A dual-focus forming method for both a 0.6 mm disk and a 1.2 mm disk, which prevents the increase of wave-front aberration caused by a refractive lens, utilizes a hologram lens having hologram devices respectively formed on the receive and emitting-planes of a transparent plate. The ...http://www.google.de/patents/US5721629?utm_source=gb-gplus-sharePatent US5721629 - Dual-focus forming method and apparatus thereof
