In this paper we present the mass functions in the substellar regime of three young open clusters , IC 348 , \sigma Orionis and Pleiades , as derived using the data from the 2 Micron All Sky Survey ( 2MASS ) catalogue which has a limiting magnitude of K _ { s } \sim 15 , and the latest version of the Guide Star Catalogue ( GSC ) which has a limiting magnitude of F \footnote { F refers to the POSS II IIIa - F passband } \sim 21 .
Based on recent evolutionary models for low mass stars , we have formulated the selection criteria for stars with masses below 0.5 M _ { \odot } .
Using a statistical approach to correct for the background contamination , we derive the mass function of objects with masses ranging from 0.5 M _ { \odot } down to the substellar domain , well below the Hydrogen Burning Mass Limit .
The lowest mass bins in our analysis are 0.025 , 0.045 and 0.055 M _ { \odot } for IC 348 , \sigma Orionis and Pleiades , respectively .
The resultant slopes of the mass functions are 0.8 \pm 0.2 for IC 348 , 1.2 \pm 0.2 for \sigma Orionis and 0.5 \pm 0.2 for Pleiades , which are consistent with the previous results .
The contribution of objects below 0.5 M _ { \odot } to the total mass of the cluster is \sim 40 % , and the contribution of objects below 0.08 M _ { \odot } to the total mass is \sim 4 % .