| 摘要 |
PURPOSE:To obtain a small-sized, lightweight lens of two-group, two-element constitution for optical disks by using the 1st lens which is a spherical or aspherical lens whose distance to an object image is set substantially infinite and the 2nd lens whose surfaces are both spherical having positive power. CONSTITUTION:The lens for optical disks consists of two aspherical lenses having the 1st and the 2nd positive-power surfaces or has one spherical lens on its light-source side, and a plastic material which is relatively low in refractive index and light-width is used. Further, the 1st lens is arranged between a semiconductor laser and an optical disk on the semiconductor laser side and the 2nd lens is arranged on the optical disk side. the lens uses an optical disk lens of two-group, two-element constitution whose numerical aperture is >=0.1 on the semiconductor side and >=0.4 on the optical disk side; the 1st lens is a spherical or aspherical lens whose distance to its object point is set substantially infinite and the 2nd lens is an aspherical lens. The aspherical surface of the 2nd lens includes a term proportional to at least the value obtained by raising the height of incident to the 10th power and satisfies inequalities. |
