Drive mechanism for a zoom lens

Abstract: A zoom lens barrel is disclosed with includes a stationary barrel (12). A rotatable cam ring (22) is supported by the stationary barrel (12) and is adapted to move along an optical axis direction in association with rotation of the rotatable cam ring. A lens guide ring (24) is adapted to move together with the cam ring (22) along the optical axis direction, and the cam ring (22) is adapted to rotate relative to the lens guide ring (24), in association with axial movement of the cam ring. Cam grooves (22a, 22b, 24a, 24b) are provided for guiding the movement of at least two movable front and rear lens groups, with at least one groove being formed on the cam ring (22). Lens guide grooves are formed on the lens guide ring and are adapted to correspond to the cam grooves of the cam ring. At least one guide pin (36) is provided which is adapted to extend through an associated cam groove and an associated lens guide groove. The cam grooves and lens guide grooves are shaped such that the movable lens groups can be moved along a predetermined track by the movement which results from axial movement and relative rotation of the cam ring and the lens guide ring.

Description: The present invention generally relates to a drive mechanism for a zoom lens adapted for use in a camera. A drive mechanism of this kind is described in US-A-4681 406. Recently developed compact cameras have minimized their width and height dimensions to limits which are essentially set by the film size and the camera aperture size. To the contrary, reduction of the thickness of the camera is restricted or limited by the length of the camera lens when retracted into the body of the camera. When retracted, the required length of the lens (hereafter also referred to as the "accommodation length") increases as the displacement of the groups of lenses in the zoom lens increases, resulting in the need to use a longer cam ring to move the lens groups. Thus, if required displacement of the lenses in the lens group is not equal to the desired length of the cam ring, it is possible that even when the lens is retracted, the cam ring will still project outwardly from the camera body, thereby resulting in a relatively large thickness camera. Thus, the problem to be solved by the present invention is to provide drive mechanism for a zoom lens by which the thickness of the camera in which the lens is positioned, when the lens is retracted or accommodated, is decreased without decreasing the accuracy or precision of movement of the lens. The invention solves this problem by the features described in the main claim. Advantageous further developments are specified in the subclaims. The present inventor has recognized that one present obstacle or bar to reducing the thickness of the camera is the use of a cam ring which rotates at a fixed axial position to move the lenses in a lens group between a photographing position and a lens accommodating (or retracted) position within a conventional lens barrel. Accordingly, the present invention provides a drive mechanism without using a cam ring which rotates at a fixed axial position. The present invention starts from a cam ring which is rotatably supported by a stationary barrel so that the cam ring will move in the optical axis direction in accordance/association with rotation of the cam ring. The cam ring can be provided with at least two cam grooves for front and rear lens groups in order to determine the displacement of the lens groups. With this arrangement of a zoom lens barrel, because the cam ring moves along the direction of the optical axis during rotation of the cam ring, displacement of the lens groups, which is determined by the profiles of the respective cam grooves, can be increased. In this manner, it is possible to shorten the accommodation length of the lens to which the lens group is retracted (beyond the zooming range). This permits the overall thickness of the camera to be desirably reduced to a certain degree. According to the present invention, the zoom lens comprises a lens guide ring which moves together with the cam ring along the optical axis direction and which is rotated relative to the cam ring in accordance/association with axial and rotational movement of the cam ring. Cam grooves are provided on the cam ring for each of at least two movable front and rear lens groups. Lens guide grooves are formed on the lens guide ring in order to correspond to the cam grooves of the cam ring, and at least one guide pin can be provided which extends through an associated cam groove and an associated lens guide groove. The cam grooves and the lens guide grooves are shaped such that the movable lens groups can be moved along a predetermined track by the movement which results from the axial movement of, and relative rotation between, the cam ring and the lens guide ring. With such an arrangement, because the cam ring is advanced while rotating, the angle of inclination of the cam grooves can be decreased from what they would need to be if the cam ring only rotated in a single axial position. This contributes to providing for highly precise movement of the lens groups. Specifically, when the zoom lens barrel has a zooming section and a macro transfer section, in which the lens group is moved from one extreme zooming position to the macro-photographing range, the lead angles, i.e., the inclination angles of the cam grooves of the zooming section and the macro-transferring section, can be oriented so that they are opposite to each other with respect to a direction which is parallel to the optical axis. In accordance with the present invention, because the cam ring and the lens guide ring supporting the lens groups move the lens groups along the optical axis direction, and because the lens groups can be moved along the optical axis direction by relative movement of the cam ring and the lens guide ring, the accommodation length of the movable lens groups can be further shortened, thereby resulting in a camera which is compact, small and thin. Further, in accordance with the present invention, a relatively large axial displacement of the cam ring, resulting from both angular and axial displacement of the cam ring, can be ensured. Additionally, the axial displacement of the movable lens groups relative to angular displacement of the cam ring can be decreased by using a lead angle of the cam groove of the macro-transferring section which is opposite to the direction of that in the zoom section with respect to the optical axis, thereby resulting in more precise movement of the movable lens groups. Specifically, because the cam ring and the lens guide ring, which rotates relative to the cam guide ring, move along the direction of the optical axis while supporting the lens groups, so that resultant movement of the cam ring and the lens guide ring will effect axial movement of the lens groups, it is possible to increase displacement of the lens groups along the optical axis, in the normal photographing (i.e., zoom) range, even while using a cam ring and lens guide ring with decreased or reduced optical axial lengths; thus, a camera incorporating the same will have a relatively small thickness with an increased photographic (focal length) range. Further, because the cam grooves have opposed lead angles which are inclined in opposite directions with respect to a direction which is parallel to the optical axis of the zooming section and a macro-transferring section, displacement of the lens groups can be decreased in comparison to the angular displacement of the cam ring, thereby resulting in highly precise movement of the lens groups, i.e., greater angular displacement can result in increased precision of resultant axial lens movement. A further development of the present invention enables correct autofocus detection and measurement in a microphotography mode. This is achieved by providing a selectively movable optical element which is rotatably spring biased into a position in front of a light receiving element of an autofocus system, by using the helicoidal threads attached to the outer periphery of a cam ring. A further development of the present invention resides in a system for guiding movement of a flexible printed circuit board. The FPC board is bent over itself to form several loops, and can be adhesively (or otherwise, e.g., by a mechanical member) connected to camera components at spaced locations. The FPC board is positioned to avoid interfering with camera components and operation. A still further development of the present invention is to guide movement of a lens guide ring. This can be achieved, e.g., without undue mechanical tolerances, by securing a plate with deformable portions to the guide ring. Another development of the present invention enables easy opening and closing of a shutter barrier mechanism. This is accomplished via the relative axial displacement, e.g., of a cylindrical lens cover with respect to a lens guide ring, and should be designed to overcome the adverse effects of any errors which occurred during the manufacture and/or assembly of camera components. Still an additional development of the present invention avoids undesirable engagement between threaded rotating components of a camera, by designing tolerances into threaded areas (e.g., by using inclined surfaces) to facilitate threading engagement and to avoid blocking type engagement. The present invention will be discussed in greater detail hereinafter with specific reference to the drawings which are attached hereto, in which like reference numerals are used to represent similar parts throughout the several views, and wherein: Fig. 1 is a longitudinal sectional view of the upper half of a zoom lens barrel capable of macro-photography, shown in a position in which the lenses are retracted or accommodated, according to one embodiment of the present invention; Fig. 2 is a view which is similar to Fig. 1, with the apparatus shown at a WIDE extremity position; Fig. 3 is a view similar to Fig. 1, with the apparatus shown at a TELE extreme position; Fig. 4 is a view similar to Fig. 1, with the apparatus shown at a MACRO photographing position; Fig. 5 is a developed or plan view of a cam ring, a lens guide ring, and an inner helicoid ring; Fig. 6 is an explanatory or schematic view illustrating the relationship between displacement of the cam grooves and the lenses; Fig. 7 is an explanatory view illustrating the relationship between the cam grooves and the lenses in a known camera, and is labeled as prior art; Fig. 8 is a perspective view of a brush provided on an outer helicoidal element in order to detect the angular position of a cam ring; Fig. 9 is a plan view of a code plate which is placed into sliding contact with the brush on the helicoid illustrated in Fig. 8; Fig. 10 is a longitudinal