| 摘要 |
PURPOSE: A technique of extending a focal distance is provided to drive a very small-sized lens finely to enable focus control in a wide range and miniaturize an optical pick-up head for use in a CD or DVD. CONSTITUTION: The distance between a convex lens(1) and a concave lens(2) is controlled to adjust a focus(4) on which parallel beams are focused. The concave lens is placed in the focus(3) of the convex lens while the convex lens being fixed, and the concave lens is moved finely, to largely move the focus on which the parallel beams are focused. |
