Lens barrel and imaging apparatus

The lens barrel includes a stationary tube, a cam ring, and a rectilinear motion tube. The rectilinear motion tube is moved by the rotation of the cam ring in the optical axis direction. A lens frame holding a lens is moved by a driving unit (feed screw and a motor) in the optical axis direction. The stationary tube includes a main guide bar in the optical axis direction. The rectilinear motion tube includes another main guide bar in the optical axis direction. The lens frame includes first and second fitting portions slidably supported by the main guide bars in the optical axis direction, and the first and second fitting portions are disposed separately in the optical axis direction, and the main guide bars are disposed in different positions around the optical axis.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a lens barrel of a retractable lens structure used for cameras such as a digital video camera, and an imaging apparatus.

Description of the Related Art

In digital video cameras, such a structure is known in which a guide bar is used to hold a lens frame in order to reduce tilt of the lens while zooming as much as possible. Holding portions of the lens frame can be arranged separately in a longitudinal direction of a guide bar. As a result, tilt of the lens can be restricted and the shift of the image can be prevented. However, the long guide bar causes the lens barrel to limit the size thereof to be smaller. Japanese Patent Application Laid-open No. 8-94905 discusses a driving mechanism for a movable member using a plurality of guide shafts and a linear motor, in a retractable lens barrel for a video camera.

In the structure discussed in Japanese Patent Application Laid-open No. 8-94905, the length of the guide bar holding the zoom lens is restricted within the entire length of the lens barrel in a retracted state. Therefore, compared with a non-retractable lens barrel, the moving range of the lens while zooming and the optical element holding accuracy are restricted.

SUMMARY OF THE INVENTION

The present invention is directed to a lens barrel including an optical element movable in an optical axis direction and a driving mechanism thereof, capable of keeping a moving range of the optical element and optical element holding accuracy when capturing an image, and reducing an entire length of the lens barrel when not capturing an image.

According to an aspect of the present invention, a lens barrel includes a lens holding member, a first lens barrel holding a first guide member, a second lens barrel holding a second guide member, wherein one end of the lens holding member is held by the first guide member, and the other end of the lens holding member is held by the second guide member, wherein the second guide member protrudes on an object side with respect to the first guide member in an optical axis direction with a shift from a retracted state to a ready for imaging state, wherein, in the imaging state, the lens holding member moves in the optical axis direction guided by the first guide member and the second guide member which protrudes to the object side from the first guide member.

According to the present invention, when capturing an image, the moving range and the optical element holding accuracy of the optical element can be maintained, and when not capturing an image, the entire length of the lens barrel can be reduced.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings. The present invention is applicable to a lens barrel including a mechanism capable of moving an optical element such as a zoom lens and a focus lens in an optical axis direction, and an optical apparatus and an imaging apparatus including the lens barrel.

Referring toFIG. 1toFIG. 9, a lens barrel according to a first exemplary embodiment of the present invention is described below.

FIG. 1is a cross sectional view along an optical axis direction illustrating a lens barrel in a usable state (ready for image capturing) according to the present exemplary embodiment. Hereinbelow, a position where an optical element movable along an optical axis direction is extended on the object side is defined as a ready-for-imaging position, and a position where the optical element is retracted on an image plane side in a retracted state is defined as a retracted position. The object side (i.e., left side inFIG. 1) is defined as an optical axis direction front side, the image plane side (i.e., right side inFIG. 1) is defined as an optical axis direction back side, and a near side to the optical axis is defined as an inner side. The positional relationship of the optical elements will be described based on the definition.

The lens barrel includes a stationary tube (first barrel) and a movable unit. The movable unit movable relative to a stationary tube1includes a cam member (cam ring2), a rectilinear motion member (rectilinear motion tube3, i.e., second lens barrel), and a holding member (lens frame4). The cam ring2is a third barrel attached to the stationary tube1to be movable around the optical axis, and is driven to be rotated by a drive source such as a motor (not illustrated). For example, when a stepping motor is used as a drive source, the rotation amount of the cam ring2is controlled by counting pulses.

FIG. 2Ais a front view of the lens barrel seen from the optical axis direction front side.FIG. 3is a cross sectional view illustrating a retracting operation of the lens barrel.FIG. 4is a cross sectional view illustrating a cam structure. As illustrated inFIG. 4, the movement of the cam ring2in the optical axis direction is restricted by a bayonet claw13of the stationary tube1in a state where the cam ring2is built in an imaging apparatus, including the retracted state of the lens barrel when not capturing an image and extended state of the lens barrel when capturing an image.

Rectilinear motion guides11(refer toFIG. 2AandFIG. 4) are provided on the inner peripheral surface of the stationary tube1, and are groove portions provided along the optical axis direction according to the present exemplary embodiment. A rectilinear motion tube3is moved by the rotation of the cam ring2in the optical axis direction. On the outer peripheral surface of the rectilinear motion tube3at the back end side, a plurality of cam followers31is provided. The cam followers31protrude outward. The rectilinear motion guides11restrict the rotation of the cam followers31around the optical axis. As illustrated inFIG. 2A, the plurality of rectilinear motion guides11is provided at three positions in a circumferential direction around the optical axis, to restrict movement of the rectilinear motion tube3in all directions other than the optical axis direction. The three cam followers31are provided on the rectilinear motion tube3respectively corresponding to the rectilinear motion guides11. The cam followers31abut against cam grooves21to move the rectilinear motion tube3back and forth along the cam grooves21in the optical axis direction caused by the rotation of the cam ring2.

