JP5185799B2 - Zoom lens and image pickup apparatus including the same - Google Patents

Description

  The present invention relates to a zoom lens and an imaging apparatus including the zoom lens.

  As a zoom lens advantageous for increasing the zoom ratio, the zoom lens has a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power. There is known a zoom lens that enlarges the distance between the first lens group and the second lens group and reduces the distance between the second lens group and the third lens group when zooming to the telephoto end.

  In particular, the second lens group proposed by the present applicant is composed of a negative lens, a positive lens, and a negative lens in order from the object side, which is advantageous for aberration correction near the telephoto end, but is small in size. A zoom lens that achieves a zoom ratio of about 5 times is known from Patent Documents 1 and 2. The zoom lenses disclosed in these patent documents have a zoom ratio of about 5 times.

JP 2008-107559 A JP 2008-76493 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a zoom lens and an image pickup apparatus including the zoom lens that are more advantageous for achieving a higher zoom ratio while ensuring miniaturization and optical performance.

In order to solve the above-described problems and achieve the object, the zoom lens of the present invention includes a first lens group having a positive refractive power and a second lens group having a negative refractive power in order from the object side to the image side. A third lens group having positive refracting power, and during zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group is increased, and the second lens group The distance from the third lens group is reduced, and in order from the object side to the image side, the second lens group has a negative lens component having a negative refractive power and a negative lens component having negative refractive power, a concave surface on the object side, and a convex surface on the image side. A positive meniscus lens and a negative lens whose object side surface is concave, and the object side surface of the positive meniscus lens and the image side surface of the negative lens in the second lens group satisfy the following conditional expression (1) : combined system of the positive meniscus lens and the negative lens in the second lens group satisfies the following conditional expression (5) It is characterized by a door.
−3.0 <(r _2GPO −r _2GNI ) / (r _2GPO + r _2GNI ) <0.33 (1)
−0.1 <f _2G / f _2GR <0.1 (5)
However,
r _2GPO is the paraxial radius of curvature of the object side surface of the positive meniscus lens in the second lens group,
r _2GNI is the paraxial radius of curvature of the image side surface of the negative lens in the second lens group,
f _2G is the focal length of the second lens group,
f _2GR is the focal length of the composite system of the positive meniscus lens and the negative lens in the second lens group,
It is.

  In the present invention, the lens groups are arranged as described above, and the interval between the lens groups is changed as described above to easily obtain a high zoom ratio. Then, in order to correct the axial aberration that becomes conspicuous in the vicinity of the telephoto end, the second lens group is arranged in an array of a negative lens component, a positive lens, and a negative lens from the object side.

  The lens component means a lens body having only two refractive surfaces in contact with air on the optical axis, that is, the object side surface and the image side surface.

  In the present invention, the positive lens in the second lens group is a positive meniscus lens having a concave object side surface and a convex image side surface, and a negative lens having a concave object side surface is disposed on the image side. With this configuration, the negative lens component on the object side and the air lens sandwiched between the positive meniscus lens are biconvex, and the negative refracting power is shared, which is advantageous for correcting axial aberrations.

  Conditional expression (1) is a positive meniscus lens and a negative lens for reducing the spherical aberration in the second lens group and reducing the thickness of the second lens group itself, which is advantageous for downsizing and a high zoom ratio. The shape is specified.

  By making sure that the lower limit of conditional expression (1) is not exceeded, the image side surface of the second lens group is prevented from being a strong concave surface, which is advantageous in reducing off-axis aberrations. The negative refracting power of the object side surface of the positive meniscus lens is ensured so as not to exceed the upper limit of conditional expression (1), and the image side surface of the second lens group is prevented from having a strong positive refracting power. This is advantageous for aberration correction and thinning of the second lens group.

  In the case where the zoom lens has a focusing mechanism, the zoom lens has a configuration in which the lens is focused on the farthest distance. Similarly, in the following configurations, when the zoom lens has a focusing mechanism, it is configured in a state in which it is focused on the farthest distance.

  In the above-described invention, it is more preferable to satisfy one or more items of the configuration described below.

  In the zoom lens of the present invention, it is preferable that the positive meniscus lens and the negative lens in the second lens group are cemented.

  By cementing the positive meniscus lens of the second lens group and the negative lens on the image side to form a cemented lens component, it becomes easy to reduce aberration fluctuations due to mutual lens decentration. In addition, it becomes easy to secure the curvature of the joint surface, which is advantageous for aberration correction.

In the zoom lens of the present invention, it is preferable that the positive meniscus lens and the negative lens in the second lens group satisfy the following conditional expression (2).
_{0.005 <n 2GP -n 2GN <0.7} ··· (2)
However,
n _2GP is the refractive index of the d-line of the positive meniscus lens in the second lens group,
n _2GN is the refractive index of the d-line of the negative lens in the second lens group,
It is.

  Conditional expression (2) is a condition for ensuring the positive refractive power at the cemented surface in the cemented lens component.

  The difference in refractive index between the positive meniscus lens and the negative lens is ensured so as not to fall below the lower limit of conditional expression (2). This makes it easy to give the cemented surface an appropriate positive refractive power, which is advantageous for correcting spherical aberration and various off-axis aberrations near the wide-angle end.

  The refractive index difference between the positive meniscus lens and the negative meniscus lens is moderately suppressed so as not to exceed the upper limit of the conditional expression (2). This is advantageous for correcting lateral chromatic aberration.

