Abstract:
An impact resistant zoom lens with a common focusing and zooming ring includes a camera mountable main barrel, front and rear axially movable lens carrying mounts, a control ring rotatably and slidably engaging the barrel and affixed to the front mount, an axial sleeve helicoid coupled to the first mount, a cylindrical cam rotatably supported by the barrel and longitudinally stationary therein and followers carried by the axial sleeve rearwardly thereof and by the rear mount and slidably engaging respective cam slots in the cam and guide tracks in the barrel. In order to prevent damage to the lens mechanism attendant to an impact on the front mount abutment members or faces are located on the front mount or sleeve and have large areas in stop engagement when the front mount is in its rearmost position with the follower movable therewith being shortly spaced from the rear end of the respective cam slot. Similarly related faces or members may be provided for limiting the forward movement of the front mount.

Description:
The present invention relates to an improved shock resistant structure in a zoom lens barrel having an optical system in which the lens element on the side closest to the object is axially moved both in the focusing and zooming operations, and being constructed so that both the focusing and zooming operations are performed by a manual operation of a single operating ring. 
     A type of zoom lens of the aforesaid nature is described in U.S. Pat. No. 3,663,093, issued on July 29, 1972, and, for example, includes a mechanism as shown in outline in FIG. 1 of the drawings herein, its optical system comprising a front first movable lens group L1 on the side closest to the object and a rear second movable lens group L2 on the camera side. Rotation or axial movement of a single operating ring 2 formed integrally with a lens mounting frame 1 holding first movable lens group L1 will move first movable lens group L1 along or move both first and second movable lens groups L1 and L2 along the optical axis, thereby providing focusing and zooming. Specifically, rotation of operating ring 2 rotates frame 1 integral with operating ring 2, holding frame 1 being guided by a helicoid 7 formed on the inner peripheral face of a sleeve portion of a holding frame 6 which is prevented from rotating by a pin 4 carried by frame 6 and slidably engaging an axial slot 5 in a fixed cylinder 3 and controllably movable only along the direction of the optical axis, to move along the optical axis together with first movable lens group L1 upon rotation of operating ring 2, whereby focusing is effected. When operating ring 2 is longitudinally moved along the optical axis, holding frames 1 and 6 are simultaneously moved with operating ring 2 in the direction of the optical axis, with pin 4 on frame 6 being guided by slot 5 in fixed cylinder 3. A cam ring 9 which rotatably engages an outer peripheral groove 8 formed in fixed cylinder 3 receives a follower pin 4 projecting through slot 5 of fixed cylinder 3 in a lead or cam groove 10 in cam ring 9. Thus, the cam ring 9 is rotated by way of the engagement of axially moving pin 4 with lead groove 10 when holding frame 6 is longitudinally moved in the direction of the optical axis in association with operating ring 2. Cam ring 9 is provided with a cam groove 11 for second movable lens group L2, and engaging cam groove 11 is a follower pin 14 which is carried by a mounting frame 12 holding second movabe lens group L2 and coaxially disposed inside fixed cylinder 3 and which extends through another axial slot 13 of fixed cylinder 3. When cam ring 9 is rotated as described above, pin 14 is pushed by cam groove 11 to move along slot 13 to cause the movement of holding frame 12 in the direction of the optical axis together with second movable lens group L2 in a similar manner to the movement of first movable lens group L1 together with operating ring 2 along the optical axis. Second movable lens group L2 is moved under the action of cam groove 11 at a speed or rate different from that of first movable lens group L1. When operating ring 2 is moved along the optical axis, zooming is thus thereby effected. It should be noted that an outer cylinder or sleeve 15 formed integrally with fixed cylinder 3 covers the outside of cam ring 9. An indicating cylinder or sleeve 16 with distance graduations and the like on its outer surface is located outside outer cylinder 15 and telescopes the operating ring 2. Formed in the inside face of the front end of indicating cylinder 16 is an annular groove 18, which is slidably engaged by a follower pin 17 carried on holding frame 6, thus permitting relative rotation between indicating cylinder 16 and holding frame 6 allowing the latter not to rotate while effecting their integral axial movement only. In addition, indicating cylinder 16 carries a follower pin 20 which engages an axial track or groove 19 in the inside face of operating ring 2, the maximum shift of holding frame 1, i.e., its focusing amount being controlled by pin 20 and groove 19. A mount 23 detachably mounts the lens barrel on a camera body (not shown) and is formed integrally with fixed cylinder 3. An operating holder 24 is held when mounting or detaching the lens barrel on or from the camera body. 
