| 摘要 |
PURPOSE:To reduce eccentric error sensitivity even when an aspherical lens is molded out of plastics, by using two positive lenses whose 1st surface only is made aspherical, and specifying the condition of the aspherical surface. CONSTITUTION:The condenser lens 1 for an optical disk consists of the 1st lens 2 and the 2nd lens 3 which are both positive lenses; the 1st surface of the 1st lens 2 on a light source side is an aspherical surface 2a, and the 2nd surface and the 3rd and 4th surfaces of the 2nd lens 3 are spherical surfaces 2b, and 3a and 3b. The 1st and the 2nd lenses 2 and 3 differ in diameter slightly and are fitted fixedly in a lens barrel 4 in the same direction; and the center curvatures, refractive indexes, focal lengths, etc., are determined so that the 1st aspherical surface satisfies a conditional inequality. |
