KR101778071B1 - Imaging Lens System - Google Patents

Abstract

The present invention relates to a small photographing lens which is small in pixel size and which can be combined with a phase sensor having a small size and a high resolution to enable the realization of a high resolution camera. The small-sized photographing lens of the present invention is a small-sized photographing lens comprising, in order from the object side, a first lens having a diaphragm, a positive refractive power and a convex shape on the object side, a second lens having a negative refractive power, Lens, a third lens in the form of a meniscus having a positive refractive power and concave on the object side, and a fourth lens having a negative refractive power and being convex on the object side, wherein the Abbe number of the first, third and fourth lenses is 40-50.

Description

Imaging Lens System < RTI ID = 0.0 >

The present invention can be applied to a smart phone or a portable terminal by entering a photographing lens system and having the function of a camera or applying it to a digital camera.

In recent years, the portability of smart phones and portable terminals has been further emphasized, and as a result of the development of displays, a compact and high resolution imaging lens is required. In recent years, there are many cases in which four lenses are used to secure high performance through aberration correction.

Conventionally, a lens system using four lenses uses an aspherical lens for miniaturization and high performance of an optical system. In this case, precision processing is difficult in the case of an aspheric lens. This results in a decrease in productivity. In addition, a wide-angle capability is required to photograph an object more widely.

However, in the prior art, the angle of view is narrowed to 61 °, and the F number is 2.7 to 2.8, which is dark.

US 8,068,290B2 US 7,453,654 B2

SUMMARY OF THE INVENTION It is an object of the present invention to provide a photographing lens system which is easy to process a lens and can be miniaturized and can be made high-definition.

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

Therefore, the photographing lens system of the present invention is a photographing lens system comprising, from the object side, a diaphragm, a first lens having a positive refractive power and a convex shape on the object side, a first lens having a negative refractive power, A third lens having a positive refractive power and a meniscus shape whose object side is concave, and a fourth lens having a negative refractive power and being convex on the object side, wherein the first, third and fourth lenses The Abbe's number is from 40 to 50.

When the Abbe number of the first lens is Vd1 and the Abbe number of the second lens is Vd2, the following conditional expression can be satisfied.

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

The following conditional expression can be satisfied for the first lens.

1.68 < TTL / 2y < 1.73 ------------------------------ (2)

Here, TTL is the distance from the first surface of the first lens to the image surface, and y is half of the diagonal length on the image plane.

The object-side surface of the fourth lens may have a positive refractive power and a convex inflection point in a direction away from the optical axis.

Further, the third lens may satisfy the following conditional expression.

1.40 < K3 / Kt | <1.85 ----------------------------- (3)

Here, K3 is the refractive power of the third lens, and Kt is the refractive power of the entire lens system.

Further, the first lens may satisfy the following conditional expression.

0.75 < K1 / Kt | <0.90 ----------------------------- (4)

Here, K1 is the refractive power of the first lens, and Kt is the refractive power of the entire lens system.

Further, the second lens may satisfy the following conditional expression.

0.45 < K2 / Kt | <0.65 ----------------------------- (5)

Here, K2 is the refractive power of the second lens, and Kt is the refractive power of the entire lens system.

In this case, the fourth lens may satisfy the following conditional expression.

0.85 < K4 / Kt | &Lt; 1.40 ---------------------------- (6)

Here, K4 is the refractive power of the fourth lens, and Kt is the refractive power of the entire lens system.

According to the present invention, it is possible to design a small-sized, high-performance, low-sensitivity product for easy application to a portable terminal product having a small size and high resolution image sensor.

