JPS6489027A - Focus controller - Google Patents

Abstract

PURPOSE:To correctly and stably execute the lead-in of a focus by operating a focus control means just after a detecting means detects that a light beam on a recording carrier is made into a prescribed converging condition. CONSTITUTION:At the time of starting the lead-in of the focus, a convergent lens 5 is approached to a disk 7, a focus position is located to an upper part than an information carrier surface, the convergent lens 5 is lowered from the position, the loop of a control system is closed at a point where the focus position passes the information carrier surface slightly, and the focus is led in. Consequently, since a first surface to appear in a focus dislocation signal at the time of distancing the convergent lens 5 is the information carrier surface, a focus lead-in level can be made small regardless of the intensity of the focus dislocation signal, and the information carrier surface can be correctly detected. Since the focus lead-in level can be made small, the focus control is operated very in the vicinity of the information carrier surface. Thus, the lead-in of the focus control can be correctly and stably executed.