KR101538657B1 - Compact zoom lens - Google Patents

Abstract

A zoom lens is disclosed. The disclosed zoom lens includes a first lens group including a light path changing member sequentially arranged from an object side to an image side and having a positive refractive power and changing an optical axis direction; A second lens group having negative refractive power; A third lens group having a positive refractive power; And a fourth lens group having a positive refractive power and composed of two lenses of a positive lens and a negative lens; The second lens group moves from the object side to the image side, and the fourth lens group moves from the image side to the object side, and satisfies the following expression.

4.5 < ft / fw &lt; = 5

Here, ft and fw are the focal length at the telephoto end and the focal length at the wide-angle end, respectively.

Description

Compact zoom lens {Compact zoom lens}

The disclosed zoom lens relates to a zoom lens having a compact and compact structure and having an image stabilization function.

2. Description of the Related Art In recent years, imaging optical devices such as digital cameras or digital camcorders using imaging devices such as CCD (Charge Coupled Device) and CMOS (Complementary Metal-Oxide Semiconductor) have been rapidly and widespread.

Such an imaging optical apparatus is required to have a high magnification and a high performance such as an anti-shake function. In addition, portability is emphasized, and various designs for high performance and small size and light weight have been proposed.

In order to meet the demand for miniaturization, a lens-type lens structure is generally used in which a lens is led to a predetermined position at the time of photographing a camera, and a lens is housed inside the camera when photographing is not performed. Such a structure can reduce the thickness of the camera and improve the portability by narrowing the interval of each lens group whenever possible. In addition, in order to realize thinning, the number of lens groups must be reduced, and at the same time, there is a difficulty in securing high optical performance due to high-definition.

A bendable zoom lens structure is proposed in which the optical path of the lens optical system is bent and used, that is, a lens group is arranged along a bent optical axis. Even in this case, it is difficult to achieve the correction of the shaking motion and the downsizing together with the high-aspect ratio. For example, in general, the bending-type optical systems are made up of a group 5 lens group to achieve a high magnification and an optical system miniaturization, and the moving amount of the magnification group is shortened to make it compact. However, It is difficult to set an optical system for correcting deterioration. There is a problem that the number of lenses of the first lens group or the fourth lens group has to be increased in order to achieve a high magnification and a high resolution.

In this way, the number of total lens groups and the number of lenses in each group must be appropriately determined in relation to optical performance, and it is necessary to design a zoom lens having an image stabilization function in addition to miniaturization and high magnification.

According to the above-mentioned necessity, the embodiments of the present invention are intended to provide a small, high magnification zoom lens having an image stabilization function.

A zoom lens according to an embodiment of the present invention includes: a first lens group that is sequentially arranged from an object side to an image side and includes a light path changing member having a positive refractive power and changing an optical axis direction; A second lens group having negative refractive power; A third lens group having a positive refractive power; And a fourth lens group having a positive refractive power and composed of two lenses of a positive lens and a negative lens; The second lens group moves from the object side to the image side, and the fourth lens group moves from the image side to the object side, and satisfies the following expression.

4.5 < ft / fw &lt; = 5

Here, ft and fw are the focal length at the telephoto end and the focal length at the wide-angle end, respectively.

And the third lens group is configured to move in a direction orthogonal to the optical axis to correct an image shake due to hand shake.

The optical path changing member may be formed of a prism that tilts the optical axis in a 90 degree direction.

Wherein the second lens group is composed of four lenses in order from the object side to the image side in order, negative, positive, negative, and positive refractive power.

The second lens group includes at least one aspherical surface of at least one surface, and further includes at least one lens having a refractive index Nd satisfying the following equation.

Nd > 1.95

The positive lens and the negative lens of the fourth lens group may be cemented to each other, and the following formula can be satisfied.

1.98 < G4f / f11 < 3.2

Here, f11 is the focal length of the first lens on the object side of the fourth lens group, and G4f is the focal length of the cemented lens of the fourth lens group.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following drawings, like reference numerals refer to like elements, and the size of each element in the drawings may be exaggerated for clarity and convenience of explanation.

FIGS. 1, 3, and 5 are views showing the optical arrangement of the zoom lens according to the first, second, and third embodiments of the present invention at the wide-angle end, the middle end, and the telephoto end, respectively. Referring to the drawings, the zoom optical system includes, in order from the object OBJ side to the image IMG side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, A third lens group G3 and a fourth lens group G4 having a positive refractive power. An infrared filter and a cover glass may be further provided on the upper side of the fourth lens group G4. The first lens group G1 includes a light path changing member P for changing an optical axis.

