KR100882717B1 - Zoom lens - Google Patents

Abstract

A zoom lens is provided. The present invention includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, which are sequentially positioned from an object side to an image side. 3.6 <Tw / fw <4.1 when changing from the wide-angle end to the telephoto end, where Tw is the distance from the first lens plane of the first lens group to the last lens plane of the third lens group at the wide-angle end. The conditional expression of the effective focal length in the telephoto end and the third lens of the first lens group are 15 <Vd <20, 1.85 <nd <1.95 (where Vd is the Abbe number of the lens with respect to the d line, and nd is the d line. The refractive index of the lens) is satisfied simultaneously. According to the present invention, since the number of lenses constituting the zoom lens is small and the optical length is short, it is suitable for an imaging optical system using a solid-state image sensor, and is suitable for mounting a small terminal such as a mobile phone.

Zoom lens, optics, camera, mobile terminal, mobile phone, wide-angle end, telephoto end, tele end.

Description

Zoom lens

1 is a view showing the configuration of a conventional zoom lens.

2 is a diagram illustrating a configuration of a zoom lens according to an exemplary embodiment of the present invention.

3 is an aberration graph at the wide-angle end according to an embodiment of the present invention.

4 is an aberration graph at an intermediate stage according to an embodiment of the present invention.

5 is an aberration graph in the telephoto end according to an embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

100 First lens group 200 Second lens group

300 Third Lens Group 110 First Lens

120 Second Lens 130 Third Lens

210 4th lens 220 5th lens

230 6th Lens 240 Aperture

310 Seventh Lens 400 Imaging Device

500 infrared filter

The present invention relates to a zoom lens.

Recently, a compact digital camera or a digital video camera using a solid-state image sensor such as a CCD or a CMOS is embedded in a mobile phone or a mobile communication terminal. Such imaging devices tend to be miniaturized, and accordingly, miniaturization of zoom lenses provided in the imaging devices is required.

1 is a view showing the configuration of a conventional zoom lens. 1 is a view showing the configuration of a zoom lens composed of a conventional three groups of lens groups. Figure 1 (a) is a state of the zoom lens in the wide-angle end, Figure 1 (b) is a state of the zoom lens in the middle end, Figure 1 (c) is a state of the zoom lens in the telephoto end.

In FIG. 1, the conventional zoom lens includes a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having positive refractive power. Among the lenses included in the lens group G1, Gln, which is a refractive index of at least one lens, satisfies the following conditional expression.

<Condition> 1.90 <G1n <2.00

In FIG. 1, the distance between the first lens group G1 and the second lens group G2 decreases when the conventional zoom lens is shifted from the wide mode to the tele mode, and the second lens group ( The distance between G2) and the third lens group G3 increases, and the distance between the third lens group G3 and the fixture on the image side decreases. In the conventional zoom lens of FIG. 1, the first lens group G1 is composed of two lenses, one of the two lenses has positive refractive power, and the second lens group G2 is composed of three lenses, at least The two lenses are bonded to each other, and the third lens group G3 is composed of one lens having positive refractive power.

Such a conventional zoom lens achieves miniaturization by reducing the number of lenses, and has advantages of excellent telecentric characteristics, high aspect ratio, and high imaging performance, but is mounted in a small terminal such as a mobile phone or a PDA in its size. There is a problem that it is not suitable to be. In addition, there is a problem in that the overall length is not constant at the time of change.

The present invention has been made to solve the above problems, the number of lenses is small and the optical length is short, suitable for the imaging optical system using a solid-state image sensor, and provides a zoom lens suitable for mounting a small terminal such as a mobile phone There is a purpose.

It is another object of the present invention to provide a zoom lens having the same length of optical field at the time of shifting between the wide end and the telephoto end.

