GB2309543A

GB2309543A - Moving lens extreme position detecting device

Info

Publication number: GB2309543A
Application number: GB9701433A
Authority: GB
Inventors: Hiroshi Nomura; Kazuyoshi Azegami; Takamitsu Sasaki
Original assignee: Asahi Kogaku Kogyo Co Ltd
Current assignee: Pentax Corp
Priority date: 1996-01-26
Filing date: 1997-01-24
Publication date: 1997-07-30
Anticipated expiration: 2017-01-24
Also published as: GB9701433D0; GB2309543B

Abstract

A lens drive mechanism includes: first and second members positioned adjacent each other, the second member 50 supporting a lens group (L2), the second member being movable relative to the first member 40 along an optical axis of the lens group; a first guide shaft 51 extending in a direction of the optical axis and being supported by the first member to be guided in the direction of the optical axis, one end of the first guide shaft being secured to the second member; a screw shaft 43 extending in the direction of the optical axis and having a first thread formed thereon, one end of the screw shaft being secured to the second member, the screw shaft being positioned adjacent to the first guide shaft; and a device for detecting whether the lens group is located at an extremity of its predetermined movable range relative to the first member along the optical axis. The detecting device includes a connecting member 306 secured to the other end of each of the screw shaft 43 and the first guide shaft 51, and optionally a photosensor 301, and a light interrupting member 302.

Description

MOVING LENS POSITION DETECTING DEVICE The present invention relates to a device for detecting a position of a moving lens group, which is driven to move along an optical axis thereof (e.g., a lens group moved for focusing), in order to stop the moving lens group at an extremity of a predetermined movable range of the moving lens group when the moving lens group moves to the extremity thereof.

A conventional lens drive mechanism in which a moving lens group is driven to move along an optical axis thereof by a feed screw shaft, on which a male thread is formed, is well known. Such a conventional lens drive mechanism is generally provided with a device for guiding the moving lens group along the optical axis, and a device for driving the moving lens group to move forward or backward along the optical axis. The moving lens group guiding device is separately and independently provided from the moving lens group driving device. In addition, a device for detecting whether the moving lens group reaches an extremity of a predetermined moving range thereof so as to stop the moving lens group at the extremity when the moving lens group moves thereto, is sometimes further provided along with the conventional lens drive mechanism. Such a detecting device is also independently and separately provided from either the moving lens group guiding device or the -moving lens group driving device.

An object of the present invention is to provide a device, provided in a lens such as a photographic lens, for detecting a position of such a moving lens group in order to stop the moving lens group at an extremity of a predetermined movable range thereof when the moving lens group moves to the extremity, in which the number of components of the lens can be reduced and in which the detecting device ensures a stable movement of the moving lens group along the optical axis thereof.

According to an aspect of the present invention, there is provided a lens drive mechanism including: first and second members positioned adjacent to each other, the second member supporting a lens group, the second member being movable relative to the first member along an optical axis of the lens group; a first guide shaft extending in a direction of the optical axis, the first guide shaft being supported by the first member to be guided in the direction of the optical axis, one end of the first guide shaft being secured to the second member; a screw shaft extending in the direction of the optical axis and having a first thread formed thereon, one end of the screw shaft being secured to the second member, the screw shaft being positioned adjacent to the first guide shaft; and a device for detecting whether the lens group is located at an extremity of a predetermined movable range of the lens group relative to the first member along the optical axis, the detecting device including a connecting member secured to the other end of each of the screw shaft and the first guide shaft.

Preferably, the lens drive mechanism further includes a gear rotatably supported on the first member so as not to move in the direction of the optical axis relative to the first member, the gear including a hole at an axial center thereof on an inner periphery of which is formed a second thread, wherein the gear is rotatably fitted on the screw shaft with the second thread meshing with the first thread.

Preferably, the detecting device further includes a photosensor fixed on the first member and a light interrupting member slidably supported on the first member in the direction of the optical axis to be sensed by the photosensor.

Preferably, the photosensor is a photointerrupter.

Preferably, a movable range of the light interrupting member is shorter than the predetermined movable range of the lens group in the direction of the optical axis, and wherein the connecting member comes into contact with the light intercepting member when the lens group. moves to a predetermined position within the predetermined movable range thereof.

Preferably, the connecting member includes an engaging portion integrally formed therewith, and wherein the engaging portion firstly comes into contact with the light interrupting member and subsequently moves the light interrupting member in the direction of the optical axis so that the light interrupting member interferes with a light path of the photo interrupter when the lens group is driven to move to the extremity.

Preferably, the lens drive mechanism further includes a shutter having a plurality of shutter blades, wherein the first member supports the shutter.

Preferably, the lens drive mechanism further includes a motor for driving the shutter, the motor being supported by the first member.

Preferably, the lens drive mechanism further includes a drive mechanism for driving the gear to rotate on the screw shaft.

Preferably, the drive mechanism includes a motor for driving the gear to rotate on the screw shaft, the motor being supported by the first member.

Preferably, the lens drive mechanism further includes a coil spring fitted on the first guide shaft between the first and second members so as to bias the second member in a direction along the optical axis away from the first member.

Preferably, the lens drive mechanism further includes a second guide shaft extending from the first member to the second member in the direction of the optical axis, one end of the second guide shaft being secured to the second member.

Preferably, the second guide shaft is slidably supported on the first member in the direction of the optical axis so as to prevent the second member from rotating about the screw shaft with respect to the first member.

Preferably, the first and second guide shafts are positioned substantially opposite to each other relative to the optical axis.

Preferably, the light interrupting member is continuously biased toward the second member by a spring.

Preferably, a photographic lens or zoom lens of a lens shutter type of camera is provided including the lens drive mechanism.

Preferably, a zoom lens including a front lens group and a rear lens group is provided with the lens drive mechanism, wherein the lens group supported by the second member is the rear lens group.

According to another aspect of the present invention, there is provided a lens shutter type of camera which includes a photographic lens system including a front lens group and a rear lens group, and a unit assembled separately from other parts of the lens shutter type of camera, the rear lens group being provided as a component of the unit, wherein the unit includes: a shutter mounting stage which supports a shutter including a plurality of shutter blades; a lens supporting member which supports the rear lens group, the lens supporting member being movable along an optical axis of the rear lens group relative to the shutter mounting stage without rotating about the optical axis; a guide shaft extending in a direction of the optical axis, the guide shaft being supported by the shutter mounting stage to be guided in the direction of the optical axis, a rear end of the guide shaft being secured to the lens supporting member; a rear lens group driving mechanism for driving the rear lens group to move along the optical axis thereof relative to the front lens group, the rear lens group driving mechanism including a gear and a screw shaft, the gear being rotatably supported on the shutter mounting stage so as not to move in the direction of the optical axis relative to the shutter mounting stage, the gear including a hole at an axial center thereof on an inner periphery of which is formed a female thread, the screw shaft extending in the direction of the optical axis and having a male thread formed thereon, one end of the screw shaft being secured to the lens supporting member, the gear being rotatably fitted on the screw shaft with the female thread meshing with the male thread, the screw shaft being positioned adjacent to the guide shaft; and a device for detecting whether the rear lens group is located at an extremity of a predetermined movable range of the rear lens group relative to the shutter mounting stage along the optical axis, the detecting device including a connecting member secured to the other end of each of the screw shaft and the guide shaft.

Preferably, the lens shutter type of camera further includes a first moving barrel, a second moving barrel and a third moving barrel concentrically arranged in this order from the optical axis, wherein the front lens group is positioned in and fixed to the first moving barrel, and further wherein the unit is positioned in and fixed to the first moving barrel behind the front lens group.

According to another aspect of the present invention, there is provided a unit, including: first and second members positioned adjacent to each other, the first member supporting a shutter including a plurality of shutter blades, the second member supporting a lens group, the second member being movably supported relative to the first member along an optical axis of the lens group; a detector for detecting whether the lens group is located at an extremity of a predetermined movable range of the lens group relative to the first member along the optical axis, the detector including a photosensor fixed on the first member and a light interrupting member which is capable of interrupting a light path of the photosensor and slidably supported on the first member in a direction of the optical axis, wherein a movable range of the light interrupting member is shorter than the predetermined movable range of the lens group in the direction of the optical axis; and an engaging member fixed to the second member, wherein the engaging member engages with the light interrupting member to interrupt the light path when the lens group moves to the extremity.

