KR20090097692A - Compact zoom lens - Google Patents

Abstract

Compact zoom lens are provided to perform a magnification operation by moving the location of each lens group from the process. A first optic group(G1) is installed at the location which it is most near from the object side(O). The first optic group has the definition refractive power. The second lens group(G2) is installed at the next location of the first optic group. The second lens group has the refractive power of the part. The third lens group(G3) is installed at the next location of the second lens group. The third lens group has the definition refractive power. The fourth lens group(G4) is installed at the next location of the third lens group. The fourth lens group has the definition refractive power. In the wide angle edge, the magnification process to the telephoto shift is performed by moving the location of each lens group. In the magnification process, interval between the second lens group and the first optic group are increased. In the magnification process, interval between the third lens group and the second lens group drop. In the magnification process, interval between the fourth lens group and the third lens group are increased. In the fourth lens group is the magnification process, the upper side movement and focal point correction are achieved.

Description

Compact zoom lens

The present invention relates to a compact and inexpensive zoom lens.

Recently, digital cameras and video cameras having solid-state imaging devices such as charge coupled devices (CCDs) and complementary metal-oxide semiconductors (CMOS) are widely used. In particular, demand for megapixel camera modules has been demanded, and cameras having high-definition performance and more than 5 million pixels have emerged in entry-level digital cameras. An imaging optical device such as a digital camera or a mobile phone camera using an imaging device such as a CCD or a CMOS requires a small size, light weight, and low cost.

In order to satisfy the demand for miniaturization, a penetrating barrel is often used to store the lens in a fixed position when the camera is photographed and to be stored inside the camera when the camera is not photographed. Such penetrating cameras should be as narrow as possible when storing the lens group, so that the thickness of the camera can be reduced and portability can be improved. In order to realize miniaturization and thinning in the penetrating barrel, the number of lens groups must be reduced. On the other hand, high optical performance due to high pixel size must be secured.

In order to reduce size, increase magnification, and reduce cost while minimizing the high magnification ratio in 4 lens group types, it is necessary to minimize manufacturing sensitivity by minimizing the number of lenses and to minimize productivity and manufacturing cost. If a large number of lenses are used, it is advantageous to miniaturize by reducing the number of lenses, but it is difficult to reduce the cost. When using more than 9 lenses, it is advantageous to correct aberration or secure a high ratio, but it is difficult to miniaturize.

It is an object of the present invention to provide a compact and inexpensive zoom lens.

The present invention includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, in order from the object side. The shifting is performed by shifting the position of each lens group when changing from the telephoto end to the telephoto end, wherein the first lens group includes one lens, and the second lens group includes three lenses. Provide a satisfactory zoom lens.

<Conditional expression>

4 ≤ ft / fw ≤ 6

1.90 ≤ Nd2 ≤ 2.05

Where fw is the focal length of the whole optical system at the wide end, ft is the focal length of the whole optical system at the telephoto end, and Nd2 is the refractive index of the last lens from the object side of the second lens group.

The lens of the first lens group may be configured as an aspherical lens.

All the lenses of the second lens group may be configured as spherical lenses.

The second lens group may include a first meniscus lens having negative refractive power in order from an object side and a convex object side, a lens having positive refractive power, and a second meniscus lens having a negative refractive power and convex on the object side. have.

The zoom lens according to the exemplary embodiment of the present invention may satisfy the following conditional expression.

<Conditional expression>

1.6 ≤ (D2w-D2t) / fw ≤ 2.0

Where D2w is the distance from the object side to the last lens of the second lens group and the first lens of the third lens group at the wide-angle end, and D2t is the last and third lens of the second lens group from the object side at the telephoto end. The distance to the first lens of the group, fw represents the focal length of the whole optical system at the wide-angle end, respectively.

The first lens from the object side of the third lens group may be an aspherical lens.

The third lens group may include a bonded lens.

The fourth lens group includes a meniscus positive lens that is convex toward the object side, and the positive lens may be manufactured using a material having a refractive index of 1.8 or more.