Three guide bars6a,6b, and6cillustrated inFIG. 1are guide members configuring a guide portion for the lens frame4. In the present exemplary embodiment, the main guide bars6aand6b, and the sub guide bar6care used. Hereinbelow, the main guide bar6a(first guide bar) is also referred to as a fixed guide bar, and the main guide bar6b(second guide bar) is also referred to as a movable guide bar. Each of the fixed guide bar6a, the movable guide bar6b, and the sub guide bar (third guide bar)6cis formed of a metallic material (e.g., stainless steel) in a circular cylindrical shape.

The fixed guide bar6aconstituting a first guide portion and the sub guide bar6cconstituting a third guide portion are attached to the stationary tube1and held so as to extend in parallel to the optical axis direction. The movable guide bar6bconstituting the second guide portion are attached to the rectilinear motion tube3and held so as to extend in parallel to the optical axis direction. As illustrated inFIG. 2A, the movable guide bar6band the fixed guide bar6aare arranged on a circle around the optical axis in a different phase relationship. In other words, a plane including a central axis of the movable guide bar6band the optical axis, and a plane including a central axis of the fixed guide bar6aand the optical axis are arranged with a predetermined angle therebetween. The reason of this arrangement is that, in order to constitute a retractable structure, it is difficult to arrange the two main guide bars to be overlapped in the front view inFIG. 2A. Further, the movable guide bar6band the fixed guide bar6aare different in distance from the optical axis, because they are fixed to different parts.

By arranging the sub guide bar6cin a position as far as possible to the movable guide bar6band the fixed guide bar6a, rotational backlash around the optical axis can be reduced. As illustrated inFIG. 2A, the sub guide bar6cis positioned at an opposite side of the fixed guide bar6aacross the optical axis.

A first fitting portion9a, a second fitting portion9b, a third fitting portion9care provided on the lens frame4respectively for the fixed guide bar6a, the movable guide bar6b, and the sub guide bar6c. The first fitting portion9ais a first guided portion guided by the fixed guide bar6a. The second fitting portion9bis a second guided portion guided by the movable guide bar6b. The third fitting portion9cis a third guided portion guided by the sub guide bar6c.

The lens frame4is a holding member that hold a lens5. The second fitting portion9bis fitted with the movable guide bar6bto restrict the movement of the lens frame4in a plane orthogonal to the optical axis so that the lens frame4can move back and forth in the optical axis direction. The first fitting portion9ais fitted with the fixed guide bar6ato restrict the movement of the lens frame4in a plane orthogonal to the optical axis so that the lens frame4can move back and forth in the optical axis direction.FIG. 2Bis a cross sectional view of the first fitting portion9aand the second fitting portion9bcut by a plane orthogonal to the optical axis. The first fitting portion9aand the second fitting portion9bare provided with shaft hole portions respectively fitted with the fixed guide bar6aand the movable guide bar6b. The movement of the lens frame4is restricted in a plane orthogonal to the optical axis, and the lens frame4is guided along the optical axis direction. Further, as illustrated inFIG. 1, the first fitting portion9aand the second fitting portion9bare positioned separately to each other in the optical axis direction. The longer the separation distance between the first fitting portion9aand the second fitting portion9bis (see L1 inFIG. 1), less easily the lens5held by the lens the frame4tilts with respect to the fixed guide bar6aand the movable guide bar6b.

The third fitting portion9cis fitted with the sub guide bar6cwith a small gap so that the lens frame4can move back and forth in the optical axis direction. The third fitting portion9cis, in order to avoid multiple fittings with the first fitting portion9aand the second fitting portion9b, in a fitting state so as to restrict the rotation direction of the lens frame4around the optical axis. Specifically, as illustrated inFIG. 2C, the third fitting portion9chas a notch portion to guide the lens frame4only in the direction restricting the rotation in a plane orthogonal to the optical axis. With this structure, decentering of the lens frame4in the plane orthogonal to the optical axis is restrained.

As described above, by using the three guide bars, decentering and tilting of the lens5held by the lens frame4do not easily occur with respect to the optical axis direction, holding accuracy of the lens5with respect to the optical axis direction can be maintained and can move back and forth only in the optical axis direction.

Next, the driving unit for moving the lens frame4back and forth in the optical axis direction will be described below with reference toFIGS. 7A and 7B.FIG. 7Aillustrates the driving unit viewed from the optical axis direction, andFIG. 7Billustrates a rack41viewed from a direction orthogonal to the optical axis.

