KR20210012213A - Miniature image pickup lens system - Google Patents

Abstract

The present invention relates to a compact photographing lens system loaded and used in a mobile phone, a tablet PC, a drone, etc. According to the present invention, the compact photographing lens system, in order from an object side, comprises: a first plastic lens which has a negative refractive power, and is formed such that an object-side surface thereof and an image surface thereof are convex towards an object; an aperture; a second plastic lens which has a positive refractive power, and is formed such that an object-side surface thereof is convex towards the object and an image surface thereof is convex upwards; a third plastic lens which has a negative refractive power, and is formed such that an object-side surface thereof is concave towards the object and an image surface thereof is convex upwards; a fourth plastic lens which has a positive refractive power, and is formed such that an object-side surface thereof is concave towards the object and an image surface thereof is convex upwards; and a fifth plastic lens which has a negative refractive power, is formed such that the center of an object-side surface thereof and the center of an image surface thereof are concave upwards, has one or more inflection points, and becomes more convex upwards towards the edge thereof. Accordingly, the MTF of a photographing optical system is stably maintained, and high resolution and weight reduction are realized. The curved shape and sensitivity are supplemented by properly arranging the refractive power of components from the object-side surface to the image surface to contribute to image quality degradation prevention and production.

Description

Compact image pickup lens system {Miniature image pickup lens system}

The present invention relates to a compact imaging lens system mounted and used in mobile phones, tablet PCs, drones, and the like.

Due to the development of the communication environment and the multifunctionalization of communication devices, camera functions of portable devices are being treated as basic specifications, and mobile phones, tablet PCs, and drones with small-sized imaging devices are rapidly spreading.

In particular, in the mobile phone imaging optical system, as the development of silicon semiconductor technology makes it possible to miniaturize pixels, the miniaturization of imaging modules such as CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) has rapidly progressed. The trend of high specification/high functionality of the camera module itself such as the variable aperture and the mounting of a DRAM stacked image sensor continues, and the adoption of dual, triple, and quadruple camera modules is increasing, and the number of mounted devices increases, and accordingly, various lenses are required. In accordance with such industry trends, optical lenses constituting an imaging module are also becoming high-pixel, miniaturized, and diversified.

For miniaturization of mobile lenses, aspheric plastic lenses are used mainly in mobile optical systems rather than glass lenses in order to limit the number of components and length, to realize weight reduction according to miniaturization, and to secure mass production and processability.

Plastic lenses have disadvantages in that they are less durable or less physicochemical compared to glass and the burden of manufacturing a mold, but they are widely used due to advantages such as mass production and cost reduction due to the application of precision injection molding technology.

If the total length of the lens is reduced under limited conditions for miniaturization and high specification/high functionality of the mobile lens, the surface angle of the lens increases due to the limitation of the lens thickness or the spacing between lenses, and thus the refractive angle increases. This results in a deterioration in sensitivity to change. This affects the decrease in the mass production yield and productivity of the optical lens.

In addition, in general, in the configuration of a mobile lens, the first lens is composed of a lens made of a low-refractive material, so that the refractive power is relatively strongly disposed at the front end of the entire lens system, increasing the sensitivity and causing light loss from the beginning.

Korean Patent Application No. 10-2012-0158535

Accordingly, the present invention was invented in view of the above circumstances, and by arranging the first lens with a low refractive power, the sensitivity at the front end is reduced to improve assembly performance, productivity, and minimize light loss, and the refractive power of the lens, An object of the present invention is to provide a compact imaging lens system that implements an image of 8 million pixels by appropriately arranging a shape, a lens configuration, an incidence angle of a chief ray, a distance between lenses, and a lens thickness.

