JP5958018B2 - Zoom lens, imaging device - Google Patents

Description

  The present invention relates to a zoom lens suitable for a digital camera, a video camera, a silver salt film camera, an image pickup apparatus having the zoom lens, and a zoom lens manufacturing method.

  2. Description of the Related Art Conventionally, there is a zoom lens used in an imaging apparatus such as a digital camera in which chromatic aberration is corrected using a lens made of glass having anomalous dispersion (see, for example, Patent Documents 1 to 3).

JP-A-8-248317 Japanese Patent Laid-Open No. 2002-62478 JP 2007-108398 A

  However, in the conventional zoom lens, correction of the secondary spectrum of chromatic aberration is insufficient.

  The present invention has been made in view of such a situation, and has a zoom lens having high optical performance capable of satisfactorily correcting various aberrations including the secondary spectrum of chromatic aberration over the entire zoom range, and the zoom lens. An object is to provide an imaging device and a method of manufacturing a zoom lens.

In order to achieve the above object, a zoom lens according to the present invention includes, in order from the object side along the optical axis, a first lens group having a positive refractive power, a second lens group having a negative refractive power, And a rear group including one or more lens groups. When zooming from the wide-angle end state to the telephoto end state, the interval between the adjacent lens groups changes, and the first lens group with respect to the image plane Moves toward the object side, and the second lens group includes a plurality of lenses including a negative lens and a positive lens, and at least one of the negative lenses satisfies the following conditional expressions (1) and (2): At least one positive lens satisfies the following conditional expressions (3A) and (4).
(1) 60.0 <νdn
(2) θgFn− (0.644−1.68 × 10 ⁻³ · νdn)> 0.000
However,
νdn: Abbe number θgFn of the material of the negative lens: Partial dispersion ratio of the material of the negative lens (3A) 39.61 ≦ νdp ≦ 44.17
(4) θgFp− (0.644−1.68 × 10 ⁻³ · νdp) <0.000
However,
νdp: Abbe number of the material of the positive lens θgFp: Partial dispersion ratio of the material of the positive lens Further, the zoom lens according to the present invention is a first lens having a positive refractive power in order from the object side along the optical axis. And a second lens group having a negative refractive power, and a rear group including one or more lens groups, and the distance between adjacent lens groups upon zooming from the wide-angle end state to the telephoto end state The second lens group includes, in order from the object side along the optical axis, a first negative lens, a second negative lens, a positive lens, and a third negative lens. At least one of the first negative lens, the second negative lens, and the third negative lens satisfies the following conditional expressions (1) and (2), and the positive lens has the following conditional expression (3): And (4) is satisfied.
(1) 60.0 <νdn
(2) θgFn− (0.644−1.68 × 10 ⁻³ · νdn)> 0.000
However,
νdn: Abbe number θgFn of the material of the negative lens: Partial dispersion ratio of the material of the negative lens (3) 35.0 <νdp <70.0
(4) θgFp− (0.644−1.68 × 10 ⁻³ · νdp) <0.000
However,
νdp: Abbe number θgFp of the material of the positive lens: Partial dispersion ratio of the material of the positive lens

  An image pickup apparatus according to the present invention includes the zoom lens.

  According to the present invention, a zoom lens having high optical performance capable of satisfactorily correcting various aberrations including a secondary spectrum of chromatic aberration over the entire zoom range, an image pickup apparatus having the same, and a method of manufacturing the zoom lens Can be provided.

It is sectional drawing which shows the lens structure of the zoom lens which concerns on 1st Example of this invention. FIG. 4 is a diagram illustrating various aberrations of the zoom lens according to Example 1 during infinite focus, where (a) shows a wide-angle end state, (b) shows an intermediate focal length state, and (c) shows a telephoto end state. . FIG. 5 is a diagram illustrating a wavelength characteristic graph of chromatic aberration when the zoom lens according to Example 1 is focused at infinity, where (a) is a wide-angle end state, (b) is an intermediate focal length state, and (c) is a telephoto end state. Respectively. It is sectional drawing which shows the lens structure of the zoom lens which concerns on 2nd Example of this invention. FIG. 6 is a diagram illustrating various aberrations of the zoom lens according to Example 2 during focusing at infinity, where (a) shows a wide-angle end state, (b) shows an intermediate focal length state, and (c) shows a telephoto end state. . It is a figure which shows the wavelength characteristic graph of the chromatic aberration at the time of infinity focusing of the zoom lens which concerns on 2nd Example, (a) is a wide angle end state, (b) is an intermediate | middle focal distance state, (c) is a telephoto end state. Respectively. It is sectional drawing which shows the outline of the camera provided with the zoom lens of this invention. It is a figure which shows the outline of the manufacturing method of the zoom lens which concerns on this invention.

