Zoom lens barrel assembly

Abstract

A zoom lens barrel assembly includes a plurality of lens barrels including a rearmost lens barrel, secured to a camera body, and a frontmost lens barrel. At least one adjacent pair of lens barrels are connected to each other via a helicoid structure. The frontmost lens barrel and a first adjacent lens barrel are connected to each other via a cam structure. The helicoid structure allows the adjacent pair of the lens barrels to rotate and move in an optical axis direction relative to each other while the zoom lens barrel assembly moves from a retracted position to a minimally extended position for a photographing operation. At least a portion of the helicoid structure includes a slip region which allows the pair of adjacent lens barrels to rotate without relatively moving along the optical axis.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens barrel assembly, and in particular, to a multi-stage-extension zoom lens barrel assembly having a lens barrier.

2. Description of the Related Art

There are concurrent needs to increase magnification of camera zoom lenses and to miniaturize them. For this reason, modern zoom lenses are constructed as a multi-stage-extension zoom lens barrel assembly. A multi-stage-extension zoom lens barrel assembly employs a helicoid structure or a cam structure to connect barrels and allow them to move relative to one another. Although the cam structure permits a high degree of freedom in terms of how much a lens barrel can extend outwards for a predetermined rotation angle of the barrel, it is difficult to ensure rigidity and light-blocking performance of the lens barrel with this structure. However, the helicoid structure ensures rigidity and light-blocking performance of the lens barrel although this structure allows the lens barrel to extend outward only by a fixed amount for a predetermined rotation angle of the barrel. For this reason, the helicoid structure is considered more suitable for use in multi-stage extension lens barrel assemblies.

A typical zoom lens barrel assembly includes a lens barrier on the frontmost end thereof. This lens barrier is opened and closed by making use of relative movement between the frontmost barrel having the lens barrier and an adjacent barrel. When there are many stages (sub-barrels) in a barrel assembly, however, the relative displacement between the lens barrels may become too small to provide sufficient stroke length required for the opening/closing of the lens barrier. In particular, in the case of a wide-angle zoom lens, in which the optical system has a small length at the wide-angle extremity, displacement of the lens barrel assembly from its retracted position, where the length of the barrel assembly and thus the length of the optical system are smallest, to the wide-angle extremity is small. If helicoid structures are used in such a zoom lens barrel assembly, leads of the helicoids of each barrel need to be close to each other in order to effectively make use of the length of the zoom lens barrel. This makes displacement of each lens barrel substantially equal to one another. As a result, sufficient stroke length required for the opening/closing of the lens barrier cannot be achieved.

To cope with above problems, only the frontmost lens barrel is constructed to have a cam structure so that the frontmost lens barrel extends outward by a larger amount for a small rotation angle and causes the other lens barrels to extend only by a small amount. While sufficient stroke can be achieved, the lead for advancing the frontmost lens barrel to open the lens barrier becomes too large. This can cause too large a resistance when the lens barrel is retreated, which affects the strength of the lens barrel. In addition, if only the frontmost lens barrel extends outward by a large amount, tension is undesirable exerted on a flexible printed board, which connects a shutter unit mounted on the frontmost lens barrel to a circuit board in a camera body.

As an alternative approach, the other lens barrels that are connected to the frontmost lens barrel can be each constructed to have a cam structure in order to provide a section or sections that allow the zoom lens barrel to extend outward only by a small amount, or do not extend outward at all, when the barrels are rotated. In this construction, the sufficient stroke length for the opening/closing of the lens barrier is provided within a rotation range between the retracted position and the wide-angle extremity. Such cam structures, however, make it difficult to ensure sufficient rigidity of the zoom lens barrel assembly. It should be noted that the rearmost lens barrel cannot be constructed as a cam structure since the driving force needs to be transmitted through gears to the first lens barrel.

SUMMARY OF THE INVENTION

In view of the above-described drawbacks of the conventional lens barrel assemblies, the present invention provides a novel zoom lens barrel assembly structure that not only enhances the rigidity of multi-stage-extension zoom lens barrel, but also provides a sufficient stroke length needed for the opening/closing of a lens barrier.

For example, a zoom lens barrel assembly is provided, including a plurality of lens barrels including a rearmost lens barrel, secured to a camera body, and a frontmost lens barrel. At least two adjacent lens barrels, of the plurality of lens barrels arranged between the camera body and the frontmost lens barrel, are connected to each other via a helicoid structure. The frontmost lens barrel and a first adjacent lens barrel are connected to each other via a cam structure. The helicoid structure allows the at least two adjacent lens barrels to rotate and move in an optical axis direction relative to each other while the zoom lens barrel assembly moves from a retracted position to a minimally extended position for a photographing operation. At least a portion of the helicoid structure includes a slip region which allows the at least two adjacent lens barrels to rotate without relatively moving along the optical axis.

A barrier mechanism can be provided on the frontmost lens barrel, the barrier mechanism being opened and closed via movement of the frontmost lens barrel in the optical axis direction as the zoom lens barrel assembly moves between the retracted position and the minimally extended position, and by relative rotation of the at least two adjacent lens barrels via the slip region.

It is desirable for the first adjacent lens barrel connected to the frontmost lens barrel via the cam structure to be connected to a second adjacent lens barrel via a second helicoid structure which causes the connected the first and second adjacent lens barrels to rotate and move along the optical axis relative to each other as the zoom lens barrel assembly moves from the retracted position to the minimally extended position, the second helicoid structure also including a slip region which allows the first adjacent lens barrel and the second adjacent lens barrel to rotate without relatively moving along the optical axis.

In another embodiment, a four-stage-extension zoom lens barrel is provided, including a first barrel connected to a fixed barrel secured to a camera body, the first barrel being movable so as to retreat and advance relative to the fixed barrel; a second barrel connected to the first barrel; a third barrel connected to the second barrel; a frontmost fourth barrel connected to the third barrel; wherein the first, second, and third barrels are each supported, and are movable in an optical axis direction, via a helicoid structure. The frontmost fourth barrel and the third barrel are connected to each other by a cam structure so as to be movable in an optical axis direction. A barrier mechanism is provided on the frontmost fourth barrel. The helicoid structures for moving the second barrel and the third barrel in the optical axis direction each allow the second and the third barrels to rotate and relatively move in the optical axis direction as the zoom lens barrel moves between a retracted position and a minimally extended position for a photographing operation, each the helicoid structure having a slip region which allows the second and third barrels to rotate without relatively moving in the optical axis direction. The barrier mechanism is opened and closed by a relative movement of the third barrel and the frontmost fourth barrel in the optical axis direction as the slip sections allow the second and the third barrels to rotate.

It is desirable for the fourth barrel to be connected to the third barrel via the cam structure so that the fourth barrel moves in the optical axis direction relative to the third barrel without rotating, and the barrier mechanism to be opened and closed by the relative movement of the third barrel and the fourth barrel in the optical axis direction in the slip section of the third barrel.

It is desirable for the slip section of the helicoid structure of the second barrel to have a different slip angle than the slip section of the helicoid structure of the third barrel.

The helicoid structure having the slip section can include a female helicoid formed on one of two adjacent barrels of the first through third barrels and a male helicoid formed on the other of the two adjacent barrels, and the female helicoid can include a helicoid slip region that permits rotation of the male helicoid when the two adjacent barrels are in a retracted position.

In another embodiment, a zoom lens barrel assembly is provided, including a plurality of lens barrels including a rearmost lens barrel secured to a camera body, and a frontmost lens barrel. The frontmost lens barrel and a first adjacent lens barrel are connected to each other via a cam structure. The first adjacent lens barrel is connected to a second adjacent lens barrel via a helicoid structure so that the first and second adjacent lens barrels relatively rotate and relatively move in the optical axis direction as the zoom lens barrel assembly moves between a retracted position and a minimally extended position for a photographing operation, the helicoid structure including a helicoid slip region which allows the first and second adjacent lens barrels to relatively rotate without relatively moving along the optical axis. The helicoid structure having the helicoid slip region includes a female helicoid formed on one of the first and second adjacent lens barrels and a male helicoid formed on the other of the first and second adjacent lens barrels. The female helicoid includes a helicoid slip region which permits rotation of the male helicoid when the first and second adjacent lens barrels are in the retracted position. A circumferential groove is formed along each of opposing thrust surfaces of the helicoid slip region.

The helicoid structure having the helicoid slip region and the circumferential groove can constitute a helicoid ring, the helicoid ring being formed by injection-molding a plastic material into a mold.

In another embodiment, a zoom lens barrel assembly is provided, including a pair of lens barrels connected to each other via a helicoid structure, the helicoid structure including a helicoid slip region which allows the pair of the lens barrels to relatively rotate without relatively moving along the optical axis. The helicoid structure having the helicoid slip region includes a female helicoid formed on one of the pair of lens barrels and a male helicoid formed on the other of the pair of lens barrels. The female helicoid includes the helicoid slip region which allows rotation of the male helicoid when the pair of lens barrels are in a predetermined position. A circumferential groove is formed along each of opposing thrust surfaces of the helicoid slip region of the female helicoid.

In another embodiment, a zoom lens barrel assembly is provided, including a plurality of lens barrels, at least two lens barrel of the plurality of lens barrels including a helicoid structure for allowing one lens barrel of the at least two lens barrels to rotate and extend and retreat as the zoom lens barrel assembly moves from a retracted position to a minimally extended position for a photographing operation. The helicoid structure includes a helicoid slip section for allowing the one lens barrel to rotate without relatively moving along the optical axis, the helicoid structure including a female helicoid formed on one of the at least two lens barrels and a male helicoid formed on the other of the at least two lens barrels, the male and the female helicoids including a helicoid slip region that allows the at least two lens barrels to rotate and prevents the at least two lens barrels from moving along the optical axis when one of the at least two lens barrels is retracted into the other. An eccentricity-preventing member provided on the at least two lens barrels for allowing the at least two lens barrels to slidably and closely engage with each other so as to slide circumferentially and slide in the optical axis direction, the eccentricity-preventing member guiding rotation of the at least two lens barrels via the helicoid slip section when one of the at least two lens barrels is retreated and slightly advanced with respect to the other of the at least two lens barrels.

