It took another 10-15 years before technology advanced to the point where the scientiœc community could afford to deploy AO on major telescopes. The œrst generation of AO systems used light from a bright star to “sense” the ¬uctuations in the atmosphere and commanded a deformable mirror (DM) to remove the phase ¬uctuations (Tyson, 2000). At present, virtually all large (8-10 m [26-32 ft]) telescopes and a large number of (4-5 m-class [26-32 ft]) telescopes have AO systems. With large telescopes, AO does not just provide higher angular resolution, but can dramatically reduce the cost of instruments. AO on a large telescope dramatically reduces the Area*Solid angle product (A*Omega) of the starlight, which means that an instrument such as a high-resolution spectrometer can be dramatically smaller, and hence cheaper.