JP5265316B2 - Zoom lens and image pickup apparatus having the zoom lens - Google Patents

Description

  The present invention relates to a zoom lens suitable for a compact digital camera and an image pickup apparatus including the zoom lens.

  In recent years, digital cameras (electronic cameras) have a number of categories in a wide range from high-functional types for business use to portable popular types. Among these categories, the portable popular type category is a high-magnification and inexpensive video that covers a wide focal length range from the wide-angle end to the telephoto end. Technology for realizing cameras and digital cameras is being demanded.

  The biggest bottleneck in reducing the depth direction of the camera is the thickness from the most object-side surface to the imaging surface of the optical system, particularly the zoom lens system. The mainstream of camera body thinning technology in recent years has been to adopt a so-called collapsible lens barrel in which the optical system protrudes from the camera body during shooting but is housed when carried. However, if a retractable lens barrel is employed, it takes time to start from the lens storage state to the use state, which is not preferable in terms of convenience. Further, if the lens group closest to the object is movable, it is not preferable in terms of waterproofing and dustproofing.

  On the other hand, recently, there is no startup time (lens protruding time) of the camera as seen in a collapsible lens barrel, it is preferable in terms of waterproofing and dustproofing, and the depth direction is extremely thin. In order to achieve this, some optical systems (optical axis) have been configured to bend with reflective optical members such as mirrors and prisms. The lens group on the most object side is a fixed-position lens group, and the reflecting optical member is provided therein, and the subsequent optical path is bent in the vertical or horizontal direction of the camera body, and the depth direction dimension is made as thin as possible. .

On the other hand, most of the portable category video cameras and digital cameras have a field angle of about 30 ° at the wide-angle end, but a wide-angle camera with a wider shooting area is also expected.
Examples of wide-angle zoom lenses that employ a bending optical system include those disclosed in Japanese Patent Application Laid-Open Nos. 2004-354871 and 2004-354869.

Japanese Patent Application Laid-Open No. 2004-354871 JP 2004-354869 A

  However, the zoom lens described in Patent Document 1 has a large field angle of about 37 °, but the zoom ratio is only about 2.8 times. The zoom lens described in Patent Document 2 has an angle of view of about 37 ° and a zoom ratio of about 3.7, but has a large overall length.

  The present invention has been made in view of the above, and does not have a start-up time (lens protruding time) to use the camera as seen in a retractable lens barrel, and is preferable in terms of waterproofing and dustproofing. The optical path (optical axis) of the optical system is bent with a reflective optical member such as a prism to make the camera extremely thin in the depth direction, and it has high optical specifications and performance such as well-corrected chromatic aberration. An object of the present invention is to provide a zoom lens that is thin and has a short overall length, and an electronic imaging device equipped with the zoom lens.

  In order to solve the above-described problems and achieve the object, an electronic imaging device of the present invention includes, in order from the object side, a first lens group having positive power (refractive power) and a second lens having negative power. In a zoom lens composed of a group, a third group having a positive power, a fourth lens group having a positive power, and a five group having a negative power, the zoom lens has a zoom ratio from the wide angle end to the telephoto end. The first lens group and the third group are fixed with respect to the image plane. At least the second group and the fourth group move, and the first lens group is for bending the negative lens and the optical path in order from the object side. And a positive lens and a positive lens.

  With such a configuration, it is possible to reduce the thickness in the depth direction by bending the optical path in the first lens group, and to change the magnification by moving the second lens group and the fourth lens group. To achieve a high zoom ratio. By giving negative power to the fifth lens group and enlarging with the fifth lens group, the focal length from the first lens group to the fourth lens group can be shortened, thereby enabling miniaturization.

  Further, when the angle of view is widened, the lens diameter is increased and the distortion is further increased. Here, by arranging negative refractive power closer to the object side than the reflecting surface of the first lens group, the lens diameter is reduced, and distortion occurring in the first lens group is reduced, and negative power is applied to the fifth lens group. It can be countered by placing.

  Furthermore, by fixing the first lens group with respect to the image plane, there is no time to start up the camera in use, and the structure is preferable in terms of waterproofing and dustproofing. In order to reduce the size and increase the zoom ratio, it is necessary to increase the refractive power of the first lens unit. However, color coma and secondary spectrum are generated at this time. Therefore, by allocating the positive refractive power of the first lens group to the two positive lenses, it is possible to satisfactorily correct the coma chromatic aberration generated at the telephoto end, which is insufficiently corrected with one positive lens, and deteriorate performance. And color bleeding can be prevented.

