KR101904059B1 - Subminiature image pickup lens system for preventing inner reflection - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-small imaging lens system used in a mobile phone, a tablet PC camera, and the like. The micro-lens imaging lens system includes: a first plastic lens having a positive refractive power, the object side surface and the upper surface being convexly formed on the object side; A second plastic lens having a negative refractive power and having both an object side surface and an upper side surface formed convex toward the object side; A third plastic lens having a negative refractive power and having both an object side surface and an upper side surface formed to be convex upward; A fourth plastic lens having a positive refractive power and having both an object side surface and an upper side surface formed to be convex upward; A fifth plastic lens having a negative refractive power, the center of the object side surface being concave toward the object side and convex toward the periphery, the center of the image side being concave upward and convex toward the periphery; And the following condition is satisfied.
1.15 < AL11 / AL52 < 1.2
AL52 <AL11 <40
Here, AL11 is the maximum surface angle of the object side surface of the first plastic lens, and AL52 is the maximum surface angle of the upper surface of the fifth plastic lens.
According to such a configuration, it is possible to provide an ultra-small imaging lens system that can control the surface angle with respect to the existing optical system to mitigate surface reflection, prevent deterioration of image quality, and contribute to productivity improvement.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a subminiature image pickup lens system,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-small imaging lens system used in a mobile phone, a tablet PC camera, and the like.

Recently, as the design of the smart phone has become slimmer, the size of the image sensor chip can be made smaller, the lens of smaller diameter can be used, and the focal length can be reduced, thereby reducing the size of the camera module.

In an image sensor composed of CCD or CMOS, the pixel size constituting the light receiving portion of the image sensor is reduced in order to obtain a desired resolution without increasing the chip size.

In order to achieve higher resolution (MTF performance) with smaller sensor pixel size, it is increasingly desired to improve the resolution by increasing the number of lenses or utilizing a glass material having high transmittance and refractive index. In particular, in recent years, more than 13 million high-resolution mobile imaging lens systems are often constructed by mixing five or more plastic lenses or some glass lenses.

When a plastic lens and a glass lens are mixed with each other to achieve the above object, the cost of the lens is increased. In order to improve the performance of the lens module and improve the light transmittance, it is necessary to reduce the total length of the lens in order to reduce the size of the lens within a limited range. If the lens surface is refracted by the lens surface, The angle formed by the optical axis and the optical axis becomes large.

These characteristics result in poor tolerance to tolerances, which can degrade yield and productivity. In addition, as the number of constituent lenses increases, the reflected light is increased, and the light reflected from the lens surface or the flange portion is re-reflected from each other. Therefore, unnecessary light rays, irrelevant to the imaging, are incident on the imaging surface, . This may lead to deterioration of the quality of the captured image.

Korean Patent Application No. 10-2012-0158535

SUMMARY OF THE INVENTION [0008] Accordingly, the present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an ultra-small imaging lens system which is designed to provide an image that is ultra- have.

According to an aspect of the present invention, there is provided an ultra-small imaging lens system comprising: a first plastic lens having positive refractive power and having an object-side surface and an upper surface convexly formed on an object side; A second plastic lens having a negative refractive power and having both an object side surface and an upper side surface formed convex toward the object side; A third plastic lens having a negative refractive power and having both an object side surface and an upper side surface formed to be convex upward; A fourth plastic lens having a positive refractive power and having both an object side surface and an upper side surface formed to be convex upward; A fifth plastic lens having a negative refractive power, the center of the object side surface being concave toward the object side and convex toward the periphery, the center of the image side being concave upward, and convex toward the periphery; And the following condition is satisfied.

1.15 < AL11 / AL52 < 1.2

AL52 <AL11 <40

Here, AL11 is the maximum surface angle of the object side surface of the first plastic lens, and AL52 is the maximum surface angle of the upper surface of the fifth plastic lens.

The micro-imaging lens system satisfies the following conditions.

0.71 < (R4o-R4i) / (R4o + R4i) < 1

T45 / CT4 < 0.5

Here, R4o is the radius of curvature of the object side surface of the fourth plastic lens, R4i is the radius of curvature of the image side surface of the fourth plastic lens, T45 is the radius of curvature of the image side surface of the fifth plastic lens And CT4 is the center thickness of the fourth plastic lens.

The micro-imaging lens system satisfies the following conditions.

1.0 < TTL / F < 1.2

Here, TTL is the total length of the lens system, and F is the focal length of the entire lens system.

According to the present invention, it is possible to provide an ultra-small imaging lens system capable of reducing the surface reflection by controlling the surface angle with respect to the existing optical system, preventing degradation of image quality, contributing to productivity, .

