JP6460711B2 - Zoom lens and imaging apparatus having the same - Google Patents

Description

  The present invention relates to a zoom lens and an image pickup apparatus having the same, and is suitable for an image pickup optical system used in an image pickup apparatus such as a digital camera, a video camera, a TV camera, a surveillance camera, and a silver salt film camera.

  An imaging optical system used in an imaging apparatus (camera) is required to be a small zoom lens that includes a wide shooting angle of view and has high resolution. In addition, when used in an imaging apparatus, it is desired that autofocus (automatic focusing) can be performed at high speed and with high accuracy. A phase difference method is often used as an autofocus method when capturing a still image. On the other hand, recent single-lens reflex cameras are required to have a moving image shooting function and to be able to autofocus during moving image shooting.

  As an autofocus method when shooting a moving image, a high-frequency detection method (TV-AF method) is often used in which the in-focus state of the imaging optical system is evaluated by detecting a high-frequency component in the imaging signal. In an image pickup apparatus using the TV-AF method, a focus lens group (a lens group that moves during focusing) is vibrated at high speed in the optical axis direction (hereinafter referred to as “wobbling”) to detect a deviation direction from an in-focus state. .

  Then, after wobbling, a signal component in a specific frequency band of the image region is detected from the output signal of the image sensor, and the optimum position in the optical axis direction of the focus lens group in a focused state is calculated. Thereafter, the focus lens group is moved to the optimum position, and focusing is completed. At the time of moving image shooting, it is necessary to drive the focus lens group at high speed in the optical axis direction in order to shorten the focusing time (focus time). In moving image shooting, it is necessary to drive the focus lens group as quietly as possible so that the motor drive sound is not recorded.

  Therefore, in order to reduce the load on the motor as much as possible, the focus lens group is strongly required to be small and light. The fact that the focus lens group is small and light is the same in an imaging apparatus that uses a phase difference method as an autofocus method. 2. Description of the Related Art Conventionally, a negative lead type zoom lens in which a lens group having a negative refractive power is disposed closest to the object side is known as a zoom lens having a wide angle of view and a small system as a whole. Among negative lead type zoom lenses, zoom lenses in which focusing is performed using a small and lightweight lens group are known (Patent Documents 1 to 3).

  In Patent Documents 1 and 2, the first lens unit to the fourth lens unit having negative, positive, positive, and negative refractive powers are sequentially arranged from the object side, and zooming is performed by changing the interval between adjacent lens units. A zoom lens that performs focusing in groups is disclosed. In Patent Document 3, the first to fifth lens units having negative, positive, positive, negative, and positive refractive powers are sequentially arranged from the object side to the image side, and zooming is performed by changing the interval between adjacent lens units. A zoom lens that performs focusing with two lens groups is disclosed.

JP 08-062499 A JP 2011-107269 A JP 2009-251112 A

  There is a strong demand for zoom lenses used in imaging devices that have a wide angle of view and that the entire lens system is small, that the focus lens group is compact and lightweight, that focusing can be performed at high speed, and that there is little variation in aberrations during focusing. Yes. In order to make the focus lens group small and light, it is necessary to reduce the number of lenses constituting the focus lens group. However, when the number of constituent lenses of the focus lens group is reduced, the residual aberration of the focus lens group increases. For this reason, aberration fluctuations increase during focusing, and it becomes difficult to obtain good optical performance over the entire object distance from a long distance to a short distance.

  On the other hand, if the power of the focus lens group is reduced in order to reduce aberration fluctuations during focusing, the amount of movement during focusing increases, and the total lens length increases. In order to obtain a zoom lens with a compact, wide field angle, high-speed focusing and low aberration fluctuation during focusing, the number of lens groups, the refractive power of each lens group, and the selection of the focus lens group and the lens It is important to set the configuration appropriately. If these settings are not appropriate, it will be difficult to obtain a zoom lens having a small overall system, a wide angle of view, and high optical performance over the entire object distance.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a zoom lens that is small in size and has a wide angle of view, has little aberration fluctuation during zooming, and can obtain high optical performance over the entire object distance.

The zoom lens of the present invention is
A first lens group having a negative refractive power, a second lens group having a positive refractive power including an aperture stop, a third lens group having a positive refractive power, and a negative lens having a negative refractive power, which are arranged in order from the object side to the image side. A zoom lens having a fourth lens group, wherein an interval between adjacent lens groups changes during zooming, and the third lens group moves during focusing;
The third lens group consists of one lens,
When the lateral magnification of the third lens group at the telephoto end is β3t , the focal length of the second lens group is f2, and the focal length of the entire lens system at the telephoto end is ft .
−0.20 <β3t <0.15
0.4 <f2 / ft <0.62
It satisfies the following conditional expression.

In addition, the zoom lens according to the present invention includes a first lens group having a negative refractive power, a second lens group having a positive refractive power including an aperture stop, and a first lens having a positive refractive power, which are arranged in order from the object side to the image side. A third lens group, a fourth lens group having a negative refractive power, and during zooming at infinity , the distance between the first lens group and the second lens group, and the third lens group and the fourth lens The distance between the groups changes, and the third lens group moves during focusing, whereby the distance between the second lens group and the third lens group and the distance between the third lens group and the fourth lens group change . A zoom lens,
When the lateral magnification of the third lens group at the telephoto end is β3t,
−0.20 <β3t <0.15
It satisfies the following conditional expression.