sectional view of a zoom lens barrel illustrating a mechanism for detecting the angular position of a cam ring, similar to the view shown in Fig. 1, according to a second embodiment of the present invention; Fig. 10A is a longitudinal sectional view of a zoom lens barrel illustrating an alternate (third) embodiment of the mechanism of Fig. 1; Fig. 11 is a developed or plan view of the angular position detecting mechanism illustrated in Fig. 10, a cam ring, a lens guide ring, and an inner helicoid ring; Fig. 12 is an exploded perspective view of the zoom lens barrel which is shown in Figs. 1-4, and of a close distance (i.e., macro) correcting mechanism for an object distance measuring device; Fig. 13 is a front elevational view of the apparatus illustrated in Fig. 12; Figs. 14A and 14B are a front elevational view of the close distance correcting optical element shown in Fig. 12, in inoperative and in operative positions, respectively; Fig. 15 is a partially cut away or broken prospective view of a mechanism for housing a flexible printed circuit board connected to the shutter unit of a zoom lens barrel, as shown in Figs. 1-4; Fig. 16 is a cross-sectional view of the mechanism of Fig. 15; Fig. 17 is an exploded perspective view of the zoom lens barrel illustrated in Figs. 1-4, in combination with a light barrier mechanism; Figs. 18A and 18B are longitudinal sectional views of a zoom lens barrel having a barrier mechanism as shown in Fig. 17, and is shown in a closed position in which the barriers are closed and an open position in which the barriers are open, respectively; Figs. 19A and 19B are front elevational views of the barrier mechanism illustrated in Fig. 17, corresponding to the views of Figs. 18A and 18B, respectively; Fig. 20 is a longitudinal sectional view of a lens barrel driving mechanism as shown in Figs. 1-4; Fig. 21 is a developed or plan view of the lens barrel driving mechanism shown in Fig. 20, a cam ring, a lens guide ring, and an inner helicoid; Fig. 22 is a perspective view of the main portion of a lens barrel driving mechanism; Fig. 23 is an exploded perspective view of the main elements which are illustrated in Fig. 22; Fig. 24 is an enlarged perspective view of a main portion of the structure of Fig. 23; Fig. 25 is a developed or plan view of the structure illustrated in Fig. 24; Fig. 26 is an exploded perspective view of a zoom lens barrel mechanism as shown in Figs. 1-4, in combination with a flange back adjusting mechanism; Fig. 27 is a front elevational view of a part of the mechanism of Fig. 26, illustrating adjustment of the flange back using an adjusting tool; Fig. 27A is a front elevational view of an alternate embodiment of the mechanism illustrated in Fig. 27; Fig. 28 is a perspective view of a camera having a flange back adjusting mechanism; and Fig. 29 is a longitudinal sectional view of a zoom lens barrel including the flange back adjusting mechanism illustrated in Fig. 26. A. Zoom lens barrel In the illustrated embodiment, the present invention is used in a zoom lens barrel having a macro photographic function; although many of the features can equally well be used in a camera without such a function. Figs. 1, 2, 3 and 4 illustrate the lens in a retracted position, a WIDE extremity position, a TELE extremity position, and a MACRO photographing position, respectively. It can thus be easily understood from the drawings of Figs. 1-4 (and particularly Fig. 1) that the accommodation or retracted length of the lens barrel in accordance with the present invention is small. As illustrated in Fig. 1, a stationary barrel 12 is secured to a camera body 11, preferably of a lens shutter type of zoom lens camera The camera body 11 includes an outer rail 13 and an inner rail 14, respectively, which serve as a film guide. Inner and outer rails 13 and 14 further define a film holding plane. In the illustrated embodiment, front and rear lens groups 15 and 16, respectively, can be retracted to, and accommodated within, a position which is very close to the film holding plane. Additionally, annular members such as cam ring 22 are relatively small, and, accordingly, the accommodation length of the camera can be decreased. A female helicoid ring 18 having inner peripheral helicoid teeth or threads 18a is secured to, and inside of, stationary barrel 12 by set screws 19. The female helicoid ring 18 is screw/ threadably engaged by a male helicoid ring 20 having outer peripheral helicoid teeth or threads 20a. Cam ring 22 is secured to male helicoid ring 20 by set screws 21, as illustrated in Fig. 5. A gear 20b is formed on the outer periphery of male helicoid ring 20; the gear has threads or teeth, each of which extends parallel to the optical axis, as illustrated in Fig. 5. Gear 20b extends at the same angle of inclination as the lead angle of helicoid teeth 20a of male helicoid ring 20, i.e., it is parallel to the direction of each of the teeth or threads 20a, as shown in Figure 5. Cam ring 22 is rotated in both forward and reverse directions by a driving motor, described in detail hereinafter, through a pinion which meshes with gear 20b, so that when the male helicoid ring 20 is rotated, cam ring 22 is moved in the optical axis direction in accordance with the lead angle of helicoid teeth 20a, all while the cam ring is rotating. Lens guide ring 24 is fitted into the inner periphery of cam ring 22 so as to move together with cam ring 22 along the optical axis direction, and so that it will rotate relative to cam ring 22. Lens guide ring 24 includes a linear movement guide plate 26 which is secured to the rear end of the lens guide ring 24 by set screws 25. Linear movement guide plate 26 includes at least one outer projection which are each engaged in a respective lens guide ring guide groove 27 formed on the interior surface of stationary barrel 12. As one example, four projections and grooves are shown in Figure 16. Each guide groove 27 is provided in the form of a straight groove, which extends along (i.e., parallel to) the optical axis direction in the embodiment which is shown in the figures. An annular groove 28 is provided between the linear movement guide plate 26 and the rear end of lens guide plate 24; an inner flange 29 on the rear end of cam ring 22 is relatively rotatably fitted within annular groove 28, so that lens guide ring 24 can move along the optical axis direction together with movement of cam ring 22. Guide ring 24 cannot, however, rotate, due to the presence of guide groove(s) 27, which engages plate 26 to prevent rotation. Cam ring 22 can, of course, rotate relative to (and about) lens guide ring 24. Front and rear lens groups 15 and 16 are secured to front lens group frame 30 and rear lens group frame 31, respectively, which are both located inside the lens guide ring 24. Front lens group frame 30 is connected to helicoid ring 33, which is itself secured to shutter block 32. The shutter block is secured to a front lens group moving frame 34, which is provided along its outer periphery with at least three guide pins 35. Rear lens group frame 31 is provided along its outer periphery with at least three guide pins 36. As illustrated in Figs. 1 and 3, the guide pins are shown at the same axial positions, thereby making it possible to show only one such pin; Figures 2 and 4, however, illustrate the pins at axially spaced positions (as does, e.g. , Fig. 17). Shutter block 32 rotates driving pin 32a over an angular displacement corresponding to an object distance which is detected by an object distance measuring device (not illustrated) in order to rotate the front lens group frame 30, which is associated with driving pin 32a, via pin 30a. In this fashion, front lens group frame 30 is moved along the optical axis direction in accordance with movement of the helicoid in order to effect focusing, in a well-known fashion. Shutter block 32 also operates shutter blades 32b in accordance with a signal representing the brightness of an object which has been detected. A cylindrical lens cover 38 is provided which is integral with front lens group moving frame 34, and a decorative cylinder 39 is provided which covers the outer peripheries of lens guide ring 24 and cam ring 22, which are adapted to respectively project from the outer shell 11a of the camera body. Cam ring 22 is provided with a front lens group cam groove 41 and a rear lens group cam groove 42 within which guide pins 35 and 36, respectively, are fitted. Lens guide ring 24 is provided with lens guide grooves 43 and 44 which, respectively, correspond to the front lens group cam groove 41 and the rear lens group cam groove 42. As shown in the embodiment of Figs. 1-4, lens guide grooves 43 and 44 are straight grooves which extend in the direction of the optical axis. Guide pin 35 extends through both the front lens group cam groove 41 and the lens guide groove 43, and guide pin 36 extends through both the rear lens group cam groove 42 and the lens guide groove 44. The profiles of front lens group cam groove 41, lens guide groove 43, and rear lens group cam groove 42, as well as lens guide groove 44, are determined such that movable lenses or lens groups 15 and 16 are moved along a predetermined axial track in accordance with the axial movement of cam ring 22 and lens guide ring 24 effected by rotation of the male helicoid ring 20, and by relative rotation of cam ring 22 with respect to lens guide ring 24. As shown in Fig. 5, the section ℓ 1 of the front lens group cam groove 41 and the rear lens group cam groove 42 represents the normal photographing range (i.e., the zooming section), section ℓ 2 represents the MACRO transferring section, which is connected to the TELE extremity position of zooming section ℓ 1, and section ℓ 3 represents a lens accommodating or retracted section connected to the WIDE extremity position of zooming section ℓ 1, respectively. MACRO transferring section ℓ 2 has a lead angle which is opposite to the angle of inclination of zooming section ℓ 1, with respect to a direction which is parallel to the optical axis. Specifically, assuming that the lead angle of the zooming section ℓ 1 is positive (+), then the lead angle of the MACRO transferring section ℓ 2 will be negative (-). The zoom lens as constructed operates as detailed hereinafter. When male helicoid ring 20 is rotated in forward and reverse directions, the male helicoid ring 20 will move along the optical axis direction while rotating, in accordance with the lead angle of helicoid teeth 20a, since the female helicoid ring 18 which is engaged by the male helicoid ring 20 is secured to stationary barrel 12. Namely, cam ring 22, which is secured to male helicoid ring 20, is rotated together with the male helicoid ring 20 and will be moved along the optical axis direction in accordance with the lead angle of the helicoid teeth 