JP2009128693A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact zoom lens capable of securing sufficient backfocusing to a focal distance. <P>SOLUTION: This zoom lens has three lens groups L1-L3 having negative refractive power, positive refractive power and negative refractive power in this order from an object side toward an image side, a space between the first lens group L1 and the second lens group L2 is reduced in a telephoto-end, compared with a wide angle end, and a space between the second lens group L2 and the third lens group L3 increases therein. The respective lens groups are set with the proper refractive power arrangement, in particular, the constitution and the refractive power arrangement in the second lens group are set properly, in the zoom lens. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a zoom lens, and is suitable for, for example, a photographing lens for a camera.

  In recent years, a zoom lens having a small size and high image quality has been demanded as a photographing lens of a lens shutter type digital still camera or a focal plane shutter type single-lens reflex camera.

  In order to reduce the size of the zoom lens, when a complicated zoom type (for example, multi-group) is adopted, the entire lens system tends to be enlarged. For this reason, in order to realize a small zoom lens, a zoom type as simple as possible is preferable.

  2. Description of the Related Art As a zoom type that is simple and easily secures back focus at the wide-angle end, a two-group zoom lens that is composed of two lens groups having negative and positive refractive powers in order from the object side is known.

  However, although the two-group zoom lens has a simple configuration, it is difficult to simultaneously realize downsizing and high performance (high image quality). Therefore, a device is required for the zoom configuration.

In order to achieve both miniaturization and high performance, a three-group zoom lens in which a lens group having a negative refractive power is further arranged on the image plane side of the two-group zoom lens is known. (Patent Documents 1 to 4)
Japanese Patent Registration No. 2988031 Japanese Examined Patent Publication No. 61-61655 JP-A-6-230286 JP 2005-292348 A

  By the way, in a digital single-lens reflex camera, while using a lens mount in common with a conventional single-lens reflex camera for a silver salt film, a solid-state image pickup device (referred to as an APS-C size) having a small size for a 35 mm film is used. What has been commercialized. In a digital single-lens reflex camera using such a small-size image sensor, when an angle of view equivalent to that of a silver-salt film single-lens reflex camera is to be realized, a photographing lens having a shorter focal length is required. This means that a longer back focus is required in terms of a focal length ratio than a 35 mm film photographing lens shared by a lens mount.

  The zoom lenses disclosed in Patent Documents 1 to 4 are all assumed to be 35 mm full size. For this reason, when assuming application to a digital single-lens reflex camera using a small-size image sensor that shares a lens mount, the back focus is not sufficiently secured with respect to the focal length at the wide-angle end, and an equivalent angle of view. Is difficult to realize.

  An object of the present invention is to provide a compact and high-performance zoom lens that ensures a sufficient back focus with respect to a focal length.

  In order to achieve the above object, the zoom lens of the present invention sets the lens group to an appropriate refractive power arrangement, and particularly appropriately sets the configuration and refractive power arrangement in the second lens group.

Specifically, there are three lens groups of negative, positive, and negative refractive power in order from the object side to the image side, and during zooming from the wide angle end to the telephoto end, the first lens group and the second lens group A zoom lens in which the distance is decreased and the distance between the second lens group and the third lens group is increased, and the second lens group is moved in order from the object side to the image side, the second A lens group having a positive refractive power, and an aperture It consists of a stop and a second B lens group having a positive refractive power. Further, the focal length of the entire system at the wide angle end is fw, and the focal lengths of the first lens group, the second lens group, and the third lens group are f1, f2, and f3, and the focal lengths of the second A lens group and the second B lens group, respectively. Are f2A and f2B, respectively.
-1.2 <f2 / f1 <-0.9
−0.2 <fw / f3 <−0.01
0.5 <f2A / f2B <1.1
Set to satisfy the following conditions.

  According to the present invention, it is possible to realize a small and high-performance zoom lens that ensures a sufficient back focus with respect to the focal length.

Embodiments of the zoom lens according to the present invention will be described below with reference to the drawings.
FIG. 1 is a lens cross-sectional view at the wide-angle end of the zoom lens according to the first exemplary embodiment. FIGS. 2A and 2B are longitudinal aberration diagrams of the zoom lens of Example 1 at the wide-angle end and the telephoto end, respectively.