The compact imaging lens system according to the present invention for realizing the above-described object includes: a first plastic lens having negative refractive power in order from an object side, and having an object side surface and an image side surface convexly formed toward the object side; iris; A second plastic lens having positive refractive power, the object side surface being convex toward the object side and the image side surface being convex toward the image side; A third plastic lens having negative refractive power, the object side surface being concave toward the object side and the image side surface being convex toward the image side; A fourth plastic lens having positive refractive power, the object side surface being concave toward the object side and the image side surface being convex toward the image side; A fifth plastic lens having negative refractive power, the object-side surface center and the image-side surface center being concave upward, having one or more inflection points, and being convex toward the image side toward the periphery; Includes.

Further, the compact imaging lens system satisfies the following conditions.

0 <｜K1/Vd1｜-｜∑Kn/Vdn｜ <0.004

Here, K1 is the refractive power of the first plastic lens, Kn is the refractive power of the n (n = 2-5)-th lens, Kn = 1/fn (fn: focal length of the n-th lens), and Vd1 is the first 1 is the Abbe number of the plastic lens, and Vdn is the Abbe number of the n (n = 2-5)th lens.

Further, the compact imaging lens system satisfies the following conditions.

｜K1｜+｜K3｜+｜K5｜ <｜K2｜+｜K4｜

0.1 <｜F/f1｜ <0.4

Here, Kn is the refractive power of the n-th lens, Kn = 1/fn (fn: focal length of the n-th lens), F is the focal length of the entire lens system, and f1 is the focal length of the first plastic lens.

Further, the compact imaging lens system satisfies the following conditions.

1.3 <TTL/F <1.5

0.455 <BFL/F

Here, TTL is the total length of the lens system, F is the focal length of the entire lens system, and BFL is the distance from the point where the image-side surface of the fifth plastic lens and the optical axis meet to the image surface.

Further, the compact imaging lens system satisfies the following conditions.

Vd1 <30

Vd2 <60

31 <｜Vd1-Vd2｜ <34

Here, Vd1 is an Abbe number of the first plastic lens, and Vd2 is an Abbe number of the second plastic lens.

According to the present invention, the MTF of the imaging optical system is stably maintained, while high resolution and light weight are realized, and the curvature shape and sensitivity are supplemented by appropriately arranging the refractive power of the components from the object side to the image side to prevent image quality degradation. And a compact imaging lens system that can contribute to production.

1 is a diagram showing a configuration of an imaging lens system according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a flow of light rays when photographing an object in the imaging lens system of FIG. 1.
3 is a spherical aberration diagram according to an embodiment of the imaging lens system of FIG. 1.
4 is an astigmatism diagram according to an embodiment of the imaging lens system of FIG. 1.
5 is a distortion aberration diagram according to an embodiment of the imaging lens system of FIG. 1.
6 is an MTF graph according to an image height in the embodiment of the imaging lens system of FIG. 1.
7 is a graph showing a change in MTF performance according to a focus position in the embodiment of the imaging lens system of FIG. 1.

Hereinafter, the configuration and operation of a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. Here, in adding reference numerals to elements of each drawing, it should be noted that only the same elements are marked with the same numerals as possible, even if they are indicated on different drawings.

1 is a diagram showing a configuration of an imaging lens system according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a flow of light rays when photographing an object in the imaging lens system of FIG. 1. 3 is a spherical aberration diagram according to an embodiment of the imaging lens system of FIG. 1. 4 is an astigmatism diagram according to an embodiment of the imaging lens system of FIG. 1. 5 is a distortion aberration diagram according to an embodiment of the imaging lens system of FIG. 1. 6 is an MTF graph according to an image height in the embodiment of the imaging lens system of FIG. 1. 7 is a graph showing a change in MTF performance according to a focal position in the embodiment of the imaging lens system of FIG. 1.

The imaging lens system 100 includes a first plastic lens (L1), a diaphragm 101, a second plastic lens (L2), a third plastic lens (L3), a fourth plastic lens (L4) in order from the object side, It includes a fifth plastic lens (L5), an optical filter 160, and an upper surface (image sensor) 170.

The first plastic lens L1 is made of plastic, has negative refractive power, and the object side surface 111 and the image side surface 112 are formed to be convex toward the object side. At least one of the object-side surface 111 and the image-side surface 112 of the first plastic lens L1 may be formed as an aspherical surface, and preferably, both surfaces may be formed as an aspherical surface.

