Realization of a bi-aspherical objective lens for the Philips Video Long Play system

An objective lens for focusing monochromatic laser light on an optical video disk has been machined in polymethyl methacrylate on a lathe numerically controlled by a computer. The objective is a single-element lens and has two steeply aspherical surfaces. It has a numerical aperture of 0.43, and its field has a diffraction-limited quality over a radius of 300 μm. Some details of the computer-numerically controlled hydraulic lathe are given.