  According to the present invention, it is possible to obtain a zoom lens that is small in size and has a wide angle of view, has little aberration fluctuation during zooming, and can obtain high optical performance over the entire object distance.

Lens sectional view of Example 1 Optical path diagram of part of FIG. (A), (B), (C) Aberration diagrams when focusing on infinity in Example 1 (A), (B), (C) Aberration diagram when focusing on a short distance in Example 1 Lens sectional view of Example 2 (A), (B), (C) Aberration diagrams when focusing on infinity in Example 2 (A), (B), (C) Aberration diagrams when focusing on a short distance in Example 2 Lens sectional view of Example 3 (A), (B), (C) Aberration diagrams when focusing on infinity in Example 3 (A), (B), (C) Aberration diagram when focusing on a short distance in Example 3 Lens cross section of Reference Example 1 (A), (B), (C) Aberration diagrams when focusing on infinity in Reference Example 1 (A), (B), (C) Aberration diagrams when focusing on a short distance in Reference Example 1 Schematic diagram of the main part of the imaging device

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The zoom lens of the present invention includes a first lens group having a negative refractive power, a second lens group having a positive refractive power including an aperture stop, and a third lens having a positive refractive power, which are arranged in order from the object side to the image side. And a fourth lens unit having a negative refractive power. The distance between adjacent lens units changes during zooming. The third lens group moves during focusing. In addition, the zoom lens according to the present invention includes a first lens group having a negative refractive power, a second lens group having a positive refractive power including an aperture stop, and a first lens having a positive refractive power, which are arranged in order from the object side to the image side. It has three lens groups and a fourth lens group with negative refractive power.

During zooming at infinity, the distance between the first lens group and the second lens group and the distance between the third lens group and the fourth lens group change. As the third lens group moves during focusing, the distance between the second lens group and the third lens group and the distance between the third lens group and the fourth lens group change . Here, the lens group is a lens element that moves integrally during zooming or focusing, and may have at least one lens, and does not necessarily have to have a plurality of lenses. A partial group having one or more lenses separated by a change in the lens interval in the optical axis direction.

  FIG. 1 is a lens cross-sectional view at the wide angle end according to Embodiment 1 of the present invention. FIG. 2 is a lens cross-sectional view at the telephoto end when focusing on infinity in a part of FIG. 3A, 3B, and 3C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end when focusing on infinity according to the first embodiment. 4A, 4 </ b> B, and 4 </ b> C are the wide-angle end (imaging lateral magnification −0.10 ×), the intermediate zoom position (imaging lateral magnification −0.17 ×), and the telephoto end of the first embodiment. It is an aberration diagram in (imaging lateral magnification -0.32 times).

  FIG. 5 is a lens cross-sectional view at the wide angle end according to Embodiment 2 of the present invention. 6A, 6B, and 6C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end when focusing on infinity according to the second embodiment. 7A, 7B, and 7C show the wide angle end (imaging lateral magnification -0.10 times), the intermediate zoom position (imaging lateral magnification -0.17 times), and the telephoto end of the second embodiment. It is an aberration diagram in (imaging lateral magnification -0.32 times).

  FIG. 8 is a lens cross-sectional view at the wide-angle end according to Embodiment 3 of the present invention. 9A, 9B, and 9C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end when focusing on infinity according to the third embodiment. 10A, 10B, and 10C show the wide angle end (imaging lateral magnification -0.10 times), the intermediate zoom position (imaging lateral magnification -0.17 times), and the telephoto end of the third embodiment. It is an aberration diagram in (imaging lateral magnification -0.32 times).

FIG. 11 is a lens cross-sectional view at the wide-angle end of Reference Example 1 of the present invention. 12A, 12B, and 12C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end when focusing on infinity according to Reference Example 1. FIG. 13A, 13B, and 13C show the wide angle end (imaging lateral magnification -0.10 times), the intermediate zoom position (imaging lateral magnification -0.17 times), and the telephoto end of Reference Example 1. FIG. 6 is an aberration diagram at (imaging lateral magnification−0.32 times). FIG. 14 is a schematic diagram of a main part of the imaging apparatus of the present invention.

  The zoom lens of each embodiment is an imaging optical system used in an imaging apparatus such as a video camera, a digital camera, or a silver salt film camera. In the lens cross-sectional view, the left side is the object side (front), and the right side is the image side (rear). The zoom lens of each embodiment may be used for a projector. In this case, the left side is the screen side and the right side is the projected image side.

  In the lens cross-sectional view, OL is a zoom lens. i indicates the order of the lens groups from the object side, and Li is the i-th lens group. SP is an aperture stop. IP is an image plane. When used as an imaging optical system for a video camera or a digital still camera, the imaging surface of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor is used for a silver salt film camera. Corresponds to the film surface.