  In addition, by fixing the third lens unit at the time of zooming, an aperture stop is installed in the vicinity of the third lens unit, so that the lens diameter can be reduced. Further, in order to reduce the size, it is necessary to increase the refractive power of the fifth lens group. By using two cemented lenses in the fifth lens group, the off-axis chromatic aberration and the Petzval sum of the entire optical system can be obtained. It becomes possible to correct well so that becomes small.

The zoom lens of the present invention desirably satisfies the following conditional expression (1).
0 <D ₅ / f _w <0.7 (1)
However,
D ₅ is the axial distance between the first cemented lens and the second cemented lens in the fifth lens group,
f _w is the focal length of the entire zoom lens system at the wide-angle end.

  Conditional expression (1) appropriately defines the distance on the optical axis between the first cemented lens and the second cemented lens in the fifth lens group. If the upper limit of conditional expression (1) is exceeded, the interval becomes large, and miniaturization becomes difficult. If the lower limit of conditional expression (1) is not reached, the lenses interfere with each other when a manufacturing error occurs in the lens frame, and the lens cannot be held.

The reflective optical element in the first lens group is preferably composed of a prism, and desirably satisfies the following conditional expression (2).
N _dp > 1.9 (2)
N _dp is the refractive index of the prism.

  By configuring the reflective optical element with a prism, the optical path length can be kept short. For this reason, the space | interval of a 1st lens and an aperture stop can be shortened. As a result, the entrance pupil can be made shallower and the size can be reduced. In addition, by satisfying conditional expression (2), the optical path length can be kept shorter, so that downsizing is possible.

Furthermore, it is desirable to satisfy the following conditional expression (3).
ν _d12 > 60 (3)
Here, ν _d12 is an average value of the Abbe numbers of the first positive lens and the second positive lens in the first lens group.
By satisfying conditional expression (3), it is possible to satisfactorily correct off-axis chromatic aberration caused by the first lens group having a strong refractive power for downsizing.

Moreover, it is desirable to satisfy the following conditional expression (4).
1.0 <| f ₅ / f _w | <3.0 (4)
However,
f ₅ is the focal length of the fifth lens group,
f _w is the focal length of the entire zoom lens system at the wide-angle end.

  Conditional expression (4) appropriately defines the power of the fifth lens group. If the upper limit of conditional expression (4) is exceeded, the power of the fifth lens group will become weak and it will be difficult to reduce the size. Below the lower limit of conditional expression (4), it becomes difficult to correct curvature of field and off-axis chromatic aberration.

Furthermore, it is desirable that the following conditional expression (5) is satisfied.
30 <ν _d52 −ν _d51 <70 (5)
However,
ν _d51 is the Abbe number of the object side lens of the object side cemented lens in the fifth lens group,
ν _d52 is the Abbe number of the image side lens of the cemented lens on the object side in the fifth lens group.

  Conditional expression (5) relates to the cemented lens of the fifth lens group. This is a conditional expression for satisfactorily correcting off-axis chromatic aberration. If the lower limit of conditional expression (5) is not reached, the occurrence of off-axis chromatic aberration due to the cemented surface is reduced and the correction becomes insufficient. On the other hand, if the upper limit of conditional expression (5) is exceeded, a glass material with no versatility must be used, which increases the cost, which is not preferable.

Moreover, it is desirable to satisfy the following conditional expression (6).
2.0 <f ₁ / f _w <5.0 (6)
However,
f ₁ is the focal length of the first lens group,
f _w is the focal length of the entire zoom lens system at the wide-angle end.

  Conditional expression (6) appropriately defines the power of the first lens group. If the upper limit of conditional expression (6) is exceeded, the entrance pupil becomes deep and the lens diameter becomes large. If the lower limit of conditional expression (6) is not reached, it will be difficult to correct off-axis aberrations and chromatic aberrations.

Furthermore, it is desirable that the following conditional expression (7) is satisfied.
1.0 <| f _lL11 / f _w | <4.0 (7)
However,
f _lL11 is the focal length of the negative lens in the first lens group,
f _w is the focal length of the entire zoom lens system at the wide-angle end.

  Conditional expression (7) appropriately defines the power of the negative lens of the first lens group. In order to make the entrance pupil shallow and to enable optical path bending physically, it is preferable to increase the power of the negative lens of the first lens group.

