Lens barrel

A lens barrel includes an optical system including a short focal length for a wide angle of view; and an ND filter in the shape of a disc which is provided on an optical axis of the optical system. An optical density of the ND filter decreases in a direction radially outwards from a center of the ND filter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens barrel which includes a short focal length for a wide angle of view.

2. Description of the Related Art

Compact zoom cameras having a zoom lens whose focal length at the wide-angle extremity is approximately 28 mm, 35 mm or 38 mm have been popularized in recent years.

Such conventional compact zoom cameras have a problem where the illumination of the marginal area of an image is smaller than that of the center of the image due to the optical properties of the lens. Specifically, in compact cameras the vignetting factor tends to be small (approximately 50 percent, image height≈0.9Y) due to the lens design, thus resulting in a lack of light quantity of marginal rays even if the diaphragm is set to a small aperture.

To combat this problem, a compact zoom camera in which an iris diaphragm is incorporated in a shutter unit has been produced. However, such a shutter unit is complicated in structure and difficult to be controlled, which may cause deterioration in precision of the aperture size to thereby lose half the initial effect of adopting the diaphragm shutter.

To combat this problem, another type of compact zoom camera has been produced having a zoom lens to which modifications are made (e.g., redesigning the zoom lens a large-diameter zoom lens). However, such a modification inevitably increases the size of the compact zoom camera.

SUMMARY OF THE INVENTION

The present invention provides a lens barrel having a simple structure, which minimizes reduction in light quantity of marginal rays.

According to an aspect of the present invention, a lens barrel is provided, including an optical system including a short focal length for a wide angle of view; and an ND filter in the shape of a disc which is provided on an optical axis of the optical system; wherein an optical density of the ND filter decreases in a direction radially outwards from a center of the ND filter.

It is desirable for the ND filter to include a high optical density portion in the shape of a circle which is provided at a center of the ND filter; and a low optical density portion provided around the high optical density portion. A diameter of the high optical density portion is smaller than effective aperture of the optical system.

It is desirable for the ND filter to be fixed to a lens frame which supports at least one lens element of the optical system.

The optical system can include a plurality of lens groups which are fixed to a corresponding plurality of lens frames, the ND filter being fixed to one of the plurality of lens frames.

The lens barrel can further include a shutter unit, wherein the ND filter is fixed to the shutter unit.

It is desirable for the ND filter to include a transparent optical element; and a coating which is applied to a surface of the transparent optical element. A diameter of the coating is smaller than the effective aperture of the optical system.

It is desirable for the ND filter to include at least two portions having different optical densities.

The transparent optical element can be in the shape of a disc.

The lens barrel can be a zoom lens or a telescoping type zoom lens.

It is desirable for the high optical density portion to include at least two portions having different optical densities which are arranged concentrically with respect to the center of the ND filter.

In another embodiment, a lens barrel is provided, including an optical system including a short focal length for a wide angle of view; and an ND coating applied to at least one lens element of the optical system; wherein an optical density of the ND coating decreases in a direction radially outwards from an optical axis of the lens element.

It is desirable for the ND coating to include a high optical density portion in the shape of a circle which is positioned at a center of the ND coating, and a low optical density portion positioned around the high optical density portion. A diameter of the high optical density portion is smaller than effective aperture of the optical system.

The optical system can include a plurality of lens groups. The ND coating is applied to a frontmost lens group of the plurality of lens groups.

The optical system can include a plurality of lens groups. The ND coating is applied to a rearmost lens group of the plurality of lens groups.

It is desirable for the ND coating to be in the shape of a circle having a diameter smaller than the effective aperture of the optical system.

It is desirable for the ND coating to include at least two portions having different optical densities.

The optical system can include a plurality of lens groups, the ND coating being applied to one of the plurality of lens groups.

The lens barrel can be a zoom lens or a telescoping type zoom lens.

It is desirable for the high optical density portion to include at least two portions having different optical densities which are arranged concentrically with respect to the center of the ND coating.