Preferably, the unit further includes: a guide shaft extending in the direction of the optical axis, the guide shaft being supported by the first member to be guided in the direction of the optical axis, one end of the guide shaft being secured to the second member; a screw shaft extending parallel to the guide shaft and having a male thread formed thereon, one end of the screw shaft being secured to the second member; and a connecting member secured to the other end of each of the screw shaft and the guide shaft, the engaging member being provided on the connecting member.

Preferably, the screw shaft is positioned adjacent to the guide shaft.

Preferably, the unit further includes a gear rotatably supported on the first member so as not to move in the direction of the optical axis relative to the first member, the gear including a hole at an axial center thereof on an inner periphery of which is formed a female thread, wherein the gear is rotatably fitted on the screw shaft with the female thread meshing with the male thread.

Preferably, the unit further includes a motor for driving the shutter, the motor being supported by the first member.

Preferably, the unit further includes a drive mechanism for driving the gear to rotate on the screw shaft.

Preferably, the unit further includes a coil spring fitted on the guide shaft between the first and second members so as to bias the second member in the direction of the optical axis away from the first member.

Preferably, the unit further includes another guide shaft extending from the first member to the second member in the direction of the optical axis, one end of the another guide shaft being secured to the second member.

Preferably, the another guide shaft is slidably supported on the first member in the direction of the optical axis so as to prevent the second member from rotating about the screw shaft with respect to the first member.

Preferably, the guide shaft and the another guide shaft are positioned substantially opposite to each other relative to the optical axis.

Preferably, a photographic lens or zoom lens of a lens shutter type of camera is provided including the unit according to claim 21.

According to yet another aspect of the present invention, there is provided a moving member position detecting arrangement including: a first moving member guided along a predetermined path to a predetermined position; a photosensor; and a second moving member movably supported relative to the photosensor to actuate the photosensor when the first moving member moves to the predetermined position.

Preferably, a movable range of the second moving member is shorter than a movable range of the first moving member.

Preferably, the moving member position detecting arrangement further includes a separate member provided separately from the first moving member, the first moving member being movable relative to the separate member, wherein the photosensor and the second moving member are supported by the separate member.

Preferably, the second moving member is guided in a direction parallel to at least a part of the predetermined path.

Preferably, the first moving member supports a lens group and is guided along an optical axis of the lens group.

Preferably, the predetermined position corresponds to an extremity of a movable range of the first moving member.

An example of the present invention will now be described below in detail with reference to the accompanying drawings in which similar elements are indicated by similar reference numerals, and wherein: Figure 1 is an enlarged schematic perspective view showing a part of a zoom lens barrel; Figure 2 is a schematic perspective view showing the part of the zoom lens barrel shown in Figure 1 in an engaged state; Figure 3 is an enlarged exploded perspective view of a part of the zoom lens barrel; Figure 4 is a schematic perspective view illustrating a state where an AF/AE shutter unit of the zoom lens barrel is mounted to a first moving barrel; Figure 5 is an exploded perspective view illustrating main parts of the AF/AE shutter unit of the zoom lens barrel shown in Figure 1, 2, 3 or 4; Figure 6 is an enlarged schematic perspective view of a third moving barrel of the zoom lens barrel; Figure 7 is a front elevational view of a fixed lens barrel block of the zoom lens barrel; Figure 8 is a sectional view of an upper part of the zoom lens barrel in a maximum extended state; Figure 9 is a sectional view of an upper part of the zoom lens barrel, illustrating main elements in a housed state; Figure 10 is a sectional view of the upper part of the zoom lens barrel shown in Figure 9 in the maximum extended state; Figure 11 is a sectional view of an upper part of the zoom lens barrel in the housed state; Figure 12 is an exploded perspective view of the overall structure of the zoom lens barrel; Figure 13 is a block diagram of a controlling system for controlling an operation of the zoom lens barrel; Figure 14 is an exploded perspective view of a lens drive mechanism of the zoom lens barrel; Figure 15 is a schematic plan view of a part of the lens drive mechanism shown in Figure 14; Figure 16 is a schematic sectional view of the lens drive mechanism; Figure 17 is a schematic sectional view of the lens drive mechanism in a state different from the state shown in Figure 16; Figure 18 is an enlarged perspective view of a linear guide barrel shown in Figure 12; Figure 19 is a sectional view of an upper part of a lens supporting barrel which supports a front lens group therein, and a lens fixing ring which is to be screw-engaged with the lens supporting barrel; Figure 20 is an enlarged perspective view of the lens supporting barrel shown in Figure 19; and Figure 21 is an enlarged sectional view of a part of the lens fixing ring shown in Figure 19.

Figure 13 is a schematic representation of various elements which comprise a preferred embodiment of a zoom lens camera to which the present invention is applied. A concept of the present zoom lens camera will now be described with reference to Figure 13.

The zoom lens camera is provided with a zoom lens barrel (zoom lens) 10 of a three-stage delivery type (telescoping type) having three moving barrels, namely a first moving barrel 20, a second moving barrel 19 and a third moving barrel 16, which are concentrically arranged in this order from an optical axis 0. In the zoom lens barrel 10 two lens groups are provided as a photographic optical system, namely a front lens group L1 having positive power and a rear lens group (moving lens group) L2 having negative power.

In the camera body, a whole optical unit driving motor controller 60, a rear lens group driving motor controller 61, a zoom operating device 62, a focus operating device 63, an object distance measuring apparatus 64, a photometering apparatus 65, and an AE (i.e., automatic exposure) motor controller 66, are provided. Although the specific focusing system of the object distance measuring apparatus 64, which is used to provide information regarding the object-tocamera distance, does not form part of the present invention, one such suitable system is disclosed in commonly assigned U.K. Patent Application No. 2298331, filed on February 22, 1996, and published on 28 August 1996.

Although the focusing systems disclosed in U.K. Patent Application No.

2298331 are of the so-called "passive" type, other known autofocus systems (e.g., active range finding systems such as those based on infrared light and triangulation) may be used. Similarly, a photometering system as disclosed in the above-noted U.K. Patent Application No. 2298331 could be implemented as photometering apparatus 65.

The zoom operating device 62 can be provided in the form of, for example, a manually-operable zoom operating lever (not shown) provided on the camera body or a pair of zoom buttons, e.g., a "wide' zoom button and a "tele" zoom button, (not shown) provided on the camera body. When the zoom operating device 62 is operated, the whole optical unit driving motor controller 60 drives a whole optical unit driving motor 25 to move the front lens group L1 and the rear lens group L2, rearwardly or forwardly without regard to a focal length and a focal point thereof. In the following explanation, forward and rearward movements of the lens groups L1 and L2 by the whole optical unit driving motor controller 60 (the motor 25) are referred to as the movement toward "tele" and the movement toward "wide" respectively, since forward and rearward movements of the lens groups L1 and L2 occur when the zoom operating device 62 is operated to "tele" and "wide" positions.

The image magnification of the visual field of a zoom finder 67 provided in the camera body varies in sequence with the variation of the focal length through the operation of the zoom operating device 62. Therefore, the photographer can perceive the variation of the focal length by observing the variation of image magnification of the visual field of the finder. In addition, the focal length, set by the operation of the zoom operating device 62, may be perceived by a value indicated on an LCD (liquid crystal display) panel (not shown) or the like.

When the focus operating device 63 is operated, the whole optical unit driving motor controller 60 drives the whole optical unit driving motor 25. At the same time the rear lens group driving motor controller 61 drives a rear lens group driving motor 30. Due to the driving of the whole optical unit driving motor controller 60 and the rear lens group driving motor controller 61, the front and rear lens groups L1 and L2 are moved to respective positions corresponding to a set focal length and a detected object distance and thereby the zoom lens is focused on the subject.

Specifically, the focus operating device 63 is provided with a release button (not shown) provided on an upper wall of the camera body. A photometering switch and a release switch (both not shown) are synchronized with the release button. When the release button is half-depressed (half step), the focus operating device 63 causes the photometering switch to be turned ON, and the object distance measuring and photometering commands are respectively input to the object distance measuring apparatus 64 and the photometering apparatus 65.

