JP2009098449A - Zoom lens and imaging apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens easily reconciling miniaturization with increase in variable power ratio. <P>SOLUTION: This zoom lens includes: a front side lens group having negative refractive power at the wide angle end; and a rear side lens group having positive refractive power at the wide angle end in that order from the object side. The front side lens group has: a first lens group that is arranged on the closest side to the object and has the positive refractive power; and a second lens group that is arranged closer to the image side than the first lens group and has the negative refractive power. The distance between the first lens group and the second lens group becomes larger at the telescopic end than at the wide angle end. The rear side lens group has a third lens group that is positioned on the object side at the telescopic end than at the wide angle end, has a distance from the second lens group shorter at the telescopic end than at the wide angle end, and also has positive refractive power establishing a condition: 0.01<f<SB>3</SB>/f<SB>t</SB><0.16. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  In recent years, digital cameras that take an image of an object using an image sensor such as a CCD or a CMOS sensor instead of a silver salt film camera have become mainstream. Furthermore, it has come to have a number of categories in a wide range from high-functional types for business use to compact popular types. Some of these categories have a zoom ratio of about 10 times, while others have a higher zoom ratio than that and are stored in the camera body when not in use and become compact.

  For example, as a zoom lens having a zoom ratio of about 10 times or higher, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens having a positive refractive power from the object side. A type having a lens group is known from the following patent documents.

Japanese Patent Laid-Open No. 11-5244 Japanese Patent Laid-Open No. 11-6958 JP 2006-171055 A JP 2007-10695 A JP 2007-3554 A

  However, the zoom lenses disclosed in these documents 1, 2, and 3 have a zoom ratio of about 10 times. In addition, the zoom lenses proposed in Documents 4 and 5 have a long zoom lens length at the telephoto end. For this reason, it is easy to increase the size of the lens barrel for driving the lens and increase the number of lens barrels for multi-stage copper sinking, which is disadvantageous for making the entire camera compact when retracted.

  The present invention has been made in view of such problems, and an object thereof is to provide a zoom lens that can easily achieve both a reduction in size and a high zoom ratio. Furthermore, it is providing the imaging device provided with such a zoom lens.

In order to solve the above-described problems and achieve the object, the zoom lens of the present invention includes:
From the object side,
A front lens group having negative refractive power at the wide-angle end;
It consists of a rear lens group with positive refractive power at the wide-angle end,
The front lens group
A first lens group disposed on the most object side and having a positive refractive power;
A second lens group disposed on the image side of the first lens group and having a negative refractive power;
The distance between the first lens group and the second lens group is larger at the telephoto end than at the wide-angle end;
The rear lens group is
The basic configuration is to have a third lens group having a positive refracting power and a smaller distance from the second lens group at the telephoto end than at the wide-angle end.

In this way, the front lens group and the rear lens group at the wide angle end have a lens arrangement like a retrofocus type, which is advantageous for securing the angle of view at the wide angle end.
Then, by increasing the distance between the first lens group and the second lens group, it becomes easy to ensure the zooming function by the second lens group having negative refractive power.
Then, by bringing the third lens group having positive refractive power of the rear lens group closer to the second lens group, the third lens group can easily have a zooming function.

In the first zoom lens of the present invention, the above-described zoom lens gives the third lens group a refractive power that satisfies the conditional expression (1), and the third lens group is located closer to the wide-angle end. It is moved so as to be located on the object side at the telephoto end.
0.01 <f ₃ / _ft <0.16 (1)
However,
f ₃ is the focal length of the third lens group,
_ft is the focal length of the entire zoom lens system at the telephoto end,
It is.

  By increasing the refractive power of the third lens unit relative to the refractive power of the entire zoom lens system at the telephoto end, it becomes easier to secure the positive refractive power of the rear group at the wide-angle end, and at the wide-angle end. This is advantageous for shortening the overall length of the zoom lens and shortening the focal length at the wide-angle end.

  In addition, moving the third lens group having positive refractive power toward the object side is more advantageous for securing the zooming load by the third lens group, and shortening the total length at the telephoto end or at the telephoto end. This is advantageous for shortening the overall length of the.

Conditional expression (1) specifies the refractive power of the third lens group.
By making sure that the lower limit of conditional expression (1) is not exceeded, the number of lenses for suppressing the occurrence of aberrations (mainly spherical aberration) in the third lens group can be easily reduced, which is advantageous for downsizing.
By making sure that the upper limit of conditional expression (1) is not exceeded, it becomes easier to secure the zooming burden of the third lens group, which is advantageous for achieving a compact and high zooming ratio.

  Furthermore, the first lens group may be positioned closer to the object side at the telephoto end than at the wide angle end. This is advantageous in increasing the zoom ratio and shortening the overall length at the wide angle end.

In the second zoom lens of the present invention, the first lens group has a refractive power that satisfies the conditional expression (2) in the basic zoom lens described above, and the first lens group has a wide angle. It is moved so that it is positioned closer to the object side at the telephoto end than at the end.
_{0.15 <f 1 / f t <} 0.50 ··· (2)
However,
f ₁ is the focal length of the first lens group,
_ft is the focal length of the entire zoom lens system at the telephoto end,
It is.

  By making the refractive power of the first lens unit relative to the refractive power of the entire zoom lens system at the telephoto end larger than that of the prior art, it is more advantageous for securing the zooming burden by the second lens unit having a negative refractive power. Become. In addition, since the first lens unit is positioned closer to the object side at the telephoto end than at the wide angle end, the overall length of the zoom lens at the wide angle end can be reduced, and the first and second lens groups can be reduced in the radial direction. It will be advantageous. Furthermore, it becomes easy to reduce the change of the F number accompanying the high zoom ratio.

Conditional expression (2) specifies the refractive power of the first lens group.
By making sure that the lower limit of conditional expression (2) is not exceeded, it is easy to reduce the number of lenses for suppressing the occurrence of aberrations in the first lens group (mainly spherical aberration at the telephoto end), and the first lens. This is advantageous for downsizing the group.
By making sure that the upper limit of conditional expression (2) is not exceeded, it becomes easier to secure the zooming burden of the second lens group, and the zoom ratio is increased while suppressing the amount of change in the distance between the first and second lens groups. This is advantageous for shortening the overall length of the zoom lens at the telephoto end.

  Furthermore, it is preferable that the third lens group be positioned closer to the object side at the telephoto end than at the wide angle end. This is advantageous for securing the zooming function of the third lens group.

  It is preferable to satisfy both the first zoom lens and the second zoom lens at the same time in order to further improve the balance between a high zoom ratio and a reduction in the overall length of the zoom lens.

  In any one of the above-described zoom lenses, it is preferable that any one or more of the following configurations are satisfied.

It is preferable that the second lens group satisfies the following conditions.
0.01 <| f ₂ | / _ft <0.10 (3)
However,
f ₂ is the focal length of the second lens group,
It is.