  In the zoom lens of the present invention, it is preferable that the negative lens in the second lens group is a negative meniscus lens having a convex image side surface.

  This is advantageous for ensuring the function of canceling off-axis aberrations near the wide-angle end.

In the zoom lens of the present invention, it is preferable that the second lens group satisfies the following conditional expression (3).
−0.10 <r _2GFI / (r _2GPO + r _2GNI ) <0 (3)
Where r _2GFI is the paraxial radius of curvature of the image side surface of the negative lens component in the second lens group.

  Conditional expression (3) specifies a preferable shape in order to further improve the compatibility between the thinning of the second lens group and the aberration correction function of the two lenses on the image side in the second lens group.

  The absolute value of the paraxial radius of curvature of the object side surface of the positive meniscus lens and the image side surface of the negative lens is not reduced too much so as not to fall below the lower limit of conditional expression (3). It is advantageous for thinning.

  By making sure that the upper limit of conditional expression (3) is not exceeded, the lens action of the object side surface of the positive meniscus lens and the image side surface of the negative lens can be secured, which is advantageous for securing the aberration correction function.

In the zoom lens according to the present invention, it is preferable that the second lens group satisfies the following conditional expression (4).
−0.4 <r _2GPO / r _2GNI <4.0 (4)

  Conditional expression (4) specifies a preferable ratio of the paraxial curvature radius of the object side surface of the positive meniscus lens and the image side surface of the negative lens.

  The image side surface of the negative lens is prevented from having a large negative refractive power so as not to fall below the lower limit of conditional expression (4). As a result, it becomes easy to ensure the function of canceling off-axis aberrations near the wide-angle end. Alternatively, by appropriately suppressing the curvature of the object side surface of the positive meniscus lens, it is easy to prevent the second lens group from becoming large due to interference between the object side surface and the image side surface of the negative lens component on the object side.

  The upper limit of conditional expression (4) is not exceeded so that the image side surface of the negative lens does not become a convex surface having a large curvature. This is advantageous for reducing the thickness of the second lens group. Alternatively, by appropriately securing the curvature of the concave surface on the object side surface of the positive meniscus lens, it is easy to reduce spherical aberration due to the sharing of negative refractive power, which is advantageous for increasing the zoom ratio.

  Conditional expression (5) specifies a preferable focal length of a composite type composed of a positive meniscus lens and a negative lens in the second lens group.

  The absolute value of the refractive power of the synthesis system is reduced so as not to fall below the lower limit of conditional expression (5) and to exceed the upper limit. This is advantageous for insufficient or excessive correction of spherical aberration on the telephoto side, and is advantageous for increasing the zoom ratio.

In the zoom lens of the present invention, it is preferable that the negative lens component in the second lens group satisfies the following conditional expression (6).
0.85 <( _r2GFO + _r2GFI ) / ( _{r2GFO- r2GFI} ) <1.1
... (6)
However,
r _2GFO is the paraxial radius of curvature of the object side surface of the negative lens component of the second lens group,
r _2GFI is the paraxial radius of curvature of the image side surface of the negative lens component of the second lens group,
It is.

  Conditional expression (6) specifies a preferable shape of the negative lens component which is the front lens component in the second lens group.

  By making sure that the lower limit of conditional expression (6) is not exceeded, the influence of off-axis aberrations near the wide-angle end can be easily suppressed. By not exceeding the upper limit of conditional expression (6), the thickness of the second lens group can be easily reduced.

  In the zoom lens of the present invention, it is preferable that the image side surface of the negative lens in the second lens group is a convex aspherical surface whose positive refractive power increases as the distance from the optical axis increases.

This is more advantageous for correcting off-axis aberrations near the wide-angle end while suppressing the thickness of the second lens group on the optical axis.
Further, since this aspherical surface is always convex regardless of the distance from the optical axis, it is advantageous in terms of manufacturing.

In the zoom lens of the present invention, the positive meniscus lens and the negative lens in the second lens group are cemented, and the thickness on the optical axis of the cemented lens component constituted by these two lenses is expressed by the following conditional expression (7 ) Is preferably satisfied.
0.2 <D _2GR / D _2G <0.5 (7)
However,
D _2GR is the thickness of the cemented lens component in the second lens group on the optical axis,
D _2G is the thickness of the second lens group on the optical axis,
It is.

  Thereby, it becomes an advantageous shape for securing negative refractive power while suppressing the thickness or outer diameter of the second lens group.

  By making sure that the lower limit of conditional expression (7) is not exceeded, the absolute value of the curvature of the cemented surface in the cemented lens component can be secured, which is advantageous for aberration correction. Alternatively, it is advantageous for reducing the outer diameter of the second lens group.

  By not exceeding the upper limit of conditional expression (7), the thickness of the second lens group can be reduced.

  In the zoom lens of the present invention, the zoom lens includes, in order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power. And a fourth lens group having positive refracting power, and it is preferable that the distance between the third lens group and the fourth lens group changes during zooming from the wide-angle end to the telephoto end.

  The fourth lens group having positive refractive power is advantageous for ensuring the function of separating the exit pupil from the image plane.

  An image pickup apparatus according to the present invention includes any one of the above-described zoom lenses and an image pickup element that is disposed on the image side of the zoom lens and converts an image formed on the image pickup surface by the zoom lens into an electric signal. And a processing circuit that converts a signal formed on the imaging surface and including distortion of the zoom lens into a signal corrected for distortion.