In another embodiment, a photographing lens is provided, including a plurality of lens elements, and at least one ND filter positioned on an optical axis of the plurality of lens elements. An optical density of the ND filter decreases in a direction radially outwards from the optical axis.

The ND filter can be provided as a disc-shaped filter provided separately from the plurality of lens elements.

The ND filter can be provided as a coating applied to at least one of the plurality of lens elements.

The present disclosure relates to subject matter contained in Japanese Patent Applications Nos. 2002-351713 and 2002-351714 (both filed on Dec. 3, 2002) which are expressly incorporated herein by reference in their entireties.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 through 2Cshow a first embodiment of a lens barrel according to the present invention. As can be appreciated fromFIGS. 1 through 2C, the lens barrel50is a telescoping type zoom lens of a camera which is provided with four external telescoping barrels: a first external barrel (lens support barrel)17, a second external barrel (cam ring)19, a third external barrel21and a fourth external barrel24which are concentrically arranged about an optical axis55aof a photographing optical system55of the lens barrel50. The photographing optical system55of the lens barrel50includes a first lens group (lens element)1, a second lens group (lens element)2, a third lens group (lens element)3, a diaphragm (diaphragm blades)14, a shutter (shutter blades)15, a fourth lens group (lens element)4, and a fifth lens group (lens element)5, in that order from the object side (the left side as viewed inFIG. 1). The lens barrel50is provided around the fourth external barrel24with a housing38which supports the first through fourth external barrels17,19,21and24so that each of the first through fourth external barrels17,19,21and24can move forward and rearward with respect to each other along the optical axis55a. In the following descriptions, the front side and the rear side refer to the object side (the left side as viewed inFIG. 1) and the film side (the right side as viewed inFIG. 1), respectively.

The fourth external barrel24is coupled to the housing38by engagement of a male helicoid with a female helicoid which are formed on the fourth external barrel24and the housing38, respectively. Likewise, the third external barrel21is coupled to the fourth external barrel24by engagement of a male helicoid with a female helicoid which are formed on the third external barrel21and the fourth external barrel24, respectively. Likewise, the second cam ring19is coupled to the third external barrel21by engagement of a male helicoid with a female helicoid which are formed on the cam ring19and the third external barrel21, respectively. The first external barrel (lens support barrel)17is coupled to the cam ring19by a cam mechanism provided therebetween.

The fourth external barrel24is fitted into the housing38, and a second helicoid ring25is fixed to a rear end surface of the fourth external barrel24. The second helicoid ring25is engaged with an axial groove38aparallel to the optical axis55aformed on an inner peripheral surface of the housing38. Due to this engagement of the second helicoid ring25with the axial groove38a, the fourth external barrel24, together with the second helicoid ring25, can move along the optical axis55awith respect to the housing38.

The lens barrel50is provided inside the fourth external barrel24with a third linear guide ring23which is fitted into the fourth external barrel24. The third linear guide ring23is provided on an inner peripheral surface thereof with a plurality of inclined lead slots23awhich are inclined with respect to the optical axis direction (i.e., the direction parallel to the optical axis55a). The third external barrel21is fitted into the third linear guide ring23, and a first helicoid ring22is fixed to a rear end of the third external barrel21. The fourth external barrel24is provided on an inner peripheral surface thereof with a plurality of linear guide grooves24a(only one of them appears inFIG. 1) which extend parallel to the optical axis55a. A plurality of guide followers29(only one of them appears inFIG. 1) which are fixed to an outer peripheral surface of the first helicoid ring22pass through the plurality of inclined lead slots23ato be engaged in the plurality of linear guide grooves24a, respectively. With this engagement of the guide followers29with both the inclined lead slots23aand the linear guide grooves24a, the third external barrel21and the first helicoid ring22are linearly guided by the third linear guide ring23in the optical axis direction.

