Perfluorinated polymer colloids with low refraction index are prepared via emulsion polymerization. The characterization is done using small-angle X-ray scattering and dynamic light scattering. The independently obtained particle size distributions are in remarkable mutual agreement and give evidence for the monodispersity of our particles. The small-angle scattering signal of such monodisperse samples is influenced by the resolution of the experimental setup. We discuss a method to take such instrumental contributions into consideration and show that the divergence of the primary beam is the most important factor using a pinhole camera with flat single-crystal monochromator.