Conditional expression (3) specifies a preferable refractive power of the second lens group from the viewpoint of compactness and a balance between optical performance.
By making sure that the lower limit of conditional expression (3) is not exceeded, spherical aberration and field curvature in the second lens group can be easily suppressed.
By not exceeding the upper limit of conditional expression (3), it is advantageous for securing the zooming function of the second lens group, and it is advantageous for miniaturizing the lens barrel by shortening the entire length of the zoom lens.

Moreover, it is preferable that the relationship between the first lens group and the second lens satisfies the following conditions.
1.26 <ΣD1 / ΣD2 <3.00 (4)
However,
ΣD1 is the thickness of the first lens group on the optical axis,
ΣD2 is the thickness of the second lens group on the optical axis,
The thickness of the lens group on the optical axis is the actual distance from the object side surface of the lens closest to the object side to the image side surface of the lens closest to the image side in each lens group.
It is.

Conditional expression (4) specifies a preferred ratio of the thickness of the first lens group to the thickness of the second lens group.
When securing the angle of view at the wide-angle end to obtain a high zoom ratio, it is preferable to satisfactorily correct the spherical aberration near the telephoto end and the curvature of field near the wide-angle end.
The thickness of the second lens group is suppressed so as not to fall below the lower limit of conditional expression (4), and the thickness on the optical axis of the first lens group is secured, so that the refractive power of the first lens group This is advantageous for securing the effective diameter at the wide-angle end when the angle of view is widened, correcting spherical aberration near the telephoto end, and correcting curvature of field near the wide-angle end.
By suppressing the increase in the size of the first lens group so as not to exceed the upper limit of conditional expression (4), it is advantageous for the reduction in size. Or it becomes easy to ensure the refractive power and optical performance of the second lens group by appropriately securing the thickness of the second lens group.

In addition, it is preferable that the second lens group includes two negative lenses and one positive lens.
Even if the negative power of the second lens group is shared by the two negative lenses and the aberration is canceled by one positive lens, the second lens group can have a zooming function, This is advantageous in reducing the thickness of the lens group and reducing aberration fluctuations.

In addition, it is preferable that a fourth lens group having a positive refractive power is disposed on the image side of the third lens group, and an aperture stop is disposed between the second lens group and the fourth lens group. .
The fourth lens group makes it easier to separate the exit pupil from the image plane, which is advantageous for securing the peripheral light amount when using an imaging device such as a CCD or CMOS sensor.

Furthermore, it is preferable that the zoom lens is a four-group zoom lens.
By using a four-unit zoom lens in which the refractive power arrangement of the lens group is positive, negative, positive in order from the object side, the burden on the mechanism that drives the lens group can be reduced.

When zooming from the wide-angle end to the telephoto end,
The first lens unit moves so that it is positioned closer to the object side at the telephoto end than at the wide-angle end,
The second lens group moves,
The third lens group moves so that it is closer to the object side at the telephoto end than at the wide-angle end,
The fourth lens group moves,
The aperture stop moves to be closer to the object side at the telephoto end than at the wide-angle end.
It is preferable.

By moving each lens group, it becomes easy to reduce aberration fluctuations accompanying a high zoom ratio and to adjust the amount of movement of the lens group.
Further, by moving the aperture stop to the object side at the telephoto end rather than the wide-angle end, the size of the third lens group can be easily reduced, and the degree of freedom of the movement range of the second and third lens groups. Is preferable because it is easy to ensure.

  At that time, the first lens group may be moved only to the object side, or may be moved along a locus convex toward the object side or the image side. The second lens group may be moved only to the object side, or may be moved along a locus convex toward the object side or the image side. The third lens group may be moved only toward the object side, or may be moved along a locus convex toward the object side. The fourth lens group may be moved so as to be closer to the object side at the telephoto end than to the wide-angle end, or may be moved so as to be closer to the image side. It may be moved monotonously, or may be moved along a locus convex toward the object side or the image side.

In addition, it is preferable that the fourth lens group having a positive refractive power moves so as to be closer to the image side at the telephoto end than at the wide-angle end.
By providing the fourth lens group with a multiplying action, the amount of movement of the lens group that moves during zooming can be reduced, which is advantageous for ensuring a zoom ratio and reducing the size of the lens frame.

The fourth lens group is the most image side lens group in the zoom lens, and it is preferable that the following condition is satisfied.
0.05 <f ₄ / _ft <0.30 (5)
However,
f ₄ is the focal length of the fourth lens group,
It is.

Arranging the fourth lens group closest to the image side is advantageous in adjusting astigmatism.
Conditional expression (5) specifies a preferable refractive power of the fourth lens group.
It is preferable to suppress overcorrection of astigmatism so as not to fall below the lower limit of conditional expression (5), and to suppress undercorrection so as not to exceed the upper limit of conditional expression (5).
When the above conditional expressions (1), (2), (3), (4), and (5) are satisfied at the same time, it is easy to share the refractive power of each lens group, and the size is reduced while maintaining a high zoom ratio. It is even more advantageous to perform.

  Also, it has an aperture stop and a shutter positioned between the second lens group and the third lens group, and the brightness stop and shutter are integrated with the third lens group at the telephoto end rather than the wide angle end. It is preferable to move to the side.

  As a result, the entrance pupil can be positioned close to the object side, and the exit pupil can be moved away from the image plane. In addition, since the off-axis light beam height is low, the shutter unit does not need to be enlarged, and the dead space when moving the aperture stop and the shutter unit can be reduced.

  In addition, by moving the aperture stop, it is possible to effectively correct spherical aberration and achieve an effect in terms of performance, and it is possible to appropriately control the entrance pupil position and the exit pupil position. That is, the beam height of the off-axis light beam at the wide-angle end and the beam height of the off-axis light beam at the telephoto end can be balanced, and the outer diameter of the first lens unit and the outer diameter of the lens unit closest to the image plane are balanced. It becomes possible to make it compact. In particular, reducing the outer diameter of the first lens group at the wide-angle end effectively leads to a compact size in the lens thickness direction. In addition, since it is possible to control the variation of the exit pupil position during zooming, when using an image sensor such as a CCD or CMOS, the angle of light incident on the image sensor is kept within an appropriate range. It is possible to prevent the occurrence of brightness shading at the corners of the screen.

The first lens group preferably includes a negative lens and a positive lens.
This makes it easy to reduce chromatic aberration near the telephoto end, which becomes noticeable when the zoom ratio is increased.
Furthermore, if the first lens group includes a cemented lens having a negative lens and a positive lens, it is possible to suppress deterioration of optical performance due to relative decentering of the lens due to assembly errors, contributing to yield improvement and cost reduction. To do.

