CN107850756B

CN107850756B - Photographic lens system

Info

Publication number: CN107850756B
Application number: CN201680041670.5A
Authority: CN
Inventors: 金星佑; 金成河; 李晋炯; 大内佑辉; 高野一史; 山田光昭; 须田康裕
Original assignee: Doosung Chemis Corp; Osaka Gas Chemicals Co Ltd
Current assignee: Doosung Chemis Corp; Osaka Gas Chemicals Co Ltd
Priority date: 2015-05-14
Filing date: 2016-05-16
Publication date: 2020-09-08
Anticipated expiration: 2036-05-16
Also published as: KR20160134053A; WO2016182409A1; KR101778070B1; TWI601977B; TW201710735A; CN107850756A

Abstract

The present invention relates to a photographing lens system which is small in size due to a small pixel size and can realize a high-resolution camera by having a high resolution. The photographic lens of the invention comprises the following components in sequence from the object side: an aperture; a first lens having positive refractive power and a convex object side; a second lens having a negative refractive power and having a concave upper side; a third lens having a positive refractive power; and a fourth lens having a negative refractive power, the object side being convex, and the image side being concave. In this case, the object side of the third lens has a concave spherical surface. The first lens has an Abbe number of 40 to 50. According to the present invention, a viewing angle of 78 ° or more and an F-number of 2.4 or less can be realized.

Description

Photographic lens system

Technical Field

The present invention can be mounted in a smart phone or a portable terminal to realize the function of a camera, or can be applied to a digital camera.

Background

Recently, with further emphasis on portability of smartphones or portable terminals and development of display devices, small-sized and high-resolution photographing lenses are required. Recently, four lenses are often used to ensure high performance by aberration correction.

As described in US8,068,290B2, US7,453,654B2, and the like, an aspherical lens has been used for a lens system using four lenses in the past for the purpose of downsizing and improving performance of the optical system. In this case, precision machining is difficult for the aspherical lens. As a result, productivity is deteriorated. Meanwhile, a wide-angle performance for photographing an object more widely is required.

However, in the conventional technique, the viewing angle (ang1e 0F view) is 61 °, narrow, and the F number (F number) is 2.7 to 2.8, dark.

Disclosure of Invention

Technical subject

The present invention is made to solve various problems including the above-described problems, and an object of the present invention is to provide a photographic lens system which is easy in lens processing and can be reduced in size and high in pixel count.

Another object of the present invention is to provide a compact photographing lens system having excellent wide-angle performance.

Technical scheme

Accordingly, the photographing lens system of the present invention includes, in order from an object side: the lens comprises a diaphragm, a first lens, a second lens, a third lens and a fourth lens.

The first lens has positive refractive power and has a convex object side. The second lens has negative refractive power, and the image side is concave. The third lens has a positive refractive power. The fourth lens has negative refractive power, and has a convex object-side shape and a concave image-side shape. In this case, the object side of the third lens has a concave spherical surface. The first lens has an Abbe number of 40 to 50.

Optionally, when the abbe number of the first lens is Vd1 and the abbe number of the second lens is Vd2, the following conditional expression is satisfied:

19<Vd1-Vd2<29--------------------------------(1)。

further optionally, the third and fourth lenses have abbe numbers of 50 to 60.

Optionally, the first lens satisfies the following conditional expression:

1.02<f/f1<1.06-----------------------------(2)，

where f is the effective focal distance of the overall lens system, and f1 is the effective focal distance of the first lens.

Further optionally, the second lens satisfies the following conditional expression:

0.50<|f/f2|<0.57-----------------------------(3)，

where f is the effective focal distance of the overall lens system, and f2 is the effective focal distance of the second lens.

Further optionally, the third lens satisfies the following conditional expression:

2.00<f/f3<2.10-----------------------------(4)，

where f is the effective focal distance of the overall lens system, and f3 is the effective focal distance of the third lens.

Further, optionally, the fourth lens satisfies the following conditional expression:

1.72<|f/f4|<1.75-----------------------------(5)，

where f is the effective focal distance of the overall lens system, and f4 is the effective focal distance of the fourth lens.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to realize a small-sized, high-performance, low-sensitivity design for manufacturing, and to easily apply the present invention to a small-sized, high-resolution portable terminal product having an image sensor.

Drawings

Fig. 1 is a structural view of a photographing lens system according to a preferred embodiment of the present invention.

Fig. 2 is a structural view of a photographing lens system according to another preferred embodiment of the present invention.

