JPH09218346A - Optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a telephoto lens which causes no performance deterioration even when a hand shake is corrected. SOLUTION: This optical system has a 1st lens group Gr1 which has positive refracting power, a 2nd lens group Gr2 which has negative refracting power, and a 3rd lens group Gr3 which has positive refracting power in order from an object side. For focusing from an infinite-distance body to a finite-distance body, the 2nd lens group Gr2 is moved to the image side, and hand-shake corrections are made by moving the 3rd lens group Gr3 as a hand shape correcting lens group at right angles to the optical axis. This optical system satisfies a conditional inequality of 1.1 <|βb(1-βa )|<4.5, where βa is the power of the hand shake correcting lens group and βb is the power of the lens group more on the image side than the hand shake correcting lens group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system, and more specifically, to a telephoto system having a camera shake correction function capable of preventing image blur caused by camera shake (for example, vibration during hand-held shooting of a camera). Related to the optical system.

[0002]

2. Description of the Related Art Hitherto, most of the causes of failure in photographing have been camera shake and out of focus. However, in recent years,
With the introduction of autofocus mechanisms in most of the cameras and the improvement of the focusing accuracy of the autofocus mechanisms, the failure of taking pictures due to out-of-focus has been almost eliminated. However, the problem of photography failure due to camera shake remains unsolved, and there is a high possibility that camera shake will occur especially in the case of a telephoto lens with a long focal length, so there is a growing demand for an image stabilization function in the telephoto optical system. It ’s just.

As a telephoto optical system having a camera shake correction function, a system has been proposed in which some lens groups are decentered for correction. For example, in Japanese Patent Laid-Open No. 63-115126, a telephoto monofocal lens is divided into a fixed lens group and a correction lens group in order from the object side, and the correction lens group is moved in the direction perpendicular to the optical axis to correct the image blur. An optical system for performing is proposed. Further, Japanese Patent Application Laid-Open No. 2-135408 proposes an optical system for correcting camera shake by moving the second lens unit or the third lens unit in a direction perpendicular to the optical axis with a positive, negative, positive and negative configuration. Further, in Japanese Patent Application Laid-Open No. 7-270724, an optical system having a positive / negative positive configuration, in which the second lens group is used for focusing, and the third lens group is moved in the direction perpendicular to the optical axis, is provided. Proposed.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention JP-A-63-115126
In the optical system described in the publication, the image stabilizing lens group is moved by 2 mm to correct an image blur of 2 mm on the image plane.
This means that a movement amount of 2 mm is necessary to correct the blur of about 0.4 degree. That is, JP-A-63-115126
In the optical system described in the publication, since the correction sensitivity of the camera shake correction lens group is small, the movement amount of the camera shake correction lens group becomes too large when the camera shake angle is large. If the amount of movement of the lens increases, the lens diameter must be increased accordingly.
There is a problem that the whole becomes large.

Further, in Japanese Patent Laid-Open No. 7-270724, the camera shake correction angle is evaluated at about 0.2 degree, but when hand-held shooting of a night view or the like, a larger camera shake occurs. Therefore, in order to enable handheld shooting of night scenes,
The camera shake correction angle must be made larger than 0.2 degrees, but in that case, aberration deterioration cannot be tolerated.

Further, the optical system described in Japanese Patent Laid-Open No. 2-135408 has a problem that a large-aperture telephoto lens cannot be provided because the aperture ratio of the lens is not large.

The present invention has been made in view of these points, and has a large correction sensitivity of the camera shake correction lens group, has a satisfactory optical performance corresponding to a sufficiently large camera shake angle, and has a camera shake correction function. It is an object of the present invention to provide an optical system having a large aperture ratio telephoto system, which has

[0008]

To achieve the above object, the present invention provides a first lens group having a positive refracting power in order from the object side, a second lens group having a negative refracting power, and a positive refracting power. A third lens group having power, and focusing from an object at infinity to an object at a finite distance is performed by moving the second lens group to the image side, and an image stabilizing lens included in the third lens group It is characterized in that the camera shake correction is performed by moving the group perpendicularly to the optical axis and that the following conditional expression is satisfied.

