Lens for optical disk

Abstract

Abstract PURPOSE:To especially correct the chromatic aberration satisfactorily by being a three-group four-sheet constituting lens, and specializing the relation of the focal length of all systems and the first group lens, the Abbe's number of the positive lens and the negative lens in the first lens and the curvature radius of the sticking surface of the first group lens. CONSTITUTION:The lens is a three-group four-pieces constituting lens and satisfies formulas 1-3. Here, f is the synthesized focal length of total lens system, f1 is the focal length of the first group lens, nu+ and nu- are Abbe's num ber of the positive lens and the negative lens in the first group lens and r2 is the curvature radius of the sticking surface of the first group lens. When f1 is smaller than the lower limit, the negative spherical aberration quantity to occur at the first group lens comes to be too large, and reversely, when it is larger than the upper limit, the burden of the third group lens and the correction of the spherical aberration comes to be hard. When ¦nu+-nu-¦ is larger than the upper limit, the action to the correction of the chromic aberration is too small, and when ¦r2¦ is large than the upper limit, the achromatic action by the positive lens and the negative lens in the first group lens comes to be small and the correction of the chromatic aberration is short.

Inventors

• 👤 Takahiro Sugiyama
• 👤 孝浩 杉山

Bibliographic Details