The aperture 101 controls the amount of light passing through the lens by adjusting the size of the hole (incident pupil).

The second plastic lens L2 is made of plastic, has positive refractive power, and the object-side surface 121 is convex toward the object and the image-side surface 122 is convex upward. At least one of the object-side surface 121 and the image-side surface 122 of the second plastic lens L2 may be formed as an aspherical surface, and preferably, both surfaces may be formed as an aspherical surface.

The third plastic lens L3 is formed of plastic and has negative refractive power, and the object-side surface 131 is concave toward the object and the image-side surface 132 is convex upward. At least one of the object-side surface 131 and the image-side surface 132 of the third plastic lens L3 is formed as an aspherical surface, and preferably, both surfaces may be formed as an aspherical surface.

The fourth plastic lens L4 is formed of plastic and has positive refractive power, and the object-side surface 141 is concave toward the object and the image-side surface 142 is convex toward the image. At least one of the object-side surface 141 and the image-side surface 142 of the fourth plastic lens L4 may be formed as an aspherical surface, and preferably, both surfaces may be formed as an aspherical surface.

The fifth plastic lens L5 is made of plastic, has negative refractive power, the center of the object-side surface 151 and the center of the image-side surface 152 are concave upward, and have one or more inflection points, and are convex upward toward the periphery. Is formed. At least one of the object-side surface 151 and the image-side surface 152 of the fifth plastic lens L5 may be formed as an aspherical surface, and preferably, both surfaces may be formed as an aspherical surface.

In the present invention, the first plastic lens (L1), the second plastic lens (L2), the third plastic lens (L3), the fourth plastic lens (L4), the fifth plastic lens (L5) are all made of plastic, It realizes reduction of aberrations and miniaturization and weight reduction of the optical system, and it is possible to improve productivity because it is a high-pixel and excellent assembly property. In addition, each lens includes at least one aspherical surface to reduce cost and suppress aberration.

The imaging lens system 100 of the present invention satisfies Conditional Expression 1 below.

0 <｜K1/Vd1｜-｜∑Kn/Vdn｜ <0.004 [Conditional Expression 1]

Here, K1 is the refractive power of the first plastic lens L1, Kn is the refractive power of the n (n = 2-5)th lens, Kn = 1/fn (fn: focal length of the nth lens), and Vd1 is It is the Abbe number of the first plastic lens L1, and Vdn is the Abbe number of the n (n = 2-5)-th lens.

이고, The thin lens focal length formula is

ego,

을 참조하여, 단렌즈 굴절력을 계산하면,

Referring to, calculating the single lens refractive power,

In, K _d /V _d denotes the prime lens refractive power derived from the thin lens focal length formula.

Where, f: focal length, n: refractive index

r ₁ : radius of curvature for S1 plane, r ₂ : radius of curvature for S2 plane

C ₁ : S1 surface curvature, C ₂ : S2 surface curvature

N _d : Refractive index at the center wavelength (587.6 nm)

N _F : refractive index at the blue reference wavelength (486.1 nm), N _C : refractive index at the red reference wavelength (656.3 nm)

△K: The refractive power of the prime lens

K _d : Refractive power at the center wavelength (587.6 nm)

K _F : refractive power at the blue reference wavelength (486.1 nm), K _C : refractive power at the red reference wavelength (656.3 nm)

Conditional Expression 1 is a conditional expression for comparing the size of the total refractive power of the first plastic lens L1 and the total refractive power from the second plastic lens L2 to the fifth plastic lens L5, and the refractive power deviation based on the aperture 101 As it converges to 0, it has a better refractive power (K) arrangement structure, which reduces overall sensitivity and improves assembly and productivity.