The rack41provided on the lens frame4is rotatable around the optical axis with a rotation shaft41aas a supporting point. The rack41is provided on the lens frame4to be movable together with the lens frame4in the optical axis direction. A coil portion of a torsion spring42is attached to a rotation shaft41a. One arm portion of arm portions of the torsion spring42is attached to a spring hook portion41bof the rack41, and the other arm portion is attached to a spring hook portion43provided on the lens frame4. The torsion spring42is a urging member for applying to the rack41a clockwise rotational force in the paper surface ofFIG. 7.

At the contact portion of the rack41and a feed screw7, as illustrated inFIG. 7B, a threaded portion41cis formed. The pitch of the threaded portion41cis set to be the same as the screw-pitch of the feed screw7, and the rack41and the feed screw7are screwed together. The feed screw7is provided on the rotation shaft of a motor8(seeFIGS. 1, 3A, and 3B), and the feed screw7is rotated together with the rotation of the motor8. With the configuration described above, the rack41configures a driving mechanism for not restricting the lens frame4from moving in an in-plane direction orthogonal to the optical axis to allow the lens frame4to move only in the optical axis direction. As a result, the lens frame4can move back and forth in the optical axis direction without being interfered with the restriction by the fitting with the guide bar.

For example, when a stepping motor is used as the motor8, the relative amount of movement of the lens frame4moving along the optical axis direction can be detected by counting the number of pulses. A position detection unit15using a photointerrupter (seeFIGS. 1, 3A, and 3B), for example, is mounted on the inner periphery of the stationary tube1on the rear end side thereof. A light-shielding portion45is attached on the rear end face of the lens frame4. The position detection unit15detects the position in the optical axis direction at which the light-shielding portion45overlaps the position detection unit15. Using the position detection unit15and the light-shielding portion45, a drive control unit (not illustrated) manages the absolute position of the lens frame4in the optical axis direction. The drive control unit counts the number of pulses of the motor8after detecting the absolute position of the lens frame4in the optical axis direction to detect the position of the lens frame4in the optical axis direction at any time.

Next, the locking structure for prohibiting the movement of the rectilinear motion tube3in the extended state of the rectilinear motion tube3will be described. The lens barrel includes a lock mechanism for the rectilinear motion tube3to stabilize the relative positional accuracy between the fixed guide bar6aand the movable guide bar6b. Referring toFIGS. 8A and 8B, the lock mechanism will be described in detail.FIG. 8Ais a cross sectional view along the optical axis direction illustrating a state where the rectilinear motion tube3is locked in a ready-for-imaging state.FIG. 8Bis an arrow view seen from a direction indicated by an arrow T inFIG. 8A.

A locking spring25is attached in the cam groove21of the cam ring2by screwing or bonding. A through hole portion22is provided on the cam ring2so that the locking spring25can be inserted easily. As illustrated inFIG. 8B, the locking spring25is formed in U-shape, and urges the cam follower31in a direction in which the U-shape is opened. The space of the U-shape of the locking spring25becomes wider as approaching the tip end thereof. The locking spring25is attached in a state where the end portion thereof closer to the cam groove21is opened toward the left side inFIG. 8B. In the ready-for-imaging state, the cam follower31is not in contact with the cam groove21, and is urged toward the left side inFIG. 8Bby the force of the locking spring25. The urged cam follower31is pressed against an abutting face portion12of the rectilinear motion guide11. The abutting face portion12is an end face portion of the front end side forming the rectilinear motion guide11. The cam follower31is not formed in circular cylindrical shape, and as illustrated inFIG. 8B, the cam follower31has a planar portion on the side contacting the abutting face portion12of the stationary tube1. The planar portion of the cam follower31and the abutting face portion12of the stationary tube1are processed in advance to secure relative accuracy. In a state where the cam follower31is pressed against the abutting face portion12by the force of the locking spring25, the relative accuracy between the movable guide bar6band the fixed guide bar6acan be sufficiently secured. In the present exemplary embodiment, the three cam followers31are arranged circumferentially around the optical axis (seeFIG. 2A), the locking springs25are arranged at three positions in the phases corresponding to the three cam followers31. As described above, in the ready-for-imaging state, since the relative positional accuracy between the movable guide bar6band the fixed guide bar6ais secured, the lens frame4can be moved back and forth in the optical axis direction with high accuracy.

Next, referring toFIG. 9, the retracting operation of the lens barrel will be described. It is assumed that, at the starting time point of the sequence, the lens barrel is in a ready-for-imaging state, and the lens5is located at the imaging position. Hereinbelow, the retracting operation while shifting from the ready-for-imaging state to the not ready-for-imaging state, will be described.

In step S101, the drive control unit controls the motor8to operate, and moves the lens frame4to the end position of the image plane side. The lens barrel has come into the state illustrated inFIGS. 3A and 5A. The drive control unit can perform the operation control of the motor8according to the number of the pulse count value required to move the lens frame4, since the drive control unit grasps the position of the lens frame4by the pulse count value of the motor8. In the present exemplary embodiment, the position detection unit15is disposed on the near side to the image plane (seeFIGS. 1 and 3). Therefore, even if any deviation in the pulse count information of the motor8occurs by some reason, the relationship between the pulse count value and the absolute position can be corrected by the drive control unit recognizing the absolute position of the lens frame4in the optical axis direction at the time the lens frame4has come near the image plane side.

