Patent ID: 8085627

Claim:
A lens position control method comprising: a moving step of moving an objective lens relative to a master disc in which a resist material has been formed as a film onto a substrate, thereby changing a distance between said objective lens and a surface of said master disc, said movement being controlled by limit data setting forth a relative travel limit between said objective lends and said master disc; a detecting step of detecting with a photodetector a return laser beam which has been transmitted through said objective lens and reflected back by said surface of said master disc; a step of stopping said relative movement between said objective lens and said master disc at a focal point position when said master disc is located at or near a focal point of said objective lens and said return laser beam is detected by said photodetector; a step of rewriting limit data to data corresponding to a position obtained by adding a movement permission amount to the focal point position, the movement permission amount being smaller than a working distance of said objective lens, to establish a stop position; and a step of stopping said relative movement between said objective lens and said surface of said master disc at said stop position determined by said limit data when said return laser beam is not detected.