  FIG. 3 is a lens cross-sectional view at the wide-angle end of the zoom lens according to the second exemplary embodiment. 4A and 4B are longitudinal aberration diagrams of the zoom lens of Example 2 at the wide-angle end and the telephoto end, respectively.

  FIG. 5 is a lens cross-sectional view at the wide-angle end of the zoom lens according to the third exemplary embodiment. FIGS. 6A and 6B are longitudinal aberration diagrams of the zoom lens of Example 3 at the wide-angle end and the telephoto end, respectively.

  FIG. 7 is a lens cross-sectional view at the wide-angle end of the zoom lens according to the fourth exemplary embodiment. 8A and 8B are longitudinal aberration diagrams of the zoom lens of Example 4 at the wide-angle end and the telephoto end, respectively.

  FIG. 9 is a lens cross-sectional view at the wide-angle end of the zoom lens according to the fifth exemplary embodiment. FIGS. 10A and 10B are longitudinal aberration diagrams of the zoom lens of Example 5 at the wide-angle end and the telephoto end, respectively.

Examples 1 to 5 correspond to Numerical Examples 1 to 5 described later, respectively.
In the lens cross-sectional views shown in FIGS. 1, 3, 5, 7, and 9, L1 is a first lens unit having negative refractive power (optical power = reciprocal of focal length), and L2 is a second lens having positive refractive power. The group L3 is a third lens group having a negative refractive power. Reference numerals 2A and 2B respectively denote a second A lens group having a positive refractive power and a second B lens group having a positive refractive power that constitute the second lens group L2. (Negative) or (positive) such as “L1 (negative)” in each lens cross-sectional view represents the sign of the refractive power of the lens group. In the lens cross-sectional view, the left side is the object side (front), the right side is the image side (rear), and the first lens group L1, the second lens group L2, and the third lens group L3 are arranged in order from the object side to the image side. Has been.

  SP is an aperture stop, and FP is a flare cut stop. IP is the image plane. When the zoom lens of this embodiment is used as a photographing optical system of a digital single-lens reflex camera, the image plane IP corresponds to an imaging plane of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor. When used as a photographing optical system for a silver salt film camera, the image plane IP corresponds to a film plane.

  In the aberration diagrams shown in FIGS. 2, 4, 6, 8, and 10, spherical aberration, astigmatism, distortion, and lateral chromatic aberration of the zoom lens of each example are shown. In the diagram showing spherical aberration, the vertical axis is the F number (Fno). The solid line d represents the d line, and the two-dot chain line g represents the g line. The vertical axis in the diagram representing astigmatism, distortion, and lateral chromatic aberration is the image height (Y). In the diagram showing astigmatism, the broken line ΔM represents the meridional image plane of the d line, and the solid line ΔS represents the sagittal image plane. Distortion is represented by the d-line, and lateral chromatic aberration is represented by the g-line with reference to the imaging position of the d-line.

  The arrows in the lens cross-sectional view indicate the movement trajectory of each lens group (plotting the position of each lens group with respect to the zoom position) when zooming from the wide-angle end to the telephoto end. In the zoom lenses of Examples 1 to 5, the distance between the first lens unit L1 and the second lens unit L2 at the telephoto end is smaller than that at the wide angle end during zooming, and the second lens unit L2 and the third lens unit are reduced. The second lens unit L2 moves toward the object side so that the distance from L3 increases. The first lens unit L1 draws a convex locus on the image side during zooming from the wide-angle end to the telephoto end in order to compensate for fluctuations in the image plane position accompanying the movement of the second lens unit, which is the main variable power group. Moving.

  The third lens unit L3 in Examples 1 to 3 does not move during zooming, whereas the third lens unit L3 in Examples 4 and 5 moves toward the object side during zooming from the wide-angle end to the telephoto end. Moving.

  In addition, the flare cut stop FP of Examples 1 and 2 moves integrally with the second lens unit L2 during zooming. On the other hand, the flare cut stops FP of Examples 3 to 5 are indicated by arrows while zooming from the wide-angle end to the telephoto end while changing the distance from the second lens unit L2 (independent of the second lens unit L2). Move to the object side.

  Focusing is performed by moving the first lens group along the optical axis.