  If the upper limit of conditional expression (7) is exceeded, the entrance pupil will remain deep, and if a certain angle of view is to be secured, the diameter and size of each optical element constituting the first lens group will be enlarged, and the optical path will be bent. It becomes difficult to be physically established. If the lower limit of conditional expression (7) is not reached, the possible magnification of the lens unit that moves for zooming following the first lens unit is close to zero, the amount of movement increases, or the zooming ratio decreases. In addition to the above problem, it is difficult to correct off-axis aberrations such as distortion and chromatic aberration.

  Further, it is desirable that the image side surface of the cemented lens closest to the image plane in the fifth lens group has a shape with a concave surface facing the image side. By adopting such a configuration, the light beam can be bounced up on the final surface, so that the light beam height in the fifth lens group is reduced, and the lens diameter can be reduced.

  An image pickup apparatus (electronic image pickup apparatus) according to the present invention includes any one of the zoom lenses described above and an image pickup element that is disposed on the image side of the zoom lens and converts an optical image formed by the zoom lens into an electric signal. It is characterized by providing.

  According to the present invention, there is no start-up time (lens projecting time) of the camera as seen in a retractable lens barrel, which is preferable in terms of waterproofing and dustproofing, and has a very thin depth direction. Therefore, it is easy to take a configuration that bends the optical path (optical axis) of the optical system with a reflective optical member such as a prism, and provides a zoom lens with a short overall length while having high optical specifications and performance such as well-corrected chromatic aberration. can do.

  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 3 of the zoom lens according to the present invention will be described below. FIGS. 1 to 3 show lens cross-sectional views of the wide-angle end (a), the intermediate focal length state (b), and the telephoto end (c) when focusing on an object point at infinity in Examples 1 to 3, respectively. 1 to 3, the first lens group is G1, the second lens group is G2, the brightness (aperture) stop is S, the third lens group is G3, the fourth lens group is G4, and the fifth lens group is G5. The parallel flat plate constituting the low-pass filter provided with the wavelength band limiting coat for limiting the infrared light 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.

  The numerical data is data in a state where the subject is focused on an object at infinity. The unit of length of each numerical value is mm, and the unit of angle is ° (degree). Further, the zoom data are values at the wide-angle end (WE), the intermediate zoom state (ST) defined in the present invention, and the telephoto end (TE).

  As shown in FIG. 1, the zoom lens of Example 1 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 first lens group having a positive refractive power. A three-lens group G3, a brightness (aperture) stop S, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a negative refractive power are arranged.

  At the time of zooming from the wide angle end to the telephoto end, the first lens group G1 is fixed. The second lens group G2 moves to the image side. The third lens group G3 is fixed. The fourth lens group G4 moves to the object side. The fifth lens group G5 is fixed.

  In order from the object side, the first lens group G1 includes a negative meniscus lens having a convex surface directed toward the object side, a prism, a biconvex positive lens, and a biconvex positive lens. The second lens group G2 includes a biconcave negative lens and a cemented lens of a positive meniscus lens having a convex surface facing the image side and a biconcave negative lens. The third lens group G3 is composed of a positive meniscus lens having a convex surface directed toward the object side. The fourth lens group G4 includes a cemented lens which is formed by a biconvex positive lens and a negative meniscus lens having a convex surface directed toward the image side. The fifth lens group G5 includes a cemented lens of a negative meniscus lens having a convex surface directed toward the object side and a positive meniscus lens having a convex surface directed toward the object side, and a cemented lens composed of a biconvex positive lens and a biconcave negative lens. .

  The aspherical surface includes both surfaces of a biconvex positive lens on the object side of the first lens group G1, both surfaces of a biconcave negative lens on the object side of the second lens group G2, and both surfaces of a positive meniscus lens of the third lens group G3. And 7 surfaces of the biconvex positive lens of the fourth lens group G4 and the object side surface.

  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 first lens group having a positive refractive power. A three-lens group G3, a brightness (aperture) stop S, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a negative refractive power are arranged.

  At the time of zooming from the wide angle end to the telephoto end, the first lens group G1 is fixed. The second lens group G2 moves to the image side. The third lens group G3 is fixed. The fourth lens group G4 moves to the object side. The fifth lens group G5 is fixed.