Referring to FIG. 1, a zoom lens according to an exemplary embodiment of the present invention may include a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, in order from the object side O. A third lens group G3 having a positive refractive power, and a fourth lens group G4 having a positive refractive power, and the position of each lens group when changing from a wide angle end to a telephoto end when changing from a wide angle end to a telephoto end. Shifting is performed. When shifting, the distance between the first lens group G1 and the second lens group G2 increases, and the distance between the second lens group G2 and the third lens group G3 decreases, and the third The distance between the lens group G3 and the fourth lens group G4 increases. The fourth lens group G4 performs image shift and focus position correction when shifting.

The first lens group G1 includes a first lens 1 having a biconvex aspherical surface. By using an aspherical lens for the first lens group G1, it is easy to secure an angle of view at the wide-angle end, and also effective distortion correction can be performed. Due to the development of aspherical processing technology, it is possible to process lenses with an outer diameter of 15mm or more, and the cost increase due to the use of aspherical lenses is not significant by using low cost materials. It is also advantageous for the compact optical system because it is composed of only one lens. The second lens group G2 includes a second lens 2 having negative refractive power in order from an object side, a third lens 3 having negative refractive power, and a fourth lens 4 having positive refractive power. . The second lens 2 may be a meniscus lens in which the object side O is convex, and the fourth lens 4 may be a meniscus lens in which the object side is convex. In the second lens group G2, the lenses may be manufactured at low cost by forming spherical lenses instead of aspherical surfaces. On the other hand, the lens of the second lens group (G2) is made of a high refractive material to minimize the lens thickness and to be advantageous for distortion and astigmatism correction.

The third lens group G3 includes a fifth lens 6 and a joint lens in which one positive lens 7 and one negative lens 8 are bonded to each other. Aspherical aberration is used in the fifth lens 6 to minimize spherical aberration, and magnification of chromatic aberration generated at the time of shifting using the bonded lens is minimized. In particular, the positive lens of the bonded lens is manufactured using a low dispersion material having a small difference in refractive index according to the wavelength of light, thereby minimizing the occurrence of chromatic aberration even at high magnification of 5 times or more. The spherical aberration of the wide-angle end and the telephoto end can be corrected by using the first lens on the object side of the third lens group as an aspherical surface.

The fourth lens group G4 includes a meniscus positive lens 9 which is convex toward the object side. The positive lens 9 uses a material having a refractive index of 1.8 or more so that the incident angle of the light beam does not increase. Through the above configuration, it is possible to obtain a high-performance compact optical system in the government correction group 4 type.

Meanwhile, the zoom lens according to the embodiment of the present invention may be configured to satisfy the following conditional expression.

4 ≤ ft / fw ≤ 6

1.90 ≤ Nd2 ≤ 2.05

Where fw is the focal length of the whole optical system at the wide end, ft is the focal length of the whole optical system at the telephoto end, and Nd2 is the refractive index of the last lens from the object side of the second lens group. In general, in order to achieve a compact optical system in the four-group type of government correction, it is advantageous to use a large number of aspherical lenses by reducing the number of lenses in the entire optical system. However, as the use of aspherical lenses increases, the sensitivity of the entire optical system increases and it becomes difficult to minimize manufacturing costs. In the present invention, only two aspherical lenses are used, which is advantageous for making a compact, low cost optical system. Equation 1 defines the zoom ratio of the wide-angle end and the telephoto end of the entire optical system, and a high magnification compact optical system of 4 times or more and 6 times or less can be obtained. Equation 2 defines the refractive index of the last lens from the object side in the second lens group, and is a conditional expression for minimizing the optical system without using an aspherical lens in the second lens group.

