Zoom lens barrel and image pickup apparatus having the same

A zoom lens barrel capable, even if it has an image shake correction mechanism and a diaphragm mechanism, of decreasing a distance between lens groups of a photographing optical system of the lens barrel, whereby the lens barrel size can be reduced and the magnification can be increased, and capable of preventing a collision between diaphragm blades of the diaphragm mechanism and the lens groups from occurring when vibration, impact, or the like is applied to the lens barrel. When apart of an image shake correction lens intrudes into an aperture of diaphragm blades, a restricted portion of a lens holding member and a restricting portion of a diaphragm restrict a maximum movement of the lens holding member in a direction perpendicular to the optical axis, thereby restricting a maximum amount of movement of the image shake correction lens in the direction perpendicular to the optical axis.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens barrel and an image pickup apparatus provided with the lens barrel.

2. Description of the Related Art

An image pickup apparatus such as a digital camera mounted with a zoom lens barrel has been demanded to have a high photographing magnification and a thin thickness. This poses a problem that a movement stroke of a photographing lens group must be increased while reducing the lens barrel size.

Nevertheless, there has widely been used a camera that has a lens barrel provided with an iris diaphragm for changing the amount of incident light to cope with various photographing conditions. In such a camera, a movement of a photographing lens group is restricted by the iris diaphragm provided in the lens barrel.

In a case, for example, that the iris diaphragm is disposed between photographing lens groups, these lens groups cannot relatively be moved toward each other much closer than the thickness of the iris diaphragm. In another case that one of photographing lens groups includes an image shake correction lens that is movable in a direction perpendicular to an optical axis, the photographing lens groups must be disposed taking account of a maximum amount of movement of the image shake correction lens.

Conventionally, there has been proposed an image pickup apparatus having a lens barrel in which a diaphragm is provided on a portion of an object-side lens surface of a lens (lens group) (see, Japanese Laid-open Patent Publication No. 2004-053633).

However, the diaphragm of the proposed image pickup apparatus has an aperture of a fixed diameter, and accordingly, if a target F number in design is determined at one of wide-angle and telephoto ends, an F number at another of the wide-angle and telephoto ends is determined by a focal distance. Thus, if an attempt is made to increase the diaphragm aperture diameter at the wide-angle end, the diaphragm aperture diameter at the telephoto end also increases. To obviate this, the number of lenses must be increased, so that the lens barrel size cannot be reduced.

There has also been proposed a lens barrel frame that includes a lens having a convex spherical portion (Japanese Laid-open Patent Publication No. H10-111444).

However, in a case that an image shake correction lens movable in a direction perpendicular to the optical axis is used in the proposed lens barrel frame, interference can occur between the image shake correction lens and diaphragm blades when vibration, impact, or the like is applied to the lens barrel frame in a state that the convex spherical portion of the lens intrudes into an aperture of the diaphragm blades, resulting in a fear that the image shake correction lens and/or the diaphragm blades are damaged. It is therefore difficult to apply the construction disclosed in Japanese Laid-open Patent Publication No. H10-111444 to a lens barrel provided with an image shake correction lens.

SUMMARY OF THE INVENTION

The present invention provides a zoom lens barrel and an image pickup apparatus having the same that are capable, even if the lens barrel has an image shake correction mechanism and a diaphragm mechanism, of decreasing a distance between lens groups of a photographing optical system of the lens barrel, whereby the lens barrel size can be reduced and the photographing magnification can be increased, and capable of preventing a collision between diaphragm blades of the diaphragm mechanism and the lens groups from occurring when vibration, impact, or the like is applied to the lens barrel.

According to one aspect of this invention, there is provided a zoom lens barrel having a photographing optical system movable between photographing positions and a retracted position in a direction of an optical axis, which comprises an image shake correction mechanism having an image shake correction lens that constitutes a part of the photographing optical system and having a lens holding member that is configured to hold the image shake correction lens and movable in a direction perpendicular to the optical axis, and a restriction unit configured to restrict a maximum amount of movement of the lens holding member in the direction perpendicular to the optical axis to thereby restrict a maximum amount of movement of the image shake correction lens in the direction perpendicular to the optical axis.