1 is a configuration diagram of a photographing lens system according to a preferred embodiment of the present invention.
2 is a configuration diagram of a photographing lens system according to another preferred embodiment of the present invention.
3 is a configuration diagram of a photographing lens system according to another preferred embodiment of the present invention.
Fig. 4 is an aberration diagram relating to longitudinal spherical aberration, astigmatism, and distortion of the photographing lens system of Fig. 1;
Fig. 5 is an aberration diagram relating to longitudinal spherical aberration, astigmatism, and distortion of the photographing lens system of Fig. 2;
Fig. 6 is an aberration diagram relating to longitudinal spherical aberration, astigmatism, and distortion of the photographing lens system of Fig. 3;

Hereinafter, an automatic machining apparatus according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. The terminology used herein is a term used to properly express the preferred embodiment of the present invention, which may vary depending on the intention of the user or operator or the custom in the field to which the present invention belongs. Therefore, the definitions of these terms should be based on the contents throughout this specification.

Figs. 1, 2 and 3 respectively show photographing lens systems 10, 20, and 30 according to the first, second, and third embodiments of the present invention. In Figures 1 and 2, R1, R2, R3, ... Represents the radius of curvature of the object side / upper surface of the diaphragm, lens or optical filter, and D1, D2, D3, ... The distance between the diaphragm, the lens or the optical filter or the diaphragm, the central thickness of the lens or the optical filter.

1, 2, and 3, the photographing lens systems 10, 20, and 30 according to the first, second, and third embodiments of the present invention are arranged in order from the object side to the image side, The first lens L1, the second lens L2, the third lens L3 and the fourth lens L4 in order from the object side. An optical member such as a filter LF may further be interposed between the fourth lens L4 and the upper surface Si.

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

The second lens L2 has a negative refractive power. In this case, the second lens L2 is a meniscus lens whose object side is a paraxial plane shape and the image side is convex. Typically, the lens that determines performance in a lens system made up of four lenses is a first lens and a second lens. In this case, the sensitivity of the second lens L2 is high, and therefore the centering of the second lens is important. In the present invention, at least the paraxial area on the object side of the second lens L2 is a planar shape. In other words, the curvature of at least the paraxial area of the object side surface of the second lens L2 is infinite. Accordingly, the tilt value along the decenter of the lens, which is the physical displacement from the optical axis to the mechanical axis, becomes zero. Accordingly, it is possible to greatly reduce the variation with respect to the astigmatism and the surface curvature according to the tilting, so that a compact photographic lens system with low manufacturing sensitivity can be obtained, and the lens can be assembled easily and quickly.

The object-side surface of the second lens may be entirely planar, and may be flat only in the paraxial area as shown in Fig. 1, and may have a non-planar shape, for example, concave or convex in its peripheral area.

The third lens L3 is a meniscus lens having positive refractive power and concave on the object side.

The fourth lens L4 has a negative refractive power. The upper surface of the fourth lens L4 may have an inflection point. For example, since the upper surface has an inflection point, the upper surface of the fourth lens L4 is in the form of a concave in the optical axis, and may be in the form of a convex meniscus lens as it is further away from the optical axis. Accordingly, it is possible to reduce the angle of incidence of principal ray incident on the image plane, reduce spherical aberration, astigmatism, and the like, thereby enhancing resolution of the lens.

The object side surface of the fourth lens L4 may have an inflection point. In other words, the object side surface of the fourth lens L4 can be changed into a meniscus shape having a convex shape on the optical axis and concave in the direction away from the optical axis.

The diaphragm St is located between the object-side surface and the image-side surface of the first lens in the paraxial area, and is located on the object side of the first lens at the object side in the region deviated from the optical axis The overall length (total length) of the lens system can be reduced, and the lens can be reduced in its outer diameter.

According to the present invention, the first lens L1 has a biconvex shape. Accordingly, the processing of the first lens is easy. In addition, since the second lens L2 has a negative refractive index, it is possible to shorten the optical electric field and to serve as an effective image height of the central ray going to the periphery.

In this case, the Abbe number of the first, third, and fourth lenses L1, L3, and L4 may be 40 to 50. Conventionally, the Abbe number of the first, third and fourth lenses is about 55. In the present invention, since the Abbe number of the first, third and fourth lenses (L1, L3, L4) is 40 to 50, the angle of view can be widened and the object side of the second lens have.