The present invention for achieving the above object comprises a first lens group having a negative refractive power, a second lens group having a positive refractive power, a positive refractive power, including a flat lens having a zero refractive power sequentially positioned from the object side to the image side And having a third lens group, wherein 3.6 <Tw / fw <4.1 when varying from the wide end to the telephoto end, where Tw is the last lens of the third lens group from the first lens plane of the first lens group at the wide end. The distance to the surface, fw, satisfies the conditional formula of the effective focal length from the telephoto end.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. First of all, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals have the same reference numerals as much as possible even if displayed on different drawings. In describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

2 is a diagram illustrating a configuration of a zoom lens according to an exemplary embodiment of the present invention. FIG. 2 (a) is a view of a zoom lens in a wide mode, FIG. 2 (b) is a view of a zoom lens in a middle mode, and FIG. 2 (c) is a telephoto end. This is the zoom lens in mode.

In FIG. 2, the zoom lens includes three lens groups of the first lens group 100, the second lens group 200, and the third lens group 300 sequentially positioned from the object side to the image side. The first lens group 100 includes a flat lens having a zero refractive power and has negative refractive power, the second lens group 200 has positive refractive power, and the third lens group 300 has positive refractive power. An image pickup device 400 for converting an image signal into an electrical signal is positioned on the image side, and an infrared filter 500 for blocking infrared rays is positioned between the third lens group 300 and the image pickup device 400.

In FIG. 2, the zoom lens is 3.6 <Tw / fw <4.1 when changing from the wide end to the telephoto end (where Tw is the third lens group 300 from the first lens surface of the first lens group 100 at the wide end). The distance to the end of the lens plane, fw is the effective focal length from the telephoto end).

In FIG. 2, the first lens group 100 includes a first lens 110, a second lens 120, and a third lens 130 sequentially positioned from an object side to an image side.

The first lens 110 is a flat lens having a refractive power of zero and is fixed at the time of shifting.

The second lens 120 is formed with a concave surface toward the image side.

The third lens 130 has a convex surface formed toward the object side. In an embodiment of the present invention, the third lens 130 has a ratio of 15 <Vd <20, 1.85 <nd <1.95 (where Vd is the Abbe's number of the lens with respect to the d line, and nd is the refractive index of the lens with respect to the d line). The conditional expression can be satisfied.

In one embodiment of the present invention, at least one or more of the second lens 120 or the third lens 130 has negative refractive power.

The second lens group 200 includes a fourth lens 210 having a positive refractive power, a fifth lens 220 having a positive refractive power, and a sixth lens 230 having a negative refractive power, which are sequentially positioned from an object side to an image side. Is done.

The fourth lens 210 has a convex surface formed toward the object side and has positive refractive power. In one embodiment of the present invention, at least one surface of the fourth lens 210 may be aspheric.

The fifth lens 220 has a convex surface formed on the image side and has a positive refractive power.

The sixth lens 230 has a concave surface formed on the image side and has negative refractive power. In one embodiment of the present invention, at least one surface of the sixth lens 230 may be aspheric.

In one embodiment of the present invention, the aperture 240 for adjusting the amount of light may be positioned between the fourth lens 210 and the fifth lens 220. The aperture 240 is used to limit the amount of light in the optical system, and as the tightening uses only the center of the lens, the aberration of the lens is reduced while the depth of focus is increased.

The third lens group 300 includes a seventh lens 310 having a positive refractive power of a plastic material. In the seventh lens 310, the central region of the lens is convex, concave toward the periphery of the lens, and at least one surface is aspheric. Since it is difficult to form an aspherical lens from a glass material, in the present invention, it is preferable that the seventh lens 310 uses a plastic lens.

As shown in FIG. 2, the distance between the first lens group 100 and the second lens group 200 decreases when shifting from the wide-angle end of FIG. 2 (a) to the telephoto end of FIG. 2 (c), The distance between the second lens group 200 and the third lens group 300 increases, and the distance between the third lens group 300 and the imaging device 400 decreases.

