A technique for improving the quality of the image produced by an astronomical telescope in which the optical system compensates for changes in the quality of seeing - constantly varying distortions produced by refraction in the Earth’s atmosphere. The distortion is corrected by the rapid bending of a small, very thin mirror placed a short distance before the focus. To be effective, the system needs an image sensor, a microprocessor and actuators to apply forces to the thin mirror, all of which must have response times shorter than a hundredth of a second.