     As shown in FIG. 3 (a) and (b), the zoom lens has a stop 27 and a circumferentially elongated recess 26 engaged by stop 27 respectively provided on fixed cylinder 3 and cam ring 9 in order to restrict the rotation of cam ring 9 relative to fixed cylinder 3 to a predetermined amount upon zooming operation. The construction for restricting the amount of rotation of cam ring 9 serves to assure the smooth zooming operation at all times by pin 4 and lead groove 10 as well as by pin 14 and cam groove 11. However, the following problems may occur, although such mechanism for smooth zooming operation is provided. 
     That is, the front head 25 of the lens barrel, whether or not it is mounted on a camera body, often strikes or is struck by other objects whereby an impact force is imparted to the lens barrel head 25. The action of the impact force is generally toward the rear or straight on (in the direction shown by arrow A) or in a similar direction toward the camera. Such direction is the same as the direction along which holding frame 1 having lens barrel head 25 is moved upon zooming operation. In addition, even if the impact force acts in a completely different direction, holding frame 1 is sharply moved, in most cases, rearwardly toward the camera side (in the direction of arrow A) under the action of the impact force, since holding frame 1 is so constructed as to move axially linearly or in a simple straight direction. At this time, frame 6 helicoid connected to frame 1 is thereby sharply rearwardly moved (in the direction of arrow A). As a result, frame 6 sharply moves rearwardly when there is some room for frame 6 to reach the extreme telephoto position of zooming operation where frame 6 is most rearwardly retracted. When frame 6 reaches the extreme telephoto position of its zooming operation, an end 26a of elongated groove 26 abuts stop 27, as shown in FIG. 3(a) to prevent further rotation of cam ring 9. When cam ring 9 is stopped, pin 4 is prevented from moving whereby frames 1 and 6 are suddenly stopped from moving. Accordingly, the impact force on lens barrel head 25 acts between lead groove 10 and pin 4 which strike each other. The engaged relationship between lead groove 10 and pin 4 is very small in contact area, being approximately a line contact, resulting in a great impact load per unit area. This may cause the inner surface of lead groove 10 to be deformed into a dent or depression which, in turn, resists or interferes with subsequent zooming operation, or pin 4 to be damaged or broken, thus causing problems in precision and durability. Similar problems may occur in case frames 1 and 6 are originally positioned at its extreme telephoto position. 
     When frames 1 and 6 are moved for a zooming operation to the wide angle photography position, the direction of movement is, in general, opposite to that of the action of an impact force on lens barrel head 25. Therefore, even if an end 26b of elongated recess 26 abuts stop 27, as shown in FIG. 3(b), zooming operation toward the extreme wide angle photography position, i.e., movements of frames 1 and 6 toward the object side, is carried out manually alone, causing no impact force generally to act as described earlier. However, there exists the possibility of an impact force causing frames 1 and 6 to move in the direction of zooming operation toward extreme wide angle photograph position when, for example, operating ring 2 is otherwise accidentally restrained thereby resulting in the above-mentioned problems. In addition, similar problems, though insignificant, may occur when operating ring 2 is manually operated toward the object side without consciousness of the frames 1 and 6 being restricted in their movement to predetermined amounts, thus resulting in the disadvantage that inaccuracy and malfunction of the zooming mechanism tend to occur. 
     SUMMARY OF THE INVENTION 
     A principal object of the present invention is to provide an improved zoom lens barrel of the type which permits both zooming and focusing operations by a single operating ring. 
     Another object of the present invention is to provide a highly durable zoom lens barrel in which the internal motion transmitting mechanisms, such as cam grooves and follower pins, are prevented from being damaged or broken even if an impact force is imparted to the front end of the lens barrel. 
     Still another object of the present invention is to provide a zoom lens barrel which assures a smooth zooming operation at all times. 
