JP2013145401A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens which is especially suitable as a zoom lens for a compact high-performance digital camera, achieves a half angle-of-view of 38 degrees or more at a wide angle end, and is miniaturized in storage and provide an imaging apparatus using the zoom lens.SOLUTION: The zoom lens includes, in order from an object side along an optical axis, a first lens group I having negative refractive power, a second lens group II having negative refractive power, and a third lens group III having positive refractive power. The first lens group can be moved in the thickness direction of an imaging apparatus body. The first lens group is extended to the front in the thickness direction during photographing and stored in the imaging apparatus body during non-use. A prism folding an optical path is placed between the first lens group and the second lens group. The prism is fixed with respect to an image surface, when varying power and retracted when the first lens group is stored in the imaging apparatus body.

Description

  The present invention relates to an imaging device such as a video camera or an electronic still camera that includes a zoom lens and a solid-state imaging device such as a CCD as an imaging device, and the zoom lens as a photographing lens.

  2. Description of the Related Art In recent years, imaging devices such as digital cameras that have been widely used are required to have higher performance and smaller size, and a zoom lens used as a photographing lens of the imaging device is also required to achieve both higher performance and smaller size. In addition, there are many users who desire a wide angle of view of the photographing lens, and it is desired that the half angle of view at the wide angle end of the zoom lens is 38 degrees or more. A half angle of view of 38 degrees in a digital camera for the general public corresponds to a focal length of 28 mm when converted to a 35 mm silver salt film camera.

  In the invention described in Patent Document 1, the camera is miniaturized by using an element that bends the optical axis in the zoom lens. However, the half angle of view at the wide-angle end is about 33 degrees, which is insufficient to satisfy the demand for higher angle of view. Further, the invention disclosed in Patent Document 2 discloses a technique in which a mirror that bends the optical axis is disposed in order to reduce the size of the image pickup apparatus when the zoom lens is stored, and the mirror is retracted from the photographing position when the lens is stored. Has been. However, since the imaging element moves toward the object side at the wide-angle end side, the first lens group moves greatly toward the object side, and there is a problem in maintaining the strength and accuracy of the lens barrel. Also, the half angle of view at the wide-angle end is about 31 degrees, which is insufficient to meet the requirements. Furthermore, since distortion is also assumed to be corrected by image processing, it is 10% or more, which is unacceptable as it is, and image quality deterioration cannot be avoided by correction by image processing.

  An object of the present invention is to provide an imaging apparatus that can be miniaturized when the zoom lens is stored.

  The imaging device according to the present invention includes, in order from the object side along the optical axis, a first lens group having negative refractive power, a second lens group having negative refractive power, and a third lens having positive refractive power. In the imaging apparatus having the lens group, the first lens group is movable in the thickness direction of the imaging apparatus main body, extended forward in the thickness direction at the time of shooting, and housed in the imaging apparatus main body when not in use. A prism that bends the optical path is disposed between the lens group and the second lens group. The prism is fixed with respect to the image plane at the time of zooming, and is retracted when the first lens group is housed in the imaging apparatus main body. This is the main feature.

  The first lens group has a negative refractive power, and the negative refractive power is preceded so as to widen the angle and correct aberrations well. In addition, by arranging a prism between the first lens group and the second lens group, the lens group after the second lens group is not drawn out from the inside of the imaging device such as a camera at the time of zooming, and the lens group fed out of the camera is arranged. Since only the first lens group can be used, it is effective in improving the accuracy and strength of the lens barrel. In addition, when the lens is housed, the thickness dimension of the imaging device when the lens is housed can be reduced by retracting the prism. Incidentally, the thickness dimension of the image pickup apparatus when the lens is housed can be made approximately the thickness of the first lens group, and the image pickup apparatus can be made thin.