The lens barrel50is provided radially inside the third external barrel21with a second linear guide ring20which is fitted into the third external barrel21. The second linear guide ring20is provided with two inclined lead slots20awhich pass through the second linear guide ring20and are inclined with respect to the optical axis direction (i.e., the direction parallel to the optical axis55a). The third external barrel21is provided on an inner peripheral surface thereof with two rotation transmitting grooves21a(only one of them appears inFIG. 1) which extend parallel to the optical axis55a. Two guide followers28(only one of them appears inFIG. 1) which are fixed to an outer peripheral surface of the cam ring19at equi-angular intervals (i.e., at intervals of 180 degrees) in a circumferential direction of the cam ring19pass through the two inclined lead slots20ato be engaged in the two rotation transmitting grooves21a, respectively. Due to the engagement of the guide followers28with both the inclined lead slots20aand the rotation transmitting grooves21a, the cam ring19is linearly guided by the second linear guide ring20in the optical axis direction.

The lens barrel50is provided inside the cam ring19with a first linear guide ring18. The first linear guide ring18is supported by the cam ring19to move together with the cam ring19while allowing the cam ring19to rotate with respect to the first linear guide ring18. The first linear guide ring18is provided at a rear end thereof with a plurality of linear guide projections18awhich project radially outwards to be engaged in a plurality of linear guide grooves20bformed on an inner peripheral surface of the second linear guide ring20. This engagement of the linear guide projections18awith the linear guide grooves20ballows the first linear guide ring18to move linearly in the optical axis direction without rotating with respect to the second linear guide ring20.

The lens barrel50is provided inside the cam ring19with a lens support ring17, and is provided inside the lens support ring17with a rear lens frame9. The lens support ring17and the rear lens frame9are linearly guided in the optical axis direction by the first linear guide ring18. A rotation of the cam ring19relative to the lens support ring17causes the lens support ring17to move forward from the cam ring19in accordance with contours of a set of three cam grooves19bformed on an inner peripheral surface of the cam ring19. The set of three cam grooves19bare formed on an inner peripheral surface of the cam ring19in the vicinity of the rear end thereof at equi-angular intervals in a circumferential direction of the cam ring19. A set of three cam followers pins27radially extend through the lens support ring17at equi-angular intervals in a circumferential direction of the lens support ring17, and are fixed to the lens support ring17so that radially outer ends of the set of three cam followers pins27are engaged in the set of three cam grooves19b. A set of three cam follower rollers26are fixed to an outer peripheral surface of the lens support ring17to project radially outwards to be engaged in the set of three cam grooves19bso that a rotation of the cam ring19with respect to the lens support ring17causes the lens support ring17to move along the optical axis55ain a predetermined moving manner due to the engagement of the three cam follower rollers26with the three cam grooves19b.

The lens barrel50is provided inside the lens support ring17with a shutter unit (AF/AE shutter unit)16having the diaphragm14and the shutter15. The lens barrel50is provided inside the shutter unit16with a front lens frame6and a middle lens frame7which are supported by the shutter unit16to be movable along the optical axis55arelative to the shutter unit16. The first lens group1is supported by the front lens frame6to be fixed thereto. The second lens group2and the third lens group3are supported by the middle lens frame7to be fixed thereto with a spacer ring8being provided between the second lens group2and the third lens group3. The front lens frame6and the middle lens frame7are supported by the shutter unit16to be movable relative to each other along the optical axis55a.

The set of three cam follower pins27, which radially extend through the lens support ring17, are fixed at their radially inner ends to an outer peripheral surface of a rear lens frame moving ring10which is positioned inside the lens support ring17in the vicinity of the rear end thereof. The rear lens frame9is screwed into a rear end portion of the rear lens frame moving ring10. The fourth lens group4and the fifth lens group5are supported by the rear lens frame9to be fixed thereto. Movement of the set of three cam follower pins27in the set of three of three cam grooves19btherealong causes the rear lens frame9to move along the optical axis55a. The fourth lens group4is fixed to the rear lens frame9by a fourth lens group pressing ring12which is fitted on a front end of the rear lens frame9. The fourth lens group4and the fifth lens group5are supported by the rear lens frame9to be fixed thereto with a spacer ring11being interposed between the fourth lens group4and the fifth lens group5.