When condition 1 is satisfied, the first plastic lens (L1) has an appropriate lens refractive power arrangement with reduced sensitivity, and by lowering the refractive power of the first plastic lens (L1), performance degradation at the front of the optical system is reduced. This is a condition that can minimize the performance degradation of

If the upper limit of Conditional Expression 1 is out of the upper limit, the refractive power of the first plastic lenses L1 becomes greater than the sum of the refractive powers of the lenses disposed behind the diaphragm 101, which relatively increases the sensitivity of the first plastic lens L1. It becomes the result.

In the case of the first plastic lens L1, since the weight that affects the entire optical system on the optical path is large, as a result, if the upper limit is exceeded, the difficulty of securing the performance of the peripheral field from the center field increases, leading to a decrease in productivity.

Examples satisfying [Condition 1]

｜K1/Vd1｜-｜∑Kn/Vdn｜ = ｜(1/f1)/Vd1｜-｜∑(1/fn)/Vdn｜

｜(1/-9.55)/23.26｜-｜{(1/1.90)/55.89} + {(1/-3.17)/23.26} + {(1/1.98)/55.89} + {(1/-2.99) /55.67}｜= ｜-0.0045｜-｜-0.0011｜ = 0.0034

The imaging lens system 100 of the present invention satisfies Conditional Expression 2 below.

｜K1｜+｜K3｜+｜K5｜ <｜K2｜+｜K4｜ [Conditional Expression 2]

Here, Kn is the refractive power of the n-th lens, and Kn = 1/fn (fn: focal length of the n-th lens).

In Conditional Equation 2, the sum of the refractive power of the first plastic lens L1, the refractive power of the third plastic lens L3, and the refractive power of the fifth plastic lens L5 is the refractive power of the second plastic lens L2 and the fourth plastic lens. Since it is less than the sum of the refractive powers of (L4), it is a condition to have an appropriate lens power arrangement and reduce performance degradation due to manufacturing errors.

Conditional Equation 2 is relatively high refractive power through the second plastic lens (L2) and the fourth plastic lens (L4) through the cross-arrangement of low refractive power and high refractive power through the cross-arrangement rather than placing a high refractive power on one side. This is a condition that can minimize performance degradation through complementary actions.

Examples satisfying [Condition 2]

｜K1｜+｜K3｜+｜K5｜ <｜K2｜+｜K4｜ = ｜1/f1｜+｜1/f3｜+｜1/f5｜ <｜1/f2｜+｜1/f4｜

｜1/-9.554927｜ + ｜1/-3.167744｜ + ｜1/-2.990712｜ <｜1/1.899099｜ + ｜1 / 1.984796｜

0.754709 <1.030395

The imaging lens system 100 of the present invention satisfies Conditional Expression 3 below.

0.1 <｜F/f1｜ <0.4 [Conditional Expression 3]

Here, F is the focal length of the entire lens system, and f1 is the focal length of the first plastic lens L1.

In Conditional Equation 3, by making the ratio of the focal length of the first plastic lens L1 to the focal length of the entire optical system to be less than 0.4, it is possible to prevent an increase in spherical aberration due to the refractive power of the first plastic lens L1. , As the ratio of the focal length of the first plastic lens L1 to the focal length of the entire optical system is disposed lower than that of other lenses, it is possible to reduce performance degradation due to manufacturing errors.

Example satisfying [Condition 3]

｜F/f1｜ = ｜2.6836 / -9.554927｜ = 0.28086

The imaging lens system 100 of the present invention may satisfy Conditional Expression 4 below.

1.3 <TTL/F <1.5 [Conditional Expression 4]

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

Conditional Equation 4 is a condition for achieving high performance and miniaturization by reducing the overall length of the lens system while satisfying the high resolution. If the angle of view is deviated from the upper limit value of Conditional Expression 4, the required angle of view is satisfied, but the length of the lens system increases, making miniaturization difficult.If the length of the lens system exceeds the lower limit, the length of the entire lens system can be further reduced. Because it is small, the desired angle of view cannot be obtained.

Examples satisfying [Condition 4]

TTL/F = 3.8700 / 2.6836 = 1.4421

The imaging lens system 100 of the present invention may satisfy Conditional Expression 5 below.