In the embodiment of the present invention, the lens group number is made into a four-group structure by reducing the total length of the optical system to achieve miniaturization.

The zoom lens according to the embodiments of the present invention moves the second lens group G2 and the fourth lens group G4 along the optical axis when changing from the wide angle end to the telephoto end. For example, the second lens group G2 moves from the object side to the image side, and the fourth lens group G4 moves from the image side to the object side.

The first lens group G1 and the third lens group G3 are fixed with respect to the optical axis direction and the third lens group G3 is fixed in a direction crossing the optical axis, And is configured to move in a direction orthogonal to the optical axis. Among the conventional techniques, there is a case where the image correction is performed using the fifth group. However, since the image-forming magnification of the fifth group is low, it is necessary to perform a large amount of movement in order to perform the correction by the shaking motion. In order to constitute the optical system, the configuration of the lens group becomes complicated and the number of necessary lenses increases.

The zoom lens of the embodiment of the present invention is composed of four lens groups of positive, negative, positive, and positive, and the configuration of the lens group and the number of lenses are reduced, and the second lens group G2 and the fourth lens group G4 And the fourth lens group G4 is used as a focusing lens group that compensates for the movement of the image plane according to the change of the object distance, so that even when only two motors required for movement of the lens group are driven, Respectively.

The zoom lens according to the embodiments of the present invention has a structure favorable for downsizing and thinning, and presents a design capable of performing camera shake correction with high magnification, and the magnification satisfies the following expression.

4.5 < ft / fw &lt; = 5

Here, ft and fw are the focal length at the telephoto end and the focal length at the wide-angle end, respectively.

A more specific lens configuration will be described with reference to the drawings.

The first lens group G1 includes the optical path changing member P for changing the optical axis, and is configured to have a positive refractive power as a whole. The first lens group G1 may include three lenses including the optical path changing member P and may include a first lens 110, a light path changing member P, a second lens 120, &Lt; / RTI &gt; The first lens 110 may be a convex meniscus lens to the object side and the second lens 120 may be a positive convex lens having a positive refractive power.

As the optical path changing member P, a reflecting member, for example, a prism, which changes the optical path so that the optical axis is bent by 90 degrees, may be employed. As described above, the optical system structure that employs the optical path changing member P to fold the optical path is selected as an advantageous structure for achieving thinness. In the case of a telescopic optical system structure in which each lens group is successively piled on a straight line, the thickness of the optical system upon storage is determined depending on the number of lenses or the movement amount of the lens group, which limits the downsizing and thinning. On the other hand, The number of lenses or the amount of movement at the time of changing can be arranged so as not to affect the thickness of the digital camera employing the zoom optical system, for example.

The second lens group G2 is a lens group which takes charge of magnification upon zooming and has a negative refractive power and moves from the object side to the object side at the time of magnification from the wide angle end to the telephoto end. For example, the second lens group G2 moves monotonously or non-linearly from the object side to the image side. The second lens group G2 includes a third lens 210 as a negative lens, a fourth lens 220 as a positive lens, a fifth lens 230 as a negative lens, and a sixth lens 240 as a positive lens . The second lens group G2 may adopt an aspherical surface on at least one surface thereof, which is intended to compensate for the spherical aberration generated at the telephoto end. The fourth lens 220 and the fifth lens 230 may be cemented to each other to correct the chromatic aberration of magnification occurring at the wide angle end. In order to achieve a high resolution and a resolving power while achieving a high magnification, the second lens group G2 uses at least one lens whose refractive index Nd satisfies the following formula.

Nd > 1.95

The third lens group G3 has a positive refractive power as a whole and may include, for example, a seventh lens 310, an eighth lens 320, and a ninth lens 330, . The seventh lens 310 may be a positive lens, the eighth lens 320 may be a positive lens, the ninth lens 330 may be a negative lens, and the eighth lens 320 and the ninth lens 330 may be made up of And a bonded cemented lens can be formed. And the third lens group G3 is fixed without moving relative to the optical axis direction during magnification. The third lens group G3 is configured to move in a direction crossing the optical axis, for example, in a direction orthogonal to the optical axis, in order to correct the image shake due to the camera shake. The chromatic aberration of magnification that occurs during this movement is complemented by constructing a cemented lens with a high dispersion material and a low dispersion material. The diaphragm ST may be disposed in front of the seventh lens 310, that is, on the object side of the seventh lens 310. [

The fourth lens group G4 has a positive refractive power as a whole, moves from the upper side to the object side when changing from the wide angle end to the telephoto end, and is responsible for the top surface movement and the focal position correction. The fourth lens group G4 may be composed of a tenth lens 410 which is a positive lens and an eleventh lens 420 which is a negative lens and the tenth lens 410 and the eleventh lens 420 are joined to each other A cemented lens can be formed. A low dispersion material is used for at least one lens in the fourth lens group G4 to suppress the generation of chromatic aberration at the telephoto end according to a high magnification. In addition, the generation of astigmatism due to the surface movement due to the magnification variation is compensated by using the aspherical surface on at least one surface of the fourth lens group G4.