As shown inFIGS. 2A,2B and2C, by moving the front lens frame6, the middle lens frame7and the rear lens frame9along the optical axis55arelative to one another, the lens barrel50changes between an accommodated position (shown inFIG. 2A) and an wide-angle extremity (shown inFIG. 2B), and can change the focal length between the wide-angle extremity (shown inFIG. 2B) and the telephoto extremity (shown inFIG. 2C). Although the focal length of the photographing optical system55at the wide-angle extremity is set to 20 mm (35 mm film camera conversion) in the present embodiment of the lens barrel, reduction in light quantity of marginal rays can be minimized if the focal length of the photographing optical system55at the wide-angle extremity is set to a focal length in a wide-angle range between 20 mm and 38 mm (35 mm film camera conversion). The shutter unit16drives the front lens frame6and the middle lens frame7forward and rearward along the optical axis55awhile changing the space therebetween to perform a focusing operation.

The lens barrel50is provided at the front end of the lens support frame17with a lens barrier mechanism which automatically closes a front end aperture of the lens barrel50when the lens barrel50is retracted into the camera body as shown inFIG. 2A, i.e., when the lens barrel50is not in use. The lens barrier mechanism is provided with a decorative plate30which is fixed to the front end of the lens support frame17, and is further provided immediately behind the decorative plate30with a pair of barrier blades31and32, each of which is pivoted on an associated pivot (not shown) formed on a rear surface of the decorative plate30. When the power of the camera is turned ON and OFF, the pair of barrier blades31and32rotate together about the respective pivots to open and close a front end aperture of the lens barrel50which is formed on the decorative plate30.

The lens barrel50is provided at the rear end of the rear lens frame9with a light shield frame13having a rectangular aperture (seeFIGS. 3A and 4) which is fixed to the rear end of the rear lens frame9. The lens barrel50is provided immediately behind the rear lens frame9with a circular ND (neutral density) filter60in the shape of a disc which is fixed to a rear end surface of the light shield frame13so that a center65of the ND filter60is positioned on the optical axis55a.

As shown inFIG. 3B, the disc-shaped ND filter60is provided on the outer edge thereof with an annular filter frame61having an outer diameter substantially the same as the outer diameter of the light shield frame13. The disc-shaped ND filter60has three concentric filter portions which are formed concentrically with respect to the center65. These three concentric filter portions are a first ND portion62(diameter=dND1) serving as a central ND portion, a second ND portion63(diameter=dND2)positioned around the first ND portion62, and a third ND portion64(diameter=d0) positioned around the second ND portion63. The optical density (reflectance) of the first ND portion62is higher than those of the other two ND portions63and64. The optical density (reflectance) of the second ND portion63is slightly lower than that of the first ND portion62, but is still high so that the first ND portion62and the second ND portion63constitute a high optical density portion of the ND filter60. The optical density of the third ND portion64is much lower than that of the second ND portion63; the third ND portion64serves as a low optical density portion having a reflectance of substantially zero. The first ND portion62, the second ND portion63and the third ND portion64are provided as coatings applied to a transparent disc made of a transparent material such as glass or plastic.

Accordingly, the optical density of the ND filter60decreases stepwise in a direction radially outwards from the center65. Namely, the reflectance of the ND filter60decreases in a direction radially outwards from the center65as shown inFIG. 3C. As another embodiment of the ND filter60, the ND filter60can be modified so that the optical density decreases continuously or discontinuously in a direction radially outwards in each of the first through third ND portions62through64. In addition, the ND filter60only needs to be formed to include two or more ND portions having different optical densities; for instance, the third ND portion64can be a non-ND portion to which no coating is applied.

A broken line shown inFIG. 3Aindicates an outermost light path of the light rays of an object which pass through the outermost regions of the fourth and fifth lens groups4and5. Therefore, the effective aperture of the ND filter60is set to the diameter (d0) of the third ND portion64which is slightly smaller than the inside diameter (D) of the annular filter frame61. The diameter of the high-optical density portion of the ND filter60, i.e., the diameter (dND2) of the second ND portion63, is set to be smaller than the effective aperture of the photographing optical system which is shown by a broken line shown inFIG. 3A.