The eccentricity-preventing member can be formed as a flange which extends circumferentially and projects radially inward from an inner periphery of one of the at least two lens barrels which is provided outside of the other of the at least two lens barrels, the flange being formed in the vicinity of the helicoid slip section and slidably placed over an outer periphery of an inner lens barrel of the at least two lens barrels.

Each of the plurality of lens barrels arranged between a camera body and a frontmost lens barrel can be connected via the helicoid structure, the front most lens barrel and a first adjacent lens barrel being connected to each other via a cam structure, and wherein the first adjacent lens barrel and a second adjacent lens barrel connected thereto constitute the at least two lens barrels.

A barrier mechanism can be mounted on the frontmost lens barrel, the barrier mechanism being opened and closed by relative movement of the frontmost lens barrel and the first adjacent lens barrel in the optical axis direction as the zoom lens barrel assembly moves from the retracted position to the minimally extended position for a photographing operation.

The present disclosure relates to subject matter contained in Japanese Patent Application Nos. 2001-82089, 2001-82090 and 2001-82092 (filed on Mar. 22, 2001) which is expressly incorporated herein by reference in their entireties.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be discussed below in detail with reference to the accompanying drawings, in which:

FIG. 1 is an exploded perspective view showing components of an embodiment of a zoom lens barrel assembly of the present invention;

FIG. 2 is a cross-section showing an upper half of the zoom lens barrel assembly in a retracted state;

FIG. 3 is a cross-section showing the upper half of the zoom lens barrel assembly in a photographing position at the wide-angle extremity;

FIG. 4 is a cross-section showing the upper half of the zoom lens barrel assembly in a photographing position at the telephoto extremity;

FIG. 5 is a perspective view showing the zoom lens barrel assembly in a fully extended position;

FIG. 6 is a perspective view showing the zoom lens barrel assembly of FIG. 5 with some of the lens barrels removed;

FIG. 7 is a perspective view of the zoom lens barrel assembly of FIG. 6 in a further disassembled state;

FIG. 8 is a perspective view showing elements of a first outer barrel and a second outer barrel;

FIG. 9 is a perspective view showing an element of a third linear guide ring;

FIG. 10 is an exploded perspective view showing the third linear guide ring along with a shutter unit;

FIG. 11 is a developed view of the third linear guide ring showing a cam groove for adjusting a diaphragm;

FIG. 12 is an developed view of a cam ring showing profiles of cam grooves on the inner surface of the cam ring;

FIG. 13 is a block diagram showing a control system of the zoom lens barrel assembly, the overall structure of which is shown in FIGS. 2 through 4 ;

FIG. 14 is an explanatory developed view showing engagement of the second outer barrel, the second helicoid ring, the second linear guide ring and guide heads, in a retracted position of the zoom lens barrel assembly;

FIG. 15 is an explanatory developed view showing engagement of the second outer barrel, the second helicoid ring, the second linear guide ring and the guide heads, in a telephoto extremity position of the zoom lens barrel assembly;

FIG. 16 is an explanatory developed view showing engagement of the second outer barrel, the second helicoid ring, the second linear guide ring and the guide heads, in an assembly/disassembly position of the zoom lens barrel assembly;

FIG. 17 is a developed view showing engagement of the second outer barrel, the second helicoid ring, the second linear guide ring and the guide heads, in the assembly/disassembly position of the zoom lens barrel assembly with the second outer barrel removed;

FIG. 18A is a perspective view showing a longitudinal cross-section of the second linear guide ring 25 of the zoom lens barrel assembly;

FIG. 18B is a perspective view showing a longitudinal cross-section of the third linear guide ring 18 of the zoom lens barrel assembly;

FIG. 19 is a developed view showing the second linear guide ring of the zoom lens barrel assembly;

FIG. 20 is a developed view showing engagement of female helicoids of the second linear guide ring with male helicoids of the third outer barrel in the retracted position of the zoom lens barrel assembly;

FIG. 21 is a developed view showing engagement of the female helicoids of the second linear guide ring with the male helicoids of the third outer barrel, when the zoom lens barrel assembly extends to a slip section boundary position;

FIG. 22 is a developed view showing engagement of the female helicoids of the second linear guide ring with the male helicoids of the third outer barrel, when the zoom lens barrel assembly extends to a wide-extremity position;

FIG. 23 is a developed view of the first linear guide ring of the zoom lens barrel assembly;

FIG. 24 is a developed view showing engagement of the first linear guide ring, the second outer barrel and the second helicoid ring, when the zoom lens barrel assembly is in the retracted position;

FIG. 25 is a developed view showing engagement of the first linear guide ring, the second outer barrel and the second helicoid ring, when the zoom lens barrel assembly is in the slip section boundary position;

FIG. 26 is a developed view showing engagement of the first linear guide ring, the second outer barrel and the second helicoid ring, when the zoom lens barrel assembly is in the wide-angle extremity position;

FIG. 27A is an explanatory view showing engagement of the female helicoids and the helicoid slip section of the first linear guide ring, and the male helicoids of the second helicoid ring of the zoom lens barrel assembly when the lens barrel assembly is in the retracted state;

FIG. 27B is an explanatory view showing engagement of the female helicoids and the helicoid slip section of the first linear guide ring, and the male helicoids of the second helicoid ring of the zoom lens barrel assembly when the lens barrel assembly is in the slip section boundary section;

FIG. 27C is an explanatory view showing engagement of the female helicoids and the helicoid slip section of the first linear guide ring, and the male helicoids of the second helicoid ring of the zoom lens barrel assembly when the lens barrel assembly is in the wide-angle extremity position;

FIG. 28A is an explanatory view showing profile of the female helicoids and the helicoid slip section of the first linear guide ring;

FIG. 28B is an explanatory view illustrating the problem that arises upon manufacturing of a mold;

FIG. 28C is an explanatory view illustrating a solution to the problem proposed by an embodiment of the present invention;

FIG. 29 is a cross-section of the upper half of the zoom lens barrel assembly in the retracted state, in which a circumferential flange is formed on the inner peripheral of the first linear guide ring and on the inner peripheral of the second linear guide ring, near the respective rear ends thereof;

FIG. 30 is a cross-section of the upper half of the zoom lens barrel assembly in a photographing position at the wide-angle extremity, in which a circumferential flange is formed on the inner peripheral of the first linear guide ring and on the inner peripheral of the second linear guide ring, near the respective rear ends thereof;

FIG. 31 is an enlarged partial cross-section of the upper end of the zoom lens barrel assembly showing adjacent area of a shutter unit with lens barriers closed;

FIG. 32 is an enlarged partial cross-section of the upper end of the zoom lens barrel assembly similar to FIG. 24 , with the lens barriers open;

FIG. 33 is a perspective view of the first helicoid ring and the first outer barrel, showing a telephoto-extremity stopper of the zoom lens barrel assembly;

FIG. 34 is a developed view showing the first helicoid ring of the zoom lens barrel assembly;

FIG. 35 is a perspective view showing the bottom of the zoom lens barrel assembly in the telephoto extremity position;

FIG. 36 is a perspective view of the first helicoid ring and the first outer barrel, showing a construction to prevent a flexible printed circuit board of the zoom lens barrel assembly from interfering with the gear teeth of the first helicoid ring;

FIG. 37 is a perspective view showing the manner in which the flexible printed circuit board interferes with the gear teeth of the first helicoid ring; and

FIG. 38 is a partial enlarged perspective view showing the manner in which the flexible printed circuit board interferes with the gear teeth of the first helicoid ring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail hereinafter with reference to the accompanying drawings. In one embodiment, the present invention is applied to a four-stage-extension zoom lens barrel assembly (multi-stage-extension zoom lens barrel assembly).

As shown in FIGS. 1 through 5 , the zoom lens barrel assembly is constructed as a four-stage-extension zoom lens barrel assembly and includes a fixed barrel (rearmost barrel) 12 secured to a camera body, and a four-stage barrel unit which is retained in the fixed barrel 12 and advances and retreats along the optical axis relative to the fixed barrel 12 . The four-stage lens unit includes a first outer barrel 17 which is the rearmost barrel, a second outer barrel 23 which is the second rearmost barrel, a third outer barrel 30 which is the third rearmost barrel and is constructed as a cam ring, and a fourth outer barrel (frontmost barrel) 31 which is the fourth rearmost barrel and serves as a lens-retaining barrel.

In the zoom lens barrel assembly, the fixed barrel 12 is connected to the first outer barrel 17 , which in turn is connected to the second outer barrel 23 , which in turn is connected to the third outer barrel 30 , with each connection provided by a helicoid structure (mechanism). The helicoid mechanisms allow the barrels 17 , 23 and 30 to extend outward from, or into, each other. The fourth outer barrel 31 is connected to the third outer barrel 30 through a cam structure.

In the zoom lens barrel assembly of the present embodiment, the first outer barrel 17 and the second outer barrel 23 are made separately from helicoid rings. Furthermore, the zoom lens barrel assembly is constructed so as to be extended past the telephoto extremity position, which is the most extended position of the barrel assembly in normal operation, to an assembly/disassembly position, at which the first outer barrel 17 and the second outer barrel 23 can be removed from and mounted onto the zoom lens barrel assembly. In this embodiment, the barrel assembly is brought into the assembly/disassembly position by rotating it to an additional rotation angle of 8° from the telephoto extremity position.

Lens barriers 92 and 93 are mounted on the fourth outer barrel 31 in the front portion thereof. The lens barriers 92 and 93 are opened and closed as the fourth outer barrel 31 and the third outer barrel 30 move along the optical axis relative to each other when the barrel assembly moves between the retracted position and the minimally extended photographing position (which corresponds to the wide-angle extremity position in this embodiment).

In the zoom lens barrel assembly of the present embodiment, the helicoid structure to move the second outer barrel 23 and the third outer barrel 30 includes a slip section which permits rotation of the second and the third outer barrels 23 and 30 but does not permit relative movement thereof along the optical axis when the lens barrel assembly moves between the retracted position and the wide-angle position. In other words, the path of the telescopic movement of the lens barrel assembly from the retracted position toward the wide-angle position includes a slip section in which the second outer barrel 23 and the third outer barrel 30 rotate at the same speed and do not move relative to each other along the optical axis. In the slip section, the first outer barrel 17 rotates while moving along the optical axis, whereas the fourth outer barrel 31 does not rotate but moves relative to the third outer barrel 30 along the optical axis. This relative movement between the fourth outer barrel 31 and the third outer barrel 30 along the optical axis causes opening/closing of the barriers 92 and 93 .

