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.
While the fundamental technologies needed for segmented telescopes have been shown in the 10m Keck telescope or GTC telescope, ELTs of sizes from 50 to 100 meters signify a qualitative shift concerning wave front control due to segmentation compared to the current 10-meter technology.