  In the lens cross-sectional view, solid arrows indicate the movement trajectory of each lens unit during zooming from the wide-angle end to the telephoto end when focused at infinity. The dotted arrow indicates the movement locus of the third lens unit L3 during zooming from the wide-angle end to the telephoto end when focusing on a short distance. The arrow related to the focus indicates the moving direction during focusing from infinity to a short distance.

The zoom lens OL of Example 1 in FIG. 1 and Example 2 in FIG. 5 is arranged in order from the object side to the image side, and has a first lens unit L1 having a negative refractive power and a second lens unit L2 having a positive refractive power. The third lens unit L3 has a positive refractive power, and the fourth lens unit L4 has a negative refractive power. During zooming from the wide-angle end to the telephoto end, the first lens unit L1 moves along a convex locus toward the image side, and the second lens unit L2, the third lens unit L3, and the fourth lens unit L4 are different from each other toward the object side. Move along the trajectory. The third lens unit L3 is a focus lens unit that moves toward the object side along the optical axis during focusing from infinity to a short distance.

The zoom lens OL of Example 3 in FIG. 8 is arranged in order from the object side to the image side, the first lens unit L1 having a negative refractive power, the second lens unit L2 having a positive refractive power, and the first lens unit having a positive refractive power. The third lens unit L3 includes a fourth lens unit L4 having a negative refractive power and a fifth lens unit L5 having a positive refractive power. During zooming from the wide-angle end to the telephoto end, the first lens unit L1 moves along a locus convex toward the image side, and the second lens unit L2 to the fourth lens unit L4 move toward the object side along different tracks. The fifth lens unit L5 is stationary. The third lens unit L3 is a focus lens unit that moves toward the object side along the optical axis during focusing from infinity to a short distance.

  The zoom lens OL of Reference Example 1 in FIG. 11 is arranged in order from the object side to the image side, the first lens unit L1 having a negative refractive power, the second lens unit L2 having a positive refractive power, and the first lens unit having a positive refractive power. The third lens unit L3 includes a fourth lens unit L4 having a negative refractive power. When focusing at infinity, during zooming from the wide-angle end to the telephoto end, the first lens unit L1 moves along a convex locus toward the image side, and the second lens unit L2 and the third lens unit L3 are integrated. To the object side (with the same trajectory). The fourth lens unit L4 moves to the object side along a different locus from the other lens units.

  When focusing on a short distance, the second lens unit L2 and the third lens unit L3 move to the object side along different paths during zooming from the wide-angle end to the telephoto end. The third lens unit L3 is a focus lens unit that moves toward the object side along the optical axis during focusing from infinity to a short distance.

  Among the aberration diagrams, in the spherical aberration diagram, d is d-line and g is g-line. In the astigmatism diagram, M is a meridional image plane at the d-line, and S is a sagittal image plane at the d-line. Moreover, the figure which shows distortion has shown the distortion in d line | wire. The lateral chromatic aberration is shown for the g-line. Fno is the F number, and ω is the half angle of view. In the following embodiments, the wide-angle end and the telephoto end refer to zoom positions when the zoom lens unit is positioned at both ends of a range in which the mechanism can move on the optical axis.

  If the number of lenses constituting the focus lens group is reduced in order to reduce the size of the entire zoom lens system, the residual aberration in the focus lens group increases, and the aberration fluctuation increases during focusing. Further, if the refractive power of the focus lens group is reduced in order to reduce aberration fluctuations during focusing, the amount of movement during focusing increases, and the overall lens length of the zoom lens increases. Therefore, in order to reduce the size of the entire zoom lens system and reduce aberration fluctuations during focusing, it is important to have a lens configuration that can reduce the residual aberration of the focus lens group while sufficiently strengthening the refractive power of the focus lens group. It is.

  In general, in order to reduce aberration fluctuations during focusing, it is important to reduce changes in the incident height h of the on-axis ray and the incident height ha of the off-axis principal ray during focusing.

  The zoom lens according to the present invention includes, in order from the object side to the image side, a first lens unit L1 having a negative refractive power, a second lens unit L2 having a positive refractive power including an aperture stop SP, and a third lens unit having a positive refractive power. L3 has a fourth lens unit L4 having a negative refractive power. The third lens unit L3 is a focus lens unit. The light beam diverged by the first lens unit L1 having a negative refractive power is converged by the second lens unit L2 having a positive refractive power, and the light beam incident on the third lens unit L3 is substantially afocal at the telephoto end.

  As a result, the change in the incident height h of the on-axis light beam during focusing is reduced, and fluctuations in spherical aberration are reduced particularly during focusing at the telephoto end. Further, the third lens unit L3 is disposed relatively near the aperture stop SP. As a result, the incident height ha of the off-axis chief ray to the third lens unit L3 is reduced to reduce the variation in field curvature at the wide angle end during focusing.

  FIG. 2 is an optical path diagram at the telephoto end in the vicinity of the third lens unit L3 of the zoom lens according to the present invention. As shown in FIG. 2, in the zoom lens of the present invention, the axial light beam incident on the third lens unit L3 becomes afocal, and the incident height of the axial principal ray is reduced while reducing the change in the incident height h of the axial light beam during focusing. It turns out that ha is made small.