20a. Further, lens guide ring 24, which is mounted to cam ring 22 so that the two rings will rotate with respect to each other and move together along the optical axis direction, is moved along the direction of the optical axis, without rotating, in accordance/association with axial movement of cam ring 22. Relative rotation of cam ring 22 and lens guide ring 24 causes axial movement of moving lenses 15 and 16 in accordance with the relationship between cam groove 41 and lens guide groove 43, as well as in accordance with the relationship between cam groove 42 and lens guide groove 44. Movement of the two lens groups is best illustrated in Figure 6. As shown, rings 22 and 24 move over substantially the same distance along the optical axis direction. Thus, lenses 15 and 16 can be moved from the accommodation position, as shown in Fig. 1, to the macro-photographing position, which is illustrated in Fig. 4, as a result of the movement of cam ring 22 and lens guide ring 24. Thus, it should be appreciated that when in the accommodation position, the accommodation length of the lens is extremely small, since the cam ring 22 and lens guide ring 24 do not protrude outwardly from the outer shell 11a of the camera body or from the cylindrical lens cover 38. Specifically, cam ring 22 rotates and moves along the optical axis direction in accordance with the lead angle of helicoid teeth 20a. Accordingly, the axial lengths of cam grooves 41 and 42 can be shorter than the largest axial displacement L1 of lenses 15 and 16, by an amount which corresponds to the axial displacement L2 of cam ring 22, as shown in Fig. 6. In other words, the total length of cam ring 22 can be shorter than the largest displacement L1 of the lenses by an amount which corresponds to the axial displacement L2 of cam ring 22. On the other hand, as shown in the schematic representation of the prior art structure of Fig. 7, known cam ring 50 does not move along the optical axis direction. Consequently, in such a known cam ring 50, the axial lengths of cam grooves 51 and 52 correspond to the axial displacement of the moving lenses (i.e., to the movement of cam pins 53 and 54), and, accordingly, the axial length of cam ring 50 must be equal to or greater than the largest displacement of the lenses. In the present structure, even if lens displacement effected by cam grooves 41 and 42 is decreased by reducing the lead angles of cam grooves 41 and 42, axial displacement effected by the lead angle of the helicoid teeth 20a will not change. Specifically, assuming that the lead angles of cam grooves 41 and 42 are zero, the displacement of lenses 15 and 16 with respect to cam ring 22 will also become zero, but lenses 15 and 16 will be finally moved by a displacement which corresponds to the lead angle of helicoid teeth 20a, insofar as cam ring 22 will axially move in accordance with the lead angle of helicoid teeth 20a as shown in Fig. 6. Thus, even if the rear lens group cam groove 42 is provided in a plane which is perpendicular to the optical axis, lens 16 can be retracted into the accommodation position by rotating cam ring 22. This means that the lead or inclination angles of the rear lens group cam groove 42 and the lens guide groove 44 formed on cam ring 22 can be significantly reduced, so that the axial lengths of rear lens group cam groove 42 and lens guide groove 44 can be reduced in order to shorten the cam ring 22 and so as to increase the resulting accuracy of movement of moving lenses 15 and 16, as discussed hereinafter. The relationship between the lead angles and the cam grooves 41 and 42 becomes clear when looking at accommodation section ℓ 3 of rear lens group cam groove 42. Section ℓ 3 of groove 42, as seen in Fig. 5, is oriented so that it is perpendicular to the optical axis of cam ring 22. If cam ring 22 could only rotate, and could not also move in the optical axis direction, as is the case with the known cam ring of Figure 7, moving lenses 15 and 16 could not be retracted. However, in accordance with the present invention, since cam ring 22 can move along the optical axis direction, it is possible to retract moving lenses 15 and 16 even when the groove (i.e., slot) is perpendicular to the optical axis, unlike the situation with the illustrated prior art structure. It is important to remember that the necessary displacement of lenses 15 and 16 from the TELE extremity position to the macro-photographing range is very small in a zoom lens barrel as used in accordance with the present invention. In order to decrease the displacement of lenses 15 and 16, yet still achieve necessary displacement of the lenses, excess displacement is eliminated by the disclosed configuration of cam grooves 41 and 42. Specifically, the lead angles of macro-transferring section 2 of cam grooves 41 and 42 are negative (-) to provide a negative (-) lead angle. This results in the shorter displacement L4 of rear lens group 16 (i.e., of guide pin 36) with respect to the axial displacement of cam ring 22 in the macro-transferring section ℓ 2, than occurs in the zooming section ℓ 1. That is, the displacement of moving lenses 15 and 16 with respect to angular displacement of cam ring 22 can be reduced, as shown in Fig. 6. With such an arrangement, since the displacement of lenses 15 and 16 relative to the angular displacement of cam ring 22 is very small, it is possible to provide a sufficient angular displacement of cam ring 22 so as to result in highly precise movement of the lenses. Further, since the lead angle of the macro-transferring section ℓ 2 is minus (e.g., a negative), the total length of cam ring 22 can be reduced. In the illustrated embodiment referred to above, guide groove 27, as well as lens guide grooves 43 and 44, are all straight grooves. However, it should be appreciated that the present invention is not limited to the use of such straight grooves. Specifically, the present invention does not exclude, prevent, nor eliminate the possibility of providing guide groove 27 and lens guide grooves 43 and 44 of shapes which are other than straight, e.g., of an angled configuration. To summarize, the shapes of guide groove 27, cam grooves 41 and 42, and lens guide grooves 43 and 44 are determined so that the lens guide ring 24 will move along the optical axis direction, together with the cam ring 22, in accordance with rotation of the cam ring, and so that lenses 15 and 16 will move in the optical axis direction, along a predetermined track, in accordance with relative rotation (and axial movement) of cam ring 22 and lens guide ring 24. It should be noted that lens guide ring 24 could be provided to rotate if desired. This could be accomplished, e.g., by forming lens guide groove 27 at a predetermined angle of inclination with respect to the optical axis, rather than parallel thereto, as is shown in Fig. 5. Even if ring 24 is rotatable, however, rings 22 and 24 can still be rotatable with respect to each other, since they can be formed so as to rotate over different angular amounts with respect to each other. At least three guide pins 35 and at least three guide pins 36 are provided (in engageable association with cam grooves 41, 42 and lens guide grooves 43, 44) in order to prevent rear lens group frame 31 and front lens group moving frame 34 from being inclined with respect to the optical axis, which might occur due to the otherwise insufficient length of engagement with respect to lens guide ring 24. Thus, if a sufficient engagement length can be provided, or if there is the possibility that the incline of rear lens group frame 31 and front lens group moving frame 34 can be eliminated by providing additional guide poles or similar structure, the number of guide pins can be reduced to either one or two. Although the male helicoid ring 20 and the cam ring 22 are formed of separate members which are interconnected by set screws 21, in the illustrated embodiment, they could alternatively be molded as a single integral piece of synthetic resin or similar material. The above discussion was directed to the basic overall construction and operation of a zoom lens barrel in accordance with the present invention. The following descriptions will address additional lens mechanisms or components and combinations thereof, in accordance with other aspects of the present invention. B. Light Intercepting Mechanism A light intercepting plate 45 is positioned at the rear end of lens guide ring 24. This intercepting plate is adapted to intercept harmful light which would otherwise enter the lens barrel, along the inner peripheral wall of the lens barrel, from the circumferential portion of moving lens 16, and which would have an adverse influence on the formation of an image on the film plane. In the illustrated embodiment, the light intercepting plate 45 is formed by a radial extension of the linear movement guide plate 26, which extends in a direction away from the inner surface of barrel 12, and which is normal to the optical axis. The inner end of the light intercepting plate 45 is located in a position which generally corresponds to the circumferential portion of lens 16, as shown in Figure 2. If harmful light enters the lens barrel from the circumferential portion of lens 16, through the inner wall of the lens barrel, light will be reflected by the inner wall of the lens barrel and will reach the film plane through aperture 46. This will, in turn, cause a number of undesirable problems, e.g., a reduction of image contrast or a decrease in the coloring characteristics of color film. Such a phenomenon tends to occur particularly when the lens is located in the TELE extremity position. Namely, when in the TELE extremity position, moving lenses 15 and 16 are fed forwardly (i.e., advanced) the farthest, and, accordingly, the internal space of the lens barrel is expanded. As a result, harmful light passing the circumferential portion of lens 16 is diffused within the expanded internal space of the lens barrel. Consequently, harmful light is reflected in a complicated fashion by the inner wall of the lens barrel and reaches the film plane. Light intercepting plate 45 thus effectively intercepts harmful light which would otherwise reach the film plane, as noted above, particularly when the lens is in the TELE extremity position. While shown as integrally attached to plate 26, it is alternately possible to provide a light intercepting plate 45 which is separate from guide plate 26, and/or which is attached to other camera structure. C. Detecting Mechanism of Focal Length Information - First Embodiment A first mechanism which is provided for detecting focal length information is adapted to detect the angular position of the cam ring 22 in order to detect zoom lens focal length information. The mechanism is attached to the periphery of one ring (or an attachment thereto) which is