Simultaneous effects of shrinkage and refractive index fall of the photographic emulsion in holography

It is shown here, by means of the reciprocal statistical density and the Ewald method, that the decrease of the photographic emulsion refractive index compensates most of the effect of the thickness shrinkage in the case of a transmission three-dimensional absorbing hologram. Moreover, the « symmetric » recording of the hologram is shown to be the most interesting configuration in the case of real-time holographic interferometry where the shrinkage and the refractive index variation of the emulsion do not generate spurious fringes, if they are uniform.