BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lens barrel adapted for an optical apparatus such as a camera or the like, and more particularly to the dust-proof and drip-proof structural arrangement of a lens barrel or the like. 
     2. Description of Related Art 
     The rotating parts, such as rotary operation parts, of lens barrels are often arranged to be in a dust-proof and drip-proof structure. Generally, the dust-proof and drip-proof structure is arranged to prevent intrusion of water, dust, etc., by inserting a rubber O-ring in between a body member and a rotating member of the lens barrel. 
     However, such a dust-proof and drip-proof structural arrangement generates a large frictional force between the O-ring and the rotating member. The large frictional force necessitate exertion of a large force in operating the rotating member. The conventional arrangement thus has often made the rotating member difficult to operate, or has prevented effective utilization of space due to limitation imposed on the diameter of the O-ring. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a lens barrel which is arranged to adequately maintain a good water-proof effect and yet to excel in operability. 
     To attain the above object, in accordance with an aspect of the invention, there is provided a lens barrel which comprises fixed tubes each arranged to hold an optical unit having an optical axis, a rotating tube arranged to rotate around the optical axis with respect to the fixed tubes, wherein the rotating tube is provided, at front and rear portions thereof as viewed along the optical axis, respectively with end surfaces of ring shape having a center thereof on the optical axis, and each of the fixed tubes is provided with an end surface opposite to the associated end surface of the rotating tube, and sheet members of ring shape having a center thereof on the optical axis, each of the sheet members being disposed on a space formed by each end surface of the rotating tube and the associated end surface of the fixed tubes. 
     Further, in the lens barrel, a wave washer of ring shape having a center thereof on the optical axis, and having convex portions and concave portions as viewed along the optical axis, is disposed in the space. 
     Further, the rotating tube is a manual operation ring arranged to be manually rotated to move another optical unit along the optical axis. 
     Further, each of the fixed tubes has a sliding surface arranged to restrict movement of the rotating tube along the optical axis and to allow the rotating tube to rotate thereon, and a water-repellant agent is applied to the sliding surface. 
     Further, the sheet members are made of plastic material. 
     Further, the sheet members are made of vinyl chloride material. 
     The above and other objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a sectional view showing a lens barrel according to a first embodiment of the invention. 
     FIG. 2 is a sectional view showing essential parts of the lens barrel shown in FIG.  1 . 
     FIG. 3 is an enlarged view showing in part the essential parts of the lens barrel shown in FIG.  2 . 
     FIG. 4 is a sectional view showing essential parts of a lens barrel according to a second embodiment of the invention. 
     FIG. 5 is an enlarged view showing in part the essential parts of the lens barrel shown in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings. 
     FIGS. 1,  2  and  3  show a lens barrel according to a first embodiment of the invention. The lens barrel is either arranged to be mounted on an optical apparatus such as a camera or the like, or is arranged integrally with the optical apparatus. 
     Referring to FIG. 1, the lens barrel  1  is a photo-taking optical system having, in order from an object side, a fixed first lens group I, a second lens group II, a third lens group III and a fourth lens group IV. A mount part  100  is provided in a rear portion of the lens barrel  1  for coupling with the optical apparatus (camera). The mount part  100  is provided with contacts for communication with the optical apparatus (camera). 
     A circuit board (not shown) is arranged inside of the lens barrel  1  to form a circuit for the communication with the optical apparatus. The circuit is arranged to process signals received from the optical apparatus and to drive and control actuators  110  and  131 . 
     The second lens group II is a focusing lens group, which is arranged to be driven by the actuator  110  in accordance with a signal coming from the optical apparatus to move along an optical axis. 
     The third lens group III is an image stabilizing lens. Two angular velocity sensors (not shown) are arranged within the lens barrel  1  to detect vibrations taking place in directions which are perpendicular to each other. Signals from these sensors are processed by the circuit. Two actuators  120  (one of them being not shown) which are arranged near to the third lens group III in a state of orthogonally intersecting each other are driven according to the amounts and directions of the vibrations. Then, the third lens group III is driven by the actuators  120  in the directions perpendicular to the optical axis in such a way as to prevent image shakes from being caused by vibrations of a hand or hands holding the optical apparatus. 