Fig. 3 is a structural view of a photographing lens system according to still another preferred embodiment of the present invention.

Fig. 4 is an aberration diagram relating to longitudinal spherical aberration, astigmatic aberration, and distortion of the photographing lens system of fig. 1.

Fig. 5 is an aberration diagram relating to longitudinal spherical aberration, astigmatic aberration, and distortion of the photographing lens system of fig. 2.

Fig. 6 is an aberration diagram relating to longitudinal spherical aberration, astigmatic aberration, and distortion of the photographing lens system of fig. 3.

Detailed Description

The photographing lens system according to an embodiment of the present invention will be described in detail below with reference to the drawings. The term (termin010gy) used in this specification is a term used to properly represent the preferred embodiment of the present invention, and may be different depending on the intention of a user or an operator or the convention of the art to which the present invention pertains. Therefore, the definitions of these terms should be made based on the contents throughout the present specification.

Fig. 1, 2 and 3 show photographic lens systems of first, second and third embodiments of the present invention. In fig. 1 and 2, R1, R2, R3, … … respectively indicate radii of curvature of the object side and image side of the diaphragm, lens, or optical filter, and D1, D2, D3, … … indicate distances between the diaphragm, lens, or optical filter, or center thicknesses of the diaphragm, lens, or optical filter.

Referring to fig. 1, 2, and 3, the photographing

lens systems

10, 20, and 30 of the first, second, and third embodiments of the present invention may include a diaphragm St, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4 in order from an object side to an image (image) side. Optical components such as a filter LF (fi1ter) may also be included between the fourth lens L4 and the image plane Si.

The first lens L1 has positive refractive power and the object side is convex. In this case, the lens may be a biconvex lens.

The second lens L2 has negative refractive power and has a concave image side.

The third lens L3 has positive refractive power and the object side has a concave spherical surface. Thus, spherical aberration, astigmatic aberration, and distortion aberration can be reduced.

According to the present invention, the first lens L1 has a biconvex shape. Thus, the first lens can be easily processed. Meanwhile, the second lens element L2 has a negative refractive index, and thus can shorten the total optical length and increase the effective image height of the central light rays toward the periphery. Further, the precision machining degree can be reduced by making the image-side surface of the third lens L3 spherical.

The fourth lens L4 has a negative refractive power. Alternatively, the fourth lens L4 has a form in which the object side is convex and the image side is concave. In this case, the image side surface of the fourth lens L4 may have a inflection point. If the image side surface has a point of inflection, the image side surface of the fourth lens L4 may be concave at the beginning of the optical axis and convex meniscus-shaped as the distance from the optical axis increases. Accordingly, the incident angle of the principal ray incident on the image plane can be reduced, and spherical aberration, astigmatic aberration, and the like can be reduced, whereby the resolution of the lens can be improved.

The object side of the fourth lens L4 may have a inflection point. That is, alternatively, the object side of the fourth lens L4 has a shape in which the optical axis is convex, and becomes a concave meniscus shape in a direction away from the optical axis.

The diaphragm St may be located at the same position as the object side surface of the first lens. In this case, not only the effect of reducing the overall length (total length) of the compact photographing lens system is obtained, but also the outer diameter of the lens can be reduced, thereby achieving miniaturization.

In this case, the abbe number of the first lens L1 may be 40 to 50. In a conventional 4-lens system, the abbe number of the first lens L1 is about 55. In the present invention, by adjusting the abbe number of the first lens to 40 to 50, the object side of the second lens L2 can be made spherical while the angle of view can be further widened. In this case, it is more preferable that the abbe number of the first lens L1 may be 44 to 46.

When the abbe number of the first lens L1 is smaller than 40, the longitudinal chromatic aberration and the astigmatic aberration increase, and when the abbe number is larger than 50, the longitudinal chromatic aberration decreases, but the astigmatic aberration increases.

Meanwhile, abbe numbers of the third lens L3 and the fourth lens L4 may be 50 to 60. By adjusting the abbe numbers of the first, second, third, and fourth lenses L1, L2, L3, and L4 to 40 to 50, 20 to 30, 50 to 60, and 50 to 60, respectively, the F-number can be reduced while a high viewing angle can be obtained.

