  Using the focusing equation, the equation for the cosmological angular
diameter distance is derived, based on the ideas of Academician Ya.B.
Zel'dovich, namely, that the distribution of matter at small angles is not
homogeneous, and the light cone is close to being empty. We propose some ways
of testing a method for measuring the angular diameter distances and show that
the proposed method leads to results that agree better with the experimental
data than those obtained by the usual methods.