1.1 <| βb (1-βa) | <4.5

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 3 show lens arrangements in the infinity in-focus condition according to the first to third embodiments.

In the first embodiment of the present invention, the first lens group Gr1 having a positive refractive power, the second lens group Gr2 having a negative refractive power, and the third lens having a positive refractive power are arranged in this order from the object side. The third lens group Gr3 includes a lens group Gr3 and a fourth lens group Gr4 having a negative refracting power, and the second lens group Gr2 is moved to the image side to perform focusing from an object at infinity to an object at a finite distance. Image stabilization is performed by decentering Gr3 in parallel with the optical axis. The first lens group Gr1 includes a biconvex positive first lens L1, a second lens L2, a biconcave negative third lens L3, a fourth lens L4, and a positive meniscus fifth lens L5 having a convex surface directed toward the object side. . Second
The lens group Gr2 is composed of a cemented lens of a positive meniscus sixth lens L6 having a concave surface facing the object side and a biconcave negative seventh lens L7, and a biconcave negative eighth lens L8. The third lens group Gr3 is composed of a diaphragm and a cemented lens of a positive meniscus ninth lens L9 having a concave surface facing the object side and a negative meniscus tenth lens L10 having a concave surface facing the object side.
The fourth lens group Gr4 includes an eleventh lens L11 having a negative meniscus whose convex surface faces the object side and a twelfth lens L12 having a positive meniscus whose concave surface faces the object side. Further, it has a protective glass on the most image side.

In the second embodiment, the first lens group Gr1 having a positive refractive power, the second lens group Gr2 having a negative refractive power, and the third lens group Gr3 having a positive refractive power are sequentially arranged from the object side. And a fourth lens group Gr4 having negative refracting power. By moving the second lens group Gr2 toward the image side, focusing from an infinite object to a finite object is performed, and the third lens group Gr3 Image stabilization is performed by eccentricity parallel to the direction perpendicular to the axis. First lens group G
r1 is a biconvex positive first lens L1, a second lens L2, a biconcave negative third lens L3, a positive meniscus fourth lens L4 having a concave surface facing the object side, and a positive meniscus convex surface facing the object side. It comprises a fifth lens L5. The second lens group Gr2 is composed of a cemented lens of a positive meniscus sixth lens L6 having a concave surface facing the object side and a biconcave negative seventh lens L7, and a biconcave negative eighth lens L8. The third lens group Gr3 is composed of a stop, a biconvex positive ninth lens L9, a positive meniscus tenth lens L10 having a concave surface facing the object side, and a negative meniscus eleventh lens L11 having a concave surface facing the object side. It consists of a pair of lenses. The fourth lens group Gr4 includes a negative meniscus twelfth lens L12 having a convex surface directed toward the object side and a positive meniscus thirteenth lens L13 having a concave surface directed toward the object side.
Further, it has a protective glass on the most image side.

In the third embodiment, the first lens group Gr1 having a positive refractive power, the second lens group Gr2 having a negative refractive power, and the third lens group Gr3 having a positive refractive power are sequentially arranged from the object side. And a fourth lens group Gr4 having negative refracting power. By moving the second lens group Gr2 toward the image side, focusing from an infinite object to a finite object is performed, and the third lens group Gr3 Image stabilization is performed by eccentricity parallel to the axis. The first lens group Gr1 includes a biconvex positive first lens L1, a second lens L2, a biconcave negative third lens L3, a positive meniscus fourth lens L4 having a concave surface facing the object side, and a convex surface facing the object side. And a fifth lens L5 having a positive meniscus. The second lens group Gr2 is composed of a cemented lens of a positive meniscus sixth lens L6 having a concave surface facing the object side and a biconcave negative seventh lens L7, and a biconcave negative eighth lens L8. The third lens group Gr3 is a diaphragm, a biconvex positive ninth lens L9, a positive meniscus tenth lens L10 having a concave surface facing the object side, and a negative meniscus eleventh lens L11 having a concave surface facing the object side. It consists of a lens. The fourth lens group Gr4 includes a negative meniscus twelfth lens L12 having a convex surface directed toward the object side, a negative meniscus thirteenth lens L13 having a convex surface directed toward the object side, and a positive meniscus fourteenth lens L14 having a convex surface directed toward the object side. The cemented lens is a positive meniscus fifteenth lens L15 having a concave surface facing the object side. Further, it has a protective glass on the most image side.

