The Extremely Large Telescope consists of 798 hexagonal components. After installation, the lens width will reach 128 feet (IT Home notes: approximately 39.01 meters), making it the world's largest optical and infrared telescope.

ESO plans to start collecting light from extraterrestrial worlds, ancient galaxies, and supermassive black holes in 2028 after installation and debugging are completed.

The most advanced glass processing facilities currently available to humanity also make it difficult to cast a telescope mirror with a width exceeding 26 feet. Therefore, most telescopes are assembled from many smaller mirrors, calibrated professionally, and installed on frames.

Each mirror segment of ELT is approximately 4.5 feet wide and less than two inches thick. The glass surface must be very smooth and have a very small margin of error: less than one thousandth of the width of a human hair.

Each mirror of ELT will be glass cast by a German factory and then shipped to France for polishing with a microscopic ion beam, scanning the mirror and removing irregularities atomically.

Source: IT Home