| 摘要 |
PURPOSE:To correct satisfactorily a spherical aberration by constituting a titled lens so that a luminous flux incident surface and a luminous flux emitting surface of a single lens having a refractive index gradient in the direction vertical to an optical axis used by a reducing magnification form a plane and a convex surface, respectively. CONSTITUTION:In case a single lens having a refractive index gradient in the direction vertical to an optical axis is used by a reducing magnification, a surface of a luminous flux incident side and a surface of its luminous flux emitting side form a plane S1 and a convex surface S2 against an image field side, respectively, and a plano-convex lens is formed. A radius of the convex surface S2, a thickness of the single lens, and a focal distance are denoted as r2, (d), and (f), respectively, so as to satisfy a condition of -1.5<=r2/f<=-0.5, and 0.8<=d/f<=2.8. Also, it is desirable to satisfy 0.4<=¦r2/d¦<=0.6. In this way, a spherical aberration and a sine condition are corrected satisfactorily and easily, and this lens is suitable as a collimator lens and a pickup use objective lens of an optical disk. |
