1. Field of the Invention
The present invention relates to a cam ring used in a lens barrel and a method for manufacturing the same.
2. Description of Related Art
A lens barrel having a cam ring is commonly used in a zoom lens. The cam ring has for example, two cam grooves in which guide pins for a front and rear group of movable lenses are fitted, so that when the cam ring rotates, the movable lens groups are moved in accordance with profiles of the cam grooves to vary the focal length.
In the lens barrel as mentioned above, in the case where the cam ring is driven to rotate by an electrical drive mechanism, it is necessary to provide a gear on the outer periphery of the cam ring. To this end, a separate gear ring is secured to the outer periphery of the cam ring in a conventional lens barrel. The cam grooves are usually in the form of through openings on which the gear ring is usually superimposed. It is therefore next to impossible to form the cam ring integral with the gear ring.
The assignee of the present application has proposed a zoom lens barrel in which a cam ring is supported so as to move along an optical axis direction in accordance with the rotation thereof to decrease the length necessary for accommodating the zoom lens barrel in a camera body (Japanese Patent application No. 63-137019). In this zoom lens barrel, the cam ring is provided, on its outer periphery, with a male helicoid (thread) which serves as a rotational guide means and which is engaged by a stationary female helicoid. Also, in this zoom lens barrel, the male helicoid is provided on a helicoid ring which is made of a piece that is separate from the cam ring for the same reason as that mentioned above. The helicoid ring must be secured to the cam ring at a later time. It is also necessary to provide a gear for rotating the cam ring on the helicoid ring.