According to this invention, even if the lens barrel has an image shake correction mechanism and a diaphragm mechanism, a distance between lens groups of the photographing optical system of the lens barrel can be decreased, whereby the lens barrel size can be reduced and the photographing magnification can be increased. Furthermore, a collision between the diaphragm blades of the diaphragm mechanism and the lens groups can be prevented from occurring when vibration, impact, or the like is applied to the lens barrel.

Further features of the present invention will become apparent from the following description of an exemplary embodiment with reference to the attached drawings.

DESCRIPTION OF THE EMBODIMENTS

The present invention will now be described in detail below with reference to the drawings showing a preferred embodiment thereof.

FIGS. 1A and 1Bshow a digital camera in external front perspective view and in rear view, respectively, where the digital camera is an example of an image pickup apparatus according to one embodiment of this invention.

As shown inFIG. 1A, the digital camera20of this embodiment has its front surface on which there are disposed an auxiliary light source19for light and distance measurements, a finder21used to determine the composition of an object, a strobe22, and a lens barrel23. The lens barrel23is a zoom lens barrel that has a photographing optical system movable between photographing positions (telephoto and wide-angle positions and intermediate positions therebetween in this example) and a retracted position in a direction of an optical axis and capable of changing the photographing magnification.

On an upper surface of the digital camera20, there are disposed a release button16, a zoom switch17, and a power switch button18. As shown inFIG. 1B, a finder eyepiece24, a display25such as an LCD, and operation buttons26to31are disposed on a rear surface of the digital camera20.

FIG. 2shows in block diagram a control system of the digital camera20.

The aforementioned release button16, zoom switch17, power switch button18, display25, and operation buttons26to31are connected to a bus45. A memory41, compression/uncompression unit42, memory card drive43, drive circuit44, ROM46, CPU47, and RAM48are also connected to the bus45.

The drive circuit44is connected with a zoom mechanism32that zoom-drives the lens barrel23, a focus drive mechanism33that drives a focus lens12, a shutter drive mechanism35that drives a shutter34, a diaphragm drive mechanism36that drives a diaphragm3, and a correction lens drive mechanism49that drives an image shake correction lens. In this example, the correction lens drive mechanism49drives a second lens1(image shake correction lens) via a second lens holding member2, which are shown inFIGS. 3 to 5.

An image pickup device15(such as a CCD sensor or a CMOS sensor) and the strobe22are also connected to the drive circuit44. Under the control of the CPU47, the drive circuit44controls the drives of respective parts of the camera that are connected to the drive circuit44.

The ROM46stores a control program, etc., and the RAM48stores data required for execution of the control program. An analog signal processor37performs analog processing on image data output from the image pickup device15and outputs the processed image data to an A/D converter38.

The A/D converter38converts the analog data received from the image pickup device15into digital data and outputs the digital data to a digital signal processor39. The digital signal processor39performs predetermined processing on the digital data and outputs the processed data as image data to the memory41.

The image data stored in the memory41is compressed by the compression/uncompression unit42into e.g. JPEG or TIFF data, which is then output to and stored into a memory card that is mounted to the memory card drive43.

The image data stored in the memory41and the image data stored in the memory card can be uncompressed by the compression/uncompression unit42, and the uncompressed image data can be displayed on the display25. When image data displayed on the display25is viewed and determined by a user as being unnecessary to be retained for record purpose, the image data can be deleted by the user by operating the operation button31.

Next, with reference toFIGS. 3 to 7, a description will be given of the lens barrel23.

FIGS. 3 to 5show the lens barrel23in cross section where the photographing optical system is positioned at a TELE (telephoto) position, at a WIDE (wide-angle) position, and at a retracted position, respectively.FIGS. 6 and 7each show the iris diaphragm3and an anti-vibration base plate4of the lens barrel23in perspective view.

As shown inFIGS. 3 to 5, the lens barrel23includes a first lens holding member6that holds a first lens5, which is disposed on a side of the lens barrel closest to an object. The iris diaphragm3having diaphragm blades3bis disposed on an image surface side of the first lens holding member6. In other words, the diaphragm3is disposed rearward of the lens holding member6. A second lens holding member2that holds a second lens1is disposed on an image surface side of the iris diaphragm3, and the anti-vibration base plate4is disposed on an image surface side of the second lens holding member2. The second lens holding member2is movable relative to the first lens holding member6and relative to the anti-vibration base plate4in a direction perpendicular to the optical axis. The shutter34is mounted to an image surface side of the anti-vibration base plate4.

