Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2000-03-28
2001-02-27
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S699000
Reexamination Certificate
active
06195211
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens device whose lens barrel elements rotate relative to each other for changing the focal length, i.e. for zooming. The present invention relates more particularly to a zoom lens device having a zooming position detector mounted in a compact fashion.
2. Background Arts
A zoom lens device has at least front and rear lens groups whose positions are changed relative to a film surface and relative to each other in the direction of the optical axis of the zoom lens device. Since there is a clearance between barrels that hold the front and rear lens groups respectively, extraneous light would enter inside the zoom lens device through the clearance without any light-shielding device. JPY 5-31634 discloses a light-shielding device for a zoom lens device, which is constituted of a light-shielding ring having a resilient lip around its inner rim. The light-shielding ring is placed behind a face flange surrounding an opening of a front wall of a camera body such that the resilient lip stays in contact with the outer periphery of a lens barrel or lens cover frame that moves with the front lens group in the axial direction through the opening of the front wall.
The light-shielding ring disclosed in JPY 5-31634 is useful for a clearance around a lens barrel that moves in the axial direction relative to a fixed barrel. However, the light-shielding ring is not preferable for a lens device where a front lens frame is rotatably held in a barrel, and a front cover member having an opening for exposing the front lens is attached to a front end of the barrel, and a clearance is provided between the front lens frame and the front cover member for allowing the front lens frame to rotate relative to the front cover member. If the light-shielding ring is used for the clearance between the front cover member and the front lens frame, the outer periphery of the front lens frame would rub against the lip of the light-shielding ring as the front lens frame rotates relative to the front cover member. The friction between the front lens frame and the front cover member would raise the necessary driving force for the lens device. The lip of the light-shielding ring would sooner be worn out or heat-deformed by the frequent friction. Besides, the light-shielding ring increases the requisite number of parts necessary for the lens device.
On the other hand, it is known in the art to provide a zooming position detector in a zoom lens device. For example, JPA 50-36118 discloses a zooming position detector consisting of an encoder plate and a brush device. The encoder plate is coupled to a lens barrel of a zoom lens device through gears and a lead screw, such that the encoder plate moves in the axial direction of the zoom lens device as the lens barrel rotates for zooming. As the encoder plate moves in the axial direction, the brush device brushes conductor patterns on the encoder plate detecting signals corresponding to the rotational angle of the lens barrel. Japanese Utility Model Registration No. 2521469 discloses a zooming position detector wherein a code plate having conductor patterns are tightly provided on an outer periphery of a cam ring that rotates for zooming, whereas a brush device brushing the conductor patterns is secured to a stationary frame outside the cam ring.
Either of the prior zooming position detectors needs a mounting space outside the movable lens barrel, which inevitably enlarges the whole size of the camera.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a zoom lens device having a zooming position detector which does not need a specific space outside the zoom lens device.
Another object of the present invention is to provide a light-shielding device for preventing extraneous light entering inside a lens device through a clearance between a front cover member of the lens device and a member that is placed behind the front cover member and rotates relative to the front cover member.
To achieve the first object, a zoom lens device according to the present invention is comprised of a cylindrical lens barrel; a member that is mounted inside the lens barrel, the member being immovable in the direction of an optical axis of the zoom lens device relative to the lens barrel, but rotating about the optical axis relative to the lens barrel during zooming; a code plate mounted to one of a face of the member and an inner portion of the lens barrel that is located near the face of the member and rotates relative to the face of the member; a brush device having electric contact strips, the brush device being mounted to the other of the face of the member and the inner portion of the lens barrel, such that the electric contact strips brush the code plate while the member rotates relative to the lens barrel for zooming; and a determination device for determining a zooming position of the zoom lens device based on a rotational position of the lens barrel relative to the member that is shown by output signals from the electric contact strips.
According to a preferred embodiment, the member is a shutter unit into which a shutter mechanism and an actuator for the shutter mechanism are incorporated, and the lens barrel is a helical movement barrel that moves in the direction of the optical axis while rotating inside a barrel fixed to a camera body, whereas the shutter unit is secured to a front of an axial movement barrel that moves in the direction of the optical axis together with the helical movement barrel without rotating relative to the fixed barrel.
As the code plate and the brush device are located inside the lens barrel, they do not need any specific room outside the lens barrel of the zoom lens device.
To achieve the second object, a lens device according to the present invention is comprised of a lens barrel, an internal member that is mounted inside the lens barrel and rotatable about an optical axis of the zoom lens device relative to the lens barrel but immovable in a direction of the optical axis relative to the lens barrel, and a front cover member secured to a front end of the lens barrel, the front cover member having an opening for exposing a center portion of the internal member, wherein a front face of the internal member and a rear surface of the front cover member are engaged with each other through a labyrinth engagement, and a clearance is provided in between the internal member and the front cover member for allowing the internal member to rotate relative to the front cover member.
According to a preferred embodiment, the internal member is a front lens frame, and a circular groove is formed in one of the front face of the front lens frame and the rear surface of the front cover member; and a circular ridge is formed in the other of the front face of the front lens frame and the rear surface of the front cover member, the circular ridge being fitted in the circular groove with the clearance.
Because of the labyrinthine engagement or the meanders of the clearance, extraneous light entering through the clearance is attenuated so much that it does not reach inside the lens device.
REFERENCES:
patent: 4458990 (1984-07-01), Kawai
patent: 4912488 (1990-03-01), Berglund et al.
patent: 5510936 (1996-04-01), Aoki et al.
patent: 5528430 (1996-06-01), Hamasaki
patent: 5602681 (1997-02-01), Nakayama et al.
patent: 5854711 (1998-12-01), Kaneda
patent: 5940226 (1999-08-01), Tanaka
patent: 50-36118 (1975-04-01), None
patent: 5-31634 (1993-08-01), None
patent: 2-521469 (1996-12-01), None
Fuji Photo Film Co. , Ltd.
Mack Ricky
Young & Thompson
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