  Although distortion and astigmatism tend to be in a trade-off relationship, the distortion of the zoom lens itself can be allowed by having the processing circuit described above. This is advantageous for reducing astigmatism and reducing the size of the zoom lens.

It is more preferable that the above-described configurations and conditional expressions satisfy a plurality at the same time.
Moreover, the function can be made more reliable by performing the following for each conditional expression.

  For conditional expression (1), it is more preferable to set the lower limit value to −2.0, more preferably −1.0. The upper limit value is more preferably 0, and further preferably −0.3.

  For conditional expression (2), the lower limit value is more preferably 0.01, and even more preferably 0.1. More preferably, the upper limit value is 0.5, more preferably 0.3.

  For conditional expression (3), it is more preferable to let the lower limit value to be −0.07, more preferably −0.04. More preferably, the upper limit value is 0.0001, more preferably 0.005.

  For conditional expression (4), it is more preferable to set the lower limit to 0, more preferably 0.05. More preferably, the upper limit value is 2.0, more preferably 1.0.

  For conditional expression (5), it is more preferable to let the lower limit value to be −0.07, more preferably −0.04. More preferably, the upper limit value is 0.07, more preferably 0.04.

  For conditional expression (6), it is more preferable to set the lower limit value to 0.85, more preferably 0.92. More preferably, the upper limit value is 1.0, more preferably 0.98.

  For conditional expression (7), it is more preferable to set the lower limit value to 0.3, more preferably 0.35. More preferably, the upper limit value is 0.45, more preferably 0.41.

  According to the present invention, it is possible to provide a zoom lens that is small in size and advantageous for securing a zoom ratio, and further, an imaging apparatus including the zoom lens.

  Embodiments of a zoom lens and an imaging apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  Examples 1 to 2 of the zoom lens according to the present invention will be described below. The wide-angle end (a), the first intermediate focal length state (b), the second intermediate focal length state (c), the third intermediate focal length state ( d) Lens cross-sectional views at the telephoto end (e) are shown in FIGS. 1 to 2, the first lens group is G1, the second lens group is G2, the third lens group is G3, the fourth lens group is G4, the brightness (aperture) stop is S, and infrared light is limited. The parallel flat plate constituting the low-pass filter to which the wavelength band limiting coat is applied is indicated by F, the parallel flat plate of the cover glass of the electronic image sensor is indicated by C, and the image plane is indicated by I. In addition, you may give the multilayer film for a wavelength range restriction | limiting to the surface of the cover glass C. FIG. Further, the cover glass C may have a low-pass filter action.

  In each embodiment, the aperture stop S moves integrally with the third lens group G3. All of the numerical data is data in a state where an object at infinity is focused. The unit of length of each numerical value is mm, and the unit of angle is ° (degree). In any of the embodiments, focusing is performed by moving the fourth lens group G4. Further, zoom data is at the wide-angle end (WE), the first intermediate focal length state (ST1), the second intermediate focal length state (ST2), the third intermediate focal length state (ST3), and the telephoto end (TE). Is the value of Note that the first intermediate focal length state (WS), the second intermediate focal length state (ST), and the third intermediate focal length state (ST) are states defined by the present invention.

  As shown in FIG. 1, the zoom lens according to the first exemplary embodiment includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a brightness (aperture) stop. S, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a positive refractive power are disposed.

  During zooming from the wide angle end to the telephoto end, the first lens group G1 moves to the object side. The second lens group G2 moves to the image side after moving to the object side. The third lens group G3 moves to the object side. The fourth lens group G4 moves to the image side after moving to the image side, and then moves to the image side. The aperture stop S moves to the object side.

  In order from the object side, the first lens group G1 includes a cemented lens of a negative meniscus lens having a convex surface directed toward the object side and a biconvex positive lens. The second lens group G2 is composed of a biconcave negative lens and a positive meniscus lens having a convex surface facing the image side, that is, a positive meniscus lens having a concave object side surface and a convex image side surface, and a negative meniscus lens having a concave surface facing the object side. And a lens. The third lens group G3 includes a biconvex positive lens and a cemented lens made up of a biconvex positive lens and a biconcave negative lens. The fourth lens group G4 is composed of a biconvex positive lens.

  The aspheric surfaces are the image-side surface of the biconvex positive lens of the first lens group G1, the double-sided negative lens of the second lens group G2, the image-side surface of the negative meniscus lens, and the third lens group G3. Of the biconvex positive lens on the object side and both sides of the biconvex positive lens of the fourth lens group G4.

  As shown in FIG. 2, the zoom lens according to the second embodiment includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a brightness (aperture) stop. S, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a positive refractive power are disposed.

  During zooming from the wide angle end to the telephoto end, the first lens group G1 moves to the object side. The second lens group G2 moves to the image side after moving to the object side. The third lens group G3 moves to the object side. The fourth lens group G4 moves to the image side after moving to the image side, and then moves to the image side. The aperture stop S moves to the object side.

  In order from the object side, the first lens group G1 includes a cemented lens of a negative meniscus lens having a convex surface directed toward the object side and a biconvex positive lens. The second lens group G2 is composed of a biconcave negative lens and a positive meniscus lens having a convex surface facing the image side, that is, a positive meniscus lens having a concave object side surface and a convex image side surface, and a negative meniscus lens having a concave surface facing the object side. And a lens. The third lens group G3 includes a biconvex positive lens and a cemented lens made up of a biconvex positive lens and a biconcave negative lens. The fourth lens group G4 is composed of a biconvex positive lens.