In the photographic lens of the present invention, when the abbe number of the first lens L1 is Vd1 and the abbe number of the second lens L2 is Vd2, the following conditional expressions are preferably satisfied for the first lens L1 and the second lens L2:

19<Vd1-Vd2<29--------------------------------(1)。

if the conditional expression is smaller than the lower limit value, the focal length increases, the viewing angle decreases, and distortion and longitudinal chromatic aberration increase. When the value is larger than the upper limit value, spherical aberration and longitudinal chromatic aberration become large, and the overall distance becomes long.

In one aspect, optionally, first lens L1 has an abbe number of 40 to 50 and second lens L2 has an abbe number of 20 to 30. This makes it possible to effectively correct longitudinal chromatic aberration that increases with an increase in focal length. The color spots can be reduced by making the difference between the abbe numbers of the first lens L1 and the second lens L2 equal to or larger than 20. The stain reduced contrast (C0 ntrast). In this case, optionally, the second lens L2 has an abbe number of 20 to 25, more preferably 21 to 23.

Further, by applying a lens having an abbe number of 40 to 50 of the first lens L1, aberration can be reduced even if the object side of the third lens L3 is made spherical.

In one aspect, the first lens L1 may satisfy the following conditional expression:

1.02<f/f1<1.06-----------------------------(2)，

If f/f1 becomes smaller than 1.02, the positive refractive power of first lens L1 becomes too small, and it becomes difficult to realize a compact and short-overall-length small imaging optical system. When f/f1 is larger than 1.06, various aberrations such as coma aberration and astigmatism aberration are more likely to occur.

Meanwhile, the following conditional expression may be satisfied:

0.50<|f/f2|<0.57-----------------------------(3)，

2.00<f/f3<2.10-------------------------------(4)，

1.72<|f/f4|<1.75-----------------------------(5)，

where f2 is the effective focal distance of the second lens L2, f3 is the effective focal distance of the third lens L3, and f4 is the effective focal distance of the fourth lens L4.

If | f/f2| <0.50, coma and astigmatism aberration increase, and if | f/f2| >0.57, distortion increases.

If f/f3<2.00, spherical aberration and distortion increase, and if f/f3<2.10, distortion and chromatic aberration increase.

If | f/f4| <1.72, coma and astigmatism aberrations increase, and if | f/f4| >1.75, astigmatism aberrations, distortion, and chromatic aberrations increase.

Further, F1, F2, F3, and F4 have the above-mentioned condition that the object side of the third lens L3 has a concave spherical surface, the angle of view (Ang1e 0F view) is 75 ° or more and wide, the F-number is 2 to 2.4, and the third lens L3 is bright and can have a compact configuration.

The definition of the aspherical surface appearing in the embodiment of the present invention is as follows.

When the optical axis direction is taken as the z axis and the direction perpendicular to the optical axis direction is taken as the h axis, the aspherical shape of the lens according to the embodiment of the present invention can be expressed by the following equation 1 with the light traveling direction being positive. Where z is a distance from a vertical plane on an aspheric fixed point with respect to a coordinate point on an aspheric surface having a central optical axis height h, k is a conic (C0nic) constant, C represents a lens curvature of an aspheric vertex, and a4, a6, A8, a10, a12, a14 … …, and the like represent aspheric coefficients.

[ mathematical formula 1]

Design data of the photographing lens system of the embodiment of the present invention is analyzed below.

Table 1 shows design data of the photographing lens system 10 illustrated in fig. 1, and table 2 shows aspherical surface data. The radii of curvature in table 1 are represented in fig. 1 by R1, R2, … …, and the thickness or distance is represented in fig. 1 by D1, D2, … …. In table 1, the reason why the distance D1 between the diaphragm and the object side surface of the first lens is 0 is that the position of the diaphragm is the same as the position of the object side surface of the first lens.

The object side surface of the first lens and the image side surface of the first lens indicate that the surface of the aperture stop is located on the image side compared to the object side surface of the first lens.

[ Table 1]

Example 1

Noodle numbering	Radius of curvature	Thickness and distance	Refractive index (nd)	Dispersion value (vd)
					1	8	0.00
2*	1.277	0.34	1.5350	44.58
					3*	-2.063	0.10
4*	8	0.15	1.6418	22.44
					5*	1.852	0.20
6	-1.003	0.47	1.5311	55.73
					7*	-0.346	0.10
8*	4.626	0.20	1.5311	55.73
					9*	0.439	0.36
10	8	0.20	1.5230	54.48
					11	8	0.22
12	8	0.00

(focal distance 1.61mm, F2.2, viewing angle 80 degree.)

Denotes an aspherical surface.

