Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2002-03-21
2003-02-11
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S701000
Reexamination Certificate
active
06519096
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lens barrel which can be used as a photographing lens barrel of a camera.
2. Description of the Related Art
As an example of a conventional lens barrel in which a movable lens group provided in the lens barrel is moved in an optical axis direction to vary an axial position of the movable lens group, a lens barrel which is provided with a rotatable ring and a cam ring which is driven to rotate about the optical axis while moving in the optical axis via rotation of the rotatable ring is known in the art. A set of follower pins formed on a support frame of the movable lens group are respectively engaged in a corresponding set of cam grooves formed on the cam ring so that the cam ring rotates about the optical axis while moving forward in the optical axis direction by rotation of the rotatable ring and so that the movable lens group moves forward in the optical axis direction relative to the cam ring by rotation of the cam ring.
Moving the cam ring in the optical axis direction while moving the movable lens group in the same direction relative to the cam ring in such a manner can achieve a large amount of movement of the movable lens group in the optical axis direction, and therefore makes it possible to achieve a high zoom ratio if the lens barrel is a zoom lens barrel, in which the focal length can be varied continuously.
However, if this type of lens barrel is used as a photographing lens of a camera, when moving forward in the optical axis direction, the cam ring projects forward from the front wall of the camera to be exposed to the outside, so that the outward appearance of the lens barrel deteriorates. This is especially prominent if the lens barrel is an extendable (telescoping) type of zoom lens barrel since the amount of forward movement of the cam ring is generally large.
In addition, if the cam ring projects forward from the camera body to be exposed to the outside, the cam ring is subject to external forces directly applied thereto, which may make it impossible to move the movable lens group linearly in the optical axis direction with precision.
A conventional lens barrel having a structure wherein a cam ring which is driven to rotate about the optical axis and is provided with a set of cam grooves so that a set of follower pins formed on a support frame of the movable lens group are respectively engaged in the set of cam grooves of the cam ring, and further wherein a linear guide ring having a set of linear guide grooves for guiding the set of follower pins of the lens support frame linearly in the optical axis direction is provided between the cam ring and the movable lens group so that the movable lens group moves in the optical axis direction by rotation of the cam ring relative to the linear guide ring, is known in the art.
However, providing such a linear guide ring between the cam ring and the movable lens group increases the diameter of the cam ring. As a consequence, the diameter of the lens barrel increases.
Moreover, if an external force is applied to an outer peripheral surface of an exterior element of the lens barrel, the external force may exert a harmful effect on the movement of the movable lens group if transferred thereto. Therefore, adopting such a structure of the lens barrel is not desirable.
As an example of a conventional lens barrel in which a movable lens group positioned in the lens barrel is moved in an optical axis direction, a lens barrel having a cam ring driven to rotate about the optical axis wherein a set of follower pins fixed to the lens group are respectively engaged in a corresponding set of cam grooves on the cam ring to be guided linearly in the optical axis direction so that the movable lens group moves in the optical axis direction by rotation of the cam ring is known in the art.
In the case of moving the movable lens group in the optical axis direction by engagement of the set of cam grooves with the set of follower pins, clearances are arranged for the follower pins in the cam grooves to ensure the smooth movement of the follower pins in the cam grooves. Therefore, backlash occurs between the follower pins and the cam grooves when the movable lens groove moves, which deteriorates the performance of the focusing system. Moreover, in the case of moving a ring member, an outer peripheral surface of which serves as an exterior surface of the lens barrel in the optical axis direction, by a cam mechanism provided in the lens barrel which includes a set of follower pins formed on the ring member and a corresponding set of cam grooves formed on a cam ring, backlash occurs between the ring member and the cam ring.
Furthermore, as an example of a lens barrel, a lens barrel which is provided with a cam ring driven to rotate about the optical axis while moving in the optical axis, and a ring member positioned around the cam ring to serve as an exterior component of the lens barrel, is known in the art. A set of follower pins formed on the ring member are respectively engaged in a corresponding set of cam grooves formed on the cam ring so that the cam ring moves in the optical axis direction together with the ring member by rotation of the cam ring.
However, the ring member is subject to external forces directly applied thereto since the ring member serves as an exterior component of the lens barrel. If a large external force is applied to the ring member, the external force is transferred to the cam ring via the follower pins of the ring member to thereby deform the cam ring to the extent that one or more of the follower pins may come off the associated cam grooves, and in a severe case, the cam ring may even be damaged. To prevent this problem from occurring, the wall thickness of the cam ring can be increased and/or the cam ring can be made out of a high stiffness material for the purpose of increasing the strength of the cam ring. However, the cam ring becomes large and heavy if the wall thickness of the cam ring is increased, and the material cost and also the machining cost increase if the cam ring is made of a high stiffness material.
SUMMARY OF THE INVENTION
The present invention provides an extendable lens barrel in which a movable lens group can move in an optical axis direction by a large amount without exposing the exterior surface of the cam ring to the outside of the lens barrel when the lens barrel is extended forward. The present invention further provides a lens barrel in which a movable lens group moves in an optical axis direction with the use of a combination of a cam ring and a linear guide member, wherein the diameter of the lens barrel can be reduced and no external force is transferred to a movable lens group, even if an external force is applied to an exterior component of the lens barrel, while ensuring smooth movement of the movable lens group, wherein no backlash occurs between a movable lens group and a cam ring and between the cam ring and a ring member, which serves as an exterior component of the lens barrel, when the movable lens group and the ring member are moved in the optical axis direction, and/or wherein a cam ring is not deformed even if a large external force is applied to a ring member which serves as an exterior component of the lens barrel.
For example, in an embodiment of the present invention, a lens barrel is provided, including a cam ring which rotates about an optical axis while moving in the optical axis direction, the cam ring including at least one cam groove formed on an inner peripheral surface thereof; a movable lens frame supported by the cam ring and provided inside the cam ring, the movable lens frame being movable in the optical axis direction without rotating about the optical axis; a cam mechanism for moving the movable lens frame in the optical axis direction by an amount of movement greater than an amount of movement of the cam ring in the optical axis direction via rotation of the cam ring in accordance with a profile of the cam groove; and an outer ring which is provided around the cam
Nakamura Satoru
Nomura Hiroshi
Okuda Isao
Yamazaki Yoshihiro
Greenblum & Bernstein P.L.C.
Mack Ricky
Pentax Corporation
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