When Abbe's number is smaller than 40, the chromatic aberration and astigmatism increase. When the Abbe's number is larger than 50, the chromatic aberration decreases, but the astigmatism increases.

According to the present invention, by using a lens having an Abbe number of 40 to 50, the depth is deep and the astigmatism correction is excellent, the MTF balance at the center and the periphery is good, and the lateral chromatic aberration is equivalent to a material having Abbe's number of 55 .

In the photographing lens according to 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 first lens L1 and the second lens L2, (L2) satisfy the following conditional expression.

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

In the above conditional expression, when the value is smaller than the lower limit value, the focal length increases, the angle of view decreases, and the distortion and the chromatic aberration increase. In addition, when the upper limit is larger than the upper limit, the spherical aberration and the longitudinal chromatic aberration increase, and the total distance becomes longer.

On the other hand, the first lens L1 may have an Abbe number of 40 to 50, and the second lens L2 may have an Abbe number of 20 to 30. [ Thereby, it is possible to effectively correct the longitudinal chromatic aberration that is increased as the focal length increases. The difference in the Abbe number between the first lens L1 and the second lens L2 is made to be 20 or more, thereby reducing the color flare that reduces the contrast. In this case, the second lens L2 may have an Abbe number of 20 to 25, more preferably 21 to 23.

On the other hand, in the photographing lens according to the present invention, it is preferable that the first lens L1 satisfies the following conditional expression (2).

1.68 < TTL / 2y < 1.73 ------------------------------ (2)

Here, TTL is the distance from the object-side surface of the first lens to the image surface, y is the highest image height (i.e., half the length of the sensor diagonal line in the image plane) on the image plane And the sensor diagonal length.

If TTL / 2y exceeds 1.73, the total length of the optical system becomes long, so that the optical system can not be miniaturized. If it is smaller than 1.68, the refractive power of the lens becomes excessively large, and aberration correction through the second lens and the third lens is not easy, and consequently, a high-performance photographing lens system is not achieved.

On the other hand, the third lens L3 may satisfy the following conditional expression.

1.40 < K3 / Kt | <1.85 ----------------------------- (3)
Here, K3 is the refractive power of the third lens L3, and Kt is the refractive power of the entire lens system.

delete

In addition, the following conditional expression can be satisfied.

0.75 < K1 / Kt | <0.90 ----------------------------- (4)

0.45 < K2 / Kt | <0.65 ----------------------------- (5)

0.85 < K4 / Kt | &Lt; 1.40 ----------------------------- (6)

Here, K1 is the refractive index of the first lens L1. K2 is the refractive power of the second lens L2, and K4 is the refractive power of the fourth lens L4.

This condition means the ratio of each lens to the total refractive power. When the value exceeds the upper limit value, there is a problem that the astigmatism increases. When the value is less than the lower limit value, there is a problem that the distortion aberration becomes large.

Since the diaphragm St is located on the object side of the first lens L1 on the object side, it is possible to reduce the overall length (total length) of the photographing lens system and reduce the outer diameter of the lens, .

In this case, the first, third, and fourth lenses L1, L3, and L4 may be made of the same plastic material. The second lens may also be made of a plastic material.

The definitions of the aspheric surface in the embodiment of the present invention are as follows.

The aspheric shape of the lens according to the embodiment of the present invention is represented by the following Equation 1, assuming that the direction of the optical axis is the z axis and the direction perpendicular to the optical axis direction is the h axis, . Where z is the distance from the vertical plane on the aspherical vertex to the coordinate point on the aspheric surface with height h from the central optical axis, k is the conic constant, c is the lens curvature of the aspheric apex, and A4, A6, A8, A10 , A12, A14, and so on represent aspheric coefficients.

Hereinafter, the design data of the photographing lens system according to the embodiment of the present invention will be described.