Next, in step S102, the lock release operation is performed with the rotation of the cam ring2. As illustrated inFIG. 6A, in the ready-for-imaging state, the position of the cam follower31is located in the through hole portion22(see solid line portion). When the cam ring2is rotated with a driving mechanism (not illustrated), the locking spring25is also rotated together with the cam ring2. As a result, the pressing force by the locking spring25is released, and the cam follower31is moved to a position31aillustrated by a broken line. In this stage, the lens frame4is in an unlocked state without moving back and forth in the optical axis direction.FIG. 6Billustrates the position of the cam follower31in the rectilinear motion guide11. Viewed from the direction orthogonal to the optical axis, the position of the cam follower31illustrated in a solid line and the position31aare overlapped.

In step S103, when the cam ring2is further rotated, the cam follower31moves along the optical axis direction toward the image plane side according to the cam groove21, and reaches the retraction position31bindicated in a broken line inFIG. 6. Through the above operations, the retracting operation is completed, and the lens barrel has come into the state illustrated inFIGS. 3B and 5B.

In the present exemplary embodiment, the function of locking the rectilinear motion tube3in the imaging position to enhance the positional accuracy of the lens frame4, and the function of retracting the rectilinear motion tube3along the optical axis direction to the retracted position can be realized only by the rotation force of the cam ring2. Further, the lens frame4has been retracted in advance through the retracting operation. Accordingly, the interference between the rectilinear motion tube3and the lens frame4can be avoided. As a result, an occurrence of trouble such as the rack41overriding the thread of the feed screw7can be prevented.

According to the present exemplary embodiment, when capturing an image, the entire length of the rectilinear motion tube3is extended in the optical axis direction to be locked by the locking mechanism. As a result, tilting of the lens is less prone to occur, and lens holding accuracy can be enhanced while the travel distance of the lens can be sufficiently secured. In addition, when not capturing an image, the retracting operation is performed to store the lens barrel in the imaging apparatus main body. As a result, portability thereof is enhanced.

Next, referring toFIGS. 10A, 10B, and 11, a second exemplary embodiment of the present invention will be described. Components or portions similar to those described in the first exemplary embodiment are denoted by the same reference numerals and not described in detail below. The different points from the first exemplary embodiment will be mainly described.

FIG. 10Ais a cross sectional view cut along an optical axis illustrating a lens barrel according to the second exemplary embodiment, andFIG. 10Bis an arrow view viewed from an arrow W direction illustrated inFIG. 10A.

A first guide groove26aformed on the inner circumference surface of the stationary tube1is a first guide portion extended in a direction parallel with the optical axis direction. A second guide groove26bformed on the inner circumference surface of the rectilinear motion tube3is a second guide portion extended in a direction parallel with the optical axis direction. A second guided portion29bguided by the second guide groove26bprotrudes outside from the outer peripheral surface of the lens frame4at the front end portion thereof. The second guided portion29bis a fitting portion fitting to the second guide groove26bwith a small gap therebetween so that the lens frame4can move back and forth in the optical axis direction. A first guided portion29aguided by the first guide groove26aprotrudes outside from the outer peripheral surface of the lens frame4at the rear end portion thereof. The first guided portion29ais a fitting portion fitting to the first guide groove26awith a small gap therebetween so that the lens frame4can move back and forth in the optical axis direction.

FIG. 10Billustrates an example fitting relationship between the second guide groove26band the second guided portion29b. The second guided portion29bis a roller in a circular cylindrical shape, and the movement of the second guided portion29bin the up-and-down direction in the drawing surface ofFIG. 10Bis restricted by the second guide groove26b. Referring toFIG. 10A, the movement of the second guided portion29bin a direction orthogonal to the drawing surface ofFIG. 10Ais restricted. The first guided portion29asimilarly has a circular cylindrical shape (not illustrated), and the movement of the first guided portion29ain a direction orthogonal to the drawing surface ofFIG. 10Ais restricted by the first guide groove26a. The lens frame4is movable along the first guide groove26aand the second guide groove26bin the optical axis direction. As illustrated inFIG. 10A, the first guided portion29aand the second guided portion29bhave a positional relationship separated in the optical axis direction. As the distance between the first guided portion29aand the second guided portion29bis longer (see L2), the lens5held by the lens frame4is less easily tilted in a direction around the axis orthogonal to the drawing surface ofFIG. 10A.

