Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2000-02-09
2001-05-22
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S694000, C359S703000
Reexamination Certificate
active
06236519
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a viewfinder device. More particularly, the present invention relates to a viewfinder device in which a movable lens is moved in response to a zooming operation of a camera incorporating the viewfinder device.
2. Description Related to the Prior Art
A zoom viewfinder device is known in the art of the camera, and is structured to change its magnification in response to zooming of a taking lens of a camera in which the viewfinder is incorporated. The zoom viewfinder device includes a viewfinder optical system and a linking mechanism. The viewfinder optical system has a construction for the zooming or changing the magnification. The linking mechanism moves a movable lens for zooming in an optical axis direction within the viewfinder optical system in response to the zooming of the camera. The viewfinder optical system suitable for the zooming is a real image type in general. At least two movable lenses, which are disposed nearer to a photographic field than a focal plane, are moved for zooming.
In a zoom viewfinder with two movable lenses for the zooming, the movable lenses are moved in the optical axis direction with changes in an interval therebetween in response to the zooming of the camera. A lens holder is disposed to extend from the periphery of the movable lens. In other words, the lens holder holds the movable lens. A shaft receiving portion is formed with the lens holder. A guiding shaft extends in parallel with the optical axis direction, and is inserted in the shaft receiving portion, to keep the movable lens movable. Cam pins are formed with the lens holder. Two cam grooves are formed in a cam member or cam plate, and are engaged with respectively the cam pins. In the course of the zooming, the cam member is shifted in one of the two directions. The movable lenses are respectively moved by following curved shapes of the cam grooves, to change a magnification of the viewfinder continuously.
A follower projection projects from the lens holder. A guiding groove is formed in a body of the viewfinder, and extends in the optical axis direction. The follower projection is engaged with the guiding groove to keep the movable lens from moving minutely with respect to the guiding shaft. The guiding groove has a width greater than a width of the follower projection. In the prior art, a spring is used to bias the lens holder for the one-side positioning, so as to push the follower projection to one edge of the guiding groove, namely a guide face included in the guiding groove.
Ideas of biasing the lens holder are disclosed in various prior documents. In JP-A 4-159523, two lens holders are biased by respectively springs for the one-side positioning. In JP-A 6-250263, a single coil spring is disposed to receive insertion of the guiding shaft therein. The coil spring biases two lens holder portions for the one-side positioning. In both structures, the follower projection is kept in contact with the guide face. The movable lens can be moved in the optical axis direction without influence of play or backlash. Images in the view field of the zoom viewfinder can be kept stationary.
However, a problem arises in that bias force of the springs that are the coil springs or plate springs is likely to become load against movement of the lens holder. In JP-A 4-159523, the follower projections of the plural lens holders are pressed to the guide faces in a manner individual from one another. The influence of the bias force of the springs, therefore, is more remarkable. The number of the parts increases, to complicate the operation of assembly of the viewfinder. Also in JP-A 6-250263, portions of the coil spring must be engaged with a lens holder portion after the insertion of the coil spring in the guiding shaft. Again, this is inconsistent to good efficiency in the assembly operation.
SUMMARY OF THE INVENTION
In view of the foregoing problems, an object of the present invention is to provide a viewfinder device in which the movable lens is movable in the optical axis direction without minute movement due to play, load is reduced during movement of the movable lens, and the number of the parts and the number of assembling steps are decreased to reduce a manufacturing cost of the viewfinder.
In order to achieve the above and other objects and advantages of this invention, a viewfinder device includes a viewfinder body. At least one movable lens is accommodated in the viewfinder body. A lens moving mechanism drives the movable lens in the viewfinder body. A rectilinear guiding mechanism guides movement of the movable lens in an optical axis direction thereof, and includes first and second guide faces, the first guide face being formed inside the viewfinder body, extended in the optical axis direction, the second guide face being formed with a periphery of the movable lens, for contacting the first guide face to slide along the first guide face. A one-side positioning member keeps the second guide face pressed on the first guide face by pushing the movable lens in a direction crosswise to the optical axis direction, for absorbing play of the movable lens relative to the optical axis direction.
The viewfinder device is a zoom viewfinder device. The movable lens moves in the optical axis direction for zooming.
In a preferred embodiment, the rectilinear guiding mechanism includes a rectilinear guiding groove formed in the viewfinder body, extended in the optical axis direction, having two opposed inner faces one of which constitutes the first guide face. A follower projection is disposed to project from a periphery of the movable lens, has the second guide face, and inserted in the rectilinear guiding groove.
Furthermore, a second rectilinear guiding mechanism guides movement of the movable lens in the optical axis direction, and includes an arm portion for extending from a periphery of the movable lens. A shaft receiving hole is formed in the arm portion. A rectilinear guiding shaft extends in the optical axis direction, the rectilinear guiding shaft being inserted in the shaft receiving hole.
The at least one movable lens comprises plural movable lenses. The one-side positioning member is a single one-side positioning rod extending in the optical axis direction.
Furthermore, a holder portion has substantially a frame shape, is disposed to extend from the periphery of the movable lens. The follower projection is formed with a periphery of the holder portion.
The lens moving mechanism includes a cam plate, curved in an arc shape, for rotating about an axis parallel with the optical axis direction. A cam groove is formed in the cam plate, and has an inclination with reference to the optical axis direction. A cam follower pin is disposed to project from the arm portion, inserted in the cam groove, and pressed by a cam surface of the cam groove when the cam plate rotates, for setting the movable lens in a zoomed position.
First and second ends of the one-side positioning rod are secured to respectively front and rear ends of the rectilinear guiding groove.
In another preferred embodiment, a tape member is secured to an outside of the viewfinder body to close the rectilinear guiding groove at least partially, for keeping the one-side positioning rod pressed on the movable lens.
The movable lens, the arm portion and the follower projection are included in one piece.
REFERENCES:
patent: 4993815 (1991-02-01), Yamazaki et al.
patent: 5150260 (1992-09-01), Chigira
patent: 5241422 (1993-08-01), Shimada et al.
patent: 5363248 (1994-11-01), Horio
patent: 5461433 (1995-10-01), Nakayama et al.
patent: 4-159523 (1992-06-01), None
patent: 6-250263 (1994-09-01), None
Fuji Photo Optical Co., Ltd.
Mack Ricky
Young & Thompson
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