  The aspheric surfaces are the image-side surface of the biconvex positive lens of the first lens group G1, the double-sided negative lens of the second lens group G2, the image-side surface of the negative meniscus lens, and the third lens group G3. Of the biconvex positive lens on the object side and both sides of the biconvex positive lens of the fourth lens group G4.

  Below, the numerical data of each said Example are shown. In addition to the above, r is the radius of curvature of each lens surface, d is the thickness or spacing of each lens, nd is the refractive index at the d-line of each lens, νd is the Abbe number at the d-line of each lens, and K is the cone Each coefficient is shown.

Each aspheric shape is expressed by the following formula (I) using each aspheric coefficient in each embodiment.
However, the coordinate in the optical axis direction is Z and the coordinate in the direction perpendicular to the optical axis is Y.
Z = (Y ² / r) / [1+ {1− (1 + K) · (Y / r) ² } ^1/2 ]
^{+ A4 × Y 4 + A6 ×} Y 6 + A8 × Y 8 + A10 × Y 10 + A12 × Y 12 ··· (I)
However,
r is the paraxial radius of curvature,
K is the cone coefficient,
A4, A6, A8, A10 and A12 are the fourth, sixth, eighth, tenth and twelfth aspherical coefficients, respectively.
In the aspheric coefficient, “e−n” (n is an integer) indicates “10 ⁻ⁿ ”.

Numerical example 1
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 26.057 0.90 1.92286 20.88
2 20.324 3.80 1.58913 61.14
3 * -90.043 variable
4 * -228.052 0.80 1.85135 40.10
5 * 6.471 3.38
6 * -49.444 1.78 1.94595 17.98
7 -13.033 0.70 1.74320 49.34
8 * -200.000 variable
9 Aperture 0.00
10 * 6.084 3.32 1.59201 67.02
11 * -14.229 0.14
12 8.776 1.88 1.49700 81.54
13 -6.821 0.39 1.61293 37.00
14 4.070 Variable
15 * 22.340 2.72 1.52542 55.78
16 * -16.652 variable
17 ∞ 0.40 1.51633 64.14
18 ∞ 0.50
19 ∞ 0.50 1.51633 64.14
20 ∞ 0.40
Image plane (imaging plane) ∞

Aspheric data 3rd surface
k = 0.000
A4 = 7.76723e-06, A6 = -5.17775e-09, A8 = -3.05628e-11, A10 = 3.05364e-13,
A12 = -1.22198e-15
4th page
k = 0.000
A4 = 5.91800e-05, A6 = -2.71411e-06, A8 = 2.98672e-08, A10 = -2.27323e-10
5th page
k = 0.000
A4 = 2.01000e-04, A6 = 7.54437e-06, A8 = -3.08734e-07, A10 = 1.56410e-08,
A12 = -8.56105e-10
8th page
k = 0.000
A4 = -2.82631e-04, A6 = -6.23538e-06, A8 = 4.00871e-07, A10 = -1.47767e-08,
A12 = 2.95296e-10
10th page
k = 0.000
A4 = -4.86039e-04, A6 = -8.24264e-06, A8 = 6.61180e-07, A10 = -7.89566e-08,
A12 = 2.77593e-09
11th page
k = 0.000
A4 = 3.02859e-04, A6 = -7.10097e-06, A8 = 1.24832e-06, A10 = -1.31994e-07,
A12 = 5.25802e-09
15th page
k = 0.000
A4 = 5.85000e-05, A6 = -1.20206e-06, A8 = -7.74180e-28
16th page
k = 0.000
A4 = 2.70961e-05, A6 = -2.27806e-06, A8 = 3.88946e-28

Zoom data
WE ST1 ST2 ST3 TE
Focal length 5.10 8.85 15.44 28.03 49.05
FNO. 3.24 4.30 5.17 5.65 6.02
Angle of view 2ω 80.81 47.46 27.61 15.38 8.90

D3 0.30 3.56 9.14 16.53 21.35
D8 15.75 11.28 7.52 4.79 1.64
D14 3.01 9.27 13.43 15.84 17.63
D16 4.62 3.46 4.03 4.26 3.96

fb (in air) 6.11 4.96 5.51 5.75 5.45
Total length (in air) 44.98 48.89 55.41 62.72 65.87

Group focal length
f1 = 39.37 f2 = -7.56 f3 = 11.52 f4 = 18.60

Numerical example 2
Unit: mm

Surface data surface number rd nd νd
Object ∞ ∞
1 25.426 1.00 1.92286 20.88
2 19.907 3.80 1.58913 61.14
3 * -102.288 variable
4 * -402.206 0.81 1.85135 40.10
5 * 6.604 3.51
6 -49.800 1.78 1.94595 17.98
7 -13.033 0.71 1.74320 49.34
8 * -602.284 variable
9 Aperture 0.00
10 * 5.774 3.12 1.59201 67.02
11 * -17.713 0.15
12 9.420 1.90 1.49700 81.54
13 -5.860 0.39 1.59276 37.48
14 4.165 Variable
15 * 22.181 2.74 1.52542 55.78
16 * -16.480 variable
17 ∞ 0.40 1.51633 64.14
18 ∞ 0.50
19 ∞ 0.50 1.51633 64.14
20 ∞ 0.40
Image plane (imaging plane) ∞