  Hereinafter, a zoom lens, an imaging apparatus, and a zoom lens manufacturing method according to the present invention will be described.

First, among the terms used in this specification, a method for calculating the Abbe number νd, the partial dispersion ratio θgF, and the anomalous dispersion ΔPgF will be described. Assuming that the refractive indexes of the g-line, d-line, F-line, and C-line are Ng, Nd, NF, and NC, respectively, the Abbe number νd and the partial dispersion ratio θgF are calculated by the following formulas (A) and (B), respectively. Is done.
(A) Abbe number νd = (Nd−1) / (NF−NC)
(B) Partial dispersion ratio θgF = (Ng−NF) / (NF−NC)

Further, the anomalous dispersion ΔPgF is calculated by the following calculation formula (C).
(C) Anomalous dispersion ΔPgF = θgF− (0.644−0.00168 × νd)

Next, the zoom lens according to the present invention will be described. The zoom lens according to the present invention includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and one or more lens groups in order from the object side along the optical axis. And the distance between the first lens group and the second lens group is changed during zooming from the wide-angle end state to the telephoto end state, and the second lens group includes a plurality of negative lenses and positive lenses. And at least one negative lens satisfies the following conditional expressions (1) and (2).
(1) 60.0 <νdn
(2) θgFn− (0.644−1.68 × 10 ⁻³ · νdn)> 0.000
However,
νdn: Abbe number θgFn of the material of the negative lens: Partial dispersion ratio of the material of the negative lens

  As described above, the zoom lens according to the present invention includes, in order from the object side along the optical axis, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and one or more And a rear group including a lens group, and the distance between the first lens group and the second lens group is changed upon zooming from the wide-angle end state to the telephoto end state. With this configuration, fluctuations in distortion due to zooming are suppressed, and a high zoom ratio is ensured for the entire system.

  In the zoom lens according to the present invention, the second lens group includes a plurality of lenses including a negative lens and a positive lens, and at least one of the negative lenses has the above conditional expression ( By satisfying 1) and (2), high performance can be achieved.

  Conditional expression (1) is a conditional expression for defining an appropriate range of the Abbe number of the material of the negative lens constituting the second lens group. Conditional expression (2) is a conditional expression for defining a range of anomalous dispersion of the negative lens obtained from a partial dispersion ratio of the material of the negative lens.

  By satisfying the conditional expressions (1) and (2), the second lens group has at least one negative lens with a small dispersion and a positive value of anomalous dispersion. With this configuration, it is possible to reduce the secondary spectrum of chromatic aberration that occurs in the second lens group, thereby realizing high optical performance.

In the zoom lens according to the present invention, it is preferable that at least one positive lens in the second lens group satisfies the following conditional expressions (3) and (4).
(3) 35.0 <νdp <70.0
(4) θgFp− (0.644−1.68 × 10 ⁻³ · νdp) <0.000
However,
νdp: Abbe number θgFp of the material of the positive lens: Partial dispersion ratio of the material of the positive lens

  Conditional expression (3) is a conditional expression for defining an appropriate range of the Abbe number of the material of the positive lens constituting the second lens group. Conditional expression (4) is a conditional expression for defining a range of anomalous dispersion of the positive lens obtained from a partial dispersion ratio of the material of the positive lens.

  By satisfying conditional expressions (3) and (4), the second lens group has at least one positive lens whose dispersion is in a desired range and whose anomalous dispersion is negative. With this configuration, a combination of anomalous dispersion between the negative lens and the positive lens in the second lens group is appropriate. As a result, it is possible to further reduce the secondary spectrum of axial chromatic aberration generated in the second lens group, and to reduce axial chromatic aberration variation in the specified wavelength range over the entire zoom lens system. Become.

  In order to secure the effect of the present invention, it is desirable to set the lower limit of conditional expression (3) to 38.0. In order to secure the effect of the present invention, it is desirable to set the upper limit of conditional expression (3) to 60.0.