relatively rotatable with respect to a second ring, so that relative rotation can be detected. As shown in Figures 1-5, a code plate 48 is attached to cam ring 22 indirectly, i.e., it is attached to the outer periphery of male helicoid 20 which is attached to the cam ring. Plate 48 is secured to helicoidal ring 20 by set screws 49 and is inclined at an angle which is identical to the angle of inclination (with respect to the optical axis) of helicoid teeth or threads 20a. Outer helicoid 18 is provided, along its inner periphery, with a brush securing recess 50 (see Fig. 8) which corresponds to code plate 48. Recess 50 can be inclined, as shown, at the same angle as the angle of inclination of each of the helicoid grooves 18a (it is not so inclined, e.g., in the embodiments of Figs. 10, 10A, and 11). Brush 51, having a base portion 52, is secured to recess 50 so that it will always come into sliding contact with code plate 48. Brush 51 is positioned so that it is substantially parallel to the length of code plate 48. Code plate 48 and brush 51 together comprise a detecting mechanism for detecting the angular position of cam ring 22, i.e., for detecting information relating to the focal length of the zoom lens, the accommodated position of the lenses, and the WIDE and TELE extremity positions of the zoom lens. Code plate 48 includes conductive lands 48a and nonconductive lands 48b, as best illustrated in Fig. 9. Brush 51 includes one common terminal 51a and three terminals 51b, so that when terminals 51a and 51b come into contact with the conductive lands 48a of code plate 48, a signal "0" will be output, and, when the terminals do not come into contact with conductive lands 48a, a signal "1" will be output. The relative angular position of cam ring 22 and lens guide ring 24 can be detected by a combination of signals "1" and "0". Base portion 52 of brush 51 is connected to control board 54 through flexible printed circuit (FPC) board 53. Code plate 48, which comprises part of the angular position detecting mechanism, can be inclined with respect to rings 20 and 22, at an angle which is identical to the angle of inclination of helicoid teeth 20a, so that the code plate 48 will move in the same direction as the helicoid teeth, as noted above, and, accordingly, so that the code plate 48 will not be a bar or obstacle to reduction of the combined length of the lenses. D. Detecting Mechanism of Focal Length Information - Second and Third Embodiments Figs. 10 and 11 illustrate a second embodiment of a focal length information detecting mechanism; in this embodiment, the mechanism is also attached to a ring which is relatively rotatable with respect to a second ring. The first focal length information detecting mechanism (1) referred to above is positioned between helicoidal ring 18 and cam ring 22, and is directly attached to the outer periphery of ring 20. Alternatively, the second focal length information detecting mechanism (2), as described in this section, is provided between lens guide ring 24 and a bent portion of plate 26, which is attached to a rear surface of cam ring 22. In this embodiment code plate 48A is not inclined with respect to the optical axis, but is directly positioned on the outer periphery of cam ring 22 so that it is concentric with ring 22 about the optical axis. Code plate 48A is secured to the outer periphery of the rear end of cam ring 22 by set screws 49A (see Fig. 11). Brush 51A, which includes a base portion 52A connected to a brush securing member 55 positioned above the code plate 48A, is in continuous sliding contact with code plate 48A. Brush securing member 55 is formed by bending a portion of the guide plate 26, which is secured to the rear end of lens guide ring 24, so that the securing member is parallel with the optical axis. Code plate 48A and brush 51A together comprise a detecting mechanism for detecting the angular position of cam ring 22, i.e., for detecting zoom lens focal length information, the accommodated position of the lens, and the WIDE and TELE extremity positions of the zoom lens. The construction of both code plate 48A and brush 51A are essentially the same as those of the above-noted focal length detecting mechanism (1), as illustrated in Fig. 9. Base portion 52A of brush 51A is connected to control board 54A through a flexible printed circuit board 53A. As can readily be understood from the above discussion, the focal length information detecting mechanism is thus functionally (although not physically) positioned between cam ring 22 and lens guide ring 24. If desired, the mechanism could be physically positioned between rings 22 and 24, if adequate clearance is provided. The third embodiment of the angular position detecting mechanism (i.e., focal length detector) is illustrated in Figure 10A. In this Figure, the mechanism is physically positioned between relatively rotatable rings 22 and 24. As shown, code plate 48B is positioned on the inner peripheral surface of cam ring 22, with conductive brush 51B (having a base 52B and suitable bristles) positioned on the exterior surface of ring 24 (although the plate and brush could alternatively be oppositely disposed). Thus, relative rotation of the rings, as in the above embodiments, effects continuous sliding contact of brush 51B and plate 48B, and together define a detecting mechanism for detecting the angular position of cam ring 22. E. Operation Mechanism for the Close Distance Correcting Optical Element As illustrated in Figs. 12-14, the stationary barrel 12 has, at its front end, a lens barrel support plate 12a which lies in a plane which is normal to the optical axis. A zoom motor 12c, having a pinion 12b at one axial end, is secured to the upper portion of supporting plate 12a via a securing member which is not illustrated. Pinion 12b is exposed within stationary barrel 12, i.e., it extends outwardly of the barrel, via a gear window 12d formed in barrel 12. Lens barrel support plate 12a is provided, along an upper portion of the plate in the vicinity of gear window 12d, with a supporting recess 12e within which a close distance correcting optical device 60 is also supported. An object distance measuring device 70 is secured to stationary barrel 12. This object distance measuring device detects the object distance in accordance with a photo-induced current, which depends upon the object distance. The device includes a light emitting portion 71 and a light receiving portion 72, which is connected to the light emitting portion 71 by a connecting portion or bridge 73. The light emitting portion 71 and light receiving portion 72 (which includes, e.g., a PSD [i.e., position sensing device] as a light receiving element) are located on opposite sides of the zoom motor 12c. Object distance measuring device 70, which is known per se, detects the object distance based on the known triangulation measuring principle. Light emitting portion 71 includes, e.g., a light source such as an LED, and a projecting lens, and light receiving portion 72 includes, e.g., a PSD which is spaced from the light source by a predetermined base length, and a light receiving lens, as noted above. It should be noted that the light source, the projecting lens, and the light receiving lens (all of which are not shown) are preferably provided in a single unit or assembly. Light emitted from the light source is reflected by the object and is incident upon the PSD of the light receiving portion 72, on which the incident position (i.e., the light point) of light on the light receiving surface depends upon the object distance. The object distance can be detected by the photo-induced current, which depends upon the light point. An operation signal, which is sent in response to the detected object distance data, is supplied to shutter block 32 in order to effect automatic focusing. .The close distance correcting optical device 60 is supported within supporting recess 12e of lens barrel support plate 12a so that it will move away from and approach the light receiving portion 72 of object distance measuring device 70. The close distance correcting optical device 60 moves correcting optical element 61 (e.g., a prism) to bring it in front of light receiving portion 72 only in the macro-photographing mode, so that light reflected from the object is refracted in order to change the incident position of reflected light onto the light receiving portion 72 in the macro mode, thereby improving object distance measurement accuracy in the macro mode. The correcting optical element 61 is not limited to the illustrated embodiment, which is described in detail, e.g., in Japanese Patent Application No. 62-42,198 (corresponding to United States Application Serial No. 159,765), filed in the name of the assignee of the present invention, since the subject of the present invention is not directly directed to the details of construction of the correcting optical element 61. The correcting optical element 61 includes an opening 62 on the object side and an opening (not illustrated) on the side of the light receiving portion 72. The correcting optical element 61 also includes a mask 63 which intercepts light outside of the necessary light path. Opening 62, which is offset from the optical axis of light receiving portion 72, is provided in the form of a slit. The correcting optical element 61 has an arm 66, which is connected to a rotatable shaft 65, which is in turn pivoted about a pivot shaft 64 secured within supporting recess 12e. The correcting optical element 61 is rotatably biased by a tensile spring 67, so that element 61 will tend to move in front of the light receiving portion 72. Tensile spring 67 is connected at one end to arm 66 and at an opposed, second end, to outer helicoid 18 or to an element on the outer helicoid side. Rotatable shaft 65 is provided on its rear lower end portion with an associated projection 68, integral therewith, which includes a front end projecting into the stationary barrel 12 through window 12f of supporting recess 12e. Associated projection 68 is briefly illustrated, in Figs. 1 and 2, by an imaginary line. Projection 68 is disengagably engaged by one helicoid tooth or thread 69 of inner helicoid 20 in order to move correcting optical element 61. Helicoid tooth 69 is formed by an extension of one of the helicoid teeth 20a along gear 20b. The length of helicoid tooth 69 substantially corresponds to the section of angular displacement of cam ring 22 in which the zoom lens is located between the TELE extremity and the WIDE extremity positions, so that the helicoid tooth 69 will have a cutaway portion 69a (see Figure 14A) which is not engaged by the associated projection 68 in the macro mode of the camera. Specifically, the correcting optical element 61 is located in an inoperative or retracted position in which the associated projection 