In addition, the negative lens and the positive lens of the first lens group may be composed of independent lens components that are not cemented.
This makes it possible to more effectively correct spherical aberration at the telephoto end.
Furthermore, by making the first lens group two lenses, a negative lens and a positive lens, it is possible to further reduce the size in the optical axis direction and the radial direction.

Moreover, it is preferable to satisfy the following conditions.
9 < _ft / _fw <50 (6)
1.1 <L _t / L _w <2.0 (7)
However,
f _w is the focal length of the entire zoom lens system at the wide-angle end,
L _t is the actual distance on the optical axis from the object-side lens surface to the image plane in the first lens group at the telephoto end,
L _w is the actual distance on the optical axis from the lens surface closest to the object side in the first lens group at the wide angle end to the image plane,
It is.

Conditional expression (6) relates to the ratio of the focal lengths of the entire zoom lens system at the wide-angle end and the telephoto end.
It is preferable that the zoom lens has a high zoom ratio so as not to fall below the lower limit of conditional expression (6), taking advantage of the above-described configuration.
By not exceeding the upper limit of conditional expression (6), it becomes easy to suppress an increase in the number of lens groups and an increase in the number of lenses for ensuring optical performance.

Conditional expression (7) relates to the ratio of the total length of the zoom lens at the wide-angle end to the total length of the zoom lens at the telephoto end.
It is preferable to reduce the total length of the zoom lens at the wide-angle end so as not to fall below the lower limit of the conditional expression (7), thereby facilitating a high zoom ratio by reducing the radial direction and securing the total length at the telephoto end. .
Further, when the image pickup apparatus includes a strobe, it is necessary to consider the effect of vignetting of strobe light caused by the lens frame of the zoom lens during wide-angle shooting. By reducing the overall length of the zoom lens at the wide-angle end, it becomes easier to reduce uneven brightness due to vignetting of the strobe light without greatly separating the strobe from the zoom lens. Is advantageous.
By suppressing the change in the overall length of the zoom lens so as not to exceed the upper limit of the conditional expression (7), it is advantageous for downsizing the lens frame for driving the zoom lens.

In addition, it is preferable that the zoom lens satisfies the following conditions at the telephoto end.
5.0 <F _t <16.0 (8)
However,
_Ft is the F-number of the zoom lens at the telephoto end, and is the minimum value when the F-number is adjustable.

Conditional expression (8) specifies the F number at the telephoto end.
By making sure that the lower limit of conditional expression (8) is not exceeded, it becomes advantageous to reduce the influence of spherical aberration and lateral chromatic aberration that become noticeable when the zoom ratio is increased. This is advantageous for downsizing each lens group.
By avoiding exceeding the upper limit of conditional expression (8), it is possible to reduce the effects of camera shake that becomes noticeable when the zoom ratio is increased. It becomes easier to perform image processing.

In addition, it is preferable that all lens groups included in the zoom lens have an aspheric lens surface.
Thereby, the influence of the aberration when the zoom ratio is increased can be reduced in each lens group, which is advantageous in reducing the total number of lenses.

The total number of lenses included in the zoom lens is 8 to 12, the first and third lens groups each have a negative lens and a positive lens, and the second lens group has a positive lens and a plurality of lenses. It is preferable to have a negative lens.
By setting the total number of lenses to any one of 8 to 12, it is advantageous for downsizing and cost reduction when the lens barrel is retracted while reducing aberration fluctuations accompanying a high zoom ratio.
At this time, the first, second, and third lens groups have both positive and negative lenses, which is advantageous in reducing various aberrations in the respective lens groups, and the second lens group. By using a plurality of negative lenses in the middle, it is possible to secure the refractive power of the second lens group while suppressing the influence of aberration, which is advantageous for downsizing and a high zoom ratio.

The imaging device of the present invention is
A zoom lens and an image sensor that is disposed on the image side of the zoom lens and converts an image formed by the zoom lens into an electrical signal;
The zoom lens is at least one of the zoom lenses described above.

A zoom lens that is advantageous for achieving a high zoom ratio is provided, and retracting when not in use is advantageous for downsizing the image pickup apparatus.
Furthermore, the imaging device preferably includes a strobe.

Moreover, it is preferable that an imaging device has an image processing part which performs the signal processing which correct | amends the aberration contained in an electrical signal.
Allowing aberrations (for example, distortion aberration and chromatic aberration of magnification) of the zoom lens is advantageous for further miniaturization and higher zoom ratio.

Furthermore, it is preferable to satisfy the following conditions.
0.50 <IH _w / f _w <1.00 (9)
However,
IH _w is the maximum image height at the wide-angle end,
f _w is the focal length of the entire zoom lens system at the wide-angle end,
It is.

Conditional expression (9) specifies a preferable relationship between the focal length at the wide-angle end and the maximum image height.
It is preferable not to fall below the lower limit of conditional expression (9), which is advantageous for securing the angle of view at the wide-angle end.
It is preferable not to exceed the upper limit of conditional expression (9) so that the radial size of the first and second lens groups can be easily reduced.

  In each of the embodiments described above, the lens group arranged closest to the image side may be formed of a plastic material. The main role of the lens group on the most image side is to arrange the exit pupil position at an appropriate position and to make light rays efficiently enter an image pickup device such as a CCD or CMOS sensor. For such a role, a relatively large power is not required, and a glass material having a low refractive index such as a plastic lens can be used. Accordingly, it is possible to provide a zoom lens and an imaging device that are less expensive and less expensive.

Further, in order to cut unnecessary light such as ghost and flare, a flare stop other than the brightness stop may be arranged. Any location on the object side of the first lens group, between the first and second lens groups, between the second and third lens groups, between the third and fourth lens groups, and between the fourth lens group and the image plane It may be arranged. The frame member that holds the lens may be a flare stop. Or you may arrange | position a flare restricting member separately. Further, the flare stop may be directly printed on the lens surface of any lens in the zoom lens, or may be painted or bonded with a seal. The shape of the opening of the flare stop may be any shape such as a circle, an ellipse, a rectangle, a polygon, or a range surrounded by a function curve. Further, not only the harmful light beam but also the light beam that causes coma flare around the screen may be cut.
Each lens may be provided with an antireflection coating to reduce ghosts and flares. A multi-coat is desirable because it can effectively reduce ghost and flare. Infrared cut coating may be applied to the lens surface, cover glass, or the like.
Further, focusing for adjusting the focus is preferably performed by moving the fourth lens group.

When the fourth lens group is focused, the weight of the motor is small because the lens weight is light. Or it is easy to suppress the change in the angle of view due to focusing.
Furthermore, since there is no change in the overall length during focusing and the drive motor can be arranged inside the lens frame, it is advantageous for making the lens frame compact.
As described above, focusing is preferably performed with the fourth lens group, but focusing may be performed with the first, second, and third lens groups. Further, focusing may be performed by moving a plurality of lens groups. Further, focusing may be performed by extending the entire zoom lens. Further, focusing may be performed by extending or retracting some lenses.