     The above and other objects of the present invention will become apparent from a reading of the following description taken in conjunction with the accompanying drawings which illustrate preferred embodiments thereof. 
     In a sense, the present invention contemplates the provision of an improved zoom lens having a common focusing and zooming ring and of the general nature described above in which a follower movable with the front lens mount engages a cam slot in a cylindrical cam which controls the longitudinal movement of the rear lens mount, the improved zoom lens being characterized by the provision of a first stop face longitudinally movable with the front lens mount and a stationary second stop face carried by the camera mountable barrel section, the stop faces being in stop abutment when the front lens mount is in its rearmost position with the follower being forward of the rear end of the cam slot. 
     In an improved zoom lens, any impact imparted to the front end of the zoom lens by-passes the focusing and zooming mechanism and is transmitted directly to the camera mountable main barrel section. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a medial longitudinal cross-sectional view of a prior art zoom lens barrel; 
     FIG. 2 is a medial longitudinal cross-sectional view of a zoom lens barrel of one embodiment according to the present invention; 
     FIGS. 3 (a) (b) are evolved views respectively showing an essential part of cam ring 9 and fixed cylinder 3 of the prior art zoom lens barrel in FIG. 1; 
     FIGS. 4 (a) (b) are evolved views respectively showing an essential part of cam ring 9 and fixed cylinder 3 of the zoom lens barrel of the embodiment shown in FIG. 2; 
     FIGS. 5 through 12 are fragmentary, medial longitudinal cross-sectional views of essential parts of the second through ninth embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIGS. 2 and 4, which illustrate a first preferred embodiment of the present invention, it should be understood that the members corresponding in reference number and symbol to those in FIGS. 1 and 3 are identical in construction and function with the latter and that their further description is omitted for simplification. 
     A ring 28 is secured by means of a screw portion 29 to the inside peripheral face of the fixed cylinder 3. Ring 28 is positioned longitudinally rearwardly of or closer to the camera side than frame 6 and opposes the rear end 30 of frame 6 on the camera side. Ring 28 is secured in position to fixed cylinder 3 so that it abuts end 30 of frame 6 at the position where frame 6 is most retracted rearwardly or to the camera side (i.e., the position controlled by stop 27 and elongated recess 26) or immediately before frame 6 reaches the position when moved toward the camera side (in the direction of an arrow A). Ring 28 may be secured to fixed cylinder 3 by any suitable means in place of screw portion 29. 
     In the above embodiment, even if an impact force is imparted to lens barrel head 25 causing holding frames 1 and 6 to move in a direction rearwardly toward the camera side which corresponds to the direction of the movement of the frames 1 and 6 upon zooming operation to extreme telephoto position, the rearward movement is stopped when end 30 of frame 6 abuts stop ring 28. Holding frame 6 is stopped when it reaches the position controlled by stop 27 and elongated recess 26 where holding frame 6 is most retracted to the camera side or immediately before it reaches the said position. For example, therefore, when holding frame 6 is stopped immediately before its rearmost retractable position to the camera side, there is still a clearance between stop 27 and the end 26a of elongated recess 26, as shown in FIG. 4(a). In this condition, the cam ring 9 can be further rotated when a very high rotational force is applied thereto. Therefore, the impact force acting on lens barrel head 25 produces little effect between pin 4 and cam ring lead groove 10. As a result, the conventional problems are obviated. End 30 of holding frame 6 and ring 28 constitute together a stopper means and a stop means for absorbing the impact force. The stop means is a means for receiving the impact force while the stopper means is a means for transmitting the impact force on lens barrel head 25 to the stop means. 
     According to the first embodiment of the present invention, the impact force acts centrally on the contact portion between end 30 of holding frame 6 and ring 28. For the reasons, however, that holding frame 6 and ring 28 are held with sufficient strength by holding frame 1 and fixed cylinder 3, respectively, end 30 of holding frame 6 and ring 28 are sufficiently strong, and the contact area between both can be sufficient, the impact force can be completely absorbed by holding frame 6 and ring 28 without adversely affecting any other part. Furthermore, there is no possibility of holding frame 6 and ring 28 being damaged or broken. 
