David L. Fried

David L. Fried is a scientist, best known for his contributions to optics. Fried described what has come to be known as Fried's seeing diameter, or r0 (usually pronounced r-naught). The seeing diameter is effectively a limiting aperture due to atmospheric turbulence, and is found either empirically or statistically. The seeing diameter limits optical resolution. Note that it is a diameter, not a radius, even though r is used as the variable. Typical values for Fried's seeing diameter in the visible spectrum may range from less than 1 cm (you can detect turbulence with your eye) to 20 cm on Mt. Haleakala.