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

When the zoom lens has a focusing function, each conditional expression described above is configured in a state in which it is focused at the farthest distance.
More preferably, a plurality of the above-described configurations are satisfied at the same time.
More preferably, each conditional expression is as follows.

For conditional expression (1),
More preferably, the lower limit value is 0.05 or even 0.09.
More preferably, the upper limit value is 0.13, more preferably 0.12.
For conditional expression (2),
More preferably, the lower limit value is 0.20, more preferably 0.25.
More preferably, the upper limit value is 0.45, more preferably 0.38, and even more preferably 0.35.
Conditional expression (3)
More preferably, the lower limit value is 0.02, more preferably 0.045.
More preferably, the upper limit value is 0.075, more preferably 0.06.
For conditional expression (4),
More preferably, the lower limit value is 1.30, more preferably 1.40.
More preferably, the upper limit value is 2.50, more preferably 2.00.
For conditional expression (5),
More preferably, the lower limit is 0.09.
More preferably, the upper limit value is 0.20.
For conditional expression (6),
It is more preferable to set the lower limit value to 15, more preferably 18.
More preferably, the upper limit value is 40, and more preferably 30.
For conditional expression (7),
More preferably, the lower limit is 1.2, and more preferably 1.5.
The upper limit value is more preferably 1.8, and more preferably 1.7.
Conditional expression (8)
More preferably, the lower limit is 7.0.
More preferably, the upper limit value is 14.0, more preferably 11.2.
Conditional expression (9)
More preferably, the lower limit value is 0.60, more preferably 0.70.
More preferably, the upper limit value is 0.95, more preferably 0.85.

Further, it is more preferable in terms of aberration correction that the total number of lenses in the zoom lens is 9 or more.
Further, the total number of lenses in the zoom lens is preferably 11 or less, and more preferably 10 or less from the viewpoint of miniaturization and cost reduction.

  It is more preferable that each of the above-described inventions satisfies a plurality at the same time. For each conditional expression, only the upper limit value or lower limit value of the numerical range of the more limited conditional expression may be limited. Further, the above-described configurations may be arbitrarily combined.

  According to the present invention, it is possible to provide a zoom lens that can easily achieve a reduction in size and a high zoom ratio. Furthermore, an imaging apparatus including such a zoom lens can be provided.

    In the following examples, in order to satisfy the user's desire to expand the shooting area without sacrificing portability, the camera is downsized, the zoom ratio is increased, and the angle of view is increased. It is an inexpensive zoom lens suitable for electronic imaging devices such as CCDs and CMOS sensors that are well maintained.

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

In Examples 1 to 3, the effective imaging area is rectangular and constant in the full zoom state. Moreover, the conditional expression corresponding value in each embodiment is a value in a state in which the object point at infinity is in focus.
Focusing is performed by moving the fourth lens group, and focusing operation from a long-distance object point to a short-distance object point is performed by moving the fourth lens group to the object side.

  The parallel plate is a low-pass filter and CCD cover glass with IR cut coating. The one with only one parallel plate is a CCD cover glass. If the number of pixels increases, moire will not stand out even without a low-pass filter. IR cut coating may be applied to the lens surface or cover glass. Although the shutter is omitted in the numerical data, it is arranged close to the aperture (brightness aperture) in the lens data. Alternatively, the shutter and the aperture may be the same.

Examples 1 to 3 of the zoom lens according to the present invention will be described below. Wide angle end (a), first intermediate focal length state (b), second intermediate focal length state (c), third intermediate focal length state ( d) Lens cross-sectional views at the telephoto end (e) are shown in FIGS. 1 to 3, the first lens group is G1, the second lens group is G2, the brightness (aperture) stop is S, the third lens group is G3, the fourth lens group is G4, and red as described above. A parallel flat plate constituting a low-pass filter provided with a wavelength band limiting coat for limiting external light is indicated by F, a parallel flat plate of the cover glass of the electronic image sensor is indicated by C, and an image plane is indicated by I. In addition, you may give the multilayer film for a wavelength range restriction | limiting to the surface of the cover glass C. FIG. Further, the cover glass C may have a low-pass filter action.
Further, the front lens group includes a first lens group G1 and a second lens group G2. The rear lens group includes a third lens group G3 and a fourth lens group G4.

  All of the numerical data is data in a state where an object at infinity is focused. The unit of length of each numerical value is mm, and the unit of angle is ° (degree). Further, the zoom data includes values at the wide angle end (WE), the first intermediate zoom state (ST1), the second intermediate zoom state (ST2), the third intermediate zoom state (ST3), and the telephoto end (TE). is there.

  As shown in FIG. 1, the zoom lens of Example 1 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, an aperture stop S, A third lens group G3 having a positive refractive power and a fourth lens group G4 having a positive refractive power are disposed.

  During zooming from the wide-angle end to the telephoto end, the first lens group G1 moves only to the object side, the second lens group G2 moves only to the object side, and the third lens group G3 moves only to the object side. The fourth lens group G4 moves convexly toward the image side.

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

  The aspherical surface is an image side surface of a positive meniscus lens having a convex surface facing the object side closest to the image side of the first lens group G1, and both surfaces of a negative meniscus lens having a convex surface facing the object side of the second lens group G2. And the image side surface of the biconvex negative lens on the image side, both surfaces of the biconvex positive lens of the third lens group G3, and both surfaces of the biconvex positive lens of the fourth lens group G4. .

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

  During zooming from the wide-angle end to the telephoto end, the first lens group G1 moves only to the object side, the second lens group G2 moves only to the object side, and the third lens group G3 moves only to the object side. The fourth lens group G4 moves convexly toward the image side.

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

  An aspherical surface is an image side surface of a positive meniscus lens having a convex surface facing the image side object side of the first lens group G1, and both surfaces of a negative meniscus lens having a convex surface facing the object side of the second lens group G2. It is used on eight surfaces including the image side surface of the biconcave negative lens, both surfaces of the biconvex positive lens of the third lens group G3, and both surfaces of the biconvex positive lens of the fourth lens group G4.

  As shown in FIG. 3, the zoom lens of Example 3 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, an aperture stop S, A third lens group G3 having a positive refractive power and a fourth lens group G4 having a positive refractive power are disposed.

  During zooming from the wide-angle end to the telephoto end, the first lens group G1 moves only to the object side, the second lens group G2 moves convexly to the object side, and the third lens group G3 moves only to the object side. The fourth lens group G4 reverses the moving direction twice after moving to the image side.

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

  The aspherical surfaces are the image side surface of the biconvex positive lens of the first lens group G1, the both surfaces of the negative meniscus lens having the convex surface facing the object side of the second lens group G2, and the image side surface of the biconcave negative lens. And both surfaces of the biconvex positive lens of the third lens group G3 and both surfaces of the biconvex positive lens of the fourth lens group G4.