FIG. 11is a front view of the lens barrel according to the present exemplary embodiment.FIG. 11illustrates a phase relationship in a circumferential direction around the optical axis between the first guide groove26aand the second guide groove26b, and further illustrates a phase relationship between a third guide groove26cand a fourth guide groove26d. Seen from the optical axis direction, the third guide groove26cand the fourth guide groove26dare arranged at positions separated in a circumferential direction by phase angles of nearly 90 degrees respectively from the angle positions at which the first guide groove26aand the second guide groove26bare arranged. The third guide groove26cformed on the inner circumference surface of the rectilinear motion tube3is a guide portion extended in a direction parallel with the optical axis direction. A third guided portion29cguided by the third guide groove26cprotrudes outside from the outer peripheral surface of the lens frame4at the front end portion thereof, and is a fitting portion fitting to the third guide groove26cwith a small gap therebetween so that the lens frame4can move back and forth in the optical axis direction. Further, the fourth guide groove26dformed on the inner circumference surface of the stationary tube1is a guide portion extended in a direction parallel with the optical axis direction. A fourth guided portion29dguided by the fourth guide groove26dprotrudes outside from the outer peripheral surface of the lens frame4at the rear end portion thereof, and is a fitting portion fitting to the fourth guide groove26dwith a small gap therebetween so that the lens frame4can move back and forth in the optical axis direction.

As described above, seen from the optical axis direction, the third guide groove26cand the fourth guide groove26dare arranged to be in a phase relationship orthogonal with each other around the optical axis direction respectively with respect to the first guide groove26aand the second guide groove26b. The four guided portions provided on the lens frame4are respectively guided by the four guide grooves. Therefore, the lens5can move back and forth in a plane orthogonal to the optical axis without tilting.

According to the second exemplary embodiment, similar effect to that of the first exemplary embodiment can be obtained without using a plurality of guide bars extending in the optical axis direction.

In the present exemplary embodiment, the retractable lens structure using the cam ring2is exemplified, however, it is not limited thereto, and the present invention can be applied to lens barrels having various types of retractable lens structures.

Referring toFIG. 12toFIGS. 21A, 21B, and 21C, a lens barrel according to a third exemplary embodiment of the present invention will be described. The lens barrel may be attachable/detachable to/from a digital camera as an imaging apparatus, or may be integrally mounted with a digital camera.

FIG. 12is a cross sectional view of a lens barrel including an optical axis in a use state according to the third exemplary embodiment. On the drawing surface ofFIG. 12, the left side is the object side, and the right side is the image plane side. The stationary barrel1is a stationary barrel in the lens barrel. The cam ring2is attached to the stationary tube1to be rotatable around the optical axis. The cam ring2is rotatable between a folding side stopper211and an extending side stopper212(seeFIG. 13). A rotation stopper111is attached to the stationary tube1by using, for example, screws (not illustrated) after the cam ring2is inserted. The cam ring2is rotated by s drive source such as a motor (not illustrated). For example, when a stepping motor is used as the drive source, the rotation amount of the cam ring2can be controlled using the pulse count value. The movement of the cam ring2in the optical axis direction is, when all the time including not capturing an image or capturing an image, restricted, as illustrated inFIGS. 15A and 15B, by the bayonet claw13of the stationary tube1(seeFIG. 14) in a state incorporated in a product. The rectilinear motion guides11each configuring a rectilinear motion guide are provided in the stationary tube1(seeFIGS. 13 and 14). The rectilinear motion guides11are grooves provided along the optical axis, and restrict the cam followers31, which also function as rectilinear motion keys configuring the rectilinear motion key portions, from rotating around the optical axis. By providing three rectilinear motion guides11in a circumferential direction, all the movement to the directions other than the optical axis direction can be restricted. In the third exemplary embodiment, the cam followers31also function as the rectilinear motion keys, however, the cam followers and the rectilinear motion keys can be constituted at different positions. The cam followers31constituting the cam follower portions are provided on the rectilinear motion tube3. The cam followers31are provided at three positions corresponding to the rectilinear motion guides11. The cam followers31also contact (engage) the respective cam grooves21constituting the cam portions along the rectilinear motion guides11, and move the rectilinear motion tube3back and forth along the cam grooves21in the optical axis direction with the rotation of the cam ring2.

The main guide bar6aconstituting the second guide portion has a circular cylindrical shape made of stainless steel or the like, is attached to the rectilinear motion tube3, and held to extend in a direction parallel with the optical axis direction. The main guide bar6b(first guide portion) and the sub guide bar6c(guide portion) are attached to the stationary tube1, and held to extend in a direction parallel with the optical axis. The arrangement of the main guide bar6a, the main guide bar6b, and the sub guide bar6cwill be described with reference toFIG. 13. Referring toFIG. 13, the main guide bar6aand the main guide bar6bare disposes at different phase positions on a circle. The parts to which the main guide bar6aand the main guide bar6bare fixed are different, so that arrangement distances from the center of the optical axis are different. The reason of this structure is that it is difficult to arrange the main guide bar6aand the main guide bar6bto be overlapped in the front view to realize a retractable structure. By arranging the sub guide bar6cat a position as far as possible from the main guide bar6aand the main guide bar6b, rotational backlash of the lens frame4around the optical axis can be reduced. The first fitting portion9ais a fitting portion fitted with the main guide bar6ato restrict the movement of the lens frame4in a circular plane orthogonal to the optical axis so that the lens frame4, which is a part of the optical member, can move back and forth in the optical axis direction. Similarly, the second fitting portion9bis a fitting portion fitted with the main guide bar6bto restrict the movement of the lens frame4in the circular plane orthogonal to the optical axis so that the lens frame4can move back and forth in the optical axis direction.FIG. 15Aillustrates the first fitting portion9aand the second fitting portion9bseen in a plane orthogonal to the optical axis. The movement of the first fitting portion9aand the second fitting portion9bis restricted in the circular plane orthogonal to the optical axis by the main guide bar6aand the main guide bar6b, and the lens frame4is guided in the optical axis direction. In addition, as illustrated inFIG. 12, the first fitting portion9aand the second fitting portion9bare arranged at separated positions in the optical axis direction. As the separation distance L (seeFIG. 12) is longer, the lens5, which is a part of the optical member provided in the lens frame4, is less prone to tilt with respect to the main guide bar6aand the main guide bar6b. The third fitting portion9cis a fitting portion fitted with the sub guide bar6cwith a small gap so that the lens frame4can move back and forth in the optical axis direction. In many cases, in order to avoid the multiple fittings with the first fitting portion9aand the second fitting portion9b, the third fitting portion9cis brought into a fitting state in which the lens frame4is only restricted to rotate around the optical axis. Specifically, as illustrated inFIG. 15B, the third fitting portion9cis configured to be guided in a direction for restricting the rotation in the plane orthogonal to the optical axis. With this structure, decentering in the plane orthogonal to the optical axis can be reduced. As described above, by using three guide bars, the lens5provided in the lens frame4is less prone to be decentered and tilted with respect to the optical axis direction, and can move back and forth in the optical axis direction while maintaining the optical axis holding accuracy.

