By using dark nebulae as opaque outer screens , the luminosity function of white dwarfs and M dwarfs has been studied .
High-extinction areas towards the Orion A , Serpens and \rho Oph cloud complexes were observed , covering a volume corresponding to 464 pc ^ { 3 } in the solar neighbourhood , complete to M _ { \mathrm { V } } \sim 16.5 .
Foreground stars were selected by VRI photometry and photometric parallaxes .

The resulting foreground sample consists of 21 M dwarfs and 7 white dwarfs .
The derived M-dwarf luminosity function is consistent with previous studies , showing no substantial upturn beyond M _ { \mathrm { V } } = 16 .
The 7 white dwarfs imply a local density of 0.013 ( \pm 0.005 ) M _ { \sun } pc ^ { -3 } ( \sim 15 % of the dynamical mass in the solar neighbourhood ) supporting other recent results but obtained with a completely different method .

For the clouds , foreground-star data were used to derive independent cloud distances , while the background stars and a simple model of the Milky Way gave reliable cloud extinctions .