Below, the numerical data of each said Example are shown. Symbols are the above, f is the focal length of the entire system, BF is the back focus, f1, f2... Are the focal lengths of the lens groups, IH is the image height, _FNO is the F number, ω is the half field angle, and WE is the wide angle. ST1, ST1 is a first intermediate focal length state, ST2 is a second intermediate focal length state, ST3 is a third intermediate focal length state, TE is a telephoto end, r1, r2,... Are curvature radii of lens surfaces, d1. , D2... Are the distances between the lens surfaces, nd1, nd2... Are the d-line refractive index of each lens, and .nu.d1, .nu.d2. The total lens length described later is obtained by adding back focus to the distance from the lens front surface to the lens final surface. BF (back focus) represents the distance from the last lens surface to the paraxial image plane in terms of air.

Numerical example 1
Unit mm

Surface data Surface number rd nd νd
1 71.917 0.80 1.92286 18.90
2 37.529 4.00 1.61800 63.33
3 138.659 0.10
4 26.623 5.50 1.77250 49.60
5 * 192621.886 Variable
6 * 47.954 0.80 1.83481 42.71
7 * 6.341 2.50
8 118.332 1.60 1.94595 17.98
9 -10.823 0.80 1.83481 42.71
10 * 14.081 Variable
11 (Aperture) ∞ 0.30
12 * 5.438 2.96 1.49700 81.54
13 * -20.223 0.10
14 6.668 1.50 1.77250 49.60
15 11.000 0.70 1.84666 23.78
16 3.966 Variable
17 * 31.214 1.90 1.74330 49.33
18 * -9.711 variable
19 ∞ 0.40 1.54771 62.84
20 ∞ 0.50
21 ∞ 0.50 1.51633 64.14
22 ∞ 0.37
Image surface (light receiving surface)

Aspheric data 5th surface
k = 0.654, A4 = 4.76005e-06, A6 = -5.27460e-10, A8 = -8.76612e-12, A10 = 1.17810e-14
6th page
k = 0.000, A4 = -2.34324e-04, A6 = -3.13708e-06, A8 = 2.43681e-07, A10 = -2.99207e-09
7th page
k = 0.369, A4 = 1.12943e-04, A6 = 1.11887e-05, A8 = -1.27867e-06, A10 = 4.22626e-08
10th page
k = 0.000, A4 = -9.38012e-04, A6 = -1.97637e-05, A8 = 2.81611e-06, A10 = -1.02669e-07
12th page
k = 0.000, A4 = -5.69400e-04, A6 = 1.16631e-05, A8 = -1.28093e-06, A10 = 4.10229e-07
13th page
k = 0.000, A4 = 8.40292e-04, A6 = 3.86549e-05, A8 = -4.12799e-06, A10 = 8.33733e-07
17th page
k = 0.772, A4 = -2.37726e-04, A6 = 1.50005e-05, A8 = -2.25542e-07, A10 = 6.46375e-10
18th page
k = 0.000, A4 = 9.09060e-05, A6 = 1.72680e-05, A8 = -2.44150e-07

Various data
WE ST1 ST2 ST3 TE
Focal length 4.85 10.51 19.35 47.08 100.00
FNO. 8.00 8.00 8.00 8.00 8.00
Angle of view 2ω 80.53 37.80 21.98 9.85 4.60
BF 5.68 4.90 4.41 1.76 2.46
Total length 48.06 59.63 65.78 70.32 74.55
d5 0.20 10.00 15.08 18.40 20.19
d10 12.73 10.77 9.35 7.23 1.00
d16 5.89 10.41 13.38 19.37 27.34
d18 4.23 3.44 2.95 0.30 1.00

Numerical example 2
Unit mm

Surface data Surface number rd nd νd
1 62.968 0.80 1.92286 18.90
2 34.496 3.50 1.61800 63.33
3 155.107 0.10
4 29.363 4.00 1.77250 49.60
5 * -3588.280 Variable
6 * 59.714 0.80 1.83481 42.71
7 * 6.851 2.50
8 190.030 1.60 1.94595 17.98
9 -10.823 0.80 1.83481 42.71
10 * 14.854 variable
11 (Aperture) ∞ 0.30
12 * 5.209 2.30 1.49700 81.54
13 * -15.384 0.10
14 6.338 1.50 1.77250 49.60
15 8.181 0.70 1.90000 23.80
16 3.690 Variable
17 * 39.261 1.90 1.74330 49.33
18 * -10.366 variable
19 ∞ 0.50 1.51633 64.14
20 ∞ 0.77
Image surface (light receiving surface)

Aspheric data 5th surface
k = 0.654, A4 = 2.62061e-06, A6 = 2.58535e-09, A8 = -1.90250e-11, A10 = 3.54790e-14
6th page
k = 0.000, A4 = -2.25942e-04, A6 = -2.43816e-06, A8 = 2.41139e-07, A10 = -3.04832e-09
7th page
k = 0.736, A4 = 8.01450e-05, A6 = 1.05151e-05, A8 = -1.27831e-06, A10 = 4.22643e-08
10th page
k = 0.000, A4 = -8.43392e-04, A6 = -2.02943e-05, A8 = 2.81754e-06, A10 = -1.02665e-07
12th page
k = 0.000, A4 = -6.79145e-04, A6 = 1.27390e-05, A8 = -1.28037e-06, A10 = 4.10229e-07
13th page
k = 0.000, A4 = 8.06000e-04, A6 = 3.79038e-05, A8 = -4.12831e-06, A10 = 8.33733e-07
17th page
k = 0.206, A4 = -1.30715e-04, A6 = 1.46119e-05, A8 = -2.28610e-07, A10 = 6.27096e-10
18th page
k = 0.000, A4 = 9.09060e-05, A6 = 1.76840e-05, A8 = -2.41180e-07

Various data
WE ST1 ST2 ST3 TE
Focal length 4.64 9.70 18.11 47.11 85.12
FNO. 8.00 8.00 8.00 8.00 8.00
Angle of view 2ω 85.45 40.52 22.84 9.50 5.15
BF 5.46 4.52 3.90 1.15 2.75
Total length 43.70 54.19 60.86 67.07 71.338
d5 0.20 8.87 14.21 18.10 20.67
d10 12.77 10.46 8.59 5.72 1.00
d16 4.37 9.44 13.25 21.20 26.01
d18 4.36 3.42 2.80 0.05 1.65

Numerical Example 3
Unit mm

Surface data Surface number rd nd νd
1 47.985 0.80 1.92286 18.90
2 28.243 0.05
3 21.248 4.08 1.77250 49.60
4 * -116.425 variable
5 * 165.072 0.80 1.83481 42.71
6 * 7.304 2.03
7 -91.810 1.91 1.94595 17.98
8 -10.823 0.80 1.83481 42.71
9 * 17.995 variable
10 (Aperture) ∞ 0.30
11 * 5.280 2.46 1.49700 81.54
12 * -14.512 0.28
13 6.294 1.52 1.77250 49.60
14 8.181 0.80 2.00068 25.47
15 3.729 Variable
16 * 473.250 3.74 1.74330 49.33
17 * -11.842 Variable
18 ∞ 0.40 1.54771 62.84
19 ∞ 0.50
20 ∞ 0.50 1.51633 64.14
21 ∞ 0.37
Image surface (light receiving surface)