     A diaphragm unit  130  is disposed between the second lens group II and the third lens group III to adjust the quantity of light. To adjust the quantity of light, a signal from the optical apparatus is processed by the circuit and the actuator  131  is driven according to the processed signal to operate the diaphragm unit  130 . 
     A front fixed tube  2   a  has fitting engagement parts arranged to engage the first lens group I and screw parts arranged to have a retaining ring screwed thereon to secure the first lens group I to the fitting engagement parts. These parts are arranged in a plurality of portions. The front fixed tube  2   a  is secured to a rear fixed tube  2   b  with screws. 
     A cam tube  141  and a moving tube  142  fittingly engage the inner and outer sides of the rear fixed tube  2   b . The cam tube  141  is provided with a plurality of cam grooves for causing the moving tube  142  to move along the optical axis. The moving tube  142  is provided with cam followers  143  which are fitted in the cam grooves of the cam tube  141 . 
     The second lens group II fittingly engages the moving tube  142  and is secured to the moving tube  142  with a retaining ring. The moving tube  142  is arranged to move along the optical axis for adjusting focus when the cam tube  141  is caused to rotate either by the actuator  110  or by a driving force of a manual operation ring  4 . The actuator  110  is a known motor called as the vibration wave motor. Since the actuator and the lens driving mechanism are well known, the details of them are omitted from description. 
     A front exterior ring  3  is secured to the outside of the front fixed tube  2   a  with screws. The front exterior ring  3  is provided with a fitting engagement part  3   a  which is formed in a cylindrical shape to extend rearward in the optical axis direction from the body part  3   e  of the front exterior ring  3  and loosely engages an inner fitting engagement part  4   a  of the manual operation ring  4  with some clearance left between them. As shown in FIG. 2, the rear end surface  3   b  of the fitting engagement part  3   a  abuts on the front end surface  4   b  of the manual operation ring  4  to restrict the forward movement of the manual operation ring  4  in the optical axis direction. 
     A rear exterior ring  9  is disposed on the rear side of the manual operation ring  4 . The rear exterior ring  9  is secured to a fixed tube  2  in such a way as to have the manual operation ring  4  sandwiched between the front exterior ring  3  and the rear exterior ring  9 . 
     The manual operation ring  4  is provided with a fitting engagement part  4   c  which is formed in a cylindrical shape to extend rearward in the optical axis direction from the body part  4   e  of the manual operation ring  4  and loosely engages an inner fitting engagement part  9   a  of the rear exterior ring  9  with some clearance left between them. The rear end surface  4   d  of the fitting engagement part  4   c  abuts on the front end surface  9   b  of the rear exterior ring  9 . The rear end surface  4   d  is thus arranged to restrict the rearward movement of the manual operation ring  4  in the optical axis direction. With the rearward movement of the manual operation ring  4  in the optical axis direction thus restricted in addition to the restriction of forward movement thereof in the optical axis direction mentioned above, the manual operation ring  4  can be rotatively operated at a set position in the optical axis direction. 
     A water-repellent agent, such as grease or silicone oil, is applied to the fitting engagement parts  3   a ,  4   a ,  4   c  and  9   a . The use of the water-repellent agent not only prevents intrusion of water but also effectively smoothes the rotation of the manual operation ring  4 . Further, oil grooves  3   c  and  4   g  are formed in the outer circumferential surfaces of the fitting engagement parts  3   a  and  4   c.    
     In the case of the first embodiment, with the lens barrel arranged in the manner as described above, a circumferential groove  3   d  is formed at a portion between the body part  3   e  and the fitting engagement part  3   a  of the front exterior ring  3 , as shown in detail in FIG. 3. A washer (a sheet-like ring member)  7  and a wave washer (a pressing ring member)  8  are fitted into a void space part  5  which is formed jointly by the circumferential groove  3   d  and a rear end surface  3   f  in the optical axis direction of the body part  3   e  of the front exterior ring  3  and a front end surface  4   h  in the optical axis direction of the manual operation ring  4  which are opposed to each other. 
