Abstract: A yield which is a ratio of the weight of a ring-shaped member to that of a stock material, and a yield which is a ratio of the ring-shaped member to a blank are improved, and the cost is reduced. In a method of producing a ring-shaped member in which a ring-shaped member is obtained from a longitudinally elongated annular blank 3, a pair of linking portions 3b, 3c are outward expanded from the inner side of the blank 3, and a pair of arcuate portions 3d are pressed from the outer side toward the inner side to be pressingly expanded, thereby shaping into a ring-shaped member.

Abstract: A method of producing a ring-shaped member is provided in which a material loss is eliminated, the process cost can be reduced, and a ring-shaped member can be easily obtained from a pipe member by a small number of steps. The method includes steps of: inwardly projectingly shaping a flange portion 1c on an end portion of a metal-made pipe member 1; and cutting off the flange portion 1c from the pipe member 1, thereby obtaining a ring-shaped member 10.

Abstract: A zoom lens barrel is intended to ensure precision in dimensions for a cam groove and contribute to realization of a compact and lightweight design and reduction in cost of manufacturing. The zoom lens barrel has a cam cylinder that is a cam member having a first cam groove and second cam groove, and a lens frame having a first cam pin to be engaged with the first cam groove, and a second cam pin to be engaged with the second cam groove. When the first cam pin formed on the lens frame moves along the first cam groove, the lens frame moves over a power varying zone that is a first zone in the direction of an optical axis. When the second cam pin formed on the lens frame moves along the second cam groove, the lens frame moves over a collapsing zone that is a second zone in the direction of the optical axis.