Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2001-01-31
2003-05-27
Mai, Huy (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S700000
Reexamination Certificate
active
06570718
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens, or a zoom lens barrel, which is provided with a cam mechanism using bottomed cam grooves formed on an inner peripheral surface of a cam barrel. At least one movable lens group is moved in the direction of the optical axis of the photographic optical system in a predetermined manner in accordance with the profiles of the bottomed cam grooves by rotation of the cam barrel.
2. Description of the Related Art
A zoom lens having a cam mechanism which uses bottomed cam grooves formed on an inner peripheral surface of a cam barrel so that one or more movable lens groups guided in the direction of the optical axis of the photographic optical system (i.e., in the optical axis direction) without rotating about the optical axis are moved in a predetermined manner by rotation of the cam barrel to obtain a continuously variable focal length is known in the art. In such a cam mechanism using bottomed cam grooves, if each cam follower pin formed on a lens frame is fitted in the zoom section (an operational section for varying the focal length) of the corresponding bottomed cam groove with a predetermined amount of play, the lens group supported by the lens frame may be eccentric and/or tilt relative to the optical axis. This deteriorates the optical performance of the zoom lens.
Such eccentricity or tilt of the lens group causes substantial problems, especially in a zoom lens of a digital camera, because object images are formed on the sensitive surface of a small CCD (CCD image sensor) which is much smaller than the picture plane of conventional cameras using light sensitive film. Namely, upon assembly, every lens element of a digital camera must be optically centered, correctly spaced, and held firmly with a relatively high precision ten times greater than that required in conventional cameras using light-sensitive film. For instance, if the angle of view is constant, the focal length of a photographing lens becomes shorter as the size of the picture plane reduces, which in turn reduces the sizes of all the elements of the photographing lens such as lens elements, and lens frames. Therefore, an influence that a tolerance (e.g., 10 &mgr;m) has on the photographing lens system of a digital camera is much larger than an influence that the same tolerance has on the photographing lens system of a conventional camera using light-sensitive film. Accordingly, manufacturing error which falls within tolerance in the optical performance in the photographing optical system of a conventional camera using light-sensitive film can be out of tolerance in optical performance in the photographing optical system of a digital camera. Specifically in the photographic lens system of a digital camera, influence that eccentricity or tilt of a lens group relative to the optical axis has on the optical performance of the photographic lens system is larger than influence that a deviation of the same lens group from the original position in the optical axis direction.
To prevent such eccentricity and tilt from occurring, a mechanism for removing play between the cam follower pins and the bottomed cam grooves in which the cam followers are respectively fitted with resilient supports which support the cam follower pins has been proposed. The resilient supports become resiliently deformed in a radial direction to bias the cam follower pins against the bottomed cam grooves, respectively, to thereby remove the play between the cam follower pins and the bottomed cam grooves, so that each cam follower pin follows along the corresponding bottomed cam groove with a sufficient frictional resistance being generated therebetween.
However, according to such a play removing mechanism, if the resilient supports remain resiliently deformed over the long term, the resilient bias (i.e., the resilient biasing force) of each resilient support gradually becomes weak, which may deteriorate the performance of the mechanism.
Another problem present in a zoom lens having a cam mechanism using bottomed cam grooves, is that although each bottomed cam groove is provided with a leading section provided for leading each corresponding cam follower pin from the cam follower insertion opening of the bottomed cam groove, which is formed on the cam barrel, to the zoom section of the bottomed cam groove (which is provided for moving the lens frame between a telephoto position thereof and a wide-angle position thereof in accordance with rotation of the cam barrel) ease of assembling and disassembling the zoom lens deteriorates if each cam follower is biased against not only a portion of the bottomed cam groove, which is used during operation of the zoom lens, but also another portion of the bottomed cam groove which is not used during operation of the zoom lens since the cam mechanism cannot be assembled or disassembled smoothly due to the frictional force generated between the cam follower pins and the bottomed cam grooves.
SUMMARY OF THE INVENTION
The present invention has been devise in view of the above-mentioned problems, and accordingly, an object of the present invention is to provide a zoom lens having a cam mechanism which reliably prevents eccentricity and tilt of a lens group relative to the optical axis from occurring during operation of the zoom lens while maintaining the performance of the prevention of lens eccentricity and tilt over a long term.
Another object of the present invention is to provide a zoom lens having a cam mechanism which reliably prevents eccentricity and tilt of a lens group relative to the optical axis from occurring during operation of the zoom lens and which excels in ease of assembly and disassembly the zoom lens.
To achieve the object mentioned above, according to an aspect of the present invention, a zoom lens is provided, including a cam barrel driven to rotate about an optical axis; bottomed cam grooves formed on an inner peripheral surface of the cam barrel; a lens frame guided in an optical axis direction; cam followers which project radially from the lens frame to be respectively engaged with the bottomed cam grooves; and resilient supports which respectively support the cam followers, each of the resilient supports being resiliently deformable in a radial direction, a resilient bias of each of the resilient supports causing each of the cam followers to be biased against a corresponding bottomed cam groove of the bottomed cam grooves. Each bottomed cam groove includes a zoom section for moving the lens frame between a telephoto position and a wide-angle position thereof in the optical axis direction in accordance with a rotational movement of the cam barrel; and an accommodation section for moving the lens frame to an accommodation position thereof, wherein a photographic operation is not performed. Each bottomed cam groove is formed so that a depth of the accommodation section is greater than a depth of the zoom section in the radial direction of the cam barrel. The resilient bias of each of the resilient supports causes each of the cam followers to be biased against each of the bottomed cam grooves wherein the follower pins are respectively fitted in the bottomed cam grooves so that no play exists when each of the bottomed cam grooves is positioned in the zoom section, and each of the resilient supports is free from being elastically deformed in the radial direction so that the cam followers are respectively inserted in the bottomed cam grooves with a predetermined amount of play when each of the bottomed cam grooves is positioned in the accommodation section.
In the bottomed cam grooves includes a first set of bottomed cam grooves having same profiles and a second set of bottomed cam grooves having same profiles, the profiles of the second set of bottomed cam grooves being different from the profiles of the first set of bottomed cam grooves. The lens frame includes a first lens frame and a second lens frame. The cam followers include a first set of cam followers which are provided on the first lens frame an
Aoki Nobuaki
Nakamura Satoru
Nomura Hiroshi
Yamazaki Yoshihiro
Greenblum & Bernstein P.L.C.
Mai Huy
Pentax Corporation
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