     The inner circumferential edge of the washer  7  fittingly engages the bottom part of the circumferential groove  3   d . The rear surface of the washer  7  abuts on the front end surface  4   h  in the optical axis direction of the manual operation ring  4 . 
     The wave washer  8  is formed in a waved shape having a plurality of crests. Before the wave washer  8  is fitted into the void space part  5 , the height of the wave part of the wave washer  8  is a little larger than the size of the space part  5  in the optical axis direction. Therefore, when the manual operation ring  4  is mounted with the washer  7  and the wave washer  8  inserted into the space part  5 , the washer  7  is pushed against the front end surface  4   h  in the optical axis direction of the manual operation ring  4  by the force of resilience generated by the elastic deformation of the crest part of the wave washer  8 . 
     A circumferential groove  4   f  is formed also in a part of the manual operation ring  4  between the body part  4   e  and the fitting engagement part  4   c  of the manual operation ring  4  (see FIG.  2 ). A void space part  10  is formed by the circumferential groove  4   f  and a rear end surface in the optical axis direction of the body part  4 e of the manual operation ring  4  and a front end surface in the optical axis direction of the rear exterior ring  9  which are opposed to each other. A washer (a sheet-like ring member)  11  and a wave washer (a pressing ring member)  12  are fitted into the void space part  10 . 
     The inner circumferential edge of the washer  11  fittingly engages the bottom part of the circumferential groove  4   f . The rear surface of the washer  11  abuts on the front end surface in the optical axis direction of the rear exterior ring  9 . 
     The wave washer  12  is formed in a waved shape having a plurality of crests. Before the wave washer  12  is fitted into the void space part  10 , the height of the wave part of the wave washer  12  is a little larger than the size of the space part  10  in the optical axis direction. When the manual operation ring  4  is mounted with the washer  11  and the wave washer  12  inserted into the space part  10 , therefore, the washer  11  is pushed against the front end surface of the rear exterior ring  9  by the force of resilience generated by the elastic deformation of the crest part of the wave washer  12 . 
     The washers  7 ,  8 ,  11  and  12  are made of plastic sheet material or vinyl chloride sheet material. The resilient forces generated with the waved shapes of the washers  8  and  12  pushed are weak forces and are nothing more than a force just strong enough for pushing the washers  7  and  11  respectively against the manual operation ring  4  and the rear exterior ring  9 . 
     Each of the washers  7 ,  8 ,  11  and  12  is formed in a ring-like shape without any notched or cut part. 
     With the lens barrel arranged as described above, the washers  7  and  11  and the water-repellent agent effectively prevent water and dust from intruding from outside into the inside of the lens barrel through clearances between the fitting engagement parts  3   a ,  4   a ,  4   c  and  9   a  of the manual operation ring  4  and the exterior rings  3  and  9 . Besides, since the washers  7  and  11  are made of plastic sheet, vinyl chloride sheet or the like, the use of them makes the manual operation ring  4  more smoothly movable, requiring a less amount of operation force than the use of rubber O-rings having large friction. 
     Further, although the water-repellent agent is applied to the fitting engagement parts  3   a ,  4   a ,  4   c  and  9   a , the water-repellent agent is effectively prevented from leaking to the outside by the washers  7  and  11 . 
     FIGS. 4 and 5 show a lens barrel  21  according to a second embodiment of the invention. The basic structural arrangement of the lens barrel  21  is similar to that of the lens barrel  1  described in the first embodiment. 
     In the second embodiment, a front fixed tube  22   a  has fitting engagement parts arranged to engage a first lens group I and screw parts arranged to have a retaining ring screwed thereon to secure the first lens group I to the fitting engagement parts. These parts are arranged in a plurality of parts. The front fixed tube  22   a  is secured to a rear fixed tube  22   b  with screws. 
     A cam tube  241  and a moving tube  242  fittingly engage the inner and outer sides of the rear fixed tube  22   b . The cam tube  241  is provided with a plurality of cam grooves for causing the moving tube  242  to move along the optical axis of the lens barrel. The moving tube  242  is provided with cam followers  243  which are fitted into the cam grooves of the cam tube  241 . 
