The fabrication of an off axis three-mirror telescope on only two substrates allowing two of mirrors to be formed on a common substrate, such as by means of diamond turning. The common substrate configuration is made possible by utilizing a common vertex for both the primary and tertiary mirrors so that...http://www.google.com.au/patents/US5414555?utm_source=gb-gplus-sharePatent US5414555 - Method for the manufacture of a three-mirror optical system and the optical system resulting therefrom