  In the zoom lens according to the present invention, in order to improve performance, the second lens group includes a first negative lens, a second negative lens, and a positive lens in order from the object side along the optical axis. It is desirable to have. By adopting such a configuration, the combination of anomalous dispersion of the first and second negative lenses and the positive lens in the second lens group becomes more appropriate, and the secondary spectrum of chromatic aberration can be corrected more satisfactorily. .

  The image pickup apparatus of the present invention includes the zoom lens having the above-described configuration. Thereby, an imaging device having high optical performance can be realized.

The zoom lens manufacturing method of the present invention includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and one or more lenses in order from the object side along the optical axis. A zoom lens manufacturing method including a rear group including a group, wherein the distance between the first lens group and the second lens group changes when zooming from the wide-angle end state to the telephoto end state. The second lens group includes a plurality of lenses including a negative lens and a positive lens, and at least one of the negative lenses is configured to satisfy the following conditional expressions (1) and (2). And
(1) 60.0 <νdn
(2) θgFn− (0.644−1.68 × 10 ⁻³ · νdn)> 0.000
However,
νdn: Abbe number θgFn of the material of the negative lens: Partial dispersion ratio of the material of the negative lens.

  With such a zoom lens manufacturing method, a zoom lens having high optical performance can be manufactured.

(Numerical example)
Hereinafter, zoom lenses according to numerical examples of the present invention will be described with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a sectional view showing the lens configuration of a zoom lens ZL1 according to the first embodiment of the present invention.

  As shown in FIG. 1, the zoom lens ZL1 according to the present embodiment includes a first lens group G1 having a positive refractive power and a second lens group having a negative refractive power in order from the object side along the optical axis. G2 and a third lens group G3 having a positive refractive power.

  In the zoom lens ZL1 according to the present embodiment, when zooming from the wide-angle end state W to the telephoto end state T, the distance between the first lens group G1 and the second lens group G2 increases, and the second lens group G2 and the second lens group G2 The distance from the third lens group G3 decreases. Further, the first lens group G1 moves toward the object side, the second lens group G2 moves toward the image plane I, and the third lens group G3 moves monotonously toward the object side with respect to the image plane I.

  The first lens group G1 includes, in order from the object side along the optical axis, a positive lens L11 having a convex surface facing the object side, a negative meniscus lens L12 having a convex surface facing the object side, and a positive lens having a convex surface facing the object side And a cemented lens with L13.

  The second lens group G2 includes, in order from the object side along the optical axis, a cemented lens of a biconcave lens L21, a biconcave lens L22 and a positive meniscus lens L23 having a convex surface facing the object side, and a biconcave lens L24. The

  The third lens group G3 has, in order from the object side along the optical axis, a cemented lens of a biconvex lens L31, a biconvex lens L32, and a negative meniscus lens L33 having a concave surface on the object side, and a convex surface directed to the object side. A cemented lens of a positive meniscus lens L34, a negative meniscus lens L35 having a convex surface facing the object side, and a positive meniscus lens L36 having a convex surface facing the object side, and a positive meniscus lens L38 having a convex surface facing the object side. A cemented lens of a biconvex lens L39 and a biconcave lens L310, a cemented lens of a biconvex lens L311 and a negative meniscus lens L312 having a concave surface facing the object side, and a negative meniscus lens having a concave surface facing the object side L313 and the light beam emitted from the L313 lens forms an image on the image plane I.

Table 1 below lists specifications of the zoom lens ZL1 according to the first example of the present invention.
In [Overall specifications] in Table 1, f is the focal length of the entire variable magnification optical system, FNO is the F number, 2ω is the angle of view (unit: degree), Y is the image height, and TL is in the infinitely focused state. The entire lens length from the most object-side surface of the first lens group G1 to the image plane I is shown. W indicates a wide angle end state, M indicates an intermediate focal length state, and T indicates a focal length state in a telephoto end state.

  In [Surface data], the lens is a code assigned to each lens, the surface number is the order of the lens surface counted from the object side, r is the radius of curvature of the lens surface, d is the distance between the lens surfaces, nd is the d-line (wavelength λ = 587.6 nm), and νd represents the Abbe number for the d-line (wavelength λ = 587.6 nm). The object plane indicates the object plane, (aperture) indicates the aperture stop SP, and the image plane indicates the image plane I. Note that the radius of curvature r = ∞ indicates a plane, and the description of the refractive index of air d = 1.00000 is omitted. ΘgF represents a partial dispersion ratio, and ΔPgF represents anomalous dispersion.

