  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 pc3 in the solar neighbourhood, complete to Mv=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 Mv=16. The 7 white dwarfs imply a local
density of 0.013(+-0.005)Msun/pc3 (~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.