The focus sensitivity is defined as a ratio Δxp / Δxf of the paraxial image plane movement amount Δxp when the focus lens group is driven by a minute amount Δxf in the optical axis direction. The focus sensitivity is obtained by using the lateral magnification βf of the focus lens group and the combined lateral magnification βR of the lens group existing on the image side of the focus lens group.
Δxp / Δxf = (βf ² −1) × βR ²
Can be expressed as If the focus sensitivity is not sufficiently increased, the amount of movement of the focus lens group during focusing becomes too large, and the entire lens system becomes large.

  Making the light beam incident on the third lens unit L3 afocal means that the lateral magnification of the third lens unit L3 is substantially zero. Then, it can be seen from the above formula that it is important to increase the combined lateral magnification of the lens group existing on the image side of the focus lens group in order to sufficiently increase the focus sensitivity.

In the zoom lens of the present invention, the fourth lens unit L4 having a negative refractive power is arranged on the image side of the focus lens unit, thereby increasing the focus sensitivity and reducing the amount of movement of the focus lens unit during focusing. The entire system is downsized. Specifically, the first lens unit L1 having a negative refractive power, the second lens unit L2 having a positive refractive power including the aperture stop SP, and the third lens having a positive refractive power, which are arranged in order from the object side to the image side. The lens unit L3 includes a fourth lens unit L4 having a negative refractive power. The distance between adjacent lens units changes during zooming. Then, the third lens unit L3 moves during focusing.

Alternatively, in Reference Example 1, the first lens unit having a negative refractive power, the second lens unit L2 having a positive refractive power including the aperture stop SP, and the first lens unit having a positive refractive power, which are arranged in order from the object side to the image side. 3 lens group L3 and 4th lens group L4 of negative refractive power. During zooming at infinity, the distance between the first lens group L1 and the second lens group L2 and the distance between the third lens group L3 and the fourth lens group L4 change. When the third lens unit L3 moves during focusing, the interval between the second lens unit L2 and the third lens unit L3 and the interval between the third lens unit L3 and the fourth lens unit L4 change.

As described above, the zoom lens of the present invention is a so-called negative lead type zoom type in which the first lens unit L1 having negative refractive power is disposed on the object side, thereby ensuring a long back focus at the wide angle end. . The third lens group moves during focusing. By using the lens group in the vicinity of the aperture stop as the focus lens group, the effective diameter of the focus lens group is reduced. Then, the lateral magnification of the third lens unit L3 at the telephoto end is β3t. At this time,
−0.20 <β3t <0.15 (1)
The following conditional expression is satisfied.

  Next, the technical meaning of conditional expression (1) will be described. Conditional expression (1) defines the lateral magnification of the third lens unit L3 at the telephoto end. By making the light beam incident on the third lens unit L3 substantially afocal at the telephoto end, a change in the incident height h of the axial ray incident on the third lens unit L3 during focusing is reduced. This reduces the variation of spherical aberration during focusing at the telephoto end.

  When the upper limit of conditional expression (1) is exceeded, the incident height h of the axial ray on the third lens unit L3 changes in the direction of increasing when focusing on a short distance at the telephoto end, and the spherical aberration increases greatly on the under side. It becomes. On the other hand, when the value is below the lower limit, the spherical aberration increases on the over side.

  As described above, according to the present invention, the focusing lens group is small and light, achieves good optical performance over the entire object distance from a long distance to a short distance, and a small zoom lens can be obtained. In addition, in the present invention, it is more preferable that at least one of the following conditional expressions is satisfied.

  The focal length of the third lens unit L3 is f3, and the focal length of the entire lens system at the wide angle end is fw. Let the focal length of the fourth lens unit L4 be f4. The focal length of the second lens unit L2 is f2, and the focal length of the entire lens system at the telephoto end is ft. The lateral magnification of the fourth lens unit L4 at the telephoto end is β4t. The interval on the optical axis from the aperture stop SP at the wide-angle end to the object-side lens surface apex position of the most object-side lens in the third lens unit L3 is denoted by Lpfw. The air space between the first lens unit L1 and the second lens unit L2 at the wide angle end is D1w, and the air space between the first lens unit L1 and the second lens unit L2 at the telephoto end is D1t.

  During zooming, the distance between the second lens unit L2 and the third lens unit L3 changes. The air space between the second lens unit L2 and the third lens unit L3 at the wide-angle end when focused to infinity is D2w. Let D2t be the air space between the second lens unit L2 and the third lens unit L3 at the telephoto end when focused to infinity. The air gap between the third lens unit L3 and the fourth lens unit L4 at the wide-angle end when focused at infinity is D3w, and the third lens unit L3 and the fourth lens unit L4 at the telephoto end when focused at infinity. Is set to D3t. At this time, one or more of the following conditional expressions should be satisfied.

1.0 <f3 / fw <2.2 (2)
−1.8 <f4 / fw <−1.4 (3)
0.4 <f2 / ft < 0.62 (4)
1.5 <β4t <4.0 (5)
0.2 <Lpfw / fw <0.8 (6)
D1w> D1t (7)
D2w <D2t (8)
D3w <D3t (9)

  Next, the technical meaning of each conditional expression described above will be described. Conditional expression (2) defines the focal length of the third lens unit L3. When the upper limit of conditional expression (2) is exceeded and the positive power of the third lens unit L3 becomes weak, the amount of movement during focusing increases and the total lens length increases. Below the lower limit, the residual aberration of the third lens unit L3 becomes too large, and aberration fluctuations during focusing increase.