  In the zoom lenses of Examples 1 to 5, the image-side principal point is as close to the image side as possible so that a desired back focus can be secured at the wide-angle end where the back focus (distance from the lens final surface to the Gauss image surface) is the shortest. The refractive power is arranged so as to be positioned. That is, the entire lens system is more of a retrofocus type at the wide angle end.

  Specifically, at the wide-angle end, the second lens unit L2 and the third lens unit L3 having a positive combined refractive power are arranged as far as possible from the first lens unit L1 having a negative refractive power. . At this time, it is possible to appropriately set the refractive power of the second lens unit L2 by providing the third lens unit L3 having a negative refractive power on the image side of the second lens unit L2. As a result, the amount of movement of the second lens unit L2 during zooming is made appropriate to achieve both high optical performance and downsizing.

  On the other hand, at the telephoto end, in order to shorten the total lens length of the entire system, the refractive power is arranged such that the image side principal point is located as close to the object side as possible. That is, a lens arrangement with positive and negative refractive powers is arranged in order from the object side, and the entire lens system is close to a telephoto type.

  Specifically, at the telephoto end, the first lens unit L1 having a negative refractive power and the second lens unit L2 having a positive refractive power are brought close to each other to form a lens unit having a positive combined refractive power, and the second lens unit. The third lens unit L3 is disposed at a position away from L2 toward the image side. Thus, a telephoto type is formed to shorten the optical total length at the telephoto end.

  The second lens unit L2 includes a second A lens unit L2A having a positive refractive power, an aperture stop SP, and a second B lens unit L2B having a positive refractive power. The second lens unit L2 approaches the third lens unit L3 at the wide-angle end, and approaches the first lens unit L1 at the telephoto end. Therefore, the aperture stop SP is disposed inside the second lens unit L2 (between the second A lens unit L2A and the second B lens unit L2B), and the aperture stop SP is used for the first lens unit L1 and the third lens unit L3 during zooming. To avoid interference. Such an efficient spatial arrangement of the aperture stop SP greatly contributes to miniaturization.

  Furthermore, in order to reduce the size while securing the back focus at the wide angle end, it is necessary to appropriately set the refractive power arrangement of each lens group. In particular, as for the refractive power arrangement in the second lens unit L2, it is important to secure the back focus at the wide angle end.

Therefore, the zoom lens of the present invention is
Having three lens groups L1 to L3 having negative, positive, and negative refractive power in order from the object side to the image side;
In zooming, the distance between the first lens unit L1 and the second lens unit L2 is decreased at the telephoto end compared to the wide angle end, and the interval between the second lens unit L2 and the third lens unit L3 is increased.
The second lens unit L2 is composed of, in order from the object side to the image side, a second A lens unit L2A having a positive refractive power, an aperture stop SP, and a second B lens unit L2B having a positive refractive power.
And the refractive power arrangement of each lens group is specified so as to satisfy the following conditional expression.
-1.2 <f2 / f1 <-0.9 (1)
-0.2 <fw / f3 <-0.01 (2)
0.5 <f2A / f2B <1.1 (3)
Here, fw is the focal length of the entire system at the wide-angle end, f1, f2, and f3 are the focal lengths of the first to third lens groups, respectively, and f2A and f2B are the focal points of the second A lens group and the second B lens group, respectively. Distance.

  Conditional expression (1) defines the refractive power arrangement with respect to the ratio of the focal lengths of the first lens unit L1 and the second lens unit L2, thereby balancing back-focusing at the wide-angle end, miniaturization, and high performance. This is a condition for the purpose of illustration.

  If the lower limit of conditional expression (1) is exceeded and the refractive power of the second lens unit L2 becomes too weak compared to the first lens unit L1, it will be difficult to ensure the back focus at the wide angle end. In addition, since the amount of movement of the second lens unit L2 during zooming increases, the total optical length particularly at the telephoto end increases.

  On the other hand, if the upper limit value is exceeded and the refractive power of the second lens unit L2 becomes too strong compared to the first lens unit L1, the spherical aberration correction of the entire second lens unit L2 is insufficient and the spherical surface in the entire zoom range. Aberration is under. Further, this can be dealt with by increasing the number of lenses of the second lens unit L2 in order to correct spherical aberration, but this leads to an increase in the size and cost of the lens system.