The iris diaphragm3is an example of an iris diaphragm of this invention, which is provided in the photographing optical system. The iris diaphragm3and the diaphragm drive mechanism36(FIG. 2) constitute a diaphragm mechanism.

The second lens1is an example of an image shake correction lens of this invention that constitutes a part of the photographing optical system. The second lens1, the second lens holding member2, and the correction lens drive mechanism49(FIG. 2) constitute an image shake correction mechanism.

A first cam cylinder7is disposed on an outer peripheral side of the first lens holding member6, and cam grooves are formed in an inner periphery of the first cam cylinder7. A rectilinear guide cylinder8is disposed on an inner peripheral side of the first lens holding member6and bayonet-connected with the first cam cylinder7.

A second cam cylinder9is disposed on an outer peripheral side of the first cam cylinder7. A cam groove along which a follower of the first cam cylinder7moves is formed in an inner periphery of the second cam cylinder9. An actuating cylinder10is disposed on an outer peripheral side of the second cam cylinder9and held at its outer periphery by a cover member11.

When the actuating cylinder10is rotatably driven by the zoom mechanism32, the first cam cylinder7rotates about the optical axis and moves in the optical axis direction with the rotation of the actuating cylinder10, while the follower of the first cam cylinder7moves along the cam groove of the second cam cylinder9.

The rectilinear guide cylinder8bayonet-connected with the first cam cylinder7moves in unison with the first cam cylinder7in the optical axis direction, while being prevented from rotating by engagement with a rectilinear groove formed in the inner periphery of the second cam cylinder9.

The second lens holding member2, the iris diaphragm3, and the anti-vibration base plate4move in the optical axis direction along the cam grooves formed in the inner periphery of the first cam cylinder7, while being prevented from rotating by engagement with the rectilinear guide cylinder8.

A focus lens holding member13that holds the focus lens12is disposed between the anti-vibration base plate4and the image pickup device15. The focus lens12and the focus lens holding member13are moved in the optical axis direction by the focus drive mechanism33, whereby a focusing operation is performed. The image pickup device15is held by an image pickup device holding member14.

To increase the photographing magnification, the second lens1must be positioned as close to the first lens5as possible when the photographing optical system of the lens barrel23is at the TELE position (FIG. 3), to thereby increase a moving distance of the second lens1in the optical axis direction between the WIDE position (FIG. 4) and the TELE position.

To this end, in the present embodiment, when the photographing optical system of the lens barrel23is at the TELE position, a part of the second lens1(i.e., a convex spherical surface portion denoted by reference numeral1ainFIG. 3) intrudes into an aperture of the diaphragm blades3bof the iris diaphragm3disposed between the first lens5and the second lens1, so as to position the second lens1as close to the first lens5as possible.

In a state shown inFIG. 4where the photographing optical system of the lens barrel23is at the WIDE position, the second lens holding member2can be moved by the lens drive mechanism49in a diametral direction (i.e., in a direction perpendicular to the optical axis) until a first restricted portion2cprovided in the second lens holding member2becomes in diametral contact with a first restricting portion4cprovided in the anti-vibration base plate4. In other words, a further movement of the second lens holding member2is restricted by the engagement between the first restricted portion2cand the first restricting portion4c, thereby restricting a maximum amount of movement of the second lens holding member2and a maximum amount of movement of the second lens1in the direction perpendicular to the optical axis in a state where the photographing optical system is at the WIDE position.

Nevertheless, since the maximum amount of movement of the second lens1is relatively large, there is a possibility that the second lens1collides with the diaphragm blades3bwhen the photographing optical system of the lens barrel23is at the TELE position shown inFIG. 3, even if the maximum amount of movement of the second lens1is restricted.

To obviate this, in the present embodiment, a second restricting portion3ais provided in the iris diaphragm3as shown inFIGS. 3 and 6, and a second restricted portion2ais provided in the second lens holding member2as shown inFIGS. 3 and 7. When the second lens1intrudes into the aperture of the diaphragm blades3bin a state that the photographing optical system of the lens barrel23is at the TELE position shown inFIG. 3, the second restricting portion3aof the iris diaphragm3is disposed on the outer peripheral side of the second restricted portion2aof the second lens holding member2.