[ Table 2]

Fig. 4 shows longitudinal spherical aberration (longitudinal spherical aberration), astigmatic aberration (astigmatic aberration), and distortion (distortion) of the lens system of the small imaging lens system 10 illustrated in fig. 1.

Longitudinal spherical aberration illustrates light having wavelengths of about 650nm, 610nm, 555nm, 510nm, 470nm, and astigmatic aberration and distortion illustrate light at 555 nm.

Table 3 shows design data of the photographing lens system 20 illustrated in fig. 2, and table 4 shows aspherical surface data. The radii of curvature in table 3 are represented in fig. 2 by R1, R2, … …, and the thickness or distance is represented in fig. 2 by D1, D2, … ….

[ Table 3]

Example 2

(focal distance 1.61mm, F2.2, viewing angle 80 degree.)

Denotes an aspherical surface.

[ Table 4]

Aspherical surface coefficient of the photographic lens of example 2

Fig. 5 shows longitudinal spherical aberration (longitudinal spherical aberration), astigmatic aberration (astigmatic aberration), and distortion (distortion) of the lens system of the imaging lens system 20 illustrated in fig. 2.

Longitudinal spherical aberration illustrates light having wavelengths of about 656.28nm, 587.56nm, 546.07nm, 486.13nm, 435.83nm, and astigmatic aberration and distortion illustrate light at 587.56 nm.

Table 5 shows design data of the photographing lens system 30 illustrated in fig. 3, and table 6 shows aspherical surface data. The radii of curvature in table 5 are represented in fig. 3 by R1, R2, … …, and the thickness or distance is represented in fig. 3 by D1, D2, … ….

[ Table 5]

Example 3

Noodle numbering	Radius of curvature	Thickness and distance	Refractive index (nd)	Dispersion value (vd)
					1	8	-0.05
2*	1.277	0.37	1.5370	44.58
					3*	-2.105	0.11
4*	33.256	0.12	1.6418	22.44
					5*	1.888	0.20
6	-0.997	0.48	1.5311	55.73
					7*	-0.344	0.10
8*	4.982	0.20	1.5311	55.73
					9*	0.435	0.36
10	8	0.20	1.5230	54.48
					11	8	0.20
12	8	0.03

(focal distance 1.61mm, F2.2, viewing angle 80 degree.)

Denotes an aspherical surface.

[ Table 6]

Aspherical surface coefficient of the photographic lens of example 3

Fig. 6 shows longitudinal spherical aberration (longitudinal spherical aberration), astigmatic aberration (astigmatic aberration), and distortion (distortion) of the lens system of the small imaging lens system 30 illustrated in fig. 3.

Table 7 below shows numerical values of each example corresponding to the above conditional expressions.

[ Table 7]

Although the present invention has been described above in connection with the preferred embodiments mentioned above, modifications or variations may be made without departing from the spirit and scope of the invention. Therefore, such modifications or variations that fall within the gist of the present invention are intended to be included within the scope of the appended claims.

Industrial applicability of the invention

The present invention can be used for portable terminals such as smart phones, and devices requiring photography such as notebooks and digital cameras.

Claims

1. A photographic lens system, characterized in that,

the photographing lens system is composed of a diaphragm, a first lens, a second lens, a third lens and a fourth lens which are arranged in sequence from the object side,

the first lens has positive refractive power and an object side is convex;

the second lens has negative refractive power, and the image side of the second lens is concave;

the third lens has a positive refractive power;

the fourth lens has negative refractive power, and the object side of the fourth lens is convex and the image side of the fourth lens is concave;

the object side of the third lens has a concave spherical surface,

the first lens has an abbe number of 40 to 50,

the first lens satisfies the following conditional expression:

1.02<f/f1<1.06-----------------------------(2)，

2. The photographic lens system of claim 1,

when the abbe number of the first lens is Vd1 and the abbe number of the second lens is Vd2, the following conditional expression is satisfied:

19<Vd1-Vd2<29--------------------------------(1)。

3. the photographic lens system of claim 1,

the third lens and the fourth lens have an abbe number of 50 to 60.

4. The photographic lens system of claim 1,

the second lens satisfies the following conditional expression:

0.50<|f/f2|<0.57-----------------------------(3)，

5. The photographic lens system of claim 1,

the third lens satisfies the following conditional expression:

2.00<f/f3<2.10-----------------------------(4)，

6. The photographic lens system of claim 1,

the fourth lens satisfies the following conditional expression:

1.72<|f/f4|<1.75-----------------------------(5)，