1 is a diagram showing the configuration of an imaging lens system according to an embodiment of the present invention.
Fig. 2 is a view for tracking the flow of light when an object is photographed in the imaging lens system of Fig. 1. Fig.
3 is a spherical aberration diagram according to an embodiment of the imaging lens system of Fig.
4 is a schematic of the astigmatic gradients according to the embodiment of the imaging lens system of FIG.
5 is a distortion aberration diagram according to an embodiment of the imaging lens system of Fig.
FIG. 6A is a view showing the maximum surface angle of the object side surface of the first plastic lens of the present invention, and FIG. 6B is a view showing the maximum surface angle of the upper surface of the fifth plastic lens.
FIG. 7A shows an image image before reflecting the conditional expression of the present invention at a half angle of view of 36 DEG, and FIG. 7B shows an image image after reflecting the conditional expression of the present invention at a half angle of view of 36 DEG.
FIG. 8A shows an image image before the conditional expression of the present invention is reflected at a half angle of view of 60 DEG, and FIG. 8B shows an image image after reflecting the conditional expression of the present invention at a half angle of view of 60 DEG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals refer to like elements throughout. The same reference numerals in the drawings denote like elements throughout the drawings.

1 is a diagram showing the configuration of an imaging lens system according to an embodiment of the present invention. Fig. 2 is a view for tracking the flow of light when an object is photographed in the imaging lens system of Fig. 1. Fig. 3 is a spherical aberration diagram according to an embodiment of the imaging lens system of Fig. 4 is a schematic of the astigmatic gradients according to the embodiment of the imaging lens system of FIG. 5 is a distortion aberration diagram according to an embodiment of the imaging lens system of Fig. FIG. 6A is a view showing the maximum surface angle of the object side surface of the first plastic lens of the present invention, and FIG. 6B is a view showing the maximum surface angle of the upper surface of the fifth plastic lens.

FIG. 8A shows an image image before the conditional expression of the present invention is reflected at a half angle of view of 60 DEG, and FIG. 8B shows an image image after reflecting the conditional expression of the present invention at a half angle of view of 60 DEG.

The imaging lens system 100 of the present invention can be used by being mounted on a camera for a mobile phone, a camera for a tablet PC, and the like.

The imaging lens system 100 includes, in order from the object side, an iris 101, a first plastic lens L1, a second plastic lens L2, a third plastic lens L3, a fourth plastic lens L4, A fifth plastic lens L5, and an optical filter 140.

Aperture 101 adjusts the size of the aperture to adjust the amount of light passing through the lens.

The first plastic lens L1 has a positive refractive power and the object side surface 111 and the upper side surface 112 are formed convex toward the object side. At least one of the object side surface 111 and the upper side surface 112 of the first plastic lens L1 is formed as an aspherical surface, and preferably both surfaces are formed as an aspherical surface.

The second plastic lens L2 has a negative refracting power and both the object side surface 121 and the upper side surface 122 are formed to be convex on the object side. At least one of the object side surface 121 and the upper side surface 122 of the second plastic lens L2 is formed as an aspherical surface, and preferably both surfaces are formed as an aspherical surface.

The third plastic lens L3 has a negative refractive power and both the object side surface 131 and the upper side surface 132 are formed to be convex upward. At least one of the object side surface 131 and the upper side surface 132 of the third plastic lens L3 is formed as an aspherical surface, and preferably both surfaces are formed as an aspherical surface.

The fourth plastic lens L4 has a positive refractive power and both the object side surface 141 and the upper side surface 142 are formed to be convex upward. At least one of the object side surface 141 and the upper side surface 142 of the fourth plastic lens L4 is formed as an aspherical surface, and preferably both surfaces are formed as an aspherical surface.

The fifth plastic lens L5 has a negative refractive power, and the center of the object side surface 151 is concave toward the object side and convex toward the periphery. The center of the image side 152 is concave upward, . This shape of the object side surface 151 and the upper side surface 152 of the fifth plastic lens L5 is for uniformly spreading the light on the upper surface 170. [ In the fifth plastic lens L5, at least one of the object side surface 151 and the upper side surface 152 is formed as an aspheric surface, and preferably both surfaces are formed as aspheric surfaces.

The imaging lens system 100 having such a configuration can provide a high-resolution, light-weight image with a reduced contrast of the conventional optical system.

The imaging lens system 100 of the present invention can satisfy the following conditional expressions 1 and 2.