  In order from the object side, the first lens group G1 includes a negative meniscus lens having a convex surface directed toward the object side, a prism, a biconvex positive lens, and a biconvex positive lens. The second lens group G2 includes a biconcave negative lens and a cemented lens of a positive meniscus lens having a convex surface facing the image side and a biconcave negative lens. The third lens group G3 is composed of a positive meniscus lens having a convex surface directed toward the object side. The fourth lens group G4 includes a cemented lens which is formed by a biconvex positive lens and a negative meniscus lens having a convex surface directed toward the image side. The fifth lens group G5 includes a cemented lens of a negative meniscus lens having a convex surface directed toward the object side and a positive meniscus lens having a convex surface directed toward the object side, and a cemented lens composed of a biconvex positive lens and a biconcave negative lens. .

  The aspherical surface includes both surfaces of a biconvex positive lens on the object side of the first lens group G1, both surfaces of a biconcave negative lens on the object side of the second lens group G2, and both surfaces of a positive meniscus lens of the third lens group G3. And 7 surfaces of the biconvex positive lens of the fourth lens group G4 and the object side surface.

  As shown in FIG. 3, the zoom lens of Example 3 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 first lens group having a positive refractive power. A three-lens group G3, a brightness (aperture) stop S, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a negative refractive power are arranged.

  At the time of zooming from the wide angle end to the telephoto end, the first lens group G1 is fixed. The second lens group G2 moves to the image side. The third lens group G3 is fixed. The fourth lens group G4 moves to the object side. The fifth lens group G5 is fixed.

  In order from the object side, the first lens group G1 includes a negative meniscus lens having a convex surface directed toward the object side, a prism, a biconvex positive lens, and a biconvex positive lens. The second lens group G2 includes a biconcave negative lens and a cemented lens of a positive meniscus lens having a convex surface facing the image side and a biconcave negative lens. The third lens group G3 is composed of a positive meniscus lens having a convex surface directed toward the object side. The fourth lens group G4 includes a cemented lens which is formed by a biconvex positive lens and a negative meniscus lens having a convex surface directed toward the image side. The fifth lens group G5 includes a cemented lens of a negative meniscus lens having a convex surface directed toward the object side and a positive meniscus lens having a convex surface directed toward the object side, and a cemented lens composed of a biconvex positive lens and a biconcave negative lens. .

  The aspherical surface includes both surfaces of a biconvex positive lens on the object side of the first lens group G1, both surfaces of a biconcave negative lens on the object side of the second lens group G2, and both surfaces of a positive meniscus lens of the third lens group G3. And 7 surfaces of the biconvex positive lens of the fourth lens group G4 and the object side surface.

  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)
Here, r is a paraxial radius of curvature, K is a conical coefficient, and A4, A6, A8, A10, and A12 are fourth, sixth, eighth, tenth, and twelfth aspheric 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 74.922 0.60 2.00069 25.46
2 10.939 2.60
3 ∞ 9.00 1.90366 31.32
4 ∞ 0.20
5 * 2513.986 2.02 1.76802 49.24
6 * -18.783 0.11
7 15.826 2.80 1.49700 81.54
8 -26.891 variable
9 * -19.497 0.59 1.88300 40.76
10 * 20.748 0.20
11 -125.741 1.48 1.94595 17.98
12 -8.614 0.45 1.88300 40.76
13 9.839 Variable
14 * 6.751 1.03 1.61881 63.85
15 * 99.747 1.00
16 (Aperture) ∞ Variable
17 * 8.981 2.26 1.49700 81.54
18 -6.362 0.45 1.90366 31.32
19 -9.266 Variable
20 128.987 0.45 2.00069 25.46
21 4.568 1.70 1.49700 81.54
22 12.006 0.20
23 7.621 3.25 1.84666 23.78
24 -5.115 0.50 2.00069 25.46
25 18.681 3.35
26 ∞ 0.50 1.54880 67.00
27 ∞ 0.50
28 ∞ 0.50 1.51680 64.20
29 ∞ Variable
Image plane ∞