When the release button is fully depressed (full step), the focus operating device 63 causes the release switch to be turned ON, and according to the result of object distance measuring demand and a set focal length, the whole optical unit driving motor 25 and the rear lens group driving motor 30 are driven, and the focusing operation, in which the front lens group Ll and the rear lens group L2 move to the focusing position, is executed. Further, an AE motor 29 of an AF/AE (i.e., autofocus/autoexposure) shutter unit (electrical unit) 21 (Figure 11) is driven via the AE motor controller 66 to actuate a shutter 27. During the shutter action, the AE motor controller 66 drives the AE motor 29 to open shutter blades 27a of the shutter 27 for a specified period of time according to the photometering information output from the photometering apparatus 65.

When the zoom operating device 62 is operated, the zoom operating device 62 drives the whole optical unit driving motor 25 to move the front and rear lens groups L1 and L2 together as a whole in the direction of the optical axis 0 (optical axis direction). Simultaneous with such a movement, the rear lens group driving motor 30 may also be driven via the rear lens group driving motor controller 61 to move the rear lens group L2 relative to the front lens group L1. However, this is not performed under the conventional concept of zooming in which the focal length is varied sequentially without moving the position of the focal point. When the zoom operating device 62 is operated, the following two modes are available, namely: 1. a mode to move the front lens group L1 and the rear lens group L2 in the optical axis direction without varying the distance therebetween by driving only the whole optical unit driving motor 25; and, 2. a mode to move the front lens group L1 and the rear lens group L2 in the optical axis direction while varying the distance therebetween by driving both the whole optical unit driving motor 25 and the rear lens group driving motor 30.

In mode 1, during a zooming operation an in-focus condition cannot be obtained at all times with respect to a subject located at a specific distance. However, this is not a problem in a lens-shutter type camera, since the image of the subject is not observed through the photographing optical system, but through the finder optical system that is provided separate from the photographing optical system, and it is sufficient to only be focused when the shutter is released. In mode 2, during a zooming operation, the front lens group L1 and the rear lens group L2 are moved without regard to whether the focal point moves, and when the shutter is released, the focusing operation (focus adjusting operation) is carried out by moving both the whole optical unit driving motor 25 and the rear lens group driving motor 30.

When the focus operating device 63 is operated in at least one part of the focal length range set by the zoom operating device 62, the whole optical unit driving motor 25 and the rear lens group driving motor 30 are driven to bring the subject into focus. The amount of movement of each lens group L1 or L2 by the whole optical unit driving motor 25 and the rear lens group driving motor 30 is determined not only using subject distance information provided from the object distance measuring apparatus 64, but also by using focal length information set by the zoom operating device 62. In such a manner, when the focus operating device 63 is operated, by moving both the whole optical unit driving motor 25 and the rear lens group driving motor 30, the position of the lens groups L1, L2 can be flexibly controlled, as compared with lens movements controlled by cam.

The zoom lens camera of this embodiment can also be controlled in a different manner such that, during an operation of the zoom operating device 62, only the magnification of the zoom finder 67 and the focal length information are varied without driving either the whole optical unit driving motor 25 or the rear lens group driving motor 30. When the focus operating device 63 is operated, both the whole optical unit driving motor 25 and the rear lens group driving motor 30 are moved simultaneously according to the focal length information and the subject distance information obtained by the object distance measuring apparatus 64 to move the front lens group L1 and the rear lens group L2 to respective positions determined according to the focal length and the subject distance information.

An embodiment of the zoom lens barrel according to the above concept will now be described with reference to mainly Figures 11 and 12.

The overall structure of the zoom lens barrel 10 will firstly be described.

The zoom lens barrel 10 is provided with the first moving barrel 20, the second moving barrel 19, the third moving barrel 16, and a fixed lens barrel block 12. The third moving barrel 16 is engaged with a cylindrical portion 12p of the fixed lens barrel block 12, and moves in the optical axis direction upon being rotated. The third moving barrel 16 is provided on an inner periphery thereof with a linear guide barrel 17, which is restricted in rotation.

The linear guide barrel 17 and the third moving barrel 16 move together as a whole in the optical axis direction, with the third moving barrel 16 rotating relative to the linear guide barrel 17. The first moving barrel 20 moves in the optical axis direction with rotation thereof being restricted. The second moving barrel 19 moves in the optical axis direction, while rotating relative to the linear guide barrel 17 and the first moving barrel 20. The whole optical unit driving motor 25 is secured to the fixed lens barrel block 12. A shutter mounting stage (first member) 40 is secured to the first moving barrel 20. The AE motor 29 and the rear lens group driving motor 30 are mounted on the shutter mounting stage 40. The front lens group L1 and the rear lens group L2 are respectively supported by a lens supporting barrel (lens supporting annular member) 34 and a lens supporting barrel (second member) 50.

An O-ring 70, made of a rubber or the like, is positioned between an outer peripheral circumferential surface of the lens supporting barrel 34, in the vicinity of the front end thereof, and an inner peripheral circumferential surface of an inner flange portion 20b formed integral with the first moving barrel 20 in the vicinity of the front end thereof, as shown in Figure 11.

The O-ring 70 prevents water from penetrating the zoom lens barrel 10 at the front end thereof between the first moving barrel 20 and the lens supporting barrel 34.

As shown in Figure 19, the front lens group L1 consists of five lenses, namely, a first lens (frontmost lens) Lla, a second lens Llb, a third lens Llc, a fourth lens Lld and a fifth lens Lle in this order from an object side to an image side, i.e., from the left hand side to the right hand side as viewed in Figure 19.

A front positioning ring 36 for determining a distance between the second lens Llb and the third lens Llc is positioned and held between the second lens Llb and the third lens Llc. An outer peripheral surface of the positioning ring 36 is fitted on an inner peripheral surface of the lens supporting barrel 34. Likewise, a rear positioning ring 37 for determining a distance between the third lens Llc and the fourth lens Lld is positioned and held between the third lens Llc and the fourth lens Lld. An outer peripheral surface of the positioning ring 37 is fitted on an inner peripheral surface of the lens supporting barrel 34. The rear surface of the fourth lens Lld and the front surface of the fifth lens Lle are cemented to each other, so that the fourth and fifth lenses Lld, Lle are formed as a cemented or composite lens. A front circumferential edge Llf of the second lens Llb along the circumferential edge thereof contacts the rear surface of the first lens Lla. A rear circumferential edge Llg of the fifth lens Lle along the circumferential edge thereof contacts an inwardly-projecting flange 34b formed integral with the rear end of the lens supporting barrel 34.

A female thread 34a is formed on an inner periphery of a front part of the lens supporting barrel 34, as shown in Figure 19 or 20. A lens fixing ring 72, for fixing the first lens Lla to the lens supporting barrel 34, engages with the lens supporting barrel 34. With this arrangement, a male thread 72a formed on the outer peripheral surface of the lens fixing ring 72 meshes with the female thread 34a.

A circular abutting surface 72b is formed on the lens fixing ring 72 on an inner peripheral surface thereof. The circular abutting surface 72b comes into contact with a circumferential the lens supporting barrel 34. The supporting ring portion 34c is located inwardly from the female thread 34a in a radial direction of the lens supporting barrel 34. The inner peripheral surface of the supporting ring portion 34c, which extends in the optical axis direction, comes into contact with an outer circumferential edge or surface op of the first lens Lla. An annular positioning surface 34d, extending substantially normal to the optical axis 0, is formed on the lens supporting barrel 34 immediately behind the supporting ring portion 34c. The circumferential edge of the rear surface of the first lens Lla comes into contact with the positioning surface 34d. With this structure, the first lens Lla is immovably held between the circular abutting surface 72b and the positioning surface 34d in the optical axis direction, and the first lens Lla is immovably held by the supporting ring portion 34c in a radial direction normal to the optical axis 0.