1.15 < AL11 / AL52 < 1.2 [Conditional expression 1]

AL52 <AL11 <40 [Conditional expression 2]

Here, AL11 is the maximum surface angle of the object side surface 111 of the first plastic lens L1, and AL52 is the maximum surface angle of the upper surface 152 of the fifth plastic lens L5. The maximum surface angle means the maximum angle between the lens surface and the vertical axis. Referring to Figs. 6A and 6B, generally, the maximum surface angle is an angle at the effective diameter end.

By controlling the angle with respect to the object side surface 111 of the first plastic lens L1 which is the first surface to be incident on the optical system and the upper surface 152 of the fifth plastic lens L5 which is the surface immediately before being incident on the image sensor, It is possible to suppress the generation of reflection on the surface of the image sensor due to unnecessary light rays entering the image sensor.

If it is not more than the lower limit of the conditional expression (1), peripheral rays incident obliquely to the inside of the optical system may be irregularly reflected by the upper surface 152 of the fifth plastic lens L5 to cause a flare phenomenon. The smaller the radius of curvature is, the more the surface angle is increased, the inner reflection light is concentrated on the upper surface, and the larger the radius of curvature is, the more the surface is spread outward.

When the upper limit of conditional expression 1 is exceeded, AL11 becomes too large as compared with AL52, which makes it difficult to control surface reflection through angle control.

The reflection of the upper surface 112 of the first plastic lens L1 and the total reflection at the object side surface 111 of the first plastic lens L1 are generated on the upper surface The flare occurrence rate at which strong light enters is increased.

The reflection of the upper surface 152 of the fifth plastic lens L5 and the total reflection at the object side surface 151 of the fifth plastic lens L5 are generated when the upper limit value of the conditional expression 2 is exceeded, The reflection of the inner surface is generated.

The 40 DEG standard is a critical angle and is a standard calculated by the material refractive index 1.5348 of the first plastic lens L1 and the fifth plastic lens L5.

The reason why AL52 is lower than AL11 is that the shape of the fifth plastic lens L5 has a larger inflection point and the closer the image is to the upper surface, the higher the probability of occurrence of reflection on the inner surface.

Examples satisfying conditional formula 1: AL11 = 38 DEG, AL52 = 33 DEG

                               AL11 / AL52 = 1.1515

The imaging lens system 100 of the present invention can satisfy the following conditional expressions 3 and 4.

0.71 < (R4o-R4i) / (R4o + R4i) < 1 [Conditional Expression 3]

T45 / CT4 < 0.5 [Conditional expression 4]

Here R4o is the curvature radius of the object side surface 141 of the fourth plastic lens L4 and R4i is the curvature radius of the upper surface 142 of the fourth plastic lens L4. T45 is the distance between the upper surface 142 of the fourth plastic lens L4 and the object side surface 151 of the fifth plastic lens L5 and CT4 is the center thickness of the fourth plastic lens L4 .

The conditional expression 3 is intended to limit the shape of the fourth plastic lens L4 and induces the curvature radius of the object side surface 141 to be larger than the curvature radius of the upper side surface 142 to alleviate the occurrence of surface reflection. If the lower limit of the conditional expression (3) is exceeded, the surface angle of the fourth plastic lens (L4) becomes large, and the possibility of surface reflection by the upper surface (142) is increased.

(R4o-R4i) / (R4o + R4i) = (-7.9282 + 1.3429) / (-7.9282-1.3429) = 0.7103

According to the conditional expression (4), the optical system can be miniaturized while securing a mask insertion space for preventing surface reflection between the fourth plastic lens L4 and the fifth plastic lens L5.

When the upper limit value of the conditional expression 4 is exceeded, the fourth plastic lens L4 becomes thinner and the mass productivity is lowered due to the sensitivity effect, or the fourth plastic lens L4, which maintains a proper distance for inserting a mask The distance between the edge of the fifth plastic lens L4 and the edge of the fifth plastic lens L5 is increased so that it is impossible to shield the flange portion between the lenses by the mask insertion and the projectile There may be cases when you need to. For turning, tolerance management is required compared to the mask, foreign materials can be generated in the production and reliability test, and the unit price is also increased.

Examples satisfying conditional formula 4: T45 / CT4 = 0.2656 / 0.5368 = 0.4947

The imaging lens system 100 of the present invention can satisfy the following conditional expression (5).

1.0 < TTL / F < 1.2 [Conditional expression 5]

Here, TTL is the total length of the lens system (distance from the first surface to the top surface of the structure), and F is the focal length of the entire lens system.

The conditional expression (5) is a condition for achieving high performance and miniaturization by reducing the entire length of the lens system at the same time as satisfying the high resolution.