Next, mechanism elements for moving the lens frame4back and forth in the optical axis direction will be described. The rack41is provided on the lens frame4. Referring toFIGS. 16A and 16B, the structure around the rack41will be described in detail. The rack41is rotatable around the optical axis with the rotation shaft41aas a supporting point. In the optical axis direction, the lens frame4and the rack41are movable together. The torsion spring42urges to rotate the rack41clockwise on the drawing surface InFIG. 16A. At the contact portion of the rack41and the feed screw7, as illustrated inFIG. 16B, the threaded portion41cis formed. The pitch of the threaded portion41cis set to be the same as the screw-pitch of the feed screw7, and the rack41and the feed screw7are screwed together. The feed screw7is provided on the rotation shaft of the motor8(seeFIG. 12), and the feed screw7is rotated together with the rotation of the motor8. With the configuration described above, the rack41configures a driving mechanism for not restricting the lens frame4from moving in an in-plane direction orthogonal to the optical axis to allow the lens frame4to move back and forth only in the optical axis direction. As a result, the lens frame4can move back and forth in the optical axis direction without being interfered with the restriction by the fitting with the guide bars6ato6c. In the present exemplary embodiment, a stepping motor is used as the motor8, for example, and by counting the number of pulses, the relative movement amount in the optical axis direction can be detected. Referring toFIG. 12, the position detection unit15such as a photointerrupter can detect a position where the light-shielding portion45overlaps the position detection unit15in the optical axis direction. By using the position detection unit15and the light-shielding portion45, the absolute position of the lens frame4in the optical axis direction can be detected. As described above, by counting the number of pulses of the motor8after detecting the absolute position of the lens frame4in the optical axis direction, the position of the lens frame4in the optical axis direction can be detected at any time.

The locking mechanism includes a structure for locking the rectilinear motion tube3in the extended state to stabilize the relative positional accuracy between the main guide bar6aand the main guide bar6b. The locking mechanism will be described in detail below.FIG. 17Ais a cross sectional view along the optical axis direction in a state where the rectilinear motion tube3in the imaging state is locked. The locking spring25is a urging member made of Special Use Stainless steel (SUS), for example, and attached to the cam groove21of the cam ring2by screwing or bonding (not illustrated). The through hole portion22is provided through the cam ring2so that the locking spring25can be easily inserted.FIG. 17Bis a top view viewed from T direction inFIG. 17A, i.e., from the upper side inFIG. 17A. As illustrated inFIG. 17B, the locking spring25is formed in U-shape, and urges the cam follower31in a direction in which the U-shape is opened in a state where the barrel is locked. The balance of the urging forces will be described with reference toFIG. 17A. The locking spring25generates forces of F01 and F02 in the opening direction of the U-shape. F01 acts on the cam follower31, the cam follower31contacts the abutting face portion12, which configures a contact portion, and the cam follower31receives reaction force F03 from the stationary tube1. On the other hand, F02 acts on the cam ring2, and caused by F02, the cam ring2receives the reaction force F04 at the bayonet claw13from the stationary tube1. The reaction force F03 and the reaction force F04 act on the stationary tube1in the opposite directions to each other to be balanced.

As illustrated inFIG. 17B, the cam follower31is not in a simple cylindrical shape, and the abutting face thereof to contact the abutting face portion12is formed to be flat. The abutting face portion12is processed in advance so that relative accuracy is secured as well as the rectilinear motion tube3and the stationary tube1, and in a state where the cam follower31is pressed against the abutting face portion12, the relative accuracy between the main guide bar6aand the main guide bar6bis secured. In the present exemplary embodiment, the cam followers31are arranged circumferentially at three separate positions, and therefore the locking springs25are arranged respectively at three positions in the corresponding phases. The cam followers31are respectively pressed to the three abutting face portions12, and thereby, the thrust-direction positions of the stationary tube1and the rectilinear motion tube3are definitely determined. With this configuration, the fluctuation of the relative tilting between the stationary tube1and the rectilinear motion tube3can be reduced. As described above, in an imaging state, the attitude accuracy in tilting and shifting of the main guide bar6aand the main guide bar6bis secured. As a result, the lens frame4can move back and forth in the optical axis direction accurately.