0.42 <BFL/F [Conditional Expression 5]

Here, BFL is the distance from the point where the image-side surface of the fifth plastic lens L5 and the optical axis meet to the image surface, and F is the focal length of the entire lens system.

Conditional Equation 5 is a condition for securing a free space at the rear of the lens and at the same time securing a view angle. If it deviates from the lower limit value of Conditional Expression 5, it is easy to reduce the entire length of the lens system, but it becomes difficult to secure a free space behind the lens while satisfying the required angle of view or more.

Examples satisfying [Conditional Expression 5]

BFL/F = 1.2213/2.6836 = 0.4551

The imaging lens system 100 of the present invention may satisfy Conditional Expressions 6 to 8 below.

Vd1 <30 [Conditional Expression 6]

Vd2 <60 [Conditional Expression 7]

31 <｜Vd1-Vd2｜ <34 [Conditional Equation 8]

Here, Vd1 is the Abbe number of the first plastic lens L1, and Vd2 is the Abbe number of the second plastic lens L2.

Conditional Equation 8 is based on the difference in Abbe number between the first plastic lens (L1) having a negative refractive power and having a low Abbe number and having a low Abbe number (L1), and the second plastic lens (L2) having a positive refractive power and having a high Abbe number. Accordingly, the vertical chromatic aberration can be corrected to alleviate the chromatic aberration required for high pixels.

Conditional Equation 8 is a condition for limiting the high refractive characteristics of the first plastic lens L1. If the lower limit of the conditional expression is exceeded, the dispersion decreases, thereby reducing chromatic aberration, but it is difficult to meet the required performance due to the difference in refractive index. This may increase, resulting in unintended aberrations.

Example satisfying [Condition 8]

｜Vd1-Vd2｜ = ｜23.2614-55.8883｜ = 32.6269

Example

Hereinafter, a specific embodiment of the imaging lens system 100 to which the configuration of the present invention is applied will be described.

The table below relates to numerical data of 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 surface number indicates that it is an aspherical surface.

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

Cotton number Radius of curvature Thickness or distance (t) Refractive index (Nd) Abbe number (Vd) Remark One ∞ 0 * 2 1.7662 0.2356 1.6397 23.2614 First lens * 3 1.3014 0.1300 4 ∞ 0.0964 STOP ∞ -0.0964 iris * 6 1.4820 0.4607 1.5449 55.8883 Second lens * 7 -3.0963 0.5208 * 8 -0.8405 0.2299 1.6397 23.2614 3rd lens * 9 -1.5793 0.1013 * 10 -3.1652 0.3955 1.5449 55.8883 4th lens * 11 -0.8444 0.1000 * 12 1.5425 0.4051 1.5345 55.6762 5th lens * 13 0.7145 0.3211 14 ∞ 0.0500 15 ∞ 0.2100 1.5168 64.1664 Optical filter 16 ∞ 0.6392 17 ∞ 0.0010

Here, both surfaces 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. E used for the Conic constant and the aspheric coefficient, and the number following it, represent a power of ten.

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

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

K: Conic constant (eccentricity)

C: paraxial curvature (=1/R)

R: radius of paraxial curvature

Ai: Aspheric constant (i means the degree of aspheric coefficient)