  More preferably, the lower limit value of conditional expression (1) is set to −1.1. Moreover, it is desirable to set the upper limit of conditional expression (1) to −0.95.

  Conditional expression (2) relates to the ratio of the focal length of the entire system to the focal length of the third lens group at the wide-angle end in order to reduce the size and improve the performance. As described above, the third lens unit L3 having a negative refractive power contributes to high performance and miniaturization. By satisfying the above-described conditional expression (1) and simultaneously setting the refractive power of the third lens unit L3 so as to satisfy the conditional expression (2) at the same time, both high performance and small size can be achieved.

  If the lower limit of conditional expression (2) is exceeded and the refractive power of the third lens unit L3 becomes too strong, it becomes difficult to ensure sufficient back focus, especially at the wide-angle end, and image plane fluctuations during zooming increase. . Further, if the refractive power of the third lens unit L3 becomes too weak beyond the upper limit value, it becomes difficult to appropriately set the refractive power of the second lens unit L2, and thus the first lens unit L1. As a result, the balance of the refractive power arrangement of the entire lens system is lost, and the lens system is enlarged.

  More preferably, the lower limit value of conditional expression (2) is desirably set to -0.11. In addition, it is desirable that the upper limit value of conditional expression (2) be −0.02.

  Conditional expression (3) relates to the ratio of the focal lengths of the second A lens unit L2A and the second B lens unit L2B, mainly to ensure the back focus at the wide angle end by making the second lens unit L2 have an appropriate refractive power arrangement. This is to achieve both high performance and downsizing.

  If the lower limit of conditional expression (3) is exceeded and the refractive power of the second A lens unit L2A becomes too strong with respect to the second B lens unit L2B, the image-side principal point of the second lens unit L2 is positioned closer to the object side. Will do. As a result, the back focus of the second lens unit L2 is shortened, and as a result, it is difficult to ensure the back focus of the entire system at the wide angle end. If the refractive power of the second A lens unit L2A exceeds the upper limit and becomes too weak with respect to the second B lens unit L2B, the lens diameter of the second B lens unit L2B increases and the spherical aberration particularly at the telephoto end increases. Correction becomes difficult.

  More preferably, the lower limit value of conditional expression (3) is desirably set to 0.54. The upper limit value is desirably 0.90.

  By configuring as described above, the original object of the present invention can be realized. Hereinafter, more preferable conditions for solving various technical problems required for the zoom lens will be described.

  First, it is preferable that the second A lens unit L2A is composed of only a single lens having a positive refractive power (positive lens). If the refractive power arrangement in the second lens unit L2 is appropriately set, the second A lens unit L2A can be configured with only a positive lens in this way, which contributes to downsizing and cost reduction.

  Secondly, it is preferable that the second B lens unit L2B includes a positive lens, a negative lens, and a positive lens in order from the object side to the image side. In this way, by setting the second B lens unit L2B to a triplet configuration, it is possible to particularly favorably correct spherical aberration while the number of lenses is small.

Third, the distance (axial air space) between the second A lens unit L2A and the second B lens unit L2B is D2AB, and the most object side lens surface vertex of the second lens unit L2 is closest to the image side of the second lens unit L2. When the distance to the lens surface vertex is D2,
0.03 <D2AB / D2 <0.3 (4)
It is preferable to satisfy the following conditions.

  Conditional expression (4) relates to the ratio of the axial air space between the second A lens unit L2A and the second B lens unit L2B to the total length (axial thickness) of the second lens unit L2, and particularly considers the arrangement of the aperture stop SP. However, this is to reduce the size.

  If the second A lens unit L2A and the second B lens unit L2B are too close to each other beyond the lower limit value of the conditional expression (4), it is difficult to arrange an opening / closing mechanism for the aperture stop SP. When the upper limit is exceeded, the lens diameter of the second B lens unit L2B increases, and the total lens length at the telephoto end also increases.

  More preferably, it is desirable to set the lower limit of conditional expression (4) to 0.05. Moreover, it is desirable to set the upper limit of conditional expression (4) to 0.15.

Fourth, when the back focus at the wide angle end is bfw,
0.45 <fw / bfw <0.9 (5)
It is preferable to satisfy the following conditions.

  Conditional expression (5) is the ratio of the focal length to the back focus at the wide-angle end, and is intended to achieve a balance between ensuring sufficient back focus and miniaturization.