[Variable interval data] indicates values of the focal length f, the variable interval, and the aperture stop diameter φ.
[Lens Group Data] indicates the start surface number and focal length of each lens group.
[Conditional Expression Corresponding Value] indicates the corresponding value of each conditional expression.

  Here, “mm” is generally used as the unit of the focal length f, the radius of curvature r, and other lengths described in Table 1. However, the optical system is not limited to this because an equivalent optical performance can be obtained even when proportionally enlarged or proportionally reduced.

  In addition, the code | symbol of Table 1 described above shall be similarly used also in the table | surface of each Example mentioned later.

(Table 1) First Example [Overall Specifications]
W M T
f 72.10 135.70 291.00
FNO 4.13 4.5 5.77
2ω 13.0 6.9 3.2
Y 8.19 8.19 8.19
TL 229.4 235.8 234.5

[Surface data]
Lens surface number r d nd νd θgF ΔPgF
Object ∞
L11 1) 79.665 5.60 1.49782 82.57 0.5386 0.0328
2) ∞ 0.10
L12 3) 100.689 1.50 1.71700 47.98 0.5585 -0.0054
L13 4) 46.297 8.44 1.43700 95.10 0.5334 0.0486
5) ∞ (D5)
L21 6) -662.575 2.00 1.49782 82.57 0.5386 0.0328
7) 40.409 4.15
L22 8) -311.187 1.42 1.43700 95.10 0.5334 0.0486
L23 9) 32.875 5.45 1.80440 39.61 0.5719 -0.0060
10) 754.966 2.56
L24 11) -68.218 2.72 1.74320 49.26 0.5526 -0.0091
12) 127.941 (D12)
13) (Aperture) ∞ 1.82
L31 14) 172.791 3.14 1.49782 82.57 0.5386 0.0328
15) −120.867 17.54
L32 16) 37.806 6.28 1.43700 95.10 0.5334 0.0486
L33 17) -130.857 1.50 1.75500 52.34 0.5476 -0.0089
18) −1870.031 0.10
L34 19) 32.588 3.34 1.49782 82.57 0.5386 0.0328
20) 63.070 0.21
L35 21) 41.682 1.50 1.78590 44.17 0.5625 -0.0077
L36 22) 21.853 4.55 1.49782 82.57 0.5386 0.0328
23) 66.791 16.80
L37 24) -115.286 2.50 1.68893 31.16 0.5993 0.0072
L38 25) 41.911 3.35 1.49782 82.57 0.5386 0.0328
26) 73.108 4.00
L39 27) 1360.609 2.50 1.80100 34.92 0.5853 -0.0005
L310 28) -26.959 1.50 1.75700 47.86 0.5556 -0.0085
29) 45.736 3.98
L311 30) 44.956 4.51 1.72342 38.03 0.5830 0.0025
L312 31) −13.457 1.50 1.67003 47.14 0.5626 −0.0027
32) −64.081 2.43
L313 33) --20.903 1.50 1.88300 40.66 0.5669 -0.0092
34) −39.626 (BF)
Image plane ∞

[Variable interval data]
W M T
f 72.10 135.70 291.00
D5 2.18 28.20 42.17
D12 69.95 42.03 1.87
BF 38.77 47.05 71.93
φ 29.8 29.8 29.8

[Lens group data]
Start surface Focal length
G1 1 135.8
G2 6 −45.3
G3 13 55.9

[Values for each conditional expression]
L21:
(1) νdn = 82.57
(2) θgFn− (0.644−1.68 × 10 ⁻³ · νdn) = 0.0328
L22:
(1) νdn = 95.10
(2) θgFn− (0.644−1.68 × 10 ⁻³ · νdn) = 0.0486
L23:
(3) νdp = 39.61
(4) θgFp− (0.644−1.68 × 10 ⁻³ · νdp) = − 0.0060

  Thus, the negative lens L21 and the negative lens L22 of the second lens group G2 both satisfy the conditional expressions (1) and (2). That is, it is a negative lens having a low dispersion whose Abbe number νd is larger than 60 and anomalous dispersion having a positive value. Further, the positive lens L23 of the second lens group G2 satisfies the conditional expressions (3) and (4). That is, it is a positive lens in which the Abbe number νd is in a range larger than 35 and smaller than 70 and anomalous dispersion is a negative value.

