A number of effects which can affect the low-mass IMF derived from the local luminosity function is studied. We consider an influence of unresolved binairies, variations in fine structure of mass-luminosity relation, BC-scale, chemical composition, and evolution of brown dwarfs. The mass-luminosity relation is found to be the main factor defining the IMF. As analysis shows, different theoretical relations calculated for Pop I composition result in different IMFs /from a power law, to a lognormal one/. The presence at faintest magnitudes /Mν > 20^m/ of a large number of brown dwarfs, slowly evolving with decreasing luminosity, leads to the depletion of the luminosity function for both lognormal and power IMFs.