68 is engaged by the helicoid tooth 69, so that the correcting optical element 61 is retracted from the optical axis of light receiving portion 72 in the normal photographing position of the zoom lens, i.e., between the TELE extremity and the WIDE extremity, as is well illustrated in Fig. 14A. On the other hand, in the macro position of the zoom lens, the associated projection 68 is positioned in the cutaway portion 69a, so that the associated projection 68 will be disengaged from helicoid tooth 69, and such that the correcting optical element 61 will be brought in front of the light receiving portion 72 as shown in Fig. 14B. With such an arrangement for a close distance correcting mechanism, movement of correcting optical element 61 towards the front end of the light receiving portion of the object distance measuring device can be ensured by the noted configuration of the helicoid tooth 69 which is provided on cam ring 22. Accordingly, no special element needs to be additionally provided, thereby providing a relatively simple operating mechanism for selectively positioning the optical element 61 in front of the light receiving element 72 during macro photography. F. Guide Mechanism for the Flexible Printed Circuit Board The following discussion is directed to a guide mechanism for the flexible printed circuit board 81, which supplies an operating signal to shutter block 32. As illustrated in Fig. 3, the flexible printed circuit board 81 is connected to control circuit board 54, and is positioned or introduced within a space defined by stationary barrel 12 and cam ring 22 through a window formed in stationary barrel 12. The flexible PC board 81 is then extended rearwardly within the space located substantially along the inner surface of stationary barrel 12, so that it is introduced rearwardly through the gap which exists between projections 26a of the linear movement guide plate 26. The flexible PC board 81 is then bent forwardly, at a first bent portion 81a, and extends along the outer surface of guide plate 26 and along the inner circumference thereof, in a generally forward direction. Lens guide ring 24 is provided, along its inner periphery, with a substantially linear (flexible PC board) guide groove 82 having a bottom or base extending along (i.e., parallel to) the optical axis direction, as shown in Fig. 15. The flexible PC board 81, which extends along the inner side face of guide plate 26, extends forwardly through guide groove 82. Board 81 is bent backwardly or rearwardly at a second bent portion 81b, in the vicinity of the front end of guide groove 82 of lens guide ring 24, so that it will be superimposed onto the remaining portion of flexible PC board 81. The flexible PC board 81 extends beyond the rear ends of shutter unit 32, the lens guide cylinder 38, and the front lens groove frame 30, and is then bent forwardly at a third bent portion 81c so that it will be connected to shutter block 32. The flexible PC board 81 includes contact sections a1, a2, and a3. Portion a1 comes into contact with the rear side face of guide plate 26 and portion a2 comes into contact with the bottom of guide groove 82. Portion a3 is located in the vicinity of the second bent portion 81b. Flexible board 81 is connected along at least the above-mentioned portions a1, a2, and a3, to respective contacting members by a suitable adhesive or mechanical connector. Of course, the board can be connected to any adjacent camera components, as long as the board retains its flexibility, yet remains secured to the camera; similarly, a greater or lesser number of sections can be so adhered. Flexible board 81 is deformable, in accordance with zooming operation of the zoom lens, as detailed hereinafter. When the zoom lens is moved from its accommodation position, as shown in Fig. 1, to the WIDE extremity position shown in Fig. 2, and thereafter to the TELE extremity position as shown in Fig. 3, by the zooming motor, cam ring 22 moves along the optical axis direction while rotating, so that lens guide ring 24 will move, without rotating, together with cam ring 22. As a result, the space behind guide plate 26 is expanded, and the loop formed by the bent or deformed portion 81a of board 81 becomes relatively large. However, the extent of the expansion of the loop of bent portion 81a is relatively small, since the expansion of the loop occurs while the flexible board 81 moves in the direction of movement of lens guide ring 24. Further, because moving lens 15 and, accordingly, shutter block unit 32, are moved forward relative to lens guide ring 24 by the relative rotation of cam ring 22 and lens guide ring 24, which occurs at the same time as axial movement of cam ring 22, lens guide ring 24 and shutter block unit 32, the space between the front lens group frame 30 and the guide plate 26 is expanded during such forward movement of the cam ring. Simultaneously, the loop diameter of flexible PC board 81 expands while the third bent portion 81c moves forwardly, with the extent of expansion being small. Accordingly, movement and deformation of bent portions 81a and 81c caused by axial movement of shutter unit 32 causes the flexible PC board 81 to extend without having an adverse influence on the operation of other components and the optical system, i.e., the relatively small loop expansion does not interfere with the operation of other camera elements. Since the second bent portion 81b is bonded, at its periphery, to guide groove 82, no relative displacement of the second bent portion 81b with respect to the lens guide ring 24 will occur. Even when in the MACRO or TELE extremity positions, in which the loop of bent portions 81a and 81c is the largest, because the upper portions of these bent portions are adhered to plate 26 (or, alternatively, to stationary barrel 12) and to flexible PC board guide groove 82, respectively, neither inclination of the bent portions 81a and 81b with respect to the optical axis, nor the entrance of bent portions 81a and 81b into the light path, will occur, thereby resulting in a lack of interference with other camera components. To the contrary, when the zoom lens is returned from the TELE extremity to the WIDE extremity or the accommodation position, the space between shutter unit 32 and guide plate 26, and the space behind guide plate 26, are both reduced. Simultaneously, the length of the portions of the flexible board 81 that are superimposed on each other increases, so that the bent portions 81a and 81c are moved rearwardly to decrease their loop diameters. Specifically, the length of superimposition of the flexible PC board 81 increases and the loop diameter of the bent portions 81a and 81c decreases in accordance with rearward movement of shutter block unit 32. Accordingly, there is no possibility that the flexible PC board will interfere with other moving members, or will enter into the light path. A flexible PC board guide groove 82 is formed in the lens guide ring 24 in the illustrated embodiment, as noted above; if, however, there is a sufficient gap between the lens guide ring 24 and the cylindrical lens cover 38 through which the flexible PC board 81 can pass, guide groove 82 could be eliminated if desired. G. Mechanism for Guiding Movement of Lens Guide Ring 24 Guide plate 26 is secured to the rear end of lens ring 24 by set screws 25, as mentioned above. Guide plate 26 includes guide projections 26a, as shown in Figure 17, which are fitted within guide grooves 27 formed on the inner surface of stationary barrel 12, in order to restrict the direction of movement of lens guide ring 24. Accordingly, it is necessary to make the positions and dimensions of the guide projections 26a and guide grooves 27 exactly identical to each other in order to precisely restrict the direction of movement of the lens guide ring 24. This, however, is practically difficult to achieve. The solution, as illustrated in Fig. 16, e.g., is to utilize guide projections 26 which are elastically deformable. In this way, possible deviations in the shape and positions of the guide grooves 27 and guide projections 26a can be absorbed, or compensated for, by elastic deformation of guide projections 26a. Guide plate 26A, as shown in Fig. 16, comprises a substantially circular disk-shaped plate and has an outer periphery with a plurality of the linear movement guide projections 26a extending outwardly from the periphery of the plate. These projections are fitted into corresponding straight guide grooves 27 formed on the inner surface of stationary barrel 12. The guide grooves 27 for the lens guide ring extend along (i.e., are parallel to) the optical axis direction. In the illustrated embodiment, four guide projections 26a are spaced from one another at equiangular positions which are 90 degrees apart from each other. It should be noted that the number of guide projections 26a (and guide grooves 27) is not limited to four, and therefore can either be less than or more than four. Two (theoretically, at least one) guide projections 26a are divided by radial slits 26b into two halves which are adapted to be located on opposite sides of the optical axis and which together form a pair of elastically deformable guide pieces 26c which are adapted to be elastically deformed so that they will approach each other. Guide pieces 26c absorb or compensate for possible positional or dimensional deviations between guide projections 26a and guide grooves 27. In other words, the use of such flexible split members minimizes problems which would otherwise result from an improper fit between grooves 27 and projections 26. Specifically, guide projections 26a are fitted into associated guide grooves 27 such that, when fitted, guide pieces 26c are slightly elastically deformed so as to approach each other and reduce the width of radial slits 26b. These radial slits are connected to circumferential slits 26e which are formed in plate portion 26d of guide plate 26A, as seen in Figure 16. Circumferential slits 26e are located about the same (imaginary) circle, and contribute to relatively easy elastic deformation of the elastically deformable guide pieces 26c. As should be understood from the above, because guide projections 26a of guide plate 26A, which are fitted into corresponding guide grooves 27 of stationary barrel 12, are elastically deformable along the width-wise direction of guide grooves 27, any possible positional deviation which may occur between guide projections 26a and guide grooves 27 can be effectively compensated for, i.e., absorbed. Further, the use of such flexible guide pieces 26c makes it easier to insert guide projections 26a into associated guide grooves 27. H. Barrier Opening and Closing Mechanism Figs. 17-19 illustrate a barrier mechanism which can be advantageously incorporated into the zoom lens barrel referred to above, e.g. The