  Further, as shown in FIG. 1 and Table 1, the combination of the glass materials of the lenses constituting the first lens group G1 and the third lens group G3 is basically a positive lens having low dispersion and positive anomalous dispersion, and anomalous dispersion. Uses a combination of negative lenses with negative characteristics. By configuring the first lens group G1 and the third lens group G3 in this way, the secondary spectrum of chromatic aberration can be corrected well, but the present invention can correct chromatic aberration more satisfactorily. That is, in such a configuration of the first lens group G1 and the third lens group G3, the chromatic aberration has a greater influence on the telephoto side than on the wide angle side in the first lens group G1 and the second lens group G2. In the three lens group G3, both the wide angle side and the telephoto side are affected. On the wide-angle side, the secondary spectrum of chromatic aberration of the first lens group G1 and the third lens group G3 is corrected favorably, so that satisfactory chromatic aberration correction is possible, but the secondary spectrum generated in the second lens group G2 is It remains on the telephoto side and deteriorates the chromatic aberration on the telephoto side. Therefore, by defining the anomalous dispersion of the negative lens and the positive lens of the second lens group G2 as in the present invention, the secondary spectrum of chromatic aberration generated in the second lens group G2 is corrected, and from the wide angle side to the telephoto side. Good chromatic aberration correction is achieved.

  FIGS. 2A and 2B are graphs showing various aberrations of the zoom lens ZL1 according to the first example when the zoom lens is focused on infinity, where FIG. 2A is a wide-angle end state, FIG. 2B is an intermediate focal length state, and FIG. Respectively.

  In each aberration diagram, FNO indicates an F number, and Y indicates an image height. In the figure, d indicates an aberration curve at the d-line (wavelength λ = 587.6 nm), g indicates an aberration curve at the g-line (wavelength λ = 435.8 nm), and those not described are d-line The aberration curve at is shown. In the aberration diagram showing astigmatism, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. The aberration diagram showing coma represents the meridional coma with respect to the d-line and the g-line at each image height. In addition, in the various aberration diagrams of the following examples, the same reference numerals as those of the present example are used.

 FIGS. 3A and 3B are diagrams illustrating wavelength characteristics graphs of chromatic aberration when the zoom lens ZL1 according to the first example is focused at infinity, where FIG. 3A is a wide-angle end state, and FIG. 3B is an intermediate focal length state. (C) shows the telephoto end state.

  As is clear from the respective aberration diagrams and wavelength characteristic graphs, the zoom lens ZL1 according to the first example has excellent optical performance with various aberrations and chromatic aberrations corrected well from the wide-angle end state to the telephoto end state. I understand.

(Second embodiment)
FIG. 4 is a sectional view showing a lens configuration of a zoom lens ZL2 according to the second embodiment of the present invention.

  As shown in FIG. 4, the zoom lens ZL2 according to the present embodiment includes a first lens group G1 having a positive refractive power and a second lens group having a negative refractive power in order from the object side along the optical axis. G2 and a third lens group G3 having a positive refractive power.

  In the zoom lens ZL2 according to the present embodiment, when zooming from the wide-angle end state W to the telephoto end state T, the distance between the first lens group G1 and the second lens group G2 increases, and the second lens group G2 and the second lens group G2 The distance from the third lens group G3 decreases. Further, the first lens group G1 moves toward the object side, the second lens group G2 moves toward the image plane I, and the third lens group G3 moves monotonously toward the object side with respect to the image plane I.

  The first lens group G1 includes, in order from the object side along the optical axis, a positive lens L11 having a convex surface facing the object side, a negative meniscus lens L12 having a convex surface facing the object side, and a positive lens having a convex surface facing the object side And a cemented lens with L13.

  The second lens group G2 includes, in order from the object side along the optical axis, a negative meniscus lens L21 having a convex surface directed toward the object side, a cemented lens of a biconcave lens L22 and a biconvex lens L23, and a biconcave lens L24. The

  The third lens group G3 has, in order from the object side along the optical axis, a cemented lens of a biconvex lens L31, a biconvex lens L32, and a negative meniscus lens L33 having a concave surface on the object side, and a convex surface directed to the object side. A cemented lens of a positive meniscus lens L34, a negative meniscus lens L35 having a convex surface facing the object side, and a positive meniscus lens L36 having a convex surface facing the object side, a negative meniscus lens L37 having a convex surface facing the object side, and the object side A cemented lens with a positive meniscus lens L38 having a convex surface, a cemented lens with a positive meniscus lens L39 having a concave surface facing the object side and a biconcave lens L310, and a negative meniscus lens L312 having a concave surface facing the biconvex lens L311 and the object side And a negative meniscus lens L313 having a concave surface facing the object side, and is emitted from the L313 lens. Beam is focused on the image plane I.