When the upper limit of Equation 1 is exceeded, an optical system of 6 times or more zoom can be obtained, but it is inevitable to add a lens for aberration correction due to an increase in magnification, and thus it is difficult to obtain a compact optical system. On the other hand, if the lower limit is exceeded, a low zoom magnification optical system cannot be obtained. Equation 2 defines the refractive index value of the last lens from the object side O of the second lens group G2. If the upper limit is exceeded, the cost of the lens is increased by using a material having a high refractive index, thereby increasing the manufacturing cost. On the other hand, when the lower limit is exceeded, miniaturization is difficult because it is difficult to minimize the electric field of the optical system. In the second lens group illustrated in FIG. 1, the negative lens 8 of the bonded lens may be made of a material having a refractive index of Equation 2.

1.6 ≤ (D2w-D2t) / fw ≤ 2.0

Here, D2w is the distance from the object side to the last lens of the second lens group G2 and the first lens of the third lens group at the wide-angle end, and D2t is the distance from the object side to the last lens of the second lens group at the telephoto end. The distance to the first lens of the third lens group, fw represents the focal length of the entire optical system at the wide-angle end, respectively. For example, D2w may represent a distance from the object side surface of the fourth lens 4 of the second lens group G2 to the object side surface of the fifth lens 6 of the third lens group G3.

Equation 3 defines the amount of change in the distance between the second lens group and the third lens group as the ratio of the focal length of the wide end when the lens is shifted from the wide end to the telephoto end. If the upper limit value is exceeded, it is difficult to miniaturize the position change amount of group 2 or group 3 at the time of shifting, and if it exceeds the lower limit value, it is difficult to secure a zoom factor of 4 times or more. In general, the distance between the second lens group and the third lens group becomes narrow when shifting from the wide-angle end to the telephoto end in the 4th type of government-corrected type, and when the change in the distance between the second lens group and the third lens group increases, the high magnification optical system Can be obtained, but it becomes difficult to miniaturize, and when the change in the distance between the second lens group and the third lens group becomes small, it becomes difficult to obtain a high magnification optical system.

On the other hand, the definition of the aspherical surface in the embodiment of the present invention is as follows.

The aspherical shape of the zoom lens according to the present invention can be expressed by the following equation with the x-axis as the optical axis direction and the y-axis as the direction perpendicular to the optical axis direction. Where x is the distance from the vertex of the lens in the optical axis direction, y is the distance in the direction perpendicular to the optical axis, K is the conic constant, A, B, C, D are aspherical coefficients, c represents the inverse of the radius of curvature (1 / R) at the vertex of the lens, respectively.

The present invention specifically includes lenses according to optimization conditions for realizing miniaturization of a zoom lens through embodiments according to various designs as follows.

F is the composite focal length of the entire lens system, Fno is the F number, 2w is the angle of view, R is the radius of curvature, Dn is the center thickness of the lens or the distance between the lens, and nd is the refractive index, vd represents Abbe's number, respectively. In addition, ST represents an aperture, D1, D2, D3, and D4 represent a variable distance, and ASP represents an aspherical surface. Incidentally, in the drawings showing the embodiments, the same numbers are indicated for the lenses constituting each lens group.

<First Embodiment>

1 illustrates a wide-angle end, an intermediate end, and a telephoto end of the zoom lens according to the first embodiment, respectively.

 f; 6.1 to 17.69 to 28.98 Fno; 3.39 ~ 4.41 ~ 5.22

 2ω; 65.72-26.16-16.78

  Lens plane R Dn nd vd

  OBJ: INFINITY INFINITY

   S1: 16.73500 2.780000 1.516798 64.19

      ASP:

    K: -0.430801

    A: 0.141908E-05 B: -0.273697E-07 C: -0.306880E-09

    D: 0.000000E-00

   S2: -94.73600 D1

   S3: 124.94300 0.500000 1.815999 46.72

   S4: 5.47 100 2.340000

   S5: -28.31300 0.620000 1.883000 40.81

   S6: 96.49800 0.100000

   S7: -9.81400 1.390000 1.945945 17.98

   S8: 19.14500 D2

   ST: INFINITY 0.300000

   S10: 5.40800 1.612000 1.693500 53.20

      ASP:

      K: -0.040814

     A: -0.742822E-03 B: -0.222932E-04 C: -0.383161E-05

     D: 0.246117E-06

  S11: -20.36700 0.540000

      ASP:

      K: 0.000000

      A: 0.169853E-03 B: -0.316066E-04 C: 0.000000E-00

      D: 0.000000E-00

  S12: 6.33500 1.130000 1.496997 81.61

  S13: 230.53200 0.450000 1.846663 23.78

  S14: 3.70 100 D3

  S15: 13.80 200 1.830000 1.922860 20.88

  S16: 134.03300 D4

  S17: INFINITY 0.300000 1.516798 64.19

  S18: INFINITY 0.500000

  S19: INFINITY 0.500000 1.516798 64.19

  S20: INFINITY 0.590000

  IMG: INFINITY

Next, the variable distances D1, D2, D3, and D4 of the zoom lens according to the first embodiment are shown for the wide-angle end, the intermediate end, and the telephoto end.

Wide angle Middle Telephoto D1 0.60 7.74 10.63 D2 12.68 3.75 1.65 D3 3.54 7.07 13.34 D4 4.68 7.03 5.88

2 and 3 show spherical aberration, image curvature, and distortion aberration at the wide-angle end and the telephoto end of the zoom lens according to the first embodiment of the present invention, respectively. Top curves show tangential field curvature (T) and sagittal field curvature (S).

Second Embodiment

4 illustrates a zoom lens according to a second embodiment, and includes first, second, third, and fourth lens groups G1, G2, G3, and G4.

 f; 6.5-18.53-26.65 Fno; 3.42 to 4.52 to 5.26

 2ω; 62.44-24.01-16.82

  Lens plane R Dn nd vd

  OBJ: INFINITY INFINITY

   S1: 18.29200 2.650000 1.516798 64.19

      ASP:

      K: -0.476487

      A: 0.125001E-06 B: -0.113803E-08 C: -0.895938E-09

      D: 0.000000E-00

   S2: -71.67200 D1

   S3: 108.69100 0.500000 1.825163 44.89

   S4: 5.57 100 2.228000

   S5: -39.70700 0.550000 1.755000 52.32

   S6: 35.50400 0.100000

   S7: 9.44 300 1.470000 1.907083 20.07

   S8: 21.33500 D2

   ST: INFINITY 0.300000

   S10: 5.50 500 2.160000 1.686893 54.33

      ASP:

      K: -0.058705

      A: -0.768250E-03 B: -0.180702E-04 C: -0.326423E-05

      D: 0.191712E-06

   S11: -18.32100 0.300000

      ASP:

      K: 0.000000

      A: 0.141361E-03 B: -0.279888E-04 C: 0.000000E-00 D: 0.000000E-00

   S12: 7.21700 1.080000 1.496997 81.61

   S13: 56.00800 0.450000 1.846663 23.78

   S14: 3.85800 D3

   S15: 12.75900 1.810000 1.850544 23.32

   S16: 119.28200 D4

   S17: INFINITY 0.300000 1.516798 64.19

   S18: INFINITY 0.500000

   S19: INFINITY 0.500000 1.516798 64.19

   S20: INFINITY 0.590000

   IMG: INFINITY

Next, the variable distances D1, D2, D3, and D4 of the zoom lens according to the second embodiment are shown for the wide-angle end, the intermediate end, and the telephoto end.

Wide angle Middle Telephoto D1 0.60 7.93 9.81 D2 12.37 3.69 1.93 D3 3.45 8.90 14.08 D4 5.09 6.44 5.67

5 and 6 show spherical aberration, image curvature, and distortion aberration at the wide-angle end and the telephoto end of the zoom lens according to the second embodiment of the present invention, respectively.