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

Cotton number K A B C D E F G * 2 1.863E-01 -1.742E-01 7.813E-01 -2.295E+01 2.601E+02 -1.598E+03 5.778E+03 -1.228E+04 * 3 0.000E+00 -3.041E-01 1.156E-01 3.653E+00 -6.692E+01 5.362E+02 -2.309E+03 5.594E+03 * 6 -2.137E+00 1.292E-02 -1.514E+00 1.003E+01 -2.475E+01 -1.162E+02 1.012E+03 -3.033E+03 * 7 2.127E+00 -2.372E-01 4.557E-01 -4.241E+00 6.689E+00 8.352E+01 -6.096E+02 1.812E+03 * 8 -2.129E-01 -4.876E-01 3.108E+00 -1.875E+01 9.804E+01 -2.983E+02 5.696E+02 -6.807E+02 * 9 0.000E+00 -5.146E-01 1.037E+00 -2.304E+00 7.780E+00 -1.252E+01 1.003E+01 -3.284E+00 * 10 -2.227E+01 -7.153E-02 7.072E-02 -1.835E+00 1.024E+01 -3.161E+01 5.730E+01 -6.171E+01 * 11 -9.969E+00 -9.638E-01 4.769E+00 -1.430E+01 2.908E+01 -4.061E+01 3.776E+01 -2.218E+01 * 12 -1.167E+00 -4.915E-01 6.965E-01 -7.571E-01 5.859E-01 -3.138E-01 1.136E-01 -2.645E-02 * 13 -4.657E+00 -2.386E-01 3.158E-01 -3.110E-01 2.108E-01 -9.722E-02 2.972E-02 -5.734E-03

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

f ₁ -9.5549 F-number (=F/D) 2.07 f ₂ 1.8991 FOV 80.00 f ₃ -3.1677 TTL 3.8700 f ₄ 1.9848 OAL 3.8002 f ₅ -2.9907 FBL 0.8502 F 2.6836 BFL 1.2213

3 is a longitudinal spherical aberration diagram according to an embodiment of the present invention, showing spherical aberration according to each wavelength. Here, the spherical aberration is the only aberration of an axial object point, which is aberration caused by a change in the focal length depending on the height at which the light beam enters the entrance pupil. That is, as the incident height of the light beam increases, the spherical aberration rapidly increases. To correct this, an aspherical surface or a high refractive material should be used to minimize the change in incidence angle depending on the height of incidence. In Fig. 3, the spherical aberration is maintained at a good level.

4 is an astigmatism diagram according to an embodiment of the present invention, showing aberration characteristics of a tangential plane (T) and a sagittal plane (S) according to the height of the upper surface 160. As shown, astigmatism exhibits good properties.

In addition, the curvature of the upper surface 160 is an aberration that appears when the upper surface 160 is curved rather than a flat surface. If you focus on the center, the periphery will be blurred, and if you focus on the periphery, the center will be blurred. A slight aberration correction is possible by tightening the aperture of the diaphragm 101, but this is only corrected by the depth of field, and when the magnification increases, there is little correction effect. In the case of the curvature of the upper surface 160, when the astigmatism is corrected, the curvature of the upper surface 160 almost disappears.

5 shows a degree of distortion according to the height of the upper surface 160 in the embodiment of the present invention. Distortion aberration does not blur or blur the image, but shows the phenomenon that the image is in focus but is taken obliquely. It is mainly conspicuous at the periphery of the screen. Barrel-type distortion occurs as it faces outward from the center of the screen, and Pincushion-type distortion occurs as it faces the center of the screen. As shown, the distortion aberration exhibits good characteristics.

6 shows an MTF graph according to the image height. In the graph, the horizontal axis represents the real image height, and the vertical axis represents the modulation transfer function (MTF). Here, MTF refers to the degree to which the contrast can be decomposed when a black/white band pattern having 100% contrast passes through the lens to form an image. If an image (several types of spatial frequencies) passes through the lens system and is reproduced with the same brightness on the image surface, the modulation transfer function value becomes 1, and when the image completely disappears from the image surface, it becomes 0.

Therefore, FIG. 6 is a graph of the MTF performance according to the image height at which the image passing through the lens is formed, and it can be confirmed that even when the image height increases (away from the center of the screen), the MTF performance maintains a good state without a sharp drop. have.

7 is a graph showing MTF performance according to an out-of-focus position. On the horizontal axis of the graph, 0 in the center is the position representing the highest resolution in the distance from the image sensor, and the numbers 0.04mm and -0.04mm indicate that the distance from the image sensor is closer or farther away by moving the lens back and forth. The vertical axis represents the modulation transfer function (MTF), which represents the degree to which a pair of pixels can be resolved.