Aspheric data 3rd surface
k = 0.000
A4 = 7.44327e-06, A6 = -6.88530e-09, A8 = -1.12372e-11, A10 = 2.06551e-13,
A12 = -1.00000e-15
4th page
k = 0.000
A4 = 4.64544e-05, A6 = -2.36922e-06, A8 = -9.01530e-09, A10 = 1.21557e-09,
A12 = -1.36256e-11
5th page
k = 0.000
A4 = 1.93733e-04, A6 = 6.93971e-06, A8 = -8.10872e-08, A10 = -1.06670e-08,
A12 = -3.71534e-12
8th page
k = 0.000
A4 = -2.68285e-04, A6 = -6.07424e-06, A8 = 3.16807e-07, A10 = -2.02148e-09,
A12 = -6.37613e-11
10th page
k = 0.000
A4 = -2.90717e-04, A6 = 2.38352e-06, A8 = 1.13169e-06, A10 = -4.00317e-08,
A12 = 4.36568e-09
11th page
k = 0.000
A4 = 6.34731e-04, A6 = 9.57225e-06, A8 = 2.14702e-06, A10 = -7.56560e-08,
A12 = 1.03866e-08
15th page
k = 0.000
A4 = 5.85000e-05, A6 = -1.36284e-06, A8 = -7.74180e-28
16th page
k = 0.000
A4 = 3.98546e-05, A6 = -2.83412e-06, A8 = 1.10000e-08

Zoom data
WE ST1 ST2 ST3 TE
Focal length 5.10 8.83 15.30 28.09 48.97
FNO. 3.26 4.23 5.15 5.67 6.00
Angle of view 2ω 81.35 47.31 27.94 15.43 8.92

D3 0.30 4.38 9.14 16.45 21.40
D8 15.75 11.57 7.55 4.64 1.61
D14 2.86 8.70 13.10 15.78 17.33
D16 4.69 3.56 4.15 4.53 4.02

fb (in air) 6.18 5.05 5.64 6.03 5.51
Total length (in air) 45.01 49.64 55.36 62.82 65.77

Group focal length
f1 = 39.64 f2 = -7.58 f3 = 11.55 f4 = 18.45

  Aberration diagrams at the time of focusing on an object point at infinity in Examples 1 and 2 are shown in FIGS. In these aberration diagrams, (a) is the wide-angle end, (b) is the second intermediate focal length state, (c) is the spherical aberration (SA), astigmatism (AS), and distortion (DT) at the telephoto end. ) And chromatic aberration of magnification (CC). In each figure, “ω” indicates a half angle of view.

Next, the values of conditional expressions (1) to (7) in each example will be listed.
Example 1 Example 2
(1) (r _2GPO −r _2GNI ) / (r _2GPO + r _2GNI ) −0.6036 −0.8473
_{(2) n 2GP -n 2GN 0.2028} 0.2028
(3) r _2GFI / (r _2GPO + r _2GNI ) -0.0259 -0.0101
(4) r _2GPO / r _2GNI 0.2472 0.0827
(5) f _2G / f _2GR -0.00366 0.01449
(6) (r _2GFO + r _2GFI ) / (r _2GFO -r _2GFI ) 0.9448 0.9677
(7) D _2GR / D _2G 0.3727 0.3660

  Note that an image with distortion by the zoom lens may be corrected by signal processing. In consideration of the influence of the perspective, signal processing may be performed so as to leave a distortion of about −3% on the wide angle side.

(Correction of distortion)
By the way, when the zoom lens of the present invention is used, image distortion is digitally corrected electrically. The basic concept for digitally correcting image distortion will be described below.

  For example, as shown in FIG. 5, the magnification on the circumference (image height) of the radius R inscribed in the long side of the effective imaging surface around the intersection of the optical axis and the imaging surface is fixed, and this circumference is The standard for correction. Then, correction is performed by moving each point on the circumference (image height) of any other radius r (ω) in a substantially radial direction and concentrically so as to have the radius r ′ (ω). To do.

For example, in FIG. 5, a point P ₁ on the circumference of an arbitrary radius r ₁ (ω) located inside the circle of radius R is a radius r ₁ ′ (ω) circle to be corrected toward the center of the circle. Move to point P ₂ on the circumference. A point Q ₁ on the circumference of an arbitrary radius r ₂ (ω) located outside the circle of radius R is a radius r ₂ ′ (ω) circumference to be corrected in a direction away from the center of the circle. It is moved to the point Q ₂ of the above.

Here, r ′ (ω) can be expressed as follows.
r ′ (ω) = α · f · tan ω
However,
ω is the half angle of view of the subject,
f is the focal length of the imaging optical system (in the present invention, the zoom lens),
α is 0 or more and 1 or less.

Here, if the ideal image height corresponding to the circle (image height) of radius R is Y,
α = R / Y = R / (f · tan ω)
It becomes.

  The optical system is ideally rotationally symmetric with respect to the optical axis, that is, distortion is also generated rotationally symmetric with respect to the optical axis. Therefore, as described above, when the optically generated distortion aberration is electrically corrected, the radius inscribed in the long side of the effective imaging surface around the intersection of the optical axis and the imaging surface on the reproduced image. The magnification on the circumference of the circle of R (image height) is fixed, and the other points on the circumference of the circle (image height) of radius r (ω) are moved in a substantially radial direction to obtain a radius r ′ ( If correction can be performed by moving the concentric circles so that ω), it is considered advantageous in terms of data amount and calculation amount.