Aspheric data 5th surface
K = 0.000
A4 = -7.13154e-05, A6 = 6.27833e-07, A8 = -2.66102e-08, A10 = 1.31535e-10
6th page
K = 0.000
A4 = -5.45682e-05, A6 = -7.88180e-09, A8 = -9.38455e-09, A10 = -8.32684e-11
9th page
K = -6.262
A4 = -4.00138e-03, A6 = 3.85229e-04, A8 = -1.71963e-05, A10 = 2.93553e-07
10th page
K = 0.000
A4 = -4.56078e-03, A6 = 4.09615e-04, A8 = -1.79102e-05, A10 = 2.92599e-07
14th page
K = -0.884
A4 = -1.37697e-04, A6 = 1.44737e-04, A8 = -2.33215e-05, A10 = 1.97629e-06
15th page
K = 5.732
A4 = -2.36364e-05, A6 = 1.25503e-04, A8 = -2.04856e-05, A10 = 1.96165e-06
17th page
K = -4.183
A4 = -5.17495e-05, A6 = -1.66872e-05, A8 = 7.74677e-07, A10 = -4.59458e-08

Zoom data
Wide angle Medium Telephoto height 3.84 3.84 3.84
Focal length 5.00 11.95 25.00
FNO. 3.50 4.74 5.00
Angle of view 2ω 83.29 34.45 16.55
BF 4.85 4.85 4.85
54.16 54.16 54.16
d8 0.96 7.01 10.91
d13 10.38 4.33 0.44
d16 5.30 3.02 2.00
d19 1.77 4.06 5.07
d29 0.35 0.35 0.35

Group focal length
f1 = 13.73 f2 = -5.29 f3 = 11.65 f4 = 11.60 f5 = -8.27

Numerical example 2
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 76.701 0.60 2.00069 25.46
2 10.968 2.60
3 ∞ 9.00 1.91107 35.07
4 ∞ 0.20
5 * 1741.750 2.02 1.76802 49.24
6 * -18.848 0.11
7 15.901 2.80 1.49700 81.54
8 -26.577 Variable
9 * -20.448 0.59 1.88300 40.76
10 * 20.615 0.20
11 -110.659 1.48 1.94595 17.98
12 -8.517 0.45 1.88300 40.76
13 9.739 Variable
14 * 6.527 1.01 1.59201 67.02
15 * 110.233 1.00
16 (Aperture) ∞ Variable
17 * 8.958 2.26 1.49700 81.54
18 -6.352 0.45 1.90366 31.32
19 -9.245 Variable
20 132.378 0.45 2.00069 25.46
21 4.593 1.70 1.49700 81.54
22 12.094 0.22
23 7.660 3.24 1.84666 23.78
24 -5.146 0.50 2.00069 25.46
25 18.599 3.35
26 ∞ 0.50 1.54880 67.00
27 ∞ 0.50
28 ∞ 0.50 1.51680 64.20
29 ∞ Variable
Image plane ∞

Aspheric data 5th surface
K = 0.000
A4 = -7.60800e-05, A6 = 8.30805e-07, A8 = -3.20996e-08, A10 = 1.70536e-10
6th page
K = 0.000
A4 = -5.79720e-05, A6 = 1.23655e-07, A8 = -1.24521e-08, A10 = -6.80245e-11
9th page
K = -6.262
A4 = -4.13033e-03, A6 = 3.92004e-04, A8 = -1.74433e-05, A10 = 3.00056e-07
10th page
K = 0.000
A4 = -4.70841e-03, A6 = 4.16484e-04, A8 = -1.83375e-05, A10 = 3.10465e-07
14th page
K = -0.884
A4 = -1.87344e-04, A6 = 1.51727e-04v-2.68232e-05, A10 = 2.26539e-06
15th page
K = 5.732
A4 = -6.20753e-05, A6 = 1.24681e-04, A8 = -2.26199e-05, A10 = 2.16416e-06
17th page
K = -4.183
A4 = -5.25369e-05, A6 = -2.48415e-05, A8 = 1.65817e-06, A10 = -8.04838e-08

Zoom data
Wide angle Medium Telephoto height 3.84 3.84 3.84
Focal length 5.00 11.98 25.00
FNO. 3.50 4.74 5.00
Angle of view 2ω 83.27 34.38 16.56
BF 4.85 4.85 4.85
54.16 54.16 54.16
d8 0.96 7.03 10.91
d13 10.38 4.32 0.44
d16 5.31 3.02 2.00
d19 1.77 4.06 5.07
d29 0.35 0.35 0.35

Group focal length
f1 = 13.75 f2 = -5.29 f3 = 11.68 f4 = 11.57 f5 = -8.28

Numerical Example 3
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * -33.000 0.70 1.88300 40.76