The entire structure of the zoom lens barrel assembly will now be described with reference to FIGS. 1 through 7 . Referring to FIG. 1 , major components of the zoom lens barrel assembly are shown in an exploded view. Hereinafter, “front” refers to the direction toward an object to be photographed and “rear” refers to the direction toward the camera body (film).

Female helicoids 12 a are formed on the inner periphery of the fixed barrel 12 which is secured to a camera body 11 . The female helicoids 12 a engage with male helicoids 14 a formed on the outer periphery of a first helicoid ring 14 . Arranged on the outside of the fixed barrel 12 is a pinion 16 , which is rotated by a zooming motor 15 . The pinion 16 engages with gear teeth 14 b , which are formed on the outer periphery of the first helicoid ring 14 and extend along the male helicoids 14 a where some of the male helicoids 14 a have been removed (cut-away). The first outer barrel 17 is connected to the first helicoid ring 14 at the front end of the helicoid ring 14 .

Engagement portions 141 (see FIGS. 1 and 34 ) formed on the front end of the first helicoid ring 14 engage with engagement portions 171 formed on the rear end of the first outer barrel 17 , so that the first helicoid ring 14 integrally rotates with the first outer barrel 17 . The engagement portions 141 and 171 can be brought into disengagable engagement by sliding the first helicoid ring 14 and the first outer barrel 17 along the optical axis toward each other when the first helicoid ring 14 and the first outer barrel 17 are in a predetermined relative rotational position (assembly/disassembly position).

A first linear guide ring 18 , which is supported within the first outer barrel 17 , can be rotated relative to the first outer barrel 17 and moves along the optical axis together with the first outer barrel 17 (i.e., no relative displacement permitted along the optical axis). Linear guide projections 18 a formed on the first linear guide ring 18 engage with respective linear guide slots 12 b formed on the fixed barrel 12 , so that the first linear guide ring 18 , while being supported within the first outer barrel 17 , can only move along the optical axis (i.e., can advance and retreat) and cannot rotate relative to the fixed barrel 12 .

A pair of circumferential grooves 172 are formed on the inner periphery of the first outer barrel 17 and are separated from each other by a predetermined distance along the optical axis. A pair of keys 181 , formed on the outer periphery of the first linear guide ring 18 , engage with the respective circumferential grooves 172 . Engagement of the keys 181 with the respective circumferential grooves 172 permits rotation of the first outer barrel 17 relative to the first linear guide ring 18 while preventing the relative movement between them along the optical axis.

Thus, upon activation of the zooming motor 15 , a driving force therefrom is transmitted through a series of reduction gears 15 a and the pinion 16 to the gear teeth 14 b , to cause the first helicoid ring 14 to rotate. The rotation of the first helicoid ring 14 in turn causes the connected unit of the first helicoid ring 14 , the first outer barrel 17 and the first linear guide ring 18 , to advance and retreat along the optical axis. Consequently, the first helicoid ring 14 , together with the first outer barrel 17 , advances or retreats along the optical axis while rotating as the male helicoids 14 a mesh with the female helicoids 12 a , whereas the first linear guide ring 18 advances or retreats along the optical axis together with the first helicoid ring 14 and the first outer barrel 17 without rotating.

The engagement portions 141 and the engagement portions 171 , and the keys 181 and the circumferential grooves 172 , are respectively configured so that when the first helicoid ring 14 and the first outer barrel 17 , and the first outer barrel 17 and the first linear guide ring 18 , are in their respective predetermined relative rotational positions (assembly/disassembly positions), the first helicoid ring 14 and the first outer barrel 17 , and the first outer barrel 17 and the first linear guide ring 18 , can be moved along the optical axis toward and away from each other for engagement/disengagement.

The first helicoid ring 14 , together with the first outer barrel 17 , advances and retreats along the optical axis while rotating as the male helicoids 14 a mesh with the female helicoids 12 a , whereas the first linear guide ring 18 advances and retreats along the optical axis together with the first helicoid ring 14 and the first outer barrel 17 without rotating. A brush 19 and a code plate 20 , which are secured to the first linear guide ring 18 and to the fixed barrel 12 , respectively, detect predetermined stepped zoom positions (1 (Wide-extremity position) through 7 (Tele-extremity position)) of the first linear guide ring 18 along the optical axis with respect to the fixed barrel 12 , wherein each of the stepped zoom positions are separated by a predetermined distance. A cosmetic ring 174 is secured to the front end of the first outer barrel 17 . The brush 19 and the code plate 20 constitute a focal detecting device.

Female helicoids 18 b are formed on the inner periphery of the first linear guide ring 18 , and engage with male helicoids 21 a formed on the outer periphery of a second helicoid ring 21 . The second helicoid ring 21 includes on the outer periphery thereof a pair of guide heads 21 b , which are placed through a pair of guide slots 18 c formed in the first linear guide ring 18 and received in a pair of head guide grooves 17 a formed on the inner periphery of the first outer barrel 17 (FIGS. 6 and 7 ). The guide slots 18 c are each formed as an elongate through hole that has the same angle of inclination as the female helicoids 18 b . As shown in FIG. 8 , each head guide groove 17 a is a straight groove that extends parallel to the optical axis O of the zoom lens system. While part of each guide head 21 b that is placed through the guide slot 18 c is formed to have a cylindrical shape with a circular cross-section, an end of the guide head 21 b that is received in the head guide groove 17 a is formed as a rectangular key that extends along the head guide groove 17 a.

The second outer barrel 23 is connected to the second helicoid ring 21 at the front end of the helicoid ring 21 . As with the first helicoid ring 14 and the first outer barrel 17 , the second helicoid ring 21 and the second outer barrel 23 are connected to each other through the engagement between engagement portions (recesses) 211 formed on the front end of the helicoid ring 21 and engagement portions (projections) 231 formed on the rear end of the second outer barrel 23 such that the second helicoid ring 21 integrally rotates with the second outer barrel 23 and can integrally retreat and advance. As with the engagement portions 141 and 171 , the engagement portions 211 and 231 can be brought into disengagable engagement when the second helicoid ring 21 and the second outer barrel 23 are in a predetermined relative rotational position (assembly/disassembly position).

A second linear guide ring 25 is supported within the second outer barrel 23 , and can be rotated relative to the second outer barrel 23 and moves along the optical axis together with the second outer barrel 23 (i.e., no relative displacement thereof is permitted along the optical axis). Linear guide projections 25 a formed on the second linear guide ring 25 engage with respective linear guide slots 18 d formed on the first linear guide ring 18 , so that the second linear guide ring 25 can only move along the optical axis relative to the first linear guide ring 18 .

A pair of circumferential grooves 232 are formed on the inner periphery of the second outer barrel 23 and are separated from one another by a predetermined distance along the optical axis. A pair of keys 251 , formed on the outer periphery of the second linear guide ring 25 , engage with the respective circumferential grooves 232 . Engagement of the keys 251 with the respective circumferential grooves 232 permits rotation of the second outer barrel 23 relative to the second linear guide ring 25 while preventing the relative movement between them along the optical axis.

Thus, upon activation of the zooming motor 15 , a driving force therefrom is transmitted through the series of the reduction gears 15 a and the pinion 16 , to cause the first helicoid ring 14 and the first outer barrel 17 to advance or retreat while rotating and the first guide ring 18 , to advance or retreat along the optical axis without rotating. This in turn causes the connected unit including the second helicoid ring 21 , the second outer barrel 23 and the second linear guide ring 25 , to advance and retreat along the optical axis. Consequently, the second helicoid ring 21 and the second outer barrel 23 advance or retreat along the optical axis relative to the first outer barrel 17 due to the engagement of the guide heads 21 b with the respective guide slots 18 c and the head guide grooves 17 a , while rotating along with the first outer barrel 17 as the male helicoids 21 a mesh with the female helicoids 18 b . On the other hand, the second linear guide ring 25 advances or retreats together with the second helicoid ring 21 and the second outer barrel 23 without rotating, due to the engagement of the linear guide projections 25 a with the respective linear guide slots 18 d.

The engagement portions 211 and the engagement portions 231 , and the keys 251 and the circumferential grooves 232 , are respectively configured so that when the second helicoid ring 21 and the second outer barrel 23 , and the second outer barrel 23 and the second linear guide ring 25 , are in their respective predetermined relative rotational positions (assembly/disassembly positions), the second helicoid ring 21 and the second outer barrel 23 , and the second outer barrel 23 and the second linear guide ring 25 , can be moved along the optical axis toward and away from each other for engagement/disengagement.

As with the first linear guide ring 18 , female helicoids 25 b are formed on the inner peripheral of the second linear guide ring 25 . The female helicoids 25 b engage with male helicoids 30 a formed on the rear outer periphery of the third outer barrel (cam ring) 30 . The third outer barrel 30 also serves as a third helicoid ring and includes a pair of guide heads 30 b on the rear outer surface thereof. The pair of the guide heads 30 b are placed through a pair of guide slots 25 c formed in the second linear guide ring 25 and are received in a pair of head guide grooves 23 a formed on the inner periphery of the second outer barrel 23 (see FIGS. 8 and 14 ). While part of each guide head 30 b that is placed through the guide slot 25 c is formed to have a cylindrical shape with a circular cross-section, an end of the guide head 30 b that is received in the head guide groove 23 a is formed as a rectangular shape that extends along the head guide groove 23 a.

The guide slots 25 c are each formed as an elongate through hole that has the same angle of inclination as the female helicoids 25 b . Each head guide groove 23 a is a straight groove that extends parallel to the optical axis O.