     A second lens group II fittingly engages the moving tube  242  and is secured to the moving tube  242  with a retaining ring. The moving tube  242  is arranged, in the same manner as in the first embodiment, to move along the optical axis for adjusting focus when the cam tube  241  is caused to rotate either by an actuator or by a driving force of a manual operation ring  23 . 
     A front exterior ring  26  is secured to the outside of the front fixed tube  22   a . The front exterior ring  26  is provided with a fitting engagement part  26   a  which is formed in a cylindrical shape to extend rearward in the optical axis direction from the body part  26   e  of the front exterior ring  26  and loosely engages an inner fitting engagement part  23   a  of the manual operation ring  23  with some clearance left between them. 
     A rear exterior ring  30  is disposed on the rear side of the manual operation ring  23 , and is secured to a fixed tube (not shown) in such a way as to have the manual operation ring  23  sandwiched between the front exterior ring  26  and the rear exterior ring  30 . 
     The manual operation ring  23  is provided with a fitting engagement part  23   f  which is formed in a cylindrical shape to extend rearward in the optical axis direction from the body part  23   e  of the manual operation ring  23  and loosely engages an inner fitting engagement part  30   a  of the rear exterior ring  30  with some clearance left between them. 
     A water-repellent agent, such as grease or silicone oil, is applied to the fitting engagement parts  23   a ,  26   a ,  23   f  and  30   a . The use of the water-repellent agent not only prevents intrusion of water but also effectively smoothes the rotation of the manual operation ring  23 . Further, oil grooves  26   f  and  23   i  are formed in the outer circumferential surfaces of the fitting engagement parts  26   a  and  23   f.    
     The rear fixed tube (fixed member)  22   b  has a fitting engagement part  22   c  formed to fittingly engage the manual operation ring  23 . The fitting engagement part  22   c  is machined to have a fitting engagement groove  22   d  formed to engage cam followers  24  which are fixed with screws at a plurality of parts. The cam followers  24  are arranged at three to six equally spaced positions in the circumferential direction. 
     The manual operation ring  23  has a fitting engagement part  23   h  formed on its inner side to engage the rear fixed tube  22   b . The fitting engagement part  23   h  is machined to have a fitting engagement groove (guide groove) formed to engage the cam followers  24 . The fitting engagement part  23   h  is further machined to have inserting holes  23   c  formed in the same number of parts as the cam-follower mounting parts provided for allowing the cam followers  24  to be mounted from the outer side of the manual operation ring  23 . The manual operation ring  23  is thus arranged to be rotatively operable in a set position in the optical axis direction. 
     A groove  23   d  is formed on the outer side of the manual operation ring  23 . An operation rubber piece  25  is fitted into the groove  23   d  to prevent the inserting holes  23   c  of the manual operation ring  23  from being exposed to the outside. 
     In the second embodiment, with the lens barrel arranged in the above-stated manner, a circumferential groove  26   d  is first formed in the front exterior ring  26  at a part between the body part  26   e  and the fitting engagement part  26   a  as shown in detail in FIG. 5. A void space part  27  is formed jointly by the circumferential groove  26   d  and a rear end surface  26   g  in the optical axis direction of the body part  26   e  of the front exterior ring  26  and a front end surface  23   j  in the optical axis direction of the manual operation ring  23  which are opposed to each other. A washer (a sheet-like ring member)  28  and a wave washer (a pressing ring member)  29  are fitted into the void space part  27 . 
     The inner circumferential edge of the washer  28  fittingly engages the bottom part of the circumferential groove  26   d . The rear surface of the washer  28  abuts on the front end surface  23   j  in the optical axis direction of the manual operation ring  23 . 
     The wave washer  29  is formed in a waved shape having a plurality of crests. Before the wave washer  29  is fitted into the void space part  27 , the height of the wave part of the wave washer  29  is a little larger than the size of the space part  27  in the optical axis direction. When the manual operation ring  23  is mounted with the washer  28  and the wave washer  29  inserted into the space part  27 , therefore, the washer  28  is pushed against the front end surface  23   j  of the manual operation ring  23  by the force of resilience generated by the elastic deformation of the crest part of the wave washer  29 . 