Due to the above described structure of the ND filter60, the light rays which are passed through the outer regions of the first through fifth lens groups1through5of the photographing optical system55pass through the third ND portion64(which has a low reflectance) while the light rays which are passed through a central portion of the first through fifth lens groups1through5of the photographing optical system55pass through either the first ND portion62or the second ND portion63(each of which is high in optical density (reflectance)). Therefore, with the ND filter60, the light quantity of the light rays which are passed through a central portion of the photographing optical system55to be incident on a film surface (not shown) is reduced with a minimum reduction of the light quantity of the light rays which are passed through a marginal portion of the photographing optical system55. Consequently, the difference between marginal rays and central rays becomes smaller by the ND filter60.

FIGS. 5A and 6show another embodiment of the placement of the ND filter60, andFIGS. 5B and 7show yet another embodiment of the placement of the ND filter60.

Although the ND filter60is fixed to a rear end surface of the light shield frame13in the above illustrated embodiment of the lens barrel, the ND filter60can be fixed to a front end surface of the fourth lens group pressing ring12as shown inFIGS. 5A and 6, or provided between the spacer ring11and the fifth lens group5to be fixed therebetween as shown inFIGS. 5B and 7, as long as the center65of the ND filter60is positioned on the optical axis55a. With this arrangement, the difference between marginal rays and central rays becomes smaller.

The ND filter60can also be applied to any lens barrel other than the above described lens barrel50which has an optical system having five lens groups. Furthermore, the ND filter60can be applied to a telescoping type zoom lens provided with three or less than three external telescoping barrels, or five or more than five external telescoping barrels. Alternatively, the ND filter60can be applied to a fixed-focal-length lens having a short focal length for a wide angle of view.

Although a single ND filter is used in the above illustrated embodiment of the lens barrel, two or more ND filters can be placed on the optical axis55a.

FIGS. 8A and 9show another embodiment of the placement of the ND filter60.

The front lens frame6is provided, on an inner peripheral surface thereof at its approximate center in the optical axis direction, with an protrusion70which projects radially inwards to contact with a marginal portion of the rear surface of the first lens group1to determine the position of the first lens group1in the optical axis direction relative to the front lens frame6. As shown inFIG. 8A, the ND filter60is fixed to a rear end surface70aof the protrusion70so that the center65is positioned on the optical axis55a. With this arrangement, the difference between marginal rays and central rays becomes smaller.

FIGS. 8B and 10show another embodiment of the placement of the ND filter60. As shown inFIG. 8B and 10, the ND filter60can be fixed to a front end70bof the front lens frame6. With this arrangement, the difference between marginal rays and central rays becomes smaller.

FIGS. 11 and 12show another embodiment of the placement of the ND filter60.

As shown inFIGS. 11 and 12, the ND filter60is fixed to a rear end surface of the shutter unit16so that the center65is positioned on the optical axis55a. With this arrangement, the difference between marginal rays and central rays becomes smaller.

FIGS. 13 through 14Cshow a second embodiment of the lens barrel according to the present invention. Similar to the first embodiment of the lens barrel shown inFIG. 13, the lens barrel150is a telescoping type zoom lens of a camera which is provided with four external telescoping barrels: a first external barrel (lens support barrel)117, a second external barrel (cam ring)119, a third external barrel121and a fourth external barrel124, which are concentrically arranged about an optical axis155aof a photographing optical system155of the lens barrel150. The photographing optical system155of the lens barrel150includes a first lens group (lens element)101, a second lens group (lens element)102, a third lens group (lens element)103, a diaphragm (diaphragm blades)114, a shutter (shutter blades)115, a fourth lens group (lens element)104, a fifth lens group (lens element)105, in that order from the object side (the left side as viewed inFIG. 13). The lens barrel150is provided around the fourth external barrel124with a housing138which supports the first through fourth external barrels117,119,121and124so that each of the first through fourth external barrels117,119,121and124can move forward and rearward with respect to one other along the optical axis155a.

