While the basic technologies required for segmented telescopes have been demonstrated for the 10m Keck telescope or GTC telescope, ELTs of diameters form 50 to 100 m represent a qualitative change with respect to wave front control related to segmentation in comparison with the current 10 meters technology.
The 10m Keck telescope and GTC telescope have shown foundational technologies for segmented telescopes. In contrast, ELTs with diameters of 50 to 100 meters exhibit a qualitative improvement in wave front control through segmentation, distinguishing them from the current 10-meter technology.