If it deviates from the lower limit value of the conditional expression 5, F becomes larger than the actual image height defined by the sensor, and it becomes difficult to satisfy the required angle of view or more.

If it deviates from the upper limit value of the conditional expression 5, the required angle of view is satisfied, but the length of the lens system increases, making miniaturization difficult.

Example satisfying conditional expression 5: TTL / F = 4.2 / 3.7008 = 1.1348

As described above, the imaging lens system 100 of the present invention satisfying all or a part of the conditional expressions 1 to 5 satisfies all of the five lenses by controlling the surface angle of the conventional optical system, It is made of plastic and can save money.

In addition, in the past, the productivity of the imaging lens system 100 of the present invention can be improved due to the surface reflection because the tolerance must be strictly mitigated to improve the productivity. However, the mass production yield and the productivity can be improved due to the reduced surface reflection.

Example

Hereinafter, a specific embodiment of the imaging lens system to which the configuration of the present invention is applied will be described.

The following table relates to numerical data of the optical elements constituting the imaging lens system. The unit of distance or length value applied in the table is "mm". The symbol "*" next to the face number indicates that it is aspherical.

Table 1 below shows design data of the imaging lens system according to this embodiment.

Face number Radius of curvature Thickness or distance (t) Refractive index (Nd) Abbe number (Vd) Remarks One 0.1765 2 -0.1765 iris * 3 1.1785 0.5849 1.5348 55.730 The first lens * 4 17.1262 0.0360 * 5 31.2924 0.2200 1.6397 23.516 The second lens * 6 2.6009 0.3078 * 7 -7.0578 0.2857 1.6397 23.516 Third lens * 8 -8.1862 0.4510 * 9 -7.9282 0.5368 1.5348 55.730 The fourth lens * 10 -1.3429 0.2656 * 11 -8.1507 0.3778 1.5348 55.730 The fifth lens * 12 1.3649 0.1153 13 0.05 14 0.21 1.5230 54.478 Optical filter 15 0.6401

Here, both of the first to fifth plastic lenses L1, L2, L3, L4, and L5 are formed as aspherical surfaces.

The aspherical shape of each lens is defined by the following equation. Conic The E used for the constant and aspheric coefficients and the numbers following it represent powers of ten.

Z: Distance from the lens apex to the optical axis direction

Y: Distance from the optical axis to the lens surface (height)

K: Conic constant (eccentricity)

C: paraxial curvature (= 1 / R)

R: Paraxial radius of curvature

Ai: Aspheric constant (i means the order of the aspherical coefficient)

Table 2 below shows the conic constant and aspherical coefficient for each lens in the embodiment of the present invention.

Face number K A B C D E F * 3 -0.1736 0.9965E-02 0.9364E-01 -0.5366E + 00 0.1589E + 01 -0.2631E + 01 0.2203E + 01 * 4 77.6610 -0.1529E + 00 0.2333E + 00 0.1474E + 01 -0.6994E + 01 0.1174E + 02 -0.9320E + 01 * 5 89.3599 -0.1230E + 00 0.5441E + 00 0.4448E + 00 -0.3663E + 01 0.5709E + 01 -0.3263E + 01 * 6 9.1896 -0.2632E-01 0.1615E + 00 0.5234E + 00 -0.2141E + 01 0.5021E + 01 -0.6246E + 01 * 7 90,000 -0.3047E + 00 0.1570E + 00 -0.4402E + 00 0.8345E + 00 -0.1136E + 00 0.0000E + 00 * 8 0.0000 -0.2577E + 00 0.2294E + 00 -0.1014E + 01 0.3188E + 01 -0.5331E + 01 0.4993E + 01 * 9 26.2554 -0.1185E-01 -0.7197E-01 0.6780E-01 -0.2572E-01 0.1614E-01 -0.9542E-02 * 10 -4.6076 -0.2957E-01 -0.3872E-01 0.1235E + 00 -0.8838E-01 0.2876E-01 -0.4551E-02 * 11 -85.5063 -0.3605E + 00 0.3222E + 00 -0.1454E + 00 0.3992E-01 -0.6724E-02 0.6413E-03 * 12 -9.9405 -0.1903E + 00 0.1432E + 00 -0.7684E-01 0.2763E-01 -0.6569E-02 0.9738E-03

Table 3 below shows performance values of the imaging lens system according to the preferred embodiment of the present invention.

