Active optics is a technology used with reflecting telescopes developed in the 1980s,[1] which actively shapes a telescope's mirrors to prevent deformation due to external influences such as wind, temperature, and mechanical stress. Without active optics, the construction of 8 metre class telescopes is not possible, nor would telescopes with segmented mirrors be feasible.
This method is used by, among others, the Nordic Optical Telescope,[2] the New Technology Telescope, the Telescopio Nazionale Galileo and the Keck telescopes, as well as all of the largest telescopes built since the mid-1990s.
Active optics is not to be confused with adaptive optics, which operates at a shorter timescale and corrects atmospheric distortions.