JP2005331697A - High variable power ratio zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact and high-performance high variable power ratio zoom lens which realizes a viewing angle of the extent of 76° equivalent to that of 28 mm of a single lens reflex camera, having a 35 mm film and a zooming ratio of about 7 times, when being mounted to a lens interchangeable digital single lens reflex camera, has the back-focus equal to that of the lens interchangeable single lens reflex camera. <P>SOLUTION: The high variable power-rate zoom lens is composed of four lens groups of a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power and a fourth lens group G4, having positive refractive power in order from the object side. When power is varied from wide angle end to telephoto end, the air interval between the first lens group G1 and the second lens group G2 is enlarged; the interval between the second lens group G2 and the third lens group G3 is shortened; at the same time, the first lens group G1, the third lens group G3 and the fourth lens group G4 are moved in the direction of the object; and focusing is performed by moving the second lens group G2 to make specified conditions satisfied. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high-performance, high-magnification zoom lens that has a zoom ratio of about 7 times and a wide-angle end angle of view of about 76 degrees used in digital still cameras, video cameras, and the like.

  High-magnification zoom lenses for 35 mm film single-lens reflex cameras having a zoom ratio of about 7 times and an angle of view at the wide-angle end of about 76 degrees are disclosed in JP-A-2000-89117 and JP-A-2002-236255. There is no high-magnification zoom lens that covers from wide angle to telephoto for interchangeable-lens digital SLR cameras using APS-C size image sensors. If the lens for a 35mm film SLR camera is converted to a lens interchangeable digital SLR camera using an APS-C size image sensor to achieve the same angle of view, the image sensor will be about 0.63 times the 35mm film. Therefore, it is necessary to construct a system by scaling 0.63 times to a lens for a 35 mm film single lens reflex camera.

However, since the scaling factor is small, the scaled system has a problem in productivity because the center thickness and edge thickness of each lens or the lens interval becomes too small, and the back focus is shortened. Problems arise in the system. Designing a wide-angle, high-magnification zoom lens that achieves good productivity and lengthens back focus while maintaining compactness and high performance before scaling is not an easy task and requires new technical content.
JP 2000-89117 A JP 2002-236255 A

  The present invention covers an angle of view of about 76 degrees corresponding to 28 mm of a 35 mm film single-lens reflex camera when mounted on a digital camera using an APS-C size image sensor, and realizes a zoom ratio of about 7 times. The objective is to provide a back focus length suitable for interchangeable lens SLR cameras and a compact, high-performance, high-magnification zoom lens.

  The present invention has a zoom ratio of about 7 times while realizing a wide focal length of 18 mm, and has a back focus that is the same as that of a 35 mm film single lens reflex camera at a wide 18 mm, simultaneously with advanced aberration correction and easy manufacturing tolerances. The design contradiction that must be realized was solved by giving the following configuration and conditions.

In other words, the first lens group having a positive power, the second lens group having a negative power, the third lens group having a positive power, and the fourth lens group having a positive power are arranged in order from the object side. The first, second, and third lens groups are subject to an object while the air distance between the first lens group and the second lens group is increased and the air distance between the second lens group and the third lens group is decreased. Then, focusing was performed by extending the second lens unit, and the following conditions were satisfied.
(1) 0.40 <fW / fbW <0.55
(2) 0.43 <β3, 4W / β3, 4T <0.47
(3) 40 <r5 / d5W <100
(4) 1.1 <f3 / f4 <2.6
However,
fW: Focal length at wide angle end fbW: Back focus at wide angle end β3, 4W: Composite magnification at wide angle end of third and fourth lens groups β3, 4T: Composite magnification at telephoto end of third and fourth lens groups r5: The radius of curvature d5W of the r5 surface is the lens interval between the first lens unit and the second lens unit at the wide angle end f3: the focal length of the third lens unit f4: the focal length of the fourth lens unit.

  According to the present invention, a high-performance high-change including a wide-angle region is obtained by the power and the movement amount direction limitation of the four-group zoom lens group having positive, negative, positive, and positive refractive power in order from the object side and four conditions. Although it is a magnification zoom lens, it can realize a system with smooth movement by zooming and less aberration fluctuation.