f ₁ 2.3265 F-number (= F / D) 2.29 f ₂ -4.4036 FOV 76.7 f ₃ -87.991 TTL 4.20 f ₄ 2.9267 OAL 4.08 f ₅ -2.1469 FBL 0.85 F 3.7008 BFL 1.02

3 is a longitudinal spherical aberration diagram according to an embodiment of the present invention, and shows spherical aberration according to each wavelength. Here, the spherical aberration is an aberration caused by changing the focal distance according to the height at which a ray enters the entrance pupil, which is the only aberration of the axial object point. That is, the spherical aberration increases rapidly as the incident height of the light beam increases. In order to correct this, it is necessary to utilize an aspherical surface or minimize the change of incidence angle due to the incidence of incidents using high refractive index materials. In Fig. 3, the spherical aberration according to each wavelength is maintained at a good level.

4 illustrates the aberration characteristics of a tangential plane T and a sagittal plane S along the height of the top surface 170 as an astigmatic diagram according to an embodiment of the present invention. As shown, the astigmatism exhibits good characteristics.

Also, the curvature of the upper surface 170 is aberration appearing when the upper surface 170 is seen to be bent into a curved surface rather than a flat surface. When the focus is on the center, the periphery is blurred. When the focus is on the periphery, the center is blurred. Although a little aberration correction can be performed by tightening the aperture of the diaphragm 101, this is corrected by the depth of field, but there is little correction effect when the enlargement magnification is large. When the astigmatism is corrected in the case of the curvature of the upper surface 170, the curvature of the upper surface 170 is almost eliminated.

FIG. 5 shows distortion along the height of the top surface 170 in an embodiment of the present invention. Distortion aberration does not cause the image to be blurred or spread, but focus is oblique but oblique. Barrel type distortion occurs mainly from the center of the screen toward the outside, and a pincushion type distortion occurs from the periphery of the screen toward the center. As shown, the distortion aberration exhibits good characteristics.

FIG. 7A shows an image image before the reflection condition of the present invention (in particular, conditional expressions 1 and 2) is reflected at half angle of view of 36 DEG, and FIG. 7B shows an image image after reflecting the conditional expression of the present invention at half angle of view of 36 DEG.

Referring to FIGS. 7A and 8B, it can be seen that the application of the conditional formula of the present invention provides an image with much less surface reflection after application than before application.

As described above, the imaging lens system according to the embodiment of the present invention is designed to satisfy the conditional expressions 1 to 5. Such an imaging lens system may satisfy all of the conditional expressions, and only some of them may be satisfied.

The imaging lens system according to the present invention reduces the amount of surface reflection generated by controlling the angle of the surface, secures a high resolution through the reduced image sensor pixel size, and compensates sensitivity and secures the rear space. It is a high-performance optical system that can be applied to over 13 million high-resolution pixels that can overcome limitations of resolving power and resolution of surface aberration of conventional imaging lens, surface reflection, and the like.

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 will be.

100: imaging optical system
101: Aperture
111, 121, 131, 141, 151: object side surface
112, 122, 132, 142, 152: upper side
160: Optical filter
170: upper surface
L1: first plastic lens
L2: Second plastic lens
L3: Third plastic lens
L4: fourth plastic lens
L5: Fifth plastic lens

Claims (3)

In an ultra-small imaging lens system,
A first plastic lens having a positive refractive power, the object side surface and the upper side surface being convexly formed on the object side;
A second plastic lens having a negative refractive power and having both an object side surface and an upper side surface formed convex toward the object side;
A third plastic lens having a negative refractive power and having both an object side surface and an upper side surface formed to be convex upward;
A fourth plastic lens having a positive refractive power and having both an object side surface and an upper side surface formed to be convex upward;
A fifth plastic lens having a negative refractive power, the center of the object side surface being concave toward the object side and convex toward the periphery, the center of the image side being concave upward and convex toward the periphery;
Lt; / RTI &gt;
The following condition is satisfied.
1.15 < AL11 / AL52 < 1.2
AL52 <AL11 <40
0.71 < (R4o-R4i) / (R4o + R4i) < 1
T45 / CT4 &lt; 0.5
Here, AL11 is the maximum surface angle of the object side surface of the first plastic lens, AL52 is the maximum surface angle of the upper surface of the fifth plastic lens, R4o is the radius of curvature of the object side surface of the fourth plastic lens, T45 is the distance between the upper surface of the fourth plastic lens and the object side surface of the fifth plastic lens, and CT4 is the center thickness of the fourth plastic lens. delete The method according to claim 1,
The following condition is satisfied.
1.0 < TTL / F < 1.2
Here, TTL is the total length of the lens system, and F is the focal length of the entire lens system.

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