Zoom lens

Abstract: The invention relates to a zoom lens for a camera comprising: a) a stationary barrel (12) which is adapted to be secured to a camera body (11) having an optical axis; b) a cam ring (22) supported by said stationary barrel (12) for movement along an optical axis; c) a lens guide ring (24) adapted to move together with said cam ring (22) along said optical axis; d) at least two movable lens groups (15, 16) which are adapted to be supported by said cam ring (22) and said lens guide ring (24) to move, with respect to each other, along said optical axis; and e) a flange back adjusting mechanism comprising an outer ring (18) adapted to be attached to said stationary barrel (12) radially between said barrel (12) and said cam ring (22), said outer ring (18) being rotatably adjustable, said mechanism further comprising means for threadably engaging said outer ring (18) with said cam ring (22).

Description: This invention relates to a zoom lens according to the generic part of the independent claim. A zoom lens of this kind is described in US-A-4 681 406. Recently developed compact cameras have minimised their width and height dimensions to limits which are essentially set by the film size and the camera aperture size. Therefore, cameras of this kind do not have an interchangeable lens but a fixedly built-in lens. During assembly of the camera in the factory a so-called flange back adjustment is required in order to provide a focused image on the film plane by moving all lens groups in common after zooming adjustment is completed. Heretofore, flange back adjustment has been effected by inserting a washer having an appropriate thickness between the lens barrel and the camera body. The problem to be solved by the present invention is to provide an easier flange back adjustment which can also be done after the camera assembly. The invention solves this problem by the features described in the independent claim. Advantageous further developments are described in the dependent claims. According to the invention, the position of the zoom lens with respect to the film plane in the camera can be adjusted by simply rotating the female helicoid ring by an external force overcoming its holding force, whereby the lens groups of the zoom lens are moved in optical axis direction as a whole until the actual focal point approaches the theoretical focal point on the film plane while viewing the actual focal point. In this way the focal point can be very easily adjusted even after the camera is assembled. 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, 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 exploded perspective view of a zoom lens barrel mechanism as shown in Figs. 1-4, in combination with a flange back adjusting mechanism; Fig. 7 is a front elevational view of a part of the mechanism of Fig. 6, illustrating adjustment of the flange back using an adjusting tool; Fig. 7A is a front elevational view of an alternate embodiment of the mechanism illustrated in Fig. 7; Fig. 8 is a perspective view of a camera having a flange back adjusting mechanism; and Fig. 9 is a longitudinal sectional view of a zoom lens barrel including the flange back adjusting mechanism illustrated in Fig. 6. The present invention will now be discussed in greater detail with specific reference to the drawings which are attached hereto. 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 sane 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 rigure 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. 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. 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 lla 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 grcove 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. 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. 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. 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, moving lenses 15 and 16 could not be retracted. 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. 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. 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. 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 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 screws 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. 8 and 9. The other construction of the embodiment illustrated in Figs. 6-9 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. 7. 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. 7A) 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. 7. 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.

Claims: A zoom lens comprising: a) a stationary barrel (12) which is adapted to be secured to a camera body (11) having an optical axis; b) a cam ring (22) supported by said stationary barrel (12) for movement along an optical axis direction of a camera in association with rotation of said cam ring (22); c) a lens guide ring (24) arranged to move together with said cam ring (22) along said optical axis direction, said cam ring (22) and said lens guide ring (24) being adapted to rotate relative to each other in association with axial movement of said cam ring (22); d) at least two movable lens groups (15, 16) which are supported by said cam ring (22) and said lens guide ring (24) to move, with respect to each other, along said optical axis direction in association with axial movement and relative rotation of said cam ring (22) and said lens guide ring (24) along a predetermined track, said cam ring (22) and said lens guide ring (24) constitute means for changing the focal length of said zoom lens; characterized by e) an adjusting mechanism comprising a rotatably adjustable female helicoid ring (18A) attached to said stationary barrel (12) and threadably engaging said cam ring (22); and f) said female helicoid ring (18A) being held against rotation on said stationary barrel (12) and being rotatably adjustable by an external force overcoming its holding force. A zoom lens in accordance with claim 1, wherein said female helicoid ring (18) includes an outwardly projecting flange (18d) in a plane perpendicular to said optical axis, said flange (18d) having a circumferential edge and a sector gear (18e) on said circumferential edge, said stationary barrel (12) including a stationary flange (12a) in slidable contact with said outer ring flange (18d). A zoom lens in accordance with claim 2, wherein said stationary flange (12a) includes a shaft bore (12g) for inserting the shaft of a flange adjusting tool (350). A zoom lens in accordance with claim 2 or 3, wherein an adjusting gear (351A) is frictionally positioned on a shaft which is attached to said stationary flange (12a). A zoom lens in accordance with anyone of the foregoing claims, wherein said cam ring (22) has an attached helicoid ring (20), said attached helicoid ring (20) having an outer periphery with helicoid teeth which are adapted to be engaged by helicoid teeth of said female helicoid ring (18A).

Inventors: NOMURA HIROSHI, NOMURA, HIROSHI, NOMURA, HIROSHI, C/O ASAHI KOGAKU KOGYO K.K.
Applicants: ASAHI OPTICAL CO LTD, ASAHI KOGAKU KOGYO KABUSHIKI KAISHA
Application year: 1989
Main classification: G02B7
IPC codes: G02B7, G03B17