The paper is devoted to the investigation of the accuracy of the Rozenberg approximation for the reflection function of a semi-infinite absorbing random media. We found that this approximation can be used at y<0.5, where y= square root (1-omega (0))/(3(1-g)) . Here omega(0) is the single scattering albedo and g is the asymmetry parameter. We also propose the modified approximation, which can be used at least up to y=1-2, depending on the observation geometry.