Third Embodiment

7 shows a zoom lens according to the third embodiment.

 f; 6.1 to 17.38 to 35.99 Fno; 3.70 ~ 5.14 ~ 6.28

 2ω; 65.72-25.54-12.48

 Lens plane R Dn nd vd

  OBJ: INFINITY INFINITY

   S1: 15.10300 2.950000 1.558838 60.90

      ASP:

      K: -0.502790

     A: 0.116617E-05 B: -0.115486E-06 C: 0.299432E-09

     D: 0.000000E-00

   S2: -114.37500 D1

   S3: 67.58800 0.500000 1.883000 40.81

   S4: 4.98200 2.080000

   S5: -284.09300 0.550000 1.883000 40.81

   S6: 17.10700 0.100000

   S7: 7.96300 1.490000 1.914409 20.44

   S8: 16.54700 D2

   ST: INFINITY 0.300000

   S10: 5.12000 1.740000 1.737602 52.82

      ASP:

      K: 0.017145

      A: -0.652305E-03 B: -0.190404E-04 C: -0.258776E-05

      D: 0.515625E-07

   S11: -19.18700 0.570000

      ASP:

      K: 0.000000

      A: 0.295195E-03 B: -0.233273E-04 C: 0.000000E-00

      D: 0.000000E-00

   S12: 5.25 800 1.310000 1.496997 81.61

   S13: -11.23700 0.450000 1.859912 28.18

   S14: 3.29600 D3

   S15: 9.42900 1.570000 1.922860 20.88

   S16: 17.79400 D4

   S17: INFINITY 0.300000 1.516798 64.19

   S18: INFINITY 0.500000

   S19: INFINITY 0.500000 1.516798 64.19

   S20: INFINITY 0.580000

  IMG: INFINITY

Next, the variable distances D1, D2, D3, and D4 of the zoom lens according to the third embodiment are shown for the wide-angle end, the intermediate end, and the telephoto end.

Wide angle Middle Telephoto D1 0.60 5.71 9.38 D2 13.17 5.19 1.65 D3 4.77 7.20 12.96 D4 3.01 6.76 7.48

8 and 9 illustrate spherical aberration, image curvature, and distortion aberration at the wide-angle end and the telephoto end of the zoom lens according to the third embodiment of the present invention, respectively.

Fourth Embodiment

10 shows a zoom lens according to the fourth embodiment.

 f; 6.1 to 17.69 to 30.49 Fno; 3.47 ~ 4.66 ~ 5.65

 2ω; 65.71-25.12-14.72

  Lens plane R Dn nd vd

  OBJ: INFINITY INFINITY

   S1: 15.84600 2.900000 1.631677 56.77

      ASP:

      K: -0.348618

      A: 0.635707E-07 B: -0.319524E-07 C: 0.667098E-09

      D: 0.000000E-00

   S2: -172.58500 D1

   S3: 83.34300 0.500000 1.842123 43.55

   S4: 4.92500 2.280000

   S5: -76.98800 0.500000 1.755000 52.32

   S6: 13.61900 0.100000

   S7: 8.18 500 1.550000 2.000600 25.46

   S8: 19.88 300 D2

   ST: INFINITY 0.300000

   S10: 4.81200 1.790000 1.592898 39.88

      ASP:

      K: -0.032835

     A: -0.772867E-03 B: -0.275412E-04 C: -0.361765E-05

     D: 0.112728E-06

   S11: -12.43800 0.100000

      ASP:

      K: 0.000000

      A: 0.434382E-03 B: -0.330093E-04 C: 0.000000E-00

      D: 0.000000E-00

   S12: 5.07200 1.380000 1.496997 81.61

   S13: -12.74000 0.450000 1.849022 24.47

   S14: 3.52800 D3

   S15: 14.23 700 1.750000 1.922860 20.88

   S16: 155.81700 D4

   S17: INFINITY 0.300000 1.516798 64.19

   S18: INFINITY 0.500000

   S19: INFINITY 0.500000 1.516798 64.19

   S20: INFINITY 0.580000

   IMG: INFINITY

Next, the variable distances D1, D2, D3, and D4 of the zoom lens according to the fourth embodiment are shown for the wide-angle end, the intermediate end, and the telephoto end.