  When the lower limit of conditional expression (5) is exceeded, the back focus at the wide angle end becomes too short. When the upper limit is exceeded, the optical total length at the wide angle end increases, and the front lens diameter increases.

  Fifth, it is preferable that the first lens unit L1 has a positive lens closest to the object side.

  If sufficient back focus is secured, the total optical length tends to be long, and the front lens diameter tends to increase. In particular, since the off-axis light beam passes away from the optical axis at the wide-angle end, it is difficult to correct negative distortion occurring in the first lens unit L1 having negative refractive power. Therefore, by disposing the positive lens on the most object side of the first lens unit L1, it is possible to correct distortion while ensuring sufficient back focus.

Sixth, when the paraxial lateral magnification of the second lens unit L2 at the wide-angle end is β2w, the paraxial lateral magnification of the second lens unit L2 at the telephoto end is β2t, and the focal length of the entire system at the telephoto end is ft,
0.8 <(β2t · fw) / (β2w · ft) <1.1 (6)
It is preferable to satisfy the following conditions.

  Conditional expression (6) is the ratio between the paraxial lateral magnification of the second lens unit L2 at the wide-angle end and the telephoto end and the focal length at the wide-angle end and the telephoto end, and defines the variable magnification sharing of the second lens unit L2. It is.

  If the variable magnification share of the second lens unit L2 decreases beyond the lower limit of conditional expression (6) and the variable magnification share of the third lens unit L3 increases too much, the third lens unit L3 moves during zooming. The amount increases and the mechanism becomes complicated. On the other hand, if the upper limit is exceeded, the variable power sharing of the second lens unit L2 increases, and it becomes difficult to correct spherical aberration fluctuations associated with zooming.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist.

In the following, numerical examples 1 to 5 corresponding to the first to fifth examples will be described. In each numerical example, i indicates the order of the surface or member from the object side. Ri is a radius of curvature (unit: mm) of the i-th surface (i-th surface), and Di is a distance (unit: mm) between the i-th surface and the (i + 1) -th surface. Ni is a refractive index with respect to the d line of the i-th member. ν i is the Abbe number of the i-th member based on the d-line represented by the following equation.
νi = (Nd−1) / (NF-NC)
Nd: Refractive index for d-line (wavelength 587.6 nm) NF: Refractive index for F-line (wavelength 486.1 nm) NC: Refractive index for C-line (wavelength 656.3 nm) f is focal length (unit: mm), Fno Represents an F number, and ω represents a half angle of view. Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

(Numerical example 1)
f = 18.60-30.92-49.00 Fno = 3.92-4.71-5.88 2ω = 72.6-47.7-31.1
R 1 = 95.000 D 1 = 3.40 N 1 = 1.516330 ν 1 = 64.1
R 2 = 1069.090 D 2 = 0.10
R 3 = 39.878 D 3 = 1.50 N 2 = 1.622992 ν 2 = 58.2
R 4 = 13.955 D 4 = 7.78
R 5 = -560.767 D 5 = 1.20 N 3 = 1.622992 ν 3 = 58.2
R 6 = 21.742 D 6 = 2.49
R 7 = 19.463 D 7 = 3.00 N 4 = 1.805181 ν 4 = 25.4
R 8 = 31.934 D 8 = Variable
R 9 = 36.679 D 9 = 2.30 N 5 = 1.517417 ν 5 = 52.4
R10 = -45.492 D10 = 1.19
R11 = Aperture stop D11 = 0.60
R12 = 17.763 D12 = 2.80 N 6 = 1.517417 ν 6 = 52.4
R13 = -62.193 D13 = 0.41
R14 = -30.185 D14 = 5.26 N 7 = 1.717362 ν 7 = 29.5
R15 = 17.203 D15 = 3.02
R16 = 44.174 D16 = 2.70 N 8 = 1.571351 ν 8 = 53.0
R17 = -19.655 D17 = variable
R18 = ∞ D18 = variable
R19 = -28.420 D19 = 1.00 N 9 = 1.516330 ν 9 = 64.1
R20 = 34.814 D20 = 0.59
R21 = 119.021 D21 = 3.10 N10 = 1.516330 ν10 = 64.1
R22 = -22.847 D22 = 35.1