A third linear guide ring 33 is supported within the third outer barrel 30 , which can be rotated relative to the third outer barrel 30 and moves integrally with the third outer barrel 30 along the optical axis (i.e., no relative displacement thereof is permitted along the optical axis). The third linear guide ring 33 includes on the outer periphery thereof a plurality of linear guide projections 33 a , each of which engages with a linear guide slot 25 d formed on the inner periphery of the second linear guide ring 25 , allowing the third linear guide ring 33 to move only along the optical axis.

Thus, upon activation of the zooming motor 15 , the first helicoid ring 14 and the first outer barrel 17 advance or retreat along the optical axis while rotating. The first linear guide ring 18 advances or retreats along the optical axis together with the first helicoid ring 14 and the first outer barrel 17 without rotating. The second helicoid ring 21 and the second outer barrel 23 advance or retreat relative to each other along the optical axis while rotating together at the same rotation speed with respect to the first outer barrel 17 . The second linear guide ring 25 advances or retreats together with the second helicoid ring 21 and the second outer barrel 23 without rotating. As a result, as the male helicoids 30 a mesh with the female helicoids 25 b , the third outer barrel 30 and the third linear guide ring 33 advance or retreat along the optical axis with respect to the second outer barrel 23 , while rotating together with the second outer barrel 23 at the same rotation speed due to the engagement of the guide heads 30 b with the guide slots 25 c and the head guide grooves 23 a . The third linear guide ring 33 , with the restriction of the linear guide projections 33 a engaging the linear guide slots 25 d , advances or retreats along the optical axis together with the third outer barrel 30 without rotating. A portion of the third outer barrel 30 in front of the helicoids 30 a extends from the second outer barrel 23 and is exposed outside to form a part of the external appearance of the lens barrel.

The fourth outer barrel (lens-retaining barrel) 31 , which holds a first lens group L 1 (which includes a first sub-lens group S 1 and a second sub-lens group S 2 ), and a rear lens group frame 32 including a secured second lens group L 2 , are supported within the third outer barrel 30 , with the fourth outer barrel 31 being in front of the rear lens group frame 32 . The fourth outer barrel 31 and the rear lens group frame 32 are guided along the optical axis by the third linear guide ring 33 . Specifically, the third linear guide ring 33 includes three arm members 33 b , each having a partial cylindrical shape as shown in FIGS. 9 and 10 . Each arm member 33 b includes on respective sides thereof (i.e., the outer periphery and the inner periphery) linear guide slots 33 c and 33 d , each of which extends parallel to the optical axis O. Each guide slot 33 c slidably receives a linear guide projection (not shown) provided on the inner periphery of the fourth outer barrel 31 , whereas each guide slot 33 d slidably receives a linear guide projection 32 a provided on the outer periphery of the rear lens group frame 32 .

Front lens group cam grooves 35 for the fourth outer barrel 31 and rear lens group cam grooves 36 for the rear lens group frame 32 are formed on the inner periphery of the third outer barrel 30 . The front lens group cam grooves 35 and the rear lens group cam grooves 36 are shown in a developed view in FIG. 12 . As shown in FIG. 12 , three front lens group cam grooves 35 and three rear lens group cam grooves 36 are alternately arranged in the circumferential direction and are equally spaced from one another. Front lens group follower projections 31 a and rear lens group follower projections 32 b radially protrude from the fourth outer barrel 31 and the rear lens group frame 32 , respectively, for engaging the front lens group cam grooves 35 and the rear lens group cam grooves 36 , respectively.

Accordingly, when the zooming motor 15 is activated and the third outer barrel 30 advances or retreats along the optical axis while rotating together with the first outer barrel 17 and the second outer barrel 23 , and the third linear guide ring 33 advances or retreats along the optical axis together with the third outer barrel 30 without rotating, the fourth outer barrel 31 and the rear lens group frame 32 , while being prevented from rotating by the engagement of the linear guide projections (not shown) with the linear guide slots 33 c , advance or retreat along the optical axis on a predetermined path with respect to the third outer barrel 30 due to the engagement of the follower projections 31 a and 32 b with the respective cam grooves 35 and 36 .

The follower projections 31 a and 32 b and the respective cam grooves 35 and 36 , which cause the fourth outer barrel 31 and the rear lens group frame 32 to move toward and away from each other along the optical axis, constitute a zoom cam mechanism.

A portion of the fourth outer barrel 31 in front the follower projections 31 a extends from the third outer barrel 30 and is exposed outside to form a part of the external appearance of the lens barrel.

The above-described zoom lens barrel has a construction in which the first linear guide ring 18 , the second linear guide ring 25 , the third linear guide ring 33 , and the fourth outer barrel 31 advance and retreat linearly along the optical axis with respect to the fixed barrel 12 , without rotating.

As shown in FIG. 12 , the region of each front lens group cam groove 35 and the region of each rear lens group cam groove 36 extending between respective telephoto extremity positions (indicated as T-extremity) and retracted positions (indicated as retracted) are used in normal operations. During photographing, the follower projection 31 a and the follower projections 32 b are each guided over the normal operation region between the telephoto extremity position (T-extremity) and the wide-angle extremity position (W-extremity). The rear lens group cam groove 36 has an intermediate discontinuous position 36 a between the telephoto extremity position (T-extremity) and the wide-angle extremity position. Between the telephoto extremity position and the wide-angle extremity position, the first lens group L 1 , retained within the fourth outer barrel 31 , which is guided over the front lens group groove 35 , has a switching function in which the first sub-lens group S 1 and the second sub-lens group S 2 is switched between a mutually close position (tele mode) and a mutually distant position (wide mode). Upon switching in the first lens group L 1 , the second lens group L 2 passes the intermediate discontinuous position 36 a in the rear lens group cam groove 36 . The zoom lens system is controlled such that the intermediate discontinuous position 36 a is not used as an actual zooming range during a photographing operation (i.e., the third outer barrel 30 does not come to a stop thereat).

The lens group cam grooves 35 and 36 include an assembly/disassembly position beyond the telephoto extremity position, to which the zoom lens barrel needs to be rotated for assembly/disassembly.

A shutter unit 40 is arranged within the fourth outer barrel 31 . A front sub-lens group frame 45 and a rear sub-lens group frame 46 are fitted in the shutter unit 40 . The first sub-lens group S 1 is secured to the front sub-lens group frame 45 , and the second sub-lens group S 2 is secured to the rear sub-lens group frame 46 . The relative position of the front sub-lens group frame 45 (first sub-lens group S 1 ) with respect to the rear sub-lens group frame 46 (second sub-lens group S 2 ) along the optical axis is switched between two positions, namely, the mutually distant position for wide-angle photographing and a mutually close position for telephoto photographing. The switching is performed between the wide-angle extremity and the telephoto extremity via a focusing cam mechanism, which is driven by a bi-directional motor 53 . In each position, the sub-lens groups S 1 and S 2 are advanced or retreated along the optical axis for focusing by the bi-directional motor 53 through the focusing cam mechanism.

The shutter unit 40 is also provided behind the second sub-lens group S 2 with a lens shutter device which includes shutter sectors 60 , and a diaphragm mechanism which includes diaphragm sectors 62 (see FIGS. 2 and 3 ). In the zoom lens barrel of the present embodiment, the shutter sectors 60 are blades that serve both as a variable aperture to determine an f-number, and as a shutter. The shutter sectors 60 are electrically controlled by a control circuit 81 so that when the shutter is released, the degree of opening of the shutter sectors 60 (f-number) and time that the shutter sectors 60 remain open (shutter speed) vary depending on the exposure value. On the other hand, the diaphragm sectors 62 are provided for the purpose of limiting the maximum aperture size especially during wide-angle photographing. The degree of opening of the diaphragm sectors 62 is mechanically varied depending on how far the entire zoom lens barrel needs to extend outward. In other words, the diaphragm sectors 62 limit the aperture size so that unwanted light is not collected during wide-angle photographing.

A diaphragm drive ring 63 for opening and closing the diaphragm sectors 62 includes on the periphery thereof a lug 63 b , which engages with a diaphragm-controlling cam slot 71 formed on the inner periphery of the partial cylindrical arm member 33 b of the third linear guide ring 33 (see FIG. 10 ). Upon zooming, the third linear guide ring 33 and the shutter unit 40 (diaphragm drive ring 63 ) move relative to each other along the optical axis. This causes the lug 63 b to follow the diaphragm-controlling cam slot 71 and move in the circumferential direction. This in turn causes the diaphragm drive ring 63 to rotate and, as a result, the size of the aperture formed by the diaphragm sectors 62 is varied.

As shown in FIG. 11 , the diaphragm-controlling cam slot 71 includes a straight portion 71 a extending parallel to the optical axis O, a sloped portion 71 b sloped with respect to the optical axis O, and an opening portion 71 c opening to the front of the third linear guide ring 33 . The straight portion 71 a and the sloped portion 71 b each have substantially the same width as the lug 63 b so that the lug 63 b engages therewith with substantially no play.

Electric components of the shutter unit 40 are connected to the control circuit 81 (see FIG. 13 ) in the camera body via a flexible printed circuit board (FPC) 80 . The positions of folds in the FPC 80 move depending on the change in the relative position of the shutter unit 40 with respect to the control circuit 81 as the zoom lens barrel advances and retreats. The FPC 80 is folded into a z-shape to avoid interference with the other components of the barrel and is inserted between the outer barrels.

In the present embodiment, the FPC 80 is folded on top of itself and forms overlapped portions 801 and 802 (see FIGS. 2 and 3 ). The overlapped portions 801 and 802 are inserted from the rear side of the zoom lens barrel assembly into a gap formed between the first outer barrel 17 and the first linear guide ring 18 and a gap formed between the second outer barrel 23 and the second linear guide ring 25 , respectively. The portion of the FPC 80 that comes out from between the second outer barrel 23 and the second linear guide ring 25 extends across the third outer barrel 30 into the fourth outer barrel 31 and is connected to the shutter unit 40 at one end thereof.