As shown in Figure 21, a coating 72e is coated on the circular abutting surface 72b. The coating 72e is a waterproof coating made of a synthetic resin. In the present embodiment, "Fantas Coat SF-6 (trademark of a coating produced by the Japanese Company "Origin Denki Kabushiki Kaisha")" is used as the coating 72e. The front surface of the first lens Lla is formed very smooth, whereas the circular abutting surface 72b of the lens fixing ring 72 is not formed as smoothly (i.e., has a rough finish) as the front surface of the first lens Lla. This is because the first lens Lla is more minutely and accurately formed than the lens fixing ring 72 since the first lens Lla is a precision optical element. Due to this fact, were it not for the coating 72e on the circular abutting surface 72b, a substantial gap would be formed between the circular abutting surface 72b and the circumferential portion fp even if the circular abutting surface 72b properly and tightly in contact with the circumferential portion fp by properly screw-engaging the lens fixing ring 72 with the female thread 34a. As a result, water or moisture would be able to penetrate into the lens supporting barrel 34 through the substantial gap. However, in the present embodiment, the coating 72e is applied to the circular abutting surface 72b so as to make the surface thereof a smooth surface which does not cause to form such a substantial gap between the circular abutting surface 72b and the circumferential portion fp when the circular abutting surface 72b properly contacts the circumferential portion fp. Accordingly, the coating 72e, positioned and held between the circular abutting surface 72b and the circumferential portion fp, effectively prevents water or moisture from penetrating the lens supporting barrel 34 between the circular abutting surface 72b and the circumferential portion fp under the condition that the circular abutting surface 72b is properly and tightly in contact with the circumferential portion fp by properly screw-engaging the lens fixing ring 72 with the female thread 34a.

A circular surface 72c is formed on the lens fixing ring 72. The circular surface 72c is connected to the circular abutting surface 72b and is located immediately outward in a radial direction from the circular abutting surface 72b. A front part of the outer circumferential surface op of the first lens Lla (i.e., a circumferential edge of the first lens Lla) comes into contact with the circular surface 72c when the lens fixing ring 72 properly engages with the female thread 34a. Due to the circular surface 72c contacting the outer circumferential surface op, the watertight structure between the circular abutting surface 72b and the circumferential portion fp, that is realized by the coating 72e, is enhanced. That is, a highly efficient watertight connection between the first lens Lla and the lens fixing ring 72 is realized by providing both the coating 72e and the circular surface 72c with the lens fixing ring 72.

An annular recessed portion 34e is formed on the lens supporting barrel 34 between the female thread 34a and the supporting ring portion 34c. As shown in Figure 11, in a state where the lens fixing ring 72 is properly screw engaged with the female thread 34a, a rear end 72d of the lens fixing ring 72 is positioned in the annular recessed portion 34e with the rear end 72d not contacting the bottom (i.e., rearmost end) of the recessed portion 34e, namely, an annular space is formed in the annular recessed portion 34e between the rear end 72d and the bottom of the recessed portion 34e.

The fixed lens barrel block 12 is fixed in front of an aperture plate 14 fixed to the camera body. The aperture plate 14 is provided on a center thereof with a rectangularshaped aperture 14a which forms the limits of each frame exposed. The fixed lens barrel block 12 is provided, on an inner periphery of the cylindrical portion 12p, with a female helicoid 12a, and also a plurality of linear guide grooves 12b each extending parallel to the optical axis 0, i.e., extending in the optical axis direction. At the bottom of one of the linear guide grooves 12b, namely l2b', a code plate 13a, having a predetermined code pattern, is fixed. The code plate 13a extends in the optical axis direction and extends along substantially the whole of the length of the fixed lens barrel block 12. The code plate 13a is part of a flexible printed circuit board 13 positioned outside the fixed lens barrel block 12.

In the fixed lens barrel block 12, a gear housing 12c, which is recessed outwardly from an inner periphery of the cylindrical portion 12p of the fixed lens barrel block 12 in a radial direction while extending in the optical axis direction, is provided as shown in Figure 7 or 12. In the gear housing 12c, a driving pinion 15, extending in the optical axis direction, is rotatably held. Both ends of an axial shaft 7 of the driving pinion 15 are rotatively supported by a supporting hollow 4, provided in the fixed lens barrel block 12, and a supporting hollow 31a, provided on a gear supporting plate 31 fixed on the fixed lens barrel block 12 by set screws (not shown), respectively. Part of the teeth of the driving pinion 15 project inwardly from the inner periphery of the cylindrical portion 12p of the fixed lens barrel block 12 so that the driving pinion 15 meshes with an outer peripheral gear 16b of the third moving barrel 16, as shown in Figure 7.

On an inner periphery of the third moving barrel 16, a plurality of linear guide grooves 16c, each extending parallel to the optical axis 0, are formed. At an outer periphery of the rear end of the third moving barrel 16, a male helicoid 16a and the aforementioned outer peripheral gear 16b are provided as shown in Figure 6. The male helicoid 16a engages with the female helicoid 12a of the fixed lens barrel block 12. The outer peripheral gear 16b engages with the driving pinion 15. The driving pinion 15 has an axial length sufficient to be capable of engaging with the outer peripheral gear 16b throughout the entire range of movement of the third moving barrel 16 in the optical axis direction.

As shown in Figure 12 or 18, the linear guide barrel 17 is provided, on a rear part of an outer periphery thereof, with a rear end flange 17d. The rear end flange 17d has a plurality of engaging projections 17c each projecting away from the optical axis 0 in a radial direction. The linear guide barrel 17 is further provided, in front of the rear end flange 17d, with a retaining flange 17e. A circumferential groove 17g is formed between the rear end flange 17d and the retaining flange 17e. The retaining flange 17e has a radius smaller than the rear end flange 17d. The retaining flange 17e is provided with a plurality of cutout portions 17f. Each of the cutout portions 17f allows a corresponding engaging projection 16d to be inserted into the circumferential groove 17g, as shown in Figure 11.

The third moving barrel 16 is provided, on an inner periphery of the rear end thereof, with a plurality of engaging projections 16d. Each of the engaging projections 16d projects towards the optical axis 0 in a radial direction. By inserting the engaging projections 16d into the circumferential groove 17g, through the corresponding cutout portions 17f, the engaging projections 16d are positioned in the circumferential groove 17g between the flanges 17d and 17e (see Figure 11). By rotating the third moving barrel 16 relative to the linear guide barrel 17, the engaging projections 16d are engaged with the linear guide barrel 17.

On the rear end of the linear guide barrel 17, an aperture plate 23 having a rectangular-shaped aperture 23a approximately the same shape as the aperture 14a, is fixed.

The relative rotation of the linear guide barrel 17, with respect to the fixed lens barrel block 12, is restricted by the slidable engagement of the plurality of engaging projections 17c with the corresponding linear guide grooves 12b, formed parallel to the optical axis 0.

A contacting terminal 9 is fixed to one of the engaging projections 17c, namely 17c'. The contacting terminal 9 is in slidable contact with the code plate 13a, fixed to the bottom of the linear guide groove 12b', to generate signals corresponding to focal length information during zooming.

On the inner periphery of the linear guide barrel 17 two linear guide grooves 17a (only one of which is shown in Figure 18) and a linear guide groove 17j having a width wider than the width of either of the two linear guide grooves 17a are formed. Each linear guide groove 17a or 17j extends parallel to the optical axis 0.

A plurality of lead slots 17b are also formed on the linear guide barrel 17 as shown in Figure 12 or 18. The lead slots 17b are each formed oblique (inclined) to the optical axis 0.

The second moving barrel 19 engages with the inner periphery of the linear guide barrel 17. On the inner periphery of the second moving barrel 19, a plurality of lead grooves 19c are provided in a direction inclined oppositely to the lead slots 17b. On the outer periphery of the rear end of the second moving barrel 19 a plurality of follower projections 19a are provided. Each of the follower projections 19a has a trapezoidal cross-sectional shape projecting away from the optical axis 0 in a radial direction. Follower pins 18 are positioned in the follower projections l9a. Each follower pin 18 consists of a ring member 18a, and a center fixing screw 18b which supports the ring member 18a on the corresponding follower projection l9a. The follower projections l9a are in slidable engagement with the lead slots 17b of the linear guide barrel 17, and the follower pins 18 are in slidable engagement with the linear guide grooves 16c of the third moving barrel 16. With such an arrangement, when the third moving barrel 16 rotates, the second moving barrel 19 moves linearly in the optical axis direction, while rotating.