     It should be noted that if manufactured with high dimensional precision, ring 28 may be formed integrally with fixed cylinder 3 and it need not necessarily be of the shape of a ring. The movement of the frame 6 toward extreme wide angle photography is restricted, as shown in FIG. 4(b), by the abutment between stop 27 and the end 26b of elongated recess 26 in a similar manner to that of the prior art lens barrel. The force applied to holding frame 6 so that it is moved toward the object side (in the opposite direction of arrow A) can be absorbed similarly to the above by the construction that holding frame 1 or a sufficiently strong part of an optional member sufficiently strongly carried thereby abuts fixed cylinder 3 or a sufficiently strong part of an optional member held thereby with sufficient strength. When it is so constructed that reciprocal axial movements of holding frame 6 are restricted by the above-mentioned mechanisms, stop 27 and elongated recess 26 may be omitted. 
     Zooming operation is provided by the predetermined relative movements of lens groups L1 and L2, the movements of these lenses being highly complex in that the movement directions are inverted during zooming operation toward the extreme telephoto position and the extreme wide angle photography position. Accordingly, the principal feature of the present invention lies in stopping the movement of the holding frame for lens element on the closest side of the optical axis or the movement of a member intregrally movable therewith when holding frame 6 to which the impact force is transmitted reaches its most retracted position to the camera side and its advanced position closest to the object side or immediately before it reaches such positions, irrespective of the lens being zoomed to the extreme telephoto position or the extreme wide angle photography position. 
     FIG. 5 shows a second embodiment of the present invention in which an annular groove 31 is formed in the inner peripheral face of fixed cylinder 3 and an adjusting washer 32 is positioned therein as a receiving means in substitution for ring 28 in FIG. 2. In the present embodiment, the impact force imparted to lens barrel head 25 is received by the abutment of end 30 on holding frame 6 upon washer 32. With this construction, fabrication and assembly are greatly facilitated when compared to structure employing ring 28. 
     FIG. 6 shows a third embodiment of the present invention in which a stop plate 33 on which end 30 of holding frame 6 abuts is strongly secured to the inner circumference of fixed cylinder 3 with two or more screws 34, stop plate 33 being suitably curved to the inner circumference of fixed cylinder 3. The stop plate 33 may be of a cylindrical type. 
     FIG. 7 illustrates a fourth embodiment of the present invention in which a projection 37 which abuts a front end 36 of fixed cylinder 3 before the holding frame 6 moves to its most retracted position is integrally formed at the rear of a front end shoulder 35 of holding frame 6 so that an impact force imparted to lens barrel head 25 is received by front end 36 and projection 37 when brought into abutment, the projection 37 being of ring shape or other suitable shape. 
     FIG. 8 shows a fifth embodiment of the present invention in which a collar or washer 38 is secured to holding frame 6 by means of the follower pin 4 carried thereby. Collar 38 slidably engages the axial slot 5 in fixed cylinder 3 and is in surface contact with both sides 5a and 5b of slot 5, and is of annular shape so that it may come into surface contact with alternative ends 5c and 5d of slot 5 as it moves along the optical axis. This ensures that the impact force is received by the surface contact between either end 5c or 5d and collar 38. Collar 38 and axial groove 5 together with pin 4 cooperate with each other to restrict the movement of the holding frame 6 at either end position of the zooming operation, on the extreme telephoto position or extreme wide angle photograph position, thereby permitting the omission of stop 27 and elongated recess 26, as shown in FIG. 4. 
     FIG. 9 illustrates a sixth embodiment of the present invention in which a projection 39 is formed on the rear end of the outside peripheral face of holding frame 6, and opposing flange or shoulder portions 40 and 41 disposed in the path of an engageable with projection 39 project inwardly from the inner peripheral face of fixed cylinder 3. In the operation of the present embodiment, an impact force imparted to lens barrel head 25 is absorbed by the engagement of projection 39 with either of flange portions 40 and 41 in the manner described earlier, eliminating the need for stop 27 and elongated recess 26, as shown in FIG. 4. 