In that state, if the second lens holding member2is moved in the direction perpendicular to the optical axis by vibration, impact, or the like applied to the lens barrel23, the second restricted portion2ais brought in diametral contact with the second restricting portion3ato prevent the second lens1from moving. The maximum amount of movement of the second lens1restricted by the engagement between the second restricted portion2aand the second restricting portion3ais smaller than the maximum amount of movement of the second lens1restricted by the first restricted portion2cand the first restricting portion4cwhen the photographing optical system of the lens barrel23is at the WIDE position shown inFIG. 4.

An opening and closing range of the diaphragm blades3bis set in such a manner that the second lens1does not interfere with the diaphragm blades3b, even if the second lens holding member2is moved in the direction perpendicular to the optical axis until the second restricted portion2abecomes in contact with the second restricting portion3a.

As a result, when the photographing optical system of the lens barrel23is at the TELE position shown inFIG. 3, it is possible to prevent the second lens1from colliding with the diaphragm blades3b, even if vibration, impact, or the like is applied in a state where the spherical surface portion1aof the second lens1intrudes into the aperture of the diaphragm blades3b.

When the photographing optical system of the lens barrel23is at the retracted position shown inFIG. 5, the diaphragm3is driven by the diaphragm drive mechanism36in such a manner that the diameter of the aperture of the diaphragm blades3bis made larger than that defined when the photographing optical system is at the TELE position, thereby increasing the length of intrusion of the spherical surface portion1aof the second lens1into the aperture. As a result, the distance between the first lens5and the second lens1is decreased, thereby making it possible to reduce the size of the lens barrel23when the photographing optical system is at the retracted position.

When the photographing optical system of the lens barrel23is at the retracted position, the second restricting portion3aof the iris diaphragm3is disposed on the outer peripheral side of the second restricted portion2aof the second lens holding member2, as with the case where the photographing optical system of the lens barrel23is at the TELE position ofFIG. 3. Accordingly, if the second lens holding member2is moved in the direction perpendicular to the optical axis by vibration, impact, or the like, the second restricted portion2abecomes in contact with the second restricting portion3ato thereby prevent the second lens1from moving, so that the second lens1can be prevented from colliding with the diaphragm blades3b. The second restricted portion2aand the second restricting portion3aare an example of a restriction unit of this invention.

When the power switch button18is operated to be turned on by the user, the photographing optical system of the lens barrel23moves from the retracted position ofFIG. 5to the WIDE position ofFIG. 4. At that time, after the second lens1retreats from the aperture of the diaphragm blades3b, an origin position of the second lens1is detected.

It should be noted that the detection accuracy and the camera's optical performance can be improved by detecting the origin position of the second lens1by using the first restricting portion4cand the first restricted portion2cof the image shake correction mechanism (second lens holding member2), as compared to a case where the origin position of the second lens1is detected by using the second restricting portion3a(which is separated from the image shake correction mechanism) and the second restricted portion2a.

It should be noted that although the lens barrel23having the iris diaphragm has been described in this embodiment, the present invention is also applicable to a lens barrel having no iris diaphragm. The restriction unit can be provided in e.g. the first lens holding member. In that case, an advantage is achieved that no excessive impact is applied to the image shake correction mechanism.

As described above, in this embodiment, a movement of the second lens holding member2in the direction perpendicular to the optical axis is restricted by the engagement either between the first restricted portion2cof the second lens holding member2and the first restricting portion4cof the anti-vibration base plate4or between the second restricted portion2aof the second lens holding member2and the second restricting portion3aof the iris diaphragm3in such a manner that the maximum amount of movement of the second lens1(which is an example of an image shake correction lens of this invention) in the direction perpendicular to the optical axis changes according to the position of the photographing optical system in the optical axis direction. As a result, even if the lens barrel23has the image shake correction mechanism and the diaphragm mechanism, the distance between lens groups can be decreased, making it possible to reduce the lens barrel size and increase the photographing magnification. It is also possible to avoid a collision between the diaphragm blades3band the second lens1due to vibration, impact, or the like applied to the lens barrel.

This application claims the benefit of Japanese Patent Application No. 2011-185974, filed Aug. 29, 2011, which is hereby incorporated by reference herein in its entirety.