On the inner periphery of the second moving barrel 19, the first moving barrel 20 is engaged. The first moving barrel 20 is provided on an outer periphery of the rear thereof with a plurality of follower pins 24 each engaging with the corresponding inner lead groove l9c, and at the same time the first moving barrel 20 is guided linearly by a linear guide member 22. The first moving barrel 20 is provided at the front end thereof with a decorative plate 41 secured thereto.

As shown in Figures 1 and 2, the linear guide member 22 is provided with an annular member 22a, a pair of guide legs 22b, the two engaging projections 28a and the engaging projection 28b. The two engaging projections 28a respectively engage with the linear guide grooves 17a, and the engaging projection 28b engages with the linear guide groove 17j, so as to guide the linear guide barrel 17 along the optical axis 0 without rotating about the optical axis O. The pair of guide legs 22b project from the annular member 22a in the optical axis direction. The engaging projections 28a and 28b each project from the annular member 22a away from the optical axis 0 in a radial direction. The guide legs 22b are respectively inserted into linear guides 40c between the inner peripheral surface of the first moving barrel 20 and the AF/AE shutter unit 21.

The annular member 22a of the linear guide member 22 is connected to the rear of the second moving barrel 19, such that the linear guide member 22 and the second moving barrel 19 are capable of moving along the optical axis 0 as a whole, and in addition are capable of relatively rotating around the optical axis 0. The linear guide member 22 is further provided on the outer periphery of the rear end thereof with a rear end flange 22d. The linear guide member 22 is further provided, in front of the rear end flange 22d, with a retaining flange 22c. A circumferential groove 22f is formed between the rear end flange 22d and the retaining flange 22c. The retaining flange 22c has a radius smaller than the rear end flange 22d. The retaining flange 22c is provided with a plurality of cutout portions 22e, as shown in Figure 1 or 2, each allowing a corresponding engaging projection l9b to be inserted into the circumferential groove 22f, as shown in Figure 11.

The second moving barrel 19 is provided on an inner periphery of the rear end thereof with a plurality of engaging projections 19b, each projecting towards the optical axis O in a radial direction. By inserting the engaging projections 19b into the circumferential groove 22f through the corresponding cutout portions 22e, the engaging projections l9b are positioned in the circumferential groove 22f between the flanges 22c and 22d. By rotating the second moving barrel 19 relative to the linear guide member 22, the engaging projections 19b are engaged with the linear guide member 22. With the above structure, when the second moving barrel 19 rotates in the forward or reverse rotational direction, the first moving barrel 20 moves linearly, forwardly or rearwardly along the optical axis 0, but is restricted from rotating.

At the front of the first moving barrel 20, a barrier apparatus 35 having barrier blades 48a and 48b is mounted.

On an inner peripheral face of the first moving barrel 20 the AF/AE shutter unit 21 having the shutter 27, consisting of three shutter blades 27a, is engaged and fixed, as shown in Figure 9. The AF/AE shutter unit 21 is provided with a plurality of fixing holes 40a formed at even angular intervals on the outer periphery of the shutter mounting stage 40. Only one of the fixing holes 40a appears in each of Figures 1 through 5.

The aforementioned plurality of follower pins 24, which engage with the inner lead grooves 19c, also serve as a device for fixing the AF/AE shutter unit 21 to the first moving barrel 20. The follower pins 24 are inserted in holes 20a, formed on the first moving barrel 20, and fixed in the fixing holes 40a. With this arrangement the AF/AE shutter unit 21 is secured to the first moving barrel 20 as shown in Figure 4. In Figure 4 the first moving barrel 20 is indicated by phantom lines. The follower pins 24 may be fixed by an adhesive, or the pins 24 may be formed as screws to be screwed into the fixing holes 40a.

As illustrated in Figures 5 and 12, the AF/AE shutter unit 21 is provided with the shutter mounting stage 40, a shutter blade supporting ring 46 fixed on the rear of the shutter mounting stage 40 so as to be located inside the shutter mounting stage 40, and the lens supporting barrel 50 supported in a state of being capable of movement relative to the shutter mounting stage 40. On the shutter mounting stage 40, the lens supporting barrel 34, the AE motor 29, and the rear lens group driving motor 30, are supported.

The shutter mounting stage 40 is provided with an annular member 40f having a circular aperture 40d. The shutter mounting stage 40 is also provided with three legs 40b which project rearward from the annular member 40f. Three slits are defined between the three legs 40b. Two of the slits comprise the aforementioned linear guides 40c, which slidably engage with the respective pair of guide legs 22b of the linear guide member 22 so as to guide the movement of the linear guide member 22.

The shutter mounting stage 40 supports an AE gear train 45, which transmits a rotation of the AE motor 29 to the shutter 27, a lens driving gear train 42, which transmits rotation of the rear lens group driving motor 30 to a screw shaft (feed screw shaft) 43, photointerrupters 56 and 57, connected to a flexible printed circuit board 6, and rotating disks 58 and 59, having a plurality of radially formed slits provided in the circumferential direction. An encoder for detecting whether the rear lens group driving motor 30 is rotating and for detecting an amount of rotation of the rear lens group driving motor 30 consists of the photointerrupter 57 and the rotating disk 59. An AE motor encoder for detecting whether the AE motor 29 is rotating and for detecting an amount of rotation of the AE motor 29 consists of the photointerrupter 56 and the rotating disk 58.

The shutter 27, a supporting member 47 which pivotally supports the three shutter blades 27a of the shutter 27, and a circular driving member 49, which gives rotative power to the shutter blades 27a, are positioned between the shutter mounting stage 40 and the shutter blade supporting ring 46, secured to the shutter mounting stage 40. The circular driving member 49 is provided with three operating projections 49a at even angular intervals, which respectively engage with each of the three shutter blades 27a. As shown in Figure 5, the shutter blade supporting ring 46 is provided at a front end thereof with a circular aperture 46a and with three supporting holes 46b positioned at even angular intervals around the circular aperture 46a.

Two deflection restricting surfaces 46c are formed on the outer periphery of the shutter blade supporting ring 46.

Each deflection restricting surface 46c is exposed outwardly from the corresponding linear guide 40c and slidably supports the inner peripheral face of the corresponding guide leg 22b.

The supporting member 47, positioned in front of the shutter blade supporting ring 46, is provided with a circular aperture 47a, aligned with the circular aperture 46a of the shutter blade supporting ring 46, and with three pivotal shafts 47b (only one of which is illustrated in Figure 5) at respective positions opposite the three supporting holes 46b. Each shutter blade 27a is provided at one end thereof with a hole 27b into which the corresponding pivotal shaft 47b is inserted, so that each shutter blade 27a is rotatable about the corresponding pivotal shaft 47b.

The major part of each shutter blade 27a, that extends normal to the optical axis 0 from the pivoted end, is formed as a light interceptive portion. All three light interceptive portions of the shutter blades 27a together prevent ambient light, which enters the front lens group L1, from entering the circular apertures 46a and 47a when the shutter blades 27a are closed. Each shutter blade 27a is further provided, between the hole 27b and the light interceptive portion thereof, with a slot 27c, through which the corresponding operating projection 49a is inserted. The supporting member 47 is fixed to the shutter blade supporting ring 46 in such a manner that each shaft 47b, which supports the corresponding shutter blade 27a, is engaged with the corresponding supporting hole 46b of the shutter blade supporting ring 46.

A gear portion 49b is formed on a part of the outer periphery of the circular driving member 49. The gear portion 49b meshes with one of the plurality of gears in the gear train 45 to receive the rotation from the gear train 45. The supporting member 47 is provided, at respective positions close to the three pivotal shafts 47b, with three arc grooves 47c each arched along a circumferential direction. The three operating projections 49a of the circular driving ring 49 engage with the slots 27c of the respective shutter blades 27a through the respective arc grooves 47c. The shutter blade supporting ring 46 is inserted from the rear of the shutter mounting stage 40, to support the circular driving ring 49, the supporting member 47 and the shutter 27, and is fixed on the shutter mounting stage 40 by set screws 90 respectively inserted through holes 46x provided on the shutter blade supporting ring 46.

