Seeing - Its cause and cure

Abstract

Following Fried, the statistics of images formed by an annular telescope aperture looking through the turbulent atmosphere are calculated; the deleterious effect of a central obscuration is much larger in the presence of seeing that for the telescope alone. A method of optimizing resolution through the atmosphere is explained in detail, with particular attention to the requirements for image-motion compensation; under ideal conditions, about a factor-of-four increase in effective resolution over conventional photography can be obtained. The effective resolution can be large or smaller than the 'seeing disk', depending on the recorded signal-to-noise ratio. Some common misconceptions about image structure and motion, and various unsound proposals for beating the seeing, are criticized.