Wide angle Middle Telephoto D1 0.60 5.80 8.28 D2 12.51 3.92 1.65 D3 3.89 7.59 15.02 D4 4.53 7.50 6.53

 The following shows that the first to fourth embodiments satisfy the conditions of Equations 1, 2 and 3, respectively.

Example 1 Example 2 Example 3 Example 4 Equation 1 4.7501 4.1 5.9 4.9982 Equation 2 1.9460 1.9071 1.9144 2.0006 Equation 3 1.8088 1.6066 1.8879 1.7799

As described above, the zoom lens according to the embodiment of the present invention has a high magnification ratio and is compact and has excellent optical performance. The above embodiments are merely exemplary, and various modifications and equivalent other embodiments are possible to those skilled in the art. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the invention described in the claims below.

1 illustrates a zoom lens according to a first embodiment of the present invention for a wide-angle end, an intermediate end, and a telephoto end.

2 and 3 show aberration diagrams at the wide-angle end and the telephoto end of the zoom lens according to the first embodiment of the present invention.

4 illustrates a zoom lens according to a second embodiment of the present invention for each of a wide-angle end, an intermediate end, and a telephoto end.

5 and 6 illustrate aberration diagrams at the wide-angle end and the telephoto end of the zoom lens according to the second exemplary embodiment of the present invention.

7 illustrates a zoom lens according to a third embodiment of the present invention for each of a wide-angle end, an intermediate end, and a telephoto end.

8 and 9 illustrate aberration diagrams at the wide-angle end and the telephoto end of the zoom lens according to the third exemplary embodiment of the present invention.

FIG. 10 is a view illustrating a zoom lens according to a fourth embodiment of the present disclosure for each wide-angle end, middle end, and telephoto end.

11 and 12 illustrate aberration diagrams at the wide-angle end and the telephoto end of the zoom lens according to the fourth embodiment of the present invention.

<Description of main part of drawing>

G1 ... first lens group, G2 ... second lens group,

G3 ... 3rd lens group, G4 ... 4th lens group

D1, D2, D3, D4 ... variable distance

Claims (8)

A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, sequentially from the object side, and having a telephoto end at a wide-angle end. The shifting is performed by shifting the position of each lens group at the time of shifting, wherein the first lens group includes one lens, the second lens group includes three lenses, and satisfies the following conditional expression. A zoom lens characterized by the above. <Conditional expression> 4 ≤ ft / fw ≤ 6 1.90 ≤ Nd2 ≤ 2.05 Where fw is the focal length of the whole optical system at the wide end, ft is the focal length of the whole optical system at the telephoto end, and Nd2 is the refractive index of the last lens from the object side of the second lens group. The method of claim 1, A zoom lens, characterized in that the lens of the first lens group is composed of an aspherical lens. The method of claim 1, And all the lenses of the second lens group consist of spherical lenses. The method of claim 1, The second lens group includes a first meniscus lens having negative refractive power in order from the object side and a convex object side, a lens having positive refractive power, and a second meniscus lens having a negative refractive power and convex on the object side. A zoom lens characterized by the above. The method of claim 1, A zoom lens, which satisfies the following conditional expression. <Conditional expression> 1.6 ≤ (D2w-D2t) / fw ≤ 2.0 Where D2w is the distance from the object side to the last lens of the second lens group and the first lens of the third lens group at the wide-angle end, and D2t is the last and third lens of the second lens group from the object side at the telephoto end. The distance to the first lens of the group, fw represents the focal length of the whole optical system at the wide-angle end, respectively. The method according to any one of claims 1 to 5, And the first lens from the object side of the third lens group is an aspherical surface. The method according to any one of claims 1 to 5, And the third lens group comprises a bonded lens. The method according to any one of claims 1 to 5, The fourth lens group includes a meniscus positive lens that is convex toward the object side, and the positive lens is manufactured using a material having a refractive index of 1.8 or more.

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