  Conditional expression (3) defines the focal length of the fourth lens unit L4. If the upper limit of conditional expression (3) is exceeded and the negative power of the fourth lens unit L4 becomes too strong, the so-called telephoto power arrangement becomes so strong that it is difficult to ensure a sufficiently long back focus. Below the lower limit, it becomes easy to ensure a sufficiently long back focus, but the total lens length increases.

  Conditional expression (4) defines the focal length of the second lens unit L2. If the upper limit of conditional expression (2) is exceeded and the positive power of the second lens unit L2 becomes too weak, the amount of movement of the second lens unit L2 for zooming increases, and the entire system increases in size. If the value is below the lower limit and the positive power of the second lens unit L2 becomes too strong, spherical aberration increases at the telephoto end, and it becomes difficult to correct spherical aberration.

  Conditional expression (5) defines the lateral magnification of the fourth lens unit L4 at the telephoto end. If the upper limit of conditional expression (5) is exceeded, the focus sensitivity becomes too high, and the drive control of the third lens unit L3 during focusing becomes difficult. Below the lower limit, the focus sensitivity becomes too low, the amount of movement of the third lens unit L3 increases during focusing, and the total lens length increases.

  Conditional expression (6) defines the distance on the optical axis from the aperture stop SP at the wide-angle end to the object-side lens surface vertex position of the most object-side lens in the third lens unit L3. By disposing the aperture stop SP and the third lens unit L3 relatively close to each other in the optical axis direction, the incident height ha of the off-axis principal ray incident on the third lens unit L3 is reduced, and focusing is performed at the wide angle end. The variation in curvature of field is reduced.

  When the upper limit of conditional expression (6) is exceeded, the variation in field curvature increases during focusing at the wide-angle end. Below the lower limit of conditional expression (6), the aperture stop SP and the third lens unit L3 are too close to each other so that the aperture stop SP is positioned close to the rear of the second lens unit L2, and the entrance pupil position is the front. Get far from the ball. As a result, the effective diameter of the front lens increases. Furthermore, the number of constituent lenses of the second lens unit L2 must be reduced, and the variation of spherical aberration and field curvature increases during zooming.

  Conditional expression (7), conditional expression (8), and conditional expression (9) define the movement of each lens group during zooming. Conditional expression (7) indicates that the zooming from the wide-angle end to the telephoto end reduces the air distance between the first lens unit L1 and the second lens unit L2, thereby providing a retrofocus type power arrangement at the wide-angle end and a telephoto type power arrangement at the telephoto end. Making it easy to do.

  Conditional expression (8) reduces the total lens length by reducing the thickness of the subsequent lens group by widening the air gap between the second lens unit L2 and the third lens unit L3 during zooming from the wide-angle end to the telephoto end. It is easy to reduce the effective diameter of the ball and the effective diameter of the rear ball.

  In the zoom lens of the present invention, since the lateral magnification of the third lens unit L3 for focusing satisfies the conditional expression (1), the focus sensitivity becomes a positive value. That is, the third lens unit L3 extends to the object side during focusing to the short distance side. On the telephoto side, the payout amount due to focusing of the third lens unit L3 becomes large. Therefore, it is necessary to secure in advance an extension interval on the object side of the third lens unit L3. On the other hand, at the wide angle end, the amount of extension by focusing of the third lens unit L3 is smaller than at the telephoto end.

  Conditional expression (8) further increases the distance between the second lens unit L2 and the third lens unit L3 during zooming from the wide-angle end to the telephoto end, and ensures a sufficient movement space for the third lens unit L3. The overall length is shortened. In the zoom lens of the present invention, the distance between the second lens unit L2 and the third lens unit L3 may be constant during zooming. According to this, it becomes easy to simplify the drive control of the mechanical mechanism or the lens group.

  In this case, since it is necessary to secure a space for focusing in advance on the object side of the third lens unit L3 at the wide-angle end, the total lens length tends to increase somewhat, but the mechanical mechanism or driving control of the lens unit is simple. There are also advantages. For this reason, it is sufficient to freely select whether the distance between the second lens unit L2 and the third lens unit L3 is changed or constant during zooming, and the effect of the present invention can be obtained in any case.

  Conditional expression (9) is such that the distance between the third lens unit L3 and the fourth lens unit L4 is widened during zooming from the wide-angle end to the telephoto end, and the amount of movement of each lens unit is reduced during zooming. The mechanical mechanism is easily simplified while downsizing.

  In the zoom lens of the present invention, the zooming effect is obtained by widening the distance between the third lens unit L3 and the fourth lens unit L4 during zooming from the wide-angle end to the telephoto end. As a result, the movement amount during zooming of the second lens unit L2 is reduced, and the overall length of the lens is shortened. More preferably, the numerical ranges of the conditional expressions (1) to (6) are set as follows.