Aspheric data 4th surface
k = 0.654, A4 = 1.17011e-05, A6 = -1.96762e-09, A8 = -8.17022e-12, A10 = 5.12387e-15
5th page
k = 0.000, A4 = -8.24711e-05, A6 = -2.76503e-06, A8 = 2.27122e-07, A10 = -3.15083e-09
6th page
k = 0.787, A4 = 6.34033e-05, A6 = 1.04135e-05, A8 = -1.27967e-06, A10 = 4.22656e-08
9th page
k = 0.000, A4 = -5.37026e-04, A6 = -1.90025e-05, A8 = 2.82021e-06, A10 = -1.02639e-07
11th page
k = 0.000, A4 = -4.84682e-04, A6 = 1.18845e-05, A8 = -1.28144e-06, A10 = 4.10225e-07
12th page
k = 0.000, A4 = 8.84774e-04, A6 = 3.84287e-05, A8 = -4.12823e-06, A10 = 8.33734e-07
16th page
k = 0.000, A4 = 9.93673e-21, A6 = 1.56889e-05, A8 = -2.27236e-07, A10 = 6.31860e-10
17th page
k = 0.000, A4 = 9.09060e-05, A6 = 1.67850e-05, A8 = -2.42650e-07

Various data
WE ST1 ST2 ST3 TE
Focal length 4.84 9.46 19.43 38.31 100.77
FNO. 3.60 4.82 5.12 5.60 8.16
Angle of view 2ω 84.84 44.20 22.40 11.52 4.50
BF 5.74 5.42 4.57 6.55 2.64
Total length 43.66 50.40 59.78 67.75 69.21
d4 0.06 5.04 11.53 16.83 21.12
d9 14.64 10.80 8.50 5.21 1.27
d15 3.65 9.57 15.61 19.60 24.62
d17 4.28 3.96 3.11 5.09 1.18

Examples 4 to 6 are examples in which the zoom lenses of Examples 1 to 3 are used, respectively, and are used in an imaging apparatus that electrically corrects distortion, and the shape of the effective imaging region changes during zooming. Therefore, it is different from the embodiment corresponding to the image height and the angle of view in the zoom state.
In Examples 4 to 6, an image is recorded and displayed after electrically correcting barrel-shaped (jinkasa-shaped) distortion occurring on the wide-angle side.

In the zoom lens of this embodiment, barrel distortion occurs at the wide-angle end on the rectangular photoelectric conversion surface. On the other hand, the occurrence of distortion is suppressed near the intermediate focal length state and at the telephoto end.
In order to electrically correct the distortion, the effective imaging area has a barrel shape at the wide angle end and a rectangular shape at the intermediate focal length state or the telephoto end.
Then, the effective imaging area set in advance is image-converted by image processing and converted into rectangular image information with reduced distortion.
The maximum image height IH _w at the wide angle end is smaller than the maximum image heights IH _s1 , IH _s2 , IH _s3 in the first, second, and third intermediate focal length states and the maximum image height IH _t at the telephoto end. I have to.

In Examples 4 to 6, the length of the photoelectric conversion surface in the short side direction is the same as the length of the effective imaging region in the short side direction at the wide angle end, and the distortion after image processing is about −3%. The effective imaging area is determined so as to remain.
In view angle equivalent to 28 mm when converted to 135 mm film size, it is preferable to set the angle so that it remains about -3% in consideration of the balance between the perspective effect at the time of photographing a three-dimensional object and the barrel distortion due to distortion. .
Of course, an image obtained by converting a smaller barrel-shaped area into a rectangular shape as an effective imaging area may be recorded and reproduced.

The zoom lens of Example 4 is the same as the zoom lens of Example 1.
The zoom lens of the fifth embodiment is the same as the zoom lens of the second embodiment.
The zoom lens of the sixth embodiment is the same as the zoom lens of the third embodiment.

Data of image height and full angle of view in Example 4 are shown below.
Various data
WE ST1 ST2 ST3 TE
Focal length 4.85 19.35 100.00 10.51 47.08
FNO. 8.00 8.00 8.00 8.00 8.00
Angle of view 2ω 80.12 37.80 21.98 9.85 4.60
Image height 3.847 3.88 3.88 3.88 3.88

Data of the image height and the total angle of view in Example 5 are shown below.
Various data
WE ST1 ST2 ST3 TE
Focal length 4.64 18.11 85.12 9.70 47.11
FNO. 8.00 8.00 8.00 8.00 8.00
Angle of view 2ω 82.846 40.518 22.838 9.502 5.146
Image height 3.60 3.80 3.80 3.80 3.80

Data on the image height and the total angle of view in Example 6 are shown below.
Various data
WE ST1 ST2 ST3 TE
Focal length 4.84 9.46 19.43 38.31 100.77
FNO. 3.60 4.82 5.12 5.60 8.16
Angle of view 2ω 82.078 44.200 22.400 11.518 4.498
Image height 3.69 3.88 3.88 3.88 3.88

  Aberration diagrams at the time of focusing on an object point at infinity in Examples 1 to 3 are shown in FIGS. In these aberration diagrams, (a) is a wide angle end, (b) is a first intermediate focal length state, (c) is a second intermediate focal length state, (d) is a third intermediate focal length state, ( e) shows spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC) at the telephoto end. In each figure, “ω” indicates a half angle of view.

  As shown in FIG. 10, in Example 1 (a), Example 2 (b), and Example 3 (c), the first lens group G1, the second lens group G2, and the fourth lens group G4 are retracted. Moves to the image side along the optical axis of each lens group and retracts. Further, the third lens group (third lens group) G3 is arranged apart from the optical axes thereof and behind the first lens group G1, along with the second lens group G2 and the fourth lens group G4.

Listed below are values corresponding to conditional expressions.