1 79.821 0.60 2.00069 25.46
2 10.973 2.59
3 ∞ 9.00 1.96100 30.90
4 ∞ 0.20
5 * 766.012 2.02 1.76802 49.24
6 * -18.928 0.11
7 15.937 2.80 1.49700 81.54
8 -26.340 D8
9 * -22.052 0.59 1.88300 40.76
10 * 20.291 0.20
11 -96.261 1.48 1.94595 17.98
12 -8.346 0.45 1.88300 40.76
13 9.604 D13
14 * 6.532 1.01 1.58913 61.25
15 * 96.838 1.00
16 (Aperture) ∞ D16
17 * 8.842 2.26 1.49700 81.54
18 -6.339 0.45 1.90366 31.32
19 -9.178 D19
20 118.496 0.45 2.00069 25.46
21 4.609 1.70 1.49700 81.54
22 12.844 0.30
23 7.646 3.22 1.84666 23.78
24 -5.194 0.50 2.00069 25.46
25 17.012 3.36
26 ∞ 0.50 1.54880 67.00
27 ∞ 0.50
28 ∞ 0.50 1.51680 64.20
29 ∞ D29
Image plane ∞

Aspheric data 5th surface
K = 0.000
A4 = -7.74277e-05, A6 = 8.79224e-07, A8 = -2.95073e-08, A10 = 1.37064e-10
6th page
K = 0.000
A4 = -5.97087e-05, A6 = 1.46863e-07, A8 = -9.95442e-09, A10 = -9.62800e-11
9th page
K = -6.262
A4 = -4.41593e-03, A6 = 4.20620e-04, A8 = -1.81065e-05, A10 = 2.98418e-07
10th page
K = 0.000
A4 = -5.02756e-03, A6 = 4.46721e-04, A8 = -1.83591e-05, A10 = 2.78724e-07
14th page
K = -0.884
A4 = -3.08144e-04, A6 = 1.91185e-04, A8 = -3.28135e-05, A10 = 2.67477e-06
15th page
K = 5.727
A4 = -1.83596e-04, A6 = 1.58750e-04, A8 = -2.79802e-05, A10 = 2.57956e-06
17th page
K = -4.181
A4 = -5.83412e-05, A6 = -1.70791e-05, A8 = 5.17894e-07, A10 = -1.26157e-08

Zoom data
Wide angle Medium Telephoto height 3.84 3.84 3.84
Focal length 5.00 12.00 25.00
FNO. 3.50 4.73 5.00
Angle of view 2ω 83.21 34.31 16.57
BF 4.86 4.86 4.86
54.15 54.15 54.15
d8 0.96 7.02 10.89
d13 10.37 4.30 0.43
d16 5.26 3.01 2.00
d19 1.78 4.04 5.04
d29 0.35 0.35 0.35

Group focal length
f1 = 13.80 f2 = -5.29 f3 = 11.84 f4 = 11.41 f5 = -8.25

  Aberration diagrams at the time of focusing on an object point at infinity in Examples 1 to 3 are shown in FIGS. In these aberration diagrams, (a) is the wide angle end, (b) is the intermediate focal length state, (c) is the spherical aberration (SA), astigmatism (AS), distortion (DT), and magnification at the telephoto end. Chromatic aberration (CC) is shown. 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.
(1) D ₅ / f _w (2) N _dp (3) ν _d12 (4) | f ₅ / f _w |
Example 1 0.040 1.90366 65.39 1.65
Example 2 0.044 1.91107 65.39 1.65
Example 3 0.060 1.961 65.39 1.65

(5) ν _d52 −ν _d51 (6) f ₁ / f _w (7) | f _lL11 / f _w |
Example 1 56.08 2.74 2.57
Example 2 56.08 2.7 2.57
Example 3 56.08 2.76 2.55

Here, in order to cut unnecessary light such as ghost and flare, a flare stop other than the brightness stop may be arranged.
Between the object side of the first lens group, the first and second lens groups, the second and third lens groups, the third and fourth lens groups, and the fourth and fifth lens groups. You may arrange in any place. The frame member may be configured to cut flare rays, or another member may be configured. Also, it may be printed directly on the optical system, painted, or bonded with a seal. The shape may be any shape such as a circle, an ellipse, a rectangle, a polygon, or a range surrounded by a function curve. Further, not only harmful light beams but also light beams such as coma flare around the screen may be cut.