Table 2 below lists specifications of the zoom lens ZL2 according to Example 2 of the present invention.
(Table 2) Second embodiment [Overall specifications]
W M T
f 72.10 135.70 291.00
FNO 4.64 5.3 8.11
2ω 13.0 6.9 3.2
Y 8.19 8.19 8.19
TL 199.2 22.4 266.6

Lens surface number r d nd νd θgF ΔPgF
Object ∞
L11 1) 92.104 3.26 1.49782 82.57 0.5386 0.0328
2) ∞ 0.10
L12 3) 155.478 1.50 1.70154 41.02 0.5758 0.0003
L13 4) 71.732 4.15 1.43700 95.10 0.5334 0.0486
5) ∞ (D5)
L21 6) 187.803 2.00 1.49782 82.57 0.5386 0.0328
7) 35.516 3.02
L22 8) −101.979 1.00 1.43700 95.10 0.5334 0.0486
L23 9) 30.494 4.41 1.78590 44.17 0.5625 -0.0077
10) -270.821 2.56
L24 11) -51.875 2.72 1.72916 54.61 0.5443 -0.0084
12) 120.975 (D12)
13) (Aperture) ∞ 1.92
L31 14) 233.583 2.93 1.49782 82.57 0.5386 0.0328
15) −77.996 8.38
L32 16) 54.812 5.18 1.43700 95.10 0.5334 0.0486
L33 17) -57.644 1.50 1.71300 53.96 0.5452 -0.0086
18) −3188.705 0.10
L34 19) 34.323 3.79 1.49782 82.57 0.5386 0.0328
20) 252.290 0.21
L35 21) 72.662 1.50 1.72916 54.61 0.5443 -0.0084
L36 22) 27.228 3.71 1.49782 82.57 0.5386 0.0328
23) 109.181 16.80
L37 24) 77.693 2.50 1.67270 32.19 0.5973 0.0070
L38 25) 21.264 4.20 1.53172 48.78 0.5622 -0.0003
26) 47.722 4.00
L39 27) -928.979 2.47 1.78472 25.64 0.6157 0.0144
L310 28) -35.508 1.50 1.76200 40.11 0.5724 -0.0047
29) 54.181 3.80
L311 30) 43.786 5.14 1.71300 53.96 0.5452 -0.0086
L312 31) −16.460 1.50 1.65160 58.57 0.5416 −0.0045
32) −66.051 1.07
L313 33) −24.208 1.50 1.49782 82.57 0.5386 0.0328
34) −159.960 (BF)
Image plane ∞

[Variable interval data]
W M T
f 72.10 135.70 291.00
D5 2.19 32.19 42.19
D12 48.10 27.60 1.93
BF 50.51 64.31 124.07
φ 25 25 25

[Lens group data]
Start surface Focal length
G1 1 160.0
G2 6 −45.3
G3 13 53.7

[Values for each conditional expression]
L21:
(1) νdn = 82.57
(2) θgFn− (0.644−1.68 × 10 ⁻³ · νdn) = 0.0328
L22:
(1) νdn = 95.10
(2) θgFn− (0.644−1.68 × 10 ⁻³ · νdn) = 0.0486
L23:
(3) νdp = 44.17
(4) θgFp− (0.644−1.68 × 10 ⁻³ · νdp) = − 0.0077

  Thus, the negative lens L21 and the negative lens L22 of the second lens group G2 both satisfy the conditional expressions (1) and (2). That is, it is a negative lens having a low dispersion whose Abbe number νd is larger than 60 and anomalous dispersion having a positive value. Further, the positive lens L23 of the second lens group G2 satisfies the conditional expressions (3) and (4). That is, it is a positive lens in which the Abbe number νd is in a range larger than 35 and smaller than 70 and anomalous dispersion is a negative value.