  Conditional expression (1) defines the relationship between power and back focus at the wide-angle end. This condition is necessary for realizing a lens having a long back focus relative to the focal length at the wide angle end. If the upper limit of conditional expression (1) is exceeded, it is advantageous for correcting distortion and spherical aberration, but a wide angle of view and a long back focus cannot be realized. On the contrary, if the lower limit is exceeded, a wide angle of view and a long back focus can be realized, but aberration correction becomes difficult, and in particular, distortion aberration correction is rapidly increased.

  Conditional expression (2) is the astigmatism of the zoom position slightly on the telephoto side from the wide-angle end while using the third lens group G3 and the fourth lens group G4 for back focus adjustment in the zoom lens of the present invention. This is a condition for improving the aberration and realizing a gentle and smooth cam shape. When the numerical value increases beyond the upper limit of conditional expression (2), the zoom magnifications of the third lens group G3 and the fourth lens group G4 group become too close to the same magnification at the wide angle end, and the third lens group G3 and the fourth lens. There is a problem in optical performance that the back focus cannot be lengthened by the group G4 and the astigmatism at the position on the telephoto side from the wide angle end is overcorrected.

  Conversely, if β3, 4W and β3, 4T become smaller than the lower limit, it is good to obtain a smooth cam shape, but it becomes difficult to correct astigmatism at the wide-angle end and to make the total length compact. The total lens length at the telephoto end becomes large.

  Conditional expression (3) is a condition necessary for balancing the lens position and aberration correction of the first lens group G1 at the wide-angle end when the focus correction cam is cut in the second group of cam barrels. If the upper limit of conditional expression (3) is exceeded, the radius of curvature of the r5 surface will be small, so light rays with a wide angle of view can be bent smoothly, but this is advantageous for correcting spherical aberration and astigmatism over the entire zoom range. On the other hand, although it is preferable for improving the overall optical performance, the distance between the first lens group G1 and the second lens group G2 becomes too narrow, and there is a problem that the correction cam for focusing cannot be cut. On the contrary, if the lower limit is exceeded, the distance between the first lens group G1 and the second lens group G2 becomes wide, which is advantageous in terms of lens barrel design, but is not preferable in terms of optical performance.

  Conditional expression (4) is a condition indispensable for realizing a high zoom ratio while maintaining excellent optical performance. The power of the third lens group G3 and the fourth lens group G4 is appropriately related. This makes it possible to achieve good optical performance and easy manufacturing tolerances. If the upper limit is exceeded, the power of the fourth lens group G4 becomes strong and good for downsizing, but a situation occurs where the back focus is insufficient at the wide angle end, and when the power of the fourth lens group G4 becomes strong, the periphery of the wide angle end is increased. This is not preferable because the performance deterioration of the part becomes remarkable.

  On the contrary, if the lower limit is exceeded, the power of the fourth lens group G4 becomes weak, and it is possible to improve off-axis performance and loosen the amount of cracking, but initially the system becomes large and a compact lens is realized. Deviate from the purpose. Further, since the outer diameter of the fourth lens group G4 is increased, it is not preferable because it is difficult to manufacture the aspherical lens introduced into the fourth lens group G4, and the productivity is lowered.

  In this embodiment, a lens having a zoom ratio of about 7 times from a wide focal length of 18 mm, which is suitable for the name of a wide angle of a digital camera using an APS-C size image sensor, and having a sufficient back focus even at the wide angle end. Is realized. Then, the problem that is difficult to achieve both high aberration correction and ease of manufacture was solved by giving the following configurations and conditions.

  In the following, Numerical Example 1, Numerical Example 2, and Numerical Example 3 of the high variable magnification zoom lens according to the present invention are shown. In Numerical Example 1, Numerical Example 2, and Numerical Example 3, f is a focal length, Fno is an F number, ω is a half angle of view, ri is a radius of curvature of the i-th lens surface in order from the object side, di is the i-th lens thickness and air interval in order from the object side, and ni and vi are the i-th lens refractive index and Abbe number in order from the object side.