Table 1 shows design data of the photographing lens system 10 shown in Fig. 1, and Table 2 shows aspheric data. The curvature radii in Table 1 are R1, R2, ... The thickness or distance is represented by D1, D2, ... in Fig. It is displayed. The reason why the distance D1 between the diaphragm and the object side surface of the first lens in Table 1 is set to a negative value of -0.02 is that the position of the diaphragm in the paraxial region is different from the object side surface of the first lens, It is indicated that the surface of the diaphragm is located on the upper side of the object side surface of the first lens.

Example 1 Face number Radius of curvature Thickness, distance Refractive Index (nd) The dispersion value (vd) One Infinity -0.02 2* 1.5822 0.4700 1.53700 44.58 3 * -4.9676 0.2550 4* Infinity 0.2750 1.65760 21.53 5 * 2.1811 0.1150 6 * -2.1122 0.5900 1.53700 44.58 7 * -0.5173 0.0300 8* 1.2616 0.3200 1.53700 44.58 9 * 0.4435 0.3943 10 Infinity 0.3000 1.52529 54.47 11 Infinity 0.2979 12 Infinity 0.0028

(Focal length 2.042 mm, F2.26, angle of view 82.08, wavelength 546 nm, total distance 3.05)

* Indicates aspheric surface

The aspherical surface coefficient of the photographing lens according to Example 1 division K A4 A6 A8 A10 A12 A14 A16 A18 A20 Two sides -4.26154466 -0.0935853 0.616594 -8.28492 10.6869 90.5206 -299.752 0 0 0 3 sides 54.43909713 -0.619819 0.267205 -2.14176 0.154214 23.695 -43.8602 0 0 0 Four sides 0 -1.30436 0.165126 -2.21074 10.8436 15.3034 -9.22001 -68.0373 -200.329 430.909 5th -3.80351499 -0.482583 0.0693009 0.857987 -0.538199 -1.30804 3.24795 1.95884 -9.64714 6.01056 6 -16.55213366 0.389339 -0.824528 0.444196 0.903884 -1.22649 0.812531 -0.0115407 -0.0863097 -0.23537 7 -3.40402434 -0.587167 0.807421 -0.913647 0.482419 1.05957 -0.752082 0.0125068 0.0228352 0.00721076 8 sides -6.86119187 -0.43086 0.162629 0.0132699 -0.0102029 -0.00378609 0.00178944 0 0 0 9 -4.01003521 -0.27746 0.188285 -0.0971449 0.0255003 -0.00164525 -0.000508377 0 0 0

Fig. 4 shows longitudinal spherical aberration, astigmatism and distortion of the lens system 10 of the small imaging lens system shown in Fig.

The longitudinal spherical aberration is shown for light having wavelengths of about 650 nm, 610 nm, 555 nm, 510 nm, 470 nm, and astigmatism and distortion are shown for 555 nm light.

Table 3 shows design data of the photographing lens system 20 shown in Fig. 2, and Table 4 shows aspherical surface data. The radius of curvature in Table 3 is defined as R1, R2, ... And the thickness or distance is represented by D1, D2, ... in Fig. It is displayed. The reason why the distance D1 between the diaphragm and the object side surface of the first lens L1 in Table 3 is set to a negative value of -0.02 is because the position of the diaphragm is set to be the object side of the first lens L1 And that the surface of the diaphragm is located on the upper side of the object side surface of the first lens L1.