     A circumferential groove  23   g  is formed also in a part of the manual operation ring  23  between the body part  23   e  and the fitting engagement part  23   f  of the manual operation ring  23 . A void space part  31  is formed by the circumferential groove  23   g  and a rear end surface in the optical axis direction of the body part  23   e  of the manual operation ring  23  and a front end surface in the optical axis direction of the rear exterior ring  30  which are opposed to each other. A washer (a sheet-like ring member)  32  and a wave washer (a pressing ring member)  33  are fitted into the void space part  31 . 
     The inner circumferential edge of the washer  32  fittingly engages the bottom part of the circumferential groove  23   g . The rear surface of the washer  32  abuts on the front end surface in the optical axis direction of the rear exterior ring  30 . 
     The wave washer  33  is formed in a waved shape having a plurality of crests. Before the wave washer  33  is fitted into the void space part  31 , the height of the wave part of the wave washer  33  is a little larger than the size of the space part  31  in the optical axis direction. When the manual operation ring  23  is mounted with the washer  32  and the wave washer  33  inserted into the space part  31 , therefore, the washer  32  is pushed against the front end surface of the rear exterior ring  30  by the force of resilience generated by the elastic deformation of the crest part of the wave washer  33 . 
     The washers  28 ,  29 ,  32  and  33  are made of plastic sheet material or vinyl chloride sheet material. The resilient forces generated with the waved shapes of the wave washers  29  and  33  pushed are weak forces and are nothing more than a force just strong enough for pushing the washers  28  and  32  respectively against the manual operation ring  23  and the rear exterior ring  30 . 
     Each of the washers  28 ,  29 ,  32  and  33  is formed in a ring-like shape without any notched or cut part. 
     With the lens barrel arranged as described above, the washers  28  and  32  and the water-repellent agent effectively prevent water and dust from intruding from outside into the inside of the lens barrel through clearances between the fitting engagement parts  23   a ,  26   a ,  23   f  and  30   a  of the manual operation ring  23  and exterior rings  26  and  30 . Besides, since the washers  28  and  32  are made of plastic sheet, vinyl chloride sheet or the like, the use of them makes the manual operation ring  23  more smoothly movable, requiring a less amount of operation force than the use of rubber O-rings having large friction. 
     Further, although the water-repellent agent is applied to the fitting engagement parts  23   a ,  26   a ,  23   f  and  30   a , the water-repellent agent is effectively prevented from leaking to the outside by the washers  28  and  32 . 
     According to the invention, as described in the foregoing, sheet-like ring members are arranged to block clearances existing between fitting engagement parts of a rotating member and exterior members. Water and dust, therefore, are effectively prevented from intruding from outside into the lens barrel through the clearances between the fitting engagement parts. Besides, since the sheet-like ring members are made of plastic sheet or vinyl chloride sheet, the rotating member can be more smoothly moved and can be operated with a less operating force than a case where rubber O-rings are used. 
     Further, although a water-repellent agent such as grease, silicone oil or the like is applied to the fitting engagement parts, the use of the above-stated sheet-like ring members effectively prevents the water-repellent agent from leaking to the outside.
A lens barrel includes fixed tubes each arranged to hold an optical unit having an optical axis, a rotating tube arranged to rotate around the optical axis with respect to the fixed tubes, wherein the rotating tube is provided, at front and rear portions thereof as viewed along the optical axis, respectively with end surfaces of ring shape having a center thereof on the optical axis, and each of the fixed tubes is provided with an end surface opposite to the associated end surface of the rotating tube, and sheet members of ring shape having a center thereof on the optical axis, each of the sheet members being disposed on a space formed by each end surface of the rotating tube and the associated end surface of the fixed tubes, so that the torque of a rotating operation on the rotating tube is lessened and, yet, the lens barrel excels in dust-proof and drip-proof.