L1max is the maximum distance from the first surface of the first lens group to the reflecting surface on the optical axis before bending by the prism, and L2 is the distance from the reflecting surface to the image surface on the optical axis after bending by the prism. When
(1) 0.3 <| L1max / L2 | <1.0
It may be configured to satisfy the following conditional expression.
If the lower limit value of the above expression (1) is exceeded, the amount of extension of the first lens group becomes small, and aberration correction becomes difficult. If the upper limit is exceeded, the amount of extension of the first lens group that is extended out of the camera becomes long, which causes a problem in maintaining the accuracy and strength of the lens barrel.

  The first lens group may be composed of at least three lenses. This is because the aberration can be corrected well while widening the angle.

When the focal length of the entire system at the wide angle end is fw and the focal length of the first lens unit is f1,
(2) 1 <| f1 / fw | <5
It may be configured to satisfy the following conditional expression.
If the lower limit value of the above equation (2) is exceeded, the power of the first lens group becomes too strong, making it difficult to correct aberrations. If the upper limit is exceeded, the first lens group becomes large, and it is difficult to reduce the size of the imaging apparatus.

When the focal length of the entire system at the wide angle end is fw and the focal length f2 of the second lens group is
(3) 5 <| f2 / fw | <30
It may be configured to satisfy the following conditional expression.
If the lower limit of the above expression (3) is exceeded, the power of the second lens group becomes too strong, making it difficult to correct aberrations. If the upper limit value is exceeded, the second lens group becomes large, and it is difficult to reduce the size of the imaging device.

When the thickness of the first lens unit on the optical axis is D1, and the maximum image height is Y′max,
(4) 0.8 <| D1 / Y′max | <5
It may be configured to satisfy the following conditional expression.
If the lower limit value of the above expression (4) is exceeded, the power of the first lens group becomes too strong, making it difficult to correct aberrations. If the upper limit is exceeded, the first lens group becomes large, and it is difficult to reduce the size of the imaging apparatus.

When the interval when the first lens group and the second lens group are closest to each other on the optical axis is L3min,
(5) 2 <| L3min / Y'max | <5
It may be configured to satisfy the following conditional expression.
If the lower limit value of the above equation (5) is exceeded, the prism layout becomes difficult. On the other hand, if the upper limit value is exceeded, the prism becomes difficult to enlarge and the zoom ratio cannot be increased.

  According to the present invention, the zoom lens can be reduced in size when stored.

FIG. 2 is an optical arrangement diagram illustrating a first embodiment of a zoom lens according to the present invention in the order of wide angle end, intermediate focal length position, and telephoto end. It is an aberration curve figure in the wide angle end of the said 1st Example. It is an aberration curve figure in the intermediate focal length position of the first embodiment. FIG. 3 is an aberration curve diagram at the telephoto end of the first example. FIG. 6 is an optical arrangement diagram illustrating a second embodiment of the zoom lens according to the present invention in the order of a wide angle end, an intermediate focal length position, and a telephoto end. FIG. 6 is an aberration curve diagram at the wide-angle end of the second example. It is an aberration curve figure in the intermediate focal length position of the second embodiment. It is an aberration curve figure in the telephoto end of the said 2nd Example. 1 is an optical layout diagram illustrating an example in which a zoom lens according to the present invention is incorporated in an imaging apparatus.

  Embodiments of a zoom lens according to the present invention and an image pickup apparatus using the same will be described below. Two examples of the zoom lens are shown in the drawings.

  FIG. 1 is an optical arrangement diagram showing a configuration of a zoom lens according to a first embodiment of the present invention, and from a wide angle end shown in (a) through a specific intermediate focal length shown in (b) ( The zoom locus | trajectory at the time of zooming to the telephoto end shown to c) is shown. A first lens group I having a negative refractive power, a second lens group II having a negative refractive power, and a third lens having a positive refractive power in order from the object side (left side in the figure) along the optical axis. It includes a group III, a fourth lens group IV having a positive refractive power, a fifth lens group V having a negative refractive power, and a sixth lens group VI having a positive refractive power. An aperture stop is provided between the second lens group II and the third lens group III.