In the present invention, the first lens 110, which is the flat lens in the first lens group 100, is fixed at the shift from the wide-angle end to the telephoto end, and the second lens 120 is the remaining lens except for the first lens 110. ) And the third lens 130 move from the object side to the image side to a predetermined position and then move from the image side to the object side again.

In addition, when changing from the wide-angle end to the telephoto end, the second lens group 200 moves from the image side to the object side, and the third lens group 300 moves from the object side to the image side.

As described above, in the present invention, zooming and focus adjustment are performed while the first lens group 100, the second lens group 200, and the third lens group 300 move simultaneously. In more detail, when the second lens group 200 is zoomed while moving, aberration correction is performed through the first lens group 100 to maintain image performance, and the third lens group 300 is non-linearly. The focus adjustment is performed while moving.

Accordingly, in the present invention, the first lens group 100 is composed of a lens having a relatively low dispersion value, which satisfies the condition of small magnification chromatic aberration required for high resolution, and aspheric the second lens 120, thereby causing distortion of distortion due to zooming. Minimize In addition, by increasing the refractive power of the second lens group 200 to shorten the moving distance of the second lens group 200 necessary for zooming, the total length of the optical system is reduced.

The following is an embodiment of the present invention, the effective focal length f = 4.78mm ~ 9.56mm ~ 14.34mm, F number F / N = 3.4 ~ 5.26 ~ 6.99, the viewing angle of 2ω = 61.10 ° ~ 32.81 ° ~ 22.30 ° It is an Example tested on condition.

[Table 1] shows numerical data of elements constituting the zoom lens according to an embodiment of the present invention.

TABLE 1

Si ri di ndi vdi One ∞ 0.50 1.51680 64.20 2 ∞ variable 3 -818.620 0.80 1.68893 31.16 4 4.229 1.72 5 7.479 1.00 1.94595 17.98 6 14.402 variable 7 3.933 0.80 1.62263 58.16 8 -47.314 0.44 9 (Stop) ∞ 0.15 10 8.963 0.88 1.62041 60.34 11 -4.322 0.15 12 -8.915 0.60 1.68893 31.16 13 2.620 variable 14 1138.073 2.50 1.53100 56.00 15 -7.412 variable 16 ∞ 0.60 1.51680 64.20 17 ∞

In Table 1, Si is the surface number, ri is the radius of curvature of the i-th (i = 1 to 17) plane in order from the object-side lens plane, di is the distance on the optical axis between the i-th plane and the i + 1th plane, ndi Denotes the refractive index of the i-th face, and vdi denotes the Abbe number of the i-th face, respectively.

[Table 2] shows the distances on the optical axis between the planes according to the specific effective focal length f. In Table 2, each unit is mm.

TABLE 2

f d2 d6 d13 d15 4.78 0.50 7.84 0.64 2.50 9.56 1.70 2.32 6.50 0.98 14.34 0.50 0.15 10.67 0.15

Aspheric definition in the present invention is as follows.

(1)

(One)

(Where z is the distance along the optical axis from the vertex of the optical plane, Y is the direction perpendicular to the optical axis, c is the curvature at the vertex of the optical plane, K is the conic coefficient, A, B, C, D, E, F are aspherical coefficients)

Table 3 below shows the aspheric coefficients for each aspherical surface.

TABLE 3

Si K A B C D 3 -0.590661E + 28 0.250400E-03 -0.906600E-05 0.426233E-06 -0.144789E-07 4 -2.895625 0.382211E-02 -0.150045E-03 0.932970E-05 0.336026E-06 7 -0.395107 -0.104925E-02 -0.341991E-03 0.635653E-04 -0.951947E-04 8 -1425.095293 0.180724E-02 0.308136E-03 -0.912610E-04 -0.701484E-04 12 12.781696 13 0.003106 14 -0.352086E + 21 -0.369047E-03 -0.128550E-03 -0.367062E-05 0.259927E-06 15 0.282421 0.787190E-03 -0.208305E-03 0.268155E-05 0.131676E-06

3 is an aberration graph in a wide mode according to an embodiment of the present invention. 3 (a) is a graph showing longitudinal spherical aberration, FIG. 3 (b) is upper surface curvature, and FIG. 3 (c) is distortion aberration.

