The Instrument Group at the Dominion Astrophysical Observatory (DAO) is a group of engineers and specialists whose main work is the design, production, and testing of instrumentation for large astronomical telescopes. Areas of expertise include electronic, mechanical, optical, and software engineering. Some notable instruments that have been completed are the adaptive optics system for the Canada-France-Hawaii 3.6-metre telescope (CFHT) and a multi-object spectrograph for the Gemini North 8-metre telescope, both on Mauna Kea in Hawaii. Projects now being designed or built include a second multi-object spectrograph for Gemini South in Chile, an adaptive optics system for Gemini North, components for a wide-field camera for CFHT, and preliminary design of components for an adaptive optics system for Gemini South. Because of the operating environment of the instruments and the precise tolerances required for optical alignment, these instruments produce unique design problems that need to be solved to meet instrument specifications. The following summary is a description of the methods developed for the mounting of lenses and mirrors.