This invention relates to an optical system for lantern slide projection, especially for star projectors in planetariums, with the aim of increasing the available light for the projection. The development consists in attaining an increase in brightness and brilliance of the image as well as a reduction...http://www.google.fr/patents/US4466717?utm_source=gb-gplus-shareBrevet US4466717 - Optical system for lantern slide projection