barrier mechanism is notable in that its barriers are closed and opened by relative axial displacement of a cylindrical lens cover, including the barriers, and the lens guide ring 24. A pair of lens barriers 140 are provided on the front end of cylindrical lens cover 38. Lens barriers 140 are opened and closed in the lens accommodation section ℓ 3 in such a way that they will be closed in the accommodation position of the lens and such that they will be maintained in an open position whenever the lens is located between the accommodation position and the macro position. Although two barriers 140 are shown, one (or more than two) could also be used. Barriers 140 are pivoted to a surface of a flange portion 38a provided on the inner periphery of the front end of lens cover barrel 38, via respective pivot pins 141. Barriers 140, which are symmetrically opposed to each other, have barrier plate portions 140a which can be moved into the light path, and driving arm portions 140b which extend in opposite directions from barrier plate portions 140a, with respect to pins 141. Driving arm portions 140b are provided at their ends with pins 142 which extend rearwardly, along the optical axis direction, through the inner space, i.e., opening, in flange portion 38a. A circular disk-like intermediate ring 143 and a circular disk-like driving ring 145 for operating barriers 140 are rotatably mounted on the back of flange portion 38a. Intermediate ring 143 is provided along its inner periphery with grooves or notches 143a, within which pins 142 are engaged; and, along its outer periphery, with a projection 143b and intermediate engaging piece 143c, both of which extend rearwardly along the optical axis direction. A closing spring 144, which continuously biases lens barriers 140 to close the barriers, is provided between projection 143b and pin 145c, which itself is provided on driving ring 145. Driving ring 145 has an outer periphery with a driving arm 145a attached thereto which extends rearwardly along the optical axis direction. Driving arm 145a extends through the gap which exists between cam ring 22 and lens guide ring 24, and includes a pin 146 provided on the front end of driving arm 145a. Pin 146 is fitted into barrier opening and closing cam groove 24c which is formed in lens guide ring 24. Recess 145b is formed on the outer periphery of driving ring 145 so that the intermediate engaging piece 143c of intermediate ring 143 will be fitted into recess 145b. Driving ring 145 is continuously biased by an opening spring 147 which is provided between driving arm 145a and cylindrical lens cover 38 in order to open barriers 140. As a result, pin 146 of driving ring 145 is brought into abutment with barrier opening and closing cam groove 24c by the rotational spring force of opening spring 147. Intermediate engaging piece 143c of intermediate ring 143 is brought into contact with the inner wall of recess 145b of driving ring 145 under the rotational biasing force of closing spring 144; in this fashion, intermediate ring 143 rotates together with driving ring 145. A barrier cover 148, which covers lens barriers 140 and which includes a photographing opening 148a, is attached to the front end of lens cover barrel 38. In a barrier mechanism constructed as detailed above, pin 146 rides on an inclined portion (i.e., a barrier opening and closing drive portion) 24d of the barrier opening and closing cam groove 24c, when the zoom lens is positioned in the accommodation position illustrated in Fig. 18A. In this fashion, driving ring 145 is rotated against the force of opening spring 147 so as to close barriers 140. Consequently, intermediate ring 143 rotates in the closing direction, together with driving ring 145, so as to rotate barriers 140 so that barrier plate portions 140a will close the light path (see Figs. 18A and 19A). When motor 270 rotates, cam ring 22 also rotates and moves along the optical axis direction, as noted above, so that the front lens group moving frame 34 will move forward (with lens cover 38) relative to lens guide ring 24. Since lens cover 38, the driven or intermediate ring 143, and driving ring 145 move forward together with front lens group moving frame 34, pin 146 will move towards the portion of the barrier opening and closing cam groove 24c that extends, parallel to the optical axis, from the inclined portion 24d of the groove 24c. As a result, driving ring 145 is rotated in the barrier opening direction under the rotational biasing force of opening spring 147 so as to rotate the intermediate ring 143 in the same direction, thereby rotating barriers 140 so as to open them (see Figs. 18B and 19B). Thereafter, even if cam ring 22 is rotated from the zooming range into the macro position, pin 146 will come into slidable contact with the portion of the barrier opening and closing cam groove 24c that extends parallel to the optical axis and will thus maintain its rotational or angular position; accordingly, barriers 140 will thus be maintained in their open position. In the embodiment which is illustrated, intermediate ring 143 is positioned between barriers 140 and driving ring 145, and closing spring 144 is positioned between intermediate ring 143 and driving ring 145 to bias the driven intermediate ring 143 towards the barrier closing direction with respect to the driving ring, so that some play (i.e., space) will be provided between the intermediate engaging piece 143c, which functionally connects intermediate ring 143 and driving ring 145, and recess 145b. Thus, when driving ring 145 is rotated in the closing direction, intermediate ring 143 is rotated in the same direction, maintaining abutment of the intermediate engaging piece 143c with one of the inner walls of recess 145b, all under the biasing spring force of closing spring 144. In this fashion, barriers 140 can be rotated into the closed position. When opposed edges of the barrier plate portions 140a of barriers 140 come into contact with each other to stop rotation of barriers 140, intermediate ring 143 will stop rotating. However, driving ring 145 continues rotating further in the closing direction, thus tensing opening spring 144, since the aforementioned play does exist between recess 145b and intermediate engaging piece 143c (due to their relative sizes). The further or excess rotation of driving ring 145, as referred to above, absorbs (i.e., compensates for) possible dimensional or tolerance type errors which arise during manufacturing and assembly of components, in order to completely close barriers 140. It should be appreciated that, as an alternative structure, it will be possible to provide spring members which bias the respective barriers 140 to open the barriers in order to provide play between the pin and the recess which functionally connect barriers 140 and driving ring 145, instead of using intermediate ring 143. I. Driving Mechanism for Cam Ring 22 Male helicoid ring 20 is provided with an outer periphery having a gear 20b with teeth which extend in a direction which is parallel to the optical axis, as illustrated in Figs. 21 and 23. The teeth of gear 20b are formed by grooves defined between adjacent male helicoid teeth or threads 20a, which are spaced at a predetermined distance from each other, as shown in the illustrated embodiment, and are thus positioned along the threads. Gear 20b preferably extends over a greater distance, as viewed in the direction of the optical axis, than do any of male helicoid teeth or threads 20a. At least one of threads 20a, however, can be made longer than others (see, e.g., thread 69 of Fig. 12), is located adjacent to gear 20b, and is used to selectively position optical element 61. This thread has been previously discussed. Motor 254 drives pinion or driving gear 255, which meshes with gear 20b. Motor 254 is attached to a securing plate 256, which is provided with a reduction gear train 257 which transmits rotational force of the output shaft of motor 254 to pinion 255. Securing plate 256 is secured to stationary barrel 12. Barrel 12 and female helicoid ring 18 have respective cutaway portions 258 and 259 for receivably engaging pinion 255 and gear 20b, so that the gear 20b can be engaged by pinion 255 through the cutaway portions. Since gear 20b is formed among male helicoid teeth 20a, as noted above, even if the male helicoid ring 20 moves in the optical axis direction while ring 20 is rotated, in accordance with the lead angle of male helicoid teeth 20a, gear 20b will move along the same angled direction as the adjacent teeth, so that engagement of gear 20b with pinion 255 can be continuously maintained. In other words, the relative positions of gear 20b and pinion 255 are constant, even when ring 20 is rotated. Accordingly, when pinion 255 rotates, gear 20b (i.e. male helicoid ring 20) will rotate and move along the optical axis direction in accordance with the lead angle of male helicoid teeth 20a. Specifically, male helicoid ring 20 is not only rotated in forward and reverse directions by pinion 255, which engages gear 20b, and motor 254 which drives the pinion and gear, but is also moved in the optical axis direction during rotation thereof in accordance with the lead angle of male helicoid teeth 20a. Thus, cam ring 22 is also moved along the optical axis direction while rotating together with the male helicoid ring 20. It should be noted that because gear 20b is formed along the male helicoid teeth 20a, gear 20b is always moved so that it will engaged by pinion 255 in accordance with movement of cam ring 22. As should be noted from the above discussion, because gear 20b is spirally formed along male helicoid teeth 20a, it is not necessary that pinion 255 have teeth which are long enough to cover axial displacement of cam ring 22. As a result, there is no need to provide a large space for accommodating the pinion. Further, because it is necessary to provide the band-like gear 20b only with a width which can be engaged by pinion 255, gear 20b can be formed so that it will be partially superimposed on male helicoid teeth 20a. This makes it possible to provide a code plate, for detecting focal length, on a portion of cam ring 22 that is not covered by gear 20b. In the illustrated embodiment, when motor 254 is driven, male helicoid ring 20 and cam ring 22 are not only rotated through pinion 255 and gear 20b, but are also moved along the optical axis direction in accordance with the lead male helicoid teeth 20a. Accordingly, the tooth surfaces of pinion 255 and gear 20b also come into sliding contact with each other along the optical axis direction. In order to ensure smooth contact and separation of the gear and pinion tooth surfaces, front and rear end edges of pinion 255 can be formed as rounded, as illustrated in Fig. 20. Although the tooth traces of gear 20b and pinion 255 