Behind the shutter blade supporting ring 46, the lens supporting barrel 50, supported to be able to move relative to the shutter mounting stage 40 via guide shafts 51 and 52, is positioned. The shutter mounting stage 40 and the lens supporting barrel 50 are biased in opposite directions away from each other by a coil spring (biasing compression spring) 3 fitted on the guide shaft 51, and therefore play between the shutter mounting stage 40 and the lens supporting barrel 50 is reduced. In addition, a driving gear 42a, provided as one of the gears in the gear train 42, is provided with a female thread hole (not shown) at the axial center thereof and is restricted to move in the axial direction. The screw shaft 43, one end of which is fixed to the lens supporting barrel 50, engages with the female thread hole. Accordingly, the driving gear 42a and the screw shaft 43 together constitute a feed screw mechanism.

In such a manner, when the driving gear 42a rotates clockwise or anticlockwise due to driving by the rear lens group driving motor 30, the screw shaft 43 respectively moves forwardly or rearwardly with respect to the driving gear 42a, and therefore the lens supporting barrel 50, which supports the rear lens group L2, moves relative to the front lens group L1.

A holding member 53 is fixed at the front of the shutter mounting stage 40. The holding member 53 holds the motors 29 and 30 between the holding member 53 and the shutter mounting stage 40. The holding member 53 has a metal holding plate 55 fixed at the front thereof by set screws 99. The motors 29, 30 and the photointerrupters 56, 57 are connected to the flexible printed circuit board 6.

One end of the flexible printed circuit board 6 is fixed to the shutter mounting stage 40.

After the first, second and third moving barrels 20, 19 and 16, and the AF/AE shutter unit 21 and the like are assembled, the aperture plate 23 is fixed to the rear of the linear guide barrel 17, and an annular retaining member 33 is fixed at the front of the fixed lens barrel block 12.

A device for preventing an occurrence of jamming in a feed screw mechanism used for moving the rear lens group L2 along the optical axis 0 relative to the front lens group L1 will be hereinafter discussed.

In addition to being provided with the above-mentioned drive mechanism for moving the rear lens group L2 with respect to the first lens group L1 along the optical axis 0, the AF/AE shutter unit 21 is also provided with a device for detecting whether the rear lens group L2 reaches a predetermined initial position thereof relative to the first lens group L1 (i.e., a front extremity of a predetermined movable range of the rear lens group L2 with respect to the front lens group L1). In a focusing operation, the rear lens group L2 is firstly driven to move rearwardly from an initial position thereof, away from the first lens group L1 along the optical axis 0 by an amount necessary for focusing. Subsequently, the rear lens group L2 is driven to move back to the initial position after a shutter release operation has been completed. The rear lens group L2 is controlled so as to be located at the initial position thereof in each of the following conditions, namely, immediately after the main switch of the camera is turned ON, immediately after a shutter release operation has been completed, and when the main switch of the camera is in an OFF state.

The device for detecting whether the rear lens group L2 reaches the initial position thereof will be discussed with reference to Figures 14 through 17.

The lens supporting barrel 50 is guided along the optical axis 0 through the guide shafts 51, 52. Rear ends of the guide shafts 51, 52 are respectively fixed in bosses 50b, 50c which are integrally formed on the lens supporting barrel 50. The guide shaft 51 is slidably inserted into a bearing 51a fixed on the shutter mounting stage 40, so as to be guided in the optical axis direction. A front end of the guide shaft 52 is free, and the guide shaft 52 slidably fits in a supporting groove 40i (see Figure 5) which is formed on the shutter mounting stage 40 and recessed inwardly in a radial direction of the shutter mounting stage 40.

Due to such a structure in which the guide shaft 52 is positioned in the supporting groove 40i, when the lens supporting barrel 50 moves along the optical axis 0 with respect to the shutter mounting stage 40, the lens supporting barrel 50 is prevented from rotating about the screw shaft 43 with respect to the shutter mounting stage 40. In other words, but for the guide shaft 52, the lens supporting barrel 50 would rotate about the screw shaft 43 with respect to the shutter mounting stage 40 when the screw shaft 43 is driven to move in the optical axis direction by rotation of the driving gear 42a, even though the guide shaft 51 is provided parallel to the screw shaft 43. This is because the screw shaft 43 and the guide shaft 51 are closely arranged in parallel to each other.

The rear end of the screw shaft 43 is secured to a boss 50a formed on the shutter mounting stage 40 in the vicinity of the boss 50b. The driving gear 42a, having the female screw hole (not shown) at the axial center thereof as noted above, is rotatably fitted on the screw shaft 43, with the female screw hole engaging with a male screw formed on the screw shaft 43. The rearward movement of the driving gear 42a along the screw shaft 43 is restricted by the shutter mounting stage 40. While the forward movement of the driving gear 42a along the screw shaft 43 is restricted by a supporting ring 53a integrally formed on the holding member 53, as can be seen in Figure 14. Due to this structure, the driving gear 42a is prevented from moving along the screw shaft 43 relative to the shutter mounting stage 40. In other words, the distance between the driving gear 42a and the shutter mounting stage 40 is constant.

When the driving gear 42a is driven to rotate by the rear lens group driving motor 30, the screw shaft 43 moves along the axis thereof, i.e., along the optical axis direction, relative to the driving gear 42a, which causes the rear lens group L2, supported by the lens supporting barrel 50, to move forwardly or rearwardly along the optical axis 0 relative to the first lens group L1. In order to prevent the occurrence of backlash between the screw shaft 43 and the driving gear 42a, the coil spring 3 is fitted on the guide shaft 51 between the bearing 51a and the boss 50b, as shown in Fig. 15. Due to the coil spring 3, the lens supporting barrel 50 is always biased rearwardly away from the shutter mounting stage 40 along the optical axis 0.

This prevents backlash from occurring between the screw shaft 43 and the driving gear 42a.

A photointerrupter 301 and a light interrupting member (second moving member) 302 are provided adjacent to each other at a front end of the shutter mounting stage 40 in the vicinity of the metal holding plate 55. The photointerrupter 301 and the light interrupting member 302 together constitute a detector for detecting whether the rear lens group L2 reaches the aforementioned initial position thereof relative to the front lens group L1. The photointerrupter 301 is mounted on a part of the flexible circuit board 6 and fixed on the shutter mounting stage 40.

The light interrupting member 302 has a cylindrical body at rear and front ends of which a light intercepting plate 302a and an engaging projection 302b are integrally formed thereon, respectively.

The light interrupting member 302 is slidably fitted on a shaft 303. The front and rear ends of the shaft 303 are supported by the metal holding plate 55 and the holding member 53, respectively, as shown in Figure 16 or 17. A coil spring (biasing compression spring) 304 is disposed on the shaft 303 to be held between the metal holding plate 55 and the front end of the light interrupting member 302, so that the light interrupting member 302 is always biased rearwardly toward the shutter mounting stage 40 in the optical axis direction.

A slit 301a extending in the optical axis direction is formed on the photointerrupter 301 as shown in Figure 14.

The light intercepting plate 302a is capable of moving in the slit 301a to interrupt a light path OP formed approximately in the middle of the slit 301a. Namely, a front part of the light intercepting plate 302a is positioned inside the slit 301a but outside positioned inside the slit 301a to interrupt the light path OP when the light interrupting member 302 moves forwardly to a predetermined position, against the biasing force of the coil spring 304, as shown in Figure 15 or 16.

A stopper plate (connecting member) 306 is secured to the front end of each of the screw shaft 43 and the guide shaft 51 through a washer 305. An engaging pin (engaging member) 306a is integrally formed on the stopper plate 306.

The engaging pin 306a is capable of engaging with the engaging projection 302b of the light interrupting member 302. Namely, when the lens supporting barrel 50, which supports the rear lens group L2, moves forwardly to a predetermined position close to a front extremity of the movable range of the lens supporting barrel 50 relative to the shutter mounting stage 40, the engaging pin 306a engages with the engaging projection 302b. Thereafter, when the lens supporting barrel 50 moves further forward, the engaging pin 306a further advances to move the engaging projection 302b forwardly against the biasing force of the coil spring 304. Thereafter, when the rear lens group L2 reaches the initial position thereof relative to the front lens group L1, that is, when the lens supporting barrel 50 reaches an initial position thereof relative to the shutter mounting stage 40, the light intercepting plate 302a intercepts the light path OP.

