The work discusses the spatial scales of atmospheric optical distortions including the outer scale of turbulence and the Fried radius. It is assumed that the energy spectrum of atmospheric turbulence is not limited strictly  and the outer scale is considered in application to astronomical telescopes. In the case when the telescope diameter is larger or comparable with the outer scale the optical distortions substantially differ from the results of the Kolmogorov model. For a given diameter it is possible to introduce a certain spatial scale at distances larger than the size of which the refractive index fluctuations no longer have a significant effect on the quality of astronomical images. Estimates of the outer scale of turbulence are reported for both a atmospheric layer from 0 up to 20 km and surface layer.