extend along the optical axis direction in the illustrated embodiment, it is also (alternatively) possible to provide gear 20b and pinion 255 which have tooth traces which extend in other directions, e.g., in a direction which is perpendicular to the lead angle of male helicoid tooth 20a. J. Helicoid Engaging Mechanism Female helicoid ring 18 has a partially cutaway portion 90 in which a drive mechanism for rotating cam ring 22 is arranged within the zoom lens barrel, as discussed above. Thus, when the end face of male helicoid ring 20 enters the cutaway portion 90 during rotation of cam ring 22, part of the male helicoid ring 20 will become disengaged from one end face 90a of the cutaway portion 90. Since there is a clearance "c" (which is shown in an exaggerated fashion in Fig. 25) which exists between the female helicoid ring 18 and male helicoid ring 20 (both of which are comprised, e.g., of resinous material), there is a possibility that male helicoid 20b will interfere with the end face 18a of female helicoid 18, which is positioned into the cutaway portion 90 whenever cam ring 22 is reversed, so as to engage the two helicoids. In the worst case situation, rotation of the helicoids may be stopped by the engagement/interference referred to above. One solution to this problem, which forms part of the present invention, is illustrated in Figs. 23-25, in which the improvement is directed to the shape of the helicoid tooth surfaces. End faces 91 of cutaway portion, 90 have inclined surfaces 91a, which serve to define helicoid groove 18b between adjacent helicoid teeth 18a. The groove has a width which gradually increases in a direction towards the cutaway portion or notch 90. Inclined surfaces 91a prevent possible collision of the end faces of the helicoids which might otherwise occur due to the presence of the clearance "c" which is provided between female helicoid ring 18 and male helicoid ring 20 whenever the end face of the male ring 20, which is disengaged from female helicoid ring 18 and cutaway portion 90, comes into engagement with female helicoid ring 18, such that the end face of helicoid teeth 20a of male helicoid ring 20 can be brought into engagement with helicoid groove 18b of the female helicoid ring 18. The end faces of helicoid teeth 18a have inclined surfaces 91b which are similar to the inclined surfaces 91a, and are provided to prevent the above-noted possible collisions between the radial end faces of the female helicoid ring 18 and male helicoid ring 20. Inclined surfaces 91b can be formed by gradually decreasing the height of helicoid teeth 20 towards cutaway portion 90. It is also possible to provide similar inclined surfaces 20c on the end faces of male helicoid ring 20. As a result of tapered surfaces 91a and 91b, the grooves 186 widen, and threads 18a narrow and shorten, in a direction towards the recess or notch 90. With this arrangement, once the cam ring 22 comes to a specific rotational position in which the male helicoid ring 20 is disengaged from female helicoid ring 18 and cutaway portion 90, when the rotation of cam ring 22 has been reversed, the end face of the male helicoid ring 20 will face the end face 91 of the female ring 18 through the cutaway portion 90. At this time, the end faces of helicoid teeth 20a of the male helicoid ring 20 will be directed/conducted into the helicoid grooves 18b through inclined surfaces 91a. Accordingly, the male helicoid ring 20 will mesh with the female helicoid ring 18 in a normal fashion in order to smoothly move the cam ring 22 along the optical axis direction. As a result, there will be no failure of engagement due to the existence of the cut-away portion 90. K. Flange Back Adjusting Mechanism Flange back adjustment is effected by moving all of the lens groups so as to form a focused image on a film plane. Flange back adjustment is effected after zooming adjustment is completed (with no movement of focus being effected during zooming). In a conventional camera, flange back adjustment has been effected, e.g., by inserting a washer having an appropriate thickness between a member which supports the cam ring and the camera body. The present invention is designed to provide an easier flange back adjustment, as is illustrated in Figs. 26-29. In the illustrated embodiments, female helicoid ring 18A is rotatably adjustably supported by stationary barrel 12, so that rotation of the female helicoid ring 18A can change the relative angular position of the male helicoid ring 20 (and, accordingly, the cam ring 22), the rotation of which is restricted, and the female helicoid ring 18A, in order to move both lens group so as to effect flange back adjustment. Stationary barrel 12 has, at its front end, a stationary flange 12a which lies in a plane perpendicular to the optical axis. Female helicoid ring 18A is provided along its outer periphery with a peripheral flange 18d which lies in a plane which is normal to the optical axis and which comes into contact with flange 12a of stationary barrel 12 in order to restrict the axial position of female helicoid ring 18A and to prevent the ring from becoming inclined with respect to the optical axis. A male helicoid ring 20 rotatably engages the inner helicoidal threads or teeth 18a of ring 18A, as in the above-noted and described embodiments. Female helicoid ring 18A is immovably held by a C-shaped leaf spring 318 which is secured to stationary flange 12a by screens 317, in order to prevent it from moving in the optical axis direction. Leaf spring 318 has a plurality of elastically deformable tongues 318a which are elastically brought into contact with flange 18d. As a result, due to the friction which exists between flange 18d, flange 12a and leaf spring 318, rotation of female helicoid 18A is restricted. However, the female helicoid ring 18A can be rotated against the frictional force when an external force which overcomes the friction is applied thereto. Flange 18d includes a partial sector gear 18e which is provided on the outer periphery of the flange. Stationary flange 12a includes a shaft bearing hole 12g in which shaft 352 of a flange back adjusting jig (i.e. tool) 350 is inserted, in the vicinity of sector gear 18e. Flange back adjusting tool 350 has a pinion (i.e., an adjusting gear) 351 which is adapted to be engaged by sector gear 18e. Lock screw 319 is provided on stationary flange 12a in the area of shaft bearing hole 12g. Lock screw 319 includes a head surface 319a which is adapted to be brought into contact with flange 18d at the underside or surface of head 319a. In this fashion, whenever lock screw 319 is fastened, flange 18d can be firmly held between and by head 319a of lock screw 319, and stationary flange 12a, in order to prevent rotation of the female helicoid ring 18a. Further, when lock screw 319 is loosened, head 319a will become separated from flange 18d to permit the female helicoid ring 18a to rotate. Decorative plate 411 of camera body 410 has an insertion hole 411a into which the flange back adjusting tool 350 can be inserted so that it will be positioned oppositely with respect to shaft bearing hole 12g of stationary flange 12a. Insertion hole 411a is covered by a removable cap 415, as shown in Figs. 28 and 29. The other construction of the embodiment illustrated in Figs. 26-29 is essentially the same as that disclosed above with respect to the zoom lens barrel, i.e., wherein female helicoid ring 18A is connected to male helicoid ring (the inner ring) 20 to which cam ring 22 is secured. After flange back adjustment by the flange back adjusting mechanism noted above, cam ring 22 is rotated into a photographing position in which a picture can be taken, such as the WIDE extremity position, so that the lock screw 319 can be loosened after cap 415 is removed. Thereafter, the flange back adjusting tool is inserted into the insertion hole 411a of decorative plate 411 in order to engage gear or pinion 351 of shaft 352 of tool 350 with sector gear 18e, as shown in Fig. 27. Thereafter, flange back adjusting tool 350 is rotated so that the actual focal point will approach the theoretical focal point on the film plane, while viewing the actual focal point at the WIDE extremity. As a result, since the male helicoid ring 20 is restricted or prevented from rotating by the pinion which is engaged by gear 20b and the motor, only the female helicoid ring 18A will rotate, with the result that relative rotation of the female helicoid ring 18A with respect to the male helicoid ring 20 will cause the male helicoid ring 20 to move in the optical axis direction, in accordance with the lead angle of the helicoid teeth 20a. Thus, both lens groups L1 and L2 move together along the optical axis direction without changing the distance between them in order to adjust the focal point, i.e., the flange back. After flange back adjustment is completed, lock screw 319 is again fastened so as to lock female helicoid ring 18A. Thereafter, the flange back adjusting tool 350 is removed and insertion hole 411a is covered by cap 415. As can be easily understood from the above, flange back adjustment can be easily effected even after the camera is assembled. Although the flange back adjusting tool 350 has a pinion gear 351 as in the embodiment which is illustrated and referred to above, it is possible (as shown in Fig. 27A) to provide a gear 351A (instead of tool pinion 351) which can be engaged by sector gear 18e, on stationary flange 12a instead of on the tool 350. Gear 351A can be, e.g., frictionally fit on a shaft which is attached to the flange 12a. By providing a secure frictional fit, such that the gear 351A can only be rotated upon the application of a suitable force by a screwdriver, e.g., it should be noted that lock screw 319 can be eliminated. In such a case, the gear which is provided on stationary flange 12a would have, e.g., a cross-shaped groove or a (+) into which a screwdriver can be fitted. The screwdriver would then be used in lieu of the tool described above, e.g., and would be used to rotate gear 351A, and, therefore, sector gear 18e. This alternative construction essentially corresponds to an arrangement in which pinion 351 is rotatably supported within shaft bearing hole 12g of stationary flange 12a, and in which the shaft portion of pinion 351 would have an insertion hole for receiving the flange back adjusting tool as shown in Fig. 27. Section gear 18e and shaft bearing hole 12g can be located at optional positions, e.g., on the left side portion or the lower side portion of camera body 410. Although the present invention has been specifically described with respect to specific embodiments thereof, the embodiments are to be considered illustrative only and not restrictive, and various modifications and changes may be made without departing from the scope of the claims appended hereto.

