1. Field of the Invention
This invention relates to an optical apparatus having a helicoid member.
2. Description of the Related Art
Some of the conventional lens-barrel drawing-out mechanisms have a female helicoid tube molded with a molding material. In forming the helicoid screw thread of the female helicoid tube, either a mold is slidden toward the inside circumference side of the female helicoid tube (a split mold type) or a mold is pulled out from the female helicoid tube while rotating the mold.
However, the method of forming the screw thread by sliding the mold toward the inside circumference side requires the mold to have a complex structural arrangement, which is not only expensive but also makes the cycle of molding longer, so that a manufacturing cost of the female helicoid tube increases disadvantageoulsy. Besides, in order to slide the mold toward the inside circumference side, the screw thread must be formed in such a shape as to avoid undercutting. Therefore, as shown in FIG. 4, the angle A of the screw thread becomes large. Then, with a male helicoid tube combined with the female helicoid tube, it is difficult to control and adjust the backlash of screw engagement in the optical axis direction of the lens barrel.
Meanwhile, the other method of forming the screw thread by rotating the mold has presented the following problem, i.e., in arranging a gear part or the like in a direction different from the direction of the lead of the helicoid screw, the gear part cannot be formed with the same mold. The gear part, therefore, must be formed separately from the helicoid screw thread.