The aspherical shape is expressed by an x-axis in the optical axis direction, a y-axis in the direction perpendicular to the optical axis, a paraxial radius of curvature r, A4, A6, A8, and A10 each aspheric coefficient, and a conic coefficient A. Is represented by the following equation.
x = (y ² / r) / [1+ {1-A (y ² / r ² )} ^1/2 ] + A4y ⁴ + A6y ⁶ + A8y ⁸ + A10y ¹⁰

f = 18.72 to 48.32 to 120.38
Fno = 3.62 to 4.98 to 5.80
ω = 37.7 ° to 15.7 ° to 6.5 °

i r d n ν
[1] 118.40 1.70 1.84666 23.8
[2] 64.85 6.70 1.48749 70.4
[3] -279.53 0.20
[4] 53.65 4.44 1.65160 58.4
[5] 171.00 2.15
[6] 47.78 0.08 1.518840 52.1
[7] 44.73 1.20 1.80420 46.5
[8] 12.30 4.45
[9] -35.63 0.90 1.80420 46.5
[10] 35.72 0.65
[11] 21.18 4.28 1.74077 27.8
[12] -41.55 1.88
[13] -18.64 0.90 1.80420 46.5
[14] 89.44 0.15
[15] 490.90 1.80 1.76182 26.6
[16] -42.33 18.72
[17] 0.00 1.33
[18] 47.93 2.28 1.48749 70.4
[19] -55.87 0.15
[20] 29.60 3.11 1.49700 81.6
[21] -209.28 2.67
[22] -29.67 1.00 1.80610 33.3
[23] -546.68 5.30
[24] 66.36 2.78 1.551680 64.2
[25] -45.82 0.15
[26] 36.22 3.93 1.48749 70.4
[27] -102.74 2.20
[28] 164.09 0.15 1.5840 52.1
[29] 211.62 1.48 1.80610 40.7
[30] 24.15 1.29
[31] 77.57 3.76 1.48749 70.4
[32] -34.12

(Aspheric coefficient)
r6
A = 0.60400000D + 01
A4 = −0.71549000D−06
A6 = −0.42212900D−07
A8 = 0.44549000D-09
A10 = −0.13824000D-11
r28
A = −0.51287000D + 03
A4 = −0.97446000D−05
A6 = −0.73875000D−07
A8 = 0.12418000D-09
A10 = 0.1324400D-11

f 18.72 48.32 120.38
d5 2.15 21.65 42.93
d16 18.72 7.59 1.31
d23 5.30 1.72 0.70

(Conditional expression)
(1) fW / fbW = 0.491
(2) β3, 4W / β3, 4T = 0.448
(3) r5 / d5W = 79.527
(4) f3 / f4 = 1.745

f = 18.73 to 48.33 to 120.38
Fno = 3.66-5.07-5.84
ω = 37.7 ° to 15.9 ° to 6.5 °

i r d n ν
[1] 14.65 1.70 1.84666 23.8
[2] 63.65 7.23 1.48749 70.4
[3] -196.40 0.15
[4] 44.85 4.34 1.65160 58.4
[5] 93.51 2.15
[6] 52.84 0.08 1.5518 42.1
[7] 48.41 1.20 1.80420 46.5
[8] 12.58 4.41
[9] -33.40 1.60 1.80420 46.5
[10] 33.55 0.85
[11] 21.68 4.70 1.74077 27.8
[12] -33.47 1.82
[13] -17.76 0.90 1.80420 46.5
[14] 80.83 0.15
[15] 311.62 1.73 1.76182 26.6
[16] -49.85 17.26
[17] 0.00 1.25
[18] 40.91 2.42 1.48749 70.4
[19] -42.43 0.15
[20] 30.34 3.34 1.49700 81.6
[21] -84.68 2.31
[22] -29.43 1.00 1.80610 33.3
[23] 607.44 5.92
[24] 64.86 2.83 1.51680 64.2
[25] -44.60 0.18
[26] 44.27 3.63 1.48749 70.4
[27] -96.55 2.20
[28] 151.68 0.15 1.5840 52.1
[29] 206.36 2.25 1.80610 40.7
[30] 24.16 1.17
[31] 67.88 6.94 1.48749 70.4
[32] -41.03

(Aspheric coefficient)
r6
A = 0.6047000D + 01
A4 = 0.2155100D-05
A6 = −0.19592300D−07
A8 = 0.3275100D-09
A10 = −0.138223600D-11
r28
A = −0.41691430D + 03
A4 = −0.10273500D−04
A6 = −0.814665500D−07
A8 = 0.3227500D-10
A10 = 0.11641700D-11

f 18.73 48.33 120.38
d5 2.15 21.82 42.04
d16 17.26 6.92 1.38
d23 5.92 1.80 0.70

(Conditional expression)
(1) fW / fbW = 0.550
(2) β3,4W / β3,4T = 0.454
(3) r5 / d5W = 43.502
(4) f3 / f4 = 1.208