  As shown in FIG. 4 and Table 2, in principle, the combination of the glass materials of the lenses constituting the first lens group G1 and the third lens group G3 has low dispersion and anomalous dispersion as in the first embodiment. A combination of a positive positive lens and a negative lens having anomalous dispersion is adopted. The effect of this configuration is the same as that of the first embodiment.

  FIGS. 5A and 5B are graphs showing various aberrations of the zoom lens ZL2 according to Example 2 when focused at infinity, where FIG. 5A is a wide-angle end state, FIG. 5B is an intermediate focal length state, and FIG. 5C is a telephoto end state. Respectively.

  FIGS. 6A and 6B are diagrams illustrating wavelength characteristics graphs of chromatic aberration when the zoom lens ZL2 according to Example 2 is focused at infinity, where FIG. 6A is a wide-angle end state, and FIG. 6B is an intermediate focal length state. (C) shows the telephoto end state.

  As is apparent from the respective aberration diagrams and wavelength characteristic graphs, the zoom lens ZL2 according to the second example has excellent optical performance with various aberrations and chromatic aberrations corrected well from the wide-angle end state to the telephoto end state. I understand.

  Here, each said Example has shown the specific example of this invention, and this invention is not limited to these. The contents described below can be appropriately adopted as long as the optical performance is not impaired.

  As a numerical example of the zoom lens according to the present invention, a positive, negative, and positive three-group configuration is shown. However, the present invention is not limited to this, and other group configurations such as positive, negative, positive, and positive four are shown. It is also possible to configure a zoom lens having a group configuration, or a positive, negative, positive, negative, positive five-group configuration. Specifically, the zoom lens according to the present invention may have a configuration in which a lens or a lens group is added to the most object side or a configuration in which a lens or a lens group is added to the most image side. The lens group indicates a portion having at least one lens separated by an air interval.

  In addition, the zoom lens of the present invention has an optical axis in which a part of a lens group, an entire lens group, or a plurality of lens groups is used as a focusing lens group for focusing from an object at infinity to an object at a short distance. It is good also as a structure moved to a direction. The focusing lens group can also be applied to autofocus, and is also suitable for driving by an autofocus motor, such as an ultrasonic motor. In particular, it is preferable that at least a part of the second lens group is a focusing lens group.

  In the zoom lens of the present invention, the whole or a part of any one of the lens groups is moved so as to include a component in a direction orthogonal to the optical axis as an anti-vibration lens group, or in an in-plane direction including the optical axis. It can also be configured to correct image blur caused by camera shake by rotating (swinging). In particular, it is preferable that at least a part of the third lens group is an anti-vibration lens group.

  The lens surface of the lens constituting the zoom lens of the present invention may be a spherical surface, a flat surface, or an aspheric surface. When the lens surface is a spherical surface or a flat surface, it is preferable because lens processing and assembly adjustment are facilitated, and deterioration of optical performance due to errors in lens processing and assembly adjustment can be prevented. Further, even when the image plane is deviated, it is preferable because there is little deterioration in drawing performance. When the lens surface is aspheric, any of aspherical surfaces by grinding, a glass mold aspherical surface formed by molding glass into an aspherical surface, or a composite aspherical surface formed by forming resin on the glass surface into an aspherical surface An aspherical surface may be used. The lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

  In addition, the aperture stop SP of the zoom lens according to the present invention is preferably disposed in the vicinity of the third lens group, but the role may be substituted by a lens frame without providing a member as the aperture stop.

  Further, an antireflection film having a high transmittance in a wide wavelength range may be applied to the lens surface of the lens constituting the zoom lens of the present invention. Thereby, flare and ghost can be reduced and high contrast optical performance can be achieved.

  Next, an image pickup apparatus including the zoom lens ZL according to the present invention will be described using a digital single lens reflex camera as an example.

  FIG. 7 is a cross-sectional view schematically showing a digital single-lens reflex camera equipped with the zoom lens of the present invention. In the digital single-lens reflex camera 1 shown in FIG. 7, light from an object (subject) (not shown) is collected by the zoom lens ZL and formed on the focusing plate 5 via the quick return mirror 3. The light imaged on the collecting plate 5 is reflected a plurality of times in the pentaprism 7 and guided to the eyepiece lens 9. Thus, the photographer can observe the object (subject) image as an erect image through the eyepiece 9.