The fourth external barrel124is coupled to the housing138by engagement of a male helicoid with a female helicoid which are formed on the fourth external barrel124and the housing138, respectively. Likewise, the third external barrel121is coupled to the fourth external barrel124by engagement of a male helicoid with a female helicoid which are formed on the third external barrel121and the fourth external barrel124, respectively. Likewise, the second cam ring119is coupled to the third external barrel121by engagement of a male helicoid with a female helicoid which are formed on the cam ring119and the third external barrel121, respectively. The first external barrel (lens support barrel)117is coupled to the cam ring119by a cam mechanism provided therebetween.

The fourth external barrel124is fitted into the housing138, and a second helicoid ring125is fixed to a rear end surface of the fourth external barrel124. The second helicoid ring125is engaged with an axial groove138aparallel to the optical axis155aformed on an inner peripheral surface of the housing138. Due to this engagement of the second helicoid ring125with the axial groove138a, the fourth external barrel124, together with the second helicoid ring125, can move along the optical axis155awith respect to the housing138.

The lens barrel150is provided inside the fourth external barrel124with a third linear guide ring123which is fitted into the fourth external barrel124. The third linear guide ring123is provided on an inner peripheral surface thereof with a plurality of inclined lead slots123awhich are inclined with respect to the optical axis direction (i.e., the direction parallel to the optical axis155a). The third external barrel121is fitted into the third linear guide ring123, and a first helicoid ring122is fixed to a rear end of the third external barrel121. The fourth external barrel124is provided on an inner peripheral surface thereof with a plurality of linear guide grooves124a(only one of them appears inFIG. 13) which extend parallel to the optical axis155a. A plurality of guide followers129(only one of them appears inFIG. 13) which are fixed to an outer peripheral surface of the first helicoid ring122pass through the plurality of inclined lead slots123ato be engaged in the plurality of linear guide grooves124a, respectively. With this engagement of the guide followers129with both the inclined lead slots123aand the linear guide grooves124a, the third external barrel121and the first helicoid ring122are linearly guided by the third linear guide ring123in the optical axis direction.

The lens barrel150is provided radially inside the third external barrel121with a second linear guide ring120which is fitted into the third external barrel121. The second linear guide ring120is provided with two inclined lead slots120awhich pass through the second linear guide ring120and are inclined with respect to the optical axis direction (i.e., the direction parallel to the optical axis155a). The third external barrel121is provided on an inner peripheral surface thereof with two rotation transmitting grooves121a(only one of them appears inFIG. 13) which extend parallel to the optical axis155a. Two guide followers128(only one of them appears inFIG. 13) which are fixed to an outer peripheral surface of the cam ring119at equi-angular intervals (i.e., at intervals of 180 degrees) in a circumferential direction of the cam ring119pass through the two inclined lead slots120ato be engaged in the two rotation transmitting grooves121a, respectively. Due to the engagement of the guide followers128with both the inclined lead slots120aand the rotation transmitting grooves121a, the cam ring119is linearly guided by the second linear guide ring120in the optical axis direction.

The lens barrel150is provided inside the cam ring119with a first linear guide ring118. The first linear guide ring118is supported by the cam ring119to move together with the cam ring119while allowing the cam ring119to rotate with respect to the first linear guide ring118. The first linear guide ring118is provided at a rear end thereof with a plurality of linear guide projections118awhich project radially outwards to be engaged in a plurality of linear guide grooves120bformed on an inner peripheral surface of the second linear guide ring120. This engagement of the linear guide projections118awith the linear guide grooves120ballows the first linear guide ring118to move linearly in the optical axis direction without rotating with respect to the second linear guide ring120.