\ Focal length 18.60 30.92 49.00
Variable interval \
D 8 31.64 12.53 1.89
D17 0.00 0.00 0.00
D18 1.80 11.43 25.57

Zoom lens group data group Start surface Focal length
1 1 -27.39
2 9 26.41
3 19 -246.41

(Numerical example 2)
f = 18.60 to 31.86 to 51.32 Fno = 3.77 to 4.62 to 5.88 2ω = 72.6 to 46.4 to 29.8
R 1 = 180.000 D 1 = 3.00 N 1 = 1.516330 ν 1 = 64.1
R 2 = -500.000 D 2 = 0.10
R 3 = 41.552 D 3 = 1.50 N 2 = 1.622992 ν 2 = 58.2
R 4 = 14.378 D 4 = 7.54
R 5 = 1027.760 D 5 = 1.20 N 3 = 1.603112 ν 3 = 60.6
R 6 = 21.235 D 6 = 2.26
R 7 = 19.209 D 7 = 3.00 N 4 = 1.805181 ν 4 = 25.4
R 8 = 31.407 D 8 = variable
R 9 = 32.355 D 9 = 2.20 N 5 = 1.518229 ν 5 = 58.9
R10 = -51.429 D10 = 0.69
R11 = Aperture D11 = 0.60
R12 = 17.812 D12 = 2.80 N 6 = 1.517417 ν 6 = 52.4
R13 = -105.294 D13 = 0.41
R14 = -36.897 D14 = 5.59 N 7 = 1.717362 ν 7 = 29.5
R15 = 16.832 D15 = 2.75
R16 = 41.934 D16 = 2.70 N 8 = 1.571351 ν 8 = 53.0
R17 = -21.537 D17 = variable
R18 = ∞ D18 = variable
R19 = -25.966 D19 = 1.00 N 9 = 1.712995 ν 9 = 53.9
R20 = 46.725 D20 = 0.59
R21 = 126.642 D21 = 3.10 N10 = 1.712995 ν10 = 53.9
R22 = -22.451 D22 = 34.88

\ Focal length 18.60 31.86 51.32
Variable interval \
D 8 32.34 12.31 1.66
D17 0.00 0.00 0.00
D18 1.80 12.37 27.88

Zoom lens group data group Start surface Focal length
1 1 -28.53
2 9 26.70
3 19 -529.65

(Numerical Example 3)
f = 18.60 to 32.65 to 53.28 Fno = 3.63 to 4.55 to 5.88 2ω = 72.6 to 45.4 to 28.8
R 1 = 70.437 D 1 = 3.70 N 1 = 1.516330 ν 1 = 64.1
R 2 = 444.313 D 2 = 0.10
R 3 = 44.427 D 3 = 1.50 N 2 = 1.696797 ν 2 = 55.5
R 4 = 14.870 D 4 = 8.24
R 5 = -421.388 D 5 = 1.20 N 3 = 1.622992 ν 3 = 58.2
R 6 = 21.911 D 6 = 2.96
R 7 = 20.984 D 7 = 2.90 N 4 = 1.805181 ν 4 = 25.4
R 8 = 35.903 D 8 = Variable
R 9 = 38.649 D 9 = 2.30 N 5 = 1.517417 ν 5 = 52.4
R10 = -55.775 D10 = 0.80
R11 = Aperture D11 = 0.69
R12 = 20.793 D12 = 3.50 N 6 = 1.570989 ν 6 = 50.8
R13 = -83.812 D13 = 0.42
R14 = -33.915 D14 = 7.00 N 7 = 1.717362 ν 7 = 29.5
R15 = 18.467 D15 = 1.17
R16 = 37.923 D16 = 3.40 N 8 = 1.568832 ν 8 = 56.4
R17 = -20.900 D17 = variable
R18 = ∞ D18 = variable
R19 = -29.484 D19 = 1.00 N 9 = 1.603112 ν 9 = 60.6
R20 = 46.223 D20 = 0.50
R21 = 168.825 D21 = 3.10 N10 = 1.622992 ν10 = 58.2
R22 = -25.277 D22 = 35.32

\ Focal length 18.60 32.65 53.28
Variable interval \
D 8 31.45 11.66 1.51
D17 0.00 6.50 16.04
D18 1.80 7.05 14.76