  However, the optical image is no longer a continuous amount (due to sampling) when captured by the electronic image sensor. Therefore, strictly speaking, the circle with the radius R drawn on the optical image is not an accurate circle unless the pixels on the electronic image sensor are arranged radially.

  That is, in the shape correction of the image data represented for each discrete coordinate point, there is no circle that can fix the magnification. Therefore, it is preferable to use a method of determining the coordinates (Xi ′, Yj ′) of the movement destination for each pixel (Xi, Yj). When two or more points (Xi, Yj) have moved to the coordinates (Xi ′, Yj ′), the average value of the values possessed by each pixel is taken. If there is no moving point, interpolation may be performed using the values of the coordinates (Xi ′, Yj ′) of some surrounding pixels.

  Such a method is particularly distorted with respect to the optical axis due to manufacturing errors of an optical system or an electronic image pickup device in an electronic image pickup apparatus having a zoom lens, and the circle of the radius R drawn on the optical image is asymmetric. It is effective for correction when Further, it is effective for correction when a geometric distortion or the like occurs when a signal is reproduced as an image in an image sensor or various output devices.

  In the electronic imaging apparatus of the present invention, in order to calculate the correction amount r ′ (ω) −r (ω), r (ω), that is, the relationship between the half field angle and the image height, or the real image height r and the ideal image height. The relationship between r ′ / α may be recorded on a recording medium built in the electronic imaging apparatus.

  Note that the radius R should satisfy the following conditional expression in order to prevent the image after distortion correction from having an extremely short amount of light at both ends in the short side direction.

0 ≦ R ≦ 0.6Ls
However, Ls is the length of the short side of the effective imaging surface.

The radius R preferably satisfies the following conditional expression.
0.3Ls≤R≤0.6Ls
Furthermore, it is most advantageous to make the radius R coincide with the radius of the inscribed circle in the short side direction of the substantially effective imaging surface. In the case of correction in which the magnification is fixed in the vicinity of the radius R = 0, that is, in the vicinity of the axis, there is a slight disadvantage in terms of image quality, but the effect of reducing the size is ensured even if the angle of view is widened. it can.

The focal length section that needs to be corrected is divided into several focal zones. And approximately near the telephoto end in the divided focal zone,
r ′ (ω) = α · f · tan ω
You may correct | amend with the same correction amount as the case where the correction result which satisfies is obtained.

  However, in that case, some barrel distortion remains at the wide-angle end in the divided focal zone. Further, if the number of divided zones is increased, it becomes unnecessary to store extraneous data necessary for correction on the recording medium, which is not preferable. Therefore, one or several coefficients related to each focal length in the divided focal zone are calculated in advance. This coefficient may be determined on the basis of simulation or actual measurement.

And near the telephoto end in the divided zone,
r ′ (ω) = α · f · tan ω
A correction amount when a correction result satisfying the above is obtained may be calculated, and the final correction amount may be obtained by uniformly multiplying the correction amount by a coefficient for each focal length.

By the way, if there is no distortion in the image obtained by imaging an object at infinity,
f = y / tan ω
Is established.
Where y is the height of the image point from the optical axis (image height), f is the focal length of the imaging system (in the present invention, the zoom lens), and ω is the image point connected from the center on the imaging surface to the y position. It is an angle (subject half field angle) with respect to the optical axis in the corresponding object direction.

If the imaging system has barrel distortion,
f> y / tan ω
It becomes. That is, if the focal length f of the imaging system and the image height y are constant, the value of ω increases.

(Digital camera)
6 to 8 are conceptual diagrams of the configuration of the digital camera according to the present invention in which the zoom lens as described above is incorporated in the photographing optical system 141. FIG. 6 is a front perspective view showing the external appearance of the digital camera 140, FIG. 7 is a rear front view thereof, and FIG. 8 is a schematic cross-sectional view showing the configuration of the digital camera 140. However, FIGS. 6 and 8 show a state in which the photographing optical system 141 is not retracted. In this example, the digital camera 140 includes a photographing optical system 141 having a photographing optical path 142, a finder optical system 143 having a finder optical path 144, a shutter button 145, a flash 146, a liquid crystal display monitor 147, a focal length change button 161, When the photographic optical system 141 is retracted, including the setting change switch 162, the photographic optical system 141, the finder optical system 143, and the flash 146 are covered with the cover 160 by sliding the cover 160. When the cover 160 is opened and the camera 140 is set to the photographing state, the photographing optical system 141 enters the non-collapsed state shown in FIG. 8. When the shutter button 145 arranged on the upper portion of the camera 140 is pressed, photographing is performed in conjunction therewith. Photographing is performed through the optical system 141, for example, the zoom lens of the first embodiment. An object image formed by the photographic optical system 141 is formed on the imaging surface of the CCD 149 through a low-pass filter F and a cover glass C that are provided with a wavelength band limiting coat. The object image received by the CCD 149 is displayed as an electronic image on a liquid crystal display monitor 147 provided on the back of the camera via the processing means 151. Further, the processing means 151 is connected to a recording means 152 so that a photographed electronic image can be recorded. The recording unit 152 may be provided separately from the processing unit 151, or may be configured to perform recording / writing electronically using a flexible disk, a memory card, an MO, or the like. Further, instead of the CCD 149, a silver salt camera in which a silver salt film is arranged may be configured.