  The first lens group G1 is desirable for focusing for adjusting the focus. When focusing is performed in this group, the load on the motor is small because the lens weight is light. Focusing may be performed with another lens group. Further, focusing may be performed by moving a plurality of lens groups. Further, focusing may be performed by extending the entire lens system, or focusing may be performed by extending or retracting some lenses.

  Further, the brightness (shading) at the periphery of the image may be reduced by shifting the CCD microlens. For example, the design of the CCD microlens may be changed according to the incident angle of the light beam at each image height. Further, the amount of decrease in the peripheral portion of the image may be corrected by image processing.

  Furthermore, each lens may be provided with an antireflection coating to reduce ghosts and flares. A multi-coat is desirable because it can effectively reduce ghost and flare. Infrared cut coating may be applied to the lens surface, cover glass, or the like. In order to prevent the occurrence of ghost and flare, it is common practice to apply an antireflection coating to the air contact surface of the lens. On the other hand, the refractive index of the adhesive is sufficiently higher than the refractive index of air on the cemented surface of the cemented lens. For this reason, the reflectance is often the same as or lower than that of a single-layer coating, and it is rare to apply a coating.

  However, if an anti-reflection coating is also applied to the joint surface, ghosts and flares can be further reduced, and still better images can be obtained. In recent years, high refractive index glass materials have become widespread and have been used extensively in camera optical systems due to their high aberration correction effects. However, when high refractive index glass materials are used as cemented lenses, reflection on the cemented surface is ignored. It becomes impossible. In such a case, it is particularly effective to provide an antireflection coating on the joint surface.

  Effective use of the bonding surface coat is disclosed in JP-A-2-27301, JP-A-2001-324676, JP-A-2005-92115, USP7116482, and the like. These documents particularly describe the cemented lens surface coat in the first lens group of the positive leading zoom lens, and the cemented lens surface in the first lens group of the positive power according to the present invention is also disclosed in these documents. You just have to do it.

As the coating material to be used, Ta ₂ O ₅ , TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , HfO ₂ , CeO, which have a relatively high refractive index, depending on the refractive index of the base lens and the refractive index of the adhesive. _{2, SnO 2, in 2 O} 3, ZnO, Y 2 O 3 coating material such as a relatively low refractive index of MgF _2, SiO _2, coating materials such as Al ₂ O _3, and appropriately selected, phase condition The film thickness may be set so as to satisfy the above.

  Further, as with the coating on the air contact surface of the lens, the bonding surface coat may be a multi-coat. By appropriately combining two or more layers of coating materials and film thicknesses, it becomes possible to further reduce the reflectance and control the spectral characteristics and angular characteristics of the reflectance. Also, it is effective to coat the cemented surfaces other than the first lens group based on the same idea.

(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. 7, 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. 7, a point P ₁ on the circumference of an arbitrary radius r ₁ (ω) positioned 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 the 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 and an electronic imaging device in an electronic imaging apparatus having a zoom lens, and the circle with the radius R drawn on the optical image is It is effective for correction when it becomes asymmetric. 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 preferably satisfies the following conditional expression so that the image after distortion correction does not have 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.

Preferably, the radius R 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 approximately near the telephoto end in the divided zone,
r ′ (ω) = α · f · tan ω
It is also possible to calculate a correction amount when a correction result satisfying the above is obtained, and uniformly multiply the correction amount for each focal distance to obtain a final correction amount.

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)
The zoom lens of the present invention as described above forms an object image, and the image can be received by an electronic image sensor such as a CCD. The embodiment is illustrated below.

  FIGS. 8 to 10 are conceptual diagrams of structures in which the zoom lens according to the present invention is incorporated in the photographing optical system 141 of the digital camera. 8 is a front perspective view showing the appearance of the digital camera 140, FIG. 9 is a rear perspective view thereof, and FIG. 10 is a cross-sectional view showing the configuration of the digital camera 140. 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 145, a flash 146, a liquid crystal display monitor 147, and the like. When the shutter 145 disposed in the position is pressed, photographing is performed through the photographing optical system 141, for example, the optical path bending zoom lens according to the first embodiment in conjunction therewith. An object image formed by the photographing optical system 141 is formed on the imaging surface of the CCD 149 through a near-infrared cut filter and an optical low-pass filter F. 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 object image formed by the finder objective optical system 153 is formed on the field frame 157 of the Porro prism 155 that is an image erecting member. Behind this polyprism 155, an eyepiece optical system 159 for guiding an erect image to the observer eyeball E is disposed. Cover members 150 are disposed on the incident side of the photographing optical system 141 and the finder objective optical system 153 and on the exit side of the eyepiece optical system 159, respectively.