Next, referring to a flowchart illustrated inFIG. 18A, a flow from a non-imaging state to a ready-for-imaging state in which the rectilinear motion tube3is extended and locked by the locking springs25, will be described. In step S111, the cam ring2is rotated counterclockwise seen from the opposite side of an object, in whole range of the second cam region (regions202inFIGS. 21A, 21B, and C). The rectilinear motion tube3is extended by means of the rotation of the cam ring2, and comes into the state illustrated inFIG. 19A. In this state, the rectilinear motion tube3is not locked, and therefore the rectilinear motion tube3has backlash with respect to the stationary tube1. In step S112, the cam ring2is further rotated to cover whole range of the first cam region (regions201inFIGS. 21A, 21B, and 21C). In the first cam region, the rectilinear motion tube3does not move back and forth. The locking spring25is brought into contact with the cam follower31by the rotation of the locking spring25caused by the rotation of the cam ring2, from the state where the cam follower31and the locking spring25are not in contact with each other. Further, after rotation in the whole second cam region, the locking spring25is charged by a certain amount. As a result, as illustrated inFIG. 17A, F01 and F02 are generated, and the relative position of the stationary tube1and the rectilinear motion tube3is in a locked state. Through the sequence described above, the lens frame4is in a holding state in which the lens frame4can move back and forth in the optical axis direction. The step S113indicates a sequence in which the motor8can be driven to move the lens frame4to a desired position according to the zoom state and the focus state of the lens barrel, for example. As described above, when capturing an image, the entire length of the lens barrel is extended and locked to improve the holding accuracy of the lens such as tilting, and the optical performance can be maintained in high level. Further, in a non-image capturing state, portability is enhanced by retracting the lens barrel to reduce the size. In the present exemplary embodiment, the lens frame4whose holding accuracy is to be held is supported by the main guide bar6aand the main guide bar6b. However, even if the rectilinear motion tube3and the lens frame4are integrally formed, similar effect can be achieved.

<Lock Release and Retracting Operations>

Next, referring to a flowchart inFIG. 18B, the retracting operation will be described. At the start point of the sequence, the lens barrel is in a state ready for imaging. The sequence of the retracting operation of the lens barrel until the lens barrel comes into the non-imaging state, will be described. In step S101, the motor8is operated to move the lens frame4to a position closest to the image plane.FIGS. 19A and 20Aare cross sectional views illustrating states of the lens barrel at that time. Since the position of the lens frame4is detected by the pulse count value of the motor8, the motor8can be driven according to the required pulse count value to move the lens frame4. Further, in the present exemplary embodiment, the position detection unit15is disposed on the near side to the image plane. Therefore, even if any deviation in the pulse count information of the motor8occurs by some reason, the relationship between the pulse count value and the absolute position can be corrected by the drive control unit recognizing the absolute position of the lens frame4in the optical axis direction at the time the lens frame4has come near to the image plane.

Next, in step S102ofFIG. 18B, the cam ring2is rotated to release the lock. Referring toFIG. 21, the operation to release the lock will be described. In the imaging state, as illustrated inFIG. 21A, the cam follower31is urged by the locking spring25, and locked. From this state, the cam ring2is rotated counterclockwise seen from the opposite side of the object, the state returns to the state illustrated inFIG. 21B. The cam follower31is separated from the locking spring25and not urged thereby. In the first cam region201, the cam groove21is orthogonal to the optical axis direction. Therefore, the cam follower31does not move substantially back and forth in the optical axis direction. In the first cam region201, the torque to move the rectilinear motion tube back and forth is not required, and only the torque for resisting the frictional force generated by the urging of the locking spring25is required.

Next, in step S103inFIG. 18B, the cam ring2is rotated to retract the rectilinear motion tube3. From the state inFIG. 21B, the cam ring2is further rotated to move the cam follower31to an opposite side of the object along the optical axis, and the cam ring2is further rotated to come into the state illustrated inFIG. 21C. As a result, in the second cam region202, the rectilinear motion tube3is retracted. In this region, since the locking spring25does not act on, only the torque for moving the rectilinear motion tube3back and forth is required.

As described above, the retracting operation is completed, and the lens barrel has come in the state illustrated inFIGS. 19B and 20B. Through the above-described operation, the function of locking the rectilinear motion tube3in the imaging position to enhance the attitude accuracy of the tilting and shifting of the lens frame4, and the function of retracting the rectilinear motion tube3along the optical axis direction to the retracted position can be realized only by the rotation of the cam ring2. By directly pressing the rectilinear motion tube3and the stationary tube1not via other members, higher positional accuracy can be achieved. Further, the lens frame4has been retracted in advance. Accordingly, the interference between the rectilinear motion tube3and the lens frame4can be avoided. As a result, an occurrence of trouble such as the rack41overriding the thread of the feed screw7can be prevented.