  In the present embodiment, an appropriate number of transparent parallel plates are disposed between the sixth lens group VI and the image plane IM. These parallel plates include various filters P1 such as an optical low-pass filter and an infrared cut filter for cutting a spatial frequency higher than the limit resolution of a solid-state imaging device such as a CCD disposed on the image plane IM, and an imaging device. It is made of a cover glass or seal glass P2 for protecting the glass.

  The first lens group I includes three lenses in order from the object side: a negative meniscus lens, a biconvex lens, and a biconcave lens. The second lens group II is composed of three lenses of a biconcave lens, a biconcave lens, and a positive meniscus lens bonded to the biconcave lens in order from the object side. The third lens group III includes one positive meniscus lens. The fourth lens group IV includes three lenses, a biconvex lens, a biconcave lens, and a positive meniscus lens, which are bonded together in order from the object side. The fifth lens group V includes one negative meniscus lens. The sixth lens group VI includes one biconvex lens and the parallel plates P1 and P2. Between the first lens group I and the second lens group II, a reflective optical element composed of a plate-like mirror is disposed. Reference numeral 8 denotes a reflecting surface of the mirror.

  When zooming from the wide-angle end to the telephoto end, the first lens group I moves toward the image plane IM, and the second lens group II moves once toward the image plane IM and then moves toward the object side. Move. The third lens group III and the fourth lens group IV move toward the object side and while approaching each other little by little. The fifth lens group V moves toward the object side. The sixth lens group VI maintains a fixed position. The mirror surface indicated by reference numeral 8 maintains a fixed position during zooming.

  Table 1 lists the values of the specifications of the zoom lens according to the first example. In these specifications, f represents the focal length of the entire zoom lens system, FNO represents the F number, and ω represents the half angle of view (deg). In the lens data shown in the specifications of Table 1, the surface number indicates the order of the lens surfaces from the object side, and the surface interval indicates the interval between the lens surfaces. Surface number 8 indicates a mirror surface, and surface numbers 7 and 9 indicate virtual surfaces. Nd represents the refractive index of the medium at the d-line (λ = 587.6 nm), and ν represents the Abbe number. Note that the refractive index of air of 1.00000 is omitted.

In this embodiment, a plurality of surfaces are constituted by aspheric surfaces, and each aspheric surface is represented by the following expression. That is, an aspherical surface is defined by the following equation, where C is the reciprocal of the paraxial radius of curvature (paraxial curvature) and H is the height from the optical axis.
X = CH2 / {1 + √ (1- (1 + K) C2H2)}
+ A4 ・ H4 + A6 ・ H6 + A8 ・ H8 + A10 ・ H10
+ A12 ・ H12 + A14 ・ H14 + A16 ・ H16 + A18 ・ H18
In addition, also in the specification value of Example 2 described later, the same sign and aspherical expression as those of Example 1 are used. The unit of focal length, curvature radius, surface interval and other lengths in the specification table is generally “mm”. However, the optical system can obtain the same optical performance even when proportionally enlarged or reduced. It is not limited to.

Table 1

The surface numbers of aspheric surfaces used in the above examples and their aspheric coefficients are shown below.
[Tenth aspect]
K = 0
A4 = 1.0811E-05
A6 = −3.5325E-07
A8 = 3.4940E-08
A10 = −7.8310E−10

[16th page]
K = 0
A4 = −4.0951E−05
A6 = −1.2537E−08
A8 = −9.6408E−09
A10 = −5.5656E-11

[21st page]
K = 0
A4 = 5.1474E-04
A6 = 8.1090E-06
A8 = 2.0780E-08
A10 = 8.3320E-09

[Twenty-second surface]
K = 0
A4 = -3.7303E-04
A6 = 1.7291E-05
A8 = 5.3710E-07
A10 = −9.7877E−09