Example 2 Face number Radius of curvature Thickness, distance Refractive Index (nd) The dispersion value (vd) One Infinity -0.02 2* 1.7780 0.4100 1.53700 44.58 3 * -4.7596 0.2400 4* Infinity 0.3000 1.64850 22.44 5 * 2.6279 0.1050 6 * -1.7475 0.6100 1.53700 44.58 7 * -0.5703 0.0300 8* 0.8443 0.3000 1.53700 44.58 9 * 0.4271 0.4411 10 Infinity 0.3000 1.52529 54.47 11 Infinity 0.2930 12 Infinity 0.0039

(Focal distance 1.920 mm, F 2.28, angle of view 85.92, wavelength 546 nm, total distance 3.03)

* Indicates aspheric surface

The aspherical surface coefficient of the photographing lens according to Example 2 division K A4 A6 A8 A10 A12 A14 A16 A18 A20 Two sides -4.1783719 -0.144579 0.0517735 -4.92942 0.99122 90.5206 -299.752 0 0 0 3 sides 37.92456986 -0.678331 -0.00751181 -1.43855 -1.10353 19.2796 -41.642 0 0 0 Four sides 0 -1.21079 -0.261285 -2.23991 10.6225 13.3496 -6.63974 -64.5421 -200.329 430.909 5th 2.12381981 -0.40004 -0.143302 0.756261 -0.519419 -1.54641 2.55509 1.41527 -8.49439 6.91462 6 -12.05871778 0.462383 -0.774577 0.38235 0.640758 -1.49153 1.09778 0 0 0 7 -3.14153119 -0.557905 0.76918 -0.904013 0.491773 1.07522 -0.692688 0 0 0 8 sides -3.89643647 -0.422806 0.161953 -0.0105869 -0.0140774 -0.00154408 0.00366335 0 0 0 9 -3.07932437 -0.31466 0.218502 -0.105824 0.0214267 0.00181306 -0.00121339 0 0 0

5 shows the longitudinal spherical aberration, astigmatism and distortion of the lens system of the small imaging lens system 20 shown in Fig.

The longitudinal spherical aberration is shown for light having wavelengths of about 656.28 nm, 587.56 nm, 546.07 nm, 486.13 nm, 435.83 nm, and astigmatism and distortion are shown for 587.56 nm light.

Table 5 shows design data of the photographing lens system 30 shown in Fig. 3, and Table 6 shows aspherical surface data. In Table 5, the radius of curvature is defined as R1, R2, ... The thickness or distance is represented by D1, D2, ... in Fig. It is displayed. The reason why the distance D1 between the diaphragm and the object side surface of the first lens L1 in Table 5 is set to a negative value of -0.02 is that the position of the diaphragm in the near- 1 &lt; / RTI &gt; lens, it means that the surface of the diaphragm is above the object-side surface of the first lens.

Example 3 Face number Radius of curvature Thickness, distance Refractive Index (nd) The dispersion value (vd) One Infinity -0.020 2* 1.6908 0.4742 1.53700 44.58 3 * -4.8543 0.2322 4* Infinity 0.2994 1.65760 21.53 5 * 2.2390 0.1709 6 * -1.8870 0.5027 1.53700 44.58 7 * -0.5495 0.1000 8* 0.9771 0.2685 1.53700 44.58 9 * 0.4386 0.4411 10 Infinity 0.3000 1.52529 54.47 11 Infinity 0.2900 12 Infinity 0.0039

 (Focal length 2.081 mm, F 2.42, angle of view 80.96, wavelength 546 nm, total distance 3.08)

* Indicates aspheric surface

The aspherical surface coefficient of the photographic lens according to Example 3 division K A4 A6 A8 A10 A12 A14 A16 A18 A20 Two sides -4.0954849 -0.110298 0.291325 -5.76388 4.62112 90.5206 -299.752 -5.57817E-13 -1.62441E-13 -4.41465E-14 3 sides 40.18028102 -0.688578 0.18356 -1.55826 -0.531454 22.7275 -41.642 2.01977E-12 1.03613E-12 4.97363E-13 Four sides 0 -1.2641 0.00975009 -1.9653 11.2608 14.2052 -10.4206 -64.5421 -200.329 430.909 5th -1.53744355 -0.482079 -0.0624799 0.878365 -0.559102 -1.5906 3.03368 2.20366 -7.72172 4.39687 6 -10.40979664 0.395938 -0.784665 0.362772 0.701118 -1.37705 1.04432 -0.0123387 -0.00232928 -0.0177956 7 -3.26460421 -0.525582 0.765414 -0.871731 0.532259 1.06146 -0.838229 -0.00184354 0.000820163 0.00571661 8 sides -4.76629966 -0.427644 0.163096 0.0101026 -0.00967517 -0.00335165 0.00127391 -4.35514E-07 8.68947E-06 -1.24755E-08 9 -3.38938889 -0.30947 0.20795 -0.0977438 0.020776 0.000562362 -0.000784168 -5.74075E-06 5.04323E-07 1.54023E-06