Next, referring toFIG. 22, a fourth exemplary embodiment of the present invention will be described.

The description of the configuration similar to that of the third exemplary embodiment is omitted, and only the characteristic items in the present exemplary embodiment will be described.FIG. 22is a sectional view illustrating in detail a locking portion of the lens barrel in a use state. The locking spring25is arranged between the cam ring2and the bayonet claw13, and attached to the cam ring2. Further, the through hole portion22described in the first exemplary embodiment is not provided. Therefore, the structure in the locked state around the cam follower31is simpler. With this configuration, in the space around the cam follower31, parts are not concentrated. Therefore, enough flexibility for designing the locking spring25can be secured. The locking spring25generates a urging force between the cam ring2and the bayonet claw13provided on the stationary tube1, and acts on as indicated by F31 and F32. F31 is balanced in the cam ring2with the reaction force F34 received from the cam follower31. On the other hand, F32 is balanced in the stationary tube1with the reaction force F33 received from the cam follower31. The retracting sequence is illustrated inFIG. 18Blike that of the third exemplary embodiment. Different points will be described below with reference toFIGS. 23A to 23C.FIG. 23Aillustrates a use state, the cam ring2is located in the first cam region201, and the locking spring25and the bayonet claw13are locked.FIG. 23Billustrates a state in which the cam ring2is rotated a little, and the lock is release. When the cam ring2is further rotated, as illustrated inFIG. 23C, the cam follower31moves to the retracted position while the lock is kept released, and the retracting operation is completed.

Through the operation described above, attitude accuracy of tiling and shifting of the extended rectilinear motion tube3when capturing an image can be enhanced to maintain the optical performance to be high. In addition, in a non-image capturing state, portability can be enhanced due to the reduced size.

Next, a fifth exemplary embodiment of the present invention will be described with reference toFIGS. 24A, 24B, 25A, 25B, 25C, and 25D.

The description of the configuration similar to that of the first exemplary embodiment is omitted, and only the characteristic items in the present exemplary embodiment will be described.FIG. 25Ais a top view seen from a T direction illustrated inFIG. 27A. A locking spring26is not in simple U-shape like that of the third exemplary embodiment, and the tip end thereof is pinched. A cam follower32has two planar portions as illustrated inFIG. 24A, so that the cam follower32can contact two portions of an abutting face portion12aconfiguring a first contact portion, and an abutting face portion12bconfiguring a second contact portion having different abutting direction from that of the first contact portion. The locking spring26generates a urging force in lower left direction in the drawing surface ofFIG. 25A, and both the abutting face portions12aand12bare in contact with the cam follower32. The balance of forces will be described below. There are three locking springs26which is the same in number as the cam followers32. With this configuration, the rectilinear motion tube3is fixed not only in the optical axis direction but also in the plane orthogonal to the optical axis. Therefore, the positional accuracy of the rectilinear motion tube3can be secured with respect to the stationary tube1in decentering direction relative to the optical axis.FIG. 25BandFIG. 25Deach illustrate a state where the locking spring26deforms according to the rotation of the cam ring2.FIG. 25Billustrates a state where the rectilinear motion tube3is locked. Next,FIG. 25Cillustrates a state where the cam ring is rotated a little, and the locking spring26is deformed and on the way to override the cam follower32. Then, as illustrated inFIG. 25D, the locking spring26has overridden the cam follower32, and the deformation is released to be in a shape of the free state. Next, the balance of forces in a state where the rectilinear motion tube3is locked will be described.FIG. 24Aillustrates forces generated in a locked state. From the locking spring26, a force is generated in F20 direction. The force is divided into F01 and F11 as component forces. F01 and F11 are component forces generated in both abutting directions against the abutting face portion12aand the abutting face portion12b. The balance of forces in the optical axis direction like F01 is the same as that of the first exemplary embodiment, so that the description thereof is omitted. The balance of forces in the direction orthogonal to the optical axis like F11 will be described below. The locking spring26is fixed to the cam ring2to generate forces of F11 and F12. F11 acts on the cam follower32to cause the cam follower32to contact the abutting face portion12b, and the cam follower32receives the reaction force F13 from the stationary tube1. On the other hand, F12 acts on the cam ring2, and an extending side stopper212receives reaction force F14 from the rotation stopper111provided on the stationary tube1, as illustrated inFIG. 24B. The reaction force F13 and the reaction force F14 act on the stationary tube1in the opposite directions to be balanced.

With the configuration described above, attitude accuracy of tiling and shifting in all directions of the extended rectilinear motion tube3when capturing an image can be enhanced to maintain the optical performance to be high. In addition, in a non-image capturing state, portability can be enhanced due to the reduced size.

This application claims the benefit of Japanese Patent Application No. 2013-006890, filed Jan. 18, 2013, and NO. 2013-032013, filed Feb. 21, 2013, which are hereby incorporated by reference herein in their entirety.