The other end of the FPC 80 is pulled out from the front end of the fixed barrel 12 ( FIGS. 2 , 3 and 4 ). The miniaturized construction of the camera poses a limitation to the choice of the position at which the FPC 80 is pulled out. For this reason, the FPC 80 is positioned in the proximity of the helicoids 14 a and the gear teeth 14 b of the first helicoid ring 14 across the path of the helicoids 14 a and the gear teeth 14 b . This can result in the FPC 80 intersecting the path of ends of the gear teeth 14 b (see FIGS. 36 , 37 and 38 ). If the FPC 80 bends in such a construction, the FPC 80 may catch on an end tooth 14 b 1 of the gear teeth 14 b as shown in FIGS. 37 and 38 . However, the present embodiment employs a lead 14 a 1 formed on the first helicoid ring 14 along the path of the gear teeth 14 b for avoiding such interference (see FIG. 34 ).

Furthermore, the front end tooth 14 b 1 of the gear teeth 14 b serves as a stopper that comes into contact with a telephoto extremity stopper 101 to prevent further rotation of the first helicoid ring 14 (see FIG. 33 ). In the present embodiment, a stopper space 14 c is provided where the gear teeth 14 b terminate in order to permit engagement of the telephoto extremity stopper 101 (see FIG. 34 ).

As shown in FIG. 13 , the zooming motor 15 for the first helicoid ring 14 , the bi-directional motor 53 for the front sub-lens group frame 45 and rear sub-lens group frame 46 , and the shutter unit 40 are controlled by a control circuit (control device) 81 . Focal length information 81 a , which is set by the user (photographer) via a zoom switch or the like, detected object distance information 81 b , which is provided by a object distance measuring device, and object brightness information 81 c , which is provided by a object brightness measuring device are input to the control circuit 81 .

The above-described zoom lens barrel assembly of the present invention operates in the following manner. Upon the zooming motor 15 driving the pinion 16 , the first helicoid ring 14 and the first outer barrel 17 advance or retreat while rotating. The first linear guide ring 18 advances or retreats together with the first helicoid ring 14 and the first outer barrel 17 along the optical axis without rotating.

The second helicoid ring 21 and the second outer barrel 23 , while rotating together at the same rotation speed with respect to the first outer barrel 17 , advance or retreat relative to one another along the optical axis. The second linear guide ring 25 advances or retreats along the optical axis together with the second helicoid ring 21 and the second outer barrel 23 without rotating.

The third outer barrel 30 advances or retreats along the optical axis with respect to the second outer barrel 23 , while rotating at the same rotation speed. The third linear guide ring 33 advances or retreats along the optical axis together with the third outer barrel 30 without rotating.

The fourth outer barrel 31 advances or retreats along the optical axis without rotating (The third outer barrel 30 rotates with respect to the fourth outer barrel 31 ).

As a result, the fourth outer barrel 31 (first lens group L 1 ) and the rear lens group frame 32 (second lens group L 2 ), each guided along the optical axis in the third outer barrel 30 , move relative to each other along the optical axis on a predetermined path provided by the front lens group cam grooves 35 and the rear lens group cam grooves 36 .

For example, in the retracted state of the zoom lens barrel assembly as shown in FIG. 2 , the zoom lens barrels are substantially retracted into the camera body 11 . When the zooming motor 15 is driven in the direction to extend the barrels, the zoom lens barrel assembly extends outward to assume the photographing position at the wide-angle extremity as shown in FIG. 3 . By further driving the zooming motor 15 in the direction to extend the barrels, the zoom lens barrel assembly extends outward from the wide-angle photographing position to the photographing position at the telephoto extremity as shown in FIG. 4 .

In the present embodiment, the telephoto extremity stopper 101 serves to stop rotation of the first helicoid ring 14 in order to prevent the zoom lens barrel assembly from further extending out from the telephoto photographing position during normal operation. As shown in FIG. 33 , the telephoto extremity stopper 101 engages with the end tooth 14 b 1 of the first helicoid ring 14 , thereby preventing further rotation of the first helicoid ring 14 .

The first helicoid ring 14 is shown in a developed view in FIG. 34 . The bottom side of FIG. 34 corresponds to the front side of the zoom lens barrel assembly. The first helicoid ring 14 rotates while being led by the male helicoids 14 a to advance or retreat. The telephoto extremity stopper 101 is positioned in the path of the gear teeth 14 b since the gear teeth 14 b are formed along the male helicoids 14 a . The telephoto extremity stopper 101 is attached to the fixed barrel 12 and is externally secured to the fixed barrel 12 by a screw (see FIG. 35 ). By employing such a telephoto extremity stopper 101 , which can be externally removed from the fixed barrel 12 , the assembly/disassembly of the zoom lens barrel assembly can be facilitated.

Note that the outer diameter of the outermost ends of the gear teeth 14 b is larger than the outer diameter of the first outer barrel 17 .

By further driving the zooming motor 15 in the direction to extend the barrels with the telephoto extremity stopper 101 removed, the first helicoid ring 14 , the first outer barrel 17 and the second outer barrel 23 are made to further rotate. This causes the zoom lens barrel assembly to extend out from the telephoto photographing position to the assembly/disassembly position of the first outer barrel 17 and the second outer barrel 23 as shown in FIG. 5 . In this embodiment, the zoom lens barrel assembly is brought into the assembly/disassembly position by rotating the first helicoid ring 14 by additional 8° from the telephoto photographing position. FIG. 6 shows the zoom lens barrel assembly in the assembly/disassembly position with the first and the second outer barrels 17 and 23 removed.

By driving the zooming motor 15 in the reverse direction to retreat the barrels, the zoom lens barrel assembly is made to retreat from the assembly/disassembly position, to the telephoto photographing position, then to the wide-angle photographing position, and then to the retracted position. In practice, zooming is controlled in a stepwise manner: several focal length steps are provided between the wide-angle extremity and the telephoto extremity, and the zooming motor 15 is stopped at each focal length step to perform focusing and exposure. As described above, the region assigned to the switching of the movement of the first sub-lens group S 1 and the second sub-lens group S 2 toward and away from each other is not used for photographing. For this reason, no step is provided in this region so that the third outer barrel 30 (thus, the zooming motor 15 ) does not come to a stop in this region.

In FIG. 14 , the second outer barrel 23 , the second helicoid ring 21 , the second linear guide ring 25 and the guide heads 30 b in the retracted position are shown in a developed view as viewed from outside. In the retracted position, keys 251 , which extend in the circumferential direction on the outer periphery of the second linear guide ring 25 , engage with respective inner peripheral grooves 232 , which extend circumferentially on the inner periphery of the second outer barrel 23 , so that the second outer barrel 23 and the second helicoid ring 21 can rotate relative to one another and move together along the optical axis. A total of four keys 251 are provided on the outer circumference of the linear guide ring 25 . Two keys 251 are provided at the same circumferential position spaced apart by a predetermined length along the optical axis, and the other two keys 251 are provided at a diametrically opposite circumferential position to the other keys 251 and are spaced apart by the same predetermined length along the optical axis as that of the other two keys 251 . The guide heads 30 b are each placed in a slip region 25 c 1 of the guide slot 25 c.

The slip region 25 c 1 of the guide slot 25 c serves as a slip section for allowing the third outer barrel 30 to rotatably slip. In other words, when the guide head 30 b is in the slip region 25 c 1 and moves along the slip region 25 c 1 , rotation of the third outer barrel 30 with respect to the second linear guide ring 25 does not cause relative movement between the third outer barrel 30 and the second linear guide ring 25 along the optical axis. The slip region 25 c 1 is provided in the section between the retracted position and the wide angle extremity position of the zoom lens barrel assembly.

By further driving the zooming motor 15 in the direction to extend the barrels, the zoom lens barrel assembly is brought into the telephoto extremity position. The second outer barrel 23 , the second helicoid ring 21 , the second linear guide ring 25 and the guide heads 30 b in the telephoto extremity position are shown in FIG. 15 in a developed view similar to FIG. 14 . In the telephoto extremity position, while a portion of each key 251 has come out from the circumferential groove 232 into a free space 233 , a portion of each key 251 still remains in the circumferential groove 232 . Accordingly, the second outer barrel 23 is prevented from moving with respect to the second linear guide ring 25 along the optical axis (thus, the second outer barrel 23 does not come off the second linear guide ring 25 ). In other words, the second outer barrel 23 and the second linear guide ring 25 can rotate relative to each other but advance or retreat together along the optical axis.

At this stage, when the zooming motor 15 is driven in the direction to extend the barrels, the gear teeth 14 b of the first helicoid ring 14 engage with the telephoto extremity stopper 101 and prevent the first helicoid ring 14 from rotating further.

By removing the telephoto extremity stopper 101 , the first helicoid ring 14 is made to move freely so that the zooming motor 15 can be further driven to extend the barrels.

From the above-described telephoto extremity position, the zoom lens barrel assembly is brought into the assembly/disassembly position by removing the telephoto extremity stopper (not shown) and further driving the zooming motor 15 in the direction to extend the barrels. The second outer barrel 23 , the second helicoid ring 21 , the second linear guide ring 25 and the guide heads 30 b in the assembly/disassembly position are shown in FIG. 16 in a developed view similar to FIG. 14 . In the assembly/disassembly position, each key 251 has come out of the circumferential groove 232 and is entirely in the free space 233 . Thus, in the assembly/disassembly position, the second outer barrel 23 can be moved with respect to the second linear guide ring 25 along the optical axis. In other words, the second outer barrel 23 can be removed from (see FIG. 17 ) or mounted back onto the second linear guide ring 25 (FIG. 16 ).

By pulling out the first and the second outer barrels 17 and 23 in the assembly/disassembly position, the guide heads 21 b and 30 b can be externally exposed (see FIG. 6 ). Once the guide heads 21 b and 30 b have been removed (see FIG. 7 ), the third outer barrel 30 , the second helicoid ring 21 , and the first helicoid ring 14 can be further rotated to extend further outward for removal by the action of the helicoids. Thus, the zoom lens barrel assembly can be disassembled when in the assembly/disassembly position.

The zoom lens barrel assembly of the present invention is integrated with the camera body and is constructed such that when the zoom lens barrel is assembled to allow the camera to take pictures, rotation of the zooming motor 15 is controlled to prevent the lens barrel assembly from extending out past the telephoto photographing position to the assembly/disassembly position. If the camera needs repairing, the zooming motor 15 can be made to operate to bring the zoom lens barrel assembly from the telephoto photographing position into the assembly/disassembly position by, for example, entering special commands.