FIG. 6 shows longitudinal spherical aberration, astigmatism and distortion of the lens system of the small imaging lens system 30 shown in FIG.

The longitudinal spherical aberration is shown for light having wavelengths of about 650 nm, 610 nm, 555 nm, 510 nm, 470 nm, and astigmatism and distortion are shown for 555 nm light.

Table 7 below shows numerical values for each example according to the above-described conditional expression.

The calculated value of the embodiment according to the conditional expression Conditional expression Example 1 Example 2 Example 3 40 <Vd1 <50 44.58 44.58 44.58 40 < Vd3 < 50 44.58 44.58 44.58 40 < Vd4 < 50 44.58 44.58 44.58 19 <v1-v2 <29 23.04907 22.14277 23.04907 0.6 < K1 / Kt | <0.90 0.89037 0.77872 0.86814 0.3 < K2 / Kt | <0.8 0.61418 0.47279 0.60977 1.3 < K3 / Kt | <1.85 1.80624 1.43769 1.62978 0.7 < K4 / Kt | <1.5 1.38359 0.89288 1.15919 1.68 < TTL / 2y < 1.73

Although the present invention has been described in connection with the above-mentioned preferred embodiments, it is possible to make various modifications and variations without departing from the spirit and scope of the invention. Accordingly, it is intended that the appended claims cover all such modifications and variations as fall within the true spirit of the invention.

L1: first lens
L2: second lens
L3: Third lens
L4: fourth lens
R1, R2, ... : Radius of curvature of iris, lens or optical filter
D1, D2, ... : Distance between iris, lens or optical filter or aperture, center thickness of lens or optical filter

Claims (8)

Sequentially from the object side,
iris;
A first lens having positive refractive power and a convex shape on the object side;
A second lens having a negative refracting power, an object side on a paraxial plane and an aspherical surface on the image side;
A third lens of a meniscus shape having a positive refracting power and concave on the object side; And
And a fourth lens having negative refractive power and being convex on the object side,
Wherein the first, third, and fourth lenses have an Abbe number of 40 to 50. The method according to claim 1,
Wherein the Abbe number of the first lens is Vd1 and the Abbe number of the second lens is Vd2.
19 <Vd1-Vd2 <29 -------------------------------- (1) delete The method according to claim 1,
Wherein the object side surface of the fourth lens has a positive refractive power and a convex inflection point in a direction away from the optical axis. The method according to claim 1,
Wherein the third lens satisfies the following conditional expression.
1.40 < K3 / Kt | <1.85 ----------------------------- (3)
Here, K3 is the refractive power of the third lens, and Kt is the refractive power of the entire lens system. The method of claim 5,
Wherein the first lens satisfies the following conditional expression.
0.75 < K1 / Kt | <0.90 ----------------------------- (4)
Here, K1 is the refractive power of the first lens, and Kt is the refractive power of the entire lens system. The method of claim 5,
And the second lens satisfies the following conditional expression.
0.45 < K2 / Kt | <0.65 ----------------------------- (5)
Here, K2 is the refractive power of the second lens, and Kt is the refractive power of the entire lens system. The method according to any one of claims 5 to 7,
Wherein the fourth lens satisfies the following conditional expression.
0.85 < K4 / Kt | &Lt; 1.40 ---------------------------- (6)
Here, K4 is the refractive power of the fourth lens, and Kt is the refractive power of the entire lens system.

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