The photointerrupter 301, the light interrupting member 302, the shaft 303, the engaging pin 306a of the stopper plate 306, etc. constitute a device for detecting a position of the rear lens group L2 in order to stop the rear lens group L2 at the initial position thereof relative to the first lens group L1 when the rear lens group L2 moves to the initial position thereof.

Whether or not the rear lens group L2 reaches the initial position thereof, that is, whether or not the lens supporting barrel 50 reaches the initial position thereof, is detected by a CPU (not shown), provided in the camera for controlling various operations (focusing operation, photometering operation, etc.), by way of monitoring the output of the photointerrupter 301. When the CPU detects that the rear lens group L2 reaches the initial position thereof, the CPU controls the rear lens group driving motor 30 to stop so as not to further move the rear lens group L2 forwardly relative to the first lens group L1. Due to this structure, when the rear lens group L2 moves toward the front lens group L1, the rear lens group L2 does not move beyond the initial position thereof but surely stops at the initial position, which also prevents an occurrence of jamming of the driving gear 42a. Even if the lens supporting barrel 50 should be accidentally driven to move forwardly beyond the front extremity of the movable range of the lens supporting barrel 50 relative to the shutter mounting stage 40 by the rear lens group driving motor 30, such an occurrence of jamming of the driving gear 42a is also prevented since the coil spring 3 functions as a bumper to alleviate an impact which might occur between the shutter mounting stage 40 and the lens supporting barrel 50.

An O-ring (impact absorbing member) 307, made of an elastic member such as rubber, is fitted on the guide shaft 51 between the stopper plate 306 and the bearing 51a.

Additionally, the O-ring 307 may be formed from other types of elastic materials. The O-ring 307 usually stays at a frontmost position on the guide shaft 51 immediately behind the stopper plate 306 as shown in Figure 15, but is slidable along the guide shaft 51. The O-ring 307 serves as a bumper to alleviate an impact occurring between the stopper plate 306 and a front end 51b of the bearing 51a, and between the stopper plate 306 and the stopper ring 53a, if the lens supporting barrel 50 should be accidentally driven to move backwardly beyond a rear extremity of the movable range of the lens supporting barrel 50 relative to the shutter mounting stage 40 by the rear lens group driving motor 30.

In the above-described embodiment of the zoom lens barrel 10, although the zoom lens optical system consists of two movable lens groups, namely the front lens group L1 and the rear lens group L2, it should be understood that the present invention is not limited to the present embodiment disclosed above, but the present invention may also be applied to another type of zoom lens optical system including one or more fixed lens group.

In addition, in the above embodiment, the rear lens group Ll is provided as a component of the AF/AE shutter unit 21, and the AE motor 29 and the rear lens group driving motor 30 are mounted to the AF/AE shutter unit 21. With such a structure, the structure for supporting the front and rear lens groups L1 and L2 and the structure for driving the rear lens group L2 are both simplified. Instead of adopting such a structure, the zoom lens barrel 10 may also be realized in such a manner by making the rear lens group L2 a member separate from the AF/AE shutter unit 21, which is provided with the shutter mounting stage 40, the circular driving member 49, the supporting member 47, the shutter blades 27, the shutter blade supporting ring 46 and the like, and that the rear lens group L2 is supported by any supporting member other than the AF/AE shutter unit 21.

In the zoom lens camera of the present embodiment, the operation by rotation of the whole optical unit driving motor 25 and the rear lens group driving motor 30 will now be described with reference to Figures 8, 9, 10 and 11.

As shown in Figure 9 or 11, when the zoom lens barrel 10 is at the most retracted (withdrawn) position, i.e., the lens-housed condition, when the power switch is turned ON, the whole optical unit driving motor 25 is driven to rotate its drive shaft in the forward rotational direction by a small amount. This rotation of the motor 25 is transmitted to the driving pinion 15 through a gear train 26, which is supported by a supporting member 32 formed integral with the fixed lens barrel block 12, to thereby rotate the third moving barrel 16 in one predetermined rotational direction to advance forwardly along the optical axis 0. Therefore, the second moving barrel 19 and the first moving barrel 20 are each advanced by a small amount in the optical axis direction, along with the third moving barrel 16.

Consequently, the camera is in a state capable of photographing, with the zoom lens positioned at the widest position, i.e., the wide end. At this stage, due to the fact that the amount of movement of the linear guide barrel 17, with respect to the fixed lens barrel block 12, is detected through the relative slide between the code plate 13a and the contacting terminal 9, the focal length of the zoom lens barrel 10, i.e., the front and rear lens groups L1 and L2, is detected.

In the photographable state as above described, when the aforementioned zoom operating lever is manually moved towards a "tele" side, or the "tele" zoom button is manually depressed to be turned ON, the whole optical unit driving motor 25 is driven to rotate its drive shaft in the forward rotational direction through the whole optical unit driving motor controller 60 so that the third moving barrel 16 rotates in the rotational direction to advance along the optical axis 0 via the driving pinion 15 and the outer peripheral gear 16b. Therefore, the third moving barrel 16 is advanced from the fixed lens barrel block 12 according to the relationship between the female helicoid 12a and the male helicoid 16a. At the same time, the linear guide barrel 17 moves forwardly in the optical axis direction together with the third moving barrel 16, without relative rotation to the fixed lens barrel block 12, according to the relationship between the engaging projections 17c and the linear guide grooves 12b. At this time, the simultaneous engagement of the follower pins 18 with the respective lead slots 17b and linear guide grooves 16c causes the second moving barrel 19 to move forwardly relative to the third moving barrel 16 in the optical axis direction, while rotating together with the third moving barrel 16 in the same rotational direction relative to the fixed lens barrel block 12. The first moving barrel 20 moves forwardly from the second moving barrel 19 in the optical axis direction, together with the AF/AE shutter unit 21, without relative rotation to the fixed lens barrel block 12, due to the above-noted structures in which the first moving barrel 20 is guided linearly by the linear guide member 22 and in which the follower pins 24 are guided by the lead grooves 19c. During such movements, according to the fact that the moving position of the linear guide barrel 17 with respect to the fixed lens barrel block 12 is detected through the relative slide between the code plate 13a and the contacting terminal 9, the focal length set by the zoom operation device 62 is detected.

Conversely, when the zoom operating lever is manually moved towards a "wide" side, or the "wide" zoom button is manually depressed to be turned ON, the whole optical unit driving motor 25 is driven to rotate its drive shaft in the reverse rotational direction through the whole optical unit driving motor controller 60 so that the third moving barrel 16 rotates in the rotational direction to retract into the fixed lens barrel block 12 together with the linear guide barrel 17. At the same time, the second moving barrel 19 is retracted into the third moving barrel 16, while rotating in the same direction as that of the third moving barrel 16, and the first moving barrel 20 is retracted into the rotating second moving barrel 19 together with the AF/AE shutter unit 21. During the above retraction driving, like the case of advancing driving as above described, the rear lens group driving motor 30 is not driven.

While the zoom lens barrel 10 is driven during the zooming operation, since the rear lens group driving motor 30 is not driven, the front lens group L1 and the rear lens group L2 move as a whole, maintaining a constant distance between each other, as shown in Figure 8 or 10. The focal length input via the zoom code plate 13a and the contacting terminal 9 is indicated on an LCD panel (not shown) provided on the camera body.

At any focal length set by the zoom operating device 62, when the release button is depressed by a half-step, the object distance measuring apparatus 64 is actuated to measure a current subject distance. At the same time the photometering apparatus 65 is actuated to measure a current subject brightness. Thereafter, when the release button is fully depressed, the whole optical unit driving motor 25 and the rear lens group driving motor 30 are each driven by respective amounts dictated according to the focal length information set in advance and the subject distance information obtained from the object distance measuring apparatus 64 so that the front and rear lens groups L1 and L2 are respectively moved to specified positions to obtain a specified focal length to thereby bring the subject into focus. Immediately after the subject is brought into focus, via the AE motor controller 66, the AE motor 29 is driven to rotate the circular driving member 49 by an amount corresponding to the subject brightness information obtained from the photometering apparatus 65 so that the shutter 27 is driven to open the shutter blades 27a by a specified amount which satisfies the required exposure. Immediately after such a shutter release operation, in which the three shutter blades 27a are opened and subsequently closed, is completed, the whole optical unit driving motor 25 and the rear lens group driving motor 30 are both driven to move the front lens group L1 and the rear lens group L2 to the respective initial positions at which they were at prior to a shutter release.