[23rd page]
K = 0
A4 = −1.1249E−05
A6 = 1.8961E-05
A8 = 3.0424E-07
A10 = 3.7088E-09

[24th page]
K = 0
A4 = 4.2201E-05
A6 = 1.2781E-04
A8 = −8.5422E-06
A10 = 2.9163E-07
A12 = −3.0957E−09

[25th page]
K = 0
A4 = −4.0581E−04
A6 = 1.3772E-04
A8 = −5.2377E-06
A10 = −9.3643E−10
A12 = 4.3339E-09

The surface numbers 6, 9, 14, 17, 21, and 23 have a variable distance from the rear surface, and the variable amount is as follows.
"Variable amount"
Wide angle end Intermediate focal length Telephoto end A 12.1192 4.5297 3.2032
B 1.5966 5.1953 1.5751
C 15.6123 6.2326 0.8000
D 1.5686 1.1294 0.8000
E 9.4447 13.0293 22.2876
F 0.9000 3.5357 3.6596

The numerical values applied to the conditional expressions (1) to (5) and the numerical values (conditional expression corresponding values) obtained from the conditional expressions are as follows from the numerical values of the above-described embodiments.
(Values for conditional expressions)
L1max = 24.34
L2 = 53.66
f1 = -14.72
fw = 5.2
f2 = −67.34
D1 = 6.9
L3min = 15.42
Y′max = 4.2
(1) | L1max / L2 | = 0.50
(2) | f1 / fw | = 2.83
(3) | f2 / fw | = 12.95
(4) | D1 / Y′max | = 1.64
(5) | L3min / Y′max | = 3.67

  2, 3 and 4 are graphs showing various aberrations of the zoom lens according to Example 1. FIG. 2 shows various aberrations at the wide angle end, FIG. 3 shows a specific intermediate focal length, and FIG. 4 shows the various aberrations at the telephoto end. Represent. The solid line in the astigmatism diagram indicates the sagittal image plane, and the broken line indicates the meridional image plane. Further, the coma aberration diagram shows coma aberration at each image height. In each aberration diagram, d represents the aberration at the d-line (λ = 587.6 nm), and g represents the aberration at the g-line (λ = 435.8 nm). In the second embodiment described below, the same reference numerals as those in the first embodiment are used.

  FIG. 5 is an optical arrangement diagram showing the configuration of the zoom lens according to the second embodiment of the present invention. From the wide-angle end shown in (a), through a specific intermediate focal length shown in (b), (c) The zoom locus of each lens unit during zooming to the telephoto end shown in FIG. In the second example, the third lens group and the fourth lens group in the first example are integrated into a third lens group III, and the fifth lens group V and the sixth lens group IV in the first example are combined. The difference is that the corresponding lens groups are a 44th lens group IV and a fifth lens group V, respectively, and after the fourth lens group IV moves to the object side, it moves to the image plane IM side. Other configurations are the same as those of the first embodiment. The shapes of the individual lenses arranged in order from the object side are the same as those in the first embodiment, and only the numerical values are different. Therefore, the same components are denoted by the same reference numerals, and the description thereof is omitted. Is disclosed.

Table 2 lists specifications of the zoom lens according to the second example. In this specification, the meaning of each symbol is the same as that described for the first embodiment.
Table 2

The surface numbers of aspheric surfaces used in the above examples and their aspheric coefficients are shown below.
[Tenth aspect]
K = 0
A4 = 2.7315E-05
A6 = 1.25596E-07
A8 = 1.4873E-08
A10 = -1.7363E-10

[16th page]
K = 0
A4 = −2.7583E−05
A6 = 2.4036E-07
A8 = −1.0126E−08
A10 = −5.5963E-11

[21st page]
K = 0
A4 = 5.0262E-04
A6 = 8.0584E-06
A8 = 5.0844E-08
A10 = 5.4946E-09

[Twenty-second surface]
K = 0
A4 = -4.1668E-04
A6 = 1.5723E-05
A8 = 3.9575E-07
A10 = 4.1614E-09

