Lens for optical disk

Abstract

Abstract PURPOSE:To satisfactorily correct various aberrations (especially, chromatic aberration), and to reduce the deterioration of the performance caused by a variation of the wavelength, by constituting a lens constituted of two groups and three pieces, so that specific conditions are satisfied. CONSTITUTION:In a lens constituted of two groups and three pieces, consisting of the first group lens of a cemented lens of a positive lens and a negative lens, and the second group lens of a biconvex lens, this lens is constituted so as to satisfy the conditions of ¦upsilon1-upsilon2¦>20, ¦r2¦<f, and 0.5>f/f1>0.1. In this case, (f), upsilon1-upsilon2, r2, and f1 denote a composite focal distance of the whole lens system, a difference of Abbe numbers of two pieces of lenses for constituting the first group lens, a radius of curvature of a joint surface of the first group lens, and a composite focal distance of the first group lens, respectively. Also, in order to obtain a lens NA (numerical aperture) is larger, it is desirable that the first surface of the second group lens is aspherical. In such a way, aberration correction in case of not only a single wavelength but plural wavelengths, namely, correction for a chromatic aberration can be executed satisfactorily, and the variation of the aberration caused by the variation of the wavelength of a light source can be made as small as possible.

Inventors

• 👤 Takahiro Sugiyama
• 👤 孝浩 杉山

Bibliographic Details