In this embodiment, as with the second outer barrel 23 and the second linear guide ring 25 , the first outer barrel 17 and the first linear guide ring 18 have circumferential grooves 172 , free spaces 173 , and keys 181 . The first outer barrel 17 can be removed from, and mounted onto, the first linear guide ring 18 in the above-described assembly/disassembly position.

A lens barrier mechanism for opening and closing the barrel opening in front of the first lens group L 1 is arranged in the front portion of the fourth outer barrel 31 . The lens barrier mechanism includes a cosmetic plate 90 secured to the front portion of the fourth outer barrel 31 , a barrier drive ring 91 , which is retained in a front wall 31 b (see FIG. 2 ) of the fourth outer barrel 31 and can rotate about the optical axis O, a pair of outer barriers 92 and a pair of inner barriers 93 , which are each rotatably supported between the barrier drive ring 91 and the cosmetic plate 90 . The cosmetic plate 90 includes a projection (not shown) for rotatably supporting the outer barriers 92 and the inner barriers 93 . The outer barriers 92 and the inner barriers 93 pivot about the projection and cooperate to open and close the opening of the cosmetic plate 90 . A barrier biasing spring 94 biases each pair of the barriers 92 and 93 to close.

The barrier drive ring 91 includes a pair of barrier projections 91 a arranged at diametrically opposite ends, and a lug arm 91 b extending rearward in the optical axis direction. The barrier projections 91 a engage with the outer barriers 92 or the inner barriers 93 to transmit rotation of the barrier drive ring 91 to the barriers 92 and 93 . The lug arm 91 b is inserted through a hole (not shown) formed in the front wall 31 b arranged on the inner periphery of the front portion of the fourth outer barrel 31 into the fourth outer barrel 31 . The lug arm 91 b is shaped to slide against a guide slope 33 e formed on the front end of the partial cylindrical arm member 33 b of the third linear guide ring 33 .

A drive ring biasing spring 95 biases the barrier drive ring 91 to rotate to open the barriers 92 and 93 . The drive ring biasing spring 95 exerts a larger force than the barrier biasing spring 94 . Thus, when the barrier drive ring 91 is free to rotate by the biasing force of the drive ring biasing spring 95 , the biasing force of the drive ring biasing spring 95 is transmitted through the barrier drive ring 91 , at transmitted to the barriers 92 and 93 via the barrier projection 91 a , so that the barriers 92 and 93 are held open against the biasing force of the barrier biasing spring 94 . When the zoom lens barrel assembly is in a photographing position between the wide-angle extremity as shown in FIG. 3 and the telephoto extremity as shown in FIG. 4 , the lug arm 91 b is not in contact with the guide slope 33 e and the barrier drive ring 91 remains free, so that the barriers 92 and 93 are held open.

As the zoom lens barrel assembly shifts from the wide-angle extremity position as shown in FIGS. 3 and 32 to the retracted position as shown in FIGS. 2 and 31 , the guide slope (barrier drive surface) 33 e (see FIG. 9 ) of the third linear guide ring 33 comes into contact with the lug arm 91 b of the barrier drive ring 91 and starts sliding against the lug arm 91 b . As a result, the barrier drive ring 91 is forcibly rotated against the drive ring biasing spring 95 as it follows the guide slope 33 e . This allows the barriers 92 and 93 to rotate and close. Since the barriers 92 and 93 are released from the restriction of the barrier drive ring 91 and are biased by the biasing force of the barrier biasing spring 94 , each pair of the barriers 92 and 93 rotate to close and remain closed.

When the zoom lens barrel assembly shifts from the wide-angle extremity position to the retracted position, slip sections are utilized so that the third outer barrel 30 and the second outer barrel 23 , and the second outer barrel 23 and the first outer barrel 17 , rotate together and do not move relative to one another along the optical axis. In the present embodiment, before the entire zoom lens barrel assembly retreats to the retracted position, i.e., before the fourth outer barrel 31 retreats to the retracted position thereof with respect to the third outer barrel 30 , the second outer barrel 23 retreats along the optical axis to the retracted position thereof with respect to the first outer barrel 17 , and enters the slip section thereof (i.e., the slip region 25 c 1 of the second linear guide ring 25 ), and thereafter starts retreating while rotating together with the first outer barrel 17 ; subsequently, the third outer barrel 30 retreats along the optical axis to the retracted position thereof with respect to the second outer barrel 23 and enters the slip section thereof; and the third outer barrel 30 , the second outer barrel 23 , and the first outer barrel 17 start retreating toward the retracted position while rotating together. Accordingly, either at substantially the same time or after the guide slope 33 e of the third linear guide ring 33 comes into contact with the lug arm 91 b of the barrier drive ring 91 and starts sliding against the lug arm 91 b , the second outer barrel 23 and then the third outer barrel 30 reach their respective slip sections. As a result, the fourth outer barrel 31 retreats due to the relative rotation of the fourth outer barrel 31 with respect to the third linear guide ring 33 . Thus, the fourth outer barrel 31 and the third outer barrel 30 , and thus the third linear guide ring 33 , move along the optical axis relative to each other. This causes the barrier drive ring 91 to rotate to thereby close the barriers 92 and 93 .

Conversely, when the zoom lens barrel assembly extends out from the retracted position to the wide-angle extremity position, the first, the second, and the third outer barrels 17 , 23 and 30 , respectively extend out along the optical axis while rotating together. However, the second outer barrel 23 and the third outer barrel 30 , when in each slip section thereof, extend out together with the first outer barrel 17 toward the wide-angle extremity while rotating together with the first outer barrel 17 , whereas the fourth outer barrel 31 extends out toward the wide-angle extremity with respect to the third outer barrel 30 without relatively rotating. When the second outer barrel 23 and the third outer barrel 30 are in the slip sections thereof, the guide slope 33 e of the third linear guide ring 33 moves away from the lug arm 91 b so that the barrier drive ring 91 , actuated by the biasing force of the drive ring biasing spring 95 , rotates to open the barriers 92 and 93 . As a result, the guide slope 33 e moves away from the lug arm 91 b and the barriers 92 and 93 are completely opened before the zoom lens barrel assembly reaches the wide-angle extremity.

When the zoom lens barrel assembly extends out from the retracted position to the wide-angle extremity position, the third outer barrel 30 exits the slip section first. Thereafter, the third outer barrel 30 starts to extend with respect to the second outer barrel 23 . Subsequently, the second outer barrel 23 exits the slip section thereof (i.e., the slip region 25 c 1 of the second linear guide ring 25 ), causing the second outer barrel 23 to start extending out with respect to the first outer barrel 17 .

As described above, the opening/closing of the barriers 92 and 93 is effected by the stroke, i.e., the relative displacement between the fourth outer barrel 31 and the third outer barrel 30 along the optical axis that occurs as the zoom lens barrel assembly shifts from the retracted position to the wide-angle extremity position. Accordingly, an alternative construction is possible wherein the slip section is not provided in the third outer barrel 30 and/or the second outer barrel 23 . A large stroke is desirable for opening and closing the barriers 92 and 93 since too small a stroke can result in an excessively large driving torque. However, increasing the stroke length increases the rotation angle of the third outer barrel 30 required for opening/closing of the barriers, and as a result, the fourth outer barrel 31 extends by an excessively large amount with respect to the camera body, which can exceed the required amount for shifting the lens barrel assembly from the retracted position to the wide-angle extremity position.

Though the slip section may be provided only in the helicoid structure of the third outer barrel 30 , such a construction can result in a small stroke for the rotation angle of the lens barrel required for the extension of the lens barrel assembly from the retracted position to the wide-angle extremity position. Therefore, in such a case, the slip section needs to have a large rotation angle. Furthermore, in such a construction, relative displacement of the fourth outer barrel 31 with respect to the third outer barrel 30 along the optical axis becomes large, so that the part of the FPC 80 that extends across the third outer barrel 30 may be unfavorably tensed unless sufficient play is provided (refer to FIGS. 2 and 3 ).

To cope with such problems, the helicoid slip sections are provided both in the second outer barrel 23 and in the third outer barrel 30 in the present embodiment in order to ensure a large rotation angle of the lens barrel assembly as the lens barrel assemble shifts from the retracted position to the wide-angle extremity position. In this manner, sufficient relative displacement along the optical axis of the fourth outer barrel 31 with respect to the third outer barrel 30 is achieved for the small lead of the cam for sending out the fourth outer barrel 31 .

Construction of the slip section of the helicoids will now be described with reference to FIGS. 18 through 27 . FIG. 18A is a perspective view showing a longitudinal cross-section of the second linear guide ring 25 . FIG. 18B is a perspective view showing a longitudinal cross-section of the first linear guide ring 18 . FIG. 19 is a developed view of the second linear guide ring 25 . Each of FIGS. 20 through 22 is a developed view showing a relationship between the second linear guide ring 25 and the third outer barrel (cam/helicoid ring) 30 . FIG. 23 is a developed view of the first linear guide ring 18 . Each of FIGS. 24 through 26 is a developed view showing a relationship between the first linear guide ring 18 , the second outer barrel 23 , and the second helicoid ring 21 . Each of FIGS. 27A , 27 B and 27 C is an enlarged view showing the female helicoids 25 b and helicoid slip sections 25 b 1 of the second linear guide ring 25 , and the male helicoids 30 a of the third outer barrel 30 .

As shown in FIG. 19 , the female helicoid 25 b on the inner periphery of the second linear guide ring 25 includes a wide (in the circumferential direction) helicoid slip section 25 b 1 near the rear end (camera body side) of the second linear guide ring 25 . The helicoid slip section 25 b 1 has substantially the same length as the male helicoid 30 a of the third outer barrel 30 in the optical axis direction. Accordingly, as shown in FIG. 20 , as the male helicoid 30 a proceeds into the helicoid slip section 25 b 1 , the male helicoids 30 a and the female helicoids 25 b are released from the confinement of the flanks thereof, so that the second linear guide ring 25 and the third outer barrel 30 can rotate relative to each other with the relative movement along the optical axis being prevented. The guide slot 25 c also includes the slip section 25 c 1 to permit the rotation in the helicoid slip section 25 b 1 .