Claims: A drive mechanism for a zoom lens adapted to be attached to a camera having an optical axis, the drive mechanism comprising: a stationary barrel (12), a rotatable cam ring (22) supported by said stationary barrel (12) and including camming means (41, 42) which are adapted to receive at least one movable lens group (15, 16) and to determine the axial positions of said movable lens group (15, 16), wherein said cam ring (22) is movable parallel to said optical axis in association with its rotation, and a non rotatable lens guide ring (24) which has at least one lens guide groove (43, 44), characterized in that said non rotatable lens guide ring (24) is adapted to be moved together with said cam ring (22) by the same distance, parallel to said optical axis, the camming means (41, 42) and the at least one lens guide groove (43, 44) being shaped such that said at least one lens group (15, 16) can be moved along a predetermined track by the movement resulting from axial movement of and relative rotation between the cam ring (22) and the lens guide ring (24). The drive mechanism of claim 1, characterized by at least two cam grooves (41,42) adapted to receive movable front and rear lens groups (15,16),at least one of said cam grooves (41,42) being located on said cam ring (22); and at least one guide pin (35,36) for each lens group (15,16) which is adapted to extend through one cam groove (41) and an associated lens guide groove (43), wherein said cam grooves (41,42) and said lens guide grooves (43,44) comprise means for guiding movement of said movable lens groups (15,16) along a predetermined path in association with axial movement and relative rotation of said cam ring (22) and said lens guide ring (24). The drive mechanism of claim 1 or 2, characterized by said cam ring (22) moving said zoom lens between a normal photographing range and a macro-photographing range and being connected to said stationary barrel (12) via a helicoid (20) positioned on said cam ring (22), an optical element (61) for close distance correction being associated with said cam ring helicoid (20) such that said mechanism comprises means for moving said close distance correcting optical element (61) away from the optical axis of a light receiver (72) when said zoom lens is located in said normal photographing range, and for bringing said close distance correcting optical element (61) into the optical axis of said light receiver (72) when said zoom lens is located in a macro photographic range. A drive mechanism according to claim 1, 2 or 3, characterized by a flexible printed circuit board (81) a shutter block (32) adapted to move together with said at least one movable lens group (15,16) parallel to said optical axis, a control circuit (54) comprising means for driving and controlling said shutter block (32), said flexible printed circuit board (81) comprising means for electrically connecting said shutter block (32) and said control circuit (54), said flexible printed circuit board (81) having at least one portion extending rearwardly, within said barrel (12), from said control circuit (54) to a rear end of said lens guide ring (24), said circuit board (81) having a second portion extending forwardly along an inner surface of said lens guide ring (24), said second portion being connected to said at least one portion, wherein a third portion of said flexible printed circuit board (81) extends rearwardly from said second portion to superimpose said second and third circuit board portions, and a fourth portion of said flexible printed board (81) extends forwardly to connect said circuit board (81) to said shutter block (32), wherein said third and fourth flexible printed circuit board portions are connected to each other. The drive mechanism of anyone of the foregoing claims, characterized by a cylindrical lens cover (38) which is adapted to move, in association with said lens groups (15,16), along said optical axis direction; barriers (140) in said lens cover (38) which are adapted to open and close a photographic opening located forwardly of said movable lens groups (15,16); and a barrier opening and closing mechanism positioned in said lens cover (38) and comprising means (143,145) for opening and closing said barriers (140) in association with relative movement of said lens guide ring (24) and said lens cover (38). The drive mechanism of anyone of claims 1 to 5, characterized by said stationary barrel (12) having an inner surface with a plurality of guide grooves (27) for receiving said lens guide ring (24), said lens guide ring (24) including a guide plate (26) attached to said lens guide ring (24) having guide projections which are adapted to be fitted into said guide grooves (27), wherein at least one of said guide projections is elastically deformable in the direction of the width of said barrel guide grooves (27). The drive mechanism of anyone of claims 1 to 6, characterized by said stationary barrel (12) including a female helicoid (18); said cam ring (22) having a male helicoid (20) which is adapted to be engaged by said female helicoid (18); a cam ring gear (20b) which extends along teeth of said cam ring male helicoid (20); and a cam ring driving mechanism (254,255) having a driving gear (255) which is adapted to be engaged by said cam ring gear (20b). The drive mechanism of claim 7, characterized by, said female helicoid (18) having a cutaway portion (90) for separating engagement of said male (20) and female helicoid (18) at a predetermined angular position of said cam ring (22), wherein at least one of said female and male helicoids (18,20) have teeth (18a) which are adjacent to said cutaway portion (90), said adjacent teeth (18a) having end faces (91b) with tapered surfaces which gradually increase the width of at least one helicoid groove (18b) defined by said adjacent teeth (18a). The drive mechanism of anyone of claims 1 to 8, characterized by a flange back adjusting mechanism comprising an outer ring (18A) adapted to be attached to said stationary barrel (12), between said barrel (12) and said cam ring (22), said outer ring (18A) being rotatably adjustable, said mechanism further comprising means (18a) for threadably engaging said outer ring (18A) with said cam ring (22). The drive mechanism of claim 7, 8 or 9, characterized by, said cam ring gear (20b) being inclined with respect to its cross-section. The drive mechanism of anyone of claims 1 to 10, characterized by a female helicoid ring (18) comprising: a generally cylindrical body; a plurality of generally helical, parallel threads (18a) on an interior peripheral surface of said body; a recess (50) on said interior surface; and an electrically conductive brush (51) having a base (52) and a plurality of flexible bristles, said base (52) being attached to said recess (50). The drive mechanism of anyone of claims 3 to 11, characterized by, said cam ring (22) having a plurality of threads (69) on an exterior cam ring surface, said threads (69) comprising means for selectively engaging said optical element (61) during rotation of said cam ring (22). The drive mechanism of anyone of claims 4 to 12, characterized by, said annular guide ring (24) having at least one elongated groove (82) for retaining said flexible printed circuit board (81). The drive mechanism of claim 7, wherein one of said stationary barrel and said cam ring (12,22) has a cutaway portion (90) for separating engagement of said male (20) and female helicoid (18) at a predetermined angular position of said members (12,22), wherein said one member (18) has teeth (18a) which are adjacent to said cutaway portion (90), said adjacent teeth (18a) having end faces (91b) with tapered surfaces which gradually decrease the width of the adjacent teeth (18a) and increase the width of a groove (18b) defined between said adjacent teeth (18a), in a direction towards said cutaway portion (90).

Inventors: NOMURA HIROSHI, NOMURA, HIROSHI
Applicants: ASAHI OPTICAL CO LTD, ASAHI KOGAKU KOGYO KABUSHIKI KAISHA
Application year: 1989
Main classification: G02B7
IPC codes: G02B7