Generally, an optical system having a first lens group having a positive refracting power, a second lens group having a negative refracting power, and a third lens group having a positive refracting power in order from the object side is an object side optical system. The lens is larger, and the lens on the object side is heavier. Therefore, it is not preferable to use the first lens group as the camera shake correction lens group, since this imposes a heavy load on the camera shake correction drive system. The second lens group is a lens group that moves for focusing, and if this lens group is used for camera shake correction, it is necessary to move each focus drive system in the direction perpendicular to the optical axis. This burden becomes very large. In the present invention, the third lens group is moved in the direction perpendicular to the optical axis when the camera shake is corrected. Since this lens group is the lightest in weight and is fixed during focusing, the load on the correction drive system is small and the correction drive system can be easily arranged. At this time, it is preferable that the following conditional expression (1) is satisfied.

1.1 <| βb (1-βa) | <4.5 (1) where βa is the magnification of the image stabilizing lens group and βb is the magnification of the lens group on the image side of the image stabilizing lens group.

Incidentally, in the first to third embodiments, the third lens group Gr3 corresponds to a "camera shake correction lens group", and the fourth lens group Gr4 "a lens group on the image side of the camera shake correction lens group". Equivalent to.

The above conditional expression (1) represents the camera shake sensitivity of the camera shake correction lens group. If the upper limit of conditional expression (1) is exceeded, the camera shake correction sensitivity becomes too weak, and the amount of movement of the camera shake correction lens group becomes too large. For this reason,
Since it is necessary to widen the lens diameter of the camera shake correction lens group, the overall size is increased, which is not preferable. On the other hand, when the value goes below the lower limit of the conditional expression (1), the camera shake correction sensitivity becomes too strong, so that it is necessary to make the movement accuracy of the correction drive system and the position detection accuracy of the correction lens group extremely high.
This is not preferable because it increases the manufacturing cost. If the lower limit is set to 1.3, the cost can be further reduced. Further, if the upper limit is set to 2.5, the lens diameter of the image stabilizing lens unit can be made smaller. In the case of an optical system in which no lens unit exists on the image side of the camera shake correction lens unit, that is, in the case of an optical system having a positive / negative positive three-group structure, conditional expression (1) may be applied with βb = 1.

According to the present invention, the first lens group having a positive refractive power and the second lens group having a negative refractive power are arranged in this order from the object side.
Focusing is performed by moving the second lens group to the image side when focusing from an object at infinity to an object at a finite distance by having a third lens group having a positive refractive power. Since this type of telephoto lens is of a telephoto type as a whole, the total length can be reduced while having a long focal length. Further, since focusing is performed by the second lens group, focusing can be performed by a relatively lightweight lens group, and the lens movement amount required for focusing is small, so that the optical performance when focusing on a close distance is sufficiently high. be able to. At this time, it is preferable that the following conditional expression (2) is satisfied.

0.4 <D / f1 <1.0 (2) where f1 is the focal length of the first lens group D is the axial distance from the most object surface of the first lens group to the most image side surface.

The conditional expression (2) represents a desirable condition for obtaining a compact large-aperture telephoto lens. When the value goes below the lower limit of the conditional expression (2), the lens diameter after the second lens group further increases, and the lens system becomes large. On the other hand, if the upper limit of conditional expression (2) is exceeded, the balance between on-axis light and off-axis light will deteriorate after the second lens group, and correction after the second lens group will become difficult, resulting in good image formation. A high-performance optical system cannot be obtained. If the upper limit is set to 0.9, a better imaging performance can be obtained. If the lower limit is set to 0.5, a more compact optical system can be obtained.

