten. 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

        r: radius of curvature 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 the lens arrangement of the microscopic imaging optical system according to the first embodiment of the present invention, and FIGS. 2 (a) to 2 (c) show the number of optical systems shown in Table 1 and FIG. Indicates a roadway.

In the first embodiment, the F number FNo is 2.8, the angle of view is 65.4 degrees, and the distance TL from the object-side surface 1 to the image surface IP of the first lens L1 is 4.28 mm, the effective focal length EFL of the optical system is 3.48 mm, the focal length f1 of the first lens L1 is 2.727 mm, and the focal length f2 of the second lens L2 is -9.827 mm. The focal length f3 of the third lens L3 is 14.576 mm, and the diagonal length D of the image sensor IP is 4.5 mm.

Face number Curvature Radius (Ri) Thickness or distance (Ti) Refractive Index (Ni) Abbe (Vi) Remarks *One 1.0545 0.6500 1.487 70.4 First lens *2 4.0839 0.1415 3 ∞ 0.5738 Aperture aperture *4 -0.5725 0.3800 1.632 23.4 Second lens * 5 -0.7929 0.1000 * 6 5.7648 1.1000 1.547 56 Third lens * 7 19.4556 0.2000 *8 ∞ 0.30000 1.517 64.2 Optical filter 9 ∞ 0.83270 10 ∞ 0.00000 Top

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 formed of glass material, and the second lens L2 formed of plastic material The object side surface 4 and the image side surface 5 of the object side surface 6 and the image side surface 7 of the third lens L3 formed of a plastic material are aspherical surfaces.

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

Face number One 2 4 5 6 7 K -1.15656 30.1899 -0.24702 -0.58063 -205.0239 -500 A 0.119736 -0.13271 0.316585 0.016344 -0.038891 -0.10999 B 0.069814 0.554924 -0.85026 0.23852 0.0264505 0.046991 C -0.14912 -3.82182 8.417685 -0.23496 -0.012272 -0.02237 D 0.413927 8.140474 -20.5941 1.168811 0.0027449 0.005834 E -0.47332 -7.1654 33.4292 -0.78391 -0.000141 -0.00074 F 0 0 -5.90927 -0.05469 -2.54E-05 9.07E-06

[Second Example ]

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

3 is a lens configuration diagram showing the lens arrangement of the microscopic imaging optical system according to the second exemplary embodiment of the present invention, and FIGS. 4 (a) to 4 (c) show the number of optical systems shown in Table 3 and FIG. Indicates a roadway.

In the second embodiment, the F number FNo is 2.8, the angle of view is 65.4 degrees, and the distance TL from the object-side surface 1 to the image surface IP of the first lens L1 is 4.20 mm, the effective focal length EFL of the optical system is 3.49 mm, the focal length f1 of the first lens L1 is 2.70 mm, and the focal length f2 of the second lens L2 is -12.821 mm. The focal length f3 of the third lens L3 is 21.62 mm, and the diagonal length D of the image sensor IP is 4.5 mm.

Face number Curvature Radius (Ri) Thickness or distance (Ti) Refractive Index (Ni) Abbe (Vi) Remarks *One 1.06134 0.65000 1.487 70.4 First lens *2 4.38067 0.13622 3 ∞ 0.54599 Aperture aperture *4 -0.57357 0.38000 1.632 23.4 Second lens * 5 -0.77605 0.10000 * 6 8.38160 1.06000 1.547 56 Third lens * 7 27.55165 0.20000 8 ∞ 0.30000 1.517 64.2 Optical filter 9 ∞ 0.90897 10 ∞ 0.00000 Top

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 formed of glass material, and the second lens L2 formed of plastic material The object side surface 4 and the image side surface 5 of the object side surface 6 and the image side surface 7 of the third lens L3 formed of a plastic material are aspherical surfaces.

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

Face number One 2 4 5 6 7 K -1.24298 34.62688 -0.20437 -0.70014 -369.231 120.5883 A 0.131066 -0.14475 0.305382 0.037124 -0.04179 -0.12312 B 0.04858 0.588776 -0.17909 0.221987 0.027064 0.049324 C -0.14771 -4.0422 7.675623 -0.0825 -0.01104 -0.02169 D 0.46758 8.472023 -21.6035 1.096296 0.002631 0.005178 E -0.58218 -7.26862 38.1457 -0.95821 -0.00028 -0.00061 F 0 0 0 0 0 0

[Third Example ]

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

5 is a lens configuration diagram showing the lens arrangement of the microscopic imaging optical system according to the third embodiment of the present invention, and FIGS. 6 (a) to 6 (c) show the number of optical systems shown in Tables 5 and 5. Indicates a roadway.

In the third embodiment, the F number FNo is 2.79, the angle of view is 65.5 degrees, and the distance TL from the object-side surface 1 to the image surface IP of the first lens L1 is 4.29 mm, the effective focal length EFL of the optical system is 3.475 mm, the focal length f1 of the first lens L1 is 2.82 mm, and the focal length f2 of the second lens L2 is -30.03 mm. The focal length f3 of the third lens L3 is 79.21 mm, and the diagonal length D of the image sensor IP is 4.5 mm.