The cemented lens of the fourth lens group G4 satisfies the following expression.

1.98 < G4f / f11 < 3.2

Here, f11 is the focal length of the first lens on the object side of the fourth lens group G4, and G4f is the focal length of the cemented lens of the fourth lens group G4.

The above formula limits the ratio of the focal length of the first lens on the object side of the fourth lens group G4 to the focal length of the cemented lens. The focal length of the first lens on the object side is shortened and the refractive power is increased to increase the spherical aberration or the focal length of the cemented lens becomes longer and the refractive power is decreased to increase the moving distance when the lens is moved from the wide angle end to the telephoto end, . The refractive power of the cemented lens is increased to increase the chromatic aberration of magnification or the focal length of the first lens on the object side becomes longer and the back focal length (BFL) becomes longer, making miniaturization of the zoom lens difficult.

Hereinafter, specific lens data of various embodiments of the zoom optical system according to the present invention will be described. The definitions of aspheric surface (ASP) in the embodiments of the present invention are as follows.

Where k is a conic constant, A, B, C, and D are aspheric coefficients, c is an aspheric surface coefficient, (1 / R) of the radius of curvature at the apex of the lens.

In the following, f denotes the combined focal length of the entire zooming optical system, Fno denotes the F number, and 2ω denotes the angle of view. An asterisk (*) in the face number indicates an aspherical surface. D1, D2, D3, D4, and D5 denote the variable distances between the lens groups at the five zoom positions (Pos1-Pos5) in each embodiment.

&Lt; Embodiment 1 >

FIG. 1 shows a zoom lens according to a first embodiment. FIGS. 2A and 2B are views showing longitudinal spherical aberration, astigmatic field curvature at a wide-angle end and a telephoto end of a zoom optical system according to the first embodiment, , And distortion aberration. The longitudinal spherical aberration is shown for light with wavelengths of 656.28 (nm), 546.07 (nm), and 435.84 (nm), respectively. The surface curvature is represented by tangential field curvature (T) for light with a wavelength of 546.07 ) And a sagittal field curvature (S), and the distortion represents the light with a wavelength of 546.07 (nm).

The following is lens data of the first embodiment.

f: 7.18 to 13.93 to 33.80 Fno: 3.7 to 3.9 to 4.2 2ω: 58.4 to 29.3 to 12.1

if Radius of curvature thickness Refractive Index (nd) Abbe number (vd) OBJ infinity One 90 0.65 1.9184 19.94 2 20.096 1.275 3 infinity 8.2 1.834 37.34 4 infinity 0.35 5 * 14.816 2.378 1.75196 52.47 6 * -32.943 D1 7 -32.035 0.5 1.88457 40.44 8 7.185 0.914 9 -20.058 One 1.92286 20.88 10 -6.232 0.6 1.88271 40.82 11 42.774 0.25 12 12.492 0.8 2.0006 25.46 13 27.596 D2 14 infinity 0.5 ST infinity 0.1 16 * 6.76 1.553 1.80146 43.46 17 -30.056 0.3 18 * 6.464 1.685 1.50016 80.77 19 -12.554 0.5 1.89644 30.65 20 4.72 D3 21 * 14.186 2.525 1.4998 78.07 22 -5.835 0.5 1.83176 44.35 23 -10.299 D4 24 infinity 0.3 1.5168 64.2 25 infinity 0.5 26 infinity 0.5 1.5168 64.2 27 infinity D5 IMG infinity

The following table shows aspheric coefficients.

if K A B C D 5 -0.844157 -1.89660E-05 6.08514E-07 3.36513E-09 -5.65410E-10 6 -2.22564 -2.18536E-06 1.28247E-06 -2.54444E-08 -1.91879E-10 16 0.274536 -1.90837E-04 -1.79096E-05 2.76368E-07 -1.21471E-08 18 -0.427348 -2.68869E-04 1.84009E-05 0.00000E + 00 0.00000E + 00 21 -0.81375 8.33689E-05 2.35909E-06 -1.24167E-07 1.16708E-08

The following table shows the variable distance between lenses.