[23rd page]
K = 0
A4 = 3.8721E-05
A6 = 1.6968E-05
A8 = 3.2119E-07
A10 = 5.8564E-09

[24th page]
K = 0
A4 = −1.1077E−04
A6 = 1.717E-04
A8 = −8.4554E-06
A10 = 2.8937E-07
A12 = −3.0401E−09

[25th page]
K = 0
A4 = −8.2439E-04
A6 = 1.4677E-04
A8 = −5.4794E-06
A10 = −5.4955E-09
A12 = 4.5836E-09

The surface numbers 6, 9, 14, 17, 21, and 23 have a variable distance from the rear surface, and the variable amount is as follows.
"Variable amount"
Wide angle end Intermediate focal length Telephoto end A 16.8511 5.6661 3.1931
B 1.4759 4.4757 1.4837
C 15.7039 7.0061 0.8000
D 10.3594 13.9076 23.0246
E 0.9000 3.0498 3.1308

The numerical values applied to the conditional expressions (1) to (5) and the numerical values (conditional expression corresponding values) obtained from the conditional expressions are as follows from the numerical values of the above-described embodiments.
(Values for conditional expressions)
L1max = 29.06
L2 = 53.76
f1 = -14.10
fw = 5.2
f2 = -11.86
D1 = 7.07
L3min = 14.96
Y′max = 4.2
(1) | L1max / L2 | = 0.60
(2) | f1 / fw | = 2.71
(3) | f2 / fw | = 21.51
(4) | D1 / Y′max | = 1.68
(5) | L3min / Y′max | = 3.56

  6, 7, and 8 are graphs showing various aberrations of the zoom lens according to Example 2. FIG. 6 shows various aberrations at the wide-angle end, FIG. 7 shows a specific intermediate focal length, and FIG. 8 shows the various aberrations at the telephoto end. Represent. The solid line in the astigmatism diagram indicates the sagittal image plane, and the broken line indicates the meridional image plane. Further, the coma aberration diagram shows coma aberration at each image height. The solid line in the astigmatism diagram indicates the sagittal image plane, and the broken line indicates the meridional image plane. Further, the coma aberration diagram shows coma aberration at each image height. In each aberration diagram, d represents the aberration at the d-line (λ = 587.6 nm), and g represents the aberration at the g-line (λ = 435.8 nm).

  The zoom lens according to each embodiment described above can be incorporated as a photographic lens in an imaging apparatus such as a digital camera or a video camera. A solid-state image sensor such as a CCD is disposed as an image sensor on the image plane IM of the zoom lens. The subject image is connected to the imaging surface of the image sensor through the zoom lens, and is converted into an electrical signal corresponding to the subject image by the image sensor and output. When using the image pickup apparatus, each lens group and the mirror 8 are arranged as shown in FIGS. 1 and 5 as shown in FIGS. 1 and 5, and an arbitrary magnification can be obtained while continuously changing the magnification from the wide-angle end to the telephoto end. Shoot at the focal length position. When not in use, the lens group constituting the zoom lens is housed on the image pickup apparatus main body side.

  FIG. 9 is an example in which the zoom lens according to the present invention is incorporated in an image pickup apparatus, and conceptually shows an example of retracting the mirror 8 and storing the lens group on the image pickup apparatus main body side when not in use. In the example shown in FIG. 9, a flat mirror 8 is disposed between the first lens group I and the second lens group II. The mirror 8 is rotatably arranged while drawing a locus in a direction perpendicular to the reflecting surface around an axis provided along the lower edge of the mirror 8. When the imaging apparatus is used, the mirror 8 rotates so that the optical axis from the second lens group II to the sixth lens group VI is bent at right angles to the optical axis of the first lens group I, and the second lens. Advancing on the optical axis from group II to the sixth lens group VI. In this advancing mode of the mirror 8, both the optical axis of the first lens group I and the optical axis from the second lens group II to the sixth lens group VI are advanced in a 45 ° attitude, and the imaging device is When the lens 8 is ready for use, and therefore when each lens group is moved and zoomed, the mirror 8 is fixed in the above-mentioned advancement posture. In the imaging apparatus main body, the direction parallel to the paper surface of FIG. 9 is the thickness direction, and the left side is the front surface. The first lens group I is configured to extend forward in the thickness direction from the imaging device main body at the time of shooting, and to be accommodated within the width direction dimension in the imaging device main body when the imaging device is not used. From the second lens group II to the sixth lens group VI, the parallel plates P1 and P2, and the image plane IM of the image sensor are arranged within the widthwise dimension of the image pickup apparatus body.