This graph shows how much resolution decreases as the distance from the image sensor increases as the lens moves back and forth. In each line of the graph, it can be seen that the wider the left and right, the less the change in MTF performance according to the out of focus.

As described above, the imaging lens system 100 according to the embodiment of the present invention is designed to satisfy the conditional expressions 1 to 8. Such an imaging lens system may satisfy the entire conditional expression, or only a part of it.

According to the present invention, there is an effect of stably maintaining the MTF of an optical system and at the same time blocking unnecessary light rays, thereby improving an object recognition range and reducing weight. By properly arranging the refractive power of components from the water side to the upper side, there is an effect that can contribute to the production and prevention of image quality degradation.

In addition, in the present invention, in order to secure good MTF performance and reduce performance degradation due to manufacturing errors, the refractive power of the first plastic lens L1 is lowered to increase the refractive power of the first plastic lens L1. There is an advantage of minimizing performance degradation of the entire optical system by securing performance by lowering the refractive power of the lens L1.

In addition, in the imaging lens system of the present invention, since the lenses are all made of plastic, it is possible to reduce aberrations and realize miniaturization and weight reduction of the optical system, and each lens includes at least one aspherical surface to reduce cost and suppress the occurrence of aberrations. It is possible.

It is obvious to those of ordinary skill in the art that the present invention is not limited to the above embodiments and can be implemented with various modifications or modifications within the scope not departing from the technical gist of the present invention. will be.

100: imaging optical system
101: aperture
111, 121, 131, 141, 151: object side
112, 122, 132, 142, 152: upper side
160: optical filter
170: upper surface
L1: first plastic lens
L2: second plastic lens
L3: 3rd plastic lens
L4: fourth plastic lens
L5: fifth plastic lens

Claims (5)

In order from the object side,
A first plastic lens having negative refractive power and having an object-side surface and an image-side surface convexly formed toward the object side;
iris;
A second plastic lens having positive refractive power, the object side surface being convex toward the object side and the image side surface being convex toward the image side;
A third plastic lens having negative refractive power, the object side surface being concave toward the object side and the image side surface being convex toward the image side;
A fourth plastic lens having positive refractive power, the object side surface being concave toward the object side and the image side surface being convex toward the image side;
A fifth plastic lens having negative refractive power, the object-side surface center and the image-side surface center being concave upward, having one or more inflection points, and being convex toward the image side toward the periphery;
Small imaging lens system comprising a. The method of claim 1,
A compact imaging lens system that satisfies the following conditions.
0 <｜K1/Vd1｜-｜∑Kn/Vdn｜ <0.004
Here, K1 is the refractive power of the first plastic lens, Kn is the refractive power of the n (n = 2-5)-th lens, Kn = 1/fn (fn: focal length of the n-th lens), and Vd1 is the first 1 is the Abbe number of the plastic lens, and Vdn is the Abbe number of the n (n = 2-5)th lens. The method of claim 1,
A compact imaging lens system that satisfies the following conditions.
｜K1｜+｜K3｜+｜K5｜ <｜K2｜+｜K4｜
0.1 <｜F/f1｜ <0.4
Here, Kn is the refractive power of the n-th lens, Kn = 1/fn (fn: focal length of the n-th lens), F is the focal length of the entire lens system, and f1 is the focal length of the first plastic lens. The method of claim 1,
A compact imaging lens system that satisfies the following conditions.
1.3 <TTL/F <1.5
0.455 <BFL/F
Here, TTL is the total length of the lens system, F is the focal length of the entire lens system, and BFL is the distance from the point where the image-side surface of the fifth plastic lens and the optical axis meet to the image surface. The method of claim 1,
A compact imaging lens system that satisfies the following conditions.
Vd1 <30
Vd2 <60
31 <｜Vd1-Vd2｜ <34
Here, Vd1 is an Abbe number of the first plastic lens, and Vd2 is an Abbe number of the second plastic lens.

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