Large-aperture single lens with aspherical surfaces

摘要

A large-aperture single lens with aspherical surfaces to be used as a pickup lens for video disks, especially for tracking the video disk by directly moving the pickup lens. It is preferable that the single lens is made of plastic material in order to make it compact and light in weight. Both refractive surfaces of the single lens are arranged to have positive refractive powers in order to make the working distance of the lens long. Spherical aberration of the single lens is corrected to the degree that the diameter of the circle of confusion thereof is decided approximately by diffraction of light. Both refractive surfaces of the single lens are formed as aspherical surfaces and the shapes of the refractive surfaces are determined so as to correct aberrations including the sine condition to the required range, by taking the error to be caused at the time of manufacture into consideration.