More specifically, when the release button is fully depressed, the rear lens group driving motor 30 is driven by a certain amount corresponding to the focal length information set in advance by the zoom operating device 62 and the subject distance information obtained from the object distance measuring apparatus 64 so that the rear lens group L2 is moved backward away from the front lens group L1 to a specified position relative to the front lens group L1.

At the same time, the whole optical unit driving motor 25 is driven by a certain amount corresponding to the focal length information set in advance by the zoom operating device 62 and the subject distance information obtained from the object distance measuring apparatus 64 so that the front and rear lens groups L1 and L2 together as a whole are respectively moved to specified positions relative to the fixed lens barrel block 12 to obtain a specified focal length to thereby bring the subject into focus. Immediately after the completion of the shutter release operation, the rear lens group driving motor 30 is driven to move the rear lens group L2 forward, back to its initial position relative to the front lens group L1, at which it was at prior to a shutter release. At the same time, the whole optical unit driving motor 25 is driven to move the front and rear lens groups L1 and L2 together as a whole to respective initial positions thereof relative to the fixed lens barrel block 12, at which they were at prior to a shutter release.

As can be understood from the foregoing, according to the zoom lens barrel 10 of the present embodiment, the lens supporting barrel 50 is surely and stably guided along the optical axis 0 using only a few guide shafts, i.e.,the guide shafts 51, 52, and the movement of the screw shaft 43 in an axial direction thereof is also surely and stably transmitted to the lens supporting barrel 50 through the stopper plate 306 and the guide shaft 51, owing to the aforementioned structures wherein the screw shaft 43 is positioned adjacent to the guide shaft 51 and further wherein the single stopper plate 306 is secured to the front end of each of the screw shaft 43 and the guide shaft 51 through a washer 305. Accordingly, in the zoom lens barrel 10, a simple guiding device for guiding the rear lens group L2 along the optical axis 0 and a simple driving device for driving the rear lens group L2 to move forward or backward along the optical axis 0, which are associated with each other, are both simultaneously realized. In addition, the stopper plate 306, specifically the engaging pin 306a thereof, serves as part of a detecting device, which consists of the photointerrupter 301, the light interrupting member 302, etc., for detecting whether the rear lens group L2 reaches the initial position thereof, due to the aforementioned structures wherein the light interrupting member 302 is supported on the shutter mounting stage 40 to be guided along an axial direction thereof parallel to the optical axis O, and wherein the photointerrupter 301 is secured to the shutter mounting stage 40, and further wherein the engaging pin 306a, which is engageable with the light interrupting member 302 to intercept the light path OP of the photointerrupter 301, is formed integral with the stopper plate 306, thus resulting in the realization of an initial position detecting device having a fewer number of components.

If a light intercepting plate, that is capable of moving in the slit 301a to interrupt the light path OP, were formed on the stopper plate 306, the lens supporting barrel 50 or the like which moves along the optical axis 0 together with the rear lens group L2, it would be necessary to provide, on the AF/AE shutter unit 21, a path though which the light intercepting plate could move along the optical axis O. The length of the path would be substantially identical to the movable range of the rear lens group L2.

However, in the AF/AE shutter unit 21 of the present embodiment, such a light intercepting plate is not formed on the stopper plate 306, the lens supporting barrel 50 or the like but the light intercepting plate 302a is formed integral with the light interrupting member 302 slidably supported on the shaft 303 fixed at an approximate end of the AF/AE shutter unit 21. Due to this structure, the moving range of the light intercepting plate 302a has been rendered short, which contributes to the realization of a small-size AF/AE shutter unit 21.

The present invention is not limited solely to the three-stage delivery type of zoom lens having three moving barrels, but may be applied to a two-stage or more than three-stage delivery type of zoom lens having two or more than three moving barrels. The present invention may also be applied to any other type of zoom lens, e.g., a zoom lens used for a video camera or a still video camera.

In the present embodiment of the zoom lens barrel 10, "Fantas Coat SF-6" is used as the coating 72e. However, a different type of coating may be used as the coating 72e as long as it is waterproof and makes the circular abutting surface 72b a smooth surface to form substantially no gap between the circular abutting surface 72b and the circumferential portion fp.

Obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the 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

CLAIMS:

1. A lens drive mechanism comprising: first and second members positionable adjacent one another, said second member supporting a lens group and being movable relative to said first member along an optical axis of said lens group; a first guide shaft extending in a direction of said optical axis, said first guide shaft being supported by said first member to be guided in said direction of said optical axis, one end of said first guide shaft being secured to said second member; a screw shaft extending in said direction of said optical axis and having a first thread formed thereon, one end of said screw shaft being secured to said second member, said screw shaft being positioned adjacent said first guide shaft; and a connecting member secured to the other end of each of said screw shaft and said first guide shaft, the connecting member operating, in use, a device for detecting whether said lens group is located at an extremity of a predetermined movable range of said lens group relative to said first member along said optical axis.

2. A lens drive mechanism according to claim 1, further comprising a gear rotatably supported on said first member so as not to be movable in said direction of said optical axis relative to said first member, said gear having a hole at an axial center thereof on an inner periphery of which is formed a second thread, wherein said gear is rotatably fitted on said screw shaft with said second thread meshing with said first thread.

3 A lens drive mechanism according to claim 1 or 2, wherein said detecting device further comprises a photosensor provided on said first member and a light interrupting member slidably supported on said first member in said direction of said optical axis to be sensed by said photosensor.

4. A lens drive mechanism according to claim 3, wherein said photosensor is a photointerrupter.

5. A lens drive mechanism according to claim 3 or 4, wherein a movable range of said light interrupting member is shorter than said predetermined movable range of said lens group in said direction of said optical axis, and wherein said connecting member comes into contact with said light intercepting member when said lens group moves to a predetermined position within said predetermined movable range thereof.

6. A lens drive mechanism according to claim 4, wherein said connecting member comprises an engaging portion integrally formed therewith, and wherein, in use, said engaging portion firstly comes into contact with said light interrupting member and subsequently moves said light interrupting member in said direction of said optical axis so that said light interrupting member interferes with a light path of said photointerrupter when said lens group is driven to move to said extremity.

7. A lens driven mechanism according to any preceding claim, further comprising a shutter having a plurality of shutter blades, wherein said first member supports said shutter.

8. A lens drive mechanism according to claim 7, further comprising a first motor for driving said shutter, said first motor being supported by said first member.

9. A lens drive mechanism according to claim 2, further comprising a drive mechanism for driving said gear to rotate on said screw shaft.

10. .A' lens drive mechanism according to claim 9, wherein said drive mechanism comprises a second motor for driving said gear to rotate on said screw shaft, said second motor being supported by said first member.

11. A lens drive mechanism according to any preceding claim, further comprising a coil spring fitted on said first guide shaft between said first and second members so as to bias said second member in a direction along said optical axis away from said first member.

12. A lens drive mechanism according to any preceding claim, further comprising a second guide shaft extending from said first member to said second member in said direction of said optical axis, one end of said second guide shaft being secured to said second member.

13. A lens drive mechanism according to claim 12, wherein said second guide shaft is slidably supported on said first member in said direction of said optical axis so as to prevent said second member from rotating about said screw shaft with respect to said first member.

14. A lens drive mechanism according to claim 12 or 13, wherein said first and second guide shafts are positioned substantially opposite to each other relative to said optical axis.

15. A lens drive mechanism according to any one of claims 3 to 6, wherein said light interrupting member is continuously biased toward said second member by a spring.

16. A photographic lens of a lens shutter type of camera including said lens drive mechanism according to any preceding claim.

17. A photographic lens according to claim 16, wherein said lens is a zoom lens.

18. A zoom lens including a front lens group and a rear lens group, said zoom lens being provided with said lens drive mechanism according to any one of claims 1 to 15, wherein said lens group supported by said second member is said rear lens group.

19. A lens drive mechanism substantially as hereinbefore described with reference to Figures 15 to 17 of the accompanying drawings.

20. A zoom lens substantially as hereinbefore described with reference to Figures 15 to 17 of the accompanying drawings.