Upper panel: the ZYJHK_S VISTA transmission bands. An example of a normalized NextGen spectrum (Hauschildt et al. 1999) with T_eff = 2500 K is overplotted. Lower panel: theoretical M_J vs. J − K_S diagram. The isochrones, shifted to the distance of 10 pc (i.e., absolute magnitudes), are in the VISTA photometric system. Different curve styles correspond to different ages, as indicated in the legend. We plot in blue the isochrones computed using the NextGen/AMES-Dusty atmospheric models, and in red those computed using the NextGen/AMES-Cond models.