Digital storage and retrieval of information on optical disks offer widespread applications in several versions, such as laser vision, compact disk, and data storage. The advantages of this technique are its high storage capacity, rapid access, and favorable manufacturing costs. The technique generally consists of burning small holes called pits in a thin film deposited on a rotating optical disk. In optical data storage technology only lenses with almost rotationally symmetrical point images should be used. Due to the increase in spot size either side of the best focus position, each lens has an associated depth of focus. Objective lenses with higher-numerical-apertures call for tighter tolerances of the cover glass used to protect the information stored in the optical disk. For a wave with a wave aberration the point image spot is enlarged compared with that of a diffraction-limited ideal lens.