Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2002-03-21
2003-12-16
Ben, Loha (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S819000, C359S701000, C359S704000
Reexamination Certificate
active
06665129
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lens barrel, and also relates to a zoom lens barrel.
2. Description of the Related Art
As an example of a conventional lens barrel in which two or more lens groups move in an optical axis direction, a lens barrel in which front and rear lens groups are guided linearly in the optical axis direction without rotating about the optical axis and in which the lens support frame of each of the front and rear lens groups is provided with a set of follower pins which are respectively engaged in a corresponding set of cam grooves (cam slots) formed on a cam ring is known in the art. In this type of lens barrel, one cam groove is necessary for each follower pin formed on the lens support frame of each of the front and rear lens groups.
Accordingly, a large number of cam grooves are necessary if the lens barrel is provided with a plurality of movable lens groups. It is difficult to form a large number of cam grooves on a cam ring due to a limited circumferential area thereon. This is more serious if the diameter of the cam ring is small.
One possible solution would be to increase the pitch of each cam groove (i.e., to increase the angle of inclination of each cam groove relative to a circumferential direction of the cam ring), however, this impairs the movement of the follower pins, or may lock the follower pins. If the number of the follower pins is large, the number of the cam grooves formed on the cam ring is also large, which inevitably deteriorates the strength of the cam ring.
As an example of a conventional extendable lens barrel such as an extendable zoom lens barrel in which two or more lens groups move in an optical axis direction, an extendable lens barrel in which front and rear lens groups are guided linearly in the optical axis direction without rotating about the optical axis, and in which the lens support frame of each of the front and rear lens groups is provided with a set of follower pins which are respectively engaged in a corresponding set of cam grooves (cam slots) formed on a cam ring, is known in the art. Note that the term ‘extendable lens barrel’ refers to a lens barrel which extends and retracts so that the length thereof is shortest at an accommodation position, and is longer at a photographing position.
In such an extendable lens barrel, if the lens barrel is retracted to move each of the front and rear lens groups to an accommodation position thereof, each follower pin of the lens support frame of each lens group is accommodated and positioned at an end (accommodation position) of the associated cam groove with no gap between the follower pin and the end of the cam groove, and accordingly, each follower pin cannot move from the accommodation position thereof unless the extendable lens barrel is extended to move each of the front and rear lens groups out of the accommodation position thereof.
However, if the respective accommodation positions of the front and rear lens groups are precisely determined by the profiles of the cam grooves, the front and rear lens groups at their respective accommodation positions need to have a certain gap therebetween so as not to collide with each other, which makes it difficult to reduce the length of the extendable lens barrel in an accommodation state thereof.
In addition, since it is necessary to adjust the fixing position of at least one lens group relative to a support frame thereof in the optical axis direction when the lens group is fixed to the lens support frame during assembly, a marginal space for the fixing position adjustment needs to be secured between the respective accommodation positions of adjacent lens groups, which makes it more difficult to reduce the length of the extendable lens barrel in an accommodation state thereof.
In an extendable lens barrel which extends and retracts between an extended position (ready-to-photograph position) and an accommodation position, if it is desired to reduce the length of the extendable lens barrel in an accommodation state thereof, all of the movable lens groups positioned in the lens barrel need to be retracted in order to be as compact as possible in an accommodation position of the extendable lens barrel.
However, in the case where the extendable lens barrel is provided at the front end thereof with a photographing aperture and at least one lens barrier blade which opens and closes the photographing aperture in a plane perpendicular to the optical axis of the extendable lens barrel, a substantial gap has to be provided between the front surface of the front-end lens group and the lens barrier blade, which increases the length of the extendable lens barrel.
SUMMARY OF THE INVENTION
The present invention provides a lens barrel wherein a cam ring does not need to have a large diameter even if the lens barrel is provided with a large number of movable lens groups, and wherein the cam ring can be provided with cam grooves which ensure smooth movements of the associated follower pins while keeping any decrease in strength of the cam ring to a minimum.
The present invention also provides a lens barrel wherein each of a plurality of lens groups provided in the lens barrel can be accommodated (housed) as compact as possible while preventing adjacent lens groups from contacting with each other even if the lens barrel is of a type wherein at least one lens group is fixed to the lens support frame thereof while the fixing position of the lens group is being adjusted relative to the lens support frame thereof in the optical axis direction, or even if the lens barrel is an extendable lens barrel provided at the front end thereof with a photographing aperture and at least one lens barrier blade which opens and closes the photographing aperture.
The present invention also provides a extendable zoom lens barrel having two or more movable lens groups, wherein front and rear lens groups can be accommodated compact in size in the zoom lens barrel when it is in an accommodation state.
For example, in an embodiment, a lens barrel is provided, including first and second lens groups guided in an optical axis direction without rotating about the optical axis; a first support frame which supports the first lens group, the first support frame including a first cam follower; a second support frame which supports the second lens group, the second support frame including a second cam follower; and a cam ring which is driven to rotate about the optical axis, the cam ring including a cam groove in which the first cam follower and the second cam follower are engaged. The cam groove is formed as a continuous groove and includes a first groove portion via which the first cam follower is guided to move the first lens group, and a second groove portion via which the second cam follower is guided to move the second lens group. The cam groove is formed so that one of the first cam follower and the second cam follower enters a corresponding one of the first groove portion and the second groove portion after passing through the other of the first groove portion and the second groove portion in a preparation stage of the lens barrel.
The first groove portion can include a first zooming section for moving the first lens group to perform a zooming operation; and a first accommodation section in which the first cam follower is positioned when the first lens group is accommodated. The second groove portion can include a second zooming section for moving the second lens group to perform the zooming operation; and a second accommodation section in which the second cam follower is positioned when the first lens group is accommodated. The first zooming section, the second zooming section, the first accommodation section and the second accommodation section are arranged in that order from one end of the cam groove, so that the first cam follower passes through the second zooming section when moving between the first accommodation section and the first zooming section.
It is desirable for the first lens group to be positioned in fr
Nakamura Satoru
Nomura Hiroshi
Okuda Isao
Yamazaki Yoshihiro
Ben Loha
Greenblum & Bernstein P.L.C.
Pentax Corporation
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