From VLT to GTC and the ELTs

At Sagem-REOSC we are in the last phase of figuring of the Gran Telescopio Canarias Primary Mirror Segments and Secondary Mirror. This paper's intent is to show, from the optical manufacturer point of view, how astronomy is presently evolving from large monolithic Active Mirrors to segmented optics thus raising new manufacturing challenges. For this we will recall the work done during VLT & Gemini, gaive latest status on Gran Telescopio Canarias and make a rapid overview of the on-going Extremely Large Telescope projects with primary mirror diameter above 20-m.