| 摘要 |
In an objective lens for an optical disk of the type in which focussing is carried out by moving a unit of the entire optical system including a light source and an objective lens, variation of the numerical apertures and deterioration in performance for the focussing are not present, but it is important for reducing the weight of the unit as light as possible to minimize the distance from a light source to an information recording surface while securing an operating distance as required. The lens for that purpose is an aspherical single lens, but it is necessary, for an aspherical shape less affected by a high-order term to be easily fabricated, to make a surface on the light source side an aspherical surface, of which conical coefficient is within a predetermined range.
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