The classical inversion of forward scattered light to obtain the size distribution of spherical particles is considered. Using the diffraction approximation, the measurement points are selected so as to reduce the influence of the particle refractive index and to make the Chahine inversion scheme usable with a good convergence rate. The algorithm efficiency, in the presence of refractive-index errors and of experimental noise, is studied. An interesting behavior of the Chahine inversion scheme, in the presence of very large experimental errors, is outlined.