Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2002-02-04
2003-05-20
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S700000, C359S701000
Reexamination Certificate
active
06567222
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens apparatus for use in a liquid crystal projector, a television camera for industrial use or the like, more particularly, to a lens barrel for use in a zoom lens apparatus.
2. Description of the Related Art
A typical zoom lens apparatus employed in a liquid crystal projector, a television camera for industrial use or the like is constructed so that a cam barrel is freely fitted into a fixed barrel. The fixed barrel holds a lens system such as a zooming lens. The cam barrel is made to rotate around an optical axis to move the lens system in a direction parallel to the optical axis (hereinafter “the optical axis direction”). That is, guide holes consisting of an elongated hole extending parallel to the optical axis are formed in the fixed barrel and support pins are provided on the outer periphery of a lens mount that holds the lens system while projecting into the guide holes. Further, elongated holes constituting cams are provided in the cam barrel along a direction tilted appropriately relative to the optical axis direction. Still further, the support pins are freely inserted into the cams. This construction allows the lens system to move in the optical axis direction guided by the guide holes while being limited in its moving distance by the oblique orientation of the cams.
In recent years, there has been a strong demand for an optical device such as a liquid crystal projector provided with highly sophisticated optical performances. That is, the liquid crystal projector is required to project images clearly onto a screen even when the amount of light emitted from a light source incorporated therein is small. For this reason, in such a liquid crystal projector, it is required that a lens having a small F value is employed in the optical system. In addition, the optical system is required to increase its magnification ratio so as to be able to project an image of copy filled with small characters in clear detail. Such strong demand for highly sophisticated optical performances to be realized in the optical system may cause the following problems in the conventional lens barrel for use in a zoom lens apparatus.
In the conventional lens barrel, to ensure advantages, such as simplicity of assembling operation, ease of operation for adjusting each part, continuing resistance to thermal deformation and the like, an appropriate gap as an allowance between parts is intentionally provided (when needed) or the number of parts to be employed is reduced by reducing the number of connecting parts provided between the parts. However, even such a microscopic event that a negligible gap causes the positional distortion of the lens in the optical axis direction may adversely affect the optical performance, thereby possibly disturbing realization of highly sophisticated optical performance to be achieved in an optical device.
SUMMARY OF THE INVENTION
In consideration of the above-described problems, the present invention has been conceived. That is, an aspect of the present invention is to provide a lens barrel for use in a zoom lens apparatus to securely be able to address the needs for developing optical devices with highly sophisticated optical performance.
A lens barrel for use in a zoom lens apparatus according to the present invention comprises: a fixed barrel holding a zoom lens system, and a cam barrel freely fitted to the fixed barrel and made to rotate around an optical axis direction as an axis with respect to the fixed barrel to move the zoom lens system in the optical axis direction, in which the fixed barrel is further constructed such that an appropriate number of radial supporting projection constituting a part of an outer periphery of the fixed barrel and projecting an appropriate length in both a circumferential direction of the fixed barrel and the optical axis direction are provided on portions of the fixed barrel, the portions being located in correspondence with ends of the cam barrel while facing the associated ends thereof, and the cam barrel is supported by the supporting projections.
As the cam barrel is supported by the supporting projections, the area where the cam barrel and the fixed barrel are in contact with each other can be made small to the utmost. Therefore, the cam barrel can be made to rotate smoothly with respect to the fixed barrel.
In general, it is desirable that a zoom lens apparatus is assembled in small size and is light in weight, and further can be provided at a low price. For this reason, it is required that the fixed barrel be formed by injection molding or the like using a synthetic resin and the cam barrel be formed by processing and molding a metal such as aluminum. Note that in the case where both the fixed barrel and the cam barrel are made of a metal, manufacturing cost of a zoom lens apparatus is forced to increase, and in the case where they both are made of a synthetic resin, there possibly arises a problem that accuracy with which a zoom lens system operates in response to the rotational movement of the cam barrel varies, whereby the zoom lens apparatus cannot maintain its desired accuracy.
In the case where the fixed barrel is formed by molding a synthetic resin and the cam barrel is formed by molding a metal, as those materials have their respective coefficients of thermal expansion different from each other, there possibly arises a problem that when the fixed barrel is thermally deformed, the cam barrel cannot be rotated smoothly. In addition, in the case where the area where the fixed barrel and the cam barrel are in contact with each other is large, possibility of causing the above-described problem increases. Specifically, in such an optical device as a liquid crystal projector, as a light source generating heat is disposed next to the zoom lens apparatus, the lens barrel is easily affected by the heat. In order to address such a serious problem, as shown in the lens barrel of the present invention, the fixed barrel is formed to have supporting projections thereon such that the supporting projections are made in contact with the inner periphery of the cam barrel for guiding the cam barrel into rotational movement, thereby enabling the cam barrel to rotate smoothly to the utmost even in a state of the fixed barrel being thermally deformed.
Furthermore, the lens barrel for use in a zoom apparatus in accordance with the present invention is constructed such that the supporting projections are provided on respective ends of the fixed barrel and spaced at equal intervals, and further, the supporting projections on the respective ends of the fixed barrel are provided facing each other.
In the case where the fixed barrel is processed by using a synthetic resin, as the supporting projections on front and rear ends of the fixed barrel are provided facing each other, operation for designing a molding die assembly becomes easier.
Additionally, the lens barrel for use in a zoom lens apparatus in accordance with the present invention is constructed such that the supporting projections are provided on respective ends of the fixed barrel and spaced at equal intervals, and further, the supporting projections are alternately disposed at front and rear ends of the fixed barrel in the circumferential direction thereof.
In the event the fixed barrel is thermally deformed, the construction that the supporting projections are alternately disposed at front and rear ends of the fixed barrel in the circumferential direction thereof makes it possible to permit the deformation to equally act on the cam barrel, thereby enabling the cam barrel to maintain its smooth rotation to the utmost.
Additionally, a lens barrel for use in a zoom lens apparatus in accordance with another aspect of the present invention comprises: a fixed barrel holding a zoom lens system and at the same time, a focus lens system in a front end thereof; a cam barrel freely fitted to the fixed barrel and made to rotate around an optical axis direction as an axis with respect to the fixed barr
Fuji Photo Optical Co., Ltd.
Mack Ricky
Price Heneveld Cooper DeWitt & Litton
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