  When a release button (not shown) is pressed by the photographer, the quick return mirror 3 is retracted out of the optical path, and the light of the object (subject) collected by the zoom lens ZL forms a subject image on the image sensor 11. . Thereby, the light from the object is picked up by the image pickup device 11 and stored in a memory (not shown) as an object image. In this way, the photographer can photograph an object with the camera 1.

  With the above configuration, the digital single-lens reflex camera 1 including the zoom lens ZL according to the present invention can satisfactorily correct various aberrations including the secondary spectrum of chromatic aberration and realize high optical performance. In addition, the camera 1 of FIG. 7 may hold | maintain a photographic lens so that attachment or detachment is possible, and may be shape | molded integrally with a photographic lens. The camera may be a single-lens reflex camera or a camera that does not have a quick return mirror or the like.

Next, a method for manufacturing the zoom lens ZL of the present invention will be described.
FIG. 8 is a diagram showing an outline of a method for manufacturing the zoom lens ZL according to the present invention.

The zoom lens ZL manufacturing method of the present invention includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and one or more lens groups in order from the object side along the optical axis. A zoom lens manufacturing method including a rear group including the following steps S1 to S3 as shown in FIG.
Step S1: The zoom lens is configured such that the distance between the first lens group and the second lens group changes during zooming from the wide-angle end state to the telephoto end state.
Step S2: The second lens group includes a plurality of lenses including a negative lens and a positive lens.
Step S3: At least one negative lens in the second lens group is configured to satisfy the following conditional expressions (1) and (2).
(1) 60.0 <νdn
(2) θgFn− (0.644−1.68 × 10 ⁻³ · νdn)> 0.000
However,
νdn: Abbe number θgFn of the material of the negative lens: Partial dispersion ratio of the material of the negative lens

  According to the zoom lens manufacturing method of the present invention, a zoom lens having high optical performance can be manufactured.

ZL variable magnification optical system G1 first lens group G2 second lens group G3 third lens group SP aperture stop I image plane 1 optical device 3 quick return mirror 5 focusing plate 7 pentaprism 9 eyepiece 11 imaging element

Claims (4)

A first lens group having a positive refractive power, a second lens group having a negative refractive power, and a rear group including one or more lens groups in order from the object side along the optical axis,
During zooming from the wide-angle end state to the telephoto end state, the distance between adjacent lens groups changes, and the first lens group moves toward the object side with respect to the image plane.
The second lens group includes a plurality of lenses including a negative lens and a positive lens,
At least one negative lens satisfies the following conditional expressions (1) and (2):
The zoom lens according to claim 1, wherein at least one positive lens satisfies the following conditional expressions (3A) and (4).
(1) 60.0 <νdn
(2) θgFn− (0.644−1.68 × 10 ⁻³ · νdn)> 0.000
However,
νdn: Abbe number θgFn of the material of the negative lens: Partial dispersion ratio of the material of the negative lens (3A) 39.61 ≦ νdp ≦ 44.17
(4) θgFp− (0.644−1.68 × 10 ⁻³ · νdp) <0.000
However,
νdp: Abbe number θgFp of the material of the positive lens: Partial dispersion ratio of the material of the positive lens A first lens group having a positive refractive power, a second lens group having a negative refractive power, and a rear group including one or more lens groups in order from the object side along the optical axis,
When zooming from the wide-angle end state to the telephoto end state, the distance between adjacent lens groups changes,
The second lens group includes, in order from the object side along the optical axis, a first negative lens, a second negative lens, a positive lens, and a third negative lens.
At least one of the first negative lens, the second negative lens, and the third negative lens satisfies the following conditional expressions (1) and (2):
The zoom lens according to claim 1, wherein the positive lens satisfies the following conditional expressions (3) and (4).
(1) 60.0 <νdn
(2) θgFn− (0.644−1.68 × 10 ⁻³ · νdn)> 0.000
However,
νdn: Abbe number θgFn of the material of the negative lens: Partial dispersion ratio of the material of the negative lens (3) 35.0 <νdp <70.0
(4) θgFp− (0.644−1.68 × 10 ⁻³ · νdp) <0.000
However,
νdp: Abbe number θgFp of the material of the positive lens: Partial dispersion ratio of the material of the positive lens   The said 2nd lens group has a 1st negative lens, a 2nd negative lens, and a positive lens in order from an object side along an optical axis. Zoom lens.   An image pickup apparatus comprising the zoom lens according to claim 1.

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