Zoom lens group data group Start surface Focal length
1 1 -26.75
2 9 26.75
3 19 -323.78

(Numerical example 4)
f = 19.60 to 33.98 to 55.08 Fno = 3.66 to 4.53 to 5.88 2ω = 69.8 to 43.8 to 27.9
R 1 = 79.606 D 1 = 3.50 N 1 = 1.516330 ν 1 = 64.1
R 2 = 1027.285 D 2 = 0.10
R 3 = 49.550 D 3 = 1.50 N 2 = 1.696797 ν 2 = 55.5
R 4 = 14.954 D 4 = 7.07
R 5 = 210.970 D 5 = 1.20 N 3 = 1.622992 ν 3 = 58.2
R 6 = 23.077 D 6 = 3.04
R 7 = 20.183 D 7 = 3.40 N 4 = 1.805181 ν 4 = 25.4
R 8 = 30.868 D 8 = variable
R 9 = 31.854 D 9 = 2.30 N 5 = 1.517417 ν 5 = 52.4
R10 = -50.924 D10 = 1.19
R11 = Aperture D11 = 0.60
R12 = 20.126 D12 = 2.90 N 6 = 1.517417 ν 6 = 52.4
R13 = -143.258 D13 = 0.50
R14 = -36.670 D14 = 6.94 N 7 = 1.717362 ν 7 = 29.5
R15 = 17.763 D15 = 2.10
R16 = 35.315 D16 = 2.90 N 8 = 1.571351 ν 8 = 53.0
R17 = -22.103 D17 = variable
R18 = ∞ D18 = variable
R19 = -25.048 D19 = 1.00 N 9 = 1.516330 ν 9 = 64.1
R20 = 37.975 D20 = 0.50
R21 = 122.123 D21 = 3.20 N10 = 1.516330 ν10 = 64.1
R22 = -21.330 D22 = 36.00

\ Focal length 19.60 33.98 55.08
Variable interval \
D 8 33.04 12.29 1.45
D17 0.00 6.09 15.04
D18 1.80 7.00 14.64

Zoom lens group data group Start surface Focal length
1 1 -28.62
2 9 27.48
3 19 -281.72

(Numerical example 5)
f = 19.60 to 34.72 to 57.11 Fno = 3.59 to 4.51 to 5.88 2ω = 69.8 to 43.0 to 26.9
R 1 = 59.605 D 1 = 4.00 N 1 = 1.487490 ν 1 = 70.2
R 2 = 286.120 D 2 = 0.10
R 3 = 47.898 D 3 = 1.50 N 2 = 1.696797 ν 2 = 55.5
R 4 = 15.199 D 4 = 7.37
R 5 = 293.913 D 5 = 1.20 N 3 = 1.622992 ν 3 = 58.2
R 6 = 22.827 D 6 = 3.04
R 7 = 20.502 D 7 = 3.30 N 4 = 1.805181 ν 4 = 25.4
R 8 = 32.048 D 8 = Variable
R 9 = 31.701 D 9 = 2.30 N 5 = 1.517417 ν 5 = 52.4
R10 = -59.397 D10 = 1.19
R11 = Aperture D11 = 0.70
R12 = 20.369 D12 = 2.90 N 6 = 1.517417 ν 6 = 52.4
R13 = -104.067 D13 = 0.50
R14 = -37.823 D14 = 7.39 N 7 = 1.717362 ν 7 = 29.5
R15 = 17.809 D15 = 2.18
R16 = 37.104 D16 = 2.90 N 8 = 1.571351 ν 8 = 53.0
R17 = -22.940 D17 = variable
R18 = ∞ D18 = variable
R19 = -28.827 D19 = 1.00 N 9 = 1.516330 ν 9 = 64.1
R20 = 44.985 D20 = 0.50
R21 = 122.123 D21 = 3.20 N10 = 1.516330 ν10 = 64.1
R22 = -24.409 D22 = 34.99

\ Focal length 19.60 34.72 57.11
Variable interval \
D 8 33.90 12.32 1.35
D17 0.00 6.95 17.15
D18 1.80 5.65 11.29

Zoom lens group data group Start surface Focal length
1 1 -29.67
2 9 28.33
3 19 -426.42

  Next, an embodiment in which the zoom lens of the present invention is applied to an image pickup apparatus will be described with reference to FIG.