     FIG. 10 shows a seventh embodiment of the present invention in which an impact resistant annular flange 42 is integrally formed on the outer face of front end shoulder 35 of holding frame 6 as a substitute for the pin 17 shown in FIG. 2, flange 42 rotatably engaging an annular groove 18 formed in indicating ring 16. Flange 42 connects holding frame 6 to indicating ring 16 firmly in relation to their axial or longitudinal movement in the direction of the optical axis. On the other hand, provided on the external cylinder 15 formed integrally with fixed cylinder 3 is a shoulder portion 44 which engages the rear free end 43 of indicating ring 16 when holding frame 6 is moved to its rearmost position or immediately before it reaches such position. In the instant embodiment, an impact force imparted to lens barrel head 25 is transmitted through flange 42 to indicating ring 16 and is absorbed at the position of shoulder portion 44 formed integrally with fixed cylinder 3. In the structure of the present embodiment, stop 27 and elongated recess 26, as shown in FIG. 4, are required. 
     FIG. 11 illustrates an eighth embodiment of the present invention in which holding frame 6 and indicating ring 16 are coupled in the manner similar to that of FIG. 10. An inwardly projecting portion 45 is formed on the inner face at the rear end of indicating ring 16 so that it alternatively abuts shoulder portion 44 and another shoulder portion 46 opposed thereto which is provided on the front outer face of external cylinder 15 on fixed cylinder 3, as in FIG. 10, when holding frame 6 is moved to its rearmost or forwardmost position respectively. In the present construction, stop 27 and elongated recess 26, as shown in FIG. 4, may be omitted. 
     FIG. 12 illustrates a ninth embodiment of the present invention in which the external cylinder 15 on fixed cylinder 3 provided in each of the earlier described embodiments is eliminated, and the cam ring 9 rotatably engages the inside face of fixed cylinder 3 with its movement along the optical axis being prevented by opposing shoulder portions 47a and 47b formed proximate opposite ends of cylinder 3. Holding frame 6 longitudinally slidably engages the inside face of cam ring 9. Projecting portion 39 formed on the outer face at the rear end of holding frame 6 is provided so as to alternatively abut shoulder portions 49 and 50 opposed to each other and directed inwardly from opposite ends of the inner face of cam ring 9, respectively, when holding frame 6 is moved to its rearmost or forwardmost positions, respectively, or immediately before it reaches the respective positions. In the present embodiment, an impact force transmitted to holding frame 6 is transferred to cam ring 9 through projecting portion 39 and shoulder portion 49 or 50 and is absorbed by shoulder portion 47a or 47b. Stop 27 and elongated recess 26 may be eliminated in the present embodiment. Pin 4 engaging cam ring lead groove 10 also engages an axial groove 51 in fixed cylinder 3 in substitution for slot 5 provided in fixed cylinder 3 in the earlier embodiments. 
     The present invention is not limited to the above-mentioned embodiments and may include a variety of other similarly functioning structures. In addition, as is clear in the embodiments decribed above, stop 27 and elongated recess 26, as shown in FIG. 4, can be eliminated since holding frame 6 to be moved during zooming operation is stopped at the positions where holding frame 6 is rearmost or forwardmost, that is closest to the camera and object sides, respectively. In other words, an impact absorption mechanism for receiving an impact force which is imparted to lens barrel head 25 serves as a mechanism for restricting the rotation of cam ring 9 to a predetermined amount. Lead groove 10 and cam groove 11 may be made a cam groove and a lead groove, respectively. The stopper means and stop means may advantageously be controllable in position. 
     When, according to the present invention, an impact force is imparted or transmitted to holding frame 2 moving during zooming operation, the movement of holding frame 2 is stopped by the abutment between holding frame 2 or a sufficiently strong part of a member held thereby and fixed cylinder 3 or a sufficiently strong part of a member held thereby so as to receive the impact force. Therefore, the impact force does not act on the relatively weak parts of the zooming operation mechanism, e.g., engageable parts, such as follower pins, guide tracks such as lead grooves and cam grooves, causing parts of the zooming mechanism not to be deformed, damaged or broken and assuring a reliable and smooth operation, and high accuracy and durability for extended periods of time. In addition, the lens barrel, according to the present invention, can be provided easily and inexpensively without any complexity in construction, and many conventional zoom lens barrels may also be easily improved. 
     While there have been described and illustrated preferred embodiments of the present invention, it is apparent that numerous alterations, omissions and additions may be made without departing from the spirit thereof.