  The digital camera 140 configured in this manner is a zoom lens having a high zoom ratio and a high optical performance of the photographing optical system 141, which is about 5 times. Can be realized.

  In addition, in the example of FIG. 10, although a parallel plane board is arrange | positioned as the cover member 150, you may omit.

(Internal circuit configuration)
FIG. 11 is a configuration block diagram of an internal circuit of a 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. 11, 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 and converts the light amount of each pixel of the object image into an electric 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 downsizing while ensuring high optical performance.

FIG. 2 is a lens cross-sectional view at the wide-angle end (a), the intermediate state (b), and the telephoto end (c) when focusing on an object point at infinity according to the first exemplary embodiment of the zoom lens of the present invention. It is the same figure as FIG. 1 of Example 2 of the zoom lens of this invention. It is the same figure as FIG. 1 of Example 3 of the zoom lens of this invention. 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. FIG. 10 is an aberration diagram for Example 3 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 optical path bending 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 G5 ... 5th lens group S ... Aperture stop F ... Low pass filter C ... Cover glass P ... Prism 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 unit 140 ... digital camera 141 ... imaging optical system 142 ... imaging optical path 143 ... finder optical system 144 ... finder optical path 145 ... shutter button 146 ... flash 147 ... liquid crystal display 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

Claims (9)

In order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens having positive refractive power In a zoom lens composed of a group and a fifth lens group having negative refractive power,
At the time of zooming from the wide angle end to the telephoto end, the first lens group and the third lens group are fixed with respect to the image plane, and at least the second lens group and the fourth lens group move,
The first lens group includes, in order from the object side, a negative lens, a reflective optical element for bending an optical path, a first positive lens, and a second positive lens.
The fifth lens group includes two cemented lenses, a first cemented lens and a second cemented lens ,
The image side surface of the fifth lens closest to the image plane side of the cemented lens in the group, a zoom lens, wherein the shape der Rukoto with a concave surface facing the image side. The zoom lens according to claim 1, wherein the following conditional expression (1) is satisfied.
0 <D ₅ / f _w <0.7 (1)
However,
D ₅ is the axial distance between the first cemented lens and the second cemented lens in the fifth lens group,
f _w is the focal length of the entire zoom lens system at the wide angle end. The zoom lens according to claim 1, wherein the reflective optical element is formed of a prism and satisfies the following conditional expression (2).
N _dp > 1.9 (2)
N _dp is the refractive index of the prism. The zoom lens according to any one of claims 1 to 3, wherein the following conditional expression (3) is satisfied.
ν _d12 > 60 (3)
Here, ν _d12 is an average value of the Abbe numbers of the first positive lens and the second positive lens in the first lens group. The zoom lens according to any one of claims 1 to 4, wherein the following conditional expression (4) is satisfied.
1.0 <| f ₅ / f _w | <3.0 (4)
However,
f ₅ is the focal length of the fifth lens group,
f _w is the focal length of the entire zoom lens system at the wide-angle end. The zoom lens according to any one of claims 1 to 5, wherein the following conditional expression (5) is satisfied.
30 <ν _d52 −ν _d51 <70 (5)
However,
ν _d51 is the Abbe number of the object side lens of the cemented lens on the object side in the fifth lens group,
ν _d52 is the Abbe number of the image side lens of the cemented lens on the object side in the fifth lens group. The zoom lens according to any one of claims 1 to 6, wherein the following conditional expression (6) is satisfied.
2.0 <f ₁ / f _w <5.0 (6)
However,
f ₁ is the focal length of the first lens group,
f _w is the focal length of the entire zoom lens system at the wide angle end. The zoom lens according to any one of claims 1 to 7, wherein the following conditional expression (7) is satisfied.
1.0 <| f _lL11 / f _w | <4.0 (7)
However,
f _lL11 is the focal length of the negative lens in the first lens group,
f _w is the focal length of the entire zoom lens system at the wide angle end. A zoom lens according to any one of claims 1 to 8, and an image pickup device that is disposed on an image side of the zoom lens and converts an optical image formed by the zoom lens into an electric signal. An imaging apparatus characterized by that .

Images