  FIG. 11 is a schematic diagram of a main part of a single-lens reflex camera. In FIG. 11, reference numeral 10 denotes a photographing lens having the zoom lens 1 according to any one of Examples 1 to 5. The zoom lens 1 is held by a lens barrel 2 that is a holding member. Reference numeral 20 denotes a camera body. A quick return mirror 3 reflects the light beam from the photographing lens 10 upward. Reference numeral 4 denotes a focusing screen disposed at an image forming position of the photographing lens 10. A penta roof prism 5 converts a reverse image formed on the focusing screen 4 into an erect image. Reference numeral 6 denotes an eyepiece 6 for observing the erect image. The camera body 20 includes the quick return mirror 3, the focusing screen 4, the penta roof prism 5, the eyepiece lens 6, and the like. Reference numeral 7 denotes a photosensitive surface on which a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor or a silver salt film is disposed. At the time of photographing, the quick return mirror 3 is retracted from the optical path, and an image is formed on the photosensitive surface 7 by the photographing lens 10.

  Thus, by applying the zoom lens of the present invention to an interchangeable lens for a single-lens reflex camera or the like, an imaging apparatus having high optical performance can be realized.

  The zoom lens of the present invention can be similarly applied to a single-lens reflex camera without a quick return mirror.

2 is a lens cross-sectional view of a zoom lens of Example 1. FIG. FIG. 6 is an aberration diagram of the zoom lens according to Example 1; 6 is a lens cross-sectional view of a zoom lens according to Example 2. FIG. FIG. 6 is an aberration diagram of the zoom lens according to Example 2; 5 is a lens cross-sectional view of a zoom lens according to Example 3. FIG. FIG. 6 is an aberration diagram of the zoom lens according to Example 3; 6 is a lens cross-sectional view of a zoom lens according to Example 4. FIG. FIG. 6 is an aberration diagram of the zoom lens according to Example 4; 10 is a lens cross-sectional view of a zoom lens according to Example 5. FIG. FIG. 10 is an aberration diagram of the zoom lens according to Example 5; It is the principal part schematic of a single-lens reflex camera.

Explanation of symbols

L1 First lens group L2 Second lens group L3 Third lens group SP Aperture stop FP Flare cut stop IP Image plane

Claims (7)

In order from the object side to the image side, a first lens unit having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power are provided at the telephoto end as compared with the wide-angle end. A zoom lens that performs zooming so that the distance between the first lens group and the second lens group decreases and the distance between the second lens group and the third lens group increases;
The second lens group includes, in order from the object side to the image side, a second A lens group having a positive refractive power, an aperture stop, and a second B lens group having a positive refractive power, and the focal length of the entire system at the wide angle end. Fw, the focal lengths of the first lens group, the second lens group, and the third lens group are f1, f2, and f3, respectively, and the focal lengths of the second A lens group and the second B lens group are f2A and f2B, respectively. ,
-1.2 <f2 / f1 <-0.9
−0.2 <fw / f3 <−0.01
0.5 <f2A / f2B <1.1
A zoom lens characterized by satisfying the following conditions:   The zoom lens according to claim 1, wherein the second A lens group includes one positive lens.   The zoom lens according to claim 1 or 2, wherein the second B lens group includes a positive lens, a negative lens, and a positive lens in order from the object side to the image side. The distance between the second A lens group and the second B lens group is D2AB, and the distance from the most object-side lens surface vertex of the second lens group to the most image-side lens surface vertex of the second lens group is D2. When
0.03 <D2AB / D2 <0.3
The zoom lens according to claim 1, wherein the following condition is satisfied. When the back focus at the wide angle end is bfw,
0.45 <fw / bfw <0.9
The zoom lens according to claim 1, wherein the following condition is satisfied.   The zoom lens according to claim 1, wherein the first lens group includes a positive lens closest to the object side. When the paraxial lateral magnification of the second lens group at the wide angle end is β2w, the paraxial lateral magnification of the second lens group at the telephoto end is β2t, and the focal length of the entire system at the telephoto end is ft,
0.8 <(β2t · fw) / (β2w · ft) <1.1
The zoom lens according to claim 1, wherein the following condition is satisfied.

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