Pos 1 Pos 2 Pos 3 Pos 4 Pos 5 D1 0.600 3.272 5.942 8.610 11.285 D2 11.185 8.513 5.842 3.174 0.500 D3 10.336 7.842 5.301 3.000 3.400 D4 4.286 6.780 9.321 11.622 11.222 D5 3.922 3.923 3.923 3.924 3.925

&Lt; Embodiment 2 >

FIG. 3 shows a zoom lens according to a second embodiment. FIGS. 4A and 4B show longitudinal aberration, astigmatic field curvature at a wide-angle end and a telephoto end of a zoom optical system according to the second embodiment, , And distortion aberration.

The following is lens data of the second embodiment.

f: 7.18 to 13.93 to 33.80 Fno: 3.7 to 3.9 to 4.2 2ω: 57.6 to 27.6 to 12.4

if Radius of curvature thickness Refractive Index (nd) Abbe number (vd) OBJ infinity One 95 0.746 1.93533 18.67 2 20.447 1.154 3 infinity 8.2 1.90366 31.31 4 infinity 0.35 5 * 14.36 2.499 1.7433 49.33 6 * -31.851 D1 7 * -19.627 0.5 1.9137 32.61 8* 7.038 0.724 9 -29.257 0.98 1.92286 20.88 10 -6.075 0.6 1.83466 36.97 11 33.581 0.25 12 12.824 0.816 2.0006 25.46 13 53.295 D2 14 infinity 0.5 ST infinity 0.1 16 * 7.21 2.592 1.77225 30.73 17 -22.726 0.3 18 7.441 1.61 1.53384 73.32 19 -7.594 0.748 1.79311 23.75 20 4.732 D3 21 * 13.553 2.614 1.53407 52.32 22 -5.661 0.75 1.88615 37.83 23 -11.696 D4 24 infinity 0.3 1.5168 64.2 25 infinity 0.5 26 infinity 0.5 1.5168 64.2 27 infinity D5 IMG infinity

The following table shows aspheric coefficients.

if K A B C D 5 -0.860507 -7.32353E-07 -1.89676E-08 0.00000E + 00 0.00000E + 00 6 -1.131892 2.91967E-05 -2.20267E-08 -2.58421E-09 3.79598E-11 7 -4.858346 2.35063E-05 -1.37259E-05 2.07471E-06 -4.01804E-08 8 -0.640025 4.47843E-05 5.32234E-06 -7.35058E-07 2.29689E-07 16 0.247472 -3.17882E-04 -3.36966E-06 1.00104E-07 -1.16769E-08 21 -2 3.07733E-04 4.97769E-07 1.74618E-07 8.94290E-09

The following table shows the variable distance between lenses.

Pos1 Pos2 Pos3 Pos4 Pos5 D1 0.6 3.464 6.328 9.191 12.056 D2 11.956 9.092 6.228 3.365 0.5 D3 8.893 6.699 4.997 4.584 9.149 D4 5.044 7.238 8.939 9.352 4.787 D5 0.401 0.401 0.402 0.402 0.403

&Lt; Third Embodiment >

FIG. 5 shows a zoom lens according to a third embodiment. FIGS. 5A and 5B are views showing an astigmatic field curvature at the wide-angle end and the telephoto end of the zoom optical system according to the third embodiment, , And distortion aberration.

The following is lens data of the third embodiment.

f: 6.9 to 13.4 to 34.5 Fno: 3.7 to 3.8 to 3.9 2ω: 59.6 to 29.6 to 12.1

if Radius of curvature thickness Refractive Index (nd) Abbe number (vd) OBJ infinity One 90 0.65 1.953 19.49 2 19.571 1.262 3 infinity 8.2 1.90366 31.31 4 infinity 0.35 5 * 13.539 2.636 1.7433 49.33 6 * -35.242 D1 7 -50.108 0.5 1.97063 25.29 8 6.334 1.016 9 -12.021 0.989 1.92286 20.88 10 -5.095 0.6 1.85351 42.05 11 45.624 0.428 12 17.836 0.942 2.00069 25.46 13 -38.592 D2 14 infinity 0.2 ST infinity 0.1 16 * 6.707 2.6 1.74143 32.81 17 -23.481 0.2 18 * 6.663 1.65 1.56636 67.97 19 -7.592 0.5 1.83427 24.95 20 4.519 D3 21 * 19.928 2.663 1.52486 64.12 22 -4.695 0.5 1.86062 42.23 23 -9.894 D4 24 infinity 0.3 1.5168 64.2 25 infinity 0.5 26 infinity 0.5 1.5168 64.2 27 infinity D5 IMG infinity