Example 1 Example 2 Example 3

_{(1) f 3 / f t} 0.110 0.120 0.100
_{(2) f 1 / f t} 0.346 0.420 0.340
_{(3) | f 2 | /} f t 0.058 0.071 0.058
(4) ΣD1 / ΣD2 1.825 1.474 0.891
_{(5) f 4 / f t} 0.102 0.132 0.155
(6) Scaling ratio f _t / f _w 20.637 18.362 20.832
(7) L _t / L _w 1.548 1.630 1.581
(8) F _t 8.000 8.000 8.158
(9) IH _w / f _w 0.801 0.820 0.802
Total number of lenses 10 10 9
Image height IH 3.88 3.8 3.88

f1 34.617 35.753 34.313
f2 -5.813 -6.070 -5.812
f3 10.999 10.184 10.096
f4 10.166 11.216 15.595

Example 4 Example 5 Example 6
_{(1) f 3 / f t} 0.110 0.120 0.100
_{(2) f 1 / f t} 0.346 0.420 0.340
_{(3) | f 2 | /} f t 0.058 0.071 0.058
(4) ΣD1 / ΣD2 1.825 1.474 0.891
_{(5) f 4 / f t} 0.102 0.132 0.155
(6) Scaling ratio f _t / f _w 20.637 18.362 20.832
(7) L _t / L _w 1.548 1.630 1.581
(8) F _t 8.000 8.000 8.158
(9) IH _w / f _w 0.794 0.777 0.763
Total number of lenses 10 10 9

f1 34.617 35.753 34.313
f2 -5.813 -6.070 -5.812
f3 10.999 10.184 10.096
f4 10.166 11.216 15.595

Moreover, in order to prevent the occurrence of ghosts and flares, an antireflection coating is generally applied to the air contact surface of the lens. On the other hand, the refractive index of the adhesive is sufficiently higher than the refractive index of air on the cemented surface of the cemented lens. For this reason, the reflectance is often the same as or lower than that of a single-layer coating, and it is rare to apply a coating. However, if an anti-reflection coating is also applied to the joint surface, ghosts and flares can be further reduced, and still better images can be obtained.
In recent years, high refractive index glass materials have become widespread and have been used extensively in camera optical systems due to their high aberration correction effects. However, when high refractive index glass materials are used as cemented lenses, reflection on the cemented surface is ignored. It becomes impossible. In such a case, it is particularly effective to provide an antireflection coating on the joint surface.

Effective use of the joint surface coating is disclosed in JP-A-2-27301, JP-A-2001-324676, JP-A-2005-92115, USP 7116482, and the like. These documents particularly describe the cemented lens surface coat in the first group of the positive leading zoom lens, and the cemented lens surface in the first lens group of the positive power of the present invention is also disclosed in these documents. Just do it. As the coating material to be used, Ta ₂ O ₅ , TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , HfO ₂ , CeO, which have a relatively high refractive index, depending on the refractive index of the base lens and the refractive index of the adhesive. _{2, SnO 2, in 2 O} 3, ZnO, Y 2 O 3 coating material such as a relatively low refractive index of MgF _2, SiO _2, coating materials such as Al ₂ O _3, and appropriately selected, phase condition The film thickness may be set so as to satisfy the above.

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

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

  For example, as shown in FIG. 11, the magnification on the circumference (image height) of the radius R inscribed in the long side of the effective imaging surface around the intersection of the optical axis and the imaging surface is fixed, and this circumference is The standard for correction. Then, correction is performed by moving each point on the circumference (image height) of any other radius r (ω) in a substantially radial direction and concentrically so as to have the radius r ′ (ω). To do.

For example, in FIG. 11, a point P ₁ on the circumference of an arbitrary radius r ₁ (ω) located inside the circle of radius R is a radius r ₁ ′ (ω) circle to be corrected toward the center of the circle. Move to point P ₂ on the circumference. A point Q ₁ on the circumference of an arbitrary radius r ₂ (ω) located outside the circle of radius R is a radius r ₂ ′ (ω) circumference to be corrected in a direction away from the center of the circle. It is moved to the point Q ₂ of the above.

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

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

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

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

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

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

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

  Note that the radius R preferably satisfies the following conditional expression so that the image after distortion correction does not have an extremely short amount of light at both ends in the short side direction.

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

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

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

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

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

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

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

(Digital camera)
12 to 14 are conceptual diagrams of the configuration of the digital camera according to the present invention in which the zoom lens as described above is incorporated in the photographing optical system 141. FIG. 12 is a front perspective view showing the appearance of the digital camera 140, FIG. 13 is a rear front view thereof, and FIG. 14 is a schematic cross-sectional view showing the configuration of the digital camera 140. However, in FIG. 12 and FIG. 14, the photographing optical system 141 is not retracted. In this example, the digital camera 140 includes a photographing optical system 141 having a photographing optical path 142, a finder optical system 143 having a finder optical path 144, a shutter button 145, a flash 146, a liquid crystal display monitor 147, a focal length change button 161, When the photographic optical system 141 is retracted, including the setting change switch 162, the photographic optical system 141, the finder optical system 143, and the flash 146 are covered with the cover 160 by sliding the cover 160. When the cover 160 is opened and the camera 140 is set to the photographing state, the photographing optical system 141 enters the non-collapsed state shown in FIG. Photographing is performed through the optical system 141, for example, the zoom lens of the first embodiment. An object image formed by the photographic optical system 141 is formed on the imaging surface of the CCD 149 through a low-pass filter F and a cover glass C that are provided with a wavelength band limiting coat. The object image received by the CCD 149 is displayed as an electronic image on a liquid crystal display monitor 147 provided on the back of the camera via the processing means 151. Further, the processing means 151 is connected to a recording means 152 so that a photographed electronic image can be recorded. The recording unit 152 may be provided separately from the processing unit 151, or may be configured to perform recording / writing electronically using a flexible disk, a memory card, an MO, or the like. Further, instead of the CCD 149, a silver salt camera in which a silver salt film is arranged may be configured.

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

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

(Internal circuit configuration)
FIG. 15 is a block diagram showing the internal circuitry of the main part of the digital camera 140. In the following description, the processing means includes, for example, the CDS / ADC unit 124, the temporary storage memory 117, the image processing unit 118, and the like, and the storage means includes, for example, the storage medium unit 119.

  As shown in FIG. 15, the digital camera 140 is connected to the operation unit 112, the control unit 113 connected to the operation unit 112, and the control signal output port of the control unit 113 via buses 114 and 115. An imaging drive circuit 116, a temporary storage memory 117, an image processing unit 118, a storage medium unit 119, a display unit 120, and a setting information storage memory unit 121 are provided.

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

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

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

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

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

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

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

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

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

  As described above, the zoom lens according to the present invention is useful for a zoom lens that easily achieves both a reduction in size and a high zoom ratio.

The wide-angle end (a), the first intermediate focal length state (b), the second intermediate focal length state (c), and the third intermediate during focusing on an object point at infinity according to the first embodiment of the zoom lens of the present invention. It is a lens sectional view in a focal length state (d) and a telephoto end (e). It is the same figure as FIG. 1 of Example 2 of the zoom lens of this invention. It is the same figure as FIG. 1 of Example 3 of the zoom lens of this invention. FIG. 6 is an aberration diagram for Example 1 upon focusing on an object point at infinity. FIG. 6 is another aberration diagram for Example 1 upon focusing on an object point at infinity. FIG. 6 is an aberration diagram for Example 2 upon focusing on an object point at infinity. FIG. 10 is another aberration diagram for Example 2 upon focusing on an object point at infinity. FIG. 10 is an aberration diagram for Example 3 upon focusing on an object point at infinity. FIG. 10 is another aberration diagram for Example 3 upon focusing on an object point at infinity. It is lens sectional drawing of the retracted state in Examples 1-3. It is a figure explaining correction | amendment of a distortion aberration. It is a front perspective view which shows the external appearance of the digital camera incorporating the zoom lens by this invention. It is a rear perspective view of the digital camera. It is sectional drawing of the said digital camera. It is a block diagram of the internal circuit of the main part of the digital camera.