The lens barrel150is provided inside the cam ring119with a lens support ring117, and is provided inside the lens support ring117with a rear lens frame109. The lens support ring117and the rear lens frame109are linearly guided in the optical axis direction by the first linear guide ring118. A rotation of the cam ring119relative to the lens support ring117causes the lens support ring117to move forward from the cam ring119in accordance with contours of a set of three cam grooves119bformed on an inner peripheral surface of the cam ring119. The set of three cam grooves119bare formed on an inner peripheral surface of the cam ring119in the vicinity of the rear end thereof at equi-angular intervals in a circumferential direction of the cam ring119. A set of three cam followers pins127radially extend through the lens support ring117at equi-angular intervals in a circumferential direction of the lens support ring117, and are fixed to the lens support ring117so that radially outer ends of the set of three cam followers pins127are engaged in the set of three cam grooves119b. A set of three cam follower rollers126are fixed to an outer peripheral surface of the lens support ring117to project radially outwards to be engaged in the set of three cam grooves119bso that a rotation of the cam ring119with respect to the lens support ring117causes the lens support ring117to move along the optical axis155ain a predetermined moving manner due to the engagement of the three cam follower rollers126with the three cam grooves119b.

The lens barrel150is provided inside the lens support ring117with a shutter unit (AF/AE shutter unit)116having the diaphragm114and the shutter115. The lens barrel150is provided inside the shutter unit116with a front lens frame106and a middle lens frame107which are supported by the shutter unit116to be movable along the optical axis155arelative to the shutter unit116. The first lens group101is supported by the front lens frame106to be fixed thereto. The second lens group102and the third lens group103are supported by the middle lens frame107to be fixed thereto with a spacer ring108being provided between the second lens group102and the third lens group103. The front lens frame106and the middle lens frame107are supported by the shutter unit116to be movable relative to each other along the optical axis155a.

The set of three cam follower pins127, which radially extend through the lens support ring117, are fixed at their radially inner ends to an outer peripheral surface of a rear lens frame moving ring110which is positioned inside the lens support ring117in the vicinity of the rear end thereof. The rear lens frame109is screwed into a rear end portion of the rear lens frame moving ring110. The fourth lens group104and the fifth lens group105are supported by the rear lens frame109to be fixed thereto. Movement of the set of three cam follower pins127in the set of three of three cam grooves119btherealong causes the rear lens frame109to move along the optical axis155a. The fourth lens group104is fixed to the rear lens frame109by a fourth lens group pressing ring112which is fitted on a front end of the rear lens frame109. The fourth lens group104and the fifth lens group105are supported by the rear lens frame109to be fixed thereto with a spacer ring111being interposed between the fourth lens group104and the fifth lens group105.

As shown inFIGS. 14A,14B and14C, by moving the front lens frame106, the middle lens frame107and the rear lens frame109along the optical axis155arelative to one another, the lens barrel150changes between an accommodated position (shown inFIG. 14A) and the wide-angle extremity (shown inFIG. 14B), and can change the focal length between the wide-angle extremity (shown inFIG. 14B) and the telephoto extremity (shown inFIG. 14C). Although the focal length of the photographing optical system155at the wide-angle extremity is set to 20 mm (35 mm film camera conversion) in the present embodiment of the lens barrel, reduction in light quantity of marginal rays can be minimized if the focal length of the photographing optical system155at the wide-angle extremity is set to a focal length in a wide-angle range between 20 mm and 38 mm (35 mm film camera conversion). The shutter unit116drives the front lens frame106and the middle lens frame107forward and rearward along the optical axis155awhile changing the space therebetween to perform a focusing operation.

The lens barrel150is provided at the front end of the lens support frame117with a lens barrier mechanism which automatically closes a front end aperture of the lens barrel150when the lens barrel150is retracted into the camera body as shown inFIG. 14A, i.e., when the lens barrel150is not in use. The lens barrier mechanism is provided with a decorative plate130which is fixed to the front end of the lens support frame117, and is further provided immediately behind the decorative plate130with a pair of barrier blades131and132each of which is pivoted on an associated pivot (not shown) formed on a rear surface of the decorative plate130. When the power of the camera is turned ON and OFF, the pair of barrier blades131and132rotate together about the respective pivots to open and close a front end aperture of the lens barrel150which is formed on the decorative plate130.

