Apparatus for selectively positioning a correcting optical element in a camera

Abstract: The invention relates to an apparatus for a camera for selectively positioning a correcting optical element (61) used during macro-photography in front of the light receiver (72) of a distance measuring device. The camera has a generally cylindrical rotatable cam ring (22) as a part of its lens. The cam ring (22) has 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).

Description: The present invention relates to a camera wherein a cylindrical cam ring can be rotated about the optical axis to change the focal length of a zoom lens. A camera of this kind is described in WO-A-87/07038. This camera also has a correcting optical element which can be selectively positioned during macro-photography in front of the light receiver of a distance measuring device, whereas in the normal photographic mode it is biased away from the optical axis of the distance measuring device into a retracted position. Movement of the correcting optical element is effected by means of a projection on the cam ring which engages a flag projection on the correcting optical element as soon as the cam ring is rotated into its macro-position so that the correcting optical element is automatically brought into its correcting position. The cam ring of the above-mentioned zoom lens cannot be moved in optical axis direction. For a lens wherein the cam ring is rotated and moved along the optical axis, the known mechanism cannot be used to control the correcting optical element since said element only moves upon a rotational movement of the cam ring and of its projection. The problem to be solved by the present invention is to provide for selectively positioning a correcting optical element in a camera by means of a rotatable cam ring which moves in optical axis direction. The invention solves this problem by an apparatus described in the independent claim. Advantageous further developments are described in the dependent claims. The camera of the present invention utilises the helicoid threads on the outer periphery of the cam ring to move the correcting optical element into its correcting position. The helicoid thread guides the cam ring in optical axis direction into the macro-position during its rotation within a stationary lens barrel. One of the helicoid teeth holds the correcting optical element in its retracted position as long as the cam ring is in the normal photographing range. When the cam ring reaches the macro position in optical axis direction, the helicoid tooth disengages the correcting optical element so that it is biased into its correcting position. 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 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. 7 is a front elevational view of the apparatus illustrated in Fig. 6; Figs. 8A and 8B are a front elevational view of the close distance correcting optical element shown in Fig. 6, in inoperative and in operative positions, respectively. 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 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. 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 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. 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 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. 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. 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. 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. 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. As illustrated in Figs. 6-8, 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, 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 8A) 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. 8A. 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. 8B. 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.

Claims: A camera comprising a zoom lens, a light receiver (72) of a distance measuring device (70) a correcting optical element (61) arranged to be used during macro-photography in front of the light receiver (72) said zoom lens having a generally cylindrical rotatable cam ring (22), said cam ring (22) having a helicoid thread (20a) on an exterior cam ring surface, said thread (20a) being arranged to guide said cam ring (22) in optical axis direction between a normal photographing range and a macro position during its rotation within a stationary lens barrel (12) and comprising one helicoid tooth (69) arranged to selectively move said optical element (61) during movement of said cam ring (22) in the normal photographing range into a position retracted from the optical axis of said distance measuring device (70), said optical element (61) being biased by a spring (67) into a position in front of said light receiver (72). The camera in accordance with claim 1, wherein said light receiver (72) and said optical element (61) are positioned in a recess (12e) on said stationary lens barrel (12a), said recess (12e) having a lower opening (12f) through which a projection (68) on said optical element (61) is arranged to extend, such that said projection (68) will selectively engage said helicoid tooth (69) during rotation of said cam ring (22) in the normal photographing range. The camera in accordance with claim 1 or 2, wherein said helicoid tooth (69) has a cutaway portion (69a) corresponding to the macro position of said cam ring (22).

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