−0.17 <β3t <0.11 (1a)
1.1 <f3 / fw <2.0 (2a)
-1.7 <f4 / fw <-1.5 (3a)
0.55 <f2 / ft <0.62 (4a)
2.5 <β4t <3.0 (5a)
0.35 <Lpfw / fw <0.70 (6a)

  The third lens unit L3 is preferably composed of a single lens in order to reduce the size and weight. In the case of a single lens, it is preferable to use a low dispersion glass material. This facilitates correction of chromatic aberration. In particular, it becomes easy to reduce the variation of axial chromatic aberration during focusing at the telephoto end.

  In the zoom lens of the present invention, a part of the lens portion may be driven to have a component in a direction perpendicular to the optical axis direction at the time of image blur. According to this, image blur due to camera shake can be reduced. For example, a lens or a lens portion having a positive refractive power may be disposed on the most image surface side of the second lens unit L2, and this may be driven so as to have a component perpendicular to the optical axis direction. A fifth lens unit L5 having positive refractive power that does not move during zooming may be disposed on the image plane side of the fourth lens unit L4. If the fifth lens unit L5 having a positive refractive power is disposed near the image plane, it becomes easy to obtain good telecentricity.

  The preferred embodiments of the zoom lens according to the present invention have been described above. However, it goes without saying that the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist of the present invention.

  Next, an embodiment of a digital still camera using the zoom lens shown in each embodiment as a photographing optical system will be described with reference to FIG.

In FIG. 14, reference numeral 20 denotes a camera body, and reference numeral 21 denotes a photographing optical system formed by any one of the zoom lenses described in the first to third embodiments and the reference example 1 . Reference numeral 22 denotes a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor that receives a subject image formed by the photographing optical system 21 and is built in the camera body. A memory 23 records information corresponding to a subject image photoelectrically converted by the solid-state imaging device 22. Reference numeral 24 denotes a finder for observing a subject image formed on the solid-state image sensor 22, which includes a liquid crystal display panel or the like.

  In this way, by applying the zoom lens of the present invention to an image pickup apparatus such as a digital still camera, a small image pickup apparatus having high optical performance can be realized. The zoom lens of each embodiment can be similarly applied to a single-lens reflex camera with a quick return mirror and a mirrorless single-lens reflex camera without a quick return mirror.

Numerical examples 1 to 4 corresponding to Examples 1 to 3 and Reference Example 1 are shown below. In each numerical example, i indicates the order of the surfaces from the object side. In numerical examples, ri is the radius of curvature of the i-th lens surface in order from the object side, di is the i-th lens thickness and air spacing in order from the object side, and ndi and νdi are the i-th lens in order from the object side. The refractive index and Abbe number of the material. BF is a back focus. The aspherical shape is an X axis in the optical axis direction, an H axis in the direction perpendicular to the optical axis, a positive light traveling direction, R is a paraxial radius of curvature, and K, A2, A4, A6, A8, and A10 are aspherical surfaces. When the coefficient

Shall be given in In each aspheric coefficient, “e−x” means “10 ^−x ” . In addition to the specifications such as focal length and F number, the half angle of view and image height of the entire system are the maximum image height that determines the half angle of view, and the total lens length is the distance from the first lens surface to the image surface. The back focus BF indicates the length from the final lens surface to the image plane. Each lens group data indicates the focal length of each lens group.

  Further, the portion where the interval d between the optical surfaces is (variable) changes during zooming, and the surface interval corresponding to the focal length is shown in the separate table. Table 1 shows the calculation results of the conditional expressions based on the lens data of Numerical Examples 1 to 4 described below.

[Numerical Example 1]
Surface number rd nd νd
1 * 30.624 1.25 1.76802 49.2
2 * 12.896 7.33
3 -32.586 0.65 1.49700 81.5
4 70.270 0.10
5 26.340 1.79 2.00069 25.5
6 42.521 (variable)
7 * 13.152 2.90 1.55332 71.7
8 * -653.400 2.12
9 (Aperture) ∞ 1.16
10 13.915 2.43 1.49700 81.5
11 322.913 0.60 1.88300 40.8
12 10.988 2.15
13 52.157 2.07 1.59522 67.7
14 -51.384 (variable)
15 15.778 2.28 1.59522 67.7
16 -117.353 (variable)
17 50.869 0.80 1.69680 55.5
18 12.337 1.73
19 * -794.677 1.83 1.58313 59.4
20 * -84.232 (variable)
Image plane ∞

Aspheric data 1st surface
K = 0.00000e + 000 A 4 = 9.40841e-006 A 6 = -3.66132e-008
A 8 = 6.24277e-010 A10 = -1.39949e-012

Second side
K = 0.00000e + 000 A 4 = -2.63295e-007 A 6 = -3.24843e-008
A 8 = -1.19423e-010 A10 = 8.73890e-012

7th page
K = 0.00000e + 000 A 4 = -3.41505e-005 A 6 = 9.61114e-008
A 8 = -5.00420e-009 A10 = 2.36398e-011

8th page
K = 0.00000e + 000 A 4 = 8.38364e-006 A 6 = 1.97674e-007
A 8 = -5.61793e-009 A10 = 3.69708e-011