Further, it is preferable that the following conditional expression (3) is satisfied.

-3.1 <f1 / f2 <-2.2 (3) where f1 is the focal length of the first lens group and f2 is the focal length of the second lens group.

The above conditional expression (3) is defined by the first lens group and the second lens group.
It represents the ratio of the focal length to the lens group. Conditional expression (3)
Beyond the upper limit of, it becomes difficult to make the overall length compact, and the amount of movement of the second lens group during focusing also increases. On the other hand, when the value goes below the lower limit of the conditional expression (3), the degree of telephoto becomes too strong, and it becomes difficult to secure a sufficient back focus.

Further, it is preferable that the following conditional expression (4) is further satisfied.

3.5 <fT / fD <8.0 (4) where fT is the focal length of the entire system and fD is the focal length of the image stabilizing lens group.

Conditional expression (4) represents the ratio of the focal length of the image stabilizing lens group to the focal length of the entire system. If the upper limit of conditional expression (4) is exceeded, the refractive power of the camera shake correction lens group becomes too strong, so that aberrations occurring in the camera shake correction lens group become too large. Further, since it is necessary to use many lenses in order to suppress the aberration generated in the camera shake correction lens group, the weight of the correction lens group is increased, which is not preferable. On the other hand, when the value goes below the lower limit of the conditional expression (4), the camera shake correction sensitivity becomes too weak, and the movement amount of the camera shake correction lens group becomes too large. For this reason, the lens diameter of the camera shake correction lens group needs to be greatly increased, and the overall size is increased, which is not preferable. By setting the upper limit to 6.0, it is possible to further suppress the amount of aberration that occurs in the image stabilizing lens unit. Setting the lower limit to 4.0 is preferable because the correction sensitivity can be made stronger.

The camera shake correction lens group is a lens group having a positive refracting power, but in order to suppress chromatic aberration that occurs during camera shake correction, the camera shake correction lens group must be color-corrected by itself. For that purpose, it is preferable that the image stabilizing lens group includes a cemented lens of a positive lens and a negative lens. Further, it is preferable that the camera shake correction lens group is composed of only positive and negative cemented lenses, because the camera shake correction lens group is very compact and lightweight, and the burden on the correction drive system can be very light.

When the lens group is moved perpendicularly to the optical axis for camera shake correction, a portion where a light beam does not pass in the normal state passes in the camera shake compensation state. This may become a harmful ray and may deteriorate the imaging performance. Therefore, if a fixed diaphragm is provided on the object side of the image stabilization lens group, in the image stabilization lens group, or on the image side of the image stabilization lens group to block harmful rays during image stabilization, even in the image stabilization state. Therefore, good imaging performance can be obtained.

In each of the embodiments of the present invention, the image stabilizing lens unit is located on the image side of the aperture stop. With such a configuration, the member of the correction drive system can be arranged on the image side of the diaphragm mechanism, that is, on the lens mount side, so that the correction drive system can be arranged relatively freely, which is preferable.
Further, integrating the diaphragm mechanism and the correction drive system is very effective in reducing the number of parts.

[0030]

EXAMPLES Tables 1 to 4 below show Examples 1 to 3 of the zoom lens according to the present invention. Specifically, Table 1 shows Example 1, Table 2 shows Example 2, and Tables 3 and 4 show Example 3.
Is shown. These Examples 1 to 3 correspond to the first to third embodiments. In each example, ri (i = 1,2,
3, ...) is the radius of curvature of the i-th surface counted from the object side, di (i =
1,2,3 ...) indicates the i-th axial upper surface distance counted from the object side, and Ni (i = 1,2,3 ...), νi (i = 1,2,3 ...). ) Indicates the refractive index and Abbe number for the d-line of the i-th lens counted from the object side. Further, f is the focal length of the entire system, and FNO is the F number. Regarding the axial upper surface distances d10 and d15, the values in the infinity in-focus state and the closest distance in-focus state are shown in order from the left. The closest object distance in Example 1 is 1774.67 mm,
The closest object distance in Example 2 is 1774.95 mm, and the closest object distance in Example 3 is 1775.48 mm.