4 is an aberration graph in the middle mode according to an embodiment of the present invention. 4 (a) is a graph showing longitudinal spherical aberration, FIG. 4 (b) is upper surface curvature, and FIG. 4 (c) is distortion aberration.

5 is an aberration graph in tele mode according to an embodiment of the present invention. 5 (a) is a graph showing longitudinal spherical aberration, FIG. 5 (b) is upper surface curvature, and FIG. 5 (c) is distortion aberration.

It can be seen from the graphs of FIGS. 3 to 5 that test results according to respective wavelengths of light are shown by color. For example, when the wavelength is 656.3 [nM], it is displayed in red, and when the wavelength is 572.6 [nM], it is displayed in light blue.

While the invention has been described using some preferred embodiments, these embodiments are illustrative and not restrictive. Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the invention and the scope of the rights set forth in the appended claims.

As described above, according to the present invention, the number of lenses constituting the zoom lens is short and the optical length is short, so that the lens is suitable for an imaging optical system using a solid-state image sensor, and is suitable for mounting a small terminal such as a mobile phone.

In addition, there is an advantage that the length of the optical field is kept the same at the change between the wide end and the telephoto end.

Claims (13)

A first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power, sequentially positioned from an object side to an image side, The first lens group includes a first lens, a second lens, and a third lens, which are sequentially positioned from an object side to an image side, wherein the first lens is a flat lens having a refractive power of 0 and is fixed at variable displacement. The second lens has a concave surface on the image side, the third lens has a convex surface on the object side, When changing from wide-angle to telephoto 3.6 <Tw / fw <4.1 Where Tw is the distance from the first lens plane of the first lens group to the last lens plane of the third lens group at the wide-angle end, and fw is the effective focal length at the telephoto end. Satisfies the conditional expression of, The third lens 15 <Vd <20, 1.85 <nd <1.95 (where Vd is the Abbe's number of lens with respect to d line, and nd is the refractive index of lens with respect to d line) Zoom lens that satisfies the conditional expression. delete The method of claim 1, At least one of the second lens and the third lens has a negative refractive power. delete The method of claim 1, The second lens group is sequentially located and separated from an object side to an image side, and includes a fourth lens having positive refractive power, a fifth lens having positive refractive power, and a sixth lens having negative refractive power. The fourth lens has a convex surface formed on the object side, the fifth lens has a convex surface formed on the image side, and the sixth lens has a concave surface formed on the image side. The method of claim 5, And a zoom lens positioned between the fourth lens and the fifth lens to adjust an amount of light. The method of claim 5, At least one surface of the fourth lens and the sixth lens is an aspherical surface zoom lens. The method of claim 1, And the third lens group comprises a seventh lens having positive refractive power of plastic material. The method of claim 8, The zoom lens of the seventh lens is convex in the center of the lens, concave toward the periphery of the lens, and at least one surface thereof is a zoom lens. The method according to any one of claims 1, 3, 5 to 9, When changing from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group is decreased, the distance between the second lens group and the third lens group is increased, and to the third lens group and the imaging device. The distance of the zoom lens is decreasing. The method of claim 10, The zoom lens of the first lens group is fixed at the change from the wide-angle end to the telephoto end, and the remaining lenses except for the flat lens are moved from the object side to the image side to a predetermined position and then move from the image side to the object side again. The method of claim 10, And the second lens group moves from an image side to an object side when shifting from a wide angle end to a telephoto end. The method of claim 10, And the third lens group moves from an object side to an image side when shifting from a wide angle end to a telephoto end.

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