| 摘要 |
PURPOSE:To reduce a shift of the center of gravity of a movable member and an objective lens without adding a balancer and to lighten a load to a driving device by providing at least two lens components and satisfying two specific conditions, and also, making the surface of one lens aspherical. CONSTITUTION:The title lens is provided with at least two lens components, and a value which has measured along an optical axis a distance extending from the incident surface of the first lens component provided on the most separated position from an information recording medium such as an optical disk, etc., between these components to the center of gravity of the whole objective lens is denoted as (gc). Subsequently, when the overall length of the objective lens, that is, a distance extending from the incident surface of the first lens component to the nearest surface to the information recording medium of the lens component provided in the nearest position to the information recording medium is denoted as SIGMAd and a focal distance of the objective lens is denoted as (f), the inequalities I and II are satisfied, and also, the surface of one lens is made aspherical. In such a way, when the objective lens has been attached to a lens holder, the center of gravity of a movable member and the center of gravity of the objective lens can be allowed to approach without providing a large balancer. |
