In 1997, the primary BBSO telescope was in the class, as were the world's other high resolution solar telescopes. However, to resolve the fundamental scale in the Sun's atmosphere (photon mean free path of at the Solar surface) an aperture of at least is required. Correction of distortion by the terrestrial atmospheric distortion by adaptive optics is the enabling technology for the first facility class solar telescope built in the United States in a generation – the Goode Solar Telescope (GST). The GST is a clear aperture off-axis telescope, which feeds its unobstructed light to visible light and near-infrared (NIR) spectro-polarimeters. The GST benefits from three generations of AO, which now includes multi-conjugate AO (MCAO) in a demonstrator phase for wide-field correction. It is the only MCAO system in operation with three deformable mirrors.