Explanation of symbols

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

Claims (23)

From the object side,
A front lens group having negative refractive power at the wide-angle end;
It consists of a rear lens group with positive refractive power at the wide-angle end,
The front lens group includes:
A first lens group disposed on the most object side and having a positive refractive power;
A second lens group disposed on the image side of the first lens group and having negative refractive power;
The distance between the first lens group and the second lens group is larger at the telephoto end than at the wide angle end;
The rear lens group is
A third lens having a positive refractive power that is located closer to the object side at the telephoto end than at the wide-angle end, and has a smaller distance from the second lens group at the telephoto end than at the wide-angle end, and that satisfies the following conditions: A zoom lens comprising: a lens group.
0.01 <f ₃ / _ft <0.16 (1)
However,
f ₃ is the focal length of the third lens group,
_ft is the focal length of the entire zoom lens system at the telephoto end,
It is.   The zoom lens according to claim 1, wherein the first lens group is located closer to the object side at a telephoto end than at a wide angle end. From the object side,
A front lens group having negative refractive power at the wide-angle end;
It consists of a rear lens group with positive refractive power at the wide-angle end,
The front lens group includes:
The first lens group disposed on the most object side and having a positive refractive power;
A second lens group disposed on the image side of the first lens group and having negative refractive power;
The first lens group is positioned closer to the object side at the telephoto end than at the wide-angle end, and the distance from the second lens group is greater at the telephoto end than at the wide-angle end;
The rear lens group is
A third lens group having a positive refractive power and a distance from the second lens group that is smaller at the telephoto end than at the wide-angle end;
The zoom lens according to claim 1, wherein the first lens group satisfies the following conditions.
_{0.15 <f 1 / f t <} 0.50 ··· (2)
However,
f ₁ is the focal length of the first lens group,
_ft is the focal length of the entire zoom lens system at the telephoto end,
It is.   The zoom lens according to claim 3, wherein the third lens group is located closer to the object side at the telephoto end than at the wide-angle end. 2. The zoom lens according to claim 1, wherein the first lens group is positioned closer to the object side at the telephoto end than at the wide-angle end, and satisfies the following condition.
_{0.15 <f 1 / f t <} 0.50 ··· (2)
However,
f ₁ is the focal length of the first lens group,
It is. The zoom lens according to claim 1, wherein the second lens group satisfies the following condition.
0.01 <| f ₂ | / _ft <0.10 (3)
However,
f ₂ is the focal length of the second lens group,
It is. The imaging apparatus according to claim 1, wherein the following condition is satisfied.
1.26 <ΣD1 / ΣD2 <3.00 (4)
However,
ΣD1 is the thickness of the first lens group on the optical axis,
ΣD2 is the thickness of the second lens group on the optical axis,
The thickness of the lens group on the optical axis is the actual distance from the object side surface of the lens closest to the object side to the image side surface of the lens closest to the image side in each lens group.
It is.   The zoom lens according to claim 1, wherein the second lens group includes two negative lenses and one positive lens. A fourth lens group having a positive refractive power is disposed on the image side of the third lens group;
9. The zoom lens according to claim 1, wherein an aperture stop is disposed between the second lens group and the fourth lens group. 10.   The zoom lens according to claim 9, wherein the zoom lens is a four-group zoom lens. When zooming from the wide-angle end to the telephoto end,
The first lens group moves so as to be positioned closer to the object side at the telephoto end than at the wide-angle end,
The second lens group moves;
The third lens group moves so that it is closer to the object side at the telephoto end than at the wide-angle end,
The fourth lens group moves;
The zoom lens according to claim 9, wherein the aperture stop moves so as to be positioned closer to the object side at the telephoto end than at the wide-angle end.   The zoom lens according to claim 9, wherein the fourth lens group moves so as to be closer to the image side at the telephoto end than at the wide-angle end. The zoom lens according to claim 9, wherein the fourth lens group is a most image side lens group in the zoom lens, and satisfies the following condition.
0.05 <f ₄ / _ft <0.30 (5)
However,
f ₄ is the focal length of the fourth lens group,
It is. The zoom lens has an aperture stop and a shutter positioned between the second lens group and the third lens group,
13. The zoom lens according to claim 1, wherein the aperture stop and the shutter are integrated with the third lens group and move toward the object side at the telephoto end rather than at the wide-angle end.   The zoom lens according to claim 1, wherein the first lens group includes a negative lens and a positive lens.   The zoom lens according to claim 15, wherein the first lens group includes two lenses, a positive lens and a negative lens. The zoom lens according to claim 1, wherein the zoom lens satisfies the following condition.
9 < _ft / _fw <50 (6)
1.1 <L _t / L _w <2.0 (7)
However,
f _w is the focal length of the entire zoom lens system at the wide-angle end,
L _t is the actual distance on the optical axis from the object-side lens surface to the image plane in the first lens group at the telephoto end,
L _w is the actual distance on the optical axis from the lens surface closest to the object side to the image plane in the first lens group at the wide-angle end,
It is. The zoom lens according to claim 1, wherein the zoom lens satisfies the following condition at a telephoto end.
5.6 <F _t <16.0 (8)
However,
_Ft is the F number of the zoom lens at the telephoto end, and is the minimum value when the F number is adjustable.   19. The zoom lens according to claim 1, wherein all the lens groups included in the zoom lens have an aspheric lens surface. The total number of lenses included in the zoom lens is 8 to 12,
Each of the first and third lens groups has a negative lens and a positive lens;
The zoom lens according to any one of claims 1 to 19, wherein the second lens group includes a positive lens and a plurality of negative lenses. A zoom lens,
An image sensor that is disposed on the image side of the zoom lens and converts an image formed by the zoom lens into an electrical signal;
21. An image pickup apparatus, wherein the zoom lens is the zoom lens according to at least one of claims 1 to 20.   The imaging apparatus according to claim 21, further comprising an image processing unit that performs signal processing for correcting an aberration included in the electrical signal. The imaging apparatus according to claim 21 or 22, wherein the following condition is satisfied.
0.50 <IH _w / f _w <1.00 (9)
However,
IH _w is the maximum image height at the wide-angle end,
f _w is the focal length of the entire zoom lens system at the wide-angle end,
It is.

Images