In each of the examples, the surface with a radius of curvature marked with * indicates that it is a surface composed of an aspherical surface, and is defined by the following formula 1 representing the surface shape of the aspherical surface. And

[0032]

[Equation 1]

Here, X: height in a direction perpendicular to the optical axis Y: amount of displacement from the reference plane in the optical axis C: paraxial curvature ε: quadric surface parameter Ai: i-th order aspherical coefficient .

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

[Table 4]

FIGS. 4 to 6 show the first to third embodiments, respectively.
FIG. 6 is a longitudinal aberration diagram corresponding to. In each figure, the upper part shows the aberration in the in-focus state at infinity, and the lower part shows the aberration in the latest cemented focus state. In the spherical aberration diagram, the solid line (d) shows the spherical aberration with respect to the d line, and the broken line (SC) shows the sine condition. In the astigmatism diagram, the broken line (DM) and the solid line (DS)
Represent astigmatisms on the meridional surface and the sagittal surface, respectively.

7 to 9 are lateral aberration diagrams in the infinity focused state corresponding to Examples 1 to 3 respectively, and FIGS. 10 to 12 are the closest distance distances corresponding to Examples 1 to 3 respectively. It is a lateral-aberration figure in a focus state. In each figure, the upper 3 rows show the lateral aberration in the state where the image stabilization is performed at the image stabilization angle of 0.7 degree, and the lower 2
Steps show lateral aberrations without camera shake correction.

Table 5 shows values corresponding to the conditional expressions (1) to (4) in the first to third embodiments.

[0041]

[Table 5]

[0042]

According to the present invention, the correction sensitivity of the camera shake correction lens group is increased. For this reason, it is possible to sufficiently perform image stabilization even with a sufficiently large image stabilization angle, and
Good optical performance can be obtained before and after camera shake correction, and the optical system is suitable for a large aperture ratio telephoto system.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram according to a first embodiment of the present invention.

FIG. 2 is a lens configuration diagram according to a second embodiment of the present invention.

FIG. 3 is a lens configuration diagram of a third embodiment of the present invention.

FIG. 4 is an aberration diagram of Example 1 of the present invention.

FIG. 5 is an aberration diagram of Example 2 of the present invention.

FIG. 6 is an aberration diagram for Example 3 of the present invention.

FIG. 7 is an aberration diagram for Example 1 of the present invention when focused on an object at infinity.

FIG. 8 is an aberration diagram for Example 2 of the present invention when focused on an object at infinity.

FIG. 9 is an aberration diagram for Example 3 of the present invention when focused on an object at infinity.

FIG. 10 is an aberration diagram in Example 1 of the present invention in a state where the closest distance is in focus.

FIG. 11 is an aberration diagram of Example 2 of the present invention in a state where the closest distance is in focus.

FIG. 12 is an aberration diagram for Example 3 of the present invention in a state where the closest distance is in focus.

[Explanation of symbols]

 Gr1 ... 1st lens group Gr2 ... 2nd lens group Gr3 ... 3rd lens group (camera shake correction lens group) Gr4 ... 4th lens group

Claims (1)

[Claims] 1. A first lens element having a positive refractive power in order from the object side.
It has a lens group, a second lens group having a negative refracting power, and a third lens group having a positive refracting power, and focusing from an object at infinity to an object at a finite distance images the second lens group. The optical image is characterized by satisfying the following conditional expression while performing the image stabilization by moving the image stabilization lens group included in the third lens group perpendicularly to the optical axis. System, 1.1 <| βb (1-βa) | <4.5 where βa is the magnification of the image stabilization lens group βb: The magnification of the lens group on the image side of the image stabilization lens group.