| 摘要 |
PURPOSE:To make a titled lens small-sized and light, to use it for a semiconductor laser whose wavelength is about 8,300Angstrom , too, and also to correct sufficiently an aberration by constituting a lens system of four lenses, and also satisfying a prescribed condition. CONSTITUTION:A condensing lens for an optical disk is constituted of the first positive lens, the second negative lens, the third positive lens and the fourth positive lens in order from a light source side, so that an expression I , an expression II and an expression III are satisfied, when (f), r2, r3 and r7 denote a focal distance of the whole system, a radius of curvature of the second lens side of the first lens, a radius of curvature of the first lens side of the second lens, and a radius of curvature of the third lens side of the fourth lens, respectively. In this way, a lens system becomes small-sized and light, can be used for a semiconductor laser whose wavelength is about 8,300Angstrom , and also a condensing lens for an optical disk for correcting an aberration sufficiently can be obtained. |
