- Main mirror diameter: 42 metres
- Light collecting area: 1300 square metres
42 metre diameter
With its main mirror as large as 42 metre in diameter, this will be the largest telescope to observe in visible-light. It will be four to five times larger than the present-day state-of-the-art facilities of this kind, and will collect about 15 times more light. It will also be much larger than the two other extremely large telescope in planning, the Thirty-Meter Telescope and the Giant Magellan Telescope.
Almost 1000 segments
It is not possible, nor advised, to build such a large mirror in one piece. Instead, the 42-m mirror will be composed of about 1000 hexagonal segments, about 1.4 metre wide and 5 cm thick. The whole concept of the telescope is in fact to be modular, so that pieces can be manufactured in large quantities, thereby drastically reducing the cost. Only this approach makes the E-ELT possible within a restricted budget.