  When the image pickup apparatus is not used, the mirror 8 rotates in the direction of the arrow so as to retreat from the rear end surface of the first lens group I with the lower end edge as the rotation center as indicated by reference numeral 8A in FIG. It faces the rear end surface of I and retracts from the optical axis from the second lens group II to the sixth lens group VI and is substantially parallel to the optical axis from the second lens group II to the sixth lens group VI. Take a posture. With the posture of the mirror 8, the second lens group II moves in a direction approaching the third lens group III in the image pickup apparatus body as indicated by an arrow. The movement of the third lens group III and the rotation of the mirror 8 are for making a space for housing the first lens group I on the imaging apparatus main body side, and the first lens group I is housed in this space. .

  If the lens group and the mirror 8 are configured as shown in FIG. 9, the lens optical axis at the time of photographing can be bent at a right angle, and only the first lens group I needs to protrude from the imaging device body. The imaging apparatus main body can be thinned. In addition, since the first lens group I can be housed in the image pickup apparatus main body when not in use, the image pickup apparatus can be made more compact, and protrusions from the image pickup apparatus main body can be eliminated.

I First lens group II Second lens group III Third lens group IV Fourth lens group V Fifth lens group 8 Mirror as reflective optical element S Aperture IM Image surface

JP-A-9-138347 JP 2006-98432 A

Claims (7)

In an imaging apparatus including a first lens group having a negative refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power in order from the object side along the optical axis. ,
The first lens group is movable in the thickness direction of the imaging device main body, extended forward in the thickness direction during shooting, and housed in the imaging device main body when not used.
A prism that bends the optical path is disposed between the first lens group and the second lens group,
The imaging device is characterized in that the prism is fixed with respect to the image plane at the time of zooming, and retracts when the first lens group is housed in the imaging device body. 2. The imaging device according to claim 1, wherein the maximum value of the distance from the first surface of the first lens group to the reflecting surface on the optical axis before bending by the prism is L1max, and the optical axis after bending by the prism. An image pickup apparatus satisfying the following conditional expression when a distance from the reflection surface to the image surface is L2.
(1)
0.3 <| L1max / L2 | <1.0   The imaging apparatus according to claim 1, wherein the first lens group includes at least three lenses. 4. The imaging apparatus according to claim 1, wherein the following conditional expression is satisfied, where fw is a focal length of the entire system at a wide-angle end and f <b> 1 is a focal length of the first lens group. An imaging device.
(2)
1 <| f1 / fw | <5 5. The imaging apparatus according to claim 1, wherein the following conditional expression is satisfied, where fw is a focal length of the entire system at a wide-angle end and f 2 is a focal length of the second lens group. An imaging device.
(3)
5 <| f2 / fw | <30 6. The imaging device according to claim 1, wherein when the thickness of the first lens unit on the optical axis is D1 and the maximum image height is Y′max, the following conditional expression is satisfied. An imaging device that is characterized.
(4)
0.8 <| D1 / Y'max | <5 7. The imaging device according to claim 1, wherein the following conditional expression is satisfied when an interval when the first lens group and the second lens group are closest to each other on the optical axis is L3 min. An imaging apparatus characterized by that.
(5)
2 <| L3min / Y'max | <5

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