19th page
K = 0.00000e + 000 A 4 = -9.13968e-005 A 6 = -3.52552e-007
A 8 = -3.04020e-009

20th page
K = 0.00000e + 000 A 4 = -8.15521e-005 A 6 = -4.71310e-007
A 8 = 7.52139e-009 A10 = -1.55702e-010

Various data Zoom ratio 2.88
Wide angle Medium Telephoto focal length 18.54 31.00 53.39
F number 3.63 4.49 5.82
Half angle of view (degrees) 36.38 23.78 14.35
Image height 13.66 13.66 13.66
Total lens length 86.52 82.19 84.35
BF 24.08 31.18 41.73

d 6 26.70 11.63 0.99
d14 3.54 5.22 3.65
d16 1.00 2.97 6.79
d20 24.08 31.18 41.73

Lens group data group Start surface Focal length
1 1 -23.20
2 7 30.07
3 15 23.52
4 17 -28.19

[Numerical Example 2]
Surface number rd nd νd
1 27.507 1.25 1.76802 49.2
2 12.450 6.87
3 -61.633 0.65 1.72916 54.7
4 30.244 0.10
5 21.311 2.18 2.00069 25.5
6 43.033 (variable)
7 * 13.111 2.72 1.55332 71.7
8 * -290.652 1.53
9 (Aperture) ∞ 1.00
10 11.674 2.80 1.49700 81.5
11 637.243 0.60 1.88300 40.8
12 10.051 1.96
13 53.717 1.52 1.61800 63.3
14 -52.494 (variable)
15 14.957 2.39 1.59282 68.6
16 -50.234 (variable)
17 -65.433 0.80 1.56883 56.4
18 11.712 2.78
19 * 79.380 2.18 1.58313 59.4
20 * -62.976 (variable)
Image plane ∞

Aspheric data 7th surface
K = 0.00000e + 000 A 4 = -2.29386e-005 A 6 = 7.67504e-007
A 8 = -3.41235e-008 A10 = 6.67636e-010

8th page
K = 0.00000e + 000 A 4 = 2.14107e-005 A 6 = 1.04794e-006
A 8 = -4.24140e-008 A10 = 8.33935e-010

19th page
K = 0.00000e + 000 A 4 = -4.34796e-005 A 6 = 5.93950e-007
A 8 = -2.17013e-008

20th page
K = 0.00000e + 000 A 4 = -5.19428e-005 A 6 = 1.22451e-007
A 8 = -7.99030e-009 A10 = -1.82406e-010

Various data Zoom ratio 2.94
Wide angle Medium telephoto focal length 16.00 27.43 47.04
F number 3.62 4.50 5.82
Half angle of view (degrees) 37.55 26.47 16.19
Image height 12.30 13.66 13.66
Total lens length 78.86 74.05 77.88
BF 20.48 27.14 37.06

d 6 24.67 10.29 1.00
d14 1.38 2.64 2.92
d16 1.00 2.66 5.58
d20 20.48 27.14 37.06

Lens group data group Start surface Focal length
1 1 -21.02
2 7 27.61
3 15 19.71
4 17 -26.65

[Numerical Example 3]
Surface number rd nd νd
1 44.257 1.50 1.62041 60.3
2 15.312 3.73
3 21.211 2.00 1.52996 55.8
4 * 18.344 6.13
5 -68.793 1.25 1.62041 60.3
6 45.616 0.20
7 24.184 2.33 1.84666 23.9
8 38.930 (variable)
9 * 11.420 2.45 1.55332 71.7
10 * -511.524 1.34
11 19.131 3.29 1.74924 28.0
12 9.340 3.91
13 (Aperture) ∞ 2.50
14 93.486 1.75 1.48749 70.2
15 -42.606 (variable)
16 16.941 2.00 1.48749 70.2
17 -166.886 (variable)
18 28.743 0.80 1.77388 43.3
19 14.239 0.69
20 24.198 1.26 1.81678 45.5
21 17.727 (variable)
22 71.697 3.87 1.51633 64.1
23 -49.145 15.40
Image plane ∞

Aspheric data 4th surface
K = 0.00000e + 000 A 4 = -1.09119e-005 A 6 = -1.04581e-007
A 8 = 2.12900e-010 A10 = -1.67874e-012

9th page
K = 0.00000e + 000 A 4 = -4.89644e-005 A 6 = 2.13576e-007
A 8 = -2.94615e-008 A10 = 5.58214e-010

10th page
K = 0.00000e + 000 A 4 = 2.56643e-005 A 6 = 2.31695e-007
A 8 = -2.15460e-008 A10 = 5.09832e-010

Various data Zoom ratio 2.88
Wide angle Medium Telephoto focal length 16.54 27.00 47.59
F number 3.45 4.19 5.82
Half angle of view (degrees) 39.55 26.84 16.01
Image height 13.66 13.66 13.66
Total lens length 90.00 84.65 95.00
BF 15.40 15.40 15.40

d 8 24.93 10.08 0.80
d15 2.28 3.04 4.36
d17 1.05 4.45 8.36
d21 5.33 10.68 25.06

Lens group data group Start surface Focal length
1 1 -23.67
2 9 28.41
3 16 31.66
4 18 -25.69
5 22 57.10