The following table shows aspheric coefficients.

if K A B C D 5 -9.38336E-01 -1.64984E-05 1.12824E-07 0.00000E + 00 0.00000E + 00 6 2.96760E-01 6.87797E-06 2.65751E-07 -2.27053E-09 1.17017E-11 16 3.00035E-01 -1.92276E-04 -1.53308E-05 3.19372E-07 -1.39050E-08 18 2.82777E-01 -5.33382E-04 6.23423E-06 -1.37166E-07 0.00000E + 00 21 -1.75281E + 00 5.57905E-04 -1.44183E-05 1.53402E-06 7.74442E-09

The following table shows the variable distance between lenses.

Pos 1 Pos 2 Pos 3 Pos 4 Pos 5 D1 0.600 3.594 6.588 9.582 12.576 D2 12.476 9.482 6.488 3.494 0.500 D3 8.759 6.071 4.092 3.665 9.849 D4 4.705 7.394 9.373 9.800 3.616 D5 0.400 0.400 0.401 0.401 0.400

The following is a table showing that the embodiments of the present invention satisfy the conditions of the equations (1) to (3).

Equation 1 Equation 2 Equation 3 First Embodiment 4.7 4.71 5 Second Embodiment) 2.0 2.0 2.0 Third Embodiment 1.998 2.426 3.173

The zoom lens according to the embodiments described above can realize a camera shake correction function and a high magnification with a configuration advantageous in downsizing and thinness through the lens configuration described above.

Although the zoom lens of the present invention has been described with reference to the embodiments shown in the drawings for the sake of understanding, it should be understood that the present invention is not limited thereto and various modifications and equivalent embodiments may be made by those skilled in the art I will understand the point. Accordingly, the true scope of the present invention should be determined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an optical arrangement at a wide angle end, a middle end, and a telephoto end of a zoom lens according to a first embodiment of the present invention; FIG.

FIGS. 2A and 2B are diagrams showing spherical aberration, field curvature, and distortion at the wide-angle end and the telephoto end of the zoom lens according to the first embodiment of the present invention.

3 is a view showing optical arrangements at the wide angle end, the middle end, and the telephoto end of the zoom lens according to the second embodiment of the present invention.

4A and 4B are aberration diagrams showing spherical aberration, field curvature, and distortion at the wide angle end and the telephoto end of the zoom lens according to the second embodiment of the present invention.

FIG. 5 is a diagram showing an optical arrangement at a wide angle end, a middle end, and a telephoto end of a zoom lens according to a third embodiment of the present invention.

6A and 6B are aberration diagrams showing spherical aberration, field curvature and distortion at the wide angle end and the telephoto end of the zoom lens according to the third embodiment of the present invention.

Claims (9)

Which are sequentially arranged from the object side to the image side, A first lens group including a light path changing member having a positive refractive power and changing an optical axis direction; A second lens group having negative refractive power; A third lens group having a positive refractive power; And A fourth lens group having a positive refractive power and composed of two lenses of a positive lens and a negative lens; / RTI &gt; Wherein the first lens group and the third lens group are fixed while the second lens group is moved from the object side to the image side and the fourth lens group is moved from the image side to the object side, Wherein the positive lens and the negative lens of the fourth lens group form a cemented lens joined to each other, A zoom lens satisfying the following expression. 4.5 < ft / fw &lt; = 5 1.98 < G4f / f11 < 3.2 Here, ft and fw are the focal length at the telephoto end and focal length at the wide-angle end, f11 is the focal length of the first lens on the object side of the fourth lens group, and G4f is the focal length of the cemented lens of the fourth lens group The method according to claim 1, And the third lens group moves in a direction orthogonal to the optical axis and corrects image blur due to camera shake. The method according to claim 1, The optical path changing member comprises a prism that folds the optical axis in a 90-degree direction. The method according to claim 1, Wherein the second lens group is composed of four lenses in order from the object side to the image side in order, negative, positive, negative, and positive refractive power. 5. The method of claim 4, Wherein the second lens group uses at least one aspherical surface. The method according to claim 1, And the second lens group includes at least one lens having a refractive index Nd satisfying the following equation. Nd > 1.95 delete delete The method according to claim 1, And the fourth lens group has at least one aspherical surface.

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