Although the helicoid slip section 25 b 1 is designed to permit no movement of the male helicoid 30 a along the optical axis, helicoid slip section 25 b 1 can be designed to permit a slight movement of the male helicoid 30 a along the optical axis. Furthermore, the helicoid slip section 25 b 1 can include a thrust surface 25 b 2 (see FIG. 28A ) and the front and the rear end surfaces of the male helicoid 30 a may be configured as a flank surface to slide against the thrust surface 25 b 2 .

When the zoom lens barrel assembly is in the retracted position, the male helicoids 30 a for engaging the female helicoids 25 b are located in the respective helicoid slip sections 25 b 1 , and the guide heads 30 b placed through the guide slots 25 c are located in the respective slip sections 25 c 1 (see FIG. 20 ). As the zoom lens barrel assembly extends out from the retracted position toward the wide-angle extremity, the third outer barrel 30 , the male helicoids 30 a , and the guide heads 30 b move with respect to the second linear guide ring 25 toward the wide-angle position (toward the right-hand side in FIGS. 20 through 22 ). With the male helicoids 30 a confined in the respective helicoid slip sections 25 b 1 , the third outer barrel 30 can only rotate with respect to the second linear guide ring 25 , and the zoom lens barrel assembly proceeds to a position in which the male helicoids 30 a are positioned at the boundaries of the slip sections (slip section boundary position) (see FIG. 21 ). When the zoom lens barrel assembly is in the slip section boundary position, the male helicoids 30 a engage with the female helicoid 25 b by their flanks.

As the zoom lens barrel assembly further extends out from the slip section boundary position toward the wide-angle extremity position, the third outer barrel 30 , with the male helicoids 30 a confined by the female helicoids 25 b , moves forward with respect to the second linear guide ring 25 (toward the top of FIGS. 20 through 22 ) while rotating and being led by the female helicoids 25 b . As a result, the zoom lens barrel assembly proceeds to the wide-angle extremity position (FIG. 22 ).

Although the male helicoids 30 a are formed on the third outer barrel 30 and female helicoids 25 b are formed on the second linear guide ring 25 in the present embodiment, male helicoids can be formed on the second linear guide ring 25 and female helicoids can be formed on the third outer barrel 30 .

As with the second linear guide ring 25 and the third outer barrel 30 , the first linear guide ring 18 , the second outer barrel 23 and the second helicoid ring 21 include slip sections.

As shown in FIG. 23 , the female helicoid 18 b on the inner periphery of the first linear guide ring 18 has a wide (as viewed in the circumferential direction) helicoid slip section 18 b 1 near the rear end (camera body side) of the first linear guide ring 18 . The helicoid slip section 18 b 1 has substantially the same length as the male helicoid 21 a of the second helicoid ring 21 in the optical axis direction. Accordingly, as shown in FIG. 24 , as the male helicoid 21 a proceeds to the helicoid slip section 18 b 1 , the male helicoids 21 a and the female helicoids 18 b are released from the confinement of the flanks thereof, so that the first linear guide ring 18 and the helicoid ring 21 (and thus the second outer barrel 23 ) can rotate relative to each other with the relative movement along the optical axis being prevented. The guide slot 18 c also includes a slip section 18 c 1 which corresponds to the helicoid slip section 18 b 1 and has no lead angle.

When the zoom lens barrel assembly is in the retracted position, the male helicoids 21 a for engaging with the female helicoids 18 b are located in the respective helicoid slip sections 18 b 1 , and the guide heads 21 b placed through the guide slots 18 c are located in the respective slip sections 18 c 1 (see FIG. 24 and FIG. 27 A). As the zoom lens barrel assembly extends out from the retracted position toward the wide-angle extremity, the male helicoids 21 a and the guide heads 21 b , and thus the helicoid ring 21 and the second outer barrel 23 , move with respect to the first linear guide ring 18 toward the wide-angle position (toward the right-hand side in FIGS. 24 through 26 ). During this relative movement, with the male helicoids 21 a and the guide heads 21 b located in the helicoid slip sections 18 b 1 and in the slip sections 18 c 1 , respectively, the second outer barrel 23 and the second helicoid ring 21 can only rotate with respect to the first linear guide ring 18 , and the zoom lens barrel assembly proceeds to a position in which the male helicoids 21 a are positioned at the boundaries of the slip sections (slip section boundary position) (see FIG. 25 and FIG. 27 B). When the zoom lens barrel assembly is in the slip section boundary position, the male helicoids 21 a engage with the female helicoids 18 b by their flanks.

As the zoom lens barrel assembly further extends out from the slip section boundary position toward the wide-angle extremity position, the second outer barrel 23 and the second helicoid ring 21 , with the male helicoids 21 a confined by the female helicoids 18 b , move forward with respect to the first linear guide ring 18 (toward the top of FIGS. 24 through 26 ) and rotate while being led by the male helicoids 21 a , the female helicoids 18 b , and the guide slots 18 c . As a result, the zoom lens barrel assembly proceeds to the wide-angle extremity position (shown in FIG. 26 and FIG. 27 C).

In this embodiment, the third outer barrel 30 also has slip sections since the slipping of only the second outer barrel 23 is insufficient for the opening/closing of the barriers 92 and 93 . For the third outer barrel 30 , the slip sections are provided for the minimizing the amount of barrel advancement and adjusting the balance of barrel advancement.

Furthermore, in the present embodiment, the slip angle of the helicoid slip section 18 b 1 for slipping the second outer barrel 23 and the helicoid ring 21 is set to be larger than the slip angle of the helicoid slip section 25 b 1 for slipping the third outer barrel 30 . If the third outer barrel 30 and the second outer barrel 23 simultaneously shift from the slip section to the helicoid section, the applied load increases significantly. This effect can be reduced by the above construction.

As described above, in the zoom lens barrel assembly of the present invention, the opening/closing of the barriers 92 and 93 are performed by the slip motions of the third outer barrel 30 , the second outer barrel 23 and the relative movement of the fourth outer barrel 31 along the optical axis. In the zoom lens barrel assembly of the present embodiment, the movement of the barrier drive ring 91 for closing and opening the barriers 92 and 93 is caused by two actions, namely, the stroke action of the fourth outer barrel 31 that takes place as the barrel assembly shifts between the retracted position and the wide-angle extremity position, and the slip action of the third outer barrel 30 and the second outer barrel 23 that takes place in the respective slip sections between the retracted position and the wide-angle extremity position. Accordingly to this construction, the long stroke length of the fourth outer barrel 31 is utilized.

Referring to FIG. 28A , a part of the female helicoids 18 b of the first linear guide ring 18 is shown in an enlarged view in the vicinity of the helicoid slip sections 18 b 1 . In general, the first linear guide ring 18 is made by injection-molding a plastic material. Accordingly, a mold is machined via electrospark machining. During the electrospark machining process, however, corners, such as those of the helicoid slip sections 18 b 1 , are rounded (indicated by R in FIG. 28 B). If the corners of the helicoid slip sections 18 b 1 are rounded, the length of each thrust surface 18 b 2 of the helicoid slip section 18 b 1 along the circumference of the barrel is reduced as well as the contact area with the male helicoid 21 a . As a result, the surfaces interfere with the male helicoids 21 a . Furthermore, if the corners of the helicoid slip sections 18 b 1 are rounded, the thrust surfaces 18 b 2 can no longer support the male helicoid 21 a against the thrust force thereof with sufficient stability.

However, in the present embodiment, a circumferential groove 18 e is formed along each of the front and the rear thrust surfaces 18 b 2 of the helicoid slip section 18 b 1 , the surfaces being spaced apart from each other in the optical axis direction. As shown in FIG. 28C , this construction eliminates the problem of rounded corners. The circumferential groove 18 e is formed to be wide enough (in the optical axis direction) to eliminate the rounded corners. Preferably, the width is substantially the same as the radius of curvature of the rounded corner that would otherwise be formed by electrospark machining.

In one embodiment, a circumferential groove 25 e similar to the circumferential groove 18 e of the first linear guide ring 18 is formed along each of the front and the rear thrust surfaces 25 b 2 of each of the helicoid-slip section 25 b 1 of the second linear guide ring 25 .

When the male helicoids 21 a proceed from the helicoid slip sections 18 b 1 into the female helicoids 18 b , if the second helicoid ring 21 and the first linear guide ring 18 are not coaxially aligned or inclined with respect to each other, the end surfaces of the male helicoids 21 a may catch on the thrust surfaces 18 b 2 , preventing the male helicoids 21 a from proceeding into the female helicoids 18 b . In order to prevent such a problem, an embodiment of the present invention includes flanges (eccentricity-preventing members) 18 f and 25 f to eliminate eccentricity. The flanges 18 f and 25 f are formed on the inner peripheries of the first linear guide ring 18 and the second linear guide ring 25 , respectively, near the rear ends of the respective guide rings (see FIGS. 18 A and 18 B). The radial flanges 18 f and 25 f slidably engage with, and close the end of, the second helicoid ring 21 and the third outer barrel 30 , respectively, when the second helicoid ring 21 and the third outer barrel 30 are retreated to their respective retracted positions (see FIG. 29 ). In this state, the second helicoid ring 21 and the third outer barrel 30 rotate through the slip sections while sliding against the flanges 18 f and 25 f , respectively. In this manner, backlash between the second helicoid ring 21 and the third outer barrel 30 is prevented even when the rings are moving through the slip sections.

With this construction, the radial positions of the male helicoids 21 a and 30 a are restricted by the flanges 18 f and 25 f , and as a result, the male helicoids 21 a and 30 a can proceed from the respective helicoid slip sections 18 b 1 and 25 b 1 into the respective female helicoids 18 b and 25 b in a smooth and reliable manner. Once the male helicoids 21 a and 30 a engage with the respective female helicoids 18 b and 25 b , the helicoid mechanism causes the second helicoid ring 21 and the third outer barrel 30 to advance or retreat between the wide-angle extremity position ( FIG. 30 ) and the telephoto extremity position while rotating.