[Numerical Example 4]
Surface number rd nd νd
1 25.646 1.25 1.76802 49.2
2 11.934 7.03
3 -63.767 0.65 1.72916 54.7
4 28.511 0.10
5 20.820 2.15 2.00069 25.5
6 41.230 (variable)
7 * 15.304 2.61 1.55332 71.7
8 * -167.161 2.46
9 (Aperture) ∞ 0.99
10 11.648 2.93 1.49700 81.5
11 7509.160 0.60 1.88300 40.8
12 10.823 2.01
13 63.521 1.54 1.61800 63.3
14 -50.310 (variable)
15 15.891 2.63 1.59282 68.6
16 -36.184 (variable)
17 -67.202 0.80 1.56883 56.4
18 15.317 1.41
19 * -52.542 1.68 1.58313 59.4
20 * -39.403 (variable)
Image plane ∞

Aspheric data 7th surface
K = 0.00000e + 000 A 4 = -9.03442e-006 A 6 = 1.45626e-006
A 8 = -4.99663e-008 A10 = 9.77850e-010

8th page
K = 0.00000e + 000 A 4 = 2.24761e-005 A 6 = 1.76409e-006
A 8 = -6.04737e-008 A10 = 1.18499e-009

19th page
K = 0.00000e + 000 A 4 = -1.10966e-005 A 6 = 2.04795e-006
A 8 = 5.29592e-009

20th page
K = 0.00000e + 000 A 4 = 2.48803e-005 A 6 = 1.87886e-006
A 8 = 5.70572e-009 A10 = 4.55614e-011

Various data Zoom ratio 2.94

Focal length 16.00 27.25 47.04
F number 3.64 4.51 5.82
Half angle of view (degrees) 37.55 26.62 16.19
Image height 12.30 13.66 13.66
Total lens length 81.22 76.63 80.74
BF 22.01 29.99 40.64

d 6 24.66 10.64 1.24
d14 2.72 2.72 2.72
d16 1.00 2.45 5.29
d20 22.01 29.99 40.64

Lens group data group Start surface Focal length
1 1 -20.25
2 7 29.06
3 15 18.98
4 17 -24.45

L1 1st lens group L2 2nd lens group L3 3rd lens group L4 4th lens group L5 5th lens group

Claims (10)

A first lens group having a negative refractive power, a second lens group having a positive refractive power including an aperture stop, a third lens group having a positive refractive power, and a negative lens having a negative refractive power, which are arranged in order from the object side to the image side. A zoom lens having a fourth lens group, wherein an interval between adjacent lens groups changes during zooming, and the third lens group moves during focusing;
The third lens group consists of one lens,
When the lateral magnification of the third lens group at the telephoto end is β3t , the focal length of the second lens group is f2, and the focal length of the entire lens system at the telephoto end is ft .
−0.20 <β3t <0.15
0.4 <f2 / ft <0.62
A zoom lens satisfying the following conditional expression: The air gap between the second lens group and the third lens group at the wide-angle end when focused at infinity is D2w, and the second lens group and the third lens group at the telephoto end when focused at infinity. When the air interval is D2t,
D2w <D2t
The zoom lens according to claim 1, wherein the following conditional expression is satisfied.   3. The zoom lens according to claim 1, further comprising a fifth lens unit having a positive refractive power that does not move during zooming on an image side of the fourth lens unit. When the focal length of the third lens group is f3 and the focal length of the entire lens system at the wide angle end is fw,
1.0 <f3 / fw <2.2
The zoom lens according to any one of claims 1 to 3, characterized by satisfying the conditional expression. When the focal length of the fourth lens group is f4 and the focal length of the entire lens system at the wide angle end is fw,
−1.8 <f4 / fw <−1.4
The zoom lens according to any one of claims 1 to 4, characterized by satisfying the conditional expression. When the lateral magnification of the fourth lens group at the telephoto end is β4t,
1.5 <β4t <4.0
The zoom lens according to any one of claims 1 to 5, characterized by satisfying the conditional expression. When the interval on the optical axis from the aperture stop at the wide angle end to the object-side lens surface vertex position of the lens closest to the object side in the third lens group is Lpfw,
0.2 <Lpfw / fw <0.8
The zoom lens according to any one of claims 1 to 6, characterized by satisfying the conditional expression. When the air gap between the first lens group and the second lens group at the wide-angle end is D1w, and the air gap between the first lens group and the second lens group at the telephoto end is D1t,
D1w> D1t
The zoom lens according to any one of claims 1 to 7, characterized by satisfying the conditional expression. The air gap between the third lens group and the fourth lens group at the wide-angle end when focused at infinity is D3w, and the third lens group and the fourth lens group at the telephoto end when focused at infinity. When the air interval of D3t is
D3w <D3t
The zoom lens according to any one of claims 1 to 8, characterized by satisfying the conditional expression. An image pickup apparatus comprising: the zoom lens according to claim 1 ; and an image pickup element that receives an image formed by the zoom lens.