Face number Curvature Radius (Ri) Thickness or distance (Ti) Refractive Index (Ni) Abbe (Vi) Remarks *One 1.18326 0.60000 1.487 70.4 First lens *2 6.92164 0.11215 3 ∞ 0.64488 Aperture aperture *4 -0.58085 0.38000 1.632 23.4 Second lens * 5 -0.75176 0.10000 * 6 5.69166 0.96444 1.53 56 Third lens * 7 6.19274 0.20000 8 ∞ 0.30000 1.517 64.2 Optical filter 9 ∞ 0.98478 10 ∞ 0.00000 Top

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 formed of glass material, and the second lens L2 formed of plastic material The object side surface 4 and the image side surface 5 of the object side surface 6 and the image side surface 7 of the third lens L3 formed of a plastic material are aspherical surfaces.

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

Face number One 2 4 5 6 7 K -1.76796 92.02347 -0.31802 -0.79222 -268.589 -260.932 A 0.118832 -0.17258 0.390517 0.044195 -0.01541 -0.10432 B 0.003997 0.830445 -0.81298 0.225819 0.010559 0.04039 C -0.09688 -5.06768 9.01698 0.168682 -0.00846 -0.01559 D 0.171298 11.07652 -19.6179 0.368336 0.003435 0.003019 E -0.32189 -9.58115 21.67051 -0.46183 -0.00051 -0.00031 F 0 0 0 0 0 0

As shown in FIG. 2, FIG. 4, and FIG. 6, the optical system having excellent characteristics of the first aberration can be obtained through the above embodiments.

On the other hand, the values of the conditional formulas 1 to 6 for the above Examples 1 to 3 are as shown in Table 7.

Conditional Expression 1 (V1 / V2) Conditional Expression 2 (TL / EFL) Conditional Expression 3 (TL / D) Conditional Expression 4 (N1 / N2) Conditional Expression 5 (R1 / EFL) Conditional Expression 6 (f2 / f3) Example 1 3.0 1.23 0.951 0.91 0.303 0.674 Example 2 3.0 1.23 0.951 0.91 0.304 0.593 Example 3 3.0 1.23 0.953 0.91 0.340 0.379

As shown in Table 7, it can be seen that the first to third embodiments of the present invention satisfy conditional expressions 1 to 6.

As described above, according to the present invention, it is possible to obtain a high resolution suitable for a high-pixel sensor using only three lenses, and to realize a compact and extremely small imaging optical system with a small number of lenses. .

In addition, by using two plastic lenses, it is possible not only to reduce the weight, but also to produce an optical system that can be easily manufactured and mass-produced, and the manufacturing cost is reduced.

In addition, by configuring the first lens as a lens of low dispersion glass material, an effect of effectively correcting chromatic aberration and minimizing shop movement due to temperature change is obtained.

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 (8)

In order from the object side, A first lens of a meniscus shape having positive refractive power and convex toward the object; A second lens having a meniscus shape having negative refractive power and convex toward the image; And A third lens having positive refractive power; And the following Conditional Expression 1 regarding the Abbe's number of the first lens and the second lens. Conditional Expression 1 2.5 <V1 / V2 <3.5 Where V1: Abbe number of the first lens         V2: Abbe number of the second lens The method of claim 1, An aperture stop for removing unnecessary light from the light incident from the first lens between the first lens and the second lens; Miniature imaging optical system further comprising. The method of claim 1, The first lens is made of a glass material, The second lens and the third lens is made of a plastic material, at least one of the refractive surface of the refractive surface of the second lens and the third lens of the ultra-compact optical system characterized in that the aspherical surface. The method according to any one of claims 1 to 3, The ultra-small imaging optical system which satisfy | fills following conditional expression 2 further with respect to the dimension of an optical axis direction. [Condition Formula 2] 1.0 <TL / EFL <1.4 TL: distance from the object-side surface of the first lens to the image surface         EFL: Effective Focal Length of All Optical Systems The method according to any one of claims 1 to 3, An image sensor sensing light incident from the third lens and corresponding to an image surface; Additionally contains The ultra-small imaging optical system which satisfy | fills following conditional expression 3 further with respect to the dimension of an optical axis direction. [Condition 3] 0.8 <TL / D <1.0 TL: distance from the object-side surface of the first lens to the image surface         D: diagonal length of image sensor The method according to any one of claims 1 to 3, The ultra-compact optical system further satisfying the following conditional expression 4 with respect to the refractive index of the first lens and the second lens. Conditional Expression 4 N1 / N2 <0.95 Here, N1: refractive index of the first lens         N2: refractive index of the second lens The method according to any one of claims 1 to 3, The ultra-small imaging optical system further satisfying the following conditional expression 5 regarding the shape of the said 1st lens. Conditional Expression 5 0.30 <R1 / EFL <0.45 Where R1 is the radius of curvature of the object-side surface of the first lens.         EFL: Effective Focal Length of All Optical Systems The method according to any one of claims 1 to 3, And the following Conditional Expression 6 is further satisfied with respect to the refractive power of the second lens and the third lens. [Condition 6] 0.3 <| f2 / f3│ <0.8 Here, f2: focal length of the second lens         f3: Focal length of the third lens

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