Although in this embodiment, the flanges 18 f and 25 f are provided on the inner peripheries of the first linear guide ring 18 and the second linear guide ring 25 , respectively, similar structures with functions similar to the flanges 18 f and 25 f , such as projections, may be provided on the inner peripheries of the second helicoid ring 21 and the third outer barrel 31 . An alternative construction is possible wherein the bottom of the helicoid slip regions 18 b 1 ( 25 b 1 ) can be gradually raised so that the helicoid slip regions 18 b 1 ( 25 b 1 ) have a largest depth at a boundary region 18 b 3 ( 25 b 3 ) and have a smallest depth at a slip boundary region 18 b 4 ( 25 b 4 ), as shown in FIG. 28 C.

In this embodiment, at least one of the lens barrels except for the frontmost one is connected to the adjacent lens barrel through a helicoid structure, and at least part of the helicoid that the lens barrel follows as the lens barrel assembly moves from a retracted position to a minimally extended photographing position is formed as a slip section that allows the lens barrel to rotate without advancing or retracting. Thus, this construction not only ensures rigidity of the lens barrel assembly, but also achieves sufficient displacement between the frontmost lens barrel and other lens barrels for providing a sufficient stroke to open and close the barrier via a predetermined rotation angle.

According to this embodiment, the multi-stage-extension zoom lens barrel assembly includes a helicoid structure which causes two connected lens barrels to rotate and move along the optical axis relative to each other as the zoom lens barrel assembly moves between a retracted position and a minimally extended photographing position, and the helicoid structure includes a helicoid slip region that causes the two barrels to relatively rotate without relatively moving along the optical axis. Also, the helicoid slip region includes a female helicoid formed on one of the two barrels to be connected and a male helicoid formed on the other of the two barrels, and the female helicoid includes a helicoid slip region that permits rotation of the male helicoid when the two barrels are in the retracted position. A circumferential groove is formed along each of thrust surfaces of the helicoid slip region. Accordingly, components of the lens barrels that have the helicoid slip region can be formed with high precision and at a lower cost.

According to the above description, the zoom lens barrel assembly of the present invention, in which telescopic movement of the lens barrels is restricted by a stopper member engaging an end tooth of gear teeth on the helicoid ring, has a simple stopper construction for the lens barrels with fewer components. This construction also facilitates disassembly of the zoom lens barrel assembly since the helicoid ring can be rotated past the normal operative position to the disassembly position by simply removing the stopper member.

Furthermore, the interference-preventing member prevents the flexible printed circuit board from interfering with the gear teeth of the helicoid ring even when the FPC is placed close to the path of the end tooth of the gear teeth of the helicoid ring.

Obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention.

Claims

1. A zoom lens barrel assembly, comprising:a plurality of lens barrels including a rearmost lens barrel, secured to a camera body, and a frontmost lens barrel; wherein at least two adjacent lens barrels, of said plurality of lens barrels arranged between the camera body and the frontmost lens barrel, are connected to each other via a helicoid structure; wherein the frontmost lens barrel and a first adjacent lens barrel are connected to each other via a cam structure; wherein said helicoid structure allows said at least two adjacent lens barrels to rotate and move in an optical axis direction relative to each other while the zoom lens barrel assembly moves from a retracted position to a minimally extended position for a photographing operation; and wherein at least a portion of the helicoid structure includes a slip region which allows said at least two adjacent lens barrels to rotate without relatively moving along the optical axis.

2. The zoom lens barrel assembly according to claim 1, wherein a barrier mechanism is provided on the frontmost lens barrel, said barrier mechanism being opened and closed via movement of the frontmost lens barrel in the optical axis direction as the zoom lens barrel assembly moves between the retracted position and said minimally extended position, and by relative rotation of said at least two adjacent lens barrels via the slip region.

3. The zoom lens barrel assembly according to claim 1, wherein said first adjacent lens barrel connected to the frontmost lens barrel via said cam structure is connected to a second adjacent lens barrel via a second helicoid structure which causes the connected said first and second adjacent lens barrels to rotate and move along the optical axis relative to each other as the zoom lens barrel assembly moves from the retracted position to the minimally extended position, said second helicoid structure also including a slip region which allows said first adjacent lens barrel and said second adjacent lens barrel to rotate without relatively moving along the optical axis.

4. A four-stage-extension zoom lens barrel, comprising:a first barrel connected to a fixed barrel secured to a camera body, said first barrel being movable so as to retreat and advance relative to the fixed barrel; a second barrel connected to the first barrel; a third barrel connected to the second barrel; a frontmost fourth barrel connected to the third barrel; wherein said first, second, and third barrels are each supported, and are movable in an optical axis direction, via a helicoid structure; wherein said frontmost fourth barrel and said third barrel are connected to each other by a cam structure so as to be movable in an optical axis direction; wherein a barrier mechanism is provided on said frontmost fourth barrel; wherein the helicoid structures for moving the second barrel and the third barrel in the optical axis direction each allow the second and the third barrels to rotate and relatively move in the optical axis direction as the zoom lens barrel moves between a retracted position and a minimally extended position for a photographing operation, each said helicoid structure having a slip region which allows the second and third barrels to rotate without relatively moving in the optical axis direction; and wherein said barrier mechanism is opened and closed by a relative movement of said third barrel and said frontmost fourth barrel in the optical axis direction as said slip sections allow the second and the third barrels to rotate.

5. The four-stage-extension zoom lens barrel according to claim 4, wherein the fourth barrel is connected to the third barrel via the cam structure so that the fourth barrel moves in the optical axis direction relative to the third barrel without rotating, and the barrier mechanism is opened and closed by said relative movement of the third barrel and the fourth barrel in the optical axis direction in the slip section of the third barrel.

6. The four-stage-extension zoom lens barrel according to claim 4, wherein the slip section of the helicoid structure of the second barrel has a different slip angle than the slip section of the helicoid structure of the third barrel.

7. The four-stage-extension zoom lens barrel according to claim 4, wherein said helicoid structure having the slip section includes a female helicoid formed on one of two adjacent barrels of said first through third barrels and a male helicoid formed on the other of said two adjacent barrels, and wherein the female helicoid includes a helicoid slip region that permits rotation of the male helicoid when said two adjacent barrels are in a retracted position.

8. A zoom lens barrel assembly, comprising:a plurality of lens barrels including a rearmost lens barrel secured to a camera body, and a frontmost lens barrel; wherein the frontmost lens barrel and a first adjacent lens barrel are connected to each other via a cam structure; wherein said first adjacent lens barrel is connected to a second adjacent lens barrel via a helicoid structure so that said first and second adjacent lens barrels relatively rotate and relatively move in the optical axis direction as the zoom lens barrel assembly moves between a retracted position and a minimally extended position for a photographing operation, said helicoid structure including a helicoid slip region which allows said first and second adjacent lens barrels to relatively rotate without relatively moving along the optical axis; wherein said helicoid structure having the helicoid slip region includes a female helicoid formed on one of said first and second adjacent lens barrels and a male helicoid formed on the other of said first and second adjacent lens barrels; wherein said female helicoid includes a helicoid slip region which permits rotation of the male helicoid when said first and second adjacent lens barrels are in the retracted position; and wherein a circumferential groove is formed along each of opposing thrust surfaces of the helicoid slip region.

9. The zoom lens barrel assembly according to claim 8, wherein said helicoid structure having said helicoid slip region and said circumferential groove constitute a helicoid ring, said helicoid ring being formed by injection-molding a plastic material into a mold.

10. A zoom lens barrel assembly, comprising:a pair of lens barrels connected to each other via a helicoid structure, said helicoid structure including a helicoid slip region which allows said pair of the lens barrels to relatively rotate without relatively moving along the optical axis; wherein said helicoid structure having the helicoid slip region includes a female helicoid formed on one of said pair of lens barrels and a male helicoid formed on the other of said pair of lens barrels; wherein said female helicoid includes the helicoid slip region which allows rotation of the male helicoid when said pair of lens barrels are in a predetermined position; and wherein a circumferential groove is formed along each of opposing thrust surfaces of the helicoid slip region of the female helicoid.

11. A zoom lens barrel assembly, comprising:a plurality of lens barrels, at least two lens barrels of said plurality of lens barrels including a helicoid structure for allowing one lens barrel of said at least two lens barrels to rotate and extend and retreat as the zoom lens barrel assembly moves from a retracted position to a minimally extended position for a photographing operation; wherein said helicoid structure includes a helicoid slip section for allowing said one lens barrel to rotate without relatively moving along the optical axis, said helicoid structure including a female helicoid formed on one of said at least two lens barrels and a male helicoid formed on the other of said at least two lens barrels, the male and the female helicoids including a helicoid slip region that allows said at least two lens barrels to rotate and prevents said at least two lens barrels from moving along the optical axis when one of said at least two lens barrels is retracted into the other; and an eccentricity-preventing member provided on said at least two lens barrels for allowing said at least two lens barrels to slidably and closely engage with each other so as to slide circumferentially and slide in the optical axis direction, said eccentricity-preventing member guiding rotation of said at least two lens barrels via said helicoid slip section when one of said at least two lens barrels is retreated and slightly advanced with respect to the other of said at least two lens barrels.

12. The zoom lens barrel assembly according to claim 11, wherein said eccentricity-preventing member is formed as a flange which extends circumferentially and projects radially inward from an inner periphery of one of said at least two lens barrels which is provided outside of the other of said at least two lens barrels, said flange being formed in the vicinity of said helicoid slip section and slidably placed over an outer periphery of an inner lens barrel of said at least two lens barrels.

13. The zoom lens barrel assembly according to claim 11, wherein each of said plurality of lens barrels arranged between a camera body and a frontmost lens barrel is connected via the helicoid structure, said front most lens barrel and a first adjacent lens barrel being connected to each other via a cam structure, and wherein said first adjacent lens barrel and a second adjacent lens barrel connected thereto constitute said at least two lens barrels.

14. The zoom lens barrel assembly according to claim 11, wherein a barrier mechanism is mounted on said frontmost lens barrel, the barrier mechanism being opened and closed by relative movement of said frontmost lens barrel and said first adjacent lens barrel in the optical axis direction as the zoom lens barrel assembly moves from the retracted position to the minimally extended position for a photographing operation.