  Further, a finder objective optical system 153 is disposed on the finder optical path 144. The finder objective optical system 153 includes a plurality of lens groups (three groups in the figure) and two prisms, and includes a zoom optical system whose focal length changes in conjunction with the zoom lens of the photographing optical system 141. The object image formed by the finder objective optical system 153 is formed on the field frame 157 of the erecting prism 155 that is an image erecting member. Behind the erecting prism 155, an eyepiece optical system 159 that guides the erect image to the observer eyeball E is disposed. A cover member 150 is disposed on the exit side of the eyepiece optical system 159.

  The digital camera 140 configured in this way has the imaging optical system 141 according to the present invention, which is extremely thin when retracted, and has high zooming performance and extremely stable imaging performance in the entire zooming range. A small size and wide angle of view can be realized.

(Internal circuit configuration)
FIG. 9 is a block diagram showing the internal circuitry of the main part of the digital camera 140. In the following description, the processing means includes, for example, the CDS / ADC unit 124, the temporary storage memory 117, the image processing unit 118, and the like, and the storage means includes, for example, the storage medium unit 119.

  As shown in FIG. 9, the digital camera 140 is connected to the operation unit 112, the control unit 113 connected to the operation unit 112, and the control signal output port of the control unit 113 via buses 114 and 115. An imaging drive circuit 116, a temporary storage memory 117, an image processing unit 118, a storage medium unit 119, a display unit 120, and a setting information storage memory unit 121 are provided.

  The temporary storage memory 117, the image processing unit 118, the storage medium unit 119, the display unit 120, and the setting information storage memory unit 121 are configured so that data can be input or output with each other via the bus 122. In addition, a CCD 149 and a CDS / ADC unit 124 are connected to the imaging drive circuit 116.

  The operation unit 112 includes various input buttons and switches, and is a circuit that notifies the control unit of event information input from the outside (camera user) via these input buttons and switches.

  The control unit 113 is a central processing unit composed of, for example, a CPU and the like. The control unit 113 includes a program memory (not shown) and is input from the camera user via the operation unit 112 according to a program stored in the program memory. This is a circuit that controls the entire digital camera 140 in response to an instruction command.

  The CCD 149 receives an object image formed through the photographing optical system 141 according to the present invention. The CCD 149 is an image pickup element that is driven and controlled by the image pickup drive circuit 116, converts the light amount of each pixel of the object image into an electrical signal, and outputs the electric signal to the CDS / ADC unit 124.

  The CDS / ADC unit 124 amplifies the electric signal input from the CCD 149 and performs analog / digital conversion, and temporarily stores the raw video data (Bayer data, hereinafter referred to as RAW data) that has just been subjected to the amplification and digital conversion. This is a circuit for outputting to the storage memory 117.

  The temporary storage memory 117 is a buffer made of, for example, SDRAM or the like, and is a memory device that temporarily stores the RAW data output from the CDS / ADC unit 124. The image processing unit 118 reads out the RAW data stored in the temporary storage memory 117 or the RAW data stored in the storage medium unit 119, and performs various corrections including distortion correction based on the image quality parameter designated from the control unit 113. It is a circuit that performs image processing electrically.

  The recording medium unit 119 detachably mounts a card-type or stick-type recording medium made of, for example, a flash memory, and RAW data transferred from the temporary storage memory 117 to the card-type or stick-type flash memory. This is a control circuit of an apparatus for recording and holding image data processed by the image processing unit 118.

  The display unit 120 includes a liquid crystal display monitor, and is a circuit that displays an image, an operation menu, and the like on the liquid crystal display monitor. The setting information storage memory unit 121 stores a ROM unit in which various image quality parameters are stored in advance, and an image quality parameter selected by an input operation of the operation unit 112 among the image quality parameters read from the ROM unit. RAM section is provided. The setting information storage memory unit 121 is a circuit that controls input and output to these memories.

  In the digital camera 140 configured in this way, the imaging optical system 141 has a sufficiently wide angle range and a compact configuration according to the present invention, and the imaging performance is extremely stable at a high zoom ratio and in a full zoom ratio range. Therefore, high performance, downsizing, and wide angle of view can be realized. In addition, fast focusing operation on the wide-angle side and the telephoto side is possible.

  As described above, the zoom lens and the imaging apparatus according to the present invention are useful for securing optical performance and reducing the size while having a high zoom ratio.

The wide-angle end (a), the first intermediate focal length state (b), the second intermediate focal length state (c), and the third intermediate during focusing on an object point at infinity according to the first embodiment of the zoom lens of the present invention. It is a lens sectional view in a focal length state (d) and a telephoto end (e). The wide-angle end (a), the first intermediate focal length state (b), the second intermediate focal length state (c), and the third intermediate during focusing on an object point at infinity according to the second embodiment of the zoom lens of the present invention. It is a lens sectional view in a focal length state (d) and a telephoto end (e). FIG. 6 is an aberration diagram for Example 1 upon focusing on an object point at infinity. FIG. 6 is an aberration diagram for Example 2 upon focusing on an object point at infinity. It is a figure explaining correction | amendment of a distortion aberration. It is a front perspective view which shows the external appearance of the digital camera incorporating the retractable zoom lens by this invention. It is a rear perspective view of the digital camera. It is sectional drawing of the said digital camera. It is a block diagram of the internal circuit of the main part of the digital camera.