The lens barrel150is provided on a rear surface of the fifth lens group105with a circular ND (neutral density) coating160having a circular plan view so that a center165of the ND coating160is positioned on the optical axis155a. The ND coating160and the ND filter60are functionally the same.

As shown inFIG. 15B, the disc-shaped ND coating160has three concentric coating portions which are formed concentrically with respect to the center165. These three concentric filter portions are a first ND portion162(diameter=dND1) serving as a central ND portion, a second ND portion163(diameter=dND2) positioned around the first ND portion162, and a third ND portion164(diameter=d0) positioned around the second ND portion163. The optical density (reflectance) of the first ND portion162is higher than those of the other two ND portions163and164. The optical density (reflectance) of the second ND portion163is slightly lower than that of the first ND portion162, but is still high so that the first ND portion162and the second ND portion163constitute a high optical density portion of the ND coating160. The optical density of the third ND portion164is much lower than that of the second ND portion163; the third ND portion164serves as a low optical density portion having a reflectance of substantially zero.

Accordingly, the optical density of the ND coating160decreases stepwise in a direction radially outwards from the center165. Namely, the reflectance of the ND coating160decreases in a direction radially outwards from the center165as shown inFIG. 15C. As another embodiment of the ND coating160, the ND coating160can be modified so that the optical density decreases continuously or discontinuously in a direction radially outwards in each of the first through third ND portions162through164. In addition, the ND coating160only needs to be formed to include two or more ND portions having different optical densities; for instance, the third ND portion164can be a non-ND portion to which no coating is applied.

A broken line shown inFIG. 15Aindicates an outermost light path of the light rays of an object which pass through the outermost regions of the fourth and fifth lens groups104and105. Therefore, the effective aperture of the ND coating160is set to the diameter (d0) of the third ND portion164which is slightly smaller than the inside diameter (D) of the annular filter frame161. The diameter of the high-optical density portion of the ND coating160, i.e., the diameter (dND2) of the second ND portion163is set to be smaller than the effective aperture of the photographing optical system which is shown by a broken line shown inFIG. 15A.

Due to the above described structure of the ND coating160, the light rays which are passed through the outer regions of the first through fifth lens groups101through105of the photographing optical system155pass through the third ND portion164(which has a low reflectance), while the light rays which are passed through a central portion of the first through fifth lens groups101through105of the photographing optical system155pass through either the first ND portion162or the second ND portion163(each of which is high in optical density (reflectance)). Therefore, with the ND coating160, the difference between marginal rays and central rays becomes smaller.

FIGS. 17 and 18show another embodiment of the formation of the ND coating160, andFIGS. 19 and 20show yet another embodiment of the formation of the ND coating160.

Although the ND coating160is formed on a rear surface of the fifth lens group105in the above illustrated embodiment of the lens barrel, the ND coating160can be formed on a front surface of the fourth lens group104as shown inFIGS. 17 and 18. With this arrangement, the difference between marginal rays and central rays becomes smaller.

As another embodiment, the ND coating160can be formed on a front surface of the first lens group101as shown inFIGS. 19 and 20. With this arrangement, the difference between marginal rays and central rays becomes smaller.

Even if the ND coating160is formed on a lens surface other than the rear surface of the fifth lens group105, the front surface of the fourth lens group104and the front surface of the first lens group101, effects similar to those obtained in any one of the above described embodiments can be expected.

The ND coating160can also be applied to a lens barrel other than the above described lens barrel150which has an optical system having five lens groups. Furthermore, the ND coating160can be applied to a telescoping type zoom lens provided with three or less than three external telescoping barrels, or five or more than five external telescoping barrels. Alternatively, the ND coating160can be applied to a fixed-focal-length lens having a short focal length for a wide angle of view.

Although a single ND coating is used in the above illustrated embodiment of the lens barrel150, two or more separate ND coatings can be formed on different lens surfaces.

As can be understood from the foregoing, according to each of the above described embodiments of the lens barrels, a lens barrel having a simple structure minimizing reduction in light quantity of marginal rays is achieved.