f = 19.03-48.29-118.95
Fno = 3.70-5.06-5.82
ω = 37.3 ° to 15.8 ° to 6.6 °

i r d n ν
[1] 105.01 1.81 1.84666 23.8
[2] 61.49 6.61 1.48749 70.4
[3] -423.68 0.15
[4] 56.20 4.40 1.65160 58.4
[5] 199.78 2.15
[6] 47.31 0.08 1.551840 52.1
[7] 43.53 1.20 1.80420 46.5
[8] 11.60 4.65
[9] -34.54 0.90 1.80420 46.5
[10] 34.70 0.15
[11] 20.09 4.25 1.74077 27.8
[12] -34.31 1.89
[13] -17.22 0.90 1.80420 46.5
[14] -449.56 0.15
[15] -88.43 1.58 1.76182 26.6
[16] -34.47 19.90
[17] 0.00 1.42
[18] 61.56 2.00 1.48749 70.4
[19] -75.14 0.15
[20] 25.31 2.02 1.49700 81.6
[21] 167.30 2.90
[22] -20.81 1.00 1.80610 33.3
[23] -48.68 3.07
[24] 59.89 2.77 1.551680 64.2
[25] -42.08 0.15
[26] 69.02 3.08 1.48749 70.4
[27] -34.67 0.15
[28] 151.76 0.15 1.5840 52.1
[29] 208.24 1.00 1.80610 40.7
[30] 24.16 1.35
[31] 136.06 3.23 1.48749 70.4
[32] -34.05

(Aspheric coefficient)
r6
A = 0.6047000D + 01
A4 = −0.86000081D−06
A6 = −0.37993123D-07
A8 = 0.44003997D-09
A10 = −0.138223600D-11
r28
A = −0.49763940D + 03
A4 = −0.10221063D−04
A6 = −0.13323833D−06
A8 = 0.24456953D-09
A10 = 0.16553089D-11

f 19.03 48.32 120.38
d5 2.15 21.33 43.09
d16 19.90 8.04 1.21
d23 3.07 1.02 0.70

(Conditional expression)
(1) fW / fbW = 0.422
(2) β3,4W / β3,4T = 0.465
(3) r5 / d5W = 92.807
(4) f3 / f4 = 2.530

2 is a lens cross-sectional view of Numerical Example 1. FIG. 6 is a lens cross-sectional view of Numerical Example 2. FIG. 10 is a lens cross-sectional view of Numerical Example 3. FIG. FIG. 5 is an aberration diagram at the wide-angle end in Numerical Example 1. FIG. 6 is an aberration diagram in an intermediate area in Numerical Example 1. FIG. 3 is an aberration diagram at the telephoto end in Numerical Example 1. FIG. 6 is an aberration diagram at the wide-angle end in Numerical Example 2. FIG. 6 is an aberration diagram in an intermediate area in Numerical Example 2. FIG. 10 is an aberration diagram at the telephoto end in Numerical Example 2. FIG. 6 is an aberration diagram at the wide-angle end in Numerical Example 3. FIG. 6 is an aberration diagram in an intermediate area in Numerical Example 3. FIG. 6 is an aberration diagram at the telephoto end in Numerical Example 3.

Explanation of symbols

G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group

Claims (1)

In order from the object side, the first lens group is positive, the second lens group is negative, the third lens group is positive, and the fourth lens group is composed of four lens groups having positive refractive power, from the wide-angle end to the telephoto end. In zooming, the first, third, and fourth lens groups are enlarged while the air gap between the first lens group and the second lens group is enlarged and the gap between the second lens group and the third lens group is reduced. Moves in the object direction, focusing is performed by extending the second lens group, and the following conditional expression is satisfied:
(1) 0.40 <fW / fbW <0.55
(2) 0.43 <β3, 4W / β3, 4T <0.47
(3) 40 <r5 / d5W <100
(4) 1.1 <f3 / f4 <2.6
However,
fW: Focal length at wide angle end fbW: Back focus at wide angle end β3, 4W: Composite magnification at wide angle end of third and fourth lens groups β3, 4T: Composite magnification at telephoto end of third and fourth lens groups r5: curvature radius d5W of r5 surface: lens interval between the first and second lens units at the wide angle end f3: focal length of the third lens unit f4: focal length of the fourth lens unit

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