Explanation of symbols

G1 ... 1st lens group G2 ... 2nd lens group G3 ... 3rd lens group G4 ... 4th lens group S ... Brightness stop F ... Low pass filter C ... Cover glass I ... Image surface 112 ... Operation part 113 ... Control part 114 ... Bus 115 ... Bus 116 ... Imaging drive circuit 117 ... Temporary storage memory 118 ... Image processing part 119 ... Storage medium part 120 ... Display part 121 ... Setting information storage memory part 122 ... Bus 124 ... CDS / ADC part 140 ... Digital camera 141 ... Optical optical system 142 ... Optical optical path 143 ... Finder optical system 144 ... Optical path for finder 145 ... Shutter button 146 ... Flash 147 ... LCD monitor 149 ... CCD
150: cover member 151 ... processing means 152 ... recording means 153 ... finder objective optical system 155 ... erecting prism 157 ... field frame 159 ... eyepiece optical system 160 ... cover 161 ... focal length change button 162 ... setting change switch

Claims (11)

From the object side to the image side,
A first lens group having positive refractive power;
A second lens group having negative refractive power;
A third lens group having positive refracting power,
During zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group is enlarged, and the distance between the second lens group and the third lens group is reduced,
The second lens group, in order from the object side to the image side,
A negative lens component with negative refractive power and a side surface of the image is concave,
A positive meniscus lens having a concave object side and a convex image side;
A negative lens whose object side surface is concave;
Consists of
The object side surface of the positive meniscus lens and the image side surface of the negative lens in the second lens group satisfy the following conditional expression (1) :
The zoom lens according to claim 1, wherein a combination system of the positive meniscus lens and the negative lens in the second lens group satisfies the following conditional expression (5) .
−3.0 <(r _2GPO −r _2GNI ) / (r _2GPO + r _2GNI ) <0.33 (1)
−0.1 <f _2G / f _2GR <0.1 (5)
However,
r _2GPO is the paraxial radius of curvature of the object side surface of the positive meniscus lens in the second lens group;
r _2GNI is the paraxial radius of curvature of the image side surface of the negative lens in the second lens group,
f _2G is the focal length of the second lens group,
f _2GR is a focal length of a composite system of the positive meniscus lens and the negative lens in the second lens group;
It is.   The zoom lens according to claim 1, wherein the positive meniscus lens and the negative lens in the second lens group are cemented. The zoom lens according to claim 2, wherein the positive meniscus lens and the negative lens in the second lens group satisfy the following conditional expression (2).
_{0.005 <n 2GP -n 2GN <0.7} ··· (2)
However,
n _2GP is the refractive index of the d-line of the positive meniscus lens in the second lens group,
n _2GN is the refractive index of the d-line of the negative lens in the second lens group,
It is.   4. The zoom lens according to claim 1, wherein the negative lens in the second lens group is a negative meniscus lens having a convex image side surface. 5. The zoom lens according to claim 4, wherein the second lens group satisfies the following conditional expression (3).
−0.10 <r _2GFI / (r _2GPO + r _2GNI ) <0 (3)
Here, r _2GFI is the paraxial radius of curvature of the image side surface of the negative lens component in the second lens group. The zoom lens according to any one of claims 1 to 5, wherein the second lens group satisfies the following conditional expression (4).
−0.4 <r _2GPO / r _2GNI <4.0 (4) The zoom lens according to any one of claims 1 to 6, wherein the negative lens component in the second lens group satisfies the following conditional expression (6).
  0.85 <(r _2GFO + R _2GFI ) / (R _2GFO -R _2GFI <1.1 (6)
  However,
  r _2GFO Is the paraxial radius of curvature of the object side surface of the negative lens component of the second lens group,
  r _2GFI Is the paraxial radius of curvature of the image side surface of the negative lens component of the second lens group,
It is. The image side surface of the negative lens in the second lens group is a convex aspherical surface whose positive refractive power increases as the distance from the optical axis increases. The zoom lens according to item. The positive meniscus lens and the negative lens in the second lens group are cemented, and the thickness on the optical axis of the cemented lens component constituted by the two lenses satisfies the following conditional expression (7). The zoom lens according to claim 1, wherein the zoom lens is a zoom lens.
    0.2 <D _2GR / D _2G <0.5 (7)
  However,
  D _2GR Is the thickness on the optical axis of the cemented lens component in the second lens group,
  D _2G Is the thickness of the second lens group on the optical axis,
It is. The zoom lens, in order from the object side to the image side,
  The first lens group having positive refractive power;
  The second lens group having negative refractive power;
  The third lens group having positive refractive power;
  A fourth lens group having positive refractive power,
  The distance between the third lens group and the fourth lens group changes during zooming from the wide-angle end to the telephoto end, according to any one of claims 1 to 9. Zoom lens. The zoom lens according to any one of claims 1 to 10,
  An image sensor disposed on the image side of the zoom lens and having an imaging surface and converting an image formed on the imaging surface by the zoom lens into an electrical signal;
  An image pickup apparatus comprising: a processing circuit configured to convert a signal including distortion of the zoom lens formed on the image pickup surface into a signal obtained by correcting the distortion.

Images