an area of about , with a secondary mirror with a diameter of . However, in 2011 a proposal was put forward to reduce its size by 13% to 978 m2, for a diameter primary mirror and a diameter secondary mirror. It reduced projected costs from 1.275 billion to 1.055 billion euros and should allow the telescope to be finished sooner. The smaller secondary is a particularly important change; places it within the capabilities of multiple manufacturers, and the lighter mirror unit avoids the need for high-strength materials in the secondary mirror support spider. ESO's Director General commented in a 2011 press release that "With the new E-ELT design we can still satisfy the bold science goals and also ensure that the construction can be completed in only 10–11 years." The ESO Council endorsed the revised baseline design in June 2011 and expected a construction proposal for approval in December 2011. Funding was subsequently included in the 2012 budget for initial work to begin in early 2012. The project received preliminary approval in June 2012. ESO approved the start of construction in December 2014, with over 90% funding of the nominal budget secured. The design phase of the 5-mirror anastigmat was fully funded within the ESO budget. With the 2011 changes in the baseline design (such as a reduction in the size of the primary mirror from 42 m to 39.3 m), in 2017 the construction cost was estimated to be €1.15 billion (including first generation instruments). In 2014, the start of operations was planned for 2024. Actual construction officially began in early 2017, and , first light is planned for 2028. Planning ESO focused on the current design after a feasibility study concluded the proposed diameter, Overwhelmingly Large Telescope, would cost €1.5 billion (£1 billion), and be too complex. Both current fabrication technology and road transportation constraints limit single mirrors to being roughly per piece. The next-largest telescopes currently in use are the Keck Telescopes, the Gran Telescopio Canarias and the Southern African Large Telescope, which each use small hexagonal mirrors fitted together to make a composite mirror slightly over across. The ELT uses a similar design, as well as techniques to work around atmospheric distortion of incoming light, known as adaptive optics. A 40-metre-class mirror will allow the study of the atmospheres of extrasolar planets. The ELT is the highest priority in the European planning activities for research